The lava lake in the summit crater of Erebus has been active since at least 1972. Located in Antarctica overlooking the McMurdo Station on Ross Island, it is the southernmost active volcano on the planet. Because of the remote location, activity is primarily monitored by satellites. This report covers activity during 2023.

The number of thermal alerts recorded by the Hawai'i Institute of Geophysics and Planetology’s MODVOLC Thermal Alerts System increased considerably in 2023 compared to the years 2020-2022 (table 9). In contrast to previous years, the MODIS instruments aboard the Aqua and Terra satellites captured data from Erebus every month during 2023. Consistent with previous years, the lowest number of anomalous pixels were recorded in January, November, and December.

Table 9. Number of monthly MODIS-MODVOLC thermal alert pixels recorded at Erebus during 2017-2023. See BGVN 42:06 for data from 2000 through 2016. The table was compiled using data provided by the HIGP – MODVOLC Thermal Alerts System.

Sentinel-2 infrared images showed one or two prominent heat sources within the summit crater, accompanied by adjacent smaller sources, similar to recent years (see BGVN 46:01, 47:02, and 48:01). A unique image was obtained on 25 November 2023 by the OLI-2 (Operational Land Imager-2) on Landsat 9, showing the upper part of the volcano surrounded by clouds (figure 32).

Figure 32. Satellite view of Erebus with the summit and upper flanks visible above the surrounding weather clouds on 25 November 2023. Landsat 9 OLI-2 (Operational Land Imager-2) image with visible and infrared bands. Thermal anomalies are present in the summit crater. The edifice is visible from about 2,000 m elevation to the summit around 3,800 m. The summit crater is ~500 m in diameter, surrounded by a zone of darker snow-free deposits; the larger circular summit area is ~4.5 km diameter. NASA Earth Observatory image by Lauren Dauphin, using Landsat data from the U.S. Geological Survey.

Geologic Background. Mount Erebus, the world's southernmost historically active volcano, overlooks the McMurdo research station on Ross Island. It is the largest of three major volcanoes forming the crudely triangular Ross Island. The summit of the dominantly phonolitic volcano has been modified by one or two generations of caldera formation. A summit plateau at about 3,200 m elevation marks the rim of the youngest caldera, which formed during the late-Pleistocene and within which the modern cone was constructed. An elliptical 500 x 600 m wide, 110-m-deep crater truncates the summit and contains an active lava lake within a 250-m-wide, 100-m-deep inner crater; other lava lakes are sometimes present. The glacier-covered volcano was erupting when first sighted by Captain James Ross in 1841. Continuous lava-lake activity with minor explosions, punctuated by occasional larger Strombolian explosions that eject bombs onto the crater rim, has been documented since 1972, but has probably been occurring for much of the volcano's recent history.

Information Contacts: 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/); NASA Earth Observatory, EOS Project Science Office, NASA Goddard Space Flight Center, Goddard, Maryland, USA (URL: https://earthobservatory.nasa.gov/images/152134/erebus-breaks-through).

Rincón de la Vieja is a volcanic complex in Costa Rica with a hot convecting acid lake that exhibits frequent weak phreatic explosions, gas-and-steam emissions, and occasional elevated sulfur dioxide levels (BGVN 45:10, 46:03, 46:11). The current eruption period began June 2021. This report covers activity during July-December 2023 and is based on weekly bulletins and occasional daily reports from the Observatorio Vulcanologico Sismologica de Costa Rica-Universidad Nacional (OVSICORI-UNA).

Numerous weak phreatic explosions continued during July-December 2023, along with gas-and-steam emissions and plumes that rose as high as 3 km above the crater rim. Many weekly OVSICORI-UNA bulletins included the previous week's number of explosions and emissions (table 9). For many explosions, the time of explosion was given (table 10). Frequent seismic activity (long-period earthquakes, volcano-tectonic earthquakes, and tremor) accompanied the phreatic activity.

Table 9. Number of reported weekly phreatic explosions and gas-and-steam emissions at Rincón de la Vieja, July-December 2023. Counts are reported for the week before the Weekly Bulletin date; not all reports included these data. Courtesy of OVSICORI-UNA.

Table 10. Summary of activity at Rincón de la Vieja during July-December 2023. Weak phreatic explosions and gas emissions are noted where the time of explosion was indicated in the weekly or daily bulletins. Height of plumes or emissions are distance above the crater rim. Courtesy of OVSICORI-UNA.

According to OVSICORI-UNA, during July-October the average weekly sulfur dioxide (SO₂) flux ranged from 68 to 240 tonnes/day. However, in mid-November the flux increased to as high as 334 tonnes/day, the highest value measured in recent years. The high SO₂ flux in mid-November was also detected by the TROPOMI instrument on the Sentinel-5P satellite (figure 43).

Figure 43. Sulfur dioxide (SO2) maps from Rincón de la Vieja recorded by the TROPOMI instrument aboard the Sentinel-5P satellite on 16 November (left) and 20 November (right) 2023. Mass estimates are consistent with measurements by OVSICORI-UNA near ground level. Some of the plume on 20 November may be from other volcanoes (triangle symbols) in Costa Rica and Nicaragua. Courtesy of the NASA Global Sulfur Dioxide Monitoring Page.

Geologic Background. Rincón de la Vieja, the largest volcano in NW Costa Rica, is a remote volcanic complex in the Guanacaste Range. The volcano consists of an elongated, arcuate NW-SE-trending ridge constructed within the 15-km-wide early Pleistocene Guachipelín caldera, whose rim is exposed on the south side. Sometimes known as the "Colossus of Guanacaste," it has an estimated volume of 130 km3 and contains at least nine major eruptive centers. Activity has migrated to the SE, where the youngest-looking craters are located. The twin cone of Santa María volcano, the highest peak of the complex, is located at the eastern end of a smaller, 5-km-wide caldera and has a 500-m-wide crater. A Plinian eruption producing the 0.25 km3 Río Blanca tephra about 3,500 years ago was the last major magmatic eruption. All subsequent eruptions, including numerous historical eruptions possibly dating back to the 16th century, have been from the prominent active crater containing a 500-m-wide acid lake located ENE of Von Seebach crater.

Information Contacts: Observatorio Vulcanológico Sismológica de Costa Rica-Universidad Nacional (OVSICORI-UNA), Apartado 86-3000, Heredia, Costa Rica (URL: http://www.ovsicori.una.ac.cr/); 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/).

Bezymianny, located on Russia’s Kamchatka Peninsula, has had eruptions since 1955 characterized by dome growth, explosions, pyroclastic flows, ash plumes, and ashfall. Activity during November 2022-April 2023 included gas-and-steam emissions, lava dome collapses generating avalanches, and persistent thermal activity. Similar eruptive activity continued from May through October 2023, described here based on information from weekly and daily reports of the Kamchatka Volcano Eruptions Response Team (KVERT), notices from Tokyo VAAC (Volcanic Ash Advisory Center), and from satellite data.

Overall activity decreased after the strong period of activity in late March through April 2023, which included ash explosions during 29 March and 7-8 April 2023 that sent plumes as high as 10-12 km altitude, along with dome growth and lava flows (BGVN 48:05). This reduced activity can be seen in the MIROVA thermal detection system graph (figure 56), which was consistent with data from the MODVOLC thermal detection system and with Sentinel-2 satellite images that showed persistent hotspots in the summit crater when conditions allowed observations. A renewed period of strong activity began in mid-October 2023.

Figure 56. The MIROVA (Log Radiative Power) thermal data for Bezymianny during 20 November 2022 through October 2023 shows heightened activity in the first half of April and second half of October 2023, with lower levels of thermal anomalies in between those times. Courtesy of MIROVA.

Activity increased significantly on 17 October 2023 when large collapses began during 0700-0830 on the E flanks of the lava dome and continued to after 0930 the next day (figure 57). Ash plumes rose to an altitude of 4.5-5 km, extending 220 km NNE by 18 October. A large explosion at 1630 on 18 October produced an ash plume that rose to an altitude of 11 km (8 km above the summit) and drifted NNE and then NW, extending 900 km NW within two days at an altitude of 8 km. Minor ashfall was noted in Kozyrevsk (45 km WNW). At 0820 on 20 October an ash plume was identified in satellite images drifting 100 km ENE at altitudes of 4-4.5 km.

Figure 57. Sentinel-2 satellite images of Bezymianny from 1159 on 17 October 2023 (2359 on 16 October UTC) showing a snow-free S and SE flank along with thermal anomalies in the crater and down the SE flank. Left image is in false color (bands 8, 4, 3); right image is thermal infrared (bands 12, 11, 8A). Courtesy of Copernicus Browser.

Lava flows and hot avalanches from the dome down the SE flank continued over the next few days, including 23 October when clear conditions allowed good observations (figures 58 and 59). A large thermal anomaly was observed over the volcano through 24 October, and in the summit crater on 30 October (figure 60). Strong fumarolic activity continued, with numerous avalanches and occasional incandescence. By the last week of October, volcanic activity had decreased to a level consistent with that earlier in the reporting period.

Figure 58. Daytime photo of Bezymianny under clear conditions on 23 October 2023 showing a lava flow and avalanches descending the SE flank, incandescence from the summit crater, and a small ash plume. Photo by Yu. Demyanchuk, courtesy of IVS FEB RAS, KVERT.

Figure 59. Night photo of Bezymianny under cloudy conditions on 23 October 2023 showing an incandescent lava flow and avalanches descending the SE flank. Photo by Yu. Demyanchuk, courtesy of IVS FEB RAS, KVERT.

Figure 60. Sentinel-2 satellite images of Bezymianny from 1159 on 30 October 2023 (2359 on 29 October UTC) showing a plume drifting SE and thermal anomalies in the summit crater and down multiple flanks. Left image is in true color (bands 4, 3, 2); right image is thermal infrared (bands 12, 11, 8A). Courtesy of Copernicus Browser.

Aviation warnings were frequently updated during 17-20 October. KVERT issued a Volcano Observatory Notice for Aviation (VONA) on 17 October at 1419 and 1727 (0219 and 0527 UTC) raising the Aviation Color Code (ACC) from Yellow to Orange (second highest level). The next day, KVERT issued a VONA at 1705 (0505 UTC) raising the ACC to Red (highest level) but lowered it back to Orange at 2117 (0917 UTC). After another decrease to Yellow and back to Orange, the ACC was reduced to Yellow on 20 October at 1204 (0004 UTC). In addition, the Tokyo VAAC issued a series of Volcanic Ash Advisories beginning on 16 October and continuing through 30 October.

Geologic Background. The modern Bezymianny, much smaller than its massive neighbors Kamen and Kliuchevskoi on the Kamchatka Peninsula, was formed about 4,700 years ago over a late-Pleistocene lava-dome complex and an edifice built about 11,000-7,000 years ago. Three periods of intensified activity have occurred during the past 3,000 years. The latest period, which was preceded by a 1,000-year quiescence, began with the dramatic 1955-56 eruption. This eruption, similar to that of St. Helens in 1980, produced a large open crater that was formed by collapse of the summit and an associated lateral blast. Subsequent episodic but ongoing lava-dome growth, accompanied by intermittent explosive activity and pyroclastic flows, has largely filled the 1956 crater.

Information Contacts: Kamchatka Volcanic Eruptions Response Team (KVERT), Far Eastern Branch, Russian Academy of Sciences, 9 Piip Blvd., Petropavlovsk-Kamchatsky, 683006, Russia (URL: http://www.kscnet.ru/ivs/kvert/); Kamchatka Volcanological Station, Kamchatka Branch of Geophysical Survey, (KB GS RAS), Klyuchi, Kamchatka Krai, Russia (URL: http://volkstat.ru/); Tokyo Volcanic Ash Advisory Center (VAAC), 1-3-4 Otemachi, Chiyoda-ku, Tokyo 100-8122, Japan (URL: http://ds.data.jma.go.jp/svd/vaac/data/); Hawai'i Institute of Geophysics and Planetology (HIGP) - MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); 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/).chr

Kīlauea is the southeastern-most volcano in Hawaii 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 recently been characterized by lava effusions, spatter, and sulfur dioxide emissions in the active Halema’uma’u lava lake (BGVN 47:08). Lava effusions, some spatter, and sulfur dioxide emissions have continued during this reporting period of July through December 2022 using daily reports, volcanic activity notices, and abundant photo, map, and video data from the US Geological Survey's (USGS) Hawaiian Volcano Observatory (HVO).

Summary of activity during July-December 2022. Low-level effusions have continued at the western vent of the Halema’uma’u crater during July through early December 2022. Occasional weak ooze-outs (also called lava break outs) would occur along the margins of the crater floor. The overall level of the active lava lake throughout the reporting period gradually increased due to infilling, however it stagnated in mid-September (table 13). During September through November, activity began to decline, though lava effusions persisted at the western vent. By 9 December, the active part of the lava lake had completely crusted over, and incandescence was no longer visible.

Table 13. Summary of measurements taken during overflights at Kīlauea that show a gradual increase in the active lava lake level and the volume of lava effused since 29 September 2021. Lower activity was reported during September-October. Data collected during July-December 2022. Courtesy of HVO.

Activity during July 2022. Lava effusions were reported from the western vent in the Halema’uma’u crater, along with occasional weak ooze-outs along the margins of the crater floor. The height of the lava lake was variable due to deflation-inflation tilt events; for example, the lake level dropped approximately 3-4 m during a summit deflation-inflation event reported on 1 July. Webcam images taken during the night of 6-12 July showed intermittent low-level spattering at the western vent that rose less than 10 m above the vent (figure 519). Measurements made during an overflight on 7 July indicated that the crater floor was infilled about 130 m and that 95 million cubic meters of lava had been effused since 29 September 2021. A single, relatively small lava ooze-out was active to the S of the lava lake. Around midnight on 8 July there were two brief periods of lava overflow onto the lake margins. On 9 July lava ooze-outs were reported near the SE and NE edges of the crater floor and during 10-11 July they occurred near the E, NE, and NW edges. On 16 July crater incandescence was reported, though the ooze-outs and spattering were not visible. On 18 July overnight webcam images showed incandescence in the western vent complex and two ooze-outs were reported around 0000 and 0200 on 19 July. By 0900 there were active ooze-outs along the SW edge of the crater floor. Measurements made from an overflight on 19 July indicated that the crater floor was infilled about 133 m and 98 million cubic meters of lava had erupted since 29 September 2021 (figure 520). On 20 July around 1600 active ooze-outs were visible along the N edge of the crater, which continued through the next day. Extensive ooze-outs occurred along the W margin during 24 July until 1900; on 26 July minor ooze-outs were noted along the N margin. Minor spattering was visible on 29 July along the E margin of the lake. The sulfur dioxide emission rates ranged 650-2,800 tons per day (t/d), the higher of which was measured on 8 July (figure 519).

Figure 519. Minor spattering rising less than 10 m was visible at the E end of the lava lake within Halema‘uma‘u, at the summit of Kīlauea on 8 July 2022. Sulfur dioxide is visible rising from the lake surface (bluish-colored fume). A sulfur dioxide emission rate of approximately 2,800 t/d was measured on 8 July. Courtesy of K. Mulliken, USGS.

Figure 520. A helicopter overflight on 19 July 2022 allowed for aerial visible and thermal imagery to be taken of the Halema’uma’u crater at Kīlauea’s summit crater. The active part of the lava lake is confined to the western part of the crater. The scale of the thermal map ranges from blue to red, with blue colors indicative of cooler temperatures and red colors indicative of warmer temperatures. Courtesy of USGS, HVO.

Activity during August 2022. The eruption continued in the Halema’uma’u crater at the western vent. According to HVO the lava in the active lake remained at the level of the bounding levees. Occasional minor ooze-outs were observed along the margins of the crater floor. Strong nighttime crater incandescence was visible after midnight on 6 August over the western vent cone. During 6-7 August scattered small lava lobes were active along the crater floor and incandescence persisted above the western vent through 9 August. During 7-9 August HVO reported a single lava effusion source was active along the NW margin of the crater floor. Measurements from an overflight on 4 August indicated that the crater floor was infilled about 136 m total and that 102 million cubic meters of lava had been erupted since the start of the eruption. Lava breakouts were reported along the N, NE, E, S, and W margins of the crater during 10-16 August. Another overflight survey conducted on 16 August indicated that the crater floor infilled about 137 m and 104 million cubic meters of lava had been erupted since September 2021. Measured sulfur dioxide emissions rates ranged 1,150-2,450 t/d, the higher of which occurred on 8 August.

Activity during September 2022. During September, lava effusion continued from the western vent into the active lava lake and onto the crater floor. Intermittent minor ooze-outs were reported through the month. A small ooze-out was visible on the W crater floor margin at 0220 on 2 September, which showed decreasing surface activity throughout the day, but remained active through 3 September. On 3 September around 1900 a lava outbreak occurred along the NW margin of the crater floor but had stopped by the evening of 4 September. Field crews monitoring the summit lava lake on 9 September observed spattering on the NE margin of the lake that rose no higher than 10 m, before falling back onto the lava lake crust (figure 521). Overflight measurements on 12 September indicated that the crater floor was infilled a total of 143 m and 111 million cubic meters of lava had been erupted since September 2021. Extensive breakouts in the W and N part of the crater floor were reported at 1600 on 20 September and continued into 26 September. The active part of the lava lake dropped by 10 m while other parts of the crater floor dropped by several meters. Summit tiltmeters recorded a summit seismic swarm of more than 80 earthquakes during 1500-1800 on 21 September, which occurred about 1.5 km below Halema’uma’u; a majority of these were less than Mw 2. By 22 September the active part of the lava lake was infilled about 2 m. On 23 September the western vent areas exhibited several small spatter cones with incandescent openings, along with weak, sporadic spattering (figure 522). The sulfur dioxide emission rate ranged from 930 t/d to 2,000 t/d, the higher of which was measured on 6 September.

