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Bulletin of the Global Volcanism Network

All reports of volcanic activity published by the Smithsonian since 1968 are available through a monthly table of contents or by searching for a specific volcano. Until 1975, reports were issued for individual volcanoes as information became available; these have been organized by month for convenience. Later publications were done in a monthly newsletter format. Links go to the profile page for each volcano with the Bulletin tab open.

Information is preliminary at time of publication and subject to change.


Recently Published Bulletin Reports

Ambrym (Vanuatu) Fissure eruption in mid-December 2018 produces fountaining and lava flows; no activity evident in caldera after 17 December

Fournaise, Piton de la (France) One-day eruptive events in April and July; 5-week eruption 27 April-1 June 2018

Negra, Sierra (Ecuador) Fissure opens on NNE caldera rim 26 June 2018, NW-flank lava flows reach the sea

Great Sitkin (United States) Small phreatic explosions in June and August 2018; ash deposit on snow near summit

Alaid (Russia) Small ash plume reported on 21 August 2018

Aira (Japan) Activity increased at Minamidake and decreased at Showa crater in early 2018

Suwanosejima (Japan) Intermittent ash emission continues from January through June 2018

Etna (Italy) Degassing continues, accompanied by intermittent ash emissions and small Strombolian explosions in June and July 2018

Stromboli (Italy) Continued Strombolian activity from five active summit vents through March-June 2018

Agung (Indonesia) Ash explosions and lava dome effusion continue during January-July 2018

Fernandina (Ecuador) Brief eruptive episode 16-22 June 2018, lava flows down N flank into the ocean

Fuego (Guatemala) Pyroclastic flows on 3 June 2018 cause at least 110 fatalities, 197 missing, and extensive damage; ongoing ash explosions, pyroclastic flows, and lahars



Ambrym (Vanuatu) — January 2019 Citation iconCite this Report

Ambrym

Vanuatu

16.25°S, 168.12°E; summit elev. 1334 m

All times are local (unless otherwise noted)


Fissure eruption in mid-December 2018 produces fountaining and lava flows; no activity evident in caldera after 17 December

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


Piton de la Fournaise (France) — September 2018 Citation iconCite this Report

Piton de la Fournaise

France

21.244°S, 55.708°E; summit elev. 2632 m

All times are local (unless otherwise noted)


One-day eruptive events in April and July; 5-week eruption 27 April-1 June 2018

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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (Ecuador) — September 2018 Citation iconCite this Report

Sierra Negra

Ecuador

0.83°S, 91.17°W; summit elev. 1124 m

All times are local (unless otherwise noted)


Fissure opens on NNE caldera rim 26 June 2018, NW-flank lava flows reach the sea

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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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)

Feature Location Description
Fissure 1 Edge of the caldera in the Volcán Chico area, trending WNW, tangential to the edge of the caldera. Four kilometers in length with lava flows that moved toward both the interior of the caldera and down the flank from the beginning of the eruption until 27 June, covering an area of 14.6 km2. The flows deposited outside the crater traveled 7 km downhill, without reaching the sea, while those inside it reached a maximum distance of 1.1 km.
Fissure 2 NW of the caldera about 3 km below its edge of the caldera at an elevation of 700 m. Approximately 250 m long and produced 4-km-long lava flows from the beginning of the eruption until 27 June, covering an area of 2.2 km2; its lava did not reach the sea.
Fissure 3 WNW of the caldera about 4 km below its edge at an elevation of 550 m. Approximately 250 m long and active from the beginning of the eruption until 27 June, emitting lava flows that covered an area of about 0.4 km2. The lava flows had a length of about 2 km and did not reach the sea.
Fissure 4 NW flank at an elevation of 100 m between 7 and 8 km below the rim of the caldera. Continuously emitting lava flows throughout the eruption. It was located on the On 6 July the lava flows from this fissure reached the ocean and modified the coastline of Isla Isabela by 1.5 km2. By 25 August when active flow ceased, its lavas had covered an area of approximately 13.3 km2.
Fissure 5 Western flank at an elevation of 840 m, 1.5 km downhill from the inner edge of the caldera. Length of 170 m and covered 0.026 km2.

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).


Great Sitkin (United States) — September 2018 Citation iconCite this Report

Great Sitkin

United States

52.076°N, 176.13°W; summit elev. 1740 m

All times are local (unless otherwise noted)


Small phreatic explosions in June and August 2018; ash deposit on snow near summit

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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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/).


Alaid (Russia) — September 2018 Citation iconCite this Report

Alaid

Russia

50.861°N, 155.565°E; summit elev. 2285 m

All times are local (unless otherwise noted)


Small ash plume reported on 21 August 2018

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 (see Caption) 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 (see Caption) 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/).


Aira (Japan) — August 2018 Citation iconCite this Report

Aira

Japan

31.593°N, 130.657°E; summit elev. 1117 m

All times are local (unless otherwise noted)


Activity increased at Minamidake and decreased at Showa crater in early 2018

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).

Month No. of ash emissions at Showa crater No. of ash emissions at Minamidake crater Pyroclastic flows
Jan 2018 1 12 (4) --
Feb 2018 0 7 (3) --
Mar 2018 0 44 (17) --
Apr 2018 3 66 (50) 800 m E from Showa.
May 2018 0 96 (48) --
Jun 2018 0 35 (13) 1,300 m SW from Minamidake.
Figure (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (Japan) — August 2018 Citation iconCite this Report

Suwanosejima

Japan

29.638°N, 129.714°E; summit elev. 796 m

All times are local (unless otherwise noted)


Intermittent ash emission continues from January through June 2018

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.

Month No. of explosions Max plume height (m above crater) Dates of ashfall in village 4 km SSW No. of seismic events Other daily activity detail
Jan 2018 0 1,100 27, 31 97 Incandescence at night.
Feb 2018 1 1,100 2, 3 100 Incandescence at night.
Mar 2018 9 2,200 25, 29 251 Incandescence at night. Ejecta scattered around the crater.
Apr 2018 8 2,000 18, 28, 29 62 Incandescence at night.
May 2018 2 1,100 14 90 Incandescence at night. Ejecta scattered around the crater.
Jun 2018 -- 900 -- 275 Incandescence at night.

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.

Month VAAs issued VAA dates Plume heights
Jan 2018 1 15 1.8 km
Feb 2018 1 2 1.2 km
Mar 2018 22 17, 22(3), 23, 25(2), 26(5), 27(5), 28(3), 29(2) 1.2-3.6 km
Apr 2018 16 1, 2, 3, 4(4), 5(2), 8, 11, 24, 27, 28(2) 1.2-2.4 km
May 2018 3 1, 4, 15 1-1.8 km
Jun 2018 1 1 --
Figure (see Caption) 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 (Italy) — August 2018 Citation iconCite this Report

Etna

Italy

37.748°N, 14.999°E; summit elev. 3295 m

All times are local (unless otherwise noted)


Degassing continues, accompanied by intermittent ash emissions and small Strombolian explosions in June and July 2018

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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (Italy) — August 2018 Citation iconCite this Report

Stromboli

Italy

38.789°N, 15.213°E; summit elev. 924 m

All times are local (unless otherwise noted)


Continued Strombolian activity from five active summit vents through March-June 2018

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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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).


Agung (Indonesia) — August 2018 Citation iconCite this Report

Agung

Indonesia

8.343°S, 115.508°E; summit elev. 2997 m

All times are local (unless otherwise noted)


Ash explosions and lava dome effusion continue during January-July 2018

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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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).


Fernandina (Ecuador) — August 2018 Citation iconCite this Report

Fernandina

Ecuador

0.37°S, 91.55°W; summit elev. 1476 m

All times are local (unless otherwise noted)


Brief eruptive episode 16-22 June 2018, lava flows down N flank into the ocean

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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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).


Fuego (Guatemala) — August 2018 Citation iconCite this Report

Fuego

Guatemala

14.473°N, 90.88°W; summit elev. 3763 m

All times are local (unless otherwise noted)


Pyroclastic flows on 3 June 2018 cause at least 110 fatalities, 197 missing, and extensive damage; ongoing ash explosions, pyroclastic flows, and lahars

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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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.

Date Local time Ravine(s) Width (m) Depth (m) Block Size (m)
06 Jun 2018 1610 Seca, Mineral 30-40 4-5 2-3
06 Jun 2018 1720 Santa Teresa, Mineral and Taniluyá 30 2-3 2-3
08 Jun 2018 0240 Santa Teresa, Mineral, and Taniluyá 30 2-3 2-3
08 Jun 2018 0450 Santa Teresa, Mineral, and Taniluyá, Ceniza -- -- 2-3
09 Jun 2018 1400 Seca, Mineral, Niagara and Taniluyá 40 5 3
10 Jun 2018 1515 Seca, Mineral, Niagara and Taniluyá, Ceniza 35 3 1
11 Jun 2018 1415 Seca and Mineral 35-40 3 3
11 Jun 2018 1750 Las Lajas and el Jute 35-55 3-5 3
12 Jun 2018 1330 Las Lajas 35-45 5 3
12 Jun 2018 1425 Ceniza, Mineral 20 2 1-3
13 Jun 2018 0110 Ceniza 25 2 1-3
13 Jun 2018 1350 Las Lajas 30-40 3 3
14 Jun 2018 0145 Santa Teresa and Mineral 20-25 2 3
14 Jun 2018 1445 Taniluyá, Ceniza, rio El Gobernador, Las Lajas 30-45 3 3
15 Jun 2018 1715 Seca, Mineral 30-35 3 3
15 Jun 2018 1725 Las Lajas 30-35 2 3
15 Jun 2018 1740 Taniluyá, Ceniza 20-25 2 3
16 Jun 2018 1445 Las Lajas 30-35 2 3
17 Jun 2018 1415 Las Lajas -- -- 3
17 Jun 2018 1440 Seca, Mineral 40 2 2
18 Jun 2018 1510 Seca, Mineral 25-30 3 3
18 Jun 2018 1600 Las Lajas 40-45 2 3
20 Jun 2018 0735 Las Lajas 35-45 2-3 3
20 Jun 2018 1230 Las Lajas 30-35 3 3
20 Jun 2018 1415 Seca, Mineral, Taniluyá, Ceniza 30-35 3 3
21 Jun 2018 1940 Las Lajas 30-35 3 3
22 Jun 2018 0030 Las Lajas -- -- 3
22 Jun 2018 1450 Las Lajas -- -- 2-3
22 Jun 2018 1535 Rio Pantaleón 40 3 3
23 Jun 2018 1740 El Jute, Las Lajas, San Miguel los Lotes area -- -- 3
26 Jun 2018 1412 El Jute, Las Lajas, San Miguel los Lotes area -- -- 3
26 Jun 2018 1455 Seca, Mineral, Niagra, Ceniza -- -- 2-3
30 Jun 2018 1435 Seca, Mineral -- -- 2-3

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 (see Caption) 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).

