Landslide at Oxwich Bay, Gower Peninsula

Oxwich Bay locationOn the weekend of 19–20 December 2009, a rockfall occurred in Oxwich Bay on the Gower Peninsula, South Wales. The rockfall occurred after a prolonged period of freezing temperatures and high rainfall in the preceding months.

The Oxwich Bay landslide lies on the northern slope of Oxwich Point in Oxwich Bay on the southern coast of the Gower Peninsula, 12 miles to the west of Swansea. The northern slope of the headland is covered in ancient broadleaf woodland.

The landslide was first reported by the South Wales Evening Post on 22 December 2009: Bay landslide left giant boulders along coastline.

The BGS Landslide Response Team undertook a brief survey of the landslide on 1 January 2010 to investigate the failure. Information was collected for the BGS National Landslide Database and geological maps. This landslide is National Landslide Database ID 17649/1.

 

Close up view of the Oxwich Bay landslide.

Geology

The Oxwich Bay landslide lies within the Swansea 1:50 000 geological map sheet (247). The area is underlain by the Oxwich Head Limestone Formation, which consists of thickly bedded, fine to coarse-grained, recrystallized, grey mottled, skeletal packstones (Howells, 2007). At the site of the rockfall the beds dip at approximately 20 degrees towards the north east. Oxwich Point forms the southern limb of the Oxwich syncline. The Oxwich Head Limestone was extensively quarried along Oxwich Point and exported from the old port of Oxwich to Devon (where it was burnt and used as agricultural lime) up until the end of the 19th century. Many of the cottages in the village used to house the quarry men.

 

Map of the bedrock geology in the area of the Oxwich Bay landslide.

 

Landslide

The Oxwich Bay landslide occurred within a disused quarry when blocks of limestone dislodged from the old working face at the back of the quarry. Failure of the blocks has occurred along fractures within the limestone. It is most likely that water has penetrated into the fractures which during periods of cold weather has frozen and expanded (by approximately 9 per cent, Norikazu, 1990), increasing the pressure in the fracture and causing the rock to fail. This process is known as freeze-thaw weathering.

Evidence of previous rockfall activity is present in the form of weathered boulders of limestone (known locally as ' The Dices' ) on the foreshore in the immediate vicinity of the December 2009 landslide.

 

The Oxwich Bay landslide. Note geologist for scale with '

The Dices'

 in the foreground.

 

Close up view of Oxwich Bay landslide with '

The Dices'

 in the foreground.

 

Wide angle view of the Oxwich Bay landslide showing its position within a disused limestone quarry.

 

Contact the Landslide Response Team

British Geological Survey
Keyworth
Nottingham
NG12 5GG
E-mail: Landslides team
Telephone: 0115 936 3143
Fax: 0115 936 3276