Loud boom-like noises that rippled through parts of southern Ontario early Monday morning were likely caused by frost quakes, police say.
CP24 viewers in York Region and Kawartha Lakes reported multiple booms that echoed in the early morning hours.
Similar noises were heard north of Toronto on Christmas Eve.
Police believe cryoseisms, also known as frost quakes, are responsible for the sounds.
Frost quakes are a rare event and they occur when water seeps into the ground, freezes and then rapidly expands.
The explosive expansion of air is similar to a thunderclap, said CP24 meteorologist Bill Coulter.
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