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).

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/).

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/).

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/).

Although the current period of activity at Ambrym has been ongoing since June 1996, direct observations have been intermittent. Most recently, there have been reports of visits during January and February 2000 (BGVN 25:02 and 25:04), August-October 2000 (BGVN 26:02), and August 2001 and December 2002 (BGVN 27:12). Another report of scientific investigations from July 2000 is presented below. These observations are supplemented by MODIS data that indicate continued lava lake activity through much of 2001 and 2002.

Observations during July 2000. During 8-11 July 2000, David Nakedau and Douglas Charley reached Ambrym and camped in the caldera, after the necessary authorizations from local chiefs. On 11 July, French and Italian scientists joined the group. During the following days two stations were installed, one close to the village of Lalinda, the other on the E flank of Benbow cone. The first station, composed of a broadband STS2 seismometer, was installed on a basaltic lava flow with the aim of recording local volcano-related seismicity and tectonic earthquakes. The summit station was equipped with a short-period Mark seismometer to record the activity of the lava lake that used to be visible at Benbow until 1999 and now has drained back at a greater depth due to the Ms 7.1 earthquake of 26 November 1999. The first results from the analysis of these data are currently in press (Carniel and others, 2003).

On 11 July 2000 a visit was made to the Niri Taten Mbwelesu crater, where only fumarolic activity could be observed. The crater name means "the son of the female pig," given after its birth in 1989 near the existing Mbwelesu (the pig) and Niri Mbwelesu (the female pig). At the request of local residents, this crater was renamed Mbogon Niri Mbwelesu in December 2002 (BGVN 27:12). After more than a day of continuous rain, on 13 July the installation of the station on the Benbow rim was accomplished. During 13 July strong degassing noises were heard only sporadically from the Southern crater, which was otherwise showing low degassing rates and low-level noises. The southern crater has been observed since the first visits of Douglas Charley, and was the site where the lava lake was observed until 1999. The Northern crater, on the contrary, was not observed by Charley before 1997. Another small vent used to be present on its W side, but was completely buried by 1999 collapses. During 13 July, from the rim observations, this crater appeared to be the source of the strongest noises.

During the following days, two descents were made into Benbow using ropes, one on 14 July by Carniel and Fulle with local guides Jimmy and Isaac; the other was made on 16 July by Charley, Garaebiti, Wallez, and Jimmy. The Southern, older crater, was obstructed and conical in shape. From it's central part, significant blueish-colored degassing was observed, indicating sulfur dioxide. On 14 July visible degassing activity was not accompanied by noticeable sound. On 16 July some small explosions were observed at this vent, which ejected centimeter-sized fragments. On the N side, a fault full of sulfur deposits was visible. Numerous concentric faults were also visible around the vent on the n, E, and W sides. A significant zone of fumarolic activity was concentrated on the N flank of the vent, mainly composed of water vapor. Other small fumaroles were located around the vent. A number of pits were aligned in the W and S border, with the most significant fumarolic activity at the S side, where blueish sulfurous gas escaped continuously.

The Northern crater emitted significant water vapor plumes. To the N and to the S of the vent, two deep tracks were created by water runoff during strong rainfalls. To the E, the border of the vent was formed by rock debris, which, according to the guide Jimmy, was emplaced as a consequence of the strong 26 November 1999 earthquake. Both on 14 July and on 16 July the sound from the N crater appeared to be much lower than from the S crater, an observation opposite to the one made from the Benbow rim on 13 July. On 14 July scientists observed several more dense water vapor clouds, some of them accompanied by the fall of very small (less than 1 cm) light lithic fragments.

Marum, and the surrounding vents of Mbwelesu, Niri Mbwelesu, and Niri Taten Mbwelesu, were visited again on 16 July. Mbwelesu was intensely degassing, which often precluded direct observation of the crater. On the SE side, where a lava lake used to be, only a static mud pond could be seen. Also Taten Mbwelesu crater was showing intense degassing accompanied by strong noise, which made observation difficult. Niri Taten Mbwelesu showed intense degassing but no noise. The dropping of rocks into the pit confirmed the presence of a mud pond at the bottom, at an approximate depth of 200 m.

On 17 July the scientists left the volcano for the village of Lalinda, where they met with the custom chief and the population in order to inform them about the activity of the volcano and about the research. On the early morning of 19 July the two eruptive plumes from Ambrym's main cones were clearly visible at a distance from the island of Paama. However, only the plume produced by Marum was colored pink-orange; this observation suggests the presence of lava at shallow depth in one of its vents, although such a feature was not observed directly during the previous days.

MODVOLC Thermal Alerts, 2001-2002. MODIS detected quasi-continuous thermal alerts for Ambrym throughout 2001 and 2002 (figure 8). Moreover, these occur fairly equally in two clusters interpreted as representing Benbow and Marum (figure 9). These data provide strong evidence in favor of continued lava lake activity. The highest alert ratios for the period of -0.107 on 9 April 2001 in Marum and -0.116 on 3 November 2001 in Benbow may represent episodes of overturn. Marum appears to have been particularly active also during January-February 2002 when the anomaly usually consisted of either 4 or 6 alert-pixels (figure 9). Anomalies continued in January-February 2003.

Figure 8. MODIS thermal alerts on Ambrym during 2001-2002. Courtesy of Diego Coppola and David Rothery, The Open University.

Figure 9. Locations of alert-pixels on Ambrym during 2001-2002. The intracaldera craters are Benbow (B) and Marum (M). The base map is not independently geolocated, so the alert-pixel overlay has been migrated to place the two clusters over the likely active craters. Base map is from SEAN 14:04, modified from geological (New Hebrides Geological Survey, 1976) and pedomorphological (Quantin, 1978) maps. Courtesy of Diego Coppola and David Rothery, The Open University.

References. Quantin, P., 1978, Archipel des Nouvelles-Hébrides: Atlas des Sols et de quelques Données du Milieu: Cartes Pédologiques, des Formes du Relief, Géologiques et de la Végétation; ORSTOM (18 sheets).

Carniel, R., Di Cecca, M., Rouland, D., accepted Feb 2003, Ambrym, Vanuatu (July-August 2000): Spectral and dynamical transitions on the hours-to-days timescale: JVGR.

Geologic Background. Ambrym is a large basaltic volcano with a 12-km-wide caldera formed during a major Plinian eruption with dacitic pyroclastic flows about 1,900 years ago. A thick, almost exclusively pyroclastic sequence, initially dacitic then basaltic, overlies lava flows of a pre-caldera shield volcano. Post-caldera eruptions, primarily from Marum and Benbow cones, have partially filled the caldera floor and produced lava flows that ponded on the floor or overflowed through gaps in the caldera rim. Post-caldera eruptions have also formed a series of scoria cones and maars along a fissure system oriented ENE-WSW. Eruptions have been frequently reported since 1774, though mostly limited to extra-caldera eruptions that would have affected local populations. Since 1950 observations of eruptive activity from cones within the caldera or from flank vents have occurred almost yearly.

Information Contacts: Diego Coppola and David A. Rothery, Department of Earth Sciences, The Open University, Milton Keynes, MK7 6AA, United Kingdom; Roberto Carniel, Università di Udine, Italy (URL: http://www.swisseduc.ch/stromboli/); Douglas Charley, Sandrine Wallez, and David Nakedau, Département de la Géologie, des Mines et des Ressources en eau, Vanuatu; Marco Fulle, Osservatorio Astronomico, Trieste, Italy (URL: http://www.swisseduc.ch/stromboli/); Esline Garaebiti, Université de Clermont-Ferrand, France; Daniel Rouland, E.O.S.T., Strasbourg, France; Geneviève Roult, I.P.G., Paris, France.

Throughout 2001 and 2002, MODIS detected quasi-continuous thermal alerts at Bagana (figure 1). The most recent report is from August 1995 (BGVN 20:08). The MODIS data are presented here as valuable objective evidence of more recent activity. MODIS thermal alerts were recorded on 16 September, 3, 19, and 26 November, and 10, 12, 28, and 30 December 2000. The 2001-2002 MODIS anomalies were relatively stable with an average alert ratio of -0.63 and generally they consisted of 1 or 2 alert pixels. The maximum alert ratio detected (-0.51) occurred on 21 November 2002 when the number of alert-pixels was at its two-year maximum of 5. This is likely to indicate a higher degree of activity than usual, in which case it is likely to represent effusion of a new lava flow or a pyroclastic flow in the act of emplacement. Coordinates of alert pixels generally clustered tightly around the summit, with a slight preference towards the NW (figure 2). Activity may be genuinely concentrated on this part of the cone, but another explanation would be a 300-m error in the supposed location of the summit relative to the MODIS geocoding. However, the 5-pixel alert of 21 November 2002 is strung out towards the E, which is likely to represent an eastward-flowing lava (or pyroclastic) flow ~2 km long.

Figure 1. MODIS thermal alerts on Bagana during 2001-2002. Courtesy of Diego Coppola and David Rothery, The Open University.

Figure 2. Locations of MODIS alert-pixels on Bagana during 2001-2002. Courtesy of Diego Coppola and David Rothery, The Open University.

