Ebeko, located on the N end of Paramushir Island in the Kuril Islands, consists of three summit craters along a SSW-NNE line at the northern end of a complex of five volcanic cones. Eruptions date back to the late 18th century and have been characterized as small-to-moderate explosions from the summit crater, accompanied by intense fumarolic activity. The current eruption period began in June 2022 and has recently consisted of frequent explosions, ash plumes, and thermal activity (BGVN 47:10). This report covers similar activity during October 2022 through May 2023, based on information from the Kamchatka Volcanic Eruptions Response Team (KVERT) and satellite data.

Activity during October consisted of explosive activity, ash plumes, and occasional thermal anomalies. Visual data by volcanologists from Severo-Kurilsk showed explosions producing ash clouds up to 2.1-3 km altitude which drifted E, N, NE, and SE during 1-8, 10, 16, and 18 October. KVERT issued several Volcano Observatory Notices for Aviation (VONA) on 7, 13-15, and 27 October 2022, stating that explosions generated ash plumes that rose to 2.3-4 km altitude and drifted 5 km E, NE, and SE. Ashfall was reported in Severo-Kurilsk (Paramushir Island, about 7 km E) on 7 and 13 October. Satellite data showed a thermal anomaly over the volcano on 15-16 October. Visual data showed ash plumes rising to 2.5-3.6 km altitude on 22, 25-29, and 31 October and moving NE due to constant explosions.

Similar activity continued during November, with explosions, ash plumes, and ashfall occurring. KVERT issued VONAs on 1-2, 4, 6-7, 9, 13, and 16 November that reported explosions and resulting ash plumes that rose to 1.7-3.6 km altitude and drifted 3-5 km SE, ESE, E, and NE. On 1 November ash plumes extended as far as 110 km SE. On 5, 8, 12, and 24-25 November explosions and ash plumes rose to 2-3.1 km altitude and drifted N and E. Ashfall was observed in Severo-Kurilsk on 7 and 16 November. A thermal anomaly was visible during 1-4, 16, and 20 November. Explosions during 26 November rose as high as 2.7 km altitude and drifted NE (figure 45).

Figure 45. Photo of an ash plume rising to 2.7 km altitude above Ebeko on 26 November 2022. Photo has been color corrected. Photo by L. Kotenko, IVS FEB RAS.

Explosions and ash plumes continued to occur in December. During 1-2 and 4 December volcanologists from Severo-Kurilsk observed explosions that sent ash to 1.9-2.5 km altitude and drifted NE and SE (figure 46). VONAs were issued on 5, 9, and 16 December reporting that explosions generated ash plumes rising to 1.9 km, 2.6 km, and 2.4 km altitude and drifted 5 km SE, E, and NE, respectively. A thermal anomaly was visible in satellite imagery on 16 December. On 18 and 27-28 December explosions produced ash plumes that rose to 2.5 km altitude and drifted NE and SE. On 31 December an ash plume rose to 2 km altitude and drifted NE.

Figure 46. Photo of an explosive event at Ebeko at 1109 on 2 December 2022. Photo has been color corrected. Photo by S. Lakomov, IVS FEB RAS.

Explosions continued during January 2023, based on visual observations by volcanologists from Severo-Kurilsk. During 1-7 January explosions generated ash plumes that rose to 4 km altitude and drifted NE, E, W, and SE. According to VONAs issued by KVERT on 2, 4, 10, and 23 January, explosions produced ash plumes that rose to 2-4 km altitude and drifted 5 km N, NE, E, and ENE; the ash plume that rose to 4 km altitude occurred on 10 January (figure 47). Satellite data showed a thermal anomaly during 3-4, 10, 13, 16, 21, 22, and 31 January. KVERT reported that an ash cloud on 4 January moved 12 km NE. On 6 and 9-11 January explosions sent ash plumes to 4.5 km altitude and drifted W and ESE. On 13 January an ash plume rose to 3 km altitude and drifted SE. During 20-24 January ash plumes from explosions rose to 3.7 km altitude and drifted SE, N, and NE. On 21 January the ash plume drifted as far as 40 km NE. During 28-29 and 31 January and 1 February ash plumes rose to 4 km altitude and drifted NE.

Figure 47. Photo of a strong ash plume rising to 4 km altitude from an explosive event on 10 January 2023 (local time). Photo by L. Kotenko, IVS FEB RAS.

During February, explosions, ash plumes, and ashfall were reported. During 1, 4-5 and 7-8 February explosions generated ash plumes that rose to 4.5 km altitude and drifted E and NE; ashfall was observed on 5 and 8 February. On 6 February an explosion produced an ash plume that rose to 3 km altitude and drifted 7 km E, causing ashfall in Severo-Kurilsk. A thermal anomaly was visible in satellite data on 8, 9, 13, and 21 February. Explosions on 9 and 12-13 February produced ash plumes that rose to 4 km altitude and drifted E and NE; the ash cloud on 12 February extended as far as 45 km E. On 22 February explosions sent ash to 3 km altitude that drifted E. During 24 and 26-27 February ash plumes rose to 4 km altitude and drifted E. On 28 February an explosion sent ash to 2.5-3 km altitude and drifted 5 km E; ashfall was observed in Severo-Kurilsk.

Activity continued during March; visual observations showed that explosions generated ash plumes that rose to 3.6 km altitude on 3, 5-7, and 9-12 March and drifted E, NE, and NW. Thermal anomalies were visible on 10, 13, and 29-30 March in satellite imagery. On 18, 21-23, 26, and 29-30 March explosions produced ash plumes that rose to 2.8 km altitude and drifted NE and E; the ash plumes during 22-23 March extended up to 76 km E. A VONA issued on 21 March reported an explosion that produced an ash plume that rose to 2.8 km altitude and drifted 5 km E. Another VONA issued on 23 March reported that satellite data showed an ash plume rising to 3 km altitude and drifted 14 km E.

Explosions during April continued to generate ash plumes. On 1 and 4 April an ash plume rose to 2.8-3.5 km altitude and drifted SE and NE. A thermal anomaly was visible in satellite imagery during 1-6 April. Satellite data showed ash plumes and clouds rising to 2-3 km altitude and drifting up to 12 km SW and E on 3 and 6 April (figure 48). KVERT issued VONAs on 3, 5, 14, 16 April describing explosions that produced ash plumes rising to 3 km, 3.5 km, 3.5 km, and 3 km altitude and drifting 5 km S, 5 km NE and SE, 72 km NNE, and 5 km NE, respectively. According to satellite data, the resulting ash cloud from the explosion on 14 April was 25 x 7 km in size and drifted 72-104 km NNE during 14-15 April. According to visual data by volcanologists from Severo-Kurilsk explosions sent ash up to 3.5 km altitude that drifted NE and E during 15-16, 22, 25-26, and 29 April.

Figure 48. Photo of an ash cloud rising to 3.5 km altitude at Ebeko on 6 April 2023. The cloud extended up to 12 km SW and E. Photo has been color corrected. Photo by L. Kotenko, IVS FEB RAS.

The explosive eruption continued during May. Explosions during 3-4, 6-7, and 9-10 May generated ash plumes that rose to 4 km altitude and drifted SW and E. Satellite data showed a thermal anomaly on 3, 9, 13-14, and 24 May. During 12-16, 23-25, and 27-28 May ash plumes rose to 3.5 km altitude and drifted in different directions due to explosions. Two VONA notices were issued on 16 and 25 May, describing explosions that generated ash plumes rising to 3 km and 3.5 km altitude, respectively and extending 5 km E. The ash cloud on 25 May drifted 75 km SE.

Thermal activity in the summit crater, occasionally accompanied by ash plumes and ash deposits on the SE and E flanks due to frequent explosions, were visible in infrared and true color satellite images (figure 49).

Figure 49. Infrared (bands B12, B11, B4) and true color satellite images of Ebeko showing occasional small thermal anomalies at the summit crater on 4 October 2022 (top left), 30 April 2023 (bottom left), and 27 May 2023 (bottom right). On 1 November (top right) ash deposits (light-to-dark gray) were visible on the SE flank. An ash plume drifted NE on 30 April, and ash deposits were also visible to the E on both 30 April and 27 May. Courtesy of Copernicus Browser.

Geologic Background. The flat-topped summit of the central cone of Ebeko volcano, one of the most active in the Kuril Islands, occupies the northern end of Paramushir Island. Three summit craters located along a SSW-NNE line form Ebeko volcano proper, at the northern end of a complex of five volcanic cones. Blocky lava flows extend west from Ebeko and SE from the neighboring Nezametnyi cone. The eastern part of the southern crater contains strong solfataras and a large boiling spring. The central crater is filled by a lake about 20 m deep whose shores are lined with steaming solfataras; the northern crater lies across a narrow, low barrier from the central crater and contains a small, cold crescentic lake. Historical activity, recorded since the late-18th century, has been restricted to small-to-moderate explosive eruptions from the summit craters. Intense fumarolic activity occurs in the summit craters, on the outer flanks of the cone, and in lateral explosion craters.

Information Contacts: Kamchatka Volcanic Eruptions Response Team (KVERT), Far Eastern Branch, Russian Academy of Sciences, 9 Piip Blvd., Petropavlovsk-Kamchatsky, 683006, Russia (URL: http://www.kscnet.ru/ivs/kvert/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Copernicus Browser, Copernicus Data Space Ecosystem, European Space Agency (URL: https://dataspace.copernicus.eu/browser/).

