As neighbors in a tiny Paris, Mo., huddled around televisions Sunday for the Super Bowl, many were startled by strange noises. Some even saw flashes of light and called 911, the Associated Press reported.
Loud thuds, one by one, were also heard by Chuck Herron, like someone was dropping big snowballs on the roof of his home.
The house is more than 100 years old and creaks, Herron said, "but I'd never heard anything like that before."
A rare natural phenomenon known as a "frost quake," was experienced by the community, scientists said. It happens when moisture in the ground suddenly freezes and expands.
According to the AP, "If conditions are just right, the soil or bedrock breaks like a brittle frozen pipe, generating mysterious noises that range from an earthquake-like rumble to sharp cracking noises sometimes mistaken for falling trees."
This winter has been ripe for frost quakes, known technically as cryoseism.
Even though it has been frigid, occasional warm-ups have allowed for thawing. And the temperature swings have sometimes been abrupt.
That was the case last weekend in Missouri, where temperatures in the 40s on Saturday gave way to single-digit readings by Sunday night, the AP reported.
Within about two hours, police and emergency dispatches received several calls in Mark Twain's hometown of Hannibal, Mo., 100 miles north of St. Louis. Worried concerns filled Facebook feeds, the AP reported.
Some people compared the noise to a sonic boom that rattles windows, said Michael Hall, executive director of the 911 center that covers the Hannibal area. Others described it as sounding like "somebody banging on their house."
Apart from Missouri, states like Indiana, Michigan, Ohio, Wisconsin, and Canada reported frost quakes last month, the AP reported.
In DeKalb, Ill., Lisa Kammes and her family were getting ready for bed earlier this winter when the loud popping noises began.
"The louder ones sounded like somebody was throwing snowballs at the house," Kammes said.
Neighbors heard noises too, and several contacted police, the AP reported.
"It wasn't the regular noise you hear when your house is creaking, blowing in the wind or ice is breaking," Kammes said.
Electrical changes that occur when the freezing compresses rocks seem to cause the light flashes reported by some people.
Robert Herrmann of the Saint Louis University Earthquake Center said frost quakes are far different from real earthquakes. Tremors typically occur a mile or two underground. Frost quakes are near the surface and do not show up on seismographs, according to the AP.
"People nearby will probably notice them a lot because they are shallow, but because they do not penetrate deep within the earth, the magnitude will not be large," Herrmann said. "But the process is the same. There is something that is causing rock to move, and as the rock moves, it generates sound waves and the ground motion."
Frost quakes are most common in the northern Plains, Alex Sosnowski, AccuWeather meteorologist, said.
"It has to get suddenly colder," Sosnowski said. "If you have a mild winter, you're probably not going to have a lot of this going on."
Even though damage in these situations is rare, homeowners who experience a frost quake should check for foundation cracks and watch for damage to water and natural gas lines, experts said.
"Damage is not common, but it happens. In Waupun, Wis., a frost quake last month created a 100-foot crack in a driveway. Homeowner Dennis Olssen told authorities the boom was so loud he thought it was an explosive until he learned that neighbors experienced the same thing," the AP reported.
Kammes said the noise on that otherwise quiet night was so alarming that her husband went outside to make sure no one had damaged the home.
"When we found out what it was," she said, "it was actually a relief."
