This is a new map kindly supplied by Dr Alun Hubbard of Aberystwyth University. It shows modelled ice thicknesses and ice limits for the time of the last glacial maximum, around 20,000 years ago. A lot of "ground truthing" has to be done, but the model is a pretty sophisticated one, and fits well with what we know for most of the ice covered area. What I hadn't spotted before (because the older maps did not have this level of detail)is the thickness of the ice over the Somerset coast (about 600m) and the fact that the ice surface contours curve around in the Bristol Channel because of the "blocking effect" of the Brecon Beacons and the other uplands of South Wales. Ice always flows perpendicularly to the directions of the ice surface contours; and this is exactly right for the postulated ice stream running over the Preseli Hills, eastwards up the Bristol Channel, and deep into the heart of Somerset.
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