MUREX: a land-surface field experiment to study the annual cycle of the energy and water budgets

The MUREX (monitoring the usable soil reservoir experimentally) experiment was designed to provide continuous time series of field data over a long period, in order to improve and validate the Soil-vegetation-Atmosphere Transfer (SVAT) parameterisations employed in meteorological models. Intensive measurements were performed for more than three years over fallow farmland in southwestern France. To capture the main processes controlling land-atmosphere exchanges, the local climate was fully characterised, and surface water and energy fluxes, vegetation biomass, soil moisture profiles, surface soil moisture and surface and soil temperature were monitored. Additional physiological measurements were carried out during selected periods to describe the biological control of the fluxes. The MUREX data of 1995, 1996, and 1997 are presented. Four SVAT models are applied to the annual cycle of 1995. In general, they succeed in simulating the main features of the fallow functioning, although some shortcomings are revealed.     

Lunar helium-3 in marine sediments: Implications for a late Eocene asteroid shower

A late Eocene asteroid shower to the Earth-Moon system resulted in an increased flux of impact ejected ³He-rich lunar matter to Earth, which is recorded by a 2 Ma enduring ³He-anomaly in marine sediments.     

Crustal uplift in the Alps: why the drainage pattern matters

The Alpine drainage system comprises two large orogen-parallel drainage basins in the core of the Alps (the Rhone and Rhine valleys), and smaller orogen-normal orientated systems. Discharge of the large rivers is ≈5–10 higher than that of the small ones. In addition, the courses of the Rhone and Rhine Rivers are trapped by faults and thrusts that display lower erosional resistance than the neighbouring lithologies. Enhanced discharge of these rivers and the low erosional resistance of their bedrocks potentially enhances surface erosion. Indeed, present-day and glacial sediment yields are ≈1.6–1.7 times higher in these valleys than in the orogen-normal systems. Interestingly, rates of crustal uplift are also enhanced in the Rhine and Rhone valleys, where current rates of ≈1.4–1.6 mm yr⁻¹ are measured. The spatial coincidence between the location of enhanced erosion and maximum crustal uplift rates are interpreted to reflect a positive feedback between surface erosion and tectonic forcing.     

Additives for Slurry Shields in Highly Permeable Ground

Summary. For tunneling projects in saturated soils tunnel boring machines (TBMs) with slurry shields are widely used. However, in coarse, highly permeable soils the suspension penetrates the ground and the required support pressure cannot be built up. For the Zimmerberg Base Tunnel near Zurich permeabilities much greater than 10⁻³ m/s were expected. This value is usually considered as the critical limit for the applicability of slurry shields. Therefore it was aimed to find additives for the bentonite suspension which would allow it to attain a higher suspension pressure. For these investigations an apparatus has been developed. It allows the maximum attainable support pressure for a given suspension and a ground to be determined. It reflects the real situation, produces reproducible results and is insensitive to the inevitable variation of individual parameters. In the tests the additives polymer, sand and vermiculite were studied and their effects on the attainable maximum suspension pressure investigated. For the best combination, i.e. with a well defined proportion of the individual components, suspension pressures could be attained which were about 10 to 20 times higher than those with an ordinary bentonite suspension. Successful excavation of the Zimmerberg Base Tunnel proved the validity of the laboratory tests containing 200 kg bentonite per m³ water.     

Uncertainty estimation of pathlines in ground water models

A method is proposed to estimate the uncertainty of the location of pathlines in two-dimensional, steady-state confined or unconfined flow in aquifers due to the uncertainty of the spatially variable unconditional hydraulic conductivity or transmissivity field. The method is based on concepts of the semianalytical first-order theory given in Stauffer et al. (2002, 2004), which allows estimates of the lateral second moment (variance) of the location of a moving particle. However, this method is reformulated in order to account for nonuniform recharge and nonuniform aquifer thickness. One prominent application is the uncertainty estimation of the catchment of a pumping well by considering the boundary pathlines starting at a stagnation point. In this method, the advective transport of particles is considered, based on the velocity field. In the case of a well catchment, backtracking is applied by using the reversed velocity field. Spatial variability of hydraulic conductivity or transmissivity is considered by taking into account an isotropic exponential covariance function of log-transformed values with parameters describing the variance and correlation length. The method allows postprocessing of results from ground water models with respect to uncertainty estimation. The code PPPath, which was developed for this purpose, provides a postprocessing of pathline computations under PMWIN, which is based on MODFLOW. In order to test the methodology, it was applied to results from Monte Carlo simulations for catchments of pumping wells. The results correspond well. Practical applications illustrate the use of the method in aquifers.     

