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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

Nevados de Chillan (Chile) Explosions and pyroclastic flows continue; new dome emerges from Nicanor crater in June 2020

Bagana (Papua New Guinea) Ash plumes during 29 February-2 March and 1 May 2020

Kerinci (Indonesia) Intermittent ash emissions during January-early May 2020

Tinakula (Solomon Islands) Intermittent small thermal anomalies and gas-and-steam plumes during January-June 2020

Ibu (Indonesia) Frequent ash emissions and summit incandescence; Strombolian explosions in March 2020

Suwanosejima (Japan) Frequent explosions, ash plumes, and summit incandescence in January-June 2020

Kadovar (Papua New Guinea) Intermittent ash plumes and persistent summit thermal anomalies, January-June 2020

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

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

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

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



Nevados de Chillan (Chile) — May 2020 Citation iconCite this Report

Nevados de Chillan

Chile

36.868°S, 71.378°W; summit elev. 3180 m

All times are local (unless otherwise noted)


Explosions and pyroclastic flows continue; new dome emerges from Nicanor crater in June 2020

Nevados de Chillán is a complex of late-Pleistocene to Holocene stratovolcanoes in the Chilean Central Andes. An eruption started with a phreatic explosion and ash emission on 8 January 2016 from a new crater (Nicanor) on the E flank of the Nuevo crater, itself on the NW flank of the large Volcán Viejo stratovolcano. Strombolian explosions and ash emissions continued throughout 2016 and 2017; a lava dome within the Nicanor crater was confirmed in early January 2018. Explosions and pyroclastic flows continued during 2018 and 2019, with several lava flows appearing in late 2019. This report covers continuing activity from January-June 2020 when ongoing explosive events produced ash plumes, pyroclastic flows, and the growth of new dome inside the crater. Information for this report is provided primarily by Chile's Servicio Nacional de Geología y Minería (SERNAGEOMIN)-Observatorio Volcanológico de Los Andes del Sur (OVDAS), and by the Buenos Aires Volcanic Ash Advisory Center (VAAC).

Explosions with ash plumes rising up to three kilometers above the summit area were intermittent from late January through early June 2020. Some of the larger explosions produced pyroclastic flows that traveled down multiple flanks. Thermal anomalies within the Nicanor crater were recorded in satellite data several times each month from February through June. A reduction in overall activity led SERNAGEOMIN to lower the Alert Level from Orange to Yellow (on a 4-level, Green-Yellow-Orange-Red scale) during the first week of March, although tens of explosions with ash plumes were still recorded during March and April. Explosive activity diminished in early June and SERNAGEOMIN reported the growth of a new dome inside the Nicanor crater. By the end of June, a new flow had extended about 100 m down the N flank. Thermal activity recorded by the MIROVA project showed a drop in thermal energy in mid-December 2019 after the lava flows of September-November stopped advancing. A decrease in activity in January and February 2020 was followed by an increase in thermal and explosive activity in March and April. Renewed thermal activity from the growth of a new dome inside the Nicanor crater was recorded beginning in mid-June (figure 52).

Figure (see Caption) Figure 52. MIROVA thermal anomaly data for Nevados de Chillan from 8 September 2019 through June 2020 showed a drop in thermal activity in mid-December 2019 after the lava flows of September-November stopped advancing. A decrease in activity in January and February 2020 was followed by an increase in explosive activity in March and April. Renewed thermal activity from the growth of a new dome inside the Nicanor crater was recorded beginning in mid-June. Courtesy of MIROVA.

Weak gas emissions were reported daily during January 2020 until a series of explosions began on the 21st. The first explosion rose 100 m above the active crater; the following day, the highest explosion rose 1.6 km above the crater. The Buenos Aires VAAC reported pulse emissions visible in satellite imagery on 21 and 24 January that rose to 3.9-4.3 km altitude and drifted SE and NE, respectively. Intermittent explosions continued through 26 January. Incandescent ejecta was observed during the night of 28-29 January. The VAAC reported an isolated emission on 29 January that rose to 5.2 km altitude and drifted E. A larger explosion on 30 January produced an ash plume that SERNAGEOMIN reported at 3.4 km above the crater (figure 53). It produced pyroclastic flows that traveled down ravines on the NNE and SE flanks. The Washington VAAC reported on behalf of the Buenos Aires VAAC that an emission was observed in satellite imagery on 30 January that rose to 4.9 km altitude and was moving rapidly E, reaching 15 km from the summit at midday. The altitude of the ash plume was revised two hours later to 7.3 km, drifting NNE and rapidly dissipating. Satellite images identified two areas of thermal anomalies within the Nicanor crater that day. One was the same emission center (CE4) identified in November 2019, and the second was a new emission center (CE5) located 60 m NW.

Figure (see Caption) Figure 53. A significant explosion and ash plume from the Nicanor crater at Nevados de Chillan on 30 January 2020 produced an ash plume reported at 7.3 km altitude. The left image was taken within one minute of the initial explosion. Images posted by Twitter accounts #EmergenciasÑuble (left) and T13 (right); original photographers unknown.

When the weather permitted, low-altitude mostly white degassing was seen during February 2020, often with traces of fine-grained particulate material. Incandescence at the crater was observed overnight during 4-5 February. The Buenos Aires VAAC reported an emission on 14 February visible in the webcam. The next day, an emission was visible in satellite imagery at 3.9 km altitude that drifted E. Episodes of pulsating white and gray plumes were first observed by SERNAGEOMIN beginning on 18 February and continued through 25 February (figure 54). The Buenos Aires VAAC reported pulses of ash emissions moving SE on 18 February at 4.3 km altitude. Ash drifted E the next day at 3.9 km altitude and a faint plume was briefly observed on 20 February drifting N at 3.7 km altitude before dissipating. Sporadic pulses of ash moved SE from the volcano on 22 February at 4.3 km altitude, briefly observed in satellite imagery before dissipating. Thermal anomalies were visible from the Nicanor crater in Sentinel-2 satellite imagery on 23 and 28 February.

Figure (see Caption) Figure 54. An ash emission at Nevados de Chillan on 18 February 2020 was captured in Sentinel-2 satellite imagery drifting SE (left). Thermal anomalies within the Nicanor crater were measured on 23 (right) and 28 February. Images use Atmospheric penetration rendering (bands 12, 11, 8a); courtesy of Sentinel Hub Playground.

Only low-altitude degassing of mostly steam was reported for the first half of March 2020. When SERNAGEOMIN lowered the Alert Level from Orange to Yellow on 5 March, they reduced the affected area from 5 km NE and 3 km SW of the crater to a radius of 2 km around the active crater. Thermal anomalies were recorded at the Nicanor crater in Sentinel-2 imagery on 4, 9, 11, 16, and 19 March (figure 55). A new series of explosions began on 19 March; 44 events were recorded during the second half of the month (figure 56). Webcams captured multiple explosions with dense ash plumes; on 25 and 30 March the plumes rose more than 2 km above the crater. Fine-grained ashfall occurred in Las Trancas (10 km SW) on 25 March. Pyroclastic flows on 25 and 30 March traveled 300 m NE, SE, and SW from the crater. Incandescence was observed at night multiple times after 20 March. The Buenos Aires VAAC reported several discrete pulses of ash that rose to 4.3 km altitude and drifted SE on 20 and 21 March, SW on 25 March, and SE on 29 and 30 March. Another ash emission rose to 5.5 km altitude later on 30 March and drifted SE.

Figure (see Caption) Figure 55. Sentinel-2 Satellite imagery of Nevados de Chillan during March 2020 showed thermal anomalies on five different dates at the Nicanor crater, including on 9, 11, and 16 March. A second thermal anomaly of unknown origin was also visible on 11 March about 2 km SW of the crater (center). Images use Atmospheric penetration rendering (bands 12, 11, 8a); courtesy of Sentinel Hub Playground.
Figure (see Caption) Figure 56. Forty-four explosive events were recorded at Nevados de Chillan during the second half of March 2020 including on 19 March. Courtesy of SERNAGEOMIN webcams and chillanonlinenoticia.

In their semi-monthly reports for April 2020, SERNAGEOMIN reported 94 explosive events during the first half of the month and 49 during the second half; many produced dense ash plumes. The Buenos Aires VAAC reported frequent intermittent ash emissions during 1-13 April reaching altitudes of 3.7-4.3 km (figure 57). They reported the plume on 8 April visible in satellite imagery at 7.3 km altitude drifting SE. An emission on 13 April was also visible in satellite imagery at 6.1 km altitude drifting NE.

Figure (see Caption) Figure 57. Sentinel-2 satellite imagery captured a strong thermal anomaly and an ash plume drifting SE from Nevados de Chillan on 10 April 2020. Image uses Atmospheric penetration rendering (bands 12, 11, 8a); courtesy of Sentinel Hub Playground.

During the second half of April 2020, SERNAGEOMIN reported that only one plume exceeded 2 km in height; on 21 April, it rose to 2.4 km above the crater (figure 58). The Buenos Aires VAAC reported isolated pulses of ash on 18, 26, 28, and 30 April. During the second half of April SERNAGEOMIN also reported that a pyroclastic flow traveled about 1,200 m from the crater rim down the SE flank. The ash from the pyroclastic flow drifted SE and S as far as 3.5 km. Satellite images showed continued activity from multiple emission centers around the crater. Pronounced scarps were noted on the internal walls of the crater, attributed to the deepening of the crater from explosive activity.

Figure (see Caption) Figure 58. Tens of explosions were reported at Nevados de Chillan during the second half of April 2020 that produced dense ash plumes. The plume on 21 April rose 2.4 km above the Nicanor crater. Photo by Josefa Carrasco Acuña from San Fabián de Alico; posted by Noticias Valpo Express.

Intermittent explosive activity continued during May 2020. The plumes contained abundant particulate material and were accompanied by periodic pyroclastic flows and incandescent ejecta around the active crater, especially visible at night. The Buenos Aires VAAC reported several sporadic weak ash emissions during the first week of May that rose to 3.7-5.2 km altitude and drifted NE. SERNAGEOMIN reported that only one explosion produced an ash emission that rose more than two km above the crater during the first two weeks of the month; on 6 May it rose to 2.5 km above the crater and drifted NE. They also observed pyroclastic flows on the E and SE flanks that day. Additional pyroclastic flows traveled 450 m down the S flank during the first half of the month, and similar deposits were observed to the N and NE. Satellite observations showed various emission points along the NW-trending lineament at the summit and multiple erosion scarps. Major erosion was noted at the NE rim of the crater along with an increase in degassing around the rim.

During the second half of May 2020 most of the ash plumes rose less than 2 km above the crater; a plume from one explosion on 22 May rose 2.2 km above the crater; the Buenos Aires VAAC reported the plume at 5.5 km altitude drifting NW (figure 59). Continuing pyroclastic emissions deposited material as far as 1.5 km from the crater rim on the NNW flank. There were also multiple pyroclastic deposits up to 500 m from the crater directed N and NE during the period. SERNAGEOMIN reported an increase in steam degassing between Nuevo-Nicanor and Nicanor-Arrau craters.

Figure (see Caption) Figure 59. Explosions produced dense ash plumes and pyroclastic flows at Nevados de Chillan multiple times during May 2020 including on 22 May. Courtesy of SERNAGEOMIN.

Webcam images during the first two weeks of June 2020 indicated multiple incandescent explosions. On 3 and 4 June plumes from explosions reached heights of over 1.25 km above the crater; the Buenos Aires VAAC reported them drifting NW at 3.9 km altitude. Incandescent ejecta on 6 June rose 760 m above the vent and drifted NE. In addition, pyroclastic flows were distributed on the N, NW, E and SE flanks. Significant daytime and nighttime incandescence was reported on 6, 9, and 10 June (figure 60). The VAAC reported emission pulses on 6 and 9 June drifting E and SE at 4.3 km altitude.

Figure (see Caption) Figure 60. Multiple ash plumes with incandescence were reported at Nevados de Chillan during the first ten days of June 2020 including on 6 June, after which explosive activity decreased significantly. Courtesy of SERNAGEOMIIN and Sismo Alerta Mexicana.

SERNAGEOMIN reported that beginning on the afternoon of 9 June 2020 a tremor-type seismic signal was first recorded, associated with continuous emission of gas and dark gray ash that drifted SE (figure 61). A little over an hour later another tremor signal began that lasted for about four hours, followed by smaller discrete explosions. A hybrid-type earthquake in the early morning of 10 June was followed by a series of explosions that ejected gas and particulate matter from the active crater. The vent where the emissions occurred was located within the Nicanor crater close to the Arrau crater; it had been degassing since 30 May.

Figure (see Caption) Figure 61. A tremor-type seismic signal was first recorded on the afternoon of 9 June 2020 at Nevados de Chillan. It was associated with the continuous emission of gas and dark gray ash that drifted SE, and incandescent ejecta visible after dark. View is to the S, courtesy of SERNAGEOMIN webcam, posted by Volcanology Chile.

After the explosions on the afternoon of 9 June, a number of other nearby vents became active. In particular, the vent located between the Nuevo and Nicanor craters began emitting material for the first time during this eruptive cycle. The explosion also generated pyroclastic flows that traveled less than 50 m in multiple directions away from the vent. Abundant incandescent material was reported during the explosion early on 10 June. Deformation measurements showed inflation over the previous 12 days.

SERNAGEOMIN identified a surface feature in satellite imagery on 11 June 2020 that they interpreted as a new effusive lava dome. It was elliptical with dimensions of about 85 x 120 m. In addition to a thermal anomaly attributed to the dome, they noted three other thermal anomalies between the Nuevo, Arrau, and Nicanor craters. They reported that within four days the base of the active crater was filled with effusive material. Seismometers recorded tremor activity after 11 June that was interpreted as associated with lava effusion. Incandescent emissions were visible at night around the active crater. Sentinel-2 satellite imagery recorded a bright thermal anomaly inside the Nicanor crater on 14 June (figure 62).

Figure (see Caption) Figure 62. A bright thermal anomaly was recorded inside the Nicanor crater at Nevados de Chillan on 14 June 2020. SERNAGEOMIN scientists attributed it to the growth of a new lava dome within the crater. Image uses Atmospheric penetration rendering (bands 12, 11, 8a); courtesy of Sentinel Hub Playground.

A special report from SERNAGEOMIN on 24 June 2020 noted that vertical inflation had increased during the previous few weeks. After 20 June the inflation rate reached 2.49 cm/month, which was considered high. The accumulated inflation measured since July 2019 was 22.5 cm. Satellite imagery continued to show the growth of the dome, and SERNAGEOMIN scientists estimated that it reached the E edge of the Nicanor crater on 23 June. Based on these images, they estimated an eruptive rate of 0.1-0.3 m3/s, about two orders of magnitude faster than the Gil-Cruz dome that emerged between December 2018 and early 2019.

Webcams revealed continued low-level explosive activity and incandescence visible both during the day and at night. By the end of June, webcams recorded a lava flow that extended 94 m down the N flank from the Nicanor crater and continued to advance. Small explosions with abundant pyroclastic debris produced recurring incandescence at night. Satellite infrared imagery indicated thermal radiance from effusive material that covered an area of 37,000 m2, largely filling the crater. DEM analysis suggested that the size of the crater had tripled in volume since December 2019 due largely to erosion from explosive activity since May 2020. Sentinel-2 satellite imagery showed a bright thermal anomaly inside the crater on 27 June.

Geologic Background. The compound volcano of Nevados de Chillán is one of the most active of the Central Andes. Three late-Pleistocene to Holocene stratovolcanoes were constructed along a NNW-SSE line within three nested Pleistocene calderas, which produced ignimbrite sheets extending more than 100 km into the Central Depression of Chile. The largest stratovolcano, dominantly andesitic, Cerro Blanco (Volcán Nevado), is located at the NW end of the group. Volcán Viejo (Volcán Chillán), which was the main active vent during the 17th-19th centuries, occupies the SE end. The new Volcán Nuevo lava-dome complex formed between 1906 and 1945 between the two volcanoes and grew to exceed Volcán Viejo in elevation. The Volcán Arrau dome complex was constructed SE of Volcán Nuevo between 1973 and 1986 and eventually exceeded its height.

