Sand is a naturally occurring granular material composed of finely divided rock and mineral particles. It is defined by size, being finer than gravel and coarser than silt, Sand can refer to a textural class of soil or soil type, i. e. a soil containing more than 85% sand-sized particles by mass. The second most common type of sand is calcium carbonate, for example aragonite, for example, it is the primary form of sand apparent in areas where reefs have dominated the ecosystem for millions of years like the Caribbean. Sand is a non renewable resource over human timescales, and sand suitable for making concrete is in high demand, in terms of particle size as used by geologists, sand particles range in diameter from 0.0625 mm to 2 mm. An individual particle in this size is termed a sand grain. Sand grains are between gravel and silt, a 1953 engineering standard published by the American Association of State Highway and Transportation Officials set the minimum sand size at 0.074 mm. A1938 specification of the United States Department of Agriculture was 0.05 mm.
Sand feels gritty when rubbed between the fingers. ISO14688 grades sands as fine and coarse with ranges 0.063 mm to 0.2 mm to 0.63 mm to 2.0 mm. In the United States, sand is commonly divided into five sub-categories based on size, very fine sand, fine sand, medium sand, coarse sand, and very coarse sand. These sizes are based on the Krumbein phi scale, where size in Φ = -log2D, on this scale, for sand the value of Φ varies from −1 to +4, with the divisions between sub-categories at whole numbers. The composition of sand is highly variable, depending on the local rock sources. The gypsum sand dunes of the White Sands National Monument in New Mexico are famous for their bright, arkose is a sand or sandstone with considerable feldspar content, derived from weathering and erosion of a granitic rock outcrop. Some sands contain magnetite, glauconite or gypsum, Sands rich in magnetite are dark to black in color, as are sands derived from volcanic basalts and obsidian. Chlorite-glauconite bearing sands are typically green in color, as are sands derived from basaltic with a high olivine content, many sands, especially those found extensively in Southern Europe, have iron impurities within the quartz crystals of the sand, giving a deep yellow color.
Sand deposits in some areas contain garnets and other resistant minerals, the study of individual grains can reveal much historical information as to the origin and kind of transport of the grain. Quartz sand that is weathered from granite or gneiss quartz crystals will be angular. It is called grus in geology or sharp sand in the trade where it is preferred for concrete. Sand that is transported long distances by water or wind will be rounded, people who collect sand as a hobby are known as arenophiles
Tectonic uplift is the portion of the total geologic uplift of the mean Earth surface that is not attributable to an isostatic response to unloading. One should take into consideration the effects of denudation, within the scope of this topic, uplift relates to denudation in that denudation brings buried rocks closer to the surface. This process can redistribute large loads from a region to a topographically lower area as well – thus promoting isostatic response in the region of denudation. The timing and rate of denudation can be estimated using pressure-temperature studies, crustal thickening has an upward component of motion and often occurs when continental crust is thrust onto continental crust. The process of nappe stacking can only continue for so long, although the raised surfaces of mountain ranges mainly result from crustal thickening, there are other forces at play that are responsible for tectonic activity. All tectonic processes are driven by force when density differences are present.
A good example of this would be the large-scale circulation of the Earths mantle, lateral density variations near the surface drive plate motion. The dynamics of mountain ranges are governed by differences in the potential energy of entire columns of lithosphere. The highest rates of working against gravity are required when the thickness of the crust changes, lithosphere on the oceanward side of an oceanic trench at a subduction zone will curve upwards due to the elastic properties of the Earths crust. Orogenic uplift is the result of collisions and results in mountain ranges or a more modest uplift over a large region. Perhaps the most extreme form of uplift is a continental-continental crustal collision. In this process, two continents are sutured together and large mountain ranges are produced, the collision of the Indian and Eurasian plates is a good example of the extent to which orogenic uplift can reach. Heavy thrust faulting and folding are responsible for the suturing together of the two plates, the collision of the Indian and Eurasian plates not only produced the Himalaya, but is responsible for crustal thickening north into Siberia.
