Logo link to homepage

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

Piton de la Fournaise (France) Eruptive episodes in February-March and June 2019; multiple fissures and lava flows

Semeru (Indonesia) Decreased activity after October 2018

Heard (Australia) Thermal hotspots continue during October 2018-March 2019 at the summit and on the upper flanks

Dukono (Indonesia) Numerous ash explosions from October 2018 through March 2019

Rincon de la Vieja (Costa Rica) Occasional weak phreatic explosions continue through February 2019

Turrialba (Costa Rica) Frequent passive ash emissions continue through February 2019

San Cristobal (Nicaragua) Weak ash explosions in January and March 2019

Semisopochnoi (United States) Minor ash explosions during September and October 2018

Asosan (Japan) Multiple brief ash emission events during April and May 2019; minor ashfall in adjacent villages

Nyamuragira (DR Congo) Lava lake reappears in central crater in April 2018; activity tapers off during April 2019

Tengger Caldera (Indonesia) New explosions with ash plumes from Bromo Cone mid-February-April 2019

Karangetang (Indonesia) Activity at two craters with the N crater producing ash plumes, avalanches, pyroclastic flows, and lava flows that reached the ocean in February 2019



Piton de la Fournaise (France) — July 2019 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)


Eruptive episodes in February-March and June 2019; multiple fissures and lava flows

Short pulses of intermittent eruptive activity have characterized Piton de la Fournaise, the large basaltic shield volcano on La Réunion Island in the western Indian Ocean, for several thousand years. For the last 20 years, frequent effusive basaltic eruptions have occurred on average twice per year. The activity is characterized by lava fountains and lava flows, and occasional explosive eruptions that shower blocks over the summit area and produce ash plumes. Almost all of the recent activity has occurred within the Enclos Fouqué caldera, although past eruptions in 1977, 1986, and 1998 have occurred at vents outside of the caldera. Four separate eruptive episodes were reported during 2018; from 3-4 April, 27 April-1 June, 13 July, and 15 September-1 November (BGVN 43:12, 43:09). Two episodes from 2019 during February-March and June are covered in this report, with information provided primarily by the Observatoire Volcanologique du Piton de la Fournaise (OVPF) as well as satellite instruments.

Piton de la Fournaise experienced two eruptions during November 2018-June 2019. The first lasted from 18 February to 10 March 2019, and the second episode was 11-13 June. The episode in February-March started consisted of multiple fissures opening on the E flank of the Dolomieu crater on 18 February with lava flows that traveled several hundred meters. After a brief pause, one new fissure opened nearby on 19 February and produced up to 3 million m3 of lava in a little over four days. Although the flow rate then declined, the eruption continued until 10 March. During the last three days, 7-10 March, two new fissures opened nearby and produced large volumes of lava, bringing the total eruptive volume to about 14.5 million m3. After little activity during April and May, a small eruption occurred on the SSE outer slope of Dolomieu crater that lasted for about 48 hours on 11-13 June; multiple small flows traveled about 1,000 m down the steep flank before ceasing. The MIROVA thermal anomaly graph of log radiative power clearly showed the abruptness of the beginning and ends of the last three eruptive episodes at Piton de la Fournaise from August 2018 through June 2019 (figure 165).

Figure (see Caption) Figure 165. The MIROVA graph of thermal energy from Piton de la Fournaise from 30 July 2018 through June 2019 shows the last three eruptive episodes at the volcano. From 15 September through 1 November 2018 fissures and flows were active on the SW flank of Dolomieu crater near Rivals crater (BGVN 43:12). Fissures opened on the E flank of the crater on 18 February 2019, and after a brief pause resumed on 19 February at the foot of Piton Madoré. Lava flows remained active until 10 March 2019. A short episode of lava effusion occurred on 11-12 June 2019 on the SSE outer slope of Dolomieu crater. Courtesy of MIROVA.

Activity during November 2018-March 2019. Following the end of the 15 September-1 November 2018 eruption, seismic activity immediately below the summit remained low (with only 20 shallow and two deep earthquakes during November). The inflationary signal recorded since the beginning of September stopped, and the OVPF deformation networks did not record any significant deformation. There were 35 shallow earthquakes (0-2 km depth) below the summit crater during December, and one deep earthquake. Only 12 shallow earthquakes and one deep earthquake (greater than 2 km below the surface) were reported in January.

OVPF reported an increase in CO2 concentrations beginning in December 2018, and noted the beginning of inflation on 13 February 2019. A seismic swarm of 379 earthquakes accompanied by minor but rapid deformation (less than 1 cm) was reported on 16 February 2019. A new seismic swarm of 208 earthquakes began early on 18 February with a much larger ground deformation (10 cm of elongation of the summit zone). A volcanic tremor indicative of the arrival of magma near the surface began at 0948 that morning. Webcams indicated that eruptive fissures had opened in the NE part of the Enclos Fouqué caldera. The onset of the eruption was marked by a sudden drop in CO2 flux which then stabilized. The eruptive sites were confirmed visually around 1130. Three fissures with actively flowing lava opened on the E flank of Dolomieu Crater; the fountains of lava were less than 30 m high. The front of the longest flow had reached 1,900 m elevation after one hour. The eruption lasted a little over 12 hours and was over by 2200 that evening; it covered about 150-200 m of the hiking trail to the summit.

Seismicity remained high after the event ended, and at 1500 on 19 February 2019 another seismic swarm of 511 deep earthquakes located under the E flank at about 2.5 km depth occurred. It was not accompanied by a significant amount of deformation. At 1710 tremor signals appeared on the observatory seismographs and the first gas plumes and lava ejection were observed at 1750 and 1912, respectively. During an overflight the next day (20 February), OVPF team members observed the new eruptive site at an elevation of 1,800 m at the foot of Piton Madoré. One fissure and one fountain were active at 0620 on 20 February and the flow front was at 1,300 m elevation (figure 166). During the night of 20-21 February the flow front crossed over the "Grandes Pentes" area in the eastern half of the Enclos Fouque (figure 167).

Figure (see Caption) Figure 166. The eruption which began on 19 February 2019 on the E flank of Dolomieu crater at Piton de la Fournaise produced a lava fountain and flow which traveled down at least 500 m of elevation by the next morning when this photo was taken at 0620 local time. Courtesy of and copyright by OVPF/IPGP (Bulletin d'activité du mercredi 20 février 2019 à 11h00, Heure locale).
Figure (see Caption) Figure 167. The active fissure at Piton de la Fournaise was producing lava fountains and an active flow during the evening of 20 February 2019. Overnight the flow crossed over the "Grandes Pentes" area of the caldera. Photo courtesy of and copyright by OVPF/IPGP (Bulletin d'activité du jeudi 21 février 2019 à 14H00, Heure locale).

OVPF reported on 22 February 2019 that 22 shallow earthquakes had been reported since the eruption began on 19 February. Surface flow rates estimated from satellite data, via the HOTVOLC system (OPGC - University of Auvergne), were between 2.5 and 15 m3/s. The quantity of lava emitted between 19 and 22 February was between 1 and 3 million m3. OVPF observed the growth of an eruptive cone that was filled with a small lava lake producing ejecta during a morning overflight on 22 February. A channelized flow moved downstream from the cone and split into two lobes about 1 km from (and 200 m below) the cone (figure 168). The split in the flow occurred near the Guyanin crater. The N flowing lobe, about 50 m wide, had an actively flowing front located at 1,320 m elevation; the incandescent flow was travelling over a recent flow (likely from the previous night). The S-flowing lobe spread to 200 m wide and split into two tongues 300 m SE of Guyanin crater.

Figure (see Caption) Figure 168. During an overflight on the morning of 22 February 2019 scientists from OVPF observed a growing spatter cone with a small lava lake at Piton de la Fournaise. A channelized flow moved downstream from the fissure and split into two flows. Photo courtesy of and copyright by OVPF/IPGP (Bulletin d'activité du vendredi 22 février 2019 à 13h30, Heure locale).

Incandescent ejecta from the cone was captured in a webcam image overnight on 22-23 February 2019 (figure 169). The rate of advance of the flow slowed significantly by 24 February, but the intensity of the eruptive tremor remained relatively constant. Mapping of the lava flow on 28 February carried out by the OI2 platform (OPGC - University Clermont Auvergne) from satellite data confirmed the slow progress of the flow after 24 February (300 m in 5 days) (figure 170). The flow front was located at 1,200 m elevation, and only the N arm was active; the lava had traveled about 2.2 km from the vent by 28 February.

Figure (see Caption) Figure 169. Incandescent ejecta from the eruptive cone at Piton de la Fournaise was captured in the webcam in the early hours of 23 February 2019. Courtesy of and copyright by OVPF/IPGP (Bulletin d'activité du samedi 23 février 2019 à 13h30, Heure locale).
Figure (see Caption) Figure 170. Contours of the lava flows at Piton de la Fournaise from 18-28 February 2019 were determined from satellite data by the OI2 platform (Université Clermont Auvergne), dated 18 (red) and 19 (blue) February (top image); 20 (green), 21 (red), 22 (blue), 27 (turquoise), and 28 (pink) February (bottom image). Courtesy of and copyright by OVPF/IPGP. Top: Bulletin d'activité du vendredi 22 février 2019 à 13h30 (Heure locale); bottom: Bulletin d'activité du jeudi 28 février 2019 à 16h30 (Heure locale).

Between 28 February and 1 March 2019 a third lobe of lava appeared flowing NE from the vent on the N side of the new flow area; it split into two lobes sometime on 1 March. Very little new lava was recorded on the other lobes. By 4 March the flow rate estimated by satellite data was about 7.5 m3/s. During a site visit on the morning of 5 March OVPF scientists sampled the N lobe of the flow and bombs and tephra near the cone, and acquired infrared and visible images. They noted the continued growth of the cone which still had an open vent at the summit and a base 100 m in diameter. It was 25 m high with a 50-m-wide eruptive vent at the top (figure 171). High-temperature gas emissions and strong Strombolian activity issued from the vent. Steam emissions were present around the base of the cone, suggesting the presence of lava tunnels. A single lobe of lava flowed N from the cone.

Figure (see Caption) Figure 171. The eruptive cone at Piton de la Fournaise on 5 March 2019 had a 100-m-diameter base, 25 m of vertical height, and 50-m-wide vent at the summit. Courtesy of and copyright by OVPF/IPGP, (Bulletin d'activité du mardi 5 mars 2019 à 17h30, Heure locale).

A new fissure that opened about 150 m from the main vent on the NW flank of Piton Madoré was first observed on the morning of 6 March (figure 172); OVPF concluded that it had opened late on 5 March. A small cone was forming and a new flow traveled N from the main eruptive site. At least six new emission points were noted the following morning (7 March) around the Piton Madoré. Poor weather prevented confirmation by aerial reconnaissance that day, but in a site visit on 8 March OVPF scientists determined that the new fissure from 5 March remained active; a small cone about 10 m high had two flow lobes on the W and N sides (figure 173). A fissure that opened on 7 March was located 300 m S of the 19 February vent and oriented E-W. It was very active on the morning of 8 March with two 50-m-high lava fountains (figure 174). Samples collected by OVPF indicated that the vents of 5 and 7 March produced lava of different compositions.

Figure (see Caption) Figure 172. A new fissure that opened about 150 m from the main vent on the NW flank of Piton Madoré at Piton de la Fournaise was first observed on the morning of 6 March 2019; OVPF concluded that it had opened late on 5 March. A small cone was forming on the flank of an old one and a new flow traveled N from the main eruptive site. Courtesy of OVPF/IPGP, copyright by Helicopter Coral (Bulletin d'activité du jeudi 7 mars 2019 à 15h00 Heure locale).
Figure (see Caption) Figure 173. The 5 March 2019 fissure at Piton de la Fournaise on the NW flank of Piton Madoré still had two active flow lobes emerging from it and heading N and W on 8 March 2019. Courtesy of and copyright by OVPF/IPGP (Monthly bulletin of the Piton de la Fournaise Volcanological Observatory, March 2019).
Figure (see Caption) Figure 174. A fissure that opened on 7 March 2019 at Piton de la Fournaise was located 300 m S of the 19 February vent and oriented E-W. It was very active on the morning of 8 March 2019 with two 50-m-high lava fountains. Courtesy of and copyright by OVPF/IPGP (Monthly bulletin of the Piton de la Fournaise Volcanological Observatory, March 2019).

There was a strong increase in the eruptive tremor intensity on 7 March, related to the opening of the two new fissures on 5 and 7 March (figure 175). As a result, the surface flow estimates made from satellite data increased significantly to high values greater than 50 m3/s, with the average values on 7-8 March of around 20-25 m3/s. The increased flow rates resulted in the flows traveling much greater distances. By the morning of 9 March the active flow had reached 650-700 m above sea level. The flow front had traveled about 1 km in 24 hours. Strong seismicity had been increasing under the summit zone for the previous 48 hours. After a phase of very strong surface activity observed overnight on 9-10 March that included lava fountains 50-100 m high (figure 176), surface activity ceased around 0630 on 10 March, and seismic activity decreased significantly. OVPF noted that sudden increases in seismicity and flow rates near the end of an eruption have occurred at about half of the eruptions at Piton de la Fournaise in recent years. Lava volumes emitted on the surface between 18 February and 10 March 2019 were estimated at about 14.5 million m3 (figure 177).

Figure (see Caption) Figure 175. An infrared view of the eruptive site on the E flank of Dolomieu crater at Piton de la Fournaise on 8 March 2019 clearly showed the original fissure from 19 February (bottom right of center), the fissure on Piton Madore that opened on 5 March (right) and the fissures that opened on 7 March (upper, right of center). The combined activity produced significant thermal and seismic activity at the volcano. Courtesy of and copyright by OVPF/IPGP (Bulletin d'activité du vendredi 8 mars 2019 à 17h00, Heure locale).
Figure (see Caption) Figure 176. Lava fountains 50-100 m high were the result of very strong surface activity observed overnight on 9-10 March 2019 at Piton de la Fournaise. Surface activity ceased around 0630 on 10 March, and seismic activity decreased significantly. Photo taken on 9 March 2019 around midnight from the RN2. Courtesy of OVPF/IPGP, copyright by A. Finizola LGSR/IPGP (Bulletin d'activité du dimanche 10 mars 2019 à 19h30 Heure locale).
Figure (see Caption) Figure 177. A sudden increase in the flow rate at the end of the 18 February-10 March 2019 eruption at Piton de la Fournaise was recorded by researchers at the Université Clermont Auvergne. OVPF noted this was typical of about half of the eruptions at Piton de la Fournaise. Courtesy of OVPF/IPGP, copyright by HOTVOLC, Université Clermont Auvergne (OVPF Monthly bulletin of the Piton de la Fournaise Volcanological Observatory, March 2019).

