Geoscience Reference
In-Depth Information
3
Progressive Descent of
Weathering Fronts, other
Spatial Organization of Soils
The main objective here is to understand why soils are stratified into
horizons and why they retain this structure during their development.
For this we shall develop what we call the
weathering-front
model
. It forms
the central and unifying principle of this entire work. Then we will
study the fine
mechanisms
that can explain this vertical structuration.
This chapter could have been titled 'modelling . It is particularly
difficult compared to the others that are illustrated with many
observations made in the natural environment. But it is essential to
devote the necessary time to it because it facilitates understanding of
the rest of the volume.
3.1 VERTICAL DIFFERENTIATION OF SOILS
3.1.1 Origin of the Horizons
It is important to ask ourselves why there are horizons in soils and
why these horizons are horizontal, at least in the case of areas with
flat topography. The answer can be obtained by computer simulation
(unpublished work of the author). Let us start from a theoretical material
assumed to be
perfectly homogeneous
to 300-cm depth (it could belong to
recent alluvia). The following phenomena are simulated on this material
for all the days of four years under the climate of Montpellier:
