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Tuesday, 17 July 2012

That discordant glacier

Thanks to Chris Sugden for locating the image used in my earlier post.  He says the photo was taken from the air while flying from Knud Rasmussens Land across the southern coast of Scoresbysund, en route to the town on the other side of the sound.  This is the Volquart Boon Kyst, not far from Kap Brewster.  I should have guessed -- the bedded sediments shown in the photo are typical of this area.

So why do we find this extraordinary glacier tumbling down over a cliff onto the shore below?  Here are three photos from Google Earth:

On each of these we are zooming in closer and closer to the glacier which I think is the one in Chris's photo.  The top one of the three is an image taken when there was more snow about, but you can see the pointed headland to the west of the glacier more or less in the top centre of the image.

Along this coast there are many small, short, steep glaciers plunging down to the shore of the Sound.  They are all very strange!  The reason is that the ice shed (the glacial equivalent of a watershed) is almost at the coast here, rather than being set well inland.  Clearly what has happened is this:  there has been so much ice pouring out of the Scoresbysund fjord complex that the southern shore of the Sound has been overdeepened and eroded on a spectacular scale during the Pleistocene glaciations, leading to very dramatic landscape alteration -- the old landscape of Knud Rasmussens Land has seen the old valleys flowing north "chopped off" or eaten away by ice, leaving the old interfluve almost at the coastline.  

On the top photo you can see that the south-flowing glaciers (some quite large) have their catchment areas almost at the north coast of the peninsula.  Snow that collects on the steep and stepped north-facing slopes feeds much smaller and shorter glaciers -- they are too short and too young to have achieved very much glacial erosion, so they decant their ice over the coastal cliffs and into the sea, leaving people like me to gaze at them in wonderment....

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