Tilicho Lake origin: Valley damming by a giant rockslide

Abstract

Abstract

The origin of the Tilicho Lake, located at 4,919 meters in Nepal’s Manang district, has never been elucidated so far. In this study, based on observations along the Upper Marsyandi of a 12-km-wide deposit that exhibits typical rock avalanche facies, we propose that Tilicho lake was formed by a massive rockslide that blocked the Upper Marsyandi valley. The similar carbonate isotopic signature of the rockslide debris found in the upper Marsyandi and Phache valleys suggests the breccia deposit filled these two valleys and originated from Upper Ordovician to Middle Devonian strata. Lithologic and geomorphic arguments suggest that the rockslide resulted from the collapse of the Khansar Kan ridge, located South-East of the Tilicho lake. According to the estimated breccia deposit volume of 21 km3 made previously by Huber (2024), we realized a reconstruction of the collapsed paleosummit and a numerical modeling of the rock avalanche dynamics. The paleosummit would have culminated at around 8400 meters, and the resulting rockslide deposit would have reached an extent of about 96 km2. The modeled geometry of the rock avalanche is close to the observed one, confirming that the rockslide’s damming created Tilicho Lake and smaller lakes in Phache valley. This catastrophic event has deeply reshaped the landscape of this region, highlighting the role of large-scale rockslides in landscape evolution in mountainous regions.