Geology Reference
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Figure 126 Paris region: extent of the gypsic facies and of the collapse indicators (from
Toulemont, 1987).
1-No gypsum, 2-Extent of gypsum, 3-Collapse zones, 4-Cones of depression in the Lutetian
aquifer.
due to the karstifi cation of the gypsic masses of the Var department is in
part attributed by Nicod to the intensive exploitation of aquifers (1990,
1991, 1993, and 1999). The same observation can be made in the neighboring
department of the Alpes-Maritimes (see chap. D2-3.4).
3.3.3 Washing out of unconsolidated fi ll
In this case, it is the circulation of water in unconsolidated material that
can wash out fi ner-grained particles and locally hollow out the terrain. This
phenomenon progresses in the upslope direction and can be concentrated
in preferential pathways (internal erosion). It is generally irreversible as
long as circulation persists and reveals itself as rising aggravations, likely to
have repercussions up to the surface or to affect the base of infrastructures
and the foundations of buildings.
This concentrated washing out along fl ow channels determined by
granulometric and cementation contrasts can also affect older, silted up
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