Ambrym is a shield volcano in the Vanuatu archipelago with a 12-km-wide summit caldera containing the persistently active Benbow and Marum craters. These craters are home to multiple active vents that produce episodic lava lakes, explosions, lava flows, ash, and gas emissions. Occasional fissure eruptions occur outside of these main craters. This report covers July to December 2018 and summarizes reports by the Vanuatu Meteorology and Geohazards Department (VMGD), the Wellington Volcanic Ash Advisory Center (VAAC), and multiple sources of satellite data.

As of the beginning of the reporting period, the hazard status at Ambrym had remained at Volcanic Alert Level 2 ("Major unrest") since 7 December 2017. Monthly VMGD activity reports describe the continued activity within the two main craters, consisting of multiple lava lakes, sustained substantial degassing and steam emission, and seismic unrest. Frequent thermal anomalies were detected throughout the reporting period (figure 42). The danger areas were confined to the Permanent Exclusion Zone within a 1 km radius of Benbow crater, and the Permanent Exclusion Zone and Danger Zone A within about a 2.7 km radius of Marum crater (including Maben-Mbwelesu, Niri-Mbwelesu and Mbwelesu, see BGVN 43:07, figure 38).

Figure 42. Plot of MODIS thermal infrared data analyzed by MIROVA showing the log radiative power of thermal anomalies at Ambrym for the year ending on 1 February 2019. After the December 2018 eruption no further thermal anomalies were noted for the reporting period. Courtesy of MIROVA.

Observations and seismic data analysis by VMGD confirmed the onset of a small-scale intra-caldera fissure eruption at 0600 local time on 15 December. This new fissure produced lava fountains and lava flows with ash and gas plumes (figure 43). Footage of the eruption by John Tasso shows the fissure eruption to the SE of Marum crater producing lava fountaining. A Sentinel-2 satellite image shows a white eruption plume and two new lava flow lobes (figure 44); the actual fissure vent was hidden by the plume. The northernmost lava flow filled in the 500 x 900 m Lewolembwi crater and a smaller lobe continued to flow towards the E (figure 44). Due to this elevated activity, the Volcanic Alert Level was raised to 3 ("Minor eruption"), with the danger zones increased to a 2 km radius around Benbow crater and a 4 km radius around Marum crater. VMGD warned of additional risk within 3 km of eruptive fissures in the SE caldera area.

Figure 43. Image of the fissure eruption producing lava fountaining at Ambrym volcano, taken from a video recorded by John Tasso on 16 December 2018.

Figure 44. Satellite imagery showing the Ambrym caldera area in November-December 2018. Top: True color Landsat-8 satellite image acquired on 13 December 2018 showing the area prior to the fissure eruption. Bottom: False-color infrared Sentinel-2 composite image (bands 12, 11, and 4) showing the multiple active vents and lava lakes within Marum and Benbow craters (top third of the image, acquired on 25 November 2018), and the eruption plume and the bright orange/red lava flow fronts in the bottom of the image (acquired on 15 December 2018); the fissure is obscured by the plume. Courtesy of Sentinel-Hub Playground.

Through 16-17 December, ash and gas emission continued from Benbow and Marum craters (figures 45 and 46), accompanied by ongoing localized seismicity; earthquakes with a magnitude greater than five were felt on neighboring islands. The Wellington VAAC issued ash advisories on 16 and 17 December noting maximum cloud altitudes of approximately 8 km.

Figure 45. Ash emission from Ambrym volcano at 1600 on 16 December 2018. Webcam image courtesy of, and annotated by, VMGD.

Figure 46. Elevated atmospheric SO2 emissions from Ambrym on 17 December 2018 with a total measured mass of 23.383 kt in this scene. The units on the scale bar reflect SO2 in terms of Dobson Units (DU). Courtesy of the NASA Goddard Flight Center Atmospheric Chemistry and Dynamics Laboratory.

From 14 to 26 December, the National Volcano Monitoring Network detected over 4,500 earthquakes related to the eruptive activity, but locally felt seismicity decreased. Analysis of satellite imagery confirmed surface deformation associated with the increase in activity. Media reports from Radio New Zealand indicated that seismic activity during December resulted in ground rupture and damage to homes on the island and residents were moved to evacuation centers.

During the reporting period, thermal anomalies were frequently detected by the MODIS satellite instruments and subsequently analyzed using the MODVOLC algorithm, reflecting the lava lake activity in Benbow and Marum craters, as well additional thermal anomalies during the December 2018 fissure eruption and subsequent lava flows to the SE of the main crater area (figures 47 and 48).

Figure 47. MODVOLC Thermal Alert System from July through December 2018 showing the two active craters of Ambrym, Benbow and Marum, and the December 2018 fissure eruption. Red areas indicate approximate locations of Thermal Anomaly detections along with the number of detections. Courtesy of HIGP - MODVOLC Thermal Alerts System.

Figure 48. MODVOLC thermal alerts detected over Ambrym volcano during July 2018 through December 2018 showing hot spots located at Benbow and Marum craters and the December 2018 fissure eruption. Courtesy of HIGP - MODVOLC Thermal Alerts System.

As of 7 January 2019, Ambrym remains on Alert Level 3 with continued seismic activity. The MIROVA (Middle InfraRed Observation of Volcanic Activity) system has not detected any recent thermal anomalies, indicating the end of the fissure eruption and a reduction in activity at the main craters.

Geologic Background. Ambrym, a large basaltic volcano with a 12-km-wide caldera, is one of the most active volcanoes of the New Hebrides arc. A thick, almost exclusively pyroclastic sequence, initially dacitic, then basaltic, overlies lava flows of a pre-caldera shield volcano. The caldera was formed during a major plinian eruption with dacitic pyroclastic flows about 1900 years ago. Post-caldera eruptions, primarily from Marum and Benbow cones, have partially filled the caldera floor and produced lava flows that ponded on the caldera floor or overflowed through gaps in the caldera rim. Post-caldera eruptions have also formed a series of scoria cones and maars along a fissure system oriented ENE-WSW. Eruptions have apparently occurred almost yearly during historical time from cones within the caldera or from flank vents. However, from 1850 to 1950, reporting was mostly limited to extra-caldera eruptions that would have affected local populations.

Information Contacts: Geo-Hazards Division, Vanuatu Meteorology and Geo-Hazards Department (VMGD), Ministry of Climate Change Adaptation, Meteorology, Geo-Hazards, Energy, Environment and Disaster Management, Private Mail Bag 9054, Lini Highway, Port Vila, Vanuatu (URL: http://www.vmgd.gov.vu/, https://www.facebook.com/VanuatuGeohazardsObservatory/); Hawai'i Institute of Geophysics and Planetology (HIGP) - MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); NASA Goddard Space Flight Center (NASA/GSFC), Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, 8800 Greenbelt Road, Goddard, Maryland, USA (URL: https://so2.gsfc.nasa.gov/); Radio New Zealand, 155 The Terrace, Wellington 6011, New Zealand (URL: https://www.radionz.co.nz/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); John Tasso, Vanuatu Island Experience, Port Vatu, West Ambrym, Vanuatu (URL: http://vanuatuislandexperience.com/).

Short pulses of intermittent eruptive activity have characterized Piton de la Fournaise, the large basaltic shield volcano on Reunion Island in the western Indian Ocean, for several thousand years. The most recent episode occurred during 14 July-28 August 2017 with a 450-m-long fissure on the S flank inside the Enclos Fouqué caldera about 850 m W of Château Fort. Three eruptive episodes occurred during March-August 2018, the period covered in this report; two lasted for one day each on the N flank in April and July, and one lasting from late April through May located on the S flank. Information is provided primarily by the Observatoire Volcanologique du Piton de la Fournaise (OVPF) as well as satellite instruments.

The first of three eruptive events during March-August 2018 occurred during 3-4 April and was a 1-km-long fissure that opened in seven segments with two eruptive vents. It was located on the N flank of the central cone, just S of the Nez Coupé de Sainte Rose on the rim of the caldera. A longer lasting eruptive event began on 27 April and was located in the cratère Rivals area on the S flank of the central cone. The main fissure had three eruptive vents initially, only one of which produced lava that flowed in tunnels away from the site toward the S rim of the Enclos Fouqué caldera. The longest flow reached 3 km in length and set fires at the base of the rampart rim of the caldera. Flow activity gradually decreased throughout May, and seismic tremor ceased, indicating the end of the event, on 1 June 2018. A third, brief event on 13 July 2018 produced four fissures with 20-m-high incandescent lava and aa flows that traveled several hundred meters across the NNW flank of the central cone, covering a large section of the most popular hiking trail to the summit. The event only lasted for about 18 hours but caused significant geomorphologic change as the first flow activity in that area in several hundred years.

The MIROVA plot of thermal energy from 6 February-1 September 2018 clearly shows two of the three eruptive events that took place during that period. The 27 April to 1 June event produced an initial very strong thermal signature that decreased throughout May. Cooling after the flow ceased continued for most of June. The one-day eruptive event on 13 July was also recorded, but the similarly brief event on 3-4 April was not captured in the thermal data (figure 126).

Figure 126. The MIROVA plot of thermal energy from Piton de La Fournaise from 6 February-1 September 2018 clearly shows two of the three eruptive events that took place during that period. The longest event, from 27 April to 1 June produced an initial very strong thermal signature that decreased throughout May. Cooling after the flow ceased continued for most of June. A brief one-day eruptive event on 13 July was also recorded. A similarly brief event on 3-4 April was not recorded. Courtesy of MIROVA.

Eruptive event of 3-4 April 2018. Minor inflation and seismicity were intermittent from the end of August 2017 when the last eruptive episode ended. Significant seismic activity around the summit resumed on 23 March 2018 and accelerated through the end of the month. Inflation continued throughout March as well. A change of composition was detected in the summit fumaroles on 23 March 2018; the fluids were enriched in CO₂ and SO₂. Beginning on 3 April around 0550 local time, OVPF reported a seismic swarm and deformation consistent with magma rising towards the surface. Seismic tremor began around 1040 in an area on the N flank near the Nez Coupé de Sainte Rose. The tremor intensity continued to increase throughout the day; OVPF visually confirmed the eruption around 1150 in the morning on the upper part of the N flank (figure 127).

Figure 127. The eruptive site at Piton de la Fournaise on 3 April 2018 on the N flank near the Nez Coupé de Sainte Rose. Courtesy of OVPF (© OVPF/IPGP) (Bulletin d'activité du 03 avril 2018 à 16h30 heure locale).

A helicopter overflight in mid-afternoon revealed a 1-km-long fissure that had opened in seven distinct segments; lava fountains emerged from two of the segments. The last active segment was just below the rampart of the Nez Coupé de Sainte Rose (figure 128). Both seismic and surface eruptive activity stopped abruptly the following day at 0400.

Figure 128. The brief eruption of 3-4 April 2018 was located on the N flank of the central crater near the Nez Coupé de Sainte Rose, a point on the rampart rim of the Enclos. Courtesy of OVPF (© OVPF/IPGP) (Bulletin d'activité du 03 avril 2018 à 16h30 heure locale).

Eruptive event of 27 April-1 June 2018. OVPF reported 2.5 cm of inflation in the 15 days after the 3-4 April eruption. Seismic activity resumed at the base of the summit area on 21 April, and a new seismic swarm began at 2015 local time on 27 April. This was followed three hours later by tremor activity indicating the beginning of a new eruptive event from fissures that opened on the S flank in the area of cratère Rivals (figure 129). Four fissures opened; one on each side of the crater and one cutting across it were initially active, but activity moved the next morning to a fourth fissure just downstream from Rivals crater and extended for less than 300 m. Fountains of lava rose to 30 m during a morning overflight on 28 April. Several streams of lava quickly coalesced into a single flow heading S towards the rampart at the rim of the Enclos Fouqué (figure 130). By 0830 on 28 April the flow was less than 300 m from the rim and had destroyed an OVPF seismic station and a GPS station. The OMI instrument on the Aura satellite recorded a significant SO₂ plume from the event on 28 April (figure 131).

Figure 129. A fissure extended about 300 m S from the Rivals crater on the S flank of the cone at Piton de la Fournaise on 28 April 2018 where a new eruptive event began the previous evening. Courtesy of OVPF (© OVPF/IPGP) (Bulletin d'activité du samedi 28 avril 2018 à 10h00 heure locale).

Figure 130. The flow from the new fissure near Rival crater at Piton de la Fournaise had flowed to within 300 m of the Enclos Fouqué caldera rim by 0830 on 28 April 2018. Courtesy of OVPF (© OVPF/IPGP) (Bulletin d'activité du samedi 28 avril 2018 à 10h00 heure locale).

Figure 131. An SO2 plume of 9.51 Dobson Units (DU) drifted NW from Reunion Island on 28 April 2018 where Piton de la Fournaise began a new eruptive episode the previous evening. Courtesy of NASA Goddard Space Flight Center.

Tremor activity decreased throughout the day on 28 April while the flow continued. The surface flow rate was measured initially at 8-15 m³ per second; it had slowed to 3-7 m³ per second by late that afternoon. Three active vents were observed on the morning of 29 April that continued the next day with fountains rising about 15 m (figure 132). A small cone (less than 5 m high) had grown around the southernmost vent and the larger middle vent contained a small lava lake. Visible lava was flowing only from the middle vent. The flow consisted of three branches; the two spreading to the E were less than 150 m long while the third flow traveled W past the E Cassian crater and had reached 1.2 km in length by 1020 on 30 April. On 30 April OVPF observed a flow from the previous day that had traveled 2.6 km, reaching the foot of the S edge of the l'Enclos Fouqué rampart.

Figure 132. Lava flowed from three active vents near the Rival crater at Piton de la Fournaise on 30 April 2018. A small cone (less than 5 m high) had grown around the southernmost vent (bottom center) and the larger middle vent contained a small lava lake. Lava was actively flowing from only the middle vent. Courtesy of OVPF (© OVPF/IPGP) (Bulletin d'activité du lundi 30 avril 2018 à 16h00 heure locale).

OVPF noted on 2 May 2018 that the intensity of volcanic tremor remained stable, slight deflation was measured, and the surface flow rate was estimated from satellite data at 1-3 m³ per second. Field observations during the afternoon of 3 May indicated that most activity was occurring from the central vent which had grown into a small pyroclastic cone with incandescent ejecta and gas emissions (figure 133). A well-developed lava tunnel had a number of roof breakouts.

Figure 133. The eruptive site at Piton de la Fournaise on 3 May 2018 had two main vents, the larger pyroclastic cone produced incandescent ejecta and dense gas plumes. Courtesy of OVPF (©IPGP/OVPF) (Bulletin d'activité du vendredi 4 mai 2018 à 15h00 heure locale).

Field reconnaissance during 6-7 May confirmed that most of the activity was concentrated at the central cone with incandescent ejecta rising less than 10 m from the top, and the only source of lava was enclosed in a tunnel. The front of the flow was still active with numerous fires reported at the base of the rampart at the rim of the Enclos Fouqué. The farthest upstream cone was still active, but weak with only occasional bursts of incandescent ejecta. By 10 May the intensity of the volcanic tremor had stabilized at a low level. Two cones remained active, the upstream cone had incandescent ejections rising 10-20 m high. Lava was contained in tunnels near the cones but was exposed below the Piton de Bert (figure 134). The frontal lobe of the flow was located 3 km from the eruptive site, downstream of Piton de Bert (figure 135) at the base of the rampart rim of the Enclos. Numerous fires continued at the base of the rampart due to fresh flows (figure 136).

Figure 134. Lava flows were visible on the slope break below Piton de Bert at Piton de la Fournaise on 10 May 2018. Courtesy of OVPF (© OVPF/IPGP) (Bulletin d'activité du jeudi 10 mai 2018 à 18h30 heure locale).

Figure 135. By 10 May 2018, the front of the flow from the 27 April eruptive event at Piton de la Fournaise was located 3 km from the eruptive site downstream from Piton de Bert. Courtesy of OVPF and Google Earth (© OVPF/IPGP) (Bulletin d'activité du jeudi 10 mai 2018 à 18h30 heure locale).

Figure 136. Fires started by active lava flows affected the base of the rampart rim of the Enclos at Piton de la Fournaise on 10 May 2018. Courtesy of OVPF (© OVPF/IPGP) (Bulletin d'activité du jeudi 10 mai 2018 à 18h30 heure locale).

A minor spike in seismicity was recorded on 15 May 2018; at the same time inflation resumed underneath the caldera. The smaller, farthest upstream cone was the most active on 16 May, with 20-30 m high ejecta. A webcam view on 24 May showed that the vent on the larger pyroclastic cone was nearly closed, and that flow activity was largely contained in tunnels. Field observations that day also confirmed the overall decrease in activity; only a single incandescent zone in the lava field near the vent was observed at nightfall, although persistent degassing continued (figure 137).

Figure 137. By 24 May 2018, activity at Piton de la Fournaise from the eruptive episode that began on 27 April had diminished significantly as seen in this view of the eruptive site near the Rival crater. Photo courtesy of Cité du Volcan and OVPF (Bulletin d'activité du vendredi 25 mai 2018 à 15h00 heure locale).

An overflight on 29 May confirmed the decreasing flow activity and continued inflation. Only rare tongues of lava could be observed in the flow field. The flow front had not progressed eastward for the previous 15 days. The main cone remained open at the top with a small eruptive vent less than 5 m in diameter. Small collapses and slumps were visible on the outer flanks of the cone (figure 138). The height of the main cone was estimated at 22-25 m on 31 May and the second vent was observed to be completely closed off. OVPF reported the end of the eruption at 1430 on 1 June 2018 based on the cessation of seismic tremor (figure 139). The MODVOLC thermal alert system recorded multiple thermal alerts from 27 April through 29 May.

Figure 138. The main cone of the eruptive event at Piton de la Fournaise remained open at the top with a small eruptive vent less than 5 m in diameter on 29 May 2018 that produced abundant steam and gas. Small collapses and slumps were visible on the outer flanks of the cone. N is to the upper left of image. Courtesy of OVPF (© OVPF/IPGP ) (Bulletin d'activité du mercredi 30 mai 2018 à 15h30 heure locale).

Figure 139. The evolution of the RSAM signal (indicator of the volcanic tremor and the intensity of the eruption) at Piton de l aFournaise between 27 April 2018 at 2000 and 1430 on 1 June at the seismic station of BOR, located at the summit of the central cone. Courtesy of OVPF (© OVPF/IPGP) (Bulletin exceptionnel du vendredi 1 juin 2018 à 15h00 heure locale).

Eruptive event of 13 July 2018. Throughout June 2018, very little activity was reported; only 23 shallow seismic events were recorded during the month and no significant deformation was measured by the OVPF deformation network. OVPF reported that inflation resumed around 1 July. A sharp increase in seismicity was observed beginning at 2340 local time on 12 July followed by a seismic swarm and rapid deformation around midnight. Tremor activity was recorded beginning about 0330 on 13 July and located on the N flank. The first images of the eruption were visible in a webcam at around 0430. Four eruptive fissures were observed in an overflight that morning around 0800 that opened over a 500-m-long zone, spreading from upstream of la Chapelle de Rosemont towards Formica Leo. Incandescent ejecta rose less than 20 m and the aa lava had flowed about 200 m from the fissures (figures 140 and 142). The lava flow propagation rate was estimated at about 6 m per minute during the first hour of activity. Thereafter, the rate continued to decrease to less than 1 m per minute at the end of the eruption. After a progressive decrease of tremor, and about 3 hours of "gas flushes" that are typically observed at the end of Piton de la Fournaise eruptions (according to OVPF), the eruption stopped on 13 July at 2200 local time. Both MIROVA and MODVOLC recorded thermal anomalies from the brief one-day event (figure 126).

Figure 140. A new eruption at Piton de la Fournaise on 13 July 2018 lasted only a single day and produced a 500-m-long zone with four fissure vents located on the N flank of the cone near la Chapelle de Rosemont and flowing towards Formica Leo. Courtesy of OVPF (© OVPF/IPGP) (Bulletin d'activité du vendredi 13 juillet 2018 à 10h30 heure locale).

Figure 141. Four fissure vents on the N flank of the central cone near la Chapelle de Rosemont produced ejecta and lava flows for about 18 hours on 13 July 2018 at Piton de la Fournaise. Courtesy of OVPF (© OVPF/IPGP) (Bulletin d'activité du vendredi 13 juillet 2018 à 10h30 heure locale).

The 13 July 2018 eruption lasted about 18 hours and produced about 0.3 million m³ of lava. Lava flows covered more than 400 m of the popular hiking trail leading to the summit (figure 142 and 143) and almost completely filled the Chapelle de Rosemont (figure 144), an old vent and a characteristic feature within the Enclos Fouqué landscape that was first described in reports of the early volcano expeditions at the end of the 18th century. This area of the volcano on the NNW flank had not experienced active eruptive events for at least the past 400 years. Despite the low volume of lava emitted and its short duration, this event significantly changed the geomorphology of the area, which was quite well known and popular with visitors. Inflation resumed after the eruptive event of 13 July and a brief pulse of seismic activity was reported by OVPF on 26 July. They noted on 13 August that after about a month of inflation, seismicity and inflation both ceased.

Figure 142. The brief 13 July 2018 eruptive event covered an area on the NNW flank of the central cone that had not had active flow activity for at least 400 years. Photo taken midday on 13 July 2018. Courtesy of OVPF (© OVPF/IPGP) (July 2018 Monthly bulletin of the Piton de la Fournaise).

Figure 143. The area of the lava flows covered during the 13 July 2018 eruption are shown in white, the fissures are shown in red, and the popular hiking trail to the summit is shown in yellow. Over 400 m of the trail was covered with fresh flows. The fissures were located on the NNW flank in the area of the Chapelle de Rosemont, an old vent. The base map was produced by OVPF using aerial and ground-based photographs that were processed by means of stereophotogrammetry. Courtesy of OVPF (July 2018 Monthly bulletin of the Piton de la Fournaise).

Figure 144. Fresh, dark lava covers the Chapelle de Rosemont on 14 July 2018 after a one-day eruption at Piton de la Fournaise the previous day. The area was first described by explorers in the 18th century and had not seen recent flow activity. Courtesy of OVPF (© OVPF/IPGP) (July 2018 Monthly bulletin of the Piton de la Fournaise).

Geologic Background. The massive Piton de la Fournaise basaltic shield volcano on the French island of Réunion in the western Indian Ocean is one of the world's most active volcanoes. Much of its more than 530,000-year history overlapped with eruptions of the deeply dissected Piton des Neiges shield volcano to the NW. Three calderas formed at about 250,000, 65,000, and less than 5000 years ago by progressive eastward slumping of the volcano. Numerous pyroclastic cones dot the floor of the calderas and their outer flanks. Most historical eruptions have originated from the summit and flanks of Dolomieu, a 400-m-high lava shield that has grown within the youngest caldera, which is 8 km wide and breached to below sea level on the eastern side. More than 150 eruptions, most of which have produced fluid basaltic lava flows, have occurred since the 17th century. Only six eruptions, in 1708, 1774, 1776, 1800, 1977, and 1986, have originated from fissures on the outer flanks of the caldera. The Piton de la Fournaise Volcano Observatory, one of several operated by the Institut de Physique du Globe de Paris, monitors this very active volcano.

Information Contacts: Observatoire Volcanologique du Piton de la Fournaise (OVPF), Institut de Physique du Globe de Paris, 14 route nationale 3, 27 ème km, 97418 La Plaine des Cafres, La Réunion, France (URL: http://www.ipgp.fr/fr); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Hawai'i Institute of Geophysics and Planetology (HIGP) - MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); NASA Goddard Space Flight Center (NASA/GSFC), Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, 8800 Greenbelt Road, Goddard, Maryland, USA (URL: https://so2.gsfc.nasa.gov/).

Sierra Negra shield volcano on the Galápagos Island of Isabela has erupted six times since 1948, most recently in 2005. The eruptions of 2005, 1979, 1963, and 1953 were located in the area known as 'Volcán Chico' near the NNE rim of the summit caldera, which extends about 9 km E-W and 7 km N-S (figure 12). The lava flows generated in these eruptions were directed mainly towards the N and NE flanks of Sierra Negra, in some cases reaching Elizabeth Bay to the N and in others filling the interior of the caldera (figure 13). A new effusive eruption that occurred from 26 June through August 2018 is covered in this report with information provided primarily by Instituto Geofísico, Escuela Politécnica Nacional (IG-EPN). Additional information comes from the Washington Volcanic Ash Advisory Center (VAAC), and several sources of satellite information.

Figure 12. Sierra Negra is located on the southern part of Isabela Island in the Galápagos National Park, Ecuador. Courtesy of IG (Informe Especial Nº 2, Volcán Sierra Negra- Islas Galápagos: Descripción del estado de agitación interna y posibles escenarios eruptivos, 12 January 2018).

Figure 13. The Sierra Negra caldera with the locations of GPS stations and the fissures, vents, and flows from the 2005 eruption. From Geist et al. (2005), courtesy of IG (Informe Especial Nº 2, Volcán Sierra Negra- Islas Galápagos: Descripción del estado de agitación interna y posibles escenarios eruptivos, 12 January 2018).

Beginning in 2017, the Geophysical Institute of the National Polytechnic School (IGEPN) installed a surveillance network of six broadband seismic stations for the Galápagos volcanoes. One station is located on the NE edge of the Sierra Negra caldera and another on the SE flank. After 12 years of little activity, an increase in seismicity beneath and around the caldera became evident by July 2017 (figure 14). On 19 October 2017 (local time) the seismic monitors detected a 16-km-deep M 3.8 earthquake with an epicenter on the NE border of the caldera in the vicinity of Volcán Chico. Four additional similar earthquakes occurred within the next hour. Another earthquake of similar size occurred on 22 October; between 15 and 16 November, three earthquakes with M 3.0 or greater were recorded. The frequency of seismic activity increased significantly in December 2017, with over 550 events recorded during the first three weeks of December 2017; at least three had magnitudes greater than 3. GPS receivers showed uplift of the caldera floor of 80 cm between 2013 and 2017. InSAR interferometry data indicated substantial inflation of the caldera floor of about 70 cm between December 2016 and late November 2017, reaching a level higher than that which preceded the eruption of 2005 (figure 15).

Figure 14. The number of daily seismic events at Sierra Negra between 13 May 2015 and 23 November 2017 show a distinct increase in activity by July 2017. The colors represent different types of earthquakes; red is VT or volcanotectonic, orange is LP or Long Period, and blue is HB or Hybrid. Courtesy of IG (Informe Especial Sierra Negra N.- 2, Actividad reciente del volcán Sierra Negra – Isla Isabela, 23 November 2017).

Figure 15. Inflation of the caldera floor at Sierra Negra between December 2016 and November 2017 exceeded 70 cm. The left graph shows the displacement plotted in centimeters versus time, and the right image is the spatial deformation from the InSAR data showing inflation at the caldera (center) and on the SW coast of Isla Isabela. Figures courtesy of Falk Amelung (RSMAS) and IG (Informe Especial Sierra Negra N.- 2, Actividad reciente del volcán Sierra Negra – Isla Isabela, 23 November 2017).

By early January 2018, inflation over the preceding 12 months was close to 1 m, with a total inflation exceeding that prior to the 2005 eruption. Seismic activity, focused on two fracture zones trending NE-SW across the summit caldera, continued to increase until 26 June 2018 when a fissure opened near Volcán Chico on the NNE caldera rim. Over the next 24 hours four fissures opened on the N rim and the NW flank. Three of the fissures were active only for this period, but the fourth, on the NW flank about 7 km below the caldera rim, continued to effuse lava for all of July and most of August 2018. Lava flows reached the sea in early July. Several pulses of increased effusive activity corresponded with increased seismic, thermal, and gas-emission activity recorded by both ground-based and satellite instrumentation. By the last week of August active flows were no longer observed, although the cooling flows continued to emit thermal signals for several weeks.

