Groundwater isoscapes in a montane headwater catchment show dominance of well‐mixed storage

We conducted an integrated groundwater–surface water monitoring programme in a 3.2‐km² experimental catchment in the Scottish Highlands by sampling all springs, seepages, and wells in six, spatially extensive synoptic surveys over a 2‐year period. The catchment has been glaciated, with steep hillslopes and a flat valley bottom. There is around 70% glacial drift cover in lower areas. The solid geology, which outcrops at higher elevations, is granite and metamorphic schist. The springs and seepages generally occur at the contact between the solid geology and drift or at breaks of slopes in the valley bottom. Samples were analysed for stable isotopes, Gran alkalinity and electrical conductivity. Despite the surveys encompassing markedly different antecedent conditions, the isotopic composition of groundwater at each location exhibited limited temporal variability, resulting in a remarkable persistence of spatial patterns indicating well‐mixed shallow, groundwater stores. Moreover, line‐conditioned excess values derived from the isotope data indicated no evidence of fractionation affecting the groundwater, which suggests that most recharge occurs in winter. The alkalinity and electrical conductivity of groundwater reflected geological differences in the catchment, being highest where more weatherable calcareous rocks outcrop at higher altitudes in the catchment. Springs draining these areas also had the most variable isotope composition, which indicated that they have shorter residence times than the drift covered part of the catchment. The study showed that even in geologically heterogeneous upland catchments, groundwater can be characterized by a consistent isotopic composition, reflecting rapid mixing in the recharge zone. Our work, thus, emphasizes the critical role of groundwater in upland catchments and provides tracer data that can help constrain quantitative groundwater models.     

Characterisation of deformation and flow mechanics around porphyroclasts in a calcite marble ultramylonite by means of EBSD analysis

This paper studies the flow heterogeneity around porphyroclasts associated with greenschist facies deformation of a calcite marble shear zone. Microstructural data from electron backscatter diffraction analyses (EBSD) are used to constrain the flow mechanics of this dominantly non-coaxial type of deformation. The microstructure of the undisturbed ultramylonite (grain-size range 5–100 μm, mean 40 μm) is interpreted to represent steady-state (time-independent) flow conditions with flow planes parallel to the shear zone boundary. Single calcite porphyroclasts (grain-size 1–3 mm) caused flow perturbation in the fine-grained marble ultramylonite. It is the shape, in particular, of these rigid porphyroclasts that controls their rotational behaviour during deformation and, therefore, the development of specific flow fabrics. The flow planes around elongated-rhomboidal, stable porphyroclasts change the orientation to become roughly parallel to the porphyroclast margin, whereas the geometry of flow planes around nearly equant, rotating porphyroclasts describes a δ-type flow pattern. We infer that to some extent decoupling at the clast–matrix interface has occurred to guarantee a stable orientation of elongated porphyroclasts, but was not sufficient to reduce the rotation rate of equant clasts to zero. According to the flow deflection, the general crystallographic preferred orientation (CPO) with its single c-axis maximum perpendicular to the flow plane is rotated about an axis which is (sub)parallel to the kinematic rotation axis of the shear zone. Ultramylonite microstructures, CPOs and misorientation data are best explained by the dual operation of grain-size-insensitive (dislocation creep with recovery and recrystallization) and grain-size-sensitive (diffusion creep) mechanisms. The limited grain-size reduction around porphyroclasts suggests that the grain-size-insensitive mechanisms controlled rheology.     

Modelling transport dynamics of contaminated sediments in the headwater of a hydropower plant at the Upper Rhine River

Sediments are an essential habitat compartment in rivers, which is a subject to dynamic transport processes. In many rivers, the fine deposited sediments are contaminated with heavy metals and organic compounds. Contaminated deposits are considered as potential hot spots because of the risk of the mobilization under erosive hydraulic conditions. Numerical models for particulate contaminant transport are then necessary and can be applied to estimate and predict the potential impact of mobilized contaminants as an important contribution to sediment management. This paper focuses on the quantification of the amount of contaminated sediments resuspended during the extreme flood event in 1999 and the prediction of deposition one year after the flood event. To assess such erosive flood event, a 2D numerical transport model was developed to analyse the dynamics of erosion and sedimentation processes in the headwater of a cross dam at the Upper Rhine River. The dam consists of a weir, a hydropower plant, and a navigation lock. As the weir is operating only for flood management, a huge amount of sediment highly contaminated with the hexachlorobenzene (HCB) was deposited in the weir zone. Therefore, numerical simulations were performed to determine the spatial and temporal distribution of deposited contaminated sediments as depending on the river discharge and its distribution to the hydraulic structures. The numerical investigation presented here is taken as a retrospective analysis of the contaminated sediment dynamics in the headwater to improve future sediment management.     

