Frost quakes are rare but scary

A frost quake can seem like an earthquake, or like a nearby explosion. The ground trembles, vibrates, and cracks, often with an explosive boom or a sound like rolling thunder. Flashing lights or lightning are sometimes reported in association with frost quakes. The visual effects are probably caused when rocks are crushed in the quake.

Localized frost quakes occur in subfreezing weather. They are rare in the United States, but have been reported in the northern states from Wisconsin to New England. They can also occur farther south when a polar vortex pulls frigid weather into areas that do not usually see such bone-chilling cold.

Also called cryoseisms or ice quakes, frost quakes occur when saturated ground is frozen deep by extreme cold. Water expands when it freezes, and expanding water is the primary cause of the effect. Temperate zone frost quakes and weather are closely linked, but they can also occur when water thaws and pools beneath a glacier in the Arctic or Antarctic. The ice above slips, cracks and booms.

North American frost quakes

According to the Maine geological survey, frost quakes usually occur during a sudden freeze. The first cold of winter or a cold snap in spring might produce a cryoseism. They often occur in the coldest part of the night, though they can happen any time. Frost quakes are extremely localized, unlike earthquakes. People down the block from an ice quake may feel and hear nothing.

Many frost quakes were reported in December of 2013, in association with sudden extremely cold weather brought south by a polar vortex. Tremors were noticed from Canada to Indiana and Ohio, waking and frightening residents who had never heard such a thing before.

Glacial ice quakes

Glacial cryoseisms usually occur in summer. Many were not noticed for some time, because of the isolation of glaciers and because the seismic vibrations they give off are so low. Most seismographs listen for earth quakes, which cause higher-pitched vibrations. It turns out that these ice quakes are quite common whenever glaciers move.

The causes of frost quakes

Frost quakes often happen when the ground is not yet insulated by snow. They are more likely to occur when bare ground is saturated before a sudden freeze. Therefore, scientists believe that the startling effects are caused by a sharp freeze that penetrates the groundwater. As the water freezes, it expands and the force of the expansion is powerful enough to suddenly displace masses of earth and rock. The displacement sounds like an explosion because, in a sense, it is one.

Ice quakes on the other hand, occur because ice turns to water. Melt water that pools beneath a glacier lubricates it, so that its great mass can flow freely, at least along part of its length. The low vibrations and audible booms are the result of ice crunching along, and, to a degree, of ice falling into the sea.

Frost quakes are strange but usually harmless. They release far less energy than true earthquakes do, and therefore do much less damage. The increasing volume of ice quakes however, may be yet another warning sign of climate change.