Information Contacts: Servicio Nacional de Geología y Minería (SERNAGEOMIN), Observatorio Volcanológico de Los Andes del Sur (OVDAS), Avda Sta María No. 0104, Santiago, Chile (URL: http://www.sernageomin.cl/, https://twitter.com/Sernageomin); 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/); Buenos Aires Volcanic Ash Advisory Center (VAAC), Servicio Meteorológico Nacional-Fuerza Aérea Argentina, 25 de mayo 658, Buenos Aires, Argentina (URL: http://www.smn.gov.ar/vaac/buenosaires/inicio.php); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); #EmergenciasÑuble (URL: https://twitter.com/urgenciasnuble/status/1222943399185207296); T13, Channel 13 Press Department (URL: https://twitter.com/T13/status/1222951071443771394); Chillanonlinenoticia (URL: https://twitter.com/ChillanOnline/status/1240754211932995595); Noticias Valpo Express (URL: https://twitter.com/NoticiasValpoEx/status/1252715033131388928); Sismo Alerta Mexicana (URL: https://twitter.com/Sismoalertamex/status/1269351579095691265); Volcanology Chile (URL: https://twitter.com/volcanologiachl/status/1270548008191643651).


Bagana (Papua New Guinea) — July 2020 Citation iconCite this Report

Bagana

Papua New Guinea

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

All times are local (unless otherwise noted)


Ash plumes during 29 February-2 March and 1 May 2020

Bagana lies in a nearly inaccessible mountainous tropical rainforest area of Bougainville Island in Papua New Guinea and is primarily monitored by satellite imagery of ash plumes and thermal anomalies. After a state of elevated activity that lasted through December 2018 (BGVN 43:05, 44:06, 44:12), the volcano entered a quieter period that persisted through at least May 2020. This report focuses on activity between December 2019 and May 2020.

Atmospheric clouds often obscured satellite views of the volcano during the reporting period. When the volcano could be observed, light-colored gas plumes were often observed (figure 43). Based on satellite and wind model data, the Darwin Volcanic Ash Advisory Centre (VAAC) reported that during 29 February-2 March ash plumes rose to an altitude of 1.8-2.1 km and drifted SW and N. On 1 May an ash plume rose to an altitude of 3 km and drifted NW and W. According to both Darwin VAAC volcanic ash advisories, the Aviation Color Code was Orange (second highest of four hazard levels).

Figure (see Caption) Figure 43. Sentinel-2 image of Bagana, showing a gas plume drifting SE on 13 March 2020, during a period when the Darwin VAAC had not reported any ash explosions (Natural Color rendering, bands 4, 3, 2). Courtesy of Sentinel Hub Playground.

During the reporting period, the MIROVA (Middle InfraRed Observation of Volcanic Activity) volcano hotspot detection system recorded only intermittent thermal anomalies, all of which were of low radiative power. Sulfur dioxide emissions detected by satellite-based instruments over this reporting period were at low levels.

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

Information Contacts: Darwin Volcanic Ash Advisory Centre (VAAC), Bureau of Meteorology, Northern Territory Regional Office, PO Box 40050, Casuarina, NT 0811, Australia (URL: http://www.bom.gov.au/info/vaac/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); 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/).


Kerinci (Indonesia) — July 2020 Citation iconCite this Report

Kerinci

Indonesia

1.697°S, 101.264°E; summit elev. 3800 m

All times are local (unless otherwise noted)


Intermittent ash emissions during January-early May 2020

Kerinci is a stratovolcano located in Sumatra, Indonesia that has been characterized by explosive eruptions with ash plumes and gas-and-steam emissions. The most recent eruptive episode began in April 2018 which has included intermittent explosions and ash plumes. The previous report (BGVN 44:12) described more recent activity consisting of intermittent gas-and-steam and ash plumes which occurred during June through early November 2019. This volcanism continued through May 2020, though little to no activity was reported during December 2019. The primary source of information for this report comes from Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM) and the Darwin Volcanic Ash Advisory Centre (VAAC).

Activity during December 2019 consisted of white gas-and-steam emissions rising 100-500 m above the summit. White and brown emissions continued intermittently through May 2020, rising to a maximum altitude of 1 km above the summit on 14 April. During 3-6 and 8-9 January 2020, the Darwin VAAC and PVMBG issued notices reporting brown volcanic ash rising 150-600 m above the summit drifting S and ESE (figure 19). PVMBG published a VONA notice on 24 January at 0828 reporting ash rising 400 m above the summit. Brown emissions continued intermittently throughout the reporting period. On 1 February, volcanic ash was observed rising 300-960 m above the summit and drifting NE; PVMBG reported continuing brown emissions during 1-3 February. During 16-17 February, two VONA notices reported that brown ash plumes rose 150-400 m above the summit and drifted SW accompanied by consistent white gas-and-steam emissions (figure 20).

Figure (see Caption) Figure 19. Brown ash plume rose 500-600 m above Kerinci on 4 January 2020. Courtesy of MAGMA Indonesia via Øystein Lund Andersen.
Figure (see Caption) Figure 20. White gas-and-steam emissions rose 400 m above Kerinci on 19 February 2020. Courtesy of MAGMA Indonesia via Øystein Lund Andersen.

During 1-16 and 25-26 March 2020 brown ash emissions were frequently observed rising 100-500 m above the summit drifting in multiple directions. During 6-8 and 10-15, April brown ash emissions were reported 50-1,000 m above the summit. The most recent Darwin VAAC and VONA notices were published on 14 April, reporting volcanic ash rising 400 and 600 m above the summit, respectively; however, PVMBG reported brown emissions rising up to 1,000 m. By 25-27 April brown ash emissions rose 50-300 m above the summit. Intermittent white gas-and-steam emissions continued through May. The last brown emissions seen in May were reported on the 7th rising 50-100 m above the summit.

Geologic Background. Gunung Kerinci in central Sumatra forms Indonesia's highest volcano and is one of the most active in Sumatra. It is capped by an unvegetated young summit cone that was constructed NE of an older crater remnant. There is a deep 600-m-wide summit crater often partially filled by a small crater lake that lies on the NE crater floor, opposite the SW-rim summit. The massive 13 x 25 km wide volcano towers 2400-3300 m above surrounding plains and is elongated in a N-S direction. Frequently active, Kerinci has been the source of numerous moderate explosive eruptions since its first recorded eruption in 1838.

Information Contacts: Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM), Jalan Diponegoro 57, Bandung 40122, Indonesia (URL: http://www.vsi.esdm.go.id/); Darwin Volcanic Ash Advisory Centre (VAAC), Bureau of Meteorology, Northern Territory Regional Office, PO Box 40050, Casuarina, NT 0811, Australia (URL: http://www.bom.gov.au/info/vaac/); MAGMA Indonesia, Kementerian Energi dan Sumber Daya Mineral (URL: https://magma.vsi.esdm.go.id/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); Øystein Lund Andersen (Twitter: @OysteinLAnderse, https://twitter.com/OysteinLAnderse, URL: http://www.oysteinlundandersen.com, images at https://twitter.com/OysteinLAnderse/status/1213658331564269569/photo/1 and https://twitter.com/OysteinLAnderse/status/1230419965209018369/photo/1).


Tinakula (Solomon Islands) — July 2020 Citation iconCite this Report

Tinakula

Solomon Islands

10.386°S, 165.804°E; summit elev. 796 m

All times are local (unless otherwise noted)


Intermittent small thermal anomalies and gas-and-steam plumes during January-June 2020

Tinakula is a remote stratovolcano located 100 km NE of the Solomon Trench at the N end of the Santa Cruz. In 1971, an eruption with lava flows and ash explosions caused the small population to evacuate the island. Volcanism has previously been characterized by an ash explosion in October 2017 and the most recent eruptive period that began in December 2018 with renewed thermal activity. Activity since then has consisted of intermittent thermal activity and dense gas-and-steam plumes (BGVN 45:01), which continues into the current reporting period. This report updates information from January-June 2020 using primary source information from various satellite data, as ground observations are rarely available.

MIROVA (Middle InfraRed Observation of Volcanic Activity) analysis of MODIS satellite data showed weak, intermittent, but ongoing thermal activity during January-June 2020 (figure 41). A small cluster of slightly stronger thermal signatures was detected in late February to early March, which is correlated to MODVOLC thermal alert data; four thermal hotspots were recorded on 20, 27, and 29 February and 1 March. However, observations using Sentinel-2 satellite imagery were often obscured by clouds. In addition to the weak thermal signatures, dense gas-and-steam plumes were observed in Sentinel-2 satellite imagery rising from the summit during this reporting period (figure 42).

Figure (see Caption) Figure 41. Weak thermal anomalies at Tinakula from 26 June 2019 through June 2020 as recorded by the MIROVA system (Log Radiative Power) were intermittent and clustered more strongly in late February to early March.
Figure (see Caption) Figure 42. Sentinel-2 satellite imagery shows ongoing gas-and-steam plumes rising from Tinakula during January through May 2020. Images with atmospheric penetration (bands 12, 11, 8a) rendering; courtesy of Sentinel Hub Playground.

Three distinct thermal anomalies were observed in Sentinel-2 thermal satellite imagery on 22 January, 11 April, and 6 May 2020, accompanied by some gas-and-steam emissions (figure 43). The hotspot on 22 January was slightly weaker than the other two days, and was seen on the W flank, compared to the other two that were observed in the summit crater. According to MODVOLC thermal alerts, a hotspot was recorded on 6 May, which corresponded to a Sentinel-2 thermal satellite image with a notable anomaly in the summit crater (figure 43). On 10 June no thermal anomaly was seen in Sentinel-2 satellite imagery due to the presence of clouds; however, what appeared to be a dense gas-and-steam plume was extending W from the summit.

Figure (see Caption) Figure 43. Sentinel-2 thermal satellite images showing a weak thermal activity (bright yellow-orange) on 22 January 2020 on the W flank of Tinakula (top) and slightly stronger thermal hotspots on 11 April (middle) and 6 May (bottom) in at the summit, which are accompanied by gas-and-steam emissions. Images with atmospheric penetration (bands 12, 11, 8a) rendering; courtesy of Sentinel Hub Playground.

Geologic Background. The small 3.5-km-wide island of Tinakula is the exposed summit of a massive stratovolcano at the NW end of the Santa Cruz islands. Similar to Stromboli, it has a breached summit crater that extends from the summit to below sea level. Landslides enlarged this scarp in 1965, creating an embayment on the NW coast. The satellitic cone of Mendana is located on the SE side. The dominantly andesitic volcano has frequently been observed in eruption since the era of Spanish exploration began in 1595. In about 1840, an explosive eruption apparently produced pyroclastic flows that swept all sides of the island, killing its inhabitants. Frequent historical eruptions have originated from a cone constructed within the large breached crater. These have left the upper flanks and the steep apron of lava flows and volcaniclastic debris within the breach unvegetated.

Information Contacts: 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).


Ibu (Indonesia) — July 2020 Citation iconCite this Report

Ibu

Indonesia

1.488°N, 127.63°E; summit elev. 1325 m

All times are local (unless otherwise noted)


Frequent ash emissions and summit incandescence; Strombolian explosions in March 2020

Ibu is an active stratovolcano located along the NW coast of Halmahera Island in Indonesia. Volcanism has recently been characterized by frequent ash explosions, ash plumes, and small lava flows within the crater throughout 2019 (BGVN 45:01). Activity continues, consisting of frequent white-and-gray emissions, ash explosions, ash plumes, and lava flows. This report updates activity through June 2020, using data from the Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM), Darwin Volcanic Ash Advisory Centre (VAAC), and various satellites.

Volcanism during the entire reporting period dominantly consisted of white-and-gray emissions that rose 200-800 m above the summit drifting in multiple directions. The ash plume with the maximum altitude of 13.7 km altitude occurred on 16 May 2020. Sentinel-2 thermal satellite imagery detected multiple smaller hotspots within the crater throughout the reporting period.

Continuous ash emissions were reported on 6 February rising to 2.1 km altitude drifting E, accompanied by a hotspot visible in infrared satellite imagery. On 16 February, a ground observer reported an eruption that produced an ash plume rising 800 m above the summit drifting W, according to a Darwin VAAC notice. Ash plumes continued through the month, drifting in multiple directions and rising up to 2.1 km altitude. During 8-10 March, video footage captured multiple Strombolian explosions that ejected incandescent material and produced ash plumes from the summit (figures 21 and 22). Occasionally volcanic lightning was observed within the ash column, as recorded in video footage by Martin Rietze. This event was also documented by a Darwin VAAC notice, which stated that multiple ash emissions rose 2.1 km altitude drifting SE. PVMBG published a VONA notice on 10 March at 1044 reporting ash plumes rising 400 m above the summit. PVMBG and Darwin VAAC notices described intermittent eruptions on 26, 28, and 29 March, all of which produced ash plumes rising 300-800 m above the summit.

Figure (see Caption) Figure 21. Strombolian explosions recorded at the crater summit of Ibu during 8-10 March 2020 ejected incandescent ejecta and a dense ash plume. Video footage copyright by Martin Rietze, used with permission.
Figure (see Caption) Figure 22. Strombolian explosions recorded at the crater summit of Ibu during 8-10 March 2020 ejected incandescent ejecta and ash. Frequent volcanic lightning was also observed. Video footage copyright by Martin Rietze, used with permission.

A majority of days in April included white-and-gray emissions rising up to 800 m above the summit. A ground observer reported an eruption on 9 April, according to a Darwin VAAC report, and a hotspot was observed in HIMAWARI-8 satellite imagery. Minor eruptions were reported intermittently during mid-April and early to mid-May. On 12 May at 1052 a VONA from PVMBG reported an ash plume 800-1,100 m above the summit. A large short-lived eruption on 16 May produced an ash plume that rose to a maximum of 13.7 km altitude and drifted S, according to the Darwin VAAC report. By June, volcanism consisted predominantly of white-and-gray emissions rising 800 m above the summit, with an ash eruption on 15 June. This eruptive event resulted in an ash plume that rose 1.8 km altitude drifting WNW and was accompanied by a hotspot detected in HIMAWARI-8 satellite imagery, according to a Darwin VAAC notice.

The MIROVA (Middle InfraRed Observation of Volcanic Activity) system detected frequent hotspots during July 2019 through June 2020 (figure 23). In comparison, the MODVOLC thermal alerts recorded a total of 24 thermal signatures over the course of 19 different days between January and June. Many thermal signatures were captured as small thermal hotspots in Sentinel-2 thermal satellite imagery within the crater (figure 24).

Figure (see Caption) Figure 23. Thermal anomalies recorded at Ibu from 2 July 2019 through June 2020 as recorded by the MIROVA system (Log Radiative Power) were frequent and consistent in power. Courtesy of MIROVA.
Figure (see Caption) Figure 24. Sentinel-2 thermal satellite imagery (bands 12, 11, 8A) showed occasional thermal hotspots (bright orange) in the Ibu summit crater during January through June 2020. Courtesy of Sentinel Hub Playground.

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

Information Contacts: 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); Martin Rietze, Taubenstr. 1, D-82223 Eichenau, Germany (URL: https://mrietze.com/, https://www.youtube.com/channel/UC5LzAA_nyNWEUfpcUFOCpJw/videos, video at https://www.youtube.com/watch?v=qMkfT1e4HQQ).


Suwanosejima (Japan) — July 2020 Citation iconCite this Report

Suwanosejima

Japan

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

All times are local (unless otherwise noted)


Frequent explosions, ash plumes, and summit incandescence in January-June 2020

Suwanosejima is an active stratovolcano located in the northern Ryukyu Islands. Volcanism has previously been characterized by Strombolian explosions, ash plumes, and summit incandescence (BGVN 45:01), which continues to occur intermittently. A majority of this activity originates from vents within the large Otake summit crater. This report updates information during January through June 2020 using monthly reports from the Japan Meteorological Agency (JMA), the Tokyo Volcanic Ash Advisory Center (VAAC), and various satellite data.

