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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

Ibu (Indonesia) Daily ash explosions continue, along with thermal anomalies in the crater, October 2022-May 2023

Dukono (Indonesia) Continuing ash emissions, SO2 plumes, and thermal signals during October 2022-May 2023

Sabancaya (Peru) Explosions, gas-and-ash plumes, and thermal activity persist during November 2022-April 2023

Sheveluch (Russia) Significant explosions destroyed part of the lava-dome complex during April 2023

Bezymianny (Russia) Explosions, ash plumes, lava flows, and avalanches during November 2022-April 2023

Chikurachki (Russia) New explosive eruption during late January-early February 2023

Marapi (Indonesia) New explosive eruption with ash emissions during January-March 2023

Kikai (Japan) Intermittent white gas-and-steam plumes, discolored water, and seismicity during May 2021-April 2023

Lewotolok (Indonesia) Strombolian eruption continues through April 2023 with intermittent ash plumes

Barren Island (India) Thermal activity during December 2022-March 2023

Villarrica (Chile) Nighttime crater incandescence, ash emissions, and seismicity during October 2022-March 2023

Fuego (Guatemala) Daily explosions, gas-and-ash plumes, avalanches, and ashfall during December 2022-March 2023



Ibu (Indonesia) — June 2023 Citation iconCite this Report

Ibu

Indonesia

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

All times are local (unless otherwise noted)


Daily ash explosions continue, along with thermal anomalies in the crater, October 2022-May 2023

Persistent eruptive activity since April 2008 at Ibu, a stratovolcano on Indonesian’s Halmahera Island, has consisted of daily explosive ash emissions and plumes, along with observations of thermal anomalies (BGVN 47:04). The current eruption continued during October 2022-May 2023, described below, based on advisories issued by the Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM), daily reports by MAGMA Indonesia (a PVMBG platform), and the Darwin Volcanic Ash Advisory Centre (VAAC), and various satellite data. The Alert Level during the reporting period remained at 2 (on a scale of 1-4), except raised briefly to 3 on 27 May, and the public was warned to stay at least 2 km away from the active crater and 3.5 km away on the N side of the volcano.

According to MAGMA Indonesia, during October 2022-May 2023, daily gray-and-white ash plumes of variable densities rose 200-1,000 m above the summit and drifted in multiple directions. On 30 October and 11 November, plumes rose a maximum of 2 km and 1.5 km above the summit, respectively (figures 42 and 43). According to the Darwin VAAC, discrete ash emissions on 13 November rose to 2.1 km altitude, or 800 m above the summit, and drifted W, and multiple ash emissions on 15 November rose 1.4 km above the summit and drifted NE. Occasional larger ash explosions through May 2023 prompted PVMBG to issue Volcano Observatory Notice for Aviation (VONA) alerts (table 6); the Aviation Color Code remained at Orange throughout this period.

Figure (see Caption) Figure 42. Larger explosion from Ibu’s summit crater on 30 October 2022 that generated a plume that rose 2 km above the summit. Photo has been color corrected. Courtesy of MAGMA Indonesia.
Figure (see Caption) Figure 43. Larger explosion from Ibu’s summit crater on 11 November 2022 that generated a plume that rose 1.5 km above the summit. Courtesy of MAGMA Indonesia.

Table 6. Volcano Observatory Notice for Aviation (VONA) ash plume alerts for Ibu issued by PVMBG during October 2022-May 2023. Maximum height above the summit was estimated by a ground observer. VONAs in January-May 2023 all described the ash plumes as dense.

Date Time (local) Max height above summit Direction
17 Oct 2022 0858 800 m SW
18 Oct 2022 1425 800 m S
19 Oct 2022 2017 600 m SW
21 Oct 2022 0916 800 m NW
16 Jan 2023 1959 600 m NE
22 Jan 2023 0942 1,000 m E
29 Jan 2023 2138 1,000 m E
10 May 2023 0940 800 m NW
10 May 2023 2035 600 m E
21 May 2023 2021 600 m W
21 May 2023 2140 1,000 m W
29 May 2023 1342 800 m N
31 May 2023 1011 1,000 m SW

Sentinel-2 L1C satellite images throughout the reporting period show two, sometimes three persistent thermal anomalies in the summit crater, with the most prominent hotspot from the top of a cone within the crater. Clear views were more common during March-April 2023, when a vent and lava flows on the NE flank of the intra-crater cone could be distinguished (figure 44). White-to-grayish emissions were also observed during brief periods when weather clouds allowed clear views.

Figure (see Caption) Figure 44. Sentinel-2 L2A satellite images of Ibu on 10 April 2023. The central cone within the summit crater (1.3 km diameter) and lava flows (gray) can be seen in the true color image (left, bands 4, 3, 2). Thermal anomalies from the small crater of the intra-crater cone, a NE-flank vent, and the end of the lava flow are apparent in the infrared image (right, bands 12, 11, 8A). Courtesy of Copernicus Browser.

The MIROVA space-based volcano hotspot detection system recorded almost daily thermal anomalies throughout the reporting period, though cloud cover often interfered with detections. Data from imaging spectroradiometers aboard NASA’s Aqua and Terra satellites and processed using the MODVOLC algorithm (MODIS-MODVOLC) recorded hotspots on one day during October 2022 and December 2022, two days in April 2023, three days in November 2022 and May 2023, and four days in March 2023.

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, has contained several small crater lakes. The 1.2-km-wide outer crater is breached on the N, creating a steep-walled valley. A large cone grew ENE of the summit, and 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. The first observed and recorded eruption was a small explosion from the summit crater in 1911. Eruptive activity began again in December 1998, producing a lava dome that eventually covered much of the floor of the inner summit crater along with ongoing explosive ash emissions.

Information Contacts: Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM), Jalan Diponegoro 57, Bandung 40122, Indonesia (URL: http://www.vsi.esdm.go.id/); MAGMA Indonesia (Multiplatform Application for Geohazard Mitigation and Assessment in Indonesia), Kementerian Energi dan Sumber Daya Mineral (URL: https://magma.esdm.go.id/v1); Copernicus Browser, Copernicus Data Space Ecosystem, European Space Agency (URL: https://dataspace.copernicus.eu/browser/); 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/).


Dukono (Indonesia) — June 2023 Citation iconCite this Report

Dukono

Indonesia

1.6992°N, 127.8783°E; summit elev. 1273 m

All times are local (unless otherwise noted)


Continuing ash emissions, SO2 plumes, and thermal signals during October 2022-May 2023

Dukono, a remote volcano on Indonesia’s Halmahera Island, has been erupting continuously since 1933, with frequent ash explosions and sulfur dioxide plumes (BGVN 46:11, 47:10). This activity continued during October 2022 through May 2023, based on reports from the Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG; also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM), the Darwin Volcanic Ash Advisory Centre (VAAC), and satellite data. During this period, the Alert Level remained at 2 (on a scale of 1-4) and the public was warned to remain outside of the 2-km exclusion zone. The highest reported plume of the period reached 9.4 km above the summit on 14 November 2022.

According to MAGMA Indonesia (a platform developed by PVMBG), white, gray, or dark plumes of variable densities were observed almost every day during the reporting period, except when fog obscured the volcano (figure 33). Plumes generally rose 25-450 m above the summit, but rose as high as 700-800 m on several days, somewhat lower than the maximum heights reached earlier in 2022 when plumes reached as high as 1 km. However, the Darwin VAAC reported that on 14 November 2022, a discrete ash plume rose 9.4 km above the summit (10.7 km altitude), accompanied by a strong hotspot and a sulfur dioxide signal observed in satellite imagery; a continuous ash plume that day and through the 15th rose to 2.1-2.4 km altitude and drifted NE.

Figure (see Caption) Figure 33. Webcam photo of a gas-and-steam plume rising from Dukono on the morning of 28 January 2023. Courtesy of MAGMA Indonesia.

Sentinel-2 images were obscured by weather clouds almost every viewing day during the reporting period. However, the few reasonably clear images showed a hotspot and white or gray emissions and plumes. Strong SO2 plumes from Dukono were present on many days during October 2022-May 2023, as detected using the TROPOMI instrument on the Sentinel-5P satellite (figure 34).

Figure (see Caption) Figure 34. A strong SO2 signal from Dukono on 23 April 2023 was the most extensive plume detected during the reporting period. Courtesy of the NASA Global Sulfur Dioxide Monitoring Page.

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

Information Contacts: Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM), Jalan Diponegoro 57, Bandung 40122, Indonesia (URL: http://www.vsi.esdm.go.id/); MAGMA Indonesia (Multiplatform Application for Geohazard Mitigation and Assessment in Indonesia), Kementerian Energi dan Sumber Daya Mineral (URL: https://magma.esdm.go.id/v1); 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/); NASA Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, NASA Goddard Space Flight Center (NASA/GSFC), 8800 Greenbelt Road, Goddard, Maryland, USA (URL: https://so2.gsfc.nasa.gov/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground).


Sabancaya (Peru) — May 2023 Citation iconCite this Report

Sabancaya

Peru

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

All times are local (unless otherwise noted)


Explosions, gas-and-ash plumes, and thermal activity persist during November 2022-April 2023

Sabancaya is located in Peru, NE of Ampato and SE of Hualca Hualca. Eruptions date back to 1750 and have been characterized by explosions, phreatic activity, ash plumes, and ashfall. The current eruption period began in November 2016 and has more recently consisted of daily explosions, gas-and-ash plumes, and thermal activity (BGVN 47:11). This report updates activity during November 2022 through April 2023 using information from Instituto Geophysico del Peru (IGP) that use weekly activity reports and various satellite data.

Intermittent low-to-moderate power thermal anomalies were reported by the MIROVA project during November 2022 through April 2023 (figure 119). There were few short gaps in thermal activity during mid-December 2022, late December-to-early January 2023, late January to mid-February, and late February. According to data recorded by the MODVOLC thermal algorithm, there were a total of eight thermal hotspots: three in November 2022, three in February 2023, one in March, and one in April. On clear weather days, some of this thermal anomaly was visible in infrared satellite imagery showing the active lava dome in the summit crater (figure 120). Almost daily moderate-to-strong sulfur dioxide plumes were recorded during the reporting period by the TROPOMI instrument on the Sentinel-5P satellite (figure 121). Many of these plumes exceeded 2 Dobson Units (DU) and drifted in multiple directions.

Figure (see Caption) Figure 119. Intermittent low-to-moderate thermal anomalies were detected during November 2022 through April 2023 at Sabancaya, as shown in this MIROVA graph (Log Radiative Power). There were brief gaps in thermal activity during mid-December 2022, late December-to-early January 2023, late January to mid-February, and late February. Courtesy of MIROVA.
Figure (see Caption) Figure 120. Infrared (bands 12, 11, 8A) satellite images showed a constant thermal anomaly in the summit crater of Sabancaya on 14 January 2023 (top left), 28 February 2023 (top right), 5 March 2023 (bottom left), and 19 April 2023 (bottom right), represented by the active lava dome. Sometimes gas-and-steam and ash emissions also accompanied this activity. Courtesy of Copernicus Browser.
Figure (see Caption) Figure 121. Moderate-to-strong sulfur dioxide plumes were detected almost every day, rising from Sabancaya by the TROPOMI instrument on the Sentinel-5P satellite throughout the reporting period; the DU (Dobson Unit) density values were often greater than 2. Plumes from 23 November 2022 (top left), 26 December 2022 (top middle), 10 January 2023 (top right), 15 February 2023 (bottom left), 13 March 2023 (bottom middle), and 21 April 2023 (bottom right) that drifted SW, SW, W, SE, W, and SW, respectively. Courtesy of NASA Global Sulfur Dioxide Monitoring Page.

IGP reported that moderate activity during November and December 2022 continued; during November, an average number of explosions were reported each week: 30, 33, 36, and 35, and during December, it was 32, 40, 47, 52, and 67. Gas-and-ash plumes in November rose 3-3.5 km above the summit and drifted E, NE, SE, S, N, W, and SW. During December the gas-and-ash plumes rose 2-4 km above the summit and drifted in different directions. There were 1,259 volcanic earthquakes recorded during November and 1,693 during December. Seismicity also included volcano-tectonic-type events that indicate rock fracturing events. Slight inflation was observed in the N part of the volcano near Hualca Hualca (4 km N). Thermal activity was frequently reported in the crater at the active lava dome (figure 120).

Explosive activity continued during January and February 2023. The average number of explosions were reported each week during January (51, 50, 60, and 59) and February (43, 54, 51, and 50). Gas-and-ash plumes rose 1.6-2.9 km above the summit and drifted NW, SW, and W during January and rose 1.4-2.8 above the summit and drifted W, SW, E, SE, N, S, NW, and NE during February. IGP also detected 1,881 volcanic earthquakes during January and 1,661 during February. VT-type earthquakes were also reported. Minor inflation persisted near Hualca Hualca. Satellite imagery showed continuous thermal activity in the crater at the lava dome (figure 120).

During March, the average number of explosions each week was 46, 48, 31, 35, and 22 and during April, it was 29, 41, 31, and 27. Accompanying gas-and-ash plumes rose 1.7-2.6 km above the summit crater and drifted W, SW, NW, S, and SE during March. According to a Buenos Aires Volcano Ash Advisory Center (VAAC) notice, on 22 March at 1800 through 23 March an ash plume rose to 7 km altitude and drifted NW. By 0430 an ash plume rose to 7.6 km altitude and drifted W. On 24 and 26 March continuous ash emissions rose to 7.3 km altitude and drifted SW and on 28 March ash emissions rose to 7.6 km altitude. During April, gas-and-ash plumes rose 1.6-2.5 km above the summit and drifted W, SW, S, NW, NE, and E. Frequent volcanic earthquakes were recorded, with 1,828 in March and 1,077 in April, in addition to VT-type events. Thermal activity continued to be reported in the summit crater at the lava dome (figure 120).

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: Instituto Geofisico del Peru (IGP), Centro Vulcanológico Nacional (CENVUL), Calle Badajoz N° 169 Urb. Mayorazgo IV Etapa, Ate, Lima 15012, Perú (URL: https://www.igp.gob.pe/servicios/centro-vulcanologico-nacional/inicio); 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); 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 Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, NASA Goddard Space Flight Center (NASA/GSFC), 8800 Greenbelt Road, Goddard MD 20771, USA (URL: https://so2.gsfc.nasa.gov/); Copernicus Browser, Copernicus Data Space Ecosystem, European Space Agency (URL: https://dataspace.copernicus.eu/browser/).


Sheveluch (Russia) — May 2023 Citation iconCite this Report

Sheveluch

Russia

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

All times are local (unless otherwise noted)


Significant explosions destroyed part of the lava-dome complex during April 2023

Sheveluch (also spelled Shiveluch) in Kamchatka, has had at least 60 large eruptions during the last 10,000 years. The summit is truncated by a broad 9-km-wide caldera that is breached to the S, and many lava domes occur on the outer flanks. The lava dome complex was constructed within the large open caldera. Frequent collapses of the dome complex have produced debris avalanches; the resulting deposits cover much of the caldera floor. A major south-flank collapse during a 1964 Plinian explosion produced a scarp in which a “Young Sheveluch” dome began to form in 1980. Repeated episodes of dome formation and destruction since then have produced major and minor ash plumes, pyroclastic flows, block-and-ash flows, and “whaleback domes” of spine-like extrusions in 1993 and 2020 (BGVN 45:11). The current eruption period began in August 1999 and has more recently consisted of lava dome growth, explosions, ash plumes, and avalanches (BGVN 48:01). This report covers a significant explosive eruption during early-to-mid-April 2023 that generated a 20 km altitude ash plume, produced a strong sulfur dioxide plume, and destroyed part of the lava-dome complex; activity described during January through April 2023 use information primarily from the Kamchatka Volcanic Eruptions Response Team (KVERT) and various satellite data.

Satellite data. Activity during the majority of this reporting period was characterized by continued lava dome growth, strong fumarole activity, explosions, and hot avalanches. According to the MODVOLC Thermal Alerts System, 140 hotspots were detected through the reporting period, with 33 recorded in January 2023, 29 in February, 44 in March, and 34 in April. Frequent strong thermal activity was recorded during January 2023 through April, according to the MIROVA (Middle InfraRed Observation of Volcanic Activity) graph and resulted from the continuously growing lava dome (figure 94). A slightly stronger pulse in thermal activity was detected in early-to-mid-April, which represented the significant eruption that destroyed part of the lava-dome complex. Thermal anomalies were also visible in infrared satellite imagery at the summit crater (figure 95).

Figure (see Caption) Figure 94. Strong and frequent thermal activity was detected at Sheveluch during January through April 2023, according to this MIROVA graph (Log Radiative Power). These thermal anomalies represented the continuously growing lava dome and frequent hot avalanches that affected the flanks. During early-to-mid-April a slightly stronger pulse represented the notable explosive eruption. Courtesy of MIROVA.
Figure (see Caption) Figure 95. Infrared (bands B12, B11, B4) satellite imagery showed persistent thermal anomalies at the lava dome of Sheveluch on 14 January 2023 (top left), 26 February 2023 (top right), and 15 March 2023 (bottom left). The true color image on 12 April 2023 (bottom right) showed a strong ash plume that drifted SW; this activity was a result of the strong explosive eruption during 11-12 April 2023. Courtesy of Copernicus Browser.

During January 2023 KVERT reported continued growth of the lava dome, accompanied by strong fumarolic activity, incandescence from the lava dome, explosions, ash plumes, and avalanches. Satellite data showed a daily thermal anomaly over the volcano. Video data showed ash plumes associated with collapses at the dome that generated avalanches that in turn produced ash plumes rising to 3.5 km altitude and drifting 40 km W on 4 January and rising to 7-7.5 km altitude and drifting 15 km SW on 5 January. A gas-and-steam plume containing some ash that was associated with avalanches rose to 5-6 km altitude and extended 52-92 km W on 7 January. Explosions that same day produced ash plumes that rose to 7-7.5 km altitude and drifted 10 km W. According to a Volcano Observatory Notice for Aviation (VONA) issued at 1344 on 19 January, explosions produced an ash cloud that was 15 x 25 km in size and rose to 9.6-10 km altitude, drifting 21-25 km W; as a result, the Aviation Color Code (ACC) was raised to Red (the highest level on a four-color scale). Another VONA issued at 1635 reported that no more ash plumes were observed, and the ACC was lowered to Orange (the second highest level on a four-color scale). On 22 January an ash plume from collapses and avalanches rose to 5 km altitude and drifted 25 km NE and SW; ash plumes associated with collapses extended 70 km NE on 27 and 31 January.

Lava dome growth, fumarolic activity, dome incandescence, and occasional explosions and avalanches continued during February and March. A daily thermal anomaly was visible in satellite data. Explosions on 1 February generated ash plumes that rose to 6.3-6.5 km altitude and extended 15 km NE. Video data showed an ash cloud from avalanches rising to 5.5 km altitude and drifting 5 km SE on 2 February. Satellite data showed gas-and-steam plumes containing some ash rose to 5-5.5 km altitude and drifted 68-110 km ENE and NE on 6 February, to 4.5-5 km altitude and drifted 35 km WNW on 22 February, and to 3.7-4 km altitude and drifted 47 km NE on 28 February. Scientists from the Kamchatka Volcanological Station (KVS) went on a field excursion on 25 February to document the growing lava dome, and although it was cloudy most of the day, nighttime incandescence was visible. Satellite data showed an ash plume extending up to 118 km E during 4-5 March. Video data from 1150 showed an ash cloud from avalanches rose to 3.7-5.5 km altitude and drifted 5-10 km ENE and E on 5 March. On 11 March an ash plume drifted 62 km E. On 27 March ash plumes rose to 3.5 km altitude and drifted 100 km E. Avalanches and constant incandescence at the lava dome was focused on the E and NE slopes on 28 March. A gas-and-steam plume containing some ash rose to 3.5 km altitude and moved 40 km E on 29 March. Ash plumes on 30 March rose to 3.5-3.7 km altitude and drifted 70 km NE.

Similar activity continued during April, with lava dome growth, strong fumarolic activity, incandescence in the dome, occasional explosions, and avalanches. A thermal anomaly persisted throughout the month. During 1-4 April weak ash plumes rose to 2.5-3 km altitude and extended 13-65 km SE and E.

