Manam is a 10-km-wide island that consists of two active summit craters: the Main summit crater and the South summit crater and is located 13 km off the northern coast of mainland Papua New Guinea. Frequent mild-to-moderate eruptions have been recorded since 1616. The current eruption period began during June 2014 and has more recently been characterized by intermittent ash plumes and thermal activity (BGVN 47:11). This report updates activity that occurred from November 2022 through May 2023 based on information from the Darwin Volcanic Ash Advisory Center (VAAC) and various satellite data.

Ash plumes were reported during November and December 2022 by the Darwin VAAC. On 7 November an ash plume rose to 2.1 km altitude and drifted NE based on satellite images and weather models. On 14 November an ash plume rose to 2.1 km altitude and drifted W based on RVO webcam images. On 20 November ash plumes rose to 1.8 km altitude and drifted NW. On 26 December an ash plume rose to 3 km altitude and drifted S and SSE.

Intermittent sulfur dioxide plumes were detected using the TROPOMI instrument on the Sentinel-5P satellite, some of which exceeded at least two Dobson Units (DU) and drifted in different directions (figure 93). Occasional low-to-moderate power thermal anomalies were recorded by the MIROVA (Middle InfraRed Observation of Volcanic Activity) system; less than five anomalies were recorded each month during November 2022 through May 2023 (figure 94). Two thermal hotspots were detected by the MODVOLC thermal alerts system on 10 December 2022. On clear weather days, thermal activity was also captured in infrared satellite imagery in both the Main and South summit craters, accompanied by gas-and-steam emissions (figure 95).

Figure 93. Distinct sulfur dioxide plumes were captured, rising from Manam based on data from the TROPOMI instrument on the Sentinel-5P satellite on 16 November 2022 (top left), 6 December 2022 (top right), 14 January 2023 (bottom left), and 23 March 2023 (bottom right). Plumes generally drifted in different directions. Courtesy of the NASA Global Sulfur Dioxide Monitoring Page.

Figure 94. Occasional low-to-moderate power thermal anomalies were detected at Manam during November 2022 through May 2023, as shown in this MIROVA graph (Log Radiative Power). Only three anomalies were detected during late November, one in early December, two during January 2023, one in late March, four during April, and one during late May. Courtesy of MIROVA.

Figure 95. Infrared (bands B12, B11, B4) satellite images show a consistent thermal anomaly (bright yellow-orange) in both the Main (the northern crater) and South summit craters on 10 November 2022 (top left), 15 December 2022 (top right), 3 February 2023 (bottom left), and 24 April 2023 (bottom right). Gas-and-steam emissions occasionally accompanied the thermal activity. Courtesy of Copernicus Browser.

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: Rabaul Volcano Observatory (RVO), Geohazards Management Division, Department of Mineral Policy and Geohazards Management (DMPGM), PO Box 3386, Kokopo, East New Britain Province, Papua New Guinea; Darwin Volcanic Ash Advisory Centre (VAAC), Bureau of Meteorology, Northern Territory Regional Office, PO Box 40050, Casuarina, NT 0811, Australia (URL: http://www.bom.gov.au/info/vaac/); 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, Maryland, USA (URL: https://so2.gsfc.nasa.gov/); Copernicus Browser, Copernicus Data Space Ecosystem, European Space Agency (URL: https://dataspace.copernicus.eu/browser/).

Krakatau is located in the Sunda Strait between Java and Sumatra, Indonesia. Caldera collapse during the catastrophic 1883 eruption destroyed Danan and Perbuwatan cones and left only a remnant of Rakata. The post-collapse cone of Anak Krakatau (Child of Krakatau) was constructed within the 1883 caldera at a point between the former Danan and Perbuwatan cones; it has been the site of frequent eruptions since 1927. The current eruption period began in May 2021 and has recently consisted of explosions, ash plumes, and thermal activity (BGVN 47:11). This report covers activity during November 2022 through April 2023 based on information provided by the Indonesian Center for Volcanology and Geological Hazard Mitigation, referred to as Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG), MAGMA Indonesia, the Darwin Volcanic Ash Advisory Center (VAAC), and several sources of satellite data.

Activity was relatively low during November and December 2022. Daily white gas-and-steam plumes rose 25-100 m above the summit and drifted in different directions. Gray ash plumes rose 200 m above the summit and drifted NE at 1047 and at 2343 on 11 November. On 14 November at 0933 ash plumes rose 300 m above the summit and drifted E. An ash plume was reported at 0935 on 15 December that rose 100 m above the summit and drifted NE. An eruptive event at 1031 later that day generated an ash plume that rose 700 m above the summit and drifted NE. A gray ash plume at 1910 rose 100 m above the summit and drifted E. Incandescent material was ejected above the vent based on an image taken at 1936.

During January 2023 daily white gas-and-steam plumes rose 25-300 m above the summit and drifted in multiple directions. Gray-to-brown ash plumes were reported at 1638 on 3 January, at 1410 and 1509 on 4 January, and at 0013 on 5 January that rose 100-750 m above the summit and drifted NE and E; the gray-to-black ash plume at 1509 on 4 January rose as high as 3 km above the summit and drifted E. Gray ash plumes were recorded at 1754, 2241, and 2325 on 11 January and at 0046 on 12 January and rose 200-300 m above the summit and drifted NE. Toward the end of January, PVMBG reported that activity had intensified; Strombolian activity was visible in webcam images taken at 0041, 0043, and 0450 on 23 January. Multiple gray ash plumes throughout the day rose 200-500 m above the summit and drifted E and SE (figure 135). Webcam images showed progressively intensifying Strombolian activity at 1919, 1958, and 2113 on 24 January; a gray ash plume at 1957 rose 300 m above the summit and drifted E (figure 135). Eruptive events at 0231 and 2256 on 25 January and at 0003 on 26 January ejected incandescent material from the vent, based on webcam images. Gray ash plumes observed during 26-27 January rose 300-500 m above the summit and drifted NE, E, and SE.

Figure 135. Webcam images of a strong, gray ash plume (left) and Strombolian activity (right) captured at Krakatau at 0802 on 23 January 2023 (left) and at 2116 on 24 January 2023 (right). Courtesy of PVMBG and MAGMA Indonesia.

Low levels of activity were reported during February and March. Daily white gas-and-steam plumes rose 25-300 m above the summit and drifted in different directions. The Darwin VAAC reported that continuous ash emissions rose to 1.5-1.8 km altitude and drifted W and NW during 1240-1300 on 10 March, based on satellite images, weather models, and PVMBG webcams. White-and-gray ash plumes rose 500 m and 300 m above the summit and drifted SW at 1446 and 1846 on 18 March, respectively. An eruptive event was recorded at 2143, though it was not visible due to darkness. Multiple ash plumes were reported during 27-29 March that rose as high as 2.5 km above the summit and drifted NE, W, and SW (figure 136). Webcam images captured incandescent ejecta above the vent at 0415 and around the summit area at 2003 on 28 March and at 0047 above the vent on 29 March.

Figure 136. Webcam image of a strong ash plume rising above Krakatau at 1522 on 28 March 2023. Courtesy of PVMBG and MAGMA Indonesia.

Daily white gas-and-steam plumes rose 25-300 m above the summit and drifted in multiple directions during April and May. White-and-gray and black plumes rose 50-300 m above the summit on 2 and 9 April. On 11 May at 1241 a gray ash plume rose 1-3 km above the summit and drifted SW. On 12 May at 0920 a gray ash plume rose 2.5 km above the summit and drifted SW and at 2320 an ash plume rose 1.5 km above the summit and drifted SW. An accompanying webcam image showed incandescent ejecta. On 13 May at 0710 a gray ash plume rose 2 km above the summit and drifted SW (figure 137).

Figure 137. Webcam image of an ash plume rising 2 km above the summit of Krakatau at 0715 on 13 May 2023. Courtesy of PVMBG and MAGMA Indonesia.

The MIROVA (Middle InfraRed Observation of Volcanic Activity) graph of MODIS thermal anomaly data showed intermittent low-to-moderate power thermal anomalies during November 2022 through April 2023 (figure 138). Some of this thermal activity was also visible in infrared satellite imagery at the crater, accompanied by gas-and-steam and ash plumes that drifted in different directions (figure 139).

Figure 138. Intermittent low-to-moderate power thermal anomalies were detected at Krakatau during November 2022 through April 2023, based on this MIROVA graph (Log Radiative Power). Courtesy of MIROVA.

Figure 139. A thermal anomaly (bright yellow-orange) was visible at Krakatau in infrared (bands B12, B11, B4) satellite images on clear weather days during November 2022 through May 2023. Occasional gas-and-steam and ash plumes accompanied the thermal activity, which drifted in different directions. Images were captured on 25 November 2022 (top left), 15 December 2022 (top right), 27 January 2023 (bottom left), and 12 May 2023 (bottom right). Courtesy of Copernicus Browser.

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

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

Stromboli, located in Italy, has exhibited nearly constant lava fountains for the past 2,000 years; recorded eruptions date back to 350 BCE. Eruptive activity occurs at the summit from multiple vents, which include a north crater area (N area) and a central-southern crater (CS area) on a terrace known as the ‘terrazza craterica’ at the head of the Sciara del Fuoco, a large scarp that runs from the summit down the NW side of the volcano-island. Activity typically consists of Strombolian explosions, incandescent ejecta, lava flows, and pyroclastic flows. Thermal and visual monitoring cameras are located on the nearby Pizzo Sopra La Fossa, above the terrazza craterica, and at multiple flank locations. The current eruption period has been ongoing since 1934 and recent activity has consisted of frequent Strombolian explosions and lava flows (BGVN 48:02). This report updates activity during January through April 2023 primarily characterized by Strombolian explosions and lava flows based on reports from Italy's Istituto Nazionale di Geofisica e Vulcanologia (INGV) and various satellite data.

Frequent explosive activity continued throughout the reporting period, generally in the low-to-medium range, based on the number of hourly explosions in the summit crater (figure 253, table 16). Intermittent thermal activity was recorded by the MIROVA (Middle InfraRed Observation of Volcanic Activity) analysis of MODIS satellite data (figure 254). According to data collected by the MODVOLC thermal algorithm, a total of 9 thermal alerts were detected: one on 2 January 2023, one on 1 February, five on 24 March, and two on 26 March. The stronger pulses of thermal activity likely reflected lava flow events. Infrared satellite imagery captured relatively strong thermal hotspots at the two active summit craters on clear weather days, showing an especially strong event on 8 March (figure 255).

Figure 253. Explosive activity persisted at Stromboli during January through April 2023, with low to medium numbers of daily explosions at the summit crater. The average number of daily explosions (y-axis) during January through April (x-axis) are broken out by area and as a total, with red for the N area, blue for the CS area, and black for the combined total. The data are smoothed as daily (thin lines) and weekly (thick lines) averages. The black squares along the top represent days with no observations due to poor visibility (Visib. Scarsa). The right axis indicates the qualitative activity levels from low (basso) to highest (altissimo) with the green highlighted band indicating the most common level. Courtesy of INGV (Report 17/2023, Stromboli, Bollettino Settimanale, 18/04/2023 - 24/04/2023).

Table 16. Summary of type, frequency, and intensity of explosive activity at Stromboli by month during January-April 2023; information from webcam observations. Courtesy of INGV weekly reports.

Figure 254. Intermittent thermal activity at Stromboli was detected during January through April 2023 and varied in strength, as shown in this MIROVA graph (Log Radiative Power). A pulse of activity was captured during late March. Courtesy of MIROVA.

Figure 255. Infrared (bands B12, B11, B4) satellite images showing persistent thermal anomalies at both summit crater on 1 February 2023 (top left), 23 March 2023 (top right), 8 March 2023 (bottom left), and 27 April 2023. A particularly strong thermal anomaly was visible on 8 March. Courtesy of Copernicus Browser.

Activity during January-February 2023. Strombolian explosions were reported in the N crater area, as well as lava effusion. Explosive activity in the N crater area ejected coarse material (bombs and lapilli). Intense spattering was observed in both the N1 and N2 craters. In the CS crater area, explosions generally ejected fine material (ash), sometimes to heights greater than 250 m. The intensity of the explosions was characterized as low-to-medium in the N crater and medium-to-high in the CS crater. After intense spattering activity from the N crater area, a lava overflow began at 2136 on 2 January that flowed part way down the Sciara del Fuoco, possibly moving down the drainage that formed in October, out of view from webcams. The flow remained active for a couple of hours before stopping and beginning to cool. A second lava flow was reported at 0224 on 4 January that similarly remained active for a few hours before stopping and cooling. Intense spattering was observed on 11 and 13 January from the N1 crater. After intense spattering activity at the N2 crater at 1052 on 17 January another lava flow started to flow into the upper part of the Sciara del Fuoco (figure 256), dividing into two: one that traveled in the direction of the drainage formed in October, and the other one moving parallel to the point of emission. By the afternoon, the rate of the flow began to decrease, and at 1900 it started to cool. A lava flow was reported at 1519 on 24 January following intense spattering in the N2 area, which began to flow into the upper part of the Sciara del Fuoco. By the morning of 25 January, the lava flow had begun to cool. During 27 January the frequency of eruption in the CS crater area increased to 6-7 events/hour compared to the typical 1-7 events/hour; the following two days showed a decrease in frequency to less than 1 event/hour. Starting at 1007 on 30 January a high-energy explosive sequence was produced by vents in the CS crater area. The sequence began with an initial energetic pulse that lasted 45 seconds, ejecting predominantly coarse products 300 m above the crater that fell in an ESE direction. Subsequent and less intense explosions ejected material 100 m above the crater. The total duration of this event lasted approximately two minutes. During 31 January through 6, 13, and 24 February spattering activity was particularly intense for short periods in the N2 crater.

