(2) Issued:(20090303/0552Z)
(3) Volcano:Okmok (CAVW# 1101-29-)
(4) Current Color Code:YELLOW
(5) Previous Color Code:
(6) Source:Alaska Volcano Observatory
(7) Notice Number:2009/A5
(8) Volcano Location:N 53 deg 23 min W 168 deg 9 min
(9) Area:Aleutians Alaska
(10) Summit Elevation:3520 ft (1073 m)
(11) Volcanic Activity Summary:AVO is increasing the Aviation Color Code to YELLOW and the Volcanic Alert Level to ADVISORY for Okmok volcano. Over the past 24 hours there have been short bursts of volcanic tremor at Okmok volcano. These bursts are occurring at a rate of one per hour on average. This is the first sign significant seismic activity at the volcano since the cessation of eruption in August 2008 and represents an increase above typical background activity.

This increase in seismic activity does not necessarily indicate that an eruption will occur, or that an eruption is likely. Clouds currently obscure satellite views of the volcano. However there is no evidence that an eruption has occurred. The AVO Operations Room is currently being staffed 24/7 due to unrest at Redoubt Volcano.
(12) Volcanic cloud height:Unknown
(13) Other volcanic cloud information:Unknown
(14) Remarks:Okmok volcano was in vigorous eruption from July 12 through mid-August, 2008. Energetic, intermittent ash emission from several vents within the caldera blanketed much of the northeast portion of Umnak Island with ash and dusted Unalaska/Dutch Harbor with fine ash on several occasions. Rain-induced remobilization of debris from high on the volcano's flanks produced lahars down many drainages, forming new deltas at the coastline. A new, 200-300 m-high (660-980 ft) tephra cone developed inside the caldera at the primary eruption site. Since late August 2008, seismicity at Okmok has generally declined. The last confirmed ash emission at Okmok occurred on August 19, 2008.

Okmok volcano is a 6-mile-wide caldera that occupies most of the eastern end of Umnak Island, located 75 miles southwest of Unalaska/Dutch Harbor in the eastern Aleutian Islands. Okmok has had several eruptions in historic time typically consisting of ash emissions occasionally to over 30,000 feet ASL but generally much lower; lava flows crossed the caldera floor in 1945 and 1958. Prior to 2008, the volcano last erupted in February 1997 producing lava flows and intermittent ash emissions over the course of several months.

The nearest settlement is Nikolski, population about 35, roughly 45 miles west of the volcano. A ranch caretaker family lives at Fort Glenn on the flank of the volcano about 6 miles east of the caldera rim.
(15) Contacts:Tom Murray, Scientist-in-Charge, USGS
tlmurray@usgs.gov (907) 786-7497

Steve McNutt, Coordinating Scientist, UAF
steve@giseis.alaska.edu (907) 474-7131
(16) 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