Significant SO2 plumes were captured by the TROPOMI instrument on the Sentinel 5-P satellite throughout the 18 February-10 March eruption (figure 178). After the surface eruption ceased, shallow seismicity continued at a lower rate of about 12 earthquakes per day. The end of the eruption (7-10 March) was accompanied by a marked deflation, interpreted by OVPF as the rapid emptying of the magma reservoir. Following the end of the eruption, inflation resumed for the rest of March but then ceased. Seismicity continued at a lower level during April with an average of six shallow earthquakes per day.

Figure (see Caption) Figure 178. Multiple days of high DU value SO2 plumes were recorded by the TROPOMI instrument on the Sentinel 5-P satellite during the 18 February-10 March 2019 eruption at Piton de la Fournaise. Top row: during 18, 21, and 22 February SO2 plumes drifted SE. Middle row: during 23, 24, and 25 February the wind direction changed from SE through S to SW and left a curling trail of SO2. Bottom row: 5, 7, and 8 March showed an increase in SO2 emissions that corresponded with increased seismicity and lava flow output before the eruption ceased.

Activity during May-June 2019. OVPF reported slight inflation near the summit beginning in early May, and an increase in CO2 concentration in the soil near Plaine des Cafres and Plaine des Palmistes. Strong shallow seismicity reappeared on 27 May 2019 and recurred on 30 and 31 May. Two small seismic swarms were measured on 31 May in the early morning. A new seismic swarm beginning at 0603 on 11 June accompanied by rapid deformation suggested a new eruption was imminent. A tremor near the summit area was first noted at 0635 local time; the webcams indicated a plume of gas, but poor visibility prevented evidence of fresh lava. Around 0930 that morning OVPF confirmed that five fissures had opened on the outer SSE slope of Dolomieu crater at elevations ranging from 2480 to 2025 m (figure 179). The flow fronts were not visible due to weather. Lava fountains under 30 m in height and lava flows were present in the three lowest fissures. The flows traveled rapidly down the steep flank of the crater (figure 180).

Figure (see Caption) Figure 179. Around 0930 on the morning of 11 June 2019 OVPF confirmed that five fissures had opened on the outer SSE slope of Dolomieu crater at Piton de la Fournaise at elevations ranging from 2480 to 2025 m. Courtesy of and copyright by OVPF-IPGP and Imazpress (Bulletin d'activité du mardi 11 juin 2019 à 11h00).
Figure (see Caption) Figure 180. Thermal imaging of the 11-12 June 2019 eruptive site at Piton de la Fournaise showed multiple streams of lava traveling rapidly down the steep flank from several fissures on 11 June 2019. Courtesy of and copyright by OVPF-IPGP (Bulletin d'activité du mardi 11 juin 2019 à 11h00).

The intensity of the eruptive tremor decreased throughout the day, and by 1530 only the lowest elevation fissure was still active (figure 181). The next afternoon (12 June) images in the OVPF webcam located in Piton des Cascades indicated the flow front was at about 1,200-1,300 m elevation. Seismographs indicated that the eruption stopped around 1200 on 13 June. Poor weather obscured visibility of the flow activity. Seismic activity decreased following the eruption, but appeared to increase again beginning on 21 June, with 10 events detected on 30 June. SO2 plumes were recorded in satellite data on 11 and 12 June 2019.

Figure (see Caption) Figure 181. The intensity of the eruptive activity at Piton de la Fournaise on 11 June 2019 decreased throughout the day, and by 1530 only the lowest elevation fissure was still active. Courtesy of and copyright by OVPF-IPGP (Bulletin d'activité du mardi 11 juin 2019 à 17h45 Heure locale).

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, 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/); Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, NASA Goddard Space Flight Center (NASA/GSFC), 8800 Greenbelt Road, Goddard, Maryland, USA (URL: https://so2.gsfc.nasa.gov/).


Semeru (Indonesia) — April 2019 Citation iconCite this Report

Semeru

Indonesia

8.108°S, 112.922°E; summit elev. 3657 m

All times are local (unless otherwise noted)


Decreased activity after October 2018

The ongoing eruption at Semeru has been characterized by numerous ash explosions and thermal anomalies, but activity apparently diminished in 2018 (BGVN 43:01 and 43:09); this decreased activity continued through at least February 2019. The current report summarizes activity from 24 August 2018 to 28 February 2019.

The Indonesian volcano monitoring agency, Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM), reported ongoing daily seismicity, dominated by explosion earthquakes and emission-related events from late November through February (figure 35). Ash plumes resulting in aviation advisories by the Darwin Volcanic Ash Advisory Centre (VAAC) were reported on 4, 6-7, and 19 September, and 12 October 2018. The next significant ash plume reported by the VAAC wasn't until 24 February 2019 (table 23).

Figure (see Caption) Figure 35. Seismicity recorded at Semeru during 28 November 2018-26 February 2019. Plot shows explosion earthquakes ('Letusan'), emission-related events ('Hembusan'), felt earthquakes ('Gempa Terasa'), local tectonic events ('Tektonic Lokal'), and distant tectonic events ('Tektonic Jauh'). Courtesy of PVMBG and MAGMA Indonesia.

Table 23. Summary of ash plumes at Semeru during 25 August 2018 through February 2019. The summit is at 3,657 m elevation. Data courtesy of Darwin VAAC.

Date Plume altitude (km) Plume drift Remarks
04 Sep 2018 4.3 W --
06-07 Sep 2018 4.3 SW --
19 Sep 2018 4 SSW Possible ash-and-steam plume.
12 Oct 2018 4.5 W Discrete eruption.
24 Feb 2019 4.3 W Discrete volcanic ash eruption.

Thermal anomalies using MODIS satellite instruments processed by the MODVOLC algorithm were only recorded on 26, 28, and 30 August 2018, and 22 and 31 October 2018. The MIROVA (Middle InfraRed Observation of Volcanic Activity) system detected numerous hotspots within 5 km of the volcano during August and early September, with a significant decrease in frequency through October (figure 36); only a few scattered hotspots were recorded from November 2018 through February 2019.

Figure (see Caption) Figure 36. MIROVA plot of thermal anomalies (Log Radiative Power) at Semeru during July 2018-February 2019. Courtesy of MIROVA.

Geologic Background. Semeru, the highest volcano on Java, and one of its most active, lies at the southern end of a volcanic massif extending north to the Tengger caldera. The steep-sided volcano, also referred to as Mahameru (Great Mountain), rises above coastal plains to the south. Gunung Semeru was constructed south of the overlapping Ajek-ajek and Jambangan calderas. A line of lake-filled maars was constructed along a N-S trend cutting through the summit, and cinder cones and lava domes occupy the eastern and NE flanks. Summit topography is complicated by the shifting of craters from NW to SE. Frequent 19th and 20th century eruptions were dominated by small-to-moderate explosions from the summit crater, with occasional lava flows and larger explosive eruptions accompanied by pyroclastic flows that have reached the lower flanks of the volcano.

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/).


Heard (Australia) — April 2019 Citation iconCite this Report

Heard

Australia

53.106°S, 73.513°E; summit elev. 2745 m

All times are local (unless otherwise noted)


Thermal hotspots continue during October 2018-March 2019 at the summit and on the upper flanks

Heard Island, in the Southern Indian Ocean, includes the large Big Ben stratovolcano and the smaller, apparently inactive, Mt. Dixon. Because of the island's remoteness, satellites are the primary monitoring tool. Big Ben has been active intermittently since 1910, and was active during October 2017-September 2018 (BGVN 43:10). Activity continued during October 2018-March 2019.

Satellite photos using Sentinel Hub showed hotspots every month between October 2018 and March 2019. Because the area was frequently covered by a heavy cloud layer, most of the hotspot signals were partially obscured. Though thermal anomalies are usually seen at summit vents, on 18 October 2018 an anomaly was present about 300 m down the E flank. Similarly, on 1 January 2019, a weak anomaly beginning about 200 m down the NW flank was about 300 m long (figure 40).

The MIROVA (Middle InfraRed Observation of Volcanic Activity) system detected three hotspots, two in October and one in early November 2018, all of low radiative power. There were no MODVOLC alert pixels during this period.

Figure (see Caption) Figure 40. Sentinel-2 L1C image of Heard Island's Big Ben volcano on 1 January 2019 one summit hotspot and an elongated thermal anomaly to the NW. Scale bar (bottom right) is 200 m. The photo was taken in atmospheric penetration view (bands 12, 11, and 8A), courtesy of Sentinel Hub Playground.

Geologic Background. Heard Island on the Kerguelen Plateau in the southern Indian Ocean consists primarily of the emergent portion of two volcanic structures. The large glacier-covered composite basaltic-to-trachytic cone of Big Ben comprises most of the island, and the smaller Mt. Dixon volcano lies at the NW tip of the island across a narrow isthmus. Little is known about the structure of Big Ben volcano because of its extensive ice cover. The historically active Mawson Peak forms the island's 2745-m high point and lies within a 5-6 km wide caldera breached to the SW side of Big Ben. Small satellitic scoria cones are mostly located on the northern coast. Several subglacial eruptions have been reported in historical time at this isolated volcano, but observations are infrequent and additional activity may have occurred.

Information Contacts: Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); 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/).


Dukono (Indonesia) — April 2019 Citation iconCite this Report

Dukono

Indonesia

1.693°N, 127.894°E; summit elev. 1229 m

All times are local (unless otherwise noted)


Numerous ash explosions from October 2018 through March 2019

The eruption at Dukono that began in 1933 has showered the area with ash from frequent explosions (BGVN 43:04, 43:12). The Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG), also known as the Center for Volcanology and Geological Hazard Mitigation (CVGHM), is responsible for monitoring this volcano.

This long-term pattern of intermittent ash explosions continued during October 2018-March 2019, with ash plumes rising to between 1.5 and 2.7 km altitude, or about 300-1,500 m above the summit (table 19). Although meteorological clouds often obscured views, satellite imagery captured typical ash plumes on 28 September 2018 (figure 10) and 5 February 2019 (figure 11). Instruments aboard NASA satellites (TROPOMI and OMPS) detected high levels of sulfur dioxide near or directly above the volcano on multiple days during January-March 2019. The Alert Level remained at 2 (on a scale of 1-4), and visitors were warned to remain outside of the 2-km exclusion zone.

Table 19. Monthly summary of reported ash plumes from Dukono for October 2018-March 2019. The direction of drift for the ash plume through each month was highly variable. Data courtesy of the Darwin VAAC and PVMBG.

Month Plume Altitude (km) Notable Plume Drift
Oct 2018 1.5-2.1 --
Nov 2018 1.5-2.1 --
Dec 2018 1.5-2.4 --
Jan 2019 1.8-2.1 --
Feb 2019 1.8-2.7 --
Mar 2019 1.5-2.4 --
Figure (see Caption) Figure 10. Satellite image from Sentinel-2 (LC1 natural color) of an ash plume at Dukono on 28 September 2018 with the plume blowing towards the NE. Courtesy of Sentinel Hub Playground.
Figure (see Caption) Figure 11. Satellite image from Sentinel-2 (LC1 natural color) of an ash plume at Dukono on 5 February 2019, with the plume blowing SW. Courtesy of Sentinel Hub Playground.

Geologic Background. Reports from this remote volcano in northernmost Halmahera are rare, but Dukono has been one of Indonesia's most active volcanoes. More-or-less continuous explosive eruptions, sometimes accompanied by lava flows, occurred from 1933 until at least the mid-1990s, when routine observations were curtailed. During a major eruption in 1550, a lava flow filled in the strait between Halmahera and the north-flank cone of Gunung Mamuya. This complex volcano presents a broad, low profile with multiple summit peaks and overlapping craters. Malupang Wariang, 1 km SW of the summit crater complex, contains a 700 x 570 m crater that has also been active during historical time.

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/); 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/); Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, NASA Goddard Space Flight Center (NASA/GSFC), 8800 Greenbelt Road, Goddard, Maryland, USA (URL: https://so2.gsfc.nasa.gov/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground).


Rincon de la Vieja (Costa Rica) — April 2019 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)


Occasional weak phreatic explosions continue through February 2019

Intermittent small phreatic explosions from the acid lake of Rincón de la Vieja's active crater has most recently occurred since 2011 (BGVN 42:08, 43:03, and 43:09). This activity continued through at least February 2019. The volcano is monitored by the Observatorio Vulcanologico Sismologica de Costa Rica-Universidad Nacional (OVSICORI-UNA), and the information below comes from its weekly bulletins between 18 August 2018 and 28 February 2019. Weather conditions often prevented webcam views and estimates of plume heights. The volcano was in Activity Level 3 throughout the reporting period (volcano erupting, steady state).

According to OVSICORI-UNA, two distinct, 2-minute-long explosions occurred on 31 August 2018 beginning at 0434 and 1305. Several hours after the eruption tremor became continuous but low-frequency long-period (LP) earthquakes ceased. OVSICORI-UNA reported a gas emission late on 7 September. An unconfirmed small phreatic explosion occurred on 11 September at 0634, and another on 17 September at 1014. The seismic record showed continuous background tremor and very sporadic LP earthquakes.

Intermittent background tremor was recorded during the first half of October, along with a few emissions and phreatic explosions. Deformation measurements during October showed a contraction between the N and S of the volcano, with subsidence. On 17 October there was another phreatic explosion, and thereafter tremor disappeared and seismicity decreased. On 23 and 27 October seismic stations signaled additional possible phreatic explosions.

OVSICORI-UNA reported that a series of explosions began at 1945 on 4 November and consisted of at least three 2-minute-long episodes. The next day at 1511 a plume of water vapor and diffuse gas, recorded by a webcam and visible to residents to the N, rose about 100 m above the crater rim and drifted W. On 9 November a 2-minute-long explosion began at 1703. Another explosion on 27 November at 0237 produced a plume of water vapor and gas that rose 600 m above the crater rim and drifted SW. A short 1-minute explosion began at 1054 on 3 December.

Based on OVSICORI-UNA weekly bulletins, activity remained stable in January 2019 with small-amplitude phreatic explosions on 11, 12, and 14 January. More energetic phreatomagmatic explosions on 17 and 20 January produced lahars. Several small-amplitude explosions were detected at the end of the month. During January, a few LPs, no VTs, and intermittent tremor were recorded.

