isostasy was enunciated like principle at the end of century XIX. It is the condition of I balance that densidad presents/displays the terrestrial surface due to the difference of of its parts. It is solved in heaves ( epirogénicos ) and is based on Principle of Archimedes .
terrestrial Crust floats on Mantle like Iceberg in the ocean; or, Sial floats on Sima like a iceberg in the ocean. The basic principle is that so that a body floats on another one, this one must be denser, and so it is placed underneath. The material that floats, sinks in a variable percentage, but always it has part of emerged him. Thus, the condition of bouyancy does not depend on the size, and when the emerged part loses volume and weight, the submerged part ascends to compensate it. Each individual block, or this one plate or a block delimited by Faults tend to reach this balance. The collapse produced in a river basin where they are settling material receives the name of Subsidence
The isostatic balance can break by a tectonic movement or the defrosting of Inlandsis . The isostasy is fundamental for the relief of Earth . The continents are less dense than the mantle, and also that oceanic Crust . When continental Crust is folded accumulates great amount of materials in a concrete region. Finished the ascent, the erosion begins. material deposits, in the long run, outside the mountainous chain, and so this one loses weight and volume. The roots ascend to compensate this loss leaving in surface the materials that been have put under a greater metamórfico process, and which they have become Granite . This promoted granite, forms rigid old massive Shields or, and that does not fold before new orogenia, but it is broken forming failed Relief . Each one of the blocks in which is broken Shield, of different sizes, also tend to reach the isostatic balance. The readjustments, ascents and collapses of blocks with respect to the other, generate small Earthquakes
Where is the depth of compensation, the height of the topography and the densidad.
Since the densidades of the terrestrial interior are not known, two models were developed of almost simultaneous way. Henry Pratt proposed a depth of constant compensation , consequently, the variations of the topography are associate to lateral changes in the densidad. On the other hand, George Airy assumed a constant densidad, which implies a depth of variable compensation.
At the moment three isostatic models exist:
In the continents:
In the oceans:
Where is the densidad of the water of sea:
In the continents:
In the oceans:
According to this theory, the crust acts as an elastic plate and its inherent rigidity distribute the topographic loads on a greater region.
Although the local isostatic model continues being used like first approach the calculation of isostatic movements in response to deglaciaciones, vulcanism or orogénesis, now is commonly accepted that the external Earth layer has certain rigidity and that behaves like a thin plate, elastic in first approach. To this process is called to him litosférica Flection . The flexural behavior of the lithospere essentially depends on elastic Thickness of the lithospere .
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