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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Tuesday, 30 July 2013

Wooden "halls" predating Long Barrows in Herefordshire

This story is all over the media at the moment -- interesting.  No doubt much more to be revealed.....

Public release date: 30-Jul-2013
Contact: Mike Addelman

Two 6,000-year-old 'halls of the dead' unearthed, in UK first

The remains of two large 6000-year-old halls, each buried within a prehistoric burial mound, have been discovered by archaeologists from The University of Manchester and Herefordshire Council -- in a UK first.
The sensational finds on Dorstone Hill, near Peterchurch in Herefordshire, were thought to be constructed between 4000 and 3600 BC.
Some of the burnt wood discovered at the site shows the character of the building's structure above ground level -- in another UK first.
The buildings, probably used by entire communities, are of unknown size, but may have been of similar length to the Neolithic long barrows beneath which they were found – 70metres and 30m long.
They were, say the team, deliberately burnt down after they were constructed and their remains incorporated into the two burial mounds.
However -- much detail has been preserved in the larger barrow: structural timbers in carbonized form, postholes showing the positions of uprights, and the burnt remains of stakes forming internal partitions.
Most importantly, the core of each mound is composed of intensely burnt clay, representing the daub from the walls of the buildings.
The buildings were likely to have been long structures with aisles, framed by upright posts, and with internal partitions.
The smaller barrow contains a 7m by 2.5m mortuary chamber, with huge sockets which would have held upright tree trunks at each end.
These massive posts bracketed a linear 'trough' lined with planks, which would have held the remains of the dead.
Professor of archaeology from The University of Manchester Julian Thomas and Dr Keith Ray Herefordshire Council's County Archaeologist, co-directed the excavation.
Professor Thomas said: "This find is of huge significance to our understanding of prehistoric life-- so we're absolutely delighted.
"It makes a link between the house and a tomb more forcefully than any other investigation that has been ever carried out.
"These early Neolithic halls are already extremely rare, but to find them within a long barrow is the discovery of a lifetime."
He added: "The mound tells us quite a bit about the people who built it: they sought to memorialize the idea of their community represented by the dwelling.
"And by turning it into part of the landscape, it becomes a permanent reminder for generations to come.
"Just think of how the burning of the hall could have been seen for miles around, in the large expanse of what is now the border country between England and Wales."
Archaeologists have long speculated that a close relationship existed between houses and tombs in Neolithic Europe, and that 'houses of the dead' amounted to representations of the 'houses of the living'.
In addition to the two long mounds, the site has provided evidence for a series of later burials and other deliberate deposits, including a cremation burial and a pit containing a flint axe and a finely-flaked flint knife.
The objects have close affinities with artefacts found in eastern Yorkshire in the Late Neolithic (c. 2600 BC).
Dr Ray said: "These subsequent finds show that 1000 years after the hall burial mounds were made, the site is still important to later generations living 200 miles away – a vast distance in Neolithic terms.
"The axe and knife may not have been traded, but placed there as part of a ceremony or an ancestral pilgrimage from what is now East Yorkshire.
"So we witness an interconnected community linking Herefordshire and East Yorkshire by marriage and by descent 5000 years ago."
He added: "In the British context, the Dorstone find is unique and unprecedented.
"We were hoping our work with The University of Manchester would help us to give us a clearer picture of the origins of these long barrows- but we were surprised how clearly the story came through.
"It's very exciting for us: for 15 years I have been arguing that Herefordshire has something important to say on the national picture of our Neolithic heritage."
Images are available from the excavation
An artist's impression of a hall of the dead is available
Professor Thomas and Dr Ray are available for comment
Journalists are welcome to visit the site at any point on Monday or Tuesday
For media inquiries contact:
Mike Addelman
Press Officer
Faculty of Humanities
The University of Manchester
0161 275 0790
07717 881567

Monday, 29 July 2013

Big meltwater conduits beneath an ice stream

 This is a rather interesting paper which explains how speculation and theory can sometimes be confirmed by observation -- using new techniques which were not available in the bad old days......

