An oil platform, offshore platform, or offshore drilling rig is a large structure with facilities for well drilling to explore, extract and process petroleum and natural gas which lies in rock formations beneath the seabed. In many cases, the platform contains facilities to house the workforce as well. Most oil platforms engage in activities on the continental shelf, though they can be used in lakes, inshore waters and inland seas. Depending on the circumstances, the platform may be fixed to the ocean floor, may consist of an artificial island, or may float. Remote subsea wells may be connected to a platform by flow lines and by umbilical connections; these sub-sea solutions may consist of one or more subsea wells, or of one or more manifold centres for multiple wells. Offshore drilling presents environmental challenges, both from the produced hydrocarbons and the materials used during the drilling operation. Controversies include the ongoing U. S. offshore drilling debate. There are many different types of facilities from which offshore drilling operations take place.
These include bottom founded drilling rigs, combined drilling and production facilities either bottom founded or floating platforms, deepwater mobile offshore drilling units including semi-submersibles and drillships. These are capable of operating in water depths up to 3,000 metres. In shallower waters the mobile units are anchored to the seabed, however in deeper water the semisubmersibles or drillships are maintained at the required drilling location using dynamic positioning. Around 1891, the first submerged oil wells were drilled from platforms built on piles in the fresh waters of the Grand Lake St. Marys in Ohio; the wide but shallow reservoir was built from 1837 to 1845 to provide water to the Miami and Erie Canal. Around 1896, the first submerged oil wells in salt water were drilled in the portion of the Summerland field extending under the Santa Barbara Channel in California; the wells were drilled from piers extending from land out into the channel. Other notable early submerged drilling activities occurred on the Canadian side of Lake Erie since 1913 and Caddo Lake in Louisiana in the 1910s.
Shortly thereafter, wells were drilled in tidal zones along the Gulf Coast of Texas and Louisiana. The Goose Creek field near Baytown, Texas is one such example. In the 1920s, drilling was done from concrete platforms in Lake Maracaibo, Venezuela; the oldest offshore well recorded in Infield's offshore database is the Bibi Eibat well which came on stream in 1923 in Azerbaijan. Landfill was used to raise shallow portions of the Caspian Sea. In the early 1930s, the Texas Company developed the first mobile steel barges for drilling in the brackish coastal areas of the gulf. In 1937, Pure Oil Company and its partner Superior Oil Company used a fixed platform to develop a field in 14 feet of water, one mile offshore of Calcasieu Parish, Louisiana. In 1938, Humble Oil built a mile-long wooden trestle with railway tracks into the sea at McFadden Beach on the Gulf of Mexico, placing a derrick at its end - this was destroyed by a hurricane. In 1945, concern for American control of its offshore oil reserves caused President Harry Truman to issue an Executive Order unilaterally extending American territory to the edge of its continental shelf, an act that ended the 3-mile limit "freedom of the seas" regime.
In 1946, Magnolia Petroleum drilled at a site 18 miles off the coast, erecting a platform in 18 feet of water off St. Mary Parish, Louisiana. In early 1947, Superior Oil erected a drilling/production platform in 20 ft of water some 18 miles off Vermilion Parish, Louisiana, but it was Kerr-McGee Oil Industries, as operator for partners Phillips Petroleum and Stanolind Oil & Gas, that completed its historic Ship Shoal Block 32 well in October 1947, months before Superior drilled a discovery from their Vermilion platform farther offshore. In any case, that made Kerr-McGee's well the first oil discovery drilled out of sight of land; the British Maunsell Forts constructed during World War II are considered the direct predecessors of modern offshore platforms. Having been pre-constructed in a short time, they were floated to their location and placed on the shallow bottom of the Thames and the Mersey estuary. In 1954, the first jackup oil rig was ordered by Zapata Oil, it was designed by R. G. LeTourneau and featured three electro-mechanically-operated lattice type legs.
