Mount Agung, located on the E end of the island of Bali, Indonesia, rises above the SE rim of the Batur caldera. The summit area extends 1.5 km E-W, with the highest point on the W and a steep-walled 800-m-wide crater on the E. Recorded eruptions date back to the early 19th century. A large and deadly explosive and effusive eruption occurred during 1963-64, which was characterized by voluminous ashfall, pyroclastic flows, and lahars that caused extensive damage and many fatalities. More recent activity was documented during November 2017-June 2019 that consisted of multiple explosions, significant ash plumes, lava flows at the summit crater, and incandescent ejecta. This report covers activity reported during April-May 2022 and December 2022 based on data from the Darwin Volcanic Ash Advisory Center (VAAC).

Activity during 2022 was relatively low and mainly consisted of a few ash plumes during April-May and December. An ash plume on 3 April rising to 3.7 km altitude (700 m above the summit) and drifting N was reported in a Darwin VAAC notice based on a ground report, with ash seen in HIMAWARI-8 visible imagery. Another ash plume was reported at 1120 on 27 May that rose to 5.5 km altitude (2.5 m above the summit); the plume was not visible in satellite or webcam images due to weather clouds. An eruption was reported based on seismic data at 0840 on 13 December, with an estimated plume altitude of 3.7 km; however, no ash was seen using satellite imagery in clear conditions before weather clouds obscured the summit.

Geologic Background. Symmetrical Agung stratovolcano, Bali's highest and most sacred mountain, towers over the eastern end of the island. The volcano, whose name means "Paramount," rises above the SE rim of the Batur caldera, and the northern and southern flanks extend to the coast. The summit area extends 1.5 km E-W, with the high point on the W and a steep-walled 800-m-wide crater on the E. The Pawon cone is located low on the SE flank. Only a few eruptions dating back to the early 19th century have been recorded in historical time. The 1963-64 eruption, one of the largest in the 20th century, produced voluminous ashfall along with devastating pyroclastic flows and lahars that caused extensive damage and many fatalities.

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/).

Tengger Caldera, located at the N end of a volcanic massif in Indonesia’s East Java, consists of five overlapping stratovolcanoes. The youngest and only active cone in the 16-km-wide caldera is Bromo, which typically produces gas-and-steam plumes, occasional ash plumes and explosions, and weak thermal signals (BGVN 44:05, 47:01). This report covers activity during January 2022-December 2023, consisting of mostly white gas-and-steam emissions and persistent weak thermal anomalies. Information was provided by the Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM) and satellite imagery. The Alert Level remained at 2 (on a scale of 1-4), and visitors were warned to stay at least 1 km from the crater.

Activity was generally low during the reporting period, similar to that in 2021. According to almost daily images from MAGMA Indonesia (a platform developed by PVMBG), white emissions and plumes rose from 50 to 900 m above the main crater during this period (figure 24). During several days in March and June 2022, white plumes reached heights of 1-1.2 km above the crater.

Figure 24. Webcam image showing a gas-and-steam plume from the Bromo cone in the Tengger Caldera on 2 April 2023. Courtesy of MAGMA Indonesia.

After an increase in activity at 2114 on 3 February 2023, a PVMBG team that was sent to observe white emissions rising as high as 300 m during 9-12 February and heard rumbling noises. A sulfur dioxide odor was also strong near the crater and measurements indicated that levels were above the healthy (non-hazardous) threshold of 5 parts per million; differential optical absorption spectroscopy (DOAS) measurements indicated an average flux of 190 metric tons per day on 11 February. Incandescence originating from a large fumarole in the NNW part of the crater was visible at night. The team observed that vegetation on the E caldera wall was yellow and withered. The seismic network recorded continuous tremor and deep and shallow volcanic earthquakes.

According to a PVMBG press release, activity increased on 13 December 2023 with white, gray, and brown emissions rising as high as 900 m above Bromo’s crater rim and drifting in multiple directions (figure 25). The report noted that tremor was continuous and was accompanied in December by three volcanic earthquakes. Deformation data indicated inflation in December. There was no observable difference in the persistent thermal anomaly in the crater between 11 and 16 December 2023.

Figure 25. Webcam image showing a dark plume that rose 900 m above the summit of the Bromo cone in the Tengger Caldera on 13 December 2023. Courtesy of MAGMA Indonesia.

All clear views of the Bromo crater throughout this time, using Sentinel-2 infrared satellite images, showed a weak persistent thermal anomaly; none of the anomalies were strong enough to cause MODVOLC Thermal Alerts. A fire in the SE part of the caldera in early September 2023 resulted in a brief period of strong thermal anomalies.

Geologic Background. The 16-km-wide Tengger caldera is located at the northern end of a volcanic massif extending from Semeru volcano. The massive volcanic complex dates back to about 820,000 years ago and consists of five overlapping stratovolcanoes, each truncated by a caldera. Lava domes, pyroclastic cones, and a maar occupy the flanks of the massif. The Ngadisari caldera at the NE end of the complex formed about 150,000 years ago and is now drained through the Sapikerep valley. The most recent of the calderas is the 9 x 10 km wide Sandsea caldera at the SW end of the complex, which formed incrementally during the late Pleistocene and early Holocene. An overlapping cluster of post-caldera cones was constructed on the floor of the Sandsea caldera within the past several thousand years. The youngest of these is Bromo, one of Java's most active and most frequently visited volcanoes.

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

Saunders is one of eleven islands that comprise the South Sandwich Islands in the South Atlantic. The active Mount Michael volcano has been in almost continuous eruption since November 2014 (BGVN 48:02). Recent activity has resulted in intermittent thermal anomalies and gas-and-steam emissions (BGVN 47:03, 48:02). Visits are infrequent due to its remote location, and cloud cover often prevents satellite observations. Satellite thermal imagery and visual observation of incandescence during a research expedition in 2019 (BGVN 28:02 and 44:08) and a finding confirmed by a National Geographic Society research team that summited Michael in November 2022 reported the presence of a lava lake.

Although nearly constant cloud cover during February 2023 through January 2024 greatly limited satellite observations, thermal anomalies from the lava lake in the summit crater were detected on clear days, especially around 20-23 August 2023. Anomalies similar to previous years (eg. BGVN 48:02) were seen in both MIROVA (Middle InfraRed Observation of Volcanic Activity) data from MODIS instruments and in Sentinel 2 infrared imagery. The only notable sulfur dioxide plume detected near Saunders was on 25 September 2023, with the TROPOMI instrument aboard the Sentinel-5P satellite.

Geologic Background. Saunders Island consists of a large central volcanic edifice intersected by two seamount chains, as shown by bathymetric mapping (Leat et al., 2013). The young Mount Michael stratovolcano dominates the glacier-covered island, while two submarine plateaus, Harpers Bank and Saunders Bank, extend north. The symmetrical Michael has a 500-m-wide summit crater and a remnant of a somma rim to the SE. Tephra layers visible in ice cliffs surrounding the island are evidence of recent eruptions. Ash clouds were reported from the summit crater in 1819, and an effusive eruption was inferred to have occurred from a N-flank fissure around the end of the 19th century and beginning of the 20th century. A low ice-free lava platform, Blackstone Plain, is located on the north coast, surrounding a group of former sea stacks. A cluster of cones on the SE flank, the Ashen Hills, appear to have been modified since 1820 (LeMasurier and Thomson, 1990). Analysis of satellite imagery available since 1989 (Gray et al., 2019; MODVOLC) suggests frequent eruptive activity (when weather conditions allow), volcanic clouds, steam plumes, and thermal anomalies indicative of a persistent, or at least frequently active, lava lake in the summit crater. Due to this observational bias, there has been a presumption when defining eruptive periods that activity has been ongoing unless there is no evidence for at least 10 months.

Information Contacts: MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); NASA Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, NASA Goddard Space Flight Center (NASA/GSFC), 8800 Greenbelt Road, Goddard MD 20771, USA (URL: https://so2.gsfc.nasa.gov/); Copernicus Browser (URL: https://dataspace.copernicus.eu/browser).

Shishaldin is located on the eastern half of Unimak Island, one of the Aleutian Islands. Frequent explosive activity, primarily consisting of Strombolian ash eruptions from the small summit crater, but sometimes producing lava flows, has been recorded since the 18th century. The previous eruption ended in May 2020 and was characterized by intermittent thermal activity, increased seismicity and surface temperatures, ash plumes, and ash deposits (BGVN 45:06). This report covers a new eruption during July through November 2023, which consisted of significant explosions, ash plumes, ashfall, and lava fountaining. Information comes from daily, weekly, and special reports from the Alaska Volcano Observatory (AVO) and various satellite data. AVO monitors the volcano using local seismic and infrasound sensors, satellite data, web cameras, and remote infrasound and lightning networks.

AVO reported that intermittent tremor and low-frequency earthquakes had gradually become more regular and consistent during 10-13 July. Strongly elevated surface temperatures at the summit were identified in satellite images during 10-13 July. On 11 July AVO raised the Aviation Color Code (ACC) to Yellow (the second color on a four-color scale) and Volcano Alert Level (VAL) to Advisory (the second level on a four-level scale) at 1439. Later in the day on 11 July summit crater incandescence was observed in webcam images. Observations of the summit suggested that lava was likely present at the crater, which prompted AVO to raise the ACC to Orange (the second highest color on a four-color scale) and the VAL to Watch (the second highest level on a four-level scale). The US Coast Guard conducted an overflight on 12 July and confirmed that lava was erupting from the summit. That same day, sulfur dioxide emissions were detected in satellite images.

A significant explosion began at 0109 on 14 July that produced an ash plume that rose to 9-12 km altitude and drifted S over the Pacific Ocean (figure 43). Webcam images and photos taken around 0700 from a ship SW off Unimak Island showed small lahar deposits, which were the result of the interaction of hot pyroclastic material and snow and ice on the flanks. There was also ashfall on the SW and N flanks. A smaller explosion at 0710 generated an ash plume that rose to 4.5 km altitude. Webcam images and pilot reports showed continued low-level ash emissions during the morning, rising to less than 4.6 km altitude; those emissions included a small ash plume near the summit around 1030 resulting from a small explosion.

Figure 43. Photo of a strong ash plume that rose to 9-12 km altitude on the morning of 14 July 2023. Lahar deposits were visible on the SW flank (white arrows). Photo has been color corrected. Courtesy of Christopher Waythomas, AVO.

Seismic tremor amplitude began increasing at around 1700 on 15 July; strongly elevated surface temperatures were also reported. An ash plume rose to 4.6 km altitude and drifted SSE at 2100, based on a satellite image. A continuous ash plume during 2150 through 2330 rose to 5 km altitude and extended 125 km S. At 2357 AVO raised the ACC to Red (the highest color on a four-color scale) and the VAL to Warning (the highest level on a four-level scale), noting that seismicity remained elevated for more than six hours and explosion signals were frequently detected by regional infrasound (pressure sensor) networks. Explosions generated an ash plume that rose to 4.9 km altitude and drifted as far as 500 km SE. Activity throughout the night declined and by 0735 the ACC was lowered to Orange and the VAL to Watch. High-resolution satellite images taken on 16 July showed pyroclastic deposits extending as far as 3 km from the vent; these deposits generated lahars that extended further down the drainages on the flanks. Ash deposits were mainly observed on the SSE flank and extended to the shore of Unimak Island. During 16-17 July lava continued to erupt at the summit, which caused strongly elevated surface temperatures that were visible in satellite imagery.

Lava effusion increased at 0100 on 18 July, as noted in elevated surface temperatures identified in satellite data, increasing seismic tremor, and activity detected on regional infrasound arrays. A significant ash plume at 0700 rose to 7 km altitude and continued until 0830, eventually reaching 9.1 km altitude and drifting SSE (figure 44). As a result, the ACC was raised to Red and the VAL to Warning. By 0930 the main plume detached, but residual low-level ash emissions continued for several hours, remaining below 3 km altitude and drifting S. The eruption gradually declined and by 1208 the ACC was lowered to Orange and the VAL was lowered to Watch. High-resolution satellite images showed ash deposits on the SW flank and pyroclastic deposits on the N, E, and S flanks, extending as far as 3 km from the vent; lahars triggered by the eruption extended farther down the flanks (figure 45). Lava continued to erupt from the summit crater on 19 July.

Figure 44. Photo of an ash-rich plume rising above Shishaldin to 9.1 km altitude on 18 July 2023 that drifted SE. View is from the N of the volcano and Isanotski volcano is visible on the left-hand side of the image. Photo has been color corrected. Courtesy of Chris Barnes, AVO.

Figure 45. Near-infrared false-color satellite image of Shishaldin taken on 18 July 2023 showing ash deposits on the N, E, and S flanks extending as far as 3 km from the vent due to recent eruption events. Courtesy of Matthew Loewen, AVO.

Elevated surface temperatures were detected in satellite images during 19-25 July, despite occasional weather cloud cover, which was consistent with increased lava effusion. During 22-23 July satellite observations acquired after the eruption from 18 July showed pyroclastic flow and lahar deposits extending as far as 3 km down the N, NW, and NE flanks and as far as 1.5 km down the S and SE flanks. Ash deposits covered the SW and NE flanks. No lava flows were observed outside the crater. On 22 July a sulfur dioxide plume was detected in satellite data midday that had an estimated mass of 10 kt. In a special notice issued at 1653 on 22 July AVO noted that eruptive activity had intensified over the previous six hours, which was characterized by an hours-long steady increase in seismic tremor, intermittent infrasound signals consistent with small explosions, and an increase in surface temperatures that were visible in satellite data. Pilots first reported low-level ash plumes at around 1900. At 2320 an ash plume had risen to 9 km altitude based on additional pilot reports and satellite images. The ACC was increased to Red and the VAL to Warning at 2343. Satellite images indicated growth of a significantly higher ash plume that rose to 11 km altitude continued until 0030 and drifted NE. During the early morning hours of 23 July ash plumes had declined to 4.6 k altitude. Seismic tremor peaked at 0030 on 23 July and began to rapidly decline at 0109; active ash emissions were no longer visible in satellite data by 0130. The ACC was lowered to Orange and the VAL to Watch at 0418; bursts of increased seismicity were recorded throughout the morning, but seismicity generally remained at low levels. Elevated surface temperatures were visible in satellite data until about 0600. On 24 July pilots reported seeing vigorous gas-and-steam plumes rising to about 3 km altitude; the plumes may have contained minor amounts of ash.

During 24-25 July low level seismicity and volcanic tremor were detected at low levels following the previous explosion on 23 July. Strongly elevated surface temperatures were observed at the summit crater in satellite data. Around 2200 on 25 July seismicity began to increase, followed by infrasound signals of explosions after 0200 on 26 July. An ash plume rose to 3 km altitude at 0500 and drifted ENE, along with an associated sulfur dioxide plume that drifted NE and had an estimated mass of 22 kt. Diffuse ash emissions were visible in satellite data and rose to 6.1-7.6 km altitude and extended 125 km from the volcano starting around 1130. These ash events were preceded by about seven hours of seismic tremor, infrasound detections of explosions, and five hours of increased surface temperatures visible in satellite data. Activity began to decline around 1327, which included low-frequency earthquakes and decreased volcanic tremor, and infrasound data no longer detected significant explosions. Surface temperatures remained elevated through the end of the month.

Seismicity, volcanic tremor, and ash emissions remained at low levels during early August. Satellite images on 1 August showed that some slumping had occurred on the E crater wall due to the recent explosive activity. Elevated surface temperatures continued, which was consistent with cooling lava. On 2 August small explosive events were detected, consistent with low-level Strombolian activity. Some episodes of volcanic tremor were reported, which reflected low-level ash emissions. Those ash emissions rose to less than 3 km altitude and drifted as far as 92.6 km N. Pilots that were located N of the volcano observed an ash plume that rose to 2.7 km altitude. Seismicity began to increase in intensity around 0900 on 3 August. Seismicity continued to increase throughout the day and through the night with strongly elevated surface temperatures, which suggested that lava was active at the surface.

An ash cloud that rose to 7.6-7.9 km altitude and drifted 60-75 km NE was visible in a satellite image at 0520 on 4 August. Pilots saw and reported the plume at 0836 (figure 46). By 0900 the plume had risen to 9.1 km altitude and extended over 100 km NE. AVO raised the ACC to Red and the VAL to Warning as a result. Seismic tremor levels peaked at 1400 and then sharply declined at 1500 to slightly elevated levels; the plume was sustained during the period of high tremor and drifted N and NE. The ACC was lowered to Orange and the VAL to Watch at 2055. During 5-14 August seismicity remained low and surface temperatures were elevated based on satellite data due to cooling lava. On 9 August a small lava flow was observed that extended from the crater rim to the upper NE flank. It had advanced to 55 m in length and appeared in satellite imagery on 11 August. Occasional gas-and-steam plumes were noted in webcam images. At 1827 AVO noted that seismic tremor had steadily increased during the afternoon and erupting lava was visible at the summit in satellite images.

Figure 46. Photo showing an ash plume rising above Shishaldin during the morning of 4 August 2023 taken by a passing aircraft. The view is from the N showing a higher gas-rich plume and a lower gray ash-rich plume and dark tephra deposits on the volcano’s flank. Photo has been color corrected. Courtesy of Chris Barnes, AVO.

Strong explosion signals were detected at 0200 on 15 August. An ash cloud that was visible in satellite data extended 100 km NE and may have risen as high as 11 km altitude around 0240. By 0335 satellite images showed the ash cloud rising to 7.6 km altitude and drifting NE. Significant seismicity and explosions were detected by the local AVO seismic and infrasound networks, and volcanic lightning was detected by the World Wide Lightning Location Network (WWLLN). A sulfur dioxide plume associated with the eruption drifted over the S Bering Sea and parts of Alaska and western Canada. Seismicity was significantly elevated during the eruption but had declined by 1322. A pilot reported that ash emissions continued, rising as high as 4.9 km altitude. Elevated surface temperatures detected in satellite data were caused by hot, eruptive material (pyroclastic debris and lava) that accumulated around the summit. Eruptive activity declined by 16 August and the associated sulfur dioxide plume had mostly dissipated; remnants continued to be identified in satellite images at least through 18 August. Surface temperatures remained elevated based on satellite images, indicating hot material on the upper parts of the volcano. Small explosions were detected in infrasound data on the morning of 19 August and were consistent with pilot reports of small, short-lived ash plumes that rose to about 4.3 km altitude. Low-level explosive activity was reported during 20-24 August, according to seismic and infrasound data, and weather clouds sometimes prevented views. Elevated surface temperatures were observed in satellite images, which indicated continued hot material on the upper parts of the volcano.

Seismic tremor began to increase at around 0300 on 25 August and was followed by elevated surface temperatures identified in satellite images, consistent with erupting lava. Small explosions were recorded in infrasound data. The ACC was raised to Red and the VAL to Warning at 1204 after a pilot reported an ash plume that rose to 9.1 km altitude. Seismicity peaked at 1630 and began to rapidly decline at around 1730. Ash plumes rose as high as 10 km altitude and drifted as far as 400 km NE. By 2020 the ash plumes had declined to 6.4 km altitude and continued to drift NE. Ash emissions were visible in satellite data until 0000 on 26 August and seismicity was at low levels. AVO lowered the ACC to Orange and the VAL to Watch at 0030. Minor explosive activity within the summit crater was detected during 26-28 August and strongly elevated surface temperatures were still visible in satellite imagery through the rest of the month. An AVO field crew working on Unimak Island observed a mass flow that descended the upper flanks beginning around 1720 on 27 August. The flow produced a short-lived ash cloud that rose to 4.5 km altitude and rapidly dissipated. The mass flow was likely caused by the collapse of spatter that accumulated on the summit crater rim.

Similar variable explosive activity was reported in September, although weather observations sometimes prevented observations. A moderate resolution satellite image from the afternoon of 1 September showed gas-and-steam emissions filling the summit crater and obscuring views of the vent. In addition, hot deposits from the previous 25-26 August explosive event were visible on the NE flank near the summit, based on a 1 September satellite image. On 2 and 4 September seismic and infrasound data showed signals of small, repetitive explosions. Variable gas-and-steam emissions from the summit were visible but there was no evidence of ash. Possible summit crater incandescence was visible in nighttime webcam images during 3-4 September.

Seismicity began to gradually increase at around 0300 on 5 September and activity escalated at around 0830. A pilot reported an ash plume that rose to 7.6 km altitude at 0842 and continued to rise as high as possibly 9.7 km altitude and drifted SSE based on satellite images (figure 47). The ACC was raised to Red and the VAL to Warning at 0900. In addition to strong tremor and sustained explosions, the eruption produced volcanic lightning that was detected by the WWLLN. Around 1100 seismicity decreased and satellite data confirmed that the altitude of the ash emissions had declined to 7.6 km altitude. By 1200 the lower-altitude portion of the ash plume had drifted 125 km E. Significant ash emissions ended by 1330 based on webcam images. The ACC was lowered to Orange and the VAL to Watch at 1440. Satellite images showed extensive pyroclastic debris flows on most of the flanks that extended 1.2-3.3 km from the crater rim.

Figure 47. Webcam image taken from the S of Shishaldin showing a vertical ash plume on 5 September 2023. Courtesy of AVO.

