May 23, 2012 at 4:53 PM ET
A traffic jam on Mount Everest turned deadly last weekend, with fatalities being blamed on the bottleneck of climbers trying to ascend or descend the summit, reports from the mountain say.
At least four climbers died near the summit over the weekend and three others were said to be missing and feared dead, climbers told NBC News' Miguel Almaguer. But Alan Arnette, a climber who is blogging the 2012 Everest expedition season, reported that seven had died over the weekend.
The bottleneck developed after weeks of bad weather prevented climbers from summit attempts until Saturday. When the weather cleared, an estimated 150 people rushed to reach the peak, according to Almaguer.
"When there’s a bottleneck on Everest, you have a long line of climbers that really can’t pass one another," Arnette told Almaguer on TODAY Wednesday morning. "They’re stuck, they're using up their oxygen. And as a result they get cold and potentially make bad decisions."
This deadly combination of factors has caused fatalities in the past. In 1996, a bottleneck and bad weather led to the deaths of eight climbers in one day, an infamous event that was recounted in the book "Into Thin Air."
Jonathan Kedrowski, a climber on the peak who said he passed some of the victims while descending, recounted the tragic aftermath of this season’s bottleneck to Almaguer.
One man wasn't wearing a hat or gloves. "He was kind of looking at me kind of zombie-like," Kedrowski said. "Anybody that would pass him he would reach out and try to grab you. The gentleman’s hand was frozen solid."
It is believed some of the victims died from hypothermia and brain swelling, triggered by the high altitude and a lack of oxygen.
Among the confirmed deaths are Eberhard Schaaf, 61, from Aachen, Germany, Shriya Shah, a 32-year-old Nepal-born woman living in Canada, and a Korean, Song Won-Bin. Discovery News reported that a Nepalese official said 55-year-old Chinese climber Ha Wenyi had also been found dead.
"Schaaf died at the South Summit of Sagarmatha due to altitude sickness," said Ang Tshering Sherpa, chief of the Asian Trekking company that organized the expedition, referring to the Nepali name of the mountain. He said the body was lying on the mountain.
At least two Sherpas died last month -- one after falling into a crevasse and the other reportedly from altitude sickness, according to National Geographic magazine. More than 200 people have died climbing Everest since 1950.
Eric Simonson, Himalayan program director of International Mountain Guides, told msnbc.com that his team of 11 climbers and 11 Sherpas reached the summit on Saturday. The group, he said, were toward the front of the line as they began their attempts at 8 p.m. and started reaching the summit at 4:50 a.m. The team returned safely to their camps.
He said choppers were flying to Camp 2 on Tuesday to pick up injured climbers who successfully descended. "The full story of who was hurt and who wasn’t, who dropped out and who didn’t, won’t be known for weeks," Simonson said.
Often, he said, survival comes down to whether or not climbers are realistic about their oxygen stores. "It’s like watching the needle on your gas tank. And if you know you still have to drive 200 miles and you see the gas tank is getting down to one-quarter, you’ve got to be able to do the mental math and know you’re going to stop and fill up." For Everest climbers, this might mean abandoning a summit attempt altogether if one's oxygen is too low.
The deaths mark a controversial season on Everest. On May 5, Himalayan Experience announced that it was canceling its expedition because of safety concerns. Minimal snowpack and warm temperatures, among other factors, had led to dangerous conditions, including rock fall and avalanches, the company said.
Michael Fagin, who provides forecasting services for Everest teams and runs everestweather.com from Redmond, Wash., said the spring had been very dry and windy. In the past week, winds had reached up to 80 mph; climbers on Everest prefer them under 30 mph.
Last week, the National Geographic-North Face expedition, led by accomplished mountaineer Conrad Anker, canceled its plans to summit via the West Ridge because of icy conditions, but will still attempt to reach the peak via a different route.
Another window to summit is forecast for May 26, and Simonson expects another bottleneck as a second wave of climbers try to reach the peak.
"The bottom line is this is how it is on Mount Everest and how it has been for many years," Simonson said. "When the weather gets good, people want to summit."
Reuters contributed to this report.
Rebecca Ruiz is a reporter at msnbc.com. Follow her on Twitter here.
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