Metals in the sediments of Ensenada de San Simón (inner Rı́a de Vigo), Galicia,NW Spain

The Ensenada de San Simón is the inner part of the Rı́a de Vigo, one of the major mesotidal rı́as of the Galician coast, NW Spain. The geochemistry of its surface sediments, and the river sediments which drain into it from a granitic and metamorphic hinterland, are described. Multivariate statistical analysis of the sediment compositions (using ridge regression and mixture-modelling) enabled the major- and trace-element distributions to be accounted for in terms of both natural and anthropogenic sources: Between 60 and 80% of the Cr, Cu, Ni, Pb and Zn concentrations of the bottom sediments of the Ensenada can be explained by sediment input from the combined R. Oitaben and R. Verdugo, the R. Redondela and faecal matter from mussel rafts, but there is additional enrichment towards the mouth of the Ensenada. This enrichment is attributed to marine water entering the Ensenada from the polluted industrial areas of the adjacent Rı́a de Vigo. It is suggested that these metals are carried landwards in solution by the tidal incursion of marine water (the volume of which, on an annual basis, greatly exceeds that contributed by the rivers). Although the incoming marine waters may also be important in supplying Pb to the outer Ensenada, this element may also be delivered by land run-off, or by windborne vehicular emissions to the Ensenada as a result of the surrounding network of roads and a road bridge over the Estrecho de Rande.     

Hydrological modeling in the karst area,Rižana spring catchment,Slovenia

Karst aquifers are known for their heterogeneity and irregular complex flow patterns which make them more difficult to model and demand specific modeling approaches. This paper presents one such approach which is based on a conceptual model. The model was applied in a karst area of the catchment of Rižana spring (200 km2). It is based on the MIKE SHE code and incorporates the main hydrological processes and geological features of the karst aquifer (diffuse and concentrated infiltration, allogenic recharge, quick and slow groundwater flow, shifting groundwater divides and groundwater outflow from the catchment area). Modeling of evapotranspiration and flow in the upper part of the unsaturated zone is more detailed. For the modeling of groundwater flow in the karst aquifer, a conceptual model was applied which uses drainage function for the simulation of groundwater flow through large conduits (karst channels and large fissures). The model was calibrated and validated against the observed Rižana spring discharge which represents a measured response of the aquifer. The results of validation show that the model is able to adequately simulate temporal evolution of the spring discharge, measured by Nash–Sutcliffe coefficient (0.82) as well as overall water balance.     

Numerical analysis of hydrogeochemical data: a case study (Alto Guadalentı́n,southeast Spain)

This study examines the spatial variability of the factors obtained from the application of correspondence analysis to a hydrogeochemical data set. The goal was to synthesize the hydrogeochemical information using this multivariate statistical technique, by setting a series of factors which clarified the main properties of one aquifer. Then, a geostatistical framework to obtain a probabilistic assessment of groundwater quality was established. Experimental and theoretical semivariograms of the selected factors, considered as regionalized variables, were computed. These variographic information and factor values in the experimental sites were used in the ordinary kriging, which provides unbiased and linear estimates of the regionalized variables. These estimates were used to compile maps of the chosen factors, which explain their spatial distribution.The selected case study was the alluvial aquifer of Alto Guadalentı́n which is situated in southeast Spain, in the Internal Zones of Betic Cordilleras. These waters are chiefly SO₄ and Cl types, but HCO₃ facies are common in the central sector of the basin. High temperature, acid pH, problems of overexploitation and pollution by CO₂-gas characterise these waters. Available groundwater quality monitoring data were used to calibrate the numerical model. The present study focused on setting the main physical and chemical attributes and establishing the spatial pattern of groundwater quality and the temporal changes in this pattern.     

