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ARCHIVED REPORT
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ALASKA VOLCANO OBSERVATORY

WEEKLY UPDATE

Friday, June 4, 2004 1:40 PM ADT (2140 UTC)



ALASKA VOLCANOES



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



Bursts of volcanic tremor continue at Mount Veniaminof. The only

significant ash emissions observed this past week occurred the evening of

May 30 into the morning of May 31. These were observed using the web

camera in Perryville (

http://www.avo.alaska.edu/avo4/atlas/volc/venia/veni2004/index.htm). None

appear to have exceeded 10,000 ft. (3000 m) above sea level. Clear views

of the volcano by the web camera earlier on May 30 showed steaming from

near the base of the intracaldera cone that rarely rose above the top of

the cone (7073 ft. or 2156 m above sea level). No activity was observed in

satellite data as the volcano was largely obscured by clouds. There are no

indications that more vigorous activity is imminent or even likely.

However, activity at Veniaminof could increase rapidly, and steam and ash

emissions may pose a hazard to people and low-flying aircraft in the

vicinity of the caldera. AVO will continue to monitor activity at Mount

Veniaminof using seismic data, satellite images, internet camera data and

observer reports.



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 emissions

occurred in 2002 and in recent weeks. 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)

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. It is characterized by

weak seismic tremor and occasional discrete low-frequency earthquakes.

Small explosion signals have been recorded by the pressure sensor. Though

clouds largely obscured Shishaldin in satellite data, data acquired at 0823

UTC (0023 ADT) May 29 show the crater to continue to be warmer than

background. 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.



The following two volcanoes, Mount Gareloi and Tanaga Volcano, have been

added to our list of seismically-monitored volcanoes. Seismic networks were

installed on the volcanoes in the summer of 2003 and performed well through

this past winter.



MOUNT GARELOI VOLCANO (CAVW #1101-07)

51°47'N 178°48'W, Summit Cone Elevation 5,924 ft (1,573 m)

Current Level of Concern Color Code: GREEN



Mount Gareloi, which makes up most of Gareloi Island, is a

stratovolcano 10 km by 8 km in diameter at its base with two summits,

separated by a narrow saddle. It is located in the Aleutians approximately

160 km west of Adak, AK. Volcanic activity has been frequently reported

from Mount Gareloi since its discovery during the Bering Expedition in

1760. "Smoke" or unspecified activity was noted in 1760, 1828, 1873, and

1927; lava extrusion in 1792; minor explosive eruptions in 1790 and 1791;

and major explosive eruptions in 1922 and 1929-30. The 1929 event is the

most violent on record for Gareloi volcano. Activity was reported several

times in the 1980's, including a report in 1987 of vigorous steaming of the

crater and a narrow flow-like feature that was also steaming extending down

from the north crater rim. A compound lava flow down the south flank also

occurred in the 1980s.

In April of 1929, a phreatic eruption opened an elongate crater 1600

m in maximum diameter just below the southern summit; further explosions

produced 12 smaller craters aligned along a south- to southeast-trending

fissure. Ash layers up to 2 m thick on Ogliuga Island, located about 16 km

southeast, may be attributable at least in part to this eruption and

several centimeters of pyroclastic debris are known to have fallen on Atka

Island (about 300 km eastward) during the event.

The local seismicity at Mount Gareloi consists mainly of

low-frequency or long-period earthquakes typically occurring about 1 every

2 minutes. Approximately 4 events per day are large enough to be located.

The character of this seismicity is indicative of active magmatic or

hydrothermal processes.



TANAGA VOLCANO (CAVW #1101-08)

51°53'N 178°08'W, Summit Cone Elevation 5,197 ft (1,806 m)

Current Level of Concern Color Code: GREEN



Tanaga Volcano is the central and highest of three adjacent

stratovolcanoes at the northwest end of Tanaga Island. It is located in the

Aleutians approximately 110 km west of Adak, AK. Tanaga Volcano and the

neighboring cones roughly define an east-west trend across northern Tanaga

Island. At least four cones adjacent to Tanaga Volcano apparently have been

active in the last few thousand years. A blanket of fine ash, as much as 6

m thick covers large areas of Tanaga Island. The ash, stratified and

intercalated with thin soil layers, may have accumulated over a period of

several thousand years.

Few details are available concerning historical activity of Tanaga

Volcano, and some or all of the events attributed to it may have involved

adjacent cones in the northwest part of the island. Tanaga was reported

active throughout the period 1763-1770. Smoke was noted above the island in

1791 and 1829, and a lava flow was observed in 1914.

The local seismicity at Tanaga Volcano consists mainly of

high-frequency or volcano-tectonic earthquakes occurring about one per

week. No volcanic tremor has been observed.



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



Steve McNutt, Acting Coordinating Scientist, UAF-GI

steve@giseis.alaska.edu (907) 474-7131



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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