Greywacke or graywacke is a variety of sandstone characterized by its hardness, dark color, poorly sorted angular grains of quartz and small rock fragments or lithic fragments set in a compact, clay-fine matrix. It is a texturally immature sedimentary rock found in Paleozoic strata; the larger grains can be sand- to gravel-sized, matrix materials constitute more than 15% of the rock by volume. The term "greywacke" can be confusing, since it can refer to either the immature aspect of the rock or its fine-grained component; the origin of greywacke was problematic until turbidity currents and turbidites were understood, according to the normal laws of sedimentation, gravel and mud should not be laid down together. Geologists now attribute its formation to strong turbidity currents; these actions churn sediment and cause mixed-sediment slurries, in which the resulting deposits may exhibit a variety of sedimentary features. Supporting the turbidity current origin theory is that deposits of greywacke are found on the edges of the continental shelves, at the bottoms of oceanic trenches, at the bases of mountain formational areas.
They occur in association with black shales of deep sea origin. Greywackes are grey, yellow or black, dull-colored sandy rocks which may occur in thick or thin beds along with shales and limestones, they are abundant in Wales, the south of Scotland, the Longford Massif in Ireland and the Lake District National Park of England. They can contain a great variety of minerals, the principal ones being quartz and plagioclase feldspars, iron oxides and graphitic, carbonaceous matters, together with fragments of such rocks as felsite, slate, various schists, quartzite. Among other minerals found in them are biotite, tourmaline, apatite, hornblende, augite and pyrites; the cementing material is sometimes calcareous. As a rule greywackes do not contain fossils, but organic remains may be common in the finer beds associated with them, their component particles are not rounded or polished, the rocks have been indurated by recrystallization, such as the introduction of interstitial silica. In some districts the greywackes are cleaved, but they show phenomena of this kind much less than the slates.
Some varieties include feldspathic greywacke, rich in feldspar, lithic greywacke, rich in tiny rock fragments. Although the group is so diverse that it is difficult to characterize mineralogically, it has a well-established place in petrographical classifications because these peculiar composite arenaceous deposits are frequent among Silurian and Cambrian rocks, are less common in Mesozoic or Cenozoic strata, their essential features are their complex composition. By increasing metamorphism, greywackes pass into mica-schists, chloritic schists and sedimentary gneisses. Greywacke zone Torlesse Greywacke This article incorporates text from a publication now in the public domain: Chisholm, Hugh, ed.. "Greywacke". Encyclopædia Britannica. Cambridge University Press. National Park Service site Presidio Franciscan Greywacke/Shales
Lava is molten rock generated by geothermal energy and expelled through fractures in planetary crust or in an eruption at temperatures from 700 to 1,200 °C. The structures resulting from subsequent solidification and cooling are sometimes described as lava; the molten rock is formed in the interior of some planets, including Earth, some of their satellites, though such material located below the crust is referred to by other terms. A lava flow is a moving outpouring of lava created during a non-explosive effusive eruption; when it has stopped moving, lava solidifies to form igneous rock. The term lava flow is shortened to lava. Although lava can be up to 100,000 times more viscous than water, lava can flow great distances before cooling and solidifying because of its thixotropic and shear thinning properties. Explosive eruptions produce a mixture of volcanic ash and other fragments called tephra, rather than lava flows; the word lava comes from Italian, is derived from the Latin word labes which means a fall or slide.
The first use in connection with extruded magma was in a short account written by Francesco Serao on the eruption of Vesuvius in 1737. Serao described "a flow of fiery lava" as an analogy to the flow of water and mud down the flanks of the volcano following heavy rain; the composition of all lava of the Earth's crust is dominated by silicate minerals feldspars, pyroxenes, amphiboles and quartz. Igneous rocks, which form lava flows when erupted, can be classified into three chemical types: felsic and mafic; these classes are chemical, the chemistry of lava tends to correlate with the magma temperature, its viscosity and its mode of eruption. Felsic or silicic lavas such as rhyolite and dacite form lava spines, lava domes or "coulees" and are associated with pyroclastic deposits. Most silicic lava flows are viscous, fragment as they extrude, producing blocky autobreccias; the high viscosity and strength are the result of their chemistry, high in silica, potassium and calcium, forming a polymerized liquid rich in feldspar and quartz, thus has a higher viscosity than other magma types.
