Smithsonian / USGS Weekly Volcanic Activity Report 31 March-6 April 2021

Rachel Holsteen-Bruyere <rbruyere@xxxxxxx> · Thu, 8 Apr 2021 07:31:44 -0700

2-2-2-2-2-2-2-2-2-2-2-2-2

From: "Kuhn, Sally" <KUHNS@xxxxxx>

Smithsonian / USGS Weekly Volcanic Activity Report

31 March-6 April 2021

Sally Kuhn Sennert - Weekly Report Editor (kuhns@xxxxxx)

URL: https://volcano.si.edu/reports_weekly.cfm

New Activity/Unrest: Karymsky, Eastern Kamchatka (Russia)  |
Krysuvik-Trolladyngja, Iceland  | Pacaya, Guatemala  | Semisopochnoi,
Aleutian Islands (USA)  | Suwanosejima, Ryukyu Islands (Japan)  |
Veniaminof, United States

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 2300 UTC every Wednesday, these reports
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, but rather a summary of activity at volcanoes that meet
criteria discussed in detail in the "Criteria and Disclaimers" section.
Carefully reviewed, detailed reports about recent activity are published in
issues of the Bulletin of the Global Volcanism Network.

Note that many news agencies do not archive the articles they post on the
Internet, and therefore the links to some sources may not be active. To
obtain information about the cited articles that are no longer available on
the Internet contact the source.

New Activity/Unrest

Karymsky  | Eastern Kamchatka (Russia)  | 54.049Â°N, 159.443Â°E  | Summit
elev. 1513 m

KVERT reported that explosions at 1130 on 3 April likely caused ash plumes
to rise to 8.5 km (27,900 ft) a.s.l. above Karymsky and drift NE, based on
satellite data. The Aviation Color Code was raised to 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.

Source: Kamchatkan Volcanic Eruption Response Team (KVERT)
http://www.kscnet.ru/ivs/kvert/index_eng.php

Krysuvik-Trolladyngja  | Iceland  | 63.917Â°N, 22.067Â°W  | Summit elev. 360 m

IMO reported that the small eruption in the W part of the
KrÃ½suvÃk-TrÃ¶lladyngja volcanic system, close to Fagradalsfjall on the
Reykjanes Peninsula, continued during 31 March-6 April. Video and visitor
photographs showed spattering and lava fountaining from the two cones, and
lava flows from both cones moved W and S within the Geldingadalur valley. A
new fissure, 100-200 m long, opened about 700 m NE of the Geldingadalur
cones around noon on 5 April. During a helicopter overflight, scientists
observed a gas plume rising from the new fissure and a fast-moving lava
flow descending into the Meradalir valley to the SE. On 6 April lava from
the second fissure was advancing at a rate of 7 cubic meters per second;
lava-flow rates at the Geldingadalir site averaged 5.5 cubic meters per
second. Around midnight during 6-7 April a third fissure opened in between
the first two; all three were oriented NE-SW. Earlier on 6 April field
teams had observed a landslide in same area. Lava from the third fissure
mostly flowed SW into Geldingadalur. The Aviation Color Code remained
Orange due to the lack of ash and tephra emissions.

Geologic Summary. The KrÃ½suvÃk-TrÃ¶lladyngja volcanic system is described by
the Catalogue of Icelandic Volcanoes as an approximately 50-km-long
composite fissure swarm trending about N38Â°E, including a 30-km-long swarm
of fissures, with no central volcano. It is one of the volcanic systems
arranged en-echelon along the Reykjanes Peninsula west of Kleifarvatn lake.
The Fagradalsfjall and KrÃ½suvÃk fissure swarms are considered splits or
secondary swarms of the KrÃ½suvÃkâ??TrÃ¶lladyngja volcanic system. Small shield
volcanoes have produced a large portion of the erupted volume within the
system. Several eruptions have taken place since the settlement of Iceland,
including the eruption of a large basaltic lava flow from the Ogmundargigar
crater row around the 12th century. The latest eruption, identified through
tephrochronology, took place during the 14th century.

