Stromboli

Photo of this volcano
Google Earth icon
  Google Earth Placemark
  • Country
  • Volcanic Region
  • Primary Volcano Type
  • Last Known Eruption
  • 38.789°N
  • 15.213°E

  • 924 m
    3031 ft

  • 211040
  • Latitude
  • Longitude

  • Summit
    Elevation

  • Volcano
    Number

6 August-12 August 2014

INGV reported that during 6-10 August, a new lava overflow occurred from the crater terrace of Stromboli in the central part of the Sciara del Fuoco. This new lava flow began on 6 August accompanied by large landslides of hot material that reached tens of meters onto the ocean surface. On 7-9 August, a second lava overflow occurred from the north of the crater terrace that covered a plateau at 600 m elevation and six arms of the flow reached the sea. Explosions from lava/sea interactions produced jets of steam, ash and blocks the rose tens of meters into the air that continued 10 August.

Source: Sezione di Catania - Osservatorio Etneo (INGV)

Index of Weekly Reports


2014: June | July | August
2013: January | February
2012: November
2011: February | July | August
2010: March | July | December
2007: February | March | November
2005: October
2004: March
2003: February | March | April | June | July | August | November | December
2002: January | July | November | December
2001: October

Weekly Reports


6 August-12 August 2014

INGV reported that during 6-10 August, a new lava overflow occurred from the crater terrace of Stromboli in the central part of the Sciara del Fuoco. This new lava flow began on 6 August accompanied by large landslides of hot material that reached tens of meters onto the ocean surface. On 7-9 August, a second lava overflow occurred from the north of the crater terrace that covered a plateau at 600 m elevation and six arms of the flow reached the sea. Explosions from lava/sea interactions produced jets of steam, ash and blocks the rose tens of meters into the air that continued 10 August.

Source: Sezione di Catania - Osservatorio Etneo (INGV)


9 July-15 July 2014

INGV reported that during 30 June-1 July, small landslides occurred on Stromboli's Sciara del Fuoco. A new lava flow that began on 7 July flowed from the high part of Sciara del Fuoco (N2) and followed the path of the previous flows. A hot avalanche occurred at 0733 that reached the coastline and was followed by a lava flow. Two other lava flows began from the same location (N2); one during the afternoon of 9 July that was accompanied by small landslides and another on 10 July.

Source: Sezione di Catania - Osservatorio Etneo (INGV)


25 June-1 July 2014

INGV reported that during 29-30 June Stromboli erupted a small intracrater lava flow, a lava flow from the crater mouth on the N, and a lava flow on the Sciara del Fuoco on the S. The flows were accompanied by intense spattering and a high frequency of explosions on 29 June.

Source: Sezione di Catania - Osservatorio Etneo (INGV)


18 June-24 June 2014

INGV reported two episodes of effusive activity at Stromboli, one on 17 June and another on 22 June. Activity on 17 June occurred in the morning within the central part of the crater terrace (Bocca S2) and included explosive spattering. This activity lasted for a few hours and produced a small lava flow directed toward Pizzo Sopra la Fossa. A sharp increase in Strombolian activity began from all of the craters on 22 June, depositing voluminous material along the Sciara del Fuoco. A lava flow ~200 m long extended from the mouth of N2 (within the N part of the crater terrace). During the evening this flow slowed, and then stalled the following day when Strombolian activity decreased.

Source: Sezione di Catania - Osservatorio Etneo (INGV)


27 February-5 March 2013

Stromboli again produced small lava overflows from the crater terrace on the afternoon of 27 February through the following night, after an interval of 10 days of normal Strombolian activity. A second episode of lava overflow started on the evening of 1 March and ceased the next afternoon. Both overflows were fed by continuous spattering from vent N2, which lies at the top of a hornito perched on the N rim of the crater terrace.

Source: Sezione di Catania - Osservatorio Etneo (INGV)


13 February-19 February 2013

Sezione di Catania - Osservatorio Etneo reported that a new phase of intermittent effusive activity at Stromboli, which consisted of small overflows of lava from the crater terrace, began on 8 February and continued until the morning of 17 February. During this interval several episodes of effusive activity occurred in the N and NW sectors of the Sciara del Fuoco, producing lava flows that traveled several tens to a few hundred meters.

Lava overflows ceased on the afternoon of 10 February, but effusive activity resumed in the early morning hours of the next day. On the afternoon of 11 February, three small lava flows were visible on the upper slope of the Sciara del Fuoco; the westernmost flow traveled a few hundred meters. That evening two of these flows remained active and continued to be fed until the morning of 12 February. The more westerly of the flows then stopped, whereas the flow traveling N continued until the early afternoon.

After an interval of non-visibility due to inclement weather conditions, a new lava flow traveled NW in the evening of 12 February. This flow progressively diminished, but was still active at about 1100 on 13 February.

The vent N2, perched on the NW rim of the crater terrace, produced continuous spattering, which also fed a small lava flow parallel to the already active flow. Spattering continued for a few hours, and then diminished during the late afternoon of 14 February. Subsequently, effusive activity diminished considerably, and only very small lava overflows extended a few tens of meters NW. In the morning of 17 February, all effusive activity ceased and mild Strombolian activity resumed.

Source: Sezione di Catania - Osservatorio Etneo (INGV)


6 February-12 February 2013

On 9 February Sezione di Catania - Osservatorio Etneo reported that after about three weeks of normal explosive activity, new, small lava overflows again occurred on Stromboli's crater terrace. The first overflow started in the morning of 8 February, producing a small lava flow that descended the upper NW slope of the Sciara del Fuoco, and ceased during the afternoon. The second overflow began shortly after midnight on 9 February and produced a lava flow that traveled N. Bad weather prevented surveillance video transmission after 0125; when the transmission resumed at 1000, the feeding of the lava flow had diminished, and the active flow front was retreating upslope, generating frequent rockfalls. In the late afternoon of 9 February lava effusion ceased altogether, but resumed once more during the early morning hours of 10 February, generating a small flow that slowly advanced downslope for a few tens of meters. The lava front continuously produced incandescent rockfalls. During the day, lava emission progressively diminished, and ceased completely in the late afternoon.

Source: Sezione di Catania - Osservatorio Etneo (INGV)


23 January-29 January 2013

On 15 January Sezione di Catania - Osservatorio Etneo reported that overflowing lava from vents lying just below the rim of the northernmost explosive vent on Stromboli's crater terrace generated small lava flows that traveled down the N and NW sectors of the Sciara del Fuoco. Landslides caused by the sliding and rolling of loose rock material on the steep slope of the Sciara del Fuoco sometimes accompanied the lava flows. At night during 15-16 January, effusive activity ceased, then only very small lava overflows were observed on the evening of 17 January and during the night of 19-20 January.

Source: Sezione di Catania - Osservatorio Etneo (INGV)


9 January-15 January 2013

On 10 January Sezione di Catania - Osservatorio Etneo reported that since the morning of 23 December 2012 overflowing lava from vents lying just below the rim of the northernmost explosive vent on Stromboli's crater terrace generated small lava flows that traveled down the N and NW sectors of the Sciara del Fuoco. In addition, the rapid accumulation of spatter during intense explosive activity often generated small flows that were accompanied by numerous landslides. Major lava flows occurred on 23 December (traveling N), during 25-27 December (traveling NW), and on 7 January (traveling NW).

During the intervals between the main effusive episodes, lava was extruded at extremely low rates from the vents, resulting numerous incandescent blocks descending the Sciara del Fuoco. Sometimes small lava flows advanced for a few tens of meters before disintegrating into blocks, such as on the morning of 10 January 2013. In all cases, the effusion of lava was preceded, and often accompanied, by intense explosive activity on the crater terrace.

A report on 15 January noted that intermittent emissions of small lava flows from the crater terrace continued, sometimes accompanied by landslides caused by the sliding and rolling of loose rock material on the steep slope of the Sciara del Fuoco.

Source: Sezione di Catania - Osservatorio Etneo (INGV)


21 November-27 November 2012

Sezione di Catania - Osservatorio Etneo reported that the persistent explosive activity at Stromboli showed a clear increase on 21 November with episodes of spattering and low lava fountaining from two vents located in the N and central portions of the crater terrace.

Source: Sezione di Catania - Osservatorio Etneo (INGV)


3 August-9 August 2011

Sezione di Catania - Osservatorio Etneo reported that during the morning of 9 August a new episode of weak spattering occurred on Stromboli's crater terrace, generating a small intra-crater lava flow. The source vent was located in the central portion of the crater terrace. Regular explosive activity also continued from the vents located in the N and S parts of the crater terrace. Spattering continued into the afternoon, then ceased.

Source: Sezione di Catania - Osservatorio Etneo (INGV)


27 July-2 August 2011

Sezione di Catania - Osservatorio Etneo reported that during the late evening of 1 August a vast accumulation of incandescent material appeared at the base of Stromboli's N1 vent, the northernmost active vent within the crater terrace at about 750 m elevation. Within a few minutes, the material collapsed and slid downslope, creating two small lobes of lava. The more easterly flow descended the N slope of the Sciara del Fuoco, generating small landslides from the loose material on the slope, and marking the first lava effusion event outside of the crater since a small emission during 11-12 December 2010. The lava accumulated on a flat area near hornitos that were formed during 2002-2003, before continuing further down a steep slope. On 2 August the lava had descended to 500 m elevation and advanced very slowly. During the afternoon effusion appeared to have diminished.

Source: Sezione di Catania - Osservatorio Etneo (INGV)


6 July-12 July 2011

Sezione di Catania - Osservatorio Etneo reported that on 5 July a high pyroclastic jet formed in the S part of Stromboli's crater terrace producing tephra that fell back onto the Pizzo sopra la Fossa. Seismic data indicated that other craters on the terrace were also active. A similar but less powerful explosion occurred from the same vent on 10 July.

Source: Sezione di Catania - Osservatorio Etneo (INGV)


16 February-22 February 2011

INGV-CT reported that on 17 February a series of strong explosions from the northernmost vent of Stromboli's summit area led to the accumulation of hot scoriaceous material on the external N flank of the crater. Activity continued at elevated levels from two vents in the northern portion of the crater terrace through 23 February.

Source: Sezione di Catania - Osservatorio Etneo (INGV)


29 December-4 January 2011

INGV-CT reported that on 19 December a major explosion from a vent in the southern part of Stromboli's crater terrace occurred at 0956, coincident with explosive sequence consisting of three discrete seismic events. During the last few days of December the "S1" vent produced frequent explosions of greater intensity than those of the preceding days. Jets rose 200 m above the crater terrace. On 27 December, the frequency of the explosions rose to 11-14 per hour. The "S1" vent is immediately next to the "S" vent, the source of the 19 December explosion.

Source: Sezione di Catania - Osservatorio Etneo (INGV)


22 December-28 December 2010

INGV-CT reported that a sequence of three explosions from Stromboli's "S" vent in the S part of the crater terrace were recorded on 19 December by thermal monitoring cameras in Vancori and Pizzo. The first explosion ejected coarse-grained pyroclastic material, followed by fine-grained tephra, more than 250 m above the crater terrace. A slightly less intense explosion occurred less than a minute later. The third and weakest explosion ejected material 180-200 m above the crater, generating an ash plume that dispersed over the W and NE parts of the island.

Source: Sezione di Catania - Osservatorio Etneo (INGV)


7 July-13 July 2010

INGV-CT reported that two major explosions from Stromboli were detected by the seismic network. These explosions occurred from the SW crater area on 25 June and from the NE crater area on 30 June. Poor weather conditions prevented visual observations using the web camera monitoring system. The event on 30 June was stronger, with several explosions occurring in a short time. Fallout from incandescent blocks triggered vegetation fires.

Source: Sezione di Catania - Osservatorio Etneo (INGV)


10 March-16 March 2010

INGV-CT reported strong explosions from Stromboli on 10 March mainly from craters located in the N part of the crater terrace, a flat area in the upper part of Sciara del Fuoco (a depression cutting the NW flank of the volcano). After one of the more powerful explosions, lava flowed over the NW edge of the crater terrace for tens of meters before fragmenting and producing small landslides of hot material that likely reached the sea.

Source: Sezione di Catania - Osservatorio Etneo (INGV)


7 November-13 November 2007

Observers reported that on 5 November five active vents at Stromboli were visible at the bottom of the crater terrace, which subsided about 100 m since March 2007. Lava fountains from a vent in the SW crater were sustained for over one minute and spattering was observed from two vents in the central crater. The vents erupted about every five to ten minutes to one hour.

Source: Stromboli On-Line


14 March-20 March 2007

INGV-CT reported that the eruption at Stromboli that started on 27 February continued during 15 March. On 9 March, the vent at 400 m elevation that fed the lava flows closed and another vent opened on the N flank of the NE Crater at 550 m elevation. It remained active for less than 24 hours. After it closed, the 400-m vent re-opened and lava again flowed to the sea. On 15 March, a major explosion occurred during an effusive flank eruption.

Source: Sezione di Catania - Osservatorio Etneo (INGV)


28 February-6 March 2007

INGV-CT reported that the eruption at Stromboli that started on 27 February continued during 7 March. Lava from a fissure on the NE flank of Crater 1 (the NE crater) flowed down the Sciara del Fuoco and formed two branches that reached the sea, resulting in steam plumes and a modified coastline. Explosive activity from the summit craters ceased when the lava flowed from the fissure, but gas puffing accompanied by small landslides inside the craters started again after 3 March.

Source: Sezione di Catania - Osservatorio Etneo (INGV)


21 February-27 February 2007

Based on news reports, lava from Stromboli was observed flowing from two craters near the summit on 27 February. One lava flow traveled down the flanks more than 900 m and reached the sea. Several explosions per hour were audible.

Sources: Deutsche Presse-Agentur; United Press International


12 October-18 October 2005

A plume emitted from Stromboli that may have contained ash was visible on satellite imagery on 14 October at a height around 1.8-2.4 km (6,000-8,000 ft) a.s.l. The plume extended ~10 km NW of the volcano.

Source: Toulouse Volcanic Ash Advisory Centre (VAAC)


10 March-16 March 2004

INGV-CT reported that explosive activity at Stromboli's three summit craters increased after 10 February, leading to significant growth of the cinder cones inside the craters. Several powerful explosions, especially from Crater 1 (the NE crater) and Crater 3 (the SW crater), sent scoriae 200 m above the craters. These powerful explosions led to fallout of fresh bombs and lapilli on Il Pizzo Sopra la Fossa (an area atop the volcano about 100 m above the crater terrace) in early March. As of 8 March, Strombolian activity was occurring at the volcano, with variations in the number and frequency of explosions within normally observed limits, and the intensity of explosions at the higher limit of commonly observed activity.

Source: Sezione di Catania - Osservatorio Etneo (INGV)


10 December-16 December 2003

The Stromboli Web video camera showed a small explosion on 10 December that produced a plume to a height of ~1 km above the volcano. No ash was visible on satellite imagery.

Source: Toulouse Volcanic Ash Advisory Centre (VAAC)


5 November-11 November 2003

According to aviation reports from the U.S. Air Force, the web camera at Stromboli captured light ash emissions on 7 and 11 November. In both cases plumes rose to ~2.5 km a.s.l.

Source: Sezione di Catania - Osservatorio Etneo (INGV)


20 August-26 August 2003

INGV-CT reported that after the effusive eruption at Stromboli ceased between 21 and 22 July, explosive Strombolian activity became more common at both summit craters. Four active vents were observed within Crater 1 (the NE crater), and one funnel-shaped incandescent depression was seen within Crater 3 (the SW crater). Strombolian activity during the first half of August was very intense at Crater 1, with spattering that led to the creation of a spatter cone on the crater floor and fallout of incandescent bombs on the cone's outer flanks. Explosive activity at Crater 3 appeared to be deeper than at Crater 1 and was often accompanied by ash emission. During the first half of August thermal images of the apparently inactive flow field revealed a thermal signature within cracks on the upper flow field and within skylights along two lava tubes in the upper Sciara del Fuoco, at about 550 m elevation. Temperatures over 300°C and incandescence at these hot spots suggest endogenous growth of the apparently inactive lava flow field. Incandescence and thermal signatures at these sites were not seen between 22 and 31 July.

Source: Sezione di Catania - Osservatorio Etneo (INGV)


23 July-29 July 2003

According to INGV-CT, the eruption that began at Stromboli on 28 December 2002 ended on 22 July. Strombolian activity occurred almost continuously in July, with spatter often falling outside the rim of Crater 1 (the NE crater). Mainly degassing and sporadic ash emissions occurred at Crater 3 (the SW crater), with Strombolian explosions becoming more common during the second half of July. Erosion of the N flank of Crater 1 by landslides in the upper Sciara del Fuoco increased in July, with the 30 December 2002 landslide scar extending backward and upslope, cutting the flank of the cone just 50 m below the crater rim. Lava effusion from vents located at about 600 m elevation on the upper eastern corner of the Sciara del Fuoco decreased beginning in early June, completely stopping between 21 and 22 July.

Source: Sezione di Catania - Osservatorio Etneo (INGV)


11 June-17 June 2003

INGV-CT reported that the effusive eruption that began at Stromboli on 15 February on the upper eastern corner of the Sciara del Fuoco (a horseshoe-shaped scarp) continued until at least 16 June, with a general decrease in lava-effusion rate. During 1-6 June, there was Strombolian activity at Crater 1 (the NE crater). Most ejecta fell within the crater and pulsating dark ash was emitted. On 11 June lava flows were occasionally emitted from hornitos at 600-m elevation. Discontinuous ash emission occurred from the summit crater until mid-June. On 15 June a SAR fixed camera recorded a Strombolian explosion, with abundant ash emissions.

Source: Sezione di Catania - Osservatorio Etneo (INGV)


9 April-15 April 2003

INGV-CT reported that the effusive eruption at Stromboli, which started on 28 December 2002, continued through 8 April 2003 from vents at 600 m a.s.l. On 5 April scientists from INGV-CT observing the volcano from a helicopter saw lava flowing from three vents at 600 m and a diluted gas plume emanating from the summit craters. A few minutes after the survey began the gas plume suddenly became red and soon after juvenile, darker material was emitted from Crater 1 (the NE crater). A hot, cauliflower-shaped jet rapidly grew above the crater. Around 2-3 seconds later Crater 3 (the SW crater) emitted a hot jet of juvenile material and soon after the two jets joined together. Then a very powerful explosion occurred at 0912 that pushed the helicopter away from the crater. A mushroom-shaped dark cloud rose to ~1 km above Stromboli's summit. The base of the cloud was surrounded by a dark gray cloud similar to a base surge. Bombs, blocks, and ash fell on the volcano's NE flank above 400 m elevation, burning vegetation. Most ejecta drifted W, falling on the town of Ginostra, about 1.5 km away, and destroyed two houses.

Observations after the eruption revealed that the lava-flow field on the upper Sciara del Fuoco (a horseshoe-shaped scarp) at 600 m elevation was completely covered by a carpet of brown debris ejected from Crater 1 during the initial phase of the event. A thick steam cloud rose above the debris carpet, formed by vaporization of wet debris above the hot lava flows. Alternating pulses of black and red ash emissions rose mainly above Crater 3. The upper part of the volcano (above 700 m elevation) was completely covered by a continuous carpet of pyroclastic products. Within a few minutes after the eruption, lava flows were active again on the Sciara del Fuoco at 600 m elevation, emerging through the debris carpet. On 8 April INGV-CT scientists saw lava flowing from four vents on the Sciara del Fuoco. Two flows traveled in the middle of the scarp and blocks detaching from the lava-flow fronts generated small rockfalls that reached the sea. News about the eruption (in Italian) and photos are available on the INGV-CT website.

Source: Sezione di Catania - Osservatorio Etneo (INGV)


2 April-8 April 2003

A strong explosion at Stromboli on 5 April around 0915 produced a mushroom-shaped ash cloud that rose several hundred meters above the volcano. Rocks ejected during the explosion damaged two homes and several roads in the town of Ginostra ~ 2 km SW of Stromboli's summit. There were no reports of injuries.

Sources: Stromboli On-Line; Associated Press; Agence France-Presse (AFP)


12 March-18 March 2003

INGV-CT reported that the eruption at Stromboli, which started on 28 December 2002, continued through 12 March. In early March two major lava flows spread NE and NW from the base of the NE crater. Hot aa lava blocks detached from lava-flow fronts causing several minor rockfalls and landslides along the Sciara del Fuoco. Lava entering the sea formed steam clouds. A decrease in lava-effusion rate from the 600-m-vent on 6 March led to a regression of the most advanced flow front to 300- to 400-m-elevation, and a smaller number of active ephemeral vents along the lava-flow field. Occasionally during 5-10 March, brown-to-pink ash emissions occurred at Crater 3 (the SW crater) that were probably produced from inner-crater collapses. No explosive activity has been observed at the summit craters since the start of the flank eruption. Detailed daily reports of volcanic activity (in Italian) are available at the INGV-CT website.

Source: Sezione di Catania - Osservatorio Etneo (INGV)


19 February-25 February 2003

INGV-CT reported that the effusive eruption that began at Stromboli on 28 December 2002, continued through 25 February 2003. Between 30 December 2002 and 15 February 2003 lava flowed from a main vent located at ~500 m elevation in the middle of the Sciara del Fuoco (a horseshoe-shaped scarp), within the scar left by the 30 December 2002 landslide. Another vent, located at ~600 m elevation at the NE base of Crater 1 (NE crater), had been active several times during the eruption, forming slow, short flows that lasted a few hours to a few days. On 15 February, after a gradual decrease in effusion rate, the vent at ~500 m elevation became inactive. This was accompanied by the opening of a new vent at ~600 m elevation, which emitted small lava flows on the upper Sciara del Fuoco. A small, complex flow field was formed with several lava tubes and ephemeral vents. This was the first time since the start of the eruption that activity at the ~500-m-elevation vent completely ceased, and the first time that the ~600-m-elevation vent remained active for over 10 days. Detailed daily reports of volcanic activity (in Italian) are available at the INGV-CT website.

Source: Sezione di Catania - Osservatorio Etneo (INGV)


5 February-11 February 2003

INGV-CT reported that the effusive eruption that began at Stromboli on 28 December 2002, continued through 6 February 2003. Emission of lava occurred from a main vent located at 500 m elevation in the middle of the Sciara de Fuocco (a horseshoe-shaped scarp), within the scar left by the 30 December 2002 landslide. Another vent, located at 600 m elevation at the NE base of Crater 1, was active several times during the eruption. Slow, short lava flows were emitted from this vent for periods lasting a few hours to a few days. During peaks in effusion rate, aa lava flows reached the sea, causing phreatic explosions at the lava-flow front.

During a thermal survey from a helicopter on 12 January, arcuate cracks were seen around the S base of the volcano's summit craters. Other fractures, oriented NE-SW, cut through the craters. Collapse of the crater's bottom during early January significantly changed the morphology of the upper part of the volcano. Previously there had been three individual craters, but scientists saw that Crater 1 (NE) and 3 (SW) had joined together to form one elongate depression. Crater 2 (the middle crater) no longer existed. INGV-CT noted that no explosive activity had occurred at the summit craters since the start of the activity within the Sciara del Fuocco. News about the eruption (in Italian), thermal images, photos, and videos of the 30 December 2002 collapse event can be downloaded from the INGV-CT website.

Source: Sezione di Catania - Osservatorio Etneo (INGV)


31 December-6 January 2003

INGV-CT reported that an effusive eruption began at Stromboli's summit at the base of the NE crater (Crater 1) on 28 December and ended the following day. A survey performed on 29 December, with a thermal camera on a Civil Protection helicopter, revealed that three lava flows had spread in the eastern Sciara del Fuoco (a horseshoe-shaped scarp). The lava flows reached the sea within 30 minutes, and spanned a width of 300 m along the coast.

On 30 December at 1315 and 1322 two landslides suddenly formed along the Sciara del Fuoco. As they traveled down the volcano's flank they produced wet, fine ashfall (less than 0.1 mm in size) on the island's SE side. The first landslide had a volume of about 600,000 m3, the second about 5,000,000 m3, and they both reached the sea. Upon contact with the sea the landslides produced two tsunamis with waves that were several meters high. The tsunamis injured few people, and damaged buildings and boats in the villages of Stromboli and Ginostra. Large waves were reported as far away as the town of Milazzo, on Sicily's N coast, 60 km S of Stromboli.

INGV-CT noted that no explosive activity occurred after the start of the 28 December effusive eruption at Stromboli. In addition, no earthquakes were recorded by their seismic network except for two that were associated with the landslides. On 1 January, a thin lava flow was expanding along the Sciara del Fuoco. As of 6 January effusive activity was ongoing at Stromboli. Lava was being emitted from two vents located at 500 m and 300 m elevation in the middle of the Sciara del Fuoco. The two narrow lava flows merged together before reaching the sea. Occasional small landslides occurred from the unstable walls of the Sciara del Fuoco, covering the lava flows with thin talus. News about the eruption at Stromboli, thermal images of the 28 December flow, and photos and video of the collapse event are available on the INGV-CT website.

Source: Sezione di Catania - Osservatorio Etneo (INGV)


24 December-30 December 2002

According to an INGV-CT report, "At 1830 of 28 December a new effusive eruption started at Stromboli volcano... Strombolian activity at Stromboli was very intense since May 2002, and lava level within the craters was very high on 19 November, when a survey using a thermal camera from [a] helicopter has been carried out. In November, an overflow from the N rim of Crater 2 formed a small lava flow a few tens of meters long, which spread in the upper Sciara del Fuoco. This event has been accompanied by a greater frequency of explosion-quakes associated to the explosions. Between 7 and 10 December explosive activity from the summit craters decreased. On 11 December Strombolian activity increased again as [reflected in the] frequency of the explosions and heights of ejecta, and was particularly intense at Crater 1, the NE crater. On 28 December the height of ejecta reached 200 m above Crater 1, and the shape of explosions suggested magma very close to the crater rim. This activity climaxed at 1830 with a strong explosion that caused ash fallout on the village of Stromboli, accompanied by the opening of an eruptive fissure trending NE-SW. The fissure opened at the NE base of Crater 1. A lava flow came out from the base of the fissure, and formed three lava branches spreading within the Sciara del Fuoco. Within 30 minutes the flows reached the sea, about 1 km away, far away from the villages. The lava flows were up to 300 m wide at the shoreline, and very narrow along the steep slope of Sciara del Fuoco. A small increase in the volcanic tremor accompanied the lava flow emission, and the number of seismic events associated to the eruptive activity is still of about five shocks per hour."

"A thermal survey carried out from [a] helicopter on 29 December did not allow us to see the craters because of poor weather conditions. A thick cloud was covering the summit of the volcano above 600 m a.s.l. The lava flows below this elevation were cooling and did not show any movement, suggesting the end of the effusive phase. A map of the lava flows, today's photos of Stromboli and updated reports (in Italian) are visible on the INGV-CT web page."

According to several news articles, volcanic activity at Stromboli on 30 December caused a landslide, which entered the sea and generated a tsunami. The articles stated that in the small village of Ginostra, waves injured six people, and damaged homes and boats. Residents and tourists were evacuated to nearby Sicily.

Sources: Sezione di Catania - Osservatorio Etneo (INGV); ABC News - Australian Broadcasting Corporation; BBC News; Reuters; CNN


6 November-12 November 2002

During the end of October, there was an increase in the intensity of Strombolian activity at Stromboli. More powerful eruptions and a larger number of ash-dominated eruptions occurred than is usual.

Source: Stromboli On-Line


24 July-30 July 2002

During 5-24 July, the level of volcanic activity fluctuated at Stromboli. Small explosions occasionally occurred at Northeast Crater, while fewer occurred at Southwest Crater. The central crater was inactive. On 24 July at about 0745 a relatively large explosion produced a mushroom-shaped plume to a height of ~0.5 km above the summit. It was not known from which crater the explosion occurred.

Sources: Italy's Volcanoes; Stromboli On-Line


23 January-29 January 2002

On 23 January at 2054 a large explosion occurred at Stromboli. The explosion was accompanied by a loud noise that was heard at all of the villages on the island and ashfall that lasted for several minutes. During a visit to the summit area on 24 January, INGV-CT staff found the area SE of the summit craters near Il Pizzo Sopra la Fossa between the Bastimento and La Fossetta was covered with ash and blocks. Most of the fallout was comprised of lithic material up to 60 cm in diameter, with minor amounts of spatter up to 1.7 m long. Fine-grained material covered the crater zone and the volcano's NE flank to the village of Stromboli, ~2 km to the NE. A continuous carpet of fallout material covered the zone of Il Pizzo, a spot where many tourists visit.

Weak volcanic activity was observed during the survey; only five weak explosions occurred from Crater 1 in 2.5 hours, with none at Craters 2 and 3. Thermal imagery showed that Crater 2 was hotter than the other active craters; the high temperatures were due to spatter coating the crater's inner walls. Measurements revealed that the diameter of Crater 2 had grown from an estimated 10 m in October 2001 to about 26 m after the 23 January explosion.

Source: Sezione di Catania - Osservatorio Etneo (INGV)


17 October-23 October 2001

On 20 October at 0235 an eruption began at Stromboli. Preliminary reports stated that glowing rocks were observed being ejected from the volcano. A tourist was killed after being struck by ejecta from the eruption. Two areas of burning vegetation approximately 200 m apart were observed at 600 m elevation. Hot ejecta may have landed in these areas.

Sources: Stromboli On-Line; New York Times


Index of Monthly Reports

Reports are organized chronologically and indexed below by Month/Year (Publication Volume:Number), and include a one-line summary. Click on the index link or scroll down to read the reports.

04/1971 (CSLP 34-71) Lava flow on 3 April reaches the sea

05/1971 (CSLP 34-71) Two explosions and a small lava flow on 1 May

11/1975 (SEAN 01:02) Effusive activity began on 5 November; lava reaches the northern coast

01/1986 (SEAN 11:01) Explosions and nuée ardente, then lava flow to sea

06/1986 (SEAN 11:06) Strombolian activity; small lava flows

09/1986 (SEAN 11:09) Intermittent lava fountains from summit lava lake after lava flow production ends; tourist killed near summit vent

11/1988 (SEAN 13:11) Incandescent tephra from several vents

03/1989 (SEAN 14:03) Brief stronger explosions; one tourist injured

09/1989 (SEAN 14:09) Explosions eject bombs and spatter

10/1989 (SEAN 14:10) Frequent incandescent tephra ejection similar to 1988

04/1990 (BGVN 15:04) Lava fountaining and ash emission from several vents

08/1990 (BGVN 15:08) Strong explosions; one crater filled by tephra

09/1990 (BGVN 15:09) Continued Strombolian activity; new vents

10/1990 (BGVN 15:10) Strong tephra ejection; increased seismicity

11/1990 (BGVN 15:11) Vigorous tephra ejection and lava fountaining from summit vents

12/1990 (BGVN 15:12) Activity drops to occasional explosions; seismicity declines

04/1991 (BGVN 16:04) Explosive activity from a single crater; strong seismicity

05/1991 (BGVN 16:05) More frequent explosions

06/1991 (BGVN 16:06) Explosions eject glowing fragments and gas columns

07/1991 (BGVN 16:07) Continued explosions from two craters

08/1991 (BGVN 16:08) Continued moderate explosive activity; gas data

09/1991 (BGVN 16:09) Continued tephra ejection from several vents

10/1991 (BGVN 16:10) More frequent explosions; new zone of fumaroles

03/1992 (BGVN 17:03) Less-frequent eruptive episodes

05/1992 (BGVN 17:05) Frequent explosions; increased seismicity

06/1992 (BGVN 17:06) Small explosions and seismicity continue

08/1992 (BGVN 17:08) Frequent weak explosions; tremor

10/1992 (BGVN 17:10) Continuous spatter ejection; occasional vigorous explosions; seismicity increases

01/1993 (BGVN 18:01) Short series of violent explosions ejects tephra column

02/1993 (BGVN 18:02) Seismicity and tremor resume after 10 February explosions

04/1993 (BGVN 18:04) Explosive activity increases; detailed description of crater

05/1993 (BGVN 18:05) Strombolian activity decreases

09/1993 (BGVN 18:09) Eruptive activity and seismicity decline from high levels in May; two strong explosions in October

10/1993 (BGVN 18:10) Explosive activity ejects lithic fragments and large bombs

01/1994 (BGVN 19:01) Seismicity continues to rise following October explosions

03/1994 (BGVN 19:03) Normal Strombolian activity; crater descriptions

06/1994 (BGVN 19:06) Variable seismicity, but generally low; moderate-low activity in late May

09/1994 (BGVN 19:09) Intense activity from ten vent locations

10/1994 (BGVN 19:10) High seismicity during July-September; eruptive activity described

01/1995 (BGVN 20:01) Seismicity low and stable in late 1994

04/1995 (BGVN 20:04) Explosion on 5 March and tremor; crater observations

05/1995 (BGVN 20:05) Slight late-May increase in seismicity; crater observations

08/1995 (BGVN 20:08) Seismicity generally low from mid-June to mid-September

12/1995 (BGVN 20:11/12) Low-level ash plumes and lava fountains during September-October

02/1996 (BGVN 21:02) Intense eruptive phase followed by a drop in seismicity

04/1996 (BGVN 21:04) Increased seismicity and Crater 1 activity after mid-April

05/1996 (BGVN 21:05) Continued high levels of activity through mid-June; two larger explosions

03/1997 (BGVN 22:03) Summary of seismic and volcanic activity during May 1996-January 1997

05/1997 (BGVN 22:05) New map of the crater terrace

10/1998 (BGVN 23:10) Larger explosions in January, August, and September 1998

06/1999 (BGVN 24:06) Vents in summit craters still active; variable seismicity

01/2000 (BGVN 25:01) 1999 seismic summary and some stronger-than-usual eruptions

08/2000 (BGVN 25:08) Low-to-moderate eruptive activity January-September 2000

04/2001 (BGVN 26:04) Variable seismicity during late 2000 and early 2001; spatter ejected above crater rims

07/2001 (BGVN 26:07) Continued Strombolian activity during March-May 2001; crater morphology changes

10/2001 (BGVN 26:10) Major explosion at Stromboli kills a tourist on 20 October 2001

01/2002 (BGVN 27:01) Fallout from 23 January explosion carpets popular tourist area

07/2002 (BGVN 27:07) Increased activity beginning in June 2002 culminates in strong explosion on 24 July

12/2002 (BGVN 27:12) Landslides on 30 December cause two tsunamis; damage in nearby villages

01/2003 (BGVN 28:01) Lava emissions continue into January; crater morphology changes

04/2003 (BGVN 28:04) Strong explosion on 5 April covers much of the summit in pyroclastic deposits

05/2003 (BGVN 28:05) Lava effusion continues through mid-June; infrared satellite observations

07/2003 (BGVN 28:07) Flank eruption finished as of 22 July; activity resumed at summit craters on 17 April

08/2003 (BGVN 28:08) Explosive activity in the summit craters and thermal signatures in the lava-flow field

02/2004 (BGVN 29:02) After 10 February 2004, explosions at upper limit of that typically seen

03/2004 (BGVN 29:03) Webcams at various wavelengths document increased explosions in February 2004

04/2007 (BGVN 32:04) Flank eruption begins on 27 February 2007

03/2010 (BGVN 35:03) Explosions and lava flows in 2009; recent reports on 2007 eruption

09/2011 (BGVN 36:09) Recent activity; plumbing insights; new water vapor flux technique; hydrogeology

12/2013 (BGVN 38:12) Small-to-moderate eruptions continue through December 2013


Contents of Monthly Reports

All information contained in these reports is preliminary and subject to change.

