British mountaineer Robin Fisher became at least the eighth person this year to die while climbing Mount Everest in Nepal. He died during his descent on Saturday in the so-called "death zone," where low oxygen levels, combined with exhaustion and weakness, can prove fatal.

Robin Fisher and partner Kristyn Carriere take a selfie at Everest Base Camp, Nepal, on April 19, 2019, in this picture obtained from social media on May 26, 2019. Robin Fisher via Reuters

On Monday, officials said American Chris Kulish died on the mountain, marking the ninth fatality on the Nepali side of Everest this climbing season. A few days before Fisher's death, he posted a video to Instagram, warning that overcrowding on the mountain could prove deadly:

On "CBS This Morning" Monday, correspondent Jericka Duncan explained some of the hazards facing those climbing 29,000 feet to the summit of the world's tallest mountain.

Overcrowding

Add a record number of people, and we're seeing more deaths on the mountain than in recent years. The government of Nepal issued a record number of climbing permits this season — 381 people were given permission to ascend the world's highest peak, which can create a logjam to reach the summit.

That exposes climbers to extended periods in areas with dangerously low oxygen levels.

A shortened weather window this year has lead to a crush of climbers attempting to summit Everest all at one time. Nimral Purja's Project Possible/Facebook

Weather

Expert climbers say May is the only month where strong winds die down enough to make summiting Everest possible. This year, that window was shorter than usual, meaning more people trying to reach the summit at the same time.

The combination of these two factors leaves people in the so-called "death zone," right before the peak, much longer.

Expert climber Dr. Jon Kedrowski said, "If you're on oxygen up high, on a day where it's crowded and you have to wait on line, you can run out of oxygen, and that can lead to problems."

Climber Cory Richards said, "Too many people, one weather window, all in, there are obvious consequences to it."

Lack of regulation

Tibet's side of Everest is much more heavily regulated, and that government issues a limited number of permits. But Nepal's side is unregulated, and there is no cap on how many permits are given.

The permit system is a major economic driver for Nepal. Each permit costs $11,000 — and that doesn't include money that is spent on food and hotels, so it's unlikely that Nepal, a poor country, will change its system.

Lack of experience

Since the issuance of climbing permits is unregulated. some people who probably should not be attempting the dangerous climb can gear up and go anyway. That can also contribute to bottlenecking, as inexperienced climbers often go slower than seasoned veterans, leading to people waiting in line.

Mountaineering expert Alan Arnette, who runs a blog on climbing Everest, put it this way: "You have to be certified to scuba dive, or qualify for elite events such as the Boston Marathon or the Kona Ironman competition, but not to climb the highest mountain on Earth."