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

Friday, 28 December 2012

The Stonehenge Solutional Rills

The "periglacial stripes" -- viewed across the slope.  Note that the channels are more than a foot deep.

 The so-called "periglacial stripes" -- acknowledgement to Aerial-cam.  Note that these stripes are aligned -- more or less -- on the axis of the Avenue and on a line drawn through the Heelstone and the Slaughter Stone to the centre of the stone monument.  Significant?  Probably not.....

 The "micro morphology" of the Stonehenge site.  The contours are just 25 cm apart, showing how Stonehenge is located on a slight spur.  the Slaughter Stone and the Heelstone are clearly visible, as are the ridges which define the Avenue.  The open pit shown in the B/W photo above is located very close to the junction between the north-point line and the cross piece.


I have been giving more thought to the famous "periglacial stripes" at Stonehenge, the alignment of which is deemed by Prof MPP to be the reason why Stonehenge was built where it was.  I have argued before that this is fanciful in the extreme, since there are -- in all probability -- stripes like these all over the Stonehenge landscape. Most of them are of course NOT aligned to the Avenue or the midsummer sunrise solstice, but are aligned perpendicular to the contours, wherever those may be.

See my previous post"

MPP keeps on referring to the stripes as "periglacial" -- presumably on the basis of what he has been told by Mike Allen and Charly French.  On p 243 of his new book he refers to freeze-thaw conditions and to sediments created from the "grinding of chalk by ice into a clay flour."  Having gone along with this to a certain extent, and having pondered on this blog about periglacial stripes and how they are formed in current areas of permafrost,  I have to admit to being worried about the precise processes that might have operated here, on gradients that are very gentle indeed.  And my brow has been furrowed even more by trying to work out  how and why this ground-up "clay flour" might have been formed during the Pleistocene -- and what role it might have played in landscape modification.  Are we talking about mechanical processes, or chemical ones?

At any rate, I have now come to the view that these ridges and channels are not periglacial at all, but are simply solutional rills developed over many millennia by the straightforward process of rainwater runoff downslope being concentrated into rills or channels which are then deepened over time.  In geomorphology these are referred to as "rillenkarren" where they occur in limestone terrain -- for example around Malham in the Pennines or on the Burren in Ireland.  Have a look at the photos below:

 Rillenkarren on the surface of Carboniferous Limestone near Malham Tarn.  Note the sinuous shapes of both the rills and the ridges.

Rillenkarren on the floor of the Carlsberg Cavern in New Mexico.  Here the channels are formed by solution processes downslope from the points where aggressive groundwater drips from the roof of the cave.

Rillenkarren on the surface of chalk exposed in France.  Note that there are very close similarities between these features and those seen around Stonehenge.

In Carboniferous Limestone areas rillenkarren tend not to be very long because limestone is heavily jointed or fractured -- and where these weaknesses intersect with solutional rills running downslope the flowing water is diverted sideways, giving rise eventually to a highly complicated terrain of clints and grikes, sometimes with the tortuous channels cut to a depth of several metres.

On a gently sloping chalk surface there are fewer joints and other structural features -- the chalk body is often "massive" and coherent.  This means that these gently meandering channels may extend for hundreds of metres downslope, unto the gradient is so low that the rills cannot be maintained or deepened any longer, with the water simply ponding in hollows or sinking into the ground.

Much as I enjoy writing about periglacial processes, I really cannot see any role for them in the formation of these gullies -- and I suggest that the process of deepening the Stonehenge solutional rills has gone on for many hundreds of thousands of years -- sometimes faster, sometimes more slowly, as climatic conditions and water tables have changed.

Charly or Mike, if you are reading this, I would appreciate some information on your thinking -- why have periglacial processes been invoked here, when there really is no need for them?





10 comments:

Constantinos Ragazas said...

Brian,

Thanks for coming back to this important topic. From previous debates we agree these stripes are 'solutional'. But we disagree how these were formed.

You write,
“these ridges and channels are not periglacial at all, but are simply solutional rills developed over many millennia by the straightforward process of rainwater runoff downslope being concentrated into rills or channels which are then deepened over time.”

And furthermore,
“there are -- in all probability -- stripes like these all over the Stonehenge landscape”

If these stripes were formed by rainwater, similar stripes would also exist all over the landscape. Have any such been found elsewhere? From what I know they haven't. MPP surely knows this for sure, however.

But if such solutional stripes are confined to the Avenue and are not generally found 'all over the Stonehenge landscape' that would raise serious questions about your 'rainwater runoff' explanation of these.

But such evidence would fit well with my explanation how the Avenue stripes formed. Namely, the Avenue marks the egress channel in the ice sheet draining the meltwater retaining basin at Stonehenge.

I concede MPP's entourage of 'experts' are very intelligent and knowledgeable professional. So they must be aware of all the points you and an amateur like me are raising. So why they claim these are 'periglacial'? Could it be 'rainwater runoff' just does not fit ALL of their evidence? While 'periglacial' leaves enough uncertainty to fix their narrative?

