|Saint-Jean-Vianney was a village in the Saguenay-Lac-Saint-Jean region of Quebec, which was partially destroyed in a landslide on May 4, 1971.|
Located near the shore of the Saguenay River, Saint-Jean-Vianney was — unbeknownst to residents at the time — built atop a bed of unstable Leda clay, a type of subsoil which can liquify under stress.
Following unusually heavy rains in April 1971, the clay soil bed at Saint-Jean-Vianney became saturated with water that had failed to run off, causing pockets of clay to gradually dissolve. Over the few weeks leading up to the landslide, cracks were reported in some of the town's streets and driveways, some house foundations dropped roughly six to eight inches into the soil, and some unusual noises — including underground thumps and an untraceable sound of running water — were reported.
At 10:45 p.m. on the evening of May 4, the earth at Saint-Jean-Vianney suddenly dropped approximately 100 feet, forming a canyon through which a river of liquefied clay flowed toward the Rivière du Petit-Bras below, swallowing houses in its path. Just before midnight, the clay finally stopped flowing and began to resolidify. By the time the landslide had ended, 41 homes had been destroyed and 31 people had been killed.
The landslide created a crater of approximately 324,000 square metres in area, varying from 15 to 30 metres in depth.