Are there any relict rock glaciers in the British mountains? |
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| Authors: | David Jarman Peter Wilson Stephan Harrison |
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| Institution: | 1. Mountain Landform Research, Scotland, UK;2. Environmental Sciences Research Institute, School of Environmental Sciences, University of Ulster, Coleraine, Northern Ireland UK;3. School of Geography, Archaeology and Earth Resources, University of Exeter, Tremough Campus, Penryn, UK |
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| Abstract: | The existence of a small population of ‘relict rock glaciers’ scattered across the main British mountain areas has previously been inferred from published cases of individual sites or local clusters. Discrete debris accumulations (DDAs) of widely differing character have been identified as ice‐debris landforms (whether ‘rock glaciers’ or ‘protalus lobes’) partly from morphological, sedimentological and topo‐locational evidence, but principally by analogy with both active and relict examples in present‐day arctic/alpine environments, with consequent palaeoclimate inferences. However, re‐interpretation of several supposed rock glaciers as rock slope failures has cast doubt on both the palaeoclimatic reconstructions and the origin of the remaining features. Issues of polygenesis and mimicry/equifinality have contributed to some previous misidentifications. We re‐evaluate the 28 candidate cases based on new field and image‐analysis evidence and place them on a continuum from no ice presence through passive ice presence and glacial shaping to emplacement onto glacier ice with consequent melt‐out topography. A null hypothesis approach (that there are no relict rock glaciers in the British mountains) is pursued, and the evidence indicates that none of the 28 cases clearly warrants classification as a relict rock glacier; their characteristics can be explained without recourse to any significant forward debris movement controlled or facilitated by incorporated or underlying ice as it deforms and melts out. However, only one‐third of the candidate DDAs are attributed in whole or part to rock slope failure (sensu stricto), with other debris sources including incremental rockfall, bedrock knolls with coarse debris veneer, protalus rampart and moraine. A few cases deserve more detailed investigation of their structure, morphology and sediments within a broader local glaciological/topographical context, with multitemporal/polygenetic evolution in mind. But it is for future researchers to demonstrate that deforming ice played an incontestable part in shaping these often enigmatic DDAs, given that other causes are simpler and commoner. Copyright © 2013 John Wiley & Sons, Ltd. |
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| Keywords: | discrete debris accumulations ice‐debris landforms protalus lobes rock‐slope failures |
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