Printer friendly version
ALASKA VOLCANO OBSERVATORY
Friday, July 23, 2004 11:30 AM ADT (1930 UTC)
MOUNT VENIAMINOF VOLCANO (CAVW #1102-07)
56°10'N 159°23'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)
54°45'N 163°58'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
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
YELLOW volcano is restless; eruption may occur
ORANGE volcano is in eruption or eruption may occur at any
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
Tom Murray, Scientist-in-Charge, USGS
firstname.lastname@example.org (907) 786-7497
John Eichelberger, Coordinating Scientist, UAF-GI
email@example.com (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.