Beach Ridge Patterns in West Aceh, Indonesia - Response to Large Earthquakes along the Northern Sunda Trench
Abstract
The morphology of beach ridge plains along active margins is suitable to reconstruct coastal subsidence during large megathrust earthquakes. Here we use satellite imagery and automatic level surveys to reconstruct the build-up of a new beach ridge along a 6 kilometer long stretch of the western Acehnese coast after the complete destruction of the strand during the great Sumatra -Andaman earthquake and successive tsunami in December 2004. The western Acehnese coast is characterized by a characteristic ridge and swale topography reflecting the long-term progradation of the coastline. Whereas new beach ridges build progressively seaward, older shore-parallel ridges can be found up to 2 kilometer inland and mark former positions of the coastline. Radiocarbon dates obtained from marshy deposits in between ridges indicate an average progradation rate of 1 to 2 meter per year over the last 1000 years. As a result of co-seismic subsidence of 0.5 to 1 meter and tsunami inundation in 2004, the most seaward beach ridge was destroyed and the coastline receded on average 134 meter landward. However, by 2006 a new 55 meter wide beach had formed. In the following years the coast prograded by another 27 meters, but never fully recovered to its pre-December 2004 position. In addition to the spatial data our topographic surveys conducted in 2009, 2012 and 2013 indicate that the newly formed beach ridge stands about 80 centimeter higher than older ridges further inland. The source material for the new beach ridge is most likely sand transported seaward by the back flow of the December 2004 tsunami and temporary stored in an offshore bar. In the months and years after the tsunami regular coastal processes rework the sand bar and lead to the reconstruction of a higher beach ridge in equilibrium with the vertical displacement of the coast and the resulting higher relative sea level. Another prominent beach ridge can be found in about 650 meter distance to the shoreline and most likely formed in the aftermath of a reported pre-historic megathrust earthquake and tsunami at about 1400AD.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2013
- Bibcode:
- 2013AGUFMNH44A..07M
- Keywords:
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- 4217 OCEANOGRAPHY: GENERAL Coastal processes;
- 4300 NATURAL HAZARDS;
- 4564 OCEANOGRAPHY: PHYSICAL Tsunamis and storm surges;
- 8170 TECTONOPHYSICS Subduction zone processes