The Weekly Volcanic Activity Report: January 17 - 23, 2018

The Weekly Volcanic Activity Report: January 17 - 23, 2018

New activity unrest was reported for 5 volcanoes between January 17 and 23, 2018. During the same period, ongoing activity was reported for 13 volcanoes.

New activity/unrest: Kadovar, Papua New Guinea | Kusatsu-Shiranesan, Honshu (Japan) | Mayon, Luzon (Philippines) | Nevados de Chillan, Chile | San Miguel, El Salvador.

Ongoing activity: Agung, Bali (Indonesia) | Aira, Kyushu (Japan) | Cleveland, Chuginadak Island (USA) | Ebeko, Paramushir Island (Russia) | Great Sitkin,  Andreanof Islands (USA) | Karymsky, Eastern Kamchatka (Russia) | Kilauea, Hawaiian Islands (USA) | Klyuchevskoy, Central Kamchatka (Russia) | Pacaya, Guatemala | Sabancaya, Peru | Sheveluch, Central Kamchatka (Russia) | Sinabung, Indonesia | Turrialba, Costa Rica.

The Weekly Volcanic Activity Report is a cooperative project between the Smithsonian's Global Volcanism Program and the US Geological Survey's Volcano Hazards Program. Updated by 23:00 UTC every Wednesday, notices of volcanic activity posted are preliminary and subject to change as events are studied in more detail. This is not a comprehensive list of all of Earth's volcanoes erupting during the week. Carefully reviewed, detailed reports on various volcanoes are published monthly in the Bulletin of the Global Volcanism Network.

New activity/unrest

Kadovar, Papua New Guinea

3.608°S, 144.588°E, Elevation 365 m

RVO reported that the eruption at Kadovar continued during 18-19 and 21-22 January. Main Crater produced ash plumes that rose as high as 800 m above the summit and drifted tens of kilometers E, SE, S, and SW. Vulcanian activity was continuous, though no discrete explosions were detected. Steam plumes from the SE Coastal Vent rose 800 m above the island, and a lava dome which strongly and continuously glowed at night slowly extruded from the vent. Strong sulfur dioxide emissions were detected.

Geological summary: The 2-km-wide island of Kadovar is the emergent summit of a Bismarck Sea stratovolcano of Holocene age. Kadovar is part of the Schouten Islands, and lies off the coast of New Guinea, about 25 km N of the mouth of the Sepik River. The village of Gewai is perched on the crater rim. A 365-m-high lava dome forming the high point of the andesitic volcano fills an arcuate landslide scarp that is open to the south, and submarine debris-avalanche deposits occur in that direction. Thick lava flows with columnar jointing forms low cliffs along the coast. The youthful island lacks fringing or offshore reefs. No certain historical eruptions are known; the latest activity was a period of heightened thermal phenomena in 1976.

Kusatsu-Shiranesan, Honshu (Japan)

36.618°N, 138.528°E, Elevation 2165 m

JMA reported that at 0959 on 23 January an eruption began at Kusatsu-Shiranesan coincident with the onset of volcanic tremor; there were no indications of an impending eruption. The Alert Level was raised to 3 (on a scale of 1-5). Skiers at the popular ski resort Kusatsu Kokusai took video showing a plume of tephra and ejected bombs rising from a vent on the Motoshiranesan edifice, about 2 km SSE of Yagama Crater on Shiranesan (where all previous historical activity has been). The eruption also caused what appeared to be an avalanche. Photos and video posted in news articles showed tephra drifting E and blanketing the nearby hillside; JMA noted ashfall in Nakanojo-machi, in the Gunma Prefecture. Tephra hit a gondola, shattering glass and injuring four skiers. Material crashed through the roof of a lodge, where about 100 people had already been evacuated. Ground Self-Defense Force troops were engaging in ski training at the time of the event; one member died and seven others were injured. Emergency responders gathered at the Sanroku Station to assist. On 24 January JMA noted that volcanic earthquakes were numerous but decreasing in number, and two 2-3-minute-long periods of volcanic tremor were detected at 1015 and 1049.

