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

地球和其他行星景观记录了过去和现在的地表过程。在几千年前较冷的气候时期，冰川冰和碎片不时地筑坝堵住河流，导致今天地球上从未见过的灾难性洪水。这种“大洪水”在几乎每个大洲的景观上都留下了不可磨灭的印记，地质学家依靠罕见的洪水沉积来重建大洪水是如何塑造我们今天所看到的景观的。该项目专注于东喜马拉雅山脉独特的洪水沉积，使用新的观测、测量和计算机建模来研究灾难性洪水事件如何对陡峭、高起伏的山脉景观的演变做出贡献。该项目还利用大洪水的引人入胜的故事来开发可公开获取的K-12教育材料，将科学发现与土著知识相结合，并将支持对多名研究生和本科生的培训。这项工作的结果将有助于更准确地解释今天在地球和火星上看到的地貌的起源，以及更好地预测类似灾难性的人为模拟的危险，例如大坝坍塌后的洪水。以往的特大洪水研究主要集中在溃坝泄洪(10^6m~3/S)对基岩河道冲刷的影响。该项目将进一步探索大洪水沉积在基岩河流长期(10^3年)演变中的作用。项目组将重点研究喜马拉雅东部雅鲁藏布江-雅鲁藏布江-雅鲁藏布江水系沿线大洪水沉积的一个有据可查的例子，以：1.使用尖端分析工具确定洪水沉积的来源、沉积年龄和粒度分布；2.开发一个基于过程的数值模型，预测洪水突然堆积后基岩河道的一级变化；3.通过比较有和没有大洪水历史的喜马拉雅东部河道的形态，寻找大洪水过程的独特地形特征。这些发现将阐明大洪水造成的山间沉积物沉积是如何控制河谷演变的。最终，这些结果有可能改变侵蚀山区地貌的数值模型中考虑泥沙沉积的方式，并将为罕见的高强度洪水事件在塑造地球和火星地貌中的作用提供新的见解。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

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.