Some of Alaska's wildfires are dramatic: flames, vast plumes of smoke and firefighting battles. Here, on June 17, a helicopter releases hundreds of gallons of water onto the Stetson Creek Fire near Cooper Landing, Alaska. But even fires that look far quieter, like they're all burned out, can continue to smolder underground — and pose a dangerous threat to permafrost.
Sgt. Balinda O'Neal/U.S. Army National Guard/AP