erosion surfaces

basins 

tors

valleys

deep weathering

preglacial drainage

Sron na h-Iolaire, a half dome in the Slochd Mˇr. Glacial erosion has steepened the near face.

 

 

 

 

 

 

 

 

 

 

Distribution of granite domes on the Cairngorm Granite.

Domes

Definition: a spherical or egg-like hill, often with sheet jointing parallel to its curved surfaces

Domes are typical features of granite terrain. They reflect the 3-D structure of granite, specifically the effect of joint spacing and joint orientation. The dome is located in a zone of massive granite - the joints are widely-spaced. In contrast, the granite at the base of the dome usually can be seen to be closely jointed. The size and shape of the dome is controlled in part by the orientation and spacing of the vertical joints at its base. Square patterns give circular domes; oblong patterns give ovoid domes. The curved slopes of the dome reflect stress release from the massive granite at the core of the dome. Sheet joints develop during erosional unloading and control the detailed form of the dome.

The granite domes of the Cairngorms tend to be rather subdued features. This may reflect the fact that, prior to glaciation, the local rivers were not deeply incised into the mountain massif. Nonetheless, domes are a major feature of the terrain. On the north-eastern edge of Ben Avon, around Clach BhÓn, the domes are elongate and studded with tors. Each dome is separated from its neighbour by a linear alteration zone. On the northern slopes of Ben Macdui the domes are more spherical and the curved sheet joints can be clearly seen. Above Glen Avon, the roche moutonnÚe of Stac an Fharaidh shows a curved stoss side conforming to the sheet jointing and a cliffed lee slope, where blocks have been plucked away from the original curved slope of the spur as glacier ice has moved over the spur.

The map of the plateau around Cairn Lochan shows an elongate dome or whaleback ridge leading to the summit of this hill and a small spherical dome to the south. It seems clear that headward erosion of the corries has removed parts of these domes and this provides a new and useful measure of the extent of erosion by corrie growth.