ICE QUAKES
In January, the area around Chicago experienced widespread frost quakes, something that occurs after sudden freezing of the ground. Known as cryoseism, the phenomenon produces small earthquake-like tremors and loud booming and popping sounds. “It sort of sounds like somebody is either snapping a very large branch off a tree or maybe popping very large bubble wrap. It’s not quite gunfire, but it’s sort of like that, and it can be that loud,” said Illinois state climatologist Trent Ford. “The shaking is less common,” he added. “Those can be like small earthquakes, not nearly to thequakes need a precise set of conditions, usually occurring after a rainy period when there’s little snow on the ground, as this creates an insulation layer that slows the freezing. “What we need is for the soil to be nearly saturated with water so that there’s very little airspace to fill,” Ford said. “And then you need a rapid freeze.” Normally, soil can expand and contract as conditions change, but once it has been frozen like this it behaves as a solid so that when water in the soil freezes and expands, the soil reacts more like rock, fracturing and forming fissures. It is this process that makes the popping and booming sounds. Researchers have found that quakes are likely to occur when the temperature rapidly drops to more than minus 20°C (-4°F) at a rate of about one degree per hour. Andrew Leung, of the University of Toronto Scarborough, who researches cryoseism, says that “Since temperature typically drops at night, frost quakes are most frequently reported at night or overnight, sometimes being mistaken for a burglar breaking into the house.”
