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/).

The fissure eruption from the Bardarbunga volcanic system began on 29 August 2014 (BGVN 39:10) about 45 km NE of the subglacial caldera at what was designated the Holuhraun vent. Lava emission ended on 28 February 2015 (BGVN 40:01), after creating a lava field almost 85 km² in size. This report includes additional information provided by the Icelandic Meterological Office and NASA's Earth Observatory. Information from a report of the Icelandic Civil Protection Scientific Advisory Board, which met on 23 June 2016 to review recent data, is included below.

A scientific team working on the Vatnajökull glacier during 3-10 June 2016 did echo soundings to examine whether changes in bedrock topography within the Bardarbunga caldera could be detected from the recent eruption. No changes in the bedrock topography were apparent. There were also no indications that meltwater was accumulating within the caldera. The 65-m-deep depression in the glacier formed during the 2014-2015 activity was getting shallower due to the flow of ice into the caldera and snow accumulation, and the depression had decreased in depth by 8 m since the previous year.

Expedition scientists also measured gas emissions at ice cauldrons (figures 13 and 14), which are formed by subglacial geothermal activity, along the caldera rim; these measurements showed little change since the previous year's expedition. Seismic data showed that accumulated moment magnitude had been increasing since mid-September 2015. A total of 51 earthquakes stronger than M3 had been registered at Bardarbunga since the end of the eruption in 2015. GPS stations showed slow movement away from the caldera.

Figure 13. The edge of a cauldron at the southernmost rim of the Bardarbunga caldera, 10 June 2016. Photo by Benedikt G. Ófeigsson; courtesy of the IMO.

Figure 14. A panorama view from 7 June 2016 shows the same cauldron at Bardarbunga, with Grimsvotn in the background. Photo by Benedikt G. Ófeigsson; courtesy of the IMO.

The Advisory Board report concluded that the most probable explanations for the ground deformation and seismicity was the inflow of magma from around 10-15 km below Bardarbunga into the area from which the magma erupted at Holuhraun during 2014-2015. There were no indications of magma collecting at shallower depths.

An image posted by the NASA Earth Observatory showed the extent of the Holuhraun lava field on 5 November 2016 surrounded by snow (figure 15).

Figure 15. Acquired 5 November 2016, this image was captured by the Advanced Land Imager on the Earth Observing-1 satellite at 1000 local time. The photo has been edited to correct for the low angle of the Sun, which caused the white snow to appear reddish. Snow does appear to build up along the edges of the lava flow, where the lava is thinner. Courtesy NASA Earth Observatory.

Geologic Background. The large central volcano of Bárðarbunga lies beneath the NW part of the Vatnajökull icecap, NW of Grímsvötn volcano, and contains a subglacial 700-m-deep caldera. Related fissure systems include the Veidivötn and Trollagigar fissures, which extend about 100 km SW to near Torfajökull volcano and 50 km NE to near Askja volcano, respectively. Voluminous fissure eruptions, including one at Thjorsarhraun, which produced the largest known Holocene lava flow on Earth with a volume of more than 21 km3, have occurred throughout the Holocene into historical time from the Veidivötn fissure system. The last major eruption of Veidivötn, in 1477, also produced a large tephra deposit. The subglacial Loki-Fögrufjöll volcanic system to the SW is also part of the Bárðarbunga volcanic system and contains two subglacial ridges extending from the largely subglacial Hamarinn central volcano; the Loki ridge trends to the NE and the Fögrufjöll ridge to the SW. Jökulhlaups (glacier-outburst floods) from eruptions at Bárðarbunga potentially affect drainages in all directions.

Information Contacts: Icelandic Met Office (IMO), Reykjavík, Iceland (URL: http://en.vedur.is/); NASA Earth Observatory, EOS Project Science Office, NASA Goddard Space Flight Center, Goddard, Maryland, USA (URL: http://earthobservatory.nasa.gov/).

Recent eruptive activity at Bulusan included episodes during 6 November 2010-16 May 2011, 1 May-17 July 2015, and 22 February 2016; activity typically included phreatic explosions from the summit crater and flank vents, ash-and-steam plumes, and minor ashfall in nearby villages (BGVN 41:03). The most recent eruption began 10 June 2016 and continued through the end of the year. Information was provided by the Philippine Institute of Volcanology and Seismology (PHIVOLCS) and the Tokyo Volcanic Ash Advisory Center (VAAC).

During the reporting period of June-December 2016, the Alert Level remained at 1 (on a scale of 0-5), indicating abnormal conditions and a 4-km radius Permanent Danger Zone (PDZ). Activity consisted of intermittent phreatic explosions generating emissions of ash and steam that typically rose 70-2,500 m above the summit crater (table 7). Minor ashfall in nearby municipalities often accompanied the explosions.

In October 2016, PHIVOLCS extended the danger zone an additional 2 km as a result of a fissure that extended 2 km down the upper S flank; PHIVOLCS was concerned that active vents along the upper part of the SE flank could pose a greater risk to the populated barangays (neighborhoods) of Mapaso (Irosin), Patag (Irosin), and San Roque (Bulusan). The municipalities of Irosin and Bulusan are about 8 km SSW and 7 km ESE, respectively, of the volcano.

Table 7. Summary of volcanic activity at Bulusan, June-December 2016.

Ashfall. On 23 June 2016, minor amounts of ash fell in the barangays (neighborhoods) of Poblacion (11 km NW), Añog (12 km NW), and Bacolod (13 km NW), all in the municipality of Juban (about 12 km NW), and the municipality of Mabini (12 km NNW). A sulfur odor was detected in the neighborhoods of Mabini, Bacolod (Irosin), Añog (Juban), and Puting Sapa (Juban).

On 16 September there was ashfall in the municipalities of Casiguran (11 km NNW), Gubat (18 km NNE), and Barcelona (14 km NE). Minor amounts of ash fell during 1 October in the barangays of San Rafael, San Roque, and San Jose, all in the municipality of Bulusan. A minor explosion on 6 October caused ashfall in some areas of the municipality of Gubat, and rumbling was noted in San Roque.

A phreatic explosion on 21 October generated a plume that resulted in a thin layer of ash in Casiguran and Gubat, and trace amounts in barangays in Barcelona, Casiguran, and Gubat. On 23 October, a phreatic explosion produced trace ashfall in multiple barangays in Irosin; the most ash, 1 mm-thick deposits, were found in Puting Sapa (Juban).

On 29 December, a phreatic explosion generated an ash plume that resulted in minor amounts of ashfall in areas downwind, including several Irosin barangays (Cogon, Tinampo, Bolos, Umagom, Gulang-gulang, and Monbon) and two Juban barangays (Caladgao and Guruyan). Residents of Guruyan, Monbon, and Tinampo noted a sulfur odor.

Geologic Background. Luzon's southernmost volcano, Bulusan, was constructed along the rim of the 11-km-diameter dacitic-to-rhyolitic Irosin caldera, which was formed about 36,000 years ago. It lies at the SE end of the Bicol volcanic arc occupying the peninsula of the same name that forms the elongated SE tip of Luzon. A broad, flat moat is located below the topographically prominent SW rim of Irosin caldera; the NE rim is buried by the andesitic complex. Bulusan is flanked by several other large intracaldera lava domes and cones, including the prominent Mount Jormajan lava dome on the SW flank and Sharp Peak to the NE. The summit is unvegetated and contains a 300-m-wide, 50-m-deep crater. Three small craters are located on the SE flank. Many moderate explosive eruptions have been recorded since the mid-19th century.

Information Contacts: Philippine Institute of Volcanology and Seismology (PHIVOLCS), University of the Philippines Campus, Diliman, Quezon City, Philippines (URL: http://www.phivolcs.dost.gov.ph/); Tokyo Volcanic Ash Advisory Center (VAAC), Tokyo, Japan (URL: http://ds.data.jma.go.jp/svd/vaac/data/).

The Karangetang andesitic-basaltic stratovolcano (also referred to as Api Siau) at the northern end of the island of Siau, north of Sulawesi, Indonesia has had more than 50 historically-observed eruptions since 1675. Frequent explosive activity is accompanied by pyroclastic flows and lahars, and lava-dome growth has created multiple summit craters. Rock avalanches, observed incandescence, and satellite thermal anomalies at the summit confirmed continuing volcanic activity through 5 September 2013 (BGVN 39:01). Activity is monitored by Indonesia's Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as CVGHM, or the Center of Volcanology and Geological Hazard Mitigation), and ash plumes are monitored by the Darwin VAAC (Volcanic Ash Advisory Center). Information is also available from MODIS thermal anomaly satellite data through both the University of Hawaii's MODVOLC system and the Italian MIROVA project.

