Evaluation of gases,condensates, and SO2 emissions from Augustine volcano,Alaska: the degassing of a Cl-rich volcanic system

After the March–April 1986 explosive eruption a comprehensive gas study at Augustine was undertaken in the summers of 1986 and 1987. Airborne COSPEC measurements indicate that passive SO₂ emission rates declined exponentially during this period from 380±45 metric tons/day (T/D) on 7/24/86 to 27±6 T/D on 8/24/87. These data are consistent with the hypothesis that the Augustine magma reservoir has become more degassed as volcanic activity decreased after the spring 1986 eruption. Gas samples collected in 1987 from an 870°C fumarole on the andesitic lava dome show various degrees of disequilibrium due to oxidation of reduced gas species and condensation (and loss) of H₂O in the intake tube of the sampling apparatus. Thermochemical restoration of the data permits removal of these effects to infer an equilibrium composition of the gases. Although not conclusive, this restoration is consistent with the idea that the gases were in equilibrium at 870°C with an oxygen fugacity near the Ni–NiO buffer. These restored gas compositions show that, relative to other convergent plate volcanoes, the Augustine gases are very HCl rich (5.3–6.0 mol% HCl), S rich (7.1 mol% total S), and H₂O poor (83.9–84.8 mol% H₂O). Values of D and ¹⁸O suggest that the H₂O in the dome gases is a mixture of primary magmatic water (PMW) and local seawater. Part of the Cl in the Augustine volcanic gases probably comes from this shallow seawater source. Additional Cl may come from subducted oceanic crust because data by Johnston (1978) show that Cl-rich glass inclusions in olivine crystals contain hornblende, which is evidence for a deep source (>25km) for part of the Cl. Gas samples collected in 1986 from 390°–642°C fumaroles on a ramp surrounding the inner summit crater have been oxidized so severely that restoration to an equilibrium composition is not possible. H and O isotope data suggest that these gases are variable mixtures of seawater, FMW, and meteoric steam. These samples are much more H₂O-rich (92%–97% H₂O) than the dome gases, possibly due to a larger meteoric steam component. The 1986 samples also have higher Cl/S, S/C, and F/Cl ratios, which imply that the magmatic component in these gases is from the more degassed 1976 magma. Thus, the 1987 samples from the lava dome are better indicators than the 1986 samples of degassing within the Augustine magma reservoir, even though they were collected a year later and contain a significant seawater component. Future gas studies at Augustine should emphasize fumaroles on active lava domes. Condensates collected from the same lava-dome fumarole have enrichments ot 10⁷–10² in Cl, Br, F, B, Cd, As, S, Bi, Pb, Sb, Mo, Zn, Cu, K, Li, Na, Si, and Ni. Lower-temperature (200°–650°C) fumaroles around the volcano are generally less enriched in highly volatile elements. However, these lower-termperature fumaroles have higher concentration of rock-forming elements, probably derived from the wall rock.     

Regional-Scale Heat and Water Vapour Fluxes in an Agricultural Landscape: An Evaluation of CBL Budget Methods at OASIS

This paper evaluates convective boundary layer (CBL) budget methods as a tool for estimating regionally averaged sensible and latent heat fluxes for the study region used in OASIS (Observations at Several Interacting Scales). This is an agricultural region of mixed cropping and grazing extending about 100 km west of the town of Wagga Wagga, NSW, Australia.The analysis proceeds in three stages: first, a simpleone-dimensional model of the well-mixed layer (the CBL slab model), forced with measurements of the surface heat and evaporation fluxes, is evaluated by comparing measured and modelled CBL temperature, humidity and depths. A comparison of several entrainment schemes shows that a simple model, where the entrainment kinetic energy is parameterised as a fraction (₃) of the surface sensible heat flux, works well if is set to 0.5. Second, the slab model is coupled to a Penman–Monteith model of surface evaporation to predict regional scale evaporation and thence heat fluxes. Finally, the integral CBL budget approach, which is an inverse method using theone-dimensional slab model, is used to infer regional heat and evaporation fluxes from measured time series of CBL temperature and humidity.We find that the simple CBL slab model works reasonably well for predicting CBL depth and very well for CBL temperature, especially if approximate estimates of subsidence velocity and warming due to advection are included. Regional sensible heat fluxes estimated from the integral CBL method match those measured, although the method is very sensitive to measurement errors. Measurement-model differences were larger for short integration times, because the well-mixed assumptions are violated at particular times of the day. The corollary is that `whole-day' (0530–1530 h) estimates are in reasonable agreement with measured values. Integral methods could not be used to infer the regional evaporation flux directly because CBL humidity profiles were complex and often not well mixed until mid-afternoon. We recommend that regional evaporation fluxes be predicted either from a coupled Penman–Monteith – CBL slab model, or inferred as a residual term from estimates of the regionally averaged available energy and sensible heat flux. Furthermore, we show that inferring fluxes via integral methods will always be difficult when the scalar concentrations have either a large surface source and free atmosphere sink (in the case of water vapour and methane), or a large surface sink and upper level source (in the case of CO₂).     

