Soil and Bedrock Instability

Unstable soils and bedrock are naturally occurring hazards that pose a threat to life and property.  As a result, property or lands could be unsafe for development and site alteration. 

Through the Provincial Policy Statement (PPS ), MNR has identified hazardous sites as areas of provincial interest. Unstable soils and bedrock can become hazardous from the impacts of heavy rainfall or geological processes (earth tremors, freeze-thaw soil action), human modification, or combination of all the above.

Soil instability-slumping

Soil instability can occur where slopes or shorelines exist.  Generally, areas where precipitation is ample, land use has changed, and moderate to steep slopes exist are most at risk. 
 

Examples of Soil and Bedrock Instability Hazards found in Ontario

• Sensitive Marine Clays (Leda clays)
  These clays were deposited as sediment during the last glacial period in the Champlain Sea.  They are generally located in Eastern Ontario.  Undisturbed, the clays can appear as solid and stable.  But when disturbed by excessive vibration, shock or when they become saturated with water, the clay can turn to liquid, sometimes in minutes.
• Organic Soils
  Organic and peat soils are formed by the decomposition (breakdown) of vegetative and organic materials into humus; they lack stability to support foundations as well as drainage.
• Karst Formations
  Unstable bedrock sites in Ontario are either Karst formations or soft bedrock along valley lands or shorelines.  Karst formations are areas where water flowing over and through limestone and dolomite bedrock deposits creates sinkholes, trenches and underground caverns.

   

Given the vast variation in Ontario’s geological landmass, this last hazard poses differing levels of risk to given communities and geographic areas throughout the Ontario.  The risk can best be determined through geoscience information and historical events.