Frost boil

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Mud boils near Lapporten, Sweden Mud boils.JPG
Mud boils near Lapporten, Sweden

A frost boil, also known as mud boils, a stony earth circles, frost scars, or mud circles, [1] 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. [2] They are typically 1 to 3 metres in diameter. [3]

Contents

Frost boils are amongst the most common features of patterned ground, the pervasive process shaping the topology of soils in periglacial regions. They generally form regular patterns of polygons. Frost boils are a type of nonsorted circle, and are characterized from other circles by barren centres of mineral soil and intercircle regions filled with vegetation and peat. [4] It is named after skin boils due to similarities in their formation processes, although subsequent research has shown other methods of formation.

Frost boils have been observed on Mars, indicating the presence of periglacial processes similar to those on Earth. [5]

Formation

The most accepted theory involves cryoturbation caused by differences in moisture conditions and ground temperature. Other recent research posits that frost boils are formed by several interacting mechanisms, including differential frost heaving, load casting, convection, [6] frost cracking, mass displacement, and soil sorting. [7] The traditional model of injection, however, may still apply for some frost boils. Models generally presume soil is predominately silt or clay, for the reasons listed under the injection subsection.

Injection

Frost boils occur in soils of poorly-sorted sediments with significant silt and/or clay content. These soils include perennially frozen till, marine clay, colluvium, and other muds. These soils have low liquid limits, low plasticity limits, and high natural moisture contents. These soils liquefy and flow readily in response to slight changes to either internal or external stress, or a change in water content. [8] Localized stresses are often the result of moisture being confined in the active layer by the underlying permafrost and a semi-rigid carapace of dried surface mud, created by desiccation during the late summer. The moisture content of soils may increase during summer due to rain. Other stresses include the volumetric change of water during the freezing and thawing, and the flow of groundwater.

The subsequent increase of hydrostatic, artesian, and/or pore water pressure pressures on slopes. When internal stresses cannot be contained, the semi-rigid surface layer ruptures. The saturated mud bursts above the surface, creating a mud boil. [9]

Soil Liquefaction

This process is analogous to the formation of sand boils. Where soils are badly drained, soil temperatures are more sensitive to changes in the atmospheric temperature. Soil aggregates are less stable near the surface as freezing occurs more rapidly. Deeper soils experience longer periods of stability due to freeze drying, or cryodesiccation. Deeper soils also experience greater stresses due to the secondary refreezing of soil in late autumn. As a result, the introduction of additional water due to thaw or groundwater flows is likely to cause deeper soil to liquefy and deform like plastic. The high viscosity of water close to 0 °C promotes aggregate explosion and particle dispersion.

This process is commonplace in alpine regions where soil temperatures rarely drop below -10 °C. [10]

Cyroturbation

Frost heaving is greater at the center of frost boils when compared to the margins of frost boils due to the ice-rich conditions at the center and vegetative cover at the margins. Due to the higher moisture content, ice predominantly forms segregated ice lenses in shallow soils near the center of the frost boil. Moisture content at the margins, however, is predominantly in the form of pore ice. Ground subsistence at the center of frost boils during thawing season is correspondingly more rapid and of a greater magnitude when compared to the margins. Subsidence at the margins advances slowly in the earlier thawing period but increases to rates comparable to center by mid-summer.

Huge frost boil.jpg

Measurements conducted on frost boils in Adventdalen, Svalbard has found that the ground subsistence rates at center of frost boils of averaged 8 mm per day during late May but decreased to less than 1 mm per day in mid-July. The same found that heaving was considerably greater at centers (c. 9.5 mm per day) than margins (c. 1.6 mm per day). Correspondingly, ice core analyses conducted on frost boils has found that samples extracted from the center of Frost Boils have higher concentration of ice lenses in shallow soils, when compared to cores extracted from marginal and intercircle regions. Most ice lenses have a diameter smaller than 3 mm. [12]

Topology

Frost boils often occur in groups, and may form terraces if a series of them occur on a slope. On slopes, frost boils are sometimes protected from erosion by a thin layer of mosses and lichens which retains moisture through surface tension as sediments flow downslope to form a lobe. These landforms eventually settle like a caterpillar track.

Common characteristics of landforms created by frost boils include a bowl-shaped boil, an elevated center, a formation of an organic layer on the outer edge, and resistance of the soil surface to vegetation colonization. [13]

Drainage on frost boils differs as a result of micro relief across the frost boil surface. In warm seasons (summer), the elevated center of the frost boil is moderately well drained compared to the depressed inter boil. The permafrost table surface is also affected by differing activity across the boil. The inner boil is more active and generally has more than twice the active depth than the inter boil, which causes the permafrost table surface to be in a nearly perfect bowl shape. [14]

Biology

Frost boils may be the predominant form of topology and patterned ground in tundras. Three elements of frost boils may repeat over large areas: patches (the center of frost boils), rims, and troughs. The density of these elements are higher in the high arctic when compared to southern tundras. Each element of frost boils is a distinct microecosystem. Although vegetation is rare on patches, it may host many species of small mosses, crustose lichens, and solitary small vascular plants. Well-developed moss covers the surface of most rims and troughs. Rims and troughs are also home to a large number of herbs and small or stunted shrubs. [15]

