Everest, Mount (Tibetan, Chomo Lungma, “goddess-mother”; Nepali, Sagarmatha, “forehead in the sky”), mountain peak, south central Asia, in the Himalaya range, on the frontier of Nepal and Tibet. Mount Everest is the highest peak in the world. The summit was previously believed to be 8,848 m (29,028 ft) above sea level, according to a 1954 Indian government survey. In November 1999, using the latest global positioning system satellite equipment, the mountain\'s elevation was revised to 8,850 m (29,035 ft). The mountain is believed to rise about 4 mm (0.2 in) every year. Its English name commemorates Sir George Everest, a British military engineer who was director (1830-1843) of the Great Trigonometrical Survey of India; the location and height of the mountain (then known as Peak XV) were first recorded as part of the survey, in 1850. Geological Formation Mount Everest, like the rest of Himalaya, rose from the floor of the ancient Tethys Sea. The range was created when the Eurasian continental plate collided with the Indian subcontinental plate about 30 to 50 million years ago (see Plate Tectonics). Eventually the marine limestone was forced upwards to become the characteristic yellow band on the top of Mount Everest. Beneath the shallow marine rock lies the highly metamorphosed black gneiss of the Precambrian era, a remnant of the original continental plates that collided and forced up Himalaya. Mount Everest is covered with huge glaciers that descend from the main peak and its nearby satellite peaks. The mountain itself is a pyramid-shaped horn, sculpted by the erosive power of the glacial ice into three massive faces and three major ridges, which soar to the summit from the north, south, and west, and separate the glaciers. From the south side of the mountain, in a clockwise direction, the main glaciers are the Khumbu glacier, which flows north-east before turning south-west; the West Rongbuk glacier in the north-west; the Rongbuk glacier in the north; the East Rongbuk glacier in the north-east; and the Kangshung glacier in the east. Climate The climate of Mount Everest is naturally extreme. In January, the coldest month, the summit temperature averages -36° C (-33° F) and can drop as low as -60° C (-76° F). In July, the warmest month, the average summit temperature is -19° C (-2° F). At no time of the year does the temperature on the summit rise above freezing. In winter and spring the prevailing westerly wind blows against the peak and around the summit. Moisture-laden air rises from the south slopes of Himalaya and condenses into a white, pennant-shaped cloud pointing east; this “flag cloud” sometimes enables climbers to predict storms. When the wind reaches 80 km/h (50 mph), the flag cloud is at a right angle to the peak. When the wind is weaker, the cloud tilts up; when it is stronger, the flag tilts down. From June to September the mountain is in the grip of the Indian monsoon, during which wind and precipitation blow in from the Indian Ocean. Masses of clouds and violent snowstorms are common during this time. From November to February, in the dead of winter, the global south-west-flowing jet stream moves in from the north, beating the summit with winds of hurricane force that may reach more than 285 km/h (177 mph). Even during the pre- and post-monsoon climbing seasons, strong winds may arise suddenly. When such storms develop, sand and small stones carried aloft, as well as driving snow and ice, pose problems for climbers. Precipitation falls mostly during the monsoon season, while winter storms between December and March account for the rest. Unexpected storms, however, can drop up to 3 m (10 ft) of snow on unsuspecting climbers and mountain hikers. Base Camp, which serves as a resting area and base of operations for climbers organizing their attempts for the summit, is located on the Khumbu glacier at an elevation of 5,400 m (17,600 ft); it receives an average of 450 mm (18 in) of precipitation a year.