Glaciologists and geomorphologists have speculated for a long time about the manner in which meltwater moves beneath an ice sheet or ice stream in a polar situation.  In some parts of Antarctica there are spectacular 'labyrynths' of meltwater channels, suggesting that catastrophic meltwater flows have occurred in the past, with erosion on a massive scale being the result.  when my colleague David Sugden and I found big meltwater systems on two of the ice-free peninsulas of the South Shetlands (Byers Peninsula on Livingstone Island and Fildes Peninsula on King George Island) we wondered where all the water had come from, and also wondered whether these channels had been cut during a rapid and catastrophic melting phase at the end of the last glacial episode.

 A famous photo of the Labyrynth, by George Denton.  These channels are naturally taken to have been formed by vast amounts of meltwater, probably flowing subglacially.

The Labyrynth, in the Taylor Dry Valleys system of East Antarctica, is the most famous example of a chaotic system of connected valleys -- suggested to have been formed during the Miocene by subglacial floods.  As long ago as 1965 CA Cotton was speculating as to the origin of the "scablands" in the Wright Valley.

There is also a considerable amount of speculation in the glaciology literature about how water moves beneath great thicknesses of ice -- and how meltwater actually assists in lubricating the glacier bed and thus encourages ice movement and glacial erosion.

But naturally enough, it is virtually impossible to OBSERVE meltwater activity in real ice sheet situations where ice may be kilometres thick and where ice surface conditions may be very hostile indeed for field parties undertaking research.  Drilling projects in many parts of Antartica have revealed the presence of meltwater lakes -- some of them very large indeed -- but little has been known about where the water comes from, how it is maintained, and where it goes to.

Now a new advance in radar technology has allowed researchers to identify two different types of meltwater flow beneath very thick ice, associated with rapid ice movement.  Beneath the Thwaites Glacier in West Antarctica, Schroeder and his colleagues have used radar signals to differentiate two types of meltwater flow -- one essentially like a swamp, with no deep channels but with sheets of water interconnected and flowing extensively across the land-ice interface; and the other involving concentrated meltwater flow in distinct channels:

The authors were most interested in the implications of this work for the possible instability of the West Antarctic Ice Sheet -- but there are a number of geomorphological implications which we should note.  First, it is quite possible for large quantities of meltwater to be flowing on the bed of a very thick ice sheet or ice stream when it is operating normally -- rather than just when there is catastrophic wastage going on.  Second, extensive or areal flow and concentrated linear flow can occur beneath the same glacier, with a transition zone between the two types of flow.  Third, it appears from the work that the water is flowing uphill, on the up-glacier flank of a rock ridge -- that confirms the assumption made many hears ago that subglacial drainage operates wherever there is sufficient hydraulic pressure, regardless of ground surface slope.  Fourth, when the meltwater is concentrated into channels beneath the ice, it seems to move in distinct tunnels on the glacier bed with semi-circular or arches cross profiles.  That is interesting, because we have not had any great evidence on this until now.  We still do not know from this work whether there are deep rock-cut channels beneath the ice tunnels -- but if water is flowing in great volumes under high pressure it is almost inevitable that substantial bedrock erosion will be taking place.

There are strong implications in all of this work for the processes that might have operated in North Pembrokeshire during the Anglian and Devensian glacial episodes, when the Irish Sea Glacier cvovered much of the landscape.  For example, what does this work tell us about the cutting of the Gwaun Valley meltwater channel system, or even about the cutting of the gorge at Rhosyfelin?  Watch this space.....

Scientists Image Vast Subglacial Water System Underpinning West Antarctica’s Thwaites Glacier 

