Sandstone alterations triggered by fire-related temperatures

The aim of the study was to identify and describe changes in two different sandstone types when undergoing different environmental and extreme temperature regimes to assess the possibility of finding insolation weathering and how these sandstones would behave during and after a fire. The first step was the simulation in the laboratory of temperature regimes up to 60 °C which would correspond to extreme events that could be found in insolation cycles even in Central Europe and the second one was the temperature above 200 °C simulating in laboratory conditions the thermal regime of a potential fire situation at temperatures up to 200, 400, 600 and 800 °C. Heating the samples above 400 °C led to gradual changes in mineral composition, colour, surface roughness and physical properties reaching, eventually, total rock breakdown through spalling and granular disaggregation. The different behaviour of sandstones exposed to high temperatures is mainly caused by their different mineral composition with various ratios of minerals that are more or less chemically stable at high temperatures as well as by the differences in the porosity.     

Hybrid Model for Urban Air Pollution Forecasting: A Stochastic Spatio-Temporal Approach

Air pollution is usually driven by a complex combination of factors in which meteorology, physical obstacles, and interactions between pollutants play significant roles. Considering the characteristics of urban atmospheric pollution and its consequent impacts on human health and quality of life, forecasting models have emerged as an effective tool to identify and forecast air pollution episodes. The overall objective of the present work is to produce forecasts of pollutant concentrations with high spatio-temporal resolution and to quantify the uncertainty in those forecasts. Therefore, a new approach was developed based on a two-step methodology. Firstly, neural network models were used to generate short-term temporal forecasts based on air pollution and meteorology data. The accuracy of those forecasts was then evaluated against an independent set of historical data. Secondly, local conditional distributions of the observed values with respect to the predicted values were used to perform spatial stochastic simulations for the entire geographic area of interest. With this approach the spatio-temporal dispersion of a pollutant can be predicted, while accounting for both the temporal uncertainty in the forecast (reflecting the neural networks efficiency at each monitoring station) and the spatial uncertainty as revealed by the spatial variograms. Based on an analysis of the results, our proposed method offers a highly promising alternative for the characterization of urban air quality.     

Detection and mapping of burnt areas from time series of MODIS-derived NDVI data in a Mediterranean region

Moderate resolution remote sensing data, as provided by MODIS, can be used to detect and map active or past wildfires from daily records of suitable combinations of reflectance bands. The objective of the present work was to develop and test simple algorithms and variations for automatic or semiautomatic detection of burnt areas from time series data of MODIS biweekly vegetation indices for a Mediterranean region. MODIS-derived NDVI 250m time series data for the Valencia region, East Spain, were subjected to a two-step process for the detection of candidate burnt areas, and the results compared with available fire event records from the Valencia Regional Government. For each pixel and date in the data series, a model was fitted to both the previous and posterior time series data. Combining drops between two consecutive points and 1-year average drops, we used discrepancies or jumps between the pre and post models to identify seed pixels, and then delimitated fire scars for each potential wildfire using an extension algorithm from the seed pixels. The resulting maps of the detected burnt areas showed a very good agreement with the perimeters registered in the database of fire records used as reference. Overall accuracies and indices of agreement were very high, and omission and commission errors were similar or lower than in previous studies that used automatic or semiautomatic fire scar detection based on remote sensing. This supports the effectiveness of the method for detecting and mapping burnt areas in the Mediterranean region.     

Monitoring of heat transmission from buildings into geological environment and evaluation of soil deformation consequences in foundation engineering

In engineering geology a number of factors affecting foundation conditions are taken into consideration during engineering-geological investigations. This article deals with the factor of heat sourced from a structure (brick kiln) as a restrictive factor in foundation engineering in clay soils and introduces a documentation of soil deformation observations as an impact of the heat transmission into the geological environment. It was carried out in Southern Moravia in the Czech Republic, where the dominant foundation soils are Neogeneous clays where differential settlements of a tunnel kiln structure occurred as a result of ignoring the boundary conditions of temperature changes in the soil environment. The brick kilns caused heterogeneous spatial changes in the subsoil temperatures. This consequently resulted in differential settlements due to temperature changes originating from the kilns. The differential settlements reached as much as 150 mm. The major objective of the article is to highlight the importance of the heat transmission from buildings into the geological environment as a factor which should be considered in engineering geology and its application in planning. A new procedure for reducing or elimination of ground movements sourced from underlying clayey soils depending on the heat changes was also suggested in this context.     

