Frostheave earthquakes may become more frequent in the north and could have significant impacts on buildings and infrastructure
In 2005, residents of the small town of Rimington, Maine, USA, heard a series of loud bangs that rattled their windows and shook the ground. One resident went outside to see if the car had exploded and found a crack running through his paved driveway. According to the Maine Geological Survey, the damage was likely caused by a frostquake, also known as a frostquake.
Freezequakes are not a particularly rare phenomenon. It occurs when water in the soil freezes and expands rapidly, creating cracks in the ground. This sudden release of seismic energy is often heard as a loud crackle or thud accompanied by small tremors. A number of freeze-quake-like events have been reported in Finland, Canada, and the United States over the past two decades. Nevertheless, relatively few studies have focused on this phenomenon. One reason for this is that the phenomenon occurs more often in sparsely populated areas such as the central and northern plains and subarctic regions of the United States. But new research from Finland suggests that cryoquakes could become a more common natural disaster in the north.
In early 2016, a swarm of frost heave earthquakes shook residents of Tarbikangas, a suburb of Oulu in central Finland, destroying soil and causing cracks in roads and building foundations. The University of Oulu’s Sodankyla Geophysical Observatory, 14 kilometers away, recorded a number of unusual seismic events and also happened to be collecting data on weather conditions in a long-term environmental monitoring study that was just about to end.
Normally, a thick layer of snow protects the soil from sudden temperature changes, but on the day of the cryoquake, researchers noticed that there was very little snow on the ground. A sudden drop in temperature was recorded just before the shaking was felt. Scientists then found that freeze quakes are most likely to occur when the temperature drops below -20 degrees Celsius at a rate of 1 degree Celsius per hour.
With this information, researchers realized they could recreate the conditions that caused frost heave earthquakes and better understand when they might occur in the future. But pinpointing exactly where the freeze quakes occurred was a more difficult problem. “The problem is that frost heave earthquakes are usually small events. It’s almost impossible to observe them with normal seismic observations,” says Kari Moisio, a senior researcher at the University of Oulu. “I need an instrument near the field I want to research.”
Ahead of the winter of 2022-2023, researchers installed seismic sensors at two locations. One is on the outskirts of Oulu, and the other is further north, above the Arctic Circle, in the town of Sodankyla. Surprisingly, they found that most of Tarbikangas’s frost heave earthquakes occurred in nearby wetlands and swamps, especially those dug by irrigation canals (until now, most frost heave earthquakes occurred on plowed roads). was thought to occur near the Half of the earthquakes recorded near Sodankylä were caused by ice breaking on the Kittinen River, but here, too, many strong cold earthquakes were caused by the freezing of water in wet marshes.
Finland is one of the countries with the most wetlands in Europe. Moisio and his colleagues’ findings suggest that this may make them particularly susceptible to freeze-earthquakes. “Of course, it’s not a problem because they usually occur in uninhabited areas,” Moisio said, but recently there have been a number of frostheave earthquakes in wetlands near cities and other infrastructure. In January of this year, Tarbikangas was hit by another 26 freeze quakes, all occurring within just seven hours. This is believed to be the highest concentration phenomenon ever recorded.
These recent events have received a lot of public attention, with reports from local residents being shared on news websites and social media. This begs the question whether the number of cryoquakes is increasing, or whether increased awareness is leading more people to report cryoquakes. “It’s a very difficult question to answer with the limited amount of information we have right now, so we can’t draw any strong conclusions yet,” Moisio says. “These events appear to be more common than previously thought.”
One concern is that as the planet warms, conditions favorable for cryoquakes may occur more frequently. Climate studies show that subarctic regions experience greater variability in snow cover and temperature. Studies have already shown that in parts of Finland, snow cover has been decreasing at a rate of 2 to 4 centimeters per decade since 1961.
And while most frost quakes are small, the strongest can cause ground movements strong enough to cause damage to urban infrastructure hundreds of meters away from wetlands. The next stage of research will identify areas that may be at risk. “Just like we have hazard maps for earthquakes, we want to do the same for freeze quakes,” Moisio explains.