Smithsonian / USGS Weekly Volcanic Activity Report 5-11 May 2021

Rachel Holsteen-Bruyere <rbruyere@xxxxxxx> · Fri, 14 May 2021 12:42:27 -0700

6-6-6-6-6-6-6-6-6-6-6-6-6

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

Smithsonian / USGS Weekly Volcanic Activity Report

5-11 May 2021

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

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

New Activity/Unrest: Bulusan, Luzon (Philippines)  | Nevados de Chillan,
Chile  | 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

Bulusan  | Luzon (Philippines)  | 12.769Â°N, 124.056Â°E  | Summit elev. 1535 m

PHIVOLCS stated that unrest at Bulusan had increased, noting that 62
volcanic earthquakes were recorded during 7-10 May and 124 were recorded
during 10-11 May. Inflation of the upper flanks first recorded on 6 March
in tilt data was sustained. GPS data indicated short-term inflation
starting in late February, though the long-term pattern since July 2019
showed deflation. The data suggested shallow hydrothermal processes. The
Alert Level for Bulusan was raised to 1 on 11 May, reflecting abnormal
conditions, and the public was reminded not to enter the 4-km-radius
Permanent Danger Zone (PDZ).

Geologic Summary. Luzon's southernmost volcano, Bulusan, was constructed
along the rim of the 11-km-diameter dacitic-to-rhyolitic Irosin caldera,
which was formed about 36,000 years ago. It lies at the SE end of the Bicol
volcanic arc occupying the peninsula of the same name that forms the
elongated SE tip of Luzon. A broad, flat moat is located below the
topographically prominent SW rim of Irosin caldera; the NE rim is buried by
the andesitic complex. Bulusan is flanked by several other large
intracaldera lava domes and cones, including the prominent Mount Jormajan
lava dome on the SW flank and Sharp Peak to the NE. The summit is
unvegetated and contains a 300-m-wide, 50-m-deep crater. Three small
craters are located on the SE flank. Many moderate explosive eruptions have
been recorded since the mid-19th century.

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

Nevados de Chillan  | Chile  | 36.868Â°S, 71.378Â°W  | Summit elev. 3180 m

SERNAGEOMIN noted that sulfur dioxide emissions and thermal anomalies at
Nevados de ChillÃ¡nâ??s Nicanor Crater had both increased in March, and
inflation began on 27 March. During the second half of April the dome grew
at a higher rate, with growth concentrated on the W part. The dome was 66 m
high at the center. The L5 lava flow advanced and was about 940 m long, and
50 m thick near the flow front. The effusion rate increased on 28 April.
During 2-5 May activity was characterized by increased crater incandescence
and a series of intense explosions that destroyed part of the summit lava
dome. Dense ash plumes rose above the crater. Block-and-ash flows traveled
less than 400 m down the NE flank and pyroclastic flows traveled short
distances SW. During 4-5 May the effusion rate increased and the L5 lava
flow advanced. A new lava flow (L6) emerged on 5 May from the summit crater
and descended 100 m down the NE flank. A high-temperature elongated deposit
in between the L5 and L6 flows was visible in infrared images. The Alert
Level remained at Yellow, the second lowest level on a four-color scale.
ONEMI stated that Alert Level Yellow (the middle level on a three-color
scale) remained in place for the communities of Pinto and Coihueco, noting
that the public should stay at least 2 km away from the crater.

Geologic Summary. The compound volcano of Nevados de ChillÃ¡n 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 (VolcÃ¡n Nevado), is located at the NW
end of the group. VolcÃ¡n Viejo (VolcÃ¡n ChillÃ¡n), which was the main active
vent during the 17th-19th centuries, occupies the SE end. The new VolcÃ¡n
Nuevo lava-dome complex formed between 1906 and 1945 between the two
volcanoes and grew to exceed VolcÃ¡n Viejo in elevation. The VolcÃ¡n Arrau
dome complex was constructed SE of VolcÃ¡n Nuevo between 1973 and 1986 and
eventually exceeded its height.

