CNN  — 

Everest has always been extremely dangerous, but its most fatal years on record have generally been related to a single disastrous event.

For example, an avalanche in 2014 killed at least 12 Sherpa guides, and a series of avalanches in 2015 sparked by that year’s massive Nepal earthquake caused the deaths of at least 19 people.

This climbing season’s 11 deaths so far, though, are not related to one event but to several factors that have caused overcrowding in the most dangerous areas of the route to the summit.

Mountaineers have suggested difficult weather conditions, a lack of experience and the growing commercialization of expeditions are contributing to the danger.

“I don’t want to be so fatalistic and say it was only a matter of time, but when you have an unchecked area that is aggressively dangerous to be in … you definitely end up with disaster, unfortunately,” Les Stroud, host of the show “Survivorman,” told CNN on Tuesday.

During the week beginning May 20, crowds of climbers became stuck in a queue to the summit, above the mountain’s highest camp at 8,000 meters (26,247 feet). The summit of Mount Everest is 8,848 meters (29,029 feet) high.

Most people can only spend a matter of minutes at the summit without extra oxygen supplies, and the area where mountaineers have been delayed is known to many as the “death zone.”

British climber Robin Haynes Fisher was one of those who had warned of the dangers of overcrowding.

“With a single route to the summit, delays caused by overcrowding could prove fatal so I am hopeful my decision to go for the 25th will mean fewer people. Unless of course everyone else plays the same waiting game,” he wrote in a captioned Instagram post on May 19.

He died after suffering from what appeared to be altitude sickness at 8,600 meters (28,215 feet), while returning from the summit on Saturday.

Bad weather created limited window

The overcrowding issue was most evident in a May 22 photo that showed a lengthy line of climbers on an exposed ridge leading to the summit.

Climbers wait to reach the summit of Everest in this image taken May 22.

Alan Arnette, who has climbed Everest four times, explained that Nepal issued a record number of permits to foreigners this year. Because each of them requires a Sherpa guide, there are about 800 people trying to climb from the Nepalese side, he said.

In addition, bad weather made it so that there were only five days when people could climb toward the summit.