The Pamir Mountains, Tian Shan, Hindu Kush, deformation of continental lithosphere can take place in several possible modes. The Ozark Plateau is an uplifted area which resulted from the Permian Ouachita Orogeny to the south in the states of Arkansas, Oklahoma. Another related uplift is the Llano Uplift in Texas, a location named after its uplift features. The Colorado Plateau which includes the Grand Canyon is the result of tectonic uplift followed by river erosion. The removal of mass from a region will be compensated by crustal rebound
Gravel /ˈɡrævəl/ is composed of unconsolidated rock fragments that have a general particle size range and include size classes from granule- to boulder-sized fragments. Gravel is categorized by the Udden-Wentworth scale into granular gravel and pebble gravel, one cubic metre of gravel typically weighs about 1,800 kg. Gravel is an important commercial product, with a number of applications, many roadways are surfaced with gravel, especially in rural areas where there is little traffic. Globally, far more roads are surfaced with gravel than with concrete or tarmac, both sand and small gravel are important for the manufacture of concrete. Large gravel deposits are a geological feature, being formed as a result of the weathering. The action of rivers and waves tends to pile up gravel in large accumulations and this can sometimes result in gravel becoming compacted and concreted into the sedimentary rock called conglomerate. Where natural gravel deposits are insufficient for human purposes, gravel is often produced by quarrying and crushing hard-wearing rocks, such as sandstone, quarries where gravel is extracted are known as gravel pits.
Southern England possesses particularly large concentrations of them due to the deposition of gravel in the region during the Ice Ages. As of 2006, the United States is the leading producer and consumer of gravel. The word gravel comes from the Breton language, adding the -el suffix in Breton denotes the component parts of something larger. Thus gravel means the stones which make up such a beach on the coast. Many dictionaries ignore the Breton language, citing Old French gravele or gravelle, Gravel often has the meaning a mixture of different size pieces of stone mixed with sand and possibly some clay. American English allows small stones without sand mixed in known as crushed stone, types of gravel include, Bank gravel, naturally deposited gravel intermixed with sand or clay found in and next to rivers and streams. Also known as Bank run or River run, bench gravel, a bed of gravel located on the side of a valley above the present stream bottom, indicating the former location of the stream bed when it was at a higher level.
Creek rock, this is rounded, semi-polished stones, potentially of a wide range of types. It is used as concrete aggregate and less often as a paving surface. Crushed stone, rock crushed and graded by screens and mixed to a blend of stones and fines and it is widely used as a surfacing for roads and driveways, sometimes with tar applied over it. Crushed stone may be made from granite, dolomite, known as crusher run, DGA QP, and shoulder stone
The Cenozoic Era is the current and most recent of the three Phanerozoic geological eras, following the Mesozoic Era and covering the period from 66 million years ago to the present day. The Cenozoic is known as the Age of Mammals, because of the mammals that dominated, such as Entelodont, Paraceratherium. The extinction of many large groups such as non-avian dinosaurs and Pterosauria allowed the mammals and birds to greatly diversify. Early in the Cenozoic, following the K-Pg event, the planet was dominated by relatively small fauna, including mammals, reptiles. From a geological perspective, it did not take long for mammals, some flightless birds grew larger than humans. These species are referred to as terror birds, and were formidable predators. Mammals came to occupy almost every available niche, and some grew very large, the Earths climate had begun a drying and cooling trend, culminating in the glaciations of the Pleistocene Epoch, and partially offset by the Paleocene-Eocene Thermal Maximum.
The continents began looking roughly familiar at this time and moved into their current positions. The Cenozoic is divided into three periods, the Paleogene and Quaternary, and seven epochs, the Paleocene, Oligocene, Pliocene and Holocene. The common use of epochs during the Cenozoic helps paleontologists better organize, there is more detailed knowledge of this era than any other because of the relatively young, well-preserved rocks associated with it. The Paleogene spans from the extinction of dinosaurs,66 million years ago. It features three epochs, the Paleocene and Oligocene, the Paleocene ranged from 66 million to 56 million years ago. The Paleocene is a point between the devastation that is the K-T extinction, to the rich jungles environment that is the Early Eocene. The Early Paleocene saw the recovery of the earth, the continents began to take their modern shape, but all the continents and subcontinent India were separated from each other. Afro-Eurasia was separated by the Tethys Sea, and the Americas were separated by the strait of Panama and this epoch featured a general warming trend, with jungles eventually reaching the poles.