All times are local (= UTC + 1 hour late September-late March; + 2 hours late March-late September)

04/1971 (CSLP 34-71) Lava flow on 3 April reaches the sea

Card 1168 (06 April 1971) Lava flow on 3 April reaches the sea

"A lava flow on the Sciara del Fuoco occurred on 3 April 1971. The flow occurred on the active slope between the crater and the sea on the NW side of the volcano. The crater is at an altitude of 800 m. Lava reached the sea and the activity has momentarily stopped."

Information Contacts: Dr. Glot, International Laboratoire de Volcanologie, Paris, France; H. Tazieff, Paris, France.

05/1971 (CSLP 34-71) Two explosions and a small lava flow on 1 May

Card 1196 (06 May 1971) Two explosions and a small lava flow on 1 May

"Catania, 1 May 1971: On the first of May at 1345 two explosions with emission of ashes have been observed at the crater of Stromboli. They opened the crater which had been blocked since the explosion of 31 March 1971 by collapsed loose materials. After the two explosions on 1 May a small amount of lava was emitted and flowed down the Sciara del Fuoco. The explosive activity continues in the form of small emissions of vapor and ashes which occur at irregular intervals of at least 15 minutes. No precursory nor contemporaneous.....have been registered on the seismograph of the Geophysical Observatory at Lipari, a distance of about 15 km from Stromboli.

"Catania, 4 May 1971: The lava flow of Stromboli....the activity is reduced to its usual state."

Information Contacts: Lo Giudice and Alfredo Rittman, Instituto Internazionale di Vulcanologia, Catania, Sicily, Italy.

11/1975 (SEAN 01:02) Effusive activity began on 5 November; lava reaches the northern coast

For the first time since the spring of 1971, a new effusive phase began at 2030 on 5 November. Three summit craters were active, and lava flowing down the Sciara del Fuoco reached the N coast. By mid November effusive activity was decreasing below the 700 m level on the Sciara. The eruption had no adverse effects on the island's population or agriculture.

Further References. Villari, L., ed., 1980, The Aeolian Islands, an active volcanic arc in the Mediterranean Sea: Rendiconti Soc. Ital. Mineral. Petrol., v. 36, 185 p. + refs.

Capaldi, G., and others, 1978, Stromboli and its 1975 eruption: BV, v. 41, p. 259-285.

Information Contact: G. Nappi, IIV, Catania.

01/1986 (SEAN 11:01) Explosions and nuée ardente, then lava flow to sea

"On 6 December at 0745 an eruptive crisis with lava flow emission started at Stromboli, interrupting a 10-year period of persistent mild explosive activity during which liquid lava was constantly in the summit craters. Inception of the eruption was accompanied by a violent explosive phase and by the opening of a trough a few tens of meters wide on the NE margin of the crater platform. The newly formed eruptive trough, ~100 m long, developed from the easternmost vent of the main crater platform (825 m elevation) roughly NE down to an altitude of 680 m (figure 1). During the initial explosive phase, which lasted ~1.5 hours, ash clouds rich in steam rose to an altitude of 2,000-3,000 m. At about 0815, a small nuée ardente descended the NW flank's Sciara del Fuoco (near the Fili del Fuoco side), reaching the sea. The explosive activity was mainly confined to the newly formed trough, which was probably widened by ejection of abundant old and fumarolically altered material. The first emission of a lava flow was from a temporary vent a few tens of meters higher than the eventual main eruptive vent, preceding or accompanying the explosive phase. The first lava flow descended toward the easternmost edge of the Sciara, forming a small lava field (at the foot of Bastimento rock). Later that morning, the lava vent was displaced N to an elevation of ~680 m because of further collapse of the eruptive trough. From this point, a second lava flow started to descend the 40° steep slope of the Sciara del Fuoco, reaching the sea at about 1100.

Figure 1. Map of the summit and NW flank of Stromboli showing the newly formed eruptive gorge (1), the first lavas on the morning of 6 December 1985 (2), the lava flows of 6 December 1985-1 January 1986 (3), and the path of a nuée ardente on 6 December 1985 (4). Courtesy of Mauro Rosi and Alessandro Sbrana.

"During the following days, the lava front advanced a few tens of meters into the sea, forming a small peninsula at the NE end of the Sciara del Fuoco. Advance of the lava flow into the sea was frequently accompanied by secondary phreatic explosions and strong steaming. The lateral drainage of the degassed lava was followed by a drop of the lava level in the upper craters, changing their activity from lava fountains (5 December) to rhythmic puffs of ash clouds and continuous steaming.

"A visit to the summit on 8 December revealed a thin ashfall cover containing millimeter-sized accretionary lapilli deposited during the initial phreatomagmatic explosive phase. Outpouring of lava continued through December and January, with an average decline in lava output and a tendency to accumulate materials on the E side of the Sciara del Fuoco. Lava was still emerging on 27 January.

"Preliminary seismic investigations (Biviano and others, 1985) indicated that no relevant variations occurred in the 3 months preceding the eruption. An isolated event (M >2.5) located a few kilometers below the volcano was recorded on 18 November, ~2 weeks before the eruption. Microseismicity related to the very shallow explosivity of the volcano revealed a weak tendency to increase as the eruption approached. Preliminary analysis of the lava emitted in the first few days of the eruption indicated that the rock is a silica undersaturated shoshonitic basalt (SiO2 49.5%, Ne 1.1), containing phenocrysts of olivine, clinopyroxene, and plagioclase very similar to those erupted in historic time at Stromboli.

"The 6 December phenomena and their precise timing were reconstructed from eyewitness observations and photographs. Field investigations were performed 7-14 December and 29 December-4 January by Rosi and Sbrana (Univ of Pisa) and Giovanni Frazzetta (IIV Catania). Preliminary information on seismicity was provided by G. Neri (IIV Catania) and extracted from Biviano and others, 1985. XRF analysis of major elements was performed at the Univ of Pisa.

References. Biviano, A., Di Prima, S., Falsaperla, S., Marturano, M., Neri, G., Pellegrino, A., and Velardita, S., 1985, Relazione informativa sull'attività sismica a Stromboli: internal report to the National Group of Volcanology, CNR.

Capaldi, G., Guerra, I., Lo Bascio, A., Luongo, G., Rapolla, A., Scarpa, R., del Pezzo, E., Martini, M., Ghiara, M. R., Lirer, L., Munno, R., and La Volpe, L., 1978, Stromboli and its 1975 eruption: BV, v. 41, p.259-285.

Further References. De Fino, M., La Volpe, L., Falsaperla, S., Frazzetta, G., Neri, G., Francalanci, L., Rosi, M., and Sbrana, A., 1988, The Stromboli eruption of December 6, 1985-April 25, 1986: volcanological, petrological and seismological data: Rendiconti della Società Italiana di Mineralogia e Petrologia, v. 43, p. 1,021-1,038.

Falsaperla, S., and Neri, G., 1986, Seismic monitoring of volcanoes: Stromboli (southern Italy): Periodico di Mineralogia, v. 55, p. 153-163.

Information Contacts: M. Rosi and A. Sbrana, Univ di Pisa.

06/1986 (SEAN 11:06) Strombolian activity; small lava flows

. . . the Société de Volcanologie Genève (SVG) visited Stromboli in early April and observed continued lava production. On 3 April, two vents were active in the summit terrace. Strombolian activity at the main vent ejected tephra to 100-150 m height in explosions that occurred every 20-25 minutes. Explosions at 30-35-minute intervals from the second vent ejected only old material. An effusive vent in the upper NNE part of the Sciara del Fuoco (below and N of the main vent) quietly emitted two small lava flows. The main flow, ~1.5 m wide, moved N at ~0.5 m/s; its front was about halfway down the Sciara del Fuoco. The other flow was only 0.5 m wide and was moving more slowly, to the NNE. Activity the next day was similar, but the smaller lava flow had stopped advancing. On 5 April, Strombolian activity had declined; explosions were less frequent and tephra did not rise as far. One lava flow, ~2 m wide, was active, moving NNE at 1-1.5 m/s.

Information Contact: P. Vetsch, SVG, Switzerland.

09/1986 (SEAN 11:09) Intermittent lava fountains from summit lava lake after lava flow production ends; tourist killed near summit vent

"The effusive eruption [ended] on 25 April 1986. During the eruption, the effusive vent, at 680 m elevation on the NE side of the Sciara del Fuoco, showed a gradual decline in lava output rate. The decrease in lava output was accompanied by the development of many small flows that advanced tens to hundreds of meters downslope, often covering previously erupted materials. In the very final stage, the progressive accumulation of lava around the vent led to the growth of a small (10-m-high) exogenous dome. At the end of the eruption, the new aa lava field covered ~1/3 of the Sciara del Fuoco; despite its 37° slope, virtually all of the erupted material accumulated on the subaerial part of the edifice. At the end of the effusive phase, Stromboli returned to its normal state, with a persistent lava lake producing intermittent lava fountains in the summit craters.

"On 24 July, Dr. Perez Bastardas Albert, a 33-year-old biologist from Barcelona, Spain, was killed near the edge of the W crater while climbing the mountain with his brother (but without local authorized guides). According to ... local police ... and volcano guides, the two brothers were at the edge of the crater at about 1100 when an explosion took place. They ran away, but Dr. Perez was hit in the head by a falling block and died instantly ~15 m from the crater rim. Recovery of the body was performed the same day, but with some difficulty because of the risk of falling material."

Information Contacts: M. Rosi, Univ di Pisa; G. Frazzetta, IIV.

11/1988 (SEAN 13:11) Incandescent tephra from several vents

Geologists visited Stromboli in October and November. Surface temperatures associated with Strombolian and fumarolic activity were studied for comparison with remotely sensed data. Temperatures were recorded using a Minolta Cyclops 33 radiometer operating at [8-14 mm] wavelength.

Craters 1, 3, and 4 were estimated to be 45 m deep; the floor of Crater 2 was not seen. Crater 1 contained three active vents (figure 2). On 26 and 27 October, a circular pit ([vent 1-1]) 1 m in diameter contained lava that glowed bright orange in daylight. Infrequent incandescent scoria and gas eruptions from vent [1-1] closely followed activity in [vent 1-2], a rubbly surface ~3 m away. At 10-30-minute intervals, [1-2] was ruptured by violent emission of blue incandescent gases (visible only after dark) followed by glowing scoria ejection. Ejecta from [1-1] and [1-2] usually fell within the crater, but on one occasion fell several meters beyond the S rim. A 2-m-diameter glowing vent ([1-3]) almost continuously ejected spatter to 50 m height. The maximum brightness temperature for the lava surface in vent [1-3] was 835°C, although readings sometimes fell as low as 240°C (when taken through dense fumes that frequently accumulated within the crater).

Figure 2. Sketch of active craters at Stromboli, October-November 1988. Courtesy of C. Oppenheimer and D. Rothery.

On 28 October, vent [1-1] had increased in area four-fold but was no longer glowing visibly in daylight. Incandescent scoria, ejected at 5-30-minute intervals, usually fell inside the crater although medium-coarse ash often reached the crater rim. Tephra ejections were usually immediately preceded by brief, rapid, bluish-gray steam emission and a roaring sound. Vent [1-3] was faintly glowing in daylight. Separate activity at former site [1-2] was no longer evident.

When geologists returned 3-6 November, a large volume of dark scoria and agglutinate had accumulated within the crater. Two new incandescent cracks had developed near site [1-1] and sharp cracking noises, like pistol shots, were often heard. Activity was dominated by ~7 explosions/hour at site [1-1]. Two distinct eruption types (ejecting tephra well above the crater rim) were recognized: very brief, violent detonations expelling gases and comminuted scoria; and longer duration (5-10-second) ejections of incandescent, highly vesiculated bombs. Site [1-3] glowed brightly but erupted infrequently.

Crater 2 was inaccessible and could not be observed directly. The crater continuously emitted high volumes of thick white fume. An eruption on 28 October that ejected a brown ash plume may have originated from this crater. A very low inner wall separated craters 3 and 4, and it was difficult to determine the origin of some eruptions. Dirty-brown plumes, attributed to Crater 3, frequently reached a height of 200-300 m above the crater rim. Brief (3-8-second) powerful incandescent bomb ejections at 5-40-minute intervals deposited tephra onto the crater's outer flanks. Infrequent explosions, clearly from Crater 4, obliquely ejected incandescent scoria over the crater's E rim, accompanied by small mushrooming ash columns. On 5 November, two small glowing vents, a few meters apart, were observed on the crater floor.

Information Contacts: C. Oppenheimer and D. Rothery, Open Univ.

03/1989 (SEAN 14:03) Brief stronger explosions; one tourist injured

A series of explosions occurred in Stromboli's summit craters [26] March at [0927]. The explosions lasted a few minutes and were significantly more intense than the volcano's regular intermittent activity. Ejecta consisted of fluid bombs, blocks, and ash that were scattered within a few hundred meters of the vents. Tourists observing the volcano nearby were hit by the shower of tephra. No one was directly injured by the fallout, but a girl fell and broke her arm when panic caused a rush towards the village.

According to numerous eyewitnesses, the explosions began without premonitory activity. Seismic records from the Ginostra station (1.8 km from the crater) recorded no significant variation before or after the event. However, a slight increase in volcanic tremor amplitude and energy of seismic shocks was observed a few days before the explosions by a portable seismograph operating on the N flank (1.5 km from the vents). The rate of gas emission and frequency of explosions gradually returned to a normal level in the following days.

Further Reference. Falsaperla, S., Montalto, A., and Spampinato, S., 1989, Analysis of seismic data concerning explosive sequences on Stromboli volcano in 1989: Bolletino del Gruppo Nazionale per la Vulcanologia, 1989-1, p. 249-258.

Information Contacts: S. Falsaperla, G. Frazzetta, and E. Privitera, IIV; M. Rosi, Univ di Pisa.

09/1989 (SEAN 14:09) Explosions eject bombs and spatter

Geologists from Ruhr Univ . . . visited Stromboli 15-18 September. On 15 September between 1900 and 2100, 10 eruptions occurred from at least 3 vents, ejecting glowing spatter to 50-100 m above the crater terrace. No ash plumes were observed, and only two of the eruptions were audible from . . . Punta Labronzo, at 125 m elevation, ~2 km NNE of the craters near the N tip of the island.

Activity seemed comparatively weak and irregular during observations of the crater terrace from about 1730 on 16 September until 1000 the next day (from Pizzo sopra la Fossa, 918 m elevation). Small Strombolian explosions from at least four vents ejected bombs and spatter to <125 m above the crater rims; no ejecta reached the observation site, roughly 200 m from the vents. Individual bursts were separated by quiet intervals of 2-45 minutes. The SE walls of the active vents seemed to have grown unusually high. The southernmost vent ([1-1] or [1-2] on figure 2) was most active with about 3 explosions/hour, but bombs were rarely ejected significantly higher than the crater rim and were mostly directed obliquely S or SW, preventing close access to the crater terrace. Next to the most active vent was a second ([1-3] on figure 2) which apparently contained a lava lake. Although not visible, the lava lake's presence was suggested by a continuous glow and dull surf-like sounds. Geologists suggested that the two vents probably coalesced sometime after midnight on 17 September, as explosive activity from the first vent was much reduced and glow was also visible above it. Between 0900 and 1000, two brown ash plumes rose from the center of Crater 1 to perhaps 200 m above the vents, dropping some ash on the observation platform. A small ash plume was visible during the evening when the volcano was frequently observed from the E coast.

Craters 3 and 4 were less active, but one or two explosions/hour from Crater 4 produced the highest lava fountains (up to 100 m) and the longest eruptive episodes. Crater 3 erupted only three times during the observation period, but often made loud crashing noises without visible ejections. Two vents erupted simultaneously only once during the observation period ([1-1/1-2] and 4). No earthquakes were felt.

Information Contact: B. Behncke, Ruhr Univ, Germany.

10/1989 (SEAN 14:10) Frequent incandescent tephra ejection similar to 1988

During 5 October fieldwork, Open Univ geologists noted that morphology of the active craters appeared similar to that of late 1988. Crater 1 (see figure 2) was the most active, with two open vents at about the same positions as [1-1] and [1-3], both containing magma at or near the surface. Vent [1-1], which had developed a deeper intracrater, erupted at a mean interval of ~8 minutes [see also 15:08], often ejecting incandescent tephra over the crater's NE rim, and occasionally over the SE rim. Bombs rose as much as 150 m above the rim. Explosions from vent [1-3] were less frequent and less powerful. Crater 3 was also active, with eruptions at an average of once every 45 minutes, ejecting glowing bombs obliquely to the W, into adjoining Crater 2.

Information Contact: C. Oppenheimer, Open Univ.

04/1990 (BGVN 15:04) Lava fountaining and ash emission from several vents

Stromboli was visited on 29 March and 1-2 April. Poor weather on the 29th obscured the active summit vents until late afternoon, when six eruptive episodes were observed between 1745 and 1830. Five were accompanied by emission of dark gray to black ash plumes that rose 150-200 m above the two active vents. The activity produced lava fountains ~100 m high, often falling onto the Sciara del Fuoco. On one occasion, a large glowing block rolled down the NNW side of the Sciara to ~100 m below the vents.

Observations from the summit between 1730 on 1 April and 0200 the next morning revealed morphologic changes that had occurred in the vent area since September 1989 (14:09). Crater A [termed Crater 1 in previous reports; compare figure 2 and figure 3 below] included at least five vents, four of which were active. The vent that had been most active in September had collapsed, but a new deep vent that had formed 10-20 m to the NW produced an average of 2-3 eruptions/hour before midnight. Glowing spatter from the eruptions rarely escaped the vent, but black ash plumes rose ~100 m above the rim. Eruptions became more frequent and intense after midnight, with lava fountains rising to ~100 m above the rim, larger ash plumes, and heavy falls of bombs and spatter onto Crater A's NE rim (figure 4). Each of the eruptions was accompanied by a few seconds of deep but not very loud rumbling. In the NE part of Crater A, a cluster of open vents (several very small and three larger) contained active magma and glowed intensely at night. They emitted burning gases but no spatter.

Figure 3. Sketch map of the summit area of Stromboli showing vent configurations observed 1-2 April 1990. Courtesy of B. Behncke.
Figure 4. Oblique sketch of the summit area of Stromboli, looking roughly W. Courtesy of B. Behncke.

Crater B [coalesced from craters formerly termed 2, 3, and 4; compare figures 2 and 3 below] included at least 4 vents, and others were probably hidden from view by intense gas emission and topographic obstacles. In its center was a symmetrical spatter cone 10-15 m high with a glowing summit vent and a small steaming hornito near its SW base. The cone was covered with yellowish green sublimates and was not ejecting tephra. Vent 5, frequently active in September, erupted only once every 1-2 hours. Its eruptions lasted up to 30 seconds, sometimes consisting of several pulses of lava fountains that reached 100 m above the rim, accompanied by loud rumbling. Vigorous emission of gas (smelling strongly of H2S and [SO2]) from the E wall of Crater B obscured vent 5 from direct observation. Vent 4a, at most 2 m in diameter, was near the base of a steep pinnacle, possibly a hornito, ~10 m high. The vent produced very loud high-pressure gas emissions, sometimes lasting 20 seconds, every 20-30 minutes, feeding a very faint bluish gas column ~20-30 m high. A few were accompanied by ejection of several glowing blocks, probably from the conduit walls. A slight continuous tremor was felt from ~50 m away during one of the gas emission episodes. Vent 3, between craters A and B, remained inactive during the observation period.

During the afternoon of 3 April, ash emission reportedly became stronger and could be seen from villages on the SE and E sides of the island.

Information Contact: B. Behncke, Ruhr Univ, Germany.

08/1990 (BGVN 15:08) Strong explosions; one crater filled by tephra

An automatic telemetering short-period seismic station was installed near the active craters in October 1989 to monitor explosive activity and volcanic tremor. During that month, "normal Strombolian" activity from Craters 1 and 3 produced ~160 explosive events/day (figure 5). During the second half of November, several events with peculiar waveforms were recorded over a 4-day period. Volcano guides (who cooperate with volcanologists by noting visible activity, as reported below) observed a new cone inside Crater 1 in December 1989, and another cone that showed explosive activity between craters 1 and 2 in February 1990. In March, small cones produced bluish vapor inside Crater 3; emissions were accompanied by dull rumbling.

Figure 5. Average number of seismic events/hour recorded at Stromboli, October-November 1989 and April-July 1990. Arrow marks 18 June explosions. Courtesy of M. Riuscetti.

During the end of May and the first half of June (28 and 30 May, and 3, 4, 11, 13, and 15 June) "normal" activity was observed at craters 1 and 3 with continuous explosions and ejection of incandescent material to 10-50 m height. Crater 2 was not active during this period. Morphologic changes to the new cones in Crater 1 were not evident.

At least four large explosions occurred on 18 June between 1700 and 1710. Ejecta fell onto the NW flank's Sciara del Fuoco and ash emission could be seen from S. Bartolo village on the NE side of the island. The wall between craters 2 and 3 collapsed. After this episode, explosive activity with ejection of small glowing blocks was observed at Crater 2 (on 19, 21, 24, 25, and 28 June, and 2 July) with almost continuous noisy gas emission (on 25 June, and 4, 7, and 9 July). Craters 1 and 3 were active, with ejection of glowing material to ~100-150 m height (on 24 and 26 June, and 1, 3, 4, 5, 7, and 9 July).

An increase in the number of low-energy explosion earthquakes occurred 9-16 July, while tremor amplitude decreased slightly. The number of events saturating the seismometer then increased sharply, while low-energy shocks dropped to near the long-term mean (figure 6). Ash and lapilli emissions were continuous from the three craters, with increases in ejecta height and emission frequency after 19 July. The strong eruptive activity declined after 26 July. Crater 2 had been completely filled by tephra, but included two active vents characterized by synchronous noisy explosions. Activity at Crater 3 was dominated by prolonged silent ash emissions. Continuous strong explosions from Crater 1 have been observed since 1 August.

Figure 6. Top: detail of figure 5, showing daily average number of seismic events/hour recorded at Stromboli, 21 June-31 July, 1990. Bottom: number of events with amplitude ³ full scale (solid line) and average relative tremor amplitude (dashed line), 9 July-4 August, 1990. Mean values for the period are shown. Courtesy of M. Riuscetti.

Information Contacts: M. Riuscetti, Univ di Udine; volcano guides: Prospero Cultrera, Nino Aquilone, and Antonio Zerilli, Stromboli, Italy.

09/1990 (BGVN 15:09) Continued Strombolian activity; new vents

The number of explosions and seismometer-saturating events fluctuated during August, and were apparently inversely correlated (figure 7). The highest peak in saturating events, 86, occurred on 13 August. Average tremor amplitude increased during August, to 12% higher than in July.

Figure 7. Average number of seismic events/hour recorded at Stromboli, August 1990. The mean value for the period is shown. Courtesy of Marcello Riuscetti.

Explosive activity persisted in Crater 3, throwing cinders and ash to >100 m. Crater 2 resumed visible explosive activity with continuous rumbling 5-10 August, while Crater 1 showed fumarolic activity 6-13 August and explosive activity following the 13th. New vents opened in Crater 2's NW wall on 25 August, and subsequently in Craters 1 and 3 (figure 8). Lapilli and cinders continued to fill the craters, completely covering the two cones in Crater 1 (15:08).

Figure 8. Sketch from "Pizzo sopra la Fossa" looking NW at the summit of Stromboli, August 1990. Courtesy of Marcello Riuscetti.

Information Contact: M. Riuscetti, Univ di Udine.

10/1990 (BGVN 15:10) Strong tephra ejection; increased seismicity

At the end of August, explosive activity in Crater 1 became nearly continuous and tremor amplitude increased. The monthly average tremor amplitude was twice as high in September as in August. The daily number of events that saturated seismometers oscillated around a mean of 30 until 20 September before rapidly decreasing (figure 9). Saturating events and tremor amplitude reached a minimum during the first week in October, then remained at levels similar to those preceding the strong activity in the second half of July.

Figure 9. Number of seismometer-saturating events/day (solid line); and average tremor amplitude (dashed line) at Stromboli, mid-June to November 1990. Courtesy of M. Riuscetti.

Volcano guides reported the following activity. 1-6 September: Ejection of hot lapilli was continuous from vents 1 and 2 in crater C1 (figure 10). Violent explosions with ash emission (150-200 m high) occurred from C3. 7-12 September: Activity was similar from C1 and C3. Block ejection and gas emission took place from C2. 13-20 September: Ejection of hot lapilli and noisy gas emission occurred from C1, while continuous minor explosions ejected small blocks from C2. Tephra was filling C3, where 4 new vents were forming on 15 September. 21 September-4 October: Most activity was concentrated in C1 and C3, with frequent explosions ejecting hot lapilli to as high as 200 m.

Figure 10. Sketch from "Pizzo sopra la Fossa" looking NW at the summit of Stromboli, October 1990. Courtesy of M. Riuscetti.

Geologists visited the summit area 4-10 October. The activity was more vigorous than had been seen during 25 years of study at Stromboli. Strong explosions at 15-20-minute intervals fed powerful brown ash emissions that reached about 300 m height (from vent 4 of C3). Nearly continuous bomb ejection from vent 1 of C1 was evident at night and gases were red. Stronger explosions were synchronous from many of the vents in the 3 craters. Lava spilled out every few tenths of a second from one small cone (1) in C3. One vent (3) in C1 ejected gas nearly every second. Fumarolic activity was very intense, especially from the W rim of C3. At least 3 new vents had formed (3 in C1 and 2 & 3 in C3) with continuous whistling and rare explosions.

11-16 October: Activity continued, but with an apparent slight decline. 17-28 October: Observations from the summit area were not available, but seismicity and reports from a village at the foot of the volcano suggested decreasing activity.

Information Contact: M. Riuscetti, Univ di Udine.

11/1990 (BGVN 15:11) Vigorous tephra ejection and lava fountaining from summit vents

Although the eruption was apparently somewhat less vigorous in late October, activity observed by Boris Behncke on 7-8 November was stronger than during his previous visits in September 1989 and March-April 1990. Vigorous gas emission fed a dense plume that obscured the vent area during the day, but visibility improved after sunset and a clear view of the craters was possible after 2000 on 7 November. Although vent morphology had changed somewhat, vent configuration was much the same as in April.

The main focus of activity was a cluster of at least four vents in C1 (at the NE end of the summit crater group) that were almost continuously erupting. Intense bomb and spatter ejection started at 1717 on 7 November and continued for at least 2 hours, with loud roaring like a jet aircraft. The strongest eruptions occurred from C1's easternmost vent (1), site of nearly continuous bomb ejections in early October. On 7 November, vent 1 ejected lava fountains to 100 m height, often followed within seconds by eruptions from vent 3, the southernmost vent in C1. Individual bursts of spatter, mostly from vent 3, were accompanied by loud explosions; gas had been emitted from this vent nearly once a second in early October. Between stronger bursts, very small lava fountains were continuously active within vents 2 and 3. Spatter was ejected to ~20 m height every 10-20 seconds from vent 3 and another vent to the NE. At 0100 on 8 November, fountains rose 40-50 m from the latter vent, and loud roaring was continuing. None of the vents produced ash plumes after 1800 on 7 November. The former vent at the NE end of C1 had apparently ceased erupting and may have been buried by the growing cone at vent 1, a prominent feature that had been too small to be visible from the summit in April.

Eruptive episodes from C3 (at the SW end of the summit crater group) occurred about twice an hour, producing lava fountains that rose as much as 100 m, and sometimes diffuse brown ash plumes and light tephra falls onto the summit platform. Most episodes consisted of several pulses of fountaining over a period of ~30 seconds. A strong eruptive episode at 1710 on 7 November was followed by bursts of spatter at intervals of 10-20 seconds until 1717. Another particularly violent burst at 2000 covered most of the crater area with glowing bombs and spatter. An area of 3 pits in C3 that had contained actively degassing lava in April was occupied by two small (<1 m diameter) vents that emitted low fountains of spatter. Much of C3 had been filled with recent pyroclastics.

Information Contact: B. Behncke, Ruhr Univ, Germany.

12/1990 (BGVN 15:12) Activity drops to occasional explosions; seismicity declines

Strombolian activity, abnormally vigorous during early October, began to decline in late October, and reached "normal" levels by the end of November. On 23 November, weak fumarolic activity was observed on the W rim of Crater 3, and continuous rumbling punctuated by rare explosions were reported from vent 3 in Crater 1. No activity was observed in Crater 2. The average tremor amplitude and the number of major shocks decreased to levels lower than in June when the paroxysmal phase began (figure 9).

Information Contact: M. Riuscetti, Univ di Udine.

04/1991 (BGVN 16:04) Explosive activity from a single crater; strong seismicity

Explosive activity was at low levels from January through March, seldom exceeding the long-term average of six recorded explosions/hour (figure 11). Visits to the summit on 30 March and 9 April revealed that activity was restricted to Crater 1, and that the small cone 1 in Crater 3 had collapsed, forming a glowing red vent. The number of earthquakes exceeding instrument saturation level was quite high from the end of January to the beginning of February (~30/day), and 11-17 March (~19/day; figure 12). Average tremor amplitude returned to normal following a low in December.

Figure 11. Daily average number of seismically recorded explosion events/hour at Stromboli, January-March 1991. The mean value for the period is shown. Courtesy of M. Riuscetti.
Figure 12. Number of seismometer-saturating events/day (upper curve); and average tremor amplitude (lower curve) at Stromboli, January-March 1991. Courtesy of M. Riuscetti.

Information Contact: M. Riuscetti, Univ di Udine.

05/1991 (BGVN 16:05) More frequent explosions

The number of seismically recorded explosions increased briefly in late March and persistently from mid-April (figure 13). After mid-April, the number of earthquakes exceeding instrument saturation level decreased from an average of ~20/day since January to <2/day (figure 14). Tremor amplitude remained at "normal" levels (figure 14).

Figure 13. Average number of seismically recorded explosion events/hour at Stromboli, 15 March-15 May 1991. The mean value for the period is shown. Courtesy of M. Riuscetti.
Figure 14. Daily number of seismometer-saturating events (lower curve); and average tremor amplitude (upper curve) at Stromboli, 15 March-15 May 1991. Courtesy of M. Riuscetti.

Volcano guides reported infrequent small explosive activity at the 3 craters during visits to the summit on 10, 15, and 16 April, and 1 May. In early May, the first complete gas sampling at Stromboli was made during an inter-explosive phase at fumaroles (410°C) on the NW rim of the active crater complex (table 1).

