(CNN) -- A heightened state of alert has been issued for a remote Alaskan volcano after the detection of a drifting ash cloud, the result of what's believed to have been a lone explosion.
The U.S. Geological Survey put out an orange alert Thursday for Cleveland Volcano in the Aleutian Islands, about 940 miles southwest of Anchorage. That is third out of four possible levels on the federal agency's warning scale.
"Satellite data indicate that this is a single explosion event," the survey and Alaska Volcano Observatory said in its notice, but "more sudden explosions producing ash could occur with plumes exceeding 20,000 feet above sea level,"
A similar alert had been issued in early September, amid concerns that the volcano could be leaking from its flanks if the lava inside continued to build up. The volcano's lava dome was 262 feet in diameter on August 30, but by then in had expanded to 394 feet.
That warning was downgraded to yellow on November 3.
According to the observatory, satellites spotted a "detached drifting ash cloud" some 15,000 feet above sea level around 7 a.m. (1 p.m. ET) and moving east-southeast.
Situated 45 miles west of Nikolski by the Bering Sea, the Cleveland volcano makes up the western half of uninhabited Chuginadak Island.
Its last, most significant eruption came in February 2001, when three explosions created ash clouds that soared as high as 39,000 feet and spurred a hot avalanche that reached the water. Smaller ash emissions were detected in January, and before that in June 2009, the observatory said.
Cleveland is one of over 130 volcanoes and volcanic fields that have been discovered in Alaska. About 90 of these have been active over the past 10,000 years, including more than 50 since the mid-18th century, according to the observatory. Roughly three-quarters of all active U.S. volcanoes to erupt in the past two centuries have been in Alaska.