Geologic Background. Bagana volcano, in a remote portion of central Bougainville Island, is frequently active. This massive symmetrical cone was largely constructed by an accumulation of viscous andesitic lava flows. The entire edifice could have been constructed in about 300 years at its present rate of lava production. Eruptive activity is characterized by non-explosive effusion of viscous lava that maintains a small lava dome in the summit crater, although occasional explosive activity produces pyroclastic flows. Lava flows with tongue-shaped lobes up to 50 m thick and prominent levees descend the flanks on all sides.

Information Contacts: Diego Coppola and David A. Rothery, Department of Earth Sciences, The Open University, Milton Keynes, MK7 6AA, United Kingdom.

After three months of activity, the flank eruption at Etna that began on 27 October 2002 finished on 28 January 2003. Lava flows and Strombolian explosions in January were confined to the S-flank vent located at 2,750 m elevation. Lava flows formed a fan and covered the previous lava flow field. A decrease in effusion during January was suggested by the shorter lava flow lengths of less than 2 km, which formed a complex flow field with small lava tubes. Strombolian activity from the 2,750-m cinder cone significantly declined on 27 January and disappeared on 29 January. Lava flows slowed on 27 January, and were no longer fed by the 29th, and thus cooled down. At this time SO₂ output decreased significantly, reaching the lowest value of 2,000 tons/day on 29 January 2003. Volcanic tremor amplitude showed a marked decrease on 27 January, and on 28 January at 2240 it returned to background levels, signaling the end of the eruption.

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: Istituto Nazionale di Geofisica e Vulcanologia (INGV), Sezione di Catania Piazza Roma 2, 95123 Catania (URL: http://www.ct.ingv.it/).

Explosions, ash emission, and lava flows took place during January-February and July 2002 (BGVN 27:08). MODIS thermal alerts were recorded monthly throughout 2002. CONRED reported that during the last 3 months of 2002, a change in behavior at Fuego was characterized by an increase in Strombolian activity. Ash emission and pyroclastic flows threatened communities to the SW, which prepared for evacuation (figure 5). This report covers the period of 26 December 2002 through mid-January 2003.

Figure 5. This condensed-format map of Fuego hazards was intended as a poster when created by the Guatemalan agency CONRED. North is towards the top; the original map key and credits are truncated from this version. The map shows six different hazard zones with a gradation of expected hazards, as well as some of the critical close-in population centers and their suggested departure routes. The large population center Antigua lies off the map, 17 km NE of Fuego's summit. Courtesy of CONRED.

According to news reports, an explosive eruption and partial crater collapse occurred on 26 December 2002 around 0905. An ash cloud was generated that reached ~2 km above the volcano and drifted W toward the Yepocapa region. Neither damage nor injuries were reported.

The Washington VAAC reported that an eruption began at Fuego on 8 January 2003 around 0500. According to INSIVUMEH, as of 1100 that day the eruption continued with ash explosions and lava flow emission. A steam-and-ash column rose to 5.7 km altitude and drifted to the W. In addition, two small-to-moderate pyroclastic flows traveled down the Santa Teresa river valley. Seismic signals continued to show evidence of magma ascent, but fewer in number with 15-25 explosions per minute recorded. This suggested continued effusive emissions for a number of hours. During the eruption, ash fell in an elliptical area chiefly W of Fuego; other events included rumbling, and fumarolic activity. CONRED stated that the Alert Level was raised to Orange and several people were evacuated from the town of Sangre de Cristo. According to a news report volcanism decreased the following day, so the Alert Level was lowered from Orange to Yellow.

INSIVUMEH reported that as of 19 January moderate eruptions continued at Fuego that produced ash clouds to 1.5-3 km altitude. Ash drifted to the S and SW, depositing fine ash in the areas of Rocela, Panimache, and Palo Verde. In addition, incandescent avalanches traveled down canyons on the volcano's flanks. Table 2 shows ash advisories issued for Fuego by the Washington VAAC during January.

Table 2. Volcanic ash advisories issued for Fuego during January 2003. Courtesy Washington VAAC.

Observations during 3-13 January 2003. Craig Chesner and Sid Halsor reported continuous low-level volcanic activity and one larger event at Fuego during a 10-day site visit. Nearly continuous Strombolian-type spattering and fountaining were observed during the night of 3 January. Bombs and blocks, ejected up to several tens of meters above the summit vent, fell on the upper flanks. No ash was observed during this activity, although ashy trails were generated from ejecta tumbling down the steep southern and eastern slopes of the volcano. On 4 January, no lava fountaining was observed, and activity was characterized by steady and passive emission of a gas plume.

Energetic fountaining and spattering were observed during the night of 5 January from a vantage point on the summit of nearby Agua volcano. Fourteen Strombolian explosions occurred at intervals of 5-61 minutes during 5 hours of continuous observation. These explosions ejected incandescent material ~100 m above the cone, showering the upper flanks with blocks and bombs. Typically, each explosion was accompanied by a loud detonation and an ash plume, and led to several minutes of vigorous fountaining. This activity continued during the morning of 6 January, but by evening, no incandescent activity was apparent at the summit vent.

On the morning of 7 January, a new lava flow was noted on the southern flank, and ash trails generated from spalling blocks suggested that it was active. In the evening, vigorous lava fountaining and spattering had resumed, and the lava flow was seen descending from the summit area to the S. A nearly continuous cascade of pyroclasts produced incandescent rock falls on the upper flanks of the cone.

At 1030 on 8 January, an expansive plume of ash had developed over the summit area. Concurrent fountaining and pulsating eruptions of ash were observed from a vantage point near Alotenango, a few kilometers NE of the volcano. By 1100, the eruption column was broadening at its base, darkening in color, and extending to considerable height above the summit. The most intense phase of the eruption occurred roughly between 1145 and 1215 (figure 6). During this time, loud rumbling and swashing-like sounds accompanied continuous fountaining and frequent, energetic eruptions of ash. A bright incandescent fire fountain, several tens of meters high, was clearly observed at the base of the ash column. Twice during this time period, lateral ash columns, presumably associated with pyroclastic flows, were noted descending towards the W. A convective column engulfed the summit area and appeared to rise several kilometers to an altitude of ~2-3 times the height of the cone.

Figure 6. Image of Fuego eruption taken on 8 January around 1200. View looking W from about 10 km away. The eruption cloud was dispersed westward and the ground-hugging smaller cloud just W from the summit area may have been associated with reported pyroclastic flows. Courtesy Sid Halsor.

By 1245, eruptive activity appeared to subside with eruptions becoming less frequent and gradual lightening in color of the ash cloud. Throughout the afternoon, the ash cloud drifted westward and dispersed ash-laden air over a broad region. A circumnavigation of the volcano during the afternoon indicated no detectable ash fall along the dispersal axis at a distance of ~9 km. However, a slight discoloration of vegetation was noted to the E of Yepocapa. Intermittent low to moderate ash eruptions continued throughout the day and summit fountaining was observed at night. The following morning (9 January), no visible activity was noted over a brief observational period. However, the summit area surrounding the vent had clearly changed, being asymmetrically higher to the NW. From 10-13 January, activity was characterized by periodic low-level Strombolian explosions and associated ash plumes. These plumes could be seen from as far away as western El Salvador.

Geologic Background. Volcán Fuego, one of Central America's most active volcanoes, is also one of three large stratovolcanoes overlooking Guatemala's former capital, Antigua. The scarp of an older edifice, Meseta, lies between Fuego and Acatenango to the north. Construction of Meseta dates back to about 230,000 years and continued until the late Pleistocene or early Holocene. Collapse of Meseta may have produced the massive Escuintla debris-avalanche deposit, which extends about 50 km onto the Pacific coastal plain. Growth of the modern Fuego volcano followed, continuing the southward migration of volcanism that began at the mostly andesitic Acatenango. Eruptions at Fuego have become more mafic with time, and most historical activity has produced basaltic rocks. Frequent vigorous eruptions have been recorded since the onset of the Spanish era in 1524, and have produced major ashfalls, along with occasional pyroclastic flows and lava flows.

Information Contacts: Gustavo Chigna M. and Otoniel Matías, Instituto Nacional de Sismologia, Vulcanologia, Meteorologia e Hidrologia (INSIVUMEH), Ministero de Communicaciones, Transporto, Obras Públicas y Vivienda, 7a. Av. 14-57, zona 13, Guatemala City 01013, Guatemala (URL: http://www.insivumeh.gob.gt/); Juan Pablo Ligorria, Coordinadora Nacional para la Reducción de Desastres (CONRED), Av. Hincapié 21-72, Zona 13, Guatemala City, Guatemala; Washington Volcanic Ash Advisory Center, NOAA Satellite Services Division, NESDIS E/SP23, NOAA Science Center, Room 401, 5200 Auth Road, Camp Springs, MD 20746, USA (URL: http://www.ospo.noaa.gov/Products/atmosphere/vaac/); Craig A. Chesner, Geology/Geography Department, Eastern Illinois University, Charleston, IL 61920, USA; Sid P. Halsor, GeoEnvironmental Science and Engineering, Wilkes University, Wilkes-Barre, PA 18766; EFE via COMTEX, Prensa Libre, Siglo XXI.

