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ARCHIVED REPORT
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ALASKA VOLCANO OBSERVATORY

WEEKLY UPDATE

Friday, May 7, 2004 10:30 AM ADT (18:30 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



Unrest continues at Mount Veniaminof volcano, characterized by small,

intermittent ash emissions, low-level volcanic tremor, and small volcanic

earthquakes. During this past week, small ash emissions were observed

during periods of clear weather on May 1-3. Ash clouds rose from 1,000 to

2,000 feet above the active cone (~8,000 to 9,000 feet or ~2,400 to 2,800 m

above sea level). The internet camera system in Perryville was brought down

for repair on May 4, so no systematic visual observations of ash plumes

were made after that time, though residents reported continued activity on

May 5. However, the observed seismicity is similar to that recorded last

week, suggesting that the ash burst activity continues. Satellite imagery

shows ash deposits on the snow to distances of 5 miles (~8 km) from the

vent. A pilot reported ash as far as 20 miles (33 km) from the cone. There

are no indications that more vigorous activity is imminent or even likely.

We expect that steam and ash emissions similar to those observed this week

may continue intermittently and could pose a hazard to people and

low-flying aircraft in the vicinity of the active cone.



AVO will continue to monitor activity at Mount Veniaminof using seismic

data, satellite images, and observer reports. AVO has increased the

frequency of seismic data analysis to provide early warning of increased

activity, should it occur. Public access to archived internet camera images

(collected at Perryville) can be found at www.avo.alaska.edu.



Mount Veniaminof volcano is an andesitic stratovolcano with an ice-filled

10-km 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 (~ 300 km3) 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 a moderate Strombolian eruption from the main intracaldera

cone in the northwest sector of the caldera above Cone Glacier. The

eruption was characterized by intermittent low-level emissions of steam and

ash, and a small lava flow was extruded into the summit caldera ice field

producing an ice pit. Minor explosions producing small ash clouds very

similar to those observed this past week occurred in 2002. Previous

historical eruptions have produced ash plumes that reached 6,000 m (20,000

ft) above sea level and ash fallout that blanketed areas within about 40 km

(25 mi) of the volcano.



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, characterized by sequences

of volcanic earthquakes and seismic tremor. The number of airwaves

recorded by the seismic network has diminished, but the more sensitive

pressure sensor continues to record weak signals from the volcano. Thermal

anomalies at the summit have been observed in satellite imagery under

optimal viewing conditions. Retrospective analysis confirms that these

data, as well as similar signals observed in January 2004, are the first

thermal anomalies observed at Shishaldin since August 2000. We see nothing

at this time to indicate that an eruption is imminent. 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.



OTHER ALASKA VOLCANOES

Seismic activity is monitored in real time at 25 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,

Shishaldin, Fisher, Westdahl, Akutan, Makushin, Okmok, Great Sitkin, and

Kanaga 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].

PDF version of these definitions
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Page modified: May 27, 2014 10:23
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