Bedding structures in Indian tsunami deposits that provide clues to the dynamics of tsunami inundation

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.

Single-grain feldspar luminescence chronology of historical extreme wave event deposits recorded in a coastal lowland, Pacific coast of central Japan

“…Since then, numerous studies have developed approaches to identify the characteristics, impact and age of tsunami deposits (e.g. Dawson and Stewart, 2007;Jankaew et al, 2008;Monecke et al, 2008;Engel et al, 2010;Switzer et al, 2012;May et al, 2016). Storm surges, another major threat to coastal communities, are also the focus of research due to recent disasters like Typhoon Haiyan, which hit the Philippine coast in 2013 (e.g.…”

Ages and relative sizes of pre‐2004 tsunamis in the Bay of Bengal inferred from geologic evidence in the Andaman and Nicobar Islands

“…A suite of diagnostic characteristics are used for the identification of paleo‐tsunami deposits, including spatially extensive deposition, inland and upward fining sequences, unconformable or erosional contacts with lower strata, and marine fossil assemblages, among them. Several of these criteria have been validated through field studies of the 2004 tsunami deposits [e.g., Bahlburg and Weiss , ; Moore et al ., ; Switzer et al ., ]. The evidence left by recent tsunamis help us attribute a similar origin to comparable deposits in coastal stratigraphic sections.…”

Geoarchaeological evidence of a Chola‐period tsunami from an ancient port at Kaveripattinam on the southeastern coast of India

“…Most of these deposits can be demarcated on the basis of Table III. Aspects of 2004 tsunami sand deposits from the southeastern coast of India (Switzer et al, 2009). …”