OVSICORI-UNA reported that two small-scale explosions occurred on 1 February, along with possible events at 1906 and 1950 on 5 February and at 0120 on 6 February. An event at 0000 on 6 February was also recorded; the report noted that poor weather conditions prevented visual observations of the crater. On 16 and 17 February strong degassing was observed. No LPs were recorded, but two significant VTs were detected on 17 and 22 February near or under the crater.

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: Observatorio Vulcanologico Sismologica de Costa Rica-Universidad Nacional (OVSICORI-UNA), Apartado 86-3000, Heredia, Costa Rica (URL: http://www.ovsicori.una.ac.cr/).


Turrialba (Costa Rica) — April 2019 Citation iconCite this Report

Turrialba

Costa Rica

10.025°N, 83.767°W; summit elev. 3340 m

All times are local (unless otherwise noted)


Frequent passive ash emissions continue through February 2019

This report summarizes activity at Turrialba during September 2018-February 2019. During this period there was similar activity as described earlier in 2018 (BGVN 43:09), with occasional ash explosions and numerous, sometimes continuous, periods of gas-and-ash emissions (table 8). Data were provided by the Observatorio Vulcanologico Sismologica de Costa Rica-Universidad Nacional (OVSICORI-UNA).

Table 8. Ash emissions at Turrialba, September 2018-February 2019. Cloudy weather sometimes obscured observations. Maximum plume height is above the crater rim. Information courtesy of OVSICORI-UNA.

Date Time Max plume height Plume drift Remarks
27 Aug-05 Sep 2018 -- 100 m SW, W Continuous gas-and-ash emissions.
06 Sep 2018 -- -- -- Mostly gas, punctuated by small sporadic ash plumes.
10 Sep 2018 1210 300 m NW --
01-13 Sep 2018 -- -- -- Continuous gas-and-ash emissions.
17-18 Sep 2018 -- 300 m SW, NW --
27 Sep 2018 0915 200 m NW --
30 Sep-01 Oct 2018 -- 500 m NW, NE --
03 Oct 2018 -- -- -- Incandescence.
08 Oct 2018 0800 500 m N --
10-16 Oct 2018 -- 1,000 m Various Intermittent emissions; some explosions, including an energetic one on 14 Oct at 1712. Clouds prevented estimate of plume height.
17-23 Oct 2018 -- 200-500 m E, NW, SW Periodic gas-and-ash emissions. Frequent Strombolian events since 5 Oct.
25-30 Oct 2018 -- -- -- Periodic ash emissions when weather conditions allowed observations.
26 Oct 2018 0134 500 m NE Ashfall in neighborhoods of Coronado (San José, 35 km WSW) and San Isidro de Heredia (Heredia, 38 km W).
29 Oct 2018 0231 500 m NW --
30 Oct 2018 1406 500 m W --
24 Oct-01 Nov 2018 -- 500 m -- Continuous emissions.
01-06 Nov 2018 0530-0640 500 m SW --
02 Nov 2018 1523, 1703 500 m -- --
03 Nov 2018 0109 500 m -- Short (2-3 minutes) duration events. Ashfall reported in Coronado.
05 Nov 2018 0620 600 m NW --
06-11 Nov 2018 -- 500 m -- Low-level, continuous gas-and-ash emissions occasionally punctuated by energetic explosions that sent plumes as high as 500 m and caused ashfall in several areas downwind, including Cascajal de Coronado, Desamparados (35 km WSW), San Antonio, Guadalupe (32 km WSW), Sabanilla, San Pedro Montes de Oca, Moravia (31 km WSW), Heredia, and Coronado (San José, 35 km WSW). Weather prevented observations on 12 Nov.
13-19 Nov 2018 -- -- -- Periodic, passive ash emissions visible in webcam images or during cloudy conditions inferred from the seismic data.
22 Nov 2018 0710 100 m W --
23 Nov 2018 -- -- -- Frequent pulses of ash.
23-25 Nov 2018 -- 500 m -- Occasional Strombolian explosions ejected lava bombs deposited near the crater; residents of Cascajal de Coronado reported hearing several booming sounds.
26-27 Nov 2018 -- -- -- Passive emissions with small quantities of ash visible. Minor ashfall in San Jose (Cascajal de Coronado and Dulce Nombre), San Pedro Montes de Oca, and neighborhoods of Heredia.
28 Nov-03 Dec 2018 -- 500 m N, NW, SW Ashfall in Santo Domingo (36 km WSW) on 2 Dec.
05 Dec 2018 -- -- -- Minor emission.
06 Dec 2018 -- -- S Emission.
08 Dec 2018 0749 500 m NW --
09 Dec 2018 -- 1,000 m -- Ashfall in areas of Valle Central.
10 Dec 2018 -- -- -- Emissions periodically observed during periods of clear viewing. Ashfall in Moravia (31 km WSW) and Santa Ana, and residents of Heredia noted a sulfur odor.
11-12 Dec 2018 -- 500 m NW, SW The Tico Times stated some flights were delayed at San Jose airport, 67 km away.
13 Dec 2018 -- -- -- Pulsing ash emissions; ashfall in Guadalupe (32 km WSW) and Valle Central.
14-16 Dec 2018 -- -- W, SW Emissions with diffuse amounts of ash.
05-06 Jan 2019 0815 -- -- Increased after midnight on 6 Jan.
28 Jan-04 Feb 2019 -- -- -- Minor, sporadic ash emissions rose to low heights during most days.
01 Feb 2019 0640 1,500 m NW --
08 Feb 2019 0540 200 m -- Sporadic ash emissions for more than one hour.
11 Feb 2019 -- -- -- Very small ash emission.
13-15 Feb 2019 200-300 m NW, W, SW Almost continuous gas emissions with minor ash content.
15 Feb 2019 1330 1,000 m W --
18 Feb 2019 1310 500 m W --
21 Feb 2019 -- 300 m NW Frequent ash pulses.
22-24 Feb 2019 -- 300 m NW, SW Frequent ash emissions of variable intensity and duration. On 22 Feb ash fell in Santa Cruz (31 km WSW) and Santa Ana, and a sulfur odor was evident in Moravia.
28 Feb 2019 1050 500 m SW Ash pulses.

According to OVSICORI-UNA's annual summary for 2018, a slow decline in activity occurred after the volcano reached its highest emission rate during 2016. Activity during 2018 was consistent with an open system, generating frequent passive ash emissions. The volcano emitted ash on 58% of the days during the year. Some explosions were large enough to eject ballistics more than 400 m around the crater. Typical activity can be seen in a photo from 11 September 2018 (figure 50) and satellite imagery on 7 November 2018 (figure 51).

Figure (see Caption) Figure 50. Photo of an ash explosion at Turrialba taken on 11 September 2018. Courtesy of Red Sismologica Nacional (RSN: UCR-ICE), Universidad de Costa Rica.
Figure (see Caption) Figure 51. Sentinel-2 satellite image of an ash emission from Turrialba on 7 November 2018, taken in natural color (gamma adjusted). Courtesy of Sentinel Hub Playground.

During January into early February 2019, passive ash emissions continued irregularly and with less intensity and duration. Emissions sometimes lacked ash. In their report of 4 February 2019, OVSICORI-UNA indicated that passive ash emissions were weak and slow. For the rest of February, they characterized ash emissions as frequent, but of low intensity.

Seismic activity. On 1 November 2018 OVSICORI-UNA reported that seismicity remained high, and involved low-amplitude banded volcanic tremor along with long-period (LP) and volcano-tectonic (VT) earthquakes. In late January-early February 2019, OVSICORI-UNA reported that seismicity remained relatively stable, although a small increase was associated with the hydrothermal system. VT earthquakes were absent, and tremors had decreased in both energy and duration. The number of low-frequency LP volcanic earthquakes remained stable, although they had decreasing amplitudes. No explosions were documented, and emissions were weak and had short durations and very dilute ash content.

Thermal anomalies. No thermal anomalies were recorded during the reporting period using MODIS satellite instruments processed by MODVOLC algorithm. The MIROVA (Middle InfraRed Observation of Volcanic Activity) system detected five scattered hotspots during September-October 2018, none during November-December 2018, and two during January-February 2019. All were within 2 km of the volcano and of low radiative power.

Gas measurements. Significant sulfur dioxide levels near the volcano were recorded by NASA's satellite-borne ozone instruments only on 29 September 2018 (both NPP/OMPS and Aura/OMI instruments) and on 11 February 2019 (Sentinel 5P/TROPOMI instrument). OVSICORI-UNA's gas measuring instruments were compromised in September 2018 through January 2019 due to vandalism. In early February, however, they detected hydrogen sulfide for the first time since 2016.

Geologic Background. Turrialba, the easternmost of Costa Rica's Holocene volcanoes, is a large vegetated basaltic-to-dacitic stratovolcano located across a broad saddle NE of Irazú volcano overlooking the city of Cartago. The massive edifice covers an area of 500 km2. Three well-defined craters occur at the upper SW end of a broad 800 x 2200 m summit depression that is breached to the NE. Most activity originated from the summit vent complex, but two pyroclastic cones are located on the SW flank. Five major explosive eruptions have occurred during the past 3500 years. A series of explosive eruptions during the 19th century were sometimes accompanied by pyroclastic flows. Fumarolic activity continues at the central and SW summit craters.

Information Contacts: Observatorio Vulcanologico Sismologica de Costa Rica-Universidad Nacional (OVSICORI-UNA), Apartado 86-3000, Heredia, Costa Rica (URL: http://www.ovsicori.una.ac.cr/); Red Sismologica Nacional (RSN) a collaboration between a) the Sección de Sismología, Vulcanología y Exploración Geofísica de la Escuela Centroamericana de Geología de la Universidad de Costa Rica (UCR), and b) the Área de Amenazas y Auscultación Sismológica y Volcánica del Instituto Costarricense de Electricidad (ICE), Costa Rica (URL: https://rsn.ucr.ac.cr/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); 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://hotspot.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/); Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, NASA Goddard Space Flight Center (NASA/GSFC), 8800 Greenbelt Road, Goddard, Maryland, USA (URL: https://so2.gsfc.nasa.gov/); Costa Rica Star (URL: https://news.co.cr); The Tico Times (URL: https://ticotimes.net).


San Cristobal (Nicaragua) — April 2019 Citation iconCite this Report

San Cristobal

Nicaragua

12.702°N, 87.004°W; summit elev. 1745 m

All times are local (unless otherwise noted)


Weak ash explosions in January and March 2019

San Cristóbal has produced occasional weak explosions since 1999, with intermittent gas-and-ash emissions. The only reported explosion during the first half of 2018 was on 22 April, the first since November 2017 (BGVN 43:03). The current report covers activity between 1 August 2018 and 1 May 2019. The volcano is monitored by the Instituto Nicaragüense de Estudios Territoriales (INETER).

According to INETER, a series of explosions occurred on 9 January 2019 that lasted several hours. INETER stated that one explosion occurred at 1643; the Washington VAAC's first advisory stated that an explosion occurred at 1145 (local time). The weak explosions, which occurred after a period of heightened seismic activity, generated an ash plume that reached 200 m above the edge of the crater and drifted W. The Washington VAAC reported volcanic ash plumes on 10-11 January extending about 92 km SW, and on 24-25 January extending about 185 km WSW. A low-energy explosion was detected by the seismic network at 1550 on 4 March 2019. The event produced a gas-and-ash plume that rose 400 m above the crater rim and drifted SW.

Monitoring data reported by INETER (table 6) showed elevated levels of seismicity during October 2018 through January 2019. Sulfur dioxide was also measured at higher levels in January 2019.

Table 6. Monthly sulfur dioxide measurements and seismicity reported at San Cristóbal during August 2018-March 2019. "Most" indicates that type of seismicity was dominant that month. Data courtesy of INETER.

Month Average SO2 Total earthquakes Degassing-type earthquakes Volcano-tectonic (VT) earthquakes
Aug 2018 461 t/d 6,464 6,147 251
Sep 2018 893 t/d 9,659 9,586 73
Oct 2018 269 t/d 11,698 3,509 8,189
Nov 2018 -- 19,593 19,586 7
Dec 2018 -- 30,901 -- Most
Jan 2019 1,286 t/d 11,504 Most Very few
Feb 2019 695 t/d 3,470 Most Very few
Mar 2019 -- 3,882 Most Very few

Geologic Background. The San Cristóbal volcanic complex, consisting of five principal volcanic edifices, forms the NW end of the Marrabios Range. The symmetrical 1745-m-high youngest cone, named San Cristóbal (also known as El Viejo), is Nicaragua's highest volcano and is capped by a 500 x 600 m wide crater. El Chonco, with several flank lava domes, is located 4 km W of San Cristóbal; it and the eroded Moyotepe volcano, 4 km NE of San Cristóbal, are of Pleistocene age. Volcán Casita, containing an elongated summit crater, lies immediately east of San Cristóbal and was the site of a catastrophic landslide and lahar in 1998. The Plio-Pleistocene La Pelona caldera is located at the eastern end of the complex. Historical eruptions from San Cristóbal, consisting of small-to-moderate explosive activity, have been reported since the 16th century. Some other 16th-century eruptions attributed to Casita volcano are uncertain and may pertain to other Marrabios Range volcanoes.

Information Contacts: Instituto Nicaragüense de Estudios Territoriales (INETER), Apartado Postal 2110, Managua, Nicaragua (URL: http://webserver2.ineter.gob.ni/vol/dep-vol.html); 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).


Semisopochnoi (United States) — February 2019 Citation iconCite this Report

Semisopochnoi

United States

51.93°N, 179.58°E; summit elev. 1221 m

All times are local (unless otherwise noted)


Minor ash explosions during September and October 2018

The remote Semisopochnoi comprises the uninhabited volcanic island of the same name, ~20 km in diameter, in the Rat Islands group of the western Aleutians (figure 1). Plumes had been reported several times in the 18th and 19th centuries, and most recently observed in April 1987 from Sugarloaf Peak (SEAN 12:04). The volcano is dominated by an 8-km diameter caldera that contains a small lake (Fenner Lake) and a number of post-caldera cones and craters. Monitoring is done by the Alaska Volcano Observatory (AVO) using an on-island seismic network along with satellite observations and lightning sensors. An infrasound array on Adak Island, about 200 km E, may detect explosive emissions with a 13 minute delay if atmospheric conditions permit.