Built on the shores of the Mississippi river by the LeTourneau Company, it was launched in December 1955, christened'Scorpion'. The Scorpion was put into operation in May 1956 off Port Aransas, Texas, it was lost in 1969. When offshore drilling moved into deeper waters of up to 30 metres, fixed platform rigs were built, until demands for drilling equipment was needed in the 100 feet to 120 metres depth of the Gulf of Mexico, the first jack-up rigs began appearing from specialized offshore drilling contractors such as forerunners of ENSCO International; the first semi-submersible resulted from an unexpected observation in 1961. Blue Water Drilling Company owned and operated the four-column submersible Blue Water Rig No.1 in the Gulf of Mexico for Shell Oil Company. As the pontoons were not sufficiently buoyant to support the weight of the rig and its consumables, it was towed between locations at a draught midway between the top of the pontoons and the underside of the deck, it was noticed that the motions at this draught were small, Blue Water Drilling and Shell jointly deci
A drilling rig is a machine that creates holes in the earth's subsurface. Drilling rigs can be massive structures housing equipment used to drill water wells, oil wells, or natural gas extraction wells, or they can be small enough to be moved manually by one person and such are called augers. Drilling rigs can sample subsurface mineral deposits, test rock and groundwater physical properties, can be used to install sub-surface fabrications, such as underground utilities, tunnels or wells. Drilling rigs can be mobile equipment mounted on trucks, tracks or trailers, or more permanent land or marine-based structures; the term "rig" therefore refers to the complex equipment, used to penetrate the surface of the Earth's crust. Small to medium-sized drilling rigs are mobile, such as those used in mineral exploration drilling, blast-hole, water wells and environmental investigations. Larger rigs are capable of drilling through thousands of metres of the Earth's crust, using large "mud pumps" to circulate drilling mud through the drill bit and up the casing annulus, for cooling and removing the "cuttings" while a well is drilled.
Hoists in the rig can lift hundreds of tons of pipe. Other equipment can force acid or sand into reservoirs to facilitate extraction of the oil or natural gas. Marine rigs may operate thousands of miles distant from the supply base with infrequent crew rotation or cycle; until internal combustion engines were developed in the late 19th century, the main method for drilling rock was muscle power of man or animal. The technique of oil drilling through percussion or rotary drilling has its origins dating back to the ancient Chinese Han Dynasty in 500 BC, where percussion drilling was used to extract natural gas in the Sichuan province. Early oil and gas drilling methods were primitive as it required several technical skills; the skills involved the availability of heavy iron bits and long bamboo poles, the manufacturing of long and sturdy cables woven from bamboo fiber, levers. Heavy iron bits were attached to long bamboo cables suspended from bamboo derricks and were raised and dropped into a manually dug hole by having two to six men jumping on a lever.
Han dynasty oil wells made by percussion drilling was effective but only reached 10 meters deep and 100 meters by the 10th century. By the 16th century, the Chinese were drilling oil wells more than 2000 feet deep. A modernized variant of the ancient Chinese drilling technique was used by American businessman Edwin Drake to drill Pennsylvania's first oil well in 1859 using small steam engines to power the drilling process rather than by human muscle. In the 1970s, outside of the oil and gas industry, roller bits using mud circulation were replaced by the first pneumatic reciprocating piston Reverse Circulation drills, became obsolete for most shallow drilling, are now only used in certain situations where rocks preclude other methods. RC drilling proved much faster and more efficient, continues to improve with better metallurgy, deriving harder, more durable bits, compressors delivering higher air pressures at higher volumes, enabling deeper and faster penetration. Diamond drilling has remained unchanged since its inception.
Oil and natural gas drilling rigs are used not only to identify geologic reservoirs but to create holes that allow the extraction of oil or natural gas from those reservoirs. In onshore oil and gas fields once a well has been drilled, the drilling rig will be moved off of the well and a service rig, purpose-built for completions will be moved on to the well to get the well on line; this frees up the drilling rig to drill another hole and streamlines the operation as well as allowing for specialization of certain services, i.e. completions vs. drilling. Mining drilling rigs are used for two main purposes, exploration drilling which aims to identify the location and quality of a mineral, production drilling, used in the production-cycle for mining. Drilling rigs used for rock blasting for surface mines vary in size dependent on the size of the hole desired, is classified into smaller pre-split and larger production holes. Underground mining uses a variety of drill rigs dependent on the desired purpose, such as production, bolting and tunnelling.
