Frost heaving

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Anatomy of a frost heave during spring thaw. The side of a 6-inch (15-cm) heave with the soil removed to reveal (bottom to top):
Needle ice, which has extruded up from the freezing front through porous soil from a water table below
Coalesced ice-rich soil, which has been subject to freeze-thaw
Thawed soil on top
Photograph taken 21 March 2010 in Norwich, Vermont Anatomy of a Frost Heave.jpg
Anatomy of a frost heave during spring thaw. The side of a 6-inch (15-cm) heave with the soil removed to reveal (bottom to top):
  • Needle ice, which has extruded up from the freezing front through porous soil from a water table below
  • Coalesced ice-rich soil, which has been subject to freeze-thaw
  • Thawed soil on top
Photograph taken 21 March 2010 in Norwich, Vermont

Frost heaving (or a frost heave) is an upwards swelling of soil during freezing conditions caused by an increasing presence of ice as it grows towards the surface, upwards from the depth in the soil where freezing temperatures have penetrated into the soil (the freezing front or freezing boundary). Ice growth requires a water supply that delivers water to the freezing front via capillary action in certain soils. The weight of overlying soil restrains vertical growth of the ice and can promote the formation of lens-shaped areas of ice within the soil. Yet the force of one or more growing ice lenses is sufficient to lift a layer of soil, as much as 1 foot (0.30 metres) or more. The soil through which water passes to feed the formation of ice lenses must be sufficiently porous to allow capillary action, yet not so porous as to break capillary continuity. Such soil is referred to as "frost susceptible". The growth of ice lenses continually consumes the rising water at the freezing front. [1] [2] Differential frost heaving can crack road surfaces—contributing to springtime pothole formation—and damage building foundations. [3] [4] Frost heaves may occur in mechanically refrigerated cold-storage buildings and ice rinks.

Contents

Needle ice is essentially frost heaving that occurs at the beginning of the freezing season, before the freezing front has penetrated very far into the soil and there is no soil overburden to lift as a frost heave. [5]

Mechanisms

Historical understanding of frost heaving

Ice lens formation resulting in frost heave in cold climates. Freezing air ice lens formation.jpg
Ice lens formation resulting in frost heave in cold climates.

Urban Hjärne described frost effects in soil in 1694. [lower-alpha 1] [5] [6] [7] [8] By 1930, Stephen Taber, head of the Department of Geology at the University of South Carolina, had disproved the hypothesis that frost heaving results from molar volume expansion with freezing of water already present in the soil prior to the onset of subzero temperatures, i.e. with little contribution from the migration of water within the soil.

Since the molar volume of water expands by about 9% as it changes phase from water to ice at its bulk freezing point, 9% would be the maximum expansion possible owing to molar volume expansion, and even then only if the ice were rigidly constrained laterally in the soil so that the entire volume expansion had to occur vertically. Ice is unusual among compounds because it increases in molar volume from its liquid state, water. Most compounds decrease in volume when changing phase from liquid to solid. Taber showed that the vertical displacement of soil in frost heaving could be significantly greater than that due to molar volume expansion. [1]

Taber demonstrated that liquid water migrates towards the freeze line within soil. He showed that other liquids, such as benzene, which contracts when it freezes, also produce frost heave. [9] This excluded molar volume changes as the dominant mechanism for vertical displacement of freezing soil. His experiments further demonstrated the development of ice lenses inside columns of soil that were frozen by cooling the upper surface only, thereby establishing a temperature gradient. [10] [11] [12]

Development of ice lenses

Frost heaves on a rural Vermont road during spring thaw Frost heaves on Bragg Hill Road in Norwich Vermont in March 2012--C.jpg
Frost heaves on a rural Vermont road during spring thaw

The dominant cause of soil displacement in frost heaving is the development of ice lenses. During frost heave, one or more soil-free ice lenses grow, and their growth displaces the soil above them. These lenses grow by the continual addition of water from a groundwater source that is lower in the soil and below the freezing line in the soil. The presence of frost-susceptible soil with a pore structure that allows capillary flow is essential to supplying water to the ice lenses as they form.

