ABSTRACTIn the European Alps, high mountain environments are subject to major impacts resulting from climate change, which strongly affect human activities such as mountaineering. The purpose of the study was to examine changes in access routes to 30 high mountain huts in the Western Alps since the 1990s. Data were derived from the use of two different methods, geo-historical studies and a questionnaire, and were used to identify both the climate-related processes affecting the climbing routes and the strategies implemented by public entities, Alpine clubs, guide companies, and hut keepers to maintain acceptable safety and technical conditions. The case studies revealed issues affecting three access routes and the results from the questionnaire showed that the main processes affecting access routes were loss of ice thickness and retreat from the front of the glaciated areas. Commonly, in situ equipment was installed to facilitate access for mountaineers and/or a part of a route was relocated to a safer area. The authors conclude that in most cases, the measures were effective but they were limited by financial, ethical and legal issues, especially in protected or classified areas that could jeopardise their durability and effectiveness. 相似文献
Recently, the interest in PS-converted waves has increased for several applications, such as sub-basalt layer imaging, impedance estimates and amplitude-versus-offset analysis. In this study, we consider the problem of separation of PP- and PS-waves from pre-stacked multicomponent seismic data in two-dimensional isotropic medium. We aim to demonstrate that the finite-offset common-reflection-surface traveltime approximation is a good alternative for separating PP- and PS-converted waves in common-offset and common shot configurations by considering a two-dimensional isotropic medium. The five parameters of the finite-offset common-reflection-surface are firstly estimated through the inversion methodology called very fast simulated annealing, which estimates all parameters simultaneously. Next, the emergence angle, one of the inverted parameters, is used to build an analytical separation function of PP and PS reflection separation based on the wave polarization equations. Once the PP- and PS-converted waves were separated, the sections are stacked to increase the signal-to-noise ratio using the special curves derived from finite-offset common-reflection-surface approximation. We applied this methodology to a synthetic dataset from simple-layered to complex-structured media. The numerical results showed that the inverted parameters of the finite offset common-reflection-surface and the separation function yield good results for separating PP- and PS-converted waves in noisy common-offset and common shot gathers. 相似文献
We advance a principle directed to assigning numerical values to free parameters usually present in inversion methods. It may be formulated as: ‘Optimum estimates of free parameters in an inversion procedure must lead, in tests using synthetic data, to solutions whose geometrical expression reflects the main qualitative or semiquantitative geological characteristic of the study area.’ To this end, the interpreter should (i) specify a typical anomalous source geometry which incorporates the most relevant geological information for the study area, (ii) compute the corresponding gravity anomaly and (iii) invert the anomaly for the source geometry finding the numerical values of the free parameters that lead to a solution closest to the typical source. Application of the above methodology to synthetic and real data from the basement relief of a rift basin has asserted its efficacy. 相似文献
The volcanic rocks of the Colíder and Roosevelt formations are extensively exposed in the south-central portion of the Amazonian Craton where effusive and pyroclastic rocks have been mapped. Both units, topped by chemical sediments and oceanic facies as rhyolite and andesite lavas, rhyodacite, and porphyritic dacite, with frequent intercalations of pyroclastic and epiclastic deposits. Whole-rock geochemistry for 55 samples of rhyolitic to andesitic composition suggests the involvement of fertile mantle-derived components with E-MORB to OIB compositions. The analyzed rocks display calc-alkaline to shoshonitic affinity consistent with generation related to an active continental margin. The whole-rock Sm-Nd isotope data from selected felsic volcanic rocks of the Colíder and Roosevelt formations yield negative initial εNd values between –3 and –9, indicating the predominantly crustal nature of the parental magmas with early Archean to late Paleoproterozoic (ca. 2.5–2.0 Ga) depleted mantle model ages.
This paper presents a fundamental study on the effect of the relative humidity on the rockfill crushing strength. This aspect plays an important role in the mechanical behaviour of rockfill, and it is known that certain characteristics of the granular materials, such as compressibility and shear strength, depend on the confining stress, which is a function of the particles crushing. An increased interest has been observed regarding the effect of the relative humidity in the mechanical behaviour of rockfill. Unfortunately, limited research has been conducted until now regarding the study of individual particle crushing. Therefore, this paper thoroughly investigated particle crushing, by performing single-particle crushing tests on rockfill particles divided into four size ranges, under different relative humidity conditions. The experimental results reveal a considerable influence of the relative humidity in the studied rockfill particles, whose strength of the particles with the greatest dimensions in saturated conditions was reduced by half. Consistent macro-mechanical evidence demonstrates that particle’s size and relative humidity conditions depict the most important factors that influence particle crushing strength.
River flow variability is known to influence estuarine production, yet knowledge on its effect upon estuarine food webs dynamics
is still scarce. Stable carbon and nitrogen isotopes were used to assess the effect of river flow in the connectivity and
food web interactions between the two main fish nursery areas of the Tagus estuary. The aims of the present work were to investigate
the seasonal variation in food web structure and the exchange rate of individuals of marine juvenile fish among estuarine
nurseries, to compare the spring of a rainy year (2001) with that of an average year (2000), and to investigate the impact
of the winter floods of 2001. A low level of connectivity was observed for the fish species that use these areas as nurseries.
In low river flow conditions, two isotopically distinct food webs were established in each nursery area. These food webs were
very sensitive to small variations in the freshwater input. Winter floods seem to disrupt the localized food webs that are
established in low river flow periods, leading to the re-establishment of a wider food web. While in rainy years this wide
food web is maintained until spring, in average years the food web undergoes fragmentation into two localized and isotopically
distinctive food webs. The increase in frequency of droughts due to climate change should lower the connectivity of the estuarine
fish nurseries food webs, causing habitat fragmentation and consequent loss in complexity and resilience. 相似文献
The Ferraria thermal water emerges at the sea level in the Ferraria lava delta (western edge of S. Miguel Island, Azores)
with temperature of ca. 60°C and pH varying between 5.4 and 6.2. It is of sodium chloride type, resulting from ca. 50% seawater
mixing with an acid brackish, at ≈100°C, denoting the presence of significant CO2(g) and the progress of water–rock interactions in open system conditions. The thermal Na–Cl water is strongly enriched with
Sr and Mn and, comparatively, has low concentrations in Al, Fe and As. These elements are removed from the solution as critical
conditions for the formation of several neo-formed mineral phases are gradually attained. Thermodynamic equilibrium calculations
are consistent with this interpretation, showing that the thermal fluid can precipitate Fe3+-(hydr-)oxides, kaolinite and non-crystalline silica. Wells logging show fracture planes and pores fully/partly filled up
with polyphase botryoidal aggregates mostly composed of goethite + ferrihydrite and displaying variable adsorbed contents
of Si, P and As. These neo-formed phases result from the pristine fluid oxidation due to seawater mixing; its precipitation
is easily affected by pH and redox variations of the brackish, due to volcanic gases pressure alterations, and fluid pressure
or flow-velocity oscillation in the fractured aquifer. 相似文献
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. 相似文献