During 6-13 September elevated surface temperatures continued to be observed in satellite data, seismicity remained elevated with weak but steady tremor, and small, low-frequency earthquakes and small explosions were reported, except on 12 September. On 6 September a low-level ash plume rose to 1.5-1.8 km altitude and drifted SSE. Occasional small and diffuse gas-and-steam emissions at the summit were visible in webcam images. Around 1800 on 13 September seismic tremor amplitudes began to increase, and small explosions were detected in seismic and infrasound data. Incandescent lava at the summit was seen in a webcam image taken at 0134 on 14 September during a period of elevated tremor. No ash emissions were reported during the period of elevated seismicity. Lava fountaining began around 0200, based on webcam images. Satellite-based radar observations showed that the lava fountaining activity led to the growth of a cone in the summit crater, which refilled most of the crater. By 0730 seismicity significantly declined and remained at low levels.

Seismic tremor began to increase around 0900 on 15 September and rapidly intensified. An explosive eruption began at around 1710, which prompted AVO to raise the ACC to Red and the VAL to Warning. Within about 30 minutes ash plumes drifted E below a weather cloud at 8.2 km altitude. The National Weather Service estimated that an ash-rich plume rose as high as 12.8 km altitude and produced volcanic lightning. The upper part of the ash plume detached from the vent around 1830 and drifted E, and was observed over the Gulf of Alaska. Around the same time, seismicity dramatically decreased. Trace ashfall was reported in the community of False Pass (38 km ENE) between 1800-2030 and also in King Cove and nearby marine waters. Activity declined at around 1830 although seismicity remained elevated, ash emissions, and ashfall continued until 2100. Lightning was again detected beginning around 1930, which suggested that ash emissions continued. Ongoing explosions were detected in infrasound data, at a lower level than during the most energetic phase of this event. Lightning was last detected at 2048. By 2124 the intensity of the eruption had decreased, and ash emissions were likely rising to less than 6.7 km altitude. Seismicity returned to pre-eruption levels. On 16 September the ACC was lowered to Orange and the VAL to Watch at 1244; the sulfur dioxide plume that was emitted from the previous eruption event was still visible over the northern Pacific Ocean. Elevated surface temperatures, gas-and-steam emissions from the vent, and new, small lahars were reported on the upper flanks based on satellite and webcam images. Minor deposits were reported on the flanks which were likely the result of collapse of previously accumulated lava near the summit crater.

Elevated seismicity with tremor, small earthquakes, and elevated surface temperatures were detected during 17-23 September. Minor gas-and-steam emissions were visible in webcam images. On 20 September small volcanic debris flows were reported on the upper flanks. On 21 September a small ash deposit was observed on the upper flanks extending to the NE based on webcam images. Seismic tremor increased significantly during 22-23 September. Regional infrasound sensors suggested that low-level eruptive activity was occurring within the summit crater by around 1800 on 23 September. Even though seismicity was at high levels, strongly elevated surface temperatures indicating lava at the surface were absent and no ash emissions were detected; weather clouds at 0.6-4.6 km altitude obscured views. At 0025 on 24 September AVO noted that seismicity continued at high levels and nearly continuous small infrasound signals began, likely from low-level eruptive activity. Strongly elevated surface temperatures were identified in satellite images by 0900 and persisted throughout the day; the higher temperatures along with infrasound and seismic data were consistent with lava erupting at the summit. Around 1700 similarly elevated surface temperatures were detected from the summit in satellite data, which suggested that more vigorous lava fountaining had started. Starting around 1800 low-level ash emissions rose to altitudes less than 4.6 km altitude and quickly dissipated.

Beginning at midnight on 25 September, a series of seismic signals consistent with volcanic flows were recorded on the N side of the volcano. A change in seismicity and infrasound signals occurred around 0535 and at 0540 a significant ash cloud formed and quickly reached 14 km altitude and drifted E along the Alaska Peninsula. The cloud generated at least 150 lightning strokes with thunder that could be heard by people in False Pass. Seismicity rapidly declined to near background levels around 0600. AVO increased the ACC to Red and the VAL to Warning at 0602. The ash cloud detached from the volcano at around 0700, rose to 11.6 km altitude, and drifted ESE. Trace to minor amounts of ashfall were reported by the communities of False Pass, King Cove, Cold Bay, and Sand Point around 0700. Ash emissions continued at lower altitudes of 6-7.6 km altitude at 0820. Small explosions at the vent area continued to be detected in infrasound data and likely represented low-level eruptive activity near the vent. Due to the significant decrease in seismicity and ash emissions the ACC was lowered to Orange and the VAL to Watch at 1234. Radar data showed significant collapses of the crater that occurred on 25 September. Satellite data also showed significant hot, degassing pyroclastic and lahar deposits on all flanks, including more extensive flows on the ENE and WSW sections below two new collapse scarps. Following the significant activity during 24-25 September, only low-level activity was observed. Seismicity decreased notably near the end of the strong activity on 25 September and continued to decrease through the end of the month, though tremor and small earthquakes were still reported. No explosive activity was detected in infrasound data through 2 October. Gas-and-steam emissions rose to 3.7 km altitude, as reported by pilots and seen in satellite images. Satellite data from 26 September showed that significant collapses had occurred at the summit crater and hot, steaming deposits from pyroclastic flows and lahars were present on all the flanks, particularly to the ENE and WSW. A small ash cloud was visible in webcam images on 27 September, likely from a collapse at the summit cone. High elevated surface temperatures were observed in satellite imagery during 27-28 September, which were likely the result of hot deposits on the flanks erupted on 25 September. Minor steaming at the summit crater and from an area on the upper flanks was visible in webcam images on 28 September.

During October, explosion events continued between periods of low activity. Seismicity significantly increased starting at around 2100 on 2 October; around the same time satellite images showed an increase in surface temperatures consistent with lava fountaining. Small, hot avalanches of rock and lava descended an unspecified flank. In addition, a distinct increase in infrasound, seismicity, and lightning detections was followed by an ash plume that rose to 12.2 km altitude and drifted S and E at 0520 on 3 October, based on satellite images. Nighttime webcam images showed incandescence due to lava fountaining at the summit and pyroclastic flows descending the NE flank. AVO reported that a notable explosive eruption started at 0547 and lasted until 0900 on 3 October, which prompted a rise in the ACC to Red and the VAL to Warning. Subsequent ash plumes rose to 6-7.6 km altitude by 0931. At 1036 the ACC was lowered back to Orange and the VAL to Watch since both seismic and infrasound data quieted substantially and were slightly above background levels. Gas-and-steam emissions were observed at the summit, based on webcam images. Trace amounts of ashfall were observed in Cold Bay. Resuspended ash was present at several kilometers altitude near the volcano. During the afternoon, low-level ash plumes were visible at the flanks, which appeared to be largely generated by rock avalanches off the summit crater following the explosive activity. These ash plumes rose to 3 km altitude and drifted W. Trace amounts of ashfall were reported by observers in Cold Bay and Unalaska and flights to these communities were disrupted by the ash cloud. Satellite images taken after the eruption showed evidence of pyroclastic flows and lahar deposits in drainages 2 km down the SW flank and about 3.2 km down the NE flank, and continued erosion of the crater rim. Small explosion craters at the end of the pyroclastic flows on the NE flank were noted for the first time, which may have resulted from gas-and-steam explosions when hot deposits interact with underlying ice.

During 4 October seismicity, including frequent small earthquakes, remained elevated, but was gradually declining. Ash plumes were produced for over eight hours until around 1400 that rose to below 3.7 km altitude. These ash plumes were primarily generated off the sides of the volcano where hot rock avalanches from the crater rim had entered drainages to the SW and NE. Two explosion craters were observed at the base of the NE deposits about 3.2 km from the crater rim. Webcam images showed the explosion craters were a source of persistent ash emissions; occasional collapse events also generated ash. Seismicity remained elevated with sulfur dioxide emissions that had a daily average of more than 1,000 tons per day, and frequent small earthquakes through the end of the month. Frequent elevated surface temperatures were identified in satellite images and gas-and-steam plumes were observed in webcam images, although weather conditions occasionally prevented clear views of the summit. Emissions were robust during 14-16 October and were likely generated by the interaction of hot material and snow and ice. During the afternoon of 21 October a strong gas-and-steam plume rose to 3-4.6 km altitude and extended 40 km WSW, based on satellite images and reports from pilots. On 31 October the ACC was lowered to Yellow and the VAL was lowered to Advisory.

Activity in November was characterized by elevated seismicity with ongoing seismic tremor and small, low-frequency earthquakes, elevated surface temperatures, and gas-and-steam emissions. There was an increase in seismic and infrasound tremor amplitudes starting at 1940 on 2 November. As a result, the ACC was again raised to Orange and the VAL was increased to Watch, although ash was not identified in satellite data. An ash cloud rose to 6.1 km altitude and drifted W according to satellite data at 2000. By 0831 on 3 November ash emissions were no longer visible in satellite images. On 6 and 9 November air pressure sensors detected signals consistent with small explosions. Small explosions were detected in infrasound data consistent with weak Strombolian activity on 19 and 21 November. Seismicity started to decrease on 21 November. On 25 November gas-and-steam emissions were emitted from the vent as well as from a scarp on the NE side of the volcano near the summit. A gas-and-steam plume extended about 50 km SSE and was observed in satellite and webcam images on 26 November. On 28 November small explosions were observed in seismic and local infrasound data and gas-and-steam emissions were visible from the summit and from the upper NE collapse scarp based on webcam images. Possible small explosions were observed in infrasound data on 30 November. Weakly elevated surface temperatures and a persistent gas-and-steam plume from the summit and collapse scarps on the upper flanks. A passing aircraft reported the gas-and-steam plume rose to 3-3.4 km altitude on 30 November, but no significant ash emissions were detected.

Satellite data. MODIS thermal anomaly data provided through MIROVA (Middle InfraRed Observation of Volcanic Activity) showed a strong pulse of thermal activity beginning in July 2023 that continued through November 2023 (figure 48). This strong activity was due to Strombolian explosions and lava fountaining events at the summit crater. According to data from MODVOLC thermal alerts, a total of 101 hotspots were detected near the summit crater in July (11-14, 16-19, 23-24 and 26), August (4, 25-26, and 29), September (5, 12, and 17), and October (3, 4, and 8). Infrared satellite data showed large lava flows descending primarily the northern and SE flanks during the reporting period (figure 49). Sulfur dioxide plumes often exceeded two Dobson Units (DUs) and drifted in different directions throughout the reporting period, based on satellite data from the TROPOMI instrument on the Sentinel-5P satellite (figure 50).

Figure 48. Graph of Landsat 8 and 9 OLI thermal data from 1 June 2024 showing a strong surge in thermal activity during July through November 2023. During mid-October, the intensity of the hotspots gradually declined. Courtesy of MIROVA.

Figure 49. Infrared (bands B12, B11, B4) satellite images show several strong lava flows (bright yellow-orange) affecting the northern and SE flanks of Shishaldin on 18 July 2023 (top left), 4 June 2023 (top right), 26 September 2023 (bottom left), and 3 October 2023 (bottom right). Courtesy of Copernicus Browser.

Figure 50. Strong sulfur dioxide plumes were detected at Shishaldin and drifted in different directions on 15 August 2023 (top left), 5 September 2023 (top right), 25 September 2023 (bottom left), and 6 October 2023 (bottom right). Courtesy of NASA Global Sulfur Dioxide Monitoring Page.

Geologic Background. The symmetrical glacier-covered Shishaldin in the Aleutian Islands is the westernmost of three large stratovolcanoes in the eastern half of Unimak Island. The Aleuts named the volcano Sisquk, meaning "mountain which points the way when I am lost." Constructed atop an older glacially dissected edifice, it is largely basaltic in composition. Remnants of an older edifice are exposed on the W and NE sides at 1,500-1,800 m elevation. There are over two dozen pyroclastic cones on its NW flank, which is covered by massive aa lava flows. Frequent explosive activity, primarily consisting of Strombolian ash eruptions from the small summit crater, but sometimes producing lava flows, has been recorded since the 18th century. A steam plume often rises from the summit crater.

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/); 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/).

Ioto (Iwo-jima), located about 1,200 km S of Tokyo, lies within a 9-km-wide submarine caldera along the Izu-Bonin-Mariana volcanic arc. Previous eruptions date back to 1889 and have consisted of dominantly phreatic explosions, pumice deposits during 2001, and discolored water. A submarine eruption during July through December 2022 was characterized by discolored water, pumice deposits, and gas emissions (BGVN 48:01). This report covers a new eruption during October through December 2023, which consisted of explosions, black ejecta, discolored water, and floating pumice, based on information from the Japan Meteorological Association (JMA), the Japan Coast Guard (JCG), and satellite data.

JMA reported that an eruption had been occurring offshore of Okinahama on the SE side of the island since 21 October, which was characterized by volcanic tremor, according to the Japan Maritime Self-Defense Force (JMSDF) Iwo Jima Air Base (figure 22). According to an 18 October satellite image a plume of discolored water at the site of this new eruption extended NE (figure 23). During an overflight conducted on 30 October, a vent was identified about 1 km off the coast of Okinahama. Observers recorded explosions every few minutes that ejected dark material about 20 m above the ocean and as high as 150 m. Ejecta from the vent formed a black-colored island about 100 m in diameter, according to observations conducted from the air by the Earthquake Research Institute of the University of Tokyo in cooperation with the Mainichi newspaper (figure 24). Occasionally, large boulders measuring more than several meters in size were also ejected. Observations from the Advanced Land Observing Satellite Daichi-2 and Sentinel-2 satellite images also confirmed the formation of this island (figure 23). Brown discolored water and floating pumice were present surrounding the island.

Figure 22. Map of Ioto showing the locations of recorded eruptions from 1889 through December 2023. The most recent eruption occurred during October through December 2023 and is highlighted in red just off the SE coast of the island and E of the 2001 eruption site. A single eruption highlighted in green was detected just off the NE coast of the island on 18 November 2023. From Ukawa et al. (2002), modified by JMA.

Figure 23. Satellite images showing the formation of the new island formation (white arrow) off the SE (Okinahama) coast of Ioto on 18 October 2023 (top left), 27 November 2023 (top right), 2 December 2023 (bottom left), and 12 December 2023 (bottom right). Discolored water was visible surrounding the new island. By December, much of the island had been eroded. Courtesy of Copernicus Browser.

Figure 24. Photo showing an eruption off the SE (Okinahama) coast of Ioto around 1230 on 30 October 2023. A column of water containing black ejecta is shown, which forms a new island. Occasionally, huge boulders more than several meters in size were ejected with the jet. Dark brown discolored water surrounded the new island. Photo has been color corrected and was taken from the S by the Earthquake Research Institute, University of Tokyo in cooperation of Mainichi newspaper. Courtesy of JMA.

The eruption continued during November. During an overflight on 3 November observers photographed the island and noted that material was ejected 169 m high, according to a news source. Explosions gradually became shorter, and, by the 3rd, they occurred every few seconds; dark and incandescent material were ejected about 800 m above the vent. On 4 November eruptions were accompanied by explosive sounds. Floating, brown-colored pumice was present in the water surrounding the island. There was a brief increase in the number of volcanic earthquakes during 8-14 November and 24-25 November. The eruption temporarily paused during 9-11 November and by 12 November eruptions resumed to the W of the island. On 10 November dark brown-to-dark yellow-green discolored water and a small amount of black floating material was observed (figure 25). A small eruption was reported on 18 November off the NE coast of the island, accompanied by white gas-and-steam plumes (figure 23). Another pause was recorded during 17-19 November, which then resumed on 20 November and continued erupting intermittently. According to a field survey conducted by the National Institute for Disaster Prevention Science and Technology on 19 November, a 30-m diameter crater was visible on the NE coast where landslides, hot water, and gray volcanic ash containing clay have occurred and been distributed previously. Erupted blocks about 10 cm in diameter were distributed about 90-120 m from the crater. JCG made observations during an overflight on 23 November and reported a phreatomagmatic eruption. Explosions at the main vent generated dark gas-and-ash plumes that rose to 200 m altitude and ejected large blocks that landed on the island and in the ocean (figure 26). Discolored water also surrounded the island. The size of the new island had grown to 450 m N-S x 200 m E-W by 23 November, according to JCG.

Figure 25. Photo of the new land formed off the SE (Okinahama) coast of Ioto on 10 November showing discolored water and a small amount of black floating material were visible surrounding the island. Photo has been color corrected. Photographed by JCG courtesy of JMA.

Figure 26. Photo of the new land formed off the SE (Okinahama) coast of Ioto on 23 November showing a phreatomagmatic eruption that ejected intermittent pulses of ash and dark material that rose to 200 m altitude. Photo has been color corrected. Photographed by JCG courtesy of JMA.

The eruption continued through 11 December, followed by a brief pause in activity, which then resumed on 31 December, according to JMA. Intermittent explosions produced 100-m-high black plumes at intervals of several minutes to 30 minutes during 1-10 December. Overflights were conducted on 4 and 15 December and reported that the water surrounding the new island was discolored to dark brown-to-dark yellow-green (figure 27). No floating material was reported during this time. In comparison to the observations made on 23 November, the new land had extended N and part of it had eroded away. In addition, analysis by the Geospatial Information Authority of Japan using SAR data from Daichi-2 also confirmed that the area of the new island continued to decrease between 4 and 15 December. Ejected material combined with wave erosion transformed the island into a “J” shape, 500-m-long and with the curved part about 200 m offshore of Ioto. The island was covered with brown ash and blocks, and the surrounding water was discolored to greenish-brown and contained an area of floating pumice. JCG reported from an overflight on 4 December that volcanic ash-like material found around the S vent on the NE part of the island was newly deposited since 10 November (figure 28). By 15 December the N part of the “J” shaped island had separated and migrated N, connecting to the Okinahama coast and the curved part of the “J” had eroded into two smaller islands (figure 27).

Figure 27. Photos of the new island formed off the SE (Okinahama) coast of Ioto on 4 December 2023 (left) and 15 December 2023 (right). No gas-and-ash emissions or lava flows were observed on the new land. Additionally, dark brown-to-dark yellow-green discolored water was observed surrounding the new land. During 4 and 15 December, the island had eroded to where the N part of the “J” shape had separated and migrated N, connecting to the Okinahama coast and the curved part of the “J” had eroded into two smaller islands. Courtesy of Copernicus Browser.

Figure 28. Photo of new volcanic ash-deposits (yellow dashed lines) near the S vent on the NE coast of Ioto taken by JCG on 4 December 2023. White gas-and-steam emissions were also visible (white arrow). Photo has been color corrected. Courtesy of JMA.

References. Ukawa, M., Fujita, E., Kobayashi, T., 2002, Recent volcanic activity of Iwo Jima and the 2001 eruption, Monthly Chikyu, Extra No. 39, 157-164.

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), 1-3-4 Otemachi, Chiyoda-ku, Tokyo 100-8122, Japan (URL: http://www.jma.go.jp/jma/indexe.html); Japan Coast Guard (JCG) Volcano Database, Hydrographic and Oceanographic Department, 3-1-1, Kasumigaseki, Chiyoda-ku, Tokyo 100-8932, Japan (URL: https://www1.kaiho.mlit.go.jp/GIJUTSUKOKUSAI/kaiikiDB/kaiyo22-2.htm); Copernicus Browser, Copernicus Data Space Ecosystem, European Space Agency (URL: https://dataspace.copernicus.eu/browser/); Asahi, 5-3-2, Tsukiji, Chuo Ward, Tokyo, 104-8011, Japan (URL: https://www.asahi.com/ajw/articles/15048458).

Puracé, located in Colombia, is a stratovolcano that contains a 500-m-wide summit crater. It is part of the Los Coconucos volcanic chain that is a NW-SE trending group of seven cones and craters. The most recent eruption occurred during March 2022 that was characterized by frequent seismicity and gas-and-steam emissions (BGVN 47:06). This report covers a brief eruption during November 2023 based on monthly reports from the Popayán Observatory, part of the Servicio Geologico Colombiano (SGC).

Activity during November 2022 through November 2023 primarily consisted of seismicity: VT-type events, LP-type events, HB-type events, and TR-type events (table 4). Maximum sulfur dioxide values were measured weekly and ranged from 259-5,854 tons per day (t/d) during November 2022 through April 2023. White gas-and-steam emissions were also occasionally reported.

SGC issued a report on 25 October that noted a significant increase in the number of earthquakes associated with rock fracturing. These earthquakes were located SE of the crater between Puracé and Piocollo at depths of 1-4 km. There were no reported variations in sulfur dioxide values, but SGC noted high carbon dioxide values, compared to those recorded in the first half of 2023.

SGC reported that at 1929 on 16 November the seismic network detected a signal that was possibly associated with a gas-and-ash emission, though it was not confirmed in webcam images due to limited visibility. On 17 November an observer confirmed ash deposits on the N flank. Webcam images showed an increase in degassing both inside the crater and from the NW flank, rising 700 m above the crater.

Table 4. Seismicity at Puracé during November 2022-November 2023. Volcano-tectonic (VT), long-period (LP), hybrid (HB), and tremor (TR) events are reported each month. Courtesy of SGC.

