Role of Crystal Interlocking on the Strength of Brittle Rocks

Results of an experimental programme on heterogeneous rock-like specimens of dental plaster confirm the pronounced role of tensile microcracks on brittle failure. Microbuckling of very small rock-columns formed amid closely located tensile cracks was observed as the key incident connecting stable phenomenon of tensile cracking to unstable phenomenon of shearing and subsequent macroscopic failure. Using the classical beam and buckling theories and considering geometry of the problem a new failure criterion is proposed. As a novel attempt, this new failure criterion relates the compressive strength of rock to three basic microstructural properties, i.e. degree of crystal interlocking, average Young modulus and average tensile strength of rock forming minerals.     

The influence of recultivation technique and seed mixture on erosion stability after restoration in mountain environment

Control of erosion, and all of its after effects, from increased surface drainage and erosion to the formation of karst, is one of the essential problems when undertaking recultivation following necessary interventions in the sub-alpine and alpine vegetation stage (high zones). Average slope inclinations of 30–45% in the vicinity of ski runs, and far above in areas of natural erosion and avalanche zones, make restoration processes with sufficient erosion protection the prerequisite for success. Only a sufficient vegetation development of more than 70% ground cover stabilises the topsoil in the long term and reduces soil erosion to an acceptable degree. From 1999 to 2002, an international EU project with the participation of research groups and private firms from Austria, Italy and Germany was carried out under the direction of the Agricultural Research and Education Centre Raumberg-Gumpenstein (AREC) on five different Alpine sites at altitudes from 1,245 to 2,350 m above sea level. The aim of the work was the formulation of practice-relevant requirements for recultivation following intervention in high zones, especially following constructional measures in the vicinity of ski runs and lifts, torrent- and avalanche barriers. In a statistical comparison, the relationship between restoration techniques, seed mixtures of differing ecological value and vegetation cover was observed. The influence of application technique on erosion processes after restoration was obvious for the first two vegetation periods. Only with the additional use of mulch covers could increase surface drainage and noticeable soil loss be avoided. At high altitudes, the choice of seed mixture, irrespective of whether rapid or slow growing and independent of the extent of accompanying fertilisation, had no significance in the first two vegetation periods following sowing. In the following growing seasons, however, higher cover values were obtained with site-specific seed mixtures at three of the five experimental sites. While few species of the commercial seed mixture showed satisfactory persistency, most of the grasses and in particular the alpine leguminosae of site-specific seed mixtures increased their share during the observation period. In the long-term, sufficient protection against erosion is only guaranteed by the use of stable, enduring and ecologically adapted species.     

Image analysis applied to quantitative evaluation of chromatic impact generated by open-pit quarries and mines

One of the most important environmental impacts resulting from opencast mining, and especially quarries, is the visual impact. Evaluation of this impact considers two aspects: first, the area occupied by the quarry as seen by an observer from a specific place, and, second, the chromatic contrast existing between landscape and exploitation. In this study we develop a methodology to assess the chromatic impact in an objective and comparable form. To assess this impact we developed a method based on image analysis that allows us to obtain from a picture or image its equivalent as a function of chromatic impact, according to the sensibility of the human eye to different wavelengths. The methodology was applied to the Martinenca limestone quarry (Alcanar, Tarragona) and to Cerro Kori Kollo mine, La Joya district (Bolivia).     

Double trouble: subsidence and CO<Subscript>2</Subscript> respiration due to 1,000 years of Dutch coastal peatlands cultivation

Coastal plains are amongst the most densely populated areas in the world. Many coastal peatlands are drained to create arable land. This is not without consequences; physical compaction of peat and its degradation by oxidation lead to subsidence, and oxidation also leads to emissions of carbon dioxide (CO₂). This study complements existing studies by quantifying total land subsidence and associated CO₂ respiration over the past millennium in the Dutch coastal peatlands, to gain insight into the consequences of cultivating coastal peatlands over longer timescales. Results show that the peat volume loss was 19.8 km³, which lowered the Dutch coastal plain by 1.9 m on average, bringing most of it below sea level. At least 66 % of the volume reduction is the result of drainage, and 34 % was caused by the excavation and subsequent combustion of peat. The associated CO₂ respiration is equivalent to a global atmospheric CO₂ concentration increase of ~0.39 ppmv. Cultivation of coastal peatlands can turn a carbon sink into a carbon source. If the path taken by the Dutch would be followed worldwide, there will be double trouble: globally significant carbon emissions and increased flood risk in a globally important human habitat. The effects would be larger than the historic ones because most of the cumulative Dutch subsidence and peat loss was accomplished with much less efficient techniques than those available now.     