Arctic soils acidify over time due to the presence of aerobic bacteria which breaks down water-soluble salts within soil moisture, reducing the fertility of most periglacial regions. Cryoturbation within active frost boils may allow water containing basic salts to permeate from depth to the surface, neutralizing soil acidity and replenishing the supply of nutrients. [16] Nutrients in plant matter, particularly carbon and nitrogen, are deposited and concentrated in troughs. These nutrients are intensely recycled in each stage of ecological succession. Troughs thus have an overall higher net ecosystem production and carbon accumulation rate than patches. Other reasons contributing to the greater carbon accumulation in troughs include a higher soil moisture content that makes troughs unfavorable for decomposition. Troughs may also have a higher carbon content due to it being older and having experienced a longer period of soil formation. [17]

The presence of plants affect the development of frost boils. In the high arctic where plants are rare, physical processes of heave and soil formation are dominant. In warmer temperate regions, dense vegetation insulates inter-boil areas, lowering soil temperatures and decreasing the potential for heave. The strong contrast between vegetated inter-boil regions and center patches lead to maximum differential heave, resulting in frost boils being better developed. [18]

See also

Related Research Articles

<span class="mw-page-title-main">Permafrost</span> Soil frozen for a duration of at least two years

Permafrost is soil or underwater sediment which continuously remains below 0 °C (32 °F) for two years or more: the oldest permafrost had been continuously frozen for around 700,000 years. Whilst the shallowest permafrost has a vertical extent of below a meter (3 ft), the deepest is greater than 1,500 m (4,900 ft). Similarly, the area of individual permafrost zones may be limited to narrow mountain summits or extend across vast Arctic regions. The ground beneath glaciers and ice sheets is not usually defined as permafrost, so on land, permafrost is generally located beneath a so-called active layer of soil which freezes and thaws depending on the season.

<span class="mw-page-title-main">Scree</span> Broken rock fragments at base of cliff

Scree is a collection of broken rock fragments at the base of a cliff or other steep rocky mass that has accumulated through periodic rockfall. Landforms associated with these materials are often called talus deposits. Talus deposits typically have a concave upwards form, where the maximum inclination corresponds to the angle of repose of the mean debris particle size. The exact definition of scree in the primary literature is somewhat relaxed, and it often overlaps with both talus and colluvium.

<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">Frost heaving</span> Upwards swelling of soil during freezing

Frost heaving 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. 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 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. Differential frost heaving can crack road surfaces—contributing to springtime pothole formation—and damage building foundations. Frost heaves may occur in mechanically refrigerated cold-storage buildings and ice rinks.

<span class="mw-page-title-main">Cryoturbation</span> Mixing of soil horizons due to freezing and thawing.

In gelisols, cryoturbation refers to the mixing of materials from various horizons of the soil down to the bedrock due to freezing and thawing.

<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">Thermokarst</span> Irregular land surface of marshy hollows and small hummocks formed when permafrost thaws

Thermokarst is a type of terrain characterised by very irregular surfaces of marshy hollows and small hummocks formed when ice-rich permafrost thaws. The land surface type occurs in Arctic areas, and on a smaller scale in mountainous areas such as the Himalayas and the Swiss Alps.

<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, with the Tuktoyaktuk peninsula area having the greatest concentration at a total of 1,350. There is currently remarkably limited data on pingos.

<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 (490 ft) in diameter and can reach a height of 12 m (39 ft).

<span class="mw-page-title-main">Snow patch</span> Snow accumulation which stays longer than other snow cover

A snow patch, is a geomorphological pattern of snow and firn accumulation which lies on the surface for a longer time than other seasonal snow cover. Snow patches are known by a wide range of synonymous terms including snowpatches, snow beds, snow banks, and ice patches. Snowpatches are categorised by their longevity. Seasonal snowpatches melt prior to the return of the following winter's snowpack, semi-perennial snowpatches last occasionally to the following snowpack, while perennial snowpatches habitually last until the next winter's snowpack.

<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.

<span class="mw-page-title-main">Permafrost carbon cycle</span> Sub-cycle of the larger global carbon cycle

The permafrost carbon cycle or Arctic carbon cycle is a sub-cycle of the larger global carbon cycle. Permafrost is defined as subsurface material that remains below 0o C for at least two consecutive years. Because permafrost soils remain frozen for long periods of time, they store large amounts of carbon and other nutrients within their frozen framework during that time. Permafrost represents a large carbon reservoir, one which was often neglected in the initial research determining global terrestrial carbon reservoirs. Since the start of the 2000s, however, far more attention has been paid to the subject, with an enormous growth both in general attention and in the scientific research output.

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.

Retrogressive thaw slumps (RTS), are a type of landslide that occur in the terrestrial Arctic's permafrost region of the circumpolar Northern Hemisphere when an ice-rich section thaws. RTSs develop quickly and can extend across several hectares modifying Arctic coastlines and permafrost terrain. They are the most active and dynamic feature of thermokarst—the collapse of the land surface as ground ice melts. They are thermokarst slope failures due to abrupt thawing of ice-rich permafrost or glaciated terrains. These horseshoe-shaped landslides contribute to the thawing of hectares of permafrost annually and are considered to be one of the most active and dynamic features of thermokarst—the "processes and landforms that involve collapse of the land surface as a result of the melting of ground ice." They are found in permafrost or glaciated regions of the Northern Hemisphere—the Tibetan Plateau, Siberia, from the Himalayas to northern Greenland, and in northern Canada's Northwest Territories (NWT), the Yukon Territories, Nunavut, and Nunavik and in the American state of Alaska. The largest RTS in the world is in Siberia—the Batagaika Crater, also called a "megaslump", is one-kilometre-long and 100 metres (330 ft) deep and it grows a 100 feet (30 m) annually. The land began to sink, and the Batagaika Crater began to form in the 1960s, following clear-cutting of a section of forested area.

References

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