THE BOOK
Some of the ideas discussed in this blog are published in my new book called "The Stonehenge Bluestones" -- available by post and through good bookshops everywhere. Bad bookshops might not have it....
To order, click
HERE

Tuesday, 22 October 2019

Tasman Glacier dead ice wilderness

Moraine "wall" above the lake -- the debris is all resting on dead ice, and is very dangerous indeed.  Material is constantly sliding down into the lake.

The sharp crest of the main moraine ridge near the village.  Many people walk along the crest of the ridge -- not a good idea.  Note the dead-ice wilderness filling the whole of the glacier tough.

Scary!  Too many paths, too close to the edge.....

Annotated photo showing the moraine "wall" and the dead-ice chaos below.

Dead-ice terrain, in the Tasman Glacier valley.  Along the edge of the ice-dammed lake you can see that the terrain is all ice-cored.

Much as I love glaciers, I am genuinely scared of terrain like this. It's one of the most obvious signs of global warming.  Glaciers in all the high mountain regions of the world are melting catastrophocally, replacing areas of clean firm ice with this sort of landscape.  The Himalayan glaciers  are being transformed at an unprecedented rate.

Here is some Google satellite imagery:

Here we see the dead-ice wilderness from above.  The valley is between 2 and 3 km wide.  The meltwater lake is at the base of the photo, and the clean glacier snout is off the top of the photo.  The dead ice area covers about 24 sq km.

Close-up of part of the moraine surface.  Note the temporary meltwater lakes and the crescentic fractures where collapses have occurred.

The junction between the lateral moraine and the dead ice zone on the valley floor.  The track to the Ball hut runs on the outside of the moraine ridge, but people stop and clamber up onto the ridge crest far too frequently, just to get a better view.  Not a good idea. For the authorities, a tourist management nightmare.......



Monday, 21 October 2019

The Rhosyfelin till



Exposed till surface at Rhosyfelin -- Late Devensian

Exposed till surface in Erratic Valley, Antarctica -- modern

Geomorphology works through the use of analogies -- you initially interpret what you see on the basis of what you know from other situations. Experience is everything.  But then of course you have to go on and prove to others that your interpretation is the correct one, through the use of analytical methods of all sorts.  More and more sophisticated techniques come along all the time....

I was struck the other day by a photo of the surface of a hummocky moraine (meaning meltout till or flowtill) in the Erratic Valley, on the Antarctic Peninsula.   I thought immediately that it looked virtually identical to the till surface exposed during the Rhosyfelin archaeological dig.   I guarantee that you could switch the labels around, and nobody would be able to tell which surface is old and which is young, or which one came from where........

If you want a detailed description of the till, it's all in the QN paper published by Dyfed Elis-Gruffydd, John Downes and myself in 2015:

Brian John, Dyfed Elis-Gruffydd and John Downes (2015a). "Quaternary Events at Craig Rhosyfelin, Pembrokeshire." Quaternary Newsletter, October 2015 (No 137), pp 16-32.

https://www.researchgate.net/publication/283643851_QUATERNARY_EVENTS_AT_CRAIG_RHOSYFELIN_PEMBROKESHIRE
https://www.academia.edu/19788792/Quaternary_Events_at_Craig_Rhosyfelin_Pembrokeshire

The till surface that was exposed in the dig was so spectacular that it could not be missed, and yet it has still not been referred to in any of the archaeological papers by MPP and his team -- and not even in the articles written by geologists Ixer and Bevins.  Maybe if they had visited the site and examined the sediments, it would have helped.........  instead, the pretence has been perpetrated that somehow all of the sediments are associated with quarrying activity, and that they have no inherent interest unless they contain "evidence" of human occupation.  Strange world we live in.....