Figure 256. Webcam images of the lava flow development at Stromboli during 17 January 2023 taken by the SCT infrared camera. The lava flow appears light yellow-green in the infrared images. Courtesy of INGV (Report 04/2023, Stromboli, Bollettino Settimanale, 16/01/2023 - 22/01/2023).

An explosive sequence was reported on 16 February that was characterized by a major explosion in the CS crater area (figure 257). The sequence began at 1817 near the S2 crater that ejected material radially. A few seconds later, lava fountains were observed in the central part of the crater. Three explosions of medium intensity (material was ejected less than 150 m high) were recorded at the S2 crater. The first part of this sequence lasted approximately one minute, according to INGV, and material rose 300 m above the crater and then was deposited along the Sciara del Fuoco. The second phase began at 1818 at the S1 crater; it lasted seven seconds and material was ejected 150 m above the crater. Another event 20 seconds later lasted 12 seconds, also ejecting material 150 m above the crater. The sequence ended with at least three explosions of mostly fine material from the S1 crater. The total duration of this sequence was about two minutes.

Figure 257. Webcam images of the explosive sequence at Stromboli on 16 February 2023 taken by the SCT and SCV infrared and visible cameras. The lava appears light yellow-green in the infrared images. Courtesy of INGV (Report 08/2023, Stromboli, Bollettino Settimanale, 13/02/2023 - 19/02/2023).

Short, intense spattering activity was noted above the N1 crater on 27 and 28 February. A lava overflow was first reported at 0657 from the N2 crater on 27 February that flowed into the October 2022 drainage. By 1900 the flow had stopped. A second lava overflow also in the N crater area occurred at 2149, which overlapped the first flow and then stopped by 0150 on 28 February. Material detached from both the lava overflows rolled down the Sciara del Fuoco, some of which was visible in webcam images.

Activity during March-April 2023. Strombolian activity continued with spattering activity and lava overflows in the N crater area during March. Explosive activity at the N crater area varied from low (less than 80 m high) to medium (less than 150 m high) and ejected coarse material, such as bombs and lapilli. Spattering was observed above the N1 crater, while explosive activity at the CS crater area varied from medium to high (greater than 150 m high) and ejected coarse material. Intense spattering activity was observed for short periods on 6 March above the N1 crater. At approximately 0610 a lava overflow was reported around the N2 crater on 8 March, which then flowed into the October 2022 drainage. By 1700 the flow started to cool. A second overflow began at 1712 on 9 March and overlapped the previous flow. It had stopped by 2100. Material from both flows was deposited along the Sciara del Fuoco, though much of the activity was not visible in webcam images. On 11 March a lava overflow was observed at 0215 that overlapped the two previous flows in the October 2022 drainage. By late afternoon on 12 March, it had stopped.

During a field excursion on 16 March, scientists noted that a vent in the central crater area was degassing. Another vent showed occasional Strombolian activity that emitted ash and lapilli. During 1200-1430 low-to-medium intense activity was reported; the N1 crater emitted ash emissions and the N2 crater emitted both ash and coarse material. Some explosions also occurred in the CS crater area that ejected coarse material. The C crater in the CS crater area occasionally showed gas jetting and low intensity explosions on 17 and 22 March; no activity was observed at the S1 crater. Intense, longer periods of spattering were reported in the N1 crater on 19, 24, and 25 March. Around 2242 on 23 March a lava overflow began from the N1 crater that, after about an hour, began moving down the October 2022 drainage and flow along the Sciara del Fuoco (figure 258). Between 0200 and 0400 on 26 March the flow rate increased, which generated avalanches of material from collapses at the advancing flow front. By early afternoon, the flow began to cool. On 25 March at 1548 an explosive sequence began from one of the vents at S2 in the CS crater area (figure 258). Fine ash mixed with coarse material was ejected 300 m above the crater rim and drifted SSE. Some modest explosions around Vent C were detected at 1549 on 25 March, which included an explosion at 1551 that ejected coarse material. The entire explosive sequence lasted approximately three minutes.

Figure 258. Webcam images of the lava overflow in the N1 crater area of Stromboli on 23 March 2023 taken by the SCT infrared camera. The lava appears light yellow-green in the infrared images. The start of the explosive sequence was also captured on 25 March 2023 accompanied by an eruption plume (e) captured by the SCT and SPT infrared webcams. Courtesy of INGV (Report 13/2023, Stromboli, Bollettino Settimanale, 20/03/2023 - 26/03/2023).

During April explosions persisted in both the N and CS crater areas. Fine material was ejected less than 80 m above the N crater rim until 6 April, followed by ejection of coarser material. Fine material was also ejected less than 80 m above the CS crater rim. The C and S2 crater did not show significant eruptive activity. On 7 April an explosive sequence was detected in the CS crater area at 1203 (figure 259). The first explosion lasted approximately 18 seconds and ejected material 400 m above the crater rim, depositing pyroclastic material in the upper part of the Sciara del Fuoco. At 1204 a second, less intense explosion lasted approximately four seconds and deposited pyroclastic products outside the crater area and near Pizzo Sopra La Fossa. A third explosion at 1205 was mainly composed of ash that rose about 150 m above the crater and lasted roughly 20 seconds. A fourth explosion occurred at 1205 about 28 seconds after the third explosion and ejected a mixture of coarse and fine material about 200 m above the crater; the explosion lasted roughly seven seconds. Overall, the entire explosive sequence lasted about two minutes and 20 seconds. After the explosive sequence on 7 April, explosions in both the N and CS crater areas ejected material as high as 150 m above the crater.

Figure 259. Webcam images of the explosive sequence at Stromboli during 1203-1205 (local time) on 7 April 2023 taken by the SCT infrared camera. Strong eruption plumes are visible, accompanied by deposits on the nearby flanks. Courtesy of INGV (Report 15/2023, Stromboli, Bollettino Settimanale, 03/04/2023 - 09/04/2023).

On 21 April research scientists from INGV made field observations in the summit area of Stromboli, and some lapilli samples were collected. In the N crater area near the N1 crater, a small cone was observed with at least two active vents, one of which was characterized by Strombolian explosions. The other vent produced explosions that ejected ash and chunks of cooled lava. At the N2 crater at least one vent was active and frequently emitted ash. In the CS crater area, a small cone contained 2-3 degassing vents and a smaller, possible fissure area also showed signs of degassing close to the Pizzo Sopra La Fossa. In the S part of the crater, three vents were active: a small hornito was characterized by modest and rare explosions, a vent that intermittently produced weak Strombolian explosions, and a vent at the end of the terrace that produced frequent ash emissions. Near the S1 crater there was a hornito that generally emitted weak gas-and-steam emissions, sometimes associated with “gas rings”. On 22 April another field inspection was carried out that reported two large sliding surfaces on the Sciara del Fuoco that showed where blocks frequently descended toward the sea. A thermal anomaly was detected at 0150 on 29 April.

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

Information Contacts: Istituto Nazionale di Geofisica e Vulcanologia (INGV), Sezione di Catania, Piazza Roma 2, 95123 Catania, Italy, (URL: http://www.ct.ingv.it/en/); 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/); Copernicus Browser, Copernicus Data Space Ecosystem, European Space Agency (URL: https://dataspace.copernicus.eu/browser/).

Nishinoshima is a small island located about 1,000 km S of Tokyo in the Ogasawara Arc in Japan. The island is the summit of a massive submarine volcano that has prominent peaks to the S, W, and NE. Eruptions date back to 1973; the most recent eruption period began in October 2022 and was characterized by ash plumes and fumarolic activity (BGVN 47:12). This report describes ash plumes and fumarolic activity during November 2022 through April 2023 based on monthly reports from the Japan Meteorological Agency (JMA) monthly reports and satellite data.

The most recent eruptive activity prior to the reporting internal occurred on 12 October 2022, when an ash plume rose 3.5 km above the crater rim. An aerial observation conducted by the Japan Coast Guard (JCG) on 25 November reported that white fumaroles rose approximately 200 m above the central crater of a pyroclastic cone (figure 119), and multiple plumes were observed on the ESE flank of the cone. Discolored water ranging from reddish-brown to brown and yellowish-green were visible around the perimeter of the island (figure 119). No significant activity was reported in December.

Figure 119. Aerial photo of gas-and-steam plumes rising 200 m above Nishinoshima on 25 November 2022. Reddish brown to brown and yellowish-green discolored water was visible around the perimeter of the island. Courtesy of JCG via JMA (monthly reports of activity at Nishinoshima, November 2022).

During an overflight conducted by JCG on 25 January 2023 intermittent activity and small, blackish-gray plumes rose 900 m above the central part of the crater were observed (figure 120). The fumarolic zone of the E flank and base of the cone had expanded and emissions had intensified. Dark brown discolored water was visible around the perimeter of the island.

Figure 120. Aerial photo of a black-gray ash plume rising approximately 900 m above the crater rim of Nishinoshima on 25 January 2023. White fumaroles were visible on the E slope of the pyroclastic cone. Dense brown to brown discolored water was observed surrounding the island. Photo has been color corrected. Courtesy of JCG via JMA (monthly reports of activity at Nishinoshima, January, 2023).

No significant activity was reported during February through March. Ash plumes at 1050 and 1420 on 11 April rose 1.9 km above the crater rim and drifted NW and N. These were the first ash plumes observed since 12 October 2022. On 14 April JCG carried out an overflight and reported that no further eruptive activity was visible, although white gas-and-steam plumes were visible from the central crater and rose 900 m high (figure 121). Brownish and yellow-green discolored water surrounded the island.

Figure 121. Aerial photo of white gas-and-steam plumes rising 900 m above Nishinoshima on 14 April 2023. Brown and yellow-green discolored water is visible around the perimeter of the island. Photo has been color corrected. Courtesy of JCG via JMA (monthly reports of activity at Nishinoshima, April, 2023).

Intermittent low-to-moderate power thermal anomalies were recorded in the MIROVA graph (Middle InfraRed Observation of Volcanic Activity) during November 2022 through April 2023 (figure 123). A cluster of six to eight anomalies were detected during November while a smaller number were detected during the following months: two to three during December, one during mid-January 2023, one during February, five during March, and two during April. Thermal activity was also reflected in infrared satellite data at the summit crater, accompanied by occasional gas-and-steam plumes (figure 124).

Figure 123. Intermittent low-to-moderate thermal anomalies were detected at Nishinoshima during November 2022 through April 2023, according to this MIROVA graph (Log Radiative Power). A cluster of anomalies occurred throughout November, while fewer anomalies were detected during the following months. Courtesy of MIROVA.

Figure 124. Infrared (bands B12, B11, B4) satellite images show a small thermal anomaly at the summit crater of Nishinoshima on 9 January 2023 (left) and 8 February 2023 (right). Gas-and-steam plumes accompanied this activity and extended S and SE, respectively. Courtesy of Copernicus Browser.

Geologic Background. The small island of Nishinoshima was enlarged when several new islands coalesced during an eruption in 1973-74. Multiple eruptions that began in 2013 completely covered the previous exposed surface and continued to enlarge the island. The island is the summit of a massive submarine volcano that has prominent peaks to the S, W, and NE. The summit of the southern cone rises to within 214 m of the ocean surface 9 km SSE.

Information Contacts: Japan Meteorological Agency (JMA), 1-3-4 Otemachi, Chiyoda-ku, Tokyo 100-8122, Japan (URL: http://www.jma.go.jp/jma/indexe.html); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Copernicus Browser, Copernicus Data Space Ecosystem, European Space Agency (URL: https://dataspace.copernicus.eu/browser/).

Karangetang (also known as Api Siau), at the northern end of the island of Siau, Indonesia, contains five summit craters along a N-S line. More than 40 eruptions have been recorded since 1675; recent eruptions have included frequent explosive activity, sometimes accompanied by pyroclastic flows and lahars. Lava dome growth has occurred in the summit craters and collapses of lava flow fronts have produced pyroclastic flows. The two active summit craters are Kawah Dua (the N crater) and Kawah Utama (the S crater, also referred to as the “Main Crater”). The most recent eruption began in late November 2018 and has more recently consisted of weak thermal activity and gas-and-steam emissions (BGVN 48:01). This report updates activity characterized by lava flows, incandescent avalanches, and ash plumes during January through June 2023 using reports from Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as CVGHM, or the Center of Volcanology and Geological Hazard Mitigation), MAGMA Indonesia, the Darwin VAAC (Volcano Ash Advisory Center), and satellite data.

Activity during January was relatively low and mainly consisted of white gas-and-steam emissions that rose 25-150 m above Main Crater (S crater) and drifted in different directions. Incandescence was visible from the lava dome in Kawah Dua (the N crater). Weather conditions often prevented clear views of the summit. On 18 January the number of seismic signals that indicated avalanches of material began to increase. In addition, there were a total of 71 earthquakes detected during the month.

