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26/12/2022

Island
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Aerial image of Süderoog, a privately owned island belonging to the Halligen group of islands in Germany
An island (or isle) is an isolated piece of habitat that is surrounded by a dramatically different habitat, such as water.[1] Very small islands such as emergent land features on atolls can be called islets, skerries, cays or keys. An island in a river or a lake island may be called an eyot or ait, and a small island off the coast may be called a holm. Sedimentary islands in the Ganges delta are called chars. A grouping of geographically or geologically related islands, such as the Philippines, is referred to as an archipelago.

There are two main types of islands in the sea: continental and oceanic. There are also artificial islands, which are man-made.

Contents
1 Etymology
2 Relationships with continents
2.1 Differentiation from continents
2.2 Continental islands
2.2.1 Microcontinental islands
2.2.2 Subcontinental islands
2.2.3 Bars
2.3 Oceanic islands
2.3.1 Tectonic versus volcanic
2.3.2 Volcanic islands
2.3.2.1 Arcs
2.3.2.2 Oceanic Rifts
2.3.2.3 Hotspots
2.3.2.4 Atolls
3 Tropical islands
4 De-islanding
5 Artificial islands
6 Island superlatives
7 See also
8 References
9 External links
Etymology
The word island derives from Middle English iland, from Old English igland (from ig or ieg, similarly meaning 'island' when used independently, and -land carrying its contemporary meaning; cf. Dutch eiland ("island"), German Eiland ("small island")). However, the spelling of the word was modified in the 15th century because of a false etymology caused by an incorrect association with the etymologically unrelated Old French loanword isle, which itself comes from the Latin word insula.[2][3] Old English ieg is actually a cognate of Swedish ö and German Aue, and related to Latin aqua (water).[4]

Relationships with continents
Differentiation from continents

Dymaxion world map with the continental landmasses (Roman numerals) and 30 largest islands (Arabic numerals) roughly to scale
There is no standard of size that distinguishes islands from continents,[5] or from islets.[6]

There is a widely accepted difference between islands and continents in terms of geology.[7] Continents are often considered to be the largest landmass of a particular continental plate; this holds true for Australia, which sits on its own continental lithosphere and tectonic plate (the Australian Plate).[8]

By contrast, islands are usually seen as being extensions of the oceanic crust (e.g. volcanic islands), or as belonging to a continental plate containing a larger landmass (continental islands); the latter is the case of Greenland, which sits on the North American Plate.[9]

Continental islands
Further information: Continental shelf
Continental islands are bodies of land that lie on the continental shelf of a continent.[10] Examples are Borneo, Java, Sumatra, Sakhalin, Taiwan and Hainan off Asia; New Guinea, Tasmania, and Kangaroo Island off Australia; Great Britain, Ireland, and Sicily off Europe; Greenland, Newfoundland, Long Island, and Sable Island off North America; and Barbados, the Falkland Islands, and Trinidad off South America.

Microcontinental islands
A special type of continental island is the microcontinental island, which is created when a continent is horizontally displaced or rifted[11][12] Examples are Madagascar and Socotra off Africa, New Caledonia, New Zealand, and some of the Seychelles.[12]

Subcontinental islands
A lake such as Wollaston Lake drains in two different directions, thus creating an island. If this island has a seashore as well as being encircled by two river systems, it becomes what might be called a subcontinental island. The one formed by Wollaston Lake is very large, about 2,000,000 km2 (770,000 sq mi).[13]

Bars
Another subtype is an island or bar formed by deposition of tiny rocks where water current loses some of its carrying capacity. This includes:

barrier islands, which are accumulations of sand deposited by sea currents on the continental shelves[14][15]
fluvial or alluvial islands formed in river deltas or midstream within large rivers. While some are transitory and may disappear if the volume or speed of the current changes, others are stable and long-lived.[16]
Oceanic islands
Main article: High island
Tectonic versus volcanic
Oceanic islands are typically considered to be islands that do not sit on continental shelves. Other definitions limit the term to only refer to islands with no past geological connections to a continental landmass.[17] The vast majority are volcanic in origin, such as Saint Helena in the South Atlantic Ocean.[18] The few oceanic islands that are not volcanic are tectonic in origin and arise where plate movements have lifted up the ocean floor above the surface. Examples are the Saint Peter and Saint Paul Archipelago in the North Atlantic Ocean and Macquarie Island in the South Pacific Ocean.