Sequential limb rotation and kink-band migration recorded by growth strata,Almazán Basin,North Spain

The geometry of growth strata in the Almazán monocline demonstrates that limb rotation and kink-band migration can coexist as folding mechanisms. The Almazán Basin, showing an overall synclinal geometry, was one of the most actively subsiding areas during the Tertiary in the inner part of the Iberian plate, with more than 3500 m of preserved Tertiary non-marine sediments. They are arranged in five tectonosedimentary units, TSU (A1 to A5), bounded by unconformities at the basin borders. The southern basin border is defined by the WNW–ESE-trending Almazán monocline, that can be followed for 25 km along strike, with a maximum structural relief of about 2500 m. The maximum changes in thickness on both limbs of the monocline occur in units A2 and A3, which constrains the maximum deformation period to between the Middle/Upper Eocene (Headonian, top of A1) and Upper Oligocene/Lower Miocene (Agenian, base of A4). The detailed geometry of the Mesozoic, pre-growth, and the Tertiary growth strata of the Almazán monocline was determined from the analysis of six seismic reflection sections, at high angles or perpendicular with the fold axis. The average dip of the monocline changes from 15° in the east to more than 45° in the western sector, being replaced westwards by a north-verging, steeply dipping thrust. In some sections, growth strata in the dipping limb show rotational offlap–onlap syntectonic unconformities, with progressively decreasing dips from bottom to top, indicating that limb rotation took place during the first stages of folding. At the limits of the dipping limb (anticline and syncline), two kink bands appear in some of the sections, the one located on the syncline being more developed. Within each kink-band, beds show a constant dip of 30–40°. The axial surfaces of each kink band converge upwards in the third and fourth tecto-sedimentary units, being parallel in the older units. The fixed axial surface occurs in a down dip position with respect to the active axial surface. The geometry of growth strata indicates that the mechanism of folding followed a sequence of: (i) a first stage of large-scale limb rotation (wavelength larger than 5 km), with minor development of kink-bands in some sections, and (ii) a second stage of more localised kink-band migration, probably favoured by fault propagation in the basement.     

Identification of hydrogeochemical processes in a volcano-sedimentary aquifer of Ciénega de Chapala in Michoacán,Mexico

The present study characterized the hydrogeochemical processes of the aquifer of Ciénega de Chapala in Michoacán, Mexico. The dominant water families contained bicarbonate magnesium and sodium. In the region, water infiltrates into a fractured volcanic environment exposed in the surrounding mountains and is transmitted to the volcano-sedimentary units of the ciénega, where silicate alteration and ion exchange processes occur in the clays of the subsoil. The Gibb diagrams confirm that the main evolutionary processes in the aquifer are rock-water interactions in the local flow and evaporation in the intermediate and regional flows. The molar ratios of HCO₃/Na and Ca/Na are congruent with the type of volcano-sedimentary environment present in the area. Ternary mixing processes associated with three end members were also identified and were related to the flow systems in the area. The local flow contributes 77% of water to the system, and the intermediate and regional flows contribute 16% and 7%, respectively.     

Hazard assessment at San Martín volcano based on geological record, numerical modeling, and spatial analysis

The San Martín shield volcano, located in the Los Tuxtlas Volcanic Field, has experienced effusive shield-building activity, as well as explosive eruptions, as evidenced by direct observations during the last eruption in 1793. The threat to the surrounding villages consists principally of lahars, especially because of the tropical climate in the region. Ash fallout and lava flows represent additional hazards. In addition, the surrounding Quaternary monogenetic field includes more than 300 scoria cones and about 40 explosion craters (mainly maars) that also represent a hazard source. In the present study we constructed hazard maps using field data, orthophotos, spatial analysis, and specialized software (LAHARZ and HAZMAP) to deliminate lahar inundation zones, areas that could potentially be affected by ash fallout (including the evaluation of houses prone to roof collapse due to ash load), and the most susceptible areas for hosting future monogenetic vent formation.     

Morphometric analysis of Colangüil river basin and flash flood hazard,San Juan,Argentina

This work analyzes various morphometric characteristics of the Colangüil river basin in order to evaluate flash flood hazards. Such high-water events pose a risk to the similarly named small village located at the basin’s foot area. For this purpose, the basin is divided into seven sub-basins and some basic measurements (surface, perimeter, basin length, river beds, elevations and slope of the main river bed, and of a number of minor river beds) are calculated. These measurements permit to predict approximately the behavior of the basin in the presence of a series of theoretical rainstorms that may generate unusual runoff volumes that make up such flash floods.     

