:: wikimiki.org ::

Beach

Beach

A beach or strand is a geological formation consisting of loose rock particles such as sand, shingle, cobble, or even shell along the shoreline of a body of water.

Components

Some geologists consider a beach to be just this shoreline feature of deposited material, but William Bascom (1980) has argued that a beach is the entire system of sand set in motion by waves to a depth of ten meters (30+ feet) or more off ocean coasts. Submerged, longshore bars are therefore also part of the beach. In the Bascom approach, beaches can be viewed as either
- small systems in which the rock material moves onshore, offshore, or alongshore by the forces of waves and currents; or
- geological units of considerable size. The former are described in detail below; the larger geological units are discussed elsewhere under bars. Both types can be viewed as "beaches." bars) is spreading from the incipient dune]] There are several conspicuous parts to a beach, all of which relate to the processes that form and shape it. That part mostly above water (depending upon tide), and more or less actively influenced by the waves at some point in the tide, is termed the beach berm. The berm is the deposit of material comprising the active shoreline. The berm has a crest (top) and a face — the latter being the slope leading down towards the water from the crest. At the very bottom of the face, there may be a trough, and further seaward one or more longshore bars: slightly raised, underwater embankments formed where the waves first start to break. The sand deposit may extend well inland from the berm crest, where there may be evidence of one or more older crests (the storm beach) resulting from very large storm waves and beyond the influence of the normal waves. At some point the influence of the waves (even storm waves) on the material comprising the beach stops, and if the particles are small enough (that is, are sand), winds shape the feature. Where wind is the force distributing the grains inland, the deposit behind the beach becomes a dune. The line between beach and dune is difficult to define in the field. Over any significant period of time, sand is always being exchanged between them. The drift line (the high point of material deposited by waves) is one potential demarcation. This would be the point at which significant wind movement of sand could occur, since the normal waves do not wet the sand beyond this area. However, the drift line is likely to move inland under assault by storm waves.

How beaches are formed

Beaches are deposition landforms, and are the result of wave action by which waves or currents move sand or other loose sediments of which the beach is made as these particles are held in suspension. Alternatively, sand may be moved by saltation (a bouncing movement of large particles). Beach materials come from erosion of rocks offshore, as well as from headland erosion and slumping producing deposits of scree. A coral reef offshore is a significant source of sand particles. coral reef The shape of a beach depends on whether the waves are constructive or destructive, and whether the material is sand or shingle. Constructive waves move material up the beach while destructive waves move the material down the beach. On sandy beaches, the backwash of the waves removes material forming a gently sloping beach. On shingle beaches the swash is dissipated because the large particle size allows percolation, so the backwash is not very powerful, and the beach remains steep. Cusps and horns form where incoming waves divide, depositing sand as horns and scouring out sand to form cusps. This forms the uneven edge of a sandy beach. coral reef Some beaches are artificial; they are either permanent or temporary (For examples see Monaco, Paris, Rotterdam, Hong Kong and Singapore). There are several beaches which are claimed to be the "World's longest", including Cox's Bazar, Bangladesh (120kms), Fraser Island beach, 90 Mile Beach in Australia and 90 Mile Beach in New Zealand and Long Beach, Washington (which is about 30km). Wasaga Beach, Ontario on Georgian Bay claims to have the world's longest freshwater beach. The Marina Beach at Chennai, India, is the second longest beach in the world.

Beaches and recreation

India] Beaches have long been a popular attraction for tourism and recreation. Especially popular are seaside resorts and large white sand beaches. Of course, residents and tourists alike use beaches as a place for leisure and sport. The relatively soft formation of sand is comfortable to sit or lie on, and entering and exiting the water is far easier across a sand beach than a rocky shore. The waves present at beaches add to the enjoyment and make the sport of body surfing and related activities possible. One of the many attractions of a sand beach, especially for children, is playing with the sand, building sand castles and other constructs. Towels and mats are typical beach "furniture". In the Victorian era, many popular beach resorts were equipped with bathing machines because even the all-covering beachware of the period was considered immodest. This social standard still prevails in some Muslim countries. At the other extreme are nude beaches, where no swimware of any kind is compulsory.

Artificial beaches

The soothing qualities of a beach and the pleasant environment offered to the beachgoer are replicated in artificial beaches, such as "beach style" pools with zero-depth entry and wave pools that recreate the natural waves pounding upon a beach. In a zero-depth entry pool, the bottom surface slopes gradually from above water down to depth. Another approach involves so-called urban beaches, a form of public park becoming common in large cities. Urban beaches attempt to mimic natural beaches with fountains that imitate surf and mask city noises, and in some cases can be used as a play park.

Sounds of the beach

park Beaches are noted for their sometimes serene stillness and the rhythmic sound made by waves crashing upon the sand. To experience, listen to this sound file sound recording (1.00MB) made on a South Carolina beach at night.

Beaches as habitat

A beach is an unstable environment which exposes plants and animals to harsh conditions. Some small animals burrow into the sand and feed on material deposited by the waves. Crabs, insects and shorebirds feed on these beach dwellers. The endangered Piping Plover and some tern species rely on beaches for nesting. Sea turtles also lay their eggs on ocean beaches. Seagrasses and other beach plants grow on undisturbed areas of the beach and dunes.

Reference

- Bascom, W. 1980. Waves and Beaches. Anchor Press/Doubleday, Garden City, New York. 366 p.

