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/).

Ahyi seamount is one of a long string of submarine seamounts at the northern edge of the Northern Mariana Islands, part of the Mariana Back-arc segment of the Izu-Bonin trench in the western Pacific Ocean. 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 further activity was reported until a new eruption was detected by seismic stations and felt by divers in the immediate area in April 2014. Volcanic activity in the Commonwealth of the Northern Mariana Islands is monitored by the US Geological Survey's Volcano Hazards Program, and observations are sometimes gathered by NOAA (National Oceanic and Atmospheric Administration) expeditions. The 2014 eruption and follow-up observations from December 2014 are summarized here.

The eruption at Ahyi seamount between 24 April and 17 May 2014 (BGVN 39:02; Haney et al., 2014) was first recorded as T-phase signals that were detected by various seismometers in the Mariana Islands. Submarine explosions were also heard and felt by NOAA scuba divers conducting coral reef research on the SE coastline of Farallon de Pajaros (Uracas) Island, about 20 km NW of Ahyi. In the same area, the NOAA crew reported sighting mats of orange-yellow bubbles on the water surface that extended up to 1 km from the shoreline. T-phase seismic signals registered across the Northern Mariana Islands (NMI) seismic network at a rate of approximately 10 per hour until 8 May, and then sporadically until 17 May (Haney et al., 2014).

During mid-May, the NOAA ship Hi'ialakai gathered multibeam sonar bathymetry and took three water-column CTD casts (Conductivity, Temperature, and Depth sensor; it gives scientists a precise and comprehensive charting of the distribution and variation of water temperature, salinity, and density). The May 2014 bathymetry revealed that the minimum depth to the summit was about 90 m, notably deeper than the 60 m measured during a 2003 survey. In addition a new crater about 100 m deep had formed at the summit, replacing the summit cone. Also, a distinct landslide chute descended the SE slope 2,300 m, removing material from the head and depositing debris at the base (see figure 4, BGVN 39:02). Significant particle plumes were detected with all three CTD casts, indicating ongoing hydrothermal activity. Plumes with optical anomalies up to 0.4 NTU (nephelometric turbidity units) were found S and W of Ahyi at 100-175 m water depth, corresponding to the depth of the new summit crater. NTU's are light backscattering measurements done by optical sensors in sea water to determine the presence of hydrothermal plumes in the water column.

On 4 December 2014, the NOAA Expedition "Submarine Ring of Fire 2014 – Ironman" visited Ahyi, and again used a CTD sensor to assess the hydrothermal status of the volcano. EM122 multibeam bathymetry data imaged CO₂ gas bubbles rising from the summit (figure 5), and clearly revealed the new summit crater. When the CTD sensor and sampling package was lowered into the water, it measured a thick plume of particles indicating ongoing hydrothermal activity near 150 m depth, close to the base of the new crater that formed during the eruption in April-May 2014.

Figure 5. Three-dimensional image of the summit of Ahyi submarine volcano gathered on 4 December 2014 with the mid-water data shown above the new crater created by the April 2014 eruption. The summit crater is ~100 m deep. CO2 bubbles (in green) can be seen rising from most of the summit, suggesting that there is more than one source of venting. This image shows an area 850 m across with depths ranging from 78 (red) to 400 m (blue). No vertical exaggeration. Image courtesy of Submarine Ring of Fire 2014 - Ironman, NSF/NOAA (http://oceanexplorer.noaa.gov/explorations/ 14fire/logs/december04/media/ahyi.html).

References: Haney, M. M., Chadwick, W., Merle, S. G., Buck, N. J., Butterfield, D. A., Coombs, M. L., Evers, L. G., Heaney, K. D., Lyons, J. J., Searcy, C. K., Walker, S. L., Young, C., and Embley, R. W., The 2014 Submarine Eruption of Ahyi Volcano, Northern Mariana Islands, American Geophysical Union, Fall Meeting 2014, abstract V11B-4727.

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: National Oceanic and Atmospheric Administration (NOAA), Office of Ocean Exploration and Research, 1315 East-West Highway, Silver Spring, Maryland, USA (URL: http://oceanexplorer.noaa.gov/welcome.html); US Geological Survey, Volcano Hazards Program (USGS-VHP), 12201 Sunrise Valley Drive, Reston, VA, USA (URL: https://volcanoes.usgs.gov/index.html).

Russia's Alaid volcano, located just off the southern tip of the Kamchatka Peninsula, is the northernmost of the chain of volcanoes that comprise the Kuril archipelago. A number of strong explosive eruptions have been recorded there in the last 200 years, including VEI 4 explosions in 1790 and 1981. The last eruption occurred between 5 October and 12 December 2012 when repeated thermal anomalies and ash plumes from the summit crater were observed. A new eruption was first reported on 29 September 2015 by the Tokyo Volcanic Ash Advisory Center (VAAC) (BGVN 41:06). Alaid is monitored by the Kamchatka Volcanic Eruptions Response Team (KVERT); valuable information about this remote site is also gathered from satellite thermal infrared data reported by both the University of Hawai'i's MODVOLC system and the Italian MIROVA system.

A new eruption at Alaid was reported on 29 September 2015. It was characterized by strong thermal anomalies and intermittent gas-and-ash plumes. The thermal anomalies were interpreted by KVERT as Strombolian eruptions and lava flows. The first episode of the eruption exhibited strong thermal anomalies with only two reports of ash, and lasted until 4 January 2016. The second episode began with the reappearance of a strong thermal anomaly and an ash plume on 20 February 2016. This was followed by a series of low-level ash plumes in March and April, and ongoing strong thermal anomalies through early May. The anomalies decreased during mid-May and June, but then a large spike of intense anomalies in the first week of July was accompanied by ash plumes and observations by KVERT of Strombolian eruptions at the summit crater and a lava flow down the SW flank. Thermal activity decreased substantially following this spike, and tapered off completely by the second week of August 2016.

The Tokyo VAAC reported an eruption at Alaid at 2120 UTC on 28 September (0720 on 29 September local time) 2015. They reported it as below 6.1 km altitude, and volcanic ash was not identifiable in satellite images. KVERT raised the Aviation Color Code from Green to Yellow early on 2 October 2015 (local time) based on an intense thermal anomaly observed during the night that they interpreted to be the beginning of a new Strombolian eruption. The first thermal anomalies identified by MIROVA (Middle InfraRed Observation of Volcanic Activity) also appear during the first two days of October (figure 5). MODVOLC thermal alerts first appeared on 5 October and were essentially continuous with no more than a few days break until 4 January 2016. The MIROVA signal remained steady until about the same date when it abruptly decreased. KVERT reported consistent and usually intense thermal anomalies, when the volcano was not obscured by clouds, until 4 January. They observed anomalies in satellite images with decreasing frequency and intensity during the rest of January and into early February.

Figure 5. MIROVA thermal anomaly data for Alaid from 5 April 2015 through 13 January 2017. The first thermal anomaly is visible on 1 or 2 October 2015. The signal remained consistently in the Moderate to High range until the first week of January when it abruptly stopped. It reappeared during the third week of February and was consistently 'High' until mid-May when it decreased to 'Low' values. A sudden spike to near 'Very High' values during the first week of July corresponded with KVERT reports of Strombolian eruptions from the summit crater and a lava flow down the SW flank. Courtesy of MIROVA.

The first report of observed gas-and-steam activity (after the Tokyo VAAC report on 29 September) was by KVERT on 16 December. Visual observations from nearby Paramushir Island (45 km SE) noted a small amount of ash in the steam-and-gas plumes on 28 and 29 December. The Tokyo VAAC also reported a plume of volcanic ash at 4.6 km altitude on 29 December drifting SW. On 5 February 2016 local time KVERT lowered the Aviation Color Code (ACC) to Green, noting decreased thermal activity and only moderate continuing fumarole activity during the previous weeks. A break in the thermal activity between early January and late February is also recorded in the MIROVA data (figure 5).

Another eruptive episode began with the appearance of a strong thermal anomaly and a weak ash emission sending a plume 50 km E on 20 February UTC, leading KVERT to raise the ACC back to Yellow. Renewed MIROVA thermal anomalies appeared on 16 or 17 February (figure 5). The first MODVOLC thermal alert was reported 23 February, and they were essentially continuous (except for probable cloudy days) until 5 May 2016. MIROVA thermal anomalies values remained consistently in the 'High' (VRP of 10⁸-10⁹ Watts) range until the second week of May when they dropped back to 'Low' (VRP of 10⁶-10⁷ Watts).

KVERT reported gas-and-steam plumes containing a small amount of ash on 20 and 24 February 2016. Minor ashfall (less than 1 mm) was reported on 24 February in Severo-Kurilsk, 45 km SE on Paramushir Island. The Tokyo VAAC also reported a possible eruption that day with a plume to 3 km altitude extending NE. An ash plume was reported by KVERT and the Tokyo VAAC on 3 March 2016 at 3 km altitude drifting 52 km WSW. This prompted KVERT to raise the ACC to Orange. Ash emissions continued for the next two days, rising to 3.4-3.9 km and drifting S and SW, according to the Tokyo VAAC. KVERT reported visual data from Paramushir Island confirming an ash plume extending SW on 6 March, and satellite data showing the plume 90 km SW that same day.

Possible eruptions were again reported on 11 and 12 March 2016 by the Tokyo VAAC under 3 km altitude, and on 12 and 14 March by KVERT as visual observations from Paramushir extending 85 km E. Weak ash emissions were reported several more times in March and April rising to between 3 and 4.3 km altitude and drifting in various directions (some as far as 90 km) on 22, 26, and 30-31 March, and 1, 9, 14, 18, 21, and 24 April. KVERT noted that on 21 and 23 April the ash plumes extended about 260 km SE. Moderate thermal anomalies were reported by KVERT from mid-May through the beginning of July, and MIROVA anomalies registered in the 'Low' range during this time. KVERT reported on 12 May that satellite data showed a lava flow on the SW flank. They noted continuing thermal anomalies over the volcano during clear weather throughout May and June, but no ash plumes were reported.

KVERT and the Tokyo VAAC once again noted ash plumes that drifted 150 km SW during 3-4 July. This is consistent with an Aura/OMI image of an SO₂ plume drifting SW from Alaid on 4 July (figure 6). On 7 July, KVERT reported Strombolian activity from a new cinder cone in the summit crater and a lava flow effusing down the SW flank. A sudden spike in the MIROVA data with values rising to 10⁹ W of Radiative Power during 3-7 July (figure 5) corroborates the KVERT observation of the lava flow; the MODVOLC data also shows a strong signal between 3 and 7 July, including several alert pixels on the SW flank of the volcano (figure 7).

Figure 6. SO2 plume drifting SW from Alaid captured on 4 July 2016 by the Aura instrument on the OMI satellite. Courtesy NASA/GSFC.

Figure 7. MODVOLC thermal alert pixel data for Alaid during 3-7 July 2016 showing a multi-pixel alert at the summit likely from Strombolian activity and alert pixels on the SW flank described by KVERT as a lava flow. Green grid lines represent 0.05 decimal degrees. Courtesy of MODVOLC.