Geologic Background. Puracé is an active andesitic volcano with a 600-m-diameter summit crater at the NW end of the Los Coconucos Volcanic Chain. This volcanic complex includes nine composite and five monogenetic volcanoes, extending from the Puracé crater more than 6 km SE to the summit of Pan de Azúcar stratovolcano. The dacitic massif which the complex is built on extends about 13 km NW-SE and 10 km NE-SW. Frequent small to moderate explosive eruptions reported since 1816 CE have modified the morphology of the summit crater, with the largest eruptions in 1849, 1869, and 1885.

Information Contacts: Servicio Geologico Colombiano (SGC), Diagonal 53 No. 34-53 - Bogotá D.C., Colombia (URL: https://www.sgc.gov.co/volcanes).

Etna, located on the Italian island of Sicily, has had documented eruptions dating back to 1500 BCE. Activity typically originates from multiple cones at the summit, where several craters have formed and evolved. The currently active craters are Northeast Crater (NEC), Voragine (VOR), and Bocca Nuova (BN), and the Southeast Crater (SEC); VOR and BN were previously referred to as the “Central Crater”. The original Southeast crater formed in 1978, and a second eruptive site that opened on its SE flank in 2011 was named the New Southeast Crater (NSEC). Another eruptive site between the SEC and NSEC developed during early 2017 and was referred to as the "cono della sella" (saddle cone). The current eruption period began in November 2022 and has been characterized by intermittent Strombolian activity, lava flows, and ash plumes (BGVN 48:08). This report updates activity during July through October 2023, which includes primarily gas-and-steam emissions; during July and August Strombolian explosions, lava fountains, and lava flows were reported, based on weekly and special reports by the Osservatorio Etneo (OE), part of the Catania Branch of Italy's Istituo Nazionale di Geofisica e Vulcanologica (INGV) and satellite data.

Variable fumarolic degassing was reported at all summit craters (BN, VOR, NEC, and SEC) throughout the entire reporting period (table 15). The MIROVA (Middle InfraRed Observation of Volcanic Activity) volcano hotspot detection system based on the analysis of MODIS data showed frequent low-to-moderate power thermal anomalies during the reporting period (figure 399). During mid-August there was a pulse in activity that showed an increase in the power of the anomalies due to Strombolian activity, lava fountains, and lava flows. Infrared satellite imagery captured strong thermal anomalies at the central and southeast summit crater areas (figure 400). Accompanying thermal activity were occasional sulfur dioxide plumes that exceeded 2 Dobson Units (DUs) recorded by the TROPOMI instrument on the Sentinel-5P satellite (figure 401).

Table 15. Summary of activity at the four primary crater areas at the summit of Etna during July-October 2023. Information is from INGV weekly reports.

Figure 399. Frequent thermal activity at Etna varied in strength during July through October 2023, as shown on this MIROVA plot (Log Radiative Power). There was a spike in power during mid-August, which reflected an increase in Strombolian activity. Courtesy of MIROVA.

Figure 400. Infrared (bands B12, B11, B4) satellite images showing strong thermal anomalies at Etna’s central and Southeast crater areas on 21 July 2023 (top left), 27 August 2023 (top right), 19 September 2023 (bottom left), and 29 October 2023 (bottom right). Courtesy of Copernicus Browser.

Figure 401. Sulfur dioxide plumes that exceeded 2 Dobson Units (DUs) rose above Etna on 14 July 2023 (top left), 14 August 2023 (top right), 2 September 2023 (bottom left), and 7 October 2023 (bottom right). These plumes drifted NE, S, SE, and SW, respectively. Courtesy of NASA Global Sulfur Dioxide Monitoring Page.

Activity during July and August was relatively low and mainly consisted of degassing at the summit craters, particularly at SEC and BN. Cloudy weather prevented clear views of the summit during early July. During the night of 2 July some crater incandescence was visible at SEC. Explosive activity resumed at SEC during 9-10 July, which was characterized by sporadic and weak ash emissions that rapidly dispersed in the summit area (figure 402). INGV reported moderate Strombolian activity began at 2034 on 14 July and was confined to the inside of the crater and fed by a vent located in the E part of SEC. An ash emission was detected at 2037. A new vent opened on 15 July in the SE part of BN and began to produce continuous gas-and-steam emissions. During an inspection carried out on 28 July pulsating degassing, along with audible booms, were reported at two active vents in BN. Vigorous gas-and-steam emissions intermittently generated rings. On rare occasions, fine, reddish ash was emitted from BN1 and resuspended by the gas-and-steam emissions.

Figure 402. Webcam image taken by the Monta Cagliato camera showing an ash emission rising above Etna’s Southeast Crater (SEC) on 10 July 2023. Photo has been color corrected. Courtesy of INGV (Report 28/2023, ETNA, Bollettino Settimanale, 03/07/2023 - 09/07/2023).

Around 2000 on 13 August INGV reported a sudden increase in volcanic tremor amplitude. Significant infrasonic activity coincided with the tremor increase. Incandescent flashes were visible through the cloud cover in webcam images of SEC (figure 403). Strombolian activity at SEC began to gradually intensify starting at 2040 as seismicity continued to increase. The Aviation Color Code (ACC) was raised to Yellow (the second lowest-level on a four-color scale) at 2126 and then to Orange (the second highest-level on a four-color scale) at 2129 due to above-background activity. The activity rapidly transitioned from Strombolian activity to lava fountains around 2333 that rose 300-400 m above the crater (figure 403). Activity was initially focused on the E vent of the crater, but then the vent located above the S flank of the cone also became active. A lava flow from this vent traveled SW into the drainage created on 10 February 2022, overlapping with previous flows from 10 and 21 February 2022 and 21 May 2023, moving between Monte Barbagallo and Monte Frumento Supino (figure 404). The lava flow was 350 m long, oriented NNE-SSW, and descended to an elevation of 2.8 km. Flows covered an area of 300,000 m² and had an estimated volume of 900,000 m³. The ACC was raised to Red at 2241 based on strong explosive activity and ashfall in Rifugio Sapienza-Piano Vetore at 1.7 km elevation on the S flank. INGV reported that pyroclastic flows accompanied this activity.

Figure 403. Webcam images of the lava fountaining event at Etna during 13-14 August 2023 taken by the Milos (EMV) camera. Images show the start of the event with increasing incandescence (a-b), varying intensity in activity (c-e), lava fountaining and pyroclastic flows (f-g), and a strong ash plume (g). Courtesy of INGV (Report 33/2023, ETNA, Bollettino Settimanale, 08/08/2023 - 14/08/2023).

Figure 404. Map of the new lava flow (yellow) and vent (red) at SEC (CSE) of Etna on 13 August 2023. The background image is a shaded model of the terrain of the summit area obtained by processing Skysat images acquired during on 18 August. The full extent of the lava flow was unable to be determined due to the presence of ash clouds. The lava flow extended more than 350 m to the SSW and reached an elevation of 2.8 km and was located W of Mt. Frumento Supino. CSE = Southeast Crater; CNE = Northeast Crater; BN = Bocca Nuova; VOR = Voragine. Courtesy of INGV (Report 34/2023, ETNA, Bollettino Settimanale, 14/08/2023 - 20/08/2023).

Activity peaked between 0240 and 0330 on 14 August, when roughly 5-6 vents erupted lava fountains from the E to SW flank of SEC. The easternmost vents produced lava fountains that ejected material strongly to the E, which caused heavy fallout of incandescent pyroclastic material on the underlying flank, triggering small pyroclastic flows. This event was also accompanied by lightning both in the ash column and in the ash clouds that were generated by the pyroclastic flows. A fracture characterized by a series of collapse craters (pit craters) opened on the upper SW flank of SEC. An ash cloud rose a few kilometers above the crater and drifted S, causing ash and lapilli falls in Rifugio Sapienza and expanding toward Nicolosi, Mascalucia, Catania, and up to Syracuse. Ashfall resulted in operational problems at the Catania airport (50 km S), which lasted from 0238 until 2000. By 0420 the volcanic tremor amplitude values declined to background levels. After 0500 activity sharply decreased, although the ash cloud remained for several hours and drifted S. By late morning, activity had completely stopped. The ACC was lowered to Orange as volcanic ash was confined to the summit area. Sporadic, minor ash emissions continued throughout the day. At 1415 the ACC was lowered to Yellow and then to Green at 1417.

During the night of 14-15 August only occasional flashes were observed, which were more intense during avalanches of material inside the eruptive vents. Small explosions were detected at SEC at 2346 on 14 August and at 0900 on 26 August that each produced ash clouds which rapidly dispersed into the atmosphere (figure 405). According to a webcam image, an explosive event detected at 2344 at SEC generated a modest ash cloud that was rapidly dispersed by winds. The ACC was raised to Yellow at 2355 on 14 August due to increasing unrest and was lowered to Green at 0954 on 15 August.

Figure 405. Webcam image of an ash plume rising above Etna’s SEC at 0902 (local time) on 26 August taken by the Montagnola EMOV camera. Photo has been color corrected. Courtesy of INGV (Report 35/2023, ETNA, Bollettino Settimanale, 21/08/2023 - 27/08/2023).

Activity during September and October was relatively low and mainly characterized by variable degassing from BN and SEC. Intense, continuous, and pulsating degassing was accompanied by roaring sounds and flashes of incandescence at BN both from BN1 and the new pit crater that formed during late July (figure 406). The degassing from the new pit crater sometimes emitted vapor rings. Cloudy weather during 6-8 September prevented observations of the summit craters .

Figure 406. Webcam image (top) showing degassing from Etna’s Bocca Nuova (BN) crater accompanied by nighttime crater incandescence at 0300 (local time) on 2 September 2023 by the Piedimonte Etneo (EPVH) camera and a photo of incandescence at BN1 and the new pit crater (bottom) taken by an observatory scientist from the E rim of BN during a survey on 2 September 2023. Courtesy of INGV (Report 36/2023, ETNA, Bollettino Settimanale, 28/08/2023 - 03/09/2023).

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

Information Contacts: Sezione di Catania - Osservatorio Etneo, Istituto Nazionale di Geofisica e Vulcanologia (INGV), Sezione di Catania, Piazza Roma 2, 95123 Catania, Italy (URL: http://www.ct.ingv.it/it/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); NASA Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, NASA Goddard Space Flight Center (NASA/GSFC), 8800 Greenbelt Road, Goddard MD 20771, USA (URL: https://so2.gsfc.nasa.gov/); Copernicus Browser, Copernicus Data Space Ecosystem, European Space Agency (URL: https://dataspace.copernicus.eu/browser/).

Suwanosejima is an 8-km-long island that consists of a stratovolcano and two active summit craters, located in the northern Ryukyu Islands, Japan. Volcanism over the past century has been characterized by Strombolian explosions, ash plumes, and ashfall. The current eruption began in October 2004 and has more recently consisted of frequent eruption plumes, explosions, and incandescent ejecta (BGVN 48:07). This report covers similar activity of ash plumes, explosions, and crater incandescence during July through October 2023 using monthly reports from the Japan Meteorological Agency (JMA) and satellite data.

Thermal activity during the reporting period was relatively low; only one low-power thermal anomaly was detected during mid-July and one during early August, based on a MIROVA (Middle InfraRed Observation of Volcanic Activity) Log Radiative Power graph of the MODIS thermal anomaly data. On two clear weather days, a thermal anomaly was visible in infrared satellite images (figure 81).

Figure 81. Infrared (bands B12, B11, B4) satellite imagery showing a thermal anomaly (bright yellow-orange) at the Otake crater of Suwanosejima on 23 September 2023 (left) and 18 October 2023 (right). Courtesy of Copernicus Browser.

Low-level activity was reported at the Otake crater during July and no explosions were detected. Eruption plumes rose as high as 1.8 km above the crater. On 13 July an ash plume rose 1.7 km above the crater rim, based on a webcam image. During the night of the 28th crater incandescence was visible in a webcam image. An eruptive event reported on 31 July produced an eruption plume that rose 2.1 km above the crater. Seismicity consisted of 11 volcanic earthquakes on the W flank, the number of which had decreased compared to June (28) and 68 volcanic earthquakes near the Otake crater, which had decreased from 722 in the previous month. According to observations conducted by the University of Tokyo Graduate School of Science, Kyoto University Disaster Prevention Research Institute, Toshima Village, and JMA, the amount of sulfur dioxide emissions released during the month was 400-800 tons per day (t/d).

Eruptive activity in the Otake crater continued during August and no explosions were reported. An eruptive event produced a plume that rose 1 km above the crater at 1447 on 12 August. Subsequent eruptive events were recorded at 0911 on 16 August, at 1303 on 20 August, and at 0317 on 21 August, which produced ash plumes that rose 1-1.1 km above the crater and drifted SE, SW, and W. On 22 August an ash plume was captured in a webcam image rising 1.4 km above the crater (figure 82). Multiple eruptive events were detected on 25 August at 0544, 0742, 0824, 1424, and 1704, which generated ash plumes that rose 1.1-1.2 km above the crater and drifted NE, W, and SW. On 28 August a small amount of ashfall was observed as far as 1.5 km from the crater. There were 17 volcanic earthquakes recorded on the W flank of the volcano and 79 recorded at the Otake crater during the month. The amount of sulfur dioxide emissions released during the month was 400-800 t/d.

Figure 82. Webcam image of an ash plume rising 1.4 km above Suwanosejima’s Otake crater rim on 22 August 2023. Courtesy of JMA (Volcanic activity commentary for Suwanosejima, August 2023).

Activity continued at the Otake crater during September. Occasionally, nighttime crater incandescence was observed in webcam images and ashfall was reported. An eruptive event at 1949 on 4 September produced an ash plume that rose 1 km above the crater and drifted SW. On 9 September several eruption events were detected at 0221, 0301, and 0333, which produced ash plumes that rose 1.1-1.4 km above the crater rim and drifted W; continuous ash emissions during 0404-0740 rose to a maximum height of 2 km above the crater rim (figure 83). More eruptive events were reported at 1437 on 10 September, at 0319 on 11 September, and at 0511 and 1228 on 15 September, which generated ash plumes that rose 1-1.8 km above the crater. During 25, 27, and 30 September, ash plumes rose as high as 1.3 km above the crater rim. JMA reported that large blocks were ejected as far as 300 m from the center of the crater. There were 18 volcanic earthquakes detected beneath the W flank and 82 volcanic earthquakes detected near the Otake crater. The amount of sulfur dioxide released during the month ranged from 600 to 1,600 t/d.

Figure 83. Webcam image of an ash plume rising 2 km above Suwanosejima’s Otake crater rim on 9 September 2023. Courtesy of JMA (Volcanic activity commentary for Suwanosejima, September 2023).

Activity during early-to-mid-October consisted of occasional explosions, a total number of 13, and ash plumes that rose as high as 1.9 km above the Otake crater rim on 29 October (figure 84). These explosions are the first to have occurred since June 2023. Continuous ash emissions were reported during 0510-0555 on 1 October. Explosions were recorded at 0304, 2141, and 2359 on 2 October, at 0112 on 3 October, and at 1326 on 6 October, which produced ash plumes that rose as high as 1 km above the crater rim and drifted SW and W. An explosion was noted at 0428 on 3 October, but emission details were unknown. A total of eight explosions were recorded by the seismic network at 1522 on 14 October, at 0337, 0433, 0555, 1008, and 1539 on 15 October, and at 0454 and 0517 on 16 October. Ash plumes from these explosions rose as high as 900 m above the crater and drifted SE. Eruptive events during 25-27 and 29-30 October generated plumes that rose as high as 1.9 km above the crater and drifted SE, S, and SW. Ash was deposited in Toshima village (3.5 km SSW). Eruptive activity occasionally ejected large volcanic blocks as far as 600 m from the crater. Nighttime crater incandescence was visible in webcams. Intermittent ashfall was reported as far as 1.5 km from the crater. There were 43 volcanic earthquakes detected on the W flank during the month, and 184 volcanic earthquakes detected near the Otake crater. The amount of sulfur dioxide emitted ranged between 400 and 900 t/d.

Figure 84. Webcam image of an ash plume rising 1.9 km above Suwanosejima’s Otake crater on 29 October 2023. Courtesy of JMA (Volcanic activity commentary for Suwanosejima, October 2023).

Geologic Background. The 8-km-long island of Suwanosejima in the northern Ryukyu Islands consists of an andesitic stratovolcano with two active summit craters. The summit is truncated by a large breached crater extending to the sea on the E flank that was formed by edifice collapse. One of Japan's most frequently active volcanoes, it was in a state of intermittent Strombolian activity from Otake, the NE summit crater, between 1949 and 1996, after which periods of inactivity lengthened. The largest recorded eruption took place in 1813-14, when thick scoria deposits covered residential areas, and the SW crater produced two lava flows that reached the western coast. At the end of the eruption the summit of Otake collapsed, forming a large debris avalanche and creating an open collapse scarp extending to the eastern coast. The island remained uninhabited for about 70 years after the 1813-1814 eruption. Lava flows reached the eastern coast of the island in 1884. Only about 50 people live on the island.

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/); 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/).

Aira caldera, located in the northern half of Kagoshima Bay, Japan, contains the post-caldera Sakurajima volcano. Eruptions typically originate from the Minamidake crater, and since the 8th century, ash deposits have been recorded in the city of Kagoshima (10 km W), one of Kyushu’s largest cities. The Minamidake summit cone and crater has had persistent activity since 1955; the Showa crater on the E flank has also been intermittently active since 2006. The current eruption period began during March 2017 and has recently been characterized by intermittent explosions, eruption plumes, and ashfall (BGVN 48:07). This report updates activity during July through October 2023 and describes explosive events, ash plumes, nighttime crater incandescence, and ashfall, according to monthly activity reports from the Japan Meteorological Agency (JMA) and satellite data.

Thermal activity remained at low levels during this reporting period, according to the MIROVA (Middle InfraRed Observation of Volcanic Activity) system (figure 149). There was a slight increase in the number of anomalies during September through October. Occasional thermal anomalies were visible in infrared satellite images mainly at the Minamidake crater (Vent A is located to the left and Vent B is located to the right) (figure 150).

Table 30. Number of monthly explosive events, days of ashfall, area of ash covered, and sulfur dioxide emissions from Sakurajima’s Minamidake crater at Aira during July-October 2023. Note that smaller ash events are not listed. Ashfall days were measured at Kagoshima Local Meteorological Observatory and ashfall amounts represent material covering all the Kagoshima Prefecture. Data courtesy of JMA monthly reports.

Figure 149. Thermal activity at Sakurajima in the Aira caldera was relatively low during July through October 2023, based on this MIROVA graph (Log Radiative Power). There was an increase in the number of detected anomalies during September through October. Courtesy of MIROVA.

Figure 150. Infrared (bands B12, B11, B4) satellite images show a persistently strong thermal anomaly (bright yellow-orange) at the Minamidake crater at Aira’s Sakurajima volcano on 28 September 2023 (top left), 3 October 2023 (top right), 23 October 2023 (bottom left), and 28 October 2023 (bottom right). Vent A is located to the left and Vent B is to the right of Vent A; both vents are part of the Minamidake crater. Courtesy of Copernicus Browser.

JMA reported that during July, there were eight eruptions, three of which were explosion events in the Showa crater. Large blocks were ejected as far as 600 m from the Showa crater. Very small eruptions were occasionally reported at the Minamidake crater. Nighttime incandescence was observed in both the Showa and Minamidake crater. Explosions were reported on 16 July at 2314 and on 17 July at 1224 and at 1232 (figure 151). Resulting eruption plumes rose 700-2,500 m above the crater and drifted N. On 23 July the number of volcanic earthquakes on the SW flank of the volcano increased. A strong Mw 3.1 volcanic earthquake was detected at 1054 on 26 July. The number of earthquakes recorded throughout the month was 545, which markedly increased from 73 in June. No ashfall was observed at the Kagoshima Regional Meteorological Observatory during July. According to a field survey conducted during the month, the daily amount of sulfur dioxide emissions was 1,600-3,200 tons per day (t/d).

Figure 151. Webcam image showing a strong, gray ash plume that rose 2.5 km above the crater rim of Aira’s Showa crater at 1232 on 17 July 2023. Courtesy of JMA monthly report (Sakurajima volcanic activity explanatory material, July 2023).

There were three eruptions reported at the Minamidake crater during August, each of which were explosive. The explosions occurred on 9 August at 0345, on 13 August at 2205, and on 31 August at 0640, which generated ash plumes that rose 800-2,000 m above the crater and drifted W. There were two eruptions detected at Showa crater; on 4 August at 2150 ejecta traveled 800 m from the Showa crater and associated eruption plumes rose 2.3 km above the crater. The explosion at 2205 on 13 August generated an ash plume that rose 2 km above the crater and was accompanied by large blocks that were ejected 600 m from the Minamidake crater (figure 152). Nighttime crater incandescence was visible in a high-sensitivity surveillance camera at both craters. Seismicity consisted of 163 volcanic earthquakes, 84 of which were detected on the SW flank. According to the Kagoshima Regional Meteorological Observatory there was a total of 7 g/m² of ashfall over the course of 10 days during the month. According to a field survey, the daily amount of sulfur dioxide emitted was 1,800-3,300 t/d.

Figure 152. Webcam image showing an eruption plume rising 2 km above the Minamidake crater at Aira at 2209 on 13 August 2023. Courtesy of JMA monthly report (Sakurajima volcanic activity explanatory material, August 2023).

