A bay is a recessed, coastal body of water that directly connects to a larger main body of water, such as an ocean, a lake, or another bay. A large bay is called a gulf, sound, or bight. A cove is a type of smaller bay with narrow entrance. A fjord is a steep bay shaped by glacial activity. A bay can be the estuary of a river, such as the Chesapeake Bay, an estuary of the Susquehanna River. Bays may be nested within each other; some large bays, such as the Bay of Bengal and Hudson Bay, have varied marine geology. The land surrounding a bay reduces the strength of winds and blocks waves. Bays were significant in the history of human settlement because they provided safe places for fishing, they were important in the development of sea trade as the safe anchorage they provide encouraged their selection as ports. The United Nations Convention on the Law of the Sea called the Law of the Sea, defines a bay as a well-marked indentation whose penetration is in such proportion to the width of its mouth as to contain land-locked waters and constitute more than a mere curvature of the coast.
An indentation shall not, however, be regarded as a bay unless its area is as large as, or larger than, that of the semi-circle whose diameter is a line drawn across the mouth of that indentation. There are various ways; the largest bays have developed through plate tectonics. As the super-continent Pangaea broke up along curved and indented fault lines, the continents moved apart and left large bays. Bays form through coastal erosion by rivers and glaciers. A bay formed by a glacier is a fjord. Rias are characterised by more gradual slopes. Deposits of softer rocks erode more forming bays, while harder rocks erode less leaving headlands. Bay platform Great capes Headlands and bays
A stack or sea stack is a geological landform consisting of a steep and vertical column or columns of rock in the sea near a coast, formed by wave erosion. Stacks are formed over time by processes of coastal geomorphology, they are formed when part of a headland is eroded by hydraulic action, the force of the sea or water crashing against the rock. The force of the water weakens cracks in the headland, causing them to collapse, forming free-standing stacks and a small island. Without the constant presence of water, stacks form when a natural arch collapses under gravity, due to sub-aerial processes like wind erosion. Erosion causes the arch to collapse, leaving the pillar of hard rock standing away from the coast—the stack. Erosion will cause the stack to collapse, leaving a stump. Stacks can provide important nesting locations for seabirds, many are popular for rock climbing. Isolated steep-sided, rocky oceanic islets of volcanic origin, are loosely called "stacks" or "volcanic stacks". Stacks form in horizontally-bedded sedimentary or volcanic rocks on limestone cliffs.
The medium hardness of these rocks means medium resistance to abrasive and attritive erosion. A more resistant layer may form a capstone; the formation process begins when the sea attacks small cracks in a headland and opens them. The cracks gradually get larger and turn into a small cave; when the cave wears through the headland, an arch forms. Further erosion causes the arch to collapse, leaving the pillar of hard rock standing away from the coast—the stack. Erosion will cause the stack to collapse, leaving a stump; this stump forms a small rock island, low enough for a high tide to submerge. Ball's Pyramid, the tallest sea stack in the world List of sea stacks Rauk
Geologically, a fjord or fiord is a long, narrow inlet with steep sides or cliffs, created by a glacier. There are many fjords on the coasts of Alaska, British Columbia, Greenland, the Faroe Islands, Kamchatka, the Kerguelen Islands, New Zealand, Novaya Zemlya, Nunavut, Quebec, South Georgia Island, Washington state. Norway's coastline is estimated at 29,000 kilometres with nearly 1,200 fjords, but only 2,500 kilometres when fjords are excluded. A true fjord is formed when a glacier cuts a U-shaped valley by ice segregation and abrasion of the surrounding bedrock. According to the standard model, glaciers formed in pre-glacial valleys with a sloping valley floor; the work of the glacier left an overdeepened U-shaped valley that ends abruptly at a valley or trough end. Such valleys are fjords. Thresholds above sea level create freshwater lakes. Glacial melting is accompanied by the rebounding of Earth's crust as the ice load and eroded sediment is removed. In some cases this rebound is faster than sea level rise.