The oceans were dominated by sharks as the large reptiles that had once ruled became extinct, archaic mammals filled the world such as creodonts and early primates that evolved during the Mesozoic, and as a result, there was nothing over 10 kilograms. The Eocene Epoch ranged from 56 million years to 33.9 million years ago, in the Early-Eocene, life was small and lived in cramped jungles, much like the Paleocene. There was nothing over the weight of 10 kilograms, among them were early primates and horses along with many other early forms of mammals
In other words, a floodplain is an area near a river or a stream which floods when the water level reaches flood stage. Flood plains are made by a meander eroding sideways as it travels downstream, when a river breaks its banks and floods, it leaves behind layers of alluvium. These gradually build up to create the floor of the flood plain, floodplains generally contain unconsolidated sediments, often extending below the bed of the stream. These are accumulations of sand, loam, and/or clay, and are often important aquifers, geologically ancient floodplains are often represented in the landscape by fluvial terraces. These are old floodplains that remain relatively high above the present floodplain and it is probable that any section of such an alluvial plain would show deposits of a similar character. The floodplain during its formation is marked by meandering or anastomotic streams, oxbow lakes and bayous, marshes or stagnant pools, and is occasionally completely covered with water. When the drainage system has ceased to act or is diverted for any reason.
The floodplain differs, because it is not altogether flat and it has a gentle slope downstream, and often, for a distance, from the side towards the center. The floodplain is the place for a river to dissipate its energy. Meanders form over the floodplain to slow down the flow of water, in terms of flood management the upper part of the floodplain is crucial as this is where the flood water control starts. Artificial canalisation of the river here will have a impact on wider flooding. This is the basis of flood management. Floodplains can support particularly rich ecosystems, both in quantity and diversity, tugay forests form an ecosystem associated with floodplains, especially in Central Asia. They are a category of riparian zones or systems, a floodplain can contain 100 or even 1,000 times as many species as a river. Microscopic organisms thrive and larger species enter a rapid breeding cycle, opportunistic feeders move in to take advantage. The production of nutrients peaks and falls away quickly, however the surge of new growth endures for some time and this makes floodplains particularly valuable for agriculture.
River flow rates are undergoing change following suit with climate change and this change is a threat to the riparian zones and other flood plain forests. These forests have over time synced their seedling deposits after the peaks in flow to best take advantage of the nutrient rich soil generated by peak flow
The Devonian is a geologic period and system of the Paleozoic, spanning 60 million years from the end of the Silurian,419.2 million years ago, to the beginning of the Carboniferous,358.9 Mya. It is named after Devon, where rocks from this period were first studied, the first significant adaptive radiation of life on dry land occurred during the Devonian. Free-sporing vascular plants began to spread across dry land, forming extensive forests which covered the continents, by the middle of the Devonian, several groups of plants had evolved leaves and true roots, and by the end of the period the first seed-bearing plants appeared. Various terrestrial arthropods became well-established, Fish reached substantial diversity during this time, leading the Devonian to often be dubbed the Age of Fish. The first ray-finned and lobe-finned bony fish appeared, while the placodermi began dominating almost every aquatic environment. The ancestors of all four-limbed vertebrates began adapting to walking on land, as their strong pectoral, in the oceans, primitive sharks became more numerous than in the Silurian and Late Ordovician.
The first ammonites, species of molluscs, trilobites, the mollusk-like brachiopods and the great coral reefs, were still common. The Late Devonian extinction which started about 375 million years ago severely affected marine life, killing off all placodermi, and all trilobites, save for a few species of the order Proetida. The palaeogeography was dominated by the supercontinent of Gondwana to the south, the continent of Siberia to the north, while the rock beds that define the start and end of the Devonian period are well identified, the exact dates are uncertain. According to the International Commission on Stratigraphy, the Devonian extends from the end of the Silurian 419.2 Mya, another common term is Age of the Fishes, referring to the evolution of several major groups of fish that took place during the period. Older literature on the Anglo-Welsh basin divides it into the Downtonian, Dittonian and Farlovian stages, in the Late Devonian, by contrast, arid conditions were less prevalent across the world and temperate climates were more common.
