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Tuesday 1 February 2022

Dead ice terrain



Don't you just love dead ice terrain?  it's very dangerous, which is maybe why I have always thought it rather fascinating.  I have done many posts over the years, including this one:

https://brian-mountainman.blogspot.com/2019/10/dead-ice-terrain.html?m=0

The above photo was taken near the edge of Whisky Glacier in Antarctica, and shows what happens when detached or dead ice is melting out under a surface layer of till.  Everything moves, and you walk across this sort of terrain at your peril.........

The more I think about the nature of the deposits in bays like West Dale Bay in Pembs or Rotherslade in the Gower or Morfa Bychan on the Ceredigion coast, the more I am convinced that around 24,000 years ago, when the ice of the LGM Irish Sea Glacier was melting away, there was wholesale reorganisation - redeposition of glacially deposited materials which actually flowed or slid on a saturated surface of either ice or permafrost.  i pat=rt compant with some other geomorphologists who think that these redeposited materials are "old" glacial deposits dating from earlier glacial episodes.  I think that this explanation is more complex than it needs to be -- Occam's Razor and all that......

Unless there is some very powerful evidence that the original glacial deposits are old, I prefer to think of them as new, redeposited and rearranged probably within a few centuries of the initiation of deglaciation.

Stratified deposits at West Dale Bay.  How exactly were they laid down?


Some of the deposits at Rotherslade (photo: Hiemstra et al, 2009).  Similar deposits are seen all around the West Wales coasts, and are variously interpreted as meltout till / flowtill / rubble drift.


Stratified slope deposits at Morfa Bychan, Ceredigion.  Periglacial or glacial in origin?


I suppose some of the differences between these deposits are related to turbulent and chaotic flows of large masses of debris in some cases, where the meltout layer is quite thick -- and at the other extreme a very thin flowing or mobile layer with a frozen "sliding surface" just a few cm beneath the ground surface.  More thought needed on all this.... 











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