The Roof of the World is on the Rise
In a geological sense, India is a bit of a bully—shoving itself into Asia with enough muscle to push up the Tibetan Plateau, home of the world’s highest mountains. Political problems and rugged topography have long prevented scientists from understanding this area where continents collide, but recent satellite information is providing clues about how the “roof of the world” was built.
Jeff Freymueller of the Geophysical Institute is among a group of scientists who present new research on this topic in the latest issue of Nature. Freymueller and his colleagues use Global Positioning System satellites to track the subtle movement of Earth’s crust. GPS is a system of 24 satellites operated by the U.S. Air Force Space Command at Peterson Air Force Base in Colorado. As all 24 satellites zip around the globe at an altitude of about 12,500 feet, they broadcast radio signals that are picked up by GPS receivers. A computer within the GPS unit instantly compares the distances from the satellites to the receiver, then calculates the geometry and displays the location of the GPS unit.
Freymueller is studying one of the longest weak points in Earth’s crust, a 1,200-mile fault that forms the boundary between the Tibetan Plateau and an immense valley to the north. The Altyn Tagh fault is what geologists call a “slip-strike” fault—ground movement along the fault is side-to-side rather than up and down. For years, geologists contended that rapid movement on the fault was the result of India squeezing the Tibetan Plateau eastward toward the South China Sea, like a pumpkinseed pressed between finger and thumb. Evidence found in rocks that moved long distances over the years caused some researchers to believe that India was pushing the Tibetan Plateau eastward at a rate of about 20 millimeters each year. Using satellite measurements, Freymueller and his coworkers found that the Tibetan Plateau is sliding east at a rate of just 10 millimeters each year. While the width of 10 dimes might not seem like much to most people, it’s enough for scientists to rethink the theory of how the Himalayas are being formed.
“It’s a very, very, significant discrepancy,” Freymueller said.
The slower rate of the plateau’s movement means India isn’t squeezing the mountains quickly to the side like a pumpkinseed. Instead, India is acting more like a snowplow, forcing more and more earth into the Himalayas and other mountain ranges and heightening the plateau.
According to the few dependable GPS units stationed up high, the mountains are still growing. A GPS receiver located at the South Col camp on Mt. Everest, at an elevation of about 26,000 feet, indicates about a 5-millimeter rise each year.
Web sites for images of Tibetan Plateau:
http://www.geographic.org/maps/india_maps.html
The image at bottom of screen is best
http://www.geo.cornell.edu/grads/duncan/topo/topo.gif
false color image of the plateau
http://kaladarshan.arts.ohio-state.edu/maps/tibet.html
map of India and Tibet
