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A cold weather phenomenon known as freeze earthquakes, which produce loud popping or popping sounds and small earthquake-like tremors, was felt around Chicago during this week’s subzero temperatures.
Illinois state climatologist Trent Ford said there is no official reporting system for frost quakes that occur after the ground freezes suddenly, but he has seen and heard reports of the event on social media. It has also experienced some frost earthquakes in the past, officially known as cryozism.
“It looks like someone is either breaking a very large branch off a tree or popping very large bubble wrap. It’s not quite a gunshot, but it’s similar to that and can be just as loud,” Ford said.
“Concussion is less common,” he added. “These can be like small earthquakes, not so big that the pictures fall off the wall.”
Ford added that freeze quakes can be disturbing, especially if people are unaware, but they don’t pose a real danger. In extreme cases they can damage roads or building foundations, but this is rare.
Where and how do frost earthquakes occur?
This phenomenon is not unique to the US Midwest; Freeze earthquakes were also reported in parts of New England, Canada and Scandinavia. They can be in rural or urban areas.
Ford said frostquakes often occur in certain winter conditions; after a wet, rainy period and when there is a small amount of snow on the ground, which has an insulating effect. It is unclear how often earthquakes occur because not much research has been done on them yet.
“What we need is for the soil to be almost saturated with water so there is very little air space to fill,” he said. “And then you need a quick freeze.”
When soil is frozen it behaves like a different material. It does not shrink and swell as it normally does, but becomes more solid.
“Water in the soil freezes and expands within the soil and actually cracks or breaks the (frozen) soil, almost like a rock. It is this fracture that makes this breaking and exploding sound.”
Mapped by social media
Frost quakes caught the attention of Andrew Leung, a Climate Lab researcher at the University of Toronto Scarborough, in December 2013 when he heard what sounded like trees falling after an ice storm. Something similar happened in Southern Ontario.
“I was surprised that many others around Toronto reported hearing similar noises,” Leung said. “I felt like falling trees might not be the best explanation for this type of noise.”
Leung continued to research this phenomenon as part of his PhD and published a paper about frostquakes in the journal Citizen Empowered Mapping in 2017.
Using social media posts and climate data analysis, he mapped frost quakes in Ontario and neighboring regions in 2013 and 2014. In his thesis, Leung identified two clusters of frostquakes and the first known frostquakes in three Canadian provinces and seven U.S. states.
“Since temperatures often drop at night, freeze earthquakes are most often reported at night or during the night, sometimes mistaken for burglars breaking into the home,” he said.
While networks have been established to study and detect earthquakes, freezequakes are too local and infrequent to be systematically tracked, making social media reports particularly valuable in this case, he said.
New findings about frost earthquakes
In northern Finland, a series of relatively strong frost quakes in the city of Oulu caused concern after the seismic event damaged a house in 2016 and ripped up roads that year and again in 2021.
In the winter of 2022 and 2023, a team of Finnish researchers installed two networks of seismic devices, one in Oulu and the other further north in Sodankylä, for further investigation. Scientists shared preliminary data from their study late last year.
Kari Moisio, a senior researcher at the University of Oulu and one of the study’s authors, said they were able to identify freeze earthquakes in the seismic data they collected because the waveform was distinctive. diary soon. The team also monitored soil temperature throughout the study.
Researchers detected 11 freezequakes in the area near Oulu and 34 further north near Sodankylä during the study period.
“This is the first time we’ve been able to look at these events with such precision, at least to our understanding,” he said.
Researchers found that frostquakes are most likely to occur when temperatures drop above minus 20 degrees Celsius (minus 4 degrees Fahrenheit) at a rate of about 1 degree per hour.
Roads and other areas cleared of snow were thought to be particularly vulnerable to freeze earthquakes. However, recent research has suggested that some frost earthquakes occur in wetlands and swamps where water accumulates. These areas are often covered in snow, so this finding surprised the research team, Moisio said.
The team plans to monitor the same areas this winter and next winter to understand whether frost earthquakes are increasing. Researchers also hope to map how common freeze earthquakes are in other parts of the country.
Wetter winters and less stable winter temperatures due to climate change could lead to more frequent frost quakes, Moisio said.
“It will not snow as much in the future in Scandinavia at our latitudes,” he said.
He said there would be more rain instead.
“I think this could lead to even more dramatic events… because this will cause the water in the ground to increase.”
Leung agreed. “We have no evidence that these are becoming more frequent,” he said. “However, in theory the overall trend of decreasing snow depth due to climate change could make the ground more susceptible to frost earthquakes as snow no longer insulates the ground.”
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