Geomorphological and sedimentological evidences of palaeo-outburst flood events from TanglangLa-Gya catchment of River Indus, Ladakh, India

ABSTRACT Gya river, one of the main tributary of Indus, hosts several scattered palaeoflood deposits. The chronology, genesis and spatiotemporal relationships of these scattered deposits can throw light to the regional and global climatic fluctuations and their implications for the evolution of the valley. The valley structure of the Gya river consists of a broad middle reach alternating with narrow valleys and gorges in the upper and lower reaches which can be blocked by the slightest of sediment discharge damming the entire valley. The geomorphological, sedimentological and chronological study in this valley reveals multiple short-lived lake phases at 21–19.9 ka, 13 ka and 4.5 ka in the broader reach of the river during the transition periods when climate rapidly fluctuates between cold-dry and warm-wet. The damming in the valley is the result of the glacial lake outbursts in the head waters of the Gya catchment blocking the narrow lower reaches of the main channel by massive sediment. These lakes that are formed by valley damming contains ~108 m3 of water which subsequently breach out causing significant geomorphic changes on reach scale along the Gya river channel.