Source of the Eas Mhoir, Ben Avon in August 2003. The vein quartz shows that the stream head is located in an alteration zone in the granite.

Groundwater

Definition: water held in fractures and pores in rock, including that in the aeration zone above the water table and the saturated zone below.

Granite is a relatively impermeable rock. Fresh granite lacks significant pore spaces but all granites are criss-crossed by network of fractures that may hold water. These range from microfractures between and within mineral grains to faults and the ubiquitous joints.

The soils of the surface of the granite are free-draining and the plateau vegetation often has to withstand periods of sustained drought in settled spells at high summer. The existence of a considerable groundwater store is shown however by the steady flow from springs such as those at Wells of Dee and below the summit of Ben Avon, even after long periods without rain, such as the summer of 2003. The springs carry significant solute loads, indicating chemical weathering of regolith and bedrock (Soulsby et al. 1999).