Perturbation of isotherms below topography: constraints from tunnel transects through the Alps, Gotthard road tunnel

For many years it has been known that near surface isotherms are influenced by the topography (Lees 1910). Recently, a number of studies were pursued to quantify the effect of topography on low temperature isotherms (e.g. Stüwe et al. 1994, Mancktelow & Grasemann 1997). The magnitude of perturbation depends on several parameters: exhumation rate, geothermal gradient, wavelength and amplitude of topography, and finally by the age of surface relief change (Braun 2002).