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| '''Isostasy''' (Greek [[wikt:ἴσος|''ísos'']] "equal", [[wikt:στάσις|''stásis'']] "standstill") is a term used in [[geology]] to refer to the state of [[gravity|gravitational]] equilibrium between the [[earth]]'s [[lithosphere]] and [[asthenosphere]] such that the [[tectonic plate]]s "float" at an elevation which depends on their thickness and density.
| | If you were young, possibly we were one of those lucky persons whom didnt need fat loss help. Maybe we were chasing kids, functioning at an outside job, cooking, cleaning plus living an active lifestyle. Its not that men over 50 and post-menopausal women are not active. However usually they are less active. This could be due to bodily limitations, including arthritis, or considering they have really gotten selected to a more sedentary lifestyle inside retirement or if they are nonetheless functioning.<br><br>A popular diagnostic tool, the body mass index measures the body fat based on the weight plus [http://safedietplansforwomen.com/bmi-chart bmi chart] the height of an individual. Developed by a Belgian scientist Adolphe Quetelet, it assists to calculate how healthy a person is based on his weight and identify whether the person is underweight, obese, or obese. The relation of BMI to fatness differs for people of different age plus gender. For instance, the BMI of women is likely to be high than that of guys.<br><br>Then when the BMI is high on the bmi chart men chart, above 25, the direction of thumb for water consumption is to Drink Half Your Body Weight In Water. Overweight persons tend to want more water, because fat cells hold more water than additional fat cells in the body, according to Barbara Levine, R.D., Ph.D., the Director of the Nutrition Information Center at the New York Hospital-Cornell Medical Center. If you fit this profile, like me, merely divide a fat by 2 to decide the amount of water you will want to drink each day.<br><br>11) Subtract the lean body mass from your bodyweight. Take this number and multiply it by 100. When you receive this result, divide it by a bodyweight.<br><br>Lets start with an average brick, like the multi-colored one at appropriate. You wish To make a little brick pile which has the same proportions because the initial brick, however, is twice as big in all three dimensions. First you add a brick, in order to double the length. Next alongside that, we add two more bricks to double the width.<br><br>The Track: Most marathon training programs will include track work as it assists bmi chart women develop the quick twitch muscles to build speed and lung energy throughout a race...getting older does not imply getting less competitive:) If I am training for a marathon, it truly makes a difference for me particularly in the later miles of the race. Good article from Runner's World called "Running inside Circles".<br><br>That sounds really complicated, however, whenever we have the numbers and are making the actual calculations, it's not almost as hard as it sounds, although you surely desire a calculator of certain kind. This is how guys must measure their body fat. For women, the measurements are different.<br><br>If you think you may be usual weight obese, the number one thing you are able to do is consult your doctor, and begin to make healthier options in the life. For more info feel free to go look at a few of the hyperlinks I've provided. |
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| This concept is invoked to explain how different topographic heights can exist at the Earth's surface. When a certain area of lithosphere reaches the state of isostasy, it is said to be in ''isostatic equilibrium''. Isostasy is '''not''' a process that upsets equilibrium, but rather one which restores it (a negative feedback). It is generally accepted <ref>A.B. Watts, Isostasy and flexure of the lithosphere,Cambridge Univ. Press., 2001</ref> that the Earth is a dynamic system that responds to loads in many different ways. However, isostasy provides an important 'view' of the processes that are happening in areas that are experiencing vertical movement. Certain areas (such as the [[Himalayas]]) are ''not'' in isostatic equilibrium, which has forced researchers to identify other reasons to explain their topographic heights (in the case of the Himalayas, which are still rising, by proposing that their elevation is being "propped-up" by the force of the impacting [[Indian plate]]). | |
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| In the simplest example, isostasy is the principle of [[buoyancy]] where an object immersed in a [[liquid]] is buoyed with a force equal to the weight of the displaced liquid. On a geological scale, isostasy can be observed where the Earth's strong lithosphere exerts stress on the weaker asthenosphere which, over [[geologic timescale|geological time]] flows laterally such that the load of the lithosphere is accommodated by height adjustments.
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| The general term 'isostasy' was coined in 1889 by the American geologist [[Clarence Dutton]].
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| == Isostatic models ==
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| Three principal models of isostasy are used:
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| # The [[George Airy|Airy]]-[[Veikko Aleksanteri Heiskanen|Heiskanen]] Model - where different topographic heights are accommodated by changes in [[Crust (geology)|crustal]] thickness, in which the crust has a constant density
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| # The [[John Henry Pratt|Pratt]]-[[John Fillmore Hayford|Hayford]] Model - where different topographic heights are accommodated by lateral changes in [[Rock (geology)|rock]] [[density]].
