Sinkholes in Canada

Sinkholes in Canada are actually a very common occurrence.  Sinkholes are common where the rock below the land surface is limestone, carbonate rock, salt beds, or rocks that can naturally be dissolved by the ground water circulating through them.  While many sinkholes are caused naturally by erosion and landslides under the surface of the earth, the sinkholes in Canada are in many cases man made.  Most sinkholes in Canada form under roads, due to the rupture or cracking of water and sewage lines underneath the roads.  The harsh winter and constant freezing and defrosting of these water systems puts a great amount of stress on the pipes below the roads.  Even a small leak can cause water to gradually seep into the soil under the roads, which will compromise the ability of the soil to support the surface above.  Over time, this can cause serious damage to the pipes and roads.  In some cases, when the pipes burst, the volume of water released into the earth can create sudden sinkholes with little or no warning signs.  

Certain areas of Canada are more prone to sinkholes do to a surface or subsurface layer of soft silt, leftover from the latest ice age.  This soft soil can cause risks of subsidence, especially near train tracks in remote areas.  Due to the large amount of snow melt each year, the runoff can cause the silt to soften and erode.  If the wrong structure is built on top of this silt, the structure can be destroyed.  This issue has been addressed, and efforts are being made to use higher quality materials in the construction of roads and water lines.  Many of the older, existing roads were built with a softer clay like soil beneath them.  Officials have worked to identify current risks for sinkholes, and are attempting to reinforce these areas.  This can prove to be difficult, as it would cause road closures and is an expensive process.  

http://www.canadianunderwriter.ca/news/hole-picture/1002925051/?&er=NA

http://globalnews.ca/news/401401/a-list-of-the-worst-sinkholes-in-canada-and-around-the-world/

http://www.cbc.ca/news/canada/why-the-ground-suddenly-gives-way-1.907424