Printer friendly versionALASKA VOLCANO OBSERVATORY
Wednesday, September 20, 2006 2:25 PM AKDT (2225 UTC)
58°46'12" N153°40'19" W, Summit Elevation 6903 ft (2104 m)
Current Level of Concern Color Code: YELLOW
On Sunday evening, September 17, AVO received numerous reports of a large unusual cloud rising to heights of 20,000 ft (6,000 m) above sea level from the Cape Douglas area, about 200 miles (320 km) southwest of Anchorage and about 80 miles (140 km) northwest of Kodiak. Since our Monday, September 18 Information Release, additional data and observations of the September 17 event have been compiled from several new sources. These data confirm that the source of the large cloud observed Sunday evening was volcanic. Thus, AVO is increasing the Level of Concern Color Code for Fourpeaked volcano from “Not Assigned” to YELLOW
The exact location of the source is still unknown. Satellite and radar data suggest a source low on the flank of Fourpeaked volcano and we are assigning this activity to Fourpeaked based on this data. However, this location has not yet been confirmed by visual observations.
New details of Sunday’s event have been added since Monday afternoon:
Retrospective analysis of data from the NEXRAD Doppler radar in King Salmon show an unusual cloud starting at 12:00 PM AKDT (2000 UTC) on September 17. The maximum cloud height determined by radar during the first hour of the event was 20,000 ft (6,000 m). The radar return from the cloud continued until at least 9:45PM AKDT (0545 UTC).
A cloud of sulfur dioxide gas released during the eruption was observed by colleagues at the University of Maryland Baltimore County over Cape Douglas/Fourpeaked region on September 17, 2006 at 3:00PM AKDT (2300 UTC) using data collected by the Ozone Monitoring Instrument (OMI) on NASA’s Aura satellite.
Puff particle dispersion modeling showed that the cloud would have spread west to east as it moved northwards over the subsequent day. This is consistent with pilot reports received by AVO on the afternoon of Monday, September 18, that described a strong sulfur smell in the Stony River Valley, 300 km (180 miles) northwest of the Fourpeaked area, and from additional OMI sulfur dioxide observations of the cloud.
Although satellite data did not detect ash during this event, AVO received reports of a trace of ashfall at Nonvianuk Lake outlet (110 km, about 70 miles, west-northwest of the volcano) and near Homer (about 95 miles northeast of the volcano).
Although poor weather in the area has prevented visual observations, NEXRAD data over the past two days have not detected any further emissions. AVO staff will attempt both fixed-winged and helicopter overflights this afternoon to locate the possible vent areas and document any changes. AVO continues to monitor satellite data for further signs of activity.
Fourpeaked Mountain lies within the northeast corner of Katmai National Park and Preserve on the Alaska Peninsula, 7.5 miles (12 km) southwest of Mount Douglas. It is the likely vent for Fourpeaked volcano, a stratovolcano that is mostly surrounded (and covered) by Fourpeaked Glacier. Small isolated volcanic exposures along ridge crests and cliff faces radiate out from the ice-covered summit. The last volcanic activity at Fourpeaked was probably greater than 10,000 years ago. No recent volcanic or hydrothermal activity has been identified.
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
Tom Murray, Scientist-in-Charge, USGS
firstname.lastname@example.org (907) 786-7497
Steve McNutt, Acting Coordinating Scientist, UAF
email@example.com (907) 474-7131
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.