Smithsonian / USGS Weekly Volcanic Activity Report 28 April-4 May 2021

Rachel Holsteen-Bruyere <rbruyere@xxxxxxx> · Wed, 5 May 2021 13:07:20 -0700

4-4-4-4-4-4-4-4-4-4-4-4-4

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

Smithsonian / USGS Weekly Volcanic Activity Report

28 April-4 May 2021

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

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

New Activity/Unrest: Asosan, Kyushu (Japan)  | Dieng Volcanic Complex,
Central Java (Indonesia)  | Karymsky, Eastern Kamchatka (Russia)  | Piton
de la Fournaise, Reunion Island (France)

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

Asosan  | Kyushu (Japan)  | 32.884Â°N, 131.104Â°E  | Summit elev. 1592 m

Volcanic tremor amplitude increased at Asoson at around 2100 on 2 May,
prompting JMA to raise the Alert Level to 2 (on a scale of 1-5) at 2255.
The public was warned to stay at least 1 km away from the crater. Sulfur
dioxide emissions were low, at 200 tons per day on 3 May, and white steam
plumes rose as high as 300 m above the crater rim.

Geologic Summary. The 24-km-wide Asosan caldera was formed during four
major explosive eruptions from 300,000 to 90,000 years ago. These produced
voluminous pyroclastic flows that covered much of Kyushu. The last of
these, the Aso-4 eruption, produced more than 600 km3 of airfall tephra and
pyroclastic-flow deposits. A group of 17 central cones was constructed in
the middle of the caldera, one of which, Nakadake, is one of Japan's most
active volcanoes. It was the location of Japan's first documented
historical eruption in 553 CE. The Nakadake complex has remained active
throughout the Holocene. Several other cones have been active during the
Holocene, including the Kometsuka scoria cone as recently as about 210 CE.
Historical eruptions have largely consisted of basaltic to
basaltic-andesite ash emission with periodic strombolian and
phreatomagmatic activity. The summit crater of Nakadake is accessible by
toll road and cable car, and is one of Kyushu's most popular tourist
destinations.

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

Dieng Volcanic Complex  | Central Java (Indonesia)  | 7.2Â°S, 109.879Â°E  |
Summit elev. 2565 m

PVMBG reported that a phreatic eruption at the Sileri Crater lake (Dieng
Volcanic Complex) occurred at 1825 on 29 April, ejecting rocks 200 m S and
E and mud 400 m S and 300 m E. According to a news article a local road was
temporarily closed because rocks (about 10 cm in diameter) from the
eruption were scattered along the road and the mud made conditions
slippery. The closest residents are 1 km away. The Alert Level remained at
1 (on a scale of 1-4), and the public was warned to stay 500 m away from
the crater rim.

Geologic Summary. The Dieng plateau in the highlands of central Java is
renowned both for the variety of its volcanic scenery and as a sacred area
housing Java's oldest Hindu temples, dating back to the 9th century CE. The
Dieng volcanic complex consists of two or more stratovolcanoes and more
than 20 small craters and cones of Pleistocene-to-Holocene age over a 6 x
14 km area. Prahu stratovolcano was truncated by a large Pleistocene
caldera, which was subsequently filled by a series of dissected to youthful
cones, lava domes, and craters, many containing lakes. Lava flows cover
much of the plateau, but have not occurred in historical time, when
activity has been restricted to minor phreatic eruptions. Toxic gas
emissions are a hazard at several craters and have caused fatalities. The
abundant thermal features and high heat flow make Dieng a major geothermal
prospect.

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

Detik News
https://news.detik.com/berita-jawa-tengah/d-5551663/kawah-sileri-di-dieng-erupsi-jalur-banjarnegara-batang-ditutup?utm_term=echoboxauto

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

KVERT reported that a weak thermal anomaly over Karymsky was visible in
satellite images during 22-23 and 29 April. 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.

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

Piton de la Fournaise  | Reunion Island (France)  | 21.244Â°S, 55.708Â°E  |
Summit elev. 2632 m

OVPF reported that the eruption at Piton de la Fournaise continued during
28 April-4 May, though inclement weather obscured visual observations
during most of the week. Both craters were active, producing lava flows
that mainly traveled though lava tubes. Lava emerged from the end of the
flow field, advancing E and setting fire to local vegetation. Minor
inflation of the summit area was recorded. Lava fountaining was weak at the
smaller vent to the SE during 3-4 May and a small lava pond occupied the
crater of the larger cone, just NW at the higher elevation. On 4 May weak
fountaining at the smaller cone occasionally ejected material just above
the crater rim and the pond was active in the larger crater. The lava flow
advanced another 180 m, reaching 1,500 m elevation. According to a news
article two students in their 20s were found dead in the caldera on 22
April, near the active cones. The cause of death was not immediately known.
The Alert Level remained at 2-2.

Geologic Summary. The massive Piton de la Fournaise basaltic shield volcano
on the French island of RÃ©union in the western Indian Ocean is one of the
world's most active volcanoes. Much of its more than 530,000-year history
overlapped with eruptions of the deeply dissected Piton des Neiges shield
volcano to the NW. Three calderas formed at about 250,000, 65,000, and less
than 5000 years ago by progressive eastward slumping of the volcano.
Numerous pyroclastic cones dot the floor of the calderas and their outer
flanks. Most historical eruptions have originated from the summit and
flanks of Dolomieu, a 400-m-high lava shield that has grown within the
youngest caldera, which is 8 km wide and breached to below sea level on the
eastern side. More than 150 eruptions, most of which have produced fluid
basaltic lava flows, have occurred since the 17th century. Only six
eruptions, in 1708, 1774, 1776, 1800, 1977, and 1986, have originated from
fissures on the outer flanks of the caldera. The Piton de la Fournaise
Volcano Observatory, one of several operated by the Institut de Physique du
Globe de Paris, monitors this very active volcano.

Sources: Observatoire Volcanologique du Piton de la Fournaise (OVPF)
http://www.ipgp.fr/;

Agence France-Presse (AFP)
https://www.straitstimes.com/world/europe/two-hikers-die-on-erupting-volcano-on-frances-reunion-island

Ongoing Activity

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

JMA reported that during 26 April-3 May incandescence from Minamidake
Crater (at Aira Calderaâ??s Sakurajima volcano) was visible nightly. There
was a total of 10 explosions, producing ash plumes that rose as high has
2.4 km above the summit and ejected bombs 1.3-1.7 km away from the crater.
The Alert Level remained at 3 (on a 5-level scale), and residents were
warned to stay 2 km away from the crater.

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/

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 22-24 April that sent ash plumes to 3 km
(10,000 ft) a.s.l. and drifted NE and SW. 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

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 28 April-4 May through a
submerged inlet. The depth of the lake was about 227 m and lava continued
to circulate in the W part, though the active area continued to shrink. The
E half of the lake remained solidified and comprised about 93 percent of
the total area, based on thermal measurements acquired on 16 April. The
sulfur dioxide emission rate was 250 and 475 tons/day on 30 April and 2
May, respectively, continuing a downward trend that began in mid-April; the
recent rates suggested that the effusion rate had also decreased. 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/

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

IMO reported that the fissure eruption in the W part of the
KrÃ½suvÃk-TrÃ¶lladyngja volcanic system, close to Fagradalsfjall on the
Reykjanes Peninsula, continued during 28 April-4 May. According to a news
source, activity at the S vent of the fifth cone, which had opened on 13
April with N and S vents, intensified at around 2030 on 26 April.
Fountaining became more explosive and lava was jetted 40-50 m high. The
lava-flow rate significantly increased; lava flowed S then E and descended
a valley into Meradalir.

By 29 April activity had intensified at the fifth cone where lava ejections
reached 250 m high, but had ceased at the others. By 1 May lava flows had
traveled N in Meradalir and connected to the flows that had previously
descended into the valley from a fissure that opened on 5 April. IMO noted
that fountaining at the vent was steady until around 0000-0100 on 2 May
when it became more pulsating. Resting periods of 1-2 minutes were
punctuated by intense fountaining reaching 100-150 m high for periods of
8-12 minutes. Gas plumes with minor amounts of ash rose 800-900 m a.s.l. A
news source noted that on 2 May lava fountains rose over 300 m, the highest
to date, and were seen from Reykjavik. Ejecta set fire to vegetation on the
hill to the S of the vent, causing a smoke plume. The Aviation Color Code
remained at 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 National Broadcasting Service (RUV)
https://www.ruv.is/frett/2021/03/18/eldgosid-i-geldingadolum-i-beinni-utsendingu

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

PVMBG reported that white plumes from Lewotolok rose as high as 500 m and
drifted SE, SW, and W on most days during 27 April-3 May. Gray-and-white
plumes rose 500 m and drifted W on 30 April and 2 May. The Alert Level
remained at 3 (on a scale of 1-4) and the public was warned to stay 3 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.

