The series of deaths, over the course of the Friday ascent and Saturday descent, was the worst single accident in the history of K2 mountaineering.

The main problem was reported as an ice avalanche occurring at an area known as "the Bottleneck", which destroyed many of the climbers' rope lines.

[7] The most dangerous section of the climb is the Bottleneck, a steep couloir overhung by seracs from the ice field east of the summit.

The high risk of falling ice and avalanches means climbers aim to minimize time spent there.

His experience as the only person in the collected teams to have previously summited K2,[8] and his unofficial leadership of the HAPs and Sherpas, was sorely missed.

This forced the climbers to take the rope from the lower portion of the route and use it to prepare the lines above the Bottleneck, causing a dangerous unplanned delay in the climb schedule.

Chris Klinke pushed on for a few more hours before abandoning the ascent,[11] as did Jelle Staleman of the Norit team, who was also suffering frozen feet.

[15] When Sträng reached the body, Serbian climbers Predrag Zagorac and Iso Planić, along with their HAP Mohammed Hussein, had already arrived.

They were joined by Jehan Baig, a HAP from the French team, who had fulfilled his assisting duties and had been allowed to head down.

Several people later indicated Baig may have been suffering from high altitude sickness, since he had displayed questionable behaviour in abseiling down the Bottleneck.

Baig lost his footing and bumped into Sträng, who then urged him to let go of the rope attached to Mandić's harness, before all four climbers would be dragged down.

[16] The Serbian group aborted, wrapped Mandić's body in a flag and fastened him to the mountain, and started to descend.

Members of the Norwegian group – including Lars Flatø Nessa and Skog, who had both summitted two hours after Zerain – had almost navigated the traverse leading to the Bottleneck, when a serac broke off from above.

As it fell, it cut all the fixed lines and took with it Skog's husband Rolf Bae, who had abandoned the ascent only 100 m (330 ft) below the summit, telling Nessa to look after his wife, as he waited for her.

Nessa and Skog continued descending without the fixed lines, and managed to reach Camp IV during the night.

Chunks of ice lay scattered around the route, and the mountaineers above were stranded in darkness in the death zone above 8,000 m (26,000 ft).

According to team Norit's Dutch mountaineer Wilco van Rooijen, panic broke out among the climbers waiting above the Bottleneck.

The Norit team included a full climbing member named Pemba Gyalje, a Sherpa mountaineer who years earlier had been a support climber on Mount Everest.

Sherpa Chhiring Dorje also descended the Bottleneck with "Little" Pasang Lama (who had been stranded without an ice axe) secured to his harness.

The men had climbed up around midnight without food or oxygen, and found Go Mi-Young stranded somewhere in the Bottleneck, unsure of which route she had to take.

Confortola claimed that during the bivouac, he heard screams and saw headlights disappear below him after a roaring sound came from the serac field.

[23] The rescue efforts started in the base camp as a group was sent upwards with ropes to help those still stuck in the Bottleneck.

Later, van Rooijen reached the remaining Korean climbers (Confortola claims one of them was Kyeong-Hyo Park) and their guide Jumik Bhote.

Confortola assumed McDonnell had succumbed to high-altitude sickness and was growing delusional, believing he had to climb back up.

Van Rooijen, in his book Surviving K2, supports the theory that Karim bivouacked even higher on the mountain than himself, Confortola, and McDonnell.

Graham Bowley (a New York Times Investigative reporter), in his book No Way Down (2010),[27] is unable to refute the evidence presented by van Rooijen but still deems the photos inconclusive at best.

[citation needed] The existence of multiple plausible scenarios underscores the uncertainty, even among eyewitnesses, pertaining to the course of events on K2 that day.

In the book Buried in the Sky (2012), Amanda Padoan and Peter Zuckerman examine much more closely the Sherpa and HAP experiences of the 2008 disaster, and present plausible alternative scenarios and explanations of the events, including the possibility that McDonnell and Karim were still alive at the time of the fourth serac fall.

They evacuated the two injured and frostbitten Dutch climbers from the base camp, located approximately 5,000 metres (16,400 ft) above sea level, to Skardu.

[48] K2's summit was not reached again until 23 August 2011, when Gerlinde Kaltenbrunner (Austria), Maxut Zhumayev and Vassiliy Pivtsov (Kazakhstan), and Darek Zaluski (Poland) topped out via the North Pillar.