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Bulletin of the Global Volcanism Network

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

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


Recently Published Bulletin Reports

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).

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Bulletin of the Global Volcanism Network - Volume 20, Number 10 (October 1995)

Managing Editor: Richard Wunderman

Adatarayama (Japan)

First tremor since 1965

Aira (Japan)

Explosive activity continues

Akan (Japan)

Continued elevated seismicity

Asosan (Japan)

Isolated tremor; ejections of mud and water

Atmospheric Effects (1995-2001) (Unknown)

Lidar data from Germany and Virginia

Dukono (Indonesia)

Pilot report of plume on 25 September

Etna (Italy)

Frequent Strombolian explosions and ash emissions from Northeast Crater and Bocca Nuova

Galeras (Colombia)

Minor seismicity and fumarolic emissions

Iwatesan (Japan)

Short tremor episode

Izu-Oshima (Japan)

Minor tremor and 48 earthquakes

Izu-Tobu (Japan)

Tremor observed again

Kozushima (Japan)

Earthquake swarm ends in mid-October

Kujusan (Japan)

Additional data on the sudden aseismic eruption of 11 October

Langila (Papua New Guinea)

Ash-bearing eruption columns rise hundreds of meters

Lengai, Ol Doinyo (Tanzania)

New hornitos and lava flows observed in July

Llaima (Chile)

Minor eruption just after a M 4.0 earthquake 160 km to the east

Manam (Papua New Guinea)

Passive degassing

Merapi (Indonesia)

Pyroclastic flows travel down two river drainages

Poas (Costa Rica)

High seismicity

Rabaul (Papua New Guinea)

Minor seismicity and vapor emission

Raung (Indonesia)

Aviation report of a plume, but not seen on satellite imagery

Rincon de la Vieja (Costa Rica)

New eruption; lahars damage a bridge and lead to evacuations

Rinjani (Indonesia)

Small ash plume seen on 12 September

Ruapehu (New Zealand)

Late September-early October eruptions rival those in 1945

Ruby (United States)

Submarine eruption

Semeru (Indonesia)

Explosions and pyroclastic flows continue

Soufriere Hills (United Kingdom)

Small ash explosions continue; three new vents form; September dome grows

Tengger Caldera (Indonesia)

Eruption from Bromo sends dark ash plume 700 m above the rim

Vulcano (Italy)

Fumarolic activity notably diminished from previous years

Yellowstone (United States)

New mud volcano, minor mud flow, and associated thermal features



Adatarayama (Japan) — October 1995 Citation iconCite this Report

Adatarayama

Japan

37.647°N, 140.281°E; summit elev. 1728 m

All times are local (unless otherwise noted)


First tremor since 1965

During 27 October, volcanic tremor of about 3-minutes duration was recorded at a site 4.8 km NE of Adatara's summit (station A). This was the first case of tremor since the local observatory began observations in 1965.

Geologic Background. The broad forested massif of Adatarayama volcano is located E of Bandai volcano, about 15 km SW of Fukushima city. It consists of a group of dominantly andesitic stratovolcanoes and lava domes that rise above Tertiary rocks on the south and abut Azumayama volcano on the north. Construction took place in three main stages that began about 550,000, 350,000, and 200,000 years ago. The high point of the complex is 1728-m-high Minowasan, a dome-shaped stratovolcano north of Tetsuzan, the currently active stratovolcano. Numanotaira, the active summit crater, is surrounded by hot springs and fumaroles and is breached by the Iogawa river ("Sulfur River") on the west. Seventy-two workers of a sulfur mine in the summit crater were killed during an eruption in 1900. Historical eruptions have been restricted to the 1.2-km-wide, 350-m-deep Numonotaira crater.

Information Contacts: Volcanological Division, Seismological and Volcanological Department, Japan Meteorological Agency (JMA), 1-3-4 Ote-machi, Chiyoda-ku, Tokyo 100 Japan.


Aira (Japan) — October 1995 Citation iconCite this Report

Aira

Japan

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

All times are local (unless otherwise noted)


Explosive activity continues

Activity at Minami-dake crater became high during both early and late October. On 28 October, 9 explosive eruptions occurred and significant volcanic ash fell in Kagoshima City. During October, seismic station B (2.3 km NE of Minami-dake crater) recorded 720 earthquakes and 1,206 tremors. On 27-28 October there were seismic swarms. During October the volcano produced 31 eruptions, 23 of them explosive; the highest ash plume, on 28 October, rose 3 km above the summit crater. October ashfall (measured 10 km W at the Kagoshima Meteorological Observatory) was 117 g/m2.

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

Information Contacts: Volcanological Division, Seismological and Volcanological Department, Japan Meteorological Agency (JMA), 1-3-4 Ote-machi, Chiyoda-ku, Tokyo 100 Japan.


Akan (Japan) — October 1995 Citation iconCite this Report

Akan

Japan

43.384°N, 144.013°E; summit elev. 1499 m

All times are local (unless otherwise noted)


Continued elevated seismicity

Seismicity during October, and thus far in 1995, remained slightly higher than was typical for the past several years (figure 6). The highest daily number of earthquakes during the month took place on 2 October and consisted of 33 events (recorded at Station A, 2.3 km from Ponmachineshiri Crater). The monthly total for October consisted of 395 events.

Figure (see Caption) Figure 6. The number of daily earthquakes at Akan's station A, 1 January 1987 through October 1995. Courtesy of JMA.

Geologic Background. Akan is a 13 x 24 km caldera located immediately SW of Kussharo caldera. The elongated, irregular outline of the caldera rim reflects its incremental formation during major explosive eruptions from the early to mid-Pleistocene. Growth of four post-caldera stratovolcanoes, three at the SW end of the caldera and the other at the NE side, has restricted the size of the caldera lake. Conical Oakandake was frequently active during the Holocene. The 1-km-wide Nakamachineshiri crater of Meakandake was formed during a major pumice-and-scoria eruption about 13,500 years ago. Within the Akan volcanic complex, only the Meakandake group, east of Lake Akan, has been historically active, producing mild phreatic eruptions since the beginning of the 19th century. Meakandake is composed of nine overlapping cones. The main cone of Meakandake proper has a triple crater at its summit. Historical eruptions at Meakandake have consisted of minor phreatic explosions, but four major magmatic eruptions including pyroclastic flows have occurred during the Holocene.

Information Contacts: Volcanological Division, Seismological and Volcanological Department, Japan Meteorological Agency (JMA), 1-3-4 Ote-machi, Chiyoda-ku, Tokyo 100 Japan.


Asosan (Japan) — October 1995 Citation iconCite this Report

Asosan

Japan

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

All times are local (unless otherwise noted)


Isolated tremor; ejections of mud and water

During October the floor of Aso's active crater (Naka-dake Crater 1) remained covered by a pond of hot water. The pond's surface was disrupted by occasional fountaining up to 5-m high. Elevated tremor continued since last month, and some October days had over 200 earthquakes; the daily mean amplitude of continuous tremors sometimes reached over 0.5 þm. Personnel 800 m W of the crater (at Aso Weather Station) felt earthquakes at 1829 and 1909 on 11 and 22 October, respectively.

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: Volcanological Division, Seismological and Volcanological Department, Japan Meteorological Agency (JMA), 1-3-4 Ote-machi, Chiyoda-ku, Tokyo 100 Japan.


Atmospheric Effects (1995-2001) (Unknown) — October 1995 Citation iconCite this Report

Atmospheric Effects (1995-2001)

Unknown

Unknown, Unknown; summit elev. m

All times are local (unless otherwise noted)


Lidar data from Germany and Virginia

Lidar data from Germany for July and August (table 4) again revealed the presence of a volcanic aerosol layer centered at 17-19 km altitude. Backscattering ratios have decreased since the last reports (Bulletin v. 20, nos. 2 and 7). October lidar data from Hampton, Virginia, showed an aerosol layer at 18-19 km altitude; these values are similar to the previous report (Bulletin v. 19, no. 11). Backscatter data declined to the range of 1.22-1.25 from 1.38-1.50.

Table 4. Lidar data from Germany and Virginia, USA, showing altitudes of aerosol layers. Backscattering ratios are for the ruby wavelength of 0.69 microns. The integrated value shows total backscatter, expressed in steradians^-1, integrated over 300-m intervals from the tropopause to 30 km.

DATE LAYER ALTITUDE (km) (peak) BACKSCATTERING RATIO BACKSCATTERING INTEGRATED
Garmisch-Partenkirchen, Germany (47.5°N, 11.0°E)
07 Jul 1995 11-27 (19.7) 1.12 (1.3) --
19 Jul 1995 12-26 (19.8) 1.13 (1.3) --
21 Jul 1995 13-29 (18.0) 1.12 (1.3) --
26 Jul 1995 11-28 (19.1) 1.13 (1.3) --
31 Jul 1995 13-24 (18.8) 1.09 (1.2) --
03 Aug 1995 12-27 (17.5) 1.12 (1.3) --
Hampton, Virginia (37.1°N, 76.3°W)
23 Mar 1995 12-25 (17.8) 1.36 0.135 x 10-3
04 May 1995 12-25 (18.7) 1.3 0.104 x 10-3
19 Oct 1995 15-30 (18.1) 1.22 0.059 x 10-3
23 Oct 1995 15-30 (18.8) 1.25 0.065 x 10-3

Information Contacts: Horst Jager, Fraunhofer -- Institut fur Atmospharische Umweltforschung, Kreuzeckbahnstrasse 19, D-8100 Garmisch-Partenkirchen, Germany; Mary Osborn, NASA Langley Research Center (LaRC), Hampton VA 23665, USA.


Dukono (Indonesia) — October 1995 Citation iconCite this Report

Dukono

Indonesia

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

All times are local (unless otherwise noted)


Pilot report of plume on 25 September

A pilot report from a Qantas flight on the morning of 25 September described a plume to 6 km altitude that was drifting ESE. Visible satellite imagery failed to detect volcanic ash, but weather clouds in the SE sector were identified with infrared imagery.

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: BOM Darwin, Australia.


Etna (Italy) — October 1995 Citation iconCite this Report

Etna

Italy

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

All times are local (unless otherwise noted)


Frequent Strombolian explosions and ash emissions from Northeast Crater and Bocca Nuova

The Istituto Internazionale di Vulcanologia (IIV) report below provides an overview of activity during October. IIV reports generally summarize the temporal evolution of volcanic phenomena during the whole month, skipping some trivial details, and frame the ongoing activity in the context of phenomena over a period of years.

Reports detailing activity during short visits made by visiting volcanologists provide a different perspective on the volcanism. One such report for some days in October was provided by a team led by Open University (OU) volcanologists conducting routine deformation measurements during 9 September-14 October. Short visits to the summit craters on 7, 12, and 14 October were also made by Boris Behncke, with additional observations from Carmelo Monaco and Marcello Bianca (University of Catania), Maria Felicia Monaco (Bari University), and others.

