The Indian Ocean Tsunami: The Global Response to a Natural Disaster

3: Geological and Geomorphological Perspectives of the Tsunami on the Tamil Nadu Coast, India

65 3 Geological and Geomorphological Perspectives of the Tsunami on the Tamil Nadu Coast, India S. R. Singarasubramanian, M. V. Mukesh, K. Manoharan, P. Seralathan, and S. Srinivasalu Eastern Continental Margin of South India The Tamil Nadu coast of India extends to a length of about 1,026 km (615.6 miles). The coastal zone—the transition between the land and the sea—is a fragile, complex, and productive ecosystem. The southern part of the coast is tectonically more stable than the northern part (Rao and Rao 1985). The width of the continental shelf varies from about 10 to 45 km (6 to 27 miles) in nondeltaic areas. During the last glaciation, as a result of the lowering of the sea level, the entire continental shelf was exposed to subaerial erosion and fluvial deposition. The rivers cut across the shelf up to the edge, depositing sediments directly onto the continental slope or into the submarine valleys. During the mid-Holocene, the sea level rose rapidly, the carbonate reef growth was truncated,and submarine valleys were delinked from river sources, as they could not keep pace with the rapid sea level rise.More sediment deposit on the inner shelf created barriers and ridges. The Holocene delta progradation of the Palar and Kaveri rivers of Tamil Nadu into the offshore regime is limited, unlike other rivers of India’s east coast such as the Mahanadi, Godavari , and Krishna. 66 Singarasubramanian, Mukesh, Manoharan, Seralathan, and Srinivasalu Bathymetric Distribution The width of the continental shelf varies from between 20 km (12 miles) near Pazhaverkkadu (Pulicat) lagoon and 50 km (30 miles) at Chennai. The average width of the shelf is 25 km (15 miles) in the Puducherry-Parangipettai (Pondicherry–Porto Novo) sector, while it narrows to 15 km (9 miles) at the head of the submarine valleys. Further south, the shelf gradually widens from 35 km (21 miles) near Karaikal to 80 km (48 miles) at Kodiyakarai (Point Calimere). The average width of the near-shore zone up to a 20 m (66 feet) depth contour is 5–8 km (3–4.8 miles), but widens from Karaikal toward the south. The shelf is wider off Pulicat-Palar and Karaikal–Point Calimere, and the shelf break occurs at a deeper depth. The shelf has two distinct morphological units separated by ridge or terrace. The inner shelf has an average gradient of 1:400. Terraces occur at 54 m (178 feet), 75 m (247 feet), 85 m (280 feet), and 115 m (379 feet) depths. The outer shelf beyond 120 m (396 feet) has a relatively steeper gradient, in the order of 1:80, and the seafloor is regular at 185 m (610.5 feet),270–360 m (891–1,188 feet),and 465 m (1,534 feet) depths due to the exposure of hard substratum. The shelf break occurs at unequal depths: at 100 m (330 feet) off Pulicat lagoon,350 m (1,155 feet) off Chennai,100 m (330 feet) off Pondicherry–Porto Novo,and 110–465 m (363–1,534 feet) off Karaikal–Point Calimere.The shelf edge truncates against the head of the submarine valleys off Pondicherry– Porto Novo. The edge invariably exhibits a convex shape and is characterized by a dome-shaped substratum. The shallow Palk Bay, with a water depth of <20 m (66 feet), is designated as a wave-sheltered coast.The 5 m (16.5 feet) depth contour in Palk Bay runs at a distance of 6–10 km (3.6–6 miles) from the coast, except off Manalmelkudi, where it runs at a distance of about 30 km (18 miles). The 10 m (33 feet) depth contour south of Point Calimere and Kodiyakarai is seen at a distance of 50–55 km (30–33 miles), but toward the west it narrows down marginally. Off Manalmelkudi, a 10 m (33 feet) depth contour is located about 45 km (27 miles) from the coast. Manalmelkudi is a cuspate foreland and so both 5 and 10 m (16.5 and 33 feet) depth contours are projected offshore. But south of Manalmelkudi and up to Thanushkodi, the 10 m (33 feet) depth contour runs at a distance of 2,530 km (1,518 miles) from the coast.The coastal land and the adjoining seafloor on the Western Palk Bay, falling between the WNW-ESW trending Vedharanyam fault and the NW-SE trending Vaigai fault, have been also uplifted (Loveson, Rajamanickam, and Chandrasekar 1990). Geological and Geomorphological Perspectives of the Tsunami 67 Geomorphic Features The coastal zone of Tamil Nadu is endowed with varied landscape, such as sandy beaches, beach ridges, backwaters, estuaries, intertidal mud and sand flats, dunes, cliffs, beach rocks, deltas, lagoons, mangrove forests, and coral reef ecosystems. The coast has constantly undergone physical changes, from the geological past to the present. Many rivers bring considerable sediments, which affect shore processes significantly. The Palar River delta occupies an area of about 4,000 km2 (1,600 sq. miles). The mature stage of the Palar River is characterized by vast flood plains and lateral accretion deposits.The old stage of the river occurs in the coastal region, where it debouches into the Bay of Bengal, 5 km (3 miles) east of Sadras. The river drains an area of 17,871 km2 (7,148 sq.miles),of which 10,856 km2 (4,342 sq. miles) are in Tamil Nadu and the rest in Karnataka. The geomorphic features along the river course include mounds,dissected pediplains,flood plains, and coastal plains. The coast between Chennai and Pondicherry through Muttukadu,Mamallapuram ,and Marakkanam is a narrow sandy belt.The major geomorphic features include tidal flats, estuary, beaches, dunes, and beach ridges. The dunes are stable at their base and mobile on their crest. The coastal dune field, which is stabilized by vegetation, occurs in a very high-energy wind regime. Linear dunes along the shoreline, which are stabilized to a large extent, represent the major geomorphic features. A spit protects the low-lying marshy land at Muttukadu. Four major zones within the tidal flat were recognized at Mamallapuram , Muttukadu, and Marakkanam: (1) an outer sand flat merging with the beach dune complex and rock exposures; (2) middle sand flat; (3) sandy to silty inner flats; and (4) salt marsh (Achyuthan 2002). The coastal area between Pondicherry and Nagapattinam is occupied by various geomorphic features: beach ridges, swales, sand dunes, deltaic plain, chenniers, palaeo-tidal flats, palaeo-lagoons, salt marshes, palaeo-channels, and lagoons (Anbarasu and Rajamanickam 1997). The coastal features in and around Point Calimere include beaches, beach ridges,swales,dunes,tidal flats,palaeo-tidal flats,barrier islands,alluvial plain, chenniers, palaeo-lagoons, flood plains, mud flats, salt pans, and mangroves (Shanthi Devi and Rajamanickam 2000). The coastal landforms between Devipattinam and Mandapam were classi fied into depositional and erosional features and others (Chockalingam, Suresh Gandhi, and Rajamanickam 2000). Series of beach ridges are distinctly noticed. Sandy beaches are more prominent. Rocky beaches are characteristic 68 Singarasubramanian, Mukesh, Manoharan, Seralathan, and Srinivasalu of Mandapam to Rameshwaram.The important features in these areas include spits,swales,sand dunes,shoals,deltaic plains,sand sheets,mud flats,chennier plains, cliffs, beach rocks, sea caves, sea cliffs, and marine terraces. The coastal landforms between Mandapam and Kanyakumari are classi fied into fluvial, coastal/marine, and aeolian (Rajamanickam and Loveson 1998). Fluvial landforms include pediplains, floodplains, deltaic plains, and palaeo-channels. Marine landforms include beach ridges, swales, backwaters, marine terraces, wave-cut platforms, sea caves, beaches, spits, tidal flats, mud flats, and cuspate forelands. The aeolian landforms are stable sand dunes and teri complexes. Apart from the coastal geomorphic features, the Tamil Nadu coast is protected with a coral ecosystem in the Gulf of Mannar region. Coral reefs act as a barrier against wave action and prevent coastal erosion. There