Owing to the Gibbs–Thomson effect of the confinement of liquids in pores, water in soil can remain liquid at a temperature that is below the bulk freezing point of water. Very fine pores have a very high curvature, and this results in the liquid phase being thermodynamically stable in such media at temperatures sometimes several tens of degrees below the bulk freezing point of the liquid. [13] This effect allows water to percolate through the soil towards the ice lens, allowing the lens to grow.

Another water-transport effect is the preservation of a few molecular layers of liquid water on the surface of the ice lens, and between ice and soil particles. Faraday reported in 1860 on the unfrozen layer of premelted water. [14] Ice premelts against its own vapor, and in contact with silica. [15]

Micro-scale processes

The same intermolecular forces that cause premelting at surfaces contribute to frost heaving at the particle scale on the bottom side of the forming ice lens. When ice surrounds a fine soil particle as it premelts, the soil particle will be displaced downward towards the warm direction within the thermal gradient due to melting and refreezing of the thin film of water that surrounds the particle. The thickness of such a film is temperature dependent and is thinner on the colder side of the particle.

Water has a lower thermodynamic free energy when in bulk ice than when in the supercooled liquid state. Therefore, there is a continuous replenishment of water flowing from the warm side to the cold side of the particle, and continuous melting to re-establish the thicker film on the warm side. The particle migrates downwards toward the warmer soil in a process that Faraday called "thermal regelation." [14] This effect purifies the ice lenses as they form by repelling fine soil particles. Thus a 10-nanometer film of unfrozen water around each micrometer-sized soil particle can move it 10 micrometers/day in a thermal gradient of as low as 1 °C m−1. [15] As ice lenses grow, they lift the soil above, and segregate soil particles below, while drawing water to the freezing face of the ice lens via capillary action.

Frost-susceptible soils

Partially melted and collapsed lithalsas (heaved mounds found in permafrost) have left ring-like structures on the Svalbard Archipelago Permafrost stone-rings hg.jpg
Partially melted and collapsed lithalsas (heaved mounds found in permafrost) have left ring-like structures on the Svalbard Archipelago

Frost heaving requires a frost-susceptible soil, a continual supply of water below (a water table) and freezing temperatures, penetrating into the soil. Frost-susceptible soils are those with pore sizes between particles and particle surface area that promote capillary flow. Silty and loamy soil types, which contain fine particles, are examples of frost-susceptible soils. Many agencies classify materials as being frost susceptible if 10 percent or more constituent particles pass through a 0.075 mm (No. 200) sieve or 3 percent or more pass through a 0.02 mm (No. 635) sieve. Chamberlain reported other, more direct methods for measuring frost susceptibility. [16] Based on such research, standard tests exist to determine the relative frost and thaw weakening susceptibility of soils used in pavement systems by comparing the heave rate and thawed bearing ratio with values in an established classification system for soils where frost-susceptibility is uncertain. [17]

Non-frost-susceptible soils may be too dense to promote water flow (low hydraulic conductivity) or too open in porosity to promote capillary flow. Examples include dense clays with a small pore size and therefore a low hydraulic conductivity and clean sands and gravels, which contain small amounts of fine particles and whose pore sizes are too open to promote capillary flow. [18]

Landforms created by frost heaving

Palsas (heaving of organics-rich soils in discontinuous permafrost) may be found in alpine areas below Mugi Hill on Mount Kenya. Frost upheaval.jpg
Palsas (heaving of organics-rich soils in discontinuous permafrost) may be found in alpine areas below Mugi Hill on Mount Kenya.