Review of July-September 1995 activity. Strombolian activity resumed at Bocca Nuova on 30 July and in Northeast Crater on 2 August (BGVN 20:08). On 30 July spatter was observed inside Bocca Nuova from a new pit crater on the N part of the crater floor. The activity climaxed on 2 and 3 August, when lava jets rose above the crater rim, then stopped on the night of 4 August. Strombolian explosions during 2-3 August issued from a small vent in the lowest part of the crater. Two more Strombolian episodes occurred on 18 and 29 August. A strong explosion from Northeast Crater on 13 September sent an ash plume 100 m above the rim. Ash emissions from Bocca Nuova and Northeast Crater continued until about 20 September, but explosions were heard throughout the month (BGVN 20:09). The OU team noted light ashfall 2-3 km away in the third week of September, and heavier ashfall 50 m from the Bocca Nuova rim on 27 September.

Overview of October 1995 activity from IIV. After a short period of Strombolian activity at Bocca Nuova and Northeast Crater at the beginning of October, alternating mild Strombolian activity and ash emission characterized their activity for the rest of the month. On 8 October almost continuous rumbling noises (like roaring jets) were heard from both craters. On the morning of 12 October intense ash emissions took place from both craters. Bocca Nuova displayed small short-lived ash puffs (5-7/hour), while from the Northeast Crater a dense ash column rising as high as 900 m developed repeatedly (2/hour). IIV field parties working in the summit area reported that the ash emission were accompanied by falling rock noises. However, successive surveys observed neither juvenile nor lithic blocks on the crater rims.

After 12 October Strombolian activity progressively resumed at Northeast Crater and continued with variable intensity until the end of the month. On 19 October Strombolian activity was relatively vigorous and the scoria ejections, up to few tens of meters from the crater rim, were almost continuous. A survey on 25 October revealed an appreciable decrease of the explosion frequency. Bocca Nuova exhibited intermittent ash emissions after 12 October. As during previous activity, they originated in a depressed area of the NW crater floor. Explosions observed on 19 October were accompanied by ejection of a black (lithic?) block to a few tens of meters above the crater floor, but neither glowing at the vent or ejection of incandescent bombs were observed. After 19 October intermittent ash emission progressively decreased, and in the last week of the month weak Strombolian activity resumed at Bocca Nuova. Significant eruptions on 9 and 14 November will be reported in the next Bulletin.

Deformation measurements. Preliminary results from the OU team indicate little ground deformation since October 1994 over most of the network. Summit levelling showed insignificant movement (-5 mm near the summit, +7 mm on the N flank) apart from the area above the 1991-93 dike, which between the W side of Cisternazza and Belvedere showed a fairly consistent subsidence of 17-24 mm. Preliminary GPS computations suggested a radial expansion about the summit of ~15 mm. Dry-tilt stations showed no large tilts.

Details of 1-7 October activity. Observations from the Northeast Crater rim on the afternoon of 1 October by the OU team revealed two faintly glowing vents, ~3-5 m across, on the crater floor. The following night, bright summit glow was seen from Nicolosi (15 km S), and on the morning of 3 October loud explosions from Northeast Crater were heard from the trail 800 m W, which had been covered with a thin layer of red ash overnight. Explosions were again heard late in the afternoon from ~7 km away, and light ash fell near Monte Corbara (5 km NW). While approaching the crater at 1815 on 3 October, two guides and an Italian TV camera crew returning from the rim warned of bombs falling outside the crater. As the OU team moved towards the high ground behind the crater, a large explosion sent brightly-glowing juvenile bombs just over the rim, rolling toward them. A few seconds later a single bomb ~20 cm across landed 10 m away, 100-200 m from the rim. Similar bomb ejections to smaller distances occurred about every 2 minutes until the team descended at 1845. On 7 October, Behncke noted a dense steam-and-gas plume from Northeast Crater. Most of the plume and occasionally some ash rose from the SSE part of the crater floor; falling stones were frequently heard.

Detonations from within Bocca Nuova heard by the OU team on 1 October were only audible from the rim. One vent on 4 October was explosively exhaling gas, and the other was collapsing, producing brownish ash clouds. Behncke observed small Strombolian explosions from Bocca Nuova on 6 October, but only ash emissions the next day. On the 7 October visit, Behncke observed frequent ash plumes from Bocca Nuova accompanied by rumbling noises and the sound of falling stones; Strombolian explosions were frequent.

The Chasm (La Voragine) quietly emitted fumes on 1 October. On 4 October the OU team climbed into Southeast Crater to the edge of the vents, which emitted gas quietly and not under pressure, apart from one area just below the S rim. On 7 October, Behncke heard small explosions, but no ejections or incandescence were seen after sunset.

Details of 12-14 October activity. Between 0800 and 0900 on 12 October a series of collapses within Northeast Crater generated a thick ash cloud. Pulses of rapidly rising ash plumes resulted in a vertical column 800-1,000 m above the summit. After 0900, a dilute gas plume rose from Northeast Crater while Bocca Nuova sent frequent ash emissions 200-300 m above the summit. When Behncke reached the crater rim shortly after 1230, there were vigorous steam emission and explosions from Northeast Crater.

Behncke saw incandescent spots in the central Northeast Crater floor that gradually increased in number and intensity. Pyroclastic ejections became more frequent and vigorous, and soon the incandescent areas were hidden by gas and dilute ash plumes. The ash plumes first rose slowly to ~100 m above the crater floor, but gradually rose higher and became more heavily ash-laden. About 5 minutes after the onset of ash venting, dense convoluting ash clouds began to rise above the rim. Bomb and ash emission steadily increased. The high-pressure gas emission noise at the beginning of this activity changed to a dull rumbling connected with the ash emission. Short pulses of bomb emissions every 5-10 seconds were followed by a dark ash puff. After ~10 minutes, the ash puffs merged into a continuous column that rose hundreds of meters above the rim. Around 1345 vigorous emissions ejected black ash plumes ~1 km above the summit. Periodic ash emissions from Northeast Crater gradually became less vigorous before ceasing that evening.

On 12 October (0800-0900), the OU team heard detonations from Bocca Nuova, mainly from a vent on the E side of the floor, but the larger vent on the NW side occasionally threw 20-cm-diameter lithic blocks 30-50 m high. Ash emissions seen by Behncke after 1230 occurred every 2-5 minutes from the pit on the NW crater floor. Each emission began with block and/or bomb ejections followed by a dense ash plume. The bombs and blocks rose out of the ~50-m-deep pit but remained ~100 m below the rim, whereas the ash plumes rose 100-500 m above the summit. An open vent in the SE crater floor displayed continuous gas emission with occasional explosions that ejected dense gas clouds.

Shortly after 1700 on 14 October Behncke saw a central glowing vent in Northeast Crater. Vigorous high-pressure gas emission produced a roaring noise, and the plume was almost vapor-free. During the first 30 minutes of the visit, glowing spatter was occasionally ejected from the vent. As degassing increased, numerous incandescent spots became visible, aligned more or less concentrically around the vent. After the first half hour, Strombolian bursts became more vigorous, ejecting bombs ~50 m above the pit. About 10 minutes later, the explosions again intensified, and the crater floor around the vent, which appeared more funnel-shaped, was covered with incandescent bombs. Ejections rose ~100 m above the vent but remained far below the crater rim.

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: Massimo Pompilio, CNR Istituto Internazionale di Vulcanologia, Piazza Roma 2, 95123 Catania, Italy; John B. Murray and Fiona McGibbon, Dept. of Earth Sciences, The Open University, Milton Keynes MK7 6AA, United Kingdom; Nicki Stevens, NUTIS, Reading University, Whiteknights, P.O. Box 227, Reading RG6 2AB, United Kingdom; Phil. Sargent, Sue Elwell, and Sarah Cooper, Civil Engineering Dept., Nottingham Trent University, Burton Street, Nottingham NG1 4BU, United Kingdom; Boris Behncke, Dept. of Volcanology and Petrology, GEOMAR, Wischhofstr. 1-3, 24148 Kiel, Germany.


Galeras (Colombia) — October 1995 Citation iconCite this Report

Galeras

Colombia

1.22°N, 77.37°W; summit elev. 4276 m

All times are local (unless otherwise noted)


Minor seismicity and fumarolic emissions

Activity during August-October remained low. Fumarolic emissions continued from areas near the active cone, with a concentration of fumaroles on the W part of the summit. SO2 concentrations, obtained by the COSPEC method, remained generally low at 53-170 metric tons/day in August and < 100 t/d in September. No deformation was detected by electronic tiltmeters during August-October. Temperature measurements at La Joya and Chavas fumaroles, as well as radon measurements, have begun in order to improve the surveillance.

High-frequency seismicity during August was centered NNE of the active crater, and consisted of events of M < 2.2 Seismic activity in September was characterized by volcano-tectonic events, located mainly in three seismogenic regions: W, SW, and NNE of the active crater. Most active was the NNE source, which has shown signs of reactivation since last March. Most earthquakes had magnitudes < 1.5. Four events during September were felt by local residents, on 3, 12, 15, and 16 September, with magnitudes of 2.5, 2.0, 2.7, and 2.7, and depths of 12, 5, 8, and 8 km, respectively. The 16 September earthquake occurred in the SW region and the other three events in the NNE region.

The most significant October seismicity consisted of high-frequency events NNE of the active cone at depths of 3-7 km; magnitudes were < 3. The largest earthquake, on the morning of 15 October, was centered ~3 km NNE of the cone at 7 km depth. It had a magnitude of 3 and was felt in Pasto, Jenoy, Narino, and in other local towns.

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

Information Contacts: Pablo Chamorro and Diego Gomez, INGEOMINAS - Observatorio Vulcanologico y Sismologico de Pasto, A.A. 1795, San Juan de Pasto, Narino, Colombia (URL: https://www2.sgc.gov.co/volcanes/index.html).


Iwatesan (Japan) — October 1995 Citation iconCite this Report

Iwatesan

Japan

39.853°N, 141.001°E; summit elev. 2038 m

All times are local (unless otherwise noted)


Short tremor episode

Tohoku University seismometers near Iwate volcano continued to register tremor (BGVN 20:09). Beginning at 0009 on 20th October, the tremor lasted ~25 minutes.

