Abstract
High-magnitude storm events and earthquakes are important drivers in the evolution of mountainous landscapes because they cause extensive landsliding. Consequently, improving the understanding of the landscape response to storm and earthquake perturbations is crucial in determining how active mountainous landscapes evolve. In this study, the sediments of Lake Gunn were used to reconstruct landscape perturbations in Fiordland associated with storm events and earthquakes. Lacustrine cores were characterised using sedimentological and geochemical techniques which revealed Type 1 and Type 2 Rapidly Deposited Layers (RDLs) that record deposition from seismic shaking, along with Type 3 and Type 3B RDLs that record deposition from storm events. Radiocarbon dating and Bayesian statistical modelling using OxCal were used to produce a chronology of Lake Gunn. This chronology demonstrated Type 2 RDLs were deposited synchronously between multiple lake basins providing strong evidence for a seismic trigger. However, in two instances a lack of synchronicity was highlighted, interpreted to reflect in-lake variability in the sensitivity of subaqueous slopes to seismic shaking. Three potential correlates with ruptures on the south Westland section of the Alpine Fault, including the well-constrained 234 cal BP earthquake, were determined, supporting the conclusion distant ruptures of the Alpine Fault may play a role in the evolution of the Fiordland landscape. Although meaningful correlations could not be made with the very poorly constrained ruptures on the Fiordland Subduction Zone, this does not rule out the Fiordland Subduction Zone as a likely seismic source. This study indicates the Fiordland landscape is sensitive to seismic perturbations that are likely associated with distant seismic shaking from earthquakes generated on the Alpine Fault and in the Fiordland Subduction Zone.