Behind the Forecast: When cold makes the ground shake

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Science Behind the Forecast 2/8/19

LOUISVILLE, KY (WAVE) - Frost quakes or ice quakes are the latest weather term getting a lot of buzz recently, especially with the arctic blast the country last week.

A cryoseism (that's the scientific word for a frost quake) can occur after temperatures drop rapidly from above freezing to below zero. When this plunge happens, water below the ground freezes and expands. The lower the temperature drops, the more the ice expands as water molecules arrange themselves into a formation that has a larger volume than it's liquid form.

Eventually, the surrounding earth gives into the pressure, a crack forms on the surface and a loud, explosive-like noise is heard.

Folks in Chicago reported hearing loud booms last week as the temperature dropped to 23 below zero. In Pennsylvania, frost quakes were also reported in early January.

Experts say that frost quakes are too small to register on a seismograph, do not cause much shaking and can only be heard from around 300 feet away.

In Carmel, Indiana, a suburb of Indianapolis, the fire department had so many questions about the phenomenon last week that they posted an explanation on their Facebook page and got thousands of responses.

We’ve had several inquires over the last 24 hours about loud pops or thumps people are hearing. School may be out...

Posted by Carmel Fire Department on Wednesday, January 30, 2019

Cryoseisms typically occur during the coldest part of the night, between midnight and sunrise.

They may occur in a series of booms and shakes over a few hours or even on consecutive nights, according to the Maine Geological Survey. A study from the University of Wisconsin-Milwaukee, found that the maximum seismic activity occurred three to four hours after a significant temperature change.

For a cryoseism to occur an area must be prone to dealing with very cold air masses, the ground must be saturated from a thaw, rain or flooding before the cold air arrives, snow cover much be minor so there isn’t much insulation and the temperature drop must occur in less than 48 hours.

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