A sinkhole in Saint-Jude, Quebec
has just collapsed a house, killing a family of four inside, leading people to ask what they are, how they occur and obviously who is at risk.
Sinkholes are depressions that occur when soil or bedrock has been removed and only air remains - commonly when the rock below the land surface is limestone, carbonate rock or salt beds that have been naturally dissolved by ground water circulating through them and then the water dries up.