UIS Commission on Karst Hydrogeology and Speleogenesis
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Karstbase Bibliography Database

Devlin, R.
The situation and dynamics of the north yorkshire windypits: a geophysical and geomorphological investigation, msc thesis [engineering geology]

ub-surface slip-rift fissures and shafts, known locally as 'windypits', are numerous in the Upper Jurassic strata of the Hambleton Hills and Ryedale district of North Yorkshire. Windypits are predominantly open gull-formations, formed as a result of cambering between competent Corallian Group sandstone and limestone beds above weak clay beds of the Oxford Clay Formation. They relate to the natural pattern of steeply-dipping, widened joint-plane discontinuities, with individual blocks of caprock moving relative to one another along these surfaces. The most extensive fissure systems are up to 40m deep and over 300m long, and typically run sub-parallel to slope contours and linear topographic features, rupturing the surface above the line of maximum gradient. More complex and unpredictable structures occur where there is more than one direction of movement, resulting in a radial fissure network. Windypits have been associated with other forms of scarp recession and landslide activity, most notably the formation of unstable block detachments along vertical cliff-exposures. Aerial photographic interpretation and terrain analysis based on field observations and mapping have been used here in a detailed geomorphological investigation of windypit structures and their related landforms. They appear to play a significant role within a far more complex model of superficial slope evolution, with important consequences for rock-slope stability. The potential hazards from landslides and natural cavities are also assessed in the light of engineering geological evaluation. Shallow geophysical surveying techniques have been used to profile the electrical contrasts between void space and host rock, at a number of selected sites. It has been found that non-contacting electromagnetic conductivity methods are unsuitable for producing a discrete windypit anomaly, due to their limited depth of penetration. Tomographic resistivity techniques appear to be the most promising for accurately locating sub-surface fissures, and helping to map their true depth and full extent Comprehensive ground investigation would allow better interpretation of the geophysical data collected.

North Yorkshire, geomorphology, karst