Geologic Background. Viewed from the east, Iwatesan volcano has a symmetrical profile that invites comparison with Fuji, but on the west an older cone is visible containing an oval-shaped, 1.8 x 3 km caldera. After the growth of Nishi-Iwate volcano beginning about 700,000 years ago, activity migrated eastward to form Higashi-Iwate volcano. Iwate has collapsed seven times during the past 230,000 years, most recently between 739 and 1615 CE. The dominantly basaltic summit cone of Higashi-Iwate volcano, Yakushidake, is truncated by a 500-m-wide crater. It rises well above and buries the eastern rim of the caldera, which is breached by a narrow gorge on the NW. A central cone containing a 500-m-wide crater partially filled by a lake is located in the center of the oval-shaped caldera. A young lava flow from Yakushidake descended into the caldera, and a fresh-looking lava flow from the 1732 eruption traveled down the NE flank.

Information Contacts: Volcanological Division, Seismological and Volcanological Department, Japan Meteorological Agency (JMA), 1-3-4 Ote-machi, Chiyoda-ku, Tokyo 100 Japan.


Izu-Oshima (Japan) — October 1995 Citation iconCite this Report

Izu-Oshima

Japan

34.724°N, 139.394°E; summit elev. 758 m

All times are local (unless otherwise noted)


Minor tremor and 48 earthquakes

On 4 October, local instruments recorded volcanic tremor of short duration and small amplitude. Throughout the month a significant but undisclosed number of earthquakes occurred in the adjacent N and W coastal areas. During October there were 48 earthquakes beneath the cone.

Geologic Background. Izu-Oshima volcano in Sagami Bay, east of the Izu Peninsula, is the northernmost of the Izu Islands. The broad, low stratovolcano forms an 11 x 13 km island and was constructed over the remnants of three dissected stratovolcanoes. It is capped by a 4-km-wide caldera with a central cone, Miharayama, that has been the site of numerous historical eruptions. More than 40 parasitic cones are located within the caldera and along two parallel rift zones trending NNW-SSE. Although it is a dominantly basaltic volcano, strong explosive activity has occurred at intervals of 100-150 years throughout the past few thousand years. Historical activity dates back to the 7th century CE. A major eruption in 1986 produced spectacular lava fountains up to 1600 m height and a 16-km-high subplinian eruption column; more than 12,000 people were evacuated from the island.

Information Contacts: Volcanological Division, Seismological and Volcanological Department, Japan Meteorological Agency (JMA), 1-3-4 Ote-machi, Chiyoda-ku, Tokyo 100 Japan.


Izu-Tobu (Japan) — October 1995 Citation iconCite this Report

Izu-Tobu

Japan

34.9°N, 139.098°E; summit elev. 1406 m

All times are local (unless otherwise noted)


Tremor observed again

Mid- and late-September micro-earthquake swarms occurred offshore near Capes Kawana-zaki and Shiofuki-zaki (BGVN 20:09), an area adjacent Ito City on the E coast of the Izu Peninsula. In late September and early October pulses of seismicity continued off these Capes, trailing off toward mid-October (figure 16). Located ~5 km SW of the epicenters, Kamala Seismic Station recorded 5,881 October earthquakes. The largest earthquake struck at 1142 on 1 October with M 4.8; nearby Into City sustained a JMA-scale intensity of IV. Small-amplitude tremors occurred on both 4 October (four times), and 12 October (one time); low-frequency earthquakes took place on 4 October (four times) and 6 October (one time). Volumetric strain at Higashi-Izu and Ajiro acted in the sense of compression.

Figure (see Caption) Figure 16. Hourly earthquakes at Izu-Tobu recorded ~5 km SW of the seismic sources, September-October 1995. Courtesy of JMA.

Geologic Background. The Izu-Tobu volcano group (Higashi-Izu volcano group) is scattered over a broad, plateau-like area of more than 400 km2 on the E side of the Izu Peninsula. Construction of several stratovolcanoes continued throughout much of the Pleistocene and overlapped with growth of smaller monogenetic volcanoes beginning about 300,000 years ago. About 70 subaerial monogenetic volcanoes formed during the last 140,000 years, and chemically similar submarine cones are located offshore. These volcanoes are located on a basement of late-Tertiary volcanic rocks and related sediments and on the flanks of three Quaternary stratovolcanoes: Amagi, Tenshi, and Usami. Some eruptive vents are controlled by fissure systems trending NW-SE or NE-SW. Thirteen eruptive episodes have been documented during the past 32,000 years. Kawagodaira maar produced pyroclastic flows during the largest Holocene eruption about 3000 years ago. The latest eruption occurred in 1989, when a small submarine crater was formed NE of Ito City.

Information Contacts: Volcanological Division, Seismological and Volcanological Department, Japan Meteorological Agency (JMA), 1-3-4 Ote-machi, Chiyoda-ku, Tokyo 100 Japan.


Kozushima (Japan) — October 1995 Citation iconCite this Report

Kozushima

Japan

34.219°N, 139.153°E; summit elev. 572 m

All times are local (unless otherwise noted)


Earthquake swarm ends in mid-October

As reported in BGVN 20:09, on 6 October a M 5.6 earthquake occurred adjacent to Kozu-shima and a seismic swarm followed for the next few days. After that, seismic events continued but decreased toward the end of October; in total, during October there were 246 felt earthquakes.

Geologic Background. A cluster of rhyolitic lava domes and associated pyroclastic deposits form the small 4 x 6 km island of Kozushima in the northern Izu Islands. Kozushima lies along the Zenisu Ridge, one of several en-echelon ridges oriented NE-SW, transverse to the trend of the northern Izu arc. The youngest and largest of the 18 lava domes, 574-m-high Tenjoyama, occupies the central portion of the island. Most of the older domes, some of which are Holocene in age, flank Tenjoyama to the north, although late-Pleistocene domes are also found at the southern end of the island. Only two possible historical eruptions, from the 9th century, are known. A lava flow may have reached the sea during an eruption in 832 CE. Tenjosan lava dome was formed during a major eruption in 838 CE that also produced pyroclastic flows and surges. Earthquake swarms took place during the 20th century.

Information Contacts: Volcanological Division, Seismological and Volcanological Department, Japan Meteorological Agency (JMA), 1-3-4 Ote-machi, Chiyoda-ku, Tokyo 100 Japan.


Kujusan (Japan) — October 1995 Citation iconCite this Report

Kujusan

Japan

33.086°N, 131.249°E; summit elev. 1791 m

All times are local (unless otherwise noted)


Additional data on the sudden aseismic eruption of 11 October

On 11 October, aseismic phreatic eruptions started within the Kuju volcanic group, on Hosho (Hosyo) dome's E side (BGVN 20:09). On 12 October observers found an E-W trending line of vents ~300-m long; also, at that time an ash-bearing plume rose to ~1 km above the crater.

The eruption deposited a 100 m2 blanket of fist-sized volcanic clasts; it also emitted mud that flowed down an adjacent valley. After that, the volume and height of the plume gradually decreased until finally ash-bearing eruptions ceased at the month's end. Seismicity stayed low during October.

Geologic Background. Kujusan is a complex of stratovolcanoes and lava domes lying NE of Aso caldera in north-central Kyushu. The group consists of 16 andesitic lava domes, five andesitic stratovolcanoes, and one basaltic cone. Activity dates back about 150,000 years. Six major andesitic-to-dacitic tephra deposits, many associated with the growth of lava domes, have been recorded during the Holocene. Eruptive activity has migrated systematically eastward during the past 5000 years. The latest magmatic activity occurred about 1600 years ago, when Kurodake lava dome at the E end of the complex was formed. The first reports of historical eruptions were in the 17th and 18th centuries, when phreatic or hydrothermal activity occurred. There are also many hot springs and hydrothermal fields. A fumarole on Hosho lava dome was the site of a sulfur mine for at least 500 years. Two geothermal power plants are in operation at Kuju.

Information Contacts: Volcanological Division, Seismological and Volcanological Department, Japan Meteorological Agency (JMA), 1-3-4 Ote-machi, Chiyoda-ku, Tokyo 100 Japan.


Langila (Papua New Guinea) — October 1995 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)


Ash-bearing eruption columns rise hundreds of meters

The increased eruptive activity at Crater 2 that began during late September continued throughout October. The activity was marked by intermittent audible explosions. The bigger explosions developed plumes that rose several hundred meters above the summit crater, resulting in ashfalls on the volcano's N-NW side. Langila produced steady but weak crater glow on most nights during October; it threw incandescent lava fragments on 23-24, 26, and 31 October. Crater 3 was quiet, only giving off weak white emissions towards late October. Seismic recording restarted on 5 October after both seismographs had been inoperative since January 1995. October seismic activity was moderate.

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: Ben Talai, RVO.


Ol Doinyo Lengai (Tanzania) — October 1995 Citation iconCite this Report

Ol Doinyo Lengai

Tanzania

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

All times are local (unless otherwise noted)


New hornitos and lava flows observed in July

Intermittent explosive activity and extrusion of carbonititic lava on the crater floor began in January 1983 and continued for over ten years. Vigorous effusive and explosive activity in June 1993, perhaps the strongest of that eruptive episode, covered most of the crater floor and upper W flank with fresh lava flows and deposited ash on the flanks (BGVN 18:07-18:10). In September 1994 a deep central depression contained a hornito from which highly vesicular brown lava was erupting (BGVN 19:09).

Activity observed in mid-July 1995 was the first reported since September 1994, although the appearance of the recent flows indicated that they were a few months old. Members of the Societe de Volcanologie Geneve (SVG) visited the summit on 15 July 1995. A visit to the summit crater was also made by Celia Nyamweru on 19 July.

Activity on 15 July 1995. SVG observers reported a new active hornito (T36), ~4 m high, close to the S foot of T20 (figure 35). Fluid carbonatitic lava flows were emitted from its base through a channel in the direction of a rounded collapsed new opening ~15 m in diameter, close to T5/T9. The lava in the channel was pale brown and frothy, with a velocity estimated at 1.5 m/second; temperature was ~550 degrees C. At the end of the channel, the flow moved N through different tubes. Lava breakouts from some downstream openings were still very fluid and completely black. Both small pahoehoe and aa lava fronts were observed. Ejecta were rare from the summit vent of T36. The new lava field was mainly directed N, with one branch passing W of T20 and the other going through and filling the oval-shaped depression first noted in October 1993 (see BGVN 19:04).

Figure (see Caption) Figure 35. Sketch of the Ol Doinyo Lengai crater (~300 m wide) looking SW from the NE rim, 19 July 1995. Courtesy of Celia Nyamweru.

Activity on 19 July. At 1000 the crater was full of cloud, hiding features on the crater floor, but frequent sharp cracks, bangs, and thumps were heard, as well as bubbling noises. Conditions improved so that activity could be observed after 1115. White to brown steam was escaping continuously from the top of T20, and a little from T5T9. Sulfurous fumes were emitted from cracks on the E crater rim and wall. The lower slopes of T23 were made up of many small parallel pahoehoe flows, now soft and pale brown; T23 was not emitting steam. The new cones, T34 to T37, lay W of the depression that had been virtually filled by lava flows from these centers. T34 was a double cone, pale gray, with an open vent on its upper slope from which no steam or heat was being emitted. T35 was light brown to white, with no sign of fresh lava. T37 was a shallow circular crater W of and close to the base of T5/T9; it appeared fresh but showed no activity on 19 July.

