How much do we know about Stonehenge? Less than we think. And what has Stonehenge got to do with the Ice Age? More than we might think. This blog is mostly devoted to the problems of where the Stonehenge bluestones came from, and how they got from their source areas to the monument. Now and then I will muse on related Stonehenge topics which have an Ice Age dimension...
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
Sunday, 16 October 2011
Super-erratics -- a picture gallery
Vast Finnish erratic on the coast of Estonia
Part of the Big Rock erratic complex, Okotoks, Alberta
Large erratic in Manitoba, USA
Isolated "giant erratic" -- Patagonia
Cluster of large erratic blocks, Tierra del Fuego
Single large erratic block, Kjove Land, East Greenland
Granite erratic, Newfoundland
The House and Barn erratics, New England
The 5,000 tonne Madison Boulder, USA. Note the person for scale.
I was asked the other day whether my post about the entrainment of vast blocks of rock (maybe including whole quarries!) was a wind-up. I replied that it was slightly tongue in cheek -- but that there was a serious point to it, in that huge blocks or slabs of rock like the above are found on all continents where glaciation has occurred on a large scale. So there is absolutely no reason why these "super-erratics" cannot also have been entrained in Western Britain, under the influence of the Irish Sea Glacier during the Anglian and other glaciations.
For some of the time, erosion on the glacier bed seems to be by a "nibbling" process, with smallish boulders, blocks or slabs being lifted off the bed over and again, gradually increasing the load being transported. However, occasionally the glaciers do seem to take "bite-sized chunks" -- and glaciologists are still not sure how frequently this happens, and why. There is a reasonable theory to explain this dramatic process, but for obvious reasons observations beneath present-day glaciers are difficult!
I like the reference in one of the specialist sites to erratic blocks like these being "in temporary residence" -- on the assumption that next time round (if there is one) they will be moved onwards, sideways or even broken up by glacier ice.
And I am still quite attracted to the idea that vast chunks of rock might have been entrained from sites like Craig Rhosyfelin and Carn Goedog -- and then broken up either during transport or else following dumping at some distant location.