Main image on top: Forse Bay (Credit: MARK HICKEN / Alamy Stock Photo / PDGX7X)

Significance: a rock shelf fringing the coastline between the low and high water marks

Shore platforms are an important element of the Caithness coastline. Platforms are developed along many kilometres of low-lying coast but often missing from coastlines with high cliffs.

Shore platform development continues on the exposed coasts of Caithness. Large scars from recent block removal are widespread. After storms, the platform surface may carry impact marks where blocks have been moved across its surface. The rear of the platform is also scoured whenever beach debris is dragged across it.

Shore platform in Forse

Boulder-covered shore platform near Forse. The shore platform is emerging from beneath a tick cover of shelly till. Erosion of the till is supplying blocks to the platform surface which probably then migrate seawards. The central block stream may relate to the location of the main rip current in the bay during storms. Platform development is facilitated by the gentle dip of the flagstone.

Shore platform at St Marys

On sheltered coasts, the shore platforms may include substantial elements inherited from previous phases of marine erosion. At Gills Bay, shown below, the wide shore platform disappears beneath the eroding cliffs formed in shelly till. The ramp at the rear of the platform carries crossing striae – it predates the last glaciation.

Gills Bay shore platform

A detailed study has been made of shore platform development and cliff recession at Dounreay in relation to the hazard posed by a shaft sunk within 12 m of the cliff face and which contains radioactive waste (Hutchinson et al., 2001). The flagstones are tilted to seaward and have cross-cutting joint systems. Wave erosion of these structures has produced a saw-toothed edge to the shore platform and a series of small cuestas running across it. The erosion of the shore platform involves a range of processes:

  1. slot formation from the weathering of the less competent flagstone beds, followed by collapse of overlying blocks along joints
  2. development of cavities in mudstone units from chemical and biological weathering
  3. sheeting and flaking of mudstone surfaces
  4. abrasion of the rear of the platform by debris moved by storm waves

Similar processes operate on exposed shore platforms on Orkney. Rates of down-wearing at Dounreay are estimated at 3-4 mm/a but this ignores the occasional loss of large blocks in storms (seen at Keiss).

Shore platform in Keiss

Share This Story, Choose Your Platform!