External sites

- [http://www.unesco.org/csi/pub/source/ero9.htm UNESCO Beach erosion & formation]
- [http://www.nearctica.com/ecology/habitats/beaches.htm Beach habitats]
- Category:Landforms Category:Recreation ja:砂浜 simple:Beach

Geology

Geology (from Greek γη- (ge-, "the earth") and λογος (logos, "word", "reason")) is the science and study of the Earth, its composition, structure, physical properties, history, and the processes that shape it. It is one of the Earth sciences. Geologists have helped establish the age of the Earth at about 4.5 billion (4.5x10⁹) years, and have determined that the Earth's lithosphere, which includes the crust, is fragmented into tectonic plates that move over a rheic upper mantle (asthenosphere) via processes that are collectively referred to as plate tectonics. Geologists help locate and manage the earth's natural resources, such as petroleum and coal, as well as metals such as iron, copper, and uranium. Additional economic interests include gemstones and many minerals such as asbestos, perlite, mica, phosphates, zeolites, clay, pumice, quartz, and silica, as well as elements such as sulfur, chlorine, and helium. Astrogeology refers to the application of geologic principles to other bodies of the solar system. However, specialised terms such as selenology (studies of the Moon), areology (of Mars), etc., are also in use. The word "geology" was first used by Jean-André Deluc in the year 1778 and introduced as a fixed term by Horace-Bénédict de Saussure in the year 1779. An older meaning of the word was first used by Richard de Bury. He used it to distinguish between earthly and theological jurisprudence.

History

In China, the polymath Shen Kua (1031 - 1095) formulated a hypothesis for the process of land formation: based on his observation of fossil shells in a geological stratum in a mountain hundreds of miles from the ocean, he inferred that the land was formed by erosion of the mountains and by deposition of silt. The work on rocks Peri lithon by Theophrastus, a student of Aristotle, remained authoritative for millennia. However, its interpretation of fossils was not overturned until after the Scientific Revolution. It was translated into Latin and the other languages of Europe such as French. Georg Bauer (Georg Agricola), a physician, summarised the knowledge of mining and metallurgy in 1556. Georg Agricola (1494-1555) wrote the first systematic treatise about mining and smelting works, De re metallica libri XII, with an appendix Buch von den Lebewesen unter Tage (book of the creatures beneath the earth). He covered subjects like wind energy, hydrodynamic power, melting cookers, transport of ores, extraction of soda, sulfur and alum, and administrative issues. The book was published in 1556. By the 1700s Jean-Etienne Guettard and Nicolas Desmarest hiked central France and recorded their observations on geological maps; Guettard recorded the first observation of the volcanic origins of this part of France. James Hutton recorded his Theory of the Earth in the 1788 Transactions of the Royal Society of Edinburgh, later called uniformitarianism. William Smith (1769-1839) drew some of the first geological maps and began the process of ordering rock strata (layers) by examining the fossils contained in them. James Hutton is often viewed as the first modern geologist. In 1785 he presented a paper entitled Theory of the Earth to the Royal Society of Edinburgh. In his paper, he explained his theory that the Earth must be much older than had previously been supposed in order to allow enough time for mountains to be eroded and for sediment to form new rocks at the bottom of the sea, which in turn were raised up to become dry land. Followers of Hutton were known as Plutonists because they believed that some rocks were formed by vulcanism which is the deposition of lava from volcanoes, as opposed to the Neptunists, who believed that all rocks had settled out of a large ocean whose level gradually dropped over time. In 1811 Georges Cuvier and Alexandre Brongniart published their explanation of the antiquity of the Earth, inspired by Cuvier's discovery of fossil elephant bones in Paris. To prove this, they formulated the principle of stratigraphic succession of the layers of the earth. They were independently anticipated by William Smith's stratigraphic studies on England and Scotland. Sir Charles Lyell first published his famous book, Principles of Geology, in 1830 and continued to publish new revisions until he died in 1875. He successfully promoted the doctrine of uniformitarianism. This theory states that slow geological processes have occurred throughout the Earth's history and are still occurring today. In contrast, catastrophism is the theory that Earth's features formed in single, catastrophic events and remained unchanged thereafter. Though Hutton believed in uniformitarianism, the idea was not widely accepted at the time. catastrophism illustrated on relief globe of the Field Museum ]] By 1827 Charles Lyell's Principles of Geology reiterated Hutton's uniformitarianism, which influenced the thought of Charles Darwin. 19th Century geology revolved around the question of the Earth's exact age. Estimates varied from a few 100,000 to billions of years. The most significant advance in 20th century geology has been the development of the theory of plate tectonics in the 1960s. Plate tectonic theory arose out of two separate geological observations: seafloor spreading and continental drift. The theory revolutionised the Earth sciences. The theory of continental drift was proposed by Alfred Wegener in 1912 and by Arthur Holmes, but wasn't broadly accepted until the 1960s when the theory of plate tectonics was developed.

Important principles of geology

There are a number of important principles in geology. Many of these involve the ability to provide the relative ages of strata or the manner in which they were formed. The Principle of Intrusive Relationships concerns crosscutting intrusions. In geology, when an igneous intrusion cuts across a formation of sedimentary rock, it can be determined that the igneous intrusion is younger than the sedimentary rock. There are a number of different types of intrusions, including stocks, laccoliths, batholiths, sills and dikes. The Principle of Cross-cutting Relationships pertains to the formation of faults and the age of the sequences through which they cut. Faults are younger than the rocks they cut; accordingly, if a fault is found that penetrates some formations but not those on top of it, then the formations that were cut are older than the fault, and the ones that are not cut must be younger than the fault. Finding the key bed in these situations may help determine whether the fault is a normal fault or a thrust fault. The Principle of Inclusions and Components states that, with sedimentary rocks, if inclusions (or clasts) are found in a formation, then the inclusions must be older than the formation that contains them. For example, in sedimentary rocks, it is common for gravel from an older formation to be ripped up and included in a newer layer. A similar situation with igneous rocks occurs when xenoliths are found. These foreign bodies are picked up as magma or lava flows, and are incorporated, later to cool in the matrix. As a result, xenoliths are older than the rock which contains them. The Principle of Uniformitarianism states that, the geologic processes observed in operation that modify the Earth's crust at present have worked in much the same way over geologic time. A fundamental principle of geology advanced by the 18th century Scottish physician and geologist James Hutton, is that "The Present is the Key to the Past." In Hutton's words: "the past history of our globe must be explained by what can be seen to be happening now." The Principle of Original Horizontality states that, the deposition of sediments occurs as essentially horizontal beds. Observation of modern marine and nonmarine sediments in a wide variety of environments supports this generalisation (although cross-bedding is inclined, the overall orientation of cross-bedded units is horizontal). The Principle of Superposition states that, a sedimentary rock layer in a tectonically undisturbed sequence is younger than the one beneath it and older than the one above it. Logically a younger layer cannot slip beneath a layer previously deposited. This principle allows sedimentary layers to be viewed as a form of vertical time line, a partial or complete record of the time elapsed from deposition of the lowest layer to deposition of the highest bed. The Principle of Faunal Succession is based on the appearance of fossils in sedimentary rocks. As organisms exist at the same time period throughout the world, their presence or (sometimes) absence may be used to provide a relative age of the formations in which they are found. Based on principles laid out by William Smith almost a hundred years before the publication of Charles Darwin's theory of evolution, the principles of succession were developed independently of evolutionary thought. The principle becomes quite complex, however, given the uncertainties of fossilisation, the localisation of fossil types due to lateral changes in habitat (facies change in sedimentary strata), and that not all fossils may be found globally at the same time.