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

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 extrude lava during 23-29
April. The SW rim lava dome had an estimated volume of 1,141,850 cubic
meters on 28 April, with a growth rate of about 11,900 cubic meters per
day, and continued to shed material down the flank. A total of 12
pyroclastic flows traveled a maximum of 2 km down the SW flank.
Incandescent avalanches, recorded 113 times, traveled as far as 2 km down
the SW flank. The volume of the summit lava dome was 1,794,000 cubic meters
on 28 April, unchanged from the previous week. Electronic Distance
Measurement (EDM) data showed a distance shortening between points in the
NW at a rate of 0.5 cm per day, indicating inflation. 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/

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

INSIVUMEH reported that during 27-29 April occasional explosions at
Pacayaâ??s Mackenney Crater ejected incandescent material as high as 250 m
above the summit. On 27 April a lava flow emerged from a new fissure on the
upper SE flank traveled 200 m. At around 0500 on 29 April the seismic
network recorded signals indicating a change from mostly explosive to
mostly effusive activity. At around 0645 a new fissure opened on the N
flank, producing a lava flow that rapidly traveled N towards Cerro Chino
and then turned S and spread W and SW. Explosive activity at the fissure
was minor during 29-30 April. By 3 May the flow was almost 2.1 km long, and
continued to advanced W and SW at least through 4 May.

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/

Semeru  | Eastern Java (Indonesia)  | 8.108Â°S, 112.922Â°E  | Summit elev.
3657 m

PVMBG reported that at 0740 on 28 April an ash plume from Semeru rose 600 m
above the summit and drifted SW. The next day, at 0550, an ash plume rose
400 m and drifted S. The Alert Level remained at 2 (on a scale of 1-4),
with a general exclusion zone of 1 km and extensions to 5 km in the SSE
sector.

Geologic Summary. Semeru, the highest volcano on Java, and one of its most
active, lies at the southern end of a volcanic massif extending north to
the Tengger caldera. The steep-sided volcano, also referred to as Mahameru
(Great Mountain), rises above coastal plains to the south. Gunung Semeru
was constructed south of the overlapping Ajek-ajek and Jambangan calderas.
A line of lake-filled maars was constructed along a N-S trend cutting
through the summit, and cinder cones and lava domes occupy the eastern and
NE flanks. Summit topography is complicated by the shifting of craters from
NW to SE. Frequent 19th and 20th century eruptions were dominated by
small-to-moderate explosions from the summit crater, with occasional lava
flows and larger explosive eruptions accompanied by pyroclastic flows that
have reached the lower flanks of the volcano.

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 23-30 April. 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

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

PVMBG reported that the eruption at Sinabung continued during 28 April-4
May. Weather conditions sometimes prevented visual observations of the
volcano, though white fumarolic plumes were visible almost daily rising as
high as 500 m above the summit and drifted in multiple directions. At 0728
on 28 April an ash plume rose 1 km and drifted SSW. At 1810 an ash plume
rose 1 km and drifted SSE and an incandescent avalanche descended 1.5 km
down the SSE flank. At 2346 an ash plume rose 1.5 km and drifted W and SW,
and another incandescent rockfall traveled 1.5 km SSE. Eruptive events
produced ash plumes that rose 500-1,000 m above the summit during 30
April-1 May. Avalanches of material traveled as far as 1.5 km E and 1 km SE
during 1-3 May. 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) reported
that seismicity at SoufriÃ¨re St. Vincent (often simply referred to as â??La
Soufriereâ??) remained low during 28 April-4 May, with a few long-period,
hybrid, and volcano-tectonic earthquakes recorded daily. Multiple
significant lahars were generated by rainfall during 28-29 April. Lahars
likely descended all valleys in the Red and Orange zones, and some were hot
and visibly steaming. Trees brought down by lahars were swept to the sea;
floating logs created hazardous conditions for small boats along the
coastline. UWI-SRC and the National Emergency Management Organisation
(NEMO) both warned the public to stay away from drainages and areas prone
to flooding, and noted that lahars have caused notable erosion and damage
to drainages and parts of the coastline. Smaller lahars were recorded
during the mornings of 30 April and 1 May. Multiple lahars were detected in
likely all the volcanoâ??s drainages for a period of about six hours on 3
May, with the most intense lahars occurring during 1100-1200. Sulfur
dioxide emissions were measured from a boat near the W coast, yielding a
flux of 1,036 tons per day. Photos showed people in Sandy Bay shoveling off
ash from rooftops on 4 May. The volcano Alert Level remained at Red.