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Scientific Event Alert Network Bulletin - Volume 14, Number 04 (April 1989)

Managing Editor: Lindsay McClelland

Aira (Japan)

Summit explosions diminish

Akutan (United States)

Small ash ejections resume

Ambrym (Vanuatu)

Ash plume and lava flow; recent eruption history

Apoyeque (Nicaragua)

Lake temperature measured

Asosan (Japan)

Brief ash emission

Bagana (Papua New Guinea)

Lava flow advances; new avalanche deposits

Concepcion (Nicaragua)

Strong fuming

Galeras (Colombia)

Ash emission and strong seismicity; area residents alerted

Kilauea (United States)

Lava flows threaten houses

Langila (Papua New Guinea)

Moderate ash ejections and glow

Lengai, Ol Doinyo (Tanzania)

January inspection reveals no new lava

Lonquimay (Chile)

Continued tephra emission; cattle sickened by ash

Manam (Papua New Guinea)

Incandescent ejections and vapor release

Masaya (Nicaragua)

Lava lake drains; rockslides; gas emission

Momotombo (Nicaragua)

Burning gases from fumaroles

Niigata-Yakeyama (Japan)

Increased steaming, small ash eruption

Nyamuragira (DR Congo)

Lava erupts from summit and E flank

Poas (Costa Rica)

Crater lake gone; explosions and molten sulfur ponds

Popocatepetl (Mexico)

New fumaroles and large sulfur deposits

Rabaul (Papua New Guinea)

Seismicity and deformation at background level

Rincon de la Vieja (Costa Rica)

Crater lake sampled

Ruapehu (New Zealand)

Heat flow declines

Ruiz, Nevado del (Colombia)

Seismicity decreases

Soputan (Indonesia)

Ashfall damages houses and crops

Ulawun (Papua New Guinea)

Small ash emissions, minor seismic increases

White Island (New Zealand)

Tephra ejections continue



Aira (Japan) — April 1989 Citation iconCite this Report

Aira

Japan

31.593°N, 130.657°E; summit elev. 1117 m

All times are local (unless otherwise noted)


Summit explosions diminish

Activity . . . in April was lower than in previous years. Single explosions were registered on the 1st, 5th, and 13th. The highest cloud rose 1,600 m on 13 April. Monthly ash accumulation at the observatory was 119 g/m2.

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: JMA.


Akutan (United States) — April 1989 Citation iconCite this Report

Akutan

United States

54.134°N, 165.986°W; summit elev. 1303 m

All times are local (unless otherwise noted)


Small ash ejections resume

Small ash ejections resumed in February 1989. Observer's initials, in brackets, follow their information in the chronology below.

27 February, 1200: A small, short-lived, vertical blast of ash and steam from the summit tephra cone was observed from a small boat on the N side of Akutan Island. The plume was probably <500 m high [LP].

15 March: An atmospheric shock wave was felt at 0900 by a pilot [NS] over the W shore of Akutan volcano. A black summit eruption plume rose rapidly, its top disappearing into cloud cover at 1,800 m altitude. Near Akutan village, the plume was observed at 0900 [RP] through a break in the clouds. Black ash quickly reached an estimated 2,300 m above the volcano. During the next several hours, emissions diminished and turned gray, with only a small white steam plume evident just before noon. At 1430, a small dark-gray eruption plume was observed from the village, drifting S [DM]. During an overflight at 1500, the summit tephra cone emitted dark steam [NS and HW]. Observations of the W and SW flanks revealed fresh ash covering the snow above 600 m elevation.

16 March, morning: A very light dusting of ash that had fallen the previous night was noticed in Akutan village [DM]. At 1100 the volcano's summit region was white with fresh snow [HW].

Between 17 and 31 March: A crater on the E side of the summit cone began to emit steam at some time during this period [DM]. Previously, steam had emerged only from the cone's W side.

28-29 March: Akutan's summit was black with fresh-looking ash. Minor amounts of steam were emitted [CL].

31 March, about 1945: A large white plume was observed at least 600 m above Akutan from a U.S. Coast Guard plane [SR]. The plume top had drifted 7 km S. No eruptive activity had been seen from near the village at 1900 [LL]. No further activity was observed from 31 March until the end of the report period on 7 April.

Observers (initials in brackets): Lawrence Prokopioff, Richard Petre, David McGlashan, Harold Wilson, and Linda Logan, Akutan Village and vicinity; Nick Sias, Peninsula Airways; Craig Leth, FAA; Lieutenant Commander Steve Rapalus and his crew, U.S. Coast Guard.

Geologic Background. One of the most active volcanoes of the Aleutian arc, Akutan contains 2-km-wide caldera with an active intracaldera cone. An older, largely buried caldera was formed during the late Pleistocene or early Holocene. Two volcanic centers are located on the NW flank. Lava Peak is of Pleistocene age, and a cinder cone lower on the flank produced a lava flow in 1852 that extended the shoreline of the island and forms Lava Point. The 60-365 m deep younger caldera was formed during a major explosive eruption about 1600 years ago and contains at least three lakes. The currently active large cinder cone in the NE part of the caldera has been the source of frequent explosive eruptions with occasional lava effusion that blankets the caldera floor. A lava flow in 1978 traveled through a narrow breach in the north caldera rim almost to the coast. Fumaroles occur at the base of the caldera cinder cone, and hot springs are located NE of the caldera at the head of Hot Springs Bay valley and along the shores of Hot Springs Bay.

Information Contacts: J. Reeder, ADGGS.


Ambrym (Vanuatu) — April 1989 Citation iconCite this Report

Ambrym

Vanuatu

16.25°S, 168.12°E; summit elev. 1334 m

All times are local (unless otherwise noted)


Ash plume and lava flow; recent eruption history

On 31 April at 0730, the meteorological service in Wellington, New Zealand detected volcanic ash clouds near 16.1°S, 168.1°E on satellite images. The main cloud had an estimated diameter of 15-30 km, with streamers to 115 km NNE, and moved at a speed of ~30 km/hour. The plume height was estimated at ~6 km from an aircraft at 0350. The meteorological service in Darwin, Australia also located a steam/ash cloud on visible satellite images at 1030. NOAA infrared and visible images showed only a small cloud on 31 April at 1344 during clear weather. The following is a report from J.P. Eissen, M. Lardy, M. Monzier, L. Mollard, and D. Charley of ORSTOM (Nouméa and Port Vila).

Description and history. "Ambrym, a large stratovolcano with a 15-km-wide caldera (figure 1), is one of the most active volcanoes of the New Hebrides arc, which includes Yasur (Tanna Island), Lopevi (Lopevi Island), and the shallow submarine volcano Karua (between Epi and Tongoa Islands).

Figure (see Caption) Figure 1. Geologic features of Ambrym caldera. The 1988 and 1989 lava flow paths have been modified after Monzier and Douglas (1989). Q1 = Tuvio volcanics (old northern Ambrym volcano), Q2 = older flank volcanics, Q3 = younger flank volcanics, Q4 = Tower Peak volcanics, Q5 = undifferentiated recent caldera and flank volcanics, Q6 = NE and E Marum basaltic flows and related old cones. The area shown is outlined on the index map (inset) of the main topographic features of Ambrym Island. B = Benbow, M = Marum (active cones), To = Tower Peak, Tu = Mt. Tuvio (old volcanic centers), E = Endu village, O = Otas village, S = Sevisi village. Maps modified after geological (New Hebrides Geological Survey, 1976) and pedomorphological (Quantin, 1978) maps.

". . . . In the historical period, at least five types of activity can be distinguished. From the most to least frequent, these are: 1) intra-caldera, intermittent, Strombolian-type activity with mild extra-caldera ashfalls, but without lava flows (occurs almost every year); 2) intracaldera eruption frequently preceded by lava lake formation in the crater — generally starts with emission of a Plinian column that produces extra-caldera ashfalls, followed by intra-caldera lava flows; 3) activity similar to (2) followed by lava overflowing from the caldera (1863 (?), 1913-14, 1942 eruptions); 4) extra-caldera lava emission from fissures (1894, 1913, 1929, 1936 eruptions) — sometimes evolves toward 5) formation of pyroclastic cones, sometimes accompanied by lava flows (1888, 1915, 1929 eruptions). Several of these types of actvity have occurred consecutively in the different phases of a single eruption (as in 1913-14 and 1929, the two major Ambrym eruptions).

"On 13 November 1986, an aircraft pilot reported an increase in activity at the volcano. Ash emission became significant 17 November, but activity decreased 19-20 November. A new cone formed (Cheney, 1986) 3 km E of the active Marum cone (figure 1) and produced an intra-caldera lava flow ~4 km long (Melchior, 1988).

May 1988 activity. "On 27 May 1988, a lava lake ~50 m in diameter was observed in Mbwelesu's crater. Benbow was emitting white clouds whereas Marum and Mbwelesu were emitting dark grey clouds (Melchior, 1988). On 10 August, intracaldera lava flowed S more than 1.5 km from what appeared to be a new cone, but was possibly an extension of Mbwelesu (Cheney, 1988). The flow (still warm) extended ~5 km S (Charley, 1988). This eruption had ended by 23 August.

April 1989 activity. "At 1000 on 24 April 1989, a pilot observed a large plume rising ~3,500 m above the volcano. A lava flow from the the 1988 cone was following the same path as the 1988 flow but was a few kilometers longer. It followed the creek near Endou village (figure 1) and may or may not have extended outside the caldera [but see 14:10]. About 1 km2 of Otas village was reported to be burned. On the night of 29 April, large areas of red glow were seen from boats cruising in the area, and winds carried ash NW. Young vegetation on the S flank was burned (possibly by acid rain), and rain water had a strong taste. Local inhabitants said that the eruption was normal for the volcano even though there were more loud roaring noises and small earthquakes than in 1986 or 1988. A local pilots' strike prevented further observation of the eruption, but on 10 May the volcano was still active." The eruption apparently stopped sometime before 14 May.

