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Geologic Forces push Everest ever skyward

Mount Everest owes its great height to the collision of the Indian subcontinent and Asia some 50 million years ago. Much like a car crashing head-on with a truck, crumpling occurred when the two continents met and the result was the creation of the Himalayan Mountains. Although the northward drift of India slowed dramatically with initial collision, the two continents have continued to converge as India slides under Asia.

Prior to the initial collision between India and Asia, the vast Tethys Sea existed between the two. The sea disappeared, a victim of plate tectonics, but its presence before 50 million years ago is recorded by scraps of oceanic crust preserved in the southern Tibetan plateau. It is not surprising that scientists consider the Himalayan range to be one of the planet’s best natural laboratories for studying the mountain building process and associated seismic activity. Dr. Bilham, a geophysicist on the EVEREST team, is conducting research to better understand the processes that drive seismic activity in Nepal and to help assess the danger of destructive earthquakes in Nepal and northern India. In this century, four earthquakes of Richter Magnitude 8 or greater have occurred in the Himalayas. Scientists expect another of similar magnitude to occur yet this century, putting millions of lives at risk.

At 29,028 feet, Mount Everest is five miles up — about the cruising altitude of a jet airliner. Data collected by Dr. Bilham indicates the world’s highest mountain is creeping skyward 3 to 5 millimeters with every passing year. Every time a team reaches the summit, the climbers are essentially setting a new altitude record.

But beneath all that Himalayan snowpack, how high is this highest of mountains? In the middle of the 19th century, the mountain’s height was measured by India’s surveyors at 29,002 feet. This altitude endured for more than a century until a new survey was undertaken, once more by experts from India, under the direction of B.L. Gulatee of the Survey of India. From 1952-54, Gulatee’s surveyors took readings from as close as 30 miles to the summit, rather than the 100 miles of the previous survey, and determined the summit elevation to be the 29,028-foot (8,848-meter) figure still used today. Great care was taken to collect readings in the wintertime, after the monsoon snow of summer had been blown off the summit by the powerful winter winds, thus reducing the summit snowpack.

The task of updating the peak’s absolute height is one being pursued by EVEREST science advisor Bilham and the Museum of Science’s Honorary Director Bradford Washburn. The two began work together 10 years ago when Bilham, of the Geophysics Department of the University of Colorado, Boulder, wanted to carry out a series of precise survey observations related to earthquakes that shake Nepal and northern India. Soon thereafter, Washburn’s teams made laser observations of prisms that were carried to and placed on the summit from Namche Bazaar, Nepal, only 18 miles to the south. Scientists were trying to zero in on the summit. In September, 1992, an Italian team for the first time set up a Global Positioning System (GPS) receiver and took readings at the top of the world. Incredibly, the results of these high-tech laser and GPS readings almost exactly agreed with Gulatee’s findings of 1954. The elevation stood at 29,028 feet.

“Unfortunately, measurements of a snowdrift, no matter how carefully they are done, don’t yield altitude figures with centimeter-accuracy — which is what we need if we intend to find the rate at which Everest is rising — not just its altitude,‘ says Washburn. To attain this super-accurate data, Washburn and Bilham have been convinced of the need of two GPS stations high in Everest bedrock. One has been successfully installed near Camp IV on the South Col. Another needs to be installed on a ledge of limestone only 100 yards from Everest’s snow summit, In an area almost always scoured free of snow by the 100-mile-an-hour west-southwest gales from October to the end of April.

Over the last three years, Bilham and his students have criss-crossed the Himalaya to establish an extensive GPS receiver network of 31 GPS stations from the northern edge of the Survey of India to Rongbuk, Tingri and Lhasa in Tibet. With two complete sets of observations from these sites in 1995 and 1997 by teams directed by Washburn, the only missing link in this extraordinary GPS web is a station on Everest summit bedrock. Washburn is currently overseeing his plans as an American scientific expedition, on the 1998 Everest Expedition, carries out his instructions and completes this link.

The scientists plan to make re-observations at all stations year after year to determine the growth and movement of the Himalaya and the plates beneath these giants. Bilham reports that Everest still continues to grow 3 to 5 mm per year and is moving north-eastward at 27 mm per year as plate tectonics go their course.


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