Patterned ground

Patterned ground is the distinct and often symmetrical natural pattern of geometric shapes formed by ground material in periglacial regions. Typically found in remote regions of the Arctic, Antarctica, and the Australian outback but also found anywhere that freezing and thawing of soil alternate; patterned ground has also been observed on Mars.[1] 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.

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

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.[2][3][4][5][6][7]

Polygons

Alaska patterned ground 1973
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.[4]

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.[8]

Circles

Permafrost stone-rings hg
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.[9][4]

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.[2][4]

Stripes

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.[10][11][4]

Formation

Phoenix mission patterned ground, Mars
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.[12]

Patterned ground occurs in alpine areas with permafrost. For example, on Mount Kenya permafrost is a few centimetres (inches) below the surface in places. Patterned ground is present at 3,400 metres (11,155 ft) to the west of Mugi Hill.[13] 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.[14]

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.[12][15]

See also

References

  1. ^ "Southern Hemisphere Polygonal Patterned Ground". Mars Global Surveyor: Mars Orbiter Camera. Malin Space Science Systems. Retrieved 8 November 2013.
  2. ^ a b "Patterned Ground". Retrieved 21 September 2016.
  3. ^ Ballantyne, C.K., 1986. "Non-sorted patterned ground on mountains in the Northern Highlands of Scotland". Biuletyn Peryglacjalny, 30: 15–34.
  4. ^ a b c d e Allaby, Michael (2013). A Dictionary of Geology and Earth Sciences. Oxford University Press. p. 429. ISBN 978-0-19-107895-8.
  5. ^ Ólafur, Ingólfsson (2006). "Glacial Geology Photos". Retrieved March 4, 2007.
  6. ^ 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.
  7. ^ 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.
  8. ^ C. Michael Hogan. 2008. Black Spruce: Picea mariana, GlobalTwitcher.com, ed. N. Stromberg Archived 2011-10-05 at the Wayback Machine
  9. ^ Hallet, Bernard (2013). "Stone circles: form and soil kinematics" (PDF). Phil. Trans. R. Soc. Lond. A. 371 (2004). doi:10.1098/rsta.2012.0357.
  10. ^ King, R. B., 1971. "Boulder polygons and stripes in the Cairngorm Mountains, Scotland". Journal of Glaciology, 10: 375-386.
  11. ^ Ballantyne, Colin K. (2001). "The sorted stone stripes of Tingo Hill". Scottish Geographical Journal. 117 (4): 313–324. doi:10.1080/00369220118737131.
  12. ^ a b Easterbrook, Don J. (1999). Surface processes and landforms (2nd ed.). Prentice Hall. pp. 418–422. ISBN 978-0-13-860958-0.
  13. ^ Baker, B. H. (1967). Geology of the Mount Kenya area; degree sheet 44 N.W. quarter (with coloured map). Nairobi: Geological Survey of Kenya.
  14. ^ Allan, Iain (1981). The Mountain Club of Kenya Guide to Mount Kenya and Kilimanjaro. Nairobi: Mountain Club of Kenya. ISBN 978-9966985606.
  15. ^ Perkins, S. (17 May 2003). "Patterns from Nowhere; Natural Forces Bring Order to Untouched Ground". Science News. 163 (20): 314. doi:10.2307/4014632.

External links

Berg Peak

Berg Peak (71°32′S 161°47′E) is a prominent peak, 1,870 metres (6,140 ft) high, standing 3 nautical miles (6 km) south of El Pulgar in the northern Morozumi Range, Victoria Land, Antarctica. It was mapped by the United States Geological Survey from surveys and from U.S. Navy air photos, 1960–63, and named by the Advisory Committee on Antarctic Names for Thomas E. Berg, a geologist who wintered at McMurdo Sound in 1961, and spent three succeeding summer seasons making patterned ground studies in the area. Berg perished in the crash of a U.S. Navy helicopter near Mount McLennan, November 19, 1969. The peak lies situated on the Pennell Coast, a portion of Antarctica lying between Cape Williams and Cape Adare.