References. Charley, D., 1988, Rapport de Mission à Ambrym en Aout 1988: Document ORSTOM, Port Vila, 5 p.

Cheney, C.S., 1986, New volcanic eruption near Endu, SE Ambrym: Geology Dept Memo, 24 November 1986, 1 p.

Cheney, C.S., 1988, Volcanic activity report, Ambrym and Epi: Geology Dept Memo, 17 August 1988, 1 p.

Melchior, A.H., 1988, Rapport de Mission de Reconnaissance Volcanologique Ambrym (25-28 May 1988) et à Tanna (14 May 1988): Document ORSTOM, Nouméa, 10 p.

Quantin, P., 1978, Archipel des Nouvelles-Hébrides: Atlas des Sols et de quelques Données du Milieu: Cartes Pédologiques, des Formes du Relief, Géologiques et de la Végétation; ORSTOM (18 sheets).

Stephenson, P.J., McCall, G.J.H., Le Maitre, R.W., and Robinson, G.P., 1968, The Ambrym Island Research Project, in Warden, A.J., ed., New Hebrides Geological Survey Annual Report 1966: Port Vila, p. 9-15.

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: J. Eissen, M. Lardy, M. Monzier, ORSTOM, New Caledonia; L. Mollard, and D. Chaney, ORSTOM, Vanuatu; J. Latter, DSIR Geophysics, Wellington; S. Kusselson, SAB; J. Temakon, Dept of Geology, Mines, and Rural Water Supply, Port Vila.


Apoyeque (Nicaragua) — April 1989 Citation iconCite this Report

Apoyeque

Nicaragua

12.242°N, 86.342°W; summit elev. 518 m

All times are local (unless otherwise noted)


Lake temperature measured

Surface temperature of the lake (measured with an 8-14 micrometer bandpass radiometer) varied between 28 and 30°C during fieldwork 8 April. A water temperature measured near the N shore was 25.5°C.

Geologic Background. The Apoyeque volcanic complex occupies the broad Chiltepe Peninsula, which extends into south-central Lake Managua. The peninsula is part of the Chiltepe pyroclastic shield volcano, one of three large ignimbrite shields on the Nicaraguan volcanic front. A 2.8-km wide, 400-m-deep, lake-filled caldera whose floor lies near sea level truncates the low Apoyeque volcano, which rises only about 500 m above the lake shore. The caldera was the source of a thick mantle of dacitic pumice that blankets the surrounding area. The 2.5 x 3 km wide lake-filled Xiloá (Jiloá) maar, is located immediately SE of Apoyeque. The Talpetatl lava dome was constructed between Laguna Xiloá and Lake Managua. Pumiceous pyroclastic flows from Laguna Xiloá were erupted about 6100 years ago and overlie deposits of comparable age from the Masaya plinian eruption.

Information Contacts: C. Oppenheimer, Open Univ.


Asosan (Japan) — April 1989 Citation iconCite this Report

Asosan

Japan

32.884°N, 131.104°E; summit elev. 1592 m

All times are local (unless otherwise noted)


Brief ash emission

On 27 April, the staff of AWS visited the crater rim as they have every day for the past 20 years. A vent on the SE floor of Crater 1 was releasing yellow vapor and ash to 30 m, accompanied by larger tephra. The Aso Volcano Disaster Prevention Authority closed a 1-km area near the crater to tourists. The area was reopened 2 May, when a field survey revealed only white vapor reaching ~5-6 m above the vent.

Glow on the crater floor has been observed every night since October 1988. A maximum temperature of 232°C was measured (with a infrared radiation thermometer) at a glowing site on 18 April.

Isolated tremor remained frequent in April. The daily number of tremor episodes was 100-250, with a monthly total of ~5,760 (figure 10). Amplitude of continuous tremor remained the same.

Figure (see Caption) Figure 10. Monthly number of isolated volcanic tremor episodes at Aso (top), earthquakes (bars, bottom), and maximum plume heights (curve, bottom), 1966-April 1989. Arrows mark periods of explosions. Courtesy of JMA.

Geologic Background. The 24-km-wide Asosan caldera was formed during four major explosive eruptions from 300,000 to 90,000 years ago. These produced voluminous pyroclastic flows that covered much of Kyushu. The last of these, the Aso-4 eruption, produced more than 600 km3 of airfall tephra and pyroclastic-flow deposits. A group of 17 central cones was constructed in the middle of the caldera, one of which, Nakadake, is one of Japan's most active volcanoes. It was the location of Japan's first documented historical eruption in 553 CE. The Nakadake complex has remained active throughout the Holocene. Several other cones have been active during the Holocene, including the Kometsuka scoria cone as recently as about 210 CE. Historical eruptions have largely consisted of basaltic to basaltic-andesite ash emission with periodic strombolian and phreatomagmatic activity. The summit crater of Nakadake is accessible by toll road and cable car, and is one of Kyushu's most popular tourist destinations.

Information Contacts: JMA.


Bagana (Papua New Guinea) — April 1989 Citation iconCite this Report

Bagana

Papua New Guinea

6.137°S, 155.196°E; summit elev. 1855 m

All times are local (unless otherwise noted)


Lava flow advances; new avalanche deposits

"Observer reports and recorded seismicity indicate that increased activity . . . is continuing. Inspections on 3 and 4 March by personnel from Bougainville Island Copper Ltd. revealed that a new deposit of avalanche debris was present on the SE flank. The deposit was dark in colour and extended from the summit . . . to the mid-flank level (~1,000 m altitude). Vegetation around the edges of the deposit had been killed. The avalanche occurred sometime between 3 February and 3 March. The profile of E flank lava flow's terminus had changed, suggesting overriding of older parts of the flow by new lobes and possible advance of the flow nose.

"On 18 March, the pilot of a passing aircraft reported a lava flow on the SE flank and copious ash around and above the volcano. However, an inspection on 12 April indicated that the deposit was probably formed by a rockfall from the inactive nose of of the E flank lava flow (at ~880 m altitude). The proximal part of the flow was still active. It appeared that a new thin lobe was overriding older lava in the main flow channel. An ash mantle on the upper E flank indicated that rockfalls (detected seismically) were occurring in this area. The flow was bent to the S at ~1,150 m altitude. It may be significant that the first lobe of this now compound flow terminated at about this point.

"Since 8 March (when seismic recording . . . was restored) seismicity has been dominated by relatively long-duration, low-frequency, spindle-shaped events. This activity is attributed to rockfalls on the margin of the active lava flow. Daily totals of these events ranged between ~90 and 300. Summit activity has continued to consist of moderate to strong emission of white vapour rich in sulphur dioxide."

Geologic Background. Bagana volcano, occupying a remote portion of central Bougainville Island, is one of Melanesia's youngest and most active volcanoes. This massive symmetrical cone was largely constructed by an accumulation of viscous andesitic lava flows. The entire edifice could have been constructed in about 300 years at its present rate of lava production. Eruptive activity is frequent and characterized by non-explosive effusion of viscous lava that maintains a small lava dome in the summit crater, although explosive activity occasionally producing pyroclastic flows also occurs. Lava flows form dramatic, freshly preserved tongue-shaped lobes up to 50 m thick with prominent levees that descend the flanks on all sides.

Information Contacts: C. McKee, RVO.


Concepcion (Nicaragua) — April 1989 Citation iconCite this Report

Concepcion

Nicaragua

11.538°N, 85.622°W; summit elev. 1700 m

All times are local (unless otherwise noted)


Strong fuming

During fieldwork 24 March, fuming obscured the interior of the summit crater. Most of the gas appeared to originate below a step in the crater's inner NE wall. A zone of weak fumaroles about 30 m below the rim on the inner E crater wall had a maximum surface temperature of 42°C (measured by an 8-14 micrometer bandpass infrared thermometer from a distance of about 300 m), suggesting gas temperatures of around 100°C.

Geologic Background. Volcán Concepción is one of Nicaragua's highest and most active volcanoes. The symmetrical basaltic-to-dacitic stratovolcano forms the NW half of the dumbbell-shaped island of Ometepe in Lake Nicaragua and is connected to neighboring Madera volcano by a narrow isthmus. A steep-walled summit crater is 250 m deep and has a higher western rim. N-S-trending fractures on the flanks have produced chains of spatter cones, cinder cones, lava domes, and maars located on the NW, NE, SE, and southern sides extending in some cases down to Lake Nicaragua. Concepción was constructed above a basement of lake sediments, and the modern cone grew above a largely buried caldera, a small remnant of which forms a break in slope about halfway up the N flank. Frequent explosive eruptions during the past half century have increased the height of the summit significantly above that shown on current topographic maps and have kept the upper part of the volcano unvegetated.

Information Contacts: C. Oppenheimer, Open Univ.


Galeras (Colombia) — April 1989 Citation iconCite this Report

Galeras

Colombia

1.22°N, 77.37°W; summit elev. 4276 m

All times are local (unless otherwise noted)


Ash emission and strong seismicity; area residents alerted

Frequent ash ejection in early May was accompanied by increased seismicity (figure 1) and SO2 emission. The strong seismic swarm that began 5 April at 1000 and saturated one seismograph was not associated with eruptive activity. COSPEC measurements the next day showed a sharp rise in SO2 emission to >1,200 metric tons/day (t/d) from 30-40 t/d 19-20 March [SO2 flux rose above 1,000 t/d on four days in April, see figure 12]. Glow was observed within the active (El Pinta) vent and by mid-April rocks 2 m below the rim had reached almost 600°C. The seismic swarm and glow prompted officials to increase the alert status to "yellow." A hazard map was published in a local newspaper and residents of areas designated as hazardous were urged to move, if possible, to a safer region. As of late April, a dense water-rich gas plume continued to rise 1-2 km above the crater and low-level seismicity persisted, but no deformation was evident.

Figure (see Caption) Figure 1. Number of recorded seismic events at Galeras, 27 February-5 May 1989. Courtesy of the Observatorio Vulcanológico de Colombia and the USGS Volcano Disaster Assistance Program.