Satellite imaging coral reef resilience at regional scale. A case-study from Saudi Arabia

We propose a framework for spatially estimating a proxy for coral reef resilience using remote sensing. Data spanning large areas of coral reef habitat were obtained using the commercial QuickBird satellite, and freely available imagery (NASA, Google Earth). Principles of coral reef ecology, field observation, and remote observations, were combined to devise mapped indices. These capture important and accessible components of coral reef resilience. Indices are divided between factors known to stress corals, and factors incorporating properties of the reef landscape that resist stress or promote coral growth. The first-basis for a remote sensed resilience index (RSRI), an estimate of expected reef resilience, is proposed. Developed for the Red Sea, the framework of our analysis is flexible and with minimal adaptation, could be extended to other reef regions. We aim to stimulate discussion as to use of remote sensing to do more than simply deliver habitat maps of coral reefs.     

Die Reaktion 2 Zoisit+1 CO2 ⇌ 3 Anorthit+1 Calcit+1 H2O

The equilibrium conditions of the following reaction 2 zoisite +1 CO₂?3 anorthite+1 calcite+1 H₂O 2 Ca₂Al₃[O/OH/SiO₄/Si₂O₇]+1 CO₂?3 CaAl₂Si₂O₈+1 CaCO₃+1 H₂O have been determined experimentally at total pressures of P _j= 2000 bars, P _f =5000 bars, and P _f =7000 bars. Owing to the vertical position of the equilibrium curves in isobaric T- \(X_{{\text{CO}}_{\text{2}} }\) diagrams, the composition of the binary H₂O-CO₂ fluid phase coexisting with zoisite is independent of temperature in the temperature interval investigated. According to our experiments, orthorhombic zoisite is only stable in equilibrium with a fluid phase at a concentration of CO₂ which is less than, respectively, ca. 2 Mol% CO₂ at P _f =2000 bars, ea. 6 Mol% at P _f =5000 bars, and ca. 10 Mol% at P _f =7000 bars. Thus, the fluid phase coexisting with zoisite is rich in H₂O. While this is independent of temperature the experimental data demonstrate that the influence of pressure cannot be neglected: With increasing pressure the concentration of CO₂ of the fluid phase coexisting with zoisite can rise a little. The position of the reaction studied, which is independent of temperature and exhibits small values of \(X_{{\text{CO}}_{\text{2}} }\) ,leads to two important petrogenetic conclusions:

1. The occurrence of zoisite is an indicator for a CO₂-poor and H₂O-rich fluid composition during metamorphism of marly calcsilicates.
2. If the concentration of CO₂ of the fluid phase coexisting with zoisite exceeds the equilibrium value of \(X_{{\text{CO}}_{\text{2}} }\) calcite+anorthite+H₂O is formed from zoisite+CO₂. Thus, a considerable increase in the anorthite-content of plagioelase is possible.

     

Combining field and modelling techniques to assess rockfall dynamics on a protection forest hillslope in the European Alps

Adequate management of a mountain forest that protects downslope areas against impacts of rockfall requires insight into the dynamics of the hillslope environment. Therefore, we applied a combined approach, using field and modelling techniques, to assess the determining factors for rockfall source areas, rockfall tracks and rockfall runout zones on a forested slope in mountainous terrain. The first objective of this study was to understand why rockfall occurs in the study area. The second objective was to translate the knowledge obtained in the field into a model that simulates rockfall dynamics on a forested slope realistically. The third objective was to assess which hillslope characteristics primarily determine the distribution of active rockfall tracks. To achieve these objectives, we made a geomorphological map of the whole study area, and we measured the major discontinuity planes in the bedrock that are exposed in the rockfall source areas. Furthermore, a test site for simulation modelling within the larger study area was defined in which both a forest and a hillslope inventory were carried out. The available data and our developed rockfall simulation model allowed us to assess the slope characteristics that mainly determine the distribution of areas affected by rockfall. We found that in decreasing order of importance, both standing and felled trees, the surface roughness and rockfall resistant shrubs primarily determine the distribution of rockfall-affected areas. Simulation tests without a forest cover produced similar rockfall runout zones as fossil rockfall events identified in the field. We believe that the combined field and modelling approach is a prerequisite for understanding how forests can protect against rockfall.     

