Abstract
Abstract. Tsunami, storm and flash-flood event layers, which have been deposited over the last century on the shelf offshore Khao Lak (Thailand, Andaman Sea), are identified in sediment cores based on sedimentary structures, grain size compositions, Ti / Ca ratios and 210Pb activity. Individual offshore tsunami deposits are 12 to 30 cm in thickness and originate from the 2004 Indian Ocean Tsunami. They are characterized by (1) the appearance of sand layers enriched in shells and shell debris and (2) the appearance of mud and sand clasts. Storm deposits found in core depths between 5 and 82 cm could be attributed to recent storm events by using 210Pb profiles in conjunction with historical data of typhoons and tropical storms. Massive sand layers enriched in shells and shell debris characterize storm deposits. The last classified type of event layer represents reworked flash-flood deposits, which are characterized by a fining-upward sequence of muddy sediment. The most distinct difference between storm and tsunami deposits is the lack of mud and sand clasts, mud content and terrigenous material within storm deposits. Terrigenous material transported offshore during the tsunami backwash is therefore an important indicator to distinguish between storm and tsunami deposits in offshore environments.
Highlights
Tsunami waves propagating into shallow waters as well as related backwash flows can erode, transport and deposit significant amounts of sediments in the inner-shelf environment (e.g., Paris et al, 2010; Goto et al, 2011), here defined as 0 to 30 m water depth
Storm and flash-flood event layers, which have been deposited over the last century on the shelf offshore Khao Lak (Thailand, Andaman Sea), are identified in sediment cores based on sedimentary structures, grain size compositions, Ti / Ca ratios and 210Pb activity
The most distinct difference between storm and tsunami deposits is the lack of mud and sand clasts, mud content and terrigenous material within storm deposits
Summary
Tsunami waves propagating into shallow waters as well as related backwash flows can erode, transport and deposit significant amounts of sediments in the inner-shelf environment (e.g., Paris et al, 2010; Goto et al, 2011), here defined as 0 to 30 m water depth. The structure and texture of tsunami deposits in offshore areas mainly depend on the local sediment sources, the geomorphology of the seafloor, the tsunami wave height and the number of waves in the case of more than one wave hitting the shoreline during the run-up and backwash (Sakuna et al, 2012). Both the bathymetry and available sediments are highly variable in shallow marine environments (e.g., Dartnell and Gardner, 2004). While the tsunami’s impact increases with decreasing water depth towards the coastline, only very few offshore tsunami deposits have been
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