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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

Sangay (Ecuador) Daily ash plumes and frequent pyroclastic flows produce ashfall and lahars, January-June 2020

Karangetang (Indonesia) Incandescent block avalanches through mid-January 2020; crater anomalies through May

Masaya (Nicaragua) Lava lake level drops but remains active through May 2020; weak gas plumes

Shishaldin (United States) Intermittent thermal activity and a possible new cone at the summit crater during February-May 2020

Krakatau (Indonesia) Strombolian explosions, ash plumes, and crater incandescence during April 2020

Taal (Philippines) Eruption on 12 January with explosions through 22 January; steam plumes continuing into March

Unnamed (Tonga) Additional details and pumice raft drift maps from the August 2019 submarine eruption

Klyuchevskoy (Russia) Strombolian activity November 2019 through May 2020; lava flow down the SE flank in April

Nyamuragira (DR Congo) Intermittent thermal anomalies within the summit crater during December 2019-May 2020

Nyiragongo (DR Congo) Activity in the lava lake and small eruptive cone persists during December 2019-May 2020

Kavachi (Solomon Islands) Discolored water plumes seen using satellite imagery in 2018 and 2020

Kuchinoerabujima (Japan) Eruption and ash plumes begin on 11 January 2020 and continue through April 2020



Sangay (Ecuador) — July 2020 Citation iconCite this Report

Sangay

Ecuador

2.005°S, 78.341°W; summit elev. 5286 m

All times are local (unless otherwise noted)


Daily ash plumes and frequent pyroclastic flows produce ashfall and lahars, January-June 2020

Frequent activity at Ecuador's Sangay has included pyroclastic flows, lava flows, ash plumes, and lahars reported since 1628. Its remoteness on the east side of the Andean crest make ground observations difficult; remote cameras and satellites provide important information on activity. The current eruption began in March 2019 and continued through December 2019 with activity focused on the Cráter Central and the Ñuñurco (southeast) vent; they produced explosions with ash plumes, lava flows, and pyroclastic flows and block avalanches. In addition, volcanic debris was remobilized in the Volcan river causing significant damming downstream. This report covers ongoing similar activity from January through June 2020. Information is provided by Ecuador's Instituto Geofísico, Escuela Politécnica Nacional (IG-EPN), and a number of sources of remote data including the Washington Volcanic Ash Advisory Center (VAAC), the Italian MIROVA Volcano HotSpot Detection System, and Sentinel-2 satellite imagery. Visitors also provided excellent ground and drone-based images and information.

Throughout January-June 2020, multiple daily reports from the Washington Volcanic Ash Advisory Center (VAAC) indicated ash plumes rising from the summit, generally 500-1,100 m. Each month one or more plumes rose over 2,000 m. The plumes usually drifted SW or W, and ashfall was reported in communities 25-90 km away several times during January-March and again in June. In addition to explosions with ash plumes, pyroclastic flows and incandescent blocks frequently descended a large, deep ravine on the SE flank. Ash from the pyroclastic flows rose a few hundred meters and drifted away from the volcano. Incandescence was visible on clear nights at the summit and in the ravine. The MIROVA log radiative power graph showed continued moderate and high levels of thermal energy throughout the period (figure 57). Sangay also had small but persistent daily SO2 signatures during January-June 2020 with larger pulses one or more days each month (figure 58). IG-EPN published data in June 2020 about the overall activity since May 2019, indicating increases throughout the period in seismic event frequency, SO2 emissions, ash plume frequency, and thermal energy (figure 59).

Figure (see Caption) Figure 57. This graph of log radiative power at Sangay for 18 Aug 2018 through June 2020 shows the moderate levels of thermal energy through the end of the previous eruption in late 2018 and the beginning of the current one in early 2019. Data is from Sentinel-2, courtesy of MIROVA.
Figure (see Caption) Figure 58. Small but persistent daily SO2 signatures were typical of Sangay during January-June 2020. A few times each month the plume was the same or larger than the plume from Columbia’s Nevado del Ruiz, located over 800 km NE. Image dates are shown in the header over each image. Courtesy of NASA’s Global Sulfur Dioxide Monitoring Page.
Figure (see Caption) Figure 59. A multi-parameter graph of activity at Sangay from May 2019 to 12 June 2020 showed increases in many types of activity. a) seismic activity (number of events per day) detected at the PUYO station (source: IG-EPN). b) SO2 emissions (tons per day) detected by the Sentinel-5P satellite sensor (TROPOMI: red squares; source: MOUNTS) and by the IG-EPN (DOAS: green bars). c) height of the ash plumes (meters above crater) detected by the GOES-16 satellite sensor (source: Washington VAAC). d) thermal emission power (megawatt) detected by the MODIS satellite sensor (source: MODVOLC) and estimate of the accumulated lava volume (million M3, thin lines represent the error range). Courtesy of IG-EPN (Informe Especial del Volcán Sangay - 2020 - N°3, “Actualización de la actividad eruptiva”, Quito, 12 de junio del 2020).

Activity during January-March 2020. IG-EPN and the Washington VAAC reported multiple daily ash emissions throughout January 2020. Gas and ash emissions generally rose 500-1,500 m above the summit, most often drifting W or SW. Ashfall was reported on 8 January in the communities of Sevilla (90 km SSW), Pumallacta and Achupallas (60 km SW) and Cebadas (35 km WNW). On 16 January ash fell in the Chimborazo province in the communities of Atillo, Ichobamba, and Palmira (45 km W). Ash on 28 January drifted NW, with minor ashfall reported in Púngala (25 km NW) and other nearby communities. The town of Alao (20 km NW) reported on 30 January that all of the vegetation in the region was covered with fine white ash; Cebadas and Palmira also noted minor ashfall (figure 60).

Figure (see Caption) Figure 60. Daily ash plumes and repeated ashfall were reported from Sangay during January 2020. Top left: 1 January 2020 (INFORME DIARIO DEL ESTADO DEL VOLCÁN SANGAY No. 2020-2, JUEVES, 2 ENERO 2020). Top right: 20 January 2020 (INFORME DIARIO DEL ESTADO DEL VOLCÁN SANGAY No. 2020-21, MARTES, 21 ENERO 2020). Bottom left: 26 January-1 February 2020 expedition (Martes, 18 Febrero 2020 12:21, EXPEDICIÓN AL VOLCÁN SANGAY). Bottom right: 30 January 2020, minor ashfall was reported in the Province of Chimborazo (#IGAlInstante Informativo VOLCÁN SANGAY No. 006, JUEVES, 30 ENERO 2020). Courtesy of IG-EPN.

A major ravine on the SE flank has been the site of ongoing block avalanches and pyroclastic flows since the latest eruption began in March 2019. The pyroclastic flows down the ravine appeared incandescent at night; during the day they created ash clouds that drifted SW. Satellite imagery recorded incandescence and dense ash from pyroclastic flows in the ravine on 7 January (figure 61). They were also reported by IG on the 9th, 13th, 26th, and 28th. Incandescent blocks were reported in the ravine several times during the month. The webcam captured images on 31 January of large incandescent blocks descending the entire length of the ravine to the base of the mountain (figure 62). Large amounts of ash and debris were remobilized as lahars during heavy rains on the 25th and 28th.

Figure (see Caption) Figure 61. Sentinel-2 satellite imagery of Sangay from 7 January 2020 clearly showed a dense ash plume drifting W and ash and incandescent material from pyroclastic flows descending the SE-flank ravine. Left image uses natural color (bands 4, 3, 2) rendering and right images uses atmospheric penetration (bands 12, 11, 8A) rendering. Courtesy of Sentinel Hub Playground.
Figure (see Caption) Figure 62. Pyroclastic flows at Sangay produced large trails of ash down the SE ravine many times during January 2020 that rose and drifted SW. Top left: 9 January (INFORME DIARIO DEL ESTADO DEL VOLCÁN SANGAY No. 2020-9, JUEVES, 9 ENERO 2020). Top right: 13 January (INFORME DIARIO DEL ESTADO DEL VOLCÁN SANGAY No. 2020-14, MARTES, 14 ENERO 2020). On clear nights, incandescent blocks of lava and pyroclastic flows were visible in the ravine. Bottom left: 16 January (INFORME DIARIO DEL ESTADO DEL VOLCÁN SANGAY No. 2020-17, VIERNES, 17 ENERO 2020). Bottom right: 31 January (#IGAlInstante Informativo VOLCÁN SANGAY No. 007, VIERNES, 31 ENERO 2020). Courtesy of IG-EPN.

Observations by visitors to the volcano during 9-17 January 2020 included pyroclastic flows, ash emissions, and incandescent debris descending the SE flank ravine during the brief periods when skies were not completely overcast (figure 63 and 64). More often there was ash-filled rain and explosions heard as far as 16 km from the volcano, along with the sounds of lahars generated from the frequent rainfall mobilizing debris from the pyroclastic flows. The confluence of the Rio Upano and Rio Volcan is 23 km SE of the summit and debris from the lahars has created a natural dam on the Rio Upano that periodically backs up water and inundates the adjacent forest (figure 65). A different expedition to Sangay during 26 January-1 February 2020 by IG personnel to repair and maintain the remote monitoring station and collect samples was successful, after which the station was once again transmitting data to IG-EPN in Quito (figure 66).

Figure (see Caption) Figure 63. Hikers near Sangay during 9-17 January 2020 witnessed pyroclastic flows and incandescent explosions and debris descending the SE ravine. Left: The view from 40 km SE near Macas showed ash rising from pyroclastic flows in the SE ravine. Right: Even though the summit was shrouded with a cap cloud, incandescence from the summit crater and from pyroclastic flows on the SE flank were visible on clear nights. Courtesy of Arnold Binas, used with permission.
Figure (see Caption) Figure 64. The steep ravine on the SE flank of Sangay was hundreds of meters deep in January 2020 when these drone images were taken by members of a hiking trip during 9-17 January 2020 (left). Pyroclastic flows descended the ravine often (right), coating the sides of the ravine with fine, white ash and sending ash billowing up from the surface of the flow which resulted in ashfall in adjacent communities several times. Courtesy of Arnold Binas, used with permission.
Figure (see Caption) Figure 65. Debris from pyroclastic flows that descended the SE Ravine at Sangay was carried down the Volcan River (left) during frequent rains and caused repeated damming at the confluence with the Rio Upano (right), located 23 km SE of the summit. These images show the conditions along the riverbeds during 9-17 January 2020. Courtesy of Arnold Binas, used with permission.
Figure (see Caption) Figure 66. An expedition by scientists from IG-EPN to one of the remote monitoring stations at Sangay during 26 January-1 February 2020 was successful in restoring communication to Quito. The remote location and constant volcanic activity makes access and maintenance a challenge. Courtesy of IG-EPN (Martes, 18 Febrero 2020 12:21, EXPEDICIÓN AL VOLCÁN SANGAY).

During February 2020, multiple daily VAAC reports of ash emissions continued (figure 67). Plumes generally rose 500-1,100 m above the summit and drifted W, although on 26 February emissions were reported to 1,770 m. Ashfall was reported in Macas (40 km SE) on 1 February, and in the communities of Pistishi (65 km SW), Chunchi (70 km SW), Pumallacta (60 k. SW), Alausí (60 km SW), Guamote (40 km WNW) and adjacent areas of the Chimborazo province on 5 February. The Ecuadorian Red Cross reported ash from Sangay in the provinces of Cañar and Azuay (60-100 km SW) on 25 February. Cebadas and Guamote reported moderate ashfall the following day. The communities of Cacha (50 km NW) and Punín (45 km NW) reported trace amounts of ashfall on 29 February. Incandescent blocks were seen on the SE flank multiples times throughout the month. A pyroclastic flow was recorded on the SE flank early on 6 February; additional pyroclastic flows were observed later that day on the SW flank. On 23 February a seismic station on the flank recorded a high-frequency signal typical of lahars.

Figure (see Caption) Figure 67. Steam and ash could be seen drifting SW from the summit of Sangay on 11 February 2020 even though the summit was hidden by a large cap cloud. Ash was also visible in the ravine on the SE flank. Courtesy of Sentinel Hub Playground, natural color (bands 4, 3, 2) rendering.

A significant ash emission on 1 March 2020 was reported about 2 km above the summit, drifting SW. Multiple ash emissions continued daily during the month, generally rising 570-1,170 m high. An emission on 12 March also rose 2 km above the summit. Trace ashfall was reported in Cebadas (35 km WNW) on 12 March. The community of Huamboya, located 40 km ENE of Sangay in the province of Morona-Santiago reported ashfall on 17 March. On 19 and 21 March ashfall was seen on the surface of cars in Macas to the SE. (figure 68). Ash was also reported on the 21st in de Santa María De Tunants (Sinaí) located E of Sangay. Ash fell again in Macas on 23 March and was also reported in General Proaño (40 km SE). The wind changed direction the next day and caused ashfall on 24 March to the SW in Cuenca and Azogues (100 km SW).

Figure (see Caption) Figure 68. Ashfall from Sangay was reported on cars in Huamboya on 17 March 2020 (left) and in Macas on 19 March (right). Courtesy IG-EPN, (#IGAlInstante Informativo VOLCÁN SANGAY No. 024, MARTES, 17 MARZO 2020 and #IGAlInstante Informativo VOLCÁN SANGAY No. 025, JUEVES, 19 MARZO 2020).

Incandescence from the dome at the crater and on the SE flank was noted by IG on 3, 4, and 13 March. Remobilized ash from a pyroclastic flow was reported drifting SW on 13 March. The incandescent path of the flow was still visible that evening. Numerous lahars were recorded seismically during the month, including on days 5, 6, 8, 11, 15, 30 and 31. Images from the Rio Upano on 11 March confirmed an increase from the normal flow rate (figure 69) inferred to be from volcanic debris. Morona-Santiago province officials reported on 14 March that a new dam had formed at the confluence of the Upano and Volcano rivers that decreased the flow downstream; by 16 March it had given way and flow had returned to normal levels.

Figure (see Caption) Figure 69. Images from the Rio Upano on 11 March 2020 (left) confirmed an increase from the normal flow rate related to lahars from Sangay descending the Rio Volcan. By 16 March (right), the flow rate had returned to normal, although the large blocks in the river were evidence of substantial activity in the past. Courtesy of IG (#IGAlInstante Informativo VOLCÁN SANGAY No. 018, MIÉRCOLES, 11 MARZO 2020 and #IGAlInstante Informativo VOLCÁN SANGAY No. 023, LUNES, 16 MARZO 2020).

Activity during April-June 2020. Lahar activity continued during April 2020; they were reported seven times on 2, 5, 7, 11, 12, 19, and 30 April. A significant reduction in the flow of the Upano River at the entrance bridge to the city of Macas was reported 9 April, likely due to a new dam on the river upstream from where the Volcan river joins it caused by lahars related to ash emissions and pyroclastic flows (figure 70). The flow rate returned to normal the following day. Ash emissions were reported most days of the month, commonly rising 500-1,100 m above the summit and drifting W. Incandescent blocks or flows were visible on the SE flank on 4, 10, 12, 15-16, and 20-23 April (figure 71).

Figure (see Caption) Figure 70. A significant reduction in the flow of the Upano River at the entrance bridge to the city of Macas was reported on 9 April 2020, likely due to a new dam upstream from lahars related to ash emissions and pyroclastic flows from Sangay. Courtesy of IG-EPN (#IGAlInstante Informativo VOLCÁN SANGAY No. 032, JUEVES, 9 ABRIL 2020).
Figure (see Caption) Figure 71. Incandescent blocks rolled down the SE ravine at Sangay multiple times during April 2020, including on 4 April (left). Pyroclastic flows left two continuous incandescent trails in the ravine on 23 April (right). Courtesy of IG-EPN (INFORME DIARIO DEL ESTADO DEL VOLCÁN SANGAY No. 2020-95, SÁBADO, 4 ABRIL 2020 and INFORME DIARIO DEL ESTADO DEL VOLCÁN SANGAY No. 2020-114, JUEVES, 23 ABRIL 2020).

Activity during May 2020 included multiple daily ash emissions that drifted W and numerous lahars from plentiful rain carrying ash and debris downstream. Although there were only a few visible observations of ash plumes due to clouds, the Washington VAAC reported plumes visible in satellite imagery throughout the month. Plumes rose 570-1,170 m above the summit most days; the highest reported rose to 2,000 m above the summit on 14 May. Two lahars occurred in the early morning on 1 May and one the next day. A lahar signal lasted for three hours on 4 May. Two lahar signals were recorded on the 7th, and three on the 9th. Lahars were also recorded on 16-17, 20-22, 26-27, and 30 May. Incandescence on the SE flank was only noted three times, but it was cloudy nearly every day.

An increase in thermal and overall eruptive activity was reported during June 2020. On 1 and 2 June the webcam captured lava flows and remobilization of the deposits on the SE flank in the early morning and late at night. Incandescence was visible multiple days each week. Lahars were reported on 4 and 5 June. The frequent daily ash emissions during June generally rose to 570-1,200 m above the summit and drifted usually SW or W. The number of explosions and ash emissions increased during the evening of 7 June. IG interpreted the seismic signals from the explosions as an indication of the rise of a new pulse of magma (figure 72). The infrasound sensor log from 8 June also recorded longer duration tremor signals that were interpreted as resulting from the descent of pyroclastic flows in the SE ravine.

Figure (see Caption) Figure 72. Seismic and infrasound signals indicated increased explosive and pyroclastic flow activity at Sangay on 7-8 June 2020. Left: SAGA station (seismic component) of 7 and 8 June. The signals correspond to explosions without VT or tremor signals, suggesting the rise of a new magma pulse. Right: SAGA station infrasound sensor log from 8 June. The sharp explosion signals are followed a few minutes later (examples highlighted in red) by emergent signals of longer duration, possibly associated with the descent of pyroclastic material in the SE flank ravine. Courtesy if IG-EPN (Informe Especial del Volcán Sangay - 2020 - N°3, “Actualización de la actividad eruptiva”, Quito, 12 de junio del 2020).

On the evening of 8 June ashfall was reported in the parish of Cebadas and in the Alausí Canton to the W and SW of Sangay. There were several reports of gas and ash emissions to 1,770 m above the summit the next morning on 9 June, followed by reports of ashfall in the provinces of Guayas, Santa Elena, Los Ríos, Morona Santiago, and Chimborazo. Ashfall continued in the afternoon and was reported in Alausí, Chunchi, Guamote, and Chillanes. That night, which was clear, the webcam captured images of pyroclastic flows down the SE-flank ravine; IG attributed the increase in activity to the collapse of one or more lava fronts. On the evening of 10 June additional ashfall was reported in the towns of Alausí, Chunchi, and Guamote (figure 73); satellite imagery indicated an ash plume drifting W and incandescence from pyroclastic flows in the SE-flank ravine the same day (figure 74).

Figure (see Caption) Figure 73. Ashfall from Sangay was reported in Alausí (top left), Chunchi (top right) and Guamote (bottom) on 10 June 2020. Courtesy of IG-EPN (#IGAlInstante Informativo VOLCÁN SANGAY No. 049, MIÉRCOLES, 10 JUNIO 2020).
Figure (see Caption) Figure 74. Incandescent pyroclastic flows (left) and ash plumes that drifted W (right) were recorded on 10 June 2020 at Sangay in Sentinel-2 satellite imagery. Courtesy of Sentinel Hub Playground.

Ashfall continued on 11 June and was reported in Guayaquil, Guamote, Chunchi, Riobamba, Guaranda, Chimbo, Echandía, and Chillanes. The highest ash plume of the report period rose to 2,800 m above the summit that day and drifted SW. That evening the SNGRE (Servicio Nacional de Gestion de Riesgos y Emergencias) reported ash fall in the Alausí canton. IG noted the increase in intensity of activity and reported that the ash plume of 11 June drifted more than 600 km W (figure 75). Ash emissions on 12 and 13 June drifted SW and NW and resulted in ashfall in the provinces of Chimborazo, Cotopaxi, Tungurahua, and Bolívar. On 14 June, the accumulation of ash interfered with the transmission of information from the seismic station. Lahars were reported each day during 15-17 and 19-21 June. Trace amounts of ashfall were reported in Macas to the SE on 25 June.

Figure (see Caption) Figure 75. The ash plume at Sangay reported on 11 June 2020 rose 2.8 km above the summit and drifted W according to the Washington VAAC and IG (left). Explosions and high levels of incandescence on the SE flank were captured by the Don Bosco webcam (right). Courtesy of IG-EPN (#IGAlInstante Informativo VOLCÁN SANGAY No. 055, JUEVES, 11 JUNIO 2020 and INFORME DIARIO DEL ESTADO DEL VOLCÁN SANGAY No. 2020-164, VIERNES, 12 JUNIO 2020).

During an overflight of Sangay on 24 June IG personnel observed that activity was characterized by small explosions from the summit vent and pyroclastic flows down the SE-flank ravine. The explosions produced small gas plumes with a high ash content that did not rise more than 500 m above the summit and drifted W (figure 76). The pyroclastic flows were restricted to the ravine on the SE flank, although the ash from the flows rose rapidly and reached about 200 m above the surface of the ravine and also drifted W (figure 77).

Figure (see Caption) Figure 76. A dense ash plume rose 500 m from the summit of Sangay on 24 June 2020 and drifted W during an overflight by IG-EPN personnel. The aerial photograph is taken from the SE; snow-covered Chimborazo is visible behind and to the right of Sangay. Photo by M Almeida, courtesy of IG EPN (Jueves, 02 Julio 2020 10:29, INFORME DEL SOBREVUELO AL VOLCÁN SANGAY EL 24 DE JUNIO DE 2020).
Figure (see Caption) Figure 77. Pyroclastic flows descended the SE flank ravine at Sangay during an overflight by IG-EPN personnel on 24 June 2020. Ash from the pyroclastic flow rose 200 m and drifted W, and infrared imagery identified the thermal signature of the pyroclastic flow in the ravine. Photo by M Almeida, IR Image by S Vallejo, courtesy of IG EPN (Jueves, 25 Junio 2020 12:24, SOBREVUELO AL VOLCÁN SANGAY).

