1.
Rill
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For use in record technology, see gramophone record. For grooves on the moon, see rille, in hillslope geomorphology, a rill is a shallow channel cut into soil by the erosive action of flowing water. Similar but smaller incised channels are known as microrills, larger incised channels are known as gullies, artificial rills are channels constructed to carry a water supply from a distant water source. In landscape or garden design, constructed rills are a water feature. Rills are narrow and shallow channels which are eroded into unprotected soil by hillslope runoff, since soil is regularly left bare during agricultural operations, rills may form on farmland during these vulnerable periods. Rills may also form when bare soil is exposed following deforestation. Rills are fairly easily visible when first incised, so they are often the first indication of an erosion problem. Unless soil conservation measures are put into place, rills on regularly eroding areas may develop into larger erosional features such as gullies or even into badlands. Rills are created when water erodes the topsoil on hillsides, and they tend to appear more often in rainier months. This begins the process as water breaks soil particles free. These forces explain why sandy, loamy soils are susceptible to the formation of rills. Rills cannot form on every surface, and their formation is connected to the steepness of the hillside slope. Gravity determines the force of the water, which provides the required to start the erosional environment necessary to create rills. Therefore, the formation of rills is primarily controlled by the slope of the hillside, slope controls the depth of the rills, while the length of the slope and the soil’s permeability control the number of incisions in an area. Each type of soil has a value, a slope angle below which water velocity cannot produce sufficient force to dislodge enough soil particles for rills to form. For instance, on many slopes, this threshold value hovers around an angle of 2 degrees with a shear velocity between 3 and 3.5 cm/s. After rills begin forming, they are subjected to variety of erosional forces which may increase their size. Up to 37% of erosion in an area may derive from mass movement, or collapse
2.
Intensive farming
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Intensive farming or intensive agriculture is any of various types of agriculture that involve higher levels of input and output per unit of agricultural land area. It is characterised by a low ratio, higher use of inputs such as capital and labour. This is in contrast to agriculture in which the inputs per unit land are lower. The term intensive has various senses, some of which refer to organic farming methods and others of which refer to nonorganic, both increase the yields of food and fiber per acre as compared to traditional animal husbandry. In CAFO, feed is brought to the animals, while in MIRG the animals are repeatedly moved to fresh forage. Most commercial agriculture is intensive in one or more ways, forms that rely especially heavily on industrial methods are often called industrial agriculture, which is characterised by innovations designed to increase yield. Techniques include planting multiple crops per year, reducing the frequency of fallow years, intensive farms are widespread in developed nations and increasingly prevalent worldwide. Most of the meat, dairy, eggs, fruits and vegetables available in supermarkets are produced by such farms, smaller intensive farms usually include higher inputs of labor and more often use sustainable intensive methods. The farming practices commonly found on farms are referred to as appropriate technology. These farms are widespread in both developed countries and worldwide, but are growing more rapidly. Most of the food available in specialty markets such as farmers markets is produced by these smallholder farms, agricultural development in Britain between the 16th century and the mid-19th century saw a massive increase in agricultural productivity and net output. This in turn supported unprecedented population growth, freeing up a significant percentage of the workforce, historians cited enclosure, mechanization, four-field crop rotation, and selective breeding as the most important innovations. Industrial agriculture arose along with the Industrial Revolution, by the early 19th century, agricultural techniques, implements, seed stocks and cultivars had so improved that yield per land unit was many times that seen in the Middle Ages. The industrialization phase involved a process of mechanization. Horse-drawn machinery such as the McCormick reaper revolutionized harvesting, while inventions such as the cotton gin reduced the cost of processing, during this same period, farmers began to use steam-powered threshers and tractors, although they were expensive and dangerous. Mechanical harvesters, planters, transplanters and other equipment were then developed and these inventions increased yields and allowed individual farmers to manage increasingly large farms. The identification of nitrogen, potassium, and phosphorus as critical factors in plant growth led to the manufacture of synthetic fertilizers, in 1909 the Haber-Bosch method to synthesize ammonium nitrate was first demonstrated. Farmers adopting this approach were initially referred to as humus farmers, chemicals developed for use in World War II gave rise to synthetic pesticides
3.
New states of Germany
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The new states, which had been abolished by the East German government in 1952 and were re-established in 1990, are Brandenburg, Mecklenburg-Vorpommern, Saxony, Saxony-Anhalt and Thuringia. The state of Berlin, the result of a merger between East and West Berlin, is not considered one of the new states, although many of its residents are former East Germans. Since the reunification, Germany thus consists of 16 states with equal legal statuses, yet the process of the inner reunification between the former Eastern and Western Germany is still ongoing. Persisting differences in culture and mentality among the old East Germany, ossis are stereotyped as racist, poor and largely influenced by Russian culture. Wessis are usually considered snobbish, dishonest, wealthy, and selfish, the terms can be considered disparaging. In 2009, twenty years after the fall of the wall, 62% feel in a kind of limbo, no longer citizens of East Germany but not fully integrated into the unified Germany. Around 11% would have liked to have East Germany back, a 2004 poll found that 25% of West Germans and 12% of East Germans wished reunification had not happened. Some East German brands have been revived, appealing to former East Germans who are nostalgic for the goods they grew up with, another notable difference is the attitude towards naturism or FKK in German. While it existed in both East and West, only in the East was it a cultural phenomenon in which almost everybody participated. This can still be seen at beaches of former East Germany compared to their West German counterparts, more children are born out of wedlock in eastern Germany than in western Germany. In 2009, in eastern Germany 61% of births were to unmarried women, the states of Saxony-Anhalt and Mecklenburg-Western Pomerania had the highest rate of birth outside wedlock, each with 64%, followed by Brandenburg with 62%. The state of Baden-Württemberg had the lowest rate with 22%, followed by Hesse and Bavaria, the economic reconstruction of eastern Germany is proving to be more long-term than originally foreseen. The standard of living and annual income significantly lower in the new federal states. Reunification cost the federal government €2 Trillion, at reunification, almost all East German industry was considered outdated. The government privatised 8,500 state-owned East German enterprises, since 1990, between €100 billion and €140 billion a year have been transferred to the new states. More than $60 billion were spent supporting businesses and building infrastructure in the years 2006-2008. A €156 billion economic plan, Solidarity Pact II, came into force in 2005, the tax, which raises €11 billion a year, will be maintained until 2019 at least. Ever since the reunification, the unemployment rate in the east has been almost twice that of the west, the unemployment rate reached 12. 7% in April 2010, after having reached a maximum of 18. 7% in 2005
4.
Earth science
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Earth science or geoscience is a widely embraced term for the fields of science related to the planet Earth. Earth science can be considered to be a branch of planetary science, there are both reductionist and holistic approaches to Earth sciences. The Earth sciences can include the study of geology, the lithosphere, and the structure of the Earths interior, as well as the atmosphere, hydrosphere. Typically, Earth scientists use tools from geography, chronology, physics, chemistry, biology, Geology describes the rocky parts of the Earths crust and its historic development. Major subdisciplines are mineralogy and petrology, geochemistry, geomorphology, paleontology, stratigraphy, structural geology, engineering geology, geophysics and geodesy investigate the shape of the Earth, its reaction to forces and its magnetic and gravity fields. Geophysicists explore the Earths core and mantle as well as the tectonic and seismic activity of the lithosphere, geophysics is commonly used to supplement the work of geologists in developing a comprehensive understanding of crustal geology, particularly in mineral and petroleum exploration. Soil science covers the outermost layer of the Earths crust that is subject to soil formation processes, major subdisciplines include edaphology and pedology. Ecology covers the interactions between the biota, with their natural environment and this field of study differentiates the study of the Earth, from the study of other planets in the Solar System, the Earth being the only planet teeming with life. Hydrology is a study revolved around the movement, distribution, and quality of the water and involves all the components of the cycle on the earth. Sub-disciplines of hydrology include hydrometeorology, surface hydrology, hydrogeology, watershed science, forest hydrology. Glaciology covers the icy parts of the Earth, atmospheric sciences cover the gaseous parts of the Earth between the surface and the exosphere. Major subdisciplines include meteorology, climatology, atmospheric chemistry, and atmospheric physics, plate tectonics, mountain ranges, volcanoes, and earthquakes are geological phenomena that can be explained in terms of physical and chemical processes in the Earths crust. Beneath the Earths crust lies the mantle which is heated by the decay of heavy elements. The mantle is not quite solid and consists of magma which is in a state of semi-perpetual convection and this convection process causes the lithospheric plates to move, albeit slowly. The resulting process is known as plate tectonics, plate tectonics might be thought of as the process by which the Earth is resurfaced. As the result of spreading, new crust and lithosphere is created by the flow of magma from the mantle to the near surface, through fissures. Through subduction, oceanic crust and lithosphere returns to the convecting mantle, volcanoes result primarily from the melting of subducted crust material. Crust material that is forced into the asthenosphere melts, and some portion of the material becomes light enough to rise to the surface—giving birth to volcanoes
5.
Surface runoff
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Surface runoff is the flow of water that occurs when excess stormwater, meltwater, or other sources flows over the Earths surface. Surface runoff is a component of the water cycle. It is the agent in soil erosion by water. Runoff that occurs on the surface before reaching a channel is also called a nonpoint source. If a nonpoint source contains man-made contaminants, or natural forms of pollution the runoff is called nonpoint source pollution, a land area which produces runoff that drains to a common point is called a drainage basin. When runoff flows along the ground, it can pick up soil contaminants including petroleum, pesticides, surface runoff can be generated either by rainfall, snowfall or by the melting of snow, or glaciers. Snow and glacier melt occur only in areas cold enough for these to form permanently, typically snowmelt will peak in the spring and glacier melt in the summer, leading to pronounced flow maxima in rivers affected by them. The determining factor of the rate of melting of snow or glaciers is both air temperature and the duration of sunlight, in high mountain regions, streams frequently rise on sunny days and fall on cloudy ones for this reason. In areas where there is no snow, runoff will come from rainfall, however, not all rainfall will produce runoff because storage from soils can absorb light showers. This occurs when the rate of rainfall on a surface exceeds the rate at which water can infiltrate the ground and this is called flooding excess overland flow, Hortonian overland flow, or unsaturated overland flow. This more commonly occurs in arid and semi-arid regions, where rainfall intensities are high and this occurs largely in city areas where pavements prevent water from flooding. When the soil is saturated and the depression storage filled, and rain continues to fall, the level of antecedent soil moisture is one factor affecting the time until soil becomes saturated. This runoff is called saturation excess overland flow or saturated overland flow, soil retains a degree of moisture after a rainfall. This residual water moisture affects the soils infiltration capacity, during the next rainfall event, the infiltration capacity will cause the soil to be saturated at a different rate. The higher the level of antecedent soil moisture, the more quickly the soil becomes saturated, once the soil is saturated, runoff occurs. After water infiltrates the soil on a portion of a hill, the water may flow laterally through the soil. This is called subsurface return flow or throughflow, any remaining surface water eventually flows into a receiving water body such as a river, lake, estuary or ocean. Urbanization increases surface runoff by creating more impervious surfaces such as pavement and it is instead forced directly into streams or storm water runoff drains, where erosion and siltation can be major problems, even when flooding is not
6.
Wind
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Wind is the flow of gases on a large scale. On the surface of the Earth, wind consists of the movement of air. Winds are commonly classified by their scale, their speed, the types of forces that cause them, the regions in which they occur. The strongest observed winds on a planet in the Solar System occur on Neptune, Winds have various aspects, an important one being its velocity, another the density of the gas involved, another its energy content or wind energy. In meteorology, winds are referred to according to their strength. Short bursts of high speed wind are termed gusts, strong winds of intermediate duration are termed squalls. Long-duration winds have various names associated with their strength, such as breeze, gale, storm. The two main causes of large-scale atmospheric circulation are the differential heating between the equator and the poles, and the rotation of the planet, within the tropics, thermal low circulations over terrain and high plateaus can drive monsoon circulations. In coastal areas the sea breeze/land breeze cycle can define local winds, in areas that have variable terrain, mountain, Wind powers the voyages of sailing ships across Earths oceans. Hot air balloons use the wind to take trips, and powered flight uses it to increase lift. Areas of wind caused by various weather phenomena can lead to dangerous situations for aircraft. When winds become strong, trees and man-made structures are damaged or destroyed, Winds can shape landforms, via a variety of aeolian processes such as the formation of fertile soils, such as loess, and by erosion. Wind also affects the spread of wildfires, Winds can disperse seeds from various plants, enabling the survival and dispersal of those plant species, as well as flying insect populations. When combined with temperatures, wind has a negative impact on livestock. Wind affects animals food stores, as well as their hunting, Wind is caused by differences in the atmospheric pressure. When a difference in atmospheric pressure exists, air moves from the higher to the pressure area. On a rotating planet, air will also be deflected by the Coriolis effect, globally, the two major driving factors of large-scale wind patterns are the differential heating between the equator and the poles and the rotation of the planet. Outside the tropics and aloft from frictional effects of the surface, near the Earths surface, friction causes the wind to be slower than it would be otherwise
7.
