Recently Published Bulletin Reports
Manam (Papua New Guinea) Few ash plumes during November-December 2022
Krakatau (Indonesia) Strombolian activity and ash plumes during November 2022-April 2023
Stromboli (Italy) Strombolian explosions and lava flows continue during January-April 2023
Nishinoshima (Japan) Small ash plumes and fumarolic activity during November 2022 through April 2023
Karangetang (Indonesia) Lava flows, incandescent avalanches, and ash plumes during January-June 2023
Ahyi (United States) Intermittent hydroacoustic signals and discolored plumes during November 2022-June 2023
Kadovar (Papua New Guinea) An ash plume and weak thermal anomaly during May 2023
San Miguel (El Salvador) Small gas-and-ash explosions during March and May 2023
Semisopochnoi (United States) Occasional explosions, ash deposits, and gas-and-steam plumes during December 2022-May 2023
Ebeko (Russia) Continued explosions, ash plumes, and ashfall during October 2022-May 2023
Home Reef (Tonga) Discolored plumes continued during November 2022-April 2023
Ambae (Vanuatu) New lava flow, ash plumes, and sulfur dioxide plumes during February-May 2023
Manam (Papua New Guinea) — July 2023 Cite this Report
Manam
Papua New Guinea
4.08°S, 145.037°E; summit elev. 1807 m
All times are local (unless otherwise noted)
Few ash plumes during November-December 2022
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).
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 (Indonesia) — July 2023 Cite this Report
Krakatau
Indonesia
6.1009°S, 105.4233°E; summit elev. 285 m
All times are local (unless otherwise noted)
Strombolian activity and ash plumes during November 2022-April 2023
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.
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.
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).
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).
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
Italy
38.789°N, 15.213°E; summit elev. 924 m
All times are local (unless otherwise noted)
Strombolian explosions and lava flows continue during January-April 2023
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).
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.
Month |
Explosive Activity |
Jan 2023 |
Typical Strombolian activity with spattering and lava overflows in the N crater area. Explosions were reported from 4 vents in the N area and 1-2 vents in the CS area. The average hourly frequency of explosions was low-to-medium (1-12 events/hour). The intensity of the explosions varied from low (less than 80 m high) to medium (less than 150 m high) in the N crater area and up to high (greater than 150 m high) in the CS crater area. |
Feb 2023 |
Typical Strombolian activity with spattering in the N crater area. Explosions were reported from 2-3 vents in the N area and 1-4 vents in the CS area. The average hourly frequency of explosions was low-to-medium (1-14 events/hour). The intensity of the explosions varied from low (less than 80 m high) to medium (less than 150 m high) in the N crater area and up to high (greater than 150 m high) in the CS crater area. |
Mar 2023 |
Typical Strombolian activity with spattering and lava overflows in the N crater area. Explosions were reported from 2-3 vents in the N area and 2-4 vents in the CS area. The average hourly frequency of explosions was low-to-medium (1-18 events/hour). The intensity of the explosions varied from low (less than 80 m high) to medium (less than 150 m high) in the N crater area and up to high (greater than 150 m high) in the CS crater area. |
Apr 2023 |
Typical Strombolian activity. Explosions were reported from 2 vents in the N area and 2-3 vents in the CS area. The average hourly frequency of explosions was low-to-high (1-16 events/hour). The intensity of the explosions varied from low (less than 80 m high) to medium (less than 150 m high) in both the N and CS crater areas. |
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.
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.
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.
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.
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 (Japan) — July 2023 Cite this Report
Nishinoshima
Japan
27.247°N, 140.874°E; summit elev. 100 m
All times are local (unless otherwise noted)
Small ash plumes and fumarolic activity during November 2022 through April 2023
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.
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.
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.
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).
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 (Indonesia) — July 2023 Cite this Report
Karangetang
Indonesia
2.781°N, 125.407°E; summit elev. 1797 m
All times are local (unless otherwise noted)
Lava flows, incandescent avalanches, and ash plumes during January-June 2023
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).
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.
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.
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.
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.
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 (United States) — July 2023 Cite this Report
Ahyi
United States
20.42°N, 145.03°E; summit elev. -75 m
All times are local (unless otherwise noted)
Intermittent hydroacoustic signals and discolored plumes during November 2022-June 2023
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.
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).
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).
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 (Papua New Guinea) — June 2023 Cite this Report
Kadovar
Papua New Guinea
3.608°S, 144.588°E; summit elev. 365 m
All times are local (unless otherwise noted)
An ash plume and weak thermal anomaly during May 2023
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).
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 (El Salvador) — June 2023 Cite this Report
San Miguel
El Salvador
13.434°N, 88.269°W; summit elev. 2130 m
All times are local (unless otherwise noted)
Small gas-and-ash explosions during March and May 2023
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.
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 (United States) — June 2023 Cite this Report
Semisopochnoi
United States
51.93°N, 179.58°E; summit elev. 1221 m
All times are local (unless otherwise noted)
Occasional explosions, ash deposits, and gas-and-steam plumes during December 2022-May 2023
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.
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
Russia
50.686°N, 156.014°E; summit elev. 1103 m
All times are local (unless otherwise noted)
Continued explosions, ash plumes, and ashfall during October 2022-May 2023
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).
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.
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.
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.
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).
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
Tonga
18.992°S, 174.775°W; summit elev. -10 m
All times are local (unless otherwise noted)
Discolored plumes continued during November 2022-April 2023
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).
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
Vanuatu
15.389°S, 167.835°E; summit elev. 1496 m
All times are local (unless otherwise noted)
New lava flow, ash plumes, and sulfur dioxide plumes during February-May 2023
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.
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).
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).
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/).
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Bulletin of the Global Volcanism Network - Volume 37, Number 07 (July 2012)
Managing Editor: Richard Wunderman
Ijen (Indonesia)
2012 high seismicity, blasts, and subaqueous emissions; maps of complex
Ioto (Japan)
Mud ejections and small phreatic eruptions during early 2012
Kikai (Japan)
Low level tremor and frequent white plumes during October 2010-June 2012
Kirishimayama (Japan)
Gradual decline in activity following explosive 2011 eruptions
Obituary Notices (Unknown)
Death of volcanologist Herman Patia Principal Volcanologist at the Rabaul Volcano Observatory
Ruiz, Nevado del (Colombia)
1988-2006 monitoring captures seismic swarms, deformation, and radon emissions
Tongariro (New Zealand)
Seismicity preceded phreatic explosion; associated rainfall-fed lahar
Ijen
Indonesia
8.058°S, 114.242°E; summit elev. 2769 m
All times are local (unless otherwise noted)
2012 high seismicity, blasts, and subaqueous emissions; maps of complex
This report first documents earthquakes at or near Kawah Ijen and minor emissions within its crater lake during mid-December 2011 to mid-2012. These earthquakes and emissions were ongoing at press time.