are twentyone islands, situated at an average distance of about 8 km (4.8 miles) from the coast and running parallel to the coastline. Along this coastline both erosion and accretion takes place.Island erosion and accretion are caused mainly by the actionof waves,wave-inducedcurrents,andlongshorecurrentsalongtheshore. Tsunami Tsunamisarealessknowncoastalhazardinthispartof theglobe,incomparison to more commonly occurring hazards such as coastal floods, cyclones, coastal erosion, storm surges, oil spills, coastal pollution, and algal bloom. Tsunamis are associated with earthquakes that are always related to crustal movements or deformation leading to displacement of a water body from an equilibrium state. When large areas of the seafloor elevate or subduct suddenly, a tsunami can be generated.Its destruction capability is enormous,as it can crush homes and other coastal structures and can inundate or flood hundreds of meters of coastal lands with a run-up height of around 10 m (33 feet) or at times even up to 30 m (99 feet). Sometimes it can strip a waste beach that may have taken years to build. Tsunamis have long wavelengths (up to 500 km [300 miles]) and can travel across the open ocean with speed ranging from 500 to 1,000 km (300 to 600 miles) per hour, depending upon the water depth. As tsunamis are characterized by shallow water waves, the energy of a tsunami wave passes through the entire water column up to the seabed even in deep ocean water.When the wave approaches shallow seas and finally the coast, the wave no longer travels with the same speed as in open water; but it begins to pile up due to wave transformation , and the wave front becomes steeper and taller with less wavelength. Unlike meteorologically induced waves,tsunamis are capable of affecting deep Geological and Geomorphological Perspectives of the Tsunami 69 shelf and ocean floor.Hence,tsunamis transport sizable amounts of sediments landward, and when they finally cross the shore they dump considerable offshore sediments on the coast.They also alter geomorphic features considerably. Sometimesthetsunamiwavescausethenear-shorewatertorecede,exposingthe ocean floor, as in Kanyakumari and Tiruchendur on the coast of Tamil Nadu. The mega-earthquake occurred on December 26,2004,off the west coast of northern Sumatra (3.2760N, 95.821E), close to Sunda Trench at a water depth of about 1,300 m (4,290 feet).Its epicenter,located at a shallow depth of 10 km (6 miles) below the ocean floor, triggered a tsunami in the Indian Ocean. The tsunami hit most of the Tamil Nadu coast, with wave height varying from 3 to 10 m (9.9–33 feet). This catastrophic wave devastated the coastal regimes in eleven Asian countries. The tsunami left considerable sedimentary signatures along the coast of Tamil Nadu, either opening or closing estuaries, breaching the coastal sand dune ridges, developing long erosional channels across the beach, and dumping large quantities of sediments beyond the backshore. Inundation of Tsunami Waves in Tamil Nadu A tsunami turns into a killer wave when it crosses land, destroying life, land, and property. As the wave strikes the shore, it may inundate low-lying coastal areas, resulting in mass destruction of land and life (see fig. 3.1). The behavior of tsunami waves in the coastal area is dependent on several factors. The most important are the topography of the seafloor and the actual geomorphic condition of the coastal land. The maximum vertical height of a tsunami in the coastal area to which water is observed to rise with reference to sea level (spring tide or mean sea level) is referred to as “run-up.” The maximum horizontal distance reached by a tsunami is referred to as “inundation.” The run-up and inundation of a tsunami will vary depending upon local geomorphic features, submarine topography, orientation of the oncoming waves, tide level, and magnitude of the tsunami. Field observations were made to identify the inundation and run-up level of the December 26, 2004, tsunami along the Tamil Nadu coast by various workers. The inundation and run-up levels of some villages along the coast of Tamil Nadu are given in table 3.1. Maximum devastation was recorded in the fishing hamlets located nearer to the coast. The settlements and beach resorts located near the coast were badly affected.Some of the villages were protected by back dune ridges,as their settlements were located to the west of dunes. The wide variation noticed in the run-up and inundation within small areas was due to variation in onshore topography but also a consequence of offshore bathymetry. Concave-shaped 1 2 3 4 5 6 7 8 9 10 Cherian Nagar, Ennore Royapuram M.G.R. and Anna Square Marina Beach Srinivasapuri Elliot's Beach Basat Nagar New Beach Kudukuppam Chinnapattam 31 32 33 34 35 36 37 38 39 40 Vembar Thoothukudi Port Arogyapuram Village Librahmkuppam Village Chinnamuttam Kanyakumari Keelmanakudi Chinnavilai Village Pattupetta Village Colachal Harbor 11 12 13 14 15 16 17 18 19 20 p Kotakuppam Puducherry Nallwarkuppam Manjakuppam Tazhanguda Devanampattibnam Kuddukullam Kuddupattinam Kilinjal Village Amman Kerapattu 21 22 23 24 25 26 27 28 29 30 Nagapattinam Beach Namiyar Nagar Vellipalayam Nagapattinam Port Velanganni Beach Alatikut Village Arupudapattinam Thondi Navapasanam Dhanushkodi Fig. 3.1. Places affected by the tsunami along the Tamil Nadu coast. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 Tiruvallur Kanchipuram Vilupuram Cuddalore Thanjavur Tiruvalur Pudukkottai Tirunelveli Tuticorin Nagapattinam Nagapattinam Ramanathapuram Kanniyakumari Karaikal T A M I L N A D U SRI LANKA Gulf of Mannar INDIAN OCEAN 0 100 miles 0 100 km 50 50 Geological and Geomorphological Perspectives of the Tsunami 71 coastline in some areas appears to have amplified the run-up and inundation . Sand dune ridges protected the coast but many dune ridge breaks have led to tsunami inundation (see photos 3.1a–f and 3.2a–f) through the saddle in between ridges or breaching of the stable ridges. When stable dune ridges protect the coasts, swales, creeks, and other inlets permit the free flow of water inland. The maximum inundations recorded were through waterways like the Vellar River, the Vedharanyam canal, and the Coleroon and Gadillam rivers. The high death toll in certain villages was due to the successive wave propagations through backwaters. Satellite images show tsunami inundation in some villages in Karaikal and Kodiyakarai (photos 3.3 and 3.4). Table 3.1. Maximum inundation and run-up level of tsunami waves in some places along the Tamil Nadu coast Place Maximum inundation (m) Run-up height (m) Pulicat 405 1 Kattupalli 600 2.5 Chepauk 600 3.5 Marina Beach Road 500 4 Besant Nagar 150 2.5 Palavakkam 335 3 Injambakkam 300 4 Shozhinganallur 550 4 Muthukadu 300 3 Pattipulam 500 4.5 Mamallapuram 650 6 Pudupattinam 650 4.3 Kadalur 770 4.7 Mogaiyur 450 4.5 Paramankeni 650 5.5 Cuddalore Old Town 1,190 2.5 Kudikadu 370 3.1 Parangipettai 1,700 2.9 Nagapattinam 1,100 4.5 Akaraipettai 3,000 4 Vedharanyam 1,400 2.3 Kodiyakarai 900 2.1 Colachel 1,500 6 Melmanakudi 1,500 6 Keezhamanakudi 1,000 5 Photos 3.1a–c. Tsunami damages along the Tamil Nadu coast. (Photos by S. R. Singarasubramanian.) Photos 3.1d–f.Tsunami damages along the Tamil Nadu coast. (Photos by S. R. Singarasubramanian.) Photos 3.2a–c.Tsunami damages and invasion of seawater. (Photos by S. R. Singarasubramanian.) Photos 3.2d–f.Tsunami damages and invasion of seawater. (Photos by S. R. Singarasubramanian.) Photo 3.3. Satellite image of Karaikal before and after the tsunami, showing the inundation of villages. Photo 3.4. Satellite image of the Kodiyakarai region before and after the tsunami, showing landform changes. Geological and Geomorphological Perspectives of the Tsunami 77 Overlaying land-use patterns and the extent of tsunami inundation indicates that barren lands with lower elevation permitted the free flow of the tsunami while areas covered by vegetation and