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

Monday, 7 December 2009

More on erratic trains



Some of the boulders in the erratic train are 16m in diamater.

Thanks to Lionel Jackson for bringing this to my attention. There are more examples here of "erratic trains" -- this time strung out in the lowlands of Tierra del Fuego, and traceable back into the mountains of the Cordillera Darwin. The thousands of boulders in the erratic trains are largely unmodified by glacial abrasion, and they sit on top of moraines -- so they are interpreted, like the Foothills Erratic Train in North America, as having come from valley side avalanches descending onto moving glacier ice. The ice has carried them away on the glacier surface and has "attenuated" or strung them out -- so that what might have been a cluster to start with has been transformed into a linear feature. Interesting info, which might help us in our attempts to work out what the glacier dynamics were when the erratics were transported from Wales to the eastern side of the Bristol Channel.

Reference:
Enigmatic boulder trains, supraglacial rock avalanches, and the origin of “Darwin’s boulders,” Tierra del Fuego
by Edward Evenson et al
GSA Today, v. 19, no. 12,pp 4-10

No comments: