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Wednesday, 21 August 2013

And now for a galloping glacier......


One photo and two maps of a very strange glacier in East Greenland, on the northern flank of Nordvestfjord.   The satellite image (top) shows the Løberen Valley as it is today, with no glacier other than a pathetic remnant up towards the top of the photo.  The map in the middle shows Løberen Glacier with the snout a little way in from the coast.  And the map below shows the same glacier as a tidewater glacier, reaching all the way to the coast and calving icebergs directly into the sea. (It's the glacier above the first letter "d" in "Nordvestfjord".) 

You might be forgiven for getting confused here, or for thinking that the Danish mapmakers are rather slapdash.  But the truth of the matter is that Løberen is one of the elite surging glaciers of the world, rocketing forward (well, in glacial terms anyway) and then retreating catastrophically every now and then.  In fact, the Danes who made the maps and looked at all the aerial surveys for this area were so impressed that they called it "the sprinter" or "the runner" partly as a joke -- and that has now been accepted as the official name.

The middle map shows Oxford Gletscher -- that's the one we worked on in 1962, and we gave it its official name.  We did ice temperature measurements on it, and were mystified because there were some very strange anomalies.  What we did not realise at the time was that Oxford Gletscher also surges occasionally, and the traces of that surging behaviour were still there in the ice temperature profile.  If we had gone up the fjord a bit further, to Løberen, we would have had a much more exciting time, because in 1962 it was more or less at its surging peak, reaching the fjord.

As far as we know, the glacier was in advancing mode in 1950 - 1967, moving forward erratically through that period -- and since when it has retreated by at least 7.5 km.  We don't know how fast the glacier was moving in the main surge phase, but some glaciers can increase their velocity 100-fold during a surge, moving at more than a metre per day.  In one surge in Iceland, the glacier ice was observed to be moving at 5 m per hour.  Here it is quite possible that Løberen was advancing at a rate of c 1 km per year at the peak of the last surge.  That would give a peak advance rate of c 3m per day.

Of course, since the glacier was terminating in the sea for the period 1960 - 67, we have no means of knowing how much further it might have advanced, if it had had a nice gentle glacial trough to flow along.

2 comments:

Anonymous said...

thought you might like to see this.
The Earth over a year
http://cosmossoup.com/an-earth-year-from-above-the-northern-hemisphere/

PeteG

BRIAN JOHN said...

Nice! Thanks Pete.