The second and third subsections below present maps and background relating to the Ijen complex. As discussed in earlier reports, Ijen is the name often applied to the larger complex consisting of a large caldera and associated cones. Kawah Ijen is the name of the intracaldera cone that contains a crater with an acid briny lake 700 x 800 m in diameter. The coordinates cited in the header and Summary for this volcano refer to the approximate center of the lake (see photos of the lake in Photo Gallery and figure 4 in BGVN 32:02; Demelle and others, 2000; Takano and others, 2004). Kawah Ijen, the active vent of the complex, is known for hydrothermal and phreatic behavior in its crater lake. During this reporting interval an intrusion appears to have risen to a shallow depth beneath the crater lake. Subaqueous sulfur-bearing emissions seemingly occurred on the lake floor.
The last subsection briefly calls attention to sulfur mining near Kawah Ijen's crater lake. Laborers carry heavy loads of native sulfur across steep terrain as they breathe air rich in volcanic gases. Recent dental studies cited in this subsection compared the teeth and gums of laborers to residents living nearby who endured less exposure to the volcanic gases. They found that the laborers suffered more tooth and gum disorders.
Mid-December 2011 to mid-2012. According to a summary of activity by the Center for Volcanology and Geological Hazard Mitigation (CVGHM) and the USGS Volcano Disaster Assistance Program (VDAP), Ijen volcano has been in a state of heightened unrest centered at Kawah Ijen since May 2011, a time when teams installed, tested, and conducted training on the use of upgraded seismic instrumentation. As previously reported in BGVN 36:12, increased seismicity and fumarole temperatures caused CVGHM to raise the Alert Level from 1 to 2 (on a scale of 1-4) on 15 December 2011.
On 18 December, after observing further increases in both seismicity and degassing, CVGHM established Alert Level 3. In the next few months, scientists documented four periods of significant unrest. They occurred on 20 and 30 December 2011, 4 January 2012, and 2 March 2012.
On 1 January 2012, CVGHM recorded a swarm of earthquakes, raising concerns of renewed pressure in the then-inferred shallow magmatic system. The agency's reports also noted shifts in the rates of recent high-frequency earthquakes (believed to be associated with breaking rocks). Increases occurred in both low-frequency earthquakes and tremor (both believed to be associated with the movement of fluids). At the crater lake, debris (probably native sulfur) seen floating on the surface was judged as likely derived from emissions vented into the ~180-m-deep lake (Takano and others, 2004). Congruent with that interpretation, sulfurous-gas emissions measured just over the lake surface were very high at the time.
On 8 February 2012, after decreases in seismicity, and visual and thermal signs of unrest at Kawah Ijen, CVGHM lowered the Alert Level to 2.
Sharp increases in seismicity prevailed after 2 March 2012, which spurred CVGHM to raise the Alert Level to 3 on 12 March. Elevated crater lake temperatures (up to 43°C at 5 m depth) and gas plumes to 100-200 m above the summit had been reported. These observations led CVGHM and VDAP to suggest an intrusion of magma had reached the point where it caused perturbations to the extensive hydrothermal system in the shallow conduit and crater lake.
During 1-30 April 2012 white plumes from Kawah Ijen rose 100-200 m above the crater, and during 1-11 May diffuse white plumes rose 50-100 m above the crater. During this time and through 13 May, the amplitude and number of earthquakes gradually decreased and the crater lake water temperature decreased by 8°C. On 13 May 2012, CVGHM again lowered the Alert Level to 2. Later, on 24 July 2012, they again raised the Alert Level to 3. Authorities posted a 1.5-km-radius no-entry zone around the lake's center.
Visual and seismic observations published in CVGHM's report of 24 July 2012 indicated repeated hot air-blasts during 1-24 July. The blasts sent plumes rising to 50-100 m over the summit, and registered seismically as follows: 1-7 July, 8 blasts; 8-14 July, 12; 15-21 July, 40; and 22-24 July, 32. During those same intervals volcanic earthquakes occurred between 36 and 273 times per interval, with the maximum occurring during 15-21 July, the same interval as the largest number of air-blasts (but not the highest average rate of air blasts per day, which occurred during 22-24 July). Various other earthquake types were recorded in the same report. Although background seismicity typically had amplitudes in the range 0.5-5 mm, many of the larger amplitude air-blasts reached 20-40 mm with durations up to 18 seconds.
Maps, hazards, and Ijen's Merapi. The Ijen complex resides at the E end of Java just across the strait from Bali (figure 13, inset map). Kawah Ijen sits at the E end of the complex within the caldera (figure 13, main map).
Figures 14 and 15 illustrate foreseen hazardous areas and the regional context, including cities around the Ijen complex. The circles shown on both maps are centered around the Kawah Ijen cone and its crater lake.
Both figures 14 and 15 emphasize the attendant lahar hazards. Regarding floods and lahars, the crater lake at Kawah Ijen has a volume of ~30 million cubic meters, all or part of which could be expelled in an eruption or breakout due to crater-wall failure, an event that could send acidic brines down one or more of the drainages. About 5,000 people live within 10 km of the lake but farther away, many thousands more would be at risk in the event of large lahars.
The port cities to the N have a population of ~1.5 million and lie near the mouth of a river representing the main drainage from within the caldera, including the controlled outflow from the crater lake (figures 14 and 15).
As seen on a relief map (figure 16), Merapi (on the far E side of the caldera) forms the highest point in the complex, 2,799 m (and reflects the summit elevation value we typically provide for the complex). Merapi is the same name applied to the better-known, regularly erupting volcano in Central Java near the city of Yogyakarta. Another potential confusion is the volcano Marapi on the island of Sumatra.
Figure 16 shows the Kendeng mountains defining the caldera's arcuate topographic margin bounding the N (with elevations up to 1,559 m). The lowest point of the caldera's N rim (~850 m) occurs near Blawan village at the breach in the caldera wall. Starting at the SE, the major cones on or near the S margin (on this map) are Merapi (2,799 m, and on its flanks, Kawah Ijen at 2,386 m), Rante, and the closely spaced Pendil Djampit.
Just N of Pendil Djampit lies a fault with offset down towards the caldera (figure 17). It trends NW and curves to the N, helping to establish the path of the inferred SW caldera margin (figure 13).
A separate volcano in the GVP database, Raung (Raoeng) stratovolcano (3,332 m), forms a distant topographic feature well to the W of the flat caldera floor and SW boundary (figures 13, 16, and 17). As here defined, Raung includes two other remote cones as subfeatures. One is the cone located to Raung's NE, Soeket (Suket) stratovolcano (2,950 m). Both Suket and Raung lie along the western topographic divide for the drainage basin that feeds into the Ijen complex.