Volcanic islands
Arcs
One type of volcanic oceanic island is found in a volcanic island arc. These islands arise from volcanoes where the subduction of one plate under another is occurring. Examples are the Aleutian Islands, the Mariana Islands, and most of Tonga in the Pacific Ocean.[19][20] The only examples in the Atlantic Ocean are some of the Lesser Antilles and the South Sandwich Islands.

Oceanic Rifts
Another type of volcanic oceanic island occurs where an oceanic rift reaches the surface. There are two examples: Iceland, which is the world's second largest volcanic island, and Jan Mayen. Both are in the Atlantic.

Hotspots
A third type of volcanic oceanic island is formed over volcanic hotspots. A hotspot is more or less stationary relative to the moving tectonic plate above it, so a chain of islands results as the plate drifts. Over long periods of time, this type of island is eventually "drowned" by isostatic adjustment and eroded, becoming a seamount.[21] Plate movement across a hot-spot produces a line of islands oriented in the direction of the plate movement. An example is the Hawaiian Islands, from Hawaii to Kure, which continue beneath the sea surface in a more northerly direction as the Emperor Seamounts. Another chain with similar orientation is the Tuamotu Archipelago; its older, northerly trend is the Line Islands. The southernmost chain is the Austral Islands, with its northerly trending part the atolls in the nation of Tuvalu. Tristan da Cunha is an example of a hotspot volcano in the Atlantic Ocean.[22] Another hotspot in the Atlantic is the island of Surtsey, which was formed in 1963.[23]

Atolls
Main article: Atoll
An atoll is an island formed from a coral reef that has grown on an eroded and submerged volcanic island. The reef rises to the surface of the water and forms a new island. Atolls are typically ring-shaped with a central lagoon. Examples are the Line Islands in the Pacific and the Maldives in the Indian Ocean.[24]

26/12/2022

Plant
From Wikipedia, the free encyclopedia
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For other uses, see Plant (disambiguation).
Plants
Temporal range:
Mesoproterozoic–present
Pha.ProterozoicArcheanHad'n
Diversity of plants (Streptophyta) version 2.png
Scientific classificatione
Domain: Eukaryota
(unranked): Diaphoretickes
(unranked): Archaeplastida
Kingdom: Plantae
sensu Copeland, 1956
Superdivisions
Chlorokybophyta
Mesostigmatophyta
Spirotaenia
Chlorobionta Kenrick & Crane 1997
Chlorophyta
Streptobionta Kenrick & Crane 1997
Klebsormidiophyceae
Charophyta (stoneworts)
Chaetosphaeridiales
Coleochaetophyta
Zygnematophyta
Embryophyta Engler, 1892 (land plants)
Marchantiophyta (liverworts)
Bryophyta (mosses)
Anthocerotophyta (hornworts)
†Horneophyta
†Aglaophyta
Tracheophyta (vascular plants)
Synonyms
Viridiplantae Cavalier-Smith 1981[1]
Chlorobionta Jeffrey 1982, emend. Bremer 1985, emend. Lewis and McCourt 2004[2]
Chlorobiota Kenrick and Crane 1997[3]
Chloroplastida Adl et al., 2005 [4]
Phyta Barkley 1939 emend. Holt & Uidica 2007
Cormophyta Endlicher, 1836
Cormobionta Rothmaler, 1948
Euplanta Barkley, 1949
Telomobionta Takhtajan, 1964
Embryobionta Cronquist et al., 1966
Metaphyta Whittaker, 1969
Plants are predominantly photosynthetic eukaryotes of the kingdom Plantae. Historically, the plant kingdom encompassed all living things that were not animals, and included algae and fungi; however, all current definitions of Plantae exclude the fungi and some algae, as well as the prokaryotes (the archaea and bacteria). By one definition, plants form the clade Viridiplantae (Latin name for "green plants") which is sister of the Glaucophyta, and consists of the green algae and Embryophyta (land plants). The latter includes the flowering plants, conifers and other gymnosperms, ferns and their allies, hornworts, liverworts, and mosses.

