Geothermal gradient

The rate at which temperature increases with depth beneath Earth’s surface, usually expressed in degrees per unit of depth. It varies with location, depth, and geological setting.

Earth's internal heat: Thermal energy within Earth, supplied by its formation and by ongoing radioactive decay. This internal energy drives heat toward the surface and establishes subsurface temperature profiles.
Geothermal energy: Energy obtained from heat stored within Earth. Subsurface gradients help identify regions where heat can support useful energy production.
Temperature: A physical quantity that measures the thermal state of matter. A gradient is calculated from changes in temperature between subsurface depths.
Shallow geothermal gradient: The temperature increase per unit depth measured in the near-surface ground. It can reflect seasonal effects and groundwater movement unlike deeper regional gradients.
Heat flow: The transfer of thermal energy through a material or across a surface per unit area and time. Heat flow and the thermal conductivity of rocks determine how steep the gradient becomes.
Geothermal exploration: The investigation of geological resources and conditions suitable for geothermal energy development. Exploration combines gradient measurements with geology to locate promising reservoirs.
Depth: The distance below a reference surface or level. The gradient uses depth as its independent variable and depends on the chosen reference.
Deep geothermal gradient: The temperature increase per unit depth inferred from measurements at substantial subsurface depths. It is less influenced by daily surface changes and may differ from shallow estimates.
Thermal conductivity: A material property describing how readily heat passes through it under a temperature difference. Low-conductivity layers can sustain steeper temperature gradients for a given heat flow.
Geothermal reservoir: A permeable volume of hot rock or fluid-bearing rock that can supply geothermal energy. Its temperature at depth reflects both the regional gradient and local fluid circulation.

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