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ARCHIVED REPORT
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ALASKA VOLCANO OBSERVATORY

WEEKLY UPDATE

Friday, July 23, 2004 11:30 AM ADT (1930 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



Small steam and ash emissions accompanied by periods of volcanic tremor

continue intermittently at Mount Veniaminof Volcano. On July 22, an AVO

field crew witnessed a small ash burst rising only a few hundred meters

(<1000 feet) above the summit of the intracaldera cone at 12:29 ADT. This

type of activity is likely typical of the ash emissions at Veniaminof

either observed or inferred on the basis of seismicity over the past three

months. During periods of repose, the cone is producing variable amounts

of white steam from at least two separate craters near the top of the cone.

The surface of the snow and ice field throughout much of the caldera is

covered with a discontinuous, 1-2-mm thick ash blanket. AVO geologists

reported no ballistics (large rocks) beyond the limits of the cone, nor did

they observe cracks or other changes in the ice that would indicate

subglacial melting. Satellite views of the volcano were obscured by clouds

for much of the week. Occasional web camera views of the caldera through

breaks in the clouds showed steam emanating from the summit cone.



Though the observed ash emission of July 22 failed to reach 10,000 ft (3000

m) above sea level, activity at Veniaminof could become more vigorous

without warning, and continuing steam and ash emissions do pose a hazard to

people and low-flying aircraft in the vicinity of the caldera.

AVO will continue to monitor activity at Veniaminof using seismic data, satellite

images, internet camera data and observer reports.



Mount Veniaminof volcano is a young stratovolcano with an ice-filled 10-km

(6 mi) 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 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

characterized by intermittent. low-level emissions of steam and ash, and a

small lava flow onto the summit caldera ice field producing an ice pit.

Previous historical eruptions have produced ash plumes that reached 6,000 m

(20,000 ft) above sea level and associated ash fall within about 40 km (25

mi) of the volcano. Minor ash emissions similar to those occuring at

present were also detected in late 2002.



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. The unrest is characterized

by weak seismic tremor and occasional discrete low-frequency earthquakes.

This level of activity is similar to that observed over the past several

months. During clear satellite views of the volcano this week, no unusual

activity was noted. 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 summit. 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 27 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, Kanaga, Tanaga,

and Gareloi 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



John Eichelberger, Coordinating Scientist, UAF-GI

eich@giseis.alaska.edu (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.

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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