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Landslide geomorphology at Cayton Bay, North Yorkshire
journal contributionposted on 2023-06-07, 16:49 authored by P R Fish, Roger Moore, J M Carey
This paper describes the geomorphology of a large coastal landslide complex at Cayton Bay, North Yorkshire. The area inland of the landslide is occupied by a strategically important road and a number of properties, and knowledge of current landslide behaviour and possible future scenarios is therefore important for future planning and risk. Instability at the site is associated with a series of faults, which bring argillaceous Upper Jurassic rocks to sea-level. These soft rocks are overlain by more resistant sandstones. The sequence is capped by a thick and variable series of glacial sediments that comprise tills with inter-bedded sand and gravel lenses, deposited during the Dimlington Stadial of the Late Devensian. In connection with the development of a future coastal strategy for Cayton Bay, detailed geomorphological field mapping was conducted, which identified two major landslide systems. These include a periodically active mudslide complex at Cayton Cliff, recognized by a series of shallow scarps and benches with occasional back-tilted blocks, and an area of dormant deep-seated landslides at Tenants Cliffs, which includes a series of graben and horst structures. The origins of the landslides are unclear, but probably involved a variety of processes that led to a reduction in material shear strength or increases in pore water pressures. The timing of original failure may relate to deglaciation following the Dimlington Stadial, or to periods of wet climate in the Holocene. Since sea-levels were not higher than present in the Holocene along this stretch of the coast, coastal erosion is not thought to have been a factor. The causes of the contemporary instability are likely to be due to the combined effects of coastal erosion and of groundwater, both of which are predicted to increase in future years due to the impacts of climate change. The implications include increasing risks to coastal assets and a need to manage and mitigate such risks. The limits of Cayton Bay are defined by the headlands of Knipe Point (also known as Osgodby Point) to the north, and Yons Nab to the south (Figure 1). The geology of the bay comprises Jurassic age rocks overlain by Quaternary glacial sediments. A series of faults running through the bay have resulted in a range of lithologies being exposed at the shoreline, and this has had a significant influence on the evolution of the bay and development of the coastal cliffs. The coastal cliffs of the northern part of the bay are characterised by a large undercliff between 100m and 400m from crest to toe, which was formed by major coastal landsliding at sometime in the past. The undercliff covers an area of about 0.3km2 and comprises undulating topography that is mostly covered with woodland. The whole of Cayton Bay, including the area affected by landsliding, is a Site of Special Scientific Interest (SSSI), owing to the sites nationally important geology, rare plants and invertebrates. Monitoring of cliff instability within the bay has been conducted since 1999 as past of a regional coastal strategy study (Halcrow, 2001). The strategy study aims to support forward projections of cliff instability and recession, coastal erosion and the risk to people and assets. This paper considers the geological setting, Quaternary history, landslide geomorphology and potential landslide behaviour scenarios.
JournalJournal of the Yorkshire Geological Society
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- Geography Publications
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