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Monitoring Changes in Seafloor Morphology Using Multi-date Bathymetry data: A Case Study of the Gulf of Mannar, Southeast Coast of India
The shore between Gundar and Palar River, the sea floor is found at a depth of 3m, and this deep extends to 1.19 km from the coast. At the south of Mel Mendal coast the sea floor slopes very steeply to 7 m depth and extends to 1.44 km from the coast. Between the depths of 10 and 20 m the sea floor slopes moderately with a width of 7.52 km. At an average depth of 20 to 30 m, there is a continental slope with 16.56km width. In between 7 and 8 m depths, the sea floor is broad and has a very gentle slope. In this region particularly at latitude of 9°6'5"N and longitude of 78°32'10"E, an island, namely Shalli Island, having 9 m elevation from sea floor is encountered. On the northern and southern sides of this island, the sea floor slopes very steep, while on the eastern and western sides, the slope is gentle. Towards east from Shalli Island another island namely Nalla Tanni Island is encountered (78°34'29"E - 9°6'11"N). Around this island the sea floor slopes very gently, particularly in the northeast, east and southeastern sides of the island, which extends to a depth of 4 m from the shore of the island. Whereas northern and southwestern sides of this island, the seafloor have a very steep slope, extending to a depth of 4 m at a distance of 0.36 m from the coast of the island.
The region between Palar River mouth and Dhanushkodi shelf, the topography has some irregularities. In the area opposite to Palar River mouth, there is a gentle depressed channel, having an approximate length of 4.41 km towards south. The coast between Palar River mouth and Kalachimundal, the sea floor is found at a depth of 1 m and it extends to a distance of 0.28 km from the shore. Between these areas the sea floor gradient is very steep to a depth of 7m. The width of this area is 1.60 km. After reaching 7 m depth the sea floor rises upto 3 m depth, this depressed channel runs to a distance of 21.27 km towards northeast and south, and lies between 78°40'4'E-9°9'15"N and 78°47'37"E-9°13'8"N. The average width of this channel has been measured as 0.75 km. After reaching 3 m depth the sea floor has a sudden fall to 10 m depth. In between the two depressions, a flat-topped continental rise has been observed. The average width of the continental rise is 1.58 km and is located 5.7 km from the shore. On this rise, there are two elevated islands rising 4m from the sea floor and are located between 78°41'28"E-9°9'3"N and 78°43'32"E-9°9'4"N. These islands are called as Anaipar and Pilliyarmunai Islands. Around these islands the sea floor slopes very gently and extensively developed fringing corals are found within 2 m depth. Between 4 and 5m depth, at a lat-long of 78°45'8'E - 9°9'12"N, an island namely, Puvarasanpatti Island, having an elevation of 4.50 m from the sea floor is encountered. At a depth between 10 m and 20 the sea floor slopes gently. The width of this continental shelf is 18.17 m. In the area between Keelakkarai and Pudumadam, the seafloor is almost plain and has a depth of 3 to 4 m. This plain extends to a distance of 9.72 km from coast. In this plain some low elevated rise and Islands are observed. Located at a lat-long of 78°49'10"E-9°9'31"N an island namely Appa Island, having an elevation of 5 m from sea floor has been noticed. Around this island the sea floor slopes gently to 2 m depth. It extends to an average distance of 1.50 km. At 78°51'25"E - 9°14'2"N and 78°52'31"E - 9°14'32", two continental rise have been observed having an elevation of 1m from the sea floor. In between 4 and 5m depths, there are some low elevated islands (5.50 m from sea floor) namely Talairi, Valai and Muli Islands. They are located at an average distance of 8.45 km from Kaplar River mouth. In this region the sea floor gradient is very steep extending from 5 m depth to 10m depth and then it slopes gently upto 30 m depth.
In the coast between Pudumadam and Thoniturai, the sea floor is almost plain having a depth of 2 to 3 m. This plain extends 6.95 km from the coast. Near Senniappa Dargah and Thoniturai this plain is encountered at 2m depth and it extends to an average distance of 2.17 km from the coast of Senniappa Dargah and 0.50 km from Thoniturai coast. Along this plain some low elevated continental rise (79°5'19"E - 9°12'14"N) and chain of islands have been observed. From Senniappa Dargh to 6.65 km towards south, an island namely Musal Island having an elevation of 3.5m from sea floor is encountered. Around this island fringing corals have developed very extensively to a depth of 2 m, they extend 1.45 km towards north, 1.75 km towards northwest, 1.69 km towards west and 1.42 km towards south from the coast of the island. Around this island the sea floor slopes gently upto a depth of 2m. On the seaward side of this island, the sea floor slope is very steep to 10m depth and to an average distance of 2 m. About 6.18 km away from Marakkayarpattinam, there are two islands namely Manalli and Manalliputti Islands (79°7'26"E - 9°12'23"N and 79°8'16"E - 9°12'23"N). Around these islands, the sea floor is encountered at 1m depth and the topography of the sea floor around this island has a moderate gradient. On the seaward side of this island, the sea floor slope is very steep, between 3 m and 6 m depths. The width of this slope is 0.73 km. At a depth of 6 to 7 m a plain having a width of 3.52 km is encountered. The sea floor slopes gently between 7 and 30 m depths. In the area between Thoniturai and Pamban canal, the sea floor is encountered at a depth of 1 m and extends to an average distance of 1.07 km from the coast of Thoniturai and Velupilliyarkovil. In this area the sea floor slopes very gently upto 2 m depth. In between 2 and 3 m depths, there is a vast plain sea floor extending 3.80 km from north to south and 23.3 km from east to west. Along this plain there are low elevated chain of islands (79°10'28"E - 9°14'28"N and 79°14'16"E - 9°13'28") namely Pumurichan, Kovi, Kursadi and Shingle islands. Around these islands the sea floor is encountered at a depth of 0.5m and extends to an average distance of 0.49 km towards north, 1 km towards south, 0.19 km towards east and 0.27 km towards west. In the north of these islands the sea floor slope is steep (till a depth of 1 m) whereas it is very gentle in the south (till a depth of 3 m). In between 3 m and 10 m the sea floor slope is steep having a width of 1.83 km. From 10 to 30 m the sea floor slopes moderately. In the area between Dhanuskodi and Kundugal the sea floor is at a depth of 6 m and slopes moderately up to 30 m depth. The width of the continental shelf in this area has been measured approximately as 26.25 km.
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