School of Earth Sciences, East China University of Technology, Nanchang 330013, China; Key Laboratory of Tibetan Environment Changes and Land Surface Processes, Institute of Tibetan Plateau Research, Chinese Academy of Sciences, Beijing 100101, China.
School of Earth Sciences, East China University of Technology, Nanchang 330013, China.
Sci Total Environ. 2022 Mar 10;811:151949. doi: 10.1016/j.scitotenv.2021.151949. Epub 2021 Nov 24.
The failure of a natural dam is an extreme geological event. Palaeo-lake sediments were discovered in the broad Xigazê valley and Dazhuka-Yueju gorge in the middle reach of the Yarlung Tsangpo River in Tibet. However, the sedimentary processes, dam failure, and peak flood of the Xigazê dammed palaeo-lake are poorly understood. Hence, we conducted a field survey of eight lacustrine sedimentary terraces in the area. We divided the sedimentary processes of the palaeo-lake into five stages and deposit types: pre-palaeo-lake sediments (fluvial or aeolian deposits); early stage sediments of the palaeo-lake (coarse sand); main stage palaeo-lake sediments (clayey silt and sand), sediments following the discharge of the palaeo-lake (sand and gravel-cobbles); and cover deposits (aeolian sediments and colluvium). Additionally, the water level along the palaeo-lake was almost constant (3811 m a.s.l.). The dam was likely located at the eastern end of the Dazhuka-Yueju gorge. Based on the water level, dam location and 30-m ASTER GDEM2 data, the capacity of the palaeo-lake was estimated as 22.55 km. To separate the water volume and sediment volume, the sediment surface elevation along the palaeo-lake was simulated based on the elevations of the six lacustrine sedimentary terraces. The volume of the sediment was ~11.56 km, which was calculated from the dam location, sediment surface elevation, and the ASTER GDEM2 data. Finally, subtraction of the sediment volume from the capacity of the palaeo-lake gave a backwater volume of 10.99 km. The peak flood possibly exceeded 3.4 × 10 m/s as a moraine dam joined the discharge during the dam failure. However, the dammed event probably had a limited effect on the landforms at downstream because of the presence of another dammed palaeo-lake in the broad Zetang valley; moreover, the bedrock upstream of the dam was protected from erosion.
天然堰塞湖的溃决是一种极端的地质事件。在西藏雅鲁藏布江中游的西嘎则峡谷和达则错-玉足峡谷发现了古湖相沉积物。然而，西嘎则古堰塞湖的沉积过程、堰塞湖溃决和洪峰流量仍不清楚。因此，我们对该地区的 8 个湖相沉积阶地进行了野外调查。我们将古湖的沉积过程分为 5 个阶段和沉积类型：古湖前沉积物（河流或风成沉积物）；古湖早期沉积物（粗砂）；古湖主阶段沉积物（粘质粉砂和砂），古湖泄水后的沉积物（砂和砾石-卵石）；和覆盖沉积物（风成沉积物和崩积物）。此外，古湖水位几乎保持不变（海拔 3811 米）。大坝可能位于达则错-玉足峡谷的东端。根据水位、大坝位置和 30 米 ASTER GDEM2 数据，估算古湖容量为 22.55 公里。为了分离水量和泥沙量，根据六个湖相沉积阶地的高程，模拟了古湖的泥沙表面高程。根据大坝位置、泥沙表面高程和 ASTER GDEM2 数据，计算出的泥沙体积约为 11.56 公里。最后，从古湖的容量中减去泥沙体积，得出的回水体积为 10.99 公里。在堰塞湖溃决过程中，一条冰碛坝加入泄流，可能导致洪峰流量超过 3.4×10 m/s。然而，由于在宽阔的泽当峡谷中存在另一个古堰塞湖，堰塞事件对下游地貌的影响可能有限；此外，大坝上游的基岩免受侵蚀。