Activity during 11 April 2023. The Institute of Volcanology and Seismology, Far Eastern Branch, Russian Academy of Sciences (IVS FEB RAS) reported a significant increase in seismicity around 0054 on 11 April, as reported by strong explosions detected on 11 April beginning at 0110 that sent ash plumes up to 7-10 km altitude and extended 100-435 km W, WNW, NNW, WSW, and SW. According to a Tokyo VAAC report the ash plume rose to 15.8 km altitude. By 0158 the plume extended over a 75 x 100 km area. According to an IVS FEB RAS report, the eruptive column was not vertical: the initial plume at 0120 on 11 April deviated to the NNE, at 0000 on 12 April, it drifted NW, and by 1900 it drifted SW. KVS reported that significant pulses of activity occurred at around 0200, 0320, and then a stronger phase around 0600. Levin Dmitry took a video from near Békés (3 km away) at around 0600 showing a rising plume; he also reported that a pyroclastic flow traveled across the road behind him as he left the area. According to IVS FEB RAS, the pyroclastic flow traveled several kilometers SSE, stopping a few hundred meters from a bridge on the road between Klyuchi and Petropavlovsk-Kamchatsky.

Ashfall was first observed in Klyuchi (45 km SW) at 0630, and a large, black ash plume blocked light by 0700. At 0729 KVERT issued a Volcano Observatory Notice for Aviation (VONA) raising the Aviation Color Code to Red (the highest level on a four-color scale). It also stated that a large ash plume had risen to 10 km altitude and drifted 100 km W. Near-constant lightning strikes were reported in the plume and sounds like thunderclaps were heard until about 1000. According to IVS FEB RAS the cloud was 200 km long and 76 km wide by 0830, and was spreading W at altitudes of 6-12 km. In the Klyuchi Village, the layer of both ash and snow reached 8.5 cm (figure 96); ashfall was also reported in Kozyrevsk (112 km SW) at 0930, Mayskoye, Anavgay, Atlasovo, Lazo, and Esso. Residents in Klyuchi reported continued darkness and ashfall at 1100. In some areas, ashfall was 6 cm deep and some residents reported dirty water coming from their plumbing. According to IVS FEB RAS, an ash cloud at 1150 rose to 5-20 km altitude and was 400 km long and 250 km wide, extending W. A VONA issued at 1155 reported that ash had risen to 10 km and drifted 340 km NNW and 240 km WSW. According to Simon Carn (Michigan Technological University), about 0.2 Tg of sulfur dioxide in the plume was measured in a satellite image from the TROPOMI instrument on the Sentinel-5P satellite acquired at 1343 that covered an area of about 189,000 km2 (figure 97). Satellite data at 1748 showed an ash plume that rose to 8 km altitude and drifted 430 km WSW and S, according to a VONA.

Figure (see Caption) Figure 96. Photo of ash deposited in Klyuchi village on 11 April 2023 by the eruption of Sheveluch. About 8.5 cm of ash was measured. Courtesy of Kam 24 News Agency.
Figure (see Caption) Figure 97. A strong sulfur dioxide plume from the 11 April 2023 eruption at Sheveluch was visible in satellite data from the TROPOMI instrument on the Sentinel-5P satellite. Courtesy of Simon Carn, MTU.

Activity during 12-15 April 2023. On 12 April at 0730 satellite images showed ash plumes rose to 7-8 km altitude and extended 600 km SW, 1,050 km ESE, and 1,300-3,000 km E. By 1710 that day, the explosions weakened. According to news sources, the ash-and-gas plumes drifted E toward the Aleutian Islands and reached the Gulf of Alaska by 13 April, causing flight disruptions. More than 100 flights involving Alaska airspace were cancelled due to the plume. Satellite data showed ash plumes rising to 4-5.5 km altitude and drifted 400-415 km SE and ESE on 13 April. KVS volcanologists observed the pyroclastic flow deposits and noted that steam rose from downed, smoldering trees. They also noted that the deposits were thin with very few large fragments, which differed from previous flows. The ash clouds traveled across the Pacific Ocean. Flight cancellations were also reported in NW Canada (British Columbia) during 13-14 April. During 14-15 April ash plumes rose to 6 km altitude and drifted 700 km NW.

Alaskan flight schedules were mostly back to normal by 15 April, with only minor delays and far less cancellations; a few cancellations continued to be reported in Canada. Clear weather on 15 April showed that most of the previous lava-dome complex was gone and a new crater roughly 1 km in diameter was observed (figure 98); gas-and-steam emissions were rising from this crater. Evidence suggested that there had been a directed blast to the SE, and pyroclastic flows traveled more than 20 km. An ash plume rose to 4.5-5.2 km altitude and drifted 93-870 km NW on 15 April.

Figure (see Caption) Figure 98. A comparison of the crater at Sheveluch showing the previous lava dome (top) taken on 29 November 2022 and a large crater in place of the dome (bottom) due to strong explosions during 10-13 April 2023, accompanied by gas-and-ash plumes. The bottom photo was taken on 15 April 2023. Photos has been color corrected. Both photos are courtesy of Yu. Demyanchuk, IVS FEB RAS, KVERT.

Activity during 16-30 April 2023. Resuspended ash was lifted by the wind from the slopes and rose to 4 km altitude and drifted 224 km NW on 17 April. KVERT reported a plume of resuspended ash from the activity during 10-13 April on 19 April that rose to 3.5-4 km altitude and drifted 146-204 km WNW. During 21-22 April a plume stretched over the Scandinavian Peninsula. A gas-and-steam plume containing some ash rose to 3-3.5 km altitude and drifted 60 km SE on 30 April. A possible new lava dome was visible on the W slope of the volcano on 29-30 April (figure 99); satellite data showed two thermal anomalies, a bright one over the existing lava dome and a weaker one over the possible new one.

Figure (see Caption) Figure 99. Photo showing new lava dome growth at Sheveluch after a previous explosion destroyed much of the complex, accompanied by a white gas-and-steam plume. Photo has been color corrected. Courtesy of Yu. Demyanchuk, IVS FEB RAS, KVERT.

References. Girina, O., Loupian, E., Horvath, A., Melnikov, D., Manevich, A., Nuzhdaev, A., Bril, A., Ozerov, A., Kramareva, L., Sorokin, A., 2023, Analysis of the development of the paroxysmal eruption of Sheveluch volcano on April 10–13, 2023, based on data from various satellite systems, ??????????? ???????? ??? ?? ???????, 20(2).

Geologic Background. The high, isolated massif of Sheveluch volcano (also spelled Shiveluch) rises above the lowlands NNE of the Kliuchevskaya volcano group. The 1,300 km3 andesitic volcano is one of Kamchatka's largest and most active volcanic structures, with at least 60 large eruptions during the Holocene. The summit of roughly 65,000-year-old Stary Shiveluch is truncated by a broad 9-km-wide late-Pleistocene caldera breached to the south. Many lava domes occur on its outer flanks. The Molodoy Shiveluch lava dome complex was constructed during the Holocene within the large open caldera; Holocene lava dome extrusion also took place on the flanks of Stary Shiveluch. Widespread tephra layers from these eruptions have provided valuable time markers for dating volcanic events in Kamchatka. Frequent collapses of dome complexes, most recently in 1964, have produced debris avalanches whose deposits cover much of the floor of the breached caldera.

Information Contacts: Kamchatka Volcanic Eruptions Response Team (KVERT), Far Eastern Branch, Russian Academy of Sciences, 9 Piip Blvd., Petropavlovsk-Kamchatsky, 683006, Russia (URL: http://www.kscnet.ru/ivs/kvert/); Institute of Volcanology and Seismology, Far Eastern Branch, Russian Academy of Sciences (IVS FEB RAS), 9 Piip Blvd., Petropavlovsk-Kamchatsky 683006, Russia (URL: http://www.kscnet.ru/ivs/eng/); Kamchatka Volcanological Station, Kamchatka Branch of Geophysical Survey, (KB GS RAS), Klyuchi, Kamchatka Krai, Russia (URL: http://volkstat.ru/); Hawai'i Institute of Geophysics and Planetology (HIGP) - MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Copernicus Browser, Copernicus Data Space Ecosystem, European Space Agency (URL: https://dataspace.copernicus.eu/browser/); Kam 24 News Agency, 683032, Kamchatka Territory, Petropavlovsk-Kamchatsky, Vysotnaya St., 2A (URL: https://kam24.ru/news/main/20230411/96657.html#.Cj5Jrky6.dpuf); Simon Carn, Geological and Mining Engineering and Sciences, Michigan Technological University, 1400 Townsend Drive, Houghton, MI 49931, USA (URL: http://www.volcarno.com/, Twitter: @simoncarn).


Bezymianny (Russia) — May 2023 Citation iconCite this Report

Bezymianny

Russia

55.972°N, 160.595°E; summit elev. 2882 m

All times are local (unless otherwise noted)


Explosions, ash plumes, lava flows, and avalanches during November 2022-April 2023

Bezymianny is located on the Kamchatka Peninsula of Russia as part of the Klyuchevskoy volcano group. Historic eruptions began in 1955 and have been characterized by dome growth, explosions, pyroclastic flows, ash plumes, and ashfall. During the 1955-56 eruption a large open crater was formed by collapse of the summit and an associated lateral blast. Subsequent episodic but ongoing lava-dome growth, accompanied by intermittent explosive activity and pyroclastic flows, has largely filled the 1956 crater. The current eruption period began in December 2016 and more recent activity has consisted of strong explosions, ash plumes, and thermal activity (BGVN 47:11). This report covers activity during November 2022 through April 2023, based on weekly and daily reports from the Kamchatka Volcano Eruptions Response Team (KVERT) and satellite data.

Activity during November and March 2023 was relatively low and mostly consisted of gas-and-steam emissions, occasional small collapses that generated avalanches along the lava dome slopes, and a persistent thermal anomaly over the volcano that was observed in satellite data on clear weather days. According to the Tokyo VAAC and KVERT, an explosion produced an ash plume that rose to 6 km altitude and drifted 25 km NE at 1825 on 29 March.

Gas-and-steam emissions, collapses generating avalanches, and thermal activity continued during April. According to two Volcano Observatory Notice for Aviation (VONA) issued on 2 and 6 April (local time) ash plumes rose to 3 km and 3.5-3.8 km altitude and drifted 35 km E and 140 km E, respectively. Satellite data from KVERT showed weak ash plumes extending up to 550 km E on 2 and 5-6 April.

A VONA issued at 0843 on 7 April described an ash plume that rose to 4.5-5 km altitude and drifted 250 km ESE. Later that day at 1326 satellite data showed an ash plume that rose to 5.5-6 km altitude and drifted 150 km ESE. A satellite image from 1600 showed an ash plume extending as far as 230 km ESE; KVERT noted that ash emissions were intensifying, likely due to avalanches from the growing lava dome. The Aviation Color Code (ACC) was raised to Red (the highest level on a four-color scale). At 1520 satellite data showed an ash plume rising to 5-5.5 km altitude and drifting 230 km ESE. That same day, Kamchatka Volcanological Station (KVS) volcanologists traveled to Ambon to collect ash; they reported that a notable eruption began at 1730, and within 20 minutes a large ash plume rose to 10 km altitude and drifted NW. KVERT reported that the strong explosive phase began at 1738. Video and satellite data taken at 1738 showed an ash plume that rose to 10-12 km altitude and drifted up to 2,800 km SE and E. Explosions were clearly audible 20 km away for 90 minutes, according to KVS. Significant amounts of ash fell at the Apakhonchich station, which turned the snow gray; ash continued to fall until the morning of 8 April. In a VONA issued at 0906 on 8 April, KVERT stated that the explosive eruption had ended; ash plumes had drifted 2,000 km E. The ACC was lowered to Orange (the third highest level on a four-color scale). The KVS team saw a lava flow on the active dome once the conditions were clear that same day (figure 53). On 20 April lava dome extrusion was reported; lava flows were noted on the flanks of the dome, and according to KVERT satellite data, a thermal anomaly was observed in the area. The ACC was lowered to Yellow (the second lowest on a four-color scale).

Figure (see Caption) Figure 53. Photo showing an active lava flow descending the SE flank of Bezymianny from the lava dome on 8 April 2023. Courtesy of Yu. Demyanchuk, IVS FEB RAS, KVERT.

Satellite data showed an increase in thermal activity beginning in early April 2023. A total of 31 thermal hotspots were detected by the MODVOLC thermal algorithm on 4, 5, 7, and 12 April 2023. The elevated thermal activity resulted from an increase in explosive activity and the start of an active lava flow. The MIROVA (Middle InfraRed Observation of Volcanic Activity) volcano hotspot detection system based on the analysis of MODIS data also showed a pulse in thermal activity during the same time (figure 54). Infrared satellite imagery captured a continuous thermal anomaly at the summit crater, often accompanied by white gas-and-steam emissions (figure 55). On 4 April 2023 an active lava flow was observed descending the SE flank.

Figure (see Caption) Figure 54. Intermittent and low-power thermal anomalies were detected at Bezymianny during December 2022 through mid-March 2023, according to this MIROVA graph (Log Radiative Power). In early April 2023, an increase in explosive activity and eruption of a lava flow resulted in a marked increase in thermal activity. Courtesy of MIROVA.
Figure (see Caption) Figure 55. Infrared satellite images of Bezymianny showed a persistent thermal anomaly over the lava dome on 18 November 2022 (top left), 28 December 2022 (top right), 15 March 2023 (bottom left), and 4 April 2023 (bottom right), often accompanied by white gas-and-steam plumes. On 4 April a lava flow was active and descending the SE flank. Images using infrared (bands 12, 11, 8a). Courtesy of Copernicus Browser.

Geologic Background. The modern Bezymianny, much smaller than its massive neighbors Kamen and Kliuchevskoi on the Kamchatka Peninsula, was formed about 4,700 years ago over a late-Pleistocene lava-dome complex and an edifice built about 11,000-7,000 years ago. Three periods of intensified activity have occurred during the past 3,000 years. The latest period, which was preceded by a 1,000-year quiescence, began with the dramatic 1955-56 eruption. This eruption, similar to that of St. Helens in 1980, produced a large open crater that was formed by collapse of the summit and an associated lateral blast. Subsequent episodic but ongoing lava-dome growth, accompanied by intermittent explosive activity and pyroclastic flows, has largely filled the 1956 crater.

Information Contacts: Kamchatka Volcanic Eruptions Response Team (KVERT), Far Eastern Branch, Russian Academy of Sciences, 9 Piip Blvd., Petropavlovsk-Kamchatsky, 683006, Russia (URL: http://www.kscnet.ru/ivs/kvert/); Kamchatka Volcanological Station, Kamchatka Branch of Geophysical Survey, (KB GS RAS), Klyuchi, Kamchatka Krai, Russia (URL: http://volkstat.ru/); Hawai'i Institute of Geophysics and Planetology (HIGP) - MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Copernicus Browser, Copernicus Data Space Ecosystem, European Space Agency (URL: https://dataspace.copernicus.eu/browser/).


Chikurachki (Russia) — May 2023 Citation iconCite this Report

Chikurachki

Russia

50.324°N, 155.461°E; summit elev. 1781 m

All times are local (unless otherwise noted)


New explosive eruption during late January-early February 2023

Chikurachki, located on Paramushir Island in the northern Kuriles, has had Plinian eruptions during the Holocene. Lava flows have reached the sea and formed capes on the NW coast; several young lava flows are also present on the E flank beneath a scoria deposit. Reported eruptions date back to 1690, with the most recent eruption period occurring during January through October 2022, characterized by occasional explosions, ash plumes, and thermal activity (BGVN 47:11). This report covers a new eruptive period during January through February 2023 that consisted of ash explosions and ash plumes, based on information from the Kamchatka Volcanic Eruptions Response Team (KVERT) and satellite data.

According to reports from KVERT, an explosive eruption began around 0630 on 29 January. Explosions generated ash plumes that rose to 3-3.5 km altitude and drifted 6-75 km SE and E, based on satellite data. As a result, the Aviation Color Code (ACC) was raised to Orange (the second highest level on a four-color scale). At 1406 and 1720 ash plumes were identified in satellite images that rose to 4.3 km altitude and extended 70 km E. By 2320 the ash plume had dissipated. A thermal anomaly was visible at the volcano on 31 January, according to a satellite image, and an ash plume was observed drifting 66 km NE.

Occasional explosions and ash plumes continued during early February. At 0850 on 1 February an ash plume rose to 3.5 km altitude and drifted 35 km NE. Satellite data showed an ash plume that rose to 3.2-3.5 km altitude and drifted 50 km NE at 1222 later that day (figure 22). A thermal anomaly was detected over the volcano during 5-6 February and ash plumes drifted as far as 125 km SE, E, and NE. Explosive events were reported at 0330 on 6 February that produced ash plumes rising to 4-4.5 km altitude and drifting 72-90 km N, NE, and ENE. KVERT noted that the last gas-and steam plume that contained some ash was observed on 8 February and drifted 55 km NE before the explosive eruption ended. The ACC was lowered to Yellow and then Green (the lowest level on a four-color scale) on 18 February.

Figure (see Caption) Figure 22. Satellite image showing a true color view of a strong ash plume rising above Chikurachki on 1 February 2023. The plume drifted NE and ash deposits (dark brown-to-gray) are visible on the NE flank due to explosive activity. Courtesy of Copernicus Browser.

Geologic Background. Chikurachki, the highest volcano on Paramushir Island in the northern Kuriles, is a relatively small cone constructed on a high Pleistocene edifice. Oxidized basaltic-to-andesitic scoria deposits covering the upper part of the young cone give it a distinctive red color. Frequent basaltic Plinian eruptions have occurred during the Holocene. Lava flows have reached the sea and formed capes on the NW coast; several young lava flows are also present on the E flank beneath a scoria deposit. The Tatarinov group of six volcanic centers is located immediately to the south, and the Lomonosov cinder cone group, the source of an early Holocene lava flow that reached the saddle between it and Fuss Peak to the west, lies at the southern end of the N-S-trending Chikurachki-Tatarinov complex. In contrast to the frequently active Chikurachki, the Tatarinov centers are extensively modified by erosion and have a more complex structure. Tephrochronology gives evidence of an eruption around 1690 CE from Tatarinov, although its southern cone contains a sulfur-encrusted crater with fumaroles that were active along the margin of a crater lake until 1959.

Information Contacts: Kamchatka Volcanic Eruptions Response Team (KVERT), Far East Division, Russian Academy of Sciences, 9 Piip Blvd., Petropavlovsk-Kamchatsky, 683006, Russia (URL: http://www.kscnet.ru/ivs/); Copernicus Browser, Copernicus Data Space Ecosystem, European Space Agency (URL: https://dataspace.copernicus.eu/browser/).


Marapi (Indonesia) — May 2023 Citation iconCite this Report

Marapi

Indonesia

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

All times are local (unless otherwise noted)


New explosive eruption with ash emissions during January-March 2023

Marapi in Sumatra, Indonesia, is a massive stratovolcano that rises 2 km above the Bukittinggi Plain in the Padang Highlands. A broad summit contains multiple partially overlapping summit craters constructed within the small 1.4-km-wide Bancah caldera and trending ENE-WSW, with volcanism migrating to the west. Since the end of the 18th century, more than 50 eruptions, typically characterized by small-to-moderate explosive activity, have been recorded. The previous eruption consisted of two explosions during April-May 2018, which caused ashfall to the SE (BGVN 43:06). This report covers a new eruption during January-March 2023, which included explosive events and ash emissions, as reported by Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM) and MAGMA Indonesia.

According to a press release issued by PVMBG and MAGMA Indonesia on 26 December, primary volcanic activity at Marapi consisted of white gas-and-steam puffs that rose 500-100 m above the summit during April-December 2022. On 25 December 2022 there was an increase in the number of deep volcanic earthquakes and summit inflation. White gas-and-steam emissions rose 80-158 m above the summit on 5 January. An explosive eruption began at 0611 on 7 January 2023, which generated white gas-and-steam emissions and gray ash emissions mixed with ejecta that rose 300 m above the summit and drifted SE (figure 10). According to ground observations, white-to-gray ash clouds during 0944-1034 rose 200-250 m above the summit and drifted SE and around 1451 emissions rose 200 m above the summit. Seismic signals indicated that eruptive events also occurred at 1135, 1144, 1230, 1715, and 1821, but no ash emissions were visually observed. On 8 January white-and-gray emissions rose 150-250 m above the summit that drifted E and SE. Seismic signals indicated eruptive events at 0447, 1038, and 1145, but again no ash emissions were visually observed on 8 January. White-to-gray ash plumes continued to be observed on clear weather days during 9-15, 18-21, 25, and 29-30 January, rising 100-1,000 m above the summit and drifted generally NE, SE, N, and E, based on ground observations (figure 11).

