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37-551: Manicouagan may refer to: Manicouagan crater , an impact crater in Quebec Manicouagan Reservoir , formed when the Manicouagan impact crater was converted to a reservoir. Manicouagan Regional County Municipality, Quebec Manicouagan River Manicouagan (electoral district) Manicouagan Uapishka Biosphere Reserve Topics referred to by

74-424: A certain proportion of its mass below the surface of the water. If snow falls to the top of the iceberg, the iceberg will sink lower in the water. If a layer of ice melts off the top of the iceberg, the remaining iceberg will rise. Similarly, Earth's lithosphere "floats" in the asthenosphere. When continents collide, the continental crust may thicken at their edges in the collision. It is also very common for one of

111-425: A change in crust loading) provide information on the viscosity of the upper mantle. The basis of the model is Pascal's law , and particularly its consequence that, within a fluid in static equilibrium, the hydrostatic pressure is the same on every point at the same elevation (surface of hydrostatic compensation): h 1 ⋅ρ 1 = h 2 ⋅ρ 2 = h 3 ⋅ρ 3 = ... h n ⋅ρ n For the simplified picture shown,

148-535: A characteristic wave number As the rigid layer becomes weaker, κ {\displaystyle \kappa } approaches infinity, and the behavior approaches the pure hydrostatic balance of the Airy-Heiskanen hypothesis. The depth of compensation (also known as the compensation level , compensation depth , or level of compensation ) is the depth below which the pressure is identical across any horizontal surface. In stable regions, it lies in

185-479: A crater originally about 100 km (62 mi) wide, although erosion and deposition of sediments have since reduced the visible diameter to about 72 km (45 mi). It is the Earth's sixth-largest confirmed impact structure according to rim-to-rim diameter. Mount Babel is interpreted as the central peak of the crater, formed by post-impact uplift . 1992 radiometric dating has estimated that impact melt within

222-481: A local hydrostatic balance. A third hypothesis, lithospheric flexure , takes into account the rigidity of the Earth's outer shell, the lithosphere . Lithospheric flexure was first invoked in the late 19th century to explain the shorelines uplifted in Scandinavia following the melting of continental glaciers at the end of the last glaciation . It was likewise used by American geologist G. K. Gilbert to explain

259-490: A region, the land may rise to compensate. Therefore, as a mountain range is eroded, the (reduced) range rebounds upwards (to a certain extent) to be eroded further. Some of the rock strata now visible at the ground surface may have spent much of their history at great depths below the surface buried under other strata, to be eventually exposed as those other strata eroded away and the lower layers rebounded upwards. An analogy may be made with an iceberg , which always floats with

296-559: Is Mount Babel . The structure was created 214 (±1) million years ago, in the Late Triassic , by the impact of a meteorite 5 km (3 mi) in diameter. The lake and island are clearly seen from space and are sometimes called the " eye of Quebec ". The lake has a volume of 137.9 km (33.1 cu mi). The reservoir is located in Manicouagan Regional County Municipality in

333-528: Is defined as the Bouger anomaly minus the gravity anomaly due to the subsurface compensation, and is a measure of the local departure from isostatic equilibrium. At the center of a level plateau, it is approximately equal to the free air anomaly . Models such as deep dynamic isostasy (DDI) include such viscous forces and are applicable to a dynamic mantle and lithosphere. Measurements of the rate of isostatic rebound (the return to isostatic equilibrium following

370-444: Is different from Wikidata All article disambiguation pages All disambiguation pages Manicouagan Reservoir#Impact crater Manicouagan Reservoir (also Lake Manicouagan / m æ n ɪ k w ɑː ɡ ən , - ɡ ɒ̃ / ) is an annular lake in central Quebec , Canada, covering an area of 1,942 km (750 sq mi). The lake island in its centre is known as René-Levasseur Island , and its highest point

407-445: Is the acceleration due to gravity, and P ( x ) {\displaystyle P(x)} is the load on the ocean crust. The parameter D is the flexural rigidity , defined as where E is Young's modulus , σ {\displaystyle \sigma } is Poisson's ratio , and T c {\displaystyle T_{c}} is the thickness of the lithosphere. Solutions to this equation have

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444-449: Is the highest peak of the island, at 952 m (3,123 ft) above sea level and 590 m (1,936 ft) above the reservoir level. The Louis-Babel Ecological Reserve makes up the central part of the island. Manicouagan Reservoir lies within the remnant of an ancient, deeply eroded impact crater ( Impact structure ). The crater was formed following the impact of an asteroid with a diameter of 5 km (3 mi), which excavated