Felsic magmas can erupt at temperatures as low as 650 to 750 °C. Unusually hot rhyolite lavas, may flow for distances of many tens of kilometres, such as in the Snake River Plain of the northwestern United States. Intermediate or andesitic lavas are lower in aluminium and silica, somewhat richer in magnesium and iron. Intermediate lavas form andesite domes and block lavas, may occur on steep composite volcanoes, such as in the Andes. Poorer in aluminium and silica than felsic lavas, commonly hotter, they tend to be less viscous. Greater temperatures tend to destroy polymerized bonds within the magma, promoting more fluid behaviour and a greater tendency to form phenocrysts. Higher iron and magnesium tends to manifest as a darker groundmass, occasionally amphibole or pyroxene phenocrysts. Mafic or basaltic lavas are typified by their high ferromagnesian content, erupt at temperatures in excess of 950 °C. Basaltic magma is high in iron and magnesium, has lower aluminium and silica, which taken together reduces the degree of polymerization within the melt.
Owing to the higher temperatures, viscosities can be low, although still thousands of times higher than water. The low degree of polymerization and high temperature favors chemical diffusion, so it is common to see large, well-formed phenocrysts within mafic lavas. Basalt lavas tend to produce low-profile shield volcanoes or "flood basalt fields", because the fluidal lava flows for long distances from the vent; the thickness of a basalt lava on a low slope, may be much greater than the thickness of the moving lava flow at any one time, because basalt lavas may "inflate" by supply of lava beneath a solidified crust. Most basalt lavas are of pāhoehoe types, rather than block lavas. Underwater, they can form pillow lavas, which are rather similar to entrail-type pahoehoe lavas on land. Ultramafic lavas such as komatiite and magnesian magmas that form boninite take the composition and temperatures of eruptions to the extreme. Komatiites contain over 18% magnesium oxide, are thought to have erupted at temperatures of 1,600 °C.
At this temperature there is no polymerization of the mineral compounds, creating a mobile liquid. Most if not all ultramafic lavas are no younger than the Proterozoic, with a few ultramafic magmas known from the Phanerozoic. No modern komatiite lavas are known, as the Earth's mantle has cooled too much to produce magnesian magmas; some lavas of unusual composition have erupted onto the surface of the Earth. These include: Carbonatite and natrocarbonatite lavas are known from Ol Doinyo Lengai volcano in Tanzania, the sole example of an active carbonatite volcano. Iron oxide lavas are thought to be the source of the iron ore at Kiruna, Sweden which formed during the Proterozoic. Iron oxide lavas of Pliocene age occur at the El Laco volcanic complex on the Chile-Argentina border. Iron oxide lavas are thought to be the result of immiscible separation of iron oxide magma from a parental magma of calc-alkaline or alkaline composition. Sulfur lava flows up to 250 metres 10 metres wide occur at Lastarria volcano, Chile.
They were formed by the melting of sulfur deposits at temperatures as low as 113 °C
Igneous rock, or magmatic rock, is one of the three main rock types, the others being sedimentary and metamorphic. Igneous rock is formed through the cooling and solidification of magma or lava; the magma can be crust. The melting is caused by one or more of three processes: an increase in temperature, a decrease in pressure, or a change in composition. Solidification into rock occurs either below the surface as intrusive rocks or on the surface as extrusive rocks. Igneous rock may form with crystallization to form granular, crystalline rocks, or without crystallization to form natural glasses. Igneous rocks occur in a wide range of geological settings: shields, orogens, large igneous provinces, extended crust and oceanic crust. Igneous and metamorphic rocks make up 90–95% of the top 16 km of the Earth's crust by volume. Igneous rocks form about 15% of the Earth's current land surface. Most of the Earth's oceanic crust is made of igneous rock. Igneous rocks are geologically important because: their minerals and global chemistry give information about the composition of the mantle, from which some igneous rocks are extracted, the temperature and pressure conditions that allowed this extraction, and/or of other pre-existing rock that melted.