Figure 521. Photo of spattering occurring at Kīlauea's Halema’uma’u crater during the morning of 9 September 2022 on the NE margin of the active lava lake. The spatter material rose 10 m into the air before being deposited back on the lava lake crust. Courtesy of C. Parcheta, USGS.

Figure 522.The active western vent area at Kīlauea's Halema’uma’u crater consisted of several small spatter cones with incandescent openings and weak, sporadic spattering. Courtesy of M. Patrick, USGS.

Activity during October 2022. Activity during October declined slightly compared to previous months, though lava effusions persisted from the western vent into the active lava lake and onto the crater floor during October (figure 523). Slight variations in the lava lake were noted throughout the month. HVO reported that around 0600 on 3 October the level of the lava lake has lowered slightly. Overflight measurements taken on 5 October indicated that the crater floor was infilled a total of about 143 m and that 111 million cubic meters of lava had been effused since September 2021. During 6-7 October the lake gradually rose 0.5 m. Sulfur dioxide measurements made on 22 October had an emission rate of 700 t/d. Another overflight taken on 28 October showed that there was little to no change in the elevation of the crater floor: the crater floor was infilled a total of 143 m and 111 million cubic meters of lava had erupted since the start of the eruption.

Figure 523. Photo of the Halema’uma’u crater at Kīlauea looking east from the crater rim showing the active lava lake, with active lava ponds to the SE (top) and west (bottom middle) taken on 5 October 2022. The western vent complex is visible through the gas at the bottom center of the photo. Courtesy of N. Deligne, USGS.

Activity during November 2022. Activity remained low during November, though HVO reported that lava from the western vent continued to effuse into the active lava lake and onto the crater floor throughout the month. The rate of sulfur dioxide emissions during November ranged from 300-600 t/d, the higher amount of which occurred on 9 November.

Activity during December 2022. Similar low activity was reported during December, with lava effusing from the western vent into the active lava lake and onto the crater floor. During 4-5 December the active part of the lava lake was slightly variable in elevation and fluctuated within 1 m. On 9 December HVO reported that lava was no longer erupting from the western vent in the Halema’uma’u crater and that sulfur dioxide emissions had returned to near pre-eruption background levels; during 10-11 December, the lava lake had completely crusted over, and no incandescence was visible (figure 524). Time lapse camera images covering the 4-10 December showed that the crater floor showed weak deflation and no inflation. Some passive events of crustal overturning were reported during 14-15 December, which brought fresh incandescent lava to the lake surface. The sulfur dioxide emission rate was approximately 200 t/d on 14 December. A smaller overturn event on 17 December and another that occurred around 0000 and into the morning of 20 December were also detected. A small seismic swarm was later detected on 30 December.

Figure 524. Photo of Halema’uma’u crater at Kīlauea showing a mostly solidified lake surface during the early morning of 10 December 2022. Courtesy of J. Bard, USGS.

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/).

Nyamulagira (also known as Nyamuragira) is a shield volcano in the Democratic Republic of Congo with the summit truncated by a small 2 x 2.3 km caldera with walls up to about 100 m high. Documented eruptions have occurred within the summit caldera, as well as from numerous flank fissures and cinder cones. The current eruption period began in April 2018 and has more recently been characterized by summit crater lava flows and thermal activity (BGVN 48:05). This report describes lava flows and variable thermal activity during May through October 2023, based on information from the Observatoire Volcanologique de Goma (OVG) and various satellite data.

Lava lake activity continued during May. The MIROVA (Middle InfraRed Observation of Volcanic Activity) system recorded moderate-to-strong thermal activity throughout the reporting period; activity was more intense during May and October and relatively weaker from June through September (figure 95). The MODVOLC thermal algorithm, detected a total of 209 thermal alerts. There were 143 hotspots detected during May, eight during June, nine during September, and 49 during October. This activity was also reflected in infrared satellite images, where a lava flow was visible in the NW part of the crater on 7 May and strong activity was seen in the center of the crater on 4 October (figure 96). Another infrared satellite image taken on 12 May showed still active lava flows along the NW margin of the crater. According to OVG lava effusions were active during 7-29 May and moved to the N and NW parts of the crater beginning on 9 May. Strong summit crater incandescence was visible from Goma (27 km S) during the nights of 17, 19, and 20 May (figure 97). On 17 May there was an increase in eruptive activity, which peaked at 0100 on 20 May. Notable sulfur dioxide plumes drifted NW and W during 19-20 May (figure 98). Drone footage acquired in partnership with the USGS (United States Geological Survey) on 20 May captured images of narrow lava flows that traveled about 100 m down the W flank (figure 99). Data from the Rumangabo seismic station indicated a decreasing trend in activity during 17-21 May. Although weather clouds prevented clear views of the summit, a strong thermal signature on the NW flank was visible in an infrared satellite image on 22 May, based on an infrared satellite image. On 28 May the lava flows on the upper W flank began to cool and solidify. By 29 May seismicity returned to levels similar to those recorded before the 17 May increase. Lava effusion continued but was confined to the summit crater; periodic crater incandescence was observed.

Figure 95. Moderate-to-strong thermal anomalies were detected at Nyamulagira during May through October 2023, as shown on this MIROVA graph (Log Radiative Power). During late May, the intensity of the anomalies gradually decreased and remained at relatively lower levels during mid-June through mid-September. During mid-September, the power of the anomalies gradually increased again. The stronger activity is reflective of active lava effusions. Courtesy of MIROVA.

Figure 96. Infrared (bands B12, B11, B4) satellite images showing a constant thermal anomaly of variable intensities in the summit crater of Nyamulagira on 7 May 2023 (top left), 21 June 2023 (top right), 21 July 2023 (bottom left), and 4 October 2023 (bottom right). Although much of the crater was obscured by weather clouds on 7 May, a possible lava flow was visible in the NW part of the crater. Courtesy of Copernicus Browser.

Figure 97. Photo of intense nighttime crater incandescence at Nyamulagira as seen from Goma (27 km S) on the evening of 19 May 2023. Courtesy of Charles Balagizi, OVG.

Figure 98. Two strong sulfur dioxide plumes were detected at Nyamulagira and drifted W on 19 (left) and 20 (right) May 2023. Courtesy of NASA Global Sulfur Dioxide Monitoring Page.

Figure 99. A map (top) showing the active vents (yellow pins) and direction of active lava flows (W) at Nyamulagira at Virunga National Park on 20 May 2023. Drone footage (bottom) also shows the fresh lava flows traveling downslope to the W on 20 May 2023. Courtesy of USGS via OVG.

Low-level activity was noted during June through October. On 1 June OVG reported that seismicity remained at lower levels and that crater incandescence had been absent for three days, though infrared satellite imagery showed continued lava effusion in the summit crater. The lava flows on the flanks covered an estimated 0.6 km². Satellite imagery continued to show thermal activity confined to the lava lake through October (figure 96), although no lava flows or significant sulfur dioxide emissions were reported.

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: Observatoire Volcanologique de Goma (OVG), Departement de Geophysique, Centre de Recherche en Sciences Naturelles, Lwiro, D.S. Bukavu, DR Congo; Hawai'i Institute of Geophysics and Planetology (HIGP) - MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); NASA 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/); Charles Balagizi, Goma Volcano Observatory, Departement de Geophysique, Centre de Recherche en Sciences Naturelles, Lwiro, D.S. Bukavu, DR Congo.

The remote volcano of Bagana is located in central Bougainville Island, Papua New Guinea. Recorded eruptions date back to 1842 and activity has consisted of effusive activity that has built a small lava dome in the summit crater and occasional explosions that produced pyroclastic flows. The most recent eruption has been ongoing since February 2000 and has produced occasional explosions, ash plumes, and lava flows. More recently, activity has been characterized by ongoing effusive activity and ash emissions (BGVN 48:04). This report updates activity from April through September 2023 that has consisted of explosions, ash plumes, ashfall, and lava flows, using information from the Darwin Volcanic Ash Advisory Center (VAAC) and satellite data.

An explosive eruption was reported on 7 July that generated a large gas-and-ash plume to high altitudes and caused significant ashfall in local communities; the eruption plume had reached upper tropospheric (16-18 km altitude) altitudes by 2200, according to satellite images. Sulfur dioxide plumes were detected in satellite images on 8 July and indicated that the plume was likely a mixture of gas, ice, and ash. A report issued by the Autonomous Bougainville Government (ABG) (Torokina District, Education Section) on 10 July noted that significant ash began falling during 2000-2100 on 7 July and covered most areas in the Vuakovi, Gotana (9 km SW), Koromaketo, Laruma (25 km W) and Atsilima (27 km NW) villages. Pyroclastic flows also occurred, according to ground-based reports; small deposits confined to one drainage were inspected by RVO during an overflight on 17 July and were confirmed to be from the 7 July event. Ashfall continued until 10 July and covered vegetation, which destroyed bushes and gardens and contaminated rivers and streams.

RVO reported another eruption on 14 July. The Darwin VAAC stated that an explosive event started around 0830 on 15 July and produced an ash plume that rose to 16.5 km altitude by 1000 and drifted N, according to satellite images. The plume continued to drift N and remained visible through 1900, and by 2150 it had dissipated.

Ashfall likely from both the 7 and 15 July events impacted about 8,111 people in Torokina (20 km SW), including Tsito/Vuakovi, Gotana, Koromaketo, Kenaia, Longkogari, Kenbaki, Piva (13 km SW), and Atsinima, and in the Tsitovi district, according to ABG. Significant ashfall was also reported in Ruruvu (22 km N) in the Wakunai District of Central Bougainville, though the thickness of these deposits could not be confirmed. An evacuation was called for the villages in Wakunai, where heavy ashfall had contaminated water sources; the communities of Ruruvu, Togarau, Kakarapaia, Karauturi, Atao, and Kuritaturi were asked to evacuate to a disaster center at the Wakunai District Station, and communities in Torokina were asked to evacuate to the Piva District station. According to a news article, more than 7,000 people needed temporary accommodations, with about 1,000 people in evacuation shelters. Ashfall had deposited over a broad area, contaminating water supplies, affecting crops, and collapsing some roofs and houses in rural areas. Schools were temporarily shut down. Intermittent ash emissions continued through the end of July and drifted NNW, NW, and SW. Fine ashfall was reported on the coast of Torokina, and ash plumes also drifted toward Laruma and Atsilima.

A small explosive eruption occurred at 2130 on 28 July that ejected material from the crater vents, according to reports from Torokina, in addition to a lava flow that contained two lobes. A second explosion was detected at 2157. Incandescence from the lava flow was visible from Piva as it descended the W flank around 2000 on 29 July (figure 47). The Darwin VAAC reported that a strong thermal anomaly was visible in satellite images during 30-31 July and that ash emissions rose to 2.4 km altitude and drifted WSW on 30 July. A ground report from RVO described localized emissions at 0900 on 31 July.

Figure 47. Infrared (bands B12, B11, B4) satellite images showed weak thermal anomalies at the summit crater of Bagana on 12 April 2023 (top left), 27 May 2023 (top right), 31 July 2023 (bottom left), and 19 September 2023 (bottom right). A strong thermal anomaly was detected through weather clouds on 31 July and extended W from the summit crater. Courtesy of Copernicus Browser.

The Darwin VAAC reported that ash plumes were identified in satellite imagery at 0800 and 1220 on 12 August and rose to 2.1 km and 3 km altitude and drifted NW and W, respectively. A news report stated that aid was sent to more than 6,300 people that were adversely affected by the eruption. Photos taken during 17-19 August showed ash emissions rising no higher than 1 km above the summit and drifting SE. A small explosion generated an ash plume during the morning of 19 August. Deposits from small pyroclastic flows were also captured in the photos. Satellite images captured lava flows and pyroclastic flow deposits. Two temporary seismic stations were installed near Bagana on 17 August at distances of 7 km WSW (Vakovi station) and 11 km SW (Kepox station). The Kepox station immediately started to record continuous, low-frequency background seismicity.

Satellite data. Little to no thermal activity was detected during April through mid-July 2023; only one anomaly was recorded during early April and one during early June, according to MIROVA (Middle InfraRed Observation of Volcanic Activity) data (figure 48). Thermal activity increased in both power and frequency during mid-July through September, although there were still some short gaps in detected activity. MODVOLC also detected increased thermal activity during August; thermal hotspots were detected a total of five times on 19, 20, and 27 August. Weak thermal anomalies were also captured in infrared satellite images on clear weather days throughout the reporting period on 7, 12, and 17 April, 27 May, 1, 6, 16, and 31 July, and 19 September (figure 48); a strong thermal anomaly was visible on 31 July. Distinct sulfur dioxide plumes that drifted generally NW were intermittently captured by the TROPOMI instrument on the Sentinel-5P satellite and sometimes exceeded two Dobson Units (DUs) (figure 49).

Figure 48. Low thermal activity was detected at Bagana during April through mid-July 2023, as shown on this MIROVA graph. In mid-July, activity began to increase in both frequency and power, which continued through September. There were still some pauses in activity during late July, early August, and late September, but a cluster of thermal activity was detected during late August. Courtesy of MIROVA.

Figure 49. Distinct sulfur dioxide plumes rising from Bagana on 15 July 2023 (top left), 16 July 2023 (top right), 17 July 2023 (bottom left), and 17 August 2023 (bottom right). These plumes all generally drifted NW; a particularly notable plume exceeded 2 Dobson Units (DUs) on 15 July. Data is from the TROPOMI instrument on the Sentinel-5P satellite. Courtesy of NASA Global Sulfur Dioxide Monitoring Page.0

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: Rabaul Volcano Observatory (RVO), Geohazards Management Division, Department of Mineral Policy and Geohazards Management (DMPGM), PO Box 3386, Kokopo, East New Britain Province, Papua New Guinea; Darwin Volcanic Ash Advisory Centre (VAAC), Bureau of Meteorology, Northern Territory Regional Office, PO Box 40050, Casuarina, NT 0811, Australia (URL: http://www.bom.gov.au/info/vaac/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Hawai'i Institute of Geophysics and Planetology (HIGP) - MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); NASA Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, NASA Goddard Space Flight Center (NASA/GSFC), 8800 Greenbelt Road, Goddard, Maryland, USA (URL: https://so2.gsfc.nasa.gov/); Copernicus Browser, Copernicus Data Space Ecosystem, European Space Agency (URL: https://dataspace.copernicus.eu/browser/); Autonomous Bougainville Government, P.O Box 322, Buka, AROB, PNG (URL: https://abg.gov.pg/); Andrew Tupper (Twitter: @andrewcraigtupp); Simon Carn, Geological and Mining Engineering and Sciences, Michigan Technological University, 1400 Townsend Drive, Houghton, MI 49931, USA (URL: http://www.volcarno.com/, Twitter: @simoncarn); Radio NZ (URL: https://www.rnz.co.nz/news/pacific/494464/more-than-7-000-people-in-bougainville-need-temporary-accommodation-after-eruption); USAID, 1300 Pennsylvania Ave, NW, Washington DC 20004, USA (URL: https://www.usaid.gov/pacific-islands/press-releases/aug-08-2023-united-states-provides-immediate-emergency-assistance-support-communities-affected-mount-bagana-volcanic-eruptions).

Mayon is located in the Philippines and has steep upper slopes capped by a small summit crater. Historical eruptions date back to 1616 CE that have been characterized by Strombolian eruptions, lava flows, pyroclastic flows, and mudflows. Eruptions mostly originated from a central conduit. Pyroclastic flows and mudflows have commonly descended many of the approximately 40 drainages that surround the volcano. The most recent eruption occurred during June through October 2022 and consisted of lava dome growth and gas-and-steam emissions (BGVN 47:12). A new eruption was reported during late April 2023 and has included lava flows, pyroclastic density currents, ash emissions, and seismicity. This report covers activity during April through September 2023 based on daily bulletins from the Philippine Institute of Volcanology and Seismology (PHIVOLCS).

During April through September 2023, PHIVOLCS reported near-daily rockfall events, frequent volcanic earthquakes, and sulfur dioxide measurements. Gas-and-steam emissions rose 100-900 m above the crater and drifted in different directions. Nighttime crater incandescence was often visible during clear weather and was accompanied by incandescent avalanches of material. Activity notably increased during June when lava flows were reported on the S, SE, and E flanks (figure 52). The MIROVA graph (Middle InfraRed Observation of Volcanic Activity) showed strong thermal activity coincident with these lava flows, which remained active through September (figure 53). According to the MODVOLC thermal algorithm, a total of 110 thermal alerts were detected during the reporting period: 17 during June, 40 during July, 27 during August, and 26 during September. During early June, pyroclastic density currents (PDCs) started to occur more frequently.