Ambae, also known as Aoba, is a large basaltic shield volcano in Vanuatu. A broad pyroclastic cone containing three crater lakes (Manaro Ngoru, Voui, and Manaro Lakua) is located at the summit within the youngest of at least two nested calderas. Periodic phreatic and pyroclastic explosions have been reported since the 16th century. A large eruption more than 400 years ago resulted in a volcanic cone within the summit crater that is now filled by Lake Voui; the similarly sized Lake Manaro fills the western third of the caldera. The previous eruption ended in August 2022 that was characterized by gas-and-steam and ash emissions and explosions of wet tephra (BGVN 47:10). This report covers a new eruption during February through May 2023 that consisted of a new lava flow, ash plumes, and sulfur dioxide emissions, using information from the Vanuatu Meteorology and Geo-Hazards Department (VMGD) and satellite data.

During the reporting period, the Alert Level remained at a 2 (on a scale of 0-5), which has been in place since December 2021. Activity during October 2022 through March 2023 remained relatively low and mostly consisted of gas-and-steam emissions in Lake Voui. VMGD reported that at 1300 on 15 November a satellite image captured a strong amount of sulfur dioxide rising above the volcano (figure 99), and that seismicity slightly increased. The southern and northern part of the island reported a strong sulfur dioxide smell and heard explosions. On 20 February 2023 a gas-and-ash plume rose 1.3 km above the summit and drifted SSW, according to a webcam image (figure 100). Gas-and-steam and possibly ash emissions continued on 23 February and volcanic earthquakes were recorded by the seismic network.

Figure 99. Satellite image of the strong sulfur dioxide plume above Ambae taken on 15 November 2022. The Dobson Units (DU) exceeded 12. Courtesy of VMGD.

Figure 100. Webcam image of a gas-and-ash plume rising above Ambae at 1745 on 20 February 2023. The plume drifted SSW. Courtesy of VMGD.

During April, volcanic earthquakes and gas-and-steam and ash emissions were reported from the cone in Lake Voui. VMGD reported that activity increased during 5-7 April; high gas-and-steam and ash plumes were visible, accompanied by nighttime incandescence. According to a Wellington VAAC report, a low-level ash plume rose as high as 2.5 km above the summit and drifted W and SW on 5 April, based on satellite imagery. Reports in Saratamata stated that a dark ash plume drifted to the WSW, but no loud explosion was heard. Webcam images from 2100 showed incandescence above the crater and reflected in the clouds. According to an aerial survey, field observations, and satellite data, water was no longer present in the lake. A lava flow was reported effusing from the vent and traveling N into the dry Lake Voui, which lasted three days. The next morning at 0745 on 6 April a gas-and-steam and ash plume rose 5.4 km above the summit and drifted ESE, based on information from VMGD (figure 101). The Wellington VAAC also reported that light ashfall was observed on the island. Intermittent gas-and-steam and ash emissions were visible on 7 April, some of which rose to an estimated 3 km above the summit and drifted E. Webcam images during 0107-0730 on 7 April showed continuing ash emissions. A gas-and-steam and ash plume rose 695 m above the summit crater at 0730 on 19 April and drifted ESE, based on a webcam image (figure 102).

Figure 101. Webcam image showing a gas-and-ash plume rising 5.4 km above the summit of Ambae at 0745 on 6 April 2023. Courtesy of VMGD.

Figure 102. Webcam image showing a gas-and-ash plume rising 695 m above the summit of Ambae at 0730 on 19 April 2023. Courtesy of VMGD.

According to visual and infrared satellite data, water was visible in Lake Voui as late as 24 March 2023 (figure 103). The vent in the caldera showed a gas-and-steam plume drifted SE. On 3 April thermal activity was first detected, accompanied by a gas-and-ash plume that drifted W (figure 103). The lava flow moved N within the dry lake and was shown cooling by 8 April. By 23 April much of the water in the lake had returned. Occasional sulfur dioxide plumes were detected by the TROPOMI instrument on the Sentinel-5P satellite that exceeded 2 Dobson Units (DU) and drifted in different directions (figure 104).

Figure 103. Satellite images showing both visual (true color) and infrared (bands B12, B11, B4) views on 24 March 2023 (top left), 3 April 2023 (top left), 8 April 2023 (bottom left), and 23 April 2023 (bottom right). In the image on 24 March, water filled Lake Voui around the small northern lake. A gas-and-steam plume drifted SE. Thermal activity (bright yellow-orange) was first detected in infrared data on 3 April 2023, accompanied by a gas-and-ash plume that drifted W. The lava flow slowly filled the northern part of the then-dry lake and remained hot on 8 April. By 23 April, the water in Lake Voui had returned. Courtesy of Copernicus Browser.

Figure 104. Images showing sulfur dioxide plumes rising from Ambae on 26 December 2022 (top left), 25 February 2023 (top right), 23 March 2023 (bottom left), and 5 April 2023 (bottom right), as detected by the TROPOMI instrument on the Sentinel-5P satellite. These plumes exceeded at least 2 Dobson Units (DU) and drifted in different directions. Courtesy of the NASA Global Sulfur Dioxide Monitoring Page.

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

Information Contacts: Geo-Hazards Division, Vanuatu Meteorology and Geo-Hazards Department (VMGD), Ministry of Climate Change Adaptation, Meteorology, Geo-Hazards, Energy, Environment and Disaster Management, Private Mail Bag 9054, Lini Highway, Port Vila, Vanuatu (URL: http://www.vmgd.gov.vu/, https://www.facebook.com/VanuatuGeohazardsObservatory/); Wellington Volcanic Ash Advisory Centre (VAAC), Meteorological Service of New Zealand Ltd (MetService), PO Box 722, Wellington, New Zealand (URL: http://www.metservice.com/vaac/, http://www.ssd.noaa.gov/VAAC/OTH/NZ/messages.html); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); 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/); Copernicus Browser, Copernicus Data Space Ecosystem, European Space Agency (URL: https://dataspace.copernicus.eu/browser/).

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 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 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.

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 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, 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 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 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 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 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 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 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 (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 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 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 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 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 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 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 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 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 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 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, 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 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 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 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 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 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, 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.

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 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 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 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/).

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 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 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 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 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 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 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 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 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/).

Volcanic activity increased in August . . . with 55 eruptions . . . including 17 explosive ones. No damage was caused. The highest ash plume of the month rose to 3,200 m at 1725 on 24 August. No volcanic swarms were registered, but 861 earthquakes were detected at a station 2.3 km NW of Minamidake crater. Heavy ashfall was observed on 21 August (159 g/m²) at [KLMO]. Total ashfall . . . during August was 425 g/m².

Geologic Background. The Aira caldera in the northern half of Kagoshima Bay contains the post-caldera Sakurajima volcano, one of Japan's most active. Eruption of the voluminous Ito pyroclastic flow accompanied formation of the 17 x 23 km caldera about 22,000 years ago. The smaller Wakamiko caldera was formed during the early Holocene in the NE corner of the 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.

Activity from Crater 1 was moderate in August. However, at about 0800 on 11 September, intermittent mud ejection from the water-covered crater floor was detected seismically. Tremor registered at a station 800 m W of the crater had an amplitude of 4.8 µm. The seismic station detected similar activity on the evening of 12 September. During the daily crater visit on the morning of 14 September, several tens of stones were found outside the crater rim, within ~300 m of the crater center.

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

Information Contacts: JMA.

An . . . eruption . . . on 7 August . . . marked the first significant eruptive activity in 18 years. According to a 12 August Reuters news report, during 7-11 August Batur "spewed glowing ash and smoke more than 600 times." The Reuters report noted that a spokesman for the local governor's office said "the threat of a major volcanic blast on Indonesia's resort island of Bali appeared to lessen on Friday [12 August] after Mount Batur's activity slowed." The news report also quoted Wimpy Tjetjep (VSI): "The probability that there will be a big and destructive eruption is small."

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

Information Contacts: W. Tjetjep, VSI; Reuters.

Seismicity remained at background levels from mid-July through early September. However, during 7-14 July, a gas-and-steam plume with a small amount of ash was observed rising ~500 m above the extrusive dome. On 11 July the ash-and-steam plume rose to ~3,000 m asl and drifted generally NE. The gas-and-steam plume extended 150 m above dome through 24 July. During the week of 11-18 August a gas-and-steam plume rose ~200 m above the volcano. A small gas-and-steam plume (to 50-70 m above the volcano) continued during the last 2 weeks of August. On 2-8 September, E. Zhdanova (KVERT) observed a viscous lava flow being "squeezed" from the extrusive dome. A gas-and-ash plume reached 1 km above the volcano and extended >40 km from the volcano. The volcano was obscured by clouds during the next week.

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: V. Kirianov, IVGG.

Increased seismicity in July 1994 culminated in a phreatic explosion on 21 July, destroying the 1991 lobe and producing avalanches and ashfall. The following report, from the geology group of the CUICT at the Universidad de Colima, provides additional details about this activity based on observations from La Yerbabuena village (8 km SW of Colima).