Table 1. Chemical composition (in volume %) of fumarolic gases from Stromboli, early May 1991. Courtesy of M. Martini.

    Gas   Volume %

    H2O   60.29
    CO2   29.68
    H2S     --
    HCl    0.28
    HF     0.041
    H2      --
    N2     6.90
    O2     1.29
    B      0.0014
    Br     0.00017
    CO     0.00007
    NH4    0.00006
    CH4     --

Local residents reported a significant increase in the number of explosions on 19 May, after several weeks of weak activity. During a visit to the summit on the evening of 21 May, frequent strong explosions were observed at craters 1 and 3, with large ejections of incandescent material. Thirty explosions were counted between 2000 on the 21st and 0600 the next day. Many ejecta fell onto the N flank's Sciara del Fuoco. Crater 2 and the small cones continuously emitted gas and vapor.

Information Contacts: M. Riuscetti, Univ di Udine; M. Martini, Univ di Firenze; H. Gaudru, Société Volcanologique Européenne (SVE), Switzerland.

06/1991 (BGVN 16:06) Explosions eject glowing fragments and gas columns

The number of recorded explosion shocks remained elevated through late June (figure 15), with mean rates relatively stable near the long-term "normal value" of 6/hour. Average tremor amplitude declined slightly at the beginning of June while the number of saturating earthquakes rose sharply (figure 16). Volcano guides reported that the activity was concentrated at Crater 3, where explosions ejected glowing fragments and white gas columns that rose 100-200 m in late June. Explosions were rare from other craters, but tephra built small cones in Crater 2. White gas emission was continuous.

Figure 15. Average number of explosion events/hour at Stromboli, 18 May-21 June 1991. The mean value for the period is shown. At the end of May, the Mark L4 seismometer was replaced by a Willmore MK III set to a natural undamped frequency of 2 seconds, with the gain adjusted to keep the same overall amplitude response at 1 Hz. Courtesy of M. Riuscetti.
Figure 16. Average number of seismometer-saturating events (lower curve) and average tremor amplitude (upper curve) at Stromboli, 18 May-21 June 1991. Courtesy of M. Riuscetti.

Information Contact: M. Riuscetti, Univ di Udine.

07/1991 (BGVN 16:07) Continued explosions from two craters

The number and intensity of explosions has continued to fluctuate in recent months, with the average rate remaining slightly higher since mid-March. During a summit visit on the night of 31 July-1 August, >50 explosions were observed between 2100 and 0600. The strongest ejected incandescent material toward the edge of the summit area. Most of the explosions were from Crater 1, the rest from Crater 3, with only gas emission evident from Crater 2 and from a small cone. On this occasion and during other visits over the past several years, durations of precursory noises appeared linked to explosive vigor, with stronger explosions following noises lasting 3-5 seconds, whereas 1-2-second noises preceded weak explosions [see also 16:08].

Information Contacts: H. Gaudru, SVE, Switzerland; T. De St. Cyr, Fontaines St. Martin, France.

08/1991 (BGVN 16:08) Continued moderate explosive activity; gas data

Explosive activity was restricted to crater C1 (NE part of the summit area; figure 17) during 9 August fieldwork (by F. Iacop, Institute of Earth Sciences, Univ of Udine). C1's central cone ejected hot tephra at ~20-minute intervals, and as a result, it had grown more rapidly than the crater's other two active cones. Glow from two small radial fissures in crater C2 was clearly visible at night. Sustained noisy gas emissions occurred about once an hour. Volcano guides had reported that activity was concentrated in crater C3 (SW part of the summit area), but at its cone 1 only hot vapor emission was occurring, from two vents, on 9 August. Rare explosions, mostly ejecting tephra, took place at bocca 4. The average number of recorded earthquakes remained near the normal value of 6/hour in July, declining below that level in the month's last week (figure 18). Average tremor amplitude also remained relatively constant through the end of July, while large shocks nearly disappeared after a peak on 29 June (figure 19). [see 16:09 for 28-29 August observations].

Figure 17. Active craters at Stromboli as seen from the somma, 6 September 1991. Crosses mark small vents active during the 6 September fieldwork. Courtesy of the Société Volcanologique Européenne.
Figure 18. Average number of explosion events/hour at Stromboli, 22 June-31 July 1991. The mean value for the period is shown. Courtesy of M. Riuscetti.
Figure 19. Number of seismometer-saturating events/day (lower curve) and average daily tremor amplitude (upper curve) at Stromboli, 22 June-31 July 1991. Courtesy of M. Riuscetti.

Moderate activity was observed in early September, with explosive episodes about every 15 minutes at crater C3 and roughly hourly at C1. Activity increased in the 3 hours of observations after 2300 on 6 September, with many moderate to strong explosions from the SW part of C3. Ejections of incandescent bombs and scoria sometimes lasted several minutes. Thick white vapor plumes rose from C2 and a small cone in its center, while blue SO2-rich plumes emerged from several other vents. Explosions from C1 were vigorous, ejecting glowing fragments and dark brown columns that rose 200 m above the crater. C3's smaller explosive bursts, consisting of tephra-poor incandescent gas jets, were usually preceded by comparatively brief periods of increasing, noisy gas puffs; larger explosions that ejected a higher proportion of tephra followed longer intervals, with fewer or no precursory gas puffs. Geologists attributed this pattern to intermittent closure (by cooling) of the lava-filled conduits to gas-bubble rise from the underlying magma body, allowing higher pressure to build at depth.

Airborne COSPEC measurements by an Italian-French cooperative program in May-July indicated a total SO2 flux somewhat lower than that measured by the same means in 1980 and 1984 (1,000 ± 200 t/d average; Allard and others, in press), consistent with the current moderate activity. Geologists concluded that combined with microprobe determination of the initial and residual sulfur content of Stromboli's lava, the SO2 flux data require the degassing of 0.1 km3/year (average) of magma, three orders of magnitude more than the co-erupted volume. Thus, gas output is essentially derived from magma stored within the volcano. To assess the amount of diffuse magmatic degassing through the volcanic pile, other than from the craters, infrared mass spectrometric profiling of CO2 concentrations in the ground began on 11 September. High CO2 levels (80-90%), associated with subsurface thermal anomalies, were found to characterize the Pizzo sopra La Fossa crater terrace (at the summit rim, SE of the active craters). Concentrations gradually decreased toward the rim of this former crater, and no CO2 anomaly was detected in outer areas to the S (down to the Vancori rampart).

Reference. Allard, P., Carbonelle, J., Le Bronec, J., Metrich, N., and Zetwoog, P., Volatile flux and magma degassing budget at Stromboli volcano: Geophysical Research Letters, in review.

Information Contacts: M. Riuscetti, Univ di Udine; Patrick Allard, CNRS-CEA, France; J.C. Baubron, BRGM, France; H. Gaudru and Rolf Haubrichs, SVE, Switzerland; Yvonne Miller, Univ de Genève, Switzerland.

09/1991 (BGVN 16:09) Continued tephra ejection from several vents

Activity was moderate from August through mid-September, with occasional explosions from craters C1 and C3 (about 1-4 hourly/crater). During 1 August to 25 September, the average number of explosion shocks/hour gradually increased to the "normal" value of 6; (figure 20). Relatively low levels of activity lasted from mid-July to mid-August. The number of instrument-saturating events was low and concentrated on a few days during the second week in August, while average tremor amplitude remained relatively stable until it declined in late August (figure 21).

Figure 20. Average number of explosion shocks/hour at Stromboli, 1 August-25 September 1991. The mean value for the period is shown by the dotted line. Courtesy of M. Riuscetti.
Figure 21. Number of seismometer-saturating events/day (lower curve) and average daily tremor amplitude in volts (upper curve) at Stromboli, 1 August-25 September 1991. Courtesy of M. Riuscetti.

The following report from Jonathan Dehn and Boris Behncke, on 28-29 August activity, supplements information in 16:8. "During a visit to Stromboli's summit and craters on 28-29 August, the volcano, much less active than during visits in March-April 1990 and November 1990, was in a state similar to that observed in mid-September 1989. Eruptions came from only two vents, one at the NE end of C1 (figure 22), and the other in the center of C3. The former erupted frequently during the evening of 28 August producing fountains up to 150 m high. Such eruptions lasted at least 10 seconds and began without any noticeable premonitory signs. Bombs and spatter fell over much of the C1 area and into C2. After midnight on 29 August, explosions from this vent became much less frequent, averaging 1-2/hour. The other active vent produced ~2-4 explosions/hour but much lower fountains, and ejecta mostly fell back into C3. These explosions were often preceded by an increasingly bright glow from the interior of C3.

Figure 22. Sketch of Stromboli's crater terrace as seen from Pizzo sopra la Fossa, 28-29 August 1991. Features (such as cone at vent 3 in C1) are not to scale. Courtesy of J. Dehn and B. Behncke.

"During the night, four glowing but not erupting vents (1 and 2 in C2, and 1 and 2 in C3) could be observed, at the same positions as in late 1990. Two more vents (2 and 3) were visible within or near C1. Vent 2 appeared to be a larger pit created by collapse of the former vents 1 and 2. A symmetrical cone ~10 m high had been built around C1's vent 3, feeding a dense gas plume.

"C3 could be approached around daybreak (0530-0630) on 29 August, and observations of the crater's interior and its eruptive activity were made during a 45-minute period. The SW half of the crater was occupied by a pit ~50 m deep. This pit contained at least three active vents, of which two were open and displaying continuous glow and gas emission. Minor spattering from these vents occurred at times, often heralding eruptions from a third vent, in the center of the pit's floor, that was buried under a cover of bombs and scoriae. Eruptions from this vent fragmented the old overlying material, forming diffuse ash plumes followed by the ejection of fresh glowing spatter. All of the ejecta from C3 fell back into the pit and onto its walls, and slumping of material from the pit's walls commonly covered the vent within seconds after each eruption.

"Vents 1 and 2 (in C3) were also observed at close range. They contained small active lava ponds, or molten sulfur, and displayed pulsating gas emission. The ponds were located within a cavern, but no obvious vertical conduit was seen. The rim of C3 was covered with a thin coating of fine tephra and fresh Pele's hair, but no ejecta fell in this area during the stay on the crater rim. From 0630 until about 1100 (29 August), the end of the summit visit, eruptions were separated by intervals ranging from 10 to 40 minutes."

Information Contacts: J. Dehn and B. Behncke, GEOMAR, Kiel; M. Riuscetti, Univ di Udine.

10/1991 (BGVN 16:10) More frequent explosions; new zone of fumaroles

The number of recorded explosion shocks increased irregularly through October (figure 23), a continuation of the generally increasing trend that followed the low activity of mid-July to mid-August. Tremor amplitude also increased (figure 24). The number of seismometer-saturating events was quite low and concentrated during the last week of October, when tremor was stronger and explosions were more frequent.

Figure 23. Average number of explosion shocks/hour at Stromboli, 25 September-31 October, 1991. The mean value for the period is shown by the dotted line. Courtesy of M. Riuscetti.
Figure 24. Number of seismometer-saturating events/day (lower curve) and average daily tremor amplitude in volts (upper curve) at Stromboli, 25 September-31 October, 1991. Courtesy of M. Riuscetti.

A team from the Univ di Udine climbed the volcano during the first week in October. Two vents were active in Crater 1, the first near the E rim, the second a 30-m-high cone on its NW flank (facing the Sciara del Fuoco). Explosions produced plumes 100-150 m high, and ejected lapilli and sand-sized tephra. Crater 2 was still marked by two radial fissures with clearly visible night glow, but its rim was no longer well-defined. Cone 1 in Crater 3 continued to produce white vapor from two vents. The westernmost vent of Crater 3 appeared to be the most active, and was at the center of a rapidly enlarging chasm. It ejected clouds of black, sand-sized tephra to a maximum height of 300 m.

Along the ridge extending E from Pizzo sopra la Fossa (the observation point SE of the active craters), a zone that once consisted of a few isolated hot spots had evolved to a thermal anomaly in September (16:08) and a continuous line of fumaroles in October.

Information Contact: M. Riuscetti, Univ di Udine.

03/1992 (BGVN 17:03) Less-frequent eruptive episodes

Visitors ... in mid-March reported that activity was at a low level, with only a few eruptive episodes an hour. Despite frequent heavy rains, no dark, ash-laden phreatomagmatic eruption plumes were observed. When viewed from a ferryboat for about an hour during the morning of 18 March, the volcano erupted only once, shortly after 0730, otherwise emitting only a gas plume.

Information Contact: B. Behncke, GEOMAR, Kiel.

05/1992 (BGVN 17:05) Frequent explosions; increased seismicity

Seismic activity remained at a low level (around 100 explosions/day) from the beginning of 1992 through 8 April, when the seismic station was shut down for maintenance and conversion to a 3-component system. When operations resumed on 17 May, seismicity was unusually high, and the number of recorded events on 19 May was the largest since the station was installed in October 1989 (figure 25). Tremor amplitude briefly remained at November 1991 levels, but decreased rapidly beginning 20 May.

Figure 25. Seismicity recorded at Stromboli, January-May 1992. Open bars show the total number of seismic events/day, while solid bars tally those with ground velocities exceeding 100 mm/s. The line represents tremor energy computed using 60-second samples taken every hour, then averaged daily. Courtesy of M. Riuscetti.

Daily summit observations 10-19 May revealed that activity was concentrated in craters C1 (vent 1) and C3 (vent 4) with glowing tephra ejected to 100-150 m height. Noisy vapor emissions lasting 15-20 seconds, accompanied by modest spatter ejection, occurred from a fissure in C2, on the W rim. Very modest activity continued from the small spatter cone in C3.

During the night of 16-17 May, Beat Gasser saw activity from several vents. Loud explosions occurred ~4 times an hour from C1, ejecting lava to as much as 300 m height for 5-10 seconds. Several explosions typically occurred at intervals of 5-10 minutes, followed by ~30 minutes of repose. Between explosions, a steady red glow and lava spattering were visible inside the crater, with spatter seldom reaching the crater's outer walls. Spattering declined before explosions. Crater C2 produced noisy 10-15-second gas emissions about once an hour. Ejections of a few red tephra fragments from C2 were seen during the night. East of C2, a steady red glow was visible at night within a small vent that was the source of pulsing gas emissions at 3-second intervals. Eruptions occurred about twice an hour from C3, but like those from C1 were not evenly spaced. Two eruptions typically occurred roughly 10 minutes apart, followed by nearly an hour of quiet. The three active craters never erupted simultaneously, and their eruptions were separated by intervals of at least 5 minutes.

Information Contacts: M. Riuscetti, Univ di Udine; B. Gasser, Kloten, Switzerland.

06/1992 (BGVN 17:06) Small explosions and seismicity continue

Fieldwork during the first week in June revealed that eruptive activity was mainly concentrated in craters C1 (vent 1) and C3 (vent 4), which fed black plumes no more than 100 m high. Seismicity remained high in June (figure 26), near the 180 events/day reached in the last third of May. A minimum of 108 events was recorded on 24 June. After declining rapidly about 20 May, tremor energy returned to levels characteristic of the period since November 1991.

Figure 26. Seismicity at Stromboli, June 1992. Open bars show the number of recorded events per day, black bars those with ground velocities exceeding 100 mm/s. The curve represents the each day's average of tremor energies on hourly 60-second samples. Courtesy of M. Riuscetti.

Information Contacts: M. Riuscetti, Univ di Udine.

08/1992 (BGVN 17:08) Frequent weak explosions; tremor

Daily summit observations revealed frequent weak explosions and vigorous fumarolic activity in July and August. Tremor amplitude was constant, and seismic activity was slightly above average. Tremor amplitude, measured with hourly 60-second samples, generally averaged 0.4-0.6 v, with one day >0.7 v (3 July). There were >100 recorded seismic events per day throughout the period; 16 days had >200 events (4 August and 15-29 August); 16 and 26 August had >250. The last two weeks in August also had more strong shocks (ground velocities >100 mm/s), but no more than 50/day.

Information Contact: M. Riuscetti, Univ di Udine.

10/1992 (BGVN 17:10) Continuous spatter ejection; occasional vigorous explosions; seismicity increases

Fieldwork during the third week in October revealed that eruptive activity was mainly concentrated in crater 1, in the NE part of the summit area. Spatter ejection was nearly continuous and explosions were frequent from C1's NE vent. Rare strong explosions from vent 5 of C3 (SW summit area) fed black plumes about 200 m high. Strong noisy degassing occurred from C2, with some spatter emission from vents that had developed from pre-existing fissures. C1 had been partially filled with debris and the spatter cone in C3 destroyed.

Tremor energy and the number of earthquakes increased steadily in September and October (figure 27). The strongest activity was recorded 14-16 October with > 20 events/hour (20% with ground velocities exceeding 100 mm/s).

Figure 27. Seismicity recorded at Stromboli, September-October 1992. Open bars show the number of recorded events per day, the solid bars those with ground velocities exceeding 100 Nm/s. The curve represents tremor energy computed using 60-second samples taken every hour, then averaged daily. Courtesy of M. Riuscetti.

Information Contact: M. Riuscetti, Univ di Udine.

01/1993 (BGVN 18:01) Short series of violent explosions ejects tephra column

A short series of violent explosions occurred from the summit craters on 10 February at 1610 GMT, ejecting a large tephra column. Lithic blocks and lava fragments fell to 1 km from the summit, and heavy ashfall occurred at the village of Ginostra, ~2 km SW of the summit. Only weak degassing from the summit craters was visible during the next two days.

A sequence of three explosion earthquakes that occurred within <2 minutes of one another was recorded by the Ginostra station of the Aeolian Island Seismic Network, operated by the IIV. The last earthquake was followed by high-amplitude tremor that lasted for 8 minutes, then gradually declined. No other anomalous seismic activity was recorded during the succeeding hours, although spectral amplitude of tremor was remarkably low. No seismicity associated with the explosive activity was detected by any other stations in the IIV network. Tilt data from a shallow borehole station on the lower N flank (at Punta Labronzo) did not show any deformation suggesting significant magma storage in the volcanic edifice.

Geologists noted that the activity appears to be comparable to similar episodes in 1988 and 1989, thought to be caused by shallow gas accumulation building pressure in a feeder pipe.

Information Contacts: S. Falsaperla and L. Velardita, IIV.

02/1993 (BGVN 18:02) Seismicity and tremor resume after 10 February explosions

Seismicity between 1 November 1992 and 28 February 1993 was stable except for two episodes of heightened activity (figure 28). High tremor energy and >25 explosion-earthquakes/hour were recorded on 6 December. On 10 February, three strong explosions occurred followed by a sudden decrease of tremor to about one-sixth the energy and one-third the number of events. In the week preceding the 10 February explosions, a large number of strong shocks occurred, with a maximum of 76 on 7 February. After a few days of low seismicity following the explosions, tremor amplitude and the number of events gradually increased, reaching an isolated maximum on 22 February.

Figure 28. Seismicity recorded at Stromboli, November 1992-February 1993. Open bars show the number of recorded events/day, the solid bars those with ground velocities >100 mm/s. The lines show daily tremor energy computed by averaging daily 60-second samples. Courtesy of M. Riuscetti.

Information Contact: M. Riuscetti, Univ di Udine.

04/1993 (BGVN 18:04) Explosive activity increases; detailed description of crater

Steve Matthews and Abigail Church observed vigorous Strombolian activity on 22 April at two 20-m-high hornitos in crater C1 (figure 29). Incandescent gas explosions occurred at 3-10 second intervals, followed ~0.5 seconds later by ejection of spatter. Semi-liquid bombs up to 2 m across reached up to 100 m above the vents. Stronger activity from all three craters every 10-20 minutes consisted of gas emissions lasting as long as 15 seconds that ejected spatter as high as 250 m. These stronger events appeared to occur in pairs from craters C3 and C2. An explosion from C3's vent 4 was often followed a few minutes later by an explosion from vent 2 in C2. Within C1, these larger explosions were only produced from the NE hornito (vent 1). Many incandescent fumaroles were visible on the hornitos and the floors of all three craters. Small amounts of spatter were also ejected from the fumaroles during the strongest explosive episodes. At about 2030, shortly after sunset, lava was observed flowing slowly from a breach or bocca in the SW hornito (vent 2) in C1. When observations ended at 2200, the lava flow had divided and was beginning to form a moat around the hornitos.

Figure 29. Sketch of the summit craters and vents at Stromboli, 22 April (top), and 3 May 1993 (bottom). Crater walls could not be distinguished on 3 May due to the abundant gas and steam. Vent numbers are in parentheses. Field of view is ~200 m across. Courtesy of S. Matthews, A. Church, and S. O'Meara.

A high level of eruptive activity was reported by Steve O'Meara on 2-6 May. Roaring noises could be heard in San Vincenzo (~2.5 km NE) the afternoon of 2 May, which became periodic by late afternoon, occurring about once every 20-30 minutes. A gray fountain was observed from the lower NE slopes around 1830 that rose several hundred meters above the NE-most vent. Several strong explosions later that evening sent incandescent boulders rolling down the steep slope of the Sciara del Fuoco (figure 29). There were at least 8 vents active for several hours during summit observations the night of 3-4 May. Eruptive activity increased dramatically after the nearly full moon rose, peaked when the moon culminated in the southern sky, and waned before moonset. Lunar perigee (when the moon is closest to the Earth) occurred that night around 0100.

Vent 1 in crater C1 (figure 29) was a large dome-shaped mound with a summit crater and shallow floor filled with incandescent bombs from other vent explosions. Approximately every 30 minutes a powerful explosive blast, which sounded like a large cannon firing, violently blew the debris from the vent to heights of 200-300 m. Increased crater glow preceded these eruptions and most others. C1's vent 2 is a small cone with a peanut-shaped throat adjacent to and W of vent 1. This vent was continuously active with jetting sounds, blue flames, and spatter ejection. Thin streams of lava were erupted about every 5 minutes, with larger 100-m sprays of lava about every 15 minutes. Vent 3 in C1 (E of and adjacent to vent 1) exhibited continuous glow and erupted synchronously with either vent 1 or vent 2, ejecting material to a height of ~100 m. Occasionally, vents 1-3 would erupt together. Ejecta from vent 3 was directed slightly NE, while blasts from vents 1 and 2 were directed vertically. These explosions only lasted for a few seconds. Another less-active vent in C1, S of and adjacent to vent 1, also appeared to erupt synchronously with vents 1-3 to heights of tens of meters.

In crater C2, vent 1 had three glowing components, though only the western-most one produced sporadic minor eruptions, spraying lava ~10-30 m above its steep, narrow cone. Eruptions from vent 2 in C2 occurred every 30-45 minutes and lasted 20-40 seconds each. Eruptions began with a strong jetting sound, after which a thin spray of lava would shoot out, followed by more vigorous jetting and extensive lava production. Lava fountains reached heights of up to 150 m. Lava was visible in the vent for about a minute after each eruption, with the surface continually being fractured by escaping gases. The lava would then slowly sink into the vent until it was no longer visible, although glow remained.

Two small adjacent vents in crater C3 were each surrounded by wide, shallow cinder rims. Eruptions were more frequent at the W vent, where explosions sent material 300-400 m high about every 10 minutes during the most active periods. These eruptions occurred without warning and were accompanied by a loud roaring noise. The largest eruptions from this vent produced very broad, expansive plumes shaped like large evergreen trees, which reached 30 m above the summit of the volcano. Another vent farther S may also have erupted, but that area was obscured by fumes and steam.

The frequency of eruptions from each vent changed with time, but not the sounds, making it possible to know which vents were erupting. By the morning of 3 May, activity had declined to one large explosion and a couple of smaller ones approximately every 20 minutes. During the most active periods of the night, >20 strong eruptions occurred every hour. Activity increased again after moonrise on 4 May and remained strong into the early morning. Orange glow reflected by the clouds was observed that night in San Vincenzo. The next day, powerful eruptions continued from crater C3 and vent 1 in C1, but with less frequency. Vents 2 and 3 in C1 glowed but did not have any strong eruptions. Observations ended about 2400 on 5 May. Seven eruptions were seen from the ferry 2100-2200 on 6 May.

Marcello Riuscetti reports that Stromboli guides observed a new cone in crater C1 and renewed activity at the C3 spatter cone in mid-May. On 16 May a small lava emission occurred from the base of a cone in C3. During the night the flow traveled 30 m down the slope, reaching the feeding fissure of the 1985 eruption before stopping. The flow resumed 18 May, covering ~60 m of 1985 lava NE towards the Sciara del Fuoco. Strong tremor and frequent explosions accompanied the lava flow.

Seismicity (number and energy of shocks, tremor energy) increased in March and April after the low of 11 February (18:02). The level of seismicity was very high in April (figure 30), with nearly continuous explosions in the second and third weeks.

Figure 30. Seismicity recorded at Stromboli, March-April 1993. Open bars show the number of recorded events/day, the solid bars those with ground velocities >100 mm/s. The lines show daily tremor energy computed by averaging hourly 60-second samples. The number of daily events are off the scale for the 2nd and 3rd weeks of April due to the nearly continuous explosions during that period. Courtesy of M. Riuscetti.

Information Contacts: S. Matthews, Univ College London, London; A. Church, Natural History Museum, London; S. O'Meara, Sky & Telescope; M. Riuscetti, Univ di Udine.

05/1993 (BGVN 18:05) Strombolian activity decreases

The strong Strombolian activity that accompanied the 18 May eruptive phase had stopped by 28 May. Observations on 20 May revealed the end of lava emissions, intense Strombolian activity from the active vents of Crater 1 (E crater), and degassing from Crater 3 (W crater). Two cones were built by Strombolian activity inside Crater 1. The smaller one, only a few meters high, is located near the E rim. The second, located in the W part of Crater 1, was about 10 m high. Strombolian activity was continuous in the small E cone, with ejection of bombs to a few meters, but was discontinuous and stronger in the W cone. Frequent explosions sent incandescent juvenile scoriae to 100 m above the crater rim; they fell up to tens of meters away from the rim. Significant ejections occurred at intervals of about 8-10 minutes. The funnel-shaped bottom of Crater 3 was obstructed by material, resulting in strong bursts of gas at intervals of 20-30 minutes that formed a column up to 100 m high. The column consisted of brown, non-juvenile dust and blocks that fell back into the crater.

The intensity of Strombolian activity at Crater 1 was lower on 27 May than during the previous visit, with fewer explosions and a decreased volume of ejected material. However, gas explosions at Crater 3 were continuing with the same frequency and intensity. No sounds indicative of Strombolian activity were heard during about one hour of observation 28 May. Only weak degassing was observed from the vents in Crater 1. The degassing was interrupted at intervals of 15-20 minutes by noisy gas explosions that formed a plume up to 100 m high composed of brown, non-juvenile dust and a few scoria blocks. At Crater 3, activity was similar to previous visits, with gas explosions and brown dust emissions at intervals of 20-30 minutes.

Information Contacts: S. Calvari, IIV.

09/1993 (BGVN 18:09) Eruptive activity and seismicity decline from high levels in May; two strong explosions in October

After the eruption of a small lava flow in mid-May accompanied by high seismicity, there was an abrupt decay of seismic activity back to "normal levels" in early June (figure 31). Stromboli guides reported very low activity at the craters, with rare ejection of black ash from crater C3 and spatter from C1 during May to August. Two strong explosions felt at 0210 on 16 October destroyed the small spatter cone in C3 that was built during the October 1990 eruption. Large blocks and spatter up to 2 m in diameter were ejected as far as 500 m from the crater, and reddish ash fell on the NW slope of the volcano along the Sciara del Fuoco. One woman was injured by hot ashes while sleeping near the crater area, and some bushes caught fire along the slopes. Tremor had begun to increase around 1100 of the previous day and then fell below the detection limits of the instruments one hour after the explosions.

Figure 31. Seismicity recorded at Stromboli, May-August 1993. Open bars show the number of recorded events/day, the solid bars those with ground velocities >100 microns/second. The lines show daily tremor energy computed by averaging hourly 60-second samples. Courtesy of M. Riuscetti.

Information Contact: M. Riuscetti, Univ di Udine.

10/1993 (BGVN 18:10) Explosive activity ejects lithic fragments and large bombs

An eruptive episode in the early hours of 23 October produced some strong explosions at both Crater 1 and Crater 2, ejecting spatter and lithic clasts. Two people who spent the night near the summit were injured by incandescent material during the explosions. Crater 1 (the easternmost of the summit craters) ejected bombs that measured up to 2 m across. Many bombs fell as far as 500 m from the craters and formed a deposit that covered the area near the vents. The eruption also destroyed an E-W line of small Strombolian cones in the crater, formed by activity in May. At least two explosions in Crater 2, with minor magmatic contributions as inferred by abundant lithics, produced a wide chasm and a small pit crater. Quiet gas emissions, with no Strombolian activity, continued through October.

Explosions from Crater 3 a week earlier, on 16 October, ejected large blocks and spatter up to 500 m from the crater. Ashfall from the Crater 3 explosions injured one woman sleeping near the crater area. Activity from mid-May through August was very low, with rare ejection of black ash from Crater 3 and spatter from Crater 1. Guides reported small explosions and negligible fumarolic activity in September. Seismicity dropped abruptly in early June, and had declined to a level of <150 events/day throughout the second half of September.

Information Contacts: S. Calvari, IIV; M. Riuscetti, Univ di Udine.

01/1994 (BGVN 19:01) Seismicity continues to rise following October explosions

A sudden decrease in seismicity followed the explosive episodes of mid-October 1993. Both number of recorded events and tremor level declined to below "normal" levels (figure 32). This pattern is similar to that observed after other explosive episodes in February and May 1993. Although problems with solar panel efficiency resulted in data loss during December, an increase in seismicity was still evident through December 1993 and January 1994.

Figure 32. Seismicity recorded at Stromboli, October 1993-January 1994. Open bars show the number of recorded events/day, the solid bars those with ground velocities >100 microns/second. The lines show daily tremor energy computed by averaging hourly 60-second samples. Courtesy of R. Carniel.

Information Contact: R. Carniel, Univ di Udine.

03/1994 (BGVN 19:03) Normal Strombolian activity; crater descriptions

"On two of three visits during 9-12 March, very detailed observations of crater morphology and eruptive activity were made. The volcano continues its millennia-long eruption; the intensity of the current activity is considered normal and characteristic of Stromboli's persistent activity. A brief visit to the Pizzo Sopra la Fossa (figure 33) was carried out on the afternoon of 9 March, but due to dense weather clouds few visual observations were possible. The noise of explosions was audible every 10-15 minutes, and continuous lava splashing could be heard. Breaks in the cloud cover revealed vigorous degassing in the entire crater area.

Figure 33. Sketch map of the crater area at Stromboli. Bold numbers indicate craters, smaller numbers are vents. Courtesy of B. Behncke.

"The second summit climb and overnight stay was undertaken during much improved weather conditions, from about 1700 on 10 March until 0700 the next morning. The active craters were observed from the beginning of the visit until 0200 on 11 March. Observations were made at close range from the rim of crater 3 (the SW-most active crater) from 2130 until 2300. Eruptions from at least 3 vents all produced largely ash-free lava fountains that rose <=150 m. Vent 4 in Crater 3 (figure 34) ejected low lava fountains about every 10 minutes between 1700 and 2000, but then remained inactive for several hours. The eruptions made little noise, similar to eruptions from the same vent during visits in September 1989, March and November 1990, and August 1991. Another vent (1 & 2) was present in the NE part of Crater 3, at the location where several small incandescent pits and conelets existed in 1990-91. However, there is now a larger and deeper pit with much more vigorous activity. The pit is roughly circular and has a diameter of about 30-50 m; its bottom (and active bocca) is not visible from any accessible place on the crater rim. Nonetheless, it appears probable that there is an active, vigorously spattering lava pond in the pit.

Figure 34. Sketch of Stromboli's crater 3 seen from the SE rim of crater 1, 12 March 1994. Made from a composite photograph. View is to the SW. Courtesy of B. Behncke.

"During the 90-minute observation from the crater rim, remarkable fluctuations in pit activity were seen. There would be a period of very low-level activity (up to 5 minutes long) when little or no spatter was thrown above the pit lip. Then bombs and spatter would be obliquely projected against the S wall of the pit for several minutes. This was followed by more vigorous vertical fountains of gradually increasing height. For ~ 10-20 minutes there would be a stupendous display of such fountains until a sequence of very large fountains (up to 100 m high) marked the end of increased activity. The heat of the large fountains could be felt on the crater rim; fortunately, no bombs fell closer than 25 m to the vantage point. Three such large fountains, or fountaining sequences, were observed during the stay on the crater rim.

"Crater 2 was inactive and not visible, but vent 4 at the SW end of Crater 1 had very violent and loud eruptions every 20-30 minutes, sometimes at shorter intervals. These eruptions began instantaneously with crashing sounds and ejection of a very thin, tall, vertical incandescent column. Within ~1 second, another fountain would shoot obliquely from a second vent a few meters away and jet right through the first column; these eruptions lasted <5 seconds. Several of them were followed within the next few minutes by a series of up to four more eruptions of gradually decreasing intensity. Many bombs from the oblique fountains fell into the adjacent pit with continuous spattering. Similar activity continued after our departure to make observations from Pizzo Sopra la Fossa. Loud crashing noises from vent 4 of Crater 1 were frequently heard during attempts to sleep below the observation platform and the next morning when descending towards the village of Stromboli.

