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Is Canada at risk of catastrophic sinkholes?


"A beautiful sinkhole in the North Karst sector of South Nahanni National Park, Northwest Territories," - Derek Ford
"A beautiful sinkhole in the North Karst sector of South Nahanni National Park, Northwest Territories," - Derek Ford

Staff writers

March 7, 2013 — With the deadly Florida sinkhole still fresh on many people's minds, Canadians may be wondering what the risk is here at home.

Photo taken from a Winnipeg newspaper in the 1970s, showing the kind of sudden collapse that is dangerous in inhabited areas (Derek Ford)
Photo taken from a Winnipeg newspaper in the 1970s, showing the kind of sudden collapse that is dangerous in inhabited areas (Derek Ford)

Last Thursday a large sinkhole opened up in southern Florida killing a 36-year-old man who was sleeping in his bed at the time. Just days later, a second sinkhole surfaced in the same neighbourhood. 

"The sinkholes that are giving trouble in southern Florida are developed in limestone, a soluble rock underneath a cover of sand and gravel, which houses like the one that collapsed are constructed on," says Derek Ford, a retired professor of physical geography and geology at McMaster University in Hamilton, Ontario. "Catastrophic sinkholes like this open up very rapidly and there was a time 25 years ago when Florida was averaging 18 catastrophic collapses on its highways per month." 

While catastrophic sinkholes are much less frequent in Canada, there are some sinkhole hazards in a few areas across the country. 

"In Canada, sinkholes develop on limestone and more frequently on gypsum, which is comparatively rare, but there is some in Nova Scotia and southwestern Ontario and a few patches elsewhere," adds Ford. 

He says a couple of problems have also arisen in Montreal, as well as suburban areas of Winnipeg, the front ranges of the Rockies and in parts of British Columbia, particularly on Vancouver Island.

"We've seen quite a lot of recent collapses up in the Northwest Territories as well as global warming is starting to melt the permafrost there."

According to Ford, hazard can arise in inhabited areas of southern Canada when aquifers are over pumped. 

"That's the cause of much of the problems in Florida too," he adds.

Wood Buffalo, Alberta. Collapse here is from below the water table and you can see where new ones are about to breakthrough in spots of stressed (yellow) vegetation. (Derek Ford)
Wood Buffalo, Alberta. Collapse here is from below the water table and you can see where new ones are about to breakthrough in spots of stressed (yellow) vegetation. (Derek Ford)

In comparison however, the risk of large sinkholes across Canada is much lower. 

"In Florida, the rocks are quite young. The limestone rocks form in tropical regions and it's a long time since Canada was cruising in the tropics, so our rocks are older and much harder." 

Ford says the rocks are likely to suffer during periods of glaciation, when the glaciers are receding and tremendous quantities of melt water have been poured into the ground.

Experts warn that aside from studying the geology and avoiding hazardous areas to build, there aren't many warning signs that a sinkhole will occur.

"Unless you put seismologists or recording instruments into the ground to hear the thump of rocks fall 20-30 metres below the surface, there really isn't much you can do," says Ford. "Simply put, just don't build your home on gypsum."

He adds that if you get a small sinkhole developing on your property, which can be more common in Canada, be sure to fill them in right away and don't pump too hard underneath.

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