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Friday, 10 December 2010

Calculating isostatic loading and rebound

This is one of the BRITICE models, for which I thank Dr Alun Hubbard and colleagues.  I'm posting it here because it has a bearing on the discussion on this blog about isostatic loading and rebound during the Devensian and other glaciations.  This model shows calculated ice thicknesses -- if you click on it to enlarge, and then examine it carefully, you will see that the THICKEST ice was off the NE coast of Scotland, whereas over the west coast of Scotland, which is maybe where the highest part of the ice dome was located, the high mountain terrain means that in many places the ice was less than 500m thick.  Another area of very thick ice was in the Irish Sea basin, centred on the Isle of Man.

The general rule, ie that 1,000m of ice leads to about 330m of crustal depression, is VERY difficult to apply in such circumstances.  If you were to try to draw a map of isobases -- showing lines of equal isostatic depression -- it would be incredibly difficult to get it right, since elastic effects, crustal warping (influenced by local geology) and regional tectonic trends also come into play.  Then in those areas where the sea is flooding back in, 100m of potential isostatic recovery may convert to less than 70m, because a water column will take the place of an ice column.  I don't think we are yet anywhere near getting an accurate isobase map for the UK.  But we have to try, because I think this area of research is crucial in understanding coastal sediment sequences, the history of Doggerland etc.

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