"The summit was climbed a third time during daylight on 12 March, and a visit was made to the craters from 0900 until 1100. All of the craters are significantly deeper than during visits in March 1990 and August 1991. The pit (vent 1 & 2) in Crater 3 (figure 34) was still continuously spattering and ejecting small lava fountains, but there were fewer large fountains. Vent 4 in Crater 3 ejected low lava fountains ~ 3 times, but was hidden by dense gas-and-steam clouds most of the time. Striking changes have occurred in Crater 1, probably during the violent explosions of October 1993. All cinder cones observed within this crater in 1990-91 have vanished; now there is an elongate chasm up to 60 m deep that appears to have a large but inactive fissure on its floor. An irregularly shaped vent in the NE portion of the crater, not active 10-11 March, erupted several times. These eruptions had durations of up to 30 seconds and produced low (~50 m) fountains mixed with very dense steam-and-gas plumes and accompanied by relatively loud rumblings. The gas plumes made the stay on the crater rim inconvenient but did not cause other problems.

"The most impressive eruptions came from vents 3 & 4 at the SW end of Crater 1. These vents lie within a larger depression of highly irregular shape; one bocca continuously emitted a bluish gas column at high pressure from a mouth maybe 2 m in diameter. Most eruptions came without any warning, especially when gas plumes caused poor visibility. However, several were preceded by brief roaring noises. The eruptions themselves began with immense crashing noises that were heart-rending at a distance of <= 50 m. Initially a diffuse ash plume would boil up from vent 3 and turbulently shoot to ~ 50 m, then large but continuously fragmenting incandescent lava lumps would be ejected at extremely high velocity. Great turbulence within the rising fountain violently tossed and turned the bombs, which therefore did not travel along the parabolic trajectories commonly observed during Strombolian eruptions. At times there were very loud but brief gas emissions from this vent that did not develop into eruptions; one particularly violent eruption was followed by several minutes of powerful degassing.

"After the end of the 12 March summit visit, ash plumes from vent 4 in Crater 1 became more common. During departure from the island on the morning of 14 March, a dense brown ash plume rose several hundred meters above the weather clouds that covered the summit."

Information Contact: B. Behncke, Geomar, Kiel, Germany.

06/1994 (BGVN 19:06) Variable seismicity, but generally low; moderate-low activity in late May

Visual observations made by volcano guides in April indicated moderate activity, in terms of both the number and vigor of the eruptions; pyroclastic material rarely reached the crater rims. Field work was carried out by R. Carniel, F. Iacop, and G. Salemi (Univ of Udine) during 21-26 May to study the correlation of external activity with seismicity. Activity at the middle crater (C2) during this period consisted of fumarolic emission, without explosions or strong degassing. The lava pond in the pit of the SW crater, C3 (19:03), displayed almost continuous spattering. This activity could be distinguished by short intervals of noise during the day, and by the red light reflected by gas above the vent at night. Neither the surface of the pond nor the fumarolic vents could be seen. Two other vents closer to the SW rim of C3 were also active. The first exhibited moderate explosions. The other produced a few small explosions on 22 May, but much more vigorous activity on 24 and 25 May during the peak of tremor (figure 35), with high, black, mushroom-shaped columns; pyroclastic material fell well beyond the SW crater rim. Within the NE crater (C1), two active vents were observed. The first, in the front towards the Sciara del Fuoco, was characterized by very high and long-lasting explosions (up to 40 seconds). The second, near the boundary with C2, produced smaller explosions; during the night a pale reddish light could be seen that intensified a few seconds before the explosions began.

Figure 35. Seismicity recorded at Stromboli, May-June 1994. Open bars show the number of recorded events/day, the solid bars those with ground velocities >100 microns/second (instrument saturation level). The line shows daily tremor energy computed by averaging hourly 60-second samples. Courtesy of Roberto Carniel.

Following increased seismic activity in December 1993 and January 1994 (19:01), seismicity was fairly constant through February and early March (<150 events/day), except for a brief increase during the last week of February (150-200 events/day). On 10 March, the number of seismic events/day increased into the 200-250 range, and remained at that level through the end of the month. Starting on 12 March, tremor energy showed a general decrease, and the number of stronger seismic events increased. This pattern has been observed several times in the past. The summit visits by Boris Behncke on 9-12 March (19:03) took place during a period of higher seismicity and tremor energy. Seismicity decreased again on 28 March to around 200 events/day, and by 10 April the rate had declined to ~ 150 events/day; it remained stable at that level for two weeks. Tremor amplitude during this time fluctuated, but generally seemed to decrease. Tremor energy increased abruptly on 25 April, just two days before the number of daily events again decreased.

During May, tremor energy decreased and the daily number of events increased compared to April, peaking at 173 events on 8 May (figure 35). Tremor energy increased from 14 to 24 May before steadily decreasing in June. The number of recorded events increased in June, with a maximum of 175 on 10 June, and there were a considerable number of larger events. Larger events are defined as those with ground velocities >100 mm/second, saturating the seismic station located very close to the crater area.

Information Contact: R. Carniel, Univ di Udine.

09/1994 (BGVN 19:09) Intense activity from ten vent locations

Extraordinarily intense activity was observed 21-22 August during an ascent and 8 hours on the summit (Pizzo sopra la Fossa). Significant morphologic changes had taken place in the crater area since March 1994 (19:03). Due to the vigorous activity, the craters could not be approached; however, the position and shape of eruptive vents were visible due to the filling of the craters. During the observation period, 10 boccas produced eruptions (compared with 4 in March), most of which were generally clustered and showed sympathetic to simultaneous activity. There were rarely any 10-minute intervals without eruptions, and for periods of up to several hours there was continuous lava fountaining from up to 3 vents at the same time. There was no regularity in the succession, size, or timing of the eruptions. Crater 2 was inactive.

Crater 1, the NE-most active crater, had 6 active boccas, most of which had formed spatter cones. None of these cones had been present during the crater visits in March; during the present visit, however, Crater 1 was filled almost to its rim with cones and erupted pyroclastics. Growth of these spatter cones since March had been much more vigorous than the formation of the earlier cones (1986-93), which were destroyed by explosions in October 1993. Only 5 months before this visit, Crater 1 had been a deep (>60 m) chasm, with no indication of incipient cones. The new cones were, after only 5 months of growth, larger than the pre-October 1993 cones.

The northernmost two vents, 1A and 1B, formed a broad, flat cone ~5 m high that displayed continuous incandescence. Vent 1A formed a crater 5-10 m wide on top of the cone and was the site of frequent brief lava fountains, but also had periods of quasi-continuous lava jetting and spraying. The focus of the explosions was apparently very close to the surface judging from the broad angle of the jets that sprayed large clumps of lava over a wide area, thus contributing to the broad, flat shape of the cone. The largest fountains from 1A rose higher than Pizzo sopra la Fossa, maybe to heights of 250 m. Vent 1B on the NE flank only became active towards the closing stages of the largest eruptions of 1A, ejecting a narrow fountain obliquely NE.

A cluster of vents was present in the central part of Crater 1, the most active among them (2A) was located on top of a tall, steep, spatter cone about 20-25 m high. Vent 2A (diameter <=3 m) was the site of activity ranging from continuous spattering to vigorous, long-lasting fountains that reached heights >250 m. There were at least four periods of continuous and vigorous fountaining, at 1930-2000, 2300-2400 (21 August), 0100-0200, and 0700-0800 (22 August), spraying rapid successions of lava 100 m above the vent and producing a continuous loud roaring sound. All fountains from 2A were vertical and relatively narrow. Frequently the entire cone was covered by cascading spatter forming small, rootless flows. Towards the morning of 22 August, the upper ~3 m of the cone was destroyed by vigorous gas emissions and explosive fountaining. Vent 2B, on the SE flank of cone 2A, was somewhat wider (<=5 m) and had formed a low, flat conelet. Its activity was restricted to minor oblique ejections of spatter towards the E that always preceded major activity from cone 2A. A very small incandescent vent (2C) was present on the S flank of 2A; it did not eject any solid material.

In the SW sector of Crater 1, two similarly shaped spatter cones (3A & 3B) were each ~10 m high. They were at the site of the twin boccas of March (labeled #4 at that time). The activity of these boccas was stupendously symmetrical, producing a pair of equally shaped narrow, tall (> 100 m) vertical fountains of equal height, initially of bluish burning gas followed by the ejection of lava fragments. Magmatic eruptions lasted up to 15 seconds and were accompanied by very loud crashing noises.

Crater 3, largely filled with new pyroclastic material, had two principal eruptive sites that had not developed into cones due to the wide dispersal of ejecta beyond the crater. Vent 1 lay in the NE part of Crater 3, at the site of the pit containing the active lava pond 5 months earlier. The vent was very small (<=3 m diameter) and had built a low mound of very large agglutinated bombs to above the almost level surface of pyroclastics filling the crater. Activity from this bocca was highly irregular, with repose periods of >30 minutes, and continuous fountaining episodes up to 60 minutes long. Larger fountains every 10-45 minutes sprayed incandescent tephra up to 150 m high. During periods of continuous fountaining, the focus of the explosions migrated towards the surface, as evidenced by the increasingly wide angle of the fountains. The vent area was covered by a continuous sheet of incandescent spatter, but no lava outflow took place.

The most impressive eruptions took place from a cluster of three closely spaced, continuously incandescent vents (2) at the SW end of Crater 3, probably corresponding to vents 3 and 4 in March (19:03). Eruptions began instantaneously and sent very broad jets to heights of up to 300 m, covering an area far beyond the crater rim. During daylight, some of these eruptions produced spectacular plumes that rose up to 500 m above the vents (350 m above the summit). The eruptions made little noise, but sometimes produced heat waves that could be intensely felt on Pizzo sopra la Fossa. At times, two eruptions occurred within a 5-minute period, whereas others were separated by up to 60 minutes.

During the week preceding and 10 days after the visit, occasional large ash puffs (up to 350-400 m above the summit) were seen from neighboring islands, and frequent lava fountains were seen at night from N Lipari Island (26 August) and Alicudi Island (30-31 August), indicating that Stromboli was in a state of increased activity at least from mid-August until the end of the month.

Information Contacts: G. Giuntoli and B. Behncke, GEOMAR, Kiel, Germany.

10/1994 (BGVN 19:10) High seismicity during July-September; eruptive activity described

Following the slow decrease of tremor energy during June, all seismicity increased in July (figure 36). Tremor energy reached an unusually high peak on 27 July; at the same time, a peak in the number of events was recorded. Although more events were recorded on 19 July (864), that was a period of almost continuous explosive activity. A considerable number of saturating events were recorded after 20 July. Volcano guides observed very strong external activity, with pyroclastic material often reaching the usual tourist zones. A decline in tremor energy was observed after 10 August; a slow increase then followed, reaching a new maximum at the end of the month. The number of recorded events followed a similar trend. Another major decrease in tremor energy characterized the first half of September; later fluctuations remained in a "low-energy" range. Vigorous eruptions seen on 21-22 August occurred during a period of low seismicity compared to late July and late August.

Figure 36. Seismicity recorded at Stromboli, 27 June-29 September 1994. Open bars show the number of recorded events/day, the solid bars those with ground velocities >100 Nm/s (instrument saturation level). The line shows daily tremor energy computed by averaging hourly 60-second samples. The seismic station is located 300 m from the craters at 800 m elevation. Courtesy of R. Carniel.

Observations of crater activity were made by R. Carniel (Univ of Udine) during field work with R. Schick (Univ of Stuttgart) and collaborators at the end of September and early October. Similar observations were made by geologists from Open Univ during 1-13 October, with detailed explosion counts for 3 hours on 1 October, 4 hours on the 5th, and one hour on the 9th. Explosions sent incandescent ejecta, ash, and/or gas to heights of <=300 m, from as many as 10 active vents (figure 37). No active vents were observed in Crater 2, but a hornito (2/1) was visible, and there was minor degassing from an unknown source. Brightness temperatures of fumaroles along the zone E of the Pizzo Sopra la Fossa (39-77°C) were measured by Open Univ geologists with a Minolta/Land Cyclops Compac 3 hand-held radiometer (8-14 mm).

Figure 37. Sketch map of the active craters at Stromboli, 1-13 October 1994. Courtesy of A. Harris [and A. Maciejewski].

Within Crater 1 in late September, Carniel noted three cones ~25 m high that had been built during the very strong activity in July and August (1/5, 1/6, & 1/7; figure 37). Continuous red glow at night could be seen from the top of each. Two other Crater 1 vents were active, the first (1/4) producing short, lateral explosions with large pyroclasts ejected onto the Sciara del Fuoco, and the second closer to Pizzo producing longer and higher explosions (<=200 m). Directed explosions suggested the possibility of a third vent close to the second one. When one of the two W-most cones in Crater 1 erupted (typically with strong degassing and little pyroclastic material) the other exhibited weak degassing. When the second vent erupted, the red glow from the remaining cone strengthened, sometimes with minor degassing.

Crater 1 contained six active vents during visits by Open Univ scientists. Explosions from vents 1/1 (~2/hour), 1/2 (4-9/hour), and 1/3 (0-2/hour) sent incandescent ejecta, occasionally with ash, to heights of 30-250 m. Glow was seen above 1/1 and 1/2 on the night of 5 October. Up to 40% of the ejecta from 1/2 and 1/3 fell outside of the crater area. These explosions were often followed by a gradually fading gas-jet noise of variable length. Explosions seen by the Open Univ team from 1/4 (2/hour) sent incandescent ejecta, including bombs and spatter, 30-150 m E onto the Sciara del Fuoco. On 5 October hornito 1/5 was the source of gas-jet eruptions, and a small amount of incandescent ejecta rose ~50 m; during 10 October more ejecta were seen in 100-m-high gas jets. Hornito 1/7 constantly degassed, and its summit vent was incandescent with a continuous gas flare 1-2 m high. On 10 October this flare increased 1-2 seconds before vent 1/3 erupted. Hornito 1/6 and vents 1/8 and 1/9 vents were only degassing.

The lava pond in Crater 3 had become a small spatter cone (3/2) when observed by Carniel, with a hole through which magma could be seen; activity was limited to degassing. One vent produced high, black, mushroom-shaped columns, and the second (in front towards Pizzo) sent pyroclasts >200 m above the craters. The opening of a new vent was also observed. Explosions from Crater 3 on 28 September were stronger, although less frequent, than from Crater 1. On 5 October the same sequence was observed, with the second vent exploding first and fewer pyroclasts ejected near the end of the explosion by a very small vent to the right of the older one. Guides reported that this vent was first observed on 1 October, when similar explosions from the small vent ejected spatter.

Open Univ geologists noted that only vent 3/2 was active on 1 October, with 3 emissions/hour of brown ash and blocks. By 5 October the quantity of ash emitted had decreased, but the amount of incandescent ejecta had increased, and more frequent explosions (5/hour) were accompanied by loud detonations. Ejecta rose 80-300 m, with some material landing outside of the crater or on the inner crater wall. During night observations on 5 October vent 3/2 would start erupting ~1-3 seconds after 3/1. On 8 October, Crater 3 released gas, sometimes accompanied by minor amounts of ejecta <30 m above the crater rim, and small brown ash clouds 30-100 m high. Similar activity on 9 October was accompanied by an increasing amount of brown ash and incandescent ejecta. During 1 October small lava fountains from vents 3/3 and 3/4 were simultaneous with gas emissions from 3/3. Vent 3/4 was also continuously active with puffs of gas (~1/second). The interior of vent 3/4 was incandescent by day, and glow was observed above 3/1, 3/2, and 3/3 at night. During the night of 5 October the brightness temperature of 3/4 was measured as 873°C, using a Minolta/Land Cyclops 152 hand-held radiometer (0.7-1.1 mm), similar to October 1988 (13:11). Incandescent gas puffs were seen above 3/4 during the night of 10 October. Only minor gas emission was observed from vent 3/5.

Information Contacts: R. Carniel, Univ di Udine; A. Harris and A. Maciejewski, Open Univ.

01/1995 (BGVN 20:01) Seismicity low and stable in late 1994

After the decrease in tremor intensity that characterized the first half of September, seismic activity generally remained stable from the end of September to mid-December (figure 38). Tremor intensity remained fairly constant, and the number of recorded events was consistently ~300/day. In contrast, the number of major events (ground speed >100 µm/s) started increasing in October and reached a maximum of 141 shocks on 14 November, which represents 38% of the total number of recorded events. This could suggest a greater source depth for the explosions, although visual observations are needed to support this hypothesis. The number of major shocks then decreased to "normal" values during late November and early December.

Figure 38. Seismicity recorded at Stromboli, 1 October-9 December 1994. Open bars show the number of recorded events/day, the solid bars those with ground velocities >100 µm/s (instrument saturation level). The line shows daily tremor energy computed by averaging hourly 60-second samples. The seismic station is located 300 m from the craters at 800 m elevation. Courtesy of Roberto Carniel.

Information Contact: R. Carniel, Univ di Udine.

04/1995 (BGVN 20:04) Explosion on 5 March and tremor; crater observations

Due to funding problems, the power supply to the 3-component summit seismic station maintained by the University of Udine was interrupted from 10 December 1994 until 13 January 1995. The previous report (BGVN 20:01) described seismic activity through 9 December. This station has been operating since 1989, but may be permanently shut down in June if funding is not continued.

Stromboli island was visited by Giada Giuntoli and Boris Behncke on 19-24 April. Generally, the volcano showed much less activity than during a previous visit in August 1994, but an increase was evident on 23 April, resulting in the resumption of eruptions from Crater 1, which had been inactive for several weeks. Behncke also provided a review of crater morphology changes since 1989.

Seismicity, early 1995. Throughout 13 January-4 April the daily number of shocks remained roughly constant at 200-400 (figure 39). On 26 February tremor intensity began to decrease, and for a few days its average value remained stable below 3 Volts x seconds (Vs). However, the number of major shocks remained high. On 5 March a large explosion accompanied the return of tremor intensity to more usual values of around 5 Vs. The explosion threw pyroclastic material towards Forgia Vecchia and Fossetta, a depression SW of the crater area. The ejecta rose high enough to be clearly seen from the village of Stromboli, where the explosion was strongly felt. Tremor level continued to increase following the explosion; after a short decrease it quickly increased again to a peak of 10.8 Vs on 30 March. The number of major shocks decreased after 13 March. The increase in tremor intensity after the 5 March event did not match the behavior recorded after the explosions of 10 February 1993 and 16 October 1993 (BGVN 18:01, 18:02, and 18:09). On those occasions a remarkable decrease of all seismicity, and of the tremor level in particular, was noted immediately afterwards.

Figure 39. Seismicity recorded at Stromboli, 13 January-4 April 1995. Open bars show the number of recorded events/day, the solid bars those with ground velocities >100 micron/s (instrument saturation level). The line shows daily tremor energy computed by averaging hourly 60-second samples. The seismic station is located 300 m from the craters at 800 m elevation. Courtesy of Roberto Carniel.

Activity on 20 April 1995. During a summit visit on 20 April between 0000 and 1500, activity was low compared to previous visits (September 1989, March and November 1990, August 1991, and March and August 1994); only three vents were erupting, in contrast to 10 in August. A detailed record of the eruptions was made for ~4 hours (table 2). The most notable change was the almost complete inactivity of Crater 1 (figures 40 and 41), which had contained at least six erupting vents in August 1994. Only vent 1/3 displayed some brief weak explosions, mostly of burning gas carrying a few incandescent fragments from the conduit walls. Crater 2 was not erupting, as in March and August 1994, but was the site of loud gas emissions.

Table 2. Eruptive activity at Stromboli observed between 0800 and 1210 on 20 April 1995, from Pizzo sopra la Fossa. Courtesy of Boris Behncke.

    Time Crater-Vent Description

    0800  1-3  Brief (1 sec) gas explosion
    0810  1-3  Explosion (2 sec) with dark fumes
    0811  3-2  Very small explosion, no bombs visible
    0811  3-1  Strong bomb ejection to ~30 m
    0813  3-2  Lava fountain (15 sec) with some ash, to ~60 m above crater terrace
    0816  1-3  Brief thud with gas puff
    0825  3-2  Small, low fountain inside crater (5 sec)
    0830  2-?  Loud gas emission, no solid ejections (2-3 sec)
    0845  3-2  Small ash explosion (10 sec) to 30 m
    0857  3-2  Small ash explosion (5 sec)
    0859  3-2  Large bomb and ash fountain to 80 m (10 sec)
    0902  3-2  Small bomb fountain with no ash to 30 m (5 sec)
    0906  3-2  Very small explosion (mainly gas) inside crater (4 sec)
    0908  3-2  Large bomb and ash fountain to 50 m, ash plume to 250 m (10 sec)
    0912  1-3  Small gas explosion (2 sec)
    0937  3-1  Single burst of large bombs to 30 m
    0944  3-1  Bomb ejection to ~20 m
    0952  1-3  Brief (1 sec) gas burst
    0954  3-1  Large bomb ejection with very large (up to 5 m) clots to ~30 m
    1010  3-2  Ash fountain to 150 m
    1043  3-2  Vigorous bomb and ash fountain; bombs to 80 m; dense ash column to >200 m (~30 sec)
    1045  1-3  Small gas explosion (1 sec)
    1110  3-2  Large bomb and ash fountain similar to that of 1043
    1124  1-3  Small gas explosion (1 sec)
    1132  1-3  Small gas explosion (1 sec)
    1136  3-2  Bomb and ash fountain, ash to >200 m
    1148  3-1  Abundant very large bombs to ~25 m; "whooshing" sound
    1152  3-1  Similar to 1148 but with less bombs
    1155  3-1  Similar to 1148 but with less bombs
    1207  1-3  Small gas explosion (1 sec)
    1208  3-2  Bomb fountain to <50 m, no ash (5 sec)

The most active vents were in Crater 3. Vent 3/1 activity consisted of almost continuous low spattering from a small lava pond with occasional bursts to ~60 m above the vent; similar activity was seen in March 1994 (BGVN 19:03). Rare bursts of large incandescent lava clots (up to 5 m in diameter) were accompanied by faint "whooshing" noises. Only twice were bombs ejected beyond the pit of 3/1, onto the NE wall of Crater 3. Eruptions from vent 3/2 occurred at intervals ranging from 2 minutes to >1 hour (see table 1), with periods of more frequent eruptions alternating with periods of very low activity. For example, six eruptions occurred during a 25-minute period (0845-0910), while from 0910 until 1210 there were only five more. Some of these eruptions consisted of loud gas emissions with very low spatter fountains, but most produced incandescent fountains 80-100 m high. Between sunrise on 20 April (at about 0700) and noon, the eruptions produced ash plumes up to 250 m high. Most of the ejected material fell back into the pit, but sometimes the entire NW rim of Crater 3 was covered with pyroclastics, and bombs rolled down the Sciara del Fuoco.

Activity on 21 and 23 April 1995. When observed from Punta Labronzo, on the N side of the island, on the evening of 21 April activity consisted of frequent low lava fountains from vent 3/2 and fluctuating incandescence over vent 3/1. Small ash plumes produced by eruptions from 3/2 were driven down the Sciara del Fuoco by strong winds. A dramatic change was evident late on 23 April, when the volcano was again observed from Punta Labronzo. Crater glow was much more intense, though still intermittent, and a persistent glow was visible at a small spot in the gap on the NE rim of Crater 1 (formed by the 5 March explosion). Vent 3/2 erupted as during the preceding days with somewhat larger ash plumes. However, a vent in the N part of Crater 1 ended the period of unusual inactivity of this crater, erupting spectacularly at intervals of 10-25 minutes. These eruptions were very brief (<5 seconds) and produced cannon-shot-like bangs. Narrow incandescent columns rose obliquely to at least 150 m above the vent before falling onto the Sciara del Fuoco, depositing abundant incandescent material on the steep slope. For 3-5 minutes, incandescent material would cascade down to about half of the Sciara's extension, with a few large blocks tumbling farther. None appeared to reach the sea during the 1-hour observation period.

Evolution of crater morphology, 1989-95. Stromboli has had, since at least the early 1970's, three craters (figure 40) along a NE-SW trend with a varying number of active vents. Most of these vents are remarkably stable in both location and eruptive behavior, while a few others shift locally and develop into clusters of closely connected vents or unite to form larger ones.

Figure 40. Sketch map of the summit area of Stromboli, April 1995, showing the three craters and locations of vents. Courtesy of Boris Behncke.

Morphologic changes occur almost continuously, with alternating constructive and destructive processes. Periods of spatter-cone growth and crater filling usually last from a few months to several years and are followed by either crater-floor subsidence or explosive disruption of the cones. Cone growth was continuous from at least 1989 (maybe 1986) until October 1993, interrupted only by small-scale cone collapse and minor explosions. At the same time, the craters were filled to their rims with tephra and minor lava flows (as in May 1993; BGVN 18:04). Two large explosions in October 1993 blew out all of the material from the craters, leaving deep (>60 m) and wide chasms with near-vertical walls, still present in March 1994 (BGVN 19:03). New spatter cones grew rapidly during unusually vigorous activity in the summer and autumn of 1994, reaching much larger dimensions than the 1989-93 cones. In March 1995, parts of these cones were again removed by powerful explosions similar to, but smaller than, the October 1993 explosions. Also during early 1995, subsidence in Crater 3 created two pits at least 50 m deep.

Crater 1 has been the site of the most pronounced spatter-cone growth during 1989-95. Very small cones rarely formed at vent 3/1 and within the one vent of Crater 2. Most of the filling of craters 2 and 3 was due to the accumulation of pyroclastics. Three large, steep-sided cones and several smaller ones grew within Crater 1 between March and August 1994, the largest at vent 1/2 in the central portion of the crater, reaching ~30 m above its base. A powerful explosion in March 1995 blew out a pit 60-70 m in diameter and some 40 m deep with vertical walls, removing half of the cone (figure 41), and exposing the now-inactive conduit. Some of the smaller 1994 cones were also destroyed during the March explosion. The "twin cones" above vents 1/4 and 1/5 had grown much larger since August 1994, reaching ~25 m above their bases. Crater 2 had changed little since the summer of 1994. The small (~5 m high) hornito in its center, first observed in October 1994 (BGVN 19:10) was still present.

Figure 41. View of the crater terrace from Pizzo Sopra la Fossa, 20 April 1995. Courtesy of Boris Behncke.

Crater 3, which had been filled with pyroclastics in August 1994, had two major depressions at the sites of vents 3/1 and 3/2. These depressions differ from the explosion pit in Crater 1, lacking its vertical walls and sharp rim, and may have formed in response to the lowering of the magmatic column sometime during November 1994 when the period of high-level activity ended. Another major change since 1989 is the significant upward growth of the entire crater terrace, most notable on the NW side facing the Sciara del Fuoco. This change is also evident on the profile views of Crater 1 taken from an observation point ~400 m NW (figure 42). Since the early and mid-20th century, the crater terrace has grown upwards by 50-100 m, completely burying the formerly conspicuous Filo di Baraona (figure 40), a frequently cited reference point in older literature at the SW end of the crater terrace. The highest point of the crater terrace is the SW rim of Crater 3, lying at ~780-800 m elevation (some 40 m above its NE rim), at the site of the former Filo di Baraona. This is significantly higher than the ~725 m estimated by Hornig-Kjarsgaard and others (1993).

Figure 42. Comparative profile views of Crater 1 from the NE, illustrating the repeated growth and destruction of spatter cones between September 1989 and April 1995. The June 1993 sketch is based on photographs taken by Jon Dehn (Geological Survey of Japan, Hokkaido) and shows two lava lobes (arrows) from the vigorous May 1993 activity extending downslope. Courtesy of Boris Behncke.

Reference. Hornig-Kjarsgaard, I., Keller, J., Koberski, K., Stadlbauer, E., Francalanci, L., and Lenhart, R., 1993, Geology, stratigraphy and volcanological evolution of the island of Stromboli, Aeolian arc, Italy: Acta Vulcanologica, v. 3, p. 21-68.

Information Contacts: Roberto Carniel, Dipartimento di Georisorse e Territorio, via Cotonificio 114, I-33100 Udine, Italy (Email carniel@udstsa.dgt.uniud.it); Giada Giuntoli and Boris Behncke, GEOMAR Research Center, Dept. of Volcanology and Petrology, Christian-Albrechts-Universitat zu Kiel, Wischhofstr. 1-3, 24148 Kiel, Germany (Email: bbehncke@geomar.de).

05/1995 (BGVN 20:05) Slight late-May increase in seismicity; crater observations

During the 5 April-10 June reporting interval, the most significant low-intensity period occurred between 27 April and 6 May (figure 43), with an average of <100 events/day, quite low compared to ~270 events/day for January-March 1995. Late 1990 to early 1991 activity, as recorded by a one-component instrument, and seismic reports after the larger eruptive phases of 1993, also showed low levels of seismicity. This low activity may be an aftereffect of the 5 March explosion, rather than precursory to a new large explosion, although this is a great simplification of complex volcano dynamics. Seismic data from April and May are particularly interesting because of an eruption forecast made by C. Blot for 20 April +-15 days, based on two deep shocks recorded beneath Stromboli Island. Local authorities also declared an alert (restricted access) during almost the same period because of the anomalous decrease in volcanic activity, in anticipation of a large explosive event.

Figure 43. Seismicity reported at Stromboli, 5 April-10 June. Open bars show the number of recorded events/day, the solid bars those with ground velocities >100 µ/s (instrument saturation level). The line shows daily tremor energy computed by averaging hourly 60-second samples. The seismic station is located 300 m from the craters at 800 m elevation. Courtesy of Roberto Carniel.

The second half of May was characterized by a reprise in the total number of recorded events and in the number of events that saturated the acquisition system with ground velocities >100 µ/s. Access limitations imposed by local authorities were also eased once normal activity resumed. A slight decrease in seismicity characterized early June, with ~100-150 events/day, only a few major shocks, and continued low tremor intensity.

During 30 April-1 May Richard Pichl observed powerful explosions every 20-25 minutes, throwing incandescent ejecta from a vent in the northernmost part of Crater 1 onto the Sciara del Fuoco, each accompanied by a "cannon-shot" bang. There was also a 1-2 hour period of continuous, violent degassing. A second vent in the central part of the crater erupted once during the night. Black ash plumes rose from Crater 3; no incandescent ejecta were reported. There was unusually strong fumarolic activity from numerous sources within Crater 1.

On the night of 23-24 May, SVE members observed explosive Strombolian activity from the Pizzo Sopra after several weeks of weak activity. Vent 3/1 (figure 44) was the most active, with intense explosions at ~15-25 minute intervals sending incandescent ejecta ~100 m above Crater 3. Vent 3/2, inside a small depression, displayed continuous incandescence with occasional weak jets and sprays of lava. Vent 1/1 ejected incandescent material every 30-40 minutes SW onto the outer slope of Crater 1 and the rim of Crater 3. Two hornitos near the rim of Crater 1 exhibited weak vapor emissions. Yellow sulfur deposits surrounded several fumaroles on the external slope of Crater 1. Intense vapor emissions from several areas in Craters 1 and 3 were observed.

Figure 44. Sketch of the active craters at Stromboli, 24 May 1995. View is from the Pizzo Sopra looking NW. Courtesy of H. Gaudru.

Information Contacts: Roberto Carniel, Dipartimentto di Georisorse e Territorio, via Cotonificio 114, I-33100 Udine, Italy (Email: carniel@udstsa.dgt.uniud.it); Henry Gaudru, Societe Volcanologique Europeenne (SVE), C.P. 1 - 1211 Geneva 17, Switzerland; Richard Pichl, Institute of Hydrogeology, Engineering Geology & Applied Geophysics, Charles University, Prague, Czech Republic.

08/1995 (BGVN 20:08) Seismicity generally low from mid-June to mid-September

The only significant tremor variations for the period 11 June-15 September 1995 were between 12 and 27 August, when intensity slowly increased (figure 45). The following four days were characterized by a rapid return of the intensity to the range observed throughout the first half of September. Noteworthy is the lack of a great number of saturating events compared to March-May 1995, including the 5 March explosion (BGVN 20:04 and 20:05). This means that explosive activity was either less energetic or shallower, with more energy released towards the air than into seismic waves. The total number of recorded events showed a rise and subsequent decrease from mid-June to mid-July, with two minima of 50-60 events/day and a maximum of almost 200 events/day recorded on 26 June. Another rise starting in mid-July reached values of 260-280 events on 28 August and 3 September, corresponding to the period of decreased tremor.

Figure 45. Seismicity detected at Stromboli, 11 June-15 September 1995. Open bars show the number of recorded events/day, the solid bars those with ground velocities >100 µ/s (instrument saturation level). The line shows daily tremor energy computed by averaging hourly 60-second samples. The seismic station is located 300 m from the craters at 800 m elevation. Courtesy of Roberto Carniel.