The Devonian Period is formally broken into Early and Late subdivisions, the rocks corresponding to those epochs are referred to as belonging to the Lower and Upper parts of the Devonian System. Early Devonian The Early Devonian lasted from 419.2 ±2.8 to 393.3 ±2.5 and began with the Lochkovian stage, which lasted until the Pragian. It spanned from 410.8 ±2.8 to 407.6 ±2.5, and was followed by the Emsian, which lasted until the Middle Devonian began,393. 3±2.7 million years ago. Middle Devonian The Middle Devonian comprised two subdivisions, first the Eifelian, which gave way to the Givetian 387. 7±2.7 million years ago. Late Devonian Finally, the Late Devonian started with the Frasnian,382.7 ±2.8 to 372.2 ±2.5, during which the first forests took shape on land. The first tetrapods appeared in the record in the ensuing Famennian subdivision. This lasted until the end of the Devonian,358. 9±2.5 million years ago, the Devonian was a relatively warm period, and probably lacked any glaciers
Pearl River Delta
The Pearl River Delta, known as Zhujiang Delta or Zhusanjiao, is the low-lying area surrounding the Pearl River estuary, where the Pearl River flows into the South China Sea. It is one of the most densely urbanized regions in the world and is a hub of China. This region is considered an emerging megacity. The nine largest cities of PRD had a population of 57.15 million at the end of 2013. According to the World Bank Group, the PRD has become the largest urban area in the world in size and population. The river delta, known as the Golden Delta of Guangdong, is formed by three rivers, the Xi Jiang, Bei Jiang, and Dong Jiang. The flat lands of the delta are criss-crossed by a network of tributaries and distributaries of the Pearl River, the Pearl River Delta is actually two alluvial deltas, separated by the core branch of the Pearl River. The Bei Jiang and Xi Jiang converge to flow into the South China Sea and Pearl River in the west, the Xi Jiang begins exhibiting delta-like characteristics as far west as Zhaoqing, although this city is not usually considered a part of the PRD region.
After passing through the Lingyang Gorge and converging with the Bei Jiang, major distributaries of the Xi include Donghui Shuidao, Jiya Shuidao, Hutiaomen Shuidao, Yinzhou Hu, and the main branch of the Xi Jiang. Jiangmen and Zhongshan are the major found in the western section of the delta. The Bei Jiang enters the plains at Qingyuan but doesnt begin to split until near Sanshui. From here the two main distributaries are Tanzhou Shuidao and Shunde Shuidao which form multiple mouths along the west side of the Pearl Rivers estuary. Two other distributaries, Lubao Yong and Xinan Yong, split from the Bei further north, the other major city in the north section of the delta is Foshan. The Dong Jiang flows through Huizhou into the delta and it begins diverging northeast of Dongguan into many distributaries, including the Dongguan Shuidao. Distributuares enter the Pearl River as far north as Luogang and as far south as Hu Men, saltwater crocodiles were present within the Pearl River estuary during antiquity.
The eastern side of the PRD, dominated by foreign capital, is the most developed economically, the western areas, dominated by local private capital, are open for development. New transport links between Hong Kong and Zhuhai in the PRD are expected to open up new areas for development, further integrate the cities, and facilitate trade within the region. 1985, the PRD had been dominated by farms and small rural villages, but after the economy was reformed and opened
Guilin, formerly romanized as Kweilin, is a prefecture-level city in the northeast of Chinas Guangxi Zhuang Autonomous Region. It is situated on the west bank of the Li River and its name means Forest of Sweet Osmanthus, owing to the large number of fragrant sweet osmanthus trees located in the city. The city has long been renowned for its scenery of karst topography and is one of Chinas most popular tourist destinations, in 314 BC, a small settlement was established along the banks of the Li River. During the Qin Dynastys campaigns against the state of Nanyue, the first administration was set up in the area around Guilin. In 111 BC, during the reign of Emperor Wu of the Han Dynasty, Shi An County was established, in AD507, the town was renamed Guizhou. Guilin prospered in the Tang and Song dynasties but remained a county, the city was a nexus between the central government and the southwest border, and it was where regular armies were placed to guard that border. Canals were built through the city so that supplies could be directly transported from the food-productive Yangtze plain to the farthest southwestern point of the empire.
