A new approach to the relief of Great Britain: III. Derivation of the contribution of neotectonic movements and exceptional regional denudation to the present relief

Abstract

This paper builds on the contribution of relative rock resistance to contrasts in the relief of Britain, to establish the contribution of other factors. These include the slope of the major rivers towards the sea, itself in part a function of the size of material eroded from the headwater uplands and thus of their lithology and the steepness of their valleyside slopes. The pattern of denudational unloading and thus of isostatic uplift is mapped and compared with actual mean altitude. It is shown that the sum of predicted isostatic uplift and local base-level is closely related to the current mean altitude of our uplands. The predicted mean height based on the six equations for each rock resistance class relating mean altitude to river distance can also be compared with actual mean elevation. This shows positive departures which are most readily explained by neotectonic uplift, notable in the Scottish Highlands, the Alston Block of the northern Pennines and Fforest Fawr in South Wales. Negative departures may be due to relative neotectonic subsidence, as in Buchan, where there is coincidence with positive gravity anomalies. However, most negative departures can be linked with severe glacial erosion, especially in such areas as westernmost Scotland, the Lake District, the Vale of Belvoir and the Wash/Fens Basin where evidence for deep glacial erosion is already strong. Regional height differences related to the major structural regions of Britain are calculated; they make a smaller contribution to differences in average elevation, and thus to the overall relief of Britain.