Pratt, John Henry -

(1809-1871): British geophysicist. He proposed "isostasy," the principle that mountains are high because they have deep roots of less dense material than the upper mantle that provide for a gravitational force corresponding to the difference in weight of root and mantle material. Isostasy is important in modeling ice age climate because the buildup and decay of large ice masses changes the elevation of the continental crust that bears the ice.