Patterned ground

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The patterned ground below Mugi Hill on Mount Kenya lies in an area of seasonal frost. Frost upheaval.jpg
The patterned ground below Mugi Hill on Mount Kenya lies in an area of seasonal frost.
A pingo and polygonal ground near Tuktoyaktuk, Northwest Territories, Canada Melting pingo wedge ice.jpg
A pingo and polygonal ground near Tuktoyaktuk, Northwest Territories, Canada

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. [2] [3] 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.

Contents

Types

Patterned ground can be found in a variety of forms. Typically, the type of patterned ground in a given area is related to the prevalence of larger stones in local soils and the frequency of freeze-thaw cycles. [4] [5] [6] [7] [8] [9]

Patterned ground in the form of soil polygons located in the hyper-arid Atacama Desert. Patterned ground located in the Atacama Desert (Chile).jpg
Patterned ground in the form of soil polygons located in the hyper-arid Atacama Desert.

Polygons

Polygonal soil patterns, typical of the Arctic Tundra Alaska patterned ground 1973.jpg
Polygonal soil patterns, typical of the Arctic Tundra

Polygons can form either in permafrost areas (as ice wedges) or in areas that are affected by seasonal frost. The rocks that make up these raised stone rings typically decrease in size with depth. [6]

In the northern reaches of the Canadian Boreal forests, when bogs reach a eutrophic climax and create a sedge mat, tamarack larch and black spruce are often the early colonists within such a polygonal climax sedge mat. [11]

Circles

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

Circles range in size from a few centimeters to several meters in diameter. Circles can consist of both sorted and unsorted material, and generally occur with fine sediments in the center surrounded by a circle of larger stones. Unsorted circles are similar, but rather than being surrounded by a circle of larger stones, they are bounded by a circular margin of vegetation. [12] [6]

Steps

Steps can be developed from circles and polygons. This form of patterned ground is generally a terrace-like feature that has a border of either larger stones or vegetation on the downslope side, and can consist of either sorted or unsorted material. [4] [6]

Stripes

Periglacial stone stripes in Antarctica Periglacial stone stripes.jpg
Periglacial stone stripes in Antarctica

Stripes are lines of stones, vegetation, and/or soil that typically form from transitioning steps on slopes at angles between 2° and 7°. Stripes can consist of either sorted or unsorted material. Sorted stripes are lines of larger stones separated by areas of smaller stones, fine sediment, or vegetation. Unsorted stripes typically consist of lines of vegetation or soil that are separated by bare ground. [14] [15] [6]

It has been conjectured that periglacial stripes on Salisbury Plain in England, that happened by chance to align with the solar sunrise at mid summer and sun set at mid winter , gave rise to awe and veneration by prehistoric people that eventually culminated in the building of the Stonehenge. [16]

Formation

Patterned ground in the polar region of Mars. Phoenix mission patterned ground, Mars.jpg
Patterned ground in the polar region of Mars.

In periglacial areas and areas affected by seasonal frost, repeated freezing and thawing of groundwater forces larger stones toward the surface, as smaller stones flow and settle underneath larger stones. At the surface, areas that are rich in larger stones contain much less water than highly porous areas of finer grained sediments. These water-saturated areas of finer sediments have a much greater ability to expand and contract as freezing and thawing occur, leading to lateral forces which ultimately pile larger stones into clusters and stripes. Through time, repeated freeze-thaw cycles smooth out irregularities and odd-shaped piles to form the common polygons, circles, and stripes of patterned ground. [17]

Patterned ground occurs in alpine areas with freeze thaw cycles. For example, on Mount Kenya seasonal frost layer is a few centimetres (inches) below the surface in places. [1] Patterned ground is present at 3,400 metres (11,155 ft) to the west of Mugi Hill. [18] These mounds grow because of the repeated freezing and thawing of the ground drawing in more water. There are blockfields present around 4,000 metres (13,123 ft) where the ground has cracked to form hexagons. Solifluction occurs when the night temperatures freeze the soil before it thaws again in the morning. This daily expansion and contraction of the soil prevents the establishment of vegetation. [19]

Frost also sorts the sediments in the ground. Once the mantle has been weathered, finer particles tend to migrate away from the freezing front, and larger particles migrate through the action of gravity. Patterned ground forms mostly within the active layer of permafrost. [17] [20]

See also

Related Research Articles

Permafrost Soil frozen for a duration of at least two years

Permafrost is ground that continuously remains below 0 °C (32 °F) for two or more years, located on land or under the ocean. Most common in the Northern Hemisphere, around 15% of the Northern Hemisphere or 11% of the global surface is underlain by permafrost, including substantial areas of Alaska, Greenland, Canada and Siberia. It can also be located on mountaintops in the Southern Hemisphere and beneath ice-free areas in the Antarctic.