4-5 May. After 10 hours of gradual increases in both background tremor (<1 mm peak to peak) and small long-period seismic events, ash was erupted between 0613 and 0830 on 4 May. Although emission rates were low, column heights reached 3.3 km. Ash composed of lithic particles and some plagioclase crystals fell towards the SW and E; a light dusting of ash fell on Pasto (population 350,000) at the volcano's E foot. Seismicity fluctuated between low and moderate levels for the next 11 hours before ash emission resumed at 1743. There were no recognizable immediate seismic precursors but the onset of the activity was accompanied by increased tremor. The rate of ash emission was again low, with the column pulsing at times to 2.9 km height. Both the plume and tremor diminished to low levels at 1855, but ash emission continued until 1940. Most of the ash was blown SW, and 1 mm of dust-sized tephra fell on Consaca, roughly 13 km WSW of the vent. EDM lines showed no change during the activity.

The ash eruption resumed at 0638, accompanied by an impulsive seismic signal, and tremor increased rapidly to an average peak-to-peak amplitude of 2 mm. The column grew to 1.2 km height by 0712, 1.9 km by 0726, and stabilized as a pulsing column to 2.8 km height between 0728 and 0825. The eruption column and tremor then decreased rapidly to low levels. The plume was broad and dense, dropping sheets of ash mainly within a few kilometers W of the vent. On the vent's E rim, the new deposit was ~25 cm thick, with the first layer a wet mud, probably from the lake that had occupied the bottom of the vent. Surge units were found in the deposit, as were lithic blocks that averaged about 15 cm in diameter. Only a thin film of ash fell at Consaca and other areas to the W and SW. However, the press reported that rescue workers evacuated ~2,000 residents of the Consacá area because of the ashfall. Activity around 1100 was accompanied by pulses of 4-5-Hz tremor and some long-period events. Ash was blown to the N, falling over La Florida and Nariño (8 km NNW and 7.5 km N of the vent). The EDM line across the caldera showed no change after the 4-5 May activity, but there may have been slight deflation on lines from the caldera rim to the active cone.

6 May. Ash emission resumed on 6 May at about 0900, producing a broad, pulsing column that fluctuated between 2.5 and 3.2 km height until darkness prevented further observations (about 1800). The rate of ash emission was intermediate between that of 4 May and the more vigorous activity of 5 May. Only low-level tremor and occasional long-period events accompanied the 6 May activity.

7-9 May. Harmonic tremor (1.3-1.4 Hz) began on 7 May at 0730 and continued for 38 minutes. Amplitudes reached 5 mm peak-to-peak and the tremor could be detected throughout the seismic net to 10 km from the vent. A similar signal reappeared at 0900, lasting for 40 minutes, and a pattern of intermittent tremor continued until 1400, with each episode building to larger amplitudes (as much as 1.5 cm peak-to-peak). The tremor typically occurred in 1.35-Hz packets with wavelengths of 10 seconds. The next-to-last tremor episode ceased abruptly after two large A-type events were recorded. During the last and strongest episode, many small A-type shocks were imbedded in the tremor. The A-type events were centered 3-3.5 km below the vent and 1-7 km to its S. The strong tremor was succeeded by bands of higher frequency tremor with much lower amplitude (<1 mm peak-to-peak). Minor ash emission continued 7 and 8 May. Ash was blown N on 7 May but did not reach La Florida, Nariño, or Jenoy (6 km NNE of the vent). The 8 May ash fell only near the crater. Frequent tremor episodes continued 8 May: 45 minutes of 2-3-Hz tremor that began gradually at 0614; low-frequency (1.54 Hz) banded tremor that began at 0800 and reached 23 mm amplitude about noon, decreasing in amplitude around 1540; amplitude increased again at 1600, to 20 mm, before declining at 1650 and stabilizing at 2-3 mm. Tremor decreased gradually from 9 May at 2000, to a maximum of 1 mm amplitude. Ash emission then stopped, and eruptive activity had not resumed as of 16 May.

The five days of ash emission prompted school closings and an increase in alert status to "orange" on 9 May. No immediate evacuations were ordered but officials asked residents to be ready for instructions if an eruption occurs. The Galeras Volcano Workshop that began 8 May with 50 participants from Central and South America will study the activity and hazards response.

Tephra deposits. An area of ~33 km2 was enclosed within the 3 mm ashfall isopach, including the TELECOM and television sites, 1.5 km to the S, and Nariño, 7.5 km N of the crater. The volume of tephra deposits was calculated at ~4 x 105 m3. The 7 cm of fine ash deposited at the S rim of El Pinta crater 19 February-3 May was overlain by more than 5 m of tephra that accumulated 4-9 May. A preliminary grain-size analysis shows a large fraction of fine (<1 mm) material (table 1). Some coarser layers of the early May tephra included scoria; in one layer (G) it was clearly altered, but in another horizon (E) it included abundant crystals in a very glassy matrix.

Table 1. Grain-size distribution of tephra deposited 4-9 May at Galeras, on the S rim of El Pinta crater. Thicknesses of individual layers (in cm) are supplemented by cumulative thickness of post-19 February tephra; only 7 cm of the section fell 19 February-3 May. The weight percent of six size fractions: <0.5, 0.5-1, 1-2, 2-4, 4-6.5, and >6.5 cm are shown. Courtesy of INGEOMINAS.

Layer ID Layer Thickness Cumulative Thickness 0-0.5 cm 0.5-1 cm 1-2 cm 2-4 cm 4-6.5 cm 6.5+ cm
B 3 cm 501 cm 26.6 32.2 27.3 8.6 5.5 --
C 7 cm 498 cm 96.0 2.3 1.0 0.5 0.3 --
D 12 cm 491 cm 44.6 27.3 20.4 6.1 1.6 --
E 22 cm 469 cm 5.0 4.1 6.1 7.9 30.9 46.0
F 32 cm 447 cm 38.8 33.0 17.9 5.2 5.2 --
G 43 cm 415 cm 6.9 8.1 7.5 6.5 6.5 24.1

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: H. Cepeda and B. Pulgarin, INGEOMINAS, Popayán; M. Calvache, F. Muñoz, and R. Méndez, INGEOMINAS, Manizales; I. Mejía and E. Parra, INGEOMINAS, Medellín; M. Mercado, Popayán; N. Banks, USGS; Deutche Presse-Agentur; Agence France-Presse.


Kilauea (United States) — April 1989 Citation iconCite this Report

Kilauea

United States

19.421°N, 155.287°W; summit elev. 1222 m

All times are local (unless otherwise noted)


Lava flows threaten houses

Kilauea's . . . eruption continued to feed lava through tubes into the ocean near Kupapau Point during April. Surface lava breakouts along the W tube were active 1-12 April and extended from ~300 m (top of the fault scarp) to 70 m altitude. Lava traveled along the W side of the flow field, entering the E margin of the Royal Gardens subdivision (figure 60). A major breakout on the 13th at ~500 m elevation remained active throughout the month. Large surface flows burned forest to the W and on 25 April passed within 50 m of an occupied home . . . . Access to the upper subdivision, as well as several houses, were threatened. By the end of the month, the flow had reached 60 m elevation and slowed, but was still active. Surface activity from the E tube at the top of the fault scarp was sporadic in early April but ceased after the 10th. The terminus of a breakout from the central tube was active just above the Kapaahu kipuka but stagnated after the 12th. The lava breakouts from the W tube on the 13th apparently lowered the magma supply to the E and central tubes, causing their flows to stagnate. The active portion of the seacoast bench that had formed since the 23 March collapse measured 160 x 60 m at the beginning of the month. Following two large collapses on 13 April (at 2024) and 22 April (at 2307), the bench continued to rebuild.

Figure (see Caption) Figure 60. Sketch map showing lava flows produced from Kupaianaha, July 1986-April 1989, and the current lava tube system. The April surface flows were mostly confined to the 1986-89 flow field. Courtesy of HVO.

The lava pond at Kupaianaha was 20-25 m below the rim during April. Lava was observed in the crater bottom of Pu`u `O`o . . . for most of the month, ranging from spatter to a sizeable lava pond that covered much of the crater floor. Gas pistoning events were witnessed at mid-month. By the 25th, only glowing holes in the rubble at the crater bottom could be seen.

Most of April's 18 strongly recorded seismic events . . . were tightly clustered beneath Kilauea's summit and S flank. Shallow events (0-5 km depth) continued to be recorded. The number of intermediate-depth long-period events beneath the summit decreased and developed a fluctuating pattern after a persistent high rate in March. Increasingly longer bursts of deep tremor (40-60 km depth), at near-regular time intervals during the first half of the month decreased thereafter. Low-level tremor continued beneath Pu`u `O`o and Kupaianaha. Relatively steady tremor amplitude beneath Pu`u `O`o was interrupted 13-17 April by short gas piston bursts and long intervals of banded tremor, correlated with increased activity in the crater. Tremor returned to a relatively steady state in the latter part of the month. Low-amplitude signals from lava entering the sea near Kupapau Point continued to be recorded.

Geologic Background. Kilauea, which overlaps the E flank of the massive Mauna Loa shield volcano, has been Hawaii's most active volcano during historical time. Eruptions are prominent in Polynesian legends; written documentation extending back to only 1820 records frequent summit and flank lava flow eruptions that were interspersed with periods of long-term lava lake activity that lasted until 1924 at Halemaumau crater, within the summit caldera. The 3 x 5 km caldera was formed in several stages about 1500 years ago and during the 18th century; eruptions have also originated from the lengthy East and SW rift zones, which extend to the sea on both sides of the volcano. About 90% of the surface of the basaltic shield volcano is formed of lava flows less than about 1100 years old; 70% of the volcano's surface is younger than 600 years. A long-term eruption from the East rift zone that began in 1983 has produced lava flows covering more than 100 km2, destroying nearly 200 houses and adding new coastline to the island.

Information Contacts: C. Heliker and R. Koyanagi, HVO.


Langila (Papua New Guinea) — April 1989 Citation iconCite this Report

Langila

Papua New Guinea

5.525°S, 148.42°E; summit elev. 1330 m

All times are local (unless otherwise noted)


Moderate ash ejections and glow

"The slightly stronger activity from Crater 2 reported in March continued in April, although fluctuations in the level of activity were evident. The volcano was quiet at the beginning of the month. Between 5 and 23 April, moderate ash emissions were observed, accompanied by weak to strong rumbling sounds. Most ash fell near the volcano. On most nights during this period, weak red glow was observed above Crater 2. Activity subsided between 24 and 28 April, but on the 29th and 30th returned to the levels seen at mid-month. Seismic records were unavailable between 14 and 30 April. During the first half of the month, seismicity was at a low level with only 0-1 explosion earthquakes/day."

