Jan Theiler works at the top of a mountain in Switzerland that has been made safe for novice skiers and walking tourists, and part of his job is to make sure it remains that way.
In the middle of the summer of 2017, a tower holding a ski lift above one of the intermediate trails had drifted slightly out of position, which was neither unexpected nor uncommon because both the tower and the trail are built on a glacier, and glaciers move. It does not matter that the ice has been tamed and groomed and that snow buses haul people across it to a monolith tottering at the edge: Beneath the surface snow, the glacier is constantly in motion, flexing and flowing with such force that anything on it, or under it, or in it, is going to move, too.
Usually the movements are imperceptible. Like stop-motion photography, the shifts and lurches aren’t apparent until the frames are played back at speed. In 22 years working on the glacier, Theiler has seen the gradual but dramatic changes, the way it recedes year after year, the summer meltwater outpacing the winter snowfall. The slab creeps across a little less of Les Diablerets, a massif in the Alps of western Switzerland, each year, the blue-gray of the edges swirled like a tide pool on limestone slowly exposed by the seasons.
Theiler needs the big machine to nudge the tower back in place, the 34-ton Caterpillar parked near the bottom of the run. He drives one of the snow buses across the glacier, big treads churning through the midsummer slush. Ahead, in the light of the late afternoon, he sees a dark patch that hadn’t been there a few days before.
He thinks it looks like mud.