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Thursday, 28 March 2013

Ice-moulded slabs on Carningli

Ice-moulded slab on Carningli.


This is a photo taken today of a beautiful ice-moulded slab on the south side of Carningli, near Newport in Pembrokeshire.  Just up the road from where we live......

To my great shame (I thought I knew every inch of the mountain) I had not spotted this before -- maybe because you sometimes miss things in the landscape if the light is not right.  Anyway, today the light was exactly right, and there it was, revealed in all its glory.

I don't know of any other process that can mould a rock surface like this apart from long-continued meltwater flow.  But in this location there is no evidence for a fluvioglacial origin for these features -- so overriding glacier ice it has to be.

I have dithered a lot in the past on the question of whether the Devensian ice of the Irish Sea Glacier flowed over Carningli, or round it, or just skidded to a halt somewhere on its northern flank.  However, this is near the western end of the craggy mountain, on the south-facing slope where there are great banks of scree, broken bedrock and occasional rock outcrops.  The ice here must have been flowing down the slope, from north to south -- there is now no doubt in my mind that the ice surface in the Devensian was above the summit of Carningli, and that ice flowed at least as far as the Gwaun Valley.  The abundant ice-moulded slabs on the summit ridge of the mountain, and on its flanks overlooking the town of Newport, all add to the evidence of quite intensive ice action, with the whole of the local landscape submerged beneath ice.

(There is still a chance that we are looking at Anglian glacial features here -- but that would mean they are 450,000 years old, and they look far too fresh.  Some more cosmogenic dating is needed........)

So this evidence matches that which I recently described in my post about the Gernos Fawr moraine on the SOUTH side of the Gwaun Valley, about 3 km due south from the photo location.

http://brian-mountainman.blogspot.co.uk/2013_02_01_archive.html






3 comments:

Constantinos Ragazas said...

Brian,

If you really believe that long groove on bluestone 68 was made by Neolithic people, I have a bridge to sell you!

Kostas

BRIAN JOHN said...

You will no doubt tell us, Kostas, the natural process by which it WAS made......

Constantinos Ragazas said...

Brian,

No it wasn't Nature either that made this groove!

But if this bluestone was one of the stones at Stonehenge set by the Atkinson reconstruction (as was bluestone 69, for example), then it is likely this groove was made by PEOPLE much later than the Neolithic. And at a time when they had a purpose and the tools to do it. Perhaps the Romans or even Medieval people.

Stonehenge existed for at least 5000 years. Why must everything in it be 5000 years old too?

Kostas