The Weekly Volcanic Activity Report: February 3 - 9, 2021

New activity/unrest was reported for 5 volcanoes from February 3 to 9, 2021. During the same period, ongoing activity was reported for 15 volcanoes.

New activity/unrest: Etna, Sicily (Italy) | Merapi, Central Java (Indonesia) | Raung, Eastern Java (Indonesia) | Sarychev Peak, Matua Island (Russia) | Semisopochnoi, United States.

New activity/unrest

Etna, Sicily (Italy)

37.748°N, 14.999°E, Summit elev. 3320 m

INGV reported that Strombolian activity from all four of Etna’s summit craters, the Southeast Crater (SEC), the Northeast Crater (NEC), Bocca Nuova (BN), and Voragine (VOR), was visible during 1-7 February; the last time that had occurred was during 1998-1999. The strongest and almost continuous Strombolian explosions at SEC originated from two vents in the E part of the top of the cone. Tephra accumulated near the top of the cone and rolled down the flanks. Minor ash emissions rapidly dispersed. Less-intense Strombolian activity occurred at the S vent. Intra-crater Strombolian activity at NEC sometimes produced nighttime crater incandescence. Strombolian activity at BN sometimes ejected coarse material beyond the crater rim, and rare ash emissions that had diffuse ash content. On 5 February scientists observed explosions from three vents at the bottom of the crater that had formed cinder cones. Nearby was another cone that occasionally produced dense emissions that rapidly dispersed. Strombolian activity at VOR ejected material that sometimes rose above the crater rim and generated diffuse ash emissions. On 5 February lava flowed into BN, overlapping flows from the previous week.

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

Merapi, Central Java (Indonesia)

7.54°S, 110.446°E, Summit elev. 2910 m

BPPTKG reported that the 2021 lava dome continued to grow just below Merapi’s SW rim during 29 January-4 February. One pyroclastic flow descended the SW flank as far as 600 m. The 2021 lava dome volume was an estimated 117,400 cubic meters on 4 February, with a growth rate of about 12,600 cubic meters per day. A comparison of photos taken on 21 January and 4 February showed that the morphological changes in the summit area were attributed to the growth of the 2021 lava dome as well as from a new dome slowly growing in the summit crater. Electronic Distance Measurement (EDM) data showed no notable deformation. Seismic activity was lower than the previous week. BNPB noted that a total of 537 people remained evacuated (190 people from Sleman Regency and 347 from Klaten) as of 3 February. The Alert Level remained at 3 (on a scale of 1-4), and the public were warned to stay 5 km away from the summit.

Geologic summary: 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.

Raung, Eastern Java (Indonesia)

8.119°S, 114.056°E, Summit elev. 3260 m

PVMBG reported that daily gray ash plumes rose as high as 1 km above Raung’s summit and drifted S and E during 3-6 February. Ash plumes rose 1.2-2 km above the summit during 7-9 February and drifted SE and E. Incandescence from the crater was often seen reflected in the emissions, and rumbling and roaring was sometimes heard. The Alert Level remained at 2 (on a scale of 1-4), and the public was warned to remain outside of the 2-km exclusion zone.

Geologic summary: Raung, one of Java's most active volcanoes, is a massive stratovolcano in easternmost Java that was constructed SW of the rim of Ijen caldera. The unvegetated summit is truncated by a dramatic steep-walled, 2-km-wide caldera that has been the site of frequent historical eruptions. A prehistoric collapse of Gunung Gadung on the W flank produced a large debris avalanche that traveled 79 km, reaching nearly to the Indian Ocean. Raung contains several centers constructed along a NE-SW line, with Gunung Suket and Gunung Gadung stratovolcanoes being located to the NE and W, respectively.

Sarychev Peak, Matua Island (Russia)

48.092°N, 153.2°E, Summit elev. 1496 m

KVERT reported that the eruption at Sarychev Peak continued during 29 January-5 February, characterized by lava effusion from the carter onto the N flank. A thermal anomaly was identified in satellite images on 29 January and 1 February; weather clouds prevented observations on the other days. The Aviation Color Code remained at Yellow (the second lowest level on a four-color scale).

Geologic summary: Sarychev Peak, one of the most active volcanoes of the Kuril Islands, occupies the NW end of Matua Island in the central Kuriles. The andesitic central cone was constructed within a 3-3.5-km-wide caldera, whose rim is exposed only on the SW side. A dramatic 250-m-wide, very steep-walled crater with a jagged rim caps the volcano. The substantially higher SE rim forms the 1496 m high point of the island. Fresh-looking lava flows, prior to activity in 2009, had descended in all directions, often forming capes along the coast. Much of the lower-angle outer flanks of the volcano are overlain by pyroclastic-flow deposits. Eruptions have been recorded since the 1760s and include both quiet lava effusion and violent explosions. Large eruptions in 1946 and 2009 produced pyroclastic flows that reached the sea.

Semisopochnoi, United States

51.93°N, 179.58°E, Summit elev. 1221 m

AVO reported that a 6 February satellite image of Semisopochnoi showed small ash deposits extending in a narrow strip less than 3 km N of North Cerberus Crater. The deposits were likely the result of a small explosions that occurred during the previous week. Steam emission obscured view of the summit crater. The Aviation Color Code and the Volcano Alert Level were raised to Yellow/Advisory. A second ash deposit, similar to the first, was visible in a satellite image on 7 February. This deposit extended at least 3 km NE of North Cerberus Crater. Weather clouds obscured views of the S side of the volcano. The report noted that the ash plumes associated with the deposits had not been observed; they likely rose less than 3 km (10,000 ft) a.s.l. and were short lived. The Aviation Color Code and the Volcano Alert Level were raised to Orange/Watch.

Geologic summary: Semisopochnoi, the largest subaerial volcano of the western Aleutians, is 20 km wide at sea level and contains an 8-km-wide caldera. It formed as a result of collapse of a low-angle, dominantly basaltic volcano following the eruption of a large volume of dacitic pumice. The high point of the island is Anvil Peak, a double-peaked late-Pleistocene cone that forms much of the island's northern part. The three-peaked Mount Cerberus was constructed within the caldera during the Holocene. Each of the peaks contains a summit crater; lava flows on the N flank of Cerberus appear younger than those on the south side. Other post-caldera volcanoes include the symmetrical Sugarloaf Peak SSE of the caldera and Lakeshore Cone, a small cinder cone at the edge of Fenner Lake in the NE part of the caldera. Most documented historical eruptions have originated from Cerberus, although Coats (1950) considered that both Sugarloaf and Lakeshore Cone within the caldera could have been active during historical time.

Ongoing activity

Aira, Kyushu (Japan)

31.593°N, 130.657°E, Summit elev. 1117 m

JMA reported that during 29 January-1 February incandescence from Minamidake Crater (at Aira Caldera’s Sakurajima volcano) was often visible nightly. Seven explosions generated eruption plumes that rose as high as 2 km above the crater rim and ejected bombs 1,000-1,300 km away from the crater. The sulfur dioxide emission rate was 1,100 tons per day on 2 February. The Alert Level remained at 3 (on a 5-level scale).

Geologic summary: The Aira caldera in the northern half of Kagoshima Bay contains the post-caldera Sakurajima volcano, one of Japan's most active. Eruption of the voluminous Ito pyroclastic flow accompanied formation of the 17 x 23 km caldera about 22,000 years ago. The smaller Wakamiko caldera was formed during the early Holocene in the NE corner of the Aira caldera, along with several post-caldera cones. The construction of Sakurajima began about 13,000 years ago on the southern rim of Aira caldera and built an island that was finally joined to the Osumi Peninsula during the major explosive and effusive eruption of 1914. Activity at the Kitadake summit cone ended about 4850 years ago, after which eruptions took place at Minamidake. Frequent historical eruptions, recorded since the 8th century, have deposited ash on Kagoshima, one of Kyushu's largest cities, located across Kagoshima Bay only 8 km from the summit. The largest historical eruption took place during 1471-76.

Asamayama, Honshu (Japan)

36.406°N, 138.523°E, Summit elev. 2568 m

On 5 February JMA lowered the Alert Level for Asamayama to 1 (on a scale of 1-5) noting that no deformation or crater incandescence had been detected since late November 2020, sulfur dioxide emissions had trended downward beginning in December, volcanic earthquakes were recorded only occasionally since mid-December, and the number of small-amplitude volcanic tremors were recorded occasionally and had not increased.

