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Physical criterias to distinguish a Tsunami deposit form a Storm deposit.. By, Frango C.Johnson Research Scholar Department of Civil Engineering IIT Kanpur, U.P (India) Slide 2 TSUNAMI DEPOSITS STORM DEPOSITS Different characteristics found in tsunami and storm deposits, described in the literature EVIDENCE Morphological Wash-over fans behind breached barriers Stratigraphical Fines inland Erosional basal contact Large inland extent Thins inland Fines inland Erosional basal contact Relative smaller inland extent Thins inland and becomes discontinuous Wash-over fans behind breached barriers Slide 3 EVIDENCE Sedimentological Intraclasts from underlying material Not found Loading structures at base Not found Bi-directional imbrications Unidirectional imbrications Poorly sorted (particle size ranging from mud to boulders) Relatively better sorted Sedimentary structures very seldom found Sedimentary structures more common Slide 4 EVIDENCE Geochemical Palaeontological Plant fragments Shell rich units Rafting light material Buried plants at base Plant fragments Shell rich units Not found Buried plants at base Increase in geochemical elements indicating marine origin No information found, but similar signature is expected because of marine origin Marine fossils: Mixture of marine and fresh water fossils Relative well/poorly preserved fossils Marine fossils: Increased diversity (mixture marine and brackish fossils) Relative well/poorly preserved fossils Mineralogical Significant Heavy mineral concentration Not found Slide 5 Twig orientation Aerial photograph of tsunami deposit distribution and flow directions at Arop transect, Papua New Guinea. From Gelfenbaum and Jaffe (2003) Slide 6 Tsunami deposit characteristics By : Morton et al. (2007) Slide 7 Typical Characteristics of tsunami deposits : Tsunami deposits produced as a result of onshore run- up and backwash can be very distinctive (Nanayama et al., 2000; Dawson and Shi, 2000). Tsunamis comprised both landward- and seaward- directed layers Typhoon-related storm deposits showing fore set bedding Landward of these continuous tapering sediment wedges there may be discontinuous lenses of tsunami deposited sediment (Dawson, 1994). Slide 8 Large coral-reef fragments deposited on Pakarang Beach, near Khao Lak, Thailand, by the 26 December 2004 tsunami. The high energies needed to remove these boulders may ensure they have a higher preservation potential than other tsunami-related onshore sediments. Slide 9 Tsunami sediment-Macro- and micro fauna. The macro-faunal content can range from fish remains to a wide range of shell debris. Presence of benthic foraminifera ought to be an important criterion that can be used to identify past tsunami deposits. Nanayama and Shigeno (2006) report deep water marine benthic foraminifera within the 1993 Hokkaido tsunamis, indicating that the tsunami was picking up foraminifera tests on the seabed depths of between 45 and 90 m (and implying seabed current velocities of 0.20.5 m/s). Slide 10 Slide 11 Slide 12 Slide 13 Sandy storm deposits Sandy storm deposits tend to be >30 cm thick, generally extend