Ischia landslides (Italy): a multidisciplinary approach aimed to the knowledge of soil properties

An integrated approach (chemical, hydrological, mineralogical and micro-tomographic) has been used to study the soils of the landslides occurred in the Ischia island (Italy) on April 2006. The study has been carried out on three soil profiles sampled on representative detachment crowns. The main outcome indicates: (i) presence of volcanic soils, very rich in primary glass, characterised by the presence of poorly ordered kaolinite in all horizons and expandable clay minerals only in the deepest horizons (CBb and Cb), (ii) high values of water content near saturation for all soil horizons, (iii) a relevant vertical discontinuity of soil physical properties. In particular, the deep silty horizon (Cb) retains high amounts of water at low matric potential and shows the lowest value of saturated hydraulic conductivity than the other horizons. This microtomographic analysis of this deep horizon indicates a very complex intra-aggregate pore space, which seems an important factor influencing the specific rheological behaviour of this sliding horizon. In terms of pedogenetic processes, the soils of M. Vezzi northern slope are very different from those described for other catastrophic landslides of the Campania region (Sarno, Quindici, etc.), but they have in common the presence, along the soil profile, of marked physical discontinuities surely contributing to the initiation mechanisms of the landslides.