Model of the crater-lake system. Given the recent concerns about activity in Kawah Ijen's crater lake, a simple model of the shallow crust in this area provides a way to help visualize conditions and processes in the subsurface. Figure 18 shows the general situation as put forth in a simple sketch by Alain Bernard (van Bergen and others, 2000).
van Bergen and others (2000) made the following remarks: "The lake chemistry is determined by dissolution of magmatic volatiles, fluid-rock interaction, evaporation of the lake water, dilution by meteoric water and recycling of lake water through seepage into the subsurface hydrothermal system. The lake acts as [a] chemical condenser for volatiles and as a calorimeter trapping heat supplied by a shallow magmatic reservoir. Magmatic volatiles can be supplied to the crater lake system by direct injection of magmatic vapours (SO2, H2S, HCl, and HF) via subaqueous fumaroles or via hot brines entering at the lake bottom."
van Hinsberg and others (2010) stated the following: "The crater lake of Kawah Ijen volcano represents the largest body of natural hyperacidic brine in the world (Delmelle and Bernard, 1994) and has been present since at least 1789 (cf. Bosch, 1858). It is characterised by a singularly high dissolved element load (>100 g/L) and very low pH. Fluids from the crater lake seep through [Kawah Ijen's] western flank to form the acid Banyu Pahit river, the water of which is eventually used for irrigation 40 km downstream [to the N] of the lake in the coastal plain of Asambagus."
Sulfur mining. A strongly active solfatara field (fumaroles that are characteristically sulfurous) is present in the SE part of Kawah Ijen's crater near the lakeshore, where sulfur-mining activities have existed for many decades (see figure 8 in BGVN 32:09). Local workers channel some of the fumarolic gases and molten condensates through pipes and out onto the ground. Once the liquid cools and hardens, workers break the solid sulfur into large pieces and load it into baskets for manual transport out of the crater. According to Wikipedia, miners carry loads of sulfur ore blocks ranging from 75 to 90 kg up a steep trail to the crater rim and then 3 km down the mountain to a weighing station. That and many other web sites show photos of the mining process. Among the more recent photos of the scene are those by Oliver Grunewald (2010) on the 'boston.com' web site. He points out that few of the miners possess gas masks.
Two dental studies of miners concluded that they had both higher incidence of dental erosion to the enamel on their teeth (Pranani and Wibisono, 2008) and the gum disease gingivitis (Anitasari and Wibisono, 2008). Both studies attribute these problems to exposure to sulfuric acid fumes. The studies were small (30 miners) and for comparison (control groups) used similar numbers of residents who lived around the mine but did not work as miners.
References. Anitasari, S. and Wibisono, G., 2008, Relationship between the length of sulphuric acid fumes exposure and the grade of gingivitis, Studies on the Sulphur Miners at Mount Ijen Banyuwangi East Java, Fakultas Kedokteran, Disusun oleh:NIM: G2A004170, Fakultas Kedokteran, Universitas Diponegoro, Semaran, 18 pp.
Bosch, C.J., 1858. Uitbarstingen der vulkanen Idjin en Raun (Banjoewangi). Tijdschrift voor Indische Taal-, Land- en Volkenkunde, Deel 7, 265–286.
Delmelle, P., Bernard, A., Kusakabe, M., Fischer, T.P., and Takanod, B., 2006, Geochemistry of the magmatic–hydrothermal system of Kawah Ijen volcano, East Java, Indonesia, J. of Volcanology and Geothermal Research, Vol. 97, Issues 1-4, April 2000, pp. 31-53.
Grunewald, O., 2010, Kawah Ijen at night, Updated 8 December 2010, Accessed 7 Sept 2012 (URL: http://www.boston.com/bigpicture/2010/12/kawah_ijen_by_night.html).
Topogr. Dienst, 1937, Atlas van Tropisch Nederland, original reproduced on Wikipedia Commons web site (http://commons.wikipedia.org/wiki/File:Ijen.JPG) entitled 'Ijen', Updated 17 June 2012, Accessed 29 August 2012.
Mulyana, A.R., Effendi, W., Karim, A., and Rukada, T., 2006, [Ijen hazards map, figure 14 (further citation details currently unavailable)].
Pranani, D. and Wibisono, G., 2008, The influence of sulphuric acid fumes exposure on the incidence of dental erosion, Study on sulphuric miner in Mount Ijen, Banyuwangi, East Java, Dyah Pranani, NIM: G2a004055, Fakultas Kedokteran, Universitas Diponegoro Semarang, 18 pp.
Takano, B., Suzuki, K., Sugimori, K., Ohba, T., Fazlullin, S.M., Bernard, A., Sumarti, S., Sukhyar, R., and Hirabayashi, M., 2004, Bathymetric and geochemical investigation of Kawah Ijen Crater Lake, East Java, Indonesia, J. of Volcanology and Geothermal Research, vol. 135, Issue 4, pp. 299–329.
van Bergen, M.J., Bernard, A., Sumarti, S., Sriwana, T., and Sitorus, K., 2000, Crater lakes of Java: Dieng, Kelud and Ijen, Excursion Guidebook, IAVCEI General Assembly, Bali 2000, 43 p.
van Hinsberg, V., Berlo, K., and van Bergen, M.J., 2010, Extreme alteration by hyperacidic brines at Kawah Ijen volcano, East Java, Indonesia: I. Textural and mineralogical imprint, J. of Volcanology and Geothermal Research, Vol. 198, Issues 1–2, pp. 253–263.
Geologic Background. The Ijen volcano complex at the eastern end of Java consists of a group of small stratovolcanoes constructed within the 20-km-wide Ijen (Kendeng) caldera. The north caldera wall forms a prominent arcuate ridge, but elsewhere the rim was buried by post-caldera volcanoes, including Gunung Merapi, which forms the high point of the complex. Immediately west of the Gunung Merapi stratovolcano is the historically active Kawah Ijen crater, which contains a nearly 1-km-wide, turquoise-colored, acid lake. Kawah Ijen is the site of a labor-intensive mining operation in which baskets of sulfur are hand-carried from the crater floor. Many other post-caldera cones and craters are located within the caldera or along its rim. The largest concentration of cones forms an E-W zone across the southern side of the caldera. Coffee plantations cover much of the caldera floor; nearby waterfalls and hot springs are tourist destinations.
Information Contacts: Center of Volcanology and Geological Hazard Mitigation (CVGHM), Jalan Diponegoro 57, Bandung 40122, Indonesia (URL: http://www.vsi.esdm.go.id/); Volcano Disaster Assistance Program (VDAP), US Geological Survey (USGS), 1300 SE Cardinal Court, Bldg. 10, Suite 100, Vancouver, WA 98683.
Ioto
Japan
24.751°N, 141.289°E; summit elev. 169 m
All times are local (unless otherwise noted)
Mud ejections and small phreatic eruptions during early 2012
This report first briefly notes an article discussing deformation at Ioto (also called Iwo-jima), an island located within a submerged caldera ~1,200 km S of Tokyo. Ozawa and others (2007) discuss both complex deformation measured during 2006-2007 and the extremely high rate of uplift during the last few hundred years. The rest of this report is devoted to observations by the Japan Meteorological Association (JMA) and other agencies at Ioto during October 2010 to May 2012, including more deformation, small emissions of hot mud and steam, and discolored seawater that suggested a NE flank submarine eruption.
