Geology of the Holm Islands

This module aims to introduce students to the science of geology through an online, asynchronous learning approach, using the Holm Islands as a central case study.

The Holm Islands are located where the Severn Estuary meets the Bristol Channel, and present an intriguing sight when viewed from the adjacent Welsh and English coasts.

There are two islands, Flat Holm and Steep Holm, the national boundary running between the two. Both are small and contrast greatly in their form: Flat Holm is Welsh, and Steep Holm English.

The islands are composed of folded and faulted Early Carboniferous rocks and form a link between those of similar character and age in the Barry area in south Wales and the Weston-Super-Mare area in England.  On Flat Holm, one of the rock layers present is unique to that island.

Understanding the geology of the islands helps to make connections across southern Britain of the rocks of this age and their structures: close to the front of an extensive mountain-building episode known as the Variscan Orogeny c. 300 million years ago.

Studies of the geology of the sea bed surrounding the islands indicate that they are exhumed ‘inselbergs’, hills that were present in lake flats during the Triassic period, and that during the last glaciation they were dry land separated by a deep ravine through which the River Severn flowed.

The course introduces plate tectonics, geological history, stratigraphy, sedimentary petrology, structural geology and palaeontology.

Learning and teaching

Delivered as online, self-paced learning over 10 weeks, supported by a tutor.

The course is to develop over 10 weeks from the geographical and geological setting, through geological methods of study, then geological history, and finally focus on specific ages and key locations, chronologically.

1. Geographic and geological setting
2. Geological methods of study for this course
3. Geological history prior to the Carboniferous period
4. Early part of the Carboniferous period
5. Late part of the Carboniferous period and the Variscan Orogeny
6. Permian period – crustal stretching and rifting as the incipient North Atlantic Ocean basin begins to form
7. Triassic period – creation of and sedimentation on the ‘Avon Platform’ tectonic unit and its contrast to adjacent active rift basins. Creation of ‘buried landscape.’
8. Jurassic and Cretaceous times: continuing burial of the Holm Island rocks, metalliferous mineralisation on Steep Holm during the Jurassic.
9. Landform evolution between the Cretaceous and Quaternary periods: repeated uplift and erosion cycles removing much of the Jurassic and younger rocks.
10. The Quaternary period – glacial and interglacial climates, the setting during the most recent glaciation and exhumation of the hills that today form the islands; the incised course of the River Severn between the Holm Islands; the post-glacial rise of sea level creating the Bristol Channel, Severn Estuary, and islands and present coastline. 

Approx. 20 learning hours

Coursework and assessment

A question paper to be given out at the end of the course. It is designed to be completed easily, but to reflect the range of the subject matter, testing the student’s understanding of the pre-course handout and what was described to them in the field.

Reading suggestions

• Chidlaw. 2000. A Commentary of Geology and Scenery in the West of England by AE
• Trueman. Allegro Publishing*. (Available from author).
• Green. 1992. British Regional Geology: Bristol and Gloucester Region. HMSO.
• Howells. 2007. British Regional Geology Wales. HMSO.
• British Geological Survey maps:
• 1:50 000 scale Sheet ‘Inner Bristol Channel and Severn Estuary.’
• 1:250 000 scale Sheet 51N 04W Solid Geology ‘Bristol Channel.’

Library and computing facilities

As a student on this course you are entitled to join and use the University’s library and computing facilities. Find out more about using these facilities.

Accessibility

Our aim is access for all. We aim to provide a confidential advice and support service for any student with a long term medical condition, disability or specific learning difficulty. We are able to offer one-to-one advice about disability, pre-enrolment visits, liaison with tutors and co-ordinating lecturers, material in alternative formats, arrangements for accessible courses, assessment arrangements, loan equipment and dyslexia screening.