There is a third process , called delamination . Here an unstable portion of cold root of the lithosphere drips down into the mantle , decreasing the density of the lithosphere and causing buoyant uplift . Regions can also experience uplift as a result of delamination of the lithosphere , in which an unstable portion of cold lithospheric root drips down into the mantle , decreasing the density of the lithosphere and causing buoyant uplift .