The continental crust of the Earth has a visible part above the surface and a lower, invisible one. The balance between these two is isostasy. Erosional isostasy is a ‘plausible mechanism’ (Maddy et al. (2000) Geomorph. 33, 3–4) for differential crustal movement, in which the crust realigns in response to erosional unloading and depositional loading (M. A. Summerfield 1991). The lack of evidence for significant surface denudation may suggest that erosional isostasy may be no more than a positive feedback response to uplift initiated by other influences (Maddy (1997) J. Quat. Sci. 12). Glacio-isostasy results from the cessation of pressure from glacier ice on glacier melting, with unloading leading to uplift (Lambeck (1995) J. Geol. Soc. London 152). Hydro-isostasy is similar to glacio-isostasy; here, the loading/unloading of the continental shelves due to changes in sea level may have been significant in driving continental uplift.