Rock avalanches occurred during the two days prior to the explosion at 2020 on 21 July. At La Yerbabuena it was possible to hear about 15 rock avalanches between 2230 and 2330 on 19 July, each lasting for 2-3 minutes. The day before the explosion, 11 rock avalanches with durations of 1-3 minutes were heard within 3.5 hours, but rain and fog hindered observations. On 21 July, two eyewitnesses, located 10 km (rancho El Jabalí) and 8.5 km (rancho La Joya) SSW of the volcano, respectively (figure 20), observed 30 minutes of incandescent rock avalanches down the SW flank just prior to the explosion. Following these avalanches there was a 15-second-long sharp hissing sound, a reddish glow at the summit, and then the explosion. A dark mushroom-shaped column rose above the summit and remained for about 15 minutes before dissipating. The explosion was heard within a radius of 20-35 km S of the volcano (figure 20). Rock avalanches continued throughout the rest of the night.

Figure 20. Map of the area around Colima volcano showing the limit of ashfall (dashed line) from the 21 July 1994 phreatic explosion, and the radius within which the explosion was heard (heavy line). Courtesy of Geology group at CUICT.

Light ashfall began 30 minutes after the explosion and lasted for 90 minutes. An accumulation of 36.6 g of ash was measured during the first hour within a 1 m² area at La Yerbabuena. Observations of the ash that night using a binocular microscope revealed no juvenile glass. Winds with velocities of 7.5-11.8 m/s at 3,500 m altitude transported ash as far as 35 km W, forming a deposit2 (figure 20). The ashfall caused no adverse effects to people or vegetation because of rainfall during the next few days.

Block-and-ash flows left deposits in the upper part of El Cordobán valley that stopped at 2,700 and 2,325 m elevation in two branches of the valley. Because of these deposits, civil protection authorities were notified of the possibility of lahars farther down the valleys during the current rainy season, similar to those that occurred following the 1991 eruption. Six days after deposition, temperatures at 20 cm depth in pristine block-and-ash-flow deposits were 116-282°C; some blocks yeilded temperatures of 120°C. Gas pipe structures were identified where hot vapor was escaping and forming conical features on the surface of the deposit. The block-and-ash-flow deposits had an average thickness of ~4 m and an estimated total volume of 450,000 m³ (in both branches). A massive ash-cloud surge deposit found on both sides of the El Cordobán valley was 1-2 cm thick and 50-70 m wide; brushwood and small trees were inclined in the direction of the flow, and maguey plants close to the valley rim were scorched. The ash-cloud surge extended ~500 m beyond the block-and-ash flow, and covered surrounding vegetation with 1-3 cm of ash.

A new lahar deposit was discovered at 1,650 m elevation in the Cordobán Valley. It was 80 cm thick and had enlarged the width of the channel by 1.7 m. Two eyewitnesses confirmed that at 1700 on 25 August, following three hours of rainfall, a lahar descended with the sound of rolling rocks. The lahar traveled ~10 km downslope, and covered part of a road at about 1,250 m elevation.

COSPEC flights made on 25 July and 6 August revealed an SO₂ flux of 270 metric tons/day, close to the baseline value of 300 tons/day. Seismicity recorded at the Red Sísmica de Colima (RESCO) was low for the first 48 hours after the 21 July explosion, but then increased above the level recorded in the 72 hours before the explosion. A few minor explosions were also detected seismically.

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: C. Navarro, A. Cortés, R. Saucedo, J-C. Gavilanes, J. Orozco, A. González, and I. Galindo (Director), CUICT-Universidad de Colima; G. Reyes and A. Ramírez, Centro de Investigación en Ciencias Básicas (RESCO-CICBAS), Universidad de Colima.

Long-period "screw-type" events, associated with fluid movements, appeared again on 9 August 1994. There were 18 of these events during 9-26 August, with a maximum of 2/day. These events are called "screws" because of the similarity on a seismograph record to the profile of a screw with a fine thread. This type of signal is significant at Galeras because it preceded five of the six eruptions between July 1992 and June 1993. After the 7 June 1993 eruption (18:6), 94 of these signals were recorded in July, August, September, October, and November 1993, and sporadically in January, March, and May 1994, without being followed by an eruption. However, the lack of eruptions following these occurrences does not decrease their importance. These signals, similar to those that preceded the 7 June 1993 eruption, were also the most monochromatic that have been seen, with frequencies of 2.6-3.2 Hz and durations of 20-120 seconds. These events occurred around the volcano at depths of <3 km. Some small-magnitude earthquakes were located NNE of the crater at a depth of 3-8 km; this source has remained active since the last swarm of screw-type signals between November and December 1993.

SO₂ flux measurements taken by the mobile COSPEC were low. Deformation equipment indicated no variations; apparent changes at one tiltmeter were due to electronic problems.

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, Pasto.

"During observations at 1145 on 15 July from the SW flank, a white plume rose above the volcano and extended toward the E. Two active lava domes were present on the summit, one in the S, and the other in the NE. Each generated white plumes from its top. Many fumaroles with yellow sulfur deposits covered the S side of the NE dome. A small chaotic-looking lava flow was located near the foot of the NE lava dome. It was possible to hear weak, rhythmic explosions from an area located between the two lava domes behind the summit pass, but no direct observations were possible because of the cover of rising clouds."

Geologic Background. Karangetang (Api Siau) volcano lies at the northern end of the island of Siau, about 125 km NNE of the NE-most point of Sulawesi. The stratovolcano contains five summit craters along a N-S line. It is one of Indonesia's most active volcanoes, with more than 40 eruptions recorded since 1675 and many additional small eruptions that were not documented (Neumann van Padang, 1951). Twentieth-century eruptions have included frequent explosive activity sometimes accompanied by pyroclastic flows and lahars. Lava dome growth has occurred in the summit craters; collapse of lava flow fronts have produced pyroclastic flows.

Information Contacts: H. Gaudru, C. Pittet, M. Auber, C. Bopp, and O. Saudan, EVS, Switzerland.

"Lava continued to enter the ocean in the W Kamoamoa/Lae Apuki area. Surface flows broke out on the bench, directly behind the littoral cone formed in July. These flows extended the active bench area 300-400 m W and formed a new tube parallel to the shoreline. Lava initially entered the ocean along a 500-m-wide front, but by the end of August entries had consolidated and lava entered the ocean along a 150-m-wide front. Additional breakouts resurfaced much of the older part of the bench early in the month. Small bench collapses and moderate-sized littoral explosions were observed towards mid-month. High surf on 23-24 August deposited sand and debris 50 m inland, along the entire front of the bench. Breakouts immediately behind the active ocean entries covered parts of the new bench and the storm deposit. There were no major bench collapses during the last half of August; material swept in by the storm appeared to support and slow the seaward movement of the bench.

"On 16 August a small pahoehoe flow broke out of the tube at 90 m elevation. A much larger channelized aa and pahoehoe flow broke out at 285 m on 20 August and rapidly advanced below 90 m elevation. The flow was active along its entire length, and by the end of the month fingers of active lava extended below the Paliuli fault scarp.

"The pond in Pu`u `O`o was active throughout August and its surface fluctuated at 79-84 m below the crater rim. Circulation in the pond was sluggish."

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. Mattox, HVO.

An eruption began on 8 September with lava fountaining and ash plumes that rose to an altitude of at least 8 km on 12 September. Explosive activity increased on 30 September, and on 1 October the ash column rose to >15 km altitude.

During 7-24 July, seismic stations continued to register weak intermediate-depth (10-30 km) earthquakes under the volcano (15-55/day); the duration of volcanic tremor averaged 8-22 hours/day. Weak fumarolic activity from the central crater was observed during the week of 7-14 July. Clouds frequently obscured the volcano through mid-August, but British climbers who visited the summit in early August reported no unusual activity. Seismicity increased from 24 July to 2 August, when 15-149 weak intermediate-depth earthquakes were recorded each day, accompanied by 1-20 hours/day of volcanic tremor. The number of weak intermediate-depth events decreased again during the next three weeks to 8-37 earthquakes/day. Tremor averaged 5-10 hours/day through 11 August, 3-4.5 hours/day the following week, and 5-17 hours/day by 2 September. Weak intermediate-depth earthquakes decreased from 2 to 8 September, averaging only 1-4 events/day. However, volcanic tremor was recorded for an average of 19-22 hours/day. Normal fumarolic activity was observed from the central crater early in September.

Seismic data indicated that an eruption began from the central crater at about 0400 on 8 September. Lava was observed fountaining 200-300 m above the crater from two separate vents. Gas and ash outbursts to 1 km were recorded every 10 minutes. Pilots from American Airlines reported an ash cloud as high as 11 km above sea level around 1445 on 9 September, and at 1010 the next day the cloud was reportedly moving SE at the same altitude.

On 12 September ground observers reported that the eruption sent gas and ash to 1.5 km above the crater. The ash plume reached an estimated 3 km above the 4.7-km-high volcano, to an altitude of ~8 km. The plume extended to the NE for more than 50 km and ashfall was reported in Kliuchi, [30 km NNE]. A 1-km-long lava flow was observed on the SW slope of the volcano; mudflows were also noted. Continuous volcanic tremor was recorded as far as 65 km from the volcano.

Kliuchevskoi was obscured by clouds on 13 September, but gas and ash explosions on 14 September rose 600-800 m above the crater with an ash column extending to 2 km above the crater. The ash plume was carried E for at least 50 km. A new lava flow 1.5 km long was observed on 14 September issuing from two NW-flank vents ~200 m below the crater rim. This flow is in addition to the lava flow on the SW flank of the volcano. Lava fountains were again observed extending to 200 m above the crater rim. Continuous volcanic tremor, with a maximum amplitude of 6.3 µm, was recorded at distances of 11 km from the volcano.

