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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

Pacaya (Guatemala) Strombolian explosions, multiple lava flows, and the formation of a small cone during February-July 2020

Sangeang Api (Indonesia) Two ash plumes and small thermal anomalies during February-June 2020

Stromboli (Italy) Strombolian explosions persist at both summit craters during January-April 2020

Nevado del Ruiz (Colombia) Lava dome confirmed inside Arenas crater; intermittent thermal anomalies and ash emissions, January-June 2020

Asosan (Japan) Daily ash emissions continue through mid-June 2020 when activity decreases

Aira (Japan) Near-daily explosions with ash plumes continue, large block ejected 3 km from Minamidake crater on 4 June 2020

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

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



Pacaya (Guatemala) — August 2020 Citation iconCite this Report

Pacaya

Guatemala

14.382°N, 90.601°W; summit elev. 2569 m

All times are local (unless otherwise noted)


Strombolian explosions, multiple lava flows, and the formation of a small cone during February-July 2020

Pacaya, located in Guatemala, is a highly active volcano that has previously produced continuous Strombolian explosions, multiple lava flows, and the formation of a small cone within the crater due to the constant deposition of ejected material (BGVN 45:02). This reporting period updates information from February through July 2020 consisting of similar activity that dominantly originates from the Mackenney crater. Information primarily comes from reports by the Instituto Nacional de Sismologia, Vulcanologia, Meteorologia e Hydrologia (INSIVUMEH) in Guatemala and various satellite data.

Strombolian explosions were recorded consistently throughout this reporting period. During February 2020, explosions ejected incandescent material 100 m above the Mackenney crater. At night and during the early morning the explosions were accompanied by incandescence from lava flows. Multiple lava flows were active during most of February, traveling primarily down the SW and NW flanks and reaching 500 m on 25 February. On 5 February the lava flow on the SW flank divided into three flows measuring 200, 150, and 100 m. White and occasionally blue gas-and-steam emissions rose up to 2.7 km altitude on 11 and 14 February and drifted in multiple directions. On 16 February Matthew Watson utilized UAVs (Unmanned Aerial Vehicle) to take detailed, close up photos of Pacaya and report that there were five active vents at the summit exhibiting lava flows from the summit, gas-and-steam emissions, and small Strombolian explosions (figure 122).

Figure (see Caption) Figure 122. Drone image of active summit vents at Pacaya on 16 February 2020 with incandescence and white gas-and-steam emissions. Courtesy of Matthew Watson, University of Bristol, posted on 17 February 2020.

Activity remained consistent during March with Strombolian explosions ejecting material 100 m above the crater accompanied by occasional incandescence and white and occasionally blue gas-and-steam emissions drifting in multiple directions. Multiple lava flows were detected on the NW and W flanks reaching as far as 400 m on 9-10 March.

In April, frequent Strombolian explosions were accompanied by active lava flows moving dominantly down the SW flank and white gas-and-steam emissions. These repeated explosions ejected material up to 100 m above the crater and then deposited it within the Mackenney crater, forming a small cone. On 27 April seismicity increased at 2140 due to a lava flow moving SW as far as 400 m (figure 123); there were also six strong explosions and a fissure opened on the NW flank in front of the Los Llanos Village, allowing gas-and-steam to rise.

Figure (see Caption) Figure 123. Infrared image of Pacaya on 28 April 2020, showing a lava flow approximately 500 m long and moving down the S flank on the day after seismicity increased and six strong explosions were detected. Courtesy of ISIVUMEH (Reporte Volcán de Pacaya July 2020).

During May, Strombolian explosions continued to eject incandescent material up to 100 m above the Mackenney crater, accompanied by active lava flows on 1-2, 17-18, 22, 25-26, and 29-30 May down the SE, SW, NW, and NE flanks up to 700 m on 30 May. White gas-and-steam emissions continued to be observed up to 100 m above the crater drifting in multiple directions. Between the end of May and mid-June, the plateau between the Mackenney cone and the Cerro Chiquito had become inundated with lava flows (figure 124).

Figure (see Caption) Figure 124. Aerial views of the lava flows at Pacaya to the NW during a) 18 September 2019 and b) 16 June 2020 showing the lava flow advancement toward the Cerro Chiquito. Courtesy of INSIVUMEH (Reporte Volcán de Pacaya July 2020).

Lava flows extended 700 m on 8 June down multiple flanks. On 9 June, a lava flow traveled N and NW 500 m and originating from a vent on the N flank about 100 m below the Mackenney crater. Active lava flows continued to originate from this vent through at least 19 June while white gas-and-steam emissions were observed rising 300 m above the crater. At night and during the early mornings of 24 and 29 June Strombolian explosions were observed ejecting incandescent material up to 200 m above the crater (figure 125). These explosions continued to destroy and then rebuild the small cone within the Mackenney crater with fresh ejecta. Active lava flows on the SW flank were mostly 100-600 m long but had advanced to 2 km by 30 June.

On 10 July a 1.2 km lava flow divided in two which moved on the NE and N flanks. On 11 July, another 800 m lava flow divided in two, on the N and NE flanks (figure 126). On 14 and 19 July, INSIVUMEH registered constant seismic tremors and stated they were associated with the lava flows. No active lava flows were observed on 18-19 July, though some may have continued to advance on the SW, NW, N, and NE flanks. On 20 July, lava emerged from a vent at the NW base of the Mackenney cone near Cerro Chino, extending SE. Strombolian explosions ejected incandescent material up to 200 m above the crater on 22 July, accompanied by active incandescent lava flows on the SW, N, NW, NE, and W flanks. Three lava flows on the NW flank were observed on 22-24 July originating from the base of the Mackenney cone. Explosive activity during 22 July vibrated the windows and roofs of the houses in the villages of San Francisco de Sales, El Patrocinio, El Rodeo, and others located 4 km from the volcano. The lava flow activity had decreased by 25 July, but remnants of the lava flow on the NW flank persisted with weak incandescence observed at night, which was no longer observed by 26 July. Strombolian explosions continued to be detected through the rest of the month, accompanied by frequent white gas-and-steam emissions that extended up to 2 km from the volcano; no active lava flows were observed.

Figure (see Caption) Figure 125. Photos of Pacaya on 11 July 2020 showing Strombolian explosions and lava flows moving down the N and NE flanks. Courtesy of William Chigna, CONRED, posted on 12 July 2020.
Figure (see Caption) Figure 126. Infrared image of Pacaya on 20 July 2020 showing a hot lava flow accompanied by gas-and-steam emissions. Courtesy of INSIVUMEH (BEPAC 47 Julio 2020-22).

During February through July 2020, multiple lava flows and thermal anomalies within the Mackenney crater were detected in Sentinel-2 thermal satellite imagery (figure 127). These lava flows were observed moving down multiple flanks and were occasionally accompanied by white gas-and-steam emissions. Thermal anomalies were also recorded by the MIROVA (Middle InfraRed Observation of Volcanic Activity) system during 10 August through July 2020 within 5 km of the crater summit (figure 128). There were a few breaks in thermal activity from early to mid-March, late April, early May, and early June; however, each of these gaps were followed by a pulse of strong and frequent thermal anomalies. According to the MODVOLC algorithm, 77 thermal alerts were recorded within the summit crater during February through July 2020.

Figure (see Caption) Figure 127. Sentinel-2 thermal satellite images of Pacaya showing thermal activity (bright yellow-orange) primarily as lava flows originating from the summit crater during February to July 2020 frequently accompanied by white gas-and-steam emissions. All images with "Atmospheric penetration" (bands 12, 11, 8A) rendering; courtesy of Sentinel Hub Playground.
Figure (see Caption) Figure 128. The MIROVA thermal activity graph (Log Radiative Power) at Pacaya during 10 August to July 2020 shows strong, frequent thermal anomalies through late July with brief gaps in activity during early to mid-March, late April, early May, and early June. Courtesy of MIROVA.

Geologic Background. Eruptions from Pacaya, one of Guatemala's most active volcanoes, are frequently visible from Guatemala City, the nation's capital. This complex basaltic volcano was constructed just outside the southern topographic rim of the 14 x 16 km Pleistocene Amatitlán caldera. A cluster of dacitic lava domes occupies the southern caldera floor. The post-caldera Pacaya massif includes the ancestral Pacaya Viejo and Cerro Grande stratovolcanoes and the currently active Mackenney stratovolcano. Collapse of Pacaya Viejo between 600 and 1500 years ago produced a debris-avalanche deposit that extends 25 km onto the Pacific coastal plain and left an arcuate somma rim inside which the modern Pacaya volcano (Mackenney cone) grew. A subsidiary crater, Cerro Chino, was constructed on the NW somma rim and was last active in the 19th century. During the past several decades, activity has consisted of frequent strombolian eruptions with intermittent lava flow extrusion that has partially filled in the caldera moat and armored the flanks of Mackenney cone, punctuated by occasional larger explosive eruptions that partially destroy the summit of the growing young stratovolcano.

Information Contacts: Instituto Nacional de Sismologia, Vulcanologia, Meteorologia e Hydrologia (INSIVUMEH), Unit of Volcanology, Geologic Department of Investigation and Services, 7a Av. 14-57, Zona 13, Guatemala City, Guatemala (URL: http://www.insivumeh.gob.gt/); 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); Matthew Watson, School of Earth Sciences at the University of Bristol (Twitter: @Matthew__Watson, https://twitter.com/Matthew__Watson); William Chigna, CONRED (URL: https://twitter.com/william_chigna).


Sangeang Api (Indonesia) — August 2020 Citation iconCite this Report

Sangeang Api

Indonesia

8.2°S, 119.07°E; summit elev. 1912 m

All times are local (unless otherwise noted)


Two ash plumes and small thermal anomalies during February-June 2020

Sangeang Api is a 13-km-wide island located off the NE coast of Sumbawa Island, part of Indonesia's Lesser Sunda Islands. Documentation of historical eruptions date back to 1512. The most recent eruptive episode began in July 2017 and included frequent Strombolian explosions, ash plumes, and block avalanches. The previous report (BGVN 45:02) described activity consisting of a new lava flow originating from the active Doro Api summit crater, short-lived explosions, and ash-and-gas emissions. This report updates information during February through July 2020 using information from the Darwin Volcanic Ash Advisory Center (VAAC) reports, Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, or CVGHM) reports, and various satellite data.

Volcanism during this reporting period was relatively low compared to the previous reports (BGVN 44:05 and BGVN 45:02). A Darwin VAAC notice reported an ash plume rose 2.1 km altitude and drifted E on 10 May 2020. Another ash plume rose to a maximum of 3 km altitude drifting NE on 10 June, as seen in HIMAWARI-8 satellite imagery.

The MIROVA (Middle InfraRed Observation of Volcanic Activity) analysis of MODIS satellite data detected a total of 12 low power thermal anomalies within 5 km from the summit during February through May 2020 (figure 42). No thermal anomalies were recorded during June and July according to the MIROVA graph. Though the MODVOLC algorithm did not detect any thermal signatures between February to July, many small thermal hotspots within the summit crater could be seen in Sentinel-2 thermal satellite imagery (figure 43).

Figure (see Caption) Figure 42. Thermal anomalies at Sangeang Api from 10 August 2019 through July 2020 recorded by the MIROVA system (Log Radiative Power) were infrequent and low power during February through May 2020. No thermal anomalies were detected during June and July. Courtesy of MIROVA.
Figure (see Caption) Figure 43. Sentinel-2 thermal satellite imagery using “Atmospheric penetration” (bands 12, 11, 8A) rendering showed small thermal hotspots (orange-yellow) at the summit of Sangeang Api during February through June 2020. Courtesy of Sentinel Hub Playground.

Geologic Background. Sangeang Api volcano, one of the most active in the Lesser Sunda Islands, forms a small 13-km-wide island off the NE coast of Sumbawa Island. Two large trachybasaltic-to-tranchyandesitic volcanic cones, Doro Api and Doro Mantoi, were constructed in the center and on the eastern rim, respectively, of an older, largely obscured caldera. Flank vents occur on the south side of Doro Mantoi and near the northern coast. Intermittent historical eruptions have been recorded since 1512, most of them during in the 20th century.

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/); 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).


Stromboli (Italy) — August 2020 Citation iconCite this Report

Stromboli

Italy

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

All times are local (unless otherwise noted)


Strombolian explosions persist at both summit craters during January-April 2020

Stromboli is a stratovolcano located in the northeastern-most part of the Aeolian Islands composed of two active summit vents: the Northern (N) Crater and the Central-South (CS) Crater that are situated at the head of the Sciara del Fuoco, a large scarp that runs from the summit down the NW side of the volcano. The ongoing eruption began in 1934 and has been characterized by regular Strombolian explosions in both summit craters, ash plumes, and occasional lava flows (BGVN 45:08). This report updates activity from January to April 2020 with information primarily from daily and weekly reports by Italy's Istituto Nazionale di Geofisica e Vulcanologia (INGV) and various satellite data.

Activity was consistent during this reporting period. Explosion rates ranged from 1-20 per hour and were of variable intensity, producing material that rose from less than 80 to over 250 m above the vents (table 8). Strombolian explosions were often accompanied by gas-and-steam emissions, spattering, and lava flows which has resulted in fallout deposited on the Sciara del Fuoco and incandescent blocks rolling toward the coast up to a few hundred meters down the slopes of the volcano. According to INGV, the average SO2 emissions measured 300-650 tons/day.

Table 8. Summary of activity at Stromboli during January-April 2020. Low-intensity activity indicates ejecta rising less than 80 m, medium-intensity is ejecta rising less than 150 m, and high-intensity is ejecta rising over 200 m above the vent. Data courtesy of INGV.

Month Activity
Jan 2020 Strombolian activity and degassing continued with some spattering. Explosion rates varied from 2-20 per hour. Ejected material rose 80-150 m above the N crater and 150-200 m above the CS crater. A small cone is growing on the S1 crater and has produced some explosions and ejected coarse material mixed with fine ash. The average SO2 emissions measured 300 tons/day.
Feb 2020 Strombolian activity and degassing continued. Explosion rates varied from 2-14 per hour. Ejected material rose 80-200 m above the N crater and 80-250 m above the CS crater. The average SO2 emissions measured 300 tons/day.
Mar 2020 Strombolian activity and degassing continued with discontinuous spattering. Explosion rates varied from 1-16 per hour. Ejected material rose 80-150 m above the N crater and 150-250 m above the CS crater. Intense spattering was observed in the N crater. The average SO2 emissions measured 300-650 tons/day.
Apr 2020 Strombolian activity and degassing continued with spattering. Explosion rates varied from 1-17 per hour. Ejected material rose 80-150 m above the N crater and 150-250 m above the CS crater. Spattering was observed in the N crater. The average SO2 emissions measured 300-650 tons/day.

During January 2020, explosive activity mainly originated from three vents in the N crater and at least three vents in the CS crater. Ejecta from numerous Strombolian explosions covered the slopes on the upper Sciara del Fuoco, some of which rolled hundreds of meters down toward the coast. Explosion rates varied from 2-12 per hour in the N crater and 9-14 per hour in the CS crater; ejected material rose 80-200 m above the craters. According to INGV, a small cone growing in the S1 crater produced some explosions that ejected coarse material mixed with fine ash. On 18 and 19 January a lava flow was observed, both of which originated in the N crater. In addition, two explosions were detected in the N crater that was associated with two landslide events.

Explosive activity in February primarily originated from 2-3 eruptive vents in the N crater and at least three vents in the CS crater (figure 177). The Strombolian explosions ejected material 80-250 m above the craters, some of which fell onto the upper part of the Sciara. Explosion rates varied from 3-12 per hour in the N crater and 2-14 per hour in the CS crater (figure 178). On 3 February a short-lived lava flow was reported in the N crater.

Figure (see Caption) Figure 177. A drone image showed spattering accompanied by gas-and-steam emissions at Stromboli rising above the N crater on 15 February 2020. Courtesy of INGV (Rep. No. 08/2020, Stromboli, Bollettino Settimanale, 10/02/2020 - 16/02/2020, data emissione 18/02/2020).
Figure (see Caption) Figure 178. a) Strombolian explosions during the week of 17-23 February 2020 in the N1 crater of Stromboli were seen from Pizzo Sopra La Fossa. b) Spattering at Stromboli accompanied by white gas-and-steam emissions was detected in the N1 and S2 craters during the week of 17-23 February 2020. c) Spattering at Stromboli accompanied by a dense ash plume was seen in the N1 and S2 craters during the week of 17-23 February 2020. All photos by F. Ciancitto, courtesy of INGV (Rep. No. 09/2020, Stromboli, Bollettino Settimanale, 17/02/2020 - 23/02/2020, data emissione 25/02/2020).

