Back Into Everest's "Death Zone"

High on the shoulders of the world's tallest mountain, teams of anxious climbers are gearing up in the high camps, about to push for the summit of Mt. Everest. Today marks the start of the final weather window—and the last chance this season for climbers to make the summit—with low winds and clear skies predicted on the peak through Sunday, when the spring monsoon is expected to arrive.

With everything on the line over the next few days, some experts fear that the primary summit routes—up the Southeast Ridge and via the North Face—will be choked with traffic, as they were last weekend, when four climbers died while descending Everest in the first summit window. Dr. Luanne Freer, a doctor with the Himalayan Rescue Association, told National Geographic that, based on interviews with bystanders and teammates, those deaths were probably related to high altitude cerebral edema (HACE). HACE most frequently occurs when climbers run out of supplemental oxygen. It's thought that the dead climbers—Shriya Shah, of Canada; Eberhard Schaaf, of Germany; Song Won-bin, of South Korea, and Ha Wenyi, of China—most likely ran out of oxygen due to traffic-related delays on the Southeast Ridge route. Details are still emerging from the last push, including two accounts from the CBC, one about the death of Shah (whose last words were, "Save me") and another from Canadian Sandra Leduc, who will be making her second attempt on the summit over the next day or two (and who calls Everest "a morgue").

National Geographic writer Mark Jenkins, who will also make a summit push today with a joint National Geographic/North Face team led by veteran Conrad Anker, estimated on Wednesday that 100 to 150 climbers would try to reach the top in this push. International Mountain Guides' Eric Simonson, meanwhile, put the number closer to 200. But the most recent reports, gathered from individual teams by Everest documentarian Alan Arnette, are more hopeful. The Peak Freaks team reported from the South Col that they've counted no more than 70 climbers heading to the high camps.

With information conflicting as it tends to in the forbidding environment of Mt. Everest, the best we can do is wish the climbers well as they trudge up into the dark (it's currently 9:30pm on the mountain, about the time when many teams are leaving camp), dizzying heights of the "death zone," and hope for their safe return.