Geothermal gradient

Geothermal depth level is the depth difference in which the crust is heated to a Kelvin, and thus represents the temperature thereof. Such heating occurs on average every 33 meters, so that often a gradient of 3 Kelvin per 100 meters is specified.

The geothermal depth level differs depending on by mountains. In ancient and peaceful areas of the earth's crust ( for example, in South Africa) it can be 90-125 meters, while in Europe on the Swabian Alb 11 meters, 45 meters and 50 meters in the Gotthard be achieved in the Lötschberg. These deviations are due inter alia to the locally varying mineralogy, geology, morphology, and particularly volcanic activity. Be Caused the larger temperature gradients in lower thermal conductivity of the rock and by lower effective thickness of the crust ( because it is either thin or because magma has penetrated ). The heat inside the earth comes to 50 to 70 percent from radioactive decay processes in the mantle and core of the earth and to 30 to 50 percent from the ascending residual heat from the time the Earth.

The geothermal depth level is relevant for example for geothermal energy, but also for any kind of deep drilling. In volcanically active areas, it is particularly small, however, it can come in the range of subduction zones at greater depths also to a reversal of the temperature gradient: where the temperature does not increase with depth, but decreases. This is due to that there comparatively cool surface rocks are pushed into the mantle.

The geothermal depth level was first determined in 1867 in the hole blocking I/1867, which was sunk in the Sperenberger salt dome.