Formation of an epigenetic gorge following a giant landslide damming in Kyirong River of the central Himalayas

Abstract

In tectonically active mountainous regions, large-scale landslide damming events have profound impacts on long-term fluvial landforms, such as river diversion and formation of epigenetic gorges. Here, we investigate morphometric and sedimentological evidence of an ancient large-scale landslide in the Kyirong River basin located in the central Himalayas. The ancient Kyirong landslide completely blocked the river, causing overtopping at the lowermost part of the dam crest. The river then progressively incised through the landslide deposits and the underlying bedrock, carving out the ∼300-m-deep Kyephu Gorge within the original bedrock valley walls. Unlike the conventional formation of epigenetic gorges, the new river channel of the Kyirong River is located closer to the landslide wall compared to the original channel.This unique formation model is the result of the combined effects of the landslide movement process and the distinctive topography. Through remote sensing image interpretation, field surveys, sediment layer analysis, and geomorphological parameter calculations, this study reconstructs the motion process of the Kyirong landslide and its subsequent effects on the river system. The Kyirong landslide is identified as a late Quaternary event, corresponding to a river incision rate of over 14.2 mm/year. The landslide event has caused significant changes in local geomorphological features, reshaping the evolution of the river. This study provides a specific case, demonstrating that in tectonically active regions, landslide events play a direct role in controlling the evolution of river landforms.