Recently Published Bulletin Reports
Erebus (Antarctica) Lava lake remains active; most thermal alerts recorded since 2019
Rincon de la Vieja (Costa Rica) Frequent phreatic explosions during July-December 2023
Bezymianny (Russia) Explosion on 18 October 2023 sends ash plume 8 km high; lava flows and incandescent avalanches
Kilauea (United States) Low-level lava effusions in the lava lake at Halema’uma’u during July-December 2022
Nyamulagira (DR Congo) Lava flows and thermal activity during May-October 2023
Bagana (Papua New Guinea) Explosions, ash plumes, ashfall, and lava flows during April-September 2023
Mayon (Philippines) Lava flows, pyroclastic flows, ash emissions, and seismicity during April-September 2023
Nishinoshima (Japan) Eruption plumes and gas-and-steam plumes during May-August 2023
Krakatau (Indonesia) White gas-and-steam plumes and occasional ash plumes during May-August 2023
Villarrica (Chile) Strombolian activity, gas-and-ash emissions, and crater incandescence during April-September 2023
Merapi (Indonesia) Frequent incandescent avalanches during April-September 2023
Ebeko (Russia) Moderate explosive activity with ash plumes continued during June-November 2023
Erebus (Antarctica) — January 2024
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Erebus
Antarctica
77.53°S, 167.17°E; summit elev. 3794 m
All times are local (unless otherwise noted)
Lava lake remains active; most thermal alerts recorded since 2019
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.
Year |
Jan |
Feb |
Mar |
Apr |
May |
Jun |
Jul |
Aug |
Sep |
Oct |
Nov |
Dec |
SUM |
2017 |
0 |
21 |
9 |
0 |
0 |
1 |
11 |
61 |
76 |
52 |
0 |
3 |
234 |
2018 |
0 |
21 |
58 |
182 |
55 |
17 |
137 |
172 |
103 |
29 |
0 |
0 |
774 |
2019 |
2 |
21 |
162 |
151 |
55 |
56 |
75 |
53 |
29 |
19 |
1 |
0 |
624 |
2020 |
0 |
2 |
16 |
18 |
4 |
4 |
1 |
3 |
18 |
3 |
1 |
6 |
76 |
2021 |
0 |
9 |
1 |
0 |
2 |
56 |
46 |
47 |
35 |
52 |
5 |
3 |
256 |
2022 |
1 |
13 |
55 |
22 |
15 |
32 |
39 |
19 |
31 |
11 |
0 |
0 |
238 |
2023 |
2 |
33 |
49 |
82 |
41 |
32 |
70 |
64 |
42 |
17 |
5 |
11 |
448 |
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).
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).
Rincon de la Vieja (Costa Rica) — January 2024
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Rincon de la Vieja
Costa Rica
10.83°N, 85.324°W; summit elev. 1916 m
All times are local (unless otherwise noted)
Frequent phreatic explosions during July-December 2023
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.
OVSICORI Weekly Bulletin |
Number of explosions |
Number of emissions |
28 Jul 2023 |
6 |
14 |
4 Aug 2023 |
10 |
12 |
1 Sep 2023 |
13 |
11 |
22 Sep 2023 |
12 |
13 |
29 Sep 2023 |
6 |
11 |
6 Oct 2023 |
12 |
5 |
13 Oct 2023 |
7 |
9 |
20 Oct 2023 |
1 |
15 |
27 Oct 2023 |
3 |
23 |
3 Nov 2023 |
3 |
10 |
17 Nov 2023 |
0 |
Some |
24 Nov 2023 |
0 |
14 |
8 Dec 2023 |
4 |
16 |
22 Dec 2023 |
8 |
18 |
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.
Date |
Time |
Description of Activity |
1 Jul 2023 |
0156 |
Explosion. |
2 Jul 2023 |
0305 |
Explosion. |
4 Jul 2023 |
0229, 0635 |
Event at 0635 produced a gas-and-steam plume that rose 700 m and drifted W; seen by residents in Liberia (21 km SW). |
9 Jul 2023 |
1843 |
Explosion. |
21 Jul 2023 |
0705 |
Explosion. |
26 Jul 2023 |
1807 |
Explosion. |
28 Jul 2023 |
0802 |
Explosion generated a gas-and-steam plume that rose 500 m. |
30 Jul 2023 |
1250 |
Explosion. |
31 Jul 2023 |
2136 |
Explosion. |
11 Aug 2023 |
0828 |
Explosion. |
18 Aug 2023 |
1304 |
Explosion. |
21 Aug 2023 |
1224 |
Explosion generated gas-and-steam plumes rose 500-600 m. |
22 Aug 2023 |
0749 |
Explosion generated gas-and-steam plumes rose 500-600 m. |
24 Aug 2023 |
1900 |
Explosion. |
25 Aug 2023 |
0828 |
Event produced a steam-and-gas plume that rose 3 km and drifted NW. |
27-28 Aug 2023 |
0813 |
Four small events; the event at 0813 on 28 August lasted two minutes and generated a steam-and-gas plume that rose 2.5 km. |
1 Sep 2023 |
1526 |
Explosion generated plume that rose 2 km and ejected material onto the flanks. |
2-3 Sep 2023 |
- |
Small explosions detected in infrasound data. |
4 Sep 2023 |
1251 |
Gas-and-steam plume rose 1 km and drifted W. |
7 Nov 2023 |
1113 |
Explosion. |
8 Nov 2023 |
0722 |
Explosion. |
12 Nov 2023 |
0136 |
Small gas emissions. |
14 Nov 2023 |
0415 |
Small gas emissions. |
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).
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 (Russia) — November 2023
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Bezymianny
Russia
55.972°N, 160.595°E; summit elev. 2882 m
All times are local (unless otherwise noted)
Explosion on 18 October 2023 sends ash plume 8 km high; lava flows and incandescent avalanches
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.
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.
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.
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
Kilauea (United States) — January 2023
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Kilauea
United States
19.421°N, 155.287°W; summit elev. 1222 m
All times are local (unless otherwise noted)
Low-level lava effusions in the lava lake at Halema’uma’u during July-December 2022
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.
Date: |
Level of the active lava lake (m): |
Cumulative volume of lava effused (million cubic meters): |
7 Jul 2022 |
130 |
95 |
19 Jul 2022 |
133 |
98 |
4 Aug 2022 |
136 |
102 |
16 Aug 2022 |
137 |
104 |
12 Sep 2022 |
143 |
111 |
5 Oct 2022 |
143 |
111 |
28 Oct 2022 |
143 |
111 |
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).
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.
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.
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.
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 (DR Congo) — November 2023
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Nyamulagira
DR Congo
1.408°S, 29.2°E; summit elev. 3058 m
All times are local (unless otherwise noted)
Lava flows and thermal activity during May-October 2023
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.
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.
Bagana (Papua New Guinea) — October 2023
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Bagana
Papua New Guinea
6.137°S, 155.196°E; summit elev. 1855 m
All times are local (unless otherwise noted)
Explosions, ash plumes, ashfall, and lava flows during April-September 2023
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.
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).
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 (Philippines) — October 2023
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Mayon
Philippines
13.257°N, 123.685°E; summit elev. 2462 m
All times are local (unless otherwise noted)
Lava flows, pyroclastic flows, ash emissions, and seismicity during April-September 2023
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.
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.
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 (Japan) — October 2023
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Nishinoshima
Japan
27.247°N, 140.874°E; summit elev. 100 m
All times are local (unless otherwise noted)
Eruption plumes and gas-and-steam plumes during May-August 2023
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.
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.
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).
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 (Indonesia) — October 2023
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Krakatau
Indonesia
6.1009°S, 105.4233°E; summit elev. 285 m
All times are local (unless otherwise noted)
White gas-and-steam plumes and occasional ash plumes during May-August 2023
Krakatau is located in the Sunda Strait between Java and Sumatra, Indonesia. Caldera collapse during the catastrophic 1883 eruption destroyed Danan and Perbuwatan cones and left only a remnant of Rakata. The post-collapse cone of Anak Krakatau (Child of Krakatau) was constructed within the 1883 caldera at a point between the former Danan and Perbuwatan cones; it has been the site of frequent eruptions since 1927. The current eruption period began in May 2021 and has recently consisted of 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).
