One of Alaska's most active volcanoes, a towering ice-covered cone in the Aleutian Islands, shot a cloud of ash more than 5 miles (8 km) high on Friday, triggering a warning to aviators and putting on a show that was captured in satellite imagery.
The ash burst from Shishaldin Volcano, about 670 miles (1,080 km) southwest of Anchorage, was part of an on-and-off, mostly low-level series of eruptions that began in July with a stream of lava from the crater at the peak of the 9,373-foot-tall (2,869-meter) mountain.
The ash plume was spotted by a pilot and was visible in satellite images captured from space. It drifted over the sea at least 75 miles (120 km) southeast of the volcano, the Alaska Volcano Observatory reported.
No communities were affected by ashfall or were otherwise in danger as of Friday morning, said David Fee of the University of Alaska at Fairbanks, a coordinating scientist with the observatory.
"This is a remote volcano," he said.
The National Weather Service issued an alert, and air traffic was advised to steer clear of Shishaldin, though aviators were already avoiding the volcano well before Friday because of earlier activity, Fee said.
While Friday's cloud, the largest yet of the series, was considered moderate, conditions at Shishaldin could worsen quickly.
"Shishadin remains at a heightened level of unrest, and explosions may occur with little warning," the observatory warned in a public statement. Friday's explosion lasted about an hour to 90 minutes, US Geological Survey scientist Matt Haney said.