ALASKA VOLCANO OBSERVATORY WEEKLY UPDATE
U.S. Geological Survey
Friday, July 18, 2008, 12:43 PM AKDT (Friday, July 18, 2008, 20:43 UTC)
53°23'49" N 168°9'58" W,
Summit Elevation 3520 ft (1073 m)
Current Volcano Alert Level: WATCH
Current Aviation Color Code: ORANGE
The 2008 eruption of Okmok Volcano, which began on July 12 at 11:43 AKDT (19:43 UTC), continues. The initial phase of the eruption was quite explosive and produced a wet, ash and gas-rich plume that reached 50,000 feet above sea level. Wet, coarse (sand-sized) ash fall was reported within minutes of the eruption's start at Fort Glenn, about 10 km W/SW of Okmok Caldera. A light ashfall was also reported at Unalaska/Dutch Harbor by 13:00 AKDT. Based on pilot reports, airborne photographs, and radar intensity images, the eruptive vent appears to be new, having formed to the northwest of Cone D (located east of the center of the caldera).
Over the last week, the severity of eruption has slowly declined. Pilot reports, seismicity, and satellite data all indicate that the eruption is now episodic, with occasional, ash-producing explosions occurring every 15 to 30 minutes. The plumes from these explosions appear to be limited to about 20,000 feet above sea level.
The current Okmok eruption differs from eruptions of the recent past in two important respects: it has been considerably more explosive, and it has occurred in a different place. Prior to this eruption, and at least since the late 1800s, eruptive activity had been concentrated at Cone A, in the southwestern corner of the caldera, and had been limited to relatively low-level plumes, generally less than 30,000 feet above sea level. Because of these differences, it is not a simple matter to forecast the eventual course of the current eruption based on recent past experience. Over the next several weeks to months, intermittent explosions are likely to occur, and some of these may produce ash plumes to 30,000 feet above sea level. Lava fountaining and lava flows are also possible, although these will result in hazards confined mainly within the caldera. We also cannot rule out a return to more vigorous explosions, perhaps even exceeding the size of those on July 12.
Please see http://www.avo.alaska.edu/activity/Okmok.php
for more information.
52°49'20" N 169°56'42" W,
Summit Elevation 5676 ft (1730 m)
Current Volcano Alert Level: ADVISORY
Current Aviation Color Code: YELLOW
Satellite and webcam views were mostly cloudy this week, though on July 14 and today thermal anomalies were visible at Cleveland's summit. AVO received no other reports of activity at Cleveland this week.
AVO monitors Cleveland Volcano with satellite imagery as weather allows. The lack of a real-time seismic network at Cleveland means that AVO is unable to track local earthquake activity related to volcanic unrest. Short-lived explosions of ash that could exceed 20,000 ft above sea level can occur without warning and may go undetected on satellite imagery. Please see http://www.avo.alaska.edu/activity/Cleveland.php
for more information.
OTHER ALASKA VOLCANOES
Seismic activity is monitored in real time at 31 volcanoes in Alaska. Satellite images of all Alaskan volcanoes are analyzed daily for evidence of ash plumes and elevated surface temperatures. Some volcanoes may currently display anomalous behavior but are not considered to be at a dangerous level of unrest. Wrangell, Spurr, Redoubt, Iliamna, Augustine, Fourpeaked, Snowy, Katmai, Griggs, Trident, Novarupta, Mageik, Martin, Ugashik-Peulik, Ukinrek Maars, Aniakchak, Veniaminof, Pavlof, Dutton, Isanotski, Shishaldin, Fisher, Westdahl, Akutan, Makushin, Korovin, Great Sitkin, Kanaga, Tanaga, and Gareloi volcanoes are in color code GREEN
and volcano alert level Normal. All are at or near normal levels of background seismicity. AVO did not detect ash plumes or significant elevated surface temperatures in the vicinity of any volcano.
Please see http://www.avo.alaska.edu/color_codes.php
for complete definitions of Aviation color codes and Volcanic activity alert levels.
VOLCANO INFORMATION ON THE INTERNET: http://www.avo.alaska.edu
RECORDING ON THE STATUS OF ALASKA'S VOLCANOES (907) 786-7478
John Power, Acting Scientist-in-Charge, USGS
Steve McNutt, Coordinating Scientist, UAFGI
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.