coastal dunes restricted the inundation process (Senthilnathan 2006). Beach ridges occurring at the berm crest were breached at many places through which inundation took place. Mangroves, rasaporis, fulifera, and casurina acted as barriers that restrained the force of the tsunami waves and hence it is presumed that the energy of the tsunami was dissipated.Though Pitchavaram lagoon connects tidal channels from both the Vellar and the Coleroon, the expansion of the lagoon during the tsunami was limited to a few meters only. This was due to the fact that the mangrove plants absorbed the tsunami wave energy significantly. Nagapattinam district in central coastal Tamil Nadu was the worst-affected district, with the highest death toll of 6,065 people. The death toll reported in Cuddalore district was more than 500 people. The areas adjoining the river mouths of theVellar,Chinnavaikal (Pitchavaram),and Coleroon were severely damaged; more than 1,000 lives were claimed. Sedimentological Observations The tsunami deposits are characterized by a sequence of fine sediments upward and thinning landward. This is indicative of decreasing wave energy away from the coast.Tsunami deposition is a very complicated process involving turbulent currents that cause deposition as well as erosion. It is hard to conclude that distinct sedimentary units represent separate waves or periods of run-up and backwash. However, evidence for bidirectional currents has been found from tsunami deposits in Tamil Nadu, shown by sedimentary structures.In many places the deposits have followed the maximum landward inundation of individual tsunami waves. This has caused additional erosion and sediment redeposition. But in some places back flow has taken different ways. The lower contact was unconformable or erosional and contains intraclasts of reworked material. Loading structures could be identified at the base of the deposits. This indicates a rapid sedimentation. Particle and grain size ranges from sand to fine mud, depending upon the availability of source materials—barrier, beach or dune sand, soil materials, and so on. Individual shells and shell-rich units were often present (photos 3.6a–f). Based on the sediment characteristics of the December 26, 2004, tsunami, three waves were recorded in many places along the Tamil Nadu coast. But in some places, due to the backwash, the wave signatures were not preserved. Apparently, each wave that struck the coast did not deposit a sandy layer. Alternatively, the sandy layer deposited by a wave might have been resus- Photos 3.5a–c.Tsunami-induced erosion along the coast of Tamil Nadu. (Photos by S. R. Singarasubramanian.) Photos 3.5d–f.Tsunami-induced erosion along the coast of Tamil Nadu. (Photos by S. R. Singarasubramanian.) 80 Singarasubramanian, Mukesh, Manoharan, Seralathan, and Srinivasalu pended with the passage of the next wave. Hence, there does not appear to be a one-to-one relationship between the number of waves inundating the coast and the number of sandy layers in a deposit. The base of each layer was characterized by darker sand and abundant heavy mineral content, although in no instance did the heavy minerals exceed 3%. Quartz sand is one of the most common components of the coastal sand and occurs in a variety of clear colors, including white, rose, and purple. If the surface texture of a quartz grain is not clear and glasslike, it indicates that the grain has undergone minor abrasion.Many of the surface features were induced by grinding during transportation. The grains that have been transported farthest have a more rounded shape. Some of the surface textures of quartz sand from the tsunami deposits show strong grooves of mechanical abrasion, indicating a high-energy environment of deposition. A rise in the percentage of silt and clay content after the tsunami was appreciable in certain coasts such as Nagapattinam and the central part of the Tamil Nadu coast. Such enhancement is likely due to the admixture of the fine sediments brought forward by the receding tsunami waves from the hinterland. A rise in carbonate content from 3.12 to 6.90% in tsunami deposits is attributed to the contribution of fresh debris brought forward by the onward movement of the tsunami waves. The tsunami deposits could be easily differentiated,with the presence of mudslips and beach rock fragments along the Tamil Nadu coast depending upon the offshore and onshore sediments. The coasts nearer to Chennai, Mahabalipuram, Pondicherry, Cuddalore, and Nagapattinam were affected by direct tsunami waves from a southeast direction,whereas the coastal regions in Palk Bay and the Gulf of Mannar were affected partly by direct waves, but mainly by the diffracted waves after they crossed the Sri Lankan island. Hence, the impact of the waves over the coastal settlements varied from place to place. In Vedharanyam about 18 cm (7.2 inches) of thick fresh fine sediments brought by the tsunami were deposited.Fine fresh sediments were spread along the coast and inland. In some places the water entered through erosional and older channels. Point Calimere has encountered widespread sedimentation and the formation of eroded channels due to the tsunami. The newly created channel is about 120 cm (48 inches) deep near the shore and extends up to 1 km (0.6 mile) inland. Here the beach was eroded and occupied by the sea to the extent of about 20 m (66 feet) after the tsunami. It can be evidenced by the current position of the Chola lighthouse, at present in the sea. South of Point Calimere, the erosion was less but the depositions of fine clayey fractions were more from the shore. About 15 cm (6 inches) of fine sand were Photos 3.6a–c. Deposition of tsunami-borne sediments along the Tamil Nadu coast. (Photos by S. R. Singarasubramanian.) Photos 3.6d–f. Deposition of tsunami-borne sediments along the Tamil Nadu coast. (Photos by S. R. Singarasubramanian.) Geological and Geomorphological Perspectives of the Tsunami 83 deposited over the 5 cm (2 inches) thick clayey sand. In Kodiyakarai, a layer of sediments about 30 cm (12 inches) thick was deposited near the shore, thinning as it led inland. Clayey sand was spread up to 700 m (2,310 feet) from the shore. The sediments were deposited over the medium to coarse sand along the coast. Here the new deposits were easily identifiable by the presence of shell and old clothing under them. Destruction by the tsunami waves of boats and the deposition of sediments over them indicate that the waves brought the sediments. Parallel to the shoreline in the beach, erosion is prominent and filled with water bodies. The stable dunes in these areas were breached at places or eroded. From eyewitness accounts as well as from field evidence,it is understood that the Point Calimere coast was struck by tsunami waves from both the northeast and the southeast, which means that the Palk Bay coast was affected by the refracted tsunami waves from the Bay of Bengal and the diffracted waves that came from the northern Sri Lankan island (Ramanamurthy et al. 2005). The 10 m (33 feet) bottom contour that runs between Point Calimere and Kankesanthurai in Sri Lanka across Palk Strait would have certainly played a major role in arresting the tsunami propagation into Palk Bay. Mallipattinam, Manora, Kalamangudi, Manthiripattinam, Prathabharamapattinam , Adhipattinam, Palakudi, Pudupattinam, and Vattanam encountered sedimentation in the fishing harbors. Muddy sediments from offshore transported by the tsunami waves were spread along the near shore and beaches. In some areas, like Prathabharamapattinam and Manora, the coastal fishing areas became clayey. Up to 30 cm (12 inches) of thick clay were deposited over the coarse sand on the shore and up to 20 m (66 feet) into the sea. In all these areas the beaches are shallow and wave domination is less. In the Manthiripattinam, Palakudi, Adhipattinam, Kalamangudi, Pudupattinam , and Vattanam areas, the sediments brought by the tsunami waves came 50–200 m (165–660 feet) inland. The tsunami sediments were fresh, loosely packed, medium- to fine-grained, and gray in color, with some shell fragments lying over the dark-colored medium to coarse sand. The tsunami sediments were deposited as thin layers, with some dark bands of heavy minerals in most places. Along the Thondi-Uchipuli segment,the tsunami inundation was about 30 m (99 feet). In Thondi, the waves entered up to 30 m (99 feet) inland but no sedimentation was observed.But the tsunami waves brought considerable fine sediments in some areas, depositing them on the beach, and the areas became clayey up to 22 m (72.6 feet). From Thondi to Uchipuli, less inundation and sediments were observed.This may be due to the shallowness of the near shore. 