Not so long ago, there was a big glacier here, calving into the lake........
I have been looking at a very interesting paper on the imminent demise of the biggest glacier in Austria, and I was struck by the above photo which shows how the extension of the ablation area higher and higher up the glacier eventually leads to the exposure of the headwall. Once that happens the supply of ice from the plateau or mountain ice field is shut off, and the death of the glacier becomes a certainty. Other work from Bethan Davies and her colleagues on the Juneau Icefield in Alaska has shown the same happening there.
Note from the above annotated photo how visible the headwall is, with only a small icefall from the right hand side actually maintaining an ice supply to the upper part of the glacier. Other old supply routes on the left are now labelled as "disconnections", in which feeder glaciers are now replaced by "regenerated glaciers" -- in which an ice cone below is fed by falling ice fragments coming down from a broken glacier high up on the cliff above. The regenerated glacier cannot realistically contribute much to the maintenance of the main glacier in its outlet trough.
When I was doing work in Iceland we saw the beginnings of this phenomenon on Kaldalonsjokull, one of the outlet glaciers from the Drangajokull ice cap. In the 1970s the rock headwall of the trough was beginning to appear as a dark patrch of debris, and we saw this as the beginning of the end for the glacier -- although at that time we had no idea how quickly the rate of melting would accelerate. Kaldalonsjokull does not even have any small regenerated glaciers to feed it with broken ice debris.
Kaldalon. This photo was taken in August 2000, showing a glacier that was moderately healthy, with a more or less continuous feed from the Drangajokull ice cap. But there were signs of the trough head beginning to emerge from the ice.
A recent photo of Kaldalonsjokull in NW Iceland, with the trough head now emerging from the ice, where once there was a continuous stream of ice from the ice cap above. This is a classic "disconnection".
When working with the staff of the Norwegian Glacier Museum at Fjaerland, I was impressed by the monitoring work they have been doing over a long period on the regenerated glaciers of Boyabreen and Supphellebreen on the flanks of the Jostedalsbre ice cap. Previously these had been discrete small outlet glaciers with steep gradients, occupying small subsidiary valleys on the flanks of bigger glacial troughs. It was interesting -- and depressing -- to see how over the course of a single human lifetime the gap between the top (or feeder) part of the glacier and the bottom (regeneration cone) was getting wider and wider.
Supphellebreen 1867, taken not many years after the separation of the upper and lower
segments of the glacier
Supphellebreen in 1993, showing the icefall supplying the ice fragments which accumulated to form the regenerated glacier below. The base of this strange little glacier was just 60 m above sea level.
All that's left of the glacier today -- just a very small patch of ice, which will be completely gone within a few years.
Boyabreen in 1993, some years after the glacier split into two halves. From this point on, the lower glacier became a regenerated glacier, fed entirely by ice fragments cascading down from above.
Boyabreen in 2021. The regenerated glacier is almost gone..........
Originally, we all thought that these retreating or declining small glaciers were coming back to a state of equilibrium, following the cold snap of the Little Ice Age, during which glaciers all over the northern hemisphere actually advanced for a while. But we were wrong. There is something much more serious happening here -- and it's called man-induced global warming.
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