Okmok Volcano Eruption |
Okmok Volcano Summary:
USGS News Release from July 18, 2008
Okmok Volcano on Umnak Island, Alaska continues to produce explosions and ash plumes through a newly
created vent and poses hazards to air travel in the area.
Scientists are using a combination of seismic and GPS instruments on the ground and weather
and radar satellites in space to track the progress of the eruption. Human visual
observations are limited because airborne ash obscures a view of what is happening inside the
volcano's 6-mile-diameter caldera and the area is too hazardous to enter.
"We are dealing with a scientific challenge because the volcano went from very quiet to a large
eruption, putting ash to high altitudes with almost no warning," said John Power, Acting Scientist
in Charge of the Alaska Volcano Observatory (AVO).
The powerful eruption in the Eastern Aleutian Islands began unexpectedly on July 12, sending
up a wet, ash and gas-rich plume that reached an altitude of 50,000 ft above sea level.
Heavy ash fall occurred on eastern Umnak Island. A dusting of ash fell in the busy
fishing community of Unalaska, 65 miles northeast of Okmok volcano. The ash plume soon
spanned several hundred miles across the North Pacific, causing many trans-Pacific flights
to be diverted and cancellation of flights to the Dutch Harbor airport. The gas cloud from the
eruption is now over Montana.
The eruption also destroyed or damaged seismic and deformation sensing equipment at two
monitoring stations. A third station has lost its communication pathway due to destruction at
the other two. Seismic equipment relays earthquake information and GPS equipment is used in
monitoring the deformation of the ground surface in response to magma movement. Seven seismic
stations are still operational and seismicity has gradually decreased in intensity since the
initial eruption.
At a minimum, activity at Okmok is likely to continue for days or weeks. Strong gas-driven
explosions can produce rock ballistics or larger volcanic debris that can be hurled beyond the
crater rim of the volcanic caldera, potentially landing in surrounding areas several miles away.
Fast moving clouds of ash, larger debris, and hot gas can form and flow across the caldera floor,
rise up over the caldera wall and continue to flow down Okmok's flanks. Rain mixed with ash could
create mudflows and rapid flooding along island drainages. As soon as conditions allow, AVO
scientists will travel to the volcano in order to document and understand the sudden onset of
explosive activity and repair damage to monitoring equipment.
The Okmok caldera formed during catastrophic eruptions 12,000 and 2,000 years ago. There are
about a dozen cones within the modern caldera that formed in the last 2000 years, and the most
recent eruptive activity occurred in 1945, 1958 and 1997. One violent eruption of Okmok in 1817
produced many feet of ash and "scoria" rock debris on the northeastern caldera rim, as well as
ash fall on Unalaska Island and floods that buried an Aleut village at Cape Tanak on the northeast
Bering Sea Coast of Umnak Island.
USGS is responsible for issuing timely warnings of potential volcanic disasters to affected
communities and civil authorities.
Information about the current eruption of Okmok Volcano, including activity statements, images,
background materials, and related hazards can be found at the AVO Okmok
Activity web page. |
The most comprehensive and up-to-date source of information on Okmok Volcano. |
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Aerial photo of the July 13th eruption from Alaska Pubic Radio. |
A short summary by the Smithsonian Institution's Global Volcanism Program. |
Frequent news items on worldwide volcanic activity. |
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Physical and political maps of Alaska. |
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Oblique aerial photo of Okmok Caldera taken in early June, 2007. The caldera is about 9 kilometers in diameter and 700 meters deep. Several
minor eruptions produced the cones, craters and lava flows on the caldera floor. Image by Cyrus Read, AVO/USGS.
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| Satellite Image of Okmok Volcano, a shield volcano on the northeastern portion of Umnak Island from March 25, 2005. Image Analysis Laboratory, NASA Johnson Space Center. |
| Separate steam and ash plumes stream from Okmok Volcano on July 12, 2008. The ash cloud rose to elevations of over 10,000 meters (35,000 feet). The green color of the ocean is from volcanic ash. NASA image. |
One of Okmok's important impacts is its ability to produce large volumes of volcanic ash. This article details volcanic ash and its potential impacts.
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| Cartoon showing hypothetical phreatomagmatic and Strombolian style eruptions within Okmok caldera by Jessica Larsen AVO/ADGGS. |
Okmok Hazard Assessment:
Beget, J.E., and others, 2005, Preliminary volcano-hazard assessment for Okmok Volcano,
Umnak Island, Alaska: Alaska Division of Geological & Geophysical Surveys Report of
Investigation 2004-3, 32 pages.
Download (Large PDF file). |
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| Okmok volcano is located on Umak Island, one of Alaska's Aleutian islands. Location map by Cheryl Cameron, AVO/ADGGS. |
Okmok Shaded Relief Map:
Shows the geomorphic features of Umnak Island and Okmok Volcano by Jessica Larsen, AVO/ADGGS. High resolution image. |
Geologic Maps of Okmok and Umnak Island:
Shows aerial extent of volcanic and surficial deposits, and more. AVO Maps page. |
Okmok Volcanic Hazards Map:
Shows hazard zones for pyroclastic flows, ash fall, debris avalanches, tephra and more. Alaska Division of Geological and Geophysical Surveys. High resolution image. |
Geology of Umnak and Bogoslof Islands, Aleutian Islands, Alaska:
from the USGS Investigations of Alaskan Volcanoes Series. 118 pages.
Download (Large PDF file). |
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