Analysis with C- and X-band satellite SAR data of the Portalet landslide area

This paper describes the use of the Stable Point Network technique, a Persistent Scatterer Interferometry SAR technique, for the analysis of the Portalet landslide area (Central Pyrenees, Spain). For this purpose, different SAR datasets acquired by ERS-1, ERS-2, ENVISAT and TerraSAR-X satellites have been analysed. The use of different SAR images acquired by satellite radar sensors operating at different microwave lengths has allowed for a comparative assessment and illustration of the advantages and disadvantages of these satellites for landslide detection and monitoring. In the introduction, differential interferometry and the study area are briefly described. Then the specifics of the SPN processing and the results of the different datasets are described and compared. In Analysis of the results: the Portalet landslide area, the Portalet landslide area is introduced and the radar displacement measurements are analysed with available geo-information data. Additionally, X-band measurements are compared with those gathered by a ground-based SAR for a previous project. Finally, the most relevant conclusions of this work are discussed.     

Investigating the robustness of the intraseasonal see-saw in the Indo-Pacific barotropic sea level across models

Ocean Dynamics - An intraseasonal see-saw has been observed in the Indo-Pacific barotropic sea level anomaly during boreal winters. This see-saw carries a significant amount of energy and is...     

Using Climber's Guidebooks to Assess Rock Fall Patterns Over Large Spatial and Decadal Temporal Scales: An Example from the Swiss Alps

High‐mountain geomorphic processes enjoy increasing scientific and societal interest. This is because these processes are perceived to be changing more than elsewhere and because their effects on infrastructure and tourism are significant. Rock fall is among the processes that receive most attention due to its presumed intimate relation with permafrost, which is widely degrading. However, over decadal temporal scales and for entire mountain ranges, there is very limited information on the changes in frequency and location of rock fall. This hampers our understanding. Here, I assess the value of information contained in a 146‐year record of climber's guidebooks of the Bernese Alps in Switzerland to derive changes in rock fall danger. The results show that guidebooks’ authors, themselves experienced climbers, perceived increases in rates and changes in positions of rock fall. The increases were mainly reported since the year 2000. It appears that datasets derived from guidebooks can provide valuable context for more detailed, higher resolution data sources.     

Is a regional flood signal reproducible from lake sediments?

The evolution of flood activity with global warming remains uncertain. To better assess flood–climate relationships, lake sediments are increasingly being investigated because they could provide regional flood histories long enough to cover past climate changes. However, site‐specific sedimentary processes may bias flood reconstructions. The aim of this article is to investigate these effects through the reconstruction of two distinct flood records from independent, neighbouring sedimentary basins of the same lake (Lake Allos in the Mediterranean French Alps), i.e. under the same climate conditions. Understanding of sedimentary processes is crucial in order to adapt the sampling strategy and the flood‐intensity proxy to each sedimentary system and, thereby, reconstruct a complete and reliable flood history. Thanks to this detailed approach, the main trends of the regional flood variability can be reproduced; i.e. periods of high flood‐frequency, ranges of flood‐frequency values and timing of the most intense events. In detail, some differences appeared associated to the various stream capacities to erode and transport flood sediments to the lake system, implying variable sensitivity of sedimentary systems in recording floods. Comparing regional flood records based on independent sedimentary systems from similar environments could thus be a complementary approach to assessing past flood intensity. Such an approach could open particularly interesting perspectives because reconstructing the long‐term evolution of flood intensity is a key challenge in the geosciences.     

Integrated Onshore‐Offshore Investigation of a Mediterranean Layered Coastal Aquifer

Most of the Mediterranean coastal porous aquifers are intensively exploited. Because of climatic and anthropogenic effects, understanding the physical and geological controls on groundwater distribution and flow dynamics in such aquifers is crucial. This study presents the results of a structural investigation of a system located along the coastline of the Gulf of Lions (NW Mediterranean). A key aspect of this study relies on an onshore‐offshore integrated approach combining outcrops, seismic profiles, and borehole data analysis. This multidisciplinary approach provides constraints on pore‐fluid salinity distribution and stratigraphic organization, which are crucial in assessing the modes of groundwater/seawater exchanges. Onshore, Lower Pliocene deposits dip gently seaward. They are unconformably overlain by Holocene clays in the lagoons. Offshore the Pliocene deposits either outcrop at the seabed or are buried below nonconsolidated sands infilling paleo‐valleys. Beneath the lido, the groundwater salinity distribution consists of salty pore water, overlying fresher pore water. Active circulation of groundwater masses is inferred from the geophysical results. In particular, offshore outcrops and paleo‐valleys may play an important role in salt water intrusion.     