During September, four eruptions were reported, three of which were explosion events. These events occurred at 1512 on 9 September, at 0018 on 11 September, and at 2211 on 13 September. Resulting ash plumes generally rose 800-1,100 m above the crater. An explosion produced an ash plume at 2211 on 13 September that rose as high as 1.7 km above the crater. Large volcanic blocks were ejected 600 m from the Minamidake crater. Smaller eruptions were occasionally observed at the Showa crater. Nighttime crater incandescence was visible at the Minamidake crater. Seismicity was characterized by 68 volcanic earthquakes, 28 of which were detected beneath the SW flank. According to the Kagoshima Regional Meteorological Observatory there was a total of 3 g/m² of ashfall over the course of seven days during the month. A field survey reported that the daily amount of sulfur dioxide emitted was 1,600-2,300 t/d.

Eruptive activity during October consisted of 69 eruptions, 33 of which were described as explosive. These explosions occurred during 4 and 11-21 October and generated ash plumes that rose 500-3,600 m above the crater and drifted S, E, SE, and N. On 19 October at 1648 an explosion generated an ash plume that rose 3.6 km above the crater (figure 153). No eruptions were reported in the Showa crater; white gas-and-steam emissions rose 100 m above the crater from a vent on the N flank. Nighttime incandescence was observed at the Minamidake crater. On 24 October an eruption was reported from 0346 through 0430, which included an ash plume that rose 3.4 km above the crater. Ejected blocks traveled 1.2 km from the Minamidake crater. Following this eruption, small amounts of ashfall were observed from Arimura (4.5 km SE) and a varying amount in Kurokami (4 km E) (figure 154). The number of recorded volcanic earthquakes during the month was 190, of which 14 were located beneath the SW flank. Approximately 61 g/m² of ashfall was reported over eight days of the month. According to a field survey, the daily amount of sulfur dioxide emitted was 2,200-4,200 t/d.

Figure 153. Webcam image showing an ash plume rising 3.6 km above the Minamidake crater at Aira at 1648 on 19 October 2023. Photo has been color corrected. Courtesy of JMA monthly report (Sakurajima volcanic activity explanatory material, October 2023).

Figure 154. Photo showing ashfall (light gray) in Kurokami-cho, Sakurajima on 24 October 2023 taken at 1148 following an eruption at Aira earlier that day. Courtesy of JMA monthly report (Sakurajima volcanic activity explanatory material, October 2023).

Geologic Background. The Aira caldera in the northern half of Kagoshima Bay contains the post-caldera Sakurajima volcano, one of Japan's most active. Eruption of the voluminous Ito pyroclastic flow accompanied formation of the 17 x 23 km caldera about 22,000 years ago. The smaller Wakamiko caldera was formed during the early Holocene in the NE corner of the caldera, along with several post-caldera cones. The construction of Sakurajima began about 13,000 years ago on the southern rim and built an island that was joined to the Osumi Peninsula during the major explosive and effusive eruption of 1914. Activity at the Kitadake summit cone ended about 4,850 years ago, after which eruptions took place at Minamidake. Frequent eruptions since the 8th century have deposited ash on the city of Kagoshima, located across Kagoshima Bay only 8 km from the summit. The largest recorded eruption took place during 1471-76.

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/).

Nishinoshima is a small island in the Ogasawara Arc, about 1,000 km S of Tokyo, Japan. It contains prominent submarine peaks to the S, W, and NE. Recorded eruptions date back to 1973, with the current eruption period beginning in October 2022. Eruption plumes and fumarolic activity characterize recent activity (BGVN 48:10). This report covers the end of the eruption for September through October 2023, based on information from monthly reports of the Japan Meteorological Agency (JMA) monthly reports, and satellite data.

No eruptive activity was reported during September 2023, although JMA noted that the surface temperature was slightly elevated compared to the surrounding area since early March 2023. The Japan Coast Guard (JCG) conducted an overflight on 20 September and reported white gas-and-steam plumes rising 3 km above the central crater of the pyroclastic cone, as well as multiple white gas-and-steam emissions emanating from the N, E, and S flanks of the crater to the coastline. In addition, dark reddish brown-to-green discolored water was distributed around almost the entire circumference of the island.

Similar low-level activity was reported during October. Multiple white gas-and-steam emissions rose from the N, E, and S flanks of the central crater of the pyroclastic cone and along the coastline; these emissions were more intense compared to the previous overflight observations. Dark reddish brown-to-green discolored water remained visible around the circumference of the island. On 4 October aerial observations by JCG showed a small eruption consisting of continuous gas-and-steam emissions emanating from the central crater, with gray emissions rising to 1.5 km altitude (figure 129). According to observations from the marine weather observation vessel Keifu Maru on 26 October, white gas-and-steam emissions persisted from the center of the pyroclastic cone, as well as from the NW, SW, and SE coasts of the island for about five minutes. Slightly discolored water was visible up to about 1 km.

Figure 129. Aerial photos of gray emissions rising from the central crater of Nishinoshima’s pyroclastic cone to an altitude of 1.5 km on 4 October 2023 taken at 1434 (left) and 1436 (right). Several white gas-and-steam emissions also rose from the N, E, and S flanks of the central crater. Both photos have been color corrected. Courtesy of JCG via JMA (monthly reports of activity at Nishinoshima, October, 2023).

Frequent low-to-moderate power thermal anomalies were recorded in the MIROVA graph (Middle InfraRed Observation of Volcanic Activity) during September (figure 130). Occasional anomalies were detected during October, and fewer during November through December. A thermal anomaly was visible in the crater using infrared satellite imagery on 6, 8, 11, 16, 18, 21, and 23 September and 8, 13, 21, 26, and 28 October (figure 131).

Figure 130. Low-to-moderate power thermal anomalies were detected at Nishinoshima during September through December 2023, showing a decrease in the frequency of anomalies after September, according to this MIROVA graph (Log Radiative Power). Courtesy of MIROVA.

Figure 131. Infrared (bands B12, B11, B4) satellite images showing a strong thermal anomaly at the crater of Nishinoshima on 21 September 2023 (left) and 13 October 2023 (right). A strong gas-and-steam plume accompanied the thermal activity, extending NW. Courtesy of Copernicus Browser.

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

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

Kīlauea is on the island of Hawai’i and overlaps the E flank of the Mauna Loa volcano. Its East Rift Zone (ERZ) has been intermittently active for at least 2,000 years. An extended eruption period began in January 1983 and was characterized by open lava lakes and lava flows from the summit caldera and the East Rift Zone. During May 2018 magma migrated into the Lower East Rift Zone (LERZ) and opened 24 fissures along a 6-km-long NE-trending fracture zone that produced lava flows traveling in multiple directions. As lava emerged from the fissures, the lava lake at Halema'uma'u drained and explosions sent ash plumes to several kilometers altitude (BGVN 43:10).

The current eruption period started during September 2021 and has been characterized by low-level lava effusions in the active Halema’uma’u lava lake (BGVN 48:01). This report covers three notable eruption periods during February, June, and September 2023 consisting of lava fountaining, lava flows, and spatter during January through September 2023 using information from daily reports, volcanic activity notices, and abundant photo, map, and video data from the US Geological Survey's (USGS) Hawaiian Volcano Observatory (HVO).

Activity during January 2023. Small earthquake swarms were recorded on 2 January 2023; increased seismicity and changes in the pattern of deformation were noted on the morning of 5 January. At around 1500 both the rate of deformation and seismicity drastically increased, which suggested magma movement toward the surface. HVO raised the Volcano Alert Level (VAL) to Watch (the second highest level on a four-level scale) and the Aviation Color Code (ACC) to Orange (the second highest color on a four-color scale) at 1520.

Multiple lava fountains and lava effusions from vents in the central eastern portion of the Halema’uma’u crater began on 5 January around 0434; activity was confined to the eastern half of the crater and within the basin of the western half of the crater, which was the focus of the eruption in 2021-2022 (figure 525). Incandescence was visible in webcam images at 1634 on 5 January, prompting HVO to raise the VAL to Warning (the highest level on a four-level scale) and the ACC to Red (the highest color on a four-color scale). Lava fountains initially rose as high as 50 m above the vent at the onset of the eruption (figure 526) but then declined to a more consistent 5-6 m height in the proceeding days. By 1930 that same day, lava had covered most of the crater floor (an area of about 1,200,000 m²) and the lava lake had a depth of 10 m. A higher-elevation island that formed during the initial phase of the December 2020 eruption remained exposed, appearing darker in images, along with a ring of older lava around the lava lake that was active prior to December 2022. Overnight during 5-6 January the lava fountains continued to rise 5 m high, and the lava effusion rate had slowed.

Figure 525. A reference map of Kīlauea showing activity on 6 January 2023, based on measurements taken from the crater rim at approximately 0900. Multiple eruptive vents (orange color) are on the E floor of Halema’uma’u crater effusing into a lava lake (red color). Lava from these vents flowed laterally across the crater floorcovering an area of 880,000 m2. The full extent of new lava from this eruption (red and pink colors) is approximately 1,120,000 m2. An elevated part of the lake (yellow color) that is higher in elevation compared to the rest of the crater floor was not covered in lava flows. Courtesy of USGS, HVO.

Figure 526. Image of the initial lava fountain at the onset of Kīlauea’s eruption on 5 January 2023 from a newly opened vent in the Halema’uma’u crater at 0449. This lava fountain rose as high as 50 m and ejected lava across the crater floor. Courtesy of USGS, HVO.

On 6 January at 0815 HVO lowered the VAL to Watch and the ACC to Orange due to the declining effusion rates. Sulfur dioxide emission rates ranged from 3,000-12,500 tonnes per day (t/d), the highest value of which was recorded on 6 January. Lava continued to erupt from the vents during 6-8 January, although the footprint of the active area had shrunk; a similar progression has been commonly observed during the early stages of recent eruptions at Halema’uma’u. On 9 January HVO reported one dominant lava fountain rising 6-7 m high in the E half of the crater. Lava flows built up the margins of the lake, causing the lake to be perched. On 10 January the eastern lava lake had an area of approximately 120,000 m² that increased to 250,000 m² by 17 January. During 13-31 January several small overflows occurred along the margins of the E lake. A smaller area of lava was active within the basin in the W half of the crater that had been the focus of activity during 2021-2022. On 19 January just after 0200 a small ooze-out was observed on the crater’s W edge.

Activity during February 2023. Activity continued in the E part of Halema’uma’u crater, as well as in a smaller basin in the W part of the 2021-2022 lava lake (figure 527). The E lava lake contained a single lava fountain and frequent overflows. HVO reported that during the morning of 1 February the large E lava lake began to cool and crust over in the center of the lake; two smaller areas of lava were observed on the N and S sides by the afternoon. The dominant lava fountain located in the S part of the lava lake paused for roughly 45 minutes at 2315 and resumed by midnight, rising 1-2 m. At 0100 on 2 February lava from the S part was effusing across the entire E lava lake area, covering the crusted over portion in the center of the lake and continuing across the majority of the previously measured 250,000 m² by 0400. A small lava pond near the E lake produced an overflow around 0716 on 2 February. On 3 February some lava crust began to form against the N and E levees, which defined the 250,000 m² eastern lava lake. The small S lava fountain remained active, rising 1-6 m high during 3-9 February; around 0400 on 5 February occasional bursts doubled the height of the lava fountain.

Figure 527. An aerial visual and thermal image taken of Kīlauea’s Halema’uma’u crater on 2 February 2023. The largest lava lake is in the E part of the crater, although lava has also filled areas that were previously active in the W part of the crater. The colors of the map indicate temperature, with blues indicative of cooler temperatures and reds indicative of warmer temperatures. Courtesy of USGS, HVO.

A large breakout occurred overnight during 2100 on 4 February to 0900 on 5 February on the N part of the crater floor, equal to or slightly larger in size than the E lava lake. A second, smaller lava fountain appeared in the same area of the E lava lake between 0300 and 0700 on 5 February and was temporarily active. This large breakout continued until 7 February. A small, brief breakout was reported in the S of the E lava lake around midnight on 7 February. In the W lake, as well as the smaller lava pond in the central portion of the crater floor, contained several overflows during 7-10 February and intermittent fountaining. Activity at the S small lava pond and the small S lava fountain within the E lake declined during 9-10 February. The lava pond in the central portion of the crater floor had nearly continuous, expansive flows during 10-13 February; channels from the small central lava pond seemed to flow into the larger E lake. During 13-18 February a small lava fountain was observed in the small lava pond in the central portion of the crater floor. Continuous overflows persisted during this time.

Activity in the eastern and central lakes began to decline in the late afternoon of 17 February. By 18 February HVO reported that the lava effusions had significantly declined, and that the eastern and central lakes were no longer erupting. The W lake in the basin remained active but at a greatly reduced level that continued to decline. HVO reported that this decrease in activity is attributed to notable deflationary tilt that began early on the morning of 17 February and lasted until early 19 February. By 19 February the W lake was mostly crusted over although some weak lava flows remained, which continued through 28 February. The sulfur dioxide emission rates ranged 250-2,800 t/d, the highest value of which was recorded on 6 February.

Activity during March 2023. The summit eruption at Halema’uma’u crater continued at greatly reduced levels compared to the previous two months. The E and central vents stopped effusing lava, and the W lava lake remained active with weak lava flows; the lake was mostly crusted over, although slowly circulating lava intermittently overturned the crust. By 6 March the lava lake in the W basin had stopped because the entire surface was crusted over. The only apparent surface eruptive activity during 5-6 March was minor ooze-outs of lava onto the crater floor, which had stopped by 7 March. Several hornitos on the crater floor still glowed through 12 March according to overnight webcam images, but they did not erupt any lava. A small ooze-out of lava was observed just after 1830 in the W lava lake on 8 March, which diminished overnight. The sulfur dioxide emission rate ranged from 155-321 t/d on 21 March. The VAL was lowered to Advisory, and the ACC was lowered to Yellow (the second lowest on a four-color scale) on 23 March due to a pause in the eruption since 7 March.

Activity during April-May 2023. The eruption at Halema’uma’u crater was paused; no lava effusions were visible on the crater floor. Sulfur dioxide emission rates ranged from 75-185 t/d, the highest of which was measured on 22 April. During May and June summit seismicity was elevated compared to seismicity that preceded the activity during January.

Activity during June 2023. Earthquake activity and changes in the patterns of ground deformation beneath the summit began during the evening of 6 June. The data indicated magma movement toward the surface, prompting HVO to raise the VAL to Watch and the ACC to Orange. At about 0444 on 7 June incandescence in Halema’uma’u crater was visible in webcam images, indicating that a new eruption had begun. HVO raised the VAL to Warning and the ACC to Red (the highest color on a four-color scale). Lava flowed from fissures that had opened on the crater floor. Multiple minor lava fountains were active in the central E portion of the Halema’uma’u crater, and one vent opened on the W wall of the caldera (figure 528). The eruptive vent on the SW wall of the crater continued to effuse into the lava lake in the far SW part of the crater (figure 529). The largest lava fountain consistently rose 15 m high; during the early phase of the eruption, fountain bursts rose as high as 60 m. Lava flows inundated much of the crater floor and added about 6 m depth of new lava within a few hours, covering approximately 10,000 m². By 0800 on 7 June lava filled the crater floor to a depth of about 10 m. During 0800-0900 the sulfur dioxide emission rate was about 65,000 t/d. Residents of Pahala (30 km downwind of the summit) reported minor deposits of fine, gritty ash and Pele’s hair. A small spatter cone had formed at the vent on the SW wall by midday, and lava from the cone was flowing into the active lava lake. Fountain heights had decreased from the onset of the eruption and were 4-9 m high by 1600, with occasional higher bursts. Inflation switched to deflation and summit earthquake activity greatly diminished shortly after the eruption onset.

Figure 528. Photo of renewed activity at Kīlauea’s Halema’uma’u crater that began at 0444 on 7 June 2023. Lava flows cover the crater floor and there are several active source vents exhibiting lava fountaining. Courtesy of USGS, HVO.

Figure 529. Photo of a lava fountain on the SW wall of Kīlauea’s Halema’uma’u crater on 7 June 2023. By midday a small cone structure had been built up. The fissure was intermittently obscured by gas-and-steam plumes. Courtesy of USGS, HVO.

At 0837 on 8 June HVO lowered the VAL to Watch and the ACC to Orange because the initial high effusion rates had declined, and no infrastructure was threatened. The surface of the lava lake had dropped by about 2 m, likely due to gas loss by the morning of 8 June. The drop left a wall of cooled lava around the margins of the crater floor. Lava fountain heights decreased during 8-9 June but continued to rise to 10 m high. Active lava and vents covered much of the W half of Halema’uma’u crater in a broad, horseshoe-shape around a central, uplifted area (figure 530). The preliminary average effusion rate for the first 24 hours of the eruption was about 150 cubic meters per second, though the estimate did not account for vesiculated lava and variations in crater floor topography. The effusion rate during the very earliest phases of the eruption appeared significantly higher than the previous three summit eruptions based on the rapid coverage of the entire crater floor. An active lava lake, also referred to as the “western lava lake” was centered within the uplifted area and was fed by a vent in the NE corner. Two small active lava lakes were located just SE from the W lava lake and in the E portion of the crater floor.

Figure 530. A compilation of thermal images taken of Kīlauea’s Halema’uma’u crater on 7 June 2023 (top left), 8 June 2023 (top right), 12 June 2023 (bottom left), and 16 June 2023 (bottom right). The initial high effusion rates that consisted of numerous lava fountains and lava flows that covered the entire crater floor began to decline and stabilize. A smaller area of active lava was detected in the SW part of the crater by 12 June. The colors of the thermal map represent temperature, with blue colors indicative of cooler temperatures and red colors indicative of warmer temperatures. Courtesy of USGS, HVO.

During 8-9 June the lava in the central lava lake had a thickness of approximately 1.5 m, based on measurements from a laser rangefinder. During 9-12 June the height of the lava fountains decreased to 9 m high. HVO reported that the previously active lava lake in the E part of the crater appeared stagnant during 10-11 June. The surface of the W lake rose approximately 1 m overnight during 11-12 June, likely due to the construction of a levee around it. Only a few small fountains were active during 12-13 June; the extent of the active lava had retreated so that all activity was concentrated in the SW and central parts of Halema’uma’u crater. Intermittent spattering from the vent on the SW wall was visible in overnight webcam images during 13-18 June. On the morning of 14 June a weak lava effusion originated from near the western eruptive vent, but by 15 June there were no signs of continued activity. HVO reported that other eruptive vents in the SW lava lake had stopped during this time, following several days of waning activity; lava filled the lake by about 0.5 m. Lava circulation continued in the central lake and no active lava was reported in the northern or eastern parts of the crater. Around 0800 on 15 June the top of the SW wall spatter cone collapsed, which was followed by renewed and constant spattering from the top vent and a change in activity from the base vent; several new lava flows effused from the top of the cone, as well as from the pre-existing tube-fed flow from its base. Accumulation of lava on the floor resulted in a drop of the central basin relative to the crater floor, allowing several overflows from the SW lava lake to cascade into the basin during the night of 15 June into the morning of 16 June.

Renewed lava fountaining was reported at the eruptive vent on the SW side of the crater during 16-19 June, which effused lava into the far SW part of the crater. This activity was described as vigorous during midday on 16 June; a group of observatory geologists estimated that the lava was consistently ejected at least 10 m high, with some spatter ejected even higher and farther. Deposits from the fountain further heightened and widened the spatter cone built around the original eruptive vent in the lower section of the crater wall. Multiple lava flows from the base of the cone were fed into the SW lava lake and onto the southwestern-most block from the 2018 collapse within Halema’uma’u on 17 June (figure 531); by 18 June they focused into a single flow feeding into the SW lava lake. On the morning of 19 June a second lava flow from the base of the eruptive cone advanced into the SW lava lake.

Figure 531. Nighttime photo of the upwelling area at the base of the spatter cone at Kīlauea’s Halema’uma’u crater on 17 June 2023. This upwelling feeds a lava flow that spreads out to the E of the spatter cone. Courtesy of M. Cappos, USGS.

Around 1600 on 19 June there was a rapid decline in lava fountaining and effusion at the eruptive vent on the SW side of the crater; vent activity had been vigorous up to that point (figure 532). Circulation in the lava lake also slowed, and the lava lake surface dropped by several meters. Overnight webcam images showed some previously eruptive lava still flowing onto the crater floor, which continued until those flows began to cool. By 21 June no lava was erupting in Halema’uma’u crater. Overnight webcam images during 29-30 June showed some incandescence from previously erupted lava flows as they continued to cool. Seismicity in the crater declined to low levels. Sulfur dioxide emission rates ranged 160-21,000 t/d throughout the month, the highest measurement of which was recorded on 8 June. On 30 June the VAL was lowered to Advisory (the second level on a four-level scale) and the ACC was lowered to Yellow. Gradual inflation was detected at summit tiltmeters during 19-30 June.

Figure 532. Photos showing vigorous lava fountaining and lava flows at Kīlauea’s Halema’uma’u crater at the SW wall eruptive vent on 18 June 2023 at 1330 (left). The eruption stopped abruptly around 1600 on 19 June 2023 and no more lava effusions were visible, as seen from the SW wall eruptive vent at 1830 on 19 June 2023 (right). Courtesy of M. Patrick, USGS.

