Earth Sciences

A preliminary sinkhole susceptibility analysis has been carried out in a stretch 50 km 2 in area of the Ebro valley alluvial evaporite karst (NE Spain). A spatial database consisting of a sinkhole layer and 27 thematic layers related to causal factors was constructed and implemented in a GIS. Three types of sinkholes were differentiated on the basis of their markedly different morphometry and geomorphic distribution: large subsidence depressions (24), large collapse sinkholes (23), and small cover-collapse sinkholes (447). The susceptibility models were produced analysing the statistical relationships between the mapped sinkholes and a set of conditioning factors using the Favourability Functions approach. The statistical analyses indicate that the best models are obtained with 6 conditioning factors out of the 27 available ones and that different factors and processes are involved in the generation of each type of sinkhole. The validation of two models by means of a random-split strategy shows that reasonably good predictions on the spatial distribution of future dolines may be produced with this approach; around 75% of the sinkholes of the validation sample occur on the 10% of the pixels with the highest susceptibility and about 45% of the area can be considered as safe.

An active sinkhole around 100 m long has been investigated in the city of Zaragoza (NE Spain). Subsidence activity on this depression, including the sudden occurrence of a collapse sinkhole 5 m across, led to the abandonment of a factory in the 1990s. At the present time, a building with 100 flats and shallow pad foundations partially built on the sinkhole, is affected by rapid differential settlement. The development of the sinkhole results from the karstification of the halite-and glauberite-bearing bedrock and the sagging and collapse of the overlying bedrock and alluvium, more than 30 m thick. GPR and electrical resistivity profiles have provided information on the distribution and geometry of the subsidence structure. The application of the trenching technique and geochronological methods (AMS and OSL dating) has allowed us to infer objective and practical data on the sinkhole including (1) Limits of the subsidence structure, (2) subsidence mechanisms, (3) cumulative subsidence ([408 cm), (4) subsidence rates on specific failure planes ([1.8 cm/year), (5) episodic displacement regime of some fault planes. The available information indicates that the progressive deformation recorded in the building will continue and might be punctuated by events of more rapid displacement. This work illustrates the practicality of the trenching technique for the study of sinkholes in mantled karst areas.

The objective of this work is to test a hypothesis formulated on the basis of former results which considers that there might be a ''global geomorphic change,'' due to activities related to land management and not determined by climate change, which could be causing an acceleration of geomorphic processes. Possible relationships between some geomorphic processes related to land instability (landslides or sediment generation) and potential triggering factors are analyzed in study areas in northern Spain. The analysis is based on landslide inventories covering different periods, as well as the determination of sedimentation rates. Temporal landslide and sedimentation rate trends are compared with different indicators of human activities (land-use change, logging, forest fires) and with potential natural triggers (rainfall, seismicity). The possible influence of the road network in the distribution of landslides is also analyzed. Results obtained show that there is a general increase of both landslide and sedimentation rates with time that cannot be explained satisfactorily by observed rainfall trends and even less by seismicity. Land-use change appears to be by far the main factor leading to land instability, with some changes producing up to a 12-fold increase of landslide rate. A relationship between road network and the spatial distribution of landslides has also been observed. These results do confirm the existence of an acceleration of geomorphic processes in the region, and also suggest that climate-related factors play a limited role in the changes observed.

This paper discusses the use of 222 Rn concentrations in water of natural springs as a geomorphological method to identify latent faults in low-mid term activity areas. The identification of this type of active fault may be crucial in hazard analysis, structural geomorphology and in landscape evolution analysis. The test used to identify these faults is based on the measuring of 222 Rn concentrations in water of springs linked to faults, and comparison with those obtained from springs which, although exactly the same lithological context, are not linked with faults (reference values). If the difference between the measured value and the reference value is positive then an anomaly is identified and that measurement indicates a spring linked to a latent fault. The test was applied and validated in springs linked to faults with a latent behaviour in Cantabria, Northern Spain. These faults have shown an intermittent movement over the last 50,000 years, and have contributed towards landslide processes playing a significant role in landscape evolution of the area.

This contribution illustrates the advantages of integrating conventional geomorphological methods with InSAR, ground penetrating radar and trenching for sinkhole mapping and characterization in a mantled evaporite karst area, where a significant proportion of the karstic depressions have been obliterated by artificial fills. The main practical aim of the investigation was to elucidate whether buried sinkholes overlap the areas planned for the construction of buildings and services, in order to apply a preventive planning strategy. Old aerial photographs and detailed topographic maps were the most useful sources of information for the identification of sinkholes and helped to obtain information on their chronology, either a minimum age or bracketing dates. The InSAR technique provided subsidence rate values ranging from 4.4 to 17.3 mm/yr consistent with the spatial distribution of the mapped sinkholes. This quantitative deformation data helped corroborating independently the existence of active buried sinkholes and improving the delineation of their limits. The GPR profiles contributed to the precise location of sinkhole edges, provided information on the geometry of buried sinkholes and deformation structures and helped to site trenches and to rule out the existence of sinkholes in particular areas. The main input derived from the trenches includes: (1) Confirming or ruling out anomalies of the GPR profiles attributable to subsidence. (2) Precise location of the edge of some filled sinkholes. (3) Information on subsidence mechanisms recorded by various deformation structures and cumulative subsidence magnitude. (4) Calculating minimum long-term subsidence rates using radiocarbon dates obtained from deformed sinkhole deposits. (5) Unequivocal evidence of active subsidence in areas assigned for the construction of buildings.