Linking landscape morphological complexity and sediment connectivity

Connectivity relates to the coupling of landforms (e.g. hillslopes and channels) and the transfer of water and sediment between them. The degree to which parts of a catchment are connected depends largely on the morphological complexity of the catchment's landscape. Landscapes can have very different and distinct morphologies, such as terraces, V‐shaped valleys or broad floodplains. The objective of this study is to better understand and quantify the relation between landscape complexity and catchment connectivity. We hypothesize that connectivity decreases with increasing landscape morphological complexity. To quantify the connectivity–complexity relationship virtual digital elevation models (DEMs) with distinct morphologies were used as inputs into the landscape evolution model LAPSUS to simulate the sediment connectivity of each landscape. Additionally, the hypothesis was tested on six common real DEMs with widely different morphologies. Finally, the effects of different rainfall time series on catchment response were explored. Simulation results confirm the hypothesis and quantify the non‐linear relation. Results from the exploration of sediment connectivity in response to sequences of rainfall events indicate that feedback between erosion and deposition are more important for certain landscape morphologies than for others: for a given rainfall input, a more effective sediment connectivity and erosion response may be expected from rolling or V‐shaped catchments than from dissected or stepped landscapes. Awareness of the differences in the behaviour and response of different morphologies to catchment processes provides valuable information for the effective management of landscapes and ecosystems through efficiently designed soil and water conservation measures. Copyright © 2013 John Wiley & Sons, Ltd.     

The Lac Des Iles Palladium Deposit,Ontario, Canada part I. The effect of variable alteration on the Offset Zone

The recently discovered Offset Zone of the Mine Block Intrusion of the Lac des Iles Complex hosts palladium mineralization with unusually high Pd/Pt and Pd/Ir ratios in rocks that range from relatively unaltered norite to amphibolites and chlorite–actinolite–talc schist. Quantitative assessment of the effect of progressive alteration using mineral modes was done using total silicate H₂O as a monitor of reaction progress (ξ = moles H₂O added to form alteration minerals per 100 g of rock). Major mineral modal variations define three reaction regions: (1) ξ?=?0.00–0.03, characterized by epidote/clinozoisite formation and some amphibole; (2) ξ?=?0.03–0.23, characterized by formation of chlorite, amphibole, quartz muscovite/sericite, and calcite after plagioclase?+?pyroxene; and (3) ξ?=?0.23–0.28, characterized by the formation of talc after earlier formed amphibole. Epidote occurs as an incongruent product from the destruction of plagioclase that is itself lost as the reaction proceeds. Pyroxene is altered at about twice the rate of plagioclase, resulting in pyroxene-rich protoliths to be more altered than those relatively enriched in plagioclase. Major elements variations largely reflect variations in the plagioclase/pyroxene ratio of the protolith, but compositional trends suggest a loss of Na with reaction progress. The base metal sulfides chalcopyrite, pyrrhotite, and pentlandite show decreasing abundance with reaction progress, forming pyrite (± magnetite) as an intermediate reaction product that also is lost as the reaction proceeds. Millerite is overall low but increases slightly. A more limited data set on the platinum-group minerals suggests that platinum-group element (PGE)-arsenides increase whereas PGE-sulfides and PGE-Bi-tellurides decrease with reaction progress. Assuming ore element concentrations in the protolith were constant and similar to relatively fresh norites, Pd increases modestly, by 5 %, whereas Pt decreases by about 65 % in the most altered rocks. Similarly, Cu, Au, and S decrease by 60, 82, and 94 %, respectively, in the most altered rocks. The antithetical behavior of Pd and the fact that Pd enrichment is not seen in altered dikes suggest that the Pd originally was enriched in the more melanocratic protoliths that are most extensively altered and that Pd also was lost in part. These results are consistent with the mineralization having been a high-temperature event that predated the amphibolite/greenschist alteration.     

