| Karst rocks such as limestone, dolomite, anhydrite, gypsum, or salt can be dissolved
physically by water or chemically by water enriched with carbon dioxide. The dissolution
driven by water flowing through the karst aquifer either occurs along fractures and bedding
partings in telogenetic rocks, or within the primary interconnected pore space in eogenetic
rocks. The enlargement of either fractures or pores by dissolution creates a large secondary
porosity typical for karst rocks, which is often very heterogenously distributed and results in
preferential flow pathes in the sub-surface, with cavities as large-scale end members of the
sub-surface voids.
Once the sub-surface voids enlarged by dissolution grow to a certain size, the overburden
rock can become instable and voids and caves can collapse. Depending of the type of
overburden, the collapse initiated at depth propagates towards the surface and finally results
in a collapse structure, such as collapse dolines, sinkholes, and tiangkengs on the very large
scale.
We present results from geophysical surveys over existing karst structures based on
gravimetric, electrical, and geomagnetical methods. We have chosen two types of dolines,
solution and collapse dolines, to capture and compare the geophysical signals resulting from
these karst structures. We compare and discuss our geophysical survey results with
simplified theoretical models describing the evolution of the karst structure and
three-dimensional structural models for the current situation derived for the different
locations. |