In 1921, Guilin became one of the headquarters of the Northern Expeditionary Army led by Dr. Sun Yat-sen, in 1940, the city acquired its present name. Guilin administers seventeen county-level divisions, including six districts, nine counties and it has a total area of 27,809 square kilometres. The topography of the area is marked by karst formations, the Li River flows through the city. Winter begins dry but becomes progressively wetter and cloudier, spring is generally overcast and often rainy, while summer continues to be rainy though is the sunniest time of year. The monthly 24-hour average temperature ranges from 7.9 °C in January to 28.0 °C in July, and the annual mean is 18.84 °C. The annual rainfall is just above 1,900 mm, and is delivered in bulk from April to June, with monthly percent possible sunshine ranging from 14% in March to 53% in September, the city receives 1,487 hours of bright sunshine annually. Population,4,747,963 Urban population,975,638 Ethnic groups, Yao, Miao and Dong The GDP per capita was ¥19435 in 2009, ranked no.125 among 659 Chinese cities.
However, since the 1950s Guilin has electronics and agricultural equipment, medicine and buses, food processing, including the processing of local agricultural produce, remains the most important industry. More recent and modern industry feature high technology and the tertiary industry characterized by tourism trading, the airport is Guilin Liangjiang International Airport. Arriving to North Station, high-speed trains between Guilin and Changsha and Beijing came into operation in December 2013, in December 2014, high-speed operations began connecting Guangzhou, Shenzhen and Shanghai. It will bring much convenience for people come to Guilin and it takes only about 2 or 3 hours from Guangzhou to Guilin,7 hours from Shanghai to Guilin and 11 hours from Beijing to Guilin
A tributary or affluent is a stream or river that flows into a larger stream or main stem river or a lake. A tributary does not flow directly into a sea or ocean and the main stem river drain the surrounding drainage basin of its surface water and groundwater, leading the water out into an ocean. A confluence, where two or more bodies of water together, usually refers to the joining of tributaries. The opposite to a tributary is a distributary, a river or stream that branches off from, distributaries are most often found in river deltas. Right tributary and left tributary are terms stating the orientation of the relative to the flow of the main stem river. These terms are defined from the perspective of looking downstream, where tributaries have the same name as the river into which they feed, they are called forks. These are typically designated by compass direction, for example, the American River receives flow from its North and South forks. The Chicago Rivers North Branch has the East and Middle Fork, the South Branch has its South Fork, forks are sometimes designated as right or left.
Here, the handedness is from the point of view of an observer facing upstream, for instance, Steer Creek has a left tributary which is called Right Fork Steer Creek. Tributaries are sometimes listed starting with those nearest to the source of the river, the Strahler Stream Order examines the arrangement of tributaries in a hierarchy of first, second and higher orders, with the first-order tributary being typically the least in size. For example, a second-order tributary would be the result of two or more first-order tributaries combining to form the second-order tributary, another method is to list tributaries from mouth to source, in the form of a tree structure, stored as a tree data structure
Karst topography is a landscape formed from the dissolution of soluble rocks such as limestone and gypsum. It is characterized by underground drainage systems with sinkholes and caves and it has been documented for more weathering-resistant rocks, such as quartzite, given the right conditions. Subterranean drainage may limit surface water, with few to no rivers or lakes, the English word karst was borrowed from German Karst in the late 19th century. The German word came into use before the 19th century, according to the prevalent interpretation, the term is derived from the German name for the Karst region, a limestone plateau above the city of Trieste in the northern Adriatic. Scholars disagree, however, on whether the German word was borrowed from Slovene, the Slovene common noun kras was first attested in the 18th century, and the adjective form kraški in the 16th century. The Slovene words arose through metathesis from the reconstructed form *korsъ, the word is of Mediterranean origin, believed to derive from some Romanized Illyrian base.
