Scientists in Alaska are worried that a massive volcano on a remote island about a thousand miles southwest of Anchorage is primed to erupt and spew a giant ash plume that could paralyze intercontinental travel.

The Alaska Volcano Observatory on Tuesday bumped the alert status for the Cleveland Volcano from yellow to orange - one step below the highest alert level.
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© Kym Yano/APAlaskan scientists have raised the alert level for Cleveland Volcano to Orange from Yellow.
"Renewed eruptive activity of Cleveland Volcano has been observed in satellite data," the observatory said, noting that a new 130-foot lava dome - a visible bulge of gathering lava - had formed in the mountaintop's crater.

The group said there have been "no observations" of explosive activity, but cautioned it "remains possible for intermittent, sudden explosions of blocks and ash to occur at any time, and ash clouds exceeding 20,000 feet above sea level."

Cleveland Volcano, also known as Mount Cleveland, is a 5,675-foot peak located on the Aleutian Islands, the chain of more than 300 volcanic islands extending from mainland Alaska that mark the barrier between the Pacific Ocean and the Bering Sea.

About 90% of air freight from Asia to North America and Europe flies over Alaska, along with some 20,000 commercial travelers a day, according to CNN.

Experts say a significant eruption could lead to a shutdown of the airspace, sparking the worst travel nightmare since a giant ash curtain from an Iceland volcano grounded millions of global travelers in April 2010.

"If there is an explosion and (ash) reaches high altitudes, it will causes flights to be rerouted and ultimately canceled," University of Alaska Fairbanks scientist Steve McNutt told CNN.

Cleveland Volcano has not erupted since Dec. 25 and Dec. 29, but those rumbles merely popped an earlier lava dome that had built up during the fall and didn't lead to any major disasters.

Its last major blow was in February, 2001, when three "explosive events" shot ash clouds 39,000 feet into the sky and poured flaming fountains of molten rock into the sea, the observatory said.