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GVP/USGS Weekly Volcanic Activity Report
18-24 April 2007
http://www.volcano.si.edu/reports/usgs/
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New Activity/Unrest: | Concepción, Nicaragua | Lopevi, Vanuatu | Nevado
del Huila, Columbia | Piton de la Fournaise, Reunion Island
Ongoing Activity: | Anatahan, Mariana Islands | Bulusan, Philippines |
Chikurachki, Russia | Fuego, Guatemala | Karymsky, Russia | Kilauea, USA
| Kliuchevskoi, Russia | Rabaul, Papua New Guinea | Reventador, Ecuador
| Santa María, Guatemala | Shiveluch, Russia | Soufrière Hills,
Montserrat | St. Helens, USA | Tungurahua, Ecuador | Ubinas, Perú
New Activity/Unrest
CONCEPCIÓN Nicaragua 11.538°N, 85.622°W; summit elev. 1,700 m
INETER reported that explosions in the crater of Concepción on 22 April
produced ash-and-gas plumes that drifted WSW.
Geologic Summary. Volcán Concepción is one of Nicaragua's highest
volcanoes and is also one of its most active. The symmetrical volcano
forms the NW half of the dumbbell-shaped island of Ometepe in Lake
Nicaragua. Concepción is connected to neighboring Madera volcano by a
narrow isthmus. N-S-trending fractures cutting across the volcano are
associated with spatter cones, cinder cones, and maars located on the
middle N flank and on the lower S flank down to Lake Nicaragua.
Concepción has had frequent moderate explosive eruptions in the past
century, most of which have originated from a small summit crater.
Source: Instituto Nicaragüense de Estudios Territoriales (INETER)
http://www.ineter.gob.ni/
Concepción Information from the Global Volcanism Program
http://www.volcano.si.edu/world/volcano.cfm?vnum=1404-12=
LOPEVI Central Islands, Vanuatu 16.507°S, 168.346°E; summit elev. 1,413 m
Based on pilot reports and satellite imagery, the Wellington VAAC
reported that ash plumes from Lopevi rose to altitudes of 2.4-4.6 km
(8,000-15,000 ft) a.s.l. during 21-24 April. Plumes drifted E on 21 April.
Geologic Summary. The small 7-km-wide conical island of Lopevi is one of
Vanuatu's most active volcanoes. A small summit crater containing a
cinder cone is breached to the NW and tops an older cone that is rimmed
by the remnant of a larger crater. The basaltic-to-andesitic volcano has
been active during historical time at both summit and flank vents,
primarily on the NW and SE sides, producing moderate explosive eruptions
and lava flows that reached the coast. Historical eruptions at the
1,413-m-high volcano date back to the mid-19th century. The island was
evacuated following eruptions in 1939 and 1960. The latter eruption,
from a NW-flank fissure vent, produced a pyroclastic flow that swept to
the sea and a lava flow that formed a new peninsula on the western coast.
Source: Wellington Volcanic Ash Advisory Center (VAAC)
http://www.ssd.noaa.gov/VAAC/OTH/NZ/messages.html
Lopevi Information from the Global Volcanism Program
http://www.volcano.si.edu/world/volcano.cfm?vnum=0507-05=
NEVADO DEL HUILA Columbia 2.93°N, 76.03°W; summit elev. 5,365 m
Based on satellite imagery, the Washington VAAC reported that an ash
eruption from Nevado del Huila on 18 April produced a plume that drifted
SW and dissipated. On 22 April, INGEOMINAS reported that during aerial
observations, fumarolic activity was observed from a fissure first noted
on 19 February. The fissure was approximately 2.3 km long and 0.2 km
wide. A resultant plume rose to an altitude of 10.4 km (34,100 ft)
a.s.l. Another fissure, extending about 2 km from the SW to the NE
sector of Pico Central, also produced fumarolic emissions. Mudflows in
the Páez and Símbola rivers originating on Pico Central primarily swept
through the Oso ravine on the E flank and Bellavista ravine on the W flank.
