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A cold weather phenomenon known as frost quakes, which make loud booming or popping sounds and cause small earthquake-like tremors, were felt around Chicago this week during the period of freezing temperatures.
Illinois State Climatologist Trent Ford said there is no formal reporting system for frostquakes, which occur after a sudden freezing of the ground, but he had seen and heard reports of the phenomenon on social media. He has also experienced some frostquakes in the past, officially known as cryoseism.
“It sounds a bit like someone breaking off a very large branch from a tree or perhaps popping very large bubble wrap. It’s not really gunfire, but it is, and it can be so loud,” Ford said.
“The shaking is less common,” he added. “Those can be like small earthquakes, not nearly as bad as pictures falling off the wall.”
Earthquakes can be disturbing, especially if people are not aware of them, but they pose no real danger, Ford added. In extreme cases they can cause damage to roads or building foundations, but this is rare.
Where and how frostquakes occur
The phenomenon is not unique to the US Midwest; Frostquakes have also been reported in New England, Canada and parts of Scandinavia. They can occur in rural or urban areas.
Frostquakes typically occur under certain winter conditions, Ford said — after a wet, rainy period and when there is little snow, which has an insulating effect, on the ground. How often the earthquakes occur is unclear, as not much research has been done on them.
“What we need is for the soil to be almost saturated with water so that there is very little air space to fill,” he said. “And then you need a quick freeze.”
Once the ground is frozen, it behaves like a different material. It becomes firmer and does not shrink and swell as normal.
“That water in the ground freezes and expands… in the ground and cracks or breaks the (frozen) ground almost like a rock. So it is that breaking that makes the popping and booming sound.”
Mapped by social media
Frost earthquakes caught the attention of Andrew Leung, a researcher at the Climate Lab at the University of Toronto Scarborough, when he heard what sounded like the sound of falling trees after an ice storm in December 2013. He went online to tweet about it and saw that others in southern Ontario had experienced something similar.
“I was surprised that many others in Toronto reported hearing similar noises,” Leung said. “I felt like fallen trees might not be the best explanation for such noise.”
Leung started researching the phenomenon as part of his PhD and published an article on frostquakes in the journal Citizen Empowered Mapping in 2017.
Using social media posts and analysis of climate data, he mapped frostquakes in Ontario and neighboring regions in 2013 and 2014. Leung identified two clusters of frostquakes and the first known frostquakes in three Canadian provinces and seven US states, according to his thesis.
“Since temperatures generally drop at night, frostquakes are most often reported at night or at night, sometimes being mistaken for a burglar breaking into the house,” he said.
Although networks have been set up to study and detect earthquakes, frostquakes are too local and rare to monitor systematically, making social media posts particularly valuable in this case, he said.
New findings on frostquakes
In northern Finland, a series of relatively strong frostquakes in the city of Oulu raised concerns after the seismic phenomenon damaged a house in 2016 and tore up roads that year and again in 2021.
During the winter of 2022 and 2023, a team of Finnish researchers installed two networks of seismic instruments, one in Oulu and one further north in Sodankylä, to conduct further research. The scientists shared preliminary data from their research at the end of last year.
They were able to identify the frostquakes in the seismic data they collected because the waveform is distinctive, says Kari Moisio, a senior researcher at the University of Oulu and one of the authors of the study, which he said would be published in a scientific journal. diary soon. The team also monitored soil temperatures over the course of the study.
The researchers discovered 11 frostquakes at the Oulu site and 34 further north at Sodankylä during the study period.
“To our understanding, this is the first time we have been able to look at these events so closely,” he said.
Freezequakes are likely to occur when temperatures drop rapidly to more than minus 20 degrees Celsius (minus 4 degrees Fahrenheit) at a rate of about 1 degree per hour, the researchers found.
Roads and other areas cleared of snow were thought to be particularly vulnerable to frost tremors. However, the latest study suggested that some frostquakes occurred in wetlands and swamps, where water accumulates. These areas typically had snow cover, Moisio said, so the finding surprised the research team.
To understand whether frostquakes are increasing, the team plans to monitor the same areas this winter and next. The researchers also hope to map how often frostquakes occur in other parts of the country.
Moisio said wetter winters and less stable winter temperatures due to climate change could make frostquakes more common.
“There won’t be as much snow in Scandinavia in the future at these latitudes where we are,” he said.
Instead, he said, it will rain more.
“This could, I think, cause even more dramatic events … because it will increase the water in the subsurface.”
Leung agreed. “We have no evidence that they are becoming more common,” he said. “However, the overall decreasing trend in snow depth due to climate change could theoretically make the ground more susceptible to frost tremors, as snow no longer insulates the ground.”
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