GVP/USGS Weekly Volcanic Activity Report 24-30 May 2006

Kristi Diller <Kristi.Diller@xxxxxxx> · Wed, 31 May 2006 16:10:18 -0700

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GVP/USGS Weekly Volcanic Activity Report 24-30 May 2006
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From: Gari Mayberry <mayberry@xxxxxxxxxxxxxx>

GVP/USGS Weekly Volcanic Activity Report
24-30 May 2006
http://www.volcano.si.edu/reports/usgs/

New Activity/Unrest: | Aoba, Vanuatu | Karthala, Comoros Islands 

New Activity/Unrest 

AOBA Vanuatu 15.40°S, 167.83°E; summit elev. 1,496 m

According to news reports, on 28 May aerial observations by scientists from the
Department of Geology and Mines revealed that Lake Voui of Aoba volcano had
changed from blue to red in color. Aoba remains at an Alert level 2, which means
the crater area is restricted. 

Geologic Summary. Aoba is a massive 2,500 cu km basaltic shield volcano that is
the most voluminous volcano of the New Hebrides archipelago. A pronounced
NE-SW-trending rift zone dotted with scoria cones gives the 16 x 38 km island an
elongated form. A broad pyroclastic cone containing three crater lakes is
located at the summit of the Hawaiian-style shield volcano within the youngest
of at least two nested calderas, the largest of which is 6 km in diameter.
Post-caldera explosive eruptions formed the summit craters of Lake Voui (also
spelled Vui) and Lake Manaro Ngoru about 360 years ago. A tuff cone was
constructed within Lake Voui about 60 years later. The latest known flank
eruption, about 300 years ago, destroyed the population of the Nduindui area
near the western coast.

Sources: Commission of Volcanic Lakes (CVL)
http://www.ulb.ac.be/sciences/cvl/aoba/Ambae1.html, 
The Age News
http://www.theage.com.au/news/World/Lake-atop-Vanuatu-volcano-turns-red/2006/05/29/1148754920617.html

KARTHALA Comoros Islands, Indian Ocean 11.75°N, 43.38°E; summit elev. 2,361 m;
All times are local (= UTC + 3 hours)  

According to the Toulouse VAAC, the Meteorology Office and Observatory of
Comores reported an eruption of Karthala of gas and steam on 28 May at about
2105. During 28-29 May from 2300 to 0930, a thin sulfur-dioxide plume extending
60 km NW was visible on satellite imagery. On 29 May, at about 0830,
volcanologists flew above the crater and confirmed that only steam and sulfur
dioxide had been emitted. According to a news article, a lava lake fed by a
central fountain was also observed.

Geologic Summary. The southernmost and largest of the two shield volcanoes
forming Grand Comore Island (also known as Ngazidja), Karthala contains a 3 x 4
km summit caldera generated by repeated collapse. Elongated rift zones extend to
the NNW and SE from the summit of the Hawaiian-style shield, which has an
asymmetrical profile that is steeper to the S. Historical eruptions have
modified the morphology of the compound, irregular summit caldera. More than
twenty eruptions have been recorded since the 19th century from both summit and
flank vents. Many lava flows have reached the sea on both sides of the island,
including during many 19th-century eruptions from the summit caldera and vents
on the northern and southern flanks.

Sources: Toulouse Volcanic Ash Advisory Center
http://www.ssd.noaa.gov/VAAC/OTH/FR/MSG1491426.03.txt, Reuters
http://today.reuters.co.uk/news/newsArticle.aspx?type=scienceNews&storyID=2006-05-30T100721Z_01_L29707275_RTRIDST_0_SCIENCE-COMOROS-VOLCANO-DC.XML&archived=False

Ongoing Activity 

ANATAHAN Mariana Islands, central Pacific Ocean 16.35°N, 145.67°E; summit elev.
788 m; All times are local (= UTC + 10 hours)

Based on a pilot report, the Washington VAAC reported that an ash plume from
Anatahan reached an altitude of 3 km (10,000 ft) a.s.l. on 29 May and drifted W.
Emissions from the E crater of vog (volcanic fog), steam, and a gas plume were
visible on satellite imagery at about 1333 and increased prior to generation of
the ash plume. A report issued from the Washington VAAC on 30 May at 0535
indicated a faint, low-level gas-and-ash plume extending from the summit. 

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.