Activity continued to increase during the first week of February. Material from Main Crater traveled as far as 800 m down the Batuawang (S) and Batang (W) drainages and as far as 1 km W down the Beha (W) drainage on 4 February. On 6 February 43 earthquake events were recorded, and on 7 February, 62 events were recorded. White gas-and-steam emissions rose 25-250 m above both summit craters throughout the month. PVMBG reported an eruption began during the evening of 8 February around 1700. Photos showed incandescent material at Main Crater. Incandescent material had also descended the flank in at least two unconfirmed directions as far as 2 km from Main Crater, accompanied by ash plumes (figure 60). As a result, PVMBG increased the Volcano Alert Level (VAL) to 3 (the second highest level on a 1-4 scale).

Figure 60. Photos of the eruption at Karangetang on 8 February 2023 that consisted of incandescent material descending the flanks (top left), ash plumes (top right and bottom left), and summit crater incandescence (bottom right). Courtesy of IDN Times.

Occasional nighttime webcam images showed three main incandescent lava flows of differing lengths traveling down the S, SW, and W flanks (figure 61). Incandescent rocks were visible on the upper flanks, possibly from ejected or collapsed material from the crater, and incandescence was the most intense at the summit. Based on analyses of satellite imagery and weather models, the Darwin VAAC reported that daily ash plumes during 16-20 February rose to 2.1-3 km altitude and drifted NNE, E, and SE. BNPB reported on 16 February that as many as 77 people were evacuated and relocated to the East Siau Museum. A webcam image taken at 2156 on 17 February possibly showed incandescent material descending the SE flank. Ash plumes rose to 2.1 km altitude and drifted SE during 22-23 February, according to the Darwin VAAC.

Figure 61. Webcam image of summit incandescence and lava flows descending the S, SW, and W flanks of Karangetang on 13 February 2023. Courtesy of MAGMA Indonesia.

Incandescent avalanches of material and summit incandescence at Main Crater continued during March. White gas-and-steam emissions during March generally rose 25-150 m above the summit crater; on 31 March gas-and-steam emissions rose 200-400 m high. An ash plume rose to 2.4 km altitude and drifted S at 1710 on 9 March and a large thermal anomaly was visible in images taken at 0550 and 0930 on 10 March. Incandescent material was visible at the summit and on the flanks based on webcam images taken at 0007 and 2345 on 16 March, at 1828 on 17 March, at 1940 on 18 March, at 2311 on 19 March, and at 2351 on 20 March. Incandescence was most intense on 18 and 20 March and webcam images showed possible Strombolian explosions (figure 62). An ash plume rose to 2.4 km altitude and drifted SW on 18 March, accompanied by a thermal anomaly.

Figure 62. Webcam image of intense summit incandescence and incandescent avalanches descending the flanks of Karangetang on 18 March 2023. Photo has been color corrected. Courtesy of MAGMA Indonesia.

Summit crater incandescence at Main Crater and on the flanks persisted during April. Incandescent material at the S crater and on the flanks was reported at 0016 on 1 April. The lava flows had stopped by 1 April according to PVMBG, although incandescence was still visible up to 10 m high. Seismic signals indicating effusion decreased and by 6 April they were no longer detected. Incandescence was visible from both summit craters. On 26 April the VAL was lowered to 2 (the second lowest level on a 1-4 scale). White gas-and-steam emissions rose 25-200 m above the summit crater.

During May white gas-and-steam emissions generally rose 50-250 m above the summit, though it was often cloudy, which prevented clear views; on 21 May gas-and-steam emissions rose 50-400 m high. Nighttime N summit crater incandescence rose 10-25 m above the lava dome, and less intense incandescence was noted above Main Crater, which reached about 10 m above the dome. Sounds of falling rocks at Main Crater were heard on 15 May and the seismic network recorded 32 rockfall events in the crater on 17 May. Avalanches traveled as far as 1.5 km down the SW and S flanks, accompanied by rumbling sounds on 18 May. Incandescent material descending the flanks was captured in a webcam image at 2025 on 19 May (figure 63) and on 29 May; summit crater incandescence was observed in webcam images at 2332 on 26 May and at 2304 on 29 May. On 19 May the VAL was again raised to 3.

Figure 63. Webcam image showing incandescent material descending the flanks of Karangetang on 19 May 2023. Courtesy of MAGMA Indonesia.

Occasional Main Crater incandescence was reported during June, as well as incandescent material on the flanks. White gas-and-steam emissions rose 10-200 m above the summit crater. Ash plumes rose to 2.1 km altitude and drifted SE and E during 2-4 June, according to the Darwin VAAC. Material on the flanks of Main Crater were observed at 2225 on 7 June, at 2051 on 9 June, at 0007 on 17 June, and at 0440 on 18 June. Webcam images taken on 21, 25, and 27 June showed incandescence at Main Crater and from material on the flanks.

MIROVA (Middle InfraRed Observation of Volcanic Activity) analysis of MODIS satellite data showed strong thermal activity during mid-February through March and mid-May through June, which represented incandescent avalanches and lava flows (figure 64). During April through mid-May the power of the anomalies decreased but frequent anomalies were still detected. Brief gaps in activity occurred during late March through early April and during mid-June. Infrared satellite images showed strong lava flows mainly affecting the SW and S flanks, accompanied by gas-and-steam emissions (figure 65). According to data recorded by the MODVOLC thermal algorithm, there were a total of 79 thermal hotspots detected: 28 during February, 24 during March, one during April, five during May, and 21 during June.

Figure 64. Strong thermal activity was detected during mid-February 2023 through March and mid-May through June at Karangetang during January through June 2023, as recorded by this MIROVA graph (Log Radiative Power). During April through mid-May the power of the anomalies decreased, but the frequency at which they occurred was still relatively high. A brief gap in activity was shown during mid-June. Courtesy of MIROVA.

Figure 65. Incandescent avalanches of material and summit crater incandescence was visible in infrared satellite images (bands 12, 11, 8A) at both the N and S summit crater of Karangetang on 17 February 2023 (top left), 13 April 2023 (top right), 28 May 2023 (bottom left), and 7 June 2023 (bottom right), as shown in these infrared (bands 12, 11, 8A) satellite images. The incandescent avalanches mainly affected the SW and S flanks. Sometimes gas-and-steam plumes accompanied the thermal activity. Courtesy of Copernicus Browser.

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: 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); Badan Nasional Penanggulangan Bencana (BNPB), National Disaster Management Agency, Graha BNPB - Jl. Scout Kav.38, East Jakarta 13120, Indonesia (URL: http://www.bnpb.go.id/); Darwin Volcanic Ash Advisory Centre (VAAC), Bureau of Meteorology, Northern Territory Regional Office, PO Box 40050, Casuarina, NT 0811, Australia (URL: http://www.bom.gov.au/info/vaac/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Hawai'i Institute of Geophysics and Planetology (HIGP) - MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); Copernicus Browser, Copernicus Data Space Ecosystem, European Space Agency (URL: https://dataspace.copernicus.eu/browser/); IDN Times, Jl. Jend. Gatot Subroto Kav. 27 3rd Floor Kuningan, Jakarta, Indonesia 12950, Status of Karangetang Volcano in Sitaro Islands Increases (URL: https://sulsel.idntimes.com/news/indonesia/savi/status-gunung-api-karangetang-di-kepulauan-sitaro-meningkat?page=all).

Ahyi seamount is a large, conical submarine volcano that rises to within 75 m of the ocean surface about 18 km SE of the island of Farallon de Pajaros in the Northern Marianas. The remote location of the seamount has made eruptions difficult to document, but seismic stations installed in the region confirmed an eruption in the vicinity in 2001. No new activity was detected until April-May 2014 when an eruption was detected by NOAA (National Oceanic and Atmospheric Administration) divers, hydroacoustic sensors, and seismic stations (BGVN 42:04). New activity was first detected on 15 November by hydroacoustic sensors that were consistent with submarine volcanic activity. This report covers activity during November 2022 through June 2023 based on daily and weekly reports from the US Geological Survey.

Starting in mid-October, hydroacoustic sensors at Wake Island (2.2 km E) recorded signals consistent with submarine volcanic activity, according to a report from the USGS issued on 15 November 2022. A combined analysis of the hydroacoustic signals and seismic stations located at Guam and Chichijima Island, Japan, suggested that the source of this activity was at or near the Ahyi seamount. After a re-analysis of a satellite image of the area that was captured on 6 November, USGS confirmed that there was no evidence of discoloration at the ocean surface. Few hydroacoustic and seismic signals continued through November, including on 18 November, which USGS suggested signified a decline or pause in unrest. A VONA (Volcano Observatory Notice for Aviation) reported that a discolored water plume was persistently visible in satellite data starting on 18 November (figure 6). Though clouds often obscured clear views of the volcano, another discolored water plume was captured in a satellite image on 26 November. The Aviation Color Code (ACC) was raised to Yellow (the second lowest level on a four-color scale) and the Volcano Alert Level (VAL) was raised to Advisory (the second lowest level on a four-level scale) on 29 November.

Figure 6. A clear, true color satellite image showed a yellow-green discolored water plume extending NW from the Ahyi seamount (white arrow) on 21 November 2022. Courtesy of Copernicus Browser.

During December, occasional detections were recorded on the Wake Island hydrophone sensors and discolored water over the seamount remained visible. During 2-7, 10-12, and 16-31 December possible explosion signals were detected. A small area of discolored water was observed in high-resolution Sentinel-2 satellite images during 1-6 December (figure 7). High-resolution satellite images recorded discolored water plumes on 13 December that originated from the summit region; no observations indicated that activity breached the ocean surface. A possible underwater plume was visible in satellite images on 18 December, and during 19-20 December a definite but diffuse underwater plume located SSE from the main vent was reported. An underwater plume was visible in a satellite image taken on 26 December (figure 7).

Figure 7. Clear, true color satellite images showed yellow-green discolored water plumes extending NE and W from Ahyi (white arrows) on 1 (left) and 26 (right) December 2022, respectively. Courtesy of Copernicus Browser.

Hydrophone sensors continued to detect signals consistent with possible explosions during 1-8 January 2023. USGS reported that the number of detections decreased during 4-5 January. The hydrophone sensors experienced a data outage that started at 0118 on 8 January and continued through 10 January, though according to USGS, possible explosions were recorded prior to the data outage and likely continued during the outage. A discolored water plume originating from the summit region was detected in a partly cloudy satellite image on 8 January. On 11-12 and 15-17 January possible explosion signals were recorded again. One small signal was detected during 22-23 January and several signals were recorded on 25 and 31 January. During 27-31 January a plume of discolored water was observed above the seamount in satellite imagery (figure 8).

Figure 8. True color satellite images showed intermittent yellow-green discolored water plumes of various sizes extending N on 5 January 2023 (top left), SE on 30 January 2023 (top right), W on 4 February 2023 (bottom left), and SW on 1 March 2023 (bottom right) from Ahyi (white arrows). Courtesy of Copernicus Browser.

Low levels of activity continued during February and March, based on data from pressure sensors on Wake Island. During 1 and 4-6 February activity was reported, and a submarine plume was observed on 4 February (figure 8). Possible explosion signals were detected during 7-8, 10, 13-14, and 24 February. During 1-2 and 3-5 March a plume of discolored water was observed in satellite imagery (figure 8). Almost continuous hydroacoustic signals were detected in remote pressure sensor data on Wake Island 2,270 km E from the volcano during 7-13 March. During 12-13 March water discoloration around the seamount was observed in satellite imagery, despite cloudy weather. By 14 March discolored water extended about 35 km, but no direction was noted. USGS reported that the continuous hydroacoustic signals detected during 13-14 March stopped abruptly on 14 March and no new detections were observed. Three 30 second hydroacoustic detections were reported during 17-19 March, but no activity was visible due to cloudy weather. A data outage was reported during 21-22 March, making pressure sensor data unavailable; a discolored water plume was, however, visible in satellite data. A possible underwater explosion signal was detected by pressure sensors at Wake Island on 26, 29, and 31 March, though the cause and origin of these events were unclear.

Similar low activity continued during April, May, and June. Several signals were detected during 1-3 April in pressure sensors at Wake Island. USGS suggested that these may be related to underwater explosions or earthquakes at the volcano, but no underwater plumes were visible in clear satellite images. The pressure sensors had data outages during 12-13 April and no data were recorded; no underwater plumes were visible in satellite images, although cloudy weather obscured most clear views. Eruptive activity was reported starting at 2210 on 21 May. On 22 May a discolored water plume that extended 4 km was visible in satellite images, though no direction was recorded. During 23-24 May some signals were detected by the underwater pressure sensors. Possible hydroacoustic signals were detected during 2-3 and 6-8 June. Multiple hydroacoustic signals were detected during 9-11 and 16-17 June, although no activity was visible in satellite images. One hydroacoustic signal was detected during 23-24 June, but there was some uncertainty about its association with volcanic activity. A single possible hydroacoustic signal was detected during 30 June to 1 July.