According to news articles, the eruption during 17-18 April caused
damage to houses and destroyed 19 bridges along the Páez and Símbola
rivers. Several kilometers of a highway, used to transport goods and
medicines to the population, were also destroyed. INGEOMINAS noted that
there were no reported deaths or injuries as a result of the eruption.
Geologic Summary. Nevado del Huila, the highest active volcano in
Colombia, is an elongated N-S-trending volcanic chain mantled by a
glacier icecap. The andesitic-dacitic volcano was constructed within a
10-km-wide caldera. Volcanism at Nevado del Huila has produced six
volcanic cones whose ages in general migrated from south to north. Two
glacier-free lava domes lie at the southern end of the Huila volcanic
complex. The first historical eruption from this little known volcano
took place in the 16th century. Two persistent steam columns rise from
the central peak, and hot springs are also present.
Sources: Instituto Colombiano de Geología y Minería (INGEOMINAS)
http://www.ingeominas.gov.co/,
Washington Volcanic Ash Advisory Center (VAAC)
http://www.ssd.noaa.gov/VAAC/messages.html,
Associated Press
http://news.yahoo.com/s/ap/20070418/ap_on_re_la_am_ca/colombia_volcano_3,
Associated Press
http://news.yahoo.com/s/ap/20070420/ap_on_re_la_am_ca/colombia_volcano_1
Nevado del Huila Information from the Global Volcanism Program
http://www.volcano.si.edu/world/volcano.cfm?vnum=1501-05=
PITON DE LA FOURNAISE Réunion Island, Indian Ocean 21.23°S, 55.71°E;
summit elev. 2,631 m
OVPDLF reported that the eruption of Piton de la Fournaise from the
S-part of the Grand Brûlé continued during 18-24 April. Tremor in this
area remained very low throughout the reporting period. On 22 April, a
large plume was visible from where lava flows met the sea. On 23 April,
abundant lava flows in Grand Brûlé traveled in lava tubes. A collapsed
lava-tube ceiling resulted in the formation of a hornito.
Geologic Summary. The massive Piton de la Fournaise shield volcano on
the island of Réunion is one of the world's most active volcanoes. Most
historical eruptions have originated from the summit and flanks of
Dolomieu, a 400-m-high lava shield that has grown within the youngest of
three large calderas. This latter caldera is 8 km wide and is breached
to below sea level on the eastern side. More than 150 eruptions, most of
which have produced fluid basaltic lava flows within the caldera, have
been documented since the 17th century.
Source: Observatoire Volcanologique du Piton de la Fournaise (OVPDLF)
http://ovpf.univ-reunion.fr/
Piton de la Fournaise Information from the Global Volcanism Program
http://www.volcano.si.edu/world/volcano.cfm?vnum=0303-02=
Ongoing Activity
ANATAHAN Mariana Islands, central Pacific Ocean 16.35°N, 145.67°E;
summit elev. 788 m
Based on satellite imagery and aerial observation on 15 April,
Anatahan’s crater lake emitted diffuse steam-and-gas plumes. Tremor
increased and remained elevated on 20 April.
Geologic Summary. The elongate, 9-km-long island of Anatahan in the
central Mariana Islands consists of large stratovolcano with a 2.3 x 5
km, E-W-trending compound summit caldera. The larger western caldera is
2.3 x 3 km wide, and its western rim forms the island's 790-m high
point. Ponded lava flows overlain by pyroclastic deposits fill the floor
of the western caldera, whose SW side is cut by a fresh-looking smaller
crater. The 2-km-wide eastern caldera contained a steep-walled inner
crater prior to the 2003 eruption whose floor was only 68 m above sea
level. Sparseness of vegetation on the most recent lava flows on
Anatahan had indicated that they were of Holocene age, but the first
historical eruption of Anatahan did not occur until May 2003, when a
large explosive eruption took place forming a new crater inside the
eastern caldera.
