NASA - National Aeronautics and Space Administration

“This lake wasn’t here 50 years ago.” Katey Walter Anthony, an ecologist at the University of Alaska-Fairbanks, dips her paddle into the water as her kayak glides across the lake. “Years ago, the ground was about three meters taller and it was a spruce forest,” she says. Big Trail Lake is a thermokarst lake, which means it formed due to permafrost thaw. Permafrost is ground that stays frozen year round; the permafrost in interior Alaska also has massive wedges of actual ice locked within the frozen ground. When that ice melts, the ground surface collapses and forms a sinkhole that can fill with water. Thus, a thermokarst lake is born.