The Glaciation of Devon and Cornwall

There has been an interesting debate on this topic over the years, with some support in the 1940's and 1950's for glacial activity on the higher parts of the SW Peninsula, then a period in which glaciation went out of fashion, with most Pleistocene landscape change put down to periglacial and fluvial processes, and then within the last few years a growing recognition of the role played in many parts of the world by thin, cold-based glaciers in protecting the landscape at times when there may have been intense glacial streaming and erosion in the lowlands and in glaciated troughs.  Interestingly enough, the authors of the Geological Conservation Review for SW England (1998) dismissed the idea of glaciation in the SW out of hand, while getting quite tangled up in the debates about the giant erratics on the coast, and the glacial deposits found in pockets along the Bristol Channel coasts of Devon, Somerset and Cornwall.  Not entirely logical, you might say -- and I might agree.

Stephan Harrison, in the book called "The Glaciations of Wales and Adjacent Areas" (2005) takes a much more nuanced approach, and argues for intermittent small, thin ice caps over Dartmoor, Exmoor and other uplands -- and he cites a good deal of evidence which is difficult to interpret except by reference to glacier ice.  More recently the modelling exercises undertaken as part of the BRITICE project has also led the research team to the view that there WERE thin ice caps over the uplands of Dartmoor, Exmoor, Preseli and the Yorkshire Moors at the peak of the Devensian Glaciation, around 20,000 years ago.

If you look at the maps above you will see that there is --  and was -- considerable high ground across the SW Peninsula, capable of supporting extensive caps of snow and firn for long periods, and even true glacier ice during the coldest and snowiest parts of the Devensian.  For the most part, the ice will have been largely immobile and frozen to its bed, but there may have been some movement (and the creation of till and even morainic features) in the deeper valleys on E- and NE-facing slopes.

I postulate that c 20,000 years there were thin ice caps on all of the "high plateax" and "high hills" areas shown on the top map.  Lower plateax and hills might well have had a more or less continuous cover of snow and firn patches, which occasionally melted out during warmer episodes.  In the lowlands and valleys there would have been less extensive snow cover, but still permafrost -- so periglacial processes would have been active.

Wherever the edge of the Devensian Irish Sea Glacier might have been (somewhere in the Bristol Channel,  maybe quite close to the coastline) the intensity of glaciation in the SW Peninsula might not have been great enough to depress the land surface sufficiently for iceberg transport of erratics in the manner seen during earlier glacial episodes.