Geologic Background. Langila, one of the most active volcanoes of New Britain, consists of a group of four small overlapping composite basaltic-andesitic cones on the lower eastern flank of the extinct Talawe volcano. Talawe is the highest volcano in the Cape Gloucester area of NW New Britain. A rectangular, 2.5-km-long crater is breached widely to the SE; Langila volcano was constructed NE of the breached crater of Talawe. An extensive lava field reaches the coast on the north and NE sides of Langila. Frequent mild-to-moderate explosive eruptions, sometimes accompanied by lava flows, have been recorded since the 19th century from three active craters at the summit of Langila. The youngest and smallest crater (no. 3 crater) was formed in 1960 and has a diameter of 150 m.

Information Contacts: C. McKee, RVO.


Ol Doinyo Lengai (Tanzania) — April 1989 Citation iconCite this Report

Ol Doinyo Lengai

Tanzania

2.764°S, 35.914°E; summit elev. 2962 m

All times are local (unless otherwise noted)


January inspection reveals no new lava

On 12 January, a field party heard magma bubbling at depth but saw no liquid lava. Photographs taken from the E rim by Mr. [Bay] Forrest indicated that hornitos within the crater remained unchanged since the last inspections in late November and mid-December 1988. The extent of lava that had entered the S crater in December had not changed, and the crater floors were covered by light-colored, older lava, with no signs of dark, fresh flows. The darkest feature was a cone (T10) near the base of the E wall. Although minor spattering similar to that observed at T4/T7 in June 1988 could have covered T10's surface, there had been no significant change in its shape. Fumaroles were visible on the E part of the saddle, but the crater walls and W part of the saddle were largely cloud-covered.

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: C. Nyamweru, Kenyatta Univ; B. Forrest, Rift Valley Academy, Kijabe, Kenya.


Lonquimay (Chile) — April 1989 Citation iconCite this Report

Lonquimay

Chile

38.379°S, 71.586°W; summit elev. 2832 m

All times are local (unless otherwise noted)


Continued tephra emission; cattle sickened by ash

The eruption . . . was continuing in early May. Eruption clouds in April and early May, composed mainly of dark brown ash and water vapor, rose 500-1,500 m from Navidad Crater. The number of recorded seismic events had declined to 2-3/day.

Estimates of the volume of the lava flow vary, and are made difficult by the flow's very irregular thickness, which has been increasing faster than the area covered by lava. Hugo Moreno estimated that through March ~150 x 106 m3 of lava had been extruded. The lava flow's W lobe essentially stopped advancing in mid-February, but the E front continued to move down the Lolco River valley. Little additional advance of the lava flow was noted in April and early May. The position of the flow as of 5 April is shown in figure 11.

Figure (see Caption) Figure 11. Map showing the lava flows as of 5 April 1989. Courtesy of Hugo Moreno Roa.

About 10,000 cattle have been suffering the effects of ashfall since December. Many have lost >100 kg in weight and are dying. Analyses by specialists at the Univ Austral determined that the animals are being affected by overdoses of fluorine from the ash. Ash has fallen in various directions (see table 5). The localities most affected are Maillin del Treile, El Naranjo (both roughly 20 km ESE of the active crater), and Comunidad Bernardo Nanco, home to about 80 families, the majority of which depend for their livelihoods on animal raising. Losses are estimated at about $2,000,000 (US). Local authorities and the Ministries of Agriculture and Health are taking emergency measures. Forest fires have burned valuable native trees, including coigüe (Nothfogus dombeyi) and araucaria (Araucaria araucana).

Geologic Background. Lonquimay is a small, flat-topped, symmetrical stratovolcano of late-Pleistocene to dominantly Holocene age immediately SE of Tolguaca volcano. A glacier fills its summit crater and spills down the S flank. It is dominantly andesitic, but basalt and dacite are also found. There is an E-W fissure, although the prominent NE-SW Cordón Fissural Oriental fissure zone cuts across the entire volcano, that produced a series of NE-flank vents and cinder cones, some of which have been the source of voluminous lava flows, including those during 1887-90 and 1988-90 that traveled up to 10 km.

Information Contacts: O. González-Ferrán, Univ de Chile; G. Fuentealba and P. Riffo, Univ de la Frontera; H. Moreno, Univ de Chile.


Manam (Papua New Guinea) — April 1989 Citation iconCite this Report

Manam

Papua New Guinea

4.08°S, 145.037°E; summit elev. 1807 m

All times are local (unless otherwise noted)


Incandescent ejections and vapor release

"Activity remained at a low inter-eruptive level during April. Both Southern and Main Craters released white vapours at weak to moderate rates. Blue vapour was also emitted from Southern Crater on 9, 13, and 22-23 April. Weak deep rumbling sounds from Southern Crater were heard occasionally 11-30 April. The summit was obscured by clouds on most nights, but during clear conditions on the 11th, glow and weak ejections of incandescent lava fragments were observed above Southern Crater. Volcano-seismicity remained at a normal inter-eruptive level with daily earthquake totals ranging between ~700 and 1,200. Tilt measurements showed no trends."

Geologic Background. The 10-km-wide island of Manam, lying 13 km off the northern coast of mainland Papua New Guinea, is one of the country's most active volcanoes. Four large radial valleys extend from the unvegetated summit of the conical 1807-m-high basaltic-andesitic stratovolcano to its lower flanks. These "avalanche valleys" channel lava flows and pyroclastic avalanches that have sometimes reached the coast. Five small satellitic centers are located near the island's shoreline on the northern, southern, and western sides. Two summit craters are present; both are active, although most historical eruptions have originated from the southern crater, concentrating eruptive products during much of the past century into the SE valley. Frequent historical eruptions, typically of mild-to-moderate scale, have been recorded since 1616. Occasional larger eruptions have produced pyroclastic flows and lava flows that reached flat-lying coastal areas and entered the sea, sometimes impacting populated areas.

Information Contacts: C. McKee, RVO.


Masaya (Nicaragua) — April 1989 Citation iconCite this Report

Masaya

Nicaragua

11.984°N, 86.161°W; summit elev. 635 m

All times are local (unless otherwise noted)


Lava lake drains; rockslides; gas emission

A local newspaper (the Barricada, citing Alain Creusot) reported that on 7 March, the level of the active lava lake in Santiago's crater had dropped considerably (since late February). Spatter was occasionally ejected outside the vent. The lake apparently drained on 9 March. Geologists visited the crater on 14 March and measured a temperature of 76.6°C on the surface of the frozen lake (all reported temperatures were measured by an 8-14 micrometer bandpass infrared thermometer from a distance of about 300 m unless otherwise stated). The two incandescent vents that first appeared on 23 February (14:02) were still present in the lake's N corner. The temperature of the hottest glowing vent was 667°C. On 16 and 18 March, fumes collected in the crater and limited observations. By 28 March, debris from rockslides on the SW inner wall of the crater had covered the site of the former lake, at least 175 m below the floor of Santiago Crater. Gas emission was strong. The two incandescent vents (maximum surface temperature 607°C) remained visible at night. On 12 April, the frequency of rockslides (audible about every 5 minutes) had increased significantly. Most occurred on the SW inner wall of the crater and many lasted for minutes. When geologists drove past Masaya on 18 April the amount of fuming appeared to have dramatically decreased.

Geologic Background. Masaya is one of Nicaragua's most unusual and most active volcanoes. It lies within the massive Pleistocene Las Sierras pyroclastic shield volcano and is a broad, 6 x 11 km basaltic caldera with steep-sided walls up to 300 m high. The caldera is filled on its NW end by more than a dozen vents that erupted along a circular, 4-km-diameter fracture system. The twin volcanoes of Nindirí and Masaya, the source of historical eruptions, were constructed at the southern end of the fracture system and contain multiple summit craters, including the currently active Santiago crater. A major basaltic Plinian tephra erupted from Masaya about 6500 years ago. Historical lava flows cover much of the caldera floor and have confined a lake to the far eastern end of the caldera. A lava flow from the 1670 eruption overtopped the north caldera rim. Masaya has been frequently active since the time of the Spanish Conquistadors, when an active lava lake prompted attempts to extract the volcano's molten "gold." Periods of long-term vigorous gas emission at roughly quarter-century intervals cause health hazards and crop damage.

Information Contacts: C. Oppenheimer, Open Univ.


Momotombo (Nicaragua) — April 1989 Citation iconCite this Report

Momotombo

Nicaragua

12.423°N, 86.539°W; summit elev. 1270 m

All times are local (unless otherwise noted)


Burning gases from fumaroles

A maximum gas temperature of 880°C was measured (by a thermocouple) at fumarole ##9, inside the crater, on 15 April. Flames that extended up to 40 cm from vents were visible at night. Most were pale orange but some gases burned with a blue flame.

Geologic Background. Momotombo is a young stratovolcano that rises prominently above the NW shore of Lake Managua, forming one of Nicaragua's most familiar landmarks. Momotombo began growing about 4500 years ago at the SE end of the Marrabios Range and consists of a somma from an older edifice that is surmounted by a symmetrical younger cone with a 150 x 250 m wide summit crater. Young lava flows extend down the NW flank into the 4-km-wide Monte Galán caldera. The youthful cone of Momotombito forms an island offshore in Lake Managua. Momotombo has a long record of Strombolian eruptions, punctuated by occasional stronger explosive activity. The latest eruption, in 1905, produced a lava flow that traveled from the summit to the lower NE base. A small black plume was seen above the crater after a 10 April 1996 earthquake, but later observations noted no significant changes in the crater. A major geothermal field is located on the south flank.

Information Contacts: C. Oppenheimer, Open Univ.


Niigata-Yakeyama (Japan) — April 1989 Citation iconCite this Report

Niigata-Yakeyama

Japan

36.921°N, 138.036°E; summit elev. 2400 m

All times are local (unless otherwise noted)


Increased steaming, small ash eruption

A white steam plume was rising from the volcano's upper E flank during observations by the staff of Takada Weather Station (from sites 10-20 km away) 1 May 1987-September 1988. Emissions gradually declined, and after a 9 November 1988 visit, no plume was observed.

