This is a nice one. From the wonderful Glaciers Online website. I've seen such things, but hadn't realised they had a technical name -- juddermarks. As in all the best detective stories, the thing that has done all the damage disappears without trace, in the warmth of the sun.......
When there are bits of brash ice floating in shallow water on a rising or falling tide (or this could happen in a shallow lake) the ice fragments may be jerked along the gravel or mud flats, marking them as they travel. You need rather placid water for this to happen -- or wave action will disturb the judder marks.
What you end up with is a series of tracks on a small patch of sediments, apparently starting and finishing without reason -- almost as if a caterpillar tractor had descended from the heavens and then travelled a few metres before taking off again.....
There now. Isn't that interesting? Another piece of rather useless information for the lexicon.......
ReplyDeletePossibly mentioned here previously , if so apologies .
http://www.youtube.com/watch?v=u1hoiHvOeGc
Not aligned on the sunrise by any chance?
ReplyDeleteBrian,
ReplyDeleteThis is a wonderful example of how water, ice and wind can conspire to create 'earthworks that shape the landscape and produce an enigma!
Some years ago you posted on some huge erratics and “empty pits” along the SW sea coast, revealed after a strong storm. These 'empty pits' were also explained by similar action.
I observed then (and you agreed then) there should be such juddermarks 'scrapings' on the bedrock. As stones frozen onto the ice sheet edge were moved about by sea-wave action; lifting the ice sheet edge on the shore and moving the erratic into a new position creating a new 'empty pit'. Only problem, there were NO such scrape marks on the bedrock!
As I recall, you favored a “flotilla of icebergs” carrying a cargo of erratics on shore! My explanation then (which you summarily rejected then) was these 'empty pits' were created by ice blocks falling over the ice edge and eventually melting in place; leaving the empty pits behind.
Kostas
Chris,
ReplyDeleteAs natural as such juddermarks are, they wouldn't 'align with MPP'.
Kostas