Geomorphic and Sedimentological Changes in the East Coast of Tamilnadu by Indian Ocean Tsunami-2004
Total Page：16
File Type：pdf, Size：1020Kb
International Journal of Environmental Science and Development, Vol. 2, No. 3, June 2011 Geomorphic and Sedimentological Changes in the East Coast of Tamilnadu by Indian Ocean Tsunami-2004 S.R.Singarasubramanian, M.V.Mukesh and K.Sujatha beaches are characteristic of Mandapam to Rameswaram. Abstract—The coastal zone of Tamilnadu was worst affected The important features in these areas include spits, swales, by the December, 2004 Tsunami. Most of the east coast of sand dunes, shoals, deltaic plains, sand sheets, mud flats, Tamilnadu was affected by the tsunami waves. Except the chenier plains, cliffs, beach rocks, sea caves, sea cliffs and region between Point Calimere and Thoothukudi were very marine terraces. meagerly affected. The rest of entire coastal region was affected along with the coastal communities. In some regions Apart from the coastal geomorphic features, the erosion was prominent with a large scale inundation and Tamilnadu coast is protected with coral ecosystem in the deposition was prominent in some places. The coastal dunes Gulf of Mannar region. Coral reefs act as a barrier against and river systems were completely altered. wave action and prevent coastal erosion. There are 21 islands, situated at an average distance of about 8 km from Index Terms——Coastal morphology, Tsunami, Inundation. the coast and running parallel to the coastline. Along these coastline both erosion and accretion takes place. Island erosion and accretion are caused mainly by the action of I. INTRODUCTION waves, wave induced currents and long shore currents along The coastal zone of Tamilnadu is endowed with varied the shore. landscape such as sandy beaches, beach ridges, backwaters, On 26th December, 2004, the deadliest tsunami a new estuaries, intertidal mud and sand flats, dunes, cliffs, beach word in the Indian history triggered by a massive earthquake rocks, deltas, lagoons, mangrove forests and coral reef of magnitude 9.0, at 6.29 IST was the largest recorded ecosystems. The coast has been constantly undergoing worldwide in 40 years. The earthquake epicenter lies at physical changes in the geological past and at present. Many Lat.3° 7'N and Long. 95° 7'E in the Indian Ocean off the rivers bring considerable sediments, which affect shore west coast of Sumatra islands, Indonesia. processes significantly. The coast between Chennai and Pondicherry through Muttukadu, Mammallapuram and Marakkanam is a narrow II. STUDY AREA sandy belt. The major geomorphic features include tidal Study area forms the tsunami affected east coast of flats, estuary, beaches, dunes and beach ridges. The dunes Tamilnadu extends from Vellar River to Thoothukudi. are stable at their base and mobile on their crest. The coastal Coastal geomorphic features were studied by field survey, dune field, which is stabilized by vegetation, occurs in a using toposheets and satellite pictures. The sedimentation very high-energy wind regime. Linear dunes along the changes were studied by means of digging pits and shoreline, which are stabilized to a large extent, represent analyzing the samples at 2 or 5 cm interval. The inundation the major geomorphic features. was noted with the remnant water marks and by transported The coastal area between Pondicharry and Nagapattinam debris during the tsunami. Original dune height was is occupied by various geomorphic features. The varying measured from the eroded parts and uprooted vegetation. geomorphic features like beach ridges, swales, sand dunes, deltaic plain, chenniers, palaeo-tidal flats, palaeo-lagoons, salt marshes, palaeo-channel and lagoon are seen in the area III. DISCUSSION (Anbarasu and Rajamanickam 1997). The coastal features in The coastal area between Vellar estuary and and around Point Calimere include beaches, beach ridges, Muzhukkuthurai was occupied by prominent 4 to 6 m stable swales, dunes, tidal flats, palaeo tidal flat, barrier islands, sand dunes with lot of vegetation, ridges are prominent. alluvial plain, chenier, palaeo lagoons, flood plains, mud These dunes run parallel to the coast. In the study area flats salt pan, mangrove etc.(Shanthi Devi and M.G.R.Tittu, Muzhukkuthurai, Karaikal, Nagapattinam and Rajamanickam, 2000). Velankanni were the major coastal regions destructed by the The coastal landforms between Devipattinam and tsunami waves. Mandapam were classified into depositional, erosional There was a long sand dune of 3m height protecting the features and others (Chockalingam et. al. 2000). Rocky Tittu running parallel to the coast. Apart from this major sand dune there was lot of stable dunes with vegetation. Run-up height in M.G.R. Tittu was more than 3m and Manuscript received March 9, 2011. completely inundated the island. Inundation in inland area in S.R.Singarasubramanian*, M.V. Mukesh and K.Sujatha, Department of Muzhukkuthurai was 1000 to 1200m (Table-1) from the Earth Sciences, Annamalai University, Annamalainagar-608 002, coast and run-up height was 1.2m in the