Infrared imagery taken during the overflight on 24 June identified three significant thermal anomalies in the large ravine on the SE flank (figure 78). Analysis by IG scientists suggested that the upper anomaly 1 (125°C) was associated with explosive activity that was observed during the flight. Anomaly 2 (147°C), a short distance below Anomaly 1, was possibly related to effusive activity of a small flow, and Anomaly 3 (165°C) near the base of the ravine that was associated with pyroclastic flow deposits. The extent of the changes at the summit of Sangay and along the SE flank since the beginning of the eruption that started in March 2019 were clearly visible when images from May 2019 were compared with images from the 24 June 2020 overflight (figure 79). The upper part of the ravine was nearly 400 m wide by the end of June.

Figure (see Caption) Figure 78. A thermal image of the SE flank of Sangay taken on 24 June 2020 indicated three thermal anomalies. Anomaly 1 was associated with explosive activity, Anomaly 2 was associated with effusive activity, and Anomaly 3 was related to pyroclastic-flow deposits. Image prepared by S Vallejo Vargas, courtesy of IG EPN (Jueves, 02 Julio 2020 10:29, INFORME DEL SOBREVUELO AL VOLCÁN SANGAY EL 24 DE JUNIO DE 2020).
Figure (see Caption) Figure 79. Aerial and thermal photographs of the southern flank of the Sangay volcano on 17 May 2019 (left: visible image) and 24 June 2020 (middle: visible image, right: visible-thermal overlay) show the morphological changes on the SE flank, associated with the formation of a deep ravine and the modification of the summit. Photos and thermal image by M Almeida, courtesy of IG EPN (Jueves, 02 Julio 2020 10:29, INFORME DEL SOBREVUELO AL VOLCÁN SANGAY EL 24 DE JUNIO DE 2020).

Geologic Background. The isolated Sangay volcano, located east of the Andean crest, is the southernmost of Ecuador's volcanoes and its most active. The steep-sided, glacier-covered, dominantly andesitic volcano grew within horseshoe-shaped calderas of two previous edifices, which were destroyed by collapse to the east, producing large debris avalanches that reached the Amazonian lowlands. The modern edifice dates back to at least 14,000 years ago. It towers above the tropical jungle on the east side; on the other sides flat plains of ash have been sculpted by heavy rains into steep-walled canyons up to 600 m deep. The earliest report of a historical eruption was in 1628. More or less continuous eruptions were reported from 1728 until 1916, and again from 1934 to the present. The almost constant activity has caused frequent changes to the morphology of the summit crater complex.

Information Contacts: Instituto Geofísico, Escuela Politécnica Nacional (IG-EPN), Casilla 17-01-2759, Quito, Ecuador (URL: http://www.igepn.edu.ec/); 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/); Washington Volcanic Ash Advisory Center (VAAC), Satellite Analysis Branch (SAB), NOAA/NESDIS OSPO, NOAA Science Center Room 401, 5200 Auth Rd, Camp Springs, MD 20746, USA (URL: www.ospo.noaa.gov/Products/atmosphere/vaac, archive at: http://www.ssd.noaa.gov/VAAC/archive.html); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); Arnold Binas (URL: https://www.doroadventures.com).


Karangetang (Indonesia) — June 2020 Citation iconCite this Report

Karangetang

Indonesia

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

All times are local (unless otherwise noted)


Incandescent block avalanches through mid-January 2020; crater anomalies through May

The Karangetang andesitic-basaltic stratovolcano (also referred to as Api Siau) at the northern end of the island of Siau, north of Sulawesi, Indonesia, has had more than 50 observed eruptions since 1675. Frequent explosive activity is accompanied by pyroclastic flows and lahars, and lava-dome growth has created two active summit craters (Main to the S and Second Crater to the N). Rock avalanches, observed incandescence, and satellite thermal anomalies at the summit confirmed continuing volcanic activity since the latest eruption started in November 2018 (BGVN 44:05). This report covers activity from December 2019 through May 2020. Activity is monitored by Indonesia's Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as CVGHM, or the Center of Volcanology and Geological Hazard Mitigation), and ash plumes are monitored by the Darwin VAAC (Volcanic Ash Advisory Center). Information is also available from MODIS thermal anomaly satellite data through both the University of Hawaii's MODVOLC system and the Italian MIROVA project.

Increased activity that included daily incandescent avalanche blocks traveling down the W and NW flanks lasted from mid-July 2019 (BGVN 44:12) through mid-January 2020 according to multiple sources. The MIROVA data showed increased number and intensity of thermal anomalies during this period, with a sharp drop during the second half of January (figure 40). The MODVOLC thermal alert data reported 29 alerts in December and ten alerts in January, ending on 14 January, with no further alerts through May 2020. During December and the first half of January incandescent blocks traveled 1,000-1,500 m down multiple drainages on the W and NW flanks (figure 41). After this, thermal anomalies were still present at the summit craters, but no additional activity down the flanks was identified in remote satellite data or direct daily observations from PVMBG.

Figure (see Caption) Figure 40. An episode of increased activity at Karangetang from mid-July 2019 through mid-January 2020 included incandescent avalanche blocks traveling down multiple flanks of the volcano. This was reflected in increased thermal activity seen during that interval in the MIROVA graph covering 5 June 2019 through May 2020. Courtesy of MIROVA.
Figure (see Caption) Figure 41. An episode of increased activity at Karangetang from mid-July 2019 through mid-January 2020 included incandescent avalanche blocks traveling up to 1,500 m down drainages on the W and NW flanks of the volcano. Top left: large thermal anomalies trend NW from Main Crater on 5 December 2019; about 500 m N a thermal anomaly glows from Second Crater. Top center: on 15 December plumes of steam and gas drifted W and SW from both summit craters as seen in Natural Color rendering (bands 4,3,2). Top right: the same image as at top center with Atmospheric penetration rendering (bands 12, 11, 8a) shows hot zones extending WNW from Main Crater and a thermal anomaly at Second Crater. Bottom left: thermal activity seen on 14 January 2020 extended about 800 m WNW from Main Crater along with an anomaly at Second Crater and a hot spot about 1 km W. Bottom center: by 19 January the anomaly from Second Crater appeared slightly stronger than at Main Crater, and only small anomalies appeared on the NW flank. Bottom right: an image from 14 March shows only thermal anomalies at the two summit craters. Courtesy of Sentinel Hub Playground.

A single VAAC report in early April noted a short-lived ash plume that drifted SW. Intermittent low-level activity continued through May 2020. Small SO2 plumes appeared in satellite data multiple times in December 2019 and January 2020; they decreased in size and frequency after that but were still intermittently recorded into May 2020 (figure 42).

Figure (see Caption) Figure 42. Small plumes of sulfur dioxide were measured at Karangetang with the TROPOMI instrument on the Sentinel-5P satellite multiple times during December 2019 (top row). They were less frequent but still appeared during January-May 2020 (bottom row). Larger plumes were also detected from Dukono, located 300 km ESE at the N end of North Maluku. Courtesy of Global Sulfur Dioxide Monitoring Page.

PVMBG reported in their daily summaries that steam plumes rose 50-150 m above the Main Crater and 25-50 m above Second Crater on most days in December. The incandescent avalanche activity that began in mid-July 2019 also continued throughout December 2019 and January 2020 (figure 43). Incandescent blocks from the Main Crater descended river drainages (Kali) on the W and NW flanks throughout December. They were reported nearly every day in the Nanitu, Sense, and Pangi drainages, traveling 1,000-1,500 m. Incandescence from both craters was visible 10-25 m above the crater rim most nights.

Figure (see Caption) Figure 43. Incandescent block avalanches descended the NW flank of Karangetang as far as 1,500 m frequently during December 2019 and January 2020. Left image taken 13 December 2019, right image taken 6 January 2020 by PVMBG webcam. Courtesy of PVMBG, Oystein Anderson, and Bobyson Lamanepa.

A few blocks were noted traveling 800 m down Kali Beha Barat on 1 December. Incandescence above the Main crater reached 50-75 m during 4-6 December. During 4-7 December incandescent blocks appeared in Kali Sesepe, traveling 1,000-1,500 m down from the summit. They were also reported in Kali Batang and Beha Barat during 4-14 December, usually moving 800-1,000 m downslope. Between 5 and 14 December, gray and white plumes from Second Crater reached 300 m multiple times. During 12-15 December steam plumes rose 300-500 m above the Main crater. Activity decreased during 18-26 December but increased again during the last few days of the month. On 28 December, incandescent blocks were reported 1,500 m down Kali Pangi and Nanitu, and 1,750 m down Kali Sense.

Incandescent blocks were reported in Kali Sesepi during 4-6 January and in Kali Batang and Beha Barat during 4-8 and 12-15 January (figure 44); they often traveled 800-1,200 m downslope. Activity tapered off in those drainages and incandescent blocks were last reported in Kali Beha Barat on 15 January traveling 800 m from the summit. Incandescent blocks were also reported traveling usually 1,000-1,500 m down the Nanitu, Sense, and Pangi drainages during 4-19 January. Blocks continued to occasionally descend up to 1,000 m down Kali Nanitu through 24 January. Pulses of activity occurred at the summit of Second Crater a few times in January. Steam plumes rose 25-50 m during 8-9 January and again during 16-31 January, with plumes rising 300-400 m on 20, 29, and 31 January. Incandescence was noted 10-25 m above the summit of Second Crater during 27-30 January.

Figure (see Caption) Figure 44. Incandescent material descends the Beha Barat, Sense, Nanitu, and Pangi drainages on the NW flank of Karangetang in early January 2020. Courtesy of Bobyson Lamanepa; posted on Twitter on 6 January 2020.

Activity diminished significantly after mid-January 2020. Steam plumes at the Main Crater rose 50-100 m on the few days where the summit was not obscured by fog during February. Faint incandescence occurred at the Main Crater on 7 February, and steam plumes rising 25-50 m from Second Crater that day were the only events reported there in February. During March, steam plumes persisted from the Main Crater, with heights of over 100 m during short periods from 8-16 March and 25-30 March. Weak incandescence was reported from the Main Crater only once, on 25 March. Very little activity occurred at Second Crater during March, with only steam plumes reported rising 25-300 m from the 22nd to the 28th (figure 45).

Figure (see Caption) Figure 45. Steam plumes at Karangetang rose over 100 m above both summit craters multiple times during March, including on 26 March 2020. Courtesy of PVMBG and Oystein Anderson.

The Darwin VAAC reported a continuous ash emission on 4 April 2020 that rose to 2.1 km altitude and drifted SW for a few hours before dissipating. Incandescence visible 25 m above both craters on 13 April was the only April activity reported by PVMBG other than steam plumes from the Main Crater that rose 50-500 m on most days. Steam plumes of 50-100 m were reported from Second Crater during 11-13 April. Activity remained sporadic throughout May 2020. Steam plumes from the Main Crater rose 50-300 m each day. Satellite imagery identified steam plumes and incandescence from both summit craters on 3 May (figure 46). Faint incandescence was observed at the Main Crater on 12 and 27 May. Steam plumes rose 25-50 m from Second Crater on a few days; a 200-m-high plume was reported on 27 May. Bluish emissions were observed on the S and SW flanks on 28 May.

Figure (see Caption) Figure 46. Dense steam plumes and thermal anomalies were present at both summit craters of Karangetang on 3 May 2020. Sentinel 2 satellite image with Natural Color (bands 4, 3, 2) (left) and Atmospheric Penetration rendering (bands 12, 11, 8a) (right); courtesy of Sentinel Hub Playground.

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/); 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/); 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/); 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/); Øystein Lund Andersen (Twitter: @OysteinLAnderse, https://twitter.com/OysteinLAnderse, URL: http://www.oysteinlundandersen.com); Bobyson Lamanepa, Yogyakarta, Indonesia, (URL: https://twitter.com/BobyLamanepa/status/1214165637028728832).


Masaya (Nicaragua) — June 2020 Citation iconCite this Report

Masaya

Nicaragua

11.985°N, 86.165°W; summit elev. 594 m

All times are local (unless otherwise noted)


Lava lake level drops but remains active through May 2020; weak gas plumes

Masaya, which is about 20 km NW of the Nicaragua’s capital of Managua, is one of the most active volcanoes in that country and has a caldera that contains a number of craters (BGVN 43:11). The Santiago crater is the one most currently active and it contains a small lava lake that emits weak gas plumes (figure 85). This report summarizes activity during February through May 2020 and is based on Instituto Nicaragüense de Estudios Territoriales (INETER) monthly reports and satellite data. During the reporting period, the volcano was relatively calm, with only weak gas plumes.

Figure (see Caption) Figure 85. Satellite images of Masaya from Sentinel-2 on 18 April 2020, showing and a small gas plume drifting SW (top, natural color bands 4, 3, 2) and the lava lake (bottom, false color bands 12, 11, 4). Courtesy of Sentinel Hub Playground.

According to INETER, thermal images of the lava lake and temperature data in the fumaroles were taken using an Omega infrared gun and a forward-looking infrared (FLIR) SC620 thermal camera. The temperatures above the lava lake have decreased since November 2019, when the temperature was 287°C, dropping to 96°C when measured on 14 May 2020. INETER attributed this decrease to subsidence in the level of the lava lake by 5 m which obstructed part of the lake and concentrated the gas emissions in the weak plume. Convection continued in the lava lake, which in May had decreased to a diameter of 3 m. Many landslides had occurred in the E, NE, and S walls of the crater rim due to rock fracturing caused by the high heat and acidity of the emissions.

During the reporting period, the MIROVA (Middle InfraRed Observation of Volcanic Activity) volcano hotspot detection system recorded numerous thermal anomalies from the lava lake based on MODIS data (figure 86). Infrared satellite images from Sentinel-2 regularly showed a strong signature from the lava lake through 18 May, after which the volcano was covered by clouds.

Figure (see Caption) Figure 86. Thermal anomalies at Masaya during February through May 2020. The larger anomalies with black lines are more distant and not related to the volcano. Courtesy of MIROVA.

Measurements of sulfur dioxide (SO2) made by INETER in the section of the Ticuantepe - La Concepción highway (just W of the volcano) with a mobile DOAS system varied between a low of just over 1,000 metric tons/day in mid-November 2019 to a high of almost 2,500 tons/day in late May. Temperatures of fumaroles in the Cerro El Comalito area, just ENE of Santiago crater, ranged from 58 to 76°C during February-May 2020, with most values in the 69-72°C range.

Geologic Background. Masaya is one of Nicaragua's most unusual and most active volcanoes. It lies within the massive Pleistocene Las Sierras caldera and is itself a broad, 6 x 11 km basaltic caldera with steep-sided walls up to 300 m high. The caldera is filled on its NW end by more than a dozen vents that erupted along a circular, 4-km-diameter fracture system. The Nindirí and Masaya cones, the source of historical eruptions, were constructed at the southern end of the fracture system and contain multiple summit craters, including the currently active Santiago crater. A major basaltic Plinian tephra erupted from Masaya about 6,500 years ago. Historical lava flows cover much of the caldera floor and there is a lake at the far eastern end. A lava flow from the 1670 eruption overtopped the north caldera rim. Masaya has been frequently active since the time of the Spanish Conquistadors, when an active lava lake prompted attempts to extract the volcano's molten "gold." Periods of long-term vigorous gas emission at roughly quarter-century intervals have caused health hazards and crop damage.

Information Contacts: Instituto Nicaragüense de Estudios Territoriales (INETER), Apartado Postal 2110, Managua, Nicaragua (URL: http://www.ineter.gob.ni/); 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/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground).


Shishaldin (United States) — June 2020 Citation iconCite this Report

Shishaldin

United States

54.756°N, 163.97°W; summit elev. 2857 m

All times are local (unless otherwise noted)


Intermittent thermal activity and a possible new cone at the summit crater during February-May 2020

Shishaldin is located near the center of Unimak Island in Alaska, with the current eruption phase beginning in July 2019 and characterized by ash plumes, lava flows, lava fountaining, pyroclastic flows, and lahars. More recently, in late 2019 and into January 2020, activity consisted of multiple lava flows, pyroclastic flows, lahars, and ashfall events (BGVN 45:02). This report summarizes activity from February through May 2020, including gas-and-steam emissions, brief thermal activity in mid-March, and a possible new cone within the summit crater. The primary source of information comes from the Alaska Volcano Observatory (AVO) reports and various satellite data.

Volcanism during February 2020 was relatively low, consisting of weakly to moderately elevated surface temperatures during 1-4 February and occasional small gas-and-steam plumes (figure 37). By 6 February both seismicity and surface temperatures had decreased. Seismicity and surface temperatures increased slightly again on 8 March and remained elevated through the rest of the reporting period. Intermittent gas-and-steam emissions were also visible from mid-March (figure 38) through May. Minor ash deposits visible on the upper SE flank may have been due to ash resuspension or a small collapse event at the summit, according to AVO.

Figure (see Caption) Figure 37. Photo of a gas-and-steam plume rising from the summit crater at Shishaldin on 22 February 2020. Photo courtesy of Ben David Jacob via AVO.
Figure (see Caption) Figure 38. A Worldview-2 panchromatic satellite image on 11 March 2020 showing a gas-and-steam plume rising from the summit of Shishaldin and minor ash deposits on the SE flank (left). Aerial photo showing minor gas-and-steam emissions rising from the summit crater on 11 March (right). Some erosion of the snow and ice on the upper flanks is a result of the lava flows from the activity in late 2019 and early 2020. Photo courtesy of Matt Loewen (left) and Ed Fischer (right) via AVO.

On 14 March, lava and a possible new cone were visible in the summit crater using satellite imagery, accompanied by small explosion signals. Strong thermal signatures due to the lava were also seen in Sentinel-2 satellite data and continued strongly through the month (figure 39). The lava reported by AVO in the summit crater was also reflected in satellite-based MODIS thermal anomalies recorded by the MIROVA system (figure 40). Seismic and infrasound data identified small explosions signals within the summit crater during 14-19 March.

Figure (see Caption) Figure 39. Sentinel-2 thermal satellite images (bands 12, 11, 8A) show a bright hotspot (yellow-orange) at the summit crater of Shishaldin during mid-March 2020 that decreases in intensity by late March. Courtesy of Sentinel Hub Playground.
Figure (see Caption) Figure 40. MIROVA thermal data showing a brief increase in thermal anomalies during late March 2020 and on two days in late April between periods of little to no activity. Courtesy of MIROVA.

AVO released a Volcano Observatory Notice for Aviation (VONA) stating that seismicity had decreased by 16 April and that satellite data no longer showed lava or additional changes in the crater since the start of April. Sentinel-2 thermal satellite imagery continued to show a weak hotspot in the crater summit through May (figure 41), which was also detected by the MIROVA system on two days. A daily report on 6 May reported a visible ash deposit extending a short distance SE from the summit, which had likely been present since 29 April. AVO noted that the timing of the deposit corresponds to an increase in the summit crater diameter and depth, further supporting a possible small collapse. Small gas-and-steam emissions continued intermittently and were accompanied by weak tremors and occasional low-frequency earthquakes through May (figure 42). Minor amounts of sulfur dioxide were detected in the gas-and-steam emissions during 20 and 29 April, and 2, 16, and 28 May.

Figure (see Caption) Figure 41. Sentinel-2 thermal satellite images (bands 12, 11, 8A) show occasional gas-and-steam emissions rising from Shishaldin on 26 February (top left) and 24 April 2020 (bottom left) and a weak hotspot (yellow-orange) persisting at the summit crater during April and early May 2020. Courtesy of Sentinel Hub Playground.
Figure (see Caption) Figure 42. A Worldview-1 panchromatic satellite image showing gas-and-steam emissions rising from the summit of Shishaldin on 1 May 2020 (local time) (left). Aerial photo of the N flank of Shishaldin with minor gas-and-steam emissions rising from the summit on 8 May (right). Photo courtesy of Matt Loewen (left) and Levi Musselwhite (right) via AVO.

Geologic Background. The beautifully symmetrical Shishaldin is the highest and one of the most active volcanoes of the Aleutian Islands. The glacier-covered volcano is the westernmost of three large stratovolcanoes along an E-W line in the eastern half of Unimak Island. The Aleuts named the volcano Sisquk, meaning "mountain which points the way when I am lost." A steam plume often rises from its small summit crater. Constructed atop an older glacially dissected volcano, it is largely basaltic in composition. Remnants of an older ancestral volcano are exposed on the W and NE sides at 1,500-1,800 m elevation. There are over two dozen pyroclastic cones on its NW flank, which is blanketed by massive aa lava flows. Frequent explosive activity, primarily consisting of Strombolian ash eruptions from the small summit crater, but sometimes producing lava flows, has been recorded since the 18th century.

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


Krakatau (Indonesia) — June 2020 Citation iconCite this Report

Krakatau

Indonesia

6.102°S, 105.423°E; summit elev. 155 m

All times are local (unless otherwise noted)


Strombolian explosions, ash plumes, and crater incandescence during April 2020

Krakatau, located in the Sunda Strait between Indonesia’s Java and Sumatra Islands, experienced a major caldera collapse around 535 CE, forming a 7-km-wide caldera ringed by three islands. On 22 December 2018, a large explosion and flank collapse destroyed most of the 338-m-high island of Anak Krakatau (Child of Krakatau) and generated a deadly tsunami (BGVN 44:03). The near-sea level crater lake inside the remnant of Anak Krakatau was the site of numerous small steam and tephra explosions. A larger explosion in December 2019 produced the beginnings of a new cone above the surface of crater lake (BGVN 45:02). Recently, volcanism has been characterized by occasional Strombolian explosions, dense ash plumes, and crater incandescence. This report covers activity from February through May 2020 using information provided by the Indonesian Center for Volcanology and Geological Hazard Mitigation, also known as Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG), the Darwin Volcanic Ash Advisory Center (VAAC), and various satellite data.