Activity during January-early June 2018. Elevated seismicity continued into 2018 with a M 3.8 event recorded on 6 January 2018 that was felt by tourists, guides, and Galápagos National Park officials. Tens of additional smaller events continued throughout the month, reaching more than 100 seismic events per day a few times; the earthquakes were located below the caldera at a depth of less than 8 km. A M 4.1 event on 10 January was located at a depth of 7 km. By 12 January, the total inflation of the caldera since the beginning of 2017 was 98 cm (figure 16).

Figure 16. Seismicity and deformation at Sierra Negra between 13 May 2015 and 28 December 2017. The orange line represents the cumulative VT earthquakes, and the blue points record the inflation in cm of the floor accumulated since the beginning of 2015. A change in slope of both curves is evident at the end of 2017 indicating the rate of increase of inflation and seismicity. Courtesy of IG (Informe Especial Nº 2, Volcán Sierra Negra- Islas Galápagos: Descripción del estado de agitación interna y posibles escenarios eruptivos, 12 January 2018).

IG reported 14 seismic events with magnitudes ranging from 3.0-4.6 between 1 January and 19 March 2018. A M 4.4 event on 18 January was located less than 1 km below the surface with an epicenter on the S rim of the caldera. A M 4.1 event on 27 February was also located less than 1 km below the surface. A M 4.6 event on 14 March was the largest to date at Sierra Negra and was located only 0.3 km below the surface. Measurements of CO₂, SO₂, and H₂S made at the Azufral fumarole field (figure 17) on the W rim of the caldera in early February did not have values significantly different compared to May 2014 and September 2017. With the continued increase in frequency and magnitude of shallow seismic activity, IG noted the increased risk of renewed eruptive activity, and noted that most of the active flows of the last 1,000 years were located on the N flank (figure 18).

Figure 17. A fumarole field near Azufral on the W rim of the Sierra Negra caldera on 6 February 2018 remained unchanged after several months of increased seismicity in the area. Photo by M. Almeida, courtesy of IG-EPN (Informe Especial del Volcán Sierra Negra (Islas Galápagos) -2018 - Nº 3, Actualizado del estado de agitación interna y posibles escenarios eruptivos, 19 March 2018).

Figure 18. Simplified geologic map of Sierra Negra with lava flows colored as a function of relative age (modified from Reynolds et al., 1995), courtesy of IG (Informe Especial del Volcán Sierra Negra (Islas Galápagos) -2018 - Nº 3, Actualizado del estado de agitación interna y posibles escenarios eruptivos, 19 March 2018).

Increases in seismicity continued into early June. IG noted that on 25 May 2018, 104 seismic events were recorded, the largest number in a single day since 2015. A M 4.8 event on 8 June was accompanied by over 40 other smaller earthquakes. The earthquake epicenters were mainly located on the edges of the crater in two NE-SW trending lineaments; the first covered the N and W edges of the crater and the second trended from the NE edge to the S edge. Deformation data indicated the largest displacements were at the caldera's center, compared with lower levels of deformation outside of the caldera.

Eruption of 26 June-late August 2018. IG reported an increase in seismicity and a M 4.2 earthquake on 22 June 2018. A larger M 5.3 earthquake was detected at 0315 on 26 June, 5.3 km below the caldera. The event was felt strongly on the upper flanks and in Puerto Villamil (23 km SE). About 8 hours later, at 1117, an earthquake swarm characterized by events located at 3-5 km depth was recorded. A M 4.2 earthquake took place at 1338 and was followed by increasing amplitudes of seismic and infrasound signals. Parque Nacional Galápagos staff then reported noises described as bellows coming from the Volcán Chico fissure vent, which, coupled with the seismicity and infrasound data, suggested the start of an eruption. About 20 minutes later IG described a thermal anomaly identified in satellite images in the N area of the caldera near Volcán Chico and Park staff observed lava flowing towards the crater's interior as well as towards the N flank in the direction of Elizabeth Bay (figure 19).

Figure 19. Lava flows descended from the N flank of Sierra Negra to Elizabeth Bay on 26 June 2018 from four distinct fissure vents (numbered). Fissure 1 was located near Volcan Chico on the caldera rim, and fissures 2, 3, and 4 were located on the N flank. Details of the fissures are discussed later in the report. Video of the flow was captured by Nature Galápagos. Photo courtesy of AFP and BBC News, annotated and reprinted by IG (Informe Especial N° 16 – 2018, Volcán Sierra Negra, Islas Galápagos, Actualización de la Actividad Eruptiva, Quito, 23 de Julio del 2018).

The Washington VAAC reported an ash plume visible in satellite imagery late on 26 June at 10.6 km altitude drifting SW. By the following morning, a plume of ash mixed with SO₂ was drifting W at 8.2 km altitude. IG reported a new ash emission late on 27 June drifting NW at 6.1 km altitude. A substantial SO₂ plume emerged on 27 June and was recorded by the OMI and OMPS satellite-based instruments drifting SW that day and the next (figure 20). The MODVOLC thermal alert system confirmed the beginning of the eruption with over 100 alert pixels recorded on 27 June and over 50 the following day. The MIROVA system recorded an abrupt, very high thermal signal beginning on 26 June (figure 21). Seismic and acoustic data indicated a gradual decrease of activity after the initial outburst, but effusive lava flows continued on 27 June.

Figure 20. A large plume of SO2 was emitted from Sierra Negra on 27 June 2018 at the beginning of the latest eruptive episode. It drifted SW the following day, as seen in these images captured by the OMPS instrument on the Suomi NPP satellite. Courtesy of NASA Goddard Space Flight Center.

Figure 21. The MIROVA project graph of thermal energy at Sierra Negra from 31 January 2018 through September 2108 shows the start of the lava flows on 27 June 2018 (UTC). Pulses of high thermal energy continued through late August when flow activity ceased; cooling of the flows continued into September 2018. Courtesy of MIROVA.

During 27 and 28 June, IG scientists were able to make a site visit to capture thermal, photographic, and physical evidence of the new lava flows (figure 22). A composite thermal image showed the extent of flows that traveled down the N flank as well as into the caldera (figure 23). A temperature of 580°C was measured near the eruptive fissure, and the surface temperatures averaged about 60°C, although some flows were measured as high as 200°C. The temperature inside a fracture on a lava flow was measured at 975°C (figure 24). Pelée hair and "spatter" bombs were visible around the eruptive fissures.

Figure 22. The lava flows of 26 June 2018 at Sierra Negra emerged from a fissure on the N flank of the caldera rim and other fissures on the N flank and flowed N. N is to the right. Photo by Benjamin Bernard, courtesy of IG (Volcán Sierra Negra, Informe de campo 27-28 junio2018, Termografía, Cartografía, y muestreo de los nuevos flujos de lava, sector de Volcán Chico).

Figure 23. Composite thermal images of the new lava flows at Sierra Negra taken on 27 June 2018 reveal the flows that emerged from the Volcán Chico fissure zone; most flows traveled N down the flank, a few (on the left) traveled down into the caldera. Images by Silvia Vallejo, courtesy of IGEPN (Volcán Sierra Negra, Informe de campo 27-28 junio2018, Termografía, Cartografía, y muestreo de los nuevos flujos de lava, sector de Volcán Chico).

Figure 24. The temperature of incandescent lava within a fresh flow at Sierra Negra was measured at 975°C on 27 June 2018. Left image by Francisco Vásconez; thermal image by Silvia Vallejo, courtesy of IGEPN (Volcán Sierra Negra, Informe de campo 27-28 junio2018, Termografía, Cartografía, y muestreo de los nuevos flujos de lava, sector de Volcán Chico).

Pahoehoe and aa flows along with lava tunnels were visible in drone images. The visible fissures were slightly arcuate and aligned in a general ENE direction, similar to the fissures of 1979 and 2005 in the vicinity of Volcán Chico. The largest flow was more than 150 m long; they reached up to 130 m wide in the flat areas, but only between 25 and 35 m wide where they were channeled on the steeper slope. In the flatter areas they had characteristics of pahoehoe with a smooth surface, a sometimes rounded texture and lava tunnels (figure 25), while in the channelized areas with a steeper slope they had a rougher surface and were characterized as aa (figure 26). The flows averaged 0.5-1 m thick and in several places the lava filled fissures or previous depressions. The samples of pahoehoe that were collected were all aphanitic with no crystals, strongly iridescent, and vesiculated with fluid textures that indicated a high gas content and low viscosity.

Figure 25. Pahoehoe flows, spatter, and a collapsing lava tunnel were visible near fissure 1 (above 'Spatter') at Sierra Negra when imaged by a drone during a field visit on 27-28 June 2018 shortly after the new eruptive episode began. This image covers the area near the top center of the image in figure 22 close to the fissure. Photos were taken by a drone flying 60 m above the flows by Benjamin Bernard, courtesy IGEPN (Volcán Sierra Negra, Informe de campo 27-28 junio2018, Termografía, Cartografía, y muestreo de los nuevos flujos de lava, sector de Volcán Chico).

Figure 26. Aa flows formed as lava traveled down the steeper parts of the N flank of Sierra Negra on 26 June 2018, seen in this drone image taken during a field visit on 27-28 June. This image general location can be seen in the bottom right area in figure 22. Photos were taken by a drone flying 60 m above the flows by Benjamin Bernard, courtesy IGEPN (Volcán Sierra Negra, Informe de campo 27-28 junio2018, Termografía, Cartografía, y muestreo de los nuevos flujos de lava, sector de Volcán Chico).

A small seismic event followed by several hours of tremor was recorded at 1552 on 1 July; a short while later National Park staff observed active lava flows on the NW flank. On 4 July, IG reported a M 5.2 earthquake that was 5 km deep; it was followed by 68 smaller seismic events. On 7 July seismic tremor activity indicating another pulse of magmatic activity was recorded by a station on the NE edge of the caldera at 1700. At the same time, satellite data showed an increase in the intensity of the thermal anomaly on the NW flank; Parque Nacional Galápagos staff confirmed strong visible incandescence in an area near the beach. Tremor activity continued on 8 July, although the amplitude gradually decreased.

The Washington VAAC reported an ash plume visible in satellite imagery on 2 July at 6.1 km altitude drifting SW. Later in the day a concentrated plume interpreted to be primarily steam and gas extended about 260 km SW. On 8 July ash could be seen moving both W and SW in satellite imagery at 2.7-3.0 km altitude. Later that day ash was visible extending about 115 km SW from the summit and other gases extended 370 km W. That evening the ash plume extended about 190 km SW at 3.7 km altitude. Gas-and-ash plumes were observed continuously drifting SW for the next three days (9-11 July) at 3.7 km altitude to a distance of about 80 km. On 13 July, two areas of ash and gas were seen in satellite imagery moving 25 km NW from the summit and up to 45 km SW at altitudes of 3.9 and 2.4 km respectively. A low-level ash plume on 16 July extended 30 km SW from the summit at 2.4 km altitude; incandescence was also visible in the webcam. The next day ash and gas emissions extended about 120 km SW at a similar altitude. Ongoing steam, gas, and ash emissions were seen in satellite imagery and in the webcam extending 110 km NW from the summit on 19 July at 3.4 km altitude. The Washington VAAC reported an ash plume on 30 July that rose to 3.4 km altitude and drifted SW. Strong SO₂ emissions were recorded by both the OMPS and OMI satellite instruments throughout July 2018 (figure 27).

Figure 27. SO2 plumes from Sierra Negra exceeded 2 Dobson Units (DU) nearly every day during July 2018. Data gathered by the OMPS satellite instrument showed a large plume drifting SW on 2 July (top left), and a more narrow stream of SO2 drifting SW on 3 July (top right). The OMI satellite instrument captured large W-drifting plumes on 12 (bottom left) and 14 (bottom right) July. Courtesy of NASA Goddard Space Flight Center.

In a report issued by IGEPN covering activity through 23 July 2018, they noted that at least four fissures had initially opened on 26 June at the start of the eruption (see numbers in figure 19 at the beginning of this report, and figure 31 at the end). Fissure 1, the longest at 4 km, was located at the edge of the caldera in the area of Volcán Chico; lava flows from this fissure traveled 7 km down the flanks, and over 1 km within the interior of the caldera. NW-flank fissures 2, 3, and 4 were much smaller (about 250 m long). Fissures 1-3 were active only until 27 June; fissure 4 continued to be active throughout July. Lava from this fissure reached the ocean on 6 July.

Gas and possible volcanic ash extended 35 km SW of the summit on 4 August at 1.5 km altitude; this was the last report of an ash plume by the Washington VAAC for the eruption. Daily reports from IGEPN indicated that nightly incandescence from advancing flows continued into August. Occasional low-level steam and gas plumes were also visible. Pulses of lava effusion on 4 and 9 August were accompanied by major episodes of seismic tremor activity and substantial SO₂ plumes (figure 28). On 15 August satellite images showed lava from fissure 4 continuing to enter the ocean. The area where the lavas entered the sea were far from any human population or agricultural activities and only accessible by boats.

Figure 28. At Sierra Negra, large SO2 plumes were recorded by the OMPS instrument on the Suomi NPP satellite at the same time that an increase in seismic activity and effusion were noted on both 4 (left) and 9 (right) August 2018. Courtesy of NASA Goddard Space Flight Center.

Throughout the ongoing eruption, pulses of thermal activity detected by MODIS infrared satellite sensors correlated with increases in seismic activity and observed flow activity. The MIROVA plot showed a high level of heat flow from the onset of the eruption on 26 June gradually decreasing in intensity through mid-August (figure 21). This was followed by a significant drop in heat flow and gradual cooling thereafter. After the initial fissure activity near the crater rim on 26-27 June, all subsequent activity was concentrated farther down the N flank at fissure 4 and is reflected in the number of pixels concentrated in that area of the MODVOLC plot of thermal alerts from June-September 2018 (figure 29).

Figure 29. MODVOLC thermal alert locations corresponded to the locations of the observed flow activity at Sierra Negra, showing the sustained thermal activity from the mid-flank fissure 4 that lasted from late June through mid-September 2018. Courtesy of HIGP - MODVOLC Thermal Alerts System .

The number of seismic events recorded during the eruptive episode had increased between 26 June and 30 July 2018 to an average of 265 per day. The peak was recorded on 29 June with 940 earthquakes. Between 31 July and 23 August, the average number was 121 per day, still higher than the level of 38 per day prior to the beginning of the eruption on 26 June. IG reported a continuous decline in activity during the last two weeks of August 2018. After the initial burst of effusive activity during 26-27 June, five additional pulses of increased thermal, seismic, and gas-emission activity were observed in multiple sources of data on 1-2, 7-8, and 31 July, and 4 and 9 August (figure 30).

Figure 30. Multiple parameters of data from the eruption of Sierra Negra from 21 June to 30 August 2018. The dashed green line marks the start of the eruption, while the pale green vertical bars indicate the different eruptive pulses recorded throughout the eruption. a) Seismic energy data (RSAM) recorded by station VCH1, in a window between 1-8 Hz (location shown in figure 31); b) Time series of degassing of SO2 recorded by the OMI and OMPS satellites instruments; c) thermal anomalies recorded by MODVOLC. Courtesy of IGEPN (Informe Especial N°18 – 2018, Volcán Sierra Negra, Islas Galápagos, "Terminación de episodio ruptive actual", Quito, 31 de Agosto del 2018), also published in Vasconez et al (2018).

In a summary report on 31 August 2018, IG reported that the eruption was divided into two main phases. The first and most energetic phase lasted one day (26 June) and was characterized by the opening of five fissures (table 2) located on the rim and N and NW flanks, and creation of lava flows that traveled as far as 7 km from the vents (figure 31). Lava was only active from all five fissures during the first day of the eruption, covering an area greater than 17 km². During the rest of the eruption from 27 June-23 August, about 13 km² of lava was produced from fissure 4, with lava reaching the sea on 6 July and expanding the coastline by 1.5 km². Detailed descriptions of the fissures provided by IGEPN are given in the following section. By 25 August the lava flows covered an area of 30.6 square kilometers. Activity continued to decline the last week of August with decreased seismicity, gas emission, and no surficial activity visible.

Figure 31. Map of the 26 June-August 2018 eruption of Sierra Negra volcano. The eruptive fissures are numbers and shown in yellow and described in detail in the next section. The coastline with Elizabeth Bay is shown in blue, and the lava flows appear in red. The green points include GPS and seismic stations, the epicenter of the earthquake of 5.3 MLV on 26 June, El Cura (control station of the Galápagos National Park) and the panoramic vista visited by tourists. Courtesy of IGEPN (Informe Especial N°18 – 2018, Volcán Sierra Negra, Islas Galápagos, "Terminación de episodio ruptive actual", Quito, 31 de Agosto del 2018), also published in Vasconez et al (2018).

Table 2. Descriptions of the five fissures active during the June-August 2018 eruption of Sierra Negra (see figure 31 for locations). Courtesy of IGEPN (Informe Especial N°18 – 2018, Volcán Sierra Negra, Islas Galápagos, "Terminación de episodio ruptive actual", Quito, 31 de Agosto del 2018)

References: Davidge L, Ebinger C, Ruiz M, Tepp G, Amelung F, Geist D, Cote D, Anzieta J, 2017, Seismicity patterns during a period of inflation at Sierra Negra volcano, Galápagos Ocean Island Chain. Earth and Planetary Science Letters. 462. DOI: 10.1016/j.epsl.2016.12.021.

Geist D, Naumann T R, Standish J J, Kurz M D, Harpp K S, White W M , Fornari D, 2005, Wolf Volcano, Galapagos Archipelago: Melting and magmatic evolution at the margins of a mantle plume. Journal of Petrology 46:2197-2224.

Vasconez F, Ramón P, Hernandez S, Hidalgo S, Bernard B, Ruiz M, Alvarado A., La Femina P, Ruiz G, 2018, The different characteristics of the recent eruptions of Fernandina and Sierra Negra volcanoes (Galápagos, Ecuador), Volcanica 1(2): 127-133. DOI: 10.30909/vol.01.02.127133.

Geologic Background. The broad shield volcano of Sierra Negra at the southern end of Isabela Island contains a shallow 7 x 10.5 km caldera that is the largest in the Galápagos Islands. Flank vents abound, including cinder cones and spatter cones concentrated along an ENE-trending rift system and tuff cones along the coast and forming offshore islands. The 1124-m-high volcano is elongated in a NE direction. Although it is the largest of the five major Isabela volcanoes, it has the flattest slopes, averaging less than 5 degrees and diminishing to 2 degrees near the coast. A sinuous 14-km-long, N-S-trending ridge occupies the west part of the caldera floor, which lies only about 100 m below its rim. Volcán de Azufre, the largest fumarolic area in the Galápagos Islands, lies within a graben between this ridge and the west caldera wall. Lava flows from a major eruption in 1979 extend all the way to the north coast from circumferential fissure vents on the upper northern flank. Sierra Negra, along with Cerro Azul and Volcán Wolf, is one of the most active of Isabela Island volcanoes.

Information Contacts: Instituto Geofísico (IG), Escuela Politécnica Nacional, Casilla 17-01-2759, Quito, Ecuador (URL: http://www.igepn.edu.ec ); Washington Volcanic Ash Advisory Center (VAAC), Satellite Analysis Branch (SAB), NOAA/NESDIS OSPO, NOAA Science Center Room 401, 5200 Auth Rd, Camp Springs, MD 20746, USA (URL: www.ospo.noaa.gov/Products/atmosphere/vaac, archive at: http://www.ssd.noaa.gov/VAAC/archive.html); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Hawai'i Institute of Geophysics and Planetology (HIGP) - MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); NASA Goddard Space Flight Center (NASA/GSFC), Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, 8800 Greenbelt Road, Goddard, Maryland, USA (URL: https://so2.gsfc.nasa.gov/); Nature Galápagos (Twitter: @natureGalápagos, https://twitter.com/natureGalápagos).

Episodic recent and historic volcanic activity has been reported at Great Sitkin, located about 40 km NE of the community of Adak in the Aleutian Islands. Prior to the recent 2018 activity, the last confirmed eruption in 1974 produced at least one ash cloud that likely exceeded an altitude of 3 km (figures 1 and 2). This eruption extruded a lava dome that partially destroyed an existing dome from a 1945 eruption. Most recently, a small steam explosion was reported on 10 June 2018. In response, the Alaska Volcano Observatory (AVO) raised the Aviation Color Code (ACC) to Yellow (Advisory) from the previous Green (Normal).

Figure 1. Eruption of Great Sitkin volcano in 1974. Photo taken from Adak Island, Alaska, located 40 km SW of the volcano. Photographer/Creator: Paul W. Roberts; courtesy of AVO/USGS (color corrected).

Figure 2. Worldview-3 satellite image of Great Sitkin on 21 November 2017 showing the crater, areas of 1974 and 1945 lava flows, and steam (indicated by the red arrow) from the reported seismic swarm and steam event ending in 2017. Photographer/Creator: Chris Waytomas; image courtesy of AVO/USGS.

AVO had previously reported that a seismic swarm had been detected beginning in late July 2016 and continuing through December 2017. Steam from the crater was also observed during this time period, in late November 2017 (figure 2). The seismicity was characterized by earthquakes typically less than magnitude 1.0 and at depths from near the summit to 30 km below sea level. Most earthquakes were in one of two clusters, beneath the volcano's summit or just offshore the NW coast of the island. Possible explosion signals were observed in seismic data on 10 January and 21 July 2017, but no confirmed emissions were observed locally or detected in infrasound data or satellite imagery.

The most recent eruption at Great Sitkin produced a small steam explosion which was detected in seismic data at 1139 local time on 10 June 2018 (figure 3). The explosion was followed by seismic activity which began diminishing after 24 hours, and by 15-16 June had returned to background levels.

Figure 3. View of Great Sitkin steaming on 10 July 2018. Photographed from Adak Island, Alaska, approximately 40 km SW. Photo by Alain Beauparlant; image courtesy of AVO/USGS (color corrected).

Due to heavy cloud cover on 10 June 2018, satellite views were obscured. Subsequent satellite data collected on 11 June showed an ash deposit on the surface of the snow extending to about 2 km SW from a vent in the summit crater (figure 4). Minor changes in the vicinity of the summit crater were observed from satellite data, including possible fumaroles north of the main crater. On 17 June an aerial photograph showed minor steaming at the vent (figure 5).

Figure 4. Satellite view of the Great Sitkin crater at 2300 UTC on 11 June 2018 showing an ash deposit extending for about 2 km to the SW. Ash was likely deposited during the brief explosion on 10 June 2018. Minor steaming from a vent through the 1974 lava flow is also visible in this image. View is from the southwest. Photographer/Creator: David Schneider; image courtesy of AVO/USGS.

Figure 5. Aerial photo showing minor steaming at the summit of Great Sitkin, 17 June 2018. A small ash deposit extends SW from the vent. Photographer: Alaska Airlines Captain Dave Clum; image courtesy of AVO/USGS.

Another small phreatic explosion was observed in seismic data at 1105 local time on 11 August. Small local earthquakes preceded the event but were not recorded following the explosion. The event is similar to three other phreatic explosions that have occurred over the past 2 years.

Geologic Background. The Great Sitkin volcano forms much of the northern side of Great Sitkin Island. A younger parasitic volcano capped by a small, 0.8 x 1.2 km ice-filled summit caldera was constructed within a large late-Pleistocene or early Holocene scarp formed by massive edifice failure that truncated an ancestral volcano and produced a submarine debris avalanche. Deposits from this and an older debris avalanche from a source to the south cover a broad area of the ocean floor north of the volcano. The summit lies along the eastern rim of the younger collapse scarp. Deposits from an earlier caldera-forming eruption of unknown age cover the flanks of the island to a depth up to 6 m. The small younger caldera was partially filled by lava domes emplaced in 1945 and 1974, and five small older flank lava domes, two of which lie on the coastline, were constructed along northwest- and NNW-trending lines. Hot springs, mud pots, and fumaroles occur near the head of Big Fox Creek, south of the volcano. Historical eruptions have been recorded since the late-19th century.

Information Contacts: Alaska Volcano Observatory (AVO), a cooperative program of a) U.S. Geological Survey, 4200 University Drive, Anchorage, AK 99508-4667 USA (URL: https://avo.alaska.edu/), b) Geophysical Institute, University of Alaska, PO Box 757320, Fairbanks, AK 99775-7320, USA, and c) Alaska Division of Geological & Geophysical Surveys, 794 University Ave., Suite 200, Fairbanks, AK 99709, USA (URL: http://dggs.alaska.gov/).

Sporadic ash and gas-and-ash plumes and strong thermal anomalies were reported from Alaid, in Russia's Kurile Islands, between 29 September 2015 and 30 September 2016 (figure 8). The Kamchatka Volcanic Eruptions Response Team (KVERT), which monitors the volcano, interpreted the thermal anomalies as Strombolian activity and a lava flow (BGVN 42:04). The current report summarizes activity during October 2016 through August 2018.

Figure 8. Aerial photo of the Alaid summit area on 28 April 2016, with fresh lava filling the crater, a cinder cone in the southern part of the crater, and a lava flow on the SW flank. Photo by L. Fugura; courtesy of IVS FEB RAS, KVERT.

According to KVERT weekly reports, the Aviation Color Code for Alaid was Green (Volcano is in normal, non-eruptive state) throughout the reporting period. The only reported activity was from the Tokyo Volcanic Ash Advisory Center, which reported that on 21 August 2018, an ash plume identified in Himawari-8 satellite images rose to an altitude of 2.7 km (about 500 m above the summit) and drifted SE. The plume was clearly visible on imagery starting at 0830 Japan Standard Time (UTC + 9 hours), and remained noticeable for at least 4 hours. There were no other satellite or ground-based observations of this activity.

Figure 9. Himawari-8 satellite image from 21 August 2018 at 1030 JST (UTC + 9 hours) showing a small ash plume drifting SE from Alaid towards Paramushir Island. Alaid is the small island NW of the larger Paramushi Island and directly W of the southern tip of the Kamchatka Peninsula. Courtesy of Himawari-8 Real-time Web.

Geologic Background. The highest and northernmost volcano of the Kuril Islands, 2285-m-high Alaid is a symmetrical stratovolcano when viewed from the north, but has a 1.5-km-wide summit crater that is breached widely to the south. Alaid is the northernmost of a chain of volcanoes constructed west of the main Kuril archipelago. Numerous pyroclastic cones dot the lower flanks of this basaltic to basaltic-andesite volcano, particularly on the NW and SE sides, including an offshore cone formed during the 1933-34 eruption. Strong explosive eruptions have occurred from the summit crater beginning in the 18th century. Reports of eruptions in 1770, 1789, 1821, 1829, 1843, 1848, and 1858 were considered incorrect by Gorshkov (1970). Explosive eruptions in 1790 and 1981 were among the largest in the Kuril Islands during historical time.

Information Contacts: Tokyo Volcanic Ash Advisory Center (VAAC), 1-3-4 Otemachi, Chiyoda-ku, Tokyo, Japan (URL: http://ds.data.jma.go.jp/svd/vaac/data/); Kamchatka Volcanic Eruptions Response Team (KVERT), Far Eastern Branch, Russian Academy of Sciences, 9 Piip Blvd., Petropavlovsk-Kamchatsky, 683006, Russia (URL: http://www.kscnet.ru/ivs/kvert/); Institute of Volcanology and Seismology, Far Eastern Branch, Russian Academy of Sciences (IVS FEB RAS), 9 Piip Blvd., Petropavlovsk-Kamchatsky 683006, Russia (URL: http://www.kscnet.ru/ivs/eng/); Himawari-8 Real-time Web, developed by the NICT Science Cloud project in NICT (National Institute of Information and Communications Technology), Japan, in collaboration with JMA (Japan Meteorological Agency) and CEReS (Center of Environmental Remote Sensing, Chiba University) (URL: https://himawari8.nict.go.jp/).

