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Topic: Isostasy

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  Isostasy - Wikipedia, the free encyclopedia
Isostasy is a term used in Geology to refer to the state of gravitational equilibrium between the Earth's lithosphere and asthenosphere such that the tectonic plates "float" at an elevation which depends on their thickness and density.
In the simplest example, isostasy is the principle observed by Archimedes in his bath, where he saw that when an object was immersed, an amount of water equal in volume to that of the object was displaced.
On a geological scale, isostasy can be observed where the Earth's strong lithosphere exerts stress on the weaker asthenosphere which, over geological time flows laterally such that the load of the lithosphere is accommodated by height adjustments.
en.wikipedia.org /wiki/Isostasy   (799 words)

Isostasy is the balance between surface topographic loads and subsurface compensation.
The diagram to the right shows the two traditional interpretations of isostasy, the Pratt model in which compensation is achieved by lateral density variations in the crust, and the Airy model in which compensation is achieved by thickness variations in the crust.
Barell also recognized that for isostasy to be dynamic, i.e., to remain valid during mountain building and erosion, the "rigid" lithosphere must "float" on a "fluid" layer that can flow to allowed the lithosphere to adjust in response to changed in the topographic load.
www.es.mq.edu.au /courses/GEOS260/Lithosphere1.html   (1830 words)

Isostasy explains the vertical distribution of Earth's crust.
George Bedell Airy proposed that the density of the crust is everywhere the same and the thickness of crustal material varies.
There are two theories of the mechanism of isostasy, the Airy hypothesis and the Pratt hypothesis, both of which have validity.
www.tiscali.co.uk /reference/encyclopaedia/hutchinson/m0006406.html   (314 words)

 Lecture 28, Earth Dynamics
Isostasy represents the theory that the outer parts of the earth are in a state of dynamic equilibrium such that the surface elevation depends on the mean density of the underlying rock.
The first hint of isostasy was provided in the middle of the eighteenth century when Piere Bouguer participated in a survey to measure the length of a degree of latitude at the equator.
At the same time that these models of isostasy were being developed, other scientists were learning to probe the deep interior of the earth.
earth.unh.edu /esci658/docs/lecture_28.html   (1706 words)

 BC Education - Geology 12 - Internal Processes and Structures (Isostasy)   (Site not responding. Last check: 2007-11-07)
The concept of isostasy is used to explain many of the vertical movements of the earth's crust.
Introduce the concept of isostasy by presenting a photograph of a raised beach terrace and having students propose hypotheses for the origin of the feature.
Have students demonstrate the principle of isostasy using floating blocks or slabs of foam rubber alternately loaded and unloaded with weights.
www.bced.gov.bc.ca /irp/esg/12intiso.htm   (402 words)

 Search Results for isostasy - Encyclopædia Britannica
American geodesist who investigated isostasy, a principle that rationalizes the tendency of dense crustal rocks to cause topographic depressions and of light crustal rocks to cause topographic...
The investigations of isostasy described above are statistical in approach in that they are directed toward determining depth of compensation and lithospheric thickness from large data sets without...
According to this principle, the level of the Earth's crust is determined by its density; lighter...
www.britannica.com /search?query=isostasy&submit=Find&source=MWTEXT   (289 words)

 Isostasy   (Site not responding. Last check: 2007-11-07)
Talk about icebergs and their unseen underwater "roots." A talk about isostatic rebound of continents from the melting of continental glaciers during the last ice age was also very interesting to the students.
Isostasy is the process by which the lithospheric plates, which are "floating" on the mantle, adjust vertically to achieve an equilibrium (the crust and upper mantle have a uniform density.) Because oceanic crust has a higher density than continental crust, it adjusts lower into the mantle.
This condition is augmented by the fact that oceanic crust is thinner and therefore has less mass to compensate for through buoyant displacement of the mantle.
visearth.ucsd.edu /VisE_teach/lessons/Isostasy_LP.html   (622 words)

 GEOS 112: Isostasy
You might have encountered the principle of isostasy before: In Physics it is often called hydrostatic equilibrium, which describes the equilibrium between the weight of an object and the buoyant force as it floats in a liquid.
In geology isostasy describes the floating of less denser crustal material (oceanic or continental) on denser mantle material.
Airy and Pratt, stating that mountains are composed of less dense material floating on a denser substrate.
www.trincoll.edu /~cgeiss/GEOS_112/isostasy/isostasy.htm   (917 words)

