THE BOOK
Some of the ideas discussed in this blog are published in my book called "The Bluestone Enigma" -- available by post and through good bookshops everywhere. Bad bookshops might not have it....
To order, click
HERE

Thursday, 14 October 2010

Glacial action on limestone hills



Above, Cheddar Gorge.  Below, Revdal in the Karstryggen, East Greenland.  Thje big limestone gorge is in deep shadow.  NB that the scale is twenty times smaller in the case of Cheddar Gorge -- so the Revdal Gorge is truly enormous.  Note also how much more "jagged" Cheddar Gorge is.....

I've been thinking about the glaciation of the Mendips -- having touched on it before on a number of occasions.  Because limestone (like chalk) acts a bit like a sponge when it is wetted, it has a number of interesting effects when it is overridden by ice.  If a glacier is warm-based, it flows partly by sliding on its bed, lubricated by a film of water.  If the temperature at the ice-rock interface is above the pressure melting point, then water should be present -- but what happens if that water then sinks into the limestone, creating what is in effect a DRY glacier bed similar to that of polar or cold-based glaciers?  This is still imperfectly understood, and there has been much speculation too about whether permafrost which is present at the time of glacier advance across a limestone area will create an impermeable bed.....

One of the interesting things about some glaciated limestone pavements is the relative absence of till and other traces of ice activity, with the limestone scraped clean and left maybe with a litter of erratics.   But what about the effects of meltwater floods either subglacially or beyond the ice edge during deglaciation?  Is Cheddar Gorge truly a glacial meltwater channel?  There are similarities with an area called Karstryggen in East Greenland -- a bare limestone plateau across which I walked with colleagues in 1962.  There is remarkably little there in the way of glacial features -- but it has certainly been glaciated several times in the past.

Must look into this a bit further......

No comments: