Wind stripes, Ronas Hill

Lee slope sand sheet, with vegetation cover. In the foreground is a bare deflation surface

  Ronas Hill

Wind-related effects

With wind speeds well in excess of 100 mph recorded almost annually, it is no surprise that the exposed hill tops of Shetland display a range of small features from wind erosion and deposition.

Deflation surfaces have been described from Ronas Hill. Here loss of vegetation has led to exposure of gritty regolith and the removal of the finer material to form extensive deflation surfaces. The effectiveness of the wind-scour can be gauged from the calibre of the gravel lag. On Ronas the loss of vegetation may have been a relatively recent occurrence for 'islands' of vegetated regolith are found amid the deflated areas (Ball and Goodier, 1974), although the edges of the 'islands' appear to have been stable for the last 35 years.

Wind stripes are strips of vegetated and bare ground that lie perpendicular to the prevailing wind. On Ronas Hill, the vegetated stripes are 0.2-1.7 m wide and may be retreating downwind as the exposed face is eroded and vegetation colonises the leeward slope of the stripe.

On lee slopes, there has been an accumulation of blown sand to form vegetated mini-dunes or sand sheets. The sand deposits contain thin organic bands that appear to relate to periods of sand stability.