A 14-minute eruption by an Alaska volcano sent an ash cloud to 30,000 feet in the Aleutian Islands. The Alaska Volcano Observatory says Bogoslof Volcano erupted at 3:17 a.m. Tuesday.
Ash clouds above 20,000 feet can harm airliners flying between Asia and North America.
The observatory raised the aviation alert code to "warning," its highest level.
Winds were blowing to the northeast, which would push a cloud into the Bering Sea.
The observatory says the cloud was not expected to drop ash on Aleutian communities or the mainland.
A cloud was not immediately spotted but the World Wide Lightning Location Network detected lightning strokes with the volcanic cloud.
Bogoslof has erupted periodically since mid-December. The volcano is 850 miles southwest of Anchorage.