Activity during July-August 2023. During July, the eruption paused; no lava was erupting in Halema’uma’u crater. Nighttime webcam images showed some incandescence from previously erupted lava as it continued to cool on the crater floor. During the week of 14 August HVO reported that the rate in seismicity increased, with 467 earthquakes of Mw 3.2 and smaller occurring. Sulfur dioxide emission rates remained low, ranging from 75-86 t/d, the highest of which was recorded on 10 and 15 August. On 15 August beginning at 0730 and lasting for several hours, a swarm of approximately 50 earthquakes were detected at a depth of 2-3 km below the surface and about 2 km long directly S of Halema’uma’u crater. HVO reported that this was likely due to magma movement in the S caldera region. During 0130-0500 and 1700-2100 on 21 August two small earthquake swarms of approximately 20 and 25 earthquakes, respectively, occurred at the same location and at similar depths. Another swarm of 50 earthquakes were recorded during 0430-0830 on 23 August. Elevated seismicity continued in the S area through the end of the month.

Activity during September 2023. Elevated seismicity persisted in the S summit with occasional small, brief seismic swarms. Sulfur dioxide measurements were relatively low and were 70 t/d on 8 September. About 150 earthquakes occurred during 9-10 September, and tiltmeter and Global Positioning System (GPS) data showed inflation in the S portion of the crater.

At 0252 on 10 September HVO raised the VAL to Watch and the ACC to Orange due to increased earthquake activity and changes in ground deformation that indicated magma moving toward the surface. At 1515 the summit eruption resumed in the E part of the caldera based on field reports and webcam images. Fissures opened on the crater floor and produced multiple minor lava fountains and flows (figure 533). The VAL and ACC were raised to Warning and Red, respectively. Gas-and-steam plumes rose from the fissures and drifted downwind. A line of eruptive vents stretched approximately 1.4 km from the E part of the crater into the E wall of the down dropped block by 1900. The lava fountains at the onset of the eruption had an estimated 50 m height, which later rose 20-25 m high. Lava erupted from fissures on the down dropped block and expanded W toward Halema’uma’u crater. Data from a laser rangefinder recorded about 2.5 m thick of new lava added to the W part of the crater. Sulfur dioxide emissions were elevated in the eruptive area during 1600-1500 on 10 September, measuring at least 100,000 t/d.

Figure 533. Photo of resumed lava fountain activity at Kīlauea’s Halema’uma’u crater on 10 September 2023. The main lava fountain rises approximately 50 m high and is on the E crater margin. Courtesy of USGS, HVO.

At 0810 on 11 September HVO lowered the VAL and ACC back to Watch and Orange due to the style of eruption and the fissure location had stabilized. The initial extremely high effusion rates had declined (but remained at high levels) and no infrastructure was threatened. An eruption plume, mainly comprised of sulfur dioxide and particulates, rose as high as 3 km altitude. Several lava fountains were active on the W side of the down dropped block during 11-15 September, while the easternmost vents on the down dropped block and the westernmost vents in the crater became inactive on 11 September (figure 534). The remaining vents spanned approximately 750 m and trended roughly E-W. The fed channelized lava effusions flowed N and W into Halema’uma’u. The E rim of the crater was buried by new lava flows; pahoehoe lava flows covered most of the crater floor except areas of higher elevation in the SW part of the crater. The W part of the crater filled about 5 m since the start of the eruption, according to data from a laser rangefinder during 11-12 September. Lava fountaining continued, rising as high as 15 m by the morning of 12 September. During the morning of 13 September active lava flows were moving on the N and E parts of the crater. The area N of the eruptive vents that had active lava on its surface became perched and was about 3 m higher than the surrounding ground surface. By the morning of 14 September active lava was flowing on the W part of the down dropped block and the NE parts of the crater. The distances of the active flows progressively decreased. Spatter had accumulated on the S (downwind) side of the vents, forming ramparts about 20 m high.

Figure 534. Photo of a strong lava fountain in the E part of Kīlauea’s Halema’uma’u crater taken on the morning of 11 September 2023. The lava fountains rise as high as 10-15 m. Courtesy of J. Schmith, USGS.

Vigorous spattering was restricted to the westernmost large spatter cone with fountains rising 10-15 m high. Minor spattering occurred within the cone to the E of the main cone, but HVO noted that the fountains remained mostly below the rim of the cone. Lava continued to effuse from these cones and likely from several others as well, traveled N and W, confined to the W part of the down-dropped block and the NE parts of Halema’uma’u. Numerous ooze-outs of lava were visible over other parts of the crater floor at night. Laser range-finder measurements taken of the W part of the crater during 14-15 September showed that lava filled the crater by 10 m since the start of the eruption. Sulfur dioxide emissions remained elevated after the onset of the eruption, ranging 20,000-190,000 t/d during the eruption activity, the highest of which occurred on 10 September.

Field crews observed the eruptive activity on 15 September; they reported a notable decrease or stop in activity at several vents. Webcam images showed little to no fountaining since 0700 on 16 September, though intermittent spattering continued from the westernmost large cone throughout the night of 15-16 September. Thermal images showed that lava continued to flow onto the crater floor. On 16 September HVO reported that the eruption stopped around 1200 and that there was no observable activity anywhere overnight or on the morning of 17 September. HVO field crews reported that active lava was no longer flowing onto Halema’uma’u crater floor and was restricted to a ponded area N of the vents on the down dropped block. They reported that spattering stopped around 1115 on 16 September. Nighttime webcam images showed some incandescence on the crater floor as lava continued to cool. Field observations supported by geophysical data showed that eruptive tremor in the summit region decreased over 15-16 September and returned to pre-eruption levels by 1700 on 16 September. Sulfur dioxide emissions were measured at a rate of 800 t/d on 16 September while the eruption was waning, and 200 t/d on 17 September, which were markedly lower compared to measurements taken the previous week of 20,000-190,000 t/d.

Geologic Background. Kilauea overlaps the E flank of the massive Mauna Loa shield volcano in the island of Hawaii. Eruptions are prominent in Polynesian legends; written documentation since 1820 records frequent summit and flank lava flow eruptions interspersed with periods of long-term lava lake activity at Halemaumau crater in the summit caldera until 1924. The 3 x 5 km caldera was formed in several stages about 1,500 years ago and during the 18th century; eruptions have also originated from the lengthy East and Southwest rift zones, which extend to the ocean in both directions. About 90% of the surface of the basaltic shield volcano is formed of lava flows less than about 1,100 years old; 70% of the surface is younger than 600 years. The long-term eruption from the East rift zone between 1983 and 2018 produced lava flows covering more than 100 km2, destroyed hundreds of houses, and added new coastline.

Information Contacts: Hawaiian Volcano Observatory (HVO), U.S. Geological Survey, PO Box 51, Hawai'i National Park, HI 96718, USA (URL: http://hvo.wr.usgs.gov/).

Tinakula is a remote 3.5 km-wide island in the Solomon Islands, located 640 km ESE of the capital, Honiara. The current eruption period began in December 2018 and has more recently been characterized by intermittent lava flows and thermal activity (BGVN 48:06). This report covers similar activity during June through November 2023 using satellite data.

During clear weather days (20 July, 23 September, 23 October, and 12 November), infrared satellite imagery showed lava flows that mainly affected the W side of the island and were sometimes accompanied by gas-and-steam emissions (figure 54). The flow appeared more intense during July and September compared to October and November. According to the MODVOLC thermal alerts, there were a total of eight anomalies detected on 19 and 21 July, 28 and 30 October, and 16 November. Infrared MODIS satellite data processed by MIROVA (Middle InfraRed Observation of Volcanic Activity) detected a small cluster of thermal activity occurring during late July, followed by two anomalies during August, two during September, five during October, and five during November (figure 55).

Figure 54. Infrared (bands B12, B11, B4) satellite images showed lava flows mainly affecting the W flank of Tinakula on 20 July 2023 (top left), 23 September 2023 (top right), 23 October 2023 (bottom left), and 12 November 2023 (bottom right). Some gas-and-steam emissions accompanied this activity. Courtesy of Copernicus Browser.

Figure 55. Low-power thermal anomalies were sometimes detected at Tinakula during July through November 2023, as shown on this MIROVA plot (Log Radiative Power). A small cluster of thermal anomalies were detected during late July. Then, only two anomalies were detected during August, two during September, five during October, and five during November. Courtesy of MIROVA.

Geologic Background. The small 3.5-km-wide island of Tinakula is the exposed summit of a massive stratovolcano at the NW end of the Santa Cruz islands. It has a breached summit crater that extends from the summit to below sea level. Landslides enlarged this scarp in 1965, creating an embayment on the NW coast. The Mendana cone is located on the SE side. The dominantly andesitic volcano has frequently been observed in eruption since the era of Spanish exploration began in 1595. In about 1840, an explosive eruption apparently produced pyroclastic flows that swept all sides of the island, killing its inhabitants. Recorded eruptions have frequently originated from a cone constructed within the large breached crater. These have left the upper flanks and the steep apron of lava flows and volcaniclastic debris within the breach unvegetated.

Information Contacts: 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/).

Ahyi seamount is located ~20 km SE of Farallon de Pajaros and was discussed in the Bulletin associated with volcanic unrest in 1979 (SEAN 04:01) and in 2001 (BGVN 26:05). The evidence for a 2014 eruption at Ahyi seamount includes seismicity, noises heard by divers and felt aboard a vessel in the area, and a follow-up research cruise to Ahyi that measured a hydrothermal plume and significant bathymetric changes since the last survey in 2003. This report is revised from an earlier version.

The U.S. Geological Survey (USGS) reported that, beginning about 0635 local time on 24 April 2014 (2035 on 23 April 2014, UTC), seismometers in various locations in the Mariana Islands began recording T-phase signals interpreted as stemming from an undersea eruption in an area to the N of Pagan island near the island of Uracas (also known as Farallon de Pajaros). Note that throughout this report, at the suggestion of William Chadwick of NOAA, 'T-phase signals' have been used in lieu of 'earthquakes' since all the eruption-related signals were hydroacoustic (from underwater explosions) rather than seismic body-waves. See the final section of this report for a brief definition of T-phase waves. The eruption was ultimately tracked to Ahyi seamount (figures 2 and 3).

Figure 2. Map of the western Pacific margin showing the Northern Mariana Islands with the location of Ahyi volcano added. Original map from Magellan Graphix (1957).

Figure 3. (left) A bathymetric map showing the islands and seamounts making up the Mariana island arc. The rectangular box on that map delineates the N part of the arc that is shown on the map at right. (right) A larger scale bathymetric map that highlights features in the vicinity of Ahyi seamount; within the yellow-lined box is the islands unit of the Mariana Trench Marine National Monument. Maps courtesy of Susan Merle, Oregon State University and NOAA-PMEL.

Seismometers that recorded the 2014 T-phase signals included those on Saipan, Pagan, Sarigan, and Anatahan islands (figure 2). The USGS reported recording T-phases during 24 April through 8 May 2014. During this same period, hydroacoustic sensors on Wake Island (~2,300 km ENE from Ahyi) also received signals. The recorded events all indicated that the source of the hydroacoustic signals was at or near Ahyi seamount, but the accuracy of the initially determined locations remained uncertain because there are other active volcanic seamounts in the area.

On 25 April 2014 the Aviation Color Code was raised by the USGS from Unassigned (Volcanic Alert Level: Unassigned) to Yellow (Volcanic Alert Level: Advisory). As of 29 May, USGS had received no reports of an eruption plume or any evidence that eruptive products had reached the surface. Satellite images showed nothing indicative of a volcanic eruption. On 29 May the Aviation Color Code was lowered by the USGS to Unassigned (Volcanic Alert Level: Unassigned).

At the time of the T-phase signals in April 2014, submarine explosions were heard and felt by scuba divers conducting coral reef research in the area. Chip Young, leader of the Hi'ialakai expedition working in the area as part of a coral reef survey by the NOAA Pacific Islands Fisheries Science Center (PIFSC), provided the following information on 28-29 April 2014. At this stage, the source of the signals was still a mystery.

"While we were diving [on 26 April at Farallon de Pajaros (FDP)] we could hear eruptions underwater. It wasn't casual, in fact, it sounded like bombs exploding with the concussion felt through your body. I don't know how close we were to the event, none of the…divers saw volcanic activity, but at least one explosion was so powerful, that it reverberated through the hull of the ship and the crew onboard thought that something had happened to the ship (at the time they didn't realized we too were hearing these explosions under water)."

"The first divers' comments about hearing something underwater started at Asuncion (4/24-4/25). We were at FDP on [26 April] and to my best guess, the massive explosion that I previously wrote about occurred 0100-0230 26 APR 14 UTC on the SE side of FDP. There were plenty of other explosions throughout the day, but that was the largest one I experienced. There were conglomerates/mats of orange+yellow bubbles on the surface of the water on the SE coastline of FDP as well. We had a very calm day at FDP, so the mats/sludge stretched on for 20-30 ft [~7-9 m] or more. These could have been from Ahyi, but visual disturbances near Ahyi weren't specifically made because we passed there in the early [morning] on the way to FDP and then in the evening on the way to Maug. We did hear explosions underwater at Maug too. I heard distant explosions, which I assumed were from FDP, but there were closer ones too. Not as violent as the sounds we heard at FDP, but 'cracks' for sure."

During the height of the T-phase swarm, explosive signals from the underwater eruption source in the vicinity of Ahyi were occurring at a rate of ~20 per hour. On 16 May 2014, the USGS reported that over the preceding week, T-phase signals had greatly diminished.

Verification of 2014 Ahyi eruption. A subsequent expedition took place during 12-18 May, after the eruption T-phases had stopped. This expedition, led by Chip Young and Dave Butterfield aboard the R/V Hi'ialakai, was working at Maug island (~50 km SSE of Ahyi) and conducted several water-column CTD (conductivity-temperature-depth) casts in the area. They found a hydrothermal plume coming from Ahyi. In addition, they collected new bathymetric data over the summit of Ahyi, which showed the depth changes that confirmed that Ahyi was indeed the source of the 2014 eruption.

According to William Chadwick, NOAA surveyed Ahyi in 2003, measuring a summit depth of 60 m. After the T-phase signals declined in mid-May 2014, the NOAA ship Hi'ialakai went over the summit and the new minimum depth was found to be 75 m. In addition, a new summit crater is evident in the 2014 bathymetry that is ~95 m deep. Bloomer and others (1989) noted a value of 137 m as Ahyi's summit depth, based on U.S. Navy Sonar Array Sounding System (SASS), an early form of multibeam sonar. This pre-2003 summit depth value is probably less accurate and therefore does not necessarily represent a true depth change between the SASS survey and 2003.

Figure 4B shows the results of multibeam sonar bathymetry over Ahyi's summit collected by the Hi'ialakai in 2014. This map was compared to their previous survey in 2003 (figure 4A) and used to compose a third map (figure 4C) showing depth differences between the two surveys. In essence, the summit elevation dropped by 25 m; a crater had developed with a floor at a depth of 195 m; and a conspicuous landslide chute descended to at least 2,300 m depth along the SE slope. Up to 125 m of material was removed from the head of the landslide chute, and constructional deposits downslope were up to 40 m thick. The map analysts noted that even though the 2014 re-survey was limited and produced an incomplete look at the entire Ahyi edifice, the changes were very clear and indicated recent eruptive activity at Ahyi.

Figure 4. Three maps (frames A, B, C) showing multibeam bathymetry and analyses of bathymetric changes between surveys of 2003 and May 2014 of Ahyi volcano (white areas signify lack of data). (A) Bathymetry of Ahyi volcano conducted 2003 showing a cone with summit at a depth of 65 m (Merle and others, 2003). (B) Ahyi map from survey conducted May 2014. The cone was gone and was replaced by a new crater with a rim at 90 m depth and a floor at 195 m depth. The current minimum summit depth for the volcano at 75 m resides near the location on figure 4B labeled "crater rim ~90 m." Extending SSE from the new crater, the research disclosed a new landslide chute descending to at least 2,300 m depth. (C) Depth changes comparing 2003 and 2014 maps. As defined on key at lower left, the cool colors signify material removed; green, no change; and warm colors, material added. Labels indicate elevation changes disclosed in the comparison (e.g. -20 m means this area is 20 m lower on the 2014 map than on the 2003 map). Map courtesy of Susan Merle, Oregon State University and NOAA/PMEL.

T-phase waves: According to Okal (2011) "T phases are defined as seismic recordings of signals having traveled an extended path as acoustic waves in the water body of the oceans. This is made possible by the 'Sound Fixing and Ranging' (SOFAR) channel, a layer of minimum sound velocity acting as a wave guide at average depths of 1,000 m. It allows the efficient propagation of extremely small signals over extremely long distances, in practice limited only by the finite size of the ocean basins."

The use of T-waves has led to much improved diagnosis of submarine vent locations. For example, Fox and Dziak (1998) described the detection of intense seismicity the NE Pacific Ocean using the T-phase Monitoring System developed by NOAA/PMEL to access the U.S. Navy's SOund SUrveillance System (SOSUS) in the North Pacific. Dziak and Fox (2002) discussed monitoring of hydroacoustic signals from the Volcano Islands arc, S of Japan (just N of the N Mariana Islands shown in figure 2), a region with frequent submarine eruptions. The signals are characterized by a narrowband, long-duration, high-amplitude fundamental centered at 10 Hz with three harmonics at 20, 30, and 40 Hz. The hydroacoustic (T-wave) signals are consistent with harmonic tremor signals observed using traditional seismic methods at active subaerial volcanoes throughout the world.

References. Bloomer, S.H., Stern, R.J., and Smoot, N.C., 1989, Physical volcanology of the submarine Mariana and Volcano Arcs, Bulletin of Volcanology, v. 51, pp. 210-224.

Bloomer, S.H., Stern, R.J., Fisk, E., and Geschwind, C.H., 1989, Shoshonitic Volcanism in the Northern Mariana Arc 1. Mineralogic and Major and Trace Element Characteristics, Journal of Geophysical Research, v. 94, no. B4, pp. 4469-4496.

Dziak, R.P., and Fox, C.G., 2002, Evidence of harmonic tremor from a submarine volcano detected across the Pacific Ocean basin, Journal of Geophysical Research, v. 107, no. B5, p. 2085.

Fox, C.G., and Dziak, R.P., 1998 (December), Hydroacoustic detection of volcanic activity on the Gorda Ridge, February-March 1996, Deep Sea Research Part II: Topical Studies in Oceanography, v. 45, no. 12, pp. 2513-2530 (DOI: 10.1016/S0967-0645(98)00081-2).

Magellan Graphix, 1997, Map: Northern Mariana Islands (territory of US) (URL: http://www.infoplease.com/atlas/state/northernmarianaislands.html).

Merle, S., Embley, R., Baker, E., and Chadwick, B., 2003, Submarine Ring of Fire 2003 - Mariana Arc R/V T.G. Thompson Cruise TN-153, February 9-March 5, 2003, Guam to Guam, Cruise Report, NOAA-PMEL (URL: http://www.pmel.noaa.gov/eoi/marianas/marianas-crrpt-03.pdf).

Okal, E.A., 2011, T Waves, in Gupta, H.K. (ed), Encyclopedia of Solid Earth Geophysics, pp. 1421-1423, Springer Netherlands (DOI: 10.1007/978-90-481-8702-7_165).

USGS, 2014 (30 April), Northern Mariana Islands Information Statement, Wednesday, April 30, 2014 5:36 AM ChST (Tuesday, April 29, 2014 19:36 UTC) (URL: http://volcanoes.usgs.gov/activity/archiveupdate.php?noticeid=10031).

USGS, 2014 (1 May), A new submarine eruption in the Northern Mariana Islands: could it happen here?, Hawaii Volcano Observatory (URL: http://hvo.wr.usgs.gov/volcanowatch/view.php?id=226).

USGS, 2014 (16 May), Current Alerts for U.S. Volcanoes, Northern Mariana Islands Weekly Update, 16 May (URL: http://volcanoes.usgs.gov/nmi/activity//status.php).

USGS, 2014 (23 May), Northern Mariana islands Weekly Update, 23 May 2014 (URL: http://volcanoes.usgs.gov/nmi/activity/index.php).

Geologic Background. Ahyi seamount is a large conical submarine volcano ~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: NOAA Pacific Marine Environmental Laboratory (NOAA-PMEL), 7600 Sand Point Way NE, Bldg #3, Seattle, WA 98115 (URL: http://www.pmel.noaa.gov/); William W. Chadwick and Susan Merle, NOAA-PMEL Earth-Ocean Interactions Program and Oregon State University; David A. Butterfield, University of Washington and NOAA-PMEL; Charles (Chip) Young, NOAA Fisheries, Pacific Islands Fisheries Science Center (PIFSC); Matt Haney, U.S. Geological Survey (USGS), Alaska Volcano Observatory (AVO), Anchorage, AK 99508; USGS Volcano Hazards Program (URL: http://volcanoes.usgs.gov/nmi/activity/); and CNMI Emergency Management Office (URL: http://www.cnmihomelandsecurity.gov.mp/).

