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Desert Pavement
A desert pavement, also called reg (in the western Sahara), serir (eastern Sahara), gibber (in Australia), or saï (central Asia) is a desert surface covered with closely packed, interlocking angular or rounded rock fragments of pebble and cobble size. They typically top alluvial fans. Desert varnish collects on the exposed surface rocks over time. Geologists debate the mechanics of pavement formation and their age. Formation Several theories have been proposed for the formation of desert pavements. A common theory suggests that they form through the gradual removal of sand, dust and other fine-grained material by the wind and intermittent rain, leaving the larger fragments behind. The larger fragments are shaken into place through the forces of rain, running water, wind, gravity, creep, thermal expansion and contraction, wetting and drying, frost heaving, animal traffic, and the Earth's constant microseismic vibrations. The removal of small particles by wind does not cont ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Desert Pavement 2
A desert is a barren area of landscape where little precipitation occurs and, consequently, living conditions are hostile for plant and animal life. The lack of vegetation exposes the unprotected surface of the ground to denudation. About one-third of the land surface of the Earth is arid or semi-arid. This includes much of the polar regions, where little precipitation occurs, and which are sometimes called polar deserts or "cold deserts". Deserts can be classified by the amount of precipitation that falls, by the temperature that prevails, by the causes of desertification or by their geographical location. Deserts are formed by weathering processes as large variations in temperature between day and night put strains on the rocks, which consequently break in pieces. Although rain seldom occurs in deserts, there are occasional downpours that can result in flash floods. Rain falling on hot rocks can cause them to shatter, and the resulting fragments and rubble strewn over the de ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Helium-3
Helium-3 (3He see also helion) is a light, stable isotope of helium with two protons and one neutron (the most common isotope, helium-4, having two protons and two neutrons in contrast). Other than protium (ordinary hydrogen), helium-3 is the only stable isotope of any element with more protons than neutrons. Helium-3 was discovered in 1939. Helium-3 occurs as a primordial nuclide, escaping from Earth's crust into its atmosphere and into outer space over millions of years. Helium-3 is also thought to be a natural nucleogenic and cosmogenic nuclide, one produced when lithium is bombarded by natural neutrons, which can be released by spontaneous fission and by nuclear reactions with cosmic rays. Some of the helium-3 found in the terrestrial atmosphere is also an artifact of atmospheric and underwater nuclear weapons testing. Much speculation has been made over the possibility of helium-3 as a future energy source. Unlike most nuclear fusion reactions, the fusion of heli ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Erg (landform)
An erg (also sand sea or dune sea, or sand sheet if it lacks dunes) is a broad, flat area of desert covered with wind-swept sand with little or no vegetative cover. The word is derived from the Arabic word ''ʿarq'' (), meaning "dune field". Strictly speaking, an erg is defined as a desert area that contains more than of aeolian or wind-blown sand and where sand covers more than 20% of the surface. Smaller areas are known as "dune fields". The largest hot desert in the world, the Sahara, covers and contains several ergs, such as the Chech Erg and the Issaouane Erg in Algeria. Approximately 85% of all the Earth's mobile sand is found in ergs that are greater than . Ergs are also found on other celestial bodies, such as Venus, Mars, and Saturn's moon Titan. Description Ergs are concentrated in two broad belts between 20° to 40°N and 20° to 40°S latitudes, which include regions crossed by the dry, subsiding air of the trade winds. Active ergs are limited to regions that ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
North Africa
North Africa, or Northern Africa is a region encompassing the northern portion of the African continent. There is no singularly accepted scope for the region, and it is sometimes defined as stretching from the Atlantic shores of Mauritania in the west, to Egypt's Suez Canal. Varying sources limit it to the countries of Algeria, Libya, Morocco, and Tunisia, a region that was known by the French during colonial times as "''Afrique du Nord''" and is known by Arabs as the Maghreb ("West", ''The western part of Arab World''). The United Nations definition includes Morocco, Algeria, Tunisia, Libya, Egypt, Sudan, and the Western Sahara, the territory disputed between Morocco and the Sahrawi Republic. The African Union definition includes the Western Sahara and Mauritania but not Sudan. When used in the term Middle East and North Africa ( MENA), it often refers only to the countries of the Maghreb. North Africa includes the Spanish cities of Ceuta and Melilla, and plazas de so ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ecoregion