Erosional processes, topographic length-scales and geomorphic evolution in arid climatic environments: the ‘Lluta collapse’, northern Chile

The Lluta collapse of northern Chile is one of the oldest recognizable landslides (>2.5 Ma) in a hyperarid continental setting. This paper develops a conceptual landscape evolution model of the Lluta collapse and analyzes the controls of mass wasting and erosion/sediment transport in channels on the topographic development. The data presented here imply that high relief along a topographic scarp, surface fracturing, elevated groundwater table during a more humid climate and an aquitard underlying permeable ignimbrites are preparatory causal factors for landsliding >2.5 Ma ago. A strong seismic event then possibly resulted in the displacement of ca. 26 km³ of mass. Subsequent modification of the landslide scar occurred by backward erosion, resulting in the establishment of a dendritic drainage network and the removal of an additional ca. 24 km³ of material. It appears that this mass was produced by mass wasting in the headwaters, and exported by high-concentrated debris flows in channels. In addition, morphometric information suggest that whereas the geometrical development of the Lluta collapse has been controlled by gravitational mass wasting, the rates of the development of this geomorphic unit have been limited by the export rates of mass and hence by the transport capacity of the flows.     

Steady-state observations of geomagnetically trapped energetic heavy ions and their implications for theory

Measurements of energetic heavy ions using the Explorer 45 and ATS-6 satellites are reviewed and the resulting implications for theory are evaluated. The measured ions are basically protons and helium ions in the energy range from 0.1 to 1 MeV/nucleon. The equatorial energetic ion distributions inside L = 4.5 are found to be very stable for extended periods of time. These ions are very closely confined to the equatorial plane and are sharply peaked as a function of L around a value designated as L_max. Beyond L = 5.0 the fluxes of these ions are more variable with order of magnitude variations being observed at L = 6.6 on the time scales of minutes, hours, or days. The region inside L = 4.5 appears to be well described by radial diffusive transport driven by fluctuations in the geomagnetic field coupled with losses due to charge exchange and Coulomb interactions with ambient hydrogen geocorona and terrestrial plasma environment. From an analysis relating the position in L-value of the maximum intensity, L_max, observed for a given ion species and energy, it is argued that the influence of fluctuations in the convection electric field as discussed by Cornwall (1972) are not effective in radially diffusing in L ions with energies greater than a few hundred kiloelectron volts per nucleon. The source of these ions remains basically undetermined and its determination must await further measurements.     

Beobachtungen bei der entwicklung des dauereies vonBrachionus calyciflorus pallas

Ohne Zusammenfassung     

Relics of an early-Panafrican metabasite–metarhyolite formation in the Brno Massif, Moravia, Czech Republic

The Brno Massif in Moravia, Czech Republic, is an important exposure of Precambrian basement in central Europe. It includes large volumes of Cadomian granitoids and a narrow fault-bounded zone with metagabbros, metadiorites, and metabasalts. This so-called Central Basic Belt also contains some metarhyolites; one of these was dated by means of the zircon evaporation method at 725 ±15 Ma. Chemical and isotope data show that the dated rock represents a mantle-derived magma which is cosanguinous with surrounding MORB-type metabasites. The data suggest that the Brno Massif hosts the oldest metabasite complex currently known in central Europe. Its formation apparently coincides with the main period of ocean-floor spreading and island-arc formation in the Panafrican orogens. This lends further support to the theory that the Brno Massif is a Gondwana-derived element. Received: 9 December 1999 / Accepted: 9 February 2000