In early oil exploration, drilling rigs were semi-permanent in nature and the derricks were built on site and left in place after the completion of the well. In more recent times drilling rigs are expensive custom-built machines that can be moved from well to well; some light duty drilling rigs are like a mobile crane and are more used to drill water wells. Larger land rigs must be broken apart into sections and loads to move to a new place, a process which can take weeks. Small mobile drilling rigs are used to drill or bore piles. Rigs can range from 100 ton continuous flight auger rigs to small air powered rigs used to drill holes in quarries, etc; these rigs use the same equipment as the oil drilling rigs, just on a smaller scale. The drilling mechanisms outlined below differ mechanically in terms of the machinery used, but in terms of the method by which drill cuttings are removed from the cutting face of the drill and returned to surface. There are many types and designs of drilling rigs, with many drilling rigs capable of switching or combining different drilling technologies as needed.
Drilling rigs can be described using any of the following attributes: Mechan
Hydrocarbon exploration is the search by petroleum geologists and geophysicists for hydrocarbon deposits beneath the Earth's surface, such as oil and natural gas. Oil and gas exploration are grouped under the science of petroleum geology. Visible surface features such as oil seeps, natural gas seeps, pockmarks provide basic evidence of hydrocarbon generation. However, most exploration depends on sophisticated technology to detect and determine the extent of these deposits using exploration geophysics. Areas thought to contain hydrocarbons are subjected to a gravity survey, magnetic survey, passive seismic or regional seismic reflection surveys to detect large-scale features of the sub-surface geology. Features of interest are subjected to more detailed seismic surveys which work on the principle of the time it takes for reflected sound waves to travel through matter of varying densities and using the process of depth conversion to create a profile of the substructure; when a prospect has been identified and evaluated and passes the oil company's selection criteria, an exploration well is drilled in an attempt to conclusively determine the presence or absence of oil or gas.
Offshore the risk can be reduced by using electromagnetic methods Oil exploration is an expensive, high-risk operation. Offshore and remote area exploration is only undertaken by large corporations or national governments. Typical shallow shelf oil wells cost US$10 – 30 million, while deep water wells can cost up to US$100 million plus. Hundreds of smaller companies search for onshore hydrocarbon deposits worldwide, with some wells costing as little as US$100,000. A prospect is a potential trap. A significant amount of geological and seismic investigation must first be completed to redefine the potential hydrocarbon drill location from a lead to a prospect. Four geological factors have to be present for a prospect to work and if any of them fail neither oil nor gas will be present. Source rock When organic-rich rock such as oil shale or coal is subjected to high pressure and temperature over an extended period of time, hydrocarbons form. Migration The hydrocarbons are expelled from source rock by three density-related mechanisms: the newly matured hydrocarbons are less dense than their precursors, which causes over-pressure.
Most hydrocarbons migrate to the surface as oil seeps. Reservoir The hydrocarbons are contained in a reservoir rock; this is a porous sandstone or limestone. The oil collects in the pores within the rock although open fractures within non-porous rocks may store hydrocarbons; the reservoir must be permeable so that the hydrocarbons will flow to surface during production. Trap The hydrocarbons are buoyant and have to be trapped within a structural or stratigraphic trap; the hydrocarbon trap has to be covered by an impermeable rock known as a seal or cap-rock in order to prevent hydrocarbons escaping to the surface Hydrocarbon exploration is a high risk investment and risk assessment is paramount for successful project portfolio management. Exploration risk is a difficult concept and is defined by assigning confidence to the presence of the imperative geological factors, as discussed above; this confidence is based on data and/or models and is mapped on Common Risk Segment Maps. High confidence in the presence of imperative geological factors is coloured green and low confidence coloured red.