Ongoing explosive activity continued into March, originating from three eruptive vents in the N crater and at least three vents in the CS crater. Ejected lapilli and bombs rose 80-250 m above the craters resulting in fallout covering the slopes in the upper Sciara del Fuoco with blocks rolling down the slopes toward the coast and explosions varied from 4-13 per hour in the N crater and 1-16 per hour in the CS crater. Discontinuous spattering was observed during 9-19 March. On 19 March, intense spattering was observed in the N crater, which produced a lava flow that stretched along the upper part of the Sciara for a few hundred meters. Another lava flow was detected in the N crater on 28 March for about 4 hours into 29 March, which resulted in incandescent blocks breaking off the front of the flow and rolling down the slope of the volcano. On 30 March a lava flow originated from the N crater and remained active until the next day on 31 March. Landslides accompanied by incandescent blocks rolling down the Sciara del Fuoco were also observed.

Strombolian activity accompanied by gas-and-steam emissions continued into April, primarily produced in 3-4 eruptive vents in the N crater and 2-3 vents in the CS crater. Ejected material from these explosions rose 80-250 m above the craters, resulting in fallout products covering the slopes on the Sciara and blocks rolling down the slopes. Explosions varied from 4-15 per hour in the N crater and 1-10 per hour in the CS crater. On 1 April a thermal anomaly was detected in satellite imagery accompanied by gas-and-steam and ash emissions downstream of the Sciara del Fuoco. A lava flow was observed on 15 April in the N crater accompanied by gas-and-steam and ash emissions; at the front of the flow incandescent blocks detached and rolled down the Sciara (figure 179). This flow continued until 16 April, ending by 0956; a thermal anomaly persisted downslope from the lava flow. Spatter was ejected tens of meters from the vent. Another lava flow was detected on 19 April in the N crater, followed by detached blocks from the front of the flow rolling down the slopes. Spattering continued during 20-21 April.

Figure (see Caption) Figure 179. A webcam image of an ash plume accompanied by blocks ejected from Stromboli on 15 April 2020 rolling down the Sciara del Fuoco. Courtesy of INGV via Facebook posted on 15 April 2020.

Moderate thermal activity occurred frequently during 16 October to April 2020 as recorded in the MIROVA Log Radiative Power graph using MODIS infrared satellite information (figure 180). The MODVOLC thermal alerts recorded a total of 14 thermal signatures over the course of nine different days between late February and mid-April. Many of these thermal signatures were captured as hotspots in Sentinel-2 thermal satellite imagery in both summit craters (figure 181).

Figure (see Caption) Figure 180. Low to moderate thermal activity at Stromboli occurred frequently during 16 October-April 2020 as shown in the MIROVA graph (Log Radiative Power). Courtesy of MIROVA.
Figure (see Caption) Figure 181. Thermal anomalies (bright yellow-orange) at Stromboli were observed in thermal satellite imagery from both of the summit vents throughout January-April 2020. Images with Atmospheric Penetration rendering (bands 12, 11, 8A); courtesy of Sentinel Hub Playground.

Geologic Background. Spectacular incandescent nighttime explosions at this volcano have long attracted visitors to the "Lighthouse of the Mediterranean." Stromboli, the NE-most of the Aeolian Islands, has lent its name to the frequent mild explosive activity that has characterized its eruptions throughout much of historical time. The small island is the emergent summit of a volcano that grew in two main eruptive cycles, the last of which formed the western portion of the island. The Neostromboli eruptive period took place between about 13,000 and 5,000 years ago. The active summit vents are located at the head of the Sciara del Fuoco, a prominent horseshoe-shaped scarp formed about 5,000 years ago due to a series of slope failures that extend to below sea level. The modern volcano has been constructed within this scarp, which funnels pyroclastic ejecta and lava flows to the NW. Essentially continuous mild Strombolian explosions, sometimes accompanied by lava flows, have been recorded for more than a millennium.

Information Contacts: Istituto Nazionale di Geofisica e Vulcanologia (INGV), Sezione di Catania, Piazza Roma 2, 95123 Catania, Italy (URL: http://www.ct.ingv.it/en/, Facebook: https://www.facebook.com/ingvvulcani/); 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).


Nevado del Ruiz (Colombia) — August 2020 Citation iconCite this Report

Nevado del Ruiz

Colombia

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

All times are local (unless otherwise noted)


Lava dome confirmed inside Arenas crater; intermittent thermal anomalies and ash emissions, January-June 2020

Columbia’s broad, glacier-capped Nevado del Ruiz has an eruption history documented back 8,600 years, and historical observations since 1570. It’s profound notoriety stems from an eruption on 13 November 1985 that produced an ash plume and pyroclastic flows onto the glacier, triggering large lahars that washed down 11 valleys, inundating most severely the towns of Armero (46 km W) and Chinchiná (34 km E) where approximately 25,000 residents were killed. It remains the second deadliest volcanic eruption of the 20th century after Mt. Pelee killed 28,000 in 1902. Ruiz remained quiet for 20 years after the September 1985-July 1991 eruption until a new explosive event occurred in February 2012; a series of explosive events lasted into 2013. Renewed activity beginning in November 2014 included ash and gas-and-steam plumes, ashfall, and the appearance of a lava dome inside the Arenas crater in August 2015 which has regularly displayed thermal anomalies through 2019. This report covers ongoing activity from January-June 2020 using information primarily from reports by the Servicio Geologico Colombiano (SGC) and the Observatorio Vulcanológico y Sismológico de Manizales, the Washington Volcanic Ash Advisory Center (VAAC) notices, and various sources of satellite data.

Gas and ash emissions continued at Nevado del Ruiz throughout January-June 2020; they generally rose to 5.8-6.1 km altitude with the highest reported plume at 7 km altitude during early March. SGC confirmed the presence of the growing lava dome inside Arenas crater during an overflight in January; infrared satellite imagery indicated a continued heat source from the dome through April. SGC interpreted repeated episodes of ‘drumbeat seismicity’ as an indication of continued dome growth throughout the period. Small- to moderate-density sulfur dioxide emissions were measured daily with satellite instruments. The MIROVA graph of thermal activity indicated a heat source consistent with a growing dome from January through April (figure 102).

Figure (see Caption) Figure 102. The MIROVA graph of thermal activity at Nevado del Ruiz from 2 July 2019 through June 2020 indicated persistent thermal anomalies from mid-November 2019-April 2020. Courtesy of MIROVA.

Activity during January-March 2020. During January 2020 some of the frequent tremor seismic events were associated with gas and ash emissions, and several episodes of “drumbeat” seismicity were recorded; they have been related by SGC to the growth of the lava dome on the floor of the Arenas crater. An overflight on 10 January, with the support of the Columbian Air Force, confirmed the presence of the dome which was first proposed in August 2015 (BGVN 42:06) (figure 103). The Arenas crater had dimensions of 900 x 980 m elongate to the SW-NE and was about 300 m deep (figure 104). The dome inside the crater was estimated to be 173 m in diameter and 60 m high with an approximate volume of 1,500,000 m3 (figures 105 and 106). In addition to the dome, the scientists also noted ash deposits on the summit ice cap (figure 107). The Washington VAAC reported an ash plume on 19 January that rose to 5.5 km altitude and drifted SW, dissipating quickly. On 30 January they reported an ash plume visible in satellite imagery extending 15 km NW from the summit at 5.8 km altitude. A single MODVOLC alert was issued on 15 January and data from the VIIRS satellite instrument reported thermal anomalies inside the summit crater on 14 days of the month. Sulfur dioxide plumes with DU values greater than 2 were recorded by the TROPOMI satellite instrument daily during the month.

Figure (see Caption) Figure 103. SGC confirmed the presence of a lava dome inside the Arenas crater at Nevado del Ruiz on 10 January 2020. The dome is shown in brown, and zones of fumarolic activity are labelled around the dome. Courtesy of SGC (El Nuevo Domo de Lava del Volcán Nevado del Ruiz y la Geomorfología Actual del Cráter Arenas 2020).
Figure (see Caption) Figure 104. A view of the Arenas crater at the summit of Nevado del Ruiz on 10 January 2020 (left) is compared with a view from 2010 (right). They were both taken during overflights supported by the Colombian Air Force (FAC). Ash deposits on the ice fields are visible in both images. Fumarolic activity rises from the inner walls of the crater in January 2020. Courtesy of SGC (El Nuevo Domo de Lava del Volcán Nevado del Ruiz y la Geomorfología Actual del Cráter Arenas 2020).
Figure (see Caption) Figure 105. The dome inside the Arenas crater at Nevado del Ruiz appeared dark against the crater rim and ash-covered ice field on 10 January 2020. Features observed include (A) the edge of the Arenas crater, (B) a secondary crater 150 m in diameter located to the west, (C) interior cornices, (D) the lava dome, (E) a depression in the center of the dome caused by possible subsidence and cooling of the lava, (F) a source of gas and ash emission with a diameter of approximately 15 m (secondary crater), and (G, H, and I) several sources of gas emission located around the crater. Courtesy of SGC (El Nuevo Domo de Lava del Volcán Nevado del Ruiz y la Geomorfología Actual del Cráter Arenas 2020).
Figure (see Caption) Figure 106. Images of the summit of Nevado del Ruiz captured by the PlanetScope satellite system on 14 March 2018 (A) and 10 January 2020 (B) show the lava dome at the bottom of Arenas crater. Courtesy Planet Lab Inc. and SGC (El Nuevo Domo de Lava del Volcán Nevado del Ruiz y la Geomorfología Actual del Cráter Arenas 2020).
Figure (see Caption) Figure 107. Ash covered the snow and ice field around the Arenas crater at the summit of Nevado del Ruiz on 10 January 2020. The lava dome is the dark area on the right. Courtesy of SGC (posted on Twitter @sgcol).

The Washington VAAC reported multiple ash plumes during February 2020. On 4 February an ash plume was observed in satellite imagery drifting 35 km W from the summit at 5.8 km altitude. The following day a plume rose to 6.1 km altitude and extended 37 km W from the summit before dissipating by the end of the day (figure 108). On 6 February an ash cloud was observed in satellite imagery centered 45 km W of the summit at 5.8 km altitude. Although it had dissipated by midday, a hotspot remained in shortwave imagery until the evening. Late in the day another plume rose to 6.7 km altitude and drifted W. Diffuse ash was seen in satellite imagery on 13 February fanning towards the W at 5.8 km altitude. On 18 February at 1720 UTC the Bogota Meteorological Weather Office (MWO) reported an ash emission drifting NW at 5.8 km altitude; a second plume was reported a few hours later at the same altitude. Intermittent emissions continued the next day at 5.8-6.1 km altitude that reached as far as 50 km NW before dissipating. A plume on 21 February rose to 6.7 km altitude and drifted W (figure 109). Occasional emissions on 25 February at the same altitude reached 25 km SW of the summit before dissipating. A discrete ash emission around 1550 UTC on 26 February rose to 6.1 km altitude and drifted W. Two similar plumes were reported the next day. On 28 and 29 February plumes rose to 5.8 km altitude and drifted W.

Figure (see Caption) Figure 108. Emissions rose from the Arenas crater at Nevado del Ruiz on 5 February 2020. The Washington VAAC reported an ash plume that day that rose to 6.1 km altitude and drifted 37 km W before dissipating. Courtesy of Camilo Cupitre.
Figure (see Caption) Figure 109. Emissions rose from the Arenas crater at Nevado del Ruiz around 0600 on 21 February 2020. The Washington VAAC reported ash emissions that day that rose to 6.7 km altitude and drifted W. Courtesy of Manuel MR.

SGC reported several episodes of drumbeat type seismicity on 2, 8, 9, and 27 February which they attributed to effusion related to the growing lava dome in the summit crater. Sentinel-2 satellite imagery showed ring-shaped thermal anomalies characteristic of dome growth within Arenas crater several times during January and February (figure 110). The VIIRS satellite instrument recorded thermal anomalies on twelve days during February.

Figure (see Caption) Figure 110. Persistent thermal anomalies from Sentinel-2 satellite imagery during January and February 2020 suggested that the lava dome inside Nevado del Ruiz’s Arenas crater was still actively growing. Atmospheric penetration rendering (bands 12, 11, 8A) courtesy of Sentinel Hub Playground.

On 4, 14, and 19 March 2020 thermal anomalies were visible in Sentinel-2 satellite data from within the Arenas crater. Thermal anomalies were recorded by the VIIRS satellite instrument on eight days during the month. Several episodes of drumbeat seismicity were recorded during the first half of the month and on 30-31 March. Distinct SO2 plumes with DU values greater than 2 were recorded by the TROPOMI satellite instrument daily throughout February and March (figure 111). The Washington VAAC reported an ash emission on 1 March that rose to 5.8 km altitude and drifted NW; it was centered 15 km from the summit when detected in satellite imagery. The next day a plume was seen in satellite imagery moving SW at 7.0 km altitude, extending nearly 40 km from the summit. Additional ash emissions were reported on 4, 14, 15, 21, 28, 29, and 31 March; the plumes rose to 5.8-6.7 km altitude and drifted generally W, some reaching 45 km from the summit before dissipating.

Figure (see Caption) Figure 111. Distinct SO2 plumes with Dobson values (DU) greater than 2 were recorded by the TROPOMI satellite instrument daily during February and March 2020. Ecuador’s Sangay produced smaller but distinct plumes most of the time as well. Dates are shown at the top of each image. Courtesy of NASA’s Sulfur Dioxide Monitoring Page.

Activity during April-June 2020. The Washington VAAC reported an ash emission that rose to 6.7 km altitude and drifted W on 1 April 2020. On 2 April, emission plumes were visible from the community of Tena in the Cundinamarca municipality which is located 100 km ESE (figure 112). The unusually clear skies were attributed to the reduction in air pollution in nearby Bogota resulting from the COVID-19 Pandemic quarantine. On 4 April the Bogota MWO reported an emission drifting SW at 5.8 km altitude. An ash plume on 8 April rose to 6.7 km altitude and drifted W. On 25 April the last reported ash plume from the Washington VAAC for the period rose to 6.1 km altitude and was observed in satellite imagery moving W at 30 km from the summit; after that, only steam and gas emissions were observed.

Figure (see Caption) Figure 112. On the evening of 2 April 2020, emission plumes from Nevado del Ruiz were visible from Santa Bárbara village in Tena, Cundinamarca municipality which is located 100 km ESE. The unusually clear skies were attributed to the reduction in air pollution in the nearby city of Bogota resulting from the COVID-19 Pandemic quarantine. Photo by Williama Garcia, courtesy of Semana Sostenible (3 April 2020).

Distinct SO2 plumes with DU values greater than 2 were recorded by the TROPOMI satellite instrument daily throughout the month. On 13 April, a Sentinel-2 thermal image showed a hot spot inside the Arenas crater largely obscured by steam and clouds. Cloudy images through May and June prevented observation of additional thermal anomalies in satellite imagery, but the VIIRS thermal data indicated anomalies on 3, 4, and 26 April. SGC reported low-energy episodes of drumbeat seismicity on 4, 9, 10, 12, 15, 16, 20, and 23 April which they interpreted as related to growth of the lava dome inside the Arenas crater. The seismic events were located 1.5-2.0 km below the floor of the crater.

Small emissions of ash and gas were reported by SGC during May 2020 and the first half of June, with the primary drift direction being NW. Gas and steam plumes rose 560-1,400 m above the summit during May and June (figure 113). Drumbeat seismicity was reported a few times each month. Sulfur dioxide emissions continued daily; increased SO2 activity was recorded during 10-13 June (figure 114).

Figure (see Caption) Figure 113. Gas and steam plumes rose 560-1,400 m above the summit of Nevado del Ruiz during May and June 2020, including in the early morning of 11 June. Courtesy of Carlos-Enrique Ruiz.
Figure (see Caption) Figure 114. Increased SO2 activity during 10-13 June 2020 at Nevado del Ruiz was recorded by the TROPOMI instrument on the Sentinel-5P satellite. Sangay also emitted SO2 on those days. Courtesy of NASA Global Sulfur Dioxide Monitoring Page.

