Collaborative Research: Geomorphic legacy of megaflood deposits on river processes and form, Eastern Himalaya

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Earth and other planetary landscapes contain a record of both past and present surface processes. During colder climate periods thousands of years ago, glacial ice and debris episodically dammed rivers, leading to catastrophic floods of a magnitude not seen on Earth today. Such “megafloods” left an indelible signature on landscapes across nearly every continent, and geologists rely on rare flood deposits to reconstruct how megafloods have shaped the landscapes we see today. This project focuses on unique flood deposits from the eastern Himalayan mountains, using new observations, measurements, and computer modeling to study how catastrophic flood events contribute to the evolution of a steep, high-relief mountain landscape. This project also uses the fascinating story of megafloods to develop publicly accessible K-12 educational materials that integrate scientific discovery with Indigenous Knowledge and will support training of multiple graduate and undergraduate students. The results of this work will help to more accurately interpret the origin of the landscapes seen on both Earth and Mars today – as well as to better predict hazards from similarly catastrophic anthropogenic analogues, such as flooding after the failure of a dam. Prior megaflood research has focused on the impact of dam-burst megaflood discharges (10^6 m3/s) on bedrock channel erosion. This project will further explore the role of megaflood deposition on the long-term (10^3 yr) evolution of bedrock rivers. The project team will focus on a well-documented example of megaflood deposition along the Yarlung-Siang-Brahmaputra river system in the eastern Himalaya to: 1. determine the source, depositional age and grain size distribution of flood deposits using cutting-edge analytical tools, 2. develop a process-based numerical model to predict first-order changes to a bedrock river channel following abrupt flood aggradation, and 3. search for a unique topographic signature of megaflood processes by comparing the morphology of eastern Himalayan river channels with and without a history of megaflooding. These findings will illuminate how intermontane sediment deposition by megafloods governs river valley evolution. Ultimately, the results have the potential to change the way sediment deposition is considered in numerical models of eroding mountainous landscapes and will provide new insight into the role of infrequent, high-magnitude flood events in shaping landscapes on both Earth and Mars.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.