During 3-10 January 2020, 13 explosions were detected from the Otake crater rising to 1.4 km altitude; material was ejected as far as 600 m away and ashfall was reported in areas 4 km SSW, according to JMA. Occasional small eruptive events continued during 12-17 January, which resulted in ash plumes that rose 1 km above the crater rim and ashfall was again reported 4 km SSW. Crater incandescence was visible nightly during 17-24 January, while white plumes rose as high as 700 m above the crater rim.

Nightly incandescence during 7-29 February, and 1-6 March, was accompanied by intermittent explosions that produced ash plumes rising up to 1.2 km above the crater rim (figure 44); activity during early February resulted in ashfall 4 km SSW. On 19 February an eruption produced a gray-white ash plume that rose 1.6 km above the crater (figure 45), resulting in ashfall in Toshima village (4 km SSW), according to JMA. Explosive events during 23-24 February ejected blocks onto the flanks. Two explosions were recorded during 1-6 March, which sent ash plumes as high as 900-1,000 m above the crater rim and ejected large blocks 300 m from the crater.

Figure (see Caption) Figure 44. Surveillance camera images of summit incandescence at Suwanosejima on 29 January (top left), 21 (middle left) and 23 (top right) February, and 25 March (bottom left and right) 2020. Courtesy of JMA (Monthly bulletin reports 511, January, February, and March 2020).
Figure (see Caption) Figure 45. Surveillance camera images of which and white-and-gray gas-and-steam emissions rising from Suwanosejima on 5 January (top), 19 February (middle), and 24 March 2020 (bottom). Courtesy of JMA (Monthly bulletin reports 511, January, February, and March 2020).

Nightly incandescence continued to be visible during 13-31 March, 1-10 and 17-24 April, 1-8, 15-31 May, 1-5 and 12-30 June 2020; activity during the latter part of March was relatively low and consisted of few explosive events. In contrast, incandescence was frequently accompanied by explosions in April and May. On 28 April at 0432 an eruption produced an ash plume that rose 1.6 km above the crater rim and drifted SE and E, and ejected blocks as far as 800 m from the crater. The MODVOLC thermal alerts algorithm also detected four thermal signatures during this eruption within the summit crater. An explosion at 1214 on 29 April caused glass in windows to vibrate up to 4 km SSW away while ash emissions continued to be observed following the explosion the previous day, according to the Tokyo VAAC.

During 1-8 May explosions occurred twice a day, producing ash plumes that rose as high as 1 km above the crater rim and ejecting material 400 m from the crater. An explosion on 29 May at 0210 produced an off-white plume that rose as high as 500 m above the crater rim and ejected large blocks up to 200 m above the rim. On 5 June an explosion produced gray-white plumes rising 1 km above the crater. Small eruptive events continued in late June, producing ash plumes that rose as high as 900 m above the crater rim.

MIROVA (Middle InfraRed Observation of Volcanic Activity) analysis of MODIS satellite data showed relatively stronger thermal anomalies in late February and late April 2020 with an additional six weaker thermal anomalies detected in early January (2), early February (1), mid-April (2), and mid-May (1) (figure 46). Sentinel-2 thermal satellite imagery in late January through mid-April showed two distinct thermal hotspots within the summit crater (figure 47).

Figure (see Caption) Figure 46. Prominent thermal anomalies at Suwanosejima during July-June 2020 as recorded by the MIROVA system (Log Radiative Power) occurred in late February and late April. Courtesy of MIROVA.
Figure (see Caption) Figure 47. Sentinel-2 thermal satellite images showing small thermal anomalies (bright yellow-orange) from two locations within the Otake summit crater at Suwanosejima. Images with “Atmospheric penetration” (bands 12, 11, 8A) rendering; courtesy of Sentinel Hub Playground.

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

Information Contacts: Japan Meteorological Agency (JMA), 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/); 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).


Kadovar (Papua New Guinea) — July 2020 Citation iconCite this Report

Kadovar

Papua New Guinea

3.608°S, 144.588°E; summit elev. 365 m

All times are local (unless otherwise noted)


Intermittent ash plumes and persistent summit thermal anomalies, January-June 2020

The steeply sloped 1.4-km-diameter Kadovar Island is located in the Bismark Sea offshore from the mainland of Papua New Guinea about 25 km NNE from the mouth of the Sepik River. Its first confirmed observed eruption began in early January 2018, with ash plumes and lava extrusion resulting in the evacuation of around 600 residents from the N side of the island (BGVN 43:03). A dome appeared at the base of the E flank during March-May 2018 (Planka et al., 2019); by November activity had migrated to a new dome growing near the summit on the E flank. Pulsating steam plumes, thermal anomalies, and periodic ash emissions continued throughout 2019 (BGVN 44:05, 45:01), and from January-June 2020, the period covered in this report. Information was provided by the Rabaul Volcano Observatory (RVO), the Darwin Volcanic Ash Advisory Center (VAAC), satellite sources, and photographs from visitors.

Activity during January-June 2020. Intermittent ash plumes, pulsating gas and steam plumes, and thermal anomalies continued at Kadovar during January-June 2020. MIROVA thermal data suggested persistent low-level anomalies throughout the period (figure 45). Sentinel-2 satellite data confirmed thermal anomalies at the summit on 5 and 25 January 2020, and an ash emission on 20 January (figure 46). Persistent pulsating steam plumes were visible whenever the skies were clear enough to see the volcano.

Figure (see Caption) Figure 45. Persistent low-level thermal activity at Kadovar was recorded in the MIROVA graph of radiative power from 2 July 2019 through June 2020. The island location is mislocated in the MIROVA system by about 5.5 km SE due to older mis-registered imagery; the anomalies are all on the island. Courtesy of MIROVA.
Figure (see Caption) Figure 46. Sentinel-2 satellite data confirmed thermal anomalies at the summit of Kadovar on 5 (left) and 25 January 2020, and an ash emission and steam plume that drifted SE on 20 January (center). Pulsating steam-and-gas emissions left a trail in the atmosphere drifting SE for several kilometers on 25 January (right). Left image uses Atmospheric penetration rendering (bands 12, 11, 8a), center and right images use Natural color rendering (bands 4, 3, 2). Courtesy of Sentinel Hub Playground.

On 2 February 2020 the Darwin VAAC reported a minor eruption plume that rose to 1.5 km altitude and drifted ESE for a few hours. Another plume was clearly discernible in satellite imagery on 5 February at 2.1 km altitude moving SE. RVO issued an information bulletin on 7 February reporting that, since the beginning of January, the eruption had continued with frequent Vulcanian explosions from the Main Vent with a recurrence interval of hours to days. Rocks and ash were ejected 300-400 m above the vent. Rumbling could be heard from Blupblup (Rubrub) island, 15 km E, and residents there also observed incandescence at night. On clear days the plume was sometimes visible from Wewak, on the mainland 100 km W. Additional vents produced variable amounts of steam. The Darwin VAAC reported continuous volcanic ash rising to 1.5 km on 22 February that extended ESE until it was obscured by a meteoric cloud; it dissipated early the next day. A small double ash plume and two strong thermal anomalies at the summit were visible in satellite imagery on 24 February (figure 47).

Figure (see Caption) Figure 47. Ash emissions and thermal anomalies continued at Kadovar during February 2020. Two small plumes of ash or dense steam rose from the summit on 24 February 2020, seen in this Natural color rendering (bands 4, 3, 2) on the left. The same image rendered in Atmospheric penetration (bands 12, 11, 8a) on the right shows two thermal anomalies in the same locations as the ash plumes. Courtesy of Sentinel Hub Playground.

The Darwin VAAC reported continuous ash emissions beginning on 13 March 2020 that rose to 1.5 km altitude and drifted SE. The plume was visible intermittently in satellite imagery for about 36 hours before dissipating. During April, pulsating steam plumes rose from two vents at the summit, and thermal anomalies appeared at both vents in satellite data (figure 48). Small but distinct SO2 anomalies were visible in satellite data on 15 and 16 April (figure 49).

Figure (see Caption) Figure 48. Steam plumes and thermal anomalies continued at Kadovar during April 2020. Top: A thermal anomaly at the summit accompanied pulsating steam plumes that drifted several kilometers SE before dissipating on 4 April 2020. Bottom left: Two gas-and-steam plumes drifted E from the summit on 9 April. Bottom right: Two adjacent thermal anomalies were present near the summit on 19 April. Top and bottom right images use Atmospheric penetration rendering (bands 12, 11, 8a), bottom left image uses Natural color rendering (bands 4, 3, 2). Courtesy of Sentinel Hub Playground.
Figure (see Caption) Figure 49. Small but distinct SO2 anomalies were detected at Kadovar on 15 and 16 April 2020 with the TROPOMI instrument on the Sentinel-5P satellite. Nearby Manam often produces larger SO2 plumes that obscure evidence of activity at Kadovar. Courtesy of NASA Global Sulfur Dioxide Monitoring Page.

Two summit vents remained active throughout May and June 2020, producing pulsating steam plumes that were visible for tens of kilometers and thermal anomalies visible in satellite data (figure 50). A strong thermal anomaly was visible beneath meteoric clouds on 8 June.

Figure (see Caption) Figure 50. During May and June 2020 thermal and plume activity continued at Kadovar. Top: Gas-and-steam plumes drifted NW from two sources at the summit of Kadovar on 19 May 2020. Bottom left: Two thermal anomalies marked the E rim of the summit crater on 28 June 2020. Bottom right: A zoomed out view of the same 28 June image shows pulsating steam plumes drifting 10 km NW from Kadovar. Top image is Natural color rendering (bands 4, 3, 2). Bottom images are Atmospheric penetration rendering (bands 12, 11, 8a) of Sentinel-2 images. Courtesy of Sentinel Hub Playground.

Visitor observations on 21 October 2019. Claudio Jung visited Kadovar on 21 October 2019. Shortly before arriving on the island an ash plume rose tens of meters above the summit and drifted W (figure 51). From the NW side of the summit crater rim, Jung saw the actively growing dome on the side of a larger dome, and steam and gas issuing from the growing dome (figure 52). The crater rim was covered with dead vegetation, ash, and large bombs from recent explosions (figure 53). The summit dome had minor fumarolic activity around the summit area and dead vegetation halfway up the flank (figure 54) while the fresh blocky lava of the actively growing dome on the E side of the summit produced significant steam and gas emissions. The growing dome produced periodic pulses of dense steam during his visit (figure 55).

Figure (see Caption) Figure 51. Views looking S show the shoreline dome at the base of the E flank of Kadovar that was active during March-May 2018 (left), and an ash plume drifting W from the summit dome located on the E side of the summit crater (right) on 21 October 2019. Copyrighted photos courtesy of Claudio Jung, used with permission.
Figure (see Caption) Figure 52. A panorama looking SE from the crater rim of Kadovar on 21 October 2019 shows the actively growing dome on the far left with a narrow plume of steam and gas being emitted. A large dome fills the summit crater; the crater rim is visible on the right. Copyrighted photo courtesy of Claudio Jung, used with permission.
Figure (see Caption) Figure 53. The crater rim of Kadovar on 21 October 2019 was covered with dead vegetation, ash, and large bombs from recent explosions. Person is sitting on a large bomb; weak fumarolic activity is visible along the rim. Copyrighted photo courtesy of Claudio Jung, used with permission.
Figure (see Caption) Figure 54. The summit dome of Kadovar on 21 October 2019 had minor fumarolic activity around most of its summit and dead vegetation half-way up the flank (left). The dead tree stumps suggest that vegetation covered the lower half of the dome prior to the eruption that began in January 2018. The fresh blocky lava of the actively growing dome on the E side of the summit dome produced significant steam and gas emissions (right). Copyrighted photos courtesy of Claudio Jung, used with permission.
Figure (see Caption) Figure 55. Dense steam from the growing dome on the E side of the summit drifted W from Kadovar on 21 October 2019. Copyrighted photo courtesy of Claudio Jung, used with permission.

Reference: Planka S, Walter T R, Martinis S, Cescab S, 2019, Growth and collapse of a littoral lava dome during the 2018/19 eruption of Kadovar Volcano, Papua New Guinea, analyzed by multi-sensor satellite imagery, Journal of Volcanology and Geothermal Research, v. 388, 15 December 2019, 106704, https://doi.org/10.1016/j.jvolgeores.2019.106704.

Geologic Background. The 2-km-wide island of Kadovar is the emergent summit of a Bismarck Sea stratovolcano of Holocene age. It is part of the Schouten Islands, and lies off the coast of New Guinea, about 25 km N of the mouth of the Sepik River. Prior to an eruption that began in 2018, a lava dome formed the high point of the andesitic volcano, filling an arcuate landslide scarp open to the south; submarine debris-avalanche deposits occur in that direction. Thick lava flows with columnar jointing forms low cliffs along the coast. The youthful island lacks fringing or offshore reefs. A period of heightened thermal phenomena took place in 1976. An eruption began in January 2018 that included lava effusion from vents at the summit and at the E coast.

Information Contacts: Rabaul Volcano Observatory (RVO), Geohazards Management Division, Department of Mineral Policy and Geohazards Management (DMPGM), PO Box 3386, Kokopo, East New Britain Province, Papua New Guinea; Darwin Volcanic Ash Advisory Centre (VAAC), Bureau of Meteorology, Northern Territory Regional Office, PO Box 40050, Casuarina, NT 0811, Australia (URL: http://www.bom.gov.au/info/vaac/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); NASA 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/); Claudio Jung (URL: https://www.instagram.com/jung.claudio/).


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).


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).


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).


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).

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Bulletin of the Global Volcanism Network - Volume 19, Number 07 (July 1994)

Managing Editor: Richard Wunderman

Aira (Japan)

Volcanism continues; 14 explosive eruptions

Arenal (Costa Rica)

Continued gas and lava emissions; sporadic Strombolian eruptions

Asosan (Japan)

Crater 1 at Nakadake still restless

Batur (Indonesia)

First significant eruptive activity in 18 years leads to ashfall 6 km WSW of the summit

Cumbal (Colombia)

Increased fumarolic activity

Etna (Italy)

Explosive degassing from La Voragine; fumarole temperatures reported

Galeras (Colombia)

Seismicity remains low; crater described and fumarole temperatures reported

Gamalama (Indonesia)

Eruptions generate ash cloud to ~5 km altitude and cause ashfall

Huila, Nevado del (Colombia)

Description of the Paez earthquake's mass wasting

Ijen (Indonesia)

Minor phreatic eruption in February described

Kanaga (United States)

Steam-and-ash plume rises 4,500 m; enlarged hot spot on imagery

Kilauea (United States)

Bench collapses and littoral explosions occur as lava flows continue to enter the ocean

Krakatau (Indonesia)

Frequent ash explosions (300-450/day) reach heights up to 500 m

Langila (Papua New Guinea)

Thick ash clouds from Crater 2 accompanied by explosion sounds

Lascar (Chile)

Moderate short-lived eruption sends plume over Argentina

Manam (Papua New Guinea)

Explosions on 5-7 July generate ash clouds and eject lava fragments

Marapi (Indonesia)

Eruption sends ash column to ~6 km above sea level; summary of 1993 activity

Masaya (Nicaragua)

Sulfur-rich plume and incandescent ejections from opening in lava lake

Merapi (Indonesia)

Increased deformation precedes a nuee ardente

Momotombo (Nicaragua)

Summit fumarole temperatures range from 238 to 655°C

Nyamuragira (DR Congo)

High lava fountains feed lava flow on NW flank

Nyiragongo (DR Congo)

Lava lake activity produces strong red glow above crater

Poas (Costa Rica)

Ashfall SW of the summit covers 56 km2

Rabaul (Papua New Guinea)

Seismicity remains low; minor subsidence

Ruapehu (New Zealand)

Relatively stable with water cooling of Crater Lake

Semeru (Indonesia)

Small ash eruptions to 500 m above the summit

Telica (Nicaragua)

Explosive eruption causes ashfall >12 km SW of the summit

Ulawun (Papua New Guinea)

White vapor emissions and low-frequency tremor

Unzendake (Japan)

Lava lobe 13 grows endogenously but then nearly stops growing in late-July

Whakaari/White Island (New Zealand)

No eruptive activity, but new shifts in leveling and magnetic data



Aira (Japan) — July 1994 Citation iconCite this Report

Aira

Japan

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

All times are local (unless otherwise noted)


Volcanism continues; 14 explosive eruptions

Sakura-jima generated 22 eruptions in July, including 14 explosive ones. None of them caused damage. The highest plume rose to 2.2 km (at 1859 on 5 July). In July, the amount of ashfall at [KLMO] was 237 g/m3. Volcanic swarms were absent in July but 520 earthquakes were detected at a seismic station 2.3 km NW of Minami-dake crater.