Information Contacts: Roberto Carniel, Dipartimento di Georisorse e Territorio, via Cotonificio 114, I-33100 Udine, Italy (Email: carniel@udgtls.dgt.uniud.it), URL: http://udgtls.dgt.uniud.it/seismol/strombol.htm).

12/1995 (BGVN 20:11/12) Low-level ash plumes and lava fountains during September-October

In contrast to very intense activity seen in summer-autumn 1994, Boris Behncke noted that activity remained low from early 1995 through October. The low level of activity, also shown by seismic data acquired by the University of Udine (see recent Bulletins), was interpreted by some researchers as a possible precursor of a more powerful eruption in the near future, resulting in a warning and access restrictions in April-May.

Eruptions during August-October produced low lava fountains and ash plumes. Activity from vent 3/1 (figure 46) consisted of night glow and spatter ejections, at times throwing bombs outside the crater. Vent 1/1 had periods of vigorous lava fountaining, often dropping incandescent bombs on the Sciara del Fuoco, particularly in early September. During dry weather, a dense gas plume often formed a hazy layer at 850-900 m altitude that extended for tens of kilometers.

Figure 46. Map of the crater terrace at Stromboli, 19-20 September 1995, showing active vents. The map was produced using EDM and triangulation measurements. Vent numbering is consistent with sketch maps from April 1995 (BGVN 20:04). Courtesy of Andy Harris and Nicki Stevens.

During a 19-20 September visit by Andy Harris and Nicki Stevens, activity was observed from five vents (figure 47). A 4-m-diameter vent in the side of a hornito (1/4), had incandescent walls and an internal temperature of 940°C, as measured with a Minolta/Land Cyclops 152 infrared (0.8-1.1 µm) thermometer. Gas-jet eruptions from this vent sent incandescent gas and minor ejecta ~50 m high. Regular explosions from vents 1/2 and 3/2 ejected bombs and brown ash clouds up to ~100 m. Seven eruptions during a 90-minute period from vent 2/1 sent bombs to a height of ~50 m. No explosions were seen from vent 3/1, but it exhibited continuous night glow and apparently quietly ejected a few bombs to no more than 10 m above the crater rim.

Observations by Behncke on 28-29 September showed that craters 2 and 3 had not changed significantly since a visit on 20 April (BGVN 20:04). Vent 3/1 showed fluctuating glow at night but had no ejections. Vent 3/2 had very weak emissions of reddish ash every 5-20 minutes. Crater 1 had been largely filled with small spatter cones during the summer of 1994, but their destruction began with a powerful phreatic explosion on 5 March 1995 (BGVN 20:04). However, the twin cones (1/4 & 5) in vent area 1/3 remained. Neither of them had erupted after September/October 1994, but an incandescent vent (~10 m wide) at the SE base of the SW cone (1/4) had brief noisy gas explosions that emitted a diffuse incandescent gas cloud.

Vigorous eruptions observed by Behncke from vent 1/1 ejected black ash plumes that occasionally rose >100 m. After dark, incandescent ejections were seen, and loud roaring noises were audible. Reports by other observers in early October disclosed continuing low-level eruptions from vents 1/1 and 3/2 and incandescence from vents 1/3 and 3/1. In addition to the vents active in September, a vent behind the twin cones in Crater 1 and a vent in the NW part of Crater 3 were active when observed by Open University geologists on 15 and 30 October.

Information Contacts: Boris Behncke and Giada Giuntoli, Department of Volcanology and Petrology, GEOMAR, Wischhofstr. 1-3, 24148 Kiel, Germany (Email: bbehncke@geomar.de, URL: http://www.geomar.de/personal/bbehncke/STROMBOLI.html); Andy Harris, Department of Earth Sciences, The Open University, Milton Keynes MK7 6AA, United Kingdom (Email: a.j.l.harris@open.ac.uk); Nicki Stevens, ESSC, University of Reading, P.O. Box 227, Reading RG2 2AB, United Kingdom.

02/1996 (BGVN 21:02) Intense eruptive phase followed by a drop in seismicity

The following presents previously unreported observations of October 1995 activity made by Roberto Carniel (University of Udine), and seismicity recorded near the summit since mid-September 1995. A contribution from the Istituto Internazionale di Vulcanologia (IIV) provides information about a significant explosive event on 16 February.

October 1995 activity. Abundant light fumarolic activity was seen in the crater area on 13 October 1995 by Carniel. A shallow lava pond in vent 3/1 (see map in BGVN 20:11/12) was inferred by continuous night glow and ejection of small spatters that sometimes reached 3-4 m above the crater rim and only rarely fell outside the vent area. The other active vent in the SW crater (vent 3/2) produced regular explosions, with ejecta reaching considerable heights. Crater 2 was quiet, exhibiting neither explosions nor the gas-jet activity that often characterizes this crater. In Crater 1, the only activity occurred at a hole in cone 1/4; it consisted of continuous gas puffing, strong glow visible during the day, and very short blasts of air and smoke. Vent 1/1 was also active, although its eruptions were not as spectacular as those from 3/2, with occasional emission of a black cloud and ejection of sufficient material to trigger noteworthy movement of pyroclasts down the Sciara del Fuoco.

Mauro Coltelli (IIV) noted that the low lava fountains reported during August-October (BGVN 20:11/12) were typical of the Strombolian activity at the volcano, which was relatively low during that period.

Seismicity recorded at the summit, September-December 1995. Seismic activity recorded by the University of Udine summit station during the last three months of 1995 showed little variation in volcanic tremor intensity (figure 47). The daily number of recorded events was low (<100) in mid-September, reached a maximum of 337 on 18 October, and then decreased again until November. This period was interesting because of rapid transitions between days of very quiet activity (3-5 and 8-9 November) and days with a greater number of events (6-7 November). The minimum of the period was reached on 8 November, with only 53 events recorded during a full day of operation. A greater number of stronger events (either more energetic or less shallow) was recorded at the end of November and in early December (high of 46 events on 4 December).

Figure 47. Seismicity detected at the summit of Stromboli, 16 September 1995-29 February 1996. Open bars show the number of recorded events/day, and the solid bars those saturating the instrument (ground velocity exceeding 100 µm/s). The line shows daily tremor intensity computed by averaging hourly 60-second samples. The seismic station is located 300 m from the craters at 800 m elevation. No data were collected during the gaps on the plot, intervals when solar panel efficiency was insufficient to provide power for continuous acquisition. In cases of partial operation, the number of recorded events and the tremor intensity were normalized to the period of acquisition. However, because stronger events (those saturating the instrument) can easily be clustered in a short period of time, they were not normalized and the plotted values show the actual numbers recorded. Courtesy of Roberto Carniel.

January-February 1996 activity. January and the first half of February showed increased seismicity, with an average of 200-300 events/day and higher tremor intensity recorded at the summit. IIV reported that explosive activity during the first half of February remained low, ranging from days with an explosion almost every hour to days with a very few explosions. The main activity consisted of Crater 3 explosions that ejected minor spatter and ash puffs. Crater 2 exhibited continuous degassing, rarely interrupted by short periods of low-level spattering. Crater 1 produced daily strong gas explosions, sometimes with minor spatter.

At 2258 GMT on 16 February the seismic stations of the IIV permanent network on Stromboli recorded a sequence of explosion events, some of which were characterized by remarkable amplitudes. The events occurred in a very short time and were followed by increased tremor amplitude lasting ~12 minutes. Thereafter, the increment of tremor amplitude gradually vanished. The seismicity marked an intense eruptive phase from the summit craters. Eyewitnesses in Stromboli village reported a strong blast followed in the next few minutes by some incandescent bombs and glow on the summit; a dark column rose 200-300 m above the craters. No significant activity was observed by local residents for the next several hours. An IIV field survey on 20 February revealed that the bombs fell on an area 200-300 m wide. Both black scoriaceous bombs, covered by Pele's hairs, and reddish fumarolized blocks were observed; the vent that produced these materials was probably in Crater 2 or 3, but no relevant morphological variation of the shape of these craters was observed.

The University of Udine summit seismic station showed a general drop in activity after the event (figure 47). This repeats the pattern already observed after the explosions of 10 February and 16 October 1993 (BGVN 18:01 and 18:09) and after the small lava flow of May 1993 (BGVN 18:09), when similar abrupt decays were observed. The following days show increasing seismicity in terms of both tremor intensity and number of events.

Information Contacts: Roberto Carniel, Dipartimento di Georisorse e Territorio, Univ. di Udine, via Cotonificio 114, I- 33100 Udine (Email: carniel@udgtls.dgt.uniud.it, URL: http://udgtls.dgt.uniud.it/seismol/strombol.htm); Mauro Coltelli, IIV (see Etna).

04/1996 (BGVN 21:04) Increased seismicity and Crater 1 activity after mid-April

Following the strong crater explosion on 16 February (BGVN 21:02), the summit seismic station of the University of Udine showed a general drop in seismic activity, as seen previously after paroxysmal phases at Stromboli (BGVN 18:01, 18:04, and 18:09). A new increase in seismic activity continued through early March with elevated average tremor intensity, while the numbers of recorded events and saturating events decreased (figure 48). After a fall in the tremor intensity on 9 and 10 March, all parameters started showing a general increasing trend that continued through the first week of April.

Figure 48. Seismicity detected at the summit of Stromboli, 1 March-15 May 1996. Open bars show the number of recorded events/day, and the solid bars those saturating the instrument (ground velocity exceeding 100 µm/s). The line shows daily tremor intensity computed by averaging hourly 60-second samples. The seismic station is located 300 m from the craters at 800 m elevation. Courtesy of Roberto Carniel.

After a brief drop in the tremor intensity (6-8 April) and in the number of events (10-11 April), a new period of increasing seismicity began. The number of recorded events suddenly increased between 15 April (286 events) and 16 April (540 events); in the following days numbers become even greater, as the seismic station was triggered almost every minute. Stromboli volcano guide N. Zerilli confirmed that on those days Crater 1 (figure 49) erupted almost continuously, with fountaining to 40-50 m above the crater. This was the source of a rapid succession of moderate explosion-quakes that caused the high number of events recorded by the station. The number of more energetic events was also high. Strong explosive activity was continuing as of 15 May.

Figure 49. Sketches of the Stromboli craters based on ground-based stereo photographs: a) October 1993 and b) April 1996. View is towards the NW. Question marks (?) on the 1993 sketch indicate areas impossible to see because of fumaroles. Vents 3/2? and 3/3? on the 1996 sketch are indirectly inferred from the trajectory of ejecta. Courtesy of Jürg Alean.

Field observations were made by J. and P. Alean, R. Carniel and F. Iacop during 21-28 April, although poor weather allowed only three summit visits. The most striking activity during the period was almost continuous spattering at vent 1/2 (figure 49b). Ejecta up to (and occasionally in excess of) 2 m in diameter were thrown at least 50 m high about every 30 minutes. For very short time periods (a few minutes) spattering activity at vent 1/2 would almost disappear, then increase and sometimes reach an intensity similar to the more normal, larger Strombolian eruptions. The latter occurred in Crater 1 from three distinct vents. On 21 April there were 20 eruptions at Crater 1 in 3.5 hours, some of them reaching heights of ~200 m. Cone 1/4 produced smoke rings on 22 April. On 28 April, Crater 1 produced 45 "normal" Strombolian explosions between 1300 and 1900 GMT, apart from the continuous spattering described above. Intense red glow from Crater 1 illuminated steam and clouds above it. This glow was one of the most intense ever seen by these scientists during their visits to the volcano; it could often be seen even from S. Vincenzo village.

Apart from fumarolic emissions, Crater 2 remained inactive. Crater 3 eruptions on 21 April were relatively small, albeit very noisy. Scoria did not reach heights of more than 100 m. It appeared as if the material was ejected from several individual vents or a fissure within the crater. A lot of ash was ejected, occasionally producing black mushroom-shaped clouds. Vent 3/1 had grown to an impressive size since 1994. They saw only one eruption from it, on 21 April at 1815 GMT; all the others were generated at vents 3/2 or 3/3. On 28 April activity at Crater 3 increased (55 eruptions between 1300 and 1900 GMT). By about 2100 GMT eruptions were occurring at intervals of 1-5 minutes, most of them exceeding 200 m in altitude. The ash content was clearly less than on 21 April, and brown ash clouds had become rare.

Figure 49 illustrates the change in crater morphology between October 1993 (figure 49a) and April 1996 (figure 49b). These sketches were drawn based on stereo photographs taken from the ground with a 35 mm single-lens reflex camera. The most striking morphological changes are probably in Crater 1, which saw the construction of a series of cones and their subsequent destruction, which led to the present configuration near vents 1/3 and 1/4. The zone around vent 1/2 in the foreground now appeared more open towards the Sciara del Fuoco, thus allowing better visibility of the crater from Punta Labronzo. Changes were also observed at vent 3/1, now better separated from Crater 2 on the rear and more connected to the rest of Crater 3 due to slumping of blocks between vents 3/1 and 3/3.

Information Contacts: Jürg Alean, Kantonsschule Zürcher Unterland, CH-8180 Bülach, Switzerland (Email: jalean@access.ch); Roberto Carniel, Dipartimento di Georisorse e Territorio, via Cotonificio 114, I-33100 Udine (Email: carniel@dgt.uniud.it, URL: http://www.ezinfo.ethz.ch/world/strombolihomee.html).

05/1996 (BGVN 21:05) Continued high levels of activity through mid-June; two larger explosions

Seismicity began slowly increasing in mid-March before a sudden jump in tremor intensity on 15-16 April (BGVN 21:04). Observations made by Marco Fulle confirmed that the elevated seismicity corresponded to increased eruptive activity. During the night of 15-16 April about 100 explosions occurred. Continuous fountains from the N part of vent 1/2 (see sketch in BGVN 21:04) rose 50 m and lasted 1-2 hours. The S part of vent 1/2 produced large explosions to heights of 150-200 m that deposited bombs on the terrace beyond vent 3/2. Activity from vent 3/1 consisted of continuous pulsing of incandescent gas and explosions every 2-3 hours. Vent 3/2 produced simultaneous explosions every 10-30 minutes from two vents. Similar activity and ~50 explosions were seen the night of 20-21 April. Additional observations included glowing ex-hornitos in vent 1/3 with regular steam pulses. Vent 3/2 explosions covered the terrace S of Crater 3 with bombs.

Observations of summit activity made during 21-28 April by Alean, Carniel, and Iacop revealed similar activity consisting of continuous spattering and intermittent explosions from Crater 1 (BGVN 21:04). Seismicity remained at high levels through mid-May (BGVN 21:04).

IIV report of 1 and 6 June explosions. At 2147 on 1 June, local seismic stations maintained by the Istituto Internazionale di Vulcanologia (IIV) recorded a powerful event lasting ~3 minutes. Eyewitnesses at Stromboli village reported a single strong blast followed by the fallout of red bombs on the upper N slope. Incandescent bombs fell on vegetation, causing a fire that was extinguished by Civil Protection aircraft in the late morning of 2 June. More than twenty tourists were visiting the summit at the time of the explosion. Some of them reported light burns caused by hot lapilli fallout and minor injuries made while escaping on the steep slope.

A field survey early on 2 June revealed that the explosion occurred at Crater 1. The chain of hornitos inside Crater 1 was blown out, leaving a large deep depression in the N side of the crater floor. The ejected material completely covered the summit, falling more than 500 m to the S and E, and reaching ~1,000 m on the N sector, where it fell on the vegetation. The deposit was made of black scoriaceous bombs, covered by Pele's hair, reddish blocks, and a small amount of fine material. On the Pizzo area, where people usually stay to observe the activity (250 m SE from the vent), the falling bombs ranged between 10 and 50 cm in size, and they covered the area with a density of 3-4/m2.

Strombolian activity after this event shortly returned to a medium intensity and a normal frequency (3-4 events/hour). In the days after there were several hours without any activity alternating to mild Strombolian activity and after 5 June spattering activity lasting several minutes was occasionally observed.

At 0452 on 6 June another strong seismic event from Crater 1 was smaller than the 1 June event and lasted ~1 minute. The eruption was recorded by the surveillance video camera on the Pizzo Sopra La Fossa, 120 m above the vent and 250 m away; the camera had been restored two days earlier. A few people observed the explosion and reported an ash column to a few hundred meters high and bomb fallout on the Sciara del Fuoco. The video showed a very fast gray-brown jet that ascended at ~30 m/second at the upper limit of the camera view; most of the bomb and block fallout was behind the camera. The ash emission lasted ~2 minutes, but at the end only overpressured steam was emitted.

After the explosion, Strombolian activity continued at Crater 1. During fieldwork that afternoon, activity was characterized by low-intensity explosions with emission of bombs and brown ash, interrupted by sporadic strong explosions that produced a larger amount of bombs followed by an almost continuous spattering for 5-15 minutes. All pyroclastic materials fell close to the craters but during the larger explosion some bombs were thrown a few hundred meters from the vents. The Strombolian activity continued through at least 10 June, showing periods of mild explosions interrupted by strong explosions and short periods of continuous spattering.

Observations on 8-9 and 11-12 June. Marco Fulle made observations from Pizzo sopra la Fossa for six hours on the night of 8-9 June. Vent 1/2 exhibited continuous fountaining 50 m high with larger pulses every 5-10 minutes and ejection of meter-sized lava clots. The vent also produced 35 explosions 100-200 m high, with bombs over the Sciara del Fuoco and the terrace up to Crater 2, and meter-sized lava clots inside Crater 1. Vent 3/1 was inactive, but vent 3/2 produced 20 explosions 50 m high with a lot of ash and bombs ejected inside the crater.

Observations from Pizzo sopra la Fossa were again made for six hours on the night of 11-12 June. Vent 1/2 again produced continuous fountaining and 46 explosions. Vent 3/1 remained inactive. Vent 3/2 generated 37 explosions 100-250 m high with minor ash. Fountaining occurred during the explosions and near-vertical jets of bombs fell S of the crater rim and over vent 3/1.

Information Contact: Mauro Coltelli, CNR Istituto Internazionale di Vulcanologia (IIV), Piazza Roma 2, Catania, Italy (Email: colt@iiv.ct.cnr.it, URL: http://www.iiv.ct.cnr.it/); Marco Fulle, Osservatorio Astronomico, Via Tiepolo 11, I-34131 Trieste, Italy (Email: fulle@ts.astro.it).

03/1997 (BGVN 22:03) Summary of seismic and volcanic activity during May 1996-January 1997

The following summarizes the interval from 15 May 1996 to 31 January 1997. Eruptive activity increased in mid-April 1996 (BGVN 21:04) and continued through mid-June with significant explosions (BGVN 21:05). A flight on 16 July 1996 documented a plume rising from Stromboli using a Wide Angle Optoelectronic Stereo Scanner (figure 50). This image of the entire island also shows older lava flows, the Sciara del Fuoco, and the Pizzo Sopra La Fossa (120 m above and 250 m SE of the vent), where people often make observations from.

Figure 50. Wide Angle Optoelectronic Stereo Scanner (WAOSS) image of Stromboli taken on 16 July 1996. Courtesy of Martin Scheele, DLR.

Figure 51 illustrates the change in crater morphology between April 1996 and September 1996. Unfortunately the morphological changes in Crater 1 (typically a site of ongoing changes) were obscured on the September stereo photographs; however, the other two craters underwent noteworthy changes. In Crater 3, the front vent (3/3), which was essentially a pit in April, had become a small cone by September as a tephra apron enclosed the vent. In the westernmost part of Crater 3, vents 3/1 and 3/2 merged into a single chasm distinct from the rest of the crater.

Figure 51. Sketches made from terrestrial stereo photographs shot on 25 April 1996 and 19 September 1996. View is towards the NW. The sketches allow comparison of morphological changes in the crater area between these two dates; vents and craters labeled 3/2? and 3/3? were inferred indirectly from ejecta trajectories; areas labeled "?" were obscured by particulate and gases. Courtesy of Jürg Alean (original photos by Alean and Carniel).

During the first half of August the activity increased at Crater 3, in particular at vent 3/1, where the magma rose to increasingly shallow levels. During 16--17 August 1996, amid vigorous seismicity (figure 52), local volcano guide Nino Zerilli saw a small lava flow discharged from vent 3/1. The lava flow proceeded for only a few meters inside the crater and stopped by the evening of 18 August. Around this same time interval magma also reached high levels in Crater 1.

On 22 August 1996 at 0230 a tourist was hit by volcanic ejecta while in a sleeping bag ~80 m from the crater. He had to be transported by helicopter to Messina for head surgery. Zerilli reported that during the previous days ejecta from Crater 3 had been thrown as far as observation sites between the Pizzo and Crater 3. Thus, this injury appeared to have been more a case of camping too close to the crater rather than an especially violent outburst that particular night.

By 26 August, vent 3/1 was completely inactive, whereas vents 3/2 and 3/3 had almost joined, and their activity consisted of very powerful Strombolian explosions sending small fragments onto the Pizzo. At Crater 1, vent 1/4 only rarely exploded but did so with strong gas jets. In contrast, vent 1/3 ceased the continuous activity that it had begun on 16 April 1996, a change interpreted as either another pause there or the end of an unusually long period of continuous spattering.

On 4 September 1996 at 1545 a blast threw incandescent pyroclastic material onto slope vegetation. This started several fires and the explosion was clearly heard and watched from the village of Stromboli. According to the local newspaper "Il Piccolo" some tourists were caught by the explosion in the crater area and six of them were slightly injured. After this, the Mayor of Lipari ordered the closure of the path to the craters. After the blast, however, Strombolian activity continued to decrease. In terms of seismicity, both the number of major events and the total number of events decreased to very low values, a situation which prevailed through the end of January 1997 (figure 52).

Figure 52. Seismicity recorded at Stromboli 15 May 1996-31 January 1997. Open bars show the number of recorded events/day, and the solid bars those saturating the instrument (ground velocity exceeding 100 µm/s). The line shows daily tremor intensity computed by averaging hourly 60-second samples. The seismic station is 300 m from the craters at 800 m elevation. Arrows highlight the two powerful explosions of 1 June and 4 September 1996. Courtesy of R. Carniel.

A visit by Carniel at the end of September revealed extremely low activity as judged by the few audible eruptions seen or heard; however, smoke often covered most of the crater area. Remarkable were some very long rumbles, which could be heard even from the village of Stromboli. These rumbles were probably associated with strong degassing from Crater 2, although this interpretation remained unconfirmed by direct observation.

Matthias Hort and Ralf Seyfried visited and photographed portions of the volcano during 30 September-2 October (figures 53 and 51). They witnessed small eruptions from vent 2 at Crater 3. These eruptions took place while Craters 1 and 2 were inactive. Rumbling noises heard on 30 September from Crater 1 disappeared within the next two days. Overall, activity gradually declined from 30 September to 2 October. According to Hort, the most spectacular event during the observation period was an ash emission that produced a plume to 100 m above the craters. Periods of up to 2 hours passed without eruption.

Figure 53. Ash and bomb emission from Crater 3 seen from Pizzo on 30 September 1996. Courtesy of Matthias Hort, GEOMAR.
Figure 54. View of vent 1 in Crater 3, 30 September 1996. Bright incandescence is seen during daylight, indicating active magma at shallow depth. Courtesy of Matthias Hort, GEOMAR.

On the evening of 10 October Boris Behncke saw two lava fountains shooting up from Crater 3 during a 5- minute interval, reaching 80-100 m above the vent (to the height of Pizzo sopra la Fossa). Each fountain lasted ~20 seconds. About 10 minutes after the second fountain, an eruption apparently occurred at Crater 1.

Unusually low seismic activity appeared on 10 November, when the seismic station recorded only 17 events within 24 hours (none of them saturating the acquisition system). Exceptionally long intervals without a single event occurred on several other days: 7 hours on 25 October, 8 hours on 10 November, 10 hours during the night between 12 and 13 November. Although the tremor intensity slowly increased from September 1996 (1-2 V.s) to January 1997 (3-5 V.s), there was no significant increase in the number of recorded events or saturating events. Thus, activity at the end of January was still considered "low to moderate."

Information Contacts: Roberto Carniel, Dipartimento di Georisorse e Territorio, via Cotonificio 114, I-33100 Udine (Email: carniel@dgt.uniud.it, URL: http://www.ezinfo.ethz.ch/world/); Jürg Alean, Kantonsschule Zürcher Unterland, CH-8180 Bülach, Switzerland (Email: jalean@access.ch); Matthias Hort, Ralf Seyfried, and Boris Behncke, Geomar Research Center for Marine Geosciences, Wischhofstrasse 1-3, 24148 Kiel, Germany (Email: bbehncke@geomar.de, URL: http://www.geomar.de/personal/bbehncke/); Martin Scheele, Institut für Weltraumsensorik (Institute for Space Sensor Technology), Deutsche Forschungsanstalt für Luft- und Raumfahrt (German Aerospace Research Establishment), Forschungszentrum Berlin-Adlershof, Rudower Chaussee 5, 12489 Berlin (Email: Martin.Scheele@dlr.de, URL: http://www.dlr.de/).

05/1997 (BGVN 22:05) New map of the crater terrace

A 7-hour visit on 23 May led to the construction of a crater terrace map (figure 55). The Crater 2 pit mapped in 1994 and 1995 had filled in and was occupied by an inactive lava flow fed from a small truncated cone. From information by Jürg Alean (BGVN 22:03) it was inferred that this flow was emplaced between 25 April and 19 September 1996. A new subsidence bowl was forming to the SE of the former Crater 2 pit. This was occupied by a pit crater and three vents (2/1, 2/2, and 2/3), none of which exhibited explosive activity. Vent 2/1, ~4 m in diameter, was the source of regular (~1/s) gas puffs and occasional gas release, and also showed night incandescence.

Figure 55. Sketch map of Stromboli's crater terrace drawn on 23 May 1997 and fitted to the map from the September 1995 EDM survey (BGVN 20:11/12). Label A indicates the pit in Crater 2 mapped in both 1994 (BGVN 19:10) and 1995. Label B designates a new subsidence bowl. Label C indicates the location of a vent and small lava flow erupted sometime between 25 April and 19 September 1996. Label D indicates the spot where hornitos existed in 1994 and 1995. Courtesy of Andy Harris.

Activity during the 23 May visit was at lower levels than seen in either October 1994 (BGVN 19:10) or September 1995 (BGVN 20:11/12). However, excellent viewing conditions revealed that major changes had occurred since the 1994 and 1995 surveys (BGVN 22:03).

During the intervals 1100-1400 and 1900-2200, no eruptions were observed from Crater 3. However, at about1400 on 24 May, an explosion from Crater 3 fed a brown ash cloud that rose ~200 m above the crater rim. This was observed from the sea.

Night-time temperature measurements obtained from Pizzo Sopra la Fossa using a Minolta/Land 152 infrared thermometer (corrected for an emissivity of 0.956) gave 2/1 vent temperatures of 670-699°C. Vents 2/2 and 2/3 (~3 x 1 m and <1 m wide, respectively) were actively degassing without incandescence. The site of hornitos in 1994 and 1995 was occupied by a pit, with a wall on the NE side.

Crater 1 was occupied by two active vents (1/1 and 1/2). Between 1055 and 1155 on 23 May eight explosions occurred from these two vents. The first two explosions sent bombs 100-200 m above the crater rim with ~20% of the ejecta landing on the upper Sciara. The following six explosions sent ejecta up to 50 m above the vent.

For the next two hours, Crater 1 exploded ~1-2 times/hour, but additional sloshing and gas release sounds were occasionally audible from Pizzo Sopra la Fossa. By the evening of 23 May, Crater 1 activity had escalated to levels similar to the 1055-1155 period. As darkness fell, an intense pulsating glow visible over Crater 1 could have been due to a small, active lava pond on the crater floor. This may have accounted for the sloshing sounds heard earlier in the day.

Stromboli, a small island N of Sicily, has been in almost continuous eruption for over 2,000 years. Its small Strombolian explosions, which hurl incandescent scoriae above the crater rim, occur several times a day, but larger eruptions are less frequent.

Information Contact: Andy Harris, HIGP/SOEST, University of Hawaii, 2525 Correa Road, Honolulu, HI 96822 USA (Email: Harris@kahana.pgd.hawaii.edu).

10/1998 (BGVN 23:10) Larger explosions in January, August, and September 1998

Moderate activity prevailed at Stromboli from January to May 1997 (BGVN 22:03). During this period there was a slight decrease in tremor intensity and a slight increase in the number of recorded events (figure 56). Events exceeding the saturation level of the summit seismic station numbered fewer than 10% of the total recorded.

Figure 56. Seismicity detected at the summit of Stromboli from January 1997 through August 1998. Gray bars show the number of recorded events/day, and the black bars those saturating the instrument (ground velocity exceeding 100 µm/s). The line shows daily tremor intensity computed by averaging hourly 60-second samples. The seismic station is located 300 m from the craters at 800 m elevation. Courtesy of Roberto Carniel.

There was a marked increase in the total number of events during June-July 1997, sometimes in excess of 300 per day. Following a month-long lapse, an even larger long-term increase began in September that continued until November 1997. There were several days in this interval when triggering of the seismic station was almost continuous and tremor intensity reached high values, behavior that usually coincided with continuous spattering at the vents. No seismic data were recorded between 24 November 1997 and 9 January 1998. Activity had returned to moderate levels by the time seismic data acquisition resumed on 10 January 1998 (figure 56). The number of daily events rapidly decreased, as did tremor intensity.

At 1130 on 16 January 1998, a strong explosion in the crater area was similar to others at Stromboli during the last few years; one comparable event occurred on 4 September 1996 (BGVN 22:03). Such explosions are not a danger to the villages of Stromboli and Ginostra (figure 57), but they may be dangerous for tourists visiting the summit because bombs easily reach the usual observation points. Another risk is that fires, started by incandescent bombs, may spread in the vegetation. In the case of the 16 January eruption, bad weather prevented tourists from climbing the volcano and rain extinguished any wildfires.

Figure 57. Sketch map of Stromboli Island, showing locations referred to in the text. Courtesy of Roberto Carniel.

A new rise in seismicity began a few days after the explosion. A peak was reached during 16-20 February; on 19 February, 405 events were recorded, and on 20 February tremor intensity was high and 43 saturating events were noted. After this increase, activity decreased steadily with only a few fluctuations until the end of April. The total number of events recorded during the decrease was sometimes <100 per day, but there were short episodes of strong volcanic tremor during 7 and 12-13 March, and a series of very strong saturating events on 25-27 March.

During May-June seismic activity increased. During July two sharp drops in the level of activity were observed: the number of events did not exceed 80 per day during 1-3 July, and went below 50 per day during 22-24 July. Tremor intensity reached the minimum of the year on 22 July. There was a slight upturn in August.

At 1726 on 23 August, another powerful explosion occurred at the craters. The strong blast was heard throughout the island, and a column of ash and lapilli shot over the craters. Incandescent bombs fell over a vast area towards Vallonazzo, Labronzo, and Forgia Vecchia. At least one other explosion followed. Several fires started in vegetation on the upper slopes; the largest one, near Forgia Vecchia, was not extinguished until the next day. Fortunately, although a high number of tourists were on the island, no one was hurt. A dark ash column was eventually replaced by a large, light ash cloud. Small lapilli fell in Ginostra. Bombs were found on the tourist path down to 750 m elevation, and in other directions bombs fell to 500 m. Authorities immediately blocked public access to the upper part of the volcano. The explosion also caused significant morphological changes to the rim of Crater 1 towards Semaforo Labronzo.

Another strong explosion, perhaps more energetic than that of 23 August, happened at 1914 on 8 September. A considerable atmospheric shock wave was reported at the village of Stromboli, and broken windows were reported near San Bartolo. Ash and small lapilli fell near Ginostra and several bush fires were started by bombs on the volcano's slopes. Unfortunately, the seismic station was not operational at the time due to a technical problem.

Stromboli, a small island N of Sicily, has been in almost continuous eruption for over 2,000 years. It is the namesake for small Strombolian explosions, which hurl incandescent scoriae above the crater rim several times a day, with infrequent larger eruptions.

Information Contacts: Roberto Carniel, Dipartimento di Georisorse e Territorio, Universitá di Udine, Via Cotonificio, 114 I-33100 Udine (Email: carniel@dgt.uniud.it); Jürg Alean, Kantonsschule Zürcher Unterland, CH-8180 Bülach, Switzerland (Email: alean@stromboli.net).

06/1999 (BGVN 24:06) Vents in summit craters still active; variable seismicity

After the strong summit explosions of 23 August and 8 September 1998 (BGVN 23:10), at least two others followed during 1998: the first at 1805 on 24 November, the second at 0245 on 28 December. Both were reported by Pierre Cottens from the village of Stromboli, with pyroclasts clearly seen from the village, reaching estimated heights of at least 700 m over the craters in November and 500 m in December, but with little ashfall over the village. Technical problems kept the seismic station maintained by the University of Udine out of service through the end of January 1999.