Figure (see Caption) Figure 10. Webcam image of the start of the explosive eruption at Marapi at 0651 on 7 January 2023. White gas-and-steam emissions are visible to the left and gray ash emissions are visible on the right, drifting SE. Distinct ejecta was also visible mixed within the ash cloud. Courtesy of PVMBG and MAGMA Indonesia.
Figure (see Caption) Figure 11. Webcam image showing thick, gray ash emissions rising 500 m above the summit of Marapi and drifting N and NE at 0953 on 11 January 2023. Courtesy of PVMBG and MAGMA Indonesia.

White-and-gray and brown emissions persisted in February, rising 50-500 m above the summit and drifting E, S, SW, N, NE, and W, though weather sometimes prevented clear views of the summit. An eruption at 1827 on 10 February produced a black ash plume that rose 400 m above the summit and drifted NE and E (figure 12). Similar activity was reported on clear weather days, with white gas-and-steam emissions rising 50 m above the summit on 9, 11-12, 20, and 27 March and drifted E, SE, SW, NE, E, and N. On 17 March white-and-gray emissions rose 400 m above the summit and drifted N and E.

Figure (see Caption) Figure 12. Webcam image showing an eruptive event at 1829 on 10 February 2023 with an ash plume rising 400 m above the summit and drifting NE and E. Courtesy of PVMBG and MAGMA Indonesia.

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

Information Contacts: Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM), Jalan Diponegoro 57, Bandung 40122, Indonesia (URL: http://www.vsi.esdm.go.id/); MAGMA Indonesia, Kementerian Energi dan Sumber Daya Mineral (URL: https://magma.esdm.go.id/v1).


Kikai (Japan) — May 2023 Citation iconCite this Report

Kikai

Japan

30.793°N, 130.305°E; summit elev. 704 m

All times are local (unless otherwise noted)


Intermittent white gas-and-steam plumes, discolored water, and seismicity during May 2021-April 2023

Kikai, located just S of the Ryukyu islands of Japan, contains a 19-km-wide mostly submarine caldera. The island of Satsuma Iwo Jima (also known as Satsuma-Iwo Jima and Tokara Iojima) is located at the NW caldera rim, as well as the island’s highest peak, Iodake. Its previous eruption period occurred on 6 October 2020 and was characterized by an explosion and thermal anomalies in the crater (BGVN 45:11). More recent activity has consisted of intermittent thermal activity and gas-and-steam plumes (BGVN 46:06). This report covers similar low-level activity including white gas-and-steam plumes, nighttime incandescence, seismicity, and discolored water during May 2021 through April 2023, using information from the Japan Meteorological Agency (JMA) and various satellite data. During this time, the Alert Level remained at a 2 (on a 5-level scale), according to JMA.

Activity was relatively low throughout the reporting period and has consisted of intermittent white gas-and-steam emissions that rose 200-1,400 m above the Iodake crater and nighttime incandescence was observed at the Iodake crater using a high-sensitivity surveillance camera. Each month, frequent volcanic earthquakes were detected, and sulfur dioxide masses were measured by the University of Tokyo Graduate School of Science, Kyoto University Disaster Prevention Research Institute, Mishima Village, and JMA (table 6).

Table 6. Summary of gas-and-steam plume heights, number of volcanic earthquakes detected, and amount of sulfur dioxide emissions in tons per day (t/d). Courtesy of JMA monthly reports.

Month Max plume height (m) Volcanic earthquakes Sulfur dioxide emissions (t/d)
May 2021 400 162 900-1,300
Jun 2021 800 117 500
Jul 2021 1,400 324 800-1,500
Aug 2021 1,000 235 700-1,000
Sep 2021 800 194 500-1,100
Oct 2021 800 223 600-800
Nov 2021 900 200 400-900
Dec 2021 1,000 161 500-1,800
Jan 2022 1,000 164 600-1,100
Feb 2022 1,000 146 500-1,600
Mar 2022 1,200 171 500-1,200
Apr 2022 1,000 144 600-1,000
May 2022 1,200 126 300-500
Jun 2022 1,000 154 400
Jul 2022 1,300 153 600-1,100
Aug 2022 1,100 109 600-1,500
Sep 2022 1,000 170 900
Oct 2022 800 249 700-1,200
Nov 2022 800 198 800-1,200
Dec 2022 700 116 600-1,500
Jan 2023 800 146 500-1,400
Feb 2023 800 135 600-800
Mar 2023 1,100 94 500-600
Apr 2023 800 82 500-700

Sentinel-2 satellite images show weak thermal anomalies at the Iodake crater on clear weather days, accompanied by white gas-and-steam emissions and occasional discolored water (figure 24). On 17 January 2022 JMA conducted an aerial overflight in cooperation with the Japan Maritime Self-Defense Force’s 1st Air Group, which confirmed a white gas-and-steam plume rising from the Iodake crater (figure 25). They also observed plumes from fumaroles rising from around the crater and on the E, SW, and N slopes. In addition, discolored water was reported near the coast around Iodake, which JMA stated was likely related to volcanic activity (figure 25). Similarly, an overflight taken on 11 January 2023 showed white gas-and-steam emissions rising from the Iodake crater, as well as discolored water that spread E from the coast around the island. On 14 February 2023 white fumaroles and discolored water were also captured during an overflight (figure 26).

Figure (see Caption) Figure 24. Sentinel-2 satellite images of Satsuma Iwo Jima (Kikai) showing sets of visual (true color) and infrared (bands 12, 11, 8a) views on 7 December 2021 (top), 23 October 2022 (middle), and 11 January 2023 (bottom). Courtesy of Copernicus Browser.
Figure (see Caption) Figure 25. Aerial image of Satsuma Iwo Jima (Kikai) showing a white gas-and-steam plume rising above the Iodake crater at 1119 on 17 January 2022. There was also green-yellow discolored water surrounding the coast of Mt. Iodake. Courtesy of JMSDF via JMA.
Figure (see Caption) Figure 26. Aerial image of Satsuma Iwo Jima (Kikai) showing white gas-and-steam plumes rising above the Iodake crater on 14 February 2023. Green-yellow discolored water surrounded Mt. Iodake. Courtesy of JCG.

Geologic Background. Multiple eruption centers have exhibited recent activity at Kikai, a mostly submerged, 19-km-wide caldera near the northern end of the Ryukyu Islands south of Kyushu. It was the source of one of the world's largest Holocene eruptions about 6,300 years ago when rhyolitic pyroclastic flows traveled across the sea for a total distance of 100 km to southern Kyushu, and ashfall reached the northern Japanese island of Hokkaido. The eruption devastated southern and central Kyushu, which remained uninhabited for several centuries. Post-caldera eruptions formed Iodake (or Iwo-dake) lava dome and Inamuradake scoria cone, as well as submarine lava domes. Recorded eruptions have occurred at or near Satsuma-Iojima (also known as Tokara-Iojima), a small 3 x 6 km island forming part of the NW caldera rim. Showa-Iojima lava dome (also known as Iojima-Shinto), a small island 2 km E of Satsuma-Iojima, was formed during submarine eruptions in 1934 and 1935. Mild-to-moderate explosive eruptions have occurred during the past few decades from Iodake, a rhyolitic lava dome at the eastern end of Satsuma-Iojima.

Information Contacts: Japan Meteorological Agency (JMA), Otemachi, 1-3-4, Chiyoda-ku Tokyo 100-8122, Japan (URL: http://www.jma.go.jp/jma/indexe.html); Japan Coast Guard (JCG) Volcano Database, Hydrographic and Oceanographic Department, 3-1-1, Kasumigaseki, Chiyoda-ku, Tokyo 100-8932, Japan (URL: https://www1.kaiho.mlit.go.jp/kaiikiDB/kaiyo30-2.htm); Copernicus Browser, Copernicus Data Space Ecosystem, European Space Agency (URL: https://dataspace.copernicus.eu/browser/).


Lewotolok (Indonesia) — May 2023 Citation iconCite this Report

Lewotolok

Indonesia

8.274°S, 123.508°E; summit elev. 1431 m

All times are local (unless otherwise noted)


Strombolian eruption continues through April 2023 with intermittent ash plumes

The current eruption at Lewotolok, in Indonesian’s Lesser Sunda Islands, began in late November 2020 and has included Strombolian explosions, occasional ash plumes, incandescent ejecta, intermittent thermal anomalies, and persistent white and white-and-gray emissions (BGVN 47:10). Similar activity continued during October 2022-April 2023, as described in this report based on information provided by Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as CVGHM, or the Center of Volcanology and Geological Hazard Mitigation), MAGMA Indonesia, the Darwin Volcanic Ash Advisory Centre (VAAC), and satellite data.

During most days in October 2022 white and white-gray emissions rose as high as 200-600 m above the summit. Webcam images often showed incandescence above the crater rim. At 0351 on 14 October, an explosion produced a dense ash plume that rose about 1.2 km above the summit and drifted SW (figure 43). After this event, activity subsided and remained low through the rest of the year, but with almost daily white emissions.

Figure (see Caption) Figure 43. Webcam image of Lewotolok on 14 October 2022 showing a dense ash plume and incandescence above the crater. Courtesy of MAGMA Indonesia.

After more than two months of relative quiet, PVMBG reported that explosions at 0747 on 14 January 2023 and at 2055 on 16 January produced white-and-gray ash plumes that rose around 400 m above the summit and drifted E and SE (figure 44). During the latter half of January through April, almost daily white or white-and-gray emissions were observed rising 25-800 m above the summit, and nighttime webcam images often showed incandescent material being ejected above the summit crater. Strombolian activity was visible in webcam images at 2140 on 11 February, 0210 on 18 February, and during 22-28 March. Frequent hotspots were recorded by the MIROVA detection system starting in approximately the second week of March 2023 that progressively increased into April (figure 45).

Figure (see Caption) Figure 44. Webcam image of an explosion at Lewotolok on 14 January 2023 ejecting a small ash plume along with white emissions. Courtesy of MAGMA Indonesia.
Figure (see Caption) Figure 45. MIROVA Log Radiative Power graph of thermal anomalies detected by the VIIRS satellite instrument at Lewotolok’s summit crater for the year beginning 24 July 2022. Clusters of mostly low-power hotspots occurred during August-October 2022, followed by a gap of more than four months before persistent and progressively stronger anomalies began in early March 2023. Courtesy of MIROVA.

Explosions that produced dense ash plumes as high as 750 m above the summit were described in Volcano Observatory Notices for Aviation (VONA) at 0517, 1623, and 2016 on 22 March, at 1744 on 24 March, at 0103 on 26 March, at 0845 and 1604 on 27 March (figure 46), and at 0538 on 28 March. According to the Darwin VAAC, on 6 April another ash plume rose to 1.8 km altitude (about 370 m above the summit) and drifted N.

Figure (see Caption) Figure 46. Webcam image of Lewotolok at 0847 on 27 March 2023 showing a dense ash plume from an explosion along with clouds and white emissions. Courtesy of MAGMA-Indonesia.

Sentinel-2 images over the previous year recorded thermal anomalies as well as the development of a lava flow that descended the NE flank beginning in June 2022 (figure 47). The volcano was often obscured by weather clouds, which also often hampered ground observations. Ash emissions were reported in March 2022 (BGVN 47:10), and clear imagery from 4 March 2022 showed recent lava flows confined to the crater, two thermal anomaly spots in the eastern part of the crater, and mainly white emissions from the SE. Thermal anomalies became stronger and more frequent in mid-May 2022, followed by strong Strombolian activity through June and July (BGVN 47:10); Sentinel-2 images on 2 June 2022 showed active lava flows within the crater and overflowing onto the NE flank. Clear images from 23 April 2023 (figure 47) show the extent of the cooled NE-flank lava flow, more extensive intra-crater flows, and two hotspots in slightly different locations compared to the previous March.

Figure (see Caption) Figure 47. Sentinel-2 satellite images of Lewotolok showing sets of visual (true color) and infrared (bands 12, 11, 8a) views on 4 March 2022, 2 June 2022, and 23 April 2023. Courtesy of Copernicus Browser.

Geologic Background. The Lewotolok (or Lewotolo) stratovolcano occupies the eastern end of an elongated peninsula extending north into the Flores Sea, connected to Lembata (formerly Lomblen) Island by a narrow isthmus. It is symmetrical when viewed from the north and east. A small cone with a 130-m-wide crater constructed at the SE side of a larger crater forms the volcano's high point. Many lava flows have reached the coastline. Eruptions recorded since 1660 have consisted of explosive activity from the summit crater.

Information Contacts: Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM), Jalan Diponegoro 57, Bandung 40122, Indonesia (URL: http://www.vsi.esdm.go.id/); MAGMA Indonesia, Kementerian Energi dan Sumber Daya Mineral (URL: https://magma.esdm.go.id/v1); 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/); Copernicus Browser, Copernicus Data Space Ecosystem, European Space Agency (URL: https://dataspace.copernicus.eu/browser/).


Barren Island (India) — April 2023 Citation iconCite this Report

Barren Island

India

12.278°N, 93.858°E; summit elev. 354 m

All times are local (unless otherwise noted)


Thermal activity during December 2022-March 2023

Barren Island is part of a N-S-trending volcanic arc extending between Sumatra and Burma (Myanmar). The caldera, which is open to the sea on the west, was created during a major explosive eruption in the late Pleistocene that produced pyroclastic flow and surge deposits. Eruptions dating back to 1787, have changed the morphology of the pyroclastic cone in the center of the caldera, and lava flows that fill much of the caldera floor have reached the sea along the western coast. Previous activity was detected during mid-May 2022, consisting of intermittent thermal activity. This report covers June 2022 through March 2023, which included strong thermal activity beginning in late December 2022, based on various satellite data.

Activity was relatively quiet during June through late December 2022 and mostly consisted of low-power thermal anomalies, based on the MIROVA (Middle InfraRed Observation of Volcanic Activity) graph. During late December, a spike in both power and frequency of thermal anomalies was detected (figure 58). There was another pulse in thermal activity in mid-March, which consisted of more frequent and relatively strong anomalies.

Figure (see Caption) Figure 58. Occasional thermal anomalies were detected during June through late December 2022 at Barren Island, but by late December through early January 2023, there was a marked increase in thermal activity, both in power and frequency, according to this MIROVA graph (Log Radiative Power). After this spike in activity, anomalies occurred at a more frequent rate. In late March, another pulse in activity was detected, although the power was not as strong as that initial spike during December-January. Courtesy of MIROVA.

The Suomi NPP/VIIRS sensor data showed five thermal alerts on 29 December 2022. The number of alerts increased to 19 on 30 December. According to the Darwin VAAC, ash plumes identified in satellite images captured at 2340 on 30 December and at 0050 on 31 December rose to 1.5 km altitude and drifted SW. The ash emissions dissipated by 0940. On 31 December, a large thermal anomaly was detected; based on a Sentinel-2 infrared satellite image, the anomaly was relatively strong and extended to the N (figure 59).

Figure (see Caption) Figure 59. Thermal anomalies of varying intensities were visible in the crater of Barren Island on 31 December 2022 (top left), 15 January 2023 (top right), 24 February 2023 (bottom left), and 31 March 2023 (bottom right), as seen in these Sentinel-2 infrared satellite images. The anomalies on 31 December and 31 March were notably strong and extended to the N and N-S, respectively. Images using “Atmospheric penetration” rendering (bands 12, 11, 8a). Courtesy of Sentinel Hub Playground.

Thermal activity continued during January through March. Sentinel-2 infrared satellite data showed some thermal anomalies of varying intensity on clear weather days on 5, 10, 15, 20, and 30 January 2023, 9, 14, 19, and 24 February 2023, and 21, 26, and 31 March (figure 59). According to Suomi NPP/VIIRS sensor data, a total of 30 thermal anomalies were detected over 18 days on 2-3, 7, 9-14, 16-17, 20, 23, 25, and 28-31 January. The sensor data showed a total of six hotspots detected over six days on 1, 4-5, and 10-12 February. During March, a total of 33 hotspots were visible over 11 days on 20-31 March. Four MODVOLC thermal alerts were issued on 25, 27, and 29 March.

Geologic Background. Barren Island, a possession of India in the Andaman Sea about 135 km NE of Port Blair in the Andaman Islands, is the only historically active volcano along the N-S volcanic arc extending between Sumatra and Burma (Myanmar). It is the emergent summit of a volcano that rises from a depth of about 2250 m. The small, uninhabited 3-km-wide island contains a roughly 2-km-wide caldera with walls 250-350 m high. The caldera, which is open to the sea on the west, was created during a major explosive eruption in the late Pleistocene that produced pyroclastic-flow and -surge deposits. Historical eruptions have changed the morphology of the pyroclastic cone in the center of the caldera, and lava flows that fill much of the caldera floor have reached the sea along the western coast.

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/); 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); NASA Worldview (URL: https://worldview.earthdata.nasa.gov/).


Villarrica (Chile) — April 2023 Citation iconCite this Report

Villarrica

Chile

39.42°S, 71.93°W; summit elev. 2847 m

All times are local (unless otherwise noted)


Nighttime crater incandescence, ash emissions, and seismicity during October 2022-March 2023

Villarrica, located in central Chile, consists of a 2-km-wide caldera that formed about 3,500 years ago, located at the base of the presently active cone. Historical eruptions date back to 1558 and have been characterized by mild-to-moderate explosive activity with occasional lava effusions. The current eruption period began in December 2014 and has recently consisted of ongoing seismicity, gas-and-steam emissions, and thermal activity (BGVN 47:10). This report covers activity during October 2022 through March 2023 and describes Strombolian explosions, ash emissions, and crater incandescence. Information for this report primarily comes from the Southern Andes Volcano Observatory (Observatorio Volcanológico de Los Andes del Sur, OVDAS), part of Chile's National Service of Geology and Mining (Servicio Nacional de Geología y Minería, SERNAGEOMIN) and satellite data.

Seismicity during October consisted of discrete long-period (LP)-type events, tremor (TR), and volcano-tectonic (VT)-type events. Webcam images showed eruption plumes rising as high as 460 m above the crater rim; plumes deposited tephra on the E, S, and SW flanks within 500 m of the crater on 2, 18, 23, and 31 October. White gas-and-steam emissions rose 80-300 m above the crater accompanied by crater incandescence during 2-3 October. There was a total of 5 VT-type events, 10,625 LP-type events, and 2,232 TR-type events detected throughout the month. Sulfur dioxide data was obtained by the Differential Absorption Optical Spectroscopy Equipment (DOAS) installed 6 km in an ESE direction. The average value of the sulfur dioxide emissions was 535 ± 115 tons per day (t/d); the highest daily maximum was 1,273 t/d on 13 October. These values were within normal levels and were lower compared to September. During the night of 3-4 October Strombolian activity ejected blocks as far as 40 m toward the NW flank. Small, gray-brown ash pulses rose 60 m above the crater accompanied white gas-and-steam emissions that rose 40-300 m high during 4-5 October. In addition, crater incandescence and Strombolian explosions that ejected blocks were reported during 4-5 and 9-11 October. Based on satellite images from 12 October, ballistic ejecta traveled as far as 400 m and the resulting ash was deposited 3.2 km to the E and SE and 900 m to the NW.

Satellite images from 14 October showed an active lava lake that covered an area of 36 square meters in the E part of the crater floor. There was also evidence of a partial collapse (less than 300 square meters) at the inner SSW crater rim. POVI posted an 18 October photo that showed incandescence above the crater rim, noting that crater incandescence was visible during clear weather nights. In addition, webcam images at 1917 showed lava fountaining and Strombolian explosions; tourists also described seeing splashes of lava ejected from a depth of 80 m and hearing loud degassing sounds. Tephra deposits were visible around the crater rim and on the upper flanks on 24 October. On 25 October SERNAGEOMIN reported that both the number and amplitude of LP earthquakes had increased, and continuous tremor also increased; intense crater incandescence was visible in satellite images. On 31 October Strombolian explosions intensified and ejected material onto the upper flanks.

Activity during November consisted of above-baseline seismicity, including intensifying continuous tremor and an increase in the number of LP earthquakes. On 1 November a lava fountain was visible rising above the crater rim. Nighttime crater incandescence was captured in webcam images on clear weather days. Strombolian explosions ejected incandescent material on the NW and SW flanks during 1, 2, and 6-7 November. POVI reported that the width of the lava fountains that rose above the crater rim on 2 November suggested that the vent on the crater floor was roughly 6 m in diameter. Based on reports from observers and analyses of satellite imagery, material that was deposited on the upper flanks, primarily to the NW, consisted of clasts up to 20 cm in diameter. During an overflight on 19 November SERNAGEOMIN scientists observed a cone on the crater floor with an incandescent vent at its center that contained a lava lake. Deposits of ejecta were also visible on the flanks. That same day a 75-minute-long series of volcano-tectonic earthquakes was detected at 1940; a total of 21 events occurred 7.8 km ESE of the crater. Another overflight on 25 November showed the small cone on the crater floor with an incandescent lava lake at the center; the temperature of the lava lake was 1,043 °C, based data gathered during the overflight.