Figure 52. Infrared (bands B12, B11, B4) satellite images show strong lava flows descending the S, SE, and E flanks of Mayon on 13 June 2023 (top left), 23 June 2023 (top right), 8 July 2023 (bottom left), and 7 August 2023 (bottom right). Courtesy of Copernicus Browser.

Figure 53. Strong thermal activity was detected at Mayon during early June through September, according to this MIROVA graph (Log Radiative Power) due to the presence of active lava flows on the SE, S, and E flanks. Courtesy of MIROVA.

Low activity was reported during much of April and May; gas-and-steam emissions rose 100-900 m above the crater and generally drifted in different directions. A total of 52 rockfall events and 18 volcanic earthquakes were detected during April and 147 rockfall events and 13 volcanic events during May. Sulfur dioxide flux measurements ranged between 400-576 tons per day (t/d) during April, the latter of which was measured on 29 April and between 162-343 t/d during May, the latter of which was measured on 13 May.

Activity during June increased, characterized by lava flows, pyroclastic density currents (PDCs), crater incandescence and incandescent rockfall events, gas-and-steam emissions, and continued seismicity. Weather clouds often prevented clear views of the summit, but during clear days, moderate gas-and-steam emissions rose 100-2,500 m above the crater and drifted in multiple directions. A total of 6,237 rockfall events and 288 volcanic earthquakes were detected. The rockfall events often deposited material on the S and SE flanks within 700-1,500 m of the summit crater and ash from the events drifted SW, S, SE, NE, and E. Sulfur dioxide emissions ranged between 149-1,205 t/d, the latter of which was measured on 10 June. Short-term observations from EDM and electronic tiltmeter monitoring indicated that the upper slopes were inflating since February 2023. Longer-term ground deformation parameters based on EDM, precise leveling, continuous GPS, and electronic tilt monitoring indicated that the volcano remained inflated, especially on the NW and SE flanks. At 1000 on 5 June the Volcano Alert Level (VAL) was raised to 2 (on a 0-5 scale). PHIVOLCS noted that although low-level volcanic earthquakes, ground deformation, and volcanic gas emissions indicated unrest, the steep increase in rockfall frequency may indicate increased dome activity.

A total of 151 dome-collapse PDCs occurred during 8-9 and 11-30 June, traveled 500-2,000 m, and deposited material on the S flank within 2 km of the summit crater. During 8-9 June the VAL was raised to 3. At approximately 1947 on 11 June lava flow activity was reported; two lobes traveled within 500 m from the crater and deposited material on the S (Mi-isi), SE (Bonga), and E (Basud) flanks. Weak seismicity accompanied the lava flow and slight inflation on the upper flanks. This lava flow remained active through 30 June, moving down the S and SE flank as far as 2.5 km and 1.8 km, respectively and depositing material up to 3.3 km from the crater. During 15-16 June traces of ashfall from the PDCs were reported in Sitio Buga, Nabonton, City of Ligao and Purok, and San Francisco, Municipality of Guinobatan. During 28-29 June there were two PDCs generated by the collapse of the lava flow front, which generated a light-brown ash plume 1 km high. Satellite monitors detected significant concentrations of sulfur dioxide beginning on 29 June. On 30 June PDCs primarily affected the Basud Gully on the E flank, the largest of which occurred at 1301 and lasted eight minutes, based on the seismic record. Four PDCs generated between 1800 and 2000 that lasted approximately four minutes each traveled 3-4 km on the E flank and generated an ash plume that rose 1 km above the crater and drifted N and NW. Ashfall was recorded in Tabaco City.

Similar strong activity continued during July; slow lava effusion remained active on the S and SE flanks and traveled as far as 2.8 km and 2.8 km, respectively and material was deposited as far as 4 km from the crater. There was a total of 6,983 rockfall events and 189 PDCs that affected the S, SE, and E flanks. The volcano network detected a total of 2,124 volcanic earthquakes. Continuous gas-and-steam emissions rose 200-2,000 m above the crater and drifted in multiple directions. Sulfur dioxide emissions averaged 792-4,113 t/d, the latter of which was measured on 28 July. During 2-4 July three PDCs were generated from the collapse of the lava flow and resulting light brown plumes rose 200-300 m above the crater. Continuous tremor pulses were reported beginning at 1547 on 3 July through 7 July at 1200, at 2300 on 8 July and going through 0300 on 10 July, and at 2300 on 16 July, as recorded by the seismic network. During 6-9 July there were 10 lava flow-collapse-related PDCs that generated light brown plumes 300-500 m above the crater. During 10-11 July light ashfall was reported in some areas of Mabinit, Legazpi City, Budiao and Salvacion, Daraga, and Camalig, Albay. By 18 July the lava flow advanced 600 m on the E flank as well.

During 1733 on 18 July and 0434 on 19 July PHIVOLCS reported 30 “ashing” events, which are degassing events accompanied by audible thunder-like sounds and entrained ash at the crater, which produced short, dark plumes that drifted SW. These events each lasted 20-40 seconds, and plume heights ranged from 150-300 m above the crater, as recorded by seismic, infrasound, visual, and thermal monitors. Three more ashing events occurred during 19-20 July. Short-term observations from electronic tilt and GPS monitoring indicate deflation on the E lower flanks in early July and inflation on the NW middle flanks during the third week of July. Longer-term ground deformation parameters from EDM, precise leveling, continuous GPS, and electronic tilt monitoring indicated that the volcano was still generally inflated relative to baseline levels. A short-lived lava pulse lasted 28 seconds at 1956 on 21 July, which was accompanied by seismic and infrasound signals. By 22 July, the only lava flow that remained active was on the SE flank, and continued to extend 3.4 km, while those on the S and E flanks weakened markedly. One ashing event was detected during 30-31 July, whereas there were 57 detected during 31 July-1 August; according to PHIVOLCS beginning at approximately 1800 on 31 July eruptive activity was dominated by phases of intermittent ashing, as well as increased in the apparent rates of lava effusion from the summit crater. The ashing phases consisted of discrete events recorded as low-frequency volcanic earthquakes (LFVQ) typically 30 seconds in duration, based on seismic and infrasound signals. Gray ash plume rose 100 m above the crater and generally drifted NE. Shortly after these ashing events began, new lava began to effuse rapidly from the crater, feeding the established flowed on the SE, E, and E flanks and generating frequent rockfall events.

Intensified unrest persisted during August. There was a total of 4,141 rockfall events, 2,881 volcanic earthquakes, which included volcanic tremor events, 32 ashing events, and 101 PDCs detected throughout the month. On clear weather days, gas-and-steam emissions rose 300-1,500 m above the crater and drifted in different directions (figure 54). Sulfur dioxide emissions averaged 735-4,756 t/d, the higher value of which was measured on 16 August. During 1-2 August the rate of lava effusion decreased, but continued to feed the flows on the SE, S, and E flanks, maintaining their advances to 3.4 km, 2.8 km, and 1.1 km from the crater, respectively (figure 55). Rockfall and PDCs generated by collapses at the lava flow margins and from the summit dome deposited material within 4 km of the crater. During 3-4 August there were 10 tremor events detected that lasted 1-4 minutes. Short-lived lava pulse lasted 35 seconds and was accompanied by seismic and infrasound signals at 0442 on 6 August. Seven collapses were recorded at the front of the lava flow during 12-14 August.

Figure 54. Photo of Mayon showing a white gas-and-steam plume rising 800-1,500 m above the crater at 0645 on 25 August. Courtesy of William Rogers.

Figure 55. Photo of Mayon facing N showing incandescent lava flows and summit crater incandescence taken at 1830 on 25 August 2023. Courtesy of William Rogers.

During September, similar activity of slow lava effusion, PDCs, gas-and-steam emissions, and seismicity continued. There was a total of 4,452 rockfall events, 329 volcanic earthquakes, which included volcanic tremor events, two ashing events, and 85 PDCs recorded throughout the month. On clear weather days, gas-and-steam emissions rose 100-1,500 m above the crater and drifted in multiple directions. Sulfur dioxide emissions averaged 609-2,252 t/d, the higher average of which was measured on 6 September. Slow lava effusion continued advancing on the SE, S, and E flanks, maintaining lengths of 3.4 km, 2.8 km, and 1.1 km, respectively. Rockfall and PDC events generated by collapses along the lava flow margins and at the summit dome deposited material within 4 km of the crater.

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

Information Contacts: Philippine Institute of Volcanology and Seismology (PHIVOLCS), Department of Science and Technology, University of the Philippines Campus, Diliman, Quezon City, Philippines (URL: http://www.phivolcs.dost.gov.ph/); 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/); William Rogers, Legazpi City, Albay Province, Philippines.

Nishinoshima, located about 1,000 km S of Tokyo, is a small island in the Ogasawara Arc in Japan. The island is the summit of a massive submarine volcano that has prominent submarine peaks to the S, W, and NE. Eruptions date back to 1973 and the current eruption period began in October 2022. Recent activity has consisted of small ash plumes and fumarolic activity (BGVN 48:07). This report covers activity during May through August 2023, using information from monthly reports of the Japan Meteorological Agency (JMA) monthly reports and satellite data.

Activity during May through June was relatively low. The Japan Coast Guard (JCG) did overflights on 14 and 22 June and reported white gas-and-steam emissions rising 600 m and 1,200 m from the central crater of the pyroclastic cone, respectively (figure 125). In addition, multiple white gas-and-steam emissions rose from the inner rim of the W side of the crater and from the SE flank of the pyroclastic cone. Discolored brown-to-green water was observed around almost the entire perimeter of the island; on 22 June light green discolored water was observed off the S coast of the island.

Figure 125. A white gas-and-steam plume rising 600 m above the crater of Nishinoshima at 1404 on 14 June 2023 (left) and 1,200 m above the crater at 1249 on 22 June 2023 (right). Courtesy of JCG via JMA (monthly reports of activity at Nishinoshima, June, 2023).

Observations from the Himawari meteorological satellite confirmed an eruption on 9 and 10 July. An eruption plume rose 1.6 km above the crater and drifted N around 1300 on 9 July. Satellite images acquired at 1420 and 2020 on 9 July and at 0220 on 10 July showed continuing emissions that rose 1.3-1.6 km above the crater and drifted NE and N. The Tokyo VAAC reported that an ash plume seen by a pilot and identified in a satellite image at 0630 on 21 July rose to 3 km altitude and drifted S.

Aerial observations conducted by JCG on 8 August showed a white-and-gray plume rising from the central crater of the pyroclastic cone, and multiple white gas-and-steam emissions were rising from the inner edge of the western crater and along the NW-SE flanks of the island (figure 126). Brown-to-green discolored water was also noted around the perimeter of the island.

Figure 126. Aerial photo of Nishinoshima showing a white-and-gray plume rising from the central crater taken at 1350 on 8 August 2023.

Intermittent low-to-moderate power thermal anomalies were recorded in the MIROVA graph (Middle InfraRed Observation of Volcanic Activity), showing an increase in both frequency and power beginning in July (figure 127). This increase in activity coincides with eruptive activity on 9 and 10 July, characterized by eruption plumes. According to the MODVOLC thermal alert algorithm, one thermal hotspot was recorded on 20 July. Weak thermal anomalies were also detected in infrared satellite imagery, accompanied by strong gas-and-steam plumes (figure 128).

Figure 127. Low-to-moderate power thermal anomalies were detected at Nishinoshima during May through August 2023, showing an increase in both frequency and power in July, according to this MIROVA graph (Log Radiative Power). Courtesy of MIROVA.

Figure 128. Infrared (bands B12, B11, B4) satellite images showing a small thermal anomaly at the crater of Nishinoshima on 30 June 2023 (top left), 3 July 2023 (top right), 7 August 2023 (bottom left), and 27 August 2023 (bottom right). Strong gas-and-steam plumes accompanied this activity, extending NW, NE, and SW. 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); Tokyo Volcanic Ash Advisory Center (VAAC), 1-3-4 Otemachi, Chiyoda-ku, Tokyo 100-8122, Japan (URL: http://ds.data.jma.go.jp/svd/vaac/data/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Copernicus Browser, Copernicus Data Space Ecosystem, European Space Agency (URL: https://dataspace.copernicus.eu/browser/).

Krakatau is located in the Sunda Strait between Java and Sumatra, Indonesia. Caldera collapse during the catastrophic 1883 eruption destroyed Danan and Perbuwatan cones and left only a remnant of Rakata. The post-collapse cone of Anak Krakatau (Child of Krakatau) was constructed within the 1883 caldera at a point between the former Danan and Perbuwatan cones; it has been the site of frequent eruptions since 1927. The current eruption period began in May 2021 and has recently consisted of Strombolian eruptions and ash plumes (BGVN 48:07). This report describes lower levels of activity consisting of ash and white gas-and-steam plumes during May through August 2023, based on information provided by the Indonesian Center for Volcanology and Geological Hazard Mitigation, referred to as Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG), MAGMA Indonesia, and satellite data.

Activity was relatively low during May and June. Daily white gas-and-steam emissions rose 25-200 m above the crater and drifted in different directions. Five ash plumes were detected at 0519 on 10 May, 1241 on 11 May, 0920 on 12 May, 2320 on 12 May, and at 0710 on 13 May, and rose 1-2.5 km above the crater and drifted SW. A webcam image taken on 12 May showed ejection of incandescent material above the vent. A total of nine ash plumes were detected during 6-11 June: at 1434 and 00220 on 6 and 7 June the ash plumes rose 500 m above the crater and drifted NW, at 1537 on 8 June the ash plume rose 1 km above the crater and drifted SW, at 0746 and at 0846 on 9 June the ash plumes rose 800 m and 3 km above the crater and drifted SW, respectively, at 0423, 1431, and 1750 on 10 June the ash plumes rose 2 km, 1.5 km, and 3.5 km above the crater and drifted NW, respectively, and at 0030 on 11 June an ash plume rose 2 km above the crater and drifted NW. Webcam images taken on 10 and 11 June at 0455 and 0102, respectively, showed incandescent material ejected above the vent. On 19 June an ash plume at 0822 rose 1.5 km above the crater and drifted SE.

Similar low activity of white gas-and-steam emissions and few ash plumes were reported during July and August. Daily white gas-and-steam emissions rose 25-300 m above the crater and drifted in multiple directions. Three ash plumes were reported at 0843, 0851, and 0852 on 20 July that rose 500-2,000 m above the crater and drifted NW.

The MIROVA (Middle InfraRed Observation of Volcanic Activity) graph of MODIS thermal anomaly data showed intermittent low-to-moderate power thermal anomalies during May through August 2023 (figure 140). Although activity was often obscured by weather clouds, a thermal anomaly was visible in an infrared satellite image of the crater on 12 May, accompanied by an eruption plume that drifted SW (figure 141).

Figure 140. Intermittent low-to-moderate power thermal anomalies were detected at Krakatau during May through August 2023, based on this MIROVA graph (Log Radiative Power). Courtesy of MIROVA.

Figure 141. A single thermal anomaly (bright yellow-orange) was visible at Krakatau in this infrared (bands B12, B11, B4) satellite image taken on 12 May 2023. An eruption plume accompanied the thermal anomaly and drifted SW. Courtesy of Copernicus Browser.

Geologic Background. The renowned Krakatau (frequently mis-named as Krakatoa) volcano lies in the Sunda Strait between Java and Sumatra. Collapse of an older edifice, perhaps in 416 or 535 CE, formed a 7-km-wide caldera. Remnants of that volcano are preserved in Verlaten and Lang Islands; subsequently the Rakata, Danan, and Perbuwatan cones were formed, coalescing to create the pre-1883 Krakatau Island. Caldera collapse during the catastrophic 1883 eruption destroyed Danan and Perbuwatan, and left only a remnant of Rakata. This eruption caused more than 36,000 fatalities, most as a result of tsunamis that swept the adjacent coastlines of Sumatra and Java. Pyroclastic surges traveled 40 km across the Sunda Strait and reached the Sumatra coast. After a quiescence of less than a half century, the post-collapse cone of Anak Krakatau (Child of Krakatau) was constructed within the 1883 caldera at a point between the former Danan and Perbuwatan cones. Anak Krakatau has been the site of frequent eruptions since 1927.

Information Contacts: Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM), Jalan Diponegoro 57, Bandung 40122, Indonesia (URL: http://www.vsi.esdm.go.id/); MAGMA Indonesia, Kementerian Energi dan Sumber Daya Mineral (URL: https://magma.esdm.go.id/v1); 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/).

Villarrica, in central Chile, consists of a 2-km-wide caldera that formed about 3,500 years ago and is located at the base of the presently active cone at the NW margin of a 6-km-wide caldera. Historical eruptions eruptions date back to 1558 and have been characterized by mild-to-moderate explosive activity with occasional lava effusions. The current eruption period began in December 2014 and has recently consisted of nighttime crater incandescence, ash emissions, and seismicity (BGVN 48:04). This report covers activity during April through September 2023 and describes occasional Strombolian activity, gas-and-ash emissions, and nighttime crater incandescence. Information for this report primarily comes from the Southern Andes Volcano Observatory (Observatorio Volcanológico de Los Andes del Sur, OVDAS), part of Chile's National Service of Geology and Mining (Servicio Nacional de Geología y Minería, SERNAGEOMIN) and satellite data.

