Once on the South Col, climbers have entered the
death zone;
altitude sickness is a significant threat at this elevation and can easily prove fatal. It is also difficult to sleep, and most climbers' digestive systems have significantly slowed or completely stopped. This is because it is more efficient at this altitude for the body to use stored energy sources than to digest new food. Most climbers will begin using supplemental oxygen here and have a maximum of only three days to make summit bids. Clear weather and low winds are critical factors in deciding whether to make a summit attempt. If the weather is not favourable within these short few days, climbers are forced to descend, many back to
Base Camp. Climbers rarely get a second chance to return to the South Col on a specific expedition. It is possible to climb to the summit of Lhotse, then along the South Col to the summit of Everest, in less than 24 hours. In certain mountaineering circles, this rare (and seldom-recorded) feat is known as the "Double Crown"; the latest well-documented attempt was by Messrs. Jocelyn Cayer and Ashish in May 2025. In 2005
Didier Delsalle of France landed a
Eurocopter AS350 B3 helicopter on the South Col. Two days later he made the first helicopter landing on the summit of Mount Everest, a feat he subsequently repeated. In May 2019 the highest weather stations in the world were installed on Everest, one at the South Col and another on a place higher up on the peak known as The Balcony as well as some other stations and locations. The weather stations are about tall and weigh . == See also ==