Temperature Related Ground Disturbance and Cryoseism

Temperature Related Ground Disturbance and Cryoseism

Temperature related ground disturbances

 

There are 4 types of ground disturbance associated with changing temperatures in cold environments – icequakes, frostquakes, ice heave, and frost heave. Only icequakes and frostquakes are cryoseisms.

Cryoseism - speed of temperature change

Icequake

An icequake can occur when lake ice expands during sudden warm periods and is unable to accommodate the change in volume.  Due to outwards propagating stress, the ice breaks, forming ridges and cracks on the shore.  This process can occur quickly enough that the seismic waves from the brittle failure of the ice are recorded on nearby seismometers.

Frostquake

Frostquakes occur when highly saturated soil (the soil is very wet) freezes quickly. This can happen when groundwater is present at or very close to the ground surface. Frostquakes have been reported in regions experiencing substantial temperature decrease over a short period (within 16–48 hours) – the sudden freezing of water to ice causes it to expand, putting enough stress on the soil to produce a fracture.

Frost heave

Frost heave occurs by the formation of ice lenses that grow increasingly larger due to the continual freezing of a continuous water supply from beneath the ground surface. For ideal conditions of frost heave to occur, water must be able to move upward from depth by the process of capillary action in which the adhesion forces between a water molecule and a soil particle are greater than the tugging force of gravity on that water molecule. As long as water from below can migrate to the freezing surface, the ice lenses will continue to grow, sometimes lifting the overlying soil as much as 30 cm or more.  Silty and loamy soils support capillary action the best and are therefore more susceptible to forming ice lenses.  Clayey soils are too dense and don’t easily transmit water to the freezing front, while gravelly soils are too porous to support capillary action.

Ice heave

Ice heave is another form of temperature related ground movement caused by frozen water. Ice heaves occur when large masses of lake ice are shoved onto the shore by strong winds during spring melt, or by the process of ice jacking.  

Ice jacking occurs when ice warms during the day and cools at night. During warm days, ice expands, radiating outward from the center of a lake. The outward expanding ice slides onto shore, sometimes pushing the sediment along the shoreline. As the temperature drops at night, however, the ice contracts, but cannot slide back into the lake. Instead, contraction cracks develop in the ice and water rises into the cracks to eventually freeze. The next day, the ice warms and expands again, but since the cracks are filled with frozen water, the ice creeps outward onto shore yet again. This jacking or ratcheting process repeats daily, causing ice to move steadily upward onto shore. Ice jacking can have serious effects on buildings close to the shoreline; damaging both the structure and the landscape.