The extremely cold weather that has chilled the American midwest to the bone has caused some startling booms in Chicago, where some of the coldest temperature readings ever were marked this week.
Chicago residents who have experienced the low of -30C (-23F) say they have heard so-called “frost quakes” as the temperatures have dropped from the polar vortex.
Geologists call them “cryoseisms”, and the loud booms are caused after a rapid drop in temperature that leads to a quick freeze of water. That rapid expansion causes the rock or soil to burst instead of expand at a slower rate, resulting in a loud bang and some possible shaking nearby.
The phenomenon has led some in the area to report thinking their homes were being broken into, or that gunshots were nearby.
And, since the shaking is much too small to be picked up by a seismograph, the phenomenon might otherwise be dismissed as a myth if it weren’t for so many accounts from people who happened to be within 300 feet of the phenomenon.
“It’s more of a noise phenomenon, like a balloon popping, than a physical danger,” Dave Call, a meteorologist at Ball State University, told USA Today. He suggested picturing a bottle full of water in a freezer expanding quickly.
But for residents in the Chicago area, that sound has been all too real.
“I thought I was crazy!” Chastity Clark Baker said on Facebook, according to local media outlet WGN. “I was up all night because I kept hearing it. I was scared and thought it was the furnace”.
Temperatures in the midwest United States are at some of the lowest in records history this week after a polar vortex extended down from up north.
At least eight people have ben reported dead from the weather, which saw temperatures dip below freezing along a large swath of the country.
Temperatures in many parts of the areas currently undergoing intense freezes are expected to rise above freezing later on in the week.