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 (Chile) — October 2023
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Villarrica
Chile
39.42°S, 71.93°W; summit elev. 2847 m
All times are local (unless otherwise noted)
Strombolian activity, gas-and-ash emissions, and crater incandescence during April-September 2023
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.
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.
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).
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 (Indonesia) — October 2023
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Merapi
Indonesia
7.54°S, 110.446°E; summit elev. 2910 m
All times are local (unless otherwise noted)
Frequent incandescent avalanches during April-September 2023
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).
Month |
Average number of avalanches per day |
Distance avalanches traveled (m) |
Apr 2023 |
19 |
1,200-2,000 |
May 2023 |
22 |
500-2,000 |
Jun 2023 |
18 |
1,200-2,000 |
Jul 2023 |
30 |
300-2,000 |
Aug 2023 |
25 |
400-2,300 |
Sep 2023 |
23 |
600-2,000 |
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.
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.
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.
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).
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
Russia
50.686°N, 156.014°E; summit elev. 1103 m
All times are local (unless otherwise noted)
Moderate explosive activity with ash plumes continued during June-November 2023
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.
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/).
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Bulletin of the Global Volcanism Network - Volume 30, Number 04 (April 2005)
Managing Editor: Richard Wunderman
Anatahan (United States)
Explosive eruption on 6 April 2005 issues highest ash plume recorded here
Awu (Indonesia)
Stable during mid- to late August 2004
Fernandina (Ecuador)
Lava flows down S flank from circumferential vents near caldera rim
Karthala (Comoros)
16 April 2005 seismicity leading to eruption; near-source tephra 1.5 m thick
Lascar (Chile)
4 May 2005 eruption sends ash over 1,000 km SE, ¾ of the way to Buenos Aires
Lengai, Ol Doinyo (Tanzania)
Tall hornito almost reaches summit elevation; more lava spills over rim
Vailulu'u (United States)
ALIA cruise discloses new cone in the summit crater
Anatahan (United States) — April 2005
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Anatahan
United States
16.35°N, 145.67°E; summit elev. 790 m
All times are local (unless otherwise noted)
Explosive eruption on 6 April 2005 issues highest ash plume recorded here
Anatahan's third historical eruption began on 5 January 2005, and is described in BGVN 29:12. Further details and satellite images were presented in BGVN 30:02, which covered events until mid-February 2005. A 5-6 April 2005 eruption cloud rose to at least 15 km altitude, which was the highest yet seen at the volcano.
Anatahan erupted almost continuously after 5 January 2005, when it started its third eruption in recorded history. An image collected by the Ozone Monitoring Instrument on NASA's Aura satellite shows atmospheric sulfur dioxide (SO2) concentrations between 31 January and 4 February 2005 (figure 14). A long SO2 plume extends NE and SW of Anatahan, and the edge of the plume covers Guam (the southernmost island) and the other Mariana Islands immediately to Anatahan's N and S.
Volcanogenic SO2 combines with water to create a sulfuric acid haze. Called "vog," this haze can cause illness and make breathing difficult. Volcanic haze grew so thick during the first week of February that the National Weather Service issued a volcanic haze advisory for Guam, where several illnesses were reported.
After mid-February 2005, eruptive activity at Anatahan steadily declined to less than 5% of the peak level attained since the eruption started on 5 January. Ash eruptions continued, and the 2003 crater floor was almost entirely covered by fresh lava out to a diameter of ~ 1 km. A MODIS image taken at 0115 on 18 February showed a plume of steam and vog extending about ~ 170 km SW of Anatahan. Seismic and acoustic records during the last week of February 2005 showed very low levels of activity. Seismic amplitudes during 23-28 February were similar to those recorded prior to the 5 January eruption. NASA MODIS (Moderate Resolution Imaging Spectroradiometer) imagery taken on 28 February showed a faint plume of vog and steam trending W of Anatahan.
During the first two weeks of March 2005 volcanic and seismic activity increased relative to the previous weeks. During 14-17 March, seismicity increased and steam rose a few hundred meters above the volcano. The inner E crater had been nearly filled with lava flows and lapilli since early January.
A small eruption began on 18 March at 1544 according to seismic data. On 19 March the Washington VAAC issued an advisory that an ash plume was visible on satellite imagery below 4 km altitude. Small explosions that began late on 20 March lasted for 14 hours. No emissions were visible on satellite imagery, but others were, later in March and April.
A strong outburst apparently began on 21 March, a day when seismicity increased significantly. Seismic amplitudes peaked on the 25th and faded out on the 26th. Near the peak on the 25th, the U.S. Air Force Weather Agency (AFWA) detected a hot spot on the island on satellite imagery and reported an ash plume briefly reaching ~ 5.8 km altitude. The plume height soon dropped to below 3 km altitude, and by near midday on the 27th the plume had changed from ash and steam to steam and vog. On the 27th the plume extended ~ 240 km SW.
On 5 April at about 2200 seismic signals began to increase slowly, and the Washington VAAC began to see increased ash on satellite imagery. On 6 April 2005 around 0300 an explosive eruption began and produced an ash plume to an initial height of ~ 15.2 km altitude, the highest in recorded history from the volcano. Seismicity peaked at the same time.
The AFWA reported an upper level ash plume at ~ 15.2 km altitude blowing E to SE and a lower level ash plume at ~ 4.6 km altitude blowing SW; the upper plume extended more than 465 km. Earth Probe TOMS data on 6 April at 1046 showed a compact sulfur-dioxide cloud drifting E of Anatahan following the eruption.
Chuck Sayon, the superintendent of American Memorial Park noted, "On Saipan at around 10 AM the skies darkened and light ash started falling . . . park operation[s] have been restricted to indoor activities due to irritation to eyes and breathing as ash starts to lightly coat the area. Schools are closed as well as the airport until further notice . . .."
On 6 April during 0400 to 0900 the seismicity at Anatahan decreased to near background. The seismicity surged for about 1 hour, with amplitudes about one-half those reached during the earlier eruption, and subsequently dropped again to near background. Prior to the 6 April eruption, during 31 March to 4 April the amplitudes of harmonic tremor varied, reaching a 2-month high on the 3rd. Small explosions occurred every one minute to several minutes, probably associated with cinder-cone formation. Steam-and-ash plumes drifted ~ 200 km, and vog drifted ~ 400 km at altitudes below ~ 2.4- 4.6 km.
The U.S. Geological Survey (USGS) (in conjunction with the Commonwealth of the Northern Mariana Islands) stated that the "eruption of 6 April 2005 was the largest historical eruption of Anatahan and expelled roughly 50 million cubic meters of ash. The eruption column and the amplitude of harmonic tremor both grew slowly over about 5 hours and both peaked about 0300 on 6 April local time . . .. The peak of the eruption lasted about one hour and then the activity declined rapidly over the following hour."
The 6 April 2005 eruption's plume was captured on satellite images. The image showed a plume that was tan or brown in color and clearly ash laden (figure 15).
Figure 16 shows SO2 concentrations in the atmosphere on 7 April 2005, over 30 hours after the large 6 April eruption. SO2 emissions from the eruption were measured by the Ozone Monitoring Instrument (OMI) on NASA's EOS/Aura satellite. OMI detects the total column amount of SO2 between the sensor and the Earth's surface and maps this quantity as it orbits the planet. A new perspective on the vertical distribution of the SO2 is revealed by combining the OMI data with coincident measurements made by the Microwave Limb Sounder (MLS), also part of the Aura mission.
The MLS data crisscross the OMI image and clearly show that some, but not all, of the SO2 measured by OMI to the volcano's E was in the upper troposphere or above. At these altitudes, SO2—and the sulfate aerosols that form from it—can stay in the atmosphere and affect the climate for a longer period of time. A weaker SO2 signal was also measured in the same region during the nighttime MLS overpass, which crosses the image from upper right to lower left. The daytime data, running from upper left to lower right, coincide with the OMI measurements. The MLS data west of Anatahan show no significant SO2 signal, indicating that the SO2 measured by OMI in this region was in the lower troposphere.
