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Wednesday, 23 January 2013

Ice marginal lakes come and go....


A photomosaic of ice fronts, marginal lakes and outwash plain on the south coast of Iceland.  The sea is right at the bottom edge of the photo.  This is a very high definition image -- click to enlarge as much as possible, and you will pick out great detail.  Note that some meltwater streams follow the ice edge before decanting into marginal lakes, which in turn decant into the sea.  The meltwater routes are well marked -- here and there we see distinct channels being formed, but because almost all of the features beyond the ice edge are made of unconsolidated sediments in this case, the channels are ephemeral.


South Greenland ice sheet edge.  I suspect that this photo was taken in the autumn, after the fall of the first snows of winter.  the lakes are still ice-free.  there are a lot of them -- and if you zoom in you can see some spillways snaking away from the ice front, along depressions or natural cols in the undulating bedrock terrain.


Another South Greenland ice sheet edge, with abundant meltwater filling low-lying parts of the landscape but not actually impounded by the ice edge.  The overall slope of the land surface is away from the higher foreground towards the top right corner of the photo.  If you look carefully you can see that most streams are flowing away from the camera position.  there are some rock-cut spillways or channels.  The lakes in the foreground are full, whereas those in the distance have had higher water levels than those of today -- you can see the light-coloured strips along the waters edge -- these are strandlines, maybe just a few metres above present lake levels.  This is a very dynamic environment.  Each lake has a different history and a different duration.

5 comments:

Dave Maynard said...

Last night, Crymych and district were staging a re-enactment of the end of the Devensian with rainwater and melted snow running all over the place, including the existing spillways!

BRIAN JOHN said...

Ah -- a pity I missed it! Mind you, here at the entrance to the Cwm Gwaun spillway we had a pretty passable imitation too.....

Constantinos Ragazas said...

Such collective memory, passed on from generation to generation, must surely mean the episode was not all that long ago. RJL would argue (in his latest post) just 1900 years ago. If so, and the rivers and lakes were much wider then, wouldn't this also suggest Crag Rhosyfelin was engulfed in water more recently too? Placing MPP's “human quarry” in water!

Kostas

BRIAN JOHN said...

There is no collective memory, Kostas.
End of story.

Victor said...

This is cool!