The last ash plume was observed by the Tokyo VAAC on 3 July 2016. The final thermal alert was recorded by MODVOLC on 7 July. MIROVA anomalies continued steadily, however, at low levels through the first week in August before ceasing. Two additional MIROVA anomalies appeared briefly in the first and last weeks of September. KVERT reported thermal anomalies continuing until early August. They also noted a gas-and-steam plume extending 155 km NE on 26 July. In their VONA (Volcano Observatory Notice for Aviation) issued on 11 August 2016 at 2305 UTC (1105 on 12 August KST), KVERT lowered the ACC to Yellow based on decreasing intensity of thermal anomalies, and no additional ash plumes since 4 July; they lowered it again to Green on 19 August (local time) citing no further evidence for volcanic activity since the last thermal anomaly on 11 August.

Geologic Background. The highest and northernmost volcano of the Kuril Islands, Alaid is a symmetrical stratovolcano when viewed from the north, but has a 1.5-km-wide summit crater that is breached open to the south. This basaltic to basaltic-andesite volcano is the northernmost of a chain constructed west of the main Kuril archipelago. Numerous pyroclastic cones are present the lower flanks, particularly on the NW and SE sides, including an offshore cone formed during the 1933-34 eruption. Strong explosive eruptions have occurred from the summit crater beginning in the 18th century. Reports of eruptions in 1770, 1789, 1821, 1829, 1843, 1848, and 1858 were considered incorrect by Gorshkov (1970). Explosive eruptions in 1790 and 1981 were among the largest reported in the Kuril Islands.

Information Contacts: Kamchatka Volcanic Eruptions Response Team (KVERT), Far East Division, Russian Academy of Sciences, 9 Piip Blvd., Petropavlovsk-Kamchatsky, 683006, Russia (URL: http://www.kscnet.ru/ivs/); 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/); Hawai'i Institute of Geophysics and Planetology (HIGP), MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/, http://modis.higp.hawaii.edu/); 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/).

Large lava flows descend the flanks of Alaska's Cleveland volcano, located on Chuginadak Island in the Aleutians, slightly over 1,500 km SW of Anchorage (figure 18). However, dome growth and destruction by frequent small ash explosions have been more typical behavior in recent years; historical activity, including three large (VEI 3) eruptions, is recorded back to 1893. The Alaska Volcano Observatory (AVO) and the Anchorage Volcanic Ash Advisory Center (VAAC) are responsible for monitoring activity and notifying air traffic of aviation hazards associated with Cleveland. This report summarizes activity between July 2011 and June 2014, and provides details of activity from June 2014 through February 2017.

Figure 18. Morning sunlight illuminates the southeast-facing slopes of the Islands of the Four Mountains on 15 November 2013 in this photograph taken from the International Space Station (ISS). The islands, part of the Aleutian Island chain, are the upper slopes of volcanoes rising from the sea floor: Carlisle, Cleveland, Herbert, and Tana. Carlisle and Herbert volcanoes are distinct cones and form separate islands. Cleveland and the Tana volcanic complex form the eastern and western ends respectively of Chuginadak Island; clouds obscure the connecting land area. Astronaut photograph ISS038-E-3612 acquired with a Nikon D3S digital camera using a 400 mm lens, provided by the ISS Crew Earth Observations experiment and Image Science & Analysis Laboratory, Johnson Space Center. The image was taken by the Expedition 38 crew. It has been cropped and enhanced to improve contrast, and lens artifacts have been removed. Caption by William L. Stefanov, Jacobs at NASA-JSC. Courtesy of NASA Earth Observatory.

Summary of activity during July 2011-June 2014. Dome growth and destruction characterized activity at Cleveland during 2011-2014. Eruptive episodes are challenging to determine due to weather conditions and the remoteness of the volcano; detectible ash plumes are intermittent, and thermal anomalies caused by dome growth are often obscured in satellite imagery. Seismic and infrasound data on explosions often provide valuable information. Dome growth was clearly documented between late July and October 2011 (BGVN 36:08, 37:01). An ash cloud observed on 29 December 2011 was followed by observations of dome growth in satellite data on 30 January 2012. Significant ash explosions occurred during April and June 2012 (BGVN 38:10). AVO also reported ash plumes on 12 July and 20 August 2012. Another small ash cloud was noted by AVO on 10 Nov 2012.

Details of the 2013 activity are provided in Dixon et al. (2015) and summarized here. Elevated temperatures in mid-January 2013 were followed by observations of a new lava dome that measured 100 m in diameter on 30 January 2013, and a second lava extrusion on 9 February. Elevated surface temperatures were intermittently observed until the next ash explosion on 4 May 2013, which was followed by a larger series of explosions on 6 May that filled the crater with tephra and created flowage deposits on the NE, E, and SE flanks. On 26 July, analysis of a satellite images suggested a new lava flow within the summit crater.

From August through 28 December 2013 the infrasound and seismic networks detected a number of additional explosions and periods of infrasonic tremor (see table 8 in Dixon et al., 2015). Most of these events did not have an accompanying ash signal in AVHRR satellite images, suggesting minor to no ash emissions. A detectible ash cloud on 30 December 2013 was preceded by strongly elevated surface temperature readings in the summit area on 28 December (BVGN 39:08). Ash plumes were again detected at the summit on 2 January, 25 February, and 6 March 2014. Cleveland was quiet for almost three months until an explosion on 5 June with a weak ash signal was detected.

Summary of activity during June 2014-February 2017. The growth and explosive destruction of six lava domes at Cleveland were recorded between June 2014 and February 2017. Although an explosion on 5 June 2014 was the last recorded explosion with confirmed ash until 14 June 2015, thermal and visual satellite evidence suggested dome growth activity during July-September and late November 2014. Weakly elevated surface temperatures at the summit were intermittent through February 2015. Minor ash deposits on the flanks were observed on 14 June 2015 in addition to stronger elevated surface temperatures, suggesting a new dome growth episode. An explosion on 21 July 2015 was thought to have destroyed the dome, and strongly elevated surface temperatures indicating new dome growth continued through July and August.

Moderately-elevated surface temperatures were detected at the summit in satellite data from January through 16 April 2016 when a new explosion was recorded. Satellite views in late April indicated that the August 2015 lava dome had been replaced with a small cinder cone within the summit crater. Explosions with no ash reported occurred twice in May, before the extrusion of a small amount of lava forming a new lava dome was observed on 17 May 2016, and which continued to grow for about one week. Moderately-elevated surface temperatures reappeared in mid-July, and field crews observed incandescence in a vent at the summit in late July. Satellite thermal anomalies were persistent from mid-May through September 2016. A new explosion on 24 October 2016 destroyed the dome emplaced in May; satellite views in November showed a deep pit within the summit crater. Weakly elevated surface temperatures reappeared in early December 2016. Moderately-elevated surface temperatures reappeared on 31 January 2017, [followed on 3 February by satellite observations that indicated] a new dome of similar size to earlier ones was once again filling the summit crater.

Activity during June 2014-February 2015. An ash-bearing explosion occurred in the late evening hours of 5 June 2014, resulting in a detached cloud with a weak ash signal observed in a satellite image that rapidly dissipated; no additional ash explosions were observed over the next 12 months. Weakly elevated surface temperatures were observed in satellite data on 7 July, and a vigorous steam-and-gas plume was observed on 8 and 9 July. Typical steam-and-gas emissions and persistent elevated surface temperatures in the summit crater were noted in satellite observations during clear periods through July and August, but AVO received no reports from pilots or mariners of any eruptive activity. Scientists working on the island in early August noted incandescence and puffing activity of steam and gas at the summit, and witnessed several small rockfall events. A newly installed webcam and other geophysical equipment at station CLCO near Concord Point on the SE coast of Chuginadak Island, about 15 km E of the volcano's summit, became operational in September 2014. In mid-September several rockfall signals were detected by the new local seismic network, and indicated the continued instability of volcanic debris on the steep upper flanks of the volcano.

Elevated surface temperatures were observed at the summit on clear days with occasional minor steaming visible in webcam images from late September to late October 2014. On 14 November AVO reported that vigorous steaming from the summit crater was observed in webcam images during the prior week, although they remarked that steam emissions are routinely observed at Cleveland and do not necessarily indicate an increase in unrest. On 28 November, they noted that a small mound of lava in the crater was observed in clear satellite views earlier that week that may have corresponded with the appearance of a faint thermal signal in the satellite data; the lava possibly extruded around 24 November. Satellite views on 19 December 2014 showed weakly elevated surface temperatures at the summit vent.

Low-density gas emissions and weakly elevated surface temperatures in the summit region were observed on 1 January 2015, and during clear weather up to 9 January. After this, nothing of note was observed in satellite or webcam images, and no significant activity was detected in seismic or infrasound (air pressure) data until weakly elevated surface temperatures were again detected in satellite data on 25 February. A low-level steam-and-gas plume emanated from the summit on 24 February, and again was identified in multiple satellite images on 28 February. During March, April, and May 2015, no significant activity, except for occasional steaming from the summit crater, was observed during periods of clear weather, causing AVO to downgrade both the Aviation Color Code (ACC) and the Volcano Alert Level (VAL) to Unassigned on 28 May 2015.

Activity during June 2015-March 2016. AVO issued a new VONA (Volcano Observatory Notice for Aviation) on 17 June 2015 returning the Aviation Color Code to Yellow (Yellow is 2nd lowest on a 4-color scale), and the Volcano Alert Level to Advisory (also 2nd lowest on a 4-level scale). This was based on satellite detection of elevated surface temperatures at the summit and an image from 14 June showing very minor ash deposits on the upper flanks. They interpreted the increase in temperature as consistent with renewed growth of the small lava dome within the crater. Elevated summit surface temperatures were again observed on 30 June, and during three clear days in early July. On 21 July AVO detected an explosion in both infrasound and seismic data, and raised the ACC to Orange and the VAL to WATCH. Satellite views were obscured by clouds, though a dusting of ash on the upper flanks was noted by a nearby field crew and recorded by the webcam later in the day. The explosion destroyed the dome that had formed in November 2014. Strongly elevated surface temperatures were recorded at the summit during the last week of July, including a thermal alert pixel from the MODVOLC system on 31 July.

Slightly elevated surface temperatures were recorded at the summit during the first week of August 2015. On 4 August, a field crew working in the area reported a small amount of lava covering the crater floor. Surface temperatures of the cooling lava measured by the crew were in the range of 550-600°C. Minor ash-and-gas emissions were also observed. A small explosion occurred on 6 August at 2203 AKDT, but no ash cloud was identified. Strongly elevated surface temperatures suggestive of lava effusion were noted in satellite data through 18 August, and weakly elevated temperatures were recorded for the rest of August and September. A small swarm of earthquakes was detected on 29 August.