Most fjords are deeper than the adjacent sea. Fjords have a sill or shoal at their mouth caused by the previous glacier's reduced erosion rate and terminal moraine. In many cases this sill causes large saltwater rapids. Saltstraumen in Norway is described as the world's strongest tidal current; these characteristics distinguish fjords from rias, which are drowned valleys flooded by the rising sea. Drammensfjorden is cut in two by the Svelvik "ridge", a sandy moraine that during the ice cover was under sea level but after the post-glacial rebound reaches 60 m above the fjord. Jens Esmark in the 19th century introduced the theory that fjords are or have been created by glaciers and that large parts of Northern Europe had been covered by thick ice in prehistory. Thresholds at the mouths and overdeepening of fjords compared to the ocean are the strongest evidence of glacial origin, these thresholds are rocky. Thresholds are related to sounds and low land where the ice could spread out and therefore have less erosive force.
John Walter Gregory argued that fjords are of tectonic origin and that glaciers had a negligible role in their formation. Gregory's views were rejected by subsequent research and publications. In the case of Hardangerfjord the fractures of the Caledonian fold has guided the erosion by glaciers, while there is no clear relation between the direction of Sognefjord and the fold pattern; this relationship between fractures and direction of fjords is observed in Lyngen. Preglacial, tertiary rivers eroded the surface and created valleys that guided the glacial flow and erosion of the bedrock; this may in particular have been the case in Western Norway where the tertiary uplift of the landmass amplified eroding forces of rivers. Confluence of tributatry fjords led to excavation of the deepest fjord basins. Near the coast the typical West Norwegian glacier spread out and lost their concentration and reduced the glaciers' power to erode leaving bedrock thresholds. Bolstadfjorden is 160 m deep with a treshold of only 1.5 m, while the 1,300 m deep Sognefjorden has a threshold around 100 to 200 m deep.
Hardangerfjord is made up of several basins separated by thresholds: The deepest basin Samlafjorden between Jonaneset og Ålvik with a distinct treshold at Vikingneset in Kvam. Hanging valleys are common along U-shaped valleys. A hanging valley is a tributary valley, higher than the main valley and were created by tributary glacier flows into a glacier of larger volume; the shallower valley appears to be ` hanging' above a fjord. Waterfalls form at or near the outlet of the upper valley. Hanging valleys occur under water in fjord systems; the branches of Sognefjord are for instance much shallower than the main fjord. The mouth of Fjærlandsfjord is about 400 m deep; the mouth of Ikjefjord is only 50 meters deep while the main fjord is around 1,300 m at the same point. During the winter season there is little inflow of freshwater. Surface water and deeper water are mixed during winter because of the steady cooling of the surface and wind. In the deep fjords there is still fresh water from the summer with less density than the saltier water along the coast.
Offshore wind, common in the fjord areas during winter, sets up a current on the surface from the inner to the outer parts. This current on the surface in turn pulls dense salt water from the coast across the fjord threshold and into the deepest parts of the fjord. Bolstadfjorden has a threshold of only 1.5 m and strong inflow of freshwater from Vosso river creates a brackish surface that blocks circulation of the deep fjord. The deeper, salt layers of Bolstadfjorden are deprived of oxygen and the seabed is covered with organic material; the shallow threshold creates a strong tidal current. During the summer season there is a large inflow of river water in the inner areas; this freshwater gets mixed with saltwater creating a layer of brackish water with a higher surface than the ocean which in turn sets up a current from the river mouths towards the ocean. This current is more salty towards the coast and right under the surface current there is a reverse current of saltier water from the coast.
In the deeper
Clay is a finely-grained natural rock or soil material that combines one or more clay minerals with possible traces of quartz, metal oxides and organic matter. Geologic clay deposits are composed of phyllosilicate minerals containing variable amounts of water trapped in the mineral structure. Clays are plastic due to particle size and geometry as well as water content, become hard and non–plastic upon drying or firing. Depending on the soil's content in which it is found, clay can appear in various colours from white to dull grey or brown to deep orange-red. Although many occurring deposits include both silts and clay, clays are distinguished from other fine-grained soils by differences in size and mineralogy. Silts, which are fine-grained soils that do not include clay minerals, tend to have larger particle sizes than clays. There is, some overlap in particle size and other physical properties; the distinction between silt and clay varies by discipline. Geologists and soil scientists consider the separation to occur at a particle size of 2 µm, sedimentologists use 4–5 μm, colloid chemists use 1 μm.
