Kikori is a small town in the Gulf Province of Papua New Guinea .
88-571: Kikori lies in the delta of the Kikori River at the head of the Gulf of Papua . This area is particularly biologically rich with a diversity of ecosystems and densely forested, with an intricate system of rivers. The geography is that of limestone karst country, with clay type soils. Oil exploitation in Kikori has been operating for several years. Its first commercial oil deposits were found there by
176-432: 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
264-700: A numerical system , called "the Polybius square ," mentioned in Hist. X.45.6 ff. . This idea also lends itself to cryptographic manipulation and steganography . Modern implementations of the Polybius square, at least in Western European languages such as English , Spanish , French , German and Italian , generally use the Roman alphabet in which those languages are written. However, Polybius himself
352-412: 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
440-669: A universal history documenting the rise of Rome in the Mediterranean in the third and second centuries BC. It covered the period of 264–146 BC, recording in detail events in Italy, Iberia, Greece, Macedonia, Syria, Egypt and Africa, and documented the Punic Wars and Macedonian Wars among many others. Polybius's Histories is important not only for being the only Hellenistic historical work to survive in any substantial form, but also for its analysis of constitutional change and
528-616: A certain hagiographic tone when writing of his friends, such as Scipio, and subject to a vindictive tone when detailing the exploits of his enemies, such as Callicrates, the Achaean statesman responsible for his Roman exile. As a hostage in Rome, then as client to the Scipios, and after 146 BC, a collaborator with Roman rule, Polybius was probably in no position to freely express any negative opinions of Rome. Peter Green advises that Polybius
616-493: 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
704-495: 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
792-533: 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
880-399: 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
968-545: 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
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#17327837181541056-529: A historian. According to Edward Tufte , he was also a major source for Charles Joseph Minard 's figurative map of Hannibal 's overland journey into Italy during the Second Punic War . In his Meditations On Hunting , Spanish philosopher José Ortega y Gasset calls Polybius "one of the few great minds that the turbid human species has managed to produce", and says the damage to the Histories
1144-573: 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
1232-605: A long commentary of his Histories and a biography. Polybius was a close friend and mentor to Scipio Africanus the Younger , and had a lasting influence on his decision-making and life. Polybius was born around 198 BC in Megalopolis , Arcadia , when it was an active member of the Achaean League . The town was revived, along with other Achaean states, a century before he was born. Polybius's father, Lycortas ,
1320-439: 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
1408-423: 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
1496-447: 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
1584-558: Is a universal history which describes and explains the rise of the Roman Republic as a global power in the ancient Mediterranean world . The work documents in detail political and military affairs across the Hellenistic Mediterranean between 264 and 146 BC, and in its later books includes eyewitness accounts of the sack of Carthage and Corinth in 146 BC, and the Roman annexation of mainland Greece after
1672-551: 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
1760-419: 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. Polybius Polybius ( / p ə ˈ l ɪ b i ə s / ; ‹See Tfd› Greek : Πολύβιος , Polýbios ; c. 200 – c. 118 BC ) was a Greek historian of the middle Hellenistic period . He is noted for his work The Histories ,
1848-591: 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
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#17327837181541936-485: Is considered by some to be the successor of Thucydides in terms of objectivity and critical reasoning , and the forefather of scholarly, painstaking historical research in the modern scientific sense. According to this view, his work sets forth the course of history's occurrences with clearness, penetration, sound judgment, and, among the circumstances affecting the outcomes, he lays special emphasis on geographical conditions. Modern historians are especially impressed with
2024-549: Is exemplified in that of Philip II , who Polybius believed exhibited both excellent military prowess and skill, as well as proficient ability in diplomacy and moral leadership. His beliefs about Philip's character led Polybius to reject the historian Theopompus ' description of Philip's private, drunken debauchery. For Polybius, it was inconceivable that such an able and effective statesman could have had an immoral and unrestrained private life as described by Theopompus. The consequences of bad leadership are also highlighted throughout
2112-634: Is lost as well. Another missing work was a historical monograph on the events of the Numantine War . The largest Polybian work was, of course, his Histories , of which only the first five books survive entirely intact, along with a large portion of the sixth book and fragments of the rest. Along with Cato the Elder (234–149 BC), he can be considered one of the founding fathers of Roman historiography . Livy made reference to and uses Polybius's Histories as source material in his own narrative. Polybius
2200-548: 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
2288-578: The Achaean War . While Polybius's Histories covers the period from 264 BC to 146 BC, it mainly focuses on the years 221 BC to 146 BC, detailing Rome's rise to supremacy in the Mediterranean by overcoming their geopolitical rivals: Carthage, Macedonia, and the Seleucid empire. Books I-II are The Histories ' introduction, describing events in Italy and Greece before 221/0 BC, including
