A practical approach to assessing moraine dam stability in High Mountain Asia

Glacial lakes store hundreds to millions of cubic metres of water, but are commonly impounded by unconsolidated, loosely packed moraine dams. Here we present a numerical modelling approach to evaluate dam stability, using limit equilibrium analyses (Geostudio SEEP/W) to generate look-up tables that describe a factor of safety (FoS) under various conditions. We find that in steady-state, an idealised moraine slope may be considered stable (FoS ≥ 2) and that peak ground accelerations greater than 0.5 g are required to induce failure (FoS < 1). We also find that rockslope failures must be substantial (>250,000 m 3 ), falling into deep water (> 100 m), and within 500 m of the dam crest, to generate an initial overtopping wave > 10 m. We apply these outputs to four moraine dams in High Mountain Asia to provide a framework for practitioners to use when assessing glacial lake hazards, based solely on geometric and seismic parameters.