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Bedding structures in Indian tsunami deposits that provide clues to the dynamics of tsunami inundation
| Content Provider | Semantic Scholar |
|---|---|
| Author | Switzer, Adam D. Srinivasalu, Seshachalam Thangadurai, N. Ram, Vinutha |
| Copyright Year | 2011 |
| Abstract | The 2004 Indian Ocean tsunami deposited an extensive sandsheet on the coastal plain of SE India. At particular sites, the sedimentary bedding in the sandsheet provides evidence of variable energy conditions and flow during inundation of the coast. Trenching of the deposits at sites where only unidirectional flow was observed allowed the investigation of changes in hydrodynamics recorded in bedding structures without the added complexity of return flows and reworking. A high-velocity initial surge is recorded as upper flow regime (UFR) plane bedding. Following the initial high flow a period of falling flow velocity and quiescence occurs where sediments settle out of suspension, often resulting in a reverse graded bed that transitions to a graded (fining-up) bed. As water levels begin to decline after maximum inundation sheet flow caused the formation of inversely graded (coarsening-up) beds or a return to UFR conditions. At one site the final stages of tsunami inundation is recorded as small channels that have an erosional base and are filled with graded sediments that exhibit complex patterns of sedimentation. Pits excavated in areas of unidirectional flow allow the development of a sedimentary model for tsunami sediment dynamics across flat topography under unidirectional flow conditions. Despite recent advances, the hydrodynamics of tsunami inundation and the inherent relationship between inundation hydrodynamics and sedimentary bedding in tsunami deposits remain poorly understood. Much can be learnt from the careful study and interpretation of modern tsunami deposits as they provide a valuable and powerful analogue to palaeostudies, and provide insights into the dynamics of erosion and deposition during tsunami inundation and back flow (e.g. Le Roux & Vargas 2005; Dawson & Stewart 2007; Hawkes et al. 2007; Jaffe & Gelfenbaum 2007; Morton et al. 2007; Paris et al. 2007, 2008; Srinivisalu et al. 2007; Choowong et al. 2008a, b; Komatsubara et al. 2008; Naruse et al. 2010). Owing to the relative rarity and geographical distribution of tsunami, few descriptions are available of the sedimentary structures and facies of onshore tsunami deposits (e.g. Gelfenbaum & Jaffe 2003; Nanayama & Shigeno 2006; Bahlburg & Weiss 2007; Hawkes et al. 2007; Hori et al. 2007; Morton et al. 2007; Paris et al. 2007; Umitsu et al. 2007; Choowong et al. 2008a, b; Naruse et al. 2010). Investigations of sedimentary processes associated with modern tsunami are extremely important in the interpretation of tsunami deposits in the geological record as many identified tsunami signatures or features can be equally attributed to storm surge or other depositional processes (Witter et al. 2001; Switzer et al. 2005; Dawson & Stewart 2007; Jaffe & Gelfenbaum 2007; Kortekaas & Dawson 2007; Morton et al. 2007; Switzer & Jones 2008a, b; Switzer & Burston 2010). Recent studies on tsunami-deposited sandsheets, such as those deposited by tsunami events in 1983 at Nihonkai-chubu (Minoura & Nakaya 1991), the 1992 Flores (Shi et al. 1995; Minoura et al. 1997), 1993 at Hokkaido–Nansei-oki (Nishimura & Miyaji 1995; Sato et al. 1995; Nanayama et al. 2000), 1994 in Java (Dawson et al. 1996), 1998 in Papua New Guinea (e.g. Gelfenbaum & Jaffe 2003) and the recent 2004 Indian Ocean tsunami (e.g. Szczucinski et al. 2005, 2007; Bahlburg & Weiss 2007; Hawkes et al. 2007; Hori et al. 2007; Morton et al. 2007; Paris et al. 2007; Srinivasalu et al. 2007; Umitsu et al. 2007; Choowong et al. 2008a, b; Naruse et al. 2010), are of considerable importance in understanding the dynamics of tsunami inundation in different coastal settings. The tsunami run-up process is very complex, and it is pertinent to any study of onshore tsunami deposits that analysis of the likely pre-event morphology, sedimentary environments and sediment dynamics of the seabed, nearshore and onshore systems be considered. One of the most widely recognized sedimentary signatures for tsunami inundation is landwards-tapering wedges From: Terry, J. P. & Goff, J. (eds) 2012. Natural Hazards in the Asia–Pacific Region: Recent Advances and Emerging Concepts. Geological Society, London, Special Publications, 361, 61–77, http://dx.doi.org/10.1144/SP361.6 # The Geological Society of London 2012. Publishing disclaimer: www.geolsoc.org.uk/pub_ethics at Nanyang Technological University on June 13, 2012 http://sp.lyellcollection.org/ Downloaded from |
| File Format | PDF HTM / HTML |
| Alternate Webpage(s) | https://earthobservatory.sg/files/publications/pdf/Geological%20Society,%20London,%20Special%20Publications-2012-Switzer-61-77.pdf |
| Language | English |
| Access Restriction | Open |
| Content Type | Text |
| Resource Type | Article |
