| Summary: | In connection with observations made on the impact of beach placer mining, a study area extending from Poompuhar to Nagoor, in Tamil Nadu, had been chosen for regular profiling and sediment sampling since April 2003. The on-set of the tsunami of 26th December 2004 encouraged continuation of the study in order to understand the sudden changes in the sedimentological processes caused by this tsunami. As a profiling survey of the area had been completed on 16th December 2004, an exact quantum of erosion level caused by the tsunami was determined for several stations. Except for Nagoor, all other stations showed erosion of the beaches, with a maximum of 2.5 m, particularly in the Karaikkal area. The study identified two major geomorphologic parts, the first extending from northern Poompuhar to Karaikkal and the second from southern Karaikkal to Nagoor. Changes in the geomorphologic characters observed at these two areas were attributed to the nature of the inner shelf bathymetry. The different beach profiles for the pre- and post-tsunami periods that were prepared through trend analysis, clearly show huge deposition of sediments on the Nagoor beaches. The influence of inlets in Karaikkal, Poompuhar and Nagoor are strongly indicated by the nature of sediments that were deposited on beaches at these locations. When the sediment texture of pre-tsunami deposits is compared with that of post- tsunami deposits, a characteristic shift in kurtosis is observed on all the beaches, while skewness and mean establish a shift on beaches that eroded. Examination of heavy mineral composition in sediments indicates a dramatic shift in concentration, ranging from 19 to 76 % in the Nagoor area. Further study of sedimentological process may shed additional light on tsunami impacts on any beach in the study area, particularly because of the ongoing monitoring and the availability of past baseline records.
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