Black Glacier

Black Glacier (71°40′S 164°42′E) is a broad tributary to the Lillie Glacier flowing northeast, marking the southeast extent of the Bowers Mountains, a major mountain range situated in the geographical location of Victoria Land, Antarctica. The glacier was first mapped by the United States Geological Survey from ground surveys and from U.S. Navy air photos, 1960–62, and named by the Advisory Committee on Antarctic Names for Robert F. Black, former geologist of the University of Wisconsin, project leader for Antarctic patterned ground studies, who carried out research in the McMurdo Sound region during several summer seasons in the 1960s. The glacier lies situated on the Pennell Coast, a portion of Antarctica lying between Cape Williams and Cape Adare.

Casius quadrangle

The Casius quadrangle is one of a series of 30 quadrangle maps of Mars used by the United States Geological Survey (USGS) Astrogeology Research Program. The quadrangle is located in the north-central portion of Mars’ eastern hemisphere and covers 60° to 120° east longitude (240° to 300° west longitude) and 30° to 65° north latitude. The quadrangle uses a Lambert conformal conic projection at a nominal scale of 1:5,000,000 (1:5M). The Casius quadrangle is also referred to as MC-6 (Mars Chart-6). Casius quadrangle contains part of Utopia Planitia and a small part of Terra Sabaea.

The southern and northern borders of the Casius quadrangle are approximately 3,065 km and 1,500 km wide, respectively. The north to south distance is about 2,050 km (slightly less than the length of Greenland). The quadrangle covers an approximate area of 4.9 million square km, or a little over 3% of Mars’ surface area.

Common surface features of Mars

The common surface features of Mars include dark slope streaks, dust devil tracks, sand dunes, Medusae Fossae Formation, fretted terrain, layers, gullies, glaciers, scalloped topography, chaos terrain, possible ancient rivers, pedestal craters, brain terrain, and ring mold craters.

Cryoturbation

In gelisols (permafrost soils), cryoturbation (frost churning) refers to the mixing of materials from various horizons of the soil down to the bedrock due to freezing and thawing.

Cryoturbation occurs to varying degrees in most gelisols. The cause of cryoturbation lies in the way in which the repeated freezing of the soil during autumn causes the formation of ice wedges at the most easily erodible parts of the parent rock. If the parent rock is hard, this can cause quite deep erosion of the rock over many years. As this process continues, during the summer when an active layer forms in the soil this eroded material can easily move both from the soil surface downward and from the permafrost table upward.

As this process occurs, the upper soil material gradually dries out (because the soil moisture moves from the warm surface layer to the colder layer at the top of the permafrost) so that it forms a granular structure with many very distinctive crystalline shapes (such as ice lenses). Separation of coarse from fine soil materials produces distinctive patterned ground with different types of soil.

The extent of cryoturbation in gelisols varies considerably: it occurs much more on exposed sites (where turbels dominate everywhere) than in sheltered sites such as valleys (where orthels are not significantly affected by cryoturbation form).

Deuteronilus Mensae

Deuteronilus Mensae is a region on Mars 937 km across and centered at 43.9°N 337.4°W / 43.9; -337.4. It covers 344°–325° West and 40°–48° North. Deuteronilus region lies just to the north of Arabia Terra and is included in the Ismenius Lacus quadrangle. It is along the dichotomy boundary, that is between the old, heavily cratered southern highlands and the low plains of the northern hemisphere. The region contains flat-topped knobby terrain that may have been formed by glaciers at some time in the past. Deuteronilus Mensae is to the immediate west of Protonilus Mensae and Ismeniae Fossae. Glaciers persist in the region in modern times, with at least one glacier estimated to have formed as recently as 100,000 to 10,000 years ago. Recent evidence from the radar on the Mars Reconnaissance Orbiter has shown that parts of Deuteronilus Mensae do indeed contain ice.

