On Saturday, the mountain, located on the state's southwestern peninsula, began to erupt at a low level, prompting scientists to raise an early warning. On Monday, that alert level was raised again to "watch" as pilots observed a 22,000-foot-high smoke plume rising from the peak, reports the International Business Times.
Elevated ground surface temperatures and satellite images of smoke plumes are both criteria that the Alaska Volcano Observatory uses to distinguish an "erupting" volcano from normal levels of background seismic activity.
Oh, and some campers noticing lava spilling down the northeast side of the volcano.
Pavlof is one of Alaska's most active volcanoes, having erupted dozens of times since 1980. Last year, an eruption caused several flight cancellations due to its location in the Aleutian Range, directly beneath commercial airline paths between North America and Asia.