Quantification of the impact of glacial erosion on the British Isles

Publication of the offshore geological maps, scale 1:500 000, by the British Geological Survey has allowed estimation of the volume of Quaternary sediments on and at the margin of the continental shelf; total volume is about 80 000 km(3). Estimates of the volume of glacial deposits left by a single glaciation are 4000 km(3) on the present land surface and from 7000 to 13 000 km(3) on the drowned continental shelf. Each ice advance has removed virtually all the deposits of its predecessor and moved them to build up a wedge of deposits on the edge of the shelf. Each glaciation creates new deposits and leaves behind a discontinuous sheet of till and associated deposits with an average thickness of about 17 m. The accumulated deposits found offshore represent an average depth of erosion, for both the present land area and the continental shelf, of 125-155 m. The repeated process of erosion of older sediments and creation of new accounts for the essentially monoglacial record of most of the British land area. The cumulative erosion has modified 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 much of the shelf. Overall rates of erosion by ice over the Quaternary period greatly exceed those for unglaciated Britain.