Several people in the Chicago area have reported hearing loud booms in the last couple of days, and given the sudden and extreme drop in temperatures due to the polar vortex, people have started suggesting that the cause of the noise and tremors might be “frost quakes”.
Frost quakes, also known as cryoseisms or ice quakes, only happen when several conditions are met. This makes them both difficult to predict and difficult to confirm once they have happened. According to a recent study, for a frost quake to occur you need four things. The region needs to be susceptible to sudden drops in temperature. The ground needs to be soaked in water and also have very little snow cover. And most importantly, you need the temperature to rapidly drop from near freezing to tens of degrees below zero.
What happens next is quite straightforward. The water in the ground freezes and as it does so, it expands and puts pressure on the soil. The ground comes under a considerable amount of stress which is relieved explosively. This can cause tremors and a loud boom. The effects are usually extremely localized and they might not register on seismographs if they’re not close enough.
The noise in and around Chicago was reported by local news station WGN TV, with various Twitter users confirming that they have heard the booms too. Still, frost quakes might not have been the cause of the sounds and it could be difficult to confirm whether they were.
The term "frost quake" might not be a household name but the phenomenon has been documented in the northeastern portion of the American continent for at least two centuries. And over the last few years, they have been reported in the news more and more frequently. This could be because people can more easily wonder online and ask “hey, what was that loud bang?”, but it could also mean that these events are becoming more common. Researchers suspect that climate change might have made the conditions that lead to cryoseisms more likely.
While there shouldn’t be any more frost quakes in the Midwest, the frosty temperatures will continue for another few days and people in the area are advised not to stay outside for long.
[H/T: Live Science]