Frost weathering
Encyclopedia
Frost weathering is a collective name for several mechanical weathering
processes induced by stresses created by the freezing of water into ice
. The term serves as an umbrella term for a variety of processes such as frost shattering, frost wedging and cryofracturing. The process may act on a wide range of spatial and temporal scales, from minutes to years and from dislodging mineral grains to fracturing boulder
s. Frost weathering is mainly driven by the frequency and intensity of freeze-thaw cycles and the properties of the materials subject to weathering. It is most pronounced in high altitude and latitude areas and is especially associated with alpine
, periglacial
, subpolar maritime and polar climate
s but occurs wherever freeze-thaw cycles are present.
, its volume increases by nine percent. Under specific circumstances, this expansion is able to displace or fracture rock. At a temperature of -22 °C, ice growth is known to be able to generate pressures of up to 207MPa
, more than enough to fracture any rock. For frost weathering to occur by volumetric expansion, the rock must have almost no air that can be compressed to compensate for the expansion of ice, which means it has to be water-saturated and frozen quickly from all sides so that the water does not migrate away and the pressure is exerted on the rock. These conditions are considered unusual, restricting it to a process of importance within a few centimeters of a rock's surface and on larger existing water-filled joints in a process called ice wedging.
Not all volumetric expansion is caused by the pressure of the freezing water; it can be caused by stresses in water that remains unfrozen. When ice growth induces stresses in the pore water that breaks the rock, the result is called hydrofracture. Hydrofracturing is favoured by large interconnected pores or large hydraulic gradients in the rock. If there are small pores, a very quick freezing of water in parts of the rock may expel water, and if the water is expelled faster than it can migrate, pressure may rise, fracturing the rock.
Since research in physical weathering begun around 1900, volumetric expansion was, until the 1980s, held to be the predominant process behind frost weathering. This view was challenged in 1985 and 1986 publications by Walder and Hallet. Nowadays researchers such as Matsuoka and Murton consider the "conditions necessary for frost weathering by volumetric expansion" as unusual.
Certain frost-susceptible soils expand or heave
upon freezing as a result of water migrating via capillary action
to grow ice lens
es near the freezing front. This same phenomenon occurs within pore spaces of rocks. The ice accumulations grow larger as they attract liquid water from the surrounding pores. The ice crystal growth weakens the rocks which, in time, break up. It is caused by the expansion of ice when water freezes, putting considerable stress on the walls of containment. This is actually a very common process in all humid, temperate areas where there is exposed rock, especially porous rocks like sandstone
. Sand can often be found just under the faces of exposed sandstone where individual grains have been popped off, one by one. This process is often termed frost spalling. In fact, this is often the most important weathering process for exposed rock in many areas.
Similar processes can act on asphalt pavements, contributing to various forms of cracking and other distresses, which, when combined with traffic and the intrusion of water, accelerate rutting, the formation of pothole
s, and other forms of pavement roughness.
Weathering
Weathering is the breaking down of rocks, soils and minerals as well as artificial materials through contact with the Earth's atmosphere, biota and waters...
processes induced by stresses created by the freezing of water into ice
Ice
Ice is water frozen into the solid state. Usually ice is the phase known as ice Ih, which is the most abundant of the varying solid phases on the Earth's surface. It can appear transparent or opaque bluish-white color, depending on the presence of impurities or air inclusions...
. The term serves as an umbrella term for a variety of processes such as frost shattering, frost wedging and cryofracturing. The process may act on a wide range of spatial and temporal scales, from minutes to years and from dislodging mineral grains to fracturing boulder
Boulder
In geology, a boulder is a rock with grain size of usually no less than 256 mm diameter. While a boulder may be small enough to move or roll manually, others are extremely massive....
s. Frost weathering is mainly driven by the frequency and intensity of freeze-thaw cycles and the properties of the materials subject to weathering. It is most pronounced in high altitude and latitude areas and is especially associated with alpine
Alpine climate
Alpine climate is the average weather for a region above the tree line. This climate is also referred to as mountain climate or highland climate....
, periglacial
Periglacial
Periglacial is an adjective originally referring to places in the edges of glacial areas, but it has later been widely used in geomorphology to describe any place where geomorphic processes related to freezing of water occur...