Fields or related disciplines

- Earth science
- Economic geology
- Mining geology
- Petroleum geology
- Engineering geology
- Environmental geology
- Geoarchaeology
- Geochemistry
- Biogeochemistry
- Isotope geochemistry
- Geochronology
- Geodetics
- Geomicrobiology
- Geomorphology
- Geophysics
- Glaciology
- Historical geology
- Hydrogeology or geohydrology
- Marine geology
- Mineralogy
- Paleoclimatology
- Paleontology
- Micropaleontology
- Palynology
- Petrology
- Plate tectonics
- Sedimentology
- Seismology
- Soil science
- Pedology (soil study)
- Speleology
- Stratigraphy
- Biostratigraphy
- Structural geology
- Volcanology

Regional geology

- Geology of the Alps
- Geology of the Himalaya
- Geology of Victoria (Australia)

United Kingdom

- Geology of Dorset
- Geology of Hampshire
- Geology of Hertfordshire

United States

- Geology of the Bryce Canyon area(Utah)
- Geology of the Canyonlands area (Utah)
- Geology of the Capitol Reef area (Utah)
- Geology of Connecticut
- Geology of the Death Valley area (California)
- Geology of the Grand Canyon area (Arizona)
- Geology of the Grand Teton area (Wyoming)
- Geology of the Lassen area (California)
- Geology of Mount Shasta (California)
- Geology of the Yosemite area (California)
- Geology of the Zion and Kolob canyons area (Utah)
- Glacial geology of the Genesee River (New York, Pennsylvania)

National geology

- Geology of Australia
- Geology of Victoria
- Geology of Iran
- Geology of India
- Geology of Sikkim
- Geology of the United States of America
- Geology of California
- Geology of the Grand Canyon area
- Geology of the United Kingdom
- Geology of Japan

Planetary geology

- Geology of Mars
- Geology of the Moon

External links

- James Hutton's [http://www.mala.bc.ca/~johnstoi/essays/Hutton.htm Theory of the Earth]
- James Hutton's [http://www.uwmc.uwc.edu/geography/hutton/hutton.htm Theory of the Earth & Abstract of the Theory of the Earth] Category:Geology ko:??? ja:??? th:?????????

Sand

Sand is an example of a class of materials called granular matter. Sand is a naturally occurring, finely divided rock, comprising particles or granules ranging in size from ¹⁄₁₆ to 2 millimeters. An individual particle in this range size is termed a sand grain. The next smaller size class in geology is silt: particles below ¹⁄₁₆ mm down to ¹⁄₂₅₆ mm (0.004 mm) in size. The next larger size class above sand is gravel, with particles ranging up to 64 mm (see grain size for standards in use). The most common constituent of sand in inland continental settings and non-tropical coastal settings is silica (silicon dioxide), usually in the form of quartz which because of its chemical inertness and considerable hardness is quite resistant to weathering. However, the composition of sand varies according to local rock sources and conditions. The bright white sands found in tropical and subtropical coastal settings are ground-up limestone. Arkose is a sand or sandstone with considerable feldspar content which is derived from the weathering and erosion of a usually nearby granite. Some locations have sands that contain magnetite, chlorite, glauconite, or gypsum. Sands rich in magnetite are dark to black in color, as are sands derived from volcanic basalts. The chlorite-glauconite bearing sands are typically green in color, as are sands derived from basalts (lavas) with a high olivine content. The gypsum sand dunes of the White Sands National Monument in New Mexico are famous for their bright, white color. Sand deposits in some areas contain garnets and other resistant minerals, including some small gemstones. Sand is transported by wind or water and deposited in the form of beaches, dunes, sand spits, sand bars, and the like. In most deserts, sand is a dominant constituent of the soil. The study of sand is called arenology.

Uses of sand

arenology Sand is often a principal component of the aggregate used in the preparation of concrete. Sand manufactured at rock crusher plants for use as an aggregate is called mansand. Graded sand is used as an abrasive in sandblasting and is also used in media filters for filtering water. Brick manufacturing plants use Sand as an additive with a mixture of clay and other materials for manufacturing bricks. Sandy soils are ideal for certain crops such as watermelons and peanuts and are often preferred for intensive dairy farming because of their excellent drainage characteristics. Sandbags are used for protection against floods and gun fire. They can be easily transported when empty, and filled with local sand. People, especially children, love to play with sand on a beach or in a sandpit. See sand art and play for details.