AVO lowered the ACC to Yellow and the VAL to ADVISORY on 14 October 2015, citing the likely cessation of lava effusion, while minor steaming, weakly elevated surface temperatures, and slightly above-background seismicity continued through November 2015. Exceptionally clear weather during late November allowed many views of the volcano, showing only modest steaming from the summit. Elevated surface temperatures were detected twice during December, and an increase in frequency of small VT (Volcano-Tectonic) events was noted on 22 and 23 December, but otherwise no significant seismicity or emissions (other than steam plumes) were detected.

Moderately-elevated surface temperatures were detected at the beginning of the second week in January 2016, followed by several small earthquakes per day during the third week, and weakly elevated temperatures. Low-level seismicity and elevated surface temperatures were next observed during the last week of February; a brief burst of small local earthquakes was recorded on 28 February followed by weakly elevated surface temperatures during the first week of March. Moderately-elevated surface temperatures were again observed during the last week of March.

Activity during April-September 2016. A new explosion on 16 April 2016 was detected in both infrasound and seismic data, but satellite views were obscured by clouds. AVO raised the ACC to Orange until 29 April, when they noted that recent satellite imagery indicated that the August 2015 lava dome had been replaced with a small cinder cone within the summit crater; seismic activity remained lower after the explosion. Another explosion on 5 May at 1844 local time led AVO to raise the ACC back to Orange, although no ash emissions were observed above the cloud deck. A brief explosive event on 10 May was detected by pressure sensors near the volcano, and again no ash was reported.

A small volume of lava was extruded from the summit on 17 or 18 May, as confirmed in satellite data. The low-relief, 50-m-diameter dome was similar in size and shape to the ten domes observed since 2011, the most recent of which was extruded and destroyed earlier in May. During the week of 20 May, this lava dome enlarged to about 60 m in diameter. Dome growth appeared to have paused or ceased by 23 May. Weakly elevated surface temperatures were observed in mostly clear views by satellite on 25 and 26 May, which is consistent with the presence of the new lava dome. The Aviation Color Code was lowered from Orange to Yellow by AVO on 3 June when no other signs of eruptive activity were observed. Occasional clear satellite views detected weakly elevated surface temperatures that AVO interpreted as consistent with cooling lava during June 2016.

The MIROVA infrared data suggests ongoing thermal anomalies from late May through September 2016 (figure 19). AVO reported weakly-to-moderately-elevated surface temperatures reappearing during the second and third weeks of July. Field crews conducted an overflight during the last week of July and observed incandescence from a vent in the summit crater. Low-level steam plumes and minor degassing were observed a number of times during August. A small swarm of earthquakes occurred on 29 August; owing to the small number of telemetered seismometers on Cleveland, the locations and magnitudes of the earthquakes could not be determined precisely. Thermal anomalies were observed in satellite data during the last week of August and slightly elevated surface temperatures were observed on clear satellite images a number of times in September.

Figure 19. MIROVA data from 18 January 2016 to 18 January 2017 showing a persistent thermal anomaly from Cleveland starting about the time of the observation of the new lava dome (17 or 18 May) through late September 2016. A new thermal anomaly appears in late December 2016. AVO reported elevated surface temperatures on 6 January 2017. Courtesy of MIROVA.

Activity during October 2016-February 2017. AVO detected an explosion at 1310 local time on 24 October 2016 that was heard by residents in Nikolski (75 km E), prompting AVO to raise the ACC to Orange and the VAL to WATCH. No evidence of an eruption cloud was detected above the weather cloud present at 8.5 km altitude, and no ashfall was reported in Nikolski. However, clear post-explosion webcam views of the volcano showed a darkened area around the summit crater which may have been the result of minor ash fallout. Narrow dark streaks were also observed extending down the upper snow-covered part of the edifice, which according to AVO may have been produced by small flows of meltwater and ash. They lowered the ACC back to Yellow on 4 November 2016. Satellite views from early November indicated that the lava dome emplaced in late May was mostly destroyed in the 24 October explosion, and was replaced with a deep pit within the summit crater. Minor steaming was observed from the summit during a few periods of clear weather in November.

Observations of weakly-elevated surface temperatures returned 8 and 9 December, with minor steaming at the summit observed on clear days. A MIROVA thermal anomaly signal reappeared around 25 December. This was followed by AVO's observation of weak-to-moderate elevated surface temperatures during first week of January 2017. Low-level steam plumes were seen on clear days later in the month. Moderately-elevated surface temperatures appeared in satellite data on 31 January. [On 3 February 2017 the appearance of a new dome] led AVO to raise the ACC to Orange. Satellite observations indicated that a new lava dome had been extruded and was partially filling the summit crater. The new dome was about 70 m in diameter and similar in size to previous lava domes that have developed on the floor of the crater.

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

Geologic Background. The beautifully symmetrical Mount Cleveland stratovolcano is situated at the western end of the uninhabited Chuginadak Island. It lies SE across Carlisle Pass strait from Carlisle volcano and NE across Chuginadak Pass strait from Herbert volcano. Joined to the rest of Chuginadak Island by a low isthmus, Cleveland is the highest of the Islands of the Four Mountains group and is one of the most active of the Aleutian Islands. The native name, Chuginadak, refers to the Aleut goddess of fire, who was thought to reside on the volcano. Numerous large lava flows descend the steep-sided flanks. It is possible that some 18th-to-19th century eruptions attributed to Carlisle should be ascribed to Cleveland (Miller et al., 1998). In 1944 it produced the only known fatality from an Aleutian eruption. Recent eruptions have been characterized by short-lived explosive ash emissions, at times accompanied by lava fountaining and lava flows down the flanks.

Information Contacts: Alaska Volcano Observatory (AVO), a cooperative program of a) U.S. Geological Survey, 4200 University Drive, Anchorage, AK 99508-4667 USA (URL: http://www.avo.alaska.edu/), b) Geophysical Institute, University of Alaska, PO Box 757320, Fairbanks, AK 99775-7320, USA, and c) Alaska Division of Geological & Geophysical Surveys, 794 University Ave., Suite 200, Fairbanks, AK 99709, USA (URL: http://www.dggs.alaska.gov/); Anchorage Volcanic Ash Advisory Center (VAAC), Alaska Aviation Weather Unit, NWS NOAA US Dept of Commerce, 6930 Sand Lake Road, Anchorage, AK 99502-1845(URL: http://www.ssd.noaa.gov/); Hawai'i Institute of Geophysics and Planetology (HIGP), MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); 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/).

Recent activity at Copahue through January 2016 (BGVN 41:03) consisted of gas and steam plumes with minor amounts of ash. This report, based on information obtained from the Buenos Aires Volcanic Ash Advisory Center (VAAC), the Southern Andes Volcanological Observatory (OVDAS), and the Servicio Nacional de Geología y Minería (National Geology and Mining Service) (SERNAGEOMIN), covers similar activity from mid-January through December 2016. Volcano Alert Levels were maintained by SERNAGEOMIN (on a four-color scale) and by the Chilean Oficina Nacional de Emergencia del Ministerio del Interior (National Office of Emergency of the Interior Ministry) (ONEMI), on a three-color scale), for alerts to individual communes in the region.

Reports from the Buenos Aires VAAC between 13 January and 26 March 2016, based on Significant Meteorological Information (SIGMET) notices, satellites, and webcam views, indicated continuous gas-and-steam plumes containing minor amounts of ash. The plumes rose as high as 3.3-4.3 km altitude (during 24-25 and 28 February) and drifted as far as 160 km (trending SE and SW) between 28 January and 2 February, and more generally as far as 150 km in a variety of directions.

The Buenos Aires VAAC next reported steam-and-gas emissions, possibly containing minor amounts of ash on 11 June, based on webcam recordings. OVDAS-SERNAGEOMIN reported an eruption during 16-30 June characterized by phreato-magmatic explosions and Strombolian activity. During an overflight on 3 July, SERNAGEOMIN scientists observed Strombolian activity from a pyroclastic cone that was forming on the floor of El Agrio crater (figure 17).

Figure 17. Photo taken during an overflight of Copahue on 3 July 2016 showing Strombolian activity from a pyroclastic cone on the floor of El Agrio crater. Courtesy of SERNAGEOMIN.

Based on webcam and satellite views, the Buenos Aires VAAC reported that during 7-8 July diffuse gas-and-steam plumes with minor amounts of ash rose to an altitude of 3 km and drifted E and SE. The Alert Level remained at Yellow (second highest level on a four-color scale).

Activity renewed in September and lasted through December 2016. Based on satellite and webcam images, notices from the Buenos Aires VAAC after 23 September described gas and water vapor plumes with minor ash content rising above the summit. The plumes rose as high as 5.2 km a.s.l. (during 23-25 and 27-29 November) and drifted based on wind direction SW, S, SSE, ESE, SE, E, ENE, NE, and N. On 2 December OVDAS-SERNAGEOMIN reported that activity continued to be dominated by weak Strombolian explosions, likely from a pyroclastic cone forming on the floor of El Agrio crater. The last VAAC reports of activity during 2016 were for gas-and-ash emissions to altitudes of 3.6-3.9 km drifting in S and E directions.

The only MODVOLC thermal anomaly during the entire reporting period was on 26 October 2016 (1 pixel). The MIROVA volcano hotspot detection system, also based on analysis of MODIS data, detected low level thermal anomalies that became more frequent during the latter part of June through early July 2016 and thereafter occurred less often. The last anomalies recorded by MIROVA (as of early April 2017) were in about the third week of December 2016 (figure 18).

Figure 18. Plot of thermal anomalies at Copahue as recorded by the MIROVA system (Log Radiative Power), April 2016-March 2017. Courtesy of MIROVA.

At some point after the December 2016 activity, SERNAGEOMIN lowered the Alert Level to Green, the lowest of the four levels. No additional reports of activity were issued from any agency through March 2017.

Geologic Background. Volcán Copahue is an elongated composite cone constructed along the Chile-Argentina border within the 6.5 x 8.5 km wide Trapa-Trapa caldera that formed between 0.6 and 0.4 million years ago near the NW margin of the 20 x 15 km Pliocene Caviahue (Del Agrio) caldera. The eastern summit crater, part of a 2-km-long, ENE-WSW line of nine craters, contains a briny, acidic 300-m-wide crater lake (also referred to as El Agrio or Del Agrio) and displays intense fumarolic activity. Acidic hot springs occur below the eastern outlet of the crater lake, contributing to the acidity of the Río Agrio, and another geothermal zone is located within Caviahue caldera about 7 km NE of the summit. Infrequent mild-to-moderate explosive eruptions have been recorded since the 18th century. Twentieth-century eruptions from the crater lake have ejected pyroclastic rocks and chilled liquid sulfur fragments.

Information Contacts: Servicio Nacional de Geología y Minería, (SERNAGEOMIN), Observatorio Volcanológico de Los Andes del Sur (OVDAS), Avda Sta María No. 0104, Santiago, Chile ( URL: http://www.sernageomin.cl/); Oficina Nacional de Emergencia - Ministerio del Interior (ONEMI), Beaucheff 1637/1671, Santiago, Chile (URL: http://www.onemi.cl/); Buenos Aires Volcanic Ash Advisory Center (VAAC), Servicio Meteorológico Nacional-Fuerza Aérea Argentina, 25 de mayo 658, Buenos Aires, Argentina (URL: http://www.smn.gov.ar/vaac/buenosaires/inicio.php?lang=es); 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/).