Sources: Servicio Nacional de GeologÃa y MinerÃa (SERNAGEOMIN)
http://www.sernageomin.cl/;

Oficina Nacional de Emergencia-Ministerio del Interior (ONEMI)
http://www.onemi.cl/

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
4-11 May. Both craters were active, producing lava flows that mainly
traveled though lava tubes. Lava emerged from the end of the flow field,
advancing E to 1,200 m elevation by 8 May, 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 and a small lava pond
continued to occupy the crater of the larger cone, just NW a higher
elevation. Gas plumes rose from both craters, though the plumes from the
smaller crater were denser. An 11 May report stated that the larger cone
was 35 m tall and 226 m in diameter at its base. 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.

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

Ongoing Activity

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

JMA reported that during 3-10 May incandescence from Minamidake Crater (at
Aira Calderaâ??s Sakurajima volcano) was visible nightly. There were four
explosions and four non-explosive events during 3-7 May, producing ash
plumes that rose as high has 2.5 km above the summit and ejecting bombs
0.8-1.1 km away from the crater. Very small eruptive events were recorded
during 7-10 May. The sulfur dioxide emission rate was 1,300 tons per day on
19 May. 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 4-6 May that sent ash plumes to 2.5 km
(8,200 ft) a.s.l. and drifted N and SE. A thermal anomaly was identified in
satellite data on 5 May. 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

Fuego  | Guatemala  | 14.473Â°N, 90.88Â°W  | Summit elev. 3763 m

INSIVUMEH reported that 5-12 explosions per hour were recorded during 4-11
May at Fuego, generating ash plumes as high as 1.1 km above the crater rim.
Shock waves sometimes rattled buildings around the volcano. Ashfall was
reported daily in several areas downwind, including Morelia (9 km SW),
PanimachÃ© I and II (8 km SW), Santa SofÃa (12 km SW), El Porvenir (8 km
ENE), Sangre de Cristo (8 km WSW), and San Pedro Yepocapa (8 km NW). Block
avalanches descended the Ceniza (SSW), Seca (W), Trinidad (S), TaniluyÃ¡
(SW), Las Lajas (SE), and Honda drainages, often reaching vegetated areas.
Explosions ejected incandescent material 100-450 m above the summit during
4-8 May.

Geologic Summary. VolcÃ¡n Fuego, one of Central America's most active
volcanoes, is also one of three large stratovolcanoes overlooking
Guatemala's former capital, Antigua. The scarp of an older edifice, Meseta,
lies between Fuego and Acatenango to the north. Construction of Meseta
dates back to about 230,000 years and continued until the late Pleistocene
or early Holocene. Collapse of Meseta may have produced the massive
Escuintla debris-avalanche deposit, which extends about 50 km onto the
Pacific coastal plain. Growth of the modern Fuego volcano followed,
continuing the southward migration of volcanism that began at the mostly
andesitic Acatenango. Eruptions at Fuego have become more mafic with time,
and most historical activity has produced basaltic rocks. Frequent vigorous
historical eruptions have been recorded since the onset of the Spanish era
in 1524, and have produced major ashfalls, along with occasional
pyroclastic flows and lava flows.

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

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 29-30 April and 1 May; weather clouds prevented
observations during 2-7 May. 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

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 at a low rate during 5-11 May
through a submerged inlet. The depth of the lake was 229 m by 11 May. 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 200-300 tons per day during 5-7
May, and 150 tons per day on 10 May, continuing a downward trend that began
in mid-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/

