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ISOSTATIC EQUILIBRIUM AND MECHANICAL EQUILIBRIUM |
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| The sketch below represents a schematic cross-section through a lithospheric plate. Although the thicknesses of both the crust and the lithospheric mantle vary, isostatic equilibrium is maintained. Isostatic equilibrium implies that it exists a depth, called the compensation depth, below which the pressure is hydrostatic. In other terms, at or below the compensation level, the weight of vertical columns with the same cross-sectional areas standing on the same equipotential surface are the same. Isostasy controls the elevation of the surface of each column. Despite being in isostatic equilibrium this plate is not in mechanical equilibrium. Lateral variations of density along a given equipotential surface indeed produce gravitational forces (body forces) acting inside the lithospheric plate. |
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