Between 13 May 2000 and 30 January 2003, thermal alerts on Heard Island occurred on the following dates: 24 May; 3, 5, and 6 June; 25 September; 29 October; 5, 15, 19, and 24 November; 16, 17, 26, and 30 December 2000; and 2 February 2001 (figure 7). Since then no further thermal alerts have been recorded. There have been no reports of May-June 2000 activity on Heard Island published in the Bulletin. However, Rothery and Coppola are confident that the MODIS data prove high-temperature volcanic activity at these times. The late-2000 period of MODIS thermal alerts is substantiated by reports from ships and helicopters. The first of these, "fumarolic activity" on 19 October (BGVN 25:11), is 24 days later than the first MODIS thermal alert in this period. A fresh lava flow was suspected but unproven on 3 February (BGVN 26:02), and two incandescent vents were photographed on the same day (BGVN 26:03). The interpretation of the MODIS data is that lava effusion is likely. The locations of the alert pixels (figure 8) suggest that activity was on the WSW side of the summit, and may have extended about halfway to the shore.

Figure 7. MODIS detected alerts on Heard during January 2000-March 2001. Courtesy of Diego Coppola and David Rothery, The Open University.

Figure 8. Locations of alert-pixels on Heard during 2001-2002. Grid squares are 1 km on a side. Base map from BGVN 17:05 (after Barling, 1990). Courtesy of Diego Coppola and David Rothery, The Open University.

Reference. Barling, J., 1990, Heard and McDonald Islands, in Le Masurier, W., and Thomson, J., eds., Volcanoes of the Antarctic Plate and southern Oceans: American Geophysical Union, Washington DC, p. 435-441.

Geologic Background. Heard Island on the Kerguelen Plateau in the southern Indian Ocean consists primarily of the emergent portion of two volcanic structures. The large glacier-covered composite basaltic-to-trachytic cone of Big Ben comprises most of the island, and the smaller Mt. Dixon lies at the NW tip of the island across a narrow isthmus. Little is known about the structure of Big Ben because of its extensive ice cover. The active Mawson Peak forms the island's high point and lies within a 5-6 km wide caldera breached to the SW side of Big Ben. Small satellitic scoria cones are mostly located on the northern coast. Several subglacial eruptions have been reported at this isolated volcano, but observations are infrequent and additional activity may have occurred.

Information Contacts: David A. Rothery and Diego Coppola, Department of Earth Sciences, The Open University, Milton Keynes MK 6AA, United Kingdom.

During most of April 2002, residents of Popondetta Town, ~21 km NNE of Lamington, and villages near the volcano were besieged by rumors of the volcano showing signs of renewed activity. Later investigations found no evidence of volcanism. Some of the rumors included fire and "smoke" from the volcano, felt earthquakes, and noises. As a result of the rumors, a couple of schools closed, some residents buried their belongings for safekeeping, and others prepared to evacuate. At the time it was difficult for the Rabaul Volcano Observatory (RVO) to confirm or deny the reports because the monitoring equipment for Lamington had not been operating since October 2001.

Based on information from Geoscience Australia and satellite imagery, the Darwin VAAC reported that an E-drifting ash cloud from Lamington seemed to be evident on satellite imagery on 22 April at 1711. The height of the cloud was not known due to thunderstorms in the area making it difficult to detect ash. However, on 23 April at 1105 a flight service reported that no volcanic activity was evident at Lamington. By 26 April Darwin VAAC had concluded that the suspicious cloud was not related to volcanism.

Investigations by the Geological Survey of PNG (RVO and PMGO) of the Department of Mining were carried out during 21-25 April (courtesy of funding from AusAID). On 28 April 2002, RVO reported that, after 3-4 weeks of rumor and speculation suggesting Lamington was showing signs of renewed volcanic activity, none had occurred. Monitoring equipment was restored during the trip, and seismic recordings during those few days showed no seismicity. A very brief aerial inspection of the summit area showed no concrete evidence of renewed volcanic activity. There were no changes in the topographical features or vegetation to indicate recent activity. Small amounts of vapor were being emitted from a few fumarole locations, but that activity was not a new development. There have been no additional reports of unusual activity or increased seismicity through February 2003.

Geologic Background. Lamington is an andesitic stratovolcano with a 1.3-km-wide breached summit crater containing a lava dome that rises above the coastal plain of the Papuan Peninsula of New Guinea north of the Owen Stanley Range. A summit complex of lava domes and crater remnants tops a low-angle base of volcaniclastic deposits dissected by radial valleys. A prominent broad "avalanche valley" extends northward from the breached crater. Ash layers from two early Holocene eruptions have been identified. In 1951 a powerful explosive eruption produced pyroclastic flows and surges that swept all sides of the volcano, killing nearly 3,000 people. The eruption concluded with growth of a 560-m-high lava dome in the summit crater.

Information Contacts: Ima Itikarai, Rabaul Volcano Observatory (RVO), P.O. Box 386, Rabaul, Papua New Guinea.

Based on information from a pilot report, the Darwin Volcanic Ash Advisory Center (VAAC) reported that an ash cloud from Langila was observed on 11 July 2002 at about 0900 and rose to a height of ~3.4 km. No ash was identifiable on satellite imagery. This was the first reported activity since October 2000 (BGVN 25:11). RVO noted that the observatory at Langila was broken into in 2000 and had its radio stolen. There are no telephones nearby, and since then they have had to rely on mailed reports (very infrequent), reports from pilots, and the Darwin VAAC.

MODVOLC Thermal Alerts, 2001-2002. MODIS thermal alerts occurred on 25 May, 19 and 26 June, 12-15, 24, and 26 August, and 13 October 2002; there were no alerts in 2001. The largest number of alert pixels was 3 on 14 August. The highest alert ratio was -0.648 on 24 August. Putting these two together suggests the most intense activity in mid-late August, but this could be severely biased by cloudy days. Available maps do not allow an accurate location of the summit, and are not of a scale to provide accurate registration. However, all but one of the alert pixels are within ~1 km of each other so there appears to be a spatially restricted event consistent with a short flow (less than a few hundred meters long) or a small dome or incandescent vent a few tens of meters across, which would affect more than one pixel when the pixel boundary fell across, or very close to, the flow, dome, or vent. Both recently active craters (Crater 1 and Crater 2) are also within a 1-km area, along a NE-SW trend, similar to the orientation of the alert pixels.

Geologic Background. Langila, one of the most active volcanoes of New Britain, consists of a group of four small overlapping composite basaltic-andesitic cones on the lower E flank of the extinct Talawe volcano in the Cape Gloucester area of NW New Britain. A rectangular, 2.5-km-long crater is breached widely to the SE; Langila was constructed NE of the breached crater of Talawe. An extensive lava field reaches the coast on the N and NE sides of Langila. Frequent mild-to-moderate explosive eruptions, sometimes accompanied by lava flows, have been recorded since the 19th century from three active craters at the summit. The youngest and smallest crater (no. 3 crater) was formed in 1960 and has a diameter of 150 m.

Information Contacts: Diego Coppola and David A. Rothery, Department of Earth Sciences, The Open University, Milton Keynes, MK7 6AA, United Kingdom; Darwin VAAC, Bureau of Meteorology, Northern Territory Regional Office, PO Box 40050, Casuarina, NT 0811, Australia (URL: http://www.bom.gov.au/info/vaac/); Steve Saunders, Rabaul Volcano Observatory (RVO), P.O. Box 386, Rabaul, Papua New Guinea.

During 2001-2002, MODIS alerts occurred only in June 2001 (figure 18). The first anomaly was detected on 9 June at 2210. This consisted of three alert-pixels with a maximum alert ratio of -0.299, and can be attributed to lava flows from a new vent 200 m above sea level on the NW side of the cone, which appeared in association with a plume-forming eruption on 8 June at around 1100 (BGVN 26:08). The only other MODIS alert was 14 June at 2225 local time, and consisted of two pixels closer to the summit (figure 6). According to a local guide (BGVN 26:08), a new flow was erupted in roughly this location on 15 June. MODIS alert data provide evidence that emplacement of this flow actually began during the previous night.

Figure 18. Locations of alert-pixels on Lopevi during 2001-2002. Courtesy of Diego Coppola and David Rothery, The Open University. Base map is from BGVN 26:08; courtesy of Institut de recherche pour le développement (IRD), Vanuatu.

Geologic Background. The small 7-km-wide conical island of Lopevi, known locally as Vanei Vollohulu, is one of Vanuatu's most active volcanoes. A small summit crater containing a cinder cone is breached to the NW and tops an older cone that is rimmed by the remnant of a larger crater. The basaltic-to-andesitic volcano has been active during historical time at both summit and flank vents, primarily along a NW-SE-trending fissure that cuts across the island, producing moderate explosive eruptions and lava flows that reached the coast. Historical eruptions at the 1413-m-high volcano date back to the mid-19th century. The island was evacuated following major eruptions in 1939 and 1960. The latter eruption, from a NW-flank fissure vent, produced a pyroclastic flow that swept to the sea and a lava flow that formed a new peninsula on the western coast.

Information Contacts: Diego Coppola and David A. Rothery, Department of Earth Sciences, The Open University, Milton Keynes, MK7 6AA, United Kingdom.

