Erosional processes in the hard rock coastal cliffs at Staithes, North Yorkshire.

The processes of change on near-vertical coastal cliffs have been quantified using terrestrial photogrammetry and laser scanning. The approach allows discrete rockfall geometry to be measured, and source located in three dimensions. This paper presents the analysis of an inventory of over 100 000 discrete rockfalls, recorded from the Liassic coast at Staithes, North Yorkshire (UK), where a rock face area of over 16 000 m2 has been monitored over a 20 month period. The data obtained on three-dimensional scar geometry and source position give an insight into rockfall characteristics from a range of rock types, cliff heights and geometries. Multiple failure mechanisms such as overhang collapse, constant spalling, fragmentation and large scale, coherent rockfalls have been observed and related to rock-type controlled processes on the rock face. The spatially referenced rockfall scar data are used to assess the influence of environmental controls on variable rock mass properties, such as rock type, structure and cliff geometry. Analysis of rockfall magnitude–frequency reveals notable similarities between coastal rockfalls and inventories from non-coastal environments. The resolution of the monitoring data allows quantification of rockfalls down to volumes of 1.25 × 10− 4 m3 to be consistently sampled and measured. This complete magnitude–frequency relationship suggests that rather than evolving exclusively through isolated, sporadic losses, coastal cliff geomorphology reflects interconnected processes in which each rockfall is part of a continuum of change to the rock face. Further detailed assessment of the rock face reveals the control of the pre-failure morphology on subsequent failure patterns, for example, the quantity of rock protrusion from the cliff is positively correlated with subsequent failure volume. The continuum of activity and the controls on failure identified within these data suggest that the episodic behaviour of coastal cliffs previously assumed may have been overstated by coarser resolution monitoring data. The findings improve our understanding of the evolution of coastal cliffs and highlight areas for further research into both cliff processes and the character of rock slope failures in general