Did you wake up with a bang this morning?

Posted: January 3, 2014 - 12:00 , by Katherine Dunnell
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You may not have been dreaming when you thought you heard a loud sound in the early morning. The phenomenon is called cryoseism and was also reported on Christmas eve around the GTA. Why is this happening and what is cryoseism?  Cryoseism occurs when the ground and rock contains a significant amount of water, and as the temperatures rapidly dip, the water freezes expanding by 9%, putting stress on the surrounding rock. The stress releases explosively creating a boom as the ground cracks. The Great Lakes area seems to record many of these events, and the frequency of the ones here in Toronto have been attributed to the ice storm and the very cold temperatures we have been experiencing this winter.

Frost on window

Comments

Comment by mike collins

Re; cryoseism. I ain't buying the freezing groundshakes theory, here's why. In a severe temperature drop the ground is insulated by the snow and by this thick sheet of ice we've all been enjoying. It can be -25C air temp but it'll be less cold below. (Not sure about heat loss through ice though, I must admit I'm skating on thin ice here myself.)
So what about the noise? Because we have large areas of dense hard ice sheet, it acts like a giant sounding board amplifying any vibration. You can hear the hollow sound when you walk on top of it. The source of the vibration would come from the ice sheet not the ground. The above ground ice would expand as it froze further (perhaps the atmospheric humidity it absorbed throughout the day or the minute amounts of melt water from any solar heating). This freezing and consequent expansion would create internal pressure within the icesheet which would be relieved by cracking - like a pond does or the sea. On a large scale this would manifest in heaving fault lines or zastrugi.
My 2 centigrades worth. Thanks for your time.

cheers,
Bawheid.