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Tuesday, 7 December 2010

Salisbury Plain ice edge?


If the ice of the Irish Sea Glacier really did extend into eastern Somerset or even onto the chalk lands of Salisbury Plain, what did the ice margin look like?  My own instinct is that it was a vertical ice front (I know Kostas is going to love this!!) rather like that which we find in the high arctic parts of Greenland, where the ice is very cold and the climate is also cold and arid.  The two pictures above are typical for the ice front where it sits on an undulating land surface to the east of Nares Sound and eastwards into Peary Land.

There are some dirt layers in the ice, and some shearing, as we can see at the right hand edge of the lower photo -- but the ice is moving very slowly indeed, and this is a very different sort of environment from that which we see near the snouts of rapidly moving and rapidly disintegrating glaciers.

Why do I think these are reasonable analogies?   Well, the apparent lack of any thick layer of anything we might call till on Salisbury Plain; the signs of permafrost and periglacial action on the chalklands, the permeable nature of the chalk, which would in itself inhibit movement on the glacier bed with meltwater lubrication; and the fact that we are on the lee side of an extensive ice sheet, where precipitation and ice dynamism would have been much less than on the western or Irish flank.

And I don't think that the ice was here for very long.  If there had been a more or less static ice margin here for centuries or even millennia, there would have been a substantial morainic feature left behind afterwards, even if the ice was moving very slowly.

Needs more thought.....

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