Inherited coastal landforms

There is widespread evidence around Orkney of the emergence of erosional landforms at the coast from beneath a cover of till. Whilst long stretches of the Atlantic coasts are undergoing active erosion, more sheltered shores give examples of platforms, geos and even cliff lines that are currently being re-occupied by the sea. Raised beaches resting on raised rock platforms occur on Hoy but there are no known coastal features on Orkney above 10 m OD. Prominent abandoned cliff lines are evident from the bathymetry at around -10 and -50 m. Similar inherited landforms occur widely around the Scottish coast.

Sea level has fluctuated widely through the glacial and interglacial cycles of the Pleistocene. Rock platforms below, at and above current sea level reflect periods when sea level has become stabilised for an extended time at that level, allowing erosion to cut a prominent notch in the shoreline. For features close to present sea level, perhaps the most likely period of erosion was during the last interglacial around 125 thousand years ago.

  • 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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  • 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.

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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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