Activity during February 2020 consisted of dominantly white gas-and-steam emissions rising 300 m above the crater, according to PVMBG. According to the Darwin VAAC, a ground observer reported an eruption on 7 and 8 February, but no volcanic ash was observed. During 10-11 February, a short-lived eruption was detected by seismograms which produced an ash plume up to 1 km above the crater drifting E. MAGMA Indonesia reported two eruptions on 18 March, both of which rose to 300 m above the crater. White gas-and-steam emissions were observed for the rest of the month and early April.

On 10 April PVMBG reported two eruptions, at 2158 and 2235, both of which produced dark ash plumes rising 2 km above the crater followed by Strombolian explosions ejecting incandescent material that landed on the crater floor (figures 108 and 109). The Darwin VAAC issued a notice at 0145 on 11 April reporting an ash plume to 14.3 km altitude drifting WNW, however this was noted with low confidence due to the possible mixing of clouds. During the same day, an intense thermal hotspot was detected in the HIMAWARI thermal satellite imagery and the NASA Global Sulfur Dioxide page showed a strong SO2 plume at 11.3 km altitude drifting W (figure 110). The CCTV Lava93 webcam showed new lava flows and lava fountaining from the 10-11 April eruptions. This activity was evident in the MIROVA (Middle InfraRed Observation of Volcanic Activity) graph of MODIS thermal anomaly data (figure 111).

Figure (see Caption) Figure 108. Webcam (Lava93) images of Krakatau on 10 April 2020 showing Strombolian explosions, strong incandescence, and ash plumes rising from the crater. Courtesy of PVMBG and MAGMA Indonesia.
Figure (see Caption) Figure 109. Webcam image of incandescent Strombolian explosions at Krakatau on 10 April 2020. Courtesy of PVMBG and MAGMA Indonesia.
Figure (see Caption) Figure 110. Strong sulfur dioxide emissions rising from Krakatau and drifting W were detected using the TROPOMI instrument on the Sentinel-5P satellite on 11 April 2020 (top row). Smaller volumes of SO2 were visible in Sentinel-5P/TROPOMI maps on 13 (bottom left) and 19 April (bottom right). Courtesy of NASA Global Sulfur Dioxide Monitoring Page.
Figure (see Caption) Figure 111. Thermal activity at Anak Krakatau from 29 June-May 2020 shown on a MIROVA Log Radiative Power graph. The power and frequency of the thermal anomalies sharply increased in mid-April. After the larger eruptive event in mid-April the thermal anomalies declined slightly in strength but continued to be detected intermittently through May. Courtesy of MIROVA.

Strombolian activity rising up to 500 m continued into 12 April and was accompanied by SO2 emissions that rose 3 km altitude, drifting NW according to a VAAC notice. PVMBG reported an eruption on 13 April at 2054 that resulted in incandescence as high as 25 m above the crater. Volcanic ash, accompanied by white gas-and-steam emissions, continued intermittently through 18 April, many of which were observed by the CCTV webcam. After 18 April only gas-and-steam plumes were reported, rising up to 100 m above the crater; Sentinel-2 satellite imagery showed faint thermal anomalies in the crater (figure 112). SO2 emissions continued intermittently throughout April, though at lower volumes and altitudes compared to the 11th. MODIS satellite data seen in MIROVA showed intermittent thermal anomalies through May.

Figure (see Caption) Figure 112. Sentinel-2 thermal satellite images showing the cool crater lake on 20 March (top left) followed by minor heating of the crater during April and May 2020. Sentinel-2 satellite images with “Atmospheric penetration” (bands 12, 11, 8A) rendering; courtesy of Sentinel Hub Playground.

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

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


Taal (Philippines) — June 2020 Citation iconCite this Report

Taal

Philippines

14.002°N, 120.993°E; summit elev. 311 m

All times are local (unless otherwise noted)


Eruption on 12 January with explosions through 22 January; steam plumes continuing into March

Taal volcano is in a caldera system located in southern Luzon island and is one of the most active volcanoes in the Philippines. It has produced around 35 recorded eruptions since 3,580 BCE, ranging from VEI 1 to 6, with the majority of eruptions being a VEI 2. The caldera contains a lake with an island that also contains a lake within the Main Crater (figure 12). Prior to 2020 the most recent eruption was in 1977, on the south flank near Mt. Tambaro. The United Nations Office for the Coordination of Humanitarian Affairs in the Philippines reports that over 450,000 people live within 40 km of the caldera (figure 13). This report covers activity during January through February 2020 including the 12 to 22 January eruption, and is based on reports by Philippine Institute of Volcanology and Seismology (PHIVOLCS), satellite data, geophysical data, and media reports.

Figure (see Caption) Figure 12. Annotated satellite images showing the Taal caldera, Volcano Island in the caldera lake, and features on the island including Main Crater. Imagery courtesy of Planet Inc.
Figure (see Caption) Figure 13. Map showing population totals within 14 and 17 km of Volcano Island at Taal. Courtesy of the United Nations Office for the Coordination of Humanitarian Affairs (OCHA).

The hazard status at Taal was raised to Alert Level 1 (abnormal, on a scale of 0-5) on 28 March 2019. From that date through to 1 December there were 4,857 earthquakes registered, with some felt nearby. Inflation was detected during 21-29 November and an increase in CO2 emission within the Main Crater was observed. Seismicity increased beginning at 1100 on 12 January. At 1300 there were phreatic (steam) explosions from several points inside Main Crater and the Alert Level was raised to 2 (increasing unrest). Booming sounds were heard in Talisay, Batangas, at 1400; by 1402 the plume had reached 1 km above the crater, after which the Alert Level was raised to 3 (magmatic unrest).

Phreatic eruption on 12 January 2020. A seismic swarm began at 1100 on 12 January 2020 followed by a phreatic eruption at 1300. The initial activity consisted of steaming from at least five vents in Main Crater and phreatic explosions that generated 100-m-high plumes. PHIVOLCS raised the Alert Level to 2. The Earth Observatory of Singapore reported that the International Data Center (IDC) for the Comprehensive test Ban Treaty (CTBT) in Vienna noted initial infrasound detections at 1450 that day.

Booming sounds were heard at 1400 in Talisay, Batangas (4 km NNE from the Main Crater), and at 1404 volcanic tremor and earthquakes felt locally were accompanied by an eruption plume that rose 1 km; ash fell to the SSW. The Alert Level was raised to 3 and the evacuation of high-risk barangays was recommended. Activity again intensified around 1730, prompting PHIVOLCS to raise the Alert Level to 4 and recommend a total evacuation of the island and high-risk areas within a 14-km radius. The eruption plume of steam, gas, and tephra significantly intensified, rising to 10-15 km altitude and producing frequent lightning (figures 14 and 15). Wet ash fell as far away as Quezon City (75 km N). According to news articles schools and government offices were ordered to close and the Ninoy Aquino International Airport (56 km N) in Manila suspended flights. About 6,000 people had been evacuated. Residents described heavy ashfall, low visibility, and fallen trees.

Figure (see Caption) Figure 14. Lightning produced during the eruption of Taal during 1500 on 12 January to 0500 on 13 January 2020 local time (0700-2100 UTC on 12 January). Courtesy of Chris Vagasky, Vaisala.
Figure (see Caption) Figure 15. Lightning strokes produced during the first days of the Taal January 2020 eruption. Courtesy of Domcar C Lagto/SIPA/REX/Shutterstock via The Guardian.

In a statement issued at 0320 on 13 January, PHIVOLCS noted that ashfall had been reported across a broad area to the north in Tanauan (18 km NE), Batangas; Escala (11 km NW), Tagaytay; Sta. Rosa (32 km NNW), Laguna; Dasmariñas (32 km N), Bacoor (44 km N), and Silang (22 km N), Cavite; Malolos (93 km N), San Jose Del Monte (87 km N), and Meycauayan (80 km N), Bulacan; Antipolo (68 km NNE), Rizal; Muntinlupa (43 km N), Las Piñas (47 km N), Marikina (70 km NNE), Parañaque (51 km N), Pasig (62 km NNE), Quezon City, Mandaluyong (62 km N), San Juan (64 km N), Manila; Makati City (59 km N) and Taguig City (55 km N). Lapilli (2-64 mm in diameter) fell in Tanauan and Talisay; Tagaytay City (12 km N); Nuvali (25 km NNE) and Sta (figure 16). Rosa, Laguna. Felt earthquakes (Intensities II-V) continued to be recorded in local areas.

Figure (see Caption) Figure 16. Ashfall from the Taal January 2020 eruption in Lemery (top) and in the Batangas province (bottom). Photos posted on 13 January, courtesy of Ezra Acayan/Getty Images, Aaron Favila/AP, and Ted Aljibe/AFP via Getty Images via The Guardian.

Magmatic eruption on 13 January 2020. A magmatic eruption began during 0249-0428 on 13 January, characterized by weak lava fountaining accompanied by thunder and flashes of lightning. Activity briefly waned then resumed with sporadic weak fountaining and explosions that generated 2-km-high, dark gray, steam-laden ash plumes (figure 17). New lateral vents opened on the N flank, producing 500-m-tall lava fountains. Heavy ashfall impacted areas to the SW, including in Cuenca (15 km SSW), Lemery (16 km SW), Talisay, and Taal (15 km SSW), Batangas (figure 18).

Figure (see Caption) Figure 17. Ash plumes seen from various points around Taal in the initial days of the January 2020 eruption, posted on 13 January. Courtesy of Eloisa Lopez/Reuters, Kester Ragaza/Pacific Press/Shutterstock, Ted Aljibe/AFP via Getty Images, via The Guardian.
Figure (see Caption) Figure 18. Map indicating areas impacted by ashfall from the 12 January eruption through to 0800 on the 13th. Small yellow circles (to the N) are ashfall report locations; blue circles (at the island and to the S) are heavy ashfall; large green circles are lapilli (particles measuring 2-64 mm in diameter). Modified from a map courtesy of Lauriane Chardot, Earth Observatory of Singapore; data taken from PHIVOLCS.

News articles noted that more than 300 domestic and 230 international flights were cancelled as the Manila Ninoy Aquino International Airport was closed during 12-13 January. Some roads from Talisay to Lemery and Agoncillo were impassible and electricity and water services were intermittent. Ashfall in several provinces caused power outages. Authorities continued to evacuate high-risk areas, and by 13 January more than 24,500 people had moved to 75 shelters out of a total number of 460,000 people within 14 km.

A PHIVOLCS report for 0800 on the 13th through 0800 on 14 January noted that lava fountaining had continued, with steam-rich ash plumes reaching around 2 km above the volcano and dispersing ash SE and W of Main Crater. Volcanic lighting continued at the base of the plumes. Fissures on the N flank produced 500-m-tall lava fountains. Heavy ashfall continued in the Lemery, Talisay, Taal, and Cuenca, Batangas Municipalities. By 1300 on the 13th lava fountaining generated 800-m-tall, dark gray, steam-laden ash plumes that drifted SW. Sulfur dioxide emissions averaged 5,299 metric tons/day (t/d) on 13 January and dispersed NNE (figure 19).

Figure (see Caption) Figure 19. Compilation of sulfur dioxide plumes from TROPOMI overlaid in Google Earth for 13 January from 0313-1641 UT. Courtesy of NASA Global Sulfur Dioxide Monitoring Page and Google Earth.

Explosions and ash emission through 22 January 2020. At 0800 on 15 January PHIVOLCS stated that activity was generally weaker; dark gray, steam-laden ash plumes rose about 1 km and drifted SW. Satellite images showed that the Main Crater lake was gone and new craters had formed inside Main Crater and on the N side of Volcano Island.

PHIVOLCS reported that activity during 15-16 January was characterized by dark gray, steam-laden plumes that rose as high as 1 km above the vents in Main Crater and drifted S and SW. Sulfur dioxide emissions were 4,186 t/d on 15 January. Eruptive events at 0617 and 0621 on 16 January generated short-lived, dark gray ash plumes that rose 500 and 800 m, respectively, and drifted SW. Weak steam plumes rose 800 m and drifted SW during 1100-1700, and nine weak explosions were recorded by the seismic network.

Steady steam emissions were visible during 17-21 January. Infrequent weak explosions generated ash plumes that rose as high as 1 km and drifted SW. Sulfur dioxide emissions fluctuated and were as high as 4,353 t/d on 20 January and as low as 344 t/d on 21 January. PHIVOLCS reported that white steam-laden plumes rose as high as 800 m above main vent during 22-28 January and drifted SW and NE; ash emissions ceased around 0500 on 22 January. Remobilized ash drifted SW on 22 January due to strong low winds, affecting the towns of Lemery (16 km SW) and Agoncillo, and rose as high as 5.8 km altitude as reported by pilots. Sulfur dioxide emissions were low at 140 t/d.

Steam plumes through mid-April 2020. The Alert Level was lowered to 3 on 26 January and PHIVOLCS recommended no entry onto Volcano Island and Taal Lake, nor into towns on the western side of the island within a 7-km radius. PHIVOLCS reported that whitish steam plumes rose as high as 800 m during 29 January-4 February and drifted SW (figure 20). The observed steam plumes rose as high as 300 m during 5-11 February and drifted SW.

Sulfur dioxide emissions averaged around 250 t/d during 22-26 January; emissions were 87 t/d on 27 January and below detectable limits the next day. During 29 January-4 February sulfur dioxide emissions ranged to a high of 231 t/d (on 3 February). The following week sulfur dioxide emissions ranged from values below detectable limits to a high of 116 t/d (on 8 February).

Figure (see Caption) Figure 20. Taal Volcano Island producing gas-and-steam plumes on 15-16 January 2020. Courtesy of James Reynolds, Earth Uncut.

On 14 February PHIVOLCS lowered the Alert Level to 2, noting a decline in the number of volcanic earthquakes, stabilizing ground deformation of the caldera and Volcano Island, and diffuse steam-and-gas emission that continued to rise no higher than 300 m above the main vent during the past three weeks. During 14-18 February sulfur dioxide emissions ranged from values below detectable limits to a high of 58 tonnes per day (on 16 February). Sulfur dioxide emissions were below detectable limits during 19-20 February. During 26 February-2 March steam plumes rose 50-300 m above the vent and drifted SW and NE. PHIVOLCS reported that during 4-10 March weak steam plumes rose 50-100 m and drifted SW and NE; moderate steam plumes rose 300-500 m and drifted SW during 8-9 March. During 11-17 March weak steam plumes again rose only 50-100 m and drifted SW and NE.

PHIVOLCS lowered the Alert Level to 1 on 19 March and recommended no entry onto Volcano Island, the area defined as the Permanent Danger Zone. During 8-9 April steam plumes rose 100-300 m and drifted SW. As of 1-2 May 2020 only weak steaming and fumarolic activity from fissure vents along the Daang Kastila trail was observed.

Evacuations. According to the Disaster Response Operations Monitoring and Information Center (DROMIC) there were a total of 53,832 people dispersed to 244 evacuation centers by 1800 on 15 January. By 21 January there were 148,987 people in 493 evacuation. The number of residents in evacuation centers dropped over the next week to 125,178 people in 497 locations on 28 January. However, many residents remained displaced as of 3 February, with DROMIC reporting 23,915 people in 152 evacuation centers, but an additional 224,188 people staying at other locations.

By 10 February there were 17,088 people in 110 evacuation centers, and an additional 211,729 staying at other locations. According to the DROMIC there were a total of 5,321 people in 21 evacuation centers, and an additional 195,987 people were staying at other locations as of 19 February.

The number of displaced residents continued to drop, and by 3 March there were 4,314 people in 12 evacuation centers, and an additional 132,931 people at other locations. As of 11 March there were still 4,131 people in 11 evacuation centers, but only 17,563 staying at other locations.

Deformation and ground cracks. New ground cracks were observed on 13 January in Sinisian (18 km SW), Mahabang Dahilig (14 km SW), Dayapan (15 km SW), Palanas (17 km SW), Sangalang (17 km SW), and Poblacion (19 km SW) Lemery; Pansipit (11 km SW), Agoncillo; Poblacion 1, Poblacion 2, Poblacion 3, Poblacion 5 (all around 17 km SW), Talisay, and Poblacion (11 km SW), San Nicolas (figure 21). A fissure opened across the road connecting Agoncillo to Laurel, Batangas. New ground cracking was reported the next day in Sambal Ibaba (17 km SW), and portions of the Pansipit River (SW) had dried up.

Figure (see Caption) Figure 21. Video screenshots showing ground cracks that formed during the Taal unrest and captured on 15 and 16 January 2020. Courtesy of James Reynolds, Earth Uncut.

Dropping water levels of Taal Lake were first observed in some areas on 16 January but reported to be lake-wide the next day. The known ground cracks in the barangays of Lemery, Agoncillo, Talisay, and San Nicolas in Batangas Province widened a few centimeters by 17 January, and a new steaming fissure was identified on the N flank of the island.

GPS data had recorded a sudden widening of the caldera by ~1 m, uplift of the NW sector by ~20 cm, and subsidence of the SW part of Volcano Island by ~1 m just after the main eruption phase. The rate of deformation was smaller during 15-22 January, and generally corroborated by field observations; Taal Lake had receded about 30 cm by 25 January but about 2.5 m of the change (due to uplift) was observed around the SW portion of the lake, near the Pansipit River Valley where ground cracking had been reported.

Weak steaming (plumes 10-20 m high) from ground cracks was visible during 5-11 February along the Daang Kastila trail which connects the N part of Volcano Island to the N part of the main crater. PHIVOLCS reported that during 19-24 February steam plumes rose 50-100 m above the vent and drifted SW. Weak steaming (plumes up to 20 m high) from ground cracks was visible during 8-14 April along the Daang Kastila trail which connects the N part of Volcano Island to the N part of the main crater.

Seismicity. Between 1300 on 12 January and 0800 on 21 January the Philippine Seismic Network (PSN) had recorded a total of 718 volcanic earthquakes; 176 of those had magnitudes ranging from 1.2-4.1 and were felt with Intensities of I-V. During 20-21 January there were five volcanic earthquakes with magnitudes of 1.6-2.5; the Taal Volcano network (which can detect smaller events not detectable by the PSN) recorded 448 volcanic earthquakes, including 17 low-frequency events. PHIVOLCS stated that by 21 January hybrid earthquakes had ceased and both the number and magnitude of low-frequency events had diminished.

Geologic Background. Taal is one of the most active volcanoes in the Philippines and has produced some of its most powerful historical eruptions. Though not topographically prominent, its prehistorical eruptions have greatly changed the landscape of SW Luzon. The 15 x 20 km Talisay (Taal) caldera is largely filled by Lake Taal, whose 267 km2 surface lies only 3 m above sea level. The maximum depth of the lake is 160 m, and several eruptive centers lie submerged beneath the lake. The 5-km-wide Volcano Island in north-central Lake Taal is the location of all historical eruptions. The island is composed of coalescing small stratovolcanoes, tuff rings, and scoria cones that have grown about 25% in area during historical time. Powerful pyroclastic flows and surges from historical eruptions have caused many fatalities.

Information Contacts: Philippine Institute of Volcanology and Seismology (PHIVOLCS), Department of Science and Technology, University of the Philippines Campus, Diliman, Quezon City, Philippines (URL: http://www.phivolcs.dost.gov.ph/); Disaster Response Operations Monitoring and Information Center (DROMIC) (URL: https://dromic.dswd.gov.ph/); United Nations Office for the Coordination of Humanitarian Affairs, Philippines (URL: https://www.unocha.org/philippines); James Reynolds, Earth Uncut TV (Twitter: @EarthUncutTV, URL: https://www.earthuncut.tv/, YouTube: https://www.youtube.com/user/TyphoonHunter); Chris Vagasky, Vaisala Inc., Louisville, Colorado, USA (URL: https://www.vaisala.com/en?type=1, Twitter: @COweatherman, URL: https://twitter.com/COweatherman); Earth Observatory of Singapore, Nanyang Technological University, 50 Nanyang Avenue, Singapore (URL: https://www.earthobservatory.sg/); 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/); Relief Web, Flash Update No. 1 - Philippines: Taal Volcano eruption (As of 13 January 2020, 2 p.m. local time) (URL: https://reliefweb.int/report/philippines/flash-update-no-1-philippines-taal-volcano-eruption-13-january-2020-2-pm-local); Bloomberg, Philippines Braces for Hazardous Volcano Eruption (URL: https://www.bloomberg.com/news/articles/2020-01-12/philippines-raises-alert-level-in-taal-as-volcano-spews-ash); National Public Radio (NPR), Volcanic Eruption In Philippines Causes Thousands To Flee (URL: npr.org/2020/01/13/795815351/volcanic-eruption-in-philippines-causes-thousands-to-flee); Reuters (http://www.reuters.com/); Agence France-Presse (URL: http://www.afp.com/); Pacific Press (URL: http://www.pacificpress.com/); Shutterstock (URL: https://www.shutterstock.com/); Getty Images (URL: http://www.gettyimages.com/); Google Earth (URL: https://www.google.com/earth/).


Unnamed (Tonga) — March 2020 Citation iconCite this Report

Unnamed

Tonga

18.325°S, 174.365°W; summit elev. -40 m

All times are local (unless otherwise noted)


Additional details and pumice raft drift maps from the August 2019 submarine eruption

In the northern Tonga region, approximately 80 km NW of Vava’u, large areas of floating pumice, termed rafts, were observed starting as early as 7 August 2019. The area of these andesitic pumice rafts was initially 195 km2 with the layers measuring 15-30 cm thick and were produced 200 m below sea level (Jutzeler et al. 2020). The previous report (BGVN 44:11) described the morphology of the clasts and the rafts, and their general westward path from 9 August to 9 October 2019, with the first sighting occurring on 9 August NW of Vava’u in Tonga. This report updates details regarding the submarine pumice raft eruption in early August 2019 using new observations and data from Brandl et al. (2019) and Jutzeler et al. (2020).

