Under these conditions, heat is transported by convection rather than by conduction . Convection is a much more efficient way to transfer heat. The use of precision temperature measurements to detect water flowing into or out of fractures is the only geologic or geophysical method of identifying those fracture zones that are hydraulically conductive at depth. Daniels found that well yields increase with depth to a much greater depth than previously thought, and that well yields increase dramatically as well diameter increases. Intercrystalline porosity is absent in these rocks.
Porosity is entirely a result of brittle fracturing.
Groundwater flow in these rocks is localized along fractures. In the crystalline basement rocks beneath the Savannah River Site in South Carolina, major zones of fracture permeability have been detected by packer tests and confirmed by temperature logging. These holes were logged for temperature by Virginia Tech. Some of the data are displayed at this web site. Groundwater circulation is apparent in both holes over the depth interval 170-200 meters, as well as at shallower depths.