Seismicity during February-June 1999. The seismic station was restored on 1 February 1999, and in the first part of the month the daily number of events declined from 130 to 50-80/day (figure 58). Saturating events showed a similar trend. The second half of February was characterized by an increasing number of events, reaching a maximum of 275 events on 2 March. During this period the tremor intensity showed fluctuations around an average of 3.6 V s, with an isolated peak on 23 February.

Figure 58. Seismicity detected at the summit of Stromboli from February through June 1999. The gray bars show the number of recorded events/day, and the black bars those saturating the instrument (ground velocity exceeding 100 µm/s). The line shows daily tremor intensity computed by averaging hourly 60-second samples. The seismic station is located 300 m from the craters at 800 m elevation. Courtesy of Roberto Carniel.

During 12-20 March there was a general decrease in activity, with a minimum number of 52 seismic events recorded on 16 March, and a minimum tremor intensity of 1.8 V s on 15 March. The gain in activity was observed first in the tremor intensity, with a local maximum of 4.7 V s on 29 March, then in the number of events, which reached a high of 208 events on 30 March.

A sharp decline was observed on 7 April both in the tremor intensity (from 3.0 to 1.2) and in the number of events (from 180 to 76). Saturating events also stopped, after an average of five saturated events during the three preceding days. Seismic activity increased slightly during the following two days, and on 9 April Cottens reported two strong blasts at about 0300, separated by a few minutes. Bad weather did not allow observation of the summit area, but the noise was similar to that produced by the strong eruptions of 1998. The seismic station recorded an event with greater than usual energy, which may have been from one of the explosions. Another decrease of activity was observed the day after the explosion, with the number of daily events falling to 83 and the tremor intensity to 1.9. The following days were characterized by a slow increase in seismicity, but activity remained low to moderate for the rest of the month.

After another gap in the seismic acquisition, the activity was still low after mid-May 1999, with <100 events/day between 20-24 May. The last week of May showed a rise in the number of events, with a maximum of 183 events on 26 May. A relatively high number of saturating events was also observed, starting on 23 May and peaking on 27 May (21 saturating events) and 30 May (23 saturating events). Another minimum in the number of events (66), number of saturating events (0) and tremor intensity (1.6) was recorded on 5-6 June 1999. During several days on the island in the second half of June, seismic activity remained at low to moderate levels, with a short duration increase in the tremor intensity on 21-22 June.

Observations during 17-20 June 1999. Observations during 17-20 June allowed mapping of the crater terrace (figure 59). Observations were made over two 3-4 hour periods: 2109-0100 (18-19 June), and 2030-2320 (19 June).

Figure 59. Sketch map of Stromboli's Crater Terrace drawn on 18-19 June 1999 from Pizzo sopra la Fossa and fitted to the map produced from a September 1995 EDM survey of the Crater Terrace (BGVN 20:11/12). Courtesy of Andy Harris and Roberto Carniel

Crater 1 contained four active vents (figure 59). During the first observation period, the vicinity of Vent 1/2 was the source of persistent widespread glow; but no ejecta was observed. Vent 1/1, however, was the source of glow and near-persistent low-energy activity, characterized by repeated phases of ejecta emission separated by periods of little or no emissions. Each phase consisted of numerous pulses of ejecta. During each pulse a few (typically 1-10) bombs were ejected <10 m above the crater rim, with pulses every few seconds. Around 11 periods of this persistent, pulsing emission were observed. Each period lasted 2-29 minutes and was separated by intervals of 3-28 minutes with occasional bomb emissions. This pattern at Vent 1/1 was broken by 16 high-energy events during which explosions sent ejecta ~100 m high.

Vent 1/3 produced high-energy events only, with 18 observed during the first period. High energy events from vents 1/1, 1/3, and 1/4 were synchronized. It was difficult to distinguish eruptions from 1/4 and 1/1 from the viewing angle, so eruptions from these two vents may have been occasionally assigned to the wrong vent; the eruption counts for 1/1 and 1/4 together were therefore combined. Vents 1/3, 1/1, and/or 1/4 erupted together on 11 occasions. On these occasions ejection from each vent was either synchronous or closely linked. During such synchronized events there appeared to be no set order in terms of which of the three vents started erupting and which followed. Vents 1/1 (and/or 1/4) and 1/3 erupted on their own on 5 and 7 occasions, respectively.

As in the first observation period, glow persisted above Vent 1/2 throughout the second period. Unlike the previous evening, however, ejecta was observed from Vent 1/2, where activity followed the style observed at Vent 1/1 during the previous evening. Around eight periods of low-energy but persistent pulsing activity were observed. These lasted 3-33 minutes and were separated by 2-23-minute-long periods of apparently no emission. This pattern of activity from Vent 1/2 was interrupted by five high-energy events lasting 4-6 seconds.

Vent 1/1 issued regular gas puffs (typically one puff every 1-2 seconds), but the frequency of ejecta emission had declined, with the periods of persistent, pulsing activity observed the previous evening replaced by discrete emissions. Ejections were observed from 1/1 on nine occasions, where only one event was of the high-energy type, and the remainder were short (<40-second-long) periods during which 1-10 bombs were ejected <10 m above the rim in pulses. As in the previous period, Vent 1/3 was characterized by high-energy events only. Seven occurred during the second period, of which three were synchronous with high energy events from 1/2 or 1/1.

Although no activity or glow was observed from Crater 2, a hornito (figure 59) had grown in the vicinity of the low cone observed during May 1997 (BGVN 22:05). The area surrounding Crater 2 no longer seemed to be marked by a crater-like feature. The subsidence bowl observed SE of Crater 2 in May 1997 had developed into a deep, funnel-shaped pit, which was the source of faint glow. On a previous map (BGVN 22:05), the vent numbering indicated that this area was part of Crater 2; this interpretation is questionable and this feature could be considered a crater by itself now. On figure 59 we denote this vent as 3/3 (therefore part of Crater 3) in order to allow for easy comparison with older maps of the crater terrace (e.g., BGVN 22:03).

Crater 3 was the location of two additional active vents (figure 59). Glow was observed from vent 3/1 only after an eruption at 2317 on 18 June. Eruptions from Crater 3 were high-energy only, and typically larger (in terms of volume and height, attaining heights of 150 ± 50 m) and longer (lasting 8-23 seconds) than those from Crater 1. Nine and eleven eruptions, respectively, occurred from Crater 3 during the two observation periods.

During our descent in the early hours of 19 June there was a rock fall/slide at about 0200 lasting 1-2 minutes. Boulders from the cliffs on the N edge of the Rina Grande rolled and bounced down the Rina Grande. Owing to the steepness of this flank, once in motion the rocks probably did not stop until they reached the sea in the direction of Forgia Vecchia, crossing the route that descends the Rina Grande ash slope within seconds. Such events pose a very serious hazard to anyone using this route, especially at night.

Information Contacts: Andy Harris and Dawn Pirie, Department of Earth Sciences, The Open University, Milton Keynes, MK7 6AA, United Kingdom (Email: a.j.l.harris@open.ac.uk, d.j.pirie@open.ac.uk); Sarah Sherman, 41-485D Kalanianaole Hwy., Waimanolo, HI 96795 USA (Email: macbeanur@yahoo.com); Roberto Carniel, Dipartimento di Georisorse e Territorio, Università di Udine, Via Cotonificio, 114, I-33100 Udine (Email: carniel@dgt.uniud.it, URL: http://stromboli.net).

01/2000 (BGVN 25:01) 1999 seismic summary and some stronger-than-usual eruptions

Reports of a strong eruption on the morning of 26 August were submitted to Stromboli On-line (maintained by Jürg Alean and Roberto Carniel) by a variety of sources, including Gianfranco Cincotta, Franco Iacop, Danielle Cottens, Klaus Jäger, and others. Another strong eruption was noted on 10 October. Throughout 1999 activity apparently continued at low levels, with between 50 and 250 daily seismic events registered at the summit (figure 60).

Figure 60. Seismicity detected at the summit of Stromboli during 1999. The gray bars show the number of recorded events/day, and the black bars those saturating the instrument (ground velocity greater than 100 µm/s). The line shows daily tremor intensity computed by averaging hourly 60-second samples. The seismic station is located 300 m from the craters at 800 m elevation. Courtesy of Roberto Carniel.

The first report of the 26 August explosion came from Gianfranco Cincotta, who reported that a normal explosion from Crater 3 at 0058 was followed by a more intense one at Crater 1. Then, after a tremor, the large explosion came from the vent in front of Crater 2, which is considered part of Crater 3 for "historical" reasons but has almost reached the status of an independent crater. The event happened as the evening tourist group descended the volcano and the night group was still climbing. Pyroclastic material was clearly visible from the village and fell over a wide area, including the path section with the observation points around the 700-m level. Fortunately this time few pyroclasts reached the reed vegetation on the upper slopes. Nevertheless, Danielle Cottens saw some small fires from Scari. According to Cincotta, 10 tourists asked for medical assistance. All were slightly injured, mostly because of the sudden run from the craters. A man inside his sleeping bag on the Pizzo was slightly burned by pyroclasts.

Henrik Berger also reported via Stromboli On-line that he and friends were camping on the Pizzo the night of 25-26 August; there were a total of seven people on the summit. A normal eruption of Crater 3 produced the usual amount of ash and little glowing lava. Perhaps one minute later, at about 0057, a significant tremor occurred, immediately followed by an eruption at Crater 1. Less than one second afterwards the small incandescent middle vent exploded with a bang. Lava shot from this vent to about twice the usual height. Most pyroclasts were ejected by Crater 1. The group fled in panic as incandescent volcanic bombs up to 30 x 50 cm impacted nearby. A lot of non-glowing material was also ejected. One woman's hand was hit by a glowing piece of scoria. A girl who had been sleeping barefoot in her sleeping bag suffered minor burns on her feet and hands. On the other side of Pizzo another person suffered burns on his belly.

On 15 September Boris Behncke was at the summit and found numerous scoriaceous bombs on and around the Pizzo sopra la Fossa that had flattened upon impact; many had diameters of 20 cm or more. In one case, a bomb had fallen on the rim of one of the primitive shelters made by tourists in the summit area. Eruptive activity was at relatively low levels, and observations into Crater 3 were made for about 10 minutes. The crater floor was covered with a mixture of previously ejected scoriae and partially altered blocks fallen off the crater walls. Explosions pierced this mixture in at least two locations, and incandescent scoriae sprayed 15-20 m above the crater floor, which lay about 30 m below observation points on the S crater rim. During three hours of observation explosions occurred from up to three vents in Craters 1 and 3, and a persistent fluctuating glow was visible after nightfall in the northernmost part of Crater 1. This glow had been visible to Behncke previously during August while passing Stromboli island twice on the ferry connecting the Aeolian Islands with Naples.

Danielle Cottens reported via Stromboli On-line that while she was on the Pizzo around 1830 on 10 October the volcano was showing intense activity, with bombs often reaching the base of the Pizzo. Around 1930 she decided to go back to the village. After 30 minutes, at about 2000, a significant explosion occurred that ejected ash and scoria onto Pizzo and in the Fossetta. Other tourist groups climbing the volcano decided to go back.

Information Contacts: Stromboli On-line, maintained by Jürg Alean and Roberto Carniel (URL: http://stromboli.net); Roberto Carniel, Dipartimento di Georisorse e Territorio, Universitá di Udine, Via Cotonificio, 114 I33100 Udine (Email: carniel@dgt.uniud.it); Jürg Alean, Kantonsschule Zürcher Unterland, CH8180 Bülach, Switzerland (Email: alean@stromboli.net); Boris Behncke, Dipartimento di Scienze Geologiche, Palazzo delle Scienze, Università di Catania (DSGUC), Corso Italia 55, 95129 Catania, Italy (Email: behncke@mbox.unict.it).

08/2000 (BGVN 25:08) Low-to-moderate eruptive activity January-September 2000

Activity at Stromboli during January-September 2000 was low-to-moderate, as it was throughout 1999 (BGVN 25:01). During a field campaign on 10-19 May 2000 researchers from various universities closely observed activity at the volcano, which resulted in detailed accounts of activity at Stromboli's three main craters. During January-September several small Strombolian eruptions occurred at the volcano, with the largest reported eruptions on 4 July and 6 September 2000.

Activity during January-May 2000. During January and February 2000, low-to-moderate seismicity was recorded by the University of Udine's summit station (figure 61). During the two months there were brief periods with very few seismic events; for example on 1-7 January there were [less than 50] events/day. On 17 February, after a short gap in acquisition, the tremor intensity increased greatly from the average value of [~4 to a peak of ~8] volt seconds (V-s), but then returned to average values the following day.

Figure 61. Seismicity detected at the summit of Stromboli during January-[early October] 2000. [Data collection continued through October and will be reported in a future issue.] The yellow bars show the number of recorded events/day, and the red bars those saturating the instrument (ground velocity greater than 100 µm/s). The line shows daily tremor intensity computed by averaging hourly 60-second samples. The seismic station is located 300 m from the craters at 800 m elevation. Courtesy of Roberto Carniel.

During the first half of March seismicity was even lower than in the previous months, often with [less than 50] events/day and occasionally (1, 5-9, 11 March) as few as [less than 20] events/day (figure 61). During the second half of March, the number of events returned to normal values (100-120 events/day) and during April increased to 140-160 events/day. Despite the increase in the number of events from March to April, there was no significant variation in tremor intensity.

A technical problem prohibited the acquisition of data at the beginning of May. During 10-19 May the Universities of Udine, Florence, Hawaii, and Open University carried out a field campaign at Stromboli. During the 10 days, scientists collected near-continuous seismic, thermal, and infrasonic measurements. They also constructed an activity log that totaled ~71 hours and was divided into nine 2- to 15-hour long segments that covered all days in the observation period except 13 May. It is important to note that the number of events recorded by the seismic station are not directly comparable to the number of eruptions logged by visual observation because some eruptions may not have produced a seismic signal that was detectable by a short-period seismometer. For this survey the naming convention was changed from previous reports. The craters that were previously named 1,2, and 3, were renamed NE, Central and SW Craters, respectively.

Several active vents were observed in the NE and [SW] craters; up to five were in the NE Crater (figure 62). The western cluster (1/1) consisted of vents that emitted ejecta in three different directions: obliquely to the SW, obliquely to the NE, and symmetrically. This zone was the source of strong nighttime glow, and near-continuous sloshing/puffing sounds that were accompanied by regular emissions of single bombs between Strombolian events. The eastern cluster (1/2) consisted of two vents that would often erupt together. During the night this zone was the source of weak, intermittent glow. Vent clusters 1/1 and 1/2 were located on the floors of two coalesced depressions within the main NE Crater. The SW Crater was the location of at least two active vents (3/1) ~10 m apart on the SE portion of the crater. No night glow was observed from either vent. A zone of high-temperature fumaroles was aligned along crater-bounding fractures at the E rim of the SW Crater.

Figure 62. Sketch map of Stromboli's Crater Terrace drawn on 10-19 May 2000 from Pizzo sopra la Fossa and fitted to the map produced from a September 1995 EDM survey of the Crater Terrace (BGVN 20:11/12). Note: For this survey the naming convention was changed, craters that were previously named 1,2, and 3, were renamed NE, Central, and SW Craters, respectively. Courtesy of Andy Harris.

During 10-14 May, activity at 1/1 was characterized by emissions of molten ejecta in heavily loaded, single-shot fountains that reached heights of 50-350 m and landed as far as ~120 m away to the eastern edge of the SW Crater. Fountain heights and ejected volumes appeared to increase from 10-11 May, when maximum ejecta heights were 100-200 m, to 14 May, when ejecta reached up to 230-350 m. Bombs rarely landed within 50 m of Pizzo sopra la Fossa, which was ~140 m away from the 1/1 vent cluster. The 1/2 vent cluster was the source of pulsing, 20- to 30-second emissions of incandescent ejecta, ash, and gas. Ejecta were emitted in a diffuse spray, and ash-and-gas emissions reached <100 m above the vent. Two vents within 10 m of each other often erupted together 2-4 times per hour, with the westernmost vent usually erupting after the eastern vent began to erupt. Activity at 3/1 was characterized by 10- to 40-second emissions of gas and brown ash, containing minor ejecta. The ash clouds from 3/1 rose up to 300 m above the vent before detaching from it.

Overnight on 14-15 May the style of activity changed when all vents switched to gas-dominated emissions that reached lower heights (<75 m) than previously. Events also became increasingly quiet, such that by the evening of 15 May some emissions were completely silent. Ejections from 1/1 continued to be short, 1- to 2-second, single-shot events, but they contained low volumes of molten ejecta with minor amounts of ash. The ejections rose <75 m above the vent with gas being the dominant component. At 1/2 the emissions were gas dominated. Long-lasting emissions at 3/1 consisted almost entirely of gas and rose <100 m above the vent. This gas-dominated style of activity continued until the final day of observations on 19 May.

During the activity change the frequency of events remained relatively stable, with 11-17 events/hour. During 10-14 May the frequency decreased at 1/1 from 6-7 events/hour to 3-6 events/hour, and during 15-19 May increased at 3/1 from 2-5 events/hour to 5-8 events/hour.

The Central Crater was not active during the observation period. The hornito initially observed during July 1999 (BGVN 24:06) was the source of low-temperature fumarolic activity. The Central Crater was entirely filled, resembling a saddle between the SW and NE Craters, rather than a crater. The deep, funnel-shaped pit SE of the Central Crater that developed during 1997-99 (BGVN 24:06) appeared to be a well-established feature. Its morphology suggested that it was an eastern extension of the SW Crater with a low septum separating it from the SW Crater.

An ~5-m-wide, persistently degassing active vent (3A) was observed on the floor of the funnel-shaped pit. Another actively degassing vent (3B), which was established on the NW rim of the 3A pit during July 1999, was ~2 m wide and was not surrounded by any constructive features (e.g. hornito, spatter rampart, or crater features), suggesting that eruptions were rare or did not occur from it. A maximum temperature of 639°C was measured from the gas-heated walls of vent 3B. However, the temperature of vent 3B was variable and during low-activity periods the vent temperature fell below 550°C (the lowest detection limit of the thermal infrared thermometer). The variation in temperature was obvious during the day from increases and decreases in the vigor of degassing: vigorous degassing occurred at high temperatures, and weak degassing occurred at low temperatures. Similar variations in glow, temperature, and degassing were observed at vent 3A. The activity at 3A and 3B vents appeared to be inversely correlated; a decrease in temperature and degassing at 3B would often synchronize with an increase at 3A, and vice versa.

Overall, during the observation period a total of 916 Strombolian events were recorded, with 383, 198, 335 events occurring at vent clusters 1/1, 1/2, and 3/1, respectively. The overall eruption rate was 13 events/hour, with a range of 6-20 events/hour and a typical repose of 5 minutes (the maximum repose was 37 minutes). Breaking these statistics down by vent, 1/1, 1/2, and 3/1 were respectively active with 5, 3, and 5 events/hour, with ranges of 0-12, 0-6, and 0-9 events/hour, and mean reposes of 12, 22, and 12 minutes (the maximum repose times were 194, 136, and 117 minutes).

Activity during June to mid-August. According to Sistema Poseidon, during mid-to-late June there was frequent Strombolian activity of medium intensity, with tephra reaching ~100-150 m above the crater's edge. This activity was regular, with about one event every 20 minutes and less regular ejections of ash and secondary debris coming from a second active vent in the same crater. By the end of June activity at the other summit craters was limited to abundant steam emissions. In early August, explosive eruptions occurred primarily in the northern vent and more sporadic eruptions occurred in the southern vent.

Small eruptions on 4 July and 6 September. Stromboli On-Line reported that at about 0935 on 4 July two large explosions were separated by 1-2 seconds. Only a small amount of ash was observed from the eruptions. They also reported that at 0554 on 6 September a violent eruption woke up the population. The ash cloud from the eruption rose to at least 1 km in altitude. The timing of the eruptions is shown on the plots of event frequency and intensity during January-September (figure 61).

Information Contacts: Andy Harris, Department of Earth Sciences, The Open University, Milton Keynes, MK7 6AA, U.K. (Email: harris@pgd.hawaii.edu); Roberto Carniel, Dipartimento di Georisorse e Territorio, Università di Udine, via Cotonificio 114, I-33100 Udine, Italy (Email: carniel@dgt.uniud.it, URL: http://stromboli.net); Maurizio Ripepe, Dipartimento di Scienze della Terra, Università di Firenze, via G. La Pira 4, I-50121 Firenze, Italy (Email: maurizio@ibogfs.cineca.it); John Bailey, Department of Geology and Geophysics, SOEST, University of Hawai' i, 2525 Correa Road, Honolulu, HI 96822, USA (Email: JBailey@soest.hawaii.edu); Stromboli On-line, maintained by Jürg Alean and Roberto Carniel (URL: http://stromboli.net); Jürg Alean, Kantonsschule Zürcher Unterland, CH8180 Bülach, Switzerland (Email: alean@stromboli.net); Sistema Poseidon, a cooperative project supported by both the Italian Government and the Sicilian Regional Government, and operated by several scientific institiutions (URL: http://www.poseidon.nti.it/).

04/2001 (BGVN 26:04) Variable seismicity during late 2000 and early 2001; spatter ejected above crater rims

This report covers the period of October 2000-February 2001, describing variable activity since the last report (BGVN 25:08).

During the last three months of 2000 the seismic activity recorded by the University of Udine summit station (figure 63) remained in the low to moderate range, comparable to the previous months. Short periods were again characterized by a very low number of events. In particular, under 50 events were recorded on several days during the period 29 October-16 November. The period between late December 2000 and early January 2001 was characterized by slightly increased activity, with more than 250 events/day and a tremor intensity occasionally exceeding the value of 5 volt·seconds (V·s). A drop in seismicity at the end of January was followed by an increase in all parameters during February, with the number of seismic events again exceeding 250 per day on 20 and 21 February. "Major" seismic events, which caused instrument saturations, were concentrated in the period 17-22 February, with a peak of 44 and 48 saturating events on 20 and 21 February, respectively (figure 63). The tremor intensity showed a slower but steady growth, with values slightly over 2 V·s at the beginning of February, and near 6 V·s at the end of February.

Figure 63. Seismicity detected at the summit of Stromboli during the period October 2000 - February 2001. Open bars signify the number of recorded events per day; solid bars, saturating events (i.e. with ground velocity exceeding 100 µm/s). The line shows the daily average of tremor intensity derived from hourly 60-second samples. The seismic station is located 300 m from the craters at 800 m elevation. Courtesy of Roberto Carniel.

Jürg Alean visited the volcano several times during mid-October 2000. On 10 October 2000, he observed about 6 eruptions/hour at the Southwest Crater (formerly called Crater 3), expelling large amounts of ash, sometimes almost hiding the glowing spatters that were being ejected to moderate heights. Vent 3B glowed intensely but never ejected lava. The Northeast Crater (formerly called Crater 1) had grown substantially over the last 7 years (figure 64) and was clearly separated into two pits, both of which were glowing at night with vent 1/1 glowing more strongly (vent clusters 1/1 and 1/2 are located on the floors of two coalesced depressions within the main Northeast Crater).

Figure 64. Different sketch maps of Stromboli's Crater Terrace drawn on the basis of ground stereo photos from 1993, 1996, and 2000. These highlight the changes in the morphology of the crater area during these seven years. Other maps and sketches can be found on the Stromboli On-line website. Courtesy of Jürg Alean.

Alean reported that on 13 October Southwest Crater had more eruptions, ~10 per hour. Further, the kind of activity was different with a total absence of ash and a much longer duration of individual eruptions, some over 30 sec; spatters reached ~100 m above the crater rim. Activity had also increased at Northeast Crater: vent 1/1 delivered several eruptions/hour, mostly at an oblique angle towards Pizzo, while vent 1/2 erupted only weakly about once/hour. On 15 October, the sudden occurrence of very noisy degassing events heard several times at Stromboli village (e.g. 1106, 1125, 1145 and 1245) confirmed the variability of the eruptive activity during this week. No similar noises were heard later that day.

Roberto Carniel visited the summit crater area on 29 November 2000 and noted that there were significant changes since Alean's earlier visit in October. The hornito, located where the Central Crater (formerly called Crater 2) was located, was showing more intense degassing, and a new vent had opened between the hornito itself and vent 3B (figure 64), thus suggesting a renewal of the activity in this sector. This new vent, which Carniel labeled 3C, showed continuously puffing degassing, similar to vent 3B. At night, both were incandescent and continuously moderate spattering was observed at vent 3C, with small-sized spatters sometimes reaching the vent rim, landing on the crater terrace. Vent 3C also showed Strombolian eruptions, with vertically ejected, molten material reaching over 50 m above the rim.

Information Contacts: Roberto Carniel, Dipartimento di Georisorse e Territorio, Universitá di Udine, via Cotonificio 114, I-33100 Udine, Italy. (Email: carniel@stromboli.net); Jürg Alean, Rheinstrasse 6, CH-8193 Eglisau, Switzerland (Email: alean@stromboli.net); Stromboli On-line website, maintained by Alean and Carniel (URL: http://stromboli.net).

07/2001 (BGVN 26:07) Continued Strombolian activity during March-May 2001; crater morphology changes

This report discusses the period March-May 2001, which included a 10-day interval of field observations. Observers and instruments documented variable volcanism and seismicity ongoing since the last report (BGVN 26:04).

Seismic activity increased in early March, as recorded by the University of Udine summit station, which is located 300 m from the craters at 800 m elevation. On 13 March the number of events per day reached 200. The latter half of March was characterized by a decrease of tremor intensity and by a noteworthy number of saturating events (peaking at 63 on 20 March). In April a reprise of the tremor intensity occurred but the number of triggering seismic events decreased. May was characterized by an increased number of seismic events.

During 14 days (10-24 May) of continuous seismic, thermal, and infrasonic measurements, the authors recorded a detailed 16-hour-long log of activity, and they updated the crater terrace map (figures 65 and 66). During the period, 1,050 seismically determined Strombolian events were recorded overall. These came from the NE, Central, and SW craters, with respective craters discharging 463, 42, and 545 events, respectively. These data provide an average daily rate (over the 62-hour period) that ranged from 5 to 31 events/hour and averaged 17 events/hour. Thus, the average repose time between eruptions was ~3.5 min; the largest measured repose time for the three vents was 22 minutes.

Figure 65. A sketch map showing Stromboli's Crater. The Terrace was drawn during 10-24 May 2001 from Pizzo Sopra la Fossa and fitted to the map produced from the September 1995 EDM survey of the Crater. Note that, the prefix "2" has been used to denote Central Crater vents as opposed to the "3" prefix used BGVN 25:08. The map does not use contours, instead the long lines show the steepest gradient of the slope. Courtesy of Andy Harris.
Figure 66. A panoramic view of Stromboli's crater terrace area taken on 10 May from Pizzo Sopra la Fossa and highlighting plumes from synchronous activity at the two SW Crater vents (3/3, 3/2). Brown ash rose from 3/2 and gray ash rose from 3/3. Courtesy of Dave Rothery.

Breaking these statistics down by individual crater, the NE, Central, and SW craters had respective daily averages that ranged as follows: 2-21, 0-3, and 1-19 events/hour. The crater's average event rates were 8, 1, and 9 events/hour, respectively. This gives average repose times for the craters of 8, 69, and 7 min, respectively. For comparison, the maximum repose times at NE, Central, and SW craters were 46, 420 and 105 minutes.

As in May 2000 (BGVN 25:08), the NE Crater consisted of two smaller pits separated by a low septum, the two pits being the location of one and two active vents, respectively. Of these, the western-most vent (1/1) and eastern-most vent (1/2) were most active, with average rates of 4 and 3 events/hour, respectively, compared with ~1 event/hour for vent 1/3. The SW crater contained three active vents that often showed paired or synchronous activity. However, the exact combination of paired eruptions varied daily. For example, on 16 May, an eruption from 3/1 would often be followed by one from 3/2 within a few seconds; but, on 19 May, an eruption from 3/1 would be followed by one from 3/3. As in previous years, eruptions from the SW crater had longer durations and were richer in ash than those from the NE crater.

The frequency and style of activity at the NE crater showed significant variations. During 10-11 May, the NE crater erupted up to 10 times/hour. Events at vent 1/1 were characterized by single-shot, ejecta-loaded Strombolian eruptions, while those at vent 1/2 were long duration (typically 10-20 s), gas-rich eruptions with diffuse ejecta sprays. During 14-15 May, the eruption rate increased to 12-17 events/hour, as eruptions at 1/1 switched to longer duration (~10 s), gas-rich ejections mixed with ash and small bombs. At the same time, events from vent 1/2 contained more bombs that reached ~300 m above the crater. On 16 May, maximum eruption rates declined to 8 events/hour, and ejections from 1/1 and 1/2 were characterized by diffuse sprays of small incandescent bombs mixed with ash to ~200 m. During 17-20 May, activity from both vents was characterized by strong eruptions, often occurring in multiple pulses, with heavy bomb loads to 200-300 m above the crater, and maximum eruption rates of 21 events/hour. Activity declined by 21 May and, by 23 May, activity consisted of gas-rich eruptions with rare-to-no bombs and maximum eruption rates of 5-6 events/hour.

During 11-20 May, the eruption rate at the SW crater increased from 1-12 events/hour (11-16 May) to 6-19 events/hour (18-20 May). Events were typified by 20- to 40-second-long emissions of gas, ash, and bombs. During this period, the ash component appeared to decline and the bomb component appeared to increase. The area inundated by bombs gradually increased, reaching the outer flank of the NE crater by 17 May. Activity peaked on 22 May when strong eruptions with heavy bomb loads were observed. At this time bombs hit the cliff below the Pizzo Sopra la Fossa and cleared the lower section of the pizzo ridge where the lowest tourist shelters are located. Bombs ~0.5 m in diameter fell within 20 m of that location and the path was littered with fresh scoria tens of centimeters in diameter. By 23 May, activity had changed entirely with the eruption rate down to 5-6 events/hour and activity characterized by gas- and ash-rich ejections with few or no bombs.

The Central Crater had evolved significantly since May 2000, when the a funnel-shaped pit that had developed during 1997-99 in the SE sector of the crater (BGVN 24:06) was active with a single degassing vent only (BGVN 25:08). Over the intervening period this pit has filled and now has an inactive hornito. Since May 2000, a new hornito (2B) has developed on the rim of this pit, with a 5-10 m wide vent (2A) at its base. The 2A vent was incandescent by night and radiometer-measured temperatures were in the range 726-577°C.

The summit of the 2B hornito was occupied by an open vent that was the source of continuous gas emission with weakly formed puffs, but no eruptions during the observation period. Vent 2A was the source of vigorous degassing with well-formed puffs. Frequent vigorous phases here often sent one or two pieces of scoria to a height of 10 m above the vent rim. This vent was also the location of rare Strombolian explosions, with just 11 observed during the entire 62-hour observation period.

A new ~2 m wide vent (2C) had also opened towards the center of the Central Crater, and appeared to be the source of a small lava flow that was not observed during May 2000. The surface shows a pahoehoe form, and the flow extends around the base of the inactive hornito 2E and laps up against the back wall of the Crater Terrace (figure 65). Vent 2C was also the source of rare (24 over the entire observation period) Strombolian eruptions, characterized by loud, emissions that created well-formed column-shaped ejecta-bearing plumes.

Explanation of seismic events. In the discussion above, the number of seismic "events" is not directly comparable to the number of "eruptions" for two reasons. First, not all eruptions produce a seismic signal in the frequency range recorded by the short-period seismometer installed by University of Udine. Second, the seismic acquisition at Udine employs a trigger algorithm, which, although not perfectly efficient, has been kept constant since the installation of the 3-component station in 1992 to guarantee coherency between the graphs presented in the Bulletin.

Information Contacts: Andy Harris, Department of Earth Sciences, The Open University, Milton Keynes, MK7 6AA, U.K. (Email: harris@pgd.hawaii.edu); Roberto Carniel, Dipartimento di Georisorse e Territorio, Università di Udine, via Cotonificio 114, I-33100 Udine, Italy (Email: carniel@dgt.uniud.it, URL: http://stromboli.net); Maurizio Ripepe, Dipartimento di Scienze della Terra, Università di Firenze, via G. La Pira 4, I-50121 Firenze, Italy (Email: maurizio@ibogfs.cineca.it); Emanuele Marchetti, Dipartimento di Scienze della Terra, Università di Firenze, via G. La Pira 4, I-50121 Firenze, Italy; John Bailey, Department of Geology and Geophysics, SOEST, University of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (Email: Jbailey@soest.hawaii.edu); Scott Rowland, Department of Geology and Geophysics, SOEST, University of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (Email: scott@high.hawaii,edu); Jürg Alean, Kantonsschule Zürcher Unterland, CH8180 Bülach, Switzerland (Email: lean@stromboli.net); Dave Rothery, Department of Earth Sciences, The Open University, Milton Keynes, MK7 6AA, U.K. (Email:d.a.rothery@open.ac.uk); Jonathan Dehn, University of Alaska Fairbanks, 903 Koyukuk Drive, Fairbanks, AK 99775, USA (Email: jdehn@gi.alaska.edu); Stromboli On-line, maintained by Jürg Alean and Roberto Carniel (URL: http://stromboli.net).