481-476: The Baltic Sea and Hudson Bay . As the ice retreats, the load on the lithosphere and asthenosphere is reduced and they rebound back towards their equilibrium levels. In this way, it is possible to find former sea cliffs and associated wave-cut platforms hundreds of metres above present-day sea level . The rebound movements are so slow that the uplift caused by the ending of the last glacial period

518-680: The Côte-Nord region of Quebec, Canada, about 300 km (190 mi) north of the city of Baie-Comeau , although its northernmost part is located in Caniapiscau Regional County Municipality . Quebec Route 389 passes the eastern shore of the lake. The crater is a multiple-ring structure about 100 km (60 mi) across, with the reservoir at its 70 km (40 mi) diameter inner ring being its most prominent feature. It surrounds an inner island plateau called René-Levasseur Island and Mount Babel

555-928: The Rochechouart impact structure in France, the Saint Martin crater in Manitoba , the Obolon' crater in Ukraine , and the Red Wing crater in North Dakota . similar to the well observed string of impacts of Comet Shoemaker–Levy 9 on Jupiter in 1994. However, more recent work has found that the craters formed many millions of years apart, with the Saint Martin crater dating to 227.8 ± 1.1 Ma. While

592-560: The Pratt hypothesis as overlying regions of unusually low density in the upper mantle. This reflects thermal expansion from the higher temperatures present under the ridges. In the Basin and Range Province of western North America, the isostatic anomaly is small except near the Pacific coast, indicating that the region is generally near isostatic equilibrium. However, the depth to the base of

629-557: The Rochechouart structure formed 206.92 ± 0.20/0.32 Ma. The Manicouagan Reservoir as it presently exists was created in the 1960s, by flooding the earlier Lake Mushalagan (Mouchalagan) to the west of the central plateau and then-smaller Manicouagan to the east, by construction of the Daniel-Johnson dam . The works were part of the enormous Manicouagan or Manic series of hydroelectric projects undertaken by Hydro-Québec ,

666-521: The United States. Isostasy Although Earth is a dynamic system that responds to loads in many different ways, isostasy describes the important limiting case in which crust and mantle are in static equilibrium . Certain areas (such as the Himalayas and other convergent margins) are not in isostatic equilibrium and are not well described by isostatic models. The general term isostasy

703-403: The balancing of lithospheric columns gives: where ρ m {\displaystyle \rho _{m}} is the density of the mantle (ca. 3,300 kg m ), ρ c {\displaystyle \rho _{c}} is the density of the crust (ca. 2,750 kg m ) and ρ w {\displaystyle \rho _{w}} is the density of

740-418: The crust does not strongly correlate with the height of the terrain. This provides evidence (via the Pratt hypothesis) that the upper mantle in this region is inhomogeneous, with significant lateral variations in density. The formation of ice sheets can cause Earth's surface to sink. Conversely, isostatic post-glacial rebound is observed in areas once covered by ice sheets that have now melted, such as around

777-448: The deep crust, but in active regions, it may lie below the base of the lithosphere. In the Pratt model, it is the depth below which all rock has the same density; above this depth, density is lower where topographic elevation is greater. When large amounts of sediment are deposited on a particular region, the immense weight of the new sediment may cause the crust below to sink. Similarly, when large amounts of material are eroded away from

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814-406: The deformation of the rigid crust. These elastic forces can transmit buoyant forces across a large region of deformation to a more concentrated load. Perfect isostatic equilibrium is possible only if mantle material is in rest. However, thermal convection is present in the mantle. This introduces viscous forces that are not accounted for the static theory of isostacy. The isostatic anomaly or IA

851-411: The depth of the mountain belt roots (b 1 ) is calculated as follows: where ρ m {\displaystyle \rho _{m}} is the density of the mantle (ca. 3,300 kg m ) and ρ c {\displaystyle \rho _{c}} is the density of the crust (ca. 2,750 kg m ). Thus, generally: In the case of negative topography (a marine basin),

888-403: The flexural rigidity of the lithosphere approaches zero. For example, the vertical displacement z of a region of ocean crust would be described by the differential equation where ρ m {\displaystyle \rho _{m}} and ρ w {\displaystyle \rho _{w}} are the densities of the aesthenosphere and ocean water, g

925-500: The gravitational attraction of the nearby Andes Mountains . However, the deflection was less than expected, which was attributed to the mountains having low-density roots that compensated for the mass of the mountains. In other words, the low-density mountain roots provided the buoyancy to support the weight of the mountains above the surrounding terrain. Similar observations in the 19th century by British surveyors in India showed that this