An ash plume reported by the Darwin VAAC on 9 February 2014 that rose to an altitude of 4.3 km (2.5 km above the summit) and drifted over 80 km W was the only recorded activity at Karangetang between MODVOLC thermal anomalies on 5 September 2013 and on 8 June 2014. Additional thermal anomalies identified between June and September 2014, and increased seismicity reported by PVMBG in September, indicated ongoing activity. An ash plume was reported by the Darwin VAAC in October 2014. A spike in thermal activity was recognized during 12 January-1 February 2015. Another strong thermal signal began on 13 May that continued through 9 December 2015, when visual reports of lava flows and ash plumes were all recorded. Ash plumes were last reported by the Darwin VAAC in January 2016; night incandescence at the summit was reported by PVMBG until 15 March 2016. The Alert Level remained at 3 from September 2013 through 16 March 2016, when it was lowered to 2. Persistent low-energy thermal anomalies were captured by MIROVA throughout 2016, but there were no PVMBG observations indicating ongoing dome growth or other eruptive activity.

Activity during 2014. On 9 February 2014, the Darwin VAAC reported an ash plume rising to 4.3 km and extending over 80 km to the W based on satellite images. The next observation of activity was a single MODVOLC thermal alert pixel on 8 June 2014 located precisely over the summit. More substantial thermal anomalies appeared between 19 and 24 July, followed by two more on 2 August, after which there is a break of more than five months with no MODVOLC thermal anomalies. The MIROVA system, however, does record intermittent, low-level anomalies through early December 2014 (figure 11).

Figure 11. MIROVA Log Radiative Power Thermal Anomaly data for 29 May 2014 through 29 May 2015 at Karangetang. Activity increases during July 2014 and slowly tapers off into December before the sudden appearance of a moderate to high thermal anomaly was recorded between 12 January and 1 February 2015. Activity increases again in early April 2015. Image courtesy of MIROVA.

On 15 September 2014, PVMBG issued a report noting that seismic amplitudes were relatively high at the volcano, increasing from much lower levels on 12 September. Seismic data also indicated an increase in earthquakes indicating avalanches in late July which corresponded in time with the thermal anomalies recorded by MODVOLC and MIROVA. PVMBG observed steam plumes rising to between 100 and 150 m above the main summit crater, and to around 25 m above the second crater during the second week of September 2014, along with incandescence at the summit. The last 2014 report of activity came from the Darwin VAAC; they reported an ash plume on 20 October rising to 3 km and drifting 75 km NW.

Activity during 2015. Both the MODVOLC and MIROVA systems report the abrupt appearance of strong thermal anomalies on 12 January 2015, continuing until 1 February when they stopped just as suddenly (figure 11). A news article by a local newspaper (Jaringan Berita Terluas di Indonesia) reported that a lahar on 22 January 2015, triggered by heavy rains, descended the volcano's flanks, overflowed the banks of the Batu River, and damaged a number of public and private buildings in the village of Bahu about 7.5 km S of the volcano, and in Bebali, 4.5 km S. It also damaged the main road between the communities of Ulu and Ondong but the debris was quickly cleared by authorities.

The MIROVA system recorded thermal anomalies beginning again at the very end of March 2015 (figure 11); MODVOLC noted a single thermal alert on 13 April, and then strong, multi-pixel anomalies nearly continuously from 24 April through 11 June 2015. During the second half of April, PVMBG staff at the Volcano Observation Post in the village of Salili, 4 km SW, noted white steam plumes ranging from 50 to 350 m above the main crater and 25 m above the second crater, and incandescence from the summit. Additionally, they observed bluish-white plumes on 16 and 17 April rising to 50-150 m. They also concluded that the amplitude of seismic activity had decreased since the end of February.

Lava flows were first observed on 22 April; incandescent avalanches from the fronts of 150-m-long lava flows traveled up to 2 km down Batuawang and Kahetang drainages (E) during 22-29 April. On 26 April pyroclastic flows traveled 2.2 km along the Kahetang drainage. On 28 April explosions produced plumes and ejected incandescent material 50 m high (figure 12). Seismicity also increased from the previous week. The MIROVA data indicated a sudden spike of high thermal activity beginning around 22 April and continuing past the end of May (figure 11).

Figure 12. Incandescent lava flowing down Karangetang's flanks on 28 April 2015. Courtesy of PVMBG (G. Karangetang Activity Report, 29 April 2015).

Activity at the volcano increased significantly at the beginning of May 2015. BNPB (Badan Nasional Penanggulangan Bencana) reported that on 7 May at 1400 an eruption that ejected incandescent material and produced a dense ash plume also generated a pyroclastic flow that traveled 4 km E, leveling four houses in Kora-Kora. The next day pyroclastic flows descended the S flank 2.5 km into the Kahetang (E) and Batuawang drainages. There were no reported fatalities; 465 people were evacuated from the village of Bebali, 4.5 km S. Also on 8 May, the Darwin VAAC reported an ash plume that rose to an altitude of 3 km drifted almost 85 km E, and dissipated two days later. On 12 May another ash plume rose to an altitude of 3.7 km and drifted 55 km SW, and there were reports by the Darwin VAAC via social media of continued pyroclastic flow activity. Steam plumes rising to 400 m continued into the last week of May, along with incandescence from the summit at night. The lava flows that first appeared on 22 April were 300 m long by the end of May and continued to send block avalanches from the fronts up to 2 km down the Batuawang, Kahetang, and Keting drainages to the SW, S and SE. Seismic amplitudes continued at a high level; seismicity was dominated by signals characteristic of avalanches, with harmonic tremor frequently detected.

On 5 June 2015 BNPB reported that activity remained high; a total of 339 people (106 families) from the villages of Ulu, Salili, Belali, and Tarorane, all a few kilometers S of the summit, remained displaced since early May. PVMBG reported that on 18 June a lahar descending Batuawang drainage (E) covered a 100-m section of roadway with 25 cm of mud containing 1-m-diameter boulders. The lahar also damaged or destroyed four homes. White plumes rising 150 m above the main crater and 25 m above crater II were observed from the Volcano Observation Post in Salili during late June. Incandescence from the lava dome was also observed at night. Lava flowed from the S part of the dome; incandescent avalanches from the front of the lava flow again traveled up to 2.3 km down the Batuawang and Kahetang drainages. Seismic activity continued to be high, although the number of daily earthquake indicating avalanches had dropped below 100 per day at the end of June. MODVOLC thermal anomaly pixels were recorded on 2-4, 9, and 11 June, far fewer than in May.

PVMBG reported that during the last two weeks of July 2015, white plumes rose 250 m above the main crater and 25 m above the second crater (crater II). Incandescence from the lava dome was observed at night when skies were clear, and incandescent avalanches from the fronts of new 150-m-long lava flows traveled up to 2.3 km E down the Batuawang, Kahetang and Keting drainages. Seismicity was dominated by signals characteristic of avalanches, with rare volcanic earthquakes. The Alert Level remained at 3. During the month, fewer MODVOLC thermal alerts were recorded than during May and June, only on 4, 6, 11, and 25 July.

Seismicity related to avalanche activity increased significantly on 14 August 2015 and the number of daily events spiked on 20 August to 599, marking a period of increased activity that continued into November (figure 13). Strong MODVOLC thermal alert signals reappeared on 10 August 2015 and continued with multiple-pixel signals almost daily until 1 October when they became more intermittent. The MIROVA thermal anomaly data also corroborated increased thermal activity during this period (figure 14).

Figure 13. Seismic amplitude data (RSAM) from Karangetang, 1 January 2015 through 17 February 2016. Activity increased notably in the third week of August 2015 and remained elevated through the end of October, followed by intermittent pulses of activity through February 2016. Courtesy of PVMBG, (G. Karangetang Activity Report, 17 February 2015).

Figure 14. MIROVA thermal anomaly data for Karangetang from 14 March 2015 through 14 March 2016. The tapering of activity between May and July 2015 corresponds well with MODVOLC, seismic, and observational data for that period. Heightened activity between August and October 2015 also corresponds with increased seismic activity, abundant MODVOLC thermal anomaly pixels, visual observations of lava flows and ash plumes, and numerous VAAC reports during this time. Courtesy of MIROVA (published originally by PVMBG in G. Karangetang Activity Report, 16 March 2016).

