 Isostasy

Approximate gravitational compensation of loads by subsurface mass redistribution. Airy and Pratt models use local column balances; flexural support spreads the load laterally. Real surface topography can also be maintained by dynamic stresses.

Isostasy is a geological concept that describes the state of gravitational equilibrium between the Earth's lithosphere (the rigid outer layer of the Earth) and the underlying asthenosphere (a semi-fluid layer of the upper mantle). According to the principle of isostasy, the Earth's crust "floats" on the denser, more fluid mantle beneath it, much like an iceberg floats in water.