Geotechnical engineers distinguish between silts and clays based on the plasticity properties of the soil, as measured by the soils' Atterberg limits. ISO 14688 grades clay particles as being smaller than 2 silt particles as being larger. Mixtures of sand and less than 40% clay are called loam. Loam is used as a building material. Clay minerals form over long periods of time as a result of the gradual chemical weathering of rocks silicate-bearing, by low concentrations of carbonic acid and other diluted solvents; these solvents acidic, migrate through the weathering rock after leaching through upper weathered layers. In addition to the weathering process, some clay minerals are formed through hydrothermal activity. There are two types of clay deposits: secondary. Primary clays remain at the site of formation. Secondary clays are clays that have been transported from their original location by water erosion and deposited in a new sedimentary deposit. Clay deposits are associated with low energy depositional environments such as large lakes and marine basins.
Depending on the academic source, there are three or four main groups of clays: kaolinite, montmorillonite-smectite and chlorite. Chlorites are not always considered to be a clay, sometimes being classified as a separate group within the phyllosilicates. There are 30 different types of "pure" clays in these categories, but most "natural" clay deposits are mixtures of these different types, along with other weathered minerals. Varve is clay with visible annual layers, which are formed by seasonal deposition of those layers and are marked by differences in erosion and organic content; this type of deposit is common in former glacial lakes. When fine sediments are delivered into the calm waters of these glacial lake basins away from the shoreline, they settle to the lake bed; the resulting seasonal layering is preserved in an distribution of clay sediment banding. Quick clay is a unique type of marine clay indigenous to the glaciated terrains of Norway, Northern Ireland, Sweden, it is a sensitive clay, prone to liquefaction, involved in several deadly landslides.
Powder X-ray diffraction can be used to identify clays. The physical and reactive chemical properties can be used to help elucidate the composition of clays. Clays exhibit plasticity. However, when dry, clay becomes firm and when fired in a kiln, permanent physical and chemical changes occur; these changes convert the clay into a ceramic material. Because of these properties, clay is used for making pottery, both utilitarian and decorative, construction products, such as bricks and floor tiles. Different types of clay, when used with different minerals and firing conditions, are used to produce earthenware and porcelain. Prehistoric humans discovered the useful properties of clay; some of the earliest pottery shards recovered are from Japan. They are associated with the Jōmon culture and deposits they were recovered from have been dated to around 14,000 BC. Clay tablets were the first known writing medium. Scribes wrote by inscribing them with cuneiform script using a blunt reed called a stylus. Purpose-made clay balls were used as sling ammunition.
Clays sintered in fire were the first form of ceramic. Bricks, cooking pots, art objects, smoking pipes, musical instruments such as the ocarina can all be shaped from clay before being fired. Clay is used in many industrial processes, such as paper making, cement production, chemical filtering; until the late 20th century, bentonite clay was used as a mold binder in the manufacture of sand castings. Clay, being impermeable to water, is used where natural seals are needed, such as in the cores of dams, or as a barrier in landfills against toxic seepage. Studies in the early 21st century have investigated clay's absorption capacities in various applications, such as the removal of heavy metals from waste water and air purification. Traditional uses of clay as medicine goes back to prehistoric times. An example is Armenian bole, used to soothe an upset stomach; some animals such as parrots and pigs ingest clay for similar reasons. Kaolin clay and attapulgite have been used as anti-diarrheal medicines.
Clay as the defining ingredient of loam is one of the oldest building materials on Earth, among other
In physical geography, a dune is a hill of loose sand built by aeolian processes or the flow of water. Dunes occur in different sizes, formed by interaction with the flow of air or water. Most kinds of dunes are longer on the stoss side, where the sand is pushed up the dune, have a shorter "slip face" in the lee side; the valley or trough between dunes is called a slack. A "dune field" or erg is an area covered by extensive dunes. Dunes occur along some coasts; some coastal areas have one or more sets of dunes running parallel to the shoreline directly inland from the beach. In most cases, the dunes are important in protecting the land against potential ravages by storm waves from the sea. Although the most 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 can form under the action of water flow, on sand or gravel beds of rivers and the sea-bed; the modern word "dune" came into English from French c.
