Use of Geomorphological Information in Indirect Landslide Susceptibility Assessment

The objective of this paper is to evaluate the importance of geomorphological expert knowledge in the generation of landslide susceptibility maps, using GIS supported indirect bivariate statistical analysis. For a test area in the Alpago region in Italy a dataset was generated at scale 1:5,000. Detailed geomorphological maps were generated, with legends at different levels of complexity. Other factor maps, that were considered relevant for the assessment of landslide susceptibility, were also collected, such as lithology, structural geology, surficial materials, slope classes, land use, distance from streams, roads and houses. The weights of evidence method was used to generate statistically derived weights for all classes of the factor maps. On the basis of these weights, the most relevant maps were selected for the combination into landslide susceptibility maps. Six different combinations of factor maps were evaluated, with varying geomorphological input. Success rates were used to classify the weight maps into three qualitative landslide susceptibility classes. The resulting six maps were compared with a direct susceptibility map, which was made by direct assignment of susceptibility classes in the field. The analysis indicated that the use of detailed geomorphological information in the bivariate statistical analysis raised the overall accuracy of the final susceptibility map considerably. However, even with the use of a detailed geomorphological factor map, the difference with the separately prepared direct susceptibility map is still significant, due to the generalisations that are inherent to the bivariate statistical analysis technique.     

Remote sensing techniques for landslide studies and hazard zonation in Europe

An inventory is presented of researches concerning the use of remote sensing for landslide studies and hazard zonation as mainly carried out in the countries belonging to the European Community. An overview is given of the applicability of remote sensing in the following phases of landslide studies:

1. (1) Detection and classification of landslides. Special emphasis is given to the types of imagery required at different scales of analysis.

2. (2) Monitoring the activity of existing landslides using G.P.S., photogrammetrical techniques and radar interferometry.

3. (3) Analysis and prediction in space and time of slope failures. The different factors required in a landslide hazard study are evaluated, and the optimum remote sensing imagery for obtaining each of these factors is indicated.

Examples are given of research work carried out in these three phases from EC countries. Finally an evaluation is given of the aspects of uncertainty associated with the use of remote sensing data, and conclusions are given as to the incorporation of remote sensing techniques within the overall framework of techniques.     

Prediction of the occurrence of slope instability phenomenal through GIS-based hazard zonation

Slope instability hazard assessment is based on the analysis of the terrain conditions at sites where slope failures occurred in the past. For the analysis of the causative factors the application of geographic information systems (GIS) is an essential tool in the data analysis and subsequent hazard assessment. Three scale levels of hazard mapping are defined. A direct experience-driven mapping at reconnaissance level, a statistical approach to determine the causative factors in a quantitative susceptibility mapping and a methodology at large-scale making using of deterministic models.     

Factors underlying piping in the Basilicata region, southern Italy

Piping/tunnelling erosion is a widely spread process in the Plio-Pleistocene marine clays of the Basilicata region in southern Italy. The pipes are often closely concentrated along the surface drainage networks at different depths with a tunnel (length) and a diameter varying from just a few centimetres to some metres. The formation and evolution of pipes in the badlands can be explained through: (1) geo-structural characteristics of the clay, (2) material properties such as a high exchangeable sodium percentage, (3) favourable climatic conditions, and (4) hydraulic gradient along the path controlled by the gully or ravine bottom that is acting as a local drain. The exposure and the extension of joints at the surface and in the bedrock along the slope are the main factors required for development of the pipes. The absence of the piping erosion on the slopes, where a reasonably thick layer of the soil material covers the open joints, shows that although certain material properties and climatic conditions play an important role, they are not sufficient to develop extensive piping erosion in the area.