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Thursday, 28 February 2013

The Gernos-fawr moraine


Well now -- this is as fine a moraine as I have seen in a long time.  Its at Gernos-fawr, near the headwaters of the Gwaun River, at an altitude of 240m.  A very distinct mound in the middle of the valley, littered with boulders of all shapes and sizes, but mostly faceted and sub-rounded -- as one would expect with a deposit made largely of glacially-transported material.

Why haven't I spotted it before? The reason is that this hillock has been previously covered with gorse bushes -- and it is quite recently that the farmer / smallholder here has had the pigs in to clear it, followed by sheep, geese and chickens.  So all is now revealed......

 The Gernos-fawr moraine is at the black spot, bottom right of the image. Click to enlarge

What is the significance of this find?  Really, I haven't got a clue.  According to all my predispositions, there shouldn't be a moraine here at all, since it is on the south side of the Gwaun Channel, about 2 km distant from the hump or highest point on the valley floor.  I assume that it is Devensian in age -- so could it have been built at a glacier terminus following ice movement across the Carningli massif and across the Gwaun Channel?  That's possible, since I have speculated many times before on Carningli being completely covered by ice at the Devensian maximum.  Here is one of my earlier maps, with Gernos-fawr marked on it:


 As we can see, Gernos-fawr is very close to this suggested ice limit, given than an ice edge never is straight -- but tends to mould itself to the contours, fingering up valleys and leaving ridges ice-free.
So far so good.  Now for something I have just discovered,  having looked rather carefully at the satellite image above (the second image on this post.)  Click to enlarge, and then have a look at the area of big fields NNE of Gelli-fawr and the area to the SW of Gernos-fawr.  Do you see the slight traces of elongated curving ridges?  I have a feeling that these might be slight traces of morainic ridges, related to a lowering (retreating) ice edge.  This is rather exciting -- I must go and check them out in the field, while bearing in mind that they might be structural benches.

You saw it here first, folks.  I'm on the case.  Watch this space.....










6 comments:

chris johnson said...

How deep is the top soil here Brian?

BRIAN JOHN said...

Usually about a foot -- but in the case of the moraine utterly churned up by the wonderful activities of the porkers!

Dave Maynard said...

Brian,

Very interested in Gernos moraine.

I had a play with the aster DEM information for round there. Can I send you some screen prints?

Dave

BRIAN JOHN said...

By all means, Dave. Sounds interesting.....

Dave Maynard said...

Not so interesting, the resolution is about 30m. Gwaun valley shows up nicely. Is there a way of attaching a jpg to this?

Dave

BRIAN JOHN said...

I don't think so, Dave. Send to me as an Email attachment, and I'll see if I can post it for you.