Scree Broken rock fragments at the base of steep rock faces, that has accumulated through periodic rockfall

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.

Bolshoy Lyakhovsky Island Island in Lyakhovsky Islands, Russia

Bolshoy Lyakhovsky Island, or Great Lyakhovsky, is the largest of the Lyakhovsky Islands belonging to the New Siberian Islands archipelago between the Laptev Sea and the East Siberian Sea in northern Russia. It has an area of 5,156.6 km2 (1,991.0 sq mi), and a maximum altitude of 311 m (1,020 ft).

Hummock 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 merger 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.

Frost heaving 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.

Solifluction Freeze-thaw mass wasting slope processes

Solifluction is a collective name for gradual processes in which a mass moves down a slope related to freeze-thaw activity. This is the standard modern meaning of solifluction, which differs from the original meaning given to it by Johan Gunnar Andersson in 1906.

Thermokarst Irregular land surface of marshy hollows and small hummocks formed as permafrost thaws

Thermokarst is a terrain-type, characterised by very irregular surfaces of marshy hollows and small hummocks formed as 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.

Pingo Mound of earth-covered ice

Pingos are intrapermafrost ice-cored hills, ranging in height from 3 to 70 m and 30 to 1,000 m 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.

A periglacial lake is a lake bordering a glacier, usually found along the fringes of large ice sheets.

Needle ice 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.

Palsa 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 rises 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.

Scalloped topography is common in the mid-latitudes of Mars, between 45° and 60° north and south. It is particularly prominent in the region of Utopia Planitia, in the northern hemisphere, and in the region of Peneus and Amphitrites Paterae in the southern hemisphere. Such topography consists of shallow, rimless depressions with scalloped edges, commonly referred to as "scalloped depressions" or simply "scallops". Scalloped depressions can be isolated or clustered and sometimes seem to coalesce. A typical scalloped depression displays a gentle equator-facing slope and a steeper pole-facing scarp. This topographic asymmetry is probably due to differences in insolation. Scalloped depressions are believed to form from the removal of subsurface material, possibly interstitial ice, by sublimation. This process may still be happening at present. This topography may be of great importance for future colonization of Mars because it may point to deposits of pure ice.

Frost boil

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.

Ice lens 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.

Frost weathering 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.

Blockfield

A blockfield, felsenmeer, boulder field or stone field is a surface covered by boulder- or block-sized angular rocks usually associated with alpine and subpolar climates and periglaciation. Blockfields differ from screes and talus slope in that blockfields do not apparently originate from mass wastings. They are believed to be formed by frost weathering below the surface. An alternative theory that modern blockfields may have originated from chemical weathering that occurred in the Neogene when the climate was relatively warmer. Following this thought the blockfields would then have been reworked by periglacial action.

Ice segregation 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.

Periglaciation

Periglaciation describes geomorphic processes that result from seasonal thawing of snow in areas of permafrost, the runoff from which refreezes in ice wedges and other structures. "Periglacial" suggests an environment located on the margin of past glaciers. However, freeze and thaw cycles influence landscapes outside areas of past glaciation. Therefore, periglacial environments are anywhere that freezing and thawing modify the landscape in a significant manner.

Stone stripe

A stone stripe, also called a lava stringer, is an elongated concentration of mostly talus-like basalt rock found along a hillside or the base of a cliff. Many stone stripes occur without cliffs. A stone stripe is identified by its lack of vegetative cover. They typically occur in north central Oregon and develop at 900 to 1,100 meter elevations. Lengths can range from only a few meters to over 150 meters, and widths measure from .3 to 3 meters. Depths of the stone stripes range from 20-65 centimeters.

Polygonal patterned ground

Polygonal, patterned ground is quite common in some regions of Mars. It is commonly believed to be caused by the sublimation of ice from the ground. Sublimation is the direct change of solid ice to a gas. This is similar to what happens to dry ice on the Earth. Places on Mars that display polygonal ground may indicate where future colonists can find water ice. Low center polygons have been proposed as a marker for ground ice.

