cliffs and structure

Key sites

lang ayre

south head

The Sneck o da Smallie, base and top.

Image courtesy of Andy Gear

Cliffs: mass movement

Definition: subaerial processes of fall, slide, flow and creep that transfer debris to the foot of a slope

Rock fall and collapse, Villians of Ure. Slope instability relates to the presence of a weak band of clay and broken rocks that rests on the surface of the thick, lower lava flow and renders the upper, thin lava flows unstable.

On the variably fractured, hard rocks of the outer coast of Shetland, the dominant processes of mass movement are fall and slides. Minor rock falls occur frequently, as shown by the scars left by the fallen blocks that contrast with the black staining of more stable surfaces. Larger slides are rarer but it is surprisingly common to find signs of incipient major rock slope failures on cliff tops. The pulling apart of the rock slopes as it tilts or slips seawards is marked by gulls - deep and narrow gullies above the cliff head. Perhaps the best example is at The Smallie on Foula. Here The Sneck is a 60m deep and 1m wide cleft which extends for 50m caused by the failure of a large mass of sandstone (May and Hansom, 2003).

Stonga Banks. Gulls or linear fissures created by tension as the cliff face slips seawards