Evidence for a water system transition beneath Thwaites Glacier, West Antarctica

Dustin M. Schroeder,
Donald D. Blankenship, and
Duncan A. Young

Thwaites Glacier is one of the largest, most rapidly changing glaciers on Earth, and its landward-sloping bed reaches the interior of the marine West Antarctic Ice Sheet, which impounds enough ice to yield meters of sea-level rise. Marine ice sheets with landward-sloping beds have a potentially unstable configuration in which acceleration can initiate or modulate grounding-line retreat and ice loss. Subglacial water has been observed and theorized to accelerate the flow of overlying ice dependent on whether it is hydrologically distributed or concentrated. However, the subglacial water systems of Thwaites Glacier and their control on ice flow have not been characterized by geophysical analysis. The only practical means of observing these water systems is airborne ice-penetrating radar, but existing radar analysis approaches cannot discriminate between their dynamically critical states. We use the angular distribution of energy in radar bed echoes to characterize both the extent and hydrologic state of subglacial water systems across Thwaites Glacier. We validate this approach with radar imaging, showing that substantial water volumes are ponding in a system of distributed canals upstream of a bedrock ridge that is breached and bordered by a system of concentrated channels. The transition between these systems occurs with increasing surface slope, melt-water flux, and basal shear stress. This indicates a feedback between the subglacial water system and overlying ice dynamics, which raises the possibility that subglacial water could trigger or facilitate a grounding-line retreat in Thwaites Glacier capable of spreading into the interior of the West Antarctic Ice Sheet.

Stripes at West Kennet Avenue?

Many thanks to Pete Glastonbury and Tim Daw for the following pics:

Both of our colleagues have mentioned the discovery of "periglacial stripes" at West Kennet.  Not sure that I can see anything obvious in these photos which would lead me to say that these features are reminiscent of the strange stripes in the Stonehenge Avenue.  Maybe they are just very subtle here? 

From Pete Glastonbury:  On the West Kennet Avenue dig today the Between the Monuments project uncovered periglacial stripes.  The dig is being run by Dr Mark Gillings and Dr Josh Pollard.
The dig started with a lightning storm, which always bodes well in archaeology, and today they uncovered the edge of Mr Keillers trench last dug 79 years ago!

Would Pete and Tim care to convince us that there are stripes there?  We'll leave to one side for the moment the idea that they may be "periglacial" -- that term seems to be thrown about all the time, without the archaeologists having any clear idea what it actually means or what the processes of formation are supposed to have been.

Sunday, 28 July 2013

Stonehenge incomplete

You know that big book called "Stonehenge Complete"?  Well, maybe there should be another now, taking account of some modern thinking, called "Stonehenge Incomplete".  Should be a good seller -- anybody volunteering to be the editor?  Would EH publish it?   Hmmm-- I just remembered that before long, EH won't exist any more........

Anyway, thinking of all that, it was my birthday yesterday, and the family gave me a birthday card with this on the front.  Very apposite.

How to use a book

Since Myris and Tony referred to this book thing, and since scrolls and papyrus are obviously still popular in certain quarters, I thought I'd share this wonderful little sketch from Norway......

Back from the hols

Hello everybody -- just returned safely from 8 weeks in Sweden, having enjoyed a delightful North Sea voyage on the romantically named MV Transpulp.  Hundreds of containers of paper and 4 passengers...... and nothing to waste money on....

Have tried to publish everything I'm aware of -- but apologies if anything has gone astray.  There was a period when I was not able to pick up or send Emails properly.

Will soon be back in the swing of things....

Tuesday, 23 July 2013

Mesolithic lunar calendar?

Latest wonderful breakthrough -- Warren Field, Crathes Castle, Aberdeenshire -- according to Prof Vince Gaffney and assorted others a Mesolithic lunar calendar associated with the invention of time itself.....

A rough alignment of pits and a lot of computed jiggery-pokery?  Does anybody else share my sense of profound scepticism about all of this -- or is it just me?

Friday, 19 July 2013

Nordvest Fjord, East Greenland

Satellite image of Nordvest Fjord and Scoresby Sund -- from Google Earth.

I've been doing some research recently on East Greenland, and have become more and more impressed with the statistics concerning Nordvest Fjord.

(Mind you, I have been obsessed with this particular fjord since 1962, when I paddled along the eastern fjord wall between Nordostbugt and the Oxford Gletscher outlet, with three fellow members of the OU East Greenland Expedition.  That was pretty mad, since we were using canvas kayaks to paddle through areas of brash ice -- if the canvas had been ripped in contact with sharp ice fragments, that would have been curtains.  One doesn't survive for more than a few minutes in water that cold....)