Sakurajima is a persistently active volcano within the Aira caldera in Kyushu, Japan. The two currently active summit craters are Showa and Minamidake, both of which produce intermittent ash plumes and occasional pyroclastic flows. This report summarizes the activity from January through June 2018 as described in reports issued by the Japan Meteorological Agency (JMA) and Tokyo Volcanic Ash Advisory Center (VAAC).

The volcano remains on Alert Level 3 (out of five). A change in activity occurred in late 2017 to early 2018, with a reduction in activity at the Showa crater and a significant increase in activity at the Minamidake crater (table 19 and figure 63). During January through June 2018 a total of 260 explosions were recorded at Minamidake (135 of these were explosive), and four at Showa. Pyroclastic flows were produced on 1 April from Showa crater that travelled 800 m, and a flow reached 1,300 m from Minamidake crater on 16 June. Periodic incandescence was visible at the summit throughout the reporting period.

Table 19. Eruptive events and pyroclastic flows recorded at the active craters of Sakurajima volcano in Aira caldera. The number of events that were explosive in nature are in parentheses. Data courtesy of JMA (January to June 2018 monthly reports).

Figure 63. The number of monthly explosions at Minamidake (upper) and Showa (lower) craters of Sakurajima, Aira caldera. The first half of 2018 has seen a dramatic increase in activity at Minamidake, and a decrease in activity at Showa crater. Grey bars indicate eruptions and red bars specify explosive eruptions. Note that the scale on the two graphs are different. Courtesy of JMA (June 2018 monthly report).

In January 2018, one ash emission occurred at Showa crater and twelve occurred at Minamidake, with four of these classified as explosive eruptions. The largest ash plume reached 2,500 m above the crater on the 18th and two explosions ejected material out to a maximum of 700-800 m from the craters. Through February, three of seven ash emissions at Minamidake were explosive. The largest ash plume occurred on the 19th and reached 1,500 m above the crater. On the 27th, the crater ejected material out to 700 m from the crater.

Through March, 44 ash emissions occurred with 17 of these classified as explosive events. The largest ash plume was produced on the 26th and reached 3,400 m above the crater. An explosive eruption on 10 March ejected material out to 1,300 m from the crater. During April, Minamidake produced 66 ash emission; 50 of these were explosive (figure 64). Showa produced three events in total and an event on 1 April produced a pyroclastic flow that traveled 800 m to the E (figure 65).The largest ash plume was from Minamidake that reached 3,400 m above the crater.

Figure 64. True color Sentinel-2 satellite image of an ash plume at Sakurajima, Aira caldera, at 1056 on 12 April. The Tokyo VAAC reported that the plume that reached an altitude of 2.4 km. Courtesy of Sentinel Hub Playground.

Figure 65. Eruption of the Sakurajima Showa crater (within the Aira caldera) at 1611 on 1 April. The ash plume rose to 1,700 m above the crater and the pyroclastic flow (circled) travelled 800 m to the east. Image taken by the Kaigata webcam, courtesy of JMA (April 2018 monthly report).

Elevated activity continued at Minamidake through May, with 96 ash emissions (48 explosive), and the highest reported ash plume reaching 3,200 m above the crater on the 24th. An explosion on 5 May scattered ejecta out to 1,300 m from the crater. Activity was reduced in June with 35 ash emissions (13 explosive) from Minamidake, with an explosive event on the 16th producing an ash plume to 4,700 m above the crater and a pyroclastic flow out to 1,300 m (figure 66). This event deposited ash on nearby communities.

Figure 66. Eruption at the Sakurajima Minamidake crater (at Aira caldera) at 1607 on 16 June. The ash plume rose to 4,700 m above the crater and the pyroclastic flow (circled) traveled 1,300 m. Image captured by the Kaigata surveillance camera, courtesy of JMA (June 2018 monthly report).

Geologic Background. The Aira caldera in the northern half of Kagoshima Bay contains the post-caldera Sakurajima volcano, one of Japan's most active. Eruption of the voluminous Ito pyroclastic flow accompanied formation of the 17 x 23 km caldera about 22,000 years ago. The smaller Wakamiko caldera was formed during the early Holocene in the NE corner of the Aira caldera, along with several post-caldera cones. The construction of Sakurajima began about 13,000 years ago on the southern rim of Aira caldera and built an island that was finally joined to the Osumi Peninsula during the major explosive and effusive eruption of 1914. Activity at the Kitadake summit cone ended about 4850 years ago, after which eruptions took place at Minamidake. Frequent historical eruptions, recorded since the 8th century, have deposited ash on Kagoshima, one of Kyushu's largest cities, located across Kagoshima Bay only 8 km from the summit. The largest historical eruption took place during 1471-76.

Information Contacts: Japan Meteorological Agency (JMA), Otemachi, 1-3-4, Chiyoda-ku Tokyo 100-8122, Japan (URL: http://www.jma.go.jp/jma/indexe.html); Tokyo Volcanic Ash Advisory Center (VAAC), 1-3-4 Otemachi, Chiyoda-ku, Tokyo, Japan (URL: http://ds.data.jma.go.jp/svd/vaac/data/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground).

Suwanosejima volcano is located in the northern Ryukyu Islands in the south of Japan and has been on Alert Level 2 since December 2007. This report is a summary of activity for the period January to June 2018 and is based on information from the Japan Meteorological Agency (JMA) along with Tokyo VAAC notices.

During the reporting period, the active Ontake crater produced intermittent explosions that scattered ejecta around the crater and ash plumes to an altitude of 1.5-3 km. Ashfall was reported in a village 4 km away on 10 days during January-May 2018 (table 14). Incandescence was visible at night using monitoring equipment. Ash plumes were noted by the Tokyo Volcanic Ash Advisory Center (VAAC) throughout the reporting period (figure 32, table 15).

Table 14. Reported explosion information for Suwanosejima recorded in JMA monthly reports.

Table 15. Number of Volcanic Ash Advisories, explosion dates, and plume heights for activity at Suwanosejima. The numbers in parentheses indicate the number of events on that date; the VAACs issued column does not include advisories that note a continued episode. Drift directions were highly variable. Data courtesy of Tokyo VAAC.

Figure 32. An ash plume at Suwanosejima reached 1 km above the crater on 3 February 2018. Image captured by the Kyanpuba webcam, courtesy of JMA (February 2018 monthly report).

Geologic Background. The 8-km-long, spindle-shaped island of Suwanosejima in the northern Ryukyu Islands consists of an andesitic stratovolcano with two historically active summit craters. The summit of the volcano is truncated by a large breached crater extending to the sea on the east flank that was formed by edifice collapse. Suwanosejima, one of Japan's most frequently active volcanoes, was in a state of intermittent strombolian activity from Otake, the NE summit crater, that began in 1949 and lasted until 1996, after which periods of inactivity lengthened. The largest historical eruption took place in 1813-14, when thick scoria deposits blanketed residential areas, and the SW crater produced two lava flows that reached the western coast. At the end of the eruption the summit of Otake collapsed forming a large debris avalanche and creating the horseshoe-shaped Sakuchi caldera, which extends to the eastern coast. The island remained uninhabited for about 70 years after the 1813-1814 eruption. Lava flows reached the eastern coast of the island in 1884. Only about 50 people live on the island.

Information Contacts: Japan Meteorological Agency (JMA), Otemachi, 1-3-4, Chiyoda-ku Tokyo 100-8122, Japan (URL: http://www.jma.go.jp/jma/indexe.html); Tokyo Volcanic Ash Advisory Center (VAAC), 1-3-4 Otemachi, Chiyoda-ku, Tokyo, Japan (URL: http://ds.data.jma.go.jp/svd/vaac/data/).

Etna is the tallest active volcano in continental Europe with persistent activity at multiple summit craters and vents. The active craters are Bocca Nuova and Voragine within the Central Crater, the Northeast Crater, Southeast Crater, and the New Southeast Crater (figure 217). This report summarizes activity from April to July 2018 and is based on reports by the Istituto Nazionale di Geofisica e Vulcanologia (INGV).

Figure 217. The active summit craters of Etna volcano: the Bocca Nuova and Voragine craters that occupy the older Central Crater, the Northeast Crater (Cratere di Nord-Est), Southeast Crater (Cratere di Sud-Est), and the New Southeast Crater (Nuovo Cratere di Sud-Est). The years given in parentheses indicate when the craters formed. Photo by Marco Neri, courtesy of INGV (19 July 2018 blog).

Activity through April was characterized by degassing at the summit craters (figure 218), with modest ash emissions from the New Southeast Crater and Northeast Crater in the first week, and occasional small ash emissions at the end of the month. Reduced activity dominated by degassing continued into May with modest ash emission from the Southeast and Northeast craters during the second week, and isolated ash emissions from the Northeast Crater in the second half of the month continuing into June.

Figure 218. Degassing at the Bocca Nuova crater at the summit of Etna in late April. The top image is a photograph of the crater with the location of the bottom image, which is a thermal image showing the degassing and temperature at the vent reaching over 400°C. Courtesy of INGV (Weekly report No. 18/2018 for 24 to 30 April 2018, issued on 2 May 2018).

Throughout June the activity consisted of degassing at the summit craters with isolated diffuse ash emission from Northeast Crater (figure 219). This continued through to July until low-energy Strombolian activity commenced in the Bocca Nuova (from two vents) and Northeast craters (figures 220 and 221). The Strombolian explosions were small, lasting up to several tens of seconds, and were sometimes accompanied by red-brown ash emission. The ejected material was confined to within the craters. More energetic bursts were visible from the INGV surveillance camera located in Milo.

Figure 219. Photos of isolated dilute red-brown ash emissions from the Etna Northeast Crater on the 6 and 8 June. Courtesy of INGV (Report No. 24/2018 for the period 4 to 10 June 2018, issued on 12 June 2018).

Figure 220. A sequence of thermal infrared images of a Strombolian explosion at the Etna Bocca Nuova crater on 17 July 2018. Two vents are active (A and B), with vent B ejecting lava up to a few tens of meters above the vent. The color scale on the right of the images indicates the temperature in Celsius. Images taken by Giuseppe Salerno, courtesy of INGV (24 July 2018 INGV blog).

Figure 221. Photos of Strombolian explosions at the base of the Etna Northeast Crater on 20 and 21 July 2018. The explosions occur when gas pockets burst and eject incandescent fluid lava above the vent. Photo by Michele Mammino, courtesy of INGV (24 July 2018 blog).

Geologic Background. Mount Etna, towering above Catania, Sicily's second largest city, has one of the world's longest documented records of historical volcanism, dating back to 1500 BCE. Historical lava flows of basaltic composition cover much of the surface of this massive volcano, whose edifice is the highest and most voluminous in Italy. The Mongibello stratovolcano, truncated by several small calderas, was constructed during the late Pleistocene and Holocene over an older shield volcano. The most prominent morphological feature of Etna is the Valle del Bove, a 5 x 10 km horseshoe-shaped caldera open to the east. Two styles of eruptive activity typically occur, sometimes simultaneously. Persistent explosive eruptions, sometimes with minor lava emissions, take place from one or more summit craters. Flank vents, typically with higher effusion rates, are less frequently active and originate from fissures that open progressively downward from near the summit (usually accompanied by Strombolian eruptions at the upper end). Cinder cones are commonly constructed over the vents of lower-flank lava flows. Lava flows extend to the foot of the volcano on all sides and have reached the sea over a broad area on the SE flank.

Information Contacts: Sezione di Catania - Osservatorio Etneo, Istituto Nazionale di Geofisica e Vulcanologia (INGV), Sezione di Catania, Piazza Roma 2, 95123 Catania, Italy (URL: http://www.ct.ingv.it/it/); Blog INGVvulcani, Istituto Nazionale di Geofisica e Vulcanologia (INGV) (URL: http://ingvvulcani.wordpress.com).

Stromboli is a persistently active volcano in the Aeolian Islands, Italy, with confirmed historical eruptions going back over about 2,000 years. The active summit craters on the crater terrace are situated above the Sciara del Fuoco, a steep talus slope on the NW side of the island that leads to the Tyrrhenian Sea below. The NE crater (Area N) includes the active N1 and N2 vents, while the Central and SW craters (Area CS) contains the C, S1, and S2 vents (figures 125 and 126).

Figure 125. False color thermal Sentinel-2 satellite image of Stromboli volcano with the locations of the Sciara del Fuoco and the active craters and vents. Four of the active vents are visible in this image as bright yellow-orange areas. Image acquired on 27 June 2018 and processed using bands 12, 11, 4. Courtesy of Sentinel Hub Playground.

Figure 126. Thermal image of the Stromboli crater terrace area showing the N (area N), and the central and S (area CS) craters with the active vents. Image taken by the Pizzo webcam, courtesy of INGV (report number 11/2018 for the period 5 to 11 March, released on 13 March 2018).

Typical activity comprises degassing and multiple explosions per hour that range from tens of seconds to a few minutes, known as Strombolian activity, which is named after this particular volcano (figure 127). The activity usually consists of low-intensity explosions that eject material (ash, lapilli, and blocks) up to 80 m above the crater and medium-low intensity explosions that eject material up to 120 m above the crater. This report describes the activity at Stromboli through March to June 2018 and summarizes reports published by the Istituto Nazionale di Geofisica e Vulcanologia (INGV).

Figure 127. The daily frequency of explosions per hour produced by all the active vents at Stromboli during the period 1 January to 2 July 2018. Red indicates explosions within the N crater, green indicates activity at the central-S craters, and blue indicates the number of total events. Courtesy of INGV (report number 27/2018 for the period 25 June to 7 July, released on 3 July 2018).

Characteristic Strombolian activity occurred throughout March, typically consisting of 5-11 events per hour that ejected material up to 120 m above the craters. High-energy explosive events occurred on 7 and 18 March, both lasting around 40 seconds and ejecting material to a height of 400 m (figures 128 and 129).

Figure 128. A high-energy explosive event on 7 March 2018 at the N2 vent of Stromboli. Top images (frames a to c) are thermal images, with the corresponding visible images across the bottom (frames d to f). Images were taken by the Pizzo webcams, courtesy of INGV (report number 11/2018 for the period 5 to 11 March, released on 13 March 2018).

Figure 129. Thermal infrared images of the high-energy explosive event on 18 March 2018 at Stromboli. The images show approximately 40 seconds of the explosive sequence recorded by the Pizzo webcam, courtesy of INGV (report number 12/2018 for the period 12 to 18 March, released on 20 March 2018).

Typical Strombolian activity continued through April with 6-12 explosive events per hour, with two high-energy explosive events on 24 and 26 April that lasted nine and three minutes, respectively. Both events ejected material across the Sciara del Fuoco, producing ash plumes and lava fountaining (figure 130). Low to medium-low intensity activity continued through May and June, with explosions per hour in the range of 3-15 and 6-13, respectively.

Figure 130. INGV noted an intense explosive sequence on 26 April 2018 at Stromboli. Top images (frames A to C) show the thermal signature of the explosion; bottom images (frames G to I) are the corresponding visible images. The sequence produced abundant ash, incandescent material, lava fountaining, and ejected large blocks to a height of 250 m above the vent that then fell around the crater and on the Sciara del Fuoco. Courtesy of the INGV (Blog INGVvulcani entry for 16 July 2018).

Geologic Background. Spectacular incandescent nighttime explosions at this 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 island 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 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 for more than a millennium.

Information Contacts: Istituto Nazionale di Geofisica e Vulcanologia (INGV), Sezione di Catania, Piazza Roma 2, 95123 Catania, Italy (URL: http://www.ct.ingv.it/en/); Blog INGVvulcani, Istituto Nazionale di Geofisica e Vulcanologia (INGV) (URL: https://ingvvulcani.wordpress.com/2018/07/16/stromboli-e-le-sue-esplosioni/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground).

After a large, deadly explosive and effusive eruption during 1963-64, Indonesia's Mount Agung was quiet until a new eruption began in November 2017 (BGVN 43:01). A lava dome emerged into the summit crater at the end of November and intermittent plumes of ash rose as high as 3 km above the summit through the end of the year. Activity continued into 2018 with explosions that produced ash plumes rising multiple kilometers above the summit, and the growth of the lava dome within the summit crater. Information about the ongoing eruptive episode comes from Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG), also known as the Indonesian Center for Volcanology and Geological Hazard Mitigation (CVGHM), the Darwin Volcanic Ash Advisory Center (VAAC), and multiple sources of satellite data. This report covers the ongoing eruption from January through July 2018.

Intermittent explosions with ash plumes were reported at Agung several times during January 2018, including Strombolian activity on 19 January. Activity decreased significantly by the end of the month; only one explosion with ash was reported during February. Two ash plumes were reported in March and three were reported each month during April and May. A more substantial explosion in mid-June produced an ash plume that rose to 7 km altitude. A series of deep-seated earthquakes during the third week of June was followed by large explosions and new effusions of lava inside the summit crater beginning on 28 June. A strong thermal signal also appeared on 28 June that gradually diminished during July. Intermittent plumes of steam and ash recurred daily until 19 July; plume heights rose up to 3 km above the summit on several occasions. Strombolian explosions on 2 and 8 July sent ejecta as far as 2 km from the summit. Explosive activity became more intermittent during the last two weeks of the month; the last reported explosion was on 27 July.

Activity during January-May 2018. During most days of January 2018 when fog was not obscuring the summit, PVMGB reported plumes of steam and minor ash rising about 500 m above the summit. In addition, intermittent explosions produced higher, denser ash plumes that rose 1,000-2,500 m above the summit several times. Ash plumes on 1 and 2 January rose to 1,000 and 1,500 m above the summit; incandescence was observed at the summit on both nights, and trace ashfall was reported at the Rendang Post on 2 January. The Darwin VAAC reported the ash plume on 1 January at 6.1 km altitude moving SW. A single MODVOLC thermal alert was recorded on 4 January. On 5 January PVMGB lowered the evacuation radius from 10 to 6 km, permitting the return of thousands of displaced people to their homes. Approximately 17,000 people in seven villages within 6 km of Agung were still under evacuation orders from the events of late 2017.

The Agung Volcano Observatory issued VONA's (Volcano Observatory Notice for Aviation) on 4, 8, 9, 11, 15, 17, 19, 23, 24, and 30 January relating to the larger explosions and ash plumes. On 11 January, an ash plume rose to 2,500 m above the summit and drifted N and NE (figure 29). Another 2,500-m-high ash plume on 19 January was accompanied by Strombolian activity at the summit for several hours, and incandescent ejecta that traveled 1,000 m from the crater. Ashfall was later reported in Tulamben village in the Kubu district (9 km NE) and in Purwekerti village in the Abang district (14 km ENE). Visual monitoring using drones carried out on 22 January showed that the volume of the lava dome was relatively unchanged at around 20 million m³. The summit was obscured by fog for the last week of the month.

Figure 29. An eruption at Agung on 11 January 2018 sent an ash plume to 2,500 m above the summit. Courtesy of MAGMA Indonesia and PVMBG (Erupsi Gunung Agung 11 Januari 2018 17:54 WITA).

Activity decreased noticeably in late January and February. Steam and minor ash plumes rose only 50-800 m above the summit for most of the month. As a result of the decrease in activity, PVMBG lowered the Alert Level from Level IV to Level III (on a four-level scale) on 10 February 2018. The radius of evacuation was also lowered from 6 to 4 km. A single explosion on 14 February sent an ash plume to 1,500 m above the summit.

For most of March 2018, steam plumes rose less than 400 m above the summit. VONA's were issued by the Agung Volcano Observatory for ash plumes twice, on 12 March (local time) when a plume rose 800 m above the summit and drifted E, and on 26 March when the ash plume rose to 500 m and drifted NW. During much of April 2018, steam plumes rose less than 300 m above the summit; weather obscured views of the summit for most of the last week of the month. AVO issued VONA's for ash plumes on 6, 11 and 30 April; the plumes on 6 and 11 April rose 500 m and drifted W and SW respectively. The Darwin VAAC reported a series of four short-lived explosions with ash plumes on 11 April; they each dissipated within a few hours. PVMBG reported another explosion on 15 April that produced an ash plume that also rose 500 m. The plume on 30 April rose 1,500 m and drifted SW.

Similar activity persisted throughout May 2018. Steam plumes generally rose 50-100 m above the summit crater each day. In addition, explosions were reported on 9, 19, and 29 May. PVMBG reported that no ash plume was observed on 9 May, due to fog obscuring the summit, but the ash plume on 19 May rose to 1,000 m above the summit and drifted SE, and the ash plume on 29 May rose 500 m and drifted SW.

Activity during June and July 2018. The volcano was covered in fog for much of the first two weeks of June. A short-lived explosion on 10 June 2018 was reported by PVMBG, but meteoric clouds obscured the summit. The Darwin VAAC noted the plume in a satellite image drifting W at about 4.6 km altitude. An explosion on 13 June produced an ash plume that rose 2,000 m above the summit and drifted WSW (figure 30). Another explosion was recorded on 15 June, but the summit was obscured, and no ash cloud was visible to ground observers. However, the Darwin VAAC reported the plume visible in satellite imagery at 7 km altitude (about 4 km above the summit) drifting SW and S for most of the day before dissipating. Ashfall was reported about 7 km W in the village of Puregai. PVMBG reported white and gray emissions on 17 June that rose 500 m.

Figure 30. An ash plume at Agung on 13 June 2018 rose about 2,000 m above the summit and drifted WSW. View is looking N. Courtesy of PVMBG (Information on G. Agung Eruption, 13 June 2018).

An explosion during the evening (local time) of 27 June 2018 produced an ash plume that rose 2,000 m from the summit and drifted W. Another explosion the following morning produced a sustained ash cloud that lasted for several hours and again caused ashfall around the village of Puregai. It rose to about 2,000 m above the summit and drifted W and SW (figure 31).

Figure 31. A sustained ash eruption began early on 28 June 2018 at Agung (top) and lasted well into the afternoon (bottom). Photo from a PBVBG webcam, posted on Twitter by Sutopo Purwo Nugroho‏ (BNPB).

PVMBG noted in late June that inflation of 5 mm had occurred since 13 May 2018. They reported that the ash plumes on 28 June caused some airlines to cancel flights to Bali, and ashfall was reported in several villages in Bangli and areas to the W and SW the following day (figure 32). The International Gusti Ngurah Rai (IGNR) airport (60 km SW) in Denpasar, the Blimbing Sari Airport (128 km W) in Banyuwangi, and the Noto Hadinegoro Airport (200 km W) in Jember closed for portions of the day on 29 June (ANTARA News).

Figure 32. Settlement and plantation areas were coated with ash from Mount Agung in Pemuteran Village (10 km W) on 29 June 2018. Courtesy of Tempo.com and ANTARA/Nyoman Budhiana.

Incandescence overnight on 28-29 June indicated fresh effusions of lava at the summit; they were accompanied by ash emissions that rose 1,500-2,500 m. Thermal satellite images recorded on 29 June indicated significant hotspots within the crater with thermal energy reaching 819 Megawatts; this was the largest amount of thermal energy recorded during the 2017-2018 activity, significantly higher than the maximum recorded of 97 Megawatts reached at the end of November 2017. The MIROVA data clearly reflected the sudden surge of thermal energy into the summit crater at the end of June (figure 33).

Figure 33. A large spike in thermal energy beginning on 28 June 2018 signaled a new surge of lava into the summit crater at Agung. This MIROVA plot of Log Radiative Power showed pulses of activity in early January, May, and early June, followed by the much larger surge of heat in late June that tapered off throughout July. Inset shows the nighttime incandescence on 28 June 2018 that resulted from the new effusion of lava. Photo taken at the PGMBG Webcam in Batu Lompeh (15 km N). Graph courtesy of MIROVA, photo courtesy of PVMBG (Press Release of Mount Agung's Latest Activities, June 29 to 3:00 p.m.)

The Darwin VAAC reported continuous emissions of ash beginning on 28 June that drifted to the W for over 24 hours. The height was initially reported by ground observers at 3.7 km altitude but was raised to 7 km altitude a few hours later, based on satellite imagery and pilot reports. By late that day, an upper plume (at 7 km) drifted SW and a second plume drifted W at 5.5 km altitude. By late on 29 June the continuous ash plume was drifting NW at 4.9 km altitude; it finally dissipated early on 30 June. In addition to large ash plumes and a major thermal anomaly, a substantial SO₂ plume also emerged from Agung on 28-29 June 2018. The plume drifted W over Java and then dispersed to the NW over the next 24 hours (figure 34). A lingering, smaller plume was still visible two days later.

Figure 34. A substantial SO2 plume was released from Agung during 28-29 June 2018 and captured by both the OMPS instrument on the Suomi satellite (upper images) and the OMI instrument on the Aura satellite (lower images). The plume first appeared on 28 June (top left) and was much larger the next day (top right). By 30 June it was dissipating over Java to the W and N (bottom left). A smaller plume drifted SW two days later (bottom right). Courtesy of NASA Goddard Space Flight Center.

A series of discrete eruptions lasting from late on 30 June through 2 July 2018 produced ash plumes that rose from 3.7 to 5.5 km altitude and drifted NW and W, according to the Darwin VAAC. Effusive activity continued to increase during the first week of July 2018 with the continued growth of the lava dome in the summit crater. PVMBG reported an additional volume of lava of 4 million m³ erupted from 28 June through the middle of July bringing the size of the dome to about 27 million m³. The frequency of explosions peaked on 2 July when Strombolian activity sent incandescent ejecta 2 km from the summit in all directions (figure 35).

Figure 35. The eruption of Mount Agung on 2 July 2017 produced Strombolian activity and incandescent ejecta that traveled 2 km from the summit crater in all directions. Courtesy of ANTARA News/HO/BMKG.

Several VONA's issued during 2-3 July reported multiple explosions that sent ash plumes 700-2,000 m above the summit. Eighteen explosions were reported by PVMBG between 1 and 8 July. The Darwin VAAC noted a substantial explosion early on 2 July that produced a plume that rose to 7.6 km altitude and drifted W. The remains of the ash plume were discernable in satellite imagery about 250 km W of Agung by the end of the day. The ash plume on 4 July rose 2,500 m above the summit (figure 36).

Figure 36. An explosion at Agung on 4 July 2018 produced an ash plume that rose 2,500 m above the summit, according to PVMBG. Courtesy of PVMBG (Information on G. Agung Eruption, July 4, 2018).

Strombolian activity was reported again on 8 July 2018 (figure 37). The Darwin VAAC reported intermittent explosions every day from 3-19 July, with ash plumes rising to altitudes from 3.7 to 6.7 km. Additional explosions were reported on 21, 24, 25, and 27 July (figure 38); ash plumes rose 700-2,000 m and drifted W or SE. MODVOLC thermal alerts resumed on 27 June, and multiple daily alerts persisted on most days through the end of July.

Figure 37. Strombolian activity at Agung recurred for the third time in 2018 on 8 July 2018. Courtesy of PVMBG (Agung Strombolian Eruption Today July 8, 2018).

Figure 38. A dense ash plume rose about 2,000 m above Mount Agung on 27 July 2018 at 1406 local time. Courtesy of PVMBG (Information on G. Agung Eruption, 27 July 2018).

Geologic Background. Symmetrical Agung stratovolcano, Bali's highest and most sacred mountain, towers over the eastern end of the island. The volcano, whose name means "Paramount," rises above the SE caldera rim of neighboring Batur volcano, and the northern and southern flanks extend to the coast. The summit area extends 1.5 km E-W, with the high point on the W and a steep-walled 800-m-wide crater on the E. The Pawon cone is located low on the SE flank. Only a few eruptions dating back to the early 19th century have been recorded in historical time. The 1963-64 eruption, one of the largest in the 20th century, produced voluminous ashfall along with devastating pyroclastic flows and lahars that caused extensive damage and many fatalities.

