Isostasy

Isostasy is the gravitational equilibrium in which Earth's crust and lithosphere are supported by the underlying mantle, with elevation shaped by thickness and density.

Airy isostasy: An isostatic model in which crust of uniform density varies in thickness, with deeper roots beneath higher terrain. It explains topographic relief through variations in crustal thickness.
Crust: Earth's outermost solid layer, divided into thinner oceanic crust and thicker continental crust. Differences in its thickness and composition create contrasting isostatic elevations.
Isostatic rebound: The uplift of Earth's crust after removal of a large load, such as a melting ice sheet. It describes the landscape response when loading no longer maintains equilibrium.
Isostatic equilibrium: A state in which buoyant support balances the gravitational load of crust and lithosphere. It names the balance that the different isostatic models describe.
Pratt isostasy: An isostatic model in which columns of equal depth have different densities, producing different surface elevations. It balances elevation differences through lateral density variation rather than crustal roots.
Density: Mass per unit volume, a physical property that affects how materials respond to gravity. Density differences help determine which crustal columns sit higher.
Gravity anomaly: A difference between measured gravity and the value predicted by a reference model. Gravity anomalies help locate mass excesses or deficits relevant to compensation.
Dynamic topography: Long-wavelength surface elevation caused by mantle flow and its stresses on the lithosphere. It can create elevation that is not explained by static buoyant compensation alone.
Flexural isostasy: An isostatic model in which the lithosphere bends elastically under loads instead of compensating locally at each point. It accounts for loads distributed across a mechanically strong lithosphere.
Gravitational potential energy: The energy an object has because of its position in a gravitational field. Isostatic balance concerns the gravitational effects of masses at different elevations.

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