Hazards of sand

Bags of sand now typically carry labels warning the user to wear respiratory protection and avoid breathing the fine silica dust. There have been a number of lawsuits in recent years where workers have sought damages after they developed silicosis, a lung disease caused by inhalation of fine silica particles. People have been severely injured and even killed after digging sand "caves" in large dunes, sandhills, or even on beaches when the cave or tunnel collapsed upon them.

Cobble

Cobble is a geologic term for a rock or rock fragment with a grain size with dimensions between 64–256 mm (2.5–10 inch). Rounded cobble sized rocks are used as a construction material for road and street surfacing: see cobblestone. A cobble is also a shallow bottomed, low draught fishing boat. A coble is also a familiar term for the Hawfinch. Category:Sedimentology

Water

:This article focuses on water as it is experienced in everyday life. See water (molecule) for information on the chemical and physical properties of pure water (H₂O, hydrogen oxide). Water (from the Old English word wæter; c.f German "Wasser", from PIE
- wod-or, "water") is a tasteless, odorless, and nearly colorless (it has a slight hint of blue) substance in its pure form that is essential to all known forms of life and is known also as the most universal solvent. Water is an abundant substance on Earth. It exists in many places and forms. It appears mostly in the oceans and polar ice caps, but also as clouds, rain water, rivers, freshwater aquifers, and sea ice. On the planet, water is continuously moving through the cycle involving evaporation, precipitation, and runoff to the sea. Water fit for human consumption is called potable water. This natural resource is becoming more scarce in certain places as human population in those places increases, and its availability is a major social and economic concern.

Molecular properties

Forms of water

potable water] Water takes many different shapes on earth: water vapor and clouds in the sky, waves and icebergs in the sea, glaciers in the mountain, aquifers in the ground, to name but a few. Through evaporation, precipitation, and runoff, water is continuously flowing from one form to another, in what is called the water cycle. Because of the importance of precipitation to agriculture, and to mankind in general, different names are given to its various forms: while rain is common in most countries, other phenomena are quite surprising when seen for the first time. Hail, snow, fog or dew are examples. When appropriately lit, water drops in the air can refract sunlight to produce rainbows. Similarly, water runoffs have played major roles in human history as rivers and irrigation brought the water needed for agriculture. Rivers and seas offered opportunity for travel and commerce. Through erosion, runoffs played a major part in shaping the environment providing river valleys and deltas which provide rich soil and level ground for the establishment of population centers. Water also infiltrates the ground and goes into aquifers. This groundwater later flows back to the surface in springs, or more spectacularly in hot springs and geysers. Groundwater is also extracted artificially in wells. Because water can contain many different substances, it can taste or smell very differently. In fact, humans and other animals have developed their senses to be able to evaluate the drinkability of water: animals generally dislike the taste of salty sea water and the putrid swamps and favor the purer water of a mountain spring or aquifer.

Water in biology

From a biological standpoint, water has many distinct properties that are critical for the proliferation of life that set it apart from other substances. Water carries out this role by allowing organic compounds to react in ways that ultimately allows replication. It is a good solvent and has a high surface tension, and thus allows organic compounds and living things to be transported in it. Fresh water has its greatest density at 4°C, then becoming less dense as it freezes or heats up from this point. As a stable, polar molecule prevalent in the atmosphere, it plays an important atmospheric role as an absorber of infrared radiation, crucial in the atmospheric greenhouse effect without of which, the average surface temperature would be −18° Celsius. Water also has an unusually high specific heat, which plays many roles in regulating global and regional climate, such as the Gulf Stream climate, allowing life to survive. Water is a very good solvent, chemically not unlike ammonia, and dissolves many types of substances, such as various salts and sugar, and facilitates their chemical interaction, which aids complex metabolisms. Some substances, however, do not mix well with water, including oils and other hydrophobic substances. Cell membranes, composed of lipids and proteins, take advantage of this property to carefully control interactions between their contents and external chemicals. This is facilitated somewhat by the surface tension of water. Water drops are stable due to the high surface tension of water caused by the strong intermolecular forces called cohesive forces. This can be seen when small quantities of water are put onto a nonsoluble surface such as polythene: the water stays together as drops. On extremely clean glass the water may form a thin film because the molecular forces between glass and water molecules (adhesive forces) are stronger than the cohesive forces. This property plays a key role in plant transpiration. A simple but environmentally important and unique property of water is that its common solid form, ice, floats on the liquid. This solid phase is less dense than liquid water, due to the geometry of the strong hydrogen bonds which are formed only at lower temperatures. For almost all other substances and for all other 11 uncommon phases of water ice except ice-XI, the solid form is more dense than the liquid form. Fresh water is most dense at 4°C, and will sink by convection as it cools to that temperature, and if it becomes colder it will rise instead. This reversal will cause deep water to remain warmer than shallower freezing water, so that ice in a body of water will form first at the surface and progress downward, while the majority of the water underneath will hold a constant 4°C. This effectively insulates a lake floor from the cold. While this behavior may seem obvious, even intuitive, it should be noted that almost all other chemicals are denser as solids than they are as liquids, and freeze from the bottom up. Life on earth has evolved with and adapted itself to the important features of water. The existence of abundant liquid, vapor and solid forms of water on Earth has been an important factor in the abundant colonization of Earth's various environments by life-forms adapted to those varying and often extreme conditions. Civilizations have historically flourished around rivers and major waterways; Mesopotamia, the so-called cradle of civilization, is situated between two major rivers. Large metropolises like London, Paris, New York, and Tokyo owe their success in part to their easy accessibility via water and the resultant expansion of trade. Islands with safe water ports, like Singapore and Hong Kong, have flourished for precisely this reason. In places such as North Africa and the Middle East, where water is scarcer, access to clean drinking water was and is a major factor in human development.

