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A comprehensive analysis of the distribution of landslides was completed in the Upper Tiber River basin, central Italy. Landslide occurrence was ascertained through a large-scale inventory obtained through air-photo-interpretation (API) and local field surveys. Lithological and bedding information was obtained through photo-geological and field mapping, aided by the review of geological maps and reports. The probability density of landslide areas was found comparable to statistics obtained by investigators in other areas of the world. Adoption of empirical relationships to link landslide area and volume allowed estimating the total volume of landslide material in the 4098 km 2 catchment in excess of 5.9 x 10(9) m(3). Statistics of terrain elevation and slope in stable areas were found different from those in landslide areas. In particular, modal terrain slope in landslide areas was less steep (11.9 degrees) than that in areas where landslides were not mapped (13.3 degrees). Analysis of the landslide and slope areas revealed that a relationship exists between the size of the slope and the size of the most common landslide. Analysis of the spatial relationship between landslides and the geological setting revealed that slope failures are most abundant where soft and weak rocks crop out, and where bedding is chaotic or disorganized. Where rocks are regularly bedded, landslide abundance is largest in dip-slopes. These new findings are important to understand the long-term evolution of the Upper Tiber River basin, and may prove useful in the assessment of landslide hazard and risk. (c) 2007 Elsevier B.V. All rights reserved.

Landslide inventory maps are effective and easily understandable products for both experts, such as geomorphologists, and for non experts, including decision-makers, planners, and civil defense managers. Landslide inventories are essential to understand the evolution of landscapes, and to ascertain landslide susceptibility and hazard. Despite landslide maps being compiled every year in the word at different scales, limited efforts are made to critically compare landslide maps prepared using different techniques or by different investigators. Based on the experience gained in 20 years of landslide mapping in Italy, and on the limited literature on landslide inventory assessment, we propose a general framework for the quantitative comparison of landslide inventory maps. To test the proposed framework we exploit three inventory maps. The first map is a reconnaissance landslide inventory prepared for the Umbria region, in central Italy. The second map is a detailed geomorphological landslide map, also prepared for the Umbria region. The third map is a multi-temporal landslide inventory compiled for the Collazzone area, in central Umbria. Results of the experiment allow for establishing how well the individual inventories describe the location, type and abundance of landslides, to what extent the landslide maps can be used to determine the frequency-area statistics of the slope failures, and the significance of the inventory maps as predictors of landslide susceptibility. We further use the results obtained in the Collazzone area to estimate the quality and completeness of the two regional landslide inventory maps, and to outline general advantages and limitations of the techniques used to complete the inventories.

In recent years, growing population and expansion of settlements and life-lines over hazardous areas have largely increased the impact of natural disasters both in industrialized and developing countries. Third world countries have difficulty meeting the high costs of controlling natural hazards through major engineering works and rational land-use planning. Industrialized societies are increasingly reluctant to invest money in structural measures that can reduce natural risks. Hence, the new issue is to implement warning systems and land utilization regulations aimed at minimizing the loss of lives and property without investing in long-term, costly projects of ground stabilization. Government and research institutions worldwide have long attempted to assess landslide hazard and risks and to portray its spatial distribution in maps. Several different methods for assessing landslide hazard were proposed or implemented. The reliability of these maps and the criteria behind these hazard evaluations are ill-formalized or poorly documented. Geomorphological information remains largely descriptive and subjective. It is, hence, somewhat unsuitable to engineers, policy-makers or developers when planning land resources and mitigating the effects of geological hazards. In the Umbria and Marche Regions of Central Italy, attempts at testing the proficiency and limitations of multivariate statistical techniques and of different methodologies for dividing the territory into suitable areas for landslide hazard assessment have been completed, or are in progress, at various scales. These experiments showed that, despite the operational and conceptual limitations, landslide hazard assessment may indeed constitute a suitable, cost-effective aid to land-use planning. Within this framework, engineering geomorphology may play a renewed role in assessing areas at high landslide hazard, and helping mitigate the associated risk.

Seventeen alluvial fans in the Po Plain, between the Ticino and Mincio Rivers, in Northern Italy were identified and studied. The research was carried out following a semi-quantitative approach that combined display and analysis of altitude data, interpretation of morphometrical maps, and comparative inspection of geomorphological maps. Boundaries between fans were drawn interactively on a shaded relief image, computed from a 50 m resolution digital terrain model prepared interpolating 5 and 1 metre contour lines. For each fan, or for each portion making up a larger fan, geometric and morphometric criteria were computed. Fan morphometric criteria were compared to the present drainage basins morphological setting. The relationship between fan area and drainage basin area shows positive allometry, with the slope of the regression line lower than that commonly proposed for both arid and humid regions.

The study has divided Italy into eight major topographic divisions (provinces) and 30 minor divisions (sections) that are similar to N. Fenneman's units of the United States. Provinces and sections are generally consistent with observed morphology. The new units were defined step-wise in a semi-quantitative approach that combined an unsupervised three-class cluster analysis of four derivatives of altitude, visual interpretation of morphometric maps (including shaded relief), and comparative inspection of small-scale geological and structural maps. The four variables are altitude, slope curvature, frequency of slope reversal, and elevation-relief ratio. Highland, upland, and lowland topographic types were identified. The variables were computed from a 230 m resolution digital terrain model, regridded from the original 230 m DEM obtained by mosaicking the entire Italian mean elevation archive.