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ARCHIVED REPORT
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ALASKA VOLCANO OBSERVATORY

INFORMATION RELEASE

Monday, July 26, 2004 12:05 PM ADT (2005 UTC)



MOUNT SPURR VOLCANO (CAVW#1103-04)

61o18' N 152o15' W, Summit Elevation 11,070 ft (3,374 m)

Previous Level of Concern Color Code: Green

Current Level of Concern Color Code: YELLOW



AVO has identified an increase in earthquake activity beneath the summit of

Mount Spurr volcano located about 130 km (80 mi) west of Anchorage. Some

of these earthquakes can be interpreted to reflect the beginning stages of

volcanic unrest. Because this is a notable departure from the normal

background seismicity of the volcano, AVO is raising the level of concern

color code to YELLOW. However, there are no indications that an eruption

is imminent. Often this type of seismicity will decline without producing

an eruption.



Retrospective analysis suggests that the current increase began slowly,

perhaps as early as February 2004. At present, AVO is locating 15-20

earthquakes below the volcano each day. This is a rate greater than any

observed since the last eruptive period in 1992. All earthquakes are less

than magnitude 1.5 and range in depth between 1 and 6 km (0.6 and 4 miles)

below sea level. To date, relatively few earthquakes have been located

beneath the Crater Peak vent, the site of the 1953 and 1992 eruptions. The

current earthquake activity differs markedly from that seen prior to the

1992 eruption, which started with a small cluster of earthquakes directly

beneath Crater Peak nearly a year before the eruption began.



AVO geologists visited Spurr by fixed-wing aircraft on July 15 and observed

no indications of recent volcanic activity. On July 11, a pilot flying by

the volcano reported a sulfur smell and new area of steaming, but neither

was noted during the AVO flight, although a significant portion of the

Crater Peak area was obscured by low clouds. AVO geologists did document

several fresh-looking, dark debris flow/avalanche deposits on the southeast

and south face of the summit dome complex suggesting water flow at the

surface, but this may simply reflect recent unseasonably warm and sunny

conditions.



AVO will continue to monitor activity at Mount Spurr closely using seismic

data, satellite images, and overflights, and will issue further information

releases as appropriate.



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

side of Cook Inlet. The only historical eruptions in 1953 and 1992

occurred at the Crater Peak flank vent located 3.5 km (2 mi) south of the

Spurr summit. 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 in Anchorage in

1953. The summit dome complex of Mount Spurr is largely covered in ice;

its last known eruption was approximately 5,000 years ago. Primary hazards

from future eruptons at Mount Spurr and Crater Peak include far-traveled

ash clouds, ash fall, pyroclastic flows, and lahars or mudflows that could

impact drainages primarily on the south and east sides of the volcano.



The volcano-hazard assessment for Mount Spurr Volcano is available from the

AVO web site: http://www.avo.alaska.edu/avo4/products/hazard.htm





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



Chris Nye, Acting Coordinating Scientist, UAF-GI

cnye@giseis.alaska.edu (907) 474-7430



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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