Lake Sarez – The Potential Hazard Assessment Based on the Natural Analogues of The Anticipated Hazard Chain

Abstract

Lake Sarez, situated in the Central Pamir Mountains of Tajikistan, was formed in 1911 when the Murgab River was blocked by the massive (~2.2 km³) Usoi rockslide triggered by a M7.3–7.7 earthquake. The resulting lake, containing approximately 16–17 km³ of water behind a 500 m-high natural dam, represents a significant transboundary hazard to populations along the Bartang–Panj–Amu Darya River system across Tajikistan, Afghanistan, Uzbekistan, and Turkmenistan. Although the Usoi dam is presently considered stable against seepage and internal deformation, satellite radar interferometry (InSAR) data from Envisat and Sentinel-1 (2003–2006, 2015–2020, 2023–2024) show active slope movements of up to 250 mm/year on the right- and left-bank slopes, covering 5 km² and 2 km², respectively. These indicate evolving deep-seated landslides capable of generating catastrophic impulse waves if they collapse into the lake. Analysis of global rockslide-induced wave events suggest that a right-bank collapse of ~0.5 km³ could reach velocities over 200 km/h, producing waves with runups exceeding 100 m, potentially overtopping the dam and initiating rapid erosion. Due to uncertainties in slope geometry and dam properties, deterministic modeling is limited; hence, hazard assessment relies on natural analogues. Gradual controlled lowering of the lake, alongside international cooperation, is recommended to prevent potential disaster, and timely proactive interventions are feasible only during the current stable phase.