The NoToVE-2004 (Northern Tonga Vents Expedition) research cruise on the RV Southern Surveyor (SS11/2004) from the Australian CSIRO Marine National Facility traveled to the northern Tonga Arc and discovered several submarine basalt-to-rhyolite volcanic centers (Arculus, 2004). One of these volcanic centers 50 km NW of Vava’u was the unnamed seamount (volcano number 243091) that had erupted in 2001 and again in 2019, unofficially designated “Volcano F” for reference purposes by Arculus (2004) and also used by Brandl et al. (2019). It is a volcanic complex that rises more than 1 km from the seafloor with a central 6 x 8.7 km caldera and a volcanic apron measuring over 50 km in diameter (figures 19 and 20). Arculus (2004) described some of the dredged material as “fresh, black, plagioclase-bearing lava with well-formed, glassy crusts up to 2cm thick” from cones by the eastern wall of the caldera; a number of apparent flows, lava or debris, were observed draping over the northern wall of the caldera.

Figure (see Caption) Figure 19. Visualization of the unnamed submarine Tongan volcano (marked “Volcano F”) using bathymetric data to show the site of the 6-8 August 2020 eruption and the rest of the cone complex. Courtesy of Philipp Brandl via GEOMAR.
Figure (see Caption) Figure 20. Map of the unnamed submarine Tongan volcano using satellite imagery, bathymetric data, with shading from the NW. The yellow circle indicates the location of the August 2019 activity. Young volcanic cones are marked “C” and those with pit craters at the top are marked with “P.” Courtesy of Brandl et al. (2019).

The International Seismological Centre (ISC) Preliminary Bulletin listed a particularly strong (5.7 Mw) earthquake at 2201 local time on 5 August, 15 km SSW of the volcano at a depth of 10 km (Brandl et al. 2019). This event was followed by six slightly lower magnitude earthquakes over the next two days.

Sentinel-2 satellite imagery showed two concentric rings originating from a point source (18.307°S 174.395°W) on 6 August (figure 21), which could be interpreted as small weak submarine plumes or possibly a series of small volcanic cones, according to Brandl et al. (2019). The larger ring is about 1.2 km in diameter and the smaller one measures 250 m. By 8 August volcanic activity had decreased, but the pumice rafts that were produced remained visible through at least early October (BGVN 44:11). Brandl et al. (2019) states that, due to the lack of continued observed activity rising from this location, the eruption was likely a 2-day-long event during 6-8 August.

Figure (see Caption) Figure 21. Sentinel-2 satellite image of possible gas/vapor emissions (streaks) on 6 August 2019 drifting NW, which is the interpreted site for the unnamed Tongan seamount. The larger ring is about 1.2 km in diameter and the smaller one measures 250 m. Image using False Color (urban) rendering (bands 12, 11, 4); courtesy of Sentinel Hub Playground.

The pumice was first observed on 9 August occurred up to 56 km from the point of origin, according to Jutzeler et al. (2020). By calculating the velocity (14 km/day) of the raft using three satellites, Jutzeler et al. (2020) determined the pumice was erupted immediately after the satellite image of the submarine plumes on 6 August (UTC time). Minor activity at the vent may have continued on 8 and 11 August (UTC time) with pale blue-green water discoloration (figure 22) and a small (less than 1 km2) diffuse pumice raft 2-5 km from the vent.

Figure (see Caption) Figure 22. Sentinel-2 satellite image of the last visible activity occurring W of the unnamed submarine Tongan volcano on 8 August 2019, represented by slightly discolored blue-green water. Image using Natural Color rendering (bands 4, 3, 2) and enhanced with color correction; courtesy of Sentinel Hub Playground.

Continuous observations using various satellite data and observations aboard the catamaran ROAM tracked the movement and extent of the pumice raft that was produced during the submarine eruption in early August (figure 23). The first visible pumice raft was observed on 8 August 2019, covering more than 136.7 km2 between the volcanic islands of Fonualei and Late and drifting W for 60 km until 9 August (Brandl et al. 2019; Jutzeler 2020). The next day, the raft increased to 167.2-195 km2 while drifting SW for 74 km until 14 August. Over the next three days (10-12 August) the size of the raft briefly decreased in size to less than 100 km2 before increasing again to 157.4 km2 on 14 August; at least nine individual rafts were mapped and identified on satellite imagery (Brandl et al. 2019). On 15 August sailing vessels observed a large pumice raft about 75 km W of Late Island (see details in BGVN 44:11), which was the same one as seen in satellite imagery on 8 August.

Figure (see Caption) Figure 23. Map of the extent of discolored water and the pumice raft from the unnamed submarine Tongan volcano between 8 and 14 August 2019 using imagery from NASA’s MODIS, ESA’s Sentinel-2 satellite, and observations from aboard the catamaran ROAM (BGVN 44:11). Back-tracing the path of the pumice raft points to a source location at the unnamed submarine Tongan volcano. Courtesy of Brandl et al. (2019).

By 17 August high-resolution satellite images showed an area of large and small rafts measuring 222 km2 and were found within a field of smaller rafts for a total extent of 1,350 km2, which drifted 73 km NNW through 22 August before moving counterclockwise for three days (figure f; Jutzeler et al., 2020). Small pumice ribbons encountered the Oneata Lagoon on 30 August, the first island that the raft came into contact (Jutzeler et al. 2020). By 2 September, the main raft intersected with Lakeba Island (460 km from the source) (figure 24), breaking into smaller ribbons that started to drift W on 8 September. On 19 September the small rafts (less than 100 m x less than 2 km) entered the strait between Viti Levu and Vanua Levu, the two main islands of Fiji, while most of the others were stranded 60 km W in the Yasawa Islands for more than two months (Jutzeler et al., 2020).

Figure (see Caption) Figure 24. Time-series map of the raft dispersal from the unnamed submarine Tongan volcano using multiple satellite images. A) Map showing the first days of the raft dispersal starting on 7 August 2019 and drifting SW from the vent (marked with a red triangle). Precursory seismicity that began on 5 August is marked with a white star. By 15-17 August the raft was entrained in an ocean loop or eddy. The dashed lines represent the path of the sailing vessels. B) Map of the raft dispersal using high-resolution Sentinel-2 and -3 imagery. Two dispersal trails (red and blue dashed lines) show the daily dispersal of two parts of the raft that were separated on 17 August 2019. Courtesy of Jutzeler et al. (2020).

References: Arculus, R J, SS2004/11 shipboard scientists, 2004. SS11/2004 Voyage Summary: NoToVE-2004 (Northern Tonga Vents Expedition): submarine hydrothermal plume activity and petrology of the northern Tofua Arc, Tonga. https://www.cmar.csiro.au/data/reporting/get file.cfm?eovpub id=901.

Brandl P A, Schmid F, Augustin N, Grevemeyer I, Arculus R J, Devey C W, Petersen S, Stewart M , Kopp K, Hannington M D, 2019. The 6-8 Aug 2019 eruption of ‘Volcano F’ in the Tofua Arc, Tonga. Journal of Volcanology and Geothermal Research: https://doi.org/10.1016/j.jvolgeores.2019.106695

Jutzeler M, Marsh R, van Sebille E, Mittal T, Carey R, Fauria K, Manga M, McPhie J, 2020. Ongoing Dispersal of the 7 August 2019 Pumice Raft From the Tonga Arc in the Southwestern Pacific Ocean. AGU Geophysical Research Letters: https://doi.orh/10.1029/2019GL086768.

Geologic Background. A submarine volcano along the Tofua volcanic arc was first observed in September 2001. The newly discovered volcano lies NW of the island of Vava'u about 35 km S of Fonualei and 60 km NE of Late volcano. The site of the eruption is along a NNE-SSW-trending submarine plateau with an approximate bathymetric depth of 300 m. T-phase waves were recorded on 27-28 September 2001, and on the 27th local fishermen observed an ash-rich eruption column that rose above the sea surface. No eruptive activity was reported after the 28th, but water discoloration was documented during the following month. In early November rafts and strandings of dacitic pumice were reported along the coast of Kadavu and Viti Levu in the Fiji Islands. The depth of the summit of the submarine cone following the eruption determined to be 40 m during a 2007 survey; the crater of the 2001 eruption was breached to the E.

Information Contacts: Jan Steffen, Communication and Media, GEOMAR Helmholtz Centre for Ocean Research, Kiel, Germany; Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground).


Klyuchevskoy (Russia) — June 2020 Citation iconCite this Report

Klyuchevskoy

Russia

56.056°N, 160.642°E; summit elev. 4754 m

All times are local (unless otherwise noted)


Strombolian activity November 2019 through May 2020; lava flow down the SE flank in April

Klyuchevskoy is part of the Klyuchevskaya volcanic group in northern Kamchatka and is one of the most frequently active volcanoes of the region. Eruptions produce lava flows, ashfall, and lahars originating from summit and flank activity. This report summarizes activity during October 2019 through May 2020, and is based on reports by the Kamchatkan Volcanic Eruption Response Team (KVERT) and satellite data.

There were no activity reports from 1 to 22 October, but gas emissions were visible in satellite images. At 1020 on 24 October (2220 on 23 October UTC) KVERT noted that there was a small ash component in the ash plume from erosion of the conduit, with the plume reaching 130 km ENE. The Aviation Colour Code was raised from Green to Yellow, then to Orange the following day. An ash plume continued on the 25th to 5-7 km altitude and extending 15 km SE and 70 km SW and reached 30 km ESE on the 26th. Similar activity continued through to the end of the month.

Moderate gas emissions continued during 1-19 November, but the summit was obscured by clouds. Strong nighttime incandescence was visible at the crater during the 10-11 November and thermal anomalies were detected on 8 and 10-13 November. Explosions produced ash plumes up to 6 km altitude on the 20-21st and Strombolian activity was reported during 20-22 November. Degassing continued from 23 November through 12 December, and a thermal anomaly was visible on the days when the summit was not covered by clouds. An ash plume was reported moving to the NW on the 13th, and degassing with a thermal anomaly and intermittent Strombolian activity then resumed, continuing through to the end of December with an ash plume reported on the 30th.

Gas-and-steam plumes continued into January 2020 with incandescence noted when the summit was clear (figure 33). Strombolian activity was reported again starting on the 3rd. A weak ash plume produced on the 6th extended 55 km E, and on the 21st an ash plume reached 5-5.5 km altitude and extended 190 km NE (figure 34). Another ash plume the next day rose to the same altitude and extended 388 km NE. During 23-29 Strombolian activity continued, and Vulcanian activity produced ash plumes up to 5.5 altitude, extending to 282 km E on the 30th, and 145 km E on the 31st.

Figure (see Caption) Figure 33. Incandescence and degassing were visible at Klyuchevskoy through January 2020, seen here on the 11th. Courtesy of KVERT.
Figure (see Caption) Figure 34. A low ash plume at Klyuchevskoy on 21 January 2020 extended 190 km NE. Courtesy of KVERT.

Strombolian activity continued throughout February with occasional explosions producing ash plumes up to 5.5 km altitude, as well as gas-and-steam plumes and a persistent thermal anomaly with incandescence visible at night. Starting in late February thermal anomalies were detected much more frequently, and with higher energy output compared to the previous year (figure 35). A lava fountain was reported on 1 March with the material falling back into the summit crater. Strombolian activity continued through early March. Lava fountaining was reported again on the 8th with ejecta landing in the crater and down the flanks (figure 36). A strong persistent gas-and-steam plume containing some ash continued along with Strombolian activity through 25 March (figure 37), with Vulcanian activity noted on the 20th and 25th. Strombolian and Vulcanian activity was reported through the end of March.

Figure (see Caption) Figure 35. This MIROVA thermal energy plot for Klyuchevskoy for the year ending 29 April 2020 (log radiative power) shows intermittent thermal anomalies leading up to more sustained energy detected from February through March, then steadily increasing energy through April 2020. Courtesy of MIROVA.
Figure (see Caption) Figure 36. Strombolian explosions at Klyuchevskoy eject incandescent ash and gas, and blocks and bombs onto the upper flanks on 8 and 10 March 2020. Courtesy of IVS FEB RAS, KVERT.
Figure (see Caption) Figure 37. Weak ash emission from the Klyuchevskoy summit crater are dispersed by wind on 19 and 29 March 2020, with ash depositing on the flanks. Courtesy of IVS FEB RAS, KVERT.

Activity was dominantly Strombolian during 1-5 April and included intermittent Vulcanian explosions from the 6th onwards, with ash plumes reaching 6 km altitude. On 18 April a lava flow began moving down the SE flank (figures 38). A report on the 26th reported explosions from lava-water interactions with avalanches from the active lava flow, which continued to move down the SE flank and into the Apakhonchich chute (figures 39 and 40). This continued throughout April and May with sustained Strombolian and intermittent Vulcanian activity at the summit (figures 41 and 42).

Figure (see Caption) Figure 38. Strombolian activity produced ash plumes and a lava flow down the SE flank of Klyuchevskoy on 18 April 2020. Courtesy of IVS FEB RAS, KVERT.
Figure (see Caption) Figure 39. A lava flow descends the SW flank of Klyuchevskoy and a gas plume is dispersed by winds on 21 April 2020. Courtesy of Yu. Demyanchuk, IVS FEB RAS, KVERT.
Figure (see Caption) Figure 40. Sentinel-2 thermal satellite images show the progression of the Klyuchevskoy lava flow from the summit crater down the SE flank from 19-29 April 2020. Associated gas plumes are dispersed in various directions. Courtesy of Sentinel Hub Playground.
Figure (see Caption) Figure 41. Strombolian activity at Klyuchevskoy ejects incandescent ejecta, gas, and ash above the summit on 27 April 2020. Courtesy of D. Bud'kov, IVS FEB RAS, KVERT.
Figure (see Caption) Figure 42. Sentinel-2 thermal satellite images of Klyuchevskoy show the progression of the SE flank lava flow through May 2020, with associated gas plumes being dispersed in multiple directions. Courtesy of Sentinel Hub Playground.

Geologic Background. Klyuchevskoy (also spelled Kliuchevskoi) is Kamchatka's highest and most active volcano. Since its origin about 6000 years ago, the beautifully symmetrical, 4835-m-high basaltic stratovolcano has produced frequent moderate-volume explosive and effusive eruptions without major periods of inactivity. It rises above a saddle NE of sharp-peaked Kamen volcano and lies SE of the broad Ushkovsky massif. More than 100 flank eruptions have occurred during the past roughly 3000 years, with most lateral craters and cones occurring along radial fissures between the unconfined NE-to-SE flanks of the conical volcano between 500 m and 3600 m elevation. The morphology of the 700-m-wide summit crater has been frequently modified by historical eruptions, which have been recorded since the late-17th century. Historical eruptions have originated primarily from the summit crater, but have also included numerous major explosive and effusive eruptions from flank craters.

Information Contacts: Kamchatka Volcanic Eruptions Response Team (KVERT), Far Eastern Branch, Russian Academy of Sciences, 9 Piip Blvd., Petropavlovsk-Kamchatsky, 683006, Russia (URL: http://www.kscnet.ru/ivs/kvert/); 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/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground).


Nyamuragira (DR Congo) — June 2020 Citation iconCite this Report

Nyamuragira

DR Congo

1.408°S, 29.2°E; summit elev. 3058 m

All times are local (unless otherwise noted)


Intermittent thermal anomalies within the summit crater during December 2019-May 2020

Nyamuragira (also known as Nyamulagira) is located in the Virunga Volcanic Province (VVP) in the Democratic Republic of the Congo and consists of a lava lake that reappeared in the summit crater in mid-April 2018. Volcanism has been characterized by lava emissions, thermal anomalies, seismicity, and gas-and-steam emissions. This report summarizes activity during December 2019 through May 2020 using information from monthly reports by the Observatoire Volcanologique de Goma (OVG) and satellite data.

According to OVG, intermittent eruptive activity was detected in the lava lake of the central crater during December 2019 and January-April 2020, which also resulted in few seismic events. MIROVA (Middle InfraRed Observation of Volcanic Activity) analysis of MODIS satellite data shows thermal anomalies within the summit crater that varied in both frequency and power between August 2019 and mid-March 2020, but very few were recorded afterward through late May (figure 88). Thermal hotspots identified by MODVOLC from 15 December 2019 through March 2020 were mainly located in the active central crater, with only three hotspots just outside the SW crater rim (figure 89). Sentinel-2 thermal satellite imagery also showed activity within the summit crater during January-May 2020, but by mid-March the thermal anomaly had visibly decreased in power (figure 90).

Figure (see Caption) Figure 88. The MIROVA graph of thermal activity (log radiative power) at Nyamuragira during 27 July through May 2020 shows variably strong, intermittent thermal anomalies with a variation in power and frequency from August 2019 to mid-March 2020. Courtesy of MIROVA.
Figure (see Caption) Figure 89. Map showing the number of MODVOLC hotspot pixels at Nyamuragira from 1 December 2019 t0 31 May 2020. 37 pixels were registered within the summit crater while 3 were detected just outside the SW crater rim. Courtesy of HIGP-MODVOLC Thermal Alerts System.
Figure (see Caption) Figure 90. Sentinel-2 thermal satellite imagery (bands 12, 11, 8A) confirmed ongoing thermal activity (bright yellow-orange) at Nyamuragira from February into April 2020. The strength of the thermal anomaly in the summit crater decreased by late March 2020, but was still visible. Courtesy of Sentinel Hub Playground.

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: Information contacts: Observatoire Volcanologique de Goma (OVG), Departement de Geophysique, Centre de Recherche en Sciences Naturelles, Lwiro, D.S. Bukavu, DR Congo; 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/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/exp.


Nyiragongo (DR Congo) — June 2020 Citation iconCite this Report

Nyiragongo

DR Congo

1.52°S, 29.25°E; summit elev. 3470 m

All times are local (unless otherwise noted)


Activity in the lava lake and small eruptive cone persists during December 2019-May 2020

Nyiragongo is located in the Virunga Volcanic Province (VVP) in the Democratic Republic of the Congo, part of the western branch of the East African Rift System and contains a 1.2 km-wide summit crater with a lava lake that has been active since at least 1971. Volcanism has been characterized by strong and frequent thermal anomalies, incandescence, gas-and-steam emissions, and seismicity. This report summarizes activity during December 2019 through May 2020 using information from monthly reports by the Observatoire Volcanologique de Goma (OVG) and satellite data.

In the December 2019 monthly report, OVG stated that the level of the lava lake had increased. This level of the lava lake was maintained for the duration of the reporting period, according to later OVG monthly reports. Seismicity increased starting in November 2019 and was detected in the NE part of the crater, but it decreased by mid-April 2020. SO2 emissions increased in January 2020 to roughly 7,000 tons/day but decreased again near the end of the month. OVG reported that SO2 emissions rose again in February to roughly 8,500 tons/day before declining to about 6,000 tons/day. Unlike in the previous report (BGVN 44:12), incandescence was visible during the day in the active lava lake and activity at the small eruptive cone within the 1.2-km-wide summit crater has since increased, consisting of incandescence and some lava fountaining (figure 72). A field survey was conducted on 3-4 March where an OVG team observed active lava fountains and ejecta that produced Pele’s hair from the small eruptive cone (figure 73). During this survey, OVG reported that the level of the lava lake had reached the second terrace, which was formed on 17 January 2002 and represents remnants of the lava lake at different eruption stages. There, the open surface lava lake was observed; gas-and-steam emissions accompanied both the active lava lake and the small eruptive cone (figures 72 and 73).

Figure (see Caption) Figure 72. Webcam image of Nyiragongo in February 2020 showing an open lava lake surface and incandescence from the active crater cone within the 1.2 km-wide summit crater visible during the day, accompanied by white gas-and-steam emissions. Courtesy of OVG (Rapport OVG February 2020).
Figure (see Caption) Figure 73. Webcam image of Nyiragongo on 4 March 2020 showing an open lava lake surface and incandescence from the active crater cone within the 1.2 km-wide summit crater visible during the day, accompanied by white gas-and-steam emissions. Courtesy of OVG (Rapport OVG Mars 2020).

MIROVA (Middle InfraRed Observation of Volcanic Activity) analysis of MODIS satellite data continued to show frequent strong thermal anomalies within 5 km of the summit crater through May 2020 (figure 74). Similarly, the MODVOLC algorithm reported multiple thermal hotspots almost daily within the summit crater between December 2019 and May 2020. These thermal signatures were also observed in Sentinel-2 thermal satellite imagery within the summit crater (figure 75).

Figure (see Caption) Figure 74. Thermal anomalies at Nyiragongo from 27 July through May 2020 as recorded by the MIROVA system (Log Radiative Power) were frequent and strong. Courtesy of MIROVA.
Figure (see Caption) Figure 75. Sentinel-2 thermal satellite imagery (bands 12, 11, 8A) showed ongoing thermal activity (bright yellow-orange) in the summit crater at Nyiragongo during January through April 2020. Courtesy of Sentinel Hub Playground.

Geologic Background. One of Africa's most notable volcanoes, Nyiragongo contained a lava lake in its deep summit crater that was active for half a century before draining catastrophically through its outer flanks in 1977. The steep slopes of a stratovolcano contrast to the low profile of its neighboring shield volcano, Nyamuragira. Benches in the steep-walled, 1.2-km-wide summit crater mark levels of former lava lakes, which have been observed since the late-19th century. Two older stratovolcanoes, Baruta and Shaheru, are partially overlapped by Nyiragongo on the north and south. About 100 parasitic cones are located primarily along radial fissures south of Shaheru, east of the summit, and along a NE-SW zone extending as far as Lake Kivu. Many cones are buried by voluminous lava flows that extend long distances down the flanks, which is characterized by the eruption of foiditic rocks. The extremely fluid 1977 lava flows caused many fatalities, as did lava flows that inundated portions of the major city of Goma in January 2002.

