Irish Sea Glacier
The Irish Sea Glacier (glacier in the Irish Sea ) was a huge glacier during the last cold period , possibly even several times from its original region in what is now Scotland and Ireland across the Irish Sea, the Isle of Man , Anglesey and Pembrokeshire expanded. It reached its maximum extent possibly during the so-called Anglian Glaciation and was still extensive during the late Devensian Glaciation (last maximum of the glaciation).
It was the only clearly delimitable glacier in the Irish Sea and extended for about 700 km from its origin to the southern end. It is sometimes referred to as the “Ice Stream” because it was apparently not bounded by ice-free land areas, but by highland areas that were just as ice-covered. At its greatest extent, the glacier extended to the coasts of Somerset and Cornwall , along the south coast of Ireland and even as far as the Isles of Scilly .
The current was in the St George's Channel pressed by a relatively narrow channel because ice from the Irish Ice Sheet in the west and the Welsh Ice Sheet (Welsh Ice Cap) to the east flowed together there. In places the glacier was therefore possibly only 80 km wide.
Once the ice crossed this eye of the needle, it spread (at least during the Anglian Glaciation ) into a broad tongue, in the area that is now formed by the Celtic Sea and the entrance to the Bristol Channel . On the eastern flank of the glacier, banding, glacier deposits and "erratic trains" show that the ice side of the Welsh Ice Sheet at the Brecon Beacons has been pushed south, so that the ice in the Irish Sea flowed parallel to the coast of South Wales and reached the English coast at the Somerset Levels , between Exmoor and the Mendips . How far inland the glacier stretched is unknown, but there are scattered glacial deposits in the Bridgwater and Glastonbury area - possibly the glacier's easternmost limits. In the west the glacier reached to Cork Harbor (Ireland). The maximum width is assumed to be 320 km. However, "old" glacial deposits in South Wales and Pembrokeshire are still not precisely dated.
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There is also a scientific discussion about the glaciation of the Isles of Scilly. The ice of the Irish Sea Glacier has been shown to press against the north coast of the islands, and more and more evidence suggests that this occurred over a period of approximately 24,000 years ago. During the same period of glaciation, the ice sheet extended along the Irish coast west to Cork and with the southern tip to about 100 km southwest of the Isles of Scilly. Research suggests that the ice ran aground everywhere and only touched water in a few places. This also corresponds to the view that the sea level was around 120 m lower then than it is today. Only in the extreme southwest could the ice have been lying on the water and the glaciers could have calved . According to one theory, the glacier penetrated so far south because the glacier tongue was partly driven by the high pressure of pore water in the easily deformable sea sediments at the bottom. According to this, parts of South Wales, the Bristol Channel and the coasts of South West England would have remained ice-free.
However, glaciers move according to the rules of physics and a long, narrow glacier tongue with a smooth elongated profile is difficult to explain in this way. Tightly constrained "valley glaciers" (trough glaciers) do not exist in tundra landscapes, as they must have prevailed in the area in question at the time. In addition, the glacier bed even rises to the south. Under these conditions, glacier ice would normally build up and "overflow" to the sides. It can be assumed that the glacier was about 2,000 m high at its southern tip and about 2,250 m in the St. George's Channel, above the Isle of Anglesey and about 2,500 m above the Isle of Man . Accordingly, the mountains of Wales and Eastern Ireland must have been buried under a thick sheet of ice and the Bristol Channel would have been filled with ice during the last major glaciation.
Research from 2007 also suggests that the area beyond the South Ireland End Moraine was covered by an Irish Ice Sheet during and after the last major glaciation, as was parts of the area beyond the South Wales End Moraine .
Another mystery is the extent to which the longitudinal profile of the Irish Sea Glacier, during its greatest extent, corresponded to the equilibrium profile . Observations of similar situations on Marie-Byrd-Land , West Antarctica , suggest that the ice cover over the mountains could have been about 800 m less than predicted.
Individual evidence
- ^ CA Lewis, AE Richards: The Glaciations of Wales and adjacent areas. Logaston Press 2005: 228ff.
- ^ RK Smedley & al: New age constraints for the limit of the British – Irish Ice Sheet on the Isles of Scilly. In: Journal of Quaternary Science 2017, 32 (1): 48-62.
- ↑ "Praise surge partially propagated by high porewater pressures within deformable marine substrates." JD Scourse; MFA Furze: Chapter Glacial marine geology of the Celtic Shelf and Goban Spur. & Porcupine continental margin. In: Isles of Scilly Field Guide. QRA 2006: 23-27.
- ↑ C. O'Cofaigh; DJA Evans: Radiocarbon Constraints on the age of the maximum advance of the British-Irish Ice Sheet in the Celtic Sea. In: Quaternary Science Reviews. vol. 26, 2007: 1197-1203.
- ^ DE Sugden: Selective glacial erosion and weathering zones in the coastal mountains of Marie Byrd Land, Antarctica. In: Geomorphology. vol. 67, 2004: 317-334.
literature
- CA Lewis, AE Richards: The Glaciations of Wales and adjacent areas. Logaston Press 2005: 228ff.
- KN Jansson, NF Glasser: Paleaeoglaciological events in the Brecon Beacons area. In: Quaternary of the Brecon Beacons Field Guide, QRA 2007, 23-35.