Information Contacts: Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM), Jalan Diponegoro 57, Bandung 40122, Indonesia (URL: http://www.vsi.esdm.go.id/); MAGMA Indonesia, Kementerian Energi dan Sumber Daya Mineral (URL: https://magma.vsi.esdm.go.id/); Darwin Volcanic Ash Advisory Centre (VAAC), Bureau of Meteorology, Northern Territory Regional Office, PO Box 40050, Casuarina, NT 0811, Australia (URL: http://www.bom.gov.au/info/vaac/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Hawai'i Institute of Geophysics and Planetology (HIGP) - MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); NASA Goddard Space Flight Center (NASA/GSFC), Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, 8800 Greenbelt Road, Goddard, Maryland, USA (URL: https://so2.gsfc.nasa.gov/); Sutopo Purwo Nugroho?, BNPB, Twitter (URL: https://twitter.com/Sutopo_PN); TEMPO.CO, Tempo Building, Jl. Palmerah Barat No. 8, South Jakarta 12210, Indonesia (URL: https://nasional.tempo.co/read/1102118/pvmbg-energi-thermal-erupsi-gunung-agung-kali-ini-paling-besar); ANTARANEWS.com, ANTARA guesthouse lt 19, Jalan Merdeka Selatan No. 17, Jakarta Pusat, Indonesia, (URL: https://en.antaranews.com).

Eruptions at Fernandina Island in the Galapagos often occur from vents located around the caldera rim along boundary faults and fissures, and occasionally from side vents on the flank. The last eruption in September 2017 lasted for about one week and originated from a fissure at the SW rim of the caldera. A new eruption in June 2018 lasted for less than a week and originated from a fissure on the N flank of the volcano. Information about the latest eruption was provided by Ecuador's Institudo Geofisica, Escuela Politécnica Nacional (IG-EPN), the Dirección del Parque Nacional Galápagos (PNG), the Washington Volcanic Ash Advisory Center (VAAC), and several sources of satellite data.

A seismic swarm on 16 June 2018 preceded a brief eruptive episode at Fernandina that lasted from 16 to 22 June. Lava erupted from a radial fissure and quickly flowed to the sea down the N flank. Emissions were primarily gas with low ash content and included substantial SO₂. After two days of activity, seismicity returned to background levels on 18 June. Park Officials reported only cooling flows and lava no longer entering the sea by 21 June 2018.

Eruption of June 2018. The first evidence of a new eruptive event at Fernandina began as a seismic swarm on 16 June 2018. The largest event (M 4.1) was located 4 km off the NE flank of the island. An active eruption was confirmed a few hours later by guides on a passing boat and by satellite images which indicated a thermal anomaly on the N flank. The eruption consisted of a lava flow on the NNE flank and a gas plume that rose 2-3 km and drifted SW (figure 32). The lava flow quickly reached the ocean, generating steam and gas explosions that were visible from Canal Bolívar, the narrow channel on the NE side of Isla Fernandina that separates it from Isla Isabela (figure 33).

Figure 32. Lava from a new eruption at Fernandina flowed quickly down the N flank of the island to the ocean on 16 June 2018, according to Parque Nacional Galapagos officials. Courtesy of Parque Nacional Galapagos.

Figure 33. Explosions produced large plumes of steam as lava reached the ocean on the N flank of Fernandina on 16 June 2018. Courtesy of Parque Nacional Galapagos.

Observations by PNG officials and visitors indicated that lava flows came from a radial fissure on the NNE flank, and produced gas plumes with low ash content that rose 2-3 km and drifted more than 250 km WNW (figures 34 and 35). The Washington VAAC detected an ash and gas plume in visible satellite imagery drifting W from the summit at 2.4 km altitude late in the day on 16 June, along with a significant thermal signature in infrared imagery. A second gas-and-ash plume at the same altitude drifted WNW the following day for a few hours before dissipating. After two days of intense eruptive activity, seismic tremor activity had declined significantly to background levels by noon on 18 June.

Figure 34. Incandescent lava flows from the eruption of Fernandina produced large plumes of water vapor as they reached the sea during the evening of 16 June 2018. Courtesy of Parque Nacional Galapagos.

Figure 35. Incandescent lava reached the sea during 16-18 June 2018 at Fernandina from a brief eruptive episode. The lava flowed down the N flank. Courtesy of CNH Tours, posted 20 June 2018.

‏A strong pulse of SO₂ emissions that drifted W was recorded by satellite instruments on 17 and 18 June 2018 (figure 36). The MODVOLC thermal alert system also recorded a surge of over 100 thermal anomalies from infrared satellite imagery that lasted from 17 to 22 June. More than half of the anomalies appeared on 17 June. The alert pixels were all clustered on the N flank. The MIROVA system also record the spike in thermal activity on 17 June and indicated that the heat source was more than 5 km from the summit (figure 37).

Figure 36. A strong pulse of SO2 issued from Fernandina on 17 June 2018 and was recorded by the OMPS instrument on the SUOMI NPP satellite. The plume drifted W and measured at about 27 Dobson Units (DU). Courtesy of NASA Goddard Space Flight Center.

Figure 37. The MIROVA system log radiative power measurement for Fernandina showed a spike of thermal activity on 16-17 June 2018 that coincided with the fissure eruption that sent lava flows down the N flank of the volcano into the sea. The black bars indicate a heat source more than 5 km from the summit. The MODVOLC thermal alert system detected over 100 thermal alerts at Fernandina between 17 and 22 June 2018, concurring with observations of lava flows on the N flank of the volcano. Courtesy of MIROVA and MODVOLC.

By 21 June 2018 PNG officials reported that lava was no longer reaching the ocean, but steam from cooling flows was visible at the coastline and over the area of the new flows (figure 38).

Figure 38. By 21 June 2018 active lava flows were no longer reaching the ocean at Fernandina, although steam from cooling lava was still visible near the coast and along the N flank. Courtesy of Parque Nacional Galapagos.

Geologic Background. Fernandina, the most active of Galápagos volcanoes and the one closest to the Galápagos mantle plume, is a basaltic shield volcano with a deep 5 x 6.5 km summit caldera. The volcano displays the classic "overturned soup bowl" profile of Galápagos shield volcanoes. Its caldera is elongated in a NW-SE direction and formed during several episodes of collapse. Circumferential fissures surround the caldera and were instrumental in growth of the volcano. Reporting has been poor in this uninhabited western end of the archipelago, and even a 1981 eruption was not witnessed at the time. In 1968 the caldera floor dropped 350 m following a major explosive eruption. Subsequent eruptions, mostly from vents located on or near the caldera boundary faults, have produced lava flows inside the caldera as well as those in 1995 that reached the coast from a SW-flank vent. Collapse of a nearly 1 km3 section of the east caldera wall during an eruption in 1988 produced a debris-avalanche deposit that covered much of the caldera floor and absorbed the caldera lake.

Information Contacts: Instituto Geofísico (IG), Escuela Politécnica Nacional, Casilla 17-01-2759, Quito, Ecuador (URL: http://www.igepn.edu.ec/); Dirección del Parque Nacional Galápagos (DPNG), Av. Charles Darwin y S/N, Isla Santa Cruz, Galápagos, Ecuador (URL: http://www.galapagos.gob.ec/, Twitter: @parquegalapagos); Hawai'i Institute of Geophysics and Planetology (HIGP) - MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); NASA Goddard Space Flight Center (NASA/GSFC), Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, 8800 Greenbelt Road, Goddard, Maryland, USA (URL: https://so2.gsfc.nasa.gov/); Cultural and Natural Heritage Tours, Galapagos, (CNH Tours), 14 Kilbarry Crescent, Ottawa, Ontario, K1K 0G8, Canada (URL: https://www.cnhtours.com/, Twitter: @CNHtours).

Guatemala's Volcán de Fuego was continuously active throughout the first half of 2018; it has been erupting vigorously since 2002 with historical observations of eruptions dating back to 1531. These eruptions have resulted in major ashfalls, pyroclastic flows, lava flows, and damaging lahars. Large explosions with a significant number of fatalities occurred during 3-5 June 2018 and are covered in this report of activity from January-June 2018. Reports are provided by the Instituto Nacional de Sismologia, Vulcanología, Meteorología e Hidrologia (INSIVUMEH) and the National Office of Disaster Management (CONRED); aviation alerts of ash plumes are issued by the Washington Volcanic Ash Advisory Center (VAAC). Satellite data from NASA, NOAA, and other sources provide valuable information about heat flow and gas emissions. Numerous media outlets provided photographs of the eruptive activity.

Summary of activity, January-June 2018. The first eruptive event of 2018 occurred during 31 January-1 February and lasted for about 20 hours. It included pyroclastic flows, lava flows, incandescent ejecta, ash plumes that rose to 7 km altitude, and ashfall more than 60 km from the volcano. Four lava flows emerged during the event, and the longest traveled 1,500 m down the Seca ravine. Multiple daily explosions that generated ash plumes continued through May 2018. Ash plumes usually rose to 4.2-4.9 km altitude (400-1,200 m above the summit) and drifted up to about 15 km from the volcano in the prevailing wind directions. Ashfall was often reported from communities within 10 km of the summit, most commonly to the W and SW, but also occasionally to the N and NE. Incandescent ejecta rose up to 300 m above the summit during periods of increased activity; block avalanches of the incandescent material descended the major drainages on all flanks, often as far as the vegetated areas several hundred m below the summit.

The first lahar of the year was reported on 9 April; additional lahars occurred several times during May after rainy periods. They were generally 20-30 m wide and 1-2 m deep, carrying debris 1-2 m in diameter. A lava flow was active in the Ceniza ravine for the second half of May, moving up to 1,000 m from the summit during heightened activity on 22 May, and again on 2 June.

The second major eruptive event of 2018, and the largest and deadliest explosive activity in recent history at Fuego, began with a strong explosion on the morning of 3 June 2018. Multiple explosions throughout the day produced an ash plume that was observed in satellite data at 15.2 km altitude, and a strong SO₂ plume that drifted N and NE. Numerous large pyroclastic flows generated by the explosions throughout the day descended multiple ravines around the flanks. The most heavily damaged communities were San Miguel Los Lotes and El Rodeo, 10 km SE of the summit at the base of Las Lajas ravine. Most infrastructure in the communities was buried in ash; there were 110 reported fatalities, and at least 197 people reported missing and presumed dead. Additional explosions two days later caused a brief halt in recovery efforts as more pyroclastic flows covered the same area.

Abundant rainfall that began on 6 June 2018 led to over 30 lahars throughout the rest of the month, inundating all of the major ravines and tributaries of the Rio Pantaleón and Rio Gobernador and causing additional infrastructure damage to bridges and roads. The lahars were often 30-40 m wide, 3 m deep, and carried volcanic blocks and debris up to 3 m in diameter. Explosive activity declined to background levels by the middle of June, but daily explosions with ash plumes and incandescent avalanche blocks continued for the remainder of the month, with continued reports of ashfall in communities within 15 km of the summit.

Activity during January-February 2018. During January 2018, plumes of steam rose to 4.3-4.5 km altitude, drifting primarily W, SW, and S. Activity included 3 to 8 explosions per hour that generated ash plumes, which rose to about 4.3-4.8 km altitude (figure 82). Explosions on 19 January increased to 7-13 per hour, and produced ash plumes that drifted more than 15 km W, SW, and S. Incandescent ejecta rose 100-300 m above the crater and traveled up to 400 m from the crater, in some cases reaching vegetated areas. The SW flank was the most affected by ashfall; it was reported in the communities of San Pedro Yepocapa, Escuintla, Sangre de Cristo, Finca Palo Verde, El Porvenir, Santa Sofía, Morelia, Paniché I and II, Rochela, and Ceilán. Block avalanches traveled down the Seca, Taniluyá, Cenizas and Las Lajas ravines. On 28 January, seismic station FG3 registered an increase in pulses of tremor activity. MODVOLC thermal alerts were issued during 17 days in January. The Washington VAAC issued multiple daily aviation alerts on 22 days of the month.

Figure 82. Moderate explosions produced a plume of ash at Fuego on 14 January 2018 that drifted W a few hundred meters above the summit, seen in this view from SW of the volcano. Courtesy of INSIVUMEH (Informe mensual de la actividad del Volcan de Fuego, Enero 2018).

The first major eruptive event of 2018 occurred during 31 January-1 February and lasted for about 20 hours. It included pyroclastic flows, lava flows, incandescent ejecta, ash plumes that rose to 7 km altitude, and ashfall more than 60 km W, SW, and NE from the volcano (figure 83). Explosive activity increased to 5-8 events per hour, incandescent material rose up to 300 m above the crater, and ejecta traveled 300 m.

Figure 83. The first major eruptive event of 2018 at Fuego produced ash plumes, pyroclastic flows, lava flows and incandescent ejecta on 1 February. Photo taken from the N (adjacent Acatenango in the foreground) by Ruben Merida, courtesy of INSIVUMEH (Informe Mensual de la Actividad del Volcan de Fuego, Febrero 2018).

The substantial ash plume produced from the event drifted tens of kilometers to the W and SW (figures 84 and 85). The SW flank was the area most affected by ashfall, where communities of San Pedro Yepocapa and Escuintla, Sangre de Cristo, Palo Verde, El Porvenir, Santa Sofia, Morelia, Paniché I and II are located. Ashfall also occurred 10-25 km NE in La Rochela, San Andrés Osuna, La Reina, Ciudad Vieja, Antigua Guatemala, and in the WSW part of Guatemala City.

Figure 84. A dense ash plume drifts W and SW from Fuego on 1 February 2018. Image taken by the Operational Land Imager (OLI) on Landsat 8. Courtesy of NASA Earth Observatory.

Figure 85. A closeup of Fuego (see box in figure 84) on 1 February 2018 shows an ash plume drifting W and fresh ash and pyroclastic flow deposits around the summit during the first major eruptive event of 2019. Image taken by the Operational Land Imager (OLI) on Landsat 8. Courtesy of NASA Earth Observatory.

Four lava flows emerged during the eruptive event; a 1,500-m-long flow traveled down the Seca ravine, a 700-m-long flow traveled down the Ceniza ravine, and flows in Las Lajas and La Honda canyons traveled 800 m from the summit. Numerous pyroclastic flows also descended the Honda and Seca ravines, and smaller pyroclastic flows descended the Trinidad and Las Lajas ravines (figure 86).

Figure 86. Pyroclastic flows descended short distances down several ravines (barrancas) at Fuego on 1 February 2018. Courtesy of INSIVUMEH (Informe Mensual de la Actividad del Volcan de Fuego, Febrero 2018).

La Honda ravine had not been affected by pyroclastic flows since 1974; they traveled 5.8 km down that ravine (figure 87), and 4.2 km down the Seca ravine. About 2,880 residents of Escuintla (20 km SE) and Alotenango (8 km E) were evacuated during these events. Significant concentrations of SO₂ were detected on 1 February by the Ozone Mapper Profiler Suite (OMPS) on the Suomi National Polar-orbiting Partnership (Suomi-NPP) satellite (figure 88).

Figure 87. Pyroclastic flow deposits covered several kilometers of barranca La Honda on 6 February 2018 from the events which occurred on 1 February. Courtesy of INSIVUMEH (Informe Mensual de la Actividad del Volcan de Fuego, Febrero 2018).

Figure 88. Significant concentrations of SO2 drifted SW on 1 February from the eruptive event at Fuego; they were recorded by the Ozone Mapper Profiler Suite (OMPS) on the Suomi National Polar-orbiting Partnership (Suomi-NPP) satellite. Courtesy of NASA Earth Observatory and NASA Goddard Space Flight Center.

Multiple daily explosions with ash plumes continued throughout the rest of February; plumes generally rose to 4.5-4.7 km altitude, and ashfall was reported in communities 10-20 km from the volcano in various directions. Block avalanches descended barrancas Seca, Taniluyá, and Ceniza on most days. Incandescence at night was visible up to 200 m above the crater. MODVOLC thermal alerts were issued on 8 days of the month, and the Washington VAAC issued multiple daily aviation alerts throughout the month.

Activity during March-May 2018. Constant activity continued during March and April 2018, without any major eruptive episodes. Continuous degassing, explosions with ash plumes (figure 89), incandescent ejecta, and daily block avalanches were reported. Steam plumes rose daily to 4.2-4.4 km altitude and usually drifted NW, W, SW, or S. Explosions averaged 4-9 per hour and produced ash plumes that rose to 4.3-4.8 km altitude drifting more than 20 km NW, W, SW, and S. Incandescent ejecta was measured up to 300 m above the crater and traveled a similar distance down the flanks. Block avalanches sent debris up to a kilometer down the major drainages most days. The MODVOLC system recorded thermal alerts during 20 days of March and 22 days of April. The communities most affected by near-daily ashfall, on the SW flank, included San Pedro Yepocapa and Escuintla, Sangre de Cristo, Palo Verde Estate, El Porvenir, Santa Sofia, Morelia, and Paniché I and II. The Washington VAAC issued multiple daily aviation alerts nearly every day during both months.

Figure 89. The ash plume on 13 April 2018 at Fuego was typical of the activity during March and April. Courtesy of INSIVUMEH (Reporte Semanal de Monitoreo: Volcán de Fuego (1402-09), Semana del 07 al 13 de abril de 2,018).

On 9 April the first lahar of the year descended the Seca canyon and the El Mineral channel, tributaries of the Pantaleón River. It was 10 m wide and 1.5 m deep, carrying abundant debris. In special bulletins released on 14 and 16 April INSIVUMEH noted increased explosive activity occurring at a rate of up to 10 explosions per hour, with ash plumes that rose to 4.8 km altitude. This was followed by a report of a lava flow during the evening of 16 April that traveled 1,300 m down the Seca Ravine.

Activity during the first two weeks of May 2018 was similar in character to the previous two months. Steam plumes rose to 4.1-4.3 km altitude, ash plumes rose to 4.5-4.8 km altitude from explosions that occurred at a rate of 4-8 per hour and drifted SW and W, and ashfall was reported in San Pedro Yepocapa, Morelia, El Por-venir, Sangre de Cristo, Santa Sofía, Finca Palo Verde, Panimaché I y II and other nearby communities. Incandescent ejecta rose 150-300 m high and was thrown 50 m from the crater; shockwaves from the explosions were felt 20-25 km away.

A lahar 12 m wide and 1.5 m deep descended the Seca Ravine on 10 May, dragging tree trunks and volcanic blocks as large as 1.5 m in diameter. A 500-m-long lava flow was reported in the barranca Ceniza on the afternoon of 15 May. Explosions occurred at a rate of 5-7 per hour on 16 May, and ash plumes rose as high as 7.8 km altitude and drifted 20 km W and SW, causing ashfall in Panimaché and Morelia. A moderate-sized lahar traveled down the El Jute ravine on 16 May after rains the previous night. During the afternoons of 16, 17, and 18 May lahars flowed down the Seca ravine from the recent abundant rainfall; they were 20 m wide, 1-2 m deep, and carried tree trunks and blocks 1-2 m in diameter. They grew to 25-30 m wide as they reached the confluence with the Rio Pantaleón, and the odor of sulfur was reported.

A lava flow in the barranca Ceniza was active for a distance of 900 m on 17 May, 600 m on 18 May, and 150 m on 19 May. Occasional sounds were audible more than 30 km from Fuego on 20 May from the 6-8 explosions that occurred every hour. Incandescent pulses rose 250 m above the crater during the night. The lava flow was active again to 700-800 m down the Ceniza ravine on 21 May. Overall activity increased to 10-15 weak to moderate explosions per hour on 22 May. The ash plumes rose to 4.3-4.7 km altitude and drifted 15 km S. Incandescent ejecta rose 300 m above the crater and lava flowed 1,000 m down the Ceniza ravine. On 23 May pulses of incandescent material rose 200-350 m above the crater and generated block avalanches that traveled down the Seca, Ceniza, and Las Lajas ravines as far as the vegetated areas. The lava flow in the Ceniza ravine was active up to 800 m from the summit that day. Explosions had decreased to 5-7 per hour by 24 May; the lava flow was still active 800 m down the Ceniza on 25 May.

The Fuego Observatory reported lahars on 25 May in the Seca and Mineral ravines that were 35 m wide and 1.5 m deep carrying abundant volcanic material. They blocked access between the communities of Yepocapa and Morelia, Santa Sofia, and others on the SW flank. Weak explosions and incandescence continued during the last week of the month, with low-level ash plumes drifting generally S, although poor visibility obscured most observations. Ash advisory reports from the Washington VAAC were more intermittent during May than the previous few months, with reports issued on 13 days of the month. The MODVOLC system reported thermal alerts on 16 days during May. The MIROVA project Log Radiative Power plot for the first six months of 2018 showed constant levels of activity similar to that during 2017 (see figure 73, BGVN 43:02) through the beginning of June, with a spike during the eruptive episode of 31 January-1 February (figure 90). The thermal signal ceased abruptly after the explosive events of early June.

Figure 90. The MIROVA project Log Radiative Power plot for Fuego for the first six months of 2018 showed constant levels of activity similar to that during 2017 (see figure 73, BGVN 43:02) through the beginning of June, with a spike during the eruptive episode of 31 January-1 February. Thermal activity ceased abruptly after the explosive events of early June. Courtesy of MIROVA.

Fuego was characterized by ongoing moderate activity during the first two days of June. Steam plumes rose to 4.5 km altitude and drifted S, and 5-8 moderate explosions per hour produced ash plumes that rose to 4.6-4.8 km altitude and drifted 8-20 km S and SE. Moderate to strong shock waves from the explosions caused roofs to vibrate 15-20 km away on the S flank. Pulses of incandescent ejecta rose 100-200 m above the crater and created block avalanches that descended the Seca, Ceniza and Las Lajas ravines as far as the vegetated areas; fine-grained ash fell in Panamiche I. On 2 June lahars descended the Seca, Rio Mineral, Cenizas, Trinidad and Jute ravines, and a lava flow was reported moving 1,000 m down the Ceniza ravine.

Eruptive events of 3-5 June 2018. The second major eruptive event of 2018, and the deadliest in the recent history of Fuego, began with a strong explosion in the early morning of 3 June 2018. The ash plume rose rapidly to 6 km altitude and initially drifted W and SW. It generated large pyroclastic flows that traveled down the Seca, Santa Teresa, and Ceniza ravines and into the communities of Sangre de Cristo and San Pedro Yepocapa on the W flank. Strong explosions continued throughout the day and generated additional large pyroclastic flows in the Seca, Cenizas, Mineral, Taniluyá, Las Lajas, and Honda ravines with devastating consequences to numerous communities around the volcano (figures 91-94).

Figure 91. Large pyroclastic flows descended multiple flanks of Fuego on 3 June 2018 causing significant fatalities and extensive property damage in adjacent communities. View is from Alotenango, 8 km E of the summit. Photo Credit: Orlando Estrada/AFP/Getty, courtesy of The Express.

Figure 92. A large pyroclastic flow on 3 June 2018 descended the Las Lajas ravine adjacent to La Reunión Golf Course, 7 km SE of the summit of Fuego. Courtesy of Matthew Watson, volcanologist.

Figure 93. The pyroclastic flows at Fuego on 3 June 2018 descended multiple ravines and damaged or destroyed a number of roadways and bridges. Photo Credit: AFP/Getty, courtesy of The Express.

Figure 94. After the pyroclastic flows at Fuego descended on 3 June 2018, the Las Lajas ravine adjacent to La Reunión Golf Course 7 km SE of the summit was filled with steaming ash and debris. Courtesy of GeoGis.

The Washington VAAC reported explosions later in the day that generated an ash plume that drifted NE at 9.1 km altitude and E at 15.2 km altitude. The Suomi NPP satellite captured an image of the ash plume rising above the cloud cover at 1300 local time (figure 95). Ashfall of tephra and lapilli was reported more than 25 km away in the village of La Soledad; in addition, the municipalities of Quisache (8 km NW), Acatenango (12 km NW), San Miguel Dueñas (10 km NE), Alotenango (8 km ENE), Antigua Guatemala (18 km NE), Chimaltenango (22 km N), and other areas NW and N of the volcano were impacted with ashfall. La Aurora airport in Guatemala City was closed for two days. In addition to the ash plume, a large plume of SO₂ was recorded drifting N and E from the volcano at an altitude of 8 km shortly after the explosions were reported (figure 96).

Figure 95. The ash plume from a large explosion at Fuego on 3 June 2018 rose above the cloud cover to over 15 km altitude and was imaged by the Visible Infrared Imaging Radiometer Suite (VIIRS) on Suomi NPP at 1300 local time. Courtesy of NASA Earth Observatory.

Figure 96. A substantial plume of sulfur dioxide (SO2) was detected by the Ozone Mapping Profiler Suite (OMPS) on Suomi NPP satellite after the large eruption at Fuego on 3 June 2018. The image shows concentrations of sulfur dioxide in the middle troposphere at an altitude of 8 kilometers as detected by OMPS. Michigan Tech volcanologist Simon Carn noted that this appeared to be the "highest sulfur dioxide loading measured in a Fuego eruption in the satellite era." Courtesy of NASA Earth Observatory and Goddard Earth Sciences Data and Information Services Center (GES DISC).

The pyroclastic flows down the SE flank were especially devastating to the communities in their path, covering roofs and vehicles with ash and debris (figure 97-100) and killing scores of people. The communities of San Miguel Los Lotes about 9 km SE of the summit and El Rodeo (10 km SE), both in Escuintla Province, were severely damaged from the pyroclastic flows, with most of the fatalities and missing people reported from those communities.

Figure 97. The pyroclastic flows that traveled down the SE flank of Fuego on 3 June 2018 were especially devastating to the communities in their path. This image taken two days later on 5 June shows how the low-lying areas around the ravine are buried in ash from the fast-moving pyroclastic flow, but the higher areas (like the golf course on the right) are relatively free of ash and debris (see figure 94). Courtesy of BBC and Getty Images.

Figure 98. The pyroclastic flows from the eruption at Fuego on 3 June 2018 buried buildings up to 2 m deep in ash and debris in the community of San Miguel Los Lotes, Escuintla Province. Photo by Luis Echeverria/Reuters, courtesy of the Telegraph.

Figure 99. Numerous vehicles were swept away in the pyroclastic flows that descended through the village of San Miguel Los Lotes, Escuintla on 3 June 2018 during the eruption at Fuego. This photo was taken on 5 June as rescue workers continued to search the town. Courtesy of Reuters and the Express.

Figure 100. The pyroclastic flows that traveled through El Rodeo on 3 June 2018 from the large eruption at Fuego contained both fine-grained ash and large angular boulders of volcanic rocks. Rescue workers were forced to evacuate the town on 5 June as additional pyroclastic flows threatened the already devastated community. Courtesy of the Associated Press (AP Photo/Rodrigo Abd).

Figure 101. Most of the village of El Rodeo, 10 km SE of the summit of Fuego, was buried by ash and debris from a pyroclastic flow on 3 June 2018. Rescue workers searched the village while heavy equipment repaired roadways on 5 June. Photo by Rodrigo Abd, courtesy of the Associated Press.

Explosions continued until early evening on 3 June, when pyroclastic flow activity finally diminished. The debris from the pyroclastic flows resulted in lahars descending the Pantaleón, Mineral, and other drainages, leading to the evacuations of the communities of Sangre de Cristo, Finca Palo Verde, Panimache and others that evening. Explosive activity returned to lower levels the following day with dense ash plumes rising to 4.5-4.6 km altitude from 5-7 weak explosions that occurred every hour. Abundant fine ash rose from the ravines filled with pyroclastic flow material from the previous day and drifted SW, W, NW, and N, affecting communities up to 25 km away in those directions. The Washington VAAC reported remnants of the ash plume drifting 300 km ENE on 4 June.