Frost heaving creates raised-soil landforms in various geometries, including circles, polygons and stripes, which may be described as palsas in soils that are rich in organic matter, such as peat, or lithalsa [19] in more mineral-rich soils. [20] The stony lithalsa (heaved mounds) found on the archipelago of Svalbard are an example. Frost heaves occur in alpine regions, even near the equator, as illustrated by palsas on Mount Kenya. [21]

In Arctic permafrost regions, a related type of ground heaving over hundreds of years can create structures, as high as 60 metres, known as pingos, which are fed by an upwelling of ground water, instead of the capillary action that feeds the growth of frost heaves. Cryogenic earth hummocks are a small formation resulting from granular convection that appear in seasonally frozen ground and have many different names; in North America they are earth hummocks; thúfur in Greenland and Iceland; and pounus in Fennoscandia.

Polygonal forms apparently caused by frost heave have been observed in near-polar regions of Mars by the Mars Orbiter Camera (MOC) aboard the Mars Global Surveyor and the HiRISE camera on the Mars Reconnaissance Orbiter. In May 2008 the Mars Phoenix lander touched down on such a polygonal frost-heave landscape and quickly discovered ice a few centimetres below the surface.

In refrigerated buildings

Cold-storage buildings and ice rinks that are maintained at sub-freezing temperatures may freeze the soil below their foundations to a depth of tens of meters. Seasonally frozen buildings, e.g. some ice rinks, may allow the soil to thaw and recover when the building interior is warmed. If a refrigerated building's foundation is placed on frost-susceptible soils with a water table within reach of the freezing front, then the floors of such structures may heave, due to the same mechanisms found in nature. Such structures may be designed to avoid such problems by employing several strategies, separately or in tandem. The strategies include placement of non-frost-susceptible soil beneath the foundation, adding insulation to diminish the penetration of the freezing front, and heating the soil beneath the building sufficiently to keep it from freezing. Seasonally operated ice rinks can mitigate the rate of subsurface freezing by raising the temperature of the ice. [22]

See also

Footnotes

  1. In the section II. Fl. Om Jord och Landskap i gemeen (II. About the soil and the landscape in general) of his book, Hiärne mentions the phenomenon of "earth casting" or "earth heaving", in which, after the spring thaw, large chunks of sod appear to have been ripped from the ground and tossed: "3. Whether one sees in other places in Sweden, Finland and Iceland, etc., as has so happened in Uppland and in Närke in Viby parish, royal Vallby, that the earth itself with turf and all [in pieces] up to a few cubits long and wide has been thrown upwards which 20 or more men could not do, and a large pit is left afterwards." (3. Om man seer uti andre Orter i Swerige / Fin-Est och Lif-land / etc. så wara stedt / som hår i Upland / och i Nårike i Wijby Sochn / Kongz Wallby / at Jorden sig med Torff och all till någre Alnars Långd och bredd har opkastat det 20 eller flere Karlar teke hint göra / och en stoor Graff effter sig lemnat.) Urban Hjärne, Een kort Anledning till åtskillige Malm- och Bergarters, Mineraliers, Wäxters, och Jordeslags sampt flere sällsamme Tings, effterspöriande och angifwande [A brief guide to discovering and specifying various types of ores and mountains, minerals, plants, and soils, together with several unusual things] (Stockholm, Sweden: 1694). Available on-line at: National Library of Sweden.

Related Research Articles

<span class="mw-page-title-main">Frost</span> Coating or deposit of ice

Frost is a thin layer of ice on a solid surface, which forms from water vapor that deposits onto a freezing surface. Frost forms when the air contains more water vapor than it can normally hold at a specific temperature. The process is similar to the formation of dew, except it occurs below the freezing point of water typically without crossing through a liquid state.

<span class="mw-page-title-main">Weathering</span> Deterioration of rocks and minerals through exposure to the elements

Weathering is the deterioration of rocks, soils and minerals through contact with water, atmospheric gases, sunlight, and biological organisms. Weathering occurs in situ, and so is distinct from erosion, which involves the transport of rocks and minerals by agents such as water, ice, snow, wind, waves and gravity.