The Rabaul Volcano Observatory (RVO) reported that the Strombolian eruption from Southern Crater of Manam on 20 May (BGVN 27:05) ended the next day after the last ash-laden clouds were released. Activity then declined to emissions of very small amounts of thin white vapor. A seismograph was installed at Warisi village on the SE side of the island on 22 May 2002. This is the first seismograph to be deployed since Manam Observatory was shut down on 16 January 2001. During 22-24 May seismicity was at a moderate level, mainly associated with many low-frequency volcanic earthquakes. During 25 May-2 June seismicity declined and fluctuated at a low level. At 1351 on 31 October 2002 a pilot reported "light brown dust/smoke" from Manam drifting S toward the main coastline at an estimated height of ~3.0 km. A possible thin low-level plume was seen on satellite imagery extending ~18.5 km N at 1425 that day, but was not seen on later imagery.

MODVOLC Thermal Alerts, 2001-2002. Throughout 2001 and 2002, thermal alerts for Manam occurred only in April and May 2002. The first alert occurred on 7 April and may reflect the tail end of 14-31 March activity reported by RVO when ejection of red incandescent lava fragments was observed (BGVN 27:05). MODIS detected no thermal alerts during that period, which could be a result of cloud cover or because activity was too slight or too intermittent to have triggered an alert.

The number of alert pixels and the value of the alert ratio both increased to a peak on 20 May, the date of a moderate-sized Strombolian eruption reported by RVO. The eruption continued until about 1400 on 20 May. Subsequently, activity declined and consisted of forceful ash emission in moderate volumes (BGVN 27:05). The biggest MODIS anomaly on 20 May was detected at 1015 with 10 alert-pixels and a maximum ratio of 0.178. This is five hours after the first known report of activity. After 12 hours the anomaly was smaller with seven alert-pixels and a maximum alert ratio of -0.322. On 21 May the decreasing thermal anomaly was represented by one alert-pixel with a ratio of -0.783.

During the earlier part of May, MODIS alerts suggested noteworthy activity at Manam that has not, to our knowledge, been reported elsewhere. The anomaly dropped briefly to a minimum on 16 May, which could reflect a lull in activity or partial cloud cover.

The centers of most alert-pixels for Manam lie systematically NW of the summit (figure 11). Bearing in mind that the strongest anomaly should occur at the summit and that ejecta appears to have gone mostly to the SE (BGVN 27:05), there is likely a systematic error in geolocation for this volcano on the MODIS thermal alerts site. The shift between the reported daytime and nighttime alert locations on 20 May could be a related effect, attributable to a 20° difference in satellite zenith angle between these two passes.

Figure 11. Locations of alert-pixels on Manam during 2001-2002. Grid squares are 1 km. Base map is from BGVN 21:12 (after Palfreyman and Cooke, 1976). Courtesy of Diego Coppola and David Rothery, The Open University.

Reference. Palfreyman, W.D., and Cooke, R.J.S., 1976, Eruptive history of Manam volcano, Papua New Guinea in Johnson R.W. (ed.), Volcanism in Australasia, Elsevier, Amsterdam, p. 117-131.

Geologic Background. The 10-km-wide island of Manam, lying 13 km off the northern coast of mainland Papua New Guinea, is one of the country's most active volcanoes. Four large radial valleys extend from the unvegetated summit of the conical basaltic-andesitic stratovolcano to its lower flanks. These valleys channel lava flows and pyroclastic avalanches that have sometimes reached the coast. Five small satellitic centers are located near the island's shoreline on the northern, southern, and western sides. Two summit craters are present; both are active, although most observed eruptions have originated from the southern crater, concentrating eruptive products during much of the past century into the SE valley. Frequent eruptions, typically of mild-to-moderate scale, have been recorded since 1616. Occasional larger eruptions have produced pyroclastic flows and lava flows that reached flat-lying coastal areas and entered the sea, sometimes impacting populated areas.

Information Contacts: Ima Itikarai, Rabaul Volcano Observatory (RVO), P.O. Box 386, Rabaul, Papua New Guinea; Darwin VAAC, Bureau of Meteorology, Northern Territory Regional Office, PO Box 40050, Casuarina Northern Territory 0811 Australia (URL: http://www.bom.gov.au/info/vaac/); Diego Coppola and David A. Rothery, Department of Earth Sciences, The Open University, Milton Keynes, MK7 6AA, United Kingdom.

An eruption began at Nyamuragira on 25 July 2002 (BGVN 27:07). Flights on 1 and 3 August confirmed that the eruption was continuing at a high rate, but another look on 27 September showed that the eruption had ceased (BGVN 27:10). The eruption was observed in MODIS thermal satellite imagery (1-km² pixel size).

Initial activity was detected on 25 July at 2040 UTC, with a large (57-pixel) thermal anomaly on the S and N flanks of the volcano. The anomaly grew in size, with an image on 27 July showing a large anomaly on the N flank and a subordinate anomaly on the S flank. On all subsequent days the anomaly was limited to the N flank. The anomaly reached a maximum size of 78 pixels on 1 August, at which point it extended approximately 12-15 pixels (or around 12-15 km) along its longest dimension (figure 23). After this point the size and intensity of the anomaly rapidly diminished (detected anomalies after mid-August were no more than 8 pixels in size). The last detected anomaly at Nyamuragira occurred on 1 October. Figures 24 and 25 show the number of anomalous pixels and the sum of the radiance for the entire eruptive event.

Figure 23. MODIS imagery on 1 August 2002 showed the maximum number of anomalous pixels (78) for the July-August eruption at Nyamuragira. Courtesy HIGP/SOEST.

Figure 24. Total number of anomalous pixels visible on MODIS imagery during and following the July-August 2002 eruption of Nyamuragira. Courtesy HIGP/SOEST.

Figure 25. Sum of the radiance values for bands 21 and 32 on MODIS imagery during and following the July-August 2002 eruption of Nyamuragira. Courtesy HIGP/SOEST.

Geologic Background. Africa's most active volcano, Nyamulagira (also known as Nyamuragira), is a massive high-potassium basaltic shield about 25 km N of Lake Kivu and 13 km NNW of the steep-sided Nyiragongo volcano. The summit is truncated by a small 2 x 2.3 km caldera that has walls up to about 100 m high. Documented eruptions have occurred within the summit caldera, as well as from the numerous flank fissures and cinder cones. A lava lake in the summit crater, active since at least 1921, drained in 1938, at the time of a major flank eruption. Recent lava flows extend down the flanks more than 30 km from the summit as far as Lake Kivu; extensive lava flows from this volcano have covered 1,500 km2 of the western branch of the East African Rift.

Information Contacts: Matt Patrick, Andy Harris, Luke Flynn, Robert Wright, Harold Garbiel, and Eric Pilger, HIGP/SOEST, University of Hawaii at Manoa, HI 96822 USA.

During mid-December 2002 through early February 2003, eruptions at Tavurvur continued from three vents at different times. The eruptions were characterized by slow, thick convoluted ash plumes occurring at irregular intervals and rising about several hundred to thousands of meters above the summit. Occasionally they became forceful. Throughout the report period light to pale gray ash plumes drifted in various directions, resulting in ashfall in the town of Rabaul, Matupit Island, Malaguna village, and other areas. During 20-27 January ash emissions were associated with discrete short-duration seismic events and slightly longer duration events. The former event types were pronounced during 20-27 January, but on 26 and 27 January seismicity changed to the low-amplitude medium-to-long duration type.

Generally, the seismicity fluctuated at low-to-moderate levels. A period of harmonic tremor was recorded on the morning of 18 December 2002. That day, the Rabaul Volcano Observatory (RVO) reported that the gaps between emissions seemed to have lengthened over the previous 24 hours. During 19-20 December, occasional larger explosions showered the flanks with rocks. Following the explosions ash-poor plumes were gently emitted from the whole area of the Northern Crater. During 20-23 December there was a slight increase in the number of volcanic earthquakes due to more ash emissions. The increase in volcanic earthquakes tapered off over the next few days.

Ground deformation measurements from real-time GPS showed no significant changes. On 24 January RVO reported that the electronic tiltmeter had been showing a slow inflation during the previous 2 months. That trend ceased by 27 January, when ground-deformation measurements from real-time GPS changed to show an inflationary trend through 2 February. Long-duration, low-amplitude earthquakes occurred through at least 10 February.

MODVOLC Thermal Alerts, 2001-2002. During 2001 and 2002, MODIS alerts occurred only during April-September 2001 and June-December 2002. These anomalies were always represented by a single alert-pixel, except for 26 May 2001, 4 July 2001, and 22 October 2002, which each had two alert-pixels. The maximum alert ratio was on 4 July 2001 when it reached -0.26. The center coordinates of all the alert-pixels plot within 1 km of each other, in a cluster centered ~1 km W of Tavurvur (figure 37), which is the only site of known activity during this period. This high degree of repeatability offset from the likely seat of the anomaly at the summit vent suggests a systematic error in geolocation.

Figure 37. Locations of alert-pixels at Rabaul during 2001-2002. Base map from BGVN 25:07 (modified from Almond and McKee, 1982). Courtesy of Diego Coppola and David Rothery, The Open University.