Daikoku seamount lies in the Northern Seamount Province of the Mariana Arc, and is about 850 km due N of Guam in the western Pacific Ocean. The summit is about 325 m below sea level and was first shown to be hydrothermally active in 2003 (figure 3). NOAA (National Oceanic and Atmospheric Administration) has conducted four expeditions to the Northern Mariana Islands in 2003, 2004, 2006, and 2014 under their Ocean Explorer program, specifically to study the volcanoes and the marine life they support. A comparison of the bathymetry recorded in 2003 and 2014 suggests that an explosion may have occurred at Daikoku during that interval, and both geochemical data and rock sampling indicate ongoing hydrothermal activity. In 2016, a research cruise conducted by the Schmidt Ocean Institute included a visit to Daikoku that revealed sulfur chimney formation.

Figure 3. Bathymetry and other data gathered on the 2003 NOAA Ocean Explorer Program's 'Submarine Ring of Fire 2003' expedition at the Mariana Arc between 9 February and 5 March 2003. The stars indicate submarine volcanoes where evidence of hydrothermal activity was found. The volcanoes were mapped in high resolution, and sampled with a CTD, as indicated by the open black circles on the tracklines. The red dots represent the location of the deployed hydrophones and the red line represents the location of the back-arc spreading center. Daikoku is located in the Northern Seamount Province of the Mariana Arc. Courtesy of NOAA's 'Submarine Ring of Fire 2003' expedition.

Geochemical sampling of the seawater is carried out with an instrument package that measures conductivity, temperature, and depth, commonly referred to as a CTD. Turbidity of the water, which estimates the concentration of particulate matter suspended in the plumes, is also measured. The CTD carries bottles for seawater sampling which is then geochemically analyzed.

On 15 April 2004 the NOAA 'Submarine Ring of Fire 2004' expedition made a single dive at Daikoku and noted warm water present over large areas of sandy sediment deposits near the summit, and small flatfish in great abundance in the venting areas. The 'Submarine Ring of Fire 2006' expedition again visited Daikoku on 4 May 2006 and discovered a "cauldron" of molten sulfur (BGVN 31:05). They also observed extensive sulfur crusts in the vicinity of the cauldron, suggesting past emissions of liquid sulfur; they were able to sample a large piece of sulfur crust (figure 4). At that time, they also mapped two large craters on the summit. One pit was reported as over 100 m deep and about 80 m in diameter, and a large plume of white fluid was observed rising out of it.

Figure 4. Sulfur crusts near the Diakoku "cauldron" were observed insitu as well as sampled by the ROV. Upper Image: Sulfur crusts in the vicinity of the sulfur cauldron (BGVN 31:05) imply past emissions of liquid sulfur at Daikoku. Lower Image: The Jason remotely operated vehicle (ROV) holds up a large piece of the sulfur crust that was sampled at Daikoku on 4 May 2006. The lasers- two red dots in the images- are 10 cm apart. Courtesy of Submarine Ring of Fire 2006 expedition, NOAA Ocean Explorer Program.

Researchers from the NOAA Ocean Explorer program visited Daikoku again on 14 December 2014 during its 'Submarine Ring of Fire 2014 – Ironman' expedition, which was conducted from the R/V (Research Vessel) Revelle between 29 November and 22 December 2014. They gathered geochemical and bathymetric data which they were able to compare with 2003 data. The CTD information gathered in 2014 showed very strong plumes coming from the top of the seamount. The plumes had high turbidity, low pH, strong anomalies in reduced chemicals, and very high levels of hydrogen (figure 5).

Figure 5. Cross-section over the top of Daikoku seamount measured on 14 December 2014 with the results from a CTD tow (black line), showing turbidity anomalies (warm colors indicate high particle concentrations) in the plume. Courtesy of 'Submarine Ring of Fire 2014 – Ironman' expedition, NOAA/PMEL, NSF.

The 2014 bathymetry data revealed two summit craters; the larger one measured 150 m across and 100 m deep on the N side of the summit with a crater floor depth of 452 m below sea level, and the smaller one, about 50 m across on the NE flank, had a crater floor depth of 443 m below sea level. The bathymetry data from 2003 show only one small crater on the N side of the summit about 50 m across with a floor depth of 400 m below sea level (figure 6). The larger pit appeared to be about 70 m wider in 2014 than in 2006.

Figure 6. Bathymetric comparison of data collected at the Daikoku summit during the 2014 expedition (top) and in 2003 (bottom). The summit crater was significantly larger, and confirmed to be hydrothermally active by the CTD tow and midwater data collected by the 2014 expedition. A second crater has also appeared on the NE flank of the volcano. Arrows with numbers represent the depth below sea level (Z) in meters. Courtesy of 'Submarine Ring of Fire 2014 – Ironman' expedition, NSF/NOAA.

On 3 and 4 December 2016, the Schmidt Ocean Institute Research Vessel R/V Falkor traveled to the Mariana back-arc with a multidisciplinary team of scientists to gather evidence of active hydrothermal vents and the life they support. They were able to make two ROV (Remotely Operated Vehicle) dives at Daikoku and collected data on the seamount and sea life living there. On their first dive they observed (and sampled) a fissure with a sulfur chimney caked with yellow sulfur, emitting white bubbles and particulates in 70°C water (figure 7).

Figure 7. An active sulfur chimney at Daikoku on 3 December 2016 was videoed and sampled by the Schmidt Ocean Institute expedition. Upper Image: A fissure at Daikoku on 3 December 2016 with a yellow sulfur-caked chimney emitting white bubbles and particulates in 70°C water. Lower Image: The sulfur chimney was sampled by the ROV SuBastian for chemical analysis. Courtesy of Schmidt Ocean Institute, Expedition FK161129.

On their second dive on 4 December 2016, they collected tube worms and crabs, and recorded the formation of "sulfur needles," tadpole-shaped fragments of sulfur that were previously observed in sampled sediments and seen floating in the water column. They appear to form when gas bubbles (probably CO₂) rise through molten sulfur, forming a coating of sulfur around the bubble before the gas escapes (figure 8). Their video shows a sulfur chimney caked with yellow sulfur emitting yellow, white, and orange droplets of sulfur.

Figure 8. Tadpole shaped "sulfur needles" coat the side of a sulfur chimney at Daikoku on 4 December 2016 as gas bubbles coated with sulfur rise through the chimney and drip residue around the sides. A video recording was also made of the chimney emitting bubbles (https://schmidtocean.org/cruise-log-post/daikoku-dive-2-sulfur-good/). Courtesy of Schmidt Ocean Institute, Expedition FK161129.

The cruise scientists used the ship's EM302/710 multibeam echosounder to get a 2-m-resolution image of the summit crater, which they combined with water column data to create an image showing both the bathymetry of the volcano and the shape of the hydrothermal plume emitting from the summit (figure 9).

Figure 9. Multibeam echosounder data reveals the topography of the summit at Daikoku on 4 December 2016 as well as the shape of the hydrothermal plume emitting from the summit. Courtesy of Schmidt Ocean Institute, Expedition FK161129.

Geologic Background. The conical summit of Daikoku seamount lies along an E-W ridge SE of Eifuku and rises to within 323 m of the sea surface. A steep-walled, 50-m-wide crater on the N flank, about 75 m below the summit, is at least 135 m deep and was observed to emit cloudy hydrothermal fluid. During a NOAA expedition in 2006, scientists observed a convecting black pool of liquid sulfur with a partly solidified, undulating sulfur crust at a depth of 420 m below the summit. Gases, particulates with the appearance of smoke, and liquid sulfur were bubbling up from an edge of the sulfur pool.

Information Contacts: Office of Ocean Exploration and Research, National Oceanic and Atmospheric Administration (NOAA), 1315 East-West Highway, Silver Spring, MD 20910, USA (URL: http://oceanexplorer.noaa.gov/, Cruise logs at: http://oceanexplorer.noaa.gov/explorations/03fire/logs/summary/summary.html, http://oceanexplorer.noaa.gov/explorations/04fire/logs/april15/april15.html, http://oceanexplorer.noaa.gov/explorations/06fire/logs/may4/may4.html, http://oceanexplorer.noaa.gov/explorations/14fire/logs/december14/december14.html); Schmidt Ocean Institute, 555 Bryant Street #374, Palo Alto, CA 94301, USA (URL: https://schmidtocean.org/, https://schmidtocean.org/cruise/searching-life-mariana-back-arc/).

After an eruption in April 2009 (BGVN 34:12), Kerinci was quiet until it erupted again in December 2011. The Indonesian agency responsible for volcano monitoring is the Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG), also known as the Center for Volcanology and Geological Hazard Mitigation (CVGHM). Since mid-December 2011 there have been four instances where there was an emission of ash, qualifying the event as an eruption. These took place in December 2011, June 2013, and twice in 2016. The eruptions in 2016 were separated by five months, so are treated as distinct eruptions.

PVMBG mentioned in its 2015 reports on Kerinci that an eruption on 15 December 2011 generated an ash plume that rose about 600 m above the summit (summit elevation is 3.8 km). No other details were given.

A brief eruption was reported by PVMBG on 2 June 2013, from 0843 to 0848, that generated an ash plume 1 km above the crater. Ashfall as thick as 5 mm was reported in areas to the E, including Tangkil (7.5 km SE). In a Jakarta Post story, a resident of Sungai Rumpun village (about 10 km SE) reported hearing a loud bang and black plumes with a sulfur odor. The article noted that several villages in Gunung Tujuh district (an area that includes the SE flank of the volcano) received heavy ashfall, but it was washed off the crops by rain.

Although PVMBG reported white plumes during 1 February-12 July 2015 that rose 50-300 m and drifted E and W, no clear eruptive activity was noted. Seismicity during this period was dominated by signals indicating emissions and shallow volcanic earthquakes. Climbers who reached the summit around this time (exact dates not reported, images uploaded 17 January 2016) photographed steam plumes (figure 1) and solid lava flows (figure 2) in the crater.

Figure 1. Photo of a steam plume rising from the Kerinci summit crater. Date not reported; uploaded 17 January 2016. Courtesy of Bernhard Huber.

Figure 2. Photo of the crater floor at Kerinci showing solidified lava flows and steam. Date not reported; uploaded 17 January 2016. Courtesy of Bernhard Huber.

Based on satellite images and ground reports from PVMBG, the Darwin Volcanic Ash Advisory Centre (VAAC) reported that during 15 days between 31 March and 9 June 2016 ash plumes rose to altitudes of 4.0-4.9 km and drifted N, NW, NE, E, and WSW. On 29 April an ash plume rose to an altitude of 6.1 km.

Figure 3. Photo of Kerinci showing a plume rising from the summit crater on 9 June 2016. Courtesy of Luke Mackin.