84 Singarasubramanian, Mukesh, Manoharan, Seralathan, and Srinivasalu From information gathered from the local communities, it was understood that the tsunami propagation was very slow and was from the southeast. Due to the reduction in velocity, the inundation may have been less and deposition was also meager. The coastal stretch between Rajamadam and Devipattinam, about 80 km (48 miles), has only one or occasionally two beach ridges with an elevation of 1–2 m (3.3–6.6 feet). The low coastal elevations, small number of beach ridges, and low sand dunes along the western and northern sides of Palk Bay is attributable to small fluctuations in sea level. The coastal dune heights vary between 1 and 2 m (3.3 and 6.6 feet) only. However, along the Devipattinam and Mandapam coastal belt, three to four series of beach ridges are observed. The Mandapam coast of Palk Bay is also characterized by 2–3 m (6.6 –9.9 feet) high coralline terraces. The northeastern part of the Rameshwaram coast in Palk Bay is occupied by shallow lagoons. Sand dunes with heights varying from 3 to 6 m (9.9 to 19.8 feet) are well developed along the southeastern tail portion of the island. The coastal regions between Rameshwaram and Vembar in the Gulf of Mannar were not affected much by the tsunami waves.Only swelling of the sea was seen by the local communities,and therefore the inundation and resultant sedimentation were very much less compared with that of other northern and central coastal regions of Tamil Nadu. However,the coastal stretch betweenVaippar and Thoothukudi was affected considerably by tsunami waves. In Taruvakulam, very thick sedimentation, up to 120 cm (48 inches), was recorded, though inundation was only 150 m (495 feet) inland. The coastal geomorphology was completely altered. Thick sedimentation in the northern part of Taruvakulam led to the seaward expansion of beach. The sediments were fresh, medium to fine, loosely packed, and layered. Here rich, heavy minerals were deposited as thin bands over the pretsunami sediments by tsunami waves. The segregation of heavy minerals into fine and coarse was observed. The coarse heavy minerals were deposited away from the coast, while the fine ones were found near the coast (5 to 20 m [16.5 to 66 feet] from the coast). Vellapatty, near Thoothukudi, was also affected by sedimentation due to the tsunami waves. The inundation was up to 75 m (247.5 feet) inland. A thin layer of tsunami sediments (10–15 cm [4–6 inches]) was deposited over the pre-tsunami coarser beach sediments. The layering was prominent, with thin, dark-colored bands of sediments.The fresh sediments brought by the tsunami were identified based on their freshness, color, and textural differences from the older sediments. Oxidation of fresh sediments was observed. Geological and Geomorphological Perspectives of the Tsunami 85 South of Thoothukudi harbor, sedimentation was recorded up to 500 m (1,650 feet) inland. Tsunami waves moved inland by eroding a channel, 15 m (49.5 feet) wide near the coast and becoming narrower inland. Sedimentation took place in and around the channel. Fresh, fine, and loose layering of sediments was noticed inland. The thickness is about 50 cm (20 inches). Dark banding of sediments is prominent. In Pulavali, the tsunami waves moved inland into dense scrubs. The inundation was up to 60 m (198 feet) inland. Erosion along the shoreline is prominent . Fine sediments (30 cm [12 inches] thick) layered with dark colors were observed over the eroded surface along the coast. The southern sector of the Tamil Nadu coast includes Palayakayal, Punnakayal ,Kayalpattinam,Virapandipattinam,and Tiruchendur.The Tamiraparani River joins the sea through two inlets, Palayakayal and Punnakayal. Erosion caused by tsunami waves was prominent in the backwater channels. Tsunami waves entered up to 2,100 m (6,930 feet) inland through the channels. A fresh fining-up sequence about 23 cm (9.2 inches) thick was observed in the estuarine region. The deposition of coarse sand thins toward the northwest in the areas running almost perpendicular to the estuaries. Widespread deposition of fine sediments with some coral and broken shell fragments was observed in these regions. Along the estuarine bank rip-up clasts could be recorded, with some shell debris. In Kayalpattinam, the tsunami inundation was up to 1,100 m (3,630 feet) from the shore.A backwater channel about 15 m (49.5 feet) in width was filled withtsunamisediments.Thethicknessof thesediments’fining-upsequencewas about 70 cm (28 inches), at a distance of 100 m (330 feet) from the shoreline. After the tsunami event, the near shore became shallow. Due to the filling of the channel, the fishing communities find it difficult to operate their powerboats in the near-shore area. InVirapandipattinam,the tsunami waves eroded 20 to 25 m (8 to 10 inches) of the beach. Due to the erosion, the beach became steep. The fresh tsunami sediments were deposited over the prominent older coarse sediments with shell fragments. About 56 cm (22.4 inches) of sediments were deposited by the tsunami wave. Even after the tsunami, erosion of the coastline continued in the region. In Tiruchendur, the effect of tsunami waves was less. Tsunami waves eroded the coastline in some localities but not all. The steep height of the coast in Tiruchendur prevented the waves’ inundation inland. Here the retreat of waves up to 20 m (66 feet) was observed by the local communities during the tsunami. 86 Singarasubramanian, Mukesh, Manoharan, Seralathan, and Srinivasalu Tsunami Effect on Coral Islands The shelf width off Pamban in the Gulf of Mannar is about 25 km (15 miles) (Hari Narain, Kaila, and Verma 1968) and the shelf break occurs at about 200 m (660 feet) depth. The shelf is very wide off the coast between Sippikulam and Tuticorin. The 20 m (66 feet) depth contour lies at a distance of 30 km (18 miles) between Rameshwaram Island and Valinokkam and about 40–45 km (25–28 miles) between Valinokkam and Tuticorin. The Rameshwaram and Tuticorin coast is characterized by the presence of twenty-one coral islands of varying sizes arranged in an en echelon manner within the 20 m depth contour. Between Tuticorin and Tiruchendur, the 20 m depth contour runs about 25–30 km (15–18 miles) from the coast, but from Tiruchendur to Kanyakumari, the 20 m depth contour is aligned very close to the coast. On the other hand, the 50 m (165 feet) depth contour east of Tiruchendur lies at a distance of about 30 km (18 miles). The shelf is very wide between Tiruchendur and Kanyakumari. Off Chinnamuttom and eastern Kanyakumari , the shelf width is nearly 80 km (48 miles), and the shelf break occurs at about 60 m (198 feet) depth. The tsunami inundation between Kanyakumari andArokkiapuram ranged between 150 and 210 m (495 and 693 feet), as the coast is moderately elevated and consists of a number of pocket beaches and low cliffs, as at Vattakotai and Idinthakarai.The Panchal,Periyathalai,Perumanel,and Kulasekharapattinam segments are low-lying coastal plains and so tsunami inundation reached up to 500 m (1,650 feet). The coast is raised coast consisting of coralline terraces. Similar to what happened on the