On 13 February 2014, the Indonesian National Board for Disaster Management (Badan Nasional Penanggulangan Bencana-BNPB) reported that a major eruption occurred at Kelut (also known as Kelud) volcano in East Java, Indonesia. Ground-based observers had little insight about the ash plume height, but a number of satellite observations helped to constrain the height and other eruption parameters such the direction of plume movement. CALIPSO satellite data revealed that a rapidly rising portion of the plume ejected material up to an altitude exceeding ~26 km, well into the tropical stratosphere. Most of the less rapidly rising portions of the plume remained lower, at 19-20 km altitude. The 2014 eruption destroyed a dome emplaced in the volcano's caldera during the previous eruption in 2007 (BGVN 33:03 and 33:07). According to BNPB in a report issued on 18 February 2014, ~7 people were killed and ~100,000 evacuated. At least one commercial aircraft flew into the plume, later landing successfully but incurring costly engine damage.

This report discusses the pre- and syn-eruption observations from the early January through 25 February 2014. Much of the detailed reporting used here came from the Indonesian Centre for Volcanology and Geological Hazard Mitigation (CVGHM; also known as Pusat Vulkanologi dan Mitigasi Bencana Geologi, PVMBG). Kelut is located just S of Surabaya (Surabaja), Indonesia's second largest city (see figure 8 in BGVN 33:03).

Pre-eruption. According to CVGHM, the lake-water temperature in the crater increased 5.5°C during 10 September 2013 to 2 February 2014. During 1 January-2 February 2014 the number of shallow volcanic earthquakes at Kelut volcano increased. During 3-10 February 2014, seismic activity at Kelut was dominated by both shallow and deep volcanic earthquakes; some hypocenters were 3 km below the summit. Real-time Seismic-Amplitude Measurement (RSAM, a gauge of volcanic seismicity) values increased on 6 and 9 February 2014. Inflation was detected at one station.

Peaks of pre-eruptive seismicity occurred during 15-16 and 28 January, and 2-13 February. Table 3 also portrays the available early 2014 seismic data from CVGHM, but it can be hard to see the aforementioned detail because the various entries on table's rows generally summarize multiple days and some of the time intervals differ. The number of deep volcanic earthquakes fluctuated but generally increased overall. Earthquakes often occurred at 2-8 km depth. Based on these observations, on 2 February the Alert Level was raised to from 1 to 2 (on a scale with increasing severity in the range 1-4). Tiltmeter data on 10 February indicated inflation.

Table 3. Seismicity at Kelut volcano during January and into 13 February 2014. Note that the data stream changed abruptly on 13 February when four of Kelut's 5 seismic stations were destroyed by eruptive material. Courtesy of CVGHM.

Crater lake water temperatures continued to increase after September 2013, particularly during 23 January-9 February. Temperatures decreased slightly when measured on 10 February. On 10 February, based on the factors noted above, CVGHM increased the Alert Level to 3. This excluded visitors and residents from within a 5-km radius of the crater.

Eruption on 13 February. At 2115 on 13 February the Alert Level for Kelut was raised to 4, extending the exclusionary zone to a 10-km radius. As noted above, BNPB reported that a major eruption occurred less than two hours later at 2250, followed by another large explosion at 2330. NASA reported that satellite images showed the Kelut eruption about 2 hours later on 13 February 2014 at ~2315 local time (1615 UTC).

According to a Darwin VAAC (2014) weekly activity report, the eruption was seen on the hourly MTSAT-2 IR satellite for 1632 UTC (2332 local time) on 13 February, where it appeared as a rapidly expanding cloud. More details came from 10-minute IR data being used on a special basis in the High Ice Project in Darwin, which captured the eruption clearly as a small cluster of cold pixels on a 1610 UTC (2310 local time) IR image. Later analysis found a small low altitude plume as early as 1540 UTC (2240 local time) at Kelut on the MTSAT-1R satellite; this is the earliest reported start time for the eruption.

According to CVGHM, ash plumes rose to an altitude of 17 km and caused ashfall in areas NE, NW, W, and elsewhere as far as Pacitan (133 km WSW), Kulon Progo (236 km W), Temanggung (240 km WNW), and Banyuwangi (228 km E). As ash began to blanket parts of the region, 40 airline flights were cancelled; impacted airports included Juanda (81 km NE), Adi Sucipto Yogya (208 km W), and Adi Sumarmo Solo (175 km WNW). News articles reported that flights in and out of seven airports were cancelled or rerouted.

Figures 15 and 16 show satellite images of the plume taken on 13 February 2014. The image at the top of figure 15 portrays the scene at 0030 local time and the trace of the path across it taken by the satellite. At ~1813 UTC on 13 February. CALIPSO (Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation). CALIPSO flew over the plume deploying CALIOP (a lidar instrument, essentially a laser range finder that creates a profile of clouds and particles in the atmosphere). This is one of the favored instruments for cloud height measurement. It is part of the A-Train, a constellation of multiple satellites and instruments that follow the same track on polar orbits and cross the equator within seconds to minutes of each other. This allows near-simultaneous observations. CALIOP data revealed that the Kelut ash cloud was generally at an altitude of 18-19 km, with some cloud/ash material reaching a maximum height of ~26 km. This is sufficiently high, and the A-Train data capabilities are sufficiently large to cause great interest, and more refined estimates of height and other parameters are likely to follow.

Figure 15. Figure 15 (top and bottom). At 0030 local time (1730 UTC 13 February) on 14 February, the Visible Infrared Imaging Radiometer Suite (VIIRS) on the Suomi NPP satellite acquired the top image as the gray circular ash plume over Kelut reached above a lighter-colored weather-cloud deck. Forty minutes later, at 0110 local time (1810 UTC 13 February), the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) satellite flew over the plume with its lidar instrument. The instrument recorded the ash cloud at nearly 20 km altitude, with sections of the plume reaching to nearly 26 km. Courtesy of NASA Earth Observatory; image by Jesse Allen, using data provided by the CALIPSO team; caption by Holli Riebeek.

Figure 16. A cross-section through the Kelut volcanic plume from data acquired on 14 February 2014. The image zooms in on CALIPSO data for the tallest parts of the volcanic cloud (using the CALIOP data). The white line shows the approximate troposphere-stratosphere boundary. Some wave structure (small white oscillations) is apparent in the umbrella region. The vertical scale on the left shows computed altitude, and on the lower right shows the color scale for intensity of the 532 nm wavelength backscatter. The horizontal scale and labels at the bottom of the figure shows the latitude, longitude, and time in UTC for the vertical sounding across the transect. The red trace across the bottom of the figure shows land topography, with the volcano at the center. The AIRS (atmospheric infrared sounder) determined SO2 brightness temperature differences (BTD-scale at upper right) referring to features such as the red stars, where AIRS detected SO2 towards the edge of the cloud. Courtesy of Carn and Telling (2014).

Figure 17 shows a view of an eruption at 0030 local time on 14 February. In Figure 18, a plane, service vehicle, and boarding area are shown covered by ash at Yogyakarta airport, 215 km E of Kelut. Closer to the volcano, ashfall and tephra blocks 5-8 cm in diameter caused structures to collapse, including schools, homes, and businesses.

Figure 17. A photo of the eruption of Kelut at 0030 on 14 February 2014, with lightning being generated in the ash plume. Courtesy of Volcano Discovery web site (URL: http:pic.twitter.com/ypy7kx9615 / @hilmi_dzi).

Figure 18. Image of a tan-colored ash blanket covering the landscape, including a parked jet liner and service vehicle, at Yogyakarta airport, 215 km W of Kelut, taken 14 February 2014. Image from NBC News web site (BIMO SATRIO / EPA).

As a result of this eruption, four of the five Kelut seismic stations were destroyed, after which, volcanic and low-frequency earthquakes were not recorded. Subsequently, available seismicity recorded at the one remaining station, 5 km away, was dominated by continuous tremor with amplitudes ranging from 0.5 to 15 mm. That station later recorded declining seismicity during 14-20 February. Two more seismic stations were installed on 16 February, 2-3 km from the crater.

On 14 February, gray-to-black plumes rose 400-600 m above the crater, and on 15 February grayish white plumes rose as high as 3 km (figure 19).

Figure 19. The eruption of Kelut (labeled just to the right of the image's center) on 13 February 2014 sent a large plume of ash drifting W across Java and over the Indian Ocean. This satellite image, acquired 14 February, shows widespread tan atmospheric discoloration from the ash plume. According to an advisory issued by the Australian Bureau of Meteorology, ash had reached 13 km in altitude, prompting the closure of several airports. Three people were killed, and Indonesian authorities have evacuated more than 75,000 people from their homes. NASA Earth Observatory, image by Jesse Allen and caption by Adam Voiland, using data from the Land Atmosphere Near real-time Capability for EOS (LANCE).

On 14 February BNPB reported that the eruption had killed four people (but later estimates were higher): one died due to a collapsing wall, one from ash inhalation, and two from "shortness of breath." All four victims lived within 7 km of Kelut in the regency of Malang, an area that received ashfall up to 20 cm thick.

By 0600 on 14 February, BNPB reported that the number of displaced people reached 100,248, but the report also noted that volcanic activity had declined. Later that day BNPB noted that 76,388 people remained evacuated. Seismicity continued to decline and was at moderate levels during 15-17 February. During 16-20 February white plumes rose as high as 1 km and drifted N, NE, and E. Data from satellite instruments provided a 14 February 2014 image on sulfur dioxide (SO₂) from Kelut (figure 20). The plume had spread primarily W of the volcano.

Figure 20. Sulfur dioxide burdens measured from Kelut (red triangle) over the Indonesian island of Java and Indian Ocean in the early morning of 14 February 2014 following the Kelut eruption. This image is based on data from the IASI instrument on the MetOp mission. Courtesy of European Space Agency (2014).

Heavy rain on 18 February caused lahars in Ngobo, Mangli (Kediri, 35 km WNW), Bladak (Blitar, 20 km SW), and Konto (Malang, 35 km E). BNPB noted that the lahars flooded five houses and one mosque, and destroyed two homes and one bridge. An 18 February BNPB report noted that a total of 7 people in Malang regency had died, and that the ashfall had affected farms, including cattle health and dairy production, and the water supply. Damage to infrastructure in Malang included 3,782 houses, 20 government buildings, 251 schools, 9 hospitals, and 36 churches.

The Alert Level was lowered from 4 to 3 on 20 February and to 2 on 28 February based on decreased amplitude of tremors and thick clouds of white smoke continuously emitted from the crater instead of dark grey. At this point, visitors and residents were prohibited from approaching the crater within a radius of 5 km, but residents outside of this zone were permitted to return home.

Only a single pixel MODVOLC satellite thermal alert was measured during the interval from 13 February through March 2014. The alert occurred at 1515 hours UTC on 20 February 2014, the first alert measured since nearly daily alerts from Kelut's last eruption, 18 November 2007-23 January 2008. During the February 2014 eruption, cloudy weather over Kelut was a major factor that precluded some alerts from being measured, but those visualized suggest that the recent Kelut eruption continued until at least 20 February 2014.

A satellite image made available thanks to the International Charter Space and Major Disasters (2014) was acquired on 18 February and interpreted by the U.S. Geological Survey. The image reveals the impact of the eruption on the summit area and regions peripheral to it (figure 21).

Figure 21. Satellite image of the crater area of Kelud, acquired on 18 February 2014. The former dome was destroyed during the 14 February eruption and significant ash and debris were deposited on the volcano slopes and in the river channels from lahars and pyroclastic flows around the volcano. Steam can be seen rising from the central crater. Courtesy of International Charter Space and Major Disasters (2014); source was WorldView, acquired 18/02/2014 by DigitalGlobe Inc.; map produced by USGS, and found online at Klemetti (2014c).

Later visits disclosed that the 2014 eruption had left a large crater 400 m in diameter and destroyed the 2007 dome, parking area, and access stairs in the crater (see figures 22 and 23).

Figure 22. Photograph of the inner dome in Kelut volcano taken in 2010, showing the then- existing lava dome from the 2007 eruption and the access stairs to the crater, both of which were destroyed by the February 2014 eruption. Image courtesy of Zahidayat / Flickr, from Klemetti (2014b).

Figure 23. (Left) The Kelut lava dome that grew in the crater in 2007, photographed 30 October 2011 by Andersen (2011). In front of the dome was the small portion of what was left of the volcanic lake that used to fill the crater. (Right) The crater of Kelut seen on the morning of 18 February 2014 (photo by Suwarno, a local photographer, via Andersen), showing that the 2014 eruption forcefully removed the dome. Comparison figure came from Andersen (2014).

A group of photographs taken by Oystein Lund Andersen (2014) during a visit from 22 to 23 February show after-eruption images, including steam rising from the crater area, ash and volcanic bombs deposited 2-5 km from Kelut's crater, and damage to trees and other vegetation by pyroclastic flows (for example, Figures 24 and 25). In addition, photographs showed that steam continued to rise from the crater through 25 February 2014. Andersen observed that activity at the volcano has decreased, but it was still unknown what exactly the situation at the vent is, whether or not a new lava dome is forming there.

Figure 24. Steaming pyroclastic flow deposits in one of the valleys below the crater, a once forested area ~1 km SW of the crater. Photo taken at 1157 on 22 February 2014. Courtesy of Andersen (2014).

Figure 25. A lush green forest once stood here, now covered by deposits from a pyroclastic flow and scattered remains of large felled trees. Photo taken at 1205 on 22 February 2014. Courtesy of Andersen (2014).

Airliner encounters plume. A commercial A320 airliner carrying passengers from Perth, Australia, to Jakarta, Indonesia, encountered an ash plume from Kelut near Indonesia on 14 February 2014. The incident was reported by the West Australian (Perth) newspaper and the Sydney Morning Herald (14 February). The reports noted that the airliner left Perth on 14 February 2014 at 0225 local time and flew through the ash cloud before arriving safely in Jakarta at 0550 local time. The estimated cost to replace the two engines of the Airbus aircraft was reported to be $20 million (US dollars). The A320 was grounded after the flight.

Morning Herald reporter Amanda Hoh (2014) reported that a "flight from Perth to Jakarta on Friday morning was filled with smoke after the plane flew into Indonesia's volcanic ash cloud…Richard Craig, from Perth, was on a flight to Jakarta at about 5am on Friday [14 February] when he said the plane suddenly flew into the ash cloud about 30 minutes before landing" Passenger Craig was quoted to have said "It was just starting to get light then it suddenly went quite dark and what I thought was smoke appeared in the cabin out the front, started coming out of the air vent and alarm went off and beeped a few times," he said. "There was an unusual smell. It wasn't like smoke, a slightly sweet smell. More like a very fine smoke…" The smoke cleared within a few minutes and Craig noted that the pilot announced that "it was a volcanic ash cloud and that 'no one was aware of it in the area.'" The plane landed safely.

Summary of damage. According to the International Federation of Red Cross and Red Crescent Societies (IFRC) (2014), "over the first few days the eruption affected 201,228 people (58,341 families) from 35 villages in three districts: Blitar, Kediri, and Malang... As of 14 February 2014, there had been seven fatalities and 70 people in hospitals in serious condition suffering from ash inhalation. Around this time the number of internally displaced persons (IDPs) had reduced to 100,248 people who had evacuated and camped across the province in 172 IDP camps set up to cater for their basic needs... In addition to the volcanic ash, heavy rain fell and produced cold lahar flooding in Malang, Kediri and Blitar districts. This caused further damage to buildings, farm lands, and roads."

Table 4 gives data on damage to structures in the 3 affected districts surrounding Kelut through February 2014. The figures are expected to increase once a more thorough assessment is made.

Table 4. An initial assessment of the damage to housing and other buildings as a result of Kelut eruption volcanic ash. Courtesy of IFRC (2014).

As reported on 24 February 2014 in the Jakarta Globe (Pitaloka, 2014), "torrential rain in East Java on 23 February 2014 prompted local officials to impose a safety curfew over some areas affected by the eruption of Mount Kelud for fear that rainwater could mix with volcanic dust, triggering mud flows." The Head of the Malang Disaster Mitigation Agency, Hafi Lutfi, said rain had triggered landslides that damaged several sections of mountain road. "A mud flow in Padansari village on Thursday [13 February] washed away two houses and two bridges, although no casualties were reported... Volcanic mud was carried down the mountain's slopes by the river, which flows through Kasembon, Ngantang and Pujon subdistricts" (figure 26).

Figure 26. Villagers stand on the remains of a bridge washed out in Malang district near Pandansari village. The bridge succumbed to water mixed with volcanic material from Mount Kelut's eruption on 19 February 2014. From Pitaloka (2014); EPA photo by Fully Handoko.

Lutfi was reported to have stated further that the "impact of Mount Kelud's eruption will extend far beyond the initial cleanup efforts. Fruit farmers reportedly lost more than Rp 24 billion ($2 million) in revenue as ash and debris destroyed whole fields of apples, durian and rambutan that were ready for harvest. The trees, covered in a thick coating of ash, had withered from lack of sunlight."

Background. The CVGHM reported that activity at Kelut last occurred in 2007, beginning with an increase in seismic activity and an eruption in October 2007. The activity ended with an effusive eruption on 3-4 November 2007 resulting with a crater lake surrounding a central lava dome (BGVN 33:03, 33:07, and 37:03).

References. Andersen, O.L., 2014 (22 February), Kelud Volcano, East-Java, Indonesia (URL: http://www.oysteinlundandersen.com/Volcanoes/Kelud/Kelud-Volcano-Indonesia-February-2014.html)

Andersen, O.L., 2011 (30 October), Mt. Kelud Volcano, Indonesia, 30 October 2011(URL: http://www.oysteinlundandersen.com/Volcanoes/Kelud/Kelud-Volcano-Indonesia-October-2011.html).

Carn, S., and Telling, J., 2014, Kelut 2014, IAVCEI (International Association of Volcanology and Chemistry of the Earth's Interior) Remote Sensing Commission (RSC) (URL: https://sites.google.com/site/iavceirscweb/eruptions/kelut-2014)

CIMSS Satellite Blog, 2014 (13 February), Eruption of the Kelut volcano in Java, Indonesia (URL: http://cimss.ssec.wisc.edu/goes/blog/archives/14910 ).

European Space Agency (ESA), 2014 (14 February), Kelut volcano grounds air travel, ESA Observing the Earth web site (URL: http://www.esa.int/Our_Activities/Observing_the_Earth/Kelut_volcano_grounds_air_travel).

Hoh, A., 2014 (14 February), Volcano eruption cancels Bali, Phuket flights and closes Indonesian airports, The Sydney Morning Herald (URL: 14http://www.smh.com.au/travel/travel-incidents/volcano-eruption-cancels-bali-phuket-flights-and-closes-indonesian-airports-20140214-32qd8.html)

International Charter Space and Major Disasters, (2014), Mount Kelud volcanic eruption in Indonesia (URL: http://www.disasterscharter.org/web/charter/activation_details?p_r_p_1415474252_assetId=ACT-481)

International Federation of Red Cross and Red Crescent Societies, 2014 (3 March), Emergency plans of action (EPofA), Indonesia: Volcanic eruption - Mt. Kelud (URL: http://reliefweb.int/sites/reliefweb.int/files/resources/MDRID009dref.pdf).

Klemetti, E., 2014a (11 February), Indonesian Eruption Update for February 11, 2014: Kelut and Sinabung (URL: http://www.wired.com/wiredscience/2014/02/indonesias-kelut-placed-highest-alert/)

Klemetti, E., 2014b (13 February), Significant Eruption Started at Indonesia's Kelut (URL: http://www.wired.com/wiredscience/2014/02/significant-eruption-started-indonesias-kelut/).

Klemetti, E., 2014c (24 February), Kelud, Before and After the Eruption (URL: http://www.wired.com/wiredscience/2014/02/kelud-eruption/).

National Aeronautics and Space Administration (NASA) Goddard Space Flight Center, 2014 (13 February), Kelut (Kelud) Eruption- February 13, 2014 (URL: http://so2.gsfc.nasa.gov/pix/special/2014/kelut/Kelut_summary_Feb14_2014.html)

Pitaloka, D.A., 2014 (24 February), Torrential Rain Worsens Kelud Misery, Jakarta Globe (URL: http://www.thejakartaglobe.com/news/torrential-rain-worsens-kelud-misery).

Volcano Discovery, 2014 (2 March), Kelut volcano news (URL: http://www.volcanodiscovery.Kelut volcano news & eruption updates _ 27 Sep 2007 - 2 Mar 2014.htm).

Geologic Background. The relatively inconspicuous Kelud stratovolcano contains a summit crater lake that has been the source of some of Indonesia's most deadly eruptions. A cluster of summit lava domes cut by numerous craters has given the summit a very irregular profile. Satellitic cones and lava domes are also located low on the E, W, and SSW flanks. Eruptive activity has in general migrated in a clockwise direction around the summit vent complex. More than 30 eruptions have been recorded since 1000 CE. The ejection of water from the crater lake during the typically short but violent eruptions has created pyroclastic flows and lahars that have caused widespread fatalities and destruction. After more than 5,000 people were killed during an eruption in 1919, an engineering project to drain the crater lake lowered the surface by more than 50 m. The 1951 eruption deepened the crater by 70 m, leaving 50 million cubic meters of water after the damaged drainage tunnels were repaired. Following more than 200 deaths in the 1966 eruption, a new deeper tunnel was constructed, and the lake's volume before the 1990 eruption was only about 1 million cubic meters.

