Beach ridge patterns in West Aceh, Indonesia, and their response to large earthquakes along the northern Sunda trench. (1st April 2015)

• Record Type: Journal Article
• Authors: Monecke, Katrin; Templeton, Caroline K.; Finger, Willi; Houston, Brian; Luthi, Stefan; McAdoo, Brian G.; Meilianda, Ella; Storms, Joep E.A.; Walstra, Dirk-Jan; Amna, Razali; Hood, Neil; Karmanocky, Francis J.; Nurjanah, ; Rusydy, Ibnu; Sudrajat, Sam Unggul
• Is Part Of: Quaternary science reviews. Volume 113(2015)
• Page Start: 159
• Page End: 170
• Publication Date: 2015-04-01
• Subjects: Paleoseismology -- Coastal morphology -- Beach ridge plain -- December 2004 Sumatra-Andaman earthquake -- 2004 Indian Ocean tsunami -- Aceh (Indonesia); Geology, Stratigraphic -- Quaternary -- Periodicals; Stratigraphie -- Quaternaire -- Périodiques; 551.79
• DOI: 10.1016/j.quascirev.2014.10.014
• Languages: English
• ISSNs: 0277-3791

Abstract

Abstract: The morphology of beach ridge plains along active margins can be used 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 10 km long stretch of the western Acehnese coast after the complete destruction of the beach during the great Sumatra -Andaman earthquake and successive tsunami in December 2004. The western Acehnese coast is characterized by ridge and swale topography reflecting the long-term progradation of the coastline. Radiocarbon dates obtained from marshy deposits in between ridges indicate an average progradation rate of 1.3–1.8 m per year over the last 1000 years. As a result of coseismic subsidence of 0.5–1 m and tsunami inundation in 2004, the most seaward beach ridge was destroyed and the coastline receded on average 110 m landward representing 65–85 years of average progradation. However, by 2006 a new 22 m wide ridge had formed. In the following years the coast prograded by an additional 30 m, but has not yet recovered to its pre-December 2004 position. In addition to the spatial data, topographic surveys conducted in 2009, 2012 and 2013 indicate that the crest of the newly formed beach ridge is 0.8–1.3 m higher than the crests of older beach ridges further inland. The source material for the new ridge is most likely sand transported seaward by the back flow of the 2004 tsunami and stored on the upper shoreface. In the months and years after the tsunami, this sediment is reworked by regular coastal processes and transported back to shore, leading to the reconstruction of a higher beach ridge in equilibrium with the vertical displacement of the coast and the resulting higher relative sea level. The preservation potential of the newly formed ridge depends on sediment availability within the coastal system to balance coastal profile adjustments due to rapid postseismic uplift. In Aceh, the preservation of seismically modified beach ridge morphology seems likely and another prominent ridge can be found in 640 m distance to the shoreline. It most likely formed in the aftermath of a previous megathrust earthquake and tsunami about 600 years ago matching sediment and coral records for this region. Highlights: We quantify coastal change in Aceh, Indonesia, since the 2004 Indian Ocean tsunami. We observe a higher beach ridge forming in response to coseismic land level change. We suggest that beach ridge plains along active margins form paleoseismic archives.