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Frost Quakes Frighten Some Chilled by Polar Vortex January 10, 2014
Frozen Toronto skyline.
Toronto residents were among those rattled by frost quakes during the New Year's deep freeze.
The most brutal chill in decades, which plunged the American Midwest and parts of southern Canada into a sudden deep freeze, also triggered loud booms that sounded like explosions or falling trees.

Meteorologists assured nervous residents that the sounds were being caused by a relatively rare phenomenon known as “frost quakes.”

The booms occur when water in the soil freezes and expands in extreme cold, causing the ground to suddenly fracture like a jar of water in the freezer.

Also known as cryoseisms, they can only happen when the ground has been saturated by heavy rain shortly before a quick freeze sets in.

Such conditions have not occurred on a large scale in decades, leaving some people witnessing the quakes for the first time in their lives.

Environment Canada meteorologist Geoff Coulson told the Toronto Star that one jolting metropolitan Toronto was the first he had experienced in 30 years.

Photo: David Wing Flickr