Diacria quadrangle

The Diacria quadrangle is one of a series of 30 quadrangle maps of Mars used by the United States Geological Survey (USGS) Astrogeology Research Program. The quadrangle is located in the northwestern portion of Mars’ western hemisphere and covers 180° to 240° east longitude (120° to 180° west longitude) and 30° to 65° north latitude. The quadrangle uses a Lambert conformal conic projection at a nominal scale of 1:5,000,000 (1:5M). The Diacria quadrangle is also referred to as MC-2 (Mars Chart-2). The Diacria quadrangle covers parts of Arcadia Planitia and Amazonis Planitia.

The southern and northern borders of the Diacria quadrangle are approximately 3,065 km (1,905 mi) and 1,500 km (930 mi) wide, respectively. The north to south distance is about 2,050 km (1,270 mi) (slightly less than the length of Greenland). The quadrangle covers an approximate area of 4.9 million square km, or a little over 3% of Mars’ surface area. The Phoenix Lander’s landing site (68.22° N, 234.25° E) lies about 186 km north of the northeastern quarter of the Diacria quadrangle. The landscape viewed by the Phoenix lander is probably representative of a large portion of the terrain in the northern Diacria quadrangle.

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.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. 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.

HiWish program

HiWish is a program created by NASA so that anyone can suggest a place for the HiRISE camera on the Mars Reconnaissance Orbiter to photograph. It was started in January 2010. In the first few months of the program 3000 people signed up to use HiRISE. The first images were released in April 2010. Over 7000 suggestions were made by the public; suggestions were made for targets in each of the 30 quadrangles of Mars. Selected images released were used for three talks at the 16th Annual International Mars Society Convention. Below are some of the over 4,224 images that have been released from the HiWish program as of March 2016.

Hutton (Martian crater)

Hutton is a crater in the Mare Australe quadrangle of Mars, located at 71.8° south latitude and 255.4° west longitude. It is 99 km in diameter and was named after James Hutton, a British geologist (1726-1797). Many areas of Mars show patterned ground. Sometimes the ground has the shape of polygons. In other places, the surface has low mounds arranged in chains. Patterned ground is common in cold climates on Earth when the soil contains water that is often frozen. Patterned ground is visible below in the image of Hutton Crater.

Lomonosov (Martian crater)

Lomonosov is a crater on Mars, with a diameter close to 150 km. It is located in the Martian northern plains. Since it is large and found close (64.9° north) to the boundary between the Mare Acidalium quadrangle and the Mare Boreum quadrangle, it is found on both maps. The topography is smooth and young in this area, hence Lomonosov is easy to spot on large maps of Mars.

The crater was named in 1973 in honour of Mikhail V. Lomonosov.

The impact that created the crater has been identified as a possible source of tsunami waves which washed the shores of an ancient ocean formerly present in the basin Vastitas Borealis.

Mare Acidalium quadrangle

The Mare Acidalium quadrangle is one of a series of 30 quadrangle maps of Mars used by the United States Geological Survey (USGS) Astrogeology Research Program. The quadrangle is located in the northeastern portion of Mars’ western hemisphere and covers 300° to 360° east longitude (0° to 60° west longitude) and 30° to 65° north latitude. The quadrangle uses a Lambert conformal conic projection at a nominal scale of 1:5,000,000 (1:5M). The Mare Acidalium quadrangle is also referred to as MC-4 (Mars Chart-4).The southern and northern borders of the quadrangle are approximately 3,065 km and 1,500 km wide, respectively. The north to south distance is about 2,050 km (slightly less than the length of Greenland). The quadrangle covers an approximate area of 4.9 million square km, or a little over 3% of Mars’ surface area. Most of the region called Acidalia Planitia is found in Acidalium quadrangle. Parts of Tempe Terra, Arabia Terra, and Chryse Planitia are also in this quadrangle.

This area contains many bright spots on a dark background that may be mud volcanoes. There are also some gullies that are believed to have formed by relatively recent flows of liquid water.