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

Information Contacts: JMA.


Arenal (Costa Rica) — July 1994 Citation iconCite this Report

Arenal

Costa Rica

10.463°N, 84.703°W; summit elev. 1670 m

All times are local (unless otherwise noted)


Continued gas and lava emissions; sporadic Strombolian eruptions

At . . . Crater C, July marked another month of continued gas and lava emissions, and sporadic Strombolian eruptions. During July, the lava flow that began at the end of April continued to erupt and flow down an established channel. During 23 days in July, seismic station VACR (2.7 km NE of crater C) recorded an average of 18 events/day. These were interspersed with days having very low seismicity and tremor. Beginning on 23 July, Strombolian-type eruptions became common, and during 23-30 July they were seen 52 times. In some cases these eruptions were accompanied by sounds similar to a jet or steam engine. On 28 July tremor reached an amplitude of 27 mm at a frequency below 2.5 Hz.

Geologic Background. Conical Volcán Arenal is the youngest stratovolcano in Costa Rica and one of its most active. The 1670-m-high andesitic volcano towers above the eastern shores of Lake Arenal, which has been enlarged by a hydroelectric project. Arenal lies along a volcanic chain that has migrated to the NW from the late-Pleistocene Los Perdidos lava domes through the Pleistocene-to-Holocene Chato volcano, which contains a 500-m-wide, lake-filled summit crater. The earliest known eruptions of Arenal took place about 7000 years ago, and it was active concurrently with Cerro Chato until the activity of Chato ended about 3500 years ago. Growth of Arenal has been characterized by periodic major explosive eruptions at several-hundred-year intervals and periods of lava effusion that armor the cone. An eruptive period that began with a major explosive eruption in 1968 ended in December 2010; continuous explosive activity accompanied by slow lava effusion and the occasional emission of pyroclastic flows characterized the eruption from vents at the summit and on the upper western flank.

Information Contacts: E. Fernández, J. Barquero, V. Barboza, R. Van der Laat, F. de Obaldia, and T. Marino, OVSICORI; G. Soto, G. Alvarado, and F. Arias, ICE; M. Mora, C. Ramirez, and G. Peraldo, Univ de Costa Rica.


Asosan (Japan) — July 1994 Citation iconCite this Report

Asosan

Japan

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

All times are local (unless otherwise noted)


Crater 1 at Nakadake still restless

Crater 1 remained restless through July, but the intensity of activity became more moderate compared to the last two months. Through July the average amplitude of continuous tremor was around 0.1 µm.

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

Information Contacts: JMA.


Batur (Indonesia) — July 1994 Citation iconCite this Report

Batur

Indonesia

8.242°S, 115.375°E; summit elev. 1717 m

All times are local (unless otherwise noted)


First significant eruptive activity in 18 years leads to ashfall 6 km WSW of the summit

Beginning on 4 August, the daily number of A-type volcanic earthquakes increased to 14; two days later 125 events were registered. An eruption on 7 August from the E part of the summit, Batur Crater III, caused ashfall as far as ~6 km WSW (figure 1). Ash covered Kintamani on the caldera rim, one of Bali's famous tourist attractions. Incandescent lava fragments and black smoke were ejected to heights of 300 m. None of the larger lava fragments fell outside of the active crater. News reports indicated that the eruption generated 960 explosions through 11 August. Volcanic tremor recorded by the VSI on 13 August had a maximum amplitude of 4.5 mm, but was increasing. By 14 August, when lava reached the surface, the tremor amplitude was 23 mm.

Figure (see Caption) Figure 1. Map of the Batur caldera, showing hazard zones, selected towns, and extent of ashfall from the eruption that began on 7 Aug 1994. The inner caldera is not shown, but includes most of danger zones I and II. Courtesy of VSI.

As of 18 August, no evacuations from the area around the . . . volcano had taken place. About 180,000 people live in Bangli Regency, but only ~500 live in what a spokesman called the "critical region." Batur was declared off-limits for climbers on 7 August, and local villagers were put on alert. An official at a monitoring center said tourists who evaded guards and climbed the mountain were taking large risks. According to press reports, the eruptions have not reduced the number of visitors to the popular resort island; Batur's crater attracts ~300 people every day. Many observe the volcanic activity from Kintamani, on the crater rim (figure 1).

Geologic Background. The historically active Batur is located at the center of two concentric calderas NW of Agung volcano. The outer 10 x 13.5 km wide caldera was formed during eruption of the Bali (or Ubud) Ignimbrite about 29,300 years ago and now contains a caldera lake on its SE side, opposite the satellitic Gunung Abang cone, the topographic high of the complex. The inner 6.4 x 9.4 km wide caldera was formed about 20,150 years ago during eruption of the Gunungkawi Ignimbrite. The SE wall of the inner caldera lies beneath Lake Batur; Batur cone has been constructed within the inner caldera to a height above the outer caldera rim. The Batur stratovolcano has produced vents over much of the inner caldera, but a NE-SW fissure system has localized the Batur I, II, and III craters along the summit ridge. Historical eruptions have been characterized by mild-to-moderate explosive activity sometimes accompanied by lava emission. Basaltic lava flows from both summit and flank vents have reached the caldera floor and the shores of Lake Batur in historical time.

Information Contacts: VSI; AP; Reuters; UPI; ANS; D. Shackleford, Fullerton CA, USA.


Cumbal (Colombia) — July 1994 Citation iconCite this Report

Cumbal

Colombia

0.95°N, 77.87°W; summit elev. 4764 m

All times are local (unless otherwise noted)


Increased fumarolic activity

"Cumbal . . . (figure 1), has been showing signs of possible reactivation during the past year. New fumaroles have appeared and the gas column has grown noticeably larger. Cumbal was visited by volcanologists from INGEOMINAS and the Univ de Montréal on 11-15 July 1994. A portable seismometer was installed . . . at 4,185 m elev, ~580 m below the summit. Both high-frequency and long-period events were recorded, as well as some possible tremor episodes. Several fumarole fields at the summit (figure 2) exhibited maximum temperatures as follows: El Verde, 378°C; El Tábano, 191°C; La Desfondada, 132°C; La Plazuela, 99°C; La Grieta-verde, 84°C; Vecino a la verde, 80°C. El Tábano is a new fumarole field that appeared in early 1994. For comparison, in 1988 El Verde had measured temperatures of 150-326°C. The El Verde fumaroles produced audible noise. Most of the gas column at Cumbal appeared to emanate from the El Verde fumaroles."

Figure (see Caption) Figure 1. Location map showing Cumbal volcano and the city of Cumbal. Modified from Mendez (1989).
Figure (see Caption) Figure 2. Sketch map of the crater area of Cumbal, July 1994, showing fumarole locations. Courtesy of INGEOMINAS.

Reference. Mendez F., R.A., 1989, Catálogo de los volcanes actives de Colombia: Bol. Geol., v. 30, no. 3, 75 p.

Geologic Background. Many youthful lava flows extend from the glacier-capped Cumbal volcano, the southernmost historically active volcano of Colombia. The volcano is elongated in a NE-SW direction and is composed primarily of andesitic-dacitic lava flows. Two fumarolically active craters occupy the summit ridge: the main crater on the NE side and Mundo Nuevo crater on the SW. A young lava dome occupies the 250-m-wide summit crater, and eruptions from the upper E flank produced a 6-km-long lava field. The oldest crater lies NNE of the summit crater, suggesting SW-ward migration of activity. Explosive eruptions in 1877 and 1926 are the only known historical activity. Thermal springs are located on the SE flanks.

Information Contacts: G. Patricia Cortes and R. Torres Corredor, INGEOMINAS, Pasto; J. Stix and M. Heiligmann, Univ de Montréal.


Etna (Italy) — July 1994 Citation iconCite this Report

Etna

Italy

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

All times are local (unless otherwise noted)


Explosive degassing from La Voragine; fumarole temperatures reported

The following describes [fieldwork] on 1-27 June and 10-18 July 1994.

"As during visits in June-July and September-October 1993, Northeast Crater was blocked and inactive, but collapse was continuing around the edge with minor rockfalls every few minutes or so. Southeast Crater was also little changed from 1993, with a quietly degassing vent under the SE rim, but no indication of gas coming out under pressure. There was strong high-temperature fumarolic activity around the crater rim, temperatures being generally highest in the cracks.

"The Chasm (La Voragine) had a single vent in its floor measuring ~ 8 x 10 m, discharging gas continuously under pressure in rhythmic puffs at a rate of ~ 30 puffs/min. On 17 June and 12 July only, distinct explosions could be heard at the rate of 1-8/min. These were the first signs of explosive activity since the end of the 1991-93 eruption, and an indication that the Strombolian degassing that has characterized the summit over the past few hundred years is resuming.

"Bocca Nuova vent was degassing almost totally silently from two vents, one to the SE and one to the W; however, on 27 June when the weather was calm, 13 very faint gas puffs/min could be heard. The SE vent seemed similar to last year, measuring ~ 10 m in diameter, but the W vent had collapsed and enlarged considerably, now measuring perhaps as much as 50 m in diameter. On the early morning of 16 June a reddish tinge to the plume above Bocca Nuova was first noticed. Upon closer inspection on 17 June, the SE vent was seen to be pouring out thick clouds of red dust, apparently a result of internal collapse within the vent, while the W vent continued to emit white fume only. Dust emission intensified in the following days, causing the downwind side (S through W) of the summit to become a striking red color. The activity was continuing in mid-July.

"The levelling traverse showed comparatively small vertical movements since September 1993. The area near Belvedere, and other areas over the dyke intruded during the 1991-93 eruption, had subsided by up to 2 cm, as had the NE rift zone near Monte Pizzillo. During the same period, a small area ~1 km SW of the summit inflated by just over 1 cm. Horizontal movements measured since October 1993 showed generally small or insignificant changes, with nearly all lines recording changes of >1 cm. Only two stations appear to have moved by more than this; a station on the E edge of Southeast Crater had shifted 3 cm E relative to nearby stations, and a station close to the NW edge of the Bocca Nuova had moved 2 cm W. These movements are consistent with expansion of the central magma column as it refills.

"Surface temperatures were measured between 1 and 27 June at four active fumarole areas with a Minolta/Land Cyclops Compac 3 hand-held radiometer (8-14 mm). Temperatures were not corrected for spectral emissivity, so all radiant temperatures are given here as brightness temperatures. On the NE rift zone, nine areas of fumaroles were observed near the N edge of the 1966-67 lavas (between 2,450 and 2,500 m altitude). Temperatures for fumaroles at the two lowest of these areas ranged between 33 and 50°C. Another area of fumaroles observed at the upper rim of the W wall of the Valle del Bove around Belvedere, above the 1991-93 dyke, had temperatures in the 57.5-84.7°C range. Temperatures measured at fumaroles and cracks in the still-cooling 1991-93 lava-flow field in the Valle del Bove were between 85 and 221°C. The locations and temperatures of fumarole areas measured in the vicinity of the summit craters are given in table 5. Temperatures of the vents within the central craters were also measured from the crater rim: 342°C for the Chasm vent, and 159 and 81.5°C, respectively, for the SE and W vents of Bocca Nuova. Active fumaroles were observed, but not measured, along the 1991-93 fissure zone and 14 December 1991 cones and flows between Southeast Crater and Belvedere, along the October 1986 fissure zone, and in the Valle del Bove below Monte Simone."

Table 5. Fumarole temperatures in the vicinity of Etna's summit craters, measured on 18 and 27 June, and 14 October 1994. Courtesy of Andrew Harris, Open University.

Date Fumarole / Rift Locations Temperature (°C)
27 Jun 1994 NE Crater - at N rim 50.4-65.0
27 Jun 1994 NE Crater - rifts at NW rim 56.0-141
27 Jun 1994 NE Crater - at dip in NW rim 45.5-97.4
27 Jun 1994 NE Crater - at E rim 51.4-85.6
18 Jun 1994 Bocca Nuova - on N slope 40.5-75.6
18, 27 Jun 1994 Bocca Nuova - inside N rim 42.2-54.3
27 Jun 1994 Bocca Nuova - rifts at N rim 52.0-74.4
18 Jun 1994 Bocca Nuova - at SW rim 52.0-65.7
18, 27 Jun 1994 Central Craters - at S rim 40.6-82.6
27 Jun 1994 Between central and SE Craters 59.1-81.3
18, 27 Jun 1994 SE Crater - rifts and fumarole at N rim 51.2-312
27 Jun 1994 SE Crater - rifts and fumarole at W rim 60.0-208
14 Oct 1994 NE Crater - fumarole at N rim 39.2-77.4
14 Oct 1994 NE Crater - rifts at NW rim 153-246
14 Oct 1994 NE Crater - fumarole at W flank 50.4-74.2
14 Oct 1994 NE Crater - fumarole at W rim 41.0-210
14 Oct 1994 NE Crater - fumarole at S rim 50.5-221
14 Oct 1994 Bocca Nuova - fumarole at N flank 50.1-75.5
14 Oct 1994 Bocca Nuova - rifts and fumarole at N rim 47.3-74.5
14 Oct 1994 Bocca Nuova - fumarole at SW rim 50.0-72.4
14 Oct 1994 Central Craters - fumarole at S rim 49.2-82.4
14 Oct 1994 Fumarole between central and SE craters 50.2-82.8
14 Oct 1994 SE Crater - rifts and fumarole at N rim 57.5-482
14 Oct 1994 SE Crater - rifts and fumarole at NW rim 56.4-218
14 Oct 1994 SE Crater - rifts and fumarole at W rim 46.8-99.5
14 Oct 1994 SE Crater - rifts and fumarole at S rim 49.9-88.0
14 Oct 1994 SE Crater - rifts and fumarole at E rim 68.5-180
14 Oct 1994 SE Crater - rifts and fumarole at NE rim 52.2-121

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: J. Murray and A. Harris, Open Univ; L. Platt, Sheffield Univ; D. Renouf, UK.


Galeras (Colombia) — July 1994 Citation iconCite this Report

Galeras

Colombia

1.22°N, 77.37°W; summit elev. 4276 m

All times are local (unless otherwise noted)


Seismicity remains low; crater described and fumarole temperatures reported

Seismicity during June and July showed no significant changes. . . . Low-frequency seismicity was at very low levels during June, although a "screw-type" event did occur; this type of event was numerous before eruptions in 1992-93. Shallow "butterfly-type" activity during the first half of June was similar to May, when the number of events decreased notably. These small-amplitude, short-duration, high-frequency events, interpreted as caused by fluid movement or rock fracture at shallow depths (<2 km) near the active cone, increased in number in the second half of June and through July. During June the fracture events were located N of the volcano, near the source that was active during November-December 1993, with other fracture events to the NE or closer to the crater. Additional sources were W and S of the crater. Fracture activity within the crater consisted of very small magnitude events (M <2.3) at depths between 2.1 and 9.7 km.

The active inner cone was visited on 21 July 1994 by volcanologists from INGEOMINAS and the Univ de Montréal. The morphology of the cone was modified considerably by the eruptions of 1992-93, which seem to have progressively deepened the crater to the present level of 200-300 m (figure 71). Prior to dome emplacement during October-November 1991 the crater was ~ 150 m deep; after dome growth in 1991-92, the crater was ~80 m deep. A N-S trending fracture, named Novedad, now breaches the S crater rim. Partial collapse of the crater rim and blocks 10-20 cm in size were noted on the N side of the cone.