Therefore, these maps are called Traffic Light Maps, while the full procedure is referred to as Play Fairway Analysis. The aim of such procedures is to force the geologist to objectively assess all different geological factors. Furthermore, it results in simple maps that can be understood by non-geologists and managers to base exploration decisions on. Bright spot On a seismic section, coda that have high amplitudes due to a formation containing hydrocarbons. Chance of success An estimate of the chance of all the elements within a prospect working, described as a probability. Dry hole A boring. See Dry hole clause Flat spot Possibly an oil-water, gas-water or gas-oil contact on a seismic section. Full Waveform Inversion A supercomputer technique use in conjunction with seismic sensors to explore for petroleum deposits offshore. Hydrocarbon in place amount of hydrocarbon to be contained in the prospect; this is calculated using the volumetric equation - GRV x N/G x Porosity x Sh / FVF Gross rock volume amount of rock in the trap above the hydrocarbon water contact Net sand part of GRV that has the lithological capacity for being a productive zone.
Net reserve part of net sand that has the minimum reservoir qualities. Net/gross ratio proportion of the GRV formed by the reservoir rock Porosity percentage of the net reservoir rock occupied by pores Hydrocarbon saturation some of the pore space is filled with water - this must be discounted Formation volume factor oil shrinks and gas expands when brought to the surface; the FVF converts volumes at reservoir conditions to storage and sale conditionsLead Potential accumulation is poorly defined and requires more data acquisition and/or eva
A Mediterranean climate or dry summer climate is characterized by rainy winters and dry summers, with less than 40 mm of precipitation for at least three summer months. While the climate receives its name from the Mediterranean Basin, these are located on the western coasts of continents, between 30 and 45 degrees north and south of the equator between oceanic climates towards the poles, semi-arid and arid climates towards the equator. In essence, due to the seasonal shift of the subtropical high-pressure belts with the apparent movement of the Sun, a Mediterranean climate is an intermediate type between these other climates, with winters warmer and drier than oceanic climates and summers imitating sunny weather in semi-arid and arid climates; the resulting vegetation of Mediterranean climates are the garrigue or maquis in the Mediterranean Basin, the chaparral in California, the fynbos in South Africa, the mallee in Australia, the matorral in Chile. Areas with this climate are where the so-called "Mediterranean trinity" of agricultural products have traditionally developed: wheat and olive.
Most large, historic cities of the Mediterranean basin lie within Mediterranean climatic zones, including Algiers, Beirut, İzmir, Marseille, Rome and Valencia. Examples of major cities with Mediterranean climates that lie outside of the historic Mediterranean basin include major examples as Adelaide, Cape Town, Dushanbe, Los Angeles, Perth, San Francisco and Victoria. Under the Köppen climate classification, "hot dry-summer" climates and "cool dry-summer" climates are referred to as "Mediterranean". Under the Köppen climate system, the first letter indicates the climate group. Temperate climates or "C" zones have an average temperature above 0 °C, but below 18 °C, in their coolest months; the second letter indicates the precipitation pattern. Köppen has defined a dry summer month as a month with less than 30 mm of precipitation and with less than one-third that of the wettest winter month. Some, use a 40 mm level; the third letter indicates the degree of summer heat: "a" represents an average temperature in the warmest month above 22 °C, while "b" indicates the average temperature in the warmest month below 22 °C.
Under the Köppen classification, dry-summer climates occur on the western sides of continents. Csb zones in the Köppen system include areas not associated with Mediterranean climates but with Oceanic climates, such as much of the Pacific Northwest, much of southern Chile, parts of west-central Argentina, parts of New Zealand. Additional highland areas in the subtropics meet Cs requirements, though they, are not associated with Mediterranean climates, as do a number of oceanic islands such as Madeira, the Juan Fernández Islands, the western part of the Canary Islands, the eastern part of the Azores. Under Trewartha's modified Köppen climate classification, the two major requirements for a Cs climate are revised. Under Trewartha's system, at least eight months must have average temperatures of 10 °C or higher, the average annual precipitation must not exceed 900 mm. Thus, under this system, many Csb zones in the Köppen system become Do, the rare Csc zones become Eo, with only the classic dry-summer to warm winter, low annual rainfall locations included in the Mediterranean type climate.
