Geothermal depth

Info point for the Sper I / 1867 borehole in Sperenberg

The geothermal depth is the difference in depth at which the earth's crust warms up by one Kelvin , and is therefore the reciprocal of the corresponding temperature gradient :

${\displaystyle \mathrm {Tiefenstufe={\frac {1}{Temperaturgradient}}} }$

Such heating occurs on average every 33 meters, so that a gradient of 3 Kelvin per 100 meters is often given:

${\displaystyle \mathrm {{\frac {33m}{1K}}\approx {\frac {1}{\frac {3K}{100m}}}} }$

The geothermal depth varies depending on the crust structure and the tectonic situation. In old and quiet areas of the earth's crust (for example in South Africa ) it can be between 90 and 125 meters per K, while in Europe on the Swabian Alb it is 11 meters, in the Lötschberg 45 meters and in the Gotthard 50 meters per K. These deviations are u. a. due to the locally varying mineralogy , geology , morphology and especially volcanic activity . The smaller depth levels are caused, i. H. the larger temperature gradients, due to the lower thermal conductivity of the rock and due to the lower effective thickness of the earth's crust (because it is either thin or because magma has penetrated).

The heat in the Earth's interior comes to 50 to 70 percent from radioactive decay processes in the Earth's mantle and the Earth's core and 30 to 50 percent of the ascending residual heat from the time of formation of the earth .

The geothermal depth is z. B. relevant for geothermal energy , but also for any type of deep drilling . In volcanically active areas it is particularly small, i.e. H. the temperature gradient is particularly large, although in the area of subduction zones at greater depths there can also be a reversal of the temperature gradient: there the temperature does not increase with depth, but rather it decreases . This is due to the fact that comparatively cool surface rocks are drawn into the earth's mantle there.

Measurements of the temperature increase in the earth's interior were z. B. carried out by Louis Cordier in France around 1827. At a particularly deep bore, the bore Sper I / 1867 that in the Sperenberger salt dome m 1271.6 drilled was sent determines 1867 in more detail.

literature

• Werner Zeil: Brinkmanns Abriss der Geologie, first volume: General Geology . 12th edition. Ferdinand Enke Verlag, Stuttgart 1980, ISBN 3-432-80592-6 , p. 217 .

Individual evidence

1. ↑ The geological peculiarity of Sperenberg. Förderverein Heimatstube Sperenberg e. V., archived from the original on May 8, 2012 ; accessed on January 19, 2020 .