Orkney is a dissected landmass drowned by postglacial sea level rise. A drop in sea level of just 35 m would unite the archipelago into a single island. The individual islands may represent hills that formed the watershed areas of preglacial drainage basins but it is linear glacial erosion which has separated one island from another and severed Orkney from the rest of Scotland.

It is difficult to reconstruct a preglacial drainage pattern on Orkney but the division of the islands into hill masses may have begun when rivers flowing to the Atlantic and North Sea excavated valleys between them. Godard (1956) reconstructs an ancient drainage system with rivers draining SE via Westray Firth and Scapa Flow

Smaller islands may have been isolated from their neighbours by marine erosion but the limited duration of current sea level requires that such erosion belongs to the last interglacial or earlier.

Sea bed topography off Orkney. Land contours ignored.

  • The outer coast of Orkney is an outstanding location to study the erosion of hard rock coasts. Evidence of major erosion is not hard to find. The great bowl of Enegars corrie is losing its edge to the sea. The egg-shaped headland of Marwick Head is a dome half lost.

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  • Amongst the many beauties of Orkney are the beaches which fringe the bays and ayres of the inner coast. These are dynamic forms, changing shape with the seasons and gradually retreating landward as sea level rises.

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  • World coasts have seen sea-level variation of approximately 100 metres within the past 11,500 years through melting of the ice caps. When the ice caps melt the sea level rises globally (eustatically). The relative sea-level at any location is measured proportionate to the nearby land, which is itself subject to tectonic movement both up and down.

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