Geologic summary: Asamayama, Honshu's most active volcano, overlooks the resort town of Karuizawa, 140 km NW of Tokyo. The volcano is located at the junction of the Izu-Marianas and NE Japan volcanic arcs. The modern Maekake cone forms the summit and is situated east of the horseshoe-shaped remnant of an older andesitic volcano, Kurofuyama, which was destroyed by a late-Pleistocene landslide about 20,000 years before present (BP). Growth of a dacitic shield volcano was accompanied by pumiceous pyroclastic flows, the largest of which occurred about 14,000-11,000 BP, and by growth of the Ko-Asama-yama lava dome on the east flank. Maekake, capped by the Kamayama pyroclastic cone that forms the present summit, is probably only a few thousand years old and has an historical record dating back at least to the 11th century CE. Maekake has had several major plinian eruptions, the last two of which occurred in 1108 (Asamayama's largest Holocene eruption) and 1783 CE.

Dukono, Halmahera (Indonesia)

1.693°N, 127.894°E, Summit elev. 1229 m

Based on satellite and wind model data, and information from PVMBG, the Darwin VAAC reported that during 3-4, 6-7, and 9 February ash plumes from Dukono rose to 1.5-2.1 km (5,000-7,000 ft) a.s.l. and drifted S, SW, and NE. The Alert Level remained at 2 (on a scale of 1-4), and the public was warned to remain outside of the 2-km exclusion zone.

Geologic summary: Reports from this remote volcano in northernmost Halmahera are rare, but Dukono has been one of Indonesia's most active volcanoes. More-or-less continuous explosive eruptions, sometimes accompanied by lava flows, occurred from 1933 until at least the mid-1990s, when routine observations were curtailed. During a major eruption in 1550, a lava flow filled in the strait between Halmahera and the north-flank cone of Gunung Mamuya. This complex volcano presents a broad, low profile with multiple summit peaks and overlapping craters. Malupang Wariang, 1 km SW of the summit crater complex, contains a 700 x 570 m crater that has also been active during historical time.

Ebeko, Paramushir Island (Russia)

50.686°N, 156.014°E, Summit elev. 1103 m

Volcanologists in Severo-Kurilsk (Paramushir Island), about 7 km E of Ebeko, observed explosions during 29 January and 1-2 February that sent ash plumes to 2.3 km (7,500 ft) a.s.l. and drifted E. The Aviation Color Code remained at Orange (the second highest level on a four-color scale).

Geologic summary: 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.

Ibu, Halmahera (Indonesia)

1.488°N, 127.63°E, Summit elev. 1325 m

PVMBG reported that during 3-9 February gray-and-white ash plume from Ibu rose 200-800 m above the summit and drifted in multiple directions. The Alert Level remained at 2 (on a scale of 1-4), and the public was warned to stay at least 2 km away from the active crater and 3.5 km away on the N side.

Geologic summary: The truncated summit of Gunung Ibu stratovolcano along the NW coast of Halmahera Island has large nested summit craters. The inner crater, 1 km wide and 400 m deep, contained several small crater lakes through much of historical time. The outer crater, 1.2 km wide, is breached on the north side, creating a steep-walled valley. A large parasitic cone is located ENE of the summit. A smaller one to the WSW has fed a lava flow down the W flank. A group of maars is located below the N and W flanks. Only a few eruptions have been recorded in historical time, the first a small explosive eruption from the summit crater in 1911. An eruption producing a lava dome that eventually covered much of the floor of the inner summit crater began in December 1998.

Karymsky, Eastern Kamchatka (Russia)

54.049°N, 159.443°E, Summit elev. 1513 m

KVERT reported that a thermal anomaly over Karymsky’s summit crater was visible in satellite images on 2 February. Weather clouds obscured views on the other days during 30 January-5 February. The Aviation Color Code remained at Orange (the second highest level on a four-color scale).

Geologic summary: Karymsky, the most active volcano of Kamchatka's eastern volcanic zone, is a symmetrical stratovolcano constructed within a 5-km-wide caldera that formed during the early Holocene. The caldera cuts the south side of the Pleistocene Dvor volcano and is located outside the north margin of the large mid-Pleistocene Polovinka caldera, which contains the smaller Akademia Nauk and Odnoboky calderas. Most seismicity preceding Karymsky eruptions originated beneath Akademia Nauk caldera, located immediately south. The caldera enclosing Karymsky formed about 7600-7700 radiocarbon years ago; construction of the stratovolcano began about 2000 years later. The latest eruptive period began about 500 years ago, following a 2300-year quiescence. Much of the cone is mantled by lava flows less than 200 years old. Historical eruptions have been vulcanian or vulcanian-strombolian with moderate explosive activity and occasional lava flows from the summit crater.

