Just after the ice storm that covered the North Country Dec. 21 through 23, people in seven states in the U.S. reported hearing loud sounds and feeling varying degrees of shaking in the ground — not your ordinary frost heaves. Geologists explained the unusual events as cryoseisms.
Cryoseisms — also called frost quakes or ice quakes — are caused by sudden freezing deep underground. When water saturates the ground and the temperature drops suddenly from above freezing to below zero, the water freezes and expands. The freezing can occur rapidly especially when there is no snow to insulate the ground. At the moment when a large water-logged area freezes, the resulting expansion is forceful enough to feel like an explosion.
Cryoseismic events don’t correspond to specific geologic sites — they are more likely to be based on the specific weather pattern that favors rapid freezing. The ice-quaking phenomenon is linked to the speed of temperature change. Ice quakes are more common between midnight and dawn because this is the coldest part of the night.
In December and early January people reported sounds and ground shaking all over the local area but also in many locations in Canada, Vermont, Rhode Island, Michigan, Wisconsin and even Texas. Witnesses who experienced the recent ice quakes attributed what they heard and felt to a wide range of possible sources: trains braking; snow plows dropping blades onto a paved road; a tree falling on a house; a refrigerator falling over; the sonic boom of an airplane; fireworks; walls cracking; cannons; thunder; gun fire; pipes bursting; and Santa’s sleigh making a rough landing on the roof.
According to Andrew LaCroix, writing in Earthquake News, the vibrations of an ice quake usually don’t travel as far as an earthquake because they don’t “release much energy compared with a true earthquake caused by dislocation of rock within the earth.” The exact location of a quake can be hard to find because cracks can melt in and close or be covered by subsequent snowfall. But if successively larger underground areas freeze and expand, pressure can continue to mount and cause booming sounds for several days.
John Ebel, a professor of geophysics at Boston College, explains that lights can also be associated with ice quakes because there are electrical changes that happen in rocks when they get squeezed, causing visual effects like lightning.
While the sound of ice forming underground is fairly uncommon, the sound of ice forming on water is one well known to ice anglers, pond hockey players and Nordic skaters. These sounds spike the adrenaline of anyone on the ice.
Andreas Bick, a recording artist, writes in his blog, “In my experience, thin ice is especially interesting for acoustic phenomena; it is more elastic and sounds are propagated better across the surface. Snowfall, on the other hand, has a muffling effect and the sound can only travel to a limited extent. The ice sheet acts as a huge membrane across which the cracking and popping sounds spread.”
The closest sound I’ve heard to ice freezing is the twang-bang of big sheets of corrugated metal and the blaster sound effects in Star Wars. If you don’t plan to be on the ice this winter do some Googling — there are some stunningly beautiful audio recordings on the Internet made by various artists and ice fishermen.
Elizabeth Lee is a licensed guide who lives in Westport. She leads recreational and educational programs focused in the Champlain Valley throughout the year. Contact her at firstname.lastname@example.org.