A Remote Sensing Assesment of the 2004 Sumatra Tsunami
A Remote Sensing Assesment of the 2004 Sumatra Tsunami

ES 771 Remote Sensing
By: Graham Markowitz, Michael Lewis, Harry Jenkins

Emporia State University
Remote Sensing, Fall 2010

Figure (left) - The initial pulses of the tsunami within bay region. Courtesy of J.T. and Caroline Malatesta http://oceanworld.tamu.edu/resources/oceanography-book/tsunamis.htm

Figure (right) - Deposition of large grain sediment along beach-line. Credit: Image courtesy of Nikos Kaligeris) http://www.sciencedaily.com/releases/2007/06/070618133738.htm

INTRODUCTION

On December 26, 2004 a 9.0 magnitude earthquake occurred in the Indian Ocean when the stress along a fault line was released. According to the USGS report the displacement was as much as 6 meters between the India and Burma plate. The source of the tsunami was the displacement of the plates. After the end of the event more the 150,000 were reported dead. The wave was barely notice in the open ocean; it was not until the wave was just offshore when it was estimated to be more than 15 meters high. The wave spread several hundred meters inland. Besides the immediate cost of lives, the tsunami drastically altered the surrounding landscape.

Due to the growing population in rural portion of the world, remotely sensed imagery provides information about damages caused by natural hazards. When studying large or small areas, remotely sensed imagery allows for an increase in efficiently when assessing ground measurements. The time originally applied for ground survey measurements can be decreased by analyzing remotely sensed data. Satellite imagery has been used to study the earth’s surface since the late 1970’s. The first photographs of earth were taken during the space mission Apollo, mercury, and Gemini. The earliest multispectral data began in the 1960s which allowed for the separation of bands within an image. Presently, images with less than one meter resolution are available depicting variations in vegetation, geology, and anthropogenic modifications.

The combination of remotely sensed images and GIS programs such as IDRIS Taiga allows researcher to determine pre and post-natural hazard settings. Imagery acquired after the particular event allows researcher to determine the land-cover affected by natural hazard. Satellite imagery provides in-depth interpolation of the region by providing several angles of the target area. Remotely sensed imagery not only allows emergency personal to coordinate disaster relief efforts but also in monitoring mitigation and resilience of the area affected. In this study, multispectral imagery has been be used to determine alterations and resilience of the landscape once affected by the Sumatra tsunami of 2004.

Process

Our initial project was to look at the destruction, change, and regrowth of a portion of Sumatra following the December 26th 2004 Tsunami however upon an exhaustive search through available Landsat data we found the best available images were found only a year and a half out from the event but upon inspection of those images we found much regrowth had indeed occurred.

Our area of interest was identified by looking for three images in the same location in heavily affected Northern Sumatra facing the Indian Ocean that included a mostly cloud free view of the same area prior to Dec 26th, 2004, one within three months of the event, and one as far out in the future from the event. We identified three images from the landsat series, two being 4-5TM and one L7 prior to SLC failure.

These images were downloaded via Earth Explorer from the USGS. The images were reviewed using ArcInfo and a clipped by a shapefile created from a portion showing the least cloud cover. The selected image is situated on the western coast of Northern Sumatra just south of Banda Aceh.

With all bands clipped to the desired location these were imported to Idrisi and haze corrected using scalar subtraction followed by stretching through scalar multiplication. Natural color and 147 band combination images were then created for visual analysis. To quantitatively analyze the images a cluster analysis was also performed on all three images.

Clusters 6, 10, and 14 in the February image appear to be representative of tidal destruction. The sum (area) of clusters 6, 10, and 14 is an approximation of the total area of land alteration in this image due to the tsunami.

Analysis

May 2000 visible

Dense tropical forest cover steep terrain inland with heavily eroded and mature water channels leaving the mountain region and depositing into the ocean in an area heavily embayed with large sedimentary features such as broad pocket beaches and tombolos. The island in the southern portion of the image was attached via a tombolo feature, built up though sediment brought out by a river mouth at that location. The coastal plains appear sedimentary in origin from the erosion of the inner mountains through the action of ample precipitation. Image acquisition before the tsunami depicts smooth fine grained beaches following a convex arc. The narrow to non-existent coastal is highly variable in breadth and appears to be the primary focus of human activity in the form of light to moderate density occupation and subsistence agriculture. No agricultural facilities appear of substantial size and built-up–areas appear small in size. Turbidity in the water indicates a northward longshore drift.