Most plants are multicellular organisms. Green plants obtain most of their energy from sunlight via photosynthesis by primary chloroplasts that are derived from endosymbiosis with cyanobacteria. Their chloroplasts contain chlorophylls a and b, which gives them their green color. Some plants are parasitic or mycotrophic and have lost the ability to produce normal amounts of chlorophyll or to photosynthesize, but still have flowers, fruits, and seeds. Plants are characterized by sexual reproduction and alternation of generations, although asexual reproduction is also common.

There are about 320,000 known species of plants, of which the great majority, some 260,000–290,000, produce seeds.[5] Green plants provide a substantial proportion of the world's molecular oxygen,[6] and are the basis of most of Earth's ecosystems. Plants that produce grain, fruit, and vegetables also form basic human foods and have been domesticated for millennia. Plants have many cultural and other uses, as ornaments, building materials, writing material and, in great variety, they have been the source of medicines and psychoactive drugs. The scientific study of plants is known as botany, a branch of biology.

Contents
1 Definition
1.1 Current definitions of Plantae
1.2 Algae
1.3 Fungi
2 Diversity
2.1 Evolution
2.2 Embryophytes
2.3 Fossils
3 Structure, growth, and development
3.1 Factors affecting growth
3.1.1 Effects of freezing
3.2 DNA damage and repair
3.3 Plant cells
4 Physiology
4.1 Photosynthesis
4.2 Immune system
4.3 Internal distribution
5 Genomics
6 Ecology
6.1 Distribution
6.2 Ecological relationships
6.3 Competition
7 Importance
7.1 Cultivation
7.1.1 Food
7.1.2 Medicines
7.1.3 Nonfood products
7.1.4 Aesthetic uses
7.2 Scientific and cultural uses
7.3 Negative effects
8 See also
9 References
10 Further reading
11 External links
Definition
All living things were traditionally placed into one of two groups, plants and animals. This classification may date from Aristotle (384 BC – 322 BC), who made the distinction between plants, which generally do not move, and animals, which often are mobile to catch their food. Much later, when Linnaeus (1707–1778) created the basis of the modern system of scientific classification, these two groups became the kingdoms Vegetabilia (later Metaphyta or Plantae) and Animalia (also called Metazoa). Since then, it has become clear that the plant kingdom as originally defined included several unrelated groups, and the fungi and several groups of algae were removed to new kingdoms. However, these organisms are still sometimes considered plants, particularly in informal contexts.[citation needed]

The term "plant" generally implies the possession of the following traits: multicellularity, possession of cell walls containing cellulose, and the ability to carry out photosynthesis with primary chloroplasts.[7][8]

Current definitions of Plantae
When the name Plantae or plant is applied to a specific group of organisms or taxon, it usually refers to one of four concepts. From least to most inclusive, these four groupings are:

26/12/2022

From Wikipedia, the free encyclopedia
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This article is about the structure. For the card game, see Contract bridge. For other uses, see Bridge (disambiguation) and Bridges (disambiguation).

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Bosphorus Bridge in Istanbul, Turkey

Underneath the Fort Pitt Bridge in Pittsburgh, Pennsylvania, USA

The old stone-made arch bridge over the Kerava River in Kerava, Finland
A bridge is a structure built to span a physical obstacle (such as a body of water, valley, road, or rail) without blocking the way underneath. It is constructed for the purpose of providing passage over the obstacle, which is usually something that is otherwise difficult or impossible to cross. There are many different designs of bridges, each serving a particular purpose and applicable to different situations. Designs of bridges vary depending on factors such as the function of the bridge, the nature of the terrain where the bridge is constructed and anchored, and the material used to make it, and the funds available to build it.

The earliest bridges were likely made with fallen trees and stepping stones. The Neolithic people built boardwalk bridges across marshland. The Arkadiko Bridge (dating from the 13th century BC, in the Peloponnese) is one of the oldest arch bridges still in existence and use.