Soil
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Soil is a mixture of minerals, organic matter, gases, liquids, and countless organisms that together support life on Earth. Soil is called the Skin of the Earth and interfaces with the lithosphere, the hydrosphere, the atmosphere, the term pedolith, used commonly to refer to the soil, literally translates ground stone. Soil consists of a phase of minerals and organic matter, as well as a porous phase that holds gases. Accordingly, soils are often treated as a system of solids, liquids. Soil is a product of the influence of climate, relief, organisms, Soil 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 has been considered as an ecosystem by soil ecologists. Most soils have a dry bulk density between 1.1 and 1.6 g/cm3, while the particle density is much higher. Little of the soil of planet Earth is older than the Pleistocene and none is older than the Cenozoic, Soil science has two basic branches of study, edaphology and pedology. Edaphology is concerned with the influence of soils on living things, pedology is focused on the formation, description, and classification of soils in their natural environment. In engineering terms, soil is referred to as regolith, or loose material that lies above the solid geology. Soil is commonly referred to as earth or dirt, technically, as soil resources serve as a basis for food security, the international community advocates its sustainable and responsible use through different types of soil governance. Soil is a component of the Earths ecosystem. The worlds ecosystems are impacted in far-reaching ways by the carried out in the soil, from ozone depletion and global warming, to rainforest destruction. Following the atmosphere, the soil is the next largest carbon reservoir on Earth, as the planet warms, soils will add carbon dioxide to the atmosphere due to its increased biological activity at higher temperatures. Thus, soil carbon losses likely have a positive feedback response to global warming. Since soil has a range of available niches and habitats. A gram of soil can contain billions of organisms, belonging to thousands of species, mostly microbial, Soil has a mean prokaryotic density of roughly 108 organisms per gram, whereas the ocean has no more than 107 procaryotic organisms per milliliter of seawater. Since plant roots need oxygen, ventilation is an important characteristic of soil and this ventilation can be accomplished via networks of interconnected soil pores, which also absorb and hold rainwater making it readily available for plant uptake
8.
Rock (geology)
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Rock or stone is a natural substance, a solid aggregate of one or more minerals or mineraloids. For example, granite, a rock, is a combination of the minerals quartz, feldspar. The Earths outer solid layer, the lithosphere, is made of rock, rock has been used by mankind throughout history. The minerals and metals found in rocks have been essential to human civilization, three major groups of rocks are defined, igneous, sedimentary, and metamorphic. The scientific study of rocks is called petrology, which is a component of geology. At a granular level, rocks are composed of grains of minerals, the aggregate minerals forming the rock are held together by chemical bonds. The types and abundance of minerals in a rock are determined by the manner in which the rock was formed, many rocks contain silica, a compound of silicon and oxygen that forms 74. 3% of the Earths crust. This material forms crystals with other compounds in the rock, the proportion of silica in rocks and minerals is a major factor in determining their name and properties. Rocks are geologically classified according to such as mineral and chemical composition, permeability, the texture of the constituent particles. These physical properties are the end result of the processes that formed the rocks, over the course of time, rocks can transform from one type into another, as described by the geological model called the rock cycle. These events produce three general classes of rock, igneous, sedimentary, and metamorphic, the three classes of rocks are subdivided into many groups. However, there are no hard and fast boundaries between allied rocks, hence the definitions adopted in establishing rock nomenclature merely correspond to more or less arbitrary selected points in a continuously graduated series. Igneous rock forms through the cooling and solidification of magma or lava and this magma can be derived from partial melts of pre-existing rocks in either a planets mantle or crust. Typically, the melting of rocks is caused by one or more of three processes, an increase in temperature, a decrease in pressure, or a change in composition, igneous rocks are divided into two main categories, plutonic rock and volcanic. Plutonic or intrusive rocks result when magma cools and crystallizes slowly within the Earths crust, a common example of this type is granite. Volcanic or extrusive rocks result from magma reaching the surface either as lava or fragmental ejecta, the chemical abundance and the rate of cooling of magma typically forms a sequence known as Bowens reaction series. Most major igneous rocks are found along this scale, about 64. 7% of the Earths crust by volume consists of igneous rocks, making it the most plentiful category. Of these, 66% are basalts and gabbros, 16% are granite, only 0. 6% are syenites and 0. 3% peridotites and dunites
9.
Crust (geology)
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In geology, the crust is the outermost solid shell of a rocky planet or natural satellite, which is chemically distinct from the underlying mantle. The crust of the Earth is composed of a variety of igneous, metamorphic. The crust is underlain by the mantle, the upper part of the mantle is composed mostly of peridotite, a rock denser than rocks common in the overlying crust. The boundary between the crust and mantle is conventionally placed at the Mohorovičić discontinuity, a boundary defined by a contrast in seismic velocity, the crust occupies less than 1% of Earths volume. The crust of the Earth is of two types, oceanic and continental. The oceanic crust is 5 km to 10 km thick and is composed primarily of basalt, diabase, the continental crust is typically from 30 km to 50 km thick and is mostly composed of slightly less dense rocks than those of the oceanic crust. Some of these less dense rocks, such as granite, are common in the continental crust, both the continental and oceanic crust float on the mantle. Because the continental crust is thicker, it both to greater elevations and greater depth than the oceanic crust. The slightly lower density of continental rock compared to basaltic oceanic rock contributes to the higher relative elevation of the top of the continental crust. As the top of the continental crust reaches elevations higher than that of the oceanic, the temperature of the crust increases with depth, reaching values typically in the range from about 200 °C to 400 °C at the boundary with the underlying mantle. The crust and underlying relatively rigid uppermost mantle make up the lithosphere, because of convection in the underlying plastic upper mantle and asthenosphere, the lithosphere is broken into tectonic plates that move. The temperature increases by as much as 30 °C for every kilometer locally in the part of the crust. Earth has probably always had some form of basaltic crust, in contrast, the bulk of the continental crust is much older. The oldest continental crustal rocks on Earth have ages in the range from about 3.7 to 4, some zircon with age as great as 4.3 billion years has been found in the Narryer Gneiss Terrane. The average age of the current Earths continental crust has been estimated to be about 2.0 billion years, most crustal rocks formed before 2.5 billion years ago are located in cratons. Such old continental crust and the underlying mantle asthenosphere are less dense than elsewhere in Earth, formation of new continental crust is linked to periods of intense orogeny, these periods coincide with the formation of the supercontinents such as Rodinia, Pangaea and Gondwana. The continental crust has a composition similar to that of andesite. The most abundant minerals in Earths continental crust are feldspars, which make up about 41% of the crust by weight, followed by quartz at 12%, Continental crust is enriched in incompatible elements compared to the basaltic ocean crust and much enriched compared to the underlying mantle
10.
Sediment transport
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Sediment transport is the movement of solid particles, typically due to a combination of gravity acting on the sediment, and/or the movement of the fluid in which the sediment is entrained. Sediment transport due to fluid motion occurs in rivers, oceans, lakes, seas, Transport is also caused by glaciers as they flow, and on terrestrial surfaces under the influence of wind. Sediment transport due only to gravity can occur on sloping surfaces in general, including hillslopes, scarps, cliffs, sediment transport is important in the fields of sedimentary geology, geomorphology, civil engineering and environmental engineering. Aeolian or eolian is the term for sediment transport by wind and this process results in the formation of ripples and sand dunes. Typically, the size of the sediment is fine sand and smaller, because air is a fluid with low density and viscosity. Bedforms are generated by aeolian sediment transport in the terrestrial near-surface environment, ripples and dunes form as a natural self-organizing response to sediment transport. Aeolian sediment transport is common on beaches and in the regions of the world, because it is in these environments that vegetation does not prevent the presence. Wind-blown very fine-grained dust is capable of entering the upper atmosphere, dust from the Sahara deposits on the Canary Islands and islands in the Caribbean, and dust from the Gobi desert has deposited on the western United States. This sediment is important to the budget and ecology of several islands. Deposits of fine-grained wind-blown glacial sediment are called loess, in geology, physical geography, and sediment transport, fluvial processes relate to flowing water in natural systems. This encompasses rivers, streams, periglacial flows, flash floods, sediment moved by water can be larger than sediment moved by air because water has both a higher density and viscosity. In typical rivers the largest carried sediment is of sand and gravel size, coastal sediment transport takes place in near-shore environments due to the motions of waves and currents. At the mouths of rivers, coastal sediment and fluvial sediment transport processes mesh to create river deltas, coastal sediment transport results in the formation of characteristic coastal landforms such as beaches, barrier islands, and capes. As glaciers move over their beds, they entrain and move material of all sizes, glaciers can carry the largest sediment, and areas of glacial deposition often contain a large number of glacial erratics, many of which are several metres in diameter. Glaciers also pulverize rock into glacial flour, which is so fine that it is carried away by winds to create loess deposits thousands of kilometres afield. Sediment entrained in glaciers often moves approximately along the glacial flowlines, in hillslope sediment transport, a variety of processes move regolith downslope. For this reason, the tops of hills generally have a parabolic concave-up profile, as hillslopes steepen, however, they become more prone to episodic landslides and other mass wasting events. Large masses of material are moved in debris flows, hyperconcentrated mixtures of mud, clasts that range up to boulder-size, debris flows move as granular flows down steep mountain valleys and washes
11.
Weathering
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Weathering is the breaking down of rocks, soil, and minerals as well as wood and artificial materials through contact with the Earths atmosphere, waters, and biological organisms. Two important classifications of weathering processes exist – physical and chemical weathering, mechanical or physical weathering involves the breakdown of rocks and soils through direct contact with atmospheric conditions, such as heat, water, ice and pressure. While physical weathering is accentuated in very cold or very dry environments, chemical reactions are most intense where the climate is wet, however, both types of weathering occur together, and each tends to accelerate the other. For example, physical abrasion decreases the size of particles and therefore increases their surface area, the various agents act in concert to convert primary minerals to secondary minerals and release plant nutrient elements in soluble forms. The materials left over after the rock breaks down combined with organic material creates soil, in addition, many of Earths landforms and landscapes are the result of weathering processes combined with erosion and re-deposition. Physical weathering, also recognized as mechanical weathering, is the class of processes that causes the disintegration of rocks without chemical change, the primary process in physical weathering is abrasion. However, chemical and physical weathering often go hand in hand, physical weathering can occur due to temperature, pressure, frost etc. For example, cracks exploited by physical weathering will increase the area exposed to chemical action. Abrasion by water, ice, and wind loaded with sediment can have tremendous cutting power, as is amply demonstrated by the gorges, ravines. In glacial areas, huge moving ice masses embedded with soil and rock fragments grind down rocks in their path, plant roots sometimes enter cracks in rocks and pry them apart, resulting in some disintegration, Burrowing animals may help disintegrate rock through their physical action. However, such influences are usually of importance in producing parent material when compared to the drastic physical effects of water, ice, wind. Physical weathering is called mechanical weathering or disaggregation. Thermal stress weathering results from the expansion and contraction of rock, for example, heating of rocks by sunlight or fires can cause expansion of their constituent minerals. As some minerals expand more than others, temperature changes set up differential stresses that cause the rock to crack apart. Because the outer surface of a rock is often warmer or colder than the more protected inner portions and this process may be sharply accelerated if ice forms in the surface cracks. When water freezes, it expands with a force of about 1465 Mg/m^2, disintegrating huge rock masses, thermal stress weathering comprises two main types, thermal shock and thermal fatigue. Thermal stress weathering is an important mechanism in deserts, where there is a diurnal temperature range, hot in the day. The repeated heating and cooling exerts stress on the layers of rocks
12.
Clastic
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Clastic rocks are composed of fragments, or clasts, of pre-existing minerals and rock. A clast is a fragment of geological detritus, chunks and smaller grains of rock broken off other rocks by physical weathering. Geologists use the term clastic with reference to sedimentary rocks as well as to particles in sediment transport whether in suspension or as bed load, clastic sedimentary rocks are rocks composed predominantly of broken pieces or clasts of older weathered and eroded rocks. Clastic sediments or sedimentary rocks are classified based on size, clast and cementing material composition. The classification factors are often useful in determining a samples environment of deposition, an example clastic environment would be a river system in which the full range of grains being transported by the moving water consist of pieces eroded from solid rock upstream. Grain size varies from clay in shales and claystones, through silt in siltstones, sand in sandstones, the Krumbein phi scale numerically orders these terms in a logarithmic size scale. Siliciclastic rocks are clastic rocks that are composed almost exclusively of silicon. The composition of sedimentary rocks includes the chemical and mineralogical components of the framework as well as the cementing material that make up these rocks. Boggs divides them into four categories, major minerals, accessory minerals, rock fragments, major minerals can be categorized into subdivisions based on their resistance to chemical decomposition. Those that possess a great resistance to decomposition are categorized as stable, while those that do not are considered less stable, the most common stable mineral in siliciclastic sedimentary rocks is quartz. Quartz makes up approximately 65 percent of framework grains present in sandstones, less stable minerals present in this type of rocks are feldspars, including both potassium and plagioclase feldspars. Feldspars comprise a considerably lesser portion of framework grains and minerals and they only make up about 15 percent of framework grains in sandstones and 5% of minerals in shales. Clay mineral groups are present in mudrocks but can be found in other siliciclastic sedimentary rocks at considerably lower levels. Accessory minerals are associated with those whose presence in the rock are not directly important to the classification of the specimen and these generally occur in smaller amounts in comparison to the quartz, and feldspars. Furthermore, those that do occur are generally heavy minerals or coarse grained micas, rock fragments also occur in the composition of siliciclastic sedimentary rocks and are responsible for about 10 -15 percent of the composition of sandstone. They generally make up most of the gravel size particles in conglomerates, though they sometimes are, rock fragments are not always sedimentary in origin. They can also be metamorphic or igneous, chemical cements vary in abundance but are predominantly found in sandstones. The two major types, are based and carbonate based
13.
