Oldfield Estuary is an estuary in the Goldfields-Esperance region of Western Australia .
75-471: The estuary has a length of 3 kilometres (2 mi) and is no wider than 600 metres (1,969 ft) with a total area of approximately 1 square kilometre (0 sq mi). The estuary has a main basin area of about 0.5 square kilometres (0 sq mi) and the rest is flood and tidal delta . The Oldfield River and the Munglinup River both discharge into the estuary. Uncleared bushland surrounds
150-432: A density current that deposits its sediments as turbidites . When the river water is less dense than the basin water, as is typical of river deltas on an ocean coastline, the delta is characterized by hypopycnal flow in which the river water is slow to mix with the denser basin water and spreads out as a surface fan. This allows fine sediments to be carried a considerable distance before settling out of suspension. Beds in
225-485: A common location for civilizations to flourish due to access to flat land for farming, freshwater for sanitation and irrigation , and sea access for trade. Deltas often host extensive industrial and commercial activities, and agricultural land is frequently in conflict. Some of the world's largest regional economies are located on deltas such as the Pearl River Delta , Yangtze River Delta , European Low Countries and
300-520: A date can be assigned is his reference to the death in AD ;23 of Juba II , king of Maurousia ( Mauretania ), who is said to have died "just recently". He probably worked on the Geography for many years and revised it steadily, but not always consistently. It is an encyclopaedic chronicle and consists of political, economic, social, cultural, and geographic descriptions covering almost all of Europe and
375-537: A delta but enter into the sea in the form of an estuary . Notable examples include the Gulf of Saint Lawrence and the Tagus estuary. In rare cases, the river delta is located inside a large valley and is called an inverted river delta . Sometimes a river divides into multiple branches in an inland area, only to rejoin and continue to the sea. Such an area is called an inland delta , and often occurs on former lake beds. The term
450-728: A descriptive history of people and places from different regions of the world known during his lifetime. Although the Geographica was rarely used by contemporary writers, a multitude of copies survived throughout the Byzantine Empire . It first appeared in Western Europe in Rome as a Latin translation issued around 1469. The first printed edition was published in 1516 in Venice . Isaac Casaubon , classical scholar and editor of Greek texts, provided
525-533: A fan. The more often the flow changes course, the shape develops closer to an ideal fan because more rapid changes in channel position result in a more uniform deposition of sediment on the delta front. The Mississippi and Ural River deltas, with their bird's feet, are examples of rivers that do not avulse often enough to form a symmetrical fan shape. Alluvial fan deltas, as seen by their name, avulse frequently and more closely approximate an ideal fan shape. Most large river deltas discharge to intra-cratonic basins on
600-399: A few main distributaries. Once a wave-dominated or river-dominated distributary silts up, it is abandoned, and a new channel forms elsewhere. In a tidal delta, new distributaries are formed during times when there is a lot of water around – such as floods or storm surges . These distributaries slowly silt up at a more or less constant rate until they fizzle out. A tidal freshwater delta is
675-535: A flat arid area splits into channels that evaporate as it progresses into the desert. The Okavango Delta in Botswana is one example. See endorheic basin . The generic term mega delta can be used to describe very large Asian river deltas, such as the Yangtze , Pearl , Red , Mekong , Irrawaddy , Ganges-Brahmaputra , and Indus . The formation of a delta is complicated, multiple, and cross-cutting over time, but in
750-573: A hypocynal delta dip at a very shallow angle, around 1 degree. Fluvial-dominated deltas are further distinguished by the relative importance of the inertia of rapidly flowing water, the importance of turbulent bed friction beyond the river mouth, and buoyancy . Outflow dominated by inertia tends to form Gilbert-type deltas. Outflow dominated by turbulent friction is prone to channel bifurcation, while buoyancy-dominated outflow produces long distributaries with narrow subaqueous natural levees and few channel bifurcations. The modern Mississippi River delta
825-439: A mature delta with a distributary network. Another way these distributary networks form is from the deposition of mouth bars (mid-channel sand and/or gravel bars at the mouth of a river). When this mid-channel bar is deposited at the mouth of a river, the flow is routed around it. This results in additional deposition on the upstream end of the mouth bar, which splits the river into two distributary channels. A good example of