Geological summary: The summit of Kusatsu-Shiranesan volcano, located immediately north of Asama volcano, consists of a series of overlapping pyroclastic cones and three crater lakes. The andesitic-to-dacitic volcano was formed in three eruptive stages beginning in the early to mid Pleistocene. The Pleistocene Oshi pyroclastic flow produced extensive welded tuffs and non-welded pumice that covers much of the east, south and SW flanks. The latest eruptive stage began about 14,000 years ago. All historical eruptions have consisted of phreatic explosions from the acidic crater lakes or their margins. Fumaroles and hot springs that dot the flanks have strongly acidified many rivers draining from the volcano. The crater was the site of active sulfur mining for many years during the 19th and 20th centuries.

Mayon, Luzon (Philippines)

13.257°N, 123.685°E, Elevation 2462 m

PHIVOLCS reported that during 16-17 January Mayon’s seismic network recorded 143 lava collapse events associated with rockfalls along the front and margins of advancing lava and pyroclastic flows in the Miisi (S), Matanag (SE), and Buyuan (SE) drainages. These events generated ash plumes that drifted SW. During 17-20 January effusion of lava at the summit and collapse events continued. Two pyroclastic flows traveled around 3 km down the Miisi drainage. Rockfall events were generated by the collapsing lava front and margins of the advancing 3-km-long lava flow in the Miisi drainage, and from the summit into the Matanag, Buyuan, and Bonga (SE) drainages. Ash plumes continued to drift SW. Sulfur dioxide gas emissions were 1,478 tonnes/day on 18 January and 1,131 tonnes/day on 19 January. During 20-21 January there were 14 rockfall events and 10 pyroclastic flows recorded by the seismic network. 

During 21-22 January there were 64 rockfall events and one pyroclastic flow recorded. Strombolian activity generated lava fountains 500 and 200 m high at 1045 on 21 January and at 0225 on 22 January, respectively. Ash plumes rose 1.3 km high and drifted SW, causing ashfall in Oas and Guinobatan (12 km SW). Lava flowed more voluminously, adding to the advancing Miisi lava flow (over 3 km long) and feeding two new lava flows on the Bonga and upper Buyuan drainages. 

At 1243 on 22 January an eight-minute-long phreatomagmatic event generated a dense, 5-km-high ash plume that drifted W. Ashfall was reported in the municipalities of Guinobatan, Camalig (11 km SSW), Oas, Polangui (20 km WNW), and Iriga City (34 km NW). The event also generated pyroclastic flows that traveled as far as 4 km down multiple drainages including Miisi, Bonga, Buyuan, Basud, San Andres, Buang, Anoling. PHIVOLCS raised the Alert Level to 4 (on a 0-5 scale) and extend the Danger Zone to an 8-km radius. A minor event at 1725 produced a 500-m-high ash plume. Between 2137 on 22 January and 0525 on 23 January there were five episodes of intense and sporadic lava fountaining, each lasting 3-30 minutes. The lava fountains rose 500-700 m high, and generated ash plumes that rose 2.5-3 km above the crater. The events fed lava flows on the Miisi and Bonga drainages, sprayed near-vent lava spatter, and fed incandescent rockfalls around the summit area. The Buyuan lava flow was 200 m long. According to news articles posted on 23 January about 40,000 people have been evacuated, and airports in the cities of Legazpi City (13 km SSE) and Naga (66 km NW), and on the nearby island of Masbate (100 km S) were closed.

Geological summary: Beautifully symmetrical Mayon volcano, which rises to 2462 m above the Albay Gulf, is the Philippines' most active volcano. The structurally simple volcano has steep upper slopes averaging 35-40 degrees that are capped by a small summit crater. Historical eruptions at this basaltic-andesitic volcano date back to 1616 and range from strombolian to basaltic plinian, with cyclical activity beginning with basaltic eruptions, followed by longer term andesitic lava flows. Eruptions occur predominately from the central conduit and have also produced lava flows that travel far down the flanks. Pyroclastic flows and mudflows have commonly swept down many of the approximately 40 ravines that radiate from the summit and have often devastated populated lowland areas. Mayon's most violent eruption, in 1814, killed more than 1200 people and devastated several towns.

