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 current eruption at Dukono has been ongoing since 1933, with frequent explosions and ash plumes between August 2014 and March 2017 (BGVN 42:06). Similar activity has continued during April 2017-March 2018. Monitoring of the volcano is the responsibility of the Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG), also known as the Center for Volcanology and Geological Hazard Mitigation (CVGHM).

Thermal measurements made by MODIS satellite instruments and processed by MIROVA show regular low-to-moderate thermal anomalies from April to October 2017 (figure 8), but none after December 2017 or in early 2018. MODVOLC analyses of thermal satellite data identified anomalies on 11 April, 29 April, 9 July, 1 August, and 21 August 2017.

Figure 8. Thermal anomalies recorded by the MIROVA system for the year ending 9 March 2018. Courtesy of MIROVA.

Explosions were frequently reported by both PVMBG and the Darwin Volcanic Ash Advisory Centre (VAAC), with ash plumes rising only a few hundred meters above the Malupang Warirang crater and drifting in various directions (table 17). Some plumes during this reporting period drifted for more than 100 km, with the longest reaching 230 km W on 27 May 2017.

Table 17. Monthly summary of reported ash plumes from Dukono for March 2017-March 2018. The direction of drift for the ash plume through each month is highly variable; only notable significant plumes are listed. Data courtesy of Darwin VAAC and PVMBG.

According to NASA Goddard Space Flight Center, SO₂ emissions are commonly detected from Dukono, but usually only at low levels, using the Ozone Monitoring Instrument (OMI) aboard NASA's Earth Observing System (EOS) Aura satellite and the Ozone Mapping and Profiler Suite (OMPS) aboard the NASA/NOAA Suomi National Polar-orbiting Partnership (SNPP) satellite. The strongest emissions captured in satellite data during this report period was on 6 March 2018 (figure 9).

Figure 9. Sulfur dioxide emissions from Dukono can be identified using the Ozone Monitoring Instrument (OMI) on NASA's Aura satellite, as seen in this example from 6 March 2018. The highest amount of SO2 (red) is centered over the volcano. Courtesy of NASA Goddard Space Flight Center.

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

Information Contacts: Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM), Jalan Diponegoro 57, Bandung 40122, Indonesia (URL: http://www.vsi.esdm.go.id/); 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/); NASA Goddard Space Flight Center (NASA/GSFC), Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, 8800 Greenbelt Road, Goddard, Maryland, USA (URL: https://so2.gsfc.nasa.gov/).

Ethiopia's Erta Ale basaltic shield volcano has had at least one active lava lake since the mid-1960s, and possibly much earlier. Two active craters (North Pit and South Pit) within the larger oval-shaped Summit Caldera have exhibited periodic lava fountaining and lava lake overflows over the years. A new eruptive event located about 3 km SE of the Summit Crater appeared on 21 January 2017. Activity at the eruption site increased during subsequent months, sending lava flows several kilometers NE and SW from a newly formed lava lake. This report discusses activity from February 2017 through March 2018 as the flows traveled as far as 16 km from the main vent. Information comes from satellite thermal and visual imagery, and photographs and reports from ground-based expeditions that periodically visit the site.

Summary of activity, February 2017-March 2018. The 21 January 2017 activity at Erta Ale was the first time a vent outside of the Summit Caldera has been observed (figure 50). The initial vent or vents created multiple lava flows that traveled generally NE and SW from their sources, creating at least one lava lake that persisted for about a year (figure 51). The flows began inside an older caldera at a location about 3 km SE of the South Pit Crater, but eventually overflowed the caldera rim in multiple directions. As the flow fields enlarged, thermal imagery captured hot-spots along the flows that were likely produced by breakouts, skylights into lava tunnels, and hornitos, as well as multiple surges of flows across the growing fields (figure 52). The imagery also showed the locations of the advancing flow fronts which had reached over 5 km SW of the source by August 2017 and over 16 km NE of the source by March 2018, eventually reaching the alluvial plain NE of Erta Ale. Thermal anomaly data indicated that the maximum thermal energy output happened in April 2017, gradually decreasing through March 2018. The far NE front of the northeast flow field was still active at end of March 2018.

Figure 50. The summit of Erta Ale has two oblong NW-trending calderas. The northern Summit Caldera contains the North Pit Crater and the South Pit Crater. The North Pit Crater has had a solidified lava lake with a large hornito emitting magmatic gases and incandescence at night, and the South Pit Crater has had an active lava lake for many years that last overflowed its rim during mid-January 2017. The new eruption began at vents located about 3 km SE of the South Pit Crater near the northern rim of a second caldera referred to here as the Southeast Caldera, on 21 January 2017. The new eruption had not yet begun in this 16 January 2017 image. See figure 46 (BGVN 42:07) for additional images the following week that show the first flows from the new vents. Images copyright by Planet Labs Inc., 3 m per pixel resolution, and used with permission under a Creative Commons license (CC BY-SA 4.0), annotated by GVP.

Figure 51. A new lava lake formed during late January 2017 at the new eruption site about 3 km SE of the South Pit Crater at Erta Ale, inside the Southeast Caldera. This view is likely from the rim of the Southeast Caldera, looking SE or E, taken in February 2017. Visitors were not able to get closer to the vent due to the active flows for several months. Copyrighted photo by Stefan Tommasini, used with permission.

Figure 52. An active new pahoehoe lava field flowed over older lava flows inside the Southeast Caldera at Erta Ale during February 2017. This photo was likely taken from the northern or western rim of the Southeast Caldera. Copyrighted photo by Stefan Tommasini, used with permission.

When the new eruptive episode began, the lava lake at the South Pit Crater drained rapidly to around 80-100 m below the rim, according to visitors to the site a few weeks later. The crater was emitting a strong thermal signal by early March 2017 as the lake level rose again. Visitors in April witnessed a fluctuating lake level rising and falling by up to 20 m every 30 minutes over several days. The thermal signal remained strong at the South Pit Crater through March 2018. Due to significant political instability in the area, ground visits are intermittent, but high-quality photographs were taken in February 2017, December 2017, and January 2018 that show the new lava lake and parts of the new flow fields.

Activity during late January-March 2017. The new eruptive event at Erta Ale began in late January 2017 at the northern end of the Southeast Caldera located; the first lava flows observed were locatedabout 3 km SE from the main Summit Caldera (figure 45 (BGVN 42:07) and figure 50). Two separate vent areas appeared active initially. The northern vent sent lava flows to the NE for several kilometers and to the SW a much shorter distance. The southern vent sent a stream of lava to the S. By the end of January 2017 the North and South Pit Craters at the Summit Caldera were still thermally active, but the signals were much stronger from the new vent areas in the Southeast Caldera (figure 53). A faint thermal signal from about 5 km E of the northern vent suggested the extent of the new flows in that direction.

Figure 53. A Sentinel-2 image from 29 January 2017 shows the initial activity at the new Southeast Caldera vents of Erta Ale (labelled Event 1 and Event 2). Weak thermal signals are apparent from the North and South Pit Craters (Pit Crater Nord, Pit Crater Sud) within the Summit Caldera, and much stronger thermal signals are evident from two areas inside the Southeast Caldera. A faint signal from about 5 km E of the new vents indicates possible flow activity breaking out of lava tubes in that region (Skylight). Courtesy of ESA/Copernicus with annotations provided by Culture Volcan (Le point sur l'activité des volcans Etna, Erta Ale, Fuego, Piton de la Fournaise et Bogoslof, 3 février 2017).

A small group of travelers led by Ethiopian geologist Enku Mulugeta visited Erta Ale during the first half of February 2017. They reported that within the main Summit Caldera, the hornito in the North Pit Crater had collapsed and the lava lake in the South Pit Crater was about 80-100 m below the caldera floor level. The eruption in the Southeast Caldera was still very active, and they photographed the sizable new lava field which contained numerous pahoehoe flows, actively spattering hornitos, and a large lava lake (figures 51, 52, and 54). During the following months activity remained high both at the new eruption site and at the Summit Caldera where the lava lake in the South Pit Crater gradually rose back up to about 50 m below the caldera floor. Culture Volcan annotated a series of Sentinel-2 satellite thermal images which show the progression of the lava flows through the following year.

Figure 54. A large new lava field quickly formed inside the Southeast Caldera at Erta Ale after the beginning of the new eruptive event in late January 2017. When photographed here in February 2017, pahoehoe flows had spread outward from a central vent area (glow at top center) for over a kilometer in multiple directions. View is likely to the E from the W rim of the Southeast Caldera. Copyrighted photo by Stefan Tommasini, used with permission.

By 10 March 2017 only the southern vent area was active inside the Southeast Caldera. It continued to feed the lava field; lava was actively flowing S from the vent towards the W rim of the Southeast Crater, and NE, breaking out from lava tubes which blocked the thermal signal until about 2.6 km NE of the vent (figure 55). Thermal signals from both the North and South Pit Craters were distinct and stronger than in late January.

Figure 55. The thermal signals at both the North and South Pit Craters at Erta Ale were stronger in this 10 March 2017 image than in late January. Only one main source of lava is apparent at the Southeast Caldera. Lava flows directly from the primary vent SW towards the W rim of the caldera, and also surfaces from tunnels about two kilometers NE in an actively moving lava front. Courtesy of ESA/Copernicus with annotations provided by Culture Volcan (Un point sur l'activité des volcans Etna et Erta Ale, 13 mars 2017).

A site visit to the South Pit Crater on 20 March 2017 demonstrated that the lake level had risen significantly since its drop in early February, and was once again actively convecting (figure 56). By the end of March 2017, satellite thermal imagery made clear the increasing thermal signal at the South Pit Crater, and in the Southeast Caldera, the major increase in effusion to the NE from the main vent. The width of the flow field had increased to about 1,400 m, and the farthest front was about 3,400 m NE from the vent (figure 57). The lava at the source measured about 180 x 75 m in size, suggesting a lava lake; a smaller overflow to the SW appeared to have reached the W rim of the Southeast Caldera by 30 March 2017 near the area where a new flow had first appeared in a 23 January 2017 satellite image (see figure 46, BGVN 42:07).

Figure 56. The South Pit Crater of Erta Ale on 20 March 2017 had risen significantly from its drop in February and was actively convecting. Photo by Jean-Michel Escarpit, courtesy of Cultur Volcan (Un point sur l'activité des volcans Fuego, Manam et Erta Ale, 22 mars 2017).

Figure 57. The thermal signal at the South Pit Crater continued to increase in this 30 March 2017 satellite image of Erta Ale. The main vent in the Southeast Caldera had dimensions of about 180 x 75 m, suggesting a lake had formed. A large increase in the thermally active area to the NE indicated that the flow field was expanding significantly in that direction, with a few small thermal anomalies between the lake and lava field suggesting a number of small flows or lava tube breakouts. Flow activity also continued to the SW reaching the W rim of the Southeast Crater where lava had flowed past the crater rim in late January (see figure 46, BGNV 42:07). Courtesy of ESA/Copernicus with annotations provided by Culture Volcan (Un point sur l'activité des volcans Klyuchevskoy et Erta Ale, 31 mars 2017).

Activity during April-May 2017. In the next Sentinel-2 satellite image from 9 April (figure 58), the distance to the farthest front of the lava flow had increased to about 4,600 m from the lava lake, and a new flow had appeared a few hundred meters east of the lake that extended about 1,100 m ENE from its source. Lava also flowed SW from the source to the SW rim of the Southeast Crater, appearing to pond against and flow slightly beyond the rim.

Figure 58. The lava flows continued to extend NE from their source inside the Southeast Crater at Erta Ale in this Sentinel-2 satellite image from 9 April 2017. The farthest edge of the northeast flow front was about 4,600 m from the lake. A new arm of lava flowed more than a kilometer ENE from its source close to the lake. Another thermal signature SW of the lake indicated an accumulation of lava near or slightly spilling over the SW rim of the Southeast Crater. Courtesy of ESA/Copernicus with annotations provided by Culture Volcan (Le point sur l'activité des volcans Erta Ale et Bogoslof, 16 avril 2017).

A group visited Erta Ale during 11-15 April 2017 in collaboration with Addis Ababa University geologist Enku Mulugeta. They noted that fluctuating lava lake levels at the South Pit Crater were cycling every 30 minutes or so between 40 and 50 m below the caldera floor (figures 59 and 60). Lava tubes from the walls of the crater would feed the lake with fresh lava after it drained. Two coalesced hornitos, about 7 m high, were present in the NE part of the crater, emitting SO₂ gas and occasional lava. At the North Crater Pit, noisy degassing of SO₂ from several hornitos at the center of the solidified crust was apparent. Observers at the Southeast Caldera could see the lava lake with the top about 10 m below its crater rim, and minor fountaining during the night, but they were not able to get closer than about 700 m due to the active flows.

Figure 59. The lava lake level at the South Pit Crater at Erta Ale during April 2017 was fluctuating by 10-20 m every 30 minutes or so. The high-stand of the lava is shown here. Courtesy of Toucan Photo.

Figure 60. The lava lake level at the South Pit Crater at Erta Ale during April 2017 was fluctuating by 10-20 m every 30 minutes or so. The low stand of the lava is shown here as the lava drains away. Courtesy of Toucan Photo.

By the end of April 2017 satellite thermal imagery indicated that the northeast flow field at the Southeast Caldera extended more than 7 km NE from the lake and was curving towards the E (figure 61). The lava lake was still thermally active, as was the South Pit Crater to the NW.

Figure 61. Sentinel-2 satellite imagery of Erta Ale on 29 April 2017 shows the growth of the northeast lava field from earlier in the month to more than 7 kilometers from its source. The South Pit Crater was still active, as was the source of the northeast lava field. Courtesy of ESA/Copernicus with annotations provided by Culture Volcan (L'activité effusive reste soutenue à l'Erta Ale, 3 mai 2017).

Eleven days later, activity was quite different in the Southeast Caldera. Satellite imagery from 9 May 2017 (figure 62) showed a new, relatively narrow but bright lava flow moving NE for 2-3 km originating in a location slightly NE of the original lava lake; activity farther NE had diminished from the previous image. A subsequent image on 18 May looked similar, but by 19 May the narrow flow had been replaced by a much broader area of thermal anomaly in the region immediately E of the source. By 29 May 2017, the source of the lava appeared to have shifted several hundred meters SE of the earlier location, and a strong thermal signal once again extended NE across the northeast flow field from the new source for about two kilometers (figure 63).

Figure 62. A Sentinel-2 satellite image of Erta Ale on 9 May 2017 showed a shift to the NE in the location of the source of the active flows. A new narrow flow had traveled 2-3 km NE from a source located NE of the lava lake. The more distant northeast flow field had a much smaller thermal signature than on 29 April. Courtesy of ESA/Copernicus with annotations provided by Culture Volcan (Breakout sur le volcan Erta Ale, 11 mai 2017).

Figure 63. A significant shift to the SE in the location of the lava source from a few weeks earlier is apparent in this Sentinel-2 satellite image of Erta Ale captured on 29 May 2017. A strong thermal anomaly trended NE across the northeast flow field for about two kilometers. Courtesy of ESA/Copernicus with annotations provided by Culture Volcan (Erta Ale: une éruption vraiment exceptionnelle, 11 juin 2017).

Activity during June-August 2017. The rapidly changing flow field was significantly different again less than two weeks later in satellite imagery captured on 8 June 2017. Lava was flowing N, SE, and S across the northeast lava field, extending beyond the rim of the Southeast Caldera to the N and E. Another very strong thermal signal emerged from the SW corner of the Southeast Caldera where lava was flowing W and S outside the caldera rim forming a new southwest lava field (figure 64).

Figure 64. A Sentinel-2 satellite image of Erta Ale on 8 June 2017 shows significant changes in the location of the active flow fields from less than two weeks earlier. The South Pit Crater in the Summit Caldera still had a strong thermal signal suggesting an active lake in the crater. Flows in the Southeast Caldera appeared to be moving N, E, and S across the northeast lava field, and a new area with flows moving S and W from the SW rim of the Southeast Caldera formed the new Southwest lava field. Courtesy of ESA/Copernicus with annotations provided by Culture Volcan (Erta Ale: une éruption vraiment exceptionnelle, 11 juin 2017).

