Remobilisation of deep Na-Cl waters by a regional flow system in the Alps: Case study of Saint-Gervais-les-Bains (France)     

Romain Sonney  François-David Vuataz 《Comptes Rendus Geoscience》2010,342(2):151-161

The hydrothermal system of Saint-Gervais-les-Bains, France is located in a south western low-elevation point of the Aiguilles Rouges crystalline Massif. The crystalline rocks are not directly outcropping in the studied area but certainly exist beyond 300 m depth. Uprising waters are pumped from two different aquifers below the Quaternary deposits of the Bon Nant Valley. In the Lower Trias-Permian aquifer crossed by De Mey boreholes (27–36 °C), the ascending Na-SO₄ and high-Cl thermal water from the basement (4.8 g/L) is mostly mixed by a Ca-SO₄ and low-Cl cold water circulating in the autochthonous cover of the Aiguilles Rouges Basement. The origin of the saline thermal water probably results from infiltration and circulation in the basement until it reaches deep thrust faults with leaching of residual brines or fluid inclusions at depth (Cl/Br molar ratio lower than 655). The dissolution of Triassic halite (Cl/Br > 1000) is not possible at Saint-Gervais-les-Bains because the Triassic cold waters have a low-Cl concentration (< 20 mg/L). Water–rock interactions occur during the upflow via north–south strike-slip faults in the basement and later on in the autochthonous cover. For the De Mey Est borehole, gypsum dissolution is occurring with cationic exchanges involving Na, as well as low-temperature Mg dissolution from dolomite in the Triassic formations. The aquifer of imbricated structures (Upper-Middle Trias) crossed by the Lépinay well (39 °C) contains thermal waters, which are strongly mixed with a low-Cl water, where gypsum dissolution also occurs. The infiltration area for the thermal end-member is in the range 1700–2100 m, close to the Lavey-les-Bains hydrothermal system corresponding to the Aiguilles Rouges Massif. For the Ca-SO₄ and low-Cl end-member, the infiltration area is lower (1100–1300 m) showing circulation from the Mont Joly Massif. The geothermometry method indicates a reservoir temperature of probably up to 65 °C but not exceeding 100 °C.  相似文献   

The influence of soil interstitial waters on the physicochemistry of major,minor and trace metals in stream waters of the green lakes valley,Front Range,Colorado     

M. Iggy Litaor 《地球表面变化过程与地形》1993,18(6):489-504

The influence of soil interstitial waters on the physicochemical characteristics of major, minor and trace metals in stream waters of an alpine watershed, Front Range, Colorado was assessed. Dissolution of Ca-aluminosilicate minerals, ion exchange reactions and the magnitude of solute flux within the alpine soil environment account for most of the observed concentrations of major, minor and trace metals in the alpine stream waters. The rate of mineral dissolution and magnitude of solute flux during the summer of 1989 was greatly affected by anthropogenic disturbance which resulted in large amounts of colloidal material and freshly exposed mineral surfaces. The alpine ecosystem responded very quickly to this disturbance. The magnitude of solute flux in the soil environment was also highly dependent on the duration and intensity of rain events, as well as the location of the site along the slope. Transport of most trace metals in the stream waters was achieved by adsorption onto colloidal surfaces of Al–Si hydroxides smaller than 0·45 μm.  相似文献   

Soil loss variation within a Colorado Alpine area     

Michael J. Bovis  Colin E. Thorn 《地球表面变化过程与地形》1981,6(2):151-163

The areally weighted surface erosion for Niwot Ridge, an alpine interfluve in the Colorado Front Range, is 10⁻¹ mm/y. This may be subdivided into rates for three generalized cover types: tundra meadow, 10⁻² mm/y; dry tundra, 10⁻¹ mm/y; late-lying snow patches, 10° mm/y. Tundra meadow (about 50 per cent of the interfluve area) yields about 5 per cent of the eroded material; dry tundra (35 per cent of the area) contributes slightly less than 50 per cent of the eroded material; while nivation hollows occupied by late-lying snow patches occupy only about 3 per cent of the area they contribute 50 per cent of the eroded material. The bulk of the surficial erosion is accomplished between June and September, primarily by rainsplash, except where snowmelt is important. The overall estimated surface lowering rate presented here is substantially higher than those reported previously.  相似文献   

Computation of travel times and rays in a medium of two-dimensional velocity distribution     

K. Aric  R. Gutdeutsch  A. Sailer 《Pure and Applied Geophysics》1980,118(2):796-806

A ray-tracing computer program is described for a two-dimensional velocity distribution defined by the local wave velocitiesv _{i, j} in points at arbitrary depthv _{i, j} below the surface points with the horizontal coordinatesx _i . The velocity variation is assumed to be linear in the triangles formed by three neighbouring points. Travel times and rays are then calculated after the exact analytic formulae for any position of the source within the model. No assumptions other than of a piecewise linear velocity structure are made. A first-order discontinuity can be approximated by a thin layer with a strong velocity gradient and refracted waves or wide-angle reflections obtained in this way. As an example,P-wave rays were computed for section No. 05 of the Alpine Longitudinal Profile. The model includes a low-velocity channel which is cut off on the eastern side, first-order discontinuities and a sediment basin.Paper presented at the ESC-Workshop Meeting Seismic Waves in Laterally Inhomogeneous Media, Liblice, 1978.  相似文献   