Kilauea, Hawaiian Islands (USA)

19.421°N, 155.287°W, Summit elev. 1222 m

HVO reported that lava from a vent on the inner NW wall of Kilauea’s Halema`uma`u Crater streamed down the cone into a perched lava lake during 3-9 February. The western half of the lake dropped from 213 m on 3 February to 211 m on 4 February and stayed at that level during 5-6 February; the drop in lake level was likely the result of summit deflation that was detected by tiltmeters. The lake level had risen to 214 m by the morning of 7 February coincident with the onset of summit inflation. A small dome fountain was visible at the entry point of lava into the lake on 8 February. The stagnant E half of the lake, separated by a series of surface cracks, was about 5 m lowed than the W half.

Geologic summary: Kilauea, which overlaps the E flank of the massive Mauna Loa shield volcano, has been Hawaii's most active volcano during historical time. Eruptions are prominent in Polynesian legends; written documentation extending back to only 1820 records frequent summit and flank lava flow eruptions that were interspersed with periods of long-term lava lake activity that lasted until 1924 at Halemaumau crater, within the summit caldera. The 3 x 5 km caldera was formed in several stages about 1500 years ago and during the 18th century; eruptions have also originated from the lengthy East and SW rift zones, which extend to the sea on both sides of the volcano. About 90% of the surface of the basaltic shield volcano is formed of lava flows less than about 1100 years old; 70% of the volcano's surface is younger than 600 years. A long-term eruption from the East rift zone that began in 1983 has produced lava flows covering more than 100 km2, destroying nearly 200 houses and adding new coastline to the island.

Klyuchevskoy, Central Kamchatka (Russia)

56.056°N, 160.642°E, Summit elev. 4754 m

KVERT reported that Strombolian and sometimes Vulcanian activity at Klyuchevskoy continued during 29 January-5 February and lava advanced down the Apakhonchich drainage on the SE flank. A large bright thermal anomaly was identified daily in satellite images. Steam-and-gas plumes with some ash rose to 6 km (19,700 ft) a.s.l. and drifted 92 km in multiple directions. The Aviation Color Code remined at Orange (the second highest level on a four-color scale).

Geologic summary: Klyuchevskoy (also spelled Kliuchevskoi) is Kamchatka's highest and most active volcano. Since its origin about 6000 years ago, the beautifully symmetrical, 4835-m-high basaltic stratovolcano has produced frequent moderate-volume explosive and effusive eruptions without major periods of inactivity. It rises above a saddle NE of sharp-peaked Kamen volcano and lies SE of the broad Ushkovsky massif. More than 100 flank eruptions have occurred during the past roughly 3000 years, with most lateral craters and cones occurring along radial fissures between the unconfined NE-to-SE flanks of the conical volcano between 500 m and 3600 m elevation. The morphology of the 700-m-wide summit crater has been frequently modified by historical eruptions, which have been recorded since the late-17th century. Historical eruptions have originated primarily from the summit crater, but have also included numerous major explosive and effusive eruptions from flank craters.

Lewotolo, Lomblen Island (Indonesia)

8.274°S, 123.508°E, Summit elev. 1431 m

PVMBG reported that the eruption at Lewotolo continued during 3-9 February. Gray-and-white ash plumes rose 200-700 m above the summit and drifted E and SE. During 5-9 February Strombolian explosions ejected material 100-350 m above the summit and incandescent material was ejected 300-500 m SE from the crater. Rumbling and occasional banging sounds were reported. The Alert Level remained at 3 (on a scale of 1-4) and the public was warned to stay 4 km away from the summer crater.

Geologic summary: The Lewotolo (or Lewotolok) stratovolcano occupies the eastern end of an elongated peninsula extending north into the Flores Sea, connected to Lembata (formerly Lomblen) Island by a narrow isthmus. It is symmetrical when viewed from the north and east. A small cone with a 130-m-wide crater constructed at the SE side of a larger crater forms the volcano's high point. Many lava flows have reached the coastline. Eruptions recorded since 1660 have consisted of explosive activity from the summit crater.

Pacaya, Guatemala

14.382°N, 90.601°W, Summit elev. 2569 m

On 6 February INSIVUMEH reported increased Strombolian activity and a higher number of explosions at Pacaya’s Mackenney Crater. The explosions rattled nearby houses and ejected ballistics as far as 500 m from the crater. Ash plumes rose as high as 650 m above the summit and drifted 5 km W, NW, and N. Ashfall was reported in areas downwind including San Francisco de Sales, El Cedro, Calderas, El Bejucal, and Mesías Altas. Lava effusion also increased and two active lava flows, 800 and 1,200 m long, were advancing. On 8 February ash plumes rose almost 600 m and drifted 30 km NW and W, and 10 km N. Explosions ejected ballistics as far as 300 m from the crater.

