At the highest point in Shetland - 450 metres - discover fascinating features that are normally found on high mountains or within the Arctic Circle.
The granite of Ronas Hill formed about 360 million years ago as molten magma cooled beneath the ancient Caledonian Mountain chain. It is exposed at the surface today due to earth movements and the erosion of overlying rocks. It is a type of granite called granophyre made of the minerals potassium feldspar (which gives the deep red colour), white quartz and black biotite mica.
The climate on top of the hill is comparable with that of the Cairngorms which are three times as high! The summit is covered with ice-shattered boulders and grains picked from the bedrock by frost. Alternate freezing and thawing causes ‘solifluction’ terraces of shattered rock to work their way down the hillside. Vegetation at the front of the terraces is buried as gravel moves downslope but spreads forwards to colonise the bare surface of the terrace below. In places the wind blows fine grains of granite into miniature dunes creating sheltered areas colonised by plants.
Ronas is home to 15 species of Arctic-alpine plants, including Alpine Lady’s Mantle and Mountain Azalea. Glaciers scoured the plateau to the north, creating a ‘cnoc and lochan’ landscape of small rock mounds called roches moutonnnées and hollows containing small lakes.
