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Flow-like landslides triggered by rainfall are a major concern in the peri-Vesuvian region of southern Italy. On December 19th, 2019, a landslide occurred along the Crocelle slope (Sarno Mountains), which had previously experienced a similar event in February 1986. This study was conducted to assess the characteristics of this event in terms of triggering and propagation conditions and, with reference to the 1986 landslide, to evaluate the evolution of residual landslide hazards at recurring landslide sites. Data collection included field surveys, visual analysis of a Unmanned Aerial Vehicle (UAV)-based photogrammetric model, geotechnical laboratory testing, rainfall and slope stability analysis, and propagation modeling. Results suggest that the landslide i) originated below a trail, ii) involved an initial volume of 450 m3, which did not significantly grow due to the limited entrainment of slope sediments, iii) was initiated after 13 h of rainfall (return period ∼4 years), and iv) propagated along a channel with an estimated velocity of up to 10 m/s. Comparison of the 2019 event with the 1986 event revealed a significant difference in terms of landslide magnitude (i.e., volume), potentially due to the occurrence of multiple events, which may have led to the temporal depletion of available materials along a slope repeatedly affected by landslides, and possibly to the different behavior of primary layered deposits (involved in the 1986 event) compared to reworked deposits (involved in the 2019 event). This suggests a reduction in the residual landslide hazard associated with a decrease in the expected magnitude and frequency of prospective events. • The 2019 Palma Campania landslide was initiated following 13 h of precipitation; • The landslide encompassed reworked pyroclastic deposits underneath a trail; • The landslide propagated within a channel with a velocity of up to 10 m/s; • Slope failure is facilitated by prior hydrological conditions; • Slope-scale landslide hazard potentially decreases due to multiple landslides. [ABSTRACT FROM AUTHOR]

Thickness and stratigraphic settings of soils covering slopes potentially control susceptibility to initiation of rainfall-induced shallow landslides due to their local effect on slope hydrological response. Notwithstanding the relevance of the assessment of hazard to shallow landsliding at a distributed scale by approaches based on a coupled modelling of slope hydrological response and slope stability, the spatial variability of soil thickness and stratigraphic settings are factors poorly considered in the literature. Under these premises, this paper advances the well-known case study of rainfall-induced shallow landslides involving ash-fall pyroclastic soils covering the peri-Vesuvian mountains (Campania, southern Italy). In such a unique geomorphological setting, the soil covering is formed by alternating loose ash-fall pyroclastic deposits and paleosols, with high contrasts in hydraulic conductivity and total thickness decreasing as the slope angle increases, thus leading to the establishment of lateral flow and an increase of pore water pressure in localised sectors of the slope where soil horizon thickness is less. In particular, we investigate the effects, on hillslope hydrological regime and slope stability, of irregular bedrock topography, spatial variability of soil thickness and vertical hydraulic heterogeneity of soil horizons, by using a coupled three-dimensional hydrological and a probabilistic infinite slope stability model. The modelling is applied on a sample mountain catchment, located on Sarno Mountains (Campania, southern Italy), and calibrated using physics-based rainfall thresholds derived from the literature. The results obtained under five simulated constant rainfall intensities (2.5, 5, 10, 20 and 40 mm h−1) show an increase of soil pressure head and major failure probability corresponding to stratigraphic and morphological discontinuities, where a soil thickness reduction occurs. The outcomes obtained from modelling match the hypothesis of the formation of lateral throughflow due to the effect of intense rainfall, which leads to the increase of soil water pressure head and water content, up to values of near-saturation, in narrow zones of the slope, such as those of downslope reduction of total soil thickness and pinching out of soil horizons. The approach proposed can be conceived as a further advance in the comprehension of slope hydrological processes at a detailed scale and their effects on slope stability under given rainfall and antecedent soil hydrological conditions, therefore in predicting the most susceptible areas to initiation of rainfall-induced shallow landslides and the related I-D rainfall thresholds. Results obtained demonstrate the occurrence of a slope hydrological response depending on the spatial variability of soil thickness and leading to focus slope instability in specific slope sectors. The approach proposed is conceived to be potentially exportable to other slope environments for which a spatial modelling of soil thickness would be possible. [ABSTRACT FROM AUTHOR]

Deep-seated landslides are important agents of relief shaping and can have substantial impact on human settlements. Many examples are present in the Campania region of southern Italy, where the association of complex lithostratigraphic and structural geologic conditions might have effect on landslide initiation and evolution. On this basis and considering the effect that the deep-seated landslide have had in the last years on the urban settlement, the Buonalbergo landslide was analyzed in terms of decadal kinematics and geological control and insights in prospective evolution were provided. The analysis of data derived by geological and landslide field mapping, settlement damage analysis, Persistent Differential Interferometry SAR data analysis, and Finite Elements stability analysis revealed i) the approximately constant rate movement of the landslide in the last three decades with a consistent enlargement of its area, ii) the presence of a large overturned anticline, characterized by a complex lithostratigraphic arrangement and multiple discontinuity sets, iii) the presence of faults responsible for morphological depression development, iv) a rotational mechanism characterizing the upper sector of the landslide and the ongoing translational sliding of blocks located at its toe and v) the effect of potential pore pressure scenarios on prospective kinematics (i.e. single to multiple stages creep) with the observed constant rate movement potentially related to a pore pressure at the landslide base ranging between 300 and 400 kPa. Result interpretation suggests i) the role of the structural and lithostratigraphic setting of the slope as predisposing factor for landslide development, ii) the potential of fold-related fabric in controlling landslide geometry and fragmentation, iii) the possible occurrence of multiple landslide events affecting the slope affected by the deep-seated landslide and iv) the potential of hydrologic conditions in modulating landslide velocity and evolution toward slope failure. The relevance of results is related to the representativeness of the Buonalbergo landslide as common process in the Apennine context in terms of potential long-term morphologic evolution of the slope and the existence of many landslides that develop in similar geological conditions driving sediment production and inducing persistent topographic changes in mountainsides. [ABSTRACT FROM AUTHOR]