By 4 June, CONRED had increased the Alert Level to red for the communities of Escuintla (22 km SE), Alotenango (8 km E), Sacatepéquez, Yepocapa (8 km NW), Santa Lucía Cotzumalguapa (22 km SW), and Chimaltenango, and opened 13 evacuation shelters in the area. CONRED initially reported on 5 June that 3,271 people were evacuated, 46 were injured and there were 70 known fatalities as a result of the pyroclastic flows and lahars on 3 June. A state of emergency was declared in all three of the provinces (Departments) of Escuintla, Sacatepéquez and Chimaltenango surrounding the volcano.

The number of block avalanches increased on 5 June as a result of 8-10 moderate explosions per hour; ash plumes and pyroclastic flow debris created persistent ash in the air around the volcano. The avalanches traveled 800-1,000 m down Las Lajas and Santa Teresa ravines. On 5 June, a pyroclastic flow descended the El Jute and Las Lajas ravines at 1410 local time. INSIVUMEH reported an increase in explosive activity a few hours later; dense ash plumes rose to 6 km altitude and drifted E and NE. Another pyroclastic flow descended the Las Lajas around 1928 local time that evening. These new pyroclastic flows led CONRAD to evacuate the additional communities of La Reyna, El Rodeo, Cañaveral I and IV, Hunnapu, Magnolia, and Sarita located on the Palín-Escuintla highway, and the highway itself was also closed (figure 102).

Figure 102. Pyroclastic flows descended the flanks of Fuego on 5 June 2018, causing additional damage after the major eruption two days earlier. The view is from the community of El Rodeo, 10 km SE, heavily damaged at the beginning of the eruption. Photo Credits: Rodrigo Abd/AP/REX/Shutterstock, courtesy of the Associated Press.

Activity during 6-30 June 2018. Weak to moderate explosions continued at Fuego on 6 June with ash plumes rising to 4.7 km altitude and drifting W and SW. Significant rainfall in the area that afternoon around 1610 resulted in lahars descending the Seca and Mineral ravines, tributaries of the Rio Pantaleón. One lahar was 30-40 m wide and 4-5 m deep emanating warm sulfurous gases; it carried fine-grained material similar to cement, rocks and debris 2-3 m in diameter, and tree trunks. The communities around the mouths of the ravines and near the Pantaleón Bridge were most affected. New lahars about an hour later descended the Santa Teresa, Mineral and Taniluyá ravines, also tributaries of the Pantaleón River. These lahars were about 30 m wide, 2-3 m deep, and carried similar cement-like fine grained material down the Pantaleón along with blocks 2-3 m in diameter and tree trunks.

Seismic station FG3 recorded a pyroclastic flow descending Las Lajas and El Jute ravines at 2140 local time on 7 June. INSIVUMEH estimated that it produced an ash cloud that rose to 6 km altitude and drifted W and SW. INSIVUMEH issued five special bulletins on 8 June reporting numerous lahars and pyroclastic flows. Lahars descended Santa Teresa, Mineral, and Taniluyá ravines into the Pantaleón around 0240 local time; they were 30 m wide, 2-3 m deep, and carried 2-3-m-diameter blocks and tree trunks. Another surge of lahars registered on the seismogram about two hours later in the same ravines and also in the Ceniza, additionally affecting the Achiguate River. A pyroclastic flow descended Las Lajas ravine at 0820 in the morning, producing another 6-km-high ash cloud. Two more similar pyroclastic flows in the same area were recorded at the seismic station at 1945 and 2040 local time that evening.

During the afternoon of 9 June, lahars descended the Seca, Mineral, Niagara and Taniluyá, generating the largest lahar to date for the year in the Pantaleón River. It was 40 m wide and 5 m deep carrying abundant blocks up to 3 m in diameter and other debris down the W flank. Later that evening explosive activity continued at a rate of 4-7 per hour, dispersing ash plumes up to 15 km W and SW from the summit at an altitude of 4.2-4.4 km. The explosions were audible up to 10 km in all directions. The same ravines and also the Ceniza were affected by new lahars 35 m wide and 3 m deep the following afternoon as a result of the constant rains in the area. Rains continued on 11 June and resulted in strong lahars descending the Seca and Mineral ravines around 1415 local time with diameters of 35-40 m and depths of 3 m. Another strong lahar descended Las Lajas and el Jute ravines in the evening at 1750 local time; these had widths ranging from 35-55 m and depths up to 5 m.

INSIVUMEH reported an increase in explosive activity beginning in the morning of 12 June 2018, producing ash plumes that rose up to 5 km altitude and drifted NE and N 15-25 km. This activity also produced a pyroclastic flow down the Seca ravine around 0730 local time with an ash cloud that rose about 6 km and drifted N and NE. That afternoon a strong lahar descended the Las Lajas ravine, carrying blocks 3 m in diameter in a hot, thick flow that was 35-45 m wide and up to 5 m deep. Since there were no longer distinct channels in the ravine, the material spread out in a wide fan flowing towards the area around El Rodeo. Additional smaller lahars descended the Ceniza and Mineral ravines later that afternoon. By 12 June 2018 CONRED reported that 110 fatalities had been confirmed, 197 additional people were missing, and over 12,500 people had been evacuated since the 3 June explosions began.

On 13 June, a small pyroclastic flow descended the Ceniza ravine around 0630. It was the last pyroclastic flow reported during June. Beginning with the first post-eruption lahars on 6 June, multiple lahars occurred every day during 8-18, 20-23, 26, and 30 June (table 18). The barrancas of Seca, Mineral, Santa Teresa, Taniluyá, Niagra, Ceniza, Las Lajas, El Jute, Rio El Gobernador, and Rio Pantaleón were all impacted by the lahars; they ranged in size from smaller flows that were 20 m wide and 2 m deep carrying blocks 1-3 m in diameter to the largest which were over 40 m wide, up to 5 m deep and carried blocks as large as 3 m in diameter. The flows were warm or hot, carrying tree trunks and other debris, and had strong sulfurous odors. Communities adjacent to the ravines could feel the vibrations of the flows as they passed. As many of the ravines were full of ash and rocks from the pyroclastic flows, new channels were formed and the flows spread out in fans as they descended, further threatening the communities around the flanks of the volcano.

Table 18. Lahars at Fuego were reported 33 separate times between 6 and 30 June 2018; many reports included multiple simultaneous lahars in drainages around all the flanks. Data courtesy of INSIVUMEH.

Explosions continued daily through the end of June 2018 at rates ranging from 4 to 9 explosions per hour, creating block avalanches that descended all the major ravines. Ash plumes rose to 4.2-4.9 km altitude (500-1,000 m above the summit) and drifted in multiple directions. On 18 and 22 June, fine-grained ashfall was reported in Panimache, Morelia, Sangre de Cristo, and Palo Verde. By 24 June, satellite imagery revealed that elevated heat was still discernable in several ravines that had been filled with pyroclastic flow debris earlier in the month (figure 103). Explosions on 27 and 28 June sent ash plumes W and ashfall was reported in Sangre de Cristo, Yepocapa, and communities a few km W of Fuego.

Figure 103. Elevated thermal signals in drainages filled with pyroclastic flows were still apparent in satellite imagery at Fuego on 24 June 2018, three weeks after a major explosive event. Courtesy of NASA Earth Observatory.

Geologic Background. Volcán Fuego, one of Central America's most active volcanoes, is one of three large stratovolcanoes overlooking Guatemala's former capital, Antigua. The scarp of an older edifice, Meseta, lies between 3763-m-high Fuego and its twin volcano to the north, Acatenango. Construction of Meseta dates back to about 230,000 years and continued until the late Pleistocene or early Holocene. Collapse of Meseta may have produced the massive Escuintla debris-avalanche deposit, which extends about 50 km onto the Pacific coastal plain. Growth of the modern Fuego volcano followed, continuing the southward migration of volcanism that began at Acatenango. In contrast to the mostly andesitic Acatenango, eruptions at Fuego have become more mafic with time, and most historical activity has produced basaltic rocks. Frequent vigorous historical eruptions have been recorded since the onset of the Spanish era in 1524, and have produced major ashfalls, along with occasional pyroclastic flows and lava flows.

Information Contacts: Instituto Nacional de Sismologia, Vulcanologia, Meteorologia e Hydrologia (INSIVUMEH), Unit of Volcanology, Geologic Department of Investigation and Services, 7a Av. 14-57, Zona 13, Guatemala City, Guatemala (URL: http://www.insivumeh.gob.gt/); Coordinadora Nacional para la Reducción de Desastres (CONRED), Av. Hincapié 21-72, Zona 13, Guatemala City, Guatemala (URL: http://conred.gob.gt/www/index.php); Hawai'i Institute of Geophysics and Planetology (HIGP) - MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); NASA Earth Observatory, EOS Project Science Office, NASA Goddard Space Flight Center, Goddard, Maryland, USA (URL: http://earthobservatory.nasa.gov/); NASA Goddard Space Flight Center (NASA/GSFC), Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, 8800 Greenbelt Road, Goddard, Maryland, USA (URL: https://so2.gsfc.nasa.gov/); Washington Volcanic Ash Advisory Center (VAAC), Satellite Analysis Branch (SAB), NOAA/NESDIS OSPO, NOAA Science Center Room 401, 5200 Auth Rd, Camp Springs, MD 20746, USA (URL: www.ospo.noaa.gov/Products/atmosphere/vaac, archive at: http://www.ssd.noaa.gov/VAAC/archive.html); Associated Press (URL: https://apnews.com/); AFP/Getty, Agence France-Presse (URL: http://www.afp.com/); BBC News (URL: https://www.bbc.com/); The Telegraph (URL: https://www.telegraph.co.uk/); Reuters (http://www.reuters.com/); The Express (URL: https://www.express.co.uk); Matthew Watson, School of Earth Sciences at the University of Bristol, Twitter: @Matthew__Watson), (URL: https://twitter.com/Matthew__Watson); GeoGis, Twitter: @jlescriba, (URL: https://twitter.com/jlescriba).

Ambrym Island was investigated by John Seach and Perry Judd during a climb into the caldera 1-8 January 1999. A lava lake in Benbow cone was present during 1-3 January but was covered by deposits from an avalanche that occurred overnight 4-5 January. Fumarolic and Strombolian activity was observed at other craters.

Activity at Benbow. Benbow crater was climbed from the S, after which observers lowered themselves using ropes 200 m down from the crater rim to a point where they could observe the crater interior. In the center of the crater, an active lava lake was seen 220 m below the observation point. The lava lake was ~40 m in diameter and constantly in motion. Large explosions caused lava fountains that reached 100 m high. Bombs glowed for up to one minute in daylight and radiated great heat. Bombs could be heard landing on the side of the pit where they caused glowing avalanches. At night a strong glow from the lava lake was visible in the sky over Benbow.

Elsewhere inside Benbow crater, Pele's hair covered the ground and fumaroles were active on the NE crater wall. Acid rain burned eyes and skin. Heavy rainfall caused many waterfalls to form inside the crater rim and a shallow brown pond formed on the floor of the first level.

During 4-5 January violent Strombolian explosions could be heard almost hourly. Each series of explosions lasted 5-10 minutes and produced dark ash columns above the crater. At some time during these explosions an avalanche on the W side of the lava lake crater completely covered the lava lake. No night glow was visible above the crater after the night of 5 January.

On 6 January Benbow crater was entered again. The wall collapse that covered the lava lake was confirmed visually. In the location of the former lava lake was a depression of rubble with two small, glowing vents nearby. The entire crater was clear of magmatic gases. Three violent Strombolian eruptions were viewed from the crater rim in the afternoon. Bombs were thrown 300 m into the air and dark ash clouds were emitted.

Activity at Niri Mbwelesu Taten. This small collapse pit continuously emitted white, brown, and blue vapors. Red deposits covered the crater walls. A small amount of yellow deposits covered the S wall. Fumarole temperatures were 66 to 69°C at a point 40 m SE of the pit. On 6-7 January numerous deep, loud degassings were heard from a distance of 4 km.

Activity at Niri Mbwelesu. Pungent, sulfurous-smelling white vapor was emitted from this crater. Periods of good visibility enabled views 200 m down from the crater rim, but the bottom could not be seen. Rockfalls were heard inside the crater.

Activity at Mbwelesu. Excellent visibility to the bottom of this crater enabled detailed observations of the lava lake. Night observations were also obtained. The lava lake was in constant motion and splashing lava out over the sides of the pit. The lake was at a lower level than during observations made three months earlier (BGVN 23:09). Large explosions sent lava fountains up to 100 m in height and threw lava onto the sides of the pit causing glowing avalanches. During one night observation a 20 x 5 m section of the crater wall broke off and fell into the lava lake. The 60-m-wide lake radiated heat that could be felt from the viewing area 380 m away. North of the lava lake was a circular vent 20 m in diameter that glowed brilliantly from magma inside and huffed out burning gasses every 20 seconds. Foul gas, smelling of rotten fish, was emitted from the crater. South of the lava lake was an elongated vent (40 x 10 m) that spattered lava every 5-10 seconds and sent showers of glowing orange lava spray 150 m high.

On the S side of Mbwelesu, fumarole temperatures averaged 43°C at 10 m from the crater edge. On the SE side, 40 m from the crater edge, fumaroles measured 57°C. On 4 January ashfall occurred on the S side of the caldera.

Geologic Background. Ambrym, a large basaltic volcano with a 12-km-wide caldera, is one of the most active volcanoes of the New Hebrides arc. A thick, almost exclusively pyroclastic sequence, initially dacitic, then basaltic, overlies lava flows of a pre-caldera shield volcano. The caldera was formed during a major plinian eruption with dacitic pyroclastic flows about 1900 years ago. Post-caldera eruptions, primarily from Marum and Benbow cones, have partially filled the caldera floor and produced lava flows that ponded on the caldera floor or overflowed through gaps in the caldera rim. Post-caldera eruptions have also formed a series of scoria cones and maars along a fissure system oriented ENE-WSW. Eruptions have apparently occurred almost yearly during historical time from cones within the caldera or from flank vents. However, from 1850 to 1950, reporting was mostly limited to extra-caldera eruptions that would have affected local populations.

Information Contacts: John Seach, P.O. Box 16, Chatsworth Island, NSW, 2469, Australia.

During February, seismic and volcanic activity at Bezymianny increased in intensity, causing the hazard status to be raised from Green to Yellow on 16 February and then to Orange on 25 February. The activity decreased on the 26th and the "Level of Concern Color Code" was reduced to Yellow. In the first two weeks of the month, numerous weak earthquakes were registered under the volcano, and fumarolic plumes rising up to a few hundred meters above the summit occurred frequently.

Starting on 15 February and continuing the following week, seismicity rose above background levels and 20-40 shallow earthquakes were registered every day. The hazard status was raised to Yellow. Fumarolic plumes continued to rise to a few hundred meters above the summit, and could be seen when not obscured by clouds. Satellite images during the week indicated a persistent thermal anomaly possibly caused by rock avalanches from the summit dome.

The hazard status was raised to Orange on 25 February after volcanic tremor began under the volcano and continued for ~6 hours. Two large explosions during that period each lasted several minutes and a gas-and-ash plume rose 5 km above the summit. Satellite images that morning showed an ash-rich plume heading SE. Over the next few days, using satellite imagery, the ash cloud was tracked for 1,500 km to the SE, but by early on the 27th the cloud had dissipated. Activity declined after the 25th and the hazard status was reduced to Yellow.

On 27-28 February the seismicity was above background levels. Low-level spasmodic tremor continued to be recorded. On the morning of 28 February a steam-and-gas plume rose 300 m. The volcano was obscured by clouds after 28 February.

Geologic Background. Prior to its noted 1955-56 eruption, Bezymianny had been considered extinct. The modern volcano, much smaller in size than its massive neighbors Kamen and Kliuchevskoi, was formed about 4700 years ago over a late-Pleistocene lava-dome complex and an ancestral edifice built about 11,000-7000 years ago. Three periods of intensified activity have occurred during the past 3000 years. The latest period, which was preceded by a 1000-year quiescence, began with the dramatic 1955-56 eruption. This eruption, similar to that of St. Helens in 1980, produced a large horseshoe-shaped crater that was formed by collapse of the summit and an associated lateral blast. Subsequent episodic but ongoing lava-dome growth, accompanied by intermittent explosive activity and pyroclastic flows, has largely filled the 1956 crater.

Information Contacts: Olga Chubarova, Kamchatka Volcanic Eruptions Response Team (KVERT), Institute of Volcanic Geology and Geochemistry, Piip Ave. 9, Petropavlovsk-Kamchatsky, 683006, Russia; Tom Miller, Alaska Volcano Observatory (AVO), a cooperative program of a) U.S. Geological Survey, 4200 University Drive, Anchorage, AK 99508-4667, USA (URL: http://www.avo.alaska.edu/), b) Geophysical Institute, University of Alaska, PO Box 757320, Fairbanks, AK 99775-7320, USA, and c) Alaska Division of Geological & Geophysical Surveys, 794 University Ave., Suite 200, Fairbanks, AK 99709, USA.

The unusually large 10 February explosion was followed by collateral reports by (a) F. Núñez-Cornú, G. Réyes-Davila, and C. Suárez-Plascenia and (b) John B. Murray. In addition, this summary of the interval 26 February to 16 March benefitted from press releases from the Colima Volcano Observatory. These three sources are discussed in separate sections below.

Geophysical signature of the 10 February explosion. F. Núñez-Cornú, G. Réyes-Davila, and C. Suárez-Plascencia provided the following report.

"On 10 February at 0145 an explosive event occurred at Colima's summit dome; this generated a shock wave that broke windows and opened gates in the small town of Juan Barragan, 8.75 km SE of the summit. The sonic wave was also heard in the towns of Tonila, Quesería, San Marcos, Atenquique, El Fresnito, Ejido de Atenquique, and up to 28 km NE of the volcano at Ciudad Guzman.

"This was the biggest explosion reported for the volcano in the last 80 years; the resulting exhalation emitted both ash and lava blocks (bombs made up of both fresh and altered components). A substantial amount of incandescent tephra fell and started fires on both the volcano's upper slopes and on Nevado de Colima's S slopes; most of the fires were extinguished by snow and rain storms during the subsequent 48 hours.

"As summarized in table 8, a seismic event took place hours before the explosion, at 2231 of 9 February; it was followed by other volcanic and tremor signals at about 0100; some of these precursory events saturated the amplitude response of analog instruments at stations EZV4 (Somma) and EZV7 (Volcancito). Four additional large, post-eruptive seismic events also occurred. These strong events were observed clearly at farther stations EZV3 (Nevado, 5.8 km from the summit), and EZV2 (Cerro Grande, 25 km from the summit)."

Table 8. Noteworthy seismic events around the time of the 10 February 1999 explosion at two Colima seismic stations (EZV3 and EZV2); the earliest reading (on the top line) took place the night before the explosion. See text for station locations. Courtesy of F. Nunez-Cornu, G. Reyes-Davila, and C. Suarez-Plascencia.

"Currently the Jalisco civil defense operates an observational base called Nevado located 900 m NW from the summit of Nevado de Colima.

"Since the end of November 1998, three seismic instruments (MarsLite with LE3d (1 Hz) sensors) were deployed to complement the RESCO network at the volcano. To improve spatial resolution the authors moved one of these instruments to El Playon on 11 February. On the way to El Playon we observed fires on the southern slopes of Nevado out to a maximum distance of 4.5 km from the volcano's summit.

"On the road at a spot 2.9 km NE of the summit and at 3,120 m elevation we found several impact craters. The first one contained an andesite block with dimensions of 0.37 x 0.44 x 0.43 m. Several small impacts occurred nearby. We found another impact pit near the road, 100 m away from the first site but at similar distance and direction from the summit. This pit measured 1.94 x 0.70 m on the surface and had a depth of 0.60 m. It contained a partially buried andesite block (identified as R3) that measured 0.60 x 0.41 x 0.70 m. The block's temperature was 40°C. The pit sat in a spot surrounded by 10- to 15-m-tall trees; their lack of visible damage suggested a near vertical angle of impact, which we estimated as 80-85°.

"At 70 m away from block R3 we found a volcanic bomb that struck the middle of the road. The bomb consisted of hydrothermally altered volcanic breccia (identified as R4, figure 34), which had shattered on the road over an area 1.73 x 1.64 m; the bomb failed to excavate a crater.

Figure 34. Impact crater R4, created by Colima's 10 February 1999 explosion. Courtesy of F. Nunez-Cornu, G. Reyes-Davila, and C. Suarez-Plascencia.

"In traveling across El Playon we observed dozens of impacts, but elected to stay the minimum time possible in order to reduce exposure to hazards. Most of the bombs seen and sampled consisted of either andesite resembling the new dome or hydrothermally altered andesite, perhaps from the 1987 crater wall. When visiting the same area on 26 February, we found the small and medium impact craters difficult to identify; most of the impacts below trees were covered by newly fallen leaves."

Leveling survey and field examination of the 10 February bombs. On 28 February, John B. Murray, assisted by members of the Colima fire department (Mitchell Ventura, Filiberto de la Mora, and Juan Carlos Martinez) measured two branches of a N-flank leveling traverse last surveyed in January 1997. The first branch, which was 740 m long, left the Playon vehicle track and followed the path up Volcancito passing through stations Porte de Colima (1.3 km from the volcano's summit) and Albergue (1.9 km from the summit). The movement measured since 1997 showed subsidence at stations nearest the volcano totaling 13 mm for the entire section. This was nearly double the subsidence measured during 1995-97, an interval without any lava emission. There was also 13 mm of subsidence seen during 1990-92, an interval which included lava emission (in 1991).

The second branch of the leveling traverse began at Albergue station and ended at Voltaire station, a spot 2.3 km from the summit. Compared to 1997, the Albergue station had subsided just over 8 mm relative to the Voltaire station. Little significant change occurred here during 1995-97 (1 mm rise) and 1990-92 (0.4 mm rise). During a 15-year interval (1982-97) these two stations subsided a total of only 6 mm, and thus looks like a small though significant change in movement. Most of the change (5.6 mm) was measured between two stations 160 m apart at a distance of 2 km from the summit. The possibility of a small error cannot be ruled out, although the movement does follow the same sense throughout this section of the leveling traverse.

The total subsidence between the farthest (2.3 km) and the nearest (1.3 km) station to the summit was 22 mm. This is rather larger than during the 1991 crisis, when the subsidence between the same two stations was 13 mm. Viewing this movement as deflation of a magma chamber (Murray, 1993), this may simply be a reflection of the rather larger output of the volcano in 1998-99 compared to 1991. However, equally tenable is the hypothesis that the movement is due to volcano spreading, or even to Colima's slow slipping down the southern flanks of the larger Nevado volcano, on whose southern slopes Colima is situated. Increases in the rate of subsidence were also observed following the Mexican earthquake of 1985, as well as during the 1991 crisis described above. Although the subsidence during 1997-99 is greater than previously measured, there is nothing in the measurements to suggest that the volcano is building up to a bigger eruption, or to distinguish between the Mogi deflation or downslope slipping models.

The distribution of volcanic bombs from the 10 February explosion was noted at sites along the leveling traverse. Table 9 lists the estimated average distance between impact craters at the various sites where measurements were made. Murray and co-worker identified fragments that varied in size between 10 and 70 cm in diameter, there being no noticeable trend in size between bombs found in the region 1.3 to 2.8 km from the summit. The largest bomb crater found had taken away one third of the road on the north edge of the 1869 lava flow near station Hector, a spot 2.1 km from the summit. This crater was at least 2 m in diameter. However, the numbers of impacts per unit area decreased as distance from the volcano increased.

There is also some evidence of directed blast in table 9, there being distinctly higher concentrations of bombs NNE of the volcano (station Esteban) than at similar distances NE (station C15). Bombs appeared to be of two distinct types: 1) solid, dark, fresh-looking andesitic rocks with high density and no sign of vesiculation, and 2) crumbly, light-colored, altered, vesicular, pumice-like ejecta with low density (guessed at around 1,000 kg/m³) There did not appear to be any predominance of one type or the other with distance from the volcano.

Table 9. Average spacing of N-flank bomb strikes that were found after Colima's 10 February 1999 explosion. Courtesy of John B. Murray.

A bomb found near the campsite, 1.75 km from the summit, left evidence of its trajectory as it had smashed a 10 cm branch of a tree just before landing. The bomb itself was of solid andesite, and had fractured into several pieces on landing, but it appeared to have had an original diameter of about 40 cm. It had made an impact crater ~1 m in diameter and 50 cm deep. Using the level as a horizontal marker, three measurements of the angle between the broken branch and the crater bottom gave 44 ± 3° from the horizontal.

Six fire sites were inspected and described; usually these were associated with a bomb, but not always. At first, these fire sites went unnoticed because they chiefly consumed low-growing vegetation, and in no case was a completely burned tree to be found. The view towards the volcano from the Playon was unaffected, as green bushes and trees were seen as usual.

For example, at fire site 3, located 2 km NNE of the summit (N side of road, just past bend near station Esteban) we found an isolated pumice bomb 20 cm across, but without burnt vegetation in contact. However, the bomb ignited grass clumps 2 and 3.5 m away; none of the grass between the bomb and the clumps had been affected.

Most fire sites were close to bombs, usually burning on the side away from the volcano. However, most were not in direct contact with the bomb in question, but centered around dry vegetation, particularly tall grass clumps, succulents, small bushes, and (occasionally) trees. The grass and succulents were not dead, but had fresh green shoots sprouting from the top. Presumably because of the high water content, only the dry, dead leaves at the base of the succulents were burned, but there were large areas where succulents were affected in this way, the adjacent vegetation being quite unaffected. There was often no obvious associated bomb in the vicinity. Similarly with grass clumps, there would be gaps of 2 or 3 m between burned clumps, from which the fire had apparently spread radially for a short distance before going out, with no sign of burning of the dry, low grass cover in between. However, not all bombs in the same area had the same effect. In some cases, the only sign of burning was directly beneath the bomb itself, where the grass was singed black but still fairly intact. Yet in places nearby, the landscape had clearly been very slowly burned over an extensive area 10 to 30 m wide, and in one case discussed below, it was still burning.

Murray goes on to comment: "The odd characteristics of these fire sites suggests the possibility of an abnormal ignition mechanism. It seems that ignition depended in many cases not on the proximity to the source of heat (bombs) but rather on the characteristics of the ignited vegetation. It was as if in certain (sometimes quite extensive) areas those low-growing plants below a certain water content, or containing appropriate oils would ignite, and the rest would not. This implies a very high air temperature close to the ground over areas in some cases tens of meters across. The most obvious source of these high temperatures would seem to be hot gas, usually emanating from bombs but not always so. Where associated with bombs, the isolated fire sites would always be on the side facing away from the summit. In other words, there is evidence that extensive degassing took place from bombs upon impact; and that there might also have been some local associated ground-hugging nuees of a weak and intermittent type."

Explosion on 28 February 1999. Murray also noted that "At 1715 on 28 February, while examining the distant bombs and impact craters 2.8 km NE of the summit on the forest road outside the caldera, we heard a distant, faint rushing sound coming from the summit, resembling a large rockfall or an aircraft. On looking up, a large whitish-grey convective cloud, like a cumulus cloud, could be seen rising from the summit and blowing in our direction. It had clearly started some time previously and was already stretching some distance towards us. A heavy rain of ash began nine minutes later, at 1724, ceasing at ~1731. The ashfall, which was sampled, sounded like large raindrops hitting the leaves in the nearby forest but on spreading out a sheet of paper on the ground, only sand-sized ash particles could be seen accumulating on it. At the end of the shower, there was one particle every centimeter approximately, the largest particle being ~ 2 mm across, and the smallest just under 0.5 mm. From the sound of the particles falling in the trees round about, it sounded as if much larger particles were involved in the shower, but none of these fell on the spread-out paper."

