Distribution of tors on Dartmoor gives clues to the existence of an ice cap: Image by Nigel Cox
Have our previous estimates of glacier limits been wrong? Generations of British geography students have drawn a line on the map between the rivers Severn and Thames to represent the southernmost limit of the last glacial ice sheet. Now, a new study has produced evidence of glaciation further south, on the bleak Devon moorland of Dartmoor.
Dartmoor: Beyond the Ice?
In his book, The Hidden Landscape, geologist Richard Fortey distinguishes between the granite masses of northern Britain which “have an almost terrifying monumentality in the face of assault by ice and weather” and those of the south-west, which “lay beyond the margin of the massive ice advance … [and] have had time to respond to the elements at comparative leisure.”
This is the conventional wisdom – that Dartmoor was shaped not by ice but by periglacial forces operating close to an ice mass. It is to these conditions, allied to earlier chemical weathering, that we attribute the formation of Dartmoor’s famous granite tors, the exposed rock molded into fantastic shapes.
Evidence for Glaciation of Dartmoor
The new research looks at several different lines of evidence for glaciation, not least the distribution of the tors themselves. These tend to occur on the edges of the moor: their absence at its center suggests that a small ice cap covered the higher central areas, either destroying existing tors or preventing their formation.
Using aerial photographs, the study looks in detail at landforms on the moor which, being poorly-developed and blurred by later erosion, haven’t previously been attributed to glacial action. Though both erosional and depositional features have been identified, it is the glacial moraines which, according to lead author David Evans, provide the most important evidence.
According to Professor Evans, the report’s findings are significant, demonstrating “that glacier ice existed in Britain much further south than previously thought and that this was on a landscape that was previously regarded as never touched by ice and therefore an iconic ancient weathered landscape.”
Click to Read Page Two: Redrawing the Map of the Ice Age
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