inland. Tamilnadu, India,Corresponding author: email: [email protected] 179 International Journal of Environmental Science and Development, Vol. 2, No. 3, June 2011 TABLE 1 INUNDATION AND RUN UP HEIGHTS OF THE TSUNAMI WAVES IN separated from each other by marked troughs. The crests are SOME LOCATIONS flat and range in height from 0.5 to 2m. They are stabilized S.No. Place Maximum Inundation (m) by the vegetation. After the mega tsunami event the sand 1. Muzhukkuthurai 1200 2. Parangipettai 1700 dunes were breached in many places and the coastal 3. Nagapattinam 1100 geomorphology has changed. In many places the channels 4. Akaraipettai 3000 were diverted or filled with sediments or new formations of 5. Vedharanyam 1400 erosional structures were observed. Most of the coastal 6. Kodiakkarai 1500 regions become steep in some places and shallow in some 7. Point Calimere 1000 8. Melmanakudi 1500 places due to the differential erosion and accretion of 9. Keezhamanakudi 1000 sediments by tsunami waves. 10. Thoothukudi 75 In Kodiakarai the sediment and water inundation was 11. Thondi 30 upto 1500m (Table-1) from the shore. Parallel to the 12. Vellapatty 75 13. Colachal 1500 shoreline in the beach, erosion is prominent and filled with 14. Melmanakudi 1500 water bodies. The stable dunes in these areas were breached 15. Keezhamanakudi 1000 at places or eroded (Fig 1. C). Point Calimere has encountered a wide spread sedimentation and formation of eroded channels due to tsunami. The entire stable 2m high dunes was eroded (Fig 1. D). The newly created channel was about 120cm deep near the shore and extends upto 1km inland. Here the beach was eroded and occupied by sea for about 20m after tsunami. In areas like Mallipattinam, Manora, Kalamangudi, Manthiripattinam, Prathabharamapattinam, Adhipattinam, Palakudi, R.Pudupattinam and Vattanam encountered sedimentation in the fishing harbors. The recent sediments brought down by the tsunami waves were spread in inland. In some areas like Prathabharamapattinam and Manora, the coastal fishing areas become clayey. In all these areas the beaches are shallow and wave domination is less. In Thondi, Mullimanal, Tiruppalakudi, Devipattinam and Uchipuli regions the tsunami waves entered upto 25 to 30m inland. In Thondi, the waves entered up to 30m (Table-1) inland and the sedimentation was not observed in inland, only water inundation was observed. From Thondi up to Uchipuli, less inundation of sediments was observed. This may be due to the shallow beaches and their locations. Vaippar, the projected coast encountered erosion normally was not affected by much sedimentation by Fig 1. A- Deposition and alteration of coast near Vellar; B- Erosion of tsunami. Taruvakulam, Vellapatty, Pulavali and stale dune at M.G.R.Tittu; C-Erosional water bodies at Vedharanyam; D- Erosion of 2m high stable dune at Point Calimere; E- Parallel bedding with Thoothukudi Harbor guest house were affected by tsunami basal erosional contact with Pre tsunami sediments at Kodiampalayam; F- waves. In Taruvakulam the shoreline was filled with Erosion base and deposition of sediments with erosional structures near sediments to an extent of about 120cm thick with 150m Poompuhar. length and 20m width along the coast. Coastal morphology In most of the coastal regions the sand dunes protecting was completely altered. Thick sedimentation in the northern the coast was completely eroded by the waves (Fig 1. B). part of Taruvakulam leads to the extent of beach towards the The tsunami waves not only alter the geomorphic features sea. Vellapatty, near Thoothukudi was also affected by the but also bring voluminous sediments from the shelf. The sedimentation due to the tsunami waves. The inundation is stable palaeo dunes were breached by the tsunami waves. up to 75m inland (Table-1). The sediments were deposited Development of sand bars perpendicular to the coast was over the normal coarser beach sediments as thin layers. noticed in the south near M.G.R.Tittu (Singarasubramanian, Behind the Harbor Guest House in Thoothukudi, the et.al. 2009). This evidenced the change in coastal sedimentation was up to 500m inland from the shore morphology and wave direction after tsunami. Small (Singarsubramanian, et. al. 2006). uplands could be seen in near the mouth of Vellar (Fig 1. A) In the southern sector of the study area includes immediately after tsunami, but slowly they became flat and Palayakayal, Punnakayal, Kayalpattinam,Virapandipattinam merged. and Tiruchendur. The estuaries of Tamiraparani River enter A prominent spit is occurring near Thoothukudi, running the sea in Palayakayal and Punnakayal. The estuary is wide few kilometers in length. It joins with main land and spread. The erosion due to tsunami waves was prominent in forming Tombolo. Beach ridges are found to be the back water channels. Tsunami waves enter up to 2100m discontinuous. Sand dunes are formed at interface between inland through the channels. In Virapandipattinam, the sea and land. They bordered the high tide mark and extend tsunami waves erode 20 to 25m of beach from the shore. inland upto 2 to 5 km.