A model for the lithosphere that accounts for isostatic anomalies by assuming there is a level of compensation that lies at a constant depth everywhere. Below the level of compensation all rocks have the same density, but above it density decreases as topographic elevation increases. For a column of material anywhere on Earth, the mass lying above the level of compensation will be the same, and ρ‎_ch a constant, where ρ‎_c is the density of the crust and h the topographic elevation. If the rocks are on the sea bed, then ρ‎_ch + ρ‎_wd is a constant, where ρ‎_w is the density and d the depth, of sea water. See also airy model.

Pratt model