Impact of the tsunami and earthquake of 26th December 2004 on the vital coastal ecosystems of the Andaman and Nicobar Islands assessed using RESOURCESAT AWiFS data

doi:10.1016/j.jag.2008.02.010

International Journal of Applied Earth Observation and Geoinformation

Volume 10, Issue 2, June 2008, Pages 229-237

https://doi.org/10.1016/j.jag.2008.02.010 Get rights and content

Abstract

Tsunami waves struck the Indian coast on 26th December 2004 affecting the Andaman and Nicobar group of islands. A quick assessment of the status of the vital coastal ecosystems has been made using pre- and post-tsunami Advance Wide Field Sensor (AWiFS) data of Indian satellite RESOURCESAT with an accuracy of 87–90% and the Kappa ranging from 0.8696 to 0.9053. Among the coastal ecosystems the coral reefs have suffered the maximum with the Nicobar reefs (69% eroded and 29% degraded) bearing the brunt more than the Andaman reefs (54% eroded and 22% degraded). Significant improvement to the condition of the reef damaged due to backwash has been noted. About 41% of the Sentinel reef area has undergone significant improvement. The continuance of the erosion of the southwestern Andaman reefs is due to the impact of recurring earthquakes. The impact on mangroves of both the groups of islands has been due to uprooting as well as inundation of seawater and resulting stagnation. Changes are expected in community structure of mangroves as a result of tsunami.

Introduction

Tsunami waves struck the Indian coast on 26th December 2004 affecting the Andaman and Nicobar group of islands, Tamil Nadu, Andhra Pradesh and Kerala coasts. A tsunami is not a single wave but a series of traveling ocean waves generated by the geological changes near or below the ocean floor. The recent tsunami was set off as a result of a massive earthquake in the region registering a magnitude of 9.3, with its epicentre under the sea (more than 8.9 km below the sea bed), off the northern tip of the Indonesian archipelago near Aceh. These waves traveled as far as 6400 km from the epicentre. The tsunami moves rapidly across the ocean (900 km/h) and takes the form of destructive high waves along shallow coastal waters (10 m height and a speed of 40 km/h).

A tsunami can damage marine ecosystems through its initial surge and the ensuing backwash, the latter of which may carry sediments and debris from land. The sediments and debris can smother and scrape seafloor habitats, such as coral, while introducing toxins and disease agents to the ecosystem. The physical forces of a tsunami are powerful enough to cause meter-wide coral boulders to tumble across the seafloor.

Satellite data was used to rapidly assess the damage caused by the recent Asian tsunami, particularly on the coastal wetlands of the affected areas. Selected coral reefs were also monitored to study the status of the ecosystems after 8–11 months.

The Andaman and Nicobar Islands bore the maximum brunt as they are located closest to the epicentre and were in the closest direct path of the tsunami. This paper describes the status of the coral reefs and the coastal wetlands of the Andaman and Nicobar group of islands after the tsunami struck. The Andaman and Nicobar groups of islands located in the southeast of the Bay of Bengal (Fig. 1) between 6°45′N and 13°14′N latitudes and 92°12′E and 93°57′E longitudes consist of about 350 islands, of which only 38 are inhabited along with a number of exposed islets and rocks, and the land area is about 8500 km² (Anon, 1987). The general orientation of the islands is north south. The islands are characterized by three interconnected natural ecosystems – Forest, Mangrove and Marine ecosystems that are the result of typical topographical, climatological and soil characteristics of the area.

Section snippets

Methods and material studied

AWiFS data of RESOURCESAT-1 was used for rapid assessment of the damage to ecosystems and subsequent monitoring. LISS III data of RESOURCESAT-1 with a resolution of 23 m were used along with AWiFS data for selected areas to study the status of the coral reefs currently. Details of the data used for the study are given in Table 1.

Data of the period October–December 2004 helped to assess the status of the coastal habitats just before the tsunami event. For studying the condition of these habitats

Results and analyses

Sai et al. (2004) and Sharma (2004) have pointed the usefulness of RESOURCESAT AWiFS data in monitoring the natural resources due to its improved quantization level (10-bit data) as compared to the LISS III data of Indian Remote Sensing Satellite 1C and 1D and RESORCESAT LISS III and LISS IV data. The inclusion of SWIR band helped in monitoring the vegetation and the increased temporal capability was an edge over the other Indian Remote Sensing Satellites in monitoring the coastal resources

Discussion and conclusion

RESOURCESAT AWiFS data helped in assessing the impact of the natural hazard on coastal resources rapidly. Among the coastal ecosystems the coral reefs have suffered the maximum damage. The Nicobar reefs have been totally eroded at most of the places. Fig. 6 aptly summarizes the impacts of tsunami and earthquake of 26th December 2004. Out of total 223.7 km² area occupied by Nicobar reefs prior to tsunami, only 10 km² of reef remained just after tsunami with 154 km² eroded and 65.8 km² damaged due to

Acknowledgements

The authors are thankful to the Director, Space Applications Centre, and Deputy Director, Remote Sensing Applications and Image Processing Area, Space Applications Centre, Ahmedabad, for providing guidance and facility to carry out this work. We are also thankful to Central Agricultural Research Institute, Port Blair for providing us logistics support and expertise for carrying out ground observations.

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Impact of the tsunami and earthquake of 26th December 2004 on the vital coastal ecosystems of the Andaman and Nicobar Islands assessed using RESOURCESAT AWiFS data

Abstract

Introduction

Section snippets

Methods and material studied

Results and analyses

Discussion and conclusion

Acknowledgements

Continental Shelf Resour.

Remote Sensing Environ.

Mangroves in India, Status Report

Application of multi-level remote sensing survey to mangrove forest resource management in the Philippines

Tsunamis

Digital analysis of remote sensing data for monitoring the ecological status of the mangrove forests of Sunderbans in Bangladesh

Digital coastal resources inventory map of Pak Panang region, Thailand, using digital mapping system and Landsat MSS data

The determination of optimal threshold levels for change detection using various accuracy indices

Photogrammetric Eng. Remote Sensing

Remote sensing handbook for tropical coastal management

Application of remote sensing in the study of developmental impact of a marine park in Malaysia

Monitoring the development impacts on the coastal resources of Pulau Redang Marine Park by remote sensing