ANCHORAGE, Alaska >> A volcano in Alaska’s remote Aleutian Islands has begun oozing lava, a signal that the mountain could explode and send up an ash cloud that could threaten aircraft.

Satellite images show lava is building in the crater at the summit of 5,675-foot Cleveland Mountain on an uninhabited island about 940 miles southwest of Anchorage, according to the Alaska Volcano Observatory.

“It’s forming a dome-shaped accumulation in the crater,” said Chris Waythomas of the U.S. Geological Survey, the observatory’s acting scientist in charge. “We call these things ‘lava domes.’ It looks like a muffin top.”

Lava domes form a lid on a volcano’s “plumbing,” including the chamber holding the magma. When they grow big enough, lava domes become unstable and will sometimes collapse, decompressing the magma chamber and leading to an explosion, Waythomas said.

“They can seal up the conduit and prevent gasses from escaping and lead to an explosive event,” he said.

Such an explosion from of the volcano on Chuginadak Island could send an ash cloud 20,000 feet or more into the air, the observatory said.

The nearest village, Nikolski, is on another island about 50 miles east and has 18 permanent residents. In previous eruptions of Cleveland Volcano, the village was not considered to be in harm’s way.

“The plume would have to head directly to Nikolski to cause any problems,” such as ash that could cause respiratory problems or damage engines, Waythomas said. If the village uses surface water for drinking, ash could temporarily foul it.

The larger threat from ash clouds is to aircraft.

Alaska’s Redoubt Volcano blew on Dec. 15, 1989, and sent ash 150 miles away into the path of a KLM jet carrying 231 passengers. Its four engines flamed out. The jet dropped more than 2 miles, from 27,900 feet to 13,300 feet, before the crew was able to restart all engines and land the plane safely at Anchorage.

The Federal Aviation Administration and the airline industry get concerned for trans-Pacific flights when an ash cloud has the potential to exceed the 20,000-foot threshold, as Cleveland Volcano has done in the past.

“Generally anything above that altitude can be hazardous to overflying aircraft,” he said.

Cleveland Volcano’s last major eruption was in 2001. It has had bursts of activity nearly every year since then, Waythomas said.

The lava dome now measures 540 feet in diameter, up from 490 feet Sept. 9. Waythomas said a satellite image indicated the lava dome was about 65 feet below the low point on the crater rim. 

“The crater is starting to fill up,” he said. “This could take another week or two and it will be there. And then we’re not sure what will happen.”

The lava flow may stop, or lava could spill over and descend the mountain’s flank.

“It may not do anything explosive. It may just ooze over,” Waythomas said. “Or it could cause the dome itself to collapse just because it becomes unstable at that point. It’s on a steep slope and there’s nothing holding it up there.”

The observatory, a joint program between the U.S. Geological Survey, the University of Alaska Geophysical Institute and the state Division of Geological and Geophysical Surveys, was formed in response to the 1986 eruption of Mount Augustine.

In announcements about Cleveland Volcano, the observatory warns that it does not have a real-time seismic network on the remote volcano and cannot track its earthquake activity, forecast imminent eruptions or even confirm explosive, ash-producing events.

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Alaska Volcano Observatory, http://www.avo.alaska.edu