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The Khumbu Icefall is an icefall at the head of the Khumbu Glacier. The icefall is found at 5,486 metres (17,999 ft) on the Nepali slopes of Mount Everest not far above Base Camp and southwest of the summit. The icefall is regarded as one of the most dangerous stages of the South Col route to Everest's summit. The Khumbu glacier that forms the icefall moves at such speed that large crevasses open with little warning. The large towers of ice or seracs found at the icefall have been known to collapse suddenly. Huge blocks of ice tumble down the glacier from time to time; they range in size from cars to large houses. It is estimated that the glacier advances 3 to 4 feet (0.91 to 1.22 m) down the mountain every day.
Most climbers try to cross the icefall during the very early morning, before sunrise, when it has partially frozen during the night and is less susceptible to moving. As the intense sunlight warms the area, the friction between the ice structure lessens and increases the chances of crevasses opening or blocks to fall. The most dangerous time to cross the Khumbu Icefall is generally in mid- and late-afternoon. Strong, acclimatized climbers can ascend the icefall in just a few hours, while climbers going through it the first time - due to a lower level of acclimatization, being understandably very careful, and lack of experience with ice ladder and climbing techniques - can make the journey take 10–12 hours. "Camp I" on Everest's South Col route is typically just a bit beyond the top of the Khumbu icefall.
On occasion, a climber will experience a large block of ice crashing down in their vicinity. The resulting blast of displaced air and snow can result in a billowing cloud of light ice and snow being deposited on a climber. This is sometimes referred to as a "dusting." To those that have experienced it, it is a very unnerving experience. If a climber is caught in an avalanche or other "movement" event in the icefall, there is very little one can do except prepare oneself for potentially being trapped by heavy blocks of ice, or immediate movement afterwards to try and rescue others. It is virtually impossible to run away, or even know which way to run.
People who have died in the icefall and whose bodies have not been recovered have reportedly shown up at the base of the icefall many years later as the ice continually migrates downward toward Everest base camp. In those cases, the bodies have been recovered and given proper burials.
Since the structures are continually changing, crossing the Khumbu Icefall is extremely dangerous. Even extensive rope and ladder crossings cannot prevent loss of life. Many people have died in this area, such as a climber who was crushed by a 12-story block of solid ice. Exposed crevasses may be easy to avoid, but crevasses buried under snow can form treacherous snow bridges through which unwary climbers can fall.
- UNITEC Institute of Technology. "Hillary Challenge". Ministry of Education, Wellington, New Zealand. Retrieved 2009-01-30.