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GRAVITATIONAL POTENTIAL ENERGY and GRAVITATIONAL FORCE |
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This sketch illustrates the variation with depth of the lithostatic pressure along two lithospheric columns, B and C, in isostatic equilibrium. It is assumed here that the crust (pink) and the mantle (green) have the same densities in both column and that there is no density difference between the lithospheric mantle and the asthenosphere. Because it has a thicker crust, column C stands above column B. Consequently the lithostatic pressure at any depth within the crust of column C is a higher than the lithostatic pressure at the same depth in column B. Below the compensation depth (here the base of crust in column C) the lithostatic pressure is the same in both column.
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| The Gravitational Potential Energy (GPE, in MPa) of both columns is given by the area beneath the r.g.z curves (orange area for column B, and yellow area, extending underneath the orange area, for column C). The gravitational force (Fg in Nm-1) that C and B applies to each other is equal to the difference of their respective GPE (surface area of the yellow area). An excess in GPE in column C (Fg<0) will drive extension, whereas a deficit (Fg>0) will drive contraction. |
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Fg = |
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