Geologic Background. Ahyi seamount is a large conical submarine volcano that rises to within 75 m of the ocean surface ~18 km SE of the island of Farallon de Pajaros in the northern Marianas. Water discoloration has been observed there, and in 1979 the crew of a fishing boat felt shocks over the summit area, followed by upwelling of sulfur-bearing water. On 24-25 April 2001 an explosive eruption was detected seismically by a station on Rangiroa Atoll, Tuamotu Archipelago. The event was well constrained (+/- 15 km) at a location near the southern base of Ahyi. An eruption in April-May 2014 was detected by NOAA divers, hydroacoustic sensors, and seismic stations.

Information Contacts: US Geological Survey, Volcano Hazards Program (USGS-VHP), 12201 Sunrise Valley Drive, Reston, VA, USA, https://volcanoes.usgs.gov/index.html; Copernicus Browser, Copernicus Data Space Ecosystem, European Space Agency (URL: https://dataspace.copernicus.eu/browser/).

Kadovar is a 2-km-wide island that is the emergent summit of a Bismarck Sea stratovolcano. It lies off the coast of New Guinea, about 25 km N of the mouth of the Sepik River. Prior to an eruption that began in 2018, a lava dome formed the high point of the volcano, filling an arcuate landslide scarp open to the S. Submarine debris-avalanche deposits occur to the S of the island. The current eruption began in January 2018 and has comprised lava effusion from vents at the summit and at the E coast; more recent activity has consisted of ash plumes, weak thermal activity, and gas-and-steam plumes (BGVN 48:02). This report covers activity during February through May 2023 using information from the Darwin Volcanic Ash Advisory Center (VAAC) and satellite data.

Activity during the reporting period was relatively low and mainly consisted of white gas-and-steam plumes that were visible in natural color satellite images on clear weather days (figure 67). According to a Darwin VAAC report, at 2040 on 6 May an ash plume rose to 4.6 km altitude and drifted W; by 2300 the plume had dissipated. MODIS satellite instruments using the MODVOLC thermal algorithm detected a single thermal hotspot on the SE side of the island on 7 May. Weak thermal activity was also detected in a satellite image on the E side of the island on 14 May, accompanied by a white gas-and-steam plume that drifted SE (figure 68).

Figure 67. True color satellite images showing a white gas-and-steam plume rising from Kadovar on 28 February 2023 (left) and 30 March 2023 (right) and drifting SE and S, respectively. Courtesy of Copernicus Browser.

Figure 68. Infrared (bands B12, B11, B4) image showing weak thermal activity on the E side of the island, accompanied by a gas-and-steam plume that drifted SE from Kadovar on 14 May 2023. Courtesy of Copernicus Browser.

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

Information Contacts: 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/); 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/); Copernicus Browser, Copernicus Data Space Ecosystem, European Space Agency (URL: https://dataspace.copernicus.eu/browser/).

San Miguel in El Salvador is a broad, deep crater complex that has been frequently modified by eruptions recorded since the early 16th century and consists of the summit known locally as Chaparrastique. Flank eruptions have produced lava flows that extended to the N, NE, and SE during the 17-19th centuries. The most recent activity has consisted of minor ash eruptions from the summit crater. The current eruption period began in November 2022 and has been characterized by frequent phreatic explosions, gas-and-ash emissions, and sulfur dioxide plumes (BGVN 47:12). This report describes small gas-and-ash explosions during December 2022 through May 2023 based on special reports from the Ministero de Medio Ambiente y Recursos Naturales (MARN).

Activity has been relatively low since the last recorded explosions on 29 November 2022. Seismicity recorded by the San Miguel Volcano Station (VSM) located on the N flank at 1.7 km elevation had decreased by 7 December. Sulfur dioxide gas measurements taken with DOAS (Differential Optical Absorption Spectroscopy) mobile equipment were below typical previously recorded values: 300 tons per day (t/d). During December, small explosions were recorded by the seismic network and manifested as gas-and-steam emissions.

Gas-and-ash explosions in the crater occurred during January 2023, which were recorded by the seismic network. Sulfur dioxide values remained low, between 300-400 t/d through 10 March. At 0817 on 14 January a gas-and-ash emission was visible in webcam images, rising just above the crater rim. Some mornings during February, small gas-and-steam plumes were visible in the crater. On 7 March at 2252 MARN noted an increase in degassing from the central crater; gas emissions were constantly observed through the early morning hours on 8 March. During the early morning of 8 March through the afternoon on 9 March, 12 emissions were registered, some accompanied by ash. The last gas-and-ash emission was recorded at 1210 on 9 March; very fine ashfall was reported in El Tránsito (10 km S), La Morita (6 km W), and La Piedrita (3 km W). The smell of sulfur was reported in Piedra Azul (5 km SW). On 16 March MARN reported that gas-and-steam emissions decreased.

Low degassing and very low seismicity were reported during April; no explosions have been detected between 9 March and 27 May. The sulfur dioxide emissions remained between 350-400 t/d; during 13-20 April sulfur dioxide values fluctuated between 30-300 t/d. Activity remained low through most of May; on 23 May seismicity increased. An explosion was detected at 1647 on 27 May generated a gas-and-ash plume that rose 700 m high (figure 32); a decrease in seismicity and gas emissions followed. The DOAS station installed on the W flank recorded sulfur dioxide values that reached 400 t/d on 27 May; subsequent measurements showed a decrease to 268 t/d on 28 May and 100 t/d on 29 May.

Figure 32. Webcam image of a gas-and-ash plume rising 700 m above San Miguel at 1652 on 27 May 2023. Courtesy of MARN.

Geologic Background. The symmetrical cone of San Miguel, one of the most active volcanoes in El Salvador, rises from near sea level to form one of the country's most prominent landmarks. A broad, deep, crater complex that has been frequently modified by eruptions recorded since the early 16th century caps the truncated unvegetated summit, also known locally as Chaparrastique. Flanks eruptions of the basaltic-andesitic volcano have produced many lava flows, including several during the 17th-19th centuries that extended to the N, NE, and SE. The SE-flank flows are the largest and form broad, sparsely vegetated lava fields crossed by highways and a railroad skirting the base of the volcano. Flank vent locations have migrated higher on the edifice during historical time, and the most recent activity has consisted of minor ash eruptions from the summit crater.

Information Contacts: Ministero de Medio Ambiente y Recursos Naturales (MARN), Km. 5½ Carretera a Nueva San Salvador, Avenida las Mercedes, San Salvador, El Salvador (URL: http://www.snet.gob.sv/ver/vulcanologia).

Semisopochnoi is located in the western Aleutians, is 20-km-wide at sea level, and contains an 8-km-wide caldera. The three-peaked Mount Young (formerly Cerberus) was constructed within the caldera during the Holocene. Each of these peaks contains a summit crater; the lava flows on the N flank appear younger than those on the S side. The current eruption period began in early February 2021 and has more recently consisted of intermittent explosions and ash emissions (BGVN 47:12). This report updates activity during December 2022 through May 2023 using daily, weekly, and special reports from the Alaska Volcano Observatory (AVO). AVO monitors the volcano using local seismic and infrasound sensors, satellite data, web cameras, and remote infrasound and lightning networks.

Activity during most of December 2022 was relatively quiet; according to AVO no eruptive or explosive activity was observed since 7 November 2022. Intermittent tremor and occasional small earthquakes were observed in geophysical data. Continuous gas-and-steam emissions were observed from the N crater of Mount Young in webcam images on clear weather days (figure 25). On 24 December, there was a slight increase in earthquake activity and several small possible explosion signals were detected in infrasound data. Eruptive activity resumed on 27 December at the N crater of Mount Young; AVO issued a Volcano Activity Notice (VAN) that reported minor ash deposits on the flanks of Mount Young that extended as far as 1 km from the vent, according to webcam images taken during 27-28 December (figure 26). No ash plumes were observed in webcam or satellite imagery, but a persistent gas-and-steam plume that might have contained some ash rose to 1.5 km altitude. As a result, AVO raised the Aviation Color Code (ACC) to Orange (the second highest level on a four-color scale) and the Volcano Alert Level (VAL) to Watch (the second highest level on a four-level scale). Possible explosions were detected during 21 December 2022 through 1 January 2023 and seismic tremor was recorded during 30-31 December.

Figure 25. Webcam image of a gas-and-steam plume rising above Semisopochnoi from Mount Young on 21 December 2022. Courtesy of AVO.

Figure 26. Webcam image showing fresh ash deposits (black color) at the summit and on the flanks of Mount Young at Semisopochnoi, extending up to 1 km from the N crater. Image was taken on 27 December 2022. Image has been color corrected. Courtesy of AVO.

During January 2023 eruptive activity continued at the active N crater of Mount Young. Minor ash deposits were observed on the flanks, extending about 2 km SSW, based on webcam images from 1 and 3 January. A possible explosion occurred during 1-2 January based on elevated seismicity recorded on local seismometers and an infrasound signal recorded minutes later by an array at Adak. Though no ash plumes were observed in webcam or satellite imagery, a persistent gas-and-steam plume rose to 1.5 km altitude that might have carried minor traces of ash. Ash deposits were accompanied by periods of elevated seismicity and infrasound signals from the local geophysical network, which AVO reported were likely due to weak explosive activity. Low-level explosive activity was also detected during 2-3 January, with minor gas-and-steam emissions and a new ash deposit that was visible in webcam images. Low-level explosive activity was detected in geophysical data during 4-5 January, with elevated seismicity and infrasound signals observed on local stations. Volcanic tremor was detected during 7-9 January and very weak explosive activity was detected in seismic and infrasound data on 9 January. Weak seismic and infrasound signals were recorded on 17 January, which indicated minor explosive activity, but no ash emissions were observed in clear webcam images; a gas-and-steam plume continued to rise to 1.5 km altitude. During 29-30 January, ash deposits near the summit were observed on fresh snow, according to webcam images.

The active N cone at Mount Young continued to produce a gas-and-steam plume during February, but no ash emissions or explosive events were detected. Seismicity remained elevated with faint tremor during early February. Gas-and-steam emissions from the N crater were observed in clear webcam images on 11-13 and 16 February; no explosive activity was detected in seismic, infrasound, or satellite data. Seismicity has also decreased, with no significant seismic tremor observed since 25 January. Therefore, the ACC was lowered to Yellow (the second lowest level on a four-color scale) and the VAL was lowered to Advisory (the second lowest level on a four-color scale) on 22 February.

Gas-and-steam emissions persisted during March from the N cone of Mount Young, based on clear webcam images. A few brief episodes of weak tremor were detected in seismic data, although seismicity decreased over the month. A gas-and-steam plume detected in satellite data extended 150 km on 18 March. Low-level ash emissions from the N cone at Mount Young were observed in several webcam images during 18-19 March, in addition to small explosions and volcanic tremor. The ACC was raised to Orange and the VAL increased to Watch on 19 March. A small explosion was detected in seismic and infrasound data on 21 March.

Low-level unrest continued during April, although cloudy weather often obscured views of the summit; periods of seismic tremor and local earthquakes were recorded. During 3-4 April a gas-and-steam plume was visible traveling more than 200 km overnight; no ash was evident in the plume, according to AVO. A gas-and-steam plume was observed during 4-6 April that extended 400 km but did not seem to contain ash. Small explosions were detected in seismic and infrasound data on 5 April. Occasional clear webcam images showed continuing gas-and-steam emissions rose from Mount Young, but no ash deposits were observed on the snow. On 19 April small explosions and tremor were detected in seismic and infrasound data. A period of seismic tremor was detected during 22-25 April, with possible weak explosions on 25 April. Ash deposits were visible near the crater rim, but it was unclear if these deposits were recent or due to older deposits.

Occasional small earthquakes were recorded during May, but there were no signs of explosive activity seen in geophysical data. Gas-and-steam emissions continued from the N crater of Mount Young, based on webcam images, and seismicity remained slightly elevated. A new, light ash deposit was visible during the morning of 5 May on fresh snow on the NW flank of Mount Young. During 10 May periods of volcanic tremor were observed. The ACC was lowered to Yellow and the VAL to Advisory on 17 May due to no additional evidence of activity.

Geologic Background. Semisopochnoi, the largest subaerial volcano of the western Aleutians, is 20 km wide at sea level and contains an 8-km-wide caldera. It formed as a result of collapse of a low-angle, dominantly basaltic volcano following the eruption of a large volume of dacitic pumice. The high point of the island is Anvil Peak, a double-peaked late-Pleistocene cone that forms much of the island's northern part. The three-peaked Mount Cerberus (renamed Mount Young in 2023) was constructed within the caldera during the Holocene. Each of the peaks contains a summit crater; lava flows on the N flank appear younger than those on the south side. Other post-caldera volcanoes include the symmetrical Sugarloaf Peak SSE of the caldera and Lakeshore Cone, a small cinder cone at the edge of Fenner Lake in the NE part of the caldera. Most documented eruptions have originated from Young, although Coats (1950) considered that both Sugarloaf and Lakeshore Cone could have been recently active.

Information Contacts: Alaska Volcano Observatory (AVO), a cooperative program of a) U.S. Geological Survey, 4200 University Drive, Anchorage, AK 99508-4667 USA (URL: https://avo.alaska.edu/), b) Geophysical Institute, University of Alaska, PO Box 757320, Fairbanks, AK 99775-7320, USA, and c) Alaska Division of Geological & Geophysical Surveys, 794 University Ave., Suite 200, Fairbanks, AK 99709, USA (URL: http://dggs.alaska.gov/).