The first alert was detected on 26 April 2001, and can be related to a change in activity on Tavurvur from occasional sub-continuous ash emissions to frequent, short-duration ash expulsions on 25 April (BGVN 26:06). From 21 May to 2 June MODIS detected a series of anomalies characterized by a single pixel (two pixels on 26 May) with a low alert ratio averaging -0.774. For this period RVO reported incandescent explosions that lessened in frequency and vigor towards the end of May but picked up again on 30 May when explosions produced dark ash clouds that rose to 1-1.5 km above the vent. On 1-2 June activity was dominated by strong discrete explosions. At night, red incandescent lava fragments were visible (BGVN 26:10). On 4 July 2001 MODIS detected a moderate anomaly coincident with Tavurvur cone, characterized by two alert-pixels with a maximum alert ratio of -0.263. The anomaly was much smaller on 6 July. Reports by RVO (BGVN 26:10) indicated a quiet period from 20 June through July and most of August marked by emission of thin, white vapor. Activity remained low throughout September and October (BGVN 26:10). MODIS detected a single alert-pixel on 17 September, possibly corresponding to the last ash-producing activity in early September 2001.

The next MODIS alerts were in 2002 on 14 June, 19 September, 22 October, 21 November, and 25 December. These were single pixels except for the 22 October anomaly, which was 2 pixels in size. This may represent the aftermath of a large explosion on 20 October that produced a thick, dark ash plume that rose 3 km (BGVN 27:11).

Reference. Almond, R.A., and McKee, C.O., 1982, Location of volcano-tectonic earthquakes within the Rabaul Caldera: Geological Survey of Papua New Guinea Report 82/19.

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

Information Contacts: Ima Itikarai, Rabaul Volcano Observatory (RVO), P.O. Box 386, Rabaul, Papua New Guinea; Diego Coppola and David A. Rothery, Department of Earth Sciences, The Open University, Milton Keynes, MK7 6AA, United Kingdom.

The MODIS Thermal Alerts website (http://modis.higp.hawaii.edu/) is the first truly global high-temperature thermal monitoring system for volcanic activity. This system is capable of detecting and documenting changes in active lava flows, lava domes, lava lakes, strongly incandescent vents, and hot pyroclastic flows. No alert is likely to be triggered by an ash cloud. MODIS cannot see through weather clouds and is also liable to miss events of less than several hours duration. Nevertheless, MODIS is capable of adding significant information to the record of global volcanic activity.

As described by Flynn and others (2001), Wright and others (2002), and Rothery and others (2003), the MODIS Thermal Alerts website provides a series of maps updated every 24 hours to show 'thermal alerts' based on night-time (approximately 2230 local time) infrared data from the Moderate Resolution Imaging Spectroradiometer (MODIS) instrument that is carried by NASA's Terra and Aqua satellites. Thermal alerts are based on an 'alert ratio' (3.9 µm radiance - 12 µm radiance) / (3.9 µm radiance + 12 µm radiance) and an alert is triggered whenever this ratio has a value more positive than -0.8. This threshold value was chosen empirically by inspection of images containing known volcanic sites at high temperature, and is the most negative value that avoids numerous false alarms. There are also some day-time alerts (at approximately 1030 local time) based on the same algorithm. These incorporate a correction for estimated solar reflection and a more stringent threshold, whereby the alert ratio must be more positive than -0.6 to trigger an alert.

In order to bring this valuable tool to the attention of a wider community, Dave Rothery and Diego Coppola have provided an analysis of volcanic activity detected by MODIS in Melanesia from January 2001 to December 2002, which they relate as fully as possible to conventional observations in the Bulletin of the Global Volcanism Network. In the cases of Manam, Rabaul, Ulawun, and Pago there is a high degree of correspondence between MODIS alerts and independently derived observations. In the cases of Bagana, Tinakula, and Ambrym the MODIS alerts represent the only hitherto reported evidence of activity during 2001-2002. Lopevi and Yasur are intermediate cases, where MODIS adds significantly to what has previously been reported. All the 'new' activity is not necessarily unknown to local volcanologists (though this may be so in some cases), and in fact additional information from local sources would help to refine the MODIS interpretation. However, the MODIS Thermal Alerts provide a useful source of near real-time information that is openly available for the benefit of the global volcanism community.

Graphs of the 'alert ratio' and number of alerted pixels indicate the magnitude of every anomaly detected during the period. In some cases these are accompanied by maps indicating the center coordinates of the alerted pixels. The original pixels are 1 x 1 km squares, which means that the true site of a spatially small anomaly that has triggered an alert can be anywhere within a 1-km box surrounding the center point. The geolocational accuracy of MODIS pixel coordinates is generally reckoned to be better than 1 km, but may become worse for high volcanoes, especially when seen close to the edge of an imaging swath (when the satellite can be more than 45 degrees away from the zenith). Furthermore, for some of the more remote volcanoes MODIS scientists believe there may remain significant map-location errors.

References. Flynn, L.P., Wright R., Garbeil, H., Harris, A.J.L., and Pilger, E., 2001, A global thermal alert system using MODIS: initial results from 2000-2001: Advances in Environmental Monitoring and Modelling, no. 3, Monitoring volcanic hotspots using thermal remote sensing, edited by Harris, A.J.L., Wooster, M.J., and Rothery, D. A. (http://www.kcl.ac.uk/kis/schools/hums/geog/advemm/vol1no3.html).

Wright, R., Flynn, L., Garbeil, H., Harris, A., and Pilger, E., 2002, Automated volcanic eruption detection using MODIS: Remote Sensing of Environment, v. 82, p. 135-155.

Rothery, D.A., Thorne, M.T., and Flynn, L., 2003, MODIS thermal alerts in Britain and the North Sea during the first half of 2001: International Journal of Remote Sensing, v. 24, p. 817-826.

Geologic Background. Special announcements or information of general interest not linked to any specific volcano.

Information Contacts:

The effusive eruption at Stromboli, which began 28 December 2002, continued into January 2003. Effusion of lava occurred at a main vent located at 500 m elevation in the middle of the Sciara del Fuoco, within the scar remaining after the 30 December 2002 landslide. The position of this vent has been rather stable since its opening, also on 30 December. Another vent, located at 600 m elevation at the NE base of Crater 1, has been active several times during the eruption, forming low-effusion rate, short lava flows lasting from a few hours to a few days. Effusion rates along the Sciara del Fuoco from the 500 m vent were very variable. During peaks in effusion rate, aa lava flows were reaching the sea causing phreatic explosions at the front. A decrease in effusion rate formed a fan of thin, narrow lava flows spreading on the upper flow field without reaching the sea.

Activation of the 600 m vent occurred each time the 500 m vent showed a marked decrease in effusion rate, suggesting a temporary magma level rise within the feeder conduit of the volcano. This observation was confirmed by an approximately 50°C increase in temperature at the bottom of the craters during activation of the 600 m vent, recorded during daily thermal mapping from a helicopter.

Lava flow emission along the Sciara del Fuoco formed a very thick flow field within the landslide scar of 30 December. Occasional small landslides from the unstable walls of the Sciara cover the lava flows with talus, increasing the thickness and instability of the flow field.

During a helicopter-borne thermal survey carried out on 12 January, arcuate cracks were detected around the southern base of the summit craters of the volcano. Other fractures, oriented NE-SW, cut through the craters. These probably result from drainage of magma in the upper part of the conduit. Collapse of the crater floor in early January significantly changed the morphology of the upper part of the volcano. Crater 2 (the middle crater) has disappeared, and Crater 1 (NE) and Crater 3 (SW) were joined together to form a unique, elongate depression. No explosive activity has been detected at the summit craters of the volcano since the start of the effusion within the Sciara del Fuoco.

Geologic Background. Spectacular incandescent nighttime explosions at Stromboli have long attracted visitors to the "Lighthouse of the Mediterranean" in the NE Aeolian Islands. This volcano has lent its name to the frequent mild explosive activity that has characterized its eruptions throughout much of historical time. The small island is the emergent summit of a volcano that grew in two main eruptive cycles, the last of which formed the western portion of the island. The Neostromboli eruptive period took place between about 13,000 and 5,000 years ago. The active summit vents are located at the head of the Sciara del Fuoco, a prominent scarp that formed about 5,000 years ago due to a series of slope failures which extends to below sea level. The modern volcano has been constructed within this scarp, which funnels pyroclastic ejecta and lava flows to the NW. Essentially continuous mild Strombolian explosions, sometimes accompanied by lava flows, have been recorded for more than a millennium.

Information Contacts: Istituto Nazionale di Geofisica e Vulcanologia (INGV), Sezione di Catania Piazza Roma 2, 95123 Catania (URL: http://www.ct.ingv.it/).

Following an eruption and tsunami from Tinakula (figure 1) during September-December 1971 (CSLP Cards 1297, 1300, and 1301), there were brief reports of large steam plumes and ash plumes in June 1984 (SEAN 09:06) and June 1985 (SEAN 10:06). This report includes observations from a variety of sources. John Seach has provided information about activity during 1989-90 and 1995, as well as some insight into hazards faced by island residents in the area. Passengers on tour expedition ships noted continuing activity in May 1999 and November 2002. MODIS thermal alerts were triggered on three occasions during January-April 2001. In April 2002 excellent observations of eruptive activity were made by scientists on an Australian research vessel.

Figure 1. Sketch map of Tinakula island based on work and publications by G.W. Hughes (1972) and colleagues and summarized by Eissen and others (1991).