An analysis of changes experienced during the last century by certain indicators of the intensity of geomorphic processes in northern Spain is presented, in order to test a previously formulated hypothesis. The hypothesis, already tested in the Rio de la Plata Basin, is that there is a global geomorphic change which implies an acceleration of geomorphic processes in general, and that such acceleration is mainly due to the transformation of land surface by human activities, not to climate factors. Sedimentation rates obtained in eight estuaries in northern Spain, through Pb-210 and Cs-137 dating of sediment cores, show a general increase since the beginning of last century, and particularly after the 1950s. Similar increases in landslide frequency have been formerly observed in some areas of the same region. Trends of change in sedimentation rates have been compared with those of potential natural (rainfall) and human (indicators of the intensity of human activities that can contribute to land-surface transformation) drivers. There seems to be no relationship between rainfall and sedimentation rate trends but the magnitude and trends of several indicators of human activity are similar to those of the latter. Data on landslide frequency obtained in a small study area also show a possible relationship with land-use change and infrastructure development, but not with rainfall. The results described are coherent with the hypothesis and suggest that the process described could have a global character. If this is so, the worldwide observed increase in flood and landslide disasters might be a characteristic of the Anthropocene and due to human-induced geomorphic change, rather than climate change (also human-induced), as often assumed.

A detailed sinkhole map has been produced in a stretch of the Ebro Valley (40.8 km 2 ) including the western sector of Zaragoza city (NE Spain). During the last few decades, around 70% of the original sinkhole area has been filled with anthropogenic sediments causing the disappearance of 137 ha of wetlands. The interstratal karstification of salts (halite and glauberite) and a WNW-ESE-trending joint set have played a major control in the development of sinkholes. Three morphometric types of sinkholes have been differentiated, each attributed to a specific subsidence mechanism inferred from the paleosinkholes exposed in the surrounding of Zaragoza city; sagging of bedrock and cover, collapse of bedrock and cover, and collapse of cover material related to the downward migration of particles through dissolutional conduits. Each type of sinkhole is characterised by a distinctive behaviour in terms of controlling factors, spatio-temporal distribution and kinematics, and consequently the proposed differentiation may have a practical utility. The vast majority of the subsidence damage identified in the area occurs within the boundaries of pre-existing sinkholes identifiable in old aerial photographs and topographical maps. This fact demonstrates that the application of preventive planning strategies based on detailed geomorphological maps would have allowed avoidance of most of the large financial losses caused by subsidence in the area, of the order of hundreds of thousands of euros per year.

A quantitative procedure for mapping landslide risk is developed from considerations of hazard, vulnerability and valuation of exposed elements. The approach based on former work by the authors, is applied in the Bajo Deba area (northern Spain) where a detailed study of landslide occurrence and damage in the recent past (last 50 years) was carried out. Analyses and mapping are implemented in a Geographic Information System (GIS).

Multiple sinkhole susceptibility models have been generated in three study areas of the Ebro Valley evaporite karst (NE Spain) applying different methods (nearest neighbour distance, sinkhole density, heuristic scoring system and probabilistic analysis) for each sinkhole type separately (cover collapse sinkholes, cover and bedrock collapse sinkholes and cover and bedrock sagging sinkholes). The quantitative and independent evaluation of the predictive capability of the models reveals that: (1) The most reliable susceptibility models are those derived from the nearest neighbour distance and sinkhole density. These models can be generated in a simple and rapid way from detailed geomorphological maps. (2) The reliability of the nearest neighbour distance and density models is conditioned by the degree of clustering of the sinkholes. Consequently, the karst areas in which sinkholes show a higher clustering are a priori more favourable for predicting new occurrences. The predictive capability of the best models obtained in this research is significantly higher (12.5-82.5%) than that of the heuristic sinkhole susceptibility model incorporated into the General Urban Plan for the municipality of Zaragoza. Although the probabilistic approach provides lower quality results than the methods based on sinkhole proximity and density, it helps to identify the most significant factors and select the most effective mitigation strategies and may be applied to model susceptibility in different future scenarios.

A methodological proposal for the assessment of impacts due to linear infrastructures such as motorways, railways, etc. is presented. The approach proposed includes a series of specific issues to be addressed for each geomorphological feature analysed-both dstaticT and ddynamicT-as well as a series of steps to be followed in the process.

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 km 2 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

A quantitative method for assessing sinkhole susceptibility and hazard has been developed and independently tested in an evaporite karst of NE Spain. Three genetic types of sinkholes have been mapped: 947 small cover-collapse sinkholes, 23 large collapse sinkholes and 24 large subsidence depressions. By analysing the statistical relationships between the sinkholes and the potential conditioning factors, susceptibility models have been developed. These were evaluated using several strategies that have allowed us to assess quantitatively the quality of the models. The best susceptibility model for the small collapse sinkholes was transformed into a hazard map by considering the frequency and average size of an independent population of new occurrences. The susceptibility and hazard models obtained indicate that it is possible to produce reasonably good predictions on the distribution and frequency of sinkholes in the study area.