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/).

Home Reef is a submarine volcano located in the central Tonga islands between Lateiki (Metis Shoal) and Late Island. The first recorded eruption occurred in the mid-19th century, when an ephemeral island formed. An eruption in 1984 produced a 12-km-high eruption plume, a large volume of floating pumice, and an ephemeral island 500 x 1,500 m wide, with cliffs 30-50 m high that enclosed a water-filled crater. Another island-forming eruption in 2006 produced widespread pumice rafts that drifted as far as Australia; by 2008 the island had eroded below sea level. The previous eruption occurred during October 2022 and was characterized by a new island-forming eruption, lava effusion, ash plumes, discolored water, and gas-and-steam plumes (BGVN 47:11). This report covers discolored water plumes during November 2022 through April 2023 using satellite data.

Discolored plumes continued during the reporting period and were observed in true color satellite images on clear weather days. Satellite images show light green-yellow discolored water extending W on 8 and 28 November 2022 (figure 31), and SW on 18 November. Light green-yellow plumes extended W on 3 December, S on 13 December, SW on 18 December, and W and S on 23 December (figure 31). On 12 January 2023 discolored green-yellow plumes extended to the NE, E, SE, and N. The plume moved SE on 17 January and NW on 22 January. Faint discolored water in February was visible moving NE on 1 February. A discolored plume extended NW on 8 and 28 March and NW on 13 March (figure 31). During April, clear weather showed green-blue discolored plumes moving S on 2 April, W on 7 April, and NE and S on 12 April. A strong green-yellow discolored plume extended E and NE on 22 April for several kilometers (figure 31).

Figure 31. Visual (true color) satellite images showing continued green-yellow discolored plumes at Home Reef (black circle) that extended W on 28 November 2022 (top left), W and S on 23 December 2022 (top right), NW on 13 March 2023 (bottom left), and E and NE on 22 April 2023 (bottom right). Courtesy of Copernicus Browser.

Geologic Background. Home Reef, a submarine volcano midway between Metis Shoal and Late Island in the central Tonga islands, was first reported active in the mid-19th century, when an ephemeral island formed. An eruption in 1984 produced a 12-km-high eruption plume, large amounts of floating pumice, and an ephemeral 500 x 1,500 m island, with cliffs 30-50 m high that enclosed a water-filled crater. In 2006 an island-forming eruption produced widespread dacitic pumice rafts that drifted as far as Australia. Another island was built during a September-October 2022 eruption.

Information Contacts: 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/).

Despite their infrequent recent reporting in the Bulletin, lidar measurements remain relevant when discussing the atmospheric impact of volcanic eruptions. As discussed below, following the large-scale atmospheric perturbation caused by Pinatubo, smaller atmospheric perturbations have been infrequent, but the eruption of Shishaldin in April 1999 produced aerosol layers that were detected in North America and Europe (Bulletin v. 24, no. 4).

Reports about atmospheric effects of volcanic activity were last provided as follows: Bulletin v. 26, no. 5, "Volcanic aerosol optical thicknesses derived from lunar eclipse observations;" Bulletin v. 24, no. 4, "Tracing recent ash by satellite-borne sensors and ground-based lidar;" Bulletin v. 23, no. 12, "Lidar data from Garmisch-Partenkirchen, Germany;" and Bulletin v. 23, no. 11, "Lidar data from Hampton, Virginia, USA."

NASA lidar measurements at Virginia, USA. Mary Osborn provided measurements from the 48-inch ground-based lidar system at NASA Langley Research Center (table 18) since May 1999. All measurements were taken at a wavelength of 694 nm. Their 48-inch lidar system was out of commission for ~8 months in late 1999 and early 2000, as they used some of its components to conduct the SAGE III Ozone Loss Validation Experiment (SOLVE). That campaign took place during November 1999-March 2000 based out of Kiruna, Sweden.

Table 18. Lidar data from Virginia, USA, for May 1999-December 2001 showing altitudes of aerosol layers. Backscattering ratios are for the ruby wavelength of 0.69 µm. The integrated values show total backscatter, expressed in steradians^-1, integrated over 300-m intervals from the tropopause to 30 km. Courtesy of Mary Osborn.

Figure 13 presents an overview of stratospheric integrated aerosol backscatter since 1974. A slight increase in stratospheric integrated backscatter occurred during late 1998-99, at least partly attributed to the Shishaldin event and several smaller eruptions. After that, the stratospheric integrated backscatter returned to the "background" aerosol loading measured in 1978-1979. Although the current level of stratospheric aerosol loading remains low, another major volcanic eruption could change the situation quite suddenly.

Figure 13. A plot of the 48-inch lidar data versus time showing the stratospheric integrated aerosol backscatter measured since 1974. Important volcanic eruptions that may have led to increased northern mid-latitude aerosol loading are noted on the time axis. Courtesy of Mary Osborn.

Geologic Background. The enormous aerosol cloud from the March-April 1982 eruption of Mexico''s El Chichón persisted for years in the stratosphere, and led to the Atmospheric Effects section becoming a regular feature of the Bulletin thorugh 1989. Lidar data and other atmospheric observations were again published intermittently between 1995 and 2001; those reports are included here.

Information Contacts: Mary Osborn, NASA Langley Research Center (LaRC), MS 475, Hampton, VA 23681, USA.

During September 2001 through early January 2002, seismicity at Bezymianny remained at or near background levels, although one mid-December outburst was striking. Weak fumarolic activity was observed on 15, 18, and 20 September, on 8, 12, 27, and 29 October, on 1 November, and during 1-2, 6, and 8-10 January. Weak shallow earthquakes were registered under the volcano beginning on 10 November. The earthquakes became stronger beginning on 22 November, but seismicity remained near background levels. Gas-and-steam plumes were observed throughout the report period reaching 50-800 m above the dome and extending up to 60 km from the volcano.

On 16 December, a plume reached 4 km above the dome and extended 60 km NW. The plume appeared dark from 20 km away. Plumes on 8-10 January extended 5-20 km S and NW. On 10 and 12-13 December, gas-and-steam plumes rose to 300 m above the volcano and extended 40 km W, SW, and SE.

Thermal anomalies were observed on satellite imagery several times during December 2001 and early January 2002 (table 1). On 10 December, a four-pixel thermal anomaly was visible, along with a faint, ash-poor plume that extended 87 km SE from the volcano.

Table 1. Thermal anomalies visible on satellite imagery at Bezymianny during December 2001 through 6 January 2002. The anomaly was centered over the dome on 12-13 December 2001. Courtesy KVERT.

The Concern Color Code was raised from Green ("volcano is dormant" ) to Yellow ("volcano is restless"). Activity increased during 14-21 December, when many weak shallow earthquakes occurred within the edifice and other local shallow seismic events (possible avalanches) were registered. The Concern Color Code was increased to Orange ("eruption may occur at any time") until around 25 December, when seismicity decreased again. The Concern Color Code was reduced to Green by the end of 2001 and remained there through at least 25 January.

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: Olga Chubarova, Kamchatka Volcanic Eruptions Response Team (KVERT) (URL: http://www.kscnet.ru/ivs/kvert/); Tom Miller, Alaska Volcano Observatory (AVO) (URL: https://www.avo.alaska.edu/); Tokyo Volcanic Ash Advisory Center, Tokyo, Japan (URL: https://ds.data.jma.go.jp/svd/vaac/data/).

The Afar National Regional State has approved a program to grant access to Erta Ale volcano by either land or air transportation. The program, which will precede the formation of a "National Park of Volcanoes," enables visitation by natural science field workers. It also allows for traditional mining and salt transportation by caravans and seeks to protect the traditional life of the region's inhabitants.

Observations during 14 November 2000. Luigi Cantamessa (Géo-Découverte), accompanied by government representatives, visited the N part of the elliptical summit caldera (figure 7) on 14 November 2000. Little had changed since last described in December 1995 (BGVN 20:11/12), but continued collapse of the N crater wall was noted. Dense smoke came from the S rim of the crater, with a very strong smell of sulfur, as in the past. GPS measurements of elevation indicated that the E wall of the N crater was ~600 m high and the N rim, the highest point of the volcano, was ~15 m higher.

Figure 7. Aerial photograph showing the N part of the Erta Ale caldera. In this view looking generally W, the inactive northern crater (with fumarolic emissions) is on the right and the southern crater with an active lava lake is on the left. Courtesy of L. Cantamessa, Géo-Découverte.

The S crater (figure 8), in the central part of the caldera, contained a molten lava lake and had undergone some changes since the 1995 visit. A portion (1-2 m thick) of the NE wall had collapsed. The level of the lava lake, still in the W part of the crater, showed significant variations. The terraces on the E side of the crater appear to have been swamped by lava, after which the lake level apparently receded. The present level appeared to be lower than in 1995. A terrace of 2-3 m width now surrounds the lake at the foot of the crater walls. Intense activity was observed at the lake's surface. There were rapid movements of the surface from S to N. Many lava fountains reached ~10-15 m high.

Figure 8. Aerial photograph looking down into the southern crater of Erta Ale. The crater is about 145 m in diameter, with an active lava lake. Courtesy of L. Cantamessa, Géo-Découverte.

Observations during 29-30 January 2001. An expedition sponsored by Aventure et Volcansmade crater observations for 48 hours during 29-30 January 2001. Because of the extremely dry and hot climate that prevails in this region, smoke or vapor rarely obscured visual observations. The N crater exhibited only fumarolic activity, but due to thick fumes from its southern portion, gas masks were necessary for those who climbed into the crater.

The S crater was determined to be ~170 x 130 m, with the active lava lake (figure 9) on the W side having a diameter of ~121 m. The lava lake was located, based on GPS measurements, at 13° 36' 11" N, 40° 39' 49" E. Cyclic activity, approximately every 4 hours, consisted of the thin, dark crust on the lake surface splitting and causing a "fantastic" bubbling of the liquid lava across the entire ~12,000 m² of the lake surface. Vigorous degassing created lava fountains 10-20 m high. Several times local collapses were seen which mainly affected the vertical walls in the SE part of the crater. The level of the lava lake remained stable.

Figure 9. Evening photograph showing the active lava lake in the southern crater of Erta Ale during 29-30 January 2001. Molten lava can be seen around the edges and through fractures in the cooled surface of the lake. Courtesy of Guy de Saint-Cyr, Aventure et Volcans.

Observations during 13-18 February 2001. Between 13 and 18 February 2001 two groups from the Société de Volcanologie (SVG), in an expedition organized by Géo-Découverte, reached the volcano by land and by helicopter (3 days later). The principal topographic elements in the N part of the caldera were the subject of GPS and telemetric measurements. The active S crater contained an elliptical lake (80 x 100 m) with a surface level 80 m below the rim and lava fountains rising 5-10 m high.

The relative absence of gas in the active crater allowed excellent observations. Over a period of 14 hours, Yves Bessard and Alain de Chambrier recorded details of the activity occurring at the lava lake, including lake movements and lava fountains. The surface of the lake was renewed approximately every 10 minutes. A continuous video recording over a period of 77 minutes was also taken from the edge of the lava lake at the bottom of the crater.

Systematic measurements of fumarole temperatures were made, primarily on the edge of the N crater and the external N edge of the caldera; values ranged from 60°C to more than 260°C at the strongly active N-crater fumaroles.

The last previous thermal measurements at Erta Ale were carried out in the 1970s by a team led by Haroun Tazieff; the most recent temperatures reported in the literature were obtained from infra-red satellite data (work mainly carried out by Oppenheimer, Francis, and Rothery). The thermal measurements collected by Marc Caillet, Steven Haefeli, and Pierre-Yves Burgi during 13-15 February 2001 are summarized below; more details on this fieldwork will be published in a journal paper.

The SVG team used a pyrometer, which works by remotely measuring the infrared radiations emitted by the lava, for the temperature measurements. Temperature calculations need an emissivity factor, the determination of which required an approach to the lava lake. For the temperature measurement of the crust, the only accessible part of the lake, the following protocol was followed. Using a steel wire, a steel sheet of 18 x 18 cm (8 mm thickness) containing a hole in which the thermocouple was inserted was deposited on the crust of the lake. Because of the distance separating the terrace from the lake (estimated at 15 m), this required the coordination of three people (Marc Caillet, Steven Haefeli, and Pierre-Yves Burgi). Caillet, standing where the ambient temperature reached 300°C, was equipped with a reflective cloth and used a large 8-m steel pole to move the thermocouple away from the wall.

Once the steel sheet was in contact with the lake's crust, temperature measurements were carried out every 30 seconds for 10 minutes, then each minute during the next 20 minutes, until the temperature stabilized. The temperature recorded at this time was 350°C. A pyrometric measurement in the same area of the thermocouple indicated a temperature of 342°C (with an emissivity index set to 0.9 on the pyrometer). By combining the temperatures obtained with the thermocouple and the pyrometer, and knowing the wavelength used by the pyrometer, an emissivity factor of 0.74 was determined. By collecting a sample of basalt, it was possible to confirm this value by the use of a furnace.

