Earth heat
Geothermal Gradient Explorer
A geothermal gradient describes how temperature changes with depth. Enter a surface temperature, gradient and depth to see what a simple linear model predicts, then compare that result with the limits of real geology.
Explore temperature with depth
There is no single geothermal gradient for Earth
Measured geothermal gradients vary substantially. A U.S. Geological Survey study of the conterminous United States reported many regional values between about 15 and 35 °C per kilometre, while higher and lower gradients occur elsewhere and even within the same region.
Gradient and heat flow are related but different
A temperature gradient describes how temperature changes with distance. Heat flow also depends on the thermal conductivity of the rock. Two regions can therefore have different gradients even when their heat flows are similar.
Groundwater and geology can bend the profile
Advection by groundwater, changes in lithology, sediment compaction, magmatic heat sources and hydrothermal circulation can all change the observed temperature-depth relationship. A straight-line extrapolation becomes increasingly uncertain as depth and geological complexity increase.
Sources and further reading
- U.S. Geological Survey: Geothermal gradients in the conterminous United States.
- Read the geothermal heat guide for the sources of Earth’s internal heat and how it reaches the surface.