Defintion: any area with a tundra climate, such as mountainous areas in mid-latitudes, or where frost processes are active or permafrost occurs in some form.
Two generations of periglacial feature exist on Orkney:
- features active today or earlier in the Holocene
- features formed under intensely cold conditions during the Loch Lomond Stadial and the early phases of deglaciation
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. The relict forms reflect, at least in part, more severe periglacial conditions when permafrost may have been widespread. The former presence of ground ice allowed heave processes to move much bigger blocks than is currently possible and enhanced frost weathering generated large volumes of scree and other angular rubble.
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.
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.
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. ...
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.