Information Contacts: Indonesian Centre for Volcanology and Geological Hazard Mitigation – CVGHM (also known as Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG)), Jalan Diponegoro 57, Bandung 40122, Indonesia (URL: http://www.vsi.esdm.go.id/); Darwin Volcanic Ash Advisory Centre (VAAC), Australian Bureau of Meteorology, Northern Territory Regional Office, PO Box 40050, Casuarina NT 0811, Australia (URL: http://www.bom.gov.au/info/vaac); MODVOLC, Hawai'i Institute of Geophysics and Planetology (HIGP) 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/); Badan Nasional Penanggulangan Bencana (BNPB – Indonesian National Board for Disaster Management), Jl. Ir.H.Juanda No. 36 Jakarta Pusat, Indonesia (URL: http://www.bnpb.go.id); CIMSS (NOAA's Cooperative Institute for Meteorological Satellite Studies), University of Wisconsin – Madison's Space Science and Engineering Center (SSEC) (URL: http://cimss.ssec.wisc.edu/goes/blog/about); NOAA Satellite and Information Service, Automated OMI SO2 Alert System, High SO2 Concentration Areas (URL: http://satepsanone.nesdis.noaa.gov/pub/OMI/OMISO2/Alert/alert.html); National Aeronautics and Space Administration (NASA) Goddard Space Flight Center (URL: http://so2.gsfc.nasa.gov); European Space Agency (URL: http://www.esa.int); West Australian (Perth) news (URL: http://au.news.yahoo.com/a/21467336/); Sydney Morning Herald (URL: http://www.smh.com.au); Andersen, Oystein Lund (URL: http://www.oysteinlundandersen.com/); IAVCEI Remote Sensing Commission website (URL: https://sites.google.com/site/iavceirscweb/eruptions/kelut-2014); and Simon Carn, Department of Geological and Mining Engineering and Sciences, Michigan Technical University, Houghton, MI.

According to the Rabaul Volcanological Observatory, a "small (probably submarine) eruption was reported to have taken place at Ritter Island on 18 April 2014 (figures 2 and 3). At about 1700 hours, an earthquake was felt at Kampalap village on Umboi Island. At the same time the level of sea rose a little over normal but was confined to the beach at Kampalap. At around 0000 hours on 19 April, another felt earthquake occurred. The earthquakes were estimated to have an intensity at Kampalap of between II to III. No floating debris where seen, and no ash or damage was reported."

Figure 2. Location maps for Ritter Island. The upper map shows the region of Papua New Guinea containing Ritter Island and other volcanoes, and the lower map is enlargement of the center of the upper map focused on Ritter Island. From Saunders and Kuduon (2009).

Figure 3. Oblique aerial view of Ritter Island photographed in 2006 by John Holder (the originator of Oceanic Expeditions) from SW looking NE, with some of the location names. From Saunders and Kuduon (2009).

A Rabaul Volcanological Observatory (RVO) report by Saunder and Kuduon (2009) noted past possible geothermal activity on Ritter Island that had not been previously reported. According to their report, "In 1997 a patrol officer (Hita Mesere) in a media release relayed reports from Councilor Nalong (Kampalap Village?) of an explosive eruption and large waves reaching nearby villages. In the preparation of this report Mr. Mesere was contacted and he confirmed that he and officers from the Morobe PDO flew over Ritter after this event and saw white smoke coming from 'boiling' in the sea, close to land in the South Bay (Mesere, 2009 Pers. Comm.)."

The report concluded that "Ritter is active, both volcanically and geomorphologically. More volcanic activity can be expected. Seismically this will probably not be as intense as in the early 1970's, as the conduit seems now to be open. Volcanic phenomena may however increase in importance if the cone continues to grow towards the surface and magma is erupted into an environment of lower hydrostatic pressures. There seems to be two causes of eruptive activity, one is the rise of fresh magma at the site of the submarine cone and the other is slope instability causing water to come into contact with residual hot rocks leading to small hydrovolcanian events close inshore of Ritter."

The RVO report also included the following table (table 1) showing past observations of possible geothermal activity on Ritter Island.

Table 1. Dates and details of reported post-collapse activity at Ritter. From of Saunders and Kuduon (2009).

Tsunami of 1888. Several recent papers have revisited the 13 March 1888 collapse of Ritter Island volcano that generated a catastrophic tsunami. According to Ward and Day (2003), "In the early morning of 1888 March 13, roughly 5 km³ of Ritter Island Volcano fell violently into the sea northeast of New Guinea. This event, the largest lateral collapse of an island volcano to be recorded in historical time, flung devastating tsunami tens of meters high on to adjacent shores. Several hundred kilometers away, observers on New Guinea chronicled 3 min period waves up to 8 m high, that lasted for as long as 3 h. These accounts represent the best available first-hand information on tsunami generated by a major volcano lateral collapse." Eyewitness accounts noted the lack of explosive activity accompanying the collapse. In this paper, the authors simulated the Ritter Island landslide as constrained by a 1985 sonar survey of its debris field and compare predicted tsunami with historical observations.

Ray and others (2014) reported that, based on primary and secondary eyewitness accounts on the morning of 13 March 1888 "there is no clear evidence for a coincident [to the collapse] or causal magmatic explosive eruption. One report suggests that there was activity (perhaps phreatic or phreatomagmatic explosions?) prior to the collapse that lead some of the resident local communities to seek higher ground, but evidence for precursory flank movements or changes in eruptive style have not been found in the historical accounts."

References. Ray, M.J., Day, S., and Downes, H., 2014, The growth of Ritter Island volcano, Papua New Guinea, and the lateral collapse landslide and tsunami of 1888: new insights from eyewitness accounts, EGU General Assembly 2014, Geophysical Research Abstracts, v. 16, EGU2014-1305.

Saunders, S., and Kuduon, J., 2009, The June 2009 Investigation Of Ritter Volcano, With A Brief Discussion On Its Current Nature, Rabaul Volcanological Observatory Open File Report OFP 003/2009, 25 pp.

Ward, S.N., and Day, S. 2003. Ritter Island—lateral collapse and the tsunami of 1888. Geophysics Journal International, v. 154, pp. 891-902.

Geologic Background. Prior to 1888, Ritter Island was a steep-sided, nearly circular island about 780 m high between Umboi and Sakar Islands. Several historical explosive eruptions had been recorded prior to 1888, when large-scale slope failure destroyed the summit of the conical basaltic-andesitic volcano, leaving the arcuate 140-m-high island with a steep west-facing scarp. Devastating tsunamis were produced by the collapse and swept the coast of Papua New Guinea and offshore islands. Two minor post-collapse explosive eruptions, during 1972 and 1974, occurred offshore within the largely submarine 3.5 x 4.5 km breached depression formed by the collapse.

Information Contacts: Rabaul Volcanological Observatory, P.O. Box 386, Rabaul, Papua New Guinea.

Previously reported activity from Sangay volcano (figure 14) included ash plumes as late as 23 May 2013 and satellite infrared thermal alerts ending in early May 2013 (BGVN 36:01). In that previous report, satellite thermal alerts from the MODVOLC system were noted to have persisted and as late as 4 May 2013. That lack of alerts continued as late as 16 July 2013 when the MODVOLC website was last checked. Since that reporting, there have been no new updates regarding Sangay on the website of the Instituto Geofisico (IG), the aviation reports have not mentioned Sangay, and other news of Sangay behavior has also been generally lacking.

Figure 14. (Inset at bottom) A regional map showing Sangay with respect to large rivers and other features surrounding Sangay. Orange line is the PanAmerican highway, which passes near Río Bamba on the map's N. Major rivers (blue) are primary routes of lahars. (Main map) A hazards map for Sangay made with hazards focus and compiling the results of multiple kinds of modeling. Key (in Spanish) notes that the upper three colors were based on slope angle (H/L) with text noting gradation of hazards in those regions from pyroclastic flows, lava flows, ash falls, volcanic bombs, rock falls, and proximal lahars. The lower three colors on the key represent inferred gradations of lahar hazard at distance from the volcano. Dashed envelopes in red refer to boundaries for small and moderate sizes of ash falls. White line shows inferred boundary for an E directed debris avalanche. Base map is from the Instituto Geografico Militar (IGM). Taken from an online poster by Ordóñez and others, 2014).

Absence of MODVOLC and aviation alerts does not necessarily translate to a lack of eruptions. The MODVOLC system imposes a reasonably high threshold to the infrared data acquired from space. Factors such as weather conditions, snow pack, and geometry of the vent area may play a role. Emissions of spatter, ash fall, and small pyroclastic flows could easily be missed. Assessments are generally best made in conjunction with information at the volcano. The current eruption began on 8 August 1934 and is thus far confirmed only through 23 May 2013.

Hazard modeling and products. In late 2013 to early 2014 IG released a poster discussing Sangay hazards (Ordóñez and others, 2014), some of the results of which we reprint here (figures 14, 15, and 16). Figure 14 contains IGEPN's recently published a map of volcanic hazards associated with Sangay, which resides in the Cordillera Real between the cities of Río Bamba and Macas. The IG and others have generally considered Sangay one of the most active volcanoes in South America. The poster noted historical records of its eruptive activity dating back to 1628 (Hall, 1977) and in the last century some important periods of activity were recorded during 1903, 1934-1937, 1941-1942, 1975-1976, and 1995 to the present (Monzier et al.. 1999). Observations of surface activity carried out in the past 40 years allowed scientists to recognize some important morphological changes at the summit of the volcano, including the emergence of new craters, dome growth, extrusion of lava flows, local explosions and ash emissions, and relatively small pyroclastic flows.

Figure 15. Modeled ash fall blanket from a hypothetical eruption at Sangay of moderate size. The key (in Spanish) refers to the colors in the key and on the isopach map, with thicknesses in millimeters. Taken from an online poster by Ordóñez and others (2014).

Figure 16. Modeled ash fall blanket from a hypothetical eruption at Sangay of large size. The key (in Spanish) refers to the colors in the key and on the isopach map, with thicknesses in millimeters. Taken from an online poster by Ordóñez and others (2014).

A larger suite of volcanic hazards models is not shown here but includes results VolcFlow. Ash3D, Tephra2, and LAHARZ. The data used for the simulations were obtained from the few geological studies in this volcano (Hall, 1977; Monzier et al, 1999; Johnson et al, 2003). Sangay is judged in some ways analogous to Tungurahua volcano, because of its chemical composition, and it similar lava rheology and eruptive style of volcanic flows.

During August-September 2013, IG installed seismic monitoring instruments (broad band and infrasound ) and for the measurement of sulfur dioxide (SO₂) in the southwestern flank of the volcano Sangay. These tools facilitate the monitoring of internal and surface activity of the volcano which will give an early warning of a potential hazards.

With regard to monitoring, during August-September 2013 IG personnel installed ~4 km southwest of Sangay volcano, permanent telemetered monitoring system consisting of a broadband seismic sensor, infrasound, and gas monitoring.

Figures 15 and 16 show the respective modeled results for a moderate and large eruption. To define the zones affected by ash fall, the modeling used the following computer routines based on assumptions and approaches discussed in the literature: Ash3d (Mastin and others, 2012) and Tephra2 (Banadonna and others, 2005). Some input data came from inferences and interpretations of descriptions by Monzier and others (1999) and from analogy with recent eruptions at Tungurahua. Plume heights were assumed to reach 10-15 km in altitude and the magma volumes in the plumes were assumed to be on the order of 0.001-0.005 km³ (dense-rock equivalent, DRE). Wind field data came from the Global Forecast System (NOAA, US National Weather Service, Environment Modeling Center). LAHARZ (Schilling, 1998), a modeling approach, was also taken to estimate the extent and coverage of lahars seen in figure 14. (The poster includes other maps on this topic as well.)

References. Bonadonna, C, Connor CB, Houghton BF, Byrne M, Laing A, Hincks T., 2005, Probabilistic modeling of tephra dispersal: Hazard assessment of a multi-phase eruption at Tarawera, New Zealand; J. Geophys. Res., 110, B03203.

Hall M. (1977). El Volcanismo en Ecuador. Publicación del Instituto Panamericano de Geografía e Historia, Sección nacional del Ecuador, Quito. 120pp.

Mastin, L, Schwaiger H, Denlinger R., 2012, User's Guide to Ash3d: A 3-D Eulerian Atmospheric Tephra Transportation and Dispersion Model, U.S. Geological Survey Open File Report.

Monzier M, Robin C, Samaniego P, Hall M, Cotten J, Mothes P, Arnaud N., 1999, J. Volcanol. Geotherm. Res. 90, 49-79.

Ordóñez J., Vallejo S., Bustillos J., Hall M., Andrade D., Hidalgo S., and Samaniego P., (Document created, December 2013; Accessed online July 2014), Volcan Sangay---Peligros Volcanicos Potenciales, Instituto Geofísico, Escuela Politécnica Nacional (IG-ESPN) (URL: http://www.igepn.edu.ec/volcan-sangay/mapa-de-peligros.html ).

Schilling S. (1998). LAHARZ: GIS programs for automated mapping of lahar-inundation hazard zones. US Geological Survey Open-File Report 98-638; 79 pp.

Geologic Background. The isolated Sangay volcano, located east of the Andean crest, is the southernmost of Ecuador's volcanoes and its most active. The steep-sided, glacier-covered, dominantly andesitic volcano grew within the open calderas of two previous edifices which were destroyed by collapse to the east, producing large debris avalanches that reached the Amazonian lowlands. The modern edifice dates back to at least 14,000 years ago. It towers above the tropical jungle on the east side; on the other sides flat plains of ash have been eroded by heavy rains into steep-walled canyons up to 600 m deep. The earliest report of an eruption was in 1628. Almost continuous eruptions were reported from 1728 until 1916, and again from 1934 to the present. The almost constant activity has caused frequent changes to the morphology of the summit crater complex.

Information Contacts: Instituto Geofísico-Escuela Politécnica Nacional (IG), Casilla 17-01-2759, Quito, Ecuador (URL: http://www.igepn.edu.ec/); Washington Volcanic Ash Advisory Center (VAAC), Satellite Analysis Branch (SAB), NOAA/NESDIS E/SP23, NOAA Science Center Room 401, 5200 Auth Rd, Camp Springs, MD 20746, USA (URL: http://www.ospo.noaa.gov/Products/atmosphere/vaac/); and 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/).

Due to elevated seismic activity, the Indonesian Center for Volcanology and Geologic Hazard Mitigation (CVGHM) issued an alert for Sangeang Api volcano on 21 May 2014. On 30 May 2014 at 1555, CVGHM reported an eruption of the island volcano that generated an explosive eruption column of ash and sulfur dioxide into the atmosphere, extending >3 km above the summit (figure 8). While the 13-km-wide island of Sangeang has no permanent settlements or residents, dozens of farmers cultivate land on the island during the growing and harvest seasons. Photographs of the eruption showed several pyroclastic flows coming down the volcano summit to the S and E that may be hazardous to anyone of the island. On 30 May, the Alert Level was raised from 2 to 3 (on a scale of 1-4). Civil authorities evacuated 135 people from within 1.5 km of the volcano to the mainland (nearby Sumbawa Island), with the result that no one was reported to have been killed or injured during the eruption.

Figure 8. Eruption plume rising from Sangeang Api volcano on 30 May 2014, photographed to the N from Sambawa Island. Note the distinctive lenticular white cloud condensed from uplifted moist air carried by the rising plume. Pyroclastic flows can also be seen moving down along the S and E sides of the volcano. Courtesy of Anonymous (2014).

Based on satellite images, pilot observations, and the Indonesian Meteorological Office, the Darwin VAAC reported that on 30 May an ash plume rose to an maximum altitude of 15.2 km and drifted 440 km E and 750 km SE (figure 9).

Figure 9. After erupting, the Sangeang Api volcano sent an ash plume to the E, along with a distinctive lenticular white cloud condensed from uplifted moist air. Pilots in the area reported seeing the cloud rising to 19.8 km, spreading over a 40 km area. Photograph taken on 30 May 2014 by Sofyan Efendi looking N during a commercial flight from Bali to the fishing town of Labuan Bajo; from Hall (2014).

The Indonesian Regional Disaster Management Agency (BNPB) reported that on 31 May two larger explosions occurred at 1330 and 2242 hrs. According to the VAAC, ash plumes from these two explosions rose to altitudes of 13.7-15.2 km and drifted 280 km NW (and other various directions, including S). Later in the day the ash plumes, including one from the previous day, eventually became detached. Ashfall affected many areas in the Bima Regency on the mainland, including Wera, and prompted the evacuation of 7,328 people from four villages within a radius of 8 km from Sangeang Api. The Bima and Tambolaka airports were temporarily closed. According to a news article, all flights to and from the Darwin International Airport in Australia on 31 May were canceled (figure 10). The VAAC noted that ash plumes rose to an altitude of 4.3 km on 1 June and drifted W and SW (figure 11). During 2-3 June ash plumes rose to altitudes of 3-4.3 km and drifted 45 km W. Based on analyses of satellite imagery and wind data, the Darwin VAAC reported that on 14 June an ash plume from Sangeang Api rose to an altitude of 2.1 km and drifted 55 km NW.

Figure 10. The Moderate Resolution Imaging Spectroradiometer (MODIS) aboard the Terra satellite captured imagery of the eruption plume from Sangeang Api (dark brown line on the image extending from the volcanic island to the SE) at 0235 UTC (1035 local time) on 31 May 2014. Ash drifted SE, shutting down airports in Bima, Indonesia, and Darwin, Australia. Service to Darwin resumed by 1 June, but Bima remained shut down as of 2 June, according to the Jakarta Globe. Other satellites have observed the ash plume as well. A near real-time tool developed by University of Wisconsin and NOAA scientists estimated that the plume reached an altitude of at least 12 to 14 km based on observations from multiple weather satellites. The Ozone Mapping & Profiler Suite on Suomi NPP also observed ash drifting toward Australia on 31 May. NASA image courtesy Jeff Schmaltz LANCE/EOSDIS MODIS Rapid Response Team, GSFC; Caption by Adam Voiland. From NASA Earth Observatory (2014, 3 June).

Figure 11. Landsat 8 satellite collected this true-color image of an ash plume rising from the Sangeang Api, an island volcano just of the coast of Sumbawa Island, Indonesia, on 1 June 2014. Note that on this day the plume is being blown W and then SW as compared with the previous day shown in figure 8. NASA Earth Observatory images by Robert Simmon, using Landsat 8 data from the USGS Earth Explorer. From NASA Earth Observatory (2014, 1 June).

During the period from 2-17 June, thin to thick white smoke was ejected as high as 200-500 m. Seismic activity during the major part of the eruption is shown on Table 4; as of 17 June, seismicity continued to decline. The Alert Level was reduced from 3 to 2 (on a scale of 1-4) on 17 June.

Table 4. Numbers of daily earthquakes measured for 3 days during and after the eruption of Sangeang Api, as reported by CVGHM. 'VB' represents shallow volcanic earthquakes; 'VA' represents deep volcanic earthquakes; 'TL' represents local earthquake tectonics; 'X' indicates activity present; 'nr' is not reported .

MODVOLC and other satellite imaging. Satellite infrared measurements of thermal alerts over this Sangeang Api volcano eruption first appeared as 2 pixels (an area of thermal anomaly of ≥2 km²) at 1405 UTC on 30 May 2014. These were the first thermal alerts measured over Sangeang Api since 20 October 2013. From 30 May 2014 through 7 July, satellite crossings measured alerts of between 1 and 9 pixels (areas of ≥1 to ≥9 km², respectively) daily until 1500 UTC on 30 June; the 9-pixel thermal alert was measured 20 June 2014 at 1425 UTC (figure 12). (Note: As an explanation for this technique, the MODVOLC web site states that "Using infrared satellite data provided by the Moderate Resolution Imaging Spectroradiometer (MODIS), scientists at the Hawai'i Institute of Geophysics and Planetology, University of Hawai'i, have developed an automated system [MODVOLC] which maps the global distribution of thermal hot-spots in near-real-time, and displays the results on this web-site." A paper by Wright and others (2004) states that "Although MODIS pixels are nominally 1 km, pixel size increases with distance from nadir and at the edges of the MODIS swath (where the scan angle reaches ±55°) MODIS pixels measure ~2.08 km in the along-track, and ~4.83 km in the across-track direction.")

Figure 12. MODVOLC image for the period 30 May to 7 July 2014 of thermal alerts measured on Sangeang Api volcano. The volcano lies on the island of Sangeang just off the Indonesian island of Sumbawa. The central array of pixels trending E-W are for those alerts measured for the period 30 May - 30 June 2014. Courtesy of MODVOLC.

Figures 13 and 14 show satellite images of ash plume temperature and SO₂ plume from Sangeang Api volcano on 30 and 31 May 2014, respectively. The plume is obviously drifting to the E and S toward Australia.

Figure 13. Composite of the Day-Night Band (DNB, red-to-yellow) at 750m resolution and the IR11.45 (I5, color scale at the top) channel at 375m resolution, image made 30 May 2014 at 1745 UTC. The DNB shows two craters at Sangeang Api volcano, Doro Api and Doro Mantoi. The brighter one was emanating the big plume with temperature values down to -196.5 K (76.6 °C) at the top. The secondary crater was emanating some material, but at much lower level so could hardly be seen. Courtesy of EUMETSAT (2014).

Figure 14. SO2 measured from the Sangeang Api volcano plume on 31 May 2014 at 0535 UTC. The volcano is located at the W end of the measured area. Courtesy of NOAA.

