You're sound asleep on a cold, wintry night, and all of a sudden a loud boom wakes you up. A few things on your shelves rattle for a second or two, then all is silent.
Was it an earthquake? Maybe, but the real culprit is likely a frost quake, a geological phenomenon brought on by winter weather. Unlike earthquakes, frost quakes are non-tectonic seismic events, meaning they are not caused by the shifting of the Earth's tectonic plates.
Also known as cryoseisms, frost quakes are caused by a sudden rapid freezing of ground and bedrock, usually when temperatures go from above freezing to below zero.
As moisture absorbed in the rock and soil freezes, it expands. This puts a great amount of stress on the areas around it.
Eventually, the stress is too much and the soil and rock will crack in an "explosive" manner, creating a loud sound and even shaking the ground surface.
Since temperatures are coldest in the overnight hours, most people experience frost quakes in the middle of the night, often waking up because of them.
According to the Maine Geological Survey, frost quakes can even leave cracks in the ground.
Cryoseisms are often very localized events, but multiple quakes can happen over a particular area. This may explain why people in multiple counties in Indiana felt frost quakes in the early morning hours of Feb. 10, as reported by WTHR in Indianapolis.
Early morning lows were below zero across the state, as cold as 18 degrees below at Frankfort Airport. The NWS reported that the temperatures on Feb. 10 were the coldest seen in the state since January 2009.
Unsettled weather for the extended Labor Day weekend will be across the Southeast, Upper Midwest, northern Rockies and the Four Corners.
The combination of moisture from Erika and a non-tropical system will drench areas from Florida to the Georgia coast through the middle of the week.
A stormy weather pattern will prevail through September across much of southern South America.
A rapid shutdown of tropical activity and an end to hurricane season in early September is not likely this year, despite a strong El Nino.
Tropical Depression 14-E is several hundred miles southwest of Mexico and is expected to slowly strengthen into a tropical storm.
Heat will be erased by an autumnlike air mass across parts of northern Europe.
East Coast (1775)
Matecumbe Key, FL (1935)
Labor Day Hurricane hit Florida. Pressure at Matecumbe Key dipped to 26.35"/892.3 mb. Most intense hurricane ever to hit the U.S. with 200-mph wind. Tide of 15 feet; 408 dead.
Mecca, CA (1950)
126 degrees - highest ever for U.S. in Sept.