In this article, the results of a study aimed to assess the landslide susceptibility in the Calaggio Torrent basin (Campanian Apennines, southern Italy) are presented. The landslide susceptibility has been assessed using two bivariate-statistics-based methods in a GIS environment. In the first method, widely used in the existing literature, weighting values (Wi) have been calculated for each class of the selected causal factors (lithology, land-use, slope angle and aspect) taking into account the landslide density (detachment zones + landslide body) within each class. In the second method, which is a modification of the first method, only the landslide detachment zone (LDZ) density has been taken into account to calculate the weighting values. This latter method is probably characterized by a major geomorphological coherence. In fact, differently from the landslide bodies, LDZ must necessarily occur in geoenvironmental classes prone to failure. Thus, the calculated Wi seem to be more reliable in estimating the propensity of a given class to generate failure. The thematic maps have been reclassified on the basis of the calculated Wi and then overlaid, with the purpose to produce landslide susceptibility maps. The used methods converge both in indicating that most part of the study area is characterized by a high-very high landslide susceptibility and in the location and extent of the low-susceptible areas. However, an increase of both the high-very high and moderate-high susceptible areas occurs in using the second method. Both the produced susceptibility maps have been compared with the geomorphological map, highlighting an excellent coherence which is higher using method-2. In both methods, the percentage of each susceptibility class affected by landslides increases with the degree of susceptibility, as expected. However, the percentage at issue in the lowest susceptibility class obtained using method-2, even if low, is higher than that obtained using method-1. This suggests that method-2, notwithstanding its major geomorphological coherence, probably still needs further refinements.

In this paper, two simple GIS-based methodologies have been used to assess the landslide susceptibility in a basin located in Southern Italy. The methodologies at issue, based on the spatial distribution of landslides and/or of causal factors, are bivariate statistics-based and expert-based, respectively. The spatial distribution of both the landslides and the causal factors has been investigated by integrating pre-existing and original data, which have been processed using ArcView GIS 3.2 software. The obtained results, consisting of landslide susceptibility maps have been compared and discussed. The bivariate statistics-based method has provided the most satisfying results. On the contrary, the expert-based method has provided a classification of the study area in terms of landslide susceptibility which does not completely fit with the surveyed spatial distribution of the landslides.

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Irpinia (Province of Avellino, Campania Region) is a historical–geographical region of Southern Italy inhabited in pre-Roman times by the ancient Samnite tribe of the Irpini, from which the name originates. This area is characterized by both low population density and high naturalness; located on the axial sector of the southern Apennine orogenic chain, the area possesses a complex hilly and mountainous orography, with predominantly agricultural and forest land uses. In this geographical context, there are many relevant geological/geomorphological sites, witnessing a wide geodiversity attributable to complex geological evolution and relief morphogenesis. The extensive bio-geodiversity has thus led to widespread geotourism practices. Irpinia is favored for its beautiful landscapes, rich cultural heritage, and typical small towns, often enhanced by quality certifications; moreover, geotourism activities are often associated with other forms of sustainable tourism. Starting from this geographical framework, the article analyzes eight attractive geosites that represent the geotouristic value of the entire Irpinia area well. The analysis was conducted using well-known qualitative and quantitative assessment methods. The results obtained, emphasizing the salient aspects of geodiversity, can be used in planning the usability of the sites and, more generally, planning for the Irpinian landscape in a geo-ecotouristic sense.

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