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

Information Contacts: V. Kirianov, IVGG; J. Lynch, SAB.

"Eruptive activity at Crater 2 continued in August. Except for a quiet period during 1-11 August, on most days thick columns of mushroom-shaped grey-brown ash clouds were released. Light ashfall in coastal areas downwind was reported on 12 and 26 August. One explosion noise was heard on the 12th, and occasional rumbling noises were heard on the 17th and 23rd. Steady weak red glow was seen on 1 and 15 August.

"Crater 3 activity was generally low. Throughout August, Crater 3 produced weak emissions of thin, pale-grey and occasionally blue vapour. After the 26th the volume of blue emissions became moderate. The 30th marked the beginning of occasional moderate to thick emissions of grey-brown ash clouds producing light ash fall on the N and NW sides of the volcano.

"Seismicity was low throughout the month. Daily totals of volcanic earthquakes were between 1 and 5."

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: I. Itikarai, R. Stewart, and C. McKee, RVO.

On 25 August 1994 Llaima volcano began a new eruptive episode. Its last eruption started on 17 May, generating an ash column >4 km high, subglacial lava, lahars, and flooding. The subglacial lava left a melted ice channel down the SW side of the volcano. From a point ~5.4 km W of the summit (Las Paraguas) at 0900 and 0915 on 21 August people felt two earthquakes of intensity II and III. On 25 August, beginning at 0900, observers heard explosions from the principal crater, and at 1135 the first ash column became visible.

Between 1630 and 1800 on 26 August, a gas-and-ash cloud rose 350 m above the summit and a portion of the cloud extended along the ice channel. Continuing from 1930 through the night, the eruption increased in intensity, ejecting gases and incandescent tephra up to 500 m above the summit; some tephra fell as far away as the summit's outer flanks. On 27-28 August the volcano was completely cloud covered, preventing direct visual observations. Some sources reported feeling continuous explosion shocks throughout 27 August, and one source felt 3 clear explosion shocks at 5-second intervals on 28 August. These observations suggested continuing eruptions.

Several seismic stations were installed during the crisis; the first began operation at 1458 on 26 August. During its first 21.2 hours of operation station El Trueno, located 18 km WNW of the principal crater (N of Cherquenco village), revealed harmonic tremor with a predominant frequency of 1.1 Hz. It is fitting to emphasize that in this situation the gain of the seismic system was relatively low (66 on a MEQ-800 instrument), and in May higher gains were in use (78 and 84). In essence, the August tremor had higher amplitude than it did in a roughly 6-hour post-effusive period associated with the May eruption. In addition, other high-frequency signals were detected during parts of 26-27 August, which are still under study. In the last 15 hours of this interval the record contains banded tremor predominantly of 1.0 Hz frequency.

A second seismic station began operation at 1046 on 27 August when a portable MEQ-800 (filter 0-5, gain 72) was installed. Station MELI was placed 14.5 km from the principal crater (N of Melipeuco, a town 20 km SSE of the volcano). The instrument detected harmonic tremor of 1.0-1.2 Hz frequency at roughly 4-5 episodes/minute. The tremor signal was thought to arise from magma-water contact in Llaima's magma-laden conduit system. Tremor of the same frequency continued for the first 6 hours of 28 August (0000-0600), but grew in amplitude and frequency range (to 1.5 Hz). Banded tremor appeared, possibly indicating pressurization processes associated with the ascent of a new batch of magma from depth. In the interval 1100 to 1752 on 28 August the seismicity remained roughly constant, although there was a tendency toward increased energy release.

A third station, installed at 1300 on 27 August, was located 1.1 km from Lago Verde, 7 km E from the principal crater. During 1300-1700 this instrument received such strong tremor signal that it had to be set at minimum gain (60). Later, the station was moved farther away, to Pangueco, 10 km from the principal crater.

On 28 August, scientists monitoring the volcano made several "General Recommendations." These included an Orange alert, 72 hours of vigilant watching of the seismic data, warnings to stay away from Llaima's drainages, and to remain attentive for further official instructions.

A new eruptive phase started at midnight on 28 August when a strong explosion produced a gas-and-ash column. The column was observed in Melipeuco beginning at 0300 when the sky cleared. The activity decreased noticeably by 0510 but reactivated so that between 0640 and 0940 puffs of gas-and-ash in the crater reached 100-600 m above the rim. Thereafter they decayed and grew weak though constant. Between 1120 and 1209 pyroclastic emissions reactivated, discharging a continuous column to 1,000 m above the crater with explosions producing dense scrolls every 5 seconds (VEI = 2).

A 4-hour overflight began at 1125 on 29 August. During that interval the plume mainly rose 400-500 m, but sometimes 1,000 m, above the principal crater's rim. Strong winds came from the W, carrying a visible plume at least 80 km toward the Andean passes "Pino Hachado" and "El Arco" along the Argentine border. The plume lay between 3,200 and 4,000 m altitude; vapor appeared to be absent in both the plume and the column suggesting a very magmatic eruption. The source vent was a 100-m-diameter crater in the E side of the principal crater, surrounded by a small spatter-cone covering the crater floor. From mid-day until 1700 erupted material rose 600-1,000 m and the wind continued to carry the plume E. At 1740 the eruptive intensity decreased but at 1818 it increased, again sending ash 600-700 m above the crater. After 1930 frequent intermittent explosions tossed more ejecta onto the spatter cone verifying its mode of the construction.

Seismicity monitored at station MEI captured the 29 August midnight explosion noted above. In the interval from 2200 on 28 August to 0100 on 29 August, the seismic record showed increased tremor amplitude (3-5 mm at a gain setting of 66) at frequencies of 1.1-1.2 Hz. Later, from 0200-0430, tremor frequency remained stationary at 1.1 Hz, amplitude dropped, and intervals of banded tremor prevailed. Further decreases in amplitude occurred later (0841-1909, 29 August), and while the frequency range of the tremor remained approximately stationary, tremor dropped to a level from where it only appeared episodically.

On 28 or 29 August the Emergency Committee met with members of the community to explain Llaima's activity, including a summary of the eruption character and fundamentals to help maintain civil calm and at the same time to convey potential hazards. Civil calm was called for owing to preparedness by the regional government, community groups, Carabineros, firefighters, the Chilean Air Force, and other groups. Hazard status remained at alert-level Orange.

On 30 August the ash eruption intensified; column height oscillated 2-3.7 km above the crater (corresponding to VEI 2). At 1603 the first dense, vapor-rich ejection took place; 38 minutes later an intermediate phase began, with vapor discharge accompanied by increased amounts of ash. The highest ash column during this phase ascended to 1.5 km above the crater. Vapor-rich and ash-rich phases alternated for ~ 3 hours (until 1901). At 2100 venting stopped. On 31 August, vapor discharge became pronounced around 0900 and continued until 1600.

Beginning at 2000 on 30 August and again at 0155 on 31 August, there was continuous tremor in the 0.9-1.0 Hz frequency range followed by ~ 40 minutes of banded tremor of similar frequency. Seismic quiet prevailed during the next 6 hours at stations MELI and PANG. Seismicity also remained low from 31 August until at least 0941 on 2 September.

Figure 7 shows a sketch of the crater seen during a 1 September overflight of Llaima (in a Chilean Air Force aircraft); the flight took place during calm, clear weather and visibility into the principal crater was excellent. The crater's normally snow-and-ice-covered surface was completely blackened by ashfall; about 15 fumaroles remained, yet ash-emissions were absent. A small cone covered most of the crater floor, its 100-m-diameter, funnel-shaped source vent lay adjacent to the SE crater wall (figure 8). On 1 September, the fissure of melting ice created by the 17 May subglacial lava flow still continued to send up a significant vapor plume. Although mostly westerly winds were noted by observers, the weak ash distribution was over a wide arc, ranging from compass bearings 190-310 (figure 9). There were two lobes of heavier deposition, one toward the N, the other ESE.

Because of decreases in both volcanic and seismic activity, around 2 August scientists lowered the hazard status from Orange to Yellow. However, they expressed concern about potential restriction or blockage of the vent by new deposits in the main crater. They were also concerned about the recent shift in seismic character compared to the previous 4 years.

Figure 7. Sketch looking down on Llaima's principal crater at 1500 on 1 September. Courtesy of Hugo Moreno.

Figure 8. Preliminary cross section of Llaima's crater showing estimates of the fill thickness and the funnel-shaped vent from the recent eruption. Courtesy of Hugo Moreno.

Figure 9. Zones of major ash cover from the Llaima eruptions in late-August. The ESE lobe reached about 6 km from the source, the length of the N lobe was unreported. Courtesy of Hugo Moreno.

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

Information Contacts: H. Moreno1, M. Murillo, M. Petit-Breuilh, and P. Peña, SERNAGEOMIN, Temuco. 1Also at Univ de Chile, Santiago.

"During our visit to the summit zone on 8 July, intense fumaroles escaped from several parts of the Tompaluan crater floor. This fumarolic activity was mainly concentrated in the N where an intracaldera structure was covered by yellow sulfur deposits. Many other fumaroles with sulfur deposits were also located in the S, E, and W parts of the crater. Temperatures measured with an electronic thermometer at the E fumaroles showed a maximum value of 95-96°C. The fumarolic gases were mainly composed of H₂O and H₂S."