Source: Emergency Management Office of the Commonwealth of the Mariana
Islands and the US Geological Survey Hawaiian Volcano Observatory
http://hvo.wr.usgs.gov/cnmi/index.html
Anatahan Information from the Global Volcanism Program
http://www.volcano.si.edu/world/volcano.cfm?vnum=0804-20=
BULUSAN Luzon, Philippines 12.770°N, 124.05°E; summit elev. 1,565 m
PHIVOLCS reported on 17 April that seismicity from Bulusan increased
significantly during 16-17 April. Ground deformation surveys conducted
in March and April indicated 4 mm of inflation on the NNE flank. Steam
plumes from the crater and fissures rose to altitudes of 1.8 km (5,900
ft) a.s.l. and drifted WSW.
Geologic Summary. Luzon's southernmost volcano, Bulusan, was constructed
within the 11-km-diameter dacitic Irosin caldera, which was formed more
than 36,000 years ago. A broad, flat moat is located below the prominent
SW caldera rim; the NE rim is buried by the andesitic Bulusan 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 of Bulusan volcano 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 at Bulusan since the mid-19th century.
Source: Philippine Institute of Volcanology and Seismology (PHIVOLCS)
http://www.phivolcs.dost.gov.ph/
Bulusan Information from the Global Volcanism Program
http://www.volcano.si.edu/world/volcano.cfm?vnum=0703-01=
CHIKURACHKI Kuril Islands, Russia 50.325°N, 155.458°E; summit elev. 1,816 m
KVERT reported that bursts of volcanic bombs from Chikurachki were
observed by hunters on 15 April. Ash plumes were seen on satellite
imagery drifting SE on 14 April and WNW during 15-16 April. Ash plumes
rose to altitudes of 3.8 km (12,500 ft) a.s.l. and drifted N on 18
April. The Level of Concern Color Code remained at Orange
<http://www.avo.alaska.edu/color_codes.php>.
Geologic Summary. Chikurachki, the highest volcano on Paramushir Island
in the northern Kuriles, is actually a relatively small cone constructed
on a high Pleistocene volcanic edifice. Oxidized scoria deposits
covering the upper part of the young cone give it a distinctive red
color. Lava flows from 1,816-m-high Chikurachki reached the sea and form
capes on the NW coast; several young lava flows also emerge from beneath
the scoria blanket on the eastern flank. The more erosionally modified
Tatarinov group of six volcanic centers is located immediately to the S
of Chikurachki. Tephrochronology gives evidence of only one eruption in
historical time from Tatarinov, although its southern cone contains a
sulfur-encrusted crater with fumaroles that were active along the margin
of a crater lake until 1959.
Source: Kamchatkan Volcanic Eruption Response Team (KVERT)
http://www.kscnet.ru/ivs/kvert/updates.shtml
FUEGO Guatemala 14.47°N, 90.88°W; summit elev. 3,763 m
INSIVUMEH reported that on 20 and 23 April, Strombolian activity was
observed at Fuego; incandescent material was ejected about 50-75 m above
the summit and blocks descended 300 m down the S and W flanks. On 20
April, sounds resembling locomotives accompanied the eruption, and lava
overflowed the crater on the S flank and traveled 100 m. The Washington
VAAC reported that an intense hotspot seen on satellite imagery on 21
April was likely caused by a lava flow to the SW, according to
information from INSIVUMEH. A plume drifting SW was also visible on
satellite imagery and may have been a result of fires started by lava
flows; the plume may have also contained light ash and gas. On 23 April,
INSIVUMEH reported that pyroclastic flows and incandescent avalanches
traveled down SE and SW ravines. Ash explosions caused light ashfall in
areas S of the volcano and fumarolic and gas plumes rose to an altitude
of 4 km (13,000 ft) a.s.l.
Geologic Summary. Volcán Fuego, one of Central America's most active
volcanoes, is one of three large stratovolcanoes overlooking Guatemala's
former capital, Antigua. The scarp of an older edifice, Meseta, lies
between 3,763-m-high Fuego and its twin volcano to the N, Acatenango.
Construction of Meseta volcano continued until the late Pleistocene or
early Holocene, after which growth of the modern Fuego volcano continued
the southward migration of volcanism that began at Acatenango. Frequent
vigorous historical eruptions have been recorded at Fuego since the
onset of the Spanish era in 1524, and have produced major ashfalls,
along with occasional pyroclastic flows and lava flows. The last major
explosive eruption from Fuego took place in 1974, producing spectacular
pyroclastic flows visible from Antigua.
