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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 len ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Gelisol
Gelisols are an order in USDA soil taxonomy. They are soils of very cold climates which are defined as containing permafrost within of the soil surface. The word "Gelisol" comes from the Latin meaning "to freeze", a reference to the process of cryoturbation that occurs from the alternating thawing and freezing characteristic of Gelisols. In the World Reference Base for Soil Resources (WRB), most Gelisols belong to the Cryosols. In soil taxonomy, Gelisols key out before the Histosols. In the WRB, the Histosols key out before the Cryosols. Organic permafrost soils are therefore Gelisols (Histels) in the soil taxonomy and Histosols (Cryic Histosols) in the WRB. Structurally, Gelisols may have a B horizon and more commonly have an A horizon and/or O horizon resting on the permafrost. Because soil organic matter accumulates in the upper layer, most Gelisols are black or dark brown in soil color, followed by a shallow mineral layer. Despite the influence of glaciation in mo ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Soil Horizon
A soil horizon is a layer parallel to the soil surface whose physical, chemical and biological characteristics differ from the layers above and beneath. Horizons are defined in many cases by obvious physical features, mainly colour and texture. These may be described both in absolute terms (particle size distribution for texture, for instance) and in terms relative to the surrounding material, i.e. 'coarser' or 'sandier' than the horizons above and below. The identified horizons are indicated with symbols, which are mostly used in a hierarchical way. Master horizons (main horizons) are indicated by capital letters. Suffixes, in form of lowercase letters and figures, further differentiate the master horizons. There are many different systems of horizon symbols in the world. No one system is more correct—as artificial constructs, their utility lies in their ability to accurately describe local conditions in a consistent manner. Due to the different definitions of the horizon sym ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Permafrost
Permafrost () is soil or underwater sediment which continuously remains below for two years or more; the oldest permafrost has 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 . 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. Around 15% of the Northern Hemisphere or 11% of the global surface is underlain by permafrost, covering a total area of around . This includes large areas of Alaska, Canada, Greenland, and Siberia. It is also located in high mountain regions, with the Tibetan Plateau being a prominent example. Only a minority of permafrost exists in the Southern Hemi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Soil
Soil, also commonly referred to as earth, is a mixture of organic matter, minerals, gases, water, and organisms that together support the life of plants and soil organisms. Some scientific definitions distinguish dirt from ''soil'' by restricting the former term specifically to displaced soil. Soil consists of a solid collection of minerals and organic matter (the soil matrix), as well as a porous phase that holds gases (the soil atmosphere) and water (the soil solution). Accordingly, soil is a three- state system of solids, liquids, and gases. Soil is a product of several factors: the influence of climate, relief (elevation, orientation, and slope of terrain), organisms, and the soil's parent materials (original minerals) interacting over time. It continually undergoes development by way of numerous physical, chemical and biological processes, which include weathering with associated erosion. Given its complexity and strong internal connectedness, soil ecologists ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Bedrock
In geology, bedrock is solid rock that lies under loose material ( regolith) within the crust of Earth or another terrestrial planet. Definition Bedrock is the solid rock that underlies looser surface material. An exposed portion of bedrock is often called an outcrop. The various kinds of broken and weathered rock material, such as soil and subsoil, that may overlie the bedrock are known as regolith. Engineering geology The surface of the bedrock beneath the soil cover (regolith) is also known as ''rockhead'' in engineering geology, and its identification by digging, drilling or geophysical methods is an important task in most civil engineering projects. Superficial deposits can be very thick, such that the bedrock lies hundreds of meters below the surface. Weathering of bedrock Exposed bedrock experiences weathering, which may be physical or chemical, and which alters the structure of the rock to leave it susceptible to erosion. Bedrock may also experience subsur ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ice Wedge
An ice wedge is a crack in the ground formed by a narrow or thin piece of ice that measures up to 3–4 meters in length at ground level and extends downwards into the ground up to several meters. During the winter months, the water in the ground freezes and expands. Once temperatures reach −17 degrees Celsius or lower, the ice that has already formed acts like a solid and expands to form cracks in the surface known as ice wedges. As this process continues over many years ice wedges can grow, up to the size of a swimming pool. Ice wedges usually appear in a polygonal pattern known as ice wedge Polygon, polygons. The cracks can also be filled with materials other than ice, especially sand, and are then called sand wedges. Formation There are many theories that attempt to explain the origin of ice wedges but only one has been consistently supported by most prominent scientists: the thermal contraction theory. Thermal contraction theory The thermal contraction theory posits th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Parent Rock
In the earth sciences, parent rock, also sometimes ''substratum'', is the original rock from which younger rock or soil is formed. In soil formation, the parent rock (or parent material) normally has a large influence on the nature of the resulting soil; for example, clay soil is derived from mudstone while sandy soil comes from the weathering of sandstones. Parent rock can be sedimentary, igneous or metamorphic. In the context of metamorphic rocks, the parent rock (or protolith) is the original rock before metamorphism occurred. See also *Bedrock * Regolith *Floater Floaters or eye floaters are sometimes visible deposits (e.g., the shadows of tiny structures of protein or other cell debris projected onto the retina) within the eye's vitreous humour ("the vitreous"), which is normally transparent, or between ... References Petrology Regolith {{rock-stub ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Active Layer
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 (in temperate climates) will decrease as depth increases. If the winter temperature is below the freezing point of water, a frost front will form in the soil. This "frost front" is the boundary between frozen and unfrozen soil, and with the coming of spring and summer, the soil is thawed, ''always from the top down''. If the heating during summer exceeds the cooling during winter, the soil will be completely thawed during the summer and there will be no permafrost. This occurs when the mean annual temperature is above 0 °C (32&nbs ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ice Lens
Ice lenses are bodies of ice formed when moisture, diffusion, diffused within soil or rock (geology), 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 (geology), lens, wedging the soil or rock apart. Ice lenses grow parallel to the surface and several centimeters to several decimeters (inches to feet) deep in the soil or rock. Studies from 1990 have demonstrated that rock fracture by ice segregation (i.e., the fracture of intact rock by ice lenses that grow by drawing water from their surroundings during periods of sustained subfreezing temperatures) is a more effective weathering process than the freeze-thaw process which older texts proposed."Periglacial weathering and headwall erosion in cirque glacier bergschrunds"; Johnny W. Sanders, Kurt M. Cuffey, Jeffrey R. Moore, Kelly R. MacGregor and Jeffrey L. Kavana ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Patterned Ground
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. 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 l ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Pedology
Pedology (from Greek: πέδον, ''pedon'', "soil"; and λόγος, ''logos'', "study") is a discipline within soil science which focuses on understanding and characterizing soil formation, evolution, and the theoretical frameworks for modeling soil bodies, often in the context of the natural environment. Pedology is often seen as one of two main branches of soil inquiry, the other being edaphology which is traditionally more agronomically oriented and focuses on how soil properties influence plant communities (natural or cultivated). In studying the fundamental phenomenology of soils, e.g. soil formation (aka pedogenesis), pedologists pay particular attention to observing soil morphology and the geographic distributions of soils, and the placement of soil bodies into larger temporal and spatial contexts. In so doing, pedologists develop systems of soil classification, soil maps, and theories for characterizing temporal and spatial interrelations among soils. There are a few ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
