Valley of 10,000 Smokes, Alaska

This year was the 100th anniversary of the Katmai-Novarupta-Valley of 10,000 Smokes eruption in Alaska, probably the largest eruption of the 20th century. When you erupt ~30 cubic kilometers of ash and volcanic debris, it lingers in the environment, especially in locations without abundant vegetation. The ash can be easily remobilized by winds, as we see in November 2012 image of ash blowing out from Katmai over Kodiak Island (above), or by rain, as happens around places like Pinatubo to form lahars. So, even though the eruption may have been a century ago, the lingering hazards remain.

Image: NASA