ST. LOUIS – Chuck Herron heard the loud thud, then another and another. It sounded 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 he had "never heard anything like that before."
As his neighbors in tiny Paris, Mo., watched the Super Bowl on Sunday, many were startled by similar strange noises. Some even saw flashes of light and called 911.
Scientists say the community experienced a rare natural phenomenon known as a "frost quake," which happens when moisture in the ground suddenly freezes and expands. If conditions are just right, the soil or bedrock breaks, generating mysterious noises that range from an earthquake-like rumble to sharp cracking sounds sometimes mistaken for falling trees.
This winter has been ripe for frost quakes, known technically as cryoseism. The weather has been frigid, but 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.
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."
Frost quakes were reported last month in Canada and in Indiana, Michigan and Ohio.
