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Sunday, 26 November 2017

BRITICE Glacial Map 2 -- a mixed blessing



I suppose we should welcome the publication of a big new paper, with multiple authors, describing the compilation of the latest version (No 2) of the BRITICE map of the British Isles.  The map is much more detailed than the first one, and that is to be welcomed, and the accompanying paper makes interesting reading.  The BRITICE project fieldwork is now wound up, but I dare say that there are many papers still to be published, from what has been a very large project involving large numbers of geomorphologists and other specialists.  They have done a vast amount of fieldwork, both on land and at sea..... or have they?

Here is a link to the paper:

http://onlinelibrary.wiley.com/doi/10.1111/bor.12273/full

Clark, C. D., Ely, J. C., Greenwood, S. L., Hughes, A. L. C., Meehan, R., Barr, I. D., Bateman, M. D., Bradwell, T., Doole, J., Evans, D. J. A., Jordan, C. J., Monteys, X., Pellicer, X. M. & Sheehy, M. 2017 : BRITICE Glacial Map, version 2: a map and GIS database of glacial landforms of the last British–Irish Ice Sheet. Boreas. https://doi.org/10.1111/bor.12273. ISSN 0300-9483.

Abstract



During the last glaciation, most of the British Isles and the surrounding continental shelf were covered by the British–Irish Ice Sheet (BIIS). An earlier compilation from the existing literature (BRITICE version 1) assembled the relevant glacial geomorphological evidence into a freely available GIS geodatabase and map (Clark et al. 2004: Boreas 33, 359). New high-resolution digital elevation models, of the land and seabed, have become available casting the glacial landform record of the British Isles in a new light and highlighting the shortcomings of the V.1 BRITICE compilation. Here we present a wholesale revision of the evidence, onshore and offshore, to produce BRITICE version 2, which now also includes Ireland. All published geomorphological evidence pertinent to the behaviour of the ice sheet is included, up to the census date of December 2015. The revised GIS database contains over 170 000 geospatially referenced and attributed elements – an eightfold increase in information from the previous version. The compiled data include: drumlins, ribbed moraine, crag-and-tails, mega-scale glacial lineations, glacially streamlined bedrock (grooves, roches moutonnĂ©es, whalebacks), glacial erratics, eskers, meltwater channels (subglacial, lateral, proglacial and tunnel valleys), moraines, trimlines, cirques, trough-mouth fans and evidence defining ice-dammed lakes. The increased volume of features necessitates different map/database products with varying levels of data generalization, namely: (i) an unfiltered GIS database containing all mapping; (ii) a filtered GIS database, resolving data conflicts and with edits to improve geo-locational accuracy (available as GIS data and PDF maps); and (iii) a cartographically generalized map to provide an overview of the distribution and types of features at the ice-sheet scale that can be printed at A0 paper size at a 1:1 250 000 scale. All GIS data, the maps (as PDFs) and a bibliography of all published sources are available for download from: https://www.sheffield.ac.uk/geography/staff/clark_chris/britice.

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So is the new map reliable, and is it of any use to the rest of the world as a teaching and research aid? Yes, and yes again. But I have major reservations about the fact that the map is available as a "zoom in" version, rather like the BGS geology map available on their viewing facility. Clearly much of the data has been input on a very small scale, so that when we zoom in to look at a part of the countryside at a scale of 1:50,000 or maybe 1:10,000 the result becomes nonsensical, with straight edges to lakes and moraines (for example) that bear no relationship to the details of local topography.

We can only judge things on the basis of what we know, and so I have taken a long hard look at what the map tells us about that area around Preseli and Carningli (my home area). Even given that the map shows "last glaciation features" and nothing older, what we see makes no sense at all.

Glacial Lake Teifi and the surrounding area, from the BRITICE Glacial Map 2

Hypothetical "Glacial Lake Nevern" and other features in the Preseli - Carningli area, 


from BRITICE Glacial Map 2

The outlines of Glacial Lake Teifi more or less coincide with what we see in assorted published papers, but the other information shown on the map is very scanty indeed for the Cardigan - Moylgrove area. That must disappoint many of the authors who have published their research findings, with considerable local detail on the record. When we zoom in on Preseli and the hypothetical area of "Lake Nevern" we find even more problems.  Why is "Lake Nevern"  shown at all?  So far as I am aware, nobody since Charlesworth in 1929 has taken it at all seriously, and many papers by a variety of authors have shown that the "evidence" for it does not withstand scrutiny.  The paper authors site "George 1970"as their source of information, but George was simply citing (very uncritically) Charlesworth, and provided no evidence for this so-called lake.  Careless.   As readers of this blog will know, there are a few places where thin laminated (lake?) sediments appear to be present on the northern flank of Preseli, but they are better explained by short-lived ponding of meltwaters in complex terrain in a dead-ice environment.  I have called this "Lake Brynberian" -- a possible small lake of limited duration and extent.   There are other fluvioglacial landforms and moraines in this area which are in the literature.  They should have been mapped, but have not been.  And where did that impounded lake at Pontfaen come from?  I am aware of no evidence in support of it.

https://brian-mountainman.blogspot.co.uk/2015/05/lake-brynberian-further-thoughts.html

The impression is gained that this map has been produced by researchers accessing satellite and bibliographic data and sitting in front of computer screens, unlike the BGS bedrock and sedimentary map for the UK which has been based largely upon the field notes of surveyors working in the field. Black mark for BRITICE, and glowing praise for the BGS.  In the abstract to the paper, the authors state:  "All published geomorphological evidence pertinent to the behaviour of the ice sheet is included, up to the census date of December 2015."  That is patently not true.  There are abundant references in the literature (just a few of them by me, and many others as well) that have clearly not been consulted.

Then we come to the map showing the wider Late Devensian context, reproduced above from Figure 11 in the article text.  The authors still insist that there was a long "surge" lobe pushing far out into the south-western approaches.  I don't know of any sea-floor or sedimentary evidence that supports it,  and I do not know what glaciological theories have been summoned up in its creation, but it sure doesn't look like any other glacier ever seen on Planet Earth.  It was probably dreamed up by some guys as a way of explaining the short-lived advance onto the northern coast of the Isles of Scilly, but there cannot possibly have been an ice edge more or less at sea-level in western Pembrokeshire and simultaneously more or less at sea-level in the Isles of Scilly, more than 200 km to the south, with ice flow as shown on the map.  The ice must have come from the NW, not the NE, and in an unconstrained situation such as that of the outer Bristol Channel, the eastern ice edge must have been far to the east of that shown on the map.  The map also ignores published evidence of Devensian ice affecting the area around the mouth of Milford Haven.  You can do some searches on this blog for more information.



Overall, this new paper, and the map, are useful contributions from the BRITICE team.  But rubbish in, rubbish out.  Now we need some serious fieldwork, on the ground, involving people who know what they are looking at.  Apparently these days they call it "ground truthing" ---- and it is apparent that we all need more of it.



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