MLS measures thermal emissions from the Earth's limb, so unlike the OMI sensor it also collects data at night. It is designed to measure vertical profiles of atmospheric gases that are important for studying the Earth's ozone layer, climate, and air quality, such as SO2. These images, derived from preliminary, unvalidated OMI and MLS data, show MLS SO2 columns (filled circles) measured every 165 km along the Aura orbit, plotted over the OMI SO2 map. The MLS SO2 columns shown here are derived from profile measurements made from the upper troposphere into the stratosphere (~ 215-0 hPa (hectoPascal, 102 Pa) or ~ 12 km altitude and above), and the circles do not represent the actual size of the MLS footprint, which is roughly 165 x 6 km.
Anatahan's morphological changes were highlighted in before (pre-eruption) versus after (post-eruption) images (figure 17). Seismicity decreased at Anatahan after 6 April and during 7-11 April was at very low levels, near background. On 11 April, a steam-and-ash plume rose ~ 2.7 km altitude and drifted ~ 280 km WSW.
Occasional data from Anatahan revealed that seismicity appeared to increase during 24-25 April. During 20-25 April, a continuous thin plume of ash-and-steam rose to less than ~ 3 km altitude and drifted more than 185 km from the volcano. Harmonic tremor dropped dramatically on 1 May after being at high levels for several days. During 27 April to 1 May, the main ash-and-steam plume rose to ~ 3 km altitude According to a news article, the volcanic plume from Anatahan reached Philippine airspace on 4 May.
On 5 May an extensive ash-and-steam plume to 4.5 km altitude was visible in all directions. Ash extended 770 km N, 130 km S (to northern Saipan), and 110 km W. Vog extended in a broad swath from 3,000 km W, over the Philippines, to 1,000 km N of Anatahan. By 9 May harmonic tremor amplitude had decreased to near-background levels, with a corresponding drop in eruptive activity. As of 10 May AFWA was reporting ash to about 3 km altitude extending 400 km W and an area of vog less than half that noted on 5 May.
On 11 May AFWA reported thick ash rising to 4.2 km altitude and moving WNW. The thick ash extended in a triangular shape from the summit 444 km to the WSW through 510 km to the NW. A layer of thin ash at 3 km altitude extended another 1,000 km beyond the thick ash. A broad swath of vog extended over 2,200 km W nearly to the Philippines and over 1,400 km NNW of Anatahan. Although the ash plume diminished over the next few days and was not as thick, it remained significant, rising to 2.4 km and extending 370 km WNW on the 13th. Scientific personnel from the Emergency Management Office and the USGS working the next day at a spot 2-3 km W of the active vent heard a continuous roaring sound. They also saw ash and steam rising by pure convection, not explosively, to 3 km altitude.
Reference. Chadwick, W.W., Embley, R.W., Johnson, P.D., Merlea, S.G., Ristaub, S., and Bobbitta, A., 2005, The submarine flanks of Anatahan volcano, Commonwealth of the Northern Mariana Islands: Jour. of Volcanology and Geothermal Res. (In press, June 2005).
Geologic Background. The elongate, 9-km-long island of Anatahan in the central Mariana Islands consists of a large stratovolcano with a 2.3 x 5 km compound summit caldera. The larger western portion of the caldera is 2.3 x 3 km wide, and its western rim forms the island's high point. Ponded lava flows overlain by pyroclastic deposits fill the floor of the western caldera, whose SW side is cut by a fresh-looking smaller crater. The 2-km-wide eastern portion of the caldera contained a steep-walled inner crater whose floor prior to the 2003 eruption was only 68 m above sea level. A submarine cone, named NE Anatahan, rises to within 460 m of the sea surface on the NE flank, and numerous other submarine vents are found on the NE-to-SE flanks. Sparseness of vegetation on the most recent lava flows had indicated that they were of Holocene age, but the first historical eruption did not occur until May 2003, when a large explosive eruption took place forming a new crater inside the eastern caldera.
Information Contacts: Juan Takai Camacho and Ramon Chong, Emergency Management Office of the Commonwealth of the Northern Mariana Islands (CNMI/EMO), PO Box 100007, Saipan, MP 96950, USA (URL: http://www.cnmihsem.gov.mp/); Simon Carn, Joint Center for Earth Systems Technology (JCET), University of Maryland Baltimore County (UMBC), 1000 Hilltop Circle, Baltimore, MD 21250, USA; Hawaiian Volcano Observatory (HVO), U.S. Geological Survey, PO Box 51, Hawaii National Park, HI 96718, USA (URL: https://volcanoes.usgs.gov/observatories/hvo/); Charles Holliday, U.S. Air Force Weather Agency (AFWA), Offutt Air Force Base, Nebraska 68113, USA; Randy White and Frank Trusdell, U.S. Geological Survey, 345 Middlefield Road, Menlo Park, CA 94025-3591 USA (URL: https://volcanoes.usgs.gov/nmi/activity/); Saipan Tribune, PMB 34, Box 10001, Saipan, MP 96950, USA (URL: http://www.saipantribune.com/); Operational Significant Event Imagery (OSEI) team, World Weather Bldg., 5200 Auth Rd Rm 510 (E/SP 22), NOAA/NESDIS, Camp Springs, MD 20748, USA (URL: https://www.nnvl.noaa.gov/); Washington Volcanic Ash Advisory Center (VAAC), Satellite Analysis Branch, NOAA/NESDIS E/SP23, NOAA Science Center Room 401, 5200 Auth Road, Camp Springs, MD 20746, USA (URL: http://www.ssd.noaa.gov/); Chuck Sayon, American Memorial Park, Saipan, MP 96950, USA; NASA Earth Observatory (URL: http://earthobservatory.nasa.gov/).
Awu
Indonesia
3.689°N, 125.447°E; summit elev. 1318 m
All times are local (unless otherwise noted)
Stable during mid- to late August 2004
Awu's eruption on 6 June 2004 and its elevated seismicity in early August 2004 was previously reported (BGVN 29:10). This report covers the last half of August 2004, which had not been reported on previously. Since the 6 June eruption, observation of the summit failed to reveal any significant changes (table 3). The hazard status of Awu during this August report remained at Level 2, having been elevated to 4 (the highest on a scale of 1 to 4) at the time of the 6 June eruption and then lowered on 14 June.
Table 3. Seismicity at Awu during August 2004 as reported by DVGHM.
Date |
Deep Volcanic (A-type) |
Shallow Volcanic (B-type) |
Tectonic |
09 Aug-15 Aug 2004 |
-- |
-- |
75 |
16 Aug-22 Aug 2004 |
2 |
1 |
81 |
23 Aug-29 Aug 2004 |
2 |
-- |
102 |
Geologic Background. The massive Gunung Awu stratovolcano occupies the northern end of Great Sangihe Island, the largest of the Sangihe arc. Deep valleys that form passageways for lahars dissect the flanks of the volcano, which was constructed within a 4.5-km-wide caldera. Powerful explosive eruptions in 1711, 1812, 1856, 1892, and 1966 produced devastating pyroclastic flows and lahars that caused more than 8000 cumulative fatalities. Awu contained a summit crater lake that was 1 km wide and 172 m deep in 1922, but was largely ejected during the 1966 eruption.
Information Contacts: Dali Ahmad, Directorate of Volcanology and Geological Hazard Mitigation (DVGHM), Jalan Diponegoro 57, Bandung 40122, Indonesia (URL: http://www.vsi.esdm.go.id/).
Fernandina (Ecuador) — April 2005
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Fernandina
Ecuador
0.37°S, 91.55°W; summit elev. 1476 m
All times are local (unless otherwise noted)
Lava flows down S flank from circumferential vents near caldera rim
On the morning of 13 May 2005, a new eruption started on uninhabited Fernandina volcano (figure 5). Fernandina last erupted in 1995 (figure 6), and had been quiet and seemingly unchanged when a team from the Ecuadorian Institute of Geophysics (IG) flew over it in late March 2005. On 11 May an M 5.0 earthquake occurred with an epicenter ~ 30 km E of Fernandina's center. Only two other earthquakes have been located by the U.S. Geological Survey (USGS) within 100 km of Fernandina in last 4.5 years (M 4.0 on 23 February 2005 and M 4.6 on 16 April 2005), both having epicenters ~ 70-80 km SE of Fernandina's center. A seismic station, installed by the IG in 1996 on the NE coast of the island, was out of service at the time of eruption.