2376-603: The First Punic War , Rome's wars with the Gauls, the rise of the Achaean League (Polybius's own constitution), and the re-establishment of Macedonian power in Greece under Antigonus III Doson and Philip V of Macedon . Books III-XXXIX describe in detail political and military affairs in the leading Mediterranean states, including affairs in ancient Rome and ancient Carthage , ancient Greece and ancient Macedonia , and
2464-662: 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
2552-586: The Histories . Polybius saw, for instance, the character and leadership of the later Philip V of Macedon , one of Rome's leading adversaries in the Greek East, as the opposite of his earlier exemplary namesake. Philip V became increasingly tyrannical, irrational and impious following brilliant military and political success in his youth; this resulted, Polybius believed, in his abandonment by his Greek allies and his eventual defeat by Rome in 197 BC. Other important themes running throughout The Histories include
2640-532: 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
2728-497: The Seleucid empire and Egypt, explaining their increasing " συμπλοκή" (symplokē) or interconnectedness and how they each contributed to Rome's rise to dominance. Only books I-V survive in full; the rest are in varying states of fragmentation. Three discursive books on politics, historiography and geography break up the historical narrative: Polybius held that historians should, if possible, only chronicle events whose participants
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2816-506: The 16th century. Consequently, in the late 16th century, Polybius's works found a greater reading audience among the learned public. Study of the correspondence of such men as Isaac Casaubon , Jacques Auguste de Thou , William Camden and Paolo Sarpi reveals a growing interest in Polybius's works and thought during the period. Despite the existence of both printed editions in the vernacular and increased scholarly interest, however, Polybius remained an "historian's historian", not much read by
2904-608: The Aetolians, the Carthaginians and the Cretans. Other historians perceive considerable negative bias in Polybius's account of Crete ; on the other hand, Hansen notes that the same work, along with passages from Strabo and Scylax , proved a reliable guide in the eventual rediscovery of the lost city of Kydonia . Polybius was responsible for a useful tool in telegraphy that allowed letters to be easily signaled using
2992-700: 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
3080-578: The Greeks and the Macedonians). While Polybius was not the first to advance this view, his account provides the most cogent illustration of the ideal for later political theorists. A key theme of The Histories is good leadership, and Polybius dedicates considerable time to outlining how the good statesman should be rational, knowledgeable, virtuous and composed. The character of the Polybian statesman
3168-608: The Kutubu Joint Venture (KJV) which has since constructed a pipeline to the Gulf of Papua and is actively extracting oil from the region. It is the site of Kikori Airport . Kikori has a tropical rainforest climate ( Köppen Af ) with very heavy rainfall year-round. Temperatures in Kikori are uniformly hot and humidity extremely uncomfortable. The town has an average annual rainfall of around 5,700 millimetres or 220 inches, making it and surrounding Gulf Province one of
3256-503: 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
3344-472: 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
3432-471: The aim of obtaining firsthand knowledge of historical sites. He apparently interviewed veterans to clarify details of the events he was recording and was similarly given access to archival material. Little is known of Polybius's later life; he most likely accompanied Scipio to Spain, acting as his military advisor during the Numantine War . He later wrote about this war in a lost monograph . Polybius probably returned to Greece later in his life, as evidenced by
3520-594: The annual strategia (chief generalship). Polybius's political career was cut short in 168 BC, however; as a consequence of the final defeat of the Antigonid kingdom in the Third Macedonian War , 1,000 Achaeans (including Polybius) with suspect allegiances were interned in Rome and its surrounding area. Polybius's father, Lycortas, was a prominent advocate of neutrality during the Roman war against Perseus of Macedon in 171-168 BC. Lycortas attracted
3608-1256: 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,
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3696-422: 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
3784-450: 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
3872-449: The conditions there. Polybius was charged with the difficult task of organizing the new form of government in the Greek cities, and in this office he gained great recognition. In the succeeding years, Polybius resided in Rome , completing his historical work while occasionally undertaking long journeys through the Mediterranean countries in the furtherance of his history, in particular with
3960-619: 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
4048-603: The education of his sons, Fabius and Scipio Aemilianus (who had been adopted by the eldest son of Scipio Africanus ). Polybius remained on cordial terms with his former pupil Scipio Aemilianus and was among the members of the Scipionic Circle . When Scipio defeated the Carthaginians in the Third Punic War , Polybius remained his counsellor. The Achaean hostages were released in 150 BC, and Polybius
4136-414: 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
4224-506: 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
4312-411: The geography surrounding one's subject matter to supply an accurate version of events. Polybius himself exemplified these principles as he was well travelled and possessed political and military experience. He consulted and used written sources providing essential material for the period between 264 BC to 220 BC, including, for instance, treaty documents between Rome and Carthage in the First Punic War ,