Geologic summary: Eruptions from Pacaya, one of Guatemala's most active volcanoes, are frequently visible from Guatemala City, the nation's capital. This complex basaltic volcano was constructed just outside the southern topographic rim of the 14 x 16 km Pleistocene Amatitlán caldera. A cluster of dacitic lava domes occupies the southern caldera floor. The post-caldera Pacaya massif includes the ancestral Pacaya Viejo and Cerro Grande stratovolcanoes and the currently active Mackenney stratovolcano. Collapse of Pacaya Viejo between 600 and 1500 years ago produced a debris-avalanche deposit that extends 25 km onto the Pacific coastal plain and left an arcuate somma rim inside which the modern Pacaya volcano (Mackenney cone) grew. A subsidiary crater, Cerro Chino, was constructed on the NW somma rim and was last active in the 19th century. During the past several decades, activity has consisted of frequent strombolian eruptions with intermittent lava flow extrusion that has partially filled in the caldera moat and armored the flanks of Mackenney cone, punctuated by occasional larger explosive eruptions that partially destroy the summit of the growing young stratovolcano.

Popocatepetl, Mexico

19.023°N, 98.622°W, Summit elev. 5393 m

CENAPRED reported that each day during 3-9 January there were 14-34 steam, gas, and ash emissions from Popocatépetl. Minor crater incandescence from the crater was visible during a few of the nights. An explosion at 2138 on 6 February generated an eruption plume with low ash content that rose 2 km above the summit and drifted NE. The Alert Level remained at Yellow, Phase Two (middle level on a three-color scale).

Geologic summary: Volcán Popocatépetl, whose name is the Aztec word for smoking mountain, rises 70 km SE of Mexico City to form North America's 2nd-highest volcano. The glacier-clad stratovolcano contains a steep-walled, 400 x 600 m wide crater. The generally symmetrical volcano is modified by the sharp-peaked Ventorrillo on the NW, a remnant of an earlier volcano. At least three previous major cones were destroyed by gravitational failure during the Pleistocene, producing massive debris-avalanche deposits covering broad areas to the south. The modern volcano was constructed south of the late-Pleistocene to Holocene El Fraile cone. Three major Plinian eruptions, the most recent of which took place about 800 CE, have occurred since the mid-Holocene, accompanied by pyroclastic flows and voluminous lahars that swept basins below the volcano. Frequent historical eruptions, first recorded in Aztec codices, have occurred since Pre-Columbian time.

Sheveluch, Central Kamchatka (Russia)

56.653°N, 161.36°E, Summit elev. 3283 m

KVERT reported that a thermal anomaly over Sheveluch was identified in satellite images on 29 January as well as 2 and 4 February. Weather clouds obscured views of the volcano on the other days during 30 January-5 February. The Aviation Color Code remained at Orange (the second highest level on a four-color scale).

Geologic summary: The high, isolated massif of Sheveluch volcano (also spelled Shiveluch) rises above the lowlands NNE of the Kliuchevskaya volcano group. The 1300 km3 volcano is one of Kamchatka's largest and most active volcanic structures. The summit of roughly 65,000-year-old Stary Shiveluch is truncated by a broad 9-km-wide late-Pleistocene caldera breached to the south. Many lava domes dot its outer flanks. The Molodoy Shiveluch lava dome complex was constructed during the Holocene within the large horseshoe-shaped caldera; Holocene lava dome extrusion also took place on the flanks of Stary Shiveluch. At least 60 large eruptions have occurred during the Holocene, making it the most vigorous andesitic volcano of the Kuril-Kamchatka arc. Widespread tephra layers from these eruptions have provided valuable time markers for dating volcanic events in Kamchatka. Frequent collapses of dome complexes, most recently in 1964, have produced debris avalanches whose deposits cover much of the floor of the breached caldera.

Sinabung, Indonesia

3.17°N, 98.392°E, Summit elev. 2460 m

PVMBG reported that the eruption at Sinabung continued during 3-9 February, though weather conditions sometimes prevented visual confirmation. Dense white plumes rose as high as 1 km above the summit and drifted in multiple directions. An eruptive event was recorded on 5 February but was not seen, and on 6 February a pyroclastic flow traveled 2.5 km down the flank. The Darwin VAAC noted that ash plumes rose to 3 km (10,000 ft) a.s.l. and drifted W and NNW that same day. On 7 February ash plumes rose 1 km above the summit and drifted E, SE, and S, causing ashfall in the Karo Regency. The Alert Level remained at 3 (on a scale of 1-4), with a general exclusion zone of 3 km and extensions to 5 km in the SE sector and 4 km in the NE sector.