Astronomical position of Earth and impact on its water

Mesopotamia The coexistence of the solid, liquid, and gaseous phases of water on Earth is vital to the origin, evolution, and continued existence of life on Earth. However, if the Earth's location in the solar system were even marginally closer or further from the Sun (ie, a million miles or so), the conditions which allow the three forms to be present simultaneously would be far less likely to exist. Earth's mass allows gravity to hold an atmosphere. Water vapor and carbon dioxide in the atmosphere provides a greenhouse effect which helps maintain a relatively steady surface temperature. If Earth were less massive, a thinner atmosphere would cause temperature extremes preventing the accumulation of water except in polar ice caps (as on Mars). According to the solar nebula model of the solar system's formation, Earth's mass may be largely due to its distance from the Sun. The distance between Earth and the Sun and the combination of solar radiation received and the greenhouse effect of the atmosphere ensures that its surface is neither too cold nor too hot for liquid water. If Earth were more distant, most water would be frozen. If Earth were nearer to the Sun, its higher surface temperature would limit the formation of ice caps, or cause water to exist only as vapor. In the former case, the low albedo of oceans would cause Earth to absorb more solar energy. In the second case, a runaway greenhouse effect and inhospitable conditions similar to Venus would result. It has been proposed that life itself may maintain the conditions that have allowed its continued existence. The surface temperature of Earth has been relatively constant through geologic time despite varying solar flux, indicating that a dynamic process governs Earth's temperature via a combination of greenhouse gases and surface or atmospheric albedo. This proposal is known as the Gaia hypothesis.

Human uses of water

Gaia hypothesis All known forms of life depend on water. Water is a vital part of many metabolic processes within the body. Significant quantities of water are used during the digestion of food. (Note however that some bacteria and plant seeds can enter a cryptobiotic state for an indefinite period when dehydrated, and come back to life when returned to a wet environment) About 72% of the fat free mass of the human body is made of water. To function properly the body requires between one and seven litres of water per day to avoid dehydration, the precise amount depending on the level of activity, temperature, humidity, and other factors. It is not clear how much water intake is needed by healthy people. However, for those who do not have kidney problems, it is rather difficult to drink too much water, but (especially in warm humid weather and while exercising) dangerous to drink too little. People do often drink far more water than necessary while exercising, however, putting them at risk of water intoxication, which is frequently fatal. The "fact" that a person should consume eight glasses of water per day cannot be traced back to a scientific source. However, leading dieticians and nutritionists will tell you that this is the RDI (Recommended Daily Intake) of water. [http://ajpregu.physiology.org/cgi/content/full/283/5/R993]. The latest dietary reference intake report by the National Research Council recommended 2.7 liters of water total (including food sources) for women and 3.7 liters for men[http://www.iom.edu/report.asp?id=18495]. Water is lost from the body in urine and feces, through sweating, and by exhalation of water vapor in the breath. Humans require water that does not contain too much salt or other impurities. Common impurities include chemicals and/or harmful bacteria, such as crypto sporidium. Some solutes are acceptable and even desirable for perceived taste enhancement and to provide needed electrolytes.

Water as a precious resource

:See water resources for information about fresh water supplies. fresh water Because of the growth of world population and other factors, the availability of drinking water per capita is shrinking. The issue of water shortage can be solved through more production, better distribution and less waste of it. For this reason, water is a strategic resource for many countries. Many battles and wars, such as the Six-Day War in the Middle East, have been fought to gain access to it. Experts predict more trouble ahead because of the world's growing population, increasing contamination through pollution, and global warming. UNESCO's World Water Development Report (WWDR, 2003) from its World Water Assessment Program indicates that, in the next 20 years, the quantity of water available to everyone is predicted to decrease by 30%. 40% of the world's inhabitants currently have insufficient fresh water for minimal hygiene. More than 2.2 million people died in 2000 from diseases related to the consumption of contaminated water or drought. In 2004, the UK charity WaterAid reported that a child dies every 15 seconds due to easily preventable water-related diseases. Some have predicted that clean water will become the "next oil", making Canada, with this resource in abundance, possibly the richest country in the world.

Regulating water distribution

Drinking water is often collected at springs or extracted from artificial borings in the ground, or wells. Building more wells in adequate places is thus a possible way to produce more water assuming the aquifers can supply an adequate flow. Other water sources are the rainwater and river or lake water. This surface water, however, must be purified for human consumption. This may involve removal of undissolved substances, dissolved substances and harmful microbes. Popular methods are filtering with sand which only removes undissolved material while chlorination and boiling kill harmful microbes. Distillation does all three functions. More advanced techniques exist, such as reverse osmosis. Desalination of abundant ocean or seawater is a more expensive solution used in coastal arid climates. The distribution of drinking water is done through municipal water systems or as bottled water. Governments in many countries have programs to distribute water to the needy at no charge. Others argue that the market mechanism and free enterprise are best to manage this rare resource, and to finance the boring of wells or the construction of dams and reservoirs. Reducing waste, that is using drinking water only for human consumption, is another option. In some cities, such as Hong Kong, sea water is extensively used for flushing toilets citywide in order to conserve fresh water resources. Polluting water may be the biggest single misuse of water; to the extent that a pollutant limits other uses of the water, it becomes a waste of the resource, regardless of benefits to the pollutor. Pharmaceuticals consumed by humans often end up in the waterways and can have detrimental effects on aquatic life if they bioaccumulate and if they are not biodegradable.

