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A small glacial cirque basin on Exmoor, Somerset Stephan Harrison

Lookup NU author(s): Dr Ed Anderson, Dr David Passmore


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Geomorphological and sedimentological investigations at the Punchbowl on Exmoor, north Somerset, have demonstrated evidence of cirque basin glaciation, some 30 km south of the accepted southern limit of Anglian ice cover in this area. The Punchbowl is a steep-sided, north-facing basin that has a subdued arcuate ridge at its mouth. Analysis of macrofabrics, clast form and roundness and particle size on sediments forming the ridge indicate it to consist of glacial diamict deposited as a terminal moraine. Further evidence supporting the presence of a former cirque basin glacier at this site is derived from basin morphology and a striated sandstone boulder. Palaeoglacier reconstruction gives a surface area of 0.38 km2, a maximum thickness of 46.5 m and a maximum basal shear stress value of 51 kPa. The ELA of the former glacier has been calculated at 334 m OD. There is no evidence for multiple glaciations at this site, and, in the absence of dating controls on the moraine, the glacier is provisionally assumed to have formed during severe climatic conditions associated with the southerly advance of ice sheets during the Anglian cold stage or during the Dimlington Stadial. Development of a glacier at this location appears to have been a rare event during the Quaternary, and may have been facilitated by accumulation of windblown snow from the adjacent plateau. © 1998 Geologists' Association.

Publication metadata

Author(s): Anderson E, Passmore D

Publication type: Article

Publication status: Published

Journal: Proceedings of the Geologists' Association

Year: 1998

Volume: 109

Issue: 2

Pages: 149-158

Print publication date: 01/01/1998

ISSN (print): 0016-7878

ISSN (electronic):