Vertical variation of heat flow density in the continental crust

Terrestrial heat flow density is a key parameter in understanding the past, present and future development of our planet. Most phenomena studied in deep crustal geophysics are temperature dependent and therefore reliable assesments of deep temperatures are necessary. Most heat flow measurements have been made in drill holes which are shallow (< 1 km) in comparison to the thicknesses of the crust and lithosphere. The recent findings in deep drilling projects (e.g. the Kola deep hole in Russia and the KTB hole in Germany) have yielded results which suggest that there is a distinct contrast between heat flow densities measured in the uppermost 1 km and values measured at deeper levels. The factors contributing to the vertical variation in the uppermost few kilometres are discussed with special emphasis on palaeoclimatic ground surface temperature changes and groundwater circulation in the bedrock.