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ARCHIVED REPORT
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SHISHALDIN VOLCANO



Based on satellite imagery and pilot reports received by the Federal Aviation Administration, Shishaldin Volcano on Unimak Island in the eastern Aleutian Islands erupted yesterday sometime around 6:30 pm AST (0330 UTC). Between 6:30 and 8:00 pm AST (0330 and 0500 UTC) Saturday, December 23, pilots reported an ash plume as high as 35,000 feet above sea level; prevailing winds at that altitude carried the plume primarily north and northwest. AVO analysis of a satellite image from 7:12 pm Saturday shows a possible small ash plume extending approximately 50 km northwest of Shishaldin. This morning, AVO received a report of a possible very light ashfall at approximately 1:30 am (1030 UTC) in Cold Bay, 56 mi (90 km) northeast of Shishaldin; this ash would have been carried from the volcano by westerly low altitude winds.



Shishaldin Volcano is located near the center of Unimak Island in the eastern Aleutian Islands. It is a spectacular symmetric cone with a summit elevation of 9373 ft (2875 m) above sea level. A small summit crater produces a steady, vigorous cloud of steam with occasional small amounts of ash. Shishaldin is one of the most active volcanoes in the Aleutian volcanic arc, erupting at least 27 times since 1775. The most recent eruptive period occurred in 1986-1987; activity consisted of minor steam and ash emissions that continued for several months. The nearest village is False Pass, 20 mi (32 km) east-northeast of the volcano.



Based on the record of historic activity at Shishaldin, additional eruptions of ash may continue intermittently for days or weeks. The Alaska Volcano Observatory will continue to monitor the situation through pilot reports and analysis of satellite images.



NOTE: Due to the partial shutdown of the Federal Government, the Alaska Volcano Observatory is currently operating with reduced staff. However, we continue to seismically monitor Spurr, Redoubt, Iliamna, and Augustine volcanoes. A computerized alarm system is capable of

notifying AVO seismologists during non-business hours

should unusual seismic activity occur.

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].

PDF version of these definitions
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URL: avo.alaska.edu/activity/avoreport_archives.php
Page modified: May 27, 2014 10:23
Contact Information: AVO Web Team

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