Sources: Instituto Nacional de Sismologia, Vulcanologia, Meteorologia, e
Hidrologia (INSIVUMEH)
http://www.insivumeh.gob.gt/geofisica/boletin%20formato.htm,
Washington Volcanic Ash Advisory Center (VAAC)
http://www.ssd.noaa.gov/VAAC/messages.html
Fuego Information from the Global Volcanism Program
http://www.volcano.si.edu/world/volcano.cfm?vnum=1402-09=
KARYMSKY Kamchatka Peninsula, Russia 54.05°N, 159.43°E; summit elev. 1,536 m
Seismic activity at Karymsky was above background levels during 13-20
April. Ash plumes from explosions occurred during 13-20 April and may
have reached altitudes of 4 km (13,000 ft) a.s.l. during 15-16 April and
drifted E. Based on visual observation, a gas-and-steam plume rose to an
altitude of 2.5 km (8,200 ft) a.s.l. on 19 April and a possible new lava
flow was seen on the SW flank. A thermal anomaly in the crater was
detected on satellite imagery during 14-16 April. Based on pilot
reports, satellite imagery, and observations in the
Petropavlovsk-Kamchatsky Flight Information Region (FIR), the Tokyo VAAC
reported that an ash plume rose to an altitude of 7.6 (25,000 ft) a.s.l.
and drifted SE. The Level of Concern Color Code remained at Orange
<http://www.avo.alaska.edu/color_codes.php>.
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 about 7,600-7,700 radiocarbon years ago.
Construction of the Karymsky stratovolcano began about 2,000 years
later. The latest eruptive period began about 500 years ago, following a
2,300-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. Most seismicity preceding Karymsky
eruptions has originated beneath Akademia Nauk caldera, which is located
immediately S of Karymsky volcano and erupted simultaneously with
Karymsky in 1996.
Sources: Kamchatkan Volcanic Eruption Response Team (KVERT)
http://www.kscnet.ru/ivs/kvert/updates.shtml,
Tokyo Volcanic Ash Advisory Center (VAAC)
http://www.ssd.noaa.gov/VAAC/OTH/JP/messages.html
Karymsky Information from the Global Volcanism Program
http://www.volcano.si.edu/world/volcano.cfm?vnum=1000-13=
KILAUEA Hawaii, USA 19.43°N, 155.29°W; summit elev. 1,222 m
During 18-24 April, lava from Kilauea continued to flow SE across a lava
delta into the ocean at the Kamokuna entry, but lava was not seen
entering the ocean at East Lae'apuki. Incandescence was intermittently
visible from several breakouts on the Pulama pali and from several vents
in the Pu'u 'O'o crater. Earthquake activity was scattered at the summit
and S-flank areas. Tremor remained at moderate levels.
Geologic Summary. Kilauea, one of five coalescing volcanoes that
comprise the island of Hawaii, is one of the world’s most active
volcanoes. Eruptions at Kilauea originate primarily from the summit
caldera or along one of the lengthy E and SW rift zones that extend from
the caldera to the sea. About 90% of the surface of Kilauea is formed by
lava flows less than about 1,100 years old; 70% of the volcano's surface
is younger than 600 years. The latest Kilauea eruption began in January
1983 along the E rift zone. This long-term ongoing eruption from Pu`u
`O`o-Kupaianaha has produced lava flows that have traveled 11-12 km from
the vents to the sea, paving broad areas on the S flank of Kilauea and
adding new land beyond the former coastline.
Source: US Geological Survey Hawaiian Volcano Observatory
http://volcano.wr.usgs.gov/hvostatus.php
Kilauea information from the Global Volcanism Program
http://www.volcano.si.edu/world/volcano.cfm?vnum=1302-01-
KLIUCHEVSKOI Kamchatka Peninsula, Russia 56.06°N, 160.64°E; summit elev.
