Alberto González-Díez

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.

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.

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.

A Comprehensive Approach to Investigate Maltese Coastal Landslides

ABSTRACT SOLDATI, M., BONACHEA, J., BRUSCHI, M.V., CORATZA, P., DEVOTO, S., GONZÁLEZ-DIAZ, A., MANTOVANI, M., PASUTO, A., PIACENTINI, D., REMONDO, J and SCHEMBRI, J.A., 2011. A Comprehensive Approach to Investigate Maltese Coastal Landslides. In: Micallef, A. (ed.), MCRR3-2010 Conference Proceedings, Journal of Coastal Research, Special Issue, No. 61, pp. 472–473. Grosseto, Tuscany, Italy, ISSN 0749-0208. This paper presents geomorphological and engineering-geological studies carried out along the north-western coast of Malta by research groups belonging to the University of Modena and Reggio Emilia (Italy), the National Research Council (Italy), the University of Malta and the University of Cantabria (Spain). The research are funded by Fondazione Cassa di Risparmio di Modena and the European Centre for Geomorphological Hazards (CERG) and focus on the evolution of coastal landslides with emphasis on the issues of hazard and risk, with respect to the recreational infrastructures present in the area and to the several tourists that visit this stretch of coast. The area of study extends for about 12 km2 in Northern Malta and elevation ranges from the coast to about 110 m above the sea level. In this part of the Island, slope failures are abundant and strictly linked to lithological and structural factors. In fact, in the north-western area of Malta, between Paradise Bay and Gnejna Bay, three geological units outcrop that deeply control the morphological setting and the evolution of landscape: Globigerina Formation, Blue Clay Formation and Upper Coralline Formation. The Upper Coralline Limestone, the younger Formation of Malta Island, forms a karst plateau, bordered by vertical cliffs of varying heights, which ranges from a few meters to 30 m. At the foot of the limestone slopes Blue Clays Formation crops out which develops gently slopes that in some cases can reach directly the sea. The different mechanical behaviour of clays and limestone favours the development of lateral spreading phenomena, which occur in particular at Anchor Bay, at Ghajn Tuffieha Bay and along the western sector of Marfa Ridge. The occurence of this type of mass movement causes the presence of vertical joints and cracks near the calcareous slopes, due to the fragile response of rock material. Properties of the cracks, such as their aperture and persistence, depend on the different stages of lateral spreading phenomena; in the areas where the phase of evolution is more mature fractures reach lengths that can exceed 200 meters. A consequence of the presence of these wide discontinuities is the accumulation of large boulders along the coast, due to the detachament and fall of blocks from the vertical cliffs. The deposits are wide and the blocks are slowly scattered on the large terrace gently sloping towards the sea. In order to study and understand the complex evolution of coastal slope failures, a multidisciplinary approach has been applied and a complex system of monitoring has been installed. The research carried out so far has included a retrospective study of slope instability events along the north-west coast of Malta, collection and analysis of climatic data, multi-temporal analysis of aerial photos, geomorphological survey and mapping. In addition, the research plan foresees LIDAR surveys and radar interferometric analyses. The results obtained have permitted to outline the causes and evolution of coastal landslides in the north-western coast of Malta, with specific focus on rock spreading phenomena whose movement velocity and direction have been monitored since 2006 in two field sites. GPS network are located at Il-Qarraba and Anchor Bay. The analysis of monitoring data has shown that lateral spreading phenomena are active in both sites and that the displacements range from a few mm/yr to more then 3 cm/yr. The integration of new monitoring data to be acquired will permit the evaluation and mapping of landslide hazard. The final results of the research are aiming at providing local authorities with a sound knowledge of coastal instability phenomena which might be useful for future land planning and in managing geomorphological risk issues.

Open image in new windowThe Application of ERT for the Geometrical Analysis of the Sebrango Landslide, (Cantabrian Range, Spain)

Electrical resistivity tomography (ERT) was applied to the geometrical characterization of the Sebrango Landslide reactivation (Cantabrian Range, Spain), which threatened the villages of Sebrango and Los Llanos on June 2013. The Sebrango Landslide is a 1.2 km-long landslide that episodically affects a hillslope located at the northern margin of the Deva River, at the northern sector of the Liebana Syncline. ERT surveying offered the opportunity to investigate the unexposed geometry of the landslide just after finishing the 2013 paroxysmal stage, while other surveying techniques, as core logging, were ruled out for safety and local government regulation during the hazard emergency. The obtained resistivity images provided information on the thickness of the terrain involved by the landslide, on the location of the inner rupture surfaces, and on the groundwater flow pattern within the hillslope. The results suggest that the landslide involves a 40–60 m-thick mass of complex structure. The resistivity images show a profuse groundwater flow within the slid mass, especially in the header area affected by the 2013 reactivation. The images also show a preferential groundwater flow longitudinally to the axis of a secondary landslide lobe, at the eastern sector of the landslide body, pointing to this sector is that actually shows greater deformation, as opposed to the main lobe oriented NW-SE. The landslide geophysical model was constrained by a core logging and monitoring campaign conducted during the subsequent months. From a geomorphological perspective, our results suggest that the particular entrenchment dynamics of the Deva River is playing a key role as a preparatory landslide factor.

La integración del conocimiento sobre la Cordillera Cantábrica: hacia un observatorio inter-autonómico del cambio global

Delgado L.A. 2018. Landscape Heterogeneity and tree species diversity in a tropical forest. Development and validation of a methodological proposal. Ecosistemas 27(1): 105-115. Doi.: 10.7818/ECOS.1475 Many landscapes exist as unstable spatial-temporal mosaics where changes in patterns of biodiversity are affected by nature processes and the dynamic interaction between social and ecological factors. It is a consequence of the natural dynamics of socio-economic systems that regulate man-made tropical forests. However, a significant proportion of studies have made generalizations about the relative values of biodiversity, without taking into account the high levels of internal heterogeneity in the biophysical properties and land uses of each site. The purpose of this study is to propose and validate a methodology to delimit the heterogeneity of the landscape based on criteria that integrate the coupling of human-ecological systems such as: space-time dynamics of deforestation and fragmentation; complexity of the landscape structure; current and historical land use and biophysical variability. For this, the use of satellite images, landscape metrics, field work, documentary review and multivariate analysis were combined. The proposed methodology is intended to help guide the empirical delimitation of landscape heterogeneity as a prerequisite for the selection of similar landscapes and forest patches in studies of the diversity of tree species, in order to provide an opportunity to control the possible difficulties caused by variability in the proportion of forests, landscape configuration and successional states, in estimating its effects on forest richness and floristic composition.