Sources: Icelandic Meteorological Office (IMO) http://en.vedur.is/;

Icelandic Coast Guard https://www.lhg.is

Pacaya  | Guatemala  | 14.382Â°N, 90.601Â°W  | Summit elev. 2569 m

INSIVUMEH reported that explosions at Pacayaâ??s Mackenney Crater during
30-31 March produced gas-and-ash plumes that rose 1.8 km above the summit
and drifted up to 50 km S, SW, W, and NW. Explosions ejected blocks as high
as 150 m above the summit. Lava flows on the W flank advanced to 3 km long
and were near La BreÃ±a; the flows overtook an unoccupied building on the
Campo Alegre farm that was used for monitoring and visitor services. The
flow front was about 500 m from the town of El Patrocinio. Incandescent
blocks detached from the end of the lava flow and set fire to vegetation.
During 31 March-2 April explosions ejected incandescent blocks as high as
225 m above the summit. Ash plumes rose 500 m and drifted 20 km S and SW.
The SW-flank lava flows remained active. Explosions continued during 3-6
April, with ash plumes rising as high as 1 km and drifting 6-20 km W, SW,
and S. The lava flow continued to be active on the SW flank, setting fire
to local vegetation. Strombolian activity ejected material 300 m high
during 5-6 April.

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 AmatitlÃ¡n 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.

Source: Instituto Nacional de Sismologia, Vulcanologia, Meteorologia, e
Hidrologia (INSIVUMEH) http://www.insivumeh.gob.gt/

Semisopochnoi  | Aleutian Islands (USA)  | 51.93Â°N, 179.58Â°E  | Summit
elev. 1221 m

AVO reported that a small plume from Semisopochnoiâ??s North Cerberus crater
was visible in a satellite image on 31 March. Steam obscured the crater
during the first part of 1 April. Later that day an ash plume was visible,
and was followed by a sulfur dioxide plume an hour later. At 2200 a plume
rose to an altitude below 3 km (10,000 ft) a.s.l. No activity was
identified in partly cloudy images during 2-6 April. The Aviation Color
Code and the Volcano Alert Level remained at Orange and Watch, respectively.

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 eruptions have originated
from Cerberus, although Coats (1950) considered that both Sugarloaf and
Lakeshore Cone could have been recently active.

Source: US Geological Survey Alaska Volcano Observatory (AVO)
https://avo.alaska.edu/

Suwanosejima  | Ryukyu Islands (Japan)  | 29.638Â°N, 129.714Â°E  | Summit
elev. 796 m

JMA reported that during 30-31 March large volcanic bombs were ejected at
least 41 times from Suwanosejima's Ontake Crater as high as 800 m above the
crater rim and to distances as far as 1 km. The Alert Level was raised to 3
(on a 5-level scale) at 0330 on 31 March and the public was warned to stay
outside a 2 km radius of the crater. The increased activity prompted an
overflight that same day where scientists confirmed several hundred
high-temperature bomb deposits with a thermal camera within a 1 km radius.
Explosions at 2205 on 30 March and 0257 on 31 March ejected bombs onto the
S and SE flanks, respectively. Grayish-white emissions rose from the
crater. After 1500 eruption plumes rose as high as 1.4 km above the crater
rim. The number of explosions decreased; two per day were recorded during
1-2 April and one was recorded on 3 April. The Alert Level was lowered to 2
on 5 April and the public was warned to stay 1 km away from the crater.

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: Japan Meteorological Agency (JMA) http://www.jma.go.jp/jma/

Veniaminof  | United States  | 56.17Â°N, 159.38Â°W  | Summit elev. 2507 m

AVO reported that during 31 March-1 April clear satellite and web camera
images of Veniaminof showed no signs of emissions. On 2 April the Volcano
Alert Level was lowered to Advisory and the Aviation Color Code was lowered
to Yellow. Satellite data showed elevated surface temperatures, especially
over the flank-vent lava flows through 4 April. Low-level ash emissions
were recorded by the webcam on 5 April, prompting AVO to raise the Volcano
Alert Level and Aviation Color Code to Watch and Orange, respectively.
Tephra deposits were visible to the SE.

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

Source: US Geological Survey Alaska Volcano Observatory (AVO)
https://avo.alaska.edu/

Ongoing Activity

Aira  | Kyushu (Japan)  | 31.593Â°N, 130.657Â°E  | Summit elev. 1117 m

JMA reported that during 29-30 March explosions at Minamidake Crater (at
Aira Caldera's Sakurajima volcano) produced ash plumes that rose as high as
2.7 km above the crater rim and ejected bombs 600-900 m away. An explosion
was recorded on 4 April. An explosion at 0641 on 5 April ejected bombs
800-1,100 m away from the crater and generated an ash plume that rose up to
3 km above the crater rim. 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.