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#1733093080602900-423: A sedimentary deposit formed at the boundary between an upland stream and an estuary, in the region known as the "subestuary". Drowned coastal river valleys that were inundated by rising sea levels during the late Pleistocene and subsequent Holocene tend to have dendritic estuaries with many feeder tributaries. Each tributary mimics this salinity gradient from its brackish junction with the mainstem estuary up to
975-447: A simple delta three main types of bedding may be distinguished: the bottomset beds, foreset/frontset beds, and topset beds. This three-part structure may be seen on small scale by crossbedding . Human activities in both deltas and the river basins upstream of deltas can radically alter delta environments. Upstream land use change such as anti-erosion agricultural practices and hydrological engineering such as dam construction in
1050-487: A valuable source of information on the ancient world of his day, especially when this information is corroborated by other sources. He travelled extensively, as he says: "Westward I have journeyed to the parts of Etruria opposite Sardinia; towards the south from the Euxine [Black Sea] to the borders of Ethiopia; and perhaps not one of those who have written geographies has visited more places than I have between those limits." It
1125-518: A very rocky mountain, called the Trojan mountain; beneath it there are caves, and near the caves and the river a village called Troy, an ancient settlement of the captive Trojans who had accompanied Menelaus and settled there. Strabo commented on volcanism ( effusive eruption ) which he observed at Katakekaumene (modern Kula , Western Turkey). Strabo's observations predated Pliny the Younger who witnessed
1200-569: Is "... pro-Roman throughout the Geography. But while he acknowledges and even praises Roman ascendancy in the political and military sphere, he also makes a significant effort to establish Greek primacy over Rome in other contexts." In Europe , Strabo was the first to connect the Danube (which he called Danouios) and the Istros – with the change of names occurring at "the cataracts," the modern Iron Gates on
1275-542: Is a good example of a fluvial-dominated delta whose outflow is buoyancy-dominated. Channel abandonment has been frequent, with seven distinct channels active over the last 5000 years. Other fluvial-dominated deltas include the Mackenzie delta and the Alta delta. A Gilbert delta (named after Grove Karl Gilbert ) is a type of fluvial-dominated delta formed from coarse sediments, as opposed to gently sloping muddy deltas such as that of
1350-460: Is a major sign that Mars once had large amounts of water. Deltas have been found over a wide geographical range. Below are pictures of a few. Strabo Strabo ( / ˈ s t r eɪ b oʊ / ; Greek : Στράβων Strábōn ; 64 or 63 BC – c. 24 AD ) was a Greek geographer , philosopher , and historian who lived in Asia Minor during the transitional period of
1425-576: Is called by the Ionians ", including describing the outflow of silt into the sea and the convexly curved seaward side of the triangle. Despite making comparisons to other river systems deltas, Herodotus did not describe them as "deltas". The Greek historian Polybius likened the land between the Rhône and Isère rivers to the Nile Delta, referring to both as islands, but did not apply the word delta. According to
1500-484: Is not known when he wrote Geographica , but he spent much time in the famous library in Alexandria taking notes from "the works of his predecessors". A first edition was published in 7 BC and a final edition no later than 23 AD, in what may have been the last year of Strabo's life. It took some time for Geographica to be recognized by scholars and to become a standard. Alexandria itself features extensively in
1575-431: Is proper,' he observes in continuation, ' to derive our explanations from things which are obvious, and in some measure of daily occurrences, such as deluges, earthquakes, volcanic eruptions, and sudden swellings of the land beneath the sea; for the last raise up the sea also, and when the same lands subside again, they occasion the sea to be let down. And it is not merely the small, but the large islands also, and not merely
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#17330930806021650-538: Is so named because the shape of the Nile Delta approximates the triangular uppercase Greek letter delta . The triangular shape of the Nile Delta was known to audiences of classical Athenian drama ; the tragedy Prometheus Bound by Aeschylus refers to it as the "triangular Nilotic land", though not as a "delta". Herodotus 's description of Egypt in his Histories mentions the Delta fourteen times, as "the Delta, as it