Contents
1 Etymology
2 History
3 Types of bridges
3.1 Structure types
3.2 Fixed or movable bridges
3.3 Double-decked bridges
3.4 Viaducts
3.5 Multi-way bridge
3.6 Bridge types by use
3.7 Bridge types by material
4 Analysis and design
5 Aesthetics
6 Bridge maintenance
7 Bridge traffic loading
7.1 Traffic loading on long span bridges
8 Bridge vibration
8.1 Vehicle-bridge dynamic interaction
9 Bridge failures
10 Bridge health monitoring
11 Visual index
12 See also
13 References
14 Further reading
15 External links
Etymology

The Stone Bridge in Skopje, North Macedonia

The Siosepol bridge over Zayandeh River is an example of Safavid dynasty (1502–1722) bridge design. Isfahan, Iran.

The 13th century Wetherby Bridge spans the River Wharfe.
The Oxford English Dictionary traces the origin of the word bridge to an Old English word brycg, of the same meaning.[1] The word can be traced directly back to Proto-Indo-European *bʰrēw-. The word for the card game of the same name has a different origin.

History

Seasonal bridge north of Jispa, H.P., India. 2010

Bridges in Amsterdam, Netherlands
The simplest and earliest types of bridges were stepping stones. Neolithic people also built a form of boardwalk across marshes; examples of such bridges include the Sweet Track and the Post Track in England, approximately 6000 years old.[2] Undoubtedly, ancient people would also have used log bridges; that is a timber bridge[3] that fall naturally or are intentionally felled or placed across streams. Some of the first man-made bridges with significant span were probably intentionally felled trees.[4]

Among the oldest timber bridges is the Holzbrücke Rapperswil-Hurden crossing upper Lake Zürich in Switzerland; the prehistoric timber piles discovered to the west of the Seedamm date back to 1523 BC. The first wooden footbridge led across Lake Zürich, followed by several reconstructions at least until the late 2nd century AD, when the Roman Empire built a 6-metre-wide (20 ft) wooden bridge. Between 1358 and 1360, Rudolf IV, Duke of Austria, built a 'new' wooden bridge across the lake that has been used to 1878 – measuring approximately 1,450 metres (4,760 ft) in length and 4 metres (13 ft) wide. On April 6, 2001, the reconstructed wooden footbridge was opened, being the longest wooden bridge in Switzerland.

The Arkadiko Bridge is one of four Mycenaean corbel arch bridges part of a former network of roads, designed to accommodate chariots, between the fort of Tiryns and town of Epidauros in the Peloponnese, in southern Greece. Dating to the Greek Bronze Age (13th century BC), it is one of the oldest arch bridges still in existence and use. Several intact arched stone bridges from the Hellenistic era can be found in the Peloponnese.[5]

Samuel Beckett Bridge in Dublin, Ireland
The greatest bridge builders of antiquity were the ancient Romans.[6] The Romans built arch bridges and aqueducts that could stand in conditions that would damage or destroy earlier designs. Some stand today.[7] An example is the Alcántara Bridge, built over the river Tagus, in Spain. The Romans also used cement, which reduced the variation of strength found in natural stone.[8] One type of cement, called pozzolana, consisted of water, lime, sand, and volcanic rock. Brick and mortar bridges were built after the Roman era, as the technology for cement was lost (then later rediscovered).

In India, the Arthashastra treatise by Kautilya mentions the construction of dams and bridges.[9] A Mauryan bridge near Girnar was surveyed by James Princep.[10] The bridge was swept away during a flood, and later repaired by Puspagupta, the chief architect of emperor Chandragupta I.[10] The use of stronger bridges using plaited bamboo and iron chain was visible in India by about the 4th century.[11] A number of bridges, both for military and commercial purposes, were constructed by the Mughal administration in India.[12]

Although large Chinese bridges of wooden construction existed at the time of the Warring States period, the oldest surviving stone bridge in China is the Zhaozhou Bridge, built from 595 to 605 AD during the Sui dynasty. This bridge is also historically significant as it is the world's oldest open-spandrel stone segmental arch bridge. European segmental arch bridges date back to at least the Alconétar Bridge (approximately 2nd century AD), while the enormous Roman era Trajan's Bridge (105 AD) featured open-spandrel segmental arches in wooden construction.[citation needed]

Rope bridges, a simple type of suspension bridge, were used by the Inca civilization in the Andes mountains of South America, just prior to European colonization in the 16th century.

