Slope instabilities in differently vegetated recent volcanic deposits

Vegetation has an important role on slope stability and erosion through hydrological and mechanical processes. Especially plants transpiration and roots uptake can preserve a large amount of matric suction during and after a rainfall event. Soils properties as the water infiltration rate, the moisture content, the organic matter content and the aggregate stability are affected by plants cover as well. The presence of vegetation and its effect on soil moisture also implies an increase of shear strength. Moreover, plants roots increase the tensile strength and the overall shear strength of the vegetated soils, because of their ability to sustain tension, and to occupy the space of soil pores. Trees and shrubs roots produce significant cohesion-like aliquots of strength into shallow soil deposits and increase subsurface drainage, impacting the pronenesse of shallow landslides. Thus, vegetation acts on most of the soil properties which control the slope instability.

Volcanic eruptions can drastically change hillslope hydrology by removing or burying the vegetation in large areas. Events of rainfall-induced slope instability and erosion in differently vegetated recent volcanic deposits are here investigated using a distributed physically-based numerical model. The model considers the effect of vegetation through an additional amount of cohesion due to plants roots, the leaf area index, the average height of plants, the storage capacity of plant cover. Several sets of parameters are considered, and the effect of differently aged vegetation covers on the stability recent volcanic deposits stability is analysed.