Similar seismicity, crater incandescence, and gas-and-steam emissions continued during December. On 1 December incandescent material was ejected 80-220 m above the crater rim. During an overflight on 6 December, intense gas-and-steam emissions from the lava lake was reported, in addition to tephra deposits on the S and SE flanks as far as 500 m from the crater. During 7-12 December seismicity increased slightly and white, low-altitude gas-and-steam emissions and crater incandescence were occasionally visible. On 24 December at 0845 SERNAGEOMIN reported an increase in Strombolian activity; explosions ejected material that generally rose 100 m above the crater, although one explosion ejected incandescent tephra as far as 400 m from the crater onto the SW flank. According to POVI, 11 explosions ejected incandescent material that affected the upper SW flank between 2225 on 25 December to 0519 on 26 December. POVI recorded 21 Strombolian explosions that ejected incandescent material onto the upper SW flank from 2200 on 28 December to 0540 on 29 December. More than 100 Strombolian explosions ejected material onto the upper W and NW flanks during 30-31 December. On 30 December at 2250 an explosion was detected that generated an eruptive column rising 120 m above the crater and ejecting incandescent material 300 m on the NW flank (figure 120). Explosions detected at 2356 on 31 December ejected material 480 m from the crater rim onto the NW flank and at 0219 material was deposited on the same flank as far as 150 m. Both explosions ejected material as high as 120 m above the crater rim.

Figure (see Caption) Figure 120. Webcam image of a Strombolian explosion at Villarrica on 30 December 2022 (local time) that ejected incandescent material 300 m onto the NW flank, accompanied by emissions and crater incandescence. Courtesy of SERNAGEOMIN (Reporte Especial de Actividad Volcanica (REAV), Region De La Araucania y Los Rios, Volcan Villarrica, 30 de diciembre de 2022, 23:55 Hora local).

During January 2023, Strombolian explosions and lava fountaining continued mainly in the crater, ejecting material 100 m above the crater. Gas-and-steam emissions rose 40-260 m above the crater and drifted in different directions, and LP-type events continued. Emissions during the night of 11 January including some ash rose 80 m above the crater and as far as 250 m NE flank. POVI scientists reported about 70 lava fountaining events from 2130 on 14 January to 0600 on 15 January. At 2211 on 15 January there was an increase in frequency of Strombolian explosions that ejected incandescent material 60-150 m above the crater. Some ashfall was detected around the crater. POVI noted that on 19 January lava was ejected as high as 140 m above the crater rim and onto the W and SW flanks. Explosion noises were heard on 19 and 22 January in areas within a radius of 10 km. During 22-23 January Strombolian explosions ejected incandescent material 60-100 m above the crater that drifted SE. A seismic event at 1204 on 27 January was accompanied by an ash plume that rose 220 m above the crater and drifted E (figure 121); later that same day at 2102 an ash plume rose 180 m above the crater and drifted E.

Figure (see Caption) Figure 121. Webcam image of an ash plume at Villarrica on 27 January rising 220 m above the crater and drifting E. Courtesy of SERNAGEOMIN (Reporte Especial de Actividad Volcanica (REAV), Region De La Araucania y Los Rios, Volcan Villarrica, 27 de enero de 2023, 12:35 Hora local).

Seismicity, primarily characterized by LP-type events, and Strombolian explosions persisted during February and March. POVI reported that three explosions were heard during 1940-1942 on 6 February, and spatter was seen rising 30 m above the crater rim hours later. On 9 February lava fountains were visible rising 50 m above the crater rim. On 17 February Strombolian explosions ejected material 100 m above the crater rim and onto the upper SW flank. Webcam images from 20 February showed two separate fountains of incandescent material, which suggested that a second vent had opened to the E of the first vent. Spatter was ejected as high as 80 m above the crater rim and onto the upper NE flank. A sequence of Strombolian explosions was visible from 2030 on 20 February to 0630 on 21 February. Material was ejected as high as 80 m above the crater rim and onto the upper E flank. LP-type earthquakes recorded 1056 and at 1301 on 27 February were associated with ash plumes that rose 300 m above the crater and drifted NE (figure 122). Crater incandescence above the crater rim was observed in webcam images on 13 March, which indicated Strombolian activity. POVI posted a webcam image from 2227 on 18 March showing Strombolian explosions that ejected material as high as 100 m above the crater rim. Explosions were heard up to 8 km away. On 19 March at 1921 an ash emission rose 340 m above the crater and drifted NE. On 21 and 26 March Strombolian explosions ejected material 100 and 110 m above the crater rim, respectively. On 21 March Strombolian explosions ejected material 100 m above the crater rim. Low-intensity nighttime crater incandescence was detected by surveillance cameras on 24 March.

Figure (see Caption) Figure 122. Photo of an ash plume rising 300 m above the crater of Villarrica and drifting NE on 27 February 2023. Courtesy of SERNAGEOMIN (Reporte Especial de Actividad Volcanica (REAV), Region De La Araucania y Los Rios, Volcan Villarrica, 27 de febrero de 2023, 11:10 Hora local).

Infrared MODIS satellite data processed by MIROVA (Middle InfraRed Observation of Volcanic Activity) detected an increase in thermal activity during mid-November, which corresponds to sustained Strombolian explosions, lava fountaining, and crater incandescence (figure 123). This activity was also consistently captured on clear weather days throughout the reporting period in Sentinel-2 infrared satellite images (figure 124).

Figure (see Caption) Figure 123. Low-power thermal anomalies were detected during August through October 2022 at Villarrica, based on this MIROVA graph (Log Radiative Power). During mid-November, the power and frequency of the anomalies increased and remained at a consistent level through March 2023. Thermal activity consisted of Strombolian explosions, lava fountains, and crater incandescence. Courtesy of MIROVA.
Figure (see Caption) Figure 124. Consistent bright thermal anomalies were visible at the summit crater of Villarrica in Sentinel-2 infrared satellite images throughout the reporting period, as shown here on 19 December 2022 (left) and 9 February 2023 (right). Occasional gas-and-steam emissions also accompanied the thermal activity. Images use Atmospheric penetration rendering (bands 12, 11, 8a). Courtesy of Sentinel Hub Playground.

Geologic Background. The glacier-covered Villarrica stratovolcano, in the northern Lakes District of central Chile, is ~15 km south of the city of Pucon. A 2-km-wide caldera that formed about 3,500 years ago is located at the base of the presently active, dominantly basaltic to basaltic-andesite cone at the NW margin of a 6-km-wide Pleistocene caldera. More than 30 scoria cones and fissure vents are present on the flanks. Plinian eruptions and pyroclastic flows that have extended up to 20 km from the volcano were produced during the Holocene. Lava flows up to 18 km long have issued from summit and flank vents. Eruptions documented since 1558 CE have consisted largely of mild-to-moderate explosive activity with occasional lava effusion. Glaciers cover 40 km2 of the volcano, and lahars have damaged towns on its flanks.

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/); Proyecto Observación Villarrica Internet (POVI) (URL: http://www.povi.cl/); 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).


Fuego (Guatemala) — April 2023 Citation iconCite this Report

Fuego

Guatemala

14.473°N, 90.88°W; summit elev. 3763 m

All times are local (unless otherwise noted)


Daily explosions, gas-and-ash plumes, avalanches, and ashfall during December 2022-March 2023

Fuego, one of three large stratovolcanoes overlooking the city of Antigua, Guatemala, has been vigorously erupting since January 2002, with recorded eruptions dating back to 1531 CE. Eruptive activity has included major ashfalls, pyroclastic flows, lava flows, and lahars. Frequent explosions with ash emissions, block avalanches, and lava flows have persisted since 2018. More recently, activity remained relatively consistent with daily explosions, ash plumes, ashfall, avalanches, and lahars (BGVN 48:03). This report covers similar activity during December 2022 through March 2023, based on information from the Instituto Nacional de Sismologia, Vulcanología, Meteorología e Hidrologia (INSIVUMEH) daily reports, Coordinadora Nacional para la Reducción de Desastres (CONRED) newsletters, and various satellite data.

Daily explosions reported throughout December 2022-March 2023 generated ash plumes to 6 km altitude that drifted as far as 60 km in multiple directions. The explosions also caused rumbling sounds of varying intensities, with shock waves that vibrated the roofs and windows of homes near the volcano. Incandescent pulses of material rose 100-500 m above the crater, which caused block avalanches around the crater and toward the Santa Teresa, Taniluyá (SW), Ceniza (SSW), El Jute, Honda, Las Lajas (SE), Seca (W), and Trinidad (S) drainages. Fine ashfall was also frequently reported in nearby communities (table 27). MIROVA (Middle InfraRed Observation of Volcanic Activity) analysis of MODIS satellite data showed frequent, moderate thermal activity throughout the reporting period; however, there was a brief decline in both power and frequency during late-to-mid-January 2023 (figure 166). A total of 79 MODVOLC thermal alerts were issued: 16 during December 2022, 17 during January 2023, 23 during February, and 23 during March. Some of these thermal evets were also visible in Sentinel-2 infrared satellite imagery at the summit crater, which also showed occasional incandescent block avalanches descending the S, W, and NW flanks, and accompanying ash plumes that drifted W (figure 167).

Table 27. Activity at Fuego during December 2022 through March 2023 included multiple explosions every hour. Ash emissions rose as high as 6 km altitude and drifted generally W and SW as far as 60 km, causing ashfall in many communities around the volcano. Data from daily INSIVUMEH reports and CONRED newsletters.

Month Explosions per hour Ash plume altitude (max) Ash plume distance (km) and direction Drainages affected by block avalanches Communities reporting ashfall
Dec 2022 1-12 6 km WSW, W, SW, NW, S, SE, NE, and E, 10-30 km Santa Teresa, Taniluyá, Ceniza, El Jute, Honda, Las Lajas, Seca, and Trinidad Panimaché I and II, Morelia, Santa Sofía, El Porvenir, Finca Palo Verde, Yepocapa, Yucales, Sangre de Cristo, La Rochela, Ceilán, San Andrés Osuna, and Aldea La Cruz
Jan 2023 1-12 5 km W, SW, NW, S, N, NE, E, and SE, 7-60 km Ceniza, Las Lajas, Santa Teresa, Taniluyá, Trinidad, Seca, Honda, and El Jute Panimaché I and II, Morelia, Santa Sofía, El Porvenir, Palo Verde, Yucales, Yepocapa, Sangre de Cristo, La Rochela, Ceylon, Alotenango, and San Andrés Osuna
Feb 2023 1-12 4.9 km SW, W, NW, and N, 10-30 km Santa Teresa, Taniluyá, Ceniza, Las Lajas, Seca, Trinidad, El Jute, and Honda Panimaché I and II, Morelia, Santa Sofía, Palo Verde, San Pedro Yepocapa, El Porvenir, Sangre de Cristo, La Soledad, Acatenango, El Campamento, and La Asunción
Mar 2023 3-11 5 km W, SW, NW, NE, N, S, SE, and E, 10-30 km Seca, Ceniza, Taniluyá, Las Lajas, Honda, Trinidad, El Jute, and Santa Teresa Yepocapa, Sangre de Cristo, Panimaché I and II, Morelia, Santa Sofía, El Porvenir, La Asunción, Palo Verde, La Rochela, San Andrés Osuna, Ceilán, and Aldeas
Figure (see Caption) Figure 166. Thermal activity at Fuego shown in the MIROVA graph (Log Radiative Power) was at moderate levels during a majority of December 2022 through March 2023, with a brief decline in both power and frequency during late-to-mid-January 2023. Courtesy of MIROVA.
Figure (see Caption) Figure 167. Frequent incandescent block avalanches descended multiple drainages at Fuego during December 2022 through March 2023, as shown in these Sentinel-2 infrared satellite images on 10 December 2022 (top left), 4 January 2023 (top right), 18 February 2023 (bottom left), and 30 March 2023 (bottom right). Gray ash plumes were also occasionally visible rising above the summit crater and drifting W, as seen on 4 January and 30 March. Avalanches affected the NW and S flanks on 10 December, the SW and W flanks on 18 February, and the NW, W, and SW flanks on 30 March. Images use Atmospheric penetration rendering (bands 12, 11, 8a). Courtesy of Sentinel Hub Playground.

Daily explosions ranged between 1 and 12 per hour during December 2022, generating ash plumes that rose to 4.5-6 km altitude and drifted 10-30 km in multiple directions. These explosions created rumbling sounds with a shock wave that vibrated the roofs and windows of homes near the volcano. Frequent white gas-and-steam plumes rose to 4.6 km altitude. Strombolian activity resulted in incandescent pulses that generally rose 100-500 m above the crater, which generated weak-to-moderate avalanches around the crater and toward the Santa Teresa, Taniluyá, Ceniza, El Jute, Honda, Las Lajas, Seca, and Trinidad drainages, where material sometimes reached vegetation. Fine ashfall was recorded in Panimaché I and II (8 km SW), Morelia (9 km SW), Santa Sofía (12 km SW), El Porvenir (8 km ENE), Finca Palo Verde, Yepocapa (8 km NW), Yucales (12 km SW), Sangre de Cristo (8 km WSW), La Rochela, Ceilán, San Andrés Osuna, and Aldea La Cruz. INSIVUMEH reported that on 10 December a lava flow formed in the Ceniza drainage and measured 800 m long; it remained active at least through 12 December and block avalanches were reported at the front of the flow. A pyroclastic flow was reported at 1100 on 10 December, descending the Las Lajas drainage for several kilometers and reaching the base of the volcano. Pyroclastic flows were also observed in the Ceniza drainage for several kilometers, reaching the base of the volcano on 11 December. Ash plumes rose as high as 6 km altitude, according to a special bulletin from INSIVUMEH. On 31 December explosions produced incandescent pulses that rose 300 m above the crater, which covered the upper part of the cone.

Activity during January 2023 consisted of 1-12 daily explosions, which produced ash plumes that rose to 4.2-5 km altitude and drifted 7-60 km in multiple directions (figure 168). Incandescent pulses of material were observed 100-350 m above the crater, which generated avalanches around the crater and down the Ceniza, Las Lajas, Santa Teresa, Taniluyá, Trinidad, Seca, Honda, and El Jute drainages. Sometimes, the avalanches resuspended older fine material 100-500 m above the surface that drifted W and SW. Ashfall was recorded in Panimaché I and II, Morelia, Santa Sofía, El Porvenir, Palo Verde, Yucales, Yepocapa, Sangre de Cristo, La Rochela, Ceylon, Alotenango, and San Andrés Osuna. Intermittent white gas-and-steam plumes rose to 4.5 km altitude and drifted W and NW.

Figure (see Caption) Figure 168. Webcam image showing an ash plume rising above Fuego on 15 January 2023. Courtesy of INSIVUMEH.

There were 1-12 daily explosions recorded through February, which generated ash plumes that rose to 4.2-4.9 km altitude and drifted 10-30 km SW, W, NW, and N. Intermittent white gas-and-steam emissions rose 4.5 km altitude and drifted W and SW. During the nights and early mornings, incandescent pulses were observed 100-400 m above the crater. Weak-to-moderate avalanches were also observed down the Santa Teresa, Taniluyá, Ceniza, Las Lajas, Seca, Trinidad, El Jute, and Honda drainages, sometimes reaching the edge of vegetated areas. Occasional ashfall was reported in Panimaché I and II, Morelia, Santa Sofía, Palo Verde, San Pedro Yepocapa, El Porvenir, Sangre de Cristo, La Soledad, Acatenango, El Campamento, and La Asunción. On 18 February strong winds resuspended previous ash deposits as high as 1 km above the surface that blew 12 km SW and S.

During March, daily explosions ranged from 3-11 per hour, producing ash plumes that rose to 4-5 km altitude and drifted 10-30 km W, SW, NW, NE, N, S, SE, and E. During the night and early morning, crater incandescence (figure 169) and incandescent pulses of material were observed 50-400 m above the crater. Weak-to-moderate avalanches affected the Seca, Ceniza, Taniluyá, Las Lajas, Honda, Trinidad, El Jute, and Santa Teresa drainages, sometimes reaching the edge of vegetation. Frequent ashfall was detected in Yepocapa, Sangre de Cristo, Panimaché I and II, Morelia, Santa Sofía, El Porvenir, La Asunción, Palo Verde, La Rochela, San Andrés Osuna, Ceilán, and Aldeas. Weak ashfall was recorded in San Andrés Osuna, La Rochela, Ceylon during 8-9 March. A lahar was reported in the Ceniza drainage on 15 March, carrying fine, hot volcanic material, tree branches, trunks, and blocks from 30 cm to 1.5 m in diameter. On 18 March lahars were observed in the Las Lajas and El Jute drainages, carrying fine volcanic material, tree branches and trunks, and blocks from 30 cm to 1.5 m in diameter. As a result, there was also damage to the road infrastructure between El Rodeo and El Zapote.

Figure (see Caption) Figure 169. Sentinel-2 infrared satellite image showing Fuego’s crater incandescence accompanied by a gas-and-ash plume that drifted SW on 25 March 2023. Images use bands 12, 11, 5. Courtesy of INSIVUMEH.

Geologic Background. Volcán Fuego, one of Central America's most active volcanoes, is also one of three large stratovolcanoes overlooking Guatemala's former capital, Antigua. The scarp of an older edifice, Meseta, lies between Fuego and Acatenango to the north. Construction of Meseta dates back to about 230,000 years and continued until the late Pleistocene or early Holocene. Collapse of Meseta may have produced the massive Escuintla debris-avalanche deposit, which extends about 50 km onto the Pacific coastal plain. Growth of the modern Fuego volcano followed, continuing the southward migration of volcanism that began at the mostly andesitic Acatenango. Eruptions at Fuego have become more mafic with time, and most historical activity has produced basaltic rocks. Frequent vigorous historical eruptions have been recorded since the onset of the Spanish era in 1524, and have produced major ashfalls, along with occasional pyroclastic flows and lava flows.

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).

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Bulletin of the Global Volcanism Network - Volume 16, Number 05 (May 1991)

Managing Editor: Lindsay McClelland

Aira (Japan)

Frequent explosions continue

Arenal (Costa Rica)

Strombolian activity and seismicity increase, then decline; block lava flows on S and SW flanks

Barren Island (India)

Explosions and lava flows from NE flank vent

Colima (Mexico)

Continued lava dome growth; increased avalanching follows earthquakes and tremor episodes

Deception Island (Antarctica)

Stronger earthquakes; anomalous water temperature in caldera center

Etna (Italy)

Strong degassing

Galeras (Colombia)

More seismic events but lower energy release; thermal activity remains moderate

Gede-Pangrango (Indonesia)

Brief earthquake swarm

Guallatiri (Chile)

Strong fumarolic activity

Irazu (Costa Rica)

Tectonic earthquake swarm

Kavachi (Solomon Islands)

Continued explosions from new island

Kilauea (United States)

E rift lava continues to flow through tubes into the ocean

Langila (Papua New Guinea)

Ash emission resumes; steady glow

Lascar (Chile)

High crater temperatures detected by satellite

Lewotobi (Indonesia)

Ash emission follows increased seismicity

Lokon-Empung (Indonesia)

Increased gas emission, then ash eruption

Manam (Papua New Guinea)

Ash ejection declines to weak vapor emission

Merapi (Indonesia)

Continued seismicity but lava dome unchanged

Obituary Notices (Unknown)

Deaths of three volcanologists (Maurice and Katia Krafft, Harry Glicken) at Unzen

Ontakesan (Japan)

Earthquake swarms and tremor; renewed steam emission from 1979 vent

Pinatubo (Philippines)

Major stratospheric cloud, pyroclastic flows, and new summit caldera; >300 killed by eruption and typhoon

Poas (Costa Rica)

Strong gas emission; rain adds water to nearly dry crater lake

Rabaul (Papua New Guinea)

Continued low-level seismicity; slight uplift

Rincon de la Vieja (Costa Rica)

More details on 8 May eruption and deposits

Ruiz, Nevado del (Colombia)

Frequent lithic ash emissions; occasional vigorous earthquake swarms

Sabancaya (Peru)

Vigorous Vulcanian activity; mudflows force daily clearing of river channel

San Jose (Chile-Argentina)

New fumarole field on upper S flank

Soputan (Indonesia)

Explosion sounds and incandescence; frequent seismicity

Stromboli (Italy)

More frequent explosions

Ulawun (Papua New Guinea)

Large gas plume and numerous weak earthquakes

Unzendake (Japan)

41 killed by pyroclastic flow from lava dome

Whakaari/White Island (New Zealand)

Ash emission from new vent; continued deformation



Aira (Japan) — May 1991 Citation iconCite this Report

Aira

Japan

31.5772°N, 130.6589°E; summit elev. 1117 m

All times are local (unless otherwise noted)


Frequent explosions continue

Frequent explosions continued through mid-June, with 17 recorded in May and 20 as of 19 June, bringing the year's total to 142. The highest ash clouds rose 3,000 m on 3 May and 2300 m on 18 June. An air shock from a 10 May explosion broke a window, the first explosion damage since December 1990.