The August 27, 2014, rock avalanche and related impulse water waves in Fuquan,Guizhou, China

At about 8:30 p.m. on 27 August 2014, a catastrophic rock avalanche suddenly occurred in Fuquan, Yunnan, southwestern China. This landslide and related impulse water waves destroyed two villages and killed 23 persons. The impulse waves occurred after initiation of the landslide, caused by the main part of the slide mass rapidly plunging into a water-filled quarry below the source area. The wave, comprising muddy water and rock debris, impacted the opposite slope of the quarry on the western side of the runout path and washed away three homes in Xinwan village. Part of the displaced material traveled a horizontal distance of about 40 m from its source and destroyed the village of Xiaoba. To provide information for potential landslide hazard zonation in this area, a combined landslide–wave simulation was undertaken. A dynamic landslide analysis (DAN-W) model is used to simulate the landslide propagation before entering the quarry, while Fluent (Ansys Inc., USA) is used to simulate the impulse wave generation and propagation. Output data from the DAN-W simulation are used as input parameters for wave modeling, and there is good agreement between the observed and simulated results of the landslide propagation. Notably, the locations affected by recordable waves according to the simulation correspond to those recorded by field investigation.     

Geochemical evaluation of Niger Delta sedimentary organic rocks: a new insight

A geochemical evaluation of Niger Delta organic matter was carried out using supercritical fluid extraction (SFE) sample preparation procedure. Comparison of geochemical significance of gas chromatographic data of rock extracts of SFE with those of Soxhlet extraction method from previous studies was made in order to establish the usefulness of SFE in geochemical exploration. The assessment of geochemical character of the rock samples from the comparison and interpretation of other geochemical parameters were used to give more insights into understanding the source rocks characteristics of onshore and shelf portions of the Niger Delta Basin. The results of the gas chromatographic (GC) analysis of the rock extracts across the lithostratigraphic units show that Pr/Ph, Pr/nC₁₇, Pr/nC₁₈, CPI and odd/even preference ranged from 0.07 to 12.39, 0.04 to 6.66, 0.05 to 13.80, 0.12 to 8.4 and 0.06 to 8.12, respectively. The Rock-Eval pyrolysis data and geochemical ratios and parameters calculated from the GC data showed that most of the samples are mature and have strong terrestrial provenance while a few samples have strong marine provenance. The few marine source rocks are located in the deeper depth horizon. Pr/Ph and standard geochemical plots indicate that most of samples were derived from organic matter deposited in less reducing conditions, i.e. more of oxidizing conditions while a few samples have predominantly influence of reducing conditions. The results of trace metal analysis of older samples from Agbada Formation also indicate marine and mixed organic matter input deposited in less reducing conditions. The results obtained in this study are comparable with those obtained from previous studies when Soxhlet extraction method was used and also indicated the presence of more than one petroleum systems in the Niger Delta.     

Late Quaternary changes in surface productivity and oxygen minimum zone (OMZ) in the northwestern Arabian Sea: Micropaleontologic and sedimentary record at ODP site 728A

Changes in the abundance of selected planktic foraminiferal species and some sedimentological parameters at ODP site 728A were examined to understand the fluctuations in the surface productivity and deep sea oxygenation in the NW Arabian Sea during last ∼540 kyr. The increased relative abundances of high fertility taxa, i.e., Globigerinita glutinata and Globigerina bulloides mainly during interglacial intervals indicate intense upwelling. Strong SW summer monsoon probably increased the upwelling in the western Arabian Sea during interglacial intervals and caused high surface productivities due to the lateral transport of eutrophic waters. Most of the glacial periods (i.e., MIS 2, 4, 6, 8 and 12) are characterized by higher relative abundances of Neogloboquadrina pachyderma and Neogloboquadrina dutertrei associated with Globigerinoides ruber. The more stratified condition and deep mixed layer due to increased NE winter monsoon are mainly responsible for the higher relative abundances of N. pachyderma during glacial periods. Some of the glacial intervals (i.e., MIS 6 and 8) are also characterized by pteropod spikes reflecting deepening of aragonite compensation depth (ACD) and relatively less intense oxygen minimum zone (OMZ) in this region due to deep sea mixing and thermocline ventilation, and relatively less intense surface productivity during winter monsoon. The interglacial periods are largely devoid of pteropod shells indicating more aragonite dissolution due to increased intensity of OMZ in the northwestern Arabian Sea.     

