Geothermal Gradient

geothermal gradient [¦jē·ō¦thər·məl ′grād·ē·ənt]

(geophysics)

The change in temperature with depth of the earth.

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Geothermal Gradient 

the amount by which the temperature of rock rises per 100 meters’ increase in the depth of the deposits. The average gradient for crust depths that are accessible to direct temperature measurement is taken to be approximately 3° C. It varies from place to place as a function of the shape of the earth’s surface, thermal conductivity of the rock, subterranean water circulation, the proximity of volcanic foci, and the various chemical reactions taking place in the earth’s crust. The regular rise in temperature with increasing depth shows the existence of heat flow from the interior of the earth to its surface. The amount of this flow is equal to the product of the geothermal gradient and coefficient of thermal conductivity.