Sources: Emergency Management Office of the Commonwealth of the Mariana Islands
and the US Geological Survey Hawaiian Volcano Observatory
http://volcanoes.usgs.gov/update.html#cnmi
Washington Volcanic Ash Advisory Center
http://www.ssd.noaa.gov/VAAC/ARCHIVE/ANAT/2006E291935.html

Anatahan Information from the Global Volcanism Program 
http://www.volcano.si.edu/world/volcano.cfm?vnum=0804-20=

BARREN ISLAND Andaman Islands, Indian Ocean, India 12.29°N, 93.88°E; summit
elev. 354 m; All times are local (= UTC + 5 1/2 hours)

Based on a pilot report, the Darwin VAAC reported an ash plume from Barren
Island on 26 May that reached an altitude below 3 km (10,000 ft) a.s.l. and
drifted N at 1230.

Geologic Summary. Barren Island, a possession of India in the Andaman Sea about
135 km NE of Port Blair in the Andaman Islands, is the only historically active
volcano along the N-S-trending volcanic arc extending between Sumatra and Burma
(Myanmar). The 354-m-high island is the emergent summit of a volcano that rises
from a depth of about 2,250 m. The small, uninhabited 3-km-wide island contains
a roughly 2-km-wide caldera with walls 250-350 m high. The caldera, which is
open to the sea on the W, was created during a major explosive eruption in the
late Pleistocene that produced pyroclastic-flow and -surge deposits. The
morphology of a fresh pyroclastic cone that was constructed in the center of the
caldera has varied during the course of historical eruptions. Lava flows fill
much of the caldera floor and have reached the sea along the western coast
during eruptions in the 19th century and more recently in 1991 and 1995.

Source: Darwin Volcanic Ash Advisory Center
http://www.bom.gov.au/products/IDD41295.shtml 

BULUSAN Luzon, Philippines 12.770°N, 124.05°E; summit elev. 1,565 m; All times
are local (= UTC + 8 hours)

A phreatic ash explosion was recorded by the seismograph network at Bulusan
between 2117 and 2130 on 25 May. Light ashfall ranging from trace amounts to
deposits 2 mm thick was reported from the W and SW villages of Bacolod,
Sankayon, Puting Sapa, Rangas, Mapili, Caladgao, and Buraburan in the
municipality of Juban and Bolos in the municipality of Irosin.

PHIVOLCS reported that the ash explosion was more-or-less typical of activity at
Bulusan during its current period of unrest and they expect more explosions to
occur. Bulusan was at Alert Level 1, with a Permanent Danger Zone of 4
kilometers around the summit. 

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
http://www.phivolcs.dost.gov.ph/ 

Bulusan Information from the Global Volcanism Program 
http://www.volcano.si.edu/world/volcano.cfm?vnum=0703-01= 

CLEVELAND Aleutian Islands, USA 52.82°N, 169.95°W; summit elev. 1,730 m

The ash plume from Cleveland observed from the International Space Station on 23
May, drifted SW and had mostly dissipated by 24 May. No further activity was
recorded. On 26 May AVO downgraded the Concern Color Code from Yellow to "Not
Assigned" <http://www.avo.alaska.edu/color_codes.php>.

Geologic Summary. The symmetrical Mount Cleveland stratovolcano is situated at
the western end of the uninhabited dumbbell-shaped Chuginadak Island in the
east-central Aleutians. The 1,730-m-high stratovolcano is the highest of the
Islands of Four Mountains group and is one of the most active in the Aleutians.
Numerous large lava flows descend its flanks. It is possible that some 18th to
19th century eruptions attributed to Carlisle (a volcano located across the
Carlisle Pass Strait to the NW) should be ascribed to Cleveland. In 1944
Cleveland produced the only known fatality from an Aleutian eruption. Recent
eruptions from Mt. Cleveland have been characterized by short-lived explosive
ash emissions, at times accompanied by lava fountaining and lava flows down the
flanks.

Sources: Alaska Volcano Observatory
http://www.avo.alaska.edu/activity/avoreport.php?view=update
Washington Volcanic Ash Advisory Center
http://www.ssd.noaa.gov/VAAC/ARCHIVE/CLEV/2006E241436.html\

Cleveland Information from the Global Volcanism Program
http://www.volcano.si.edu/world/volcano.cfm?vnum=1101-24-

FUEGO Guatemala 14.47°N, 90.88°W; summit elev. 3,763 m

On 29 May, INSIVUMEH reported that fumarolic emissions from Fuego reached a
height of ~125 m above the volcano (~12,750 ft a.s.l.). Lava flows extended ~400
m SW toward the Ceniza River. Avalanches occurred from the lava-flow fronts.
Incandescent material was propelled from the crater tens of meters. Plumes
reached heights of 200 m above the crater (13,000 ft a.s.l.) and dispersed W and NW.