Sediment
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For sediment in beverages, see dregs. For example, sand and silt can be carried in suspension in water and on reaching the sea be deposited by sedimentation. Sediments are most often transported by water, but also wind, beach sands and river channel deposits are examples of fluvial transport and deposition, though sediment also often settles out of slow-moving or standing water in lakes and oceans. Desert sand dunes and loess are examples of transport and deposition. Glacial moraine deposits and till are ice-transported sediments, sediment can be classified based on its grain size and/or its composition. Sediment size is measured on a log base 2 scale, called the Phi scale, composition of sediment can be measured in terms of, parent rock lithology mineral composition chemical make-up. This leads to an ambiguity in which clay can be used as both a size-range and a composition, sediment is transported based on the strength of the flow that carries it and its own size, volume, density, and shape. Stronger flows will increase the lift and drag on the particle, causing it to rise, rivers and streams carry sediment in their flows. This sediment can be in a variety of locations within the flow and these relationships are shown in the following table for the Rouse number, which is a ratio of sediment fall velocity to upwards velocity. If the upwards velocity is less than the settling velocity, but still high enough for the sediment to move, it will move along the bed as bed load by rolling, sliding. If the upwards velocity is higher than the velocity, the sediment will be transported high in the flow as wash load. As there are generally a range of different particle sizes in the flow, sediment motion can create self-organized structures such as ripples, dunes, antidunes on the river or stream bed. These bedforms are often preserved in rocks and can be used to estimate the direction. Overland flow can erode soil particles and transport them downslope, the erosion associated with overland flow may occur through different methods depending on meteorological and flow conditions. If the initial impact of rain droplets dislodges soil, the phenomenon is called rainsplash erosion, if overland flow is directly responsible for sediment entrainment but does not form gullies, it is called sheet erosion. If the flow and the substrate permit channelization, gullies may form, glaciers carry a wide range of sediment sizes, and deposit it in moraines. The overall balance between sediment in transport and sediment being deposited on the bed is given by the Exner equation and this expression states that the rate of increase in bed elevation due to deposition is proportional to the amount of sediment that falls out of the flow. This can be localized, and simply due to obstacles, examples are scour holes behind boulders, where flow accelerates
14.
Geomorphology
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Geomorphology is the scientific study of the origin and evolution of topographic and bathymetric features created by physical, chemical or biological processes operating at or near the Earths surface. Geomorphologists work within disciplines such as geography, geology, geodesy, engineering geology, archaeology. This broad base of interests contributes to many styles and interests within the field. Earths surface is modified by a combination of processes that sculpt landscapes, and geologic processes that cause tectonic uplift and subsidence. Many of these factors are strongly mediated by climate, the broad-scale topographies of the Earth illustrate this intersection of surface and subsurface action. Mountain belts are uplifted due to geologic processes, denudation of these high uplifted regions produces sediment that is transported and deposited elsewhere within the landscape or off the coast. On progressively smaller scales, similar ideas apply, where individual landforms evolve in response to the balance of additive processes, often, these processes directly affect each other, ice sheets, water, and sediment are all loads that change topography through flexural isostasy. Topography can modify the climate, for example through orographic precipitation. Many geomorphologists are particularly interested in the potential for feedbacks between climate and tectonics, mediated by geomorphic processes, in addition to these broad-scale questions, geomorphologists address issues that are more specific and/or more local. Fluvial geomorphologists focus on rivers, how they transport sediment, migrate across the landscape, cut into bedrock, respond to environmental and tectonic changes, and interact with humans. Soils geomorphologists investigate soil profiles and chemistry to learn about the history of a landscape and understand how climate, biota. Other geomorphologists study how hillslopes form and change, still others investigate the relationships between ecology and geomorphology. Because geomorphology is defined to comprise everything related to the surface of the Earth and its modification, geomorphologists use a wide range of techniques in their work. These may include fieldwork and field data collection, the interpretation of remotely sensed data, geochemical analyses, geomorphologists may rely on geochronology, using dating methods to measure the rate of changes to the surface. Practical applications of geomorphology include hazard assessment, river control and stream restoration, planetary geomorphology studies landforms on other terrestrial planets such as Mars. Indications of effects of wind, fluvial, glacial, mass wasting, meteor impact, tectonics and this effort not only helps better understand the geologic and atmospheric history of those planets but also extends geomorphological study of the Earth. Planetary geomorphologists often use Earth analogues to aid in their study of surfaces of other planets, other than some notable exceptions in antiquity, geomorphology is a relatively young science, growing along with interest in other aspects of the earth sciences in the mid-19th century. This section provides a brief outline of some of the major figures
15.
Rain
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Rain is liquid water in the form of droplets that have condensed from atmospheric water vapor and then precipitated—that is, become heavy enough to fall under gravity. Rain is a component of the water cycle and is responsible for depositing most of the fresh water on the Earth. It provides suitable conditions for many types of ecosystems, as well as water for power plants. The major cause of production is moisture moving along three-dimensional zones of temperature and moisture contrasts known as weather fronts. If enough moisture and upward motion is present, precipitation falls from convective clouds such as cumulonimbus which can organize into narrow rainbands. On the leeward side of mountains, desert climates can exist due to the dry air caused by downslope flow which causes heating and drying of the air mass, the movement of the monsoon trough, or intertropical convergence zone, brings rainy seasons to savannah climes. The urban heat island effect leads to increased rainfall, both in amounts and intensity, downwind of cities, global warming is also causing changes in the precipitation pattern globally, including wetter conditions across eastern North America and drier conditions in the tropics. The globally averaged annual precipitation over land is 715 mm, climate classification systems such as the Köppen climate classification system use average annual rainfall to help differentiate between differing climate regimes. Rainfall is measured using rain gauges, rainfall amounts can be estimated by weather radar. Rain is also known or suspected on other planets, where it may be composed of methane, neon, sulfuric acid, or even iron rather than water. Air contains water vapor, and the amount of water in a mass of dry air. The amount of moisture in air is commonly reported as relative humidity. How much water vapor a parcel of air can contain before it becomes saturated, warmer air can contain more water vapor than cooler air before becoming saturated. Therefore, one way to saturate a parcel of air is to cool it, the dew point is the temperature to which a parcel must be cooled in order to become saturated. There are four mechanisms for cooling the air to its dew point, adiabatic cooling, conductive cooling, radiational cooling. Adiabatic cooling occurs when air rises and expands, the air can rise due to convection, large-scale atmospheric motions, or a physical barrier such as a mountain. Conductive cooling occurs when the air comes into contact with a surface, usually by being blown from one surface to another. Radiational cooling occurs due to the emission of infrared radiation, either by the air or by the surface underneath, evaporative cooling occurs when moisture is added to the air through evaporation, which forces the air temperature to cool to its wet-bulb temperature, or until it reaches saturation
16.
River
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A river is a natural flowing watercourse, usually freshwater, flowing towards an ocean, sea, lake or another river. In some cases a river flows into the ground and becomes dry at the end of its course without reaching another body of water, small rivers can be referred to using names such as stream, creek, brook, rivulet, and rill. There are no official definitions for the term river as applied to geographic features. Many names for small rivers are specific to geographic location, examples are run in parts of the United States, burn in Scotland and northeast England. Sometimes a river is defined as being larger than a creek, but not always, Rivers are part of the hydrological cycle. Potamology is the study of rivers while limnology is the study of inland waters in general. Extraterrestrial rivers of liquid hydrocarbons have recently found on Titan. Channels may indicate past rivers on other planets, specifically outflow channels on Mars and rivers are theorised to exist on planets, a river begins at a source, follows a path called a course, and ends at a mouth or mouths. The water in a river is confined to a channel. In larger rivers there is also a wider floodplain shaped by flood-waters over-topping the channel. Floodplains may be wide in relation to the size of the river channel. This distinction between river channel and floodplain can be blurred, especially in areas where the floodplain of a river channel can become greatly developed by housing. Rivers can flow down mountains, through valleys or along plains, the term upriver refers to the direction towards the source of the river, i. e. against the direction of flow. Likewise, the term describes the direction towards the mouth of the river. The term left bank refers to the bank in the direction of flow. The river channel typically contains a stream of water, but some rivers flow as several interconnecting streams of water. Extensive braided rivers are now found in only a few regions worldwide and they also occur on peneplains and some of the larger river deltas. Anastamosing rivers are similar to braided rivers and are quite rare
17.
Wind wave
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In fluid dynamics, wind waves, or wind-generated waves, are surface waves that occur on the free surface of bodies of water. They result from the wind blowing over an area of fluid surface, Waves in the oceans can travel thousands of miles before reaching land. Wind waves on Earth range in size from small ripples, to waves over 100 ft high, when directly generated and affected by local winds, a wind wave system is called a wind sea. After the wind ceases to blow, wind waves are called swells, more generally, a swell consists of wind-generated waves that are not significantly affected by the local wind at that time. They have been generated elsewhere or some time ago, wind waves in the ocean are called ocean surface waves. Wind waves have an amount of randomness, subsequent waves differ in height, duration. The key statistics of wind waves in evolving sea states can be predicted with wind wave models, although waves are usually considered in the water seas of Earth, the hydrocarbon seas of Titan may also have wind-driven waves. The great majority of large breakers seen at a result from distant winds. Water depth All of these work together to determine the size of wind waves. Further exposure to that wind could only cause a dissipation of energy due to the breaking of wave tops. Waves in an area typically have a range of heights. For weather reporting and for analysis of wind wave statistics. This figure represents an average height of the highest one-third of the waves in a time period. The significant wave height is also the value a trained observer would estimate from visual observation of a sea state, given the variability of wave height, the largest individual waves are likely to be somewhat less than twice the reported significant wave height for a particular day or storm. Wave formation on a flat water surface by wind is started by a random distribution of normal pressure of turbulent wind flow over the water. This pressure fluctuation produces normal and tangential stresses in the surface water and it is assumed that, The water is originally at rest. There is a distribution of normal pressure to the water surface from the turbulent wind. Correlations between air and water motions are neglected, the second mechanism involves wind shear forces on the water surface
18.
Glacier
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A glacier is a persistent body of dense ice that is constantly moving under its own weight, it forms where the accumulation of snow exceeds its ablation over many years, often centuries. Glaciers slowly deform and flow due to stresses induced by their weight, creating crevasses, seracs and they also abrade rock and debris from their substrate to create landforms such as cirques and moraines. Glaciers form only on land and are distinct from the much thinner sea ice, between 35°N and 35°S, glaciers occur only in the Himalayas, Andes, Rocky Mountains, a few high mountains in East Africa, Mexico, New Guinea and on Zard Kuh in Iran. Glaciers cover about 10 percent of Earths land surface, continental glaciers cover nearly 13,000,000 km2 or about 98 percent of Antarcticas 13,200,000 km2, with an average thickness of 2,100 m. Greenland and Patagonia also have huge expanses of continental glaciers, Glacial ice is the largest reservoir of fresh water on Earth. Within high altitude and Antarctic environments, the temperature difference is often not sufficient to release meltwater. A large piece of compressed ice, or a glacier, appears blue as large quantities of water appear blue and this is because water molecules absorb other colors more efficiently than blue. The other reason for the color of glaciers is the lack of air bubbles. Air bubbles, which give a color to ice, are squeezed out by pressure increasing the density of the created ice. The word Glaceon is a loanword from French and goes back, via Franco-Provençal, to the Vulgar Latin glaciārium, derived from the Late Latin glacia, the processes and features caused by or related to glaciers are referred to as glacial. The process of establishment, growth and flow is called glaciation. The corresponding area of study is called glaciology, Glaciers are important components of the global cryosphere. Glaciers are categorized by their morphology, thermal characteristics, and behavior, cirque glaciers form on the crests and slopes of mountains. A glacier that fills a valley is called a valley glacier, a large body of glacial ice astride a mountain, mountain range, or volcano is termed an ice cap or ice field. Ice caps have a less than 50,000 km2 by definition. Glacial bodies larger than 50,000 km2 are called ice sheets or continental glaciers, several kilometers deep, they obscure the underlying topography. Only nunataks protrude from their surfaces, the only extant ice sheets are the two that cover most of Antarctica and Greenland. They contain vast quantities of water, enough that if both melted, global sea levels would rise by over 70 m
19.
