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When continents collide

Geologists find a new active fault in Nepal that potentially links climate with mountain building
Arjun Heimsath
Arjun Heimsath

A Dartmouth researcher is part of a team that has discovered a new active "thrust fault" at the base of the Himalaya in Nepal. This new fault likely accommodates some of the subterranean pressure caused by the continuing collision of the Indian subcontinent with Asia.

The study, titled "Active out-of-sequence thrust faulting in the central Nepalese Himalaya," was published in the Apr. 21 issue of the journal Nature.

"This work tackles one of the fundamental questions in my field," said Arjun Heimsath, Assistant Professor of Earth Sciences and an author on the paper. "We are trying to determine whether climate is driving erosion, which may in turn impact tectonics, or whether tectonic forces drive erosion that subsequently influences climate. It's sometimes called the classic chicken-or-egg problem in geomorphology."

The researchers argue that this evidence quantifies a connection between erosion rates and tectonic forces, which might lead to a new understanding of how the growth of the Himalaya plays a role in global climate change. The new fault is found in an area where there is a dramatic change in the structure of the landscape, and it is in a region where the rainfall and erosion rates are among the highest in the world.

Heimsath explained that as India continues to collide with Asia, the Himalayan Mountain Range grows a centimeter or more each year, and then the monsoons help bring about the erosion of the same mountains. The new active fault is at the base of the Great Himalaya in Central Nepal, about 60 miles from Kathmandu. Here, the landscape changes from low relief and gently sloping hills to steep, high mountains, and the researchers discovered that the erosion rates increase by a factor of four with the transition in topography.

"We used two different techniques of dating minerals in sediments to determine erosion rates spanning the last several thousand years as well as several million years," he said. "There was corroboration over drastically different time scales of erosion rates from several watersheds, suggesting a close connection between erosion and tectonics."

A lenticular cloud forms above the high peak of Manasulu
A lenticular cloud forms above the high peak of Manasulu (elev. 26,915 feet) in the Nepalese Himalaya. This cloud formation is a typical example of how the jet stream can affect cloud formations over the mountains, and is indicative of the high climactic gradient across the region.  Arjun Heimsath, Assistant Professor of Earth Sciences, took this photo from his field camp in Nepal, where he studied the interaction between erosion rates, tectonic forces and climate change.  (photo by Arjun Heimsath)

Heimsath and colleagues speculate that there may be some sort of feedback mechanism between erosion and tectonic movement, which might help reduce the potential energy accumulated by the uplift of the Himalaya and the formation of the Tibetan plateau, a vast region where the mean elevation is over 16,000 feet.

"The incredible mass of this uplifted plateau is struggling for someplace to go, and it's possible that focused erosion processes, which remove material at a high rate along the base of the Himalaya, are enabling a reduction in this accumulated potential energy. It's a continent-sized physics problem," he said.

Co-authors on this study are Cameron Wobus, Kelin Whipple and Kip Hodges, all from the Department of Earth, Atmospheric and Planetary Sciences at the Massachusetts Institute of Technology. Wobus, a current PhD student at MIT, earned his M.S. from Dartmouth's Department of Earth Sciences in 1997.

The research was funded by a National Science Foundation Continental Dynamics Program grant awarded to Heimsath.

By SUSAN KNAPP

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Last Updated: 12/17/08