Qualitative landslide susceptibility assessment by multicriteria analysis: A case study from San Antonio del Sur,Guantánamo,Cuba

Landslide hazard mapping is essential for regional landslide hazard management. The main objective of this study is to construct a rainfall-induced landslide hazard map of Luhe County, China based on an automated machine learning framework (AutoGluon). A total of 2241 landslides were identified from satellite images before and after the rainfall event, and 10 impact factors including elevation, slope, aspect, normalized difference vegetation index (NDVI), topographic wetness index (TWI), lithology, land cover, distance to roads, distance to rivers, and rainfall were selected as indicators. The WeightedEnsemble model, which is an ensemble of 13 basic machine learning models weighted together, was used to output the landslide hazard assessment results. The results indicate that landslides were mainly occurred in the central part of the study area, especially in Hetian and Shanghu. Totally 102.44 s were spent to train all the models, and the ensemble model WeightedEnsemble has an Area Under the Curve (AUC) value of 92.36% in the test set. In addition, 14.95% of the study area was determined to be at very high hazard, with a landslide density of 12.02 per square kilometer. This study serves as a significant reference for the prevention and mitigation of geological hazards and land use planning in Luhe County.     

Approaches for tsunami risk assessment and application to the city of Cádiz, Spain

Tsunamis can represent a significant risk to the population and cause huge economic damage in many costal regions. In order to be able to identify risk hot spots and implement targeted risk reduction measures, decision makers need to have a clear picture of the risk situation in their countries or regions. This work reviews existing approaches for tsunami risk assessment and recommends a five-step process for assessing tsunami risk. As a case study, a qualitative risk assessment for a worst-case tsunami scenario was carried out to understand the tsunami risk to the population in Cádiz. Moreover, a sensitivity analysis of the tsunami hazard input parameters was performed as a strong influence of the variability of the input parameters on the resultant tsunami hazard and risk zonation maps was observed. The study shows that regardless of the assumptions made a non-negligible tsunami risk to Cádiz exists.     

Space–time distribution of ancient and active alluvial karst subsidence: examples from the central Ebro Basin,Spain

Space and time variations of alluvial karst subsidence in the central Ebro Basin are analysed in trenches (paleodolines), aerial photographs (historical dolines) and field surveys (present-day active dolines). The measured subsidence rates, as well as a comparison between densities of paleodolines computed in randomly selected scan-lines and density of active dolines computed in maps, suggest that present-day subsidence in favourable areas is more intense than that of Pleistocene times. According to diachronic maps drawn from (a) different aerial photographs taken after 1946 and (b) field surveys on deformations in urbanized areas, subsidence behaved as a nearly steady process while the whole area was used for agriculture. In contrast, rapid changes (through periods of several tens of years) have occurred in urbanized areas, in which dolines expand their boundaries through small marginal collapses, shifting sharply their sinking centres to neighbouring sites. These rapid changes do not have an equivalent in observed paleodolines.     

Late Quaternary volcanic record from lakes of Michoacán,central Mexico

This paper describes the initial stages of the development of a tephrochronology for the region of the Michoacán–Guanajuato volcanic field (MGVF) in central Mexico. There are two elements to this: the geochemical characterisation of volcanic glass and the linkage of tephra deposits to eruptions of known age. The MGVF is dominated by cinder cones and shield volcanoes which erupt only once. There are only two stratovolcanoes (multiple eruptions) which are common elsewhere in the Trans-Mexican Volcanic Belt. Tephras were sampled from sub-aerial sites close to cones of known age and from lake sediment cores from the Zirahuén, Pátzcuaro and Zacapu basins in the State of Michoacán. Multiple samples were collected to ensure that each tephra was well represented. The glass was analysed by electron microprobe and found to be calc-alkaline in composition. SiO₂ abundances varied from 52% to 75%. Full results are available at http://www.geo.ed.ac.uk/tephra/. The ages of the dated cones ranged from the 20th century AD to ca 17,000 ¹⁴C years BP. Tephras from eruptions of El Jabali (3840 ¹⁴C years BP), Jorullo (1759–1774) and Paricutín (1943–1952) have been identified in lake cores. These provide a means of correlating between basins and have the potential to provide a basis for understanding the volcanic history of this area and for dating a wider range of sediment sequences.     