Mannar coast,both diffracted tsunami waves from the southern Sri Lankan coast and waves traveling westward in the Indian Ocean affected the southwestern coast of India. Kizhmanakudi and Melmanakudi ,coastal settlements located on the southern and northern banks of the Palayar River, respectively, were inundated for ten hours, and seawater entered up to 1,500 m (4,950 feet) inland.The bridge connecting the two coastal villages was thrown nearly 50 m (165 feet) up the estuary. Even the coastal settlements behind the 4–6 m (13.2–19.8 feet) high cliffs and elevated beaches were not spared. As the tsunami wave approach was from the south and southwest, the coastal settlements located north of the rocky promontories or groins were affected only partially. But settlements south of the rocky promontories, such as Azhikkal, Pillaithoppu, Muttom, Kottilpadu, and Colachal, were severely affected. Four coral islands situated off Thoothukudi were studied for post-tsunami sedimentological aspects. On Pandian Island, the tsunami deposited some Geological and Geomorphological Perspectives of the Tsunami 87 debris and scrubs along the coast and inland.Sediments ranging from medium to coarse size were deposited as layers over the very coarse sand with coral debris. About 8 cm (32 inches) of thick,gray,medium sand brought by tsunami waves were deposited over the dirty, yellow, compact older sediments inland (about 12 m [39.6 feet] from the shoreline). The medium sand was transported and deposited even in the fly ash pond near the island. Koswari,Van, and Kariyashuli islands also experienced sedimentation. On Van Island, the deposition of medium-sized sediments over the coarser fractions was observed. About 30 cm (12 inches) of fresh, medium-sized sand was deposited with thin dark bands of sediments over the coarse to very coarse sand. On Koswari Island, fine clayey material was deposited along the shore. A thick layer of fine- to medium-sized heavy mineral deposits parallel to the shore was prominent on Kariyashuli Island.About 30 cm thick alternate medium and coarse sediments were deposited with shell and coral fragments on Kariyashuli Island. Sediment Characteristics Large tsunamis may significantly disturb the permanent sedimentation regimes of coastal areas,and landward-tapering units of sand extending far inland constitute the commonest signature of tsunamigenic flooding in intermediate to slightly reflective coastal environments.A tsunamigenic event will most probably be locally sourced,and the associated disturbance will likely leave signatures related to changes in the composition of sediment rather than texture and with physical and chemical properties translated to geochemical proxies of salinity or unusual plankton contribution to the total fossil content. Tsunami waves produced by any processes will vertically displace the sea surface. Tsunamis are capable of affecting deep shelf and even oceanic floors. Most open-ocean tsunami waves have the required wavelengths (up to 100 km [60 miles]) but not the amplitude (a few meters maximum) to significantly move sediment in deep water. Tsunami deposits can be recognized primarily as rapidly deposited, tabular, and extensive unusually coarse layers laid down (or at least reworked) by traction currents within fine-grained sections, but it is very difficult to differentiate them from storm and hurricane deposits. Very rapid deposition was indicated by plants found bent over and buried by the sand or removed by the tsunami, leaving an erosive base to the deposit: the lower part of the tsunami included rip-up clasts of the underlying muddy layer (depending upon the coastal sediments). Few internal structures were found, although in a few places some faint horizontal stratification could be observed. The sedimentological investigation of tsunami deposits is a fairly new field 88 Singarasubramanian, Mukesh, Manoharan, Seralathan, and Srinivasalu of research (Dawson 1999).The impact of tsunami waves on coastlines is unlike that of storm waves,because tsunami waves have greater wavelengths and wave periods.If there is a sufficient sediment supply,tsunami waves are constructive as they move inland and transport a variety of grain sizes, ranging from silt to boulders. The retreating waves can remobilize and erode sediments (Keating , Whelan, and Brock 2004). Literature on tsunami deposits may be organized into three primary categories (Whelan and Kelletat 2003): large clasts (e.g., boulders), coarse and fine sediments (e.g., gravel, sand, silt), and other, fairly obscure deposits such as washover fans. The nature of tsunami deposits is largely determined by sediment supply. The most commonly investigated tsunami deposits are fine sediments that occur as sediment sheets. Grain-size parameters are widely used as indicators of environment differentiation (Friedman 1961; Duane 1964) and depend on factors such as availability of source material, medium of transport, physiography and geomorphology of the area, winds, waves, climate, and long shore currents (King 1972; Swift 1976). Textural attributes like mean, standard deviation, skewness, and kurtosis of sediments are used to reconstruct the depositional environment (Amaral 1977).The physical process assumption was that these different statistical parameters reflect differences in the transporting and depositing mechanisms of fluid flow (Sahu 1964; Greenwood 1969). Identification of tsunami deposits was based on several criteria, including differences in grain size and color. Sedimentary deposits from the tsunami were found in most places where significant inundation occurred. For tsunami deposits that were overlying a known preexisting surface that was texturally distinct, such as from soils, identification was fairly simple, whereas if the underlying material was beach sand that was similar both texturally and visually, identification was more difficult. In tsunami deposits, grain size generally fines upward and rip-up clasts may be present. The base of the deposits erodes the underlying structures, and a heavy mineral layer may be present at the base. Underlying sands were often trampled, while tsunami sands were relatively undisturbed. Many of the deposits had multiple layers. It was very difficult to differentiate the tsunami sediments from the normal beach sand, since the tsunami deposits did not show much difference from the beach sand. The mud content was also very low except in the low-lying zones, where the tsunami water column was trapped for a considerable time. In some transects the heavy mineral accumulation was considerable. Field investigation to study the sedimentary signatures left by the December 26,2004,Indian Ocean Tsunami was carried out on certain shores with normal profiles along the coast of Tamil Nadu between Injambakkam and Cuddalore. Geological and Geomorphological Perspectives of the Tsunami 89 Tsunami deposits were identified in three different coastal settings: (1) muddy; (2) fluvial; and (3) sandy beach along the coastal tract from south of Chennai. Tsunamigenic sediments (2–40 cm [0.8–16 inches] thick) were found deposited up to 620 m (2,046 feet) inland. Thickness of the deposits varied from site to site, generally thinning out within 15 m (49.5 feet) of the limit of inundation. The tsunami deposits were identified away from the coastal zone above the agricultural soil, where the demarcation is very distinct. The typical thickness was 40 cm (16 inches) at 100 m (330 feet) from the shoreline and thinning landward. The beach face and berm showed no evidence of deposition from the tsunami.On the berm the exposed roots of some shrubs indicated the erosion of sediments up to a height of 30 to 40 cm (12 to 18 inches). The zone of erosion extended up to 50 m (165 feet) from the shore. The tsunami sand deposits often contained two or more similar layers. The thicknesses of the layers were not uniform. The thickness of tsunamigenic sediments varied