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: H. Gaudru, C. Pittet, M. Auber, C. Bopp, and O. Saudan, EVS, Switzerland.

Part of the EVS report follows. "During our observations at 1100 on 9 July intense and noisy gas emissions (like a jet engine) occurred near the low NW part of the inner wall of the crater. These gas emissions generated a gray-white plume. This area of the crater was covered by many yellow sulfur deposits. A strong smell of hydrogen sulfide was also noted. An important solfatara zone surrounded the NW, N, NE, and E sides of the green, ~40,000 m³, acidic crater lake. Two small geysers, the one in the N and the other in the NW, were very active (2-3 m height). Several boiling basins and mud pots were active around the lake. It was not possible to get down into the crater without rock climbing equipment, because the crater walls were very steep." EVS observers also proposed that a low part of the S wall had collapsed.

Geologic Background. The elongated Mahawu volcano immediately east of Lokon-Empung volcano is the northernmost of a series of young volcanoes along a SSW-NNE line near the margin of the Quaternary Tondano caldera. Mahawu is capped by a 180-m-wide, 140-m-deep crater that sometimes contains a small crater lake, and has two pyroclastic cones on its N flank. Historical activity has been restricted to occasional small explosive eruptions recorded since 1789. In 1994 fumaroles, mudpots, and small geysers were observed along the shores of a greenish-colored crater lake.

Information Contacts: H. Gaudru, C. Pittet, M. Auber, C. Bopp, and O. Saudan, EVS, Switzerland.

"Increased activity at Southern Crater began on 8 August following a week of low-level activity. This change initiated with weak emissions of thick grey ash clouds. On the 9th, the emissions changed to forceful ejections of thick grey-brown ash clouds that caused light ashfall on the NW side of the volcano. Activity subsided after the 11th, but started again on the 18th and continued until 30 August. The thick grey-brown ash columns rose ~400-1,000 m above the summit. Most of the ash ejections were associated with explosion and low roaring and/or rumbling noises. Incandescent lava fragment projections were seen on 23 and 26-30 August.

"Activity from Main Crater consisted of emissions of weak-to-moderate white vapour through August. No noises or night glows were observed. Seismicity remained at low levels throughout the month except for a brief period during 21-29 August when it was moderate. This coincided with the period of thick brown ash cloud emissions and incandescent lava fragment projections. On average, ~1,200 volcanic earthquakes were recorded each day."

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: I. Itikarai, R. Stewart, and C. McKee, RVO.

Two STS2 broad-band seismometers were deployed on 27-29 July by collaborators of the Geophysical Laboratory of GMU and Martin Beisser of GFZ-Potsdam. The researchers investigated signal coherency at different points on the volcano to find suitable sites for a multi-station seismic array that will make permanent records at a 50-Hz sampling rate. The researchers measured Merapi seismicity at a base station located at Klathakan (1.8 km WNW of the summit between 1,200-1,300 m elev), the site of a seismic station for the last eight years. The second station was mobile and GPS-equipped; however, for the following comparisons and discussion the mobile site remained 400 m N of the base station.

Figure 10 shows amplitude data for three components of volcanic shock from the mobile station. The volcanic shock event that began at 1750 and 37 seconds on 27 July is here termed Event A. Figure 11 shows the arriving signals and allows for a visual comparison of the coherency in the vertical component (top two plots), and two orthogonal horizontal components (lower four plots). From visual inspection, the best coherency appeared in the vertical-component data. Some other types of events received appeared to show less coherency between the two sites.

Figure 10. A seismic event on Merapi received at the mobile station showing 3-component amplitude data. The event shown began at 1750 and 37 seconds on 27 July 1994 and is termed "Event A." Courtesy of A. Brodscholl.

Figure 11. The first five seconds of Event A on Merapi (27 July 1994) as received at the broadband base and mobile stations (400-m separation). The records show considerable coherency. Courtesy of A. Brodscholl.

Figure 12 shows three components of a previously undetected tremor type, a tremor preceded by or superimposed on a long-period pulse. On the record, the interval of greatest short-period amplitude came after the pulse's maximum. Examples of this kind of tremor were seen three times in 12 hours. Whether these events are common on Merapi and elsewhere still remains uncertain.

Figure 12. Merapi seismic record from the mobile station showing an example of tremor coming after the maximum of a long-period pulse. These pulses and temporally associated tremors were seen three times in a 12-hour period and were not previously detected. Courtesy of A. Brodscholl.

[The reported low-frequency signal was later found to be caused by instrumental problems not recognized at the time of submission.]

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: M. Beisser, GFZ-Potsdam, Germany; A. Brodscholl, GMU.

The eruptive activity . . . continued until 27 July, when seismic tremor ended and no more glow was observed. The lava flow moved over the 1971 Rugarama flow and partially filled Lake Magera at the W Precambrian escarpment. Heavy steaming from the unfilled portion of the lake was observed on 23 August during an overflight. Fumarolic activity was also observed along the 1989 fissure (figure 14), and the fresh lava plain in and around the pit crater appeared much larger than before. At the S end of the 1989 fissure a new solfataric area was noticed; a feature not formed during the 1989 or 1991 eruptions. Zairian scientists who visited the crater on 25 August observed ash emission from the 1989 fissure and confirmed that there had been fresh lava extrusion in the central crater. No evidence of lava flows on the S slope of the volcano was observed.

Figure 14. Summit caldera of Nyamuragira, 25 August 1994, showing lava flows from 1989 (black) and 1994 (cross-hatched). Courtesy of N. Zana.

Geologic Background. Africa's most active volcano, Nyamulagira (also known as Nyamuragira), is a massive high-potassium basaltic shield about 25 km N of Lake Kivu and 13 km NNW of the steep-sided Nyiragongo volcano. The summit is truncated by a small 2 x 2.3 km caldera that has walls up to about 100 m high. Documented eruptions have occurred within the summit caldera, as well as from the numerous flank fissures and cinder cones. A lava lake in the summit crater, active since at least 1921, drained in 1938, at the time of a major flank eruption. Recent lava flows extend down the flanks more than 30 km from the summit as far as Lake Kivu; extensive lava flows from this volcano have covered 1,500 km2 of the western branch of the East African Rift.

Information Contacts: N. Zana, Centre de Recherche en Géophysique, Kinshasa.

On the night of 22-23 June, glow above the central crater [indicated] a reactivation of the lava lake. A seismic station on the S slope of the volcano recorded a low-frequency microearthquake at 0232 on 23 June that may have coincided with the initial lava outburst; there were no felt earthquakes before this event. Long-period tremors recorded at Katale station ceased ~2 hours after the initial lava outburst. However, tremor activity increased significantly at 2355 later that same day.

A National Park team that visited the summit reported three active vents inside the crater, the northern-most of which had formed a small scoria cone. On 1 July, four lava fountains were active. Intense lava emission was accompanied by increasing tremor amplitude recorded at local seismic stations. Continuous activity lasted until about 17 July, but decreased notably after 4 July. Additional episodes of lava lake activity occurred during 13-15 August, 19-21 August, and from about 1920 on 25 August through the 29th. The rate of lava fountaining . . . seemed to be lower than that observed during 1982. Lava fountain heights of 30-40 m were also less than the 80-100 m heights reached in 1982. The level of the fresh lava lake was ~5-10 m below the 1982 lava lake height, and the lake was confined close to the central vent in an area of ~120-150 m.

Renewed lava lake activity was preceded by a general increase in amplitude and frequency of long-period volcanic earthquakes. Volcanic tremor and earthquake swarms were recorded on 5-9 January, 20 January, and 16 May 1994. Records from the S-flank seismic station (Bulengo) indicated increased seismicity in the SW Virunga area; the frequent volcanic tremor and microearthquakes recorded at this station were not recorded at other stations outside the Nyiragongo field. A seismic swarm on 5 January 1993 was dominated by A-type volcanic events with focal depths of <5 km. On 21 November 1990 a M 4.5 earthquake was centered on the S flank. This event, felt in Goma with an intensity of MM V-VI, resulted in cracked walls of several brick houses and the death of one woman caused by a falling concrete platform. There were several aftershocks, and tremor activity was recorded for several days.

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

Information Contacts: N. Zana, Centre de Recherche en Géophysique, Kinshasa.

Lahars from the upper slopes of Pinatubo began again in June 1994, induced by monsoon rains. This volcanic hazard has been frequent in the drainages of Pinatubo during every monsoon season following its June 1991 eruption. Tropical cyclones brought continuous rains on the Pinatubo area in June. Lahars developed in the major drainage channels of the O'Donnell (NE), Sacobia (E), Pasig-Potrero (SE), Marella-Santo Tomas (SW), and Bucao (NW) rivers. On the SE flank, the lahar crisis was more dramatic along the Pasig-Potrero River because it had captured the upper reaches of the Sacobia River in October 1993. The following report, from the Philippine Institute of Volcanology and Seismology, summarizes lahar activity during June-August 1994.

The first lahars were noted on 23 June. Other lahars on 10 July caused damage in downstream villages. They passed under Mancatian Bridge 2 and then curved to the left side of the Pasig-Potrero channel towards Bancal, in barangay Maliwalu (figure 31). These lahars resulted in 2-3 m of deposition on the Mancatian area (from the Angeles-Porac Road to ~2 km upstream) and at least 2 m of in-dike deposition, decreasing to 1-m-thick deposits near Bancal.

