Snap! Crackle! Boom! Did a quake startle you awake?
Strange sounds have been heard across Ontario as the province goes through a deep freeze.
Perhaps you heard loud booms during late December and early January that woke you at night. You may have checked the Earthquakes Canada website to confirm there were no recorded earthquakes in your area. If that’s the case, maybe you experienced a frost quake — a phenomenon called cryoseism.
What is this strange phenomenon? It’s simple. The noise comes from the cracking of the ground when the groundwater freezes — sort of a shallow underground land explosion. But don’t worry.
The ground isn’t exploding, so you won’t see piles of broken rock in the bush near your community.
When temperatures drop suddenly, the groundwater near the surface of the Earth can freeze.
When a body of groundwater freezes, the resulting ice block expands by about nine per cent compared to the size of the original water body. This is a critical trigger. The expanded ice needs more room to exist in the ground, so the freezing water has to push the solid ground away to make space for the expanding body of ice.
The ground is strong, but there is a big force associated with the expansion of water when it turns to ice. When the freeze takes place quickly, the land cannot adjust and it may crack suddenly. BAM! A frost quake occurs. The cracking and breaking of the ground can create a loud boom. The noise sounds a bit like taking a dry piece of wood and bending it until it breaks with a loud crack. You may have experienced a variation of this phenomenon if you’ve ever left a can of pop outside on a cold winter night. In the morning, you see the result of freezing water: the can was ripped apart by the expanding ice.
For cryoseism, or frost quake, to occur, three factors appear to be key. First, a rapid drop in temperature to well-below freezing is needed. Second, the ground must be saturated with water due to rain, sleet, snowmelt, or flooding. Finally, the area must have little or no snow cover to insulate the ground. Geologically, areas of permeable materials, such as sand or gravel, are susceptible to frost action and are more likely sources of a frost quake.
Frost quakes may occur in late fall, early winter, during a January thaw, or during a deep freeze in spring after snow melt. Because it is normally colder at night, many cryoseisms occur between midnight and dawn.
Big frost quakes may have visible signs as well as the noise. In the affected area, surface cracks may appear where the land split apart underground. Some people report seeing distant flashing lights before or during a frost quake, possibly due to electrical changes when rocks are affected.
Some may wonder if we can distinguish between an earthquake and a frost quake. Frost quakes may be mistaken for minor earthquakes because they both can cause the ground to shake and crack, and both may be accompanied by loud thundering or booming sounds.
Some geologists suggest that it may be possible to distinguish frost quakes from earthquakes based on local weather and geological conditions. For example, a quake immediately after a big drop in temperature, in an area of stable rock, is likely a frost quake. After a frost quake, there is usually little to no continued quaking activity. This differs from earthquakes where aftershocks can be felt for hours or days. Also, not all frost quakes are picked up by earthquake monitoring sensors because of the characteristics of the ground shaking.
Historically, frost quakes are more common in the Great Lakes and St. Lawrence River area.
One reason may be the large number of people who live in this area who hear and report the events. The weather patterns may be another reason because this area enjoys weather swings from melting, to rain, to freezing rain, to bitterly cold temperatures all within a few hours. The increase in reports across southern Ontario in December 2013 and January 2014 may reflect the ice storm and the cold temperatures that followed.
I have heard stories from several Far North First Nation communities about loud booms and distant flashing lights, and have been asked if an earthquake occurred. In fact, during my last visit with Cat Lake First Nation in December 2013, several people reported being awakened in the night by a loud noise and asked if there could have been an earthquake. There is no record of an earthquake on the Earthquakes Canada seismic monitoring network but, it was a bitterly cold week and the snow cover was still relatively thin. Was this a frost quake?
I have heard similar stories from communities along Hudson Bay that included lights on the horizon. Perhaps frost quakes are more common in the Far North than assumed? Perhaps it is lake or Hudson Bay ice that is expanding and cracking, or the freezing of the groundwater related to melting permafrost that created the event? Perhaps the explanation is a cryoseism event? Mysteries of Ontario beneath our feet!
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