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 caldera, along with several post-caldera cones. The construction of Sakurajima began about 13,000 years ago on the southern rim and built an island that was joined to the Osumi Peninsula during the major explosive and effusive eruption of 1914. Activity at the Kitadake summit cone ended about 4,850 years ago, after which eruptions took place at Minamidake. Frequent eruptions since the 8th century have deposited ash on the city of Kagoshima, located across Kagoshima Bay only 8 km from the summit. The largest recorded eruption took place during 1471-76.

Information Contacts: JMA.


Arenal (Costa Rica) — May 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)


Strombolian activity and seismicity increase, then decline; block lava flows on S and SW flanks

On 20 April, seismic explosion signals became moderately more frequent, and seismicity increased to >40 recorded earthquakes/day (RSN network). Seismicity was similar in May, with a daily average of 20 recorded earthquakes and a maximum of 43 (Univ Nacional network). Strombolian explosive activity was stronger, more voluminous, and more frequent, especially on 19-26 May when explosions vibrated windows and were heard 34 km SE (in Quesada). Several explosions were recorded at a seismic station 98 km away (Juan Diaz). Plumes rose to 1 km height above Crater C, depositing ash to Chambacú (17.5 km NE) and La Palma (4 km N). After 26 May, seismic and eruptive activity returned to normal levels. Gas emission continued with periodic, smaller explosions; plumes were carried predominantly to the NE, W, and SW. Block lava flows continued down the SW and S flanks, reaching 700 m elevation by the end of April.

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

Information Contacts: E. Fernández, J. Brenes, V. Barboza, and T. Marino, OVSICORI; R. Barquero, ICE.


Barren Island (India) — May 1991 Citation iconCite this Report

Barren Island

India

12.278°N, 93.858°E; summit elev. 354 m

All times are local (unless otherwise noted)


Explosions and lava flows from NE flank vent

Reports of strong emissions of "thick smoke" on 30 April prompted a visit to the island on 16 May by geologists from the GSI [see additional information about the start of the eruption in 16:10]. Lava poured continuously from a subsidiary vent on the NE face of the central volcanic cone, travelling N into a valley, then W along the course of the 1803 lava flow (figure 1). An area of ~800 x 200 m had been covered by fresh lava, with an average thickness of 5-6 m. Explosions at the vent occurred at intervals of several seconds, ejecting bombs, lapilli, and ash to heights >50 m.

Figure (see Caption) Figure 1. Geologic sketch map of Barren Island, by D. Haldar, T. Laskar, and J.K. Biswas. Courtesy of the GSI.

On 7 June at 1602, John Deed, pilot of Thai Airways International flight 307, observed a gray to dark-gray plume rising ~3 km above the summit and extending roughly 90 km NE. No lava was visible.

Geologic Background. Barren Island, a possession of India in the Andaman Sea about 135 km NE of Port Blair in the Andaman Islands, is the only historically active volcano along the N-S volcanic arc extending between Sumatra and Burma (Myanmar). It is the emergent summit of a volcano that rises from a depth of about 2250 m. The small, uninhabited 3-km-wide island contains a roughly 2-km-wide caldera with walls 250-350 m high. The caldera, which is open to the sea on the west, was created during a major explosive eruption in the late Pleistocene that produced pyroclastic-flow and -surge deposits. Historical eruptions have changed the morphology of the pyroclastic cone in the center of the caldera, and lava flows that fill much of the caldera floor have reached the sea along the western coast.

Information Contacts: Director General, GSI; Deputy Director General, GSI Eastern Region; T. Fox, ICAO.


Colima (Mexico) — May 1991 Citation iconCite this Report

Colima

Mexico

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

All times are local (unless otherwise noted)


Continued lava dome growth; increased avalanching follows earthquakes and tremor episodes

During the weeks preceding 5 June, volcanic seismicity recorded by RESCO remained at low levels, showing only a few avalanches/day. Poor visibility prevented daily visual observations from the city of Colima, but sporadic observations from sites near the volcano (Yerbabuena and La Joya) have shown strong fumarolic activity (mainly vapor and a small grayish plume) and continued growth of the dome extrusion.

On 6 June between about 0000 and 0200, a tremor episode was clearly recorded by station EZV7 (at Volcancito, ~1 km NE of the summit), but was barely detectable at other stations. Activity then returned to previous levels. A second tremor episode, much stronger and clearly recorded by several stations, occurred between about 1800 and 2100, after which seismicity again returned to relative quiet. The activity was interpreted as probably being of phreatic origin, given recent rainfall in the region. Witnesses about 13 km from the volcano (in the Tonila area) reported conspicuous incandescence at the crater.

A third seismic episode, on 8 June between about 2000 and 2200, consisted of four large, complex shallow earthquakes followed by almost monochromatic harmonic tremor. The caretaker at nearby La Joya reported hearing four explosions followed by strong sustained whistling. On 9 June, a few small closely-spaced B-type earthquakes seemed to mark the onset of another tremor episode, but it did not materialize and no further tremor activity had been recorded as of 13 June.

During the evening of 9 June, there was an increase in both the number and duration of avalanche events, which remained of small magnitude. Long-duration avalanches continued as of 13 June, but their numbers had decreased. Geophysicists noted that the increased number and duration of avalanches on 9 June was similar to that observed before the 16 April dome collapse. No deep seismicity, indicating stress at depth, has been detected, but the tremor, not previously observed, suggested changes in activity requiring careful monitoring.

Geologic Background. The Colima 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 scarp, 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 recorded 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: F. Alejandro Nava, Francisco Núñez-Cornú, Gilberto Ornelas-Arciniega, Ariel Ramírez-Vázquez, G.A. Reyes-Dávila, Hector Tamez, and R. García, CICT, Universidad de Colima; Z. Jiménez, I. Yokoyama, and S. de la Cruz-Reyna, UNAM.


Deception Island (Antarctica) — May 1991 Citation iconCite this Report

Deception Island

Antarctica

62.9567°S, 60.6367°W; summit elev. 602 m

All times are local (unless otherwise noted)


Stronger earthquakes; anomalous water temperature in caldera center

"Spanish-Argentine volcanological, geophysical, and geodetic scientists visited Deception Island during the 1990-91 austral summer (28 November 1990-13 March 1991) to provide measurements of the background activity. The present activity generally has remained unchanged from previous years.

"A digital microseismic network was installed to record the local and regional seismic activity for 3 months (figure 3). On 14 January, a M 3.2 earthquake was recorded on the NE sector of the island. After this event the seismic activity changed dramatically compared to that recorded during the previous 4 summers, increasing in magnitude and decreasing in frequency. In general, the epicenters are related to the 1970 eruption vents and they are associated with the fissure system (figure 4). Episodes of volcanic tremors were also recorded in Fumarole Bay.

Figure (see Caption) Figure 3. Daily number of seismic events recorded by a temporary digital microseismic network at Deception Island, 14 December 1990-23 February 1991. Courtesy of Ramón Ortiz.
Figure (see Caption) Figure 4. Epicenters of earthquakes (mb >1.2) recorded at Deception Island, 1 December 1990-23 February 1991. Courtesy of Ramón Ortiz.

"During the 1990-91 fieldwork, more than 300 gravimetric measurements were carried out, the magnetic map of the island was completed, and temperatures in fumaroles and hot soils were monitored. A volcanologically oriented GPS network was established and four GPS benchmarks (Argentine Station, Pendulum Cove, Fumarole Bay, and Whalers Bay) were measured with double-frequency receivers. Finally, three dry-tilt stations were installed in Telefon Bay (1970 eruption area), Crater Lake (1842 eruption sector), and Fumarole Bay.

"The Spanish Oceanographic vessel Las Palmas recorded water temperature and salinity distribution in Port Foster. An area of anomalous temperature was detected in the central part of the caldera."

Geologic Background. Ring-shaped Deception Island, at the SW end of the South Shetland Islands, NE of Graham Land Peninsula, was constructed along the axis of the Bransfield Rift spreading center. A narrow passageway named Neptunes Bellows provides an entrance to a natural harbor within the 8.5 x 10 km caldera that was utilized as an Antarctic whaling station. Numerous vents along ring fractures circling the low 14-km-wide island have been reported active for more than 200 years. Maars line the shores of 190-m-deep Port Foster caldera bay. Among the largest of these maars is 1-km-wide Whalers Bay, at the entrance to the harbor. Eruptions during the past 8,700 years have been dated from ash layers in lake sediments on the Antarctic Peninsula and neighboring islands.

Information Contacts: R. Ortiz, Museo Nacional de Ciencias Naturales, Spain; J. Viramonte, Univ Nacional de Salta, Argentina; R. Soto, Real Instituto y Observatorio de la Armada, Spain.


Etna (Italy) — May 1991 Citation iconCite this Report

Etna

Italy

37.748°N, 14.999°E; summit elev. 3357 m

All times are local (unless otherwise noted)


Strong degassing

Nearly continuous degassing was observed ... on 24 May. Northeast Crater's active vent was slightly incandescent and weakly emitting gas. Normal degassing, with sporadic rumbling, occurred at La Voragine, whose elliptical vent E of the central crater floor had reopened. The floors of Bocca Nuova and Southeast Crater were not visible due to their strong degassing.

Geologic Background. Mount Etna, towering above Catania on the island of Sicily, has one of the world's longest documented records of 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 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; Franco Emmi, Etna guide.


Galeras (Colombia) — May 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 seismic events but lower energy release; thermal activity remains moderate

The number of seismic events (high-frequency, low-frequency, and long-period) increased during May, while seismic energy release and reduced displacement decreased from April values (figures 40 and 41). The high-frequency activity (M 0.5-1.9) was centered W of the crater at 2-8 km depth. Tremor episodes were less frequent and had lower reduced displacements than in April. The tiltmeter 0.9 km E of the crater (Crater Station) continued to show deformation, with 20 µrad inflation (tangential component) in May, for a total inflation since September of 102 µrad. Other stations showed oscillations or only very low cumulative inflation.

Figure (see Caption) Figure 40. Daily number of high-frequency events (bottom) and energy release (top) at Galeras, May 1991. Courtesy of INGEOMINAS.
Figure (see Caption) Figure 41. Daily number of long-period events (bottom) and reduced displacement (top) at Galeras, May 1991. Courtesy of INGEOMINAS.

SO2 flux, measured by COSPEC, varied between low and moderate levels. Fumarole temperatures in Besolima fissure continued to decrease (436°C in May compared to 468°C in April), while temperatures remained fairly constant at Deformes (254°C compared to 250-265°C since December 1990) and Calvache (89°C compared to 88-92°C since December 1989).

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 open 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 eruptions since the time of the Spanish conquistadors.

Information Contacts: INGEOMINAS-OVP.


Gede-Pangrango (Indonesia) — May 1991 Citation iconCite this Report

Gede-Pangrango

Indonesia

6.786°S, 106.983°E; summit elev. 3026 m

All times are local (unless otherwise noted)


Brief earthquake swarm

Three shocks were felt (intensities I-III) on 30 April. Seismicity later returned to normal levels (10-15 events/day) during the second week of May (table 1).

Table 1. Number of earthquakes at Gede, May 1991. Courtesy of VSI.

Dates Deep Volcanic (VT) Shallow Volcanic Tectonic
01-04 May 1991 22 51 47
05-11 May 1991 197 635 9
12-18 May 1991 8 16 20
19-25 May 1991 23 8 9
26-31 May 1991 9 8 13

Geologic Background. The two peaks of the Gede-Pangrango volcanic complex overlook the major cities of Cianjur, Sukabumi, and Bogor, situated to the E, S, and NW, respectively. The summit of Gunung Pangrango, constructed over the NE rim of a 3 x 5 km caldera, forms the high point. Many lava flows are visible on the flanks of the younger Gunung Gede to the SE of Pangrango. The steep-walled summit crater has migrated about 1 km NNW over time. Two large debris-avalanche deposits are present on its flanks, one of which underlies the city of Cianjur. Activity recorded since the 16th century has typically consisted of small short explosive eruptions.

Information Contacts: W. Modjo, VSI.


Guallatiri (Chile) — May 1991 Citation iconCite this Report

Guallatiri

Chile

18.42°S, 69.092°W; summit elev. 6071 m

All times are local (unless otherwise noted)


Strong fumarolic activity

Two strongly active zones of fumaroles were observed during a summit visit on 2 November 1990. The more intense fumaroles, 80 m below the . . . summit, produced a plume 200 m high accompanied by a jet-engine noise. Some boiling mud pools were also seen. The second zone, on the S side of the volcano at ~3,000 m elev, contained about 10 fumaroles. The volcano was otherwise snow-covered.

Geologic Background. One of northern Chile's most active volcanoes, Volcán Guallatiri is a symmetrical ice-clad stratovolcano at the SW end of the Nevados de Quimsachata volcano group. It lies just W of the border with Bolivia and is capped by a central dacitic dome or lava complex, with the active vent situated on its S side. Thick lava flows are prominent on the lower N and W flanks of the andesitic-to-rhyolitic volcano. Minor explosive eruptions have been reported since the beginning of the 19th century. Intense fumarolic activity with "jet-like" noises continues, and numerous solfataras extend more than 300 m down the W flank.

Information Contacts: P. Vetsch and R. Haubrichs, SVG, Switzerland.


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

Irazu

Costa Rica

9.979°N, 83.852°W; summit elev. 3436 m

All times are local (unless otherwise noted)


Tectonic earthquake swarm

A large swarm of tectonic earthquakes was recorded just S of the crater from 2 January through the end of February. On 25 May, a rapid increase in the number of tectonic earthquakes marked the start of a second swarm in the same zone. A shock located about 1 km E of the crater was felt on 28 May (M 3.5), and two others centered near the crater were felt on 5 June at 0534 (M 3.5) and 0540 (M 3.2). Scientists believe that the seismicity may represent reactivation of the fault zone involved in the M [7.6] earthquake that occurred about 90 km ESE on 22 April. No changes in surface activity at the volcano were reported.

Geologic Background. The massive Irazú volcano in Costa Rica, immediately E of the capital city of San José, covers an area of 500 km2 and is vegetated to within a few hundred meters of its broad summit crater complex. At least 10 satellitic cones are located on its S flank. No lava effusion is known since the eruption of the 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 main crater, which contains a small lake. The first well-documented 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. Phreatic activity reported in 1994 may have been a landslide event from the fumarolic area on the NW summit (Fallas et al., 2018).

Information Contacts: R. Barquero, ICE; Mario Fernández, Red Sismológica Nacional (RSN), Univ de Costa Rica; ACAN news service, Panamá City, Panamá.


Kavachi (Solomon Islands) — May 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)


Continued explosions from new island

Pilots from Solomon Islands Airways reported that "the volcano is still active and increasing in size, though slowly" as of 14 June. Photographs taken on 12 May (by Rod Marsland, a Rabaul-based pilot) show the island to have been ~110 m in diameter, with a 15-m-diameter crater (assuming a height of 25 m based on an average of several visual estimates). Lava was being ejected to 30 m height in the photos. The new island's exact location remains uncertain.

Geologic Background. Named for a sea-god of the Gatokae and Vangunu peoples, Kavachi is 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: P. de Saint-Ours, RVO.


Kilauea (United States) — May 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)


E rift lava continues to flow through tubes into the ocean

Lava . . . continued to flow into the sea at two sites on the W side of the flow field (figure 79). More than 95% of the lava advanced through the Wahaula tube system, which divided a few hundred meters from the coast and fed the W and E entry points in the Poupou area. The W Poupou entry has been persistently explosive, continuing to throw tephra onto a large littoral cone on the old sea cliff. Growth of the littoral cone halted in May as erosional mechanisms (weather and cliff collapse) kept pace with explosive activity at the lava/sea interface. Below the old sea cliff, the W entry had built a small bench that extended <10-15 m into the ocean and was easily broken up by high surf. The E branch of the tube continued to feed the E Poupou entry points, which in previous months had built a sizeable 2-level bench below the old sea cliff. Throughout May, there were at least two major entry points off this bench. In early May, fluid lava flows broke out onto the E bench from its junction with the old sea cliff, covering the W side of the bench and entering the ocean. Successive overflows and inflation (perhaps caused by lava underplating) continued to build the lower bench, and by the end of the month it was within 1-2 m of the upper bench.

Figure (see Caption) Figure 79. Lava produced by Kīlauea's Kupaianaha vent, 1983-91. Arrows indicate flow in tubes and crosses at the coast mark sites where lava was entering the ocean in May 1991. Surface flows are shown above the tube's E and W branches. Courtesy of HVO.

Small lava flows broke out during May from the Wahaula tube between ~180 m (600 ft) elevation and the flat area near the coast. Two large flows were active. One (Waiaka) moved downslope atop the Wahaula tube in April, turning E off the tube near the coast and entering the ocean 17 April-2 May. This flow's activity declined during the first 2 weeks in May, and the flow was stagnant by the 16th. In mid-May, a new (Paradise) flow broke away from the Wahaula tube between 150 and 180 m elevation (500-600 ft) and established a new tube to the E. By the end of May, this flow was entering the ocean at the same site as the Waiaka flow.

A lava pond remained in the bottom of Pu`u `O`o crater through May. Kupaianaha's lava pond remained completely crusted over. Fume from the pond area diminished significantly, and the primary area of degassing shifted from the Kupaianaha shield area to a skylight in the tube system near 620 m (2,050 ft) elevation. In early May, all of the skylights along the Wahaula tube overflowed, closing some of those at lower elevations. The upper skylights remained open, and observations of times required for logs thrown into the upper skylight to reach the lower skylight yielded lava velocities of 1.4 m/s.

Geologic Background. Kilauea overlaps the E flank of the massive Mauna Loa shield volcano in the island of Hawaii. Eruptions are prominent in Polynesian legends; written documentation since 1820 records frequent summit and flank lava flow eruptions interspersed with periods of long-term lava lake activity at Halemaumau crater in the summit caldera until 1924. The 3 x 5 km caldera was formed in several stages about 1,500 years ago and during the 18th century; eruptions have also originated from the lengthy East and Southwest rift zones, which extend to the ocean in both directions. About 90% of the surface of the basaltic shield volcano is formed of lava flows less than about 1,100 years old; 70% of the surface is younger than 600 years. The long-term eruption from the East rift zone between 1983 and 2018 produced lava flows covering more than 100 km2, destroyed hundreds of houses, and added new coastline.

Information Contacts: T. Moulds, HVO.


Langila (Papua New Guinea) — May 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)


Ash emission resumes; steady glow

"After 7 months of quiescence, Crater 3 was reactivated. Resumption of activity, which started on 16 May, was manifested by the release of moderately thick white-to-grey vapour clouds with occasional blue vapours, and the recording of explosion earthquakes (2-20/day). After 18 May, deep rumbling noises and/or loud Vulcanian explosions were heard at the Cape Gloucester observation post . . . and light ashfalls occurred on the NW flank of the volcano. A weak steady red glow was observed over this crater at the end of the month.

"Activity at Crater 2 . . . did not seem to be affected. This crater kept on releasing moderate to weak emissions of white vapour and displayed a steady weak night glow."

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: D. Lolok and P. de Saint-Ours, RVO.


Lascar (Chile) — May 1991 Citation iconCite this Report

Lascar

Chile

23.37°S, 67.73°W; summit elev. 5592 m

All times are local (unless otherwise noted)


High crater temperatures detected by satellite

On 8 January, radiant flux from the crater was near the highest levels since 1984, as demonstrated by Open Univ researchers using data from Landsat TM bands 5 and 7 (1.55-1.75 and 2.08-2.35 µm wavelength, respectively) (figure 8). The January images are the third in a set of three night images that have been used to provide improved estimates of radiated power output at Lascar. Previous estimates were based on daylight images (Glaze and others, 1989). No reflected sunlight is mingled with the thermal signal in night images, yielding more reliable thermal radiance values.

