Dewatering of warm-based ice

I've been looking at James Scourse's 1997 chapter in the big Stonehenge book, called "Transport of the Stonehenge Bluestones: testing the glacial hypothesis."  It's an interesting chapter designed to systematically demolish the theories of Kellaway and Thorpe et al about glaciual transport.  It's particularly interesting because the archaeological establishment has decided to accept it as THE glaciological and geomorphological assessment of the situation -- because of course it all sounds very learned, and because it suits them very well to be able to say "The best glaciological advice we have is that glacial transport of the bluestones to Stonehenge was impossible."    James Scourse himself, in the last sentence of the chapter, claims that he has "eliminated the impossible" from the debate about bluestone transport, thereby agreeing that the human transport of the stones -- however improbable -- actually happened.

As I have said before, scientists should not really use the word "impossible" because it may come back like a boomerang and hit them between the eyes.  I will return in due course to some to James's glaciology, which I think is pretty dodgy or selective (I think he puts up a number of Aunt Sallies just in order to knock them down), but for the moment I just want to think about the implications of ice close to an ice sheet margin flowing across highly permeable bedrock -- namely chalk.  I came across some discussions in the North American literature to the "dewatering" of warm-based ice when it is flowing across limestone or chalk.  This would presumably slow down or stop basal sliding and would then only permit movement by internal deformation, shearing etc.  What would the implications of this be for till emplacement and for the transport and dumping of erratics?

I'm of course aware that in Eastern England there is a lot of chalky till around, which implies that chalk was easily eroded by overriding ice and that the ice that did the eroding had plenty of basal lubrication ..........

Not sure who reads this blog, but if anybody has any thoughts on this, all comments gratefully received!

Stonehenge -- process and purpose

Silbury Hill and Stonehenge -- powerful religious symbols?  Or just strange places built by engineers having fun?

The latest book on Silbury Hill -- being sold flat out by EH on the Today programme, and no doubt to the rest of the media as well -- seems to make the point that the famous mound went through so many different phases of building that there may not have been any coordinated or deliberate "purpose" to it at all.  It sort of just grew....... with every generation having a go at it, and making it a bit bigger than it was before.  So the PROCESS became more important than the purpose.  If there was a purpose (and people don't build things without a purpose) it may have varied with each generation -- and I like to think that the builders had no religious or symbolic purpose at all, but maybe wanted to build something which would simply impress neighbouring tribal groups.  "Yah boo sucks -- our mound is bigger than yours.  So there!"  Children and grandchildren all continued in the grand tradition of showing off, and maybe there was a sort of resigned sigh that went up from the tribe every decade or so, when mound-building time came around, as they carried on something started by great-great grandfather.  Maybe they groaned:  "God knows why we are doing this, but in honour of his memory, we'd better just carry on with it."  So they concentrated on the techniques or the processes of transporting loads of rubble onto the mound, stabilising slopes, maintaining a pleasing conical shape etc etc... just because they wanted to demonstrate that they were capable of doing it.

For a long time I have had a similar idea about Stonehenge.  The builders were so short of stones, and so indecisive, that they moved stones around all the time, with one temporary stone setting following another.  Then, when they ran out of stones completely, ran out of energy, and started to lose interest in the Stonehenge project (if it could ever have been called that) the whole thing ground to a halt.  It's not at all outrageous to suggest that during all these phases of pottering about, the builders were more obsessed with processes than they were with purposes.  How do we set very large stones in the ground, and how do we stabilise them? How do we extrapolate from woodworking techniques (with mortise and tenon joints, tongue and groove fittings etc) into working with very hard stones?  How do we get the lintels up onto the sarsens?  How do we get them to stay there once they are up and roughly in position?

OK -- the builders of both Silbury Hill and Stonehenge may well have been mathematical geniuses, and spiritual to boot, but that doesn't alter my view that these monuments have more to do with engineering experimentation than with the worship of ancestors or with planetary alignments.

Who owns Stonehenge images?

This is a photo of Stonehenge.  It's mine.  If EH wants it, they can have it, for a small fee to be negotiated........

Who owns images of Stonehenge?  Simple question -- and a simple answer:  "It's a free world.  If I take a picture, even of something owned by somebody else,  the picture is mine -- and I may do with it what I will."  But no, says English Heritage, we own Stonehenge, and if you make money out of a picture taken of the ancient ruin, we want a royalty from you." 

That's what they told a picture agency, and when the press got hold of the story and made a bit of a fuss, they made matters worse by issuing the following:

--------------------------------------------------
Email from English Heritage...
Ms R L McKellar
English Heritage
Customer Services
Po Box 569
SWINDON
SN2 2YP

Thank you for your email regarding photography at Stonehenge.
English Heritage looks after Stonehenge on behalf of the nation. But we do not control the copyright of all images of Stonehenge. And we have never tried to do so. We have no problem with photographers sharing images of Stonehenge on Flickr and similar not-for-profit image websites. We encourage visitors to the monument to take their own photographs.
If a commercial photographer enters the land within our care with the intention of taking a photograph of the monument for financial gain, we ask that they pay a fee and abide by certain conditions. English Heritage is a non-profit making organisation and this fee helps preserve and protect Stonehenge for the benefit of future generations. The majority of commercial photographers respect this position and normally request permission in advance of visiting.
I am sorry for any confusion caused by a recent email sent to a picture library.
Yours sincerely
Rae Mckellar
Correspondence Team Manager

----------------------------------------

Naturally enough, the forums and blogs are now full of extremely rude comments about EH, which is apparently trying to ape what the National Trust does with its properties.  The whole thing is insane.   For a start, how do you define a "commercial photographer" -- and then what about "intention"?  If a commercial photographer visits the site to have a nice picnic in the sun, and takes a few photos while he is there, and then sells them, is that OK?  And what about "financial gain" -- if a photographer sells some pics just in order to cover his costs, is that OK?