4400-466: 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
4488-477: The historian was able to interview, and was among the first to champion the notion of factual integrity in historical writing. In the twelfth volume of his Histories , Polybius defines the historian's job as the analysis of documentation, the review of relevant geographical information, and political experience. In Polybius's time, the profession of a historian required political experience (which aided in differentiating between fact and fiction) and familiarity with
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#17327837181544576-551: The history of the Greek historian Phylarchus , and the Memoirs of the Achaean politician, Aratus of Sicyon . When addressing events after 220 BC, he continued to examine treaty documents, the writings of Greek and Roman historians and statesmen, eye-witness accounts and Macedonian court informants to acquire credible sources of information, although rarely did he name his sources (see, exceptionally, Theopompus ). Polybius wrote several works, most of which are lost. His earliest work
4664-406: 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
4752-594: 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
4840-583: 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
4928-731: The later books of The Histories was preserved in Byzantine anthologies. His works reappeared in the West first in Renaissance Florence . Polybius gained a following in Italy, and although poor Latin translations hampered proper scholarship on his works, they contributed to the city's historical and political discourse. Niccolò Machiavelli in his Discourses on Livy evinces familiarity with Polybius. Vernacular translations in French, German, Italian and English first appeared during
5016-408: The least wet months of November and December and a striking contrast to the rainlessness of those same trade winds in relatively nearby Northern Australia . This Gulf Province geography article 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 the waters of
5104-481: The machines Archimedes created for the defense of Syracuse against the Romans, where Polybius praises the 'old man' and his engineering in the highest terms, and an analysis of the usefulness of astronomy to generals (both in the Histories ). Polybius was considered a poor stylist by Dionysius of Halicarnassus , writing of Polybius's history that "no one has the endurance to reach [its] end". Nevertheless, clearly he
5192-674: The manner in which Polybius used his sources, particularly documentary evidence as well as his citation and quotation of sources. Furthermore, there is some admiration of Polybius's meditation on the nature of historiography in Book 12. His work belongs, therefore, amongst the greatest productions of ancient historical writing. The writer of the Oxford Companion to Classical Literature (1937) praises him for his "earnest devotion to truth" and his systematic pursuit of causation. It has long been acknowledged that Polybius's writings are prone to
5280-477: The many existent inscriptions and statues of him there. The last event mentioned in his Histories seems to be the construction of the Via Domitia in southern France in 118 BC, which suggests the writings of Pseudo-Lucian may have some grounding in fact when they state, "[Polybius] fell from his horse while riding up from the country, fell ill as a result and died at the age of eighty-two". The Histories
5368-606: The mixed constitution. Polybius's discussion of the separation of powers in government, of checks and balances to limit power, and his introduction of "the people", all influenced Montesquieu 's The Spirit of the Laws , John Locke 's Two Treatises of Government , and the framers of the United States Constitution . The leading expert on Polybius for nearly a century was F. W. Walbank (1909–2008), who published studies related to him for 50 years, including
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#17327837181545456-543: The most important teachers of constitutional theory. Since the Age of Enlightenment , Polybius has in general held appeal to those interested in Hellenistic Greece and early Republican Rome, while his political and military writings have lost influence in academia. More recently, thorough work on the Greek text of Polybius, and his historical technique, has increased the academic understanding and appreciation of him as
5544-433: The narrative of the historical events, Polybius also included three books of digressions. Book 34 was entirely devoted to questions of geography and included some trenchant criticisms of Eratosthenes , whom he accused of passing on popular preconceptions or laodogmatika . Book 12 was a disquisition on the writing of history, citing extensive passages of lost historians, such as Callisthenes and Theopompus . Most influential
5632-524: 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
5720-610: The public at large. Printings of his work in the vernacular remained few in number—seven in French, five in English ( John Dryden provided an enthusiastic preface to Sir Henry Sheers' edition of 1693) and five in Italian. Polybius's political analysis has influenced republican thinkers from Cicero to Charles de Montesquieu to the Founding Fathers of the United States . John Adams , for example, considered him one of
5808-487: 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
5896-579: 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
5984-414: 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
6072-440: The role of Fortune in the affairs of nations, how a leader might weather bravely these changes of fortune with dignity, the educational value of history and how it should demonstrate cause and effect (or apodeiktike ) to provide lessons for statesmen, and that historians should be "men of action" to gain appropriate experience so as to understand how political and military affairs are likely to pan out ( pragmatikoi ). Polybius
6160-399: 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
6248-514: 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,
