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ARCHIVED REPORT
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ALASKA VOLCANO OBSERVATORY

INFORMATION RELEASE

Friday, November 25, 2005 11:20 AM AKST (2020 UTC)




CLEVELAND VOLCANO (CAVW#1101-24-)

52.8232°N 169.9431°W, Summit Elevation 5676 ft (1730 m)

Current Level of Concern Color Code: Not Assigned

Previous Level of Concern Color Code: YELLOW



Activity at Cleveland Volcano in the east central Aleutians appears to have diminished. Clear satellite views this morning show no thermal anomaly. AVO has not detected a temperature anomaly in the vicinity of the volcano since November 6. Following the brief ash burst on October 7, no further ash emissions have been noted. Based on this trend, the likelihood of significant ash-producing events has decreased, and AVO is terminating Level of Concern Color Code YELLOW. Cleveland Volcano is not monitored with seismic instrumentation, therefore we do not assign Color Code GREEN.



Cleveland volcano forms the western half of Chuginadak Island, a remote and uninhabited island in the east central Aleutians. It is located about about 75 km (45 mi.) west of the community of Nikolski, and 1500 km (940 mi.) southwest of Anchorage. The volcano's most recent significant eruption began in February, 2001 and had 3 explosive events that produced ash clouds as high as 12 km (39,000 ft) above sea level. This eruption also produced a rubbly lava flow and hot avalanche that reached the sea. The most recent minor ash emissions were observed in July 2005.



TANAGA VOLCANO (CAVW#1101-08-)

51.885°N 178.1458°W, Summit Elevation 5925 ft (1806 m)

Current Level of Concern Color Code: GREEN

Previous Level of Concern Color Code: YELLOW



Over the past several weeks, seismic activity beneath young volcanic vents on Tanaga Island has decreased significantly from levels seen in early October. Satellite views of the island have shown no anomalous temperatures or evidence of ash emission. Based on the decay of earthquake counts and frequency of tremor episodes, the likelihood of an eruption has diminished. Therefore, AVO is downgrading the Level of Concern Color Code to GREEN.



Tanaga Island lies in the Andreanof Islands approximately 100 km (62 miles) west of the community of Adak and 2025 km (1260 miles) SW of Anchorage. The northern half of the island is home to the Tanaga volcanic complex, comprising three main volcanic edifices. Historically active Tanaga volcano is the tallest of these (1,806 m or 5,925 ft) and lies in the center of the complex. Immediately west of Tanaga volcano lies Sajaka, a 1,354 m (4,443 ft)-high compound edifice with an older cone to the east that collapsed into the sea within the last few thousand years, and a new cone that has grown in the breach. The new cone is 1,312 m (4,305 ft) high and consists of steeply dipping, interbedded cinders and thin, spatter-fed lava flows. To the east of Tanaga lies Takawangha, which is separated from the other active volcanic vents by a ridge of older rock. Takawangha's 1,449 m (4,754 ft)-high summit is mostly ice-covered, except for four young craters that have erupted ash and lava flows in the last few thousand years. Parts of Takawangha's edifice are hydrothermally altered and may be unstable, and could produce localized debris avalanches. No historical eruptions are known from Sajaka or Takawangha; however, field work shows that recent eruptions have occurred and it is possible that historic eruptions attributed only to Tanaga may instead have come from these other vents.







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@gi.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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