from place to place depending upon the coastal morphology. Near Cuddalore the thickness varied from 30 to 80 cm (12 to 32 inches) in the open foreshore beaches. In estuaries the thickness went up to 90 cm (36 inches), as in Devanampattinam, and 25–65 cm (10–26 inches) at Pitchavaram.In the foreshore beaches of small embayed/ coast areas,the thickness was higher (45 cm [18 inches] at Sothikuppam and 55 cm [22 inches] at Mulukkuthurai) than on open beaches.In the central part of the Tamil Nadu coast, the thickness of tsunamigenic sediments varied from 1 to 60 cm (0.4 to 24 inches).Very fine clay layers deposited over the paddy fields as high saline soils could be observed near Nagapattinam and Point Calimere away from the coast. The sediment thickness was less along the coast between south of Point Calimere and Thoothukudi. In these regions the impact of the tsunami was less,since they were shadowed by Sri Lanka.The coasts along these regions had maximum water inundation of about 150–200 m (495–660 feet), with fine clay sediments occupying the shallow coast.Near Thoothukudi,in the Taruvakulam, Pulavali, and Harbour region, the inundation was greater, up to 500–700 m (1,650–2,310 feet), and the sediments were deposited by tsunami waves.Sedimentation and erosion were prominent along the projecting coasts in this region.The inundation of sediments was up to 500 m (1,650 feet) in the southern part, i.e., along Tiruchendur, Kanyakumari and Colachel. The sediments were fine to medium or even coarser than the normal tidal sediments. The tsunami sediment characteristics differ from coast to coast depending upon the offshore and near-shore sediments. In Tamil Nadu the sediments were finer in the northern and central part, clayey between the central and southern, and coarser in the southern part. 90 Singarasubramanian, Mukesh, Manoharan, Seralathan, and Srinivasalu From the examination of tsunamigenic sediments from several cores, it is seen that textural parameters vary with depth: the tsunami deposits are coarser than pre- and post-tsunami deposits. The coarser nature of the tsunamigenic sediments is due to the fact that the powerful tsunami waves, with heights varying from 1 to 5 m (3.3 to 16.5 feet) while striking the coast, winnowed the finer fractions either landward (in the case of low-lying coasts, estuaries, and tidal inlets) or seaward, if the coast was steep. Hence the tsunami deposits are in a sense lag deposits. Tsunamigenic sediments are usually larger in grain size than surrounding sediments, indicating higher-energy conditions. The pre- and post-tsunami sediments show more or less uniform textural characteristics. In many cores, the pre- and post-tsunami sediments reveal the variations of regular spring and neap tidal cycles. But the tsunamigenic sediments, though coarser than pre- and post-tsunami, show only marginal variation in mean grain size with depth without any grading due to rapid sedimentation .One of the main reasons for the coarser nature of the tsunamigenic sediment may be that sediments would have been derived from the plunge point and near shore and added to the existing beach sediments. Analyses of vertical core sediments reveal the difference between the tsunami and seasonal sediments. Statistical parameters of vertical core give the approximate thickness of the tsunamigenic sediments. The mean values range between 1 ø to 2 ø, indicating the medium-sand category, in part of north and central Tamil Nadu,and 2 ø to 3 ø (finesand)in thesouthof centralTamilNadu, and 0 ø to 1 ø (coarse sand) on the southern part of the Tamil Nadu coast. The mean size revealed the fluctuation in energy conditions.The mean size indicates that the fine sand was deposited in moderately low-energy conditions and the medium sand was deposited in moderate-energy conditions. The mean size hence revealed that different energy conditions led to the deposition of these kinds of sediments in different locations. The coarser fractions deposited by the tidal cycle might have been carried back by the high-energy tsunami waves in the northern and central part of the coast (Singarasubramanian, Mukesh, and Manoharan 2005; Singarasubramanian et al. 2006). But in the southern part, the diffracted tsunami waves eroded the rocky surfaces of the beach and deposited them along the coast. Standard deviation (1 ø) measures the sorting of sediments and indicates the fluctuations in the kinetic energy or velocity conditions of the depositing agent (Sahu 1964).The sediments ranged from very well sorted to poorly sorted in nature. The sorting character of sediments indicates the type of wave and energy condition in the depositing medium.This kind of sorting nature of the sediments may be due to the intermixing and influx of the sediments from Geological and Geomorphological Perspectives of the Tsunami 91 the sea as well as the river. The presence of fine sand of a well-sorted nature suggests effective wave action. Down core variations clearly demarcate the tsunamigenic and tidal sediments along the coast. This infers that, depending upon the coastal morphology and available offshore sediments, the deposits will vary from place to place along the Tamil Nadu coast. Skewness measures the asymmetry of a frequency distribution. The symmetry of the samples varies from strongly fine skewed to strongly coarse skewed. The strongly fine-skewed and fine-skewed sediments generally imply the introduction of fine material or removal of coarser fraction (Friedman 1961) or the winnowing of sediments (Duane 1964). The fine-skewed nature of sediments indicates excessive riverine input. The positive skewness of sediments indicates the unidirectional transport (channel) or the deposition of sediments in a sheltered low-energy environment (Brambati 1969). Friedman (1962) suggested that extreme high or low values of kurtosis imply that part of the sediment achieved its sorting elsewhere in a high-energy environment. The tsunami sediments range from leptokurtic to mesokurtic, depending upon the energy flow and sediment load of the wave. The variation in the kurtosis values is a reflection of the flow characteristics of the depositing medium (Seralathan and Padmalal 1994; Baruah, Kotoky, and Sarma 1997). Finer size and dominant leptokurtic sediments reflect maturity of the sand, and variation in the sorting values is likely due to the continuous addition of finer/coarser materials in varying proportions (Prabhakara Reo et al.2001).The mesokurtic nature of sediments indicates that the original characters of sediments existed during the deposition without any mixing of populations or that a single supply of sediments was maintained (Mohan and Rajamanickam 2001). The frequency curves of the sediments collected from different parts of the coast show some similarities. In some cases the frequency curves of tsunamigenic sediments show a bimodal nature with coarse tail.The bimodal nature of the sediments is an indication that the sediments have more than one source. Similarly, the frequency curves of the tsunamigenic sediments show distinct traction population.In tsunamigenic sediments fine populations are considerably less prevalent along the southern Tamil Nadu coast. On the other hand, the pre- and post-tsunami sediments show considerable fine population. This clearly shows that during the tsunami wave attack the fines were deflated and would have been transported either landward or seaward. In the northern and central coast of Tamil Nadu the coarser fractions are smaller. Hence, this reveals that the size characteristics of tsunamigenic sediments depend upon the available source materials. A rise in the percentage of silt and clay (2.34–6.70%) after the tsunami was 92 Singarasubramanian, Mukesh, Manoharan, Seralathan, and Srinivasalu observed in some coastal transects.Such enhancement is likely to be due to the admixture of fine sediments brought forward by the receding tsunami waves from the hinterland