In terms of modes of occurrence, igneous rocks can be either extrusive. Intrusive igneous rocks make up the majority of igneous rocks and are formed from magma that cools and solidifies within the crust of a planet, surrounded by pre-existing rock; the mineral grains in such rocks can be identified with the naked eye. Intrusive rocks can be classified according to the shape and size of the intrusive body and its relation to the other formations into which it intrudes. Typical intrusive formations are batholiths, laccoliths and dikes; when the magma solidifies within the earth's crust, it cools forming coarse textured rocks, such as granite, gabbro, or diorite. The central cores of major mountain ranges consist of intrusive igneous rocks granite; when exposed by erosion, these cores may occupy huge areas of the Earth's surface. Intrusive igneous rocks that form at depth within the crust are termed plutonic rocks and are coarse-grained. Intrusive igneous rocks that form near the surface are termed subvolcanic or hypabyssal rocks and they are medium-grained.
Hypabyssal rocks are less common than plutonic or volcanic rocks and form dikes, laccoliths, lopoliths, or phacoliths. Extrusive igneous rocks known as volcanic rocks, are formed at the crust's surface as a result of the partial melting of rocks within the mantle and crust. Extrusive solidify quicker than intrusive igneous rocks, they are formed by the cooling of molten magma on the earth's surface. The magma, brought to the surface through fissures or volcanic eruptions, solidifies at a faster rate. Hence such rocks are smooth and fine-grained. Basalt is lava plateaus; some kinds of basalt solidify to form long polygonal columns. The Giant's Causeway in Antrim, Northern Ireland is an example; the molten rock, with or without suspended crystals and gas bubbles, is called magma. It rises; when magma reaches the surface from beneath water or air, it is called lava. Eruptions of volcanoes into air are termed subaerial, whereas those occurring underneath the ocean are termed submarine. Black smokers and mid-ocean ridge basalt are examples of submarine volcanic activity.
The volume of extrusive rock erupted annually by volcanoes varies with plate tectonic setting. Extrusive rock is produced in the following proportions: divergent boundary: 73% convergent boundary: 15% hotspot: 12%. Magma that erupts from a volcano behaves according to its viscosity, determined by temperature, crystal content and the amount of silica. High-temperature magma, most of, basaltic in composition, behaves in a manner similar to thick oil and, as it cools, treacle. Long, thin basalt flows with pahoehoe surfaces are common. Intermediate composition magma, such as andesite, tends to form cinder cones of intermingled ash and lava, may have a viscosity similar to thick, cold molasses or rubber when erupted. Felsic magma, such as rhyolite, is erupted at low temperature and is up to 10,000 times as viscous as basalt. Volcanoes with rhyolitic magma erupt explosively, rhyolitic lava flows are of limited extent and have steep margins, because the magma is so viscous. Felsic and intermediate magmas that erupt do so violently, with explosions driven by the release of dissolved gases—typically water vapour, but carbon dioxide.
Explosively erupted pyroclastic material is called tephra and includes tuff and ignimbrite. Fine volcanic ash is erupted and forms ash tuff deposits, which ca
Coal is a combustible black or brownish-black sedimentary rock, formed as rock strata called coal seams. Coal is carbon with variable amounts of other elements. Coal is formed if dead plant matter decays into peat and over millions of years the heat and pressure of deep burial converts the peat into coal. Vast deposits of coal originates in former wetlands—called coal forests—that covered much of the Earth's tropical land areas during the late Carboniferous and Permian times; as a fossil fuel burned for heat, coal supplies about a quarter of the world's primary energy and two-fifths of its electricity. Some iron and steel making and other industrial processes burn coal; the extraction and use of coal causes much illness. Coal damages the environment, including by climate change as it is the largest anthropogenic source of carbon dioxide, 14 Gt in 2016, 40% of the total fossil fuel emissions; as part of the worldwide energy transition many countries use less coal. The largest consumer and importer of coal is China.