References. Anonymous, 2014 (30 May), Massive volcano eruption: Sangeang Api volcano - Sunda Islands, Indonesia, Before Its News web site (http://beforeitsnews.com/environment/2014/05/massive-volcano-eruption-sangeang-api-volcano-sunda-islands-indonesia-2502094.html).

EUMETSAT, 2014, Eruption of Sangeang Api volcano: There were a series of spectacular eruptions from the Indonesian volcano Sangeang Api at the end of the May. URL: http://www.eumetsat.int/website/home/Images/ImageLibrary/DAT_2235292.html

NASA Earth Observatory, 2014 (3 June), Sangeang Api Erupts (URL: http://earthobservatory.nasa.gov/IOTD/view.php?id=83799).

NASA Earth Observatory, 2014 (1 June), Sangeang Api Eruption (URL: http://earthobservatory.nasa.gov/NaturalHazards/view.php?id=83887&eocn=image&eoci=nh_viewall)

Wright, R., Flynn, L.P, Garbeil, H., Harris, A.J.L., and Pilger, E., 2004, MODVOLC: near-real-time thermal monitoring of global volcanism, Journal of Volcanology and Geothermal Research, v. 135, pp. 29-49.

Hall, J., 2014 (30 May), Pictured from a passenger plane: Menacing 12-mile-high ash cloud looms over Indonesia's 'Mountain of Spirits' after volcano erupts, Daily Mail (URL: http://www.dailymail.co.uk/news/article-2644253/Incredible-moment-huge-volcano-erupts-Indonesia-sending-ash-spewing-thousands-feet-sky.html).

Geologic Background. Sangeang Api volcano, one of the most active in the Lesser Sunda Islands, forms a small 13-km-wide island off the NE coast of Sumbawa Island. Two large trachybasaltic-to-tranchyandesitic volcanic cones, Doro Api and Doro Mantoi, were constructed in the center and on the eastern rim, respectively, of an older, largely obscured caldera. Flank vents occur on the south side of Doro Mantoi and near the northern coast. Intermittent eruptions have been recorded since 1512, most of them during in the 20th century.

Information Contacts: Indonesian Centre for Volcanology and Geological Hazard Mitigation – CVGHM (also known as Pusat Vulkanologi dan Mitigasi Bencana Geologi - PVMBG)), Jalan Diponegoro 57, Bandung 40122, Indonesia (URL: http://www.vsi.esdm.go.id/); MODVOLC, Hawai'i Institute of Geophysics and Planetology (HIGP) 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/); DARWIN VAAC (Darwin Volcanic Ash Advisory Centre), Bureau of Meteorology, Northern Territory Regional Office, PO Box 40050, Casuarina, NT 0811, Australia (URL: http://www.bom.gov.au/info/vaac/); Badan Penanggulangan Bencana Daerah (BPBD), Indonesian Regional Disaster Management Agency (URL: http://bpbd.malangkab.go.id/); and Badan Nasional Penanggulangan Bencana (BNPB), Indonesian National Disaster Management Agency (URL: http://www.bnpb.go.id/).

INETER reported that during 2013, Telica was one of the main contributors to Nicaragua's volcanic seismicity (along with Momotombo, San Cristóbal, Cerro Negro, and Concepción). Of the total seismicity detected in Nicaragua, 28% was associated with the volcanic chain.

Throughout 2013, white, low-level gas plumes rose over 200 m above the crater. Field observers saw incandescence from the crater floor and heard jetting sounds. This activity was slightly diminished in May and peaked in late September.

In March 2013, a group of students from Chalmers University of Technology, Switzerland, surveyed the crater with an FTIR spectrometer to determine SO₂ flux (figure 34). Overall, during 5-21 March, SO₂ flux averaged 175 tons/day with the maximum value of 250 tons/day recorded on 17 March. The group returned to Telica in March 2014 and found fluxes of similar levels (figure 34).

Figure 34. SO2 flux measured from Telica during 5-22 March 2013 by students from the Chalmers University of Technology, Switzerland. Courtesy of Vladimir Conde, Chalmers University of Technology.

On 25 September 2013, small explosions were detected from the crater that released gas and ash. There were four explosions during 0725-1605; the largest occurred at 0725 and generated a plume 50 m above the crater rim. The other three explosions were less energetic and did not eject material beyond the crater. During a field visit that day, INETER scientists observed incandescence from a new vent within the crater as well as small fractures crossing the crater floor. An infrared thermometer measured a maximum of 505°C from the active vent.

A field survey team observed strong degassing from the crater on 8 October. The main source of the gas was the SW wall and jetting sounds were also noted.

2014. Low-level degassing continued during January-June 2014. Jetting sounds and incandescence from the crater occurred less frequently based on field visits by INETER scientists. Seismicity in January and February was elevated; 11,182 and 26,355 volcano-tectonic (VT) earthquakes were detected respectively. In April 2014, seismicity was greatly reduced (2,454 earthquakes) and was dominated by paired earthquakes known as doublets (also detected in January 2014).

During a field visit on 22 May 2014, INETER scientists noted that, while incandescence was still visible, gas emissions were greatly reduced and the jetting sounds were absent. The active vent within the crater appeared to be covered and possibly blocked by rockfalls originating from the crater walls. Emissions, jetting sounds, and incandescence were also reduced in June 2014.

Geologic Background. Telica, one of Nicaragua's most active volcanoes, has erupted frequently since the beginning of the Spanish era. This volcano group consists of several interlocking cones and vents with a general NW alignment. Sixteenth-century eruptions were reported at symmetrical Santa Clara volcano at the SW end of the group. However, its eroded and breached crater has been covered by forests throughout historical time, and these eruptions may have originated from Telica, whose upper slopes in contrast are unvegetated. The steep-sided cone of Telica is truncated by a 700-m-wide double crater; the southern crater, the source of recent eruptions, is 120 m deep. El Liston, immediately E, has several nested craters. The fumaroles and boiling mudpots of Hervideros de San Jacinto, SE of Telica, form a prominent geothermal area frequented by tourists, and geothermal exploration has occurred nearby.

Information Contacts: Virginia Tenorio, Instituto Nicaragüense de Estudios Territoriales (INETER), Apartado Postal 2110, Managua, Nicaragua (URL: http://www.ineter.gob.ni).

On 5 August 2012, White Island erupted, following rapid water level rises in the crater lake. Minor ash emission continued to as late as 17 August (BGVN 37:06). This report describes activity during September 2012-January 2014. Unless otherwise stated, information was compiled from GeoNet reports. Major events during the reporting interval include a spiny dome first viewed in December 2012, several months of explosive phreatic activity in early 2013, and discrete explosive eruptions during the latter half of 2013. Magma last surfaced at White Island in 2000 in an explosive eruption that ejected molten lava (BGVN 25:08). GeoNet, a monitoring project funded by the Earthquake Commission, is operated by New Zealand's GNS Science which produces an on-line Volcanic Alert Bulletin. It monitors volcano events by webcam, and acoustic and seismic instruments. Periodically, in situ temperature, fumarole and spring chemical sampling, deformation, gas data, and visual narratives were also recorded. Surveillance includes a mini DOAS network and may also airborne visual observations, photos, and IR images.

GeoNet currently describes White Island as the most active of New Zealand's volcanoes. During 2012 and 2013 normal seismic activity was interspersed with periods of heightened activity. GeoNet reported minor ash, seismicity, gas emissions, dome building, and changes at the crater and crater lakes. Two significant eruptions occurred after a period of reduced activity in 2013: one in August and the other in October. In January 2014, GeoNet volcanologists reported low seismicity. During a single year, tour companies estimated that over 10,000 tourists visited White Island from NZ's North Island ~45 km to the S. Safety of visitors to the island and surrounding waters depends on Volcanic Alert Bulletins. The NZ volcano alert levels ranged from 0 (low risk) to 5 (high risk); Aviation Alert colors ranged from Green (low risk), to Yellow, to Orange and then to Red (high risk). These two alert types were frequently updated, based on spikes in activity. For example in August 2013, Alert Levels ranged from 1 to 2 and Aviation Colour Codes shifted from Yellow to Green to Red to Orange and back to Yellow.

Ashfall in 2012 and a spiny lava dome. In a Volcanic Alert Bulletin issued on 12 December 2012, GNS reported that after the 5 August eruption, a spiny done was formed. In the 26 July 2013 report, phreatic and steam driven activity was observed beginning in December with minor ash emissions interspersed and continuing into the following year. Degassing and tremors were frequent with varying intensities (figure 55). The figure records seismicity as root square amplitude mean (RSAM) on the ordinate plotted along the time line abscissa from June 2007 to December 2013. The tremors were generally attributed to fluid movement (magma, geothermal water, and steam) at an undetermined depth in the crust.

Figure 55. White Island seismicity as root square amplitude mean (RSAM) on the ordinate plotted along the time line abscissa from June 2007 to December 2013. Figure by Brad Scott; courtesy New Zealand's Geological and Nuclear Sciences (GNS Science).

In December 2012, two airborne observations were conducted. GNS volcanologists on 10 December viewed for the first time a small spiny lava dome in the crater active during August 2012. The dome emerged in the vent active in a spot adjacent to two other venting areas (figure 56). GNS reporting attributed the dome morphology to a cooled carapace thrust upward by injection of magma deeper in the dome. Several spines protruded from the roughly 20-30 m diameter dome base (figure 57). Tour operators to the island commented that the dome was visible weeks before the volcanologists viewed it. The actual date of formation remained unstated and possibly unknown.

Figure 56. Aerial view of White Island's active crater. A lava dome juts up adjacent to the front edge of an active oval vent near the prominent lake in the center of the image. The image was taken from a helicopter on 10 December 2012 looking W at ~600 m from the active vents. Photo by Brad Scott; courtesy GNS Science.

Figure 57. Magnified view of the 10 December 2012 image showing the spiny lava dome (about 20-30 m diameter). The hot lake in the foreground sits adjacent to the active vent. Courtesy of GeoNet. Image by B. J. Scott, GNS Science.

Airborne observations on 20 December 2012 found the lava dome unchanged. Several small lakes occupied parts of the area formally covered by a large lake viewed before the August eruption. Infrared temperatures taken during the flight found the dome to be 187°C, the actively upwelling hot lake S of the dome to be 71°C, and the cool lake on the N side of the dome to be 35°C. 20 December airborne measurements resulted in a gas flux rate for SO₂ of 400 metric tons/day (t/d), for CO₂: 1,300 t/d, and for H₂S₂; 10 t/d.

Ashfall after the August 2012 eruption to the end of 2012 was unreported in the 2012 Volcanic Alert Bulletin archive. However, in the 26 July 2013 report, GeoNet summarized the December 2012-February 2013 activity as an eruption sequence interspersed with phreatic, steam driven activity and very minor ash emissions. Ashfall in December 2012 and January-February 2013 are reported in table 12. Exact ashfall dates were unreported due to the minor nature of ashfall events and irregular visits. Table 12 summarizes eruptive activity at White Island during this report period.

Table 12. December 2012-11 October 2013 eruptive activity at White Island. Column headings are eruptions, seismicity, and a brief eruptive narrative. Dates in the second column from the right came from Volcanic Alert Bulletin reports. Notes refer to image and video records found in the Reference section under GNS. Courtesy of GNS.

Ashfall in 2013, 20 August eruption, and 11 October eruption. On 1 January 2013, GNS volcanologists reported the spiny lava dome (figure 58) remained unchanged from December 2012. The lava dome temperature was 200-240°C, up from 187°C in December, and the nearby 'hot lake' was 70-80°C, unchanged from December.

GNS volcanologist Brad Scott, who visited the island, commented in the 22 January Volcano Alert Bulletin "the hydrothermal activity is some of the most vigorous I have seen at White Island for many years." Scott also reported the hot lake had disappeared, replaced by a small tuff cone. That cone was the main point of emission for steam and gas. On 30 January 2013, the active vent continued to produce intermittent vigorous bursts of mud, rock, steam, and gas rising 50-100 m high without detectable ash in the plume. On 31 January, gas fluxes were 2,000 metric tons per day (t/d) for carbon dioxide (CO₂), 600 t/d for sulfur dioxide (SO₂), and 19 t/d for hydrogen sulfide (H₂S).

Figure 58. This is the same photo seen in figure 56, but in this case it shows infrared temperatures of White Island's dome and lakes taken on 7 January 2013. The active vent continued to produce vigorous bursts of mud, rock, steam, and gas reaching 50-100 m high. Ash was not carried into the plume at the time of this photo. The small lake to the left is the cool lake (35°C) and the lava-dome crater is partially hidden under the steam plume. Courtesy of GeoNet. Image by Brad Scott, GNS Science.

On 7 February, SO₂ and CO₂ rates were similar to measurements in January: SO₂ was 560 t/d and CO₂ was 1,800 t/d. The main steam and gas plume came from the ash cone occupying the previous hot lake crater. Small explosive eruptions in the active crater and seismicity, which had been occurring for three weeks prior to the week of 11 February, became less intense.

During 23-24 February 2013 minor ash erupted from the active vent. Tremor was consistent with the level of unrest seen over the past month. On 25 February, the ash emissions had ceased and had been replaced by steam-and-gas explosions from the active vent. The level of volcanic tremor increased, associated with the reappearance of fluids in the vent area (figure 55). The unrest was among the most vigorous that Scott had observed during visits to White Island. He was quoted in the 25 February report to say "the unrest continues and we continue to see small scale explosive events. Larger explosive eruptions can occur at any time with little or no warning. As always a high level of caution should be taken if visiting the island."

The crater on 4 March 2013 contained an ash cone surrounded by water (figure 59), which replaced the previous hot lake as the primary source of steam in the crater. On 29 April 2013, GNS reported that ash had ceased being emitted at an undisclosed date during the first part of the month. In April, low to moderate seismic tremor was detected, while degassing continued. Rainfall during April caused the two lakes to combine. The maximum lake temperature was ~ 62°C. The lava dome temperature was ~200°C.

Figure 59. A 4 March 2013 image looking W ~600 m from the crater. A new ash cone formed at the hot lake emitted gas and steam. N of the ash cone sits the cool lake. Image by B. J. Scott, GNS Science.

During April, May, and June 2013 the crater lake reformed. On 9 July 2013 GNS reported small volcanic earthquakes occurred approximately every 70 seconds, with changing amplitude and frequency. GNS volcanologists visiting on 26 July observed gas venting through the small lake with debris ejected 20-30 m vertically. By 5 August this minor venting had declined and tremor had decreased to near-background levels (see figure 55).

A small eruption took place in August 2013 detected by a constellation of instruments on White Island which included audio receivers, seismometers, temperature sensors, and IR sensors. The eruption was captured on video media by several cameras near the crater rim and a camera stationed ~45 km S at NZ's North Island (figure 60). The eruption occurred at 1023 on 20 August 2013 (NZ local time) and continued for about 10 minutes. As seen from the mainland, it mainly produced a steam plume rising to ~4 km, and slowly trending W before dispersing (figure 61). The eruption originated from a vent in the active crater that had been experiencing very small mud eruptions in early to mid-August 2013. This eruption was preceded by strong tremor.

Figure 60. Map locating GNS video camera which resides at Whakatane on NZ's North Island ~50 km S of White Island. It recorded the 20 August 2013 eruption seen in the next figure. Map courtesy of 100% New Zealand (2014) and revised by GVP.

Figure 61. Image of White Island taken from Whakatane WebCam video of the 20 August 2013 eruption. The image was in the GNS 22 August 2013 report. Courtesy of Geonet.

The N rim webcam captured visual and thermal infrared images of the eruption. Both the N Island camera and the N rim camera video links were included in the GNS 22 August report. The 20 August eruption ejected mud and rocks a short distance from the vent and produced large volumes of white steam. Weather radar observations suggested that the steam also contained a small proportion of volcanic ash. The hazards posed by the eruption were restricted to the island or possibly vessels anchored nearby. By 21 August 2013, White Island activity had diminished. Volcanologists flying over the island on 23 August observed the return of a small lake. Steam emissions chiefly emerged from the cone area, but their intensity dropped as the small lake reformed. SO₂, CO₂, and H₂S gases recorded during the flight had diminished to pre-eruption levels.

The 7 October GNS report described the changes associated with the August 2013 eruption. A new basin further to the NE of the previous lake filled with water. The lava dome area appeared unchanged while nearby a small pond had formed. Landslides had altered several of the main crater walls, the result of processes most likely related to weather events. Daily SO₂ gas flux measured the previous month ranged from 117 to 662 t/d, typical of the last 12-18 months but higher than before July 2012. In early October it remained elevated.

A moderate but potentially dangerous eruption emerged on 11 October 2013. The eruption sequence began 4 October, with a small energetic steam emission followed by intensified tremor. On 8 October, a period of strong seismicity prevailed accompanied by acoustic signals, and a minor steam and mud eruption that produced a steam plume. During the evening of 11 October, a moderate explosive eruption lasted ~1 minute based on data from acoustic and seismic sensors. The N rim camera images showed that the eruption emerged from the crater's central vent. The explosive eruption produced an ash cloud that expanded across the main crater floor. New mud deposited on the crater floor was evident in the web camera images taken the following day (figure 63). The deposit was thick enough to bury much of the small scale topography on parts of the crater floor. This image and the muddy stratigraphic layer established the baseline for subsequent changes created by volcanism and erosion.

Figure 62. On 12 October 2013 at 0650, the crater floor and walls lie draped beneath fresh deposits of dark gray mud from the eruption the night before. Courtesy of Geonet.

The October 2013 mud eruption was the largest of recent events. GNS volcanologists estimated it would have been life threatening to people on the island. Volcanic tremor gradually decreased after 11 October returning to levels equivalent to the middle of the prior week (see figure 55). The mud deposited on 11 October 2013 had clearly begun to erode by early December 2013. Around this time a new camera on the W rim captured active steam-and-gas plumes from several vents and the large lake seen in 2012 (figure 63). On 23 December 2013 GNS reported an absence of eruptive activity since the 11 October eruption. Seismicity remained low; gas flux, variable. Average daily SO₂ flux ranged from 300 to over 1,000 t/d. Prior to 2012, daily averages were generally less than 300 t/d.

Figure 63. An 11 December 2013 image showing gullies and rills as erosion set in on the fresh mud coating within the crater formed by the 11 October 2013 eruption. Several vents produced active steam plumes and the lake had returned. Courtesy of GNS.

January 2014 changes to the crater and rate of gas emitted. During several January visits, GNS Science staff observed a continued rise in water level of the crater lake, reaching ~5 m higher than in late 2013. The average daily SO₂ flux ranged from 133 to 924 t/d. GNS volcanologists reported an absence of further eruptive activity since the 11 October 2013 eruption.

On 15 January 2014, a thermal infrared image was taken by a portable infrared sensor pointed W from the western crater rim (figure 64). The image shows part of the Crater Lake (oval labeled El1), the area of the 2012 lava extrusion below the lake (large rectangular box labeled Ar1), and a hot fumarole on the S edge of the Crater Lake (small rectangle in the center labeled Ar2). Maximum temperatures were 58°C at the lake, 285°C forAr1, and 297°C for Ar2. These observations confirmed that hot volcanic gases were still passing through these vents.

Figure 64. Thermal infrared image taken on 15 January 2014, with scale at right and areas with analysis at upper left. The oval area (El12) includes part of the Crater Lake, and the area of the 2012 lava extrusion (in rectangular Ar1). The smaller rectangle, Ar2, includes a hot fumarole on the southern edge of the Crater Lake. Courtesy of GeoNet.

References.

100% New Zealand, accessed 5 May 2014, New Zealand Map (URL: http://www.newzealand.com/int/map/).

GNS (22 August 2013), White Island eruption 20 August 2013 - 5x speed, (URL: http://info.geonet.org.nz/display/volc/2013/08/20/White+Island+Eruption.)

GNS (22 August 2013), White Island eruption 20 August 2013 Crater rim - 5x speed, (URL: http://info.geonet.org.nz/display/volc/2013/08/20/White+Island+Eruption).

GNS (14 October 2012), Un-named video clip URL reference in body of GNS report (URL: http://info.geonet.org.nz/pages/viewpage.action?pageId=7241739).

Geologic Background. The uninhabited Whakaari/White Island is the 2 x 2.4 km emergent summit of a 16 x 18 km submarine volcano in the Bay of Plenty about 50 km offshore of North Island. The island consists of two overlapping andesitic-to-dacitic stratovolcanoes. The SE side of the crater is open at sea level, with the recent activity centered about 1 km from the shore close to the rear crater wall. Volckner Rocks, sea stacks that are remnants of a lava dome, lie 5 km NW. Descriptions of volcanism since 1826 have included intermittent moderate phreatic, phreatomagmatic, and Strombolian eruptions; activity there also forms a prominent part of Maori legends. The formation of many new vents during the 19th and 20th centuries caused rapid changes in crater floor topography. Collapse of the crater wall in 1914 produced a debris avalanche that buried buildings and workers at a sulfur-mining project. Explosive activity in December 2019 took place while tourists were present, resulting in many fatalities. The official government name Whakaari/White Island is a combination of the full Maori name of Te Puia o Whakaari ("The Dramatic Volcano") and White Island (referencing the constant steam plume) given by Captain James Cook in 1769.

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