January 19, 2014

Expanding upon mystery of recent sounds, shaking

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. 

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