Friday, 18 October 2019

Dead ice terrain

Unterer Grindelwaldgletscher in the Alps.  Debris-covered snout with many additions coming from valley side rockfalls

Chukhung Glacier, Nepal

Erratic Valley, Antarctic Peninsula.  Exposure of surface till in an area of hummocky moraine

Crusoe Glacier snout, Axel Heiberg Island.  Bedrock exposures adding rockfall debris to mixed morainic and fluvioglacial materials

Khumbu Glacier, Nepal.  Ice-cored moraines

Fox Glacier, New Zealand

Rohn Glacier, Alaska.  Dead ice terrain on the glacier flank, with meltwater lakes


Bing satellite image of the terminal moraine loop and dead ice terrain, Roslin Gletscher, East Greenland.  In 1962 we walked across that little lot -- it was a bit hairy at times.......


High-resolution Google Earth image of part of the same dead ice topography.  The glacier snout is just off the photo at top left.  Some of the trapped lakes are fed by debris-rich meltwater streams (buff colour) and others are isolated (blue).

Till characteristics and nomenclature






If you have ever wondered about diamictons and tills, and all things related to glacial deposition, you can always read the text by David Sugden and myself (if you can get a copy!) or --if you are short of time -- just take a look at this.  It's a fascinating little web site, with great illustrations:

https://web.viu.ca/earle/geol305/Glacial%20Tills.pdf

I have always subscribed to the view that if something looks like a till, it probably is a till -- and that it is probably NOT an ancient deposit redistributed or rearranged under periglacial conditions over many thousands of years.  I am a man who likes his Occam's Razor;  the most parsimonious explanation of things is always what I look for, unless I am dragged away from it by something unexpected or spectacular.  The spat about the Caldey Island "diamicton" comes to mind..........

Since I have worked in so many glacier snout environments characterised by complete chaos, I am even rather sceptical about giving different till types names -- but I suppose there are always those who like to classify things.  I am equally cautious about the significance of fabric analyses, given that what happened here may not really have anything to do with what happened there, or a bit above, or a bit below.  In a chaotic ice wastage environment, anything can happen, and usually does.  Where a glacier is melting away, in a "dead ice environment", the environment is far from dead -- it becomes highly dynamic and mobile, with slumps and slides all over the place and a vast amount of sediment redistribution.  In these environments, field workers sometimes lose their lives when fragile ice bridges collapse without warning and where debris is suddenly mobilised on a steep melting ice slope.  If you happen to be standing in the wrong place at the wrong time time, too bad........

But some principles do apply.  We do have lodgement tills in Pembrokeshire, in the exposures of clay-rich Irish Sea tills at Abermawr, Mwnt, Whitesands, Druidston and elsewhere -- and in those exposures we can see deformation features and much else besides, if we subject the till to "micro-fabric analyses."

Elsewhere, and above the lodgement tills, we find something much more akin to chaos, in what was referred to in the old days as "rubble drift" --  patches of flow till, intermittent and discontinuous beds of sands and gravels, some blocks of incorporated frost-shattered slope breccia, and both subglacial and supraglacial meltout tills.  The tills that I have been describing on the Pembrokeshire coast, from multiple locations, have been emplaced in these rather chaotic environments at a time of catastrophic ice wastage -- I doubt that any of them have accumulated by lodgement on a glacier bed.

A textbook example of a flowtill  -- or is it a debris flow?  Does it matter?

A textbook example of a meltout till.  This one might be sublacial, but then again it might have formed supraglacially.  Again, does it matter?

Fresh till from Popplestones, Bryher, Isles of Scilly.  Probably a meltout till.

Stony matrix-supported till on the north slope of Preseli.  Probably a meltout till.

Clifftop till, Bullslaughter Bay, South Pembrokeshire.  Probably a meltout till.

Clifftop till near Ceibwr.  Another meltout till?

Stony clifftop till at Madoc's Haven.  Yet another meltout till.....

Controversy is the lifeblood of science


My little dispute with John Hiemstra and others over the nature of a small deposit on Caldey Island is quite fun, and it reminds me that disputation and controversy lie right at the heart of science.  One might even say that it provides the lifeblood of science....... and it is inevitable and necessary because, as Karl Popper pointed out long ago, science can only advance through a process of falsification.  If scientists concentrate on hypothesis confirmation everything stagnates -- and working hypotheses are replaced by ruling hypotheses.  We end up with "assumptive" and potentially corrupt research.  Now where have we heard that before?