10/2001 (BGVN 26:10) Major explosion at Stromboli kills a tourist on 20 October 2001

Continuing Strombolian activity resulted in crater-morphology changes during March-May 2001 (BGVN 26:07). Similar activity has continued at Stromboli (figure 67), with a major explosion occurring on 20 October.

On 20 October 2001 at 0237 ejecta from a major explosion at the active vents reached a group of tourists a few hundred meters away near Pizzo sopra La Fossa, severely injuring a woman who died a few days later at Messina hospital. On behalf of the Italian Civil Protection, Franco Barberi and others visited the crater on 21 October. The following is their report, including a summary of field observations, information provided by a Stromboli guide, and a brief examination of images recorded by a video camera at Pizzo sopra La Fossa managed by the Section of Catania of the Istituto Nazionale di Geofisica e Vulcanologia.

Figure 67. Seismicity detected near the summit of Stromboli during May-early November 2001. The gray-shaded bars signify the number of recorded events per day; the much smaller solid-black bars signify saturating events (i.e. with ground velocity exceeding 100 µm/s). The line shows the daily average of tremor intensity derived from hourly 60-second samples. The seismic station is located 300 m from the craters at 800 m elevation. Courtesy of Jürg Alean and Roberto Carniel.

Major explosion on 20 October 2001. In the days preceding the explosion, since at least the afternoon of 16 October, Stromboli's activity was intense at crater 3 and less intense at craters 1 and 2. A strong explosion from crater 2 occurred at about 0100 on 17 October and was followed by a lingering prolonged incandescence within the crater indicating that magma was very near to the surface. The situation remained almost the same, with fluctuations, until the morning of 19 October, when activity decreased. It again gained vigor in the afternoon and during the following night, mostly from crater 1 and subordinately from crater 2. Activity at crater 3 was less frequent compared with that of the preceding days.

The major explosion at 0237 of 20 October is clearly visible on the recorded images. The ejected material was mostly made of large blocks of strongly altered old lava. At Pizzo sopra La Fossa, where the tourists were located, several blocks of these old lavas were observed, with a maximum size of 40 x 40 x 20 cm, and clear impact pits in the loose soil (a dozen over a surface of 40 m2). Fresh scoriaceous material was rare, making it difficult to assess whether any juvenile clasts were associated with emission of the solid blocks. Fresh scoriae were abundant descending the path that approaches crater 3. The guide confirmed that in the days preceding the accident, glowing scoriae from crater 3 landed on the path to the crater rim.

Examination of the freshly ejected material revealed two previously recognized pumice and scoria suites. Some fresh material showed the intermingling of black scoria and golden pumice characteristic of type "b" of the major explosions of Stromboli described in the background section below. The nature of emitted products indicates that the explosion of 20 October was of type "a." Both types of major explosions appear to have occurred within a couple of days.

The 20 October explosion produced a new crater hole, a few ten's of meters across, between craters 1 and 3 near a small pre-existing hornito. For a few hours after the explosion, activity remained high at crater 1 and some glowing scoria set fire to vegetation in the upper part of a neighboring small valley. On the morning of 21 October, the activity had returned to normal levels, with Strombolian explosions at about 20-minute intervals, mostly from crater 1.

Civil protection implications. Every year thousands of tourists climb Stromboli, attracted by its persistent activity. The Pizzo sopra La Fossa is an ideal site for observation, as it dominates the crater terrace hosting the active craters a few hundred meters below (see maps in BGVN 15:04). The sudden occurrence of major explosive bursts, with ejecta landing on Pizzo sopra La Fossa, represents a threat for these tourists. Accordingly, access to the crater zone is prohibited and it is forbidden to spend the night there. However, there is no apparent enforcement of the restrictions, and there are only a few warning notices at the beginning of the path. For many years Italian volcanologists have, in vain, suggested that local authorities build appropriate shelters at Pizzo sopra La Fossa, to allow tourists to observe the volcanic activity in reasonably safe conditions. The 20 October incident could have been avoided. For example, the tourists could have heeded the suggestion to immediately leave the zone, given by the guide, who found them at that dangerous site 4 hours before the explosion.

The search for possible geophysical and geochemical precursors of these major explosions continues. It remains the main objective of the volcanological research on Stromboli (Carapezza and Federico, 2000).

Background on petrology and eruption dynamics. Activity occurs mostly from three craters, conventionally named 1 to 3 from NE to SW. The craters are located at ~750 m elevation within the "crater terrace," a flat area in the upper part of Sciara del Fuoco, a depression cutting the NW flank of the volcano.

The ordinary persistent activity of the volcano (Strombolian), is characterized by continuous emission of steam and gas, frequent explosions of moderate energy, and a magma column at persistently high levels in the conduit that feeds the eruptive vents. During the normal Strombolian activity, explosions occur on average every 10-20 minutes and produce jets of gas, fragments of black, crystal-rich (~50% of phenocrysts), shoshonitic scoriae, and solid blocks of pre-existing lavas, usually strongly altered, ripped from the conduit walls. The jet height is around 200-300 m and ejecta fall mostly within the crater terrace without affecting the Pizzo sopra La Fossa zone and the access paths (Barberi and others, 1993).

This ordinary activity is periodically interrupted, on average twice a year, by more violent explosions that may be associated with lava-flow emission. Jets reach a height up to 500 m, and molten as well as solid fragments fall over an area with a radius of several hundred meters. The summit zone is frequently visited by tourists. Much rarer are the so-called "eruptive paroxysms" that occur on average every 5-15 years and may also affect the inhabited zones of the island (Stromboli and Ginostra villages) with showers of bombs and blocks, ash falls, glowing avalanches, and even small tsunamis (Barberi and others, 1993).

From the nature of the erupted products, two different types of major explosions have been identified at Stromboli (Barberi and others, 1993): a) events characterized by the emission of mainly solid old lava blocks, with subordinate fragments of new magma. They are probably produced by the sudden expansion of over-pressured gas pockets accumulated in proximity to the magma column in zones with obstructed conduits; b) sudden and violent lava fountains with high emission rates of vesiculated glowing magma fragments and minor solid blocks. During these events, in addition to the usual black scoriae of the ordinary Strombolian activity, and closely intermingled with them, are crystal poor (~10% of phenocrysts) golden pumices. The chemical compositions of the two types of lapilli are nearly identical, and the black scoria is interpreted as the degassed and largely crystallized equivalent of the golden pumice (Bertagnini and others, 1999; Metrich and others, 2001). Therefore, the major type "b" explosions seem generated by the injection of a discrete volume of deep, gas-rich, and largely liquid magma, into the cooler, crystal-rich, more viscous and degassed magma permanently present in the upper part of the eruptive system.

References. Barberi, F., Rosi, M., and Sodi, A., 1993, Volcanic hazard assessment at Stromboli based on review of historical data: Acta Vulcanol. 3, p.173-187.

Bertagnini, A., Coltelli, M., Landi, P., Pompilio, M., and Rosi, M., 1999, Violent explosions yield new insight into dynamics of Stromboli volcano: Eos, Transactions of the American Geophysical Union, v. 80, p. 633, 636.

Carapezza, M.L., and Federico, C., 2000, The contribution of fluid geochemistry to the volcano monitoring of Stromboli: J. Volcanol. Geoth. Res., v. 95, p. 227-245.

Metrich, N., Bertagnini, A., Landi, P., and Rosi, M., 2001, Crystallization driven by decompression and water loss at Stromboli volcano (Aeolian Islands, Italy): J. Petrol., v. 42, no. 8, p. 1471-1490.

Information Contacts: Franco Barberi, Dipartimento di Scienze Geologiche, Università di Roma Tre, Largo San L. Murialdo 1, 00146 Roma (Email: fbarbe@tin.it); Maria Luisa Carapezza, Gruppo Nazionale per la Vulcanologia, INGV, Via Nizza 128, 00198 Roma (Email: carapezza@ingv.it); Jürg Alean, Kantonsschule Zürcher Unterland, CH8180 Bülach, Switzerland (Email: lean@stromboli.net); Roberto Carniel, Dipartimento di Georisorse e Territorio, Università di Udine, via Cotonificio 114, I-33100 Udine, Italy (Email: carniel@dgt.uniud.it, URL: http://stromboli.net).

01/2002 (BGVN 27:01) Fallout from 23 January explosion carpets popular tourist area

On 23 January at 2054 a large explosion occurred at Stromboli. The explosion was accompanied by a loud noise that was heard at all of the villages on the island and ashfall that lasted for several minutes.

On 24 January, staff from Istituto Nazionale di Geofisica e Vulcanologia - Sezione di Catania (INGV-CT) visited the area SE of the summit craters near Il Pizzo Sopra la Fossa between the Bastimento and La Fossetta. They found the area covered with ash and blocks, mostly comprised of lithic material, with some clasts up to 60 cm in diameter, and with minor amounts of spatter up to 1.7 m long. No golden-colored pumice was found, which typically characterizes the most energetic events of Stromboli (Bertagnini and others, 1999). The greatest density of lithics on the ground was found in a ~200-m-wide belt between the craters and Il Pizzo. Spatter was more frequent NE of Il Pizzo. Fine-grained material covered the crater zone and the volcano's NE flank to the village of Stromboli, ~2 km to the NE. A continuous carpet of fallout material covered the zone of Il Pizzo, a spot where many tourists visit. The explosion would have posed a serious threat to tourists had it occurred during a visit. Fallout from the eruption also damaged equipment located near the summit.

During the 2.5 hours of the survey observers recorded only five weak explosions from Crater 1 and none from Craters 2 and 3. This activity was much weaker than that observed after the major explosion of 20 October 2001 (BGVN 26:10), when 15 explosions were recorded from Crater 1 and 8 from Crater 3 during a 1-hour period.

Thermal images on 24 January showed that Crater 2 had a higher temperature than the other active craters. Maximum temperatures recorded at this crater were 320°C averaged over a pixel area of 40 cm, much higher than the 200°C recorded on 20 October 2001. The high temperatures were due to spatter coating the crater's inner walls following the 23 January explosion. Measurements also revealed that the diameter of Crater 2 had grown from an estimated 10 m in October to ~26 m after the January explosion.

From the type and distribution of erupted products and the morphological changes observed at the craters, observers suggested that the eruptive event of 23 January could be related to the obstruction of the conduit of one of the craters. Gas pressure within the conduit probably built up until a major explosion occurred, ejecting mostly lithics. Conduit opening was followed by intense magmatic explosions and spatter fallout. During the present phase, observers were concerned by the lack of explosive activity at Crater 3. This may suggest an obstruction of this crater, which might be followed by a new violent episode similar to the one on 23 January.

Reference. Bertagnini A., Coltelli M., Landi P., Pompilio M., and Rosi M., 1999, Violent explosions yield new insights into dynamics of Stromboli volcano: EOS Transactions, AGU, v. 80, n. 52, p. 633-636.

Information Contacts: Sonia Calvari, Massimo Pompilio and Daniele Andronico, Istituto Nazionale di Geofisica e Vulcanologia - Sezione di Catania (INGV-CT) Piazza Roma 2, 95123 Catania, Italy.

07/2002 (BGVN 27:07) Increased activity beginning in June 2002 culminates in strong explosion on 24 July

Except for the large explosion on 23 January 2002 (BGVN 27:01), activity at Stromboli was subdued until late June. However, activity fluctuated during 5-23 July (figure 68) and culminated with an explosion on the 24th. The explosion was observed (and photographed) from the harbor of the village of Stromboli by Boris Behncke and a group of French excursionists. Thermal camera and infrared spectrometer measurements were performed on 16 May and 22 June.

Figure 68. Seismic activity at Stromboli during January through mid-August 2002. Major events (those saturating the seismic station) became prominent starting in mid-June. Courtesy of Stromboli On-Line.

On 9 July, most activity was concentrated at several vents within the NE crater; the most vigorous vent was located farthest NE. Explosions sent bursts of incandescent bombs up to 150 m above this vent, with many directed obliquely toward the NE. The SW crater produced only a few weak explosions, while the central crater was inactive and remained so through 23 July.

On 17 July, the activity was much weaker; explosions occurred only at the most northeastern vent of the NE crater and produced jets of bombs that rose only a few tens of meters high. On 23 July the same vent produced incandescent jets up to 150 m high, some directed toward the Sciara del Fuoco, with spectacular cascades of bombs rolling toward the sea. Two smaller vents in the SW part of the NE crater were the site of smaller simultaneous explosions. Rather long-lived small explosions came from the SW crater and were often accompanied by ash plumes.

The explosion at about0745 on 24 July produced a brown, mushroom-shaped plume that rose ~500 m above the summit. The explosion occurred as a single burst followed by weaker ash emissions. While a loud detonation was heard in the village of Stromboli, no noise was noted at the village harbor. As a consequence of the explosion, light ash fell over the harbor area and on a number of nearby vessels. It is not known which crater produced the explosion and whether there were any persons present at the summit. Viewed from the neighboring island of Panarea during the evening of 24 July, the volcano continued its normal explosive activity with incandescent bursts at intervals of several tens of minutes.

Thermal camera and infrared spectrometer measurements by Instituto Nazionale di Geofisica e Vulcanologia (INGV). On 16 May and 22 June, a Fourier transform infrared (FTIR) spectrometer (figure 69) and FLIR thermal camera (figure 70) measurements of activity were performed on Crater 1 [NE Crater] and Crater 3 [SW Crater] from Pizzo Sopra la Fossa. Time, location, and estimates of intensity of periodic explosions were recorded.

Figure 69. Photo showing the FTIR spectrometer instrument located at Pizzo Sopra la Fossa during measurements of Crater 1 in May and June 2002. Courtesy INGV.
Figure 70. Photo showing the FLIR thermal camera located at Pizzo Sopra la Fossa during measurements of Crater 1 in May and June 2002. Courtesy INGV.

On 16 May, activity at the summit was primarily located at Crater 1 and consisted of relatively weak explosions containing smaller amounts of pyroclasts than had been seen in the preceding months. Examples of some explosions recorded with the FLIR are shown in figure 71.

Figure 71. FLIR images of Stromboli taken on 16 May 2002. Crater 1a at 1314 (top) shows pyroclastics estimated to be ~ 40 m above the source. Crater 1b at 1319 (bottom) has only a gas cavity visible. Temperature ranges vary with each image. Courtesy INGV.

On 22 June, FTIR and FLIR measurements were made from Pizzo Sopra la Fossa, observing all three craters. Measurements began at 1142 and concluded at 1350. Activity at the summit was primarily located at Crater 1 and consisted of explosions that propelled scoria to a maximum height of ~250 m above the craters. Occasional ash emissions were observed from Craters 1a and 3. The activity was of significantly greater intensity compared with that observed in May. Figure 72 shows the resulting images from measurements taken with the FLIR camera.

Figure 72. FLIR images of Stromboli taken on 22 June 2002. Crater 1a at 1150 (top) and Crater 3 at 1220 (bottom). Temperature ranges vary with each image. Courtesy INGV.

Information Contacts: Boris Behncke, Dipartimento di Scienze Geologiche, Universita di Catania, Corso Italia 55, 95129 Catania, Italy (URL: http://stromboli.net/boris); Instituto Nazionale di Geofisica e Vulcanologia (INGV); Sezione di Catania (URL: http://www.ct.ingv.it/); Stromboli On-Line (URL: http://www.stromboli.net/).

12/2002 (BGVN 27:12) Landslides on 30 December cause two tsunamis; damage in nearby villages

Following heightened seismicity during June-July 2002 that culminated in an explosion on 24 July (BGVN 27:07), major activity lessened until late December.

On 28 December, an effusive eruption started at the base of Crater 1 of the NE Crater in the summit area. This eruption ended on 29 December and a helicopter-borne thermal camera survey that day revealed three lava flows that had spread in the eastern Sciara del Fuoco and had reached the sea. Along the coast, the joined flows were ~300 m wide, but were no longer being fed.

Visibility improved on 30 December, when a new survey found an eruptive fissure running NE. The fissure started from the base of Crater 1 at ~700 m elevation and spread down to ~600 m elevation, along a length of ~200 m. On 30 December observers saw a ~200-m-long lava flow emitted from the base of the fissure, spreading in the upper Sciara del Fuoco into a small depression.

Landslides and tsunami. On 30 December at 1315 and 1322 two landslides formed along the Sciara del Fuoco. They reached the sea accompanied by fine (0.1 mm grain-size) wet dust falling on the SE flank of the island (from rock collisions during the landslides). The volume of the first landslide was estimated at ~6 x 106 m3 of rock while the second was smaller at ~5 x 106 m3 of rock. These landslides detached the lava from the 28 December eruption along the slope together with a large portion of the ground below.

The large volume of rock crashing into the sea caused two tsunamis, each with waves several meters high. The waves spread onto the villages of Stromboli and Ginostra damaging buildings and boats and injuring several people (according to news reports, six people were evacuated by helicopter and taken to two hospitals on Sicily). Large waves were reported on the northern coast of Sicily, 60 km S of Stromboli. The two separate landslides were formed from two distinct bodies of rock, and left a ridge on the Sciara del Fuoco wall between them. This ridge may collapse in the future; its volume is estimated to be similar to that of the first landslide.

As of 6 January 2003, the effusive eruption and thin lava flows continued along the Sciara del Fuoco. Two vents located at ~500 m and ~300 m elevation in the middle of the Sciara del Fuoco were feeding two narrow flows that merged and reached the sea. Occasional small landslides from the unstable walls of the Sciara covered the lava flows with a thin talus. Concern over another major landslide had diminished due to several small-volume rockfalls from the walls of the depression. The summit craters had not shown any explosive activity since the start of the eruption on 28 December, and no earthquakes were recorded by the indigenous seismic network. Two shocks recorded by INGV seismic stations were directly related to the spreading of the two landslides on the Sciara del Fuoco.

Previous tsunamis at Stromboli occurred in 1930, 1944, and 1954. These were related either to paroxysmal eruptive activity, to landslides along the Sciara del Fuoco, or to pyroclastic flows, but not associated with lava flow venting.

Information Contacts: Sonia Calvari, Instituto Nazionale di Geofisica e Vulcanologia (INGV); Sezione di Catania (URL: http://www.ct.ingv.it/, Email: calvari@ct.ingv.it); Stromboli On-Line (URL: http://www.stromboli.net/).

01/2003 (BGVN 28:01) Lava emissions continue into January; crater morphology changes

The effusive eruption at Stromboli, which began 28 December 2002, continued into January 2003. Effusion of lava occurred at a main vent located at 500 m elevation in the middle of the Sciara del Fuoco, within the scar remaining after the 30 December 2002 landslide. The position of this vent has been rather stable since its opening, also on 30 December. Another vent, located at 600 m elevation at the NE base of Crater 1, has been active several times during the eruption, forming low-effusion rate, short lava flows lasting from a few hours to a few days. Effusion rates along the Sciara del Fuoco from the 500 m vent were very variable. During peaks in effusion rate, aa lava flows were reaching the sea causing phreatic explosions at the front. A decrease in effusion rate formed a fan of thin, narrow lava flows spreading on the upper flow field without reaching the sea.

Activation of the 600 m vent occurred each time the 500 m vent showed a marked decrease in effusion rate, suggesting a temporary magma level rise within the feeder conduit of the volcano. This observation was confirmed by an approximately 50°C increase in temperature at the bottom of the craters during activation of the 600 m vent, recorded during daily thermal mapping from a helicopter.

Lava flow emission along the Sciara del Fuoco formed a very thick flow field within the landslide scar of 30 December. Occasional small landslides from the unstable walls of the Sciara cover the lava flows with talus, increasing the thickness and instability of the flow field.

During a helicopter-borne thermal survey carried out on 12 January, arcuate cracks were detected around the southern base of the summit craters of the volcano. Other fractures, oriented NE-SW, cut through the craters. These probably result from drainage of magma in the upper part of the conduit. Collapse of the crater floor in early January significantly changed the morphology of the upper part of the volcano. Crater 2 (the middle crater) has disappeared, and Crater 1 (NE) and Crater 3 (SW) were joined together to form a unique, elongate depression. No explosive activity has been detected at the summit craters of the volcano since the start of the effusion within the Sciara del Fuoco.

Information Contact: Istituto Nazionale di Geofisica e Vulcanologia (INGV), Sezione di Catania Piazza Roma 2, 95123 Catania (URL: http://www.ct.ingv.it/, Email: calvari@ct.ingv).

04/2003 (BGVN 28:04) Strong explosion on 5 April covers much of the summit in pyroclastic deposits

On the morning of 5 April, scientists from INGV-CT were conducting a daily helicopter flight with a portable thermal camera, surveying the active lava flow field on the upper sector of the Sciara del Fuoco, above a flat zone at the base of the 28 December 2002 eruptive fissure. Three vents along this surface were feeding small lava flows, and the summit craters were producing a very diluted gas cloud. A few minutes after the start of the survey, which began about 0900, the gas plume from the craters being blown W was suddenly crossed by a reddish ash emission, which was interpreted as resulting from further collapses within the craters. However, the red ash was soon replaced by darker juvenile material coming from Crater 1 (the NE crater) that formed a hot jet with a cauliflower shape rapidly growing above the crater. A few seconds later, Crater 3 also produced a hot jet of juvenile material. Data from the seismic network confirmed that the explosion began at 0912.

The eruptive process then evolved very rapidly, with jets from craters 1 and 3 joining together. A very powerful explosion pushed the helicopter away from the crater. A mushroom-shaped dark cloud rose from the craters, expanding vertically to an altitude of ~2 km, 1 km above the volcano's summit (figure 73). The eruptive cloud was surrounded at its base by a dark-gray cloud, while it was still expanding vertically and assuming the mushroom shape. Bombs, ash, and blocks fell on the NE flank above 400 m elevation, burning vegetation. Most of the ejecta drifted W, falling on Ginostra (~1.5 km from the summit) and destroying two houses; no people were injured.

Figure 73. Photograph of the expanding eruption plume at Stromboli on 5 April 2003. Courtesy of INGV.

Continuing the helicopter survey after the eruption, observers saw that the lava-flow field on the upper Sciara del Fuoco was completely covered by a brown carpet of debris ejected from Crater 1 during the initial phase of the event. A thick steam cloud rose above the debris due to vaporization from the wet material by the underlying lava flows. Meanwhile, several alternating black and reddish pulses occurred, mainly from Crater 3. Several fingers of light-brown debris were expanding from the NW flank of Crater 1 along the mid-section of the Sciara del Fuoco. The upper part of the volcano above 700 m elevation was completely covered by pyroclastic products. Within a few minutes after the start of the eruption, the upper Sciara del Fuoco had active flows emerging from the layer of debris covering the lava-flow field. The explosive event caused abundant emission of pumice mixed with small brown scoria. The pumice contained small crystals and was very vesiculated. Lithic fragments of lava with light-gray groundmass and centimeter-sized crystals of pyroxene were common in the pumice.

A helicopter survey on 8 April showed four active vents pouring lava onto the upper Sciara del Fuoco at 590 m elevation. Two of the flows were expanding along the middle Sciara del Fuoco, causing detachment of blocks from the flow front and small rockfalls that reached the sea. Within the summit craters a thick layer of debris had accumulated following the event of 5 April.

Information Contact: Sonia Calvari, Istituto Nazionale di Geofisica e Vulcanologia, Piazza Roma 2, 95123 Catania, Italy (URL: http://www.ct.ingv.it/, Email: calvari@ct.ingv.it).

05/2003 (BGVN 28:05) Lava effusion continues through mid-June; infrared satellite observations

The latest eruptive episode from Stromboli began on 28 December 2002 (BGVN 28:01) and included a significant explosion on 5 April (BGVN 28:04). This report includes field observations provided by the Istituto Nazionale di Geofisica e Vulcanologia (INGV) through mid-June 2003. Thermal alerts based on infrared satellite imagery over the course of this eruption have been compiled and summarized by scientists at The Open University.

Activity during 17 April-16 June 2003. Effusion of lava from vents located at ~600 m elevation, on the upper eastern corner of the Sciara del Fuoco, continued until 16 June with a generally decreasing effusion rate. This caused a significant increase in the thickness of the lava field formed since 15 February to over 50 m. Since the 5 April eruption, the summit craters of the volcano have been blocked by fallout material obstructing the conduit. Small, occasional, short-lived explosions of hot juvenile material were observed on 17 April during a helicopter survey with a hand-held thermal camera, and on 3 May from the SAR fixed camera located at 400 m elevation on the E rim of the Sciara del Fuoco.

The effusion rate from the 600-m-elevation vents on the Sciara del Fuoco showed a significant decline between 1 and 4 May, when inflation of the upper lava flow field was detected through daily helicopter-borne thermal surveys. Inflation stopped on 6 May, when two new vents opened on the inflated crust of the flow field, causing drainage and spreading new lava flows along the Sciara del Fuoco. Between the end of May and early June, gas-rich magma was extruded from the 600 m vents on the upper Sciara del Fuoco. Spattering built up two hornitos, which in a few days reached an estimated height of over 6 m. This activity was accompanied by lava flow effusion along the upper Sciara del Fuoco, with lava descending to 150 m elevation.

On 1 June, Strombolian activity resumed at Crater 1 (NE crater). It was revealed first through helicopter-borne thermal surveys, and then by direct observations from the eastern Sciara del Fuoco rim. Most of the ejecta fell within the crater, and from the lower slopes of the volcano only pulsating dark ash emissions were observed. Strombolian activity stopped around 6 June, and occasional lava flows occurred at the hornitos at 600 m elevation on 11 June. The summit craters showed discontinuous ash emission until mid-June, and the SAR fixed camera at 400 m elevation showed a Strombolian explosion with abundant ash emission on the night of 15 June.

MODVOLC Thermal Alerts. MODIS thermal anomalies for Stromboli covering the period from the start of MODIS data acquisition over Europe in May 2000 until the present were compiled using data available at http://modis.higp.hawaii.edu/.

With the exception of single-pixel alerts on 8 July and 19 September 2000 (with alert ratios of -0.798 and -0.794, both barely above the -0.800 automatic detection threshold of the thermal alerts algorithm), activity at Stromboli remained below the automatic detection threshold until November 2002 (figure 74). In that month there were two single-pixel alerts, barely above detection threshold (-0.790 on 12 November and -0.792 on 28 November). Thermal infrared radiance was higher than ever before at the time of the MODIS overpass on 20 December 2002, when there was a two-pixel alert, with alert ratios of -0.667 and -0.749.

Figure 74. Alert-ratio, number of alert pixels, and summed 4 µm (MODIS band 21) spectral radiance for MODIS thermal alerts on Stromboli between 1 November 2002 and 13 May 2003. MODIS data courtesy of the HIGP MODIS Thermal Alert Team.

These five dates were the only MODIS thermal alerts prior to the start of effusive activity on 28 December 2002 (BGVN 27:12 and 28:01). The source of the radiance to trigger these alerts was evidently incandescence at one or more of the active vents. In the case of a volcano such as Stromboli, prior to December 2002, isolated thermal alerts are more likely to represent the chance coincidence of a short-lived peak of incandescence with the time of MODIS overpass, rather than a sustained emission of infrared radiation. However the November-December 2002 thermal alerts can with hindsight be seen to have been indicators of enhanced activity in the lead-up to the 28 December effusive eruption.

On 28 December 2002 MODIS recorded its highest ever alert ratio at Stromboli (+0.419) and highest summed radiance at 4.0 µm (MODIS band 21) in a seven-pixel alert, corresponding to the daily MODIS overpass at 2115 UTC. This is a record of radiance from 300-m-wide lava flows from the NE crater (BGVN 27:12). Subsequent to that date, thermal alerts have occurred persistently at Stromboli, and evidently reflect ongoing lava effusion. The general trend of the highest alert ratio on each date, the number of alert pixels, and the summed 4.0 µm radiance for all alert pixels on each date shows an exponential decline.

There are no thermal alerts for 3-7 April 2003 inclusive, which could be because of cloud cover. There is thus no direct record of the explosion on the morning of 5 April that completely covered the upper 200 m of the volcano with bombs. However, the mild intensification of subsequent thermal-alerts indicates slight re-invigoration of the on-going lava effusion.

Information Contacts: Sonia Calvari, Istituto Nazionale di Geofisica e Vulcanologia, Piazza Roma 2, 95123 Catania, Italy (URL: http://www.ct.ingv.it/, Email: calvari@ct.ingv.it); David A Rothery and Diego Coppola, Department of Earth Sciences, The Open University, Milton Keynes, MK7 6AA, United Kingdom (Email: d.a.rothery@open.ac.uk, diego.coppola@unito.it). MODIS data courtesy of the HIGP MODIS Thermal Alert Team.

07/2003 (BGVN 28:07) Flank eruption finished as of 22 July; activity resumed at summit craters on 17 April

Effusion of lava from vents located at about 600 m elevation on the upper eastern corner of the Sciara del Fuoco decreased in early June and completely stopped between 21 and 22 July. The decreasing effusion rate caused shorter lava flows, which during July did not spread below 600 m elevation. The upper part of the lava flow field, formed since 15 February on the upper Sciara del Fuoco, reached an estimated thickness of more than 50 m as a result of the slower rate.

[After] the 5 April eruption (BGVN 28:04), the summit craters of the volcano [were] blocked by fallout debris obstructing the conduit. [By 17 April the blockage was apparently cleared because] small, occasional, and short-lived explosions of juvenile, hot material were observed at Crater 3 (the SW crater) [that day] during a helicopter survey with a hand-held thermal camera, and at Crater 1 (the NE crater) on 3 May from the SAR fixed camera located at 400 m on the eastern rim of the Sciara del Fuoco.

Strombolian activity from Crater 1 (NE crater) became more frequent and intense in June, and almost continuous in July, with spatter often falling outside the crater. In July, Crater 3 (SW crater) activity consisted mainly of degassing and sporadic ash emissions, with Strombolian explosions becoming more common in the second half of July.

Erosion of the N flank of Crater 1 by landslides in the upper Sciara del Fuoco increased in July, with the 30 December 2002 landslide scar extending backward and upslope, cutting the flank of the cone 50 m below the crater rim.

Information Contact: Sonia Calvari, Istituto Nazionale di Geofisica e Vulcanologia, Piazza Roma 2, 95123 Catania, Italy (URL: http://www.ct.ingv.it/, Email: calvari@ct.ingv.it).

08/2003 (BGVN 28:08) Explosive activity in the summit craters and thermal signatures in the lava-flow field

The latest effusive eruption at Stromboli ended between 21 and 22 July (BGVN 28:07), when active lava flows on the upper Sciara del Fuoco were no longer visible. Since then explosive Strombolian activity became more common at both summit craters. Four active vents were observed within Crater 1 (the NE crater), and there was one funnel-shaped incandescent depression within Crater 3 (the SW crater). Strombolian activity during the first half of August was very intense at Crater 1, causing a spatter cone to form on the crater floor and incandescent bombs to fall on the outer flanks. Explosive activity at Crater 3 was apparently deeper, and was often accompanied by ash emission.

During the first half of August, thermal images of the apparently inactive lava flow field revealed thermal signatures within cracks on the upper flow field, and within skylights along two lava tubes in the upper Sciara del Fuoco, at ~550 m elevation. Temperatures of over 300°C, and incandescence of these hot spots, suggest endogenous growth. Incandescence and thermal signatures at these sites were not observed between 22 and 31 July.

Information Contact: Sonia Calvari, Istituto Nazionale di Geofisica e Vulcanologia, Piazza Roma 2, 95123 Catania, Italy (URL: http://www.ct.ingv.it/, Email: calvari@ct.ingv.it).

02/2004 (BGVN 29:02) After 10 February 2004, explosions at upper limit of that typically seen

According to aviation reports from the U.S. Air Force, the web camera at Stromboli captured shots of light ash emissions on 7 and 11 November 2003. In both cases plumes rose to ~ 2.5 km elevation. The Stromboli Web video camera showed a small explosion on 10 December 2003 that produced a plume to a height of ~ 1 km above the volcano. No ash was visible on satellite imagery.

The Istituto Nazionale di Geofisica e Vulcanologia (INGV) in Catania reported that explosive activity at Stromboli's three summit craters increased after 10 February 2004, leading to significant growth of the cinder cones inside the craters. Several powerful explosions, especially from Crater 1 (the NE crater) and Crater 3 (the SW crater), sent scoriae 200 m above the rims. These powerful explosions led to fallout of fresh bombs and lapilli on Il Pizzo Sopra la Fossa (an area atop the volcano about 100 m above the crater terrace) in early March. As of 8 March, Strombolian activity was occurring at the volcano, with variations in the number and frequency of explosions within normally observed limits, and the intensity of explosions at the higher limit of commonly observed activity.

Information Contacts: Istituto Nazionale di Geofisica e Vulcanologia (INGV), Sezione di Catania Piazza Roma 2, 95123 Catania, Italy (URL: http://www.ct.ingv.it/, Email: calvari@ct.ingv); Toulouse VAAC, Météo-France, 42 Avenue G. Coriolis, 31057 Toulouse, France (URL: http://www.meteo.fr/aeroweb/info/vaac/, Email: vaac@meteo.fr); AGI Online news service, Italy (URL: http://www.agi.it/).

