Is erosion helping Himalayas to grow?

August 05, 2003

Does erosion, which occurs over years or decades, influence mountain-building, which requires eons? Do surface forces like wind and rivers contribute to tectonic shifts miles below the earth's surface?

Are erosion and tectonics combining to cause the edge of Tibet to slide away, geologically speaking, from the main body of Tibet? Peter Zeitler and Anne Meltzer, professors of earth and environmental sciences at Lehigh, are leading an international study of erosion and tectonic processes near Namche Barwa, which at 23,000 feet is the highest peak in the eastern Himalayas.

Zeitler and Meltzer recently completed an international study of Nanga Parbat, the 26,000-foot peak that dominates the western end of the Himalayas.

Both peaks stand in an area characterized by highly active tectonic processes below the earth and extreme erosion on the surface. Both rise from spectacular gorges and patrol the watersheds of large rivers - the Indus (Nanga Parbat) and the Tsangpo (Namche Barwa) - that are contributing to the turbulent forces shaping the Himalayas.

"The deep gorges of the Indus and Tsangpo rivers expose, uniquely to our knowledge, [about] 7,000 meters of relief, actively deforming metamorphic rocks, and granites," Zeitler and Meltzer wrote in GSA Today, the magazine of the Geological Society of America.

In both cases, Zeitler and Meltzer believe, the rivers erode gorges deep enough to weaken the earth's crust, encouraging an upward surge of hot metamorphic and mountain-forming rock that they have termed a "tectonic aneurysm."

"We believe that the manner and rate at which surface rocks are being chiseled away by erosion affects what is happening 10 to 30 kilometers below the earth's surface," says Zeitler.

Zeitler and Meltzer are leading 16 researchers from seven institutions in a project titled "Geodynamics of Indentor Corners" that has received $2.2 million through the National Science Foundation's highly competitive Continental Dynamics Program.

The researchers are combining short-timescale seismological, geomorphic and GPS (global positioning system) measurements with observations made over a longer period of time, including geochronologic, petrologic and structural measurements.

These results will be integrated with three-dimensional modeling and analyzed against the backdrop of a fourth dimension - time.

The researchers in the Namche Barwa project represent Lehigh, Stanford University, the Massachusetts Institute of Technology, Otago University (New Zealand), the University of Maine, the Chengdu Institute (China), the University of Washington, and the State University of New York at Albany.

In addition to analyzing and dating samples of surface rocks, the researchers will deploy up to 70 seismometers to listen to earthquakes, including local and regional events as well as those on different continents. By comparing the arrival times and form of seismic waves generated by the earthquakes, the seismometers will help researchers infer the composition and temperature of rocks in the subsurface, as well as detect the presence of any melts.

The seismometers will be made available to the researchers through Incorporated Research Institutions for Seismology (IRIS), a university research consortium of which Meltzer is former director.

Zeitler and Meltzer have traveled twice to Tibet for field study, and plan more trips over the next four years.

Lehigh University

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