During June 2017, the most aggressive flow activity contributed to significant growth of the southwest lava field. By 28 June, infrared imaging detected flow fronts 4,500 m SW of the vent; they had extended to about 5,100 m, nearing the base of the SW flank of Erta Ale, by 5 July (figure 65). Flow activity also persisted in the northeast flow field with activity concentrated about 1.5 km NE of the vent on 28 June. Movement increased at the northeast flow field beginning in late June and it had extended to about 3.5 km NE of the lava lake by 5 July 2017.

Figure 65. Lava flow activity at the Southeast Caldera of Erta Ale during June 2017 was concentrated in the growing southwest flow field which had extended about 5,100 m from its lava lake source by 5 July 2017 in this Landsat 8 satellite image. The northeast flow field began extending farther NE during the first week of July, reaching 3,500 m from the lake by 5 July. Courtesy of ESA/Copernicus and NASA/USGS with annotations provided by Culture Volcan (Un point sur l'activité des volcans Copahue et Erta Ale, 8 juillet 2017).

Significant movement to the NE in the northeast flow field was apparent in satellite images beginning on 21 July 2017; the head of the flow had reached about 9.5 km from the lava lake by 28 July 2017, mostly focused in a narrow channel (figure 66). Activity decreased in the southwest flow field during July; the lava front had advanced only a few hundred meters by the end of July from its position on 5 July.

Figure 66. The northeast flow field at Erta Ale lengthened significantly during July 2017; the leading edge was about 9.5 km NE of the lava lake by 28 July 2017, as captured in this Sentinel-2 satellite image. The southwest flow field had extended just a few hundred meters SW from its location on 5 July. The distance between the South Pit Crater and the Southeast Caldera lava lake is about 2.7 km. Courtesy of ESA/Copernicus with annotations provided by Culture Volcan (Les actus du jour: Katla en alerte jaune et quelques changements à l'Erta Ale, 29 juillet 2017).

During August 2017, lava continued to flow from the Southeast Caldera lava lake in two directions. The northeast flow front extended to 12 km from the vent by 17 August and had reached over 14 km by 7 September. The southwest flow field, while it remained in roughly the same area, had a decreased but still significant thermal signature in early September, suggesting continued but diminished activity throughout the period (figures 67).

Figure 67. During August 2017, lava continued to flow in two directions from the Southeast Caldera lava lake at Erta Ale. The northeast flow field had reached over 14 km from the lake by 7 September 2017 when this Landsat 8 satellite image was taken. The Southwest flow field, while it remained in roughly the same area, still had a significant thermal signature suggesting continued activity. Courtesy of ESA/Copernicus and NASA/USGS with annotations provided by Culture Volcan (volcan Erta Ale: ça continue; Fernandina: c'est moins sûr, 12 septembre 2017).

Activity during September-December 2017. In a Sentinel-2 satellite image from 26 September 2017, it was clear that the South Crater Pit was still thermally active, and that the southwest flow field had largely cooled with only a small area on its NW edge still producing a thermal anomaly (figure 68). In contrast, the northeast flow field had advanced about 1 km in the previous three weeks and was less than a kilometer from the edge of the valley alluvium. It finally reached the edge of the older lava field and began to advance across the alluvium NE of the volcano, more than 16 km from the lava lake, on 16 October 2017 (figure 69). Based on satellite imagery, Cultur Volcan interpreted that activity slowed significantly during November 2017, and while the thermal signal remained strong near the head of the flow, it did not advance significantly across the alluvium.

Figure 68. The South Pit Crater at Erta Ale still had an active lava lake on 26 September 2017 in this Sentinel-2 satellite image. The southwest lava field had largely cooled, with only a small thermal anomaly along it NW edge. The northeast lava field continued to be active; it had advanced about 1 km NE in about three weeks and was about 650 m from the edge of the alluvium. A significant number of hotspots along the northeast lava flow suggest that several skylights existed into lava tubes or there were small breakouts. Courtesy of ESA/Copernicus with annotations provided by Culture Volcan (Les actus du jour: Heard Island, Erta Ale, Pacaya, Fuego, Sangay, Ol Doynio Lengai, 5 octobre 2017).

Figure 69. Erta Ale's northeast flow field reached the alluvium about 16 km E of the Southeast Caldera lava lake by 16 October 2017, as recorded in this Sentinel-2 satellite image. The distance between the ends of the two easternmost tongues of lava is about 1 km. Courtesy of ESA/Copernicus with annotations provided by Culture Volcan (Erta Ale: ça y est, le champ de lave entre dans la plaine!, 18 octobre 2017).

Visitors to the South Pit Crater in mid-December 2017 reported that its lava lake continued to be active and its level was about 60 m below the rim. They were also able to visit the Southeast Caldera lava lake, 2.7 km SE of the South Pit Crater, and take photographs from its rim; it was about 200 m long and 100 m wide and filled with slowly convecting lava (figures 70, 71). Satellite imagery from 25 December 2017 showed the active lake at the South Pit Crater, the active lake at the Southeast Caldera, and numerous skylights and overflows along the 16-km-long northeast flow field (figure 72).

Figure 70. The Southeast caldera lava lake at Erta Ale, its surface crusted over with slightly cooled lava, with dimensions of about 200 x 100 m in mid-December 2017. Photograph by FB88, courtesy of Culture Volcan (Un point sur l'activité à l'Erta Ale, 31 décembre 2017).

Figure 71. The Southeast Caldera lava lake at Erta Ale was slowly convecting during mid-December 2017. Photographed by FB88, courtesy of Culture Volcan (Un point sur l'activité à l'Erta Ale, 31 décembre 2017).

Figure 72. Sentinel-2 satellite imagery from 25 December 2017 of Erta Ale showed the active lake at the South Pit Crater (Summit lava lake), the active lake at the Southeast Caldera (Rift-Zone lava lake), and numerous skylights and overflows along the 16-km-long northeast flow field. Courtesy of ESA/Copernicus with annotations provided by Culture Volcan (Un point sur l'activité à l'Erta Ale, 31 décembre 2017).

Activity during January-March 2018. By mid-January 2018 thermal activity was concentrated a few kilometers back from the front of the northeast flow, about 12 km from the lava lake (figure 73). A Volcano Discovery tour group visited during 13-26 January 2018 and was able to access and photograph both the North and South Pit Craters and the new lake and flow fields around the Southeast Caldera with ground-based and aerial drone photography (figures 74-84).

Figure 73. By 19 January 2018, thermal activity at Erta Ale's northeast flow field was concentrated a few kilometers back from the front of the flow, about 12 km from the Southeast Caldera lava lake. The South Pit Crater and Southeast Caldera lava lakes are visible on the left. Small hot-spots near the Southeast Caldera lava lake could be hornitos or skylights into lava tubes. Courtesy of ESA/Copernicus with annotations provided by Culture Volcan (Le point sur l'activité des volcans Erta Ale, Kadovar (Mis à jour) et Nevados de Chillan, 21 janvier 2018).

Figure 74. In this aerial view taken during 13-26 January 2018 by a drone of the central part of Erta Ale's Summit Caldera, steam plumes rose from the North Pit Crater (left) and South Pit Crater (right). The fresh black lava around the South Pit Crater overflowed onto the caldera floor in January 2017 shortly before the beginning of the eruptive events in the Southeast Caldera a few kilometers to the south. Copyrighted photo by Stefan Tommasini, used with permission.

Figure 75. The North Pit Crater inside the Summit Caldera at Erta Ale contained a large collapsed vent in January 2018 that formed after the magma drained away from the crater in January 2017. Photo taken during 13-26 January 2018. Copyrighted photo by Stefan Tommasini, used with permission.

Figure 76. The lava lake in the South Pit Crater of Erta Ale's Summit Caldera was tens of meters below the rim in January 2018. Magma drained away and parts of the crater walls collapsed in January 2017, followed by repeated filling and draining of the lava lake during 2017. Photo taken during 13-26 January 2018. Copyrighted photo by Stefan Tommasini, used with permission.

Figure 77. This aerial view by drone shows the large lava lake that formed at Erta Ale's Southeast Caldera during 2017; it was still slowly convecting in January 2018. The lake dimensions were about 100 x 200 m. Photo taken during 13-26 January 2018. Copyrighted photo by Stefan Tommasini, used with permission.

Figure 78. Recently cooled black crust is overrun and consumed by molten lava that quickly cools and crusts over in Erta Ale's Southeast Caldera lava lake in January 2018. Photo taken during 13-26 January 2018. Copyrighted photo by Stefan Tommasini, used with permission.

Figure 79. Lava appears to flow into the Southeast Caldera lava lake at Erta Ale from a vent at the far edge and slowly spread across the lake during January 2018. Photo taken during 13-26 January 2018. Copyrighted photo by Stefan Tommasini, used with permission.

Figure 80. Lava splashes as it flows into the Southeast Caldera lava lake at Erta Ale in January 2018. Photograph by Anastasia Ganuschenko taken during 13-26 January 2018, courtesy of Volcano Discovery.

Figure 81. Downwelling consumes lava inside the Southeast Caldera lava lake at Erta Ale in January 2018. Photo taken during 13-26 January 2018. Copyrighted photo by Stefan Tommasini, used with permission.

Figure 82. Incandescence is visible inside a hornito that formed through lava spattering along the new flows in the Southeast Caldera at Erta Ale in January 2018. Photograph by Anastasia Ganuschenko taken during 13-26 January 2018, courtesy of Volcano Discovery.

Figure 83. Many layers of fresh Pahoehoe lava flows were cool enough to walk on in some areas of the Southeast Caldera lava fields in January 2018. Photo taken during 13-26 January 2018. Copyrighted photo by Stefan Tommasini, used with permission.

Figure 84. Fresh lava flows were easily distinguished from older ones by their silver hue and dark black crust at Erta Ale's Southeast Caldera lava fields in January 2018. Photo taken during 13-26 January 2018. Copyrighted photo by Stefan Tommasini, used with permission.

By late March 2018 no thermal signal appeared in satellite imagery at the site of the Southeast Caldera lava lake, although the South Pit Crater was still visible. A large increase in the area of fresh flows and multiple thermal anomalies were present at the flow front of the northeast lava field 14-16 km from the former lava lake (figure 85). During the second half of March, the flow progressed several hundred meters out into the alluvial plain.

Figure 85. Sentinel-2 satellite imagery captured on 15 March 2018 showed a large increase in the area of fresh lava flows at the NE front of the northeast lava field at Erta Ale when compared with an image from 19 January 2018. Over the next ten days, images showed the narrow finger of lava that just touches the alluvium in this image creep about a kilometer out into the alluvial plain. Courtesy of Courtesy of ESA/Copernicus, published by Cultur Volcan (Les actus volcaniques du jour: Erta Ale, Maly-Semiachik, Suwanose-Jima et Ebeko, 28 mars 2018).

MIROVA thermal anomaly data. The MIROVA thermal anomaly data captures information about the distance of the anomalies from the summit as well as the radiative power released from Erta Ale. Both sets of information agree well with observations from the Sentinel-2 and Landsat satellite data. The plot of distance from the summit (figure 86) shows that during August 2016-mid-January 2017 the thermal anomalies were located very close to the summit point, representing heat flow from both the South and North Pit Craters within the Summit Caldera. Beginning on 21 January 2017, the jump in location of the anomalies corresponded with the beginning of the eruption in the Southeast Caldera. The MIROVA thermal anomalies progressed farther from the summit point during March and April 2017, when the northeast flow field was lengthening to the NE. The thermal signal jumps back closer to the summit point in early May corresponding to when new breakouts were spotted near the Southeast Caldera lava lake; the flows again traveled away from the lake during June and July 2017. Active lava flows from mid-August 2017 through March 2018 were visible in satellite imagery 12-16 km from the lava lake, which is reflected in the MIROVA data (figure 86).

Figure 86. MIROVA data showing the distance from the summit point of thermal anomalies at Erta Ale. Upper graph is the year ending 18 July 2017. Lower graph is the year ending 9 March 2018. They correspond well with locations of thermal anomalies that appear in numerous satellite images during that time. Note the distance scale change. See text and earlier figures for details. Courtesy of MIROVA.

The MIROVA data for the radiative power released from Erta Ale during August 2016-March 2018 also corresponds well with satellite and ground observations (figure 87). The levels of radiative power were moderate and constant during August 2016 to mid-January 2017 when only the lava lake and hornitos at the South and North Pit Craters were active (see also figure 47, BGVN 42:07). A moderate spike in the radiative power corresponds to the overflow of the South Pit Crater during 16-20 January 2017, followed by a large spike in radiative power on 21 January when the eruption started in the Southeast Caldera. This was followed by an extended period of increased radiative power as extensive flow fields formed in the Southeast Caldera. The graph is also able to distinguish the movement of the flows from near the Southeast Caldera lava lake to farther away and then near again during March-June 2017. The radiative power graph from 10 March 2017-9 March 2018 clearly shows a gradual decrease in the amount of radiative power over the period, suggesting a decline in flow activity, which corresponds well to satellite observations.

Figure 87. MIROVA plots of radiative power at Erta Ale for 18 July 2016-18 July 2017 (upper) and 9 March 2017-9 March 2018 (lower). Note the different y-axis scales for VRP due to the large spike on 21 January 2017 at the beginning of the Southeast Caldera eruptive episode. The plots record both the movement of the flow fields away from and closer to the summit point during March-June 2017, and then the gradual decrease in radiative energy from May 2017 through early March 2018. Courtesy of MIROVA.

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

Information Contacts: European Space Agency (ESA), Copernicus (URL: http://www.esa.int/Our_Activities/Observing_the_Earth/Copernicus; Robert Simon, Sr., Data Visualization Engineer, Planet Labs Inc. (URL: http://www.planet.com/) [Images used under https://creativecommons.org/licenses/by-sa/4.0/]; Cultur Volcan, Journal d'un volcanophile (URL: https://laculturevolcan.blogspot.com); Toucan Photo (URL: http://www.toucan.photo/); Tom Pfeiffer, Volcano Discovery (URL: http://www.volcanodiscovery.com/); 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/); Stefan Tommasini (URL: http://vulkane-und-natur.de/).

Italy's Mount Etna on the island of Sicily has had historically recorded eruptions for the past 3,500 years and has been erupting continuously since September 2013 through at least March 2018. Lava flows, explosive eruptions with ash plumes, and lava fountains commonly occur from its major summit crater areas that include the North East Crater (NEC), the Voragine-Bocca Nuova (or Central) complex (VOR-BN), the South East Crater (SEC) (formed in 1978), and the New South East Crater (NSEC) (formed in 2011). A new crater, referred to as the "Cono della sella" or CdS, emerged during early 2017 in the saddle between SEC and NSEC (figure 206).

Figure 206. A modified digital elevation model (DEM) of the summit area at Etna showing the major craters. The hatched black lines highlight the rims of the summit craters: BN = Bocca Nuova, which contains the NW depression (BN-1) and the SE depression (BN-2); VOR = Voragine with an active vent on its E rim that opened in August 2016; NEC = Northeast Crater; SEC = South-East Crater; NSEC = New Southeast Crater; and "Cono della Sella" or CdS, which emerged in early 2017, shown in red. The yellow dots indicate the locations of significant degassing vents at VOR, BN, and NSEC. Courtesy of INGV (Report 51/2017, Bollettino settimanale sul monitoraggio vulcanico, geochimico e sismico del vulcano Etna, 11/12/2017-17/12/2017, issue date-19/12/2017).

The most recent eruptive episode began with ash emissions from a new vent in the saddle between NSEC and SEC on 20 January 2017, followed by Strombolian activity a few days later (BGVN 42:10). Activity intensified at the end of February when the first of several lava flows emerged from this and other adjacent vents. By mid-March 2017, Strombolian activity, ash emissions, and lava flows had created a cone higher than the adjacent NSEC and SEC cones, referred to as the "Cono della Sella" (CdS) or saddle cone. An effusive episode at the end of April 2017 sent flows down both the N and S flanks of the new cone from multiple vents. Intermittent Strombolian activity and persistent fumarolic activity continued from multiple crater areas, and minor ash emissions were observed a few times through August 2017. The Osservatorio Etneo (OE), which provides weekly reports and special updates on activity, is run by the Catania Branch of Italy's Istituo Nazionale di Geofisica e Vulcanologica (INGV). This report uses information from INGV to summarize events between September 2017 and March 2018.

