The first stages of erosion by ice sheets: Evidence from central Europe A.M. Hall a, ⁎, P. Migoń b a School of GeoSciences, University of Edinburgh, Edinburgh EH8 9XP UK b Department of Geography and Regional Development, University of Wroclaw, pl. Universytecki 1, 50-137 Wroclaw, Poland abstract article info Article history: Received 5 January 2010 Received in revised form 4 August 2010 Accepted 6 August 2010 Available online 18 August 2010 Keywords: Preglacial inheritance Granite Glacial erosion Inselberg Roche moutonnée Grus In almost all former and presently glaciated areas of the world, glaciers have modified or even transformed pre-glacial terrain during the many cold stages of the Pleistocene. In consequence, the early stages in the development of glacial landscapes have been overprinted or erased by later phases of erosion. The Sudetes in central Europe provide exceptional opportunities to examine the inception of glacial erosion. Evidence of a long geomorphic evolution before glaciation, with the development of etch surfaces, deep weathering covers and the preservation of Neogene kaolinitic sediments, provides a direct analogue to other lowland crystalline terrains as existed immediately prior to Pleistocene glaciation. Large granite intrusions exist in the Sudetes and its Foreland that support hills that range in size from small tors to large domes. These terrains experienced only thin ice cover for short periods when the Scandinavian ice sheet reached its Pleistocene maximum limits in Marine Isotope Stage (MIS) 12 (Elsterian) at 440–430 ka and MIS 8 (Early Saalian) at 250–240 ka. In each of four study areas beyond, at and within the limits of glaciation we have mapped Glacial Erosion Indicators, glacial landform assemblages that indicate progressive glacial modification of the pre-glacial granite terrain. We find that glacial erosion increases with distance from the ice margin, due to greater ice thickness and longer ice cover, but has had only limited impact. On hills, regolith was stripped by moving ice, tors were demolished, and blocks were entrained. However, indicators of more advanced glacial erosion, such as lee- side cliffs and glacial streamlining, are absent, even from granite domes that lay beneath ~ 500 m of ice. The survival of tors beneath ice cover and the removal of tor superstructure by glacial erosion are confirmed. The presence of glacially-modified tors in areas covered only by Elsterian ice implies that the tors existed before 440 ka. Moreover, the contrast between blockfield-covered slopes found above Elsterian and Saalian glacial trimlines on summits of granite, gabbro and basalt hills in the Sudetic Foreland and glacially-stripped surfaces at lower elevations implies only limited regeneration of blockfields since 430 and 240 ka. The first stages of roche moutonnée formation are recognised in the exhumation of tor stumps but development of lee-side steps remains very limited. Granite domes retain a pre-glacial morphology and local examples of hill asymmetry are determined by structural, rather than glaciological controls. Development of roches moutonnées and asymmetric and streamlined hills by glacial erosion has not occurred in the Sudetes despite the passage of largely warm-based ice sheets 80–500 m thick that persisted for 5–20 ka. © 2010 Elsevier B.V. All rights reserved. 1. Introduction Whilst landscapes of little or no glacial erosion have been recognised in many formerly glaciated areas (see summary in Benn and Evans, 1998), the changes brought about at the inception of glacial erosion have only recently begun to be identified (André, 2004; Hall and Sugden, 2007). This limited understanding reflects the present condition of almost all former and presently glaciated areas of the world, where pre-glacial terrain has been modified or transformed by glacial erosion during the many cold stages of the Pleistocene. In consequence, landforms created early in the development of glacial landscapes have been overprinted or erased by later phases of erosion and so are difficult to decipher. Yet understanding the geomorphic changes that take place at the inception of glacial erosion is important for several reasons. Differences between the weathered and perme- able materials of the pre-glacial landscape and the hard rock or drift- covered substrates more typical of glacier beds in the Late Pleistocene may have led to important differences in ice sheet behaviour (Clark and Pollard, 1998). Reliable recognition of relict landforms is required in order to identify patterns of erosion in glaciated landscapes (Hall and Sugden, 1987) and for former glacier basal thermal regimes to be reconstructed (Kleman and Stroeven, 1997; Stroeven et al., 2002; Harbor et al., 2006). Models of the progressive development of landforms of glacial erosion, including roches moutonnées (Jahns, 1943; Sugden et al., 1992; Glasser, 2002) and domes (Matthes, 1930; Ebert and Hätterstrand, 2010) also need to be tested against field Geomorphology 123 (2010) 349–363 ⁎ Corresponding author. Tel.: + 44 131 311 6969; fax: + 44 131 3081. E-mail addresses: am.hall@fettes.com (A.M. Hall), piotr.migon@uni.wroc.pl (P. Migoń). 0169-555X/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.geomorph.2010.08.008 Contents lists available at ScienceDirect Geomorphology journal homepage: www.elsevier.com/locate/geomorph