– It Was So Cold in Canada, the Ground Exploded (Gizmodo, Jan 7, 2014):
Even before the polar vortex put large swathes of the US into a deep freeze, subzero temperatures in Canada were causing frost quakes. A few nights ago, residents around Ontario woke up to mysterious booms—like an explosion or falling tree. Turns it was just the cold.
Like a glass jar of water in the freezer, the ground can crack as liquid water expands while freezing into ice. Frost quakes, or cryoseisms, require a sharp temperature drop: It must be warm enough for water to first saturate the ground and then suddenly cold enough for a quick freeze. The explosions are so loud because frost quakes happen so close to the surface. And as disruptive as they sound, they’re unlikely to be dangerous.
Frost quakes have also been reported in the midwest and New England, but they are generally quite rare. Environment Canada meteorologist Geoff Coulson told the Toronto Star it was the first he experienced in 30 years. [Toronto Star via Outside]