Skateraw - detail of the base of the Main Postglacial Raised Beach, with a dyke of till injected into an open joint of the raised shore platform

Shoreline sequences between Dunbar and Belhaven, after Sissons (1967).

ITRP Inter-tidal rock platform

MPRB Main Postglacial Raised Beach, itself resting on a raised shore platform

RRP Raised rock platform, with crag and tail

 

shore platforms

raised rock platforms

inherited coastal landforms Orkney

Belhaven

Chapel Point

 

 

Complex rock shore line east of North Berwick.

The inter-tidal rock platform is being extended slowly by undercutting of the margins of a slightly higher level developed on more resistant rocks. This higher platform level passes beneath the main postglacial raised beach. The backing cliffs are partly vegetated and covered with slope deposits and fronted by the raised beach. The image is taken from a basanite dyke that stands proud of both platforms.

Ancient coastal landforms

Definition: shore platforms and cliffs that predate the last ice sheet

Raised rock platforms at Dunbar

In a number of locations along the rock coasts of south-east Scotland there are signs of inheritance of fragments of shore platforms and cliffs from before passage of the last sheet. Typical evidence includes

  • Till cover on the rear of the platform or in fissures in the cliff face
  • Striae or ice moulding of the platform
  • Development of shore platforms several hundred metres wide in sheltered locations
  • Lags of glacial boulders resting on the shore platform. The immobility of the boulders indicates very limited wave action on the platform

The survival of old shore platform fragments raises interesting questions about the effectiveness of glacial erosion, the age of the platforms and rates of shore platform erosion at the present day.

A small number of localities have been described where glacial till either rests on the shore platform or in fissures beneath the shore platform surface (Hall, 1989). The till appears to rest on the rear of platform fragment and on the break of slope between the inter-tidal rock platform and a low raised rock platform. The latter localities imply that two old shore platforms exist at elevations close to sea level around Dunbar.

The best known example of an ice-moulded raised shore platform lies east of Dunbar (Sissons, 1967). A short distance west of the town centre a raised rock platform cuts clean across a volcanic neck and rises gently inland to a rocky knoll that was clearly an island in an ancient sea. A tail of till stretches eastwards from this ancient island. The sequence of events thus seems to be

  • formation of the shore platform and island at sea level
  • uplift of the platform
  • glaciation of the platform and formation of a crag and tail

If the shore platform is old then clearly also the cliff may have a long history. The cliffs east of North Berwick are capped by till and fronted in places by a raised beach that protects the cliff base from erosion. Here the inter-tidal shore platform is being fashioned by lowering of the weak rocks that form a higher platform just above mean sea level.