Sainte-Monique Landslide: What Happened in Quebec

Fernand Therrien left his house in Sainte-Monique only minutes before it vanished into a crater. He escaped with his life on May 21, 2025—but his home did not. The landslide that followed has since been classified as one of the biggest quick clay collapses the province has seen in recent years, with authorities estimating the scar stretched roughly 760 meters long and 150 meters wide near the Nicolet River.

Date of incident: May 21, 2025 · Location: Sainte-Monique, Quebec · Crater size: 760 meters long, 150 meters wide (expert estimate) · Impact: One house destroyed · Fundraising: Nearly $40,000 raised

What is the address of the Sainte-Monique landslide?

The landslide struck along the rang du Haut-de-l’Île, a rural road in the municipality of Sainte-Monique-de-Nicolet, part of the Centre-du-Québec region. The site sits in the MRC of Nicolet-Yamaska, roughly 200 to 300 feet from a stream that was subsequently swept away in the event. According to geolocatable data, the coordinates place the crater near latitude 46.13890 and longitude -72.49700.

The property belonged to Fernand Therrien, whose house was situated along the upper stretch of land overlooking a local waterway. Civil Security officials noted that while Sainte-Monique has a history of smaller ground movements, an event of this scale had not occurred recently in the sector.

Proximity to Nicolet River

The rang du Haut-de-l’Île lies several kilometers from the Nicolet River itself, though local waterways played a role in the disaster. A swollen stream near the Therrien property was cited as a likely contributing factor in the days leading up to the slide, with erosion undercutting the unstable slope. Authorities noted that the stream was carried away in the landslide, potentially explaining part of the mechanism behind the collapse.

Affected property details

The destroyed residence belonged to Fernand Therrien. Video footage from the scene showed the aftermath: a gaping wound in the landscape where the house once stood, surrounded by agricultural land. Two neighboring farms in the immediate sector were also assessed as at-risk following the incident, according to Radio-Canada reporting.

What happened in the Sainte-Monique de Nicolet landslide?

At approximately 6 a.m. on May 21, 2025, residents in Sainte-Monique reported hearing a loud rumble as nearly 100 meters of land shifted along the rang du Haut-de-l’Île. The resulting crater measured roughly 300 meters wide by 100 meters long according to initial authority estimates, though subsequent expert assessment placed the dimensions at 760 meters long by 150 meters wide with a depth near 25 meters.

Fernand Therrien had left his residence only minutes before it was swallowed. His narrow escape was confirmed by Civil Security officials, who stated that had he remained inside, the outcome could have been fatal. No injuries were reported among the seven residents evacuated from the area.

Timeline of the slide

• May 21, 2025, 6 a.m.: Major landslide occurs; Fernand Therrien’s house swept away; crater forms
• May 22, 2025: Fundraising begins for the affected family; nearly $40,000 collected within days
• June–July 2025: Soil samples collected from the site for laboratory analysis
• September 18, 2025: Municipal officials announce stabilization plans for early October
• October 2025: Initial stabilization work begins; trimming of crater scar with long-reach machinery
• March 2026: Rock reinforcement of adjacent waterway completed at a cost of approximately $800,000

Immediate impacts

Two residences were evacuated immediately following the slide, affecting seven people in total. Two farms in the sector were flagged as potentially at risk. Heavy rainfall in the preceding days and a swollen stream were identified as contributing factors, according to Le Nouvelliste reporting. Experts contacted by EOS Science described the event as a textbook quick clay landslide—the kind that has devastated communities across Canada’s sensitive clay regions for generations.

What is the current status after the Sainte-Monique landslide?

Rock reinforcement work on the unnamed stream adjacent to the crater was completed by March 2026, representing the first major phase of stabilization. The Ministry of Transport and Sustainable Mobility has not yet finished additional geological testing at the site, which would be required before residents could receive full clearance to return.

As of March 29, 2026, two families—including those whose homes were not destroyed—remained unable to return to their residences. Families living in the area have expressed ongoing concerns about soil fragility, and officials acknowledge that psychological impacts from the evacuation persist alongside the physical recovery.