Evolution in sea ice from 1978 to 2012

In this paper, the intra-annual and interannual variability of the sea ice is analysed over the period 1979–2012 from the data and images facilitated by the “National Snow and Ice dates Center”. These data are related to the annual average temperature. The annual average of the marine ice surface area (1979–2012) is very similar in both poles, although its temporary evolution is opposed in both hemispheres. In the Arctic Ocean there is an abrupt reduction of the surface area of the ice during this period. As opposed to it, the marine seas surrounding the Antarctic show an increase of the extension of the ice, especially in the last 15 years, with a maximum value in 2012. With respect to the total of the marine ice over the period 1979–2012, there is an overall deficit balance, because the reduction of the Arctic ice is greater than the increase of the Antarctic ice.     

3D alluvial aquifer reconstruction in polluted areas by means of GPR (Sabiñánigo,N Spain)

Assumptions of simple geometries for alluvial deposits (related to main rivers) can preclude determination of complexities that are revealed as fundamental controls in underground flow. Although subhorizontal contacts between alluvial and substratum materials are expected, previous sedimentary or erosional processes can result in irregular geometries, only accessible through detailed analysis. The studied case presents the 3D reconstruction of a Quaternary terrace in the proximities of Sabiñánigo (Southern Pyrenees, Northeastern Spain), lying on homogeneous Eocene marls. The studied area is located in an industrialized area supporting strongly pollutant chemical industry (chlorinated pesticides) for the past 50 years. The objective of the study was to constrain the groundwater pathway along the area to subsequently analyze leakage of chemicals to the water table. In order to reveal preferred flow paths, a detailed characterization of the internal structure of the alluvial deposits (0.5–13 m thick) and their relations with the Tertiary substratum was carried out by means of ground penetrating radar (GPR, 50 and 100 MHz antennas). The obtained models permit identifying several topographic highs in the alluvial/substratum contact, determining preferred pathways in water flow, favoring particular conditions associated with low levels of the water table. The presented results support the interest of application of GPR surveys in order to characterize the groundwater pathways in expected homogeneous areas and their importance in order to establish the contaminant surveillance network.     

GIS application for regional assessment of seismically induced slope failures in the Sierra Nevada Range,South Spain,along the Padul Fault

Complete rupture of the Padul Fault represents one of the largest plausible earthquakes in the Sierra Nevada Range, one of the most seismically active regions of Spain. We performed a regional assessment of earthquake-triggered slope instabilities in the western part of the range to determine the most likely types of failures from such an earthquake in the region and suggest where such failures have a higher likelihood of occurring. These results are broadly useful for management of regional life-lines and future development. First, a slope-instability inventory of the Sierra Nevada was produced to identify the most common instability types. Subsequently, the Newmark’s sliding rigid-block methodology, implemented in a geographic information system, was used to obtain the distribution of Newmark displacements in the area considering a M _w 6.6 earthquake on the Padul Fault. The Newmark displacements were then compared to the distribution of the inventoried slope instabilities to identify the areas where seismicity could reactivate old slope instabilities or generate new ones, and to identify the involved landslide typology. The most likely seismically induced slope instabilities in the Sierra Nevada are rock falls and rock slides. These types of instabilities could be triggered by Newmark displacements of 2 cm or less.     

A software solution for point counting. Petrographic thin section analysis as a case study

In the field of geology, as in many other fields, a common problem is the analysis of 2D sections. An example of this is the petrographic study of rock samples, i.e., the quantification of its mineral components and the percentages of each phase present in it. Conventionally, this quantification has been determined by point counting performed on thin sections. Although point counting is very time consuming, it is of common use in several domains including geology, biology, medicine, and materials sciences, among others. Point counting in thin sections is normally conducted through mechanical or electromechanical devices attached to a microscope; such devices are very expensive, offer limited functionality, and are very time consuming. In this contribution, we introduce an interactive visualization application called Rock.AR that reduces the amount of time required to apply this technique and simplify its work flow. It provides visual tools like distortion techniques, overview + detail, and statistics to assist the technique. A comparison between this application and similar tools through users' experiences is provided. We compare the time it takes to complete a session of point counting and the tools' usability.     