Ash plumes were again reported on 15-19, and 21 November 2016 based on observations of satellite data by the Darwin VAAC. The plumes rose to altitudes of 4.3-4.6 km and drifted NE, ENE, SE, and S. On 15 and 17 November they drifted almost 30 km downwind. The Alert Level remained at 2 (on a scale of 1-4), where it has been since September 2007, and PVMBG advised residents and visitors not to enter an area within 3 km of the summit.

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

Information Contacts: 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/); Bernhard Huber (URL: https://www.flickr.com/photos/97278656@N08/, https://creativecommons.org/licenses/by-nc-nd/2.0/); Luke Mackin (URL: https://www.flickr.com/photos/wildsumatra/, https://creativecommons.org/licenses/by-nc-sa/2.0/); Jakarta Post (URL: http://www.thejakartapost.com/news/2013/06/02/mt-kerinci-erupts.html).

Klyuchevskoy has been quite active for many decades, with eruptive periods alternating with less active times (BGVN 35:06, 38:07, and 39:10). Recent eruptions took place during August-December 2013, with another period of activity beginning in January 2015 and continuing at least into March 2015 (BGVN 39:10). MODVOLC thermal alert pixels, based on MODIS satellite data, were frequent starting on 3 January but had stopped after 26 February 2015. Moderate activity continued until 10 May 2015, when the eruption that began in January ended. Eruptive activity was again observed in late August 2015, and fluctuating activity has continued through March 2017. The Kamchatkan Volcanic Eruption Response Team (KVERT) is responsible for monitoring this volcano, and is the primary source of information. Times are in UTC (local time is UTC + 12 hours).

Activity during April-July 2015. KVERT lowered the Aviation Color Code (ACC) to Green, the lowest of four levels, on 6 April 2015, although moderate gas-and-steam activity continued. On 13 April, gas-and-steam emissions increased at 0840, and continued at least through 1215 on 14 April, with incandescence at the summit possibly indicative of renewed Strombolian activity. KVERT raised the ACC from Green to Yellow. Strong gas-and-steam activity continued through the rest of April; the plumes sometimes contained small amounts of ash. Satellite data showed a weak thermal anomaly when not obscured by clouds, and incandescence at the summit was occasionally observed. On 18 April, KVERT reported that Strombolian activity was continuing, and that a webcam had recorded a narrow ash plume rising 1-2 km and drifting 100 km SE; the ACC was raised to Orange. Satellite images showed a weak thermal anomaly during 16-17 and 23 April; a gas plume containing a small amount of ash drifted 147 km E on 21 April. On 26 April the ACC was lowered to Yellow; KVERT noted that gas-and-steam activity and tremor continued.

Satellite data showed ash-bearing plumes during 2-5 May that drifted more than 450 km SE, and moderate activity continued through 9 May. The ACC was briefly raised to Orange before again being set at Yellow on 12 May. Moderate activity prevailed though the rest of the month. Satellite data showed occasional gas-and-steam plumes, sometimes containing small amounts of ash; weak thermal anomalies were often observed over the volcano when clouds did not obscure viewing.

On 22 May, KVERT described activity as weak. This remained the case through 27 August 2015. Gas-and-steam emissions continued, and satellite data often showed a thermal anomaly when the volcano was not obscured by clouds. Gas-steam plumes drifted 20 km SE on 26-27 May. On 20 July, the ACC was lowered to Green.

Activity during August 2015-March 2016. On 27 August, KVERT reported that a moderate Strombolian explosion had occurred, which continued into 28 August. At 1544 UTC on 27 August, incandescence of the crater was observed. The ACC was raised to Yellow.

Thereafter, through 17 September 2015, KVERT described activity as moderate, with moderate gas-steam activity. Strombolian explosions occurred on 27-28 August and 8-10 September. Satellite data showed occasional weak thermal anomalies when the volcano was not obscured by clouds. On 13-14 September, a diffuse ash plume rose to about 1.5 km and drifted E.

During 24 September-30 November 2015, KVERT described the activity as a "weak explosive eruption." According to video data, moderate gas-and-steam activity continued and a weak thermal anomaly was sometimes observed when the volcano was not obscured by clouds. Occasionally, incandescence of the summit volcanic crater was noted.

KVERT again described activity as moderate during December 2015-March 2016, with strong gas-steam emissions, although the volcano was usually either quiet or obscured by clouds. KVERT reported thermal anomalies each month, ranging from two during December 2015 to 12 during both January and February 2016. Video often recorded incandescence at the summit during the latter part of December.

Activity during April 2016-November 2016. On 3 April 2016, activity increased with Strombolian explosions. Detection of very frequent thermal anomalies by the MODVOLC system began again on 8 April and continued being reported almost daily through 2 November 2016. Thermal data identified by the MIROVA system showed strong anomalies over the same time period (figure 18). The MIROVA data also indicated a steady increase in radiative power beginning in the second half of May 2016.

Figure 18. Plots of MODIS thermal data detected at Klyuchevskoy during the year ending on 23 March 2017. The data analyzed by the MIROVA system is presented as radiative power (top) and log radiative power (bottom). Courtesy of MIROVA.

Strong gas-steam emissions continued, and plumes extended to about 100 km SE on 10 April and about 55 km NE on 14-15 April. Satellite data by KVERT through June showed persistent intense thermal anomalies when not obscured by clouds. On 24 April, activity increased again. According to video and satellite data, a lava flow began to effuse on the S and SE flank of the volcano (along Apakhonchich chute). An ash plume drifted about 500 km SW on 23-24 April. The ACC was raised to Orange.

The explosive-effusive eruption continued from May through September 2016. Lava continued to effuse along the SE flank. Satellite data showed an ash plume extending 88 km SE on 2 May, up to 80 km E and SE on 13 May and 16 May, 47 km W on 13 June, about 30 km E on 18 June, and 60 km W and E on 27-28 June. Gas-steam plumes drifted about 60 km W and E on 27 and 28 June. On 24 June, at 2115 and 2350 UTC, video data showed two rock collapses into the Apakhonchich chute and ash plumes drifted W, then NW. According to video and satellite data, Strombolian activity of the summit crater continued on 24 June.

According to video data, the eruption intensified on 6 July. Strong explosions sent ash to an altitude of 7.5 km and the plumes drifted about 350 km SW, S, and SE. A large bright thermal anomaly was observed all that week. On 6-7 July, dense ash plumes drifted about 400 km SE and E, and numerous ash plumes were observed thereafter through September. Bursts of volcanic bombs shot up to 200-300 m above the summit crater and up to 50 m above the cinder cone into the Apakhonchich chute along the SE flank. Lava continued to flow on the SE flank along the chute (figure 19). Strong gas-steam activity within two volcanic centers emitted various amounts of ash. On 10, 13 and 15 September, explosions shot ash up to an altitude of 7 km and ash plumes extended for about 50 km SE and NE.

Figure 19. Photo of Klyuchevskoy on 25 August 2016 with ash-containing emissions and lava streaming from the cone into the Apakhonchich chute. Courtesy of Denis Bud'kov/Bernard Duick.

During the second week of September, KVERT reported that lava began to effuse on the E and SW flanks. Explosions sent ash up to an altitude of 7.5 km and ash plumes extended for about 530 km in various directions. Small ash layers were observed over Koryaksky and Avachinsky volcanoes on 8 September. On 10, 13, 15, and 20-22 September, explosions sent ash up to an altitude of 6-7 km and ash plumes extended for up to 165 km in various directions. In their 29 September and 6 October reports, KVERT noted that bursts of volcanic ash that rose above the summit crater and cinder cone fell into Apakhonchich chute.

Explosions during the first week of October sent ash to an altitude of 5-6 km and plumes extended about 260 km E. On 7-8 October, gas-steam plumes containing ash drifted about 390 km E and SE. By 13 October, activity had apparently diminished, with moderate gas-steam emissions containing some ash. A weak thermal anomaly was noted on 7 and 12 October.

By 20 October the explosive-effusive activity had returned with a lava flow on the E flank, a large strong thermal anomaly, and strong gas-steam emissions containing various amounts of ash. Explosions sent ash to 5-6 km altitude and plumes extended for about 300 km E, SE, and NW on 14 and 18-19 October. On 20-21 and 23-27 October explosions sent ash up to an altitude of 5-7 km; gas-steam plumes containing ash extended for about 335 km in various directions. On 30-31 October and 1-3 November, explosions sent ash up to an altitude of 5-8 km and gas-steam plumes containing ash extended for about 277 km E and SE. Strong thermal anomalies detected from satellite by the MODIS instrument decreased significantly in strength after 2 November.

On 3-5 November, ash plumes extended up to 116 km E. KVERT's report on 10 November noted that activity had decreased significantly during the previous week. Lava effusion onto the flanks was last noted on 3 November; the next day the thermal anomaly was weaker. Ash plumes were last detected in satellite images during 3-4 November. The ACC was lowered to Yellow on 7 November. However, moderate activity continued and thermal anomalies and Strombolian activity could still be observed. Strong gas-and-steam emissions continued. On 16 November, an ash plume extended up to 85 km NW. KVERT reported a daily thermal anomaly visible in satellite images during 18-25 November.

Activity during December 2016-March 2017. Thermal anomaly data after early November 2016 was not sufficient to cause alerts on MODVOLC, and was seen to be very weak and fluctuating in MIROVA plots before ending completely in mid-February 2017 (see figure 19). On 26 December KVERT reported that a weak thermal anomaly had been detected and that gas-and-steam plumes sometimes contained small amounts of ash. Over the next few months the ACC was frequently changed between Yellwo and Orange, depending on the ash plume hazard to aviation.

Explosions on 1 January 2017 generated ash plumes that rose to an altitude of 5 km and drifted 114 km SE, resulting in KVERT raising the ACC to Orange. Daily satellite imagery showed a thermal anomaly over the volcano during 2-6 January. Gas-and-steam emissions sometimes with minor ash, along with thermal anomalies, continued through 20 January. During 9-10 January ash plumes drifted 160 km ESE, and on 22 January an ash plume rose to 5-5.5 km and drifted 45 km E.

KVERT reported that a thermal anomaly was identified in satellite data during 25 February and 1-3, 5, and 8-9 March. At 1340 on 2 March a gas, steam, and ash plume recorded by the webcam rose to altitudes of 8-9 km and drifted 110 km NE and NW. Explosions on 8 March produced ash plumes that rose to 5.5 km altitude and drifted about 20 km NW. As of 24 March gas-and-steam emissions continued to rise from the crater, and a weak thermal anomaly was sometimes identified in satellite images, but no explosions had been detected since 8 March. On 24 March the ACC was lowered to Green.

A gas, steam, and ash plume identified in satellite data on 28 March rose to altitudes of 5-6 km and drifted 108 km ENE, resulting in the ACC being raised to Yellow. Another ash plume the next day that rose to as high as 7.5 km altitude and drifted 75 km SW prompted an Orange ACC status. Additional explosions during 27-30 March generated ash plumes to an altitude of 7 km that drifted 300 km in multiple directions.

