THEORY OF ISOSTASY BY JOLLY (1925) - Geography for You


Joly, presented his views on isostasy in the year 1925. He disapproved the view of Hayford and Bowie about the existence of level of compensation at the depth of about 100 km on the ground that the temperature at this depth would be so high that it would cause complete liquefaction and thus level of compensation would not be possible.

He further refuted the concept of Hayford and Bowie that ‘density varies above the level of compensation but remains uniform below the level of compensation’ on the ground that such condition would not be possible in practice because such condition would be easily disturbed by the geological events and thus the level of compensation would be disturbed.

According to Joly there exists a layer of 10-mile (16 km) thickness below a shell of uniform density. The density varies in this zone of 10-mile thickness. It, thus, Joly assumed the level of compensation as not a linear phenomenon but a zonal phenomenon. In other words, he did not believe in a ‘line (level) of compensation’ rather he believed in a ‘zone of compensation’ (of 10-mile thickness).

Thus, we also find a glimpse of the law of floatation (it may be noted that Joly did not mention this, we only infer the idea of floatation from Joly’s concept) and his concept is closer to the Airy’s concept rather than the concept of Hayford and Bowie.

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