China mines account for half the world's coal, followed by India with about a tenth. Australia accounts for about a third of world coal exports followed by Russia; the word took the form col in Old English, from Proto-Germanic *kula, which in turn is hypothesized to come from the Proto-Indo-European root *gu-lo- "live coal". Germanic cognates include the Old Frisian kole, Middle Dutch cole, Dutch kool, Old High German chol, German Kohle and Old Norse kol, the Irish word gual is a cognate via the Indo-European root. Coal is composed of macerals and water. Fossils and amber may be found in coal. At various times in the geologic past, the Earth had dense forests in low-lying wetland areas. Due to natural processes such as flooding, these forests were buried underneath soil; as more and more soil deposited over them, they were compressed. The temperature rose as they sank deeper and deeper; as the process continued the plant matter was protected from biodegradation and oxidation by mud or acidic water.
This trapped the carbon in immense peat bogs that were covered and buried by sediments. Under high pressure and high temperature, dead vegetation was converted to coal; the conversion of dead vegetation into coal is called coalification. Coalification starts with dead plant matter decaying into peat. Over millions of years the heat and pressure of deep burial causes the loss of water and carbon dioxide and an increase in the proportion of carbon, thus first lignite sub-bituminous coal, bituminous coal, lastly anthracite may be formed. The wide, shallow seas of the Carboniferous Period provided ideal conditions for coal formation, although coal is known from most geological periods; the exception is the coal gap in the Permian -- Triassic extinction event. Coal is known from Precambrian strata, which predate land plants—this coal is presumed to have originated from residues of algae. Sometimes coal seams are interbedded with other sediments in a cyclothem; as geological processes apply pressure to dead biotic material over time, under suitable conditions, its metamorphic grade or rank increases successively into: Peat, a precursor of coal Lignite, or brown coal, the lowest rank of coal, most harmful to health, used exclusively as fuel for electric power generation Jet, a compact form of lignite, sometimes polished.
Bituminous coal, a dense sedimentary rock black, but sometimes dark brown with well-defined bands of bright and dull material It is used as fuel in steam-electric power generation and to make coke. Anthracite, the highest rank of coal is a harder, glossy black coal used for residential and commercial space heating. Graphite is difficult to ignite and not used as fuel. Cannel coal is a variety of fine-grained, high-rank coal with significant hydrogen content, which consists of liptinite. There are several international standards for coal; the classification of coal is based on the content of volatiles. However the most important distinction is between thermal coal, burnt to generate electricity via steam. Hilt's law is a geological observation, the higher its rank, it applies if the thermal gradient is vertical. The earliest recognized use is from the Shenyang area of China where by 4000 BC Neolithic inhabitants had begun carving ornaments from black lignite. Coal from the Fushun mine in northeastern China was used to smelt copper as early as 1000 BC.