The Darwin VAAC reported that on 28 August 2015 a pyroclastic cloud was observed on satellite. The ash plume rose to an altitude of 2.4 km and drifted 55 km ENE. They also observed a number of ash plumes between 10 and 17 September that rose as high as 3 km and drifted up to 130 km generally E. Lava fountains as high as 300 m were observed from the Volcano Observation Post in Salili during 9-16 September. Debris fell as far as 300 m from the summit crater into the Kinali River. Incandescent avalanches from the fronts of 200-m-long lava flows traveled up to 2.5 km down the Batuawang, Kahetang, Keting, and Batang drainages; brownish smoke was observed at the end of the Batuawang flows. The Alert Level remained at 3.

During October 2015, MODVOLC thermal anomaly pixels became more intermittent, appearing on 10 days during the month, far fewer than September. Steam plumes from the main crater were observed from Salili up to 150 m above the crater along with incandescence on clear nights. Lava flows remained active 200 m from the crater still sending pyroclastic avalanches down the Batuawang, Kahetang, Keting, and Batang drainages up to 2 km from the lava fronts. The flows had increased to 600 m long between 19 and 22 October and the avalanches continued. Most seismicity decreased in early October, except harmonic tremor, suggesting that magma movement inside the volcano persisted. The Darwin VAAC reported that on 8 October an ash plume rose to an altitude of 2.7 km and drifted 65 km E and that during 18 October ash plumes rose to an altitude of 2.1 km and drifted 75-95 km NE. Constant harmonic tremors for 6 hours on 20 October indicated magma was still active.

Seismicity continued its steady decline since early September during November (figure 13), although tremor activity continued. Incandescence was still visible from the lava dome at night according to PVMBG, and the incandescent avalanches were still travelling up to 1.5 km down the Batuawang and Kahetang drainages. Steam plumes rose generally 50-200 m, and occasionally 400 m from the main crater. A lahar in Batuawang drainage flowed as far as the village of Bebali and covered about 50 m of the Ondong-Ulu highway on 20 November, similar to the event of 18 June. MODVOLC recorded only two thermal anomaly pixels at the summit, both on 25 November.

By December 2015, incandescence was still observed at the crater from the Volcano Observatory in Salili, but steam plumes rarely exceeded 150 m. A single MODVOLC thermal anomaly pixel, was recorded on 9 December, and spikes in seismic amplitudes were recorded on 21 and 22 December.

Activity during 2016. According to PVMBG, Karangetang was quiet during most of January 2016, although incandescence was reported from the main crater, and plumes of bluish and white smoke rose 50-100 m. There were no reports of active lava flows or incandescent avalanches, but the accumulation of material in the Batuawang drainage made the possibility of damaging lahars during the rainy season very high. The relatively constant number of shallow (VB) earthquakes suggested that the lava dome was growing slowly; there was a two-fold increase in RSAM values during the month (figure 13). Based on analyses of satellite imagery and wind data, the Darwin VAAC reported three ash plumes during the month; on 12 January an ash plume rose to an altitude of 5.2 km and drifted 65 km NW, on 14 January a steam-and-ash plume rose to an altitude of 5.2 km and drifted over 35 km W, and the next day an ash-and-steam plume rose to an altitude of 2.7 km and drifted about 20 km SW.

Incandescence continued at the summit during February and early March 2016 along with bluish-white plumes rising 25-100 m from the summit crater. Seismic energy values (RSAM) remained elevated during February, suggesting continued growth of the lava dome. The last MODIS thermal anomaly observed by PVMBG was on 8 March. Although they continued to observe incandescence 10-25 m above the summit and bluish-white emissions to 150 m through 15 March, they lowered the Alert Level from 3 to 2 on 16 March, noting that even though the RSAM seismic energy values were still above normal, they had been stable for some time. The MIROVA Thermal Anomaly Radiative Power data from March 2016 also showed a significant decline in thermal energy released from the volcano compared with the period from late April through November 2015 (figure 14). Although no further reports were issued by PVMBG or Darwin VAAC, the thermal anomalies detected by MIROVA continued at low to moderate levels during 2016, suggesting a persistent heat source at the volcano (figure 15).

Figure 15. MIROVA Log Radiative Power Thermal Anomaly data for Karangetang from 14 Dec 2015 through 14 December 2016 showing continued low-energy thermal anomalies during the period. Courtesy of MIROVA.

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/); Badan Nasional Penanggulangan Bencana (BNPB), National Disaster Management Agency, Graha BNPB - Jl. Scout Kav.38 East Jakarta 13120 (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/); 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/, http://modis.higp.hawaii.edu/cgi-bin/modisnew.cgi); 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/); Jaringan Berita Terluas di Indonesia, http://www.jpnn.com/read/2015/01/23/283204/Awas,-Lahar-Dingin-Karangetang-Kembali-Mengancam.

Explosions occurred at Marapi (not to be confused with the better known Merapi on Java) during August 2011; March, May, and September 2012; and February 2014 (BGVN 40:05). This report discusses activity during 2015 and 2016. All information was provided by the Indonesian Center of Volcanology and Geological Hazard Mitigation (PVMBG, also known as CVGHM). During the reporting period, the Alert Level remained at 2 (on a scale of 1-4); residents and visitors were advised not to enter an area within 3 km of the summit.

According to PVMBG, diffuse white plumes rose as high as 300 above Marapi's crater during February-25 May 2015, 150 m above the crater during 1 August-16 November 2015, and 250 m above the crater during 1 November 2015-19 January 2016. Inclement weather often prevented observations.

Seismicity fluctuated during this time, dominated by earthquakes centered a long distance from the volcano. However, tremor increased significantly during August 2015 through at least the middle of January 2016 (figure 4). A phreatic explosion at 2233 on 14 November 2015, generated an ash plume, and ashfall was noted in Panyalaian and Aia Angek on the SW flank.

Figure 4. Types and daily number of earthquakes recorded at Marapi during 1 January 2015-18 January 2016. Key: eruptive earthquakes (Letusan), emission-type "blowing" earthquakes (Hembus), shallow earthquakes (VB), deep earthquakes (VA), local earthquakes (Lokal), and long-distance earthquakes (Jauh). The terms shallow and deep were not quantified. Courtesy of PVMBG (23 January 2016 report).

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

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

Evidence of submarine volcanism at Monowai has been frequently observed since October 1977, when the Royal New Zealand Air Force (RNZAF) noted a plume of discolored water above the seamount. Most subsequent eruptions have been determined based on additional observations of discolored water or the seismic detection of acoustic waves (T waves or T phases) caused by explosive activity. Monitoring reports are provided by New Zealand's GeoNet through their website and other publications. The hydro-acoustic signals are most frequently detected by seismometers in Rarotonga (Cook Islands) or by the Polynesian Seismic Network (Réseau Sismique Polynésien, or RSP) in Tahiti. Research visits over the past 20 years have resulted in many detailed analyses of morphological changes due to volcanism and subsequent collapses.

Some of those results have been reviewed in previous Bulletin reports. This issue will focus on reviewing eruptive episodes after a sector-collapse event on 24 May 2002, which caused anomalous seismic signals originally thought to be explosive in nature. Following the May 2002 event, no activity was detected until T phases were recorded during 1-24 November 2002 (figure 28 and see BGVN 28:02). The next eruptive period began on 10 April 2003 (figure 28 and see BGVN 28:05) and continued until a seismic swarm on 14 August 2004 (BGVN 28:11, 30:07), which included the building of a new cone and ended just prior to a bathymetric survey from the R/V Tangaroa in September 2004. Another sequence of swarms began on 2 March 2005 and continued until 27 June 2006. Although there appear to have been small signals in September 2006, scientists at the Laboratoire de Géophysique, Commissariat à l'Energie Atomique (CEA/DASE/LDG) reported that there were 6 months of quiet after the June 2006 swarms (BGVN 32:01).

Figure 28. Monitoring data from the Polynesian Seismic Network showing T wave swarms at Monowai throughout January 2002-December 2007. The times of the September 2004 and May 2007 bathymetric surveys (dashed vertical lines), and the time of the anomalous 24 May 2002 swarm (arrows) are shown. (top) Number of T wave events per day. (bottom) Amplitudes of T wave events, in nanometers as recorded at station TVO in Tahiti. Note unusually high amplitude of the 24 May 2002 event, interpreted as the sector collapse between the 1998 and 2004 surveys. Modified from Chadwick et al. (2008).