On 16 September 2018 increased seismicity was detected at 0831, prompting AVO to raise the Aviation Color Code (ACC) to Yellow and Volcano Alert Level (VAL) to Advisory. Retrospective analysis of satellite data acquired on 10 September revealed small ash deposits on the N flank of Mount Cerberus, possibly associated with two bursts of tremor recorded on 8 September (figure 5). This new information, coupled with intensifying seismicity and a strong tremor signal recorded at 1249 on 17 September, resulted in AVO raising the ACC to Orange and the VAL to Watch. Seismicity remained elevated on 18 September with nearly constant tremor recorded by local sensors. At the same time, no ash emissions were observed in cloudy satellite images and no eruptive activity was recorded on regional pressure sensors at Adak.

Figure (see Caption) Figure 1. Minor ash deposits can be seen on the south and west flanks of the N cone of Mount Cerberus, Semisopochnoi Island, in this ESA Sentinel-2 image from 1200 on 10 September 2018. Also note probable minor steam emissions obscuring the crater of the N cone. Image courtesy of AVO.

During 19-25 September 2018 seismicity remained elevated, alternating between periods of continuous and intermittent bursts of tremor. Tremor bursts at 1319 on 21 September and at 1034 on 22 September produced airwaves detected on a regional infrasound array on Adak Island; no ash emissions were identified above the low cloud deck in satellite data, and the infrasound detections likely reflected an atmospheric change instead of volcanic activity.

Seismicity remained elevated during 3-9 October 2018, with intermittent bursts of tremor. No volcanic activity was detected in infrasound or satellite data. On 11 October satellite data indicated partial erosion of a tephra cone in the crater of Cerberus's N cone. A crater lake about 90 m in diameter filled the vent. The data also suggested that the vent had not erupted since 1 October. Seismicity remained elevated and above background levels. The next day AVO lowered the Aviation Color Code to Yellow and the Volcano Alert Level to Advisory, noting the recent satellite data results and lack of tremor recorded during the previous week. AVO reported that unrest continued during 11-24 October.

An eruptive event began at 2047 on 25 October 2018, identified based on seismic data; strong volcanic tremor lasted about 20 minutes and was followed by 40 minutes of weak tremor pulses. A weak infrasound signal was detected by instruments on Adak Island. The Aviation Color Code was raised to Orange (the second highest level on a four-color scale) and Volcano Alert Level was raised to Watch (the second highest level on a four-level scale). A dense meteorological cloud deck prevented observations below 3 km, but a diffuse cloud was observed in satellite data rising briefly above the cloud deck, though it was unclear if it was related to eruptive activity. Tremor ended after the event, and seismicity returned to low levels.

Small explosions were detected by the seismic network at 2110 and 2246 on 26 October 2018, and 0057 and 0603 on 27 October. No ash clouds were identified in satellite data, but the volcano was obscured by high meteorological clouds. Additional small explosions were detected in seismic and infrasound data during 28-29 October; no ash clouds were observed in partly-cloudy-to-cloudy satellite images.

AVO reported on 31 October 2018 that unrest continued. Two small explosions were detected, one just before 0400 and the other around 1000. Satellite views were obscured by clouds at the time, and no ash clouds were observed. Unrest continued through 1 November, at which time the satellite link and the seismic line failed. On 21 November the ACC was lowered to Yellow and the VAL was lowered to Advisory.

Geologic Background. Semisopochnoi, the largest subaerial volcano of the western Aleutians, is 20 km wide at sea level and contains an 8-km-wide caldera. It formed as a result of collapse of a low-angle, dominantly basaltic volcano following the eruption of a large volume of dacitic pumice. The high point of the island is 1221-m-high Anvil Peak, a double-peaked late-Pleistocene cone that forms much of the island's northern part. The three-peaked 774-m-high Mount Cerberus volcano was constructed during the Holocene within the caldera. Each of the peaks contains a summit crater; lava flows on the northern flank of Cerberus appear younger than those on the southern side. Other post-caldera volcanoes include the symmetrical 855-m-high Sugarloaf Peak SSE of the caldera and Lakeshore Cone, a small cinder cone at the edge of Fenner Lake in the NE part of the caldera. Most documented historical eruptions have originated from Cerberus, although Coats (1950) considered that both Sugarloaf and Lakeshore Cone within the caldera could have been active during historical time.

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/).


Asosan (Japan) — July 2019 Citation iconCite this Report

Asosan

Japan

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

All times are local (unless otherwise noted)


Multiple brief ash emission events during April and May 2019; minor ashfall in adjacent villages

Japan's 24-km-wide Asosan caldera on the island of Kyushu has been active throughout the Holocene. Nakadake has been the most active of 17 central cones within the caldera for 2,000 years. Historical eruptions have been primarily basaltic to basaltic-andesitic ash eruptions, with periodic Strombolian activity, all from Nakadake Crater 1. The most recent major eruptive episode began in late November 2014 and continued through 1 May 2016. Another eruption, with the largest ash plume in 20 years, occurred on 8 October 2016. Asosan remained quiet until renewed activity from Crater 1 began in mid-April 2019; it is covered in this report, through the end of June 2019. The Japan Meteorological Agency (JMA) provides monthly reports of activity; the Tokyo Volcanic Ash Advisory Center (VAAC) issues aviation alerts reporting on possible ash plumes.

Asosan remained quiet during 2017 and 2018 with steam plumes rising a few hundred meters from Crater 1 and low levels of SO2 emissions; a warm acidic lake was present within the crater. Fumarolic activity from two areas on the S and SW wall of the crater rim generated occasional thermal anomalies in satellite data and incandescence at night. A brief period of increased seismicity was reported in mid-March 2019. An increase in seismic amplitude on 14 April 2019 preceded a small explosion on 16 April; it produced an ash plume which rose 200 m above the crater rim and drifted NW. It was followed by additional small explosions on 19 April. A new explosion on 3 May produced minor ashfall in adjacent communities; ash emissions were reported multiple times during May with plumes reaching 1,400 m above the crater rim. No additional ash emissions were reported in June.

Activity during 2017 and 2018. JMA reported that no eruptions occurred during 2017. Amplitudes of volcanic tremor increased somewhat during March but were generally low for the rest of the year. The earthquake hypocenters were mostly located near the active crater at around sea level. SO2 emissions were slightly less than 1,000 tons per day (t/d) from January through April; for the rest of the year they ranged from 600 to 2,500 t/d. The Alert Level had been lowered from 2 to 1 on 7 February 2017 where it remained throughout the year. Steam plumes generally rose no more than 600 m above the active crater rim (figure 42). JMA noted that from January to June they often observed crater incandescence at night with a high-sensitivity surveillance camera; Sentinel-2 satellite images also captured thermal anomalies a few times (figure 43). The green lake inside the crater persisted throughout the year with water temperatures of 50-60°C. Two fumaroles were present with high-temperature gas emissions on the SW and S crater walls. Temperatures at the S crater wall were over 600°C from February to May; they decreased to 320-560°C during the rest of the year (figure 44). Sulfur deposits were visible around the SW crater wall fumarole during July.

Figure (see Caption) Figure 42. Steam plumes that rose around 600 m above Nakadake Crater 1 at Asosan were typical activity throughout 2017. Images taken with JMA webcam on 9 June (top left), 22 August (top right), 12 November (bottom left), and 20 December (bottom right) 2017. Courtesy of JMA (Aso volcano monthly activity reports, Fukuoka District Meteorological Observatory, Regional volcano monitoring and warning center).
Figure (see Caption) Figure 43. Sentinel-2 images captured thermal anomalies at the S rim of the green lake at Asosan's Nakadake Crater 1 on 16 February (left) and 27 May 2017 (right). JMA reported that incandescence was occasionally visible during the night from January-June from the same area. Courtesy of Sentinel Hub Playground.
Figure (see Caption) Figure 44. High-temperature gas and steam from fumaroles on the S wall of the Nakadake Crater 1 at Asosan on 24 August (top) and 17 November 2017 (bottom) were persistent all year, with temperatures ranging from 300 to over 600°C. The green lake inside the crater persisted throughout the year as well with water temperatures of 50-60°C. Courtesy of JMA (Aso volcano monthly activity reports, Fukuoka District Meteorological Observatory, Regional volcano monitoring and warning center).

The Alert Level did not change at Asosan during 2018, and no eruptions were reported. Sulfur dioxide emissions fluctuated between 400 and 1,800 t/d throughout the year. Steam plumes generally rose less than 500 m above the active crater (figure 45); incandescence was observed at night during May-October and sometimes observed in satellite imagery as thermal anomalies (figure 46). The temperature of the green lake inside the crater ranged from 58 to 75°C throughout the year. The thermal anomaly on the S wall of the crater was consistently in the 300-500°C range, and had a high temperature in April of 580°C; in December the high temperature had risen to 738°C (figure 47). A brief increase in the number of isolated tremors occurred during March, with 1,044 reported on 4 March, exceeding the previous maximum of 1,000 on 27 October 2014. Seismicity also increased briefly during June, with more than 400 events reported each day on 8, 18, and 20 June. The Minami Aso village Yoshioka fumarole zone, located about 5 km W of Nakadake Crater 1, continued to produce modest steam plumes throughout 2017 and 2018 (figure 48).

Figure (see Caption) Figure 45. Typical steam plumes at Asosan during 2018 rose around 500 m above the Nakadake Crater 1. Images are from 4 March (top left), 22 July (top right), 17 August (lower left), and 13 September 2018 (lower right). Courtesy of JMA (Aso volcano monthly activity reports, Fukuoka District Meteorological Observatory, Regional volcano monitoring and warning center).
Figure (see Caption) Figure 46. Nighttime incandescence was reported by JMA during May-October 2018 from the S rim of Nakadake Crater 1 at Asosan; Sentinel-2 satellite images (bands 12, 4, 2) captured thermal anomalies from the same area numerous times during 2018 including on 16 June (top left), 26 July and 19 September (middle row), and 18 and 23 November (bottom row). JMA photographed incandescence at night on 17 July 2018 at the S fumarole area (top right). Courtesy of Sentinel Hub Playground and JMA (Aso volcano Monthly Report for July 2018).
Figure (see Caption) Figure 47. The "Green Tea Pond" inside Nakadake Crater 1 at Asosan had temperatures that ranged from 58 to 75°C during 2018 (top row, 26 March 2018); the thermal anomaly on the S wall of the crater consistently had temperatures measured in the 300-500°C range and the SW fumarole area had somewhat lower temperatures (bottom row, 22 June 2018). Courtesy of JMA (monthly Asosan reports for March, May, and June 2018).
Figure (see Caption) Figure 48. The Minami Aso village Yoshioka fumarole zone, located about 5 km W of Nakadake Crater 1 at Asosan, continued to produce modest steam plumes throughout 2017 and 2018. It is shown here on 20 December 2017 (top) and 12 March 2018 (bottom). Courtesy of JMA (December 2017 and March 2018 monthly volcano reports).

Activity during 2019. Steam plumes rose to 800 m above the crater rim during January 2019. Overall activity increased slightly during February; SO2 emissions peaked at 2,200 t/d early in the month; they ranged from 800 to 1,800 t/d for most of the month. The amplitude of volcanic tremor also increased slightly during February. A further increase in tremor amplitude on 11 March 2019 prompted JMA to raise the Alert Level from 1 to 2 the following morning. Volcanic tremor amplitude decreased on 15 March; JMA determined that activity had decreased, and the Alert Level was lowered back to 1 on 29 March 2019. The amount of water in the crater decreased significantly between 27 February and 20 March, exposing part of the crater floor.

The surface temperature of the lake rose during the first part of 2019; it was 78°C in February and 84°C in March. Steam plumes rose to 1,200 m above the crater rim during March and April. SO2 emissions rose to 4,500 t/d on 12 March but dropped to a lower range of 1,300-2,400 for the rest of the month. Another surge in SO2 emissions on 12 April 2019 to 3,600 t/d prompted a special report from JMA the following day. SO2 emissions varied from about 1,700 to 4,100 t/d during the month; values remained high during the second half of the month. JMA noted that the color of the water in the lake inside Nakadake Crater 1 changed from green to gray after 4 April. Fountains of muddy water were periodically observed; they reached 15 m high on 9 April. The temperatures of both the lake (82°C) and around the two fumarole areas (S area about 530°C, SW area about 310°C) remained constant during April and similar to March.

A large increase in the amplitude of volcanic tremor early on 14 April 2019 prompted JMA to raise the Alert Level from 1 to 2 later in the day. The epicenters of the earthquakes were very shallow, located within 1 km beneath the crater. A small eruption occurred at 1828 on 16 April at Nakadake Crater 1; it produced a gray and white plume that rose 200 m above the crater rim and was the first eruption since 8 October 2016 (figure 49). Incandescence was observed inside the crater on 3 and 17 April. The amplitude of seismic tremors decreased on 18 April. Three very small eruptions on 19 April produced ash and steam plumes that rose 500 m above the crater rim. During a site visit that day JMA measured a high-temperature area that produced incandescence from the bottom of the crater at night (figure 50).

Figure (see Caption) Figure 49. The first eruption since October 2016 at Nakadake Crater 1 at Asosan on 16 April 2019 sent an ash plume 200 m above the crater rim (top). Incandescent gas appeared on the crater floor the next day (bottom). Courtesy of JMA (Aso volcano monthly activity reports, April 2019, Fukuoka District Meteorological Observatory, Regional volcano monitoring and warning center).
Figure (see Caption) Figure 50. Three small explosions on 19 April 2019 at Asosan's Nakadake Crater 1 produced small ash emissions that rose 500 m above the crater rim (top). A strong thermal signal also appeared from the bottom of the crater. Courtesy of JMA (Aso volcano monthly activity reports, April 2019, Fukuoka District Meteorological Observatory, Regional volcano monitoring and warning center).

A new eruption began at 1540 on 3 May that lasted until 0620 on 5 May (figure 51). Initially the ash plume rose 600 m above the crater rim, but a few hours later the volume of ash increased, and the plume reached 2 km above the crater rim for a brief period. Incandescence was visible from the webcam. The Tokyo VAAC reported the ash plume at 3 km altitude drifting SE on 3 May. Later in the day it rose to 3.7 km altitude and drifted SW. During a field survey the following day (4 May) JMA reported a steam and ash plume rising from the center of the active crater. The infrared thermal imaging camera recorded the temperature of the plume at about 500°C (figure 52).

