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Monday, 7 November 2011

Glacier porn

Now that the good Sir David is awakening the consciousness of the nation with respect to the wonders of the Frozen Planet (all that stuff about "a world beyond imagination" etc etc) I thought I'd stick this photo up.  I came across it the other day, and immediately thought it was one of the most beautiful polar images I'd ever seen.  So I thought I'd share it......  no particular connection to Stonehenge.

There's a whole glaciology lecture contained in this photo -- but I'll spare you the details.  Enjoy!!

By the way, it's from the SE part of Greenland.  Click to enlarge.

2 comments:

Anonymous said...

NO NO NO
Give us the details!
That is what many of us read this for.
Jean-Robert Sabot

BRIAN JOHN said...

I didn't think you cared! That only goes to show that one must not make assumptions....

These big outlet glaciers are not flowing from the Greenland Ice Sheet, but from a very large independent ice cap which is in the centre of the photo in the middle distance. Beyond that there is broken terrain with more deep troughs containing outlet glaciers. On the big glaciers we can see the medial and lateral moraine ridges, picked out by shadows -- some of them are very large. Note how each medial moraine can be traced back to a junction between two glaciers -- so two lateral moraine combine to form a medial moraine ridge. Most of the debris in these ridges is "superficial" in the sense that it has come from frost-shattered scree falling down the mountainsides above the ice surface.

The upland massif in the centre of the photo (flat-bedded sediments -- probably Permian?) is being broken up by glacial processes -- valley glaciers and cirque glaciers galore. This broken terrain extends under the main ice cap away into the distance -- a good illustration of the manner in which ice caps and ice sheets develop their own dome-shaped profiles independent of what the terrain is like underneath.

The remaining bits of the upland plateau have all got their own little ice caps on them -- this is exactly what Henry Patton is trying to model just now for the Welsh Ice Cap of the Devensian -- with independent small ice caps on all of the peripheral uplands, sometimes independent and sometimes coalescing, depending on the waxing and waning of climate.

Another interesting thing is the evidence here for a supply of snow down onto the cirgue glaciers from avalanching off the edges of the ice caps on the plateau above. This avalanching also helps to carry broken bedrock debris down onto the edges of all the big glaciers -- thus contributing to the building of the lateral moraines.