QUANTIFICATION OF THE IMPACT OF GLACIAL EROSION ON THE BRITISH-ISLES

Publication of the offshore geological maps, scale 1:500 000, by the B ritish Geological Survey has allowed estimation of the volume of Quate rnary sediments on and at the margin of the continental shelf; total v olume is about 80 000 km(3). Estimates of the volume of glacial deposi ts left by a single glaciation are 4000 km(3) on the present land surf ace and from 7000 to 13 000 km(3) on the drowned continental shelf. Ea ch ice advance has removed virtually all the deposits of its predecess or and moved them to build up a wedge of deposits on the edge of the s helf. Each glaciation creates new deposits and leaves behind a discont inuous sheet of till and associated deposits with an average thickness of about 17 m. The accumulated deposits found offshore represent an a verage depth of erosion, for both the present land area and the contin ental shelf, of 125-155 m. The repeated process of erosion of older se diments and creation of new accounts for the essentially monoglacial r ecord of most of the British land area. The cumulative erosion has mod ified the uplands on more resistant rocks, producing glacial erosional forms which have long been recognized. Erosion has been several times more effective on the weaker rocks flooring our major lowlands and mu ch of the shelf. Overall rates of erosion by ice over the Quaternary p eriod greatly exceed those for unglaciated Britain.