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| # The [[Vening Meinesz]], or [[flexural isostasy]] model - where the [[lithosphere]] acts as an [[Elasticity (physics)|elastic]] plate and its inherent rigidity distributes local topographic loads over a broad region by bending.
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| Airy and Pratt isostasy are statements of buoyancy, while [[flexural isostasy]] is a statement of buoyancy while deflecting a sheet of finite elastic strength.
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| === Airy ===
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| [[File:Airy Isostasy.jpg|thumb|right|Airy isostasy, in which a constant-density crust floats on a higher-density mantle, and topography is determined by the thickness of the crust.]]
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| [[File:Backstripping and eustasy correction.jpg|thumb|Airy isostasy applied to a real-case basin scenario, where the total load on the mantle is composed by a crustal basement, lower-density sediments and overlying marine water]]
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| The basis of the model is the [[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). In other words:
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| h<sub>1</sub>⋅ρ<sub>1</sub> = h<sub>2</sub>⋅ρ<sub>2</sub> = h<sub>3</sub>⋅ρ<sub>3</sub> = ... h<sub>n</sub>⋅ρ<sub>n</sub>
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| For the simplified picture shown the depth of the mountain belt roots (b<sub>1</sub>) are:
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| <big><math> (h_1+c+b_1)\rho_c = (c\rho_c)+(b_1\rho_m) </math></big>
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| <big><math> {b_1(\rho_m-\rho_c)} = h_1\rho_c </math></big>
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| <big><math> b_1 = \frac{h_1\rho_c}{\rho_m-\rho_c} </math></big>
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| <br />
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| where <math> \rho_m </math> is the density of the mantle (ca. 3,300 kg m<sup>-3</sup>) and <math> \rho_c </math> is the density of the crust (ca. 2,750 kg m<sup>-3</sup>). Thus, we may generally consider:
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| <big>b<sub>1</sub> ≅ 5⋅h<sub>1</sub></big> | |
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| In the case of negative topography (i.e., a marine basin), the balancing of lithospheric columns gives:
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| <br />
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| <big><big><math> c\rho_c = (h_w\rho_w)+(b_2\rho_m)+[(c-h_w-b_2)\rho_c] </math></big>
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| <br />
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| <big><math> {b_2(\rho_m-\rho_c)} = {h_w(\rho_c-\rho_w)} </math></big>
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| <br />
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| <big><math> b_2 = (\frac{\rho_c-\rho_w}{\rho_m-\rho_c}){h_w} </math></big>
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| <br />
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| where <math> \rho_m </math> is the density of the mantle (ca. 3,300 kg m<sup>-3</sup>), <math> \rho_c </math> is the density of the crust (ca. 2,750 kg m<sup>-3</sup>) and <math> \rho_w </math> is the density of the water (ca. 1,000 kg m<sup>-3</sup>). Thus, we may generally consider:
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| <big>b<sub>2</sub> ≅ 3.2⋅h<sub>w</sub></big>
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| === Pratt ===
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| For the simplified model shown the new density is given by: <math> \rho_1 = \rho_c \frac{c}{h_1+c} </math>, where <math>h_1</math> is the height of the mountain and c the thickness of the crust.
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| === Vening Meinesz / flexural ===
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| 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 the flexural rigidity of the lithosphere approaches 0.
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| ==Isostatic effects of deposition and erosion==
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| 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 a region, the land may rise to compensate. Therefore, as a mountain range is eroded down, 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 are eroded away and the lower layers rebound upwards again.
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| An analogy may be made with an [[iceberg]] - it always floats with a certain proportion of its mass below the surface of the water. If more ice is added to the top of the iceberg, the iceberg will sink lower in the water. If a layer of ice is somehow sliced off the top of the iceberg, the remaining iceberg will rise. Similarly, the Earth's lithosphere "floats" in the asthenosphere.
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| ==Isostatic effects of plate tectonics==
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| When continents collide, the continental crust may thicken at their edges in the collision. If this happens, much of the thickened crust may move ''downwards'' rather than up as with the iceberg analogy. The idea of continental collisions building mountains "up" is therefore rather a simplification. Instead, the crust ''thickens'' and ''the upper part of the thickened crust'' may become a mountain range.{{fact|date=July 2012}}
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| However, some continental collisions are far more complex than this, and the region may not be in isostatic equilibrium, so this subject has to be treated with caution.{{fact|date=July 2012}}
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| ==Isostatic effects of ice sheets==
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| {{Main|post-glacial rebound}}
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| The formation of [[ice sheets]] can cause the 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 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 cliff]]s and associated [[wave-cut platform]]s 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]] is still continuing.
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| In addition to the vertical movement of the land and sea, isostatic adjustment of the Earth also involves horizontal movements. It can cause changes in the [[Earth's gravity|gravitational field]] and [[Rotation of Earth|rotation rate of the Earth]], [[polar wander]], and [[earthquake]]s.
