What Is Frost Wedging?

Frost wedging is a type of mechanical weathering caused by frost and ice. Water expands when it freezes, and repeated cycles of freezing and thawing slowly weaken the structural integrity of porous and cracked rocks. Over time, frost wedging enlarges tiny cracks into huge fissures. The fissures eventually split the rock completely.

Frost wedging is a slow, cyclical process. During the day, liquid water warmed by the sun trickles into microscopic pores, cracks and spaces in rock. When the sun sets and the temperature drops, the water freezes and expands by 9 percent, exerting pressure on the surrounding rock. When the sun rises again, the frost melts and the water flows deeper into the expanded crack, where it freezes after sunset.

The most obvious evidence of frost wedging is the flat, plate-like surface created when the expanded rock joints finally split. Huge rock formations shaped by glaciers often display such sharp, flat faces. Frost wedging occurs only in climates that are cool to cold throughout the year. Canada, Scandinavia, northern Russia and Antarctica are particularly prone to this kind of weathering.

All types of weathering take place over time. However, biological factors that weaken rock serve as catalysts, decreasing the amount of time necessary for drastic change to happen. For example, moss and lichen weaken and destabilize small cracks in the rocks where they grow, making the material more vulnerable to the effects of expanding frost.