Although still exhibiting intermittent volcanism, activity at Etna was at low levels during September 2017-March 2018. A comparison of the thermal activity of that period with the previous interval of November 2016-August 2017 (figure 186, BGVN 42:10) demonstrates the order of magnitude decrease from the earlier period (figure 207). Persistent degassing occurred throughout this interval, often with incandescent gas and periodic ash emissions resulting from continued subsidence around crater vents and from small explosive events. Ashfall was reported once in the cities S of Etna in mid-January 2018, and a minor episode of Strombolian activity and ash emissions took place at the eastern vent of NSEC in mid-February 2018.

Figure 207. Thermal activity at Etna was substantially decreased compared to earlier in 2017 (figure 186, BGVN 42:10) as seen in this MIROVA graph that plots data for the year ending on 12 July 2018. Courtesy of MIROVA.

Activity during September-December 2017. Active degassing at the beginning of September 2017 occurred from the vent at the E rim of the Voragine crater (VOR), and from the NW vent of Bocca Nuova (BN-1) (figure 208). At the Northeast Crater (NEC) and the SE Crater (SEC)-New South East Crater (NSEC) complex, which included the new "Cono del Sella" (CdS), there was widespread degassing from the fumarolic fields located in the bottoms and walls of the craters. Minor explosive activity was reported on 19 September 2017 from BN and NSEC, and nighttime incandescence was reported from the other craters. On 20 September small sporadic ash emissions were noted from NSEC and VOR. Incandescence at night was observed at the SEC-NSEC complex for the remainder of the month, and strong degassing continued at the VOR vent.

Figure 208. Active degassing was evident at the summit craters of Etna on 24 August 2017. a) degassing from Bocca Nuova (BN). b) the active vent on the E rim of Voragine (VOR) was mostly steam. Courtesy of INGV (Report 35/2017, Bollettino settimanale sul monitoraggio vulcanico, geochimico e sismico del vulcano Etna, 21/08/2017-27/08/2017, issue date 29/08/2017).

Occasional ash emissions were observed during the second week of October 2017 from the Cono della Sella (CdS) (figure 209). A minor ash emission was also reported on 16 October from the SEC-NSEC complex. Minor emissions of brown ash were reported from BN-1 during the last week of October. In the late afternoon of 26 October, a single explosion occurred at one of the three mouths of the Cono della Sella crater. The explosion generated a short jet of incandescent material and a small ash plume that quickly dispersed.

Figure 209. An ash emission occurred on 13 October 2017 from the Cono della Sella (CdS) at Etna. These images were taken from the M. Cagliato (left) and La Montagnola (right) webcams. Intense degassing from VOR was also visible in the La Montagnola image. Courtesy of INGV (Report 42/2017, Bollettino settimanale sul monitoraggio vulcanico, geochimico e sismico del vulcano Etna, 09/10/2017-15/10/2017, issue date 17/10/2017).

Cloudy weather during November resulted in limited visibility for much of the month. A small, isolated explosion containing minor ash occurred at SEC on 14 November 2017. During the third week of November, a new pit crater appeared at the bottom of NEC that measured 70 x 50 m (figure 210), and intense degassing was observed from BN-1. Frequent small ash emissions were reported from CdS during 24-26 November. In the last week of the month, pulsating degassing from the craters could be detected during periods of limited visibility, as well as a series of explosions with ash emissions from SEC.

Figure 210. A new pit crater opened at the bottom of NEC at Etna during the third week of November 2017. A) Map of the summit crater area (DEM 2014) showing the pit crater location at the bottom of the NEC and one of the main fumaroles at the bottom (orange arrow). B) View of the bottom of NEC from the S on 23 November 2017, the orange arrow is the fumarole and the white hatched line indicates the rim of the new pit crater. C) The S flank of the NEC, showing the locations of the thermal cameras that created the images of the new pit in images D and E. Courtesy of INGV, (Report 48/2017, Bollettino settimanale sul monitoraggio vulcanico, geochimico e sismico del vulcano Etna, 20/11/2017-26/11/2017, issue date 28/11/2017).

Degassing from the summit craters persisted throughout December 2017 with intermittent incandescence observed from fumaroles at NSEC. A few ash emissions were recorded from CdS, including overnight on 14-15 December (figure 211).

Figure 211. Minor degassing, fumaroles, and incandescence were recorded at the summit craters of Etna in early December 2017. a) Degassing from BN and VOR on the morning of 13 December 2017, seen from the S. b) Image taken from the high-resolution webcam at Monte Cagliato (EMCH, E side of Etna) showing incandescence at the E vent of NSEC in the early hours of 12 December 2017. c) Puff of ash emitted by CdS on the morning of 15 December 2017, recorded by the Montagnola (EMOV) webcam. Courtesy of INGV (Report 51/2017, Bollettino settimanale sul monitoraggio vulcanico, geochimico e sismico del vulcano Etna, 11/12/2017-17/12/2017, issue date 19/12/2017).

Activity during January-March 2018. Similar activity continued throughout January 2018; a small ash emission was observed from CdS on 5 January, and a puff of brown ash emerged from NSEC the next day. Incandescence degassing also continued from the NSEC vents. During the second week of the month, 20 small explosive events were observed from the eastern vent at NSEC, although cloud cover obscured the summit for much of the time. Minor ash emissions continued from NSEC for the rest of the month, along with nighttime incandescence, especially strong from BN-1. On 22 January a modest ashfall affected the communities S of Etna including the city of Catania (27 km S); the lack of visibility prevented identification of which crater produced the ash. By the end of the month, the pit crater at the base of NEC had expanded, causing erosion of the inner E wall (figure 212). In spite of the low level of activity during this period, SO₂ emissions were occasionally recorded with satellite instruments. The most significant SO₂ plumes were measured during the last few days of January (figure 213).

Figure 212. Activity during January 2018 at Etna included strong incandescence from BN-1, numerous small explosive events from NSEC, and expansion of the pit crater at the base of NEC. The hatched black lines highlight the edge of the summit craters: BN = Bocca Nuova, including the NW depression (BN-1) and the SE depression (BN-2); VOR = Voragine; NEC = Northeast Crater; SEC = South-East Crater; NSEC = New Southeast Crater. The yellow dots indicate the positions of the degassing vents of VOR, NEC and NSEC (E vent and "Cono della Sella"). The yellow dots with a red border indicate the vents characterized by strong incandescence (BN-1) and occasional ash emissions (NSEC, E vent). Courtesy of INGV, Report 06/2018, Bollettino settimanale sul monitoraggio vulcanico, geochimico e sismico del vulcano Etna, 29/01/2018-04/02/2018, issue date, 06/02/2018).

Figure 213. Significant SO2 plumes were measured from Etna on 29 (left) and 31 (right) January 2018 by the OMI instrument on NASA's Aura satellite. Courtesy of NASA Goddard Space Flight Center.

Two weak ash emissions occurred at NSEC during the first week of February 2018. The frequency of explosions increased during 15-16 February to 1-2 events per hour, producing moderate amounts of brown-gray ash and incandescent pyroclastic material (figure 214); heightened activity lasted for several days. The explosions were heard 20 km E and S from the summit. Faint, non-explosive emissions of gray ash were observed on the morning of 17 February 2018 from NEC (figure 215).

Figure 214. Ash and incandescent material were ejected from the E vent of NSEC at Etna during 17 February 2018. a) Ash emission from the E vent at NSEC viewed by the Tremestieri Etneo webcam from the S flank on the morning of 17 February 2018. b) Incandescent material ejected during one of the explosions from the same vent, on the evening of 17 February 2018. Photo by Michele Mammino, used by INGV with permission of the author. Courtesy of INGV (Report 08/2018, Bollettino settimanale sul monitoraggio vulcanico, geochimico e sismico del vulcano Etna, 12/02/2018-18/02/2018 (issue date 20/02/2018).

Figure 215. A weak ash emission rose from Etna's NEC at 1005 local time on 17 February 2018, as seen by the Zafferana Etnea webcam. Courtesy of INGV, Report 08/2018, Bollettino settimanale sul monitoraggio vulcanico, geochimico e sismico del vulcano Etna, 12/02/2018-18/02/2018, issue date 20/02/2018).

Degassing continued at the summit craters for the remainder of February and throughout March 2018. During an inspection by INGV on 10 March, the expansion of the pit crater at the bottom of NEC was noted, as was continuing collapses of the internal walls which produced minor ash emissions. Activity at the E vent of NSEC included a minor ash emission on 2 March 2018; occasional ejection of incandescent pyroclastic material and modest ash emissions continued throughout the month (figure 216). The ash emissions occurred at irregular intervals, varying from a few tens of minutes to a few hours, more frequently in the last days of the month.

Figure 216. Explosive activity from the vent on the E side of NSEC at Etna, taken from the Tremestieri Etneo webcam on the S flank on 8 March 2018. Ash emissions were accompanied by incandescent tephra that landed on the flanks. Photographic sequence by B. Behncke. Courtesy of INGV, Report 11/2018, Bollettino Settimanale, 05/03/2018-11/03/2018, issue date 13/03/2018).

Geologic Background. Mount Etna, towering above Catania on the island of Sicily, has one of the world's longest documented records of volcanism, dating back to 1500 BCE. Historical lava flows of basaltic composition cover much of the surface of this massive volcano, whose edifice is the highest and most voluminous in Italy. The Mongibello stratovolcano, truncated by several small calderas, was constructed during the late Pleistocene and Holocene over an older shield volcano. The most prominent morphological feature of Etna is the Valle del Bove, a 5 x 10 km caldera open to the east. Two styles of eruptive activity typically occur, sometimes simultaneously. Persistent explosive eruptions, sometimes with minor lava emissions, take place from one or more summit craters. Flank vents, typically with higher effusion rates, are less frequently active and originate from fissures that open progressively downward from near the summit (usually accompanied by Strombolian eruptions at the upper end). Cinder cones are commonly constructed over the vents of lower-flank lava flows. Lava flows extend to the foot of the volcano on all sides and have reached the sea over a broad area on the SE flank.

Information Contacts: Sezione di Catania - Osservatorio Etneo, Istituto Nazionale di Geofisica e Vulcanologia (INGV), Sezione di Catania, Piazza Roma 2, 95123 Catania, Italy (URL: http://www.ct.ingv.it/it/ ); 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/); NASA Goddard Space Flight Center (NASA/GSFC), Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, 8800 Greenbelt Road, Goddard, Maryland, USA (URL: https://so2.gsfc.nasa.gov/).

The first confirmed historical eruption at Kadovar began around mid-day local time on 5 January 2018, according to witnesses. The steeply-sloped island is approximately 1.4 km in diameter and is located about 25 km NNE from the mouth of the Sepik River on the mainland of Papua New Guinea (figure 1). This report covers activity from the beginning of the eruption on 5 January through March 2018. Information about the eruption is provided by the Rabaul Volcano Observatory (RVO), the Darwin Volcanic Ash Advisory Center (VAAC), satellite sources, news reports, and local observers. A possible eruption was witnessed by explorers in 1700; no other activity was reported until an outbreak of thermal activity in 1976 (NSEB 01:14-01:11, SEAN 03:09) and a short period of seismic unrest in 2015, according to RVO.

Figure 1. Kadovar Island is located about 25 km NNE from the mouth of the Sepik River on the mainland of Papua New Guinea. Nearby active volcanoes include Blup Blup (12 km N) and Bam (21 km W); residents of Kadovar were evacuated initially to Blup Blup before being moved to an area near Wewak, the nearest community on the mainland, about 105 km W. The red triangles are Holocene volcanoes, and the blue (cyan) triangles are Pleistocene volcanoes. Base map courtesy of Google Earth.

Ash and steam emissions from Kadovar were first reported on 5 January 2018. After about 24 hours, more than half of the island was covered by volcanic debris. Activity intensified over the next two weeks; RVO identified five distinct vents located at the summit and along the SE coast. Dense ash plumes and steam rose from the summit vents, and a slowly-extruding lava flow emerged from a vent near the shoreline on the SE flank. Persistent steam and intermittent ash plumes were produced from the summit vent through the end of March. The lava flow grew outward from the shore for tens of meters before collapsing in early February, but it reappeared a few days later. By the end of the first week of March 2018 the flow was about 17 m above sea level; its growth rate had slowed, adding only one meter by late March.

The NOAA/CIMSS Volcanic Cloud Monitoring system generated an alert for an ash cloud moving WNW, as imaged by S-NPP VIIRS, at 0330 UTC on 5 January 2018; Himawari-8 imagery subsequently showed that the eruption began around 0220 UTC. The Darwin VAAC reported two discrete ash plumes drifting W at 2.1 km altitude during the day. After local reports of the eruption Samaritan Airlines flew administrators from the Wewak district to investigate, enabling photographs of ash and steam emissions (figure 2).

Figure 2. Steam and ash emerged from a vent near the summit of Kadovar Island and drifted WNW on 5 January 2018. The view is looking NW with the SE flank of Kadovar in the foreground. In the upper photo, the island in the background is Viai Island about 30 km NW. Photo by Ricky Wobar, administrator of the Wewak district. Courtesy of Samaritan Aviation, posted on Facebook on 5 January 2018.

The following day, 6 January 2018, photos from a Samaritan Air flight showed that dark gray ash and steam plumes rising from a crater on the SE side of the summit had intensified (figures 3 and 4). It was estimated that 50 or 60% of the island was covered in volcanic debris, which appeared to be primarily ash along with some pyroclastic flows. According to the International Federation of Red Cross and Red Crescent Societies (IFRC), the entire population of Kadovar, about 600 people who lived on the N side of the island, was relocated to nearby Blup Blup Island which is home to about 800 residents. RVO reported minor ashfall on Kairiru and Mushu islands (115 km WNW), and on mainland Papua New Guinea at Mt. Uru in Yangoru (130 km W), Woginara (140 km W), and the Wewak District (100 km W).

Figure 3. Ash and steam plumes rose from distinct vents on the SE side of the summit at Kadovar. View is to the NE, with Blup Blup volcano located about 12 km in the distance. Photo by Ricky Wobar likely taken on 6 January 2018, published by ABC News on 8 January 2018. Courtesy of ABC News.

Figure 4. Ash and steam emissions intensified from vents at the summit of Kadovar Island on 6 January 2018. Posted on Facebook, 6 January 2018 by Samaritan Aviation.

Also on 6 January 2018, missionary Brandon Buser set out from Wewak to visit Bam by boat. He observed the steam and ash plumes of Kadovar from about 75 km away. About 25 km W of the island, he felt falling ash. From a few hundred meters offshore he witnessed the ash and steam plumes rising from near the summit as he circled the S and E sides of the island (figures 5-8).

Figure 5. Locations of the following photographs of the eruption at Kadovar on 6 January 2018 correspond closely to the purple spots where the boat slowed down on its trip around the island. North is to the top. Numbers indicate approximate locations of the following figures 6-12. Courtesy of Brandon Buser. Base map courtesy of Google Earth.

Figure 6. An ash plume drifted NW from the summit of Kadovar as viewed from a boat a few hundred meters off the SW flank on 6 January 2018. Courtesy of Brandon Buser.

Figure 7. Ash drifted WNW from Kadovar and also covered the vegetation on the SSW flank on 6 January 2018 in this view from a boat a few hundred meters off the SSW flank. Courtesy of Brandon Buser.

Figure 8. Dark ash and white steam both rose from vents at the summit of Kadovar on 6 January 2018. Debris and ashfall killed and denuded the trees on the SE flank, and covered the ground. View is from a boat a few hundred meters off the SE flank. Courtesy of Brandon Buser.

While preparing to head E to Bam, Buser witnessed an explosion that sent large plumes of ash and steam skyward from the SE flank, and a significant cloud of volcanic debris was ejected outward and down the SE flank; large boulders fell into the ocean. Heading rapidly E away from the eruption, he took additional photographs (figures 9-12).

Figure 9. Dark gray ash and white steam billowed up from a vent near the summit of Kadovar on 6 January 2018 at the start of an explosion. The denuded vegetation and bare slopes on the SE flank indicated the extent of the recent activity. The view is from a boat a few hundred meters offshore of the NE flank. Courtesy of Brandon Buser.

Figure 10. An explosion witnessed at Kadovar on 6 January 2018. Steam rose from a vent near the summit (right), dark gray ash billowed up from the SE flank, and brown dust and debris descended the SE flank into the ocean (left) in this view from a few hundred meters off the NE flank. Courtesy of Brandon Buser.

