Some of the ideas discussed in this blog are published in my new book called "The Stonehenge Bluestones" -- available by post and through good bookshops everywhere. Bad bookshops might not have it....
To order, click

Sunday 4 September 2016

Malaspina ice edges

This is a wonderful new image from the European Space Agency showing the Malaspina piedmont glacier in Alaska -- formed on the lowland plain beyond the mountain front.  It's really high definition -- enlarge by clicking...... there is a lot of snow on the glacier and on the mountains -- I suspect it's a spring or autumn satellite image.  (It's a false-colour image, showing up green vegetation as red.) Some of the summer images show up the details on the ice surface much more clearly.  Take this one, for example (from NASA):

What really interests me is the contact between the main piedmont lobe and the flanking glaciers.  Here I have enlarged the images from the right and left flanks:

The piedmont glacier itself is a good analogy for the manner in which the Irish Sea Glacier might have behaved in the Celtic Sea.  The above "ice edge" images might give us a guide to what may have been going on in Cardigan Bay between the Irish Sea Glacier and the ice mass coming down from the Welsh Ice Cap.

The elongated glacier lobe shown by Chris Clark and others (in a number of publications) is in my view a non-starter -- you don't get lobes like that in unconstrained situations.

See this: 

This is my most recent attempt at defining how a big piedmont glacier might have looked, about 20,000 years ago:

This is for the Devensian -- note that I have the whole of Pembrokeshire covered by ice.  I can't see any way, glaciologically, of keeping South Pembs ice free. More on this soon......


wuga said...

I always assumed that Milford Haven would have been a Fjord rather than a Ria if South pembs had been glaciated.

BRIAN JOHN said...

No Paul -- fjords will only form where there is a massive amount of ice to be discharged from an upland area towards the lowlands -- as in East Greenland, western Norway, parts of Arctic Canada, Chile etc. Once the ice is channelled, there is tremendous downcutting power, and deeper and deeper fjords can be cut. The situation in Pembrokeshire is quite wrong for the formation of fjords -- instead of channelled ice flow, there must have been areal or extensive flow across an undulating ground surface, with relatively little erosion except on upstanding hill masses like Carn Llidi.

wuga said...

Thanks Brian. I was taught Geology at Pembroke Comp 40 years ago and I vaguely remember Ria/No glaciation theory.
I suppose our romantic nature would love the idea of anceient tribesmen hauling rocks from a "special" place..ah well..
The Preseli's are special, of course.
Bringing my son "home" at the end of the month hoping to show him some of the wonders of Pembrokeshire..if the weather allows.
Incidentally great sight that I have, sadly, only just discovered.

BRIAN JOHN said...

I wonder who told you that if there are rias there are no glaciations involved? Typical, I suppose, of the rather simplified "truths" that children are told they must believe if they are to get through their exams. As ever, the truth is more complicated, and it was our jobs as university teachers to encourage students to think for themselves and to be sceptical about everything. I've been out of the system for a long time now, but I hope that is still what goes on at universities.....