Landslide susceptibility and hazard assessment in San Ramón Ravine, Santiago de Chile, from an engineering geological approach

Debris flows and soil and rock slides are among the main geological hazards in the mountain foothills of Central Chile. Geological risk associated with the development of landslides, especially debris flows triggered in the basins of ravines that drain into the capital city, Santiago, has increased in time due to accelerated urban expansion. A landslide hazard evaluation in the San Ramón Ravine, located within the foothills of Santiago is presented. Hazard evaluation is based on a methodology that combines the determination of landslide susceptibility calculated by integration of conditioning factors, with the assessment of slope failure and runout probabilities incorporating geotechnical engineering approaches. The methodology is appropriate for medium or subregional scale studies with limited data. The results show that in San Ramón Ravine the landslide hazard consists mainly of debris flows, rock block slides, rock falls and shallow soil slides. Among these, debris flows are the most important due to the urban area that can be affected. Other case studies show that the method can be used in other regions with minor adaptations for territorial planning or for engineering and environmental purposes.     

Reflectance spectroradiometry applied to a semi-quantitative analysis of the mineralogy of the N4ws deposit,Carajás Mineral Province,Pará, Brazil

Quantifying the abundance and physicochemical properties of minerals using reflectance spectroradiometry in the visible, near infrared and shortwave infrared (400–2500 nm) regions is an important tool in mineral exploration. In this study, the reflectance spectra of drill cores from the world-class N4WS iron deposit located in the Carajás Mineral Province, Brazil, were obtained. These spectra were validated using X-ray fluorescence (XRF) geochemical analyses and thin sections. The reflectance spectra were collected using a FieldSpec 3 spectroradiometer (ASD, Boulder, Colorado, USA) in 10 drill cores. The mineralogy of the deposit is mainly hematite, with lesser amounts of magnetite, goethite, quartz, kaolinite, gibbsite, smectite, talc, carbonate and chlorite. The mineralogy of the iron deposit was extracted from the spectral data using the geometry (depth and wavelength) of absorption features across the reflectance spectrum removed from the continuum. The depth of the absorption features is proportional to the mineral abundance, and the wavelength is proportional to the mineral chemical composition. The diagnostic absorption features of each mineral were used to determine the mineral abundance and composition. The final products include the abundance of iron (hydro) oxide (11.6% root-mean-square error [RMSE] Fe₂O₃); abundance of aluminous clays (RMSE 6% Al₂O₃); abundance of talc (8% RMSE MgO); identification of clay type (kaolinite, montmorillonite or gibbsite); composition of carbonate (dolomite vs. calcite); and composition of chlorite (Mg vs. Fe). The mineral abundance and composition results provided an effective characterisation of the ore, protore and host rocks and showed variations within the ore body.     

Insights into petrogenesis of the Jálama pluton (Central Iberian Zone,western Spain)

The Jálama pluton (JP) is a Variscan peraluminous granitoid that intruded into low-grade metasediments from the Central Iberian Zone (CIZ). It comprises a sillimanite-bearing two-mica monzogranite in the inner zone, followed by a tourmaline-bearing two-mica monzogranite, and a marginal tourmaline-muscovite leucogranite in the northern half of the pluton. Microgranitoid enclaves and metasedimentary xenoliths occur locally in monzogranites. The change in rock type from the central monzogranite to the marginal leucogranite corresponds to decreasing TiO₂, MgO, FeO, CaO, Sr, Ba, Zr, and ΣREE, and increasing SiO₂, Na₂O, P₂O₅, Rb, Li, Cs, Ta, Sn, and W. Fe/(Fe+Mg) ratios in biotite, muscovite and tourmaline increase with increasing Fe/(Fe+Mg) in bulk rock, suggesting an important control of the bulk-rock composition on mineral chemistry. The high peraluminosity, the low CaO and high P contents, as well as the similarity of ε(Nd)₃₀₀ values in both the granites and metasediments of the southern CIZ constitute strong evidences for a crustal origin of the granite suite, probably by melting of these metasedimentary rocks. Field and petrographic observations, together with mineralogical and geochemical data, suggest that assimilation and mingling/mixing acted in concert with fractional crystallization during the formation of the JP. These processes may also have been important in the evolution of other granitoids from this region.     

