********************************************
GVP/USGS Weekly Volcanic Activity Report
21-27 February 2007
http://www.volcano.si.edu/reports/usgs/
********************************************
New Activity/Unrest: | Kliuchevskoi, Russia | Nevado del Huila, Columbia
| Stromboli, Italy | Tungurahua, Ecuador | White Island, New Zealand
Ongoing Activity: | Karymsky, Russia | Kilauea, USA | Langila, Papua New
Guinea | Manam, Papua New Guinea | Rabaul, Papua New Guinea | Sangay,
Ecuador | Santa María, Guatemala | Shiveluch, Russia | Soufrière Hills,
Montserrat | St. Helens, USA | Ubinas, Perú
New Activity/Unrest
KLIUCHEVSKOI Kamchatka Peninsula, Russia 56.06°N, 160.64°E; summit elev.
4,835 m
Seismic activity at Kliuchevskoi continued at above background levels
during 16-22 February. Based on observation and video data,
gas-and-steam plumes rose to an altitude of 5.3 km (17,400 ft) a.s.l.
and drifted E. These plumes possibly contained some ash. A thermal
anomaly at the summit was seen on satellite imagery during 16-19 and 21
February. Based on information from KEMSD and satellite imagery, the
Tokyo VAAC reported that eruption plumes possibly reached altitudes of
6.1 km (20,000 ft) a.s.l. and drifted E during 22-23 February.
According to a news article, ash particles up to 2 mm in diameter fell
on the village of Klyuchi, about 40 km N on 26 February.
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
http://www.kscnet.ru/ivs/kvert/updates.shtml,
Tokyo Volcanic Ash Advisory Center (VAAC)
http://www.ssd.noaa.gov/VAAC/OTH/JP/messages.html,
RIA Novosti http://en.rian.ru/russia/20070226/61238497.html
Kliuchevskoi Information from the Global Volcanism Program
http://www.volcano.si.edu/world/volcano.cfm?vnum=1000-26=
NEVADO DEL HUILA Columbia 2.93°N, 76.03°W; summit elev. 5,365 m
INGEOMINAS reported that seismic activity from Nevado del Huila remained
elevated during 21-23 February. On 21 February, steam plumes rose to
altitudes of 5.7 km (18,700 ft) a.s.l. and drifted W. On 24 February,
fumarolic activity from the central and N areas on the volcano was not
seen during aerial observations.
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.
Source: Instituto Colombiano de Geología y Minería (INGEOMINAS)
http://www.ingeominas.gov.co/
Nevado del Huila Information from the Global Volcanism Program
http://www.volcano.si.edu/world/volcano.cfm?vnum=1501-05=
STROMBOLI Aeolian Islands, Italy 38.79°N, 15.21°E; summit elev. 926 m
Based on news reports, lava from Stromboli was observed flowing from two
craters near the summit on 27 February. One lava flow traveled down the
flanks more than 900 m and reached the sea. Several explosions per hour
were audible.
Geologic Summary. Spectacular incandescent nighttime explosions at
Stromboli volcano have long attracted visitors to the "Lighthouse of the
Mediterranean." Stromboli, the NE-most of the Aeolian Islands, has lent
its name to the frequent mild explosive activity that has characterized
its eruptions throughout historical time. The small, 926-m-high island
of Stromboli is the emergent summit of a volcano that grew in two main
eruptive cycles, the last of which formed the western portion of the
island. The active summit vents are located at the head of the Sciara
del Fuoco, a horseshoe-shaped scarp formed as a result of slope failure
that extends to below sea level and funnels pyroclastic ejecta and lava
flows to the NW. Essentially continuous mild Strombolian explosions,
sometimes accompanied by lava flows, have been recorded at Stromboli
since Roman times.