or from the prograding tsunami waves from offshore. A rise in the percentage of carbonate content from 3.12 to 6.90% in tsunami deposits, particularly along the Poompuhar coast, is attributed to fresh debris brought forward by the onward tsunami waves. In the case of organic matter, one could find no appreciable rise among the pre- and post-tsunami sediments (table 3.2). The December 2004 tsunami altered not only the sediment texture along the coast, but also the heavy mineral concentrations. Depending upon the available sources along the coast/offshore, tsunami waves either enhanced the heavy mineral concentrations or totally eroded them. They deposited more etched, angular, or pitted heavy minerals with overgrowth texture along the coast compared to the normal seasonal deposits in certain localities like Poompuhar and Karaikal. The concentration of certain heavy minerals enriched in particular grain size compared to seasonal deposits may be due to the highenergy waves. The concentration of ilmenites along the coast clearly points out that these heavies are from offshore sediments.This enrichment of heavies in certain localities must have been from the offshore sediments brought by tsunami waves. The assemblage of heavy minerals was not significant to the study of tsunamigenic deposits except for interpretation based on the textural attribute rather than concentration along the east coast. As quartz sand is one of the most common components of coastal sand,it is Table 3.2. Pre- and post-tsunami sediment characteristic variation Location Clay content (%) Organic material (%) Calcareous fragments (%) Pretsunami Posttsunami Pretsunami Posttsunami Pretsunami Posttsunami Poompuhar 0.6–4.3 1.17–3.74 0.2–0.29 1–1.18 0.59–3.44 0.58–6.9 Chinnankudi 0.59–1.18 1.15–1.29 0.29–0.3 0.38–0.5 1.38–1.78 0.7–4.28 Kuttiyandavar 0.3–0.8 0.5–4.3 0.2–0.22 0.1–0.2 2–2.5 1.5–2 Chandirapadi 0.3–0.9 0.2–0.9 0.1–0.2 0.1–0.4 0.7–1.5 0.8–0.9 Kottucherimedu 0.5–0.6 0.5–0.8 0.1–0.2 0.1–0.2 0.9–2.2 0.8–2 Vadakkuvanjiyur 0.2–1.2 0.4–1.4 0.1–0.2 0.1–0.2 0.7–2.4 1.3–2.5 Nagore Beach 0.59–2.34 0–2.66 0–1.08 0.1–0.61 0.68–1.48 0.5–0.79 Source: Rajamanickam 2006. Geological and Geomorphological Perspectives of the Tsunami 93 appropriate to discuss some of the surface characteristics of the quartz mineral from tsunami deposits. Quartz can demonstrate such surface morphology as conchoidal fractures, microfractures, crystalline nodes, quartz overgrowths, microblocks, abrasion textures, and weathering textures. Many of these features were induced by grinding during transportation. The grains that were transported the furthest have a more rounded shape. Some of the surface textures of quartz sand from the tsunami deposits of the study area show strong grooves of mechanical action. This indicates that this feature is formed as a result of a high-energy environment.The quartz grains carry either straight or slightly curved grooves caused probably by the collision of sharp-edged sand grains, indicating that these textures are of littoral origin. Surface features of mechanical processes are also seen in the sand grain of tsunami deposits. Some grains exhibit intense chemical dissolution. The grains have a series of subparallel indentations probably produced by a portion of one grain slipping across another.The quartz grains illustrate a clear,strong groove of mechanical action modified by chemical action.Grains with a blocky conchoidal breakage pattern are of littoral origin. Some rounded quartz grains exhibit mechanical “V” pits subsequently modified by chemical weathering. Changes in Faunal Assemblages The study of microfossils within tsunami deposits is relatively new (Dawson and Shi 2000). Hemphill-Haley (1995, 1996) demonstrated the value of diatom analysis in identifying tsunami deposits on the coasts of Washington, Oregon, and Vancouver Island. Intertidal and marine diatoms in far-inland tsunami deposits indicate that sand was transported landward from a marine source rather than downstream as a fluvial deposit. Diatom analysis can also be used to determine the landward extent of tsunami flooding beyond the range of stratigraphic markers (Hemphill-Haley 1995, 1996). Unusually well-preserved diatoms in tsunami deposits relative to the underlying and overlying strata indicate rapid burial. However, Hemphill-Haley warns that diatoms alone cannot differentiate tsunami deposits from storm or seiche deposits, and they should be used in combination with other evidence for earthquakes. The presence of Ammonia beccarii really does not give any clues as to the provenance of the tsunami sediments along the coast. It is unambiguously considered a cosmopolitan species worldwide,with its living specimens having been recovered from hyposaline to hypersaline environments.Records from the Indian regions also point to its adaptability in a variety of habitats. Ammonia dentata is known to occur in the shelf areas, ranging from near-shore regions 94 Singarasubramanian, Mukesh, Manoharan, Seralathan, and Srinivasalu to relatively deeper waters in the Bay of Bengal.Sediments from the inner shelf, however,yielded specimens of the same species with long and slender spines at relatively greater water depths and with higher mud content in the substrate. This could be attributed to the adaptability of this species to a wide range of environmental conditions, i.e., the turbulent near shore to the relative calm of the inner-shelf region. Asterorotalia trispinosa (Thalmann) specimens recovered from the tsunami sediments have only short and blunt spines,thus indicating that the sediments have been derived from the inner-shelf region.Amphistegina radiata is typically an inner-shelf species that flourishes on sandy substrates at depths ranging from 15 to 40 m (49.5 to 132 feet) (Rajeshwara Rao 1998). Fresh specimens of this species in the subsamples are indicative of derivation of sediments from water depths of at least 15 m.Bathymetry of the area shows that the 15 m (49.5 feet) depth contour runs at about 3–4 km (1.8–2.4 miles), suggesting that the sediments might have been derived from the inner shelf. The presence of species such as the elphidiids and Pararotalia nipponica (Asano) indicate that the sediments were derived from the near-shore region,as these taxa are typically near-shore-dwelling ones.Sediments along the Ennore, Kalpakkam,Mamallapuram to Cuddalore,Nagapattinam,Karaikal,andVedharanyam regions of the east coast of Tamil Nadu were comprised of 50% or more reworked foraminiferal specimens,indicating that the tsunami sediments could have been derived from a water depth of at least 55 m (181 feet). According to Hussain (2006), the following species are distributed in the estuarine/creek (brackish water) tsunami sediments of Ennore to Cuddalore: Bairdoppilata alcyonicola, Bairdoppilata sp.cf. cushmani, Basslerites liebaui, Callistocythere flavidofusca intricatoides, Caudites javana, Mutilus pentoekensis , Neocytheromorpha sp., Neomonoceratina iniqua, N. jaini, N. porocostata, Paradoxostoma bhatiai, Paranesidea fracticorallicola, Spinoceratina spinosa, Stigmatocythere indica, S.kingmai, and Tanella gracilis. He also indicates the presence of composite fauna of foraminifera of benthic nature.Among them,Milliolina occupies the dominant place followed by Rotalina and others.Among the genera,Ammonia, Quinqueloculina, and Elphidium are dominant, followed by Pararotalia, Nonion, etc. The living species are rare and cosmopolitan in nature. The genera Ammonia and Quinqueloculina are distributed in all the stations. All the foraminifers recorded are benthic forms and preferably thrive in the inner-shelf environment,except Globigerina, which is planktonic and generally occurs in relatively deeper environments. All the ostracodes recorded are benthic forms and occur in neritic and upper bathyl zones. Most of the forms are less ornamented, and few are moderately Geological and Geomorphological Perspectives of the Tsunami 