Ancient Forests in European drylands: Holocene palaeoecological record of Mazarrón,south-eastern Spain

This paper presents a new Holocene palaeoecological record from coastal south-eastern Spain, a region characterised by high plant species diversity, varied physiography, high risk of desertification, and a history of human pressure on the landscape that stretches to antiquity. The pollen sequence shows four main vegetation phases: the first characterised by mixed forests of Pinus and evergreen Quercus accompanied by broad-leaved mesophilous trees, and a diversity of Mediterranean scrub; the second phase is characterised by mesophytic decline and expansion of Artemisia; a third, mid-Holocene phase of thermo-mesophytic maxima with prevalence of forested landscapes; and, finally, the progressive opening of the landscape with sparse pines, halo-xerophytic grasslands and sclerophyllous brushwood. The current treeless situation of south-eastern Spain is a relatively recent feature resulting from a dramatic change in the ecological structure of the regional landscapes. This paper stresses the continued vulnerability of these arid systems in the face of a changing climate. This sequence adds to previous palaeobotanical records (pollen and charcoal) and archaeological reports to suggest that deforestation started earlier in low-elevation areas and river basins than in the inland mountains and platforms, a factor that appears in connection to human exploitation of the natural environment.     

Contributions of boron isotopes to understanding the hydrogeochemistry of the coastal detritic aquifer of Castellón Plain,Spain

The Castellón Plain alluvial aquifer, Spain, is intensively exploited to meet the demand for agricultural irrigation and industrial water supply. The geochemistry of its groundwater shows complex salinization in the northern and southern parts of the aquifer, with significant pollution from human origin in the central portion. Boron content and B isotope geochemistry are useful for distinguishing between various sources of pollution and their relative importance in different parts of this aquifer. Boron concentrations in the groundwater vary between 0.01 and 0.85 mg/L. In the more saline groundwaters, found at the northern and southern ends of the study area, the presence of B is linked to inputs from seawater and water with a calcium-magnesium sulphate facies, which feed the aquifer and clearly influence the chemistry of its waters. Evidence of B adsorption processes in some samples is shown by the low B/Cl ratios and the high values of δ¹¹B. In the central portion of the aquifer, the high B/Cl ratios and the strongly negative δ¹¹B are related to pollution of human origin.     

The structure and tectonic evolution of the Aguilón fold-nappe,Sierra Alhamilla,Betic Cordilleras,SE Spain

Detailed structural work in the Sierra Alhamilla, SE Spain, shows that the Aguilón nappe, comprising Triassic and older metasedimentary rocks, is a fold-nappe. The most prominent set of small-scale folds changes from dominantly N-vergent in the upper, right-way-up limb to S-vergent in the greatly thinned lower limb. The nappe closes to the north, and must have been emplaced in this direction. Nappe formation was accompanied by small-scale folding and extensive solution-transfer producing a pronounced differentiated crenulation cleavage. These structures overprint an earlier set of folds and cleavage, and are overprinted in turn by late N-vergent structures. The lower limb of the nappe was thinned and disrupted during continued nappe transport.Pre-Triassic schist in the core of the nappe was affected by medium-grade metamorphism of probable post-Triassic age. The contact with low-grade Permo-Triassic sediments above and below the schist coincides with a distinct change in metamorphic grade. This contact may be a post-metamorphic extensional fault that is now folded around the nappe, which suggests that nappe formation was preceded by extensional faulting. This is consistent with gravity spreading as the driving process for nappe emplacement.