Cotopaxi is an almost perfectly symmetrical cone standing 5,897 metres over the Ecuadorian highlands, an hour south of Quito, and the glacier that gives it that shape is also the dangerous part. Lava is not the problem here. When magma heats the summit the ice can melt within hours and come down the valleys as lahars, fast slurries of mud and rock that travel far beyond any lava. That is what happened in 1877, and tens of thousands now live along those same paths, around Latacunga and out toward Quito, so the mountain is watched constantly and evacuation routes are marked. At its feet the ground is páramo, the cold tussock grassland of the high Andes, gold in low light and dotted with spiky red chuquiraga. Herds of wild horses graze it and pay you almost no attention. A flat trail loops the glacier-fed Limpiopungo lagoon, where Andean gulls and ducks work the shallows. On a calm morning the cone stands doubled in the water, before the mountain wraps itself in its own cloud.
The José Ribas refuge sits at about 4,800 metres, reached by a steep path of loose volcanic sand that takes you up from a car park high on the flank. It is a short walk and a hard one: the air up there holds so little oxygen that you stop to breathe every few minutes. On a clear day the clouds are below you rather than overhead. That is as far as most people go. Summit parties leave the refuge around midnight, while the snow is still frozen hard and falling ice least likely. The rest of the night goes on crossing the glacier by headlamp, in crampons and roped to a guide, taking the last thousand metres slowly. They reach the top at first light, and it takes several days of acclimatising in the highlands beforehand to have a real chance. Andean peoples held this mountain holy long before the Inca arrived, reading its eruptions as omens. The valleys living in the path of the next one are farming the soil the last ones left.