Definition: all material between fresh bedrock and the ground surface, including weathered bedrock, deposits and soil.

Although bedrock reaches the surface along much of the coast, in most parts of Orkney it is covered by variable depths of regolith. Apart from covers of till and dune sand, the regolith is composed largely of weathered bedrock. Evidence of intense frost-shattering and associated cryoturbation is found at a number of sites. The condition of prehistoric stone monuments indicates that frost-shattering is of limited effectiveness today and the frost weathering may relate to the cold conditions which prevailed during the Lateglacial. Chemical weathering associated with soil development has also generated a metre or more of regolith, particularly on calciferous sandstones and flagstones which are susceptible to decalcification. Deep chemical weathering is not widespread, a reflection of the effectiveness of glacial erosion on the islands.

Hill of Cruaday. Unweathered flagstones covered by frost-shattered bedrock. Spade for scale.

Rip-block till resting on flags and covered by a thin layer of head and soil. The head is a periglacial deposit reworked by frost-shattering and cryoturbation form the underlying till. Birsay.

Key sites

  • The landscape of Orkney before the Ice Age can be reconstructed from the fragments of ancient landforms that have escaped erosion by the great ice sheets.

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  • Around 15 thousand years ago, the last ice sheet disappeared to leave a barren, scoured terrain. As temperatures rose rapidly, pioneer plants arrived from the south and the low ground was soon carpeted with a rich herbaceous cover.

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  • Active periglacial features are confined to the hill tops of Hoy and reflect a prevailing environment of high wind speeds, heavy but now short-lived snowfalls, high ground moisture levels, and frequent freeze thaw cycles in winter.

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  • Orkney is a sandstone lowland moulded by the passage of ice sheets. Glacial erosion has smoothed and rounded hills and ridges on land and excavated the major firths of Hoy Sound, Eynhallow Sound and Westray Firth and to establish the archipelago. Local glaciers developed at intervals on Hoy to carve striking corries and valleys. ...

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  • Orkney has a stunning array of coastal scenery which is amongst the most impressive in the British Isles. The wonderful variety reflects the interaction of rock type, glaciation and sea level change in one of the highest energy marine environments in the world.

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