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Saturday, 7 November 2015

Pro-glacial lakes - Russell Glacier, W Greenland


These amazing photos of pro-glacial ice-dammed lakes are from the Russell Glacier, West Greenland.  I don't think they are 2 photos of the same lake, but the photos were taken several years apart, so it's possible.

In the top photo the edge of the glacier is blocking off a possible meltwater escape route at the tip of a spur, and a very large lake has been partly drained.  The original shoreline is easily visible; because it's so fresh there is a stark contrast between the vegetated area on top of the spur and the barren area (with many bedrock outcrops) on the lower slopes.  If you look carefully at the slope beyond the area of floating brash ice, you can see a whole series of other faint shoreline traces, formed at short-lived water level stillstands during a protracted period of lake draining.  (These are the sorts of things David Sigden and I looked for very intensively during our fieldwork in Greenland and Antarcica -- but this time theu were associated with sea-level stillstands over a long period of isostatic recovery.....)

The bottom photo is even more spectacular, showing the old lake shoreline even more clearly, and showing the exposed lake bed as well.  Probably this photo was taken in the same year that the lake was drained.  On the lake floor, meltwater streams have already started to incise themselves into the old lake floor sediments.

According to the descriptions in the literature, the only way that these lakes can drain is by the thinning and "lifting" of the glacier ice off its bedrock floor, allowing meltwater torrents to escape via rather complex conduit networks on or near the glacier bed.  These processes are, of course, very difficult to observe......

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