It has been suggested that the word may derive from the Proto-Indo-European root karra- rock, the name may be connected to the oronym Karsádios oros cited by Ptolemy, and perhaps to Latin Carusardius. The development of karst occurs whenever acidic water starts to break down the surface of bedrock near its cracks, as the bedrock continues to degrade, its cracks tend to get bigger. As time goes on, these fractures will become wider, if this underground drainage system does form, it will speed up the development of karst formations there because more water will be able to flow through the region, giving it more erosive power. The carbonic acid that causes karstic features is formed as rain passes through the atmosphere picking up carbon dioxide, once the rain reaches the ground, it may pass through soil that can provide much more CO2 to form a weak carbonic acid solution, which dissolves calcium carbonate. The oxidation of sulfides leading to the formation of acid can be one of the corrosion factors in karst formation.
As oxygen -rich surface waters seep into deep anoxic karst systems, they bring oxygen, sulfuric acid reacts with calcium carbonate, causing increased erosion within the limestone formation. This chain of reactions is, This reaction chain forms gypsum, the karstification of a landscape may result in a variety of large- or small-scale features both on the surface and beneath. On exposed surfaces, small features may include solution flutes, limestone pavement, medium-sized surface features may include sinkholes or cenotes, vertical shafts, disappearing streams, and reappearing springs. Large-scale features may include limestone pavements and karst valleys, mature karst landscapes, where more bedrock has been removed than remains, may result in karst towers, or haystack/eggbox landscapes. Beneath the surface, complex underground systems and extensive caves. Some of the most dramatic of these formations can be seen in Thailands Phangnga Bay, calcium carbonate dissolved into water may precipitate out where the water discharges some of its dissolved carbon dioxide.
Rivers which emerge from springs may produce tufa terraces, consisting of layers of calcite deposited over extended periods of time, in caves, a variety of features collectively called speleothems are formed by deposition of calcium carbonate and other dissolved minerals
Limestone is a sedimentary rock, composed mainly of skeletal fragments of marine organisms such as coral and molluscs. Its major materials are the minerals calcite and aragonite, which are different crystal forms of calcium carbonate, about 10% of sedimentary rocks are limestones. The solubility of limestone in water and weak acid solutions leads to karst landscapes, most cave systems are through limestone bedrock. The first geologist to distinguish limestone from dolomite was Belsazar Hacquet in 1778, like most other sedimentary rocks, most limestone is composed of grains. Most grains in limestone are skeletal fragments of organisms such as coral or foraminifera. Other carbonate grains comprising limestones are ooids, peloids and these organisms secrete shells made of aragonite or calcite, and leave these shells behind when they die. Limestone often contains variable amounts of silica in the form of chert or siliceous skeletal fragment, some limestones do not consist of grains at all, and are formed completely by the chemical precipitation of calcite or aragonite, i. e. travertine.
Secondary calcite may be deposited by supersaturated meteoric waters and this produces speleothems, such as stalagmites and stalactites. Another form taken by calcite is oolitic limestone, which can be recognized by its granular appearance, the primary source of the calcite in limestone is most commonly marine organisms. Some of these organisms can construct mounds of rock known as reefs, below about 3,000 meters, water pressure and temperature conditions cause the dissolution of calcite to increase nonlinearly, so limestone typically does not form in deeper waters. Limestones may form in lacustrine and evaporite depositional environments, calcite can be dissolved or precipitated by groundwater, depending on several factors, including the water temperature, pH, and dissolved ion concentrations. Calcite exhibits a characteristic called retrograde solubility, in which it becomes less soluble in water as the temperature increases. Impurities will cause limestones to exhibit different colors, especially with weathered surfaces, Limestone may be crystalline, granular, or massive, depending on the method of formation.
Crystals of calcite, dolomite or barite may line small cavities in the rock, when conditions are right for precipitation, calcite forms mineral coatings that cement the existing rock grains together, or it can fill fractures. Travertine is a banded, compact variety of limestone formed along streams, particularly there are waterfalls. Calcium carbonate is deposited where evaporation of the leaves a solution supersaturated with the chemical constituents of calcite. Tufa, a porous or cellular variety of travertine, is found near waterfalls, coquina is a poorly consolidated limestone composed of pieces of coral or shells. During regional metamorphism that occurs during the building process, limestone recrystallizes into marble