The impact of water on human culture

Water is considered a purifier in most religions, including Christianity, Islam, Judaism, and Shinto. For instance, baptism in Christian churches is done with water. In addition, a ritual bath in pure water is performed for the dead in many religions including Judaism and Islam. In Islam, the daily Salah can only be done after ablution (Wodoo), that is, washing parts of the body in clean water. In Shinto, water is used in almost all rituals to cleanse a person or an area. Water is often believed to have spiritual powers. In Celtic mythology, Sulis is the local goddess of thermal springs; in Hinduism, the Ganga is also personified as a goddess. Alternatively, gods can be patrons of particular springs, river or lakes: for example in Greek and Roman mythology, Peneus was a river god, one of the three thousand Oceanids. The Greek philosopher Empedocles held that water is one of the four classical elements along with fire, earth and air, and was regarded as the ylem, or basic stuff of the universe. Water was considered cold and moist. In the theory of the four bodily humours, water was associated with phlegm. Water was also one of the Five Elements in traditional Chinese philosophy, along with earth, fire, wood, and metal. A common misconception about water is that it is a powerful conductor of electricity. Any electrical properties observable in water are due to the ions of mineral salts and carbon dioxide dissolved in it. Water does self-ionize (two water molecules become one hydroxide anion and one hydronium cation), but only at a very slight, almost immeasurable level. Pure water can also be electrolized into oxygen and hydrogen gases but without any dissolved ions, this is a very slow process and thus very little current is conducted. Many bottled water companies exploit another common misconception, advertising both purity and taste, even though pure water is tasteless.

External links

- [http://www.lsbu.ac.uk/water/phase.html Phase diagrams of water]
- [http://www.publicforuminstitute.org/issues/oceans/index.htm Oceans and Water Issues Page]
- [http://www.greenfacts.org/water-disinfectants/index.htm Scientific Facts on Water disinfectants] A faithful summary by GreenFacts of a leading scientific consensus report on Drinking Water Disinfectants published by the International Programme on Chemical Safety of the WHO.
- [http://www.hkc22.com/residentialwater.html Residential water problems and markets] Study paper from Helmut Kaiser Consultancy
- [http://www.hkc22.com/watermarketsworldwide.html Water markets worldwide] Study paper from Helmut Kaiser Consultancy
- [http://www.worldwaterforum.org/ World Water Forum]
- [http://www.unesco.org/water/wwap/ World Water Assessment Program]
- [http://unesdoc.unesco.org/images/0012/001295/129556e.pdf United Nations' World Water Development Report]
- [http://www.gemswater.org/ United Nations GEMS/Water Programme]
- [http://www.lsbu.ac.uk/water/ Water Structure and Behaviour]
- [http://www.wateraid.org/ WaterAid]
- [http://www.sahra.arizona.edu/newswatch/ SAHRA—Global Water Newswatch]
- [http://www.siwi.org/ Stockholm International Water Institute] (SIWI)
- [http://www.c-win.org/ California Water Impact Network (C-WIN)]
- [http://news.bbc.co.uk/2/hi/science/nature/3752590.stm BBC: The water debate]
- [http://www.geocities.com/tapvsbottled/ Tap Water Vs Bottled Water] - Interesting site providing facts about tap and bottled water.
- [http://www.emagazine.com/september-october_2003/0903feat1.html E the Environmental Magazine piece on bottled water] (Oct 2003).
- [http://www.iapws.org/ International Association for the Properties of Water and Steam]
- [http://ga.water.usgs.gov/edu/watercycle.html US Geological Survey: Comprehensive discussion of the water cycle, in many languages]
- [http://www.dartmouth.edu/~etrnsfer/water.htm Why is water blue?]
- [http://www.water.org.uk/home/resources-and-links/water-for-health/ask-about/adults Water requirements in adults]
- [http://www.hkc22.com/environmentaltechnology.html/ Climate change raises markets for environmental technology, drinking water and clean energies]

References

- OA Jones, JN Lester and N Voulvoulis, Pharmaceuticals: a threat to drinking water? TRENDS in Biotechnology 23(4): 163, 2005
- Category:Beverages Category:Hydrology Category:Materials Category:Natural resources Category:Nutrition zh-min-nan:Chúi als:Wasser ko:물 ja:水 ms:Air simple:Water th:น้ำ

Bar (landform)

In geography, a bar is a linear shoaling landform feature within a body of water. Bars tend to be long and narrow (linear) and develop where a current (or waves) promote deposition of particles, resulting in localized shallowing (shoaling) of the water. Bars can appear in the sea, in a lake, or in a river. They are typically composed of sand, although could be of any particulate matter that the moving water has access to and is capable of shifting around (for example, soil, silt, gravel, cobble, shingle, or even boulders). The size of the particles comprising a bar is related to the size of the waves or the strength of the currents moving the material, but the availability of material to be worked by waves and currents is also important. A vessel run aground on a bar is arguable worse off than one run aground on stationary rocks, because of the destructive capacity of the shifting action. The term bar can apply to landform features over a considerable range in size, from just a few meters in a small stream to marine depositions stretching for hundreds of kilometres along a coastline, often called barrier islands. In a nautical sense, a bar is a shoal, similar to a reef: a shallow formation of (usually) sand that is a navigation or grounding hazard. It therefore applies to a silt formation that shallows the entrance to or the course of a river or creek.

Sandbars and longshore bars

Bars that occur at or off the shoreline of a sea or a lake are related to beaches and might be considered offshore features of a beach (Bascom, 1980). At times when larger waves attack the beach berm, some of the beach material is redistributed offshore to become a longshore bar or sandbar, possibly visible at low tide. This bar forms (sometimes seaward of a trough) where the waves are breaking, because the breaking waves set up a shoreward current with a compensating counter-current along the bottom. Sand carried by the offshore moving bottom current is deposited where the current reaches the wave break (Bascom, 1980). Other longshore bars may lie further offshore, representing the break point of even larger waves, or the break point at low tide.

Bars as geological units

In addition to longshore bars discussed above that are relatively small features of a beach, the term bar can be applied to larger geological units that form off a coastline as part of the process of coastal erosion. These include spits and baymouth bars that form across the front of embayments and rias. A tombolo is a bar that forms an isthmus between an island or offshore rock and a mainland shore. The largest of the geological units of this kind are the barrier islands, such as occur along the East Coast of the United States, as well as along the Gulf coast. In places of reentrants along a coastline (such as inlets, coves, rias, and bays), sediments carried by a longshore current will fall out where the current dissipates, forming a spit. An area of water isolated behind a large bar is called a lagoon. Over time, lagoons may silt up, becoming salt marshes. See also: geomorphology, earth science.