Official press releases. A 26 February update by the Colima Volcano Observatory stated that chemical analysis of Colima's water and ash had indicated insignificant risk to human health. At this time the established security limit was set at 10-10.5 km from the summit. Evacuated settlements included Yerbabuena, Causenta, Atenguillo, El Fresnal, La Cofradía, Juan Barragán, El Agostadero, Los Machos, El Alpizahue, El Saucillo, and El Borbollón. The local populations were advised to avoid a long list of drainages, as well as to hand-carry important documents, and to advise authorities of those requiring help in order to secure transport in case of more extensive evacuations. Meanwhile, during the previous 24 hours the monitored parameters indicated relative quiet, suggesting possible voluntary return to evacuated areas at noon on 2 March if these conditions persisted. The 5 March update noted degassing events during the previous 24 hours, the majority of these around 1400 on 5 March. The 16 March update mentioned the recent occurrence of both degassing and minor ash emissions

Reference. Murray, J.B., 1993, Ground deformation at Colima Volcano, Mexico, 1982 to 1991: Geofisica Internacional, v. 32, no. 4, p. 659-669.

Geologic Background. The Colima volcanic complex is the most prominent volcanic center of the western Mexican Volcanic Belt. It consists of two southward-younging volcanoes, Nevado de Colima (the 4320 m high point of the complex) on the north and the 3850-m-high historically active Volcán de Colima at the south. A group of cinder cones of late-Pleistocene age is located on the floor of the Colima graben west and east of the Colima complex. Volcán de Colima (also known as Volcán Fuego) is a youthful stratovolcano constructed within a 5-km-wide caldera, breached to the south, that has been the source of large debris avalanches. Major slope failures have occurred repeatedly from both the Nevado and Colima cones, and have produced a thick apron of debris-avalanche deposits on three sides of the complex. Frequent historical eruptions date back to the 16th century. Occasional major explosive eruptions (most recently in 1913) have destroyed the summit and left a deep, steep-sided crater that was slowly refilled and then overtopped by lava dome growth.

Information Contacts: F. Nunez-Cornu^1,4, G. Reyes-Davila², and C. Suarez-Plascencia^3,4; 1) Laboratoria Sismologia, University of Guadelajara, Guadelajara, Mexico; 2) RESCO, University of Colima, Colima, Mexico; 3) Department of Geology, University of Guadelajara, Guadelajara, Mexico; 4) U. Est. Proteccion Civil Jalisco; Colima Volcano Observatory, Universidad de Colima, Av. Gonzalo de Sandoval 444, Colima, Colima 28045, Mexico (URL: https://portal.ucol.mx/cueiv/); J.B. Murray, Department of Earth Sciences, The Open University, Milton Keynes MK7 6AA, England.

The following report summarizes activity observed at Etna from January through February 1999. Bocca Nuova exhibited minor explosive activity through early February, but Northeast Crater and Voragine were quiet. Southeast Crater had seven distinct eruptive episodes between 5 January and 4 February; the latest was accompanied by the opening of a new eruptive fissure at its southeastern base. The information for this report was compiled by Boris Behncke at the Istituto di Geologia e Geofisica, University of Catania (IGGUC), and posted on his internet web site. The compilation was based on personal summit visits, observations from Catania, and other sources cited in the text.

Activity at Southeast Crater (SEC) until 23 January. After one week of relative quiet, the sixteenth eruptive episode of SEC since 15 September occurred shortly before noon on 5 January; this was preceded by weak Strombolian activity that started around midnight. The paroxysmal phase was characterized by vigorous fountaining, and lava flowed towards the northeast while tephra was driven southwest by the strong wind. Loud detonations were audible in towns on the flanks of Etna.

Episode 17, during the night of 9-10 January, was preceded by mild Strombolian activity; the paroxysmal phase occurred shortly after midnight. Lava presumably flowed NE again and tephra fell NE; Fiumefreddo, ~8 km SW of Taormina, received a light showering of ash. Loud detonations during the final phase were audible over a wide area, and clear weather conditions permitted many in the Catania area to watch the spectacular display.

After the shortest repose interval observed since early in the current eruptive sequence in September, episode 18 took place on the morning of 13 January, between about 0630 and 0930. Visibiliby was hampered by clouds, but loud detonations were audible in a wide area around the volcano. Ash fell as far as Giarre, ~15 km E.

The next eruptive episode occurred on 18 January, shortly after 0800, and lasted ~ 45 minutes. Minor Strombolian and effusive activity had occurred earlier during the night. As in preceding episodes, the culminating phase was characterized by initial strong lava fountaining which gradually became more ash-rich, generating a dense eruption column. Due to calm conditions, the column rose several kilometers above the summit (3 km as estimated from Catania) and attained a spectacular mushroom shape visible in the morning sky from all around the volcano. At the SEC cone itself, the heavy fallout and rapid accumulation of pyroclastics led to frequent avalanches, especially on the steep eastern side. After 0830, dull explosion sounds were audible to as far as Catania, accompanying the rhythmic uprush of dark ash. The activity declined rapidly at 0845, but ash emissions became again more forceful after 0900 and continued sporadically for several hours, accompanied by sliding of hot pyroclastics from the steep E side of the cone. No information was available about lava flows although it is likely that they occurred, possibly on the NE side of SEC.

SEC erupted again after only two days and four hours of inactivity, shortly after noon on 20 January. Increased gas emission began at ~ 1215, and by 1240 a lava fountain appeared at the vent of the SE Crater cone. This fountain rapidly rose to a height of several hundred meters, and the column which rose above it became more and more ash-rich. Less than 15 minutes after the onset of the eruption there occurred the first slides of hot pyroclastics from the upper part of the cone, and five minutes later the whole cone and part of Etna's main summit cone were veiled by a black curtain of falling bombs and scoriae. By 1300, the vertical eruption column had risen several kilometers above Etna's summit. Ten minutes later the activity began to decline rapidly, and by 1315 the eruptive episode was essentially over, with only a few ash puffs being emitted during the following 30 minutes.

During a summit visit by Boris Behncke and Giovanni Sturiale (IGGUC) on 21 January, the crater was completely quiet, and only a few weak fumaroles played on the SW and E crater rims. The cone at SEC had grown higher than 3,250 m, about as high as the rim of the former Central Crater (filled by lavas and pyroclastics in the 1950's and 60's). While its flanks were steep and regular on most sides, obliterating any trace of the pre-1998 crater rim, a deep V-shaped notch was present in the northern crater rim through which lava had spilled onto the cone's flanks during recent eruptive episodes. These lavas had formed a fan-shaped lava field on the northeastern base of the cone, extending to the rim of Valle del Bove.

Behncke and Sturiale also investigated the pyroclastic deposits of the recent eruptive episodes which extended in relatively narrow fans from SEC in various directions. During the 18 and 20 January epidsodes, most fallout had occurred in a radius of <1 km from the cone, mainly on the SE side of the former Central Crater where 0.5-1 m of pyroclastics had accumulated since late 1998. Meter-sized bombs had fallen up to 500 m from SEC, creating spectacular impact craters. Among the most peculiar features of the recent eruptive products was a small lahar on the southwestern side of SEC which extended ~300 m from the base of its cone; this was probably produced during the 5 January episode. Records of lahars are relatively rare in the recent history of Etna, the most notable occurring in 1755.

On the morning of 23 January, SEC was the site of yet another eruptive episode that began at about 0630 and probably lasted less than one hour. Due to the absence of wind, an eruption column rose several kilometers above the summit then drifted slowly SE. In Catania, the ashfall was not dense, but people in the streets felt particles entering in the eyes; these particles were less than 1 mm in diameter and left a thin, discontinuous film on the ground. More serious effects were caused by the fallout in the upper southern parts of the mountain where skiing was rendered impossible by scoria on the snow. The repose period between this and the previous eruptive episode was two days and 18 hours.

There appears to have been no significant seismic or eruptive activity between 23 January and 4 February; the few clear views during that period revealed no morphological changes.

The January eruptive episodes continued to build the SEC cone, which has changed beyond recognition from its mid-1998 appearance. The large crater formed in 1990 at the summit of the SEC cone was completely filled, and a new, tall summit grew over it, burying any trace of the 1990 crater and much of the lava flows erupted from mid-1997 to late July 1998. After the 23 January episode the cone's new summit was at ~ 3,270 m elevation, almost 90 m higher than the highest point of the 1990 crater rim in 1997.

New eruptive fissure opens on 4 February. A new eruptive episode from SEC began at 1600, producing a spectacular eruption column visible from Catania and all around the mountain. Like previous episodes, this event was characterized by vigorous fire-fountaining, tephra emission, and lava, and was preceded by a gradual increase in gas emissions and then mild Strombolian activity. The activity began to culminate at around 1600 when a tall fountain jetted from the summit crater of the cone, and lava spilled through the breach in the N crater rim.

Sometime around 1630, the SE side of the cone fractured, and a new vent opened about halfway down the cone's flank, producing a tall lava fountain 250-350 m high and feeding a dense, ash-laden eruption column. An eruption column rose ~ 2-3 km above the summit before being driven SE, dropping fine ash on the flanks. Lava soon began to flow SE from this vent (figure 75). At about 1640, a row of incandescent spots appeared below the newly formed vent, indicating that a fissure had begun to propagate downslope from the base of the SEC cone. Vigorous lava fountaining and tephra emission from the new vent on the SE flank of SEC diminished rapidly shortly after 1700, but activity continued at the smaller vents on the fissure below that vent, at ~ 2,950 m elevation, and lava advanced rapidly towards the rim of Valle del Bove. At nightfall, both this lava flow and the lava erupted at the beginning of the episode onto the northern side of SEC were brightly incandescent and well visible from towns on the eastern side of the volcano, causing rumors of the opening of fractures on both sides of the cone. However, the northern flow soon stagnated and cooled, and no further lava emission occurred on that side for the remainder of February.

Figure 75. Sketch map showing Etna's summit craters SEC, Voragine (V), and Bocca Nuova (BN). The approximate extent of lava flows emitted during the 4 February eruption are in medium gray and those following the 4 February eruption are in black. Flows erupted from 1971 to 1993 are shown in light gray. Courtesy of Boris Behncke.

On 5 February, lava had begun to spill into Valle del Bove, forming a cascade on its steep western wall. The flow advanced very slowly, and had not yet reached the valley floor (at ~2,000 m elevation) on the next day when the new eruptive fissure was visited by Behncke and Giuseppe Scarpinati (L'Association Volcanologique Européenne, LAVE). Mild explosive activity was building several hornitos in the upper part of the ~100-m-long, SE-trending fissure at the base of the SEC cone while lava was issuing from numerous vents along the whole length of the fissure, feeding several channellized flows and some minor a`a flows. The effusion rate was estimated at 5 m³/s or more, significantly higher than during previous mainly effusive eruptions near Etna's summit craters (mainly at NE Crater in the 1970's) and similar to the effusion rates of some of Etna's flank eruptions. Pahoehoe lava was abundant around the effusive vents. The cone of SEC was found to be fractured from its summit down to its base, but only the main 4 February vent appeared to have produced significant eruptive activity while only minor spatter and scoriae were found in the part of the fracture between that vent and the still-active fissure.

On 15 February, Behncke and Scarpinati again visited the eruptive fissure and observed its activity for about 4 hours. By that day the lava spilling into the Valle del Bove had reached ~ 2,000 m elevation. There was no sign that the activity was diminishing, and the effusion rate remained perhaps as high as 5 m³/s.

Lava continued to issue from a number of effusive vents on the active fissure, forming at least two main rivers and several smaller and short-lived flows. In the course of a few hours Behncke and Scarpinati saw some of the lesser flows cease and others reactivate, forming blocky a`a while the more vigorous and long-lived flows moved in well-defined channels and showed no significant flux variations. Numerous short lava tubes, well-developed flow channels, and secondary vents had formed. Most effusive activity occurred ~50-100 m downslope from the upper end of the fissure, but several vents were also higher upslope. In the uppermost part of the fissure, numerous hornitos had formed, most of them concentrated in three clusters, and this area had countless incandescent vents producing high-pressure gas emission accompanied by a persistent hissing noise. The largest hornitos formed thin, vertical spires up to 3 m high while others were small humps a few tens of centimeters high. There was little explosive activity; only one vent in the uppermost hornito cluster rarely ejected incandescent pyroclastics.

Similar activity continued through the end of February. Lava flowed into the Valle del Bove, forming numerous lobes that moved on top or adjacent to earlier flows, and the farthest flow fronts did not extend much beyond 2,000 m elevation, remaining above the Monti Centenari, a cluster of cones formed during the 1852-53 eruption on the floor of Valle del Bove. The flow field gradually widened to ~500 m on the rim, and flows were issuing from numerous ephemeral vents on the W slope of the Valle.

Activity at Bocca Nuova (BN), Voragine, and Northeast Crater (NEC). Little significant activity occurred at these craters during January-February 1999 except for a brief resurgence of activity at BN during the week preceding the 4 February SEC events. During the 21 January visit by Behncke and Sturiale, spattering and Strombolian activity occurred deep within the large crater in the southeastern part of BN, accompanied by dense gas emission.

The cone in the northwestern part of BN produced violent noisy explosions every few minutes which ejected fountains of bombs high above the crater rim; ejecta frequently fell outside the crater, mostly to the W but in a few cases also SW and S. Between the explosions, deep-seated minor activity occurred within the 50-80-m-wide crater of the cone. No effusive activity had taken place in BN since it was invaded by lava from Voragine on 22 July 1998.

Bright crater glow was visible above BN in the first nights of February, the first time in about five months. This glow persisted during the night of 3-4 February but was much weaker on the evening of 4 February, indicating a drop of the magma level, probably related to the opening of the eruptive fissure on the SE base of SEC earlier that day. During the following week, only infrequent weak glows were visible above BN and then vanished altogether.

Very little activity except profuse steaming was observed within the Voragine during the 21 January visit by Behncke and Sturiale, who were able to descend into this crater and arrived at the "diaframma," the septum that separates the Voragine from Bocca Nuova. The floor of the crater was very flat in its eastern part, while a cluster of four craters with low cones occupied its central-western portion. The central crater, ~50 m wide and 30 m deep, was completely quiet; on its W side a much shallower, ~20-m-wide crater contained a 2-m-wide degassing hole with overhanging walls on whose floor numerous incandescent spots could be seen. A small crater with a diameter of less than 20 m, and ~ 10 m deep, lay on the SE side of the central crater. The largest crater in the Voragine was in the SW part of the Voragine and was between 70 and 100 m wide and more than 50 m deep with very steep and unstable walls, so that its floor could not be seen. Eruptive activity occurred at depth; as could be judged from the noises this was similar to the activity observed in the southeastern BN vents on the same day. A fifth vent that was active in August and early September 1998 on the crest of the "diaframma" appeared to have collapsed into the large SW vent, and only a part of its cone remained standing.

Geologic Background. Mount Etna, towering above Catania, Sicily's second largest city, has one of the world's longest documented records of historical volcanism, dating back to 1500 BCE. Historical lava flows of basaltic composition cover much of the surface of this massive volcano, whose edifice is the highest and most voluminous in Italy. The Mongibello stratovolcano, truncated by several small calderas, was constructed during the late Pleistocene and Holocene over an older shield volcano. The most prominent morphological feature of Etna is the Valle del Bove, a 5 x 10 km horseshoe-shaped caldera open to the east. Two styles of eruptive activity typically occur, sometimes simultaneously. Persistent explosive eruptions, sometimes with minor lava emissions, take place from one or more summit craters. Flank vents, typically with higher effusion rates, are less frequently active and originate from fissures that open progressively downward from near the summit (usually accompanied by Strombolian eruptions at the upper end). Cinder cones are commonly constructed over the vents of lower-flank lava flows. Lava flows extend to the foot of the volcano on all sides and have reached the sea over a broad area on the SE flank.

Information Contacts: Boris Behncke, Istituto di Geologia e Geofisica (IGGUC), Palazzo delle Scienze, Università di Catania, Corso Italia 55, 95129 Catania, Italy.

Seismicity remained low during January and February 1999. Volcano-tectonic (VT) earthquakes were common from two sources at depths of 0.2-18.8 km and had a coda magnitude range between -0.6 and 3. The first area was below the active cone, and the second was NNE of Galeras. The most significant VT event registered on 3 January at 0714 with a coda magnitude of 3, an epicenter ~14 km NNE of the volcano, and felt earthquakes in Pasto. Other types of VT events located toward the E flank have been called "trenes" (trains) because they are recorded consecutively, to make up packets of 2-5 events. They were small events, recorded at only four of the nine stations in the Galeras network. Those events had a depth range of 3.3-7.3 km and a coda magnitude range between -0.6 and 0.9.

Previous VT events at times have preceded seismic sequences, such as those during November-December 1993 and March 1995, as well as a small seismic sequence in July 1997. However, events have also been recorded in periods of no seismic sequences.

Quasi-monochromatic volcanic tremor episodes were recorded during 4-6 January. The maximum amplitudes were obtained on the E-W components of the broadband stations whereas the minimal amplitudes were recorded on the vertical components of those stations. The spectral frequencies show stable values with small variations of 0.5 Hz. Analysis of the tremor episodes suggested that the source directions of these events were toward the active cone of the volcano.

The electronic tiltmeter Peladitos, on the E flank of Galeras, showed stable behavior with small variations (<1 µrad) in both radial and tangential components. The Chorrillo and Huairatola portable tiltmeters showed stable behavior in the tangential components whereas the radial components continued a descending trend that began at the end of September 1998. Through 26 January, the cumulative decline in the Chorrillo radial component was ~35 µrad, and the Huairatola radial component decline was ~600 µrad.

Most of the radon stations showed stable behavior of the Rn-222 gas emission with changes <200 pCi/l. In contrast, the Meneses-1 station showed variations of ~ 3,300 pCi/l on an ascending trend; the Meneses-3 stations, ~2,700 pCi/l on a descending trend.

When the Alfa Deformes fumarole was measured in December 1998, it had a pH of 0.6. The next measurement, in May 1998, revealed a pH of 2.3, followed by a gradual decline to a value of 0.3 on 25 February. Measured fumarole temperatures generally remained stable, although the La Joya fumarole had increased to 181°C on 6 March from 148°C on 25 February. Scientists observed numerous fissures emitting gas during a summit visit, as well as cracks that could generate small landslides on the main cone.

Geologic Background. Galeras, a stratovolcano with a large breached caldera located immediately west of the city of Pasto, is one of Colombia's most frequently active volcanoes. The dominantly andesitic complex has been active for more than 1 million years, and two major caldera collapse eruptions took place during the late Pleistocene. Long-term extensive hydrothermal alteration has contributed to large-scale edifice collapse on at least three occasions, producing debris avalanches that swept to the west and left a large horseshoe-shaped caldera inside which the modern cone has been constructed. Major explosive eruptions since the mid-Holocene have produced widespread tephra deposits and pyroclastic flows that swept all but the southern flanks. A central cone slightly lower than the caldera rim has been the site of numerous small-to-moderate historical eruptions since the time of the Spanish conquistadors.

Information Contacts: Observatorio Vulcanológico y Sismológico de Pasto (OVSP), Carrera 31, 18-07 Parque Infantil, PO Box 1795, Pasto, Colombia (URL: https://www2.sgc.gov.co/volcanes/index.html).

The Instituto Geofísico (IG-EPN) monitors seismic events, crustal deformation, geochemistry, and records visual observations at Guagua Pichincha. This volcano consists of a 2-km-wide caldera, breached to the west, on whose floor lies a dome complex and the present explosion craters. The following report summarizes their daily observations from 1 January to 31 March 1999. During this period, a Yellow alert status persisted.

Bad weather often prevented or hindered visual observations. Guards at the refuge station and visiting scientists frequently reported noises and the strong smell of sulfur from the fumaroles. COSPEC data from 16 January and 13 March showed only background concentrations of SO₂ from the fumaroles, following the maximum concentrations yet recorded (170 t/day) on 10 December. Ash-and-steam plumes from dome fumaroles, when visible, ranged from 100 to 800 m in height, while explosion plumes reached 3 km. The 1981 explosion crater had increased in diameter and almost absorbed the September 1998 crater.

People living along the Cristal river (W flank) confirmed the seismic detection of small debris flows and floods that were generated on 7 and 27 January, 2, 16, and 21 February, and 1 March, all related to intense rainfalls; these traveled down the Rio Cristal at least 10-15 km. Estimated volumes are between 0.3 and 1 x 10^-6 m³ with estimated peak discharges of 100-250 m³/s.

Phreatic explosions covered the dome and the interior of the caldera with ash and rocks. A guard at the refuge station and Civil Defense personnel found 2-5 mm of new ash and new impact craters in the Terraza area following the explosions of 21 and 23 January. Analysis of the ash showed no juvenile material, suggesting that magma had not ascended. Ballistically ejected rock fragments up to 30 cm in diameter were found 1-1.5 km S and SE of the dome, the result of phreatic explosions in this time period.

Volcano-tectonic (VT), long-period (LP), and hybrid earthquakes, sometimes in multiples, occurred almost daily throughout January, February, and March. Phreatic explosions were frequent during that period, occurring on average once per day in February and March. Daily LP event counts varied between 1 and 40, but many days had few VT or LP events. Still, 24 VT events occurred on 28 February and 1 March. .High-frequency tremor episodes of a few minutes to as much as four hours (9 February) duration were recorded, but possible associated effects in at the caldera summit could not be confirmed due to bad weather. Some rockfalls in the caldera were heard by the refuge guards while tremor episodes were occurring.

On 9 February and 14 March instruments detected 16 and 70 tectonic earthquakes along the N part of the Quito fault. The largest events had magnitudes of 3.7 and 4.0, respectively. It had been speculated that these events represented sympathetic responses to stresses produced by the volcano's magma chamber. This idea came from an earlier observation of an "on-off scenario" where the presence earthquakes in the N Quito area correlated with little seismicity registering under the caldera, and vice versa.

Reduced displacement measurements (RDs) of phreatic explosions ranged from those too small to measure to several that were 20 cm² or greater. Some of these larger RDs, such as those on 18 and 28 January, and 13, 19, and 28 February, were the largest since October 1998. The one on 28 February was the largest yet recorded. A summary of seismic events since August 1998 is presented in table 2.

Table 2. Monthly summaries of explosions and seismic events at Guagua Pichincha, August 1998-March 1999. Courtesy IG-EPN.

Geologic Background. Guagua Pichincha and the older Pleistocene Rucu Pichincha stratovolcanoes form a broad volcanic massif that rises immediately to the W of Ecuador's capital city, Quito. A lava dome is located at the head of a 6-km-wide breached caldera that formed during a late-Pleistocene slope failure ~50,000 years ago. Subsequent late-Pleistocene and Holocene eruptions from the central vent in the breached caldera consisted of explosive activity with pyroclastic flows accompanied by periodic growth and destruction of the central lava dome. One of Ecuador's most active volcanoes, it is the site of many minor eruptions since the beginning of the Spanish era. The largest historical eruption took place in 1660, when ash fell over a 1000 km radius, accumulating to 30 cm depth in Quito. Pyroclastic flows and surges also occurred, primarily to then W, and affected agricultural activity, causing great economic losses.

Information Contacts: Instituto Geofísico, Escuela Politécnica Nacional, Apartado 17-01-2759, Quito, Ecuador.

Local residents first noticed thick gray ash emissions from the summit on 18 December 1998 (corrected from BGVN 24:01); this information reached the Volcanological Survey of Indonesia (VSI) Gamkonora volcano observatory on the 31st. On 2 January personnel from VSI who went to the island to take COSPEC measurements of the SO₂ release observed a loud eruption that caused up to 3 mm of ashfall in and around Tugure Batu Village. The eruption lasted 35 minutes and generated a plume 1,000 m high. Another eruption observed on 5 January 1999 lasted for 60 minutes. Thunderclaps from the summit were heard on 16 January and a night glow from ejecta was evident above the summit area. Residents also reportedly saw lava at the crater rim. The seismometer from Gamkonora (an RTS PS-2) was installed ~2 km from the summit of Ibu on 3 February along with an ARGOS satellite system tiltmeter.

Field observations on 11 March revealed continuing eruptions and rumbling noises, but the larger eruptions (accompanied by booming and thick ash ejection) had decreased to a rate of one every 15-20 minutes. When observed on 2 February larger eruptions occurred every 5 minutes. Seismograph records are still dominated by explosion events; during 9-15 March there were 779 events, increased from 673 events the previous week.

Geologic Background. The truncated summit of Gunung Ibu stratovolcano along the NW coast of Halmahera Island has large nested summit craters. The inner crater, 1 km wide and 400 m deep, contained several small crater lakes through much of historical time. The outer crater, 1.2 km wide, is breached on the north side, creating a steep-walled valley. A large parasitic cone is located ENE of the summit. A smaller one to the WSW has fed a lava flow down the W flank. A group of maars is located below the N and W flanks. Only a few eruptions have been recorded in historical time, the first a small explosive eruption from the summit crater in 1911. An eruption producing a lava dome that eventually covered much of the floor of the inner summit crater began in December 1998.

Information Contacts: R. Sukhyar and Dali Ahmad, Volcanological Survey of Indonesia (VSI), Jalan Diponegoro No. 57, Bandung 40122, Indonesia (URL: http://www.vsi.esdm.go.id/).

During fieldwork on Santa Ana volcano in February, increased steaming was observed at the summit of Izalco relative to levels of previous years. Strong fumarolic activity occurred along the entire circumference of the 250-m-wide summit crater, with the exception of the NE side facing Cerro Verde. Activity was most vigorous at a vent on the N side of the crater floor, but was also strong along much of the inner rim of the crater and along its outer flanks. Steaming was observed over broad areas on the outer southern flanks to ~50 m below the rim, and on the W flank immediately N of a shoulder of the cone at ~1,800 m elevation, roughly 150 m below the summit. Activity had earlier been noticed to have increased in November 1998 following Hurricane Mitch. Most of the steaming was water vapor, and the increased activity was attributed to saturation of the still-warm cone by heavy rains accompanying the hurricane.

Geologic Background. Volcán de Izalco, El Salvador's youngest volcano, was born in in 1770 CE on the southern flank of Santa Ana volcano. Frequent strombolian eruptions from Izalco provided a night-time beacon for ships, causing the volcano to be known as El Faro, the "Lighthouse of the Pacific." During the two centuries prior to the cessation of activity in 1966, Izalco built a steep-sided, 650-m-high stratovolcano truncated by a 250-m-wide summit crater. Izalco has been one of the most frequently active volcanoes in North America, and its sparsely vegetated slopes contrast dramatically with neighboring forested volcanoes. Izalco's dominantly basaltic-andesite pyroclasts and lava flows are geochemically distinct from those of both Santa Ana and its fissure-controlled flank vents. Lava flows were mostly erupted from flank vents and deflected southward by the slopes of Santa Ana, traveling as far as about 7 km from the summit of Izalco.

Information Contacts: Carlos Pullinger, Calle Padres Aguilar 448, Colonia Escalon, San Salvador, El Salvador; Demetrio Escobar, Centro de Investigaciones Geotecnicas (CIG), Final Blvd. Venezuela y calle a La Chacra, Apdo. Postal 109, San Salvador, El Salvador; Lee Siebert and Paul Kimberly, Global Volcanism Program, Smithsonian Institution.

Krakatau erupted on 5 February 1999 accompanied by thunderclaps and an ash plume that reached a height of ~1,000 m above the summit. The activity continued until 10 February with ash plumes reaching ~100-300 m above the summit. The continuing sporadic eruptions deposited small amounts of ash over most of the island; a deposit of ~0.3 mm was measured near the observatory. On 11 February, the glow of ejecta was observed reaching ~25 m above the summit and continued during the night.

Activity decreased early during the week of 9-15 March. Weak booming noises were heard twice on 9 and 10 March, but plumes were not observed. At the end of the week booming noises were rare, and a white-gray ash plume was seen on 14 March that rose 100-300 m above the summit. The current activity is a continuation of eruptions that began in 1992.