I have another little dispute with James Scourse on the extent of glacier ice across the Isles of Scilly.  That's OK too -- and I hope James might agree with me that by testing ideas and scrutinizing evidence more closely, we will all get closer to the truth. 


When I sit down and think about it, I recall scores of disputes in my own field of glacial geomorphology,  some resolved and others not.  Right at the beginning of my career I had a dispute with Prof Fred Shotton over the age of the glacial deposits in Western Britain.  On that, I was right and he was wrong.  The dispute over the position of the Devensian ice edge in West Wales has involved scores of researchers over the years, and it still rolls on.  Right now, there is a somewhat acrimonious dispute (not involving me!) relating to the age of the last glacial ice to have affected Lundy Island:


How many scientific controversies are represented by the lines on this map?

Not so long ago there was another big row about the glaciation of Dartmoor.  Going back fifty years or more, Eddie and Sybil Watson had an ongoing dispute with virtually everybody else about the nature of the pseudo-stratified deposits along the Ceredigion coast.  There have been big arguments about the nature and age of the deposits covered by peat in the Somerset Levels.  That involved Prof Clarence Kidson and others.  In Scotland Prof Brian Sissons was notoriously disputatious, and argued fiercely with everybody about everything, verbally and in print!  Intense scrutiny was everything to him, and he scared the living daylights out of many a PhD student -- but he was not always right, and taught people to assemble their evidence properly and to interpret it carefully. Prof Dai Bowen had a huge row with Prof Danny McCarroll and many others about the use of amino acid dating techniques,  and the consequences of "over-interpreting" the results from an inadequately understood new technology.  The old ideas about matching erosion surfaces in the landscape, espoused by Professors Wooldridge and Linton and other senior professors were disputed, bit by bit, by younger geomorphologists, and were eventually abandoned on the grounds that they were far too simplistic and were not properly supported by field evidence.   I could go on a great length........

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This is an interesting extract from a recent article:

Why do scientists disagree in the first place? One set of potential causes focuses on the experts themselves. One or more of the experts may be making an inaccurate claim because of incompetence (i.e., they are not experts at all [5]) and/or the fundamental limits of human judgment [6], or they may be intentionally or unintentionally biasing claims because of idiosyncratic attitudes, beliefs, or personal interests [7]. Another expert-focused cause might be different methodological choices that stem from individual scientists’ skills or preferences, or from historical developments in their respective fields or sub-disciplines. Alternatively, disagreements among experts within scientific fields may be due to irreducible uncertainty of the world itself and could be conceived of as a part of the normal process of science [8, 9]. From this perspective, it is inevitable that experts will disagree when confronting complex and uncertain real-world problems. It is the complexity and inherent uncertainty of the world that leads to disagreements about how to conceptualize problems, the research methods that should be used, etc. From a conceptual standpoint, these various expert- and world-focused reasons are neither logically nor practically mutually exclusive. For any given dispute among scientists there might be multiple causes, and these causes might differ from one dispute to another.

Source:  

Why do scientists disagree? Explaining and improving measures of the perceived causes of scientific disputes.  By Nathan F. Dieckmann, Branden B. Johnson
Plosone
Published: February 7, 2019
https://doi.org/10.1371/journal.pone.0211269

Here is another short extract from Wikipedia:

A scientific controversy is a substantial disagreement among scientists. A scientific controversy may involve issues such as the interpretation of data, which ideas are most supported by evidence, and which ideas are most worth pursuing.   Controversies between scientific and non-scientific ideas are not within the realm of science and are not true scientific controversies.[1]

This brings me, inevitably, to the dispute over the transport of the bluestones, which I am happy to acknowledge and play my part in, but which is ignored or denied by Mike Parker Pearson and his colleagues.  Are we involved in a scientific controversy, or are we not?  Well, if we say, for the sake of argument, that archaeologists are not scientists but storytellers, it might be argued that they are NOT involved in a scientific dispute!  

