GEOMORPHOLOGICAL AND SEDIMENTOLOGICAL CHANGES DURING AND AFTER THE DECEMBER-2004 INDIAN OCEAN TSUNAMI NEAR THE VELLAR RIVER AND THE M.G.R. ISLAND AREA OF THE CENTRAL TAMIL NADU COAST, INDIA

The present study reviews geomorphic changes and sediment characteristics in the Vellar river and the M.G.R. island in the Cuddalore District, of Tamilnadu, India, caused by the 26th December, 2004 Indian Ocean Tsunami. The island has an area of about 12,000 m2 and it is separated from the mainland by a channel. It is bounded to the east by the Vellar River and to the north and south by the Muzhukkuthurai lagoon. A vegetated coastal dune with a length of about 1.5 km protected the island. Tsunami waves ranging in height from 4 to 6 meters breached the dunes, caused erosion and carried debris of destroyed coastal buildings westward to more than 50 m inland. The tsunami run up was up to 1.3 m. Very fine sand with a thickness of one meter filled the Muzhukkuthurai lagoon in the west. Heavy erosion resulted in a steep beach gradient. Sediments transported from the SE and the SSE direction resulted in greater accretion along the intertidal region. The sediment layer exhibited trampled and load structures, indicating deposition by the flooding and receding motion of the water, moving at high velocity. The sediments ranged from fine to medium in size and were well sorted.