Irish Sea Ice stream --flowline hypotheses

Above is my latest attempt to portray the likely flowlines of both the Irish Sea Ice Stream and the Welsh Ice cap during the LGM, around 26,000 years ago.  I'm now quite convinced that there was no ice-free enclave or corridor across central and south Pembrokeshire.

The main points from this map:

1.  I have adjusted the flowlines on the map for the areas adjacent to the junction line between Irish Sea ice and Welsh ice to avoid direct head-on collisions!  As Bethan Davies, a very experienced glaciologist, has pointed out, if there was active and powerful ice coming both from east and west, the ice streams must fave flowed in parallel along the junction itself.

2.  The ice edge shown on the eastern side of the Welsh Ice Cap may not be very accurate, and may not represent the local LGM since things were probably not synchronous on the west and east flanks.  Also, Patton et al (2013) suggested that topographic features show streaming ice flowing broadly from SW towards NE in several of the outlet glacier troughs in the Welsh Borders.  Were there dramatic switches of iceflow direction in different phases of the glacial cycle?

https://www.researchgate.net/publication/248381137_The_last_Welsh_Ice_Cap_Part_2_-_Dynamics_of_a_topographically_controlled_icecap#fullTextFileContent

3.  The junction shown to the west may be out by 10 - 15 km in places, especially on the Cardigan Bay coast.  I have shown it somewhere near New Quay, but Neil Glasser and colleagues have suggested it was further up the coast towards Aberaeron, and a number of researchers have recorded Irish Sea till at Llanon.    Eddie and Sybil Watson claimed that there is Irish Sea till at Morfa Bychan, almost as far north as Aberystwyth.  Glasser et al have also postulated that when the Irish Sea ice started to melt back, there was a distinct Teifi Glacier for which there are recognisable retreat stages or short-lived ice edge oscillations.  How powerful this glacier or ice stream was at the time of peak glaciation is still a matter for speculation, and there are records of Irish Sea glacial deposits almost as far upstream as Llandysul.

4.  The position of the junction line between the mouth of the Teifi and Carmarthen Bay is a matter of speculation.

5.  We assume that the eastern part of Carmarthen Bay was affected by Welsh ice fed southwards along the Taf and Tywi valleys.

6.  Was the contact zone off the tip of Gower, or did Irish Sea ice impinge upon the southern part of the peninsula?  There are "Irish Sea erratics" in some Gower deposits, but there is no agreement on when they were transported and dumped.  It may be somewhat too simple to just refer to them as "Anglian erratics", as Peter Kokelaar has done.

7.  The lobe of Welsh ice pushing out into Swansea Bay seems now to be quite widely accepted, especially since the discovery of crescentic lobes or ridges during sea-floor investigations.  these are widely interpreted as end moraines associated with the Tawe Glacier.

8.  The southern edge of the LGM Welsh Ice Cap, shown running across Glamorgan approx between Porthcawl and Cardiff seems to be quite widely accepted nowadays, as mentioned on other posts on this blog.

 

This (above) is one of my earlier attempts to define probable flowlines, shown together with the suggested LGM ice edge (black line) as shown in various BRITICE-CHRONO publications. I'm now convinced that the black line in West Wales has no significance whatsoever.   The Contact between the two ice masses, shown with the blue line, is probably not that accurate in Cardigan Bay and Pembrokeshire.  As mentioned above, the Irish Sea ice was powerful enough to push much further east, probably affecting the Ceredigion coast as far north as Llanon and maybe even to Morfa Bychan.

This BGS map (above) is very useful in that it defines the valley glaciers associated with the Welsh Ice Cap, which must have been quite well defined during the early and late phases of the Devensian glacial episode.  However, the LGM ice edge shown across North Pembrokeshire is highly speculative, and is not supported by field evidence.  If we ignore that yellow line, the iceflow directions do make considerable sense.

One of my earlier attempts, showing a prominent Teifi Glacier pushing out almost as far as the coast at Poppit and Gwbert.  Neil Glasser and colleagues have shown that it was probably not capable of doing that at the LGM, and indeed Irish Sea till does seem to penetrate well inland, suggesting that the ice from the NW was dominant.