Figure (see Caption) Figure 71. Sketch map (top) and perspective view (bottom) of the Galeras crater, July 1994. Small ovals represent fumaroles; crater depth is ~200-300 m. View is from the west. Drawn by Milton Ordonez, INGEOMINAS.

Some low-pressure fumaroles were noted in the deepest part of the crater, but gas was being emitted mainly in the shallower W and SW sectors. At Deformes fumarole, on the SW flank of the cone, temperature was measured and gas samples were collected for analysis. Maximum temperature was 138°C, significantly cooler than the ~200°C recorded in December 1992 and January 1993 (Zapata G., 1992; Goff et al., 1993). Besolima, generally the hottest measured fumarole on the cone's outer flanks, had largely disappeared. Las Chavas fumarole showed very low activity with a maximum temperature of 105°C. A new fumarole near the W rim of the cone, named Nuevas, had temperatures of 208 and 392°C. This fumarole is in the area where Florencia fumarole and remnants of the lava dome (destroyed in July 1992) had temperatures of 640°C on 26 November 1992 (Zapata G., 1992).

Stationary COSPEC measurements of SO2 in June from five points around the volcano showed low levels of gases (18-176 t/d), similar to the measurements obtained using the mobile COSPEC (79-217 t/d). July degassing was concentrated on the W periphery of the active cone, with low concentrations of SO2 (<220 t/d) measured by COSPEC.

Electronic tiltmeter variations in June at the Peladitos station were 2.4 µrad in the tangential component and 7.8 µrad in the radial component. The Crater tiltmeter fluctuated in June due to electronic problems; no deformation was observed in July. On 7 July the Agua Tibia springs, located in the Rio Azufral valley 5 km W of the active cone, had a temperature of 21°C and pH of 5.

References. Zapata G., J.A., 1992, Visita al crater del volcan Galeras: INGEOMINAS Internal Report, 30 November 1992, 2 p.

Goff, F., McMurtry, G.M., Adams, A.I., and Roldán-M., A., 1993, Stable isotopes and tritium of magmatic water at Galeras volcano, Colombia: EOS, Trans. Am. Geophys. Union, 74(43), p. 690.

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

Information Contacts: R. Corredor and C. Gonzalez, INGEOMINAS, Pasto; J. Stix and M. Heiligmann, Univ de Montréal.


Gamalama (Indonesia) — July 1994 Citation iconCite this Report

Gamalama

Indonesia

0.8°N, 127.33°E; summit elev. 1715 m

All times are local (unless otherwise noted)


Eruptions generate ash cloud to ~5 km altitude and cause ashfall

A NOTAM that originated from the Ujung Pandang FIR on 6 May 1994 requested that all aircraft avoid the area around Gamalama volcano. VSI did not note any unusual activity on that day, and no ash cloud was detected on satellite imagery. The warning only noted that the height of "dust" was variable.

Members of the SVE visited Gamalama at 1130 on 21 July. Summit activity consisted of violent degassing from the summit crater, producing a white-gray plume above the volcano; no solid material was ejected during the observations. A small active fumarolic area on the W crater rim exhibited yellow sulfur deposits. White vapor was rising from a large crack on the E crater rim, a part of the crater that appeared to be very unstable. The bottom of the crater could not be seen from the rim.

VSI reported that activity from the main crater increased with a sudden eruption on 5 August 1994 at 2125. The eruption produced an ash cloud to a height of 3,000 m above the summit . . . and accompanying ash falls. A felt earthquake a few minutes before the eruption had an intensity of MM II-III. Volcanic tremor recorded since 10 August preceded another eruption at about 2400 on 13 August from the same location. A news report indicated that explosions on 14 August caused ashfall in Ternate (~ 4 km SE), and that 5-20 minor explosions/day had occurred in recent days.

Following eruptions in May 1993 (18:5 & 7; and VSI, 1993a), seismicity steadily decreased to low levels by the end of June; vapor emission stopped by the end of August 1993 (VSI, 1993b). Seismicity began increasing again in December 1993 (VSI, 1993b), and explosions were reported during January-March 1994 (19:05).

Geologic Background. Gamalama is a near-conical stratovolcano that comprises the entire island of Ternate off the western coast of Halmahera, and is one of Indonesia's most active volcanoes. The island was a major regional center in the Portuguese and Dutch spice trade for several centuries, which contributed to the thorough documentation of Gamalama's historical activity. Three cones, progressively younger to the north, form the summit. Several maars and vents define a rift zone, parallel to the Halmahera island arc, that cuts the volcano. Eruptions, recorded frequently since the 16th century, typically originated from the summit craters, although flank eruptions have occurred in 1763, 1770, 1775, and 1962-63.

Information Contacts: W. Tjetjep, VSI; H. Gaudru, C. Pittet, M. Auber, C. Bopp, and O. Saudan, EVS, Switzerland; BOM Darwin, Australia; AP; Radio Republik Indonesia.


Nevado del Huila (Colombia) — July 1994 Citation iconCite this Report

Nevado del Huila

Colombia

2.93°N, 76.03°W; summit elev. 5364 m

All times are local (unless otherwise noted)


Description of the Paez earthquake's mass wasting

The destructive earthquake-triggered mudflows of 6 June (19:5) were the subject of a preliminary report (Casadevall and others, 1994) following an investigation by a team from INGEOMINAS and the USGS during 30 June-9 July. What follows is a summary of that report, which includes first-hand observations on slope-failure and transport of loosened material.

The M 6.4 earthquake that struck on 6 June 1994 is now termed the Paez earthquake. Although the preliminary epicenter determination was W of the volcano's summit, a more recent estimate places it on Nevado del Huila's SSW flank, several kilometers N of the village of Irlanda (figure 1; BGVN 19:5). Prior to the earthquake, normal background seismicity prevailed; a series of aftershocks also took place beneath the volcano.

Earthquake damage was attributed to shaking, mass movement of loosened material, and flooding. The volcano's topography and volcanic deposits contributed to the disaster, but the primary area of landslides lay S of the main volcanic edifice and reached a maximum elevation of ~3,000 m. Aerial observers on 7 July saw no changes in either the vigor of fumaroles present near the summit or in the distribution and surface appearance of glaciers. Though dislodged ice was noted in news reports, none was found during fieldwork. The latest estimates on direct human impact from the earthquake are >150 fatalities, 500 people listed as missing, and 20,000 people displaced. Six bridges and >100 km of roads were destroyed.

All mass movement due to slope failure was previously called "mudflows" (19:5). The new report uses more precise terminology (Varnes, 1978), and provides an English-Spanish glossary that includes these and other terms: (a) rock, soil, and earth falls, (b) various kinds of slides including earth slides and debris slides, (c) rock avalanches, (d) debris avalanches, and (e) earth flows. According to this scheme, the bulk of the observed slides were earth slides derived from weathered residual soils that have developed on the bedrock. Lack of bedrock involvement and the limited amount of translations that involved bouncing, rolling, or falling resulted in few mass movements categorized as rock avalanches.

Nearly all of the 6 June earthquake-triggered landslides originated on slopes of >=30°. In this steep terrain they mainly began as shallow slips in residual soils. The soils had been saturated a few weeks prior to the earthquake by heavy rains. Reduced shear strength because of the saturated soils was a major factor in the observed slope failures and the velocity of the downslope movements. Typically these water-charged slides were ~ 1-2 m thick, and immediately liquified, transforming into either debris avalanches or earth flows moving rapidly downslope. In total, these processes stripped >50% of the vegetation from the steep hillsides. The slides themselves caused little direct damage since the steep slopes were generally uninhabited.

Adjacent to the volcano, in up-river villages such as Irlanda and Wila, damage took place as the mobile earth flows ran across relatively flat terrace surfaces. Earth flows in Irlanda were only 2 m thick, but they destroyed the houses and structures in their path. Some of the damage at Irlanda may have been caused by a high-velocity earth flow that began on the opposite side (the E side) of Rio Paez and crossed over.

The 1994 debris flows in the Rio Paez were cohesive (>3% of sediment with <0.004 mm size), which means that they remain intact and travel long distances. On the other hand, large previous debris flows preserved in lateral terraces along the river are of the noncohesive type that transformed into hyperconcentrated flows as they moved downstream. The noncohesive debris flows are thought to have been more closely related to past explosive volcanism and provide one means of analyzing past behavior at Huila. This point is noteworthy because the headwaters of the Rio Paez provide the drainage for almost the entire volcano. Because the bulk of debris flows must travel down the Rio Paez, study of the deposits along it should provide a thorough record of the volcano's seismically and magmatically generated deposits.

The report noted several analogous cases of "widespread stripping of saturated materials and vegetative cover from steep slopes" during seismic loading. One case involved the M 6.1 and 6.9 earthquakes of March 1987 in NE Ecuador. Those earthquakes triggered an estimated 75-110 million m3 of mass wasting, killed an estimated 1,000 people, destroyed a major oil pipeline, and caused US $1 billion in damages. These events are also of interest because Mount Rainier (Washington State, USA) contains a gravitationally unstable zone of altered rock high on its edifice. The zone could detach during seismic loading and move downslope, eventually reaching heavily populated areas.

Researchers continue to watch the volcano to see if the recent seismicity causes any changes to its normally passive hydrothermal system. Monitoring is done from an observatory in Popayan, 83 km SW.

References. Casadevall, T.J., Schuster, R.L., and Scott, K.M., 29 July 1994, Preliminary report on the effects of the June 6, 1994 Sismo de Paez (Paez earthquake), Southern Colombia: U.S. Geological Survey Response Team, 15 p.

Varnes, D.J., 1978, Classification of mass movements, in Schuster, R.L., and Krizek, R.J. (eds.), Landslides: Analysis and Control: U.S. National Academy of Sciences, Transportation Research Board Special Report 176, p. 11-33.

Geologic Background. Nevado del Huila, the highest peak in the Colombian Andes, is an elongated N-S-trending volcanic chain mantled by a glacier icecap. The andesitic-dacitic volcano was constructed within a 10-km-wide caldera. Volcanism at Nevado del Huila has produced six volcanic cones whose ages in general migrated from south to north. The high point of the complex is Pico Central. Two glacier-free lava domes lie at the southern end of the volcanic complex. The first historical activity was an explosive eruption in the mid-16th century. Long-term, persistent steam columns had risen from Pico Central prior to the next eruption in 2007, when explosive activity was accompanied by damaging mudflows.

Information Contacts: INGEOMINAS, Popayan; T. Casadevall, USGS.


Ijen (Indonesia) — July 1994 Citation iconCite this Report

Ijen

Indonesia

8.058°S, 114.242°E; summit elev. 2769 m

All times are local (unless otherwise noted)


Minor phreatic eruption in February described

At 0915 on 3 February 1994, a small phreatic eruption took place from the S part of the crater lake. Coincident with the eruption, lake level rose ~1 m. Visual and seismic activity then returned to normal through July. During 7-14 August, the number of volcanic earthquakes and tremor increased compared to earlier in August. The temperature of the light-green crater lake was 39-42°C.

Geologic Background. The Ijen volcano complex at the eastern end of Java consists of a group of small stratovolcanoes constructed within the large 20-km-wide Ijen (Kendeng) caldera. The north caldera wall forms a prominent arcuate ridge, but elsewhere the caldera rim is buried by post-caldera volcanoes, including Gunung Merapi, which forms the high point of the complex. Immediately west of the Gunung Merapi stratovolcano is the historically active Kawah Ijen crater, which contains a nearly 1-km-wide, turquoise-colored, acid lake. Picturesque Kawah Ijen is the world's largest highly acidic lake and is the site of a labor-intensive sulfur mining operation in which sulfur-laden baskets are hand-carried from the crater floor. Many other post-caldera cones and craters are located within the caldera or along its rim. The largest concentration of cones forms an E-W zone across the southern side of the caldera. Coffee plantations cover much of the caldera floor, and tourists are drawn to its waterfalls, hot springs, and volcanic scenery.

Information Contacts: VSI.


Kanaga (United States) — July 1994 Citation iconCite this Report

Kanaga

United States

51.923°N, 177.168°W; summit elev. 1307 m

All times are local (unless otherwise noted)


Steam-and-ash plume rises 4,500 m; enlarged hot spot on imagery

On the morning of 15 July a pilot observed steam plumes rising from multiple vents to ~600 m above the summit. FWS personnel in Adak . . . reported steam plumes during 16-22 July. A distinct hot spot . . . was seen on a satellite image from 0906 on 22 July. FWS personnel aboard the RV Tiglax observed incandescent flows on the flank of Kanaga during the night of 27-28 July; low-level steaming from the summit area was continuing. Also in late July the FWS crew saw a blocky lava flow entering the sea on the NW flank, forming a new headland and small cove. Pilots reported incandescent flows on the NW flank during the following week, and steam plumes to 1,500 m altitude. On 10 August the RV Tiglax passed within ~3 km of shore and the crew observed the two NW-flank lava flows for the first time during daylight. Steam was rising from where the flows were entering the sea, and a strong SO2 odor was detected. Satellite imagery again recorded hot spots . . . during 2-12 August.

At 0500 on 18 August, the FAA received a pilot report of "glowing" at the summit. Pilots reported a light gray, dense steam cloud at 0800 rising to 4,500 m above the summit that had a mushroom-shaped top and was trailing to the E. A satellite infrared image taken at 0836 showed a summit hot spot twice as large as that seen in recent weeks, suggesting an increase in heating associated with production of lava flows. Also visible in the image was a plume extending 15-20 km NE; enhancements of calibrated data suggested that the plume may have contained some ash. Throughout the day, pilots and FWS personnel in Adak observed an eruption cloud consisting of a white, dominantly steam portion, which rose to ~4,500 m altitude, and a vigorously roiling, gray, ash-bearing portion that rose to an estimated 2,400-3,000 m altitude. A loud rumbling, similar to the sound of a freight train, was heard in Adak all afternoon and into the evening. Prevailing winds carried the plume NE, and a light curtain of fallout was observed. Satellite images from 1133 and about 2000 on 18 August showed a plume drifting NE.

The summit hot spot, which on 18 August appeared to have doubled in size, persisted on a satellite image from 1004 on 19 August. No plume was visible that day, although cloud cover may have obscured it. FWS observers reported continued rumbling from the direction of the volcano. Kanaga continued to erupt minor amounts of ash during 20-21 August, interfering with local air traffic and dropping a light dusting of ash on the community of Adak. As of midday on 22 August, analysis of satellite imagery indicated a possible plume, containing minor ash, drifting generally ESE from the volcano over Adak. The FAA enforced a 24-km restricted flight zone around Kanaga until 1430 to minimize the possibility of aircraft encountering an ash cloud during instrument approach and departure. Poor weather obscured the volcano through the morning of 22 August. However, no ash cloud was seen from Adak as visibility improved through the day.

Pilots and other observers continued to report and photograph avalanches of hot fragmental debris cascading down the N flank of the volcano into the ocean. Although AVO has been unable to clearly discern the source of this material, it likely represents collapse of a growing lava dome or ejection of hot blocks of lava from near or within the summit crater. Based on the last eight months of activity, continuing episodes of ash eruption accompanied by avalanching of hot debris down the volcano's flanks can be expected. Depending on wind conditions and the size of a given eruptive episode, additional ashfall on Adak is possible.

. . . .The eruption has been characterized by intermittent, low-level steam and ash emissions producing plumes rarely rising over 3,000-4,500 m altitude and drifting a few tens of kilometers downwind. Although tracking of ash fallout is limited due to the remote location of Kanaga, it appears from satellite imagery that detectable fallout has been confined to within a few tens of kilometers of the volcano. On 22 August, AVO learned that several very light dustings of fine ash on the N portions of Adak had occurred over the past few months.

Geologic Background. Symmetrical Kanaga stratovolcano is situated within the Kanaton caldera at the northern tip of Kanaga Island. The caldera rim forms a 760-m-high arcuate ridge south and east of Kanaga; a lake occupies part of the SE caldera floor. The volume of subaerial dacitic tuff is smaller than would typically be associated with caldera collapse, and deposits of a massive submarine debris avalanche associated with edifice collapse extend nearly 30 km to the NNW. Several fresh lava flows from historical or late prehistorical time descend the flanks of Kanaga, in some cases to the sea. Historical eruptions, most of which are poorly documented, have been recorded since 1763. Kanaga is also noted petrologically for ultramafic inclusions within an outcrop of alkaline basalt SW of the volcano. Fumarolic activity occurs in a circular, 200-m-wide, 60-m-deep summit crater and produces vapor plumes sometimes seen on clear days from Adak, 50 km to the east.