But of course there is a scientific dispute going on, and it has been running for almost exactly a century.  HH Thomas was a geologist, and so was Geoffrey Kellaway, and although they (as far as I know) never met, they certainly disputed the glacial and human transport hypotheses, as did other scientists including Olwen Williams-Thorpe and her team, James Scourse and Christopher Green.  More recently Rob Ixer, a professional geologist, has been very happy to dispute many points relating to his petrology and provenancing research, and also the glacial and human transport theses, on the pages of this blog, but not in published articles.  In those, whether writing with Richard Bevins as a specialist geologist or as a part of a team of specialists from many disciplines, he has studiously maintained the pretence that his ideas are universally accepted and that there are no disputes in progress.  Because he is a scientist and I am a scientist, this is a proper scientific controversy, and for it to go unacknowledged strays very close to the realm of scientific malpractice -- as I have said many times before.  

To a degree, I suppose we can partly forgive MPP and his archaeology colleagues because they are not scientists and do not fully understand what I am talking about...........   


Thursday, 17 October 2019

Caldey Island -- a till or not a till?




In the summer issue of Quaternary Newsletter Prof John Hiemstra and several colleagues published a short note on the "diamicton" at Ballum's Bay on Caldey Island, which I have referred to on a number of occasions on this blog.

https://brian-mountainman.blogspot.com/2011/08/devensian-till-at-bullums-bay-caldey.html

I have been convinced since 2011 that this deposit is a Late Devensian till, and I have not changed my mind.  Anyway, I encouraged John and others to go and have a look at it, which they duly did, and they decided that it is "probably" an old Anglian deposit which has been redistributed and redeposited under periglacial conditions in the Late Devensian -- some way from the nearest glacier.  Their article is available on Researchgate, where it can be scrutinised.

https://www.researchgate.net/publication/333998714_Caldey_%27Kald_ey%27_in_Old_Norse_was_literally_a_%27cold_island%27_but_was_it_under_Devensian_ice

I didn't like their line of reasoning, and say so in the new edition of QN, just published:

https://www.researchgate.net/publication/336614738_COMMENT_ON_CALDEY_'KALD_EY'_IN_OLD_NORSE_WAS_LITERALLY_A_'COLD_ISLAND'_BUT_WAS_IT_UNDER_DEVENSIAN_ICE_QUATERNARY_RESEARCH_FUND_REPORT_BY_JOHN_HIEMSTRA_ET_AL

I didn't expect them to row back on their earlier opinions, and of course they have responded to my published points by saying that they still think they are right -- and to give a proper picture of their arguments I have added their comments after my own.  All good fun.

Of course, it's easy for them to say that I am basing my conclusions on "basic" rather than intensive fieldwork and on my detailed knowledge of the Pembrokeshire coastal exposures -- and they are right that I have no detailed laboratory studies or dating results to back up what I am saying.  The joys of being old, retired and disreputable!

But I will maintain, until something strong comes along to prove me wrong, that the Caldey till exposure is unexceptional, and that there are many other similar till exposures along the south Pembrokeshire coast -- as itemised on this blog -- that show that the Late Devensian ice pressed far to the east.  I repeat -- their explanation of the deposit as a "redistributed ancient till" is more convoluted than it needs to be, and is unsupported by any convincing evidence.


Of course, none of us ever looks at an exposure in a completely impartial way, and I dare to suggest that John and his colleagues may be just a little influenced, in their attitude to the Ballum' Bay exposure, by their interpretation of some of the deposits on the Gower coast, and at Rotherslade in particular.  They claim that in the cliffs on the south Gower coast there are great thicknesses of "redistributed till" which were rearranged beyond the edge of Late Devensian ice.  On balance, I disagree with that too, since I consider that the authors have not demonstrated in their paper that the studied deposits were not simply deposited (and maybe rearranged) in a highly dynamic and changeable ice wastage environment at or near the peak of the Late Devensian glaciation.........