Acquisition of temperatures at various lake locations was carried out by pyrometry. Continuous pyrometric measurements were taken over periods of several tens of minutes (with a measurement each second) and were collected on a portable computer. The crust, many faults, and lava fountains were the three types of areas considered. These measurements were made from the edge of the pit and from the lower terrace. The measurements made near the lake were of primary importance because both the absorption of radiation by magmatic gases between the source and the observer and the enlarging of the pyrometer field of view with distance are two factors which tend to distort measurements. A difference of about 25°C was observed between the maxima measured from the edge and the bottom of the pit. In addition, the temperature measurements were taken at night in order to avoid any pollution due to the solar radiation (which can distort values up to 90%). The highest recorded temperature, 1,217°C, was found in a lava fountain. The temperature of the crust of the lake was very variable, 290°C near the cliffs to 520°C in the center of the lake, with an average of 474°C.

Geologic Background. The Erta Ale basaltic shield volcano in Ethiopia has a 50-km-wide edifice that rises more than 600 m from below sea level in the Danakil depression. The volcano includes a 0.7 x 1.6 km summit crater hosting steep-sided pit craters. Another larger 1.8 x 3.1 km wide depression elongated parallel to the trend of the Erta Ale range is located SE of the summit and is bounded by curvilinear fault scarps on the SE side. Basaltic lava flows from these fissures have poured into the caldera and locally overflowed its rim. The summit caldera usually also holds at least one long-term lava lake that has been active since at least 1967, and possibly since 1906. Recent fissure eruptions have occurred on the N flank.

Information Contacts: Luigi Cantamessa, Geó-Découverte, 12-14 rue de Cendrier, CH-1201 Geneva, Switzerland (URL: http://geo-decouverte.ch/); Annie Buard, Christophe Toussaint, Jean Claude Boissonnet, Philippe Roy, and Guy de Saint-Cyr, Aventure et Volcans, 73 cours de la Liberté, 69003 Lyon, France; P. Vetsch, Marc Caillet, Steven Haefeli, and Pierre-Yves Burgi, Société de Volcanologie (SVG), PO Box 6423, CH-1211 Geneva 6, Switzerland (URL: http://www.volcan.ch/).

An eruption began on 5 January 2002 and continued until 16 January. The eruption, which sent lava to the sea, followed several months of increased seismicity. The most recent previous eruption occurred during 11 June-7 July 2001 (BGVN 26:07).

Seismicity during October 2001-January 2002. During 3-9 October the Observatoire Volcanologique du Piton de la Fournaise (OVPDLF) reported that, beginning in early September, seismicity increased to ~10 events per day. Seismic activity further increased during early October, with up to 40 daily earthquakes. In the first half of October an average of 16 earthquakes per day occurred; in the second half the daily average increased to 26 events. On 5 November seismometers registered 129 earthquakes, an anomalously large number. Their hypocenters plotted at 0.62 km under the N edge of Bory Crater. In November, ~30-50 earthquakes occurred per day.

During late September through mid-October, the volcano was at Alert Level 1, and significant tilt variations were detected S of Dolomieu Crater. These events occurred simultaneously with the widening of fissures at two extensometer stations on the N and S flanks, suggesting slight summit inflation. The extensometer variations were ~3-4 times smaller than those during previous eruptions. Seismicity disappeared until the end of December, but increased again during 26-30 December when the daily earthquake counts were 17, 49, 62, and 70.

On 26 January 2002 a total of 17 earthquakes occurred, including two M 1.8 events. The earthquakes were mostly located 0.5-1.5 km below sea level, and their epicenters were beneath the N edge of Bory to Dolomieu craters. Extensometers at Magne and Chateau Fort continued to reveal slow opening of cracks, reaching 0.27 mm on 27 January.

On that same day 49 earthquakes were recorded, including events of M 2.2, 2.0, and 1.8. On 28 December during 0400-1000 a total of 48 earthquakes registered. The extensometers at Magnes and Château Fort continued to show a slow opening of the cracks. The tiltmeters, which had remained stable since the beginning of December, showed a resumption of inflation. On 29 January seismometers recorded 62 earthquakes, including an M 2.3 event. On 30 January a total of 70 earthquakes included M 2.2 and 2.0 events. Opening of the cracks at Magnes and Chateau Fort continued to progress and reached 0.28 mm.

New eruption during 5-16 January 2002. An eruption began at 2300 on 5 January and ended at 1615 on 16 January. On 5 January fire fountaining occurred and lava flowed from four cracks that opened in the NE part of l'Enclos Fouqué caldera and continued towards the foot of the Nez Coupé de Sainte Rose, a feature located on the E side of the active field of lava flows (see map showing the location of previous fissures there in BGVN 23:09). By 6 January only two cracks remained active and lava flows reached ~1,100 m elevation on the projecting ledge of the Plaine des Osmondes.

On 6 January at 2100 the eruption was visible from Piton Sainte Rose and from the National Road RN2. During 7-9 January, the eruption continued but tremor progressively decreased. On 9 January the tremor was half that of the previous day and almost no fire-fountaining was visible. Other seismicity persisted, although on 7 January only four low-magnitude earthquakes were detected. By 8 January the reading on the Château Fort extensometer had decreased only slightly since the eruption began. Readings at the Magnes extensometer continued to increase slightly.

A field excursion around this time found no further incandescent lava visibly flowing at distance from the vent areas. Observers noted that the initial flow did not extend beyond the Plaine des Osmondes. On the other hand, the interior of the eruption cone was still hot, strong degassing was audible, and small, nearly continuous projections of molten material took place, although the emitted volume was negligible.

Tremor decreased during 7-11 January. As few as 8 small shallow earthquakes were recorded per day. On 12 January tremor started to increase almost continually in comparison to the previous day, and numerous earthquakes were recorded ~4 km beneath the Plaine des Osmondes, near the N caldera wall.

During the evening of 12 January, a new fissure opened at the base of the rampart in the lower part of the Plaine des Osmondes. Lava flowed from a lava tunnel down into the Grand Brûlé close to the northern rampart. On 14 January lava flowed across the highway on its way to the ocean, entering it at 1540. By 15 January tremor was stable and 160 earthquakes were recorded over a 24-hour period on the N side of the volcano. At 0600 a swarm of low-frequency earthquakes was recorded in the NE rift zone.

After 12 days of lava emission and associated tremor, the eruption ended on 16 January, marked by a sudden, large decrease in lava emission at 1610 and the termination of tremor at 1910. After the eruption ended a large number of long-period earthquakes were recorded below the summit and the Plaine des Osmondes, indicating the continued presence of magma beneath the NE rift zone. The total lava volume emitted was estimated to be 10-15 x 10⁶ m³.

Geologic Background. Piton de la Fournaise is a massive basaltic shield volcano on the French island of Réunion in the western Indian Ocean. Much of its more than 530,000-year history overlapped with eruptions of the deeply dissected Piton des Neiges shield volcano to the NW. Three scarps formed at about 250,000, 65,000, and less than 5,000 years ago by progressive eastward slumping, leaving caldera-sized embayments open to the E and SE. Numerous pyroclastic cones are present on the floor of the scarps and their outer flanks. Most recorded eruptions have originated from the summit and flanks of Dolomieu, a 400-m-high lava shield that has grown within the youngest scarp, which is about 9 km wide and about 13 km from the western wall to the ocean on the E side. More than 150 eruptions, most of which have produced fluid basaltic lava flows, have occurred since the 17th century. Only six eruptions, in 1708, 1774, 1776, 1800, 1977, and 1986, have originated from fissures outside the scarps.

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

During 1 October 2001 through at least 6 January 2002, activity at Ijen was higher than normal, though low visibility often restricted visual observation of the summit. Activity included heightened continuous tremor, shallow volcanic (B-type) earthquakes, and one small explosion earthquake (table 2). No deep volcanic (A-type) earthquakes were reported.

Table 2. Summary of seismicity at Ijen during 1 October 2001- 6 January 2002. The left-hand column shows time intervals; the other columns indicate the number of earthquakes or maximum tremor amplitudes seen during the time intervals. Courtesy of the Volcanological Survey of Indonesia (VSI).

During 1-7 October a thin, white, low-pressure plume was observed reaching ~50-100 m above the summit. Ijen volcano remained at Alert Level 2 (on a scale of 1-4) through at least 6 January 2002.

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

Information Contacts: Dali Ahmad, Volcanological Survey of Indonesia (VSI), Jalan Diponegoro No. 57, Bandung 40122, Indonesia (URL: http://www.vsi.esdm.go.id/).

During May 2001 through at least early January 2002, seismic activity at Kerinci was dominated by small explosion earthquakes. Plumes were visible above the summit and generally drifted E throughout most of the report period (table 1). Minor explosions occurred and on 9 August an explosion was accompanied by a booming sound heard by people working in rice fields around the volcano. At 0925 the same day a brown, high-pressure plume was observed reaching 700 m above the summit. The plume was visible drifting NNE for ~5 minutes.

Table 1. Seismicity at Kerinci during 7 May 2001 through 6 January 2002. The left-hand column shows time intervals; the adjacent four columns indicate the number of earthquakes or maximum tremor amplitudes seen during the time intervals; the right-hand column adds comments about plume heights. Courtesy VSI.

Eruptive activity stopped briefly during mid-August. During 0800-1200 on 9 September, explosive activity produced a brown ash plume that rose 500 m above the summit. Gas pressure was low in early November and seismic activity decreased slightly. The volcano remained at Alert Level 2 (on a scale of 1-4) throughout the report period.

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

Information Contacts: Dali Ahmad, Volcanological Survey of Indonesia (VSI), Jalan Diponegoro No. 57, Bandung 40122, Indonesia (URL: http://www.vsi.esdm.go.id/).

During September 2001 through at least early 2002, minor seismic events occurred and tremor remained low to moderate at Kīlauea's summit and at Pu`u `O`o. Tiltmeters across the volcano showed some deformation, which is normal for Kīlauea. A significant tilt event occurred on 9 December, but was not accompanied by unusual seismicity or change in eruptive activity. A survey of vertical and horizontal movement concluded that during 2001 Kīlauea's summit continued to subside at a maximum rate of 7cm/year as magma moved from the summit reservoir to the Pu`u `O`o vent; the S flank moved seaward at a maximum rate of 7cm/year. Lava broke out of the tube system and continued to flow down the Paluma Pali slope, resulting in bench growth at the new Kamoamoa ocean entry.

Geophysical activity. Small deflation events occurred at Kīlauea's summit on 12, 13, and 28 September, a large decrease followed by tremor on 17 October. By 21 October tremor at Pu`u `O`o became rather continuous; however, short bursts of higher amplitude tremor returned by 24 October. During 1-8 November weak, long-period earthquakes occurred frequently at the summit. On 8 December rapid deflation (~2.4 µrad) took place at Kīlauea's summit, followed shortly thereafter by deflation (~1.9 µrad) at Pu`u `O`o cone. On 9 December abrupt inflation (6 µrad) at Kīlauea's summit was followed by much weaker inflation at Pu`u `O`o. Strong earthquakes and tremor accompanied the inflation. A shallow M 3.4 earthquake was registered beneath the SE corner of the caldera. The end of summit inflation and beginning of deflation were notably abrupt. By 10 December, seismicity had returned to normal levels at the summit and tremor at Pu`u `O`o remained moderate.

On 1 January during 1200-2300, deflation occurred at Kīlauea's summit (~2.3 µrad), followed shortly thereafter by deflation (~2.5 µrad) at Pu`u `O`o cone. On 3 January during 1210-1950, inflation (~1.6 µrad) was again recorded at Kīlauea's summit. A small deflation followed on 11 January.

Through mid-January numerous small, long-period earthquakes with bursts of tremor registered at Kīlauea's summit and tilt across the volcano showed no significant deformation.

Lava flow. On 6 September a surface lava flow broke out in the E part of the flow field at an elevation of ~ 600 m on the Pulama Pali slope. The lava followed the route of the E tube from the top to the base of the slope, across the coastal flat and into the ocean at the E Kupapa`u ocean entry. On 13 September two surface flows were active along the W tube system of the Pulama Pali slope. During 28-29 September, a lava flow located W of the active flow field began to enter the ocean at a new area S of an old Kamoamoa camping area. The new W flow developed a tube system by 30 September that could reroute lava from East Kupapa'u to the Kamoamoa entry.

Throughout October lava broke out of the Kamoamoa tube system and flowed on the surface along the entire Puluma Pali slope. Flows increased along the main tube and E Kupapa'u. Around 13 November the Kamoamoa flow was confined to the tube system with at least five points of sea entry. Through the end of November, lava was mostly confined to the tube systems with a few surface flows that broke out of the tubes and produced patches of incandescence.

During December, surface flows and breakouts occurred along all tube systems from just below Pu`u `O`o to the coast. On 10 December, major breakouts were in progress just below Pu`u `O`o. On 18 December two parallel flows moved down Pulama Pali, both along the track of the Kamoamoa tube. The flows, which were sluggish and more than half crusted over, broke out from the tube in the upper half of the slope and descended to the lower third before becoming entirely crusted over. On 20 December a 3-m tall hornito formed at an elevation of ~700 m from a break in the roof of the main lava tube (figure 153).