Information Contacts: Observatoire Volcanologique de Goma (OVG), Departement de Geophysique, Centre de Recherche en Sciences Naturelles, Lwiro, D.S. Bukavu, DR Congo; 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/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground).


Kavachi (Solomon Islands) — May 2020 Citation iconCite this Report

Kavachi

Solomon Islands

8.991°S, 157.979°E; summit elev. -20 m

All times are local (unless otherwise noted)


Discolored water plumes seen using satellite imagery in 2018 and 2020

Kavachi is a submarine volcano located in the Solomon Islands south of Gatokae and Vangunu islands. Volcanism is frequently active, but rarely observed. The most recent eruptions took place during 2014, which consisted of an ash eruption, and during 2016, which included phreatomagmatic explosions (BGVN 42:03). This reporting period covers December 2016-April 2020 primarily using satellite data.

Activity at Kavachi is often only observed through satellite images, and frequently consists of discolored submarine plumes for which the cause is uncertain. On 1 January 2018 a slight yellow discoloration in the water is seen extending to the E from a specific point (figure 20). Similar faint plumes were observed on 16 January, 25 February, 2 March, 26 April, 6 May, and 25 June 2018. No similar water discoloration was noted during 2019, though clouds may have obscured views.

Figure (see Caption) Figure 20. Satellite images from Sentinel-2 revealed intermittent faint water discoloration (yellow) at Kavachi during the first half of 2018, as seen here on 1 January (top left), 25 February (top right), 26 April (bottom left), and 25 June (bottom right). Images with “Natural color” rendering (bands 4, 3, 2); courtesy of Sentinel Hub Playground.

Activity resumed in 2020, showing more discolored water in satellite imagery. The first instance occurred on 16 March, where a distinct plume extended from a specific point to the SE. On 25 April a satellite image showed a larger discolored plume in the water that spread over about 30 km2, encompassing the area around Kavachi (figure 21). Another image on 30 April showed a thin ribbon of discolored water extending about 50 km W of the vent.

Figure (see Caption) Figure 21. Sentinel-2 satellite images of a discolored plume (yellow) at Kavachi beginning on 16 March (top left) with a significant large plume on 25 April (right), which remained until 30 April (bottom left). Images with “Natural color” rendering (bands 4, 3, 2); courtesy of Sentinel Hub Playground.

Geologic Background. Named for a sea-god of the Gatokae and Vangunu peoples, Kavachi is one of the most active submarine volcanoes in the SW Pacific, located in the Solomon Islands south of Vangunu Island. Sometimes referred to as Rejo te Kvachi ("Kavachi's Oven"), this shallow submarine basaltic-to-andesitic volcano has produced ephemeral islands up to 1 km long many times since its first recorded eruption during 1939. Residents of the nearby islands of Vanguna and Nggatokae (Gatokae) reported "fire on the water" prior to 1939, a possible reference to earlier eruptions. The roughly conical edifice rises from water depths of 1.1-1.2 km on the north and greater depths to the SE. Frequent shallow submarine and occasional subaerial eruptions produce phreatomagmatic explosions that eject steam, ash, and incandescent bombs. On a number of occasions lava flows were observed on the ephemeral islands.

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


Kuchinoerabujima (Japan) — May 2020 Citation iconCite this Report

Kuchinoerabujima

Japan

30.443°N, 130.217°E; summit elev. 657 m

All times are local (unless otherwise noted)


Eruption and ash plumes begin on 11 January 2020 and continue through April 2020

Kuchinoerabujima encompasses a group of young stratovolcanoes located in the northern Ryukyu Islands. All historical eruptions have originated from the Shindake cone, with the exception of a lava flow that originated from the S flank of the Furudake cone. The most recent previous eruptive period took place during October 2018-February 2019 and primarily consisted of weak explosions, ash plumes, and ashfall. The current eruption began on 11 January 2020 after nearly a year of dominantly gas-and-steam emissions. Volcanism for this reporting period from March 2019 to April 2020 included explosions, ash plumes, SO2 emissions, and ashfall. The primary source of information for this report comes from monthly and annual reports from the Japan Meteorological Agency (JMA) and advisories from the Tokyo Volcanic Ash Advisory Center (VAAC). Activity has been limited to Kuchinoerabujima's Shindake Crater.

Volcanism at Kuchinoerabujima was relatively low during March through December 2019, according to JMA. During this time, SO2 emissions ranged from 100 to 1,000 tons/day. Gas-and-steam emissions were frequently observed throughout the entire reporting period, rising to a maximum height of 1.1 km above the crater on 13 December 2019. Satellite imagery from Sentinel-2 showed gas-and-steam and occasional ash emissions rising from the Shindake crater throughout the reporting period (figure 7). Though JMA reported thermal anomalies occurring on 29 January and continuing through late April 2020, Sentinel-2 imagery shows the first thermal signature appearing on 26 April.

Figure (see Caption) Figure 7. Sentinel-2 thermal satellite images showed gas-and-steam and ash emissions rising from Kuchinoerabujima. Some ash deposits can be seen on 6 February 2020 (top right). A thermal anomaly appeared on 26 April 2020 (bottom right). Sentinel-2 atmospheric penetration (bands 12, 11, 8A) images courtesy of Sentinel Hub Playground.

An eruption on 11 January 2020 at 1505 ejected material 300 m from the crater and produced ash plumes that rose 2 km above the crater rim, extending E, according to JMA. The eruption continued through 12 January until 0730. The resulting ash plumes rose 400 m above the crater, drifting SW while the SO2 emissions measured 1,300 tons/day. Ashfall was reported on Yakushima Island (15 km E). Minor eruptive activity was reported during 17-20 January which produced gray-white plumes that rose 300-500 m above the crater. On 23 January, seismicity increased, and an eruption produced an ash plume that rose 1.2 km altitude, according to a Tokyo VAAC report, resulting in ashfall 2 km NE of the crater. A small explosion was detected on 24 January, followed by an increase in the number of earthquakes during 25-26 January (65-71 earthquakes per day were registered). Another small eruptive event detected on 27 January at 0148 was accompanied by a volcanic tremor and a change in tilt data. During the month of January, some inflation was detected at the base on the volcano and a total of 347 earthquakes were recorded. The SO2 emissions ranged from 200-1,600 tons/day.

An eruption on 1 February 2020 produced an eruption column that rose less than 1 km altitude and extended SE and SW (figure 8), according to the Tokyo VAAC report. On 3 February, an eruption from the Shindake crater at 0521 produced an ash plume that rose 7 km above the crater and ejected material as far as 600 m away. As a result, a pyroclastic flow formed, traveling 900-1,500 m SW. The previous pyroclastic flow that was recorded occurred on 29 January 2019. Ashfall was confirmed in the N part of Yakushima Island with a large amount in Miyanoura (32 km ESE) and southern Tanegashima. The SO2 emissions measured 1,700 tons/day during this event.

Figure (see Caption) Figure 8. Webcam images from the Honmura west surveillance camera of an ash plume rising from Kuchinoerabujima on 1 February 2020. Courtesy of JMA (Weekly bulletin report 509, February 2020).

Intermittent small eruptive events occurred during 5-9 February; field observations showed a large amount of ashfall on the SE flank which included lapilli that measured up to 2 cm in diameter. Additionally, thermal images showed 5-km-long pyroclastic flow deposits on the SW flank. An eruption on 9 February produced an ash plume that rose 1.2 km altitude, drifting SE. On 13 February a small eruption was detected in the Shindake crater at 1211, producing gray-white plumes that rose 300 m above the crater, drifting NE. Small eruptive events also occurred during 20-21 February, resulting in gas-and-steam emissions that rose 200 m above the crater. During the month of February, some horizontal extension was observed since January 2020 using GNSS data. The total number of earthquakes during this month drastically increased to 1225 compared to January. The SO2 emissions ranged from 300-1,700 tons/day.

By 2 March 2020, seismicity decreased, and activity declined. Gas-and-steam emissions continued infrequently for the duration of the reporting period. The SO2 emissions during March ranged from 700-2,100 tons/day, the latter of which occurred on 15 March. Seismicity increased again on 27 March. During 5-8 April 2020, small eruptive events were detected, generating ash plumes that rose 900 m above the crater (figure 9). The SO2 emissions on 6 April reached 3,200 tons/day, the maximum measurement for this reporting period. These small eruptive events continued from 13-20 and 23-25 April within the Shindake crater, producing gray-white plumes that rose 300-800 m above the crater.

Figure (see Caption) Figure 9. Webcam images from the Honmura Nishi (top) and Honmura west (bottom) surveillance cameras of ash plumes rising from Kuchinoerabujima on 6 March and 5 April 2020. Courtesy of JMA (Weekly bulletin report 509, March and April 2020).

Geologic Background. A group of young stratovolcanoes forms the eastern end of the irregularly shaped island of Kuchinoerabujima in the northern Ryukyu Islands, 15 km W of Yakushima. The Furudake, Shindake, and Noikeyama cones were erupted from south to north, respectively, forming a composite cone with multiple craters. All historical eruptions have occurred from Shindake, although a lava flow from the S flank of Furudake that reached the coast has a very fresh morphology. Frequent explosive eruptions have taken place from Shindake since 1840; the largest of these was in December 1933. Several villages on the 4 x 12 km island are located within a few kilometers of the active crater and have suffered damage from eruptions.

Information Contacts: Japan Meteorological Agency (JMA), 1-3-4 Otemachi, 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 100-8122, Japan (URL: http://ds.data.jma.go.jp/svd/vaac/data/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground).

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Bulletin of the Global Volcanism Network - Volume 23, Number 09 (September 1998)

Managing Editor: Richard Wunderman

Ambrym (Vanuatu)

Long-active lava lake continues to hold bubbling lava

Azul, Cerro (Ecuador)

Flank and caldera eruptions continue

Colima (Mexico)

Explosion on 6 July follows seven months of seismic unrest

Etna (Italy)

Summary of summit eruptive activity during August 1997-January 1998

Fournaise, Piton de la (France)

Activity ends with fissure eruptions outside the caldera

Guagua Pichincha (Ecuador)

Phreatic discharges and shallow, near-vent seismicity continue

Hokkaido-Komagatake (Japan)

Phreatic eruption spreads ash 25 October

Iwatesan (Japan)

Nearby M 6.2 earthquake on 3 September, but volcano still slumbering

Klyuchevskoy (Russia)

Explosions, ash 2-3 September raise concern to yellow alert

Lengai, Ol Doinyo (Tanzania)

New cones, vigorous activity since February

Masaya (Nicaragua)

Integrated scientific studies of the caldera area

Obituary Notices (Unknown)

Death of Oleg Volynets in Petropavlovsk-Kamchatsky

Popocatepetl (Mexico)

Several episodes of ash emission during September

Sete Cidades (Portugal)

Seismic swarm on submarine flank

Sheveluch (Russia)

Ash explosions and pyroclastic flow during 3 September

Soufriere Hills (United Kingdom)

Continuing decrease in activity; hazards reassessed

Yasur (Vanuatu)

Ongoing eruption, felt earthquake, and fresh glass chemical analysis



Ambrym (Vanuatu) — September 1998 Citation iconCite this Report

Ambrym

Vanuatu

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

All times are local (unless otherwise noted)


Long-active lava lake continues to hold bubbling lava

This long-active caldera was visited by John Seach during 4-7 September 1998. At Niri Mbwelesu Taten, a small collapse pit, strong degassing was observed as well as yellow sulfurous deposits on the NW wall. During the night, degassing was heard from a distance of 4 km and white vapor tinged with blue was constantly emitted from the pit.

Niri Mbelesu crater was constantly full of vapor resulting in poor visibility. But bubbling lava was heard and at night the clouds reflected a red glow from the crater.

At Mbwelesu crater, an active elongated lava lake (~100 x 30 m) was observed. The larger explosions threw lava high into the air and onto the crater wall. To the east of the lava lake a smaller elongated vent contained lava. On the NW wall of the crater was a circular vent 20 m in diameter from which no lava was extruded.

Benbow crater was climbed from the S. The sound of bubbling lava was heard but not observed, and there was a very intense night glow.

Geologic Background. Ambrym, a large basaltic volcano with a 12-km-wide caldera, is one of the most active volcanoes of the New Hebrides Arc. A thick, almost exclusively pyroclastic sequence, initially dacitic then basaltic, overlies lava flows of a pre-caldera shield volcano. The caldera was formed during a major Plinian eruption with dacitic pyroclastic flows about 1,900 years ago. Post-caldera eruptions, primarily from Marum and Benbow cones, have partially filled the caldera floor and produced lava flows that ponded on the floor or overflowed through gaps in the caldera rim. Post-caldera eruptions have also formed a series of scoria cones and maars along a fissure system oriented ENE-WSW. Eruptions have apparently occurred almost yearly during historical time from cones within the caldera or from flank vents. However, from 1850 to 1950, reporting was mostly limited to extra-caldera eruptions that would have affected local populations.

Information Contacts: John Seach, P.O. Box 16, Chatsworth Island, N.S.W. 2469, Australia.


Cerro Azul (Ecuador) — September 1998 Citation iconCite this Report

Cerro Azul

Ecuador

0.92°S, 91.408°W; summit elev. 1640 m

All times are local (unless otherwise noted)


Flank and caldera eruptions continue

This eruption began between 1229 and 1304 on 15 September (BGVN 23:08). The event was first recognized by University of Hawaii scientists monitoring thermal images from the GOES-8 geostationary satellite. A dominant plume reaching over 150 km SW developed between 1345 and 1545 on 15 September, and a minor plume trended NW carried by the prevailing surface winds. Overflights revealed two new vents in the summit caldera, and a flank fissure eruption 8 km SE of the caldera (figure 1).

Figure (see Caption) Figure 1. Photograph of the S part of Isabela Island, taken from the Space Shuttle in 1983, showing the site of the September 1998 flank eruption. Puerto Villamil and the scientific station at Tomas de Berlanga (or Santo Tomas) are the only inhabited locations on the island. White zones over the island are clouds. Courtesy of the GOES Hotspot Monitoring System.

The first scientists reaching the volcano were from Ecuador's Instituto Geofísico-Escuela Politécnica Nacional (IG-EPN) and ORSTOM. They described the flank eruption site as a SE-directed radial fissure, 400-500 m long, and between 680 and 630 m elevation. Lava fountaining (to ~200 m) built an elongate cinder cone 50 m high during the team's 19-25 September observations. The main cone was breeched on the E, issuing flows that traveled over 8 km E before turning S toward the sea. During the night of 24-25 September a break in the main cone fed a new flow to the SE. All were 3-5-m-thick aa flows, and the longest ended 2 km from the coast.

University of Idaho graduate student Rachel Ellisor arrived on the night of 22 September, and described additional details of the flank eruption, including a smaller cone (NW of the main cone) with low fountains feeding a flow moving more directly S toward the sea. This flow was sampled daily; its velocity ranged from 0.001 to 10-20 km/hour and its thickness was described as 2-3 m at the front but 10-12 m in the interior. Gas clouds billowed from the fissure's SE end, and fountains issued from the main vent.

Ellisor took a 1 October overflight and described the intracaldera flows. One issued from a small vent (20-30 m high) on the S bench and flowed NW onto the caldera floor, while a larger cone (~60 m high) on the W caldera floor fed flows eastward into the shallow lake. Intracaldera activity had ended by 1 October.

Returning to the flank eruption, Ellisor reported that three large cones (60-80 m high) had been built in a N-S orientation. The mid-September flows (to the E, then S) had stagnated on the coastal flats, and their thickness was estimated at 5-15 m (interior) to 1-3 m (fronts). Increased activity on 6 October fed new flows building a channel system directly S of the main fissure. Ellisor's most recent report was dated 13 October, but GOES-8 images showed a thermal anomaly continuing through 4 November, the eruption's 51st day.

During 19-25 September, scientists from IG-EPN and ORSTOM installed three digital and one analog seismic station between the coast and the active vent. The distance between end stations was 8.5 km. Seismic signals registered during the study were composed of permanent tremor with an amplitude of 20 µm/s (2.4 km from the vent) and with a dominant frequency of 1.6 Hz. No rock-fall or long-period events were registered. One station 4 km from the vent continued working after the group returned to Quito.

Geologic Background. Located at the SW tip of the J-shaped Isabela Island, Cerro Azul contains a steep-walled 4 x 5 km nested summit caldera complex that is one of the smallest diameter, but at 650 m one of the deepest in the Galápagos Islands. The shield volcano is the second highest of the archipelago. A conspicuous bench occupies the SW and west sides of the caldera, which formed during several episodes of collapse. Youthful lava flows cover much of the caldera floor, which has also contained ephemeral lakes. A prominent tuff cone located at the ENE side of the caldera is evidence of episodic hydrovolcanism. Numerous spatter cones dot the western flanks. Fresh-looking lava flows, many erupted from circumferential fissures, descend the NE and NW flanks. Historical eruptions date back only to 1932, but Cerro Azul has been one of the most active Galápagos volcanoes since that time. Solfataric activity continues within the caldera.

Information Contacts: P. Samaniego, F. Desmulier, J.P. Metaxian, M. Ruiz, and M. Vaca, Instituto Geofísico, Escuela Politécnica Nacional, AP 17-01-2759, Quito, Ecuador; ORSTOM (L'Institut Français de Recherche Scientifique pour le Développement en Coopération), AP 17-11-6596, Quito, Ecuador (URL: http://www.ird.fr/); Rachel Ellisor and Dennis Geist, Dept. of Geology and Geological Engineering, University of Idaho, Moscow, ID 83843 USA (URL: https://www.uidaho.edu/sci/geology/); Peter Mouginis-Mark and Luke Flynn, GOES Hotspot Monitoring System, Hawaii Institute of Geophysics and Planetology, University of Hawaii, 2525 Correa Road, Honolulu, Hawaii 96822 USA (URL: http://modis.higp.hawaii.edu/).


Colima (Mexico) — September 1998 Citation iconCite this Report

Colima

Mexico

19.514°N, 103.62°W; summit elev. 3850 m

All times are local (unless otherwise noted)


Explosion on 6 July follows seven months of seismic unrest

After seven months of seismic unrest (small swarms, with durations lasting some few hours to as much as 90 hours), at 1858 on 6 July an explosion at the summit dome was similar in behavior and about half of the magnitude of an explosion in 1994.

A microbarograph 8 km SW of the summit at La Yerbabuena failed to register the explosion's shock wave, and the events were not noticed by residents of that settlement or La Becerrera (12 km SW of the summit), nor were these effects noticed by rangers at Rancho El Jabali (12 km SSW of the summit). Residents did report light rain and a bit of thunder and lightning at 1900, which may have helped conceal, or have been confused with, the sound of the explosion.

Seen through a microscope, plant leaves contained ash residue left after rainfall: mineral particles and hydrothermally altered rock fragments under 0.5 mm in diameter, often of light cream color, and similar to those collected at Yerbabuena after the 1994 explosion.

Melchor Ursua of the Civil Defense reported that at 1900 residents of Tonila (13.5 km SE of the summit) observed a small black mushroom cloud rise above the summit accompanied by the sound of thunder or explosion. At 2300 that day from La Yerbabuena, observers Navarro, Breton, and Santaana saw fumarolic gases blown around the W face of the volcano, but in the faint moonlight he failed to discern any glow or ash from the crater.

The last seismic crisis started around 2200 on 2 July 1998 and ended at 1858 on 6 July: a vigorous swarm of earthquakes, which according to Gabriel Reyes comprised ~1,000 events a day for the last 3 days. One event with coda magnitude (Mc) 3.5-4.0 gained registry at all network stations including those near the coast at Tecoman and Armeria; it was interpreted as related to the above-discussed explosion. The seismic quiet afterwards consisted of zero events in a pattern reminiscent of 1994 when quiet prevailed for about 12 hours.

Noteworthy swarms during 1997 occurred on 20 March, 16, 21, and 30 June, 28 November, and 5 December. Compared to the 1997 swarms, this one (2-6 July 1998) was the largest and most energetic.

During the latest swarm the volcano was only visible from 0800 to 1000. After 160 mm of rain had fallen at La Yerbabuena, a lahar swept downslope between 1400 and 1800 on 2 July, blocking passage across the Becerrera River valley 12.5 km SW of the summit.

During 1900-2000 on 7 July, the seismic station closest to the W flank (SOMA, 1.7 km NW from the summit) registered strong, continuous mass wasting and later, during 2200-2300, a relatively strong volcanic event. Seismic quiet returned later, but vigorous fumarolic emissions were blown W. An update on 28 October noted that for a few weeks after the explosion the volcano displayed unrest, including about 23 seismic swarms, each enduring for 2 to 6-8 hours. All the seismic information was provided by the Colima seismic network (RESCO). The last swarm occurred on 25 October and prevailed for 13 hours.

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

Information Contacts: Carlos Navarro Ochoa, Colima Volcano Observatory, Universidad de Colima, Ave. 25 de Julio 965, Colima 28045, Colima, México.


Etna (Italy) — September 1998 Citation iconCite this Report

Etna

Italy

37.748°N, 14.999°E; summit elev. 3320 m

All times are local (unless otherwise noted)


Summary of summit eruptive activity during August 1997-January 1998

The following report summarizes activity observed at each of the four summit craters of Etna from August 1997 through 15 January 1998. Events through 8 January 1998 at Bocca Nuova, Southeast Crater, Northeast Crater, and Voragine are described below separately. A seismic crisis during 9-12 January was followed by a brief decrease in activity at all of the craters. Significant eruptive episodes after mid-January 1998 will be described in future issues.