<span class="mw-page-title-main">Supercooling</span> Lowering the temperature of a liquid below its freezing point without it becoming a solid

Supercooling, also known as undercooling, is the process of lowering the temperature of a liquid below its freezing point without it becoming a solid. It is achieved in the absence of a seed crystal or nucleus around which a crystal structure can form. The supercooling of water can be achieved without any special techniques other than chemical demineralization, down to −48.3 °C (−54.9 °F). Supercooled water can occur naturally, for example in the atmosphere, animals or plants.

<span class="mw-page-title-main">Hummock</span> Small knoll or mound above ground

In geology, a hummock is a small knoll or mound above ground. They are typically less than 15 meters (50 ft) in height and tend to appear in groups or fields. Large landslide avalanches that typically occur in volcanic areas are responsible for formation of hummocks. From the initiation of the landslide to the final formation, hummocks can be characterized by their evolution, spatial distribution, and internal structure. As the movement of landslide begins, the extension faulting results in formation of hummocks with smaller ones at the front of the landslide and larger ones in the back. The size of the hummocks is dependent on their position in the initial mass. As this mass spreads, the hummocks further modify to break up or merge to form larger structures. It is difficult to make generalizations about hummocks because of the diversity in their morphology and sedimentology. An extremely irregular surface may be called hummocky.

<span class="mw-page-title-main">Talik</span>

A talik is a layer of year-round unfrozen ground that lies in permafrost areas. In regions of continuous permafrost, taliks often occur underneath shallow thermokarst lakes and rivers, where the deep water does not freeze in winter and thus the soil underneath does not freeze either. Sometimes closed, open, and through taliks are distinguished. These terms refer to whether the talik is surrounded by permafrost, open at the top, or open both at the top and above an unfrozen layer beneath the permafrost.

<span class="mw-page-title-main">Active layer</span>

In environments containing permafrost, the active layer is the top layer of soil that thaws during the summer and freezes again during the autumn. In all climates, whether they contain permafrost or not, the temperature in the lower levels of the soil will remain more stable than that at the surface, where the influence of the ambient temperature is greatest. This means that, over many years, the influence of cooling in winter and heating in summer will decrease as depth increases.

<span class="mw-page-title-main">Pingo</span> Mound of earth-covered ice

Pingos are intrapermafrost ice-cored hills, 3–70 m (10–230 ft) high and 30–1,000 m (98–3,281 ft) in diameter. They are typically conical in shape and grow and persist only in permafrost environments, such as the Arctic and subarctic. A pingo is a periglacial landform, which is defined as a non-glacial landform or process linked to colder climates. It is estimated that there are more than 11,000 pingos on Earth. The Tuktoyaktuk peninsula area has the greatest concentration of pingos in the world with a total of 1,350 pingos. There is currently remarkably limited data on pingos.

In fluid statics, capillary pressure is the pressure between two immiscible fluids in a thin tube, resulting from the interactions of forces between the fluids and solid walls of the tube. Capillary pressure can serve as both an opposing or driving force for fluid transport and is a significant property for research and industrial purposes. It is also observed in natural phenomena.

<span class="mw-page-title-main">Drunken trees</span> Stand of trees displaced from their normal vertical alignment

Drunken trees, tilted trees, or a drunken forest, is a stand of trees rotated from their normal vertical alignment.

<span class="mw-page-title-main">Needle ice</span> Ice column formed when liquid groundwater rises into freezing air

Needle ice is a needle-shaped column of ice formed by groundwater. Needle ice forms when the temperature of the soil is above 0 °C (32 °F) and the surface temperature of the air is below 0 °C (32 °F). Liquid water underground rises to the surface by capillary action, and then freezes and contributes to a growing needle-like ice column. The process usually occurs at night when the air temperature reaches its minimum.

<span class="mw-page-title-main">Patterned ground</span>

Patterned ground is the distinct and often symmetrical natural pattern of geometric shapes formed by the deformation of ground material in periglacial regions. It is typically found in remote regions of the Arctic, Antarctica, and the Outback in Australia, but is also found anywhere that freezing and thawing of soil alternate; patterned ground has also been observed in the hyper-arid Atacama Desert and on Mars. The geometric shapes and patterns associated with patterned ground are often mistaken as artistic human creations. The mechanism of the formation of patterned ground had long puzzled scientists but the introduction of computer-generated geological models in the past 20 years has allowed scientists to relate it to frost heaving, the expansion that occurs when wet, fine-grained, and porous soils freeze.

