Catastrophic sediment transport preconditioned by warm storms

Cascading sediment flows in extratropical mountain ranges could be enhanced by an increasing frequency of warmer storms over the next century. We present analysis of the geomorphological and sedimentological impact of two rain-induced catastrophic sediment transport events that occurred just 54 days apart on the Rio Teno, Central Chilean Andes. Despite the second storm generating 50-80% smaller peak flood magnitudes and 1.3 times fewer mass movements, we find evidence for the catastrophic reworking of riverbed sediments that scale in magnitude with the first event. We argue that beyond the individual disruptive event, warm storms have the potential to prime mountain river systems for subsequent sediment transport events during smaller floods. To forecast the evolution of sediment fluxes from mountain ranges over the next century, we therefore need to go beyond assuming a simple relationship between sediment export and the frequency of sediment mobilising flood events to consider the disproportional response of the sediment system to smaller floods following more frequent warm storms.