1790, which in turn came from Middle Dutch dūne. Dunes are made of sand-sized particles, may consist of quartz, calcium carbonate, gypsum, or other materials; the upwind/upstream/upcurrent side of the dune is called the stoss side. Sand is pushed or bounces up the stoss side, slides down the lee side. A side of a dune that the sand has slid down is called a slip face; the Bagnold formula gives the speed. Five basic dune types are recognized: crescentic, star and parabolic. Dune areas may occur in three forms: simple and complex. Barchan dunes are crescent-shaped mounds which are wider than they are long; the lee-side slipfaces are on the concave sides of the dunes. These dunes form under winds that blow from one direction, they form separate crescents. When the sand supply is greater, they may merge into barchanoid ridges, transverse dunes; some types of crescentic dunes move more over desert surfaces than any other type of dune. A group of dunes moved more than 100 metres per year between 1954 and 1959 in China's Ningxia Province, similar speeds have been recorded in the Western Desert of Egypt.
The largest crescentic dunes on Earth, with mean crest-to-crest widths of more than three kilometres, are in China's Taklamakan Desert. See lunettes and parabolic dues, for dunes similar to crescent-shaped ones. Abundant barchan dunes may merge into barchanoid ridges, which grade into linear transverse dunes, so called because they lie transverse, or across, the wind direction, with the wind blowing perpendicular to the ridge crest. Seif dunes are linear dunes with two slip faces; the two slip faces make them sharp-crested. They are called seif dunes after the Arabic word for "sword", they may be more than 160 kilometres long, thus visible in satellite images. Seif dunes are associated with bidirectional winds; the long axes and ridges of these dunes extend along the resultant direction of sand movement. Some linear dunes merge to form Y-shaped compound dunes. Formation is debated. Bagnold, in The Physics of Blown Sand and Desert Dunes, suggested that some seif dunes form when a barchan dune moves into a bidirectional wind regime, one arm or wing of the crescent elongates.
Others suggest. In the sheltered troughs between developed seif dunes, barchans may be formed, because the wind is constrained to be unidirectional by the dunes. Seif dunes are common in the Sahara, they range up to 300 km in length. In the southern third of the Arabian Peninsula, a vast erg, called the Rub' al Khali or Empty Quarter, contains seif dunes that stretch for 200 km and reach heights of over 300 m. Linear loess hills known; these hills appear to have been formed during the last ice age under permafrost conditions dominated by sparse tundra vegetation. 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 near topographic barriers. In the southeast Badain Jaran Desert of China, the star dunes are up to 500 metres tall and may be the tallest dunes on Earth.
Oval or circular mounds that lack a slipface. Dome dunes occur at the far upwind margins of sand seas. Fixed crescentic dunes that form on the leeward margins of playas and river valleys in arid and semiarid regions in response to the direction of prevailing winds, are known as lunettes, source-bordering dunes and clay dunes, they may be composed of clay, sand, or gypsum, eroded from the basin floor or shore, transported up the concave side of the dune, deposited on the convex side. Examples in Australia are up to 6.5 km long, 1 km wide, up to 50 metres high. They occur in southern and West Africa, in parts of the western United States Texas. U-shaped mounds of sand with convex noses trailed by elongated arms are parabolic dunes; these dunes are formed from blowout dunes where the erosion
American Society of Civil Engineers
The American Society of Civil Engineers is a tax-exempt professional body founded in 1852 to represent members of the civil engineering profession worldwide. Headquartered in Reston, Virginia, it is the oldest national engineering society in the United States, its constitution was based on the older Boston Society of Civil Engineers from 1848. The American Society of Civil Engineers represents more than 150,000 members of the civil engineering profession in 177 countries. Through the expertise of its active membership, ASCE is a leading provider of technical and professional conferences and continuing education, the world’s largest publisher of civil engineering content, an authoritative source for codes and standards that protect the public. ASCE stands for the "American Society of Civil Engineers"; the society was chartered under this full legal name when it was incorporated on April 17, 1877 in New York state. ASCE's membership has long been composed of civil engineers and affiliate members who are not students or classically trained engineers or scientists.