Figure 11. A large explosion at Kadovar witnessed on 6 January 2018. Light gray steam and ash rose from near the summit and drifted NW covering the N half of the island in ash; a large eruption of dark gray ash shot upward from a different vent on the SE flank surrounded by dust and debris that traveled outward at its base. Larger debris caused splashing in the water off the SE flank (left). View is from a few kilometers off the NE flank. Courtesy of Brandon Buser.

Figure 12. The plumes of steam, ash, and debris from the explosion moments earlier at Kadovar on 6 January 2018 rose and began to drift NW covering the island. Blocks landing in the ocean on the SE flank created spray along the shoreline (left). View is from a boat a few kilometers NE of the island. Courtesy of Brandon Buser.

The Darwin VAAC reported on 6 January 2018 that a continuous ash plume was identifiable in satellite imagery moving W and WNW at 2.1 km altitude. By 7 January, the plume could be identified about 220 km WNW in satellite images (figure 13). During their return trip from Bam on 8 January 2018, the missionaries again circled the island and noted that the eruption seemed to be occurring from different vents. The island was covered in ash, and they became covered with wet ash as they traveled under the drifting ash plume. The Darwin VAAC reported the plume drifting WNW extending about 185 km on 8 January. They also noted that the influence of the sea breeze was also spreading minor ash to the SW. Continuous ash emissions were observed by the Darwin VAAC through 11 January, drifting W and NW at 2.1 km altitude.

Figure 13. The Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA's Aqua satellite captured the eruption of Kadovar that began two days earlier on 7 January 2018 as a plume of ash and steam that streamed NW from its crater. A second smaller plume, also drifting NW, is visible SE of Kadovar from unrelated activity at nearby Manam, one of Papua New Guinea's most active volcanos. Brown-green plumes visible in the water S of Kadovar near the coast of the mainland, are caused by sediment from the Sepik and Ramu rivers on the mainland. Courtesy of NASA Earth Observatory.

RVO reported a significant escalation in activity during 12-13 January 2018. An explosion during the previous night ejected large incandescent boulders from the fracture on the SE flank. Residents on Blup Blup (15 km N) could see incandescence high on the volcano's flank. During a flyover on 13 January, RVO noted variable steam and gas emissions rising to 1 km above the Main Crater and identified five distinct vents (figure 14). The SE Coastal Vent was very active with dense white steam emissions rising 600 m from the vent (figure 15). A dome of lava was visible at the base of the steam plume, but no incandescence was observed. The Southern Coastal Vent had been vigorously steaming a few days earlier, and RVO interpreted it to be the source of the incandescent blocks in the explosion a few days before.

Figure 14. A sketch map of the five newly identified vents at Kadovar, 14 January 2018, from an RVO overflight the previous day. Courtesy of RVO (VOLCANO INFORMATION BULLETIN- No. 08 14/01/2018).

Figure 15. A vigorous steam plume rose from the SE Coastal Vent at Kadovar on 13 January 2018 while an ash plume rose from Main Crater at the summit. Photo by the office of Allan Bird, Governor of East Sepik Province. Courtesy of RVO (VOLCANO INFORMATION BULLETIN- No. 08 14/01/2018).

Reports of continuous ash emissions at 2.1 km altitude drifting WNW from the Darwin VAAC resumed on 16 January. A brief emission to 3.7 km was also noted that day. Pilot reports on 17 and 18 January indicated that ash was still in the area as high as 3-3.7 km altitude drifting W. The reports of emissions from the Darwin VAAC continued through 24 January. Ash emissions were generally continuous at altitudes from 2.4 to 3 km, although low level emissions of primarily steam and gas were observed on 20 January that included intermittent phases of increased ash content. The plume drift direction was variable, with periods when ash drifted S and SE in addition to the generally prevailing NW and W directions.

During 18-22 January 2018, the Main Crater continued to produce moderate to dark gray ash plumes that rose 500-800 m above the summit, drifting locally S and SE, and a continuous steam plume from the SE Coastal Vent rose as high as 800 m above the island. An incandescent lava flow slowly extruded from the SE Coastal Vent. By the last week of January, the ash plumes were only rising about 100 m above the Main Crater and drifting W; weak incandescence was still observed at night. The white steam plume from the SE Coastal Vent rose closer to 400 m above the island. RVO estimated that the lava flow had risen to about 50 m above sea level and extended 150-200 m out from the coast.

In their report on 2 February 2018, RVO noted that the lava flow continued to grow. A distinct lobe had pushed out from the seaward nose of the flow, by about 20-30 m; it appeared to be channeled by levees which had developed at the flow's sides. At 1830 local time on 1 February, a collapse of the side of the flow facing Blup Blup was observed; it resulted in a plume of gray ash and then vigorous steaming at the collapse site, which also was incandescent at night. The main body of the flow significantly bulged upwards, with a distinct 'valley' visible between the bulge and the island's flank.

RVO reported that on 9 February the lava flow at the SE Coastal Vent had collapsed, causing 5-6 minor tsunamis less than 1 m high that were observed by residents on Blup Blup's E and W coasts. The waves were reported at 1050, before the main collapse of the dome. In a 12 February report, RVO noted that activity from Main Crater consisted of white plumes rising 20 m and drifting a few kilometers SE accompanied by weak nighttime crater incandescence. Activity renewed at the SE Coastal Vent shortly after the collapse of the flow on 9 February 2018; lava re-emerged a few days later, connecting a lava island to the coastline again. Continuous steam emissions from both the Main Crater and the SE Coastal Vent were interrupted by dark ash plumes on 16 and 20-22 February, and occasional explosions were heard by residents on nearby islands. Minor ashfall was reported on Blup Blup on 21 and 22 February.

Eruptive activity continued during March 2018, although at a slower rate. The Main Crater generally produced continuous emissions of white steam and intermittent explosions with dark ash plumes; incandescence was usually visible at night from Blup Blup. According to the Darwin VAAC, a pilot reported an ash plume at 3.9 km altitude drifting SE on 2 March; it was not visible in satellite imagery due to meteoric clouds. The lava flow extruding from the SE Coastal Vent continued to grow, creating a dome that grew from 7-8 m above sea level to 10-17 m above sea level by 8 March. Dark ash emissions from the vent and nighttime incandescence were common. The growth rate slowed later in the month, and only one meter of change was observed between 10 and 20 March.

Satellite data. The MIROVA project recorded thermal anomalies from Kadovar in early January and early March 2018 (figure 16). MODVOLC thermal alerts were issued on three days; 15 and 22 January, and 7 February 2018. During January, small SO₂ plumes were recorded by NASA satellites on four occasions (figure 17).

Figure 16. The MIROVA project thermal anomaly graph for Kadovar from 11 May 2017 through March 2018. The first anomaly in early January 2018 correlates with observations of the first reported explosion. Courtesy of MIROVA.

Figure 17. SO2 plumes from Kadovar were detected several times during January 2018 by the OMI instrument on NASA's Aura satellite. Courtesy of NASA Goddard Space Flight Center.

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: 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, Contact: steve_saunders@mineral.gov.pg, ima_itikarai@mineral.gov.pg; Darwin Volcanic Ash Advisory Centre (VAAC), Bureau of Meteorology, Northern Territory Regional Office, PO Box 40050, Casuarina, NT 0811, Australia (URL: http://www.bom.gov.au/info/vaac/); NASA Earth Observatory, EOS Project Science Office, NASA Goddard Space Flight Center, Goddard, Maryland, USA (URL: http://earthobservatory.nasa.gov/); NASA Goddard Space Flight Center (NASA/GSFC), Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, 8800 Greenbelt Road, Goddard, Maryland, USA (URL: https://so2.gsfc.nasa.gov/); NOAA, Cooperative Institute for Meteorological Satellite Studies (CIMSS), Space Science and Engineering Center (SSEC), University of Wisconsin-Madison, 1225 W. Dayton St., Madison, Wisconsin 53706, USA (URL: http://cimss.ssec.wisc.edu/); International Federation of Red Cross and Red Crescent Societies (IFRC) (URL: http://www.ifrc.org/); Samaritan Aviation (URL: http://samaviation.com/, https://www.facebook.com/samaritanaviation/); Brandon Buser (URL: https://ethnos360.org/missionaries/brandon-and-rachel-buser, https://www.facebook.com/brandon.buser.35); ABC News (URL: http://www.abc.net.au/news/2018-01-08/tsunami-warning-for-communities-near-erupting-png-volcano/9311544); Google Earth (URL: https://www.google.com/earth/).

Recent activity at Karymsky has consisted of ash explosions on 4 June and 20 September 2017, separated by a period of relative quiet (BGVN 42:11). The volcano was quiet after 20 September until another ash explosion on 4 December 2017. This report covers activity from 1 December 2017 through March 2018, using information compiled from the Kamchatka Volcanic Eruptions Response Team (KVERT) and the Tokyo Volcanic Ash Advisory Center (VAAC). According to KVERT, an explosion on 27 January 2018 was last through at least 31 March.

Based on satellite data, KVERT reported that an explosion began at about 0630 on 4 December 2017 and generated an ash cloud that rose to an altitude of 2.7 km and drifted 200 km E. An ash cloud 16 x 12 km in dimension was identified in satellite images about three hours after the explosion, 92 km E of the volcano. The Aviation Color Code was raised from Green to Orange (the second highest level on a four-color scale). A thermal anomaly was identified in satellite data during 3 and 5-6 December.

According to KVERT, another ash plume was identified in satellite data drifting 114 km ENE on 14 December. No further ash emissions were noted afterward; the Aviation Color Code was thus lowered on 24 December to Yellow.

A small ash cloud was identified in satellite imagery drifting near Karymsky on 18 January 2018, and a thermal anomaly was identified on 19 and 23 January. Gas-and-steam plumes drifted 30 km NE and NW on 21 and 25 January, and an ash plume drifted about 100 km NE on 23 January. An explosion at 1430 on 27 January generated ash plumes that rose to an altitude of 5.2 km and drifted 80 km NE-NNE, prompting KVERT to raise the Aviation Color Code to Orange.

Moderate gas-and-steam emissions continued during February and March. Thermal anomalies were detected in satellite images on 3, 9, and 18 February, and 23-26 March; during other days, the volcano was either quiet or obscured by clouds. The Aviation Color Code remained at Orange through the end of the reporting period.

Geologic Background. Karymsky, the most active volcano of Kamchatka's eastern volcanic zone, is a symmetrical stratovolcano constructed within a 5-km-wide caldera that formed during the early Holocene. The caldera cuts the south side of the Pleistocene Dvor volcano and is located outside the north margin of the large mid-Pleistocene Polovinka caldera, which contains the smaller Akademia Nauk and Odnoboky calderas. Most seismicity preceding Karymsky eruptions originated beneath Akademia Nauk caldera, located immediately south. The caldera enclosing Karymsky formed about 7600-7700 radiocarbon years ago; construction of the stratovolcano began about 2000 years later. The latest eruptive period began about 500 years ago, following a 2300-year quiescence. Much of the cone is mantled by lava flows less than 200 years old. Historical eruptions have been vulcanian or vulcanian-strombolian with moderate explosive activity and occasional lava flows from the summit crater.

Information Contacts: Kamchatka Volcanic Eruptions Response Team (KVERT), Far Eastern Branch, Russian Academy of Sciences, 9 Piip Blvd., Petropavlovsk-Kamchatsky, 683006, Russia (URL: http://www.kscnet.ru/ivs/kvert/); Tokyo Volcanic Ash Advisory Center (VAAC), 1-3-4 Otemachi, Chiyoda-ku, Tokyo, Japan (URL: http://ds.data.jma.go.jp/svd/vaac/data/).

The large Kusatsu-Shiranesan volcanic complex comprises three overlapping pyroclastic cones and numerous summit craters; it is located about 150 km NW of Tokyo in the Gunma Prefecture of central Japan. Intermittent short-lived historic activity has been reported from the northernmost Shiranesan cone since the beginning of the 19th century. An explosion at the southernmost Motoshiranesan cone in January 2018 resulted in one fatality and several injuries. Information about the event was gathered from the Japan Meteorological Agency (JMA) and various news sources.

Summary of activity during 1976-2014. Small phreatic explosions in the Mizugama and Yugama craters at the northernmost part of the Kusatsu-Shiranesan volcanic complex occurred in 1976, 1982, and 1983 (figure 14). Larger ash-bearing explosions in November and December 1983 sent tephra 30-40 km to communities downwind to the SE from the Yugama and adjacent Karagama craters on the Shiranesan cone. Intermittent increases in seismic activity near the Yugama crater coincided with water discoloration in the crater lake, and possible ejections of debris from hydrothermal activity in 1989 and 1996. Increased hydrothermal activity was noted on the N flank of Yugama during 2013-2014. Seismic swarms, deformation, thermal, and fumarolic activity increased briefly during early June 2014 in the area around the Yugama crater lake, but no eruption was observed. In late June 2014, JMA reported dying vegetation in a forested area 3 km SW of the Motoshiranesan summit area.

Figure 14. Subfeatures of the Kusatsu-Shiranesan volcanic complex as seen in Google Earth imagery, looking N. The northernmost bleached area includes the historically active Yugama, Mizugama, and Karagama craters, part of the Shiranesan cone. In the center of the complex is the Ainomine cone which has a ski area on the S flank. The southernmost edifice is the Motoshiranesan cone which has multiple craters at its summit, including Kagamiike or "Mirror pond". The explosions of 23 January 2018 occurred at Kagamiike and the adjacent crater to the N, in area referred to by JMA as Honkonoyama. Courtesy of Google Earth.

Activity during 2014-2017. Seismicity remained elevated from March to mid-August 2014 around the Yugama crater area. Ground deformation data suggested inflation between March 2014 and April 2015 in that area. Field surveys conducted on 4-5 and 10-11 November 2014 indicated fumarolic areas on the N and NE flanks of the Mizugama crater, but no other significant activity. Short-lived increases in seismicity were observed during January-February 2015. A field survey in May 2015 confirmed ongoing thermal activity on the N and NE wall of the Yugama crater, and the N and NE flank of the Mizugama crater. A small-amplitude, 2-minute-long tremor during late June 2015 was the first since January 2013; it was not accompanied by eruptive activity. The fumarolic activity on the N wall of the Yugama Crater was higher during a field survey in October 2015 than in had been the previous May.

Thermal activity was ongoing at Yugama and Mizugama craters during 2015-2017 along with intermittent fumarolic activity in the same general area, but no significant seismicity was reported. By June 2017 the decrease in the concentration of components derived from high-temperature volcanic gas in the lake, and the stable low-level seismicity in the area, led JMA to lower the warning level from 2 to 1 (on a 5 level scale) on 7 June 2017; they noted that the thermal activity continued around the Yugama crater throughout the rest of the year (figures 15-17).

Figure 15. A minor thermal anomaly persisted inside the NE crater wall at Yagama Crater at Kusatsu-Shiranesan throughout 2015-2017. Both visual (upper) and thermal (lower) images were taken during an overflight on 1 November 2017. View is to the north. Courtesy of JMA (Volcanic activity monthly report, Kusatsu-Shirane, November 2017).

Figure 16. Thermal anomalies persisted on the N and NE flank of the Mizugama crater at Kusatsu-Shiranesan during 2015-2017. These visual (upper) and thermal (lower) images were captured on 1 November 2017. Courtesy of JMA (Volcanic activity monthly report, Kusatsu-Shirane, November 2017).

Figure 17. Daily earthquake frequency at Kusatsu-Shiranesan during 1 January 2011-30 November 2017. Although earthquake counts temporarily increased during March-August 2014 and in January and February 2015, no eruptive activity was reported. Courtesy of JMA (Volcanic activity monthly report, Kusatsu-Shirane, November 2017).

Activity during January-March 2018. JMA reported that at 0959 on 23 January 2018 an eruption began at Kusatsu-Shiranesan coincident with the onset of volcanic tremor which prompted JMA to raise the Alert Level to 3 (on a scale of 1-5); there had been no prior indications of an impending eruption. Skiers at the popular Kusatsu Kokusai ski resort, located on the Ainomine cone, took video showing a plume of tephra and ejected bombs rising from vents around the Kagamiiki and adjacent crater at the summit of the Motoshiranesan cone (see Information Contacts for Mainichi for video link). Motoshiranesan is immediately adjacent S of the Ainomine cone and about 2 km SSE of the Yagama Crater on the Shiranesan cone where all previous historical activity had been reported (figures 14 and 18).

