Finding tsunami causing landslide deposits in the lakes of New Zealand
Description of Research Project
I am a NERC PhD student funded through the IAPETUS Doctoral Training Programme and CASE partnered with the British Geological Survey. My project focuses on identifying landslide deposits within lakes and fiords in New Zealand. Landslides are a common geomorphological process in mountainous landscapes and are an effective means of maintaining an equilibrium, limiting the growth of mountains. Seismic shaking in particular can trigger widespread failure and mobilisation of slopes of sufficient relief. Rock avalanches, highly mobile landslides, are very effective agents of erosion, and, can be highly destructive, particularly if they reach settlements. Within a terrestrial setting, landslide deposits are subject to post failure modification and erosion by high rates of geomorphic processes, removing evidence of past events. The spatial and temporal frequency of these events remains poorly understood and so the risks posed are underestimated. In former glaciated environments, lakes and fiords are common and provide a unique geomorphic setting that can preserve landslide deposits, allowing for capture of the record of past large landslides. If these landslides post-date lake formation and or relative sea level rise, a landslide-tsunami might also have occurred, which poses further risks the wider area.
The South Island of New Zealand is a highly seismically active area. The Alpine Fault runs along the western front of the Southern Alps and is one of the most active plate tectonics on Earth. The fault has a 600 km long onshore expression and is believed to be capable of generating great earthquakes (ML >8). The Alpine Fault has not sustained a large magnitude earthquake since ca. AD 1717 and the time since this rupture is close to the average estimated recurrence interval of the fault (c. 200-300 years). Thus, the probability of a ML >8 earthquake along the Alpine Fault is 34% in the next 20 years and 54% in the next 100 ! years.
An earthquake of this magnitude is expected to generate shaking which will reach Modified Mercalli Intensity (MM) of VII or higher across the Southern Alps, including numerous waterside population centres. This will be sufficient to trigger landsliding across the Southern Alps and many will enter the fiords and lakes. This in turn could generate hazardous tsunamis. These pose large risks to many waterside developments along lake shores in this rapidly developing tourist region. Tsunami hazard assessment requires the spatial distribution and sizes of landslides to be known in order to ascertain their tsunami potential. Currently in New Zealand, there is only a partial inventory of terrestrial deposits and limited investigation of submarine deposits in the lakes and fiords. Additionally, the lack of a long historical archive in New Zealand (from ca. 1840 AD onwards) means there are only a few documented landslide tsunamis in some of the fiords in New Zealand.
The methodology will encompass the application of an integrated suite of boat-mounted geophysical survey equipment. Sonar will be used to generate high resolution bathymetric maps of lake basins to identify landslide deposits. Lakes Wanaka and Wakatipu have been identified as potential survey locations from previous research. Where landslide deposits are obscured by lacustrine sediments, sub-bottom profiling can be used to locate the buried deposits due to the difference in acoustic signals of lacustrine sediments and landslide deposits. Using conservative estimates of lake sedimentation rates (8-10 mm/yr), it is anticipated that < 13,000 years of sedimentary record can be analysed in some locations. This approach will allow a size, spatial and temporal pattern of landslides into lakes to be identified. Whilst most deposits are likely to be associated with subaerial sources, there is also the possibility of identifying submarine landslides from delta collapse for example, which may have had potential to generate tsunamis. Ident! ificatio n of both subaerial and submarine sources will assist in future hazard management both for landslide and tsunami risk within the lakes and fiords of New Zealand.
- GEO3144 Landslides from Pole to Pole
- GEO2137 Key Methods in Physical Geography
Qualifications and Achievements
- 2014-2015: MSc Water Hazards, Risk and Resilience, University of Dundee
- 2010-2014: Bsc Geography, University of Dundee
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