Landslide processes and Andosols: the case study of the Campania region

The general goal of this research has been the study of soils connected to the initiation mechanisms of debris flow landslide in the Campania region. More specifically the following aims were investigated: 1) a regional scale analysis concerning the relationship between soil types and landslide initiation mechanisms in Campania; 2) a local scale analysis on selected sites where hydropedological landslide initiation processes were explored. The study was conducted in the following step: (i) analysis of historical reports; (ii) georeferencing of the main landslide detachment crown in Campania; (iii) morphological description and sampling of selected profiles located in the detachment crown; (iv) chemical and physical (hydrological) analysis; (v) hydrological physically based modelling for water balance simulation at the time of landslides. The analysis has clearly shown that the most important Campanian debris flow landslide occurred in mountains very fertile forest (mostly chestnut) ecosystem with complex sequences of Andosols both as surface and buried soils. Such soils have a high allophane and imogolite content, high water retention properties and well developed tixotropy. These features along with the high slope and/or the slope discontinuity (roads, cliff) seem to have played a very important rule in the landslide initiation mechanisms. From the outputs of the regional scale analysis, few selected sites (5 soil profiles) were investigated with a detailed analysis of the hydropedological processes affecting landslide initiation mechanisms. Bulk and undisturbed (steel cylinders) samples were collected in each soil horizon for standard chemical analysis and for determining hydraulic properties by the Wind method. Physically based water balance models have been applied. More specifically, the knowledge of water retention and hydraulic conductivity functions along with the knowledge of the boundary conditions enable the solution of the Richard equation and therefore the inference of water balance in the period of the landslide. Functional properties (i.e. water content at specific depth, soil weight at specific depth) were then defined and obtained as an integrated model output for estimating the susceptibility of the soil system to landslide initiation processes.