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Devastating slide in Quebec 'was like the end of the world' Add to ...

In the third period of the hockey game, with their beloved Habs on the way to victory, the Préfontaine family was nestled around the big TV in their basement living room when the land gave way with a ferocious roar.

The first hint for some of the neighbours in Saint-Jude, a village about 50 kilometres northeast of Montreal, came when power was cut to their own television sets. Others heard the noise when thousands of tons of clay that had been still for 10,000 years went rolling down the river bank. They thought an earthquake had struck, so they set out along Salvail Road to see what had happened.

At the bottom of a new gully, Richard Préfontaine and Lyne Charbonneau, along with their two daughters, 12-year-old Amélie and nine-year-old Anaïs, were trapped. With their house up to the eaves in mud, officials confirmed all four dead Tuesday evening, nearly 24 hours after the slide.





After the land caved in, neighbours came upon the immense hole in the earth, as long as a kilometre, which cut the paved road along the rolling river valley with two 10-metre cliffs.

"The trees were gone, the earth was gone, it was like the end of the world," said Herman Gagnon, who was among the first to come upon the crater.

The cause of the destruction is as common as dirt - or rather a layer of unstable clay that lies beneath it. Millennia ago, a huge body of water known to geologists as the Champlain Sea covered an area from Ottawa to Quebec City. The clay and thin layer of topsoil were left behind when the Champlain Sea, itself a product of ice age glaciers, receded.







The Leda clay, as it is called, is a slide waiting to happen. Didier Perret, a research scientist with Natural Resources Canada, says the "sensitive" clays are found throughout southern Ontario and southern Quebec. When the clay is disturbed - perhaps by erosion of a river bank - a slide or "earth flow" occurs. Major slides happen every two years or so on slopes in this region, but most occur in places that are not inhabited.

"When not disturbed, these clays behave very well," he said, "but when they are [disturbed] they behave like fluid."

Deposits of Leda clay can be 15 to 100 metres deep, and typically sit below a layer of sand about one or two metres deep and on top of a layer of till.

The salt water environment in which the clays were deposited is what makes them unstable, said geological engineering professor Erik Eberhardt of the University of British Columbia.

"Clays that are deposited in fresh water are like a deck of cards," Dr. Eberhardt said. "But the clays deposited in the salt water environment, they stack end-to-end in a way that would look like a card house. So if I hit a deck of cards, it wouldn't do anything, but if I hit a card house … it would come tumbling down and flatten."

That appears to be what happened just before 9 p.m. on Monday. The Préfontaine house dropped at least 20 metres and moved about 150 metres closer to the Salvail River before it was buried nearly to the green metal roof in mud and water.



Power poles, displaced about 100 metres down the hill, still stood, their tips now several metres below ground level. A man driving a red pickup truck drove off the edge of the new cliff, near the Préfontaine home, plunging into the mud. He was not seriously hurt, police said.

Search and rescue teams spent a full day digging and draining away a soupy mixture of clay and water, using a backhoe to dismantle the 15-year-old family home. They planned to work around the clock to rescue survivors or get the bodies out of the basement.

"Our crews saw in Haiti, and we've seen in mine disasters, how there can be pockets where people survive for days," said Michel C. Doré, the co-ordinator of the rescue effort for the provincial Public Security Ministry.

Anxious family members stood about a kilometre away, waiting for word. "I still can't believe it," said Sébastien Charbonneau, Lyne's teenage son from a previous relationship. Sporting his Habs cap and hoodie, he skirted a police roadblock and set out on foot to get a better look.

What he saw had the appearance of a combination earthquake and meteor strike. The slumping ground collapsed from 10 to 20 metres toward the river. Blocks of clay were strewn about, some capped with closely-trimmed lawn.

The family dog, Foxy, survived tied to a tree. The dog appeared to be dead at first but snarled and snapped at rescuers before they led it away to waiting family.

Mr. Préfontaine, an electrician, was known in the village as a nature enthusiast. He was often spotted in his canoe on the Salvail River, taking photos of birds.

"They are lovely people, and they had the nicest house on this road," said Lucette Arpin, a neighbour who broke news of the slide to Ms. Charbonneau's son Monday night.

Ms. Charbonneau worked in a nearby daycare. In the Grade 4 class of the younger girl, Anaïs, her empty desk was a heavy presence for classmates.

"Every class has a life of its own, and an empty desk is very difficult for everyone," said Chantal Chagnon, principal of Aux-Quatre-Vents elementary school in Saint-Jude.

Village mayor Yves de Bellefeuille said the area along the river valley had been designated as a "low risk area" for landslides, although much of the St. Lawrence River Valley, where most Quebeckers live, sits on a slippery layer of clay.

Several small, fresh slides dot the bank of the Salvail River along the few kilometres of highway from Saint-Jude to the Préfontaine home. A bit farther down the road, the wreckage of an old collapsed bridge still sits alongside a stream.

Mr. de Bellefeuille said three dozen homes sit along this stretch of river and he's received dozens of calls from concerned residents. He and provincial experts say the area is safe.

"If we wanted to move everyone away from areas with this kind of ground, we would have to move a lot of very large population centres," said Mr. Doré.

"This is the reality we live in, but it's rare to see something on this scale."

With a report from Wency Leung

Sensitive deposits of leda clay, found in parts of Ontario and Quebec, can be 15 to 100 metres deep and typically sit below a layer of sand (about one or two metres deep) and on top of a layer of till.

Glaciers that covered the south of Ontario and Quebec with about two to three kilometres of ice 20,000 years ago are responsible for the clay deposits, according to Didier Perret of Natural Resources Canada. As the glaciers thawed, water from the Atlantic Ocean poured into the area, creating the Champlain Sea, which stretched between Ottawa and Quebec City. As the climate chnaged, the Champlain Sea eventually retreated, leaving the clays behind, he says.

The salt water environment, in which they were deposited, is what made them unstable, said geological engineering professor Erik Eberhardt of University of B.C. "Clays that are deposited in fresh water are like a deck of cards," Dr. Eberhardt says. "But the clays deposited in the salt water environment, they stack end-to-end in a way that would look like a card house. So if I hit a deck of cards, it wouldn't do anything, but if I hit a card house...it would come tumbling down and flatten."

Dr. Eberhardt says a change in water pressure in the ground or any type of tremor can trigger a collapse. Mr. Perret adds that one of the main triggers of previous landslides in the area is river bank erosion, which can be worsened by rainfall and melting snow.

Wency Leung

Follow on Twitter: @Perreaux

 

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