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

Information Contacts: El Servicio Geológico Colombiano (SGC), Diagonal 53 No. 34-53 - Bogotá D.C., Colombia (URL: https://www.sgc.gov.co/volcanes, https://twitter.com/sgcol); 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/); Hawai'i Institute of Geophysics and Planetology (HIGP) - MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); NASA Worldview (URL: https://worldview.earthdata.nasa.gov/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); Camilo Cupitre (URL: https://twitter.com/Ccupitre/status/1225207439701704709); Manuel MR (URL: https://twitter.com/ElPlanetaManuel/status/1230837262088384512); Semana Sostenible (URL: https://sostenibilidad.semana.com/actualidad/articulo/fumarola-del-nevado-del-ruiz-fue-captada-desde-tena-cundinamarca/49597); Carlos-Enrique Ruiz (URL: https://twitter.com/Aleph43/status/1271800027841794049).


Asosan (Japan) — July 2020 Citation iconCite this Report

Asosan

Japan

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

All times are local (unless otherwise noted)


Daily ash emissions continue through mid-June 2020 when activity decreases

Japan's 24-km-wide Asosan caldera on the island of Kyushu has been active throughout the Holocene. Nakadake has been the most active of 17 central cones for 2,000 years; all historical activity is from Nakadake Crater 1. The largest ash plume in 20 years occurred on 8 October 2016. Asosan remained quiet until renewed activity from Crater 1 began in mid-April 2019; explosions with ash plumes continued through the first half of 2020 and are covered in this report. The Japan Meteorological Agency (JMA) provides monthly reports of activity; the Tokyo Volcanic Ash Advisory Center (VAAC) issues aviation alerts reporting on possible ash plumes, and Sentinel-2 satellite images provide data on ash emissions and thermal activity.

The Tokyo VAAC issued multiple daily reports of ash plumes from Nakadake Crater 1 from 1 January-14 June 2020. They were commonly at 1.8-2.1 km altitude, and often drifted E or S. JMA reported that ashfall continued downwind from the ash plumes until mid-June; seismic activity was relatively high during January and February and decreased steadily after that time. The measured SO2 emissions ranged from 1,000-4,900 tons per day through mid-June and dropped to 500 tons per day during the second half of June. Intermittent thermal activity was recorded at the crater through mid-May.

Explosive activity during January-June 2020. Ash plumes rose up to 1.1 km above the crater rim at Nakadake Crater 1 during January 2020 (figure 70). Ashfall was confirmed downwind of an explosion on 7 January. During February, ash plumes rose up to 1.7 km above the crater, and ashfall was again reported downwind. The crater camera provided by the Aso Volcano Museum occasionally observed incandescence at the floor of the crater during both months. Incandescence was also occasionally observed with the Kusasenri webcam (3 km W) and was seen on 20 February from a webcam in Minamiaso village (8 km SW).

Figure (see Caption) Figure 70. Ash plumes rose up to 1.1 km above the Nakadake Crater 1 at Asosan during January 2020 (left) and up to 1.7 km above the crater during February 2020 (right) as seen in these images from the Kusasenri webcam. Ashfall was reported downwind multiple times. Courtesy of JMA (Volcanic activity commentary material for Mt. Aso, January and February 2020).

During March 2020, ash plumes rose as high as 1.3 km. Ashfall was reported on 9 March in Ichinomiyamachi, Aso City (figure 71). In field surveys conducted on the 18th and 25th, there was no visible water inside the crater, and high-temperature grayish-white plumes were observed. The temperature at the base of the plume was measured at 300°C (figure 72).

Figure (see Caption) Figure 71. Ashfall from Asosan appeared on 9 March 2020 in Ichinomiyamachi, Aso City around 10 km N. Courtesy of JMA (Volcanic activity commentary material for Mt. Aso, March 2020).
Figure (see Caption) Figure 72. During a field survey of Nakadake Crater 1 at Asosan on 25 March 2020, JMA staff observed a gray ash plume rising from the crater floor (left). The maximum temperature of the ash plume was measured at about 300°C with an infrared thermal imaging device (right). Courtesy of JMA (Volcanic activity commentary material for Mt. Aso, March 2020).

Occasional incandescence was observed at the bottom of the crater during April and May 2020; ash plumes rose 1.1 km above the crater on most days in April and were slightly higher, rising to 1.8 km during May, although activity was more intermittent (figure 73). A brief increase in SO2 activity was reported by JMA during field surveys on 7 and 8 May; satellite data captured small plumes of SO2 on 1 and 6 May (figure 74). A brief increase in tremor amplitude was reported by JMA on 16 May.

Figure (see Caption) Figure 73. Although activity at Asosan’s Nakadake Crater 1 was more intermittent during April and May 2020 than earlier in the year, ash plumes were still reported most days and incandescence was seen at the bottom of the crater multiple times until 15 May. Left image taken 11 May 2020 from the Kusachiri webcam; right image taken from the crater webcam on 10 May provided by the Aso Volcano Museum. Courtesy of JMA (Volcanic activity commentary material for Mt. Aso, May 2020).
Figure (see Caption) Figure 74. The TROPOMI instrument on the Sentinel-5P satellite detected small but distinct SO2 plumes from Asosan on 1 and 6 May 2020. Additional small plumes are visible from Aira caldera’s Sakurajima volcano. Courtesy of NASA’s Global Sulfur Dioxide Monitoring Page.

The last report of ash emissions at Nakadake Crater 1 from the Tokyo VAAC was on 14 June 2020. JMA also reported that no eruption was observed after mid-June. On 8 June they reported an ash plume that rose 1.4 km above the crater. During a field survey on 16 June, only steam was observed at the crater; the plume rose about 100 m (figure 75). In addition, a small plume of steam rose from a fumarole on the S crater wall.

Figure (see Caption) Figure 75. A steam plume rose about 100 m from the floor of Nakadake Crater 1 on 16 June 2020. A small steam plume was also observed by the S crater wall. Courtesy of JMA (Volcanic activity commentary material for Mt. Aso, June 2020).

Thermal activity during January-June 2020. Sentinel-2 satellite data indicated thermal anomalies present at Nakadake Crater 1 on 2 January, 6 and 21 February, 16 April, and 11 May (figure 76). In addition, thermal anomalies from agricultural fires appeared in satellite images on 11 February, 7 and 17 March (figure 77). The fires were around 5 km from the crater, thus they appear on the MIROVA thermal anomaly graph in black, but are likely unrelated to volcanic activity (figure 78). No thermal anomalies were recorded in satellite data from the Nakadake Crater 1 after 11 May, and none appeared in the MIROVA data as well.

Figure (see Caption) Figure 76. Thermal anomalies appeared at Asosan’s Nakadake Crater 1 on 2 January, 6 and 21 February, 16 April and 11 May 2020. On 2 January a small ash plume drifted SSE from the crater (left). On 6 February a dense ash plume drifted S from the crater (center). Only a small steam plume was visible above the crater on 21 February (right). Images use Atmospheric penetration rendering (bands 12, 11, 8A), courtesy of Sentinel Hub Playground.
Figure (see Caption) Figure 77. Thermal anomalies from agricultural fires located about 5 km from the crater appeared in satellite images on 11 February, and 7 and 17 March 2020. Although a dense ash plume drifted SSE from the crater on 11 February (left), no thermal anomalies appear at the crater on these dates. Images use Atmospheric penetration rendering (bands 12, 11, 8A), courtesy of Sentinel Hub Playground.
Figure (see Caption) Figure 78. The MIROVA project plot of Log Radiative Power at Asosan from 29 June 2019 through June 2020 shows only a few small thermal alerts within 5 km of the summit crater during January-June 2020, and a spike in activity during February and March located around 5 km away. These data correlate well with the Sentinel-2 satellite data that show intermittent thermal anomalies at the summit throughout January-May and agricultural fires located several kilometers from the crater during February and March. Courtesy of MIROVA.

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

Information Contacts: Japan Meteorological Agency (JMA), 1-3-4 Otemachi, Chiyoda-ku, Tokyo 100-8122, Japan (URL: http://www.jma.go.jp/jma/indexe.html); 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/); 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).


Aira (Japan) — July 2020 Citation iconCite this Report

Aira

Japan

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

All times are local (unless otherwise noted)


Near-daily explosions with ash plumes continue, large block ejected 3 km from Minamidake crater on 4 June 2020

Sakurajima rises from Kagoshima Bay, which fills the Aira Caldera near the southern tip of Japan's Kyushu Island. Frequent explosive and occasional effusive activity has been ongoing for centuries. The Minamidake summit cone has been the location of persistent activity since 1955; the adjacent Showa crater on its E flank has also been intermittently active since 2006. Numerous explosions and ash-bearing emissions have been occurring each month at either Minamidake or Showa crater since the latest eruptive episode began in late March 2017. This report covers ongoing activity at Minamidake from January through June 2020; the Japan Meteorological Agency (JMA) provides regular reports on activity, and the Tokyo VAAC (Volcanic Ash Advisory Center) issues tens of reports each month about the frequent ash plumes.

Activity continued during January-June 2020 at Minamidake crater with tens of explosions each month. The Tokyo VAAC issued multiple daily reports of ash emissions during January and February. Less activity occurred during the first half of March but picked up again with multiple daily reports from mid-March through mid-April. Emissions were more intermittent but continued through early June, when activity decreased significantly. JMA reported explosions with ash plumes rising 2.5-4.2 km above the summit, and ejecta traveling generally up to 1,700 m from the crater, although a big explosion in early June send a large block of tephra 3 km from the crater (table 23). Thermal anomalies were visible in satellite imagery on a few days most months and were persistent in the MIROVA thermal anomaly data from November 2019 through early June 2020 (figure 94). Incandescence was often visible at night in the webcams through early June; the Showa crater remained quiet throughout the period.

Table 23. Monthly summary of eruptive events recorded at Sakurajima's Minamidake crater within the Aira Caldera, January through June 2020. The number of events that were explosive in nature are in parentheses. No events were recorded at the Showa crater during this time. Ashfall is measured at the Kagoshima Local Meteorological Observatory (KLMO), 10 km W of Showa crater. Data courtesy of JMA (January to June 2020 monthly reports).

Month Ash emissions (explosive) Max plume height above crater Max ejecta distance from crater Total amount of ashfall (g/m2) Total ashfall previous month
Jan 2020 104 (65) 2.5 km 1,700 m 75 (12 days) 280,000 tons
Feb 2020 129 (67) 2.6 km 1,800 m 21 (14 days) 230,000 tons
Mar 2020 26 (10) 3.0 km 1,700 m 3 (8 days) 360,000 tons
Apr 2020 51 (14) 3.8 km 1,700 m less than 0.5 (2 days) 160,000 tons
May 2020 51 (24) 4.2 km 1,300 m 19 (8 days) 280,000 tons
Jun 2020 28 (16) 3.7 km 3,000 m 71 (9 days) 150,000 tons
Figure (see Caption) Figure 94. Persistent thermal anomalies were recorded in the MIROVA thermal energy data for the period from 2 July 2019 through June 2020. Thermal activity increased in October 2019 and remained steady through May 2020, decreasing abruptly at the beginning of June. Courtesy of MIROVA.

Explosions continued at Minamidake crater during January 2020 with 65 ash plumes reported. The highest ash plume rose 2.5 km above the crater on 30 January, and incandescent ejecta reached up to 1,700 m from the Minamidake crater on 22 and 29 January (figure 95). Slight inflation of the volcano since September 2019 continued to be measured with inclinometers and extensometers on Sakurajima Island. Field surveys conducted on 15, 20, and 31 January measured the amount of sulfur dioxide gas released as very high at 3,400-4,700 tons per day, as compared with 1,000-3,000 tons in December 2019.

Figure (see Caption) Figure 95. An explosion at the Minamidake summit crater of Aira’s Sakurajima volcano on 29 January 2020 produced an ash plume that rose 2.5 km above the crater rim and drifted SE (left). On 22 January incandescent ejecta reached 1,700 m from the summit during explosive events. Courtesy of JMA (Sakurajima Volcanic Activity Commentary, January 2020).

About the same number of explosions produced ash plumes during February 2020 (67) as in January (65) (figure 96). On 10 February a large block was ejected 1,800 m from the crater, the first to reach that far since 5 February 2016. The tallest plume, on 26 February rose 2.6 km above the crater. Sentinel-2 satellite imagery indicated two distinct thermal anomalies within the Minamidake crater on both 1 and 6 February (figure 97). Activity diminished during March 2020 with only 10 explosions out of 26 eruptive events. On 21 March a large bomb reached 1,700 m from the crater. The tallest ash plume rose 3 km above the crater on 17 March. Scientists noted during an overflight on 16 March that a small steam plume was rising from the inner wall on the south side of the Showa crater; a larger steam plume rose to 300 m above the Minamidake crater and drifted S (figure 98). Sulfur dioxide emissions were similar in February (1,900 to 3,100 tons) and March (1,300 to 3,400 tons per day).

Figure (see Caption) Figure 96. An ash plume rose from the Minamidake crater at the summit of Aira’s Sakurajima volcano on 6 February 2020 at 1752 local time, as seen looking S from the Kitadake crater. Courtesy of JMA (Sakurajima Volcanic Activity Commentary, February 2020).
Figure (see Caption) Figure 97. Sentinel-2 satellite imagery revealed two distinct thermal anomalies within the Minamidake crater at Aira’s Sakurajima volcano on 1 and 6 February 2020. Images use Atmospheric penetration rendering (bands 12, 11, 8A). Courtesy of Sentinel Hub playground.
Figure (see Caption) Figure 98. During an overflight of Aira’s Sakurajima volcano on 16 March 2020, JMA captured this view to the SW of the Kitadake crater on the right, the steam-covered Minamidake crater in the center, and the smaller Showa crater on the left adjacent to Minamidake. Courtesy of JMA and the Maritime Self-Defense Force 1st Air Group P-1 (Sakurajima Volcanic Activity Commentary, March 2020).

During April 2020, ejecta again reached as far as 1,700 m from the crater; 14 explosions were identified from the 51 reported eruptive events, an increase from March. The tallest plume, on 4 April, rose 3.8 km above the crater (figure 99). The same number of eruptive events occurred during May 2020, but 24 were explosive in nature. A large plume on 9 May rose to 4.2 km above the rim of Minamidake crater, the tallest of the period (figure 100). On 20 May, incandescent ejecta reached 1,300 m from the summit. Sulfur dioxide emissions during April (1,700-2,100 tons per day) and May (1,200-2,700 tons per day) were slightly lower than previous months.

Figure (see Caption) Figure 99. A large ash plume at Aira’s Sakurajima volcano rose from Minamidake crater at 1621 on 4 April 2020. The plume rose to 3.8 km above the crater and drifted SE. Courtesy of JMA (Sakurajima Volcanic Activity Commentary, April 2020).
Figure (see Caption) Figure 100. Activity continued at Aira’s Sakurajima volcano during May 2020. A large plume rose to 4.2 km above the summit and drifted N in the early morning of 9 May (left). The Kaigata webcam located at the Osumi River National Highway Office captured abundant incandescent ejecta reaching 1,300 m from the crater during the evening of 20 May. Courtesy of JMA (Sakurajima Volcanic Activity Commentary, May 2020).

A major explosion on 4 June 2020 produced 137 Pa of air vibration at the Seto 2 observation point on Sakurajima Island. It was the first time that air vibrations exceeding 100 Pa have been observed at the Seto 2 station since the 21 May 2015 explosion at the Showa crater. The ash plume associated with the explosion rose 1.5 km above the crater rim. During an 8 June field survey conducted in Higashisakurajima-cho, Kagoshima City, a large impact crater believed to be associated with this explosion was located near the coast 3 km SSW from Minamidake. The crater formed by the ejected block was about 6 m in diameter and 2 m deep (figure 101); fragments found nearby were 10-20 cm in diameter (figure 102). A nearby roof was also damaged by the blocks. Smaller bombs were found in Kurokami-cho, Kagoshima City, around 4- 5 km E of Minamidake on 5 June; the largest fragment was 5 cm in diameter. Multiple ash plumes rose to 3 km or more above the summit during the first ten days of June; explosions on 4 and 5 June reached 3.7 km above the crater (figure 103). Larger than normal inflation and deflation before and after the explosions was recorded during early June in the inclinometers and extensometers located on the island. Incandescence at the summit was observed at night through the first half of June. The Tokyo VAAC issued multiple daily ash advisories during 1-10 June after which activity declined abruptly. Two brief explosions on 23 June and one on 28 June were the only two additional ash explosions reported in June.