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

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

Guatemala's Pacaya volcano has a 450-year record of observations of frequent activity, in addition to confirmed radiocarbon dating of eruptions over the last 1,500 years. Its location, approximately 30 km south of the capital of Guatemala City, makes it both a popular tourist attraction as a national park, and a hazard to the several million people that live within 50 km. Activity during the last 50 years has been characterized by extensive lava flows, bomb-laden Strombolian explosions, and large and small ash plumes that have dispersed ash to cities and towns across the region.

This report summarizes activity at Pacaya during the long-lived 2004-2010 eruptive episode, and continues with the details of activity during the next eruption between March 2013 and April 2014. Most of the information is provided by the Instituto Nacional de Sismologia, Vulcanologia, Meteorologia e Hydrologia (INSIVUMEH), the Coordinadora Nacional para la Reducción de Desastres (CONRED) of Guatemala, and the Washington Volcanic Ash Advisory Center (VAAC), which provides air traffic advisories. Information is also gathered from remote sensing satellite data provided through the University of Hawai'i's MODVOLC program and from Google Earth images.

Renewed Strombolian activity was observed on 19 July 2004 after two years of mostly steam emissions, and again in early December 2004. Intermittent Strombolian explosions accompanied near-continuous lava flows down most flanks of MacKenney Cone from December until 11 September 2005. An explosion on 9 March 2006 was the beginning of a new, lengthy episode characterized by extensive lava flows and few significant ash plumes. Multiple strong thermal anomalies were recorded every month from March 2006 through June 2010, excepting December 2006. It climaxed with a major explosion of ash and lava flows during 27- 28 May 2010, and ended with the last Strombolian explosions recorded on 26 October 2010. After two and a half years of quiet, a new period of Strombolian activity began on 5 March 2013, which included intermittent lava flows. This continued until an outbreak of more extensive lava flows during the second half of January 2014. After a final burst of lava flows in early March, a small ash plume on 10 April 2014 was the last reported activity for four months.

Activity during June 2004-September 2005. Renewed periods of near-continuous tremor and frequent long-period earthquakes were recorded during June- August 2004, after the end of visible incandescence from a long-lived lava lake in June 2001. Incandescence was first reported on 14 June 2004, followed by ejection of lava fragments from a vent at the bottom of the central crater of MacKenney Cone on 19 July (BGVN 30:10). Incandescence was observed during the next few months, and tephra was expelled from the cone during 7-9 December 2004.

A sequence of substantial lava flows was first observed by INSIVUMEH in January 2005; strong thermal signatures were initially captured by MODVOLC beginning on 24 December 2004 and persisted until 28 August 2005. During this period, most of the lava flows covered the NW, N, and NE flanks of the central crater, but some extended up to 300 m down the W and SW flanks (figure 62). An INSIVUMEH report from 2008 noted that in March and April 2005 the growth of N-S oriented cracks on the MacKenney Crater created a new vent on the cone's ENE side. In just a few days, the flow field from this vent grew to about 800 m long and curved westward down the N flank, filling much of the depression formed by the cracks in the subsequent months (BGVN 33:08).

Figure 62. Two MODVOLC images of Pacaya showing locations of lava flows during 2005. Upper image shows lava flows during 1-15 April 2005. Flows are located NW, N, and NE of MacKenney Cone as well as to the W in a longer flow. During August 2005 (lower image), active flows were concentrated NE and E of the cone with residual cooling observed to the W and SW. Courtesy of HIGP MODVOLC Thermal Alerts System.

Strombolian explosions reached 100 m above the crater, and avalanches of ejected incandescent blocks produced small ash clouds to low levels during much of 2005. Thermal anomalies ceased at Pacaya after 28 August 2005, although observations by INSIVUMEH of occasional Strombolian activity and ejected bombs were made until 11 September. After that, only weak incandescence was reported in early November and January 2006; a new Strombolian explosion occurred on 9 March 2006.

Activity during 2006-2009. The Strombolian explosions that began on 9 March 2006 ejected material tens of meters above the volcano in pulses of activity lasting 10-30 seconds; on 12 March material rose 250 m above MacKenney Cone. Significant lava flows began in late March, advancing about 150 m from the S and SW edges of the crater. A new flow on 13 April was reported by INSIVUMEH as issuing from a parasitic cone, at the ENE base of the main cone, and was 125 m long by 17 April. During the rest of 2006, lava flows from this vent reached lengths of more than 800 m NW of the summit cone and covered an area N, NE, and NW of the cone, known as the 'meseta' (plateau) popular with visitors to the Park (see figures 39, 40, and 41, BGVN 33:08). The Washington VAAC issued only one ash advisory in 2006, on 28 August, and noted possible ash emissions at 3 km altitude drifting 16 km W.

Throughout 2007, 2008, and 2009, multiple vigorous lava flows traveled in different directions from MacKenney Cone. The new lava flows that emerged from a vent on the ENE flank during March and April 2006 also continued to flow NE and N, and then curved to the W in multiple branches, covering large areas of the plateau between the active cone and the three older cones (Cerro Grande, Cerro Chiquito and Cerro Chino) to the N. These flows were most active through November 2008 (figure 63). Flows down the S and SW flanks continued intermittently and reached lengths of several hundred meters. They were most active between August 2008 and the end of 2009; reaching 800 m long in December 2008. Lava flow volume and explosive activity increased during April 2009; the flows traveled down the S and SW flanks for distances up to 400 m. During July, they traveled as far as 600 m down the flanks, and remained vigorous throughout the rest of the year.

Figure 63. Location and extent of thermal anomalies from lava flows and Strombolian activity at Pacaya during April and November 2008. Upper image: Thermal anomalies suggest that lava flows during the first half of April 2008 were primarily issuing from a vent on the NE flank and flowing N, NW, and NE, and not originating from MacKenney Cone. Lower image: By November 2008, there were extensive flows from the summit crater flowing W and SW, as well as to areas N of the cone. Courtesy of HIGP MODVOLC Thermal Alerts System.

Strombolian explosions were intermittent during this three year period, only reported a handful of times in January, June, and December 2007, February, May, and July 2008, and March and April 2009, with explosions of material to a few tens of meters above the summit cone. These explosions often created gas plumes reported by INSIVUMEH to altitudes of 2-3 km. They reported that material from explosions in March 2009 enlarged the cones in the summit crater, and vigorous degassing contributed to substantial noise. A small spatter cone, 4 m high, was detected in the S part of the crater in late April.

There were only three series of VAAC reports during 2007-2009, two in 2007 and one in 2008. A small ash plume was observed on 6 April 2007 at 4.6 km altitude that drifted less than 10 km SSE before dissipating. On 17 November 2007 a narrow plume was observed in satellite imagery extending 15-25 km NW of the summit at an altitude of 4.3 km. A brief emission of gas and possible ash was reported on 2 November 2008, but dissipated within three hours.

Activity during 2010. During January 2010, the lava flows that had descended the S, SW, and W flanks of MacKenney Cone since 2006 ceased flowing. Strombolian explosions were observed again in early February and new flows originating from a depression on the NE flank of the cone traveled 400 m down the E and NE flanks toward the meseta. Avalanches of blocks from the flow fronts set fire to local vegetation. Significant tephra explosions reached up to 150 m high in late February and lava flows traveled 800 m E (figure 64). Multiple lava flows on the SW flank of MacKenney cone on 20 May 2010 traveled 1.6 km, farther than previously recorded flows.

Figure 64. Significant new lava flows at Pacaya can be identified moving E from the NE flank of MacKenney Cone beginning in February 2010 on this map of MODVOLC thermal alerts. The flows that had been active through January to the W and SW were cooling but still produced a thermal signature visible in this MODVOLC image from the second half of March 2010. Courtesy of HIGP MODVOLC Thermal Alerts System.

This increasing activity culminated in a large Strombolian eruption on 27 and 28 May 2010. On 29 May a 90-m-wide lava flow traveled SSE down the flank at an estimated rate of 100 m per hour and burned three houses on the Pacaya Grande ranch (see details in BGVN 39:05). The eruption was characterized in a report from CONRED as having constant explosions that ejected material 500 m into the air. INSIVUMEH reported a continuing series of explosions 5-10 seconds apart that ejected black ash up to 1 km above the crater on 28 May.

Numerous weather clouds prevented the Washington VAAC from determining an altitude of the ash plume until late on 28 May, when it was visible in satellite imagery at about 13 km altitude. Ash plumes drifted 20-30 km NW, causing ashfall as thick as 10 cm in areas downwind, including in Guatemala City, about 30 km NNE. INSIVUMEH reported 5-7 mm of ashfall during 27-28 May at the Aurora International Airport. CONRED reported on 28 May that about 1,600 people had been evacuated from six towns 3-4 km W, NNW, N, and NNE, and that the airport was closed. According to a map posted by CONRED, blocks fell in areas as far as 12 km NE, and ash was reported in areas E of Chinautla, 37 km NNE. Reuters News Agency reported that one person (a reporter) died and three children were missing.

The lava flow moving down the SSE flank of MacKenney Cone was shown by MODVOLC thermal alert pixels that persisted through much of June 2010 (figure 65). The lava flowed to within 450 m of several properties including El Chupadero, located 2-2.5 km S of the crater, and disrupted an access road from El Caracol (3 km SW) and Los Pocitos (5.5 km S).

Figure 65. Thermal alert pixels seen in MODVOLC data show the area of lava flows at Pacaya extending down the SSE flank of MacKenney Cone from the summit and from a vent on the SSE side of the cone during June 2010, damaging property in its path. Courtesy of HIGP MODVOLC Thermal Alerts System.

Intermittent Strombolian activity continued into June 2010, with tephra ejected as high as 700 m above the crater. The lava flows on the SE flank remained active through mid-June and had traveled as far as 3.5 km before cooling. By late June, the cone was primarily emitting white and blue fumarolic plumes to several hundred meters. Significant ash emissions and small pyroclastic flows were again reported during the last two weeks of July, causing an evacuation of 150 people from nearby areas. A Washington VAAC report on 22 July noted a plume at an altitude of 4.1 km drifting N, that produced ashfall within 10 km. Strombolian explosions on 24 and 25 July were strong enough to cause a MODVOLC thermal alert pixel at the summit, and to eject tephra blocks onto the flanks.

The last eruptive events of this multi-year eruption were ash plumes emitted in August and Strombolian activity in October 2010. Small ash plumes rose to 800 m above the crater causing ashfall 5 km away on 2 and 3 August. This was followed by a burst of Strombolian explosions during 21-22 and 26 October. After this, only fumarolic emissions of primarily water vapor were reported at Pacaya until a plume of ash-and-gas was reported by INSIVUMEH on 5 March 2013.

A comparison of a geologic map prepared by INSIVUMEH's Rudiger Escobar Wolf in 2010 (also published in BGVN 39:05) and a Google Earth image from December 2010 readily shows the impact of the extensive flows at Pacaya during the 2006-2010 eruptive episode (figure 66).

