From Wikipedia

Touching The Void

Touching the Void is a book by Joe Simpson recounting the true story of Simpson's and Simon Yates' disastrous and near-fatal climb of the 6,344-metre (20,813 foot) Siula Grande in the Peruvian Andes in 1985.

Although previously attempted, Yates and Simpson were the first people to ascend to the summit of Siula Grande via the almost vertical west face. Disaster struck, however, on the descent. Simpson slipped down an ice cliff and landed awkwardly, smashing his tibia into his knee joint and breaking it. The pair, whose trip had already taken longer than they intended because of bad weather on the ascent, had run out of fuel for their stove, which they needed to melt ice and snow for drinking water, and needed to descend quickly to their base camp, about 3,000 feet below.

They proceeded by tying two one hundred and fifty foot-long ropes together and then tying themselves to each end. Yates dug himself into a hole in the snow and lowered Simpson down the mountain on the 300 feet of rope. However because the two ropes were tied together, the knot wouldn't go through the belay plate, so Simpson would have to stand on his good leg to give Yates enough slack to unclip the rope, and then thread the rope back through the lowering device, with the knot on the other side. A second disaster struck when Yates was lowering Simpson down the mountain, and lowered him off a cliff. He (Yates) was in a belay seat, much higher up the mountain, and Yates could not see or hear Simpson, but felt all his weight on the rope. Simpson could not climb up because of his broken leg, and Yates could not pull him back up as his belay seat was slowly crumbling up. Neither of them could do anything to save both of them.

Yates had two choices: stay in that same position and wait for the belay seat to break, which would probably have resulted in both their deaths, or he could cut the rope and then climb down to see where Simpson was. As Yates could not see Simpson, he had no idea whether he was hanging over a cliff or simply a few feet from the ground but unable to find secure footing. Yates decided that the only logical step was to cut the rope. Unfortunately, below Simpson at the bottom of the cliff was a deep crevasse, and he knew he would fall into it. When Yates cut the rope, Simpson plummeted down the cliff and into the crevasse.

The next day, Yates carried on descending the mountain by himself. When he reached the crevasse he realised the situation that Simpson had been in, and what had happened when he cut the rope. After calling for Simpson, he was forced to assume that he had died either from the fall or during the night and so continued down the mountain alone.

Simpson was, however, still alive and on a ledge inside the crevasse. He had survived a 100 ft fall, with a broken leg. When he regained consciousness, he took in the rope, and discovered the end was cut, and he realised what Simon had done. He eventually abseiled from his landing spot on an ice bridge (which broke his fall and therefore presumably saved his life) to presumably the bottom of the crevasse, a thin ice roof, and crawled out back onto the glacier via a side opening.

From there, he spent three days without food and only splashes of water from melting ice, crawling and hopping five miles back to the base camp. Almost completely delusional, he reached the base camp a few hours before Yates intended to leave the camp to return to civilization.

Simpson's survival is widely regarded by mountaineers as amongst the most amazing pieces of mountaineering lore.