An air traffic controller in the region said small planes have flown around the plumes from Pavlof Volcano. Ash would have to rise tens of thousands of feet to threaten larger planes.
The eruption began Monday, and a photograph shows lava spraying out from the summit of the volcano, located 625 miles (1,000 kilometers) southwest of Anchorage. The Alaska Volcano Observatory said clouds of ash, steam and gas have occasionally reached the 20,000-foot (6,000-meter) level and have been visible from the nearby communities of Cold Bay and Sand Point.
Onsite seismic instruments have detected an increase in the force of tremors from the 8,262-foot (2,500-meter) volcano.
Typically, Pavlof eruptions are gas-rich fountains of lava that can shoot up to a few thousand feet. But its ash clouds are usually less dense than the plumes of more explosive volcanoes that pose a greater hazard to aircraft, scientists say.
Pavlof is among the most active volcanoes in the Aleutian arc, with nearly 40 known eruptions, according to the observatory.
The volcano last erupted in 2007. During the 29-day eruption, Pavlof emitted mud flows and erupting lava, as well as ash clouds up to 18,000 feet (5,500 meters) high, according to Power.
In early May, Cleveland Volcano, on an uninhabited island in the Aleutian Islands, experienced a low-level eruption. Satellite imagery shows the volcano has continued to discharge steam, gas and heat in the past week. New analysis of earlier images showed a small lava flow going over the southeast rim of the summit crater, the observatory said.
There has been no new imagery in recent days because of overcast skies in the area, Power said.
No ash clouds have been detected in more than a week from Cleveland, which is not monitored with seismic instruments.
The volcano is a 5,675-foot (1,800-meter) peak on a remote island 940 miles (1,500 kilometers) southwest of Anchorage. Cleveland's most recent significant eruption began in February 2001 and sent ash clouds up to 39,000 feet (12,000 meters) above sea level. It also produced a rocky lava flow and hot debris that reached the sea.