Figure (see Caption) Figure 101. A large crater measuring 6 m wide and 2 m deep was discovered 3 km from the Minamidake crater in Higashisakurajima, part of Kagoshima City, on 8 June 2020. It was believed to be from the impact of a large block ejected during the 4 June explosion at Aira’s Sakurajima volcano. Photo courtesy of Kagoshima City and JMA (Sakurajima Volcanic Activity Commentary, June 2020).
Figure (see Caption) Figure 102. Fragments 10-30 cm in diameter from a large bomb that traveled 3 km from Minamidake crater on Sakurajima were found a few days after the 4 June 2020 explosion at Aira. Courtesy of JMA, photo courtesy of Kagoshima City (Sakurajima Volcanic Activity Commentary, June 2020).
Figure (see Caption) Figure 103. An ash plume rose 3.7 km above the Minamidake crater at Aira’s Sakurajima volcano on 5 June 2020 and was recorded in Sentinel-2 satellite imagery. Image uses Atmospheric penetration rendering (bands 12, 11, 8A). Courtesy of Sentinel Hub playground.

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

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


Nevados de Chillan (Chile) — July 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).


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).


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/).

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Bulletin of the Global Volcanism Network - Volume 16, Number 07 (July 1991)

Managing Editor: Lindsay McClelland

Aira (Japan)

Frequent explosions; aircraft windshield damaged

Ambae (Vanuatu)

Caldera lake bubbling; burned vegetation

Ambrym (Vanuatu)

Ash emissions and lava lake activity continue

Arenal (Costa Rica)

Increased Strombolian activity; seismicity

Colima (Mexico)

Block lava flow advances; new dome lobe; seismicity

Etna (Italy)

Strombolian activity and continued strong degassing

Fournaise, Piton de la (France)

Brief lava production follows seismicity, deformation, and magnetic changes

Galeras (Colombia)

More small explosions; increased seismicity and deformation

Gaua (Vanuatu)

Increased fumarolic activity; vegetation killed

Hudson, Cerro (Chile)

SO2 circles globe; aircraft encounter ash over Australia; >1 km3 airfall on Argentina

Irazu (Costa Rica)

Seismicity remains high; crater lake level rises

Kavachi (Solomon Islands)

May-June submarine eruption ends; temporary island eroded away

Kilauea (United States)

Continued E rift lava production; summit earthquake swarm

Kuwae (Vanuatu)

Summit at 2-3 m depth; no visible fumarolic activity; sulfur odor

Langila (Papua New Guinea)

Tephra emission and seismicity

Lewotobi (Indonesia)

Strombolian activity

Lopevi (Vanuatu)

No fumarolic activity

Manam (Papua New Guinea)

Stronger ash emission

Mauna Loa (United States)

Summit earthquake swarm

Ontakesan (Japan)

Decreasing seismicity

Pacaya (Guatemala)

Explosive eruptions destroy cone and crater; crop damage; evacuations

Pinatubo (Philippines)

Ash emissions decreasing; typhoons trigger large lahars

Poas (Costa Rica)

Continued degassing; seismicity

Rincon de la Vieja (Costa Rica)

Seismicity and tremor

Ruiz, Nevado del (Colombia)

Seismicity remains at low levels; small ash emissions

Sabancaya (Peru)

Earthquake swarm damages towns and triggers mudslides; 20 people reported dead

Santa Maria (Guatemala)

Explosions and avalanches; plumes to 600 m height

Stromboli (Italy)

Continued explosions from two craters

Suretamatai (Vanuatu)

Fumarolic activity

Taal (Philippines)

Abnormal seismicity continues

Unzendake (Japan)

Continued dome growth and pyroclastic flow generation; dome history reviewed

Yasur (Vanuatu)

Continued block and ash emissions; small episodic lava lakes



Aira (Japan) — July 1991 Citation iconCite this Report

Aira

Japan

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

All times are local (unless otherwise noted)


Frequent explosions; aircraft windshield damaged

Eighteen explosions occurred . . . in July . . ., bringing the yearly total to 171. Ejecta from an explosion at 1057 on 5 August struck the windshield of a Boeing 737 airliner 13 minutes later as it flew at an altitude of 1.2 km, 10 km N of the volcano. A crack 50 cm long formed in the outer surface of the windshield, but the plane (domestic flight ANK 793) landed its 122 passengers and five crew safely. Dense weather clouds had prevented the pilot from seeing the eruption plume. This was the first incident of in-flight damage since 24 June 1986, and the 12th near the volcano since 1975. A car windshield a few kilometers from the crater was cracked by ejecta from another explosion (at 1249) the same day. These were the third and fourth cases of explosion-related damage in 1991.

On 23 July, the month's highest ash cloud rose 2,500 m. Prevailing wind directions prevented ash from being deposited at [KLMO]. Earthquake swarms, not unusual for Sakura-jima, were recorded on 1, 2, 9, 15, 18, 21, and 22 July.

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.


Ambae (Vanuatu) — July 1991 Citation iconCite this Report

Ambae

Vanuatu

15.389°S, 167.835°E; summit elev. 1496 m

All times are local (unless otherwise noted)


Caldera lake bubbling; burned vegetation

"Three anomalous 'boiling' areas with large bubbles and burned vegetation were observed at Lake Vui on 13 July, by P. Fogarty (Chief Pilot of VANAIR). This was the first time he had observed such a phenomenon, and he noted that the vegetation had still been green in May. An aerial survey of the two summit calderas was carried out (during a VANAIR flight) on 24 July. At that time, no strong degassing was visible, but 3 areas of discolored water (each several tens of meters in diameter) were noticeable in the crater lake. Burned vegetation was observed up to the crater rim, 120 m above the water. On 26 July, microseismicity in the caldera was very weak and without any volcanic characteristics.

"Although continuous weak solfataric activity occurs beneath Lake Vui (Warden, 1970), an anomalously strong SO2 degassing is believed to have occurred between May and July. This event was unnoticed by island residents, but since Aoba has been quiet for 300 years, vigilance for this kind of phenomenon must be improved. The existence of a summit caldera lake, numerous lahar deposits, and thick layers of ash (vesiculated and accretionary lapilli) demonstrate the hazards that would accompany renewed activity. Thus, as a precaution, a seismological station was installed in July on the SW flank of the volcano.

Reference. Warden, A.J., 1970, Evolution of Aoba caldera volcano, New Hebrides: BV, v. 34, p. 107-140.

Geologic Background. The island of Ambae, also known as Aoba, is a massive 2,500 km3 basaltic shield that is the most voluminous volcano of the New Hebrides archipelago. A pronounced NE-SW-trending rift zone dotted with scoria cones gives the 16 x 38 km island an elongated form. A broad pyroclastic cone containing three crater lakes (Manaro Ngoru, Voui, and Manaro Lakua) is located at the summit within the youngest of at least two nested calderas, the largest of which is 6 km in diameter. That large central edifice is also called Manaro Voui or Lombenben volcano. Post-caldera explosive eruptions formed the summit craters about 360 years ago. A tuff cone was constructed within Lake Voui (or Vui) about 60 years later. The latest known flank eruption, about 300 years ago, destroyed the population of the Nduindui area near the western coast.

Information Contacts: C. Robin and M. Monzier, ORSTOM, Nouméa, New Caledonia; M. Lardy and C. Douglas, ORSTOM, Vanuatu; C. Mortimer, Dept. of Geology, Mines, and Rural Water Supply, Vanuatu; J. Eissen, ORSTOM, France.


Ambrym (Vanuatu) — July 1991 Citation iconCite this Report

Ambrym

Vanuatu

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

All times are local (unless otherwise noted)


Ash emissions and lava lake activity continue

"Aerial surveys on 13 and 24 July (VANAIR flights) showed puffs of gas and ash rising several hundred meters above Mbuelesu crater, and weak degassing from Benbow crater. Mbuelesu's lava lake, ~100 m in diameter and very deep in the crater, was still present. Activity has remained more or less constant since 1990, and no new lava flows have been observed since 1989."

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

Information Contacts: C. Robin and M. Monzier, ORSTOM, New Caledonia; M. Lardy and C. Douglas, ORSTOM, Vanuatu; C. Mortimer, Dept of Geology, Mines, and Rural Water Supply, Vanuatu; J. Eissen, ORSTOM, France.


Arenal (Costa Rica) — July 1991 Citation iconCite this Report

Arenal

Costa Rica

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

All times are local (unless otherwise noted)


Increased Strombolian activity; seismicity

Strombolian activity, lava effusion, and seismicity all increased in July . . . . The number of volcanic earthquakes rose to a maximum of 59 recorded events/day on 11 July (figure 39). Seismometers recorded intermittent, vigorous tremor episodes, several hours long (6-hour average duration), especially at the beginning of the month.

Figure (see Caption) Figure 39. Daily number of earthquakes at Arenal, July 1991. Courtesy of the Instituto Costarricense de Electricidad.

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: R. Barquero and Guillermo Alvarado, ICE.


Colima (Mexico) — July 1991 Citation iconCite this Report

Colima

Mexico

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

All times are local (unless otherwise noted)


Block lava flow advances; new dome lobe; seismicity

Block lava continued to advance down the main cone's SW flank, generating small avalanches from the flow front and levees. Avalanches have also occurred from the summit area, similar to those that preceded the partial collapse of the newly extruded dome on 16 April. A new lobe was observed in the W part of the summit area on 28 July. Poor weather has severely limited observations of the summit, so the date of the new lobe's extrusion is not known.

On 3 August at about 0600, a NW-flank seismic station (EZV4) recorded the beginning of signals that formed a distinctive wave package with a periodicity of about 15-20 seconds. By 5 August at 1200, the amplitude of these signals had nearly doubled and the periodicity had dropped to 10 seconds. The next day at about 0100, seismicity decreased to nearly background levels, but at 0900 sustained harmonic tremor was registered by EZV4 and other nearby stations (EZV3, 5, and 6); heavy rain during the second week in July had damaged the seismic station about 1 km NE of the summit (EZV7, at Volcancito), and poor weather has prevented it from being re-established. Harmonic tremor continued until 8 August at about 0600. During the increased seismicity, the plume was vigorous and a dense white color.

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

Information Contacts: Francisco Núñez-Cornú, Julián Flores, F. Alejandro Nava, R. Saucedo, G.A. Reyes-Dávila, Ariel Ramírez-Vázquez, J. Hernández, A. Cortés, and Hector Tamez, CICT, Universidad de Colima; Z. Jiménez and S. de la Cruz-Reyna, UNAM.


Etna (Italy) — July 1991 Citation iconCite this Report

Etna

Italy

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

All times are local (unless otherwise noted)


Strombolian activity and continued strong degassing

Strong degassing continued .. during fieldwork in June and July. Strombolian activity was reported at a vent in the NE part of Southeast Crater. Small explosions occurred almost continuously, with more powerful blasts ejecting material to the level of the crater rim occurring every 10-15 minutes (in July). Meanwhile, a vent in the center of the crater gently degassed. In June, occasional emissions of small (<20 cm) sublimate-covered lithic blocks and scoria occurred from a 20 x 10 m pit in Northeast Crater. Lava was visible within the vent, which continued to glow through July. The vent widened internally, giving the appearance of a large chamber inclined in the direction of La Voragine. The elliptical vent at La Voragine crater (reopened prior to a 24 May visit; 16:05) showed incandescence in July, but not in June. Degassing continued from numerous fumaroles within the crater. The floor of Bocca Nuova crater was hidden by large quantities of gas in June, but in July two scoria cones were seen gently emitting vapor. At night, a strongly degassing vent on the SE side of the crater emitted tongues of incandescent gas at 15-minute intervals. A fumarole (56°C) was observed on the October 1989 fracture where it crossed the Canalone Della Montagnola at an altitude of ~ 2,200 m.

The following is from Steve Saunders. "A resurvey, in July, of an EDM network (67 lines) on the upper S flank showed a shortening of the majority of the lines (56), suggesting that minor deflation had occurred since the previous survey in July 1990. At that time, length increases along most lines were interpreted as resulting from minor inflation of the upper flanks since November 1989."

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: H. Gaudru, EVS, Switzerland; T. De St. Cyr, Fontaines St. Martin, France; S. Saunders, West London Institute of Higher Education; W. McGuire, Cheltenham and Glouster College of Higher Education.


Piton de la Fournaise (France) — July 1991 Citation iconCite this Report

Piton de la Fournaise

France

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

All times are local (unless otherwise noted)


Brief lava production follows seismicity, deformation, and magnetic changes

A short eruption occurred on 19-20 July, following a slight increase in seismicity that began 24 June (figure 28), and immediately preceded by a shallow microearthquake swarm. Almost 80 earthquakes (M <1.5), located beneath the S flank of the summit cone at depths of <1 km, were recorded from 0256 to 0350 on 19 June. At 0350, the appearance of tremor signaled the start of lava outflow.

Figure (see Caption) Figure 28. Daily number of earthquakes (top), measured tilt at Dolomieu station 100 m S of the crater (middle), and difference of magnetic field from the reference station 3.5 km W of the fissure (bottom) at Piton de la Fournaise, 30 May-19 July 1991. Courtesy of J. Toutain.

EDM (sampled every 5 minutes) and radial tilt measurements (every minute) at a station (DOLO) ~200 m from the eruptive fissure (figure 29) showed relatively slow inflation beginning at 0310 (figure 30), believed associated with the beginning of intrusion from the magma reservoir. At 0340, radial tilt began to increase rapidly (up to 54 µrad/min), while EDM indicated a rapid decrease in the distance between the rims of the two summit craters. Inflation led to southward tilting (mean azimuth, 175°) of the DOLO station area. Rapid deflation began at 0350, corresponding with the start of tremor, and lasted until 0434. Deflation occurred at maximum rates of 48 µrad/min, causing DOLO to tilt roughly N (azimuth ~10°).

Figure (see Caption) Figure 29. Sketch map showing the summit area of Piton de la Fournaise and the 19 July 1991 lava flows. Courtesy of J.P. Toutain.
Figure (see Caption) Figure 30. Deformation at Piton de la Fournaise, 0140-0500 on 19 July 1991. Top: EDM, sampled every 5 minutes at Dolomieu. Middle: tilt measurements, sampled every minute at Dolomieu and Soufriere; bold lines=radial component, normal lines=tangential component. Bottom: measured strain, sampled every minute at Dolomieu; Z=vertical, X and Y= horizontal components. Arrow indicates start of eruption. Stations are shown in Figure 33. Courtesy of J. Toutain.

The magnetic field near the eruptive vents (station 6) showed a clear decreasing trend beginning on 16 June (figure 28). On 19 July, a rapid magnetic field increase was measured, corresponding with the onset of the eruption.

Lava was emitted from two vents along an eruptive fissure, one inside and one outside of the summit (Dolomieu) crater (figure 29). Lava fountains, 30 m high, were observed during the morning of the 19th and flow velocity was estimated at 3-4 m/sec that afternoon. Lava flowed E through the Grandes Pentes area, covering ~ 1 x 106 m2, with a total volume estimated at 5 x 106 m3. The eruption lasted until about 2000 on 20 July.

Geologic Background. The massive Piton de la Fournaise basaltic shield volcano on the French island of Réunion in the western Indian Ocean is one of the world's most active volcanoes. Much of its more than 530,000-year history overlapped with eruptions of the deeply dissected Piton des Neiges shield volcano to the NW. Three calderas formed at about 250,000, 65,000, and less than 5000 years ago by progressive eastward slumping of the volcano. Numerous pyroclastic cones dot the floor of the calderas and their outer flanks. Most historical eruptions have originated from the summit and flanks of Dolomieu, a 400-m-high lava shield that has grown within the youngest caldera, which is 8 km wide and breached to below sea level on the eastern side. More than 150 eruptions, most of which have produced fluid basaltic lava flows, have occurred since the 17th century. Only six eruptions, in 1708, 1774, 1776, 1800, 1977, and 1986, have originated from fissures on the outer flanks of the caldera. The Piton de la Fournaise Volcano Observatory, one of several operated by the Institut de Physique du Globe de Paris, monitors this very active volcano.

Information Contacts: J. Toutain and P. Taochy, OVPDLF; P. Bachelery, Univ de la Réunion; J-L. Cheminée, P. Blum, A. Hirn, J. LePine, and J. Zlotnicki, IPGP; F. Garner and I. Appora, Univ Paris VI.


