Case History
Submarine Landslides on the South-Eastern Australian Margin
S. Clarke (School of Geosciences, University of Sydney)
D.W. Airey (School of Civil Engineering, University of Sydney)
P. Yu (School of Geosciences, University of Sydney)
T. Hubble (School of Geosciences, University of Sydney)
1. INTRODUCTION
The consequences of submarine landslides include damage to seabed infrastructure (communications cables and buried pipelines), subsidence of coastal areas and the generation of tsunamis (Masson et al.,2009). Our failure to understand the causes of these phenomena means that submarine landslides present a significant risk to coastal and offshore development, and have on occasion resulted in the halting of offshore developments. It has been established that large submarine landslides can produce tsunamis, such as the earthquake triggered submarine slides in 1929 (Grand Banks, USA; Fine et al., 2005) and 1988 (Aitape, Papua New Guinea; Tappin et al., 2001) which both resulted in significant casualties. The large loss of life and damage to infrastructure from the Indian Ocean tsunami of 2004 (Lay et al., 2004) and the recent Japanese event have increased interest in the tsunamigenic potential of large submarine slides. Australia is vulnerable to tsunamis with 85% of the population living within 50 km of the coast and much of the critical infrastructure located close to the coast. It has been suggested (Dominy-Howes, 2008) that the maximum credible tsunami could cover mainly in 6 m of water, and while the possibility of such an event has major implications for risk assessment and siting of critical infrastructure, the likelihood cannot be sensibly determined.
The geological record contains many examples of submarine landslides, which can vary in scale from minor shallow slides to very large slides, such as the Storegga slides off the Norwegian coast which have a total volume of over 3000 km3 (Haflidason et al., 2005). Statistics on known landslides on the eastern continental slope of North America, which has geological similarities to Australia’s eastern margin, have been published by Masson et al. (2006). These show that between 30oN and 45oN there are 152 large landslides affecting an area of nearly 40000 km2. Most failures occur on slopes of between 1o and 7o, with the greatest number of failures occurring on slopes of 3.5o. The area affected by failures decreases as the slope increases, and the depth of water at the slide head ranges from 250 m to 2500 m, with the greatest number of failures occurring at water depths of around 1000 m. Despite extensive literature on the nature and causes of submarine landslides, their dynamics and triggering processes are not well understood (Locat and Lee, 2002; Bardet et al., 2003). One of the principal reasons for this is the limited data on the physical and mechanical properties of the sediments, particularly from the slide plane, as these materials have not traditionally been collected.
In Australia, studies of the southeastern (SE) Australian continental slope (Jenkins and Keene, 1992; Glenn et al., 2008; Boyd et al., 2010) have been very limited until recently. Evidence of submarine landslides on the SE Australian margin was first reported by Jenkins and Keene (1992), but it was not until high resolution, multi-beam bathymetric data became available (Glenn et al., 2008; Boyd et al., 2010) that the true distribution of these slides could be established. The recent collection of high-resolution multibeam echo-sounding and sub-bottom profiling data has provided a detailed view of mass-transport features over a 900 km length of the margin. A wide range of slide features has been detected as well as a series of canyons which cut through the slope sediments. The submarine slides range in scale from hundreds of
small slides with volumes of <0.5 km3 up to the largest documented slide which has a volume of 20 km3
(Boyd et al., 2010).
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