THERE ARE ABOUT TEN ROUTES to the top from K2’s 16,750-foot base camp, but most expeditions make their way up the Abruzzi Spur, a series of steep ridgelines on the southeast flank. Several dozen successful teams have also taken a more direct ridgeline, the Cesen Route, on the south side of the peak. Both approaches stop at three camps en route to a shared camp four, situated at 25,000 feet on the mountain’s prominent shoulder. In August, the seven teams were divided between the two routes, with most ascending the Abruzzi. Above camp four, some three dozen climbers merged into a single narrow column.

Everest also has two main routes with four standard camps, but K2 is 20 degrees steeper on average and is located 545 miles farther north. It's 785 feet shorter than Everest, but the climbing is more technical, more exposed to falling rock and ice, and the peak is subject to harsher weather. The result is a mountain that claims many more lives for each successful summit bid. Everest has been climbed roughly 3,000 times, with hundreds of new names added to the list every year. K2 has seen only 299 ascents—and in many years, nobody summits. According to logs compiled by ExplorersWeb, 10.3 percent of K2 summiters have died on the descent. That’s more than five times Everest’s fatality rate for summiters, 1.82 percent. Among elite climbers, K2 is known as "the mountaineer's mountain." It's also called "the savage mountain."

"K2 is the holy grail," says American Ed Viesturs, who's climbed all of the world's 8,000-meter peaks, including K2, without supplemental oxygen. "A climb of K2 is more important than a climb of Everest. People are willing to push longer and harder for it." The mountain's prestige beckons mountaineers, as does its relative affordability. Since 2003, the Pakistani government has attempted to boost tourism by cutting prices on Himalayan-climbing permits by up to 95 percent. It now costs a mere $6,000 for a team of seven to attempt the mountain.

Still, there's no evidence to suggest that inexperienced mountaineers are suddenly flocking to K2. The use of hired Nepalese and Pakistani porters—aberrant a decade ago—is becoming more common, but guided expeditions are still rare. (One was there this year, although none of those climbers were involved in the August mayhem.) Everest, by comparison, is dominated by commercial expeditions.

"Commercial climbing has no place on K2 like on easier mountains like Broad Peak, Gasherbrum II, or even Everest," wrote Nazir Sabir, president of the Alpine Club of Pakistan, in an open letter after the disaster.

Which raises an obvious question: How did a group of veteran mountaineers get themselves into so much trouble?

THE SUMMIT BID BEGAN with a meeting in base camp in late July, after forecasts had predicted a good weather window on August 1. On crowded peaks, climbers generally work together to improve everyone's chances of reaching the top safely. This year, with ten expeditions on the mountain—including teams from Singapore, Korea, Spain, Serbia, the Netherlands, France, Italy, Norway, and the U.S., as well as a multinational group—communication was especially important.

Van Rooijen, who'd arrived with his Dutch squad several weeks before the other teams, organized the communal effort. Each expedition would be tasked with carrying ropes and other shared gear up the mountain, piling it up at camp four in preparation for the final push. At 10 P.M. on July 31, an advance team—comprising the strongest climber from each expedition—would leave camp four to fix the ropes through the Bottleneck and Traverse. The team would be led by Korean climber Kim Jae Soo, and it included Pakistani porter Shaheen Baig, the only climber on the mountain who’d been through the Bottleneck and knew where to set the ropes.

Shaheen Baig never made it to camp four, however. He turned back sick at camp two. According to Chhiring Dorje Sherpa and Chris Klinke, of the American expedition, when the time came for the rope-fixing team to start working, they discovered that they were short-handed and that some teams hadn't brought enough line. The search for more equipment and manpower delayed the advance team for more than two hours, the first of a series of setbacks that would keep all but one climber out well past dark.