Geologic Background. The renowned volcano Krakatau (frequently misstated as Krakatoa) lies in the Sunda Strait between Java and Sumatra. Collapse of the ancestral Krakatau edifice, perhaps in 416 CE, formed a 7-km-wide caldera. Remnants of this ancestral volcano are preserved in Verlaten and Lang Islands; subsequently Rakata, Danan and Perbuwatan volcanoes were formed, coalescing to create the pre-1883 Krakatau Island. Caldera collapse during the catastrophic 1883 eruption destroyed Danan and Perbuwatan volcanoes, and left only a remnant of Rakata volcano. This eruption, the 2nd largest in Indonesia during historical time, caused more than 36,000 fatalities, most as a result of devastating tsunamis that swept the adjacent coastlines of Sumatra and Java. Pyroclastic surges traveled 40 km across the Sunda Strait and reached the Sumatra coast. After a quiescence of less than a half century, the post-collapse cone of Anak Krakatau (Child of Krakatau) was constructed within the 1883 caldera at a point between the former cones of Danan and Perbuwatan. Anak Krakatau has been the site of frequent eruptions since 1927.

Information Contacts: R. Sukhyar and Dali Ahmad, Volcanological Survey of Indonesia (VSI), Jalan Diponegoro No. 57, Bandung 40122, Indonesia (URL: http://www.vsi.esdm.go.id/).

The following report is based on photos taken between September and November 1998. Most of the photos were taken by local mountain guide Burra Ami Gadiye. Sketches and descriptions of the photos were provided by Celia Nyamweru of St. Lawrence University.

Lava from within the crater breached the rim, causing small lava flows down the outer crater wall; the breach on the NW probably occurred in late October, and the breach on the E began in early November. Small, narrow tongues of pahoehoe lava erupted continuously from vents around the upper slopes of cones T37S, T37N, and T40 (figure 55). Most of these flows moved E or NE, although a few moved W. The tops of T37S and T37N were built up into broad cones with jagged crowns. Some growth also occurred at T40. Little change was apparent on any of the other cones that were in existence in August (BGVN 23:10). In mid-November a new cone, which has been numbered T50, formed at the base of the SE wall.

Figure 55. View of Ol Doinyo Lengai looking N from the summit on 29 September 1998. Traced by Celia Nyamweru from a photo by B.A. Gadiye.

Activity during September and October. Narrow flows of pahoehoe lava emerged in late September from vents close to the summit of T37S and flowed E and W. The westward-flowing lava reached the center of the crater; the eastward-flowing lava reached the rim of T24 and the base of the crater wall. These flows were very dark in color suggesting they were still fluid or only very recently formed. The summit of T37S had a jagged profile (figure 56), replacing the broad dome seen in August.

Figure 56. View of Ol Doinyo Lengai looking NW from SE crater rim as seen on 29 September 1998. Traced by C. Nyamweru from photographs by B. A. Gadiye.

Small, narrow, very dark colored pahoehoe flows emerged in early October from vents close to the summits of T37S and T40 (figure 57). Behind T40 and to the right of T45, the T37 cluster showed some dark lava extending westwards from its summit past T47, the very tall narrow cone in front of the south wall. Cone T40 had fresh lava extending from the summit onto its lower slopes.

Figure 57. Photograph of Ol Doinyo Lengai taken on 3 October 1998 of the view S from the N crater rim. Courtesy B.A. Gadiye.

In another photo on 7 October (figure 58), the top of T37S was dark brown, in striking contrast with the very pale brown lower slopes. Surrounding cones were pale brown. A large dark brown flow from a source between T45 and T37 extended around the eastern slope of T45. The flow showed no sign of whitening along the edges of the slabs, unlike the flow in front of it, and, therefore, might have been only a few hours old. The E crater wall was estimated to be 5 m high based on the appearance of a person in one photo. This was not an estimate of the lowest point on the crater wall.

Figure 58. Photograph of Ol Doinyo Lengai taken on 7 October 1998 of the view SW from the E crater rim. Courtesy B.A. Gadiye.

Activity during November. In early November fresh, black, shiny, pahoehoe lava flowed from a vent between T45 and T37S. Gadiye noted the source of the flow as the cone T5T9. Only the very top of T5T9 remained visible, since the remainder was covered by 20 m of lava. Another lava flow originated from a vent on the S slope of T40 and flowed around the E side of this cone. According to Gadiye the crater had filled and lava was pouring over the NW rim. A few weeks later he took two photographs, noting that the lava was spilling over the crater rim on the E and had burned the grass on the slope. The lava in one of these photos (taken just outside the rim) consisted of brown and gray smooth pahoehoe flows that did not seem to be more than 10 to 20 cm thick. Judging from the pale color, it had probably undergone weathering during the weeks since it flowed.

Aerial photographs taken late in November showed several narrow tongues of very dark lava over an older surface of white and pale brown lava. These dark flows originated from the slopes of T37S and from the cluster of cones around T37N1. A narrow white streak that overflowed the rim on the NW side was probably recent lava. A few days later fresh pahoehoe flows effused from T37S and T37N and flowed E toward the crater wall and the remains of the rim of T24 (figure 59). In this area was a new cone near the base of the S wall: a low circular feature, just out of view in figure 59, which Gadiye described as "a new cone near the SE rim that is boiling and giving out a lot of steam." This has been designated T50. Lava was seen to be overflowing the NW rim. T37S had a very jagged appearance and there also seemed to have been considerable growth at T37N1, between T37S and T45. Some fresh pahoehoe, very dark over the white older flows, was also visible farther west on the crater floor, near the T44/T48/T49 cone cluster.

Figure 59. Photograph of Ol Doinyo Lengai taken on 24 November 1998 looking SW from the crater floor. Courtesy of B.A. Gadiye.

Geologic Background. The symmetrical Ol Doinyo Lengai is the only volcano known to have erupted carbonatite tephras and lavas in historical time. The prominent stratovolcano, known to the Maasai as "The Mountain of God," rises abruptly above the broad plain south of Lake Natron in the Gregory Rift Valley. The cone-building stage ended about 15,000 years ago and was followed by periodic ejection of natrocarbonatitic and nephelinite tephra during the Holocene. Historical eruptions have consisted of smaller tephra ejections and emission of numerous natrocarbonatitic lava flows on the floor of the summit crater and occasionally down the upper flanks. The depth and morphology of the northern crater have changed dramatically during the course of historical eruptions, ranging from steep crater walls about 200 m deep in the mid-20th century to shallow platforms mostly filling the crater. Long-term lava effusion in the summit crater beginning in 1983 had by the turn of the century mostly filled the northern crater; by late 1998 lava had begun overflowing the crater rim.

Information Contacts: Celia Nyamweru, Department of Anthropology, St. Lawrence University, Canton, NY 13617 USA (URL: http://blogs.stlawu.edu/lengai/).

During 1963-82 ash emissions, lava flows, lava fountains, and Strombolian explosions occurred intermittently at Lopevi. In 1968-69 activity mainly affected the SE flank (figure 1), where two lava flows from the summit reached the sea. The twenty-year pattern of activity ended with emission of a major plume that rose to 6,000 m on 24 October 1982 (SEAN 07:010).

Figure 1. View of the SE flank of Lopevi volcano, looking toward the NW in May 1995. Paama Island, from which recent observations were made, and Ambrym Island, a currently active volcano, are in the background (to the N). Courtesy IRD; photo by P. Evin, IRD.

Since then, activity had been generally fumarolic. Eruptive activity resumed in July 1998. A series of Strombolian explosions in the main 1963 crater (just NW of the central crater) was observed during November 1998. On 29, 30, and 31 December 1998, Strombolian explosions and Vulcanian emissions were observed from the island of Paama every 4-5 minutes.

Sporadic eruptive activity observed between the end of December 1998 and March 1999 was confined to the 1963 crater on the NW flank (figure 2). The appearance of this large crater, at ~900 m elevation, ruined the perfect conic profile of Lopevi, a rare volcano of the archipelago without a caldera.

Figure 2. View of the active crater on Lopevi's NW flank as seen in January 1999. Courtesy IRD; photo by J-M. Bore, IRD.

Lopevi, an island ~6 km in diameter, 1,450 m high, and 3,500 m above the seafloor, is one of the most active of the Vanuatu archipelago. The first written description came from Captain Cook, who in 1774 entered in his ship's log that the volcano was "seemingly without activity." Volcanic crises reported since 1863 appear to have occurred in cycles of ~15-20 years. In 1960, following a significant Plinian eruption from the NW flank, a series of pyroclastic flows, lava flows, Strombolian activity, and fumarolic emissions were observed during one month. In 1963, over a period of several months, large quantities of flowing lava and ash spread through ~ 1,000 ha in the NW part of the island.

Geologic Background. The small 7-km-wide conical island of Lopevi, known locally as Vanei Vollohulu, is one of Vanuatu's most active volcanoes. A small summit crater containing a cinder cone is breached to the NW and tops an older cone that is rimmed by the remnant of a larger crater. The basaltic-to-andesitic volcano has been active during historical time at both summit and flank vents, primarily along a NW-SE-trending fissure that cuts across the island, producing moderate explosive eruptions and lava flows that reached the coast. Historical eruptions at the 1413-m-high volcano date back to the mid-19th century. The island was evacuated following major eruptions in 1939 and 1960. The latter eruption, from a NW-flank fissure vent, produced a pyroclastic flow that swept to the sea and a lava flow that formed a new peninsula on the western coast.

Information Contacts: Michel Lardy, Institut de recherche pour le développement (IRD), B.P. 76, Port Vila, Vanuatu; Douglas Charley and Roland Priam, Department of Geology, Mines and Water Resources, PMB 01, Port Vila, Vanuatu.

Explosive activity resumed on 2 January 1999 at Pacaya for the first time since the end of a major eruptive episode on 19 September 1998. Current activity has consisted of small explosions that ejected ash without incandescent material. Beginning on 8 January, the number of explosions increased from 100-200/day to more than 400/day, reaching a peak of ~ 550 on 21 January (figure 19). Explosion counts declined to ~200/day by the end of the month. Volcanologists from INSIVUMEH and the Smithsonian Institution observed frequent small ash eruptions during a 1 February visit. The explosions were not accompanied by detonations, and produced billowing gray-to-brown ash columns that rose ~100 m above the vent. They observed that two vents produced explosions; the largest explosions originated from the westernmost and lower of two vents in the breached crater. Intense fumarolic activity occurred from the inclined floor of the summit crater, its rim, and the outer flanks.

Figure 19. Daily explosion counts at Pacaya during January 1999. Courtesy of INSIVUMEH.

Significant changes to the morphology of MacKenney cone had occurred since a strong explosive eruption on 18-19 September 1998. That eruption left a major breach 20-25 m wide that extended SW. By the time of the 1 February visit, erosion had widened the breach to 70-80 m. At its head, the breach had nearly vertical walls more than 50 m deep, and formed a gully that extended more than 1 km down to ~1,800 m elevation. The NE side of the crater was also notched, but not nearly as deeply. Fractures and down-dropped blocks of summit agglutinate material along the crater rim also showed this SW-NE orientation in line with the location of two flank vents active during September 1998. The breach gives MacKenney cone a twin-peaked appearance when viewed from the W flank (figure 20). The present form of the crater increases the possibility of future eruptive or collapse events being directed toward the W-flank village of El Patrocinio (figure 21).

Figure 20. A prominent gully extends more than 1 km down the SW flank of Pacaya from the twin-peaked summit of MacKenney cone, 1 February 1999. The dark lava flow at the lower right was one of two emplaced from flank vents at the end of the 18-19 September 1998 eruption. Photograph courtesy of Lee Siebert.

Figure 21. Sketch map of Pacaya and nearby towns. Hachured arcuate line indicates the caldera rim. Contour interval 100 m; contour intervals around MacKenney crater are approximate. Courtesy of INSIVUMEH.

The accumulation of spatter and ejecta from the September 1998 explosions had built MacKenney cone to a height about 30-35 m above an older cone immediately SE of MacKenney crater. The older cone, the previous vantage point for observing explosive activity from Pacaya, had itself grown about 10 m in the past decade from the accumulation of ejecta from MacKenney crater. The height of MacKenney cone now exceeds that of Cerro Grande, a vegetated ~2,560-m-high prehistorical cone of Pacaya located 2 km NE of MacKenney.

September 1998 eruption. A major explosive and effusive eruption took place on 18-19 September (table 3). During the first 17 hours of the eruption, a 1.2-km-long lava flow descended WNW into the caldera moat and down the flank of the volcano to the Montanas las Granadillas area SW of Cerro Chino. From 1700-2200 an explosive eruption ejected ash columns to 5 km above the crater, producing ashfall to the SW and NNW. Fine ashfall caused the closing of the international airport in Guatemala City for 35 hours. About 1 m of volcanic bombs were deposited on the caldera rim. Pyroclastic avalanches of incandescent ejecta mantled the upper half of the cone. One 3-m-wide impact crater was formed at the base of the lava flow near El Patrocinio, and 1-m-wide impact craters were found as far as 5 km from the vent. During the final explosive phase, the SW rim of MacKenney crater collapsed, forming a debris avalanche that traveled 2 km down the SW flank to ~1,500 m elevation. Coarse blocks littered the surface of the deposit, whose light color contrasted with that of adjacent dark-colored lava flows.

Table 3. Summary of major eruptive events at Pacaya volcano from January 1987 to September 1998.

Several lava flows accompanied the explosive activity (figure 22). The longest of these traveled ~4 km from a notch in the NE crater rim. The flow initially descended northward into the caldera moat where it was deflected by the caldera wall, flowed across the moat, and then down the SW flank to 1,760 m elevation before diverging around a small kipuka and scorching trees at its northern margin below Cerro Chino. Much of the caldera moat was covered by lava flows of the September eruption, and the prominent 1984 spatter cone low on the N flank was nearly buried.

Figure 22. Photograph of the lava flow (foreground) that descended from Pacaya's caldera moat down the W flank. This flow and the two dark lobes above it originated from MacKenney cone during the 18-19 September 1998 eruption. Light-colored tephra deposits between the flows mantle previous lava flows. Photograph taken on 1 February 1999. Courtesy of Paul Kimberly, SI.

At the end of the eruption, two small lava flows took place from flank vents on opposite sides of the cone. A vent on the upper NE flank at ~2,450 m elevation produced a short lava flow that reached the caldera moat. A vent on the lower SW flank at ~1,800 m elevation (figure 22) produced a short lava flow that divided into two lobes, one traveling to the SW and the other to the south.

Summary of 1987-1998 activity. Routine explosive activity characteristic of Pacaya occurred through much of the period from 1987 to the present but is not listed in table 3. Strong explosive eruptions in January 1987 and June 1991 destroyed the upper part of MacKenney cone, deepening and widening the crater, after which renewed eruptions reconstructed the cone. Major eruptions on 7 and 14 June 1995 destroyed the WNW side of the crater, leaving two notches at the summit. Debris from the 7 June collapse slammed into the caldera wall at Cerro Chino, 1 km NW of the summit, and produced a secondary hot cloud that swept over Cerro Chino, destroyed a radio antenna, and affected houses within 2 km of the active vent. The shockwave threw INSIVUMEH observer Pastor Alfaro down a slope, fracturing his leg. The 7 June event produced a 2.5-km-high plume. The second collapse on 14 June produced an avalanche that traveled SW toward El Rodeo and was accompanied by a 4-km-high plume. Lava flows subsequently traveled 2 km. Figure 23 shows RSAM plots for 1995-98.

Figure 23. Plot of seismic activity at Pacaya as represented by Real-time Seismic Amplitude Measurement (RSAM) counts during January 1995-December 1998. Courtesy of INSIVUMEH.

A strong explosive eruption on 20 May 1998 produced a 4-km-high ash column. Incandescent bombs burned trees on the SSW flank of Cerro Grande, 2 km N of the crater, and scoria fall damaged vegetation and crops. Two persons in the settlement of San Francisco de Sales, 2.5 km NE of the crater, were injured by falling scoria blocks. The ash plume was primarily blown to the NE, with a lesser plume to the SW (figure 24). Ash fell from 1300-1600 in the villages and towns within 5 km of the volcano. During 1400-1830 ash fell in the capital city of Guatemala, causing closure of the international airport. Ashfall covered an area of 800 km², and had an estimated volume of ~2.3 x 10⁶ m³. The eruption caused the evacuation of 254 residents from surrounding villages to the town of San Vicente de Pacaya. Lava flows during the 20 May eruption traveled down the N, W, and SW flanks and had a volume of 6.3 x 10⁵ m³.

Figure 24. Isopachs of the 20 May 1998 explosive eruption from Pacaya volcano. Courtesy of Otoniel Matias, INSIVUMEH.

Geologic Background. Eruptions from Pacaya, one of Guatemala's most active volcanoes, are frequently visible from Guatemala City, the nation's capital. This complex basaltic volcano was constructed just outside the southern topographic rim of the 14 x 16 km Pleistocene Amatitlán caldera. A cluster of dacitic lava domes occupies the southern caldera floor. The post-caldera Pacaya massif includes the ancestral Pacaya Viejo and Cerro Grande stratovolcanoes and the currently active Mackenney stratovolcano. Collapse of Pacaya Viejo between 600 and 1500 years ago produced a debris-avalanche deposit that extends 25 km onto the Pacific coastal plain and left an arcuate somma rim inside which the modern Pacaya volcano (Mackenney cone) grew. A subsidiary crater, Cerro Chino, was constructed on the NW somma rim and was last active in the 19th century. During the past several decades, activity has consisted of frequent strombolian eruptions with intermittent lava flow extrusion that has partially filled in the caldera moat and armored the flanks of Mackenney cone, punctuated by occasional larger explosive eruptions that partially destroy the summit of the growing young stratovolcano.

Information Contacts: Otoniel Matias, Instituto Nacional de Sismologia, Vulcanologia, Meteorologia e Hydrologia (INSIVUMEH), Ministerio de Communicaciones, Transporte y Obras Publicas, 7A Avenida 14-57, Zona 13, Guatemala City, Guatemala; Lee Siebert and Paul Kimberly, Global Volcanism Program, National Museum of Natural History, Room E-442, Smithsonian Institution, Washington DC 20560-0119.

Seismicity under the volcano was about at background levels from December 1998 through February 1999. On 2 February a M 2 earthquake was located at 23 km depth. Weak volcanic tremor and small earthquakes were registered during the first half of February, and on 21 February a 6-minutes series of shallow earthquakes was detected. The Level of Concern Color Code remained Green.

The volcano was frequently obscured by clouds, making observations only intermittently possible. Fumarolic plumes rising 50-400 m were noted on 10 December, 8, 13-14, and 20 January, 6-7, 13, 16-18, and 22 February. Higher plumes, in the range of 700-800 m above the summit, were observed on 21 and 23 January, and 5 February. On 10 and 15 February fumarolic plumes rose 1,000 m.

Geologic Background. The high, isolated massif of Sheveluch volcano (also spelled Shiveluch) rises above the lowlands NNE of the Kliuchevskaya volcano group. The 1300 km3 volcano is one of Kamchatka's largest and most active volcanic structures. The summit of roughly 65,000-year-old Stary Shiveluch is truncated by a broad 9-km-wide late-Pleistocene caldera breached to the south. Many lava domes dot its outer flanks. The Molodoy Shiveluch lava dome complex was constructed during the Holocene within the large horseshoe-shaped caldera; Holocene lava dome extrusion also took place on the flanks of Stary Shiveluch. At least 60 large eruptions have occurred during the Holocene, making it the most vigorous andesitic volcano of the Kuril-Kamchatka arc. Widespread tephra layers from these eruptions have provided valuable time markers for dating volcanic events in Kamchatka. Frequent collapses of dome complexes, most recently in 1964, have produced debris avalanches whose deposits cover much of the floor of the breached caldera.

Information Contacts: Olga Chubarova, Kamchatka Volcanic Eruptions Response Team (KVERT), Institute of Volcanic Geology and Geochemistry, Piip Ave. 9, Petropavlovsk-Kamchatsky, 683006, Russia; Tom Miller, Alaska Volcano Observatory (AVO), a cooperative program of a) U.S. Geological Survey, 4200 University Drive, Anchorage, AK 99508-4667, USA (URL: http://www.avo.alaska.edu/), b) Geophysical Institute, University of Alaska, PO Box 757320, Fairbanks, AK 99775-7320, USA, and c) Alaska Division of Geological & Geophysical Surveys, 794 University Ave., Suite 200, Fairbanks, AK 99709, USA.

During the first week of February, National Weather Service personnel in Cold Bay, 93 km ENE of Shishaldin, observed anomalous steaming. On 9 February a vigorous steam plume rose as high as 1,830 m above the vent and a long plume drifted downwind. Satellite imagery taken that day showed a thermal anomaly at the vent in addition to the steam plume. The steam activity decreased during the week, becoming only light puffs rising a few meters above the vent; however, the thermal anomaly at the vent persisted. A newly installed seismic net recorded slightly elevated seismicity beginning at the end of January.

The hazard status was raised to Yellow on 18 February due to the persistence of the thermal anomaly and the identification of low-level seismic tremor. Pilots and ground observers reported a large steam plume rising to 5,800 m on 18 February. No ash was detected on satellite imagery. Cloudy weather precluded ground observations for most of the following week.

Shishaldin volcano, located near the center of Unimak Island in the eastern Aleutian Islands, is a spectacular symmetrical cone with a basal diameter of approximately 16 km. A small summit crater typically emits a noticeable steam plume with occasional small amounts of ash. Shishaldin is one of the most active volcanoes in the Aleutian volcanic arc, situated near that part of the arc where the maximum rate of subduction occurs. It has erupted at least 27 times since 1775. Major explosive eruptions occurred in 1830 and 1932, and eight historical eruptions have produced lava flows. Steam and minor ash emission began in March 1986 and continued intermittently through mid-February, 1987. A poorly documented short-lived eruption of steam and ash, perhaps as high as 10 km, occurred in December 1995 (BGVN 21:01). Fresh ash was noted on the upper flanks and crater rim but no specific eruptive event was identified for the deposits.

Geologic Background. The beautifully symmetrical volcano of Shishaldin is the highest and one of the most active volcanoes of the Aleutian Islands. The 2857-m-high, glacier-covered volcano is the westernmost of three large stratovolcanoes along an E-W line in the eastern half of Unimak Island. The Aleuts named the volcano Sisquk, meaning "mountain which points the way when I am lost." A steady steam plume rises from its small summit crater. Constructed atop an older glacially dissected volcano, it is Holocene in age and largely basaltic in composition. Remnants of an older ancestral volcano are exposed on the west and NE sides at 1500-1800 m elevation. There are over two dozen pyroclastic cones on its NW flank, which is blanketed by massive aa lava flows. Frequent explosive activity, primarily consisting of strombolian ash eruptions from the small summit crater, but sometimes producing lava flows, has been recorded since the 18th century.

Information Contacts: Alaska Volcano Observatory, a cooperative program of a) U.S. Geological Survey, 4200 University Drive, Anchorage, AK 99508-4667, USA (URL: http://www.avo.alaska.edu/), b) Geophysical Institute, University of Alaska, PO Box 757320, Fairbanks, AK 99775-7320, USA, and c) Alaska Division of Geological & Geophysical Surveys, 794 University Ave., Suite 200, Fairbanks, AK 99709, USA.

Several small dome collapses, some that were initially explosive, generated pyroclastic flows in December. Episodes of ash venting occurred almost daily and seismicity was dominated by volcano-tectonic earthquakes and rockfalls. The number of volcano-tectonic earthquakes declined toward the end of December but the number of long-period signals, corresponding to ash venting, increased slightly. Some explosive eruptions during early- to mid-January generated substantial ash clouds. Brief episodes of ash venting, correlating with seismic tremor, became shorter and weaker toward the end of January. Small-volume pyroclastic flows were generated by dome collapse, but some flows may have been generated by fountain collapse during small explosive eruptions. The average SO₂ flux was elevated throughout December and January. Eastward movement of the Long Ground and Tar River GPS sites continued.

Visual observations.Daily periods of volcanic tremor during December coincided with steam-and-ash venting. On 8 December mudflows occurred all around the volcano.

A pyroclastic flow generated by dome collapse on 14 December reached the sea at the Tar River delta. Deposits were fluidized, fine-grained material with very few blocks. A large ash cloud was generated that rose rapidly to ~6,100 m. Ash fell W and NW of the volcano, attaining a thickness of 2 mm in Salem and containing accretionary lapilli up to 2 mm in diameter. On 19 December a pyroclastic flow reached the Tar River delta in less than five minutes. Powerful black jets of ash and rock burst from the dome at the onset of the event but it is unclear if this explosive activity preceded or followed the dome collapse. The small deposit was almost entirely confined to the incised channel in the Tar River valley on top of the 14 December deposits. On 21 December, at the onset of a sudden large seismic signal, dense black jets of ash and vigorously convecting ash clouds escaped from the main vent in the 3 July scar. Ballistic blocks rose 80 m above the vent. Very vigorous ash venting continued for more than 30 minutes after the initial explosion. A minor dome collapse on 27 December resulted in a small-volume pyroclastic flow reaching the Tar River delta. Poor visibility hampered observations, but a significant ash cloud was generated.

Minor ash venting took place on 1 and 5 January. At 0358 on 7 January, a large long-period seismic signal immediately preceded a 30-minute episode of tremor (usually associated with vigorous ash venting). Later the same day, a small dome collapse generated a pyroclastic flow that traveled half-way down the Tar River valley and a low-level ash cloud that moved W over Plymouth. On 13 January an explosive event generated an ash cloud to 6,100 m and a pyroclastic flow. The onset of the seismic signal had a long-period component, and a pressure wave was recorded at Long Ground. A booming sound was reported by many. The pyroclastic-flow deposit in the Tar River valley was small in volume but its extent suggested that the flow had been very mobile. Narrow small-volume pyroclastic-flow deposits were observed S of the dome as far as the former position of Galway's Soufriere. Two small dome-collapse pyroclastic flows occurred on 14 January. At 0827 on 15 January a small explosive event generated an ash cloud that rose to 4,600 m. The cloud moved NW and light ashfall affected Salem and Old Towne. Ash venting continued in pulses for 15 minutes. Another small explosion on 16 January generated an ash cloud to 3,000 m. Rockfalls were triggered on the inner walls of the 3 July scar and on the outer SE and NE flanks of the dome. A minor dome-collapse pyroclastic flow on 20 January almost reached the sea at the Tar River delta. The resulting steam-rich plume dissipated rapidly. Several brief (20 minute) episodes of tremor preceded by a rockfall corresponded to weak ash venting on 24 January. Further short episodes of ash venting occurred on 25 and 27 January.

Clear conditions on 26 and 27 January enabled MVO staff to survey the dome (figure 44). The canyon, which had been incised through the dome, was clearly visible. It bisected the dome in a NW-SE direction from the top of Tar River Valley to the top of Gages Valley. The inner walls of the canyon were vertical and surfaces looked fresh because of repeated small rockfalls.

Figure 44. Photograph of the dome area at Soufriere Hills taken in late January 1999. This was used to calculate the dome volume and shows an exceptionally clear view of the gully running through the dome. Courtesy MVO; photograph by Richard Herd and Chloe Harford.

Seismicity. Seismicity in December consisted chiefly of volcano-tectonic earthquakes and rockfall signals. Many of the latter were associated with small pyroclastic flows or venting. Small clusters of earthquakes were located under George's Hill to the NW of the dome, under Roaches Yard to the SE, and under Hermitage Estate to the NE.

Overall, January was quiet seismically. Pyroclastic-flow signals had low-frequency precursors. These events were associated with booming noises and were followed by periods of vigorous ash venting, suggesting the collapses were caused by violent degassing of the dome.

