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Mineralogical, geochemical and grain-size composition of soil and pore-water chemistry parameters were characterized on both eroded (south-facing) and non-eroded (north-facing) clayey-silt slopes in the Basilicata region (southern Italy).Only a few grain-size parameters and clay mineralogy discriminate eroded from noneroded substrates. Compared with the latter, the former have fractions of over 63 µ µ µ µ µm and 1-4 µ µ µ µ µm lower and fractions 4-63 µ µ µ µ µm higher. Grain-size characters of crusts did not discriminate with respect to substrate.Bulk rock mineralogy was not distinctive, but the clay mineral assemblage shows that the eroded slope is enriched in kaolinite, mixed layers (illite-smectite) and chlorite, whereas illite decreases, although overlaps are common.Chemical data enable discrimination between eroded and non-eroded slopes. pH, SAR (sodium adsorption ratio), TDS (total dissolved salts) and PS (percentage of sodium) are distinctive parameters for both eroded and non-eroded slopes. TDS increases in depth in the non-eroded slope, whereas the maximum TDS is just below the crust in the eroded one. On average, eroded substrates are higher in pH, SAR and PS than non-eroded ones. The ESP (exchangeable sodium percentage) of the eroded slope has a higher value than the non-eroded one. Crusts are less dispersive than eroded substrates, and non-eroded substrates behave as crusts. This suggests that the portion of the slope most severely exposed to weathering tends to stabilize, due to strong decreases in SAR, PS and ESP. Several diagrams reported in the literature show similarly anomalous crust samples on eroded slopes, compared with other samples coming from greater depths on eroded slopes. In the present case study, the exchangeable form of Na characterizes crusts more than the soluble form.This study describes the erosional mechanism, which involves morphological and geographic exposure and climatic elements, as well as grain size, mineralogy, chemistry and exchangeable processes of soils.

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Abstract. Silty sands and clayey silts taken from a landslide in the Agri Valley have been analysed in order to study the role of sediment composition in the slope stability and the development of a slip zone. A geognostic hole was used to collect samples and monitor movements. A slip zone at a depth of about 14 m was identified. Compositional and physical-mechanical characterisation of samples was carried out. Some compositional characters, such as a 32-2 µm grain-size fraction, clay mineral content, cation exchange capacity and total nitrogen, increase in the slip zone. Some correlations have been found between geotechnical properties (residual shear strength and residual friction angle) and the same compositional characters, which can therefore be considered possible factors influencing slope stability.