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

A devastating landslide that engulfed a home and created a massive 300-meter crater in a rural road in central Quebec has left many puzzled about how such an event could occur. When we typically think of landslides, we envision rocks and debris cascading down a slope, not a flat expanse of land collapsing in on itself. However, in southern Quebec, this type of landslide is quite common due to the region’s topography and clay-rich soil.

Simon Legault, a science communicator with Ouranos, Quebec’s climatology and climate change innovation hub, explained that the St. Lawrence Valley is predominantly covered in clay, making landslides more likely. He described landslides as the “movement of soil,” often manifesting as a muddy slide or soil losing its consistency and slowly drifting into lower areas, such as the nearby stream in Sainte-Monique.

According to data from the Quebec government, approximately 100 landslides and instances of unstable ground are reported to municipal authorities each year, with clay soil and proximity to waterways increasing the likelihood of such events. These occurrences are more frequent in the spring and fall, or during extreme weather events.

Professor Philippe Gachon from Université du Québec à Montreal highlighted the significance of Wednesday’s landslide, noting its unprecedented magnitude in recent Quebec history. He emphasized clay soil as a landslide risk and attributed the decreased stability of the land to increasingly extreme weather conditions.

Clay soil can become unstable due to excessive rainfall or prolonged dry spells, both of which Quebec has experienced in recent years. As climate change leads to more erratic weather patterns, understanding the water cycle in the province becomes crucial to mitigate the risk of landslides. Gachon warned that Quebec is vulnerable to hydrological “whiplash” from alternating wet and dry periods, underscoring the need for proactive measures in a changing climate.

Both Legault and Gachon believe that climate change will heighten the risk of landslides in the future. With projections indicating increased rainfall and earlier spring thaws, the ground will become more saturated, potentially leading to liquefaction and ground movement. While the risk of landslides may rise, it can be mitigated through proper land management practices.

Currently, 40% of reported landslides in Quebec are linked to human activities that impact slope stability. These activities include constructing buildings on hillsides, excavating at the base of slopes, altering water flow towards slopes, and deforestation. Municipal and provincial authorities are working to identify high-risk areas and educate the public about landslide risks.

In conclusion, as climate change continues to reshape our environment, understanding and addressing the factors that contribute to landslides will be crucial for safeguarding communities and infrastructure in Quebec. By adopting sustainable land management practices and raising awareness among the population, we can mitigate the impact of landslides and ensure the safety of all residents.