Nevados de Chillan, Chile

36.868°S, 71.378°W, Elevation 3180 m

Servicio Nacional de Geología and Minería (SERNAGEOMIN) Observatorio Volcanológico de Los Andes del Sur (OVDAS) reported continuing explosive activity during 1-15 January associated with a low rate of lava-dome growth in the active crater. Gas plumes from the explosions rose less than 1 km above the crater rim, and sporadic incandescence associated with some explosions was recorded at night. The lava-dome growth rate was low at 1,360 m3/day, determined by photos taken during overflights on 9 and 12 January. The total volume of the lava dome was an estimated 37,000 m3. The Alert Level remained at Yellow, the middle level on a three-color scale, and the public was reminded not to approach the craters within a 4-km radius.

Geological summary: The compound volcano of Nevados de Chillán is one of the most active of the Central Andes. Three late-Pleistocene to Holocene stratovolcanoes were constructed along a NNW-SSE line within three nested Pleistocene calderas, which produced ignimbrite sheets extending more than 100 km into the Central Depression of Chile. The largest stratovolcano, dominantly andesitic, Cerro Blanco (Volcán Nevado), is located at the NW end of the group. Volcán Viejo (Volcán Chillán), which was the main active vent during the 17th-19th centuries, occupies the SE end. The new Volcán Nuevo lava-dome complex formed between 1906 and 1945 between the two volcanoes and grew to exceed Volcán Viejo in elevation. The Volcán Arrau dome complex was constructed SE of Volcán Nuevo between 1973 and 1986 and eventually exceeded its height.

San Miguel, El Salvador

13.434°N, 88.269°W, Elevation 2130 m

SNET reported that during 14-17 January there were four gas-and-ash emissions from San Miguel that rose no higher than 300 m above the crater rim. The report noted that prior to each emission seismicity decreased and then suddenly increased.

Geological summary: The symmetrical cone of San Miguel volcano, one of the most active in El Salvador, rises from near sea level to form one of the country's most prominent landmarks. The unvegetated summit rises above slopes draped with coffee plantations. A broad, deep crater complex that has been frequently modified by historical eruptions (recorded since the early 16th century) caps the truncated summit, also known locally as Chaparrastique. Radial fissures on the flanks of the basaltic-andesitic volcano have fed a series of historical lava flows, including several erupted during the 17th-19th centuries that reached beyond the base of the volcano on the N, NE, and SE sides. The SE-flank flows are the largest and form broad, sparsely vegetated lava fields crossed by highways and a railroad skirting the base of the volcano. The location of flank vents has migrated higher on the edifice during historical time, and the most recent activity has consisted of minor ash eruptions from the summit crater.

Ongoing activity

Agung, Bali (Indonesia)

8.343°S, 115.508°E, Elevation 2997 m

PVMBG reported that the eruption at Agung continued during 17-23 January, with gas-and-steam plumes rising from the crater punctuated by occasional ash emissions. An event at 2126 on 17 January generated a plume that rose 1.5 km above the crater rim and drifted E. An event was recorded at 1944 on 18 January, though fog prevented confirmation of a plume. At 1920 on 19 January a Strombolian event produced an ash plume that rose as high as 2.5 km and drifted E, and ejected incandescent material as far as 1 km from the crater. Incandescence emanated from the crater for about two hours after the event. White-to-gray plumes rose 500 m during 22-23 January. The Alert Level remained at 4 (on a scale of 1-4) and the exclusion zone continued at a 6-km radius.

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

Aira, Kyushu (Japan)

31.593°N, 130.657°E, Elevation 1117 m

JMA reported that two of the nine events at Minamidake crater (at Aira Caldera’s Sakurajima volcano) were explosive during 15-22 January. Plumes rose as high as 2.5 km above the crater rim, and material was ejected as far as 500 m from the crater. During field observations on 16 January scientists measured a high amount of sulfur dioxide emissions at 2,600 tons/day; the last measurement was 1,800 tons/day on 25 December 2017. The Alert Level remained at 3 (on a 5-level scale).

Geological 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.