Figure 31. Pinatubo lahar deposit map along the Pasig-Potrero River between Mancatian and Santa Rita, 3 August 1994. Courtesy of PHIVOLCS.

On 19 July, lahars cut through the Mancatian portion of the left dike and encroached on several houses at and near its outer base (figure 31). Aggradation on the left side of the channel forced the active channel to shift towards the right inner dike, so subsequent lahars (25 July) aggraded the right portion of the diked area. Average aggradation along the Mancatian area was ~3 m. Succeeding lahars (26 and 30-31 July) overtopped and breached the inner right dike ~600 m upstream from the road. The breach allowed the lahars to bury areas outside of the inner dike with 2 m of debris. Downstream, strong lahar flows (even as early as 19 July) breached the left dike at Bancal. The breach, ~100 m wide, allowed the lahars to be delivered as far as barangay San Antonio, Bacolor. The bulk of the lahars that passed through the breach were deposited at barangays Potrero and Cotod. Deposits in these areas were as thick as 4 m, especially very near the dike. Deposits in barangay San Antonio and Duat areas were 20-100 cm thick.

Significant deposition in the Mancatian area along the right side of the channel shifted the active flow back towards the left side of the channel so that by 1 August the lahars were again battering the left dike. The active channel maintained this course as of early September.

The passage of Typhoon Ritang on 6-7 August did not bring much rain over the Pinatubo area. However, the lahars generated filled the Pasig-Potrero River from the Delta 5 watchpoint (figure 32) to barangay Mancatian, and caused additional deposition at the alluvial fan area. In-channel aggradation left only a few meters of freeboard along some of the channel and lahars overflowed at the left bank, near the base of Delta 5. The overflowing lahar buried part of an old fan area between Pasig-Potrero River and Sapang Ebus (Taug River) with 0.2-2.0 m of debris. The overflow started on the afternoon of 6 August. The Typhoon Ritang lahars that were conveyed all the way down to the alluvial fan reaches had observed discharges of 60-300 m³/s upon reaching Mancatian. These laminar lahars further aggraded the Cotod and Potrero area by 50-100 cm.

Figure 32. Pinatubo lahar deposit map between the Pasig-Potrero River and Sapang Ebus, 17 August 1994. Courtesy of PHIVOLCS.

After Typhon Ritang and beginning on 8 August, lahars continuously flowed in the Pasig-Potrero River. These non-streaming hyperconcentrated streamflow lahars had an average discharge of 6 m³/s at Delta 5 and 3 m³/s at Mancatian. It is suspected that these lahars were triggered by the breaching of a lake, because no rainfall was recorded by the Upper Sacobia rain gage during 8-16 August. Lahars with the same characteristics were observed in 1991 and 1992 during the release of water from lakes formed on the pyroclastic-flow field by the damming of tributaries with lahar and secondary pyroclastic-flow deposits.

On 16 August, shortly after a large secondary explosion and possibly a secondary pyroclastic flow on the Sacobia pyroclastic-flow field, lahars in the Pasig-Potrero River suddenly ceased and the river became dry. Debris from the secondary pyroclastic flow might have temporarily dammed the river because continuous lahars resumed on 20 August. Aerial surveys on 19 and 30 August revealed several lakes, the biggest of which was in the same location as the 1992 lake. A breach on the outer left dike ~500 m downstream of the Angeles-Porac road allowed these continuous non-rainfall lahars to be delivered and deposited at the alluvial fan area outside of the dike. The accumulation of sediment caused extensive damage outside of the left dike from Barangay Manibaug-Pasig down to Barangay San Antonio in Bacolor, Pampanga.

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. Arboleda and M. Matinez, PHIVOLCS.

As usual, seismicity during July and August consisted primarily of B-type events (figure 3). During these two months, B-type events were recorded more frequently than during much of January-March and less frequently than during much of May. Type-A, -AB, and -B seismic events at Popocatépetl were defined in 19:1.

Guillermo González-Pomposo and Carlos Valdés-González noted that when B-type seismicity increased in July and August, A- and AB-type seismicity declined. Both A- and AB-type seismicity remained at 0-1 events/day for July-August, except for two days when one or the other type reached 2 events/day. Overall, during July type-A events took place 4 times, type-B events 150 times, and type-AB events 6 times. During August type-A events took place 5 times, type-B events 165 times, and type-AB events 6 times.

In contrast with the moderate levels of seismicity seen in July and August, early July ultraviolet absorption correlation spectrometry (COSPEC) measurements made by ASU and UNAM researchers indicated a prodigious SO₂ flux: a minimum of 575 metric tons/day (t/d) and an estimated "true flux" of 2,700-3,500 t/d. Their report on the 5,420-m-high volcano follows.

"We were able to make a driven traverse [using an automobile] of the plume of Popocatépetl on 1 July, 1994. The data showed an SO₂ flux of 575 t/d, if a standard wind velocity of 1 m/s was assumed; this must be considered as the absolute minimum. Our best estimate of the true wind velocity was based on the National Airport measurements at 5 km above sea level (on 2 July) of 5 m/s. Therefore, our best estimate of the true flux was 2,900 t/d. An estimate of the uncertainty in this flux is complicated by measurements made on 2 July using the Trimble GPS (Global Positioning System) instrument on board the chartered aircraft. One aircraft traverse, at the crater level, suggested a wind velocity of ~30 m/s. So, we are reporting what seems to be a minimum realistic SO₂ flux.

"At ~0900 on 1 July, the sky was relatively clear and the plume was visibly blowing to the SW. It appeared to rise a few hundred meters above the crater, before being blown by the wind. The white, cloudy plume remained visible for tens of kilometers, perhaps a hundred kilometers. By the time we were on the road that passes around the W margin of the base of Popocatépetl and Iztaccíhuatl, the cloud cover became sufficient to block any certain view of the plume. At 1700 in the afternoon, however, we were in the saddle between Popocatépetl and Iztaccíhuatl and had another very clear view of the plume. Its appearance then was similar to the way it had looked before, suggesting approximate stability for intervals of hours and days. Using the standard approach (Stoiber and others, 1983), we mounted the COSPEC on the passenger seat of the van, with the telescope looking vertically, and drove at roughly constant velocity (~30-40 km/hr). The traverse was more than 40 km in total length, with its center being at a point approximately straight W of the volcano's crater. Good maps facilitated geometrical corrections to allow for portions of the traverse not normal to the plume's axis.

"The airplane traverses made on 2 July used a plane flown by Sergio Zambrano who used his on-board GPS instrument to minimize all of the usual uncertainties concerning location, aircraft velocity, length of traverse, and angle between the traverse and the plume axis. However, the one measurement that we did not recognize adequately while airborne was the ability to realistically estimate wind velocity at the elevation of the plume, as it was dispersed. The five traverses gave extremely repeatable graphs [on the strip chart records] and the estimated flux was 3,100 ± 400 t/d (using the 5 m/s wind velocity measurement from the National Airport). Because we failed to recognize the possibility of using the GPS instrument for measuring the wind velocity we cannot accept the one [~30 km/hr] measurement as well constrained. If it were true, then the SO₂ flux was enormous.

"Our measurements of SO₂, by two different COSPEC methods on two different days, were remarkably similar. The plume looked very homogeneous, when we were able to see it on these two days. The increase in SO₂ flux since measured by T. Fisher and others by aircraft on 1 February 1994 (1,200 ± 400 t/d) is very difficult to escape [19:1]. An increased gas flux is also consistent with the visual impression of H. Delgado upon climbing to the crater rim in August, that the gas emissions were greater with more loud sounds from the fumaroles within the crater."

Although the reported SO₂ flux is strikingly large for a volcano not in eruption, it is too small to confirm with the satellite-borne TOMS, which detects masses of SO₂ greater than about 5 kilotons (Bluth and others, 1992). Popocatépetl looms over the México and Puebla valleys, potentially threatening over 20 million people.

References. Bluth, G.J.S., Doiron, S.D., Schnetzler, C.C., Krueger, A.J., and Walter, L.S., 1992, Global tracking of the SO₂ clouds from the June, 1991 Mount Pinatubo eruptions: Geophysical Research Letters, v. 19, no. 2, p. 151-154.

Stoiber, R.E., Malinconico, Jr., L.L., and Williams, S.N., 1983, Use of the correlation spectrometer at volcanoes, in Forecasting Volcanic Events, H. Tazieff and J.C. Sabroux (eds.): Elsevier, New York, p. 425-444.

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

Information Contacts: Departamento de Sismología y Volcanología, Instituto de Geofísica, UNAM; Stanley N. Williams and Tobias Fisher, Arizona State Univ, USA; Claus Siebe and Hugo Delgado, Instituto de Geofísica, UNAM, Circuito Exterior. 1 Also at Benemérita Univ Autónoma de Puebla, México.

Vulcan and Tavurvur, two vents on opposite sides of Rabaul Caldera (figures 15 and 12), erupted on the morning of 19 September and sent ash as high as 18 km asl. This caldera forms a sheltered harbor whose N end is occupied by Rabaul, New Britain's largest city. The report of August seismicity was sent from RVO on 9 September. Satellite interpretations are courtesy of NOAA, with TOMS data from the NASA Goddard Space Flight Center. Although communication with Rabaul was cut off for many days, RVO reports were received for 23 and 27 September. Information based on reports from local and international news services is noted, and may not be accurate.

