Eleven people have died scaling the peaks of Mount Everest this year in a particularly crowded season atop the world's highest mountain.

Government officials in Nepal blamed bad weather limiting the number of days people can attempt to summit the mountain. Veteran mountaineers said overcrowding and inexperience can kill climbers.

"There were more people on Everest than there should be," Kul Bahadur Gurung with the Nepal Mountaineering Association told The Associated Press.

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What made this season so deadly? Is it uncharacteristic for the treacherous peak that has claimed more than 200 lives? These are the numbers that explain what's happening atop Everest:

At least 11 deaths

Most of the 11 fatalities on Mount Everest's peaks this year were because of complications related to altitude sickness.

It's the highest number of climbers killed since 2015 when more than a dozen climbers and Sherpas died, most in an avalanche at base camp. In 2014, 16 Sherpas died in an avalanche.

Climbers and Sherpas die almost every year on the dangerous mountain, often because of altitude sickness, exposure, falls or natural disasters such as avalanches.

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Among the dead this year: Americans Christopher Kulish, 62, and Don Cash, 55, who died within a week of each other.

The two men were on separate expeditions, but both were realizing their goal of joining the Seven Summits Club, a membership earned when a person climbs the tallest mountain on each of the seven continents.

Both men reached Everest's summit but died shortly after as they descended, probably because of complications from altitude sickness.

381 permits

A record-breaking 381 people were issued permits to climb Everest this year by Nepal's government. The actual number of people on the mountain is at least double that, including the Sherpas who do much of the work for the climbers.

As a result, there has been a record number of successful summits – more than 825, said Alan Arnette, a Colorado climber who summited Mount Everest on his fourth attempt in 2011 and who keeps a blog of Everest climbing seasons. That number includes Sherpas and climbers in Nepal and China.

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Climbers can approach the peak from the north in Tibet or the south in Nepal. China and Nepal issue permits each year to track how many climbers are on the mountain and to add additional revenue for the countries.

This year, the Chinese government increased restrictions around the permits it gave out. Nepal has no limit and requires little other than a doctor’s signature to climb Everest.

$11,000 per permit

Nepal, one of the world's poorest countries, has a booming climbing industry that brings in $300 million each year. Each permit to climb Mount Everest costs $11,000, said Mohan Krishna Sapkota, secretary at the Ministry of Tourism and Civil Aviation.

Nepalese government officials said they have no plans to limit the number of permits but admitted that climber inexperience may contribute to the problem.

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Though some blame the overcrowding on the record number of permits, others point to the growing number of expedition companies that are willing to bring novice climbers.

"The easy headline is, 'Overcrowding is killing people on Everest,' " Arnette said. "But the root cause … is low-cost guide companies bringing in a new demographic of climbers who don't belong there. Limiting the number of permits isn't the solution. People should have to have climbed an 8,000-meter peak, and they need to tighten up who can guide there because right now they let anybody guide.''

More than 29,000 feet

Regardless of the number of people at the top, the climb to Everest's summit always carries risk. Mount Everest's peak sits more than 29,000 feet above sea level. The area between Camp Four at 26,240 feet and the summit is known as the "death zone."

Oxygen levels are so low in the "death zone" that climbers cannot stall for long before completing the summit and coming back down. Without an extra oxygen supply, the conditions will prove fatal.

"Once you get above about 25,000 feet, your body just can't metabolize the oxygen," Grayson Schaffer, editor of Outside magazine, told NPR. "Your muscles start to break down. You start to have fluid that builds up around your lungs and your brain. Your brain starts to swell. You start to lose cognition. Your decision making starts to become slow. And you start to make bad decisions.

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"And all of this is happening in the face of, you know, each person trying to sort of reach their ultimate dream."

The long line to the top

Though many may conjure images of a serene snow-capped peak when they envision Everest, one photo has defined perceptions around the mountain this season.

Standing in a single-file line near the top of the massive cliff, dozens of climbers in brightly colored jackets appeared to litter the edge of the mountain.

The photo was taken by veteran climber Nirmal Purja last week while descending the summit and has become the poster for the overcrowding issue this season.

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"The photo is so stunning, and to many people, it seems offensive to see so many people crowded on this high peak," said Colorado climber Jim Davidson, who summited Mount Everest in 2017. "It is out of line with the mystical and romantic image of Mount Everest. So because of the photo, we seem to be over-attributing overcrowding as causing these deaths."

Davidson said the photo is not representative of what the mountain looks like most of the time. The photo captures the root of what others said may be to blame for the deaths this year: too few windows to summit.

Poor weather has limited the number of days climbers can even attempt to reach the top. Coupled with the record number of climbers, that's forced more people into the "death zone" at once, slowing the lines to the top at dangerous altitudes.

"Every minute counts there," Eric Murphy, a mountain guide from Washington who climbed Everest for a third time May 23, told The Associated Press. He said what should have taken 12 hours took 17 hours.

Miles Blumhardt reports for the Fort Collins Coloradoan. Contributing: The Associated Press

Follow Miller and Blumhardt on Twitter: @RyanW_Miller and @MilesBlumhardt.