‘Ottawa’ What Went Down in Ottawa? The Science of Sinkholes Explained
Sinkholes that open up vast chasms in the ground — sometimes big enough to swallow cars, houses or even three-storey buildings — may seem like Mother Nature throwing a massive tantrum.
But there’s a science to how they form. Here’s how it works.
Andres Plana/Metro
Sinkholes can form in lots of ways. They’re especially common in areas where the bedrock contains bases like calcium carbonate, which react with acid in rainwater and groundwater. Ontario’s abundant limestone is calcium carbonate.
Water seeps into the rock’s nooks and crannies, dissolving it and opening up a cavern underground that may not be visible above.
When it gets big enough and close enough to the surface, the “roof,” often made of clay or soil, can cave in, sometimes quite quickly and dramatically. Presto: Sinkhole!
Sinkholes: Often our fault
Human activity is often to blame for sinkholes: pumping of groundwater, construction of sewer lines, mining. A disturbance that prevents surface water from being able to drain away, causing it to collect underground, could be a recipe for a sinkhole. Under a downtown street in Ottawa this week, a water main broke, but it’s not yet clear if the break caused the sinkhole, or the reverse.