Sources: Deutsche Presse-Agentur
http://news.monstersandcritics.com/europe/news/article_1270023.php/Sirens_sound_as_Stromboli_Volcano_erupts_in_Italy,
United Press International
http://www.upi.com/NewsTrack/Top_News/20070227-114319-5348r/
Stromboli Information from the Global Volcanism Program
http://www.volcano.si.edu/world/volcano.cfm?vnum=0101-04=
TUNGURAHUA Ecuador 1.47°S, 78.44°W; summit elev. 5,023 m
Volcanic tremor and long-period earthquakes from Tungurahua began at
approximately 2100 on 23 February. On 24 February at 0310, tremor
amplitude increased. Incandescent material was ejected 800 m above the
summit and fell on the flanks about 1 km below the summit. An eruption
plume drifted NW and roaring noises were audible. Gravel and sand-sized
ash reportedly fell at Pillate (8 km W) and San Juan (40 km WSW) and in
places accumulated up to 3 mm thick. Deposits of ash 2 mm thick were
reported from Bilbao (8 km W), Cotaló (8 km NW), Manzano (8 km SW), and
Choglontus (W).
On 25 February, 12 moderate to large explosions occurred according to
seismic interpretation. Based on satellite imagery, MWO, pilot reports,
and the IG, the Washington VAAC reported that ash plumes rose to
altitudes of 7.6-12.2 km (25,000-40,000 ft) a.s.l. during 24-25
February. Plumes drifted SW and NW.
On 26 February, a plume with no ash content rose to 6 km (19,700 ft)
a.s.l. and drifted W. Later that day, two explosions produced ash plumes
that 7 km (23,000 ft) a.s.l. and again drifted W. On 27 February,
incandescent material was ejected above the summit and fell on the
flanks about 500 m down the flanks. Noises produced by material rolling
down the flanks and “cannon shots” were heard during 25-27 February.
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.
Sources: Instituto Geofísico-Escuela Poltécnica Nacional
http://www.igepn.edu.ec/,
Washington Volcanic Ash Advisory Center (VAAC)
http://www.ssd.noaa.gov/VAAC/messages.html
Tungurahua Information from the Global Volcanism Program
http://www.volcano.si.edu/world/volcano.cfm?vnum=1502-08=
WHITE ISLAND Bay of Plenty, New Zealand 37.52°S, 177.78°E; summit elev.
321 m
Based on pilot and volcanologist reports, the Wellington VAAC reported
that a steam plume from White Island rose to an altitude of 3.0 km
(10,000 ft) a.s.l. on 23 February.
Geologic Summary. The uninhabited 2 x 2.4 km White Island, one of New
Zealand's most active volcanoes, is the emergent summit of a 16 x 18 km
submarine volcano in the Bay of Plenty about 50 km offshore of North
Island. The 321-m-high island consists of two overlapping
stratovolcanoes; the summit crater appears to be breached to the SE
because the shoreline corresponds to the level of several notches in the
SE crater wall. Throughout the short historical period beginning in 1826
the volcano has had long periods of continuous hydrothermal activity and
steam release, punctuated by small-to-medium eruptions. Its activity
also forms a prominent part of Maori legends. The most recent eruptive
episode, which began on 7 March 2000, included the largest eruption at
White Island in the past 20 years on 27 July.
Source: Wellington Volcanic Ash Advisory Center (VAAC)
http://www.ssd.noaa.gov/VAAC/OTH/NZ/messages.html
White Island Information from the Global Volcanism Program
http://www.volcano.si.edu/world/volcano.cfm?vnum=0401-04=
Ongoing Activity
KARYMSKY Kamchatka Peninsula, Russia 54.05°N, 159.43°E; summit elev. 1,536 m
Seismic activity at Karymsky was above background levels during 16-22
February, with 100-180 shallow earthquakes occurring daily. Ash plumes
may have reached altitudes of 3.0 km (9,900 ft) a.s.l. during the
reporting period. A thermal anomaly in the crater was detected on
satellite imagery during 16-19 February. Based on satellite imagery and
information from KEMSD, the Tokyo VAAC reported that eruption plumes
rose to altitudes of 4.0-5.2 km (13,000-17,000 ft) a.s.l. on 22 and 27
February. 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
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 21-27 February, lava from Kilauea continued to flow from lava
deltas into the ocean at the East Lae'apuki, Kamokuna, and East
Ka'ili'ili entries. Incandescence was intermittently visible from
several breakouts on the pali and from several vents in Pu'u 'O'o's
crater. On 22 February, HVO field crews reported gas jetting from vents
on the S side of Pu’u ‘O’o. Tremor at Kilauea's summit continued at low
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-
LANGILA New Britain Island, Papua New Guinea 5.53°S, 148.42°E; summit
elev. 1,330 m
On 13 and 14 February, eruptive activity at Langila's Crater 2 consisted
of continuous emissions of gray ash plumes. During 15-23 February the
emissions became forceful. Plumes rose to an altitude of 2.3 km (7,500
ft) a.s.l. and drifted SE and SW. Occasional roaring noises were heard
accompanying emissions. Incandescence was observed at the summit.