Information Contacts: AVO.


Kilauea (United States) — July 1994 Citation iconCite this Report

Kilauea

United States

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

All times are local (unless otherwise noted)


Bench collapses and littoral explosions occur as lava flows continue to enter the ocean

"The . . . eruption continued throughout July with more lava entering the ocean in the W Kamoamoa/Lae Apuki area. On the morning of 8 July, a piece of the Kamoamoa bench, ~4,000 m2, fell into the ocean. Littoral explosions following the collapse deposited a small amount of spatter on the delta. A wave associated with the collapse event deposited blocks on the surface of the delta, 40 m inland of the sea cliff. One line of stations, set up to monitor movement of cracks on the active bench, disappeared into the ocean with the collapse. Following the event, the remaining lines recorded several centimeters of seaward movement. The cracks on the bench continued to widen throughout the month. Some of the larger cracks contained standing water.

"Surface activity was confined mostly to the W Kamoamoa/Lae Apuki bench; however, on 11 July, a surface flow broke out of the active tube on Pali Uli. This flow did not reach the ocean before stagnating. There were no significant changes in the Pu`u `O`o lava pond, which was 79 m below the crater rim in July.

"The ocean entries were intermittently explosive, following the 8 July collapse, due to smaller collapses along the front of the bench. Littoral explosions increased in frequency and magnitude later in the month. The most dramatic event began on the afternoon of 26 July. By the following day, large spatter bursts had built a 10-m-high littoral cone on the leading edge of the Kamoamoa/Lae Apuki bench. Explosive activity was initially episodic but was continuous by at least 1810 on 27 July. At 2025 a cascade of lava, about 5 m wide, ripped out of the tube on Pali Uli, from the same area as the 11 July flow. Within 50 minutes, the explosive activity at the ocean had subsided. The cascade on Pali Uli fed flows that eventually stagnated the following day. Activity at the ocean paused briefly, but by 1112 on 28 July, plumes were again visible off the Kamoamoa/Lae Apuki bench. Surface flows broke out on the bench, and by the end of the month extended the bench 5-10 m W."

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

Information Contacts: T. Mattox, HVO.


Krakatau (Indonesia) — July 1994 Citation iconCite this Report

Krakatau

Indonesia

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

All times are local (unless otherwise noted)


Frequent ash explosions (300-450/day) reach heights up to 500 m

Ash explosions continued at a rate of 300-450/day in early August. The height of the ash columns, measured from the [Pasuaran Observatory] during clear weather, ranged from 150 to 500 m above the summit, with incandescent projections evident at night. The sporadic eruptions have deposited ash over almost the entire island. During the second week of August, explosion earthquakes averaged 460 events/day. Occasionally, explosion sounds were heard and vibrations felt at the observatory.

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: VSI.


Langila (Papua New Guinea) — July 1994 Citation iconCite this Report

Langila

Papua New Guinea

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

All times are local (unless otherwise noted)


Thick ash clouds from Crater 2 accompanied by explosion sounds

"Eruptive activity at Crater 2 continued during July, while Crater 3 activity was at a low level. Throughout the month, Crater 2's normal moderate emissions of thin white-grey vapour were disrupted by forceful ejections of thick, mushroom-shaped, grey-brown ash clouds accompanied by low explosion and rumbling sounds. These caused fine ashfall NW of the volcano. On 16 and 22 July, the ash clouds rose several thousands of meters above the crater. Steady weak night glow was reported on 26 July and there was fluctuating weak-bright glow on the 29th. Crater 3 continued to emit small volumes of mostly white vapour, sometimes with blue and grey vapour. There were no audible sounds or night glow reported during July. Seismic activity throughout the month remained at a low level with between 1 and 7 small low-frequency earthquakes/day."

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

Information Contacts: B. Talai, R. Stewart, and C. McKee, RVO.


Lascar (Chile) — July 1994 Citation iconCite this Report

Lascar

Chile

23.37°S, 67.73°W; summit elev. 5592 m

All times are local (unless otherwise noted)


Moderate short-lived eruption sends plume over Argentina

Renewed Vulcanian activity during 20-26 July generated plumes up to ~9,000 m altitude, ~4,000 m above the summit . . . . On 20 July at 1630 a grayish column 400-500 m high was emitted from the crater. The next day at 1230 a brownish eruptive column rose 3,000-4,000 m and immediately drifted NE. Very fine ashfall was reported in Salar de Olaroz in the Argentine Puna, 120 km NE of the vent. At 1430 on 23 July another eruption plume to a height of 3,000-4,000 m was blown NNE. No ashfall was reported in the Argentine Puna following this activity.

A single short-lived Vulcanian explosion at about 1200 on 26 July generated a column and NNE-trending plume that soon detached from the volcano; prevailing high-level winds then shifted the plume toward the E. Witnesses from Toconao (35 km NW) and San Pedro de Atacama (70 km NW) reported a moderate explosion followed by a dark-colored mushroom-shaped column that slowly rose to 4,000 m height. Pilots from Aerolineas Argentinas, AeroMonterrey, and Lineas Aereas de Chile reported to the Argentina National Metereological Service that the plume, ~30 km wide and 200 km long, reached an altitude of 9,000 m. Ashfall was only reported in areas close to the volcano. No ashfall was reported in the small village of Catua along the Chilean-Argentine border, 80 km E of Lascar. Immediately after the eruption the volcano showed very diminished activity, with weak white fumarolic plumes that hardly rose above the crater rim. From 27 July to 4 August the volcano exhibited normal fumarolic activity.

Infrared images of the 26 July ash cloud were captured by Raúl Rodano and Luis Ganz from the Meteosat 3 satellite (figure 22). An image taken at 1346 on 26 July showed an ESE-directed plume 50 x 20 km in size, reaching an altitude between 3,600 and 5,400 m (figure 22, top). At 1523 another image showed a 130-km-long plume with the trailing edge located 60 km from Lascar (figure 22, middle). On the E side of the plume, a core (40 km in diameter) developed vertically and reached ~7,000 m altitude. The lower levels of the plume were oriented ESE, following the general atmospheric circulation. Because of wind-shear between 5,400 and 7,000 m, the plume was reoriented NNE by upper-level winds (200°- 70 km/hour). On the image taken at 1631, the plume is 180 km long and 100 km from the source (figure 22, bottom). Based on analysis of this imagery, the NNE-oriented E end of the plume reached an estimated maximum height of 7,500 m. Although the sky was cloudy by 1830, scattered parts of the NNE-oriented plume could be seen 80 km E of Jujuy, Argentina, drifting E at 80 km/hour at an estimated altitude of 4,500 m. With frame animation it was possible to discern the dispersed plume reaching Presidente Roque Saenz Pena city, 800 km E of Lascar, at 2009 on 26 July.

Figure (see Caption) Figure 22. Infrared images of the 26 July 1994 plume from Lascar (white area) taken from the Meteosat 3 satellite. At 1346 (top) the small plume (50 x 20 km) was moving ESE. By 1523 (middle) the trailing edge of the 130-km-long detached plume was located 60 km from the volcano. On the image taken at 1631 (bottom), the plume was 100 km from the source, 180 km long, and the E end was oriented NNE. Approximate location of Lascar is shown by the black triangle; Jujuy, Argentina, is indicated by the white square. Courtesy of Raúl Rodano and Luis Ganz.

These eruptions comprise the fourth period of Vulcanian activity following the large subplinian eruption of 19-20 April 1993. Eruptions were also reported in August and December 1993, and February 1994. All are thought to have been caused by blockage of the degassing magmatic system due to collapse of the dome formed in the late stages of the April 1993 eruption. The present morphology of the crater is unknown, although this renewed activity suggests further subsidence of the crater floor due to conduit degassing. Lascar, the most active volcano of the northern Chilean Andes, contains five overlapping summit craters along a NE trend. Prominent lava flows descend its NW flanks.

Reference. Gardeweg P., M.C., 1994, La Explosion del 26 de Julio, 1994, X Informe sobre el comportamiento del Volcan Lascar: Informe Inedito, Biblioteca Servicio Nacional de Geologia y Mineria, 4 p.

Geologic Background. Láscar is the most active volcano of the northern Chilean Andes. The andesitic-to-dacitic stratovolcano contains six overlapping summit craters. Prominent lava flows descend its NW flanks. An older, higher stratovolcano 5 km E, Volcán Aguas Calientes, displays a well-developed summit crater and a probable Holocene lava flow near its summit (de Silva and Francis, 1991). Láscar consists of two major edifices; activity began at the eastern volcano and then shifted to the western cone. The largest eruption took place about 26,500 years ago, and following the eruption of the Tumbres scoria flow about 9000 years ago, activity shifted back to the eastern edifice, where three overlapping craters were formed. Frequent small-to-moderate explosive eruptions have been recorded since the mid-19th century, along with periodic larger eruptions that produced ashfall hundreds of kilometers away. The largest historical eruption took place in 1993, producing pyroclastic flows to 8.5 km NW of the summit and ashfall in Buenos Aires.

Information Contacts: M. Gardeweg, SERNAGEOMIN, Santiago; J. Viramonte, R. Becchio, I. Petrinovic, and R. Arganaraz, Instituto Geonorte Univ Nacional de Salta, Argentina; B. Coira and A. Perez, Instituto de Geologia Universidad de Jujuy, Argentina; R. Rodano and L. Ganz, Aerolineas Argentinas Weather Division, Buenos Aires, Argentina; H. Corbella, CONICET - Argentine Museum of Natural Sciences, Buenos Aires.


Manam (Papua New Guinea) — July 1994 Citation iconCite this Report

Manam

Papua New Guinea

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

All times are local (unless otherwise noted)


Explosions on 5-7 July generate ash clouds and eject lava fragments

"During July, there was a brief increase in the level of activity from Southern Crater, while Main Crater activity continued to remain at a low level. Activity from Southern Crater was low from 1 to 4 July with gentle emissions of small volumes of white vapour. From 1430 on 5 July onwards, activity increased as weak deep-sounding explosions were heard at 5-10 minute intervals accompanying forceful emissions of grey-brown ash clouds. Incandescent lava fragments were seen being ejected from Southern Crater during the evening until the activity stopped at 2130. Ash emissions continued to occur until 7 July, and only one explosion was heard on 6 July. For the remainder of the month, activity at Southern Crater continued at the normal low level, with only white vapour emissions and blue vapour observed on 12 and 15 July.

"Throughout the month Main Crater continued to emit white vapour, weak to moderate in volume. A whitish-grey plume was seen on 31 July. No sounds were heard and no night glow was observed.

"Seismic activity remained at a low-moderate level throughout the month, with small fluctuations in the number and amplitude of low-frequency earthquakes. On average ~1,170 earthquakes/day were recorded, and there was a brief quiet period from 25 to 27 July when <500 earthquakes/day were recorded. There were no significant tilt changes in July.

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

Information Contacts: B. Talai, R. Stewart, and C. McKee, RVO.


Marapi (Indonesia) — July 1994 Citation iconCite this Report

Marapi

Indonesia

0.38°S, 100.474°E; summit elev. 2885 m

All times are local (unless otherwise noted)


Eruption sends ash column to ~6 km above sea level; summary of 1993 activity

An eruption at 0016 on 12 August 1994 sent an ash column to ~6 km altitude, a height of 3,200 m above the summit. Another explosion at 0046 ejected ash 280 m high. From the observatory ~7 km from the crater, observers noted incandescent projections as high as 300 m above the crater rim, accompanied by explosion sounds and vibrations. Ashfall in and around the city of Bukittinggi . . . ranged from 0.5 to 1 mm thick. Shallow volcanic earthquakes were recorded after the explosions, but gradually decreased.

Eruptions during the first half of 1993 (VSI, 1993a) produced lapilli and ash that were deposited in a radius of 1.5-3 km from the active crater. A dark gray column rose as high as 1,200 m above the summit . . . , but was usually in the 400-500 m range. Explosion earthquakes from January to July 1993 fluctuated between 1 and 77 events/day. The frequency of explosions increased in July 1993, but then decreased from August through December (VSI, 1993b). These explosions during Jul-Dec 1993 deposited lapilli and ash within a 750-m-radius of the active crater. Incandescent material fell within a few tens of meters of the crater rim. Average plume height in the second half of 1993 was 400-800 m, reaching a maximum of 3,200 m above the summit. Throughout 1993, deep volcanic earthquakes (A-type) were detected at a rate of 6-41/month. Between 42 and 338 shallow (B-type) events were recorded each month.

Geologic Background. Gunung Marapi, not to be confused with the better-known Merapi volcano on Java, is Sumatra's most active volcano. This massive complex stratovolcano rises 2,000 m above the Bukittinggi Plain in the Padang Highlands. A broad summit contains multiple partially overlapping summit craters constructed within the small 1.4-km-wide Bancah caldera. The summit craters are located along an ENE-WSW line, with volcanism migrating to the west. More than 50 eruptions, typically consisting of small-to-moderate explosive activity, have been recorded since the end of the 18th century; no lava flows outside the summit craters have been reported in historical time.

Information Contacts: VSI.


Masaya (Nicaragua) — July 1994 Citation iconCite this Report

Masaya

Nicaragua

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

All times are local (unless otherwise noted)


Sulfur-rich plume and incandescent ejections from opening in lava lake

Scientists from FIU and INETER visited Masaya for about an hour on the afternoon of 26 May 1994 and noted that the two incandescent openings (5-7 m in diameter) in the cooling lava lake observed on 1 March near the N wall of Santiago crater (BGVN 19:03) had coalesced into a single opening 10-12 m long. A sulfur-rich plume was being emitted from the opening at a rate of several pulses/minute; the pulses were accompanied by jetting sounds easily heard from the S rim. Fresh, black ash covered the crater floor immediately SW of the opening. INETER scientists reported that small Strombolian explosions ejected incandescent material from the opening several times during May and June 1994.

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: Peter C. La Femina, Michael Conway, and Andrew MacFarlane, FIU; Christian Lugo, INETER.


Merapi (Indonesia) — July 1994 Citation iconCite this Report

Merapi

Indonesia

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

All times are local (unless otherwise noted)


Increased deformation precedes a nuee ardente

A nuée ardente erupted around 1400 on 16 July 1994, an event preceded by a clear increase in tilt several days before the eruption. Figure 9 shows tilt measurements during the interval 1-18 July. One set of measurements came from a site on Merapi's summit (Goa Jepang, ~2,900 m elevation); the other set of measurements came from a cave on Merapi's S flank (~1,000 m elevation).

Figure (see Caption) Figure 9. Tilt at Merapi recorded at both the summit and in a cave on the S flank, 1-18 July 1994 Courtesy of Arnold Brodscholl.

The daily temperature variation in the cave is<1°C, suggesting little influence from temperature there (left-hand scale). The daily record of tilt varied significantly less at the cave site (typically <100 µrad) than at the summit site (typically ~150 µrad), an observation consistent with the more stable temperature in the cave.

Tilt began increasing at both sites roughly five days prior to the eruption. During this interval the tilt at both sites correlated consistently overall, and moderately at the finer-scale. Tilt ceased to track consistently near the end of the eruption, when the flank site underwent a dramatic decrease, a turn-around that began prior to the end of the eruption. Summit tilt measurements in January 1993 were similar to those presented here but then measurements at the cave site were a rarity, leaving the increased tilt without confirmation.