, subpolar maritime and polar climate
Polar climate
Regions with a polar climate are characterized by a lack of warm summers . Regions with polar climate cover over 20% of the Earth. The sun shines 24 hours in the summer, and barely ever shines at all in the winter...
s but occurs wherever freeze-thaw cycles are present.
Volumetric expansion
When water freezes to iceIce
Ice is water frozen into the solid state. Usually ice is the phase known as ice Ih, which is the most abundant of the varying solid phases on the Earth's surface. It can appear transparent or opaque bluish-white color, depending on the presence of impurities or air inclusions...
, its volume increases by nine percent. Under specific circumstances, this expansion is able to displace or fracture rock. At a temperature of -22 °C, ice growth is known to be able to generate pressures of up to 207MPa
MPA
-Academic degrees:* Master of Professional Accountancy* Master of Public Administration* Master of Public Affairs* Master of Physician's Assistant-Chemicals:* Medroxyprogesterone acetate, also known by the brand name Depo-Provera* Morpholide of pelargonic acid...
, more than enough to fracture any rock. For frost weathering to occur by volumetric expansion, the rock must have almost no air that can be compressed to compensate for the expansion of ice, which means it has to be water-saturated and frozen quickly from all sides so that the water does not migrate away and the pressure is exerted on the rock. These conditions are considered unusual, restricting it to a process of importance within a few centimeters of a rock's surface and on larger existing water-filled joints in a process called ice wedging.
Not all volumetric expansion is caused by the pressure of the freezing water; it can be caused by stresses in water that remains unfrozen. When ice growth induces stresses in the pore water that breaks the rock, the result is called hydrofracture. Hydrofracturing is favoured by large interconnected pores or large hydraulic gradients in the rock. If there are small pores, a very quick freezing of water in parts of the rock may expel water, and if the water is expelled faster than it can migrate, pressure may rise, fracturing the rock.
Since research in physical weathering begun around 1900, volumetric expansion was, until the 1980s, held to be the predominant process behind frost weathering. This view was challenged in 1985 and 1986 publications by Walder and Hallet. Nowadays researchers such as Matsuoka and Murton consider the "conditions necessary for frost weathering by volumetric expansion" as unusual.
Ice segregation
Frost heaving
Frost heaving results from ice forming beneath the surface of soil during freezing conditions in the atmosphere. The ice grows in the direction of heat loss , starting at the freezing front or boundary in the soil...
upon freezing as a result of water migrating via capillary action
Capillary action
Capillary action, or capilarity, is the ability of a liquid to flow against gravity where liquid spontanously rise in a narrow space such as between the hair of a paint-brush, in a thin tube, or in porous material such as paper or in some non-porous material such as liquified carbon fiber, or in a...
to grow ice lens
Ice lens
An Ice Lens or ice lenses are formed when moisture, diffused within soil or rock, accumulates in a localized zone. The ice initially accumulates within small collocated pores or pre-existing crack, and, as long as the conditions remain favorable, continues to collect in the ice layer or ice lens,...
es near the freezing front. This same phenomenon occurs within pore spaces of rocks. The ice accumulations grow larger as they attract liquid water from the surrounding pores. The ice crystal growth weakens the rocks which, in time, break up. It is caused by the expansion of ice when water freezes, putting considerable stress on the walls of containment. This is actually a very common process in all humid, temperate areas where there is exposed rock, especially porous rocks like sandstone
Sandstone
Sandstone is a sedimentary rock composed mainly of sand-sized minerals or rock grains.Most sandstone is composed of quartz and/or feldspar because these are the most common minerals in the Earth's crust. Like sand, sandstone may be any colour, but the most common colours are tan, brown, yellow,...
. Sand can often be found just under the faces of exposed sandstone where individual grains have been popped off, one by one. This process is often termed frost spalling. In fact, this is often the most important weathering process for exposed rock in many areas.
Similar processes can act on asphalt pavements, contributing to various forms of cracking and other distresses, which, when combined with traffic and the intrusion of water, accelerate rutting, the formation of pothole
Pothole
A pothole is a type of disruption in the surface of a roadway where a portion of the road material has broken away, leaving a hole.- Formation :...
s, and other forms of pavement roughness.