"The ground is shaking," a man's voice says, sounding incredulous. "Shit," he says, amid giggles of disbelief from others. Then, seconds later, the camera swings around to see something truly horrifying: a wall of snow and debris descending from all directions, about to engulf a collection of tents. The video was uploaded to a YouTube channel operated by Jost Kobusch, a German mountaineer attempting to climb Everest, on Sunday.