Source: Japan Meteorological Agency (JMA) http://www.jma.go.jp/jma/

Dukono  | Halmahera (Indonesia)  | 1.693Â°N, 127.894Â°E  | Summit elev. 1229 m

Based on satellite and wind model data, the Darwin VAAC reported that
during 31 March-6 April ash plumes from Dukono rose to 2.4 km (8,000 ft)
a.s.l. and drifted E, SE, and SSE. 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.

Sources: Darwin Volcanic Ash Advisory Centre (VAAC)
http://www.bom.gov.au/aviation/volcanic-ash/darwin-va-advisory.shtml;

Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as CVGHM)
http://vsi.esdm.go.id/

Ebeko  | Paramushir Island (Russia)  | 50.686Â°N, 156.014Â°E  | Summit elev.
1103 m

Volcanologists in Severo-Kurilsk (Paramushir Island), about 7 km E of
Ebeko, observed explosions during 25 and 28-29 March that sent ash plumes
up to 2.5 km a.s.l. (8,200 ft) and drifted in different directions. 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.

Source: Kamchatkan Volcanic Eruption Response Team (KVERT)
http://www.kscnet.ru/ivs/kvert/index_eng.php

Etna  | Sicily (Italy)  | 37.748Â°N, 14.999Â°E  | Summit elev. 3320 m

INGV reported continuing episodes of lava fountaining, intra-crater
explosive activity, and discontinuous ash emissions at Etnaâ??s Southeast
Crater (SEC) during the week of 29 March-4 April, though weather conditions
often prevented visual observations. Gas emissions rose from the other
summit craters and occasional explosive activity was visible; puffs of ash
sometimes rose from Voragine Crater during 31 March-2 April.

At 0707 on 31 March a loud explosion was followed by several ash puffs,
marking the beginning of the 17th lava-fountaining episode since they began
on 16 February. At around 1100 a thermal anomaly at the S base of SEC was
visible during an overflight and in thermal camera images. Explosive
activity increased by late afternoon and several lava flows effused from
the S-base vent. The main part of the flow traveled towards the Valle del
Bove with other smaller flows traveled S and SW. Two other vents at the S
base had opened by evening and one ejected spatter a few tens of meters
high. Periods of lava fountaining began through the night, and the main
lava flow descended the W wall of the Valle del Bove. Strombolian activity
intensified at 1950, with an eruption plume that rose to 1.2 km (4,000 ft)
a.s.l. and drifted SSW. Lava fountaining began at around 0100 on 1 April.
At 0218 lava overflowed the E rim of SEC and headed towards the Valle del
Bove, running parallel to the flows from the S base.

Lava fountains continued to be visible during the morning of 1 April and
intense Strombolian activity produced dense ash plumes that drifted S. By
0940 the eruption plume had risen to 9 km (29,500 ft) a.s.l. and drifted
SSW. Lava fountaining ceased around 1000 and the eruption plume rose to 5.5
km (18,000 ft) a.s.l. and drifted S. Ash fell in Milia, Nicolosi, and
Catania and lapilli (1 cm in diameter) fell in Rifugio Sapienza. Lava
effusion and flow advancement continued; lava from the S base of SEC spread
out like a fan. A series of loud bangs were audible in the late morning and
ash emissions continued until the afternoon. Lava overflowed the E rim of
SEC at 1040, and a SSE flow entered the Valle del Bove at the SW wall.
Explosive activity began to decline at 1320, and effusive activity waned
overnight during 1-2 April.

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.

Source: Sezione di Catania - Osservatorio Etneo (INGV)
http://www.ct.ingv.it/

Gareloi  | United States  | 51.79Â°N, 178.794Â°W  | Summit elev. 1573 m

AVO reported that a loss of operation and communication with all seismic
stations on Gareloi was likely due to snow cover. Both the Aviation Color
Code and the Volcano Alert Level were changed to Unassigned, reflecting the
lack of this data to detect unrest. The observatory noted that regional
infrasound networks, lightning detection, and satellite images will be used
to monitor and detected unrest.

