There’s a lot of underground activity in Maine. Geologically speaking, that is.
Every year the state records at least one earthquake between magnitude 3 and 3.9, which is enough to swing a hanging lamp or rattle some dishes. In between there are a handful of lesser quakes.
In Maine, there are also seasonal seismic events called cryoseisms or, more commonly, frost quakes. These happen when heavily saturated ground rapidly freezes. The water in the soil expands until it starts pushing against the soil and into the cracks of rocks around it.
That pressure builds until it actually breaks the rocks or fractures the soil. When that happens it can sound like snow sliding off a roof or, as one homeowner in Nova Scotia described, like a bowling ball being dropped on his roof.
Maine gets its fair share of frost quakes, but they rarely reach the bowling ball on the roof level, according to Henry Berry, physical geologist at the Maine Geological Survey.
When they do occur, Berry said, people often mistake them for small earthquakes.
“It’s really hard to know the difference unless you ask,” Berry said.
Since the Maine Geologic Survey constantly records all seismic activity in the state, as long as you note the exact time you observe a sound or shake, geologists can check what was going on at that exact moment.
“You can look at our website and see if any earthquakes were reported,” Berry said. “If you want to report your observation to us, we need to know the time before we check the seismic reports because you are asking us to find a tiny wiggly line in a whole bunch of wiggly lines.”
Frost quakes tend to be very localized, according to Berry. The vibrations they create don’t travel far. But since they do occur just below the surface, they can be pretty impressive if you are right on top of one.
In 2005, a frost quake large enough to shake the ground and crack a paved driveway was reported in Limington. The homeowner said it was loud enough that he thought his car had exploded.
Frost quakes tend to happen between midnight and dawn during the coldest part of the night. If conditions are just right, there may be a series of booms over a few hours.
Those conditions need to line up just right, according to Don Dumont, warning coordinator meteorologist with the National Weather Service office in Caribou.
“You need a shallow amount of snow,” Dumont said. “You need moisture in the soil and really cold, sub-zero temperatures.”
Lack of snow cover means the saturated soil has little to insulate it when very cold, arctic air rushes into the area. That creates a rapid freeze and expansion.
“You get that pressure release and it makes booms and cracks,” Dumont said. “A good analogy is when you step on your deck on a really cold morning and it cracks loudly.”
Current snow depth and meteorological conditions favor frost quakes near the coast, Dumont said.
Over time, the conditions needed for frost quakes in Maine are increasing with extreme weather events on the rise due to climate change.
“Maine winters are warming and as part of a changing climate, we are seeing a tendency for more extreme weather events,” according to Sean Birkel, Maine state climatologist at the University of Maine Climate Change Institute. “In winter this can mean patterns that bring extreme cold followed by extreme warmth.”
While there are no hard data on what it means in terms of frost quakes, Birkel said scientific observations are showing these extreme events are creating conditions they need.
“One of the factors is a warming ocean surface that increases evaporation and overall more moisture entering the atmosphere,” he said. “That means there is more moisture available for precipitation and that is, in part, fueling more rainfall.”
Berry would love to see more people reporting any suspected cryoseismic activity, given that they do not register on the seismic monitoring equipment. They can be reported through email to the Maine Geological Survey at [email protected].
“For us to determine if there was a frost quake, we need human beings to tell us,” Berry said.
