Previously unknown fault provides new insights on Himalayan mountain building

MIT and Dartmouth scientists have identified a previously unrecognized, active fault in the Nepalese Himalayas. The discovery, published in the April 21 issue of Nature, provides new insights into how the mountains evolved and helps explain why the transition between the high Himalayan Ranges and their gently sloping foothills is so abrupt.

“This project started with the simple observation that the landscape of the central Nepalese Himalaya seems to be telling us something about deformation at depth in the Earth’s crust,” said Cameron Wobus, lead author on the paper and a graduate student in MIT’s Department of Earth, Atmospheric and Planetary Sciences (EAPS).

“The interdisciplinary approach we’ve taken to the problem has confirmed this intuition, and has demonstrated the existence of a surface-breaking thrust fault many kilometers north of where most geologists believe active deformation is focused. It’s an exciting development and it forces us to think more creatively about how mountain ranges like the Himalaya evolve.”

Wobus’ co-authors are EAPS Professors Kelin Whipple and Kip Hodges, and Assistant Professor Arjun Heimsath of Dartmouth.

The newly discovered fault is at the southern edge of the high Himalayan ranges in central Nepal, about 60 miles northwest of Katmandu. Farther south, the landscape is characterized by gently sloping hills. The researchers discovered that there is a sharp change in both erosion and rock uplift rates across the fault. The erosion rates to the north are four times higher than those to the south.

As a result, they speculate that there may be a feedback mechanism between erosion and tectonic deformation. Hodges notes that this is a new perspective on mountain building. “Rapid erosion related to the Indian monsoon is most intense at the approximate position of the newly discovered fault. Our hypothesis is that the modern geodynamics of the range front is indicative of coordinated high precipitation and active deformation. And it would be a very exciting development if we are right that deformational processes close to the surface of the Earth are interdependent with climatic processes.”

Such a relationship is consistent with theory, according to Whipple, but “definitive field evidence for this sort of dynamic feedback has been elusive. Our work in Nepal moves us toward a better resolution of the strength of climate-tectonics interactions and the temporal and spatial scales over which they operate.”