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ARCHIVED REPORT
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SHISHALDIN VOLCANO



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 noticable steam plume 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 late 1995 and early 1996 and consisted of minor explosions that produced low level steam and ash emissions.



During the past week, National Weather Service personnel in Cold Bay, 58 miles (93 km) east-northeast of the volcano, observed anomalous steaming at Shishaldin volcano. On Tuesday, a vigorous steam plume rose as high as 6000 feet (1830 m) above the vent and a long plume drifted downwind. Satellite imagery on that same day showed the steam plume and a thermal anomaly at the vent. The steam activity decreased throughout the week to light puffs rising a few hundred feet above the vent, however the thermal anomaly at the vent persists. A new seismic net monitoring Shishaldin volcano recorded slightly elevated seismicity beginning the end of January, but the seismicity currently has not reached a level to indicate that a major eruption is expected. As long as the thermal anomaly persists, a low-level ash burst could occur with little or no warning.



OTHER ALASKA VOLCANOES



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

Novarupta, Trident, Mageik, Martin, Aniakckak, Pavlof,

Dutton, Akutan, Isanotski, Fisher, Westdahl, and

Makushin volcanoes are all at or near normal levels of

background seismicity.

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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Page modified: May 27, 2014 10:23
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