While the R/V Sonne was on site conducting a bathymetric survey during 1-4 May 2007 (Chadwick et al, 2008), scientists heard booming sounds and saw slicks and bubbles on the surface (BGVN 33:03). That activity was part of an eruptive period that began on 12 December 2006 and continued into at least early November 2007 (figure 29 and see BGVN 32:01). A "big acoustic event" was detected by the Polynesian Seismic Network (Réseau Sismique Polynésien, or RSP) on 8 February 2008 (BGVN 33:03).

Figure 29. Monitoring data from the Polynesian Seismic Network showing the T wave swarms at Monowai in December 2006 and January 2007. (top) Number of events per day, (bottom) amplitude at station TVO in nanometers. Modified from Chadwick et al. (2008).

A network of 23 ocean-bottom seismometers (OBS) and hydrophones was deployed in July 2007 over the fore-arc just to the E of Monowai at distances of 70-250 km to acquire data about local seismicity associated with subduction (Grevemeyer et al., 2016). The instruments also detected T waves and direct wave signals from the ongoing explosive activity. Analysis by Grevemeyer et al. (2016) showed that between deployment and recovery at the end of January 2008 there had been more than 2,000 events associated with Monowai, clustered into 13-15 major sequences that each lasted between several hours to about two days. Quiet periods between the event sequences varied between 1 and 70 days.

Intermittent activity during 2009 was described in a GeoNet posting from 6 January 2010. Activity was noted in early and mid-May, early July, mid-September (figure 30), late October (figure 31), mid-November, late November to early December, and mid-December 2009 based on seismic data recorded in Rarotonga, Cook Islands. On 27 October the RNZAF overflew the area and confirmed the activity, observing discolored sea water related to suspended sediment and precipitates. Another flight in May 2010 did not show similar activity. A summary of 2010 activity in New Zealand by GeoNet noted continued evidence of small-scale eruptive activity on the Rarotonga seismic record during the year (no dates given), but no activity was confirmed by surface observations.

Figure 30. Seismic data from Rarotonga showing an eruption at Monowai during 13-17 September 2009. Courtesy of GNS.

Figure 31. Aerial photo of discolored water near Monowai on 27 October 2009. Photo taken by Royal New Zealand Air Force, courtesy of GeoNet.

[Discolored water with gas bubbles and a sulfurous odor was observed during a planned swath mapping visit by the R/V Sonne on 14 May 2011 (Peirce and Watts, 2011).] According to Metz et al. (2016), explosive eruptions took place over [17-22 May] as detected by T phase waves recorded at broadband seismic stations on Rarotonga (Cook Islands), Papeete (Tahiti), and the Marquesas Islands. Signals were also received at an International Monitoring System hydrophone array (maintained by the Comprehensive Nuclear-Test-Ban Treaty Organization) near Ascension Island, ~15,800 km from the seamount in the equatorial South Atlantic Ocean. A second round of mapping by R/V Sonne on the return transit was accomplished on 1-2 June, [following the explosive activity]. Watts et al. (2012) showed that there had been a depth change to the summit of 18.8 m between two surveys (BGVN 37:06), which was attributed to the growth of a cone or lava spine during the intervening eruption. There was an additional visual confirmation of activity in August 2011, and GeoNet stated that activity was continuing in September. The 2011 volcanic summary by GeoNet again noted undated evidence of small-scale activity seen in the Rarotonga seismic data.

Seismicity during 1-4 June 2012 indicated another period of significant activity, which was confirmed by discolored seawater in the area observed from an RNZAF flight on 3 June. Seismographs in Rarotonga recorded eruptive activity during 3-19 August 2012 (figure 32). A posting from GeoNet on 2 October noted that Monowai had "not been active recently."

Figure 32. Seismic data from Rarotonga showing an eruption at Monowai during 3-19 August 2012. Courtesy of GNS.

There were no GeoNet reports of activity during 2013. However, the R/V Sonne was planning to add to the time series of maps of Monowai while making a final transit to Auckland (Werner et al., 2013). While they were approaching the seamount on 1 January 2014, with a summit estimated to be ~60 m below the surface based on 2011 bathymetry data, scientists noticed a light yellowish water discoloration and a faint rumble. The cruise report further noted that during profiling close to the summit a "sudden and significant increase in volcanic activity with explosive hydroclastic eruptions was accompanied by thunder and shock waves rapidly spreading out on the water surface." Pumice was also collected in the vicinity, but the source volcano was not known.

In a GeoNet volcanic activity update on 10 November 2014, Brad Scott observed that there had been eruptions detected during approximately 16-22 and 23-27 October, and 1-5 November (figure 33) based on T phase waves measured at Rarotonga, but the activity appeared to be weaker than that seen in 2009 and 2012. Confirming these observations was material seen floating on the ocean surface over the seamount by a RNZAF airplane on 31 October 2014 (figure 34). GeoNet noted that volcanic activity regularly occurs about 3-10 days a month; the yearly summary said the seamount erupted often in 2014.

Figure 33. Eruptive activity at Monowai during October-November 2014 identified on a seismic amplitude plot recorded from the Rarotonga T phase seismic monitoring site. Courtesy of GeoNet.

Figure 34. Aerial view from a RNZAF airplane of the ocean over Monowai showing floating debris (pumice) on 31 October 2014. Courtesy of GeoNet.

There were no reports of activity during 2015, but a plume of discolored water was once again seen by the RNZAF on 19 May 2016. According to a 16 November 2016 GeoNet update by Brad Scott, activity was recorded for about 24 hours over 11-12 November. The report noted that this type of activity is seen a few days every month.

References: Chadwick, W.W., Jr., Wright, I.C., Schwarz-Schampera, U., Hyvernaud O., Reymond, D., and de Ronde, C.E.J., 2008, Cyclic eruptions and sector collapses at Monowai submarine volcano, Kermadec arc: 1998-2007, GeochemistryGeophysicsGeosystemsG3, v. 9, p. 1-17 (DOI: 10.1029/2008GC002113).

Grevemeyer, I., Metz, D., and Watts, A., 2016, Submarine explosive activity and ocean noise generation at Monowai Volcano, Kermadec Arc: constraints from hydroacoustic T-waves: EGU General Assembly 2016.

Peirce C, Watts A, 2011, R/V Sonne SO 215 - Cruise Report, The Louisville Ridge - Tonga Trench collision: Implications for subduction zone dynamics: Durham, Department of Earth Sciences, Durham University.

Metz, D., Watts, A.B., Grevemeyer, I., Rodgers, M., and Paulatto, M., 2016 (22 February), Ultra-long-range hydroacoustic observations of submarine volcanic activity at Monowai, Kermadec Arc, Geophysical Research Letters, v. 43, no. 4, p. 1529-1536.

Watts, A.B., Peirce, C., Grevemeyer, I., Paulatto, M., Stratford, W., Bassett, D., Hunter, J.A., Kalnins, L.M., and de Ronde, C.E.J., 2012 (13 May), Rapid rates of growth and collapse of Monowai submarine volcano in the Kermadec Arc, Nature Geoscience, v. 5, p. 510-515 (DOI: 10.1038/ngeo1473).

Werner, R., D. Nürnberg, and F. Hauff, 2013, RV SONNE — Cruise report SO 225, Helmholtz-Zentrum fur Ozeanforschung Kiel (GEOMAR) (DOI: 10.3289/GEOMAR_REP_NS_5_2012).

Geologic Background. Monowai, also known as Orion seamount, is a basaltic stratovolcano that rises from a depth of about 1,500 to within 100 m of the ocean surface about halfway between the Kermadec and Tonga island groups, at the southern end of the Tonga Ridge. Small cones occur on the N and W flanks, and an 8.5 x 11 km submarine caldera with a depth of more than 1,500 m lies to the NNE. Numerous eruptions have been identified using submarine acoustic signals since it was first recognized as a volcano in 1977. A shoal that had been reported in 1944 may have been a pumice raft or water disturbance due to degassing. Surface observations have included water discoloration, vigorous gas bubbling, and areas of upwelling water, sometimes accompanied by rumbling noises. It was named for one of the New Zealand Navy bathymetric survey ships that documented its morphology.

Information Contacts: New Zealand GeoNet Project, a collaboration between the Earthquake Commission and GNS Science, Wairakei Research Centre, Private Bag 2000, Taupo 3352, New Zealand (URL: http://www.geonet.org.nz/).