962-516: The impact structure has an age of 214 ± 1 million years. A later estimate found an age of 215.4 ± 0.16 Ma. As this is more than 12 million years before the end of the Triassic, the impact that produced the crater cannot have been the cause of the Triassic–Jurassic extinction event . It was suggested that the Manicouagan crater may have been part of a multiple impact event which also formed

999-476: The peak period of the winter cold, the lake surface is usually lower, since the turbines run all the time at peak load to meet the huge electrical heating needs of the province. The surface of the lake also experiences low levels in the extreme periods of heat in New England during the summer, since in that period Hydro-Québec sells electrical energy to the joint New England grid and individual utilities in

1036-478: The plates to be underthrust beneath the other plate. The result is that the crust in the collision zone becomes as much as 80 kilometers (50 mi) thick, versus 40 kilometers (25 mi) for average continental crust. As noted above , the Airy hypothesis predicts that the resulting mountain roots will be about five times deeper than the height of the mountains, or 32 km versus 8 km. In other words, most of

1073-722: The provincial electrical utility. The complex of dams is also called the Manic-Outardes Project because the rivers involved are the Manicouagan and the Outardes . The reservoir acts as a giant headpond for the Manicouagan River, feeding the Jean-Lesage generating station (Manic-2), René-Lévesque generating station (Manic-3), and Daniel-Johnson Dam ( Manic-5 ) generating stations downstream. In

1110-419: The same term [REDACTED] This disambiguation page lists articles associated with the title Manicouagan . If an internal link led you here, you may wish to change the link to point directly to the intended article. Retrieved from " https://en.wikipedia.org/w/index.php?title=Manicouagan&oldid=1109273498 " Category : Disambiguation pages Hidden categories: Short description

1147-434: The thickened crust moves downwards rather than up, just as most of an iceberg is below the surface of the water. However, convergent plate margins are tectonically highly active, and their surface features are partially supported by dynamic horizontal stresses, so that they are not in complete isostatic equilibrium. These regions show the highest isostatic anomalies on the Earth's surface. Mid-ocean ridges are explained by

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1184-408: The thickness of the crust. This hypothesis was suggested to explain how large topographic loads such as seamounts (e.g. Hawaiian Islands ) could be compensated by regional rather than local displacement of the lithosphere. This is the more general solution for lithospheric flexure , as it approaches the locally compensated models above as the load becomes much larger than a flexural wavelength or

1221-560: The uplifted shorelines of Lake Bonneville . The concept was further developed in the 1950s by the Dutch geodesist Vening Meinesz . Three principal models of isostasy are used: Airy and Pratt isostasy are statements of buoyancy, but flexural isostasy is a statement of buoyancy when deflecting a sheet of finite elastic strength. In other words, the Airy and Pratt models are purely hydrostatic, taking no account of material strength, while flexural isostacy takes into account elastic forces from

1258-401: The water (ca. 1,000 kg m ). Thus, generally: For the simplified model shown the new density is given by: ρ 1 = ρ c c h 1 + c {\displaystyle \rho _{1}=\rho _{c}{\frac {c}{h_{1}+c}}} , where h 1 {\displaystyle h_{1}} is the height of the mountain and c

1295-587: The word 'isostasy' in 1889 to describe this general phenomenon. However, two hypotheses to explain the phenomenon had by then already been proposed, in 1855, one by George Airy and the other by John Henry Pratt . The Airy hypothesis was later refined by the Finnish geodesist Veikko Aleksanteri Heiskanen and the Pratt hypothesis by the American geodesist John Fillmore Hayford . Both the Airy-Heiskanen and Pratt-Hayford hypotheses assume that isostacy reflects

1332-503: Was a widespread phenomenon in mountainous areas. It was later found that the difference between the measured local gravitational field and what was expected for the altitude and local terrain (the Bouguer anomaly ) is positive over ocean basins and negative over high continental areas. This shows that the low elevation of ocean basins and high elevation of continents is also compensated at depth. The American geologist Clarence Dutton use

1369-486: Was coined in 1882 by the American geologist Clarence Dutton . In the 17th and 18th centuries, French geodesists (for example, Jean Picard ) attempted to determine the shape of the Earth (the geoid ) by measuring the length of a degree of latitude at different latitudes ( arc measurement ). A party working in Ecuador was aware that its plumb lines , used to determine the vertical direction, would be deflected by

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