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.

Source: Instituto Nacional de Sismologia, Vulcanologia, Meterologia, e
Hidrologia, http://www.insivumeh.gob.gt/geofisica/boletin%20formato.htm

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

Based on interpretations of seismic and satellite data, KVERT reported that ash
explosions from the summit crater of Karymsky continued during 20-26 May. On 27
May, the Tokyo VAAC reported an ash plume an elevation of 3.7 km (12,000 ft)
a.s.l.  KVERT warned that activity from the volcano could affect nearby
low-flying aircraft. Karymsky remained at Concern Color Code 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.

Source: Kamchatkan Volcanic Eruption Response Team
http://www.kscnet.ru/ivs/kvert/updates.shtml, 
Tokyo Volcanic Ash Advisory Center
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 24-30 May, lava from Kilauea continued to flow off of a lava delta into
the ocean at the East Lae`apuki entry. Incandescence was visible from East Pond
Vent, January Vent, and Drainhole during 24-30 May, and from South Wall Complex
on 24 and 30 May. Tremor remained at a very typical moderate level at Pu`u `O`o.
Small amounts of inflation and deflation occurred during the report period. 

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 about 104 km2 of land on the S flank of
Kilauea and building more than 200 hectares of new land. 

Source: US Geological Survey Hawaiian Volcano Observatory
http://volcanoes.usgs.gov/update.html

Kilauea information from the Global Volcanism Program 
http://www.volcano.si.edu/world/volcano.cfm?vnum=1302-01-

MANAM offshore New Guinea, Papua New Guinea 4.10°S, 145.06°E; summit elev. 1,807 m

According to the Darwin VAAC, an ash plume from Manam was visible on satellite
imagery on 24 and 25 May, extending ~100 km WNW.  On 26 May, an ash plume
visible on satellite imagery reached an altitude below 3 km (10,000 ft) a.s.l.
and drifted 48 km WNW. According to RVO (Rabaul Volcano Observatory), low-level
activity occurred on 30 May.

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: Darwin Volcanic Ash Advisory Center
http://www.bom.gov.au/products/IDD41300.shtml

MERAPI  central Java, Indonesia 7.542°S, 110.442°E; summit elev. 2,947 m 

The Alert Level at Merapi remained at 4, the highest level, during 24-30 May. On
24-25 May, lava flows were observed moving SW towards the Krasak River and SE
towards the Gendol River. According to news reports, on 27 May a M 6.3
earthquake that killed about 5,400 resulted in a three-fold increase in activity
at Merapi. According to CVGHM, an M 5.9 earthquake coincided with pyroclastic
flows of unknown origin that extended 3.8 km SW toward the Krasak River. During
28-30 May, multiple pyroclastic flows reached a maximum of 3 km SE toward the
Gendol River and 4 km SW toward the Krasak and Boyong Rivers. Gas plumes reached
a height above the volcano of 500 m (11,300 ft a.s.l.) on 25 May, 1,200 m
(13,600 ft a.s.l.) on 26 May, 100 m (10,000 ft a.s.l.) on 29 May, and 900 m
(12,600 ft a.s.l.) on 30 May.

Residents remained evacuated from villages within a 7 km radius from the
volcano's summit and within 300 m of the banks of Krasak/Bebeng, Bedog, and
Boyong Rivers to the SW, and Gendol River to the SE.

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 N of the major city of Yogyakarta. The steep-sided modern Merapi
edifice, its upper part unvegetated due to frequent eruptive activity, was
constructed to the SW of an arcuate scarp cutting the eroded older Batulawang
volcano. Pyroclastic flows and lahars accompanying growth and collapse of the
steep-sided active summit lava dome have devastated cultivated and inhabited
lands on the volcano's western-to-southern flanks and caused many fatalities
during historical time. The volcano is the object of extensive monitoring
efforts by the Merapi Volcano Observatory of the Volcanological Survey of Indonesia.

Sources: Center of Volcanology and Geological Hazard Mitigation (CVGHM)
http://www.cnn.com/2006/WORLD/asiapcf/05/17/indonesia.volcano/index.html, 
The Canadian Press  http://www.cbc.ca/cp/world/060529/w052998.html,
Merapi Information from the Global Volcanism Program 
http://www.volcano.si.edu/world/volcano.cfm?vnum=0603-25=

SOUFRIÈRE HILLS Montserrat, West Indies 16.72°N, 62.18°W; summit elev. 1,052 m

During 24-30 May, lava-dome growth continued at Soufrière Hills. On 23 May, the
new lava dome was observed for the first time since the 20 May dome collapse.
The new lava dome was darker than the previous lava dome and on 25 May, reached
a height of 767 m. Rockfalls were observed on the NE and SW sectors of the new
lava dome. The largest of several active vents were on the W side of the dome
and were responsible for ash-venting episodes. 