03/2004 (BGVN 29:03) Webcams at various wavelengths document increased explosions in February 2004

Explosive activity at the summit craters of Stromboli volcano resumed in early June 2003, before the end of the effusive eruption that finished between 21 and 22 July 2003. Eruptive activity at this volcano is monitored by Istituto Nazionale di Geofisica e Vulcanologia (INGV-CT). They have installed two web cameras at an elevation of 920 m on Il Pizzo Sopra la Fossa and at an elevation of 400 m along the E margin of the Sciara del Fuoco, the depression on the N flank of the volcano. Additionally, a web thermal camera is located at the 400-m elevation site noted above, and a web infrared camera is positioned at Il Pizzo Sopra la Fossa. The 2 cameras (thermal and video) at the 400-m elevation site give important insights when visibility is insufficient at the more distant cameras. The infrared camera at Il Pizzo provides both a continuous view of the activity at the summit craters and a quantification of the energy released by the explosions at the three summit craters through an automated system called VAMOS (Cristaldi and others, 2004).

According to aviation reports from the U.S. Air Force, the web camera at Stromboli captured shots of light ash emissions on 7 and 11 November 2003. In both cases plumes rose to ~ 2.5 km altitude. According to the Toulouse VAAC the Stromboli Web video camera showed a small explosion on 10 December that produced a plume to a height of ~ 1 km above the volcano. No ash was visible on satellite imagery.

According to the INGV-CT, explosive activity at the three summit craters increased after 10 February 2004, leading to a significant growth of the cinder cones inside the craters. Several powerful explosions, especially from crater 1 (the NE-crater) and crater 3 (the SW-crater) carried scoriae 200 m above the craters. These explosions led to fallout of fresh bombs and lapilli on Il Pizzo Sopra la Fossa (the top of the volcano, ~ 100 m above the crater terrace) in early March. Samples of lapilli and scoriae collected on Stromboli by local guides have been analyzed with the scanning electron microscope and microanalysis instruments of INGV-CT (Corsaro and others, 2004). Measurements of glass compositions indicated that products erupted until 25 February 2004 are related to the black scoriaceous volcanics normally erupted during Strombolian activity. Golden basaltic pumices were absent from available samples; such pumices at this volcano have been generally associated with paroxysmal explosive events (Bertagnini and others, 1999) such as that of 5 April 2003. Analysis of components carried out on several ash samples allowed scientists at INGV-CT to recognize sideromelane and tachylite as the main components, making up ~ 80% of the erupted ash (Andronico and others, 2004). The activity of this volcano as of 8 March 2004 can be described, fittingly, as Strombolian with variations in the number and frequency of explosions within normally observed limits, and intensity of explosions at the higher limit of commonly observed activity.

References. Andronico, D., Caruso, S., Cristaldi, A., and Del Carlo, P., 2004, Caratterizzazione delle ceneri emesse dallo Stromboli nel Gennaio-Febbraio 2004: INGV-CT Internal Report, Prot. int. n° UFVG2004/034.

Corsaro, R.A., Miraglia, L., and Zanon, V., 2004, Caratterizzazione dei vetri presenti nei prodotti emessi dallo Stromboli durante il mese di febbraio: 2004 INGV-CT Internal Report, Prot. int. UFVG2004/033.

Cristaldi, A., Contelli, M., and Mangiagli, S., 2004, Rapporto settimanale sull'attivit eruttiva dello Stromboli: 22-29 Febbraio 2004. INGV-CT Internal Report, Prot. int. n° UFVG2004/031 [download at http://www.ct.ingv.it/].

Bertagnini, A., Coltelli, M., Landi, P., Pompilio, M., and Rosi, M., 1999, Violent explosions yield new insights into dynamics of Stromboli volcano. Eos, American Geophysical Union Transactions, 80, 52: 633-636.

Information Contacts: Sonia Calvari, Istituto Nazionale di Geofisica e Vulcanologia, Piazza Roma 2, 95123 Catania, Italy (URL: http://www.ct.ingv.it/, Email: calvari@ct.ingv.it); Charles Holliday, Air Force Weather Agency (AFWA), Satellite Applications Branch, Offutt AFB, NE 68113-4039, USA (Email: charles.holliday@afwa.af.mil).

04/2007 (BGVN 32:04) Flank eruption begins on 27 February 2007

According to Sonia Calvari of Istituto Nazionale di Geofisica e Vulcanologia (INGV-CT), a flank eruption started on Stromboli volcano on 27 February 2007 and continued to at least 15 March. Compared to the previous flank eruption during 2002-2003, lava effusion was about an order of magnitude greater. Initially, a NE fissure opened on the NE flank of the NE-crater, and lava emitted from the fissure formed three branches and rapidly reached the sea (figure 75).

Figure 75. Lava from Stromboli reaching the sea on 27 February 2007. Courtesy of the INGV-CT 2007 Stromboli eruption web site.

Late on the eruption's first day, the three initial flows stopped and a new vent opened at the E Margin of the Sciara del Fuoco at about 400 m elevation. In a few days, this vent emitted sufficient lava to build a lava bench several tens of meters wide, which significantly modified the coastline. These lava emissions stopped for a few hours on 9 March, after which another vent opened at about 550 m elevation on the N flank of the NE-crater, almost in the same position as one of the vents of the 2002-2003 eruption. The 550-m vent was active for less than 24 hours and, when it ceased emitting lava, the 400-m vent reopened, again feeding lava to the sea.

On 15 March 2007, while the effusion from the 400-m vent continued, a major explosion occurred at 2137 (2037 UTC). This event, similar to that on 5 April 2003 (BGVN 28:04), was recorded by all the INGV-CT monitoring web cams. As in 2003, the 2007 event occurred during a flank effusive eruption, when the summit craters were obstructed by debris fallen from the crater rims. Still images and videos can be downloaded from the INGV-CT webpage dedicated to the 2007 Stromboli eruption.

Satellite imagery. Satellite imagery revealed an ash plume fanning SSE from the eruption site beginning at 1215 UTC on 27 February 2007. Another eruption was observed on MET-8 split-window IR (infrared) imagery on the same day at 1830 UTC. Ash then blew SSE at 46-56 km/hour.

Information Contacts: Sonia Calvari, Istituto Nazionale di Geofisica e Vulcanologia Sezione di Catania, Piazza Roma 2, 95123 Catania, Italy (Email: calvari@ct.ingv.it, URL: http://www.ct.ingv.it/); INGV-CT 2007 Stromboli eruption website (URL: http://www.ct.ingv.it/stromboli2007/main.htm); U.S. Air Force Weather Agency (AFWA)/XOGM, Offutt Air Force Base, NE 68113, USA (Email: Charles.Holliday@afwa.af.mil).

03/2010 (BGVN 35:03) Explosions and lava flows in 2009; recent reports on 2007 eruption

Sonia Calvari of the Istituto Nazionale di Geofisica e Vulcanologia (INGV) reported that the 2007 eruptive episode at Stromboli started on 27 February and finished on 2 April (BGVN 32:04) Additional details about this eruption can be found in Barberi and others (2009) and Calvari and others (2010). Eruptions later in 2007 and during 2008 will be reported in a later issue; summaries of activity in 2009 and January 2010 are included below.

Activity during 2009. The summit activity in 2009 was very unusual, producing four or five intracrater lava flows. Lava within the crater depression was extruded on 22-25 April, 3 May, and 30 August 2009. On 8 November a major explosion from the vents in the central crater fragmented and destroyed part of the E flank of the cinder cone there. The explosion produced an eruptive column over 350 m high that drifted SE and was soon followed by a lava flow from the widened central vent. The lava flow spread within the crater depression for a few minutes and reached a maximum distance of ~ 60 m. After the 8 November explosion, activity returned to background levels.

Strong seismic activity was recorded on 24 November 2009. Observers saw an explosive eruption cloud and the emission of a lava flow. Ejecta fallout affected the summit area, particularly the Pizzo sopra la Fossa, where numerous volcanic bombs landed. Also affected was the eastern downwind flank, where a layer of pumice was deposited on the beach. The fallout of incandescent material caused some vegetation fires on the E flank. After this explosive activity, seismicity returned to the level previously observed.

Activity during January 2010. According to the INGV website, at 1912 UTC on 4 January 2010, the network of surveillance cameras recorded an explosion that affected the central vent area. During a first phase, coarse pink pyroclastic materials (bombs and possibly lithic particles) were erupted from the entire crater terrace. A second phase followed with the emission of a small ash plume. Beginning at 0757 UTC on 7 January, the IR camera located on the Pizzo sopra la Fossa showed spattering lava in the central portion of the crater, leading to a series of lava flows; the lava stopped around 0100 UTC on 8 January. At 1448 UTC on 10 January, the INGV network of surveillance cameras recorded a strong explosion that affected the N portion of the crater, causing a major fallout of volcanic bombs at Pizzo sopra la Fossa and high on the NE part of the volcano.

References. Barberi, F., Rosi, M., and Scendone, R. (eds), 2009, The 2007 eruption of Stromboli: Journal of Volcanology and Geothermal Research, v. 182, no. 3-4, p. 123-280.

Calvari, S., Lodato, L., Steffke, A., Cristaldi, A., Harris, A.J.L., Spampinato, L., and Boschi, E., 2010, The 2007 Stromboli eruption: Event chronology and effusion rates using thermal infrared data: Journal Geophysical Research, Solid Earth, 115, B4, B04201, doi:10.1029/2009JB006478.

Information Contact: Sonia Calvari, Istituto Nazionale di Geofisica e Vulcanologia (INGV), Sezione di Catania, Piazza Roma 2, 95123 Catania, Italy (Email: calvaria@ct.ingv.it, URL: http://www.ingv.it/).

09/2011 (BGVN 36:09) Recent activity; plumbing insights; new water vapor flux technique; hydrogeology

Activity at Stromboli (figure 76), since February 2010 (BGVN 35:03) through 11 October 2011 was generally of medium to low intensity, with minor fluctuations typical for Stromboli. Istituto Nazionale di Geofisica e Vulcanologia (INGV) reported occasional episodes of increased activity; note that the dates provided below are illustrative and by no means all-inclusive. This generally occurred as either more intense explosions or increased spattering (figure 77). More intense explosions often generated coarse pyroclastics and/or expelled erupted products farther than during typical activity, sometimes to the summit platform (Pizzo sopra la Fossa) overlooking the active craters, and beyond. For example, some specific pronounced events took place on 19 December 2010, 5 August, and 5 September 2011.

Figure 76. Index map (inset) and aerial photograph of Stromboli, showing the active vents and Sciara del Fuoco, a Pleistocene landslide scarp. Underlined names indicate coastal towns. Index map courtesy of Ginkgo Maps; aerial photograph courtesy of the Italian Air Force.
Figure 77. Photograph of an eruption at Stromboli at approximately 1930 on 15 July 2011 showing spattering behavior. Courtesy of Tom Pfeiffer, Volcano Discovery.

On 30 June 2010, incandescent material thrown from the vent caused small fires on the upper flanks of the volcano. Increased spattering activity often resulted in intra- and, less frequently, extra-crater lava flows (figure 78a and b, respectively) such as those seen during 18-23 October 2010, 1-2 August, and 7 September 2011. The extra-crater lava flows of 1-2 August from the northernmost vent were the first observed since December 2010; they extended only a few hundred meters downslope (figure 78a). Extra-crater lava flows were often accompanied by land- or rock-slides down Sciara del Fuoco, fed by material that broke free from lava flow fronts and rolled down slope (e.g. 1 August 2011).

Figure 78. Intra-crater (a) and extra-crater (b) lava flows at Stromboli. (a) Spatter fed lava flow emitted from a small cone on the SW rim of the crater terrace; a small group of glowing vents can be seen at bottom left (circled). Photographed during the night of 11-12 August 2011 by Gijs de Reijke. (b) Aerial view of the summit area of Stromboli, highlighting extra-crater lava flows onto Sciara del Fuoco. The northern (N) and southern (S) vent areas are labeled in red; lava flows were emitted during 11-12 December 2010 (1, yellow), 1-2 August 2011 (2, pink), and on 18 August 2011 (3, red). Photo by Mauro Coltelli; courtesy of Istituto Nazionale di Geofisica e Vulcanologia (INGV).

Some of the parameters reported by INGV during February 2010 to October 2011 included seismic, deformation, visual observation, and gas flux. The flux of CO2 and SO2, and particularly the CO2/SO2 ratio measured in the plumes, provided insight into the provenance of the generally discreet gas discharges ("gas slugs") that regularly burst upon reaching Stromboli's vent. INGV reported that a coupled increase in the CO2/SO2 ratio and decrease of SO2 flux (seen, for example, during the weeks of 5-12 and 19-26 September 2011) indicated an increased contribution of volatiles from deeper portions of the magmatic system.

Recent insight into magma generation. A study of erupted ash textures and compositions by D'Oriano and others (2011) yielded results comparable with the implications of the CO2/SO2 ratio reported by INGV. The authors use the commonly accepted terms for two separate populations of magma at Stromboli; these terms are presented and used herein.

"LP magmas" are those with low porphyricity (similar sized phenocrysts) that are considered to have relatively deeper origins and simple cooling histories. "HP magmas" are those with high porphyricity (multiple size populations of phenocrysts) that are considered to reside in a shallow reservoir in the crust and have more complex, multiple stage cooling histories.

D'Oriano and others (2011) found that there is a coupled, possibly persistent ascent of deep-derived CO2 and small amounts of LP magma. They concluded that the coupled ascent of LP magma and CO2 is transient and does not disturb the HP magma that resides in the shallow reservoir. See figure 79 for a schematic of the plumbing and magma storage zones of Stromboli.

Figure 79. Schematic cross-section of Stromboli showing the crustal plumbing system and highlighting HP and LP magma storage zones. From Aiuppa and others (2010), based upon earlier works.

New technique for measuring plume water vapor concentration. LIDAR (Light Detection and Ranging) has been used for the first time to measure water vapor flux of a volcanic plume. Fiorani and others (2011) used a CO2 laser-based LIDAR system called ATLAS (Agile Tuned Lidar for Atmospheric Sensing) at Stromboli to measure both wind speed and water vapor concentration of the erupted plume. When combined, the measurements yielded water vapor flux of the plume. Their measurements agreed with measurements obtained from traditional methods, and were the first such measurements at an active volcano.

Hydrogeology of Stromboli. A detailed geophysical survey of Stromboli revealed some hydrogeological features of the volcano (figure 80). Revil and others (2011) conducted a survey measuring electrical resistivity, soil CO2 concentrations, soil temperature, and self-potential along two profiles (a and b, figures 80 and 81). Their survey focused on the Pizzo crater (near the active vents), and the Rina Grande sector collapse on the E side of the island. They published a detailed schematic interpretation of fluid-flow pathways along the two profiles (figure 81).

Figure 80. Geologic map of Stromboli. Red dots denote geophysical profiles of Revil and others (2011); (a) profile across Pizzo crater, near the active vents, and (b) profile down the length of the Rino Grande sector collapse, on the E flank of Stromboli. The two profiles are coincident to the W of Neo-Stromboli crater. Modified from Revil and others (2011).
Figure 81. Interpretive hydrogeology diagram of Revil and others (2011) at Stromboli highlighting fluid flow pathways along two profiles; (a) profile across Pizzo crater, and (b) profile down the length of the Rino Grande sector collapse. See legend at right; areas in gray indicate the inferred extent of the hydrothermal system; orange lines and arrows indicate hot water flow; gray arrows indicate gas discharge; black solid and dashed lines indicate faults. See Revil and others (2011) for further details.

The authors identified an unconfined aquifer above the villages of Scari and San Vincenzo. They stated that the Rina Grande sector collapse is the "most important structural control for magmatic and hydrothermal fluids" in the upper part of the Stromboli edifice, and that it hosts the two main diffuse degassing areas of the edifice. They further concluded that the hydrothermal system reaches shallow levels in the lower part of the Rina Grande collapse (profile b, figures 80 and 81). This fact, they wrote, "raises questions about the mechanical stability of this [E] flank of the edifice".

References. Aiuppa, A., Bertagnini, A., Métrich, N., Moretti, R., Di Muro, A., Liuzzo, M., Tamburello, G., 2010, A model of degassing for Stromboli volcano, Earth and Planetary Science Letters, v. 295, no. 1-2, p. 195-204 (DOI: 10.1016/j.epsl.2010.03.040).

D'Oriano, C., Bertagnini, A., and Pompilio, M., 2011, Ash erupted during normal activity at Stromboli (Aeolian Islands, Italy) raises questions on how the feeding system works, Bulletin of Volcanology, v. 73, no. 5, p. 471-477 (DOI:10.1007/s00445-010-0425-0).

Fiorani, L., Colao, F., Palucci, A., Poreh, D., Aiuppa, A., and Giudice, G., 2011, First-time lidar measurement of water vapor flux in a volcanic plume, Optics Communications, v. 284, no. 5, p. 1295-1298 (DOI:10.1016/j.optcom.2010.10.082).

Revil, A., Finizola, A., Ricci, T., Delcher, E., Peltier, A., Barde-Cabusson, S., Avard, G., Bailly, T., Bennati, L., Byrdina, S., Colonge, J., Di Gangi, F., Douillet, G., Lupi, M., Letort, J., and Tsang Hin Sun, E., 2011, Hydrogeology of Stromboli volcano, Aeolian Islands (Italy) from the interpretation of resistivity tomograms, self-potential, soil temperature and soil CO2 concentration measurements, Geophysical Journal International, v. 186, no. 3, p. 1078-1094 (DOI:10.1111/j.1365-246X.2011.05112.x).

Information Contacts: Boris Behncke andMauro Coltelli, Istituto Nazionale di Geofisica e Vulcanologia (INGV), Sezione di Catania, 95125 Catania (URL: http://www.ct.ingv.it/); Ginkgo Maps (URL: http://www.ginkgomaps.com/); Italian Air Force (URL: www.aeronautica.difesa.it); Tom Pfeiffer, Volcano Discovery (URL: http://www.volcanodiscovery.com/); Gijs de Reijke, Arnhem High School, Nijmegen, Netherlands.

12/2013 (BGVN 38:12) Small-to-moderate eruptions continue through December 2013

An HTML version of this report is not available, please read this report as a PDF file.

Spectacular incandescent nighttime explosions at Stromboli volcano have long attracted visitors to the "Lighthouse of the Mediterranean." Stromboli, the NE-most of the Aeolian Islands, has lent its name to the frequent mild explosive activity that has characterized its eruptions throughout much of historical time. The small, 924-m-high island of Stromboli is the emergent summit of a volcano that grew in two main eruptive cycles, the last of which formed the western portion of the island. The Neostromboli eruptive period from about 13,000 to 5000 years ago was followed by formation of the modern Stromboli edifice. The active summit vents are located at the head of the Sciara del Fuoco, a prominent horseshoe-shaped scarp formed about 5000 years ago as a result of the most recent of a series of slope failures that extend to below sea level. The modern volcano has been constructed within this scarp, which funnels pyroclastic ejecta and lava flows to the NW. Essentially continuous mild strombolian explosions, sometimes accompanied by lava flows, have been recorded at Stromboli for more than a millennium.

Summary of Holocene eruption dates and Volcanic Explosivity Indices (VEI).

Start Date Stop Date Eruption Certainty VEI Evidence Activity Area or Unit
1934 Feb 2 2014 Jun 30 (continuing) Confirmed 2 Historical Observations Summit craters and Sciara del Fuoco
1932 Jun 3 1932 Jun 3 Confirmed 2 Historical Observations
1910 May 1931 Jul Confirmed 3 Historical Observations Summit craters and Sciara del Fuoco
1890 1907 May 29 Confirmed 3 Historical Observations
1857 1889 Jun 26 Confirmed 3 Historical Observations Summit craters and Sciara del Fuoco
1558 (in or before) 1857 Confirmed 3 Historical Observations Summit craters and Sciara del Fuoco
0950 ± 50 years Unknown Confirmed 2 Historical Observations
0550 ± 50 years Unknown Confirmed 3 Historical Observations
0250 ± 50 years Unknown Confirmed 2 Historical Observations
0150 ± 50 years Unknown Confirmed 2 Historical Observations
0050 ± 50 years Unknown Confirmed 2 Historical Observations
0050 BCE ± 50 years Unknown Confirmed 2 Historical Observations
0210 BCE ± 10 years Unknown Confirmed 2 Historical Observations
0350 BCE ± 50 years Unknown Confirmed 2 Historical Observations
4050 BCE (?) Unknown Confirmed 3 Radiocarbon (uncorrected) Secche di Lazzaro pyroclastics
4250 BCE (?) Unknown Confirmed 2 Magnetism NE flank (Punta Lena lava flow)
4550 BCE (?) Unknown Confirmed 0 Magnetism Northern flank (Vallonazzo)
4800 BCE ± 300 years Unknown Confirmed 2 Magnetism Northern flank
5050 BCE (?) Unknown Confirmed 0 Magnetism Northern flank (Vallonazzo lava flow)
5550 BCE (?) Unknown Confirmed 0 Magnetism Northern flank (Labronzo)
5800 BCE ± 300 years Unknown Confirmed 0 Magnetism NE flank (Nel Camnestrà lava flow)
6050 BCE (?) Unknown Confirmed 0 Magnetism Northern flank (Vallonazzo)

This compilation of synonyms and subsidiary features may not be comprehensive. Features are organized into four major categories: Cones, Craters, Domes, and Thermal Features. Synonyms of features appear indented below the primary name. In some cases additional feature type, elevation, or location details are provided.



Synonyms
Strongyle


Cones
Feature Name Feature Type Elevation Latitude Longitude
Filo dello Zolfo Vent
Malo Passo Vent
Neostromboli Stratovolcano
Paleostromboli Stratovolcano
Pizzo Sopra la Fossa Tuff cone 918 m
San Bartolo Vent 650 m
Sciara Vent
Strombolicchio Cone 49 m
Timpone del Fuoco Shield volcano 147 m
Torrione Vent
Vancori Stratovolcano 924 m
Vigna Vecchia Cone


Craters
Feature Name Feature Type Elevation Latitude Longitude
Cavoni Submarine crater
Fossa Crater
Fossetta Crater
Labronzo Crater
Nel Cannestrà Fissure vent 450 m
Pizzo Crater
Roisa Fissure vent 250 m
The island of Stromboli is seen in this aerial view with the top of the photo facing NW. The volcano, in continuous activity for more than 1300 years, was constructed in two cycles, the last of which formed the western side of the island. A "smoke" plume trails to the south from the active vent at the head of the horseshoe-shaped scarp, Sciara del Fuoco. The scarp, which extends to sea level, was created by a massive Pleistocene landslide, and serves to funnel pyroclastic ejecta and lava flows to the west.

Photo by the Italian Air Force.
The rising sun brightens the slopes of Stromboli volcano, the "Lighthouse of the Mediterranean." This view shows the NE tip of the island with the Rina Grande valley at the left. The principal historically active vent of Stromboli lies at the head of the Sciarra del Fuoco, a prominent horseshoe-shaped scarp on the opposite side of the island. Stromboli, the NE-most of the Aeolian Islands, has lent its name to the frequent mild explosive activity that has characterized its eruptions throughout much of historical time.

Photo by Guiseppina Kysar, 1999 (Smithsonian Institution).

The following references have all been used during the compilation of data for this volcano, it is not a comprehensive bibliography. Discussion of another volcano or eruption (sometimes far from the one that is the subject of the manuscript) may produce a citation that is not at all apparent from the title.

Andronico D, Pistolesi M, 2010. The November 2009 paroxysmal explosions at Stromboli. J Volc Geotherm Res, 196: 120-125.

Arrighi S, Rosi M, Tanguy J-C, Courtillot V, 2004. Recent eruptive history of Stromboli (Aeolian Islands, Italy) determined from high-accuracy archeomagnetic dating. Geophys Res Lett, 35: L19603, doi:10.1029/2004GL020627.

Baldi P, Coltelli M, Fabris M, Marsella M, Tommasi P, 2008. High precision photogrammetry for monitoring the evolution of the NW flank of Stromboli volcano during and after the 2002-2003 eruption. Bull Volc, 70: 703-715.

Barberi F, Civetta L, Rosi M, Scandone R, 2009. Chronology of the 2007 eruption of Stromboli and the activity of the Scientific Synthesis Group. J Volc Geotherm Res, 182: 123-130.

Barberi F, Rosi M, Sodi A, 1993. Volcanic hazard assessment at Stromboli based on review of historical data. Acta Vulc, 3: 173-187.

Bertagnini A, Landi P, 1996. The Secche di Lazzaro pyroclastics of Stromboli volcano: a phreatomagmatic eruption related to the Sciara del Fuoco sector collapse. Bull Volc, 58: 239-245.

Bosman A , Chiocci F L, Romagnoli C, 2009. Morpho-structural setting of Stromboli volcano revealed by high-resolution bathymetry and backscatter data of its submarine portions. Bull Volc, 71: 1007-1019.

Calvari S, Spampinato L, Lodato L, 2006. The 5 April 2003 vulcanian paroxysmal explosion at Stromboli volcano (Italy) from field observations and thermal data. J Volc Geotherm Res, 149: 160-175.

Cortes J A, Wilson M, Condliffe E, Francalanci L, Chertkoff D G, 2005. The evolution of the magmatic system of Stromboli volcano during the Vancori period (26-13.8 ky). J Volc Geotherm Res, 147: 1-38.

Di Roberto A, Bertagnini A, Pompilio M, Gamberi F, Marani M P, 2008. Newly discovered submarine flank eruption at Stromboli volcano (Aeolian Islands, Italy). Geophys Res Lett, 35: L16310, doi:10.1029/2008GL034824.

Di Roberto A, Bertagnini A, Pompilio M, Gamberi F, Marani M P, Rosi A M, 2008. Newly discovered submarine flank eruption at Stromboli volcano (Aeolian Islands, Italy). Geophys Res Lett, 35: L16310, doi:10.1029/2008GL034824.

Favalli M, Karatson D, Mazzuoli R, Pareschi M T, Ventura G, 2005. Volcanic geomorphology and tectonics of the Aeolian archipelago (Southern Italy) based on integrated DEM data. Bull Volc, 68: 157-170.

Finizola A, Sortino F, Lenat J-F, Aubert M, Ripepe M, Valenza M, 2003. The summit hydrothermal system of Stromboli. New insights from self-potential, temperature, CO2 and fumarolic fluid measurements, with structural and monitoring implications. Bull Volc, 65: 486-504.

Francalanci L, Tommasini S, Conticelli S, 2004. The volcanic activity of Stromboli in the 1906-1998 AD period: mineralogical, geochemical and isotope data relevant to the understanding of the plumbing problem. J Volc Geotherm Res, 131: 179-211.

Gabbianelli G, Romagnoli C, Rossi P L, Calanchi N, 1993. Marine geology of the Panarea - Stromboli area (Aeolian Archipelago, southeastern Tyrrhenian Sea). Acta Vulc, 3: 11-20.

Gillot P-Y, Keller J, 1993. Radiochronological dating of Stromboli. Acta Vulc, 3: 69-77.

Giordano G, Porreca M, Musacchio P, Mattei M, 2008. The Holocene Secche de Lazzaro phreatomagmatic succession (Stromboli, Italy): evidence of pyroclastic density current origin deduced by facies analysis and AMS flow directions. Bull Volc, 70: 1221-1236.

Green J, Short N M, 1971. Volcanic Landforms and Surface Features: a Photographic Atlas and Glossary. New York: Springer-Verlag, 519 p.

Harris A, Dehn J, Patrick M, Calvari S, Ripepe M, Lodato L, 2005. Lava effusion rates from hand-held thermal infrared imagery: an example from the June 2003 effusive activity at Stromboli. Bull Volc, 68: 107-117.

Hornig-Kjarsgaard I, Keller J, Koberski U, Stadlbauer E, Francalanci L, Lenhart R, 1993. Geology, stratigraphy and volcanological evolution of the island of Stromboli, Aeolian arc, Italy. Acta Vulc, 3: 21-68.

Imbo G, 1965. Italy. Catalog of Active Volcanoes of the World and Solfatara Fields, Rome: IAVCEI, 18: 1-72.

Kokelaar, Romagnoli C, 1995. Sector collapse, sedimentation and clast population evolution at an active island-arc volcano: Stromboli, Italy. Bull Volc, 57: 240-262.

Landi P, Francalanci L, Pompilio M, Rosi M, Corsaro R A, Petrone C M, Nardini I, Miraglia L, 2006. The December 2002-July 2003 effusive event at Stromboli volcano, Italy: insights into the shallow plumbing system by petrochemical studies. J Volc Geotherm Res, 155: 263-284.

Lodato L, Spampinato L, Harris A, Calvari S, Dehn J, Patrick M, 2007. The morphology and evolution of the Stromboli 2002-2003 lava flow field: an example of a basaltic flow field emplaced on a steep slope. Bull Volc, 69: 661-679.

McGregor A D, Lees J M, 2004. Vent discrimination at Stromboli volcano, Italy. J Volc Geotherm Res, 137: 169-185.

Pasquare G, Francalanci L, Garduno V H, Tibaldi A, 1993. Structure and geologic evolution of the Stromboli volcano, Aeolian Islands, Italy. Acta Vulc, 3: 79-89.

Quidelleur X, Gillot P-Y, Filoche G, Lefevre J-C, 2005. Fast geochemical changes and rapid lava accumulation at Stromboli Island (Italy) inferred from K-Ar dating and paleomagnetic variations recorded at 60 and 40 ka. J Volc Geotherm Res, 141: 177-193.

Renzulli A, Santi P, 1997. Sub-volcanic crystallization of Stromboli (Aeolian Islands, southern Italy) preceding the Sciara del Fuoco sector collapse: evidence from monzonite lithic suite. Bull Volc, 59: 10-20.

Romagnoli C, Kokelaar P, Rossi P L, Sodi A, 1993. The submarine extension of Sciara del Fuoco feature (Stromboli Is.): morphologic characterization. Acta Vulc, 3: 91-98.

Rosi M, 1980. Isola Stromboli. Rendiconti Soc Italiana Min Petr, 36: 345-368.

Rosi M, Bertagnini A, Landi P, 2000. Onset of the persistent activity at Stromboli volcano (Italy). Bull Volc, 62: 294-300.

Speranza F, Pompilio M, D'Ajello Caracciolo F, Sagnoti L, 2008. Holocene eruptive history of the Stromboli volcano: constraints from paleomagnetic dating. J Geophys Res, 113: B09101, doi:1029/2007JB005139.

Tanner L H, Calvari S, 2004. Unusual sedimentary deposits on the SE side of Stromboli volcano, Italy: products of a tsunami caused by the ca. 5000 years BP Sciara del Fuoco collapse?. J Volc Geotherm Res, 137: 329-340.

Tibaldi A, 2003. Influence of cone morphology on dykes, Stromboli, Italy. J Volc Geotherm Res, 126: 79-95.

Tibaldi A, 2001. Multiple sector collapses at Stromboli volcano, Italy: how they work. Bull Volc, 63: 112-125.

Tinti S, Maramai A, Armigliato A, Granziani L, Manucci A, Pagnoni G, Zaniboni F, 2006. Observations of physical effects from tsunamis of December 30, 2002 at Stromboli volcano, southern Italy. Bull Volc, 68: 450-461.

Volcano Types

Stratovolcano
Cinder cone(s)

Tectonic Setting

Subduction zone
Continental crust (> 25 km)

Rock Types

Major
Trachyandesite / Basaltic trachy-andesite
Andesite / Basaltic Andesite
Basalt / Picro-Basalt
Minor
Trachyte / Trachyandesite
Trachybasalt / Tephrite Basanite

Population

Within 5 km
Within 10 km
Within 30 km
Within 100 km
2,225
2,225
3,894
1,347,563

Affiliated Databases

Large Eruptions of Stromboli Information about large Quaternary eruptions (VEI >= 4) is cataloged in the Large Magnitude Explosive Volcanic Eruptions (LaMEVE) database of the Volcano Global Risk Identification and Analysis Project (VOGRIPA).
WOVOdat WOVOdat is a database of volcanic unrest; instrumentally and visually recorded changes in seismicity, ground deformation, gas emission, and other parameters from their normal baselines. It is sponsored by the World Organization of Volcano Observatories (WOVO) and presently hosted at the Earth Observatory of Singapore.
EarthChem EarthChem develops and maintains databases, software, and services that support the preservation, discovery, access and analysis of geochemical data, and facilitate their integration with the broad array of other available earth science parameters. EarthChem is operated by a joint team of disciplinary scientists, data scientists, data managers and information technology developers who are part of the NSF-funded data facility Integrated Earth Data Applications (IEDA). IEDA is a collaborative effort of EarthChem and the Marine Geoscience Data System (MGDS).
Smithsonian Collections Search the Smithsonian's NMNH Department of Mineral Sciences collections database. Go to the "Search Rocks and Ores" tab and use the Volcano Name drop-down to find samples.