Cleveland, Chuginadak Island (USA)

52.825°N, 169.944°W, Elevation 1730 m

Based on recent satellite data AVO reported on 19 January that a new lava flow had been emplaced within Cleveland’s summit crater sometime since the last observations of elevated surface temperatures on 5 January. Elevated surface temperatures were identified in satellite images during 19-22 January. No activity was detected by seismic or infrasound sensors during 20-23 January. The Aviation Color Code remained at Orange and the Volcano Alert Level remained at Watch.

Geological summary: Beautifully symmetrical Mount Cleveland stratovolcano is situated at the western end of the uninhabited, dumbbell-shaped Chuginadak Island. It lies SE across Carlisle Pass strait from Carlisle volcano and NE across Chuginadak Pass strait from Herbert volcano. Cleveland is joined to the rest of Chuginadak Island by a low isthmus. The 1730-m-high Mount Cleveland is the highest of the Islands of the Four Mountains group and is one of the most active of the Aleutian Islands. The native name for Mount Cleveland, Chuginadak, refers to the Aleut goddess of fire, who was thought to reside on the volcano. Numerous large lava flows descend the steep-sided flanks. It is possible that some 18th-to-19th century eruptions attributed to Carlisle should be ascribed to Cleveland (Miller et al., 1998). In 1944 Cleveland produced the only known fatality from an Aleutian eruption. Recent eruptions have been characterized by short-lived explosive ash emissions, at times accompanied by lava fountaining and lava flows down the flanks.

Ebeko, Paramushir Island (Russia)

50.686°N, 156.014°E, Elevation 1103 m

Based on observations by volcanologists in Severo-Kurilsk (Paramushir Island), about 7 km E of Ebeko, explosions during 11-12, 14-16, and 18 January generated ash plumes that rose as high as 3.1 km (10,200 ft) a.s.l. Minor ashfall was reported in Severo-Kurilsk during 15-16 and 18 January. The Aviation Color Code remained at Orange (the second highest level on a four-color scale).

Geological 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.

Great Sitkin, Andreanof Islands (USA)

52.076°N, 176.13°W, Elevation 1740 m

On 18 January AVO reported that seismicity at Great Sitkin had declined over the past two months to near background levels. In addition, no significant activity was observed in satellite data during this time period and no steam plumes were noted. AVO lowered the Aviation Color Code and Volcano Alert Level to Green/Normal.

Geological summary: The 1740-m-high Great Sitkin volcano forms much of the northern side of Great Sitkin Island. A younger parasitic volcano capped by a small, 0.8 x 1.2 km ice-filled summit caldera was constructed within a large late-Pleistocene or early Holocene scarp formed by massive edifice failure that truncated an ancestral volcano and produced a submarine debris avalanche. Deposits from this and an older debris avalanche from a source to the south cover a broad area of the ocean floor north of the volcano. The 1740-m-high summit lies along the eastern rim of the younger collapse scarp. Deposits from an earlier caldera-forming eruption of unknown age cover the flanks of the island to a depth up to 6 meters. The small younger caldera was partially filled by lava domes emplaced in 1945 and 1974, and five small older flank lava domes, two of which lie on the coastline, were constructed along northwest- and NNW-trending lines. Hot springs, mud pots, and fumaroles occur near the head of Big Fox Creek, south of the volcano. Historical eruptions have been recorded at Great Sitkin since the late-19th century.

Karymsky, Eastern Kamchatka (Russia)

54.049°N, 159.443°E, Elevation 1513 m

KVERT reported that a small ash cloud was identified in satellite data drifting near Karymsky on 18 January. The Aviation Color Code remained at Yellow (the second lowest level on a four-color scale).

Geological 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, Elevation 1222 m

During 17-23 January HVO reported that the lava lake continued to rise, fall, and spatter in Kilauea’s Overlook crater. Surface lava flows were active above and on the pali, and on the coastal plain. Early in the morning on 19 January rocks from the inside of Halema’uma’u crater fell into the lava lake producing a short-lived explosion of spatter and wallrock that blanketed an area around the former visitor overlook. Debris fell as far as the Halemaumau parking lot.

Geological summary: Kilauea volcano, which overlaps the east 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 sq km, destroying nearly 200 houses and adding new coastline to the island.