T36 was a compound cone of which T36A was the largest component; it was composed of cascades of pahoehoe lava, some whitened and others black and very fresh. T36B was a rounded dome with a small vent at its base from which lava was emitted. T36C appeared to have a crack along its crest that emitted gas-rich lava. T36B and T36C were ~5 m apart and very close in elevation. Activity from hornito cluster T36 (figure 36) consisted of clots of lava thrown ~1 m above T36B, gas-rich lava escaping from the top of hornito T36C and flowing down its N slope, and very fluid, black shiny lava escaping from a small crack (T36E) on the lower slopes of this feature and flowing N across very recent pahoehoe. At 1137 a small spray of gas-rich lava escaped from hornito T36D, on the W side of T36. Warm pahoehoe flows on the W slope of T36,

Figure (see Caption) Figure 36. Details of hornito cluster at Ol Doinyo Lengai. 19 July 1995. Asterisks indicate areas of active lava emission. Courtesy of Celia Nyamweru.

Crater morphology. Features from June 1993 and earlier (see map in BGVN 19:04) were still visible, but major new cones had formed in the area between T5/T9, T20, and T23 (figure 35). T5/T9 remained a very prominent feature, and the tops of the T8, T14, and T15 cones remained visible, although all were surrounded by many younger lava flows. T24, T26, and T30 were not inspected closely, but there seemed to be no change in these large features in the S part of the crater; they were gray and white, with no sign of recent activity. West of T36 were two low lava domes with pale brown open craters, now inactive. To the W of them, on the edge of F34, was a low wide feature, possibly a collapsed cone, probably the features identified as T22, T31, and T32 in September 1993 (BGVN 18:09). There was also a rather new hornito in this area.

Recent pahoehoe flows ~10 cm thick had reached the base of the E, N, and NW walls. Crater walls appeared lowest to the NW. The rugged F34 and F35 lava flows of June 1993 were heavily weathered and beginning to soften and crumble. They were quite dark gray; a great contrast to the flows that had formed over the last several months (thin pahoehoe flows that whiten within a few weeks of eruption). No recent ash was observed on the outer slopes of the cone, the crater rim, or the inner walls; the vegetation was green and healthy. Brown vegetation was observed in a few areas near the base of the inner wall, probably due to contact with hot lava reaching the wall, and on part of the S wall below the summit.

This symmetrical stratovolcano in the African Rift Valley rises abruptly above the plain S of Lake Natron. It is the only volcano known to have erupted carbonatite tephra and lavas in historical time. The cone-building stage of Ol Doinyo Lengai ended about 15,000 years ago and was followed by periodic Holocene ejections. Historical eruptions have consisted of smaller tephra ejections and emission of numerous natrocarbonatite lava flows on the floor of the summit crater.

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

Information Contacts: Celia Nyamweru, Department of Anthropology, St. Lawrence University, Canton NY 13617, USA; M. Vigny and P. Vetsch, Societe de Volcanologie Geneve, B.P. 298, CH-1225 Chenebourg, Switzerland.


Llaima (Chile) — October 1995 Citation iconCite this Report

Llaima

Chile

38.692°S, 71.729°W; summit elev. 3125 m

All times are local (unless otherwise noted)


Minor eruption just after a M 4.0 earthquake 160 km to the east

Beginning on 13 October 1995 Llaima started emitting gases and occasional ash; in addition, during the night the northern principal crater glowed a rose color. Dominant winds dispersed the eruptive columns toward the SE on 13 October. Three days later, Llaima started emitting a continuous, strong blast of steam that occasionally also contained dark-gray scrolls bearing fine-grained ash. The resulting plume blew NE.

On the night of 20-21 October, the principal crater discharged a strong explosion. Wind carried ash toward the SW, depositing it on the alpine ice. Some ash fell over the Trufultruful valley and the valley's most eastern flanking hills, forming a band or stripe up to 12 km in length.

On 21 October between 1600 and 1800 the volcano gave off a continuous, intense column of vapor and ash. That night, between 2300 and 0100 in the town of Conguillio, residents heard an explosion accompanied by subterranean noises. The following night, observers saw a "ring of fire" over the principal crater, an effect thought to indicate the presence of lava within the crater.

The Servicio Sismologico de la Universidad de Chile reported that seismic activity one day before the eruption, on 12 October, included a M 4.0 earthquake that struck the region; its depth was 70 km; its epicenter fell at the extreme S end of Lake Lieulleu in the Cordillera de Nahuelbuta (38.28°S, 73.408°W), a spot about 160 km E of Llaima. During 20 and 22 October, portable seismometers picked up 1.0-1.5 Hz tremor; on 20 October the tremor appeared about 15-20 seconds before the above-mentioned explosion. It should be noted that such sub-continuous episodes of 1.0-1.5 Hz tremor are relatively rare at Llaima.

The 13-22 October eruptions followed fumarolic activity (BGVN 20:02) and, before that, an outbreak of ash-bearing eruptions in late August 1994 (BGVN 19:08). On the basis of the above behavior, the 24 October SERNAGEOMIN report stated that the volcano had been assigned an alert status of yellow. Llaima, an ice- and snow-covered stratovolcano, is one of the largest and most active in Chile; it erupted in 1990, 1992, and 1994.

Geologic Background. Llaima, one of Chile's largest and most active volcanoes, contains two main historically active craters, one at the summit and the other, Pichillaima, to the SE. The massive, dominantly basaltic-to-andesitic, stratovolcano has a volume of 400 km3. A Holocene edifice built primarily of accumulated lava flows was constructed over an 8-km-wide caldera that formed about 13,200 years ago, following the eruption of the 24 km3 Curacautín Ignimbrite. More than 40 scoria cones dot the volcano's flanks. Following the end of an explosive stage about 7200 years ago, construction of the present edifice began, characterized by Strombolian, Hawaiian, and infrequent subplinian eruptions. Frequent moderate explosive eruptions with occasional lava flows have been recorded since the 17th century.

Information Contacts: Hugo Moreno1, Gustavo Fuentealba, and Paola Pena, Observatorio Volcanologico de los Andes del Sur, SERNAGEOMIN, Temuco, Chile.


Manam (Papua New Guinea) — October 1995 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)


Passive degassing

Activity was low during October. During the month, both summit craters released only white vapors at low to moderate rates and both audible sounds and summit-crater night glow were absent. During the first three weeks of October, the daily totals of low-frequency earthquakes were at 200-500, but by month's end they increased to 800-1,300. Coincident with the increase, earthquake amplitudes also rose by ~50%. No visual changes accompanied the increase in seismicity. However, data from tiltmeters (4 km SW of the summit) showed a deflation of approximately 1.5 m µrad beginning around the second half of the month.

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: Ben Talai, RVO.


Merapi (Indonesia) — October 1995 Citation iconCite this Report

Merapi

Indonesia

7.54°S, 110.446°E; summit elev. 2910 m

All times are local (unless otherwise noted)


Pyroclastic flows travel down two river drainages

During August-October 1995 pyroclastic flows ("glowing avalanches") continued flowing down the Boyong River; others entered the Krasak River and reached ~1-1.5 km from the source. Seismic activity was dominated by multiphase and lava-avalanche (rockfall) earthquakes. The number of multiphase earthquakes increased in October to 793 events, compared to 186 in September. Earthquakes associated with lava avalanches or rock falls gradually decreased from 1,195 events in August to 806 in September and 605 in October (figure 16). Shallow volcanic (B-type) earthquakes (~1 km depth) were recorded on 25 October and a deep volcanic (A-type) earthquake (2.7 km depth) was detected on 30 October. Observations in October indicated an inflation associated with 40 µrad of tilt. Measurement of SO2 by COSPEC indicated that the emission rate during October fluctuated between 18 and 112 t/d (average 63).

Figure (see Caption) Figure 16. Seismicity at Merapi, June-October 1995. Courtesy of VSI.

Geologic Background. Merapi, one of Indonesia's most active volcanoes, lies in one of the world's most densely populated areas and dominates the landscape immediately north of the major city of Yogyakarta. It is the youngest and southernmost of a volcanic chain extending NNW to Ungaran volcano. Growth of Old Merapi during the Pleistocene ended with major edifice collapse perhaps about 2000 years ago, leaving a large arcuate scarp cutting the eroded older Batulawang volcano. Subsequently growth of the steep-sided Young Merapi edifice, its upper part unvegetated due to frequent eruptive activity, began SW of the earlier collapse scarp. Pyroclastic flows and lahars accompanying growth and collapse of the steep-sided active summit lava dome have devastated cultivated lands on the western-to-southern flanks and caused many fatalities during historical time.

Information Contacts: W. Tjetjep, VSI.


Poas (Costa Rica) — October 1995 Citation iconCite this Report

Poas

Costa Rica

10.2°N, 84.233°W; summit elev. 2708 m

All times are local (unless otherwise noted)


High seismicity

During October, tremor at Poás reached 101 hours; the last time tremor rose over 12 hours/month was May-September 1994, an interval when tremor ranged between 49 and 307 hours/month. The number of minor earthquakes, which were predominantly of low frequency, continued to climb during the month of October, reaching 9,838 events. This was a value ~8% larger than the total for September, the previous month with the most seismic activity in 1995.

The crater lake has risen consistently: by ~5 m during June-October (ICE), and by ~30 cm in the last month (OVSICORI-UNA). During October 1995, the fumarole on the W terrace appeared to have decreased its emissions compared to recent months (< 50-m-high steam plumes), and others on the lake's NW and SW sides also had diminished output. Fumaroles on the S and SW crater wall produced steam columns reaching 100 m tall. During October, bubbling in the lake still continued. During October OVSICORI-UNA scientists measured the temperatures at several sites: pyroclastic cone, 93°C; fumaroles on the S and SW sides of the crater, 95-97°C; the lake in the inactive crater (Lake Botos), 15°C; and the lake in the active crater, 30°C.

Head scarps of landslides that emanate from the dome and flow toward the lake displayed ongoing mass wasting; ICE workers mentioned that this mass wasting may have been triggered by recent heavy rains. In addition, ICE reported that on 17 September (at 0548) a M 3.9 earthquake struck; it had a depth of 5 km and an epicenter 1.6 km SW of the main crater. At the summit, the earthquake's intensity was MM III-IV.

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

Information Contacts: E. Fernandez, E. Duarte, and V. Barboza, Observatorio Vulcanologico y Sismologico de Costa Rica, Universidad Nacional (OVSICORI-UNA); Mauricio Mora, Escuela Centroamericana de Geologia, Universidad de Costa Rica; G.J. Soto, Oficina de Sismologia y Vulcanologia del Arenal y Miravalles: OSIVAM, Instituto Costarricense de Electricidad (ICE).


