|
|
|
Application of RS and GIS in Damage Assessment and Rehabilitation of 26th December 2004 Great Indian Ocean Tsunami Event in Car Nicobar Island, India
Arun Kumar
Department of Earth Sciences Manipur University Imphal 795003 India
ABSTRACT:
The Car Nicobar Islands was one of the several islands in Indian Ocean which were severally damaged by the Great Tsunami on 26 December 2004. The great tsunami event caused the devastation, loss of life and property in south and south East Asia. The objectives of the study are to assess the changes in the coastal features of the Car Nicobar Island using various indicators such as the tsunami height, run up elevation, water flow direction, erosion, sand deposition, and coastal subsidence. Andaman & Nicobar Islands are summit of the submarine mountain range lying on the great tectonic suture zone extending from Eastern Himalaya along the Myanmar border to Arakan and finally Sumatra and Lesser Sunda. The IRS P-6 satellite data has been found to be very useful in this regard. The digital analysis of the digital satellite data was done by using the image processing software (ERDAS IMAGINE 8.4) and DTM to quantify the tsunami height (15m), run up elevation (2-19 m), inundation (295-1203 m), and coastal responses. The settlement and coconut plantation has been severely damaged on the island, which is assessed by using GIS analysis of the pre and post satellite data.
1 INTRODUCTION:
The Car Nicobar Islands was one of the several islands which were severally damaged by the Great Tsunami on 26 December 2004. The origin of tsunami was series on undersea earthquakes, the largest being measured 9.3 M. The direct consequence of Great Earthquake, that ruptured the sea floor up to 100 km in places, was displacement of a huge volume of water that translated into tsunami of colossal proportion. The great tsunami event caused the devastation and a loss of life in south and south East Asia including the Andaman and Nicobar Islands. The geological formations represent a period of sedimentation from Cretaceous to Sub Recent period. The Nicobar Islands are part of a great island arc created by the collision of the Indo- Australian Plate with Eurasia. The collision lifted the Himalaya and most of the Indonesian islands, and created a long arc of highlands and islands, which includes the Arakan Yoma range of Myanmar, the Andaman and Nicobar islands, and the islands off the west coast of Sumatra, including the Banyak Islands and Mentawai Islands (http://www.Forest.nic.in/frstisland1. htm). These islands are the summits of a submarine mountain range lying on the great tectonic suture zone extending from the Eastern Himalayas along the Myanmar border to the Arakan and finally Sumatra and Lesser Sundas. The geological formations represent a period of sedimentation from Cretaceous to Sub-
Recent period. The surface deposits of gravel beds and raised soil covers that are of recent origin seem to be of Holocene age (> 10,000 yrs). The present configuration of these islands took shape only about 26 million years ago. These islands have a tropical climate and temperature ranges from 22º C to 28ºC. Rainfall is heavy due to annual monsoons and measures around 3000 to 3800 mm each year. The physiography of these islands is characterised by undulating topography and intervening valleys. There is no major perennial fresh water river in the islands. There are several rain fed streams. The coastal lines of these islands are wavy with large number of bays and lagoons. Soil cover is thin, varying from 2m to 5m. The coastal flats have an admixture of sand, silty and clay with fine fragments of coral lime. The vegetation of the Nicobars is typically divided into the coastal mangrove forests and the interior evergreen and deciduous Tropical and subtropical moist broadleaf forests. The present studies are made in Car Nicobar islands to assess the damages of tsunami and find out the geological evidences for tsunami characterization using RS data and GIS software. The objectives of the study are to assess the changes in the various coastal features of the island using various indicators such as the tsunami height, run up elevation, water flow direction, erosion, sand deposition, and coastal subsidence.
2 GREAT EVENTS OF 26 DECEMBER 2004:
The Great Earthquake of December 26 2004 that occurred off the west coast of Northern Sumatra took place at the interface between the India and Burma plates, where Burma plate has been referred by Andaman/Nicobar Ridge that acts as a small tectonic plate (Curray et.al., 1982). The event was considered as a mega thrust earthquake referring to the large cracking of the plate boundary. The mega thrust earthquakes often generate large tsunamis that can cause damage over a much wider area than is directly affected by ground shaking near the earthquake's rupture. Tsunami was generated in the fast slip area (first 650 km at taut length) and the waves propagated in all directions. As a result, strongest waves hit the coasts of Indonesia, Thailand and other nearby areas (Andaman & Nicobar Islands) which are closely located on the east of the epicenter. The devastation in the Nicobar Islands was due to a 10-15 m high tsunami following the 2004 Indian Ocean earthquake. At least 3000 people were believed to have been killed on the disaster. Historical data does not provide a very realistic estimate of earlier tsunami events in the island, however, 31.12.1881 tsunami which was caused by an earthquake of magnitude 7.9 Ms has been recorded by the National Geophysical Data center, NOAA, USA (www.ngdc.noaa.gov/nmdc/servlet/showdatadatasets). The other referred earthquakes and volcanic eruptions of 1847(M?), 1883 (Volcanic eruption) and 1941(M 7.7 Mw) might have caused the tsunami hazards or not in the region is still unrevealed. The possible clues can be explored by trenching the beaches, study their profiles and date them by TL/OSL dating technique to ascertained the historical and pre historical tsunamis in the region.
|
|
|