There is a mounting body of evidence that superwaves, produced either by submarine landslides or by the impact of asteroids or comets in the ocean, have flooded continental lowlands. On continents, there is firm evidence that the catastrophic release of impounded water, possibly resulting from impact events, has led to grand deluges. Moreover, in special circumstances, rising seas have poured over sills to fill low-lying basins. All these lines of evidence add weight to the idea that some landscape features are caused by diluvial, rather than by fluvial, processes. Thus, neodiluvialism goes some way to vindicating the beliefs held by the old diluvialists before the dogma of uniformitarianism silenced them. It would perhaps be unwise to draw too close a parallel between the old diluvialism and the new diluvialism. Suffice it to remark that the diluvial metamorphosis of the landscape that superwaves and superfloods might inflict, and the diluvial metamorphosis of the landscape wrought by the conjectural floods of the old diluvialists, are in most respects very similar. Before Charles Lyell, it was commonplace to interpret virtually all gravel and boulder deposits as a sure sign of the catastrophic action of flowing water. After 175 years of gradualistic explanations of flood deposits, it seems fair, with the general acceptance of the bombardment hypothesis and the sure knowledge that huge floods have occurred in the past, to look again at catastrophic explanations (cf. Baker 2002). Interestingly, evidence for a diluvial origin of landscapes and sediments comes from not so much the finding of previously unnoticed phenomena, as from the reinterpretation of well-known landscape and sedimentary features.