UNDERSTANDING OUR PLANET Q/A #6 – What geologic processes might cause the forces that can hold a region out of isostatic equilibrium? – 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. It was ascertained that disturbances of the isostatic equilibrium are the result of the active geotectonic process and that isostatic forces are passive as tectonic factor. In the geological time scale the readjustment takes place instantaneously, therefore isostatic anomalies of gravity may be considered as direct indications of the modern tectonic activity. However, some continental collisions are far more complex than this, and the region may not be in isostatic equilibrium. Certain areas (such as the Himalayas) are not in isostatic equilibrium, in the case of the Himalayas, by proposing that their elevation is being “propped-up” by the force of the impacting Indian plate.
Note : Isostasy is the principle of buoyancy 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.