Examples

- Abidjan, Côte d'Ivoire
- Ap Lei Chau - Ap Lei Pai, Hong Kong
- Barnegat Bay, New Jersey, United States
- Cape Canaveral, Florida, United States
- Cape St. Paul, Ghana
- Cheung Chau, Hong Kong
- Galveston Island, Texas, United States
- Great Yarmouth, England
- Lung Kwu Chau, Hong Kong
- Looe Pool, Cornwall, England
- Long Island, New York, United States
- Macao Isthmus, Macao
- Miami Beach, Florida, United States
- Minnesota Point, Duluth, Minnesota, United States
- Ninety Mile Beach, Victoria, Australia
- Ocean City, Maryland, United States
- Padre Island, Texas, United States
- Pamlico Sound, North Carolina, United States
- Port Said, Egypt
- Pui O, Hong Kong
- Sha Chau, Hong Kong
- Shek O Headland - Tai Tau Chau, Hong Kong
- Sriharikota, Andhra Pradesh, India
- Stinson Beach, California, USA
- The Coorong, South Australia, Australia
- Twin Lakes, California, United States
- Wadden islands, also known as West Frisian Islands, along the Dutch, German, and Danish coasts. The largest group of barrier islands on Earth.
- Winona, Minnesota, United States
- Yim Tin Tsai - Ma Shi Chau, Hong Kong

References

- Bascom, W. 1980. Waves and Beaches. Anchor Press/Doubleday, Garden City, New York. 366 p. Category:Landforms

Dune

:This article is about the sand formations, for other meanings see Dune (disambiguation). Dune (disambiguation)] In physical geography, a dune is a hill of sand built by eolian (wind-related) processes. Bare dunes are subject to shifting location and size based on their interaction with the wind. The "valley" or trough between dunes is called a slack. Some coastal areas have one or more sets of dunes running parallel to the shoreline directly inland from the beach. In most such cases the dunes are important in protecting the land against potential ravages by storm waves from the sea. Although the most widely distributed dunes are those associated with coastal regions, the largest complexes of dunes are found inland in dry regions and associated with ancient lake or sea beds. Dunes also form under the action of water flow (Alluvial processes), on sand or gravel beds of rivers, estuaries and the sea-bed.

Types of dune

Crescentic

The most common dune form on Earth (and on Mars) is the crescentic. Crescent-shaped mounds generally are wider than long. The slipface is on the dune's concave side. These dunes form under winds that blow from one direction, and they also are known as barchans, or transverse dunes. Some types of crescentic dunes move faster over desert surfaces than any other type of dune. A group of dunes moved more than 100 meters per year between 1954 and 1959 in China's Ningxia Province; similar rates have been recorded in the Western Desert of Egypt. The largest crescentic dunes on Earth, with mean crest-to-crest widths of more than 3 kilometers, are in China's Taklamakan Desert.

Linear

Straight or slightly sinuous sand ridges typically much longer than they are wide are known as linear dunes. They may be more than 160 kilometers long. Linear dunes may occur as isolated ridges, but they generally form sets of parallel ridges separated by miles of sand, gravel, or rocky interdune corridors. Some linear dunes merge to form Y-shaped compound dunes. Many form in bidirectional wind regimes. The long axes of these dunes extend in the resultant direction of sand movement.

Star

Radially symmetrical, star dunes are pyramidal sand mounds with slipfaces on three or more arms that radiate from the high center of the mound. They tend to accumulate in areas with multidirectional wind regimes. Star dunes grow upward rather than laterally. They dominate the Grand Erg Oriental of the Sahara. In other deserts, they occur around the margins of the sand seas, particularly near topographic barriers. In the southeast Badain Jaran Desert of China, the star dunes are up to 500 meters tall and may be the tallest dunes on Earth.

Dome

Oval or circular mounds that generally lack a slipface, dome dunes are rare and occur at the far upwind margins of sand seas. Badain Jaran Desert]

Parabolic

U-shaped mounds of sand with convex noses trailed by elongated arms are parabolic dunes. Sometimes these dunes are called U-shaped, blowout, or hairpin dunes, and they are well known in coastal deserts. Unlike crescentic dunes, their crests point upwind. The elongated arms of parabolic dunes follow rather than lead because they have been fixed by vegetation, while the bulk of the sand in the dune migrates forward. ;

Combined types

Badain Jaran Desert, one of the tallest in the world.]] Occurring wherever winds periodically reverse direction, reversing dunes are varieties of any of the above types. These dunes typically have major and minor slipfaces oriented in opposite directions. All these dune types may occur in three forms: simple, compound, and complex. Simple dunes are basic forms with a minimum number of slipfaces that define the geometric type. Compound dunes are large dunes on which smaller dunes of similar type and slipface orientation are superimposed, and complex dunes are combinations of two or more dune types. A crescentic dune with a star dune superimposed on its crest is the most common complex dune. Simple dunes represent a wind regime that has not changed in intensity or direction since the formation of the dune, while compound and complex dunes suggest that the intensity and direction of the wind has changed.

Coastal dunes

Dunes form on coasts where the backshore can support and onshore winds encourage the accumulation of sand blown inland from off a beach. Any part of the upper beach, once dry, can lose sand to the wind, especially if the sand is fine, and dune formation proceeds in the direction towards which the predominant wind direction is blowing. Dunes provide privacy and shelter from the wind.