The large eruption of 29 August 2014 at the Tavurvur stratovolcano of Rabaul caldera, on the NE tip of New Britain Island in Papua New Guinea, followed a period of minor ash eruptions earlier in the year (BGVN 39:08). The volcano has been intermittently active since a major eruption in September 1994, which was its first eruption in over 50 years. During the 1994 eruption, a lava flow, tephra ejection, and an ash plume rising to 18 km caused the evacuation of over 50,000 people from the surrounding area, significant damage to nearby Rabaul Town, several deaths, and disrupted air traffic for several days (BGVN 19:08, 19:09). Additional information for the 2014 eruption, and subsequent activity covered in this report, was compiled by the Rabaul Volcano Observatory (RVO) and issued by the Department of Mineral Policy and Geohazards Management of Papua New Guinea (DMPGM). Aviation alerts for Rabaul are issued by the Darwin Volcanic Ash Advisory Center (VAAC). A number of news outlets also covered the eruption with photographs, videos, and interviews of local residents.

A Strombolian eruption at Tavurvur began shortly after 0330 local time on 29 August 2014. This was followed by an ash plume rising to 18 km altitude. Smaller explosions at irregular intervals continued through 0641 on 30 August. After this, plumes of white vapor and slightly bluish gas returned, except for an ash plume reported on 12 September and a small explosion on 18 September. The volcano remained quiet after this and through 2016, although ground deformation data indicated a gradual inflation of about 6 cm over the period.

Activity during August-December 2014. Prior to August 2014, DMPGM reported that ground deformation measurements from the GPS station on Matupit Island (3 km W) had been showing increasing inflation, first detected in March 2014 (figure 67). In the days immediately before the 29 August 2014 eruption, Tavurvur had been emitting a diffuse plume of white vapor. An explosion occurred on 6 August, and an inspection of the summit crater on 8 August revealed an incandescent area covered by debris.

Figure 67. Locations of ground deformation (red), seismic (green) and thermal (orange) monitoring stations around Tavurvur volcano at Rabaul Caldera, New Britain Island, Papua New Guinea. Matupit Island is the peninsula immediately W of Tavurvur. Image courtesy WOVOdat.

The activity on 29 August 2014 started slowly between 0330 and 0400 local time and then developed into a Strombolian eruption accompanied by loud explosions, roaring, and rumbling. The stronger explosions generated shockwaves which rattled windows and doors in the area. At dawn, the eruption plume could be seen blowing W over the Malguna villages, about 8 km NW, at an altitude of 3,000 m (figure 68). Rabaul Town, 7 km NW of Tavurvur, was initially affected by ash, as was Volavolo (20 km W), but a shift in wind direction sent the plume in a more WNW direction by mid-morning. Villages to the E and S were not affected by ash, but ashfall was reported in Keravat, about 25 km SW. High levels of seismic tremor were recorded during the eruption.

Figure 68. Eruption of Mt. Tavurvur, the active stratovolcano of Rabaul caldera, on 29 August 2014. The ash plume rose to 18 km altitude and dispersed ash to the W and NW of the volcano. Courtesy of OLIVER BLUETT/AFP/Getty Images, printed in The Washington Post.

DMPGM reported that the Strombolian eruption had begun to subside around 0645, and by 0700 only a diffuse white plume was being emitted and seismicity had decreased. Another report at 1600 noted that strong explosions continued throughout the day at irregular intervals, producing ash plumes that rose rapidly to 1,000 m above the summit before drifting NW. The explosions also ejected lava fragments of various sizes in all directions 500 to 1,000 m from the summit crater (figure 69). Shock waves accompanied the loud explosions and rattled buildings within several kilometers of the volcano. Intermittent explosions at increasing intervals continued into the following night generating incandescent lava fragments around the summit. Seismicity was dominated by discrete events that were associated with the explosions. The strong explosions ceased at 0641 on 30 August, and no incandescence was observed after that. By the morning of 31 August, seismicity had decreased from 80 events/hour to 15/hour. According to DMPGM, the eruption deposited a significant amount of ash and scoria on the hillsides of Rabaul Town and Malaguna Villages to the NW.

Figure 69. Incandescent lava exploding from Tavurvur (Rabaul Caldera) on 29 August 2014. Courtesy of Emma Edwards, reported at Traveller.com.

The initial ash plume from the eruption was first observed in satellite imagery by the Darwin VAAC around 0900 local time on 29 August, and rose to over 18 km altitude. The upper part of the plume was originally drifting SW, then changed to NW, and the lower part at 4.3 km altitude was moving NW. By late morning, the plume was moving in three directions at different altitudes; NW at 4.3 km, S at 16.7 km, and W at 18.3 km. The high-level ash from the original eruption had dissipated by the evening on 30 August, but low-level plumes to 2.1 km were still reported.

A substantial SO₂ plume was recorded by the OMI Instrument on the Aura Satellite on 29 August, and was still measurable a day later (figure 70) drifting S. The MODVOLC thermal anomaly system recorded anomalous pixels at Rabaul captured by MODIS satellite data between 29 August and 1 September 2014.

Figure 70. SO2 plumes captured by the OMI instrument on the AURA satellite from Rabaul on 29 and 30 August 2014. Rabaul is the triangle at the top right corner of the crescent shaped island of New Britain at the center of the image. Courtesy of NASA/GSFC.

From 1 to 17 September emissions consisted of variable amounts of diffuse to dense white vapor and small traces of diffuse blue vapor. Southeast winds were recirculating significant amounts of fine ash back into the atmosphere. A plume was reported by the Darwin VAAC on 12 September at 3 km altitude, drifting NW. Seismicity had decreased to very low levels with only 10-30 events recorded per day during the first half of September. A single small explosion occurred at 1242 on 18 September according to DMPGM that produced a small, light-gray ash plume that rose a few hundred meters above the summit crater before dissipating to the NW.

A site inspection of Tavurvur crater was conducted by DMPGM on 23 September 2014, and they observed significant changes in the crater since the 29 August eruption. The crater floor was filled with blocky lavas, and thus much shallower than when last observed prior to the eruption. Three or four areas of active emissions were present within the crater, and the rim was covered with large blocks of lava. By the end of September, seismicity had dropped to less than 10 low-frequency earthquakes per week. In mid-October DMPGM observed that the ground deformation data from the Matupit GPS station indicated that there had been an inflation of about 4 cm since the benchmark reached on 29 August during the eruption. Ground deformation was stable during November. During a field inspection of the summit crater on 9 December 2014, scientists measured a temperature of 310°C at a hot spot on the upper flank. Numerous patches of diffuse white vapor emissions were present at different places on the inner walls of the crater, and the crater floor seemed to have subsided slightly since the prior visit.

Activity during 2015 and 2016. A report by DMPGM from March 2015 noted that Tavurvur remained quiet with the summit crater releasing various amounts of diffuse white vapor, which was slightly denser during periods of rain. There was no observed incandescence or noise, and seismicity was low, with only a small number of both high-frequency and volcano-tectonic earthquakes recorded on 10 and 13 February. Ground deformation data indicated a general inflationary trend since September 2014 of about 5 cm. Monthly reports issued by DMPGM in March and April indicated little activity at Tavurvur, and stability of the ground deformation data. On 17 May 2015 a strong, earthquake of M 5.1 originating NE of Rabaul Caldera 1-2 km offshore from Korere and Nodup (about 9 km NW of Tavurvur) generated a swarm of aftershocks in the same area. They occurred at a depth of about 9 km and caused several small landslides in various places on the N flank of Kombiu, another stratovolcano at Rabaul about 2.5 km NE of Tavurvur.

Tavurvur remained quiet from September through November with occasional diffuse white vapor plumes rising from the summit caldera, and no volcanic earthquakes reported. While a long-term inflationary trend continued through November, shorter term fluctuations up and down of a few centimeters in the ground deformation data were also observed. The trend of vertical uplift between January 2015 and December 2016 showed an increase of approximately 6 cm during the period (figure 71).

Figure 71. Vertical uplift at the Matupit GPS station for Rabaul between 1 January 2015 and 1 December 2016. The trend shows a gradual inflation of about 6-7 cm. Courtesy of DMPGM (Volcano Information Bulletin No. 12-122016, 4 December 2016).

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

Information Contacts: Department of Mineral Policy and Geohazards Management (DMPGM), Volcano Observatory, Geohazards Management Division, 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/); 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/, http://modis.higp.hawaii.edu/cgi-bin/modisnew.cgi); NASA Goddard Space Flight Center (NASA/GSFC), Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, Goddard, Maryland, USA (URL: https://so2.gsfc.nasa.gov/); World Organization of Volcano Observatories (WOVOdat), hosted by Earth Observatory of Singapore, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798 www.wovodat.org; The Washington Post, http://www.washingtonpost.com/news/morning-mix/wp/2014/08/29/photos-in-papua-new-guinea-mount-tavurvur-explodes-in-spectacular-style/); Traveller.com, http://www.traveller.com.au/qantas-reroutes-flights-as-pngs-rabaul-volcano-erupts-109utz .

An eruption at Sheveluch has been ongoing since 1999, and the activity there was previously described through February 2015 (BGVN 42:01). During March-August 2015, the same type of activity prevailed, with lava dome extrusion, incandescence, hot block avalanches, fumarolic activity, and occasional strong explosions that generated ash plumes. Most of the following data comes from Kamchatka Volcanic Eruption Response Team (KVERT) reports. During this period the Aviation Color Code remained at Orange (the second highest level on a four-color scale).

KVERT reported that during 27 February-15 May 2015, lava-dome extrusion onto the N flank continued to be accompanied by incandescence, hot block avalanches, and fumarolic activity. This activity diminished somewhat during 22 May-14 July, when lava-dome extrusion was accompanied only by fumarolic activity. However, heightened activity resumed during 15 July-31 August, when KVERT reported that lava-dome extrusion was accompanied by fumarolic activity, dome incandescence, and hot avalanches.

Between 28 February and the middle of April 2015, strong explosions generated ash plumes that rose to 7-12 km altitude. Ash drifted as much as 885 km in various directions, and ash fell in Ust-Kamchatsk (85 km SE) at least twice in March. Based on KVERT reports, ash plumes on 15 June and 5-6 July only rose as high as 3.3-5 km in altitude.

A daily thermal anomaly was detected 27 February-15 May, except when cloud cover obscured views. During 16-30 May, thermal anomalies were only detected occasionally in satellite images, but became more frequent thereafter, depending on cloud cover. KVERT reported that during 10 July-31 August, satellite images again detected an almost daily thermal anomaly over the dome.

Thermal anomalies based on MODIS satellite instruments analyzed using the MODVOLC algorithm were infrequent during the reporting period, in contrast to the almost daily hotspots reported by KVERT. One hotspot was detected in March, April, and June, none in May, four in July, and eight in August.

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

Information Contacts: Kamchatka Volcanic Eruptions Response Team (KVERT), Far Eastern Branch, Russian Academy of Sciences, 9 Piip Blvd., Petropavlovsk-Kamchatsky, 683006, Russia (URL: http://www.kscnet.ru/ivs/kvert/); 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/).

The latest eruption of Sinabung that began mid-September 2013 (BGVN 38:09) had persisted through April 2016 (BGVN 41:09). This report describes the continuing activity from May-October 2016, and unfortunately included a fatality. Data were primarily drawn from reports issued by the Indonesian Center of Volcanology and Geological Hazard Mitigation (PVMBG, CVGHM), the Darwin Volcanic Ash Advisory Centre (VAAC), and the Badan Nacional Penanggulangan Bencana (National Disaster Management Authority, BNPB).

Inclement weather sometimes prevented visual observations. Throughout the reporting period, the Alert Level remained at 4 (on a scale of 1-4), indicating that the public should remain outside of a 3-km radius; those within 7 km of the volcano on the SSE sector, and within 6 km in the ESE sector, and 4 km in the NNE sector should evacuate.

According to the Darwin VAAC and PVMBG reports, a number of ash plumes were observed each month (table 6). They generally rose to altitudes of 3.3-5.5, although one rose as high as 5.9 km.

Table 6. Ash plumes with altitudes and drift directions reported at Sinabung from May 2016 to October 2016. Weather clouds often prevented observations. Courtesy of PVMBG, Darwin VAAC, and BNPB.

According to BNPB, a lahar passed through Kutambaru village, 20 km NW of Sinabung and near the Lau Barus River, at 1545 on 9 May 2016, killing a boy and injuring four more. One person was missing. A news article (Okezone News) noted that three houses were also damaged.

BNPB reported that a pyroclastic flow descended the flanks at 1648 on 21 May, killing six people and critically injuring three more. A later CBS news account on 22 May indicated that seven people had died, with two in critical condition. The victims were gardening in the village of Gamber, 4 km SE from the summit crater, in the restricted zone. The report noted that activity remained high; four pyroclastic flows descended the flanks on 21 May.

On 3 July, BNPB reported that the eruption continued at a very high level. Lava was incandescent as far as 1 km down the SE and E flanks, and multiple avalanches were detected. An explosion at 1829 generated an ash plume that rose 1.5 km and drifted E and SE, causing ashfall in Medan (55 km NE). There were 2,592 families (9,319 people) displaced to nine shelters, and an additional 1,683 families in temporary shelters waiting for relocation.

According to BNPB, on 24 August, observers at the PVMBG Sinabung observation post noted a marked increase in seismicity and counted 19 pyroclastic flows and 137 avalanches from the early morning until the late afternoon. Foggy conditions obscured visual observations through most of the day, although incandescent lava as far as 500 m SSE and 1 km ESE was noted in the morning, and a pyroclastic flow was seen traveling 3.5 km ESE at 1546. The lava dome had grown to a volume of 2.6 million cubic meters. Activity remained very high on 25 August; pyroclastic flows continuously descended the flanks, traveling as far as 2.5 km E and SE, and 84 avalanches occurred during the first part of the day.

Thermal anomalies. During the reporting period, thermal anomalies, based on MODIS satellite instruments analyzed using the MODVOLC algorithm, occurred during one to five days every month. Only three days had more than one pixel (1, 3 May, 8 October). The Mirova (Middle InfraRed Observation of Volcanic Activity) volcano hotspot detection system, also based on analysis of MODIS data, detected thermal anomalies every month during the reporting period within 5 km of the volcano, with the heaviest concentration in May and fewest in September and October.

Geologic Background. Gunung Sinabung is a Pleistocene-to-Holocene stratovolcano with many lava flows on its flanks. The migration of summit vents along a N-S line gives the summit crater complex an elongated form. The youngest crater of this conical andesitic-to-dacitic edifice is at the southern end of the four overlapping summit craters. The youngest deposit is a SE-flank pyroclastic flow 14C dated by Hendrasto et al. (2012) at 740-880 CE. An unconfirmed eruption was noted in 1881, and solfataric activity was seen at the summit and upper flanks in 1912. No confirmed historical eruptions were recorded prior to explosive eruptions during August-September 2010 that produced ash plumes to 5 km above the summit.

Information Contacts: 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/); Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM), Jalan Diponegoro 57, Bandung 40122, Indonesia (URL: http://www.vsi.esdm.go.id/); Darwin Volcanic Ash Advisory Centre (VAAC), Bureau of Meteorology, Northern Territory Regional Office, PO Box 40050, Casuarina, NT 0811, Australia (URL: http://www.bom.gov.au/info/vaac/); Hawai'i Institute of Geophysics and Planetology (HIGP), MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Okezone News (URL: http://news.okezone.com/); CBS News (URL: http://www.cbsnews.com/).

Mount Veniaminof, located on the Alaska Peninsula, has a large glacier-filled summit caldera that formed around 3,700 years ago. A cone within the crater has been the source of at least 13 eruptions in the last 200 years that included intermittent steam and ash emissions, incandescent lava flows, and Strombolian activity. Prior to an eruptive episode that began in June 2013, lava had last erupted during Strombolian activity in February 2005; subsequent minor ash emissions occurred later in 2005, November 2006, and February 2008. Pilots reported ash plumes in January and June 2009, but the Alaska Volcano Observatory (AVO) concluded that the plumes were steam-only. Veniaminof is closely monitored by AVO and the Anchorage Volcanic Ash Advisory Center (VAAC). The Federal Aviation Administration (FAA) also has a web camera in Perryville, 35 km E of the volcano. This review draws heavily from a USGS report on the June through October 2013 eruption (Dixon et al., 2015).

Beginning on 7 June 2013, a several-day period of increasing levels of seismic tremor indicated the start of a largely effusive eruption from the intracaldera cinder cone (figure 17). The first ash plume was observed on 13 June. Over the next four months, numerous emissions rose to altitudes generally below 4.6 km and coated the flanks of the cone with ash, Strombolian explosions were visually observed several times, and lava flowed down the N and S flanks of the active cone and advanced onto the surrounding ice-filled caldera creating ice cauldrons. The eruption constructed a new spatter cone within the summit crater of the main active cone. Activity had ceased by 17 October 2013. A brief period of elevated seismicity occurred during October and November 2015, but no eruptive activity was recorded.

