Landslides in iliolitic and marly formations. Examples from north-westem Greece

Landslides in iliolitic and marly formations are investigated at two representative sites in northern Greece. The first case concerns an iliolitic tectonic formation between Pindos and Ionian flysch while the second concerns the marls of the molasses of the Mesohellenic Basin. Both areas present a high relief, with steep slopes and significant rainfall. The above formations were studied using both in situ and laboratory techniques. According to our study, these formations present more or less similar mechanical properties, but different behaviour in relation to landslide occurrence; they are very hard in dry conditions but lose their resistance rapidly under wet conditions. In the first case, the rainwater penetrates the iliolite causing landslides of soil type. In the second the rainwater does not penetrate the marl creating a surface saturated zone. The material drys rapidly creating cracks and flakes which accumulate at the toe of the slope. This weathering causes caving at the base of the overlying sandstone which presents toppling and sliding phenomena.