The U.S. Midwest has been gripped by the lowest temperatures it has seen in years. People around the region started hearing strange “booms” and popping noises. This phenomenon is known as a frost quake, or cryoseism.
What causes a "Frost Quake"?
Frost quakes occur when extremely cold temperatures lead to rapid freezing in the ground after it has been saturated. These low temperatures that reached below 0 degrees Fahrenheit (-18 degrees Celsius).are caused by an unusually cold Arctic air mass.
NASA's Atmospheric Infrared Sounder instrument aboard the Aqua satellite captured the polar vortex as it moved southward from central Canada into the U.S. Midwest from Jan. 20 through Jan. 29. The lowest temperatures are shown in purple and blue and range from -40 degrees Fahrenheit (also -40 degrees Celsius) to -10 degrees Fahrenheit (-23 degrees Celsius).
As temperatures began to drop below the freezing point, the absorbed water began to freeze.
As water freezes, it expands outward. This creates more stress and more stress as more water freezes. After a certain point, the ice breaks or cracks creating these "booms". With temperatures still falling, the freezing effect will be enhanced.
These frost quakes are most commonly heard at night when there is less noise. They also tend to occur more at night when temperatures are at their lowest
What is a Frost quake? The strange physics of water
The sound of loud booms heard and associated with a “frost quake” is actually the sound of soil that’s been compressed at high pressure and result in sudden breaks, causing a loud cracking sound.
That’s the frost quake, or cryoseism, the scientific name for a crack in the soil that was previously saturated with water or ice.
All that pressure is caused by water that has permeated underneath the surface of the ground that suddenly freezes because of a massive blast of low temperatures, like a polar vortex.
As we all have learned this in Physics 101: water expands when it freezes.
Slowly, all the spaces in the soil are used up which cause the soil pressure to build. Eventually, the pressure reaches a critical point and the soil gives way to release the pressure. As the pressure is being released, it causes cracking or thundering noises. Snow is an effective insulator, so shallow or no snow cover is also a necessary requirement for this deep freezing.
Should people feel worried?
These frost quakes are most commonly heard at night when there is less noise. They also tend to occur more at night when temperatures are at their lowest. Frost quakes are not known to cause injuries or damage.
Though the sound of a frost quake can be scary, they aren’t dangerous.
For those in winter’s icy grip this week, the real danger is the cold temperatures themselves, which can cause hypothermia if a person heads outside without proper clothing.