Figure (see Caption) Figure 8. Spectral radiance from Lascar measured in 2 short-wavelength infrared bands, 2 December 1984-8 January 1991. Solid line, Landsat TM band 7 (2.08-2.35 µm); dashed line, Landsat TM band 5 (1.55-1.75 µm). Courtesy of D. Rothery and C. Oppenheimer.

The following is from D. Rothery and C. Oppenheimer. "Two of the night images are shown in figure 9. The 12 November 1989 image shows a strong equidimensional radiant anomaly in a position that corresponds to the lava dome, with some isolated radiant pixels just beyond the edges that are probably sites of fumaroles. The 26 March 1990 image shows a much reduced radiant anomaly, following the 20 February 1990 explosive eruption.

Figure (see Caption) Figure 9. Night images of Lascar's active dome on 12 November 1989 (left) and 26 March 1990 (right), recorded at 2.08-2.35 µm wavelengths (Landsat TM band 7). N is toward the top. The individual pixels are ~30 m across. An image recorded on 8 January 1991 is almost identical to the 12 November 1989 image. Courtesy of D. Rothery and C. Oppenheimer.

"Field observations at the summit of Lascar on 23-24 March and 4 April 1990 showed that there were sites of incandescence over regions of the collapsed dome, and that some fumaroles elsewhere were also incandescent. Temperatures of up to 940°C were estimated by the use of an infrared thermometer.

"The most recent image (8 January 1991, not shown here) is almost indistinguishable from the 12 November 1989 image, which suggests a return to earlier conditions."

Reference. Glaze, L.S., Francis, P.W., and Rothery, D.A., 1989, Measuring Thermal Budgets of Active Volcanoes; Nature, v. 338, p. 144-146.

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

Information Contacts: D. Rothery and C. Oppenheimer, Open Univ.


Lewotobi (Indonesia) — May 1991 Citation iconCite this Report

Lewotobi

Indonesia

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

All times are local (unless otherwise noted)


Ash emission follows increased seismicity

Ash was erupted to 800 m height, and deposited to 7 km NE and 4 km NW, on 11-13 May. Gas emission continued through the end of May, with 84 emission events recorded during the last week. Twelve shallow and seven deep volcanic earthquakes were also recorded during the last week in May.

Geologic Background. The Lewotobi edifice in eastern Flores Island is composed of the two adjacent Lewotobi Laki-laki and Lewotobi Perempuan stratovolcanoes (the "husband and wife"). Their summits are less than 2 km apart along a NW-SE line. The conical Laki-laki to the NW has been frequently active during the 19th and 20th centuries, while the taller and broader Perempuan has had observed eruptions in 1921 and 1935. Small lava domes have grown during the 20th century in both of the summit craters, which are open to the north. A prominent cone, Iliwokar, occurs on the E flank of Perampuan.

Information Contacts: W. Modjo, VSI.


Lokon-Empung (Indonesia) — May 1991 Citation iconCite this Report

Lokon-Empung

Indonesia

1.358°N, 124.792°E; summit elev. 1580 m

All times are local (unless otherwise noted)


Increased gas emission, then ash eruption

Gas emissions to 450 m height were observed during the morning and afternoon of 10 May. One week later (17-18 May), ash was erupted to 200-400 m height. Seismicity then decreased, with one deep and three shallow volcanic earthquakes recorded during the last week of May, down from six deep and nine shallow events the second week of the month.

Geologic Background. The Lokong-Empung volcanic complex, rising above the plain of Tondano in North Sulawesi, includes four peaks and an active crater. Lokon, the highest peak, has a flat craterless top. The morphologically younger Empung cone 2 km NE has a 400-m-wide, 150-m-deep crater that erupted last in the 18th century. A ridge extending 3 km WNW from Lokon includes the Tatawiran and Tetempangan peaks. All eruptions since 1829 have originated from Tompaluan, a 150 x 250 m crater in the saddle between Lokon and Empung. These eruptions have primarily produced small-to-moderate ash plumes that sometimes damaged croplands and houses, but lava-dome growth and pyroclastic flows have also occurred.

Information Contacts: W. Modjo, VSI.


Manam (Papua New Guinea) — May 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)


Ash ejection declines to weak vapor emission

". . . Manam has returned to the low non-erupting pattern displayed since early 1989. Both Main and Southern Craters released thin white vapour emissions. Grey ash-laden clouds commonly rose over Southern Crater until 20 May, associated with weak rumbling noises, presumably due to rockfalls within that crater. No night glow was reported from either crater. Tiltmeter measurements showed a slight radial inflation of ~1 µrad."

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: D. Lolok and P. de Saint-Ours, RVO.


Merapi (Indonesia) — May 1991 Citation iconCite this Report

Merapi

Indonesia

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

All times are local (unless otherwise noted)


Continued seismicity but lava dome unchanged

Seismic activity remained unchanged, with three volcanic earthquakes recorded during the first week in May, and seven during the last week in May. No changes were visible at the summit dome.

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

Information Contacts: W. Modjo, VSI.


Obituary Notices (Unknown) — May 1991 Citation iconCite this Report

Obituary Notices

Unknown

Unknown, Unknown; summit elev. m

All times are local (unless otherwise noted)


Deaths of three volcanologists (Maurice and Katia Krafft, Harry Glicken) at Unzen

Volcanology has lost three of its most valuable professionals and our network has lost three of our most faithful contributors. Maurice and Katia Krafft, 45 and 44, were natives of Alsace who blended art and science in unique ways. They were famous not only for their superb photography and books, but for the enthusiasm and humor that made friends for them throughout the world. Always a close team, they were scholarly, selective collectors of volcanological literature and art. They had recently compiled guidebooks to the Comores and Zaire, a history of volcanology, a beautiful book of still photographs, and an informative IAVCEI video on volcanic hazards.

Harry Glicken, 33, was a Californian working as a post-doctoral fellow at Tokyo Metropolitan University. His study of the 1980 debris avalanche at Mt. St. Helens was a landmark. His brief but geographically diverse research career took him to Indonesia, Alaska, the Caribbean, and Japan, where he worked on the 1888 Bandai eruption, and most recently on pyroclastic surge deposits from Oshima volcano. All three of these fine people had much yet to give to volcanology, and we mourn their loss.

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

Information Contacts:


Ontakesan (Japan) — May 1991 Citation iconCite this Report

Ontakesan

Japan

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

All times are local (unless otherwise noted)


Earthquake swarms and tremor; renewed steam emission from 1979 vent

Many earthquakes and tremor episodes have been detected by a seismometer near the volcano since April, bringing seismicity to its highest levels since the start of regular seismic monitoring in 1988. Earthquake swarms were recorded on 20, 23, and 27 April, and 12 and 13 May, with tremor on 27 and 28 April, and 2 and 12-16 May (figure 8). In mid-May, steam began to emerge from a vent formed in the last eruption (in 1979) that had remained quiet since soon after the eruption ended. Similar seismicity continued in June, and as of the 19th, 170 earthquakes and eight tremor episodes had been recorded.

Figure (see Caption) Figure 8. Daily number of earthquakes (top) and tremor episodes (bottom) at On-take, January-May, 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.


Pinatubo (Philippines) — May 1991 Citation iconCite this Report

Pinatubo

Philippines

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

All times are local (unless otherwise noted)


Major stratospheric cloud, pyroclastic flows, and new summit caldera; >300 killed by eruption and typhoon

After more than 2 months of increasing seismicity, deformation, and emission of small plumes, a series of strong explosions culminated in one of the largest eruptions of this century. The 15-16 June climactic phase lasted more than 15 hours, sending tephra to 30 km altitude, generating voluminous pyroclastic flows, and leaving a small caldera in the former summit region. Ten days later, the aerosol cloud formed a nearly continuous band that stretched 11,000 km from Indonesia to Central Africa. Timely evacuations saved many lives, but the combined effects of the eruption and a typhoon killed more than 300 people.

Figure (see Caption) Figure 4. Map of southern Luzon Is., showing some towns and river valleys.

Minor activity, April-May. Renewed activity was signaled by an explosion on 2 April, at the E end of Pinatubo's geothermal area, about 1.5 km NW of the summit (see 16:4). The explosion devastated about 1 km2 of forested land, stripped leaves and vegetation over several square kilometers, and ejected small steam/ash clouds, depositing ash 10 km away. About 2,000 people were evacuated from a zone of 10-km radius. After the explosion, a line of new fumaroles, roughly 1 km long with six main vents, had developed. Emissions, voluminous and at extremely high pressure, were carried W onto a zone of dead and dying vegetation. Respiratory and eye irritation forced about 5,000 W-flank residents to leave the area.

A seismometer installed on 5 April recorded 50-90 events/day through 10 May. Earthquakes (located beginning 6 May) were dominantly centered 4-8 km NW of the summit (figure 5) at 3-6 km depth, and had magnitudes of 0.1-1.5 (averaging about M 1.0).

Figure (see Caption) Figure 5. Epicenters of earthquakes (crosses) recorded near Pinatubo (dotted outline), 6-24 May (top), 25 May-5 June (middle), and 6-9 June (bottom) 1991. Courtesy of David Harlow.

Increased activity, late May-early June. Emissions from the vents increased in volume, with two large pulses observed on 25 and 26 May. Some ash was reported. SO2 flux, measured by COSPEC, rose from 500 t/d on 13 May to 5,000 t/d on 28 May, but dropped again to 1,700 t/d on 30 May and 1,800 t/d on 3 June. Seismicity continued slightly NW of the fumaroles (at 2-6 km depth), and an increasing number of earthquakes were recorded directly beneath the fumaroles (at 0-2 km depth) at the end of May. A "blast event" during the evening of 3 June produced ash and was immediately followed by harmonic tremor lasting 30 minutes. A similar tremor event was recorded the next day at around 1200. The SO2 flux had dropped to 280 t/d by 4 June.

Increased earthquake amplitudes and more frequent tremor were noted in early June. PHIVOLCS issued an Alert Level 3 announcement (indicating a possible major pyroclastic eruption within 2 weeks) on 5 June. Geologists interpreted the shallow seismicity and harmonic tremor to be caused by the upward movement of magma, and the drop in gas flux to suggest a blockage of escaping gas and an accompanying pressure buildup.

Seismicity increased over the next few days, from about 1,000 to 2,000 recorded earthquakes/day, associated with 25 microradians of tilt recorded on the upper E flank. Most epicenters were just NW of the summit. An explosion at 1640 on 7 June from the main vent near the center of the line of fumaroles (at the head of the Maronut River) ejected ash to 8,000 m height. The explosion occurred about 40 minutes into an hour-long episode of harmonic tremor. At 1700, PHIVOLCS announced an increase to Alert Level 4 (eruption possible within 24 hours) and ordered the evacuation of an area up to 21 km from the summit. About 12,000 residents were evacuated (from Zambales, Tarlac, and Pampanga Provinces).

Ash emission continued the next day, producing plumes about 5,000 m high and depositing ash to 25 km W. Helicopter reconnaissance in the morning confirmed the extrusion of a lava dome (100 x 60 m, and 30 m high) near the main vent on the volcano's N flank. The press reported that ash emission was continuing on 9 June (table 1) from two craters, with ash falling as far as the South China Sea (~35 km W). Seismographs near the volcano recorded continuous harmonic tremor.

Table 1. Eruptive episodes from Pinatubo, 9-17 June 1991. Times of eruption onsets are from PHIVOLCS and the USGS; times of initial satellite observations of eruptive episodes are shown in the second column. Plume altitudes are from NOAA. Altitudes given in the text are generally ground-based, and often higher than the NOAA estimates. Satellite data were compiled by James Lynch, NOAA/NESDIS, based on analysis of visible/infrared weather satellite imagery. Data in this table are very preliminary and will change as analyses of ground and satellite observations continue.

Date Eruption Time Detection Time Maximum Plume Altitude Direction of Movement Horizontal Extent (time after eruption)
09 Jun 1991 -- 0931 2 km NW less than 1 x 104 km2 (2 hrs)
11 Jun 1991 -- 1631 3.5 km WSW less than 1 x 104 km2 (2 hrs)
12 Jun 1991 0851 0931 17-19 km WSW 5.5 x 104 km2 (8 hrs)
12 Jun 1991 2250 2331 17-19 km WSW 1.1 x 105 km2 (8 hrs)
13 Jun 1991 0840 0931 17-19 km WSW 1 x 105 km2 (6 hrs)
14 Jun 1991 1309 1331 20-22 km WSW 5 x 104 km2 (4 hrs)
14 Jun 1991 1408 1431 20-22 km WSW 6 x 104 km2 (5 hrs)
14 Jun 1991 1853 1931 23-25 km WSW 7.5 x 104 km2 (6 hrs)
14 Jun 1991 2018 Indistinguishable from 1853 eruption on satellite images.
14 Jun 1991 2321 2331 23-25 km WSW 5 x 104 km2 (3 hrs)
15 Jun 1991 0114 0131 23-25 km WSW 1.5 x 105 km2 (4 hrs)
15 Jun 1991 0220 Indistinguishable from 0114 eruption on satellite images.
15 Jun 1991 0555 0631 20-22 km WSW 1.1 x 105 km2 (3 hrs)
15 Jun 1991 0611 Indistinguishable from 0555 eruption on satellite images.
15 Jun 1991 0809 0831 20-22 km WSW 1.1 x 105 km2 (3 hrs)
15 Jun 1991 0831 Indistinguishable from 0809 eruption on satellite images.
15 Jun 1991 1027 1031 35-40 km WSW 1 x 106 km2 (12 hrs)
15 Jun 1991 1027 1031 35-40 km WSW 1.5 x 106 km2 (18 hrs)
15 Jun 1991 1027 1031 35-40 km WSW 2.2 x 106 km2 (24 hrs)
15 Jun 1991 1027 1031 35-40 km WSW 2.7 x 106 km2 (36 hrs)
Initial, strongest phase of the climactic eruption, apparent on infrared imagery until 2131; column over the volcano reached 35-40 km height; extensive ash plume at 25-30 km. Ash from this phase comprised >95% of the extensive plume.
15 Jun 1991 1117 Indistinguishable from the 1027 eruption on satellite images.
15 Jun 1991 1221 Indistinguishable from the 1027 eruption on satellite images.
15 Jun 1991 1252 Indistinguishable from the 1027 eruption on satellite images.
15 Jun 1991 1342 Indistinguishable from the 1027 eruption on satellite images.
15 Jun 1991 1342 2231 26-28 km WSW --
The second phase of the climactic eruption continued until 0231 on 16 Jun, with a ball-shaped column over the volcano.
16 Jun 1991 -- 0331 23-25 km WSW --
The third phase, smaller than the second,, was characterized by a wedge-shaped plume from the volcano; apparent on satellite imagery until 0731.
16 Jun 1991 -- 1031 5-6 km WSW 1.5 x 104 km2 (3 hrs)
16 Jun 1991 -- 1231 5-6 km WSW less than 1 x 104 km2 (2 hrs)
16 Jun 1991 -- 1431 5-6 km WSW 1.5 x 104 km2 (3 hrs)
16 Jun 1991 -- 2031 4-5 km WSW less than 1 x 104 km2 (2 hrs)
17 Jun 1991 1300 1300 3.5 km WSW less than 1 x 104 km2 (2 hrs)

The evacuation of Clark Air Base (~15 km E of the volcano) was ordered by the U.S. Air Force at 0500 on 10 June. Almost 14,500 servicemen and their families were moved to Subic Bay Naval Base (30 km SSW), while 1,500 personnel remained at Clark. Preliminary hazard maps placed Clark Air Base at the E edge of pyroclastic-flow hazard zones, and flanked by potential mudflow hazard zones. Voluminous ash-laden steam clouds were emitted on 11 June.

Initial strong explosions, 12-early 15 June. A tephra column rose to about 20 km on 12 June, as an explosive episode at 0851 signalled the start of a major pyroclastic phase. The explosions were preceded by around 12-16 hours of continuous tremor and several smaller explosions. Numerous shocks had been felt by scientists working on the volcano earlier in the morning. Pyroclastic flows advanced at least 5 km and perhaps as much as 15 km down the Maronut, O'Donnell, and Marella Rivers on the NW, N, and SW flanks of the volcano, respectively. Six hundred of the remaining 1,500 military personnel at Clark Air Base were evacuated and thousands of people fled adjacent Angeles (population 300,000). All residents within a 20-km radius of the volcano were warned to leave.

The press reported that a smaller explosion occurred at 1149, then explosive activity declined after a few hours. Prevailing winds carried the eruption plume WSW, depositing ash more than 30 km away, but ashfall also apparently occurred N of the volcano, reportedly covering an aerial gunnery range. A small rain-induced mudflow occurred in the Maronut River valley at about 1830 on 12 June.

Weather satellite images showed that the eruption plume had separated from the volcano by 1330, after reaching about 330 km length (figure 6). By 1830, winds had sheared the plume into three different layers; material at 15-18 km altitude traveling WSW at 100 km/hour; at 6-9 km altitude, W at 55 km/hour; and at 6-9 km altitude, WNW at 35 km/hour. The Nimbus-7 satellite's TOMS instrument detected a significant amount of SO2 during its pass over the area about 2.5 hours after the onset of the explosion. Aviation authorities warned aircraft to avoid the plumes and closed several air routes W of the volcano (A461, A583, B460, R77, R93, R468, and R471).

Figure (see Caption) Figure 6. Infrared image from the NOAA 10 polar-orbiting weather satellite on 15 June at about 1830, showing the massive cloud from the climactic explosive phase. Temperature estimates suggest that the main body of the plume is at about 30 km altitude, with the eruption column directly over the volcano rising to 35-40 km. The apparent boundary between sections of the cloud is probably a sampling artifact. Material NE of the volcano is probably at a lower altitude than the bulk of the cloud to the W and SW. Numerous faint bands are evident within the plume in false-color versions of the image. Courtesy of NOAA/NESDIS.

Another large explosive pulse occurred between 2250 and 2305 on 12 June, producing an eruption column that briefly rose to 25 km altitude before declining to a sustained elevation of about 20 km. Tephra fell to the W, NW, and SW, with pumice lapilli falling to 15 km distance, and coarse sand-sized tephra to more than 20 km from the volcano. A similar explosion at 0840 on 13 June lasted for 8 minutes and sent an ash column to 25 km altitude, following about an hour of long-period earthquakes. Satellite images showed large plumes extending [WSW] from the volcano after both explosions.

After a lull of about 28 hours, explosions resumed at 1309 on 14 June, ejecting tephra to 25 km altitude. Intermittent small pulses occurred at 1353 and 1408. Pyroclastic flows in the NW flank's Maronut valley extended 15 km to Sitio Ugik, site of an evacuation camp until increased shallow seismicity prompted additional warnings just before the start of the latest series of explosions. Ash fell to the S, SE, and SW. Another explosion at 1853 sent ash to 24 km altitude and additional pyroclastic flows to the NW. Strong rains during several of the explosive pulses generated mudflows in drainages where pyroclastic-flow deposits and airfall tephra had previously been emplaced.

By 14 June, 79,000 people had been evacuated, including about 15,000 from Clark Air Base. Civil Defense officials reported that four people had been killed, 24 injured, and four were missing in the series of explosions.

A small explosion at 2018 on 14 June sent an ash cloud to 6 km. A period of harmonic tremor preceded a strong explosion at 2321 that produced a column to >20 km [see also 16:6]. Ashfall was reported in San Marcelino (25 km SW) and San Narciso (30 km WSW). Explosions on 15 June at 0114 and about 0220 produced pyroclastic flows that moved down the SW flank.

Climactic explosions, 15-16 June. An explosion at 0555 on 15 June fed a 20-22 km-high ash column [see also 16:6], marking the onset of strong sustained activity that included the climactic explosions and lasted until early 16 June. Effects of the eruption were exacerbated by heavy rains and strong winds from typhoon Yunya. Much of the summit region was removed by explosions or collapse, leaving a caldera 2-3 km in diameter centered slightly north of the former summit.

Pyroclastic flows generated by the first 15 June explosion extended 8-10 km down the N, NNE, NNW flanks. Additional explosions were reported at 0611, 0809, and 0831. Before the strongest activity began, PHIVOLCS expanded the radius of the official danger zone from 30 to 40 km and expressed concern about the possibility of a caldera-forming eruption. The expanded danger zone included Clark Air Base, Subic Naval Base, and their neighboring cities of Angeles and Olongapo. Additional evacuees brought the total to about 200,000. Several thousand military dependents were sent back to the United States.

