Rocks may look solid, but there are enough cracks and voids in them so that with a good rain, they fill with water like a sponge. An odd property of water is that it is one of the rare substances that gains volume (about 9%) when it changes to a solid state. Thus, when water seeps into small fractures and voids, then freezes during a cold night or winter, its volume increases so that the ice in a fracture acts like a wedge, pushing and shoving apart the surrounding rocks.
The wedging action of a single freeze may not alone be capable of cracking open a “solid” rock. But over even a short geologic period of several thousands of years, the freezing wedge can be repeated thousands of times. A state of constant freeze, such as in the Antarctic, is not as effective as in a climate of rapidly fluctuating conditions between freezing and melting. Such conditions of repetitive hard freezes are common in Alpine and periglacial regions. Many of the mountains we view today bear the scars of ice fracturing from the repetitive hard freezes dating from the latest days of the latest ice age.
The effects of ice fracturing can be seen everywhere in the mountains of more temperate zones. It aids processes of surficial rock exfoliation, and can even be the cause of splitting off sides of mountains hundreds of meters in size. Yet is it a commonly overlooked geologic process within rocks examined by geologists in the hot summer months. In the winter, look out: rock falls are often the result of ice fracturing.
Photo by Anna Batsi
Rassios, Ghikas, Batsi, 2013. The Birth of Meteora.