1725-641: The Greater Tokyo Area . The Ganges–Brahmaputra Delta , which spans most of Bangladesh and West Bengal and empties into the Bay of Bengal , is the world's largest delta. The Selenga River delta in the Russian republic of Buryatia is the largest delta emptying into a body of fresh water, in its case Lake Baikal . Researchers have found a number of examples of deltas that formed in Martian lakes . Finding deltas
1800-526: The Nile Delta and Colorado River Delta are some of the most extreme examples of the devastation caused to deltas by damming and diversion of water. Historical data documents show that during the Roman Empire and Little Ice Age (times when there was considerable anthropogenic pressure), there was significant sediment accumulation in deltas. The industrial revolution has only amplified the impact of humans on delta growth and retreat. Ancient deltas benefit
1875-698: The Roman Republic into the Roman Empire . He is best known for his work Geographica ("Geography"), which presented a descriptive history of people and places from different regions of the world known during his lifetime. Additionally, Strabo authored historical works, but only fragments and quotations of these survive in the writings of other authors. Strabo was born to an affluent family from Amaseia in Pontus (in present-day Cappadocia ) in around 64 BC. His family had been involved in politics since at least
1950-544: The Aegean Sea. Around 25 BC, he sailed up the Nile until he reached Philae , after which point there is little record of his travels until AD 17. It is not known precisely when Strabo's Geography was written, though comments within the work itself place the finished version within the reign of Emperor Tiberius . Some place its first drafts around 7 BC, others around AD 17 or AD 18. The latest passage to which
2025-514: The Aristotelian Xenarchus and Tyrannion who preceded him in teaching Strabo, Athenodorus was a Stoic and almost certainly the source of Strabo's diversion from the philosophy of his former mentors. Moreover, from his own first-hand experience, Athenodorus provided Strabo with information about regions of the empire which Strabo would not otherwise have known about. Strabo is best known for his work Geographica ("Geography"), which presented
2100-552: The Euxine [Black Sea] was so great, that its bed must be gradually raised, while the rivers still continued to pour in an undiminished quantity of water. He therefore conceived that, originally, when the Euxine was an inland sea, its level had by this means become so much elevated that it burst its barrier near Byzantium, and formed a communication with the Propontis [Sea of Marmara], and this partial drainage had already, he supposed, converted
2175-678: The Greek geographer Strabo , the Cynic philosopher Onesicritus of Astypalaea , who accompanied Alexander the Great 's conquests in India , reported that Patalene (the delta of the Indus River ) was "a delta" ( Koinē Greek : καλεῖ δὲ τὴν νῆσον δέλτα , romanized: kalei de tēn nēson délta , lit. 'he calls the island a delta'). The Roman author Arrian 's Indica states that "the delta of
2250-474: The Mediterranean and Near East, especially for scholarly purposes, was popular during this era and was facilitated by the relative peace enjoyed throughout the reign of Augustus (27 BC – AD 14). He moved to Rome in 44 BC, and stayed there, studying and writing, until at least 31 BC. In 29 BC, on his way to Corinth (where Augustus was at the time), he visited the island of Gyaros in
2325-592: The Mediterranean: Britain and Ireland, the Iberian Peninsula, Gaul, Germania, the Alps, Italy, Greece, Northern Black Sea region, Anatolia, Middle East, Central Asia and North Africa. The Geography is the only extant work providing information about both Greek and Roman peoples and countries during the reign of Augustus. On the presumption that "recently" means within a year, Strabo stopped writing that year or
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2400-497: The Mississippi. For example, a mountain river depositing sediment into a freshwater lake would form this kind of delta. It is commonly a result of homopycnal flow. Such deltas are characterized by a tripartite structure of topset, foreset, and bottomset beds. River water entering the lake rapidly deposits its coarser sediments on the submerged face of the delta, forming steeping dipping foreset beds. The finer sediments are deposited on
2475-649: The Romanian/Serbian border. In India , a country he never visited, Strabo described small flying reptiles that were long with snake-like bodies and bat-like wings (this description matches the Indian flying lizard Draco dussumieri ), winged scorpions, and other mythical creatures along with those that were actually factual. Other historians, such as Herodotus , Aristotle , and Flavius Josephus , mentioned similar creatures. Charles Lyell , in his Principles of Geology , wrote of Strabo: He notices, amongst others,