Figure 18. Locations and images of the active vents at Kusatsu-Shiranesan during the eruptive event of 23 January 2018. Upper left: View is looking W at the Motoshiranesan summit craters. The crater with the pond in Box 1 is Kagamiike (yellow Japanese characters). Boxes 1 and 2 in the upper left photo are enlarged in the lower photos. Upper right topographic map shows the locations in red of the three vents. The upper red line and dot correspond to the vents shown in the lower right box 2. The lower red bar on the topographic map (near the small pond) corresponds to the vent shown in the lower left image as box 1. Courtesy of JMA (Volcanic activity monthly report, Kusatsu-Shirane, January 2018).

Photos and video posted in news articles showed tephra shooting tens of meters into the air, drifting E, and blanketing the nearby hillside (figure 19); JMA noted ashfall in Nakanojo-machi, in the Gunma Prefecture, about 8 km E. Tephra hit a gondola, shattering glass and injuring four skiers (figure 20). Material fell through the roof of a lodge, where about 100 people had already been evacuated. Ground Self-Defense Force troops were engaging in ski training at the time of the event; one member died from the impact of large tephra blocks, and seven others were injured.

Figure 19. Tephra from Mount Kusatsu-Shiranesan covers the N flank of the Motoshiranesan cone and much of the Ainomine cone in this view to the W taken on 23 January 2018. Photo by Suo Takeuma, AP, courtesy of CNN (Japanese man killed by falling rocks after volcano erupts at ski resort, 23 January 2018).

Figure 20. Fist-sized tephra blocks and ash ejected from the eruption of Mount Kusatsu-Shiranesan cover the floor of a damaged gondola at the Kusatsu Kokusai Ski Resort on 24 January 2018, courtesy of The Mainichi Japan (Damaged ski resort gondolas show the power of Gunma Pref. volcanic eruption, 25 January 2018).

The following day, on 24 January 2018, JMA noted that volcanic earthquakes were numerous but decreasing in number, and two 2-3-minute-long periods of volcanic tremor were detected at 1015 and 1049. Minor but elevated seismicity continued through 30 January, punctuated by periods of tremor. The largest fissure where the eruption occurred was oriented E-W, located just inside the N rim of the northernmost crater at the Motoshiranesan summit (figure 21). Kenji Nogami, a professor at the Tokyo Institute of Technology, confirmed that the event appeared to have been "a typical phreatic eruption" (Japan Times).

Figure 21. The largest fissure vent active in the 23 January 2018 explosion at Kusatsu-Shiranesan was still surrounded by ash and tephra when photographed during an overflight on 28 January 2018. The summit ropeway station of the ski area is at the image top just NW of the explosion vent. Courtesy of The Mainichi (Visitor traffic plunges in Kusatsu hot spring resort after deadly eruptions, 30 January 2018).

The Tokyo Volcanic Ash Advisory Center issued a single volcanic ash advisory on 23 January indicating a possible eruption, but it was not identifiable from satellite data. Observations made on 14 February 2018 confirmed the presence of the vents in the Kagamiike and adjacent crater, but there was no evidence of thermal activity and little fumarolic activity in the area (figure 22). Seismicity decreased steadily after the explosion on 23 January 2018 through the end of March 2018 and no further activity was reported (figure 23).

Figure 22. Vents from the 23 January 2018 eruption at Kusatsu-Shiranesan were still visible at the craters on 14 February 2014 during a helicopter overflight by JMA. The upper image, looking W, shows the large vent at the N side of the crater immediately N of the Kagamiike crater, as well as a smaller vent located to the W on the E flank of the adjacent slope. The lower image shows two smaller vents on the inner wall of the adjacent Kagamiike crater. Courtesy of JMA (Volcanic activity monthly report, Kusatsu-Shirane, February 2018).

Figure 23. Seismicity decreased steadily at Kusatsu-Shiranesan after the explosion on 23 January 2018. Graph shows the number of daily seismic events during 1 January-31 March 2018. Courtesy of JMA (Volcanic activity monthly report, Kusatsu-Shirane, March 2018).

Geologic Background. The Kusatsu-Shiranesan complex, located immediately north of Asama volcano, consists of a series of overlapping pyroclastic cones and three crater lakes. The andesitic-to-dacitic volcano was formed in three eruptive stages beginning in the early to mid-Pleistocene. The Pleistocene Oshi pyroclastic flow produced extensive welded tuffs and non-welded pumice that covers much of the E, S, and SW flanks. The latest eruptive stage began about 14,000 years ago. Historical eruptions have consisted of phreatic explosions from the acidic crater lakes or their margins. Fumaroles and hot springs that dot the flanks have strongly acidified many rivers draining from the volcano. The crater was the site of active sulfur mining for many years during the 19th and 20th centuries.

Information Contacts: Japan Meteorological Agency (JMA), Otemachi, 1-3-4, Chiyoda-ku Tokyo 100-8122, Japan (URL: http://www.jma.go.jp/jma/indexe.html); The Mainichi (URL: http://mainichi.jp/english/, eruption video URL-https://mainichi.jp/movie/video/?id=121708141#cxrecs_s); The Japan Times (URL: https://www.japantimes.co.jp/); Cable News Network (CNN), Turner Broadcasting System, Inc. (URL: http://www.cnn.com/).

Steep-sloped and symmetrical Mayon has recorded historical eruptions back to 1616 that range from Strombolian fountaining to basaltic and andesitic flows, as well as large ash plumes, and devastating pyroclastic flows and lahars. A lava dome that grew during August-October 2014 resulted in rockfalls, pyroclastic flows, and lava flows from the summit crater that led to evacuations in nearby communities (BGVN 41:03). Activity declined during November and December 2014 and remained low throughout 2015. By February 2016 the Alert Level was reduced to 0 (on a 0-5 scale) by the Philippine Institute of Volcanology and Seismology (PHIVOLCS) which monitors the volcano. A seismic swarm in August 2016, and the beginning of a new eruption in January 2018 are covered in this report with information provided primarily by PHIVOLCS.

After a brief seismic swarm in August 2016, Mayon remained quiet until a phreatic explosion on 13 January 2018 sent an ash plume 2,500 m above the summit and scattered ash over numerous nearby communities. The growth of a new lava dome sent lava flows down the flanks and ash plumes multiple kilometers above the summit during subsequent weeks. Lava fountaining produced incandescence at the summit for many weeks. Lava collapse events from the flow fronts sent pyroclastic density currents (PDC's) down multiple ravines during January and February 2018. Lava fountaining activity became nearly continuous at the beginning of February but began to taper off by mid-month. Flows had reached as far as 4.5 km down ravines, and lava-collapse generated pyroclastic density currents reached 5 km from the summit crater. The pyroclastic activity continued through February from the gravity-driven collapsing flow fronts even though fountaining and lava effusion had decreased. Brief periods of fountaining and gravity-driven lava flow were noted throughout March 2018, but activity had essentially ceased by month's end.

Activity during 2016-2017. Very low seismicity of 0-2 volcanic earthquakes per day was typical for January and early February 2016; the largest number recorded was 12 on 9 January. On 12 February 2016, PHIVOLCS noted that seismicity had remained at baseline levels of 0-2 earthquakes per day for the previous six months, indicating that rock fracturing associated with magmatic activity had diminished. Ground deformation information suggested a return to pre-2014 eruption positions, and low levels of SO₂ flux had been consistent since November 2015. They reduced the Alert Level to 0.

Increasing SO₂ flux above 1,000 tons/day beginning in July 2016 was accompanied by ground deformation measurements suggesting renewed inflation. A brief swarm of 146 earthquakes was recorded by the Mayon Volcano Observatory's seismic network from 3-6 August; they were located 10 km away on the SE flank. This change led PHIVOLCS to raise the Alert Level back to 1 on 8 September 2016. Seismicity and SO₂ levels remained very low through the end of 2016, but GPS data suggested continued inflation. Slight inflation was recorded throughout 2017. Rare days of small seismic swarms of more than 10 earthquakes occurred during 2017, but otherwise seismicity and SO₂ flux values remained within background levels.

Activity during January 2018. A sudden phreatic eruption at 1621 local time on 13 January 2018 sent a gray steam-and-ash plume 2,500 m above the summit that drifted SW. The activity lasted for a little under two hours. Traces of ash fell on the Barangays of Anoling (4 km SW), Sua (6 km SW), Quirangay (9 km SW), Tumpa (9 km SW), Ilawod (10 km SW), and Salugan (8 km SW) in the city of Camalig and in the Barangays of Tandarora (26 km WSW), Maninila (8 km SW), and Travesia (10 km SW) in the municipality of Guinobatan. Incandescence at the summit crater was first observed a few hours later. As a result, PHIVOLCS raised the Alert Level from 1 to 2 early the next day.

Two more phreatic explosions occurred the following morning (14 January) at 0849 and 1143 that each produced ash plumes, but they were largely obscured by summit clouds. Minor amounts of ash were reported in Camalig. By the evening, PHIVOLCS had raised the Alert Level again to 3 after three explosions, 158 rockfall events, and the observation of bright incandescence at the summit crater. By 2000 on 14 January they noted the growth of a new lava dome and the beginnings of a lava flow towards the southern flank.

Two lava collapse events on the morning on 15 January each lasted 5-10 minutes. They originated from the lava flow front and produced rockfall and small-volume pyroclastic density currents. Ash plumes drifted SW and rained ash on Travesia, Muladbucad Grande, Maninila, Masarawag, Poblacion, Iraya, Ilawod, Calzada, Inamnan Grande, Inamnan Pequeno, Maguiron, Quitago and Mauraro in the municipality of Guinobatan and on the Baranguays of Cabangan, Anoling, Sua, Tumpa, Quirangay, Gapo, and Sumlang, and Baranguays 1 to 7 in the municipality of Camalig. A degassing event at 1107 produced a grayish to dirty white ash column that rose to a maximum of height of approximately 1,000 m above the summit before drifting WSW.

Lava effusion continued from the summit during 16-21 January 2018 with flows down the Mi-isi and Bonga gullies and occasional short-duration lava fountaining. Tens of daily lava collapse events accompanied the growth of the flow in the Mi-isi gully which had reached about 3 km from the summit by 18 January. Debris from the growing summit dome also descended the Matanag and Buyuan Gullies. Pyroclastic density currents descended the Mi-isi, Matanag, and Buyuan Gullies. Ash plumes rose up to 2 km and drifted SW from the summit crater and caused ashfall in Camalig, Guinobatan, and Polangui (figures 26-28).

Figure 26. Mayon emitted ash and steam along with pyroclastic density currents that flowed down the SW flank on 16 January 2018. View is looking N from S of the airport in Lagazpi City, Philippines, about 12 km S. Courtesy of The Express, photo from European Pressphoto Agency.

Figure 27. Pyroclastic density currents (PDC's) descended the W flank of Mayon on 16 January 2018. Incandescence at the base of the PDC was also visible. Lava was fountaining at the summit and incandescent blocks were rolling down the Mi-isi drainage on the S flank. Image taken near Legazpi city, 12 km S. Courtesy of The Express, photo from European Pressphoto Agency.

Figure 28. Lava flows at Mayon descended the Mi-isi drainage on the S flank and were visible from Legazpi city on 17 January 2018. Courtesy of The Express, photo from European Pressphoto Agency.

Activity increased on 22 January 2018 with lava fountains at the summit reaching 200-500 m high, the lava flow into the Mi-isi drainage extending beyond 3 km, and two new flows in the Bonga gully and upper Buyuan watershed. A dense 5-km-tall ash plume erupted at 1243 during a phreatomagmatic event that lasted for 8 minutes (figure 29). It generated pyroclastic density currents in several drainages within 4 km of the summit vent including Mi-isi, Bonga, Buyuan, Basud, San Andres, Buang, Anoling and other minor drainages. Ash was blown W and fell on the municipalities of Guinobatan, Camalig, Oas, Polangui and Iriga City. Five additional episodes of lava fountaining to 700 m occurred overnight that fed the Mi-isi and Bonga gully flows, and generated ash plumes to 2.5 and 3 km above the summit. This increase in activity led PHIVOLCS to raise the Alert Level to 4. By the following day, more than 50,000 people had evacuated to emergency shelters and civil aviation authorities temporarily closed airports in the cities of Legazpi and Naga.

Figure 29. The Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA's Aqua satellite acquired this image of the area around Mayon in the Philippines on 22 January 2018. The image combines natural-color data with thermal infrared bands (7-2-1). The substantial ash plume from the explosion that day rose to 10.9 km altitude and drifted NW and W, and the emerging lava dome appeared as a thermal hotspot at the summit. Courtesy of NASA Earth Observatory.

Numerous episodes of intense lava fountains during the nights of 23-26 January each lasted from a few minutes to more than an hour. They generated 150-600 m high fountains and continued to feed the flows in the Mi-isa and Bonga gullies. Ash plumes also rose from 0.5-5 km above the crater. The Mi-isa gully flow remained at 3 km from the summit, and the Buyuan flow had reached 1 km by 24 January. Pyroclastic density currents in the Mi-isi, Lidong/Basud, and Buyuan drainages were also observed. The PDCs in the Buyuan drainage traveled more than 5 km from the summit crater (figures 30-33).

Figure 30. Ash and steam plumes rose from the summit crater of Mayon while lava flows descended drainages on the S flank as seen from the town of Daraga, 10 km S, on 23 January 2018. Courtesy of The Express, photo from European Pressphoto Agency.

Figure 31. An ash plume rises, likely from a pyroclastic density current, in a drainage on the SE flank of Mayon, a few kilometers N of the town of Daraga on 23 January 2018. Courtesy of The Express, photo from European Pressphoto Agency.

Figure 32. Ash and pyroclastic density currents emerged from the summit of Mayon on 24 January 2018, sending ashfall to nearby communities and filling drainages with pyroclastic debris. Image taken from Daraga, 10 km S. Courtesy of The Express, photo from European Pressphoto Agency.

Figure 33. Lava flows were very active on the S flank of Mayon, visible from about 12 km SSE in Legazpi on 25 January 2018. Courtesy of The Express, AFP/Getty Images.

By the evening of 26 January 2018, the lava fountaining episodes had transitioned into aseismic lava effusion, feeding incandescent flows into the Bonga and Mi-isi gullies on the S flank, and advancing the flow in the Bonga significantly downslope to 1.8 km. Fewer fountaining episodes continued during 27-28 January. Heavy rainfall during 28-29 January remobilized deposits from pyroclastic density currents and generated sediment-laden stream flows in several channels (figure 34) and channel-confined lahars on the Binaan Channel.

Figure 34. Sediment-laden streams posed hazards to residents of Camalig (11 km SW) at Mayon on 28 January 2018 after heavy rains and numerous PDC's had filled the drainages with debris. Courtesy of The Express, photo from European Pressphoto Agency.

A significant increase in lava effusion and fountaining at the summit during the evening of 29 January 2018 fed PDCs into the Mi-isi and Bonga Gullies, and resulted in significant ashfall in Camalig and Guinobatan to the SW. Intermittent lava fountaining to 200 m, flow-front collapses that generated PDC events, low-level ash emissions, and slow lava effusion from the summit crater continued during 30 January-4 February (figures 35 and 36). The Mi-isi and Basud lava flows had advanced to 3.2 and 3.6 km, respectively, from the summit crater by 1 February, and the Bonga-Buyuan flow had advanced 4.3 km by 3 February.

Figure 35. Steam-and-ash plumes rose steadily above Mayon on 31 January 2018. Image taken at the port in Legazpi City, about 15 km S. Courtesy of The Express, Getty Images.

Figure 36. Lava effusion at the summit of Mayon had decreased from a week earlier (see figure 33) by 31 January 2018. Courtesy of The Express, Getty Images.

Activity during February-March 2018. Lava fountaining reached 550 m above the summit crater on 5 February and increased to near-continuous activity the next day. Lava flows and incandescent rockfalls were observed throughout the night in the Mi-isi and Bonga-Buyuan channels. High volumes of incandescent lava flows advanced to 3.2, 4.5, and approximately 3.0 km down the Mi-isi, Bonga-Buyuan and Basud channels. Pyroclastic density currents from the collapsing flow fronts reached 4.6, 4.4, and 4.2 km from the summit crater in the same drainages during 7 February. Near-continuous fountaining accompanied by steam plumes that rose up to 800 m continued through 10 February.