Information for this report was compiled by Boris Behncke at the University of Catania and published on his internet web site. The compilation was based on personal visits to the summit, telescopic observations from Catania, monitoring of images posted on the internet from the camera maintained by the Istituto Internazionale di Vulcanologia (IIV), and other sources.

Visits to the summit craters in late September and early October 1997 revealed continuing vigorous activity from Bocca Nuova and Southeast Crater while more sporadic activity was occurring at the Voragine and Northeast Crater. This pattern continued through November and December. The overall activity on 8 January 1998 at Bocca Nuova, Northeast Crater, and Voragine was notably diminished; it was the lowest observed in six months.

Activity at Bocca Nuova. During late August, lava ejections from Bocca Nuova (BN) became significantly more vigorous. Both eruptive centers in this crater often ejected lava bombs outside the crater, with many falling on its S rim. Occasional explosions ejected bombs on the lower S flank of the central cone. The number of active vents in Bocca Nuova increased to seven on 28 August, but was down to five just two days later. The bombardment and explosions led to collapse on the E side of Bocca Nuova, lowering the septum between BN and Voragine (informally named "diaframma" among local volcanologists), and eroding the remains of a 1964 cone.

Visits to the summit in late September and early October revealed continuing activity. As of 14 October, Bocca Nuova's activity was gradually increasing, and the crater was being filled in. The northern of its two eruptive centers had a broad cone with a crater 50-100 m wide, which at times was completely filled with fountaining lava. Fountains often sent spatter and bombs high above the rim, and large ejecta fell outside the crater up to 100 m away. Bombs as large as 40 cm in diameter fell onto the area where the best views of the erupting cone in BN are obtained. Explosions in the SE eruptive center at times sent pyroclastic material all over the S flank of Etna's summit cone.

On 6 November the northern eruptive center was vigorously active. The cone at that site had grown to ~50 m below the NW crater rim. The SE eruptive center was much less violent than in previous months; on the crater wall above it a large overhanging hollow had been carved out by explosions. On the evening of 6 November, Strombolian explosions occurred at intervals of 1-5 seconds, with some jets rising up to 200 m above the cone's summit. An episode of spectacular lava fountaining from BN occurred on 25 November when huge bursts of incandescent bombs developed into a continuous fountain from the SE eruptive center. On 28 November the clouds over the mountain cleared, permitting the view of a huge vapor column rising almost vertically to about 1,500 m above the summit. This unusually large plume was due to an approaching cold front that led to increased condensation.

Explosive activity and gas emissions within BN accompanied a lava flow from Southeast Crater during 9-11 December. Intermittent activity on 12 December, stronger than during the previous 17 days, ejected high bursts of incandescent bombs from BN's southeastern vents. Activity through 15 December was very vigorous, and eruptions continued through 21 December. Glow was visible above BN's two eruptive centers on 26 December and over the E part of the crater on 31 December.

On the evening of 7 January, several jets of incandescent bombs rose over the SE crater lip, and a few bombs fell onto the remains of the 1964 cone. As of 8 January the large cone in the N part of the crater floor had partially collapsed, creating a crater ~150 m in diameter. Frequent rockfalls occurred within this crater. Subsidence of the cone and the adjacent crater floor had created a set of circumferential fractures several meters wide. The most recent activity at this eruptive center appears to have been the extrusion of a lava flow that covered the E and SE sides of the BN floor. The vents at the SE eruptive center were the site of weak Strombolian explosions every 10-15 minutes. Most, if not all, activity occurred from the lowermost vent in the SW part of the eruptive center. A complex cone around these vents had grown notably since the visit on 6 November 1997, with the rim of the highest vent being at about the same elevation as the N rim of Bocca Nuova. Large parts of the crater wall above the SE eruptive center had collapsed, probably before the most recent cone growth (all collapse debris was buried).

Activity at Southeast Crater. Strombolian and effusive activity continued from Southeast Crater (SEC), whose intracrater cone could be seen on 1 September through a gap in the NE crater rim from coastal areas to the E. During a visit on 30 August, lava fountains rose up to 150 m above the cone, and three vents were active. There had been significant infilling of the deep southern part of SEC since effusive activity shifted to the cone's NW flank sometime before 11 August. Before then, lava had repeatedly spilled onto the SE flank of the cone.

Visits to the summit craters in late September and early October revealed continuing vigorous activity. While effusive vents were active on the W base of the cone from 10 August to mid-September, lava again issued from E-flank vents in late September, causing renewed overflows onto the outer SW flank of the cone. By mid-October the cone within SEC had grown to about the height of the highest point on the crater rim. Explosive activity was the same as during previous months, and lava effusion continued from the flanks of the cone.

At dusk on 2 November there were continuous Strombolian bursts from SEC. A visit on 6 November revealed very weak and erratic Strombolian activity. For the first time in many months there was no lava effusion at SEC, although guides at Torre del Filosofo reported that a small lava flow had spilled over the low SE rim of the crater three days earlier. After sunset on 6 November, Strombolian bursts from SEC could be seen from Catania (Palazzo delle Scienze).

Telescope observations from the roof of the Palazzo delle Scienze in Catania on 3-4 December revealed vigorous Strombolian activity at SEC and significant growth of its central conelet, which stood much higher than the surrounding crater rims. Activity on the evening of 5 December was documented with the IIV camera until bad weather hid the summit. At dusk, activity at SEC increased, and strong explosions heralded lava emission to the NE side of the intracrater cone. A more significant lava flow was erupted from SEC on the late afternoon of 9 December, accompanied by vigorous explosive activity at the intracrater cone and within Bocca Nuova. The SEC lava flow overrode previous flows on the SE flank of the cone.

The 9 December lava flow was visible on 11 December, contrasting against freshly fallen snow. Seen from Palazzo delle Scienze, this flow extended much farther downslope than previous flows on the SE flank of the cone, but its front was still several hundred meters from the steep W flank of Valle del Bove. The flow had apparently stopped (no steam was visible at the contact of the lava with the snow). Two smaller lava lobes were erupted onto the SE flank of SEC's cone, about two-thirds of the way down the cone's flank. The active central cone appeared to have lost some height during the strong explosions; Strombolian activity was still vigorous and at times accompanied by weak ash emissions. Vigorous activity at SEC, with some large explosions, continued during 12-15 December, with lava flows spilling over the SE rim and some SE-flank lava extending far beyond the base of the cone. The new flow passed only about 600 meters NE from the Torre del Filosofo mountain hut, ~1 km from SEC. As of 17 December the lava flows erupted from SEC during the previous few days were still confined to the SE flank of the cone. None of the new flows had extended as far as those on 9 and 12-13 December. Over 20-21 December, nearly continuous explosive activity at the SEC intracrater cone sent lava onto its SE and SSE flanks. The cone regained the height lost after 5 December. A 22 December afternoon episode of vigorous lava fountaining as high as 200 m from SEC lasted about 1 hour. A lava flow erupted onto the SE flank of SEC appeared to be no longer than ~200 m.

Activity at SEC in late December and early January was spectacular. On 25 December, continuous Strombolian activity occurred from the central conelet and lava flowed down the SE flank to its base, covering previous flows. Three active lava flows were visible on the SE flank on the 26th. Sometime between early 29 and early 30 December, more lava flows spilled down the S flank of SEC, and a peculiar flow moved down on the SW flank, bifurcating on the lower slope. On the evening of the 30th, active flows were visible on the S flank while the SW flow only showed incandescence in its upper part. On the evening of 31 December, incandescent lava was visible on the lip of SEC in many places while active flows were descending on the S flank. On 7 January the SW flow was incandescent along its full length, with the W lobe extending to the base of the SEC cone.

On 8 January Southeast Crater gave off continuous Strombolian explosions from two vents at the summit of the intracrater cone and lava emission from its SE base. The summit of the cone was distinctly (~5-7 m) higher than the highest point ("Fortino") on the NE rim of SEC. Lateral growth of the cone was most significant in the N and NE parts of SEC where all lava flows and effusive vents active between July and September 1997 had been buried. The lava field surrounding the central cone had risen significantly, causing overflows on the E, SE, S, and SW sides. Only a segment of the NE crater rim stood a few meters above the lava fill; the W and NW part of the rim stood 20 m above the lava field and the cone's base. Three craters were present on the central cone, two of which were erupting. Activity would occur from one vent at any given time while the other was silent. The N vent ejected bombs and scoriae onto the N and NW crater rim and beyond. The S vent produced loud bangs and showered the E and SE flanks of the cone with pyroclastics. The effusive vent on the SE side of the cone had crusted over, and lava issued only on the SW rim of SEC where it overflowed, forming a narrow (1.5 m) flow with distinct lateral levees extending to the base of the SEC cone. The flow bypassed a cone formed in 1971 on its E side; when reaching the almost horizontal plain below the steep SW flank of SEC, it broadened and thickened notably and advanced slowly in the direction of the 1971 "Observatory cone." Within 3.5 hours on 8 January, the flow front advanced ~15 m through thick snow, forming an offshoot on the W side of the ~20-m-wide lava front. None of the other flows on the S flank of SEC showed any signs of movement or incandescence. The distance from the Torre del Filosofo mountain hut to the nearest flow front was ~1 km; the active flow did not threaten this structure.

Activity at Northeast Crater. During the second half of July Northeast Crater (NEC) occasionally ejected incandescent bombs from a deep pit in the central part of the crater; fine ash fell outside the pit. Visits to the summit craters in late September and early October revealed sporadic activity. NEC frequently emitted ash plumes during the first week of October, and on the evening of 10 October, incandescent ejections rose as high as 50 m above the crater rim. Strong gas emission was occurring from NEC on 11 December. NEC was essentially quiet on 8 January, with only light steam emissions from its central pit and some of the June-August 1996 vents in the SW part of the crater. Steam emission was more abundant, and at times pulsating, from a collapse pit in the S part of the crater. This pit was also the site of frequent avalanching and rockfalls that generated plumes of brown ash. No fresh magmatic products were found in the vicinity of the central and southern pits.

Activity at Voragine. A small cone began to form on the floor of Voragine in late July, and Strombolian activity was observed on 5 August. On 30 August, the cone was mildly steaming, and the surrounding deposit of black scoriae was partly covered by blocks that had collapsed from the septum between Voragine and Bocca Nuova. The first effusive activity from the Voragine in many years occurred in late September, forming a small lava field on the crater floor. Strombolian activity was weak on 28 September but very vigorous on 9 October; one day later it was again weak. The Voragine was explosively active from the central conelet on 6 November, and another weakly explosive vent had formed at the SW base of the diaframma between the Voragine from Bocca Nuova.

The cone in the central part of the Voragine was quiet on 8 January, with only slight emission of bluish gas. Its horseshoe-shaped crater was open to the SE; a small lava flow had issued from the open side of the cone. The vent on the SW side of the crater floor, which was first observed on 6 November 1997, had enlarged and was surrounded by a low half-cone leaning against the base of the diaframma. This vent produced weak explosions that mainly expulsed hot gas and a few pyroclasts. When viewed from the E rim of the Voragine, the conduit of this vent was seen to be inclined SW, diving below the diaframma.

Seismic crisis of 9-12 January 1998. The most intense seismic crisis during the current eruptive cycle occurred during 9-12 January and caused widespread media attention. From the afternoon of 9 January through 11 January about 200 earthquakes occurred in an area on the W and SW flanks of the volcano. The strongest shock (M 3.7) damaged a church in Biancavilla. No other damage or injuries were reported. Most epicenters were between Monte Nunziata and Monte Palestra, two ancient cones on the W flank. Seismicity diminished late on 10 January.

Strong ash emissions from BN on the morning of 11 January indicated further collapse in that crater, caused by earlier subsidence of the magmatic column. It is assumed that the magma intruded into a new fracture within the W side of the volcanic edifice. On 12 January ash emission from BN was almost continuous, but strong ash emissions also occurred from NEC. Activity at SEC continued with Strombolian bursts and emission of lava flows onto the SW, S, and SE flanks of the cone. The peculiar SW flow seemed to be waning; during the previous few days it had formed several minor lobes adjacent to the main one; the flow front seemed to have reached the base of the 1971 "Observatory cone."

Another seismic swarm occurred below the W flank on the afternoon of 12 January, with twelve earthquakes in 20 minutes, the strongest being M 3.1. Epicenters were closer to the summit craters than those of the preceding swarm, clustering 2-3 km E of Monte Palestra. Focal depths were ~4 km below sea level; no damage was reported. No significant change was noted in the eruptive activity at Southeast Crater, which had three active flows moving down its SW, S, and SE flanks.

Summit activity during 13-15 January 1998. Strombolian activity on the evening of 13 January at the intracrater cone in SEC was vigorous, while active lava was only visible near the crater rim in three places. A very faint glow reappeared at the SE eruptive center in BN. Strong ash emissions occurred from BN throughout the day. Seismic and eruptive activity were low on 14 January. The only visibly active crater was SEC, which was vigorous on the 13th but showed a marked diminution of activity towards midnight. At nightfall on 14 January SEC had very few and weak explosions, and there was no active lava flow on its outer flanks. No glow was visible above BN. This was the lowest level of activity observed in about a year. Seismic activity resumed late on 14 January with a series of about ten weak earthquakes below the W flank (Monte Palestra area) and several shocks beneath the SW slope, some 5 km above Biancavilla. Hypocenters were ~6 km below the surface on the W flank but much shallower on the SW flank. Activity at SEC dropped to very low levels: very few and weak explosions from the intracrater cone were observed on 14 January and no active lava was visible on the outer flanks of the crater.

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

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


Piton de la Fournaise (France) — September 1998 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)


Activity ends with fissure eruptions outside the caldera

The eruption that began in March (BGVN 23:03) diminished during August and September. Observatoire Volcanologique du Piton de la Fournaise (OVPF) considers the eruption ended. The most significant activity during the last two months took place outside the caldera.

A small fissure eruption began on 9 August north of the caldera. Lava issued from this fissure, which was located ~500 m from the caldera wall near Nez Coupé Sainte Rose (figure 49). The initial eruption lasted only 24 hours, but a second fissure eruption began 14 August in the same area closer to the caldera wall. No fountains were observed with the second fissure, although the lava was very fluid. Flows eventually measured 200-300 m wide and ~2 km long. They moved parallel to the caldera wall until 14 September when they stopped ~500 m above Trou Caron. Some of the lava reached the edge of the caldera and spilled over onto the Plaine des Osmondes through three separate rivulets. A flow that was moving towards the upper part of Bois Blanc (a village located on the east coast) stopped by 25 August.

Figure (see Caption) Figure 49. Map of the NE quadrant of Piton de la Fournaise showing important craters and other features. The dark tone represents the caldera wall, the light-gray areas indicate the extent of lava flows dating from 1972. The medium-gray shows flows since March 1998. Courtesy of OVPF.

During September, some night incandescence due to the lava lake at Piton Kapor was seen. Only weak tremor was observed. Beginning 5 September some gas-piston events were recorded; these had likely taken place before, but had remained undetected during stronger episodes of tremor.

This eruption, including all tremor and degassing at Piton Kapor, ended 21 September, after 196 days of activity. It thus comprised the volcano's longest and one of it's most voluminous eruptions of this century.

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: Thomas Staudacher, Observatoire Volcanologique du Piton de la Fournaise (OVPF), 14 RN3, le 27Km, 97418 La Plaine des Cafres, La Réunion, France.


Guagua Pichincha (Ecuador) — September 1998 Citation iconCite this Report

Guagua Pichincha

Ecuador

0.171°S, 78.598°W; summit elev. 4784 m

All times are local (unless otherwise noted)


Phreatic discharges and shallow, near-vent seismicity continue

The volcanic crisis near Quito (figure 10) continued with a series of phreatic discharges and an E-dipping zone of earthquakes that rose to within a few kilometers of the surface (figure 2). With potentially dramatic significance to Ecuador's Capital (1995 urban population, 1,270,000 residents; suburban, 258,000 residents), the eruption has spurred a strong educational response in both the regional press and on an official web site. These discourses have repeated noteworthy points: the volcano's last vigorous eruption was in 1660; its recurrence intervals have oscillated between about 400 and 600 years; its last major eruption took place 338 years ago; and its phreatic eruptions have repeated during the past 15 years. Phreatic eruptions began on on 7 August (BGVN 23:08); since then the Instituto Geofísico, Escuela Politécnica Nacional (IG-EPN) has made available daily reports on activity during 30 September to 27 October, which we summarize here.

Figure (see Caption) Figure 10. Simplified schematic showing Guagua Pichincha, Quito's urban areas (elongate zone with selected roads), and hazard designations associated with the volcano. Revised from a color hazard map on the IG-EPN website and keyed as follows: 1) Maximum danger (including major risks of hot volcanic flows, lahars, and ashfall - requiring total evacuation); 2) Minor danger (minor risk of ash clouds, hot volcanic flows, and lahars - areas immediately abandoned should an eruption be either imminent or large); 3) Lahar risk along drainage areas; and 4-6) graded risk of ashfalls. The bold arrows help identify the location of source vents and portray ejecta trajectories representative of those that might occur during an eruption. For more detail, see Hall and von Hillebrandt (1988). Courtesy of the Instituto Geofisico, Escuela Politécnica Nacional.

Activity and observations. The epicenters of located earthquakes during April-October 1988 generally clustered around the caldera (figure 11). This was particularly the case for volcano-tectonic (VT) earthquakes, which in cross-section view tended to lie underneath the caldera. The located long-period (LP) events generally propagated from greater depths and in cross-section view defined a broad E-dipping zone. Thus far in the crisis there has been an alternating pattern of seismicity and seismically detected explosions (figure 12). During late September through late October there were often 1-2 daily explosions.

Figure (see Caption) Figure 11. (top) Located seismic events at Guagua Pichincha during April-October 1998 were mainly centered around the caldera. The abbreviations VT and LP refer to volcano-tectonic and long-period events. The LP events showed a tendency to lie farther outboard, on the volcano's E slopes. (bottom) A cross section showing hypocenters for the same seismic events, which reveals the E-dipping attitude of located events. Courtesy of the Instituto Geofisico, Escuela Politécnica Nacional.
Figure (see Caption) Figure 12. Histograms for Guagua Pichincha showing both the daily number of earthquakes, including (a) volcano tectonic (VT), (b) long-period (LP), (c) multiphase (MP), and (d) the daily number of seismically detected explosions. Courtesy of the Instituto Geofisico, Escuela Politécnica Nacional.

On 3 October observers confirmed the presence of new fumaroles on the dome's W edge; nearby, in the headwaters of the Rio Cristal, they noted a new fumarole field. A phreatic explosion was heard at 0400 on 5 October by residents of Lloa. The explosion was the thirty-first such event in the sequence initiated on 7 August. It ranked among the most energetic seen to this point of the crisis, comparable to those on 8 and 24 August, and 29 September. The 5 October explosion followed 50 minutes of tremor registered at station YANA (7 km NE of the crater; "C" on figure 13). Small seismic events continued until 0800 that day. This explosion left a fresh ash layer in the caldera that revealed a new vent near the older one but above it to the S.

Figure (see Caption) Figure 13. Contour map (200-m interval) indicating noteworthy sites surrounding Guagua Pichincha, including the valley embracing Quito and some of the key W-slope rivers that drain the breached caldera and environs. The map indicates settlements of Nono and Lloa (darkened rectangles) and seismic stations installed and maintained by various groups (open rectangles). These stations are designated by the following call letters: A, FARH; B, NONO; C, YANA; D, PINO; E, QWR; F, TERV; G, GGP; H, (uncertain); J, TOAZ; K, PIEZ; L, JORG; and M, MGUL. Courtesy of the Instituto Geofisico, Escuela Politécnica Nacional.

The seismic swarm NE of the caldera (BGVN 23:08) continued; between June and early October there were 3,200 events; ~10 had a magnitude (MR) over 3.9. On 4 October instruments detected ~30 earthquakes, the strongest MR 3.5. A MR 3.6 earthquake struck this zone on 10 October and was felt locally in the settlements of Pomasqui and San Antonio.

Measured deformation was not detected for the interval 15 September-7 October. Although not plotted, tremor has occurred. For example, at 2214 on 7 October station PINO detected tremor for 19 minutes while station YANA registered it for 7 minutes. On 11 and 12 October tremor followed phreatic explosions and in the former case, prevailed for 20 minutes at stations near the crater.

Mass wasting on the SE flank ~11 km from the caldera (in Quito's San Roque sector) on 9 October covered an old school, part of a church, threatened several smaller structures, and blocked vehicular traffic. Roughly 20 people were evacuated.

On 12 October condensing gases escaping the dome at a fumarole called "La Locomotora" rose 200 m. Around this time the 1981 explosion crater also emitted a moderate flow of gray gases but new fractures or fumaroles were absent.

At 1621 on 14 October a phreatic explosion at the 1981 vent sent fine material over the NE part of the caldera and left a visible coating ~300 m up the caldera walls. The associated grayish-white plume formed a ~3-km-tall column. Clear weather enabled residents of Quito to see the plume. Geophysical instruments detected the event at widely scattered locations. COSPEC registered the first clear SO2 signal, a 300 ppm concentration in the plume. Guards at a local observation post smelled strong sulfur, particularly when gases from La Locomotra fumarole blew past.

An explosion at 0947 on 16 October sent a plume to ~2 km. Again, Quito residents saw the plume, but an explosion the next morning was shrouded from view by weather clouds. The latter explosion was considered moderate; it was associated with ~5 minutes of tremor centered around 1.2-Hz frequency and scientists working nearby (at station PINO) saw a gray-white cloud develop. A 17 October explosion was shrouded in clouds. The phreatic explosions on 14, 15, 16, and 17 October yielded respective reduced seismic displacements of 11, 4.2, 9.8, and 3.2 cm2.