Succession on coastal dunes

wind]] As a dune forms, plant succession occurs. The conditions on an embryo dune are harsh, with salt spray from the sea carried on strong winds. The dune is well drained and often dry. Rotting sea weed brought in by storm waves adds enough nutrients to allow pioneer species to colonise the dune. These pioneer species are marram grass, sea wort grass and other sea grasses in England. These plants are well adapted to the harsh conditions of the fore dune, typically having deep roots which reach the water table, root nodules that produce nitrogen compounds, and protected stoma, reducing transpiration. The deep roots also bind the sand together, and the dune grows into a fore dune as more sand is blown over the grasses. The grasses add nitrogen to the soil, meaning other, less hardy plants can then colonise the dunes. Typically these are heathers and gorses. These too are adapted to the low soil water content and have small, prickley leaves which reduce transpiration. Heathers add humus to the soil, but have a pH of lower than 7, so make the soil slightly acidic. Heathers are usually replaced by coniferous trees which can tolerate the low pH. Coniferous forests and heathland are common climax communities for sand dune systems. Young dunes are called yellow dunes, dunes which have high humus content are called grey dunes. Leaching occurs on the dunes, washing humus into the slacks, and the slacks may be much more developed than the exposed tops of the dunes. For the snow analogue to a sand dune see sastruga.

Sub-Aqueous dunes

Sub-Aqueous (underwater) dunes form on a bed of sand or gravel under the actions of water flow. They are ubiquitous in natural channels such as rivers and estuaries, and also form in engineered canals and pipelines. Dunes move downstream as the upstream slope is eroded and the sediment deposited on the downstream or lee slope. These dunes most often form as a continuous 'train' of dunes, showing remarkable similarity in wavelength and height. Dunes on the bed of a channel significantly increase flow resistance, their presence and growth playing a major part in river flooding.

Longitudinal and Transverse Dunes

Longitudinal dunes, also called Seif dunes, elongate parallel to the prevailent wind, possibly caused by a larger dune having its smaller sides blown away. Seif dunes are sharp-crested and are common in the Sahara. They range up to 300 m (900 ft) in height and 300 km (200 mi) in length. Seif dunes are thought to develop from barchans if a change of wind direction occurs. The new wind direction will lead to the development of a new wing and the overdevelopment of one of the original wings. If the prevailing wind then becomes dominant for a lengthy period of time the dune will revert to its barchan form, with one exaggerated wing. Should the strong wind then return the exaggerated wing will further extend so that eventually it will be supplied with sand when the prevailing wind returns. The wing will continue to grow under both wind conditions, thus producing a seif dune. On a seif dune the slip face develops on the side facing away from the strong wind, while the slip face of a barchan faces the direction of movement. In the sheltered troughs between highly developed seif dunes barchans may be formed because the wind is unidirectional. A transverse dune is horizontal to the prevailing wind, probably caused by a steady buildup of sand on an already existing minuscule mound. Also, the tranversional altitude of the stratosphere exceeds expectations of the previously identifiedj

Lithified dunes

A lithified (consolidated) sand dune is a type of sandstone that is formed when a marine or eolian sand dune becomes compacted and hardened. Once in this form, water passing through the rock can carry and deposit minerals, which can alter the hue of the rock. Cross-bedded layers of stacks of lithified dunes can produce the cross-hatching patterns, such as those seen in Zion National Park. A local slang term used for these consolidated dunes is "slickrock", a name that was introduced by pioneers of the old west because their steel-rimmed wagon wheels could not gain purchase on the rock.

References & Links

- The Physics of Blown Sand (1941) by Ralph Bagnold

Examples

- The Kelso Dunes, in the Mojave desert of California.

Sand dune plains

:(large expanses of dunes)
- Great Sand Dunes National Park
- Mesquite Flat Dunes, USA
- Western Sahara
- White Sands National Monument
- Rig-e Jenn in the Central Desert of Iran
- The Great Sand Dunes of southwest Saskatchewan
- Southeastern Shore of Lake Michigan
- Imperial Sand Dunes near Brawley, California
- Guadalupe-Nipomo Dunes, Central Coast California, see Dunes Center, Guadalupe, CA

Sand dune systems

:(coastal dunes featuring succession)
- Studland, Dorset, England
- Murlough Sand Dunes, Newcastle, Co Down, Northern Ireland
- Morfa Harlech Sand Dunes, Snowdonia, North West Wales

External Links

- [http://www.geographyinaction.co.uk/Magilligan/Mag_intro.html Magilligan Dunes, Northern Ireland]

Dune

Types of dune

Crescentic

Linear

Star

Dome

Oval or circular mounds that generally lack a slipface, dome dunes are rare and occur at the far upwind margins of sand seas. Badain Jaran Desert]

Parabolic

Combined types

Coastal dunes

Succession on coastal dunes

Sub-Aqueous dunes

Longitudinal and Transverse Dunes

Lithified dunes

References & Links

- The Physics of Blown Sand (1941) by Ralph Bagnold

Examples

- The Kelso Dunes, in the Mojave desert of California.

Sand dune plains

Sand dune systems

:(coastal dunes featuring succession)
- Studland, Dorset, England
- Murlough Sand Dunes, Newcastle, Co Down, Northern Ireland
- Morfa Harlech Sand Dunes, Snowdonia, North West Wales

External Links

- [http://www.geographyinaction.co.uk/Magilligan/Mag_intro.html Magilligan Dunes, Northern Ireland]

Landform

A landform comprises a geomorphological unit. Landforms are categorised by characteristics such as elevation, slope, orientation, stratification, rock exposure, and soil type. Landforms by name include berms, mounds, hills, cliffs, valleys, and so forth. Oceans and continents exemplify highest-order landforms. A number of factors, ranging from plate tectonics to erosion and deposition can generate and affect landforms. Biological factors can also influence landforms -- see for example the role of plants in the development of dune systems and salt marshes, and the work of corals and algae in the formation of coral reefs. coral reefs

List of landforms

- alas
- continent
- limestone pavement
- plain and plateau
- rock formations