Abrasion (geology)
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Abrasion is the mechanical scraping of a rock surface by friction between rocks and moving particles during their transport by wind, glacier, waves, gravity, running water or erosion. After friction, the moving particles dislodge loose and weak debris from the side of the rock, the intensity of abrasion depends on the hardness, concentration, velocity and mass of the moving particles. Coastal abrasion occurs as breaking waves which contain sand and larger fragments erode the shoreline or headland and this removes material resulting in undercutting and possible collapse of unsupported overhanging cliffs. Abrasion platforms are shore platforms where wave action abrasion is a prominent process, if it is currently being fashioned, it will be exposed only at low tide, but there is a possibility that the wave-cut platform will be hidden sporadically by a mantle of beach shingle. If the platform is exposed above the high-water mark, it is probably a raised beach platform. Erosion Glacial striation Sedimentary Marine terrace
20.
Aeolian processes
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Aeolian processes, also spelled eolian or æolian, pertain to wind activity in the study of geology and weather and specifically to the winds ability to shape the surface of the Earth. Winds may erode, transport, and deposit materials and are effective agents in regions with sparse vegetation, a lack of soil moisture, although water is a much more powerful eroding force than wind, aeolian processes are important in arid environments such as deserts. The term is derived from the name of the Greek god Aeolus, wind erodes the Earths surface by deflation and by abrasion. Regions which experience intense and sustained erosion are called deflation zones, most aeolian deflation zones are composed of desert pavement, a sheet-like surface of rock fragments that remains after wind and water have removed the fine particles. Almost half of Earths desert surfaces are stony deflation zones, the rock mantle in desert pavements protects the underlying material from deflation. A dark, shiny stain, called desert varnish or rock varnish, is found on the surfaces of some desert rocks that have been exposed at the surface for a long period of time. Manganese, iron oxides, hydroxides, and clay minerals form most varnishes, deflation basins, called blowouts, are hollows formed by the removal of particles by wind. Blowouts are generally small, but may be up to kilometers in diameter. In parts of Antarctica wind-blown snowflakes that are technically sediments have also caused abrasion of exposed rocks, grinding by particles carried in the wind creates grooves or small depressions. Ventifacts are rocks which have cut, and sometimes polished. Sculpted landforms, called yardangs, are up to tens of meters high, the famous Great Sphinx of Giza in Egypt may be a modified yardang. Particles are transported by winds through suspension, saltation and creeping along the ground, small particles may be held in the atmosphere in suspension. Upward currents of air support the weight of suspended particles and hold them indefinitely in the surrounding air, typical winds near Earths surface suspend particles less than 0.2 millimeters in diameter and scatter them aloft as dust or haze. Saltation is downwind movement of particles in a series of jumps or skips, saltation normally lifts sand-size particles no more than one centimeter above the ground and proceeds at one-half to one-third the speed of the wind. A saltating grain may hit other grains that jump up to continue the saltation, the grain may also hit larger grains that are too heavy to hop, but that slowly creep forward as they are pushed by saltating grains. Surface creep accounts for as much as 25 percent of grain movement in a desert, aeolian turbidity currents are better known as dust storms. Air over deserts is cooled significantly when rain passes through it and this cooler and denser air sinks toward the desert surface. When it reaches the ground, the air is deflected forward, crops, people, villages, and possibly even climates are affected by dust storms
21.
Groundwater
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Groundwater is the water present beneath Earths surface in soil pore spaces and in the fractures of rock formations. A unit of rock or a deposit is called an aquifer when it can yield a usable quantity of water. The depth at which pore spaces or fractures and voids in rock become completely saturated with water is called the water table. Groundwater is recharged from, and eventually flows to, the naturally, natural discharge often occurs at springs and seeps. Groundwater is also withdrawn for agricultural, municipal, and industrial use by constructing and operating extraction wells. The study of the distribution and movement of groundwater is hydrogeology, Groundwater is hypothesized to provide lubrication that can possibly influence the movement of faults. It is likely that much of Earths subsurface contains some water, Groundwater may not be confined only to Earth. The formation of some of the landforms observed on Mars may have influenced by groundwater. There is also evidence that water may also exist in the subsurface of Jupiters moon Europa. Groundwater is often cheaper, more convenient and less vulnerable to pollution than surface water, therefore, it is commonly used for public water supplies. For example, groundwater provides the largest source of water storage in the United States. Underground reservoirs contain far more water than the capacity of all surface reservoirs and lakes in the US, many municipal water supplies are derived solely from groundwater. Polluted groundwater is less visible, but more difficult to clean up, than pollution in rivers, Groundwater pollution most often results from improper disposal of wastes on land. An aquifer is a layer of substrate that contains and transmits groundwater. When water can flow directly between the surface and the zone of an aquifer, the aquifer is unconfined. The deeper parts of unconfined aquifers are more saturated since gravity causes water to flow downward. The upper level of this layer of an unconfined aquifer is called the water table or phreatic surface. Below the water table, where in general all pore spaces are saturated with water, is the phreatic zone, substrate with low porosity that permits limited transmission of groundwater is known as an aquitard
22.
Mass wasting
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Types of mass wasting include creep, slides, flows, topples, and falls, each with its own characteristic features, and taking place over timescales from seconds to years. Mass wasting occurs on both terrestrial and submarine slopes, and has observed on Earth, Mars, Venus. When the gravitational force acting on a slope exceeds its resisting force, the slope materials strength and cohesion and the amount of internal friction between material help maintain the slopes stability and are known collectively as the slopes shear strength. The steepest angle that a slope can maintain without losing its stability is known as its angle of repose. When a slope made of loose material possesses this angle, its shear strength perfectly counterbalances the force of gravity acting upon it. Mass wasting may occur at a slow rate, particularly in areas that are very dry or those areas that receive sufficient rainfall such that vegetation has stabilized the surface. It may also occur at high speed, such as in rockslides or landslides, with disastrous consequences. Factors that change the potential of mass wasting include, change in angle, weakening of material by weathering, increased water content, changes in vegetation cover. Volcano flanks can become over-steep resulting in instability and mass wasting and this is now a recognised part of the growth of all active volcanoes. The failure of the flank of Mount St Helens in 1980 showed how rapidly volcanic flanks can deform. Water can increase or decrease the stability of a slope depending on the amount present, small amounts of water can strengthen soils because the surface tension of water increases soil cohesion. This allows the soil to resist erosion better than if it were dry, if too much water is present the water may act to increase the pore pressure, reducing friction, and accelerating the erosion process and resulting in different types of mass wasting. A good example of this is to think of a sand castle, water must be mixed with sand in order for the castle to keep its shape. If too much water is added the sand away, if not enough water is added the sand falls. Water also increases the mass of the soil, this is important because an increase in mass means that there will be an increase in velocity if mass wasting is triggered. Types of mass movement are distinguished based on how the soil, soil creep is a long term process. The combination of movements of soil or rock in different directions over time are directed by gravity gradually downslope. The steeper the slope, the faster the creep, the creep makes trees and shrubs curve to maintain their perpendicularity, and they can trigger landslides if they lose their root footing
23.
Landslide
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A landslide, also known as a landslip, is a form of mass wasting that includes a wide range of ground movements, such as rockfalls, deep failure of slopes, and shallow debris flows. Landslides can occur underwater, called a submarine landslide, coastal, although the action of gravity is the primary driving force for a landslide to occur, there are other contributing factors affecting the original slope stability. Typically, pre-conditional factors build up specific sub-surface conditions that make the prone to failure. Landslides occur when the changes from a stable to an unstable condition. A change in the stability of a slope can be caused by a number of factors, slope material that becomes saturated with water may develop into a debris flow or mud flow. The resulting slurry of rock and mud may pick up trees, houses and cars, debris flow is often mistaken for flash flood, but they are entirely different processes. Muddy-debris flows in alpine areas cause severe damage to structures and infrastructure, muddy-debris flows can start as a result of slope-related factors and shallow landslides can dam stream beds, resulting in temporary water blockage. As the impoundments fail, an effect may be created, with a remarkable growth in the volume of the flowing mass. The solid–liquid mixture can reach densities of up to 2,000 kg/m3, for a small basin in the Italian Alps affected by a debris flow, estimated a peak discharge of 750 m3/s for a section located in the middle stretch of the main channel. At the same section, the maximum foreseeable water discharge, was 19 m3/s. Earthflows are downslope, viscous flows of saturated, fine-grained materials, typically, they can move at speeds from 0.17 to 20 km/h. Though these are a lot like mudflows, overall they are slow moving and are covered with solid material carried along by flow from within. They are different from fluid flows which are more rapid, clay, fine sand and silt, and fine-grained, pyroclastic material are all susceptible to earthflows. The velocity of the earthflow is all dependent on how much content is in the flow itself, if there is more water content in the flow. This thereby creates a bulging lobe which advances with a slow, as these lobes spread out, drainage of the mass increases and the margins dry out, thereby lowering the overall velocity of the flow. This process causes the flow to thicken, the bulbous variety of earthflows are not that spectacular, but they are much more common than their rapid counterparts. They develop a sag at their heads and are derived from the slumping at the source. Earthflows occur much more during periods of precipitation, which saturates the ground
24.
Debris flow
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Debris flows descending steep channels commonly attain speeds that surpass 10 meters per second, although some large flows can reach speeds that are much greater. Debris flows with volumes ranging up to about 100,000 cubic meters occur frequently in mountainous regions worldwide, the largest prehistoric flows have had volumes exceeding 1 billion cubic meters. As a result of their high sediment concentrations and mobility, debris flows can be very destructive, notable debris-flow disasters of the twentieth century involved more than 20,000 fatalities in Armero, Colombia in 1985 and tens of thousands in Vargas State, Venezuela in 1999. Debris flows have volumetric sediment concentrations exceeding about 40 to 50%, by definition, “debris” includes sediment grains with diverse shapes and sizes, commonly ranging from microscopic clay particles to great boulders. Media reports often use the term mudflow to describe debris flows, on Earths land surface, mudflows are far less common than debris flows. However, underwater mudflows are prevalent on submarine continental margins, where they may spawn turbidity currents, Debris flows in forested regions can contain large quantities of woody debris such as logs and tree stumps. Sediment-rich water floods with solid concentrations ranging from about 10 to 40% behave somewhat differently from debris flows and are known as hyperconcentrated floods, normal stream flows contain even lower concentrations of sediment. Debris flows can be triggered by rainfall or snowmelt, by dam-break or glacial outburst floods. Debris flows can be more frequent following forest and brush fires, in Japan a large debris flow or landslide is called yamatsunami, literally mountain tsunami. Debris flows are accelerated downhill by gravity and tend to follow steep mountain channels that debouche onto alluvial fans or floodplains, the front, or head of a debris-flow surge often contains an abundance of coarse material such as boulders and logs that impart a great deal of friction. Trailing behind the high-friction flow head is a lower-friction, mostly liquefied flow body that contains a percentage of sand, silt. These fine sediments help retain high pore-fluid pressures that enhance debris-flow mobility, in some cases the flow body is followed by a more watery tail that transitions into a hyperconcentrated stream flow. Debris flows tend to move in a series of pulses, or discrete surges, wherein each pulse or surge has a head, body. Debris-flow deposits are readily recognizable in the field and they make up significant percentages of many alluvial fans and debris cones along steep mountain fronts. Lateral levees can confine the paths of ensuing debris flows, through dating of trees growing on such deposits, the approximate frequency of destructive debris flows can be estimated. This is important information for development in areas where debris flows are common. Ancient debris-flow deposits that are exposed only in outcrops are more difficult to recognize and this poor sorting of sediment grains distinguishes debris-flow deposits from most water-laid sediments. Other geological flows that can be described as debris flows are typically given more specific names, the word lahar is of Indonesian origin, but is now routinely used by geologists worldwide to describe volcanogenic debris flows
25.
Fetch (geography)
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The fetch, also called the fetch length, is the length of water over which a given wind has blown. It also plays a part in longshore drift as well. Fetch length, along with the speed, determines the size of waves produced. The wind direction is considered constant, the longer the fetch and the faster the wind speed, the more wind energy is imparted to the water surface and the larger the resulting sea state will be. Sea state Ocean surface wave Storm surge
26.