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| == Eustasy and relative sea level change ==
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| {{Main|Eustasy}}
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| Eustasy is another cause of relative [[sea level change]] quite different from isostatic causes. The term ''eustasy'' or ''eustatic'' refers to changes in the amount of water in the oceans, usually due to [[global climate change]]. When the Earth's climate cools, a greater proportion of water is stored on land masses in the form of glaciers, snow, etc. This results in falling global sea levels (relative to a stable land mass). The refilling of ocean basins by [[glacial meltwater]] at the end of ice ages is an example of eustatic [[sea level rise]].
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| A second significant cause of eustatic sea level rise is thermal expansion of sea water when the Earth's mean temperature increases. Current estimates of global eustatic rise from tide gauge records and [[satellite altimetry]] is about +3 mm/a (see 2007 IPCC report). Global sea level is also affected by vertical crustal movements, changes in the rotational rate of the Earth, large scale changes in [[continental margin]]s and changes in the spreading rate of the [[ocean floor]].
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| When the term ''relative'' is used in context with ''sea level change'', the implication is that both eustasy and isostasy are at work, or that the author does not know which cause to invoke.
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| Post-glacial rebound can also be a cause of rising sea levels. When the sea floor rises, which it continues to do in parts of the northern hemisphere, water is displaced and has to go elsewhere.
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| ==References==
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| {{Reflist}}
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| ==Further reading==
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| * Lisitzin, E. (1974) "Sea level changes". Elsevier Oceanography Series, 8
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| *{{cite book |author=AB Watts |year=2001 |title=Isostasy and Flexure of the Lithosphere |publisher= Cambridge University Press |isbn=0-521-00600-7 |url=http://books.google.com/books?id=CNkiZU7enWUC&printsec=frontcover#v=onepage&q=&f=false}} A very complete overview with much of the historical development.
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| ==See also==
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| * [[Clarence Dutton]], who coined the term ''isostasy'' in 1889
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| * [[John Fillmore Hayford]]
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| * [[William Bowie]]
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| * [[Marine terrace]]
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| ==External links==
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| * {{Cite EB1922|Isostasy|author=[[Richard Dixon Oldham]]}}
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| [[Category:Geodynamics]]
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| [[Category:Geology]]
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| [[Category:Geomorphology]]
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| [[Category:Buoyancy]]
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If you were young, possibly we were one of those lucky persons whom didnt need fat loss help. Maybe we were chasing kids, functioning at an outside job, cooking, cleaning plus living an active lifestyle. Its not that men over 50 and post-menopausal women are not active. However usually they are less active. This could be due to bodily limitations, including arthritis, or considering they have really gotten selected to a more sedentary lifestyle inside retirement or if they are nonetheless functioning.
A popular diagnostic tool, the body mass index measures the body fat based on the weight plus bmi chart the height of an individual. Developed by a Belgian scientist Adolphe Quetelet, it assists to calculate how healthy a person is based on his weight and identify whether the person is underweight, obese, or obese. The relation of BMI to fatness differs for people of different age plus gender. For instance, the BMI of women is likely to be high than that of guys.
Then when the BMI is high on the bmi chart men chart, above 25, the direction of thumb for water consumption is to Drink Half Your Body Weight In Water. Overweight persons tend to want more water, because fat cells hold more water than additional fat cells in the body, according to Barbara Levine, R.D., Ph.D., the Director of the Nutrition Information Center at the New York Hospital-Cornell Medical Center. If you fit this profile, like me, merely divide a fat by 2 to decide the amount of water you will want to drink each day.
11) Subtract the lean body mass from your bodyweight. Take this number and multiply it by 100. When you receive this result, divide it by a bodyweight.
Lets start with an average brick, like the multi-colored one at appropriate. You wish To make a little brick pile which has the same proportions because the initial brick, however, is twice as big in all three dimensions. First you add a brick, in order to double the length. Next alongside that, we add two more bricks to double the width.
The Track: Most marathon training programs will include track work as it assists bmi chart women develop the quick twitch muscles to build speed and lung energy throughout a race...getting older does not imply getting less competitive:) If I am training for a marathon, it truly makes a difference for me particularly in the later miles of the race. Good article from Runner's World called "Running inside Circles".
That sounds really complicated, however, whenever we have the numbers and are making the actual calculations, it's not almost as hard as it sounds, although you surely desire a calculator of certain kind. This is how guys must measure their body fat. For women, the measurements are different.
If you think you may be usual weight obese, the number one thing you are able to do is consult your doctor, and begin to make healthier options in the life. For more info feel free to go look at a few of the hyperlinks I've provided.