Abstract
ABSTRACTThree maps are presented that portray the periglacial geomorphology of the three summit areas of Bodmin Moor, Cornwall, SW England, including Brown Willy (scale 1:2630), Kilmar/Bearah/Sharp tors (scale 1:3335) and Rough/Little Rough/Showery tors (scale 1:2175). Landform elements include castellated tors with well-developed cantilevered or precariously balanced corestones, summit blockfields, rock-fronted lobes thought to record former permafrost creep, patterned ground (stripes) and lower slope accumulations of crudely stratified growan or weathered granite residue. The altitudinal arrangement of these periglacial landforms appears to be a signature of a well-established periglacial landsystem and hence the Bodmin Moor granite massif is a suitable exemplar for a mature upland periglacial landsystem unaffected by glacierization.
Highlights
Apparent on Main Maps 1–3 are clear lobate-shaped assemblages of boulders which represent boulderfronted lobes, many being several tens of metres wide, of the type previously identified by Miller (1990) as gelifluction lobes, debris tongues and block streams emerging from summit blockfields (Figures 1 and 4). Slopes covered by such prominent assemblages of boulders are often termed ‘clitter slopes’ on Dartmoor (Albers, 1930; Green & Eden, 1973; Linton, 1949, 1955; Waters, 1964), where Harrison, Anderson, and Winchester (1996) have invoked a genesis of permafrost creep of boulders after they have collapsed from tor stacks due to the process of macrogelifraction and thereby they could be regarded as mini rock glaciers
Dartmoor has traditionally been championed as the exemplar of ancient periglaciated landscapes, in the British Isles, the recent identification of evidence for potential glaciation of the area has questioned this long standing notion
Mapping of the landforms on the highest summits of Bodmin Moor indicates that this granite massif is a more suitable exemplar for a mature upland periglacial landsystem unaffected by glacierization
Summary
Recent proposals that the uplands of southwest Britain formerly hosted glacier ice at some time during the Quaternary Period (Evans, Harrison, Vieli, & Anderson, 2012a, 2012b; Harrison, 2001; Harrison, Anderson, & Passmore, 1998, 2001; Harrison, Knight, & Rowan, 2015) have fundamentally questioned traditional interpretations of the geomorphology of the region as having evolved exclusively through periglacial processes and are landscapes of great periglacial antiquity (e.g. Linton, 1955). The notion of glaciation having affected the granite uplands of SW England was entertained as long ago as the midnineteenth century (Ormerod, 1869), the subtlety of the geomorphological evidence for glaciation in such peripheral regions (Evans, 2016) resulted in it being overlooked in relation to the more prominent periglacial landforms and deposits It is surprising, that little systematic mapping of periglacial landforms has ever been undertaken on the granite uplands, an important exception being the assessment of Cox Tor and its environs by te Punga (1956, 1957), Gerrard (1988) and Miller (1990), where altiplanation terraces and spectacular examples of ‘clitter’ (blockfield) landforms such as boulder lobes and boulder runs were identified and used as exemplars of periglacial landscape maturity. This project is designed to test the feasibility of assessing landform types, distribution and patterns using aerial photography in a landscape characterized by plateau extents and altitudes that elsewhere in the region have been proposed to be sufficient to generate glacier ice during the Quaternary glacial cycles
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