Seismicity during April consisted of long period (LP) events and tremor (TRE); a total of 9,413 LP-type events and 759 TR-type events were detected throughout the month. Nighttime crater incandescence persisted and was visible in the degassing column. Sulfur dioxide data was obtained using Differential Absorption Optical Spectroscopy Equipment (DOAS) that showed an average value of 1,450 ± 198 tons per day (t/d) during 1-15 April and 1,129 ± 201 t/d during 16-30 April, with a maximum daily value of 2,784 t/d on 9 April. Gas-and-steam emissions of variable intensities rose above the active crater as high as 1.3 km above the crater on 13 April. Strombolian explosions were not observed and there was a slight decrease in the lava lake level.

There were 14,123 LP-type events and 727 TR-type events detected during May. According to sulfur dioxide measurements taken with DOAS equipment, the active crater emitted an average value of 1,826 ± 482 t/d during 1-15 May and 912 ± 41 t/d during 16-30 May, with a daily maximum value of 5,155 t/d on 13 May. Surveillance cameras showed continuous white gas-and-steam emissions that rose as high as 430 m above the crater on 27 May. Nighttime incandescence illuminated the gas column less than 300 m above the crater rim was and no pyroclastic emissions were reported. A landslide was identified on 13 May on the E flank of the volcano 50 m from the crater rim and extending 300 m away; SERNAGEOMIN noted that this event may have occurred on 12 May. During the morning of 27 and 28 May minor Strombolian explosions characterized by incandescent ejecta were recorded at the crater rim; the last reported Strombolian explosions had occurred at the end of March.

Seismic activity during June consisted of five volcano-tectonic (VT)-type events, 21,606 LP-type events, and 2,085 TR-type events. The average value of sulfur dioxide flux obtained by DOAS equipment was 1,420 ± 217 t/d during 1-15 June and 2,562 ± 804 t/d, with a maximum daily value of 4,810 t/d on 17 June. White gas-and-steam emissions rose less than 480 m above the crater; frequent nighttime crater incandescence was reflected in the degassing plume. On 12 June an emission rose 100 m above the crater and drifted NNW. On 15 June one or several emissions resulted in ashfall to the NE as far as 5.5 km from the crater, based on a Skysat satellite image. Several Strombolian explosions occurred within the crater; activity on 15 June was higher energy and ejected blocks 200-300 m on the NE slope. Surveillance cameras showed white gas-and-steam emissions rising 480 m above the crater on 16 June. On 19 and 24 June low-intensity Strombolian activity was observed, ejecting material as far as 200 m from the center of the crater to the E.

During July, seismicity included 29,319 LP-type events, 3,736 TR-type events, and two VT-type events. DOAS equipment recorded two days of sulfur dioxide emissions of 4,220 t/d and 1,009 t/d on 1 and 13 July, respectively. Constant nighttime incandescence was also recorded and was particularly noticeable when accompanied by eruptive columns on 12 and 16 July. Minor explosive events were detected in the crater. According to Skysat satellite images taken on 12, 13, and 16 July, ashfall deposits were identified 155 m S of the crater. According to POVI, incandescence was visible from two vents on the crater floor around 0336 on 12 July. Gas-and-ash emissions rose as high as 1.2 km above the crater on 13 July and drifted E and NW. A series of gas-and-steam pulses containing some ash deposited material on the upper E flank around 1551 on 13 July. During 16-31 July, average sulfur dioxide emissions of 1,679 ± 406 t/d were recorded, with a maximum daily value of 2,343 t/d on 28 July. Fine ash emissions were also reported on 16, 17, and 23 July.

Seismicity persisted during August, characterized by 27,011 LP-type events, 3,323 TR-type events, and three VT-type events. The average value of sulfur dioxide measurements taken during 1-15 August was 1,642 ± 270 t/d and 2,207 ± 4,549 t/d during 16-31 August, with a maximum daily value of 3,294 t/d on 27 August. Nighttime crater incandescence remained visible in degassing columns. White gas-and-steam emissions rose 480 m above the crater on 6 August. According to a Skysat satellite image from 6 August, ash accumulation was observed proximal to the crater and was mainly distributed toward the E slope. White gas-and-steam emissions rose 320 m above the crater on 26 August. Nighttime incandescence and Strombolian activity that generated ash emissions were reported on 27 August.

Seismicity during September was characterized by five VT-type events, 12,057 LP-type events, and 2,058 TR-type events. Nighttime incandescence persisted. On 2 September an ash emission rose 180 m above the crater and drifted SE at 1643 (figure 125) and a white gas-and-steam plume rose 320 m above the crater. According to the Buenos Aires VAAC, periods of continuous gas-and-ash emissions were visible in webcam images from 1830 on 2 September to 0110 on 3 September. Strombolian activity was observed on 2 September and during the early morning of 3 September, the latter event of which generated an ash emission that rose 60 m above the crater and drifted 100 m from the center of the crater to the NE and SW. Ashfall was reported to the SE and S as far as 750 m from the crater. The lava lake was active during 3-4 September and lava fountaining was visible for the first time since 26 March 2023, according to POVI. Fountains captured in webcam images at 2133 on 3 September and at 0054 on 4 September rose as high as 60 m above the crater rim and ejected material onto the upper W flank. Sulfur dioxide flux of 1,730 t/d and 1,281 t/d was measured on 3 and 4 September, respectively, according to data obtained by DOAS equipment.

Figure 125. Webcam image of a gray ash emission rising above Villarrica on 2 September 2023 at 1643 (local time) that rose 180 m above the crater and drifted SE. Courtesy of SERNAGEOMIN (Reporte Especial de Actividad Volcanica (REAV), Region De La Araucania y Los Rios, Volcan Villarrica, 02 de septiembre de 2023, 17:05 Hora local).

Strong Strombolian activity and larger gas-and-ash plumes were reported during 18-20 September. On 18 September activity was also associated with energetic LP-type events and notable sulfur dioxide fluxes (as high as 4,277 t/d). On 19 September Strombolian activity and incandescence were observed. On 20 September at 0914 ash emissions rose 50 m above the crater and drifted SSE, accompanied by Strombolian activity that ejected material less than 100 m SSE, causing fall deposits on that respective flank. SERNAGEOMIN reported that a Planet Scope satellite image taken on 20 September showed the lava lake in the crater, measuring 32 m x 35 m and an area of 0.001 km². Several ash emissions were recorded at 0841, 0910, 1251, 1306, 1312, 1315, and 1324 on 23 September and rose less than 150 m above the crater. The sulfur dioxide flux value was 698 t/d on 23 September and 1,097 t/d on 24 September. On 24 September the Volcanic Alert Level (VAL) was raised to Orange (the third level on a four-color scale). SENAPRED maintained the Alert Level at Yellow (the middle level on a three-color scale) for the communities of Villarrica, Pucón (16 km N), Curarrehue, and Panguipulli.

During 24-25 September there was an increase in seismic energy (observed at TR-events) and acoustic signals, characterized by 1 VT-type event, 213 LP-type events, and 124 TR-type events. Mainly white gas-and-steam emissions, in addition to occasional fine ash emissions were recorded. During the early morning of 25 September Strombolian explosions were reported and ejected material 250 m in all directions, though dominantly toward the NW. On 25 September the average value of sulfur dioxide flux was 760 t/d. Seismicity during 25-30 September consisted of five VT-type events, 1,937 LP-type events, and 456 TR-type events.

During 25-29 September moderate Strombolian activity was observed and ejected material as far as the crater rim. In addition, ash pulses lasting roughly 50 minutes were observed around 0700 and dispersed ENE. During 26-27 September a TR episode lasted 6.5 hours and was accompanied by discrete acoustic signals. Satellite images from 26 September showed a spatter cone on the crater floor with one vent that measured 10 x 14 m and a smaller vent about 35 m NE of the cone. SERNAGEOMIN reported an abundant number of bomb-sized blocks up to 150 m from the crater, as well as impact marks on the snow, which indicated explosive activity. A low-altitude ash emission was observed drifting NW around 1140 on 28 September, based on webcam images. Between 0620 and 0850 on 29 September an ash emission rose 60 m above the crater and drifted NW. During an overflight taken around 1000 on 29 September scientists observed molten material in the vent, a large accumulation of pyroclasts inside the crater, and energetic degassing, some of which contained a small amount of ash. Block-sized pyroclasts were deposited on the internal walls and near the crater, and a distal ash deposit was also visible. The average sulfur dioxide flux measured on 28 September was 344 t/d. Satellite images taken on 29 September ashfall was deposited roughly 3 km WNW from the crater and nighttime crater incandescence remained visible. The average sulfur dioxide flux value from 29 September was 199 t/d. On 30 September at 0740 a pulsating ash emission rose 1.1 km above the crater and drifted NNW (figure 126). Deposits on the S flank extended as far as 4.5 km from the crater rim, based on satellite images from 30 September.

Figure 126. Webcam image of a gray ash plume rising 1.1 km above the crater of Villarrica at 0740 (local time) on 30 September 2023. Courtesy of SERNAGEOMIN (Reporte Especial de Actividad Volcanica (REAV), Region De La Araucania y Los Rios, Volcan Villarrica, 30 de septiembre de 2023, 09:30 Hora local).

Infrared MODIS satellite data processed by MIROVA (Middle InfraRed Observation of Volcanic Activity) showed intermittent thermal activity during April through September, with slightly stronger activity detected during late September (figure 127). Small clusters of thermal activity were detected during mid-June, early July, early August, and late September. According to the MODVOLC thermal alert system, a total of four thermal hotspots were detected on 7 July and 3 and 23 September. This activity was also intermittently captured in infrared satellite imagery on clear weather days (figure 128).

Figure 127. Low-to-moderate power thermal anomalies were detected at Villarrica during April through September 2023, according to this MIROVA graph (Log Radiative Power). Activity was relatively low during April through mid-June. Small clusters of activity occurred during mid-June, early July, early August, and late September. Courtesy of MIROVA.

Figure 128. Consistent bright thermal anomalies (bright yellow-orange) were visible at the summit crater of Villarrica in infrared (bands B12, B11, B4) satellite images, as shown on 17 June 2023 (top left), 17 July 2023 (top right), 6 August 2023 (bottom left), and 20 September 2023 (bottom right). Courtesy of Copernicus Browser.

Geologic Background. The glacier-covered Villarrica stratovolcano, in the northern Lakes District of central Chile, is ~15 km south of the city of Pucon. A 2-km-wide caldera that formed about 3,500 years ago is located at the base of the presently active, dominantly basaltic to basaltic andesite cone at the NW margin of a 6-km-wide Pleistocene caldera. More than 30 scoria cones and fissure vents are present on the flanks. Plinian eruptions and pyroclastic flows that have extended up to 20 km from the volcano were produced during the Holocene. Lava flows up to 18 km long have issued from summit and flank vents. Eruptions documented since 1558 CE have consisted largely of mild-to-moderate explosive activity with occasional lava effusion. Glaciers cover 40 km2 of the volcano, and lahars have damaged towns on its flanks.

Information Contacts: Servicio Nacional de Geología y Minería (SERNAGEOMIN), Observatorio Volcanológico de Los Andes del Sur (OVDAS), Avda Sta María No. 0104, Santiago, Chile (URL: http://www.sernageomin.cl/); Proyecto Observación Villarrica Internet (POVI) (URL: http://www.povi.cl/); Sistema y Servicio Nacional de Prevención y Repuesta Ante Desastres (SENAPRED), Av. Beauchef 1671, Santiago, Chile (URL: https://web.senapred.cl/); Buenos Aires Volcanic Ash Advisory Center (VAAC), Servicio Meteorológico Nacional-Fuerza Aérea Argentina, 25 de mayo 658, Buenos Aires, Argentina (URL: http://www.smn.gov.ar/vaac/buenosaires/inicio.php); 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/).

Merapi, located just north of the major city of Yogyakarta in central Java, Indonesia, has had activity within the last 20 years characterized by pyroclastic flows and lahars accompanying growth and collapse of the steep-sided active summit lava dome. The current eruption period began in late December 2020 and has more recently consisted of ash plumes, intermittent incandescent avalanches of material, and pyroclastic flows (BGVN 48:04). This report covers activity during April through September 2023, based on information from Balai Penyelidikan dan Pengembangan Teknologi Kebencanaan Geologi (BPPTKG), the Center for Research and Development of Geological Disaster Technology, a branch of PVMBG which specifically monitors Merapi. Additional information comes from the Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM), MAGMA Indonesia, the Darwin Volcanic Ash Advisory Centre (VAAC), and various satellite data.

Activity during April through September 2023 primarily consisted of incandescent avalanches of material that mainly affected the SW and W flanks and traveled as far as 2.3 km from the summit (table 25) and white gas-and-steam emissions that rose 10-1,000 m above the crater.

Table 25. Monthly summary of avalanches and avalanche distances recorded at Merapi during April through September 2023. The number of reported avalanches does not include instances where possible avalanches were heard but could not be visually confirmed as a result of inclement weather. Data courtesy of BPPTKG (April-September 2023 daily reports).

BPPTKG reported that during April and May white gas-and-steam emissions rose 10-750 m above the crater, incandescent avalanches descended 500-2,000 m on the SW and W flanks (figure 135). Cloudy weather often prevented clear views of the summit, and sometimes avalanches could not be confirmed. According to a webcam image, a pyroclastic flow was visible on 17 April at 0531. During the week of 28 April and 4 May a pyroclastic flow was reported on the SW flank, traveling up to 2.5 km. According to a drone overflight taken on 17 May the SW lava dome volume was an estimated 2,372,800 cubic meters and the dome in the main crater was an estimated 2,337,300 cubic meters.

Figure 135. Photo showing an incandescent avalanche affecting the flank of Merapi on 8 April 2023. Courtesy of Øystein Lund Andersen.

During June and July similar activity persisted with white gas-and-steam emissions rising 10-350 m above the crater and frequent incandescent avalanches that traveled 300-2,000 m down the SW, W, and S flanks (figure 136). Based on an analysis of aerial photos taken on 24 June the volume of the SW lava dome was approximately 2.5 million cubic meters. A pyroclastic flow was observed on 5 July that traveled 2.7 km on the SW flank. According to the Darwin VAAC multiple minor ash plumes were identified in satellite images on 19 July that rose to 3.7 km altitude and drifted S and SW. During 22, 25, and 26 July a total of 17 avalanches descended as far as 1.8 km on the S flank.

Figure 136. Photo showing an incandescent avalanche descending the flank of Merapi on 23 July 2023. Courtesy of Øystein Lund Andersen.

Frequent white gas-and-steam emissions continued during August and September, rising 10-450 m above the crater. Incandescent avalanches mainly affected the SW and W flanks and traveled 400-2,300 m from the vent (figure 137). An aerial survey conducted on 10 August was analyzed and reported that estimates of the SW dome volume was 2,764,300 cubic meters and the dome in the main crater was 2,369,800 cubic meters.

Figure 137. Photo showing a strong incandescent avalanche descending the flank of Merapi on 23 September 2023. Courtesy of Øystein Lund Andersen.

Frequent and moderate-power thermal activity continued throughout the reporting period, according to a MIROVA (Middle InfraRed Observation of Volcanic Activity) analysis of MODIS satellite data (figure 138). There was an increase in the number of detected anomalies during mid-May. The MODVOLC thermal algorithm recorded a total of 47 thermal hotspots: six during April, nine during May, eight during June, 15 during July, four during August, and five during September. Some of this activity was captured in infrared satellite imagery on clear weather days, sometimes accompanied by incandescent material on the SW flank (figure 139).

Figure 138. Frequent and moderate-power thermal anomalies were detected at Merapi during April through September 2023, as shown on this MIROVA plot (Log Radiative Power). There was an increase in the number of anomalies recorded during mid-May. Courtesy of MIROVA.

Figure 139. Infrared (bands B12, B11, B4) satellite images showed a consistent thermal anomaly (bright yellow-orange) at the summit crater of Merapi on 8 April 2023 (top left), 18 May 2023 (top right), 17 June 2023 (middle left), 17 July 2023 (middle right), 11 August 2023 (bottom left), and 20 September 2023 (bottom right). Incandescent material was occasionally visible descending the SW flank, as shown in each of these images. Courtesy of Copernicus Browser.

Geologic Background. Merapi, one of Indonesia's most active volcanoes, lies in one of the world's most densely populated areas and dominates the landscape immediately north of the major city of Yogyakarta. It is the youngest and southernmost of a volcanic chain extending NNW to Ungaran volcano. Growth of Old Merapi during the Pleistocene ended with major edifice collapse perhaps about 2,000 years ago, leaving a large arcuate scarp cutting the eroded older Batulawang volcano. Subsequent growth of the steep-sided Young Merapi edifice, its upper part unvegetated due to frequent activity, began SW of the earlier collapse scarp. Pyroclastic flows and lahars accompanying growth and collapse of the steep-sided active summit lava dome have devastated cultivated lands on the western-to-southern flanks and caused many fatalities.

