Mount Spurr is not the kind of lava-spewing volcano familiar from Hawaii, but instead has historically ejected huge plumes of volcanic ash as high as 45,000 feet into the atmosphere, disrupting air travel between the United States and Asia via the great circle routes that link places like New York and Tokyo by following the curve of the earth.

Mount Spurr in Alaska is showing signs of unrest, such as hundreds of small earthquakes beneath the surface. The volcano could be getting ready to erupt soon, with experts saying the chance of eruption is 50-50.