Why is climbing Mount Everest so dangerous?

Crossing the Khumbu Icefall can be particularly dangerous. [Via The Conversation]

Khumbu Icefall

Of all deaths from 1950 to 2019 in non-Sherpa climbers during a summit bid on Mount Everest, about 35 per cent were caused by falls, with other leading causes being exhaustion (22 per cent), altitude illness (18 per cent) and exposure (13 per cent).

In Sherpa deaths over the same period, 44 per cent were attributable to avalanches. One 2014 avalanche took the lives of 16 Sherpas.

Almost 84 per cent of deaths in non-Sherpa climbers occurred on their descent - after either successfully reaching the top of Mount Everest, or after turning back before reaching the summit.

While some deaths on descent are related to falls, most are linked to extreme fatigue and exhaustion, or sustained exposure to extremely low levels of oxygen.

In Sherpas, most deaths occur on the lower sections of the climb where they spend lots of time preparing the expedition route and are exposed to greater risk of trauma-related death.

Low oxygen at extreme altitude

At Mount Everest base camp (5,364m), oxygen availability is about 50% of that at sea level. At the summit, oxygen availability decreases to less than 30%.

In these high-altitude, low-oxygen environments, climbers are at significant risk of acute mountain sickness, high-altitude pulmonary oedema, and high-altitude cerebral oedema.

Acute mountain sickness is the less severe of the three conditions and is associated with symptoms such as headache, nausea, loss of appetite, and in some cases vomiting and fatigue. Generally, it can resolve following further acclimatisation and rest, or descent to lower altitudes. It rarely evolves into a life-threatening condition.

However, with continued exposure to high altitude, more severe conditions can develop.

High-altitude pulmonary oedema is caused by the accumulation of fluid in the lungs. This leads to excessive breathlessness and a dry cough that can evolve into one that produces a foamy, pink sputum.

High-altitude cerebral oedema is caused by excess fluid in the brain and leads to severe headache, confusion, dizziness, loss of balance, and ultimately coma or death, if untreated.

Almost all non-Sherpa climbers on Mount Everest summit attempt to climb with supplemental oxygen tanks to assist their physical performance and mitigate the risk of developing these conditions.

Ultimately, however, for some climbers, this is not enough and even if they successfully reach the summit, they succumb to the environment or high-altitude-related illness on their descent back to base camp.