Geologic Summary. The 8 x 10 km Gareloi Island, the northernmost volcano of
the Delarof Group at the western end of the Andreanof Islands, consists of
a stratovolcano with two summits and a prominent SE-trending fissure. The
fissure was formed during an eruption in 1929 and extends from the southern
summit to the sea. Steep sea cliffs that are cut into rocks of an older,
eroded center are found on the SW coast, and submarine deposits of three
debris avalanches produced by edifice collapse are found offshore. Young
lava flows cover the older volcano from the summit to the coast along three
broad axes trending NW, ENE, and S. The 1929 eruption originated from 13
craters along a 4-km-long fissure. Phreatic explosions were followed by the
ejection of glassy pumice, lapilli, scoria, and older blocks, as well as by
the emission of four short, steep lava flows, one of which reached the SE
coast.

Source: US Geological Survey Alaska Volcano Observatory (AVO)
https://avo.alaska.edu/

Kilauea  | Hawaiian Islands (USA)  | 19.421Â°N, 155.287Â°W  | Summit elev.
1222 m

HVO reported that the W vent on the inner NW wall of Kilauea's Halema`uma`u
Crater continued to supply the lava lake during 31 March-6 April. Lava
flowed at a low rate from the main vent into the lake through crusted-over
channels and submerged inlets. The total depth of the lake measured about
225 m and lava continued to circulate in the W part; the E half of the lake
remained solidified and expanded toward the W. The sulfur dioxide emission
rate was 1,200 tons/day on 1 April. HVO field crews observed weak
spattering from two areas at the W vent during 1-2 April. The Aviation
Color Code remained at Orange and the Volcano Alert Level remained at Watch.

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.

Source: US Geological Survey Hawaiian Volcano Observatory (HVO)
https://volcanoes.usgs.gov/observatories/hvo/

Langila  | New Britain (Papua New Guinea)  | 5.525Â°S, 148.42Â°E  | Summit
elev. 1330 m

Based on analyses of satellite imagery and wind model data, the Darwin VAAC
reported that on 5 April an ash plume from Langila rose to 1.5 km (5,000
ft) a.s.l. and drifted SW.

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

Source: Darwin Volcanic Ash Advisory Centre (VAAC)
http://www.bom.gov.au/aviation/volcanic-ash/darwin-va-advisory.shtml

Lewotolok  | Lembata Island (Indonesia)  | 8.274Â°S, 123.508Â°E  | Summit
elev. 1431 m

PVMBG reported that the Strombolian eruption at Lewotolok continued during
30 March-6 April. Gray-and-white ash plumes rose as high as 700 m above the
summit and drifted in multiple directions, though rainy weather conditions
prevented visual observations during 2-3 and 5 April. Incandescent material
was ejected 300-500 m above the summit and 500 m SE during 30-31 March;
eruptive events were recorded by the seismic network on the other days but
not visually confirmed. Rumbling was occasionally noted. According to news
articles secondary lahars from Cyclone Seroja destroyed homes, and impacted
as many as 300, in several villages to the SW; mud-and-debris flows and
flooding severely impacted other parts of Indonesia and killed at least 70
people. The Alert Level remained at 3 (on a scale of 1-4) and the public
was warned to stay 4 km away from the summit crater.

Geologic Summary. The Lewotolok (or Lewotolo) 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.

Sources: Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known
as CVGHM) http://vsi.esdm.go.id/;

Reuters
https://news.yahoo.com/landslides-destroy-houses-indonesia-cyclone-073738358.html
;

South China Morning Post
https://www.scmp.com/news/asia/southeast-asia/article/3128464/indonesia-deploys-helicopters-search-survivors-after

Merapi  | Central Java (Indonesia)  | 7.54Â°S, 110.446Â°E  | Summit elev.
2910 m

BPPTKG reported that the lava dome just below Merapiâ??s SW rim and the lava
dome in the summit crater both continued to grow during 26 March-1 April.
The SW rim lava-dome volume was an estimated 1,060,000 cubic meters on 1
April, with a growth rate of about 13,400 cubic meters per day, and
continued to shed material down the flank. A total of 14 pyroclastic flows
traveled a maximum of 1.8 km down the SW flank. Incandescent avalanches,
recorded 158 times, traveled as far as 1.1 km down the SW flank. The summit
lava dome had grown to 70 m tall and produced one incandescent avalanche.
Minor ashfall was reported in Ngadirojo, Stabelan (4 km NW), Takeran,
Tlogolele (5 km NW), Selo (3 km NNW), Pos Babadan (4 km NW), and Pasar
Talun (12 km W). The Alert Level remained at 3 (on a scale of 1-4), and the
public was 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.