Moderate steam emission was seen again on 30 March 1989, with a white vapor plume rising 100-150 m from 2 areas on the upper E flank. Steam from the upper NE flank rose about 30-50 m on 15 April. Four days later, steam with a small amount of ash was emitted to about 100-150 m above the upper E flank, the first sighting of a gray plume since May 1987. Observations from Sasagamine (about 8 km SE) on 26 April revealed gray plumes rising 250-300 m from many sites on the upper E flank. A 30 April steam plume, about 300-400 m high and blown 600 m by the wind (figure 2), was the highest since May 1987. Access to the volcano has been closed to tourists.

Figure (see Caption) Figure 2. Height of steam plumes at Niigata-Yake-yama, 1987-91. Courtesy of JMA.

Geologic Background. Niigata-Yakeyama, one of several Japanese volcanoes named Yakeyama ("Burning Mountain"), is a very young andesitic-to-dacitic lava dome in Niigata prefecture in central Honshu, near the Japan Sea. The small volcano rises to 2400 m and was constructed on a base of Tertiary mountains 2000 m high beginning about 3100 years ago. Three major magmatic eruptions took place in historical time, producing pyroclastic flows and surges and lava flows that traveled mainly down the Hayakawa river valley to the north and NW. The first of these eruptions took place about 1000 years ago (in 887 and possibly 989 CE) and produced the Hayakawa pyroclastic flow, which traveled about 20 km to reach the Japan Sea, and the massive Mae-yama lava flow, which traveled about 6.5 km down the Hayakawa river valley. The summit lava dome was emplaced during the 1361 eruption, and the last magmatic eruption took place in 1773 CE. Eruptive activity since 1773 has consisted of relatively minor phreatic explosions from several radial fissures and explosion craters that cut the summit and flanks of the dome.

Information Contacts: JMA.


Nyamuragira (DR Congo) — April 1989 Citation iconCite this Report

Nyamuragira

DR Congo

1.408°S, 29.2°E; summit elev. 3058 m

All times are local (unless otherwise noted)


Lava erupts from summit and E flank

An eruption that began on 23 April in Nyamuragira's summit crater was reported by the Vice Conservator of the Institut Zairois pour la Conservation de la Nature, Parc National des Virunga. On the 24th at 1418, three lava fountains emerged from a fissure on the SSE flank of the volcano. Incandescence was visible from the village of Gisenyi, Rwanda, roughly 30 km from the vent. The resulting lava flow passed between Kitazungurwa and Rugarambiro cones, diverted around Gitebe cone, and flowed along lava erupted in 1981-82 from Rugarambiro (figure 6). By the 26th, the flow had reached Nyasheke-South and was ~6 km from Kakomero, the base camp for climbers at the park entrance.

On the night of the 26th, lava emerged from the W side of the Kanamaharagi cone (formed during the 1905 eruption), building a new parasitic cone (also named Kanamaharagi) at ~1,860 m altitude. Lava fountains up to 200 m high and large amounts of tephra were emitted 30 April-1 May. As of 6 May, the volcano was still erupting.

Geologic Background. Africa's most active volcano, Nyamuragira, is a massive high-potassium basaltic shield about 25 km N of Lake Kivu. Also known as Nyamulagira, it has generated extensive lava flows that cover 1500 km2 of the western branch of the East African Rift. The broad low-angle shield volcano contrasts dramatically with the adjacent steep-sided Nyiragongo to the SW. The summit is truncated by a small 2 x 2.3 km caldera that has walls up to about 100 m high. Historical eruptions have occurred within the summit caldera, as well as from the numerous fissures and cinder cones on the flanks. A lava lake in the summit crater, active since at least 1921, drained in 1938, at the time of a major flank eruption. Historical lava flows extend down the flanks more than 30 km from the summit, reaching as far as Lake Kivu.

Information Contacts: S. Peyer and H. Peyer, Gisenyi, Rwanda; H-L. Hody, GEOVAR, Kigali, Rwanda.


Poas (Costa Rica) — April 1989 Citation iconCite this Report

Poas

Costa Rica

10.2°N, 84.233°W; summit elev. 2708 m

All times are local (unless otherwise noted)


Crater lake gone; explosions and molten sulfur ponds

Until mid-April, thermal activity remained similar to that observed in March, with boiling mud springs and vigorous fumaroles in the crater lake, which has been shrinking since early 1987. Two ponds of molten sulfur (115°C) have persisted since 16 March at the former site of small sulfur and mud cones 50 m SE of the center of the inner crater (figure 14). Small pyroclastic sulfur cones surrounded the lakes, collapsing occasionally.

Figure (see Caption) Figure 14. Sketch map of the inner crater at Poás and its features, April 1989. Courtesy of Gerardo Soto.

On 12 April, the crater lake was convecting vigorously, but shallow areas were visible. The lake level dropped about 2 m during the following week, and by 19 April only a few small mud pools remained. The characteristic geyser-type phreatic activity through the crater lake changed 18-19 April with the lake's near disappearance. Cypressoid vertical columns continuously rose about 25 m above the former center of the lake and began to build a mud/pyroclastic cone. On 19 April, small bursts of gas and mud that contained sulfur particles emerged through the mud surface to heights of about 10 m, rarely to 25-30 m. Steaming was continuous. Activity had increased slightly the next day, but magnetometer traverses that passed about 100 m from the active area showed no changes since the last measurements on 3 April. Phreatic bursts reached about 50 m height on 21 April. Using a thermocouple, Jorge Barquero measured a liquid temperature of 116°C in one of the sulfur ponds. On 22 April at around 1000, a dark mushroom-shaped column developed, convecting to 200-300 m height. Fine mud, sulfur, and burning gases (possibly hydrogen) were ejected until 1032. Fine yellow material fell on the W side of the inner crater [see also 14:05]. Ejection of lithic material stopped suddenly and the plume reverted to its normal white color. About 15 minutes later, continuous geysering of dark sediment and gas was observed for 2-3 minutes. Clouds obscured the summit at 1130. At 2100, after weather had cleared, the base of the plume was suddenly illuminated by a pink-orange light for about 2 minutes. No sounds were audible other than those accompanying the continuing phreatic activity. The light stopped suddenly and was thought to have been generated by burning gases.

During observations on 23 April, a thick white plume coalesced from numerous vents, two of which were discharging a mixture of white condensed steam and yellow sulfur. Dark cypressoid plumes were emitted every few seconds. At least one vent continuously discharged fine dark material. At 0717, a pink-orange light was again seen at the base of a continuous white plume on the SW side of the crater bottom. The light remained visible for 2.5 minutes, and geologists believed that it was generated by burning gases. A brightness temperature of 158°C was recorded (with an 8-14 micrometer bandpass infrared thermometer), but the measurement was made from almost 1 km distance and geologists suspected that the temperature was probably several hundred degrees higher. Phreatic activity from at least six of the vents expelled blocks to about 50 m height and occasionally to 100 m or more, generally vertically but sometimes obliquely. Most of the ejecta fell within 10-20 m of the vents, building cones to about 10 m height with funnel-shaped craters up to 5 m in diameter. The ejecta appeared dry and included blocks more than 20 cm across. Radiant temperatures of dark plumes were only about 80°C as measured from about 150 m away. Activity occasionally reached a level at which at least one of the six or more phreatic vents was erupting at a given time. Booming noises and sounds like a jet engine were occasionally heard. From nearer the vents, sounds like pistol shots were audible.

The two ponds of dark brown, very fluid, bubbling liquid, apparently sulfur, were about 50 cm below the former crater lake floor in steep-sided pits. One, roughly elliptical, was about 20 m across, while the other was dumbbell-shaped and about 10 m long. A terrace of solid sulfur had developed at the edge of the liquid, and the sides and rims of the pits were coated by bright yellow sulfur sublimates. A moderate amount of visible condensate rose from their surfaces and the smell of SO2 was strong. No surface burning was evident. Blocks of pale-colored altered rock (probably former lake sediments) floated on the sulfur ponds, suggesting a density substantially above 1 g/cm3. Remnants of the former crater lake had a maximum surface infrared radiometer temperature of 97°C.

Four geologists (G. Alvarado, M. Fernández, G. Soto, and D. Stevenson) descended to the bottom of the inner crater on 25 April. The activity had built at least three new cones, aligned with the sulfur ponds along a N30°W trend. The cones, 10-12 m high, were continuously active, emitting vertical columns of mud, sulfur, gases, and rocks to 30-70 m (occasionally 100 m) height for some seconds. Optical radiometer temperatures of the plumes were 75-90°C. Lesser thermal features (fumaroles, small hot lakes, and boiling mud springs) were found around the periphery of the cones. A small fault scarp, parallel to the line of cones, cut the sediments. The faulting was interpreted as the result of subsidence caused by the removal of the eruptive products, and a decrease in the internal pore pressure of the subsurface hydrothermal regime. At noon, the geologists were surprised by (but escaped unscathed from) a sudden eruption of sulfur, mud, and gases (some burning) that formed a thick vertical column nearly 400 m high, with a minimum radiometer temperature of 459°C. Sulfur and mud fell on the W wall of the crater and over the rim (toward Cerro Pelón). Other similar eruptions deposited greenish-gray mud within the crater.

The column from a larger eruption on 28 April between 0500 and 0600 reached an estimated height of 1.5-2 km and dropped fine mud to 2.5 km S of the source [see also 14:05]. The next day, the central mud cone (which had reached about 20 m height) ejected vertical columns of mud and sulfur to 200 m height. The small SW mud cone was in nearly continuous activity, emitting brown-gray lithic ash that was carried W by the wind. The gases were sulfurous, strongly yellow- and orange-colored, and rose in a vertical convective column to 350 m height. Eruptive characteristics were similar on 30 April and 1 May, but with columns to 1-1.5 km high on the 1st. The wind carried the fine lithic ash and mud toward the W onto various towns (including Bajos de Toro, Zarcero, and Sarchí).

Activity decreased 2 and 3 May. On the 3rd, ash was measured on the crater rim, reaching 1 mm thickness at point A (figure 15) and 2 mm at point B. Particles reached medium-grained ash size and were lithic, dominantly mud/clay granules of sulfide/sulfate sediments with a high percentage of solutes.

Figure (see Caption) Figure 15. Distribution of ash at Poás, and sites where thicknesses were measured 3 May 1989. Sketch and data from G. Soto.

Seismicity has visibly declined. Volcanic earthquakes totaled 4,240 in April, for a mean of 141/day (figure 16). Seismicity continued to be dominated by B-type events, although their number had decreased. The most significant change was the appearance of tremor episodes with durations of 4-10 minutes. The change in seismic pattern was interpreted by Morales et al. (1988) as the change from magma-water interaction in a medium that is not open (B-type signals) to one that is partially open (continuous train of B-type signals or tremors).

