Joshua Nathan Jones, Sarah J Boulton , Georgina Bennett , Martin Stokes , Michael R. Z. Whitworth 

In mountainous environments, quantifying the drivers of mass-wasting is fundamental for understanding landscape evolution and improving hazard management. Here, we quantify the magnitudes of mass-wasting caused by the Asia Summer Monsoon (ASM), extreme rainfall and earthquakes in the Nepal Himalayas. Using a newly compiled 30-year mass-wasting inventory, we establish empirical relationships between monsoon-triggered mass-wasting and ASM precipitation before quantifying how other mass-wasting drivers have perturbed this relationship. We find that perturbations up to 5 times greater than that expected from the ASM alone are caused by rainfall events with 5 to 30 year return periods and short-term (< 2 year) earthquake-induced landscape preconditioning. In 2015, the landscape preconditioning induced perturbation is found to be strongly controlled by the topographic signature of the Gorkha earthquake, whereby high Peak Ground Acceleration (PGA) coincident with excess topography (rock volume above a landscapes threshold angle) amplifies landscape damage.