“Could a single, sharp boom on a bitter night come from the ground itself?” In some areas of the Midwest, the sound comes unannounced: a sudden crack that can reverberate down a block and wake people up. In the winter, such a sound is sometimes referred to as an “icequake” or “frost quake,” a phenomenon that can sometimes be mistaken, especially if windows shake or walls shudder for a brief moment.
Frost quakes are a weather-related earthquake that is a small, shallow shake caused by the rapid freezing of water in the ground, which expands and causes the ground to break apart, resulting in a sound that is like a balloon popping in an empty room. The process was clearly described by AccuWeather senior meteorologist Adam Douty: Because water expands when it freezes, it can literally push dirt and rocks apart. If this happens all at once, for example, if a rock under pressure bursts apart, it can create the sound and earthquake-like sensation.
They may be felt personally because they occur close to home.
There are a few ingredients that are in line. The temperature is the most important factor, but it is not just “cold” because it is a rapid drop. In one of the explanations, frost quakes are associated with air suddenly dropping to subzero temperatures within 12 to 48 hours, which is enough time for the underground water to freeze solid and expand. Water availability is also important, as the saturated soil from wet weather can be the fuel. Snow, surprisingly, can lower the chances. A thicker layer will work like insulation; in one of the explanations, six inches of snow can be enough to prevent the soil from freezing because it will make the cracking less likely.
This explains why some cold snaps are loud and others are quiet. It also explains why frost quakes appear regularly in areas that experience quick freeze cycles, which are common in the Northeast and Alaska, and also in Canada and Iceland. In the Midwest, they are noticed during extreme cold snaps when there is enough moisture in the ground to freeze quickly.
For people living through a boom, it is useful to distinguish between frost quakes and tectonic earthquakes. Meteorologists have termed frost quakes as events that do not relate to the movement of plates; they are more like freeze-thaw damage but on a massive and sudden scale. One meteorologist who has explained the phenomenon in a household way is Dave Call, a meteorologist at Ball State University. He has explained the phenomenon as follows: “It’s like a liquid in a container expanding in a freezer until it bursts. It can be loud, but it’s not a hazard.”
Confusion continues because there is more than one explanation for winter booms. An overview of mysterious booms by the U.S. Geological Survey introduces a possible cause for some booms: very small earthquakes that are shallow. These events can produce high-frequency vibrations that can be heard by people in the area. Another possible cause, according to the same overview, is structures themselves. Houses and other materials can expand and contract in extreme cold, producing sounds like snaps, pops, and bangs that may seem to come from outside when they do not.
What makes this week different is the extent of the cold and the length of the dangerous conditions. NOAA has issued warnings of “dangerously cold air that will persist across a large area of the country, with snow and ice creating impacts that can last beyond the storm. When the cold air is in residence and the ground is ready and wet, “above the occasional midnight boom can be part of winter’s less-discussed soundtrack.”
