HR: 17:50h
AN: T24A-07    [Abstracts]
TI: Sedimentary deposits from the July 17th 2006 Java tsunami on the West Australian coastline
AU: * Prendergast, A L
EM: amy.prendergast@ga.gov.au
AF: Geoscience Australia, GPO BOX 378, Canberra, ACT 2600, Australia
AB: On July 17th 2006, an Mw = 7.7 earthquake south of Java generated a tsunami that devastated parts of the Javanese coast, killing more than 500 people. The tsunami also affected parts of the Western Australian coast. Within a week of the event, a post tsunami survey was carried out near Steep Point, Western Australia. 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. Eyewitnesses reported three waves in the tsunami wave train, the second being the largest. A topographic survey using kinematic GPS with accuracies of 0.02 metres in the horizontal and 0.04 metres in the vertical recorded inundation depths of between 1-2 m, inundation of up to 200 m inland, and a maximum recorded run-up of 7.9 m AHD (Australian Height Datum). The tsunami caused widespread erosion in the littoral zone, extensive vegetation damage, destroyed several campsites (including transporting a large vehicle ten metres inland) and deposited extensive sediment sheets over coastal dunes. At their seaward edge, these sediments are up to 14 cm thick, tapering landwards over approximately 200 m. The deposits are composed of moderately well sorted, medium grained silicic sand with some gravel and organic debris. A basal unconformity defines the boundary between tsunami sediments and underlying aeolian dune sand. Buried green vegetation stems with roots traceable to the lower dune unit occur within the tsunami deposit. No roots are present within the tsunami-deposited sediments. This is taken as evidence for the recent mobilisation of the sediments within the tsunami sediment sheet. Evidence for up to three individual waves is preserved as normally graded sequences mantled by layers of dark grey, organic-rich fine silty sand. Grainsize and microfossil analyses are in progress. 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.
DE: 3022 Marine sediments: processes and transport
DE: 4235 Estuarine processes (0442)
DE: 4558 Sediment transport (1862)
DE: 4800 OCEANOGRAPHY: BIOLOGICAL AND CHEMICAL (0460)
DE: 9330 Australia
SC: Tectonophysics [T]
MN: 2007 Joint Assembly