4,835 m
During 13-20 April, Strombolian activity occurred at Kliuchevskoi, based
on observations and video data. Seismic activity continued above
background levels and a thermal anomaly in the crater was detected on
satellite imagery. Fumarolic activity intensified during 15 and 17-18
April. Gas-and-steam plumes possibly containing small amounts of ash
rose to altitudes of 6.3-7.2 km (20,700-23,600 ft) a.s.l. during 15 and
17-18 April and drifted in multiple directions. Based on pilot reports,
satellite imagery, and observations in the Petropavlovsk-Kamchatsky
Flight Information Region (FIR), the Tokyo VAAC reported several
E-drifting ash plumes. They rose to altitudes of 5.2 (17,000 ft) a.s.l.
and 8.8 km (29,000 ft) on 18 and 22 April, respectively. On 24 April,
KVERT reported mudflows and phreatic activity at lava flow fronts on the
NW flank. Resultant ash plumes rose from the lava flow fronts to an
altitude of 3.5 km (11,500 ft) a.s.l. The Level of Concern Color Code
remained at Orange <http://www.avo.alaska.edu/color_codes.php>.
Geologic Summary. Kliuchevskoi is Kamchatka's highest and most active
volcano. Since its origin about 7,000 years ago, the beautifully
symmetrical, 4,835-m-high basaltic stratovolcano has produced frequent
moderate-volume explosive and effusive eruptions without major periods
of inactivity. More than 100 flank eruptions have occurred during the
past 3,000 years, mostly on the NE and SE flanks of the conical volcano
between 500 m and 3,600 m elevation. The morphology of its 700-m-wide
summit crater has been frequently modified by historical eruptions,
which have been recorded since the late-17th century. Historical
eruptions have originated primarily from the summit crater, but have
also included major explosive and effusive eruptions from flank craters.
Sources: Kamchatkan Volcanic Eruption Response Team (KVERT)
http://www.kscnet.ru/ivs/kvert/updates.shtml,
Kamchatkan Volcanic Eruption Response Team (KVERT) via the Volcano
Listserv http://www.volcano.si.edu/reports/volclist/,
Tokyo Volcanic Ash Advisory Center (VAAC)
http://www.ssd.noaa.gov/VAAC/OTH/JP/messages.html
Kliuchevskoi Information from the Global Volcanism Program
http://www.volcano.si.edu/world/volcano.cfm?vnum=1000-26=
RABAUL New Britain Island, Papua New Guinea 4.271°S, 152.203°E; summit
elev. 688 m
RVO reported that during 16-25 April, white-to-gray emissions from
Rabaul caldera's Tavurvur cone generated plumes that rose a few hundred
meters and drifted multiple directions. Based on reports from RVO and
satellite imagery, the Darwin VAAC reported that a diffuse plume rose to
an altitude of 1.5 km (5,000 ft) a.s.l. on 18 April and drifted SW.
Occasionally during 18-23 April, moderately-sized explosions led to
darker gray plumes. During 22-25 April, light ashfall was reported in
Rabaul town. Weak roaring noises occasionally accompanied the emissions.
A slight glow was seen from crater at night and small amounts of
incandescent material were rarely ejected from the crater during 16-23
April.
Geologic Summary. The low-lying Rabaul caldera on the tip of the Gazelle
Peninsula at the NE end of New Britain forms a broad sheltered harbor.
The outer flanks of the 688-m-high asymmetrical pyroclastic shield
volcano are formed by thick pyroclastic-flow deposits. The 8 x 14 km
caldera is widely breached on the E, where its floor is flooded by
Blanche Bay. Two major Holocene caldera-forming eruptions at Rabaul took
place as recently as 3,500 and 1,400 years ago. Three small
stratovolcanoes lie outside the northern and NE caldera rims.
Post-caldera eruptions built basaltic-to-dacitic pyroclastic cones on
the caldera floor near the NE and western caldera walls. Several of
these, including Vulcan cone, which was formed during a large eruption
in 1878, have produced major explosive activity during historical time.
A powerful explosive eruption in 1994 occurred simultaneously from
Vulcan and Tavurvur volcanoes and forced the temporary abandonment of
Rabaul city.
