Seismic evidence for a two-stage origin of the October 2026 Budhi Gandaki landslide in the Nepal Himalaya

Christopher Calvelage , Shuye Huang, Chan-Mao Chen, Binhao Wang, Beth Pratt-Sitaula, John Mitchell McLaughlin

On 10 October 2026 a rock avalanche left the south face of the Chamar massif, Nepal, ran 8.7 km down the Ungilung and dammed the Shyar above the Budhi Gandaki. Single-force inversions of one regional and 28 teleseismic records resolve four force pulses 23–26 s apart, alternating westward and eastward. Flow simulations released from the face favor two stages of failure, a smaller one at the onset of the high-frequency signal and the main body 40–60 s later, together 6–21 Mm3, reaching the Shyar in three minutes.