Our previous report on Ioto (Iwo-jima), discussed a submarine eruption off the SE coast that occurred in September 2001, and a small phreatic eruption at Idogahama, a beach on the NW coast of the island, in October 2001 (BGVN 26:09). Ioto is mildly seismically active with many fumaroles and occasional phreatic explosions, but the volcano has not experienced a magmatic eruption in 400 years (Newhall and Dzurisin, 1988; Lowenstern and others, 2006; Yokoyama and Nazzaro, 2002; and Ukawa and others, 2006).
The locations of the major volcanoes of Japan, including the island of Ioto, are shown in figure 5. Figure 6 is a map of Ioto, summarizing its topography and past eruption sites.
Deformation. Ozawa and others (2007) noted that the overall pattern of deformation seen in the last several hundred years averaged to ~0.25 m of uplift per year, but often exceeded uplift rates of 1 m per year. They plotted uplift and subsidence during January 2006-late 2007 from satellite radar interferometry. Concluding that the deformation pattern is very complicated both spatially and temporally, the authors noted that "In August of 2006, subsidence which had continued from 2003 rapidly changed to uplift, and an increase of seismicity was also observed simultaneously." They divided the uplift during August 2006-late 2007 into 3 stages. The authors used gravity and magnetic data to constrain the shape of the shallow intruding magma under the island's main edifice (Motoyama, also spelled Moto-yama) centered in the bulbous NE portion of the island (figure 6). They described the intruding magma body as having a funnel shape, narrowing towards the bottom and centered about the main topographic high. The authors' modeling suggested that the block of material trapped within the funnel was variously displaced during each of the deformation stages, shifting the block depending on where the magma pooled.
JMA reports. The following material summarizes activity from October 2010 to May 2012, based on monthly volcanic activity reports from JMA. JMA reports on Ioto between November 2001 and September 2010 are not available in English; translations into English resumed in October 2010.
In October 2010, Japan's National Research Institute for Earth Science and Disaster Prevention (NIED) reported that seismicity remained at a low level. GPS observations by the Geospatial Information Authority of Japan (GSI) indicated that an episode of uplift that had ceased around October 2009 resumed in May 2010. N-S baseline displacement (extension) accelerated during late September-early October 2010, accompanied by an eastward deformation in the central part of the island. The uplift slowed after mid-November 2010. This upheaval followed one that occurred during August 2006-October 2009.
During 29-30 January 2011, aerial observations were conducted in cooperation with the Japan Maritime Self-Defense Force (JMSDF). No change in the distribution of thermal anomalies or emissions was detected since the last observation in July 2010.
According to NIED and GSI, both shallow seismicity and the rate of uplift at Ioto increased in February 2011 and continued through at least January 2012. GPS measurements showed a rapid southward displacement at the S part of island. Moreover, between 26 August and 2 September 2011, a local westward displacement was observed SW and SE of Motoyama.
A field survey during 16-18 November 2011 revealed that the water level in Asodai crater (along the fault of the same name, figure 6) had risen compared with the last observation during 29-30 January 2011. The temperature of the muddy water at the bottom of the pit was estimated to be ~100°C, the same as that observed in January 2011. Associated discharges reached a maximum height of 20 m above the crater. No change in the distribution of thermal anomalies or emissions was detected since the last observation in January 2011.
On 10 February 2012, JMSDF reported a mud ejection at an old crater (another depression along the Asodai fault, a spot sometimes called "Million Dollar Hole"). According to field surveys on 14 and 15 February, three major ejection sites were aligned in the N-S direction, the deepest being about 13 m. Mud was ejected to distances of up to 100 m NE of the main vent. No seismicity was observed to be associated with this event, but JMA believed a very small phreatic explosion probably occurred during early February. The maximum temperature of the mud was 96.6°C. Another mud ejection occurred on 7 March in the same area, and mud was ejected up to 60 m WNW. Ash emissions also rose from Asodai, but not from Idogahama.
During another field survey from 7 to 9 March 2012, further mud ejections were noted from the same area as the previous events on the island's W side. In addition, a very small phreatic eruption was noted, with tremor (90-minute duration) and intermittent ejections of steam plumes, mud, and small rocks. Emissions rose 20 m above the crater, and small amounts of ash rose more than 10 m and scattered within 20 m in every direction. During that time, the water level in Asodai crater was higher than that observed during the 16-18 November observation.
During 5-6 April 2012, volcanic tremor and intermittent earthquakes were recorded, and two apparently very small phreatic eruptions were reported. This was accompanied by intermittent noises and emissions at the old crater to the W of the island. According to GSI, ground deformation and seismic activity were greater than usual during 27-28 April, but both subsided after 4 May.
During 29-30 April, the ocean NE of the island was discolored, suggesting an offshore underwater eruption. An aerial observation conducted by the Japan Coast Guard (JCG) on 16 May revealed that discoloration persisted, but in smaller areas. On the N part of the island, steam plumes rose to heights of up to 10 m on 30 April.
During May 2012, ground deformation was almost static. Seismic activity diminished, and no volcanic tremors were observed. Based on camera monitoring, emissions from Asodai crater were low, and no emissions were noted in Idogahama.
References. Lowenstern, J.B., Smith, R.B., and Hill, D.P., 2006, Monitoring super-volcanoes: geophysical and geochemical signals at Yellowstone and other large caldera systems, Phil. Trans. R. Soc. A 364, p. 2055-2072.
Yokoyama, I., and Nazzaro, A., 2002, Anomalous crustal movements with low seismic efficiency-Campi Flegrei, Italy and some examples in Japan, Annals of Geophysics, v. 45, no. 6, p. 709-722.
Newhall, C.G., and Dzurisin, D., 1988, Historical unrest at large calderas of the world, U.S. Geological Survey Bulletin 1855: 1108 p, 2 vol, pgs. 509-520.
Ukawa, M., Fujita, E., Ueda, H., Kumagai, T., Nakajima, H., and Morita, H., 2006, Long-term geodetic measurements of large scale deformation at Iwo-jima caldera, Japan, J. of Volcanology and Geothermal Research, v. 150, p. 98-118.
Ozawa, T., Ueda, H., Ukawa, M., and Miyazaki, S., 2007, Temporal change in crustal deformation related to volcanic activity of Iwo-jima observed by PALSAR/InSAR, Proceedings of the First Joint PI Symposium of ALOS, Data Nodes for ALOS Science Program (DIS 10).
Geologic Background. Ioto, in the Volcano Islands of Japan, lies within a 9-km-wide submarine caldera. The volcano is also known as Ogasawara-Iojima to distinguish it from several other "Sulfur Island" volcanoes in Japan. The triangular, low-elevation, 8-km-long island narrows toward its SW tip and has produced trachyandesitic and trachytic rocks that are more alkalic than those of other volcanoes in this arc. The island has undergone uplift for at least the past 700 years, accompanying resurgent doming of the caldera; a shoreline landed upon by Captain Cook's surveying crew in 1779 is now 40 m above sea level. The Motoyama plateau on the NE half of the island consists of submarine tuffs overlain by coral deposits and forms the island's high point. Many fumaroles are oriented along a NE-SW zone cutting through Motoyama. Numerous recorded phreatic eruptions, many from vents on the W and NW sides of the island, have accompanied the uplift.
