The Erosional and Depositional Potential of Holocene Tibetan Megafloods Through the Yarlung Tsangpo Gorge, Eastern Himalaya: Insights From 2D Hydraulic Simulations
The Erosional and Depositional Potential of Holocene Tibetan Megafloods Through the Yarlung Tsangpo Gorge, Eastern Himalaya: Insights From 2D Hydraulic Simulations
复制标题
DOI：
10.1029/2021jf006498
复制
发表时间：
2022-04
期刊：
影响因子：
--
通讯作者：
Susannah M. Morey;K. Huntington;Michael D. Turzewski;Mahathi Mangipudi;David R. Montgomery
中科院分区：
文献类型：
--
作者：
Susannah M. Morey;K. Huntington;Michael D. Turzewski;Mahathi Mangipudi;David R. Montgomery
在地球和火星上观测到了间歇性大洪水（≥106 m3/s）的深刻影响。来自青藏高原山谷阻塞冰川的第四纪特大洪水可能在雅鲁藏布江峡谷的地貌演变和喜马拉雅山东部的山脉景观中发挥重要作用。我们使用的第一个2D数值模拟的一个megaflasts来源于重建的81 km 3西藏湖泊洪水水力学分析和研究的侵蚀和沉积潜力的大洪水在山区景观。模拟洪水历时>60 h，洪峰流量3.1 × 106 m3/s。我们发现，淹没的功能，如梯田，狭窄的山谷部分，紧曲流弯曲，和overtoped山脊的影响所观察到的最大深度（370米），速度（76米/秒）和床剪切应力（>100千帕）的位置，创建动态模式的侵蚀潜力。因此，很难预测当地（≤1公里）的模式，无论是单位流功率或洪水功率较小的突发洪水的巨型侵蚀潜力。然而，当预测区域（≥25 km）的量级转移时，两者都是有用的。峡谷下游的洪水区域部分经历较低的河床剪切应力和<5 kW/m2的洪水功率，这表明有可能发生显著沉积。我们认为，在大洪水期间，现代河道内的巨石和山坡上的细粒颗粒的广泛沉积可能会阻碍随后的侵蚀，并影响整个洪水通道的河道宽度和纵向形式。我们的研究结果表明，山区大洪水的遗产包括广泛的侵蚀和沉积。
Profound effects of episodic megafloods (≥106 m3/s) have been observed on Earth and Mars. Quaternary megafloods sourced from valley‐blocking glaciers on the Tibetan Plateau likely play an important role in the geomorphic evolution of the Yarlung‐Tsangpo Gorge and mountain landscape of the eastern Himalaya. We use the first 2D numerical simulation of a megaflood sourced from a reconstructed 81 km3 Tibetan lake to analyze flood hydraulics and examine the erosional and depositional potential of megafloods in mountain landscapes. The simulated flood has a duration >60 hr and a peak discharge of 3.1 × 106 m3/s. We find that the extent of inundated features like terraces, narrow valley sections, tight meander bends, and overtopped ridges influences locations of observed maximum depth (370 m), speed (76 m/s), and bed shear stress (>100 kPa), creating dynamic patterns of erosive potential. Consequently, it is difficult to predict local (≤1 km) patterns of megaflood erosional potential from either unit stream power or flood power from smaller magnitude outburst floods. However, both are useful when predicting regional (≥25 km) order‐of‐magnitude shifts in megaflood flood power. Portions of the flood domain downstream of the Gorge experience lower bed shear stresses and flood power <5 kW/m2, indicating potential for significant deposition. We suggest widespread deposition of boulders within the modern channel and fine‐grained particles on hillslopes during a megaflood likely impedes subsequent erosion and affects channel width and longitudinal form throughout the flood pathway. Our findings show the legacy of megaflooding in mountainous terrain includes both extensive erosion and deposition.