Figure (see Caption) Figure 51. An explosion at Asosan's Nakadake Crater 1 on 3 May 2019 produced an ash plume that reached 2 km above the crater rim (top) and incandescence visible from the webcam (bottom). Courtesy of JMA (Aso volcano monthly activity reports, April 2019, Fukuoka District Meteorological Observatory, Regional volcano monitoring and warning center).
Figure (see Caption) Figure 52. During a site visit on 4 May 2019, staff from JMA witnessed an ash and steam plume rising from the bottom of Nakadake Crater 1 at Asosan (top). The infrared thermal imaging camera recorded the temperature of the plume at about 500°C (bottom). Courtesy of JMA (Aso volcano monthly activity reports, May 2019, Fukuoka District Meteorological Observatory, Regional volcano monitoring and warning center).

Ash fell on the S flank, and a small amount of ashfall on 4 May was confirmed by evidence on a car windshield in Takamori Town (6 km S), Kumamoto Prefecture (figure 53). Ashfall was also reported in Takamori-machi, Minami Aso village (9 km SW), and part of Yamato-cho (25 km SW), also in the Kumamoto Prefecture. SO2 emissions were measured as high as 4,000 t/d on 4 May. Additional explosions with ash plumes were reported from Asosan on 9, 12-16, 29, and 31 May; the plumes rose from 200 to 1,400 m above the crater rim but were not visible in satellite imagery. The TROPOMI instrument on the Sentinel-5 satellite captured SO2 plumes on 3 and 26 May 2019 (figure 54).

Figure (see Caption) Figure 53. Ashfall was reported on 4 May 2019 in Takamori Town, Kumamoto Prefecture, from the eruption at Asosan's Nakadake Crater 1 on 3 May 2019. Courtesy of JMA (Aso volcano monthly activity reports, May 2019, Fukuoka District Meteorological Observatory, Regional volcano monitoring and warning center).
Figure (see Caption) Figure 54. Plumes of SO2 from Asosan were recorded by the TROPOMI instrument on the Sentinel-5P satellite on 3 (left) and 26 (right) May 2019. Courtesy of NASA Goddard Space Flight Center.

Steam plumes rose to 1,700 m above the crater rim during June 2019 (figure 55). During field visits on 6 and 25 June diffuse ash emissions were observed rising from the center of the active crater, but they did not extend significantly above the crater rim (figure 56). The maximum temperature of the plume was measured at about 340°C with a thermal imaging camera. Almost all of the water in the crater bottom had evaporated since early May; incandescence continued to be observed within the crater at night with the high-resolution webcam (figure 57).

Figure (see Caption) Figure 55. Steam plumes rose to 1,700 m above the crater rim at Asosan's Nakadake Crater 1 on 10 June 2019. Courtesy of JMA (Aso volcano monthly activity reports, June 2019, Fukuoka District Meteorological Observatory, Regional volcano monitoring and warning center).
Figure (see Caption) Figure 56. Plumes of gas and minor ash were visible at Asosan's Nakadake Crater 1 during site visits by JMA on 6 (left) and 25 (right) June 2019. Courtesy of JMA (Aso volcano monthly activity reports, June 2019, Fukuoka District Meteorological Observatory, Regional volcano monitoring and warning center).
Figure (see Caption) Figure 57. Incandescent gas was visible from the vent at Asosan's Nakadake Crater 1 on 18 (left) and 25 (right) June 2019. Courtesy of JMA (Aso volcano monthly activity reports, June 2019, Fukuoka District Meteorological Observatory, Regional volcano monitoring and warning center).

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: 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); Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, NASA Goddard Space Flight Center (NASA/GSFC), 8800 Greenbelt Road, Goddard, Maryland, USA (URL: https://so2.gsfc.nasa.gov/).


Nyamuragira (DR Congo) — May 2019 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 lake reappears in central crater in April 2018; activity tapers off during April 2019

The Virunga Volcanic Province (VVP) in the Democratic Republic of the Congo is part of the western branch of the East African Rift System. Nyamuragira (or Nyamulagira), a high-potassium basaltic shield volcano on the W edge of VVP, includes a lava field that covers over 1,100 km2 and contains more than 100 flank cones in addition to a large central crater (see figure 63, BGVN 42:06). A lava lake that had been active for many years emptied from the central crater in 1938. Numerous flank eruptions were observed after that time, the most recent during November 2011-March 2012 on the NE flank. This was followed by a period of degassing with unusually SO2-rich plumes from April 2012 through April 2014 (BGVN 42:06). The lava lake reappeared during July 2014-April 2016 and November 2016-May 2017, producing a strong thermal signature. After a year of quiet, a new lava lake appeared in April 2018, reported below (through May 2019) with information provided by the Observatoire Volcanologique de Goma (OVG), MONUSCO (the United Nations Organization working in the area), and satellite data and imagery from multiple sources.

Fresh lava reappeared inside the summit crater in mid-April 2018 from a lava lake and adjacent spatter cone. Satellite imagery and very limited ground-based observations suggested that intermittent pulses of activity from both sources produced significant lava flows within the summit crater through April 2019 when the strength of the thermal signal declined significantly. Images from May 2019 showed a smaller but persistent thermal anomaly within the crater.

Activity from October 2017-May 2019. Indications of thermal activity tapered off in May 2017 (BGVN 42:11). On 20 October 2017 OVG released a communication stating that a brief episode of unspecified activity occurred on 17 and 18 October, but the volcano returned to lower activity levels on 20 October. There was no evidence of thermal activity during the month. The volcano remained quiet with no reports of thermal activity until April 2018 (figure 73).

Figure (see Caption) Figure 73. Sentinel-2 satellite images (bands 12, 4, 2) indicated no thermal activity at Nyamuragira on 19 November (top left), 14 December 2017 (top right) and 18 January 2018 (bottom). However, Nyiragongo (about 13 km SE) had an active lava lake with a gas plume drifting SW on 18 January 2018 (bottom right). Courtesy of Sentinel Hub Playground.

OVG reported the new lava emissions beginning on 14 April 2018 as appearing from both the lava lake and a small adjacent spatter cone (figure 74). The first satellite image showing thermal activity at the summit appeared on 18 April 2018 (figure 75) and coincided with the abrupt beginning of strong MIROVA thermal signals (figure 76). MODVOLC thermal alerts also first appeared on 18 April 2018. An image of the active crater taken on 9 May 2018 showed the lake filled with fresh lava and two adjacent incandescent spatter cones (figure 77).

Figure (see Caption) Figure 74. Fresh lava reappeared at Nyamuragira's crater during April 2018 from the lava lake (left) and the adjacent small spatter cone (right). Courtesy of OVG (Republique Democratique du Congo, Ministere de la Recherche Scientifique, Observatoire Volcanologique de Goma, Direction Generale Goma, Rapport Avril 2018).
Figure (see Caption) Figure 75. The first satellite image (bands 12, 4, 2) indicating renewed thermal activity at the Nyamuragira crater appeared on 18 April 2018; the signal remained strong a few weeks later on 3 May 2018. Courtesy of Sentinel Hub Playground.
Figure (see Caption) Figure 76. A strong thermal signal appeared in the MIROVA graph of Log Radiative Power on 18 April 2018 for Nyamuragira, indicating a return of the lava lake at the summit crater. Courtesy of MIROVA.
Figure (see Caption) Figure 77. Fresh lava filled the lake inside the crater at Nyamuragira on 9 May 2018. Two spatter cones were incandescent with gas emissions. Courtesy of OVG (Republique Democratique du Congo, Ministere de la Recherche Scientifique, Observatoire Volcanologique de Goma, Direction Generale Goma, Rapport Mai 2018).

Satellite images confirmed that ongoing activity from the lava lake remained strong during June -September 2018 (figure 78). A mission to Nyamuragira was carried out by helicopter provided by MONUSCO on 20 July 2018; lava lake activity was observed along with gas emissions from the small spatter cone (figure 79). OVG reported increased volcanic seismicity during 1-3 and 10-17 September 2018, and also during October, located in the crater area, mostly at depths of 0-5 km.

Figure (see Caption) Figure 78. Sentinel-2 satellite images (bands 12, 4, 2) confirmed that ongoing activity from the lava lake at Nyamuragira remained strong during June-September 2018, likely covering the crater floor with a significant amount of fresh lava. Image are from 12 June (top left), 7 July (top right), 17 July (middle left), 22 July (middle right), 11 August (bottom left), and 20 September (bottom right). Courtesy of Sentinel Hub Playground.
Figure (see Caption) Figure 79. The crater at Nyamuragira on 20 July 2018 had an active lava lake and adjacent incandescent spatter cone with gas emissions. Courtesy of OVG (Republique Democratique du Congo, Ministere de la Recherche Scientifique, Observatoire Volcanologique de Goma, Direction Generale Goma, Rapport Juillet 2018).

Personnel from OVG and MONUSCO (United Nations Organization Stabilization Mission in DR Congo) made site visits on 11 October and 2 November 2018 and concluded that the level of the active lava lake had increased during that time (figure 80). On 2 November OVG measured the height from the base of the active cone to the W rim of the crater as 58 m (figure 81).

Figure (see Caption) Figure 80. OVG scientists reported a rise in the lake level between site visits to the Nyamuragira crater on 11 October (top) and 2 November 2018 (bottom). Top image courtesy of MONUSCO and Culture Vulcan, bottom image courtesy of OVG (Republique Democratique du Congo, Ministere de la Recherche Scientifique, Observatoire Volcanologique de Goma, Direction Generale Goma, Rapport Octobre 2018).
Figure (see Caption) Figure 81. On 2 November 2018 scientists from OVG measured the height from the base of the active cone to the W rim of the crater as 58 m. Courtesy of OVG (Republique Democratique du Congo, Ministere de la Recherche Scientifique, Observatoire Volcanologique de Goma, Direction Generale Goma, Rapport Octobre 2018).

Seismicity remained high during November 2018 but decreased significantly during December. Instrument and access issues in January 2019 prevented accurate assessment of seismicity for the month. The lava lake remained active with periodic surges of thermal activity during November 2018-March 2019 (figure 82). Multiple images show incandescence in multiple places within the crater, suggesting significant fresh overflowing lava.

Figure (see Caption) Figure 82. The active lava lake at Nyamuragira produced strong thermal signals from November 2018 through March 2019 that were recorded in Sentinel-2 satellite images (bands 12, 4, 2). Several images suggest fresh lava cooling around the rim of the crater in addition to the active lake. A relatively cloud-free day on 19 November 2018 (top left) revealed no clear thermal signal, but a strong signal was recorded on 29 November (top right) despite significant cloud cover. Images from 13 and 28 January 2019 (second row) both showed evidence of incandescent lava in multiple places within the crater. The thermal signal was smaller and focused on the center of the crater on 12 and 27 February 2019 (third row). Images taken on 9 and 19 March 2019 clearly showed incandescent material at the center of the crater and around the rim (bottom row). Courtesy of Sentinel Hub Playground.

On 12 April 2019 a Ukrainian Aviation Unit supported by MONUSCO provided support for scientists visiting the crater for observations and seismic analysis. Satellite data confirmed ongoing thermal activity into May, although the strength of the signal appeared to decrease (figure 83). MODVOLC thermal alerts ceased after 8 April, and the MIROVA thermal data also confirmed a decrease in the strength of the thermal signal during April 2019 (figure 84).

Figure (see Caption) Figure 83. Sentinel-2 satellite data (bands 12, 4, 2) confirmed ongoing thermal activity at Nyamuragira into May 2019. The thermal anomalies on 18 April (left) and 3 May (right) 2019 were smaller than those recorded during previous months. Courtesy of Sentinel Hub Playground.
Figure (see Caption) Figure 84. The MIROVA graph of thermal activity (log radiative power) at Nyamuragira from 16 July 2018 through April 2019 showed near-constant levels of high activity through April 2019 when it declined. This corresponded well with satellite and ground-based observations. Courtesy of MIROVA.

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: Observatoire Volcanologique de Goma (OVG), Departement de Geophysique, Centre de Recherche en Sciences Naturelles, Lwiro, D.S. Bukavu, DR Congo; Katcho Karume, Director; Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); 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/); MONUSCO, United Nations Organization Stabilization Mission in the DR Congo (URL: https://monusco.unmissions.org/en/, Twitter: @MONUSCO); Cultur Volcan, Journal d'un volcanophile (URL: https://laculturevolcan.blogspot.com), Twitter: @CultureVolcan).


Tengger Caldera (Indonesia) — May 2019 Citation iconCite this Report

Tengger Caldera

Indonesia

7.942°S, 112.95°E; summit elev. 2329 m

All times are local (unless otherwise noted)


New explosions with ash plumes from Bromo Cone mid-February-April 2019

The 16-km-wide Tengger Caldera in East Java, Indonesia is a massive volcanic complex with numerous overlapping stratovolcanos (figure 11). Mount Bromo is a pyroclastic cone that lies within the large Sandsea Caldera at the northern end of the complex (figure 12) and has erupted more than 20 times during each of the last two centuries. It is part of the Bromo Tengger Semeru National Park (also a UNESCO Biosphere Reserve) and is frequently visited by tourists. The last eruption from November 2015 to November 2016 produced hundreds of ash plumes that rose as high as 4 km altitude; some of them drifted for hundreds of kilometers before dissipating and briefly disrupted air traffic. Only steam and gas plumes were observed at Mount Bromo from December 2016 to February 2018 when a new series of explosions with ash plumes began; they are covered in this report with information provided by the Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as CVGHM) and the Darwin Volcanic Ash Advisory Centre (VAAC). Copyrighted ground and drone-based images from Øystein Lund Andersen have been used with permission of the photographer.

Figure (see Caption) Figure 11. The Tengger Caldera viewed from the north Mount Bromo issuing steam in the foreground and Semeru volcano in the background on 30 September 2018. Courtesy of Øystein Lund Andersen, used with permission.
Figure (see Caption) Figure 12. Aerial view of the Bromo Cone in Tengger Caldera seen from the west on 30 September 2018. Courtesy of Øystein Lund Andersen, used with permission.

PVMBG lowered the Alert Level at Bromo on 21 October 2016 from III to II near the end of an eruptive episode lasting nearly a year. The last VAAC report was issued on 12 November 2016 (BGVN 41:12) noting that the last ash emission had been observed the previous day drifting NW at 3 km altitude. Throughout 2017 and 2018 Bromo remained at Alert Level II, with no unusual activity described by PVMBG. During 1-2 September 2018, a wildfire in the Bromo Tengger Semeru National Park burned 65 hectares of savannah (figure 13); the fire produced 12 MODVOLC thermal alerts around the Tengger Caldera rim. No reports of increased volcanic activity were issued by PVMBG during the period.

