Editing Isostasy (section)

=== Airy ===
[[File:Airy Isostasy.jpg|thumb|right|Airy isostasy, in which a constant-density crust floats on a higher-density mantle, and topography is determined by the thickness of the crust.]]
[[File:Backstripping and eustasy correction.jpg|thumb|Airy isostasy applied to a real-case basin scenario, where the total load on the mantle is composed by a crustal basement, lower-density sediments and overlying marine water]]

The basis of the model is [[Pascal's law]], and particularly its consequence that, within a fluid in static equilibrium, the hydrostatic pressure is the same on every point at the same elevation (surface of hydrostatic compensation):<ref name=Watts2001/>{{sfn|Kearey|Klepeis|Vine|2009|p=43}}

h<sub>1</sub>⋅ρ<sub>1</sub> = h<sub>2</sub>⋅ρ<sub>2</sub> = h<sub>3</sub>⋅ρ<sub>3</sub> = ... h<sub>n</sub>⋅ρ<sub>n</sub>

For the simplified picture shown, the depth of the mountain belt roots (b<sub>1</sub>) is calculated as follows:

:<math> (h_1+c+b_1)\rho_c = (c\rho_c)+(b_1\rho_m) </math>
:<math> {b_1(\rho_m-\rho_c)} = h_1\rho_c </math>
:<math> b_1 = \frac{h_1\rho_c}{\rho_m-\rho_c} </math>

where <math> \rho_m </math> is the density of the mantle (ca. 3,300&nbsp;kg m<sup>−3</sup>) and <math> \rho_c </math> is the density of the crust (ca. 2,750&nbsp;kg m<sup>−3</sup>). Thus, generally:
<br />
:''b''<sub>1</sub> ≅ 5⋅''h''<sub>1</sub>

In the case of negative topography (a marine basin), the balancing of lithospheric columns gives:

:<math> c\rho_c = (h_2\rho_w)+(b_2\rho_m)+[(c-h_2-b_2)\rho_c] </math>
:<math> {b_2(\rho_m-\rho_c)} = {h_2(\rho_c-\rho_w)} </math>
:<math> b_2 = (\frac{\rho_c-\rho_w}{\rho_m-\rho_c}){h_2} </math>

where <math> \rho_m </math> is the density of the mantle (ca. 3,300&nbsp;kg m<sup>−3</sup>), <math> \rho_c </math> is the density of the crust (ca. 2,750&nbsp;kg m<sup>−3</sup>) and <math> \rho_w </math> is the density of the water (ca. 1,000&nbsp;kg m<sup>−3</sup>). Thus, generally:
<br />
:''b''<sub>2</sub> ≅ 3.2⋅''h''<sub>2</sub>