The use of isotope geochemistry in landslide research: recent applications in the northern Apennines of Italy

To date, the hydrological and mechanical processes involved in landslide triggering mechanisms are far to be fully understood. In particular, in the last decade, the scientific community is trying to integrate multidisciplinary approaches to gain further insights in the knowledge of landslide initiation and evolution. Among them, hydrochemistry and isotope geochemistry are current investigation tools which are used by an increasing number of researchers worldwide. This paper aims at pointing out the potentiality of isotopic analyses for unraveling water recharge processes taking place in two large clay)rich lands lides in the northern Apennines of Italy: Ca’ Lita (Province of Reggio Emilia) and Berceto (Province of Parma). With reference to this sector of the mountain chain, geological and hydrogeological settings were highly complicated by the tectonic stresses developed during the Apennines emplacement; one of the results is the frequent mismatch between hydrogeological and hydrological catchments boundaries. Moreover, in several cases, the presence of faults allows the rising of deep fluids from the oilfields hosted at depth. These aliquots act as a further recharge into the slopes, often involved in landsliding, which must be taken into account both for a hydrological (i.e., the amount of this peculiar water cannot be properly assessed by a common hydrogeological balance) and a mechanical point of view (i.e., influence of the pore water chemical composition on geotechnical properties). The research combines in)situ monitoring together with hydrochemical and isotopic (stable and radiogenic isotope) analyses. The continuous monitoring of groundwater levels, electrical conductivity and temperature are coupled with groundwater sampling followed by determination of major ions (Na+, K+, Mg 2+, Ca2+, Cl−, HCO−1,SO2−4), tracers (such as Btot and Sr2+), and isotopes (∂ 18O, ∂2H and 3H). Moreover, leaching experiments on soil samples are being carried out to simulate the reactions that occur when landslide materials are leached by rainfall water. With these tools, in the Ca’ Lita landslide, an oil)field)origin aliquot of groundwater has been assessed and successively quantified. In the Berceto landslide, the hydrogeological boundaries have been properly defined and a hydraulic connection with the Baganza River has been demonstrated.