Tsunami unlikely to have redrawn coastlines

Tsunami unlikely to have redrawn coastlines

Emma Ross, Associated Press, Jakarta

Aerial images of tsunami-battered coastlines suggest the world
map may be changed forever, with chunks of land sinking into the
sea. But did the quake and the killer wave it spawned really
significantly reshape the Indian Ocean's outline? Scientists say
probably not.

Almost all the apparent land fragmentation is likely due to
temporary flooding, experts say. However, there are signs - still
too early to verify -- that a handful of isolated Indian islands
near the center of the quake or its aftershocks may indeed have
changed.

Cecep Subarya, of Indonesia's National Coordination Agency for
Surveys and Mapping, says no new islands have been spotted, and
no existing islands have been seen to vanish or split up off the
northwest coast of Indonesia's Sumatra island, the earthquake's
epicenter.

Nor has Sumatra's coast been reshaped, he said.
Experts say nearly all the rest of the region is too far from the
epicenter for the physical geography to have been affected. Those
areas look different now because of flooding from the tsunami,
but the water will recede.

One exception may be the Andaman and Nicobar islands. Experts
say it's possible that the Indian archipelago, some of it about
150 kilometers (90 miles) off northwestern Sumatra and in the
general location of strong aftershocks, may have been changed for
good.

Local Coast Guard Commander Anil Pokhariyal said his aerial
survey of the islands indicated that one may have been cut in two
and another divided into three since the disaster. A third
island, Sentinelese, appears to be reshaped, he said.

"A long stretch of coral reef, which used to be under the sea,
has now emerged overland," he said. "The island appears to have
tilted -- one side submerged and the other emerging above water."

However, it is not yet clear whether such reported changes are
due to the tsunami, which creates only temporary changes, or to
the quake, which can make permanent ones, said Christophe Vigny,
a geophysicist at France's National Center for Scientific
Research in Paris.

In Sumatra, study results due within the next three weeks will
verify whether any apparent changes are the result of temporary
floodwater cover or real remolding, Subarya said. If the
landscape has been reformed, he said, it is likely to have been
only by centimeters (fractions of inches) -- an invisible
difference.

He said the entire island had apparently moved a few
centimeters closer to India immediately after the quake, but
measurements taken Tuesday showed it has mostly moved back in the
week since the disaster.

Major immediate landscape changes are more likely to be caused
by volcanoes than earthquakes, scientists say. For instance, the
1883 explosive eruption of Indonesia's volcanic Krakatoa island
left only one-third of the island above sea level and formed
nearby new islands of pumice and ash.

The Dec. 26 tsunami hammered some Indian Ocean coastlines
harder than others, and scientists say several factors explain
why.

Part of the reason was the wave's shape, Vigny said.
It formed in a north-south line along the quake's fault line,
sending the water's full force east toward Thailand and West
toward Sri Lanka and India. Bangladesh escaped unscathed because
its coast is relatively far north of the epicenter and faces
south.

Myanmar has reportedly suffered less than some neighboring
countries. However, scientists believe its proximity to Sumatra
means it likely took a hard hit, and are skeptical of the ruling
military junta's claims of light damage.

"Many scientists think the wave should have hit the southern
coast of Myanmar. There is no reason why the wave should not get
there," Vigny said.

Another reason the tsunami's impact varied in neighboring
locations is that, while the wave's height is almost uniform in
deep water, its force and behavior are influenced by the shape of
the ocean floor when it approaches land. The sea floor shape can
either focus or hamper the wave, and since every basin is
slightly different, so is every wave.

For example, a steep drop-off from the coastline to the open
sea -- rather than a shallow slope -- can form a natural barrier
that tames a wave's ferocity.
"Every wave has its own interaction with the coastline," Vigny
said.

Concerning demographics, experts say they do not expect the
heavy death toll, which includes a lot of children, to have any
impact on the makeup of populations because younger people are
already heavily represented in many affected areas. Also, the
total death toll in each country, especially Indonesia, is still
a fraction of the population and not enough to make a demographic
dent.

On the Net:

Digital Globe satellite photos of tsunami damage to coastlines:
http://www.digitalglobe.com/tsunami-gallery.html

National University of Singapore satellite Asian tsunami photos:
http://www.crisp.nus.edu.sg/tsunami/tsunami.html