Figure 66. Comparison of 2010 geologic map (also published in BGVN 39:05) and a Google Earth image dated 12 December 2010 showing the impact of the lava flows at Pacaya from the 2006-2010 eruption. Geologic map from INSIVUMEH, imagery from Google Earth.

Activity during March 2013-August 2014. Pacaya remained quiet between October 2010 and March 2013 except for intermittent pulses of seismicity and minor water vapor and gas emissions. An increase in explosions was noted beginning late in 2012, but only steam plumes were observed rising less than 500 m above the summit during January and February 2013. A single MODVOLC thermal alert pixel captured on 2 Feb 2013 to the SE of MacKenney Cone is likely the result of agricultural, not volcanic, activity.

The first report of renewed activity was on 5 March 2013 when INSIVUMEH noted that a thin plume of brown ash accompanied the fumarolic plumes, and dispersed to the S. Weak gas-and-ash plumes recurred several more times during March. On 24 April tephra was ejected 25 m high by weak explosions; incandescence and explosions were detected the next day and again on 29 April. Incandescence was regularly observed during May, and more substantial Strombolian activity started on 20 May and carried through to the end of the month. Tephra ejections rose to 25 m above the crater, and continuous explosions a few minutes apart that ejected bombs and generated rumbles, were heard 4 km away. An explosion on 30 May ejected ash and lapilli 200 m above the crater that was then deposited within 400 m of the crater.

Strombolian activity on 27 June 2013 again ejected small amounts of tephra that were deposited on the W flank. An investigation of the summit crater of MacKenney Cone during June determined that a 15 m high cone had been the source of the most recent explosive activity. An increase in seismicity in late July indicated the continued growth of the pyroclastic cone which had risen to 4 m above the crater rim by 24 July, doubling its total height from June to more than 30 m high. Weak explosions and incandescence were observed the next night, and a Strombolian eruption on 30 July lasted for four hours and ejected material 250 m above the cone. A diffuse ash plume drifted 2 km N, causing ashfall in areas downwind, and another ash plume drifted 5 km S. A prominent hot spot at the summit was reported by the Washington VAAC.

During 9 and 10 August seismicity increased again and Strombolian explosions ejected tephra 200 m above MacKenney Crater and onto the flanks, 400 m from the crater, causing small avalanches on the flanks. Another explosion during the night of 14-15 August produced a 300-m-long lava flow that traveled W from MacKenney Crater; new emissions of ash and gases to 500 m above the crater were reported by the Washington VAAC the next day. Tremors and explosions of incandescent material continued through August and the first half of September ejecting material and sending small ash plumes a few kilometers above the cone. Incandescence was reported as visible from the capital to the N by mid-September. Two MODVOLC thermal anomaly pixels were recorded on 30 August and 3 September confirming the increased thermal activity reported by INSIVUMEH.

In late November 2013 INSIVUMEH reported that activity remained unchanged with weak explosions, gas emissions and tephra ejections continuing. Pilots reported that ash plumes rose to 2.7 km and drifted 10 km SW. This continued into early January 2014 when activity at the main crater increased; seismographs recorded constant tremor, and beginning on 11 January, INSIVUMEH observed tephra explosions to 100 m, gas plumes to 600 m, and new craters on the E, S, and W flanks that produced extensive new lava flows. These flows emitted strong thermal anomaly signatures that were captured by MODVOLC for the next two weeks (figure 67).

Figure 67. MODVOLC thermal alert images from Pacaya on individual days during January 2014 show the extent of new lava from multiple vents on the E, S, and W flanks of MacKenney Cone. The green dot is the summit crater at MacKenney Cone. Clockwise from top left: a) 11 January, thermal signatures N and SW of the summit crater; b) 13 January, the strongest signals are from the SW and SW flanks; c) 19 January, fewer signals suggest a pause in the flows; d) 20 January, renewed flows on the S flank. Courtesy of HIGP MODVOLC Thermal Alerts System.

At the beginning of this event (on 11 January) CONRED reported evacuations from Villa Canales (14 km NW), El Chupadero (2-2.5 km S), and San Vicente Pacaya (5 km NW). Lava flows had reached 3 km by 13 January. A report on 21 January noted that the S-flank lava flow was 3.6 km long and continued to slowly advance, burning vegetation (figure 68) between the Rodeo and Los Pocitos roads.

Figure 68. An a'a lava flow at Pacaya burning its way through a forest on 11 January 2014. Courtesy of CONRED.

Volcanologists observed that the cone in MacKenney Crater had been completely destroyed during the January events, leaving a deep crater that produced fumarolic activity. The Washington VAAC noted an ash plume on 11 January that rose to 3.4 km and extended 55 km SSW from the summit. After that, a prominent hot spot was visible but there was no further indication of ash in satellite imagery. Separate Google Earth images captured in December 2013 and April 2014 show the extent of the new lava flows on the S flank of MacKenney Cone (figure 69) during January 2014.

Figure 69. Two Google Earth images of the S flank of MacKenney Cone at Pacaya before and after lava flows during January 2014. Upper image is dated 30 December 2013. Lower image is dated 9 April 2014. An image dated 30 March also shows the new flows, but was much hazier. Note that the location of MODVOLC thermal alerts in figure 67d matches the location of January 2014 lava flows. Courtesy of Google Earth.

The next episode of activity began with increased gas-and-vapor plumes during 27-28 February 2014 and included ejection of fine pyroclastic material 600 m S and SW from the crater. INSIVUMEH and CONRED noted increased activity on 2 March; at 0515 Strombolian activity at MacKenney Crater ejected material as high as 800 m and lava flows descended the W flank (figure 70). Explosions produced dense ash plumes that initially rose 2.5 km and drifted 15 km S, SW, and W. Ashfall was reported in El Rodeo (4 km WSW), Patrocinio (about 5 km W), and Francisco de Sales (5 km N). By the next day, activity had decreased, but lava flows traveled up to 1.3 km S and ejected tephra drifted 600 m S and SW. Small explosions and lava flows continued to be active for the next week. MODVOLC thermal alerts were captured around the summit on 2 and 3 March, but no additional thermal alerts were recorded in 2014. The Washington VAAC also noted emissions of gas and volcanic ash on 2 March that rose to 4.9 km altitude and extended over 200 km W before the end of the day. By 3 March an area of light ash remained 370 km W of the volcano off the southern Mexico coast and dissipated during the day.

Figure 70. The eruption of Pacaya on 2 March 2014. The lava fountain (reddish) can be seen at the summit vent. Courtesy of CONRED.

After INSIVUMEH reported a small ash plume on 10 April 2014, only minor episodes of increased seismicity and steam plumes rising a few tens of meters above the summit were observed through August.

Geologic Background. Eruptions from Pacaya are frequently visible from Guatemala City, the nation's capital. This complex basaltic volcano was constructed just outside the southern topographic rim of the 14 x 16 km Pleistocene Amatitlán caldera. A cluster of dacitic lava domes occupies the southern caldera floor. The post-caldera Pacaya massif includes the older Pacaya Viejo and Cerro Grande stratovolcanoes and the currently active Mackenney stratovolcano. Collapse of Pacaya Viejo between 600 and 1,500 years ago produced a debris-avalanche deposit that extends 25 km onto the Pacific coastal plain and left an arcuate scarp inside which the modern Pacaya volcano (Mackenney cone) grew. The NW-flank Cerro Chino crater was last active in the 19th century. During the past several decades, activity has consisted of frequent Strombolian eruptions with intermittent lava flow extrusion that has partially filled in the caldera moat and covered the flanks of Mackenney cone, punctuated by occasional larger explosive eruptions that partially destroy the summit.

Information Contacts: Instituto Nacional de Sismologia, Vulcanologia, Meteorologia e Hydrologia (INSIVUMEH), Unit of Volcanology, Geologic Department of Investigation and Services, 7a Av. 14-57, Zona 13, Guatemala City, Guatemala (URL: http://www.insivumeh.gob.gt/); Coordinadora Nacional para la Reducción de Desastres (CONRED), Av. Hincapié 21-72, Zona 13, Guatemala City, Guatemala (URL: http://conred.gob.gt/www/index.php); 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: http://www.ospo.noaa.gov/Products/atmosphere/vaac/, archive at: http://www.ssd.noaa.gov/VAAC/archive.html); 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/); Google Earth (URL: https://www.google.com/earth/); Reuters News Agency (URL: http://www.reuters.com/article/us-guatemala-volcano-idUSTRE64R11M20100528?pageNumber=2).

Mount Rokatenda, or Paluweh, on the island of Palu'e, lies north of the primary volcanic arc that cuts across Flores Island in Indonesia's Lesser Sunda Islands, and has seen infrequent activity in modern times. The previous eruption in 1985 from a summit lava dome spread 3 cm of ash over villages on the W side of the island. This report is a summary of the October 2012 to August 2013 eruption, and an update through 2016 that includes information provided by Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM), the Darwin Volcanic Ash Advisory Center (VAAC), and the University of Hawai'i's MODVOLC thermal alert reporting system. Numerous news reports also covered the major explosions during 2013.

Two brief periods of increased seismicity in April 2009 and January 2012 were the only recorded activity at Paluweh since 1985, prior to an eruption that began in October 2012 and continued through August 2013. PVMBG noted the beginning of lava dome growth on 8 October. A substantial number of MODVOLC thermal alert pixels from MODIS satellite data were first recorded on 11 October 2012 and recurred regularly through 20 July 2013. The first ash plumes were reported by the Darwin VAAC on 11 November 2012 and continued several times each month through May 2013, and then again in late June and during 10-12 August. Plumes generally rose to 2-3 km and drifted between 50 and 100 km in various directions, although a large ash plume on 3 February 2013 rose to higher than 13 km and drifted over 500 km SE, S and SW, briefly impacting air travel in NW Australia. A major explosion on 10 August 2013 created a large pyroclastic flow to the NW from the summit that killed five people on the beach. No further explosions were specifically dated after 12 August 2013, and seismicity gradually decreased over the next several months.

Activity during October 2012-April 2013. PVMBG noted lava dome growth, incandescent avalanches, pyroclastic flows, and ash plumes during October 2012 through January 2013. Ejecta as large as 6 cm in diameter was deposited up to 3 km from the summit, and ashfall affected the entire island, averaging 2 cm thick in places; lahars and ash damaged homes and infrastructure on the island (BGVN 39:01). A large eruption on 2 February 2013, which produced a 13-km-high ash plume the next day, generated a substantial SO₂ signature, pyroclastic flows to the S and SW, and avalanches. Residents of eight villages were evacuated and significant ashfall was reported up to 1 mm thick in Ende (60 km S on East Nusa Tenggara Island). Thick ashfall was also reported in Ona (SE part of the island) and thin deposits were reported in other areas of the island to the W, N, and E. During a field expedition on 7 February, PVMBG staff observed that about 25% of the S portion of the dome was lost; the lava-dome volume had been an estimated 5.1 million cubic meters on 13 January, prior to the explosion.

