Isostasy

Rationale: C.E. Dutton coined the term 'Isostasy' in 1889 in his paper to the Philosophical Society of Washington to describe the gravitational equilibrium of the Earth's crust.

Rationale: Airy assumed that the density of the crustal blocks is uniform (approximately 2.67 g/cm³), and the mountains float because they have deeper roots of the same density displacing the denser mantle.

Rationale: Pratt argued that the density of crustal blocks varies laterally—mountains have lower density, plateaus medium density, and ocean floors highest density—all resting on a uniform depth of compensation.

Rationale: Pratt's model is summarized as 'uniform depth, varying density', whereas Airy's model is summarized as 'uniform density, varying depth (thickness/roots)'.

Rationale: Vening Meinesz introduced flexural isostasy in 1931, proving that the Earth's lithosphere has flexural rigidity and can distribute loads over a broader regional area.

Rationale: The depth of compensation is a hypothetical plane where the total pressure exerted by the overlying columns is equalized, regardless of surface elevations.

Rationale: Using the buoyancy formula based on density contrasts (approx. 4:1 to 5:1 ratio depending on exact density values used), a 1 km high mountain requires a substantial root, roughly 4 to 5 km deep below normal crustal thickness.

Rationale: Post-glacial rebound (crustal uplift following the melting of Pleistocene ice sheets) is the classic and most direct observable evidence of ongoing isostatic adjustment.

Rationale: The asthenosphere is ductile and relatively weak, permitting the buoyant lithospheric blocks to float and adjust vertically.

Rationale: Both Airy and Pratt developed their respective theories in 1855 in response to geodetic survey anomalies (deflection of the plumb line) observed near the Himalayas in India.

Rationale: Oceanic crust is composed mainly of basaltic rocks (density ~3.0 g/cm³) which are denser than granitic/felsic continental crust (~2.7 g/cm³).

Rationale: As erosion removes mass from the surface, the mountain's weight decreases, causing the crust to buoyantly rise (isostatic rebound) to compensate for the lost mass.

Rationale: Pratt's model posits variable density and uniform depth of compensation, meaning no varying roots are required.

Rationale: Seismic studies show that large variations in crustal thickness (roots) actually exist beneath major mountain chains, proving Airy's root concept to be more physically realistic than pure Pratt compensation.

Rationale: It comes from the Greek words 'iso' (equal) and 'stasios' (standing).

Rationale: Gravimeters measure local gravitational acceleration, helping scientists calculate gravity anomalies (like Free-air and Bouguer anomalies) to test isostatic equilibrium.

Rationale: Local compensation (as assumed by Airy and Pratt) means each vertical column acts independently, unlike regional compensation where elastic bending distributes the load.

Rationale: Vening Meinesz used submarine pendulum gravity measurements in East Indies and ocean trenches to formulate the regional flexural isostasy theory.

Rationale: Oceanic crust is thinner and denser than continental crust, causing it to float at a lower level in the denser asthenosphere mantle.