Galápagos National Park workers in western Galápagos were apparently the first to witness the eruption, and IG technicians recognized it on satellite imagery. The University of Hawaii presents hotspot images on their website. Their GOES data lacked hotspots at 0930, but a clear and strong one had developed on the S flank by 0945. Francisco Dousdebes (of Metropolitan Touring) placed the eruption's start time at 0935. S-flank hotspots were comparatively extensive by 1015. The Washington VAAC issued their first full advisory at 1315. Their notices reported that the W-directed plume rose to ~ 5 km altitude, and the S-directed plume went to 9 km; both were visible as late as 1745 on 13 May, depicting the leading portions of Fernandina' s ash plume more than 200 km from the volcano
An overflight of the eruption on the 13th by the National Park resulted in a report by Patricio Ramón and Hugo Yepes, and the eruption was confirmed by Washington Tapia, director of the Galápagos National Park. That evening, Galápagos resident Greg Estes telephoned Dennis Geist to report that the eruptive source was a "circumferential vent near [the] summit, S side . . . 6 km long with an eruptive zone 50 m across." It was uncertain how this fissure was related to the 1981 eruption site (figure 2 and SEAN 09:03). IG also noted that tephra had fallen on neighboring Isabela Island, in the areas of the volcanoes Wolf and Ecuador (~ 40 km from the vent, figure 1).
At 0537 on the second morning, 14 May, the Washington VAAC reported low level ash/steam not visible in infrared imagery, but at 0746, 1½ hours after sunrise, a plume of ash extended ~ 130 km to the W and was moving at 18 km/hour at 1,800 m elevation. The GOES thermal anomaly was greatly diminished by 0930, and remained low to non-existent until resumption around 1415. That afternoon, an overflight by Godfrey Merlen, Wacho Tapia, and Alan Tye (Charles Darwin Research Station) resulted in the fullest report to date.
They said that although the vent area was obscured by clouds, topography suggested a 4.5 km long fissure vent near the S rim, with activity having progressed from SW (near the first and uppermost flows of the 1995 radial fissure eruption) to the E (figure 1). The lava flows "had begun to pond on the gentler outer skirt of the island," and were then 5.5 km from the coast (~ 5 km from the vents). They thought it unlikely that the flows would reach the sea. A follow-up news report in El Comercio (Quito) quoted Tapia as identifying five flows down the S flank. Only one remained incandescent. At 1745 on 14 May, Washington VAAC reported a plume remaining to the NW, but—lacking detectable ash—they discontinued advisories. Thermal anomalies on the GOES satellite remained strong, however, until the next morning.
The report also noted that, "As on previous eruptions, such as that on Cerro Azul in 1998, lava passing through vegetated areas has caused small fires, but these have not spread far from the lava tongues themselves before going out. Most of the new flows have passed over unvegetated older lava, and damage to Fernandina's vegetation is limited."
The team also flew over Alcedo volcano on Isabela, where Project Isabela staff had reported increased fumarole activity. Steam was rising from the "new" fumarole sites (active since the 1990s) and from the area of sulfur deposits and fumaroles in the southwestern area of the rim, but this activity did not appear unusual.
On 15 May, the GOES thermal anomaly was gone before noon, but returned near midnight (about 2330), over a smaller area, and it remained through sunrise (0615) on 16 May. Small anomalies were visible the next several nights (when contrast with adjacent cold flows was strongest), but there was no obvious evidence of continued feeding of the new flows.
The complex thermal anomalies detected in MODIS satellite imagery (provided by the University of Hawaii), were abundant around the time of eruption. They spread over Fernandina's rim, in some cases in the caldera, and broadly over the S flank. They continued through at least the rest of May.
The Washington VAAC reported that a weak hotspot started 29 May 2005 at 1945 (30 May at 0145 UTC) and a very short narrow plume of ash and gases appeared in multi-spectral imagery at 2145 (30 May at 0345 UTC). No ground confirmation of an eruption was available, and there was a layer of low-level weather cloud over the island. At that time, the plume appeared to dissipate as it moved away at ~ 18 km/hour.
Geologic Background. Fernandina, the most active of Galápagos volcanoes and the one closest to the Galápagos mantle plume, is a basaltic shield volcano with a deep 5 x 6.5 km summit caldera. The volcano displays the classic "overturned soup bowl" profile of Galápagos shield volcanoes. Its caldera is elongated in a NW-SE direction and formed during several episodes of collapse. Circumferential fissures surround the caldera and were instrumental in growth of the volcano. Reporting has been poor in this uninhabited western end of the archipelago, and even a 1981 eruption was not witnessed at the time. In 1968 the caldera floor dropped 350 m following a major explosive eruption. Subsequent eruptions, mostly from vents located on or near the caldera boundary faults, have produced lava flows inside the caldera as well as those in 1995 that reached the coast from a SW-flank vent. Collapse of a nearly 1 km3 section of the east caldera wall during an eruption in 1988 produced a debris-avalanche deposit that covered much of the caldera floor and absorbed the caldera lake.
Information Contacts: Patricio Ramón and Hugo Yepes, Geophysical Institute (IG), Escuela Politécnica Nacional, Apartado 17-01-2759, Quito, Ecuador (URL: http://www.igepn.edu.ec/); Alan Tye, Charles Darwin Research Station, Puerto Ayora, Santa Cruz, Galapagos Islands, Ecuador (URL: http://www.darwinfoundation.org/); Washington Volcanic Ash Advisory Center (VAAC), Satellite Analysis Branch, NOAA/NESDIS E/SP23, NOAA Science Center Room 401, 5200 Auth Road, Camp Springs, MD 20746, USA (URL: http://www.ssd.noaa.gov/); Tom Simkin, Dept. of Mineral Sciences, National Museum of Natural History, Smithsonian Institution, Washington, DC 20013-7012, USA; National Earthquake Information Center, U.S. Geological Survey, Box 25046, DFC, MS 966, Denver, CO 80225-0046, USA (URL: https://earthquake.usgs.gov/); MODIS Thermal Alert System; University of Hawaii and Manoa, 168 East-West Road, Post 602, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu).
Karthala
Comoros
11.75°S, 43.38°E; summit elev. 2361 m
All times are local (unless otherwise noted)
16 April 2005 seismicity leading to eruption; near-source tephra 1.5 m thick
After a long period of quiescence following the 1991 phreatic eruption, Karthala's seismicity rebounded starting in July 2000 (BGVN 25:10). In October 2000, more than 20 seismic events per day were recorded.
The local observatory and a key source for this report is the Karthala Volcano Observatory (KVO; Netter and Cheminée, 1997). They maintain close ties with the Centre National de Documentation et de Recherche Scientifique des Comores (CNDRS), Reunion Island University, the Institut de Physique du Globe de Paris, Piton de la Fournaise Volcanological Observatory, and various universities in France.
Activity during October 2000-March 2004. Between October 2000 and January 2003, relatively low seismicity was detected beneath Karthala's summit. The seismicity slowly increased. During January instruments recorded 51 earthquakes on the 5th, 58 on the 10th, and 50 on the 11th. During the month of April 2003 instruments registered 732 (i.e. averaging ~ 24 each day).
Seismic instruments detected several short earthquake swarms, each comprised of ~ 150 earthquakes. These swarms took place on 25 March and in April 2003, and each lasted several hours. Moreover, seismologists witnessed another swarm consisting of 183 events on 15 May. Except for that latter swarm, Karthala's seismicity was relatively quiet for 35 days after the 25 April swarm. A photo of the Chahalé crater from the year 2003, well before the April 2005 eruption, appears in figure 6. (For a map of Karthala's summit, see BGVN 16:08.)