Lava fountaining became sporadic and weak beginning on 11 February. Heavy rainfall during 13 February generated channel-confined lahars in the Anoling channel. By 14 February, lava flows remained at 3.3 km, 4.5 km, and 900 m down the Mi-isi, Bonga and Basud gullies, and PDCs had deposited material to distances of 4.6, 4.5, and 4.2 km in the same drainages. Intermittent lava fountaining continued through 22 February. The fountains generally rose 100-600 m above the summit and were often audible more than 10 km from the summit.

Quieter lava effusion with fewer fountaining events was more typical behavior beginning on 23 February. Numerous episodes of lava-collapse pyroclastic density currents were visually observed on the Mi-isi, Basud, and Bonga-Buyuan Gullies within 2-4 kilometers of the summit crater during the second half of February. Deflation of the lower slopes that began on 20 February was recorded by electronic tiltmeter, consistent with the transition to seismically quieter lava effusion at the summit crater. However, the overall electronic tiltmeter and the continuous GPS data indicated that the volcano was still inflated relative to October and November 2017 levels.

Weak fountaining, lava effusion, and degassing were noted during 25-28 February. The sporadic fountains generated plumes that rose 800 m, and weak effusion continued to feed the flows in the drainages. Gravity-driven lava flow movement and degassing with ash plumes rising 600 m above the summit were the primary activity at Mayon on 1 March, although occasional lava fountaining events were still observed. Based on the decrease in activity at the summit, the decrease in seismicity, continued deflation, and significantly lower SO₂ emissions, PHIVOLCS lowered the Alert Level to 3 on 6 March 2018.

Brief periods of weak fountaining and lava flows were observed during 7-24 March. The fountaining generated dark gray ash plumes that rose 100-300 m above the summit crater before drifting SW, and were sometimes audible more than 10 km from the summit crater. At night, lava flows continued moving downslope within 3.3, 4.5, and 1.9 km of the crater in the Mi-isi, Bonga, and Basud gullies. Steam plumes rose as high as 2.5 km above the summit before drifting SW on 7 March. Intermittent bluish steam-laden plumes rose to 700 m before drifting SW on 14 March. A slight inflation of the lower flanks beginning on 11 March 2018 was recorded by electronic tiltmeters through at least 22 March. Overall deformation data indicated that the edifice was still inflated relative to pre-eruption baselines.

Beginning around 24 March 2018, the primary activity consisted of intermittent lava collapse events in the Mi-isi gully located between 4-5 km from the summit and steam-laden plumes that drifted SW from the summit. Lava flow effusion at the crater was last detected on 18 March. Ground deformation since 20 February 2018 recorded deflation despite short-term episodes of inflation of its lower and middle slopes, and incandescence at the summit had diminished from intense to faint. Lava flows had begun to stabilize, producing fewer rockfalls and infrequent pyroclastic density currents, the last of which was observed on 27 March 2018. This continued decrease in activity led PHIVOLCS to lower the Alert Level to 2 on 29 March 2018.

VAAC, SO₂, and MIROVA information. The Tokyo VAAC reported the first ash emission from Mayon on 13 January 2018 as a plume that rose to 5.2 km altitude and drifted SW. Many subsequent ash emissions were obscured by meteoric clouds and were only occasionally observed in satellite imagery. The ash plume from the large explosion on 22 January was observed in satellite imagery at 10.9 km altitude drifting NW. Numerous daily VAAC reports were issued through February; they were intermittent in March, ending on 23 March 2018. Plumes generally were reported at 5.2-7.6 km altitudes. Small sulfur dioxide plumes were captured by the OMI and OMPS satellite instruments on several days between 22 and 31 January 2018 (figure 37).

Figure 37. SO2 anomalies from Mayon were captured by the OMPS and OMI instruments on the SUOMI and AURA satellites during January 2018. Upper left: 22 January 2018; upper right: 23 January 2018; lower left: 26 January 2018; lower right: 31 January 2018. Courtesy of NASA Goddard Space Flight Center.

The MIROVA project thermal anomaly graph of log radiative power clearly captured the onset of activity at Mayon in mid-January 2018 (figure 38). Thermal activity increased through early February and then slowly decreased through mid-March 2018 when lava effusion ended.

Figure 38. The sudden onset of thermal activity at Mayon is apparent in this MIROVA project graph of log radiative power for the year ending on 11 May 2018. The data is based on the satellite-based MODIS infrared thermal imagery. Thermal activity peaked at the end of January and dropped off gradually through mid-March 2018; it then decreased abruptly after that. Courtesy of MIROVA.

Geologic Background. Symmetrical Mayon, which rises above the Albay Gulf NW of Legazpi City, is the most active volcano of the Philippines. The steep upper slopes are capped by a small summit crater. Recorded eruptions since 1616 CE range from Strombolian to basaltic Plinian, with cyclical activity beginning with basaltic eruptions, followed by longer term andesitic lava flows. Eruptions occur predominately from the central conduit and have also produced lava flows that travel far down the flanks. Pyroclastic flows and mudflows have commonly swept down many of the approximately 40 ravines that radiate from the summit and have often damaged populated lowland areas. A violent eruption in 1814 killed more than 1,200 people and devastated several towns.

Information Contacts: Philippine Institute of Volcanology and Seismology (PHIVOLCS), Department of Science and Technology, University of the Philippines Campus, Diliman, Quezon City, Philippines (URL: http://www.phivolcs.dost.gov.ph/); Tokyo Volcanic Ash Advisory Center (VAAC), 1-3-4 Otemachi, Chiyoda-ku, Tokyo, Japan (URL: http://ds.data.jma.go.jp/svd/vaac/data/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); NASA Earth Observatory, EOS Project Science Office, NASA Goddard Space Flight Center, Goddard, Maryland, USA (URL: http://earthobservatory.nasa.gov/); NASA Goddard Space Flight Center (NASA/GSFC), Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, 8800 Greenbelt Road, Goddard, Maryland, USA (URL: https://so2.gsfc.nasa.gov/); The Express (URL: https://www.express.co.uk); European Pressphoto Agency (EPA) (URL: http://www.epa.eu/); Getty Images (URL: https://www.gettyimages.com/); Agence France Presse (AFP) (URL: https://www.afp.com/).

Located 60 km SE of Mexico City, frequent historical eruptions have been reported from Popocatépetl going back to the 14th century. Activity increased in the mid-1990s after about 50 years of quiescence, and the current eruption, which has been ongoing since January 2005, has included frequent ash plumes and numerous episodes of lava-dome growth and destruction within the 500-m-wide summit caldera. Multiple emissions of steam and gas occur daily, rising generally 1-4 km above the 5.4-km-elevation summit; many contain small amounts of ash. Larger, more explosive events that generate ashfall in neighboring communities often occur every week.

Activity through July 2017 was typical of the ongoing eruption with near-constant emissions of water vapor, gas, and minor ash, as well as multiple explosions every week with ash-plumes and incandescent blocks sent down the flanks (BGVN 42:09). This report covers similar activity through February 2018. Information about Popocatépetl comes from daily reports provided by México's Centro Nacional de Prevención de Desastres (CENAPRED); ash emissions are also reported by the Washington Volcanic Ash Advisory Center (VAAC). Satellite visible and thermal imagery and SO₂ data also provide important observations.

Near-constant emissions of steam and gas, often with minor ash content, were typical activity for throughout August 2017-February 2018. Intermittent larger explosions with plumes of moderate ash content that generated ashfall in nearby communities were reported in most months, including several times during October and November 2017, reaching communities as far as 70 km away. Incandescence at the summit was often observed on clear nights, and Strombolian activity that sent incandescent blocks several hundred meters down the flanks occurred at least once each month during September 2017-January 2018. The tallest ash plumes during the period reached 9.1 km altitude in mid-October and 10.3 km altitude at the end of January 2018. Thermal anomalies were persistently detected in satellite data throughout the period, and SO₂ plumes were recorded every month with satellite instruments.

Activity during August-September 2017. The Washington VAAC reported satellite observations of an ash plume extending 55 km W of the summit at 6.4 km altitude on 31 July 2017; the plume was mostly gas and steam with a small amount of ash. CENAPRED reported ashfall in Ozumba (18 km W) on 1 August from a plume that rose 2 km above the summit. They also noted numerous low-intensity explosions with steam, gas, and ash during 5-7 August. A small explosion early on 14 August produced a 500-m-high plume with minor ash content that drifted SW. Two explosions later in the day generated ash plumes that rose 0.8 and 1.5 km from the summit and drifted W (figure 94). Another explosion on 15 August produced a plume over 1 km in height with moderate ash content. On 21 August CENAPRED reported an ash plume that rose 4 km and drifted NW (figure 95). The Washington VAAC reported this plume extending 33 km W from the summit at 7.6 km altitude. Later in the day the ash cloud was observed about 230 km W of the summit, and a new cloud at a slightly lower altitude had drifted 45 km NW.

Figure 94. An ash plume drifted W from Popocatépetl on 14 August 2017 as seen from the Tlamacas webcam located about 5 km N of the volcano. Courtesy of CENAPRED.

Figure 95. An ash plume at Popocatépetl rose 4 km above the summit on 21 August 2017 and drifted over 200 km W before dissipating. View is from the Altzomoni webcam, located about 10 km N of the summit. Courtesy of CENAPRED.

CENAPRED noted 22 explosions with ash during 25-26 August that drifted N and NW. They were observed in satellite imagery by the Washington VAAC at 7.6 km altitude. Eleven explosions with small amounts of ash were reported by CENAPRED on 27 August. There were daily explosions during 28-31 August, but weather clouds obscured views of the summit. Incandescence at the summit crater was observed on many clear nights during August.

During 1-11 September 2017 cloudy conditions generally prohibited observations of the summit, but low-intensity emissions of steam and gas were briefly observed, many containing minor ash. Five explosions with minor ash emissions were reported by CENAPRED on 12 September; the Washington VAAC noted the ash plume in satellite imagery at 6.7 km altitude drifting slowly N. CENAPRED reported 22 explosions with ash and incandescent rocks on the NE flank during 12-13 September.

The Washington VAAC reported ash plumes on 13 September at 8.2 km altitude, on 18 September at 6.4 km altitude drifting W, and on 23 September near 7 km altitude moving to the NNE. Numerous explosions were reported by CENAPRED during 27 and 28 September (figure 96). The Washington VAAC reported the dense ash plume from these explosions at 6.7 km altitude drifting WSW. It extended 130 km W of the volcano by early afternoon on 27 September. CENAPRED reported that an explosion late on 30 September sent incandescent fragments 0.8 km from the crater and produced a dense ash column that rose more than 2 km above the summit.

Figure 96. A dense ash emission from Popocatépetl on 27 September 2017 extended 130 km W before dissipating as viewed from the Altzomoni webcam, located about 10 km N of the summit. Courtesy of CENAPRED.

Activity during October-November 2017. The ash plume from the explosion late on 30 September 2017 was visible in satellite imagery the following morning located 15 km SW from the summit at 7.9 km altitude according to the Washington VAAC. CENAPRED reported three explosions on 2 October and five explosions the next day, causing ashfall in Atlautla (17 km W), Tepetlixpa (21 km W), and Ozumba. Three explosions on 5 October resulted in ashfall in Totolapan (32 km W), Tlalnepantla (40 km W), and Cuernavaca (64 km W), and closer to the volcano in Ecatzingo (15 km SW), Atlautla, and Tepetlixpa. Lahars were also observed on the W flank, but there were no reports of damage. Two more explosions on 6 October led to ashfall reported from Zacualpan de Amilpas (30 km SW) and Tetela del volcán (18 km SW) (figure 97). The Washington VAAC reported the 6 October emissions at 6.4 km altitude.

Figure 97. Webcam image showing one of the two explosions on 6 October 2017 at Popocatépetl that caused ashfall in Zacualpan de Amilpas (30 km SW) and Tetela del volcán (18 km SW). The Tlamacas webcam is located about 5 km N of the volcano. Courtesy of CENAPRED.

The first of two explosions on 7 October 2017, shortly after midnight, produced a plume that rose over 2 km and drifted SW with ashfall reported in Tetela del volcán; incandescent blocks were also sent down the flanks (figure 98). The second explosion produced an ash plume that rose 3 km and drifted NNE. The Washington VAAC reported continuing ash emissions during 7-11 October. Numerous plumes rose to 5.8-9.1 km altitude and drifted in several different directions; the plume extended 130 km SW from the summit on 10 October. CENAPRED reported three explosions on 8 October (figure 99) and two on 9 October. Numerous low-intensity exhalative events during 10-12 October produced ash plumes less than 1 km above the crater that drifted SW. Ashfall was reported in several communities during this time including Ozumba, México City (60 km NW), Milpa Alta (45 km NW), Xochimilco (56 km NW), Tlalpan (68 km NW), Coyoacán (66 km NW), Iztapalapa (57 km NW), Magdalena Contreras (72 km NW), and Iztacalco (64 km NW).

Figure 98. Incandescent blocks visible in this image traveled down the flanks of Popocatépetl during the early morning of 7 October 2017. The Tlamacas webcam is located about 5 km N of the volcano. Courtesy of CENAPRED.

Figure 99. Multiple explosions from Popocatépetl on 8 October 2017, including the one seen here, caused ashfall in several communities NW of the volcano. The Tlamacas webcam is located about 5 km N of the volcano. Courtesy of CENAPRED.

CENAPRED noted incandescence at the crater during most nights from 14 to 31 October, as well as steam, gas, and minor ash from hundreds of low-intensity emission events each day. The Washington VAAC reported ash emissions visible in satellite imagery on 16, 20-22, and 26 October drifting in several different directions at altitudes of 5.8-7.6 km. The plume observed on 22 October reached 60 km from the summit before dissipating. CENAPRED reported two explosions with ash plumes each day during 25-27 October. The Washington VAAC reported an ash plume on 29 October at 6.1 km altitude drifting E about 35 km from the summit, and another at 6.7 km the following day along with an infrared hotspot visible at the summit.

The Washington VAAC issued multiple daily ash advisories throughout November 2017. CENAPRED reported hundreds of daily low intensity emissions of gas and steam that often contained minor ash; the plumes generally rose about 1 km above the summit and most often drifted SW. They also observed incandescence at the crater on all clear nights. They reported Strombolian activity on 3 November in the early morning that lasted for several hours. Explosions early on 4 November resulted in minor ashfall in Yecapixtla (29 km SW) and Zacualpan de Amilpas and other areas to the SW. A Strombolian episode later that day lasted for about an hour and resulted in minor ashfall in Tetela del Volcán. Another explosion that night sent incandescent fragments 200 m down the flanks.

An explosion on 6 November sent an ash plume 2.5 km above the summit crater that drifted SW and sent incandescent fragments 500 m down the flank. Another explosion during the early morning of 7 November produced a 2-km-high ash plume. Moderate amounts of ash rose 1 km above the summit on 8 November. There were three explosions on 10 November; the largest produced a 3-km-high ash plume that drifted SW. Continuous low-level emission of gas and ash on 14 November resulted in ashfall reported in Totolapan, Yecapixtla, Ocuituco (23 km SW), Tetela del Volcán, and Ecatzingo. An explosion on 17 November sent an ash plume 2.5 km above the summit that drifted SW. During 18-19 November five explosions caused ash plumes to rise 2 km above the summit and incandescent blocks to fall down the E flank.

Around 1030 on 20 November, seismic activity increased and was accompanied by a constant plume of steam, gas, and moderate ash that rose about 1.5 km and drifted E. During 20-21 November eight explosions were reported, with five more the following day. During the afternoon of 23 November a continuous ash emission that lasted 90 minutes drifted SSE at 2 km above the summit, and spread ash over communities to the SSE including Huaquechula (30 km SSE), Tepeojuma (38 km SE), Atlixco (23 km SE), and Izúcar de Matamoros (50 km SE) (figure 100). Another significant ash emission during the afternoon of 24 November sent a column of ash to 4 km above the summit, drifting SSE; it lasted for almost two hours (figure 101). The Washington VAAC reported the plume at 8.5 km altitude. Ashfall was reported in San Pedro Benito Juárez (12 km SE) and Atlixco. Late that evening, an explosion sent incandescent fragments 1 km down the flanks and generated an ash plume that rose to 2.5 km above the summit and also drifted SSE.

Figure 100. A continuous ash emission at Popocatépetl that lasted for 90 minutes drifted SSE at 2 km above the summit, and spread ash over several communities to the SSE on 23 November 2017. The Tlamacas webcam is located about 5 km N of the volcano. Courtesy of CENAPRED.