Figure 15. NW tip of the Gazelle Peninsula, New Britain Island, papua New Guinea, showing the road network (dashed lines), towns (dots), and volcanic centers (triangles). Modified from McKee and others, 1985.

Figure 12. Map of the Rabaul Caldera showing recently active volcanic vents and extinct composite cones (modified from Almond and McKee, 1982). [copy from 18:03]

August seismicity. The total number of detected events for August was 448 . . . . The month was quiet until 25-28 August when 227 earthquakes were detected, with more than half of them on the 26th. Unusually for Rabaul, these earthquakes tended to be discrete events not occurring in swarms. Only 34 of the August events were located, 25 of them during 25-28 August. Most located earthquakes were along the ring fault near Tavurvur, or offshore to the S and SW; 17 hypocenters had location errors ofL 2.6, but none of the earthquakes were felt. On 28 August, the caldera network recorded what appeared to be a low-frequency earthquake. Signals with a dominant frequency of ~1 Hz recorded on some of the inner network stations were very complicated with no clear phase arrivals or onsets. These signals probably originated close to the Matupit Island seismometer. No seismicity was recorded after 29 August.

Seismic precursors, 18-19 September. RVO reported that at 0300 on 18 September, a M 5.1 earthquake occurred beneath the harbor. An aftershock sequence from this event merged into an intensifying swarm of high-frequency (A-type) earthquakes. Peak intensity of this swarm occurred around 2400 that night with ~2 felt events/minute, but then tapered off slightly toward morning. By 0600 on 19 September the eruption had begun. Thus, only 27 hours of unusual seismicity preceded the eruption. Inspection of the seismograms since the onset of the eruption revealed several long-period events in the 12 hours prior to the M 5.1 earthquake.

Initial eruptive activity, 19 September. Tavurvur began erupting around 0600 on 19 September, followed by an explosion from Vulcan ~1-1.5 hours later. RVO volcanologist Patrice de Saint-Ours was quoted in press reports that day as stating that the pattern of eruptions was very similar to 1937, and that the vents were no longer visible from the observatory because of the ash cloud, estimated by ground observers to be >3 km high. Most press reports described thick mushroom-shaped pulses of ash rising from the vents, hot ash falling near the vents, and loud explosion noises. Aerial video footage showed vigorous, thick, light-brown ash columns, and the surface of the harbor covered with ash and floating pumice. Other press reports on 19 September stated that Rabaul town was covered with 20-25 cm of ash, and that thunderstorms mixed rain with the ash, forming a heavy mud that damaged buildings and vegetation. The press reports also described columns of gray ash rising thousands of meters into the air, ejecta as large as trucks, and "black muddy rain." Ash fell across New Britain and New Ireland.

A pilot report received at Port Moresby at 1034 placed the top of the volcanic ash cloud between 15 and 18 km altitude. A later pilot report noted the presence of drifting ash ~185 km SW of Rabaul well above 6 km altitude. GMS satellite imagery as late as 2132 on 19 September revealed an obvious plume fanning out to the S through WNW. The W part of the plume was tracking W and WNW at ~110 km/hour, and had moved across central Papua New Guinea; plume height was estimated to be 21-30 km, well into the stratosphere. The S part of the plume, at an altitude of 12-18 km, had begun to move SE at ~55 km/hour around an upper tropospheric ridge. A satellite infrared image taken a few hours earlier, at 1800 on the 19th (figure 16), showed similar plume morphology. Initial estimates of plume height during the first two days of activity were between 18 and 30 km. Space Shuttle astronauts who observed and photographed the plume (figure 17) estimated its height as at least 18 km based on altitudes of storm clouds in the area.

Figure 16. Infrared satellite image of the ash plume from Rabaul, 1800 on 19 September 1994, about 12 hours after the start of the eruption. Courtesy of George Stephens, NOAA/NESDIS.

Figure 17. Photograph of plumes from Rabaul taken by Space Shuttle astronauts roughly 24 hours after the start of the 19 September 1994 eruption. Oblique view is to the SW. The cloud-covered island in the foreground is New Ireland, and the papua New Guinea mainland is in the distance. The eruption column rose to 18 km where it flattened out and was blown W in a fan-shaped plume. A layer of yellow-brown ash was blown towards the N by lower level winds. NASA photograph STS064-116-064, courtesy of Cindy Evans.

Eruptive activity, 20-23 September. Video of the eruption, taken from a helicopter about 1.5 days after its start, showed massive, gray-to-black ash columns billowing vigorously from Vulcan and Tavurvur. The maximum height of the cloud was reported by the press to be ~20 km, with blocks as big as cars falling into the harbor. Black ash appeared to be falling over a wide area and scenes from Rabaul town showed buildings and vegetation blanketed by ash.

Night winds on 19 September, which were generally blowing NNE-NE (taking the ash over New Ireland), changed direction at dawn on the 20th and started blowing N-NNW, and as the afternoon progressed the winds became more westerly. By 1532 on 20 September the plume had narrowed compared to previous GMS satellite images and the core was moving WSW at ~55 km/hour at an altitude of ~12 km. As night fell on 20 September the cloud had reached the main island of Papua New Guinea between Lae and Milne Bay; residents in the town of Lae, 600 km away, reported ashfall.

On 21 September, witnesses said huge mushroom clouds of dense, black smoke and debris continued to rise high above Tavurvur and Vulcan. Much of the falling ash combined with rain, turning to a heavy mud mixture that demolished some houses and destroyed coconut plantations. The airport was buried under debris, many roads were blocked, and the harbor was covered with debris and floating pumice.

The plume was still moving WSW at 1832 on 21 September at ~7.5 km altitude, and was visible for up to 90 km SW of the origin. Soon after this time the plume was no longer clearly visible on GMS imagery, indicating that strong explosive activity, which had ejected ash high into the atmosphere almost continuously since about 0600 on 19 September, had declined. Some residents returned to Rabaul town during a brief respite from the falling ash. However, by the morning of 22 September Vulcan was ejecting massive amounts of whitish ash and Tavurvur was emitting dark blackish-gray ash. GMS satellite imagery for 1230 on 22 September revealed a new mid-high level plume that was ~40 km long and moving WSW. The plume was estimated to be at ~7.5 km altitude, and could still be seen at 1530 on GMS infrared images.

A report from RVO for the period from 1500 on 22 September through 0900 the next day indicated that volcanic and seismic activity remained relatively stable. Steady emissions continued from Tavurvur with a dark gray ash-and-vapor cloud rising ~2 km and blowing NE over Rabaul town. Low rumbling sounds accompanied the stronger emissions. At night, incandescent ejecta could be seen falling on the NW flank, but incandescence was rarely visible in the eruptive column due to its high ash content. Intermittent pulses of stronger activity from Vulcan produced jets of a vapor-rich ash at intervals of 5-15 minutes. Collapse of the column generated pyroclastic surges that traveled 2-5 km from the vent, mostly to the NE. Generally there was a low volume of ash in the eruption cloud. The column height was about 1.5 km. At night witnesses saw incandescent ejecta accumulate around the vent at the beginning of each pulse.

An aerial inspection by volcanologists at 1620-1640 on 22 September revealed little morphological change at Tavurvur, with the active vent located on the W side of the 1937 crater. At Vulcan, the only active vent was near sea level on the breached NE-flank crater. Eruptions were Surtseyan, highly explosive, and vapor-rich with low ash content. No great deformation was noted since the start of the eruption. Overall, volcano-seismic activity showed a steady small decline during 20-22 September. During the inspection, visibility over Rabaul was generally very good, but there were occasional ash falls.

On the morning of 27 September, RVO reported that Vulcan was no longer erupting, but an ash plume from Tavurvur was still present, and there was an ashy haze over Rabaul town. Seismicity had decreased to about the detection limit using the RSAM averaging method. The observatory reported ~40 mm of fine powdery ash at their location, and ~50 cm of ash at the airport, with the ash-fall layer thickening rapidly towards Matupit Island. The press initially reported up to a meter of ash in Rabaul town, but later estimates were consistently around 75 cm for most areas. No accurate mapping of the ashfall has been completed. Press reports on 25 September estimated that 25% of the buildings in the greater Rabaul area had been completely destroyed, and that another 50% had significant structural damage. Preliminary damage assessments reported on 27 September by the UNDHA indicated that 40% of the buildings in the area had been seriously damaged.

Satellite-based SO₂ data. The Meteor-3 satellite overflew the eruption plume . . . at 1538 on 19 September. Preliminary results from the TOMS instrument showed SO₂ column amounts no higher than background and a slight column ozone increase in the region that was most likely due to the presence of SO₂. Another pass at 1520 on 20 September showed an SO₂ plume of ~45,000 km², with an SO₂ mass estimated at a maximum of 80 kilotons (kt) ± 50%. At 1503 the next day, preliminary results showed that the estimated size of the SO₂ plume was 50,000 km², with an SO₂ mass estimated at 70 kt ± 50%. The SO₂ detected on 21 September had probably been produced since the overflight on the previous day because the small tropospheric plume noted at that time would have either dispersed or been chemically converted within 24 hours. Preliminary data from the overflight at 1430 on 23 September showed an estimated size of at least 40,000 km² for the SO₂ plume, with an estimated SO₂ mass of 35 kt ± 50%. By 1410 on 24 September, SO₂ column amounts were no higher than background levels in the vicinity of the volcano.

