wind

periglaciation

Streetmap extract

 

 

Roga Field

Turf-banked solifluction lobes

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Ronas Hill. Glacially-disturbed blockfields, frost-shattered granite, deflation surfaces and wind crescents

Ronas Hill

Significance: a 450m high hilltop that shows a range of features developed in response to contemporary and past wind and frost action

At least three generations of periglacial feature may exist on the Ronas plateau:

  • 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, except in high summer, and frequent freeze thaw cycles. The relict forms reflect, at least in part, more severe periglacial conditions when permafrost may have been widespread. The former presence of permafrost allowed heave processes to operate to the base of the former active layer, thereby allowing much bigger blocks to move than is currently possible. Significantly perhaps, there are few signs of the development of large stone-banked solifluction lobes or patterned ground on Ronas Hill, suggesting that the duration or severity of periglacial conditions may be less than in the high Cairngorms.