NSFGEO-NERC Collaborative Research: Coupling Erosion, Weathering, and Hydrologic Function in an Active Orogenic System

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Mountain ranges are some of the most spectacular features of the Earth’s surface, but their importance extends far beyond their photogenic nature. Mountains play critical roles in sustaining key natural resources, such as supplying fresh water to large human populations. Mountainous regions are the site of many destructive natural hazards, such as landslides and floods. In addition, mountains are where fresh rocks are exposed to water and the atmosphere, resulting in chemical reactions that can modify carbon dioxide and climate over geologic time. These processes are all closely interconnected, yet they have been largely studied in isolation. This project will examine the physical and chemical transformation of rock together with the flow of water and Earth materials within the scope of one integrated research endeavor. The project will examine these processes in a valley in the Himalaya Mountains of Nepal where topography changes from more subdued in the south to high mountains in the north. Cutting-edge techniques for documenting the nature and rate of landscape change will be applied to determine the role of mountains in the Earth system. Models that illustrate how all these processes interact and the effects they produce will be developed to forecast future changes and apply the results to other regions. The research will involve training of multiple graduate and undergraduate researchers and will involve collaboration among researchers from four countries. The collisional boundaries between Earth’s tectonic plates produce dramatic mountain ranges that generate destructive natural hazards as well as chemical and physical exchanges that control the surface environment. This project will comprise a multi-disciplinary investigation of four interrelated problems: (1) how rock is transformed physically and chemically during exhumation in tectonically-active mountains; (2) how the steep mountainous topography of active orogens develops, and particularly what the role is for landslides; (3) how water makes its way from precipitation, through the subsurface, and into streams and rivers draining active orogens; and (4) how chemical weathering depends on tectonic and climatic conditions in these settings. The project will investigate the Melamchi Khola valley in central Nepal, where a pronounced south-to-north gradient in exhumation rate offers an ideal opportunity to document system-level relationships among tectonics, topographic evolution, erosion, hydrology, and chemical weathering in an archetypal setting of collisional tectonics. The research will (1) characterize rock mass across scales from the micron to kilometer, including via geophysical imaging, borehole drilling, and rock testing; (2) quantify water transit times and chemical weathering reactions and fluxes, via groundwater dating, stream and spring monitoring, and reactive transport modeling; and (3) develop models of landscape evolution that account for the interconnected processes that regulate landslides, which are the primary vehicles for hillslope erosion in these settings. The project includes diverse opportunities for student education, development of international collaboration. A summer school for early-career researchers will expand the educational reach, and a short course on active source seismology will be held in Kathmandu to broaden the training opportunities for Nepali scientists.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.