Frost Quake (noun, “Frahst Kwayk”)

In winter, a sudden drop in temperature can trigger a frost quake. During one of these events, the ground splits with a loud boom and shakes like an earthquake but on a much smaller scale. People who have felt a frost quake say it feels like a car ran into their building.

Frost quakes happen when water from rainfall, snowmelt or flooding soaks into the ground, filling all available spaces. The soil becomes saturated, like a sponge filled with water. And when a cold front bringing Arctic air plunges temperatures outside well below freezing — say, about –15° Celsius (5° Fahrenheit) — water in the soil begins to freeze.

As water freezes, its molecules line up in a specific crystal structure. This causes solid ice to take up more space than liquid water. As freezing water expands underground, it presses against nearby soil, and pressure builds. The pressure eventually becomes so great that it causes the frozen soil to crack, allowing one section to slide past another. This sliding is similar to what happens during an earthquake. But earthquakes begin deep underground, and frost quakes occur close to the surface.

People are more likely to hear the boom of shattering ground from a frost quake than they are to feel the jolt it creates. That’s because shaking is limited to a small area — sometimes just a few hundred meters (or feet). Some can be felt a few kilometers (a mile or two) away.

Frost quakes are less likely to happen when snow blankets the ground. That’s because snow insulates the soil, protecting it from dropping air temperatures. Although Arctic air may make us shiver, those super-cold temperatures aren’t able to freeze water in the soil.

Frost quakes are just one type of cryoseism (CRY-oh-SY-zum). That is, a seismic event caused by the cracking of frozen ground. The other type is an ice quake, which takes place in glaciers or lake ice. Frost quakes only occur in frozen soil or rock.

In a sentence

Frost quakes resemble earthquakes, but they are much smaller and cause minimal damage.

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