The whole thing is a PR disaster, and if EH does have a cunning scheme, it will be impossible to police, with almost a million visitors coming onto the site each year.  Anyway, Stonehenge is owned by the public.  That means ME.  It's my monument, and I hereby give permission to all and sundry to make as many images as they like and to sell them to whoever might be happy to part with a few quid, or a few pence, or even something they want to barter.  That's my contribution to the national economy in these straightened times.  So that's all right then.

Erratic speculations

Three pictures from at area that might be expected to supply erratic material into the Irish Sea Glacier as it flowed across this area on its way towards Salisbury Plain.  Top:  one of the tors on the ridge crest.
Middle: a perched block (locally derived) on the same tor.  Below:  rocky outcrop (one of many) in among the gnarled oak trees of Tycanol Wood.  In the lower part of the wood, the rocks are partly rhyolites.  The tors are made of dolerite.

Tycanol and Carnedd Meibion Owen

Thinking about the cave in Tycanol Wood, not far from Newport (Pembs), I got to wondering why no erratic material from this area has yet been discovered on Salisbury Plain.  Material has been found from near Brynberian (Pont Saeson) and from Carn Alw and Carn Goedog on the north flank of the main Preseli ridge.  These are classic entrainment environments for ice moving from NW to SE, as I have explained previously on this blog.  Ice which is moving upslope in order to cross a barrier which is transverse to the direction of movement would be expected to shear over the summit, with erratic material entrained and then sheared high into the heart of the glacier.  Lionel Jackson and I explored this idea in our EARTH magazine article in 2008:

http://www.earthmagazine.org/earth/article/1a1-7d8-c-1f

Rob Ixer and Richard Bevins (and maybe others as well) are examining some of the other "erratic litter" material from the Stonehenge environs, concentrating on the rhyolites which the OU team long ago identified as having potentially great importance.  Where did these rhyolites and other complex igneous / metamorphic fragments come from?  It's already been suggested by geologists in print that they might have come from the outcrops of the Fishguard Volcanic series which outcrop on the N Pembs coast from the Pen Caer Peninsula to the Dinas area.  But there are also igneous inclusions (including ash beds) in the Ordovician sedimentary rocks on the coast between Dinas and Newport.  Those rocks also extend well inland, and indeed the vast igneous province in this area (with intrusions and extrusions, and lots of sediments as well) incorporate the dolerite and other outcrops on the eastern parts of the Presely Hills.  It's these outcrops (seen best in the tors on the ridge) which have attracted most attention in the past.

Right in the heart of the perfect entrainment area is the ridge which is now partly clothed by Tycanol Wood and which has the splendid tors of Carnedd Meibion Owen on its summit.  There are  craggy outcrops of rhyolite in among the trees as well, and some exposed rock faces on the hill slopes.

I would't mind betting that sooner or later, erratic material will be found from these rhyolite outcrops somewhere on Salisbury Plain.

The Druid's Cave

What with all the recent talk about Druidism being recognized as a religion, it's worth reminding ourselves of the strong link which the Druids have with Carningli and the neighbourhood.  Laurence Main, who visits Carningli often, is a practising Druid, and he looks on the mountain as a special and sacred place.  Another place which has a tradition of Druidic connections is the cave in the upper part of Tycanol Wood;  according to local legends (mostly invented by small boys) Druidic ceremonies were conducted there in the days when the Iron Age was on its way out and the Age of the Saints was on the way in.  It's not much of a cave really, but it is just about habitable, I suppose, and here is a charming story about it:

The Man in the Cave

Simon Hughes was a member of a large family living at Fachongle Ganol in the early years of the twentieth century.  He was conscripted into the Army during the First World War and undertook military training, but he became a conscientious objector and “escaped” from his barracks.  He made his way back to Cilgwyn and went into hiding.  Army officers and the police hunted for him, but he moved from house to house and the community closed ranks in order to protect him.  On one occasion he was having dinner in the cottage called Fachongle Ganol when an Army sergeant with a troop of soldiers tracked him down and hammered on the front door.  Mr and Mrs Hughes kept the soldiers talking while Simon escaped through the back door.  For much of the time he was reputed to have lived in the “Druid’s Cave” in Tycanol Wood.  The local police made a great show of hunting for him, but always contrived to fail in their endeavours.  At the end of the war he came out of hiding and left the district.  He became a shop-keeper, ending his days as manager of the Co-operative Store in Tonypandy.

From the sublime to the ... erm, utilitarian.....

Water and Ice

Click to enlarge.

An amazing picture widely circulated by the National Geographic Magazine as a piece of wallpaper.  It's not just a fantastic photo -- but much more.  It shows an extraordinary relationship between water and ice.  It's very unusual to find standing water in a meandering stream channel like this.  The water has been much higher -- you can see the "strandlines" on the flanks of the channel.  Meltwater on a big glacier or ice sheet margin usually dives down through deep pits called moulins.

I'm not sure what's going on here -- maybe the whole of the base of the glacier is saturated, and the water level represents a water-table within the glacier.  That's seriously bad news.  A very unhealthy glacier indeed, and definitely on the way out.