Figure (see Caption) Figure 13. A wall of fire in the Bromo Tengger Semeru National Park savanna during 1-2 September 2018 produced thermal alerts that were not related to volcanic activity at the Bromo Cone in Tengger Caldera. Image courtesy of the park authority, reported by Mongabay. MODVOLC thermal alerts courtesy of Hawai'i Institute of Geophysics and Planetology (HIGP).

After slightly more than two years of little activity other than gas and steam plumes, ash emissions resumed from the Bromo Cone on 18 February 2019. After a brief pause, a new explosion on 10 March marked the beginning of a series of near-daily ash emissions that lasted for the rest of March, producing ash plumes that rose to altitudes ranging from 3.0 to 5.2 km and drifted in many different directions. A new series of ash emissions began on 6 April, rising to 3 km and also drifting in multiple directions. Ash emission density decreased during the month; plumes were only rising a few hundred meters above the summit by the end of April and consisted of mostly steam and moderate amounts of ash.

Activity during February-April 2019. PVMBG reported that at 0600 on 18 February 2019 an eruption at Tengger Caldera's Bromo Cone generated a dense white-and-brown ash plume that rose 600 m and drifted WSW. The plume was not visible in satellite imagery, according to the Darwin VAAC. The Alert Level remained at 2 (on a scale of 1-4). After a few weeks of quiet a new explosion on 10 March (local time) produced a white, brown, and gray ash plume that rose 600 m above the summit; the plume was visible in satellite imagery extending SW. Increased tremor amplitude was also reported on 10 March. A new emission the next morning produced similar ash plumes that drifted S, SW, and W at 3 km altitude. On the morning of 12 March (local time) a continuous ash plume was observed in satellite imagery at 3.4 km altitude drifting SW. The plume drifted counterclockwise towards the S, E, and NE throughout the day and continued to drift NE and SE on 13 March. The altitude of the plume was reported at 4.3 km later that day based on a pilot report.

Continuous brown, gray, and black ash emissions were reported by PVMBG during 14-19 March at altitudes ranging from 3 to 3.9 km; they drifted generally NE to NW. Ashfall was noted around the crater and downwind a short distance. The Darwin VAAC reported continuous ash emissions to 5.2 km altitude drifting SE on 20 March. It was initially reported by a pilot and partially discernable in satellite imagery before dissipating. Ongoing ash emissions of variable densities and colors ranging from white to black were intermittently visible in satellite imagery and confirmed in webcam and ground reports at around 3.0 km altitude during 21-25 March (figures 14-17). Ashfall impacted the closest villages to Bromo, including Cemara Lawang (30 km NW), which was covered by a thin layer of ash. A few trees in the area were toppled over by the weight of the ash. The plume altitude increased slightly on 26 March to 3.7-3.9 km, drifting N and NE. The higher altitude plume dissipated early on 28 March, but ash emissions continued at 3.0 km for the rest of the day.

Figure (see Caption) Figure 14. Ash drifted NNE from the Bromo Cone in Tengger Caldera on 23 March 2019. Courtesy of Øystein Lund Andersen (drone image), used with permission.
Figure (see Caption) Figure 15. Ash drifted N from the Bromo Cone in Tengger Caldera on 23 March 2019. The Batok Cone is on the right, Segera Wedi is behind Bromo, and Semeru is in the far background. Courtesy of Øystein Lund Andersen, used with permission.
Figure (see Caption) Figure 16. A few trees toppled from ashfall in the vicinity of the Bromo Cone in Tengger Caldera on 24 March 2019. Courtesy of Øystein Lund Andersen, used with permission.
Figure (see Caption) Figure 17. Ash plumes from the Bromo Cone in Tengger Caldera on 24 March 2019 caused ashfall in communities as far as 30 km away. View is from the floor of the Sandsea Caldera. Courtesy of Øystein Lund Andersen, used with permission.

After just a few days of quiet, new ash emissions rising to 3.0 km altitude and drifting SE were reported by both PVMBG (from the webcam) and the Darwin VAAC on 6 April 2019. By the next day the continuous ash emissions were drifting N, then E during 8-10 April, and S during 11 and 12 April. A new emission seen in the webcam was reported by the Darwin VAAC on 15 April (UTC) that rose to 3.0 km and drifted W. Ash plumes were intermittently visible in either webcam or satellite imagery until 17 April rising 500-1,000 m above the crater; from 19-25 April only steam plumes were reported rising 300-500 m above the summit. A minor ash emission was reported from the webcam on 26 April that rose to 3.0 km altitude and drifted NE for a few hours before dissipating. PVMBG reported medium density white to gray ash plumes that rose 400-600 m above the crater for the remainder of the month.

Geologic Background. The 16-km-wide Tengger caldera is located at the northern end of a volcanic massif extending from Semeru volcano. The massive volcanic complex dates back to about 820,000 years ago and consists of five overlapping stratovolcanoes, each truncated by a caldera. Lava domes, pyroclastic cones, and a maar occupy the flanks of the massif. The Ngadisari caldera at the NE end of the complex formed about 150,000 years ago and is now drained through the Sapikerep valley. The most recent of the calderas is the 9 x 10 km wide Sandsea caldera at the SW end of the complex, which formed incrementally during the late Pleistocene and early Holocene. An overlapping cluster of post-caldera cones was constructed on the floor of the Sandsea caldera within the past several thousand years. The youngest of these is Bromo, one of Java's most active and most frequently visited volcanoes.

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/); 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/); 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/); Øystein Lund Andersen (Twitter: @OysteinLAnderse, https://twitter.com/OysteinLAnderse, URL: http://www.oysteinlundandersen.com); Mongabay, URL: https://news.mongabay.com/2018/09/fires-tear-through-east-java-park-threatening-leopard-habitat/.


Karangetang (Indonesia) — May 2019 Citation iconCite this Report

Karangetang

Indonesia

2.781°N, 125.407°E; summit elev. 1797 m

All times are local (unless otherwise noted)


Activity at two craters with the N crater producing ash plumes, avalanches, pyroclastic flows, and lava flows that reached the ocean in February 2019

Karangetang (also referred to as Api Siau) is an active volcano on the island of Siau in the Sitaro Regency, North Sulawesi, Indonesia. It produces frequent small eruptions that include gas-and-steam plumes, ash plumes, avalanches, lava flows, incandescent ballistic ejecta, and pyroclastic flows. This report covers May 2018-May 2019 and summarizes reports by Indonesia's Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as CVGHM, or the Center of Volcanology and Geological Hazard Mitigation), and the Darwin VAAC (Volcanic Ash Advisory Center), and satellite data. During this time, increased activity resulted in a lava flow that reached the ocean and cut road access to communities.

No activity was reported during May through October 2018. During this time, Sentinel-2 thermal images showed elevated temperatures in the main active crater and gas-and-steam plumes dispersing in different directions (figure 17). On 4 July, the Darwin VAAC reported a "weak" ash plume to an altitude of 3 km that drifted NE, only based on satellite imagery. There were few thermal signatures detected by the MIROVA algorithm from May through November (figure 18).

Figure (see Caption) Figure 17. Incandescence and weak steam-and-gas plumes at the southern crater of Karangetang on 9 May and 17 August 2018. This was common in cloud-free images acquired during this time. Sentinel-2 false color (bands 12, 11, 4) images courtesy of Sentinel Hub Playground.
Figure (see Caption) Figure 18. MIROVA log radiative power plot of MODIS infrared data for June 2018 through April 2019. There was little thermal energy detected before December, after which levels remained high until they began declining in March 2019. Courtesy of MIROVA.

Steam plumes were observed from two craters during November 2018 (figures 19 and 20). There was a significant increase in seismicity on 22 to 23 November, followed by a sharp decline on the 24th. The first MODVOLC thermal alert was issued on 25 November. At 1314 on 25 November an ash plume rose to at least 500 m above the N crater and the Aviation Color Code was raised to Orange. A Sentinel-2 thermal image acquired on this day showed elevated temperatures at both south and north craters, with accompanying gas-and-steam plumes. After the increase in seismicity and detected thermal energy, activity progressed to lava flow extrusion, avalanches, and pyroclastic flows triggered from the lava flow. The lava flow originated from the north crater (Kawah Dua) and moved towards the NNW. Avalanches accompanied the flow from the crater and down the lava flow surface. The Volcano Alert level was increased from II to III on 20 December at 1800 (on a scale of I to IV).

Figure (see Caption) Figure 19. White gas-and-steam plumes emanating from two craters at Karangetang at 0630 on 16 November 2018. Courtesy of MAGMA Indonesia via Øystein Lund Andersen.
Figure (see Caption) Figure 20. An ash plume from the N crater (left) and a gas-and-steam plume from the S crater (right) of Karangetang at 0703 on 26 November 2018. Courtesy of MAGMA Indonesia via Øystein Lund Andersen.

Throughout January 2019 activity consisted of small ash plumes up to 600 m above the N crater (figure 21) and continued lava flow activity. On 17 January Kompas TV reported that heavy ashfall impacted several villages. Lava and avalanches traveled as far as 0.7-1 km W towards the Sumpihi River and 1-2 km NE down the Kali Batuare throughout the month.

Figure (see Caption) Figure 21. A small ash plume on 31 January 2019 at Karangetang. Courtesy of MAGMA Indonesia via Øystein Lund Andersen.

Video taken on 3 February 2019 shows the lava flow covering the road and continuing down the steep slope with multi-meter-scale incandescent blocky lava fragments on the surface dislodging and triggering small avalanches. By 5 February the lava flow reached over 3.5 km down the Malebuhe River drainage on the NW flank and into the ocean where a lava delta was growing with dense steam plume rising above by the 11th (figures 22-26). Drone footage from 9 February shows the lava flow across the section of road had a width of about 160 m and a width of about 140 m at the coast. Gas-and-steam and ash plumes were noted most days, reaching up to 600 m above the crater and dominantly dispersing to the E (figure 27). By 11 February there had been 190 people evacuated.

Figure (see Caption) Figure 22. The lava flow front at Karangetang nearing the ocean on 5 February 2019. Courtesy of MAGMA Indonesia.
Figure (see Caption) Figure 23. The lava flow entering the ocean at Karangetang in early February 2019. Photos posted on 11 February; courtesy of BNPB.
Figure (see Caption) Figure 24. Locations of activity observations at Karangetang in November 2018 and February 2019. 27 November 2018: the descent of lava from the Kawah Dua crater (N crater) to about 700-1000 m away, towards the Sumpihi River and Kinali Village. 2 February 2019: the descent of lava 2.5 km NW, 500 m from the highway. 5 February 2019: the lava flow reached the sea. Courtesy of BNPB.
Figure (see Caption) Figure 25. Sentinel-2 thermal satellite images of Karangetang during November 2018 through February 2019 showing elevated temperatures at two craters, gas-and-steam plumes, and a lava flow moving to the NW (bright yellow-orange). Sentinel-2 false color (bands 12, 11, 4) images courtesy of Sentinel Hub Playground.
Figure (see Caption) Figure 26. View of the active lava flow on Karangetang at the ocean entry in early February 2019. Photo posted on 12 February; taken by Ungke Pepotoh, courtesy of Agence France-Presse.
Figure (see Caption) Figure 27. Ashfall from Karangetang on Siau Island as seen from Pehe port on 7 February 2019. Photo courtesy of The New Indian Express, AFP / Ungke Pepotoh.

On 13 February 2019 avalanches continued from the northern crater to 700-1000 m W towards the Sumpihi River and 1-2 km NE towards Kali Batuare. KOMPAS TV reported a statement by PVMBG describing a decrease in activity, including lava avalanches, but with elevated seismicity on the 12 February. Throughout this period of elevated activity both seismicity (figure 28), along with plume heights and directions (figure 29), were variable. On 22 February the Darwin VAAC reported an ash plume, due to a pyroclastic flow, rising to an altitude of 3.7 km.

Figure (see Caption) Figure 28. Graph showing the variable seismicity at Karangetang during 1 November 2018 to 8 February 2019. Courtesy of PVMBG.
Figure (see Caption) Figure 29. Graph showing gas-and-steam plume heights in meters above the crater from 1 November 2018 to 8 February 2019, with the plume dispersal directions indicated in the box. Modified from data courtesy of PVMBG.

Throughout March 2019 PVMBG reported the continuation of a low rate of lava effusion at the north crater, avalanches, and gas-and-steam plumes rising up to 500 m above the crater. The Darwin VAAC reported an ash plume on 7 March that rose to an altitude of 2.7 km that dispersed to the SW. Minor ash emissions were reported by the Darwin VAAC on 6 April that rose to 2.1 km altitude and drifted SE. In mid-April, activity increased in the southern crater and on 15 April a pyroclastic flow traveled 2 km towards the Kahetang and Batuawang rivers. Another ash advisory was issued for an ash plume up to 2.4 km altitude on 16 April. Small gas-and-steam plumes continued through the month.

Geologic Background. Karangetang (Api Siau) volcano lies at the northern end of the island of Siau, about 125 km NNE of the NE-most point of Sulawesi island. The stratovolcano contains five summit craters along a N-S line. It is one of Indonesia's most active volcanoes, with more than 40 eruptions recorded since 1675 and many additional small eruptions that were not documented in the historical record (Catalog of Active Volcanoes of the World: Neumann van Padang, 1951). Twentieth-century eruptions have included frequent explosive activity sometimes accompanied by pyroclastic flows and lahars. Lava dome growth has occurred in the summit craters; collapse of lava flow fronts have produced pyroclastic flows.

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/); Badan Nasional Penanggulangan Bencana (BNPB), National Disaster Management Agency, Graha BNPB - Jl. Scout Kav.38, East Jakarta 13120, Indonesia (URL: http://www.bnpb.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/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); 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/); Agence France-Presse (URL: http://www.afp.com/); Kompas TV, Menara Kompas Lt. 6, Jl. Palmerah Selatan No.21, Jakarta Pusat 10270 Indonesia (URL: https://www.kompas.tv/article/39190/abu-gunung-karangetang-tutup-permukiman-warga); The New Indian Express (URL: http://www.newindianexpress.com/world/2019/feb/08/emergency-declared-on-indonesian-island-after-volcanic-eruption-1936173.html); Øystein Lund Andersen (Twitter: @OysteinLAnderse, https://twitter.com/OysteinLAnderse, URL: https://www.oysteinlundandersen.com).

