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Tuesday, 10 July 2012

A Discordant Glacier in Greenland


This is a truly amazing photo -- not because it's particularly beautiful, but because of what it shows.  I have never seen such a thing before.  Right in the middle of the photo there is a very active (heavily crevassed) glacier flowing between local ice caps and snowfields.  Nothing strange about that -- but look at the snout.  The ice suddenly plunges as an icefall over a steep precipice at the coast, piling up at the shoreline on the edge of a frozen sea.  This is a winter photo -- it would be interesting to see what this all looks like in the summer.

Normally when you see an icefall such as this, the ice is descending very rapidly from a tributary glacier at a higher level to a larger glacier flowing in a deeper trough, in which the ice surface is at a lower level.

What we have is a glacier in a hanging valley -- it is discordant because the floor of the trough occupied by the glacier is not very deep, and it is not at all graded to the floor of any glacier that might be a part of a larger ice drainage system.  Hanging valleys are almost always tributary valleys, left high and dry because the main valley, carrying a much greater volume of active ice, has been eroded down to a much lower level.  That is not the case here, for what we see is a coastal cliffline.

This might of course be within a fjord, in which case there would at one time have been a big glacier in occupation of the area on the right of the photo.

Are we looking at a "new" glacier here, carrying ice which previously flowed off in another direction, and now starting to excavate a trough?  That's a possibility, since strange confluences and abrupt changes of direction are not at all uncommon in East Greenland -- one of the things which makes this an endlessly fascinating area for glaciologists and glacial geomorphologists.

The image comes from one of Chris Sugden's YouTube videos.  If you see this post, Chris, can you give a precise location for the image?

7 comments:

Anonymous said...

Brian quoting from your post,

“The ice suddenly plunges ... piling up at the shoreline on the edge of a frozen sea.”


Could similar conditions have existed during the Younger Dryas with glaciers 'piling up' over a frozen Bristol Channel? And could these glaciers advancing over Preseli have entrained erratics onto the frozen sea surface to later be carried to Salisbury Plain?

Interesting!

Kostas

BRIAN JOHN said...

No chance of that, Kostas. During the Younger Dryas, the evidence shows that the glaciers which did exist were all in the high mountains of the British Isles, well away from the coast.

Anonymous said...

Perhaps my timing is off?

Kostas

BRIAN JOHN said...

Both the timing and the process, Kostas. I don't see anything like this happening, anywhere in Britain, at any stage during the Pleistocene. The geographical and glaciological conditions were very different.

Anonymous said...

Thanks, Brian

I appreciate your thoughts on this. Current accepted thinking by geologists and archeologists alike is that Salisbury Plain was never glaciated too. Contrary to your claims and common sense. Not too far at Dartmoor west and south of Salisbury Plain we now know ice existed during the Younger Dryas –- thanks to the work of Stephan Harrison and others. So who knows what science will reveal about the geomorphology of Salisbury Plain back then in the future.

My sense tells me 'local ice cover'. Your expertise tells you not!

Kostas

Anonymous said...

Hello Brian
Thank you for your comments on "Tunumi - The East Greenland Coast". This particular image was taken looking west from the flight path, on the north shore of Scoresbysund. The ice fall is into the fjord.
Chris

BRIAN JOHN said...

Thanks Chris

I think I have spotted the precise location on Google Earth -- very interesting, and I think I now have an explanation for what's going on here. I'll do another post......