Phillips (Martian crater)

Phillips Crater is a crater in the Mare Australe quadrangle of Mars, located at 66.7° south latitude and 45.1° west longitude. It is 190.2 km in diameter and was named after John Phillips, a British geologist (1800–1874), and Theodore E. Philips, a British astronomer (1868–1942).

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.Patterned ground forms in a mantle layer, called latitude dependent mantle, that fell from the sky when the climate was different.On Mars, researches have found patterned ground that formed from fractures and patterned ground formed by the arrangement of boulders. It is not yet clear what caused boulders to form patterns, but it does not seem that fractures caused the boulders to move around.

Ross (Martian crater)

Ross is an impact crater in the Thaumasia quadrangle of Mars located at 57.7 S and 107.84 W. It is 82.51 km in diameter. It was named after Frank E. Ross, an American astronomer (1874-1960). The crater's name was approved in 1973.Gullies and polygonal patterned ground have been observed in and around Ross crater.

Scalloped topography

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 (direct transition of a material from the solid to the gas phase with no intermediate liquid stage). 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.A study published in Icarus, found that the landforms of scalloped topography can be made by the subsurface loss of water ice by sublimation under current Martian climate conditions over periods of tens of thousands of Mars years. Scalloped depressions are thought to begin with a small trigger like a small impact, local darkening, erosion, or cracks from thermal contraction. Cracks are common in ice-rich ground on the Earth. Their model predicts that these scalloped depression will develop when the ground has large amounts of pure ice, up to many tens of meters in depth. So, scalloped features can serve as markers for large deposits of pure ice. Ice in and around scalloped topography is not just in the pore spaces of the ground it is excess ice, probably 99% pure as was found by the Phoenix mission. The shallow Subsurface Radar (SHARAD), aboard the Mars Reconnaissance Orbiter can detect ice-rich layers only when thicker than 10–20 meters over wide areas; it has discovered ice in the region of scalloped topography.The details on the formation of scalloped topography still being worked out. One study, published in 2016 in Icarus proposes a five step process.

Major changes in the planet’s tilt change the climate. This climate change causes an icy mantle to form.

Various conditions cause the mantle to thaw or evaporate.

Meltwater moves in the ground, at least to the depth of the scalloped depressions.

Freezing and thawing of the ice produces masses of ice (ice lenses).

With another tilt change the climate changes and masses of ice sublimate, resulting in scalloped depressions.In Utopia Planitia, a series of curvilinear ridges parallel to the scarp are etched on the floor of large scalloped depressions, possibly representing different stages of scarp erosion. Recently, other researchers have advanced an idea that the ridges represent the tops of layers. Sometimes the surface around scalloped terrain or scalloped topography displays "patterned ground", characterized by a regular pattern of polygonal fractures. These patterns indicate that the surface has undergone stress, perhaps caused by subsidence, desiccation, or thermal contraction. Such patterns are common in periglacial areas on Earth. Scalloped terrains in Utopia Planitia display polygonal features of different sizes: small (about 5–10 m across) on the scarp, and larger (30–50 m across) on the surrounding terrains. These scale differences may indicate local difference in ground ice concentrations.

Terrain softening

The landscape polewards of around 30 degrees latitude on Mars has a distinctively different appearance to that nearer the equator, and is said to have undergone terrain softening. Softened terrain lacks the sharp ridge crests seen near the equator, and is instead smoothly rounded. This rounding is thought to be caused by high concentrations of water ice in soils. The term was coined in 1986 by Steve Squyres and Michael Carr from examining imagery from the Viking missions to Mars.