An ecoregion (ecological region) or ecozone (ecological zone) is an ecologically and geographically defined area that is smaller than a bioregion, which in turn is smaller than a biogeographic realm. Ecoregions cover relatively large areas of land or water, and contain characteristic, geographically distinct assemblages of natural communities and species. The biodiversity of flora, fauna and ecosystems that characterise an ecoregion tends to be distinct from that of other ecoregions. In theory, biodiversity or conservation ecoregions are relatively large areas of land or water where the probability of encountering different species and communities at any given point remains relatively constant, within an acceptable range of variation (largely undefined at this point). Three caveats are appropriate for all bio-geographic mapping approaches. Firstly, no single bio-geographic framework is optimal for all taxa. Ecoregions reflect the best compromise for as many taxa as possibl ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Australia
Australia, officially the Commonwealth of Australia, is a sovereign ''Sovereign'' is a title which can be applied to the highest leader in various categories. The word is borrowed from Old French , which is ultimately derived from the Latin , meaning 'above'. The roles of a sovereign vary from monarch, ruler or ... country comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands. With an area of , Australia is the largest country by area in Oceania and the world's sixth-largest country. Australia is the oldest, flattest, and driest inhabited continent, with the least fertile soils. It is a megadiverse country, and its size gives it a wide variety of landscapes and climates, with deserts in the centre, tropical Forests of Australia, rainforests in the north-east, and List of mountains in Australia, mountain ranges in the south-east. The ancestors of Aboriginal Australians began arriving from south east Asia approx ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Utah
Utah ( , ) is a state in the Mountain West subregion of the Western United States. Utah is a landlocked U.S. state bordered to its east by Colorado, to its northeast by Wyoming, to its north by Idaho, to its south by Arizona, and to its west by Nevada. Utah also touches a corner of New Mexico in the southeast. Of the fifty U.S. states, Utah is the 13th-largest by area; with a population over three million, it is the 30th-most-populous and 11th-least-densely populated. Urban development is mostly concentrated in two areas: the Wasatch Front in the north-central part of the state, which is home to roughly two-thirds of the population and includes the capital city, Salt Lake City; and Washington County in the southwest, with more than 180,000 residents. Most of the western half of Utah lies in the Great Basin. Utah has been inhabited for thousands of years by various indigenous groups such as the ancient Puebloans, Navajo and Ute. The Spanish were the first Europ ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Newspaper Rock
Newspaper Rock State Historic Monument is a Utah state monument featuring a rock panel carved with one of the largest known collections of petroglyphs. It is located in San Juan County, along Utah State Route 211, northwest of Monticello and south of Moab. It is along the relatively well-traveled access road into the Needles district of Canyonlands National Park, from US 191 and from the park boundary. The rock is a part of the vertical Wingate sandstone cliffs that enclose the upper end of Indian Creek Canyon, and is covered by hundreds of petroglyphs—one of the largest, best preserved and easily accessed groups in the Southwest. The petroglyphs feature a mixture of human, animal, material and abstract forms. Newspaper Rock was designated a State Historical Monument in 1961, and was added to the National Register of Historic Places listings in San Juan County, Utah as Indian Creek State Park in 1976. Petroglyphs The first carvings at the Newspaper Rock site wer ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Desert Varnish
Desert varnish or rock varnish is an orange-yellow to black coating found on exposed rock surfaces in arid environments. Desert varnish is approximately one micrometer thick and exhibits nanometer-scale layering. Rock rust and desert patina are other terms which are also used for the condition, but less often. Formation Desert varnish forms only on physically stable rock surfaces that are no longer subject to frequent precipitation, fracturing or wind abrasion. The varnish is primarily composed of particles of clay along with oxides of iron and manganese. There is also a host of trace elements and almost always some organic matter. The color of the varnish varies from shades of brown to black. It has been suggested that desert varnish should be investigated as a potential candidate for a " shadow biosphere". However, a 2008 microscopy study posited that desert varnish has already been reproduced with chemistry not involving life in the lab, and that the main component is actuall ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Desert Pavement Evolution
A desert is a barren area of landscape where little precipitation occurs and, consequently, living conditions are hostile for plant and animal life. The lack of vegetation exposes the unprotected surface of the ground to denudation. About one-third of the land surface of the Earth is arid or semi-arid. This includes much of the polar regions, where little precipitation occurs, and which are sometimes called polar deserts or "cold deserts". Deserts can be classified by the amount of precipitation that falls, by the temperature that prevails, by the causes of desertification or by their geographical location. Deserts are formed by weathering processes as large variations in temperature between day and night put strains on the rocks, which consequently break in pieces. Although rain seldom occurs in deserts, there are occasional downpours that can result in flash floods. Rain falling on hot rocks can cause them to shatter, and the resulting fragments and rubble strewn over the de ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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