Figure 17. Topographic map of Mount Veniaminof showing the margin of the caldera (red dashed line) and the active cone within the caldera (black circle). Seismic stations VNWF and VNHG were the most fully operable of the network in June 2013. The caldera is 10 km in diameter. Courtesy of AVO/UAFGI, 19 June 2013 (AVO database image URL: http://www.avo.alaska.edu/images/image.php?id=50831).

Gradually increasing low-frequency tremor was recorded on two seismograph stations at Veniaminof, along with elevated surface temperatures of the intracaldera cinder cone recorded via satellite images on 7 June 2013. This led AVO to increase the 4-level Aviation Color Code and the Volcano Alert Level from Green/Normal to Yellow/Advisory the next day. By 13 June, seismicity levels and elevated surface temperatures at the summit of the cinder cone (as measured by satellite images) indicated an eruption was likely underway, causing AVO to raise the Aviation Color Code and the Volcano Alert Level to Orange/Watch. Observation of an ash plume at an altitude of 3.7 km by a pilot that evening along with a lava flow effusing from the intra-caldera cinder cone confirmed the eruption.

Residents in Perryville (32 km SSE) and Port Moller (77 km WSW) also observed ash emissions at about 2330 local time that evening. The first VAAC report around the same time listed the ash plume at 4.3 km altitude, drifting NNE. Ash deposits on the snow-covered caldera floor, and lava on the cone, were visible in satellite images on 14 June. The first MODVOLC thermal anomaly pixels from MODIS satellite data also appeared on 14 June. On 18 June the web camera in Perryville captured short-lived ash plumes rising to less than 4.6 km, and residents in Sandy River (33 km W) reported visible plumes to similar altitudes the next day. The 100-m-wide lava flow extended 500 m down the SW flank of the cone onto the adjacent snow and ice field by 18 June. Interaction of the lava with the caldera snow-and-ice field generated water-rich ash plumes. Clear satellite views the following day showed active flow lobes advancing over the ice at the base of the cone.

In subsequent weeks, three flows descended the S flank, and minor amounts of ash accumulated on the caldera floor. Strombolian activity was captured by infrared satellite imagery, from the FAA web camera in Perryville, and from several local lodges and remote camps (figure 18).

Figure 18. Telephoto view of erupting Mount Veniaminof, 9 July 2013. Photograph was taken from Sandy River about 32 km W of the volcano. Bright orange incandescence indicates lava fountaining from the vent hidden from view within the crater atop the cinder cone. At times, the eruption was characterized by closely spaced bursts that produced 'puffs' of ash. Courtesy of AVO/USGS. Photograph by William Jasper, used with permission (AVO database image URL: http://www.avo.alaska.edu/images/image.php?id=56303 ).

On 16 July 2013 an AVO geologist visited the caldera by helicopter, making observations and taking the first close-up photographs documenting the lava flows and ice cauldron formation (figure 19). Images of the vent area showed a new cone of accumulated spatter nested within the summit crater of the main cone.

Figure 19. Southwestern flank of the intracaldera cone at Mount Veniaminof on 16 July 2013 showing lava flows emplaced during the eruptive activity occurring in June and July 2013, and a new cone formed from eruptive spatter. View is toward the east. The flows appear similar to those produced during the 1993 eruption. Courtesy of AVO/USGS. Photograph by Chris Waythomas, 16 July 2013 (AVO database image URL: http://www.avo.alaska.edu/images/image.php?id=51301 ).

Strong MODVOLC thermal alert pixels, up to 12 per day, continued almost daily through the end of July. A pilot report from 0800 AKDT on 25 July described an ash plume to 100 m above the erupting cone dispersing 25 km to the S, and a "river of lava" flowing from the intracaldera cone. Numerous reports from the Anchorage VAAC between 27 and 31 July confirmed ash plumes rising as high as 4.6 km altitude and drifting up to 20 km NW.

After a brief period of quiet in early August 2013, activity resumed with lava flows and ash plumes on 11 August. On 12 August, satellite imagery confirmed incandescence from the cone and an ash plume was also observed from Perryville. A second overflight under clear skies by AVO geologists on 18 August revealed ash covering the immediate area of the glacier and the lava flows, and an active incandescent flow down the S flank into the ice cauldrons where the hottest parts of the flows were still in contact with ice and water. The S-flank lava flows had coalesced and largely melted into the surrounding ice (figures 20 and 21).

Figure 20. A small puff of ash emerges from the active cone inside the Veniaminof caldera on 18 August 2013. A fan of lava flows active earlier in the summer descends the southern flank of the cone onto glacial ice, producing white steam clouds and depressions where melting has occurred. The surrounding glacier is darkened by recent ashfall. Courtesy of USGS/AVO. Photograph by Game McGimsey (AVO database image URL: http://www.avo.alaska.edu/images/image.php?id=55761 ).

Figure 21. Aerial view of the eruption at Veniaminof's intracaldera cone on 18 August 2013, from an overflight co-sponsored by the National Geographic Society. The cone rises about 300 m above the surrounding icefield. An incandescent orange stream of lava is emerging from the active cone. Steam billows from the pit at the base of the cone where the lava encounters and melts ice and snow creating an ice cauldron. The small, ash-rich plume rising just above the vent produced a diffuse ash cloud that drifted downwind. Courtesy of AVO/USGS. Photograph by Game McGimsey, AVO/USGS (AVO database image at URL: http://www.avo.alaska.edu/images/image.php?id=56211 ).

Strombolian explosions of incandescent lava and minor ash emissions were observed at the central active vent on 18 August during the flyover. Two new lava flows were also observed issuing from the NE flank of the new cone. Forward Looking Infrared Radiometer (FLIR) images delineated the lava flows and hot spatter on the cone (figure 22). As measured by the FLIR, maximum temperatures reached 700° to 800°C.

Figure 22. Forward Looking Infrared Radiometer (FLIR) image of the erupting intracaldera cone of Mount Veniaminof on 18 August 2013. In this oversaturated image (due to low thermal imagery setting), the active lava flows (hottest) are red and the lava fountaining at the summit is easily visible. These lava flows are on the NE flank of the cone. Maximum temperatures recorded were between 700° and 800° C. Courtesy of USGS/AVO. FLIR image by Game McGimsey (AVO database image URL: http://www.avo.alaska.edu/images/image.php?id=57831).

The Anchorage VAAC reported ash plumes on 20 and 21 August 2013 rising to 3.7 km altitude moving SE within a few kilometers of the summit. Residents of Perryville reported rumbling noises, explosions, and trace ashfall on 20 August. Similar, low-level ash plumes and persistent thermal anomalies were detected during the remainder of August. A noted increase in activity on 30 August included elevated levels of continuous tremor, lava fountaining, and ash emissions as high as 6.1 km altitude; this was some of the strongest unrest detected since the eruption began in June. Trace amounts of ashfall were again reported in Perryville. Lava effusion, fountaining, and nearly continuous small ash plumes continued through the first week in September. Satellite and aerial images on 6 and 7 September indicated further development of the flows on the NE flank and expansion of the ice cauldron as well as a new lobe of lava advancing southward from the NE flank ice cauldron (figure 23).

Figure 23. Aerial view of Mount Veniaminof erupting on 7 September 2013. Note the white water vapor clouds indicating that hot lava is interacting with snow and ice. A gray-brown ash column rises from the active vent. The advancing flows in foreground are on the southeastern flank of the cone and were the last flows emplaced in the 2013 eruption. The summit ice field is darkened with recent ash fall. Courtesy AVO/USGS. Photograph by Joyce Alto, used with permission (AVO database image URL: http://www.avo.alaska.edu/images/image.php?id=56424).

MODVOLC thermal alert pixels ceased on 8 September 2013; the last September satellite imagery detection of volcanic ash emissions as reported by the Anchorage VAAC was on 9 September. By 19 September no evidence of active lava flows was observed in satellite images; seismicity had begun to decrease during the week, and the eruption appeared to be waning. This short-lived period of quiescence ended on 6 October when MODVOLC pixels reappeared through 11 October, suggesting active lava effusion. An ash plume reported by the Anchorage VAAC on 11 October rose to 6.1 km altitude (the highest of this eruption) and trace amounts of ash were reported in the communities of Chignik Lake and Chignik Lagoon, 40-55 km E of the active vent; it was the last VAAC report of an ash plume in 2013. On 17 October AVO noted that seismicity had decreased during the previous week and satellite observations during periods of clear weather showed no evidence of eruptive activity. The Aviation Color Code/Volcano Alert Level was lowered to Yellow/Advisory. Seismicity remained slightly above background levels through the following June, although no further activity was reported. The Alert Level was lowered to Green/Normal on 9 July 2014.