Below 30 degrees of latitude, impact craters have steep walls; well-defined, sharp rims; and flat or smoothly bowl-shaped floors. Ridges on intercrater plains come to similarly well-defined, pointed crests. However, above this latitude, these same features appear very different. The crests seen on ridges and crater rims appear strongly rounded and much more poorly defined. The relief (height) of features is somewhat reduced. Small craters are noticeably less common. In other words, terrain which elsewhere looked sharp here looks "soft". This texture has also been described as "smooth", or "rolling". Softened craters are also commonly infilled with concentric patterns on their floors.On Earth, diffusive creep of soils is associated with rounded hillslopes. Squyres and Carr thus attributed the softened texture to accelerated viscous creep in shallow soils near the surface, and went on to associate this accelerated creep with the presence of ground ice at these latitudes. This conclusion has been largely borne out by subsequent research. In the late 1980s some attempts were made to link terrain softening with dust and aeolian processes, though this hypothesis has largely been superseded by more recent observations.Terrain softening is one of a suite of features seen in the midlatitudes of Mars—also including lobate debris aprons, lineated valley fill, concentric crater fill, latitude dependent mantle, patterned ground, viscous flow features, arcuate ridges, recurring slope lineae, and gullies—whose form and distribution strongly suggest the abundance of ice at the surface.

Utopia Planitia

Utopia Planitia (Greek and Latin: "Nowhere Land Plain"—loosely, the plain of paradise) is a large plain within Utopia, the largest recognized impact basin on Mars and in the Solar System with an estimated diameter of 3,300 km. It is the Martian region where the Viking 2 lander touched down and began exploring on September 3, 1976. It is located at the antipode of Argyre Planitia, centered at 46.7°N 117.5°E / 46.7; 117.5. It is also in the Casius quadrangle, Amenthes quadrangle, and the Cebrenia quadrangle of Mars.

Many rocks at Utopia Planitia appear perched, as if wind removed much of the soil at their bases. A hard surface crust is formed by solutions of minerals moving up through soil and evaporating at the surface. Some areas of the surface exhibit what is called "scalloped topography", a surface that seems to have been carved out by an ice cream scoop. This surface is thought to have formed by the degradation of an ice-rich permafrost.On November 22, 2016, NASA reported finding a large amount of underground ice in the Utopia Planitia region of Mars. The volume of water detected has been estimated to be equivalent to the volume of water in Lake Superior. (image)

Vastitas Borealis

Vastitas Borealis (Latin, 'northern waste' ) is the largest lowland region of Mars. It is in the northerly latitudes of the planet and encircles the northern polar region. Vastitas Borealis is often simply referred to as the northern plains, northern lowlands or the North polar erg of Mars. The plains lie 4–5 km below the mean radius of the planet, and is centered at 87.73°N 32.53°E / 87.73; 32.53. To the north lies Planum Boreum. A small part of Vastitas Borealis lies in the Ismenius Lacus quadrangle.

The region was named by Eugene Antoniadi, who noted the distinct albedo feature of the Northern plains in his book La Planète Mars (1930). The name was officially adopted by the International Astronomical Union in 1973.Although it is not an officially recognized feature, the North Polar Basin makes up most of the lowlands in the Northern Hemisphere of Mars. As a result, Vastitas Borealis lies within the North Polar Basin, while Utopia Planitia, another very large basin, is adjacent to it. Some scientists have speculated the plains were covered by a hypothetical ocean at some point in Mars' history and putative shorelines have been suggested for its southern edges. Today these mildly sloping plains are marked by ridges, low hills, and sparse cratering. Vastitas Borealis is noticeably smoother than similar topographical areas in the south.

In 2005 the European Space Agency's Mars Express spacecraft imaged a substantial quantity of water ice in a crater in the Vastitas Borealis region. The environmental conditions at the locality of this feature are suitable for water ice to remain stable. It was revealed after overlaying frozen carbon dioxide sublimated away at the commencement of the Northern Hemisphere Summer and is believed to be stable throughout the Martian year.A NASA probe named Phoenix landed safely in a region of Vastitas Borealis unofficially named Green Valley on 25 May 2008 (in the early Martian summer). Phoenix landed at 68.218830°N 234.250778°E. The probe, which will remain stationary, collected and analyzed soil samples in an effort to detect water and determine how hospitable the planet might once have been for life to grow. It remained active there until winter conditions became too harsh around five months later.

Landforms
Processes
Soils and deposits
Biomes and ecotones
Climate

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