Rabaul (Papua New Guinea) — October 1995 Citation iconCite this Report

Rabaul

Papua New Guinea

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

All times are local (unless otherwise noted)


Minor seismicity and vapor emission

The volcanoes at Rabaul Caldera continued to remain quiet in October. Tavurvur's summit area released bluish white vapors at very low rates; however, the emission rates rose during rainy days at the end of the month. No emissions came from Vulcan.

Only 19 earthquakes were recorded in October. Two of the 13 low-frequency earthquakes originated from Tavurvur while the rest came from either within or just outside the caldera's N sector. The six high-frequency earthquakes took place on the 20th (2 earthquakes), 23rd (2), 26th (1), and 29th (1). Most of these high-frequency earthquakes occurred in the caldera's NE sector (Namanula area). One high-frequency earthquake (ML 1.9, on the 23rd) originated near Tavurvur at about 1 km depth. October ground deformation remained very low.

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

Information Contacts: Ben Talai, RVO.


Raung (Indonesia) — October 1995 Citation iconCite this Report

Raung

Indonesia

8.119°S, 114.056°E; summit elev. 3260 m

All times are local (unless otherwise noted)


Aviation report of a plume, but not seen on satellite imagery

An aviation report stated that at 1705 on 15 August "smoke" from Raung at an altitude of 6 km was drifting W. Following this report, aviation notices were posted in Indonesia, New Zealand, and Australia for the next 24 hours. No plume was observed by Australian meteorologists on satellite imagery from 1800 on 15 August through 2050 the next day.

The last reported eruption, which occurred sometime between January and June 1993, generated an ash column 600 m above the rim and caused ashfall in the surrounding area.

Geologic Background. Raung, one of Java's most active volcanoes, is a massive stratovolcano in easternmost Java that was constructed SW of the rim of Ijen caldera. The unvegetated summit is truncated by a dramatic steep-walled, 2-km-wide caldera that has been the site of frequent historical eruptions. A prehistoric collapse of Gunung Gadung on the W flank produced a large debris avalanche that traveled 79 km, reaching nearly to the Indian Ocean. Raung contains several centers constructed along a NE-SW line, with Gunung Suket and Gunung Gadung stratovolcanoes being located to the NE and W, respectively.

Information Contacts: BOM Darwin, Australia.


Rincon de la Vieja (Costa Rica) — October 1995 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)


New eruption; lahars damage a bridge and lead to evacuations

A new phreatomagmatic eruption followed three months of declining seismicity. During 1995 the number of local earthquakes peaked in July and then progressively decreased (figure 10). Prior to the eruption, during October, OVSICORI-UNA reported that park rangers who ascended to the main summit saw increased degassing and noted the appearance of fumaroles along cracks at the E and NE crater margins. Rangers described the crater lake's color as green and the smell as strong and sulfurous.

Figure (see Caption) Figure 10. The number of monthly earthquakes at Rincón de la Vieja volcanic complex recorded 5 km SW of the active crater (station RIN3), January-October 1995. The seismic system failed to operate on 29 October; the three events recorded during the rest of the month were all of low frequency (

ICE described the eruption as phreatomagmatic, beginning at 1504 on 6 November, and climaxing on 8 November with 25 explosions. They noted the ash-bearing and steam-rich columns rose to 1 and 4 km, respectively, above the crater. Ash blew WSW; medium- to fine-grained ash reached up to 30 km from the volcano (Santa Rosa National Park).

According to ICE, on 9 November the eruption entered a steam-rich phase. Columns typically rose 200 m, but sometimes as much as 1.5 km after some steam explosions.

During the course of the eruption, ballistic ejecta were thrown over a zone extending to ~1 km N. Ejecta formed lahars that followed two key rivers (Penjamo and Azul rivers) and their tributaries. Heavy rains beginning on 10 and continuing on 11 November triggered secondary lahars and associated floods; a bridge 7 km N of the crater (Penjamo bridge) was damaged but not destroyed, interrupting traffic flow. During this episode, lahars along a tributary of the Penjamo river produced a gully 8-m deep and 25-m wide, isolating some inhabitants.

Initial inspections of ash and the lahar matrix indicated that they mainly consisted of hydrothermally altered fragments, lake-sediment mud, and vesiculated glassy andesite fragments.

Some residents living near the volcano were evacuated to a safe village 9 km NW of the crater. News reports on 8 November by both Associated Press and Deutsche Presse-Agentur stated that about 100 families were evacuated. Two days later Enrique Coen reported relocation of 300 families.

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: E. Fernandez, E. Duarte, and V. Barboza, Observatorio Vulcanológico y Sismológico de Costa Rica, Universidad Nacional (OVSICORI-UNA), Apartado 86-3000, Heredia, Costa Rica; G.J. Soto, Oficina de Sismologia y Vulcanologia del Arenal y Miravalles: OSIVAM, Instituto Costarricense de Electricidad (ICE), Apartado 10032-1000, San José, Costa Rica; Enrique Coen, Departamento de Fisica, University Nacional, Heredia, Costa Rica; Associated Press; Deutsche Presse-Agentur.


Rinjani (Indonesia) — October 1995 Citation iconCite this Report

Rinjani

Indonesia

8.42°S, 116.47°E; summit elev. 3726 m

All times are local (unless otherwise noted)


Small ash plume seen on 12 September

A NOTAM about volcanic activity from Rinjani was issued by the Bali Flight Information Region on the morning of 12 September. An ash cloud was reportedly drifting SW with the cloud top around 4 km altitude. As of 1200 that day, Australian meteorologists had not observed a significant plume on satellite imagery. Synoptic Analysis Branch analysts detected no ash cloud on either visible or infrared GMS imagery. However, at 1600 the Bureau of Meteorology in Darwin advised aviators that a weak low-level plume was intermittently evident on satellite imagery as far as 28 km SW of the volcano.

Geologic Background. Rinjani volcano on the island of Lombok rises to 3726 m, second in height among Indonesian volcanoes only to Sumatra's Kerinci volcano. Rinjani has a steep-sided conical profile when viewed from the east, but the west side of the compound volcano is truncated by the 6 x 8.5 km, oval-shaped Segara Anak (Samalas) caldera. The caldera formed during one of the largest Holocene eruptions globally in 1257 CE, which truncated Samalas stratovolcano. The western half of the caldera contains a 230-m-deep lake whose crescentic form results from growth of the post-caldera cone Barujari at the east end of the caldera. Historical eruptions dating back to 1847 have been restricted to Barujari cone and consist of moderate explosive activity and occasional lava flows that have entered Segara Anak lake.

Information Contacts: BOM Darwin, Australia; SAB.


Ruapehu (New Zealand) — October 1995 Citation iconCite this Report

Ruapehu

New Zealand

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

All times are local (unless otherwise noted)


Late September-early October eruptions rival those in 1945

Ruapehu's current eruptive period began with a vent-clearing blast on 29 June 1995 and a series of larger eruptions began on 23 September (BGVN 20:09). More recently available information (in Immediate Report RUA 95/06) highlighted 18 and 20 September observations summarized below. These are followed by brief comments on eruptions during October.

Activity during 18-20 September. An eruption at 0805 on 18 September was accompanied by a ML 3.6 earthquake; the eruption produced the largest lahar down the ESE flank since 1975. The ESE drainage is called the Whangaehu River. Two days later, at 0122 on 20 September, another eruption associated with a smaller earthquake (ML 3.2) also sent a smaller lahar down the Whangaehu River.

At roughly 0800 on 18 September the ski field manager heard what he initially thought was wind noise while he was inside a ski lodge building on Ruapehu's flanks, a spot 400 m N of the Whangaehu channel (Aorangi lodge at Tukino). He went closer to the river and saw a 12-18 m deep lahar in the narrow channel.

Later that day, a flood warning gauge 27 km downstream was triggered at 1123, suggesting the lahar moved at an average speed of roughly 2.3 m/s (8.3 km/hour). By around noon at Tukino the lahar was 40-m wide and had covered the snow up to 20-30 m above the Whangaehu valley floor. The lahar's surface rose about 11 m on the outside of one turn. A preliminary estimate of peak flow was >1,000 m3/s; the local velocity, 15 m/s. An early phase of the lahar had cut out 2-3 m of ice and snow formerly filling the valley.

The 18 September lahar arrived at a point 57 km downstream from Crater Lake (Karioi) at 1515, 7 hours after the eruption. Volume of the lahar at this point was estimated (by groups identified as NUWA Wanganui and ECNZ) at ~2 x 105 m3; the peak flow, at ~34 m3/s. The lahar destroyed a hiking bridge, leaving only its 0.2-m-high concrete abutments on either side of the river.

The smaller 20 September lahar arrived at 57 km downstream (Karioi) 8 hours after the eruption; its size there was estimated at ~0.9 x 105 m3; its peak flow, at ~21 m3/s. In an area above ~2,000 m elevation, the 18 and 20 September lahar deposits were separated by an intervening snow layer. Still higher, above ~2,400 m elevation, both lahars had emerged from the upper Whangaehu valley's snow and ice tunnel system. Lahars passing through and over the uppermost part of this system had produced considerable new crevasses and collapse features in the snow and ice. On 20 September, collapsed holes downstream of the large ice cave (located below the crater lake's drainage point at Outlet, figure 19) were filled with non-steaming water that had apparently cooled. The ice cave itself appeared largely intact.

Figure (see Caption) Figure 19. (above) Survey points for deformation studies at Ruapehu (prior to the disappearance of Crater Lake). (below) Summary of deformation between stated stations and given time intervals. Courtesy of IGNS.

A helicopter was used to visit the crater on 20 September. A large column of steam rose from the waterfall immediately below Outlet. A large volume of lake water continued to spill over the waterfall even though recent eruptions through the lake had expelled substantial lahar-forming discharges. Ash from the 18 September eruption was plastered on some steep slopes. Ash from the 20 September eruption was plastered on the new snow around the lake margins. On the E side of the lake there was a N-trending, 100-m-long lobe of ash on the glacier surface. Scoria clasts found near Outlet (the largest, 20-50 cm across) formed a continuous layer trapped behind a low lava ridge. Their distribution suggested they were deposited by a passing surge rather than as impacting ballistics. Absence of snow on the surface of the scoria indicated they had probably arrived during the 20 September eruption and some clasts still had warm interiors. Sampled clasts were black in color, and consisted of an unaltered plagioclase-, augite-, orthopyroxene-bearing andesite. The lack of Fe-Ti oxides makes them similar to 1966 ejecta; in contrast, ejecta from 1971 and 1975 did contain minor amounts of Fe-Ti oxides. Three ash samples collected from within the crater contained lapilli up to 25 mm in diameter and composed of angular lithic material. Ash finer than 2-mm diameter was dominated by gray shiny spheroids and globules of sulfur with lesser amounts of gray comminuted lake bed material.