Galeras (Colombia) — July 1991 Citation iconCite this Report

Galeras

Colombia

1.22°N, 77.37°W; summit elev. 4276 m

All times are local (unless otherwise noted)


More small explosions; increased seismicity and deformation

Seismicity and emissions began to increase at the end of July, leading to the evacuation of 11 people working on the summit . . . in early August. Released seismic energy (see figure 52) and reduced displacement (figure 42) of long-period earthquakes reached the highest values since the start of monitoring in February 1989. Amplitudes and durations for long-period events showed slow increases, as well. Tremor was recorded in low-frequency bands and modulated packs, with small variations in amplitude and period.

Figure (see Caption) Figure 42. Daily reduced displacement of long-period earthquakes at Galeras, July-August 1991. Courtesy of INGEOMINAS.

Long-period events, shallow in origin and often associated with gas-and-ash emissions, increased to >100/day by mid-August. The number of gas-and-ash emissions increased correspondingly. Plume heights reached 2 km and ash was deposited to 8 km N and NW. Head-sized blocks, hot to the touch, were periodically ejected onto the crater rim.

Inflation, continuing since September 1990, increased dramatically during the first half of August, when 265.8 µrad tangential and -180.6 µrad radial deformation were measured (figure 43) 0.9 km E of the crater ("Crater" electronic tiltmeter). The resultant inflation vector was 321.35 µrad with an azimuth of 115.81°.

Figure (see Caption) Figure 43. Tangential (top curve) and radial (bottom curve) deformation at the Crater electronic tiltmeter at Galeras, January-August 1991. Courtesy of INGEOMINAS.

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: INGEOMINAS-OVP; S. Williams and M. Calvache, Arizona State Univ.


Gaua (Vanuatu) — July 1991 Citation iconCite this Report

Gaua

Vanuatu

14.27°S, 167.5°E; summit elev. 797 m

All times are local (unless otherwise noted)


Increased fumarolic activity; vegetation killed

"An increase in fumarolic activity was noted by VANAIR pilots since April. On 13 July, a detailed aerial survey was conducted over the island during a VANAIR flight. Strong continuous degassing was observed, forming a dense white plume from the SE crater of Mt. Gharat cone. The NW slopes of the cone were largely denuded of vegetation, and the area of the caldera affected by the prevailing SE trade winds had burned vegetation. Due to this increasing activity, we plan to install a seismological station to monitor the volcano as soon as possible.

"Gaua is a composite volcano with a large (8 x 6 km) central caldera occupied by Lake Letas (428 m elev). Mt. Gharat (797 m elev) is an active basaltic cone located near the center of this caldera. Only solfataric activity was recorded from 1868 to 1962 (Mallick and Ash, 1975). Beginning in 1962, central crater explosions with frequent associated ash columns were reported nearly every year until 1977. Information on activity from 1977 to 1990 is scarce, but the volcano was probably quiet, with only minor steam emissions from the SE crater." [BVE reported strong gas emission in mid-1980, a black plume on 9 July 1981, and a brown plume with tephra on 18 April 1982.]

Reference. Mallick, D.I.J., and Ash, R.P., 1975, Geology of the southern Banks Islands: New Hebrides Geological Survey Regional Report, 33 p.

Geologic Background. The roughly 20-km-diameter Gaua Island, also known as Santa Maria, consists of a basaltic-to-andesitic stratovolcano with an 6 x 9 km wide summit caldera. Small parasitic vents near the caldera rim fed Pleistocene lava flows that reached the coast on several sides of the island; several littoral cones were formed where these lava flows reached the sea. Quiet collapse that formed the roughly 700-m-deep caldera was followed by extensive ash eruptions. Construction of the historically active cone of Mount Garat (Gharat) and other small cinder cones in the SW part of the caldera has left a crescent-shaped caldera lake. The symmetrical, flat-topped Mount Garat cone is topped by three pit craters. The onset of eruptive activity from a vent high on the SE flank in 1962 ended a long period of dormancy.

Information Contacts: C. Robin and M. Monzier, ORSTOM, Nouméa, New Caledonia; M. Lardy and C. Douglas, ORSTOM, Vanuatu; C. Mortimer, Dept. of Geology, Mines, and Rural Water Supply, Vanuatu; J. Eissen, ORSTOM, France.


Cerro Hudson (Chile) — July 1991 Citation iconCite this Report

Cerro Hudson

Chile

45.9°S, 72.97°W; summit elev. 1905 m

All times are local (unless otherwise noted)


SO2 circles globe; aircraft encounter ash over Australia; >1 km3 airfall on Argentina

On 12 August, the volcano entered a paroxysmal phase, after four days of lesser explosive activity. Tephra was ejected to 16-18 km height, falling up to 1,000 km SE on the Falkland Islands, and with estimates of >1 km3 deposited in Argentina [but see 16:8]. Ash leacheate analyses showed unusually high levels of fluorine. The SO2-rich plume produced by the eruption was rapidly transported around the world, returning to Chile within 7 days. Airline pilots reported sighting the plume as it passed near Melbourne, Australia (roughly 15,000 km from the volcano).

Initial strong explosive activity, 8-10 August. The following quoted material is from José A. Naranjo. "Just 20 years after the previous activity, Hudson started a new eruption on 8 August at 1820. Local inhabitants who were evacuated from the Huemules River (to the W) reported small precursory seismic activity 3-4 hours before the first explosion. The eruption started with a phreato-magmatic explosion that produced a column almost 7-10 km high. Immediately following the initial explosion, a dense, ash-laden column (light brown-greyish in color) formed, reaching ~12 km. Intense lightning discharged from the mushroom-shaped cloud. Activity steadily decreased through 11 August, when direct observation of the summit showed that the 8 August eruption vent was on the W side of the caldera (10 x 7 km; figure 1). The caldera floor was covered by glacial ice estimated to be at least 40 m thick, and having a volume of about 2.5 km3. In addition, a flank valley, extending 10 km NW from the summit to Huemules valley, is filled with a tongue of ice from the main summit glacier. This terminates at the Huemules Valley, which extends onward ~35 km W to the coast.

Figure (see Caption) Figure 1. Sketch map of the summit area of Hudson, 11 August 1991. Courtesy of José Naranjo.

"Prevailing winds during clear weather carried the column NNE (figure 2) over Puerto Chacabuco (50 km away), where 5-7 mm of ash was deposited. At Puerto Aisén (~ 65 km NNE), ash accumulations reached 5 mm in 16 hours. Lava was observed beneath glacial ice near the vent, flowing down to Ventisquero ('glacial tongue') Huemules. Between 3 and 4 hours after the main explosion, a jökullhaup flowed down the Huemules valley to the coast. A 2-m-thick deposit of ash- to lapilli-sized sand and 0.2-5-m-diameter ice blocks was randomly dispersed near the delta. These ice blocks probably floated in the mudflow." The press reported that the flow increased the river width from 80 m to 170 m.

Figure (see Caption) Figure 2. Map showing the location of Hudson and the direction of ash dispersal on 8-9 and 12-15 August 1991. Courtesy of José Naranjo.

Late on 9 August, a NOTAM reported the plume at 11-12 km altitude. Although the eruption remained nearly continuous, intensity declined. By 10 August, Ladeco (Chilean Airlines) pilots reported the plume at ~ 6 km altitude.

"Eleven people were evacuated from along the Huemules River on 11 August. Direct observations at 1250 showed an explosion from a new vent (Crater 2), about 2.5 km SSE of the first vent (Crater 1; figure 1). The new white-and-black explosion cloud was smaller and spread laterally, developing black, cold pyroclastic-ice flows around the vent, similar to the original. White-grey columns, reaching 3 km height, were observed up to the last direct observation at 1630 on 11 August.

Paroxysmal activity, 12-15 August. "A second, larger eruption started at about 1200 on 12 August. Bad weather prevented aerial observation, but heavy ashfall was reported at Río Murta (60 km SSE) at 1245, and 7 minutes later at Río Tranquilo, 20 km farther S. The ashfall was accompanied by intense lightning, and a sulfur odor. At 1300, ashfall was reported at Puerto Guadal (105 km S). The eruption was directly observed on a commercial flight at 1430. The dense, brown-grey cauliflower-shaped cloud, carried SE, was visible from 4 km altitude, but clearly reached >10 km, with more than a 5-km thickness. One explosion was observed rising at a rate of 1.9 km/min. Observations ended at 1440.

"Since 12 August the eruption has continued without variation, and the plume has been carried SE. On 13 August at 1415, a black ash-laden column was reported from a commercial airplane at >10 km altitude. Pumice fall was since reported beginning 14 August, and coarse lapilli up to 5 cm in diameter fell 55 km SE."

Although weather clouds obscurred the eruption plume to visible and infrared satellite images on the 12th and much of the 13th, preliminary data from the Nimbus-7 satellite (TOMS) indicated 250,000 metric tons of SO2, within a disconnected section of the eruption cloud near the Falkland Islands at about 1100 on the 13th. Beginning at about 2000, a continuous, narrow, eruption plume was visible on AVHRR (NOAA 9 and 11) and GOES satellite images, gradually extending 1200 km SE, beyond the Falkland Islands, at ~12 km altitude. The plume became disconnected from the volcano at about 1200 on 14 August, by which time, Naranjo reported, the eruptive column reached a stable altitude of 16 km. TOMS data from 1100 on the 14th revealed a segment of SO2-rich plume (probably the same as on the 13th) near South Georgia Island (2,600 km ESE of the volcano), and a second, smaller segment over the Falkland Islands. No other SO2-rich plume was visible.

Intense seismic activity was felt on 14 August at 1630, 60 km SSE, where 3-cm-diameter pumice was falling. A continuous eruption began again at about 2000, when satellite images (GOES and NOAA 9 and 11) showed that the plume was carried SE at 185 km/hr (100 knots) at stratospheric altitudes of 17-18 km (figure 3). Seismicity increased, with felt earthquakes at Coyhaique (80 km NE) beginning at 2200, and a series of five large earthquakes (M>5) detected near Hudson by the WWSSN beginning at 2238 (table 1). Early on the 15th, the plume extended 1,500 km SE, past the Falkland Islands, where it divided into two components, one travelling E, the other S, both quickly becoming diffuse. At its widest point (the Falkland Islands), the plume was 370 km wide. Infrared satellite imagery showed the plume before it disconnected from the volcano at 1130. TOMS data from 1100 on the 15th (figure 4) showed the plume already disconnected from the volcano, and containing roughly twice as much SO2 as on the 13th (missing data prevented more accurate determinations). No additional emissions have been reported as of 23 August.

Figure (see Caption) Figure 3. Infrared image from the NOAA 10 polar orbiting weather satellite on 15 August 1991 at about 0800, showing the ash plume extending SE from Hudson. Temperature estimates suggest that the plume is at aboout 17-18 km altitude. Courtesy of G. Stephens.

Table 1. Earthquakes near Hudson recorded by the Worldwide Standardized Seismic Net on 14-15 August 1991. Original, very preliminary data are replaced by information from the National Earthquake Information Center's Preliminary Determination of Epicenters.

Date Time Latitude Longitude Magnitude Depth
14 Aug 1991 2238:15 45.6°S 72.6°W 5.2 mb --
15 Aug 1991 0039:08.5 45.7°S 72.6°W 5.3 mb --
15 Aug 1991 0250:37.9 45.8°S 72.5°W 5.3 mb --
15 Aug 1991 0546:15.7 45.7°S 73.2°W 5.7 Ms 13 km
15 Aug 1991 0816:19.3 45.6°S 71.9°W 5.3 mb --

Eruption plume migration. The eruption plume of 14-15 August was rapidly carried E by the "Roaring Forties" winds as shown by TOMS data (figure 4), reaching Australia (15,000 km E) on 20 August. There the following report was compiled from airline information by Alfred Prata:

Figure (see Caption) Figure 4. Preliminary data from the TOMS on the Nimbus-7 satellite showing a polar view of an eruption cloud from Hudson on 20 August 1991 at about 1100 (local time). Each dot represents SO2 values above 10 milliatmosphere-cm (100 ppm-m), within an area 50 km across. The prominent concentration of SO2 to the left represents the cloud's position 24 hours after that to the right, but both are 20 August because they straddle the International Date Line. Envelopes surrounding the cloud's position at approximately 1100 (local time) on 15, 16, and 18 August have been added to illustrate its passage around the globe. Courtesy of Scott Doiron.

"On 20 August, Australian Airlines flight FL418 (Airbus) from Melbourne to Sydney reported an encounter with a strange hazy cloud 260 km NE of Melbourne at about 0230. The haze was faint grey, much like the material often trapped under a temperature inversion, and had a brownish-orange tinge. The haze appeared uniform (not wispy) and there was no evidence of any trace of debris. Associated with this was a strong smell of sulfurous gas which entered the aircraft and was noticed by the crew and passengers. The return flight departed Sydney at about 0400 and encountered the same haze in roughly the same place at 0445. The aircraft was in the haze for 5-10 minutes (75-150 km) and did not change their flight level (FL330, ~10 km altitude). A NOTAM was issued for the period of the evening of the 20th through the morning of the 22nd." The cloud was also reported by pilots from Qantas and Ansett, as late as 2000 on the 20th.

The Atmospheric Research Division of CSIRO were able to discriminate the plume, ~ 500 km long and 100 km wide, on an AVHRR image by ratioing bands 4 and 5. TOMS data showed the plume continuing its eastward path, reaching Chile on 21 August.

Deposits and post-eruptive activity. Intense fumarolic activity continued from a 2-km fissure (oriented N20°E) on the WNW caldera margin during a 23 August overflight. Weaker fumarolic activity was observed on the interior slopes of the 500-m-diameter Crater 1, located 400 m E of the fissure (figure 1). The fissure and Crater 1 were the site of activity 8-10 August.

A black flow (probably lava), with shades of reddish-brown, extended about 3.5 km from the extreme N end of the fissure, onto Ventisquero Huemules. The flow was 50-300 m wide, with several broader sections, and covered recent scoria (8-10 August) in places. Several weak vapor/gas emissions were visible. Scoriaceous pyroclastic flow deposits containing large quantities of ice and snow extended from the fissure toward the interior of the caldera, and in part, over Ventisquero Huemules toward the NW, and Huemules Valley.

Products of the 8-10 August activity were basaltic in composition. Ash samples (ranging to 0.1 mm in size) from Puerto Aisén contained abundant magnetite, pyroxene, plagioclase, and black glass shards. Silica contents of the ash were determined to be 50.98% (at Sernageomin Laboratory).

At Crater 2, believed to be the site of activity on 12-15 August, intense degassing occurred at 3 fumaroles along the S margin. Concentric cracks were visible in the thick ice surrounding the 800-m-wide Crater 2. Pumice from 12-15 August activity differed in composition from the earlier erupted material. Whole rock analyses (from Peter Bitschene) indicated a trachyandesitic composition, with ~ 60% SiO2 and 8-9% alkalies. The distal fallout ash was >98% vitric with predominant pumice and platy shards, and some entrained blocky basaltic shards.

Bitschene estimated that more than 1 km3 of tephra was deposited in Argentina's Santa Cruz province [but see 16:8]. Lakes near the volcano were highly turbid and had layers of floating pumice along their E shores. Increased sediment load resulted in the acceleration of delta growth in Lago Buenos Aires (SE; also called Lago General Carrera), and silting up of the mouth of Río Ibáñez near Puerto Ingeniero Ibáñez (75 km SE) creating a flood risk.

Roughly 50-60,000 sheep and cattle are located within the airfall zone. Extremely high values of fluorine (225 ppm water extractable) were obtained from the ash analyzed 4 days after the eruption. Alberto Villa (INTA, Univ de Chile) reported that grass samples collected at the same site had 280 ppm fluorine (on a dry basis). [but see 16:9-10]

Reference. Stern, C.R., 1991, Mid-Holocene Tephra on Tierro del Fuego (54°S) Derived from the Hudson Volcano (46°S): Evidence for a Large Explosive Eruption; Revista Geológica de Chile, v. 18, no. 2, in press.

Geologic Background. The ice-filled, 10-km-wide caldera of the remote Cerro Hudson volcano was not recognized until its first 20th-century eruption in 1971. It is the southernmost volcano in the Chilean Andes related to subduction of the Nazca plate beneath the South American plate. The massive volcano covers an area of 300 km2. The compound caldera is drained through a breach on its NW rim, which has been the source of mudflows down the Río de Los Huemeles. Two cinder cones occur N of the volcano and others occupy the SW and SE flanks. This volcano has been the source of several major Holocene explosive eruptions. An eruption about 6700 years ago was one of the largest known in the southern Andes during the Holocene; another eruption about 3600 years ago also produced more than 10 km3 of tephra. An eruption in 1991 was Chile's second largest of the 20th century and formed a new 800-m-wide crater in the SW portion of the caldera.

