The extreme cold that has affected around two-thirds of the United States in the past few days caused a wave of frost quakes in several states.
Frost quakes occur when the ground freezes and contracts suddenly, generating small earthquakes.
This event can be accompanied by intense vibrations and loud noises, especially at night, and even cause trees to fall.
Evan Webb, a meteorologist with the National Weather Service (NWS) in Kentucky, where most of these phenomena have been reported, explained to EFE on Wednesday that cryosisms, the technical term for frost quakes, occur when the ground becomes saturated due to rain or freezing rain, which penetrates the unfrozen ground, seeping in until it becomes saturated.
The expert added that this phenomenon is followed by a rapid drop in temperature, as moisture in the ground freezes and expands very quickly when it turns to ice. This expansion causes small cracks or fractures, which generate the loud booms or ‘pops’ that people have been hearing.
Since the weekend, a cold wave hit the region between Texas and the north Atlantic coast, leaving large accumulations of snow and temperatures between 15 and 20 degrees below average in some states.
The winter storm left dozens of people dead in the US as of Tuesday and caused the largest number of flight cancellations since the COVID-19 pandemic.
In addition, more than half a million homes still remained without electricity on Tuesday, with maximum temperatures around -5°C (23°F) in inland areas, which, with a feeling of -20°C (-4°F) in some states.
In this context, the population of inland regions has reported ice quakes in recent days, forcing regional NWS offices to issue reassurance notices.
»Are you troubled by strange noises in the middle of the night? Those loud booms aren’t paranormal—they’re cryoseisms (Frost Quakes)! Water in the soil is freezing, expanding & cracking under pressure. Startling but harmless. Stay Warm, We’re ready to believe you…» wrote on social media the regional service in Louisville, Kentucky.
Webb said they had received calls from several people since the weekend, when the worst of the cold snap began, reporting loud noises at night.
Videos posted on social media show the sound generated by some of these phenomena, similar to a gunshot.
The cold snap is caused by a displacement of the polar vortex, an unusual event that has brought Arctic polar air to latitudes unaccustomed to it, such as Kentucky and Tennessee.
Florida, which had escaped the winter cold so far, will experience its coldest weather in 15 years this coming weekend, with temperatures below 0°C (below 30°F) in Miami.
The vortex or mass of cold air is always present over the North Pole, but it can shift when the air in the upper atmosphere warms, suddenly weakening the wind barrier that keeps it over the Arctic.
The last major occurrence of this event in the United States took place in January 2024, when record lows were recorded in southern states such as Texas and Louisiana.
At least 40 people died during that episode of freezing temperatures, according to national media.