During the time interval from early June 2003 to January 2004 instruments registered three periods with elevated seismicity. The first interval spanned 121 days from June until the end of September 2003 and included 6,315 earthquakes. Within that interval there was a major crisis on 6th September, comprised of 345 events, some being felt by local residents (BGVN 28:08).
The second interval began on 11 October 2003, reaching its peak on 4 January 2004 (253 events) and stopped on 31 January 2004. During this interval of 113 days, instruments registered 4,431 earthquakes. The third interval, during the time period of 3 February to 5 March 2004, contained fewer earthquakes. Instruments recorded 832 events in 31 days with a maximum of 143 events per day. After the third interval, KVO recorded only low seismicity until early 2005, when daily events rose to 50-60.
Eruption during April 2005. A seismic crisis began at 0812 on 16 April. Although instruments initially received only short-period events, starting at 0914 they also registered many long-period ones. From 1055 on 16 April a continuous signal was recorded, which was interpreted as tremor marking the beginning of the eruption. At around 1400 that day inhabitants heard a rumbling coming from the volcano. A few minutes later they observed an ash column above the summit. The first ash-fall deposits began to form around 1600, developing on the island's eastern side. According to the firsts reports, ash deposition increased and continued through the night accompanied by a strong smell of sulfur.
On the morning of 17 April ash falls continued on the eastern part of the island and were heavy enough to require inhabitants to use umbrellas to get about. At midday, Jean-Marc Heintz, a pilot for Comores Aviation, flew over the west flank and observed a large plume in the direction of the Chahalé crater. He also clearly observed airborne molten ejecta.
Around 1300, observers saw a very dark plume, spreading into a mushroom shape and accompanied by lightning flashes. Some inhabitants panicked and fled the island's eastern villages. In the afternoon, residents heard rumbling. During the evening, significant rainfall generated small mudflows, and the rumbling became stronger.
At that time, authorities evacuated some eastern villages (according to Agence France Presse (AFP) this affected ~ 10,000 people). Ash there started to fall on the island's western and northern parts, notably, on the country's capital city of Moroni (~ 10 km NW of the summit) and on the Hahaya airport (~ 20 km N of Moroni, ~ 25 km NW of the summit). Figure 7 shows a photo with the base of a vigorous plume over the E flanks on the afternoon of 17 April.
KVO authorities sometimes witnessed a red color at the plume's base, interpreted as a sign of an ongoing magmatic eruption. At 2105 the KVO seismic network recorded a drastic decrease in the amplitude of the tremor. During the night of 17-18 April, wide variations of the tremor amplitude were recorded with a maximum at 0140 on 18 April and a minimum at 0430 on 18 April. Thereafter, the tremor amplitude did not increase. During the night of 17-18 April the plume and falling ash disappeared.
On an overflight of the Chahalé crater at 0830 on 18 April, KVO personnel observed major modifications at the summit (figures 8-10). A lava lake (figure 8) had replaced the water-bearing lake (figure 6) that had occupied the crater since 1991.
On 19 April a new overflight revealed the crater floor containing the lava lake, with its chilled surface emitting steam (figure 13). Lava remained confined to Chahalé crater. Around the caldera area, and particularly on its N, observers saw conspicuous tephra deposits; most of the vegetation had been destroyed (figure 14).
On 20 April a field excursion found that ash deposits varied in thickness from a few millimeters on the coast to ~ 1.5 m at the summit. Near the summit the observers recognized some post-eruptive evaporation and geothermal processes. Specifically, although the lava lake's surface had frozen, there remained sufficient heat under the surface that groundwater migrating towards to the crater's floor evaporated into steam. During another field survey on 8 May, observers noted the renewed presence of lake water inside the crater.
Reference. Netter, C., and Cheminée, J. (eds.), 1997, Directory of Volcano Observatories, 1996-1997: World Organization of Volcano Observatories (WOVO), WOVO/IAVCEI/UNESCO, Paris, 268 p.
Geologic Background. The southernmost and largest of the two shield volcanoes forming Grand Comore Island (also known as Ngazidja Island), Karthala contains a 3 x 4 km summit caldera generated by repeated collapse. Elongated rift zones extend to the NNW and SE from the summit of the Hawaiian-style basaltic shield, which has an asymmetrical profile that is steeper to the S. The lower SE rift zone forms the Massif du Badjini, a peninsula at the SE tip of the island. Historical eruptions have modified the morphology of the compound, irregular summit caldera. More than twenty eruptions have been recorded since the 19th century from the summit caldera and vents on the N and S flanks. Many lava flows have reached the sea on both sides of the island. An 1860 lava flow from the summit caldera traveled ~13 km to the NW, reaching the W coast to the N of the capital city of Moroni.
Information Contacts: Nicolas Villeneuve (CREGUR, Centre de Recherches et d'Etudes en Géographie de l'Université de la Réunion); Hamidou Nassor, and Patrick Bachèlery (LSTUR, Laboratoire des Sciences de la Terre), Université de La Réunion BP 7151, 15 Avenue, René Cassin, 97715 Saint-Denis, Reunion Island; François Sauvestre and Hamid Soulé, CNDRS, BP 169, Moroni, République Fédérale Islamique des Comores (URL: http://volcano.ipgp.jussieu.fr/karthala/stationkar.html).
Lascar
Chile
23.37°S, 67.73°W; summit elev. 5592 m
All times are local (unless otherwise noted)
4 May 2005 eruption sends ash over 1,000 km SE, ¾ of the way to Buenos Aires
Lascar, the most active volcano in northern Chile, erupted on 4 May 2005. Although the eruption was substantial, thus far there is an absence of reports from anyone who saw the eruption at close range. Preliminary assessments came mainly from satellite sensors and distant affects witnessed in Argentina. This report is based on one sent to us by Chilean Observatorio Volcanológico de los Andes del Sur (OVDAS) scientists José Antonio Naranjo and Hugo Moreno, discussing events around 4 May, with brief comments on some of Lascar's behavior in the past several years, and suggestions for future monitoring.
Lascar sits ~ 70 km SW of the intersection between Chile, Argentina, and Bolivia, ~ 300 km inland from the Chilean port city of Antofagasta. This part of the coast lies along the Atacama desert, and on flat terrain tens of kilometers W of Lascar resides a large salt pan, the Salar de Atacama (about 50 x 150 km). The settlement of Toconao is ~ 33 km NW of Lascar. Previous reports discussed field observations during 13 October 2002 to 15 January 2003, and fine ash discharged from fumaroles on 9 December 2003 (BGVN 28:03 and 29:01).
Naranjo and Moreno concluded that at roughly 0400 on 4 May an explosive eruption ejected an ash cloud to a tentative altitude on the order of 10 km that dispersed to the SE. About 2 hours later the cloud began dropping ash on Salta, Argentina. Satellite images portrayed the ash cloud's dispersal. An aviation 'red alert' was issued by the Buenos Aires Volcanic Ash Center; they saw the plume over Argentina at altitudes of 3-5 km.
Shortly after atmospheric impacts of the 4 May eruption became apparent, the Buenos Aires VAAC notified OVDAS that NW Argentine cities had reported falling ash. These cities, all SE of Lascar, included Jujuy, Salta, Santiago del Estero, and Santa Fe—locations with respective approximate distances from Lascar of 260, 275, 580, and 1,130 km. The Argentine province of Chaco, along the country's NE margin, was also noted as receiving ash. Buenos Aires (~ 1,530 km SE of Lascar) remained ~ 400 km beyond the point of the farthest detected ashfall.
Patricia Lobera, a professor in Talabre, Argentina, 17 km E of Lascar, said that eruption noises were not heard there on the morning of 4 May. When observers saw the plume from Talabre that morning they reportedly thought the plume looked similar to those on previous days.
Remotely sensed hot spots were detected on a GOES satellite image for 0339 (0639 UTC) on 4 May, showing the first evidence of an eruption. In a later image, at 0409, the thermal anomaly had increased, and the image suggested a growing, ash-bearing cloud then trending ~ 23 km to the SE. The thermal anomaly diminished in intensity by 0439, remaining diminished thereafter, but by that time the plume's leading margin extended over ~ 100 km SE and its tail had detached from the volcano. At 0509 the plume reached 170 km SE. According to a press report, at around 0600 ash fell in Salta (~ 275 km SE of Lascar).