Information Contacts: Japan Meteorological Agency (JMA), Otemachi, 1-3-4, Chiyoda-ku Tokyo 100-8122, Japan (URL: http://www.jma.go.jp/); Japan’s National Research Institute for Earth Science and Disaster Prevention (NIED), 3-1, Tennodai, Tsukuba, Ibaraki, 305-0006, Japan (URL: http://www.bosai.go.jp/e/); Geospatial Information Authority of Japan (GSI) (URL: http://www.gsi.go.jp/ENGLISH/); Japan Maritime Self-Defense Force (JMSDF) (URL: http://www.mod.go.jp/msdf/formal/english/index.html); Japan Coast Guard (JCG) (URL: http://www.kaiho.mlit.go.jp/e/index_e.htm).
Kikai
Japan
30.793°N, 130.305°E; summit elev. 704 m
All times are local (unless otherwise noted)
Low level tremor and frequent white plumes during October 2010-June 2012
Kikai was the scene of ongoing steaming and modest seismic unrest during October 2010-June 2012. As background, Kikai (also called Satsuma-Iwo-jima and Tokara-Iwo-jima), an island on the NW rim of the submerged Kikai caldera (figure 1), experienced chiefly low-level seismicity between 2002 and 2004 punctuated by stronger earthquakes and tremor, and three small eruptions during May-June 2002, June-August 2003, and March-September 2004 (BGVN 28:04 and 30:07). Almost daily plumes, most of which were white, occurred between late 2002 and at least January 2005 (BGVN 30:07).
Recent monthly reports of volcanic activity from the Japan Meteorological Agency (JMA) translated into English resumed in October 2010. Thus, in this report, we lack JMA reports between January 2005 and September 2010 and only summarize and tabulate activity after October 2010 and as late as June 2012.
In an effort to gather other information, we searched for MODVOLC thermal alerts at Kikai and found none during January 2005 to late September 2012. Only one alert appeared in the past decade. That weak alert occurred on 2 August 2003 at a point along the coast well to the NE of the crater. This was unlikely the result of eruptive causes owing to the location and extended absence of alerts at the crater and dome. Near-source thermal photography (noted by JMA and mentioned below) revealed subtle thermal anomalies suggesting elevated temperatures over parts of the dome.
According to JMA, seismicity was relatively low during October 2010-June 2012. Slight increases occurred during 28-31 October 2010 and on 21 August 2011 (Table 3). White-plumes appeared at Iodake summit crater, and their size remained above background throughout the reporting period (Table 3). An occasional night-time glow was visible with a high-sensitivity camera, during at least January-April 2011, July-August 2011, February 2012, and May-June 2012.
Table 3. Monthly summary of seismicity and plume observations at Kikai during October 2010-June 2012. All reported plumes were described as white. All reported volcanic tremor was of small amplitude and short duration. Seismicity in October 2010 was low (as shown) except for occasional increases on 28, 30 and 31 October. The tremor during February 2011 was the first to occur since February 2010. '-' indicates data not reported. Data courtesy of JMA.
Date |
Number of tremor events |
Number of earthquakes ("low" through June 2011) |
Avg. plume height (maximum height) above Iodake crater (m) |
Oct 2010 |
0 |
Low |
-- (--) |
Nov 2010 |
0 |
Low |
200 (300) |
Dec 2010 |
0 |
Low |
100 (300) |
Jan 2011 |
0 |
Low |
100 (300) |
Feb 2011 |
1 |
Low |
100 (300) |
Mar 2011 |
1 |
Low |
|
Apr 2011 |
1 |
Low |
|
May 2011 |
1 |
Low |
|
Jun 2011 |
1 |
Low |
|
Jul 2011 |
8 |
202 |
|
Aug 2011 |
0 |
244 |
|
Sep 2011 |
0 |
119 |
|
Oct 2011 |
2 |
169 |
|
Nov 2011 |
0 |
159 |
-- (600) |
Dec 2011 |
0 |
167 |
-- (300) |
Jan 2012 |
0 |
209 |
-- (300) |
Feb 2012 |
0 |
189 |
-- (200) |
Mar 2012 |
1 |
201 |
-- (400) |
Apr 2012 |
1 |
126 |
-- (300) |
May 2012 |
0 |
212 |
-- (600) |
Jun 2012 |
1 |
204 |
-- (300) |
Aerial infrared observations on 14 December 2010 and during November-December 2011 found that the distribution of thermal anomalies in the crater had not changed since previous observations in April 2008 and on 22 December 2009. In addition, according to the Japanese Coast Guard, the summit crater did not visibly change between observations on 22 October 2010 and 19 January 2011. According to a field survey on 26 November 2011, the sulfur-dioxide flux averaged 800 tons per day. In December 2011, discolored water, apparently caused by volcanic activity, was observed near the coast. No remarkable crustal change was observed by GPS during Janurary 2012-June 2012.
The journal Earth, Planets and Space produced an edition in 2002 with 16 articles devoted to Kikai caldera, Satsuma-Iwo-jima, and related topics (Shinohara and others, 2002). A video entitled "Satsuma-Iwojima, Japan" uploaded to Youtube in September 2008 shows a steaming fumarole with bright yellow (sulfur?) incrustations (str4hler, 2008).
References. Maeno, F. and Imamura, F., 2007, Numerical investigations of tsunamis generated by pyroclastic flows from the Kikai caldera, Japan, Geophysical Research Letters, Vol. 34, L23303 (DOI: 10.1029/2007GL031222).
Shinohara, H., Iguchi, M., Hedenquist, J.W., and Koyaguchi, T., 2002, Preface to special volume, Earth, Planets and Space, Vol. 54 (No. 3), pp. 173-174.
str4hler, 2008, [Video] Satsuma-Iwojima, Japan. Accessed 21 September 2012, uploaded to Youtube on 16 September 2008 (URL: http://www.youtube.com/watch?v=jyIhaEQAPlw).
Geologic Background. Multiple eruption centers have exhibited recent activity at Kikai, a mostly submerged, 19-km-wide caldera near the northern end of the Ryukyu Islands south of Kyushu. It was the source of one of the world's largest Holocene eruptions about 6,300 years ago when rhyolitic pyroclastic flows traveled across the sea for a total distance of 100 km to southern Kyushu, and ashfall reached the northern Japanese island of Hokkaido. The eruption devastated southern and central Kyushu, which remained uninhabited for several centuries. Post-caldera eruptions formed Iodake (or Iwo-dake) lava dome and Inamuradake scoria cone, as well as submarine lava domes. Recorded eruptions have occurred at or near Satsuma-Iojima (also known as Tokara-Iojima), a small 3 x 6 km island forming part of the NW caldera rim. Showa-Iojima lava dome (also known as Iojima-Shinto), a small island 2 km E of Satsuma-Iojima, was formed during submarine eruptions in 1934 and 1935. Mild-to-moderate explosive eruptions have occurred during the past few decades from Iodake, a rhyolitic lava dome at the eastern end of Satsuma-Iojima.