 Chapter 9 (Large-scale Gravity and Isostasy)
Isostasy is the ability of layer in the Earth to yield under the weight of large masses (e.g., mountains; large basins)
Isostasy follows Archimedes’ Principle, which states, “The decrease of weight [of a body] equals the weight of liquid displaced by the part of the body under the liquid surface.”  In other words, “the denser the liquid, the less far the block sinks before it floats.”  This is the way in which an iceberg floats.
Evidence for Isostasy: evidence that support the concept of isostasy has come from looking at the gravity signature across Hawaii, Greenland, and the Himalayas and comparing it to Bathymetry and/or topography.
www.unlv.edu /Colleges/Sciences/Geoscience/pub/snelson/GeopMethods/Isostacy/Isostacy.htm   (337 words)

 AllRefer.com - continent : Geology and Topography of the Continents : Floating Continents and Isostasy (Geology And ...   (Site not responding. Last check: 2007-11-07)
Evidence indicates that part of the mantle below the crust consists of semifluid rocks on which the continents and ocean basins, in effect, are floating.
A condition of gravitational balance, called isostasy, exists between different parts of the earth's crust.
The theory of isostasy claims that the continental crust floats higher than the oceanic crust because the former is composed of a thick layer of lower density rocks while the latter is composed of a thin layer of higher density rocks.
reference.allrefer.com /encyclopedia/C/continent-geology-and-topography-of-the-continents-floating-continents-and-isostasy.html   (272 words)

 Isostasy   (Site not responding. Last check: 2007-11-07)
regional isostasy, in which the lithosphere is assumed to have a finite lateral (or flexural) strength;
Because the main contributor to pressure in the Earth is the weight of the overburden, there cannot be any weight difference between two vertical columns when measured from the Earth's surface down to the level of compensation.
Note that the concept of local isostasy is one of relative weight, not absolute weight.
wwwrses.anu.edu.au /~jean/GEOL3005/Isostasy/Intro.html   (381 words)

 CLARENCE DUTTON: ISOSTASY AND GEOMORPHOLOGY REVISITED   (Site not responding. Last check: 2007-11-07)
While his scientific acumen is evident in reports on the plateaus and canyons of the West, his name is still often linked with the concept of isostasy, a term he coined in 1889 to reflect the debate then raging concerning Earth's crustal equilibrium.
The subsequent demise of Davisian geomorphology, triggered by advances in the understanding of plate tectonics, geomorphic processes, and geochronology, led to a reawakening of interest in isostasy as a concept basic to the explanation of Earth's surface relief.
Somewhat belatedly, the Colorado Plateau and the American West, together with other regions characterized by active tectonism and rapid denudation, are once again at the center of the debate regarding denudation and crustal behavior.
gsa.confex.com /gsa/2002AM/finalprogram/abstract_39123.htm   (404 words)

The processes of isostasy and eustasy involve the dynamic adjustment of the earth’s lithosphere and hydrosphere over glaciation intervals.
Isostasy is the crustal response to retain a buoyant equilibrium as a gravitational force working on a mass is exerted on the lithosphere, while an opposite force thrusts upward from the asthenosphere.
Eustasy is the temporal transgression and regression of the mean sea level relative to the local terra firma.
www.homepage.montana.edu /~geol445/hyperglac/sealevel2   (94 words)

 isostasy ::: pricing   (Site not responding. Last check: 2007-11-07)
A typical assignment will start with a short assessment of your organisation's current situation, with a firm proposal for a full implementation programme.
This will normally take 2 days on site to complete, and isostasy will charge a fixed fee of £280 per location.
You can shelf the advice at that point or continue the project without Isostasy if that suits you better.
freespace.virgin.net /david.prescott1/advice.html   (100 words)

 isostasy ::: sustainable building   (Site not responding. Last check: 2007-11-07)
Isostasy is helping some clients to realise their dream.
From virtual ruins, they are refurbishing a barn in the Yorkshire Dales which they plan to use as an arts/light engineering workshop.
Isostasy is guiding them through the sustainable refurbishment by suggesting the most cost effective solutions which meet their requirements of energy efficiently, sustainable building materials, renewable power and the minimisation of the environmental footprint of the development.
freespace.virgin.net /david.prescott1/barn.html   (116 words)