Geologic Background. Merapi, one of Indonesia's most active volcanoes, lies in one of the world's most densely populated areas and dominates the landscape immediately north of the major city of Yogyakarta. It is the youngest and southernmost of a volcanic chain extending NNW to Ungaran volcano. Growth of Old Merapi during the Pleistocene ended with major edifice collapse perhaps about 2,000 years ago, leaving a large arcuate scarp cutting the eroded older Batulawang volcano. Subsequent growth of the steep-sided Young Merapi edifice, its upper part unvegetated due to frequent activity, began SW of the earlier collapse scarp. Pyroclastic flows and lahars accompanying growth and collapse of the steep-sided active summit lava dome have devastated cultivated lands on the western-to-southern flanks and caused many fatalities.

Information Contacts: A. Brodscholl, GMU; Subandryo, VSI; B. Voight, Pennsylvania State Univ.


Momotombo (Nicaragua) — July 1994 Citation iconCite this Report

Momotombo

Nicaragua

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

All times are local (unless otherwise noted)


Summit fumarole temperatures range from 238 to 655°C

Beginning on 11 June, scientists from FIU and INETER deployed a datalogger in the crater to continuously monitor fumarole temperatures and barometric pressure. The team entered the summit crater three times along a trail that crosses an active avalanche chute and leads around to the NE crater rim. Condensate and Giggenbach-type samples were collected from fumaroles along the SW crater wall. These fumaroles were very corrosive, as indicated by the destruction of the datalogger thermocouples, and had temperatures ranging from 238 to 655°C. A voluminous plume was rising from the crater on 13 March.

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

Information Contacts: Peter C. La Femina, Michael Conway, and Andrew MacFarlane, FIU; Christian Lugo M., INETER.


Nyamuragira (DR Congo) — July 1994 Citation iconCite this Report

Nyamuragira

DR Congo

1.408°S, 29.2°E; summit elev. 3058 m

All times are local (unless otherwise noted)


High lava fountains feed lava flow on NW flank

High lava fountaining in early July took place from a new vent on the W flank, named Kimera. Located ~100 m S of the 1971 Rugarama cone, this vent became active at 2148 on 4 July, but remained active for only 4-5 days. The lava flows generally moved W until at least 10 July, when the flows reached their maximum extent. By 11 July, the small lake (Magera) at the E foot of a Precambrian escarpment was entirely filled and dried by the flow. High SO2 concentrations detected by the TOMS during 5-10 July were most likely caused by this activity at Nyamuragira and not from the lava lake at Nyiragongo. Nyamuragira also emitted levels of SO2 detectable by satellite during 17-19 July 1986 (275-375 ± 30% kt) and on 24 September 1991 (20 kt).

A press report described falls of both ash and Pele's hair during the first half of July in the Mokoto Hills, above the W escarpment of the rift ~20 km from the volcano. Several farmers reported problems caused by cattle eating ash-laden grass.

Long-term monitoring data indicated an apparent acceleration in seismo-geodetic activity in the past 10 years. Seismicity steadily increased from <200 volcanic events/month in 1960-65 to ~300-400/month in the early 1980's (figure 13). Increased seismicity after 1985 suggests an acceleration of magma supply into the volcano. The geodimeter network operating on the Nyamuragira summit has also revealed a gradual strain increase since 1980, showing that the crater is dilated.

Figure (see Caption) Figure 13. Monthly number of volcanic earthquakes at Nyamuragira, 1960-92. The short-period seismic station is located 110 km from the volcano. Vertical arrows indicate flank eruptions. Courtesy of H. Hamaguchi.

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: N. Zana, Centre de Recherche en Géophysique, Kinshasa; H. Hamaguchi, Tohoku Univ; J. Durieux, GEVA, Lyon, France; G. Benhamou, Libération newspaper, France; T. Casadevall, USGS; I. Sprod, GSFC.


Nyiragongo (DR Congo) — July 1994 Citation iconCite this Report

Nyiragongo

DR Congo

1.52°S, 29.25°E; summit elev. 3470 m

All times are local (unless otherwise noted)


Lava lake activity produces strong red glow above crater

For four days around 14 July a dense steam-and-gas plume was visible from Goma, and red glow could be seen at night. An amateur video taken on an unknown day between 19 and 24 July included a 6-second partial view of the crater that revealed a large very active lava fountain roughly in the center of the crater. A large, flat spatter cone had been built, with a least three large openings in the walls and lava flows radiating from the openings. The entire lava lake was not active. The background was hidden by gases and clouds, making it impossible to determine the elevation of the lava lake surface. Following the 1982 activity, the surface was 400 m below the crater rim. A very strong red glow was again observed above the crater during the night of 29 July. Very little red glow was reported in early August.

Another eruption within the summit lava lake began at about 1900 on 10 August. Red glow above the summit could be seen from Goma during daylight as well as at night. Press reports also stated that "ash and dust" had been emitted from the volcano. The increased activity on 10-13 August and strong red glow visible from the refugee camps caused some concern among the refugees and relief workers.

Volcanologists from Zaire, Japan, France, and the USGS were all present in Goma from 19 to 23 August. The primary purpose of the USGS scientists was to evaluate the hazards posed to the ongoing relief operations in Goma, which contained more than one million Rwandan refugees and the large Zairian population. Specific hazards addressed included the threat of active lava flows to resettlement camps and infrastructure, the threat of volcanic ash to air relief operations, and the threat of CO2 accumulation to refugees in resettlement camps along the Goma-Sake road.

During the flight to Goma on 19 August, USGS volcanologists flew over and around the crater. Although the crater floor was clearly visible, no signs of activity were observed. However, during the pre-dawn hours on 20 August, strong red glow above the main crater could be seen. Early that morning the French Army flew USGS and French volcanologists to the summit. At that time the lava lake was very active, with fountaining of lava up to 40 m above the surface of the crater floor, estimated to be ~450 m below the crater rim. Seismograms from instruments operated by Zairan scientists clearly showed this eruptive activity. The eruption-related seismicity had ended by 22 August, and no additional red glow was noted. No activity was observed during an aerial inspection the next day, but red glow was again seen early on 24 August.

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: H. Hamaguchi, Tohoku Univ; J. Durieux, GEVA; T. Casadevall and J. Lockwood, USGS; AP.


Poas (Costa Rica) — July 1994 Citation iconCite this Report

Poas

Costa Rica

10.2°N, 84.233°W; summit elev. 2708 m

All times are local (unless otherwise noted)


Ashfall SW of the summit covers 56 km2

Despite roughly 3 months of rainy weather, the colorful northernmost crater lake that evaporated this past year remained nearly dry, venting became alarmingly noisy, and in the interval from 9 July to 5 August the volcano produced a series of ash falls. These falls were carried to the SW and covered a roughly 56 km2 area.

Increased vigor of fumaroles has led to vapor columns reaching >1 km above the lake floor; the columns were blown to the W and SW. Some of the columns were red to orange in color, presumably due to combustion of sulfur. In the recent past the most vigorous fumaroles were located near the former lake's center. These fumaroles diminished in size; during July the ones located SW of the former lake were of greatest importance.

On 21 July, a fumarole S of the former lake generated a white-colored column; thermocouple measurements of the fumarole revealed a 495°C temperature. The highest pressure fumarole, also located S of the former lake, emitted a red- to orange-colored plume. Continuously jetted gases contained entrained sediment. These escaping gases had a temperature of 515°C, measured with a pyrometer aimed toward the vent. Other fumaroles issued sporadic sediment and colored gases; temperature at the dome was 81°C. ICE and ECG reported jetting gases thrusting to 350 m above the crater floor and then rising convectively to 1 km. Using infrared thermometry, temperatures as high as 700°C were measured in the S-vent area.

Ash was erupted on the night of 9 July and into the morning of 10 July. Continued reports of ash fall came from San Miguel Arriba, Trojas, San Luis de Grecia, Cajon, and Porvenir de Sarchi (figure 53). These reports continued for 2 days; later, mapping and compilation led to an ash distribution map for this and later eruptions in July (figure 53). Blocks were principally limited to the crater area, fine ash covered much of the summit area, and the finest ash blew as far as about 15 km. The fumaroles ejecting lake sediment continued to grow, and ejected ash with blocks. Such events were noted seven times in late July (24, 25, 27, 28, 29, and twice on 30 July). In general, the strongest ash eruptions were accompanied by loud jet-like noises.

Figure (see Caption) Figure 53. Distribution of ash from Poás during July 1994. Scale is approximate; roads indicated by dashed lines, rivers by solid lines, and settlements by dots. Courtesy of OVSICORI-UNA.

OVSICORI-UNA reported July seismicity from station POA2 (2.5 km SW of the active crater) in terms of several types of events (figure 54). In July, a total of 4,994 events took place. Starting on 26 July several high-frequency (volcano-tectonic) earthquakes took place each day.

Figure (see Caption) Figure 54. Poás seismicity for July 1994. Courtesy of OVSICORI-UNA.

The amount of deformation on two distance-measurement lines has, since 1973, shown a tendency toward contraction, amounting to about 0.7 and 1.8 ppm/month, respectively. Between 24 June and 5 July both lines suddenly contracted about 19 ppm. From 22 July until the end of the month there were no further significant changes. Back in the interval between 8 March and 12 May a component of two leveling lines deflated slightly (10 µrad). During the last re-occupation of the leveling lines, which took place at the end of July, one line 2 km S of the active crater had inflated by about 17 µrad.

The increased degassing has led to a variety of health and environmental problems. Crops and soils have been damaged. Residents on the W and SW flanks continue to report irritations to the throat, skin, and eyes when gases and ash enter their communities.

On the morning of 22 August an American Airlines flight reported an eruption cloud to ~6 km. Visibility over Poás was poor due to thunder storms to the E and clouds in its vicinity; satellite imagery was unable to detect the plume. Jorge Barquero described this plume as consisting of vapor and gas. A plume on the previous day reached to about 2 km above the vent; heights of these plumes were highly dependant on local wind conditions. As of 22 August, no confirmed ash-bearing plumes had erupted since 5 August.

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

Information Contacts: E. Fernández, J. Barquero, V. Barboza, R. Van der Laat, F. de Obaldia, and T. Marino, OVSICORI; G. Soto, G. Alvarado, and F. Arias, ICE; M. Mora, C. Ramirez, and G. Peraldo, UCR.


Rabaul (Papua New Guinea) — July 1994 Citation iconCite this Report

Rabaul

Papua New Guinea

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

All times are local (unless otherwise noted)


Seismicity remains low; minor subsidence

"July was relatively quiet, with 220 detected earthquakes . . . . Activity was highest in the middle of the month, with half the earthquakes occurring between 13 and 19 July, and two swarms on those days. Most of the earthquakes, including the 13 July swarm, were located on the NE portion of the ring fault on the E side of Greet Harbour at depths of 0-4 km. Most of the rest were located near the W portion of the ring fault. An exception to this was the swarm on 19 July, which was located, albeit poorly, in the center of Karavia Bay. None of the earthquakes were large enough to be felt. The largest earthquake during the month, M 2.7, occurred on 5 July. Leveling measurements on 19 July showed a very small amount of subsidence, <9 mm, at the end of Matupit Island since 27 June.

"On 13 July, signals were recorded from three earthquakes that originated outside the network, somewhere N of Rabaul. S-P times between 2 and 4 seconds were consistent with locations near Tavui caldera, an underwater caldera N of Rabaul. This caldera was only discovered in 1984 and virtually nothing is known about it. Records are currently being checked for any other seismic activity that may have come from this vicinity."

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

Information Contacts: B. Talai, R. Stewart, and C. McKee, RVO.


Ruapehu (New Zealand) — July 1994 Citation iconCite this Report

Ruapehu

New Zealand

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

All times are local (unless otherwise noted)


Relatively stable with water cooling of Crater Lake

When visited on 8 June, Crater Lake appeared a very pale, almost yellowish, gray. On 4 July, as was more typical for the recent past, the crater lake was a uniform battleship-gray with no evidence of convection or slicks. Temperature at Outlet, 22°C, was slightly higher than for June-July in past years. The lake is currently cooling following a minor heating event in early June that followed strong acoustic signals, minor earthquakes, and volcanic tremor 10-15 days earlier. These two recent visits revealed no evidence of eruptive activity.

On 4 July, unusually thick accumulations of snow prevented deformation surveys and emphasized the need to install tiltmeters in key locations to improve the continuity of monitoring. Snow and ice were removed from the ARGOS satellite installation, but the solar panel could not be located under deep snow and battery and transmission power steadily declined.

A working party coordinated by the Ministry of Civil Defence has considered developing a contingency plan for volcanic hazards. They also may adopt a system using "Volcanic Alert Levels" graded from 1 (low level) to 5 (highest level, hazardous eruption in progress).

Geologic Background. Ruapehu, one of New Zealand's most active volcanoes, is a complex stratovolcano constructed during at least four cone-building episodes dating back to about 200,000 years ago. The dominantly andesitic 110 km3 volcanic massif is elongated in a NNE-SSW direction and surrounded by another 100 km3 ring plain of volcaniclastic debris, including the Murimoto debris-avalanche deposit on the NW flank. A series of subplinian eruptions took place between about 22,600 and 10,000 years ago, but pyroclastic flows have been infrequent. A single historically active vent, Crater Lake (Te Wai a-moe), is located in the broad summit region, but at least five other vents on the summit and flank have been active during the Holocene. Frequent mild-to-moderate explosive eruptions have occurred in historical time from the Crater Lake vent, and tephra characteristics suggest that the crater lake may have formed as early as 3,000 years ago. Lahars produced by phreatic eruptions from the summit crater lake are a hazard to a ski area on the upper flanks and to lower river valleys.

Information Contacts: P. Otway, B. Scott, and A. Hurst, IGNS Wairakei.


Semeru (Indonesia) — July 1994 Citation iconCite this Report

Semeru

Indonesia

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

All times are local (unless otherwise noted)


Small ash eruptions to 500 m above the summit

Eruptive activity on 3 February 1994 produced ashfalls, lava avalanches, and pyroclastic flows, destroying a village and killing 6 people (19:01). Total volume of the pyroclastic-flow deposits was about 6 million m3.

During 5-14 August observations, visual and seismic activity . . . were normal. The daily number of explosion earthquakes fluctuated between 40 and 100 events, and volcanic tremor was occasionally recorded with a maximum amplitude of 4 mm. Ash eruptions generated clouds up to 500 m above the summit. There were no pyroclastic flows or lava avalanches.

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

Information Contacts: VSI.


Telica (Nicaragua) — July 1994 Citation iconCite this Report

Telica

Nicaragua

12.606°N, 86.84°W; summit elev. 1036 m

All times are local (unless otherwise noted)


Explosive eruption causes ashfall >12 km SW of the summit

An eruption on 31 July produced a gas-and-ash column that rose ~800 m above the 1,060-m-high summit. Ashfall was reported SW of the volcano (figure 6). Phreatic activity continued until 12 August with gas emission and minor ash explosions. Seismicity has been recorded continuously since December 1993, when a permanent telemetered seismic station (TELN: short-period, vertical-component) was installed ~500 m E of the active crater rim (figure 7). Also since December 1993, the Instituto Nicaragüense de Estudios Territoriales (INETER) has collaborated with the government, local authorities, civil defense, and the media, to educate the population about the situation at the volcano. Due to the relatively low magnitude of this eruption, it was not necessary to carry out the prepared evacuation plans.

Figure (see Caption) Figure 6. Ashfall from Telica, 31 July-6 August 1994. Courtesy of INETER.
Figure (see Caption) Figure 7. Sketch map of the summit area at Telica, showing locations of crater fumaroles (left) and seismic stations (right). Courtesy of INETER.

A seismic event on 15 June 1994 was recorded by several stations of the Nicaraguan seismic network, up to distances of ~40 km from Telica. This event at a depth of 6 km had a maximum magnitude of 2.1. The 31 July eruption was preceded by a steady increase in seismicity during 15-25 July (figure 8), recorded by station TELN. Seismicity had increased from25 events/day at the end of May. By the end of July there were up to 150 events/day.

Figure (see Caption) Figure 8. Seismicity at Telica, February-August 1994. Courtesy of INETER.