Sources: Steve Saunders, Rabaul Volcano Observatory,
Darwin Volcanic Ash Advisory Centre (VAAC)
http://www.ssd.noaa.gov/VAAC/OTH/AU/messages.html
Rabaul Information from the Global Volcanism Program
http://www.volcano.si.edu/world/volcano.cfm?vnum=0502-14=
REVENTADOR Ecuador 0.078°S, 77.656°W, summit elev. 3,562 m
On 18, 20, and 23 April, steam-and-gas emissions from Reventador hung
near the summit. On 18 April, a plume was seen drifting NW on satellite
imagery. On 20 April, a bluish haze of gases was observed. Clouds
occasionally inhibited views of the summit during 18-24 April.
Geologic Summary. Reventador is the most frequently active of a chain of
Ecuadorian volcanoes in the Cordillera Real, well E of the principal
volcanic axis. It is a forested stratovolcano that rises above the
remote jungles of the western Amazon basin. A 3-km-wide caldera breached
to the E was formed by edifice collapse and is partially filled by a
young, unvegetated stratovolcano that rises about 1,300 m above the
caldera floor. Reventador has been the source of numerous lava flows as
well as explosive eruptions that were visible from Quito in historical
time. Frequent lahars in this region of heavy rainfall have constructed
a debris plain on the eastern floor of the caldera.
Source: Instituto Geofísico-Escuela Politécnica Nacional
http://www.igepn.edu.ec/
Reventador Information from the Global Volcanism Program
http://www.volcano.si.edu/world/volcano.cfm?vnum=1502-01=
SANTA MARÍA Guatemala 14.756°N, 91.552°W; summit elev. 3,772 m
INSIVUMEH reported that explosions from Santa María's Santiaguito lava
dome complex on 20 and 23 April occasionally produced ash plumes that
rose to altitudes of 5.3 km (17,400 ft) a.s.l. The plumes drifted SW and
ashfall was reported from areas up to 9 km to the SW. On 23 April, lava
flows on the SW and NE flanks of Caliente dome produced small landslides
composed of blocks.
Based on satellite imagery, the Washington VAAC reported that diffuse
ash plumes on 18, 23, and 24 April, and gas plumes possibly containing
ash on 20 April, drifted SW and W.
Geologic Summary. Symmetrical, forest-covered Santa María volcano is one
of a chain of large stratovolcanoes that rises dramatically above the
Pacific coastal plain of Guatemala. The stratovolcano has a
sharp-topped, conical profile that is cut on the SW flank by a large,
1-km-wide crater, which formed during a catastrophic eruption in 1902
and extends from just below the summit to the lower flank. The renowned
Plinian eruption of 1902 followed a long repose period and devastated
much of SW Guatemala. The large 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
westward-younging vents, accompanied by almost continuous minor
explosions and periodic lava extrusion, larger explosions, pyroclastic
flows, and lahars.
Sources: Instituto Nacional de Sismologia, Vulcanologia, Meteorologia, e
Hidrologia (INSIVUMEH)
http://www.insivumeh.gob.gt/geofisica/boletin%20formato.htm,
Washington Volcanic Ash Advisory Center (VAAC)
http://www.ssd.noaa.gov/VAAC/messages.html
Santa María Information from the Global Volcanism Program
http://www.volcano.si.edu/world/volcano.cfm?vnum=1402-03=
SHIVELUCH Kamchatka Peninsula, Russia 56.653°N, 161.360°E; summit elev.
3,283 m
KVERT reported that seismic activity at Shiveluch continued above
background levels during 13-20 April. Based on seismic interpretation,
observation, and video data, ash-and-steam plumes possibly rose to
altitudes of 5.5-6.5 km (18,000-21,300 ft) a.s.l. throughout the
reporting period. Plumes were seen on satellite imagery drifting E, SE,
and S and a thermal anomaly was present. Base on pilot reports,
satellite imagery, KEMSD, and observations from the
Petropavlovsk-Kamchatsky Flight Information Region (FIR), the Tokyo VAAC
reported that ash plumes rose to altitudes of 4.6-6.1 km (15,000-20,000
ft) a.s.l. during 18-22 April. They drifted E. The Level of Concern
Color Code remained at Orange <http://www.avo.alaska.edu/color_codes.php>.