Ground deformation. The only area where significant deformation took place in December was on the E flank. The vectors for Long Ground showed eastward movement of these two sites amounting to 5 cm since lava stopped erupting. Most of this movement occurred during the last three months (a time of increased surface activity). The differential movement between Whites and Long Ground since June 1996 is more than 10 cm. The two sites are 733 m apart and the movement between them cannot be fit elastically. A ground inspection on 30 December revealed a possible fault between the two sites. The only surface expression is a linear break in the road and it is not currently known whether this is related to volcanic deformation or to surficial movements. The Tar River GPS pin has followed a similar movement to Long Ground throughout the eruption. The Perches site, until it was destroyed in July, followed a similar path. One possible interpretation is that a sector of the volcano including Long Ground, Perches, and Tar River is moving as a block along faults in a NE direction.

Eastward movement of Long Ground and Tar River continued in January but at a reduced rate. A local EDM network of five pins was set up on 27 January to learn whether the surface feature is a fault.

Environmental monitoring. The miniCOSPEC was used several times in December. The SO₂ flux was elevated and on 22 December and reached a peak average flux of 1,700 metric tons per day (figure 45). Sulfur-dioxide flux decreased throughout January, but generally remained elevated. Concentrations were also measured at ground level by using diffusion tubes around the island.

Figure 45. Average daily SO2 fluxes at Soufriere Hills measured by miniCOSPEC, December 1998-January 1999. The lines connecting measured points are guidelines only; the actual measured levels varied. The measurements made on 19 January showed a very low flux: observations suggested that at least part of the plume was at a very low altitude and may have been found partly below the elevation of the traversing helicopter. Data courtesy of MVO.

Ash and rainwater collection continued throughout January. Ash samples from the small explosive events tended to very coarse, with lithic and crystal fragments up to 6 mm in size in the Richmond Hill-St. Georges area. In contrast, ash generated by dome-collapse pyroclastic flows was very fine-grained.

Volume measurements. A detailed photographic and theodolite survey was conducted from twelve sites around the volcano at the end of January. A photographic survey was also conducted from the helicopter with the GPS onboard. The information has been processed to produce a detailed dome map and volume measurement. The dome had a volume of 76.8 x 10⁶ m³ and its highest point was 977 m at the top of the White River Valley. The dome was split deeply by the collapse on 3 July 1998 and by subsequent events. The N part of the dome, which comprises three main buttresses above Gages, the N flank, and Tar River, contains two-thirds of the total dome volume. The scar cuts up to 100 m into the pre-1995 crater floor and has removed a minimum of 5.4 x 10⁶ m³ of old rock from this area.

Geologic Background. The complex, dominantly andesitic Soufrière Hills volcano occupies the southern half of the island of Montserrat. The summit area consists primarily of a series of lava domes emplaced along an ESE-trending zone. The volcano is flanked by Pleistocene complexes to the north and south. English's Crater, a 1-km-wide crater breached widely to the east by edifice collapse, was formed about 2000 years ago as a result of the youngest of several collapse events producing submarine debris-avalanche deposits. Block-and-ash flow and surge deposits associated with dome growth predominate in flank deposits, including those from an eruption that likely preceded the 1632 CE settlement of the island, allowing cultivation on recently devegetated land to near the summit. Non-eruptive seismic swarms occurred at 30-year intervals in the 20th century, but no historical eruptions were recorded until 1995. Long-term small-to-moderate ash eruptions beginning in that year were later accompanied by lava-dome growth and pyroclastic flows that forced evacuation of the southern half of the island and ultimately destroyed the capital city of Plymouth, causing major social and economic disruption.

Information Contacts: Montserrat Volcano Observatory (MVO), Mongo Hill, Montserrat, West Indies (URL: http://www.mvo.ms/).

On 18 February, a gas-and-steam explosion generated a plume to 600 m above the volcano. Small (magnitudes near zero) shallow earthquakes were registered under the volcano and continued through the month, coincident with M 1.5 events at 15-30 km depth. No further unusual seismicity was reported as of mid-March.

The massive Tolbachik basaltic volcano is located at the southern end of the dominantly andesitic Kliuchevskaya volcano group. The Tolbachik massif is composed of two overlapping, but morphologically dissimilar volcanoes. The flat-topped Plosky Tolbachik shield volcano with its nested Holocene Hawaiian-type calderas up to 3 km in diameter is located east of the older and higher sharp-topped Ostry Tolbachik stratovolcano. Lengthy rift zones extending NE and SSW of the volcano have erupted voluminous basaltic lava flows during the Holocene, with activity during the past two thousand years being confined to the narrow axial zone of the rifts. The last eruptive activity, in 1975-76, vented from both the summit and SSW-flank fissures; it was the largest historical basaltic eruption in Kamchatka.

Geologic Background. The massive Tolbachik basaltic volcano is located at the southern end of the dominantly andesitic Kliuchevskaya volcano group. The massif is composed of two overlapping, but morphologically dissimilar volcanoes. The flat-topped Plosky Tolbachik shield volcano with its nested Holocene Hawaiian-type calderas up to 3 km in diameter is located east of the older and higher sharp-topped Ostry Tolbachik stratovolcano. The summit caldera at Plosky Tolbachik was formed in association with major lava effusion about 6500 years ago and simultaneously with a major southward-directed sector collapse of Ostry Tolbachik volcano. Lengthy rift zones extending NE and SSW of the volcano have erupted voluminous basaltic lava flows during the Holocene, with activity during the past two thousand years being confined to the narrow axial zone of the rifts. The 1975-76 eruption originating from the SSW-flank fissure system and the summit was the largest historical basaltic eruption in Kamchatka.

Information Contacts: Olga Chubarova, Kamchatka Volcanic Eruptions Response Team (KVERT), Institute of Volcanic Geology and Geochemistry, Piip Ave. 9, Petropavlovsk-Kamchatsky, 683006, Russia; Tom Miller, Alaska Volcano Observatory (AVO), a cooperative program of a) U.S. Geological Survey, 4200 University Drive, Anchorage, AK 99508-4667, USA (URL: http://www.avo.alaska.edu/), b) Geophysical Institute, University of Alaska, PO Box 757320, Fairbanks, AK 99775-7320, USA, and c) Alaska Division of Geological & Geophysical Surveys, 794 University Ave., Suite 200, Fairbanks, AK 99709, USA.

Volcanic-tremor levels on White Island (BGVN 23:10-23:12 and 24:01) have remained low since 22 January and low-level eruptive activity continued through mid-March. On 12 February, the low-energy hydrothermal activity within Metra Crater was dominated by gas-and-steam emissions from small fumaroles on the N and W sides of the crater. Four small ponds had formed on the crater floor. A weak gas (SO₂) and steam plume from PeeJay Vent rose 400-500 m, forming haze visible 40-50 km away.

During a visit by C.P. Wood on 13 March activity was generally constant with the ash-and-steam column rising to ~ 1,060 m and drifting many kilometers downwind, with sea discoloration from fall-out evident to 1 km from the island. PeeJay Vent was continuously emitting ash-charged gray-brown steam, but with varying intensity. During peak discharges, observers standing on the 1978/90 Crater Complex edge noted a rumbling noise from PeeJay, but no block ejection was seen. The vent diameter appeared to have increased and was an obvious funnel shape lined with whitish sublimate deposits. Ash could not be collected because of the wind direction. Metra Crater was occupied by a lurid lime-green lake, which largely filled the original crater and peripheral scallops to ~ 1 m below the rim (the old lake floor). There was no sign of thermal disturbance in the Metra lakelet. The ash surface throughout Main Crater was rain-washed and smooth (except for the route used by tourist operators), with no sign of recent impact craters near the 1978/90 Crater Complex edge.

Geologic Background. Uninhabited 2 x 2.4 km White Island, one of New Zealand's most active volcanoes, is the emergent summit of a 16 x 18 km submarine volcano in the Bay of Plenty about 50 km offshore of North Island. The island consists of two overlapping andesitic-to-dacitic stratovolcanoes; the summit crater appears to be breached to the SE, because the shoreline corresponds to the level of several notches in the SE crater wall. Volckner Rocks, four sea stacks that are remnants of a lava dome, lie 5 km NNE. Intermittent moderate phreatomagmatic and strombolian eruptions have occurred throughout the short historical period beginning in 1826, but its activity also forms a prominent part of Maori legends. Formation of many new vents during the 19th and 20th centuries has produced rapid changes in crater floor topography. Collapse of the crater wall in 1914 produced a debris avalanche that buried buildings and workers at a sulfur-mining project.

Information Contacts: Brad Scott, Wairakei Research Centre, Institute of Geological and Nuclear Sciences (IGNS) Limited, Private Bag 2000, Wairakei, New Zealand (URL: http://www.gns.cri.nz/).

In discussing the week ending on 12 September, "Earthweek" (Newman, 1997) incorrectly claimed that a volcano named "Mount Pinukis" had erupted. Widely read in the US, the dramatic Earthweek report described terrified farmers and a black mushroom cloud that resembled a nuclear explosion. The mountain's location was given as "200 km E of Zamboanga City," a spot well into the sea. The purported eruption had received mention in a Manila Bulletin newspaper report nine days earlier, on 4 September. Their comparatively understated report said that a local police director had disclosed that residents had seen a dormant volcano showing signs of activity.

In response to these news reports Emmanuel Ramos of the Philippine Institute of Volcanology and Seismology (PHIVOLCS) sent a reply on 17 September. PHIVOLCS staff had initially heard that there were some 12 alleged families who fled the mountain and sought shelter in the lowlands. A PHIVOLCS investigation team later found that the reported "families" were actually individuals seeking respite from some politically motivated harassment. The story seems to have stemmed from a local gold rush and an influential politician who wanted to use volcanism as a ploy to exclude residents. PHIVOLCS concluded that no volcanic activity had occurred. They also added that this finding disappointed local politicians but was much welcomed by the residents.

PHIVOLCS spelled the mountain's name as "Pinokis" and from their report it seems that it might be an inactive volcano. There is no known Holocene volcano with a similar name (Simkin and Siebert, 1994). No similar names (Pinokis, Pinukis, Pinakis, etc.) were found listed in the National Imagery and Mapping Agency GEOnet Names Server (http://geonames.nga.mil/gns/html/index.html), a searchable database of 3.3 million non-US geographic-feature names.

The Manila Bulletin report suggested that Pinokis resides on the Zamboanga Peninsula. The Peninsula lies on Mindanao Island's extreme W side where it bounds the Moro Gulf, an arm of the Celebes Sea. The mountainous Peninsula trends NNE-SSW and contains peaks with summit elevations near 1,300 m. Zamboanga City sits at the extreme end of the Peninsula and operates both a major seaport and an international airport.

[Later investigation found that Mt. Pinokis is located in the Lison Valley on the Zamboanga Peninsula, about 170 km NE of Zamboanga City and 30 km NW of Pagadian City. It is adjacent to the two peaks of the Susong Dalaga (Maiden's Breast) and near Mt. Sugarloaf.]

References. Newman, S., 1997, Earthweek, a diary of the planet (week ending 12 September): syndicated newspaper column (URL: http://www.earthweek.com/).

Manila Bulletin, 4 Sept. 1997, Dante's Peak (URL: http://www.mb.com.ph/).

Simkin, T., and Siebert, L., 1994, Volcanoes of the world, 2nd edition: Geoscience Press in association with the Smithsonian Institution Global Volcanism Program, Tucson AZ, 368 p.

Information Contacts: Emmanuel G. Ramos, Deputy Director, Philippine Institute of Volcanology and Seismology, Department of Science and Technology, PHIVOLCS Building, C. P. Garcia Ave., University of the Philippines, Diliman campus, Quezon City, Philippines.

Xinhua News Agency filed a news report on 27 February under the headline "Volcano erupts in Somalia" but the veracity of the story now appears doubtful. The report disclosed the volcano's location as on the W side of the Gedo region, an area along the Ethiopian border just NE of Kenya. The report had relied on the commissioner of the town of Bohol Garas (a settlement described as 40 km NE of the main Al-Itihad headquarters of Luq town) and some or all of the information was relayed by journalists through VHF radio. The report claimed the disaster "wounded six herdsmen" and "claimed the lives of 290 goats grazing near the mountain when the incident took place." Further descriptions included such statements as "the volcano which erupted two days ago [25 February] has melted down the rocks and sand and spread . . . ."

Giday WoldeGabriel returned from three weeks of geological fieldwork in SW Ethiopia, near the Kenyan border, on 25 August. During his time there he inquired of many people, including geologists, if they had heard of a Somalian eruption in the Gedo area; no one had heard of the event. WoldeGabriel stated that he felt the news report could have described an old mine or bomb exploding. Heavy fighting took place in the Gedo region during the Ethio-Somalian war of 1977. Somalia lacks an embassy in Washington DC; when asked during late August, Ayalaw Yiman, an Ethiopian embassy staff member in Washington DC also lacked any knowledge of a Somalian eruption.

A Somalian eruption would be significant since the closest known Holocene volcanoes occur in the central Ethiopian segment of the East African rift system S of Addis Ababa, ~500 km NW of the Gedo area. These Ethiopian rift volcanoes include volcanic fields, shield volcanoes, cinder cones, and stratovolcanoes.

Information Contacts: Xinhua News Agency, 5 Sharp Street West, Wanchai, Hong Kong; Giday WoldeGabriel, EES-1/MS D462, Geology-Geochemistry Group, Los Alamos National Laboratory, Los Alamos, NM 87545; Ayalaw Yiman, Ethiopian Embassy, 2134 Kalorama Rd. NW, Washington DC 20008.

Following the Ms 7.8 earthquake in Turkey on 17 August (BGVN 24:08) an Email message originating in Turkey was circulated, claiming that volcanic activity was observed coincident with the earthquake and suggesting a new (magmatic) volcano in the Sea of Marmara. For reasons outlined below, and in the absence of further evidence, editors of the Bulletin consider this a false report.

The report stated that fishermen near the village of Cinarcik, at the E end of the Sea of Marmara "saw the sea turned red with fireballs" shortly after the onset of the earthquake. They later found dead fish that appeared "fried." Their nets were "burned" while under water and contained samples of rocks alleged to look "magmatic."

No samples of the fish were preserved. A tectonic scientist in Istanbul speculated that hot water released by the earthquake from the many hot springs along the coast in that area may have killed some fish (although they would be boiled rather than fried).

The phenomenon called earthquake lights could explain the "fireballs" reportedly seen by the fishermen. Such effects have been reasonably established associated with large earthquakes, although their origin remains poorly understood. In addition to deformation-triggered piezoelectric effects, earthquake lights have sometimes been explained as due to the release of methane gas in areas of mass wasting (even under water). Omlin and others (1999), for example, found gas hydrate and methane releases associated with mud volcanoes in coastal submarine environments.

The astronomer and author Thomas Gold (Gold, 1998) has a website (Gold, 2000) where he presents a series of alleged quotes from witnesses of earthquakes. We include three such quotes here (along with Gold's dates, attributions, and other comments):

(A) Lima, 30 March 1828. "Water in the bay 'hissed as if hot iron was immersed in it,' bubbles and dead fish rose to the surface, and the anchor chain of HMS Volage was partially fused while lying in the mud on the bottom." (Attributed to Bagnold, 1829; the anchor chain is reported to be on display in the London Navy Museum.)

(B) Romania, 10 November 1940. ". . . a thick layer like a translucid gas above the surface of the soil . . . irregular gas fires . . . flames in rhythm with the movements of the soil . . . flashes like lightning from the floor to the summit of Mt Tampa . . . flames issuing from rocks, which crumbled, with flashes also issuing from non-wooded mountainsides." (Phrases used in eyewitness accounts collected by Demetrescu and Petrescu, 1941).

(C) Sungpan-Pingwu (China), 16, 22, and 23 August 1976. "From March of 1976, various large anomalies were observed over a broad region. . . . At the Wanchia commune of Chungching County, outbursts of natural gas from rock fissures ignited and were difficult to extinguish even by dumping dirt over the fissures. . . . Chu Chieh Cho, of the Provincial Seismological Bureau, related personally seeing a fireball 75 km from the epicenter on the night of 21 July while in the company of three professional seismologists."

Yalciner and others (1999) made a study of coastal areas along the Sea of Marmara after the Izmet earthquake. They found evidence for one or more tsunamis with maximum runups of 2.0-2.5 m. Preliminary modeling of the earthquake's response failed to reproduce the observed runups; the areas of maximum runup instead appeared to correspond most closely with several local mass-failure events. This observation together with the magnitude of the earthquake, and bottom soundings from marine geophysical teams, suggested mass wasting may have been fairly common on the floor of the Sea of Marmara.

Despite a wide range of poorly understood, dramatic processes associated with earthquakes (Izmet 1999 apparently included), there remains little evidence for volcanism around the time of the earthquake. The nearest Holocene volcano lies ~200 km SW of the report location. Neither Turkish geologists nor scientists from other countries in Turkey to study the 17 August earthquake reported any volcanism. The report said the fisherman found "magmatic" rocks; it is unlikely they would be familiar with this term.

The motivation and credibility of the report's originator, Erol Erkmen, are unknown. Certainly, the difficulty in translating from Turkish to English may have caused some problems in understanding. Erkmen is associated with a website devoted to reporting UFO activity in Turkey. Photographs of a "magmatic rock" sample were sent to the Bulletin, but they only showed dark rocks photographed devoid of a scale on a featureless background. The rocks shown did not appear to be vesicular or glassy. What was most significant to Bulletin editors was the report author's progressive reluctance to provide samples or encourage follow-up investigation with local scientists. Without the collaboration of trained scientists on the scene this report cannot be validated.

References. Omlin, A, Damm, E., Mienert, J., and Lukas, D., 1999, In-situ detection of methane releases adjacent to gas hydrate fields on the Norwegian margin: (Abstract) Fall AGU meeting 1999, Eos, American Geophysical Union.

Yalciner, A.C., Borrero, J., Kukano, U., Watts, P., Synolakis, C. E., and Imamura, F., 1999, Field survey of 1999 Izmit tsunami and modeling effort of new tsunami generation mechanism: (Abstract) Fall AGU meeting 1999, Eos, American Geophysical Union.

Gold, T., 1998, The deep hot biosphere: Springer Verlag, 256 p., ISBN: 0387985468.

Gold, T., 2000, Eye-witness accounts of several major earthquakes (URL: http://www.people.cornell.edu/ pages/tg21/eyewit.html).

Information Contacts: Erol Erkmen, Tuvpo Project Alp.

In December 2002 information appeared in Mongolian and Russian newspapers and on national TV that a volcano in Central Mongolia, the Har-Togoo volcano, was producing white vapors and constant acoustic noise. Because of the potential hazard posed to two nearby settlements, mainly with regard to potential blocking of rivers, the Director of the Research Center of Astronomy and Geophysics of the Mongolian Academy of Sciences, Dr. Bekhtur, organized a scientific expedition to the volcano on 19-20 March 2003. The scientific team also included M. Ulziibat, seismologist from the same Research Center, M. Ganzorig, the Director of the Institute of Informatics, and A. Ivanov from the Institute of the Earth's Crust, Siberian Branch of the Russian Academy of Sciences.

Geological setting. The Miocene Har-Togoo shield volcano is situated on top of a vast volcanic plateau (figure 1). The 5,000-year-old Khorog (Horog) cone in the Taryatu-Chulutu volcanic field is located 135 km SW and the Quaternary Urun-Dush cone in the Khanuy Gol (Hanuy Gol) volcanic field is 95 km ENE. Pliocene and Quaternary volcanic rocks are also abundant in the vicinity of the Holocene volcanoes (Devyatkin and Smelov, 1979; Logatchev and others, 1982). Analysis of seismic activity recorded by a network of seismic stations across Mongolia shows that earthquakes of magnitude 2-3.5 are scattered around the Har-Togoo volcano at a distance of 10-15 km.

Figure 1. Photograph of the Har-Togoo volcano viewed from west, March 2003. Courtesy of Alexei Ivanov.

Observations during March 2003. The name of the volcano in the Mongolian language means "black-pot" and through questioning of the local inhabitants, it was learned that there is a local myth that a dragon lived in the volcano. The local inhabitants also mentioned that marmots, previously abundant in the area, began to migrate westwards five years ago; they are now practically absent from the area.

Acoustic noise and venting of colorless warm gas from a small hole near the summit were noticed in October 2002 by local residents. In December 2002, while snow lay on the ground, the hole was clearly visible to local visitors, and a second hole could be seen a few meters away; it is unclear whether or not white vapors were noticed on this occasion. During the inspection in March 2003 a third hole was seen. The second hole is located within a 3 x 3 m outcrop of cinder and pumice (figure 2) whereas the first and the third holes are located within massive basalts. When close to the holes, constant noise resembled a rapid river heard from afar. The second hole was covered with plastic sheeting fixed at the margins, but the plastic was blown off within 2-3 seconds. Gas from the second hole was sampled in a mechanically pumped glass sampler. Analysis by gas chromatography, performed a week later at the Institute of the Earth's Crust, showed that nitrogen and atmospheric air were the major constituents.

Figure 2. Photograph of the second hole sampled at Har-Togoo, with hammer for scale, March 2003. Courtesy of Alexei Ivanov.

The temperature of the gas at the first, second, and third holes was +1.1, +1.4, and +2.7°C, respectively, while air temperature was -4.6 to -4.7°C (measured on 19 March 2003). Repeated measurements of the temperatures on the next day gave values of +1.1, +0.8, and -6.0°C at the first, second, and third holes, respectively. Air temperature was -9.4°C. To avoid bias due to direct heating from sunlight the measurements were performed under shadow. All measurements were done with Chechtemp2 digital thermometer with precision of ± 0.1°C and accuracy ± 0.3°C.

Inside the mouth of the first hole was 4-10-cm-thick ice with suspended gas bubbles (figure 5). The ice and snow were sampled in plastic bottles, melted, and tested for pH and Eh with digital meters. The pH-meter was calibrated by Horiba Ltd (Kyoto, Japan) standard solutions 4 and 7. Water from melted ice appeared to be slightly acidic (pH 6.52) in comparison to water of melted snow (pH 7.04). Both pH values were within neutral solution values. No prominent difference in Eh (108 and 117 for ice and snow, respectively) was revealed.

Two digital short-period three-component stations were installed on top of Har-Togoo, one 50 m from the degassing holes and one in a remote area on basement rocks, for monitoring during 19-20 March 2003. Every hour 1-3 microseismic events with magnitude <2 were recorded. All seismic events were virtually identical and resembled A-type volcano-tectonic earthquakes (figure 6). Arrival difference between S and P waves were around 0.06-0.3 seconds for the Har-Togoo station and 0.1-1.5 seconds for the remote station. Assuming that the Har-Togoo station was located in the epicentral zone, the events were located at ~1-3 km depth. Seismic episodes similar to volcanic tremors were also recorded (figure 3).

Figure 3. Examples of an A-type volcano-tectonic earthquake and volcanic tremor episodes recorded at the Har-Togoo station on 19 March 2003. Courtesy of Alexei Ivanov.

Conclusions. The abnormal thermal and seismic activities could be the result of either hydrothermal or volcanic processes. This activity could have started in the fall of 2002 when they were directly observed for the first time, or possibly up to five years earlier when marmots started migrating from the area. Further studies are planned to investigate the cause of the fumarolic and seismic activities.

At the end of a second visit in early July, gas venting had stopped, but seismicity was continuing. In August there will be a workshop on Russian-Mongolian cooperation between Institutions of the Russian and Mongolian Academies of Sciences (held in Ulan-Bator, Mongolia), where the work being done on this volcano will be presented.

References. Devyatkin, E.V. and Smelov, S.B., 1979, Position of basalts in sequence of Cenozoic sediments of Mongolia: Izvestiya USSR Academy of Sciences, geological series, no. 1, p. 16-29. (In Russian).

Logatchev, N.A., Devyatkin, E.V., Malaeva, E.M., and others, 1982, Cenozoic deposits of Taryat basin and Chulutu river valley (Central Hangai): Izvestiya USSR Academy of Sciences, geological series, no. 8, p. 76-86. (In Russian).

Geologic Background. The Miocene Har-Togoo shield volcano, also known as Togoo Tologoy, is situated on top of a vast volcanic plateau. The 5,000-year-old Khorog (Horog) cone in the Taryatu-Chulutu volcanic field is located 135 km SW and the Quaternary Urun-Dush cone in the Khanuy Gol (Hanuy Gol) volcanic field is 95 km ENE. Analysis of seismic activity recorded by a network of seismic stations across Mongolia shows that earthquakes of magnitude 2-3.5 are scattered around the Har-Togoo volcano at a distance of 10-15 km.

Information Contacts: Alexei V. Ivanov, Institute of the Earth Crust SB, Russian Academy of Sciences, Irkutsk, Russia; Bekhtur andM. Ulziibat, Research Center of Astronomy and Geophysics, Mongolian Academy of Sciences, Ulan-Bator, Mongolia; M. Ganzorig, Institute of Informatics MAS, Ulan-Bator, Mongolia.

An eruption at Mount Elgon was mistakenly inferred when fumes escaped from this otherwise quiet volcano. The fumes were eventually traced to dung burning in a lava-tube cave. The cave is home to, or visited by, wildlife ranging from bats to elephants. Mt. Elgon (Ol Doinyo Ilgoon) is a stratovolcano on the SW margin of a 13 x 16 km caldera that straddles the Uganda-Kenya border 140 km NE of the N shore of Lake Victoria. No eruptions are known in the historical record or in the Holocene.

On 7 September 2004 the web site of the Kenyan newspaper The Daily Nation reported that villagers sighted and smelled noxious fumes from a cave on the flank of Mt. Elgon during August 2005. The villagers' concerns were taken quite seriously by both nations, to the extent that evacuation of nearby villages was considered.

The Daily Nation article added that shortly after the villagers' reports, Moses Masibo, Kenya's Western Province geology officer visited the cave, confirmed the villagers observations, and added that the temperature in the cave was 170°C. He recommended that nearby villagers move to safer locations. Masibo and Silas Simiyu of KenGens geothermal department collected ashes from the cave for testing.

Gerald Ernst reported on 19 September 2004 that he spoke with two local geologists involved with the Elgon crisis from the Geology Department of the University of Nairobi (Jiromo campus): Professor Nyambok and Zacharia Kuria (the former is a senior scientist who was unable to go in the field; the latter is a junior scientist who visited the site). According to Ernst their interpretation is that somebody set fire to bat guano in one of the caves. The fire was intense and probably explains the vigorous fuming, high temperatures, and suffocated animals. The event was also accompanied by emissions of gases with an ammonia odor. Ernst noted that this was not surprising considering the high nitrogen content of guano—ammonia is highly toxic and can also explain the animal deaths. The intense fumes initially caused substantial panic in the area.

It was Ernst's understanding that the authorities ordered evacuations while awaiting a report from local scientists, but that people returned before the report reached the authorities. The fire presumably prompted the response of local authorities who then urged the University geologists to analyze the situation. By the time geologists arrived, the fuming had ceased, or nearly so. The residue left by the fire and other observations led them to conclude that nothing remotely related to a volcanic eruption had occurred.

However, the incident emphasized the problem due to lack of a seismic station to monitor tectonic activity related to a local triple junction associated with the rift valley or volcanic seismicity. In response, one seismic station was moved from S Kenya to the area of Mt. Elgon so that local seismicity can be monitored in the future.

Information Contacts: Gerald Ernst, Univ. of Ghent, Krijgslaan 281/S8, B-9000, Belgium; Chris Newhall, USGS, Univ. of Washington, Dept. of Earth & Space Sciences, Box 351310, Seattle, WA 98195-1310, USA; The Daily Nation (URL: http://www.nationmedia.com/dailynation/); Uganda Tourist Board (URL: http://www.visituganda.com/).