A year ago this week, 16 sherpas were killed in an avalanche above Everest base camp. Carole Cadwalladr, who travelled to the camp for The Observer, says Everest is a mirror as well as a mountain: “We see in it what we want to see. And our ideas about it fit the ideas we have about the world we live in. Lefties see exploitative labour practices, mountaineers see a corruption of the sport they love, Sherpas see economic opportunity and each year around 300 people see a fixed point against which they can test themselves.”