Geologic summary: Gunung Sinabung is a Pleistocene-to-Holocene stratovolcano with many lava flows on its flanks. The migration of summit vents along a N-S line gives the summit crater complex an elongated form. The youngest crater of this conical andesitic-to-dacitic edifice is at the southern end of the four overlapping summit craters. The youngest deposit is a SE-flank pyroclastic flow 14C dated by Hendrasto et al. (2012) at 740-880 CE. An unconfirmed eruption was noted in 1881, and solfataric activity was seen at the summit and upper flanks in 1912. No confirmed historical eruptions were recorded prior to explosive eruptions during August-September 2010 that produced ash plumes to 5 km above the summit.

Soufriere St. Vincent, St. Vincent

13.33°N, 61.18°W, Summit elev. 1220 m

University of the West Indies Seismic Research Centre (UWI-SRC) and National Emergency Management Organisation (NEMO) reported that the lava dome in Soufrière St. Vincent’s main crater continued to grow during 1-9 February. Gas data analysis conducted during a field visit showed that sulfur dioxide emissions were first detected on 1 February, suggesting that ground water was drying up and no longer interacting with the gas species. The dome had an estimated volume of 5.93 million cubic meters. Scientists observed damaged vegetation, likely caused by fire, on the NW part of the crater (just N of the dome). A report on 6 February stated that the dome continued to spread laterally N and S, with N as the dominant growth direction. Gas-and-steam continued to rise from the top of the dome as well as along the contact of the old and new domes. Scientists visited the Wallibou Hot Spring area on 7 February after a report of anomalously higher temperatures and gas odors; they collected water samples and took temperatures measurements for later analysis. Initial findings suggested the presence of hydrogen sulfide in that area and temperatures that had increased around 5-6 degrees; the lead scientist noted that based on their findings there was no increased risk associated with the hot springs. NEMPO reminded the public to avoid the volcano and that descending into the crater remained extremely dangerous. The Alert Level remained at Orange (the second highest level on a four-color scale).

Geologic summary: Soufrière St. Vincent is the northernmost and youngest volcano on St. Vincent Island. The NE rim of the 1.6-km wide summit crater is cut by a crater formed in 1812. The crater itself lies on the SW margin of a larger 2.2-km-wide caldera, which is breached widely to the SW as a result of slope failure. Frequent explosive eruptions after about 4,300 years ago produced pyroclastic deposits of the Yellow Tephra Formation, which cover much of the island. The first historical eruption took place in 1718; it and the 1812 eruption produced major explosions. Much of the northern end of the island was devastated by a major eruption in 1902 that coincided with the catastrophic Mont Pelée eruption on Martinique. A lava dome was emplaced in the summit crater in 1971 during a strictly effusive eruption, forming an island within a lake that filled the crater. A series of explosive eruptions in 1979 destroyed the 1971 dome and ejected the lake; a new dome was then built.

Suwanosejima, Ryukyu Islands (Japan)

29.638°N, 129.714°E, Summit elev. 796 m

JMA reported that incandescence at Suwanosejima’s Ontake Crater was occasionally visible at night during 29 January-5 February. Intermittent explosions produced ash plumes that rose as high as 1.2 km above the crater rim and ejected bombs 300 m away from the crater. The Alert Level remained at 2 (on a 5-level scale).

Geologic summary: The 8-km-long, spindle-shaped island of Suwanosejima in the northern Ryukyu Islands consists of an andesitic stratovolcano with two historically active summit craters. The summit is truncated by a large breached crater extending to the sea on the east flank that was formed by edifice collapse. Suwanosejima, one of Japan's most frequently active volcanoes, was in a state of intermittent strombolian activity from Otake, the NE summit crater, that began in 1949 and lasted until 1996, after which periods of inactivity lengthened. The largest historical eruption took place in 1813-14, when thick scoria deposits blanketed residential areas, and the SW crater produced two lava flows that reached the western coast. At the end of the eruption the summit of Otake collapsed forming a large debris avalanche and creating the horseshoe-shaped Sakuchi caldera, which extends to the eastern coast. The island remained uninhabited for about 70 years after the 1813-1814 eruption. Lava flows reached the eastern coast of the island in 1884. Only about 50 people live on the island.

Source: GVP

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