Figure 153. On 20 December at Kīlauea a 3-m tall hornito formed at an elevation of ~ 700 m from a break in the roof of the main lava tube. Incandescence was observed at the base of the hornito. Courtesy HVO.

During early January 2002, surface lava flows were visible on Pulama Pali coming from the Kamoamoa lava tube system. A surface flow reached 1.5-2 km down the upper portion of the flow field above the Pulama Pali slope.

Ocean entry. Through most of September lava generally continued to flow down the Pulama Pali slope, across the coastal flat, and into the ocean at the E Kupapa'u ocean entry. The ocean entry tube and the W tube carried lava that broke out on the coastal flat, and the E Kupapa'u bench remained active. Field mapping on 18 September revealed that the relatively larger W flow was within ~ 625 m of the coastline about 1.8 km W of the entry location at East Kupapa`u. Lava flows located W of the active flow field began to enter the ocean at a new area on 28-29 September. By 30 September a new lava bench and an adjacent black sand beach began to form. The new entry, fed by the W flow, was located 500-600 m seaward of the old site of Kamoamoa, 3.7 km from Chain of Craters road.

By 2 October the Kamoamoa bench had widened ten's of meters. The E bench was no longer active and showed signs of rapid erosion under heavy surf. The W bench extended 70 m farther W, reaching a length of about 190 m parallel to the shoreline and extending 60-70 m out from the old sea cliff. The feeding tube, called the Kamoamoa tube, remained small, with supply estimated to be about 15% of the total flux coming from Pu`u `O`o. By mid-October, lava continued to enter the ocean at both E Kupapa'u entries.

On 14 October surf erosion was gradually claiming the eastern part of the bench. Several small-to-moderate littoral explosions were observed at the point where lava entered the sea. By 28 October activity had decreased at the Kamoamoa entry and its bench reached 120 m from the old sea cliff. Surface flow had ended and all lava reached the bench through tubes. On 31 October a new entry point was observed roughly midway between E Kupapa'u and Kamoamoa.

Lava continued to flow into the sea at the Kamoamoa, Kupapa'u, and E Kupapa'u entries through November and December. By 18 November the Kupapa'u entry was inactive, and by 5 December much of the Kupapa'u bench had fallen into the ocean. By 20 December, the Kamoamoa bench was 360 m long, 130 m wide, and was littered with blocks and black sand.

During early January 2002, lava flowed into the ocean at the Kamoamoa entry from multiple locations, mostly at the tip of the bench and especially in the western third or quarter of the bench. The amount of lava entering the ocean at the E Kupapa'u entry was very small.

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: Hawaiian Volcano Observatory (HVO), U.S. Geological Survey, PO Box 51, Hawaii National Park, HI 96718, USA (URL: https://volcanoes.usgs.gov/observatories/hvo/).

The eruption that began on 6 February 2001 (BGVN 26:03) continued through at least early April. An update from the Goma Volcanological Observatory since our last report stated that the February eruption was preceded by swarm of low-frequency earthquakes that began on 16 December 2000. The eruption started from the summit caldera of Nyamuragira and formed four cones: two on the N flank, one on the S flank, and one inside the caldera. The two main cones were symmetrical and located on the N (Amani) and S (Tumayhini) flanks, along the fissure connecting Nyamuragira and Nyiragongo. Lava flows extended up to 15 km from the two main cones. Ash fell up to 20 km away, damaging farmland and causing health problems.

The Hawaii Institute of Geophysics and Planetology at the School of Ocean and Earth Science Technology (HIGP/SOEST) tracked the eruption using MODIS (Moderate Resolution Imaging Spectroradiometer) global hot-spot data. No hot spots were seen at Nyamuragira until 7 February 2001. Figures 20 and 21 show examples of the hot spot maps for Nyamuragira during 7-12 February.

Figure 20. On 7 February 2001 at Nyamuragira the first-detected hot spot, a ~ 7 x 5 km anomaly, was seen on MODIS satellite imagery on the N flank of the volcano centered 7-10 km due N of the summit. The rectangle indicates the area shown in the following figure. Courtesy HIGP/SOEST.

Figure 21. MODIS satellite imagery over Nyamuragira and vicinity revealed a series of hot-spot anomalies on 8, 11, and 12 February 2001. Compared to the anomaly seen on the previous day, on the 8th, the similarly situated N flank anomaly had increased in size. In addition, a second anomaly (~ 13 x 6 km) was conspicuous just SSE of the summit. On 11and 12 February the two anomalies remained similar to each other and to those on the 8 February image, though the anomalies become less circular than those of the 7 and 8 February images. The 11-12 February images contained a N-flank anomaly that trended NNE for ~ 22 km and the S-flank anomaly trended E for ~ 17 km. Courtesy HIGP/SOEST.

As of 10 March, no lava fountains were observed and all flows had stopped. Only very dense "smoke" was observed coming from the cones. Unlike previous eruptions at Nyamuragira, no significant high-frequency earthquakes were observed; these usually signal the end of the eruption.

After 15 March through at least July 2001, the same seismic patterns that preceded the February eruption were observed. During the end of June, the Goma Volcanological Observatory reported that the magnitude of the low-frequency earthquakes and the amplitude of volcanic tremor had increased significantly. Scientists believed this increased activity could signal a large eruption sometime in the near future. The high seismic activity could also be related to regeneration of the Nyamuragira lava lake or to activity of the Nyiragongo lava lake.

False eruption report, January 2002. Rumors of a new eruption at Nyamuragira circulated soon after a 17 January eruption at Nyiragongo (see this Bulletin). Ash was allegedly ejected from the N flank of Nyamuragira on 22 January, but the reports could not be confirmed because of poor visibility. According to the United Nations Office for the Coordination of Humanitarian Affairs (OCHA), volcanologists determined that ash observed in Goma on 22 January originated from the collapse of Nyiragongo's inner crater and not from a new eruption at Nyamuragira.

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: Dieudonné Wafula, Observatore Volcanologie de Goma (RDC-E), Goma, Democratic Republic of Congo; Andy Harris, Eric Pilger and Luke Flynn, Hawaii Institute of Geophysics and Planetology at the School of Ocean and Earth Science Technology (HIGP/SOEST), University of Hawaii, 2525 Correa Road, Honolulu, HI 96822; United Nations Office for the Coordination of Humanitarian Affairs (OCHA), United Nations, New York, NY 10017 USA (URL: https://reliefweb.int/).

An eruption began at Nyiragongo on 17 January 2002 with some lava flows and possibly their feeding fissure vents entering the city of Goma (~18 km S of the volcano, population ~400,000) in the Democratic Republic of Congo (DRC) and threatening refugee camps (figure 10). Encroaching lava spurred massive evacuations of the city. A great deal of conflicting information exists concerning the numbers of people killed or displaced, the amount of property destroyed, the specific paths of the lava flows, etc.

Figure 10. Sketch map showing the location of Nyiragongo and other nearby volcanoes. The boundary between the Democratic Republic of Congo (NW) and Rwanda (SE) is shown as a yellow line; roads are red, and the national park boundary is black. National park areas are lighter shades of green (in DR Congo) and blue (in Rwanda). Modified from a base map courtesy of Wheeling Jesuit University/ NASA Classroom of the Future.

The following is taken primarily from reports by the United Nations Office for the Coordination of Humanitarian Affairs (OCHA), the U.S. Agency for International Development - Office of U.S. Foreign Disaster Assistance (USAID/OFDA), and the aid organization Oxfam International.

Numerous dramatic press reports showed multiple lava flows engulfing Goma; city streets became paths for rough-surfaced lava flows, and numerous buildings collapsed, burned, or both. In the end, one of the flows passed completely through Goma to enter Lake Kivu and proceeded to build a lava delta. The lava flows damaged or destroyed agricultural areas around Goma, covered the N part of the runway at the airport, and cut off access to parts of the town. Lava flows destroyed both residential and business districts as well as a cathedral.

Authorities in Goma reported that more than 150,000 people remained there during the peak of the lava flow activity. A report from the UN and USAID/OFDA on 23 January estimated that 147 people were killed because of lava flows and seismically induced building collapses. According to Oxfam International, ~60,000 people lost their homes.

The UN report stated that up to ~250,000 people were displaced as a result of the eruption. These and possibly other displaced people were concentrated in the following places: Goma, DRC (62,500); Sake, DRC (5,000); Rutshuru, DRC (5,000); in camps along the eastern DRC frontier near Gisenyi, Rwanda (6,000-10,000); in Ruhengeri, Rwanda (4,000); in Bukavu, DRC (15,000); in surrounding areas (30,000), in six sites near the NW shore of Lake Kivu (up to 60,000) and in area villages (60,000).

17-21 January 2002 eruption. The start time of the 17 January eruption is uncertain. According to Agence France-Presse, Nyiragongo began to erupt at about 0500. USAID/OFDA reported that the eruption began at about 0930. Most reports stated that three lava flows moved down the E, W, and S flanks. During a 17 January phone conversation with BGVN editors, Richard McDonald, a missionary in the Congo region, noted that his sources had suggested that lava flows traveled to the E, N, and S. Two flows traveled directly S through Goma and divided the city in three. One of these flows continued into Lake Kivu.

MODIS (Moderate Resolution Imaging Spectroradiometer) images from 17 January at 1050 showed a substantial ash plume moving W from Nyiragongo (figure 11).

Figure 11. An annotated MODIS satellite image showing the region surrounding Nyiragongo as captured at 1050 on 17 January 2002. Lava flows are not yet conspicuous at this stage of the eruption. Instead, a W-trending ash plume is visible extending more than 150 km from the volcano. Courtesy NASA.

OCHA stated that at 1100 on 17 January observers flew over the volcano in a helicopter and reported a large lava flow approaching Goma. The lava flow cut the road between Goma and Rutshuru (to the N, figure 10). By 1430, with a small hill slowing its progress, the lava flow had reached 2 km N of the airport and was still progressing southward. The lava flow had reached a width of 2 km, and its velocity was estimated at 2-3 m/minute (0.2 km/hour), a very slow flow rate compared to those reported for the very high velocity 1977 eruption which reached up to 60-100 km/hour (see SEAN 02:03). The smaller of the two lava flows heading toward Goma cut the road leading in from the W (figure 12). OCHA reported that a fourth fissure opened during the afternoon of 17 January. A total of 14 neighboring villages were affected by the lava flows.

Figure 12. Map of Goma showing lavas from the 17-21 January 2002 eruption of Nyiragongo. Lavas from the eruption ultimately trisected Goma and one branch entered Lake Kivu. Courtesy OCHA Humanitarian Information Center (HIC).

News reports made much about fires in Goma. Fuel depots exploded and kerosene storage facilities at the airport burned. On 21 January a petrol station exploded killing ten's of people (~50 according to news reports). A UN worker in Goma reported that the air was full of ash and dust during the eruption. News reports also emphasized the fires' smoke and soot.

On 18 January, OCHA reported that tremors occurred every hour, and some were strong enough to damage buildings in Gisenyi (figure 10). Several tremors were felt as far away as at the S end of Lake Kivu in Bukavu (~125 km SE). As of 24 January, earthquakes and tremors up to M 4.7 continued in the vicinity of Nyiragongo.

Representatives from OCHA reported on 20 January that a new crater had opened on the NW side of Nyiragongo, and the temperature of some parts of Lake Kivu reached up to 40°C.

By 21 January, the rapid advance of new lava flows appeared to be over, but residual molten lava still slowly seeped into Lake Kivu, where it formed a ~100-m-wide delta. Although no new lava flows threatened the city, some scientists feared that lava entering the lake or seismic activity could disturb the lake sufficiently to release significant amounts of carbon dioxide and methane gas lying at the lake bottom. News and other scientific sources suggested a gas release was unlikely.

OCHA reported that a 22 January a flight over the volcano confirmed a lack of new activity, including the crater where only a few fumaroles were present. A system of fractures was visible along the southern slope of the volcano, starting from the eastern flank of Shaheru crater (close to the main Nyiragongo cone) and propagating down close to the outskirts of Goma. The fractures were generally meters wide, and during the eruption lava poured out from different locations and altitudes along the fracture system. The lowest lava emission point in this fracture system, as estimated from the helicopter, was at least ~2 km from Goma.

According to OCHA, volcanologists determined that ash observed in Goma on 23 January originated from the collapse of Nyiragongo's inner crater and not from a Nyamuragira eruption, as was originally (incorrectly) stated in several news reports. During a visit to Nyiragongo's main crater on 28 January, the UN Volcano Surveillance Team found that the crater floor had collapsed more than 600 m. In addition, they reported no ongoing volcanism nor any fumaroles at the bottom of the crater, although they could smell SO₂. A few weak steam vents were visible on the inner crater wall and a small gas plume was seen above the crater rim to the NE. On 28 January the volcano was at Alert Level Yellow (second on a four-color scale).

Regional seismicity. On 4 January 2002, an M 4.8 earthquake occurred near Nyiragongo. Local volcanologists had planned to visit Nyiragongo on 19 January to observe its activity, but the volcano erupted before the visit.

