May 9, 2010

World’s Largest Dam Can Be Seen From Space

A Canadian ecologist has discovered the world's largest beaver dam, located in a remote area of northern Alberta, which can be seen from space.

Researcher Jean Thie said he used satellite imagery and Google Earth software to find the dam, which is about 2,800 feet long on the southern edge of Wood Buffalo National Park.

The average beaver dam in Canada is about 32 to 328 feet long, and it is rare to even see one as big as about 1,640 feet.

The dam, which was first discovered in October 2007, is located in a virtually inaccessible part of the park south of Lac Claire about 120 miles northeast of Fort McMurray.

Thie said the construction of the dam most likely started in the mid-1970s.  He made the discovery by accident while tracking melting permafrost in Canada's far north.

"Several generations of beavers worked on it and it's still growing," he told AFP in Ottawa.

Mike Keizer, a spokesman for the park, said rangers flew over the heavily forested marshlands last year to try and "have a look."  He said they saw significant vegetation growing on the dam, suggesting it's old.

"A new dam would have a lot of fresh sticks," Keizer told AFP. "This one has grasses growing on it and it's very green."

Part of the dam may have been created by naturally fallen trees, and the beavers may have just "opportunistically filled in the gaps."

Thie said he also found two smaller dams sprouting at either side of the main dam.  He said that in 10 years, all three structures could merge into a mega-dam measuring just short of a mile in length.

The region is flat, causing the animals to build a massive structure to stem wetland water flows.  Thie said the dam was visible in NASA satellite imagery from the 1990s.

"It's a unique phenomenon," he said. "Beaver dams are among the few animal-made structures visible from space."

North American beavers build dams in order to create deep, still pools of water to protect against predators, as well as to float food and building materials.

A 2,139 feet structure originally held the record for the world's largest beaver dam in Three Forks in the U.S. state of Montana.

Thie said he found evidence that beavers were repopulating old habitats after being hunted extensively for pelts in the past centuries.

"They're invading their old territories in a remarkable way in Canada," he told AFP. "I found huge dams throughout Canada, and beaver colonies with up to 100 of them in a square kilometer."

"They're re-engineering the landscape," he added.


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