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Alert level lowered at Alaska's Cleveland volcano

Ben Anderson
Aerial photograph of the Mt. Cleveland lava and summit crater on August 8, 2011. Mt. Cleveland is on Chuginadak Island in Alaska's Aleutian chain.
Photo by Dave Withrow/NOAA
Worldview satellite image collected on August 9, 2011 of the summit crater of Cleveland Volcano. The irregularly shaped dark object in the center of the image is the newly erupted lava dome. It is surrounded by brightly colored mineral deposits produced by volcanic gas emissions. A thin steam cloud partially obscures the view.
Image courtesy of AVO/USGS, copyright 2011 DigitalGlobe
Ashfall on the Lady Gudny on July 21, 2008.
Photo courtesy Anne Hillman, KIAL/Unalaska Community Broadcasting
2008 aerial photograph of the Island of Four Mountains region, including Mount Cleveland.
Photo by Cyrus Read/ AVO, U.S. Geological Survey
The eruption of Cleveland Volcano on May 23, 2006, is featured in this image photographed by an Expedition 13 crewmember on the International Space Station.
Photo courtesy Image Analysis Laboratory, NASA Johnson Space Center
The island with a prominent caldera in left (west) of image is Herbert, just northeast of it is Carlisle, and Mount Cleveland lies almost directly east. The western flanks of Tana are visible in the lower right of the image. Photographed on January 1, 2001.
Photo courtesy Image Analysis Laboratory, NASA Johnson Space Center
Mount Cleveland is a 1,730-m (5,676 ft)-high stratovolcano in Alaska's Aleutian chain. Photographed on July 24, 1994.
Photo by M. Harbin/AVO, University of Alaska Fairbanks
A webcam image showing an eruption at Cleveland Volcano on June 19, 2012.
Alaska Volcano Observatory photo
Aerial photograph of the Mt. Cleveland lava and summit crater on August 8, 2011. Mt. Cleveland is on Chuginadak Island in Alaska's Aleutian chain.
Photo by Dave Withrow/NOAA
Annotated NOAA satellite image from 5:02 AM AST on 29 December 2011 showing a drifting ash cloud from a small eruption of Cleveland Volcano.
Photo courtesy AVO/UAF-GI
Satellite radar image from the TerraSAR-X sensor, showing the summit of Cleveland Volcano on February 10, 2012. It shows the presence of a small lava dome within the summit crater.
Image courtesy of AVO/USGS
This GeoEye IKONOS image shows a faint plume issuing from Cleveland Volcano at 2:31 PM on September 14, 2010. Red in this image highlights areas of vegetation detected by the near-infrared channel.
Photo courtesy Alaska Volcano Observatory/GeoEye
A small volcanic plume rose above remote Mount Cleveland on June 1, 2010. This false-color image was acquired by the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) aboard NASA’s Terra satellite.
Image by NASA Earth Observatory
Aerial photograph of the Mt. Cleveland lava and summit crater on August 8, 2011. Mt. Cleveland is on Chuginadak Island in Alaska's Aleutian chain.
Photo by Kym Yano/NOAA

Mount Cleveland, an active stratovolcano located in Alaska's Aleutian Islands, has been downgraded following a period of increased activity that included numerous small, explosive eruptions.

The Alaska Volcano Observatory said Saturday that Cleveland was being downgraded when the volcano had shown little or no activity since an explosion on March 13. That explosion was preceded by two other small explosions on March 8 and 10. Those explosions were detected by nearby seismic networks, since Cleveland is located on the uninhabited Chuginadak Island and has no real-time monitoring capabilities.

The alert level at Cleveland was lowered to "yellow," meaning that the volcano still has eruptive potential but activity has decreased from previous levels. Cleveland, among Alaska's most active volcanoes, has been upgraded and downgraded numerous times in the last year, including one eruption on Dec. 29 that launched a cloud of ash 15,000 feet into the sky.

In being downgraded, Cleveland joins Mount Iliamna -- a 10,000-foot volcano on the lower west side of Cook Inlet, directly across from the Kenai Peninsula -- in the yellow designation. 

Iliamna was upgraded after scientists noted an increased level of seismic activity in the vicinity of the peak in early March. A weekly report issued Saturday said that earthquake activity remained elevated, but had dropped off from the levels observed in the first weeks of March.

A flight to Iliamna on March 17 to conduct tests on emissions from the volcano, which revealed heightened levels of sulfur dioxide and carbon dioxide, indicating the presence of magma.

"It is not known, however, if this is a newly intruded magma, or whether new pathways for gas from preexisting magma have caused the increased gas flux," The AVO noted. "The amount of gas being emitted is broadly similar to levels seen in 1996-1997, when a likely magmatic intrusion but no eruption occurred at the volcano."

Scientists observed increased venting in the vicinity of the mountain but little other outward indication of extra volcanic activity on the peak. A glacier situated on the peak showed some signs of deformation, but the AVO reported that the steepness of the glacier's location has contributed to avalanches in the past.

Scientists continue to monitor Iliamna, which has never had a recorded eruption.

Casual observers around Southcentral Alaska may have been noticing some increased seismic activity of their own: several earthquakes in recent weeks have been strong and shallow enough to be felt in the heavily populated Anchorage bowl and Matanuska-Susitna Valley areas, as well as along the Kenai Peninsula. That included a minor 3.9-magnitude quake near Wasilla on Thursday and a 3.8-magnitude temblor in Cook Inlet on Tuesday.

Contact Ben Anderson at ben(at)alaskadispatch.com