Rosa Marquilla, a geologist at the University of Salta, reported that residents there noticed a mist attributed to the eruption, which hung over the city until at least to 1600, after which, the sky gradually cleared. Preliminary description of the petrography of the ash that fell in Salta came from Ricardo Pereyra (University of Salta) who saw crystal fragments (pyroxenes, feldspars, and magnetite) and fragments of volcanic glass containing plagioclase mircrolites. Lithic fragments were not observed.
The OVDAS authors concluded that, apparently since the year 2000, Lascar underwent constant degassing from an open vent within the ~ 780-m-diameter active central crater. Sporadic explosions as in July 2000 and October 2002, and in this case, 4 May 2005, could be due to diverse causes. For example, there may have been temporarily obstructed conduits at depth, local collapses blocking the vent at the crater floor, or fresh magma injection contacting groundwater. Extrusion of a viscous dome lava also might explain the sudden explosions. That circumstance would presumably lead to visibly increased fumarolic output.
Naranjo and Moreno had several suggestions for ongoing monitoring. First, they suggested developing closer long-term contacts, including people able to visually monitor the volcano directly, as well as continued systematic contact with the Buenos Aires VAAC and their satellite analysts. They recommended ongoing relations with the University of Hawaii (MODVOLC) program to remotely sense hot-spots. They went on to suggest a campaign of stereo aerial photography to detect changes in the active crater. They advocated notifying local inhabitants of the possibility of ash falls before another explosive episode. They pointed out that mountaineers should be made aware of elevated risks within 8 km of the active crater.
References. Gardeweg, M., 1989, Informe preliminar sobre la evolución de la erupción del volcán Láscar (II Región): noviembre 1989: Servicio Nacional de Geología y Minería, Informe Inédito (unpublished report), 27 p.
Gardeweg, M., and Lindsay, J., 2004, Lascar Volcano, La Pacana Caldera, and El Tatio Geothermal Field: IAVCEI General Assembly Pucón 2004, Field Trip Guide-A2, 32 p.
Gardeweg, M., Medina, E., Murillo, M., and Espinoza, A., 1993, La erupción del 19-20 de abril de 1993: VI informe sobre el comportamiento del volcán Láscar (II Región): Servicio Nacional de Geología y Minería, Informe Inédito (unpublished report), 20 p.
Geologic Background. Láscar is the most active volcano of the northern Chilean Andes. The andesitic-to-dacitic stratovolcano contains six overlapping summit craters. Prominent lava flows descend its NW flanks. An older, higher stratovolcano 5 km E, Volcán Aguas Calientes, displays a well-developed summit crater and a probable Holocene lava flow near its summit (de Silva and Francis, 1991). Láscar consists of two major edifices; activity began at the eastern volcano and then shifted to the western cone. The largest eruption took place about 26,500 years ago, and following the eruption of the Tumbres scoria flow about 9000 years ago, activity shifted back to the eastern edifice, where three overlapping craters were formed. Frequent small-to-moderate explosive eruptions have been recorded since the mid-19th century, along with periodic larger eruptions that produced ashfall hundreds of kilometers away. The largest historical eruption took place in 1993, producing pyroclastic flows to 8.5 km NW of the summit and ashfall in Buenos Aires.
Information Contacts: José Antonio Naranjo and Hugo Moreno, Programa Riesgo Volcanico, Servicio Nacional de Geologia y Mineria, Avda. Santa Maria 0104, Casilla 1347, Santiago, Chile; Gustavo Alberto Flowers, Buenos Aires Volcanic Ash Advisory Center (Buenos Aires VAAC), Servicio Meteorológico Nacional-Fuerza Aérea Argentina, 25 de mayo 658, Buenos Aires, Argentina (URL: http://www.smn.gov.ar/vaac/buenosaires/productos.php).
Ol Doinyo Lengai (Tanzania) — April 2005
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Ol Doinyo Lengai
Tanzania
2.764°S, 35.914°E; summit elev. 2962 m
All times are local (unless otherwise noted)
Tall hornito almost reaches summit elevation; more lava spills over rim
Although lava venting at Ol Doinyo Lengai continued intermittently after February 2004 (BGVN 29:02), no significant changes were detected until July 2004, a time when vigorous venting emitted substantial amounts of the low-viscosity carbonatitic lava typical at this volcano ('flash floods' of lava). This summary report covers the time interval from February 2004 through early February 2005 based on observations made by Frederick Belton, Celia Nyamweru, Bernhard Donth, and Christoph Weber. Websites devoted to Ol Doinyo Lengai, including photographs, information on the evolution, recent history, and current status of the volcano are maintained by Belton, Nyamweru, and Weber.
A map, thermal data, and some new elevation estimates. In February 2005 Weber and others collected location data with a global positioning system (GPS) receiver. Weber used this to create a sketch map of the active crater (figure 82).
In July 2004 Belton completed the third of a series of distance measurements across crater outflow areas at the crater rim (table 7). Due to the unusually strong eruption on 15 July 2004 (figure 83), deposits comprising the E overflow widened by 3 or 4 m (growing from 44 to 47 m, figure 82). Later, in January 2005, observers noticed a fourth area of overflows had become established on the N crater rim, with lavas pouring over the rim at two adjacent points there (figure 82).
Table 7. For Ol Doinyo Lengai, the width of the three extant lava outflows at the points where they spilled from the active crater ('overflows,' figure 15), as measured during 2 August 2003-29 July 2004. Two additional small overflows formed later, by January 2005, on the N crater rim. The 3-m E-overflow increase occurred during the eruption of T58C on 15 July 2004. Courtesy of Frederick Belton.
Date |
NW overflow width |
E overflow width |
W overflow width |
02 Aug 2003 |
135 m |
44 m |
17 m |
29 Jun 2004 |
135 m |
44 m |
18 m |
29 Jul 2004 |
135 m |
47 m |
18 m |
During 3-7 February 2005 Weber and others completed a series of lava and fumarole temperature measurements that appear as tables 8 and 9. The tables indicate the hottest lava and fumarole temperatures at cracks were 588°C (at T49C, February 2004) and 150°C (at T49G, June 2004), respectively. The hornitos T49C and T49G both lie near T49B, a hornito delineated on figure 82.
Table 8. Repeated maximum lava temperatures measured at Ol Doinyo Lengai during 28 August 1999 to 3 February 2005. The measurements were made employing a digital thermometer (TM 914C with a stab feeler of standard K type). The instrument was used in the 0-1200°C mode, and at least four replicate measurements were made at any one spot. Calibration was by the delta-T method; uncertainties were ± 6°C in the 0-750°C range. Courtesy of C. Weber.
Date |
Location |
Temperature (°C) |
28 Aug 1999 |
T40 lava lake |
529 |
01 Sep 1999 |
Pahoehoe flow in a tube near T40 |
519 |
01 Sep 1999 |
Aa flow still in motion at flat terrains (60 cm thick) |
516 |
03 Oct 2000 |
Pahoehoe flow in a tube near T49B |
507 |
03 Oct 2000 |
Aa flow still in slow motion at flat terrain (25 cm thick) |
496 |
11 Feb 2004 |
Pahoehoe flow in a tube near T49G |
588 |
12 Feb 2004 |
Pahoehoe flow in a tube near T49B |
579 |
13 Feb 2004 |
Aa flow not in motion anymore at flat terrain (15 cm thick) |
490 |
26 Jun 2004 |
Pahoehoe flow in slow motion (10 cm thick) flat terrain |
560 |
03 Feb 2005 |
Pahoehoe flow (15 cm thick) in motion traveling within a levee. |
561 |
03 Feb 2005 |
Aa flow not in motion anymore at flat terrain (15 cm thick) |
520 |
Table 9. Maximum fumarole temperatures measured at cracks in Ol Doinyo Lengai's crater floor over a series of visits during 28 August 1999 to 4 February 2005. Collected using the digital thermometer with procedures and parameters noted with the previous table. For locations, see map (figure 15). Courtesy of C. Weber.