Geologic Summary. The high, isolated massif of Shiveluch volcano (also
spelled Sheveluch) rises above the lowlands NNE of the Kliuchevskaya
volcano group and forms one of Kamchatka's largest and most active
volcanoes. The currently active Molodoy Shiveluch lava-dome complex was
constructed during the Holocene within a large horseshoe-shaped caldera
formed by collapse of the massive late-Pleistocene Strary Shiveluch
volcano. At least 60 large eruptions of Shiveluch have occurred during
the Holocene, making it the most vigorous andesitic volcano of the
Kuril-Kamchatka arc. Frequent collapses of lava-dome complexes, most
recently in 1964, have produced large debris avalanches whose deposits
cover much of the floor of the breached caldera. During the 1990s,
intermittent explosive eruptions took place from a new lava dome that
began growing in 1980. The largest historical eruptions from Shiveluch
occurred in 1854 and 1964.
Sources: Kamchatkan Volcanic Eruption Response Team (KVERT)
http://www.kscnet.ru/ivs/kvert/updates.shtml,
Tokyo Volcanic Ash Advisory Center (VAAC)
http://www.ssd.noaa.gov/VAAC/OTH/JP/messages.html
Shiveluch Information from the Global Volcanism Program
http://www.volcano.si.edu/gvp/world/volcano.cfm?vnum=1000-27=
SOUFRIÈRE HILLS Montserrat, West Indies 16.72°N, 62.18°W; summit elev.
1,052 m
During 13-20 April, visual observations suggested that lava-dome growth
at Soufrière Hills continued at a reduced rate. Material originating
from the lava dome’s growing E-facing shear lobe was shed down the Tar
River Valley. Heavy rains resulted in lahars in several drainages 16-17
April. During 18-20 April, a gas plume drifted N and NE and a bluish
haze containing sulfur dioxide was observed flowing down the N flanks
due to light winds coming from the S.
Geologic Summary. The complex, dominantly andesitic Soufrière Hills
volcano occupies the southern half of the island of Montserrat. The
summit area consists primarily of a series of lava domes emplaced along
an ESE-trending zone. English's Crater, a 1-km-wide crater breached
widely to the east, was formed during an eruption about 4000 years ago
in which the summit collapsed, producing a large submarine debris
avalanche. Block-and-ash flow and surge deposits associated with dome
growth predominate in flank deposits at Soufrière Hills. Non-eruptive
seismic swarms occurred at 30-year intervals in the 20th century, but
with the exception of a 17th-century eruption that produced the Castle
Peak lava dome, no historical eruptions were recorded on Montserrat
until 1995. Long-term small-to-moderate ash eruptions beginning in that
year were later accompanied by lava-dome growth and pyroclastic flows
that forced evacuation of the southern half of the island and ultimately
destroyed the capital city of Plymouth, causing major social and
economic disruption.
Source: Montserrat Volcano Observatory http://www.mvo.ms/
Soufrière Hills Information from the Global Volcanism Program
http://www.volcano.si.edu/world/volcano.cfm?vnum=1600-05=
ST. HELENS Washington, USA 46.20°N, 122.18°W; summit elev. 2,549 m
Data from deformation-monitoring instruments and observations from a
remote camera showed that during 18-24 April lava-dome growth at Mount
St. Helens continued. Seismicity persisted at low levels, punctuated by
M 1.5-2.5, and occasionally larger, earthquakes. In some instances,
clouds inhibited visual observations.
Geologic Summary. Prior to 1980, Mount St. Helens formed a conical,
youthful volcano sometimes known as the Fuji-san of America. During the
1980 eruption the upper 400 m of the summit was removed by slope
failure, leaving a 2 x 3.5 km horseshoe-shaped crater now partially
filled by a lava dome. Mount St. Helens was formed during nine eruptive
periods beginning about 40-50,000 years ago, and has been the most
active volcano in the Cascade Range during the Holocene. The modern
edifice was constructed during the last 2,200 years, when the volcano
produced basaltic as well as andesitic and dacitic products from summit
and flank vents. Historical eruptions in the 19th century originated
from the Goat Rocks area on the N flank, and were witnessed by early
settlers.
