(1) VOLCANO OBSERVATORY NOTICE FOR AVIATION (VONA)
(2) Issued:(20090929/1844Z)
(3) Volcano:Redoubt (CAVW# 1103-03-)
(4) Current Color Code:GREEN
(5) Previous Color Code:
(6) Source:Alaska Volcano Observatory
(7) Notice Number:2009/A44
(8) Volcano Location:N 60 deg 29 min W 152 deg 44 min
(9) Area:Cook Inlet-South Central Alaska
(10) Summit Elevation:10197 ft (3108 m)
(11) 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.
(12) Volcanic cloud height:Unknown
(13) Other volcanic cloud information:Unknown
(14) Contacts:John Power, Acting Scientist-in-Charge, USGS
jpower@usgs.gov (907) 786-7497

Steve McNutt, Coordinating Scientist, UAF
steve@giseis.alaska.edu (907) 474-7131
(15) Next Notice:A new VONA will be issued if conditions change significantly or alert levels are modified. While a VONA is in effect, regularly scheduled updates are posted at
http://www.avo.alaska.edu