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ARCHIVED REPORT
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Alaska Volcanoes Update

February 20, 1997, 1:30 pm AST (2230 UTC)



Okmok Volcano: 53°24' N, 168°10' W;

caldera rim elevation 3520 feet (1,073 m) elevation of erupting

cone about 2500 feet (760 m)

The small eruption that began last week continues at Okmok volcano

on Umnak Island. On Tuesday morning, February 18, U.S. Coast

Guard pilots reported an ash plume rising to between 10,000

feet and 15,000 feet ASL at the volcano. Satellite images showed

a large circular hot spot. Observers at the former Fort Glenn

military base at the east end of the island reported seeing a bright

red glare reflected from the 6,000- foot-high weather clouds above

the volcano. The red glow was visible from about 1:00 am (AST)

until sunrise. A large steam plume was subsequently observed rising

from, and covering the top of the caldera. At 1:35 pm (AST) pilots

reported an ash cloud above Okmok rising to 16,000 feet ASL

and moving slowly to the southwest. Satellite images from the

afternoon of Wednesday, February 19 showed no hotspot, but

images from this morning show a small hotspot. AVO does not have

seismic monitoring equipment on the island.



Although AVO lacks direct observations inside the caldera, the

reported activity appears to indicate that a lava-producing

eruption has occurred from an intracaldera cone located along

the south rim. The main pulse of activity began early on Tuesday

morning and subsided sometime yesterday. The south rim cone

has been the source of most of the recent historical activity.

Based on previous activity, the current eruption could continue for

weeks or months with intermittent steam and ash emission and

extrusion of intracaldera lava flows.



Okmok volcano is a 6-mile-wide caldera that occupies most of the

eastern end of Umnak Island, located 75 miles southwest of

Dutch Harbor in the eastern Aleutian Islands. Okmok has had

several eruptions in historic time typically consisting of ash

emissions occasionally to over 30,000 feet ASL but generally to

much lower altitudes; lava flows crossed the caldera floor in 1945

and 1958. The last eruption occurred November 1986 through

February 1988 and was characterized by intermittent ash

emission.



The nearest settlements are Nikolski, population about 35, about 45

miles west of the volcano, and a small number of people at the

abandoned Fort Glenn military base 10 miles east of the volcano.

AVO is closely monitoring the situation and will issue further

updates as more information becomes available.

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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