Information Contacts: Balai Penyelidikan dan Pengembangan Teknologi Kebencanaan Geologi (BPPTKG), Center for Research and Development of Geological Disaster Technology (URL: http://merapi.bgl.esdm.go.id/, Twitter: @BPPTKG); MAGMA Indonesia, Kementerian Energi dan Sumber Daya Mineral (URL: https://magma.esdm.go.id/v1); Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM), Jalan Diponegoro 57, Bandung 40122, Indonesia (URL: http://www.vsi.esdm.go.id/); Darwin Volcanic Ash Advisory Centre (VAAC), Bureau of Meteorology, Northern Territory Regional Office, PO Box 40050, Casuarina, NT 0811, Australia (URL: http://www.bom.gov.au/info/vaac/); 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/); Øystein Lund Andersen (URL: https://www.oysteinlundandersen.com/, https://twitter.com/oysteinvolcano).

Ebeko, located on the N end of Paramushir Island in Russia’s Kuril Islands just S of the Kamchatka Peninsula, consists of three summit craters along a SSW-NNE line at the northern end of a complex of five volcanic cones. Observed eruptions date back to the late 18th century and have been characterized as small-to-moderate explosions from the summit crater, accompanied by intense fumarolic activity. The current eruptive period began in June 2022, consisting of frequent explosions, ash plumes, and thermal activity (BGVN 47:10, 48:06). This report covers similar activity during June-November 2023, based on information from the Kamchatka Volcanic Eruptions Response Team (KVERT) and satellite data.

Moderate explosive activity continued during June-November 2023 (figures 50 and 51). According to visual data from Severo-Kurilsk, explosions sent ash 2-3.5 km above the summit (3-4.5 km altitude) during most days during June through mid-September. Activity after mid-September was slightly weaker, with ash usually reaching less than 2 km above the summit. According to KVERT the volcano in October and November was, with a few exceptions, either quiet or obscured by clouds that prevented satellite observations. KVERT issued Volcano Observatory Notices for Aviation (VONA) on 8 and 12 June, 13 and 22 July, 3 and 21 August, and 31 October warning of potential aviation hazards from ash plumes drifting 3-15 km from the volcano. Based on satellite data, KVERT reported a persistent thermal anomaly whenever weather clouds permitted viewing.

Figure 50. Ash explosion from the active summit crater of Ebeko on 18 July 2023; view is approximately towards the W. Photo provided by I. Bolshakov and M.V. Lomonosov MGU; courtesy of KVERT.

Figure 51. Ash explosion from the active summit crater of Ebeko on 23 July 2023 with lightning visible in the lower part of the plume. Photo provided by I. Bolshakov and M.V. Lomonosov MGU; courtesy of KVERT.

Geologic Background. The flat-topped summit of the central cone of Ebeko volcano, one of the most active in the Kuril Islands, occupies the northern end of Paramushir Island. Three summit craters located along a SSW-NNE line form Ebeko volcano proper, at the northern end of a complex of five volcanic cones. Blocky lava flows extend west from Ebeko and SE from the neighboring Nezametnyi cone. The eastern part of the southern crater contains strong solfataras and a large boiling spring. The central crater is filled by a lake about 20 m deep whose shores are lined with steaming solfataras; the northern crater lies across a narrow, low barrier from the central crater and contains a small, cold crescentic lake. Historical activity, recorded since the late-18th century, has been restricted to small-to-moderate explosive eruptions from the summit craters. Intense fumarolic activity occurs in the summit craters, on the outer flanks of the cone, and in lateral explosion craters.

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

During March 2010, the Icelandic Meteorological Office (IMO) and the Nordic Volcanological Center of the University of Iceland's Institute of Earth Sciences (IES) reported the first eruption of Eyjafjallajökull volcano in southern Iceland since 1823. The following was mostly condensed from a multitude of reports on the EIS and IMO websites, and only discusses activity through the start of the explosive summit phase. Many of the satellite images featured here came from the NASA Earth Observatory.

From 20 March to 12 April 2010 the eruption's first phase occurred from a fissure 9 km ENE of the summit, an area named Fimmvörðuháls, located between the Eyjafjallajökull and Mýrdalsjökull icecaps (figure 1). These vents on the lower E slopes were snow-covered but not under the year-round icecap found at higher elevations. Lava flows filled gullies, and quickly melted adjacent winter snow, creating small steam plumes. After apparent cessation of the fissure activity on or about 12 April, a second phase of the eruption began on 14 April (figures 2 and 3, table 1), generating ash plumes that blew E to Europe and resulted in a 20-80% decrease of airline flights for as much as a week (Wall and Flottau, 2010). As of late May the eruption continued, with occasional plumes that restricted air travel in parts of Europe.

Figure 1. Map of southern Iceland showing Eyjafjallajökull and Katla volcanoes, towns, and locations of monitoring instruments. The Mýrdalsjökull icecap overlies Katla. ("Jökull" translates to "glacier" or "icecap" in English). Index map showing some eruptive centers is from Laursen (2010). Base map courtesy of IMO.

Figure 2. Approximately N-looking interpretive cross-section cartoon drawn between Eyjafjallajökull and Katla. The eruption of 20 March was located at Fimmvörðuháls. Starting on 14 April, eruptions took place at the summit caldera. Notice the thin upper layer (blue on colored versions) representing glacial ice and the inferred common linkage at ~ 2 km depth below sea level of the conduits feeding the two active vent areas. Courtesy of Páll Einarsson (IES).

Figure 3. ASTER image of the Eyjafjallajökull-Fimmvörðuháls vents at 1350 local time on 19 April. The image shows both visible information and heat signatures from areas of anomalously high thermal infrared (IR) radiation (for colored versions, yellow is hottest, red, cooler). For the Fimmvörðuháls the thermal signature shows the extent of lava flows no longer extruding but still hot. At the summit, the vent is clearly active, with a thermal signature and a dense white plume blowing SSE. ASTER is the Advanced Spaceborne Thermal Emission and Reflection Radiometer flying on NASA's Terra satellite. Courtesy of Rob Simmon, the U.S./Japan ASTER Science Team, and Holli Riebeek, NASA Earth Observatory.

Table 1. Preliminary data regarding the 2010 eruption of Eyjafjallajökull, which started at an E-flank vent (Fimmvörðuháls) and then later shifted to the ice-covered summit caldera. The grain sizes of the second phase of the eruption were quantified by The Environment Agency of Iceland; other data courtesy of IMO and IES.

Precursory observations. The IES website contained a list of scientific papers and publications including several noting restlessness at Fimmvörðuhálsat in recent years (see Further References below). The IES reports noted that the Fimmvörðuháls eruption followed weeks of high seismicity and deformation (figure 4).

Figure 4. (top) Map of the southern Iceland GPS (Global Positioning System) network, including stations THEY, SKOG, STE1, and STE2. (bottom) Displacement measurements for selected continuous/semi-continuous GPS stations around Eyjafjallajökull from early July 2009 to early March 2010. Inset photograph is of station SKOG. Courtesy of IES.

In general terms, GPS data indicated that permanent station Thorvaldseyri (THEY; S of the volcano, figure 4) started moving S in late December 2009. In the weeks prior to the eruption, there was rapid deformation at Skogaheidi (SKOG; S of the volcano) and Steinsholt (STE1 and STE2; N of the volcano). IES identified three distinct phases in the GPS data. First, at the end of December, the southward motion of THEY. Second, at the beginning of February 2010, displacement at THEY changed to SW as SKOG began E displacement. Third, after 5 March, STE2 displaced rapidly NW and up. Scientists noticed a trend after 4 March at continuous GPS sites installed within 12 km of the eruptive site; all showed deformation at rates of up to a centimeter a day.

Seismic tremor began around 2230 on 4 March, and around that time, signal sources rose slowly towards the surface. Compared to the weeks prior to the eruption, seismicity increased rather slowly immediately prior to the eruption. However, as the eruption onset neared, geophysicists saw both the depth of earthquakes decrease and the locations of earthquakes move from the area under the summit towards the Fimmvörðuháls site.

According to Laursen (2010) "Eyjafjallajökull's so-far-unpredictable behavior offers a perfect example of the challenge facing volcanologists. Before this spring's first eruption...GPS stations on the volcano had wandered several centimeters in May of 2009 and again in December, signs that rising magma was stretching the skin of the volcano in advance of an eruption. In mid-February...Steinunn Jakobsdóttir, a geophysicist at IMO, was tracking tremors ~ 5 kilometers below Eyjafjallajökull's surface. But officials didn't order evacuations because the seismic hints weren't that dire. 'Usually when an eruption starts, a low-frequency [seismic signal] is rising when the magma is coming to the surface,' says Jakobsdóttir. Although seismic tracking placed magma closer to the surface on 19 March, this low-frequency signal was absent, so civil authorities kept the alert level at its lowest setting. But the next night, southern Icelanders reported a dark cloud glowing red above the mountain: The volcano had experienced a small eruption, one that led authorities to evacuate farmers living in its floodplains."

Eruption from Fimmvörðuháls. Late on 20 March 2010 an eruption began at Fimmvörðuháls, an area around 1,000 m elevation in a ~ 2-km-wide pass of ice-free land between Eyjafjallajökull and Mýrdalsjökull. Initially detected visually, the eruption was seen at 2352 that day as a red cloud above the site.

The eruption broke out with Hawaiian-style fire fountains (figure 5) on a ~ 500-m-long, NE-oriented fissure (at 63° 38.1' N, 19° 26.4' W). Lava flowed a short distance from the eruptive site and a minor eruption plume rose to less than 1 km altitude and blew W. Tephra fall was minor or insignificant.

Figure 5. Image of fissure eruption at Eyjafjallajökull taken 21 March 2010 by Sigrún Hreinsdóttir. Courtesy of IES.

Airborne observers during 0400-0700 on 21 March described a short eruptive fissure with fire fountaining from 10-12 vents reaching up to ~ 100 m height. Eruption tremor rose slowly until reaching a maximum at around 0700-0800 that day. No further lengthening of the fissure was detected. Lava was still limited to the immediate surroundings of the eruptive craters (runouts of less than few hundred meters). Minor ashfall occurred within a few kilometers W.

On 22 March, observations made from the ground showed lava extrusion from a series of closely-spaced vents. Prevailing E winds led to maximum scoria accumulation on a linear rim W of the NE-trending fissure. A'a lava flowed over the steep Hrunagil canyon rim creating spectacular 'lava falls.'

During 23-31 March, lava steadily issued at the initial craters, with gradual focusing towards fewer vents. Lava advanced N into the Hrunagil and Hvannárgil valleys, with continuation of intermittent lava falls (figures 6-8). Lava descending gullies generated zones of frothy rock. Extensive steam plumes occurred when advancing lava encountered water and snow. Two or three plumes were observed (one at the eruptive craters, others more pronounced in front of the advancing lava). Meltwater descended in batches into rivers valleys, and seismometers recorded relatively steady eruption tremor.

Figure 6. EO-1 ALI satellite image with annotations indicating path of lava flows from the Fimmvörðuháls vent, 24 March 2010. Note N arrow and scale at lower left. Courtesy of Robert Simmon, NASA Earth Observatory.

Figure 7. Photo showing lava falls developed when lava flows encountered steep canyon walls, 1 April 2010. Courtesy of Sigrún Hreinsdóttir, IES.

Figure 8. Map showing Fimmvörðuháls fissures and the distribution of new scoria and lava at various points in time during 21 March-7 April 2010. Table indicates cumulative areal extent of the deposits. Courtesy of EIS and Icelandic Coast Guard.

On the evening of 31 March, scientists noted the opening of a new short fissure immediately N of the previous one. This change may have been a response to changes at shallow depth in the feeder channel. Eruption tremor remained unchanged. During 31 March-6 April, lava discharged in both the old and new eruptive craters in a manner similar to before. Pronounced 'lava falls' returned to Hvannárgil valley.

During 1-2 April 2010 a team from the Italian Instituto Nazionale di Geofisica e Vulcanologia (INGV) working in collaboration with the scientists from IES conducted gas measurements at Fimmvörðuháls (Burton and others, 2010). Three measurement techniques were used: open-path FTIR (Fourier transform infrared spectroscopy), DOAS (differential optical absorption spectroscopy), and a sulfur dioxide (SO₂) imaging system. The FTIR spectrometer uses infrared radiation emitted from the erupting lavas as a source for absorption spectrometry of gases emitted from the explosive vents. Spectra are analyzed using a single-beam retrieval, which allows pathlength estimates of H₂O, CO₂, SO₂, HCl, and HF. Favorable wind conditions allowed traverse measurements under the gas plume with a DOAS spectrometer for SO₂ flux estimates.

The investigators found that the SO₂ gas flux was ~ 3,000 metric tons per day. Approximately 70% of the SO₂ flux was produced by the fissure that opened 31 March, with ~ 30% emitted by the fissure that had opened on 21 March. The overall HF flux was ~ 30 tons per day. Gas compositions emitted from the two fissures were broadly similar and rich in H₂O (over 80% by mole), less than 15% CO₂, and less than 3% SO₂. The SO₂/HCl ratio varied at the 31 March fissure on 1 and 2 April (25% and 5%, respectively).

On 5 April, eruption tremor (at 1-2 Hz recorded at the nearest seismic station, Godabunga) began to gradually decline. By 7 April lava emissions had stopped from the original craters, but continued at the 31 March fissure.

When IES surveyed the new landscape on 7 April (figure 9), they found 1.3 km² of new lava, an average thickness of new lava there of 10-12 m, and an estimated volume of eruptive material of 22-24 x 10⁶ m³. From this they computed an average emission rate of ~ 15 m³/s. The tallest new cone reached an elevation 1,067 m, ~ 82 m above the previous ground surface. Another cone with a rim at 1,032 m elevation was 47 m above the previous surface and the vent area glowed red.

Figure 9. The Fimmvörðuháls as surveyed and photographed by Freysteinn Sigmundsson and Eyjólfur Magnússon on 7 April 2010. Values shown are elevations and those in parentheses refer to the approximate net gain in elevation due to fresh deposits on the pre-eruption surface. Courtesy of IES.

By 9 April, after little change in deformation rates during the eruption, time series at continuous GPS stations N of the volcano showed sudden change, partly jumping back to pre-eruptive levels. On 11 April, eruption tremor also approached pre-eruptive levels, but visual observation revealed eruptive activity in late afternoon. Seismic tremor on 12 April reached a minimum.

Eruption from the summit caldera. The second, more explosive eruptive phase, began on 14 April 2010 at the subglacial, central summit caldera. This phase was preceded by an earthquake swarm from around 2300 on 13 April to 0100 on 14 April. Meltwater started to emanate from the icecap around 0700 on 14 April and an eruption plume was observed later that morning. The exact conditions at the summit were unknown due to cloud cover obscuring the volcano, but on 15 April an overflight imaged the erupting caldera using radar (figure 10).

Figure 10. This 15 April radar image of the Eyjafjallajökull eruption depicts the otherwise hidden scene at the cloud-covered summit caldera. The glacial snow and ice had deformed and melted, forming circular depressions (ice cauldrons) in the icecap's surface. Flooding from the melting glacier had led to the various features on and below the glacier to the N and S (illustrated by labels). The data were acquired via aircraft by the Icelandic Coast Guard during 1700-1800 on 15 April 2010. The glacier margin and surface contours came from a 2004 investigation. Courtesy of Icelandic Coast Guard and IES.

The 15 April radar image helped depict a series of vents along a 2-km-long, N-oriented fissure. Both on top of and from below, meltwater flowed down the N and S slopes. Jokulhlaups (floods of meltwater also carrying considerable debris) reached the lowlands around the volcano with peak flow around noon on 14 April, causing destruction of roads, infrastructure, and farmlands. Residents had earlier been evacuated from hazardous areas. Tephra fall began in SE Iceland. That evening, a second jokulhlaup emanated from the icecap down the Markarfljot valley, which trends E-W along the N margin of the volcano and contains extensive outwash from surrounding glaciers.

On 15 April the ash plume reached a maximum altitude of over 8 km. E-blown ash began to arrive over mainland Europe closing airspace over the British Isles and large parts of Northern Europe. Ash generation continued at a similar level. Meltwater emerged from the glacier in pulses. Debris-charged jokulhlaups were seen in the evening.

Chemical analyses of mid-April ash samples revealed fluorine-rich intermediate eruptive products with silica content of ~ 58%. The initial lavas erupted at Fimmvörðuháls had silica contents of ~ 48% (table 1).

References. Burton, M., Salerno, G., La Spina, A., Stefansson, A., and Kaasalainen, H., 2010, Gas composition and flux report, IES web site.

Laursen, L., 2010, Iceland eruptions fuel interest in volcanic gas monitoring: Science, v. 328, no. 5977, p. 410-411.

Sigmarsson, O., Óskarsson, N., Þórðarson, Þ., Larsen, and G., Höskuldsson, Á, 2010, Preliminary interpretations of chemical analysis of tephra from Eyjafjallajökull volcano (report on the IES website).

Wall, R., and Flottau, J., 2010. Out of the ashes: Rising losses and recriminations rile Europe's air transport sector: Aviation Week & Space Technology, v. 172, no. 16, p.23-25.

Further References. Dahm, T., and Brandsdóttir, B., 1997, Moment tensors of micro-earthquakes from the Eyjafjallajökull volcano in South Iceland: Geophysical Journal International, v. 130, no.1, p. 183-192, DOI:10.1111/j.1365-246X.1997.tb00997.x.