Vertical profiling of SO2 and SO above Venus’ clouds by SPICAV/SOIR solar occultations

New measurements of sulfur dioxide (SO₂) and monoxide (SO) in the atmosphere of Venus by SPICAV/SOIR instrument onboard Venus Express orbiter provide ample statistics to study the behavior of these gases above Venus’ clouds. The instrument (a set of three spectrometers) is capable to sound atmospheric structure above the clouds in several observation modes (nadir, solar and stellar occultations) either in the UV or in the near IR spectral ranges. We present the results from solar occultations in the absorption ranges of SO₂ (190–230 nm, and at 4 μm) and SO (190–230 nm). The dioxide was detected by the SOIR spectrometer at the altitudes of 65–80 km in the IR and by the SPICAV spectrometer at 85–105 km in the UV. The monoxide’s absorption was measured only by SPICAV at 85–105 km. We analyzed 39 sessions of solar occultation, where boresights of both spectrometers are oriented identically, to provide complete vertical profiling of SO₂ of the Venus’ mesosphere (65–105 km). Here we report the first firm detection and measurements of two SO₂ layers. In the lower layer SO₂ mixing ratio is within 0.02–0.5 ppmv. The upper layer, also conceivable from microwave measurements by Sandor et al. (Sandor, B.J., Todd Clancy, R., Moriarty-Schieven, G., Mills, F.P. [2010]. Icarus 208, 49–60) is characterized by SO₂ increasing with the altitude from 0.05 to 2 ppmv, and the [SO₂]/[SO] ratio varying from 1 to 5. The presence of the high-altitude SO_x species could be explained by H₂SO₄ photodissociation under somewhat warmer temperature conditions in Venus mesosphere. At 90–100 km the content of the sulfur dioxide correlates with temperature increasing from 0.1 ppmv at 165–170 K to 0.5–1 ppmv at 190–192 K. It supports the hypothesis of SO₂ production by the evaporation of H₂SO₄ from droplets and its subsequent photolysis at around 100 km.     

Partial ages: diagnosing transport processes by means of multiple clocks

The concept of age is widely used to quantify the transport rate of tracers - or pollutants - in the environment. The age focuses only on the time taken to reach a given location and disregards other aspects of the path followed by the tracer parcel. To keep track of the subregions visited by the tracer parcel along this path, partial ages are defined as the time spent in the different subregions. Partial ages can be computed in an Eulerian framework in much the same way as the usual age by extending the Constituent oriented Age and Residence Time theory (CART, www.climate.be/CART). In addition to the derivation of theoretical results and properties of partial ages, applications to a 1D model with lateral/transient storage, to the 1D advection-diffusion equation and to the diagnosis of the ventilation of the deep ocean are provided. They demonstrate the versatility of the concept of partial age and the potential new insights that can be gained with it.     

Modelling sediment dynamics due to hillslope–river interactions: incorporating fluvial behaviour in landscape evolution model LAPSUS

Landscape evolution models (LEMs) simulate the three‐dimensional development of landscapes over time. Different LEMs have different foci, e.g. erosional behaviour, river dynamics, the fluvial domain, hillslopes or a combination. LEM LAPSUS is a relatively simple cellular model operating on timescales of centuries to millennia and using annual timesteps that has had a hillslope focus. Our objective was to incorporate fluvial behaviour in LAPSUS without changing the existing model equations. The model should be able to reproduce alternating aggradation and incision in the floodplains of catchments, depending on simulated conditions. Testing was done using an artificial digital elevation model (DEM) and a demonstration of the ability for fluvial simulation was performed for a real landscape (Torrealvilla catchment, southeast Spain). Model equations to calculate sediment dynamics and water routing were similar for both hillslope and fluvial conditions, but different parameter values were used for these domains, defined based on annual discharge. Parameters changing between the domains are convergence factor p, which is used in the multiple flow algorithm to route water, and discharge and gradient exponents m and n, used in transport capacity calculations. Erodibility and ‘sedimentability’ factors K and P were changed between cold (little vegetation, high erodibility) and warm conditions (more vegetation, lower erodibility). Results show that the adapted parameters reproduced alternating aggradation – due to divergent flow in the floodplain and sediment supply under cold conditions – and incision due to reduced sediment supply and resulting clean water erosion during simulated warm conditions. The simulated results are due to interactions between hillslopes and floodplains, as the former provide the sediments that are deposited in the latter. Similar behaviour was demonstrated when using the real DEM. Sensitivity and resolution analysis showed that the model is sensitive to changes in m, n and p and that model behaviour is influenced by DEM resolution. Copyright © 2012 John Wiley & Sons, Ltd.