- 1Victoria University of Wellington, School of Geography, Environment and Earth Sciences, New Zealand
- 2University of Otago, School of Geography, Dunedin, New Zealand
- 3GNS Science, Lower Hutt, New Zealand
Mass movements on slopes adjacent to and beneath lakes and fjords can produce destructive tsunami. Reconstructing past events is crucial for understanding the extent and frequency of this hazard. Current reconstruction approaches involve identifying large landslide deposits preserved on the lakebed and analysing landslide dimensions and dynamics to estimate tsunami magnitude. However, in active tectonic settings, much of the morphological evidence is eroded or buried over time, which impedes the development of long event records that are needed to quantify lacustrine tsunami hazard.
This study tested the hypothesis that lake tsunami leave diagnostic sedimentary imprints in the stratigraphic record of lakes that can be reliably used to develop long records of tsunami frequency. The hypothesis was tested by examining the sedimentological signature and spatial heterogeneity of deposits produced by a coseismic tsunamigenic delta collapse in Lake Rotoroa, New Zealand. Extensive bathymetric mapping, seismic imaging, sediment coring and numerical modelling were used to establish evidence of a destructive lacustrine tsunami generated by the catastrophic collapse of D’Urville and Sabine River deltas between 800 - 979 CE. The delta collapse was triggered directly by the rupture of the northern section of the Alpine Fault, where the fault ruptured through the delta fronts instigating the deep-seated delta collapse with heightened tsunamigenic capacity.
Six 6-m long sediment cores distributed across the lake basin were examined to characterise the tsunami deposit. A lithofacies model for lake tsunami deposits was then developed by correlating the textural and structural characteristics of the event deposit to numerical tsunami simulations and sediment transport principles. The findings from Lake Rotoroa show that lacustrine tsunami lead to the formation of megaturbidite deposits with distinct subunits that preserve evidence of high-velocity bottom currents, prolonged water column motion, and tsunami backwash. Comparisons to historic event deposits within Lake Rotoroa and globally highlighted that lacustrine tsunami deposits consistently display diagnostic sedimentary signatures that are distinct from other event deposits.
We conclude that lake tsunami deposits can be differentiated from turbidites produced by non-tsunamigenic mass-wasting, demonstrating that lake sediment records can be used to reconstruct the frequency of lake tsunami over millennial time scales. This research presents a promising new avenue for the quantitative reconstruction of lacustrine tsunami hazard in active tectonic settings.
How to cite: Hughes, K. E., Howarth, J. D., Fitzsimons, S. J., Moody, A., and Wang, X.: Diagnostic sedimentary imprints of lacustrine tsunami: evidence from tsunamigenic fault-contact delta collapse in Lake Rotoroa, New Zealand, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14694, https://doi.org/10.5194/egusphere-egu25-14694, 2025.