In the interval 15 August-20 September the deformation of the area about Crater lake was significant and indicated moderate inflation (figures 19 and 20). The deformation survey was hampered by snow and ice, which deeply buried most survey stations. Survey mark D had been bent 70 mm out of position immediately prior to the August survey, but eccentricity corrections enable a valid comparison with all former observations at D. Maximum changes took place in the E-W direction. These changes were similar to those computed by comparing the mean of the five surveys made earlier this year to the September survey (first column, bottom of figure 19).

Non-elastic inflation of the style seen was previously noted as much as 2 weeks prior to eruptions on 8 May 1971 and 24 April 1975. This short-term inflation (lasting weeks) was also seen on 12 occasions during 1980-91; these occasions were tentatively correlated with intense heating and minor eruptions. Still, the relation between inflation magnitude and the corresponding eruption remains uncertain.

The 20 September crater visit yielded the following lake observations. The lake's temperature was 48.5°C (on 15 August it had been roughly 20 degrees C cooler, figure 20). There was a strong smell of SO2. The volume of water escaping at Outlet was estimated visually at 1 m3/s (on 15 August it was only ~50 l/s). This exceptional output was the largest seen in 24 years.

Figure (see Caption) Figure 20. Plots of Ruapehu's cross-crater deformation, crater lake temperature, and Mg/Cl ratio for 1976 through late-1995. The cross-crater deformation is approximately E-W (between stations I and J, figure 19). Courtesy of IGNS.

Lake water sampled on 20 September showed clear increases in the concentrations of Mg, Cl, and SO4 ions, and in the ratio of Mg/Cl (figure 20). The observed concentrations for 15 August and 20 September, respectively, were as follows: Mg, 584 and 713 ppm; Cl, 8,154 and 8,619 ppm; and SO4, 26,600 and 30,600 ppm. Increases in Mg began in May and pointed to dissolution of fresh andesitic material into the hydrothermal system. Although previously it was not clear if the source of Mg was juvenile or older andesites, the increased amounts of Cl and SO4 firmly established the input of fresh magmatic material.

SO4 concentrations stand at the highest levels ever recorded at Ruapehu. In the absence of synchronous increases in K, and noting that Ca continues to be controlled by gypsum solubility, it is clear that the increases in SO4 were not attributable to dissolution of secondary hydrothermal minerals. Instead the SO4 increases indicated greater SO2 flux into the lake. Assuming a lake of 9 x 106 m3, the increase in SO4 from 15 August to 20 September equates to a minimum input of ~700 metric tons/day of SO2 into the lake. This behavior differs from that observed prior to the 1971 eruptions: The indication is that the quantity of magma involved in the current activity is larger than in the 1971. Taken with the rather moderate degree of cross-crater deformation seen, the quantity of SO2 discharged into the lake indicates connection to larger volumes of degassing magma at depth.

Volcanic tremor remained at background from early July until early September; its amplitude was ~1 µm/s for signals centered around 7 Hz, and at this value or slightly lower for signals centered around 2 Hz. During a five day interval starting on 6 September, the amplitude of 2-Hz tremor increased. During the 24 hours prior to the 18 September eruption and earthquake (BGVN 20:09), predominantly 7-Hz tremor occurred, at one point doubling in amplitude. Later, ~80 minutes prior to the eruption and earthquake, tremor again increased by a factor of 2-3, with 2-Hz tremor becoming dominant. Although dramatic, Ruapehu often displays wide-ranging shifts in tremor amplitude and, in retrospect, the increased amplitudes seen would not have been a useful way to predict the eruption.

The 18 September earthquake took place at 0805, continuing for 6 minutes. Analog seismograms from the three local stations (Dome, Chateau, and Ngauruhoe) were pegged, and the M 3.6 estimate was made based on amplitude recorded by the tremor-monitoring system. After the earthquake, predominantly 2-Hz tremor prevailed, remaining at or above the pre-earthquake amplitude. Later the same day (18 September), strong 1-Hz tremor occurred--for the first time at Ruapehu since the early 1970s.

Further minor earthquakes were recorded during the next few days. On 19 September seismometers registered a ML 2.2 earthquakes as well as four other discrete earthquakes; on 20 September there were ML 3.1 and 3.2 earthquakes followed by another interval of strong 1-Hz tremor until 0900.

October eruptions. At the time of this writing, IGNS reports for October are incomplete, but a brief survey of available "Science Alert Bulletins" and aviation reports suggested that minor eruptions continued and in mid-October moderate ash-rich eruptions took place. On 11 October a plume was seen in satellite imagery; on 12 and 14 October, pilot and associated aviation reports indicated ash to at least ~10 km altitude.

The 11 October eruption was described as near-continuous moderate eruptive activity that included hot ballistic blocks and lightning. Subsequent lower intensity eruptions presumably fed the plume so that its proximal end remained attached to the volcano. The eruption deposited ash in a blanket with a tentative volume between 0.01 and 0.05 km3. Thus, the steam-rich plumes seen in the 3 weeks prior to 11 October gave way to more ash-rich plumes during this eruption. A thin blanket of ash was also deposited during the 14 October eruption.

The absence of a crater lake was confirmed on 14 October. By 17 October, partly impeded views into the crater revealed steam and ash emitted from at least three vents, and a still-dry crater floor. COSPEC measurements around this time suggested the SO2 flux was over 10,000 metric tons/day. A COSPEC flight on 21 October gave viewers their first look at a possible new lava dome, however, there were no subsequent confirmations of the dome in available reports.

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: C.J.N. Wilson, B.J. Scott, P.M. Otway, and I.A. Nairn, Institute of Geological & Nuclear Sciences (IGNS), Private Bag 2000, Wairakei, New Zealand; Bureau of Meteorology, Northern Territory Regional Office, P.O. Box 735, Darwin, NT 0801, Australia.

Correction: The most recent analysis indicates that there were 18 hydrothermal eruptions recorded between 0600 and 1640 on 20 September. Table 7 indicated "15 small phreatic eruptions witnessed."


Ruby (United States) — October 1995 Citation iconCite this Report

Ruby

United States

15.62°N, 145.57°E; summit elev. -230 m

All times are local (unless otherwise noted)


Submarine eruption

Ruby is a prominent, active submarine volcano in the Mariana Arc (2,300 km S of Tokyo) located NW of the Island of Saipan (figure 1). Although signs of an eruption were first noted by fishermen about 11 October, initial attempts to confirm their early observations failed. On 23 October fishermen reported that they could hear submarine explosions in that vicinity. A vessel from the Wildlife and Emergency Management Office of the Commonwealth of the Northern Mariana Islands confirmed these reports. An Associated Press news report stated that early on 25 October observers had seen dead fish and bubbles, and had smelled a sulfurous odor. On 27 October the Pacific Daily News reported the eruption site as 15°36'22"N, 145°34'33"E (15.6061°N, 145.5758°E). This spot clearly lies on the edifice identified by Bloomer and others (1985, p. 215) as Ruby (only ~1.7 km from the point specified in this report's heading).

Figure (see Caption) Figure 1. Index map and bathymetric map (depths in meters) showing seamounts near Saipan Island, including the known active centers Esmeralda Bank and Ruby (after Bloomer and others, 1989).

Prior to the eruption, published estimates of the summit elevation suggested a 230-m depth, a refinement an earlier estimate of 549 m (Bloomer and others, 1985, p. 215). On 6 October 1995, the Pacific Daily News report stated the summit was measured at 185-m depth. This newly reported depth remains unconfirmed. According to Mike Blackford, on 23 October a marine depth finder reportedly measured a depth of ~60 m. Although this could be a reflection off the eruptive plume, in the absence of any discussion of instrument type and calibration, this depth remains equivocal.

According to Koyanagi and others (1993), the two seismic stations nearest the eruption were on Saipan (~50 km SE of Ruby) and Pagan islands (~130 km N of Saipan), both too distant to detect subtle seismic effects. Despite the lack of a nearby seismic station, tremor appeared on seismic records at the time of the eruption and the next day. Given the temporal coincidence between the eruption and the tremor, the two were probably associated.

A fish recovered at the eruption site was found to have small particles of ash in its gills and HVO researchers planned to analyze this ash. News of the eruption caused concern about a possible local tsunami and on 25 October, the Commonwealth of the Northern Mariana Islands issued an alert.

Evidence for Ruby's active status came from 1966 hydrophone data, followed later by dredging of extremely fresh volcanic rocks bearing plagioclase, clinopyroxene, and olivine (Bloomer and others, 1985).

References. Bloomer, S.H., Stern, R.J., and Smoot, N.C., 1989, Physical volcanology of the submarine Mariana and Volcano arcs: Bull. Volcanol., no. 51, p. 210-234.

Koyanagi, R., Kojima, G., Chong, F., and Chong, R., 1993, Seismic monitoring of earthquakes and volcanoes in the Northern Mariana Islands: 1993 summary report: Prepared for the Office of the Governor, Commonwealth of the Northern Mariana Islands, Capitol Hill, Saipan MP 96950 (revised 21 February 1993), 34 p.

Geologic Background. Ruby, a basaltic submarine volcano that rises to within 230 m of the sea surface near the southern end of the Mariana arc NW of Saipan, was detected in eruption in 1966 by sonar signals (Norris and Johnson, 1969). In 1995 submarine explosions were heard, accompanied by a fish kill, sulfurous odors, bubbling water, and the detection of volcanic tremor.

Information Contacts: Robert J. Stern, Center for Lithospheric Studies, University of Texas at Dallas, Box 830688, Dallas, TX 75083-0688 USA; Robert Koyanagi, USGS Hawaiian Volcano Observatory, Hawaii Volcanoes National Park, HI 96718, USA; Ramon C. Chong, Commonwealth of the Northern Mariana Islands (CNMI), Disaster Control Office, Capitol Hill, Saipan, MP 96950 USA; Mike Blackford, Pacific Tsunami Warning Center, 91-270 Fort Weaver Road, Ewa Beach HI 96706, USA; Associated Press; Pacific Daily News.


Semeru (Indonesia) — October 1995 Citation iconCite this Report

Semeru

Indonesia

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

All times are local (unless otherwise noted)


Explosions and pyroclastic flows continue

The VSI reported that by 3 August a tongue of glowing lava had reached 300 m long; at 1932 that evening the lava collapsed to feed lava avalanches. Qantas airlines reported additional activity at 1510 on 8 August, describing volcanic "smoke" near Semeru to above 4 km. Two days later, around 1530 on 10 August, a Qantas flight reported an ash cloud to 9 km altitude with a SW drift.

