Rare ‘frost quakes’ boom through the Greater Toronto Area

Looks like our good old-fashioned Canadian winter is making the rare 'frost quake' a little less rare this season.

In the early hours of Friday, right around 2 a.m., reports of strange booming sounds around the Greater Toronto Area and even farther afield lit up social media sites as people wondered if they were being robbed, haunted, or just hearing things.

[ Related: Eastern Canada plunges into deep freeze as roller coaster winter rolls on ]

While I can't say for certain that no one reporting booms on Twitter suffered from the other three problems (well, they weren't being haunted, at least), last night there were definitely more frost quakes — or cryoseisms — happening in southern Ontario. The region first heard some of these telltale sonic booms on Christmas Eve, as temperatures plunged following the ice storm that swept across eastern Canada. With much of Southern Ontario once again in the deep freeze, it's not entirely surprising that more quakes were felt last night, even if the shocks themselves can be startling.

Cryoseisms happen when water in the ground freezes and expands, and are most common later at night when the ground has had longer to cool after sunset. Anyone who's ever put a glass jar filled with water in their freezer knows what happens when the water turns to ice (tip: if you're going to try this, first get permission from whoever owns the jar and the freezer, be sure to put the jar in a big Ziploc bag, and don't be too alarmed at the results). Since water expands when it freezes, the little veins of water filling crevices underground put tremendous pressure on the soil and rock around them when they freeze. Put enough pressure on the rock and ... BANG!

Although they're called 'frost quakes', cryoseisms are far less dangerous than the more common tectonic earthquake. They can crack the ground right at the location where they happen, so anything built on that ground might suffer some damage, but the biggest effect is the loud booms that are produced when they go off.

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These quakes aren't the only strange sounds of winter. People who have lived near lakes that freeze over are likely familiar with the booming sounds that echo off the frozen waters, like in this video of ice cracking on Lake Superior from a few years back:

Also, the Great Lakes are famous (or maybe 'infamous') for sparking off bouts of thundersnow — seemingly out-of-season thunderstorms that dump snow instead of rain. While they happen in other conditions too, lake effect snow squalls are particularly favourable for producing winter thunderstorms as the relatively warm lake water adds energy to the storm.

Frost quakes generally occur when the temperature swings significantly — you need slightly milder weather to saturate the ground with liquid water, followed by a cold snap to freeze it all quickly. Given that the Great Lakes region is having a bit of a break from the deep freeze this weekend, followed by another dose of bone-chilling air expected early next week, we could even have more of these (now perhaps somewhat less-rare) phenomena to look forward to.

(Photo courtesy: The Canadian Press)

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