Information Contacts: Japan Meteorological Agency (JMA), Otemachi, 1-3-4, Chiyoda-ku Tokyo 100-8122, Japan (URL: http://www.jma.go.jp/); MODVOLC, 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/).
Kirishimayama (Japan) — July 2012 Cite this Report
Kirishimayama
Japan
31.934°N, 130.862°E; summit elev. 1700 m
All times are local (unless otherwise noted)
Gradual decline in activity following explosive 2011 eruptions
The early 2011 eruption of Shinmoe-dake (Shinmoedake) volcano of the Kirishima Volcanic Group was characterized by sub-Plinian and Vulcanian explosions and an ~600-m-diameter lava dome that was extruded into the crater (BGVN 35:12 and 36:07, reports covering through July 2011). Fewer eruptions occurred during an ensuing decline in activity, where plumes only rose to up to 1 km above the summit. No explosions (defined as accompanying an air shock larger than 20 Pa and explosive earthquake signals) were reported by the Japan Meteorological Agency (JMA) after 11 May 2011 and through June 2012. This report discusses diminishing plume emissions and seismicity during September 2011-June 2012, and supplies more context on the entire eruptive episode. The material in this report is based on JMA monthly reports, which are now available in English with coverage starting in October 2010.
2011 eruption wanes. After the explosive eruptions during January-February 2011, eruptions (ash emissions) at Shinmoe-dake occurred through 7 September 2011. After that, JMA reported no further eruptions at least through June 2012; gas-and-steam plumes rose to a maximum of ~600 m above the crater of Shinmoe-dake after 7 September 2011 (figure (18).
Elevated seismicity continued following the cease of explosive eruptions in May 2011, but a substantial protracted decline too place during August-November 2011. In May and June 2012, JMA reported that seismicity had returned to background levels seen prior to the onset of the early 2011 explosive activity, and they reported an absence of measured tremor over the same two months (figures 18 and 19).
JMA reported that GPS baseline extension indicated "magma supply to a deeper chamber several kilometers northwest of the crater" through December 2011; the baseline extension slowed after December. JMA initially reported almost no change after January 2012, but during June 2012 the baseline distance between Ebino (~16 km NNW) and Makizono (~14 km WSW) shortened.
Observation flights conducted through various collaborations between the Japan Ground, Air, and Maritime Self-Defense Forces (JGSDF, JASDF, and JMSDF, respectively) and the Ministry of Land, Infrastructure, Transportation and Tourism (MLIT) allowed frequent aerial photography and infrared thermal measurements of the crater and edifice of Shinmoe-dake. The diameter of the lava dome within the crater remained ~600 m as of June 2012 (indicating little-to-no growth since 30 January 2011). Infrared thermal photography revealed little thermal structure to the dome, but highlighted comparatively high-temperature areas at its margins. A fissure (described as a "crack" by JMA) located on the W slope of the edifice was occasionally reported to emit plumes, and exhibited an elevated temperature compared with the rest of the edifice (figure 20). Similar aerial and thermal observations were reported as late as 10 May 2012.
The Alert Level remained at 3 (on a scale from 1-5) at the end of June 2012.
Geologic Background. Kirishimayama is a large group of more than 20 Quaternary volcanoes located north of Kagoshima Bay. The late-Pleistocene to Holocene dominantly andesitic group consists of stratovolcanoes, pyroclastic cones, maars, and underlying shield volcanoes located over an area of 20 x 30 km. The larger stratovolcanoes are scattered throughout the field, with the centrally located Karakunidake being the highest. Onamiike and Miike, the two largest maars, are located SW of Karakunidake and at its far eastern end, respectively. Holocene eruptions have been concentrated along an E-W line of vents from Miike to Ohachi, and at Shinmoedake to the NE. Frequent small-to-moderate explosive eruptions have been recorded since the 8th century.
Information Contacts: Japan Meteorological Agency (JMA), Otemachi, 1-3-4, Chiyoda-ku Tokyo 100-8122, Japan (URL: http://www.jma.go.jp/); Japan Ground Self-Defense Force (JGSDF) (URL: http://www.mod.go.jp/gsdf/english/index.html); Japan Air Self-Defense Force (JASDF) (URL: http://www.mod.go.jp/asdf/English_page/organization/formation01/); Japan Maritime Self-Defense Force (JMSDF) (URL: http://www.mod.go.jp/msdf/formal/english/index.html); Ministry of Land, Infrastructure, Transportation and Tourism (MLIT) (URL: http://www.mlit.go.jp/en/index.html).
Obituary Notices (Unknown) — July 2012 Cite this Report
Obituary Notices
Unknown
Unknown, Unknown; summit elev. m
All times are local (unless otherwise noted)
Death of volcanologist Herman Patia Principal Volcanologist at the Rabaul Volcano Observatory
One of the first homegrown volcanologists in Papua New Guinea (PNG), Herman Patia (figure 1), grew up the youngest of nine children in Gunanba, a village at the Eastern end of New Britain Island and S of Rabaul caldera. He died on 18 June 2012, two days short of his 50th birthday, in Rabaul Town after a month of unstated illness (Itikarai, 2012, which this obituary summarizes). Patia completed all his early schooling through his BS degree in PNG. He completed an MS degree at the Australian National University with a thesis on Rabaul’s petrology and geochemistry (Patia, 2004). He continued to write papers, including co-authorship on the workshop report cited below (Johnson and others, 2010).
Patia began work at Rabaul Volcano Observatory (RVO) in 1986 and rose to the position of Principal Volcanologist. RVO monitors the country’s 57 known Holocene volcanoes, some of which are quite active and close to settlements. Like many scientists working at volcano observatories, Patia’s contributions were multifaceted, spanning from research and publishing to volcano monitoring, and from mapping and hazards assessment to raising community awareness. PNG volcanoes draw international interest, and visitors recall benefitting from Herman’s advice and assistance. He was widely known as someone with both technical competence as well as an amiable, good-natured disposition.
More than once, duty dictated an immediate response to a sudden crisis, putting Patia in situations that could entail considerable risk. For example, in responding to a crisis at Langila in the early 1990’s, he and his then RVO colleague Patrice de Saint Ours survived a close call while monitoring behavior at the summit. A sudden explosion discharged incandescent lava fragments at close range. They escaped by running down the volcano’s ash- and scoria-covered flank, hot lava fragments burning holes in Patia’s backpack.
References. Itikarai, I., 2012, Patia parts with his volcanoes, Papua New Guinea Weekend Online Courier, June 2012.
Johnson, R.W., Itikarai, I., Patia, H., and McKee, C., 2010, Rabaul Volcano Workshop Report; Volcanic systems of the Northeastern Gazelle Peninsula, Papua New Guinea: synopsis, evaluation, and a model for Rabaul volcano, Rabaul Observatory Twinning Program, Dept. Of Mineral Policy and Geohazards Management (DMPGM), Government. of Papua New Guinea and Australian Agency for International Development (AusAID), Australian Government, 84 p., ISBN 978-1-921672-89-7.
