Based on satellite data showing "thermal anomalies," the Alaska Volcano Observatory has issued an eruption advisory for Cleveland Volcano, located in the Aleutian Chain about 45 miles west of Nikolski and about 150 miles west of Unalaska/Dutch Harbor. The advisory means the volcano could erupt at any moment with little further warning. The volcano lacks a seismic network, so observers are monitoring it as best they can via satellite, but if it blows, it could disrupt major air traffic routes. According to the AVO's latest status report, the volcano's most recent significant eruption began in February, 2001 and it produced 3 explosive events that produced ash clouds as high as 12 km (39,000 ft) above sea level and produced a rubbly lava flow and hot avalanche that reached the sea. Learn more from a Reuters report on the advisory, and from the AVO's Cleveland Volcano page.