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Landslide survey : High Lossit, near Machrihanish Bay, Mull of Kintyre

Ellen, R.; Whitbread, K.. 2014 Landslide survey : High Lossit, near Machrihanish Bay, Mull of Kintyre. Nottingham, UK, British Geological Survey, 22pp. (IR/14/035) (Unpublished)

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Abstract/Summary

A walkover survey was carried out from the 20th to the 21st of February 2014 to inspect a landslide at High Lossit, Mull of Kintyre, Scotland [NR 62655, 19980]. The subsidence and ground deformation associated with the landslide affected an area of approximately 12 000 sq m of rough grazing land, bordering coastal cliffs, and causing minor damage to stone walls and fencing. The reported landslide occurred within the boundary of a larger, pre-existing landslide that probably occurred following deglaciation of the area during the Late Devensian. The original landslide had an estimated area of 40 000 sq m and likely occurred by rotational failure or sliding of deeply weathered basalt of the Clyde Plateau Volcanic Formation, forming a mass movement deposit comprising angular blocks of bedrock in a matrix of gravelly clay within an area bound by a 5 to 30 m high back-scarp. The recently reported landslide (with an area of approximately 12 000 sq m) is classified as a dominantly translational slide within the older landslide deposit, with rotation at the head of the landslide, developing into a translational slide in the main body and toe. The landslide is developed in a north to north-west facing slope, in gently north-east dipping basalt of the Clyde Plateau Volcanic Formation. The cause of the recent slope failure is likely due to a combination of driving forces including excessive water ingress after prolonged heavy rainfall, and existing slope instability due to the high slope angle and presence of large blocks of heavily weathered and altered basalt. The slope has a history of instability, reflected in the pre-existing scarp of the post-Late Devensian landslide and there is evidence for active soil movement prior to the recent slip recorded by offset of a stone wall at the foot of the recent slip. Large Post-Late Devensian landslips have been identified in numerous coastal locations around the Mull of Kintyre. The causes of these large landslips are poorly understood, but in the High Lossit area, intense weathering of basalts and local faulting in addition to over-steepening of the slope through glacial erosion may have been contributing factors to slope instability soon after deglaciation. Further assessment, including detailed geological mapping, would be required to properly understand the effect of the highly weathered and altered basalt on the ground stability and to develop the ground model. To assess for likelihood of future movement, a hydrogeological study of the site would also be required as the drainage of the affected field has been altered following the landslide.

Item Type: Publication - Report (UNSPECIFIED)
Funders/Sponsors: British Geological Survey
Additional Information. Not used in RCUK Gateway to Research.: This report made open to all by D. Campbell April 2015. This item has been internally reviewed but not externally peer-reviewed
Date made live: 27 Apr 2015 12:46 +0 (UTC)
URI: http://nora.nerc.ac.uk/id/eprint/510694

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