ASCE is dedicated to the "...advancement of the science and profession of Civil engineering and the enhancement of human welfare through the activities of society members." It has about 152,000 members in about 177 countries. Its mission is to provide essential value to "...members, their careers, our partners, the public...... Facilitate the advancement of technology; the first serious and documented attempts to organize civil engineers as a professional society in the newly created United States were in the early 19th century. In 1828, John Kilbourn of Ohio, managed a short-lived "Civil Engineering Journal", editorializing about the recent incorporation of the Institution of Civil Engineers in Great Britain that same year, Kilbourn suggested that the American corps of engineers could constitute an American society of civil engineers. In 1834, an American trade periodical, the "American Railroad Journal" advocated for similar national organization of civil engineers. On December 17, 1838, a petition started circulating asking civil engineers to meet in 1839 in Baltimore, Maryland to organize a permanent society of civil engineers.
Prior to that, thirteen notable civil engineers identifiable as being from New York, Pennsylvania, or Maryland met in Philadelphia. This group presented the Franklin Institute of Philadelphia with a formal proposal that an Institution of American Civil Engineers be established as an adjunct of the Franklin..." Some of them were: Benjamin Wright. In 1969, the American Society of Civil Engineers declared Wright to be the'Father of American Civil Engineering'. William Strickland Pennsylvanians Solomon. W. Roberts, the latter being Chief Engineer for the Allegheny Portage railroad, the first crossing of the Allegheny mountains Forty engineers appeared at the February, 1839 meeting Baltimore including J. Edgar Thomson, Roberts, Edward Miller, the Maryland engineers Isaac Trimble and architect Benjamin H. Latrobe and attendees from as far as Massachusetts and Louisiana. Subsequently, a group met again in Philadelphia, led by its Secretary, Edward Miller to take steps to formalize the society, participants now included such other notable engineers as: John B.
Jervis Claudius Crozet William Gibbs McNeill George Washington Whistler Walter Gwynn J. Edgar Thompson Sylvester Welch, brother of future ASCE president Ashbel Welch Other members included Jonathan Knight and Moncure Robinson. Miller drafted up a proposed constitution which gave the society's purpose as "the collection and diffusion of professional knowledge, the advancement of mechanical philosophy, the elevation of the character and standing of the Civil Engineers of the United States." Membership in the new society restricted membership to engineers and "architects and eminent machinists were to be admitted only as Associates." The proposed constitution failed, no further attempts were made to form another society. Miller ascribed the failure due to the difficulties of assembling members due available means for traveling in the country at time. One of the other difficulties members would have to contend with was the requirement to produce each year, one unpublished paper or "...present a scientific book, plan or model, not in the possession of the Society, under the penalty of $10."
In that same period, the editor of the American Railroad Journal commented that effort had failed in part due to certain jealousies which arose due to the proposed affiliation with the Franklin Institute. That journal continued discussion on forming an engineers' organization from 1839 thru 1843 serving its own self interests in advocating its journal as a replacement for a professional society but to no avail. During the 1840s, professional organizations continued to organize in the United States; the organizers motives were to "... improve common standards, foster research, disseminate knowledge through meetings and publications." Unlike earlier associations such as the American Philosophical Society, these newer associations were not seeking to limit membership as much as pursue "... more specialized interests." Examples of this surge in new professional organizations in America were the American Statistical Association, American Ethnological Society, American Medical Association, American Association for the Advancement of Science, National Education Association.
During this same period of association incorporations on the 1840s, attempts were aga
A coral reef is an underwater ecosystem characterized by reef-building corals. Reefs are formed of colonies of coral polyps held together by calcium carbonate. Most coral reefs are built from stony corals. Coral belongs to the class Anthozoa in the animal phylum Cnidaria, which includes sea anemones and jellyfish. Unlike sea anemones, corals secrete hard carbonate exoskeletons that protect the coral. Most reefs grow best in warm, clear and agitated water. Called "rainforests of the sea", shallow coral reefs form some of Earth's most diverse ecosystems, they occupy less than 0.1% of the world's ocean area, about half the area of France, yet they provide a home for at least 25% of all marine species, including fish, worms, echinoderms, sponges and other cnidarians. Coral reefs flourish in ocean waters, they are most found at shallow depths in tropical waters, but deep water and cold water coral reefs exist on smaller scales in other areas. Coral reefs deliver ecosystem services for tourism and shoreline protection.
The annual global economic value of coral reefs is estimated between US$30–375 billion and 9.9 trillion USD. Coral reefs are fragile because they are sensitive to water conditions, they are under threat from excess nutrients, rising temperatures, oceanic acidification, sunscreen use, harmful land-use practices, including runoff and seeps. Most coral reefs were formed after the last glacial period when melting ice caused sea level to rise and flood continental shelves. Most coral reefs are less than 10,000 years old; as communities established themselves, the reefs grew pacing rising sea levels. Reefs that rose too could become drowned, without sufficient light. Coral reefs are found in the deep sea away from continental shelves, around oceanic islands and atolls; the majority of these islands are volcanic in origin. Others have tectonic origins. In The Structure and Distribution of Coral Reefs, Charles Darwin set out his theory of the formation of atoll reefs, an idea he conceived during the voyage of the Beagle.
He theorized that subsidence of the Earth's crust under the oceans formed the atolls. Darwin set out a sequence of three stages in atoll formation. A fringing reef forms around an extinct volcanic island as the ocean floor subsides; as the subsidence continues, the fringing reef becomes a barrier reef and an atoll reef. Darwin predicted that underneath each lagoon would be a bedrock base, the remains of the original volcano. Subsequent research supported this hypothesis. Darwin's theory followed from his understanding that coral polyps thrive in the tropics where the water is agitated, but can only live within a limited depth range, starting just below low tide. Where the level of the underlying earth allows, the corals grow around the coast to form fringing reefs, can grow to become a barrier reef. Where the bottom is rising, fringing reefs can grow around the coast, but coral raised above sea level dies. If the land subsides the fringing reefs keep pace by growing upwards on a base of older, dead coral, forming a barrier reef enclosing a lagoon between the reef and the land.
A barrier reef can encircle an island, once the island sinks below sea level a circular atoll of growing coral continues to keep up with the sea level, forming a central lagoon. Barrier reefs and atolls do not form complete circles, but are broken in places by storms. Like sea level rise, a subsiding bottom can overwhelm coral growth, killing the coral and the reef, due to what is called coral drowning. Corals that rely on zooxanthellae can die when the water becomes too deep for their symbionts to adequately photosynthesize, due to decreased light exposure; the two main variables determining the geomorphology, or shape, of coral reefs are the nature of the substrate on which they rest, the history of the change in sea level relative to that substrate. The 20,000-year-old Great Barrier Reef offers an example of how coral reefs formed on continental shelves. Sea level was 120 m lower than in the 21st century; as sea level rose, the water and the corals encroached on what had been hills of the Australian coastal plain.
By 13,000 years ago, sea level had risen to 60 m lower than at present, many hills of the coastal plains had become continental islands. As sea level rise continued, water topped most of the continental islands; the corals could overgrow the hills, forming cays and reefs. Sea level on the Great Barrier Reef has not changed in the last 6,000 years; the age of living reef structure is estimated to be between 8,000 years. Although the Great Barrier Reef formed along a continental shelf, not around a volcanic island, Darwin's principles apply. Development stopped at the barrier reef stage, it formed 300 -- 1,000 m from shore, stretching for 2,000 km. Healthy tropical coral reefs grow horizontally from 1 to 3 cm per year, grow vertically anywhere from 1 to 25 cm per year; as the name implies, coral reefs are made up of coral skeletons from intact coral colonies. As other chemical elements present in corals become incorporated into the calcium carbonate deposits, aragonite is formed. However