Kathy Lenniger was running her dogsled team one day along her usual route in Fairbanks, Alaska, when she suddenly splashed into overflow, fresh water spilling on top of the snow. Surprised and chilled, she returned to the parking lot, where a lanky man was loading a sled with science equipment. Nicholas Hasson, it turned out, was studying thawing permafrost — research that could shed light on the streams and sinkholes that recently materialized around Lenniger’s property and all around town.