Satellite data suggested that the climactic phase began with an explosion detected by a nearby barograph at 1027, and continued with recorded explosions at 1117, 1221, and 1252, although ground reports indicated that the strongest activity started with an explosion at 1342 (table 1). A column remained fixed over the volcano through 2131, feeding a massive cloud (figure 7). Comparison of satellite-derived eruption column temperatures with atmospheric temperature profiles from nearby radiosondes yielded an altitude of 25-30 km as the cloud spread WSW toward mainland Asia, and elevations of 35-40 km for the eruption column over the volcano. The maximum altitude of a plume can be underestimated by this technique if its temperature has not fully equilibrated with that of the surrounding air, or if more diffuse material extends above the plume's densest region. Satellite data suggest that more than 95% of the cloud was produced by this 12-hour phase. Visible-band images showed ejection of very dark-colored material throughout the day (from 0631 until 1631), in contrast to the light-colored plumes generated by other phases of the eruption. Noticeably less violent activity, seen on images from 2231 on 15 June until 0231 on 16 June, sustained a ball-shaped cloud over Pinatubo at 26-28 km altitude. Activity had declined further during a third period, from 0331 through 0731, when a wedge-shaped plume extended from the volcano.

Figure (see Caption) Figure 7. Infrared image from the NOAA 10 polar orbiting weather satellite on 15 June at about 1830, showing the massive cloud from the climactic explosive phase. Temperature estimates suggest that the main body of the plume is at about 30 km altitude, with the eruption column directly over the volcano rising to 35-40 km. The apparent boundary between sections of the cloud is probably a sampling artifact. Material NE of the volcano is probably at lower altitude than the bulk of the cloud to the W and SW (figure 7-19). Numerous faint concentric bands are evident within the plume in false-color versions of the image.

The bulk of the tephra fell to the SE, S, and SW, but airfall distribution was complicated by the typhoon's winds. Ash was carried by the typhoon to Palawan Island, 500 km SSW of the volcano. The press reported slight ashfall 150 km S (in Batangas Province) and clumps of mud fell on Clark Air Base, Angeles, and the volcano's W flank. Some falling pumice was reportedly apricot-sized. Pumice the size of marbles fell 33 km SSW (at Olongapo) where tephra fall reached 15-30 cm and more than 30 injuries and some deaths were reported. The cloud darkened Manila by 1545, 3 hours before its usual nightfall, although most ashfall amounts there were less than about 1 cm [see also 16:6].

The stratospheric cloud expanded rapidly WSW, and by 1030 the next day, its leading edge had reached the Bangkok area, more than 2,000 km away (figure 8). Preliminary Nimbus-7 satellite data showed very high concentrations of SO2 over a broad area (figure 9), with a total mass that appeared to be approximately double that of the 1982 injection from El Chichón. Light ashfalls were reported in southern Vietnam (from Da Nang to the Mekong Delta, 1,400 km W-1,800 km WSW), northern Borneo (Sabah and Sarawak, 1,000-2,000 km SW), and Singapore (2,500 km SW). By 23 June, a nearly continuous zone of enhanced SO2 as much as 30° wide extended from south of Indochina about 11,000 km to central Africa (figure 10). A small zone of apparent aerosol material had reached about 40°W. [See the Atmospheric Effects chapter for more information about the stratospheric cloud].

Figure (see Caption) Figure 8. Sketch of the major eruption cloud from Pinatubo as seen on satellite imagery on 16 June at about 1030, about 21 hours after the onset of strongest activity, and 1 hour before the SO2 data in figure 7-20. Courtesy of SAB.
Figure (see Caption) Figure 9. Preliminary SO2 data from the Total Ozone Mapping Spectrometer on the Nimbus-7 satellite, showing the major eruption cloud from Pinatubo on 16 June at about 1130, 22 hours after the start of the climactic explosions. Each number or letter represents the average SO2 value within an area 50 km across. 0 = 10-35 milliatmosphere-cm (100-350 ppm-m), 1 = 36-60 matm-cm, 2 = 61-85 matm-cm, etc.; 9 is followed by A, B, etc. Data were lost in the barred zone. Courtesy of Scott Doiron.
Figure (see Caption) Figure 10. Preliminary SO2 data from the Total Ozone Mapping Spectrometer on the Nimbus-7 satellite, showing the major eruption cloud from Pinatubo on 23 June, eight days after the climactic phase. The main body of the cloud, 11,000 km long, has reached central Africa, but a smaller advance segment apparently extended over the eastern Atlantic Ocean, bisected by the 30°W meridian. Only values > 18 matm-cm are shown. Highest values within the dense cloud reached about 75 matm-cm (over Saudi Arabia). Courtesy of Scott Doiron.

Smaller explosions continued during the next several days, but the strongest activity appeared to have ended, and people began to return to their homes. PHIVOLCS reported three periods of ash emission accompanied by tremor on 17 June. Satellite data revealed a small explosion at 1300 and a column to 5-6 km altitude was observed.The Worldwide Standardized Seismic Net detected shallow earthquakes near Pinatubo on 15 June at 1539 (M 4.9), 1831 (M 4.4), 1841 (M 5.4), 1911 (M 4.6), 1915 (M 5.5), and 2026 (M 4.7), on 16 June at 0349 (M 4.9), 0359 (M 4.8), 1008 (M 5.6), 1458 (M 4.9), 1751 (M 5.1), and 2127 (M 4.9), on 17 June at 0441 (M 5.3) and 2333 (M 4.6), and on 18 June at 1120 (M 4.6).

On 18 June geologists reported preliminary cumulative ashfall thicknesses of 15-30 cm at Clark Air Base, 15-30 cm in Olongapo, and an unconfirmed 35.5 cm in some parts of SW Luzon. At a site along the Abacan River, 37 km E of the summit, debris-flow deposits were sandwiched between a coarse basal layer and finer, sand-sized tephra. Several homes at this site had been inundated, and several others swept away by lateral stream erosion, with some resulting casualties. A similar situation was found at a second site along the Baluyot River, 34 km ESE of the summit. Several homes had been lost or buried by mud, but no deaths had occurred.

The leading edge of typhoon Yunya had reached the area by 14 June at about 2000, and strong storms began moving over the volcano at about 0500 on 15 June. The storm had weakened to light-moderate showers 24 hours later, but these persisted through the 16th. Heavy rains soaked the recently fallen tephra, adding substantially to its weight, and the wet tephra soon hardened to a concrete-like material, making it very difficult to remove. Numerous roof and building collapses resulted, and were responsible for many of the casualties from the combined effects of the eruption and typhoon. As of 19 June, the death toll had risen to more than 300.

The 15 June activity forced closure of Manila's international and domestic airports, which remained closed to arriving jet aircraft through 18 June. A limited number of outgoing flights were permitted beginning early 19 June, and propeller-driven aircraft, less vulnerable to the effects of ash clouds, offered limited air service to and from Manila. Preliminary reports indicate that [14] jets encountered ash during the eruption, most on 15 June (table 2). All landed safely, but some sustained engine and/or exterior damage.

Table 2. Preliminary summary of aircraft encounters with clouds from Pinatubo, 12-18 June 1991. Courtesy of T. Casadevall. [Including additional encounters reported in BGVN 16:07.]

Date Time Duration Location Comments
12 Jun 1991 -- 3 minutes Descent into Manila --
13 Jun 1991 0030 20 minutes S China Sea Electrostatic discharge on windscreen; no damage.
14 Jun 1991 early AM 15 minutes 750 km W of Pinatubo, 11 km altitude No significant damage.
14 or 15 Jun 1991 -- 29 minutes -- Two engines replaced; impact damage and ash buildup on engines.
15 Jun 1991 -- 15-20 minutes -- Flew through "heavy ash;" cockpit and cabin contaminated by ash.
15 Jun 1991 early AM -- 1,100 km W, 9 km altitude All four engines damaged.
15 Jun 1991 -- 12 minutes 10.5 km altitude Temperatures of all four engines rose and fluctuated; sparks from windows; ash hit aircraft; no significant exterior or engine damage.
15 Jun 1991 1600 -- Approach to Manila from S Vietnam Much ash in engines; exterior abrasion.
15 Jun 1991 evening -- Leaving Manila Black marks on exterior of left wing.
15 Jun 1991 2347 -- Approach to Manila from S Vietnam Ash, sulfur odor, electrostatic discharge, and blue-green light. No significant damage
16 Jun 1991 0130 25 minutes S China Sea Electrostatic discharge on windscreen; no damage.
16 Jun 1991 0310 30 minutes S China Sea Electrostatic discharge on windscreen; no damage.
17 Jun 1991 -- -- -- Engine 3 shutdown; heavy ash buildup in engines.
18 Jun 1991 0200 -- 11 km altitude Engine 1 stalled, engine 4 lost power; descended to 9 km to restart. Engine 1 replaced.

Further References. Pinatubo Volcano Observatory Team, 1991, Lessons from a major eruption: Mt. Pinatubo, Phillipines: EOS, v. 72, p. 545, 552-3, 555.

Woods, A. and Self, S., 1992, Thermal disequilibrium at the top of volcanic clouds and its effect on estimates of the column height: Nature, v. 355, p. 628-630.

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; R. Janda and J. Ewert, CVO; SAB; Scott Doiron, GSFC; Chris Newhall and Ellen Limburg-Santistevan, USGS Reston; David Harlow, USGS Menlo Park; T. Casadevall, USGS Denver; Nicholas Krull, FAA; Tom Fox, ICAO; NEIC; AP; UPI; Reuters.


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

Poas

Costa Rica

10.2°N, 84.233°W; summit elev. 2697 m

All times are local (unless otherwise noted)


Strong gas emission; rain adds water to nearly dry crater lake

Strong sulfur-gas emission continued from crater fumaroles in May. The crater lake, nearly dry since March, began to refill during the third week of May because of increased rainfall. Small pools coalesced to cover the entire crater floor, and warm mud was frequently ejected to several meters height from the center of the lake. The largest fumarole was in the crater's N sector, and other smaller ones were in the W and SE. Microseismicity decreased at the end of May and the volcano was considered by geologists to have returned to normal rainy season conditions. A new network of five digital seismometers was installed near the volcano by a joint RSN-French group.

Geologic Background. The broad 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 are easily accessible by vehicle from the nearby capital city of San José. A N-S-trending fissure cutting the complex stratovolcano extends to the lower N flank, where it has produced the Congo stratovolcano and several lake-filled maars. The southernmost of the two summit crater lakes, Botos, last erupted about 7,500 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 an eruption was reported in 1828. Eruptions often include geyser-like ejections of crater-lake water.

Information Contacts: R. Barquero, ICE.


Rabaul (Papua New Guinea) — May 1991 Citation iconCite this Report

Rabaul

Papua New Guinea

4.2459°S, 152.1937°E; summit elev. 688 m

All times are local (unless otherwise noted)


Continued low-level seismicity; slight uplift

"Seismicity was at a low level in May. The month's total number of earthquakes was 102 (compared to 126-140 over the last 3 months). Only five earthquakes were locatable, distributed on the NE and W sides of the caldera seismic zone. Levelling measurements on 24 May showed a slight uplift (3.5 mm at the SE end of Matupit Island)."

Geologic Background. The low-lying Rabaul caldera on the tip of the Gazelle Peninsula at the NE end of New Britain forms a broad sheltered harbor utilized by what was the island's largest city prior to a major eruption in 1994. The outer flanks of the asymmetrical shield volcano are formed by thick pyroclastic-flow deposits. The 8 x 14 km caldera is widely breached on the east, where its floor is flooded by Blanche Bay and was formed about 1,400 years ago. An earlier caldera-forming eruption about 7,100 years ago is thought to have originated from Tavui caldera, offshore to the north. Three small stratovolcanoes lie outside the N and NE caldera rims. Post-caldera eruptions built basaltic-to-dacitic pyroclastic cones on the caldera floor near the NE and W caldera walls. Several of these, including Vulcan cone, which was formed during a large eruption in 1878, have produced major explosive activity during historical time. A powerful explosive eruption in 1994 occurred simultaneously from Vulcan and Tavurvur volcanoes and forced the temporary abandonment of Rabaul city.

Information Contacts: D. Lolok and P. de Saint-Ours, RVO.


Rincon de la Vieja (Costa Rica) — May 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)


More details on 8 May eruption and deposits

The following, from the Univ Nacional, supplements last month's report from ICE.

A phreatic eruption on 8 May ejected lake sediments and ash, and produced small mudflows. The eruption followed several low-frequency earthquakes during the night of 6-7 May, and a low-frequency earthquake with a 155-second duration at 0811 on 7 May. Reports from residents of Dos Ríos de Upala (8 km NW) and from guards at Parque Nacional Rincón de la Vieja described an accompanying explosion and a 1-km-high light-colored plume with ash that traveled NW.

Seven low-frequency microearthquakes preceded the 8 May phreatic eruption. An earthquake that lasted 120 seconds, possibly associated with a small explosion, occurred 18 minutes prior to the eruption, and low-frequency tremor began 7 minutes before it.

The sound wave of the main explosion arrived at the seismometer (6 km SW) 6 seconds after the start of the eruption signal at 1017, and the instrument was saturated for 25 seconds. The subsequent 150-second signal was interpreted to record strong degassing and the initiation of mudflows. Low-frequency harmonic tremor was recorded for 30 minutes, gradually decreasing below detection limits. The main explosion produced a gray ash cloud, 5 km high, that was carried NW. Ash was deposited to 14 km NW from this (figure 1) and the approximately 10 small (columns

Figure (see Caption) Figure 1. Map showing deposits from the 8 May 1991 phreatic eruption at Rincón de la Vieja. Site numbers correspond to cross-sections in figures 2 and 3, and table 1. Courtesy of OVSICORI.

Table 1. Field observations of 8 May 1991 mudflow deposits from Rincón de la Vieja. Sites correspond to locations in figure 1. Courtesy of OVSICORI.

Site Distance Deposit width Channel width Max. flow height Deposit description
1 7.2 km 41 m 10 m 4-6 m 1.65 m of erosion.
2 6.6 km 185 m 12 m 2-3 m ~8 m deposited.
3 7.0 km 239 m -- 4-5 m 2-60 cm of fine (2-16 mm) material.
4 16.6 km -- -- 2.15 m Blocks (to 1.5 x 2.0 m) and tree trunks (50 cm diameter); 10-50-cm mantle of fine sediment.

Mudflows traveled down the N flank (along the Quebrada Azufrosa, and Río Pénjamo), destroying two small bridges and cutting off access to the towns of Buenos Aires (~12 km NE) and Gavilán. Several smaller mudflows traveled down tributaries to the Río Azul (also to the N). Erosion occurred predominantly between 1,500 and 500 m elevation. Field observations of the mudflow deposits were made at several sites (figures 2 and 3; table 1). Park guards reported small quantities of sediment transported by the Río Colorado (S flank), but no effects on the ecosystem were observed.

Figure (see Caption) Figure 2. Cross-section of 8 May 1991 Rincón de la Vieja mudflow deposits near a bridge over the Río Azul. Site location is marked in figure 1. Courtesy of OVSICORI.
Figure (see Caption) Figure 3. Cross-section of 8 May 1991 Rincón de la Vieja mudflow deposits near a bridge over the Río Pénjamo. Site location is marked in figure 1. Courtesy of OVSICORI.

Blocks (to 40 x 50 cm) with impact craters and ejected lake sediments were found near the summit during a 9 May visit. Acidity and sediment-fall had variable impacts on nearby vegetation, ranging to complete defoliation. Fumarolic activity continued, as evidenced by a strong sulfur odor, eye irritation, and breathing difficulties near the crater. Rain collected 3 km S had a pH of 3.85.

Seismicity declined to 9 low-frequency recorded earthquakes/day (9 May), with only sporadic (1-2/day) events on later days.

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: E. Fernández S., Jorge Brenes M., V. Barboza M., and Tomás Marino H., Observatorio Vulcanológico y Sismológico de Costa Rica, Univ Nacional.


Nevado del Ruiz (Colombia) — May 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)


Frequent lithic ash emissions; occasional vigorous earthquake swarms

Lithic ash emissions were frequent during May, depositing material to Manizales (30 km WNW) on 1 May. Short pulses of shallow tremor were associated with the emissions. High-frequency seismicity reached very high levels during a swarm on 8 May (figure 45), which included a M 2.1 earthquake, 2.5 km N of Arenas crater at 5 km depth. A similar swarm occurred on 14 May. Low-frequency seismicity was at a moderate level in May, with peaks of vigorous seismicity on 4 days. Deformation measurements showed no significant changes. The SO2 flux was low; the monthly average was 930 t/d, compared to ~2,740 t/d in April.

Figure (see Caption) Figure 45. Daily number of seismic events (bottom) and energy release (top) at Ruiz, May 1991. Solid line, high-frequency events; dashed line, low-frequency events. Courtesy of INGEOMINAS.

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) — May 1991 Citation iconCite this Report

Sabancaya

Peru

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

All times are local (unless otherwise noted)


Vigorous Vulcanian activity; mudflows force daily clearing of river channel

Strong Vulcanian explosions were observed during a visit on 13-19 April. The explosions, occurring every 20-30 minutes, lasted ~ 1 minute and produced 3-4-km-high, medium-gray ash clouds. Small avalanches were produced by falling blocks at the base of the eruptive columns. Quiet degassing continued between explosions. Light-gray ashfall was frequent during the visit, depositing 2 mm one night ~9.5 km SE of the summit (at Cajamarcana).

The volcano began erupting in late May 1990, reportedly ejecting ash to 7 km. By late June 1990 (15:7), activity had decreased to periodic explosions with weak ash columns 2-3 km high, but then increased slowly through November. High-frequency seismicity (>122 events recorded over one 2-week period) was usually centered ~ 10 km NE, although two earthquakes occurred under the crater. Several tremor episodes were recorded, starting in October.

The plume was black and heavy with ash during an overflight on 10 November, rising an estimated 5-8 km in distinct, but almost continuous pulses. Ash deposited on Hualca Hualca (4 km N) caused increased melting of the glaciers (estimated 20 cm of snow above the ice and berm) producing numerous mudflows. These moved down the N flank nightly, dumping an estimated 13,000 m3 of debris/day into the Majes River drainage system ~ 5 km N of the volcano. Construction crews cleared the channel daily. Airfall deposits were composed of 80% lithics and 20% glassy fragments and breadcrusted material. At one outcrop, the 1990 ash accumulations were 1 cm thick, overlying at progressively greater depth 30 cm soil, 2 cm ash, 40 cm soil, and another 2 cm ash. Eruptive activity observed on 22 December appeared about the same as it was on 10 November.

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: P. Vetsch and R. Haubrichs, SVG, Switzerland; N. Banks, CVO; Instituto Geofísico del Perú, Lima.


San Jose (Chile-Argentina) — May 1991 Citation iconCite this Report

San Jose

Chile-Argentina

33.789°S, 69.895°W; summit elev. 6070 m

All times are local (unless otherwise noted)


New fumarole field on upper S flank

A new fumarole field, 150 m below the rim on the S flank . . . was first observed in late February (figures 1 and 2). On 14 May, geologists from the Univ de Chile noted that the new activity was similar to that of earlier fumaroles associated with a small andesitic dome within the central crater.

Figure (see Caption) Figure 1.Sketch of view looking E at the San José complex, 14 May 1991. Vapor rises from within the crater and from the February 1991 fumarole field. Courtesy of O. González-Ferrán.
Figure (see Caption) Figure 2. Sketch map showing the summit region and craters of the San José complex, May 1991. Courtesy of O. González-Ferrán.

Although no earthquakes were detected at the volcano, an increase in seismicity was recorded by the Univ de Chile's seismic network throughout the roughly N-S fault zone that separates the Valle Central and the Cordillera Andina. Four events were recorded in February, 8 in March, 9 in April, and 14 in May, the largest (M 4.0 and M 3.5) on 8 and 11 April, respectively (figure 3).

Figure (see Caption) Figure 3. Sketch showing the location of San José and the epicenters of two large earthquakes, April 1991. Courtesy of O. González-Ferrán.

Geologic Background. Volcán San José lies along the Chile-Argentina border at the southern end of a volcano group that includes the Pleistocene volcanoes of Marmolejo and Espíritu Santo. The glaciated 6070-m-high Marmolejo stratovolcano is truncated by a 4-km-wide caldera, breached to the NW, that has been the source of a massive debris avalanche. San José is a 5856-m-high stratovolcano of Pleistocene-Holocene age with a broad 2 km x 0.5 km summit region containing overlapping and nested craters, pyroclastic cones, and blocky lava flows. Volcán la Engorda and Volcán Plantat, located SW of Marmolejo and NW of San Jose, have also been active during the Holocene. An 8-km-long lava flow traveled to the SW from the 1-km-wide summit crater of Espíritu Santo volcano, which overlaps the southern slope of Marmolejo. Mild phreatomagmatic eruptions were recorded from San José in the 19th and 20th centuries.

