Mt. Everest's"Death Zone" lived up to its name over the weekend as at least four climbers succumbed to the elements near the 29,035-foot summit of the world's tallest peak.
Overcrowding on the main summit route, leading to prolonged exposure and exhaustion within a low-oxygen zone that begins at 8,000 meters (about 26,000 feet), is being blamed.
The victims were identified as Eberhard Schaaf, 61, a German doctor; Shriya Shah, 33, of Canada; Song Won-bin, 44, of South Korea, and Ha Wenyi, 55, of China.
Still missing is the Chinese climber's Sherpa guide.
A mass summit attempt began Friday and Saturday as climbing teams were taking advantage of the first favorable weather window of of the season. About 150 climbers reached the top of Everest, mostly on Saturday.
But crowding had choked ascent routes, delaying summit bids of some teams by several hours.
"There was a traffic jam on the mountain on Saturday. Climbers were still heading to the summit as late as 2:30 p.m. which is quite dangerous," Gyanendra Shrestha, of Nepal's Mountaineering Department, told the Associated Press.
"With the traffic jam, climbers had a longer wait for their chance to go up the trail and spent too much time at higher altitude. Many of them are believed to be carrying limited amount of oxygen and not anticipating the extra time spent."
The Seoul-based Yonhap news agency is reporting that Song, after collapsing with fatigue, fell at an area known as The Balcony, a small platform area at 27,600 feet.
On average, a handful of climbers perish each year on Mt. Everest. This year, according to Everestnews.com, there have been at least six fatalities, and 198 successful summits.
The most tragic day on Everest, with late summit bids also a contributing factor, was May 10, 1996, when eight people died after becoming trapped in a snow storm.
That season was the most deadly on record, with 15 fatalities.