Far-field impact and coastal sedimentation associated with the 2006 Java tsunami in West Australia |
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Authors: | A L Prendergast N Brown |
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Institution: | (1) Geoscience Australia, GPO Box 378, Canberra, Australia;(2) Department of Archaeology, University of Cambridge, Downing Street, Cambridge, UK |
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Abstract: | A detailed assessment of the impact of a far-field tsunami on the Australian coastline was carried out in the Steep Point
region of Western Australia following the July 17 2006 Java tsunami. Tsunami inundation and run-up were mapped on the basis
of eyewitness accounts, debris lines, vegetation damage and the occurrence of recently deposited fish, starfish, corals and
sea urchins well above high-tide mark. A topographic survey using kinematic GPS with accuracies of 0.02 m in the horizontal
and 0.04 m in the vertical recorded flow depths of between 1 and 2 m, inundation of up to 200 m inland, and a maximum recorded
run-up of 7.9 m AHD (Australian Height Datum). The tsunami impacted the sparsely populated Steep Point coastline close to
low tide. It caused widespread erosion in the littoral zone, extensive vegetation damage and destroyed several campsites.
Eyewitnesses reported three waves in the tsunami wave train, the second being the largest. A sand sheet, up to 14 cm thick
and tapering landwards over 200 m, was deposited over coastal dunes. The deposits are predominantly composed of moderately
well-sorted, medium-grained carbonate sand with some gravel and organic debris. A basal unconformity defines the boundary
between tsunami sediments and underlying aeolian dune sand. Evidence for up to three individual waves is preserved as normally
graded sequences mantled by layers of dark grey, organic-rich fine silty sand. Given the strong wind regimes in the area and
the similarity of the underlying dune deposits to the tsunami sediments, it is likely that seasonal erosion will remove all
traces of these sediment sheets within years to decades. |
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