A view into the caldera on the morning of 18 October disclosed relatively passive outgassing from the 1981 and 1988 explosion craters. La Locomotra and other fumaroles on the central dome had clearly increased their output, feeding a plume ~700 m high. Another moderate explosion on 25 October was followed by 3 hours of tremor.

A flight on the morning of 27 October revealed only modest degassing, a 300-m-high plume, and an SO2 concentration below the COSPEC's detection limit. Minard Hall also recognized that the 1981 crater and one formed in September 1998 had coalesced. The wall isolating them had apparently been weakened by repeated phreatic eruptions.

Risk mapping. The highest risk settlements include Lloa (figures 1 and 4) and Mindo. The latter lies on the river of the same name about 22 km NW of the caldera; it lies off of maps in this report but is depicted on the larger hazard map of Hall and von Hillebrandt (1988). One branch of the Mindo river's headwaters begin just N of the breach in the caldera (figure 4). Rivers draining the breached W-flank and nearby NW-flank (e.g. Rio Cristal and Rio Mindo) were assigned a higher category of risk for lahars than any lahar-risk zones on the E flanks (figure 1).

New fieldwork has been aimed at inspecting older lahar deposits in vicinity of the settlements of Mindo and Nono. Nono, on the NNE flank (figures 2 and 4), lies at mouth of a narrow N-S valley that cuts across much of the volcano's E to NNE flanks.

Partnerships. The following describes some of the civic and media efforts to communicate volcanic hazards. On 30 September Ecuador's president requested that a safety committee be formed (Comité Especial de Seguimento, CES). The committee was charged with integrating Civil Defense, the IG-EPN, and the City of Quito. In overcast conditions on 24 August a film crew from TeleAmazonas shot footage of an explosion plume not otherwise visible in Quito. These glimpses, and later examples of widely visible plumes, surely helped residents grasp the immediacy and some of the power of the eruption.

Authorities raised the hazard status to Yellow on 1 October. On 3 October a new video system started to monitor the inner crater. This advance was supported by "Ecuavista" in coordination with "911 of the City of Quito," the phone number for the City's communications base.

A 2 October announcement told of a downtown Quito information center implemented to release daily circulars at bearing official volcanological information. Thanks to a partnership between the information center and IBM of Ecuador, the former gained access to the internet, email, and a modern computing environment The radio station "Zaracay," which can be received widely, including the urban and Mindo areas, was also designated as a conduit for public announcements.

By 7 October the seismic network consisted of 12 stations with real-time data transmission. Collaborating scientific teams and monitoring equipment have come from both the U.S. Geological Survey as well as ORSTOM (the French Scientific Research Institute for Development through cooperation). Contingency plans have surfaced, dealing with the issue of transportation during the higher stages of alert (Orange and Red). Public announcements have broached the need to maintain the integrity of the municipal infrastrucure in the event of an eruption, including crews to clean ash (from roads, power lines, etc.).

Reference. Hall, Minard, and von Hillebrandt M., Christa G., 1988, Mapa de los peligros volcanicos poteciales asociados con el volcan Guagua Pichincha; Republica del Ecuador (1:50,000).

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

Information Contacts: Instituto Geofísico, Escuela Politécnica Nacional, Apartado 17-01-2759, Quito, Ecuador; El Comercio newspaper, Quito, Ecuador (URL: http://www.elcomercio.com); El Universo newspaper, Quito, Ecuador (URL: http://www.eluniverso.com); La Hora newspaper, Quito, Ecuador (URL: http://www.lahora.com); Volcanic Disaster Assistance Program, U.S. Geological Survey, 5400 MacArthur Blvd., Vancouver, Washington 98661 USA (URL: https://volcanoes.usgs.gov/observatories/cvo/); ORSTOM, A.P. 17-11-6596, Quito, Ecuador (URL: http://www.ird.fr/).


Hokkaido-Komagatake (Japan) — September 1998 Citation iconCite this Report

Hokkaido-Komagatake

Japan

42.063°N, 140.677°E; summit elev. 1131 m

All times are local (unless otherwise noted)


Phreatic eruption spreads ash 25 October

The Japan Meteorological Agency (JMA) issued an advisory and three observation reports concerning Hokkaido-Komaga-take volcano on 25 October following a small-scale phreatic eruption that began at 0912 the same day. Ash rose in a column to a height of ~1,200 m above the crater. The eruptive activity soon declined. There were no report of injuries or damage caused by the eruption, and no evacuation order was issued.

Volcanologists surveyed the activity from a helicopter the afternoon of 25 October (figure 2). They reported that the eruption originated from the same crater that opened during the 1929 eruption, which was also the site of the March 1996 eruption. Ash covered a significant area around and to the E of the crater. The scale of this eruption apparently was smaller than that of the March 1996 eruption.

Figure (see Caption) Figure 2. An aerial view of Komaga-take showing fuming activity from the 1929 Crater about 6 hours after the 25 October 1998 eruption. View is from the SE looking towards the Komanose Rim (back) and the Sawaradake Rim (back right). The 1942 Large Fissure (middle, diagonal) and the 1996 Southern Fissure Crater (middle center) can also be seen. Hyoutan Crater (front center) is adjacent to the 1929 Crater. Photograph by Bousai Heli; courtesy of Hiromu Okada, Usu Volcano Observatory.

Volcanic tremor lasting six minutes was associated with this eruption. In addition, five volcanic earthquakes were recorded in the 12 hours following the first eruption signs.

Komaga-take is located 30 km N of Hakodate City (population 320,000). The andesitic stratovolcano has a 2-km-wide horseshoe-shaped caldera open to the E. The volcano has generated large pyroclastic eruptions, including major historical eruptions in 1640, 1856, and 1929. In the 1640 eruption, debris from a partial summit collapse entered the sea resulting in a tsunami that killed 700 people. Although the 1929 eruption was one of the largest 20th-century eruptions in Japan, it may not have had clear geophysical precursors.

Geologic Background. Much of the truncated Hokkaido-Komagatake andesitic volcano on the Oshima Peninsula of southern Hokkaido is Pleistocene in age. The sharp-topped summit lies at the western side of a large breached crater that formed as a result of edifice collapse in 1640 CE. Hummocky debris avalanche material occurs at the base of the volcano on three sides. Two late-Pleistocene and two Holocene Plinian eruptions occurred prior to the first historical eruption in 1640, which began a period of more frequent explosive activity. The 1640 eruption, one of the largest in Japan during historical time, deposited ash as far away as central Honshu and produced a debris avalanche that reached the sea. The resulting tsunami caused 700 fatalities. Three Plinian eruptions have occurred since 1640; in 1694, 1856, and 1929.

Information Contacts: J. Miyamura, Sapporo District, Japan Meteorological Agency, 1-3-4 Ote-machi, Chiyoda-ku, Tokyo 100, Japan; Hiromu Okada, Usu Volcano Observatory, Institute of Seismology and Volcanology, Hokkaido University, Sohbetsu-cho, Hokkaido 052-0103, Japan.


Iwatesan (Japan) — September 1998 Citation iconCite this Report

Iwatesan

Japan

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

All times are local (unless otherwise noted)


Nearby M 6.2 earthquake on 3 September, but volcano still slumbering

A strong earthquake occurred 10 km SW of the summit of Iwate volcano at 1658 on 3 September. The Richter magnitude was 6.1 and the depth ~7 km. The mechanism was E-W compression on a reverse fault. A N-S-trending surface rupture appeared, despite the event's non-extreme magnitude. The aftershock area resulting from the earthquake differed from typical earthquakes on Iwate and the relationship between the earthquake and the volcano, if any, is not understood. This was the largest earthquake since August 1996 when a M 5.9 tremor struck.

A 3 September Reuters news article mentioned that a powerful earthquake took place, centered in the ski resort area of Shizukuishi, a mountainous region near Iwate volcano. The report claimed the epicenter was 5 km underground and police said that the event slightly injured at least nine people.

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: Yukio Hayakawa, Faculty of Education, Gunma University, Aramaki, Maebashi 371, Japan; Reuters Limited, 1700 Broadway, New York, NY 10019 USA (URL: http://www.reuters.com/).


Klyuchevskoy (Russia) — September 1998 Citation iconCite this Report

Klyuchevskoy

Russia

56.056°N, 160.642°E; summit elev. 4754 m

All times are local (unless otherwise noted)


Explosions, ash 2-3 September raise concern to yellow alert

During 2-28 September, seismicity under the volcano was generally above background levels. Hypocenters were concentrated at two levels: near the summit crater and at depths of 25-30 km. Clouds often prevented observations.

On 2 September a fumarolic plume was observed during the daylight hours rising 50 m above the summit. Beginning at 2218 that day, a 33-minute series of explosive earthquakes was recorded, and at 2245 an ash explosion produced a plume that rose 4-5 km above the crater. On 3 September, scientists noticed that ash had been deposited in a 2-km-long zone on the NE slope. A plume of gas, with no ash content, rose 500 m above the volcano during 3-4 September, but had stopped by 5 September. Because of the increase in activity, the alert status was changed to Yellow, meaning more significant eruptions may occur.

No fumarolic plumes were seen during 8, 18, and 27 September, but plumes rising up to 100 m above the summit were seen during 13, 16, 17, 21, and 24 September. The alert color code returned to Green on 21 September, indicating normal activity.

Geologic Background. Klyuchevskoy (also spelled Kliuchevskoi) is Kamchatka's highest and most active volcano. Since its origin about 6000 years ago, the beautifully symmetrical, 4835-m-high basaltic stratovolcano has produced frequent moderate-volume explosive and effusive eruptions without major periods of inactivity. It rises above a saddle NE of sharp-peaked Kamen volcano and lies SE of the broad Ushkovsky massif. More than 100 flank eruptions have occurred during the past roughly 3000 years, with most lateral craters and cones occurring along radial fissures between the unconfined NE-to-SE flanks of the conical volcano between 500 m and 3600 m elevation. The morphology of the 700-m-wide summit crater has been frequently modified by historical eruptions, which have been recorded since the late-17th century. Historical eruptions have originated primarily from the summit crater, but have also included numerous major explosive and effusive eruptions from flank craters.

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


Ol Doinyo Lengai (Tanzania) — September 1998 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 cones, vigorous activity since February

From February through August 1998, several visitors to the crater of Ol Doinyo Lengai produced photographs and descriptions of eruptive activity. The following are taken from a summary of those visits provided by Celia Nyamweru, including detailed observations of certain hornitos made by Fred Belton and Chris Weber during their visits in June and August.

Orientation. Figure 51 locates the prominent features in the crater based on a photograph taken on 23 February 1998. A similar sketch map based on a photograph taken in February 1997 from nearly the same perspective appeared in a previous report (BGVN 23:06). Among the conspicuous new features appearing in 1998 are three large hornitos labeled T45, T46, and T47. T45 was described in February 1998 as being "possibly a new cone," but it may have been active as early as December 1997; by August it had grown to a height of ~7 m and was the dominant landmark in the E of the crater. T46 is a broad, darkly colored feature near the T20/T44 cluster. T46 was erroneously identified as T47 in the last Bulletin report. T47 is a tall, very narrow cone with a pointed top. It is located in the south-central area of the crater near the site of T23, which has nearly vanished. The cone cluster known as "A" has completely disappeared beneath recent lava.

Figure (see Caption) Figure 51. View of the crater of Ol Doinyo Lengai looking N from the S crater wall as it appeared 23 February 1998. The oblique view has a variable scale: it is ~ 300 m from T47 to C, and ~ 100 m from T47 to both T37S and T26/T27. Courtesy of C. Nyamweru from a photo by J.S. Antonio.

General appearance. During a visit to the summit on 12 March, observers noted no major changes to the crater since 23 February. Pale-brown, brown, and gray lava of differing ages covered the floor (figure 52). Pahoehoe flow patterns were clear in some areas, particularly N and NE of T45. An open vent in the T23 area contained a bubbling lava pool and steam issued from various vents. T47 was described as a very tall cone with a vertical crack and sharp peak, making it easily distinguishable from other nearby cones.

Figure (see Caption) Figure 52. Composite panoramic view to the SW from the E crater rim taken on 12 March. T45 is prominent in the foreground. The scale is oblique: it is ~ 150 m from T45 to T47 and ~ 100 m from T45 to T40. Courtesy of C. Nyamweru; photos by B.A. Gadiye.

An aerial photograph taken during May showed no important changes (figure 53). No steam or fresh lava was seen. The crater floor was covered with white or pale gray lava. A summit visit on 12 June revealed few changes (figure 54). No fresh lavas were seen, but recent flows of gray and brown lava were noticed, particularly in the area of T45 and from T37S in the direction of T24.

Figure (see Caption) Figure 53. Aerial view of the Ol Doinyo Lengai crater looking to the SE in May 1998. Courtesy of C. Nyamweru; photo by B. Wangermez.
Figure (see Caption) Figure 54. Composite panoramic view of Ol Doinyo Lengai looking SW from the E crater rim (compare with figure 52) taken on 12 June. Courtesy of C. Nyamweru; photos by B.A. Gadiye.

There were no signs of fresh surface activity when observers arrived on 17 June. The entire crater floor was grayish white and mostly soft, and no new spatter was visible on any hornito. The lowest point on the crater rim, to the NW, was 30 cm above the crater floor. T47 was the tallest cone in the crater (~11 m) and was lightly steaming. A 150-m-long steaming fracture, rich in sulfur deposits, was oriented SW-NE; the fracture passed over the site of T41 and T42, both of which had disappeared.

During visits through the first week of August, the steaming fissure was no longer visible, but a new fissure of the same type had developed. This was oriented NW-SE with its SE end located near the base of T20. T37S had two small cones recently added to the S part of its summit and a small lava flow down its W flank. A few clots of lava were ejected from T44C around 1300 on 2 August; although no taller, it showed recently added lava cascades on its N flank. At 0615 on 7 August T44 splashed black liquid lava out of its 6-m-high peak.

T37N1. On 17 June, T37N1 was open to the SE and contained a lava platform consisting of a 2-m-diameter circular pit beneath a 5-m overhanging wall. The pit opened into a cave that was ~4 m deep. A small spatter cone, 4 m W and 2.5 m above the pit, was located on the shoulder of the overhanging wall. At 0630 on 18 June a vigorously sloshing pond of very gas-rich lava rose slowly inside the circular pit. Lava was also visible through the vent of the spatter cone. Within an hour the pond overflowed and the spatter cone began ejecting lava clots up to 2 m above the cone, eventually producing pahoehoe and aa flows that traveled ~100 m ESE. This activity continued until 1200. At 1815 on 19 June a 20-minute eruption resulted in an overflow of the pond. Continuous lava fountains rose up to 1 m above the spatter cone, covering the flows from the previous day. At 1600 on 20 June an eruption lasting more than 15 hours began with a high-volume pond overflow and explosions every 2 seconds from the spatter cone. By 2245 the explosions had stopped and an orange flame was seen at the cone's vent. Lava continued to pour from the pond all night. A tube-fed flow first traveled N, then curved E as a narrow strip ~80 m long containing a single tube, and finally spread out into a wide stacked flow-field that piled up against the E rim.

At 1800 on 5 August a lava lake was seen in the cave under the spatter cone, ~5 m below the rim. At 1930 the lake began to glow dull red in the darkness, revealing that the cave was much larger than it had first appeared. The entire T37N1 hornito was hollow with a lake slowly rising inside that flowed toward the SW and entered a westward-directed tube or cave. As the lake rose higher lava appeared on the crater floor at the W base of T37N1, flowing slowly along the bottom of an old tube. Within 10 minutes the lake rose up to vent level and began to slosh over the rim, but lava could no longer be seen on the crater floor. From 2000 to 2330 the lake overflowed numerous times and lava advanced to a point near the base of T5T9. Due to frequent fluctuations in lake level, no long tubes developed; instead the flows were short and thickly stacked.

Similar activity occurred in the early morning hours of 6 August; just before 0715 the lake was ~3 m below the rim of the spatter cone, which had been increased in height and reduced in diameter during the eruption. The open interior of T37N1 filled with lava to a depth of 2 m, completely burying the pit that had contained the overflowing lava pond in June. The T37N1 spatter cone, positioned on the W side of the new, higher lava platform, was taller and had a larger vent than in June. Foaming white to pale gray carbonatite lava splashed out and fed short lava flows a few meters long down the W slope. Its vent opened into a large cave, ~8 m deep. A recent tube-fed flow from the vent extended to the W crater wall. The vesiculation of the gas-rich lava was high. Activity stopped around 1100 causing a 4-m drop of the lava level.

T48. At 0800 on 18 June (while T37N1 was erupting) T48 produced lava fountains up to 3 m high for 10 minutes, forming short aa flows on its N side. Throughout the morning of 19 June it occasionally ejected solid lapilli along with loud puffs of steam. At 2335 that night it began exploding loudly every 2 seconds and produced lava fountains up to 7 m high. After less than 2 minutes of these explosions the fountains decreased in height to 3 m but increased in volume. Each explosion covered the NW half of T48 with a thick layer of spatter that glowed dull red.

By August T48 had increased in height by at least 2 m and had produced many fresh flows extending in all directions. Aerial photographs taken by Benoit Wangermez on 1 August showed several fresh lava flows originating from vents in the approximate location of T48 and T49 extending to the NE and W crater rims. At 1300 on 2 August, low lava fountaining began from the summit vent and within an hour a lava stream was cascading down the nearly vertical SW flank of T48. Over the next 7 hours a large tube formed from the summit down the SW flank. Lava from this tube advanced past the N slope of T20 more than halfway to the WNW crater wall. Near the base of T48 the tube was ~60 cm in diameter and had several skylights from which lava often overflowed. The lava was gas-rich with a surface that appeared to be covered with gray foam.

The eruption continued all night but lava never reached the crater wall. At 0800 on 3 August a close inspection of the vertical lava tube revealed a small crack expelling hot air. Near 1000 the tube ruptured at that point, creating a powerful horizontal lava fountain that played on the N flank and base of nearby T44C. As the rupture progressed, other fountains directed at various angles of inclination developed, and eventually a flow began to form a second tube. The original tube was still full of flowing lava. By 1800 no lava was visible in the skylights. At 1930 a thin lava stream was spraying horizontally from the E side of T48's summit. At 0600 on 4 August T48 was inactive but at 0800 fountains developed on its upper east flank, creating pahoehoe and aa flows that reached the base of T40B. Similar activity continued until 2000. There was no further activity until 2330 on 5 August when a wide lava fountain sprayed horizontally for 20 minutes from just above a small ledge on the E flank, 2 m below the summit.

On 6 August at 1400 lava splashed out of two openings close to the peak of T48. Black, degassed, very liquid lava fed little lava flows reaching 8 m down the E slope. The activity stopped shortly after 1600.

T40. Sloshing lava was heard inside T40 during the entire June visit. During the night of June 19 a pahoehoe flow traveled ~10 m from a small vent in its base. Lava flowed into a cave under a low, broad hornito just NE of T40. This new lava flow was ~1 m thick. The cave had contained an impressive group of white lava stalactites. On 20 June a 3-m2 section of the SW flank collapsed into its interior.

On 2 August at 1000 occasional lava clots were being ejected from T40's summit, but this continued for only ~30 minutes. During the August visit T40 was noisily degassing. The collapse pit that formed on 20 June in the SW flank of T40 was no longer visible, having been filled in by lava. Recent flows extended a short distance SW and SE of T40, partially covering a low mound to the SE. A tall, narrow cone had very recently been formed on the summit of T40 and was the source of several very fresh aa flows extending to the base of T40.

T49. A small cone just NE of T49 extended toward the NW and grew in height between visits. Sloshing lava was frequently heard there. After several earthquakes during the night of 6 August, at 0408 on 7 August a loud explosion blew off the top and N side of T49. Rocks up to 1 m3 were thrown or rolled a few meters. A dark-red lava fountain ~15 m high continued until 0413 with a loud, jet-like noise. Pahoehoe lava with little viscosity (1-5 Pa s) splashed N of T49 and traveled NW. The flow was thin (10-20 cm) and stopped shortly after the end of the eruption. The amount of erupted lava was ~70-100 m3. Lava pearls up to 4 mm diameter and fine ash were blown over 200 m NW.

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

Information Contacts: Celia Nyamweru, Department of Anthropology, St. Lawrence University, Canton, NY 13617 USA (URL: http://blogs.stlawu.edu/lengai/); Fredrick A. Belton, 3555 Philsdale Ave., Memphis, TN 38111; Christoph Weber, Kruppstr 171, 42113 Wuppertal, Germany.


Masaya (Nicaragua) — September 1998 Citation iconCite this Report

Masaya

Nicaragua

11.985°N, 86.165°W; summit elev. 594 m

All times are local (unless otherwise noted)


Integrated scientific studies of the caldera area

Four teams of Canadian, British, and Nicaraguan volcanologists carried out studies of Masaya caldera during January-April and September 1998. The volcano was examined using correlation spectroscopy (COSPEC), microgravity, Open Path Fourier Transform Infrared spectroscopy (OP-FTIR), and soil-gas studies.

Vent degassing appeared to have increased significantly. COSPEC measurements during February-April 1998 showed SO2 flux varying from 680 t/d to a maximum of 5,580 t/d. Measurements made during the previous year (January-March 1997) showed more stable fluxes of approximately 380 t/d. Measurements in September 1998 showed flux levels varying from 320 to 1,420 t/d.

OP-FTIR measured from the Plaza Oviedo overlooking the "Santiago" pit crater showed consistent SO2/HCl and HCl/HF volume ratios of 2 and 7, respectively. Using the COSPEC-derived SO2 flux, scientists inferred HCl fluxes of 340 to 2,790 t/d and HF fluxes of 97 to 797 t/d.

CO2 soil-gas measurements at the foot of the Comalito cinder cone increased from 23 to 31.3% between March 1997 and February 1998. Fumarole temperatures also increased from 70 to 84°C during February 1998.

