Controls on fluvial sediment evacuation following an earthquake-triggered landslide: Observations from LiDAR time series

Abstract

Catastrophic sediment overloading of mountain streams in response to coseismic landsliding causes river systems to fundamentally reorganize their morphology and sediment transporting characteristics, influencing sediment yields, bedrock incision, and the coupling between erosion and tectonics. A sequence of 13 airborne LiDAR surveys of an alpine tributary of the Hāpuku River, New Zealand, reveals patterns of sediment mass balance change over 5 years following delivery of 6.6 million cubic meters of landslide debris during the 2016 magnitude 7.8 Kaikōura earthquake. The surveys reveal how mountain river systems modulate catastrophic sediment deliveries to their lower reaches through sediment storage, evolution of channel morphology, and armoring of the bed. Variations in valley width contribute to the delay and diffusion of the seismically induced disturbance “wave” as it moves across river process domains. The landslide sediment train remnants may persist for longer than the return time of their triggering mechanism, leading to a long-lived hiatus in bedrock incision in this tectonically active mountain catchment.