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Wednesday, 29 April 2015

When is a pingo not a pingo?

 A fabulous photo of De Geer Moraines (cross-valley moraines) on Baffin Island.  It is now being suggested that many of the "rampart remnants" found in Wales were formed as morainic features like these, and are not pingo remnants at all......  I am not 100% convinced, but the evidence is persuasive.

Arising out of some of the comments of recent days, I have been digging a bot more on the matter of pingos in Wales, and how common they might be........... and it appears that they are less common than we might think.

Dave mentioned that the "pingos" near Blaenporth look more like bits and pieces of eskers than the remnants of circular pingos -- good point!  The same is true of some of the Norfolk features as well -- cf the monochrome photo which I published.

In 2004, many years after the work of Edward and Sybil Watson was published, CCW announced the following project: 

Mapping and Conservation Assessment of Pingos in Wales
This was a joint CCW/University of Cardiff (Department of Earth Sciences) project undertaken as a Ph.D. study that mapped pingos (ground ice depressions) in Wales. Pingos are arguably better developed in Wales than anywhere else in the British Isles. However, prior to this study no comprehensive review of this geomorphological resource had ever been undertaken. Moreover, these are relatively small-scale and fragile landforms and, over the years, many pingos have been drained or destroyed. Many pingo basins contain significant flora and fauna, often with a thick peat deposit that contains an important pollen record which can be radiocarbon dated, thereby providing an important history of environmental change spanning some 10,000 years. Key objectives for the project were to locate all remaining pingos and similar landforms across Wales, to map and compare them, and to examine the structure of a selected few in greater detail. The study provided a framework for conserving key parts of this important geomorphological resource (either as SSSI or RIGS).

The work involved Dr Peter Brabham and a research student called Neil Ross.  There was a brief report in "Earth Heritage" No 23,  2004/5, and in 2006 Neil was awarded his doctorate for a thesis in which he examined in great detail the evidence for and against pingos in Wales.  The complete thesis can be accessed here:

Neil Ross PhD thesis 2006
A re-evaluation of the origins of Late Quaternary ramparted depressions in Wales
Neil Ross
School of Earth, Ocean and Planetary Sciences Cardiff University

(See also: Ballantyne and Harris 1994)

Here are some of the excellent illustrations from Neil's thesis.

 Map of "ramparted depressions" in Southern Britain.  Note the two main clusters -- in Wales and Norfolk.  Note that the author does NOT refer these features as "pingos"........

The distribution of so-called "pingo groups" in West wales, after Watson and Watson.

Some of the sinuous ramparts showing up on a satellite image.  This group is south of Blaenporth, in the Hirwaun Valley.

Another group of sinuous features near Ponthirwaun, in the Hirwaun Valley

Neil Ross's map of the "ramparted" features in the Hirwaun Valley.  While there are many irregularities, note that there is an approximate lineation from NE - SW.  That is perpendicular to the last direction of ice flow across this area.

Contour model showing the location of the Hirwaun Valley "ramparted features" and associated depressions.  Neil estimates that these features lie approximately at the highest level of pro-glacial Lake Teifi.  The blue contour shows the approx position of the shoreline.

I haven't had a chance to look through the whole thesis yet, but it looks to me like an impressive piece of work -- and the evidence is pretty convincing that these ridges and depressions are related to sub-glacial processes which operated near the maximum of the Late Devensian glaciation of the area.  The nature of the sediments in the depressions and in the ramparts do not suggest a periglacial origin at all  -- and Neil has done a lot of excavating and a lot of sedimentological analysis. 

Neil suggests that very few of the "pingos" recorded in Wales are actually pingos -- and grave doubt can be expressed about some of the Norfolk features as well.

So we have a nice old-fashioned controversy here.  More of which anon.

1 comment:

Dave Maynard said...

You beat me to it! I knew of the reference, but hadn't time to find it.

If we are looking for similar features, how about to the right of the road from Brian Llewelyn to Egwlyswrw?

In the field on the entrance to the Shire Horse place, there were some rampart like features bulldozed some years ago. Also closer in to Eglwyswrw are ridges with wet areas in between, which have recently had a drainage ditch across them. I've been meaning to have a quick look at those for a while looking for archaeology.