updated 1/5/2005 7:51:05 PM ET 2005-01-06T00:51:05

Water depths in parts of the Straits of Malacca, one of the world's busiest shipping channels off the coast of Sumatra, reached about 4,000 feet before last month's tsunami. Now, reports are coming in of just 100 feet  — too dangerous for shipping, if proved true.

A U.S. spy imagery agency is working around the clock to gather information, warn mariners and begin the time-consuming task of recharting altered coastlines and ports throughout the region.

Officials at the Bethesda, Md.-based National Geospatial-Intelligence Agency say the efforts will take international cooperation over months, if not years.

Thousands of navigational aides, such as buoys held in place by mushroom-shaped anchors, were carried off to new locations by 50-foot to 100-foot waves. Old shipwrecks marked on charts have been relocated, joined by new wrecks that will have to be salvaged, moved or charted.

But there might be a silver lining in the devastation.

"Maybe there's less pirates now," says Peter Doherty, who works at the agency and is chairman for the International Hydrographic Organization's commission that sends out radio navigational warnings.

He and others are hoping that the waves carried away the modern-day Blackbeards. These thieves trolled the waters in high-speed boats, armed with guns, knives and grappling hooks, which they used to climb the sides of ships to steal them and their goods.

Just how different the ocean floor looks remains largely a mystery. The bulk of the tsunami recovery effort has gone toward humanitarian relief. Gradually, however, attention will turn to what it will take to make the region's waters safe. Among the first priorities will be making the channels safe for relief shipments.

New configurations
The U.S. agency, which analyzes spy satellite imagery and produces maps and charts for the Defense Department, has so far sent out two tsunami-related warnings on a Pentagon messaging system and made them available publicly on its own Web site.

Ports of call may be heavily damaged "to include unknown new bottom configurations, ship wrecks, shoreline changes and depth limitations," according to a warning from Dec. 29.

"In addition," the notice said, "aids to navigation may be damaged, inoperable, off station or even destroyed. ... Proceed with extreme caution."

The agency has received an unconfirmed report that one area of the Strait of Malacca, which divides Malaysia and the devastated Indonesian island of Sumatra, had its depth cut from 4,060 feet to just 105 feet.

In another area of tsunami-effected waters, a merchant marine ship has logged that the depth was cut from 3,855 feet to just 92 feet.

Whole channels moved
The agency's chief hydrographer, Chris Andreasen, said experts may find that whole channels were moved by the earthquake that preceded the tsunami, shifting the ocean floor many feet, rather than the inches seen during the 1989 California quake during the World Series.

"When the plate moves, everything on it moves," Andreasen said. "There could be some pretty serious shifts."

Warnings about the new oceanic landscape go out right away. But the agency waits to update its charts until it gets final confirmation.

Among other international operations, the Navy is sending two ships to begin efforts to rechart the waters. One, the USNS John McDonnell, could arrive by next week.

It is expected to be followed by the newer USNS Mary Sears, which is awaiting final orders to head out from Japan. On board will be sonar, a dozen scientists and 34-foot vessels used to rechart the shipping channels.

The initial goal is not to study every square foot, but to understand what happened to the channels so the ports can be used to deliver relief supplies. Now, helicopters and airplanes are the primary means, said Capt. Jeffrey Best, commanding officer at the Naval Oceanographic Office at Stennis Space Center in Mississippi.

The Navy does not know what it will find. "We may have buildings or buses in the channels of the harbors," Best said.

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