2550-472: The ability to pile up and accumulate due to the sediment traveling into a steep subduction trench rather than a shallow continental shelf . There are many other lesser factors that could explain why the majority of river deltas form along passive margins rather than active margins. Along active margins, orogenic sequences cause tectonic activity to form over-steepened slopes, brecciated rocks, and volcanic activity resulting in delta formation to exist closer to
2625-514: The age of 21, Strabo moved to Rome, where he studied philosophy with the Peripatetic Xenarchus , a highly respected tutor in Augustus's court. Despite Xenarchus's Aristotelian leanings, Strabo later gives evidence to have formed his own Stoic inclinations. In Rome, he also learned grammar under the rich and famous scholar Tyrannion of Amisus . Although Tyrannion was also a Peripatetic, he
2700-1256: The basins feeding deltas have reduced river sediment delivery to many deltas in recent decades. This change means that there is less sediment available to maintain delta landforms, and compensate for erosion and sea level rise , causing some deltas to start losing land. Declines in river sediment delivery are projected to continue in the coming decades. The extensive anthropogenic activities in deltas also interfere with geomorphological and ecological delta processes. People living on deltas often construct flood defences which prevent sedimentation from floods on deltas, and therefore means that sediment deposition can not compensate for subsidence and erosion . In addition to interference with delta aggradation , pumping of groundwater , oil , and gas , and constructing infrastructure all accelerate subsidence , increasing relative sea level rise. Anthropogenic activities can also destabilise river channels through sand mining , and cause saltwater intrusion . There are small-scale efforts to correct these issues, improve delta environments and increase environmental sustainability through sedimentation enhancing strategies . While nearly all deltas have been impacted to some degree by humans,
2775-422: The bird's-foot of the Mississippi or Ural river deltas), pushing its mouth into the standing water. As the deltaic lobe advances, the gradient of the river channel becomes lower because the river channel is longer but has the same change in elevation (see slope ). As the gradient of the river channel decreases, the amount of shear stress on the bed decreases, which results in the deposition of sediment within
2850-450: The channel and a rise in the channel bed relative to the floodplain . This destabilizes the river channel. If the river breaches its natural levees (such as during a flood), it spills out into a new course with a shorter route to the ocean, thereby obtaining a steeper, more stable gradient. Typically, when the river switches channels in this manner, some of its flow remains in the abandoned channel. Repeated channel-switching events build up
2925-612: The economy due to their well-sorted sand and gravel . Sand and gravel are often quarried from these old deltas and used in concrete for highways , buildings, sidewalks, and landscaping. More than 1 billion tons of sand and gravel are produced in the United States alone. Not all sand and gravel quarries are former deltas, but for ones that are, much of the sorting is already done by the power of water. Urban areas and human habitation tend to be located in lowlands near water access for transportation and sanitation . This makes deltas
3000-574: The eruption of Mount Vesuvius on 24 August AD 79 in Pompeii : …There are no trees here, but only the vineyards where they produce the Katakekaumene wines which are by no means inferior from any of the wines famous for their quality. The soil is covered with ashes, and black in colour as if the mountainous and rocky country was made up of fires. Some assume that these ashes were the result of thunderbolts and subterranean explosions, and do not doubt that
3075-478: The estuary are saline and heavily tannin-stained . 33°52′59″S 120°47′22″E / 33.88306°S 120.78944°E / -33.88306; 120.78944 This article about a location in Western Australia is a stub . You can help Misplaced Pages by expanding it . River delta A river delta is a triangular landform created by the deposition of the sediments that are carried by
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3150-466: The estuary which has high dunes to the east and low sediments to the west. The lagoon is filled with river sediment to the north and beach sand to the south with a long high sandbar that breaks every three to four years. The estuary functions primarily as a result of wave energy. The seagrass Ruppia megacarpa is found in the estuary. The catchment area of the estuary is 30% natural vegetation and 70% cleared for cropping and pasture. The waters of
3225-531: The explanation of Xanthus the Lydian, who said that the seas had once been more extensive, and that they had afterwards been partially dried up, as in his own time many lakes, rivers, and wells in Asia had failed during a season of drought. Treating this conjecture with merited disregard, Strabo passes on to the hypothesis of Strato , the natural philosopher, who had observed that the quantity of mud brought down by rivers into
