Ferrallitization
The Ferrallitisierung is a weathering-related depletion of silicon ( desilication ) of soil in wet tropical regions with simultaneous enrichment of iron -, and aluminum oxides , aluminum chloride and kaolinite . If water rises capillary to the surface under changing humidity conditions , the topsoil is also absolutely enriched with iron ( plinthization ).
At the beginning of tropical weathering (or in the contact area with the rock ), silicates , feldspars and biotite are loosened and the rock structure is loosened. Later, these minerals are also dissolved in permeable soils. At the same time, however, iron oxides are also formed, above all goethite and hematite (if there is a high annual mean temperature and there is no organic matter), which is responsible for the characteristic reddish to reddish brown color of the earth.
If the quartz crystals are subsequently dissolved, only very few stable minerals remain. Due to the silicon that is required but is now missing, kaolinite can now also be broken down, which can lead to mass losses of up to 90% and which can explain the high erosion rates in the tropics. The strong chemical weathering in the humid tropical areas has reached depths of around 50 meters over the course of many millions of years. Due to the extensive denudation on the rinsing area , individual, weather-resistant rock blocks remain on the land surface (the so-called island mountains or wool sack blocks).
See also
literature
- Paul Schachtschabel , Fritz Scheffer : Textbook of soil science . 15th edition. Spektrum, Akademischer Verlag, Heidelberg et al. 2002, ISBN 3-8274-1324-9 .
- Herbert Kuntze , Günter Roeschmann , Georg Schwerdtfeger : Soil science . 5th, revised and expanded edition. Ulmer, Stuttgart 1994, ISBN 3-8252-8076-4 .