Stabilization efforts

The initial stabilization phase, which began in early October 2025, involved trimming and reshaping the crater walls using heavy machinery with extended reach. Engineers worked to reduce the angle of the scar and prevent further sloughing into the void. An unnamed stream located roughly 200 to 300 feet from the crater was reinforced with rock as a preventive measure to guard against further erosion.

Soil samples collected in June and July 2025 were sent for laboratory analysis, with results expected by late October of that year. The cost of the waterway stabilization work alone reached approximately $800,000, according to Via 905 FM reporting.

Return to normal

Full access to the affected properties remains restricted pending further testing by the Ministry of Transport and Sustainable Mobility. Municipal authorities continue to monitor the site, and residents have been assured that additional safety assessments are underway. The timeline for when the remaining families can safely return home has not yet been publicly confirmed.

How was the community affected by the Sainte-Monique landslide?

The immediate human toll was significant though not fatal. Seven people were evacuated from two households, and a third family’s property—the home of Fernand Therrien—was consumed entirely. The community fundraiser launched the following day collected nearly $40,000, demonstrating local solidarity with the displaced residents.

Beyond the physical destruction, the landslide has left a psychological mark. Residents of the sector have lived with uncertainty for nearly a year, watching stabilization crews work while wondering when—or if—they can safely go home. The broader Sainte-Monique area, while accustomed to occasional ground movement, had not experienced a collapse of this magnitude within recent memory.

Evacuations

Evacuation orders were issued for two residences immediately following the slide, affecting seven individuals. Two neighboring farms were also assessed as at-risk, though their occupants were not formally evacuated. The seven evacuated residents were temporarily housed with relatives or in emergency accommodations arranged by the municipality.

Fundraising for owner

A GoFundMe-style campaign raised nearly $40,000 for the Therrien family within the first 24 hours, according to local media reports. The response reflected both the generosity of the surrounding community and the recognition that the displaced family would face significant costs for temporary housing, legal documentation of their losses, and eventual resettlement.

We didn’t expect anything like this to happen here. Our street has been here for generations—we thought the ground was solid.

— Affected resident, via Radio-Canada interview

The families are asking us every day when they can go back. We don’t have an answer yet, but we know the soil is fragile and we have to be certain.

— Municipal official, as reported by Via 905 FM

What is known about the Sainte-Monique crater?

The crater left by the Sainte-Monique landslide is among the most substantial quick clay scars documented in Quebec in recent years. Expert analysis from EOS Science, which tracks landslide events globally, estimated the feature at 760 meters long and 150 meters wide, with an approximate depth of 25 meters at its deepest point. Initial measurements from authorities had placed the width nearer to 300 meters, suggesting the final extent of the collapse became clearer as surveys continued.

The crater’s elongated shape reflects the mechanics of quick clay failures, which typically propagate along weaknesses in the clay layer. Geologists note that the material can retain water in a semi-stable state for decades before a triggering event—often heavy rain, river erosion, or human construction—causes it to lose strength abruptly.

Dimensions

• Length: 760 meters (expert estimate via EOS Science)
• Width: 150 meters (expert estimate) to 300 meters (initial authority estimate)
• Depth: Approximately 25 meters
• Volume displaced: Not publicly quantified

Formation

Quick clay landslides occur when sensitive marine clay deposits—formed from glacial sediments deposited in ancient seas—experience a reduction in their natural salt content. Freshwater percolation, as from heavy rainfall or stream erosion, leaches the salt that helps the clay maintain structure. The result is a material that can behave like a liquid when disturbed.

Sainte-Monique sits atop Leda Clay, a geological formation that stretches across parts of Ontario and Quebec and has been responsible for numerous historical disasters. The 1955 Nicolet landslide, just a few kilometers away, resulted in 3 deaths, 2,000 evacuees, and $7 million in damages—reminding residents that the region carries inherent risks that have no simple engineering solution.

Related reading: Mon Dossier Santé Québec

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