Date |
Location |
Temperature (°C) |
28 Aug 1999 |
F1 |
70 |
28 Aug 1999 |
Near T49 |
82 |
03 Oct 2000 |
Near T49C |
75 |
03 Oct 2000 |
F1 |
69 |
20 Oct 2002 |
The hottest cracks in the crater floor |
124 |
20 Oct 2002 |
F1 |
78 |
30 Jun 2003 |
F1 |
86 |
30 Jun 2003 |
Near T49C |
76 |
12 Feb 2004 |
F1 |
88 |
26 Jun 2004 |
F1 |
78 |
26 Jun 2004 |
Near T49C |
150 |
04 Feb 2005 |
F1 |
84 |
Weber's team GPS measurements suggested a summit elevation of 2,960 ± 5 m. This is consistent with GPS measurements taken in October 2000, by a scientific group led by Joerg Keller, of 2,950-2,960 m (BGVN 25:12). In addition, the tallest hornito in the N-central crater rises to nearly this elevation (see discussion of T49/T56B, below).
During observations in February 2004, Weber measured the tallest hornito at the T49 location (part of T56B) in the center area of the active crater. GPS readings on top of T56B yielded an elevation of 2,886 m. This is only [74 m below the elevation of the summit]. The top of T49 is also ~ 33 m above the adjacent crater floor to the N. In addition, when he measured on 3-7 February, Weber found hornito T58C (a then recent feature) had grown to reach an elevation of ~ 2,870 m.
Observations during February 2004 to February 2005. During February 2004 visits, T56B did not erupt, but instead a new vent erupted at the T49 location (~ 10 m E of T49B, see also BGVN 29:02). This new vent was called T49G (figure 15).
A group from Volcano Expeditions International (VEI) spent 24-30 June 2004 on Lengai and found much of the scene at the vents in the crater similar to that noted in February 2004. They noted that half of the upper 10 m of hornito T56B had collapsed on its E side, and an active lava lake had formed inside this hornito with lava escaping several times through the collapsed opening to its E and flowing out ~ 200 m. The lava was rich in gas with a temperature of 560°C. The hornito T58B was also active and spattered lava many times during these days of observation. Some lava flows from T58B reached about 150 m to the S.
During 2-3 July 2004, Belton observed T58B erupt repeatedly, emitting lava and strombolian displays. The escaping lava flowed S, passing near the base of hornito T47. On 4 July, Belton saw some of the most intense activity of the month. A sequence of lavas erupted on that day and over the next few days. However, events in mid-July and later were also unusually vigorous.
The 4 July 2004 activity included strong strombolian eruptions at T58B and several collapses of its vent area, which released large cascades of lava onto the crater floor. Simultaneously, a tube-fed eruption of pahoehoe lava from the new vent T49G flowed across the NW crater rim to spill down that flank. Early on 5 July numerous eruptions of T58B sent lava flowing toward T47 at an estimated velocity of 10 m/sec. On 6 July, lava flowed out of the lake in T56B and onto the crater floor moving E and entering a cave in T45 for a short distance.
After very low activity during 7-10 July 2004, renewed flows and spatter came out on 11 July from T58B, and frequent but short (usually ~ 2 minute) episodes of loud degassing and spattering issued from the lava lake in T56B. At night, this vent emitted incandescent gas. This pattern continued until the morning of 14 July, when eruptions at T58B became more explosive and it expelled small ash clouds. On the morning of 15 July a collapse in the vent area of T58B released large rapid lava flows to the E. The episodes of degassing and spattering from T56B increased in frequency until 1500 on 15 July, when a small hole formed in the crater floor just E of T58B.
Called T58C, the hole became a newly opened vent. It began emitting visible gas puffs mixed with spatter. At this time the degassing episodes from T56B ceased. T58C then began strong degassing and squirted up intermittent lava fountains. The fountains soon fed a large lava stream moving toward the S crater wall.
By 1600 on 15 July 2004 a paroxysm at T58C was in progress, with lava forming 10- to 12-m-tall fountains and 'flash floods' that completely inundated the central-eastern crater floor (in the area between T56B, T58B, T37, T37B, T45, and T57). T58C also ejected strong jets of ash and gas. Turbulent rivers of lava flowing at more than 10 m/sec swept toward the crater's S wall and its E overflow and completely surrounded T37B and T45. Flow rate from the vent was estimated to peak at 10 m3/s.
The momentum of the rapidly outflowing lava carried it nearly 3 m up the W (upstream) side of T45 and obliterated the large cave within that cone. The associated surge of lava poured over the E crater rim and down the flank. It flooded over a 3 m wide swath of vegetation. This triggered a huge cloud of steam and smoke that resembled a small pyroclastic flow. The smoke cloud was accompanied by a loud sizzling sound. A brush fire burned along the crater rim overflow as additional floods of lava arrived. These larger-than-normal flows lasted for little more than 30 sec and were separated by periods of repose of 5 to 6 min. After sunset, incandescent gas flared from the vent during the repose periods. Weak strombolian activity was seen in T56B.
Early on 16 July 2004 the newly formed T58C was a circular pit ~ 2 m in diameter with lava sloshing violently at a depth of ~ 2 m. Two small sub-vents on the N and S edges of the pit interconnected with the main vent. Activity continued sporadically at T58B and T56B with strombolian activity and lava flows. On 21 July there was an exceptionally strong eruption of T58B with loud explosions, jetting of ash-poor clouds, and spatter thrown to above-average heights. Explosions blasted a new vent in the upper E side of T58B. At least four oval bombs 9-12 cm in length flew through the air, along with a great deal of lapilli and ash. Later examination of the bomb's interiors revealed that they all had an outer zone ~ 1.5- to 2-cm thick and a distinctive inner core.
On 23 July 2004, a sloping ~ 4 m2 oval section of the crater floor immediately SW of the new spatter cone T58C began to steam and vibrate. Tremor increased and ground movement was visible, manifested as a small section of crater floor rapidly pushed outward and then inward several centimeters, like a membrane vibrating in time to the degassing sounds of lava in T58C just behind it. Abruptly this portion of the crater floor broke outward, and a flood of lava ensued. T58C was observed to grow in height through the time when Belton left the crater on 29 July 2004.
Observations during January and February 2005. Donth reported that during his visit on 10 January 2005, hornito T49B erupted to form many effusive lava flows. For the first time, lava escaped over the northern edge of the crater (see figure 15).
During Weber's crater visit, 3-7 February 2005, the hornito T49B actively emitted lava flows that traveled to the N. Pahoehoe lava flows in motion within small levees on flat terrain were measured from 520°C up to a maximum of 561°C (table 3). The fumaroles at F1 had a maximum temperature of 84°C, and at hornito T46, a maximum of 91°C (table 4). No change in distance was measured across the CR1, CR2, and CR3 cracks cutting the upper crater walls. Adding to visitor safety concerns, which include altitude sickness, burns, falls, and impact from ejecta, Weber's team saw a spitting cobra close to the summit. An overflight by plane on 14 February showed no subsequent change, but did give an excellent view of the crater and its central hornitos (figure 16).
A flight on 14 February failed to reveal subsequent changes. But the effort provided an excellent view of the crater and its central hornitos (figure 84).
Geologic Background. The symmetrical Ol Doinyo Lengai is the only volcano known to have erupted carbonatite tephras and lavas in historical time. The prominent stratovolcano, known to the Maasai as "The Mountain of God," rises abruptly above the broad plain south of Lake Natron in the Gregory Rift Valley. The cone-building stage ended about 15,000 years ago and was followed by periodic ejection of natrocarbonatitic and nephelinite tephra during the Holocene. Historical eruptions have consisted of smaller tephra ejections and emission of numerous natrocarbonatitic lava flows on the floor of the summit crater and occasionally down the upper flanks. The depth and morphology of the northern crater have changed dramatically during the course of historical eruptions, ranging from steep crater walls about 200 m deep in the mid-20th century to shallow platforms mostly filling the crater. Long-term lava effusion in the summit crater beginning in 1983 had by the turn of the century mostly filled the northern crater; by late 1998 lava had begun overflowing the crater rim.
