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The Tunisian territory (area of diapirs) is exposed to the risks of ground movements linked to water, some of which are related to the phenomenon of dissolution of gypsum, allowing the appearance of underground cavities which present natural risks and set people in danger. The analysis of the hazard was determined by the field study coupled with the application of geophysical methods to locate and map the cavities and identify their dimensions and their positions in the subsoil. In the region of El Fahs (40 km NW of Tunis): we used a non-destructive method, georadar (GPR) with a 200 MHz antenna bandwidth, and an electric method, by using the electric tomography of which we have applicated the sequence of dipole-dipole measurement. The results obtained were examined and interpreted according to 2D profiles. The geophysical methods of GPR and electrical tomography aim to detect many calvities in different depths. However, the geological radar was able to identify several cavities and the zones of dissolution whose investigation depth did not exceed the first 3 meters. On the contrary, the electric tomography method allowing the presence of several deeper underground cavities with larger dimensions extended to 64 meters. To conclude, the geological and hydrogeological contexts of the terrain studied and on the state of the soil and subsoil allow us to better understanding the mechanisms of the establishment of the dissolution phenomenon and the appearance of cavities in the basement. The analysis of the predisposing factors present in the study area shows that the geodynamic context of the Triassic ascent takes place according to a precise thermodynamic process that favors the phenomenon of dissolution of the gypsum.

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Landslides are one of the most significant natural damaging disasters in hilly environment [1]. The location of our study area is to the north of Tunisia, home to several manifestations of land instabilities, we bring to study this area of interest by GIS and geomatic approach to reduce social economic losses due to landslides. The performance of a cartographic data base for the landslide study in the Cap-Bon region was realized through studying geologic 1/50,000 and topographic 1/25,000 maps, aster optic Remote Sensing, land observation, and climatologic seismic data. These data will be digitalized, georeferenced, vectorized, spatially analyzed, classified and geotreated in order to produce a landslides card. The findings have shown that fields with smooth and friable lithology which are located at rather important seismic zones (more than 4 at Richter's scale) have some stability. However, the most endangered zones are in the North-West around Oued El Kbir and El Ain. Realizing this work helps to determine the most hazardous zones so that policy makers have an effective field intervention.