Information Contacts: J. Naranjo, SERNAGEOMIN; H. Moreno, Univ de Chile; G. Fuentealba and P. Riffo, Univ de La Frontera; P. Bitschene, Patagonia Volcanism Project, Argentina; N. Banks, USGS; SAB, NOAA; G. Stephens, NOAA/NESDIS; S. Doiron, GSFC; B. Presgrave, NEIC; C. Stern, Univ of Colorado, Boulder; A.J. Prata, CSIRO, Australia; ICAO; Radio Nacional de Chile; AP.


Irazu (Costa Rica) — July 1991 Citation iconCite this Report

Irazu

Costa Rica

9.979°N, 83.852°W; summit elev. 3432 m

All times are local (unless otherwise noted)


Seismicity remains high; crater lake level rises

In July, the turquoise-green crater lake continued to rise, eventually covering 2/3 of the crater floor, including several fumaroles that formed during early-mid June. Sulfur deposits had been observed at some of these fumaroles. On 17 July, the lake was 150 x 100 m, with a maximum depth of 2 m. Water temperatures increased with proximity to the bubbling springs (90°C), mud pots, and roaring fumaroles, ranging from 35°C to 55°C (compared to 30-48°C in late June). The lake had pH of 3.7.

Seismicity remained at high levels in July, but was decreased in comparison to late May-June (16:5-6). July's highest seismicity occurred on the 4th, when 75 earthquakes were recorded (seismic station IRZ2, 5 km WSW, Univ Nacional network; figure 3), 34 of which occurred in a NW-SE trend. The 4 July earthquakes (M 1.5-2.7) were centered 0.6-10 km from the crater at <10 km depth. Tremor episodes and B-type earthquakes continued to be recorded in July.

Figure (see Caption) Figure 3. Daily number of earthquakes at Irazú, July 1991. Courtesy of Universidad Nacional.

Geologic Background. Irazú, one of Costa Rica's most active volcanoes, rises immediately E of the capital city of San José. The massive volcano covers an area of 500 km2 and is vegetated to within a few hundred meters of its broad flat-topped summit crater complex. At least 10 satellitic cones are located on its S flank. No lava flows have been identified since the eruption of the massive Cervantes lava flows from S-flank vents about 14,000 years ago, and all known Holocene eruptions have been explosive. The focus of eruptions at the summit crater complex has migrated to the W towards the historically active crater, which contains a small lake of variable size and color. Although eruptions may have occurred around the time of the Spanish conquest, the first well-documented historical eruption occurred in 1723, and frequent explosive eruptions have occurred since. Ashfall from the last major eruption during 1963-65 caused significant disruption to San José and surrounding areas.

Information Contacts: R. Barquero, Guillermo Alvarado, and Alain Creussot, ICE; Mario Fernández and Hector Flores, Sección de Sismología y Vulcanología, Univ de Costa Rica; J. Barquero, E. Fernández, V. Barboza, and J. Brenes, OVSICORI.


Kavachi (Solomon Islands) — July 1991 Citation iconCite this Report

Kavachi

Solomon Islands

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

All times are local (unless otherwise noted)


May-June submarine eruption ends; temporary island eroded away

An eruption built a small temporary island . . . first observed on 4 May, but its location was initially uncertain. However, more precise navigational data from the chief pilot of Western Pacific Air Services placed the activity at 9.00°S, 157.97°E, roughly 3 km NE of Kavachi's summit.

Activity apparently had not changed when, during an overflight on 5 June, [John] Monroe observed a vigorously active lava fountain roughly 25 m high and a plume that rose >2,500 m. The island's dimensions were estimated at 150-200 m long and ~50 m high. Carl Rossiter reported that divers ~45 km NE of Kavachi (at Kicha Island) felt powerful explosions while underwater on 7-8 and 12-13 June. Individual explosions occurred a few seconds apart in groups of 12-20. Explosion groups generally lasted a total of 1-2 minutes, were typically preceded and followed by rumbling, and were separated by roughly 30 minutes of quiet. No explosions were felt at other dive sites, where islands were between the observers and Kavachi.

The eruption weakened in mid-June, and the island disappeared beneath the ocean surface later in the month. No additional activity has been reported.

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

Information Contacts: R. Addison and A. Papabatu, Ministry of Natural Resources, Honiara; J. Monroe, San Jose, USA; C. Rossiter, See and Sea Travel Service, San Francisco, USA.


Kilauea (United States) — July 1991 Citation iconCite this Report

Kilauea

United States

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

All times are local (unless otherwise noted)


Continued E rift lava production; summit earthquake swarm

The . . . eruption continued through July, as lava from Kupaianaha vent flowed into the sea. The surface of Kupaianaha's lava pond remained frozen, while lava was still active at the bottom of Pu`u `O`o crater. Nearly simultaneous earthquake swarms occurred in the summit areas of Kilauea and its larger neighbor Mauna Loa.

Eruptive activity. Lava from Kupaianaha was confined to tubes as it advanced down the upper slopes, where skylights at ~650 m (2,150-2,140 ft) elevation revealed an average velocity of ~1 m/s. Active surface flows were intermittently observed in a steeper area near 350 m (1,100 ft) elevation, and additional large surface flows emerged from the tube system between there and the coast through July. One large flow, active since June, advanced on top of the main (Wahaula) tube's E branch (figure 79). Its terminus was near 40 m (140 ft) elevation on 9 July. Although the flow front was wide with many active lobes, it did not reach the coast. Numerous small breakouts were active behind its front. Another flow emerged from a tube near 180 m (600 ft) elevation, moved downslope above the tube's W branch, and reached the coastal plain on 14 July. Two fluid pahoehoe lobes were advancing toward the coast on 16 July, moving past a kipuka at 35 m (120 ft) elevation. By the end of the month, the active flow front was > 400 m wide, and small breakouts from the flow were burning vegetation in Royal Gardens subdivision.

Despite the extensive surface activity, lava continued to pour into the sea from tubes at two main entries. The tube's W branch fed two active sites (at the Poupou entry). The littoral cone at the W Poupou site continued to erode, but erosion slowed toward the end of July as a bench growing outward below the littoral cone absorbed most of the waves' force. A cycle of bench erosion and rebuilding occurred repeatedly at the E Poupou site. Undercutting by wave action removed meter-sized blocks from the cliff face, and the resulting rapid collapse and erosion generated increased spatter activity, initiating construction of a new lower bench. At the entry fed by the E branch of the tube (Paradise), a prominent mid-bench scarp was noted on 4 July. Spatter was found draped over the scarp but none was evident on the lower portion of the bench, suggesting that the lower bench grew after the collapse episode. However, no seismic evidence of collapse was noted. The lower bench grew to within 1 m of the upper bench by 26 July. By the end of the month, the lava entry point shifted from the middle to the E side of the bench. Its W side began eroding and soon developed a cliff facing the ocean.

Seismicity. Continuous volcanic tremor persisted through July at the seismic stations nearest the eruption site and near the W ocean entry. Tremor amplitudes were generally low, although occasional brief bursts of higher amplitude tremor were recorded.

Earthquake activity beneath the summit appeared to have changed slightly since mid-late June. Shallow activity (0-5 km depth) had decreased, especially from the first 3 months of 1991. Daily visual scans of analog records since mid-June suggest that the dominant frequency content of shallow harmonic events had also changed, from 3-5 Hz to 1-3 Hz. The number of deeper (5-13 km) harmonic events fluctuated through July. Between 3 and 6 July, there were swarms of both shallow and deeper long-period events, then activity declined before a second, less intense swarm of intermediate-depth long-period events occurred on 11 July. This was followed first by an increase in shallower long-period activity, then a swarm of several hundred short-period microearthquakes on 13 July between 1400 and 2300, ~2 hours after the onset of a swarm under neighboring Mauna Loa. Almost all were too small for precise location. The 13 July seismicity was not associated with obvious eruptive changes, but geophysicists believe that it may indicate changes in magmatic activity or the state of stress beneath the summit.

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. Moulds and P. Okubo, HVO.


Kuwae (Vanuatu) — July 1991 Citation iconCite this Report

Kuwae

Vanuatu

16.829°S, 168.536°E; summit elev. -2 m

All times are local (unless otherwise noted)


Summit at 2-3 m depth; no visible fumarolic activity; sulfur odor

"Kuwae is a mainly submarine caldera (~10x5 km) that, according to C14 ages, Tongan folklore, and reconnaissance fieldwork (Garanger, 1972; Crawford, 1988), is probably very young (~1,500 A.D.). The caldera is located between Epi, Laika, and Tongoa islands in the central part of Vanuatu. During the ORSTOM-CALIS cruise in May 1991, detailed bathymetric and magnetic surveys of the collapse structure were made, and data are presently under analysis. August fieldwork was carried out on Tongoa and Laika Islands in order to study caldera eruption products, their composition, and their age. Several ignimbrite units, including non-welded ash and pumice flow deposits, and thick, complex sequences of poorly-welded to densely-welded tuffs, have been discovered. C14 ages will be determined for charcoal samples from these deposits.

"During the last century, the caldera's active Karua volcanic cone has emerged at least six times, in 1897, [1901], . . . 1948, [1949], 1959, and 1971. Each period of activity was accompanied by explosions. The ephemeral island reached a maximum size of 100 m tall and 1.5 km in diameter in 1949. On 6 August, during a visit by speedboat, the submerged summit area was 50-70 m large at 2-3 m depth. No fumarolic activity was observed despite a strong sulfur smell." [Turbulence and discolored sea water were observed in 1971-74 and 1977.]

References. Crawford, A.J., 1988, Circum-Pacific Council for Energy and Mineral Resources: Earth Science Series, v. 8.

Garanger, J., 1972, Publication de la Société Océanistes, no. 30.

Geologic Background. The largely submarine Kuwae caldera occupies the area between Epi and Tongoa islands. The 6 x 12 km caldera contains two basins that cut the NW end of Tongoa Island and the flank of the late-Pleistocene or Holocene Tavani Ruru volcano on the SE tip of Epi Island. Native legends and radiocarbon dates from pyroclastic-flow deposits have been correlated with a 1452 CE ice-core peak thought to be associated with collapse of Kuwae caldera; however, others considered the deposits to be of smaller-scale eruptions and the ice-core peak to be associated with another unknown major South Pacific eruption. The submarine volcano Karua lies near the northern rim of Kuwae caldera and is one of the most active volcanoes of Vanuatu. It has formed several ephemeral islands since it was first observed in eruption during 1897.

Information Contacts: C. Robin and M. Monzier, ORSTOM, New Caledonia; M. Lardy and C. Douglas, ORSTOM,Vanuatu; C. Mortimer, Dept of Geology, Mines, and Rural Water Supply, Vanuatu; J. Eissen, ORSTOM, France.


Langila (Papua New Guinea) — July 1991 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)


Tephra emission and seismicity

"Activity of both craters remained moderately strong in July, as in June. Crater 3, which had resumed activity in mid-May, released white-to-grey vapor and ash clouds, and light ashfall occurred towards the NE of the volcano on the 6th and 8th. Occasional weak to loud explosions were heard throughout the month. Weak to bright red glow was observed on the 8th, 9th, 13th, and throughout the last week of the month.

"Activity at Crater 2 was characterized by the emission of moderate to thick pale grey ash clouds. Occasional loud to low explosions, some of which were accompanied by light ashfall, were heard during the second and last week of the month. Steady, weak night glow was visible throughout the second week and on the 22nd and 23rd.

"Seismicity remained high throughout the month, with the occurrence of explosion earthquakes and tremor. The daily number of Vulcanian explosions recorded by the summit station (LAN) reached a maximum of 40-60 between the 21st and 26th. Tremor, hardly noticeable in May, occurred almost daily in June-July (up to 100-200 minutes/day). Two types were recognized: high-frequency, discontinuous tremor periods, lasting 1-2 minutes; and lower-frequency harmonic tremor, continuous for periods of several (up to 10) minutes. The tremor became strong enough to be recorded at both the summit station (LAN) and the 9-km-distant CGA station."

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: C. McKee, RVO.


Lewotobi (Indonesia) — July 1991 Citation iconCite this Report

Lewotobi

Indonesia

8.542°S, 122.775°E; summit elev. 1703 m

All times are local (unless otherwise noted)


Strombolian activity

Press releases reported increased activity, with small eruptions occurring around 19 July. One eruption reportedly ejected incandescent material 100 m high, dropping hot ash (smelling of sulfur) onto nearby areas and causing residents to flee. At 1645 on 29 July, a 300-m-high ash cloud extending ~35 km W was reported by pilots on Qantas flight A61. By the week of 14-19 August the volcano was no longer exploding, and gas emissions, 50-100 m high, appeared to be decreasing.

Geologic Background. The Lewotobi "husband and wife" twin volcano (also known as Lewetobi) in eastern Flores Island is composed of the Lewotobi Lakilaki and Lewotobi Perempuan stratovolcanoes. Their summits are less than 2 km apart along a NW-SE line. The conical Lakilaki has been frequently active during the 19th and 20th centuries, while the taller and broader Perempuan has erupted only twice in historical time. Small lava domes have grown during the 20th century in both of the crescentic summit craters, which are open to the north. A prominent flank cone, Iliwokar, occurs on the E flank of Perampuan.

Information Contacts: W. Modjo, VSI; ICAO; UPI.


Lopevi (Vanuatu) — July 1991 Citation iconCite this Report

Lopevi

Vanuatu

16.507°S, 168.346°E; summit elev. 1413 m

All times are local (unless otherwise noted)


No fumarolic activity

"The volcano was totally quiet during overflights (VANAIR) on 4 September 1990, and 13 and 24 July 1991. . . . As with Gaua, the scarcity of information from 1977 to 1989 prevents a precise description of its activity. Nevertheless, it seems that no major event occurred during this period."

[The Bulletin of Volcanic Eruptions (BVE) reports lava flows in November 1978, ash eruptions and lava flows February-March 1979, a black eruption column on 2 July 1979, minor ash emissions on 12 September 1979, vigorous ash eruptions in April and July 1980, and an eruption cloud and lava flow on 18-20 August 1980.]

Geologic Background. The small 7-km-wide conical island of Lopevi, known locally as Vanei Vollohulu, is one of Vanuatu's most active volcanoes. A small summit crater containing a cinder cone is breached to the NW and tops an older cone that is rimmed by the remnant of a larger crater. The basaltic-to-andesitic volcano has been active during historical time at both summit and flank vents, primarily along a NW-SE-trending fissure that cuts across the island, producing moderate explosive eruptions and lava flows that reached the coast. Historical eruptions at the 1413-m-high volcano date back to the mid-19th century. The island was evacuated following major eruptions in 1939 and 1960. The latter eruption, from a NW-flank fissure vent, produced a pyroclastic flow that swept to the sea and a lava flow that formed a new peninsula on the western coast.

Information Contacts: C. Robin and M. Monzier, ORSTOM, New Caledonia; M. Lardy and C. Douglas, ORSTOM,Vanuatu; C. Mortimer, Dept of Geology, Mines, and Rural Water Supply,Vanuatu; J. Eissen, ORSTOM, France.


Manam (Papua New Guinea) — July 1991 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)


Stronger ash emission

"Activity . . . increased slightly in July, as shown by more voluminous vapour and ash emissions, stronger sounds, and the resumption of night glow over Main Crater. Emissions from Main Crater consisted of weak to moderate white-grey ash and vapour accompanied by thin blue vapour from 22 to 25 July. Occasional deep roaring noises were heard on the 4th-6th. A weak fluctuating night glow was visible 23-25 July for the first time since April. Southern Crater emitted thin to thick grey-brown ash clouds, occasionally rising to ~400-500 m above the crater rim. Booming and deep roaring noises were heard on most days throughout the month, but no night glow was observed. Seismicity was at a moderate level and tiltmeter measurements showed no change."

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: C. McKee, RVO.


Mauna Loa (United States) — July 1991 Citation iconCite this Report

Mauna Loa

United States

19.475°N, 155.608°W; summit elev. 4170 m

All times are local (unless otherwise noted)


Summit earthquake swarm

Surface deformation measurements indicate gradual reinflation of Mauna Loa's summit since its 1984 eruption. Earthquake counts have fluctuated, but have apparently increased since late 1990.

Two bursts of intermediate-depth volcanic tremor, beginning at about 1200 on 13 July, preceded a swarm of long-period earthquakes that continued for ~14 hours. Activity peaked between 2300 on 13 July and 0100 the next morning. As the long-period events gradually declined, shallow microearthquake activity increased, and continued for about 6 hours. All of the events were too small for precise location.