6336-424: 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
6424-497: The square, a letter could be deduced. In The Histories , Polybius specifies how this cypher could be used in fire signals, where long-range messages could be sent by means of torches raised and lowered to signify the column and row of each letter. This was a great leap forward from previous fire signaling, which could send prearranged codes only (such as, 'if we light the fire, it means that the enemy has arrived'). Other writings of scientific interest include detailed discussions of
6512-404: The square, the final "5,5" code point encodes the spaces in between words. Alternatively, it can denote the end of a sentence or paragraph when writing in continuous script. Five numbers are then aligned on the outside top of the square, and five numbers on the left side of the square vertically. Usually these numbers were arranged 1 through 5. By cross-referencing the two numbers along the grid of
6600-414: The suspicion of the Romans, and Polybius subsequently was one of the 1,000 Achaean nobles who were transported to Rome as hostages in 167 BC, and was detained there for 17 years. In Rome, by virtue of his high culture, Polybius was admitted to the most distinguished houses, in particular to that of Lucius Aemilius Paullus Macedonicus , the conqueror in the Third Macedonian War , who entrusted Polybius with
6688-656: 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
6776-718: 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
6864-642: The wettest lowland places on Earth – comparable to the Chocó of Colombia, the exposed monsoonal coasts of Myanmar, the Caribbean Coast of Central America, and the Alaska Panhandle . Rainfall averages at least 250 millimetres or 10 inches during every month of the year, but orographic lifting of the southeast trade winds between May and September creates a rainfall peak in those months which average over 550 millimetres or 20 inches – twice as much as
6952-418: Was Book 6, which describes Roman political, military, and moral institutions, which he considered key to Rome's success; it presented Rome as having a mixed constitution in which monarchical , aristocratic and popular elements existed in stable equilibrium. This enabled Rome to escape, for the time being, the cycle of eternal revolutions ( anacyclosis ) faced by those with singular constitutions (i.e. many of
7040-401: Was a biography of the Greek statesman Philopoemen ; this work was later used as a source by Plutarch when composing his Parallel Lives ; however, the original Polybian text is lost. In addition, Polybius wrote an extensive treatise entitled Tactics , which may have detailed Roman and Greek military tactics . Small parts of this work may survive in his major Histories , but the work itself
7128-585: Was a prominent, land-owning politician and member of the governing class who became strategos (commanding general) of the Achaean League. Consequently, Polybius was able to observe first hand during his first 30 years the political and military affairs of Megalopolis, gaining experience as a statesman . In his early years, he accompanied his father while travelling as ambassador . He developed an interest in horse riding and hunting, diversions that later commended him to his Roman captors. In 182 BC, he
7216-430: Was among the first historians to attempt to present history as a sequence of causes and effects, based upon a careful examination and criticism of tradition. He narrated his history based upon first-hand knowledge. The Histories capture the varied elements of the story of human behavior: nationalism , xenophobia , duplicitous politics, war, brutality, loyalty, valour, intelligence, reason and resourcefulness. Aside from
7304-645: Was chronicling Roman history for a Greek audience, to justify what he believed to be the inevitability of Roman rule. Nonetheless, Green considers Polybius's Histories the best source for the era they cover. For Ronald Mellor , Polybius was a loyal partisan of Scipio , intent on vilifying his patron's opponents. Adrian Goldsworthy , while using Polybius as a source for Scipio's generalship, notes Polybius's underlying and overt bias in Scipio's favour. H. Ormerod considers that Polybius cannot be regarded as an 'altogether unprejudiced witness' in relation to his bêtes noires ;
7392-732: 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
7480-414: Was given the honour of carrying the funeral urn of Philopoemen , one of the most eminent Achaean politicians of his generation. In either 170 BC or 169 BC, Polybius was elected hipparchus (cavalry officer) and was due to assist Rome militarily during the Third Macedonian War , although this never came about. This office was the second highest position of the Achaean League and often presaged election to
7568-537: Was granted leave to return home, but the next year he went on campaign with Scipio Aemilianus to Africa, and was present at the Sack of Carthage in 146, which he later described. Following the destruction of Carthage, Polybius likely journeyed along the Atlantic coast of Africa, as well as Spain. After the destruction of Corinth in the same year, Polybius returned to Greece, making use of his Roman connections to lighten
7656-429: Was widely read by Romans and Greeks alike. He is quoted extensively by Strabo writing in the 1st century BC and Athenaeus in the 3rd century AD. His emphasis on explaining causes of events, rather than just recounting events, influenced the historian Sempronius Asellio . Polybius is mentioned by Cicero and mined for information by Diodorus , Livy , Plutarch and Arrian . Much of the text that survives today from
7744-434: Was writing in Greek, and would have implemented his cipher square in the Greek alphabet. Both versions are shown here. In the Polybius square, letters of the alphabet were arranged left to right, top to bottom in a 5 × 5 square. When used with the 26-letter Latin alphabet two letters, usually I and J, are combined. When used with the Greek alphabet, which has exactly one fewer letters than there are spaces (or code points) in
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