VSI noted that during August-October small-to-moderate explosions and avalanches continued from the Jonggring Seloko summit crater. Plumes rose to a maximum of 600 m above the summit; the average plume height was 300-500 m. In August and September, pyroclastic flows often traveled down the Kember River, then descended the Kobokan River, reaching a distance of 1-3 km. The frequency of lava avalanches increased in September, extending along the Kember River for up to 500 m from the summit.

Earthquakes associated with the pyroclastic flows were variable, with 1-16 events/day through early October; after that the frequency of earthquakes decreased. Increasing numbers of volcanic earthquakes (both A-and B-type) started on 11 October and continued until the end of the month, fluctuating at 1-14 events/day (figure 8). The number of explosion earthquakes was typically 45-109/day (figure 8), except on 26 and 27 September, when there were only 33 and 24 events, respectively.

Figure (see Caption) Figure 8. Eruptive activity at Semeru as detected by seismograph, August-October 1995: pyroclastic flows and volcanic earthquakes (top), explosions and avalanche events (bottom). Courtesy of VSI.

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: W. Tjetjep, VSI; BOM Darwin, Australia.


Soufriere Hills (United Kingdom) — October 1995 Citation iconCite this Report

Soufriere Hills

United Kingdom

16.72°N, 62.18°W; summit elev. 915 m

All times are local (unless otherwise noted)


Small ash explosions continue; three new vents form; September dome grows

The observatory was moved on 1 October from the Vue Pointe Hotel to Eifel House on Bishop View Road in Old Towne. A phreatic eruption that day deposited ash across a large area, including the capital city of Plymouth. This eruption was followed by a volcano-tectonic (VT) earthquake swarm, with 70 events located beneath the volcano at depths of 1-6 km. Two of the earthquakes, at 2257 and 2319, had magnitudes of ~2.5 and were felt at the observatory; several were felt in the Long Ground area. After about 0500 on 2 October, the number of located earthquakes dropped to ~5/day. Two episodes of low-amplitude broadband tremor recorded during 1-3 October were related to steam emission. Electronic tiltmeter and EDM observations during that time revealed no significant deformation.

EDM measurements at Tar River completed on 3-4 October continued to show a shortening trend, signaling minor inflation. Shallow VT (12 located events) and long-period (2 events) seismicity continued. Moderate levels of seismicity prevailed during 4-8 October, with 30-40 shallow (< 6 km depth) VT earthquakes each day, rare felt events (M 2-2.5), and a few long-period events. No deformation was detected by electronic tiltmeter.

An explosion around 2355 on 5 October caused heavy ashfall in Plymouth and in the SW part of the island. On 5 October the government announced that over the next two days they would evacuate Plymouth's home for elderly people and the hospital, sending residents to the N part of the island.

Two eruption signals were recorded at 0235 and 0347 on 8 October, and the EDM line at Tar River continued to show minor inflation. Seismicity began decreasing on 8-9 October, when 24 earthquakes were located beneath the volcano, with a few in the Centre Hills area. A small eruption at 1356 on 9 October generated light ashfall in Amersham and Upper Gages. Vent 2 was emitting a small amount of steam again during 7-9 October. Several episodes of broadband tremor may have been caused by increased steam emission. There were only 6 located earthquakes during 9-10 October, but several episodes of broadband tremor. Another minor eruption around 0012 on 10 October caused light ashfall in Plymouth. Visual helicopter inspection of the crater revealed significant steam emission and an increase in the size of the 25 September dome (20:9).

Formation of Vent 5 on 11 October. An ash eruption at 0021 on 11 October came from a new vent on the Tar River side of the Castle Peak dome, and damaged the EDM reflector at Tar River. A small earthquake swarm accompanied this vent formation. There were two more small ash eruptions later that day at 1540 and 1700. Although no significant changes to the dome were noted, steaming continued from its top; Vent 1 was also steaming, and appeared to be larger and deeper. Scientists noted that steam emissions from the crater had generally increased.

Three more ash eruptions occurred on 12 October, at 0901, 0955, and 1114. Continuous steam emission came from several areas in the crater and Vent 5. Two episodes of broadband tremor during 12-13 October were attributed to increased steam emission. Seismicity was low, with only 22 events during 11-13 October. No deformation was detected following this latest series of explosions.

Formation of Vent 6 on 14 October. An eruption at 0708 on 14 October created another vent on the NE flank of Castle Peak dome, generated a significant amount of ash, and ejected blocks as far as the edge of Long Ground, ~1 km E of the vent. A pilot reported that the plume may have reached ~2 km altitude. Another eruption at 1058 caused no reported ashfall. Two gas venting episodes at 2200 and 2345 on the 14th were associated with a small earthquake swarm and broadband tremor episodes. Vent 2 again emitted moderate amounts of steam, accompanied by a loud roaring sound, and Vent 5 continued to emit small amounts of steam. Seismicity decreased from 18 events on 13-14 October to five events accompanied by broadband tremor on 15-16 October.

Seismicity increased again on 16-17 October with 22 events clustered in two areas: one beneath the volcano and the other just E of Windy Hill. Steam-and-ash eruptions were recorded by the seismic network at 1757 and 2245 on 16 October, and at 1150 and 1522 on the 17th. There were also several episodes of broadband tremor and ~30 minutes of low-frequency harmonic tremor starting around 0414 on 17 October. Later that morning an aerial inspection of the crater showed no significant changes and little steaming. During a second flight at 1145, a large mudflow originating within the crater moat beyond Vent 2 was seen running rapidly down the Hot River and reaching the sea. This was probably the largest mudflow (in terms of volume of material) since the current activity began.

During 17-18 October there were 12 scattered earthquakes, several periods of broadband tremor, and some intermediate-frequency tremor. Ash eruptions were recorded at 1739 on the 17th and at 0530 on the 18th. The dome area continued to emit steam, but did not increase in size.

Formation of Vent 7 on 18 October. The 31 earthquakes during 18-19 October were clustered beneath the volcano. Several broadband tremor episodes and one period of low-frequency tremor were also detected. An eruption at 1621 on the 18th was associated with the formation of a new vent within the moat area of English's Crater, just SW of Vent 1. Another eruption was recorded at 2207 on the 18th. An explosive event around 1516 on 19 October generated a mudflow down the Hot River. During 19-20 October there were 28 earthquakes located; the events were scattered throughout S Montserrat, with some clustered beneath Soufriere Hills and St. Georges Hill.

There were 15 VT earthquakes on 20-21 October concentrated around the Long Ground/Soufriere Hills area. Several eruption episodes on 21 October resulted in ashfall that affected villages in the E. Ash fell at the airport for the first time, closing it briefly. No deformation was detected at the Tar River EDM or Long Ground tilt stations. Helicopter observations revealed that Vent 1 had extended E and was responsible for the previous ashfall. There was a small mud flow down the Tar River.

An average of 35 earthquakes/day occurred during 21-23 October. They were scattered throughout S Montserrat with some concentrations in the Long Ground-Tar River area and beneath the volcano. Some broadband tremor was also recorded. Visual observation of English's Crater both from helicopter and Tar River on 22 October revealed light steam emission from vents 2 and 5. When observed on the morning of 23 October, the September dome continued to steam, and was covered with sulfur deposits; it may also have grown since last observed on 20 October. Only one other small area SE of the dome was steaming. An eruption at 1337 on 23 October produced ash deposits within the summit crater and at Tar River. Steam emission increased after this eruption.

Seismicity decreased following this eruption to 10-14 events/day through 29 October, except for 22 events on the 27th. Locations were mainly beneath the volcano, although some were centered in the Windy Hill area and other parts of S Montserrat. An eruption at 1325 on 25 October caused ashfall in the Tar River area. Eruption signals were again recorded at 2314, 2321, and 2347 on 25 October, and at 0447 on the 26th; no ashfall was reported. Several episodes of low-amplitude broadband tremor were recorded during 25-26 October. EDM measurements at Tar River on 26 October indicated a continuation of the minor inflation observed during the past several weeks.

A steam-and-ash eruption at 1317 on 27 October from Vent 1 was followed by more than 30 minutes of low-frequency tremor. Eruption signals were recorded at 0855 and 2018 on 28 October, but no ashfall was reported. Steam emission from Vent 2 was observed that afternoon. Eruptions occurred again at 0326 and 0857 on the 29th, both followed by broadband tremor. An ash-and-steam plume was seen from the observatory following the 0857 event. Steam was seen coming from Vent 1 during a helicopter flight, but no major changes were noted.

Seismicity increased on 29-30 October to 55 events; most were clustered in a region just W of Windy Hill, with some scattered in the Centre Hills and Soufriere Hills areas. Eruption signals were recorded at 2110 on the 29th, and at 0244 and 1310 on the 30th. Two small long-period events were recorded after the first eruption. Ash from the first two of these eruptions was observed in English's Crater by helicopter. The third eruption, witnessed by scientists at the Tar River EDM site, produced a high column that caused ashfall over a wide area. This ashfall was the most significant since 21 August, and was accompanied by a density current of ash in the Gages valley. The morning of 31 October visual observations revealed a significant increase in Vent 1's size, but the 25 September dome appeared unchanged.

Seismicity decreased again the next day to 23 events, but they were located in clusters in the Tar River-Long Ground area and W of Windy Hill. There were also four long-period events and several episodes of broadband tremor. One eruption at 1118 on 31 October had no reported associated ashfall. EDM measurements at Tar River again showed a slight shortening, associated with continued slow inflation of the upper part of the volcanic edifice.

Only 14 seismic events were recorded during 31 October-1 November; most were located beneath the volcano with a few in the Windy Hill and Fox's Bay area. There were three long-period events and several episodes of broadband tremor. A small eruption at 1129 on 1 November caused ashfall within the summit crater.

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

Information Contacts: Montserrat Volcano Observatory (MVO), Olde Towne.


Tengger Caldera (Indonesia) — October 1995 Citation iconCite this Report

Tengger Caldera

Indonesia

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

All times are local (unless otherwise noted)


Eruption from Bromo sends dark ash plume 700 m above the rim

On 9 September, dark gray emissions were observed reaching a height of 70 m above the rim of Bromo Crater. Volcanic tremor associated with the emission events (maximum amplitude of 1-3 mm) was recorded continuously beginning on 8 September, using a PS-2 seismograph installed 750 m from the active crater. After 10 September the plume was denser than during the March-May 1995 activity (20:03). An international Notice to Airmen (NOTAM) on the morning of 22 September reported an ash cloud with a top at ~3 km altitude and a SW drift. The height of the ash column gradually increased, peaking at 700 m (~3 km altitude) on 25 September (figure 2); during the emission, maximum tremor amplitude was 49 mm. A thick dark gray ash cloud caused ashfall in nearby villages, reported as far away as ~20 km E (around the area of Sukapura). The eruption vent, with a diameter of ~25 m, was located on the N part of the crater floor, similar to the last eruption. Ash eruptions were continuing at the end of October, but the activity was gradually decreasing. In October the maximum plume height was 200-450 m above the crater rim; the maximum tremor amplitude was 8-40 mm.

