Almost all of the landscapes in the Stockholm Archipelago are "washed" in the sense that following deglaciation at the end of the Devensian/ Weichselian Glaciation they have emerged from the sea as a result of isostatic recovery. The photo above, from the northern end of the island of Norröra, shows a typical morainic landscape with smoothed and abraded rock outcrops -- the fines have been washed out of the till as relative sea level has fallen, leaving behind a "residue" of boulders and cobbles. Two hundred years ago, sea-level here was about a metre higher than it is now -- everything seen in this photo would have been under water.
The above photo was taken way out in the middle of a stretch of open water -- a little islet made up of large boulders -- this is just the tip of a submerged moraine. During storms, waves wash right over the islet. All of the fines have been washed away. The white colouring comes from the droppings of thousands of cormorants, gulls and geese which use the islet as a perching place. The smell, up close, is not too good......
A perched boulder weighing maybe 5 tonnes, on an eroded and washed surface near the southern end of the island of Blidö.
A beautiful washed roche moutonnee on the island of Blidö. The up-glacier side is elongated and smooth -- the plucked lee side is much steeper. Here the ice moved from north to south.
Another small islet on the east side of Blidö, made up of washed moraine with boulders and cobbles of many lithologies and many different sizes. Here there are a few gravelly deposits left among the boulders on the beach.
It is intriguing to speculate on what may lie at the bottom of the Bristol Channel in the way of evidence of glacial episodes.
ReplyDeleteThere is a lot of evidence down there, as we have seen in many earlier posts. The trouble is that this is not an isostatically lifting coastline -- the land surface is sinking gradually, as is the sea floor, while sea level is now going up. Perfect for sedimentation and thickening sediments, except where tidal scour is occurring. But clues WILL be found, just as they have been on Dogger Bank etc......
ReplyDeleteSo underneath the sedimentation and thickening sediments, there will possibly be some recognisably glacial material, evidence of glaciation moving broadly southwards and eastwards. How do you expect the evidence to be revealed to Man? You imply it has been at Dogger Bank.
ReplyDeleteThe evidence is already on the record, Tony. Put "Bristol Channel" into the search box...... I don't agree with all that Gibbard and the others say, especially about this "Early Devensian" glaciation, but the earlier -- Anglian? - glacial episode seems to be very well established now.
ReplyDeleteWhat we could do with is for NASA or similar to turn their attentions to creating a robotic device, not for Mars, but for the bottom of the Bristol Channel, which would simultaneously identify rhyololite and dolerite traces/boulders and transport them up from the depths back to Angel Mountain HQ.Get Prof. Brian Kay on the blower!
ReplyDeleteI meant Prof. Brian Cox.
ReplyDelete