3300-459: The family's support for Rome might have affected their position in the local community, and whether they might have been granted Roman citizenship as a reward. Strabo's life was characterized by extensive travels. He journeyed to Egypt and Kush , as far west as coastal Tuscany and as far south as Ethiopia in addition to his travels in Asia Minor and the time he spent in Rome . Travel throughout
3375-448: The first critical edition in 1587. Although Strabo cited the classical Greek astronomers Eratosthenes and Hipparchus , acknowledging their astronomical and mathematical efforts covering geography, he claimed that a descriptive approach was more practical, such that his works were designed for statesmen who were more anthropologically than numerically concerned with the character of countries and regions. As such, Geographica provides
3450-414: The flow enters the standing water, it is no longer confined to its channel and expands in width. This flow expansion results in a decrease in the flow velocity , which diminishes the ability of the flow to transport sediment . As a result, sediment drops out of the flow and is deposited as alluvium , which builds up to form the river delta. Over time, this single channel builds a deltaic lobe (such as
3525-506: The fresh stream feeding the head of tidal propagation. As a result, the tributaries are considered to be "subestuaries". The origin and evolution of a tidal freshwater delta involves processes that are typical of all deltas as well as processes that are unique to the tidal freshwater setting. The combination of processes that create a tidal freshwater delta result in a distinct morphology and unique environmental characteristics. Many tidal freshwater deltas that exist today are directly caused by
3600-466: The geomorphology and ecosystem. Deltas are typically classified according to the main control on deposition, which is a combination of river, wave , and tidal processes, depending on the strength of each. The other two factors that play a major role are landscape position and the grain size distribution of the source sediment entering the delta from the river. Fluvial-dominated deltas are found in areas of low tidal range and low wave energy. Where
3675-412: The islands, but the continents, which can be lifted up together with the sea; and both large and small tracts may subside, for habitations and cities, like Bure, Bizona, and many others, have been engulfed by earthquakes.' Strabo commented on fossil formation mentioning Nummulite (quoted from Celâl Şengör ): One extraordinary thing which I saw at the pyramids must not be omitted. Heaps of stones from
3750-406: The lake bottom beyond this steep slope as more gently dipping bottomset beds. Behind the delta front, braided channels deposit the gently dipping beds of the topset on the delta plain. While some authors describe both lacustrine and marine locations of Gilbert deltas, others note that their formation is more characteristic of the freshwater lakes, where it is easier for the river water to mix with
3825-586: The lakewater faster (as opposed to the case of a river falling into the sea or a salt lake, where less dense fresh water brought by the river stays on top longer). Gilbert himself first described this type of delta on Lake Bonneville in 1885. Elsewhere, similar structures occur, for example, at the mouths of several creeks that flow into Okanagan Lake in British Columbia and form prominent peninsulas at Naramata , Summerland , and Peachland . In wave-dominated deltas, wave-driven sediment transport controls
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#17330930806023900-566: The land of the Indians is made by the Indus river no less than is the case with that of Egypt". As a generic term for the landform at the mouth of the river, the word delta is first attested in the English-speaking world in the late 18th century, in the work of Edward Gibbon . River deltas form when a river carrying sediment reaches a body of water, such as a lake, ocean, or a reservoir . When
3975-464: The last book of Geographica , which describes it as a thriving port city with a highly developed local economy. Strabo notes the city's many beautiful public parks, and its network of streets wide enough for chariots and horsemen. "Two of these are exceeding broad, over a plethron in breadth, and cut one another at right angles ... All the buildings are connected one with another, and these also with what are beyond it." Lawrence Kim observes that Strabo
4050-672: The left side into marshy ground, and that, at last, the whole would be choked up with soil. So, it was argued, the Mediterranean had once opened a passage for itself by the Columns of Hercules into the Atlantic, and perhaps the abundance of sea-shells in Africa, near the Temple of Jupiter Ammon , might also be the deposit of some former inland sea, which had at length forced a passage and escaped. But Strabo rejects this theory as insufficient to account for all