Were these stripes formed by 'rainwater runoff' that would not be 'myth-shattering'. MPP could easily accept this. What MPP cannot wiggle around is evidence that confirms my theory!

I loved the photos of rillenkarren in your post! The fourth one down has a remarkable resemblance to modern sculpture. A Neolithic Henry Moore perhaps? I know GeoCur will agree!

Kostas

TonyH said...

Ahhh, them clints and them grikes........sounds like it's time for a new, low-budget-in-these-times-of-recession, Spanish Spaghetti Western, starring the 85-year-old Mr Eastwood as The Archaeologist With No Name, Only Initials, but who commands a mega excavating budget. And it seems like Stonehenge DOES possess an Irish connection, but with The Burren, not Merlin.

BRIAN JOHN said...

I just don't know how widespread these features might be -- buried beneath the present land surface. Of course, the modern soil horizon will fill in the channels and "smooth off" the surface -- but I would hypothesize that solution could still be proceeding today selectively -- concentrated in the channels because that is where water flow will be concentrated. Does anybody know how many trenches have been cut across the slopes surrounding Stonehenge, and what the diggers have found?

TonyH said...

It really is quite stunning how deafening is the sound Of silence emanating from every other corner of the geomorphological world about the formation of these channels. Considering that MPP has been metaphorically shouting his theory from the computer-enhanced rooftops of Durrington Neolithic Village, via the National Geographic, Fox News, Japanese Television, etc, it is surely extremely curious, is it not, that the Academic Geomorphological Community has not shown any desire, or enthusiasm, to take a long, cool, look at Mr Parker Pearson's claims? It is as if Mr Parker Pearson stands on Holy Ground, whence no mere mortal may enter, be he scientist, atheist or agnostic. Yet the legion (and I use the word advisedly) of Indiana Jones fans are actively encouraged to readily lap up MPP's version of Landscape Formation. Mr Parker Pearson receives his accolades from the Archaeological Media on a regular basis these days. Is it, in reality, a case of being famous for all of fifteen minutes? Time will tell....

I recently met a lady from North Derbyshire who helped excavate across The Stonehenge Avenue. It would be interesting to hear her opinion, as she will know something about the natural limestone features of the Peak District.

TonyH said...

Brian, quite a lot of the land to the north of Stonehenge is owned by the National Trust, i.e. north of the now-closed/ soon-to-be-closed A344, and encompassing The Avenue as far as and beyond and east of the Avenue's "elbow"; also virtually up to the New King Barrows to Stonehenge's east and ENE. The National Trust also owns up to and including The Cursus and The Cursus Barrows. I do not know of any trenches having been cut across the slopes surrounding Stonehenge, and it is apparent how protective and guarded the National Trust is to the land it owns within the World Heritage Site.

Once the new Visitor Centre is up and running, at Airman's Corner, a good distance to Stonehenge's N.W., it is to be hoped that public interest in the origin of these landscape features at the Avenue will lead geomorphologists towards searching out a coherent explanation for them. Because, soon, the public will have increased ease of open access on foot to the Greater Stonehenge Landscape.

Anonymous said...

Interesting idea.

Would not rain water or even ice melt for that matter, not create a greater frequency distribution of cavities as shown in your examples?

The excavation by Atkinson et al 1956, shows this cross section to be 'convex' in shape so the groves are on top of the natural chalk slope, asking the water to defy gravity, by sitting in some instances on top of a high ridge.

Moreover, Atkinson's diagrams show that the five major 'group' of deep cavities are of equal distribution between each other of 1.75m. Several old 16th C. cart roads cut across the Avenue and Hawley found one in 1923 an old cart track just to the left of your aerial picture by the Heal Stone, which rut marks were the same 1.75m of width.


BRIAN JOHN said...

The gradient of the slope has something to do with it. You never get a smooth and even junction between solid rock below and regolith above -- rock always crumbles and breaks up at the interface, no matter what the physical or chemical processes may be. More research is needed into what the soil scientists and geomorphologists have found on Salisburuy Plain over the years. I wouldn't discount cart tracks and wheel ruts in some locations either....

TonyH said...

Dave Field, the landscape archaeologist formerly employed by English Heritage to work largely on Salisbury Plain, has now retired, but still resides in the Wiltshire area I believe and is involved with the Archaeology Field Group of Wiltshire Archaeology & Natural History Society these days. We have discussed his findings in the Stonehenge landscape on this blog before, and he may be able to act as a gatekeeper to the knowledge and findings of various other specialists, if he happens to read this.

TonyH said...

Nice that we managed to get some feedback by email from Prof Charly French and also Mike Lewis regarding their views on The Stripes, following me sending your Post to Professor French. Are you going to share their views withthose reading your Blog?

BRIAN JOHN said...

Yes Tony -- and thanks for initiating the discussion! some useful points worth reporting. When I get a moment or two.......