References

  1. 1 2 Grab, Stefan W.; Gatebe, Charles K.; Kinyua, Antony M. (2004). "Ground Thermal Profiles from Mount Kenya, East Africa". Geografiska Annaler: Series A, Physical Geography. 86 (2): 131–141. doi:10.1111/j.0435-3676.2004.00219.x. ISSN   0435-3676. JSTOR   3566103. S2CID   129324724.
  2. Sager, Christof; Airo, Alessandro; Arens, Felix L.; Schulze-Makuch, Dirk (2021-01-15). "New type of sand wedge polygons in the salt cemented soils of the hyper-arid Atacama Desert". Geomorphology. 373: 107481. doi: 10.1016/j.geomorph.2020.107481 . ISSN   0169-555X.
  3. "Southern Hemisphere Polygonal Patterned Ground". Mars Global Surveyor: Mars Orbiter Camera. Malin Space Science Systems. Archived from the original on 27 October 2016. Retrieved 8 November 2013.
  4. 1 2 "Patterned Ground". Archived from the original on 29 March 2017. Retrieved 21 September 2016.
  5. Ballantyne, C.K. (1986). "Non-sorted patterned ground on mountains in the Northern Highlands of Scotland". Biuletyn Peryglacjalny. 30: 15–34.
  6. 1 2 3 4 5 Allaby, Michael (2013). A Dictionary of Geology and Earth Sciences. Oxford University Press. p. 429. ISBN   978-0-19-107895-8.
  7. Ólafur, Ingólfsson (2006). "Glacial Geology Photos" . Retrieved March 4, 2007.
  8. Kessler M.A.; Werner B.T. (January 2003). "Self-organization of sorted patterned ground". Science. 299 (5605): 380–3. doi:10.1126/science.1077309. PMID   12532013. S2CID   27238820.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  9. Marchant, D.R.; Lewis, A.R.; Phillips, W.M.; Moore, E.J.; Souchez, R.A.; Denton, G.H.; Sugden, D.E.; Potter Jr., N.; Landis, G.P. (2002). "Formation of Patterned Ground and Sublimation Till over Miocene Glacier Ice in Beacon Valley, Southern Victoria Land, Antarctica". Geological Society of America Bulletin. 114 (6): 718–730. doi:10.1130/0016-7606(2002)114<0718:fopgas>2.0.co;2.
  10. Sager, Christof; Airo, Alessandro; Arens, Felix L.; Schulze-Makuch, Dirk (2021-01-15). "New type of sand wedge polygons in the salt cemented soils of the hyper-arid Atacama Desert". Geomorphology. 373: 107481. doi: 10.1016/j.geomorph.2020.107481 . ISSN   0169-555X.
  11. C. Michael Hogan. 2008. Black Spruce: Picea mariana, GlobalTwitcher.com, ed. N. Stromberg Archived 2011-10-05 at the Wayback Machine
  12. Hallet, Bernard (2013). "Stone circles: form and soil kinematics". Phil. Trans. R. Soc. Lond. A. 371 (2004): 20120357. doi: 10.1098/rsta.2012.0357 . PMID   24191111.
  13. Davies, Bethan. "stone stripes". AntarcticGlaciers.org. Retrieved 2022-03-24.
  14. King, R. B. (1971). "Boulder polygons and stripes in the Cairngorm Mountains, Scotland". Journal of Glaciology. 10 (60): 375–386. doi: 10.1017/s0022143000022073 .
  15. Ballantyne, Colin K. (2001). "The sorted stone stripes of Tingo Hill". Scottish Geographical Journal. 117 (4): 313–324. doi:10.1080/00369220118737131. S2CID   128558678.
  16. Yirka, Bob; Phys.org. "New dig suggests Stonehenge was built to align with summer and winter solstice". phys.org. Retrieved 2022-03-24.
  17. 1 2 Easterbrook, Don J. (1999). Surface processes and landforms (2nd ed.). Prentice Hall. pp. 418–422. ISBN   978-0-13-860958-0.
  18. Baker, B. H. (1967). Geology of the Mount Kenya area; degree sheet 44 N.W. quarter (with coloured map). Nairobi: Geological Survey of Kenya.
  19. Allan, Iain (1981). The Mountain Club of Kenya Guide to Mount Kenya and Kilimanjaro. Nairobi: Mountain Club of Kenya. ISBN   978-9966985606.
  20. Perkins, S. (17 May 2003). "Patterns from Nowhere; Natural Forces Bring Order to Untouched Ground". Science News. 163 (20): 314–316. doi:10.2307/4014632. JSTOR   4014632.