How K2 is climbed

In 1856 a British surveyor, Thomas Montgomerie, sketched two peaks from a hill in Kashmir about 210 kilometres away and labelled them K1 and K2, K for Karakoram. The survey used local names wherever it found them. K1 turned out to be Masherbrum. Nobody had a name for the second one that stuck, so it kept its code.

This is the view most people get, from Concordia about 15 kilometres to the south. K2 is 238 metres lower than Everest. What I hadn't realised is how alone it stands. Switch to the view from above and watch the contour lines, one every 100 metres, crowd together round it.

There's no road to K2. Expeditions drive to Askole, the last village, and walk for about a week up the Baltoro Glacier, with porters carrying everything. Most of the ice is buried under rock that has fallen from the walls on either side, which is why the lower glaciers here are grey rather than white.

At Concordia four glaciers meet and the route turns north up the Godwin-Austen Glacier, named after another surveyor. Base Camp sits on the ice at about 5,000 metres, higher than any summit in the Alps. Drag the slider to walk it.

At Base Camp each breath already holds only a little over half the oxygen it would at sea level. The body adapts. Within hours you breathe faster, and over weeks you make more red blood cells. But it adapts slowly, and mountain doctors advise that above 3,000 metres you sleep no more than about 500 metres higher than the night before.

So climbers go up and come back down. They carry loads to Camp 1, sleep there, and return to Base Camp to recover, then go higher the next time. I'd assumed the summit push was the climb. It's really the last of several. Compare the two plans.

This ridge is the Abruzzi Spur, named after the Duke of the Abruzzi, an Italian prince whose 1909 expedition picked it out as the way up. Most K2 summits have come this way since. It looks gentle from Base Camp. It isn't.

Just below Camp 2 is a crack about 30 metres tall, House's Chimney, named after Bill House, the American who first climbed it in 1938. Today it's hung with old ropes left by decades of expeditions. Point at the mountain to read how steep the ground is.

Above Camp 2 the ridge becomes the Black Pyramid, about 400 metres of dark rock and ice, steep enough that you're climbing with your hands most of the way. Camp 3 sits just above it.

Yellow on the map is 30 to 40 degrees, the angle at which snow slabs most often break away as avalanches. Dark red is steeper than 50, too steep for much snow to stay. The route weaves between them. Switch the map off to see the mountain as a climber would.

Camp 4 sits on the Shoulder, a broad slope of snow just under 8,000 metres. Above about 8,000 metres the body can't adapt any more. Climbers call it the death zone: however fit you are, you're slowly getting weaker.

I'd assumed there was less oxygen in the air up here. There isn't. It's still 21%, but the air pressure is lower, so each breath pulls in fewer molecules of everything. On the summit you get about a third of a sea-level breath. Drag the altitude and watch the oxygen fall.

Above the Shoulder the route squeezes into the Bottleneck, a gully of 50 to 60 degrees at 8,200 metres, then traverses left beneath a serac, a cliff of glacier ice hanging from the summit slopes. Everyone climbs it on one fixed rope, one person at a time.

On 1 August 2008, as climbers were coming down from the summit in the evening, part of the serac broke away and swept the ropes off the traverse. Eleven climbers died over the next two days. In 2023 Muhammad Hassan, a Pakistani high-altitude porter, fell near the Bottleneck on a morning when a long line of climbers was on the rope, and died there. Every person ahead of you is more time under the ice. Set the queue.

Achille Compagnoni and Lino Lacedelli reached the top on 31 July 1954. The night before, Walter Bonatti and the porter Amir Mahdi had carried oxygen up for them, couldn't find their tent, and spent the night in the open at about 8,100 metres. Mahdi lost all his toes to frostbite.

Compagnoni later claimed Bonatti had used some of that oxygen. Bonatti spent fifty years arguing otherwise, and in 2007 the Italian Alpine Club accepted his account. The summit itself sits on the border between Pakistan and China. Turn round and look both ways.

The summit is only halfway. You're exhausted, it's late, and the hardest ground on the mountain is below you. In 1953 an American team retreating in a storm was lowering Art Gilkey, who had a blood clot in his leg, when one climber slipped and pulled the others off with him. Pete Schoening had the rope wrapped round his ice axe, jammed behind a boulder. He held all six. Climbers still call it the Belay. Gilkey was lost in an avalanche soon after.

Between the first ascent in 1954 and January 2021, 377 people reached the top of K2 and 86 died on the mountain. Each dot is one of them.

By 2020 every 8,000-metre peak had been climbed in winter except K2. Winter there means jet-stream winds and short days, and in midwinter K2's summit air is thinner than Everest's in its climbing season, partly because K2 is eight degrees further north.

On 16 January 2021 ten Nepali climbers from three teams stopped ten metres below the summit, waited until they were all together, and walked the last steps singing their national anthem. Switch seasons and see how much daylight they had.

You leave Camp 4 in the dark with a head torch. Pick when you set off, how fast you climb, how long the queue is, and the time you'll turn round whatever happens. Most deaths on K2 come from getting the last one wrong.