Frost boil
A frost boil, also known as mud boils, a stony earth circles, frost scars, or mud circles,
Frost boils are amongst the most common features of
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
The subsequent increase of
Soil Liquefaction
This process is analogous to the formation of
This process is commonplace in alpine regions where soil temperatures rarely drop below -10 °C.[10]
Cyroturbation
Soil that are silty or loamy, as described above, can hold larger moisture contents. Thus, segregated ice lenses are formed preferentially in these locations. The soil thus experiences greater
Cyroturbation of this type is a slow process, often taking centuries for a single cycle.[11]
Internal characteristics
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.
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
References
- ^ Peterson, R. A.; D. A. Walker; V. E. Romanovsky; J. A. Knudson; M. K. Raynolds; W. B. Krantz (2003). A differential frost heave model: cryoturbation-vegetation interactions (PDF). Vol. 2. pp. 885–890.
- ^ Zhang, Xiong; Presler, Wendy (December 2012). "Use of H2Ri Wicking Fabric to Prevent Frost Boils in the Dalton Highway Beaver Slide Area, Alaska". Alaska University Transportation Center.
- ^ Van Everdingen, R. (1998). Multi-Language Glossary of Permafrost and Related Ground-Ice Terms. National Snow and Ice Data Center/World Data Center for Glaciology, Boulder, CO.
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- ISBN 9781118684931.
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- Bibcode:2003AGUFM.C21B0823S.
- Bibcode:2002AGUFM.B12A0775P.
- ^ Chernov, Y.I. & Matveyeva, N. V., 1997, ‘Arctic ecosystem in Russia’, in F.E. Wielgolaski (ed.), Ecosystems of the World, p. 411-412, Elsevier.
- ISSN 2156-2202.
- ISSN 0929-1393.
- S2CID 27092852.