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ARCHIVED REPORT
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ALASKA VOLCANO OBSERVATORY

WEEKLY UPDATE

Friday, May 21, 2004 11:30 AM ADT (19:30 UTC)



ALASKA VOLCANOES



MOUNT VENIAMINOF VOLCANO (CAVW #1102-07)

5610'N 15923'W, Summit Cone Elevation 7,073 ft (2,156 m)

Current Level of Concern Color Code: YELLOW



Unrest continues at Mount Veniaminof volcano, characterized by intermittent

volcanic tremor. These data are similar to the seismic signals recorded

last month in association with small ash plumes, suggesting that ash bursts

continue. A pilot report on May 18 indicated the presence of an ash plume

rising to heights of 1000-3000 ft (300-900 m) above the volcano's summit

(8000-10,000 ft or 2400-3000 m above sea level) and extending approximately

20 miles (32 km) northeast. Cloudy conditions have obscured observation of

Veniaminof by satellite. There are no indications that more vigorous

activity is imminent or even likely. However, activity at Veniaminof could

increase rapidly, and steam and ash emissions may pose a hazard to people

and low-flying aircraft in the vicinity of the caldera. AVO will continue

to monitor activity at Mount Veniaminof using seismic data, satellite

images, and observer reports.



Mount Veniaminof volcano is an andesitic stratovolcano with an ice-filled

10-km diameter summit caldera located on the Alaska Peninsula, 775 km (480

mi) southwest of Anchorage and 35 km (22 mi) north of Perryville.

Veniaminof is one of the largest (~ 300 km3) and most active volcanic

centers in the Aleutian Arc and has erupted at least 12 times in the past

200 years. The most recent significant eruption of the volcano occurred in

1993-95 and was a moderate Strombolian eruption from the main intracaldera

cone in the northwest sector of the caldera above Cone Glacier. The

eruption was characterized by intermittent low-level emissions of steam and

ash, and a small lava flow was extruded into the summit caldera ice field

producing an ice pit. Minor explosions producing small ash occurred in 2002

and in recent weeks. Previous historical eruptions have produced ash plumes

that reached 6,000 m (20,000 ft) above sea level and ash fallout that

blanketed areas within about 40 km (25 mi) of the volcano.



SHISHALDIN VOLCANO (CAVW #1101-36)

5445'N 16358'W, Summit Cone Elevation 9,373 ft (2,857 m)

Current Level of Concern Color Code: YELLOW



Seismic unrest continues at Shishaldin volcano, characterized by weak

seismic tremor and small explosions. On May 16 a pilot reported an ash

plume rising to 1000 ft (300 m) above Shishaldin's summit (10,400 ft or

3170 m above sea level). Satellite imagery from May 17 shows a vigorous

plume that may contain small amounts of ash emanating from the summit.

Clouds have obscured Shishaldin in satellite images taken since that time.

We see nothing at this time to indicate that more vigorous activity is

imminent. However, activity at Shishaldin could increase rapidly and ash

and gas emissions may pose a hazard to people and low-flying aircraft in

the vicinity of the active cone. AVO will continue to monitor activity at

Shishaldin volcano using seismic data, satellite images, and observer

reports.



Shishaldin volcano, located near the center of Unimak Island in the eastern

Aleutian Islands, is a spectacular symmetric cone with base diameter of

approximately 10 miles (16 km). A small summit crater typically emits a

noticeable steam plume with occasional small amounts of ash. Shishaldin is

one of the most active volcanoes in the Aleutian volcanic arc, erupting at

least 28 times since 1775. Most of Shishaldin's eruptions have consisted

of small ash and steam plumes, although the most recent eruption in

April-May 1999 produced an ash column that reached a height of 45,000 ft

above sea level.



OTHER ALASKA VOLCANOES

Seismic activity is monitored in real time at 25 volcanoes in Alaska.

Satellite images of all Alaskan volcanoes are analyzed daily for evidence

of ash plumes and elevated surface temperatures. Some volcanoes may

currently display anomalous behavior but are not considered to be at a

dangerous level of unrest.



Wrangell, Spurr, Redoubt, Iliamna, Augustine, Snowy, Griggs, Katmai,

Novarupta, Trident, Mageik, Martin, Aniakchak, Pavlof, Dutton, Isanotski,

Fisher, Westdahl, Akutan, Makushin, Okmok, Great Sitkin, and Kanaga

volcanoes are in color code GREEN. All are at or near normal levels of

background seismicity. AVO did not detect ash plumes or significant

elevated surface temperatures in the vicinity of any volcano.



ABBREVIATED COLOR CODE KEY (contact AVO for complete description):

GREEN volcano is dormant; normal seismicity and fumarolic activity

occurring

YELLOW volcano is restless; eruption may occur

ORANGE volcano is in eruption or eruption may occur at any time

RED significant eruption is occurring or explosive

eruption expected at any time



VOLCANO INFORMATION ON THE INTERNET: http://www.avo.alaska.edu

RECORDING ON THE STATUS OF ALASKA'S VOLCANOES (907) 786-7478



CONTACT INFORMATION:



Tom Murray, Scientist-in-Charge, USGS

tlmurray@usgs.gov (907) 786-7497



Steve McNutt, Acting Coordinating Scientist, UAF-GI

steve@giseis.alaska.edu (907) 474-7131



The Alaska Volcano Observatory is a cooperative program of the U.S.

Geological Survey, the University of Alaska Fairbanks Geophysical

Institute, and the Alaska Division of Geological and Geophysical Surveys.

VOLCANO ALERT LEVELS
NORMAL
Volcano is in typical background, noneruptive state or, after a change from a higher level, volcanic activity has ceased and volcano has returned to noneruptive background state.
ADVISORY
Volcano is exhibiting signs of elevated unrest above known background level or, after a change from a higher level, volcanic activity has decreased significantly but continues to be closely monitored for possible renewed increase.
WATCH
Volcano is exhibiting heightened or escalating unrest with increased potential of eruption, timeframe uncertain, OR eruption is underway but poses limited hazards.
WARNING
Hazardous eruption is imminent, underway, or suspected.

AVIATION COLOR CODES
GREEN
Volcano is in typical background, noneruptive state or, after a change from a higher level, volcanic activity has ceased and volcano has returned to noneruptive background state.
YELLOW
Volcano is exhibiting signs of elevated unrest above known background level or, after a change from a higher level, volcanic activity has decreased significantly but continues to be closely monitored for possible renewed increase.
ORANGE
Volcano is exhibiting heightened or escalating unrest with increased potential of eruption, timeframe uncertain, OR eruption is underway with no or minor volcanic-ash emissions [ash-plume height specified, if possible].
RED
Eruption is imminent with significant emission of volcanic ash into the atmosphere likely OR eruption is underway or suspected with significant emission of volcanic ash into the atmosphere [ash-plume height specified, if possible].

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