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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....
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Saturday, 5 December 2015

Things are not always what they seem



The edge of the Esplanade Platform in the Grand Canyon -- a photo from Wayne Ranney's blog.  This is fascinating, because it shows scarring and dissection on the talus apron beneath the high buff-coloured cliffs.  When I first saw this photo I thought we would see scores or even hundreds of metres of stratified talus,  built up layer by layer over thousands of not millions of years.  But no -- what we see instead, if we click to enlarge the photo, is red sandstone, almost horizontally bedded, exposed on the side of the cuttings and gullies, in some cases almost projecting through the talus surface.  The talus from the high cliffs is coloured quite differently, which is what makes this photo so spectacular.  The recent gullying has not only swept the talus veneer away, but has started to cut fresh gullies in the red sandstone as well.

So the talus apron or set of intersecting cones is not an impressively thick accumulation at all -- but just a very thin veneer over a sloping bedrock surface.  Wayne tells me that the thickest talus (for example exposed in the cutting towards the right hand edge of the photo) is 15-18m thick,  and in many places it appears to be under 5m in thickness. 

I'm very surprised!!  This looks nothing like the little theoretical talus cliff profile I posted on the blog the other day.......

Wayne Ranney's blog:
http://earthly-musings.blogspot.co.uk/2011/02/searching-origins-of-esplanade-platform.html

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