During summer, regions of Mediterranean climate are influenced by cold ocean currents which keep the weather in the region dry and pleasant. Similar to desert climates, in many Mediterranean climates there is a strong diurnal character to daily temperatures in the warm summer months due to strong heating during the day from sunlight and rapid cooling at night. In winter, Mediterranean climate zones are no longer influenced by the cold ocean currents and therefore warmer water settles near land and causes clouds to form and rainfall becomes much more likely; as a result, areas with this climate receive all of their precipitation during their winter and spring seasons, may go anywhere from 3 to 6 months during the summer without having any significant precipitation. In the lower latitudes, precipitation decreases in both the winter and summer because they are closer to the Horse latitudes, thus bringing smaller amounts of rain. Toward the polar latitudes, total moisture increases; the rainfall tends to be more evenly distributed throughout the year in Southern Europe, while in the Eastern Mediterranean and in Southern California the summer is nearly or dry.
In places where evapotranspiration is higher, steppe climates tend to prevail, but still follow the weather pattern of the Mediterranean climate. The majority of the regions with Mediterranean climates have mild winters and warm summers; however winter and summer temperatures can vary between different regions with a Mediterranean climate. For instance, in the case of winters and Los Angeles experience mild temperatures in the winter, with frost and snowfall unknown, whereas Tashkent has colder winters with annual frosts and snowfall. Or to consider summer, Athens experiences rather high temperatures in that season. In contrast, San Francisco has cool summers with daily highs around 21 °C due to
An estuary is a enclosed coastal body of brackish water with one or more rivers or streams flowing into it, with a free connection to the open sea. Estuaries form a transition zone between river environments and maritime environments, they are subject both to marine influences—such as tides and the influx of saline water—and to riverine influences—such as flows of fresh water and sediment. The mixing of sea water and fresh water provide high levels of nutrients both in the water column and in sediment, making estuaries among the most productive natural habitats in the world. Most existing estuaries formed during the Holocene epoch with the flooding of river-eroded or glacially scoured valleys when the sea level began to rise about 10,000–12,000 years ago. Estuaries are classified according to their geomorphological features or to water-circulation patterns, they can have many different names, such as bays, lagoons, inlets, or sounds, although some of these water bodies do not meet the above definition of an estuary and may be saline.
The banks of many estuaries are amongst the most populated areas of the world, with about 60% of the world's population living along estuaries and the coast. As a result, many estuaries suffer degradation from a variety of factors including: sedimentation from soil erosion from deforestation and other poor farming practices; the word "estuary" is derived from the Latin word aestuarium meaning tidal inlet of the sea, which in itself is derived from the term aestus, meaning tide. There have been many definitions proposed to describe an estuary; the most accepted definition is: "a semi-enclosed coastal body of water, which has a free connection with the open sea, within which sea water is measurably diluted with freshwater derived from land drainage". However, this definition excludes a number of coastal water bodies such as coastal lagoons and brackish seas. A more comprehensive definition of an estuary is "a semi-enclosed body of water connected to the sea as far as the tidal limit or the salt intrusion limit and receiving freshwater runoff.
This broad definition includes fjords, river mouths, tidal creeks. An estuary is a dynamic ecosystem having a connection to the open sea through which the sea water enters with the rhythm of the tides; the sea water entering the estuary streams. The pattern of dilution varies between different estuaries and depends on the volume of fresh water, the tidal range, the extent of evaporation of the water in the estuary. Drowned river valleys are known as coastal plain estuaries. In places where the sea level is rising relative to the land, sea water progressively penetrates into river valleys and the topography of the estuary remains similar to that of a river valley; this is the most common type of estuary in temperate climates. Well-studied estuaries include the Severn Estuary in the United Kingdom and the Ems Dollard along the Dutch-German border; the width-to-depth ratio of these estuaries is large, appearing wedge-shaped in the inner part and broadening and deepening seaward. Water depths exceed 30 m.