 A mixture of icebergs, old sea ice, new sea ice and brash ice fragments in Nordvest Fjord.  The new sea ice can start to form in late August, when it freezes at night.  It is not surprising that there has been no proper bathymetric survey of the fjord, and that all we have are occasional soundings.

And since you ask,  yes, we named the glacier, on which we did the first serious glaciological work in August 1962.

For maps of the territory in question, have a look here:

Back to the fjord, which is really the mother and father of all the fjords on Planet Earth.   If you go to any of the fjord sites on the web, you will find copious amounts of information about Sognefjord, Milford Sound, the fjords of Chile and even Antarctica, but very little about this one.  Strange, given that it is now well known from satellite imagery, even if not very frequently visited.  That's because access is very difficult.  The fjord extends c 217 miles (350 km) inland from the outer coast.  It's in two sections -- the outer (very broad) part is called Scoresby Sund, which is about 20 miles wide and 120 miles long, with Jameson land to the north and Milne Land and Knud Rasmussens land to the south and west, and then Nordvest Fjord proper, which pushes inland for a further 95 miles or so.  In this section the fjord is mostly less than 5 miles wide, and in places as narrow as 3.5 miles from shore to shore.  Access into the fjord system is often very difficult, even for ice-strengthened ships in the summer, because of the thick pack ice which conjests the Scoresby Sund entrance; in some years no vessels manage to get through it, and even when access is possible, the fjord is effectively shut off again early in September.

 This photo was taken near Nordost Bugt, where the narrow Nordvest Fjord opens out into Hall Bredning.  The snow-capped peaks and icefields on  the mountains across the fjord are typical of the fjord landscape.

The Nordvest Fjord - Scoresby Sund system has clearly been one of the major outlet routes for ice from the Greenland Ice Sheet, during the whole of the Pleistocene and maybe for much longer than that.  Even today the Daugaard Jensens Gletscher, near the head of the fjord, is possibly the most productive glacier in the whole of Greenland.  Because the ice here has been streaming so effectively in a narrow and constrained trough, the rate of downcutting has been impressive indeed. There are no proper bathymetric charts, but from the scattered soundings that have been made we see depths of 1372m, 1459m, 1372m, 1150m, 1237m, and 1290m between Eskimo Bugt and Syd Kap.  The deepest sounding of all is 1508m (4,947 ft).    These soundings show that the fjord is substantially deeper than Sognefjord in Norway (maximum known depth 1308m), which has just one short stretch deeper than 1200m.  But here on the flanks of Nordvest Fjord the plateau ice caps and mountain summits are almost all over 2000m (6561 ft), whereas there is little land over 1600m on the flanks of Sognefjord.  So the full depth of Nordvest Fjord over a distance of about 80 miles is approx 3300m or 11,000 feet.  I'll let somebody else work out how much material has been eroded and removed by ice from a trough of this size.......  but it is indisputable that this is the deepest, longest and most dramatic fjord system on earth.

We don't know enough about the long profile to know whether it conforms to the "ideal" long profile of Sognefjord, where we can see an incremental deepening of the trough wherever there have been supplements to the ice discharge via tributary glaciers:

I would expect something similar in the case of Nordvest Fjord.  What we do know is that where the narrow Nordvest Fjord opens out in the vicinity of Syd Kap and the Bear Islands, there is a sudden shallowing of the water, as the bedrock floor rises to approx 400-500m below sea level.  This is very similar to the situation at the mouth of Sognefjord, where ice diffluence has been associated with a reduction in erosive capacity, as we can see on the diagram above.  We don't exactly see skerries at the junction between the deep fjord and the shallow fjord, but there are some grounds and small islets which make navigation difficult and dangerous, and as in the case of Sognefjord the fjord bed rises from c 1200m to just a few tens of metres over a distance of just 4 miles.  This is called the threshold, and it explains why there is relatively little water exchange in the murky depths of the fjord; vast quantities of water are simply trapped in what is in effect a gigantic elongated basin.

Autumn colours at Syd Kap, where the fjord opens out into the wide expanse of Hall Bredning.
The uplands and icefields of Renland, with icebergs and the Bear Islands in the foreground.