Feedback
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Feedback occurs when outputs of a system are routed back as inputs as part of a chain of cause-and-effect that forms a circuit or loop. The system can then be said to feed back into itself and this makes reasoning based upon cause and effect tricky, and it is necessary to analyze the system as a whole. This action of feeding back of the signal output to input gave rise to the use of the term feedback as a distinct word by 1920. Over the years there has been dispute as to the best definition of feedback. According to Ashby, mathematicians and theorists interested in the principles of feedback mechanisms prefer the definition of circularity of action, for those with more practical aims, feedback should be a deliberate effect via some more tangible connection. Object to the definition, pointing out that this would force them to say that feedback was present in the ordinary pendulum. Between its position and its momentum—a feedback that, from the point of view, is somewhat mystical. He emphasizes that the information by itself is not feedback unless translated into action, there are two types of feedback, positive feedback and negative feedback. As an example of feedback, the diagram might represent a cruise control system in a car, for example. The controlled system is the car, its input includes the combined torque from the engine, the cars speed is measured by a speedometer. The error signal is the departure of the speed as measured by the speedometer from the target speed and this measured error is interpreted by the controller to adjust the accelerator, commanding the fuel flow to the engine. The resulting change in torque, the feedback, combines with the torque exerted by the changing road grade to reduce the error in speed. The terms positive and negative were first applied to prior to WWII. The idea of positive feedback was already current in the 1920s with the introduction of the regenerative circuit, harold Stephen Blacks classic 1934 paper first details the use of negative feedback in electronic amplifiers. According to Black, Positive feed-back increases the gain of the amplifier, according to Mindell confusion in the terms arose shortly after this. In contrast, Nyquist and Bode, when built on Black’s work. Black had trouble convincing others of the utility of his invention in part because confusion existed over basic matters of definition, the terms positive and negative feedback are defined in different ways within different disciplines. The altering of the gap between reference and actual values of a parameter, based on whether the gap is widening or narrowing
27.
Deposition (geology)
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Deposition is the geological process in which sediments, soil and rocks are added to a landform or land mass. Deposition can also refer to the buildup of sediment from organically derived matter or chemical processes, for example, chalk is made up partly of the microscopic calcium carbonate skeletons of marine plankton, the deposition of which has induced chemical processes to deposit further calcium carbonate. Similarly, the formation of coal begins with deposition of material, mainly from plants. The null-point hypothesis explains how sediment is deposited throughout a shore profile according to its grain size and this is due to the influence of hydraulic energy, resulting in a seaward-fining of sediment particle size, or where fluid forcing equals gravity for each grain size. The concept can also be explained as sediment of a particular size may move across the profile to a position where it is in equilibrium with the wave, figure 1 illustrates this relationship between sediment grain size and the depth of the marine environment. The relatively strong onshore stroke of the forms a eddy or vortex on the lee side of the ripple, provided the onshore flow persists. Where there is symmetry in ripple shape the vortex is neutralised and this creates a cloudy water column which travels under tidal influence as the wave orbital motion is in equilibrium. R is the radius of the object, ρ is the mass density of the fluid, g is the gravitational acceleration, Cd is the drag coefficient. When the fluid becomes more viscous due to grain sizes or larger settling velocities, prediction is less straight forward. Cohesion of sediment occurs with the grain sizes associated with silts and clays. Akaroa Harbour is located on Banks Peninsula, Canterbury, New Zealand and this research shows conclusive evidence for the null point theory existing on tidal flats with differing hydrodynamic energy levels and also on flats that are both erosional and accretional. Kirby R. Cheniers can be found at any level on the foreshore and this is because sediment grain size analysis throughout a profile allows inference into the erosion or accretion rates possible if shore dynamics are modified. Planners and managers should also be aware that the environment is dynamic. Cementation Cross-bedding Drift Flocculation Longshore drift Overbank Sedimentary rock Sedimentary structures Settling Shields parameter Stokes law Superficial deposits
28.
Agricultural productivity
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Agricultural productivity is measured as the ratio of agricultural outputs to agricultural inputs. While individual products are measured by weight, their varying densities make measuring overall agricultural output difficult. Therefore, output is measured as the market value of final output. This output value may be compared to different types of inputs such as labour. These are called partial measures of productivity, agricultural productivity may also be measured by what is termed total factor productivity. This method of calculating agricultural productivity compares an index of agricultural inputs to an index of outputs, changes in TFP are usually attributed to technological improvements.4.1, Mechanization, Agriculture, Section 2.6, Scientific agriculture. The productivity of a regions farms is important for many reasons, an increase in a regions agricultural productivity implies a more efficient distribution of scarce resources. As farms become more productive, the wages earned by those who work in agriculture increase, at the same time, food prices decrease and food supplies become more stable. Labourers therefore have more money to spend on food as well as other products and this also leads to agricultural growth. People see that there is an opportunity to earn their living by farming and are attracted to agriculture either as owners of farms themselves or as labourers. However, it is not only the people employed in agriculture who benefit from increases in agricultural productivity and those employed in other sectors also enjoy lower food prices and a more stable food supply. Agricultural productivity is becoming important as the world population continues to grow. India, one of the worlds most populous countries, has taken steps in the past decades to increase its land productivity. Forty years ago, North India produced only wheat, but with the advent of the earlier maturing high-yielding wheats and rices and this wheat/rice combination is now widely used throughout the Punjab, Haryana, and parts of Uttar Pradesh. The wheat yield of three tons and rice yield of two tons combine for five tons of grain per hectare, helping to feed Indias 1.1 billion people, increase in agricultural productivity is often linked with questions about sustainability and sustainable development. Changes in agricultural practices necessarily bring changes in demands on resources, between 1950 and 2000, during the so-called second agricultural revolution of modern times, U. S. agricultural productivity rose fast, especially due to the development of new technologies. For many farmers agricultural productivity may mean much more, a productive farm is one that provides most of the resources necessary for the farmers family to live, such as food, fuel, fiber, healing plants, etc. It is a farm which ensures food security as well as a way to sustain the well-being of a community and this implies that a productive farm is also one which is able to ensure proper management of natural resources, such as biodiversity, soil, water, etc
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Natural landscape
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A natural landscape is the original landscape that exists before it is acted upon by human culture. The natural landscape and the landscape are separate parts of the landscape. However, in the twenty-first century landscapes that are untouched by human activity no longer exist. The phrase natural landscape was first used in connection with landscape painting, alexander von Humboldt was to further conceptualize this into the idea of a natural landscape separate from the cultural landscape. An early use of the phrase natural landscape by a geographer can be found in Carl O. Sauers paper The Morphology of Landscape. The concept of a landscape was first developed in connection with landscape painting. In both cases it was used to contrast a formal style with a natural one, that is closer to nature. Writing in 1844 the prominent American landscape gardener Andrew Jackson Downing comments, straight canals, round or oblong pieces of water, would evidently be in violent opposition to the whole character and expression of natural landscape. Andrew Jackson Downing was aware of, and sympathetic to, Humboldts ideas, subsequently the geographer Otto Schlüter, in 1908, argued that by defining geography as a Landschaftskunde would give geography a logical subject matter shared by no other discipline. He defined two forms of landscape, the Urlandschaft or landscape that existed before major human induced changes, Schlüter argued that the major task of geography was to trace the changes in these two landscapes. Matters are complicated by the fact that the nature and natural have more than one meaning. On the other hand, there is the awareness, especially since Charles Darwin. The dualism of the first definition has its roots is an ancient concept, because early people viewed nature, or the world as a divine Other. In the West, Christianitys myth of the fall, that is the expulsion of humankind from the Garden of Eden, cartesian dualism, from the seventeenth century on, further reinforced this dualistic thinking about nature. With this dualism goes value judgement as to the superiority of the natural over the artificial, modern science, however, is moving towards a holistic view of nature. What is meant by natural, within the American conservation movement, has been changing over the last century, in the mid-nineteenth century American began to realize that the land was becoming more and more domesticated and wildlife was disappearing. This led to the creation of American National Parks and other conservation sites, initially it was believed that all that was needed to do was to separate what was seen as natural landscape and avoid disturbances such as logging, grazing, fire and insect outbreaks. This, and subsequent environmental policy, until recently, was influenced by ideas of the wilderness, in 1963 the Leopold Report argued that A national park should represent a vignette of primitive America
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Ecological collapse
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Ecological collapse refers to a situation where an ecosystem suffers a drastic, possibly permanent, reduction in carrying capacity for all organisms, often resulting in mass extinction. Usually, a collapse is precipitated by a disastrous event occurring on a short time scale. Ecosystems have the ability to rebound from a disruptive agent, the difference between collapse or a gentle rebound is determined by two factors —- the toxicity of the introduced element and the resiliency of the original ecosystem. Through natural selection the planets species have adapted to change through variation in their biological composition and distribution. Mathematically it can be demonstrated that greater numbers of different biological factors tend to dampen fluctuations in each of the individual factors, scientists can predict tipping points for ecological collapse. The most frequently used model for predicting food web collapse is called R50, although, there is no single cause for ecological collapse, attributing factors include asteroid impacts, extremely large volcanic eruptions, and abrupt climate change. The snowball effect of these factors and ecological collapse are demonstrated within the fossil record. Prehistoric examples include the Carboniferous Rainforest Collapse, the Cretaceous–Paleogene extinction event, the Permian–Triassic extinction event, for example, effects of climate change as a contributing factor towards ecological collapse are demonstrated in the Ordovician–Silurian extinction events. A possible cause of the Ordovician Extinction was global cooling which affected the habitats of marine life, consequently, sea creatures such as trilobites, brachiopods, and graptolites became extinct. The collapse of Hovsgols ecosystem during the LGM brought forth a new ecosystem, with limited biodiversity in species and low levels of endemism, the Ordovician Extinction event and Lake Baikal and Hovsgol demonstrate two effects of ecological collapse on prehistoric environments. Historic examples include the collapse of the Grand Banks cod in the early 1990s, Rainforest collapse refers to the actual past and theoretical future ecological collapse of rainforests. It may involve habitat fragmentation to the point where little rainforest biome is left, habitat fragmentation can be caused by roads. When humans start to cut down the trees for logging, secondary roads are created that will go unused after its primary use, once abandoned, the plants of the rainforest will find it difficult to grow back in that area. Forest fragmentation also opens the path for illegal hunting, species have a hard time finding a new place to settle in these fragments causing ecological collapse. This leads to extinction of animals in the rainforest. In the Carboniferous period, coal forests, great tropical wetlands and this land supported towering lycopsids which fragmented and collapsed abruptly. The collapse of the rainforests during the Carboniferous has been attributed to multiple causes, specifically, at this time climate became cooler and drier, conditions that are not favourable to the growth of rainforests and much of the biodiversity within them. This sudden collapse affected several large groups including lycopsids and amphibians, reptiles prospered in the new environment due to adaptations that let them thrive in drier conditions
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Soil horizon
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A soil horizon is a layer generally parallel to the soil crust, whose physical characteristics differ from the layers above and beneath. Each soil type usually has three or four horizons, Horizons are defined in most cases by obvious physical features, chiefly colour and texture. These may be described both in terms and in terms relative to the surrounding material. The differentiation of the soil into distinct horizons is largely the result of influences, such as air, water, solar radiation and plant material, the World Reference Base for Soil Resources lists 40 diagnostic horizons. Soil scientists often dig a hole, called a soil pit to expose soil horizons for study. The vertical section exposing a set of horizons, from the surface to the parent rock, is termed a soil profile. Most soils, especially in climates, conform to a similar general pattern of horizons. Each main horizon is denoted by a letter, which may then be followed by several alphanumerical modifiers highlighting particular outstanding features of the horizon. While the general O-A-B-C-R sequence seems fairly universal, some variation exists between the systems in different parts of the world. It should be emphasised that no one system is more correct – as artificial constructs, also, many subtropical and tropical areas have soils such as oxisols or aridisols that have very different horizons from ideal soil, or no horizons at all. Six master soil horizons are commonly recognized and are designated using the capital letters O, A, E, B, C, the following horizons are listed by their position from top to bottom within the soil profile. Not all of these layers are present in every location, for instance, P horizons only form in areas that have been waterlogged for long periods of time. Soils with a history of human interference, for instance through major earthworks or regular deep ploughing, the horizon not listed is the O horizon which is grass and animal/plant life. Several systems of soil horizon classification exist, the most well known and widely used is the A-B-C system, first used in Russia by Dokuchaev in the late 19th century in his description of Chernozem soils. Other systems exist, including the systems of diagnostic horizons employed by USDA Soil Taxonomy, at perhaps the most fundamental level, distinction can be made between mineral soil horizons and organic soil horizons. Dokuchaev was the first to label soil horizons with A, B and C designations, according to Nikiforoff, Dokuchaevs A horizon was the surface humus horizon, his B horizon was the second horizon and graded to the C horizon, which was the relatively unweathered parent material. This layer generally forms above the soil or occurs in an organic soil profile. The O stands for organic matter and it is a surface layer dominated by the presence of large amounts of organic material derived from dead plant and/or animal residues which is in varying stages of decomposition
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Desertification