Figure (see Caption) Figure 16. Number of seismic events recorded/day at Poás by the Red Sismológica Nacional, April 1989. Courtesy of Mario Fernández.

Reference. Morales, L.D., Soley, J.F., Alvarado, G.E., Borgia, A., and Soto, G., 1988, análisise espectral de algunas señales sísmicas y su relación con la actividad de los volcanes Arenal y Poás, Costa Rica: Boletín del Observatorio Vulcanológico del Arenal, año 1, no. 2, p. 1-25.

Geologic Background. The broad, well-vegetated edifice of Poás, one of the most active volcanoes of Costa Rica, contains three craters along a N-S line. The frequently visited multi-hued summit crater lakes of the basaltic-to-dacitic volcano, which is one of Costa Rica's most prominent natural landmarks, are easily accessible by vehicle from the nearby capital city of San José. A N-S-trending fissure cutting the 2708-m-high complex stratovolcano extends to the lower northern flank, where it has produced the Congo stratovolcano and several lake-filled maars. The southernmost of the two summit crater lakes, Botos, is cold and clear and last erupted about 7500 years ago. The more prominent geothermally heated northern lake, Laguna Caliente, is one of the world's most acidic natural lakes, with a pH of near zero. It has been the site of frequent phreatic and phreatomagmatic eruptions since the first historical eruption was reported in 1828. Eruptions often include geyser-like ejections of crater-lake water.

Information Contacts: G. Soto, Mario Fernández, and Héctor Flores, UCR; Guillermo Alvarado, R. Barquero, and Ileana Boschini, ICE; David Stevenson and C.M.M. Oppenheimer, Open Univ.


Popocatepetl (Mexico) — April 1989 Citation iconCite this Report

Popocatepetl

Mexico

19.023°N, 98.622°W; summit elev. 5393 m

All times are local (unless otherwise noted)


New fumaroles and large sulfur deposits

During 1986-87, a seasonal, nearly circular lake occasionally occupied the summit crater. The lake's pH was 2-2.7 and the temperature was 30°C. Continuous fumarolic activity began in August 1988. A March 1989 summit visit by Alejandro Rivera Domínguez revealed large sulfur deposits in the main and inner craters. New fumaroles (not observed in 1987-88) on the main crater wall emitted high-pressure sulfurous gas and steam to 300 m. No significant microseismicity or tilt was detected.

The Grupo de Montañismo y Exploración de la UNAM, led by Prof. José Manuel Casanova Becerra, climbed the volcano on 9 April. More than 20 new fumaroles were observed on the outer S flank about 200 m below the crater rim. These vents (up to 1 m in diameter) were not observed when the group visited the area 2 years ago. Steam columns reached 20 m height and there was a mild sulfur odor. The steam's temperature was probably near the boiling point (at about 5,100 m altitude). The average altitude of the crater rim was 5,300 m with the crater bottom 340 m below. Increased steaming (common during the season) was observed inside the crater.

One seismograph is sited near the volcano . . . . Researchers hope to build an observatory 12 km from the volcano with telemetric data capture. Current monitoring is from the Meteorological Observatory, Geophysics Dept, Univ Autónoma de Puebla, and from Yancuitlalpan Village, S of the volcano.

Geologic Background. Volcán Popocatépetl, whose name is the Aztec word for smoking mountain, rises 70 km SE of Mexico City to form North America's 2nd-highest volcano. The glacier-clad stratovolcano contains a steep-walled, 400 x 600 m wide crater. The generally symmetrical volcano is modified by the sharp-peaked Ventorrillo on the NW, a remnant of an earlier volcano. At least three previous major cones were destroyed by gravitational failure during the Pleistocene, producing massive debris-avalanche deposits covering broad areas to the south. The modern volcano was constructed south of the late-Pleistocene to Holocene El Fraile cone. Three major Plinian eruptions, the most recent of which took place about 800 CE, have occurred since the mid-Holocene, accompanied by pyroclastic flows and voluminous lahars that swept basins below the volcano. Frequent historical eruptions, first recorded in Aztec codices, have occurred since Pre-Columbian time.

Information Contacts: S. De la Cruz-Reyna, UNAM; Alejandro Rivera Domínguez, Univ Autónoma de Puebla.


Rabaul (Papua New Guinea) — April 1989 Citation iconCite this Report

Rabaul

Papua New Guinea

4.271°S, 152.203°E; summit elev. 688 m

All times are local (unless otherwise noted)


Seismicity and deformation at background level

"Activity remained at a low (background) level in April. The total number of caldera earthquakes was 146. All of the events were small (ML 0.5-1.5) and none could be located. The daily earthquake count ranged from 0 to 17. Ground deformation measurements showed no significant changes."

Geologic Background. The low-lying Rabaul caldera on the tip of the Gazelle Peninsula at the NE end of New Britain forms a broad sheltered harbor utilized by what was the island's largest city prior to a major eruption in 1994. The outer flanks of the 688-m-high asymmetrical pyroclastic shield volcano are formed by thick pyroclastic-flow deposits. The 8 x 14 km caldera is widely breached on the east, where its floor is flooded by Blanche Bay and was formed about 1400 years ago. An earlier caldera-forming eruption about 7100 years ago is now considered to have originated from Tavui caldera, offshore to the north. Three small stratovolcanoes lie outside the northern and NE caldera rims. Post-caldera eruptions built basaltic-to-dacitic pyroclastic cones on the caldera floor near the NE and western caldera walls. Several of these, including Vulcan cone, which was formed during a large eruption in 1878, have produced major explosive activity during historical time. A powerful explosive eruption in 1994 occurred simultaneously from Vulcan and Tavurvur volcanoes and forced the temporary abandonment of Rabaul city.

Information Contacts: C. McKee, RVO.


Rincon de la Vieja (Costa Rica) — April 1989 Citation iconCite this Report

Rincon de la Vieja

Costa Rica

10.83°N, 85.324°W; summit elev. 1916 m

All times are local (unless otherwise noted)


Crater lake sampled

Geologists sampled the crater lake on 6 April. The lake temperature was 45°C, determined by throwing a bottle 100 m into the lake, measuring the resulting sample with a thermocouple, and applying a cooling correction.

Geologic Background. Rincón de la Vieja, the largest volcano in NW Costa Rica, is a remote volcanic complex in the Guanacaste Range. The volcano consists of an elongated, arcuate NW-SE-trending ridge that was constructed within the 15-km-wide early Pleistocene Guachipelín caldera, whose rim is exposed on the south side. Sometimes known as the "Colossus of Guanacaste," it has an estimated volume of 130 km3 and contains at least nine major eruptive centers. Activity has migrated to the SE, where the youngest-looking craters are located. The twin cone of 1916-m-high Santa María volcano, the highest peak of the complex, is located at the eastern end of a smaller, 5-km-wide caldera and has a 500-m-wide crater. A plinian eruption producing the 0.25 km3 Río Blanca tephra about 3500 years ago was the last major magmatic eruption. All subsequent eruptions, including numerous historical eruptions possibly dating back to the 16th century, have been from the prominent active crater containing a 500-m-wide acid lake located ENE of Von Seebach crater.

Information Contacts: David Stevenson, Open Univ.


Ruapehu (New Zealand) — April 1989 Citation iconCite this Report

Ruapehu

New Zealand

39.28°S, 175.57°E; summit elev. 2797 m

All times are local (unless otherwise noted)


Heat flow declines

Since February, no discrete eruptions have been reported although steam passively rising from Crater Lake has occasionally been witnessed. When geologists visited the volcano 21-22 March, slight upwelling in the N vent area formed broken sulfur slicks. Crater Lake's temperature had fallen to 32°C (a 10.5° drop over 23 days) representing a decline in heat flow to ~10% of its previous rate. Lake level had decreased to 100-150 mm below overflow. Lake chemistry was stable, showing little change in Mg/Cl since 11 January. Minor inflation was measured across the N crater rim. On 5 April, geologists observed slightly increased upwelling in the N vent area. The lake temperature was 31.3°C. N-rim inflation had largely disappeared. NZGS geologists noted that some previous pulses of inflation/deflation have been followed by renewed lake heating (or strong seismicity). Few tremor episodes and volcanic earthquakes were recorded on seismic records through . . . 5 April.

Geologic Background. Ruapehu, one of New Zealand's most active volcanoes, is a complex stratovolcano constructed during at least four cone-building episodes dating back to about 200,000 years ago. The 110 km3 dominantly andesitic volcanic massif is elongated in a NNE-SSW direction and surrounded by another 100 km3 ring plain of volcaniclastic debris, including the Murimoto debris-avalanche deposit on the NW flank. A series of subplinian eruptions took place between about 22,600 and 10,000 years ago, but pyroclastic flows have been infrequent. A single historically active vent, Crater Lake, is located in the broad summit region, but at least five other vents on the summit and flank have been active during the Holocene. Frequent mild-to-moderate explosive eruptions have occurred in historical time from the Crater Lake vent, and tephra characteristics suggest that the crater lake may have formed as early as 3000 years ago. Lahars produced by phreatic eruptions from the summit crater lake are a hazard to a ski area on the upper flanks and to lower river valleys.

Information Contacts: P. Otway, NZGS Wairakei.


Nevado del Ruiz (Colombia) — April 1989 Citation iconCite this Report

Nevado del Ruiz

Colombia

4.892°N, 75.324°W; summit elev. 5279 m

All times are local (unless otherwise noted)


Seismicity decreases

Seismic activity (high- and low-frequency earthquakes, long-period events, and tremor) significantly decreased in April, continuing a 2-month trend. SO2 emissions measured by COSPEC varied between 700 and 3,700 t/d with a monthly average of 1,800 t/d (figure 26). No significant changes in deformation were measured.

Figure (see Caption) Figure 26. Rates of SO2 emission measured by COSPEC at Ruiz, July 1986-April 1989. Courtesy of the Observatorio Vulcanológico de Colombia.