The Ashanti built bridges over streams and rivers.[13][14] They were constructed by pounding four large forked tree trunks into the stream bed, placing beams along these forked pillars, then positioning cross-beams that were finally covered with four to six inches of dirt.[14]

During the 18th century, there were many innovations in the design of timber bridges by Hans Ulrich Grubenmann, Johannes Grubenmann, and others. The first book on bridge engineering was written by Hubert Gautier in 1716.

A major breakthrough in bridge technology came with the er****on of the Iron Bridge in Shropshire, England in 1779. It used cast iron for the first time as arches to cross the river Severn.[15] With the Industrial Revolution in the 19th century, truss systems of wrought iron were developed for larger bridges, but iron does not have the tensile strength to support large loads. With the advent of steel, which has a high tensile strength, much larger bridges were built, many using the ideas of Gustave Eiffel.[16]

The covered bridge in West Montrose, Ontario, Canada
In Canada and the United States, numerous timber covered bridges were built in the late 1700s to the late 1800s, reminiscent of earlier designs in Germany and Switzerland. Some covered bridges were also built in Asia.[17] In later years, some were partly made of stone or metal but the trusses were usually still made of wood; in the United States, there were three styles of trusses, the Queen Post, the Burr Arch and the Town Lattice.[18] Hundreds of these structures still stand in North America. They were brought to the attention of the general public in the 1990s by the novel, movie, and play The Bridges of Madison County.[19][20]

In 1927 welding pioneer Stefan Bryła designed the first welded road bridge in the world, the Maurzyce Bridge which was later built across the river Słudwia at Maurzyce near Łowicz, Poland in 1929. In 1995, the American Welding Society presented the Historic Welded Structure Award for the bridge to Poland.[21]

Types of bridges
Bridges can be categorized in several different ways. Common categories include the type of structural elements used, by what they carry, whether they are fixed or movable, and by the materials used.

Structure types
Bridges may be classified by how the actions of tension, compression, bending, torsion and shear are distributed through their structure. Most bridges will employ all of these to some degree, but only a few will predominate. The separation of forces and moments may be quite clear. In a suspension or cable-stayed bridge, the elements in tension are distinct in shape and placement. In other cases the forces may be distributed among a large number of members, as in a truss.

26/12/2022

Beach
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For other uses, see Beach (disambiguation).
"Sand beach" redirects here. For other uses, see Sand Beach (disambiguation).

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St Oswalds Bay, Dorset, England. Wild sand and shingle beaches are shaped and maintained naturally by wave actions.

Recreational beaches, such as this one on the Gold Coast of Australia, can be shaped and maintained by beach nourishment projects.[1]

A summer tourism at the Yyteri Beach in Pori, Finland.
A beach is a landform alongside a body of water which consists of loose particles. The particles composing a beach are typically made from rock, such as sand, gravel, shingle, pebbles, etc., or biological sources, such as mollusc shells or coralline algae. Sediments settle in different densities and structures, depending on the local wave action and weather, creating different textures, colors and gradients or layers of material.

Though some beaches form on inland freshwater locations such as lakes and rivers, most beaches are in coastal areas where wave or current action deposits and reworks sediments. Erosion and changing of beach geologies happens through natural processes, like wave action and extreme weather events. Where wind conditions are correct, beaches can be backed by coastal dunes which offer protection and regeneration for the beach. However, these natural forces have become more extreme due to climate change, permanently altering beaches at very rapid rates. Some estimates describe as much as 50 percent of the earth's sandy beaches disappearing by 2100 due to climate-change driven sea level rise.[2]

Sandy beaches occupy about one third of global coastlines.[2] These beaches are popular for recreation, playing important economic and cultural roles—often driving local tourism industries. To support these uses, some beaches have man-made infrastructure, such as lifeguard posts, changing rooms, showers, shacks and bars. They may also have hospitality venues (such as resorts, camps, hotels, and restaurants) nearby or housing, both for permanent and seasonal residents.

Human forces have significantly changed beaches globally: direct impacts include bad construction practices on dunes and coastlines, while indirect human impacts include water pollution, plastic pollution and coastal erosion from sea level rise and climate change. Some coastal management practices are designed to preserve or restore natural beach processes, while some beaches are actively restored through practices like beach nourishment.

