A couple of days before Christmas, Sam Cossman balanced precariously on a rock face 800 feet above one of the world’s seven permanent lava lakes, in the Marum crater on Ambrym island, Vanuatu, in the South Pacific. Dark was falling, but the orange light from the 2,000-degree molten rock below lit up the crater around him like perpetual sunset. The ActSafe powered rope ascender that was supposed to lift him and his 70 pounds of gear back up to basecamp was leaking fuel. All he could do was hug tightly to the rock wall and wait for tools and a new tank of gas to be brought down to him. Then it began to rain.
The sulfur dioxide in the air turned each falling drop into burning acid, and within moments the trickle of water down the rock face was replaced by a torrent. The ground above was mostly bare rock, so rainstorms quickly triggered flash flooding. As the water ran down the side of the crater it brought with it a hailstorm of loose rocks, before plunging into the lava below. When it hit the molten rock, thick, choking plumes of acidic steam rose back upwards.
Two days earlier, on his first descent of this expedition, Cossman had been hit hard by a falling rock. He’d lost his grip on the rope and been momentarily dazed, but luckily it had left no more than a painful bruise near his right collarbone. This time he might not be quite so fortunate. What the f— am I doing here? he thought.