<P> Mt . Everest has two main climbing routes, the southeast ridge from Nepal and the north ridge from Tibet, as well as many other less frequently climbed routes . Of the two main routes, the southeast ridge is technically easier and more frequently used . It was the route used by Edmund Hillary and Tenzing Norgay in 1953 and the first recognised of 15 routes to the top by 1996 . This was, however, a route decision dictated more by politics than by design, as the Chinese border was closed to the western world in the 1950s, after the People's Republic of China invaded Tibet . </P> <P> Most attempts are made during May, before the summer monsoon season . As the monsoon season approaches, the jet stream shifts northward, thereby reducing the average wind speeds high on the mountain . While attempts are sometimes made in September and October, after the monsoons, when the jet stream is again temporarily pushed northward, the additional snow deposited by the monsoons and the less stable weather patterns at the monsoons' tail end make climbing extremely difficult . </P> <P> The ascent via the southeast ridge begins with a trek to Base Camp at 5,380 m (17,700 ft) on the south side of Everest, in Nepal . Expeditions usually fly into Lukla (2,860 m) from Kathmandu and pass through Namche Bazaar . Climbers then hike to Base Camp, which usually takes six to eight days, allowing for proper altitude acclimatisation in order to prevent altitude sickness . Climbing equipment and supplies are carried by yaks, dzopkyos (yak - cow hybrids), and human porters to Base Camp on the Khumbu Glacier . When Hillary and Tenzing climbed Everest in 1953, the British expedition they were part of (comprising over 400 climbers, porters, and Sherpas at that point) started from the Kathmandu Valley, as there were no roads further east at that time . </P> <P> Climbers spend a couple of weeks in Base Camp, acclimatising to the altitude . During that time, Sherpas and some expedition climbers set up ropes and ladders in the treacherous Khumbu Icefall . </P>

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