According to the Washington VAAC, ash-plume emissions continued during 24-30
May. On 24 May, emission of small volumes of gas and thin ash plumes continued
and drifted W and SW.  A pilot near St. Croix (NW) reported that the ash/haze
layer reached an altitude of 1.5 km (5,000 ft) a.s.l. Ashfall was reported at
San Juan (NW) airport. During 25-30 May, ash plumes reached an altitude of 4.6
km (15,000 ft) a.s.l. and drifted W and NW. On 24-26 May, a hot spot was visible
on infrared 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
http://www.ssd.noaa.gov/VAAC/ARCHIVE/FUEG/2006E181541.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; All times
are local (= UTC - 8 hours [ or 7 hours early April - late October])

During 24-25 May, seismicity remained at levels typical of the continuing
lava-dome extrusion at Mount St. Helens. On 29 May, a M 3.1 earthquake and
simultaneous large rockfall occurred. An ash plume was produced at 0810 that
reached an altitude of 4.9 km - 6.1 km (16,000-20,000 ft) a.s.l. according to
ground observations and pilot reports. An additional pilot report suggested the
plume reached an altitude of 7.3 km (24,000 ft) a.s.l. By 1308, ash from the
event was no longer visible on satellite imagery. On 30 May, the rockfall was
confirmed to predominantly originate from the N side of the growing fin. The
volcano remained at Volcano Advisory (Alert Level 2); aviation color code Orange.

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
Washington Volcanic Ash Advisory Center
http://www.ssd.noaa.gov/VAAC/ARCHIVE/STHELEN/2006E292108.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

During 24-30 May, visual observations of Tungurahua were limited due to heavy
cloud cover. On 23 May, an ash plume reported by a pilot reached an altitude of
6.4 km (21,000 ft) a.s.l. A faint plume was visible on satellite imagery that
drifted WSW. Slight ashfall was reported to the SW in Puela on 24 May, and the
observatory reported a decrease in gas and ash emissions. On 25 May a
significant meteorological advisory (SIGMET) indicated an ash plume to an
altitude of 5 km (16,500 ft) a.s.l. On 27 and 30 May, the VAAC reported that the
Instituto Geofísico observed ash plumes at altitudes of 7.9 km (26,000 ft)
a.s.l. and 5 km (16,500 ft) a.s.l., respectively. 

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 Poltecnica Nacional
http://www.igepn.edu.ec/vulcanologia/tungurahua/actividad/informet.htm,
Washington Volcanic Ash Advisory Center
http://www.ssd.noaa.gov/VAAC/ARCHIVE/TUNG/2006E301432.html, 

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

According to a pilot report, the Buenos Aires VAAC reported that an ash plume
from Ubinas on 24 May reached an altitude of 6.7 km (22,000 ft) a.s.l. and
drifted E. On 25 May, an ash plume reached an altitude of 7 km (23,000 ft)
a.s.l. and drifted NW. On 30 May, an ash plume visible on satellite imagery
reached an altitude of 7.9 km (26,000 ft) a.s.l. and drifted E. 

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
http://www.bom.gov.au/products/Volc_ash_recent.shtml,

Ubinas Information from the Global Volcanism Program
http://www.volcano.si.edu/world/volcano.cfm?vnum=1504-02

ULAWUN New Britain Island, Papua New Guinea 5.04°S, 151.34°E; summit elev. 2,334 m

On 25 May, the Darwin VAAC reported a thin steam-and-ash plume from Ulawun that
extended 30 miles WNW.

Geologic Summary. The symmetrical basaltic to andesitic Ulawun stratovolcano is
the highest volcano of the Bismarck arc, and one of Papua New Guinea's most
frequently active. Ulawun rises above the N coast of New Britain opposite Bamus
volcano. The upper 1,000 m of the 2,334-m-high volcano is unvegetated. A
steep-walled valley cuts the NW side of the volcano, and a flank lava-flow
complex lies to the S of this valley. Historical eruptions date back to the
beginning of the 18th century. Twentieth-century eruptions were mildly explosive
until 1967, but after 1970 several larger eruptions produced lava flows and
basaltic pyroclastic flows, greatly modifying the summit crater.

Source: Darwin Volcanic Ash Advisory Center
http://www.bom.gov.au/products/IDD41305.shtml

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