 Ocean Crustal Models, Isostasy, and Rock Density   (Site not responding. Last check: 2007-11-07)
Archimedes' Principle: A body, wether completely or partially submerged, is buoyed upward by a force equal to the weight of the displaced fluid.
Isostasy: an equilibrium condition, as in the floating of the units of the lithosphere above the asthenosphere.
isostasy occurs when the buoyant force is equal to the gravitational force, i.e.
www-ocean.tamu.edu /~dkobilka/isostasy.html   (532 words)

 [No title]
In this end-member, also called Airy isostasy, the load rides just high enough in the fluid that the pressure directly beneath the load, at some arbitrary depth, is equal to that beyond the edge of the load, measured at the same depth.
This is what is implied by the name isostasy, which means equal pressure (iso- for equal, -stasia for standing or static).
If the pressures were not equal, the fluid would flow from high pressure to low, meaning that the elevations of the load would change, and the problem would not be static.
www.es.ucsc.edu /~rcoe/eart110c/Lab7_text.doc   (864 words)

 isostasy --  Encyclopædia Britannica   (Site not responding. Last check: 2007-11-07)
In the 18th century the French scientist Pierre Bouguer had observed that the deflections of the pendulum in Peru are much less than they should be...
American geodesist who investigated isostasy, a principle that rationalizes the tendency of dense crustal rocks to cause topographic depressions and of light crustal rocks to cause topographic elevations.
American civil engineer and early geodesist who established the theory of isostasy.
www.britannica.com /eb/article-9042969   (501 words)

 Crustal Isostasy Indicates Anomalous Densities Beneath Iceland
is implied (assuming isostasy and a normal 8 km thick crust for the abyssal plain).
The similarity of this value with the one inferred for Iceland, despite the large difference in age, suggests that the density contrast is compositionally, and not thermally, controlled.
Crustal isostasy indicates that the density contrast across the Icelandic Moho is 89 +/- 12 kg/m
www.ldeo.columbia.edu /users/menke/crust   (2923 words)

 Mountain Building
Explain the process of isostasy and the concept of isostatic equilibrium.
The mid-ocean ridges are 500 to 5000 km wide and cover more than 20% of the Earth's surface.
The concept of the Earth's crust in gravitational balance or equilibrium is called isostasy.
gpc.edu /~pgore/geology/geo101/mountain.htm   (443 words)

 Publisher description for Library of Congress control number 00065146   (Site not responding. Last check: 2007-11-07)
This unique book presents an overview of isostasy, a simple concept of fundamental importance to the Earth Sciences that students have traditionally found difficult to grasp.
Beginning by tracing the ideas behind local and regional models of isostasy and arguing that only flexure is in accord with geological observations, the book proceeds to describe the theoretical background, the observational evidence and the constraints that flexure has provided on physical properties of the lithosphere.
Ideal for graduate students of geophysics, geodesy and geoscience, it will also be of interest to researchers in gravity and geodesy, tectonics and basin analysis.
www.loc.gov /catdir/description/cam021/00065146.html   (203 words)

 Isostasy   (Site not responding. Last check: 2007-11-07)
For completeness, I include a brief section on isostasy.
The Earth's crust responds to loads placed upon it by sinking a bit into the denser materials that are beneath.
The Baltic Sea and the Hudson bay are both major land forms that are the result of isostatic depression, and will eventually rise above their current positions.
www.cs.umt.edu /U/johnson/research/phd_html/node17.html   (183 words)

 Oilfield Glossary: Term 'isostasy'
The balance between the elevation of the lithospheric plates and the asthenosphere is achieved by the flowage of the denser asthenosphere.
Various hypotheses about isostasy take into account density (Pratt hypothesis), thickness (Airy hypothesis), and pressure variations to explain topographic variations among lithospheric plates.
The current model consists of several layers of different density.
www.glossary.oilfield.slb.com /Display.cfm?Term=isostasy   (104 words)

 isostasy - OneLook Dictionary Search
Tip: Click on the first link on a line below to go directly to a page where "isostasy" is defined.
Isostasy : Online Plain Text English Dictionary [home, info]
By the theory of isostasy each unit column of the earth, from surface to center, has approximately the same weight, and the continents stand higher than the ocean beds chiefly because the material of the crust has there less density.
www.onelook.com /?w=isostasy   (240 words)

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