4125-458: The legendary story of Typhon takes place in this region. Ksanthos adds that the king of this region was a man called Arimus. However, it is not reasonable to accept that the whole country was burned down at a time as a result of such an event rather than as a result of a fire bursting from underground whose source has now died out. Three pits are called "Physas" and separated by forty stadia from each other. Above these pits, there are hills formed by
4200-518: The next (AD 24), at which time he is thought to have died. He was influenced by Homer , Hecataeus and Aristotle . The first of Strabo's major works, Historical Sketches ( Historica hypomnemata ), written while he was in Rome ( c. 20 BC ), is nearly completely lost. Meant to cover the history of the known world from the conquest of Greece by the Romans, Strabo quotes it himself and other classical authors mention that it existed, although
4275-542: The only surviving document is a fragment of papyrus now in the possession of the University of Milan (renumbered [Papyrus] 46). Strabo studied under several prominent teachers of various specialities throughout his early life at different stops during his Mediterranean travels. The first chapter of his education took place in Nysa (modern Sultanhisar , Turkey) under the master of rhetoric Aristodemus , who had formerly taught
4350-524: The onset of or changes in historical land use, especially deforestation , intensive agriculture , and urbanization . These ideas are well illustrated by the many tidal freshwater deltas prograding into Chesapeake Bay along the east coastline of the United States. Research has demonstrated that the accumulating sediments in this estuary derive from post-European settlement deforestation, agriculture, and urban development. Other rivers, particularly those on coasts with significant tidal range , do not form
4425-401: The phenomena, and he proposes one of his own, the profoundness of which modern geologists are only beginning to appreciate. 'It is not,' he says, 'because the lands covered by seas were originally at different altitudes, that the waters have risen, or subsided, or receded from some parts and inundated others. But the reason is, that the same land is sometimes raised up and sometimes depressed, and
4500-417: The quarries lie in front of the pyramids. Among these are found pieces which in shape and size resemble lentils. Some contain substances like grains half peeled. These, it is said, are the remnants of the workmen's food converted into stone; which is not probable. For at home in our country (Amaseia), there is a long hill in a plain, which abounds with pebbles of a porous stone, resembling lentils. The pebbles of
4575-642: The reign of Mithridates V . Strabo was related to Dorylaeus on his mother's side. Several other family members, including his paternal grandfather, had served Mithridates VI during the Mithridatic Wars . As the war drew to a close, Strabo's grandfather had turned several Pontic fortresses over to the Romans. Strabo wrote that "great promises were made in exchange for these services", and as Persian culture endured in Amaseia even after Mithridates and Tigranes were defeated, scholars have speculated about how
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#17330930806024650-480: The result of this process is the Wax Lake Delta . In both of these cases, depositional processes force redistribution of deposition from areas of high deposition to areas of low deposition. This results in the smoothing of the planform (or map-view) shape of the delta as the channels move across its surface and deposit sediment. Because the sediment is laid down in this fashion, the shape of these deltas approximates
4725-573: The river delta, causing the delta to retreat. For deltas that form further upriver in an estuary, there are complex yet quantifiable linkages between winds, tides, river discharge, and delta water levels. Erosion is also an important control in tide-dominated deltas, such as the Ganges Delta , which may be mainly submarine, with prominent sandbars and ridges. This tends to produce a "dendritic" structure. Tidal deltas behave differently from river-dominated and wave-dominated deltas, which tend to have
4800-414: The river water is nearly equal in density to the basin water, the delta is characterized by homopycnal flow , in which the river water rapidly mixes with basin water and abruptly dumps most of its sediment load. Where the river water has a higher density than basin water, typically from a heavy load of sediment, the delta is characterized by hyperpycnal flow in which the river water hugs the basin bottom as