That paper is here:

https://www.academia.edu/11862453/Reinterpreting_Rotherslade_Gower_Peninsula_implications_for_Last_Glacial_ice_limits_and_Quaternary_stratigraphy_of_the_British_Isles?auto=download

Hiemstra, J. F., Rijsdijk, K. F., Shakesby, R. A. and McCarroll, D. Reinterpreting Rotherslade, Gower Peninsula: implications for Last Glacial ice limits and Quaternary stratigraphy of the British Isles.
J. Quaternary Sci., (2008). ISSN 0267-8179









Preseli -- glacial deposits


Copy of a map by WD Evans (Plate 4 of his QJGS article) -- designed to show where the areas of exposed rock are to be found, but if you concentrate instead on the "boulder clay" or till areas, you can see just how extensive they are, both to north and south of the upland ridge.


I have been digging up some ancient papers and doctorate theses from the 1940's -- and have turned up some quite useful information.  Two researchers had interesting things to say-- WD Evans and JC Griffiths -- both of whom submitted doctorate theses to the University of London.

Sadly, it is not always easy to get at old papers -- the QJGS articles are still trapped behind paywalls, including this one:

The Geology of the Prescelly Hills, North Pembrokeshire
William David Evans
Quarterly Journal of the Geological Society, 101, 89-110, 1 October 1945, https://doi.org/10.1144/GSL.JGS.1945.101.01-04.04

Evans did not have much to say about glaciation, but Griffiths's thesis was titled "The Glacial Deposits west of the Taff, South Wales" (1940), and although in many ways it is a rather poor piece of research, he was convinced that there was at one time a Preseli ice cap, and that it may well have existed before the mountains were "overwhelmed" by Irish Sea ice.

This is an interesting map, from a 1984 NERC report on drainage in the Preseli Hills:


The stippled area covers all the land above 200m -- so this might give an indication of the extent of the intermittent ice-cap, which we have referred to on many past occasions.

Griffiths also mentioned blue clay till at Llangolman -- again I have described this before:

https://brian-mountainman.blogspot.com/2014/10/pre-devensian-glacial-deposits-south-of.html

In 1904 TJ Jehu, one of my great heroes, described a clay pit at Llyn (Grid ref SN112274) or Fagwyr Owen, to the NW of Llangolman.  This was in open country, just above the 600 ft contour.  Jehu described the clay pit as containing "boulder clay" and of being 20 ft deep -- so deep that ladders had to be used to get in and out.  The clay is bluish and very tough, and was referred to back in 1904 as "india-rubber clay."  From the map and written evidence, there may have been more than one clay pit in the vicinity.


One thing that is very confusing, on the Geology of Britain viewer, is that on a small scale, the deposits both to the north and the south of the Preseli upland are coloured blue and labelled as "till", whereas when you zoom in the deposits to the south change from blue to a muddy sort of colour, with a different label.

The blue area is described thus:
Till (Irish Sea Ice) - Diamicton. Superficial Deposits formed up to 3 million years ago in the Quaternary Period. Local environment previously dominated by ice age conditions (U).

On the other hand, the area to the south has these words attached:
Head - Diamicton, Gravel, Sand And Silt. Superficial Deposits formed up to 3 million years ago in the Quaternary Period. Local environment previously dominated by subaerial slopes (U).

So on the one hand the till is deemed to be fresh, and on the other it is deemed to be mixed up with brecciated slope deposits and other materials.  I don't know that this distinction is based on any hard evidence -- I suspect that there is simply an assumption (based on the presumptions of Dai Bowen and others) that the till to the north of Preseli is Devensian and the till to the south is Anglian -- belonging to the mythical "Penfro Till Formation."

In other words, nobody knows what is going on, and somebody needs to sort it out.

=================

Where did this till on the south side of Preseli come from?  How old is it?  I have assumed in the past that it is very old -- and therefore Pre-Devensian.  Now I am not so sure.