Source: Balai Penyelidikan dan Pengembangan Teknologi Kebencanaan Geologi
(BPPTKG) http://www.merapi.bgl.esdm.go.id/

Raung  | Eastern Java (Indonesia)  | 8.119Â°S, 114.056Â°E  | Summit elev.
3260 m

PVMBG reported that daily gray-and-white ash plumes rose 50-500 m above
Raung's summit during 31 March-5 April and drifted N and S. 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.

Source: Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known
as CVGHM) http://vsi.esdm.go.id/

Sheveluch  | Central Kamchatka (Russia)  | 56.653Â°N, 161.36Â°E  | Summit
elev. 3283 m

KVERT reported that a thermal anomaly over Sheveluch was identified in
satellite images during 28 March-2 April. On 3 April a plume of
re-suspended ash rose to 2.5 km (8,200 ft) a.sl. and drifted 250 km ESE.
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.

Source: Kamchatkan Volcanic Eruption Response Team (KVERT)
http://www.kscnet.ru/ivs/kvert/index_eng.php

Shishaldin  | Fox Islands (USA)  | 54.756Â°N, 163.97Â°W  | Summit elev. 2857 m

AVO reinstated the Green Aviation Color Code and the Normal Volcano Alert
Level for Shishaldin on 2 April, after several seismic stations again
became operational following a months-long outage, thus improving the
observatoryâ??s monitoring capability.

Geologic Summary. The beautifully symmetrical Shishaldin is the highest and
one of the most active volcanoes of the Aleutian Islands. The
glacier-covered volcano is the westernmost of three large stratovolcanoes
along an E-W line in the eastern half of Unimak Island. The Aleuts named
the volcano Sisquk, meaning "mountain which points the way when I am lost."
A steam plume often rises from its small summit crater. Constructed atop an
older glacially dissected volcano, it is largely basaltic in composition.
Remnants of an older ancestral volcano are exposed on the W and NE sides at
1,500-1,800 m elevation. There are over two dozen pyroclastic cones on its
NW flank, which is blanketed by massive aa lava flows. Frequent explosive
activity, primarily consisting of Strombolian ash eruptions from the small
summit crater, but sometimes producing lava flows, has been recorded since
the 18th century.

Source: US Geological Survey Alaska Volcano Observatory (AVO)
https://avo.alaska.edu/

Sinabung  | Indonesia  | 3.17Â°N, 98.392Â°E  | Summit elev. 2460 m

PVMBG reported that the eruption at Sinabung continued during 31 March-6
April. Weather conditions sometimes prevented visual observations of the
volcano, though daily white fumarolic plumes were visible rising as high as
500 m above the summit. Avalanches were detected daily by the seismic
network and observed traveling 500-1,500 m down the E and SE flanks. An
eruptive event produced a gray ash plume that rose 500 m above them summit
on 1 April. Pyroclastic flows went as far as 1.5 km down the E and SE
flanks. Ash plumes rose 0.7-2 km during 2-5 April and mainly drifted E and
SE. 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.

Source: Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known
as CVGHM) http://vsi.esdm.go.id/

Soufriere St. Vincent  | St. Vincent  | 13.33Â°N, 61.18Â°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 SoufriÃ¨re St. Vincentâ??s main crater continued to slowly grow during
31 March-6 April, expanding to the N and S. Gas-and-steam continued to rise
from the top of the dome, as well as along the contact with the
pre-existing 1979 dome. A swarm of volcano-tectonic (VT) earthquakes began
at 0638 on 5 April. The number and frequency of the VTs increased until
about 0830 and then stabilized. The rate declined at around 1400 and then
significantly dropped at 1600, though small VT events continued to be
detected through 1800. The events were located at depths of 6 km, slightly
deeper than the swarm events recorded during 22-25 March, located at
revised depths of 3-5 km. Several reports of felt events came from nearby
communities, including Fancy and Chateaubelair. The largest event, a M 3.5,
was recorded at 0920 and felt by local residents. The swarm was more
intense than the previous one, with an average rate of about 50 earthquakes
per hour compared with 1.5 per hour during 22-25 March. The Alert Level
remained at Orange (the second highest level on a four-color scale).

Geologic Summary. SoufriÃ¨re 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 PelÃ©e 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.

