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

This paper builds on the contribution of relative rock resistance to contra sts in the relief of Britain, to establish the contribution of other factor s. These include the slope of the major rivers towards the sea, itself in p art a function of the size of material eroded from the headwater uplands an d thus of their lithology and the steepness of their valleyside slopes. The pattern of denudational unloading and thus of isostatic uplift is mapped a nd compared with actual mean altitude. It is shown that the sum of predicte d isostatic uplift and local base-level is closely related to the current m ean altitude of our uplands. The predicted mean height based on the six equ ations for each rock resistance class relating mean altitude to river dista nce can also be compared with actual mean elevation. This shows positive de partures which are most readily explained by neotectonic uplift, notable in the Scottish Highlands, the Alston Block of the northern Pennines and Ffor est Fawr in South Wales. Negative departures may be due to relative neotect onic subsidence, as in Buchan, where there is coincidence with positive gra vity anomalies. However, most negative departures can be linked with severe glacial erosion, especially in such areas as westernmost Scotland, the Lak e 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 sma ller contribution to differences in average elevation, and thus to the over all relief of Britain. (C) 1999 Elsevier Science B.V. All rights reserved.