ELSEVIER Geomorphology 20 (1997) 29-48 Calculating Quaternary glacial erosion rates in northeast Scotland Neil F. Glasser av *, Adrian M. Hall b zyxwvutsrqponmlkjihgfedcbaZYXWVU a schoolof Biological and Earth Sciences, Liverpool John Moores University, Byrom Street, Liverpool, w 3AF, UK b Dewfment zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA of Geography, University of Edinburgh, Drummond Street, Edinburgh, Effg SW, UK Received 1 December 1995; accepted 8 January 1997 Abstract Northeast Scotland is an area exhibiting selective erosion by Quatemary ice sheets. In this area both glacial and preglacial landforms exist in close proximity. The depths of erosion which this modification represents are calculated on the assumption of various depths of preglacial weathering. A depth of erosion of between 34 and 62 m per unit area is indicated. Calculated rates of erosion are 0.021 nun a- ’ for the entire 2.3 m.y. of the Quaternary, and between 0.1 and 0.5 mm aa1 on the assumption that glacial conditions existed in this area for 500,000 years and 100,000 years, respectively. These figures are compared to the offshore sedimentary record in the adjacent west-central North Sea. The volume of sediment deposited offshore is equivalent to a depth of erosion of 195 m per unit area, yielding an average erosion rate of 0.085 mm a-i over the entire Quatemary. Rates of erosion were low in the preglacial Pliocene (0.049 mm a- ‘1 and early Quatemary (0.063 mm a-‘). The expansion of ice sheets across the area in the middle Quatematy was associated with a sharp increase in the rates of erosion (> 0.13 mm a-‘) but the last (late Devensian) ice sheet in the area was less erosive (< 0.095 mm a-‘). The estimated rates of erosion represented by the offshore sedimentary record therefore exceed the estimated rates of glacial erosion from the onsho’re geomorphological reconstruction. Keywords: glacial erosion rates; offshore sediment volumes; geomorphological reconstruction; preglacial landscape: Scotland 1. Introduction Although erosion by former ice sheets and glaciers is widely believed to be a significant component of Quaternary landscape evolution in the northern mid- latitudes, there are few reliable estimates of long-term (103-lo- ’ ka) depths and rates of glacial erosion. The aim of this paper is therefore to calculate the depth and rate of Quatemary erosion across northeast Scotland using geomorphological reconstruction. Specific attention is given to identifying the spatial ?? Corresponding author. variability of Quaternary erosion across the area and to identifying temporal variations in the rates of erosion by comparing these figures with the sedi- ment volumes in the adjacent North Sea basin. In previous discussions concerning the depths and rates of erosion achieved by former glaciers two main approaches have been used (Bennett and Glasser, 1996): (1) geomorphological reconstruction, in which the preglacial landscape is reconstructed using evidence from landforms, deposits and weath- ering covers and compared with the present land- scape; and (2) sediment volumes, in which the vol- umes of Quatemary sediments in sedimentary basins are converted into depths of rock erosion in their 0169-555X/97/$17.00 0 1997 Elsevier Science B.V. All rights reserved. PZZSO169-555X(97)00005-6