Evacuations and official response. On the night of 18-19 September, during the period of strong continuous seismicity, an estimated 30,000 people evacuated from Rabaul town and surrounding villages. Apparently, most of the people left before the eruptions began, but evacuations by road and sea to the towns of Kokopo (20 km SE) and Kerevat (~25 km SW), continued on 19 September. The airport closed just as Tavurvur began erupting. Evacuees went to missions and townships along the Gazelle Peninsula, where they were housed in camps, schools, church halls, and hospitals. Authorities were preparing to provide food and shelter for up to 70,000 people.

Ships rescued thousands of villagers off beaches near Rabaul town on 20 September. Press reports indicated that although Rabaul town was totally evacuated, there were small villages in the surrounding hills where people were trapped and taking shelter in schools and churches. As of 21 September, 45,000 people had been displaced, of whom 25,000 were located in Kokopo and the remainder at Kerevat and nearby mission and government stations. By 23 September, the UNDHA reported that a total of 53,000 people had been displaced. The only reported casualties were one boy killed when he was hit by a truck during the evacuation, and one man struck by lightning.

Following the declaration of a state of emergency in Rabaul, the Prime Minister of Papua New Guinea made a helicopter inspection on the afternoon of 19 September. NOTAMs issued from the Port Moresby Flight Information Region on 19-20 September advised pilots to exercise caution and informed them that the airspace within a 110 km radius of the Rabaul airport was closed to all air traffic unless authorized by emergency management officials. A NOTAM on the 22nd advised aircraft to avoid an abnormally colored cloud, especially yellow-brown or grayish layers. It further stated that the ash particles could contaminate engine oil and cause engine deterioration within hours. The duty manager of Air Niugini (national airline of Papua New Guinea) said all flights to and from New Britain and New Ireland provinces had been suspended. Relief flights were using an abandoned airstrip at Tokua (~20 km SE of Rabaul), which had received no ashfall.

Looting in Rabaul town was reported during both the evacuation and on 21 September, when military forces were brought in to help local police. News reports frequently mentioned looting by residents who had not evacuated or by non-residents going into the evacuated area. By the evening of 21 September, the army had sealed off all outlying roads and only allowed entry by authorized personnel.

At the request of the Papua New Guinea government, the USGS Volcano Disaster Assistance Program sent three volcanologists to Rabaul on 28 September. They took telemetered seismic stations with a PC-based data acquisition and analysis system, several telemetered tiltmeters, and other deformation-monitoring instrumentation. This equipment was requested because RVO was unable to locate earthquakes with only three seismic stations remaining in operation. The other stations were incapacitated by tsunamis, vandalism, or heavy ashfall.

References. Almond, R.A., and McKee, C.O., 1982, Location of volcano-tectonic earthquakes within the Rabaul Caldera: Geological Survey of Papua New Guinea report 82/19.

McKee, C.O., Johnson, R.W., Lowenstein, P.L., Riley, S.J., Blong, R.J., de Saint-Ours, P., and Talai, B., 1985, Rabaul caldera, Papua New Guinea: volcanic hazards, surveillance, and eruption contingency planning: Journal of Volcanology and Geothermal Research, v. 23, p. 195-237.

Mori, J., McKee, C., Itikarai, I., Lowenstein, P., de Saint-Ours, P., and Talai, B., 1989, Earthquakes of the Rabaul Seismo-Deformational Crisis September 1983 to July 1985: Seismicity on a caldera ring fault: IAVCEI Proceedings in Volcanology 1, J.H. Latter (ed.), Volcanic Hazards: Assessment and Monitoring, p. 429-462.

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: C. McKee, R. Stewart, and I. Itikarai, RVO; J. Lynch, SAB; G. Stephens, NOAA/NESDIS; I. Sprod, GSFC; C. Evans, NASA-SSEOP; G. Wheller, Volcanex International Pty Ltd, Tasmania; Kevin Vang, Macquarie Univ, Sydney; ICAO; UNDHA; AP; UPI; Reuters; Papua New Guinea Post-Courier.

Weak shallow seismic activity (1-4 events/day) continued to be registered beneath the volcano throughout July and August. Average duration of volcanic tremor was less than 30 minutes/day. The gas-and-steam plume (up to 500 m above the extrusive dome) observed during 7-14 July was blown E for about 30 km. Clouds frequently prevented observations in July and early August. Normal fumarolic activity was observed above the extrusive dome during mid-August. In late August and early September a gas-and-steam plume was observed up to ~3 km above the extrusive dome. Shallow seismicity remained at normal levels (1-5 events/day) through 12 September, with an average of 0.3 hours of tremor/day.

A strong eruption in April 1993 has been followed by a plume visible during clear weather (18:4-8 & 10-12, and 19:1-4 & 6). Prior to that eruption, the most recent explosive activity was in April 1991 (16:3). The largest historical eruptions from Shiveluch occurred in 1854 and 1964.

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: V. Kirianov, IVGG.

The EVS mounted an expedition to visit N Sulawesi volcanoes in July. They found that the morphology of Soputan's lava dome suggested continued endogenous growth. Some other parts of their Soputan report follow.

"Many fumaroles rose in different parts of the dome, mainly in its central part and in the space between the dome's foot and the crater wall. The summit area of the dome was strewn with chaotic blocks covered by white and yellow sulfur deposits. Two other fumarolic fields were located on the SW and W parts of the lava dome. Temperature measurements showed a maximum of 140°C; gases mainly consisted of H₂S, SO₂, and CO₂."

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: H. Gaudru, C. Pittet, M. Auber, C. Bopp, and O. Saudan, EVS, Switzerland.

"Seismic activity in August continued the pattern of previous months, with mainly sub-continuous low-frequency tremor and occasional larger low-frequency earthquakes. No high-frequency earthquakes were recorded."

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: I. Itikarai, R. Stewart, and C. McKee, RVO.

The lava dome grew endogenously SE to SW during mid- to late-August. The S ridge on the dome top 0moved S by ~1 m/day and rose vertically by ~0.5 m/day; the central ridge decreased in height. Crest-line measurements from 3.5 km SE of the dome confirmed the endogenous growth. EDM measurements by the JMA in cooperation with the GSJ were hampered by poor weather conditions and volcanic ash. The eruption (magmatic extrusion) rate remained at a low level. The GSJ calculated the average eruption rate from early-April to mid-July as 60,000 m³/day, based on aerial photographs. This value is similar to those for February-April, although no values for the calculation error were given.

The N and S parts of the presently growing dome had no room for talus deposition (figure 75). Therefore, the advancing dome easily triggered rockfalls in both directions that moved straight downward as pyroclastic flows. Most parts of lobe 13 collapsed during 15-29 August, generating pyroclastic flows to the SW, S, and SE, which reached the Akamatsu valley. Pyroclastic flows detected seismically at a station ~1 km WSW of the dome totaled 264 during August. Real-time monitoring of pyroclastic flows is also conducted at the UWS using four sets of visible and thermal-infrared video cameras. In late August, JMA recorded the second largest daily number of pyroclastic flows since 20 May 1991, based on signals registered at the seismic station SW of the dome. This large number of events reflected smaller distances between pyroclastic flow routes and the seismic station than was previously the case.

Figure 75. Sketch map of the lava dome at Unzen, late August 1994. Solid dome rock is shown as black. Arrows indicate the main direction of pyroclastic flows and rockfalls. Solid and dashed lines represent slope dip directions of new and old talus deposits, respectively. Volcanic gas emission points are shown by "f" symbols. Courtesy of S. Nakada, Kyushu Univ.

On the nights of 15 and 16 August, pyroclastic flows descended SE ~400 m through a deep gully, which developed during rainy seasons at the S margin of the Akamatsu valley floor. Field inspection on 24 August showed that the 15-16 products were block-and-ash-flow deposits consisting of multiple layers each ~2 m thick. The deposits included still-hot lava blocks up to 3 m across in an ash matrix, and were covered with an ashfall layer ~10 cm thick. No associated surge deposits were evident. Gently sloped depressions ~2 m across, indicating underlying fumarolic pipes, were found on the surface of the 15-16 August deposits. The depression surfaces were reddish to yellowish brown, and lava pebbles (3. Density has increased roughly with time during this eruption (1.8 to 2.5 g/cm³); there has been a roughly negative correlation between density of lava blocks and eruption rate. The SiO₂ contents of new samples were 64.7-65.1 wt.%, remaining roughly constant with previous lavas (63.5-65.5%). These results indicate that the vesicularity (porosity) of lava blocks probably decreased with time.

Pyroclastic flows moving SW passed through a gully in the S slope of the dome, crossed the Akamatsu valley floor, and came against the N wall of Mt. Iwatoko, generating frequent ash clouds. A pyroclastic flow late on 27 August traveled 2.0 km SE and produced a signal that lasted for almost 30 minutes, the longest duration since pyroclastic flows began in May 1991. Many pyroclastic flows in the last 10 days of the month had long durations, but all were considered to be triggered by small-scale collapses. On 29 August, pyroclastic flows again moved SE through the gully in the Akamatsu valley; the horizontal travel distance was ~3 km from the source. The volume of the largest pyroclastic-flow deposits during this period was estimated to be ~100,000 m³.

Microearthquakes beneath the lava dome were registered at a rate of ~50/day during the first half of August, and gradually increased in number later in the month. On 28 August, 474 earthquakes were detected at a seismic station 3.6 km SW of the dome. In total, 7,306 earthquakes were registered during August.

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

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