Scientists are raising the alert level for Cleveland Volcano in Alaska's Aleutian chain after satellite data has indicated thermal anomalies.
The Alaska Volcano Observatory today raised the level to advisory status.
There is no real-time seismic network at the volcano. Scientists say unrest there is frequent, and short-lived explosions with ash plumes up to 20,000 feet can occur without warning and may not be detected by satellites.
Cleveland is about 940 miles southwest of Anchorage, on a remote and uninhabited island in the Aleutians chain.
The observatory says the last significant eruption of the 5,676-foot volcano began in February 2001 and eventually produced a lava flow that reached the ocean. There were minor eruptions in January, June and October 2009.