It is the idea that the lighter crust must be floating on the denser underlying mantle.
It is invoked to explain how different topographic heights can exists on the Earth’s surface.
Isostatic equilibrium is an ideal state where the crust and mantle would settle into in absence of disturbing forces.
The waxing and waning of ice sheets, erosion, sedimentation, and extrusive volcanism are examples of processes that perturb isostasy.
The physical properties of the lithosphere (the rocky shell that forms Earth’s exterior) are affected by the way the mantle and crust respond to these perturbations.
Therefore, understanding the dynamics of isostasy helps us figure out more complex phenomena such as mountain building, sedimentary basin formation, the break-up of continents and the formation of new ocean basins.