The Rise and Fall of Marpha Lake, a Late Quaternary Dammed Lake in the Himalayan Rain‐Shadow With Implications to Landscape Evolution and Sediment Dynamics

Abstract Understanding landscape evolution history and sedimentary dynamics in high mountainous regions is tampered by rapid erosion of the sedimentary archives. Naturally dammed lakes provide unique snapshots of these processes and enable evaluating these processes under climatic conditions different from the present. Marpha Lake, in the Himalayan rain‐shadow of the upper Kali Gandaki, central Nepal, with its ∼450 m thick lacustrine sequence provides a rare opportunity to study these processes. Optically Stimulated Luminescence (OSL) of quartz and feldspars was used to date the full sequence of filling, breaching and sediment evacuation of the lake. The results show that the lake initiated at ∼120 ka and sediment accumulated until ∼80 ka, corresponding to the intense monsoon period of Marine Isotope Stage (MIS) 5. The calculated minimum catchment erosion rate during the lake filling is typical of modern erosion rates of the Himalayan rain shadow (∼150 mm/ka). The lake was breached at ∼30 ka and the majority of sediments were evacuated within 10 kyr. Between 80 and 30 ka, there was little sedimentation, corresponding to the Last Glacial period (MIS 2–4) associated with weaker Indian monsoon and possible ice coverage of the lake's drainage basin down to the elevation of the lake. Breaching of the dam may have been the result of ice pressure from the lake and/or ice build‐up in the pores within the dam. Thus, the sediments of Marpha Lake provide a fascinating archive for understanding how the interplay between mass movement and climate shaped the Himalayan rain shadow morphology during the Late Quaternary.