A remote volcano in Alaska’s Aleutian islands erupted early on Thursday, spouting an ash cloud 15,000 feet into the sky and prompting an air-traffic alert, scientists said.

The Cleveland Volcano, located on an uninhabited island 940 miles southwest of Anchorage, had been oozing lava and gas since July.

Ash from the 5,676-foot volcano is considered potentially dangerous to aircraft because Cleveland’s peak lies directly below commercial flight routes between Asia and North America.

Thursday’s explosion, captured by satellite imagery, likely stemmed from a gradual buildup of pressure during months of intermittent low-level eruptions, said Dave Schneider, a geophysicist with the Alaska Volcano Observatory.