Quebec's clay-rich soil raises landslide risk — even with no significant slope

Annabelle Olivier · CBC News

· Posted: May 23, 2025 4:00 AM EDT | Last Updated: 1 hr ago

A landslide that swallowed a location and near a 300-metre crater successful the mediate of a agrarian roadworthy successful cardinal Quebec connected Wednesday has near galore wondering however it could person happened. 

Usually erstwhile radical deliberation of landslides, they deliberation of a slope with rocks and debris rushing down and not a seemingly level expanse of onshore appearing to illness successful connected itself. 

As it happens, however, the benignant of landslide that deed Sainte-Monique, Que., connected Wednesday is rather communal successful confederate Quebec, owed to the province's topography and its soil.

Simon Legault, a subject communicator with Ouranos — Quebec's climatology and clime alteration innovation hub — explained that astir of the St. Lawrence Valley is covered successful clay.

He described landslides arsenic the "movement of soil."

"So what we mostly spot successful confederate Quebec is conscionable similar a muddy descent oregon conscionable ungraded that loses consistency oregon becomes a small spot much liquefied and conscionable dilatory drifts into the little onshore around," helium said.  In Sainte-Monique, that "lower land" was a adjacent stream.

According to information connected the Quebec authorities website, astir 100 landslides and incidents of unstable crushed are reported to municipal authorities each year. They hap much often successful clay ungraded and adjacent waterways, and are much predominant successful the outpouring and fall, oregon during utmost meteorological events. 

Extreme upwind makes onshore little stable

For Philippe Gachon, a prof astatine Université du Québec à Montreal's geography department, what stands retired successful Wednesday's lawsuit is the landslide's magnitude which "has seldom been seen successful caller years successful Quebec."

In a telephone interrogation with The Canadian Press, Gachon pointed to clay arsenic being a landslide hazard and added the onshore has go little unchangeable owed to much utmost upwind conditions.

Clay tin go unstable owed to excessive rainfall oregon utmost dryness, helium explained — and Quebec has seen some successful caller years.

"Clay doesn't similar erstwhile there's excessively overmuch water, and it doesn't similar it either erstwhile determination isn't capable h2o due to the fact that it has a inclination to fracture," helium said.

As utmost upwind becomes much common, helium says it's captious to amended recognize the entirety of the h2o rhythm successful the province, which helium said is susceptible to hydrological "whiplash" owed to alternating periods of utmost bedewed and dryness.

"It's wide that with clime change, we're going to look events we've ne'er experienced before, definite phenomena we've ne'er seen earlier successful history," helium said.

Climate alteration increases risk, adept says

Legault besides believes clime alteration is apt to summation the hazard of landslides successful the future.

Over the adjacent decades, helium says the state is expected to spot much rain, and an earlier onset of the outpouring thaw, allowing much h2o to penetrate into the ground.

"Water is simply a origin that tin lend to crushed question oregon landslide due to the fact that you request to person much water, oregon an excess of h2o wrong the crushed that causes that liquefaction," helium said.

The higher hazard of landslides, however, doesn't needfully mean accrued frequency, helium said, "depending connected however we accommodate the terrain." 

Currently, estimates amusement that 40 per cent of reported landslides are linked to "poor practices associated with quality activities that impact slope stability," according to Ouranos' website. 

"We person earthy landslides, but we sometimes person populations that are conscionable modifying slopes," Legault said.

Things similar gathering a operation connected apical of a hill, excavating astatine the bottommost of a slope, gathering thing that would nonstop much h2o toward a slope oregon cutting trees, are each examples of activities that could lend to expanding the hazard of landslides. 

Legault said municipal and provincial authorities are moving to amended recognize the laic of the onshore to cognize wherever risks are highest. This enactment indispensable continue, helium said, and it's important that the colonisation knows the risks arsenic well.