Signs of lava at Mount Cleveland prompted volcanologists to raise their alert level Tuesday afternoon for the Aleutian Islands volcano.
The Alaska Volcano Observatory reports "heightened or escalated unrest" and the possibility of an eruption at the 5,676-foot volcano, according to the observatory's website.
Cleveland Volcano comprises the western half of Chuginidak Island, which sits about 115 miles west of Dutch Harbor and 950 miles southwest of Anchorage.
Satellite data and visual observations in late July revealed a lava dome about 140 feet in diameter growing in the volcano's crater, said volcanologist Chris Waythomas. The dome grew another 10 feet or so between Tuesday and Wednesday, according to the observatory.
"Sometimes lava domes like that can be explosive and lead to ash production," Waythomas said.
The volcano observatory raised the advisory status from "advisory" to "watch" and the aviation warning level from yellow to orange.
Cleveland is capable of blasting volcanic ash more than 20,000 feet into the sky -- a significant danger to air traffic in the vicinity -- so staff at the observatory decided to warn aviators of a possible explosive eruption, the researcher said.
Still, it's not certain that any ash-producing eruption will occur, Waythomas said.
"This could be the end of a little pulse of magma that's come into the volcano to form a little dome in there, and that'll be that, or it could lead to something more explosive," he said.
Because of a lack of seismographic equipment at the volcano, researchers must rely on pilot observations, satellite data and a webcam sometimes obscured by clouds, Waythomas said. An eruption could occur with little or no warning, he said.
Planes flying across the North Pacific Ocean or locally between islands would have to avoid the ash cloud, Waythomas said.
The most up-to-date information on Cleveland Volcano can be found at www.avo.alaska.edu.
Reach Casey Grove at email@example.com or 257-4589.Alaska Volcano Observatory updates on Mount Cleveland
By CASEY GROVE