Figure (see Caption) Figure 2. Height of ash plume and maximum tremor amplitude at Bromo, Tengger Caldera, September-October 1995. Courtesy of VSI.

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: W. Tjetjep, VSI; BOM Darwin, Australia.


Vulcano (Italy) — October 1995 Citation iconCite this Report

Vulcano

Italy

38.404°N, 14.962°E; summit elev. 500 m

All times are local (unless otherwise noted)


Fumarolic activity notably diminished from previous years

Fumarolic activity, vigorous in the late 1980s and through 1994, notably diminished in 1995 (BGVN 20:04 and 20:06). During observations in September, the steam and gas output of the most conspicuous fumaroles, at the N rim of the Fossa Grande crater, was back to pre-1985 levels, and no longer formed sizeable gas plumes. Some of the formerly most vigorous fumaroles and steaming cracks were no longer active. Strong gas emission still occurred from fumaroles in the oversteepened and unstable Forgia Vecchia area, below the N rim of the Fossa Grande, and hydrothermal alteration continued to weaken the rock. Several blocks of strongly altered rock with volumes of ~100-500 m3 each had already detached and subsided by 10-20 cm, and may fall. However, it was uncertain whether they would reach the S margin of the village below the Fossa cone. Fumarolic activity also continued from numerous places on the beach N of the "Faraglione" and on the low isthmus connecting Vulcanello to the main body of Vulcano island. During a visit to the western-most (and most recent) crater of Vulcanello on 13 September, no evidence of recent fumarolic activity was found in its NE part where intense fumarolic activity took place until the mid-19th century.

Geologic Background. The word volcano is derived from Vulcano stratovolcano in Italy's Aeolian Islands. Vulcano was constructed during six stages during the past 136,000 years. Two overlapping calderas, the 2.5-km-wide Caldera del Piano on the SE and the 4-km-wide Caldera della Fossa on the NW, were formed at about 100,000 and 24,000-15,000 years ago, respectively, and volcanism has migrated to the north over time. La Fossa cone, active throughout the Holocene and the location of most of the historical eruptions, occupies the 3-km-wide Caldera della Fossa at the NW end of the elongated 3 x 7 km island. The Vulcanello lava platform forms a low, roughly circular peninsula on the northern tip of Vulcano that was formed as an island beginning in 183 BCE and was connected to Vulcano in about 1550 CE. Vulcanello is capped by three pyroclastic cones and was active intermittently until the 16th century. The latest eruption from Vulcano consisted of explosive activity from the Fossa cone from 1898 to 1900.

Information Contacts: Boris Behncke and Giada Giuntoli, Department of Volcanology and Petrology, GEOMAR, Wischhofstr. 1-3, 24148 Kiel, Germany.


Yellowstone (United States) — October 1995 Citation iconCite this Report

Yellowstone

United States

44.43°N, 110.67°W; summit elev. 2805 m

All times are local (unless otherwise noted)


New mud volcano, minor mud flow, and associated thermal features

On the SW flank of Sour Creek resurgent dome W of Astringent Creek in the 0.6 Ma Yellowstone caldera, is an extensive, unnamed acid sulfate hydrothermal system (figures 2 and 3). Surface expression of the ~3 km2 thermal area consists of discontinuous high temperature altered ground, turbid springs, pools, seeps, fumaroles, mud pots, a large gas- and sulfur-rich acid lake, and numerous sublimated sulfur mound deposits interspersed among low-temperature forest-covered ground.

Figure (see Caption) Figure 2. Index map of the western United States showing the location of Yellowstone Caldera.
Figure (see Caption) Figure 3. Sketch map of Yellowstone Caldera indicating the location of the recent thermal features described in this and an earlier report.

During early 1990, a significant rise in temperature in the upper NW end of the hydrothermal system began killing old-growth pine trees. Within a year, a new super-heated fumarole emerged, blanketing the downed trees and roots with a layer of hydrothermally altered coarse sand from a directed blast to the N.

The temperature and volume of dry steam venting from the deep "shaft-like" vent steadily increased over the next three years, with the temperature reaching a maximum of 104.3°C on 8 October 1994, ~11°C higher than the local boiling point. The dynamic activity of the fumarole and surrounding hot ground was only monitored about twice a year over the three years following its 1990 inception due to its remote location and restricted access.

A similar progression was previously seen during 1985 in an area ~4.5 km to the E. This area, the upper E margin of the Mushpots thermal area, sits on the W flanks of Pelican Cone (BGVN 17:03). The progression went from new hot ground and dying mature forests, to the vigorous breakout of a dry, super-heated fumarole with progressively hotter temperatures over time, followed by sudden emergence of a large and violent mud volcano. Both the 1985 and recent thermal features had similar fluid compositions.

During 1992-94 the unnamed thermal area W of Astringent Creek developed a series of seven large craters that evolved as the Mushpots thermal area did in 1985. The craters were progressively younger towards the SW, ending at the site of the current new hot ground and fumarole (figure 4). In December 1993, National Park Service research geologist R. Hutchinson predicted that the newest superheated fumarole would soon evolve into a large mud volcano.

Figure (see Caption) Figure 4. Sketch map (scale approximate) showing the surface expression of an unnamed thermal area W of Astringent Creek in Yellowstone Caldera. Coordinates for map's center are at about 44°38'06"N, 110°16'44"W. Courtesy of R. Hutchinson.

As a part of routine monitoring, the thermal area W of Astringent Creek was inspected on 7 June 1995. The former 104.3°C fumarole was replaced by a large vigorous mud pot with ejecta extensively scattered around it. In addition, two new smaller roaring fumaroles at or slightly above boiling point, three new moderate-sized churning caldrons (pits containing hot, agitated aqueous fluids), numerous smaller muddy pools, collapse pits, and frying-pan springs (audibly degassing springs) were apparent then. Extensive areas of unstable quicksand-like saturated ground made up of scalding mud were found under the fallen trees. Some regions were heavily encrusted with sulfate minerals or sulfur crystals; others were covered by baked organic matter on the pine forest's floor.

Extending NW from the largest parasitic churning caldron, below the new mud volcano crater, was a spectacular white kaoline clay mud flow (figure 4, dark shading and arrow showing flow direction). It spread rapidly to reach an average width of 13.8 m in the first 55 meters of its length in dead forest grove and eventually terminated 114 m from its source on the open, acid thermal-basin floor.

The relative freshness of the ejected mud and incorporated semi-coarse sandy material indicated that the super-heated fumarole transformed into the powerful mud volcano between mid-April and mid-May. The distribution of large mud bombs suggested that their trajectories reached 20-30 m above the crater rim. Ejecta were seen along the following compass bearings with the stated maximum distances from the crater: N, 13.6 m; E, 30.2 m; S, 25.4 m; and W, 12.1 m.

When visited on both 7 June and 9 September, the mud volcano still continued to throw mud 0.5-1.5 m high from dozens of points around the crater floor. The mud volcano crater was 13.5-m long, 11.3-m wide, and 3.9-4.9 m deep. A conservative estimate of the crater volume was 315 m3. The total area covered by the ejecta and crater was ~2,100 m2. In the SW quarter of the crater a large, slightly elevated projection was visible with an arcuate line of dry, white, probably super-heated fumarole vents.

The largest parasitic caldron had numerous points of ebullition in its irregularly shaped pool (maximum dimensions of 10.8 x 7.9 m), with a water level 0.7-1.4 m below the former forest floor. The churning water was near boiling, opaque, light tan in color, and partially covered with brown organic-rich foam derived from cooked plant material.

Each of the caldrons were interpreted as being parasitic to the mud volcano crater because they appeared to have evolved shortly after the initial fumarole collapse and then subsequently drained much of its fluids. This relationship seems to have rapidly lowered the crater floor, preventing the accumulation of a thick ejecta cone on the crater rim.

The mud volcano crater, parasitic features, vents, and the associated hot ground remain extremely dangerous and unstable. Additional alterations in the creation of new or enlarged springs, and perhaps even another mud volcano crater are anticipated. With respect to geologic hazards, the acid sulfate thermal area should be checked again in the near future. Photographs were taken on 7 June.

The Yellowstone Plateau volcanic field developed through three volcanic cycles spanning two million years and included some of the world's largest known eruptions. Eruption of the > 2,500 km3 Huckleberry Ridge Tuff ~2.1 million years ago (Ma) created a caldera more than 75 km long. The Mesa Falls Tuff erupted around 1.3 Ma, forming the 25-km-wide Island Park Caldera at the first caldera's W end. A 0.6 Ma eruption deposited the 1,000 km3 Lava Creek Tuff and associated caldera collapse created the rest of the present 45 x 75 km caldera (figure 3). Resurgent doming then occurred; voluminous (1,000 km3) intercaldera rhyolitic lava flows were erupted between 150,000 and 70,000 years ago. Phreatic eruptions produced local tephra layers during the early Holocene. Distinctive geysers, mud pots, hot springs, and other hydrothermal features within Yellowstone caldera helped lead to the establishment of the National Park in 1872.

Geologic Background. The Yellowstone Plateau volcanic field developed through three volcanic cycles spanning two million years that included some of the world's largest known eruptions. Eruption of the over 2450 km3 Huckleberry Ridge Tuff about 2.1 million years ago created the more than 75-km-long Island Park caldera. The second cycle concluded with the eruption of the Mesa Falls Tuff around 1.3 million years ago, forming the 16-km-wide Henrys Fork caldera at the western end of the first caldera. Activity subsequently shifted to the present Yellowstone Plateau and culminated 640,000 years ago with the eruption of the over 1000 km3 Lava Creek Tuff and the formation of the present 45 x 85 km caldera. Resurgent doming subsequently occurred at both the NE and SW sides of the caldera and voluminous (1000 km3) intracaldera rhyolitic lava flows were erupted between 150,000 and 70,000 years ago. No magmatic eruptions have occurred since the late Pleistocene, but large hydrothermal eruptions took place near Yellowstone Lake during the Holocene. Yellowstone is presently the site of one of the world's largest hydrothermal systems including Earth's largest concentration of geysers.

Information Contacts: Roderick A. Hutchinson, National Park Service, P.O. Box 168, Yellowstone National Park, Wyoming 82190, USA.

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 (BGVN 22:08) False Report of Mount Pinokis Eruption

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

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

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

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

UFO adherent claims new volcano in Sea of Marmara

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

Fumaroles and minor seismicity since October 2002

12/2005 (BGVN 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/).