Marco Polo, the Italian who traveled to China in the 13th century, described coal as "black stones... which burn like logs", said coal was so plentiful, people could take three hot baths a week. In Europe, the earliest reference to the use of coal as fuel is from the geological treatise On stones by the Greek scientist Theophrastus: Among the materials that are dug because they are useful, those known as anthrakes are made of earth, once set on fire, they burn like charcoa
Kingdom of Saxony
The Kingdom of Saxony, lasting between 1806 and 1918, was an independent member of a number of historical confederacies in Napoleonic through post-Napoleonic Germany. The kingdom was formed from the Electorate of Saxony. From 1871 it was part of the German Empire, it became a Free state in the era of Weimar Republic in 1918 after the end of World War I and the abdication of King Frederick Augustus III of Saxony. Its capital was the city of Dresden, its modern successor state is the Free State of Saxony. Before 1806, Saxony was part of the Holy Roman Empire, a thousand-year-old entity that had become decentralised over the centuries; the rulers of the Electorate of Saxony of the House of Wettin had held the title of elector for several centuries. When the Holy Roman Empire was dissolved in August 1806 following the defeat of Emperor Francis II by Napoleon at the Battle of Austerlitz, the electorate was raised to the status of an independent kingdom with the support of the First French Empire the dominant power in Central Europe.
The last elector of Saxony became King Frederick Augustus I. Following the defeat of Saxony's ally Prussia at the Battle of Jena in 1806, Saxony joined the Confederation of the Rhine, remained within the Confederation until its dissolution in 1813 with Napoleon's defeat at the Battle of Leipzig. Following the battle, in which Saxony — alone of all the German states — had fought alongside the French. King Frederick Augustus I was deserted by his troops, taken prisoner by the Prussians and considered to have forfeited his throne by the allies, who put Saxony under Prussian occupation and administration; this was more due to the Prussian desire to annex Saxony than to any crime on Frederick Augustus's part, the fate of Saxony would prove to be one of the main issues at the Congress of Vienna. In the end, 40% of the Kingdom, including the significant Wittenberg, home of the Protestant Reformation, was annexed by Prussia, but Frederick Augustus was restored to the throne in the remainder of his kingdom, which still included the major cities of Dresden and Leipzig.
The Kingdom joined the German Confederation, the new organization of the German states to replace the fallen Holy Roman Empire. During the 1866 Austro-Prussian War, Saxony sided with Austria, the Saxon army was seen as the only ally to bring substantial aid to the Austrian cause, having abandoned the defense of Saxony itself to join up with the Austrian army in Bohemia; this effectiveness allowed Saxony to escape the fate of other north German states allied with Austria — notably the Kingdom of Hanover — which were annexed by Prussia after the war. The Austrians and French insisted as a point of honour that Saxony must be spared, the Prussians acquiesced. Saxony joined the Prussian-led North German Confederation the next year. With Prussia's victory over France in the Franco-Prussian War of 1871, the members of the Confederation were organised by Otto von Bismarck into the German Empire, with WIlliam I as its emperor. John, as Saxony's incumbent king, was subordinate and owed allegiance to the Emperor, although he, like the other German princes, retained some of the prerogatives of a sovereign ruler, including the ability to enter into diplomatic relations with other states.
Wilhelm I's grandson Kaiser Wilhelm II abdicated in 1918 as a result of Germany's defeat in World War I. King Frederick Augustus III of Saxony followed him into abdication and the erstwhile Kingdom of Saxony became the Free State of Saxony within the newly formed Weimar Republic; the 1831 Constitution of Saxony established the state as a parliamentary monarchy. The king was named as head of the nation, he was required to follow the provisions of the constitution, could not become the ruler of any other state without the consent of the Diet, or parliament. The crown was hereditary in the male line of the royal family through agnatic primogeniture, though provisions existed allowing a female line to inherit in the absence of qualified male heirs. Added provisions concerned the formation of a regency if the king was too young or otherwise unable to rule, as well as provisions concerning the crown prince's education. Any acts or decrees signed or issued by the king had to be countersigned by at least one of his ministers, who thus took responsibility for them.
Without the ministerial countersignature, no act of the king was to be considered valid. The king was given the right to declare any accused person innocent, or alternately to mitigate or suspend their punishment or pardon them, he was given supreme power over religious matters in Saxony. He appointed the president of the upper house of the Diet, together with a proxy from among three candidates suggested by that house, appointed the president and proxy of the lower house, as well; the king was given sole power to promulgate laws, to carry them into effect, only by his consent could any proposal for a law be advanced in the Diet. He had authority to issue emergency decrees and to issue non-emergency laws that he found needful or "advantageous," though such instruments required the counter-signature of at least one of his ministers, had to be presented to the next Diet for approval, he could not, change the constitution itself or the electoral laws in this manner. He was permitted to veto laws passed by the Diet, or to send them back with proposed amendments for reconsideration.