Geologic Background. Nevado del Ruiz is a broad, glacier-covered volcano in central Colombia that covers more than 200 km2. Three major edifices, composed of andesitic and dacitic lavas and andesitic pyroclastics, have been constructed since the beginning of the Pleistocene. The modern cone consists of a broad cluster of lava domes built within the caldera of an older edifice. The 1-km-wide, 240-m-deep Arenas crater occupies the summit. The prominent La Olleta pyroclastic cone located on the SW flank may also have been active in historical time. Steep headwalls of massive landslides cut the flanks. Melting of its summit icecap during historical eruptions, which date back to the 16th century, has resulted in devastating lahars, including one in 1985 that was South America's deadliest eruption.

Information Contacts: C. Carvajal, INGEOMINAS, Manizales.


Soputan (Indonesia) — April 1989 Citation iconCite this Report

Soputan

Indonesia

1.112°N, 124.737°E; summit elev. 1785 m

All times are local (unless otherwise noted)


Ashfall damages houses and crops

On 22 April, Soputan erupted for the first time since May 1985 (10:05), sending ash and lapilli to 1,000-1,500 m above the summit. Newspapers, quoting VSI director Subroto Modjo, reported that the eruption consisted of three explosions (at 1027, 1535, and 1752), the second of which ejected most of the tephra. Earthquakes were recorded by a nearby seismograph and were felt 25 km away. As much as 15-20 cm of ash (carried E by the wind) fell nearby in parts of Tumaratas (11 km NE of Soputan) and Taraitak, and in Ampreng, Raringis, and Noongan. At least 500 houses were damaged and three classrooms collapsed [but see 14:5] in Noongan, a gathering hall collapsed in Paslaten Langowan (13 km ENE), and many trees, especially in the Gunung Potong forest area (7 km E) were knocked down. No ashfall was reported in Manado, 45 km NNE. Damage to buildings and crops was estimated at about $114,000. As a precaution, hazard warning maps were given to residents. . . . No casualties or additional explosions had been reported as of 26 April.

Geologic Background. The Soputan stratovolcano on the southern rim of the Quaternary Tondano caldera on the northern arm of Sulawesi Island is one of Sulawesi's most active volcanoes. The youthful, largely unvegetated volcano rises to 1784 m and is located SW of Riendengan-Sempu, which some workers have included with Soputan and Manimporok (3.5 km ESE) as a volcanic complex. It was constructed at the southern end of a SSW-NNE trending line of vents. During historical time the locus of eruptions has included both the summit crater and Aeseput, a prominent NE-flank vent that formed in 1906 and was the source of intermittent major lava flows until 1924.

Information Contacts: OFDA; R. Austin, Englehard Engineering, USA.


Ulawun (Papua New Guinea) — April 1989 Citation iconCite this Report

Ulawun

Papua New Guinea

5.05°S, 151.33°E; summit elev. 2334 m

All times are local (unless otherwise noted)


Small ash emissions, minor seismic increases

"Mild, intermittent, eruptive activity continued in April. Ash emissions occurred 6, 8, 11, 20-22, and 28 April, but their ash content was low, and no significant ashfalls were reported. A strong correlation between activity and preceding heavy rainfall (as observed in March) was not evident. When not producing ash, the volcano emitted white vapours at moderate rates.

"For most of the month, the volcano-seismicity consisted of occasional, small, low-frequency events. Periods of low-amplitude, discontinuous and irregular tremor were recorded between 16 and 18 April. During the last week of April (perhaps correlating with a period of moderate rainfall) discrete events were more numerous, with periods of continuous and discontinuous irregular tremor of low-moderate amplitude."

Geologic Background. The symmetrical basaltic-to-andesitic Ulawun stratovolcano is the highest volcano of the Bismarck arc, and one of Papua New Guinea's most frequently active. The volcano, also known as the Father, rises above the north coast of the island of New Britain across a low saddle NE of Bamus volcano, the South Son. The upper 1000 m is unvegetated. A prominent E-W escarpment on the south may be the result of large-scale slumping. Satellitic cones occupy the NW and E flanks. A steep-walled valley cuts the NW side, and a flank lava-flow complex lies to the south of this valley. Historical eruptions date back to the beginning of the 18th century. Twentieth-century eruptions were mildly explosive until 1967, but after 1970 several larger eruptions produced lava flows and basaltic pyroclastic flows, greatly modifying the summit crater.

Information Contacts: C. McKee, RVO.


White Island (New Zealand) — April 1989 Citation iconCite this Report

White Island

New Zealand

37.52°S, 177.18°E; summit elev. 321 m

All times are local (unless otherwise noted)


Tephra ejections continue

Donald Duck vent has intermittently ejected tephra since its formation in late January in a zone of strong fumarolic activity ~100 m NE of eruptive vents in 1978 crater (figure 11). Photographs by Geoff Green of a 4 March eruption (at about 1500-1530) show a 500-m, vigorously convoluting ash column with an incandescent base. The eruption continued for at least 45 minutes, and ash emission also began from R.F. Crater. A larger eruption between 16 and 20 March, apparently not witnessed, presumably generated a larger column. During April, Donald Duck vent continued to eject ash and threw lithic blocks to as much as 200 m S. Intermittent ash, block, and bomb ejections also continued from R.F. Crater during the month. Two bomb-ejecting eruptions from R.F. Crater since 20 March were followed by widespread ash deposition.

During 26 April fieldwork, Donald Duck vent emitted voluminous clouds of light gray gas from a vent at the base of its N wall. New ash-covered scoria bombs (first noted in early April) were present S of Donald Mound, reaching more than l m in diameter near the 1978 Crater rim. R.F. Crater (appearing deep with vertical walls) discharged a dilute cloud of gas and fine pink ash. Ash covered much of the main crater floor and walls. Impact craters and lithic blocks a few days old were abundant around Donald Mound and Donald Duck vent. Congress Crater was quiet.

Fumarole temperatures and emissions had decreased at most vents except Noisy Nellie, which continued to emit voluminous high-pressure gas. Geologists suggested that Donald Duck and R.F. Crater have been capturing heat from surrounding areas, which are cooling as a result. General deflation, in progress since mid-l987, continued with strong subsidence of the Donald Mound area. Seismicity through late April remained similar to previous months, with microearthquakes recorded most days. Activity was conspicuously banded, with individual bands lasting 1.5-24 hours, containing up to 10 medium-frequency events/minute. Activity was most prolonged around 1-2 April. Small E-type events were recorded in April on the 3rd (0854) and 8th (0115, 0931, and 2008), while small A-types occurred most days. Very few B-types were recorded.

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: I. Nairn, NZGS Rotorua.

Atmospheric Effects

The enormous aerosol cloud from the March-April 1982 eruption of Mexico's El Chichón persisted for years in the stratosphere, and led to the Atmospheric Effects section becoming a regular feature of the Bulletin. Descriptions of the initial dispersal of major eruption clouds remain with the individual eruption reports, but observations of long-term stratospheric aerosol loading will be found in this section.

View Atmospheric Effects Reports

Special Announcements

Special announcements of various kinds and obituaries.

View Special Announcements Reports

Additional Reports

Reports are sometimes published that are not related to a Holocene volcano. These might include observations of a Pleistocene volcano, earthquake swarms, or floating pumice. Reports are also sometimes published in which the source of the activity is unknown or the report is determined to be false. All of these types of additional reports are listed below by subregion and subject.

Kermadec Islands


Floating Pumice (Kermadec Islands)

1986 Submarine Explosion


Tonga Islands


Floating Pumice (Tonga)


Fiji Islands


Floating Pumice (Fiji)


Andaman Islands


False Report of Andaman Islands Eruptions


Sangihe Islands


1968 Northern Celebes Earthquake


Southeast Asia


Pumice Raft (South China Sea)

Land Subsidence near Ham Rong


Ryukyu Islands and Kyushu


Pumice Rafts (Ryukyu Islands)


Izu, Volcano, and Mariana Islands


Acoustic Signals in 1996 from Unknown Source

Acoustic Signals in 1999-2000 from Unknown Source


Kuril Islands


Possible 1988 Eruption Plume


Aleutian Islands


Possible 1986 Eruption Plume


Mexico


False Report of New Volcano


Nicaragua


Apoyo


Colombia


La Lorenza Mud Volcano


Pacific Ocean (Chilean Islands)


False Report of Submarine Volcanism


Central Chile and Argentina


Estero de Parraguirre


West Indies


Mid-Cayman Spreading Center


Atlantic Ocean (northern)


Northern Reykjanes Ridge


Azores


Azores-Gibraltar Fracture Zone


Antarctica and South Sandwich Islands


Jun Jaegyu

East Scotia Ridge


Additional Reports (database)

08/1997 (SEAN 22:08) False Report of Mount Pinokis Eruption

False report of volcanism intended to exclude would-be gold miners

12/1997 (SEAN 22:12) False Report of Somalia Eruption

Press reports of Somalia's first historical eruption were likely in error

11/1999 (SEAN 24:11) False Report of Sea of Marmara Eruption

UFO adherent claims new volcano in Sea of Marmara

05/2003 (SEAN 28:05) Har-Togoo

Fumaroles and minor seismicity since October 2002

12/2005 (SEAN 30:12) Elgon

False report of activity; confusion caused by burning dung in a lava tube



False Report of Mount Pinokis Eruption (Philippines) — August 1997

False Report of Mount Pinokis Eruption

Philippines

7.975°N, 123.23°E; summit elev. 1510 m

All times are local (unless otherwise noted)


False report of volcanism intended to exclude would-be gold miners

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.


False Report of Somalia Eruption (Somalia) — December 1997

False Report of Somalia Eruption

Somalia

3.25°N, 41.667°E; summit elev. 500 m

All times are local (unless otherwise noted)


Press reports of Somalia's first historical eruption were likely in error

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.


False Report of Sea of Marmara Eruption (Turkey) — November 1999

False Report of Sea of Marmara Eruption

Turkey

40.683°N, 29.1°E; summit elev. 0 m

All times are local (unless otherwise noted)


UFO adherent claims new volcano in Sea of Marmara

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.


Har-Togoo (Mongolia) — May 2003

Har-Togoo

Mongolia

48.831°N, 101.626°E; summit elev. 1675 m

All times are local (unless otherwise noted)


Fumaroles and minor seismicity since October 2002

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 (see Caption) 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 (see Caption) 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 (see Caption) 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.


Elgon (Uganda) — December 2005

Elgon

Uganda

1.136°N, 34.559°E; summit elev. 3885 m

All times are local (unless otherwise noted)


False report of activity; confusion caused by burning dung in a lava tube

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/).