Key sites
Periglacial landscapes
Summit of Ronas Hill, a glacially-disturbed granite blockfield with extensive deflation surfaces
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.
Three generations of periglacial feature exist on the Shetland:
- 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
- features inherited from phases of periglacial activity prior to the last ice sheet
Permafrost conditions are absent from Shetland
today and the active forms 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. Both
the Sel Ayre and Fugla Ness SSSIs show good examples of periglacial slope
deposits that predate the last ice sheet.