The Himalaya and high Tibetan Plateau are one of the most remarkable topographic features on Earth, and are widely taken to the be the classic example of continent-continent collision. In recent years a number of collaborative projects have used the region as a perfect natural laboratory for studying mountain building, and to answer basic questions about our world, like "Why are high mountains so high?" and "Does erosion have a role in mountain building?" Answers to these questions are not just important for pure theory, because active tectonic processes have an impact on humans and society, both in the way they have shaped geography and in the hazards like flooding, landsliding, and earthquakes that go with them.
     
At each end of the Himalaya, prominent syntaxes are present (seen in the figure above as the sharp bends in the range, marked by the red boxes). These syntaxes formed around the leading edges and corners of the cold Indian plate as it collided into Asia, indenting Asia and causing both uplift and lateral escape of crustal blocks. These active syntaxes can be termed "indentor corners" and clearly occupy a significant fraction of the Himalaya-Tibet system. They are the site of some of the world's most active tectonics, including young metamorphism and melting, and very rapid erosion and crustal deformation. These active processes are of interest and concern to society, as they occur in a region that is the ultimate watershed for over a billion people in south and southeast Asia. Understanding how shortening associated with collision is being taken up, what is happening at depth, and if erosion is important are all important plate-scale questions      
The syntaxes are also interesting at a more local scale. They serve as a pathway for the biggest Himalayan rivers, the Indus and the Tsangpo, as they turn south and cut spectacular gorges across the mountain belt (the turn in the Tsangpo can be seen in the image at the left, which shows the Big Bend Canyon near Namche Barwa). One goal of our project is to test a model we have proposed that links the location of these big rivers in the syntaxes, the gorges they cut, and the active young metamorphism and deformation seen in the two syntaxes, at Nanga Parbat in Pakistan and Namche Barwa in Tibet. In this model (shown as a cartooon above), the rapid cutting of a deep gorge weakens the crust enough so that it fails. Once the crust fails, deformation and strain are increasingly localized as hot rocks are brought close to the surface, leading to rapid rock uplift. This positive feedback leads to the development of big mountains that sit atop weak crust and astride big rivers (as can be seen in the image on the left).    


Using multinational research teams, our project is examining these questions using techniques of sesimology, dating, GPS, geodynamic modeling, and petrology. Beyond these basic research goals, our research will have practical outcomes as well: assessment of erosion rates and landslide hazards, documentation of precipitation, and mapping of active seismicity, faults, and seismic hazards.