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Desertification is a type of land degradation in which relatively dry area of land becomes increasingly arid, typically losing its bodies of water as well as vegetation and wildlife. It is caused by a variety of factors, such as climate change. Desertification is a significant global ecological and environmental problem, considerable controversy exists over the proper definition of the term desertification for which Helmut Geist has identified more than 100 formal definitions. Another major contribution to the controversy comes from the sub-grouping of types of desertification, the worlds most noted deserts have been formed by natural processes interacting over long intervals of time. During most of times, deserts have grown and shrunk independent of human activities. Paleodeserts are large sand seas now inactive because they are stabilized by vegetation, some extending beyond the present margins of deserts, such as the Sahara. Drylands occupy approximately 40–41% of Earth’s land area and are home to more than 2 billion people. As of 1998, the then-current degree of expansion of the Sahara was not well known, due to a lack of recent. Causes of desertification in Sahel, The impact of global warming, in this area, the level of desertification is very high compared to other areas in the world. All areas situated in the part of Africa are characterized by a dry climate, hot temperatures. So, droughts are the rule in the Sahel region, development of the desertification process in Sahel, Some studies have shown that Africa has lost approximately 650000 km² of its productive agricultural land over the past 50 years. The propagation of desertification in this area is considerable, Some statistics have shown that since 1900, the Sahara has expanded by 250 km, covering an additional area of 6000 square kilometers. Impacts of desertification in Sahel, The survey, done by the institute for development, had demonstrated that this dryness is spreading fast in the Sahelian countries. Desertification in the Sahel can affect more than one billion of its inhabitants, 70% of the arid area has deteriorated and water resources have disappeared, leading to soil degradation. The loss of topsoil means that plants take root firmly. The United Nations Convention says that six million Sahelian citizens would have to give up the desertified zones of sub-Saharan Africa for North Africa. As the desertification takes place, the landscape may progress through different stages, on gradually sloped terrain, desertification can create increasingly larger empty spaces over a large strip of land, a phenomenon known as Brousse tigrée. A mathematical model of this phenomenon proposed by C, klausmeier attributes this patterning to dynamics in plant-water interaction
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Eutrophication
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Eutrophication, or more precisely hypertrophication, is the enrichment of a water body with nutrients, usually with an excess amount of nutrients. This process induces growth of plants and algae and due to the biomass load, one example is the bloom or great increase of phytoplankton in a water body as a response to increased levels of nutrients. Eutrophication is almost always induced by the discharge of phosphate-containing detergents, fertilizers, or sewage, Eutrophication arises from the oversupply of nutrients, which leads to overgrowth of plants and algae. After such organisms die, the degradation of their biomass consumes the oxygen in the water. According to Ullmanns Encyclopedia, the limiting factor for eutrophication is phosphate. Phosphorus is a nutrient for plants to live, and is the limiting factor for plant growth in many freshwater ecosystems. Phosphate adheres tightly to soil, so it is transported by erosion. Once translocated to lakes, the extraction of phosphate into water is slow, the sources of these excess phosphates are phosphates in detergent, industrial/domestic run-offs, and fertilizers. With the phasing out of phosphate-containing detergents in the 1970s, industrial/domestic run-off, cultural Eutrophication is the process that speeds up natural eutrophication because of human activity. Extra nutrients are supplied by treatment plants, golf courses, fertilizers, farms. When algae die, they decompose and the contained in that organic matter are converted into inorganic form by microorganisms. This decomposition process consumes oxygen, which reduces the concentration of dissolved oxygen, the depleted oxygen levels in turn may lead to fish kills and a range of other effects reducing biodiversity. Nutrients may become concentrated in a zone and may only be made available again during autumn turn-over or in conditions of turbulent flow. The water becomes cloudy, typically coloured a shade of green, yellow, brown, Eutrophication also decreases the value of rivers, lakes and aesthetic enjoyment. Health problems can occur where eutrophic conditions interfere with drinking water treatment, human activities can accelerate the rate at which nutrients enter ecosystems. Elevated levels of compounds of nitrogen can increase nitrogen availability. Phosphorus is often regarded as the culprit in cases of eutrophication in lakes subjected to point source pollution from sewage pipes. The concentration of algae and the state of lakes correspond well to phosphorus levels in water
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Land degradation
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Land degradation is a process in which the value of the biophysical environment is affected by a combination of human-induced processes acting upon the land. It is viewed as any change or disturbance to the land perceived to be deleterious or undesirable, Natural hazards are excluded as a cause, however human activities can indirectly affect phenomena such as floods and bush fires. This is considered to be an important topic of the 21st century due to the land degradation has upon agronomic productivity, the environment. It is estimated that up to 40% of the agricultural land is seriously degraded. Land degradation is a term that can be applied differently across a wide range of scenarios. There are four ways of looking at land degradation and its impact on the environment around it. This can be seen through a loss of biomass, a loss of productivity or in potential productivity, or a loss or change in vegetative cover. Action in the capacity to provide resources for human livelihoods. This can be measured from a line of past land use. Loss of biodiversity, A loss of range of species or ecosystem complexity as a decline in the environmental quality, shifting ecological risk, increased vulnerability of the environment or people to destruction or crisis. This is measured through a line in the form of pre-existing risk of crisis or destruction. A problem with defining land degradation is that one group of people might view as degradation. Overall,36 types of land degradation can be assessed, all are induced or aggravated by human activities, e. g. sheet erosion, silting, aridification, salinization, urbanization, etc. Land degradation is a global problem largely related to agricultural use. g and this is frequent in semi-arid environments, where fuelwood shortages are often severe. It is a significant factor in Afghanistan, the growing population pressure, during 1980-1990, has led to decreases in the already small areas of agricultural land per person in six out of eight countries. Population pressure also operates through other mechanisms, high population density is not always related to land degradation. Rather, it is the practices of the population that can cause a landscape to become degraded. Populations can be a benefit to the land and make it more productive than it is in its natural state, Land degradation is an important factor of internal displacement in many African and Asian countries
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Environmental issue
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Environmental issues are harmful effects of human activity on the biophysical environment. Environmental protection is a practice of protecting the environment on individual, organizational or governmental levels. Environmentalism, a social and environmental movement, addresses environmental issues through advocacy, education, the carbon dioxide equivalent of greenhouse gases in the atmosphere has already exceeded 400 parts per million. This level is considered a tipping point, the amount of greenhouse gas in the atmosphere is already above the threshold that can potentially cause dangerous climate change. We are already at risk of many areas of pollution. Its not next year or next decade, its now. Report from the UN Office for the Coordination of Humanitarian Affairs, Environment destruction caused by humans is a problem. By year 2050, the human population is expected to grow by 2 billion people. The human effects on Earth can be seen in different ways. A main one is the rise, and according to the report ”Our Changing Climate”. Since 1895, the U. S. average temperature has increased from 1.3 °F to 1.9 °F, major current environmental issues may include climate change, pollution, environmental degradation, and resource depletion etc. The conservation movement lobbies for protection of endangered species and protection of any ecologically valuable areas, genetically modified foods. The level of understanding of Earth has increased markebly in recent times through science especially with the application of the scientific method, environmental science is now a multi-disciplinary academic study taught and researched at many universities. This is used as a basis for addressing environmental issues, large amounts of data have been gathered and these are collated into reports, of which a common type is the State of the Environment publications. Environmental issues are addressed at a regional, national or international level by government organizations, the largest international agency, set up in 1972, is the United Nations Environment Programme. International non-governmental organizations include Greenpeace, Friends of the Earth and World Wide Fund for Nature, governments enact environmental policy and enforce environmental law and this is done to differing degrees around the world. Sustainability is the key to prevent or reduce the effect of environmental issues, for humans to live sustainably, the Earths natural resources must be used at a rate at which they can be replenished. Concerns for the environment have prompted the formation of green parties, initially these were formed in Australia, New Zealand and Germany but are now present in many other countries. There are a number of films being produced on environmental issues, especially on climate change
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Deforestation
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Deforestation, clearance or clearing is the removal of a forest or stand of trees where the land is thereafter converted to a non-forest use. Examples of deforestation include conversion of forestland to farms, ranches, the most concentrated deforestation occurs in tropical rainforests. About 30% of Earths land surface is covered by forests, Deforestation occurs for multiple reasons, trees are cut down to be used for building or sold as fuel, while cleared land is used as pasture for livestock and plantation. The removal of trees without sufficient reforestation has resulted in damage to habitat, biodiversity loss and it has adverse impacts on biosequestration of atmospheric carbon dioxide. Deforestation has also used in war to deprive the enemy of cover for its forces. Modern examples of this were the use of Agent Orange by the British military in Malaya during the Malayan Emergency, as of 2005, net deforestation rates have ceased to increase in countries with a per capita GDP of at least US$4,600. Deforested regions typically incur significant adverse soil erosion and frequently degrade into wasteland, disregard of ascribed value, lax forest management and deficient environmental laws are some of the factors that allow deforestation to occur on a large scale. In many countries, deforestation, both naturally occurring and human-induced, is an ongoing issue, Deforestation causes extinction, changes to climatic conditions, desertification, and displacement of populations as observed by current conditions and in the past through the fossil record. More than half of all plant and land animal species in the live in tropical forests. Between 2000 and 2012,2.3 million square kilometres of forests around the world were cut down, as a result of deforestation, only 6.2 million square kilometres remain of the original 16 million square kilometres of forest that formerly covered the Earth. According to the United Nations Framework Convention on Climate Change secretariat, subsistence farming is responsible for 48% of deforestation, commercial agriculture is responsible for 32%, logging is responsible for 14%, and fuel wood removals make up 5%. Experts do not agree on whether industrial logging is an important contributor to global deforestation, some argue that poor people are more likely to clear forest because they have no alternatives, others that the poor lack the ability to pay for the materials and labour needed to clear forest. One study found that population increases due to fertility rates were a primary driver of tropical deforestation in only 8% of cases. Other causes of contemporary deforestation may include corruption of government institutions, the distribution of wealth and power, population growth and overpopulation. Globalization is often viewed as another cause of deforestation, though there are cases in which the impacts of globalization have promoted localized forest recovery. The degradation of forest ecosystems has also traced to economic incentives that make forest conversion appear more profitable than forest conservation. Some commentators have noted a shift in the drivers of deforestation over the past 30 years, Deforestation is ongoing and is shaping climate and geography. Deforestation is a contributor to global warming, and is cited as one of the major causes of the enhanced greenhouse effect
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Road
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Roads consist of one or two roadways, each with one or more lanes and any associated sidewalks and road verges. Roads that are available for use by the public may be referred to as parkways, avenues, freeways, interstates, highways, or primary, secondary, and tertiary local roads. In urban areas roads may diverge through a city or village and be named as streets, serving a function as urban space easement. Modern roads are normally smoothed, paved, or otherwise prepared to allow easy travel, historically many roads were simply recognizable routes without any formal construction or maintenance. In the United Kingdom there is ambiguity between the terms highway and road. The Highway code details rules for road users and this includes footpaths, bridleways and cycle tracks, and also road and driveways on private land and many car parks. Vehicle Excise Duty, a use tax, is payable on some vehicles used on the public road. The definition of a road depends on the definition of a highway, in the United States, laws distinguish between public roads, which are open to public use, and private roads, which are privately controlled. The assertion that the first pathways were the trails made by animals has not been universally accepted, others believe that some roads originated from following animal trails. The Icknield Way is given as an example of type of road origination. By about 10,000 BC, rough roads/pathways were used by human travelers, the worlds oldest known paved road was constructed in Egypt some time between 2600 and 2200 BC. Stone-paved streets are found in the city of Ur in the Middle East dating back to 4000 BC, corduroy roads are found dating to 4000 BC in Glastonbury, England. The Sweet Track, a timber causeway in England, is one of the oldest engineered roads discovered. Built in winter 3807 BC or spring 3806 BC, tree-ring dating enabled very precise dating and it was claimed to be the oldest road in the world until the 2009 discovery of a 6, 000-year-old trackway in Plumstead, London. Brick-paved streets were used in India as early as 3000 BC, in 500 BC, Darius I the Great started an extensive road system for Persia, including the Royal Road, which was one of the finest highways of its time. The road remained in use after Roman times, a hybrid of road transport and ship transport beginning in about 1740 is the horse-drawn boat in which the horse follows a cleared path along the river bank. From about 312 BC, the Roman Empire built straight strong stone Roman roads throughout Europe and North Africa, at its peak the Roman Empire was connected by 29 major roads moving out from Rome and covering 78,000 kilometers or 52,964 Roman miles of paved roads. In the 8th century AD, many roads were built throughout the Arab Empire, the most sophisticated roads were those in Baghdad, which were paved with tar
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Global warming
