OTTAWA -- Richard Prefontaine and his wife, Lynne Charbonneau, were watching a playoff hockey game with their two daughters on Monday night when the ground beneath their house gave way suddenly and without warning.
The houseâs bright green metal roof was all that was visible the next day in a vast mud crater near the village of St. Jude, Quebec, about 50 miles northeast of Montreal. The landslide created a hole 100 feet deep, 300 yards wide and a third of a mile long.
The family's remains were found huddled together on a couch by the television, with rescuers discovering only their golden retriever, tied to a tree, alive.
On Wednesday, officials allowed residents of several nearby houses to return home. But the family's shocking demise was a stark reminder of a hidden menace under many parts of Quebec, one that dates back 10,000 years to an ancient inland sea.
Michel A. Bouchard, a professor of geology at the University of Montreal, said the area around St. Jude rests on an unusual variety of "sensitive clay" that was originally the bed of an ancient sea. Lake Champlain is a remnant of the sea.
Because the clay formed in salt water, Professor Bouchard said, the molecular structure of its particles resembles playing cards arranged as an unstable house of cards, rather than stacked in a deck, as occurs with clay formed in fresh water. A variety of events can break the molecular bonds holding the clay particles together. When that occurs, the clay can spontaneously liquefy with little or no provocation.
"Even a fly landing on the surface can set it off," he said.
The landslide took place so quickly and silently on Monday night that many neighbors could not understand why their electricity and water supply had been disrupted. The collapse removed a large section of road, sending a pickup truck into the crater. It took the injured driver about an hour to crawl to safety.
Deadly or disruptive landslides involving the clay, sometimes known as Leda clay, take place occasionally in Quebec and eastern Ontario. In 1971, 31 people died and 40 houses were destroyed by a landslide in St.-Jean Vianney, Quebec. The town of Lemieux, Ontario, east of Ottawa, was relocated in 1991 after officials became concerned about the stability of the clay underneath the town. Two years later, a landslide consumed 42 acres near Lemieux's former location.