VOLCANO: Redoubt Aviation Color Code Change from Yellow to Green

[Kirsten Chojnicki <kchojnic@xxxxxxx>]

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Redoubt Aviation Color Code Change from Yellow to Green
From: avo-sci@xxxxxxxx
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AVO/USGS Volcanic Activity Notice 20090929_1044

Volcano: Redoubt (CAVW #1103-03-)

Current Volcano Alert Level: ADVISORY

Current Aviation Color Code: GREEN
Previous Aviation Color Code: YELLOW

Issued: Tuesday, September 29, 2009, 10:44 AM AKDT (20090929/1844Z)
Source: Alaska Volcano Observatory
Notice Number: 2009/A44
Location: N 60 deg 29 min W 152 deg 44 min
Elevation: 10197 ft (3108 m)
Area: Cook Inlet-South Central Alaska

Volcanic Activity Summary: Over the past several months, seismic
activity, volcanic gas output, ground deformation, lava dome
temperatures, and outward signs of lava dome instability at Redoubt
Volcano have been declining.   The volcano appears to have returned to
its normal background condition and for now poses no immediate threat
of eruptive activity.  Accordingly, AVO is lowering the Aviation Color
Code to GREEN and the Volcano Alert Code to NORMAL.

Since it began growing in early April 2009, the lava dome in the summit
crater at the top of the Drift glacier canyon has reached a volume of
approximately 70 million cubic meters (91 million cubic yards). Lava
domes, particularly those built on steep slopes, are typically unstable
and subject to sudden collapse. A dome collapse at Redoubt would likely
produce ash clouds and falls, hot block-and-ash flows, and downstream
flooding and lahars. However, based on the length of time since the
cessation of dome growth (more than 60 days), AVO believes the
possibility for dome collapse is small and declining toward a
background level of danger typical of many active stratovolcanoes with
steep unstable rock slopes.

Redoubt's new lava dome remains hot and gas-rich and will continue to
pose local hazards for some time. High levels of sulfur dioxide, carbon
dioxide, and hydrogen sulfide may occur near the dome, as will rock
falls and abundant steaming. Depending on wind and cloud conditions,
sulfur smells could reach populated areas and steam plumes will be
visible on occasion. Small outbursts of impounded water, not associated
with a dome collapse, are possible, but these are unlikely to pose a
threat much beyond the upper Drift River. As temperatures in the area
begin to decline and winter freeze up occurs, the likelihood of
flooding of the valleys of the lower Drift River, Rust Slough, Cannery
Creek, and Montana Bill Creek will also decline.

At this time it is not known if the volcano is entering a prolonged
period of quiet, as it did after the 1966-68 and 1989-90 eruptions when
the volcano exhibited little to no unrest for periods of about 20 years.

A resumption of eruptive activity at Redoubt in the near future is
possible, but AVO considers this scenario unlikely. Hours to days of
precursory seismicity would likely precede resumed activity, providing
AVO ample time to issue prompt forecasts of possible volcanic hazard.
 AVO continuously monitors Redoubt with an alarm system that alerts
on-call staff of potential unrest.

Contacts: John Power, Acting Scientist-in-Charge, USGS
jpower@xxxxxxxx (907) 786-7497

Steve McNutt, Coordinating Scientist, UAF
steve@xxxxxxxxxxxxxxxxx (907) 474-7131

Next Notice: A new VAN will be issued if conditions change
significantly or alert levels are modified. While a VAN is in effect,
regularly scheduled updates are posted at
http://www.avo.alaska.edu

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.

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