He was permitted to issue extraordinary decrees to obtain money for state expenditures refused by the Diet, through the
Silesia is a historical region of Central Europe located in Poland, with small parts in the Czech Republic and Germany. Its area is about 40,000 km2, its population about 8,000,000. Silesia is located along the Oder River, it consists of Upper Silesia. The region is rich in mineral and natural resources, includes several important industrial areas. Silesia's largest city and historical capital is Wrocław; the biggest metropolitan area is the Upper Silesian metropolitan area, the centre of, Katowice. Parts of the Czech city of Ostrava fall within the borders of Silesia. Silesia's borders and national affiliation have changed over time, both when it was a hereditary possession of noble houses and after the rise of modern nation-states; the first known states to hold power there were those of Greater Moravia at the end of the 9th century and Bohemia early in the 10th century. In the 10th century, Silesia was incorporated into the early Polish state, after its division in the 12th century became a Piast duchy.
In the 14th century, it became a constituent part of the Bohemian Crown Lands under the Holy Roman Empire, which passed to the Austrian Habsburg Monarchy in 1526. Most of Silesia was conquered by Prussia in 1742 and transferred from Austria to Prussia in the Treaty of Berlin. Silesia became, as a province of Prussia, a part of the German Empire and the subsequent Weimar Republic; the varied history with changing aristocratic possessions resulted in an abundance of castles in Silesia in the Jelenia Góra valley. After World War I, the easternmost part of this region, i.e. an eastern strip of Upper Silesia, was awarded to Poland by the Entente Powers after insurrections by Poles and the Upper Silesian plebiscite. The remaining former Austrian parts of Silesia were partitioned to Czechoslovakia, forming part of Czechoslovakia's German-settled Sudetenland region, are today part of the Czech Republic. In 1945, after World War II, the bulk of Silesia was transferred, on demands of the Polish delegation, to Polish jurisdiction by the Potsdam Agreement of the victorious Allied Powers and became part of Poland.
The small Lusatian strip west of the Oder–Neisse line, which had belonged to Silesia since 1815, remained in Germany. The largest town and cultural centre of this region is Görlitz. Most inhabitants of Silesia today speak the national languages of their respective countries, while before the population shifts after 1945, the majority of Silesia's population spoke German; the population of Upper Silesia is native, while Lower Silesia was settled by a German-speaking population before 1945. An ongoing debate exists whether Silesian speech should be considered a dialect of Polish or a separate language. A Lower Silesian German dialect is used, although today it is extinct, it is used by expellees who relocated to the remaining parts of Germany, as well as by Germans who stayed in their Lower Silesian home. The names of Silesia in the different languages most share their etymology—Latin and English: Silesia; the names all relate to the name of a mountain in mid-southern Silesia. The mountain served as a cultic place.
Ślęża is listed as one of the numerous Pre-Indo-European topographic names in the region. According to some Polish Slavists, the name Ślęża or Ślęż is directly related to the Old Slavic words ślęg or śląg, which means dampness, moisture, or humidity, they disagree with the hypothesis of an origin for the name Śląsk from the name of the Silings tribe, an etymology preferred by some German authors. In the fourth century BC, Celts entered Silesia, settling around Mount Ślęża near modern Wrocław, Oława, Strzelin. Germanic Lugii tribes were first recorded within Silesia in the 1st century. Slavic peoples arrived in the region around the 7th century, by the early ninth century, their settlements had stabilized. Local Slavs started to erect boundary structures like the Silesia Walls; the eastern border of Silesian settlement was situated to the west of the Bytom, east from Racibórz and Cieszyn. East of this line dwelt a related Slav tribe, the Vistulans, their northern border was in the valley of the Barycz River, north of.
