Delayed Be-10 dilution in detrital quartz following extensive coseismic landsliding: A 2016 Kaikoura earthquake case study

Large earthquakes play a major role in the topographic evolution of active orogens. Earthquake induced landslides can alter the mass balance of mountain belts for decades to centuries depending on how landslide material is transported and stored. In this study, we analysed in-situ Be-10 concentrations in fluvial sediments to capture a time series of post-earthquake denudation rates of the Tutae Putaputa vertical bar Conway River catchment, which experienced similar to 13 x 10(6) m(3) of landsliding in the 2016 Kaikoura earthquake. Be-10 concentrations were determined for detrital samples from the Conway River at the rangefront of the Seaward Kaikoura Mountains, South Island, New Zealand, and near the catchment outlet over three sampling intervals, including after significant precipitation events, 1-2 yr following the earthquake. Our results indicate somewhat higher apparent erosion rates at the rangefront (0.41-0.58 mm/yr) when compared to erosion rates incorporating lower-relief sub-catchments at the river outlet (similar to 0.28 mm/yr). No changes were found over the same time period in the Hurunui River, a neighbouring catchment that experienced negligible coseismic landsliding during the Kaikoura event. Apparent catchment-averaged erosion rates in the Conway River have remained similar to long-term exhumation rates from previously published thermochronology studies. To explain our results, we explore the observed controls on catchment-wide Be-10 concentrations in our study area, such as the spatiotemporal variability in landslide connectivity to the channel and storage within the catchment. Our results highlight that using in-situ cosmogenic Be-10 in fluvial deposits as a proxy for changes in sediment fluxes of earthquake-affected landscapes is complex and highly site-specific. (C) 2022 The Authors. Published by Elsevier B.V.