Figure 101. A substantial ash emission at Popocatépetl during the afternoon of 24 November 2017 sent a column of ash to 4 km above the summit that drifted SSE; it lasted for almost two hours. The Washington VAAC reported the plume at 8.5 km altitude. The Altzomoni webcam is located about 10 km N of the summit. Courtesy of CENAPRED.

A flyover by CENAPRED and the Federal Police on 25 November 2017 allowed evaluation of the changes in the summit crater from the recent explosions. They noted that the internal crater within the summit crater had increased its dimensions, reaching a diameter of 370 m and a depth of 110 m (figure 102). A 3-km-tall ash plume resulted from continuous emissions that began in the afternoon of 27 November and lasted for two hours. The Washington VAAC reported the plume at 7.9 km altitude. The plume drifted SSE, and dispersed ash over communities in that region including Tochimilco (16 km), Izucar de Matamoros, Atlixco, and Huaquechula.

Figure 102. During a flyover on 25 November 2017, CENAPRED observed that the increased size of the internal summit crater at Popocatépetl was 370 m in diameter and 110 m deep. Courtesy of CENAPRED.

Activity during December 2017-February 2018. The Washington VAAC issued multiple daily reports of ash emissions during 1-12 and 24-31 December 2017. CENAPRED noted hundreds of daily low-intensity emissions of gas and steam, most with small quantities of ash, throughout December, as well as multiple ash emissions on many days that rose generally 1-2.5 km above the summit. In the early morning of 2 December an explosion caused an ash plume to rise 2.5 km above the summit. A second plume rose 1 km later that day; they both drifted SSE. An explosion in the afternoon of 9 December sent an ash plume over 2.5 km above the summit that drifted NE. The Washington VAAC reported the plume at 7.6 km altitude. Later that evening Strombolian activity sent incandescent blocks down the flanks and generated an ash plume that drifted E. Incandescence was observed at the summit crater during the nights of 17-21 and 24-29 December. Continuous emissions of steam, gas, and moderate-density ash were reported drifting NW for about 90 minutes on 29 December. An explosion on 31 December at 1032 generated a 2-km-high ash plume that also drifted NW.

There were multiple daily reports of ash emissions issued by the Washington VAAC during most days of January 2018. CENAPRED noted hundreds of daily low-intensity emissions of gas and steam, many with small quantities of ash, throughout the month, as well as explosions with ash emissions on many days that generally rose 1-2.5 km above the summit. They also observed incandescence at the summit crater multiple days each week. Ongoing low-level emissions of steam, gas, and minor ash were reported during 4-5 January. During the evening of 5 January activity increased, and the ash plume rose to 800 m and drifted SE. In addition, incandescent blocks were ejected 200-300 m down the flanks for about two hours.

An explosion on 18 January 2018 generated an ash plume that rose 1.5 km above the summit and drifted E while incandescent blocks were ejected up to 700 m down the flanks. An episode of Strombolian activity in the early morning of 25 January produced an ash plume that rose 2 km above the summit and drifted N and NE, resulting in reports of ashfall in San Pedro Nexapa (14 km NE) and Amecameca (19 km NE). It lasted for about 2 hours. Four explosions were reported during the afternoon of 29 January and an explosion the following afternoon produced an ash plume that rose more than 3 km above the summit, and was dispersed to the NW. An explosion on 31 January also produced a substantial ash plume that the Washington VAAC reported at 10.3 km altitude moving NNE (figure 103).

Figure 103. An ash plume rose to 10.3 km altitude from Popocatépetl on 31 January 2018 and drifted NNE. The Altzomoni webcam is located about 10 km N of the summit. Courtesy of CENAPRED.

Activity was somewhat quieter at Popocatépetl during February 2018. The Washington VAAC reported ash emissions on 14 days during the month. CENAPRED reported tens, not hundreds, of daily low-intensity emissions of gas and steam that often contained minor amounts of ash. They also noted one or more explosions with ash emissions on many days that rose generally 1-1.5 km above the summit and drifted in various directions. During many clear days they observed nearly constant emissions of steam, gas, and minor ash that reached 500-800 m above the summit. An explosion on 20 February produced an ash plume that rose 1.5 km above the summit. Continuous steam and gas emissions during 22-23 February were accompanied by minor incandescence intermittently observed at the summit.

Satellite data. Sulfur dioxide emissions were large enough to be recorded by satellite instruments several times every month during August 2017-February 2018 (figure 104). Variable wind directions and persistent emissions produced relatively long-lived plumes that dispersed over large areas of Mexico.

Figure 104. The OMI instrument on NASA's AURA satellite recorded evidence of significant monthly SO2 emissions at Popocatépetl, including on 27 September 2017 (upper left), 13 October 2017 (upper right), 31 October 2017 (lower left) and 25 December 2017 (lower right). Variable wind directions and persistent emissions produced relatively long-lived plumes that dispersed over large areas of Mexico. Courtesy of NASA Goddard Space Flight Center.

Thermal anomaly data provided by the MIROVA project are consistent with the visual record of persistent incandescent and explosive activity at the summit (figure 105). Multiple MODVOLC thermal alerts were also recorded every month from October 2017-February 2018.

Figure 105. Thermal anomalies detected by satellite-based MODIS instruments and recorded through the MIROVA project show the pattern of continued moderate-level activity at Popocatépetl during the year ending 12 July 2018. Courtesy of MIROVA.

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

Information Contacts: Centro Nacional de Prevención de Desastres (CENAPRED), Av. Delfín Madrigal No.665. Coyoacan, México D.F. 04360, México (URL: http://www.cenapred.unam.mx/), Daily Report Archive http://www.cenapred.unam.mx:8080/reportesVolcanGobMX/BuscarReportesVolcan); Washington Volcanic Ash Advisory Center (VAAC), Satellite Analysis Branch (SAB), NOAA/NESDIS OSPO, NOAA Science Center Room 401, 5200 Auth Rd, Camp Springs, MD 20746, USA (URL: www.ospo.noaa.gov/Products/atmosphere/vaac, archive at: http://www.ssd.noaa.gov/VAAC/archive.html); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Hawai'i Institute of Geophysics and Planetology (HIGP) - MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); NASA Goddard Space Flight Center (NASA/GSFC), Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, 8800 Greenbelt Road, Goddard, Maryland, USA (URL: https://so2.gsfc.nasa.gov/).

Indonesia's Sinabung volcano has been highly active since its first confirmed Holocene eruption during August and September 2010; ash plumes initially rose up to 2 km above the summit, and falling ash and tephra caused fatalities and thousands of evacuations (BGVN 35:07). It remained quiet after the initial eruption until 15 September 2013, when a new eruptive phase began that has continued uninterrupted through February 2018. Ash plumes rising several kilometers, avalanche blocks falling several kilometers down the flanks, and deadly pyroclastic flows travelling more than 4 km have all been documented repeatedly during the last several years. Details of events during October 2017-March 2018, including the largest explosion to date on 19 February 2018, are covered in this report. Information is provided by, Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG), referred to by some agencies as CVGHM or the Indonesian Center of Volcanology and Geological Hazard Mitigation, the Darwin Volcanic Ash Advisory Centre (VAAC), and the Badan Nacional Penanggulangan Bencana (National Disaster Management Authority, BNPB). Additional information comes from satellite instruments and local observers.

When activity began in 2010, and again when eruptions resumed in 2013, many news accounts included statements that Sinabung had last been active 400 years ago, or even saying specifically that the last eruption was in 1600 CE. Those claims appear to have been caused by a misunderstanding related to the boundary time that Indonesian volcanologists use to categorize volcanoes. Those volcanoes with historical activity, defined as being about 400 years ago (corresponding to the beginning of the Dutch East India Company era), are in the "Type A" group. Those in the "Type B" group, including Sinabung prior to 2010, have not had reported activity in more than 400 years. Using charcoal associated with the most recent pyroclastic flow, Hendrasto et al. (2012) determined that the last previous eruptive activity was 1200 years before present using carbon dating techniques, or 740-880 CE (at 1 sigma).

Although activity remained high from October 2017 through March 2018, a gradual decline in the overall eruptive activity from the beginning of 2017 was apparent. The number of explosions per month generally declined, with no explosions reported during March 2018, for the first time since August 2013 (figure 45). The thermal anomaly record was similar; periods of high heat flow persisted through mid-November 2017, followed by a gradual reduction in the amount of thermal activity, although the intensity remained consistent, according to the MIROVA project (figure 46). Much of the heat flow was attributed to the dome growth at the summit; the dome was destroyed in the large explosion of 19 February 2018.

Figure 45. The number of explosions per month at Sinabung as reported by PVMBG from January 2017-March 2018. Only partial data was reported for 18-31 January 2018, and no explosions were observed during March 2018.

Figure 46. Thermal anomaly data at Sinabung from satellite-based MODIS instruments, plotted on a Log Radiative Power scale, persisted through the end of 2017 and then decreased in frequency through the end of February 2018. Much of the heat flow was attributed to a dome near the summit which was destroyed in the 19 February 2018 explosion. Graph shows thermal anomalies between 11 May 2017 and 1 April 2018. Courtesy of MIROVA.

Throughout the period from October 2017 through 19 February 2018, steam plumes were constantly rising to heights of 1,000-2,400 m above the summit. Avalanche blocks were ejected daily down the E and S flanks from 500-3,500 m, and multiple pyroclastic flows each month traveled between 1,000 and 4,600 m down the SE flank. Tens of explosions occurred monthly, generating ash plumes that rose from 500 to 5,000 m above the summit. Explosive activity was more intermittent during February than the previous months, until 19 February when the largest explosion to date occurred; it included an ash plume that rose to at least 16.8 km altitude and at least ten pyroclastic flows. In spite of the size of the explosion, no injuries or fatalities were reported as most nearby communities had been evacuated from the ongoing activity. Activity decreased substantially during March 2018; there were no explosions, block avalanches, or pyroclastic flows reported, only steam plumes rising 1,000 m above the summit.

Activity during October 2017-January 2018. During October 2017, steam plume heights reached 1,500 m above the summit. Avalanche blocks traveled down the E and S flanks 500-2,500 m, and eight pyroclastic flows traveled 1,000-4,500 m down the SE and S flanks. Ash plume heights ranged from 500 to 3,600 m above the summit. The Darwin VAAC issued 38 aviation alerts during the month. On 1 October they reported an ash plume drifting both NW at 4.6 km altitude and NE at 3.7 km. The next day, the webcam observed an ash emission that rose to 5.5 km altitude. On 4 October an ash plume was spotted in the webcam rising to 5.8 km altitude and drifting ENE. Later that day it had detached from the volcano and was seen drifting NW in satellite imagery. An ash plume on 5 October rose to 3.9 km altitude and drifted ESE. Two ash emission were reported on 7 October; the first rose to 3 km altitude, the second rose to 4.3 km, they both dissipated quickly. On 8 October, three plumes were reported. The first rose to 4.6 km and drifted WSW, the second rose to 3 km and drifted S and the third rose to 3.4 km and also drifted S. The following day, an ash plume rose to 4.6 km and drifted E. BNPB stated that on 11 October, an event at Sinabung generated an ash plume that rose 1.5 km above the crater and drifted ESE, causing ashfall in several local villages. On 12 October an event produced an ash plume that rose 2 km above the crater and was followed by pyroclastic flows traveling 1.5 and 2 km down the S and ESE flanks, respectively.

PVMBG reported ash plumes rising to 3.7 km on 11, 12, and 13 October 2017. Later on 13 October the Jakarta MWO reported an ash plume at 4.3 km. The next day PVMBG reported an ash plume at 5.5 km altitude. A plume on 15 October rose to 3 km and drifted E. A steam plume on 16 October drifted down the SE flank before drifting SE no 16 October (figure 47). On 17 October, a discrete emission rose a few hundred meters above the summit drifted NE. Later that day, an ash plume was seen in the webcam moving SE at 3.4 km. On 18 October, two ash emissions were reported. The first rose to 3.7 km and drifted E, the second rose to 3.9 km and drifted W. An ash plume rose to 4.6 km altitude on 21 October, and to 3.9 km, drifting S, on 23 October. The next day, three ash plumes were reported; the first rose to 3 km, the second to 4.6 km, and the third to 3.7, all drifting E. After five days of quiet, the webcam observed ash plumes that rose to 4.3 km on 30 October, and to 3.9 km on 31 October. Only two MODVOLC thermal alerts were issued, on 20 and 27 October.

Figure 47. A steam plume drifted down the SW flank of Sinabung before moving SE on 16 October 2017. View is from the SE. Courtesy of PVMBG.

Steam plumes were higher during November 2017, rising 2,400 m above the summit. Block avalanches traveled 500-3,000 m down the E and S flanks most days, and ten pyroclastic flows traveled between 2,000-3,500 m down the ESE and S flanks. The ash plumes rose 700-3,200 m above the summit. The Darwin VAAC issued 41 aviation alerts in November. Near-daily ash plumes were observed mostly in the webcam and occasionally in satellite imagery. They generally rose to 3.4-4.9 km altitude; the most common drift directions were S and SW. A number of times, multiple ash plumes were reported in a single day. On 14 November, four ash plumes were observed. The first rose to 3.7 km, the second and third rose to 4.6 km and drifted S and SSW, the last rose to 3.9 km and also drifted SSW. On 20 November a discrete emission produced an ash plume that rose to 5.5 km altitude and drifted SSW. Three ash plumes were recorded the next day, rising 3.9-4.6 km and drifting in multiple directions under variable winds. An ash plume on 23 November was reported by PVMBG at 6.7 km altitude drifting W, the highest noted for the month. MODVOLC thermal alerts appeared twice on 5 November, once on 14 November, and three times on 17 November.

Activity during December 2017 was similar to the previous two months; steam plumes rose 2,000 m above the summit, block avalanches traveled 500-3,500 m down the E and S flanks numerous times, and nine pyroclastic flows descended the ESE and S flanks distances ranging from 2,000 to 4,600 m. Ash plume heights were from 700-4,000 m above the summit. The Darwin VAAC issued 43 aviation alerts in December 2017. They reported ash plume heights of 3.4-4.9 km altitude on most days. Every day during 10-19 December, ash plumes were reported at altitudes of 4.6-5.5 km drifting SW, E or SE. PVMBG reported ash plumes on 26, 27 and 28 December that rose to 3.9, 5.2, and 5.5 km, respectively. BNPB reported pyroclastic flows on 27 December that traveled 3.5-4.6 km SE, and ashfall was reported in many nearby villages including Sukanalu Village (20 km SE), Tonggal Town, Central Kuta, Gamber (4 km SE), Berastepu (4 km SE), and Jeraya (6 km SE). The highest ash plume of the month rose to 6.4 km altitude on 29 December and drifted E. This was followed by another discrete ash emission the same day that rose to 5.8 km and two plumes the next day that rose to 5.2 km and drifted W. There was only one MODVOLC thermal alert issued on 7 December.

The Darwin VAAC issued 56 aviation alerts for January 2018. Multiple discrete ash emissions were reported on most days. Plume altitudes generally ranged from 3.4 to 5.5 km. A 6.1 km altitude plume was visible in satellite imagery on 18 January (figure 48). The drift directions were highly variable throughout the month. Most plumes dissipated within six hours. Incandescent blocks were reported by PVMBG falling 500-1,500 m down the ESE flank on most days when the summit was visible. They also reported a pyroclastic flow on 27 January that traveled 2,500 m ESE from the summit (figure 49). Three MODVOLC thermal alerts were issued on 6 January, and one on 12 January.

Figure 48. An ash plume rose 3,000 m from the summit of Sinabung on 18 January 2018 in this view looking at the SE flank. Photographer unknown, courtesy of Sutopo Purwo Nugroho, Twitter.

Figure 49. A pyroclastic flow descended 2,500 m down the SE flank of Sinabung on 27 January 2018 while an ash plume also drifts SE in this view of the SE flank. Photographer unknown, courtesy of Sutopo Purwo Nugroho, Twitter.

Activity during February 2018. During most of February, steam plumes rose only 1,000 m above the summit, and avalanche blocks traveled 500-2,500 m down the ESE and S flanks. Far fewer ash emissions were reported than previous months, but the largest explosive event recorded to date took place on 19 February (figure 50). The Darwin VAAC issued 29 aviation alerts during February 2018. Short-lived ash emissions were reported on 1, 3, 5, 11, and 15 February. The ash plume heights ranged from 3.4-4.6 km altitude, and they drifted S or SW.

