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By Yereth Rosen | Reuters– Fri, Sep 16, 2011ANCHORAGE, Alaska (Reuters) – A volcano in Alaska‘s Aleutian Islands has been in an unusual low-level eruption for two months, raising the spectre of an explosive eruption with little warning, officials at the Alaska Volcano Observatory said on Friday.

Cleveland Volcano, a 5,676-foot peak located 940 miles southwest of Anchorage, continues to expel lava out its crater, a low-level eruption that began in mid-July, scientists at the Alaska Volcano Observatory said.

Satellite imagery shows a lava dome growing inside the volcano’s crater. Satellite data also shows continued heat generated from the volcano, according to the observatory, a joint federal-state organization.

So far, there have been no signs of ash clouds. But those could come with little warning, scientists said.

“The big thing we’re concerned about is an explosive eruption,” said Steve McNutt of the University of Alaska Fairbanks, a coordinating scientist for the observatory.

One worry is that the dome could seal off the crater vent entirely, causing pressure to build until it is released explosively, McNutt said. Or the dome could topple, triggering a molten flow down the mountain that releases gas and ash into the atmosphere while lava and rocks tumble, he said.

While Cleveland is one of Alaska’s most active volcanoes — erupting about once a year over the past decade — its long-running lava flow and dome buildup is something different from past behavior, scientists said.

Past eruptions have been mostly brief and explosives, with relatively small ash clouds, said Chris Waythomas, acting scientist-in-charge at the observatory.

Interference with air travel is the most immediate risk posed by Alaska’s volcanoes because the peaks lie directly in the flight path used by jets traveling between Asia and the U.S. West Coast.

Jet engines can be damaged or shut down abruptly when they suck in gritty volcanic ash.

A KLM airliner abruptly dropped more than 14,000 feet when it flew through ash from erupting Redoubt Volcano in 1989. The badly damaged jet landed in Anchorage.

For scientists at the observatory, Cleveland’s remoteness poses special challenges. Scientists have not been able to station seismic instruments on Cleveland, as they have on volcanoes closer to Anchorage, so they have no real-time data.

Instead, they must rely on satellite imagery, which is often disrupted by cloud cover, and on other measurements that can be delayed.

Getting seismic equipment on Cleveland has so far proved too costly a proposition, the scientists said.

“It’s been on our list for years,” McNutt said, adding that such a project could cost up to $1 million. “It’s just a very expensive and very difficult place to work,” he said

(Editing by Dan Whitcomb and Peter Bohan)

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