Guðmundsson, M.T., and Gylfason, A.G., 2004, H?ttumat vegna eldgosa og hlaupa frá vestanverðum Mýrdalsjökli og Eyjafjallajökli. Háskólaútgáfan og Ríkislögreglustjórinn [Volcanic risk assessment run from Mýrdalsjökli and Eyjafjallajökull measurements]: University of Iceland and the National Police, 230 p.

Hjaltadottir, S., K. S. Vogfjord and R. Slunga, 2009, Seismic signs of magma pathways through the crust at Eyjafjallajokull volcanoe, South Iceland: Icelandic Meteorological Office report, VI 2009-013 (http://www.vedur.is/media/vedurstofan/utgafa/skyrslur/2009/VI_2009_013.pdf).

Hooper, A., Pedersen, R., and Sigmundsson, F., 2009, Constraints on magma intrusion at Eyjafjallajökull and Katla volcanoes in Iceland, from time series SAR interferometry, p. 13-24 in Bean, C.J., Braiden, A.K., Lokmer, I., Martini, F., and O'Brien, G.S., eds., The VOLUME project - Volcanoes: Understanding subsurface mass movement: School of Geological Sciences, University College Dublin.

Larsen, G., 1999, Gosi í Eyjafjallajökli 1821-1823 [The eruption of the Eyjafjallajökull volcano in 1821-1823]: Science Institute Research Report RH-28-99, Reykjavík, 13 p.

Pedersen, R., Sigmundsson, F., and Einarsson, P., 2007, Controlling factors on earthquake swarms associated with magmatic intrusions; Constraints from Iceland: Journal of Volcanology and Geothermal Research, v. 162, p. 73-80.

Pedersen, R., and Sigmundsson, F., 2004, InSAR based sill model links spatially offset areas of deformation and seismicity for the 1994 unrest episode at Eyjafjallajökull volcano, Iceland: Geophysical Research Letters, v. 31, L14610 doi: 10.1029/2004GL020368.

Pedersen, R., and Sigmundsson, F., 2006, Temporal development of the 1999 intrusive episode in the Eyjafjallajökull volcano, Iceland, derived from InSAR images: Bulletin Volcanology, v. 68, p. 377-393.

Sigmundsson, F., Geirsson, H., Hooper, A. J., Hjaltadottir, S., Vogfjord, K. S., Sturkell, E. C., Pedersen, R., Pinel, V., Fabien, A., Einarsson, P., Gudmundsson, M. T., Ofeigsson, B., and Feigl, K., 2009, Magma ascent at coupled volcanoes: Episodic magma injection at Katla and Eyjafjallajökull ice-covered volcanoes in Iceland and the onset of a new unrest episode in 2009: Eos (Transactions of the American Geophysical Union), v. 90, no. 52, Fall Meeting Supplement, Abstract V32B-03.

Sturkell, E., Einarsson, P., Sigmundsson, F., Hooper, A., Ófeigsson, B.G., Geirsson, H., and Ólafsson, H., 2009, Katla and Eyjafjallajökull volcanoes, p. 5-12 in Schomacker, A., Krüger. J., and Kjr, K.H., eds., The Mrdalsjökull Ice cap, Iceland - Glacial processes, sediments and landforms on an active volcano: Developments in Quaternary Sciences, v. 13.

Geologic Background. Eyjafjallajökull (also known as Eyjafjöll) is located west of Katla volcano. It consists of an elongated ice-covered stratovolcano with a 2.5-km-wide summit caldera. Fissure-fed lava flows occur on both the E and W flanks, but are more prominent on the western side. Although the volcano has erupted during historical time, it has been less active than other volcanoes of Iceland's eastern volcanic zone, and relatively few Holocene lava flows are known. An intrusion beneath the S flank from July-December 1999 was accompanied by increased seismic activity. The last historical activity prior to an eruption in 2010 produced intermediate-to-silicic tephra from the central caldera during December 1821 to January 1823.

Information Contacts: Nordic Volcanological Center, Institute of Earth Sciences, University of Iceland, Sturlugata 7, Askja, 101 Reykjavík, Iceland (URL: http://www.earthice.hi.is/page/ies_volcanoes) [contributors:Páll Einarsson, ásta Rut Hjartardóttir, Magnus Tumi Gudmundsson, Freysteinn Sigmundsson, Niels Oskarsson, Gudrun Larsen, Sigrun Hreinsdottir, Rikke Pedersen, Ingibjörg Jónsdóttir]; Icelandic Meteorological Office (IMO), Bústaðavegur 9, 150 Reykjavík, Iceland (URL: http://en.vedur.is/) [contributors:Steinunn Jakobsdóttir, Kristin S. Vogfjord, Sigurlaug Hjaltadottir, Gunnar B. Gudmundsson, Matthew J. Roberts]; The Environment Agency of Iceland, Sudurlandsbraut 24, 108 Reykjavik, Iceland (URL: http://english.ust.is/); NASA Earth Observatory (URL: http://earthobservatory.nasa.gov/); London Volcanic Ash Advisory Centre, Met Office, FitzRoy Road, Exeter, Devon EX1 3PB, United Kingdom (URL: http://www.metoffice.gov.uk/aviation/vaac/).

Eruptions from Piton de la Fournaise resumed in September 2008 after more than 16 months of quiet (BGVN 34:02). Eruptive episodes inside Dolomeiu crater, as reported by the Observatoire Volcanologique du Piton de la Fournaise (OVPDLF), took during 21 September-2 October and on 28 November 2008, with a third that began on 15 December and continued into January 2009. This report presents observations from January 2009 through January 2010.

Eruptions during 21 September 2008-4 February 2009. Eruptive phases in September, November, and December 2008 were previously described (BGVN 34:02). OVPDLF reported that the episode that began on 14 December 2008 ended on 4 February 2009. During that eruption two vents were active; lava flowed to the bottom of Dolomieu crater through lava tubes and caused the crust over the pooled area to rise. Some incandescence was noted at night and at dawn. Eruption tremor was irregular until 1 January, when it suddenly stopped. Tremor gradually rose over the next few days, but to a relatively low level, where it remained steady until slowly dropping again in early February (figure 79). Lava flows from this eruption covered an area of approximately 420 x 220 m, with a thickness of 75 m (figure 80).

Figure 79. Tremor at Piton de la Fournaise, 14 December 2008-5 February 2009. Courtesy of OVPDLF.

Figure 80. Cumulative lava flows in Dolomieu crater at Piton de la Fournaise during the September 2008-February 2009 eruption. Flows covered 420 x 220 m to a depth of 75 m. Courtesy of OVPDLF.

Activity during October 2009-January 2010. The OVPDLF reported three eruptions from the summit region at the Dolomieu crater's W wall adjacent to Bory crater between November 2009 and January 2010. The flows traveled to the E down the steep cliff toward the crater floor. These eruptions began on 5 November 2009, lasting about two days; on 14 December 2009, lasting 6 hours; and on 2 January 2010, lasting 10 days.

During 5-13 October 2009, OVPDLF reported increased seismicity (figure 81). Seismicity from 14 to 17 October indicated deformation on the N side of, and rockfalls within, the Dolomieu crater. On 18 October another seismic crisis was noted along with deformation on the N and S sides of the Dolomieu crater. Aerial observations on 19 October revealed a small new fumarole in the crater. Unspecified changes in the chemical composition of the gases were also noted. On 20 October rockfalls occured in greater number and longer duration than in previous days.

Figure 81. A graph showing the number of volcano-tectonic earthquakes/day registered between 1 July 2009 and 26 January 2010 at Piton de la Fournaise. Horizontal bars indicate eruptions. Courtesy OVPDLF.

On 4 November 2009 a magnitude 3 earthquake at 0604 was felt by some residents of the southern part of the island. Such a magnitude is uncommon at this volcano. Seismologists at the Observatory located the earthquake at 750 m below sea level, under the southwestern edge of the Dolomieu crater. Later that day, 167 earthquakes of lesser magnitude followed. The focal depths rose to ~ 1 km above sea level with epicenters below the summit.

OVPDLF reported that 30 minutes after an intense seismic event on 5 November, a tremor signal characteristic of the beginning of an eruption occurred, and a vent opened inside the southern part of the Dolomieu crater. Within another 30 minutes, a fissure on the upper SE flank propagated E, and a second fissure opened on the E flank.

Lava fountains ~ 20 m high and flows were emitted from both fissures. The glowing lava was visible from the edge of the Enclos Fouqué and from the road in the Grand Brulé. Beginning around 1500, there was a gradual decrease in the intensity of the eruption. At 0645 on 6 November, a reconnaissance was conducted by a helicopter supplied by the National Gendarmerie, which confirmed that two fissures were open in the S side, S and E of the Dolomieu summit crater. Each emitted a lava flow descending to ~ 1,970 m elevation. As of 0730 that day, the lava ceased flowing, with a gradual decrease in the intensity of the eruption tremor.

At 1730 on 14 December a seismic event preceded a rise in summit deformation (8 cm horizontal). Eruptive tremor began at 1830, and an eruption began at 1845. A system of sub-parallel fissures along the summit of Dolomieu crater fed lava flows on the S slope of the volcano, inside the Enclos Fouqué. A second fissure system opened on the E flank of the Dolomieu summit crater at 2025, and lava flows advanced down the eastern slope. This eruption ended at 0040 after a gradual decrease in magma supply. On 15 December, a visible degassing in the S and SE fissures was associated with low-intensity eruptive tremor. All of the lava flows were confined to high portions of the S and SE slopes.

Fissure-fed fountaining sent lava flows down the S flank on 14 December 2009. Another seismic event on 29 December was characterized by numerous earthquakes up to M 3 in the area W and NW of Dolomieu crater at depths of 1.1-2.2 km below the summit. Deformation was also detected. OVPDLF reported decreased seismicity and fewer landslides within Dolomieu crater on 30 and 31 December.

On 2 January 2010 a fissure eruption near the top of the W crater rim (figure 82) was preceded by a seismic event and another 3 cm of horizontal deformation. Lava fountains rose a few tens of meters high and sent lava flows into Dolomieu crater, and ash and gas plumes rose above Piton de la Fournaise. Large landslides also occurred in Bory crater (W). During 2-3 January, seismicity and the number of landslides decreased. A series of ash plumes was noted through 12 January.

Figure 82. Dolomieu crater on 2 January from its W rim showing lava flows and fountains. The dense gray plume was attributed to collapse along the steep crater wall. Courtesy of OVPDLF.

As of 4 January, the lava flows covered about 80% of the crater floor. Lava fountaining was still visible during 5-7 January and continued to erupt from a vent along a fissure high on the SW Dolomieu crater wall. The vent produced lava fountains and flows that pooled in the bottom of the crater. On 7 January the vent closed, but the previously erupted lava continued to flow for the next few days (figure 83). Seismicity decreased on 12 January and only minor gas emissions persisted. Figure 82 shows the lava flow along the axis where extensive glowing flows were visible. Some flows around this time were fed by lava tubes.

Figure 83. A photo taken on the morning of 7 January 2010 of the lava vent flows from the W wall adjacent to Bory crater at Piton de la Fournaise. Courtesy of Undervol, OVPDLF.

Geologic Background. Piton de la Fournaise is a massive basaltic shield volcano on the French island of Réunion in the western Indian Ocean. Much of its more than 530,000-year history overlapped with eruptions of the deeply dissected Piton des Neiges shield volcano to the NW. Three scarps formed at about 250,000, 65,000, and less than 5,000 years ago by progressive eastward slumping, leaving caldera-sized embayments open to the E and SE. Numerous pyroclastic cones are present on the floor of the scarps and their outer flanks. Most recorded eruptions have originated from the summit and flanks of Dolomieu, a 400-m-high lava shield that has grown within the youngest scarp, which is about 9 km wide and about 13 km from the western wall to the ocean on the E side. More than 150 eruptions, most of which have produced fluid basaltic lava flows, have occurred since the 17th century. Only six eruptions, in 1708, 1774, 1776, 1800, 1977, and 1986, have originated from fissures outside the scarps.

Information Contacts: Laurent Michon and Patrick Bachélery, Laboratoire GéoSciences Réunion, Institut de Physique du Globe de Paris, Université de La Réunion, CNRS, UMR 7154-Géologie des Systèmes Volcaniques, La Réunion, France; Guillaume Levieux, Thomas Staudacher, and Valérie Ferrazzini, Observatoire Volcanologique du Piton de la Fournaise (OVPDLF), Institut de Physique du Globe de Paris, 14 route nationale 3, 27ème km, 97418 La Plaine des Cafres, La Réunion, France (URL: http://www.ipgp.fr/fr/ovpf/actualites-ovpf/).

Ongoing volcanism, including ash explosions, pyroclastic flows, avalanches, and lahars had continued through November 2007 at Santa Maria (BGVN 32:10). Subsequent activity has been closely monitored by the Instituto Nacional de Sismologia, Vulcanologia, Meteorologia, e Hidrologia (INSIVUMEH), with input from the Washington Volcanic Ash Advisory Center (VAAC).

Activity during 2008. On 11 January 2008, INSIVUMEH reported constant avalanches of blocks from the lava flows on the W and SW flanks of Santa María's Santiaguito lava dome complex. Weak-to-moderate explosions produced ash plumes that rose to altitudes of 4.1-4.5 km and drifted SW. On 6 February, weak explosions generated white columns of water and steam and ash that rose ~ 200 m above the crater rim. There were also a few avalanches onto the W flank lava flow. Degassing on 8 February was characterized by steam and gray plumes of fine ash on the SW flank. A significant magmatic explosion that threw fine ash up to ~ 5 km altitude and drifted ~ 4 km to the SW was followed by weak explosions of steam and ash. Avalanches of blocks from the crater rim on 12 February reached the lava flows on the S and SW flanks. Two moderate explosions expelled gray ash up to ~ 4 km altitude that dispersed to the SW.

The Washington VAAC (based on satellite imagery) reported that ash "puffs" from the Santiaguito lava dome complex rose ~ 4.5 km and drifted SW on 1 April, and then rose ~ 4 km and drifted W on 2 April. During 3-7 April, small explosions produced ash plumes; ashfall was reported in surrounding areas. This was followed on 15 April by three explosions expelling ash 300-900 m above the volcano and dispersing 5 km to the SW. Constant avalanches occurred to the W and SW. On 18 April another volcanic ash emission was reported by the Washington VAAC which rose to ~ 4.8 km, drifted SW, and extended ~ 30 km. More weak to moderate explosions occurred on 21 April which expelled gray ash clouds 300-800 m above the crater rim that drifted E. This activity was repeated on 25 April; the Washington VAAC reported an ash emission which rose to ~ 4.8 km and drifted ~ 13 km SW. On 28 April explosions sent ash plumes to an altitude of 4.1 km that drifted W.

Based on observations of satellite imagery, the Washington VAAC reported that ash puffs from the Santiaguito complex drifted NW on 13 May. On 22 May, two explosions were heard and gray ash emissions rose ~ 300-600 m above the crater rim and drifted S and SW, depositing ash in the Palajunoj area. Avalanches of blocks on the SW flanks were seen and heard. A lahar descended the Nima I River to the S on 25 May.

On 3 June, a Special Bulletin was issued to warn of the potential high water conditions in the Nimá I, Nimá II, San Isidro, Drum, Samala, rivers as a result of heavy rains in the area. On 5 June, avalanches were heard on the flanks of the volcano and overflows into the Samal and Mulu Rivers were reported. A lahar on 9 June about 15 m wide and up to 2 m deep descended the Nima I River, carrying blocks up to 1 m in diameter, and smelling of sulfur.

During the morning of 19 June, six weak-to-moderate explosions produced ash plumes that rose to altitudes of 2.8-3.3 km and drifted SW and S. An incandescent lava flow accompanied by constant avalanches of blocks descended the SW flank. On 20 June, five weak-to-moderate explosions expelled gray ash up to ~ 600-800 m above the crater, spreading to the SW over the area of Palajunoj. The lava flow to the SW continued and incandescent lava could be seen at night, accompanied by constant avalanches of blocks and fine ash. A lahar traveled S down the Nima I river, carrying blocks up to 1 m in diameter. These conditions continued through 24 June.

On 4 July, an explosion produced an ash plume that rose to an altitude of 3.3 km and drifted SW. A lahar traveled S down the Nima I River, carrying tree limbs and blocks up to 50 cm in diameter. On 7-8 July, sounds resembling avalanches descending the flanks were reported; visual observations were hindered due to cloud cover. On 22 July seismic stations detected a lahar in the Nima I river. Explosions observed on 23, 28, and 29 July from the Caliente cone produced ash plumes that rose to altitudes of 2.8-3.3 km and drifted SW and W. Ashfall was reported in areas downwind. A lava flow and avalanches of blocks descended the SW flank. On 28 July, weak pyroclastic flows also traveled down the SW flank.

During 21-26 August, explosions from the Caliente cone, part of the Santiaguito complex, produced ash plumes that rose to altitudes of 2.8-3.3 km and drifted S, SW, and W. Constant degassing from the crater was noted.