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.

An analysis of geomorphic system's response to change in human and natural drivers in some areas within the Río de la Plata basin is presented. The aim is to determine whether an acceleration of geomorphic processes has taken place in recent years and, if so, to what extent it is due to natural (climate) or human (land-use) drivers. Study areas of different size, socio-economic and geomorphic conditions have been selected: the Río de la Plata estuary and three sub-basins within its watershed. Sediment cores were extracted and dated ( 210 Pb) to determine sedimentation rates since the end of the 19th century. Rates were compared with time series on rainfall as well as human drivers such as population, GDP, livestock load, crop area, energy consumption or cement consumption, all of them related to human capacity to disturb land surface. Data on river discharge were also gathered. Results obtained indicate that sedimentation rates during the last century have remained essentially constant in a remote Andean basin, whereas they show important increases in the other two, particularly one located by the São Paulo metropolitan area. Rates in the estuary are somewhere in between. It appears that there is an intensification of denudation/ sedimentation processes within the basin. Rainfall remained stable or varied very slightly during the period analysed and does not seem to explain increases of sedimentation rates observed. Human drivers, particularly those more directly related to capacity to disturb land surface (GDP, energy or cement consumption) show variations that suggest human forcing is a more likely explanation for the observed change in geomorphic processes. It appears that a marked increase in denudation, of a "technological" nature, is taking place in this basin and leading to an acceleration of sediment supply. This is coherent with similar increases observed in other regions. . The latter authors indicate that human mobilisation of rocks and unconsolidated materials could be one or two orders of magnitude greater than denudation/transport by natural processes. Also, that areas disturbed by excavation/accumulation, although relatively small, are significant contributors to sediment generation, perhaps the main one. According to , human activities have increased global sediment transport by rivers by 2.

This paper deals with landslide hazards and risk analysis of Penang Island, Malaysia using Geographic Information System (GIS) and remote sensing data. Landslide locations in the study area were identified from interpretations of aerial photographs and field surveys. Topographical/ geological data and satellite images were collected and processed using GIS and image processing tools. There are ten landslide inducing parameters which are considered for landslide hazard analysis. These parameters are topographic slope, aspect, curvature and distance from drainage, all derived from the topographic database; geology and distance from lineament, derived from the geologic database; landuse from Landsat satellite images; soil from the soil database; precipitation amount, derived from the rainfall database; and the vegetation index value from SPOT satellite images. Landslide susceptibility was analyzed using landslide-occurrence factors employing the probability-frequency ratio model. The results of the analysis were verified using the landslide location data and compared with the probabilistic model. The accuracy observed was 80.03%. The qualitative landslide hazard analysis was carried out using the frequency ratio model through the map overlay analysis in GIS environment. The accuracy of hazard map was 86.41%. Further, risk analysis was done by studying the landslide hazard map and damageable objects at risk. This information could be used to estimate the risk to population, property and existing infrastructure like transportation network. Malaysia, little attention has been paid to the people who live within landslide-prone areas. Unfortunately not much database is available about them and the measures taken to avoid loss. In this paper, efforts have been made to study landslide hazards

This contribution illustrates the advantages of integrating conventional geomorphological methods with InSAR, ground penetrating radar and trenching for sinkhole mapping and characterization in a mantled evaporite karst area, where a significant proportion of the karstic depressions have been obliterated by artificial fills. The main practical aim of the investigation was to elucidate whether buried sinkholes overlap the areas planned for the construction of buildings and services, in order to apply a preventive planning strategy. Old aerial photographs and detailed topographic maps were the most useful sources of information for the identification of sinkholes and helped to obtain information on their chronology, either a minimum age or bracketing dates. The InSAR technique provided subsidence rate values ranging from 4.4 to 17.3 mm/yr consistent with the spatial distribution of the mapped sinkholes. This quantitative deformation data helped corroborating independently the existence of active buried sinkholes and improving the delineation of their limits. The GPR profiles contributed to the precise location of sinkhole edges, provided information on the geometry of buried sinkholes and deformation structures and helped to site trenches and to rule out the existence of sinkholes in particular areas. The main input derived from the trenches includes: (1) Confirming or ruling out anomalies of the GPR profiles attributable to subsidence. (2) Precise location of the edge of some filled sinkholes. (3) Information on subsidence mechanisms recorded by various deformation structures and cumulative subsidence magnitude. (4) Calculating minimum long-term subsidence rates using radiocarbon dates obtained from deformed sinkhole deposits. (5) Unequivocal evidence of active subsidence in areas assigned for the construction of buildings.

An assessment of some consequences of human activities on geomorphic processes during the last century is presented. The effects of urban-infrastructure development and mining on direct and indirect denudation and geologic materials transport in several study areas are analysed. The temporal occurrence of landslides is analysed in another study area. Results obtained are compared with data on denudation and sediment transport from the literature, as well as with data on geomorphic disaster trends for the same period.