Observations in 1989-90 and 1995. John Seach observed Tinakula volcano from the Reef Islands (54 km ENE) from August 1989 to February 1990. Typical activity consisted of Vulcanian eruptions and ash emission to 200-400 m above the summit. Eruptions occurred in distinct bursts separated by intervals ranging from minutes to hours. Reports from sailors indicated that lava bombs frequently rolled down to the sea on the NW side of the volcano, and glowing avalanches were observed at night.

Tinakula was approached by motorized canoe on two occasions in 1995, but dangerous seas made landing impossible. Ongoing ash emissions originated from the summit area. The upper slopes of the volcano were bare and exposed to gas emissions. Regions of mass wasting on the flanks were common, and blocks of lava and rubble were found at sea level at various locations around the island. However, some of the lower flanks were covered with thick vegetation. During a Solair flight from Santa Cruz to Honiara in late September 1995, activity was observed at the summit crater with ash emissions drifting several kilometers towards the W.

The island has not been inhabited since the tsunami in 1971, but islanders from the outer Reef Islands occasionally travel to tend gardens on the SE flank. The ocean between Santa Cruz Island and Reef Islands is dangerous, with many currents and high seas regularly capsizing boats. Landing on the island is always dangerous due to prevailing swells and the lack of a suitable beach. The dominant SE trade winds blow ash and gases away from inhabited islands for most of the year, but a large eruption occurring in westerly winds may affect populations in the Reef Islands. Volcanic bombs (5 cm in diameter) of an unknown age located in villages on the Reef Islands (over 50 km away) were reported to have fallen from the sky.

Observations during May 1999. On the morning of 16 May 1999, Matthew Mumford, on a sailing expedition aboard the Akademik Shuleykin, noted as they approached Tinakula that ". . . a cloud of darkness was blown skyward before our bow. As the ash moved across the sky, the contrast of gray against the white pillows of cloud gave a clear indication of how active this volcano continues to be."

MODVOLC Thermal Alerts, 2000-2002. MODIS alerts for Tinakula on 15 January 2001, 6 March 2001, and 16 April 2001 provide objective evidence of continued volcanic activity. The maximum alert ratio was low (-0.75), indicating small-scale activity. The absence of alerts since April 2001 was judged more likely to be because the level of activity has dipped below the -0.8 alert-ratio threshold rather than because of a genuine cessation of activity.

Observations during April 2002. Scientists from the RV Franklin briefly investigated Tinakula during the SOLAVENTS expedition, 26 March-21 April 2002. A vent high up on the W flank was actively expelling gas/steam, which could be heard as a low roar 50 m from shore. Small avalanches down the steep W side were common, and one larger eruption observed from the vessel's bridge lasted about 5 minutes. Small optical transmission anomalies were detected in the water column and are probably turbidity induced-particulate plumes. A weak methane anomaly was also recorded ~2.8 km off the NW coast of Tinakula. The following is based on extracts from the daily narrative section of the cruise report (McConachy and others, 2002).

The Franklin arrived ~3.2 km off the W coast of Tinakula at 0705 on 6 April 2002 (figures 2-5) and in perfect conditions the Zodiac rescue boat was deployed with Able Seaman Graham and scientists Richard Arculus and Donn Tolia to commence water sampling. The zodiac was safely back on deck by 0815. The scientists reported a roaring noise from Tinakula's active crater heard when the boat was 50 m offshore.

Figure 2. Photo showing the N coast of Tinakula as viewed from the zodiac boat off the R/V Franklin, 6 April 2002. The landslide scarp descends to the sea on the NW side of the island. Ndeni Island can be seen in the background S of Tinakula. Photographed by Donn Tolia, Director, Geological Survey of the Solomon Islands; courtesy of CSIRO.

Figure 3. Close-up view of Tinakula showing the landslide scarp and embayment on the NW coast. The breached summit crater is mostly hidden by steam emissions. Photographed by Donn Tolia, Director, Geological Survey of the Solomon Islands; courtesy of CSIRO.

Figure 4. Photo of Tinakula taken from the RV Franklin, 6 April 2002. Photographed by Susan Belford; courtesy of CSIRO.

Figure 5. Photo of Tinakula in the distance taken from the RV Franklin, 6 April 2002. Photographed by Susan Belford; courtesy of CSIRO.

From virtually the same location a grab sample collected material from the 1971 eruption at around 950 m depth. An excellent, 75%-full load of exceptionally well-sorted black volcanic sand was recovered, consisting of plagioclase, pyroxene and red-brown fragments; no foraminifera were visible. A CTD-Hydrocast followed at around 0910. During this operation, smoke came from a vent 2/3 way up the summit on the W side of the sector collapse, and minor avalanches came down scree slopes on the N side of the collapse area. A number of light transmission anomalies were observed on the down cast and sampled on the upcast. They are most likely particle plumes following isopycnals (constant density surfaces) sloughing off the main slope.

Observations during November 2002. Passengers on the Zegrahm Expeditions cruise ship Clipper Odyssey observed that Tinakula was "active" on the morning of 18 November 2002, but no description of the activity was provided.

References. McConachy, T.F., Yeats, C.J., Arculus, R.J., Beattie, R., Belford, S., Holden, J., Kim, J., MacDonald, L., Schardt, C., Sestak, S., Stevens, B., and Tolia, D., 2002, SOLAVENTS-2002: Solomons Australia Vents Expedition Aboard the RV Franklin, 26 March-21 April 2002, edited by C.J. Yeats, CSIRO Exploration and Mining Report 1026F, 456 p.

Hughes, G.W., 1972, Geological map of Tinakula: Nendö sheet EOI 1, Soloman Geol. Survey, Honiara.

Eissen, J-P., Blot, C., and Louat, R., 1991, Chronology of the historic volcanic activity of the New Hebrides island arc from 1595 to 1991: Rapports Scientifiques et Technique, Sciences de la Terre, No. 2, ORSTOM, France.

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: Timothy F. McConachy, CSIRO Exploration and Mining, PO Box 136, North Ryde, NSW 1670, Australia (URL: http://mnf.csiro.au/); Diego Coppola and David A. Rothery, Department of Earth Sciences, The Open University, Milton Keynes, MK7 6AA, United Kingdom; John Seach, PO Box 16, Chatsworth Island, NSW 2469, Australia (URL: http://www.volcanolive.com/); Jeff and Cynthia Gneiser, Zegrahm & Eco Expeditions, 192 Nickerson Street ##200, Seattle, WA 98109, USA (URL: https://www.zegrahm.com/); Matthew Mumford, Unit 1.02, 26 Kippax Street, Surrey Hills, NSW 2010, Australia.

During mid-March 2002 through at least early February 2003, activity from the main crater and the N valley vents of Ulawun were unchanged and generally remained low. The vent in the main crater released weak-to-moderate volumes of white and white-gray vapor. The N valley vents sometimes produced very weak traces of thin white vapor. Seismicity returned to background levels after volcanic tremors ceased on 18 March 2002. Discrete low-frequency earthquakes continued to occur in small numbers. During 15-28 April the seismicity level was low, however from 29 April seismicity increased to a moderate level following an episode of continuous volcanic tremor. The tremor ceased on 25 May. In June, RVO reported that the electronic tiltmeter continued to show long-term deflation of the summit area, but the amount of change was smaller than in the previous 1-3 months. Small continuous volcanic tremors became more prominent beginning on 21 January 2003 and ceased on 27 January.

Satellite imagery showed eruption plumes on 22 and 28 August (news reports indicated continued activity that entire week), and 6-7 September 2002 (BGVN 27:08). The Darwin VAAC issued advisories about low-level ash plumes on 12 and 19 September, and an ash-and-steam cloud to ~3.7 km on 28 September. Low-level ash plumes were noted again on 2 and 16 October, with another higher plume (~3.6 km) on the 22nd. At 0630 on 3 November an Air Niugini pilot reported ash drifting ESE from the volcano at ~3 km altitude.

MODVOLC Thermal Alerts, 2001-2002. Throughout 2001 and 2002, thermal alerts for Ulawun occurred only during 26-28 April 2001. The first detected anomaly was at 2225 on 26 April and consisted of four alert-pixels with a maximum alert ratio of -0.095. By the following day the anomaly had increased in spatial dimension to eight alert-pixels although the maximum alert ratio was lower (-0.224). On 28 April at 2215 the anomaly had increased to 15 alert-pixels with a higher maximum alert ratio of -0.053. After that no more anomalies were detected.

This sequence can be related to events reported by the Rabaul Volcano Observatory (BGVN 26:06) On 26 April 2001 at 0530 a small Strombolian eruption began. This was characterized by glowing lava fragments ejected by frequent explosions followed by small pyroclastic flows. During the day activity decreased but on 27 April at 0530 another phase of Strombolian activity began. A small pyroclastic flow occurred followed by a lava flow that descended to about 500-600 m above sea-level. This is presumably the cause of the 15-pixel alert on 28 April (figure 8). A third phase of Strombolian activity began at about 0600 on 29 April. This phase was slower and more gradual, peaking at about 1800-2200 on 29 April, and did not produce a MODIS thermal alert.

Figure 8. Locations of MODIS alert-pixels on Ulawun during 2001-2002. Courtesy of Diego Coppola and David Rothery, The Open University.

