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Thursday, 9 May 2013

Two extremes

It is one of the extraordinary features of glacier ice that it can in some circumstances erode more or less vertically down into solid rock,  and in other cases flow across a wide open landscape, cleaning it up and scouring the rock surface clear of debris.

These two pictures show the extremes.  The top one is a new photo of Torres del Paine in South America, where streaming ice in a high mountain landscape has cut a series of vertical-sided troughs.  Gradient and glacial bed conditions have something to do with it -- and if there is a very dynamic situation with high accumulation, rapid movement and evacuation, and high melting rates lower down, the resultant glaciated landscape will be spectacular indeed.

In other cases, as in the Vestfold Hills area of Antarctica (shown in the lower photo) very slow ice movement in a polar glacier context may just grind away the land surface inexorably over millions of years.  There are a few patches of ancient till here, but the areally scoured rock surface is remarkably clean.  There are many ancient freshwater lakes here -- most of them frozen solidly almost down to their beds because of the extremely low temperatures experienced in the locality.  Look at the extraordinary patterns on the rock surface.  These are basalt dykes -- hundreds of them......

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