Could the Irish Sea Glacier have reached Salisbury Plain?

Two of the Boulton - Hagdorn models for the LGM maximum.  These are obviously very simplified or generalised, and the date is all wrong, but the BRITICE team has shown that the ice extended further to the SW than the model predicted -- so in some respects these models are conservative.

As one would expect, I keep this matter under constant review, and I have been looking again at one of the classic papers, by Geoff Boulton and Magnus Hagdorn, which attempted to model the LGM history of the British and Irish ice sheet.

Geoffrey Boulton, Magnus Hagdorn
Glaciology of the British Isles Ice Sheet during the last glacial cycle: form, flow, streams and lobes
Quaternary Science Reviews 25 (2006), pp 3359–3390.

A lot has happened since 2006, including more sophisticated modelling work by Henry Patton and others (already discussed on this blog), the vast research programme of the BRITICE team and an increased awareness of the role of soft sediments and a fluid bed (in the Celtic Sea arena in particular) in influencing both ice stream velocity and ice surface gradient.  It's now pretty widely accepted that the Irish Sea Ice Stream between St Georges Channel and the shelf edge had a maximum velocity of around 1 km per year and an exceptionally low surface gradient.

These models show predicted ice surface elevation and horizontal velocity on the glacier bed.

The trouble with these models --as indeed with all the others that followed within the last decade or so -- is that they are MODELS that require massive manipulations to take account of local topographt and ground surface conditions -- not to mention rock type variations, terrain roughness, and climatic and glaciological variability.  Eventually the models have to be built on so many variables that they become unworkable, requiring enormous computing power.  And when you add "ground truthing" it starts to get really confusing, because research workers still do not agree about the precise positioning of the ice edge at the maximum or at any other stage in the life of the ice sheet.  But that's science for you......... and eventually it WILL all get sorted out.

For comparison, here are two of the very old models showing approx ice surface contours and streamlines.  In the south-western segment the ice edge is more than a hundred km away from where it should be, but one thing that is accurate about these old models is the portrayal of ice stream directions perpendicular to the ice edge.  That respect for a basic glaciological principle has been forgotten about by many of the researchers within the past decade, which is why, over and again, they fail to accept that ice MUST have progressed eastwards for some distance up the Bristol Channel, both in the LGM and in earlier glacier episodes.

I'm still very convinced that the scenario during the "Greatest British Glaciation" (at least in the SW) looked something like this:

.... and that the LGM situation was something like this: