What Is a Frost Quake, and How Does One Occur?

Frost quakes (or "cryoseisms," if you want to get technical), are seismic events that typically occur in Earth’s boreal or cold, temperate regions. But don't be fooled by the name—although they exhibit rumbles and booms like earthquakes and can crack soil, building foundations, and roads, they're driven by weather rather than the motion of tectonic plates. They occur whenever water-saturated soil rapidly freezes, then expands, leading to the fracturing of underground soil and rock.

Another significant difference between these two events is that frost quakes are typically small-magnitude events and may not register on seismographs at all. Frost quakes are also highly localized and, in some cases, don't travel more than a few hundred yards away from the point of origin. They generally occur between midnight and dawn, the coldest part of the night, so it's no wonder why some people aren't familiar with them. However, if you've ever been awaken on a winter's night by what sounds like a fist banging against a wall, or the firing of a shotgun, it's possible you might have witnessed a frost quake and not even known it.

When and How Frost Quakes Occur

Just as geologists can't predict the exact location and time when an earthquake might sway the ground underfoot, meteorologists aren't able to forecast frost quakes. However, the best time to possibly experience one of these elusive events is when you're expecting rain, melting snow, or a wintry mix that’ll saturate the ground; a cold wave, such as a polar vortex outbreak, or an Alberta clipper (which has been known to lower temperatures by tens of degrees Fahrenheit in as little as 10 hours); and minimal snow cover on the ground (surprisingly, a blanket of snow can insulate the ground from rapid temperature drops).

Frost quakes begin to form when the soil is saturated from a recent rainstorm or snowstorm. Usually less than 48 hours after the precipitation ends, air temperatures will plummet from near freezing to subzero, causing soil temperatures to also drop rapidly. As soil temperatures cool to around freezing, the water droplets trapped within the soil’s pores freeze. Since water expands when it freezes into ice, a buildup of pressure stresses the surrounding soil and bedrock which is frozen itself and can’t stretch any further. With nowhere for this pressure to escape, the ground fractures, releasing a wave of seismic energy.

When a similar chain of events occurs within bodies of ice rather than water-logged soil, “ice quakes” are born. 

Recent research out of the University of Oulu in Oulu, Finland, suggests that the depth of the frozen soil layer is linked to frost quake severity; a rapid decrease in temperature creates thermal stress, and thermal stress that exceeds the strength of the frozen layer lead to frost quakes. Future research could include studying the effects of soil type on frost quake formation. If certain types of soil are found to be more conducive to these quakes, it could put forecasters one step closer to being able to predict their appearance.

Locations and Examples

Frost quakes can occur anywhere as long as the right weather conditions align. Of course, some locations, including places like Alaska, Canada, the Northeastern United States, and eastern Europe, are more prone to experiencing them than others. And research suggests frost quakes may become more prevalent due to the changing climate, so long as the conditions detailed above are present.

During the 2019 North American cold wave, when overnight lows around minus 20 degrees F were common across the Midwest, frost quakes were reported in a few major cities, including Chicago, Illinois, and Pittsburgh, Pennsylvania. 

In 2016, the town of Tavlikangas, Finland, experienced a frost quake so severe, it was picked up by an observing station nearly nine miles away. The quake's tremors caused minor damage, including rupturing a roadway. This same crack crossed the road and traveled to a nearby home, cracking its basement and one of the house's inner walls. The homeowners claimed it felt like "a truck had crashed into the wall of the house."