<span class="mw-page-title-main">Palsa</span> A low, often oval, frost heave occurring in polar and subpolar climates

Palsas are peat mounds with a permanently frozen peat and mineral soil core. They are a typical phenomenon in the polar and subpolar zone of discontinuous permafrost. One of their characteristics is having steep slopes that rise above the mire surface. This leads to the accumulation of large amounts of snow around them. The summits of the palsas are free of snow even in winter, because the wind carries the snow and deposits on the slopes and elsewhere on the flat mire surface. Palsas can be up to 150 m in diameter and can reach a height of 12 m.

<span class="mw-page-title-main">Frost boil</span> Small circular mounds of fresh soil material formed by frost action and cryoturbation

A frost boil, also known as mud boils, a stony earth circles, frost scars, or mud circles, are small circular mounds of fresh soil material formed by frost action and cryoturbation. They are found typically found in periglacial or alpine environments where permafrost is present, and may damage roads and other man-made structures. They are typically 1 to 3 metres in diameter.

<span class="mw-page-title-main">Ice lens</span> Ice within soil or rock

Ice lenses are bodies of ice 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, wedging the soil or rock apart. Ice lenses grow parallel to the surface and several centimeters to several decimeters deep in the soil or rock. Studies from 1990 have demonstrated that rock fracture by ice segregation is a more effective weathering process than the freeze-thaw process which older texts proposed.

<span class="mw-page-title-main">Frost weathering</span> Mechanical weathering processes induced by the freezing of water into ice

Frost weathering is a collective term 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 boulders. It is most pronounced in high-altitude and high-latitude areas and is especially associated with alpine, periglacial, subpolar maritime, and polar climates, but may occur anywhere at sub-freezing temperatures if water is present.

Cryosuction is the concept of negative pressure in freezing liquids so that more liquid is sucked into the freezing zone. In soil, the transformation of liquid water to ice in the soil pores causes water to migrate through soil pores to the freezing zone through capillary action.

<span class="mw-page-title-main">Ice segregation</span> Geological phenomenon

Ice segregation is the geological phenomenon produced by the formation of ice lenses, which induce erosion when moisture, diffused within soil or rock, accumulates in a localized zone. The ice initially accumulates within small collocated pores or pre-existing cracks, and, as long as the conditions remain favorable, continues to collect in the ice layer or ice lens, wedging the soil or rock apart. Ice lenses grow parallel to the surface and several centimeters to several decimeters deep in the soil or rock. Studies between 1990 and present have demonstrated that rock fracture by ice segregation is a more effective weathering process than the freeze-thaw process which older texts proposed.

<span class="mw-page-title-main">Periglaciation</span> Natural processes associated with freezing and thawing in regions close to glaciers

Periglaciation describes geomorphic processes that result from seasonal thawing and freezing, very often in areas of permafrost. The meltwater may refreeze in ice wedges and other structures. "Periglacial" originally suggested an environment located on the margin of past glaciers. However, freeze and thaw cycles influence landscapes also outside areas of past glaciation. Therefore, periglacial environments are anywhere when freezing and thawing modify the landscape in a significant manner.

Frost damage is caused by moisture freezing in the construction. Frost damage can occur as cracks, stone splinters and swelling of the material.

<span class="mw-page-title-main">Freeze-fracture</span> Freeze-fracture processes and methods

Freeze-fracture is a natural occurrence leading to processes like erosion of the earths crust or simply deterioration of food via freeze-thaw cycles. To investigate the process further freeze-fracture is artificially induced to view in detail the properties of materials. Fracture during freezing is often the result of crystallizing water which results in expansion. Crystallization is also a factor leading to chemical changes of a substance due to changes in the crystal surroundings called eutectic formation.

References

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Further reading