THERE MAY BE NO MORE DANGEROUS PLACE to watch a sunset than the top of K2. But on August 1, before all hell broke loose on the world's second-highest mountain, the weather was so calm and clear that some of the 18 climbers who'd summitted that day spent up to an hour and a half taking it in.

On the summit was Wilco van Rooijen, the leader of a Dutch expedition, who survived the ensuing ordeal and who remembers seeing tears in the eyes of a teammate who ultimately did not: Gerard McDonnell, an Irishman who’d lived and climbed in Alaska for the past decade. Both men had been seriously injured by rockfall on previous K2 attempts, but now they'd made it together. Celebrating with them, taking photographs and calling loved ones from their sat phones, were Dutchman Cas van de Gevel; Pemba Gyalje Sherpa, of Nepal, who had accompanied McDonnell up Everest in 2003; and Hugues d'Aubarede and his Pakistani porter, Karim Meherban, both members of a French team. Between 7:30 and 8 P.M., Marco Confortola, the leader of an Italian team, also reached the top.

Beneath them all, bathed in twilight, sprawled Pakistan's Karakoram Range—including Gasherbrum I and II, the world's eleventh- and thirteenth-highest mountains, and Broad Peak, the twelfth-highest. Below the 28,250-foot summit of K2, a team of three Norwegians were on their way down, moving slowly into a treacherous portion of the upper slope known as the Traverse. The Traverse is a wildly steep slope with an unstable 200-foot-tall glacier towering above it and thousands of feet of certain-death falls yawning below. After it plays out, the route descends into the Bottleneck, a narrow, 60-degree couloir. Both the Traverse and the Bottleneck are exposed to icefall from the glacier's hanging seracs.

At the front of the Norwegian group was mountaineer and polar explorer Rolf Bae, who'd turned around just shy of the top because of altitude sickness. Behind him on the rope were his wife, Cecilie Skog, and teammate Lars Naesse, who'd both reached the summit. Skog was several yards behind Bae when she heard a loud crack, followed by a palpable rumble from the darkness above. In an instant, her husband's headlamp vanished under a massive icefall. She and Naesse played their own thin beams over the debris but saw nothing but shredded ropes. They knew that Bae was gone.

Behind the Norwegians, 14 others found themselves stranded on the wrong side of the Traverse. Their fixed lines were badly damaged and their supplemental oxygen—which nine of the 14 relied on—was already running low. Things were bad, but they were about to get a lot worse. By the next day, a third of the nearly three dozen mountaineers who’d started toward the summit on August 1 would be dead.

In the immediate aftermath, news outlets and commentators quickly made comparisons to the infamous 1996 Everest disaster, chronicled by Jon Krakauer in Outside and later in his bestselling book Into Thin Air, which brought to light a growing industry of commercial guides and underexperienced climbers at the top of the world. The New York Times wrote of the K2 tragedy that “the presence of hired high-altitude porters on some of the teams raised questions about whether some of the expeditions might have been commercial, guided efforts.” The insider newsletter Expedition News published a story headlined, "The Everestification of K2." And Tyrolean climbing legend Reinhold Messner scorned the victims' "pure stupidity" in the German media.

Meanwhile, ExplorersWeb.com countered that such statements weren't warranted, and that all of the dead on K2 were, in fact, experienced mountaineers with substantial high-altitude résumés. None of the climbers caught up in the disaster were on commercially guided expeditions.

Who was right? Two months after the debacle, it seems clear that the truth lies somewhere in the middle. Direct comparisons between Everest and K2 are a mistake—the mountains are just too different—but it's obvious that grave mistakes were made in both instances: on Everest by experienced guides leading guided groups, on K2 by groups of experienced climbers. And though K2 is too difficult and dangerous a mountain ever to see Everest-size crowds—which these days can mean hundreds vying for the summit on a single day—the world's second-highest peak is suddenly facing its own crowding problem. The difference is that on K2, a few dozen climbers is all it takes to create a murderous traffic jam.