Geothermal Gradient
The rate at which Earth's interior temperature increases with increasing depth below the surface.
Governing formula
q = -k (dT / dz) (Heat Flux = Conductivity × Gradient)
SI unit
°C/km or K/km
In depth
Near Earth's surface, the mean geothermal gradient is ~25–30 °C/km in continental crust. Heat flows outward from radioactive decay and primordial core heat via conduction and mantle convection.
Examples in the real world
Deep gold mines requiring active air cooling as rock temperature exceeds 50 °C at 3 km depth.