May 2000 147

Dense tropical forest cover steep terrain inland with heavily eroded and mature water channels leaving the mountain region and depositing into the ocean in an area heavily embayed with large sedimentary features such as broad pocket beaches and tombolos. The island in the southern portion of the image was attached via a tombolo feature, built up though sediment brought out by a river mouth at that location. The coastal plains appear sedimentary in origin from the erosion of the inner mountains through the action of ample precipitation. Image acquisition before the tsunami depicts smooth fine grained beaches following a convex arc. The narrow to non-existent coastal is highly variable in breadth and appears to be the primary focus of human activity in the form of light to moderate density occupation and subsistence agriculture. No agricultural facilities appear of substantial size and built-up–areas appear small in size. Turbidity in the water indicates a northward longshore drift.

February 2005 Visible

Leupeung is completely devoid of agricultural vegetation and urbanized development seems absent. The post-tsunami image shows a new beach ridge morphology forming in locations that were once fine grained beaches. The beach ridge morphology can be depicted by deepened, linear beach forms where the fine grain sand was replaced by coarser fragments. Areas of deposition for medium to fine grained sediment were limited to a few hundred meters inland, where finer suspended sediment was deposited 1km or further inland (Fujino, S., et al., 2010). The tombolo north of Leupeung has been detahced by wave action and the isthmus has been replaced by a cove.

Other noticeable morphological features include lateral expansion of river inlets, lagoons, and bays by swell inundation. The former marshy back beach region and meandering streams in the former small coastal plain are now directly deposits into the ocean. The receding swells carried suspended sediment offshore as large waves contain more energy to entrain and suspend finer sediment (Hyndman, D., et al. 2008). The broader plains in which the village of Lamno and surrounding agricultural fields appears heavily devastated with sall but the highest areas being cleaned of vegetation and no discernable village remaining.

February 147

Vegetation has been removed completely in all areas below the high water mark of the tidal low with only areas where sheer faces meet the sea bringing vegetation up to the waters edge. The area of the former tombolo appears to have been scoured deeply as the remains of the sandbar are not visible in this image.

August 2006 Visible

Light vegetation is visible throughout the coastal plains and some redevelopment of is evident, especially is the central portion of this image as Lamno shows some reconstruction of the village and surrounding fields. The immediate morphological changes due to the tsunami were soon masked by a new set of depositional forms. The transition back to the pre-tsunami beach line occurred within a relatively brief period of time. The cove in which the tombolo used to be has begun to build a considerable beach. As the tsunami waves receded, the altered coastline was subject to normal or pre-tsunami beach forming processes (Fujino, et al., 2010). Just after a year and a half after the tsunami, the new coast began to closely resembled the old coast. Finer grained sediment was redeposited in locations that were once left bare causing the new beaches to appear wider than previous beaches, as referenced by the May 2000 image. The tombolo was washed away by the tsunami and as of one and a half years later there still did not seem to be a noticeable build-up of sediment at that location. The pocket beaches are again taking on more regularity, favoring the northern extents due to longshore currents.

August 2006 147

Vegetation is still sparse in much of the coastal plains but there is definite regrowth occurring. Some agriculture is again being undertaken in both the Lamno and Leupeung regions. Sharp divisions between vegetative and non-vegetative regions have been erased in many areas as the softened transitions demonstrate a recolonization of those regions by the native plants. In addition, other biological forms such as coral reefs are predicted to return to pre-tsunami states. Of the coral reefs damaged, there were still large amounts of the reef that were left intact. Post-tsunami surveys suggest that the damaged parts of the coral reef should regenerate and fully recover within the next 5 to 10 years (Hagan, A.B., et al. 2007).

Figure (left) - Uplifted and exposed coral reef after earthquake. Courtesy of http://blogs.discovermagazine.com/80beats/tag/tsunamis/

Figure (right) - Devastated Sumatran village and vegetation post tsunami. Courtesy of AFP, http://www.theaustralian.com.au

REFERENCES


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Last updated December 2010.