Search Bulletin Archive by Publication Date

Select a month and year from the drop-downs and click "Show Issue" to have that issue displayed in this tab.

   

The default month and year is the latest issue available.

Scientific Event Alert Network Bulletin - Volume 06, Number 10 (October 1981)

Managing Editor: Lindsay McClelland

Aira (Japan)

Frequent explosions, two incandescent columns

Atmospheric Effects (1980-1989) (Unknown)

Aircraft and satellite data on stratospheric ejecta from four eruptions

Etna (Italy)

Small plumes on satellite images

Fukujin (United States)

Water discoloration seen in January 1981, but then none through October

Fukutoku-Oka-no-Ba (Japan)

Frequent water discoloration observed during January-October 1981

Krakatau (Indonesia)

Small ash clouds

Langila (Papua New Guinea)

New lava flow, incandescent tephra, ash emission

Manam (Papua New Guinea)

Incandescent tephra, glow, ash plume

Mehetia (France)

Several months of increased seismicity

Minami-Hiyoshi (Japan)

No discolored water seen during January-October 1981

Ruapehu (New Zealand)

Increased seismicity; lower crater lake temperatures; eruption expected

Soufriere Guadeloupe (France)

Temperature, magnetic field stable

St. Helens (United States)

Lava extrusion adds new lobe to composite dome

Suwanosejima (Japan)

January-August 1981 explosions tabulated



Aira (Japan) — October 1981 Citation iconCite this Report

Aira

Japan

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

All times are local (unless otherwise noted)


Frequent explosions, two incandescent columns

Frequent explosions continued through October, when 35 were recorded. Two 100-m-high incandescent columns were recorded for 3 seconds at 0444 on 2 October. Ash clouds higher than 2 km above the summit were observed on 3, 17 and 31 October.

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, Tokyo.


Atmospheric Effects (1980-1989) (Unknown) — October 1981 Citation iconCite this Report

Atmospheric Effects (1980-1989)

Unknown

Unknown, Unknown; summit elev. m

All times are local (unless otherwise noted)


Aircraft and satellite data on stratospheric ejecta from four eruptions

Filter samples from LASL high-altitude aircraft and data from NASA's SAGE satellite provided information about the height and dispersal of the eruption cloud ejected by Ulawun in October 1980, and the LASL aircraft also collected tephra probably produced by the May 1981 eruption of Pagan.

Ulawun's brief but powerful eruption took place 6-7 October 1980, producing a cloud estimated by ground observers to have reached 7-10 km in height. On 24 October, the aircraft sampled the lower stratosphere at about 19 km altitude, between the equator and 5°N at about 80°W (just S of Panama). Data from these samples indicated atmospheric concentrations of as much as 6 parts per billion (ppb) of sulfate by mass, of which only 25-50% could be attributed to the 18 May eruption of St. Helens. The SAGE satellite detected tephra from St. Helens N of 40°N in October 1980, but also detected a large cloud of new material from 26°N to 10°S (data collection was truncated at 10°S) between 125°W and the International Date Line. SAGE next collected data from the equatorial region in mid-November, when a zone of significant particle enhancement (roughly 5 times background), extending upward from the tropopause (about 16.5 km altitude at the equator) to about 22 km, circled the globe in an irregular band 10-20° wide between 20°S and 10°N.

Pagan's eruption began 15 May. Japanese weather radar recorded the top of the eruption column at 18-20 km altitude and weather satellite images showed that the high-altitude cloud traveled SSE. Ten weeks later, filter samples collected by the LASL aircraft just S of Panama (from the equator to 5°N) on 24 July showed lower stratospheric sulfate concentrations of about 5 ppb by mass at altitudes of 18.2, 19, and 19.2 km. Between 5°N and 35°N at 16.8 km altitude (above the tropopause), sulfate concentrations were as high as 4 ppb by mass; only about 1 ppb could be attributed to material remaining from the St. Helens eruption 14 months earlier. High concentrations of sulfate aerosols and silicate particles collected at mid to high northern latitudes in early July are probably from the late April-early May eruption of Alaid. From these data, the average lower stratospheric sulfate concentration over the entire Northern Hemisphere in July 1981 was calculated to be about 2.5 ppb by mass, primarily contributed by the eruptions of Pagan and Alaid but including a little material from the St. Helens eruption. The same calculations made from July 1980 data yielded a slightly lower concentration, about 2.3 ppb by mass, with St. Helens as the dominant source. In the last decade, only two relatively brief periods can be identified as showing "background" sulfate concentrations, without a substantial volcanic component: mid-1973 through mid-1974 (about 0.34 ppb sulfate by mass), and late 1978 through late 1979 (about 0.47 ppb sulfate by mass).

Geologic Background. 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 here.

Information Contacts: W. Sedlacek, LASL; P. McCormick, NASA.


Etna (Italy) — October 1981 Citation iconCite this Report

Etna

Italy

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

All times are local (unless otherwise noted)


Small plumes on satellite images

Images returned by the NOAA 7 polar orbiting satellite continued to show occasional plume emission: on 9 October at 1442 plume roughly 75 km long, drifting to the SE, and on 1 November at 1329 a much smaller plume, roughly 20 km long was moving to the SW. No other activity was seen on the almost daily imagery between those dates.

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: M. Matson, NOAA.


Fukujin (United States) — October 1981 Citation iconCite this Report

Fukujin

United States

21.93°N, 143.47°E; summit elev. -217 m

All times are local (unless otherwise noted)


Water discoloration seen in January 1981, but then none through October

The Japan Maritime Safety Agency (JMSA) continues frequent monitoring flights over several known submarine volcanoes. [Discolored water was specifically noted, in an included table of observations, on 7 and 8 January, but not again through October 1981 (see table 1 below).]

Geologic Background. One of the larger of the submarine volcanoes of the Marianas arc, Fukujin seamount has risen on occasion to just beneath the sea surface. Intermittent periods of water discoloration have been observed since the mid-20th century, and eruptions producing floating pumice were noted on several occasions.

Information Contacts: JMSA, Tokyo; JMA, Tokyo.


Fukutoku-Oka-no-Ba (Japan) — October 1981 Citation iconCite this Report

Fukutoku-Oka-no-Ba

Japan

24.285°N, 141.481°E; summit elev. -29 m

All times are local (unless otherwise noted)


Frequent water discoloration observed during January-October 1981

The Japan Maritime Safety Agency (JMSA) continues frequent monitoring flights over several known submarine volcanoes. [Discolored water at Fukutoku-Okanoba was specifically noted, in an included table of observations, on 9 and 29 January, 12 and 20 February, 12, 13, and 16 March, 20 April, 16, 17, and 22 July, 17 August, and 17 September 1981 (see table 1 below).]

Geologic Background. Fukutoku-Oka-no-ba is a submarine volcano located 5 km NE of the pyramidal island of Minami-Ioto. Water discoloration is frequently observed from the volcano, and several ephemeral islands have formed in the 20th century. The first of these formed Shin-Ioto ("New Sulfur Island") in 1904, and the most recent island was formed in 1986. The volcano is part of an elongated edifice with two major topographic highs trending NNW-SSE, and is a trachyandesitic volcano geochemically similar to Ioto.

Information Contacts: JMSA, Tokyo; JMA, Tokyo.


Krakatau (Indonesia) — October 1981 Citation iconCite this Report

Krakatau

Indonesia

6.102°S, 105.423°E; summit elev. 813 m

All times are local (unless otherwise noted)


Small ash clouds

Explosions resumed 20 October after several months of fumarolic activity. Guy Camus and Pierre Vincent visited the volcano for four hours during the afternoon of 19 October, but noticed no premonitory activity. Explosions began between 0300 and 0400 the next morning. From Rakata Island (about 3 km SE of Anak Krakatau), Camus and Vincent noted 19 explosions in the two hours just after sunrise, before leaving the island. They had seen several others by mid-afternoon during discontinuous observations from a boat. Most were initiated by a "cannon-like" explosion from the main cone, followed by convective growth of an eruption column (typically to 400-600 m, but occasionally to [2] km in height). No noise could be heard on Rakata Island. The explosions usually lasted one to several minutes, but the last one observed by Camus and Vincent as they left the area began at 1511 and continued until 1525. Most of the eruption columns were dark, containing abundant ash but few blocks and no incandescent material. Water vapor could be seen condensing at the top of several eruption columns and lightning was occasionally observed. Ash fell on Sertung Island, about 2 km W of Anak Krakatau.

Further References. Camus, G., Gourgaud, A., and Vincent, P.M., 1987, Petrologic evolution of Krakatau (Indonesia): implications for a future activity: JVGR, v. 33, p. 299-316.

Siswowidjoyo, S., 1985, The renewed activity of Krakatau volcano after its catastrophic eruption in 1883: Proceedings of the Symposium on 100 Years Development of Krakatau and its Surroundings, Indonesian Institute of Sciences, Jakarta, p. 192-198.

Sudradjat, A., 1985, The morphological development of Krakatau volcano, Sunda Strait, Indonesia: Proceedings of the Symposium on 100 Years Development of Krakatau and its Surroundings, Indonesian Institute of Sciences, Jakarta, p. 141-146.

Geologic Background. The renowned volcano Krakatau (frequently misstated as Krakatoa) lies in the Sunda Strait between Java and Sumatra. Collapse of the ancestral Krakatau edifice, perhaps in 416 or 535 CE, formed a 7-km-wide caldera. Remnants of this ancestral volcano are preserved in Verlaten and Lang Islands; subsequently Rakata, Danan, and Perbuwatan volcanoes were formed, coalescing to create the pre-1883 Krakatau Island. Caldera collapse during the catastrophic 1883 eruption destroyed Danan and Perbuwatan, and left only a remnant of Rakata. This eruption, the 2nd largest in Indonesia during historical time, caused more than 36,000 fatalities, most as a result of devastating tsunamis that swept the adjacent coastlines of Sumatra and Java. Pyroclastic surges traveled 40 km across the Sunda Strait and reached the Sumatra coast. After a quiescence of less than a half century, the post-collapse cone of Anak Krakatau (Child of Krakatau) was constructed within the 1883 caldera at a point between the former cones of Danan and Perbuwatan. Anak Krakatau has been the site of frequent eruptions since 1927.

Information Contacts: G. Camus and P. Vincent, Univ. de Clermont-Ferrand.


Langila (Papua New Guinea) — October 1981 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)


New lava flow, incandescent tephra, ash emission

"Eruptive activity intensified in October when Crater 3 became strongly active, emitting incandescent tephra and a new lava flow. After a brief interval of ash emission on 3 October, Crater 3 began a sustained period of explosive activity on 9 October. Ejections of incandescent tephra were seen on 15 October and continued from 17 October throughout the month. The production of a new lava flow from Crater 3 was suspected on 27 October and confirmed on the 28th. The flow rate was apparently low.

"Activity at Crater 2 may have declined since late September. Vulcanian explosions occurred at intervals of several days, and periods of less-explosive ash emission were observed at the beginning and end of October. At other times, Crater 2 released white and blue vapours. Crater 2 glow was observed on 1, 3, 17, and 18 October.

"Ashfalls were reported in inhabited areas about 10 km N and W of the volcano on about 50% of days during the first half of October. Seismicity remained at a fairly low level, consisting mainly of numerous small events probably originating from Crater 3."

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.


Manam (Papua New Guinea) — October 1981 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 tephra, glow, ash plume

"Both craters showed stronger activity in October. Incandescent tephra ejections from Southern crater were seen on four nights at the beginning of the month, and on most nights from 12 October onwards. Brown or grey ash emissions from Southern crater were seen 1-9 and 21-30 October. Main crater emitted brown or grey ash on most days 1-22 October. Main crater glow was seen on 1 October, and incandescent tephra ejections on the 14th. A substantial ash plume from Main crater (reportedly several tens of kilometers long) was observed on 14 October. White and blue vapours were emitted from both craters during non-explosive intervals throughout October, and rumbling sounds from the volcano were heard on most days. No trends were shown by tiltmeter measurements, and seismic activity remained steady."

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.


Mehetia (France) — October 1981 Citation iconCite this Report

Mehetia

France

17.874°S, 148.068°W; summit elev. 389 m

All times are local (unless otherwise noted)


Several months of increased seismicity

A swarm of earthquakes centered beneath Mehetia began suddenly on 6 March and was continuing in late October. After the first two days of the swarm, characterized by numerous weak events, seismographs began to record occasional larger shocks (figure 1). The seismic energy released during the first week of the swarm greatly exceeded the previous total energy release detected by the Tahitian seismic net since the first stations were installed in 1962-63. Both the number of earthquakes (figure 2) and energy release (figure 3) varied considerably, with periods of increased activity separated by brief lulls. Epicenters were about 10 km SE of the crater. There were several groups of foci, which may indicate vertical migration, but it was impossible to compute depths of focus for most of the events. A temporary seismic station operated on Mehetia 25-30 March recorded local earthquakes at about 13 km depth.

Figure (see Caption) Figure 1. Log plot of number of events vs. magnitude at intervals of ML 0.2 recorded from Mehetia, 6 March-15 December 1981. The b value (slope) of the regression line is 1.13 ± 0.03 for the entire swarm. For the first two days of the swarm, characterized by numerous weak events, b = 1.63. Courtesy of J. Talandier.
Figure (see Caption) Figure 2. Number of recorded earthquakes (ML 0.9 or greater) per day (3-day means) at Mehetia, 6 March-early December 1981 (293 days). The total number of such events during this interval was 3,536. The Tahitian seismic net records most local events of ML 1.1 or greater, but fluctuating levels of microseismic noise prevent consistent recording of weaker events. Courtesy of J. Talandier.
Figure (see Caption) Figure 3. Seismic energy released by the Mehetia swarm (3-day intervals), 6 March-early December 1981. Courtesy of J. Talandier.

By late October, more than 3,000 local events of magnitude 0.9 (ML) or stronger had been recorded. Of these, about 30 were stronger than ML 3.0, including magnitude 4.0 and 4.3 shocks. Because of the detection limits (usually about ML 1.1, but weaker seismicity is sometimes recorded during periods of lesser microseismic noise) for events in the Mehetia area (~140 km from the nearest Tahitian net station), harmonic tremor, if any, would probably not be recorded. Talandier's extrapolation of the well-defined frequency-magnitude relationship indicates that about 50,000 events stronger than ML 0.1 have probably occurred during the swarm. Talandier also notes that the Mehetia swarm and seismicity associated with Hawaiian volcanoes showed similarities in number and magnitude of events and seismogram characteristics, as well as the detection of long-period waves that could be generated by events occurring beneath a magma chamber. No surface volcanic activity has been reported at Mehetia. The island is uninhabited, working conditions there are difficult, and no geologist has visited the area recently.