Crater and fumarole observations, March-June 1994. Beginning on 3 June, scientists from Florida International Univ (FIU) and INETER spent 15 days at Telica as part of an ongoing investigation to determine the areal extent and intensity of degassing, and the role of structural controls on degassing from the volcanic complex. A lacustrine deposit was observed in March at the S end of the crater, and a small, muddy brown lake was visible in May-June. All observations were made from the NE rim, where jetting sounds were clearly audible. Sulfur-rich steam from the crater sometimes moved down the slopes of the volcano, filling the NW valley with high concentrations of SO2; sulfur odor could occasionally be smelled on the NE slope. Residents on the flanks of the volcano stated that the activity was not unusual for this time of the year.

Fumarole temperatures near station TELN were in the 81-86°C range, similar to temperatures in September 1993 and March 1994. A low-temperature fumarole was discovered on the lower ESE slope of the ridge occupied by the seismic station. A data-logger recorded fumarole temperatures and barometric pressure for four days. Fumaroles near TELN and in the active crater exhibited increased flux since March. At times the crater fumaroles appeared to be emitting steam and gases in discrete clouds at intervals of several minutes. The most intense fumarole was in the upper NW corner of the crater (A on figure 7). Other fumaroles were observed in the lower NW corner, on the N, E, and SE crater walls, and in avalanche deposits on the S and SE parts of the crater floor. Fumarole A had temperatures of 150-160°C in July 1994 (figure 7). In the NE corner of the crater, fumarole B increased in temperature from 55°C in April to 174°C in July. Another fumarole area on the E side of the crater (C) had a temperature of 498°C in July, a significant increase from 246°C in 1990.

Eruptive activity. A relatively small explosive eruption at about 1645 on 31 July produced a gas-and-ash column that rose ~800 m above the summit. The light-gray ash cloud was driven SW by the wind, depositing about 2 mm of ash in the towns of Chichigalpa (20 km WSW), Quezalguaque (12.5 km SSW), and Posoltega (16 km SW) (figure 6). No seismic events were felt by residents near the volcano, but the sound of the explosion was heard at distances up to 10 km.

Following the 31 July eruption, phreatic activity continued in the next hours and days with varying intensity of gas emanation and ash expulsion. One of the strongest explosions, on 5 August, produced an ash column 1,200 m high. One phase of gas emission reached heights of 200-300 m above the crater rim. Gas also filled a valley W of the volcano with high concentrations of SO2, sometimes causing breathing problems for INETER scientists who traveled through the valley at a distance of ~2 km from the crater. Seismicity at shallow depths (~2 km) beneath the crater was recorded by TELN and four stations installed after the eruption began: telemetric stations TEL 2, 3, & 4, and local digital registration station TEL 5 (figure 7). The numerous weak events during the eruption were only recorded by the local seismic stations.

Chemical analyses of washed ash samples collected on different days indicated an increase of the SO42- and Cl- contents over time. Several very heavy rainfalls occurred during the eruptive period. Analyzed rainwater samples also showed high concentrations of SO42- with respect to Cl- and F2-, and a corresponding low pH level. Similar measurements two weeks before the eruption showed normal low concentrations of SO42- and Cl-.

Early eruption products consisted of very fine-grained, light-colored, blocky ash. INETER volcanologists believe that the ash was non-juvenile, and was ejected during phreatic or phreatomagmatic eruptions. Major explosions generally lasted for ~10-25 minutes. Early eruption columns were mostly white in color, and ranged from several hundred meters to 1,400 m above the vent. On 9 and 10 August, the ash was black, significantly darker than before, with correspondingly darker eruption plumes. The ash remained blocky and non-vesicular.On 10 August, 40-50 high-frequency seismic events were recorded, including one that lasted 4.5 hours. High-frequency events prior to 10 August occurred at a rate of ~70-90/day and were associated with more frequent explosions (10-20/day). The number of daily explosions also decreased to 6 on 10 August, including one major explosion that lasted for 16 minutes. An explosion at 1800 on 11 August generated a plume that rose 350 m, but only 16 high-frequency events were detected that day. On the early morning of 12 August one of the strongest explosions of this eruption occurred; activity then decreased throughout the day. By that evening the explosions had stopped and gas emanation and seismicity reached very low levels.

Seismicity had increased slightly by 16 August, five microseismic events were detected during 24 hours on 17-18 August, and on 20 August tremor lasted for 6.2 hours. However, no seismic events were detected on 21-22 August, and activity remained low as of 26 August.

On 23 August, Oto Matias (INSIVUMEH, Guatemala) arrived with a COSPEC instrument to assist INETER scientists in making SO2-flux measurements. Attempts to carry out COSPEC measurements of the SO2 concentration in the gas plume were made on 24 August, but low levels of gas emission and cloudy skies prevented good results.

Soil sampling. During three field surveys by FIU and INETER scientists in early June, >60 stations were deployed over 50 km2 to determine the concentration of radon (Rn), CO2, Hg, and He in soils. One identified anomaly had intensified between March and May/June 1994. This anomaly, ~750 m long and 250 m wide, surrounded the TELN seismic station. Along this anomaly, Hg values ranged from several tens of ppb to >2,900 ppb, He from 5,399 to 5,415 ppb, CO2 to 2.1 volume %, and Rn to 1,819 pico-Curies/liter.

San Jacinto Hot Springs. The village of San Jacinto, 9 km NE of the town of Telica and 2 km E of Santa Clara volcano, contains a field of boiling mudpots (BGVN 19:03). Soil samples for Hg and CO2 measurements were collected from the hydrothermal field in March and May/June 1994. The March samples contained CO2 concentrations up to 0.09 volume % and Hg from 6,710 to 21,512 ppb. The onset of the rainy season had resulted in an increase in both the size of the field and the steam flux since 9 March. Exploration for a new geothermal power plant was taking place approximately 250 m WNW.

Historical activity. Telica is a composite volcano located 19 km N of León at the NW end of a large volcanic complex. Known historical activity dates from a strong eruption that occurred in 1527-29. Strong activity was also noted in 1685, 1740-43, and at least 7 times in the 20th century. During several eruptions ash has damaged agricultural crops. In February 1982 several strong explosions generated ash columns of 3.5 km height and the ashfall affected nearby towns. The most recent eruption of Telica in November 1987 included Strombolian-type activity.

Eruptions in pre-historical times produced ash deposits of 50 cm thickness or more within a radius of 50 km. A volcanic hazard map (figure 9) suggests that ashfall poses the greatest threat to the local population. Lava flows have occurred, but with low frequency, most recently ~1,000 years ago. The hazard zone for pyroclastic eruptions lies within ~2 km of the crater. Lahars have occurred as a result of very strong eruptions during the rainy season.

Figure (see Caption) Figure 9. Volcanic hazards map of Telica. Hazard zones are shown for ashfall and tephra, lava flows, and column collapse. Courtesy of INETER.

Geologic Background. Telica, one of Nicaragua's most active volcanoes, has erupted frequently since the beginning of the Spanish era. This volcano group consists of several interlocking cones and vents with a general NW alignment. Sixteenth-century eruptions were reported at symmetrical Santa Clara volcano at the SW end of the group. However, its eroded and breached crater has been covered by forests throughout historical time, and these eruptions may have originated from Telica, whose upper slopes in contrast are unvegetated. The steep-sided cone of Telica is truncated by a 700-m-wide double crater; the southern crater, the source of recent eruptions, is 120 m deep. El Liston, immediately E, has several nested craters. The fumaroles and boiling mudpots of Hervideros de San Jacinto, SE of Telica, form a prominent geothermal area frequented by tourists, and geothermal exploration has occurred nearby.

Information Contacts: H. Taleno, L. Urbina, M. Navarro, O. Canales, C. Guzman, C. Buitrago, A. Izaguirre, Christian Lugo M. (Vulcanology); W. Strauch (Seismology); C. Urbina, and A. Acosta (Electronics), INETER, Managua; Peter C. La Femina, Michael Conway, and Andrew MacFarlane, Florida International Univ, USA.


Ulawun (Papua New Guinea) — July 1994 Citation iconCite this Report

Ulawun

Papua New Guinea

5.05°S, 151.33°E; summit elev. 2334 m

All times are local (unless otherwise noted)


White vapor emissions and low-frequency tremor

"The level of activity . . . was slightly lower in July . . . . The summit crater continued to emit mainly white vapour, of variable volume. Faint blue vapour emissions were seen on 3, 5, 9, and 20 July. No sounds or night glow were reported.

"Seismic activity . . . continued the pattern of previous months, with mainly sub-continuous, low-level, low-frequency tremor, and the occasional larger low-frequency earthquake. Only two high-frequency earthquakes were recorded during the month. Amplitude measurements and RSAM monitoring were made difficult at the start of the month by storm-generated noise. However, both showed a gradual increase through the month until about 23 July when there were sharp drops; gradual increases were again seen through the end of the month."

Geologic Background. The symmetrical basaltic-to-andesitic Ulawun stratovolcano is the highest volcano of the Bismarck arc, and one of Papua New Guinea's most frequently active. The volcano, also known as the Father, rises above the N coast of the island of New Britain across a low saddle NE of Bamus volcano, the South Son. The upper 1,000 m is unvegetated. A prominent E-W escarpment on the south may be the result of large-scale slumping. Satellitic cones occupy the NW and E flanks. A steep-walled valley cuts the NW side, and a flank lava-flow complex lies to the south of this valley. Historical eruptions date back to the beginning of the 18th century. Twentieth-century eruptions were mildly explosive until 1967, but after 1970 several larger eruptions produced lava flows and basaltic pyroclastic flows, greatly modifying the summit crater.

Information Contacts: B. Talai, R. Stewart, and C. McKee, RVO.


Unzendake (Japan) — July 1994 Citation iconCite this Report

Unzendake

Japan

32.761°N, 130.299°E; summit elev. 1483 m

All times are local (unless otherwise noted)


Lava lobe 13 grows endogenously but then nearly stops growing in late-July

Lobe 13 . . . grew endogenously at slow rates until late-July. Its final size was ~80 m long, 70 m wide, and 30 m high; it lies hidden behind the roughly 10x longer lobe 11, which forms the prominent bulge on figures 73 and 74.

Figure (see Caption) Figure 73. Sketch of the Unzen lava done showing features of the 22 July photograph (figure 74); view is roughly [from] the N. Vegetated surfaces are shown in black, undifferentiated dome, talus, pyroclastic-flow, and other deposits shown lightly shaded. Courtesy of S. Nakada.
Figure (see Caption) Figure 74. Photograph of the lava dome at Unzen, 22 July 1994. Taken from a helicopter looking [from] approximately N. Courtesy of S. Nakada.

In Unzen's summit area, the endogenous dome developed three E-W trending ridges along its top. The highest (central) ridge uplifted in early-July between two other ridges. The central ridge and a N ridge moved to the N at a rate of ~2 m/day during July, leaving behind the S ridge and increasing the width of a graben between them. The central ridge also rose vertically at a rate of <1 m/day. The E part of the central ridge consisted of brown-colored massive lava that was rounded, convex upward, and relatively smooth. The ridge was composed of massive lava squeezed from the interior of the dome, an effect also seen in April. When the lava reached the top of the ridge it broke and collapsed.

The ridges stopped moving N at the end of July. Occasionally there were small, low-density rockfalls to the SW in early- to mid-August. Owing to fragmentation, the massive lava of the central ridges decreased its height by ~20 m during the first two weeks in August, and at the same time the talus slope hardly advanced in any direction. These observations imply that for this two-week period in August an extremely low eruption rate (estimated at 4m3/day) prevailed.

During mid-July to early-August a continuous rain of N-directed rockfalls occurred when the N ridge became exposed at the cliff top. These rockfalls transformed into small pyroclastic flows, generally with run-out distances under 1 km. Pyroclastic flows were detected seismically at a station 1 km WSW of the dome and real-time monitoring of the dome was accomplished by four sets of visible and thermal infrared video cameras. During July this system detected 44 pyroclastic flows.

During most of July, microearthquakes beneath the dome generally took place <80 times a day. The total number of earthquakes in July was 2,488, roughly a 20% drop from the previous two months.

EDM by the JMA and the GSJ found that during late-June through mid-July the radial distance to one reflector on Unzen's N flank shortened rapidly, by tens of centimeters/day. The lack of confirmation from other reflectors suggested that the area in motion was of limited size.

Geologic Background. The massive Unzendake volcanic complex comprises much of the Shimabara Peninsula east of the city of Nagasaki. An E-W graben, 30-40 km long, extends across the peninsula. Three large stratovolcanoes with complex structures, Kinugasa on the north, Fugen-dake at the east-center, and Kusenbu on the south, form topographic highs on the broad peninsula. Fugendake and Mayuyama volcanoes in the east-central portion of the andesitic-to-dacitic volcanic complex have been active during the Holocene. The Mayuyama lava dome complex, located along the eastern coast west of Shimabara City, formed about 4000 years ago and was the source of a devastating 1792 CE debris avalanche and tsunami. Historical eruptive activity has been restricted to the summit and flanks of Fugendake. The latest activity during 1990-95 formed a lava dome at the summit, accompanied by pyroclastic flows that caused fatalities and damaged populated areas near Shimabara City.

Information Contacts: S. Nakada, Kyushu Univ; JMA.


Whakaari/White Island (New Zealand) — July 1994 Citation iconCite this Report

Whakaari/White Island

New Zealand

37.52°S, 177.18°E; summit elev. 294 m

All times are local (unless otherwise noted)


No eruptive activity, but new shifts in leveling and magnetic data

Routine monitoring visits on 23 April and 28 June 1994 found no evidence of any eruptive activity. On 23 April the floor of Princess Crater was occupied by a muddy pond that contained fresh landslide debris (see figure 21). The divide between Wade and Royce craters had been destroyed. Active fumaroles included those in TV1 Crater, and those escaping from beneath landslide debris in the Royce area.

Scientists who made brief trips on 12 and 15 May noted 5-10 m subsidence of the lake occupying the active vent area on the floor of Wade Crater; the lowered lake level persisted until at least 29 May. A triangulation survey on 28 June determined the lake to be 56 m below sea level and 92 m below the rim of the 1978/90 Crater Complex.

Deformation was surveyed in nearly ideal conditions on 28 June, achieving a good error of closure; the results showed that since 19 January 1994 a subtle but significant crater-wide uplift, typically 5-10 mm, has taken place. Stronger uplifts occurred at Donald Mound (+15 mm) and SE of Peg M (+21 mm). This kind of crater-wide inflation was last seen in the three years preceding the 1976-93 eruptions.

A magnetic survey of established sites revealed a pattern of net magnetic changes very similar to the two previous periods of measurements in 1993. A negative anomaly lay to the N of Donald Mound (-100 nT), and a positive one to the S (+60 nT). P. Rickerby noted that "these anomalies could be interpreted as resulting from shallow heating under Donald Mound (~50 m deep) and shallow cooling under TV1."

Seismicity recorded during January-June 1994 has generally showed little change; tremor in this interval has remained near background, though it has been present on 54% of the obtained records.

Geologic Background. The uninhabited Whakaari/White Island is the 2 x 2.4 km emergent summit of a 16 x 18 km submarine volcano in the Bay of Plenty about 50 km offshore of North Island. The island consists of two overlapping andesitic-to-dacitic stratovolcanoes. The SE side of the crater is open at sea level, with the recent activity centered about 1 km from the shore close to the rear crater wall. Volckner Rocks, sea stacks that are remnants of a lava dome, lie 5 km NW. Descriptions of volcanism since 1826 have included intermittent moderate phreatic, phreatomagmatic, and Strombolian eruptions; activity there also forms a prominent part of Maori legends. The formation of many new vents during the 19th and 20th centuries caused rapid changes in crater floor topography. Collapse of the crater wall in 1914 produced a debris avalanche that buried buildings and workers at a sulfur-mining project. Explosive activity in December 2019 took place while tourists were present, resulting in many fatalities. The official government name Whakaari/White Island is a combination of the full Maori name of Te Puia o Whakaari ("The Dramatic Volcano") and White Island (referencing the constant steam plume) given by Captain James Cook in 1769.

Information Contacts: T. Hunt, B. Scott, T. Kabayashi, and T. Tosha, IGNS, Wairakei; P. Rickerby, Victoria Univ, Wellington.

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