4875-401: The sea also is simultaneously raised and depressed so that it either overflows or returns into its own place again. We must, therefore, ascribe the cause to the ground, either to that ground which is under the sea, or to that which becomes flooded by it, but rather to that which lies beneath the sea, for this is more moveable, and, on account of its humidity, can be altered with great celerity. It
4950-449: The sea-shore and of rivers suggest somewhat of the same difficulty [respecting their origin]; some explanation may indeed be found in the motion [to which these are subject] in flowing waters, but the investigation of the above fact presents more difficulty. I have said elsewhere, that in sight of the pyramids, on the other side in Arabia, and near the stone quarries from which they are built, is
5025-399: The sediment is never piled up in thick sequences due to the sediment traveling and depositing in deep subduction trenches. At the mouth of a river, the change in flow conditions can cause the river to drop any sediment it is carrying. This sediment deposition can generate a variety of landforms, such as deltas, sand bars, spits, and tie channels. Landforms at the river mouth drastically alter
5100-514: The sediment source. When sediment does not travel far from the source, sediments that build up are coarser grained and more loosely consolidated, therefore making delta formation more difficult. Tectonic activity on active margins causes the formation of river deltas to form closer to the sediment source which may affect channel avulsion , delta lobe switching, and auto cyclicity. Active margin river deltas tend to be much smaller and less abundant but may transport similar amounts of sediment. However,
5175-424: The shape of the delta, and much of the sediment emanating from the river mouth is deflected along the coastline. The relationship between waves and river deltas is quite variable and largely influenced by the deepwater wave regimes of the receiving basin. With a high wave energy near shore and a steeper slope offshore, waves will make river deltas smoother. Waves can also be responsible for carrying sediments away from
5250-610: The sons of the Roman general who had taken over Pontus. Aristodemus was the head of two schools of rhetoric and grammar, one in Nysa and one in Rhodes . The school in Nysa possessed a distinct intellectual curiosity in Homeric literature and the interpretation of the ancient Greek epics. Strabo was an admirer of Homer 's poetry, perhaps as a consequence of his time spent in Nysa with Aristodemus. At around
5325-650: The trailing edges of passive margins due to the majority of large rivers such as the Mississippi , Nile , Amazon , Ganges , Indus , Yangtze , and Yellow River discharging along passive continental margins. This phenomenon is due mainly to three factors: topography , basin area, and basin elevation. Topography along passive margins tend to be more gradual and widespread over a greater area enabling sediment to pile up and accumulate over time to form large river deltas. Topography along active margins tends to be steeper and less widespread, which results in sediments not having
5400-718: The triangular shape (Δ) of the uppercase Greek letter delta . In hydrology , the dimensions of a river delta are determined by the balance between the watershed processes that supply sediment and the watershed processes that redistribute, sequester, and export the supplied sediment into the receiving basin. River deltas are important in human civilization , as they are major agricultural production centers and population centers. They can provide coastline defence and can impact drinking water supply. They are also ecologically important, with different species' assemblages depending on their landscape position. On geologic timescales , they are also important carbon sinks . A river delta
5475-426: The waters of a river , where the river merges with a body of slow-moving water or with a body of stagnant water. The creation of a river delta occurs at the river mouth , where the river merges into an ocean , a sea , or an estuary , into a lake , a reservoir , or (more rarely) into another river that cannot carry away the sediment supplied by the feeding river. Etymologically, the term river delta derives from
5550-713: Was first coined by Alexander von Humboldt for the middle reaches of the Orinoco River , which he visited in 1800. Other prominent examples include the Inner Niger Delta , Peace–Athabasca Delta , the Sacramento–San Joaquin River Delta , and the Sistan delta of Iran. The Danube has one in the valley on the Slovak–Hungarian border between Bratislava and Iža . In some cases, a river flowing into
5625-400: Was more relevantly a respected authority on geography, a fact of some significance considering Strabo's future contributions to the field. The final noteworthy mentor to Strabo was Athenodorus Cananites , a philosopher who had spent his life since 44 BC in Rome forging relationships with the Roman elite. Athenodorus passed onto Strabo his philosophy, his knowledge and his contacts. Unlike
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