Frost quakes! The science behind the shaking
Perhaps you felt it overnight-- the ground shaking in Madison. It's likely a frost quake.
The natural phenomenon that comes with a loud bang is known as a "frost quake," and it happens about once a year in Madison.
Geoscientist Lucas Zoet explains, people can't even see the wiggle in the ground because it's smaller than a strand of human hair. It can be felt, however, especially when people are close to the source.
Zoet says the two conditions have to be just right for a frost quake to occur. Water on the ground, including that from melted snow, has to be met with rapidly dropping temperatures. The water then fills the small gaps in the ground, which are normally filled with air, then freezes into ice, expands and pops.
"What we hear is that snapping of the ground as it's being ripped open by the water freezing," Zoet said.