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Perfectly round sinkholes, ancient river beds and shorelines have been revealed in what was once a fresh water Cape Breton lake.
The sinkholes on the floor of the Bras d'Or Lakes are not found in any other lake in Canada, said John Shaw, a research scientist with the Geological Survey of Canada (Natural Resources Canada),
attached to the Bedford Institute of Oceanography.
"The bottom of the lake in some places looks like Swiss cheese." It is peppered with sink holes, circular depressions, some of which are 150 metres (495 feet) deep.
"It is unique to the Bras d'Or Lakes, an amazing discovery," said Shaw, who noted one of the sink holes (30 metres deep), near Baddeck is still active, it's sinking, and will require further study.
The circular sinkholes are not all that uncommon on land in Cape Breton and can be found near gypsum deposits.
The Geological Survey of Canada has been actively surveying the lake for two years and comparing it with historical data collected by the Canadian Hydrographic Survey.
The information and what the data reveals about the lake's ecosystem, through maps and coastline is being made available to First Nations groups, organizations interested in the Bras d'Or Lakes and the province.
Shaw said the team used a new multi-beam sonar system which produced a series of images that has allowed them to uncover a number of mysteries about the lake.
"We found one or two strange objects, we are not sure what they are," he said.
The study showed that about 7,000-8,000 years ago the surrounding sea level was much lower and the Bras d'Or Lakes was a series of small fresh water lakes.
"The multi-beam sonar allowed us to see ancient beaches, shores and spits 25 metres from the present shoreline. If we could drop the level of the lake down we would seen a small lake at Whycocomagh connected by a river off Baddeck to the larger lake.
"It's a meandering river, well preserved. Sonar will give us that kind of image and we do it in colour."
A geophysical survey included the taking of sea floor samples and cores which form part of the review paper.
It was the 10-day survey in May by the team that showed the Swiss cheese-like bottom west of Baddeck caused by the dissolution of the gypsum deposits under the sea floor.
Shaw said the new data should be of interest to First Nations.
"We found ancient beaches and if ancient peoples lived on the shores of the lakes that is where we will find their remains.
"Their cultural remains are under water, that is why we don't find them on land," he pointed out.
The sonar also found a "big object" north of the Narrows, near Iona, which looks man made. It may be a large barge, he added.
The new information will be used by the Eskasoni Institute of Natural Resources and the province as they continue to develop plans related to the management of the lake and nearby land.
"There are worries about pollution, this will give people basic maps and bottom types," said Shaw whose specialty is sea level change.
A map of the coastline will be made to assess sensitivity to sea level rise and its ongoing impact on the lake.
wstewart@cbpost.com
Copyright 2003 Cape Breton Post
