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A cold weather phenomenon known as frost quakes, which make loud booming or popping sounds and release small earthquake-like tremors, was felt around Chicago during this week’s bout of below-zero temperatures.
Illinois state climatologist Trent Ford said there was no formal reporting system for frost quakes, which occur after a sudden freeze on the ground, but he had seen and heard reports of the phenomenon on social media. It has also had several frostbites, officially known as frostbite, in the past.
“It looks like someone is removing a very large branch from a tree or maybe popping very large bubble wrap. It’s not full gunfire, but it’s like that, and it can be so loud,” Ford said.
“The shaking is less common,” he said. “Those can be like small earthquakes, and not nearly as far as pictures falling off the wall.”
Frost quakes can be unsettling, especially if people aren’t aware of them, but if they don’t pose a real danger, Ford said. In extreme cases, they can damage roads or building foundations, but this is rare.
Where and how frostbites occur
The phenomenon is not unique to the US Midwest; Frost tremors were also reported in New England, Canada and parts of Scandinavia. They can occur in rural or urban areas.
Frost quakes usually occur under a certain set of winter conditions, Ford said — after a wet period of rain and when there is little snow, which has an insulating effect, on the ground. It’s not clear how common the tremors are because they haven’t been researched much yet.
“What we want 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 soil is frozen, it acts like a different material. It becomes more solid, not shrinking and swelling like it would normally.
“That water in the soil condenses and expands … within the soil and basically the (frozen) soil cracks or breaks almost like rock. So it’s that fracturing that makes (the) popping and booming sound.”
Mapped by social media
Frost tremors caught the attention of Andrew Leung, a researcher at the Climatic Laboratory at the University of Toronto Scarborough, when he heard what sounded like the sound of trees falling after an ice storm in December 2013. He went online to tweet about it and saw that there were other people. in southern Ontario they experienced something similar.
“I was surprised that many other people around Toronto reported hearing similar sounds,” Leung said. “I felt that fallen trees might not be the best explanation for that noise.”
Leung continued to investigate the phenomenon as part of his doctorate and published a paper on frost quakes 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. Leung identified two frost quake clusters and the first known frost quakes in three Canadian provinces and seven US state, according to his thesis.
“Since the temperature usually drops at night, frostbites are often reported at night or overnight, and are sometimes mistaken for a burglar breaking into the house,” he said.
Although networks have been established to study and detect earthquakes, earthquakes are too localized and frequent to be systematically monitored, making social media reports particularly valuable in this situation, said he.
New results on frost tremors
In northern Finland, a series of fairly strong earthquakes caused concern in the city of Oulu after the seismic phenomenon damaged a house in 2016 and ruptured roads that year and again in 2021.
During the winter of 2022 and 2023, a team of researchers from Finland installed two networks of seismic instruments, one in Oulu, and another further north in Sodankylä, for further investigation. The scientists shared preliminary data from their study late last year.
They were able to identify the frost quakes in the seismic data they collected because the waveforms are distinctive, said 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 Science. magazine soon. The team also tracked soil temperature during the study.
The researchers observed 11 frost tremors at the site near Oulu and 34 further north near Sodankylä over the period of the study.
“At least to our understanding, this was the first time we could look at these events so precisely,” he said.
Frost quakes 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 frostbite. However, the latest study suggested that some frost quakes 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 if frostbites are increasing, the team plans to monitor the same areas this winter and next. The researchers also hope to map how common frost quakes are in other areas of the country.
Moisio said wetter winters and less stable winter temperatures due to climate change could lead to more frequent frostbites.
“There won’t be as much snow in the future in Scandinavia at these latitudes where we are,” he said.
Instead, he said, it will rain more.
“This, I think, could create more dramatic events … because this will increase water in the subsurface.”
Leung agreed. “We have no evidence that they are becoming more frequent,” he said. “However, the general trend of reduced snow depth due to climate change can theoretically make the ground more vulnerable to frost quakes because snow is no longer insulating the ground.”
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