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Tsunami Redraws Indian Ocean Maps

Brian Handwerk
for National Geographic Channel
January 12, 2005
 
In addition to its massive death toll, December's tsunami also rearranged geographic features of the Indian Ocean on a gargantuan scale—above and below the water's surface.

Reports continue to surface of vanished islands, restructured coastlines, and uncertain shipping lanes. Geographers are responding with satellites and survey vessels to determine which areas are hardest hit. Their findings are helping and rechart maritime routes essential for the delivery of relief supplies.



David Skole and his team are using 30-meter-resolution (33 yards) satellite imagery to determine which areas were hardest hit and are most in need of help. Skole directs the Center for Global Change and Earth Observations (CGCEO) at Michigan State University. The group works in conjunction with Landsat.org, NASA, the United States Geological Survey, and other organizations.

CGCEO is concentrating much of its effort on Indonesia's Aceh Province, the heavily damaged northern region on the island of Sumatra. Even in this area that bore the brunt of the wave's destruction, the geographical impacts vary with shape of the coastline and offshore environment.

"The perspective you might get from the news is that the entire province was wiped out," Skole said. "That's not true, only about 400 to 500 square kilometers [150 to 190 square miles] were damaged along a narrow ribbon of coastline. And some pockets were worse than others."

"Unfortunately when you cross-map the damage maps with population-density maps and the locations of urban areas, you see that the areas most damaged were also the areas of high population density," he continued. "People are settling in these high-risk zones along the coastline."

Interestingly, when it comes to determining where relief efforts are most needed, satellite images are sometimes proving more reliable than reports from the scene.

"Some of these areas are remote or cut off from transportation and communication," Skole explained. "If they do have communication, people may call in and say, We need help, it's a total mess here. Well, everybody is saying that, so how do you map it?"

Skole is working to create such a relief-need map with colleagues in the Indonesian government. They're using satellite techniques they've honed over a decade-long relationship working on mapping projects related to rain forest deforestation.

"We have a global database of Landsat images from the year 2000, so we could do a before-and-after comparison," he said. "The signature of the damage is pretty striking. [We're seeing] significant coastline erosion and new islands that were once connected to the coastline."

Underwater Conditions Unknown

The National Geospatial-Intelligence Agency (NGA) is also using its satellite technology to determine which areas around the Indian Ocean are heavily damaged and most in need of assistance. NGA's maritime navigation watch is collecting on-site reports from the Indian Ocean region. Both sources describe an area that no longer matches existing maps and charts.

"In this case we see massive erosion of the islands," said Chris Andreasen, chief hydrographer at NGA's Office of Global Navigation in Bethesda, Maryland. "That sediment had to go somewhere, so I'd expect shoaling in channels and areas where vessels typically try to navigate. We have no idea what that impact is right now."

NGA is producing satellite maps and other products that indicate damaged areas and serve as crucial aids to mariners in the treacherous waters.

"Two major lighthouses are out at the north end of the Strait of Malacca," Andreasen said. "You might think [mariners] could rely on GPS instead, but it turns out that one of [the lighthouses] was also the location of [a now broken GPS transmitter] as well. You don't expect that a lighthouse would be in a location that's going to be taken out."

Along the coastlines and near ports, wrecks and debris fill the waters. Buoys and other fixed navigational aids have been wiped out.

Local authorities in charge of maintaining such operations were not spared the impact of the wave. "I think that Sri Lanka had only one [survey] vessel, and it was destroyed, and their hydrographic office was also hit by the wave," Andreasen said. "I believe that one member of their staff was killed, so they are still shoveling mud out of that office."

Ports and Approaches Are a Treacherous Maze

Help is on the way as part of the international response to the tsunami. The primary goal is to open ports to vessels capable of carrying the enormous amounts of relief supplies headed into the region.

The U.S. Navy coastal survey vessel John McDonnell is expected to arrive in the Strait of Malacca on January 14. The ship carries two small hydrographic survey launches, equipped with high-frequency sonar to operate in depths of 10 to 260 feet (3 to 80 meters).

"We don't know the shape that the channels, approaches, and harbors are in, based on debris," said Capt. Jeffrey S. Best, commanding officer of the Naval Oceanographic Office (NAVOCEANO) at Stennis Space Center, Mississippi. "There could be buildings, cars, or all kinds of things blocking those approaches. Our guys need to make sure that it's safe so that we can get the big relief ships in there."

"We just want to produce a field chart that identifies major hazards to navigation," Best continued. "Our goal is not to survey to standard. We may be asked later for an in-depth survey."

Experts say it could take several months or more to open affected Indian Ocean ports. In the shorter term, some NAVOCEANO staff are using NGA satellite images to identify sandy beaches where supplies might be brought ashore by landing craft.

On arrival, the John McDonnell will also attempt to verify reports of dangerous shoals in the Strait of Malacca—among the world's busiest shipping areas.

Unverified reports suggest that areas of the straights that were once thousands of feet deep are now as shallow as 100 feet (30 meters)—too shallow for large commercial vessels.

While identifying target relief areas and charting safe courses for supply ships are top priorities, recreating the maps altered by nature's power will be a very long-term project.

"It's going to take years if not decades to survey the whole region, because [the impact] is just huge," NGA's Andreasen said. "We've never seen anything like this before."

Tsunami in Southeast Asia: Full Coverage
The great tsunami of 2004 was one of the worst disasters in history. Read our latest news stories and learn how tsunamis are generated, where they can strike, and what you can do to protect yourself.

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