José Ramón Díaz de Terán

A methodological approach for the analysis of the temporal occurrence and triggering factors of landslides

The temporal occurrence of landslides in an area of the Cantabrian Range during the last 120,000 years is analyzed. An initial relative chronology was established on the basis of aging degree and spatial relationships between landslides and glacial and fluvial features. Ten landslide classes were thus identified and their chronological limits defined on the basis of 19 14C age determinations on fluvial and glacial deposits (including eight new ones). The chronology was tested with 14C dates obtained on landslide deposits, 10 from previous work and nine new ones. The chronological classes identified were compared with existing climate models for the region; the type and spatial distribution of landslides in each class were also analyzed. The approach made it possible to identify periods during which landslides were triggered mainly by channel incision, seismic activity and rainfall increase. Human activity played a significant role after 5000 BP and especially in the last few centuries. Mobilization of materials by slope movements has increased in the region by a factor of 10, compared to pre-Neolithic rates.

Late Quaternary climate changes and mass movement frequency and magnitude in the Cantabrian region, Spain

Abstract A reconstruction of Holocene climate changes in the Cantabrian region, based on pollen records and on complementary sedimentological, geomorphological, archaeological and oxygen isotope data is presented. The climate model thus proposed has been tested obtaining new sediment records and dating sixteen additional samples. The distribution and relative chronology of slope movements in a study area are presented. Eleven new dates have been obtained for landslide and flow deposits and a correlation between occurrence of mass movements and climate changes is proposed. The volumes affected by these movements in different periods have been calculated and rates have been obtained. Estimates of denudation rates in the study area during the Quaternary and in the Holocene are also presented and compared with the former.

Landslide risk models for decision making.

This contribution presents a quantitative procedure for landslide risk analysis and zoning considering hazard, exposure (or value of elements at risk), and vulnerability. The method provides the means to obtain landslide risk models (expressing expected damage due to landslides on material elements and economic activities in monetary terms, according to different scenarios and periods) useful to identify areas where mitigation efforts will be most cost effective. It allows identifying priority areas for the implementation of actions to reduce vulnerability (elements) or hazard (processes). The procedure proposed can also be used as a preventive tool, through its application to strategic environmental impact analysis (SEIA) of land-use plans. The underlying hypothesis is that reliable predictions about hazard and risk can be made using models based on a detailed analysis of past landslide occurrences in connection with conditioning factors and data on past damage. The results show that the approach proposed and the hypothesis formulated are essentially correct, providing estimates of the order of magnitude of expected losses for a given time period. Uncertainties, strengths, and shortcomings of the procedure and results obtained are discussed and potential lines of research to improve the models are indicated. Finally, comments and suggestions are provided to generalize this type of analysis.

Environmental diagnosis for planning and management in the high Andean region: the biosphere reserve of Pozuelos, Argentina.

A method for the identification, mapping and evaluation of integrated environmental units is described. This method is applied to the assessment and zoning of a biosphere reserve, in order to establish guidelines for the distribution of conservation and management actions. The method, based on the definition of units according to observable features, enables the diagnosis of qualities of interest for planning and management, with results that can be reproduced by different operators, if certain initial criteria are accepted. Using these criteria, initial descriptive maps can be transformed into prescriptive maps which provide the basis for management decisions.The nature and distribution of the units present in the area is shown. The allocation of land-use activities obtained using the criteria indicated above provides the basis for economic assessment of development plans. A series of conservation and development actions are proposed for the reserve.

Geomorphic Hazards in Spain

An overview of the main geomorphic hazards in Spain is presented. For each one of the processes analysed (floods, landslides, sinkholes, and coastal hazards), a brief description of their distribution, socioeconomic effects, and main causes is given. The main lines of research undertaken in recent times on these hazards, including development of new tools or techniques, are discussed. Finally, legislation and land-use planning measures for mitigation of risks due to such processes are described.

Landslide Hazard Scenarios Based on Both Past Landslides and Precipitation

The goal of this contribution is to develop a set of methods and techniques for modelling landslide hazard, in order to obtain better predictions and, therefore, to reduce the risk associated to this type of process. The research has been carried out in North-Western Guipuzcoa (Spain), an area intensely affected by shallow landslides. Hazard predictions must be based on several assumptions, termed scenarios. To propose more realistic hazard scenarios, two different approaches have been applied: on one hand, by extrapolating the trends observed from recent past landslide activity and, on the other hand and indirectly, from the empirical analyses between landslides and their main trigger (precipitation). It was necessary to get long time series of landslide occurrences, through which sound future frequency could be estimated and relationships between landslides and their predisposing factors established. The landslide inventory includes 20 time intervals ranging from the 50s of last century to the present and has been obtained by analyzing photographic images from different dates. Rainfall records of several weather stations have been analyzed, establishing correlations between landslides and precipitation intensity-duration. According to rainfall quantity, duration and intensity, as well as landslide activity, six multiple occurrence regional landslide events (MORLE), regarding rainfall extreme events, have been identified and characterized. On the basis of both types of scenarios quantitative hazard models could be obtained.