Examples of this type of estuary in the U. S. are the Hudson River, Chesapeake Bay, Delaware Bay along the Mid-Atlantic coast, Galveston Bay and Tampa Bay along the Gulf Coast. Bar-built estuaries are found in place where the deposition of sediment has kept pace with rising sea level so that the estuaries are shallow and separated from the sea by sand spits or barrier islands, they are common in tropical and subtropical locations. These estuaries are semi-isolated from ocean waters by barrier beaches. Formation of barrier beaches encloses the estuary, with only narrow inlets allowing contact with the ocean waters. Bar-built estuaries develop on sloping plains located along tectonically stable edges of continents and marginal sea coasts, they are extensive along the Atlantic and Gulf coasts of the U. S. in areas with active coastal deposition of sediments and where tidal ranges are less than 4 m. The barrier beaches that enclose bar-built estuaries have been developed in several ways: building up of offshore bars by wave action, in which sand from the sea floor is deposited in elongated bars parallel to the shoreline, reworking of sediment discharge from rivers by wave and wind action into beaches, overwash flats, dunes, engulfment of mainland beach ridges due to sea level rise and resulting in the breaching of the ridges and flooding of the coastal lowlands, forming shallow lagoons, elongation of barrier spits from the erosion of headlands due to the action of longshore currents, with the spits growing in the direction of the littoral drift.
Barrier beaches form in shallow water and are parallel to the shoreline, resulting in long, narrow estuaries. The average water depth is less than 5 m, exceeds 10 m. Examples of bar-built estuaries are Barnegat Bay, New Jersey. Fjords were formed where pleistocene glaciers deepened and widened existing river valleys so that they become U-shaped in cross s
The Valencian Community is an autonomous community of Spain. It is the fourth most populous autonomous community after Andalusia and Madrid with more than 4.9 million inhabitants. Its homonymous capital Valencia is metropolitan area in Spain, it is located along the Mediterranean coast on the east side of the Iberian peninsula. It borders with Catalonia to the north and Castilla–La Mancha to the west, Murcia to the south; the Valencian Community consists of three provinces which are Valencia and Alicante. According to its Statute of Autonomy, the Valencian people are a nationality, their origins date back to the Aragonese reconquest of the Moorish Taifa of Valencia, taken by James I of Aragon in 1238 during the Reconquista. The newly founded Kingdom of Valencia was granted wide self-government under the Crown of Aragon. Valencia experienced its golden age in the 15th century. Self-government continued after the unification of the Spanish Kingdom, but was suspended in 1707 by Phillip V of Spain as a result of the Spanish War of Succession.
Valencian nationalism resurged towards the end of the 19th century, which led to the modern conception of the Valencian Country. Self-government under the Generalitat Valenciana was reestablished in 1982 after Spanish transition to democracy. Many Valencian people speak Valencian, the region's own co-official language, a southwestern dialect of Catalan standardised by the Acadèmia Valenciana de la Llengua. Valencian is a diglossic language, repressed during Franco's dictatorship in favour of Spanish. Since it regained official status in 1982 in the Valencian Estatut d'Autonomia. Valencian has been implemented in public administration and the education system leading to an exponential increase in knowledge of its formal standard. Valencian is understood by more than half of the population living within the Valencian Community. Valencia was founded by the Romans under the name of "Valentia Edetanorum", which translates to'Valiance of the Land of the Lamb'. With the establishment of the Taifa of Valencia, the name developed to بلنسية, which became Valencia after the expulsion of the Moors.
"Valencian Community" is the standard translation of the official name in Valencian recognized by the Statute of Autonomy of 1982. This is the name most used in public administration, the media and Spanish written language. However, the variant of "Valencian Country" that emphasizes the nationality status of the Valencian people is still the preferred one by left-wing parties, civil associations, Catalan written language and major academic institutions like the University of Valencia. "Valencian Community" is a neologism, adopted after democratic transition in order to solve the conflict between two competing names: "Valencian Country" and "Former Kingdom of Valencia". On one hand, "Valencian Country" represented the modern conception of nationality that resurged in the 19th century, it became well-established during the Second Spanish Republic and on with the works of Joan Fuster in the 1960s, implying the existence of the "Catalan Countries". This nationalist subtext was opposed by anti-Catalan blaverists, who proposed "Former Kingdom of Valencia" instead in order to emphasize Valencian independence from Catalonia.