Mehetia is a well-defined cone about 1,500 m in diameter and 435 m high, with a 200-m-diameter crater at the summit. No historic eruptions have been reported, but the limited erosion of the crater and flanks, lack of vegetation at the summit, and Tahitian legends of "big fires" all indicate that eruptions probably took place less than 2,000 years ago.

Geologic Background. The 1.5-km-wide, steep-sided island of Mehetia, the youngest and SE-most of the Society Islands, lacks a well-developed fringing coral reef. The ~400-m-high island (known as Meetia or Meketia in the Tahitian and Tuamotuan languages, respectively) is the summit of a large volcano that rises 4000 m from the sea floor. An older edifice is formed of a lava flow sequence overlain by hydromagmatic deposits and strombolian ejecta. A well-preserved Holocene crater, 150 m wide and 80 m deep, is located NW of the summit and has been the source of the youngest lava flows on the island (Binard et al., 1993). Polynesian legends mention "large fires," and the lack of vegetation on some lava flows suggests that the latest activity occurred within the last 2000 years (Talandier and Custer, 1976). Other recent activity originated from a submarine crater at 2500-2700 m depth on the SE flank.

Information Contacts: J.M. Talandier, Lab. de Géophysique, Tahiti.


Minami-Hiyoshi (Japan) — October 1981 Citation iconCite this Report

Minami-Hiyoshi

Japan

23.5°N, 141.935°E; summit elev. -107 m

All times are local (unless otherwise noted)


No discolored water seen during January-October 1981

The Japan Maritime Safety Agency (JMSA) continues frequent monitoring flights over several known submarine volcanoes. [No discolored water was specifically noted, in an included table of observations, during January-October 1981 (see table 1 below).]

Geologic Background. Periodic water discoloration and water-spouting have been reported over this submarine volcano since 1975, when detonations and an explosion were also reported. It lies near the SE end of a coalescing chain of youthful seamounts, and is the only historically active vent. The reported depth of the summit of the trachyandesitic volcano has varied between 274 and 30 m. The morphologically youthful seamounts Kita-Hiyoshi and Naka-Hiyoshi lie to the NW, and Ko-Hiyoshi to the SE.

Information Contacts: JMSA, Tokyo; JMA, Tokyo.


Ruapehu (New Zealand) — October 1981 Citation iconCite this Report

Ruapehu

New Zealand

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

All times are local (unless otherwise noted)


Increased seismicity; lower crater lake temperatures; eruption expected

Ruapehu's Crater Lake has cooled from 32.5°C in late April to 11°C in early October. The temperatures recorded since late August were the lowest since detailed measurements began. Periods of low Crater Lake temperature preceded strong eruptions in June 1969 and April 1975.

The following report, from J. H. Latter, describes recent seismicity.

"The period of declining temperatures up to 7 September was seismically quiet, apart from minor volcanic tremor and associated B-type earthquakes that ended on 6 July, a short swarm of roof rock shocks from 11 to 13 July, and less than an hour of strong volcanic tremor on 24 August. In particular, there were no large B-type earthquakes, as after the April 1975 eruption, which might have suggested activity at the volcanic focus that was unable to break out at the surface. This might be interpreted as evidence that the low lake temperatures were due either to a blockage deeper than the volcanic focus (thought to be about 1 km below Crater Lake), or that heat transfer had declined or stopped, for some different reason.

"Beginning gradually on 7 September, a swarm of roof rock earthquakes marked the end of seismic quiescence. The swarm was unusually prolonged, ending on 2 October with an earthquake of magnitude 2.4 ML (i.e. quite small), which was not a true roof rock earthquake. This was well-recorded on the Tongariro National Park network and could be accurately located at 2 km below Crater Lake, which, in the model used, marks the top of the Tertiary sedimentary rocks below the volcano. Rather than being a roof rock earthquake, it was therefore a "wall rock," or perhaps even "floor rock" earthquake, for the known volcanic focus; although it is possible that it may represent a roof rock earthquake for a deeper volcanic focus (magma chamber?) below the Tertiary sedimentary rocks.

"A train of weak B-type earthquakes preceded the 2 October earthquake by about 54 hours. Volcanic tremor began about 8 hours later but lasted only a few hours. Tremor did not become common on the records until after the 2 October earthquake. Since then it has built up steadily on the records, becoming quite strong and almost continuous since 14 October. Clearly the roof rock swarm and terminating earthquake took place in response to stress caused by blockage of some kind and had the effect of removing the blockage. Since 2 October, more typical volcano-seismic activity, as shown by the tremor, has resumed.

"An unusual feature of the volcanic tremor has been that some has been of a much higher frequency than measured previously at Ruapehu. In the past, 3 Hz tremor has been thought to have been correlated with eruptions. On 7 October, tremor with dominant frequencies as high as 4.5 Hz was recorded, probably because of intrusion at shallow levels high in the volcano in very restricted or narrow spaces [see also 28 October in 6:12].

"In spite of the interesting type of recent seismic activity, it is stressed that the amount of energy released is small. Roof rock activity has peaked at a level well below that reached in November 1976 and March 1977. Furthermore, B-type earthquakes have all been small (the largest ML 2.3), and the volcanic tremor, which peaked on 18 October at about 1.9 x 106 J [and again on 25 October (~3.5 x 106 J)], was exceeded in November 1976, October 1977, October 1978, and August and October 1979. It is far below the level that prevailed before the 1971 eruptions.

"It seems likely that the present moderately high level of tremor will be associated with reheating of Crater Lake, and that eruptions will take place. But the volcano can perhaps be considered in a less dangerous state than during its recent period of low temperatures and marked roof rock activity."

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: J. Latter, DSIR, Wellington.


Soufriere Guadeloupe (France) — October 1981 Citation iconCite this Report

Soufriere Guadeloupe

France

16.044°N, 61.664°W; summit elev. 1467 m

All times are local (unless otherwise noted)


Temperature, magnetic field stable

IPG geophysicists have installed three telemetering magnetometers and established a network of 20 additional non-telemetering magnetometer stations on the flanks of Soufrière. Although significant changes in the magnetic field were recorded over periods of a few [months] during the phreatic and seismic activity of 1976-77, no variations of more than 1.5 nT were detected between August 1980 and March 1981.

IPG geophysicists also drilled two boreholes, to 77 m depth in the summit dome, and to 97 m depth immediately beside the dome. The temperature measurement at the bottom of dome borehole decreased steadily, from 97.5°C in April 1978 to 87°C in December 1980. . . . No significant temperature variation was recorded in the borehole near the dome, which remained at about 19°C through 1980. The temperature of a fumarole (Lacroix) about 80 m below the summit dropped from about 160°C in July 1978 to just over 100° by January 1979 and has remained between 96° and 98°C in 1981.

Further Reference. Zlotnicki, J., 1986, Magnetic measurements on La Soufrière volcano, Guadeloupe (Lesser Antilles), 1976-1984: A re-examination of the volcanomagnetic effects observed during the volcanic crisis of 1976-1977: JVGR, v. 30, p. 83-116.

Geologic Background. La Soufrière de la Guadeloupe volcano occupies the southern end of Basse-Terre, the western half of the butterfly-shaped island of Guadeloupe. Construction of the Grand Découverte volcano about 0.2 million years ago (Ma) was followed by caldera formation after a plinian eruption about 0.1 Ma, and then by construction of the Carmichaël volcano within the caldera. Two episodes of edifice collapse and associated large debris avalanches formed the Carmichaël and Amic craters about 11,500 and 3100 years ago, respectively. The presently active La Soufrière volcano subsequently grew within the Amic crater. The summit consists of a flat-topped lava dome, and several other domes occur on the southern flanks. Most historical eruptions have originated from NW-SE-trending fissure systems that cut across the summit and upper flanks. A relatively minor phreatic eruption in 1976-77 caused severe economic disruption when Basse-Terre, the island's capital city, which lies immediately below the volcano, was evacuated.

Information Contacts: J. Pozzi, J. Zlotnicki, G. Simon, J. Le Mouel and J. Cheminée, IPG, Paris.


St. Helens (United States) — October 1981 Citation iconCite this Report

St. Helens

United States

46.2°N, 122.18°W; summit elev. 2549 m

All times are local (unless otherwise noted)


Lava extrusion adds new lobe to composite dome

Lava extrusion that probably began 30 October added a new lobe to the composite dome in the crater, the 9th extrusive episode since the catastrophic eruption of 18 May 1980. After lava extrusion ended 10 September (SEAN 06:08), rates of displacement in the crater remained low for several weeks, as they had after earlier extrusion episodes. Sulfur dioxide emission ranged from 70 to 190 t/d 9-24 October, but showed no particular trends.

The crater floor was not quiet during this period. Inflation of the dome has caused small thrust faults to form in the surrounding crater floor. In early October, the most active thrust, S of the dome, was moving at about 1.5 cm/day, and stations on the N crater rampart showed outward movement of about 0.5 cm/day. By 24 October, these rates had increased to 14.5 and 3.5-4 cm/day respectively, and levelling profiles perpendicular to the dome showed that crater floor tilt rates had reached 400-500 µrad/day, prompting the USGS to issue an advisory prediction of renewed lava extrusion within the next 2 weeks.

Eleven laser targets were installed on the dome and distances to the targets were measured from fixed points 150-1,000 m away beginning 21-23 October. Rates of lateral expansion of the dome varied considerably, but were as much as 50 cm/day as of 25 October. Three continuously recording tiltmeters located 550, 850, and 1,050 m N of the center of the dome began returning data 13 October. No significant tilt was detected by these instruments until about noon on 26 October, when all three began to record inflation at 25-50 µrad/day. The number of local earthquakes began to increase on 27 October, and gradually became more frequent through the 29th, but most of the events were extremely small. Seismicity increased substantially between midnight and 0700 on 30 October, then all but rockfall events ceased fairly abruptly shortly after 0730. During this period, there were a few events that reached roughly M 1, but none were in the M 1.5-1.8 range typical of the larger events prior to past additions to the dome, and the total seismic energy release was much smaller than that associated with previous extrusion episodes. Inflation registered by the three continuously recording tiltmeters N of the dome flattened out on 29 October and at least one instrument began to show deflation by 0800 on the 30th.

Poor weather prevented any observations of the crater 30 October. When visibility improved early on the 31st, a substantial quantity of lava had already been extruded from the N part of the pre-existing dome's summit area. The new lobe advanced gradually down the N flank over portions of lobes extruded in April, June, and September. Geologists in the crater 31 October noted that several plastic airphoto targets N of the dome had melted and some metal fenceposts had been bent, although boards on the ground were not disturbed, indicating that a directed hot blast may have moved 200-300 m N from the dome. By the evening of 1 November, the new lava had advanced about halfway down the dome's N flank (figure 19), but was moving more slowly than the previous day. The lobe front moved roughly 20-40 m downslope during the next 24 hours, a quarter to half of the previous rate of advance. As of late 4 November, lava had nearly reached the foot of the April lobe, where a substantial pile of talus had accumulated, and appeared to be advancing slowly, but lava extrusion had stopped by 5 November. The volume of the new lobe appeared to be roughly comparable to that of previous lobes (a few million cubic meters).

Figure (see Caption) Figure 19. Sketch of the N side of the Mt. St. Helens composite dome at 1400 on 1 November 1981, looking S from the mouth of the crater. Sketch by Bobbie Myers.

The extrusion was accompanied by major deformation of the dome, particularly at the S end, where dramatic changes took place. Large blocks were thrust upwards 10-20 m and steep outward tilting was obvious. On 31 October, the four remaining laser targets on the dome showed outward movements of 1-8.2 m since the previous measurements six days earlier. However, by 2 November, expansion of the pre-existing dome had slowed to only a few centimeters per day and some areas may have been showing subsidence. Large incandescent cracks radial to the center of the new extrusion extended from top to bottom of the September lobe, and the June lobe also showed large new cracks. As during previous extrusion episodes, thrust faults stopped moving (on 1 November) and significant deformation of the crater floor had not resumed as of 10 November. SO2 emission during the extrusion peaked at 220 t/d (on 31 October) then dropped steadily, to 160 t/d 3 November, 130 t/d on the 6th, and 80 t/d on the 10th.

Geologic Background. Prior to 1980, Mount St. Helens formed a conical, youthful volcano sometimes known as the Fuji-san of America. During the 1980 eruption the upper 400 m of the summit was removed by slope failure, leaving a 2 x 3.5 km horseshoe-shaped crater now partially filled by a lava dome. Mount St. Helens was formed during nine eruptive periods beginning about 40-50,000 years ago and has been the most active volcano in the Cascade Range during the Holocene. Prior to 2200 years ago, tephra, lava domes, and pyroclastic flows were erupted, forming the older St. Helens edifice, but few lava flows extended beyond the base of the volcano. The modern edifice was constructed during the last 2200 years, when the volcano produced basaltic as well as andesitic and dacitic products from summit and flank vents. Historical eruptions in the 19th century originated from the Goat Rocks area on the north flank, and were witnessed by early settlers.

Information Contacts: T. Casadevall, D. Dzurisin, D. Peterson, D. Swanson, USGS, Vancouver, WA; C. Boyko, S. Malone, E. Endo, C. Weaver, University of Washington; R. Tilling, USGS, Reston, VA.


Suwanosejima (Japan) — October 1981 Citation iconCite this Report

Suwanosejima

Japan

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

All times are local (unless otherwise noted)


January-August 1981 explosions tabulated

During 1981, explosions from Suwanose-jima have been recorded every month through August. Observations were made from 3 km S of the active B crater (figure 1) and from Nakano-shima Island, 26 km NE. An explosion is registered when visual observation of an eruption cloud is correlated with the sound of an explosion. Aircraft crews reported three eruption clouds: 28 June, cloud height 1.2 km; 17 July, 2.4 km; and 10 August, 2.7 km.

Figure (see Caption) Figure 1. Topographic map of Suwanose-jima Island; the active vent is in Crater B. Courtesy of JMA.

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: JMA, Tokyo.

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.

Atmospheric Effects (1980-1989)  Atmospheric Effects (1995-2001)

Special Announcements

Special announcements of various kinds and obituaries.

Special Announcements

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/).