Geologic Background. The symmetrical basaltic-to-andesitic Ulawun stratovolcano is the highest volcano of the Bismarck arc, and one of Papua New Guinea's most frequently active. The volcano, also known as the Father, rises above the N coast of the island of New Britain across a low saddle NE of Bamus volcano, the South Son. The upper 1,000 m is unvegetated. A prominent E-W escarpment on the south may be the result of large-scale slumping. Satellitic cones occupy the NW and E flanks. A steep-walled valley cuts the NW side, and a flank lava-flow complex lies to the south of this valley. Historical eruptions date back to the beginning of the 18th century. Twentieth-century eruptions were mildly explosive until 1967, but after 1970 several larger eruptions produced lava flows and basaltic pyroclastic flows, greatly modifying the summit crater.

Information Contacts: Ima Itikarai, Rabaul Volcano Observatory (RVO), P.O. Box 386, Rabaul, Papua New Guinea; Darwin Volcanic Ash Advisory Center (VAAC), Bureau of Meteorology, Northern Territory Regional Office, PO Box 40050, Casuarina, NT 0811, Australia (URL: http://www.bom.gov.au/info/vaac/); Diego Coppola and David A. Rothery, Department of Earth Sciences, The Open University, Milton Keynes, MK7 6AA, United Kingdom.

Uncertain low-level eruptive activity occurred at Veniaminof in September 2002 (BGVN 27:10). During October 2002, seismicity was lower than when it was first noted in early September, although it was still above background levels. Visual observations were intermittent and inconclusive. The Alaska Volcano Observatory (AVO) received reports ranging from minor-steam and possible ash emissions, to no signs of activity. Satellite imagery on 2 October suggested an apparent gray, diffuse deposit extending across the caldera from the historically active intracaldera cinder cone. This could reflect a small explosion, vigorous steam emission, or redistribution of material by strong winds; no thermal anomalies were observed on satellite imagery. Footage obtained later, but recorded in early October, showed minor ash emission from the intracaldera cone rising ~100-200 m above the cone and drifting a short distance before dispersing. A faint covering of ash was visible on the caldera ice field extending from the base of the cone.

On 18 November AVO lowered the Concern Color Code from Yellow to Green. Since early October they had received no pilot reports or other observations of activity at the volcano. Also, they had not detected thermal anomalies in any clear satellite images. Though seismicity remained above levels recorded during summer of 2002, it remained roughly constant during the previous month at a level notably lower than in September.

Seismicity began to increase in mid-December, and on 6 January AVO raised the Concern Color Code from Green to Yellow. No thermal anomalies were detected on satellite imagery. Elevated seismicity continued through February 2003, with discrete seismic events occurring at a rate of 1-2 per minute during 21-28 February. Nearly constant periods of seismicity were recorded during the report week. Discrete seismic events occurred at rates up to 1-2 events per minute, along with moderate levels of volcanic tremor. Satellite imagery did not reveal increased surface temperatures, ash emission, or ash deposits. Visual observations on 22 January from the village of Perryville, located 35 km SSW of the volcano, revealed that white steam was rising from the intracaldera cone. The steaming was similar to that observed over the previous several months. The Concern Color Code remained at Yellow.

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

Information Contacts: Alaska Volcano Observatory (AVO), a cooperative program of a) U.S. Geological Survey, 4200 University Drive, Anchorage, AK 99508-4667, USA, 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.

The eruption that began at Pago on 3 August 2002 (BGVN 27:07-27:09 and 27:12) continued through at least early February 2003. The Rabaul Volcano Observatory (RVO) reported that slow effusion of the lava flow from the northwestern-most vent continued. The flow was still contained within the Witori Caldera. An aerial inspection on 10 December confirmed that the lava was still moving. Besides the continuing lava flow, a weak glow was observed on the night of 28 December and rumbling noises were heard for a very short period on 9 January. Rumblings noises were also reported on 4 and 9 February.

Small volcano-tectonic earthquakes continued at background levels. Variable amounts of white vapor were released from the vents. During late December and January the northwestern-most vent was releasing some bluish vapor, indicative of continuing eruption of lava from the same vent. Some booming noises were reported on 22 January from the summit area. As of 24 January 2003, reports of browning vegetation on the S part of the volcano had not been investigated due to logistical problems. However, RVO stated that a likely cause was volcanic plumes containing sulfur gases blowing to the S and SE and affecting vegetation. Ground deformation showed a lack of significant changes during December. This contrasts with the period between the start of the eruption on 3 August and the beginning of November when complex and significant movements were recorded.

MODVOLC Thermal Alerts, 2001-2002. Throughout 2001 and 2002, thermal alerts for Pago occurred only during August-December 2002 (figure 17). This period was characterized by continuous thermal anomalies first detected on 6 August at 1030 and growing to several pixels in size. At this time the anomaly consisted of a single alert-pixel with an alert ratio of -0.31. At 2250 MODIS detected five alert-pixels with a maximum alert ratio of -0.35. The alert ratio of the anomaly rose to a peak on 8 August at 1015 when a single alert-pixel had an alert ratio of -0.035.

Figure 17. MODIS detected alerts on Pago during 2001-2002. Courtesy of Diego Coppola and David Rothery, The Open University.

After that, during August detected alerts on Pago gradually decreased. On 15 August the anomaly consisted of three alert-pixels with a maximum alert ratio of -0.077, and on 22 August two alert-pixels were detected with maximum alert ratio of -0.167. The RVO reported that the eruption continued with low levels of activity during August and was characterized by the ejection of ash clouds (BGVN 27:08). The earliest date reported for lava effusion is 9 August (BGVN 27:07).

On 26 August MODIS detected five alert-pixels with a maximum alert ratio of -0.291. The anomaly decreased on 29 August when only one alert-pixel was detected (alert ratio -0.318), but had expanded by 31 August to two alert-pixels with a maximum alert ratio of -0.382, and by 2 September to four alert-pixels with a maximum alert ratio of -0.345. This series of anomalies is evidently related to lava erupted from the craters NW of the central cone during 25 August to 3 September (BGVN 27:08), during which lava flowed NE and then SW after reaching the caldera wall. The coordinates of the alert-pixels throughout the eruption were dispersed between the active vent and the caldera wall in a pattern consistent with this description (figure 18).

Figure 18. Locations of alert-pixels on Pago during 2001-2002. Courtesy of Diego Coppola and David Rothery, The Open University.

On 9 September MODIS detected a single pixel anomaly with an alert ratio of -0.275. This anomaly was probably related to the explosion(s) that produced a 1.5-km-high ash-and-steam plume visible on satellite images on 7 and 8 September (BGVN 27:08). During September and October the alert ratio became lower and varied between one and five pixels. The relatively high alert ratio of -0.441 on 2 October was probably related to continuous lava flows in the NE portion of a fissure system inside the caldera, reported by the RVO (BGVN 27:09). MODIS detected continuous anomalies during October-December 2002, attributed to continuing lava effusion. Another alert was recorded on 15 January 2003.

Geologic Background. The active Pago cone has grown within the Witori caldera (5.5 x 7.5 km) on the northern coast of central New Britain contains the active Pago cone. The gently sloping outer caldera flanks consist primarily of dacitic pyroclastic-flow and airfall deposits produced during a series of five major explosive eruptions from about 5,600 to 1,200 years ago, many of which may have been associated with caldera formation. Pago cone may have formed less than 350 years ago; it has grown to a height above the caldera rim, and a series of ten dacitic lava flows from it covers much of the caldera floor. The youngest of these was erupted during 2002-2003 from vents extending from the summit nearly to the NW caldera wall. The Buru caldera cuts the SW flank.

Information Contacts: Ima Itikarai, Rabaul Volcano Observatory (RVO), PO Box 386, Rabaul, E.N.B.P., Papua New Guinea; Diego Coppola and David A. Rothery, Department of Earth Sciences, The Open University, Milton Keynes, MK7 6AA, United Kingdom.

Eruptive activity has continued at Yasur since a more vigorous phase began in October 2001 that lasted at least into January 2002 (BGVN 27:01). This report includes details for a period of mild activity during 24-28 July 2000 (not previously included in the Bulletin). Since that time visitors noted activity continuing in October 2000 and September 2001 (BGVN 26:11), as well as October and December 2001 (BGVN 27:01). Accounts are provided below of activity during January, August, November, and December 2002. Finally, MODIS thermal-alert data confirm intermittent lower level activity in 2001, and an increase in vigor beginning in August 2002.

Observations during July 2000. Roberto Carniel, Douglas Charley, and Marco Fulle arrived on Tanna Island on 24 July 2000 and camped at the base of the E slope of the cone. The lake that used to fill part of the surrounding Ash Plain had disappeared after heavy rains during the rainy season caused the overflow of the lake, damaging several houses in the village of Sulphur Bay. In the active crater, three smaller craters were distinguished, named A, B, and C, from left to right as seen from the E rim, where local guides bring tourists. This spot lies no more than 150 m from the most active C vents (figure 30). During the visit Crater B was slightly active, while Crater A appeared dormant.

Figure 30. Photo showing the three subcraters within the active summit crater of Yasur, 24 July 2000. The N end of the island of Tanna and the Pacific Ocean can be seen in the right background. Courtesy of Marco Fulle.

