A model to account for isostasy which in the lithosphere assumes a constant density (ρ‎_c = 2 670 kg/m³), but in which topographic elevations (h) are compensated by the presence of ‘roots’ replacing high-density mantle rocks (ρ‎_m = 3 300 kg/m³) by lower-density lithospheric rocks. The depth of the root (d) is equal to hρ‎_c/(ρ‎ − ρ‎_c). See also pratt model.

Airy model