Microgravity surveys during March 1997-February 1998 showed a slight increase in gravity immediately beneath the Santiago pit crater. They also showed evidence (increased noise recorded on the meter) of significant seismic activity around the Santiago crater. Similar measurements acquired in September 1998 indicated increased seismic activity throughout the caldera.

Temperatures at the active vent, measured using a Cyclops infrared camera, ranged between 170 and 400°C. The higher measurements occurred when incandescence of the vent walls was visible. In March, a small fumarole emitting low levels of gas appeared, ~15 m from the active vent.

Geologic Background. Masaya is one of Nicaragua's most unusual and most active volcanoes. It lies within the massive Pleistocene Las Sierras caldera and is itself a broad, 6 x 11 km basaltic caldera with steep-sided walls up to 300 m high. The caldera is filled on its NW end by more than a dozen vents that erupted along a circular, 4-km-diameter fracture system. The Nindirí and Masaya cones, the source of historical eruptions, were constructed at the southern end of the fracture system and contain multiple summit craters, including the currently active Santiago crater. A major basaltic Plinian tephra erupted from Masaya about 6,500 years ago. Historical lava flows cover much of the caldera floor and there is a lake at the far eastern end. A lava flow from the 1670 eruption overtopped the north caldera rim. Masaya has been frequently active since the time of the Spanish Conquistadors, when an active lava lake prompted attempts to extract the volcano's molten "gold." Periods of long-term vigorous gas emission at roughly quarter-century intervals have caused health hazards and crop damage.

Information Contacts: Glyn Williams-Jones, Dave Rothery, Hazel Rymer, Peter Francis, and Lisa Boardman, Department of Earth Sciences, The Open University, Milton Keynes MK7 6AA, United Kingdom; Alexandre Beaulieu, Dany Harvey, Pierre Delmelle, Katie St-Amand, and John Stix, Département de Géologie, Université de Montréal, Montréal, Québec H3C 3J7, Canada; Mike Burton, Clive Oppenheimer, and Matthew Watson, Department of Geography, University of Cambridge, Downing Place, Cambridge, CB2 3EN, United Kingdom (URL: http://www.geog.cam.ac.uk/); Hélène Gaonac'h, Département des sciences de la Terre, Université du Québec - Montréal, Montréal, Québec H3C 3P8, Canada; Martha Navarro and Wilfried Strauch, INETER, Apartado Postal 2110, Managua, Nicaragua; Benjamin van Wyk de Vries, Departement des Sciences de la Terre, Universite Blaise Pascal, 63038 Clermont-Ferrand, France.


Obituary Notices (Unknown) — September 1998 Citation iconCite this Report

Obituary Notices

Unknown

Unknown, Unknown; summit elev. m

All times are local (unless otherwise noted)


Death of Oleg Volynets in Petropavlovsk-Kamchatsky

On 24 October, in Petropavlovsk-Kamchatsky, the volcano community lost a distinguished scientist and an exceptionally kind, warm human being. Oleg Volynets worked for over 39 years on the volcanoes of the NW Pacific rim, and died at the peak of an unusually productive career. His colleague Vera Ponomareva wrote that he "combined the qualities of a unique expert in Kamchatka rocks with broad knowledge in modern geochemistry. More important, he was our conscience, a true 'chevalier sans peur et sans reproche.' His death is a deep personal grief for many people." He found time to share his extensive knowledge of Russian volcanoes with us here at the Smithsonian, and we are among those "many people."

Geologic Background. Obituary notices for volcanologists are sometimes written when scientists are killed during an eruption or have had a special relationship with the Global Volcanism Program.

Information Contacts:


Popocatepetl (Mexico) — September 1998 Citation iconCite this Report

Popocatepetl

Mexico

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

All times are local (unless otherwise noted)


Several episodes of ash emission during September

Following a large ash exhalation on 8 September (BGVN 23:08), eruptive activity at Popocatépetl decreased in intensity and duration. CENEPRED reported a few moderate emissions during September that caused local ashfall.

Small-volume, discrete, short-duration emissions containing ash, sometimes accompanied by steam and gas, were recorded occasionally during the period 9-15 September. Brief episodes of harmonic tremor were also recorded. During the night of 14 September glow reflected from clouds over the crater was seen.

Moderate exhalations of steam, gas, and light ash took place during 16 September. Several brief episodes of high-frequency tremor were recorded that afternoon; the largest emissions occurred at 1546-1552, 1604, and 1611. Ashfall was reported at Amecameca, 20 km NW of the volcano. Despite bad weather that reduced visibility most of the day, a dense column of steam and gas was seen rising 700 m above the summit before being blown to the NW. Activity decreased to stable background levels on 17 September. A dense steam and gas cloud seen on the morning of 18 September dispersed to the NE; as the cloud gained altitude, its direction changed to the south. SO2 measurements showed significant increases following the 16 September explosion over levels earlier in the month.

Another moderate increase in eruptive activity began a few days later. A steam and gas column rising 1 km above the summit was observed during 20 September. Brief, moderately intense emissions of steam and gas, sometimes with light ash puffs, took place throughout the morning of 21 September. An explosion at 1148 that morning produced light ashfall in towns up to 20 km NW of Popocatépetl. A similar but less intense event occurred at 1543. Emissions decreased to relatively low levels until 1225 on 22 September when a moderate explosion lasting 7 minutes produced a steam, gas, and ash plume that rose 4 km above the summit. Visibility during 22 August was poor due to bad weather, but a large ash cloud near the crater was detected by Doppler radar. Ash was dispersed during the afternoon NW of the volcano, producing light ash falls in the suburban SE of metropolitan México City.

Following the explosion on 22 September, eruptive activity paused until a similar explosion occurred at 1829 on 23 September. This explosion lasted 6 minutes and produced a 3-km high column of steam, gas, and ash. Ash fall was reported in towns SW of the volcano. Eruptive activity soon decreased again, stabilizing at low levels of small, isolated emissions of steam and gas, typical of earlier in September. An exhalation at 1025 on 24 September was followed by 30 minutes of low-frequency harmonic tremor. An A-type earthquake of M 2.1 located 1.8 km E of the crater at a depth of 3.9 km was recorded at 2224 on 24 September, and another moderate exhalation lasting 7 minutes began at 2332.

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

Information Contacts: Servando De la Cruz-Reyna1,2 Roberto Quaas1,2 Carlos Valdés G.2 and Alicia Martinez Bringas1; 1 Centro Nacional de Prevencion de Desastres (CENAPRED) Delfin Madrigal 665, Col. Pedregal de Santo Domingo, Coyoacan, 04360, México D.F. (URL: https://www.gob.mx/cenapred/); and 2 Instituto de Geofisico, UNAM, Coyoacán 04510, México D.F., México.


Sete Cidades (Portugal) — September 1998 Citation iconCite this Report

Sete Cidades

Portugal

37.87°N, 25.78°W; summit elev. 856 m

All times are local (unless otherwise noted)


Seismic swarm on submarine flank

Since June 1998, increasing seismic activity in the vicinity of Sete Cidades volcano has resulted in occasional seismic swarms. On the night of 2-3 August about 120 events were registered in 3 hours. During that period, five earthquakes were felt along the W coast, the strongest with a magnitude of 3.1 reached a maximum intensity of V (MM) at Ginetes e Varzea. Similarly, on 2 September in Sao Miguel more than 120 events occurred beneath the sea floor over a period of about 4 hours near shore between Ponta da Ferraria and Mosteiros. One of the five felt earthquakes during this period also reached an intensity of V (MM). There were no reports of injury or damage from any of these events.

Geologic Background. Sete Cidades volcano at the western end of Sao Miguel Island contains a 5-km-wide summit caldera, occupied by two caldera lakes, that is one of the scenic highlights of the Azores. The steep-walled, 500-m-deep caldera was formed about 22,000 years ago, and at least 22 post-caldera eruptions have occurred. A large group of Pleistocene post-caldera trachytic lava domes, lava flows, and pyroclastic-flow deposits is found on the western-to-northern flanks. A nearly circular ring of six Holocene pyroclastic cones occupies the caldera floor. These have been the source of a dozen trachytic pumice-fall deposits erupted during the past 5000 years. Sete Cidades is one of the most active Azorean volcanoes. Historical eruptions date back to the 15th century and have occurred from within the caldera and from submarine vents off the west coast.

Information Contacts: João Luis Gaspar and Nicolau Wallenstein, Departamento de Geociencias, Centro de Vulcanologia, Universidade dos Açores, Rua Mae de Deus, 9500 - Ponta Delgada, Sao Miguel, Açores, Portugal.


Sheveluch (Russia) — September 1998 Citation iconCite this Report

Sheveluch

Russia

56.653°N, 161.36°E; summit elev. 3283 m

All times are local (unless otherwise noted)


Ash explosions and pyroclastic flow during 3 September

Seismicity remained generally at background levels during 2-28 September. A plume on 2-3 September was seen rising 200 m above the volcano. At 1622 on 3 September, ash explosions produced a cloud that rose 5 km above the summit, and extended 100 km NNE. Pyroclastic flows moving SW were observed at this time. The explosion was also accompanied by a 9-minute series of shallow earthquakes and tremor. The level-of-concern color code remained Green. Observation was restricted by cloud during much of the month.

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

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


Soufriere Hills (United Kingdom) — September 1998 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)


Continuing decrease in activity; hazards reassessed

The following summarizes the Montserrat Volcano Observatory's (MVO) scientific reports for July and August, except information concerning the 3 July pyroclastic flows, which was reported in BGVN 23:07.

Summary. In the weeks following the 3 July pyroclastic flows, no fresh magma reached the surface; however, vesicular ballistic blocks were recovered from craters on Perches Mountain suggesting that there may have been a small Vulcanian explosion. SO2-flux levels declined steadily throughout July to an average of 1,000 metric tons/day (t/d). Vigorous steam-and-ash venting continued from the dome-collapse scar until the end of July. Activity in August was dominated by several small dome-collapse events and a period of enhanced steam-and-ash venting in the middle of the month. The dome-collapse events were caused by the gravitational collapse of weakened dome rock. The ash venting was intense one day but waned over following days to normal levels. MiniCOSPEC results showed a peak that coincided with the enhanced venting, but there was an overall decline from ~1,000 t/d at the beginning of the month to ~500 t/d at the end of the month.

Visual observations. Ash-and-steam venting immediately after the 3 July event was vigorous. Significant pulses of steam-and-ash continued for 2-3 weeks and fumarolic activity was evident on the S and N flanks of the dome.

A steep buttress overhanging the 3 July scar collapsed on 16 August generating pyroclastic flows that reached the Tar River delta. Large fragments of the buttress were left in the area of the scar's mouth. On 19 August fumarolic activity in the scar increased in intensity: fumaroles on the back wall and at the base of the scar discharged copious quantities of steam and ash in jets. The next day activity decreased in intensity and the fumaroles were generally issuing steam only. Some of the fumaroles were temporarily buried following a rockfall within the scar on 20 August. The fumarolic activity declined steadily, and by 22 August activity had declined to levels observed in the first week of August.

Mudflows continued to be a problem in July. Mudflow deposits built up beneath the Belham Bridge until there was a clearance of only about 30 cm.

Seismicity. After 5 July, seismicity returned to levels similar to the previous month, with the exception of a swarm of volcano-tectonic earthquakes on 25 July (figure 43). This swarm had no outward manifestation at the volcano and activity returned to low levels by the next day.

Figure (see Caption) Figure 43. Seismicity recorded at Soufriere Hills by type during July and August 1998. Data courtesy of MVO.

Seismicity during August was generally low. Activity was dominated by small volcano-tectonic earthquakes located ~3 km below the dome, with occasional rockfalls and pyroclastic-flow signals. On 13 August there were two episodes (at 0519 and 1455) of pyroclastic flow in the White River valley. These flows traveled 1.8 km from the dome and were caused by the collapse of weakened dome rock. Active fumaroles on the Galways side of the dome near Chances Peak undermined part of the dome. A scar immediately above the fumarolic area is believed to be the source of the pyroclastic flows. Each episode was followed by about an hour of continuous rockfall activity. On 19 August a rockfall signal was followed by tremor, which corresponded to vigorous ash venting. The signal lasted two days and varied in amplitude. At times of highest amplitude the tremor was nearly monochromatic at 4 Hz.

Ground deformation. Measurements from GPS survey sites on the flanks of the volcano and in the N of the island indicated widespread major reductions in movement during July. The Hermitage site indicated continued slow movement NE at rate of ~0.5 cm/month. The GPS site at Perches was destroyed in the 3 July event; ballistics were scattered over Perches Mountain and the GPS site was later found at the edge of a 3.4 m diameter impact crater. The rates of movement of sites in August were within the instrumental error. The GPS kit was used for one week by volcanologists from the University of Rhode Island who were conducting a bathymetric survey of the fans at the mouths of the Tar River and White Rivers valleys.

The EDM reflector on Peak B was measured from Windy Hill. The increase in distance of 5 cm during the period May-July may have been caused partially by release associated with the 3 July collapse. The line had shortened by 9 cm between 25 January and 13 May, but between May and August the distance lengthened by a total 8 cm (within 1 cm of its original length) possibly indicating a relaxation in the confining pressure.

Volume measurements. A kinematic GPS survey of the Tar River fan was completed in July. The total volume of the fan was estimated to be 22.1 x 106 m3. A previous survey in August 1997 gave a volume of 15.7 x 106 m3. Much of the increase resulted from the 3 July collapse, which extended the fan 350 m N, although a small part of the increase was due to the accumulation of pyroclastic-flow deposits during the September-October 1997 explosion sequence (BGVN 22:10 and 22:11). The E limit of the fan, defined by a steep shelf extending into the sea, was unchanged. A small deposit was left on the S side of the fan, although above the established shoreline there was only a thin layer of pyroclastic-flow deposits.

No volume measurements were made in August. Attempts to survey the 3 July collapse scar were foiled by deteriorating weather conditions and a lack of helicopter fuel.

Environmental monitoring. MiniCOSPEC observations recommenced on 5 July. In early July SO2 flux was generally between 1,000 and 2,500 metric tons/day (t/d). On 13 July SO2 flux measured 4,150 t/d, the highest ever recorded at Montserrat. Throughout the remainder of July there was a gradual decline in SO2 flux to an average of 1,000 t/d at the end of the month. The cause of the relatively high gas flux in the apparent absence of magmatic activity was being investigated, but may relate to perturbations in the hydrothermal system caused by the dome collapse on 3 July 1998.

MiniCOSPEC measurements in early August showed a consistent SO2 flux of ~500-1000 t/d. On 19 August levels rose to 1,400 t/d as a result of enhanced venting. Towards the end of the month poor weather limited the number of COSPEC measurements, but there appeared to be a slight decrease to an average of ~500 t/d. Throughout late August the wind direction was variable due to tropical storms in the area. On occasions when the wind blew to the N or NW a strong smell of sulfurous gases was detected in the inhabited area of Montserrat.

Sulfur dioxide diffusion tubes exposed between 29 June and 13 July clearly reflect the high emissions in early July (table 31). The Plymouth area in particular was subjected to very high concentrations of gas. In the second half of July SO2 concentrations in Plymouth were reduced by half. Populated areas N of the Belham River valley were, as usual, only subjected to very low SO2 levels in July. In August there was a general decline of SO2 in the atmosphere. An additional monitoring site in the N of the island was installed to assess SO2 during shifts in wind direction.

Table 31. Sulfur dioxide diffusion-tube results, 29 June-11 August 1998. Levels are in parts per billion (ppb). Courtesy of MVO.

Station 29 Jun-13 Jul 1998 13 Jul-27 Jul 1998 27 Jul-11 Aug 1998
Police HQ, Plymouth 207.9 116.5 131.5
St. George's Hill 22.05 8.55 9.55
Weekes 5.75 4.1 2.85
MVO south 4.3 3.85 --
Lawyers 2.2 0 3.8
Vue Pointe Hotel -- -- 3.25

Hazard assessment. A meeting was held 14-16 July at McChesney's Estate to assess the current hazards and risks associated with Soufriere Hills Volcano. The meeting brought together many of the senior scientists who have worked at MVO during the three-year volcanic crisis. Those who took part were Richie Robertson, Lloyd Lynch and John Shepherd from the Seismic Research Unit in Trinidad; Simon Young, Sue Loughlin, Tony Reedman, and Gill Norton from the British Geological Survey; and many other senior scientists from around the world including Steve Sparks from Bristol University, Peter Baxter from Cambridge University, Barry Voight from Penn State University, Joe Devine from Brown University, Peter Francis from the Open University, Keith Rowley, and Willy Aspinall. Richard Luckett and Richard Herd from MVO provided up-to-date information about the current status of Soufriere Hills volcano.

Discussion was held on various aspects of the activity over the previous six months, including the event on 3 July. Related issues, including the safety of Bramble airport, were also addressed. An assessment of the level of risk associated with the volcano was undertaken. A report was presented to the government of Montserrat and the U.K. on 29 July after which the findings were made public.

According to the report, MVO judged it likely that the volcano has entered a period of repose, with the probability of no further magmatic eruptions in the next 6 months set at about 95%. MVO was confident that renewed magma ascent and escalation to dangerous levels of activity could be identified, although they cautioned that escalation might take place in a very short period of time (e.g. a matter of hours). Most of the island was perceived to be under reduced risk, but areas S of the Belham River Valley remain vulnerable to serious volcanic hazards including pyroclastic flows related to the collapse of the dome, mud flows, and exposure to fine ash. Further dome collapses were deemed likely and could affect all flanks of the volcano, especially the Tar River, Gages Valley, Plymouth area, Galways, and the NE slopes. There is potential for a variety of events to take place, including steam explosions, mud flows, and ash falls, for many years to come but the risks will decline with time. Health risk analysis showed that if magmatic activity does not resume, the potential for harmful exposure to ash will be limited and the risk of developing silicosis will be low in Zones 1 to 3. The same would apply to Population Zone 4 north of the Belham Valley after a clean-up operation has been safely completed. A public education program on the health risks of ash was recommended, including guidance on protection measures during the clean up. Certain groups could be at risk from much higher exposure (e.g. outdoor workers and asthma sufferers) and there may be unknown long-term health risks to young children.

The Volcanic Executive Group (VEG), chaired by Governor Tony Abbott, met to consider the Scientific Review. A statement from the Governor's Office following the meeting rescinded the recommendation that residents leave the Central Zone. Also, there was no longer any objection to commercial organizations operating within the Central Zone. The clean up of Friths, Salem, and Old Towne, which commenced some weeks ago, was intensified. The VEG sought advice on how to ensure that the Zone will be cleaned so that children and those with respiratory problems will not be affected on reoccupation.

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), c/o Chief Minister's Office, PO Box 292, Plymouth, Montserrat, West Indies (URL: http://www.mvo.ms/); Richard Aspin, Information & Education Unit, Emergency Dept., St Johns Village, Montserrat, Leeward Islands, West Indies.


Yasur (Vanuatu) — September 1998 Citation iconCite this Report

Yasur

Vanuatu

19.532°S, 169.447°E; summit elev. 361 m

All times are local (unless otherwise noted)


Ongoing eruption, felt earthquake, and fresh glass chemical analysis

On 9 September 1998, an earthquake was felt in a village 3 km from Yasur; simultaneously, loud explosions were heard from the volcano. When the summit was visited by John Seach during 10-11 September, five craters inside the main summit crater in the pyroclastic cone were found to be active. Crater A, large and on the S, displayed quiet explosions followed by brown ash emission. Other craters were quiet with only gas emissions. These included the smaller Crater B, in the center of the main crater; the larger Crater C, on the N; the small Crater D located W of Crater B; and Crater E, on the SW wall of the main crater.

During 4 hours of observation on 10 September, 51 explosions were observed from four craters: Crater A, 25 explosions; Crater B, 9; Crater C, 13; and Crater D, 4. Bombs thrown from Craters B, C, and D fell back into the vent or onto the crater wall. Some larger explosions, every 20-30 minutes, threw bombs 350 m high. During the night, bombs thrown onto the crater wall glowed for up to 6 minutes. The explosions and shaking were felt up to 3 km away.

A fresh bomb collected in August 1997 (BGVN 22:08) was recently analyzed by microprobe (table 1).

Table 1. Major element analysis of Yasur glass taken from an average of five analyses on fresh glass bomb collected in August 1997. All iron is shown as FeO. Microprobe analysis courtesy of Timothy O'Hearn; sample courtesy of Steve and Donna O'Meara, and Robert Benward.

Component Weight %
SiO2 58.61
TiO2 0.95
Al203 15.07
FeOt 8.68
MnO 0.25
MgO 2.49
CaO 5.44
Na2O 3.52
K2O 3.78
P2O5 0.66
Total 99.46

Geologic Background. Yasur, the best-known and most frequently visited of the Vanuatu volcanoes, has been in more-or-less continuous Strombolian and Vulcanian activity since Captain Cook observed ash eruptions in 1774. This style of activity may have continued for the past 800 years. Located at the SE tip of Tanna Island, this mostly unvegetated pyroclastic cone has a nearly circular, 400-m-wide summit crater. The active cone is largely contained within the small Yenkahe caldera, and is the youngest of a group of Holocene volcanic centers constructed over the down-dropped NE flank of the Pleistocene Tukosmeru volcano. The Yenkahe horst is located within the Siwi ring fracture, a 4-km-wide, horseshoe-shaped caldera associated with eruption of the andesitic Siwi pyroclastic sequence. Active tectonism along the Yenkahe horst accompanying eruptions has raised Port Resolution harbor more than 20 m during the past century.

Information Contacts: John Seach, P.O. Box 16, Chatsworth Island, N.S.W. 2469, Australia; Tim O'Hearn, Department of Mineral Sciences, Smithsonian Institution, Washington, DC 20560-0119 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  Obituaries

Misc 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 subject.

Additional Reports  False Reports