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

Sunday, 27 July 2014

More about glacial erosion


Two photos taken on the island of Svartloga the other day. The top one shows the streamlined whaleback forms typical of this part of the Stockholm Archipelago.  The rock surfaces here (heavily metamorphosed Pre-Cambrian granites) are on the up-glacier side of a larger roche moutonnee feature.  What is particularly interesting is the extent of fracturing on the rock surface -- the apparently random fracture pattern is obvious, except that it is not actually random at all, since there is a reason for everything in glaciated terrain.......

I'm intrigued by this top photo, since the fractures are on a rock surface which must have been under heavy compression when it was last glaciated.  Most cracks on roche moutonnee forms are seen where compression gives way to tension, near the highest point on the roche moutonnee surface.  Given a bit more time (ie a few thousand years more, maybe) and this rock surface would have been busted into bits.  Maybe we are looking at the result of pressure release, with these fractures appearing as a result of the removal of the ice load.

The bottom photo shows a moulded, smoothed and striated rock surface with some transverse fractures developing exactly where we would expect them, in readiness for the removal of the next slab or boulder as quarrying of plucking processes come into play.  The clean face at the top right of the photo is on the down-glacier flank of the roche moutonnee -- beautifully smoothed but not striated.  Sometimes these plucked faces are rough, and sometimes smooth.  The reasons for this are complex.  Another very striking feature is the colour difference between the up-glacier and down-glacier faces.  The striated (up-glacier) surface is very weathered, and is coloured grey.  The down-glacier or plucked face is a creamy pink colour -- quite unweathered and fresh.  It would be interesting to do some cosmogenic dating on faces like these, since their physical appearances suggest that on the striated face there has not been a huge amount of erosion since the last interglacial.......

Friday, 25 July 2014

More rock glaciers

Rock glacier, Kenai Mountains, Alaska

Rock glacier, Sourdough Mts, Alaska

Rock Glacier, Selwyn Mts, NWT, Canada

Rock glacier, Talkeetna Mts, Alaska (this one occupies an old cirque in the mountains)

Rock Glaciers

Rock glaciers are strange features which exist only in high latitudes, and for the most part in rugged mountain terrain.  Sometimes they look like glaciers covered in debris, but some occur in such inappropriate locations that they clearly have nothing much to do with glacier ice or glacial processes.  They can be very large and very spectacular -- but they are inadequately understood.  One requirement for them seems to be the presence of permafrost, or at least a long freezing season.  They are composed, internally, of vast amounts of rock debris with the interstices filled by  ground ice formed by the trickling downwards of melting snow which then later freezes.  Another requirement is that they must have relatively modest precipitation -- so they are found for the most part in relatively arid environments, or in places where snow cannot accumulate in sufficient quantities for snow-patches to accumulate and to be converted into firn or glacier ice.  But they certainly flow just as glaciers do -- and this is apparent on many of the surface features.  Here are three photos of rock glaciers found on the web:

The Mount Sneffels rock glacier, Unites States

Snaefell Rock Glacier, southern Iceland

Rock Glacier near McCarthy, Alaska



Tuesday, 22 July 2014

Aurochs find at Whitesands




Thanks to Tony for bringing this to my attention -- from a BBC web page.  It's based on a National Park press release.  Interesting finds -- but it would be good to know more details.  I have no idea how strong the evidence for the footprints actually is -- and I remain to be convinced that they are human, and very old.  Also, I doubt that they are 10,000 years old, unless there is strong radiocarbon dating evidence to support that contention.  From what we know about the submerged forests, their uppermost surfaces are much more likely to be between 7,000 and 5,000 years old -- since that is when the final submergence by a rising sea level is likely to have happened.  The caption to the photo of an aurochs horn calls it an "aurochs tusk"... !!!  Hmmm......

It would be good to know more about the context of the find of the aurochs horn and "the remains" which presumably mean bones.

And as for this:  "the footprints.......suggest the humans may have been tracking a large hoofed animal such as an auroch"  is pure fantasy.  The footprints were at Newgale and the aurochs was found at Whitesands.  There is nothing whatsoever to connect them, and footprints on a peat bed could have been created by anybody wandering through a wooded area for any purpose whatsoever.  But that's what archaeologists apparently do nowadays -- to hell with science; all that matters is creating a good story.  But I suppose in this case it's harmless enough.

 http://www.bbc.co.uk/go/em/fr/-/news/uk-wales-28104756

Storms reveal hunter-gatherer footprints and animal remains

More evidence of prehistoric life in west Wales has been discovered following the severe storms earlier in the year.

Ancient human and animals footprints have been found at Newgale and the remains of extinct cattle at Whitesands in Pembrokeshire.

The finds follow earlier discoveries of forests and other remains along the south and west Wales coastline.

The footprints are believed to date from around 10,000 years ago.

The discoveries were made possible after violent tides stripped large areas of sand away from beaches.

 Phil Bennett from the park authority holding the aurochs tusk
The remains of an aurochs, an extinct breed of cattle, was also found.

Pembrokeshire Coast National Park Authority's culture and heritage manager Phil Bennett said: "The footprints in the exposed peat at Newgale, which are most probably from the Mesolithic period around 10,000 years ago, suggest the humans may have been tracking a large hoofed animal such as an auroch.