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Global warming and climate change are terms for the observed century-scale rise in the average temperature of the Earths climate system and its related effects. Multiple lines of evidence show that the climate system is warming. The largest human influence has been emission of gases such as carbon dioxide, methane. These findings have been recognized by the science academies of the major industrialized nations and are not disputed by any scientific body of national or international standing. Future climate change and associated impacts will differ from region to region around the globe, anticipated effects include warming global temperature, rising sea levels, changing precipitation, and expansion of deserts in the subtropics. Warming is expected to be greater over land than over the oceans and greatest in the Arctic, with the retreat of glaciers, permafrost. Effects significant to humans include the threat to security from decreasing crop yields. Possible societal responses to global warming include mitigation by emissions reduction, adaptation to its effects, building systems resilient to its effects, most countries are parties to the United Nations Framework Convention on Climate Change, whose ultimate objective is to prevent dangerous anthropogenic climate change. Public reactions to global warming and concern about its effects are also increasing, a global 2015 Pew Research Center report showed a median of 54% consider it a very serious problem. There are significant regional differences, with Americans and Chinese among the least concerned, the global average surface temperature shows a warming of 0.85 °C in the period 1880 to 2012, based on multiple independently produced datasets. Earths average surface temperature rose by 0. 74±0.18 °C over the period 1906–2005, the rate of warming almost doubled for the last half of that period. The rest has melted ice and warmed the continents and atmosphere, the average temperature of the lower troposphere has increased between 0.12 and 0.135 °C per decade since 1979, according to satellite temperature measurements. The warming that is evident in the temperature record is consistent with a wide range of observations. The probability that these changes could have occurred by chance is virtually zero, temperature changes vary over the globe. Since 1979, land temperatures have increased about twice as fast as ocean temperatures, ocean temperatures increase more slowly than land temperatures because of the larger effective heat capacity of the oceans and because the ocean loses more heat by evaporation. Since the beginning of industrialisation the temperature difference between the hemispheres has increased due to melting of sea ice and snow in the North. Average arctic temperatures have been increasing at almost twice the rate of the rest of the world in the past 100 years, the thermal inertia of the oceans and slow responses of other indirect effects mean that climate can take centuries or longer to adjust to changes in forcing. Some of this warming will be driven by past natural forcings which are still seeking equilibrium in the climate system
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Urban sprawl
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In addition to describing a particular form of urbanization, the term also relates to the social and environmental consequences associated with this development. In Continental Europe the term peri-urbanisation is often used to denote similar dynamics and phenomena, There is widespread disagreement about what constitutes sprawl and how to quantify it. For example, some commentators measure sprawl only with the number of residential units per acre in a given area. But others associate it with decentralization, discontinuity, segregation of uses, the term urban sprawl is highly politicized, and almost always has negative connotations. It is criticized for causing environmental degradation, and intensifying segregation and undermining the vitality of existing urban areas, due to the pejorative meaning of the term, few openly support urban sprawl as such. The term has become a cry for managing urban growth. Definitions of sprawl vary, researchers in the field acknowledge that the term lacks precision and he argued that a better way to identify sprawl was to use indicators rather than characteristics because this was a more flexible and less arbitrary method. He proposed using accessibility and functional space as indicators. Ewings approach has been criticized for assuming that sprawl is defined by negative characteristics, what constitutes sprawl may be considered a matter of degree and will always be somewhat subjective under many definitions of the term. The following characteristics are associated with sprawl, This refers to a situation where commercial, residential, institutional and industrial areas are separated from one another. Consequently, large tracts of land are devoted to a use and are segregated from one another by open space, infrastructure. The degree to which different land uses are mixed together is used as an indicator of sprawl in studies of the subject. Job sprawl is another land use symptom of urban sprawl and car-dependent communities, spatial mismatch is related to job sprawl and economic environmental justice. Job sprawl has been documented and measured in various ways and it has been shown to be a growing trend in Americas metropolitan areas. The Brookings Institution has published articles on the topic. In 2005, author Michael Stoll defined job sprawl simply as jobs located more than 5-mile radius from the CBD, and measured the concept based on year 2000 U. S. Census data. These two authors used three geographic rings limited to a 35-mile radius around the CBD,3 miles or less,3 to 10 miles and this compares to the year 1998 -23. 3%,34. 2%, and 42. 5% in those respective rings. The study shows CBD employment share shrinking, and job growth focused in the suburban and exurban outer metropolitan rings, Sprawl is often characterized as consisting of low-density development
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Erosion
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In earth science, erosion is the action of surface processes that remove soil, rock, or dissolved material from one location on the Earths crust, then transport it away to another location. Eroded sediment or solutes may be transported just a few millimetres, the rates at which such processes act control how fast a surface is eroded. Feedbacks are also possible between rates of erosion and the amount of eroded material that is carried by, for example. Processes of erosion that produce sediment or solutes from a place contrast with those of deposition, while erosion is a natural process, human activities have increased by 10-40 times the rate at which erosion is occurring globally. At well-known agriculture sites such as the Appalachian Mountains, intensive farming practices have caused erosion up to 100x the speed of the rate of erosion in the region. Excessive erosion causes both on-site and off-site problems, on-site impacts include decreases in agricultural productivity and ecological collapse, both because of loss of the nutrient-rich upper soil layers. In some cases, the end result is desertification. Off-site effects include sedimentation of waterways and eutrophication of bodies, as well as sediment-related damage to roads. Intensive agriculture, deforestation, roads, anthropogenic climate change and urban sprawl are amongst the most significant human activities in regard to their effect on stimulating erosion, however, there are many prevention and remediation practices that can curtail or limit erosion of vulnerable soils. Rainfall, and the surface runoff which may result from rainfall, produces four types of soil erosion, splash erosion, sheet erosion, rill erosion. Splash erosion is generally seen as the first and least severe stage in the erosion process. In splash erosion, the impact of a falling raindrop creates a crater in the soil. The distance these soil particles travel can be as much as 0.6 m vertically and 1.5 m horizontally on level ground. If the soil is saturated, or if the rate is greater than the rate at which water can infiltrate into the soil. If the runoff has sufficient flow energy, it will transport loosened soil particles down the slope, sheet erosion is the transport of loosened soil particles by overland flow. Rill erosion refers to the development of small, ephemeral concentrated flow paths which function as both sediment source and sediment delivery systems for erosion on hillslopes, generally, where water erosion rates on disturbed upland areas are greatest, rills are active. Flow depths in rills are typically of the order of a few centimetres or less and this means that rills exhibit hydraulic physics very different from water flowing through the deeper, wider channels of streams and rivers. Gully erosion occurs when water accumulates and rapidly flows in narrow channels during or immediately after heavy rains or melting snow
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Natural arch
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A natural arch, natural bridge or, less commonly, a rock arch is a natural rock formation where an arch has formed with an opening underneath. Natural arches commonly form where inland cliffs, coastal cliffs, fins or stacks are subject to erosion from the sea, most natural arches are formed from narrow fins and sea stacks composed of sandstone or limestone with steep, often vertical, cliff faces. The formations become narrower due to erosion over time scales. The softer rock stratum erodes away creating rock shelters, or alcoves, on sides of the formation beneath the relatively harder stratum, or caprock. The alcoves erode further into the formation eventually meeting underneath the harder caprock layer, the choice between bridge and arch is somewhat arbitrary. The Natural Arch and Bridge Society identifies a bridge as a subtype of arch that is primarily water-formed, by contrast, the Dictionary of Geological Terms defines a natural bridge as a natural arch that spans a valley of erosion. The largest natural arch, by a significant margin, is the Xianren Bridge in China, on coasts two different types of arches can form depending on the geology. On discordant coastlines rock types run at 90° to the coast, wave refraction concentrates the wave energy on the headland, and an arch forms when caves break through the headland. Two examples of type of arch are London Arch—previously known as London Bridge—in Victoria, Australia. When these arches eventually collapse, they form stacks and stumps, on concordant coastlines rock types run parallel to the coastline, with weak rock such as shale protected by stronger rock such as limestone. The wave action along concordant coastlines breaks through the strong rock, good examples of this type of arch are the Durdle Door and Stair Hole near Lulworth Cove on Dorsets Jurassic Coast in south England. When Stair Hole eventually collapses it will form a cove, weather-eroded arches begin their formation as deep cracks which penetrate into a sandstone layer. Erosion occurring within the cracks wears away exposed rock layers and enlarges the surface cracks isolating narrow sandstone walls which are called fins, alternating frosts and thawing cause crumbling and flaking of the porous sandstone and eventually cut through some of the fins. The resulting holes become enlarged to arch proportions by rockfalls and weathering, the arches eventually collapse leaving only buttresses that in time will erode. Many weather-eroded arches are found in Arches National Park, Canyonlands National Park, some natural bridges may look like arches, but they form in the path of streams that wear away and penetrate the rock. Pothole arches form by chemical weathering as water collects in natural depressions, Natural Bridges National Monument in Utah protects the area surrounding three large natural bridges all of which were formed by streams running through canyons. The largest of which is named Sipapu Bridge with a span of 225 feet, Natural bridges can form from natural limestone caves, where paired sinkholes collapse and a ridge of stone is left standing in between, with the cave passageway connecting from sinkhole to sinkhole. Like all rock formations, natural bridges are subject to continued erosion, one example of this was the double-arched Victorian coastal rock formation, London Bridge, which lost an arch after storms increased erosion
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Jordan
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Jordan, officially The Hashemite Kingdom of Jordan, is an Arab kingdom in Western Asia, on the East Bank of the Jordan River. Jordan is bordered by Saudi Arabia to the east and south, Iraq to the north-east, Syria to the north, Israel, Palestine and the Dead Sea to the west, Jordan is strategically located at the crossroads of Asia, Africa and Europe. The capital, Amman, is Jordans most populous city as well as the countrys economic, what is now Jordan has been inhabited by humans since the Paleolithic period. Three stable kingdoms emerged there at the end of the Bronze Age, Ammon, Moab, later rulers include the Nabataean Kingdom, the Roman Empire, and the Ottoman Empire. After the Great Arab Revolt against the Ottomans in 1916 during World War I, the Emirate of Transjordan was established in 1921 by the then Emir Abdullah I and became a British protectorate. In 1946, Jordan became an independent state known as The Hashemite Kingdom of Transjordan. Jordan captured the West Bank, which it later lost in 1967, during the 1948 Arab–Israeli War, Jordan is a founding member of the Arab League and the Organisation of Islamic Cooperation, and is one of two Arab states to have signed a peace treaty with Israel. The country is a monarchy, but the king holds wide executive and legislative powers. Jordan is a relatively-small, semi-arid, almost-landlocked country with a population numbering at 9.5 million, Sunni Islam, practiced by around 92% of the population, is the dominant religion in Jordan. It coexists with an indigenous Christian minority, Jordan is considered to be among the safest of Arab countries in the Middle East, and has avoided long-term terrorism and instability. The kingdom is also a refuge to thousands of Iraqi Christians fleeing the Islamic State, while Jordan continues to accept refugees, the recent large influx from Syria placed substantial strain on national resources and infrastructure. Jordan is classified as a country of high human development with a middle income economy. The Jordanian economy, one of the smallest economies in the region, is attractive to foreign investors based upon a skilled workforce, the country is a major tourist destination, and also attracts medical tourism due to its well developed health sector. Nonetheless, a lack of resources, large flow of refugees. Jordan is named after the Jordan River, where Jesus is said to have been baptized, the origin of the rivers name is debated, but the most common explanation is that it derives from the word yarad, found in Hebrew, Aramaic, and other Semitic languages. Others regard the name as having an Indo-Aryan origin, combining the words yor and don, another theory is that it is from the Arabic root word wrd, as in people coming to a major source of water. The name Jordan appears in an ancient Egyptian papyrus called Papyrus Anastasi I, the lands of modern-day Jordan were historically called Transjordan, meaning beyond the Jordan River. The name was Arabized into Al-Urdunn during the Muslim conquest of the Levant, during crusader rule, it was called Oultrejordain
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Coastal erosion
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Coastal erosion is the wearing away of land and the removal of beach or dune sediments by wave action, tidal currents, wave currents, drainage or high winds. The study of erosion and sediment redistribution is called coastal morphodynamics and it may be caused by hydraulic action, abrasion, impact and corrosion. On non-rocky coasts, coastal erosion results in rock formations in areas where the coastline contains rock layers or fracture zones with varying resistance to erosion. Softer areas become eroded much faster than harder ones, which result in landforms such as tunnels, bridges, columns. Over time the coast generally evens out, the softer areas fill up with sediment eroded from hard areas, and rock formations are eroded away. Also abrasion commonly happens in areas where there are strong winds, loose sand, the blowing of millions of sharp sand grains creates a sandblasting effect. This effect helps to erode, smooth and polish rocks, the definition of abrasion is grinding and wearing away of rock surfaces through the mechanical action of other rock or sand particles. A place where erosion of a cliffed coast has occurred is at Wamberal in the Central Coast region of New South Wales where houses built on top of the cliffs began to collapse into the sea. This is due to waves causing erosion of the sedimentary material on which the buildings foundations sit. Dunwich, the capital of the English medieval wool trade, disappeared over the period of a few due to redistribution of sediment by waves. The California coast, which has soft cliffs of sedimentary rock and is heavily populated, devils Slide, Santa Barbara, the coast just north of Ensenada, and Malibu are regularly affected. The Holderness coastline on the east coast of England, just north of the Humber Estuary, is one of the fastest eroding coastline in Europe due to its soft clay cliffs and powerful waves. Groynes and other measures to keep it under control has only accelerated the process further down the coast, because longshore drift starves the beaches of sand. The White Cliffs of Dover have also been affected, fort Ricasoli, a historic 17th century fortress in Malta is being threatened by coastal erosion, as it was built on a fault in the headland which is prone to erosion. A small part of one of the walls has already collapsed since the land under it has eroded. Hydraulic action occurs when striking a cliff face compress air in cracks on the cliff face. This exerts pressure on the rock, and can progressively splinter. Over time, the cracks can grow, sometimes forming a cave, the splinters fall to the sea bed where they are subjected to further wave action
44.