Geologic Summary. Langila, one of the most active volcanoes of New
Britain, consists of a group of four small overlapping composite cones
on the lower eastern flank of the extinct Talawe volcano. Talawe is the
highest volcano in the Cape Gloucester area of NW New Britain. A
rectangular, 2.5-km-long crater is breached widely to the SE; Langila
volcano was constructed NE of the breached crater of Talawe. An
extensive lava field reaches the coast on the N and NE sides of Langila.
Frequent mild-to-moderate explosive eruptions, sometimes accompanied by
lava flows, have been recorded since the 19th century from three active
craters at the summit of Langila. The youngest and smallest crater (no.
3 crater) was formed in 1960 and has a diameter of 150 m.
Sources: Herman Patia, Rabaul Volcano Observatory,
Darwin Volcanic Ash Advisory Centre (VAAC)
http://www.ssd.noaa.gov/VAAC/OTH/AU/messages.html
Langila Information from the Global Volcanism Program
http://www.volcano.si.edu/world/volcano.cfm?vnum=0502-01=
MANAM offshore New Guinea, Papua New Guinea 4.10°S, 145.06°E; summit
elev. 1,807 m
RVO reported that Manam’s South Crater emitted gray ash plumes during
15-19 February and white vapor plumes on 21 February. Gray ash plumes
continually emitted from Main Crater rose to an altitude of 2.3 km
(7,500 ft) a.s.l. and drifted SE during 19-21 February.
Geologic Summary. The 10-km-wide island of Manam is one of Papua New
Guinea's most active volcanoes. Four large radial valleys extend from
the unvegetated summit of the conical 1,807-m-high stratovolcano to its
lower flanks. These "avalanche valleys," regularly spaced 90 degrees
apart, channel lava flows and pyroclastic avalanches that have sometimes
reached the coast. Five satellitic centers are located near the island's
shoreline. Two summit craters are present; both are active, although
most historical eruptions have originated from the southern crater,
concentrating eruptive products during the past century into the SE
avalanche valley. Frequent historical eruptions have been recorded since
1616.
Source: Herman Patia and Steve Saunders, Rabaul Volcano Observatory
Manam Information from the Global Volcanism Program
http://www.volcano.si.edu/world/volcano.cfm?vnum=0501-02=
RABAUL New Britain Island, Papua New Guinea 4.271°S, 152.203°E; summit
elev. 688 m
RVO reported that during 16-24 February, Rabaul caldera's Tavurvur cone
emitted white vapor plumes that rose to 0.9-3.7 km (3,000-12,000 ft)
a.s.l. and drifted N, W, and E. Ash clouds were emitted on 16, 19, 21,
and 23-24 February and ashfall was reported from surrounding villages on
20 February. Loud roaring noises were occasionally heard. On 22
February, a moderate explosion produced fragments that showered the
flanks. On 27 February, the Darwin VAAC reported that a diffuse plume
was visible on satellite imagery. On 28 February, RVO reported a large
explosion produced an ash plume that rose to an altitude of 2.7 km
(8,900 ft) a.s.l. and drifted NE.
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: Herman Patia and 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=
SANGAY Ecuador 2.03°S, 78.34°W; summit elev. 5,188 m
The Washington VAAC reported eruptions from Sangay based on information
from Guayaquil MWO, IG, pilot reports, and satellite imagery. Ash plumes
reached altitudes of 10.7 km (35,000 ft) a.s.l. on 23 February and 6.4
km (21,000 ft) a.s.l. on 25 February. Plumes drifted S and SW,
respectively.
Geologic Summary. The isolated Sangay volcano, located E of the Andean
crest, is the southernmost of Ecuador's volcanoes, and its most active.