Information Contacts: Christoph Weber, Volcano Expeditions International, Muehlweg 11, 74199 Untergruppenbach, Germany (URL: http://www.v-e-i.de/); Celia Nyamweru, Department of Anthropology, St. Lawrence University, Canton, NY 13617, USA (URL: http://blogs.stlawu.edu/lengai/); Frederick Belton, Developmental Studies Department, PO Box 16, Middle Tennessee State University, Murfreesboro, TN 37132, USA (URL: http://oldoinyolengai.pbworks.com/); Bernard Donth, Waldwiese 5, 66123 Saarbruecken, Germany.
Vailulu'u (United States) — April 2005
Cite this Report
Vailulu'u
United States
14.215°S, 169.058°W; summit elev. -592 m
All times are local (unless otherwise noted)
ALIA cruise discloses new cone in the summit crater
According to Hubert Staudigel (Scripps Institution of Oceanography) and Stanley Hart (Woods Hole Oceanographic Institute), Vailulu'u seamount, the most active Samoan submarine volcano, erupted between April 2001 and April 2005. It formed a 293-m-tall lava cone, which was named Nafanua after the Samoan Goddess of War. This new cone had been growing inside the 2-km-wide caldera of Vailulu'u at a minimum rate of about 20 cm/day since April 2001. Nafanua was discovered during a 2005 diving expedition with the National Oceanic and Atmospheric Agency (NOAA) research submersible Pisces V, launched from the University of Hawaii research vessel Kaimikai O Kanaloa (KOK). It is located in the originally 1,000-m-deep W crater of Vailulu'u (figures 5 to 8).
Seismic monitoring during April-June 2000 showed substantial seismicity, ~ 4 earthquakes per day with hypocenters beneath Nafanua (Konter and others, 2004; BGVN 26:06), which can now be interpreted as pre-eruption seismic activity. These observations are consistent with previous reports highlighting the volcanic and hydrothermal activity of Vailulu'u (Hart and others, 2000; Staudigel and others, 2004). The scientists suggested that continued volcanic activity could bring the summit region of Vailulu'u to a water depth of ~ 200 m. At that point, Nafanua would overtop the crater rim and further growth would require a build-up of the lower flanks, areas that rise from the 5,000-m-deep floor of the ocean.
Staudigel and Hart teamed up in April 2005 on the Hawaiian Research Vessel Kilo Moana to study the Samoan hotspot thought to underlie Vailulu'u. They named their expedition ALIA after the ancient twin-hulled canoe that Samoan warriors used to explore the SW Pacific. The Kilo Moana left Pago Pago on 4 April 2005 to study active and extinct underwater volcanoes along the chain of Samoan islands. The expedition investigated previously uncharted seamounts and the submarine portions of some islands, scattered over almost 600 nautical miles, from its most recent and quite active Vailulu'u submarine volcano in the E to Combe Island in the W.
The Nafanua cone was first mapped by using the center beam of the research vessel KOK in several crossings of the W crater. An active hydrothermal system was apparent from evidence such as the murky water that limited visibility during two submersible dives, several microbial biomats covering pillow lavas that were centimeters thick, and a large number of diffuse vents. A dive on 30 March 2005 to examine Nafanua reported "that it must have grown in the last 4 years because CTD (conductivity-temperature-depth) crossings in 2001 still were consistent with the old crater morphology ... the basal portion of the cone displayed relatively large pillows, and higher up pillows look almost like very fluid pahoehoe that collapsed and/or transitioned into aa flows. Nafanua . . . grew very fast with abundant breccia material from collapsing and draining pillows, in particular in the summit region."
On 1 April, another dive along the outer flanks of Vailulu'u found that during the up-slope transit, observers saw a few additional areas of active venting and many sites where there had been venting in the past. Large and perfectly formed pillow lavas were present in most sites, with a few areas being dominated by broken talus fragments and some having completely black glassy pillows with no oxidation, apparent evidence for relatively recent formation. The topography was extremely rough, the slope being punctuated with numerous fissure systems and edifices of pillow lava.
A primary plan for the ALIA expedition was to study the water in and around the seamount for several days using a CTD probe. To sample the inside of the volcano for a full tidal cycle, the scientists varied the depth of the CTD between 40 and 930 m (almost to the crater floor), collecting various data, including visibility. At Vailulu'u, the particulates given off by hydrothermal venting are flushed out of its caldera during each tidal cycle into the surrounding water. In 2005, a dense layer of particulates was found in the water within the crater, but the water was clear outside the crater rim. This contrasts with observations seen from the cruise in 2000, when there was a dense ring of particulates around the whole volcano. It appears that in 2005 the particulates were rising above the crater and then later sinking, instead of forming the widespread ring observed in 2000.
In addition, the expedition crew conducted dredging of the new summit of Nafanua. Staudigel and Hart noted that the rocks from the first dredge haul were quite newly formed, containing pristine olivine-phyric volcanic rocks. Abundant large vesicles in the rocks from Nafanua suggest a volatile-rich magma capable of submarine lava fountaining and explosive outgassing in shallower water. Dredging from a second site, outside of Vailulu'u, recovered rocks that were both much older and far less fragile.
References. Hart, S.R., Staudigel, H., Koppers, A.A.P., Blusztajn, J., Baker, E.T., Workman, R., Jackson, M., Hauri, E., Kurz, M., Sims, K., Fornari, D., Saal, A., and Lyons, S., 2000, Vailulu'u undersea volcano: The new Samoa: Geochemistry, Geophysics, Geosystems (G3), American Geophysical Union, v. 1, no. 12, doi: 10.1029/2000GC000108.
Konter, J.G., Staudigel, H., Hart, S.R., and Shearer, P.M., 2004, Seafloor seismic monitoring of an active submarine volcano: Local seismicity at Vailulu'u Seamount, Samoa: Geochemistry, Geophysics, Geosystems (G3), American Geophysical Union, v. 5, no. 6, QO6007, doi: 10.1029/2004GC000702.
Lippsett, L., 2002, Voyage to Vailulu'u: Searching for Underwater Volcanoes. Woods Hole Oceanographic Institution, Fathom online magazine (URL: http://www.fathom.com/feature/122477/).
Staudigel, H., Hart, S.R., Koppers, A., Constable, C., Workman, R., Kurz, M., and Baker, E.T., 2004, Hydrothermal venting at Vailulu'u Seamount: The smoking end of the Samoan chain: Geochemistry, Geophysics, Geosystems (G3), American Geophysical Union, v. 5, no. 2, QO2003, doi: 10.1029/2003GC000626.
Geologic Background. Vailulu'u, a massive basaltic seamount discovered in 1975, rises 4,200 m from the sea floor to a depth of 590 m. Located about one-third of the way between Ta'u and Rose islands at the E end of the American Samoas, it is considered to mark the current location of the Samoan hotspot. The summit contains an oval-shaped crater that is 2 km wide and 400 m deep. Two principal rift zones extend E and W from the summit, parallel to the trend of the hotspot; a third rift extends SE. The rift zones and escarpments produced by mass wasting phenomena give the seamount a star-shaped pattern. On 10 July 1973 explosions were recorded by SOFAR (hydrophone records of underwater acoustic signals). An earthquake swarm in 1995 may have been related to an eruption. Eruptive activity between April 2001 and April 2005 formed a cone almost 300 m high, named Nafanua. Repeated bathymetric mapping surveys showed depth changes, including height and width increases of Nafanua after 2005, that suggest at least intermittent activity during 1999-2017; a 2019 survey showed no further changes since 2017.
Information Contacts: Hubert Staudigel, Institute of Geophysics and Planetary Physics, Scripps Institution of Oceanography, Univ. of California, San Diego, La Jolla, CA 92093-0225, USA (URL: https://earthref.org/whoswho/ER/hstaudigel/, https://igpp.ucsd.edu/); Stanley R. Hart, Woods Holes Oceanographic Institute, Geology and Geophysics Dept., Woods Hole, MA 02543, USA; ALIA Expedition, Samoan Seamounts, R/V Kilo Moana (KM0506), supported by the San Diego Supercomputer Center and the Scripps Institution of Oceanography (URL: https://earthref.org/ERESE/projects/ALIA/).