Abstract

Fault scarps and graben features indicative of slope deformation have been observed adjacent to the rear scarps of landslides and on moorland plateaux in the Pennines. The scarps are distinct, up to 2 m high and can be traced for a maximum distance of approximately 400 m. These severely reduce the strength of the rock mass, enable groundwater to be channelled onto the upper valley slopes and may have played an important role in the initiation of first-time slope failures, and in the reactivation of older landslides. These features are similar to those recently described on the interfluves of the South Wales Coalfield valleys, and are consistent with those described as ‘block movements’ elsewhere in the world. Those in South Wales have been interpreted, by some previous investigators, as being generated during mining subsidence. However, in the Pennines, the slope and plateaux movements occur in the Namurian (Upper Carboniferous) sedimentary sequences where there has been no mining and it is therefore evident that other mechanisms are involved. In both South Wales and the Pennines steep-sided valleys have incised the moorland plateaux which in both cases are capped by strong, well-jointed cap rocks. These have exposed the underlying, much weaker, fissile mudstones which form the middle and lower slopes. These block movements in the Pennines are documented, discussed and compared with those in South Wales.

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