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/

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

JMA reported that 45 explosions at Suwanosejima's Ontake Crater produced
eruption plumes that rose as high as 1.7 km above the crater rim during
23-30 April. Large volcanic bombs were ejected 400 m from the crater.
Nighttime crater incandescence was visible during 24-25 April. The Alert
Level remained at 2 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/

Taal  | Luzon (Philippines)  | 14.002Â°N, 120.993Â°E  | Summit elev. 311 m

PHIVOLCS reported that unrest at Taal continued during 27 April-4 May.
Low-level background tremor that had begun at 0905 on 8 April continued,
along with 2-26 daily low-frequency events and 5-37 daily volcanic
earthquakes during 28 April-2 May. One hybrid event was detected during
28-29 April. Diffuse steam plumes from fumarolic vents in Main Crater rose
5-10 m on most days. Average daily sulfur dioxide emission rates were in
the 1,452-3,191 tonnes per day range. Upwelling of hot volcanic fluids in
the crater lake was accompanied by steam plumes that were 300-600 m tall on
27 April, 30 April, and 4 May. The Alert Level for Taal remained at 2 (on a
scale of 0-5). PHIVOLCS strongly recommended no entry onto the island, and
access to the Main Crater and Daang Kastila fissure (along the walking
trail) was strictly prohibited.

Geologic Summary. Taal is one of the most active volcanoes in the
Philippines and has produced some of its most powerful historical
eruptions. Though not topographically prominent, its prehistorical
eruptions have greatly changed the landscape of SW Luzon. The 15 x 20 km
Talisay (Taal) caldera is largely filled by Lake Taal, whose 267 km2
surface lies only 3 m above sea level. The maximum depth of the lake is 160
m, and several eruptive centers lie submerged beneath the lake. The
5-km-wide Volcano Island in north-central Lake Taal is the location of all
historical eruptions. The island is composed of coalescing small
stratovolcanoes, tuff rings, and scoria cones that have grown about 25% in
area during historical time. Powerful pyroclastic flows and surges from
historical eruptions have caused many fatalities.

Source: Philippine Institute of Volcanology and Seismology (PHIVOLCS)
http://www.phivolcs.dost.gov.ph/

Whakaari/White Island  | North Island (New Zealand)  | 37.52Â°S, 177.18Â°E  |
Summit elev. 294 m

GeoNet reported that a brief period of low-energy tremor and acoustic
signals was recorded at Whakaari/White Island beginning at 2230 on 29
April. During an overflight on 30 April scientists did not observe new
deposits near the active vent or thermal anomalies at the active vent area.
Gas-emission rates had been relatively unchanged since March. The brief
period of increased activity was likely caused by a series of low-energy
subterranean explosions, similar to activity observed in mid-February and
early-mid March. Seismic tremor remained at background levels. The Volcanic
Alert Level remained at 1 and the Aviation Color Code remained at Green.

Geologic Summary. The uninhabited Whakaari/White Island is the 2 x 2.4 km
emergent summit of a 16 x 18 km submarine volcano in the Bay of Plenty
about 50 km offshore of North Island. The island consists of two
overlapping andesitic-to-dacitic stratovolcanoes. The SE side of the crater
is open at sea level, with the recent activity centered about 1 km from the
shore close to the rear crater wall. Volckner Rocks, sea stacks that are
remnants of a lava dome, lie 5 km NW. Descriptions of volcanism since 1826
have included intermittent moderate phreatic, phreatomagmatic, and
Strombolian eruptions; activity there also forms a prominent part of Maori
legends. The formation of many new vents during the 19th and 20th centuries
caused rapid changes in crater floor topography. Collapse of the crater
wall in 1914 produced a debris avalanche that buried buildings and workers
at a sulfur-mining project. Explosive activity in December 2019 took place
while tourists were present, resulting in many fatalities. The official
government name Whakaari/White Island is a combination of the full Maori
name of Te Puia o Whakaari ("The Dramatic Volcano") and White Island
(referencing the constant steam plume) given by Captain James Cook in 1769.

Source: GeoNet http://www.geonet.org.nz/

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End of Volcano Digest - 3 May 2021 to 5 May 2021 (#2021-45)
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