Behaviour of radiogenic Pb in zircon during ultrahigh-temperature metamorphism: an ion imaging and ion tomography case study from the Kerala Khondalite Belt,southern India

Zircon crystals from a locally charnockitized Paleoproterozoic high-K metagranite from the Kerala Khondalite Belt (KKB) of southern India have been investigated by high-spatial resolution secondary ion mass spectrometry analysis of U–Th–Pb and rare earth elements (REE), together with scanning ion imaging and scanning ion tomography (depth-profiled ion imaging). The spot analyses constrain the magmatic crystallization age of the metagranite to ca. 1,850 Ma, with ultrahigh-temperature (UHT) metamorphism occurring at ca. 570 Ma and superimposed charnockite formation at ca. 520–510 Ma, while the ion imaging reveals a patchy distribution of radiogenic Pb throughout the zircon cores. Middle- to heavy-REE depletion in ca. 570 Ma zircon rims suggests that these grew in equilibrium with garnet and therefore date the UHT metamorphism in the KKB. The maximum apparent ²⁰⁷Pb/²⁰⁶Pb age obtained from the unsupported radiogenic Pb concentrations is also consistent with formation of the Pb patches during this event. The superimposed charnockitization event appears to have caused additional Pb-loss in the cores and recrystallization of the rims. The results of depth-profiling of the scanning ion tomography image stack show that the Pb-rich domains range in size from <5 nm to several 10 nm (diameter if assumed to be spherical). The occurrence of such patchy Pb has previously been documented only from UHT metamorphic zircon, where it likely results from annealing of radiation-damaged zircon. The formation of a discrete, heterogeneously distributed and subsequently immobile Pb phase effectively arrests the normal Pb-loss process seen at lower grades of metamorphism.     

Significance of ancient sulfide PGE and Re–Os signatures in the mantle beneath Calatrava,Central Spain

Spinel lherzolite and wehrlite xenoliths from the Cenozoic Calatrava volcanic field carry the geochemical imprint of metasomatic agents that have affected the subcontinental lithospheric mantle beneath Central Iberia. Some xenoliths (mainly wehrlites) were enriched in REE, Sr, P, and CO₂ by silicic-carbonate-rich metasomatic melts/fluids, while others record the effects of subduction-related hydrous silicate fluids that have precipitated amphibole and induced high Ti/Eu in primary clinopyroxene. The petrographic observations and geochemical data suggest that interstitial glass in the xenoliths represent the quenched products of Si-rich melts that infiltrated the mantle peridotite shortly before the entrainment of the xenoliths in the host magmas that erupted ca 2 million years ago. During their infiltration, the metasomatic melts reacted with peridotite, resulting in silica enrichment, while remobilizing grains of iron-rich monosulfide solid solution (Fe-rich Mss) initially enclosed in, or intergranular to, primary olivine and pyroxenes. In situ laser ablation inductively coupled plasma-mass spectrometry analysis of single sulfide grains reveals that the Fe-rich Mss in glass shows platinum-group element (PGE) patterns and ¹⁸⁷Os/¹⁸⁸Os compositions identical to the Fe-rich Mss occurring as inclusions in, or at grain boundaries of primary silicates. Moreover, independent of its microstructural position, Fe-rich Mss exhibits PGE and ¹⁸⁷Os/¹⁸⁸Os signatures typical of Mss either residual after partial melting or crystallized directly from sulfide melts. Our findings reveal that young metasomatic melt(s)/fluid(s) may carry remobilized sulfides with PGE and Os-isotopic signatures identical to those of texturally older sulfides in the peridotite xenolith. These sulfides thus still provide useful information about the timing and nature of older magmatic events in the subcontinental mantle.