On 10 September seismic stations detected a lahar in the Nima I River. The lahar, about 18 m wide and up to 2 m deep, carried blocks and smelled of sulfur. During 11-16 September, explosions produced ash plumes that rose to altitudes of 2.8-3.3 km and drifted SW; on 18 September, the Washington VAAC reported that an ash plume rose to an altitude of 4.3 km and drifted SSW. On 24 September explosions produced ash plumes that rose to altitudes of 2.8 km and drifted SW. Avalanches of material from lava flows descended the SW flank.

On 11 and 15 November, the Washington VAAC reported that ash puffs drifted SW. On 12 December, explosions from the Caliente dome produced an ash plume that rose to an altitude of 3.2 km and drifted SW; the Washington VAAC reported a plume to an altitude of 5.8 km. On 16 December, two ash puffs drifted W and WNW at altitudes of 4.3-4.6 km. The Washington VAAC again reported that during 17-20 and 22 December ash plumes drifted SW, W, and NW; plumes rose to an altitude of 5.8 km. On 22 December, white plumes drifted SW and avalanches occurred from the crater rim. On 23 December a small ash plume drifted NW and explosions resulted in pyroclastic flows. Ash plumes rose to an altitude of 3.3 km and drifted S and SW. On 25 December a puff of ash drifted WNW.

Activity during 2009. Activity continued into 2009 and the Washington VAAC reported that two small ash plumes drifted ESE on 1 January. During 4-5 January, gas and steam plumes possibly containing some ash drifted SW and WSW. On 5 and 6 January fumarolic plumes drifted 100 m above the crater. Five explosions produced ash plumes that rose to altitudes of 2.8-3 km and drifted W and SE. A few avalanches originating from a lava flow descended the W flank. Explosions during 30 January-3 February produced plumes that rose to altitudes of 2.6-3.2 km and drifted W, SW, and S. Avalanches that were periodically incandescent descended the S and W flanks of Caliente lava dome.

The Washington VAAC reported that on 4 February multiple ash puffs drifted W. Explosions on 6 February produced plumes that rose to altitudes of 2.8-3.1 km and also drifted SW. Ashfall was reported in areas downwind. Ash puffs on 12 February drifted WSW and W. On 16-17 February, explosions produced ash plumes that rose to altitudes of 2.7-3.3 km and drifted SW. Small pyroclastic flows on 16 February descended the SE flank and reached the Nima I River. Incandescent avalanches were noted on 17 February and fumarolic plumes drifted SW.

On 18 February, a dense ash plume drifted W, and on the 20th an explosion sent an ash plume to an altitude of 3.2 km that drifted E. On 24 February, an explosion produced a white plume that rose 500 m above the summit and drifted SW. Incandescence was seen SW of Caliente dome. On 26-27 February and 2 March, explosions produced ash plumes that rose to altitudes of 2.8-3.4 km and drifted SW. Ashfall was reported in nearby areas. Avalanches were seen SW of the Caliente dome.

Based on satellite imagery, the Washington VAAC reported that during 4-6 March ash plumes drifted W. On 6 and 10 March, ash plumes rose to 2.8-3.4 km and drifted SW, NW, and N. Ashfall was reported in areas downwind. On 12, 16, and 17 March, explosions produced ash plumes that rose to altitudes of 2.7-3.5 km and drifted E and SW. A few avalanches originated from an active lava flow and traveled down the SW flank. On 12 March an ash plume drifted S, and on 15 March, an ash plume rose to an altitude of 3 km and drifted SW and WSW.

During 24-28 April explosions produced ash plumes that drifted 5-8 km WSW, although the number of explosions had decreased during the previous few weeks. On 5, 8, and 9 June ash plumes rose to altitudes of 2.8-3.3 km and drifted SW. Gas plumes that were sometimes gray rose ~ 300-600 m above the Caliente dome, and avalanches descended the S and W flanks. On 26 and 29 June explosions produced ash plumes that rose to altitudes of 2.9-3.3 km and drifted W and SW.

On 26 June, the seismic network detected a lahar that traveled S down the Nima I River. Steam plumes and a sulfur odor rose from the deposits. The lahar was 15 m wide and 1 m thick at the toe, and carried blocks up to 1.5 m in diameter. On 2 July lahars descended both the Nimá I and Nimá II rivers, carrying tree branches and blocks 50-75 cm in diameter. The lahars were 15 and 20 m wide.

On 6 July, explosions produced ash plumes that rose to altitudes of 2.8-3.2 km and drifted W. On 31 July and 3 August, explosions produced ash plumes, and the Caliente lava dome was incandescent. On 3 August, ash plumes rose to an altitude of 3.1 km and drifted W. Fumarolic plumes rose 200 m above the dome and rumbling noises were occasionally heard.

On 28 August, another explosion was noted. On 1 September, fumarolic plumes rose 150 m above Caliente dome and drifted SW and avalanches descended the SW flank of the dome. On 14 September an explosion produced an ash plume that rose to an altitude of 3.3 km. The plume drifted SW and caused ashfall. Avalanches went to the SW.

The Washington VAAC reported that on 22 October multiple ash plumes drifted less than 20 km SW. On 23 and 26 October, explosions produced ash plumes that rose above Caliente dome to altitudes of 3-3.3 km. The plumes drifted W and SE and caused ashfall. Avalanches descended the SW flank of the dome. Degassing sounds resembling airplane engines were also heard.

On 6 November, an explosion produced a plume that rose 900 m and drifted SW. The Washington VAAC reported that on 8 November a small gas plume possibly containing ash drifted less than 10 km SSW. Another small plume was seen later that day. On 13 November, a plume drifted SW. Avalanches descended the SW flank of the dome and the Washington VAAC reported that on 16 November multiple ash plumes drifted WSW.

On 20 November, two explosions produced an ash plume that drifted SW. Avalanches descended the SW flank of the dome. An explosion on 24 November produced an ash plume the rose to an altitude of 3.3 km and drifted SE. Ashfall was reported in areas downwind.

On 11, 14, and 15 December, explosions produced ash plumes that rose to altitudes of 2.8-3.5 km and drifted W and SW. Avalanches occasionally descended the SE flank of the dome. On 15 December, explosions generated pyroclastic flows that descended the E and SW flanks. On 30 December explosions produced ash plumes that rose to altitudes of 3-3.4 km and drifted W and SW. The Washington VAAC reported that ash plumes seen on satellite imagery drifted more than 30 km WSW. Avalanches occasionally descended the SW flank of the dome.

Activity during January-April 2010. Incandescent avalanches traveled down the SW flanks on 8 January 2010. A few explosions on 5 and 11-12 January produced ash plumes that rose to altitudes of 3.1-3.4 km and drifted S, SE, and SW. Avalanches from a lava flow descended the W flank of the dome. On 21 January ashfall was reported in areas near the Santiaguito complex. The next day an explosion produced an ash plume that rose to an altitude of 3.2 km and drifted SW. An ash plume seen on satellite imagery drifted less than 10 km.

On 2 and 4 March, explosions produced ash plumes that rose to altitudes of 2.7-3.1 km and drifted E and NE. Ash fell in areas downwind. Ash fell in inhabited areas downwind. The Washington VAAC reported that on 8 March an ash plume was seen in satellite imagery drifting WNW. On 29 March, explosions produced ash plumes that rose to altitudes of 3-3.3 km and drifted W over inhabited areas. Avalanches from a lava flow descended the SW flank. On 30 March a diffuse ash plume was seen in satellite imagery.

On 20 April, explosions produced ash plumes that rose to altitudes of 2.8-3.4 km and drifted S and SE. On 26 April, ash explosions and pyroclastic flows generated ash plumes that rose to an altitude of 8.3 km and drifted NW and N. Ashfall was reported in Quetzaltenango (18 km WNW) and other areas to the W, NW, and N. According to news articles, schools in 10 communities were closed and flights were banned within a 20-km-radius of the volcano.

Geologic Background. Symmetrical, forest-covered Santa María volcano is part of a chain of large stratovolcanoes that rise above the Pacific coastal plain of Guatemala. The sharp-topped, conical profile is cut on the SW flank by a 1.5-km-wide crater. The oval-shaped crater extends from just below the summit to the lower flank, and was formed during a catastrophic eruption in 1902. The renowned Plinian eruption of 1902 that devastated much of SW Guatemala followed a long repose period after construction of the large basaltic andesite stratovolcano. The massive dacitic Santiaguito lava-dome complex has been growing at the base of the 1902 crater since 1922. Compound dome growth at Santiaguito has occurred episodically from four vents, with activity progressing E towards the most recent, Caliente. Dome growth has been accompanied by almost continuous minor explosions, with periodic lava extrusion, larger explosions, pyroclastic flows, and lahars.

Information Contacts: Instituto Nacional de Sismologia, Vulcanología, Meteorología, e Hidrologia (INSIVUMEH), Unit of Volcanology, Geologic Department of Investigation and Services, 7a Av. 14-57, Zona 13, Guatemala City, Guatemala (URL: http://www.insivumeh.gob.gt/); Washington Volcanic Ash Advisory Center, Satellite Analysis Branch (SAB), NOAA/NESDIS E/SP23, NOAA Science Center Room 401, 5200 Auth Rd, Camp Springs, MD 20746, USA (URL: http://www.ospo.noaa.gov/Products/atmosphere/vaac/); Coordinadora Nacional para la Reducción de Desastres (CONRED), Av. Hincapié; 21-72, Zona 13, Guatemala City, Guatemala (URL: http://www.conred.org/).

Volcanism at Shiveluch that has been almost continuous since 1980 remained so from May 2008 through March 2010. During that time the lava dome was active and frequently growing, and produced moderate and weak explosions (figure 18). The most active phases took place during July-October 2008, March-April 2009, and November-December 2009 (figure 19).

Figure 18. (top) A panoramic view Shiveluch looking N on 27 August 2009. The "Young Shiveluch" lava dome is degassing. (bottom) A photo taken at night on 15 September 2009 from the same perspective as the photo on left, showing lava traveling down the dome's S flank. Both photos taken from Kliuchi by Yuri Demyanchuk, IVS RAS.

Figure 19. Plots for Shiveluch indicating the number the thermal anomaly pixels from satellite observations (top plot) and numbers of earthquakes originating in or adjacent to the dome (lower plot) during May 2008 to March 2010. The arrows show the observed explosions during good visibility. The ash cloud icons indicate the most significance events (ash plumes extending more then 50 km based on satellite images). Data from KB GS RAS.

During the two years discussed, there were many short-lived ash plumes (1-3 km above the dome), ash clouds produced by rockfalls and avalanches, and strong explosions that generated long-distance plumes (those with 'ash cloud' symbols above the arrows, figure 19). The large explosive eruptions of 26 April and 23 June 2009 sent respective ash plumes to 510 km and 754 km distances (table 8). The day after the earlier event, there was clear visibility on 27 April (figure 20).

Table 8. Significant explosions and ash plumes recorded at Shiveluch from May 2008 to March 2010. Plumes lower than ~1.2 km above the dome and seen for less than 10 km from the vent were omitted. Data courtesy of KVERT.

Figure 20. Strong explosion on 26 April 2009 at Shiveluch produced a pyroclastic flow on the S slope and a resulting ash plume that extended 120 km to the NE. Photo by Yuri Demyanchuk, IVS RAS.

KVERT noted that on 11 September 2009 there were strong explosions. Based on interpretations of seismic data, the inferred ash plumes that day rose to an altitude greater than 15 km above sea level. The seismic network then detected 8 minutes of signals interpreted as pyroclastic flows from the lava dome; resulting plumes rose to an altitude of ~ 15 km. Cloud cover prevented visual observations. Ten more events characterized as ash explosions and either pyroclastic flows or avalanches were detected. Seismicity then decreased during 11-12 September. A visit during clear visibility on 13 September revealed fresh pyroclastic-flow deposits (figure 21).

Figure 21. The light area on this 13 September 2009 photo represents fresh pyroclastic-flow deposits on Shiveluch. The deposits covered the apron and extended 5 km S. Dotted-line indicates the approximate profile of the lava dome of Young Shiveluch. Photo by Yuri Demyanchuk, IVS RAS.

Seismicity. Extended intervals of low-level seismicity were detected at the dome in May and June 2008, during May to October 2009, and to some extent from January through March 2010 (figure 19, bottom). A plot of regional seismicity during December 2009-5 April 2010 in a 70-km-diameter circle around Shiveluch (figure 22) indicates SW-dipping epicenters that rise to shallow depths under Shiveluch (and similarly for other volcanoes in the Kliuchevskoi group).

Figure 22. Regional seismicity recorded during 19 December 2009 to 4 April 2010, presented in three panels. (a) A map of the region showing location and depths of earthquakes (white line is trace of cross-section AB), and the 70-km-diameter circle enclosing Shiveluch with epicenters of earthquakes plotted in (c). (b) Earthquakes projected onto the vertical plane of cross section AB. (c) Histogram showing Shiveluch's daily earthquakes with respect to time (bar height shows class (Ks) from seismic amplitude, after S.A. Fedotov), ascending curve is the cumulative number of earthquakes. Courtesy of KB GS RAS.

Geologic Background. The high, isolated massif of Sheveluch volcano (also spelled Shiveluch) rises above the lowlands NNE of the Kliuchevskaya volcano group. The 1,300 km3 andesitic volcano is one of Kamchatka's largest and most active volcanic structures, with at least 60 large eruptions during the Holocene. The summit of roughly 65,000-year-old Stary Shiveluch is truncated by a broad 9-km-wide late-Pleistocene caldera breached to the south. Many lava domes occur on its outer flanks. The Molodoy Shiveluch lava dome complex was constructed during the Holocene within the large open caldera; Holocene lava dome extrusion also took place on the flanks of Stary Shiveluch. Widespread tephra layers from these eruptions have provided valuable time markers for dating volcanic events in Kamchatka. Frequent collapses of dome complexes, most recently in 1964, have produced debris avalanches whose deposits cover much of the floor of the breached caldera.

Information Contacts: Kamchatka Volcanic Eruptions Response Team (KVERT), Institute of Volcanology and Seismology (IV&S) Far East Division, Russian Academy of Sciences (FED RAS), Kamchatka Branch of the Geophysical Service of the Russian Academy of Sciences (KB GS RAS), Piip Ave. 9, Petropavlovsk-Kamchatsky, 683006, Russia (URL: http://www.kscnet.ru/ivs, http://www.emsd.ru/~ssl/monitoring/main.htm); Yuri Demyanchuk, IV&S FED RAS; Alaska Volcano Observatory (AVO), a cooperative program of the U.S. Geological Survey, 4200 University Drive, Anchorage, AK 99508-4667, USA (URL: http://www.avo.alaska.edu/), the Geophysical Institute, University of Alaska, PO Box 757320, Fairbanks, AK 99775-7320, USA, and the Alaska Division of Geological and Geophysical Surveys, 794 University Ave., Suite 200, Fairbanks, AK 99709, USA.

Montserrat Volcano Observatory (MVO) reported a strong increase in dome growth at Soufrière Hills (figure 82) and energetic explosive activity, including pyroclastic flows and substantial ash clouds, during the 6 months ending early April 2010 (the end of this reporting interval). Energetic extrusions were particularly noteworthy during January and February 2010 (table 69). From mid-December 2009 through early April 2010 there was continuing seismicity and gas emissions (table 70) as well as weekly ash emissions and pyroclsatic flows (table 71). Partial dome collapse on 11 February 2010 led to a plume that rose to ~15 km altitude.

Figure 82. Map of Montserrat showing the pre-eruption topography of Soufrière Hills. The black circle shows the location of the MVO. The approximate outline of the Tar River delta in July 2004 is shown. Courtesy of Wadge and others (2005).

Table 69. Key features of the five Vulcanian explosions that occurred at Soufriere Hills in January and February 2010. Units in valley columns are pyroclastic-f low runout distances in kilometers. From Cole and others (2010) with due credit to Washington Volcanic Ash Advisory Center (VAAC) for satellite and aviation-based plume altitude estimates.

Table 70. Soufrière Hills seismicity and gas measurements from weekly reports between 4 December 2009 and 19 March 2010. MVO seismicity terminology as follows: Rockfall signals (featureless, high-frequency events, which correlate to large rockfalls from the dome); Volcano-tectonic (high frequencies >5 Hz, often impulsive P-phases and usually clear S-phases); Long-period (generally phaseless events with predominant frequency ~1 Hz); Hybrid (repetitive transient events of intermediate frequency, 3-5 Hz, without discernible S-phases; initial high-frequency waveforms at some stations) (MVO, 1996). Numbers refer to the total over the period indicated. Hydrochloric acid/sulfur dioxide ratios (HCl/SO₂) are derived from Fourier Transform Infrared (FTIR) gas measurements. Cycles of activity refer to rockfalls, ash venting, and pyroclastic flows. "--" indicates that data was not reported. Courtesy of MVO.

Table 71. Brief summary of dome emissions compiled from MVO reports, 4 December 2009-1 April 2010. Date entries indicated with a * are discussed in the text. Courtesy of MVO.

MVO issued a synthesis to the Scientific Advisory Committee (SAC) on volcanism between 15 August 2009 and 28 February 2010 (Cole and others, 2010). That report figures heavily in the following summary, but the included tables and comments also came from MVO reports, and there is a section on satellite thermal monitoring. Two similar earlier reports were published in 2009 (Robertson and others, 2009 and Stewart and others, 2009).