On the afternoon of 24 July the activity was moderate to high. Between 1620 and 1640 frequent spattering was observed by Carniel at the C/1 and C/2 vents. Between 1640 and 1820 eight eruptions were observed at vent C/0, with another 10 eruptions at vent C/1. On average the latter vent exhibited the bigger eruptions, in one case accompanied by gray emissions.

During the morning of 25 July the activity was again quite intense; observations were sometimes disturbed by a strong wind. Between 0825 and 0910 the explosions were mostly concentrated in the C/0 vent (six eruptions). Some of them were accompanied by the emission of brown ash at the end. During this period three silent explosions with only brown ash emitted were observed at vent B/1, completely inactive the previous day. C/1 showed only one eruption. After 20 minutes with no eruptions, from 0930 to 1130 the activity was mostly concentrated in the C/1 vent, where 17 eruptions were observed, some ended by a brown ash emission. The vent also showed about ten minutes of frequent spattering around 1120; during the same period B/1 vent produced two more silent ash eruptions and a brief spattering was observed at a vent, C/2, that looked different from C/1 but did not show any other activity after this. After 0930 vent C/0 did not show any activity.

During the afternoon, new visual observations were made by Carniel. From 1700 to 1725 very low activity was observed. Two successive silent brown ash eruptions from vent B/1 accompanied the start of a more intense phase for vent C/1. This vent erupted 15 times between 1725 and 1855, sometimes also showing continuous spattering and glow. Again no activity was seen at vent C/0.

During the morning of 26 July visual observations were made between 0835 and 1125. The first ten minutes were characterized by continuous and loud spattering at vent C/1, which showed a total of 18 explosions, some of them extremely loud and/or accompanied by the emission of gray ash. Vent C/0 showed only three eruptions, but all very loud and followed by a brown ash emission. One single silent ash eruption was observed at vent B/1 at 0945.

Carniel made other visual observations between 1700 and 1750 on the afternoon of 26 July, when the activity was characterized by a variable level of continuous spattering from vent C/1, which also showed 10 eruptions. During this period vent C/0 showed a single eruption at 1736. No activity was observed in crater B.

After a morning characterized by rain, Carniel and Fulle climbed the volcano again on the afternoon of 27 July. The air was still humid and gas stayed over the craters. The volcano was very quiet between the eruptions, with no sounds and no spattering at any vent. Between 1630 and 1730 there were 14 eruptions observed at vent C/1, but most of them were gas-rich emissions with very few bombs reaching the vent rim. Only two eruptions slightly bigger than spattering were observed at vent C/0.

On the morning of 28 July 2000, before leaving the volcano, the team made their last visual observations. Activity was moderate and visibility not very good. Many eruptions were very loud and they could be ascribed to C/1 from the sound alone, even when not visible. At 0920 a rockfall was heard from the S side of the caldera rim.

Observations during January 2002. The International Federation of Red Cross and Red Crescent Societies noted on 16 January 2002 that scientists were on alert for heightened volcanic activity at Yasur following a M 7.2 earthquake on 3 January. The earthquake produced landslides in Vanuatu's capital, Port Vila on Efate Island, and damaged buildings and bridges in the city, but there were no deaths or serious injuries. During 5 January to at least 16 January ash fell on Tanna Island, polluting water sources. The week of 6 January the Vanuatu government restricted access to the volcano's crater citing an increased risk of an eruption since the 3 January earthquake.

The Volcanic Ash Advisory Center in Wellington notified aviators of an eruption on 25 January around 1300. A pilot reported that the ash cloud rose to ~2 km altitude and slowly drifted S. The ash cloud was not visible on satellite imagery, possibly due to heavy meteorological cloud cover.

Observations during August 2002. The European Volcanological Society posted a report from the Institut de Recherche pour le Développement (IRD) on 3 September 2002. At that time the increasing level of activity at Yasur since October 2001 and the M 6 earthquake of 29 August 2002 had prompted IRD to upgrade the hazard status to Alarm Level 3, closing access to the volcano. The earthquake was strongly felt by residents of the entire district around the volcano. This was the first time since the seismic station was installed in October 1992 that a shock of such magnitude was recorded. Elders of the Yasur district confirmed that such an earthquake had not been experienced within living memory. The installation of two new seismological monitoring stations is planned, to complement the existing alarm system installed 2 km from Yasur and the Isangel station.

Observations during November 2002. On 22 November 2002 a group of passengers from the Zegrahm Expeditions cruise ship Clipper Odyssey visited the summit area. They observed Strombolian activity from one crater and heard thunderous whooshing sounds followed by thick yellow and white smoke from another.

Observations during December 2002. John Seach visited to the volcano on 7 December 2002, approaching by 4WD vehicle across the dry bed of Lake Siwi, which drained in 2000 after a collapse of the natural dam on the N end of the ash plain. Reports from Sulphur Bay village indicated that many houses were destroyed by the flooding. Flowing water from the lake eroded a 5-m-deep section of ground at the location of the dam (figure 31).

Figure 31. Erosion channel at the N end of the ash plain at Yasur caused by draining of Lake Siwi. Courtesy of John Seach.

Three fumaroles were active on the caldera wall near the parking area at the summit. The crater rim was climbed from the SE and observations made from 1700 to 1930. Yasur showed a high level of activity with up to three vents erupting simultaneously inside the main crater. Eruptions occurred every one or two seconds during the 2.5-hour stay at the summit. Most eruptions were Strombolian with glowing bombs sent up to 150 m above the crater (figure 32). Projectiles generally fell back inside the crater, but the northern-most vent occasionally sent glowing lava bombs over the N and NE crater rims. Mild Vulcanian eruptions occurred at times with ash ejected to 100 m above the crater. Bombs were ejected as either glowing orange blobs of lava or black crusted material. Eruptions were accompanied by loud explosions and ground shaking. Bombs impacting on the ash made a sound like raindrops.

Figure 32. Time-lapse night photo of a Strombolian eruption from Yasur (southern vent) on 7 December 2002. Courtesy of John Seach.

Seismic counts made by the Institute of Research and Development (Noumea) showed an increase in eruptive activity at Yasur in the beginning of December 2002 with Level 3 events increasing from 10 to 40 per hour (see BGVN 27:01 for description of seismic count data). Seismic counts remained elevated until the end of January 2003 when activity reduced to pre-December 2002 levels.

MODVOLC Thermal Alerts, 2001-2002. MODIS alerts occurred only three times in 2001 but increased in frequency, size, and alert ratio during 2002 (figure 33). The alerts that occurred in 2001, on 10 March, 4 April, and 31 August, were characterized by a single alert-pixel with very low alert ratio. Ground reports for this period noted mild eruptive activity, with vigorous Strombolian activity beginning in late December 2001 (BGVN 26:11 and 27:01). From 31 January 2002 MODIS indicates quasi-continuous activity throughout the year, which was at its most intense in the two months beginning 29 August 2002 (2210 local time). This followed the M 6 volcanic earthquake at 1500. A map of alert-pixel coordinates places them consistently E of the crater, but this may be a geolocation error rather than being indicative of a new vent.

Figure 33. MODIS thermal alerts on Yasur during 2001-2002. Courtesy of Diego Coppola and David Rothery, The Open University.

Geologic Background. Yasur has exhibited essentially continuous Strombolian and Vulcanian activity at least since Captain Cook observed ash eruptions in 1774. This style of activity may have continued for the past 800 years. Located at the SE tip of Tanna Island in Vanuatu, this pyroclastic cone has a nearly circular, 400-m-wide summit crater. The active cone is largely contained within the small Yenkahe caldera, and is the youngest of a group of Holocene volcanic centers constructed over the down-dropped NE flank of the Pleistocene Tukosmeru volcano. The Yenkahe horst is located within the Siwi ring fracture, a 4-km-wide open feature associated with eruption of the andesitic Siwi pyroclastic sequence. Active tectonism along the Yenkahe horst accompanying eruptions has raised Port Resolution harbor more than 20 m during the past century.

Information Contacts: Roberto Carniel, Università di Udine, Italy (URL: http://www.swisseduc.ch/stromboli/); Douglas Charley, Département de la Géologie, des Mines et des Ressources en eau, Vanuatu; Marco Fulle, Osservatorio Astronomico, Trieste, Italy (URL: http://www.swisseduc.ch/stromboli/); Diego Coppola and David A. Rothery, Department of Earth Sciences, The Open University, Milton Keynes, MK7 6AA, United Kingdom; John Seach, PO Box 16, Chatsworth Island, NSW 2469, Australia (URL: http://www.volcanolive.com/); Jeff and Cynthia Gneiser, Zegrahm & Eco Expeditions, 192 Nickerson Street ##200, Seattle, WA 98109, USA (URL: https://www.zegrahm.com/); International Federation of Red Cross and Red Crescent Societies, PO Box 372, CH-1211 Geneva 19, Switzerland (URL: http://www.ifrc.org/); Wellington Volcanic Ash Advisory Center (VAAC), MetService, PO Box 722, Wellington, New Zealand (URL: http://vaac.metservice.com/); Michel Lardy, Institut de Recherche pour le Développement (IRD), CRV, BP A 5 Nouméa, Nouvelle Calédonie; Société Volcanologique Européenne, C.P. 1, 1211 Geneva 17, Switzerland (URL: http://www.sveurop.org/).