Figure 50. A very large ash plume rose to 16.8 km altitude from Sinabung on 19 February 2018. Image is from several tens of kilometers from the volcano a few hours after the eruption. No fatalities were reported. Photographer unknown, courtesy of Sutopo Purwo Nugroho, Twitter.

The large explosion was first reported by the Darwin VAAC at 0255 UTC on 19 February 2018. It produced an ash plume, which was clearly observed in satellite imagery (figure 51), that quickly rose to at least 16.8 km altitude and began drifting NW (figure 52). It also produced a large SO₂ plume that was recorded by satellite instruments (figure 53). Over the next 15 hours the plume dispersed in three different directions at different altitudes. The highest part of the plume drifted NW at 13.7 km and was visible over 300 km from the summit. The lower part of the plume drifted S initially at 6.7 km and gradually lowered to 4.3 km; it was visible 75 km from the summit before dissipating. A middle part of the plume drifted NW at 9.1 km during the middle of the day. Three subsequent minor ash emissions were observed on 20 and 25 February that rose to 3.4 km altitude. There were no VAAC reports issued during March 2018. A MODVOLC thermal alert issued on 11 February was the last for several months.

Figure 51. The Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA's Terra satellite captured this natural-color image of the ash plume at Sinabung at 0410 UTC on 19 February 2018, just a few hours after it began. The ash plume rose over 16 km high and drifted in multiple directions. Courtesy of NASA Earth Observatory.

Figure 52. The large ash plume of 19 February 2018 at Sinabung, viewed here from within a few kilometers of the summit in the first hour or so after the eruption, rose quickly to over 16 km altitude. Photographer unknown, courtesy of Sutopo Purwo Nugroho, Twitter.

Figure 53. Two different Ozone Monitoring Instruments measured the SO2 plume released by Sinabung in the explosion on 19 February 2018. The upper left image was recorded about three hours after the explosions (0616-0621 UTC, 19 February 2018) by the Ozone Mapper Profiler Suite (OMPS) instrument on the Suomi NPP satellite. The upper right image was recorded about 27 hours after the explosion (0619-0802 UTC, 19 February 2018) by the Ozone Monitoring Instrument (OMI) on the Aura satellite, and shows the multi-directional dispersal of the SO2 plume during that time. The lower image uses the data captured at the same time as the upper left image and displays it using different software and detailed background information. The maximum gas concentrations reached 140 Dobson Units. Upper images courtesy of NASA Goddard Space Flight Center, and lower image courtesy of NASA Earth Observatory.

As many as 10 pyroclastic flows were observed during the 19 February explosion, traveling as far as 4.9 km SSE and 3.5 km E (figures 54 and 55). Ash and tephra as large as a few millimeters in diameter fell in areas downwind, including Simpang Empat (7 km SE), the Namanteran district, Pqyung (5 km SSW), Tiganderket (7 km W), Munthe, Kutambaru (20 km NW), Perbaji (4 km SW), and Kutarayat (figure 56 and 57).

Figure 54. A pyroclastic flow traveled several kilometers SSE from Sinabung on 19 February 2018 as tephra fell from the rising ash cloud in this view from several kilometers away to the NE. Photographer unknown, courtesy of Sutopo Purwo Nugroho, Twitter.

Figure 55. The dark gray ash plume rose skyward while the large brown pyroclastic flows traveled SE from Sinabung on 19 February 2018 as viewed from the town of Kutarakyat located 5 km NE of the volcano. Photo by Endro Rusharyanto, courtesy of the Associated Press (AP).

Figure 56. Small tephra fragments fell on the village of Gurukinayan (13 km E) and other villages SE of Sinabung during the eruption of 19 February 2018. Photographer unknown, courtesy of Sutopo Purwo Nugroho, Twitter.

Figure 57. Ash from the eruption at Sinabung on 19 February 2018 covered vegetable plants the following day in the village of Payung (5 km SSW). Photograph by Antara Foto, Ahmad Putra via Reuters.

Villagers were temporarily evacuated from nearby villages, but were able to return a few days later (figure 58). Conditions in five districts were so dark that visibility was reduced to about 5 m. In addition, ashfall was recorded as far away as the town of Lhokseumawe, 260 km N. Magma Indonesia reported that the lava dome that had been growing at the summit for some time was destroyed in the 19 February explosion (figure 59). A PVMBG volcanologist reported the volume of the destroyed lava dome was at least 1.6 million cubic meters.

Figure 58. Villagers from Gurukinayan (13 km E) were evacuated as ash spread over the town from the eruption of Sinabung on 19 February 2018, but they returned to their homes a few days later. Photographer unknown, courtesy of Sutopo Purwo Nugroho, Twitter.

Figure 59. The summit of Sinabung, before (top) and after (bottom) the large explosion of 19 February 2018. The dome size in the upper photo is similar to that shown figure 43 (BGVN 42:12) from September 2017. The lower image was taken within a week after the explosion. Courtesy of MAGMA Indonesia, via Twitter.

Reference: Hendrasto M, Surono, Budianto A, Kristianto, Triastuty H, Haerani N, Basuki A, Suparman Y, Primulyana S, Prambada O, Loeqman A, Indrastuti N, Andreas A S, Rosadi U, Adi S, Iguchi M, Ohkura T, Nakada S, Yoshimoto M, 2012. Evaluation of Volcanic Activity at Sinabung Volcano, After More Than 400 Years of Quiet. Journal of Disaster Research, vol. 7, no. 1, p. 37-44.

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: 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, Indonesia (URL: http://www.bnpb.go.id/); Sutopo Purwo Nugroho, Head of Information Data and Public Relations Center of BNPB via Twitter (URL: https://twitter.com/Sutopo_PN); MAGMA Indonesia, Kementerian Energi dan Sumber Daya Mineral (URL: https://magma.vsi.esdm.go.id/); 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/); NASA Earth Observatory, EOS Project Science Office, NASA Goddard Space Flight Center, Goddard, Maryland, USA (URL: http://earthobservatory.nasa.gov/); NASA Goddard Space Flight Center (NASA/GSFC), Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, 8800 Greenbelt Road, Goddard, Maryland, USA (URL: https://so2.gsfc.nasa.gov/); Associated Press (AP), Endro Rusharyanto, Photographer (URL: http://www.ap.org/); Reuters (http://www.reuters.com/).

Confirmed historical eruptions at Stromboli go back 2,000 years; this island volcano in the Tyrrhenian Sea has been a natural beacon with its near-constant fountains of lava for eons. Eruptive activity at the summit consistently occurs from multiple vents at both a north crater area (N Area) and a southern crater group (S or CS Area) on 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 island. Thermal and visual cameras that monitor activity at the vents are located on the nearby Pizzo Sopra La Fossa, above the Terrazza Craterica, and at a location closer to the summit craters.

Eruptive activity during January-October 2017 peaked during June and then declined through August, returning to background levels in September; it included intermittent periods of frequent explosions from both crater areas that sent ash, lapilli, and bombs across the Terrazza Craterica and onto the head of the Sciara del Fuoco (BGVN 43:02). This report covers similar activity from November 2017-February 2018. Weekly reports of activity were provided by Italy's Instituto Nazionale de Geofisica e Vulcanologia (INGV), Sezione de Catania, which monitors the gas geochemistry, deformation, and seismicity, as well as surficial activity.

An explosive sequence on 1 November 2017 followed less than two weeks after a similar event on 23 October (BGVN 43:02) in the CS Area, creating Strombolian activity that sent ejecta 300 m high. Intermittent explosions and spattering continued until the next large explosion on 1 December, also in the CS Area. A general increase in seismicity was recorded during December 2017; intense spattering in the N Area on 15 December formed a lava flow that traveled 100 m N from the rim of the vent before stopping. The number of explosive events remained high (more than 20 per hour) through December, when both the intensity and rate of activity declined significantly, reaching levels below 10 events per hour in early February, and remaining there for the rest of the month. The general levels of intensity in the N and CS Areas, apart from the larger explosive events, were variable throughout November 2017-February 2018, generally increasing during December and decreasing during January (table 3). This pattern of activity is also reflected in the variation of the thermal activity that was recorded in the MIROVA thermal data during that time (figure 117), and the MODVOLC thermal alert data which recorded two alerts in November, and 14 in December, but none after that through February 2018.

Table 3. General intensity and activity levels at the summit vents in the N Area and CS Area at Stromboli, November 2017-February 2018. Intensity values correspond to the height of the ejecta above the vent: Low = less than 80 m high, Med-Low = less than 120 m High, Medium = less than 150 m high, Med-High = sometimes to 200 m, High = over 200 m. Coarse ejecta consisted of lapilli and bombs, and fine ejecta was primarily ash and smaller lava fragments.

Figure 117. MIROVA thermal data for Stromboli for the year ending on 2 May 2018 showed a gradual increase in thermal energy during mid-November 2017, peaking in mid-December, and then decreasing rapidly in early January to low levels by the end of the month that persisted through February 2018. Courtesy of MIROVA.

On 1 November 2017 at 0829 UTC a strong explosive sequence that lasted about 2 minutes was observed in the CS Area of the Terrazza Craterica (figure 118). The first explosion sent bombs and lapilli around the slopes of the terrace and the ejecta exceeded 300 m in height. Two more explosions followed soon after, sending material about 150 m into the air.

Figure 118. The explosive sequence of 1 November 2017 at Stromboli, taken from the INGV thermal and visual cameras at the 400 m level sent ash, bombs, and lapilli as high as 300 m. The time period covered by the explosions is about two minutes. Courtesy of INGV (Report 45/2017, Bollettino settimanale sul monitoraggio vulcanico, geochimico, delle deformazioni del suolo e sismico del vulcano Stromboli del 07/11/2017).

A survey by INGV scientists during 3-5 November 2017 evaluated the effects of this and the previous explosion on 23 October on the Terrazza Craterica. They noted that a large depression with a vent at the base, formed in the CS Area after the 23 October explosions, had been significantly enlarged during the 1 November explosions. Continuous spattering and strong incandescence were observed during the survey at the 4-m-wide C vent. They also observed that the explosive activity at S2 was produced by three emission points. They noted that the N1 site consisted of a single hornito and a secondary vent on the side flank (figure 119).

Figure 119. Several changes to the Terrazza Craterica at Stromboli were visible after the two strong explosive sequences of 23 October and 1 November 2017. a) The Terrazza Craterica on 5 November 2017; b) vent C on 30 September 2017 and c) on 5 November 2017 after the two major explosions; d) vent N1 on 30 September and e) on 5 November 2017. Photograph by D. Andronicus, courtesy of INGV (Report 45/2017, Bollettino settimanale sul monitoraggio vulcanico, geochimico, delle deformazioni del suolo e sismico del vulcano Stromboli del 07/11/2017).

The 23 October 2017 explosions ejected light brown scoriaceous material S and SE, almost reaching the Pizzo Sopra La Fossa 300 m to the E. A wide band of lithic blocks was also observed on the N flank of the W part of the Valle della Luna, an open area located S of the Terrazza, over a ridge at a higher elevation. During the 1 November explosions abundant black scoriaceous material formed spatter that covered the entire Terrazza Craterica and reached the W wall of the Pizzo facing the craters. Some of this material additionally landed on the NW ridge of the Valle della Luna and on its N flank. Blocks as large as 2 m were ejected during the 1 November event, along with reddish debris that dispersed in a wide area of the Terrazza Craterica and onto the SE flank at the S end of the Pizzo.

Vent C exhibited continuous degassing activity interrupted by short spattering episodes observed mainly on 15 and 21 November 2017. During 20-24 November, a new vent opened between vents S2 and C, which was sporadically active with incandescence and small explosions of fine-grained material. Three emission points were active from the C vent area at the end of November (figure 120).

Figure 120. The two crater areas on the Terrazza Craterica at Stromboli are visible from the thermal camera on the Pizzo Sopra La Fossa, seen here on 27 November 2017. The abbreviations and arrows indicate the names and locations of the active vents. Three emission points were active at vent C at the end of November 2017. Courtesy of INGV (Report 48/2017, Bollettino settimanale sul monitoraggio vulcanico, geochimico, delle deformazioni del suolo e sismico del vulcano Stromboli del 28/11/2017).

On 1 December 2017 at 1242 UTC a strong new explosive sequence in the CS crater area was recorded by the seismic network, although weather conditions permitted only observations of incandescence during the event. A large crater was noted a few days later in the area where the three emission points had been active at vent C. A general increase in seismic activity was observed beginning on 4 December that included increases in tremor amplitude, frequency and amplitude of VLP quakes, and the amplitude of explosion earthquakes. On 9 December, numerous explosions from vent S2 combined with strong winds and sent debris as far as the Pizzo Sopra La Fossa located 300 m E (figure 121).

Figure 121. The infrared camera on the Pizzo Sopra La Fossa captured an explosion produced by vent S2 in the CS Area at Stromboli on 9 December 2017; ejecta reached the Pizzo area. Courtesy of INGV (Report 50/2017, Bollettino settimanale sul monitoraggio vulcanico, geochimico, delle deformazioni del suolo e sismico del vulcano Stromboli del 12/12/2017).

The general increase in seismicity continued into the second week of December 2017. On 15 December 2017 intense spattering began at vent N1 at 1019 UTC. At 1330 the lava overflowed the crater rim and flowed N towards the Pianoro area, the N facing slope of the Terrazza Craterica, reaching about 100 m from the rim of N1 before stopping by 1530 that afternoon (figure 122).

Figure 122. Images taken by the infrared camera at the 400 m level of the lava overflow on 15 December 2017 from the N1 vent at Stromboli. Courtesy of INGV (Report 51/2017, Bollettino settimanale sul monitoraggio vulcanico, geochimico, delle deformazioni del suolo e sismico del vulcano Stromboli del 19/12/2017).

A survey by INGV scientists on 15 December 2017 revealed that the biggest change caused by the 1 December explosion was the formation of a new cone at vent S2 (figure 123a) with an inner crater that was almost 40 m wide. Emissions of dark ash 2-3 times per hour were observed along with spattering and ejected blocks of lava. Vent C, which had been a small pit crater prior to the explosion (figure 123b), had become a small cone that was degassing from the crater, with two smaller lateral vents exhibiting weak but continuous spattering activity (figure 123c). Vent N2 was characterized by infrequent Strombolian activity (1-2 explosions per hour). Most of the activity on 15 December was at vent N1 (figure 123a, e), where INGV scientists observed a new vent with continuous and increasing spattering that soon formed a lava flow. The flow traveled quickly across the crater area. Between 1300 and 1420, 3-4 violent and prolonged explosions at N1 ejected lava fragments tens of meters from at least four emission points. The area was covered with abundant scoriaceous material with average dimensions of 5-6 cm, and numerous fragments of black scoriaceous spatter ranging in size from 20 to 40 cm long; a few were as large as 100 cm.

Figure 123. INGV scientists recorded the changes at Stromboli's summit on 15 December 2017 that resulted from the explosions of 1 December, as well as events that day that generated a short lava flow. a) the Terrazza Craterica on 15 December 2017; b) vent C on 5 November and c) on 15 December after the explosions of 1 December created a cone; d) vent N1 on 5 November and e) on 15 December; the lava flows were produced by vents N1a and N1d. Photo by D. Andronicus, courtesy of INGV (Report 51/2017, Bollettino settimanale sul monitoraggio vulcanico, geochimico, delle deformazioni del suolo e sismico del vulcano Stromboli del 19/12/2017.

Activity diminished during January 2018; low- to medium-intensity explosions were typical in the N Area and degassing continued with intermittent explosive activity at the CS Area. During February 2018 activity decreased further with the overall explosion rate averaging generally less than 10 events per hour, a significant decline after the increases in activity that began in early November 2017 (figure 124).

Figure 124. The hourly frequency of the explosive events at Stromboli as recorded by the surveillance cameras from 1 July 2017-5 March 2018, averaged by day. The information is grouped by explosions at the N Area and the CS Area, and also shown as the total average. The Total value is the sum of the average hourly frequency by day of all the explosive events produced by the active vents. Courtesy of INGV (Repprt 10/2018, Stromboli, Bollettino Settimanale, 26/02/2018 - 04/03/2018, issue date 06/03/2018).

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/).