"The discovery of the aurochs remains at nearby Whitesands would support this theory and the horns give you an idea of just how large these creatures must have been."

However Mr Bennett said there were two sides to the story, as the weather had also led to the loss of other resources.

The aurochs remains will be conserved, with the aim of putting it on display at Oriel y Parc Gallery in St Davids.

Sunday, 20 July 2014

The Quiraing Landslip, Isle of Skye


Two more fabulous photos of the Quiraing Landslip, on the Totternish Peninsula north of Portree, on the Isle of Skye.   This is the biggest landslip in the British isles,  giving rise to  a bizarre and almost "otherworldly" landscape.....
The Quiraing is a landslip located in the north-east of the Isle of Skye, north of Portree, on the Trotternish Peninsula. It is the largest landslip in Great Britain. - See more at: http://www.natureflip.com/quiraing#sthash.4ymdlGDM.dpuf





The Quiraing is a landslip located in the north-east of the Isle of Skye, north of Portree, on the Trotternish Peninsula. It is the largest landslip in Great Britain. - See more at: http://www.natureflip.com/quiraing#sthash.4ymdlGDM.dpuf

Saturday, 19 July 2014

Ness of Brodgar



There's a nice article, graphic, map and photo gallery featuring the Ness of Brodgar on the National Geographic web site, here:
http://ngm.nationalgeographic.com/2014/08/neolithic-orkney/brodgar-graphic

The article claims that a great complex of buildings and standing stones involved the quarrying and transport of "thousands of tonnes" of sandstone which was transported several miles to the site portrayed in the graphic.  But no evidence is given to support that contention.......

From the "Decoded Past" web site:

http://decodedpast.com/neolithic-scotland-heart-orkney-world-heritage-sites/4413

"The Neolithic drive towards impacting and shaping the landscape, which is evident in slightly later sites across Britain and France, probably began with agriculture. The Neolithic people learned how to move and manipulate rocks in order to make fields to grow crops and rock enclosures to keep cattle from straying.

The Stones of Stenness are true megaliths, in that they are about twenty feet tall. The 23 foot passage into Maeshowe is almost completely walled by two massive megaliths laid on their long edges. There may originally have been sixty stones in the perfect circle that is the Ring of Brodgar, although only twenty or so are still evident. Certainly, a large number of people participated in quarrying, moving and erecting the stones."

There's a quote from Neil Oliver's book:   “A whale-back ridge dominates the middle of the Brodgar peninsula, roughly halfway between the Ring of Brodgar and the Stones of Stenness, and it had always been taken for a natural feature. The fact that it lies right at the centre of this great natural amphitheatre, containing all of Orkney’s most famous ritual monuments, seemed purely a coincidence of geology.”

The award of World Heritage status in 1999 led to plans for a more thorough investigation of the area surrounding the site. This began in 2002 when a geophysical survey was undertaken across the isthmus that links the stone circles, and then the archaeologists got to work. Annual programmes of digging still continue, but by 2012, archaeologists excavated a massive walled enclosure of a dozen mainly ritual buildings.

“We have discovered a Neolithic temple complex that is without parallel in western Europe. Yet for decades we thought it was just a hill made of glacial moraine,” says discoverer Nick Card of the Orkney Research Centre for Archaeology. “In fact the place is entirely manmade, although it covers more than six acres of land.” 

Robert McKie reports in his article ‘Neolithic discovery: why Orkney is the centre of ancient Britain’.

The site contains some of the most perfectly constructed stone walling of any historical era that stood for a thousand years from about 3300 BC. In spite of being ritually ‘decommissioned,’ after excavation, it still stands to two metres in height. Anyone crossing between the two stone circles would have to pass through the site, and its buildings are not residential in character.
-------------------------------------------

There does seem to be a vast amount of stone used in these structures.  Don't have a problem with that -- if you have a big project and you have little timber available, you will use stone, from wherever you can get it.  Much of it will have been quarried or dug up close to the places where it was needed -- indeed the easy availability of stone might have been a determinant for the location of the Ness in the first place.  Other stones will have been glacial erratics,  and some monoliths might have come from places where they were easy to wedge out of the bedrock exposures.

I get a sense from the newer reports that there is a big difference between the interpretations of Colin Richards, who attaches profound significance to the act of quarrying and profound -- maybe spiritual or ritualistic -- significance to the places where the quarrying was done, and the much more utilitarian interpretations of the current digging teams on Orkney.  As far as I can see, they think that the builders of the Ness needed stone, so they went out and got it from wherever they could find it.  Nice and simple.




Tuesday, 15 July 2014

Glen Tilt -- a classic glacial trough


Glen Tilt in Perthshire is a classic U-shaped glacial trough -- except that it isn't really typical of glacial troughs at all.  It's a long, straight through valley, cut along the line of a fault, and for at least some of the time the whole valley was submerged beneath an ice sheet, with ice moving across it at an angle.  So the trough might have contained stagnant ice at that time.  But its shape reveals that it has clearly carried streaming ice at other stages of the Ice Ages, just like some of the through valleys of Greenland.