Fault scarps and fissures occur on moorland plateaux and in the vicinity of deep-seated landslides in the South Wales Coalfield, UK. These scarps may reach about 4 m in height and 3-4 km in length. The ages of the fault scarps and fissures are difficult to determine. Their relatively fresh and unweathered appearance would seem to suggest they were generated during subsidence as a result of coal mining which has taken place for some 150 years. However, their large magnitude, which make them dramatic features of the landscape, sets them apart from the much lesser features generated during coal mining subsidence in other UK coalfields. Some fault scarps seem to pre-date Ordnance Survey and British Geological Survey maps from the late 1800s-early 1900s. As total extraction (longwall) methods associated with fault reactivation had yet to develop widely at that time it is probable that mining subsidence alone could not have generated such distinct topographic features. The paper reviews the evidence of analogous non-mining fault steps and fissuring, mine abandonment plans and recent fissure treatment works to cast new light on the origin and development of these features. A conceptual model to demonstrate the causative mechanisms and evolution of fissures is also presented. The paper concludes that some fault steps and fissures developed in response to stress relief caused by deglaciation and periglacial activity and have subsequently undergone a later phase of development as a consequence of differential mining subsidence
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