The deep-seated landslides correlated with the presence of the volcanic tuffs in the Transylvanian depression (Rumania)

Abstract

The Transylvanian Basin, a vast intracarpauhian morphotecuonic area, is dominated by stratigraphic series and lithologic complexes of Neozoic age. The sedimentary layers include numerous horizons of volcanic tuffs, some of them having very wide extensions and being very thick, and others much more thinner, with an ununiform spreading. These tuffs, together with the petrographic complexes in which they were inserted, have been tectonic affected, thus appearing the domes and the diapir folds. The areas with thick horizons of volcanic tuffs are frequently accompanied by profound landslides. The studies developed in this area lead us to idea that the volcanic tuffs play a special role in the process of landslides genesis, through various aspects: the mechanic behavior of the tuff layers at lithostatic pressures, the internal microtectonization which takes place in the packets of rocks, the fact that they enable surface waters to penetrate along the fissures toward depth, the presence of the lenticular soluble materials etc. The landslides which appear in the layers of tuffs have many shapes, from which we mention: the shape of blocks phragmented in corpuses, the shape of isolated monticuli and the shape of structural terraces. The landslides corpuses are affected, later on, by microtectonic processes, which stand out in specific microforms.