Influence of ion exchange on dissolved load of alpine meltwaters     

M. Lemmens  M. Roger 《地球表面变化过程与地形》1978,3(2):179-187

Meltwaters were collected in Switzerland at the border of two alpine glaciers, the Tsanfleuron glacier resting on limestones and the Tsijiore Nouve glacier flowing over gneissic rocks. Waters were analysed by atomic absorption spectrophotometry for the four major cations. Cation exchange appears to be an essential mechanism in the explanation of the dissolved cationic content of meltwaters in the frontal zone of glaciers. This is indicated by a study of the rate and characteristics of water enrichment. The rate-determining step in the process seems to be film diffusion. The influence of this diffusion is put forward in an analysis of the rates of change in concentration of the four major cations with discharge. Glacier grinding is considered as a factor favouring cation exchange in a proglacial environment.  相似文献   

Tracking Holocene environmental changes in an alpine lake sediment core: application of regional diatom calibration, geochemistry, and pollen     

Roland Schmidt  Christian Kamenik  Christina Kaiblinger  Markus Hetzel 《Journal of Paleolimnology》2004,32(2):177-196

Diatom abundances in the surface sediment samples of 41 mountain lakes in the central Austrian Alps (Niedere Tauern) were related to environmental variables using multi-variate techniques. Canonical correspondence analysis (CCA) revealed that the pH, date of autumn mixing (A _mix), mean August water temperature (T _Aug), dissolved organic carbon (DOC), and relative water depth (Z _rel) made significant contributions to explain the diatom assemblage variation in the lakes of the training set. A weighted averaging partial least square regression and calibration model was used to establish Di-pH (R ² _boot= 0.72, RMSEP_boot= 0.131), and a thermistor measurements-based PLS model for A _mix (R ² _boot= 0.71, RMSEP_boot= 0.006 log₁₀ Julian days). The latter showed a better prediction than T _Aug, and was used in terms of climate change. These transfer functions, together with analyses of loss on ignition (LOI), the total carbon/nitrogen (C/N)-ratios, and selected pollen, were applied to an early to mid-Holocene (11.5–4 cal. ky BP) sediment core section from an Austrian Alpine treeline lake on crystalline bedrock. Additionally, passive sample scores in the CCA of the diatom training set were used to show trends in the variables DOC and Z _rel. During the early Holocene, diatoms indicative of increased pH, extended warm summers, and low water levels dominated. Between 10.2 and 7.6 cal. ky BP it was followed by diatom assemblages that indicated an increase in lake water depth and an earlier A _mix. The multi-proxy data suggest that the A _mix decline is the result of a series of snow-rich summer cool and wet climate fluctuations, which were divided by climate warming at ∼9 cal. ky BP. Increased A _mix, LOI and DOC, and the correspondent decline in the C/N-ratios, show subsequent climate warming between 7.3 and 6 cal. ky BP. The long-term trend in Di-pH indicates the impact of catchment-related processes during the early-Holocene, that were superimposed by climate.  相似文献   

Dating fluvial terraces by Th/U on pedogenic carbonate, Wind River Basin, Wyoming     

Warren D Sharp  Kenneth R LudwigOliver A Chadwick  Ronald AmundsonLaura L Glaser 《Quaternary Research》2003,59(2):139-150

Reliable and precise ages of Quaternary pedogenic carbonate can be obtained with ²³⁰Th/U dating by thermal ionization mass spectrometry applied to carefully selected milligram-size samples. Datable carbonate can form within a few thousand years of surface stabilization allowing ages of Quaternary deposits and surfaces to be closely estimated. Pedogenic carbonate clast-rinds from gravels of glacio-fluvial terraces in the Wind River Basin have median concentrations of 14 ppm U and 0.07 ppm ²³²Th, with median (²³⁰Th/²³²Th) = 270, making them well suited for ²³⁰Th/U dating. Horizons as thin as 0.5 mm were sampled from polished slabs to reduce averaging of long (≥10⁵ yr), and sometimes visibly discontinuous, depositional histories. Dense, translucent samples with finite ²³⁰Th/U ages preserve within-rind stratigraphic order in all cases. Ages for terraces WR4 (167,000 ± 6,400 yr) and WR2 (55,000 ± 8600 yr) indicate a mean incision rate of 0.26 ± 0.05 m per thousand years for the Wind River over the past glacial cycle, slower than inferred from cosmogenic-nuclide dating. Terrace WR3, which formed penecontemporaneously with the final maximum glacial advance of the penultimate Rocky Mountain (Bull Lake) glaciation, has an age of 150,000 ± 8300 yr indicating that it is broadly synchronous with the penultimate global ice volume maximum.  相似文献   