Recent plumbing system of the Krakatau volcano revealed by teleseismic earthquake distribution

Spatial and temporal analysis of global seismological data 1964–2005 reveals a distinct teleseismic earthquake activity producing a columnar-like formation in the continental wedge between the Krakatau volcano at the surface and the subducting slab of the Indo-Australian plate. These earthquakes occur continuously in time, are in the body-wave (m _b) magnitude range 4.5–5.3 and in the depth range 1–100 km. The Krakatau earthquake cluster is vertical and elongated in the azimuth N30°E, suggesting existence of a deep-rooted fault zone cutting the Sunda Strait in the SSW-NNE direction. Possible continuation of the fault zone in the SW direction was activated by an intensive 2002/2003 aftershock sequence, elongated in the azimuth of N55°E. Beneath the Krakatau earthquake cluster, an aseismic gap exists in the Wadati-Benioff zone of the subducting plate at the depths 100–120 km. We interpret this aseismic gap as a consequence of partial melting inhibiting stress concentration necessary to generate stronger earthquakes, whereas the numerous earthquakes observed in the overlying lithospheric wedge beneath the volcano probably reflect magma ascent in the recent plumbing system of the Krakatau volcano. Focal depth of the deepest events (~100 km) of the Krakatau cluster constrains the location of the primary magma generation to greater depths. The ascending magmatic fluids stress fault segments within the Sunda Strait fault zone and change their friction parameters inducing the observed tectonic earthquakes beneath Krakatau.     

Groundwater nitrate vulnerability assessment in alluvial aquifer using process-based models and weights-of-evidence method: Lower Savinja Valley case study (Slovenia)

This paper describes the implementation of process-based models reflecting relative groundwater nitrate vulnerability of the shallow alluvial Lower Savinja Valley (LSV) aquifer in Slovenia. A spatially explicit identification of the potentially vulnerable priority areas within groundwater bodies at risk from a chemical point of view is being required for cost-effective measures and monitoring planning. The shallow LSV unconfined aquifer system consists of high-permeable Holocene and middle- to low-permeable Pleistocene gravel and sand, with a maximum thickness of about 30 m, mainly covered by shallow eutric fluvisoils or variously deep eutric cambisoil. The hydrogeological parameters, e.g. the depth to the groundwater, hydrological role of the topographic slope, etc. usually used in different point count schemes are, in the case of the lowland aquifer and shallow groundwater, spatially very uniform with low variability. Furthermore, the parametric point count methods are generally not able to illustrate and analyze important physical processes, and validation of the results is difficult and expensive. Instead of a parametric point count scheme, we experimentally used the Arc-WofE extension for weights-of-evidence (WofE) modelling. All measurement locations with a concentration higher than the value of 20 mg NO₃ ⁻ per litre of groundwater have been considered as training points (173), and the three process-based models generalized output layers of groundwater recharge (GROWA), nitrate leached from the soil profile (SWAT) and groundwater flow velocity (FEFLOW), served as evidential themes. The technique is based on the Bayesian idea of phenomena occurrences probability before (prior probability) and after consideration of any evidential themes (posterior probability), which were measured by positive and negative weights as an indication of the association between a phenomena and a prediction pattern. The response theme values describe the relative probability that a 100 × 100 m spatial unit will have a groundwater nitrate concentration higher than the training points’ limit values with regard to prior probability value. The lowest probability of groundwater nitrate occurrence is in the parts of the LSV aquifer, which are known as anoxic condition areas with very likely denitrification processes. The cross-validation of the dissolved oxygen and dissolved nitrate response theme confirmed the accuracy of the groundwater nitrate prediction. The WofE model results very clearly indicate regional groundwater nitrate distribution and enable spatial prediction of the probability for increased groundwater nitrate concentration in order to plan the groundwater nitrate reduction measures and optimize the programme for monitoring the effects of these measures.