Accurate quantification of sediment conveyance following the 2016 Kaikōura earthquake, New Zealand
- 1Engineering Geology, GNS Science, Lower Hutt, New Zealand (katie.jones@gns.cri.nz)
- 2School of Geography, Environment and Earth Sciences, Victoria University of Wellington, Wellington, New Zealand
- 3School of Surveying, University of Otago, Dunedin, New Zealand
- 4Univ Rennes, CNRS, Géosciences Rennes, UMR 6118, 35000 Rennes, France
Evaluating the influence of earthquakes on erosion, landscape evolution and sediment-related hazards requires quantifying the volume and velocity of post-seismic sediment cascades. However, accurate estimates of post-earthquake sediment transfers remain rare. Following the 2016 MW7.8 Kaikōura earthquake in New Zealand, the volume of post-seismic erosion was quantified directly by measuring the ground surface change between 4 lidar surveys captured in 2016, 2017, 2019 and 2021 using the multiscale model-to-model cloud comparison (M3C2) algorithm. The lidar surveys covered the 62 km2 Hapuku and 66 km2 Kowhai river catchments within the Seaward Kaikōura Range, representing the two catchments with the highest density of co-seismic landsliding.
The total co-seismic landslide source volume for the Hapuku Catchment was 30 ± 6 M m3,the catchment being dominated by a 17 M m3 rock avalanche which dammed the Hapuku River. In the 5 years after the earthquake a total of 10.60 ± 0.22 M m3 of sediment was post-seismically eroded (equivalent to ~26% of the co-seismic landslide debris volume when considering bulking of the landslide deposit). A total of 9.71 ± 0.23 M m3 of sediment was delivered to the riverbed resulting in considerable riverbed aggradation and 3.58 ± 0.28 M m3 was inferred to have been transported beyond the rangefront of the Seaward Kaikōura Range (equivalent to ~9% of the co-seismic landslide debris). The total co-seismic landslide source volume for the Kowhai Catchment was only 13 +4/-3 M m3. Over the 5 years 2.02 ± 0.10 M m3 of sediment was post-seismically eroded, equal to ~13% of the co-seismic landslide debris volume within the catchment. The volume delivered to the riverbed, 1.29 ± 0.10 M m3 and 0.85 ± 0.13 M m3 is presumed to have been transported beyond the rangefront (equivalent to ~5% of the co-seismic landslide debris).
From these volumes, the rates at which the co-seismic landslide sediment was eroded from hillslopes, delivered off-slope to channels and exported from the range front were calculated. When projected, these rates of sediment conveyance suggest the volume of co-seismically generated sediment is likely to be evacuated from the rangefront within or close to the recurrence interval for ground motions equivalent to the Kaikōura earthquake. The Hapuku and Kowhai river catchments being examples of where co-seismic landsliding counterbalanced uplift.
How to cite: Jones, K., Howarth, J., Massey, C., Sirguey, P., Lague, D., and Bernard, T.: Accurate quantification of sediment conveyance following the 2016 Kaikōura earthquake, New Zealand, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-4588, https://doi.org/10.5194/egusphere-egu23-4588, 2023.