Marine debris on a beach in Hawaii.
Wild beaches, also known as undeveloped or undiscovered beaches, are not developed for tourism or recreation. Preserved beaches are important biomes with important roles in aquatic or marine biodiversity, such as for breeding grounds for sea turtles or nesting areas for seabirds or penguins. Preserved beaches and their associated dune are important for protection from extreme weather for inland ecosystems and human infrastructure.[2]

Contents
1 Location and profile
2 Formation
2.1 Sand colors
3 Erosion and accretion
3.1 Natural erosion and accretion
3.1.1 Causes
3.1.2 Effects on flora
3.1.3 Effects on adjacent land
3.2 Manmade erosion and accretion
3.2.1 Destruction of flora
3.2.2 Creation of beach access points
3.2.3 Concentration of runoff
3.2.4 Deprivation of runoff
3.2.5 Inappropriate beach nourishment
4 Use for recreation
4.1 History
4.1.1 Seaside resorts for the working class
4.1.2 Expansion around the world
4.2 Today
4.3 Artificial beaches
4.4 Restrictions on access
4.4.1 Private beaches
4.4.2 Public beaches
5 Access design
5.1 Concrete ramp or steps
5.2 Corduroy (beach ladder)
5.3 Fabric ramp
5.4 Foliage ramp
5.5 Gravel ramp
6 Longest beaches
7 Wildlife
8 See also
9 References
10 Works cited
11 Further reading
12 External links
Location and profile

A berm is a nearly horizontal portion that stays dry except during extremely high tides and storms. The swash zone is alternately covered and exposed by wave run-up. The beach face is the sloping section below the berm that is exposed to the swash of the waves. The wrack line (not shown here) is the highest reach of the daily tide where organic and inorganic debris is deposited by wave action. May have sand dunes.[3]
Although the seashore is most commonly associated with the word beach, beaches are also found by lakes and alongside large rivers.

Beach may refer to:

small systems where 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.

There are several conspicuous parts to a beach that relate to the processes that form and shape it. The 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 long shore 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 (sand size or smaller), winds shape the feature. Where wind is the force distributing the grains inland, the deposit behind the beach becomes a dune.

The differences between summer and winter on beaches in areas where the winter conditions are rougher and waves have a shorter wavelength but higher energy. In winter, sand from the beach is stored offshore.[3]
These geomorphic features compose what is called the beach profile. The beach profile changes seasonally due to the change in wave energy experienced during summer and winter months. In temperate areas where summer is characterised by calmer seas and longer periods between breaking wave crests, the beach profile is higher in summer. The gentle wave action during this season tends to transport sediment up the beach towards the berm where it is deposited and remains while the water recedes. Onshore winds carry it further inland forming and enhancing dunes.

Conversely, the beach profile is lower in the storm season (winter in temperate areas) due to the increased wave energy, and the shorter periods between breaking wave crests. Higher energy waves breaking in quick succession tend to mobilise sediment from the shallows, keeping it in suspension where it is prone to be carried along the beach by longshore currents, or carried out to sea to form longshore bars, especially if the longshore current meets an outflow from a river or flooding stream. The removal of sediment from the beach berm and dune thus decreases the beach profile.

If storms coincide with unusually high tides, or with a freak wave event such as a tidal surge or tsunami which causes significant coastal flooding, substantial quantities of material may be eroded from the coastal plain or dunes behind the berm by receding water. This flow may alter the shape of the coastline, enlarge the mouths of rivers and create new deltas at the mouths of streams that had not been powerful enough to overcome longshore movement of sediment.

The line between beach and dune is difficult to define in the field. Over any significant period of time, sediment 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.[4]

Formation
See also: Beach evolution

Quartz sand particles and shell fragments from a beach. The primary component of typical beach sand is quartz, or silica (SiO2).

Sand and shingle is scoured, graded and moved around by the action of waves and currents

Beach formed on a wild, untamed rocky coastline
Beaches 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. Some species of fish that feed on algae attached to coral outcrops and rocks can create substantial quantities of sand particles over their lifetime as they nibble during feeding, digesting the organic matter, and discarding the rock and coral particles which pass through their digestive tracts.

