isostasy

from WordNet (r) 3.0 (2006)

isostasy
    n 1: (geology) a general equilibrium of the forces tending to
         elevate or depress the earth's crust

from The Collaborative International Dictionary of English v.0.48

Isostasy \I*sos"ta*sy\, n. [See {Iso-}; {Stasis}.]
   The state or quality of being isostatic. Specif. (Geol.),
   general equilibrium in the earth's crust, supposed to be
   maintained by the yielding or flow of rock material beneath
   the surface under gravitative stress. By the theory of
   isostasy each unit column of the earth, from surface to
   center, has approximately the same weight, and the continents
   stand higher than the ocean beds chiefly because the material
   of the crust has there less density.
   [Webster 1913 Suppl.]