Controls on 10Be dilution in catchments affected by coseismic landsliding: a 2016 Kaikōura earthquake case-study
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Date
2021-11-17
Journal Title
Journal ISSN
Volume Title
Publisher
Australian Nuclear Science and Technology Organisation
Abstract
The 2016 Mw 7.8 Kaikōura earthquake triggered tens of thousands of landslides across the northern
Canterbury and southern Marlborough regions in the South Island of Aotearoa New Zealand. The
influence of landslides generated by this earthquake on sediment generation, transport and
deposition in stream networks has varied across the region and through time — some catchments
show significant and near-immediate responses while others show little to no change despite the
extensive landsliding. We measured 10Be concentrations in detrital quartz sands over a two-year
period in the Conway River catchment, which has a total area of ~475 km2 and had ~13 M m3 of
new landslide material liberated from hillslopes during the 2016 Kaikōura earthquake. Samples for
10Be analysis were collected at the rangefront of the Seaward Kaikōura Mountains and near the
catchment outlet on three sampling campaigns between 2017-2018. We also carried out a similar
sampling regime in the nearby Hurunui catchment, which was unaffected by the 2016 Kaikōura
earthquake. Measured 10Be concentrations were converted to basin wide mean denudation rates
using accepted GIS-based elevation and shielding programs. Our results indicate that apparent
catchment-wide erosion rates in the Conway River (i) did not change through time, (ii) have
remained similar to basin mean erosion rates for the Hurunui, (iii) overlap with the range of values
for exhumation rates of the region (from previously published low-temperature thermochronology
data), and (iv) are influenced in part by selection of grain size. We also compared our 10Be
concentrations for the Conway catchment to values derived by modelling mean landslide 10Be
concentrations constrained by local production rates, detailed mapping of all landslides across the
catchment, area-volume scaling, and landslide-channel connectivity estimates. Our modelling
estimates show that the mean 10Be concentrations derived from landslide sediment would have been
sufficient to dilute pre-earthquake catchment-wide 10Be values by up to a factor of 3. We explore
various landscape and landslide parameters that may explain the mismatch between measured and
modelled 10Be and ascertain that the combination of storage, site specific channel connectivity, and
landslide geometries/failure mechanisms likely exert first-order controls on in-situ 10Be
concentrations following such a large catchment-wide disturbance event. We conclude that using
fluvial quartz grains to characterise catchment response to landsliding and the mass balance of
earthquakes, is subject to a number of factors that are highly site-specific. © The Authors
Description
Keywords
Beryllium 10, Watersheds, Landslides, Earthquakes, New Zealand, Geologic faults, Data, Rivers
Citation
Wilkinson, C., Stahl, T., Jones, K., Fujioka, T., Fink, D., & Norton, K. (2021). Controls on 10Be dilution in catchments affected by coseismic landsliding: a 2016 Kaikōura earthquake case-study. Paper presented to the 15th International Conference on Accelerator Mass Spectrometry. ANSTO Sydney, Australia. November 15th – 19th, 2021. (pp. 78). Retrieved from: https://ams15sydney.com/wp-content/uploads/2021/11/AMS-15-Full-Program-and-Abstract-Book-R-1.pdf