The composition of the beach depends upon the nature and quantity of sediments upstream of the beach, and the speed of flow and turbidity of water and wind. Sediments are moved by moving water and wind according to their particle size and state of compaction. Particles tend to settle and compact in still water. Once compacted, they are more resistant to erosion. Established vegetation (especially species with complex network root systems) will resist erosion by slowing the fluid flow at the surface layer. When affected by moving water or wind, particles that are eroded and held in suspension will increase the erosive power of the fluid that holds them by increasing the average density, viscosity, and volume of the moving fluid.

Coastlines facing very energetic wind and wave systems will tend to hold only large rocks as smaller particles will be held in suspension in the turbid water column and carried to calmer areas by longshore currents and tides. Coastlines that are protected from waves and winds will tend to allow finer sediments such as clay and mud to precipitate creating mud flats and mangrove forests. The shape of a beach depends on whether the waves are constructive or destructive, and whether the material is sand or shingle. Waves are constructive if the period between their wave crests is long enough for the breaking water to recede and the sediment to settle before the succeeding wave arrives and breaks.

Fine sediment transported from lower down the beach profile will compact if the receding water percolates or soaks into the beach. Compacted sediment is more resistant to movement by turbulent water from succeeding waves. Conversely, waves are destructive if the period between the wave crests is short. Sediment that remains in suspension when the following wave crest arrives will not be able to settle and compact and will be more susceptible to erosion by longshore currents and receding tides. The nature of sediments found on a beach tends to indicate the energy of the waves and wind in the locality.

Constructive waves move material up the beach while destructive waves move the material down the beach. During seasons when destructive waves are prevalent, the shallows will carry an increased load of sediment and organic matter in suspension. On sandy beaches, the turbulent backwash of destructive waves removes material forming a gently sloping beach. On pebble and shingle beaches the swash is dissipated more quickly because the large particle size allows greater percolation, thereby reducing the power of the backwash, and the beach remains steep. Compacted fine sediments will form a smooth beach surface that resists wind and water erosion.

During hot calm seasons, a crust may form on the surface of ocean beaches as the heat of the sun evaporates the water leaving the salt which crystallises around the sand particles. This crust forms an additional protective layer that resists wind erosion unless disturbed by animals or dissolved by the advancing tide. Cusps and horns form where incoming waves divide, depositing sand as horns and scouring out sand to form cusps. This forms the uneven face on some sand shorelines. White sand beaches look white because the quartz or eroded limestone in the sand reflects or scatters sunlight without absorbing other colors.

Sand colors

Depiction of sands:
glass, dune, quartz
volcanic, biogenic coral, pink coral
volcanic, garnet, olivine
The composition of the sand varies depending on the local minerals and geology.[5] Some of the types of sand found in beaches around the world are:

White sand: Mostly made of quartz and limestone , it can also contain other minerals like feldspar and gypsum .[5][6]
Light-colored sand: This sand gets its color from quartz and iron ,[5] and is the most common sand color in Southern Europe[7] and other regions of the Mediterranean Basin , such as Tunisia .[5]
Tropical white sand: On tropical islands, the sand is composed of calcium carbonate from the shells and skeletons of marine organisms, like corals and mollusks , as found in Aruba .[5]
Pink coral sand: Like the above, is composed of calcium carbonate and gets its pink hue from fragments of coral, such as in Bermuda and the Bahama Islands .[5]
Black sand: Black sand is composed of volcanic rock, like basalt and obsidian, which give it its gray-black color.[5] Hawaii 's Punaluu Beach, Madeira's Praia Formosa and Fuerteventura's Ajuy beach are examples of this type of sand.[5]
Red sand: This kind of sand is created by the oxidation of iron from volcanic rocks.[6] Santorini 's Kokkini Beach or the beaches on Prince Edward Island in Canada are examples of this kind of sand.[6]
Orange sand: Orange sand is high on iron. It can also me a combination of orange limestone, crushed shells, and volcanic deposits.[6] Ramla Bay in Gozo , Malta or Porto Ferro in Sardinia are examples of each, respectively.[5]
Green sand: In this kind of sand, the mineral olivine has been separated from other volcanic fragments by erosive forces.[5] A famous example is Hawaii's Papakolea Beach , which has sand containing basalt and coral fragments.[5] Olivine beaches have high potential for carbon sequestration , and artificial greensand beaches are being explored for this process by Project Vesta .[8]

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