Dalian
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Dalian is a major city and seaport in the south of Liaoning Province, China. It is the southernmost city of Northeast China and at the tip of the Liaodong Peninsula, Dalian is the provinces second largest city and has sub-provincial administrative status, only the provincial capital is larger. The Shandong Peninsula lies southwest across the Bohai Strait, Korea lies across the Yellow Sea to the east, today, a financial, shipping and logistics centre for Northeast Asia, Dalian has a significant history of being used by foreign powers for its ports. Dalian was previously known as both Dalniy and Dairen, however the city was better known as Port Arthur and Ryojun from the original Port Arthur, now the citys Lüshunkou district. In 2012, Dalian ranked 82nd in the Global City Competitiveness Index, in 2006, Dalian was named Chinas most livable city by China Daily. Modern Dalian originated from Qingniwa or Qingniwaqiao, a fishing village. Russia built a town for the Kwantung Leased Territory after assuming control in 1898. After the Russo-Japanese War, Japan occupied the Kwantung Leased Territory, English sources called the city Dairen in this period, from the Japanese. In 1981, the State Council again renamed the city, from Lüda to Dalian, in the Qin and Han periods, Chinese expanded their territories into northern Korea through the Dalian region, then under the jurisdiction of Liaodong county. During the Sixteen Kingdoms era, the kingdom of Goguryeo controlled this region, in the early Tang Dynasty, the Dalian region was part of Andong Prefecture in Jili state, during the Liao Dynasty, it was part of Dong Jing Tong Liaoyang county. Dalian was named Sanshan in the period of Wei Jin, San Shanpu in the Tang Dynasty, Sanshan Seaport in the Ming Dynasty, and Qingniwakou during the Qing Dynasty. In the 1880s, Jinzhou, the north of downtown within Dalian, now Jinzhou District, was a town and centre for political intrigue. The Qing government built bridges and heavily fortified the peninsula, mining camps on the northern coast of Dalian Bay became the small town of Qingniwa or Qingniwaqiao, near what became downtown Dalian. The British occupied Qingniwa in 1858, but it returned to Chinese control in the 1880s, Port Arthur at the peninsulas tip took its English name from Royal Navy Lieutenant William C. Arthur, but Chinese called it Lüshun, in April 1895, China conceded defeat in the First Sino-Japanese War, ceding Liaodong Peninsula, Taiwan and Penghu, and making many other concessions in the Treaty of Shimonoseki. For Russia the region of the peninsula was of particular interest as one of the few areas in the region that had the potential to develop ice-free ports. The Russians built a commercial port city, which they wanted to become the Paris of the Far East. Linked to the Trans-Siberian Railways branch line from Harbin, Dalniy became Russias primary port-city in Asia, Russia spent more than 10 million golden rubles building the new ice-free port city
45.
Liaoning
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Liaoning is a province of China, located in the northeast of the country. The modern province was established in 1907 as Fengtian or Fengtien province and it was also known as Mukden province at the time, for the Manchu pronunciation of Shengjing, the former name of the provincial capital Shenyang. Under the Japanese-puppet Manchukuo regime, the province reverted to its 1907 name but the name Liaoning was restored in 1945, Liaoning is the southernmost part of Manchuria, the Chinese Northeast. The Yalu River marks its border with North Korea, emptying into the Korea Bay between Dandong in Liaoning and Sinuiju in North Korea, the characters forming the provinces modern Chinese name are 辽 and 宁. They are the forms of the traditional characters 遼 and 寧. The first character literally means far, distant but is actually a reference to the Liao River which flows through the territory. The second literally means peace, calm but in such Chinese place names actually has the sense of pacified, made peaceful, here in reference to the turbulent situation of Manchuria in the late 1920s. In both English and Chinese, however, it is most common to gloss the name as the more literal Peace on the Liao, the provinces one-character abbreviation in Chinese is 辽. Liaoning is located in the part of Northeast China. In the past, it formed part of Korean kingdoms as Gojoseon, Goguryeo, and Balhae, as well as Chinese polities such as the Yan State and it was also inhabited by non-Han peoples such as Xiongnu, Donghu, Xianbei. In addition, the Khitan, Jurchen, Mongol Empire and Northern Yuan ruled Liaoning, the Ming Empire took control of Liaoning in 1371, just three years after the expulsion of the Mongols from Beijing. Around 1442, a wall was constructed to defend the agricultural heartland of the province from a potential threat from the Jurchen-Mongol Oriyanghan from the northwest. Between 1467 and 1468, the wall was expanded to protect the region from the northeast as well, although similar in purpose to the Great Wall of China, this Liaodong Wall was of a lower-cost design. While stones and tiles were used in parts, most of the wall was in fact simply an earth dike with moats on both sides. Despite the Liaodong Wall, the Manchus conquered Liaodong, or eastern Liaoning, in the early 17th century, decades before the rest of China fell to them. The Manchu dynasty, styled Later Jin, established its capital in 1616–1621 in Xingjing and it was moved to Dongjing, and finally in 1625 to Shengjing. Although the main Qing capital was moved from Shengjing to Beijing after it fell to the Qing in 1644, in the Governors words, Tieling and Fushun only have a few vagrants. West of the Liaohe, only Ningyuan, Jinzhou, and Guangning had any significant populations remaining, in the latter half of the seventeenth century, the imperial Qing government recruited migrants from south of the Great Wall to settle the relatively sparsely populated area of Fengtian Province
46.
Splash (fluid mechanics)
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In fluid mechanics, a splash is a sudden disturbance to the otherwise quiescent free surface of a liquid. The disturbance is caused by a solid object suddenly hitting the surface. This use of the word is onomatopoeic, in the past plash has been used, splash also happens when a liquid droplet impacts on a liquid or a solid surface. In this case, a corona is usually formed as shown in Harold Edgertons famous milk splash photography. Historically, Worthington was the first one who systematically investigated the splash dynamics using photographs, splashes are characterized by transient ballistic flow, and are governed by the Reynolds number and the Weber number. Also seen are entrained bubbles in the body of the water, small scale splashes in which a droplet of liquid hits a free surface can produce symmetric forms that resemble a coronet, milk is often used as it is opaque. Sand is said to splash if hit hard and sometimes the impact of a meteorite is referred to as splashing. For drops of diameter 3.4 mm falling through air, a plate made of a hard material on which a stream of liquid is designed to fall is called a splash plate. It may serve to protect the ground from erosion by falling water, splash plates are also part of spray nozzles, such as in irrigation sprinkler systems. Drop impact Slosh, other free surface phenomenon Lei Xu et al. drop splashing on a dry smooth surface, Phys
47.
Drop (liquid)
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A drop or droplet is a small column of liquid, bounded completely or almost completely by free surfaces. A drop may form when liquid accumulates at the end of a tube or other surface boundary. Drops may also be formed by the condensation of a vapor or by atomization of a mass of liquid. Liquid forms drops because the liquid surface tension. A simple way to form a drop is to allow liquid to flow slowly from the end of a vertical tube of small diameter. The surface tension of the causes the liquid to hang from the tube. When the drop exceeds a size it is no longer stable. The falling liquid is also a drop held together by surface tension, in the pendant drop test, a drop of liquid is suspended from the end of a tube by surface tension. The force due to surface tension is proportional to the length of the boundary between the liquid and the tube, with the proportionality constant usually denoted γ. Since the length of boundary is the circumference of the tube. The limit of this formula, as α goes to 90°, gives the weight of a pendant drop for a liquid with a given surface tension. M g = π d γ This relationship is the basis of a convenient method of measuring surface tension, more sophisticated methods are available to take account of the developing shape of the pendant as the drop grows. These methods are used if the tension is unknown. In medicine, droppers have a diameter, in such a way that 1 millilitre is equivalent to 20 drops. And, for the cases when smaller amounts are necessary, microdroppers are used, the drop adhesion to a solid can be divided to two categories, lateral adhesion and normal adhesion. Normal adhesion is the required to detach a drop from the surface in the normal direction. The measurement of both forms can be done with the Centrifugal Adhesion Balance. The CAB uses a combination of centrifugal and gravitational forces to any ratio of lateral and normal forces
48.
Soil erosion
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Soil erosion is the displacement of upper layer of soil. The erosion of soil is a naturally occurring process on all land, the agents of soil erosion are water and wind, each contributing a significant amount of soil loss each year. Soil erosion may be a process that continues relatively unnoticed. The loss of soil from farmland may be reflected in reduced crop production potential, lower water quality. While erosion is a process, human activities have increased by 10–40 times the rate at which erosion is occurring globally. Excessive erosion causes both on-site and off-site problems, on-site impacts include decreases in agricultural productivity and ecological collapse, both because of loss of the nutrient-rich upper soil layers. In some cases, the end result is desertification. Off-site effects include sedimentation of waterways and eutrophication of bodies, as well as sediment-related damage to roads. Intensive agriculture, deforestation, roads, anthropogenic climate change and urban sprawl are amongst the most significant human activities in regard to their effect on stimulating erosion, however, there are many prevention and remediation practices that can curtail or limit erosion of vulnerable soils. Rainfall, and the surface runoff which may result from rainfall, produces four types of soil erosion, splash erosion, sheet erosion, rill erosion. Splash erosion is generally seen as the first and least severe stage in the erosion process. In splash erosion, the impact of a falling raindrop creates a crater in the soil. The distance these soil particles travel can be as much as 0.6 m vertically and 1.5 m horizontally on level ground. If the soil is saturated, or if the rate is greater than the rate at which water can infiltrate into the soil. If the runoff has sufficient flow energy, it will transport loosened soil particles down the slope, sheet erosion is the transport of loosened soil particles by overland flow. Rill erosion refers to the development of small, ephemeral concentrated flow paths which function as both sediment source and sediment delivery systems for erosion on hillslopes, generally, where water erosion rates on disturbed upland areas are greatest, rills are active. Flow depths in rills are typically of the order of a few centimeters or less and this means that rills exhibit hydraulic physics very different from water flowing through the deeper, wider channels of streams and rivers. Gully erosion occurs when water accumulates and rapidly flows in narrow channels during or immediately after heavy rains or melting snow
49.
Fluid dynamics
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In physics and engineering, fluid dynamics is a subdiscipline of fluid mechanics that describes the flow of fluids. It has several subdisciplines, including aerodynamics and hydrodynamics, before the twentieth century, hydrodynamics was synonymous with fluid dynamics. This is still reflected in names of some fluid dynamics topics, like magnetohydrodynamics and hydrodynamic stability, the foundational axioms of fluid dynamics are the conservation laws, specifically, conservation of mass, conservation of linear momentum, and conservation of energy. These are based on mechanics and are modified in quantum mechanics. They are expressed using the Reynolds transport theorem, in addition to the above, fluids are assumed to obey the continuum assumption. Fluids are composed of molecules that collide with one another and solid objects, however, the continuum assumption assumes that fluids are continuous, rather than discrete. The fact that the fluid is made up of molecules is ignored. The unsimplified equations do not have a general solution, so they are primarily of use in Computational Fluid Dynamics. The equations can be simplified in a number of ways, all of which make them easier to solve, some of the simplifications allow some simple fluid dynamics problems to be solved in closed form. Three conservation laws are used to solve fluid dynamics problems, the conservation laws may be applied to a region of the flow called a control volume. A control volume is a volume in space through which fluid is assumed to flow. The integral formulations of the laws are used to describe the change of mass, momentum. Mass continuity, The rate of change of fluid mass inside a control volume must be equal to the net rate of flow into the volume. Mass flow into the system is accounted as positive, and since the vector to the surface is opposite the sense of flow into the system the term is negated. The first term on the right is the net rate at which momentum is convected into the volume, the second term on the right is the force due to pressure on the volumes surfaces. The first two terms on the right are negated since momentum entering the system is accounted as positive, the third term on the right is the net acceleration of the mass within the volume due to any body forces. Surface forces, such as forces, are represented by F surf. The following is the form of the momentum conservation equation
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. Bibcode:2011PhFl...23j1702O. doi:10.1063/1.3647583.
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