9000 years of chironomid assemblage dynamics in an Alpine lake: long-term trends, sensitivity to disturbance, and resilience of the fauna   总被引：2，自引：0，他引：2  

Oliver Heiri  André F. Lotter 《Journal of Paleolimnology》2003,30(3):273-289

Subfossil chironomid analysis was applied to a sediment core from Sägistalsee, a small lake at present-day tree-line elevation in the Swiss Alps. During the whole 9000-year stratigraphy the chironomid fauna was dominated by taxa typical of alpine lakes. Major faunistic trends were caused by changes in accumulation rates of three taxa, namely Procladius, Stictochironomus, and Tanytarsus lugens-type. In the early Holocene Procladius was the dominant taxon. In younger samples, Stictochironomus tended to have as high or higher abundances and both taxa showed an increase in accumulation rates. A possible cause of this succession is the decrease of lake-water depth due to infilling of the lake basin and changes in associated limnological parameters. The immigration of Picea (spruce) at ca. 6500 cal. ¹⁴C yrs BP and the resulting denser woodlands in the lake's catchment may have promoted this trend. During three phases, from ca. 70–1450, 1900–2350, and 3500–3950 cal. BP, remains of Procladius, Stictochironomus, and Tanytarsus lugens-type are absent from the lake sediment, whereas other typical lake taxa and stream chironomids show no change in accumulation rate. Together with sediment chemistry data, this suggests that increased oxygen deficits in the lake's bottom water during these intervals caused the elimination of chironomids living in the deepest part of the lake. All three periods coincide with increased human activity in the catchment, as deduced from palaeobotanical evidence. Therefore, enhanced nutrient loading of the lake due to the presence of humans and their livestock in the catchment is the most likely cause of the increased anoxia. The chironomid fauna reacted the same way to intensive pasturing during the last ca. 1500 years as to Bronze Age clear-cutting and more moderate pasturing during the Bronze, Iron, and Roman Ages, suggesting that alpine lake ecosystems can be extremely sensitive to human activity in the catchment. On the other hand, the chironomid assemblages show a considerable amount of resilience to human disturbance, as the chironomid fauna reverted to the pre-impact stage after the first two periods of human activity. In recent years, even though pasturing decreased again, the chironomid fauna has only partly recovered. This is possibly due to other human-induced changes in the lake ecosystem, e.g., the stocking of the lake with fish. The chironomid stratigraphy is difficult to interpret climatologically as the strongest changes in chironomid-inferred temperatures coincide with periods of intensive human activity in the catchment.  相似文献   

Glacial erosion and geomorphology in the northwest Sierra Nevada, CA     

L. Allan James   《Geomorphology》2003,55(1-4):283

Pleistocene glacial erosion left a strong topographic imprint in the northwestern Sierra Nevada at many scales, yet the specific landforms and the processes that created them have not been previously documented in the region. In contrast, glaciation in the southern and central Sierra was extensively studied and by the end of the 19th century was among the best understood examples of alpine glaciation outside of the European Alps. This study describes glacially eroded features in the northwest Sierra and presents inferred linkages between erosional forms and Pleistocene glacial processes. Many relationships corroborate theoretical geomorphic principles. These include the occurrence of whalebacks in deep ice positions, roches moutonnées under thin ice, and occurrence of P-forms in low topographic positions where high subglacial meltwater pressures were likely. Some of the landforms described here have not previously been noted in the Sierra, including a large crag and tail eroded by shallow ice and erosional benches high on valley walls thought to be cut by ice-marginal channels.  相似文献   

Barrier jets around the Southern Alps of New Zealand and their potential to enhance alpine rainfall     

Michael J. Revell  Jeff H. Copeland  Howard R. Larsen  David S. Wratt 《Atmospheric Research》2002,61(4)

We use new data from the SALPEX'96 campaign to examine the evolution of orographically modified flow over and around New Zealand's Southern Alps. We consider prefrontal situations for which the larger-scale synoptic pattern generates an incoming northwesterly flow perpendicular to the mountain axis, calculate the nondimensional parameters which control the wind flow and determine how long it takes orographic modifications to become established. We place flows over the New Zealand Alps in a Rossby number/Blocking number parameter space and compare them with flows over other mountain ranges on the globe. Using model and aircraft data, we show the region of modified flow extends over 100 km upstream of the Southern Alps.We show 2D model simulations represent many aspects of the flow modification satisfactorily, although they tend to overdevelop the final state of the Barrier Jet flow. In 3D, using real data to force the boundaries, the migratory nature of the weather systems in the area would generally limit the time available for a modified steady state to develop. In addition, in situations where there is significant lateral variation of initial fields, the 2D results may only be applicable for a few hours.From the point of view of potential to influence alpine rainfall processes, for the case studied, the gradual uplift associated with the modified flow between 1 and 2 km above sea level extended far enough upstream in saturated air to enable cloud drops to grow to drizzle drops before reaching the much more substantial updrafts at the foot of the Alps. This allows vigorous prefrontal precipitation to occur over the foothills and mountains due largely to warm rain processes.  相似文献