Klyuchevskoy, Central Kamchatka (Russia)

56.056°N, 160.642°E, Elevation 4754 m

Based on satellite observations KVERT reported that a weak thermal anomaly over Klyuchevskoy was visible during 11-12, 15, and 17 January. Gas-and-steam plumes containing some ash drifted about 120 km W and E during 12 and 17-18 January. The Aviation Color Code remained at Orange.

Geological 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.

Pacaya, Guatemala

14.382°N, 90.601°W, Elevation 2569 m

INSIVUMEH reported that during 18-19 January Strombolian explosions at Pacaya’s Mackenney Crater ejected material 25 m above the main cone. In a special report from 20 January INSIVUMEH noted that the Strombolian activity had been cyclically building and destroying a cone within the crater. Scientists at the Observatorio del Volcan de Pacaya (OVPAC) observed a 400-m-long lava flow descending the W flank, spalling off material from the front. Strombolian explosions continued during 20-21 January, and a 200-m-long lava flow was advancing down the SW flank.

Geological 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.

Sabancaya, Peru

15.787°S, 71.857°W, Elevation 5960 m

Observatorio Vulcanológico del Sur del IGP (OVS-IGP) and Observatorio Vulcanológico del INGEMMET (OVI) reported that explosive activity at Sabancaya was similar to the previous week; there was an average of 57 explosions recorded per day during 15-21 January. Seismicity was dominated by long-period events, with signals indicating emissions. Gas-and-ash plumes rose 3.3 km above the crater rim and drifted 50 km NW. The MIROVA system detected six thermal anomalies. The sulfur dioxide flux was high, at 3,410 tons per day on 19 January. The report noted that the public should not to approach the crater within a 12-km radius.

Geological summary: Sabancaya, located in the saddle NE of Ampato and SE of Hualca Hualca volcanoes, is the youngest of these volcanic centers and the only one to have erupted in historical time. The oldest of the three, Nevado Hualca Hualca, is of probable late-Pliocene to early Pleistocene age. The name Sabancaya (meaning "tongue of fire" in the Quechua language) first appeared in records in 1595 CE, suggesting activity prior to that date. Holocene activity has consisted of Plinian eruptions followed by emission of voluminous andesitic and dacitic lava flows, which form an extensive apron around the volcano on all sides but the south. Records of historical eruptions date back to 1750.

Sheveluch, Central Kamchatka (Russia)

56.653°N, 161.36°E, Elevation 3283 m

KVERT reported that a thermal anomaly over Sheveluch was identified in satellite images during 12-19 January. The Aviation Color Code remained at Orange.

Geological summary: The high, isolated massif of Sheveluch volcano (also spelled Shiveluch) rises above the lowlands NNE of the Kliuchevskaya volcano group. The 1300 cu km 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, Elevation 2460 m

PVMBG and BNPB reported that ash plumes at Sinabung were seen rising as high as 3.5 km above the crater during 18-23 January and drifting E, SE, and W, although sometimes foggy conditions prevented visual observations. Avalanches of incandescent material traveled as far as 1.5 km down the ESE flank during 21-23 January. The Alert Level remained at 4 (on a scale of 1-4), with a general exclusion zone 3 km and extensions of 7 km on the SSE sector, and 6 km in the ESE sector, and 4 km in the NNE sector.

Geological 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. 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.

Turrialba, Costa Rica

10.025°N, 83.767°W, Elevation 3340 m

OVSICORI-UNA reported that an event at Turrialba at 0000 on 22 January generated a plume that rose 500 m above the crater rim and drifted NW.

Geological summary: Turrialba, the easternmost of Costa Rica's Holocene volcanoes, is a large vegetated basaltic-to-dacitic stratovolcano located across a broad saddle NE of Irazú volcano overlooking the city of Cartago. The massive 3340-m-high Turrialba is exceeded in height only by Irazú, covers an area of 500 sq km, and is one of Costa Rica's most voluminous volcanoes. Three well-defined craters occur at the upper SW end of a broad 800 x 2200 m summit depression that is breached to the NE. Most activity originated from the summit vent complex, but two pyroclastic cones are located on the SW flank. Five major explosive eruptions have occurred during the past 3500 years. A series of explosive eruptions during the 19th century were sometimes accompanied by pyroclastic flows. Fumarolic activity continues at the central and SW summit craters.

Source: GVP

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