The first known states in Silesia were Bohemia. In the 10th century, the Polish ruler Mieszko I of the Piast dynasty incorporated Silesia into the Polish state. During the Fragmentation of Poland and the rest of the country were divided among many independent duchies ruled by various Silesian dukes. During this time, German cultural and ethnic influence increased as a result of immigration from German-speaking parts of the Holy Roman Empire. In 1178, parts of the Duchy of Kraków around Bytom, Oświęcim, Chrzanów, Siewierz were transferred to the Silesian Piasts, although their population was Vistulan and not of Silesian descent. Between 1289 and 1292, Bohemian king Wenceslaus II became suzerain of some of the Upper Silesian duchies. Polish kings had not renounced their hereditary rights to Silesia until 1335; the province became part of the Bohemian Crown under the Holy Roman Empire, passed with that crown to the Habsburg Monarchy of Austria in 1526. In the 15th century
In earth science, erosion is the action of surface processes that removes soil, rock, or dissolved material from one location on the Earth's crust, transports it to another location. This natural process is caused by the dynamic activity of erosive agents, that is, ice, air, plants and humans. In accordance with these agents, erosion is sometimes divided into water erosion, glacial erosion, snow erosion, wind erosion, zoogenic erosion, anthropogenic erosion; the particulate breakdown of rock or soil into clastic sediment is referred to as physical or mechanical erosion. Eroded sediment or solutes may be transported just a few millimetres, or for thousands of kilometres. Natural rates of erosion are controlled by the action of geological weathering geomorphic drivers, such as rainfall; the rates at which such processes act control. Physical erosion proceeds fastest on steeply sloping surfaces, rates may be sensitive to some climatically-controlled properties including amounts of water supplied, wind speed, wave fetch, or atmospheric temperature.
Feedbacks are possible between rates of erosion and the amount of eroded material, carried by, for example, a river or glacier. Processes of erosion that produce sediment or solutes from a place contrast with those of deposition, which control the arrival and emplacement of material at a new location. 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 natural 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 eventual end result is desertification. Off-site effects include sedimentation of waterways and eutrophication of water bodies, as well as sediment-related damage to roads and houses.
Water and wind erosion are the two primary causes of land degradation. Intensive agriculture, 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, the surface runoff which may result from rainfall, produces four main types of soil erosion: splash erosion, sheet erosion, rill erosion, gully erosion. Splash erosion is seen as the first and least severe stage in the soil erosion process, followed by sheet erosion rill erosion and gully erosion. In splash erosion, the impact of a falling raindrop creates a small crater in the soil, ejecting soil particles; 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 rainfall rate is greater than the rate at which water can infiltrate into the soil, surface runoff occurs.
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. Where water erosion rates on disturbed upland areas are greatest, rills are active. Flow depths in rills are of the order of a few centimetres or less and along-channel slopes may be quite steep; this means that rills exhibit hydraulic physics different from water flowing through the deeper, wider channels of streams and rivers. Gully erosion occurs when runoff water accumulates and flows in narrow channels during or after heavy rains or melting snow, removing soil to a considerable depth. Valley or stream erosion occurs with continued water flow along a linear feature; the erosion is both downward, deepening the valley, headward, extending the valley into the hillside, creating head cuts and steep banks.
In the earliest stage of stream erosion, the erosive activity is dominantly vertical, the valleys have a typical V cross-section and the stream gradient is steep. When some base level is reached, the erosive activity switches to lateral erosion, which widens the valley floor and creates a narrow floodplain; the stream gradient becomes nearly flat, lateral deposition of sediments becomes important as the stream meanders across the valley floor. In all stages of stream erosion, by far the most erosion occurs during times of flood when more and faster-moving water is available to carry a larger sediment load. In such processes, it is not the water alone