According to Bruce W. Presgrave of the USGS National Earthquake Information Center (NEIC), there was an unusual number of tectonic earthquakes in the Goma-Nyiragongo region starting ~9 hours after Nyiragongo's alleged initial lavas at 0500. The sequence included ~100 earthquakes M 3.5 or larger. Tectonic swarms of this size occasionally appear in conjunction with volcanism. For example, seismologists noted intense protracted swarms during Miyake-jima's intrusions and eruptions during the year 2000 (BGVN 25:05, 25:07, and 25:09).

The largest earthquake to date in the sequence was M 5; it struck at 0214 on 20 January at 1.76°S, 29.08°E. The second largest, M 4.8, struck at 2201 on 17 January at 1.74°S, 29.08°E, about 17 hours after the estimated onset of the lava flows according to news reports. Though imprecisely fixed, these estimated epicenter locations are just a few ten's of kilometers WSW of Goma; and the probable uncertainty could place them closer to Goma and Nyiragongo.

In addition to registering at the two closest stations in Mbarara, Uganda (MBAR, 0.602°S, 30.738°E) and Kilima Mbogo, Kenya (KMBO, 1.127°S, 37.252°E), the earthquakes also left clear signatures on instruments at great distances, for example in China and at the South Pole, Antarctica. The earthquakes contained sharp P- and S-wave arrivals. Also, as would be expected of tectonic events at teleseismic distances, the associated signals at even the closest stations MBAR and KMBO lacked tremor. The signals were not the sort that could be expected to arise from surficial processes like sudden mass wasting, fuel explosions, building collapses, etc. First motion or minimal tensor results are not yet available.

Comparatively few news accounts discussed the seismic activity or seismically induced damage, perhaps because residents were concerned with more pressing aspects of Nyiragongo's eruption. However, NEIC has received email messages indicating that numerous earthquakes were felt near Kigali, Rwanda (~100 km E of Nyiragongo, table 2).

Table 2. Summary of earthquakes felt near Kigali, Rwanda (~ 100 km E of Nyiragongo) during 10-22 January 2002. The earthquakes were all recorded instrumentally as well. Courtesy Bruce Presgrave (NEIC) and Fr. Stephen Yavorsky, S.J.

As a result of the seismicity, many buildings collapsed in Goma. At least 25 buildings in Gisenyi were also destroyed. By 28 January seismicity had decreased and earthquakes were not large enough to be felt by the population.

Humanitarian crisis. According to OCHA and various news reports, refugees began to return to Goma just a few days after the eruption, despite the dangers that still existed in the area. USAID/OFDA reported that on the morning of 20 January, more than 15,000 people per hour were returning to Goma from points E of the city, while simultaneously 3,000 people per hour were fleeing the city to locations W. Aid workers reported that the refugees would rather return to Goma and risk another eruption than stay in displacement camps in Rwanda, which they perceived to be a hostile country. On 21 January, continuing seismic activity caused buildings to collapse, resulting in more deaths.

Poor access to people in affected parts of Goma was a problem for relief efforts. Several humanitarian groups, along with news agencies, reported that aid workers, along with returning refugees, crossed freshly crusted lava flows to access certain areas. On 18 January two out of three water pumping stations were not working.

Eye irritation and breathing difficulties were reported as a result of the ash and fumes in Goma. Health care centers were provided with medication, and all health care has been free thus far. A few suspected cases of cholera have been reported, but OCHA reported that relief agencies felt prepared for possible disease outbreaks.

According to Oxfam International, the major problems facing the people of Goma were water supply and sanitation facilities, shelter, food, medical care, and damage to schools. A qualitative helicopter assessment on 23 January indicated that ~30% of Goma was destroyed by the lava flows and that up to 50,000-60,000 people in the E of the town lost their homes. On the other hand, the 27 January map-based assessment illustrated by figure 12 concluded that lava flows had affected 4.5 km² of the city's 35 km² populated area. Thus, this analysis suggested that ~13% of Goma had been affected.

Figure 12 shows that the E portion of Goma had been cut off from the rest of the town by lava. During the first four days of the eruption, speedboats transported relief workers between the E and W parts of Goma.

On 23 January, 11 sites (in Goma and Sake) operated by the World Food Program began to distribute food and non-food items to refugees (several of these sites appear on figure 12). Other NGO's had collaborated to purchase food locally to provide food for refugees prior to this distribution, but many people had not received food since the eruption began.

A report from OCHA on 25 January confirmed that two access roads into Goma had been cut through the hardened lava and that a third would soon be completed. They reported that 50% of the water network in Goma was operational and that aid agencies had positioned bladders in areas not served by the network. Agencies planned to have the entire water network operational by 4 February. On 25 January, Oxfam reported that the operational portion of the water network still mainly serviced the western part of Goma, and that in the eastern part an estimated 100,000 people remained in dire need of drinking water. Water from Lake Kivu was determined to be potable for adults if filtered. About 22 water purification points were established for residents withdrawing lakewater.

The Goma airport reopened to small aircraft on 25 January. However, the tower was considered inoperable due to the risk of gas explosion.

As of 25 January, seismic activity continued, and monitoring in Goma suggested that some epicenters were at shallow depth beneath the city. OCHA warned that further eruptions were still possible near Goma and Lower Gisenyi. Several humanitarian efforts continued to help the people in Goma through the ongoing crisis. Further information will be forthcoming in future Bulletin reports, including more technical information from volcanologists on the scene.

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: United Nations Office for the Coordination of Humanitarian Affairs (OCHA), United Nations, New York, NY 10017 USA (URL: https://reliefweb.int/); Oxfam International, Suite 20, 266 Banbury Road, Oxford, OX2 7DL, United Kingdom (URL: https://www.oxfam.org/); Richard McDonald, c/o Independent Missionaries, Box 42, Cyangugu, Rwanda; U.S. Agency for International Development (USAID)/Office of U.S. Foreign Disaster Assistance (OFDA), Ronald Reagan Building, Washington, DC 20523-1000, USA (URL: https://www.usaid.gov/); Bruce Presgrave, USGS National Earthquake Information Center (NEIC), MS 967, Denver Federal Center, Box 25046, Denver, CO 802225, USA (URL: https://earthquake.usgs.gov/); Fr. Stephen Yavorsky, S.J., Maison Régionale Jésuite, B.P. 6039, Kigali, Rwanda; National Aeronautics and Space Administration (NASA), Washington, DC 20456-0001, USA (URL: https://www.nasa.gov/).

In mid-July 2001, the level of concern for Shiveluch was raised from Yellow to Orange (BGVN 26:08) and remained at that level until the end of November 2001 when it was returned to Yellow. During a very active period, 30 September through 1 October, the level of concern was set to Red. The level of concern remained at Yellow through early January 2002, rising briefly to Orange in mid-January and returning to Yellow at the end of the report period, 25 January 2002.

During mid-July through at least 25 January 2002, seismicity was above background levels. The lava dome, now with a summit at ~2,500 m, continued to grow. Typical activities throughout the period included explosions, some producing pyroclastic flows, ash and/or gas-and-steam plumes typically rising 1-2 km (3,500-4,500 m altitude) above the dome, and localized ash falls. Plumes drifted in various directions depending upon local wind conditions and extended from several to as much as 80 km from the volcano. As many as 60 or more earthquakes over M 1.7 (including some over M 2.0) occurred weekly, with many other weak, shallow earthquakes occurring within the volcano's edifice. Other local, shallow seismic events (possible collapses, avalanches, weak gas-ash explosions), and episodes of weak, volcanic tremor also were registered. In mid-January the earthquake rate decreased but the energy of individual events increased (maximum magnitude, 2.7).

The AVHRR satellite images of the active dome area showed thermal anomalies almost daily throughout the period. Anomalies ranged from 1 to 10 pixels in size with maximum temperatures from a few degrees C to 49°C on numerous occasions. Background temperatures typically ranged from -14 to -29° C.

Activities from the end of August to late-January 2002 include visual reports on 4 September of a gas-and-steam plume rising 1,200 m above the dome and extending 10 km E, and a pyroclastic flow ~1 km long later that day. On 11 September, several hot avalanches from the summit of the dome were observed. An explosive eruption began at 1323 on 30 September and, at 2010, another explosion sent an ash plume 9,000 m above the dome. A small circular cloud ~25 km in diameter located directly over the volcano was reported later. On 1 October, ash plumes were observed to be as high as 7,500 m above the dome with localized ashfall thicknesses in the millimeter range. This eruption was the beginning of a very active period that extended into the first week of October, e.g., eleven M 2 and nine M 1.7 earthquakes were registered during 1-4 October. On 19 November a 10-pixel thermal anomaly was observed with temperatures ranging from 0 to 49°C. A steam plume observed on 7 January extended ~100 km SE. On 14 January, continuous rock avalanches were reported by observers in Klyuchi town. Gas-and-steam plumes that week rose 1,000-1,500 m above the dome and extended 10 km SE. Seismicity decreased during 19-25 January compared to the previous week. Several gas-and-steam plumes were observed, one extending 75 km to the SE on 21 January. Thermal anomalies continued but no ash was detected in any image.

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

On 1 August 2000, Jeff and Raine Williams, aboard the sailing yacht Gryphon, reported that they spent a couple nights at Uanukuhahaki island, approximately 48 km E of the volcanic islands of Kao and Tofua. They noted that "steam can be seen rising from Tofua almost continuously." They also observed that pumice stones were scattered all along the beach at Uanukuhahaki.

Tim Worthington (Christian-Albrechts-Universität zu Kiel) notes that the activity seen on 1 August 2000 is the normal state of Tofua. In September 1999, Worthington mapped a thick compound ash layer (with three distinct units) containing abundant pumice clasts that is widespread on Kotu, Ha'afeva, Matuku, and other islands in the group 30-50 km E of Tofua and Kao. The ash represents the distal part of the pyroclastic flow sequence associated with a pre-historic caldera-forming eruption on Tofua. Other workers, including Shane Cronin (GEOMAR), are looking at these units in more detail with a view to dating the eruption. The "pumice stones" seen on Uanukuhahaki may be blocks of andesitic pumice eroded from this ash sequence.

Geologic mapping and observations, November 2000. Worthington was part of a group that spent 8 days mapping and sampling at Tofua in late November 2000. Tofua is a nearly circular island 9.5 x 7.1 km in diameter. The flanks rise steeply to a well-defined caldera rim reaching 515 m elevation in the NW and SE. The inner caldera walls are precipitous, and the caldera is occupied by a large, cold, fresh-water lake standing at 30 m elevation. The most recent volcanism took place from vents within the N half of the caldera, where there are three cinder-cone complexes.

The westernmost cinder-cone complex is densely forested and rather degraded. The easternmost complex consists of four distinct but intergrown small cinder cones with well-formed craters (two have sub-craters). A series of young rubble-topped basaltic andesite lavas were erupted from these cones and flowed towards (and into) the lake. Different degrees of vegetation on each flow suggest a recurrence interval of about 50 years, and the youngest may have been emplaced during the 1958-60 eruptions. It was mapped by visiting geologists in the early 1970s.

The northernmost cinder cone is the large and vigorously degassing Lofia, with a basal diameter of ~500 m and a summit at 380 m elevation. Lofia has a summit crater 70 m in diameter with vertical inner walls, which was completely filled by dense brownish-blue SO₂-rich steam during the visit. Intermittent chugging sounds resembling a train starting to move could be heard from the crater rim. From the yacht, occasional dull orange reflections were observed in clouds above the caldera rim on two nights. However, there was no evidence of recent spatter around the crater rim, nor any indication of significant volcanic activity since the 1958-60 eruptions.

On calm days the plume from Lofia rose above the caldera rim and was visible from nearby islands and to passing ships; more commonly it dispersed in the wind before passing the caldera rim. Numerous breadcrust bombs were plastered onto the NW caldera wall downwind from Lofia, and had welded to form a sparsely vegetated 20-m-thick rootless lava flow on the NW caldera rim. The region of sparse vegetation on the outer NW caldera wall extended from 300 to 515 m elevation, gaving the NW summit of Tofua a "burnt" appearance to passing ships. The spatter testifies to vigorous fire-fountaining at Lofia, whose summit is 130 m below and 700 m S of the caldera rim. The latest episode of this activity may have taken place during the 1958-60 eruptions, but the spatter almost certainly represents the accumulated result of many such episodes.

Geologic Background. The low, forested Tofua Island in the central part of the Tonga Islands group is the emergent summit of a large stratovolcano that was seen in eruption by Captain Cook in 1774. The summit contains a 5-km-wide caldera whose walls drop steeply about 500 m. Three post-caldera cones were constructed at the northern end of a cold fresh-water caldera lake, whose surface lies only 30 m above sea level. The easternmost cone has three craters and produced young basaltic-andesite lava flows, some of which traveled into the caldera lake. The largest and northernmost of the cones, Lofia, has a steep-sided crater that is 70 m wide and 120 m deep and has been the source of historical eruptions, first reported in the 18th century. The fumarolically active crater of Lofia has a flat floor formed by a ponded lava flow.

Information Contacts: Tim J. Worthington, Institut für Geowissenschaften, Christian-Albrechts-Universität zu Kiel, Olshausenstr. 40, D-24118 Kiel, Germany; Jeff and Raine Williams, P.O. Box 729, Funkstown, MD 21734, USA.