After the large early February 2013 explosion, many intermittent low-level ash emissions continued through the last week in May, with over 175 VAAC reports issued from the Darwin VAAC during the period. NASA's Earth Observatory (EO) identified an ash plume in MODIS satellite images drifting over 440 km SW on 24 March 2013, and discoloration of the seawater from ash W of the island (figure 7).

Figure 7. NASA image acquired 24 March 2013 with the MODIS instrument shows an ash plume from Paluweh drifting over 440 km SW across Flores Island. Light-colored ash coats the southern third of Paluweh Island, and the ocean to the W of the island is colored turquoise from ash floating near the water's surface. Courtesy of NASA, GSFC.

Another NASA-EO image captured on 19 April 2013 shows the extent of ash deposits covering areas of the S and E sides of the summit where the plumes most commonly drift. A delta extending S into the Flores Sea, which was visible in imagery on 12 February and likely created by a pyroclastic flow during the large 2-3 February explosion (figure 8), was also visible.

Figure 8. NASA-EO image of Paluweh captured 19 April 2013. Note the extent of ash covering the area of the island on the S and E sides of the summit where the plumes usually drift. It also shows a delta extending S into the Flores Sea, also visible in imagery on 12 February and likely created by a pyroclastic flow during the large 2-3 February explosion. Courtesy of NASA Earth Observatory.

Activity during May-August 2013. There was a three-week break in reported ash plumes between 25 May and 19 June when a low level plume rising to 2.4 km was observed drifting 37 km SE. After this, no further activity was reported until 10 August. A large and deadly explosion took place on 10 August, producing an ash plume that rose to 4.3 km and drifted 130 km W. Details of the explosion are given in BGVN 39:01 and additional information is provided in this report. According to PVMBG, a substantial pyroclastic flow traveled NW from the summit down the Ojaubi drainage towards a village on the beach and killed five fisherman. Rescuers noted that the ground was hot and covered with 10-20 cm of ash. NASA-EO captured images before and after the 10 August 2013 eruption where the path of the pyroclastic flow to the NW is clearly visible (figure 9).

Figure 9. NASA-EO images of Paluweh (Mt. Rokatenda) on 3 August and 4 September 2013, before and after a large eruption with a deadly pyroclastic flow that traveled NW from the summit to the ocean, killing 5 people at the beach on 10 August. The delta on the S of the island was created during an earlier eruption and pyroclastic flow on 2-3 February 2013. Courtesy of NASA Earth Observatory.

Activity during 2014-2016. In April 2014, PVMBG noted that the last major explosion had been on 10 August 2013. The last 2013 ash plume recorded by the Darwin VAAC was on 12 August 2013. Visual observations of occasional eruptive activity were noted until November 2013; small explosion earthquakes were also reported as being last recorded in November. No changes were observed in the lava dome between September 2013 and March 2014. PVMBG lowered the Alert level from III to II (on a scale of 1-4) on 7 April 2014.

No additional reports of activity at Paluweh appeared until late 2015, when PVMBG noted that steam plumes rising 75-200 m above the summit were common between August and October 2015. Seismicity remained low but variable during this time as well. From November 2015 through January 2016, steam plume heights ranged from 5-150 m. Seismicity remained low; earthquakes indicating rock avalanches and fumarolic emissions were the most common type recorded (figure 10). Paluweh remained quiet throughout 2016, although in February 2017 it was still listed by PVMBG at Alert Level II, with a potential for eruptive activity.

Figure 10. Seismic activity at Paluweh between 1 January 2015 and 13 January 2016. Vertical Axis represents daily number of events for all graphs. Guguran are avalanche events, Hembusan are emission-related events, Vulkanik Dangkal (VB) are shallow volcanic events, Vulkanik Dalam (VA) are deep volcanic events, Tektonik Local are local tectonic events, and Tektonik Jauh are distant tectonic events. Courtesy of PVMBG (Paluweh report, 18 January 2016).

Geologic Background. Paluweh volcano, also known as Rokatenda, forms the 8-km-wide island of Palu'e north of the volcanic arc that cuts across Flores Island. The broad irregular summit region contains overlapping craters up to 900 m wide and several lava domes. Several flank vents occur along a NW-trending fissure. The largest historical eruption occurred in 1928, when strong explosive activity was accompanied by landslide-induced tsunamis and lava dome emplacement. Pyroclastic flows in August 2013 resulted in fatalities.

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/); NASA Earth Observatory, EOS Project Science Office, NASA Goddard Space Flight Center, Goddard, Maryland, USA (URL: http://earthobservatory.nasa.gov/).

A brief eruption that began on 23 October 2013 was the first reported activity at Zhupanovsky since 1959 (BGVN 39:09). After another eight months of quiet, eruptive activity began again in early June 2014 that was characterized by periods of frequent, moderate, ash-generating explosions that continued through the end of that year (BGVN 39:09). As described below, similar activity continued from January 2015 through 24 March 2016, with periods of strong explosions generating ash plumes as high as 10 km altitude. Another long period of eight months without observed activity was broken by a large eruption on 20 November 2016. No additional activity was reported through March 2017. Most of the data comes from Kamchatka Volcanic Eruption Response Team (KVERT) reports. Often, the volcano is obscured by clouds. All reported dates are UTC unless otherwise noted (local = -12 hours).

Activity during 2015. According to KVERT, the moderate eruption with explosions generating ash plumes continued into 2015 (table 3). The Aviation Color Code remained Orange (third level on a four-color scale) between 1 January and 15 May 2015. After an explosion on 3 April, explosive activity waned and KVERT lowered the Aviation Color Code from Orange to Yellow (second level on a four-color scale) on 16 May. On 9 June 2015, activity increased again, with webcam and satellite images showing an ash plume rising to an altitude of 6 km. The Aviation Color Code was raised on 8 June to Orange. During an overflight on 16 July, volcanologists observed fresh deposits at the foot of the volcano from collapses of the S section of the active Priemysh Crater that likely occurred on 12 July (figures 7 and 8). Moderate activity at the crater continued through 17 July; the Aviation Color Code was lowered to Yellow on 18 June and to Green on 23 July. On 7 August KVERT reported that explosive activity had ended, but collapses of the S part of the active crater continued. On 6 August ash plumes rose to an altitude of 5 km and drifted 25-60 km SW, triggering KVERT to raise the Aviation Color Code to Yellow. The code was lowered back to Green on 13 August.

Figure 7. Photo of the summit area of Zhupanovsky showing the collapse deposits from the Priemysh cone, 16 July 2015. Photo credit to A. Plechova and V.I. Vernadsky, IGAC RAS. Courtesy of Institute of Volcanology and Seismology FEB RAS, KVERT.

Figure 8. Photo of the southern side of Zhupanovsky showing the collapse deposits from the Priemysh cone, 16 July 2015. Photo credit to A. Plechova and V.I. Vernadsky, IGAC RAS. Courtesy of Institute of Volcanology and Seismology FEB RAS, KVERT.

Table 3. Summary of reported activity at Zhupanosky, January 2015-March 2016. Data is from webcam images, satellite images, and visual observations. On many days, clouds obscured visibility. Courtesy of KVERT and Tokyo VAAC.

KVERT indicated that activity remained low until 27 November 2015 when, based on satellite images, ash plumes rose to altitudes of 5-6 km and drifted 285 km E. The Aviation Color Code was raised to Orange. IVS FED RAS (Institute Volcanology and Seismology Far East Division of the Russian Academy of Sciences) observers noted an ash explosion at 0356 on 30 November (UTC); the Tokyo Volcanic Ash Advisory Center (VAAC) reported that the resulting ash plume rose to an altitude of 9 km. Pyroclastic flow deposits 15.5 km long were observed on the S flank after the 30 November event.

According to KVERT, activity decreased after a partial collapse of the S central sector on 27 and 30 November 2015. Satellite images detected a very weak thermal anomaly over the volcano on 4 and 7 December. Moderate levels of fumarolic activity continued. On 10 December the Aviation Color Code was lowered to Yellow. By early-to-mid December 2015, only moderate levels of fumarolic activity were observed. On 17 December the Aviation Color Code was lowered to Green.

KVERT reported that thermal anomalies occurred frequently during the reporting period; often they were obscured by clouds. The only MODVOLC thermal alerts, based on MODIS anomalies, during the reporting period were during March-June 2015: on 7 March, 8 March (2 pixels), 15 March (2 pixels), 21 March (2 pixels), 20 May, and 16 June.

Activity during 2016. The eruption pattern of fluctuating activity levels continued into 2016. Based on visual observations, KVERT reported that at 1636 on 19 January 2016 (UTC), an explosion generated an ash plume that rose to an altitude of 7-8 km and drifted 20 km E (figure 9). The Aviation Color Code was raised to Orange.

Figure 9. Photo of the ash column rising from Zhupanovsky, 19 January 2016. Still image taken from webcam video. Courtesy of Institute of Volcanology and Seismology FEB RAS, KVERT.

Moderate steam-and-gas activity continued during 5 February-18 March. An explosion at 2029 on 12 February (UTC) was recorded by a video camera and generated an ash plume that rose to an altitude of 7 km and drifted E. A larger explosion visually observed a minute later generated an ash plume that rose to an altitude of 10 km and drifted 50 km SE. The Aviation Color Code was raised to Red for several hours. In a report issued at 2334 (UTC), KVERT noted that only moderate amounts of gas and steam rose from the volcano; the Aviation Color Code was lowered to Orange. Ash from the earlier explosions drifted E over Kronotsky Bay and NW. A few hours later, an ash plume was detected in satellite images rising 1 km above the volcano and drifting 288 km E.

The Tokyo VAAC recorded an explosion at 1320 on 24 March (UTC) that generated an ash plume which rose to an altitude of 8 km. After the explosion, no further activity was observed. A very weak thermal anomaly was detected over the volcano in satellite images on 1 and 10 April. The Aviation Color Code was thus lowered to Yellow on 13 April. The last thermal anomaly detection in a satellite image was on 10 April. However, moderate fumarolic activity continued. The Aviation Color Code was lowered to Green on 16 June.

At 1429 on 20 November 2016 a webcam recorded ash plumes rising to altitudes of 6-8 km and drifting 73 km E (figure 10); the Aviation Color Code was raised from Green to Orange. No further activity was observed, and on 22 November the Aviation Color Code was lowered to Yellow.

Figure 10. Photo of the ash column rising from Zhupanovsky and extending E, 20 November 2016. Still image taken from webcam video. Courtesy of Institute of Volcanology and Seismology FEB RAS, KVERT.

Geologic Background. The Zhupanovsky volcanic massif consists of four overlapping stratovolcanoes along a WNW-trending ridge. The elongated complex was constructed within a Pliocene-early Pleistocene caldera whose rim is exposed only on the eastern side. Three of the stratovolcanoes were built during the Pleistocene. An early Holocene stage of frequent moderate and weak eruptions from 7,000 to 5,000 years before present (BP) was followed by a period of infrequent larger eruptions that produced pyroclastic flows. The last major eruption took place about 800-900 BP. Recorded eruptions have consisted of relatively minor explosions from Priemysh, the third cone from the E about 2.5 km from the summit peak.

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