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 5-11 May. On 2 May pulsating high
jets of lava from crater 5 prompted authorities to widen the restricted
zone because; ash and lava could be deposited several hundred of meters
away. Cycles of lava jetting and effusion periodically continued during 3-7
May, with lava steadily enlarging the flow field. By 4 May the area of the
flow field had grown to 1.41 square kilometers, and the total volume
erupted was 23 million cubic meters. Activity was quiet for a period of
time during 8-9 May, though IMO noted that fountaining quickly resumed
during the morning of 9 May. High jets of lava occurred every 10 minutes,
sometimes with jets rising as high as 300 m. Tephra (a few centimeters in
diameter) was deposited as far as 1 km from the vent and small amounts of
tephra were reported in GrÃndavÃk. Hot deposits have caused small
vegetation fires within a few hundreds of meters around the eruption site.
On 10 May gas plumes rose higher than 2 km a.s.l. The eruption area was
closed due to local wildfires and unfavorable wind conditions. Very high
fountains were visible in Reykjavik. On 11 May lava fountains again rose up
to 300 m tall and were seen from the capital. The cone had grown to about
50 m high. 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) http://www.ruv.is/;

Institute of Earth Sciences http://www.earthice.hi.is/

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

PVMBG reported that mostly white plumes from Lewotolok rose as high as 600
m and drifted SE, W, and NW during 4-11 May. Gray-and-white plumes rose 500
m and drifted W, NW, and SE on 6 and 8 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 30 April-6
May. The SW rim lava-dome volume was an estimated 1.1 million cubic meters
on 2 May, with a growth rate of about 17,000 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 74 times, traveled as far as 2 km down the SW flank and twice went
600 m SE. The volume of the summit lava dome was 1.7 million cubic meters
on 2 May, with a growth rate of about 14,000 cubic meters per day.
Electronic Distance Measurement (EDM) data showed a distance shortening
between points in the NW at a rate of 0.6 cm per day, indicating minor
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 4-11 May the lava flow on Pacayaâ??s N flank
continued to advance, lengthening from 2.1 to 2.4 km, and spreading
laterally in some areas. Incandescent blocks detached from the flow,
especially along the flow margins and steep slopes. Occasional explosions
at the vent (near Cerro Chino) ejected incandescent material as high as 100
m. Around 0600 on 6 May explosions at the summit produced ash plumes that
drifted S. Dense ash plumes were visible drifting W and SW during 7-9 May.
On 11 May an advancing lava flow on the SW flank was 2.3 km long.

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/

Sangay  | Ecuador  | 2.005Â°S, 78.341Â°W  | Summit elev. 5286 m

IG reported a high level of activity at Sangay during 5-11 May. Seismicity
was characterized by 3-28 daily explosions, long-period earthquakes, lahar
events, and signals indicating emissions. Weather clouds and rain sometimes
prevented visual observations of the volcano, especially during 8-9 May.
Based on the Washington VAAC and occasional webcam images, ash plumes were
visible during 4-8 and 10 May rising as high as 2 km above the summit and
drifting mainly NW, W, and SW. Eruptions during midmorning and again around
noon on 7 May produced ash plumes that rose 2.3 km and drifted WSW; higher
plumes rose 5.4 km and drifted NW. Notable ashfall was reported in multiple
places in the afternoon; in Guamote (40 km WNW), in Riobamba, and AlusÃ. A
lava flow descended the SE flank. Minor amounts of ash fell in parts of the
Guayas province in the morning of 8 May. The seismic network recorded lahar
signals during 7-10 May.

Geologic Summary. The isolated Sangay volcano, located east of the Andean
crest, is the southernmost of Ecuador's volcanoes and its most active. The
steep-sided, glacier-covered, dominantly andesitic volcano grew within
horseshoe-shaped calderas of two previous edifices, which were destroyed by
collapse to the east, producing large debris avalanches that reached the
Amazonian lowlands. The modern edifice dates back to at least 14,000 years
ago. It towers above the tropical jungle on the east side; on the other
sides flat plains of ash have been sculpted by heavy rains into
steep-walled canyons up to 600 m deep. The earliest report of a historical
eruption was in 1628. More or less continuous eruptions were reported from
1728 until 1916, and again from 1934 to the present. The almost constant
activity has caused frequent changes to the morphology of the summit crater
complex.

