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ALASKA VOLCANO OBSERVATORY
Monday, May 3, 2004 07:00 PM ADT (03:00 May 4 UTC)
Shishaldin Volcano (CAVW #1101-36)
54°45'N 163°58'W, Summit Cone Elevation 9,373 ft (2,857 m)
Previous Level of Concern Color Code: GREEN
Current Level of Concern Color Code: YELLOW
Seismic activity at Shishaldin Volcano has notably changed in the last week
from discrete earthquakes to more continuous activity. Tremor has been
observed for the first time since the most recent eruption ended in May
1999. Airwaves accompanying earthquakes have been recorded by the seismic
network, suggesting that the source of the seismicity has shallowed.
Satellite data do not show any significant increases in ground temperature
at the volcano, nor have there been reports of increased steaming.
Shishaldin has had elevated levels of seismicity since the 1999 eruption.
However, the type of activity now seen is unusual, and AVO is raising the
level-of-concern color code to YELLOW. We see nothing at this time to
indicate that an eruption is imminent or even likely. However, activity at
Shishaldin could increase rapidly and AVO has increased the frequency of
seismic data analysis. AVO will continue to monitor activity 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.
ABBREVIATED COLOR CODE KEY (contact AVO for complete description):
GREEN volcano is dormant; normal seismicity and fumarolic activity
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
Tom Murray, Scientist-in-Charge, USGS
firstname.lastname@example.org (907) 786-7497
John Eichelberger, Coordinating Scientist, UAF-GI
email@example.com (907) 474-5530
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.