95 ornamented. Both foraminifera and ostracoda are less prevalent in living condition . Predated forms are almost absent in these tsunami samples. However, the samples collected were from beaches, creeks, and river-mouth upstreams. This supports the fact that the tsunami sediments have been deposited in these marginal marine water bodies. When compared to pre-tsunami samples, the offshore samples yield less organic matter, and in turn the living populations are found to be low in most of the post-tsunami deposits. Three waves struck the coast of Tamil Nadu. In general, the tsunami sedimentation along the east coast indicates that it was deposited at different times and at different inundation distances. The deposits were thinning landward. In some localities along the Tamil Nadu coast, multiple grading of sediment deposition was prominent, indicating that the deposition took place by successive waves. In the central part of the east coast of Tamil Nadu, where the wave was not dominant,the deposition of sediments was less prevalent,and the tsunami waves deposited mostly on the shore itself and made the coast clayey. The thickness of tsunamigenic deposits along the coast varied,depending upon the morphological setting. Thick deposition was noticed in the northern and southern parts of the Tamil Nadu coastal area. The south-central part was shadowed by Sri Lanka; hence, only reduced-velocity diffracted waves hit the shore, and sedimentation was less. The tsunamigenic sediments can be classi- fied based on their texture, faunal content, and, to a certain extent, their heavy mineral assemblages. Note The authors thank the Department of Science and Technology,New Delhi,for financial assistance in carrying out this study. References Achyuthan, H. 2002. Coastal response to changes in sea level since the last 4500 BP on the east coast of Tamilnadu, India. Radiocarbon 44 (1): 137–44. Amaral, E. J. 1977. Depositional environment of the St. Peter sandstone deduced by textural analysis. Journal of Sedimentary Petrology 47:32–52. Anbarasu, K., and G. V. Rajamanickam. 1997. Abandoned channels of rivers—An evidence for neotectonism. Indian Journal of Geomorphology 2:209–17. Baruah, J., P. Kotoky, and J. N. Sarma. 1997. Textural and geochemical study on river sediments:A case study on the Jhanji River,Assam.Journal of the Indian Association of Sedimentologists 16:195–206. Brambati, A. 1969. Stratigraphy and sedimentation of Siwaliks of north eastern India. Proceedings of the international seminar on intermontane basins: Geology and resources, 427–39. Chiang Mai, Thailand: International Seminar on Intermontane Basins. 96 Singarasubramanian, Mukesh, Manoharan, Seralathan, and Srinivasalu Chockalingam, M., M. Suresh Gandhi, and G.V. Rajamanickam. 2000. A study on the evolution of coastal landforms between Mandapam and Devipattinam, east coast of India. Indian Journal of Geomorphology 5:81–90. Dawson, A. G. 1999. Linking tsunami deposits, submarine slides and offshore earthquakes . Quaternary International 60:119–26. Dawson, A. G., and S. Z. Shi. 2000. Tsunami deposits. Pure Applied Geophysics 157:875–97. Duane, D. B. 1964. Significance of skewness in recent sediments, western Pamlico Sound, North Carolina. Journal of Sedimentary Petrology 34:864–74. Friedman, G. M. 1961. Distinction between dune, beach, and river sands from their textural characteristics. Journal of Sedimentary Petrology 31:514–29. ———. 1962. On sorting, sorting coefficients and the log normality of the grain-size distributions of sandstones. Journal of Geology 70:737–53. Greenwood, B. 1969. Sediment parameters and environment discrimination: An application of multivariate statistics.Canadian Journal of Earth Sciences 6:1347–58. Hari Narain, K. L. Kaila, and R. K. Verma. 1968. Continental margins of India. Canadian Journal of Earth Sciences 5:613–27. Hemphill-Haley, E. 1995. Diatom evidence for earthquake induced subsidence and tsunami 300 yr ago in southern coastal Washington. Geological Society of America Bulletin 107:367–78. ———. 1996. Diatoms as an arid aid in identifying late Holocene tsunami deposits. Holocene 6 (4): 439–48. Hussain,S.M.2006.26th tsunami causes,effects,remedial measures pre and post tsunami disaster management: A geoscientific perspective, ed. G. V. Rajamanickam, 83–115. New Delhi: New Academic. Keating,B.,F.Whelan,and J.B.Brock.2004.Tsunami deposits at Queen’s beach,Oahu, Hawaii—Initialresultsandwavemodeling.ScienceofTsunamiHazards22(1):23–43. King, C. A. M. 1972. Beaches and coasts. 2nded. New York: St. Martins. Loveson,V.J.,G.V.Rajamanickam,and N.Chandrasekar.1990.Environmentalimpacton microdeltasandswampalongthecoastof PalkBay,TamilNadu:Severalvariationand its impacts on coastal environment. Tamil University, Thanjavur, Tamil Nadu, India. Mohan,P.M.,and G.V.Rajamanickam.2001.Depositional environment inferred from the core samples of beach ridge, Mahabalipuram, east coast, Tamilnadu. Journal of the Indian Association of Sedimentologists 20 (1): 59–74. Prabhakara Rao,A.,V.Anilkumar,A.Yugandhar Rao,G.S.Ravi,and S.Krishnan.2001. Grain size parameters in the interpretation of depositional environments of coastal sediments between Bendi Creek and Vamsadhara River, east coast, India. Journal of the Indian Association of Sedimentologists 20 (1): 106–16. Rajamanickam, G.V. 2006. 26thtsunami causes, effects, remedial measures pre and post tsunami disaster management: A geoscientific perspective, ed. G. V. Rajamanickam, 68–77. New Delhi: New Academic. Rajamanickam, G. V., and V. J. Loveson. 1998. Geomorphology and evolution of the east coast from Kanyakumari to Mandapam, Tamilnadu. Indian Journal of Geomorphology 3 (2): 233–44. Geological and Geomorphological Perspectives of the Tsunami 97 Rajeschwara Rao, N. 1998. Recent foraminifera in the inner shelf of the Bay of Bengal, off Karikattukuppam. Ph.D. diss., University of Madras. Ramanamurthy, M. V., S. Sundaramoorthy, Y. Pari, P. Rangarao, P. Mishra, M. Bhat, Usha Tune, R.Venkatesan, and B. R. Subramaniyan. 2005. Inundation of sea water in Andaman Nicobar Islands and parts of Tamil Nadu coast during 2004 Sumatra tsunami. Current Science 88:1736–43. Rao, T. C. S., and B. Rao. 1985. Geophysical studies over the continental margins of east coast of India. Marine Geology 67:151–61. Sahu, B. K. 1964. Depositional mechanisms from the size analysis of clastic sediments. Journal of Sedimentary Petrology 34:73–83. Senthilnathan, D. 2006. 26th tsunami causes, effects, remedial measures pre and post tsunami disaster management: A geoscientific perspective, ed. G. V. Rajamanickam, 10–44. New Delhi: New Academic. Seralathan, P., and D. Padmalal. 1994. Textural studies of the surficial sediments of Muvattupuzha River and central Vembanad estuary, Kerala. Journal of the Geological Society of India 43:179–90. Shanthi Devi, R., and G. V. Rajamanickam. 2000. Distribution of coastal landforms between the coast of Adirampattinam and Nagapattinam,Tamilnadu.Indian Journal of Geomorphology 5:137–60. Singarasubramanian, S. R., M. V. Mukesh, and K. Manoharan. 2005. A preliminary report on coastal sediment characteristics after M 9 tsunami event along the central Tamil Nadu, east coast of India. In Sumatra tsunami on 26th December, 2004, ed. Byung Ho Choi and Fumihiko Imamura. Proceedings of Special Asia Tsunami Session at Asian and Pacific Coasts. Seoul: Hanriwon. Singarasubramanian, S. R., M. V. Mukesh, K. Manoharan, S. Murugan, D. Bakkiaraj, A. John Peter, and P. Seralathan. 2006. Sediment characteristics of the M 9 tsunami event between Rameswaram and Thoothukudi, Gulf of Mannar, southeast coast of India. International Journal of the Science of Tsunami Hazards 25 (3): 160–73. Swift, D. L. P. 1976. Coastal sedimentation: Marine sediment transport and environment management. New York: John Wiley and Sons. Whelan,F.,and D.Kelletat.2003.Analysis of tsunami deposits at Trafalgar,Spain,using GIS and GPS technology. Essener Geographische Arbeiten 35:25. ...