Source: Instituto GeofÃsico-Escuela PolitÃ©cnica Nacional (IG)
http://www.igepn.edu.ec/

Santa Maria  | Guatemala  | 14.757Â°N, 91.552Â°W  | Summit elev. 3745 m

INSIVUMEH reported that during 4-11 May daily explosions at Santa MarÃaâ??s
Santiaguito lava-dome complex generated ash plumes that rose as high as 1.1
km above the summit and drifted W, SW, and S. Collapses of blocky lava from
Caliente dome sent avalanches down the SE, S, SW, and W flanks, sometimes
reaching the base, and causing minor ashfall around the volcano. Ashfall
was also reported in San Marcos (8 km SW) and Loma Linda Palajunoj (6 km
WSW) during 5-6 and 10-11 May.

Geologic Summary. Symmetrical, forest-covered Santa MarÃa volcano is part
of a chain of large stratovolcanoes that rise above the Pacific coastal
plain of Guatemala. The sharp-topped, conical profile is cut on the SW
flank by a 1.5-km-wide crater. The oval-shaped crater extends from just
below the summit to the lower flank, and was formed during a catastrophic
eruption in 1902. The renowned Plinian eruption of 1902 that devastated
much of SW Guatemala followed a long repose period after construction of
the large basaltic-andesite stratovolcano. The massive dacitic Santiaguito
lava-dome complex has been growing at the base of the 1902 crater since
1922. Compound dome growth at Santiaguito has occurred episodically from
four vents, with activity progressing W towards the most recent, Caliente.
Dome growth has been accompanied by almost continuous minor explosions,
with periodic lava extrusion, larger explosions, pyroclastic flows, and
lahars.

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 Semeru continued to erupt during 4-11 May. Avalanches
of material traveled 200-300 m SE down the Kobokan drainage on 6 May.
Gray-and-white plumes rose 200-500 m above the summit and drifted S during
8-9 May. Avalanches of material traveled as far as 700 m down the Kobokan
drainage. 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/

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

AVO lowered the Aviation Color Code to Yellow and the Volcano Alert Level
to Advisory for Semisopochnoi on 7 May, noting that no ash emissions had
been observed nor explosions recorded since 26 April. Sulfur dioxide
emissions were recorded on 1 and 5 May, signifying continued unrest. Steam
plumes were visible rising from the N crater of Mt. Cerberus on 7 May.

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/

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 30 April-7 May. 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 4-11 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 drifting in multiple directions. Daily
avalanches descended 500-1,500 m down the E and SE flanks. At 1119 on 6 May
an ash plume rose 2 km above the summit and drifted E. At 0908 and 1519 on
7 May ash plumes rose 3 km and drifted E. Ash plumes rose 1-2.8 km and
drifted E, WNW, and W at 1044, 1656, and 1841 on 8 May; plumes were also
seen on 9 May. At 0747 on 10 May an ash plume rose 2.5 km and drifted SW.
Ash plumes on 11 May rose 700 m and drifted W at 0712, and rose 1.5 km and
drifted E at 1428. 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

On 6 May government authorities lowered the Alert Level to Orange for
SoufriÃ¨re St. Vincent (often simply referred to as â??La Soufriereâ??) based on
recommendations from University of the West Indies Seismic Research Centre
(UWI-SRC). The public was allowed to return to their homes in the Yellow
and Orange zones, though access to the Red Zone remained restricted.
UWI-SRC noted that over the previous few days continuing lahars had
mobilized boulders 5 m in diameter and were steamy in areas where they
contacted hot deposits. A small lahar signal was recorded at 0740 on 7 May.
Sulfur dioxide emissions were measured from a boat near the W coast,
yielding a flux of 208 tons per day on 9 May. Seismicity remained low
through 11 May with only a few long-period earthquakes recorded by the
seismic network.

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 35 explosions at Suwanosejima's Ontake Crater produced
eruption plumes that rose as high as 2.4 km above the crater rim during 30
April-7 May. Large volcanic bombs were ejected 700 m from the crater.
Crater incandescence was visible nightly. 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/

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End of Volcano Digest - 10 May 2021 to 14 May 2021 (#2021-48)
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