Sources: University of the West Indies Seismic Research Centre (UWI-SRC)
http://www.uwiseismic.com/;

National Emergency Management Organisation (NEMO), Government of Saint
Vincent and the Grenadines http://nemo.gov.lc/

Tanaga  | Andreanof Islands (USA)  | 51.885Â°N, 178.146Â°W  | Summit elev.
1806 m

AVO reported a loss of operation and communication with all but two seismic
stations on Tanaga, likely caused by snow cover. Both the Aviation Color
Code and the Volcano Alert Level were changed to Unassigned, reflecting the
inability to locate earthquakes to detect unrest. Monitoring will continue
with the remaining seismic stations, regional infrasound networks,
lightning detection, and satellite images.

Geologic Summary. Tanaga volcano, the second largest volcanic center of the
central Aleutians, is the central and highest of three youthful
stratovolcanoes oriented along a roughly E-W line at the NW tip of Tanaga
Island. Ridges to the east and south represent the rim of an arcuate
caldera formed by collapse of an ancestral edifice during the Pleistocene.
Most Holocene eruptions originated from Tanaga volcano itself, which
consists of two large cones, the western of which is the highest,
constructed within a caldera whose 400-m-high rim is prominent to the SE.
At the westernmost end of the complex is conical Sajaka, a double cone that
may be the youngest of the three volcanoes. Sajaka One volcano collapsed
during the late Holocene, producing a debris avalanche that swept into the
sea, after which the Sajaka Two cone was constructed within the collapse
scarp.

Source: US Geological Survey Alaska Volcano Observatory (AVO)
https://avo.alaska.edu/

Tengger Caldera  | Eastern Java (Indonesia)  | 7.942Â°S, 112.95Â°E  | Summit
elev. 2329 m

PVMBG reported that during 30 March-5 April white steam-and-gas plumes rose
50-700 m above the summit of Tengger Calderaâ??s Bromo cone. The plumes were
white to gray during 1-2 April. The Alert Level remained at 2 (on a scale
of 1-4), and visitors were warned to stay outside of a 1-km radius of the
crater.

Geologic Summary. The 16-km-wide Tengger caldera is located at the northern
end of a volcanic massif extending from Semeru volcano. The massive
volcanic complex dates back to about 820,000 years ago and consists of five
overlapping stratovolcanoes, each truncated by a caldera. Lava domes,
pyroclastic cones, and a maar occupy the flanks of the massif. The
Ngadisari caldera at the NE end of the complex formed about 150,000 years
ago and is now drained through the Sapikerep valley. The most recent of the
calderas is the 9 x 10 km wide Sandsea caldera at the SW end of the
complex, which formed incrementally during the late Pleistocene and early
Holocene. An overlapping cluster of post-caldera cones was constructed on
the floor of the Sandsea caldera within the past several thousand years.
The youngest of these is Bromo, one of Java's most active and most
frequently visited volcanoes.

Source: Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known
as CVGHM) http://vsi.esdm.go.id/

Ubinas  | Peru  | 16.355Â°S, 70.903Â°W  | Summit elev. 5672 m

Instituto GeofÃsico del PerÃº (IGP) reported that during 29 March-4 April
there were 11 volcano-tectonic earthquakes at Ubinas with magnitudes less
than 1.8, and a few seismic signals indicated emissions. Sporadic
steam-and-gas plumes rose as high as 200 m above the crater rim. On 5 April
the Alert Level was lowered to Green (the lowest level on a four-color
scale).

Geologic Summary. A small, 1.4-km-wide caldera cuts the top of Ubinas,
PerÃº's most active volcano, giving it a truncated appearance. It is the
northernmost of three young volcanoes located along a regional structural
lineament about 50 km behind the main volcanic front. The growth and
destruction of Ubinas I was followed by construction of Ubinas II beginning
in the mid-Pleistocene. The upper slopes of the andesitic-to-rhyolitic
Ubinas II stratovolcano are composed primarily of andesitic and
trachyandesitic lava flows and steepen to nearly 45 degrees. The
steep-walled, 150-m-deep summit caldera contains an ash cone with a
500-m-wide funnel-shaped vent that is 200 m deep. Debris-avalanche deposits
from the collapse of the SE flank about 3,700 years ago extend 10 km from
the volcano. Widespread Plinian pumice-fall deposits include one of
Holocene age about 1,000 years ago. Holocene lava flows are visible on the
flanks, but historical activity, documented since the 16th century, has
consisted of intermittent minor-to-moderate explosive eruptions.

Source: Instituto GeofÃsico del PerÃº (IGP) http://www.igp.gob.pe/

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End of Volcano Digest - 5 Apr 2021 to 8 Apr 2021 (#2021-36)
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