Since the dome remained active and at the same time represented the volcano's highest point, the summit elevation varied. The historical value of 915 m was a high point on the crater rim. Cole and others (2010) noted that the dome's summit was 1,050 m in September 2009, with the elevation being 1,130 m on 29 January 2010. Some taller heights involved blocky spines that did not last.

Extrusive Phase 5 activity. Extrusive Phase 4 finished on 3 January 2009 and was followed by 10 months of comparative inactivity with intermittent small pyroclastic flows and ash venting 5-7 October (BGVN 34:10). Phase 5 occurred from 4 October 2009 to 11 February 2010 (figure 83). Seismic records enabled MVO to subdivide this phase into three episodes of inferred dome growth as follows: 9 October-20 November 2009 (Episode 1); 20 November 2009-8 January 2010 (Episode 2); and 8 January-11 February 2010 (Episode 3). Cole and others (2010) noted that "A characteristic feature of Phase 5 dome growth has been the simultaneous occurrence of PFs in more than one direction, sometimes on the opposite side of the lava dome." Throughout Phase 5, ash often fell on inhabited areas.

Figure 83. Rockfall and pyroclastic flow data from the Phase 5 interval (3 October 2009 to 14 February 2010) at Soufriere Hills. Pyroclastic flows were observed by MVO staff, mainly during work hours, with each assigned to one of six drainages (flow directions) and to one of three sizes (the symbol size is proportional to the PF's size). Daily counts of rockfalls and long-period earthquakes and rockfalls (LP/RF) were determined by inspection of seismic signals (from station MBFL located at MVO). From Cole and others (2010).

Phase 5 began with a swarm of 24 volcano-tectonic (VT) earthquakes and ash venting. Gas fluxes had been low for two days prior to the onset of activity. The dome variously grew to the S, W, and N, and pyroclastic flows traveled in many directions. The eruptive style was described as "ash venting" rather than "explosions" due to the mild character of the associated seismic signals and the absence of ballistic fragments. Fallout deposits included comparatively coarse, well-sorted ash.

October dome growth mostly occurred on the S, with shed material filling the upper part of the SW flank's White River and covering what had stood as a protective wall for material traveling WSW. As a result, for the first time, substantial pyroclastic flows entered the WSW flank's Gingoes and Aymer's Ghauts, reaching the sea there with runout distances of over 4 km in those drainages.

Cyclic episodes of tremor occurred particularly during episode 2. On 23 November tremor occurred all day; it then waned and began to appear in cycles at 4-hour intervals, initially with signals of long-period and hybrid earthquakes. The tremor appeared associated with increased venting lasting 0.5-2 hours with plume heights to 5 km altitude. At 0640 on 10 December 2009, a large pyroclastic flow traveled down Tyers (Tyres) Ghaut and reached ~3.5 km from the lava dome.

Vigorous Vulcanian explosions occurred on five occasions during January-February 2010 (table 69), episode 3. All of these involved collapsing ash columns, producing fountain collapse pyroclastic flows that typically descended more than one ghaut. One explosion on 8 January, the largest by volume during January-February, sent a pyroclastic flow ~ 6 km down the Belham Valley. Two more Vulcanian explosions occurred during the night on 10 January.

Dome collapse of 11 February 2010. A large dome collapse took place in the early afternoon of 11 February, one day after a shift in dome-growth direction, and had several pulses. The collapse comprised 40-50 million cubic meters of material, and represented roughly 20% of the dome's total volume. A collapse scar ~ 300 m wide developed on the N flank of the dome. The collapse ended with vertically-directed explosions that created a new crater behind the collapsed part of the dome.

The collapse produced large pyroclastic flows and surges, mainly to the N and NE, that extended the E coastline (between Trants and Spanish Point), adding ~1 km² of new land. Two smaller flows also traveled NW and entered the Belham Valley.

A large ash column resulted from the collapse that reached ~15 km altitude, causing extensive ashfall on Guadeloupe (~60 km SE) and other parts of the eastern Caribbean. After 11 February, both seismicity and surface activity quieted but deep deformation returned. Gas measurements also indicated that the system remained active.

Pyroclastic flows traveled N and NE toward the old airport. The extensive pyroclastic-flow deposits extended the coastline 300-400 m out to sea. The coastal area impacted extended from Whites Bottom Ghaut to Trants Bay, just N of the old Bramble airport (figures 84 and 85). The effects were clearly visible on the NE flanks. Some flows, ~ 15 m thick, reached the sea at Trant's Bay. These flows extended the island's coastline up to 650 m to the E.

Figure 84. Two false-color satellite images, taken nearly 3 years apart at Soufriere Hills highlight the impact of the dome collapse of 11 February 2010. The image on the right is from 21 February 2010; the image on the left is from 17 March 2007. In colored versions of this image, red areas are vegetated, clouds are white, blue/black areas are ocean water, and gray areas are flow deposits. The large collapse scar on the N flank of the dome is visible (arrow). Several of the ghauts (valleys) on the SW side can be seen to have been nearly filled by pyroclastic flow deposits between October 2009 and February 2010. Images courtesy of NASA Earth Observatory.

Figure 85. Taken one week after the events of 11 February 2010 at Soufrière Hills, this aerial photograph shows the new pyroclastic flows at Spanish Point. Courtesy of MVO.

Towards the end of the collapse there was an energetic pyroclastic flow directed N over Streatham and Harris. This sent flows over the Harris Ridge into Bugby Hole and down the Farm River (~3.5 km from the dome) for the first time. The flows razed many buildings in both Harris and Streatham down to their foundations, and trees were felled by pyroclastic surges in the Gun Hill area and at the head of Farm River in Bugby Hole.

It was unclear whether there was any new dome growth within the crater during the week after the collapse. Night-time views of the dome revealed several small points of incandescence. Observations of the crater at the summit of the dome on 26 February found that it was then 50-100 m deep and ~200 m wide (figure 86). There was no newly extruded lava visible inside the crater.

Figure 86. Views of the inside of the new crater at the summit of the Soufrière Hills dome taken on 26 February 2010. The dark material on the left is the deposit of a fresh rockfall that probably occurred a few days before the photograph was taken. Courtesy of MVO.

Heavy rain on 8-9 March caused vigorous steaming of the hot 11 February deposits (figure 87). Strong geysering was visible at Trants near the old Bramble airport, with ash and steam fountaining occurring. In addition, lahars traveled down several drainages, including the Belham valley. Small spots of incandescence on the dome were visible again on 14 March. Occasional small pyroclastic flows and rockfalls were still occurring mainly from the western and southern parts of the dome.

Figure 87. Heavy rainfall on 8 and 9 March 2010 triggered a series of small to moderate sized pyroclastic flows. These were derived from the old dome and collapse scar. Pyroclastic flows continued to form as small amounts of cooled lava were shed from the surface. Courtesy of MVO.

MODVOLC Thermal Alerts. According to the Hawai'i Institute of Geophysics and Planetology (HIGP) Thermal Alerts System, no satellite thermal alerts were measured over Soufrière Hills between 29 March 2007 and 3 December 2008. Satellite thermal alerts were measured almost daily during 11 October 2009 through 15 February 2010. An isolated thermal alert was measured on 10 March 2010. Previously shorter periods of thermal alerts were measured during 11-29 March 2007 and 3 December 2008-3 January 2009.

References. Cole, P., Bass, V., Christopher, C., Fergus, M., Gunn, L., Odbert, H., Simpson, R., Stewart, R., Stinton, A., Stone, J., Syers, R., Robertson, R., Watts, R., and Williams, P., 2010, Report to the Scientific Advisory Committee on Montserrat Volcanic Activity, Report on Activity between 15 August 2009 and 28 February 2010, Open File Report OFR 10-01a, Prepared for SAC 14: 22-24 March 2010. Montserrat Volcano Observatory (MVO).

Robertson, R., Babal, L., Bass, V., Christopher, T., Chardot, L., Fergus, M., Fournier, N., Higgins, M., Joseph, E., Komorowski, J.-C., Odbert, H., Simpson, R., Smith, P., Stewart, R., Stone, J., Syers, R., Tsaines, B., and Williams, P., 2009, Report for the Scientific Advisory Committee on Montserrat Volcanic Activity, Prepared for SAC 13: 7-9 September 2009, MVO Open File Report 09/03.

Stewart, R., Bass, V., Chardot, L., Christopher, T., Dondin, F., Finizola, A., Fournier, N., Joseph, E., Komorowski, J.-C., Legendre, Y., Peltier, A., Robertson, R., Syers, R., and Williams, P., 2009, Report for the Scientific Advisory Committee on Montserrat Volcanic Activity, Prepared for SAC12: 9-11 March 2009, MVO Open File Report 09/01.

Wadge, G., Macfarlane, D.G., Robertson, D.A., Hale, A.J., Pinkerton, H., Burrell, R.V., Norton, G.E., and James, M.R., 2005, AVTIS: a novel millimetre-wave ground based instrument for volcano remote sensing: J. Volcanology and Geothermal Research, v. 146, no. 4, p. 307-318.

MVO, 1996, MVO/VSC Open Scientific Meeting, 27 November 1996, Seismicity of Montserrat Soufrière Hills Volcano Eruption, July 1995-November 1996 (URL: http://www.geo.mtu.edu/volcanoes/west.indies/soufriere/govt/meetings/nov1996/02.html).

Geologic Background. The complex, dominantly andesitic Soufrière Hills volcano occupies the southern half of the island of Montserrat. The summit area consists primarily of a series of lava domes emplaced along an ESE-trending zone. The volcano is flanked by Pleistocene complexes to the north and south. English's Crater, a 1-km-wide crater breached widely to the east by edifice collapse, was formed about 2000 years ago as a result of the youngest of several collapse events producing submarine debris-avalanche deposits. Block-and-ash flow and surge deposits associated with dome growth predominate in flank deposits, including those from an eruption that likely preceded the 1632 CE settlement of the island, allowing cultivation on recently devegetated land to near the summit. Non-eruptive seismic swarms occurred at 30-year intervals in the 20th century, but no historical eruptions were recorded until 1995. Long-term small-to-moderate ash eruptions beginning in that year were later accompanied by lava-dome growth and pyroclastic flows that forced evacuation of the southern half of the island and ultimately destroyed the capital city of Plymouth, causing major social and economic disruption.

Information Contacts: Montserrat Volcano Observatory (MVO), Fleming, Montserrat, West Indies (URL: http://www.mvo.ms/); Washington Volcanic Ash Advisory Center (VAAC), Satellite Analysis Branch (SAB), NOAA/NESDIS E/SP23, NOAA Science Center Room 401, 5200 Auth Rd, Camp Springs, MD 20746, USA (URL: http://www.ospo.noaa.gov/Products/atmosphere/vaac/); NASA Earth Observatory (URL: http://earthobservatory.nasa.gov/); Hawai'i Institute of Geophysics and Planetology (HIGP) Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/).

Sonia Calvari of the Istituto Nazionale di Geofisica e Vulcanologia (INGV) reported that the 2007 eruptive episode at Stromboli started on 27 February and finished on 2 April (BGVN 32:04) Additional details about this eruption can be found in Barberi and others (2009) and Calvari and others (2010). Eruptions later in 2007 and during 2008 will be reported in a later issue; summaries of activity in 2009 and January 2010 are included below.

Activity during 2009. The summit activity in 2009 was very unusual, producing four or five intracrater lava flows. Lava within the crater depression was extruded on 22-25 April, 3 May, and 30 August 2009. On 8 November a major explosion from the vents in the central crater fragmented and destroyed part of the E flank of the cinder cone there. The explosion produced an eruptive column over 350 m high that drifted SE and was soon followed by a lava flow from the widened central vent. The lava flow spread within the crater depression for a few minutes and reached a maximum distance of ~ 60 m. After the 8 November explosion, activity returned to background levels.

Strong seismic activity was recorded on 24 November 2009. Observers saw an explosive eruption cloud and the emission of a lava flow. Ejecta fallout affected the summit area, particularly the Pizzo sopra la Fossa, where numerous volcanic bombs landed. Also affected was the eastern downwind flank, where a layer of pumice was deposited on the beach. The fallout of incandescent material caused some vegetation fires on the E flank. After this explosive activity, seismicity returned to the level previously observed.

Activity during January 2010. According to the INGV website, at 1912 UTC on 4 January 2010, the network of surveillance cameras recorded an explosion that affected the central vent area. During a first phase, coarse pink pyroclastic materials (bombs and possibly lithic particles) were erupted from the entire crater terrace. A second phase followed with the emission of a small ash plume. Beginning at 0757 UTC on 7 January, the IR camera located on the Pizzo sopra la Fossa showed spattering lava in the central portion of the crater, leading to a series of lava flows; the lava stopped around 0100 UTC on 8 January. At 1448 UTC on 10 January, the INGV network of surveillance cameras recorded a strong explosion that affected the N portion of the crater, causing a major fallout of volcanic bombs at Pizzo sopra la Fossa and high on the NE part of the volcano.

References. Barberi, F., Rosi, M., and Scendone, R. (eds), 2009, The 2007 eruption of Stromboli: Journal of Volcanology and Geothermal Research, v. 182, no. 3-4, p. 123-280.

Calvari, S., Lodato, L., Steffke, A., Cristaldi, A., Harris, A.J.L., Spampinato, L., and Boschi, E., 2010, The 2007 Stromboli eruption: Event chronology and effusion rates using thermal infrared data: Journal Geophysical Research, Solid Earth, 115, B4, B04201, doi:10.1029/2009JB006478.

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

Telica exhibited extensive degassing and sporadic ash explosions during 2006-2008 (BGVN 34:08). Activity since then had decreased to a relatively low level, but degassing was continuing. This report discusses activity in 2009 and January-February 2010 based on reports from the Instituto Nicarag?ense de Estudios Territoriales (INETER) and from fieldwork by Mel Rodgers (University of South Florida) in November 2009 and March 2010.

INETER publishes a monthly bulletin on earthquakes and volcanic activity in Nicaragua. For Telica, most of the monthly data consists of in-field temperature measurements. An observation camera situated 20 km from the crater has not been functional for more than a year. The seismic instrument at Telica was frequently out of order during 2009.

On 20 May 2009, the sulfur dioxide output in the crater ranged from 106-251 tons per day. The maximum temperature of the crater was about 90-112°C in April and May 2009, but rose to 201°C in July, 251°C in August, and 302-317°C during September through November 2009. The maximum temperature of four fumaroles was also measured, which generally ranged from 67-72°C. These temperatures decreased in June 2009 and increased in August 2009 (to 76-105°C). The temperature of fumarole 4 decreased to 59°C in October; gas emission at that fumarole ceased altogether in November.

Visits in November 2009 and March 2010. Mel Rodgers detailed observations during fieldwork at the volcano in November 2009 and March 2010 conducted with Diana Roman (University of South Florida), Peter La Femina and Halldor Geirsson (Pennsylvania State University), and Alain Morales (INETER). On 24-25 November 2009, the group observed a set of elongated fractures flanking the crater floor through which incandescence and/or lava were clearly visible. A high concentration of gas and a steady gas-and-vapor plume were also observed in the crater. Multiple vigorous fumaroles were observed on the W side of the crater close to the top of the crater wall, and an intermittent jetting noise that appeared to be coming from the crater floor was audible from their position at the crater rim. A broadband seismometer was installed and, during the 24-hour visit, a high rate of long-period (LP) seismicity was recorded.

On 15 March 2010, the researchers returned and again observed incandescence within the crater. Incandescence was clearly visible through a C-shaped crack or skylight, SE of the 25 November 2009 location (figures 17 and 18). A high concentration of gas and a steady gas-and-vapor plume in the crater continued and vigorous degassing of the fumaroles on the crater floor was observed (figure 19). Intermittent jetting noises and rockfalls were audible coming from the crater, and at 2202 UTC a loud, low popping noise from the crater was heard. Data retrieved from the single station installed in November 2009 showed a high rate of LP seismicity from November 2009-March 2010.

Figure 17. Photograph taken 25 November 2009 of Telica volcano showing the relative locations of the 25 November 2009 incandescent fracture (right) and the later 15 March 2010 incandescent crack/skylight (left). Courtesy of Mel Rodgers.

Figure 18. Photograph taken 15 March 2010 showing incandescence visible in the C-shaped crack/skylight at Telica volcano. Courtesy of Mel Rodgers.

Figure 19. Photograph taken 15 March 2010 showing a view of the entire Telica crater floor. Locations of sightings of incandescence and of vigorous gas jets are indicated. Courtesy of Mel Rodgers.

A successful installation of the TESAND (Telica Seismic and Deformation) network was completed in March 2010. This network, consisting of six broadband seismometers and eight high-rate (1 Hz) continuous global positioning system stations, will be deployed for 3 years to document background LP seismicity and magmatic processes associated with quiescent volcanism.

According to the Hawai'i Institute of Geophysics and Planetology (HIGP) Thermal Alerts System, no satellite thermal alerts were measured over Telica during 2008, 2009, and through 30 April 2010.

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

Information Contacts: Instituto Nicaraguense de Estudios Territoriales (INETER), Apartado Postal 2110, Managua, Nicaragua; Mel Rodgers, University of South Florida; Hawai'i Institute of Geophysics and Planetology (HIGP) Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822 (URL: http://modis.higp.hawaii.edu/).