The 13 July activity began ~2 hours before an earthquake swarm under the summit of Kilauea. Seismicity at Mauna Loa has apparently returned to average background levels since mid-July.

Geologic Background. Massive Mauna Loa shield volcano rises almost 9 km above the sea floor to form the world's largest active volcano. Flank eruptions are predominately from the lengthy NE and SW rift zones, and the summit is cut by the Mokuaweoweo caldera, which sits within an older and larger 6 x 8 km caldera. Two of the youngest large debris avalanches documented in Hawaii traveled nearly 100 km from Mauna Loa; the second of the Alika avalanches was emplaced about 105,000 years ago (Moore et al. 1989). Almost 90% of the surface of the basaltic shield volcano is covered by lavas less than 4000 years old (Lockwood and Lipman, 1987). During a 750-year eruptive period beginning about 1500 years ago, a series of voluminous overflows from a summit lava lake covered about one fourth of the volcano's surface. The ensuing 750-year period, from shortly after the formation of Mokuaweoweo caldera until the present, saw an additional quarter of the volcano covered with lava flows predominately from summit and NW rift zone vents.

Information Contacts: P. Okubo, HVO.


Ontakesan (Japan) — July 1991 Citation iconCite this Report

Ontakesan

Japan

35.893°N, 137.48°E; summit elev. 3067 m

All times are local (unless otherwise noted)


Decreasing seismicity

Seismicity decreased in July, with 94 earthquakes and two tremor episodes recorded . . . (figure 10). Summit vents continued emitting white steam plumes but these rose weakly to ~ 100 m . . . .

Figure (see Caption) Figure 10. Daily number of earthquakes January-15 August 1991.

Geologic Background. The massive Ontakesan stratovolcano, the second highest volcano in Japan, lies at the southern end of the Northern Japan Alps. Ascending this volcano is one of the major objects of religious pilgrimage in central Japan. It is constructed within a largely buried 4 x 5 km caldera and occupies the southern end of the Norikura volcanic zone, which extends northward to Yakedake volcano. The older volcanic complex consisted of at least four major stratovolcanoes constructed from about 680,000 to about 420,000 years ago, after which Ontakesan was inactive for more than 300,000 years. The broad, elongated summit of the younger edifice is cut by a series of small explosion craters along a NNE-trending line. Several phreatic eruptions post-date the roughly 7300-year-old Akahoya tephra from Kikai caldera. The first historical eruption took place in 1979 from fissures near the summit. A non-eruptive landslide in 1984 produced a debris avalanche and lahar that swept down valleys south and east of the volcano. Very minor phreatic activity caused a dusting of ash near the summit in 1991 and 2007. A significant phreatic explosion in September 2014, when a large number of hikers were at or near the summit, resulted in many fatalities.

Information Contacts: JMA.


Pacaya (Guatemala) — July 1991 Citation iconCite this Report

Pacaya

Guatemala

14.382°N, 90.601°W; summit elev. 2569 m

All times are local (unless otherwise noted)


Explosive eruptions destroy cone and crater; crop damage; evacuations

Fourteen eruptions occurred during the most recent phase of strong explosive activity, 6 June-1 August, with the strongest and most destructive activity occurring 27-31 July. Activity was at low levels as of 15 August.

The following report from Philippe Rocher describes activity through mid-June.

"During the first half of 1991, activity was continuous and relatively quiet, with several small eruptions and lava flows from the main crater. This last cycle of activity began in November 1990. The continuous ejection of material built a cone that reached 400-500 m height. Although seismicity showed no significant changes in May, occassional pulses of increased surface activity occurred. On 11-15 May, explosion counts ranged from 1,170 to 1,730/day and a new lava flow was emitted. The cone reached 500 m high and lava traveled down the SE slope.

"On 6 June, explosive activity increased again, with explosions every 10-40 seconds and ash reaching 100-500 m heights. The next pulse occurred on 11 June. On the following day, strong explosions sent material to 500 m height and triggered avalanches that destroyed the summit of the cone. Lava flowed down the SW slope. Ash emissions to 500 m height and short lava flows characterized the next increase, lasting 4.5 hours on 14 June. On 16 June, a 10-hour episode of strong explosions ejected a black plume to 600 m height and caused avalanches that traveled to the foot of the volcano. Between the different eruptions, strong degassing continued, accompanied by B-type earthquakes and small, low-amplitude (about 1 mm) tremor episodes."

The following is from Eddy Sánchez.

"The most explosive and destructive activity during the current phase of activity began at 0100 on 27 July. Strombolian activity destroyed the main crater, and ejected ash and lapilli to the SW, principally affecting Caracol, Rodeo, and Patrocinio, the same towns affected by the eruption on 25 January 1987. Activity decreased at 0230." The press reported that three people were injured and 2,000 left homeless.

"Intense activity resumed at 1330-2230 on 30 July, with four cycles of moderate explosions, each cycle lasting 1.5 hours. Similar activity occurred the next day, when columns of fine ash and gas rose 400-1,000 m above MacKenney Crater. The last strong episode of Strombolian activity began at 0230 on 1 August, when ash clouds reached 700-1,000 m heights, with pulses and pauses of 30-60 minutes, and blocks (>=5 m in diameter) were ejected onto the flanks of the volcano.

"Local agriculture was significantly damaged by airfall from this recent phase of explosive activity. Corn and bean fields were destroyed, as well as part of the coffee crop. Airfall thicknesses ranged from 0.5 to 26 cm, with up to 5 cm in Rodeo and 15 cm in Santa Lucía Cotzumalguapa (figure 8). The ash was deposited as far as 55 km WSW (Pueblo Nuevo Tiquisate).

Figure (see Caption) Figure 8. Isopach map of airfall deposits from activity on 27-31 July 1991 at Pacaya. Base Map is a portion of Guatemala 1:250,000 sheet (ND 15-8, Dirección General de Cartografía, Guatemala City, Guatemala). Contour interval, 100 m. Courtesy of E. Sánchez.

"During the last eruption, on 1 August, INSIVUMEH recommended to emergency agencies that the approximately 1,500 residents of Caracol, Rodeo, and Patrocinio be evacuated, due to the hazard of a new violent eruption. The next day, seismic and eruptive activity decreased considerably, allowing the evacuated people to return home. Activity continued to decrease quickly, with 40 B-type microearthquakes (frequency, 4-5 Hz, and amplitude, 2.0-2.5 mm) recorded daily on 7 August. Activity as of 15 August was considered at low levels."

Geologic Background. Eruptions from Pacaya, one of Guatemala's most active volcanoes, are frequently visible from Guatemala City, the nation's capital. This complex basaltic volcano was constructed just outside the southern topographic rim of the 14 x 16 km Pleistocene Amatitlán caldera. A cluster of dacitic lava domes occupies the southern caldera floor. The post-caldera Pacaya massif includes the ancestral Pacaya Viejo and Cerro Grande stratovolcanoes and the currently active Mackenney stratovolcano. Collapse of Pacaya Viejo between 600 and 1500 years ago produced a debris-avalanche deposit that extends 25 km onto the Pacific coastal plain and left an arcuate somma rim inside which the modern Pacaya volcano (Mackenney cone) grew. A subsidiary crater, Cerro Chino, was constructed on the NW somma rim and was last active in the 19th century. During the past several decades, activity has consisted of frequent strombolian eruptions with intermittent lava flow extrusion that has partially filled in the caldera moat and armored the flanks of Mackenney cone, punctuated by occasional larger explosive eruptions that partially destroy the summit of the growing young stratovolcano.

Information Contacts: E. Sánchez, INSIVUMEH; Philippe Rocher, L.A.V.E., France; ACAN network, Panama City, Panama.


Pinatubo (Philippines) — July 1991 Citation iconCite this Report

Pinatubo

Philippines

15.13°N, 120.35°E; summit elev. 1486 m

All times are local (unless otherwise noted)


Ash emissions decreasing; typhoons trigger large lahars

Activity declined through the third week of August, although periodic explosions continued to eject material to >15 km height. Heavy rains triggered large mudflows that traveled down all major drainage systems, destroying houses and resulting in numerous casualties. The number of people killed by the eruption, mudflows, and disease (in evacuation camps) now exceeds 500. The stratospheric aerosol cloud produced by the paroxysmal activity on 15-16 June continued to disperse.

Continuing activity, to 20 August. Declining seismicity was interrupted by a M 4.5-5 volcano-tectonic earthquake at 1456 on 26 July and several felt aftershocks. Ash emission continued, often accompanied by tremor during periods of increased plume heights. Two pulses of emissions to >7.5 km at 0136 and 0203, and one to 16.4 km (as determined by radar at Clark Air Base) at 1212 on 27 July, were accompanied by low-amplitude tremor. Aviation officials were notified within 15 minutes of the onset of this more energetic activity. Relatively dry weather continued through early August.

Seismicity continued a gradual downward trend (figure 16), with a decrease in amplitude and number of long-period events, and a decrease in seismic energy released (figure 17). Small upsurges in amplitude (RSAM) corresponded to long-period earthquakes. Ash emissions were rare and did not exceed 8 km height during 8-10 August and had fewer accompanying long-period events. Occasional high-frequency earthquakes were felt at Clark Air Base with intensities up to II. Mudflow signals were seismically recorded on the 10th.

Figure (see Caption) Figure 16. Number of earthquakes per 4 hours (top) and Realtime Seismic Amplitude Measurement (bottom) at Pinatubo, 16 June-11 August 1991. Courtesy of PHIVOLCS.
Figure (see Caption) Figure 17. Accumulated RSAM energy at Pinatubo, 16 June-15 August 1991. Courtesy of PHIVOLCS.

Heavy rain triggered large mudflows on 11 August. The press reported that more than 13,000 people fled their villages, and more than 1,000 houses were destroyed. The Gumain (SE flank) and Sacobia (E flank) Rivers rose an average 1.2 m, and 300 houses were damaged along the Abacan near Mexico (~45 km E of the summit). Five large ash emissions (average height 5 km) occurred on 12 August. United Airlines pilots reported an ash cloud to >15 km altitude at about 1300 on the 12th and to 12 km the following day at 1426.

High ash emissions (maximum plume height about 13 km) and mudflows were reported on 14 August. About 5,000 people evacuated Tabon in the Pampanga region (E flank), as 96 houses were washed away. The press reported debris to 3 m deep. Mudflows on the 18th prompted another large evacuation, with 3,000 fleeing 6 towns in the Pampanga and Tarlac regions (E flank).

On 20 August, the press reported that the largest mudflows since the start of the eruption killed 31 people (primarily in Santa Rita, ~40 km NE), bringing the number of mudflow-related deaths to over 100. Flows 5 m high reportedly traveled down ten rivers, damaging more than 9,000 houses and destroying three bridges. Up to 55,000 people evacuated their homes. Ash clouds rose to 12 km high.

The press reported that by 6 August, more than 46 people (mostly children and infants) had died of various illnesses (primarily diarrhea, measles, and broncho-pneumonia) in evacuation camps. This number had increased to nearly 200 (mostly Aeta tribesmen) by 18 August, and it was reported that almost 1,500 people in the camps were suffering from disease. By 20 August, more than 500 people had died since the start of the eruption according to press reports.

Field geology. Fieldwork and evaluation of the deposits from the paroxysmal activity of 15-16 June continued. A preliminary airfall isopach map was prepared by the PHIVOLCS MGB Lahar Task Force (figure 18), and the volume of material within the 10-cm isopach was estimated to be 0.47 km3. Ash leachates indicated chloride contents to almost 1,000 ppm, and fluoride contents under 10 ppm (table 3). Petrographic analysis of pumice samples revealed the presence of anhydrite micro-phenocrysts scattered in the matrix groundmass (Bernard, and others, 1991). Pyroclastic-flow deposit volumes were estimated to total roughly 7 km3. The following report by Alain Bernard describes one of the pyroclastic-flow deposits.

Figure (see Caption) Figure 18. Preliminary isopach map of 12-16 June 1991 airfall deposits from Pinatubo. Isopachs are centimeters. Prepared by PHIVOLCS MGB Lahar Task Force.

Table 3. Preliminary fluoride and chloride contents in Pinatubo ash leachates, 12 June-4 July 1991. Ash was washed for 12 hours in a 4:1 ratio of water (distilled-deionized water, pH 5.5) to ash. The 12, 15, and 22 June samples were collected by PHIVOLCS and reported "fresh fallen," the other samples were collected shortly after falling, during dry weather. Courtesy of Alain Bernard and PHIVOLCS.

Date Location Distance from volcano F- (ppm) Cl- (ppm) pH
12 Jun 1991 San Marcelino 28 km 0.3 212 --
15 Jun 1991 Bacoor-Cavite 120 km 9.8 208 --
22 Jun 1991 O'Donnell 26.5 km 0.4 475 --
29 Jun 1991 Binoclutan 38 km 1.6 991 --
29 Jun 1991 Mapanuepe 19 km 0.05 67 3.83
30 Jun 1991 Botolan 39.5 km 0.4 803 --
03 Jul 1991 Iba 44 km 0.65 464 --
03 Jul 1991 Marella 1 10 km 0.06 11 7.9
03 Jul 1991 Marella 2 13 km 0.1 50 7.2
03 Jul 1991 Hot mudflow (on pyroclastic flow) 8 km 0.4 354 6.19
04 Jul 1991 Poonbato 23.5 km 0.5 604 --
03 Jul 1991 Burgos-Ugik 17 km 0.6 699 --

"A pyroclastic-flow deposit emplaced in the Marella River (reaching 15 km SW from the main crater) was visited on 3 July. It was still degassing, with numerous rootless fumaroles present even at low altitude at the end of the deposits. The gases emitted were mostly steam, but minor amounts of SO2 (and probably H2S) were present, since incrustations of native sulfur were observed at the mouths of these fumaroles. Strong odors of burned wood (charcoal) were also perceptible in some places, and associated with black-brown deposits at the surface of the pyroclastic-flow deposit resulting from some pyrolysis of wood buried at shallow depth beneath the deposit. Maximum temperatures of the fumarole were close to boiling, 98-99.5°C. The temperature inside of the pyroclastic-flow deposit measured at one location (~10 km from the crater) was 223°C at a depth of 70 cm.

"The surface of the deposit was a hard crust that was very easy to walk on. It looked like some recent pyroclastic-flow deposits observed on Augustine, with rounded pumice clasts (maximum size

"Numerous small cones (maximum diameter about 10 m, up to about 1-2 m high) were also present on the surface of the pyroclastic-flow deposit. These cones resulted from the activity of large steam fumaroles. At the time of the visit, two intermittent fumaroles were active in the upper portion of the deposit (~8 km from the crater) emitting a steam plume 3-4 m high mixed with fine-grained ash. A hot (88°C) stream of muddy water (65 cm wide), with the consistency of a mudflow, was also surging from the ground in the area close to these intermittent fumaroles. A water sample filtered from this stream showed a high chloride content compared to other streams and rivers travelling down the volcano (table 3). Many old tracks of other mudflows were observed on the surface of the pyroclastic flow deposit."

[Additional encounters between aircraft and ash clouds, frequent in the eruption's first days, were reported this month but included above in table 2.]

Reference. Bernard, A., Demaiffe, D., Mattielli, N., and Punongbayan, R.S., 1991, Anhydrite-bearing pumices from Mount Pinatubo: further evidence for the existence of sulphur-rich silicic magmas: Nature, v. 354, p. 139-140.

Geologic Background. Prior to 1991 Pinatubo volcano was a relatively unknown, heavily forested lava dome complex located 100 km NW of Manila with no records of historical eruptions. The 1991 eruption, one of the world's largest of the 20th century, ejected massive amounts of tephra and produced voluminous pyroclastic flows, forming a small, 2.5-km-wide summit caldera whose floor is now covered by a lake. Caldera formation lowered the height of the summit by more than 300 m. Although the eruption caused hundreds of fatalities and major damage with severe social and economic impact, successful monitoring efforts greatly reduced the number of fatalities. Widespread lahars that redistributed products of the 1991 eruption have continued to cause severe disruption. Previous major eruptive periods, interrupted by lengthy quiescent periods, have produced pyroclastic flows and lahars that were even more extensive than in 1991.

Information Contacts: R. Punongbayan, PHIVOLCS; A. Bernard, Univ Libre de Bruxelles, Belgium; T. Casadevall, USGS Denver; J. Lynch, SAB; Daily Inquirer, Manila, Philippines; AP; UPI; Reuters.