Keith-Reid, R., 2007, Profile: Detecting Volcanoes-Meet volcanologist Herman Patia, Islands Business International.
Patia, H., 2004, Petrology and geochemistry of the recent eruption history at Rabaul Caldera, Papua New Guinea: implications for magmatic processes and recurring volcanic activity. Unpubl. Masters of Philosophy thesis, Australian National University, Canberra, 111 pp. (Available at https://digitalcollections.anu.edu.au/handle/1885/7345).
Geologic Background. Obituary notices for volcanologists are sometimes written when scientists are killed during an eruption or have had a special relationship with the Global Volcanism Program.
Information Contacts:
Nevado del Ruiz (Colombia) — July 2012 Cite this Report
Nevado del Ruiz
Colombia
4.892°N, 75.324°W; summit elev. 5279 m
All times are local (unless otherwise noted)
1988-2006 monitoring captures seismic swarms, deformation, and radon emissions
Our last report on Nevado del Ruiz (BGVN 27:05) focused on a swarm of earthquakes that occurred in June 2002, when the Instituto Colombiano de Geología y Minería (INGEOMINAS) raised the Alert Level to II ("Orange", on a scale from I-IV, where the highest Alert Level is I, "Red"). Monthly reports from the INGEOMINAS Manizales Observatory became available online beginning in March 2006 and continued through the time period covered in this report, March-December 2006. We also include the long-term datasets of deformation recorded from 1988 to 2006 and radon-gas monitoring from 2002 to 2006.
INGEOMINAS characterized overall activity at Nevado del Ruiz from March to December 2006 as limited to small earthquakes, minor rockfalls, and intermittent vapor plumes. They measured continuous deformation trends (primarily from 3 tilt stations), and low levels of radon-gas emissions with a peak in March 2006 at two stations. No Alert Level was defined for this time period.
Seismicity during 2006. INGEOMINAS reported that low seismicity generally prevailed from March through December 2006; 217-673 events occurred per month at depths of 6-10 km below the summit with maximum local magnitudes of 0.95-2.3. Long period (LP) events occurred slightly more often than volcano-tectonic (VT) events; 1-5 hybrid events were detected each month except in December when these events were absent. Tremor was recorded only once in September and twice in October.
Two small VT earthquake swarms were recorded, one in March and the other in May. The swarm on 9 March occurred as a cluster of events 2-4 km deep centered to the SE of the crater (figure 49). The swarm on 29 May was characterized by ~20 events located SE of the crater with magnitudes less than 1.02.
Rockfalls, ice movement, and debris flows were also detected by the seismic network from March to December 2006. For these kinds of events, typically more than 250-600 per month were detected; however, fewer events were detected in April and June, 61 and 47 events respectively.
Vapor plumes in 2006. During most of 2006 vapor plumes were visible from the summit area of Nevado del Ruiz. Often appearing intermittently, these plumes were white or white-to-gray colored and reached 100-600 m over the crater rim. Plume emissions have been associated with the fumaroles within the summit crater.
Deformation summary. The deformation network at Nevado del Ruiz in March 2006 contained 12 dry tiltmeter stations (Piraña, Rubí, Bis, Molinos, Tumbas, Refugio, Nereidas, Pequeño, Pijao, Arenales, Alfombrales, and Recio) and four stations for leveling campaigns (Piraña, Bis, Tumbas, and Nereidas; figure 50). This network was developed to cover the W and N flanks; the S and E flanks did not have network coverage during this reporting period. Fieldwork was planned to include leveling at sites Arenales, Alfombrales, and Recio since they had not been occupied for several years. Four tilt stations showed inflation and deflation trends (Bis, Nereidas, Refugio, and Tumbas) and are discussed in the text below.
Tilt station Bis was established in late 1988 on the NW flank ~5.7 km NW of the active crater (figure 50). As seen on figure 51, inflation had been recorded at Bis from 1988 through 1999 with a cumulative tilt increase of as much as 40-60 microradians (µrad; figure 51). Since the beginning of 2000 until the end of 2004, this station recorded stable conditions with a small amount (4 µrad) of inflation. From 2004 through March 2006 there was another significant increase in the inflation trend; a cumulative 22 µrad N component and 15 µrad E component inflation.
Tilt station Nereidas was installed 4.6 km SW of the active crater and measured significant changes primarily from late March 1993 to March 2006. Inflation and deflation trends were recorded, 13 µrad N and 11 µrad E, respectively.
Station Refugio, located 2.6 km NW of the active crater, has primarily recorded stable conditions since 1990.
Station Tumbas was located on the NW flank of the volcano ~4.8 km from the crater. This station has shown deflation from both components since 2000. Since February 2005 the cumulative deflation of the N component was 7 µrad and 13 µrad in the E component. From 2005 to March 2006 there were fluctuations from this station within the measurable range of the tiltmeters.
Long-term radon gas measurements. Radon monitoring at Nevado del Ruiz has been based on six stations. In particular, INGEOMINAS has long records from stations Gualí and Hotel Termales since 2002 and 2003, respectively (figure 52). The locations of the radon gas sampling stations were not disclosed, however a 1986 map of instrumentation places the Hotel Termales (labeled "Termales" with a square and "X")and Río Gualí (marked with a circle near the river) stations within 12 km to the NW of the summit crater (figure 53). In March 2006, results from three radon monitoring sites suggested to INGEOMINAS that there was a possible correlation with the earthquake swarms detected on 9 March 2006. Stations Río Gualí, Gualí, and Rubí recorded an increase in radon emission on 5 March while stations Condor and Cajones maintained low levels (55 pico Curies per Liter, pCi/L). From April through December 2006, no major changes were noted in radon gas emissions.
Geologic Background. Nevado del Ruiz is a broad, glacier-covered volcano in central Colombia that covers more than 200 km2. Three major edifices, composed of andesitic and dacitic lavas and andesitic pyroclastics, have been constructed since the beginning of the Pleistocene. The modern cone consists of a broad cluster of lava domes built within the caldera of an older edifice. The 1-km-wide, 240-m-deep Arenas crater occupies the summit. The prominent La Olleta pyroclastic cone located on the SW flank may also have been active in historical time. Steep headwalls of massive landslides cut the flanks. Melting of its summit icecap during historical eruptions, which date back to the 16th century, has resulted in devastating lahars, including one in 1985 that was South America's deadliest eruption.
Information Contacts: Instituto Colombiano de Geología y Minería (INGEOMINAS), Volcanological and Seismological Observatory, Avenida 12 Octubre 15-47, Manizales, Colombia (URL: https://www2.sgc.gov.co/volcanes/index.html).