Big tabular bergs in Scoresby Sund -- probably from either Daugaard Jensens Gletscher or one of the other ice sheet outlet glaciers.

Ice-smoothed slabs in Syd Kap Bay, with the waters of Hall Bredning beyond.

Wednesday, 17 July 2013

Smoothed face + Plucked face

If you are lost in a fog in the Stockholm Archipelago, you can use the striations to tell you where the north-south line is, and then you can look at the rock faces around you.  The north faces of the undulating landscape are almost always smoothed and polished, as in the top photo, and the south faces are almost always rough and plucked, as in the lower photo.  These pics were taken on the west side of Rodloga Storskar -- just about 100m apart.

Plucked face of a roche moutonnee

Here's another classic glacial landform from the west side of Rodloga Storskar in the Stockholm Archipelago.  This is another piece of a roche moutonnee, but here we are looking straight at the plucked face -- ie the ice has come directly towards the camera.    The great scar left following the removal of plucked blocks is truly spectacular. 

I am rather convinced that this is the mechanism by which large blocks were dragged from the outcrops ar Rhosyfelin, during the Anglian Glaciation.......

Roche moutonnees - Stockholm Archipelago

 Ice movement directions in the Weichselian (Devensian) glacial stage, c 20,000 years ago, in Southern Sweden.  The following photos all come from within the area marked by the red circle.  With minor variations, the ice movement in the Stocholm Archipelago has  been within a few degrees of north - south.  If you are lost in a fog, without a compass, all you need to do is go ashore and look for the striations.......

 Typical small roche moutonnee on a small island off Blido, in the outer archipelago.  The smoothed (up-glacier) face is on the north side, and the rough or plucked face is on the south side.  The latter is much steeper, as we can see -- because this is the face from which blocks of rock have been dragged away.

 Another typical small roche moutonnee, on Salskaret, off Blido.  Again we can see the contrast between the northern streamlined and smoothed face, and the steeper plucked face on the south side.

This is the most beautiful small roche moutonnee I have ever seen, on the west side of Rodloga Storskar.  The roche moutonnee form is almost perfect, and to the south of what is left of the "parent rock" there are three detached blocks -- and maybe more, under the sea surface.  here we can see two of the blocks, which have not been moved very far by the overriding ice.

Here we can see all 3 of the detached blocks -- the first one is about 20m away from the parent rock.

Towards the end of the last glacial episode, the original roche moutonnee had been reduced to such a small size that the remnant was about to be broken up by the inexorable compression on the up-glacier side and the tension exerted on the rock surface on the down-glacier side.  The big crack we can see in the photo was about to be exploited, and another big block was about to be dragged from the flank of the 'parent" feature -- but then the glaciation came to an end, the ice stopped moving, and the erosional process was never completed.......

Tuesday, 9 July 2013

Ice-moulded forms

Another pic from the Stockholm Archipelago.  Classic ice moulded forms, washed bedrock surfaces and a litter of erratics left when the till in which they were embedded was washed away by wave action etc during the emergence of the coast. As Tony knows, I could probably give you a geomorphology lecture on the basis of this photo alone, but maybe not now.......

A very erratic erratic on a washed surface

One of the nice things about coming to Sweden every summer is that I get to wander about in the Stockholm Archipelago, which is like an open text-book on glacial erosional processes.  Some of the landforms and the detailed "micro-morphology" left by overriding ice are quite extraordinary -- and in part their survival after c 15,000 years of exposure, following the retreat of the Devensian ice, is down to the fact that this whole area has been subjected to considerable isostatic recovery.  The process is still going on.  This means that the rock surface shown in this photo was submerged beneath the sea  not that long ago, and that it has been "washed" by coastal processes including wave action which have removed most of the silt, clay and gravel from any till left behind when the ice retreated.  So we get these remarkably clean and smooth rock surfaces, with erratics scattered all over the place, just waiting to be photographed........

Here the bedrock is a metamorphosed Precambrian pink granite, and the erratic boulder is made of a grey gneiss which will have come from somewhere to the north.