Poas (Costa Rica) — July 1991 Citation iconCite this Report

Poas

Costa Rica

10.2°N, 84.233°W; summit elev. 2708 m

All times are local (unless otherwise noted)


Continued degassing; seismicity

An average of 239 microearthquakes, with a maximum of 485 (3 July), were recorded daily in July (figure 39), at a station 2 km SW of the crater. Of these, 29 were identified as A- and B-type earthquakes. Seismic frequencies ranged from 1.4 to 2.6 Hz. A total of 41 hours of continuous and discrete semi-harmonic tremor episodes were recorded, with durations of up to 6 hours.

Figure (see Caption) Figure 39. Daily number of earthquakes at Poás, July 1991. Courtesy of the Univ Nacional.

The crater lake's average temperature was 63°C. Fumaroles were covered as the lake level continued to rise. Area residents sporadically reported a sulfurous odor.

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: J. Barquero, E. Fernández, V. Barboza, and J. Brenes, OVSICORI.


Rincon de la Vieja (Costa Rica) — July 1991 Citation iconCite this Report

Rincon de la Vieja

Costa Rica

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

All times are local (unless otherwise noted)


Seismicity and tremor

A total of 399 microearthquakes were recorded in July (figure 4) at a seismic station (RIN3) 6 km SW of the crater. Six hours of low- and medium-frequency tremor (1.3-3.2 Hz), were recorded in episodes 12 minutes to 3 hours long. Low-frequency earthquakes were also recorded, with durations that reached 175 seconds.

Figure (see Caption) Figure 4. Daily number of earthquakes at Rincón de la Vieja, July 1991. Courtesy of OVSICORI.

Geologic Background. Rincón de la Vieja, the largest volcano in NW Costa Rica, is a remote volcanic complex in the Guanacaste Range. The volcano consists of an elongated, arcuate NW-SE-trending ridge constructed within the 15-km-wide early Pleistocene Guachipelín caldera, whose rim is exposed on the south side. Sometimes known as the "Colossus of Guanacaste," it has an estimated volume of 130 km3 and contains at least nine major eruptive centers. Activity has migrated to the SE, where the youngest-looking craters are located. The twin cone of Santa María volcano, the highest peak of the complex, is located at the eastern end of a smaller, 5-km-wide caldera and has a 500-m-wide crater. A Plinian eruption producing the 0.25 km3 Río Blanca tephra about 3,500 years ago was the last major magmatic eruption. All subsequent eruptions, including numerous historical eruptions possibly dating back to the 16th century, have been from the prominent active crater containing a 500-m-wide acid lake located ENE of Von Seebach crater.

Information Contacts: J. Barquero, E. Fernández, V. Barboza, and J. Brenes, OVSICORI.


Nevado del Ruiz (Colombia) — July 1991 Citation iconCite this Report

Nevado del Ruiz

Colombia

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

All times are local (unless otherwise noted)


Seismicity remains at low levels; small ash emissions

Seismicity was at very low levels in July, although tremor reached slightly higher levels at the beginning of the month. Deformation measurements showed no significant changes. The SO2 flux continued to fluctuate, with a monthly average of ~1,220 t/d. Two small ash emissions, restricted to the summit region, were observed during July.

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

Information Contacts: C. Carvajal, INGEOMINAS, Manizales.


Sabancaya (Peru) — July 1991 Citation iconCite this Report

Sabancaya

Peru

15.787°S, 71.857°W; summit elev. 5960 m

All times are local (unless otherwise noted)


Earthquake swarm damages towns and triggers mudslides; 20 people reported dead

A swarm of earthquakes, reported on 23-24 July, triggered mudslides that partly buried four villages. In towns within 20 km N of the volcano, the earthquakes caused many houses to collapse, especially in Maca (15 km N) which was almost completely destroyed. The press reported that 20 people were killed, 80 were injured, and 3,000 were left homeless. More than 20 earthquakes/day were reported felt (MM <=V) 75 km SE (in Arequipa). The largest of the shocks (Ms [4.7]), detected at [1444] on 23 July by the WWSSN, was centered [35] km [ENE] from the volcano at shallow depth.

Geologic Background. Sabancaya, located in the saddle NE of Ampato and SE of Hualca Hualca volcanoes, is the youngest of these volcanic centers and the only one to have erupted in historical time. The oldest of the three, Nevado Hualca Hualca, is of probable late-Pliocene to early Pleistocene age. The name Sabancaya (meaning "tongue of fire" in the Quechua language) first appeared in records in 1595 CE, suggesting activity prior to that date. Holocene activity has consisted of Plinian eruptions followed by emission of voluminous andesitic and dacitic lava flows, which form an extensive apron around the volcano on all sides but the south. Records of historical eruptions date back to 1750.

Information Contacts: NEIC; EFE network, Madrid, Spain; Agence France-Presse; Reuters; UPI; AP.


Santa Maria (Guatemala) — July 1991 Citation iconCite this Report

Santa Maria

Guatemala

14.757°N, 91.552°W; summit elev. 3745 m

All times are local (unless otherwise noted)


Explosions and avalanches; plumes to 600 m height

The volcano was in a moderate explosive phase in May, emitting gray ash clouds 300-500 m high. In June, the number of moderate to strong explosions increased daily, with plumes 400-600 m high, and ashfall on the area surrounding the volcano. Numerous collapses and large avalanches were observed on the SE slope.

Geologic Background. Symmetrical, forest-covered Santa María volcano is part of a chain of large stratovolcanoes that rise above the Pacific coastal plain of Guatemala. The sharp-topped, conical profile is cut on the SW flank by a 1.5-km-wide crater. The oval-shaped crater extends from just below the summit to the lower flank, and was formed during a catastrophic eruption in 1902. The renowned Plinian eruption of 1902 that devastated much of SW Guatemala followed a long repose period after construction of the large basaltic-andesite stratovolcano. The massive dacitic Santiaguito lava-dome complex has been growing at the base of the 1902 crater since 1922. Compound dome growth at Santiaguito has occurred episodically from four vents, with activity progressing W towards the most recent, Caliente. Dome growth has been accompanied by almost continuous minor explosions, with periodic lava extrusion, larger explosions, pyroclastic flows, and lahars.

Information Contacts: Philippe Rocher, L.A.V.E., France.


Stromboli (Italy) — July 1991 Citation iconCite this Report

Stromboli

Italy

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

All times are local (unless otherwise noted)


Continued explosions from two craters

The number and intensity of explosions has continued to fluctuate in recent months, with the average rate remaining slightly higher since mid-March. During a summit visit on the night of 31 July-1 August, >50 explosions were observed between 2100 and 0600. The strongest ejected incandescent material toward the edge of the summit area. Most of the explosions were from Crater 1, the rest from Crater 3, with only gas emission evident from Crater 2 and from a small cone. On this occasion and during other visits over the past several years, durations of precursory noises appeared linked to explosive vigor, with stronger explosions following noises lasting 3-5 seconds, whereas 1-2-second noises preceded weak explosions [see also 16:08].

Geologic Background. Spectacular incandescent nighttime explosions at this volcano have long attracted visitors to the "Lighthouse of the Mediterranean." Stromboli, the NE-most of the Aeolian Islands, has lent its name to the frequent mild explosive activity that has characterized its eruptions throughout much of historical time. The small island is the emergent summit of a volcano that grew in two main eruptive cycles, the last of which formed the western portion of the island. The Neostromboli eruptive period took place between about 13,000 and 5,000 years ago. The active summit vents are located at the head of the Sciara del Fuoco, a prominent horseshoe-shaped scarp formed about 5,000 years ago due to a series of slope failures that extend to below sea level. The modern volcano has been constructed within this scarp, which funnels pyroclastic ejecta and lava flows to the NW. Essentially continuous mild Strombolian explosions, sometimes accompanied by lava flows, have been recorded for more than a millennium.

Information Contacts: H. Gaudru, SVE, Switzerland; T. De St. Cyr, Fontaines St. Martin, France.


Suretamatai (Vanuatu) — July 1991 Citation iconCite this Report

Suretamatai

Vanuatu

13.8°S, 167.47°E; summit elev. 921 m

All times are local (unless otherwise noted)


Fumarolic activity

"During our survey, no change in activity at the major geothermal areas (Frenchman's Solfataras and Hell's Gate) was noted, with respect to descriptions by Aubert de la Rue (1937) and Hochstein (1980). Slightly superheated fumaroles (with sulfur deposits), hot springs, and boiling ponds up to 3 m in diameter occurred over a 300-m strip along the Sulfur River (E flank) between 300 to 400 m elevation. The temperature of the Sulfur River at Hell's Gate remained stable at 50°C.

"Soretimeat . . . is a composite volcano built on an ancient Pleistocene edifice. Ash emissions reported in 1860 and 1965-66 are most likely to have been from hydrothermal explosions (Ash and others, 1980)." ["Flames" were observed during an apparent eruption in 1865 (Atkin, 1868).]

References. Ash, R.P., Carney, J.N., and MacFarlane, A., 1980, Geology of the northern Banks Islands: New Hebrides Geological Survey Regional Report, p. 1-47.

Atkin, J., 1868, On volcanoes in the New Hebrides and Banks Islands: Proceedings of the Geological Society of London, v. 24, p. 305-307.

Aubert de la Rue, E., 1937, La Volcanisme aux Nouvelles Hebrides (Melanesie): BV, v. 2, p. 79-142.

Hochstein, M.P., 1980, Geology of the Northern Banks Islands: New Hebrides Geological Survey Regional Report, p. 47-49.

Geologic Background. Suretamatai volcano (also known as Soritimeat) forms much of Vanua Lava Island, one of the largest of Vanuatu's Banks Islands. The younger lavas overlie a number of small older stratovolcanoes that form the island. In contrast to other large volcanoes of Vanuatu, the dominantly basaltic-to-andesitic Suretamatai does not contain a youthful summit caldera. A chain of small stratovolcanoes oriented along a NNE-SSW line gives the low-angle volcano an irregular profile. The youngest cone, near the northern end of the chain, is the largest and contains a lake of variable depth within its 900-m-wide, 100-m-deep summit crater. Activity reported during the 19th century consisted of moderate explosive eruptions.

Information Contacts: C. Robin and M. Monzier, ORSTOM, Nouméa, New Caledonia; M. Lardy and C. Douglas, ORSTOM, Vanuatu; C. Mortimer, Dept. of Geology, Mines, and Rural Water Supply, Vanuatu; J. Eissen, ORSTOM, France.


Taal (Philippines) — July 1991 Citation iconCite this Report

Taal

Philippines

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

All times are local (unless otherwise noted)


Abnormal seismicity continues

Abnormally high levels of seismicity continued as of mid-August. Up to 5 small high-frequency earthquakes were recorded daily 9-12 August. No earthquakes were felt during this time. The main crater lake temperature remained at 31°C. Close monitoring of the volcano continued.

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

Information Contacts: R. Punongbayan, PHIVOLCS.


Unzendake (Japan) — July 1991 Citation iconCite this Report

Unzendake

Japan

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

All times are local (unless otherwise noted)


Continued dome growth and pyroclastic flow generation; dome history reviewed

The dome in Jigoku-ato crater continued to grow in an easterly direction in July, at a rate of 0.3 x 106 m3/day (figure 26). The magma supply rate remained unchanged in August, but the direction of growth became westerly. By 15 August, the dome was estimated to be 650 x 250 m and 130 m thick. On 19 July it had been 520 x 260 m, with a volume of 5.9 x 106 m3.

Figure (see Caption) Figure 26. Cumulative volumes of magma erupted from Unzen, May-July 1991. Courtesy of S. Nakada.

The number of seismically-detected pyroclastic flows and avalanches from the dome decreased in July (compared to June), showed a gradual increase late July-early August, then decreased suddenly on 12 August to only a few events/day. A total of 326 pyroclastic flows were recorded in July (down from 482 in June), and 155 during 1-15 August. Event durations were shorter than in previous months when flow signals occasionally lasted more than 300 seconds. The longest events lasted 140 seconds in July and 150 seconds in August.

Pyroclastic flows continued to travel as much as 2 km E down the Mizunashi River. None of the flows reached the evacuated areas of Shimabara and Fukae, which remained closed with 12,395 inhabitants relocated. Ash clouds from the larger pyroclastic flows rose 2 km, with ash falling mainly NE on Shimabara. Prevailing winds remained unchanged since May. Continuous ash emission from vents in the crater near the dome occurred in mid-July (16:06), and on 5-6, and 12 August, when the ash cloud rose 1.5 km. Explosive ejections of incandescent blocks to 100 m height were observed from midnight to 0200 on 12 August, presumably from a vent on the W end of the dome that continuously emitted ash throughout the day.

In contrast to the drop in pyroclastic flows on 12 August, the number of summit earthquakes and tremor episodes increased sharply on 11 August. This followed reduced seismic activity in June (230 recorded earthquakes) and July (133), compared to April (1959). More than 460 earthquakes had already been recorded in August by the 15th. Earthquake magnitudes were small and no shocks were felt, nor were changes in ground deformation detected by tiltmeters or EDM lines near the summit. Following the peak on 12 August, seismicity began to decrease. The increase in seismicity may be related to the incandescent ejections on 12 August, the active continuous ash emission, and the westward growth of the dome.

A man died on 8 August from burns suffered on 3 June, bringing the total casualties to 39 dead and three missing.

The following is a report from Setsuya Nakada on dome growth and morphology in June. "Large pyroclastic flows occurred on 3 and 8 June (figure 27), with volumes of about 0.7 x 106, and 1 x 106 m3, respectively. The E half of the lava dome collapsed during the eruption of the 3 June pyroclastic flow, leaving a 150-m-wide horseshoe-shaped depression opening to the E (figure 28). The volume of dome material left behind (referred to as W dome) was about 0.48 x 106 m3. A new lava dome formed within the depression by 8 June, obtaining pre-3 June volumes.

Figure (see Caption) Figure 27. Distribution of the 3 and 8 June 1991 pyroclastic flow deposits at Unzen. From Nakada and Kobayashi (1991).
Figure (see Caption) Figure 28. Growth pattern of the lava dome in Jigoku-ato Crater at Unzen, May-August, 1991. From Nakada and Kobayashi (1991).

"Some of the 8 June pyroclastic flows, which reached 5.5 km beyond the crater, resulted from the direct eruption of magma from the vent. An extensive area of trees was burnt by the accompanying ash clouds. Pyroclastic surge (ash-cloud surge) deposits, such as those in the deposits from 3 June, were not clearly identified. Breadcrust bombs 5 cm in diameter were ejected to 3 km NE of the crater. Half of the W dome and the entire E dome (post-3 June material) were destroyed, widening the horseshoe-shaped depression to 200 m. About 0.15 x 106 m3 of the W dome remained.

"Vulcanian explosions on 11 June ejected breadcrust and cauliflower bombs, up to 46 cm long, to 3 km distance. As a result, a depression 20-30 m in diameter formed within the crater, just above the former Jigoku-ato crater. On 17 June a continuous eruption column was observed rising from the W dome, for the first time since the start of lava extrusion.

"The E dome continued to grow and collapse along its E margin, filling a steep valley on the E slope of Jigoku-ato crater, then growing over the valley-fill deposits, a gentler surface than the original valley floor. The surface of the lava dome had the form of a petal with two lobes. These were created by extrusion near the summit of the E dome. After the middle of June, the lava surface traveled SE at a rate of 40 m/day, but the dome only lengthened a maximum of 10 m/day. By the end of June the horseshoe-shaped depression was filled with dome material, and lava blocks began to overflow NE onto the caldera floor."

Reference. Nakada, S., and Kobayashi, T., 1991, Lava dome and pyroclastic flows of the 1991 eruption at Unzen volcano: Bulletin of the Volcanological Society of Japan, v. 36, in press.

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: JMA; S. Nakada, Kyushu Univ.


Yasur (Vanuatu) — July 1991 Citation iconCite this Report

Yasur

Vanuatu

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

All times are local (unless otherwise noted)


Continued block and ash emissions; small episodic lava lakes

"Activity remained unchanged during 1990-91, with block and ash emissions and small episodic lava lakes."

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

Information Contacts: C. Robin and M. Monzier, ORSTOM, New Caledonia; M. Lardy and C. Douglas, ORSTOM, Vanuatu; C. Mortimer, Dept of Geology, Mines, and Rural Water Supply, Vanuatu; J. Eissen, ORSTOM, France.

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