According to the USGS and AVO, the 2013 eruption produced about 5 X 10⁵ m³ of erupted lava, comparable in size to the 1983 eruption. A chart of eruptive events and the real-time seismic amplitude (RSAM) time series data between 13 June and 17 October 2013 prepared by USGS/AVO illustrates the significant eruptive events of this period (figure 24). Additional details of the eruption can be found in Dixon et al., 2015.

Figure 24. Real-time seismic amplitude (RSAM) time series from seismic station VNWF (located on the lower SW flank of Veniaminof), and significant eruptive events between 9 June and 1 November 2013. The AVO Aviation Color Code during the eruption also is shown. Courtesy of USGS/AVO (figure 25, Dixon et al., 2015).

No further reports of activity from Veniaminof were issued until increased seismic activity began on 30 September 2015. This led AVO to increase the Color Code/Alert Level to Yellow/Advisory the next day. Occasional, clear web camera images from Perryville in the subsequent weeks showed small steam plumes rising from the intracaldera cone but no ash emissions or lava effusions. Slightly elevated levels of seismicity continued until the beginning of December. AVO downgraded the status from Yellow/Advisory to Green/Normal on 11 December 2015.

References: Dixon, J.P., Cameron, Cheryl, McGimsey, R.G., Neal, C.A., and Waythomas, Chris, 2015, 2013 Volcanic activity in Alaska - Summary of events and response of the Alaska Volcano Observatory: U.S. Geological Survey Scientific Investigations Report 2015-5110, 92 p., http://dx.doi.org/10.3133/sir20155110

Waythomas, C.F., 2013, Volcano-ice interactions during recent eruptions of Aleutian Arc volcanoes and implications for melt water generation: Eos Transactions, American Geophysical Union, Fall Meeting, abstract V34C-03.

Geologic Background. Veniaminof, on the Alaska Peninsula, is truncated by a steep-walled, 8 x 11 km, glacier-filled caldera that formed around 3,700 years ago. The caldera rim is up to 520 m high on the north, is deeply notched on the west by Cone Glacier, and is covered by an ice sheet on the south. Post-caldera vents are located along a NW-SE zone bisecting the caldera that extends 55 km from near the Bering Sea coast, across the caldera, and down the Pacific flank. Historical eruptions probably all originated from the westernmost and most prominent of two intra-caldera cones, which rises about 300 m above the surrounding icefield. The other cone is larger, and has a summit crater or caldera that may reach 2.5 km in diameter, but is more subdued and barely rises above the glacier surface.

Information Contacts: 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 (URL: http://www.dggs.alaska.gov/); Anchorage Volcanic Ash Advisory Center (VAAC), Alaska Aviation Weather Unit, NWS NOAA US Dept. of Commerce, 6930 Sand Lake Road, Anchorage, AK 99502-1845(URL: http://www.ssd.noaa.gov/); 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/).

Remote Zavodovski Island, located in the Southern Atlantic Ocean, is the northernmost of the South Sandwich Islands, 570 km SE of South Georgia Island. The basaltic stratovolcano on the island, known as Mount Curry, has a large lava platform extending east from two parasitic cones on the side of the main edifice. Steam emissions from the summit have been observed by researchers, fishing vessels, and tourists who visit the island to see the population of over one million chinstrap penguins. The only confirmed historical eruption was that observed in 1819 by the Russian explorer Bellingshausen. In early July 2016, a photograph of ash and steam emitting from the volcano was released by the British Antarctic Survey (BAS).

While steam plumes have been observed emitting from Mt. Curry on a number of occasions, observations of volcanic ash had not been documented in modern times until June 2016. The MODIS instrument (Moderate Resolution Imaging Spectroradiometer) on NASA's Aqua satellite captured a unique image of the interaction of low-level emissions from Zavodovski and the atmosphere on 27 April 2012 (figure 1). Aerosol particles from the volcano are key to the formation of clouds, but whether they are derived from steam plumes, magmatic gases, or volcanic ash is unclear from this image.

Figure 1. In this image that includes Zavodovski Island taken on 27 April 2012, NASA scientists interpret the sulfate aerosols from the volcano as sufficient to seed clouds in the air masses passing over the island. Note how the plume stretching north is brighter than the surrounding clouds, a result of the small aerosol particle size and the numerous small water droplets that form around them. The smaller droplets provide more surfaces to reflect light. Courtesy of NASA Earth Observatory.

The BBC conducted a filming expedition to Zavodovski in January 2015 to document the landscape of the island and the behavior of its resident chinstrap penguin colony; while there they observed regular puffs of steam rising from the summit, shown in their expedition report to the SGSSI Government (figure 2). Additional NASA MODIS satellite images of white plumes issuing from Mount Curry were captured by the South Sandwich Islands Volcano Monitoring Blog in January and December 2015, but are inconclusive as to the presence of volcanic ash.

Figure 2. Puffs of steam emerge at regular intervals from Mount Curry on Zavodovski Island in January 2015 when photographed by a BBC filming crew that spent 14 days on the island. View taken by UAV from the SW side of the island. Courtesy of SGSSI Government (BBC "One Planet" – Post-expedition report - Zavodovski Island 2015).

The plumes in 2016 first appeared in images dated 30 March and 7 April, but the plume content beyond steam is difficult to assess. Images from 1 and 13 June 2016 also show white gas plumes. The British Antarctic Survey (BAS) reported on 6 July 2016 that Mt. Curry began erupting in March 2016. A fishing observer captured an image of an ash-and-steam eruption in June 2016 (figure 3). The BAS noted that fishing vessels in the area captured photos of the eruption with "smoke" and ash drifting to the E, covering the lower slopes of the volcano, and bombs being ejected from the crater.

Figure 3. Mt. Curry on Zavodovski island emitting ash and steam plumes during June 2016. Courtesy of British Antarctic Survey. Photo by fishing observer David Virgo.

Satellite images confirmed that up to half of the island was coated with ash. On 20 July 2016 the Government of South Georgia and South Sandwich Islands issued a Navigation Warning noting that eruptions on Zavodovski and nearby Bristol Island were emitting significant ash and dust particles and advised Mariners to remain at least 3 nautical miles from the area.

Frequent satellite images of white plumes issuing from Zavodovski were captured in satellite images during the rest of 2016. On 29 August a white plume was drifting NE. Between 17 September and 10 October satellite images captured several white plumes drifting in various directions. On 1 November a grayish white plume was observed drifting E; on 19 and 20 November and 6 December white plumes were observed. A grayish-white plume was captured on 9 December drifting SSW, and on 17 December a large white plume was drifting SE.

References: BBC, 2015, BBC Natural History Unit filming expedition to Zavodovski Island, a report to the commissioners office, South Georgia Government, posted at www.gov.gs.

Geologic Background. The 5-km-wide Zavodovski Island, the northernmost of the South Sandwich Islands, consists of a single basaltic stratovolcano with two cones on the east side. Mount Curry, the island's summit, lies west of the center of the island, which is more eroded on that side. Two fissures extend NE from the summit towards the E-flank craters, and a lava platform is located along the eastern coast. The volcano was producing abundant emissions when observed in 1819 by the explorer Bellingshausen. A landing party in 1830 also reported strong emissions along with a fresh lava field on the east side from which pumice was being eroded into the ocean.

Information Contacts: British Antarctic Survey, Natural Environment Research Council, High Cross, Madingly Road, Cambridge CB3 0ET, United Kingdom (URL: https://www.bas.ac.uk/ , https://www.bas.ac.uk/media-post/penguin-colonies-at-risk-from-erupting-volcano/); Government of South Georgia and the South Sandwich Islands, Government House, Stanley, Falkland Islands, South Atlantic (URL: http://www.gov.gs/); NASA Earth Observatory, EOS Project Science Office, NASA Goddard Space Flight Center, Goddard, Maryland, USA (URL: http://earthobservatory.nasa.gov/); South Sandwich Islands Volcano Monitoring Blog (URL: http://southsandwichmonitoring.blogspot.com/).