The Northern Giudicarie and the Meran-Mauls fault (Alps,Northern Italy) in the light of new paleomagnetic and geochronological data from boudinaged Eo-/Oligocene tonalites

This study concentrates on small intrusions along two important faults of the Giudicarie fault system, the Northern Giudicarie and the Meran-Mauls fault, summarised under the term tonalitic lamellae. Magnetic fabric analyses in combination with structural field data indicate dextral strike slip deformation along the NE–SW striking northern part of the Giudicarie fault system, the Meran-Mauls fault, overprinted by younger thrusting. The regional stressfield was oriented approximately NNW–SSE during Tertiary times. The distinctive change in deformation along the Meran-Mauls fault from dextral strike slip to top-SE thrusting may be caused by a rotation or bending of the fault after the intrusion of the tonalites and the formation of their horizontal magnetic foliation. Based on the assumption of a preliminary straight Periadriatic lineament bent by the NNW-wards advancement of the Southalpine indenter, the tonalitic lamellae may be interpreted as lenses sheared off from the Adamello batholith during indentation. New U/Pb data on zircon show that some of the lamellae are of Oligocene (Rupelian), others of Late Eocene (Priabonian) age. An amphibole-gabbro lens occurring on the Meran-Mauls fault provides a Middle Eocene (Bartonian) age. Among the major Periadriatic plutons, only the southern units of the Adamello batholith also intruded in the Eocene that suggests a strong correlation between the tonalitic lamellae and the Adamello batholith. The analyses of the remanent magnetisation and the Curie point determinations argue for magnetite as the main carrier of a viscous magnetisation blocked at relatively low temperatures. This indicates slow cooling of the investigated intrusions along the Giudicarie fault system down to approximately 300°C, which is in contrast to the fast cooling determined for the Adamello intrusion units currently at the surface. The new zircon fission track data also show later cooling of the tonalites along the Giudicarie fault system when compared with the Adamello batholith in the south and the Mauls lamellae in the north, indicating that this area contains magmatic bodies exhumed from a deeper structural level than in the Adamello and the Mauls region. This may be due to important top-SE thrusting and transpressive faulting in the footwall of the Northern Giudicarie fault and the Meran-Mauls fault.     

Aerial perspective for shaded relief

ABSTRACT

Aerial perspective is an essential design principle for shaded relief that emphasizes high elevation terrain using strong luminance contrast and low elevations with low contrast. Aerial perspective results in a more expressive shaded relief and helps the reader to understand the structure of a landscape more easily. We introduce a simple yet effective method for adding aerial perspective to shaded relief that is easy to control by the mapmaker.     

Real-time raster projection for web maps

The virtual globe is the default visualization for Digital Earth applications, but it can only show one half of the Earth. This article introduces user-adjustable, on-the-fly projection of georeferenced raster images for web mapping and web GIS applications. This technique allows users to center a map on arbitrary locations, while still seeing the entire Earth surface. Modern web mapping libraries can apply map projection transformations to vector data in the browser, but they do not currently support the projection of raster images at interactive frame rates. We use the cross-platform WebGL (Web Graphics Library) graphics pipeline for hardware-accelerated projection of raster data in web browsers. Two algorithmic techniques – inverse per-fragment projection, and combined forward per-triangle and inverse per-fragment projection – for georeferenced raster imagery are documented. The resulting raster maps combine the ease of use and flexibility of interactive virtual globes with the ability to show the entire Earth. The adjustable projection of raster imagery allows users to observe global phenomena that are difficult to visualize on virtual globes or traditional maps with static projections.