Tongariro (New Zealand) — July 2012 Cite this Report
Tongariro
New Zealand
39.157°S, 175.632°E; summit elev. 1978 m
All times are local (unless otherwise noted)
Seismicity preceded phreatic explosion; associated rainfall-fed lahar
Elevated seismicity in July 2012 preceded a phreatic eruption at Tongariro on 6 August. The eruption ejected blocks of old lava from the crater area, and triggered a debris flow down a drainage on a flank of the volcano. Six days later, heavy rainfall remobilized some of the debris flow and generated a small flood/lahar that crossed a state highway. This report summarizes GeoNet alert bulletins and Taupo Civil Defense postings concerning the phreatic explosion and associated events (through 17 August 2012).
Precursory seismicity. GeoNet reported elevated numbers of volcanic earthquakes (M < 2.5) beginning on 13 July (figure 2). Seismicity then declined until 18 July, when volcanic earthquakes returned, increasing in magnitude and abundance through 20 July. The earthquakes were clustered between Emerald Lake and the SE shore of Lake Rotoaira at 2-7 km depth; a subset of the earthquakes were tightly clustered between Blue Lake and Te Maari (Te Mari) Craters within the same depth range (figures 2 and 3). As a result, the Volcano Alert Level was raised from 0 to 1 (on a scale from 0-5) and the Avation Colour Code was raised from Green to Yellow (on a four color scale; Green-Yellow-Orange-Red) on 20 July.
By 23 July, GeoNet had deployed four portable seismometers and had sampled springs and fumaroles. They reported that provisional analyses of gas samples indicated a marked increase in volcanic gases above typical mixtures of hydrothermal and volcanic gas signatures (see subsection "Ash and gas analyses" for detail). By 31 July, GeoNet had also installed a GPS instrument to monitor any deformation.
Phreatic eruption. At 2352 on 6 August, a phreatic eruption occurred from a vent located within the Te Maari Craters area. An explosion generated seismic signals that lasted a few minutes, followed by a series of discrete small earthquakes during the next few tens of minutes. Within 35 minutes, GeoNet posted an Alert Bulletin announcing that ashfall had been reported; the Volcano Alert Level was raised to 2 and the Aviation Colour Code was raised to Red. Taupo Civil Defense responded by closing State Highways 1 and 46 (to the E and N of Tongariro, respectively).
Approximately one hour after the eruption, the Cooperative Institute for Meteorological Satellite Studies (CIMSS) observed in satellite imagery that an ash plume was drifting more than 50 km E from Tongariro (figure 4). They also reported that airports had cancelled flights at Gisborne (210 km ENE), Rotorua (120 km NNE), Taupo (60 km NE), and Palmerston North (135 km S).
GeoNet reported that no volcanic tremor occurred before or after the event, and the Aviation Colour Code was reduced to Orange ~12 hours later (about 1200 on 7 August), and reduced again the next day (1500 on 8 August).
GeoNet conducted an observation flight on 8 August and photographed a variety of features discussed and illustrated in more detail below. They included: (1) a new vent area residing in a small crater, and associated steaming fissures, (2) a debris flow, and (3) impact craters.
The new vent(s) are located in the Upper Te Maari Craters area (figure 5a); low clouds prevented scientists from viewing areas higher than the lowest parts of Upper Te Maari Crater. Photographs of the area revealed a nearby steaming eruptive fissure, and more intense steaming in areas of ground that had been steaming prior to the eruption (figure 5b).
A debris flow generated by the phreatic eruption comprised rock and soil debris that blocked a stream valley draining NW from the Te Maari Craters area (figure 6). GeoNet reported water ponding around the edges, and ash that had been remobilized into slurry flows. GeoNet noted that areas of the debris flow (especially in the upper sections) had eroded into the substrate (figure 6a).
The explosion ejected blocks of lava up to 2 km from the Te Maari Craters area, leaving impact craters in vegetation and ground surfaces (figure 7). All blocks were angular, and none were steaming or surrounded by burnt vegetation; GeoNet thus concluded that the blocks comprised old (non-juvenile) lava(s) ejected from the vent area.
Ash and gas analyses. Textural analyses indicated that the ash emitted during the 6 August explosion contained little-to-no fresh (juvenile) lava, suggesting that the eruption was primarily steam driven (phreatic). GeoNet also reported that analysis of the fluorine content of the ash indicated that, except in the immediate vicinity of the volcano, there were little health or agricultural concerns.
For 9 August, GeoNet reported emissions of 2,100 tons/day of SO2, 3,900 tons/day of CO2, and 364 tons/day of H2S from vents. Sulfur (H2S) smells were reported in downwind locations during 11-12 August, and further reports were filed from the Manawatu region on 15 August. GeoNet attributed the sulfur odors to "passive degassing of magma beneath the surface of Tongariro."
Heavy rains spawn minor lahar. In concert with the 11 August release of a new, updated hazard map of Tongariro (figure 8), GeoNet warned motorists not to stop their vehicles along Highway 46 (N of Tongariro) due to hazards in that area. Following heavy rains the next morning, a minor flood/lahar crossed State Highway 46 near the S tip of Lake Rotoaira (at a location ~6 km W of Rangipo). According to the New Zealand Herald, a driver described 13-cm-deep mud crossing the road at 0830 that day. Scientists at GNS Science stressed that the lahar was not a direct result of an eruptive process, and a resident reported that the area was commonly washed out during heavy rains.
Ten days after the phreatic explosion, GeoNet reduced the Volcano Alert Level to 1, stating that minor eruptive activity, required for Volcanic Alert Level 2, had ceased. The Aviation Colour Code remained at Yellow as of 24 August 2012.
Geologic Background. Tongariro is a large volcanic massif, located immediately NE of Ruapehu volcano, that is composed of more than a dozen composite cones constructed over a period of 275,000 years. Vents along a NE-trending zone extending from Saddle Cone (below Ruapehu) to Te Maari crater (including vents at the present-day location of Ngauruhoe) were active during several hundred years around 10,000 years ago, producing the largest known eruptions at the Tongariro complex during the Holocene. North Crater stratovolcano is truncated by a broad, shallow crater filled by a solidified lava lake that is cut on the NW side by a small explosion crater. The youngest cone, Ngauruhoe, is also the highest peak.
Information Contacts: GeoNet, a collaboration between theEarthquake Commission and GNS Science (URL: http://www.geonet.org.nz/); GNS Science, Wairakei Research Center, Private Bag 2000, Taupo 3352, New Zealand (URL: http://www.gns.cri.nz/); Earthquake Commission (EQC), PO Box 790, Wellington, New Zealand (URL: http://www.eqc.govt.nz/); The Cooperative Institute for Meteorological Satellite Studes (CIMSS), a collaboration between theUniversity of Wisonsin-Madison, theNational Oceanic and Atmospheric Administration, and theNational Aeronautics and Space Administration, Space Science and Engineering Center, 1225 W. Dayton St., Madison, WI 53706 (URL: http://cimss.ssec.wisc.edu/); University of Wisconsin-Madison (UW-Madison) (URL: http://www.wisc.edu/); National Oceanic and Atmospheric Administration (NOAA) (URL: http://www.noaa.gov/about-noaa.html); National Aeronautics and Space Administration (NASA) (URL: http://www.nasa.gov/); New Zealand Herald (URL: http://www.nzherald.co.nz/).