Information Contacts: O. González-Ferrán, Univ de Chile; P. Acevedo, Univ de la Frontera, Temuco.


Soputan (Indonesia) — May 1991 Citation iconCite this Report

Soputan

Indonesia

1.112°N, 124.737°E; summit elev. 1785 m

All times are local (unless otherwise noted)


Explosion sounds and incandescence; frequent seismicity

On 22-24 May... loud booming sounds and night glow were reported from the main crater. Up to 100 seismic events were recorded/6-hour period on 28 May.

Geologic Background. The Soputan stratovolcano on the southern rim of the Quaternary Tondano caldera on the northern arm of Sulawesi Island is one of Sulawesi's most active volcanoes. The youthful, largely unvegetated volcano is the only active cone in the Sempu-Soputan volcanic complex, which includes the Soputan caldera, Rindengan, and Manimporok (3.5 km ESE). Kawah Masem maar was formed in the W part of the caldera and contains a crater lake; sulfur has been extracted from fumarolic areas in the maar since 1938. Recent eruptions have originated at both the summit crater and Aeseput, a prominent NE-flank vent that formed in 1906 and was the source of intermittent major lava flows until 1924.

Information Contacts: W. Modjo, VSI.


Stromboli (Italy) — May 1991 Citation iconCite this Report

Stromboli

Italy

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

All times are local (unless otherwise noted)


More frequent explosions

The number of seismically recorded explosions increased briefly in late March and persistently from mid-April (figure 13). After mid-April, the number of earthquakes exceeding instrument saturation level decreased from an average of ~20/day since January to

Figure (see Caption) Figure 13. Average number of seismically recorded explosion events/hour at Stromboli, 15 March-15 May 1991. The mean value for the period is shown. Courtesy of M. Riuscetti.
Figure (see Caption) Figure 14. Daily number of seismometer-saturating events (lower curve); and average tremor amplitude (upper curve) at Stromboli, 15 March-15 May 1991. Courtesy of M. Riuscetti.

Volcano guides reported infrequent small explosive activity at the 3 craters during visits to the summit on 10, 15, and 16 April, and 1 May. In early May, the first complete gas sampling at Stromboli was made during an inter-explosive phase at fumaroles (410°C) on the NW rim of the active crater complex (table 1).

Table 1. Chemical composition (in volume %) of fumarolic gases from Stromboli, early May 1991. Courtesy of M. Martini.

Gas Volume %
H2O 60.29
CO2 29.68
H2S --
HCl 0.28
HF 0.041
H2 --
N2 6.90
O2 1.29
B 0.0014
Br 0.00017
CO 0.00007
NH4 0.00006
CH4 --

Local residents reported a significant increase in the number of explosions on 19 May, after several weeks of weak activity. During a visit to the summit on the evening of 21 May, frequent strong explosions were observed at craters 1 and 3, with large ejections of incandescent material. Thirty explosions were counted between 2000 on the 21st and 0600 the next day. Many ejecta fell onto the N flank's Sciara del Fuoco. Crater 2 and the small cones continuously emitted gas and vapor.

Geologic Background. Spectacular incandescent nighttime explosions at Stromboli have long attracted visitors to the "Lighthouse of the Mediterranean" in the NE Aeolian Islands. This volcano 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 scarp that formed about 5,000 years ago due to a series of slope failures which extends 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: M. Riuscetti, Univ di Udine; M. Martini, Univ di Firenze; H. Gaudru, Société Volcanologique Européenne (SVE), Switzerland.


Ulawun (Papua New Guinea) — May 1991 Citation iconCite this Report

Ulawun

Papua New Guinea

5.05°S, 151.33°E; summit elev. 2334 m

All times are local (unless otherwise noted)


Large gas plume and numerous weak earthquakes

"Activity remained at the low, non-erupting level displayed since January 1990, gently releasing a white vapour plume and generating an average of ~200 very small low-frequency earthquakes/day.

"An aerial inspection and ground deformation survey was carried out 14-16 May. The plume emitted by the crater, although of moderate volume, seemed rich in SO2 and could distinctly be seen stretching horizontally >40 km downwind. No significant changes were noted in summit crater morphology since the last inspection in May 1990, apart from a series of cracks on the terminal cone's upper W flank, suggesting a slight inward sagging of this side of the crater rim.

"EDM and dry tilt measurements suggest that no significant deformation has occurred over the last 12 months."

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

Information Contacts: D. Lolok and P. de Saint-Ours, RVO.


Unzendake (Japan) — May 1991 Citation iconCite this Report

Unzendake

Japan

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

All times are local (unless otherwise noted)


41 killed by pyroclastic flow from lava dome

On 3 June a large pyroclastic flow formed near the summit of Fugen-dake cone and moved down the E flank, reaching the outskirts of Kita-Kamikoba, 3 km from the 20 May lava dome. Forty people were killed, including volcanologists Harry Glicken, and Maurice and Katia Krafft. The pyroclastic flow and accompanying fires destroyed more than 56 houses and portions of Shimabara were blanketed with wet ash. A larger pyroclastic flow, on 8 June, destroyed an additional 73 houses in Shimabara and Fukae, but no injuries were reported. On 11 June, ejecta from an explosive event, not associated with pyroclastic-flow activity, damaged houses and car windows in Shimabara. Ashfall was reported 250 km to the NE. Dome extrusion and pyroclastic-flow activity at Unzen continued as of 24 June.

Premonitory activity and small ash emission. Increased seismicity was initially centered in Chijiiwa Bay, 13 km W, in November 1989, and gradually migrated E in July-October 1990, when seismicity increased further and the first volcanic tremor was recorded. Following several earthquake swarms, including one on 13-14 November (centered 5 km W of the summit at shallow depth), the volcano erupted on 17 November, weakly emitting ash to heights of 300-400 m from two newly formed vents (Jigoku-ato and Tsukumo-jima) within existing craters roughly 650 m E of the summit (figure 17). Ash emissions, tremor, and swarm activity quickly ceased, but steam emission continued and seismicity remained at high levels. An earthquake swarm occurred on 15 January and tremor resumed on 25 January (figure 18).

Figure (see Caption) Figure 17. Map showing the distribution of the three facies of the 3 June pyroclastic flow at Unzen. Crosses represent locations of recovered bodies. Data from Kyushu and Kagoshima universities. Body locations from The Japan Times. Courtesy of JMA.
Figure (see Caption) Figure 18. Daily number of earthquakes (top) and tremor episodes (bottom) at Unzen, January-18 June 1991. Arrows represent resumption of explosive activity on 12 February and dome appearance on 20 May 1991. Courtesy of JMA.

Phreato-magmatic activity, February-May. A second eruption on 12 February produced 500-m ash plumes from a new 50-m-long line of small vents (named Byobu-iwa) 170 m WSW of Jigoku-ato crater and 500 m E of the summit. Deposits of ash and lapilli reached 30 cm thick (10 m E of the vent) but no incandescence was seen and no juvenile material was detected in the ash. Frequent small ash emissions continued from Byobu-iwa vent and seismicity remained at high levels.

In early April, ash emissions resumed at Jigoku-ato vent, which widened and began to eject bombs. By mid-April, Jigoku-ato was the site of the most intense activity. The Geographic Survey Institute detected a summit offset of 11 cm to the W on 12 April.

Juvenile volcanic glass was first recognized on 12 May, although emissions remained small. Shallow microseismicity beneath Jigoku-ato rose sharply the next day, and EDM measurements showed rapid inflation of the summit region.

Debris flows, 15 and 19 May. Heavy rains on accumulated ash deposits triggered debris flows along the Mizunashi River on 15 and 19 May that destroyed two bridges and caused the temporary evacuation of about 1,300 people from Shimabara.

Lava extrusion, 20-23 May. On 20 May, high-silica dacite (table 6) lava extrusion began in Jigoku-ato crater. By the following day large fractures had appeared and the dome had separated into four parts. Debris flows along the Mizunashi River continued; after the fourth debris flow, at 0252 on 21 May, about 1,100 people were evacuated. Water level in the river dropped following a debris flow at 0445, and people were allowed to return home at 0555.

Table 6. Chemical composition of eruptive products from Unzen. Sample 1 - block from 24 May 1991 pyroclastic flow. Sample 2 - surface of lava dome 1 June 1991. Sample 3 - pumice block from 8 June 1991 pyroclastic flow. Sample 4 - 1792 lava flow. Total Fe as Fe2O3. Analyses performed by XRF at Kyushu Univ, normalized anhydrous.

Component Sample 1 Sample 2 Sample 3 Sample 4
SiO2 65.92 66.03 66.18 66.1
TiO2 0.66 0.64 0.65 0.65
Al2O3 15.46 15.47 15.46 15.8
Fe2O3* 4.18 4.14 4.07 4.28
MnO 0.09 0.08 0.08 0.09
MgO 2.39 2.37 2.34 2.24
CaO 4.90 4.98 4.86 4.56
Na2O 3.85 3.77 3.80 3.78
K2O 2.39 2.35 2.41 2.39
P2O5 0.16 0.17 0.16 0.13
Total 100.02 100.00 100.01 100.02

The dome continued to grow, reaching about 110 m diameter and 44 m height (a few tens of meters above the crater rim) on 23 May, when material began spalling from its margins down the steep outer slopes. Large blocks, to 5 m in diameter (60-70 m3 volume), were observed falling from the dome, and explosive events produced grayish clouds to 100 m height. The Geological Society of Japan reported that Fugen-dake cone had expanded 89 cm from 10 to 22 May (figure 19), and that the lava dome front was moving E at 70-80 cm/hour.

Figure (see Caption) Figure 19. Results of EDM measurements between points T1 and F2 on the S flank of Fugen-dake cone at Unzen, 10 May-8 June. Shortening of this line reflects expansion of the cone as F2 moves toward T1. Data from the GSJ. Courtesy of JMA.

Pyroclastic flows begin, 24 May. At 0810 on 24 May, a large explosion was heard as a portion of the lava dome collapsed, producing a pyroclastic flow that traveled about 1 km down the E flank to within 2 km of Kita-Kamikoba. The flow discolored trees and transported blocks 10 m in diameter. Smaller collapse/pyroclastic flow events occurred at 1755 and 1920.

About 1,300 people were evacuated on 24 May because of increasing mudflow hazard along the Mizunashi River, as volcanic debris accumulated and heavy rains continued. During the evening, workers dredged material from above a dam (2 km from the summit) constructed after the November 1990 eruption to reduce the mudflow danger. By 0600 the following morning the evacuation recommendation was withdrawn and residents were allowed to return home.

Heavy rain on 25 May made observation difficult, but dust and ash from a pyroclastic flow was seen at around 1145. The lava dome continued to grow at an estimated rate of 80,000 m3/day. Rain continued on 26 May, and ash plumes 600 m high were reported, but little is known about activity at the dome.

At 1130 on 26 May, a pyroclastic flow traveled into the Mizunashi valley, injuring a worker (2.6 km from the crater) who had climbed up from the dredging area for better views of the volcano. The flow traveled 3 km, to within 600 m of Kita-Kamikoba, and deposited ash 5 km E on Shimabara. Bursts of tremor accompanied this flow and the prior pyroclastic flow at 1113, suggesting that the tremor signal could be used to detect and count pyroclastic flows (figure 20).

Figure (see Caption) Figure 20. Daily number of pyroclastic flows determined seismically at Unzen, 20 May-18 June 1991. Number represents counts of tremor lasting >30 seconds with amplitudes larger than an empirical threshold. Courtesy of JMA.

The 1130 pyroclastic flow, and the continued accumulation of debris in the river channel, prompted the evacuation of around 3,500 people from the surrounding valley. Several mudflows were reported during that evening, and rain soaked previously-deposited dust and ash to create more mud. Many people were allowed to return home the next day when the rain ceased.

Observations of the dome (27 May) revealed a v-shaped vent, from which a 60-m-wide tongue of lava was being extruded. Pyroclastic flows spawned from the margins of the lava tongue traveled along E and SE paths that joined at mid-flank. On 28 May, fluid (no longer blocky) lava overflowed the crater's E rim and moved down the outer flank, reaching about 700 m elevation by midnight.

The 26 May evacuation order was extended. Pyroclastic flows continued to form, reaching to within 500 m of Kita-Kamikoba on the 29th, and within 200 m on the 30th. Trees in the valley were burned to charcoal, suggesting that flow temperatures had increased. On 31 May, lava was observed emerging from the vent, and then avalanching 1 km down the steep slope in 30 seconds, producing a roaring sound that was heard 6 km E in Shimabara.

Pyroclastic flow kills 41, 3 June. At about 1610 on 3 June, an audible explosion and 6 minutes of recorded tremor signaled the collapse of a portion of the summit dome and lava flow. The resulting large pyroclastic flow moved down the Mizunashi River at reported speeds of up to 100 km/hour and entered Kita-Kamikoba. The core of the pyroclastic flow traveled about 3.2 km (figure 17) over a vertical drop of 1,000 m. An ash cloud surge apparently detached from the flow and traveled an additional 0.8 km, knocking down trees, burning houses, and leaving deposits up to 30 cm thick. Blasted zones occurred in places along the margins of the flow and surge. The volume of the deposits was estimated to be 7.3 x 105 m3.

All of the casualties were within an evacuated "forbidden" zone and all were caused by the detached surge. The victims consisted of: 15 members of the Japanese press, three volcanologists, four taxi drivers, a few local residents, and members of police and fire brigades. Of the 41 people listed dead, 27 bodies were recovered, four remain missing and are presumed dead, and 10 died in hospitals from burns.

Pyroclastic flows continued over the next several days, hampering rescue and recovery efforts, but were less frequent. Lava effusion occurred at a constant rate of around 105 m3/day, producing a tongue 70-80 m wide and 100 m long by 5 June. Periodic explosions produced gas/ash columns 100 m high. One helicopter was grounded due to ash-related engine problems on 6 June. On 7 June, the evacuated zone was widened to include an additional 1,500 people, bringing the total number of evacuees to more than 7,200, and a fine of $75 was imposed on people entering the evacuated area. Observers reported that despite continued growth of the dome it had not yet recovered half of its pre-3 June size.

Large pyroclastic flow, 8 June. An increase in pyroclastic flow activity occurred in the afternoon of 8 June, with numerous small flows over a 5-hour period leading to a larger flow at 1723. The evacuation zone was again widened, to include parts of Fukae, bringing the total number evacuated to about 8,500. Multiple pyroclastic flows began at 1930. Finally, from 1951 to 2016, a continuous series of pyroclastic flows traveled 5.5 km down the Mizunashi River, through parts of Shimabara and Fukae, to within 50 m of Highway 57 (2 km from the sea). Deposits reached 100 m wide and had an estimated volume of ~1.0 x 106 m3. The flows destroyed 73 houses, but no injuries were reported.

Activity continued, with an explosion (detected by infrared camera) at 2007 and a small pyroclastic flow at 2120. Ashfall from the explosion was deposited 90 km NE (in Hida) and 80 km N (in Fukuoka). Clasts 5 cm in diameter fell to 5 km.

Evacuation zones were expanded on 9 June and again on 10 June, to a total of 9,800 people. Mudflow hazards were considered high given the more than 1 x 106 m3 of debris that completely filled the Mizunashi River channel and covered the surrounding valley.

Large explosive event, 11 June. By 11 June, a 50-m-wide dome partly filled the large horseshoe-shaped depression that formed 8 June on the E side of the summit dome. A large explosive ash emission, not associated with pyroclastic-flow formation, occurred at 2359-0003, accompanied by strong tremor and sharp deflation (10 µrad; figure 21). Houses, car windows, and two helicopters were damaged by tephra clasts (d = 1.0-2.0 g/cm3) >=15 cm in diameter that fell to 3.5 km (figure 22). Ash was deposited to 130 km NE (Oita) and 250 km NE (Matsuyama, Shikoku Is.). Two hours after the explosion, 25 µrad of inflation was recorded over a 10-hour period, suggesting rising magma.

Figure (see Caption) Figure 21. Change of ground tilt 850 m W of Unzen's dome, 6-15 June, 1991. Arrows represent large eruptive events on 8 and 11 June. E up corresponds to inflation of the summit area. Data from the Joint Monitoring Group of National Universities. Courtesy of JMA.
Figure (see Caption) Figure 22. Isopleth map of maximum pumice clast sizes from the explosion at Unzen on 11 June at 2359. Data from Kyushu and Kagoshima universities. Courtesy of JMA.

Continued activity. Dome extrusion and pyroclastic-flow formation continued at Unzen as of 24 June. On 14 June, the dome was 100 m wide and 50 m high; it grew another 20 m in height by 16 June. Cracks in the dome emitted gas to 200-300 m height, and periodic explosions produced 1-km-high ash columns. The evacuation area was again expanded on 17 June, bringing the total number of evacuees to more than 10,000.

Actions by Coordinating Committee. The following is from Daisuke Shimozuru, Chairman of the Coordinating Committee for the Prediction of Volcanic Eruptions. "The Japan Meteorological Agency (JMA) dispatched an observation team in mid-October to intensify seismic observation, assisting JMA's local observatory. Early in November, volcanic tremors were observed. We were very worried about an impending eruption, and asked the Ministry for financial aid for observations by university scientists. On 9 November, the Ministry decided to provide financial aid for observations by 6 universities. The university team set up seismic and deformation nets, in cooperation with Shimabara Volcano Observatory of Kyushu Univ." A chronology of Unzen's activity and statements and warnings issued by the Coordinating Committee is shown in table 7 (see following report).

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; D. Shimozuru, Tokyo Univ of Agriculture; H. Kamata, GSJ; Public Works Research Institute, Ministry of Construction; K. Uto, USGS; M. Takahashi, SI; Kyodo News Service; The Japan Times; Asahi Shinbun; Yomiuri Shinbun; AP; UPI; Reuters.


Whakaari/White Island (New Zealand) — May 1991 Citation iconCite this Report

Whakaari/White Island

New Zealand

37.52°S, 177.18°E; summit elev. 294 m

All times are local (unless otherwise noted)


Ash emission from new vent; continued deformation

Ash-laden steam emission was reported starting 23 April and continued as of 27 May. An 18 May visit revealed that activity was centered at a newly formed vent in the NE part of 1978/91 Crater (figure 13), near a zone of hot ground first observed on 21 April. Considerable ash accumulation had already occurred in the surrounding area.

Figure (see Caption) Figure 13. Sketch map of White Island on 27 May 1991, showing the new May 91 Vent. Dots mark deformation bench marks. Contour interval, 40 m. Courtesy of DSIR.

During 27May fieldwork, the new vent (named May 91) almost continuously (>=1 pulse/second) emitted a column of gas and minor ash 500-600 m high, depositing dry material, plus some moist sub-millimeter aggregates. The vent, against the NE crater wall, was surrounded by a tuff cone 35-40 m in diameter and 8-10 m high, but no ballistic ejecta were visible. Orca and TV1 Craters quietly emitted weak steam.

Up to 95 mm of ash had accumulated since 21 May at a site 125 m SSE of May 91 vent, of which at least 25 mm was from the new vent. Tephra had infilled the small lake in the vicinity of R.F. Vent (near the SE wall of 1978/90 Crater), and small mudflows traveled across the crater floor. Ash contained a high proportion of fresh material, but lacked vesiculated clasts.

Little change was observed at the 40-45-m-deep collapse pit NW of formerly active Donald Duck Crater. Two passages (20-30 m wide) led from the pit; one connected to Donald Duck Crater (to the SE), and the other headed at least 50-60 m N towards Noisy Nellie. The SE passage contained large sulfur stalactites and stalagmites.

Deformation measurements on 27 May showed that subsidence centered at Donald Mound and Noisy Nellie continued, but at lower rates than the last measurements on 13 February. Minor uplift was measured ~200 m S of Donald Mound.

Seismicity (typically small A- and B-type earthquakes) remained at low levels since 21 April, with periods of 2-3 days without recorded events. One uncharacteristically large E-type event, similar to an event preceding the formation of TV1 Crater (BGVN 15:09) was recorded at 0538 on 23 May. Weak low-frequency tremor has been recorded since 10 May.

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

Information Contacts: B. Scott and B. Houghton, DSIR Geology & Geophysics, Rotorua; J. Cole, Univ of Canterbury, Christchurch.

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