It has been in frequent eruption for the past several centuries. The
steep-sided, 5,230-m-high glacier-covered volcano grew within
horseshoe-shaped calderas of two previous edifices, which were destroyed
by collapse to the E, producing large debris avalanches that reached the
Amazonian lowlands. The modern edifice dates back to at least 14,000
years ago. Sangay towers above the tropical jungle on the E side; on the
other sides flat plains of ash from the volcano have been sculpted by
heavy rains into steep-walled canyons up to 600 m deep. The earliest
report of an historical eruption was in 1628. More or less continuous
eruptions were reported from 1728 until 1916, and again from 1934 to the
present. The more or less constant eruptive activity has caused frequent
changes to the morphology of the summit crater complex.
Source: Washington Volcanic Ash Advisory Center
http://www.ssd.noaa.gov/VAAC/messages.html
Sangay Information from the Global Volcanism Program
http://www.volcano.si.edu/world/volcano.cfm?vnum=1502-09=
SANTA MARÍA Guatemala 14.756°N, 91.552°W; summit elev. 3,772 m
Based on satellite imagery, the Washington VAAC reported that diffuse
ash plumes from Santa María's Santiaguito lava dome complex drifted
mainly W and N during 22, 23, and 25-27 February. INSIVUMEH reported
seven explosions produced ash plumes that rose to altitudes of 4.4-4.6
km (14,400-15,100 ft) a.s.l. and drifted SW on 26 February. Avalanches
occurred from lava-flow fronts on the SW flanks and from the S edge of
Caliente Dome. A hotspot was seen on satellite imagery. On 27 February,
explosions occurring at an approximate rate of 3 per hour produced ash
plumes that reached altitudes of 4.8 km (15,700 ft) a.s.l. Occasionally
explosions were accompanied by pyroclastic flows that traveled SW.
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
Seismic activity at Shiveluch continued above background levels during
16-22 February. Based on seismic interpretation, observation, and video
data, gas-and-ash plumes rose to altitudes of 6 km (19,700 ft) a.s.l.
throughout the reporting period. Plumes drifted S, NW, and N. A large
thermal anomaly was visible on satellite imagery. The Tokyo VAAC
reported eruption plumes to altitudes of 4.6 km (15,000 ft) a.s.l. on 22
February based on information from KEMSD, KVERT, and satellite imagery.
Plumes drifted N. 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
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 16-23 February, lava-dome growth at Soufrière Hills continued and
was concentrated on the E and N sides. Small pyroclastic flows traveled
down the Tar River Valley to the E, Gages to the W, and Tyres Ghaut to
the NW. Ash venting and roaring noises originated from an area above
Gages to the SW, where a new blocky lobe was visible. Moderately-sized
pyroclastic flows traveled E down the Tar River Valley during 24-25 and
27 February. Bright incandescence at the dome was observed during the
reporting period.
Based on satellite data, pilot reports, and information from the MVO,
the Washington VAAC reported continuous ash emissions during 21-27
February. Resultant plumes rose to altitudes of 2.1-6.1 km (7,000-20,000
ft) a.s.l. and drifted mainly NE, NW, and W. A thermal anomaly was
detected in the crater on satellite imagery.
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.
Sources: Montserrat Volcano Observatory http://www.mvo.ms/,
Washington Volcanic Ash Advisory Center (VAAC)
http://www.ssd.noaa.gov/VAAC/messages.html
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 showed that during 21-27
February, the lava dome at Mount St. Helens continued to grow.
Seismicity continued at low levels, punctuated by M 1.5-2.5 and
occasionally larger earthquakes. Inclement weather 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-
UBINAS Perú 16.355°S, 70.903°W; summit elev. 5,672 m
Based on pilot reports, the Buenos Aires VAAC reported continuous
emissions from Ubinas on 21 February. Ash plumes rose to 5.5-6.7 km
(18,000-22,000 ft) a.s.l. and drifted SW.
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.
Source: 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**
Smithsonian Institution
National Museum of Natural History MRC-119
Department of Mineral Sciences
Washington, D.C., 20560
http://www.volcano.si.edu/reports/usgs/
Phone: 202.633.1805
Fax: 202.357.2476
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