Source: US Geological Survey Cascades Volcano Observatory
http://vulcan.wr.usgs.gov/Volcanoes/MSH/CurrentActivity/framework.html
St. Helens Information from the Global Volcanism Program
http://www.volcano.si.edu/world/volcano.cfm?vnum=1201-05-
TUNGURAHUA Ecuador 1.47°S, 78.44°W; summit elev. 5,023 m
IG reported that during 17-18 April, Strombolian activity from
Tungurahua was observed; incandescent material was ejected about 500 m
above the summit and blocks descended down the flanks. Lahars carring
large blocks NW down the Mandur gorge caused a road closing on 19 April.
During 17-24 April, ash plumes rose to altitudes of 5.5-9 km
(18,000-29,500 ft) a.s.l. and drifted W and N. Ashfall was reported from
areas mainly to the N, NW, W, and SW during 17, 19, 21-22, and 24 April.
On 23 April, lahars were observed in several gorges to the NW. Clouds
occasionally inhibited views of the summit during the reporting period.
Geologic Summary. The steep-sided Tungurahua stratovolcano towers more
than 3 km above its northern base. It sits ~140 km S of Quito, Ecuador’s
capital city, and is one of Ecuador's most active volcanoes. Historical
eruptions have been restricted to the summit crater. They have been
accompanied by strong explosions and sometimes by pyroclastic flows and
lava flows that reached populated areas at the volcano's base. The last
major eruption took place from 1916 to 1918, although minor activity
continued until 1925. The latest eruption began in October 1999 and
prompted temporary evacuation of the town of Baños on the N side of the
volcano.
Source: Instituto Geofísico-Escuela Poltécnica Nacional
http://www.igepn.edu.ec/
Tungurahua Information from the Global Volcanism Program
http://www.volcano.si.edu/world/volcano.cfm?vnum=1502-08=
UBINAS Perú 16.355°S, 70.903°W; summit elev. 5,672 m
INGEMMET reported that on 18 April, explosions from Ubinas produced gas
and ash plumes to altitudes of 5.9-7.7 km (19,400-25,300 ft) a.s.l.
Plumes drifted SW. Based on significant meteorological (SIGMET) notices,
satellite imagery, and pilot reports, the Buenos Aires VAAC reported
that ash plumes rose to altitudes of 5.5-7 km (18,000-28,000 ft) a.s.l.
on 17, 18, 22, and 24 April. Plumes drifted NW, SW, and SE.
Geologic Summary. A small, 1.2-km-wide caldera that cuts the top of
Ubinas, Peru's most active volcano, gives it a truncated appearance.
Ubinas is the northernmost of three young volcanoes located along a
regional structural lineament about 50 km behind the main volcanic front
of Peru. The upper slopes of the stratovolcano, composed primarily of
Pleistocene andesitic lava flows, 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 of Ubinas extend 10 km from
the volcano. Widespread plinian pumice-fall deposits from Ubinas include
some of Holocene age. Holocene lava flows are visible on the volcano's
flanks, but historical activity, documented since the 16th century, has
consisted of intermittent minor explosive eruptions.
Sources: Instituto Geológical Minero y Metalúrgico (INGEMMET)
http://www.ingemmet.gob.pe/,
Buenos Aires Volcanic Ash Advisory Center (VAAC)
http://www.ssd.noaa.gov/VAAC/OTH/AG/messages.html
Ubinas Information from the Global Volcanism Program
http://www.volcano.si.edu/world/volcano.cfm?vnum=1504-02=
**+++++++++++++++++++++++++++++++++++++**
**Sally Kuhn Sennert**
**SI/USGS Weekly Volcanic Activity Report Editor**
**Global Volcanism Program**
http://www.volcano.si.edu/reports/usgs/
Smithsonian Institution, National Museum of Natural History
Department of Mineral Sciences, MRC-119
Washington, D.C., 20560
Phone: 202.633.1805
Fax: 202.357.2476
<http://www.volcano.si.edu/reports/usgs/>++++++++++++++++++++++++++++++++++++++++++
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