The Blatten Glacier Disaster

Before.........

.... and after

There is a fascinating piece of reportage (with spectacular animation) on the BBC web site, relating to the recent disaster in the Swiss Alps.

https://www.bbc.co.uk/news/resources/idt-c7f929de-96a9-45e5-b1bb-31de82fce72d

Thank goodness there was no loss of life, since the idyllic village had already been evacuated, prior to the catastrophiv event.  I thought, before I looked into this, that the "glacier collapse" took place in the upper part of a regenerated glacier, like that of Supphellebreen at Fjaerland in Norway -- but no, this was a very small and very dynamic independent glacier (Birch Glacier) in a high mountain environment.  High rates of snow accumulation, steep slopes, and rapid ice flow under the influence of gravity, on slopes dominated by frost shattering and rockfalls. Permafrost melting and rainfall in the Alps (as distinct from snowfall) were contributary factors in causing additional debris mobility.   

The old photos show a substantial fan of debris close to the village, with no clear terminal or other moraines.

There is no doubt at all that collapses like this will now occur with increasing regularity in all of the high mountain environments where there are thousands of vulnerable glaciers of this type.......

(For very good enlargements of the images, just click on them.)

The other evening.......

 Thanks to Lynne for this photo taken at the beginning of my talk the other evening at Canolfan Bethlehem, Newport.  There was an excellent response from the audience, which included many who have also heard MPP reporting on his "discoveries" during and after his September digs in North Pembs.

Just in -- the following comment:  ".........really enjoyed your talk last week. It was so engaging that I don't think anyone minded the hard pews! We thought the talk was a nicely balanced assessment of the pros and cons of all 'the available theories' about how the Bluestones were transported. You have, as one of my bosses used to say, 'relentless pounding logic' on your side. Very well done.

An Irish erratic near Cardigan?

 

I found this small erratic of Carboniferous Limestone in the Irish Sea till at Gwbert, near Cardigan, today.  It has two beautiful brachiopod fossils in it, and as befits a far-travelled stone its surface is covered in striations.  

Where has it come from?  The best bet is thst it has come from somewhere in central Ireland, and limestones rich in braciopods seem to be especially common in the Burren area on the west coast.  Here is an example:

However, from what we know of past iceflow directions, a source somewhere near Dublin seems more likely:

Geological map opf Ireland -- the light blue tint shows the area of Carboniferous Limestone outcrops.

If the erratic really did come from Ireland, there must have been much more mixing of ice streams and erratic material in the Cardigan Bay -- St Georges Channel area than has been previously recognized............

We also have to consider Anglesey and the  North Wales coast as source areas, although the outcrops there are of very limited extent.  This is from the GeoMon Global Geopark web site:

.............highly fossiliferous limestones outcrop all long the east coast southwards from Lligwy to Penmon [and along the coast of North Wales from the Great Orme to Prestatyn]. These rocks were laid down in cycles as the sea transgressed and retreated as many as 11 times over North Wales. On Anglesey, only four of these cycles, which consist of limestone followed by sandy beds and then mudstone were deposited. The rocks are rich in brachiopods and corals and often exhibit palaeokarstic surfaces and rarer sandstone pipes.

An Anglesey origin for the erratic is, on balance, most likely since this accords most closely with the ice flow pattern shown on the map above.

An interesting dilemma.........

Gwbert raised beach platform

 

Down on the Teifi Estuary this morning checking out the situation on the east side of the river mouth. There used to be amazing exposures of Irish Sea till here (back in the 1960's) but they were destroyed with the building of new coastal defences and a new caravan park.  

The Irish Sea till is still there, in patches, resting on the old raised beach platforms which are still visible.  These are the counterparts of the raised beach platforms exposed at Poppit, on the other side of the river mouth.  There are occasional exposures of till, fluvio-glacial materials and slope breccia, but because there has been so much slumping it's almost impossible to see stratigraphic relationships. 

The higher parts of the raised beach platform seem to be well above the influence of current HWM coastal processes, so  I interpret the smoothing and rounding of bedrock undulations to glacial erosion prior to the deposition of the till.

The glaciated summit of Carn Llidi

 

 

Thanks to Hugh Thomas for posting this great pic, taken on the summit of Carn Llidi nearSt Davids.  Ice-smoothed summit mounds.  In the distance is Ramsey Island, also with glaciated summits -- the source of a great range of glacial erratics found in mid and south Pembrokeshire.

The latest on the bluestones..........

 

Tonight, 7 pm, at Canolfan Bethlehem, Newport.....

Erratic dispersal modelling -- the Irish Sea Ice Stream

Modelling erratic dispersal accounting for shifting ice flow geometries: A new method and explanations of erratic dispersal of the British–Irish Ice Sheet
R. L. Veness, C. D. Clark, J. C. Ely, J. L. Knight, A. Igneczi, S. L. BradleyVersion of Record online: 15 May 2025

https://doi.org/10.1002/jqs.3720

https://onlinelibrary.wiley.com/doi/epdf/10.1002/jqs.3720

ABSTRACT: Glacial erratics are geologically distinctive rocks transported away from their source area by ice sheets and deposited in lithologically different bedrock areas. They have attracted much scientific curiosity with >24 000 observations across the British Isles. A common misinterpretation is that they took a nearly direct line of transport from source to resting position, neglecting to change ice flow directions during ice sheet growth and decay. To rectify this, we sequentially modelled erratic time‐space trajectories at 1000‐year timesteps using ice flowlines in an empirically constrained ice sheet model simulation to predict erratic deposition areas. We addressed the processes of entrainment and deposition by combining all potential trajectories into a single footprint of possible locations. Erratic dispersal is predicted for three geologically distinctive lithologies; Shap Granite of Northern England, Galway Granite of Ireland and the Glen Fyne igneous complex from Scotland. The footprint of predicted trajectories compared against 1883 observations of erratic locations was found to successfully explain 77% of the observed erratics. Most erratics were explained by flow directions during ice retreat; however, some required earlier ice divide shifts to produce potentially long‐duration, multiphase pathways. Our analysis demonstrates the possibility of explaining many erratics without explicitly modelling the complex processes of entrainment and deposition.

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This is an interesting paper in which the authors test a modelling exercise agtainst "ground truthing" for the distribution of erratics from three different bedrock sources -- one in Ireland, one in northern England, and one in western Scotland.   Figure 4 (at the head of this post) shows the latest version of the streamlines of the Irish Sea Ice Stream as far south as the Bristol Channel, predicting where distinctive erratics from the Loch Fyne igneous complex might be found.

See this post:

https://brian-mountainman.blogspot.com/2024/08/possible-altar-stone-sources.html

and this:

https://brian-mountainman.blogspot.com/2024/08/in-praise-of-ailsa-craig.html

This new work has a bearing on the Altar Stone debate -- including the possibility that it might have come from one of the ORS sandstone outcrops in the Midland Valley of Scotland or the Southern Uplands.   We already know a lot about the distribution of Ailsa Craig erratics -- this new work suggests that other erratics from much further north -- around Loch Fyne -- might also have found their way into the Bristol Channel and onto the coasts of SW England.

I must admit to being very intrigued by the postulated streamlines for South Pembrokeshire and the Bristol Channel and by the positions of the arrow tips.  There is no ground truthing to show that there ever was a significant ice edge position where it is shown on Figure 4.  And of course it is wildly improbable that erratic-carrying ice ever did swing round in Carmarthen Bay and move north-westwards onto the coast of SE Pembrokeshire -- ie directlly opposite to the direction of ice flow across the rest of the county.   The model that created the map clearly needs some tweaking........