Blaverists have accepted the official denomination. The autonomous community can be homonymously identified with its capital "Valencia". However, this could be disregarding of the provinces of Castellón. Other more anecdotal translations have included "Land of Valencia", "Region of Valencia" and "Valencian Region"; the term "Region", carries negative connotations among many Valencians because it could deny their nationality status. The Pre-Roman autochthonous people of the Valencian Community were the Iberians, who were divided in several groups; the Greeks established colonies in the coastal towns of Saguntum and Dénia beginning in the 5th century BC, where they traded and mixed with the local Iberian populations. After the end of the First Punic War between Carthage and Rome in 241 BC, which established their limits of influence in the Ebro river, the Carthaginians occupied the whole region; the dispute over the hegemony of Saguntum, a Hellenized Iberian coastal city with diplomatic contacts with Rome, destroyed by Hannibal in 219 BC, ignited the Second Punic War, which ended with the incorporation of the region to the Roman Empire.
The Romans founded the city of Valentia in 138 BC, over the centuries overtook Saguntum in importance. After the Fall of the Western Roman Empire, during the Barbarian Invasions in the 5th century AD, the region was first invaded by the Alans and ruled by the Visigoths, until the arrival of the Arabs in 711, which left a broad impact in the region, still visible in today's Valencian landscape and culture. After the fall of the Caliphate of Cordoba, two main independent taifas were established at the region, Balansiya and Dénia, along with the small and short living taifas of Orihuela, Alpuente, Jérica and Sagunt and the short Christian conquest of Valencia by El Cid. However, the origins of present-day Valencia date back to the Kingdom of Valencia, which came into existence in the 13th century. James I of Aragon led the Christian conquest and colonization of the existing Islamic taifas with Aragonese and Catalan colonizers in 1208; the kingdom developed intensively in the 14th and 15th centuries, which are con
Headlands and bays
Both headland and bay are two coastal features that are related and found on the same coastline. A bay is a body of water—usually seawater and sometimes fresh water— surrounded by land, whereas a headland is surrounded by water on three sides. Headlands are characterized by rocky shores, intense erosion and steep sea cliffs. Bays have less wave activity and have sandy beaches. Headlands and bays form on discordant coastlines, where the land consists of bands of rock of alternating resistance that run perpendicular to the coast. Bays form where less resistant rocks, such as sands and clays, are eroded, leaving bands of stronger, or more resistant rocks, which form a headland or peninsula. Refraction of waves occurs on headlands concentrating wave energy on them, so many other landforms, such as caves, natural arches, stacks, form on headlands. Wave energy is directed at right angles to the wave crest, lines drawn at right angles to the wave crest represent the direction of energy expenditure. Orthogonals converge on headlands and diverge in bays, which concentrates wave energy on the headlands and dissipates wave energy in the bays.
In the formation of sea cliffs, wave erosion undercuts the slopes at the shoreline, which retreat landward. This accelerates mass movement; the debris from these landslides collects at the base of the cliff and is removed by the waves during storms, when wave energy is greatest. This debris provides sediment, transported through longshore current for the nearby bay. Joints in the headlands are eroded back to form caves; these gaps collapse and leave tall stacks at the ends of the headlands. These too are eroded by the waves. Wave refraction disperses wave energy through the bay, along with the sheltering effect of the headlands, this protects bays from storms; this effect means that the waves reaching the shore in a bay are weaker than the waves reaching the headland, the bay is thus a safer place for water activities like surfing or swimming. Through the deposition of sediment within the bay and the erosion of the headlands, coastlines straighten out, but the same process starts all over again.
A beach is a dynamic geologic feature that can fluctuate between advancement and retreat of sediment. The natural agents of fluctuation include waves, tides and winds. Man-made elements such as the interruption of sediment supply, such as a dam, withdrawal of fluid can affect beach stabilization. Static equilibrium refers to a beach, stable and experiences neither littoral drift nor sediment deposition nor erosion. Waves diffract around the headland and near the beach when the beach is in a state of static equilibrium. Dynamic equilibrium occurs when the beach sediments are deposited and eroded at equal rates. Beaches that have dynamic equilibrium are near a river that supplies sediment and would otherwise erode away without the river supply. Unstable beaches are a result of human interaction, such as a breakwater or dammed river. Unstable beaches are reshaped by continual erosion or deposition and will continue to erode or deposit until a state of equilibrium is reached in the bay. GeoResources - diagrams of headland and bay formation