New Data Helps Researchers Demystify 'Frost Quakes'
(Inside Science) -- On Jan. 6, 2016, residents in the outskirts of Oulu, Finland, heard a loud bang that was immediately followed by tremors and large cracks in a nearby road and building. A research station 14 kilometers away recorded the seismic event, called a "frost quake." These potentially destructive events can crack frozen soil and, as happened in Finland, create additional damage. Now scientists have new insights that shed light on why these quakes happen and when and where they might occur.
Geoscientist Jarkko Okkonen and his colleagues had collected soil, water and temperature data from central Finland between 2011 and 2015 as part of a long-term environmental study. They applied that data to a new study of frost quakes, published in September in the Journal of Geophysical Research: Earth Surface.
Researchers think frost quakes are fairly common in boreal regions across the world. However, since frost quakes often happen in sparsely populated areas, much was unknown about their specific origins. In the new study, "we were actually able to collect data on a frost quake and use that data to determine what the cause was," said study co-author Roseanna Neupauer, a hydrogeologist at the University of Colorado Boulder.
The scientists used the environmental data leading up to the 2016 event in Finland to model the environmental conditions leading up to frost quakes. They discovered frost quakes most likely occur when soil is saturated with water and close to freezing.
"If the air temperature then drops rapidly, the water freezes quickly," Neupauer said. "When water freezes, it expands, and if the stress exerted by the rapidly expanding ice on the soil exceeds the strength of the soil, you get a frost quake."
The researchers noted that a thick layer of snow could reduce the chances of frost quakes by providing thermal insulation that would keep water and ice within the snow at more stable, albeit cold, temperatures. In contrast, on the day of the frost quake in Oulu, only a thin layer of snow covered the ground.
Okkonen now wants to conduct experiments to see what kinds of soils might be more prone to frost quakes. Neupauer noted that because climate change is expected to lead to more extreme swings in temperature, "perhaps it'll become more likely that we'll see more frost quakes.