PhD title: Reconstructing the landscape response to high magnitude disturbance in active mountain belts
Assoc. Prof. Sean Fitzsimons (University of Otago)
Prof. Richard Norris (University of Otago)
Dr Marcus Vandergoes (GNS Science)
Dr Geraldine Jacobson (ANSTO)
University of Otago Prestigious Scholarship (2008)
TEC Top Achievers Doctoral Scholarship (2009-2011)
PGSF GNS Subcontract: Seismic hazards in the South Island
Humanities Division Research Grant
Landslide-induced erosion is now widely accepted as playing a crucial role in the evolution of topography in active mountain belts (Burbank et al., 1996; Dadson et al., 2003; Roering et al., 2001). High magnitude, low frequency disturbance such as earthquakes and severe storms are the predominant triggers of landsliding in active mountain settings (Chen, 2008; Hovius et al., 2000; Lin et al., 2008) and consequently, are major drivers of erosion in these systems. Despite the importance of high-magnitude low frequency disturbance in driving erosion, we only have a rudimentary understanding of the rates and magnitude of sediment produced with these events. We also have very little knowledge of the spatial and temporal variations in sediment supplied by catchments following events (landscape response).
To date, research has focused on quantifying the amount of sediment produced by catchments in response to disturbance over a few decades at most. However, mountain catchments may take many decades to adjust to disturbances such as high magnitude earthquakes (Korup, 2005; Lin et al., 2008; Pearce and Watson, 1986). Consequently, there is a need for data collected over centuries to fully understand how landscapes respond to these events.
The current research
The PhD research addresses the need for quantitative data on landscape response to high magnitude disturbance over long timeframes. The research adopts a multi-disciplinary reconstruction approach to investigate the signature of landscape response preserved in the sediment of lakes with catchments draining the Southern Alps (Fig. 1). There are three phases to the research. Each phase is designed to establish prerequisites for reconstructing landscape response to high magnitude low frequency disturbance but also address significant research questions in there own right.
Figure 1b: Photograph of Lake Mapourika showing the lake relative to the range front of the Southern Alps and the Alpine Fault (photo courtesy of GNS science).
Phase one will establish a palaeo-seismic record by identifying seismites recorded in cores (Fig. 2a) from lakes long the central section of the Alpine Fault (Fig. 2b). Seismites will be identified using a combination of core sedimentology, palaeo-ecology and correlation based on high-resolution 14C chronology and palaeo-magnetic secular variation. The lake record will extend the current palaeo-seismic record for the Alpine Faultby two thousand years. The longer and more refined record of past earthquakes will further refine our understanding of the seismic potential of the Alpine Fault and may help determine the type and range of earthquakes that are characteristic of the fault.
Figure 2a: Mackereth corer in use on Lake Paringa.
Figure 2b: Map of central South Island and cut-outs showing and the location and morphology of the lakes used in this study and their position relative to the Alpine Fault.
Phase two will develop a modern analogue to allow quantitative assessment of storm intensity to be determined from records of lake sedimentation. The modern analogue will be constructed by correlating meteorological precipitation data with the record of sedimentation events. Correlation will be achieved using 210Pb and 237Cs dating to generate chronologies for recent lake sediments that can then be wiggle-matched to the records of precipitation. Grainsize parameters will be used to develop quantitative indices for storm intensity. Using the analogue the intensity and frequency of storms will be determined for the last 3 ka. The storm record will extend over known periods of late Holocene climate change, such as the Medieval Warm Period (MWP) and Little Ice Age (LIA) (Gomez et al., 2007; Williams et al., 2004), and will contribute to our understanding of the timing and manifestation of these climatic events in the southern hemisphere.
Phase three will integrate the palaeo –seismic and –storm records to resolve the landscape response to high magnitude low frequency disturbance over a range of catchment sizes and event cycles. High resolution 14C dating will be used to temporally constrain landscape response following major disturbance, such as, Alpine Fault earthquakes. The relationship between storm intensity and sediment transport will be explored to identify thresholds in intensity above which transport begins and to establish if these thresholds vary over earthquakes cycles. High-resolution pollen analysis will be used to reconstruct the impact of individual disturbance events on catchment vegetation and to assess the feedback between vegetation disturbance caused by earthquakes and storms and erosion in the lake catchments.
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