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ARCHIVED REPORT
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ALASKA VOLCANO OBSERVATORY

WEEKLY UPDATE

Friday, September 24, 2004 10:30 AM ADT (18:30 UTC)



ALASKA VOLCANOES



MOUNT SPURR VOLCANO (CAVW#1103-04)

6118' N 15215' W, Summit Elevation 11,070 ft (3,374 m)

Current Level of Concern Color Code: YELLOW



Elevated levels of seismicity continue to be recorded at Mt. Spurr volcano.

This week, about 68 earthquakes were located within 30 km of the summit,

with an average of approximately 10 events per day. AVO measured gases

being emitted by Crater Peak and Mount Spurr during a fixed-wing flight on

September 15. The combined output of carbon dioxide (CO2) from the two

vents was approximately 2300 tons/day, an increase from the approximately

760 tons/day measured August 7-8. The gray color of the lake at the bottom

of the ice cauldron is typical of crater lakes containing dissolved sulfur

dioxide, or SO2. These observations further suggest that magma resides

beneath the volcano. However, there are no indications that an eruption is

imminent, and this type of activity does not always lead to an eruption. No

anomalous activity was observed in satellite data. AVO scientists will

attempt to overfly the summit today and obtain thermal measurements.



Mt. Spurr volcano is an ice- and snow-covered stratovolcano located on the

west side of Cook Inlet. The only known historical eruptions occurred in

1953 and 1992 from the Crater Peak flank vent located 3.5 km (2 mi) south

of the summit of Mt. Spurr. These eruptions were explosive, brief in

duration, and produced towering columns of ash that rose up to 20 km

(65,000 ft) above sea level and deposited several mm of ash on populated

areas of south-central Alaska, including approximately 6 mm of ash on

Anchorage in 1953. The summit of Mt. Spurr and the surrounding avalanche

caldera is heavily mantled by ice and snow. The last known eruption from

the summit dome of Mt. Spurr was more than 5,000 years ago. The primary

hazards associated with future eruptions from the Mt. Spurr summit vent and

from Crater Peak include far-traveled ash clouds, ash fall, pyroclastic

flows, and lahars or mudflows that could inundate drainages all sides of

the volcano, but primarily on the south and east flanks.



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



Low-level seismic tremor and intermittent tremor bursts continue to be

recorded at Mount Veniaminof Volcano. Tremor episodes likely represent

low-level ash and steam emissions similar to those observed over the past

four months, although cloudy conditions obscured views of the volcano in

web camera and satellite data. Activity at Veniaminof could, at any time,

become more vigorous, and the steam and ash emissions from the intracaldera

cone 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 occurring 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



Low-level seismic tremor continues to be recorded at Shishaldin Volcano.

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

months. No anomalous activity was observed in satellite views of the

volcano this week. 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, 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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