Sediment density structure derived from textural analysis of cross-sectional X-radiographs

Two image texture analysis procedures, autocorrelation and binary run length, quantify the scales, orientation, and isotropy of density fluctuations imaged in X-radiographs of sediment cross sections from the Arafura Sea (Australia) and Eckernförde Bay (Germany). Image texture-based results agree with traditional bulk methods in some cases and disagree in others. Advantages of imagebased techniques over bulk methods are nonintrusiveness of the approach and the ability to produce more detailed characterizations of the spatial variability present in sediment structure. The image texture-based parameterizations of density structure are interpreted with respect to environmental processes.     

Acoustic backscattering experiments in a well characterized sand sediment: data/model comparisons using sediment fluid and Biot models

As part of the sediment acoustics experiment 1999 (SAX99), backscattering from a sand sediment was measured in the 20- to 300-kHz range for incident grazing angles from 10/spl deg/ to 40/spl deg/. Measured backscattering strengths are compared to three different scattering models: a fluid model that uses the mass density of the sediment in determining backscattering, a poroelastic model based on Biot theory and an "effective density" fluid model derived from Biot theory. These comparisons rely heavily on the extensive environmental characterization carried out during SAX99. This environmental characterization is most complete at spatial scales relevant to acoustic frequencies from 20 to 50 kHz. Model/data comparisons lead to the conclusions that rough surface scattering is the dominant scattering mechanism in the 20-50-kHz frequency range and that the Biot and effective density fluid models are more accurate than the fluid model in predicting the measured scattering strengths. For 50-150 kHz, rough surface scattering strengths predicted by the Biot and effective density fluid models agree well with the data for grazing angles below the critical angle of the sediment (about 30/spl deg/) but above the critical angle the trends of the models and the data differ. At 300 kHz, data/model comparisons indicate that the dominant scattering mechanism may no longer be rough surface scattering.     

Fundamental response of pore-water pressure to microfabric and permeability characteristics: Eckernförde Bay

Ambient and dynamic in situ pore pressures were measured, and microfabric was examined in finegrained, shallow-water sediment in Eckernförde Bay, Germany. In situ permeabilities were calculated from piezometer data. Pore-water pressure decay times in sediments 0.5–1.0 m subbottom are indicative of clayey materials. Shallower sediments, although of similar classical grain size as the deeper sediments, have quicker decay times typical of silty marine sediment. Pore pressure response is a function of the microfabric, porometry, and sediment permeability. Aggregates (composed of fine-grained material, biota, and extracellular polymers) produce large pores and complex microstructure, resulting in effective permeabilities characteristic of silts.     

Physical and numerical experiments on layered convection in a density-Stratified fluid

Abstract

The formation and growth of horizontal layered convection cells in a density stratified solution of salt water subject to an impulsively applied lateral temperature gradient is investigated with physical and numerical experiments. Results indicate that lyers are induced by two mechanisms. One is the successive formation of layers due to the presence of the top and bottom boundaries. The other is the spontaneous occurrence of layers when a suitably defined Rayleigh number exceeds a critical value. It is found that well established layers are homogeneous in temperature and salinity and are separated by sharp gradients in density. Lateral heat transfer is of a periodic nature. Numerical experiments were carried out for finite and infinite geometry cases. For the finite geometry case, convection cells are generated successively inward from the horizontal boundaries. For the infinite geometry case, periodic conditions in the vertical direction are assumed. With continuous input of small perturbations, simultaneous occurrence of the convection cells is obtained at supercritical Rayleigh numbers. Criteria for determining the onset of spontaneous cells numerically are explored.     

Hillslope groundwater discharges provide localized stream ecosystem buffers from regional per- and polyfluoroalkyl substances contamination

Emerging groundwater contaminants such as per- and polyfluoroalkyl substances (PFAS) may impact surface-water quality and groundwater-dependent ecosystems of gaining streams. Although complex near-surface hydrogeology of stream corridors challenges sampling efforts, recent advances in heat tracing of discharge zones enable efficient and informed data collection. For this study, we used a combination of streambed temperature push-probe and thermal infrared methods to guide a discharge-zone-oriented sample collection along approximately 6 km of a coastal trout stream on Cape Cod, MA. Eight surface-water locations and discharging groundwater from 24 streambed and bank seepages were analysed for dissolved oxygen (DO), specific conductance, stable water isotopes, and a range of PFAS compounds, which are contaminants of emerging concern in aquatic environments. The results indicate a complex system of groundwater discharge source flowpaths, where the sum of concentrations of six PFAS compounds (corresponding to the U.S. Environmental Protection Agency third Unregulated Contaminant Monitoring Rule “UCMR 3”) showed a median concentration of 52 ± 331 (SD) ng/L with two higher outliers and three discharges with PFAS concentrations below the quantification limit. Higher PFAS concentration was related (− 0.66 Spearman rank, p < .001) to discharging groundwater that showed an evaporative signature (deuterium excess), indicating flow through at least one upgradient kettle lake. Therefore, more regional groundwater flowpaths originating from outside the local river corridor tended to show higher PFAS concentrations as evaluated at their respective discharge zones. Conversely, PFAS concentrations were typically low at discharges that did not indicate evaporation and were adjacent to steep hillslopes and, therefore, were classified as locally recharged groundwater. Previous research at this stream found that the native brook trout spawn at discharge points of groundwater recharged on local hillslopes, likely in response to generally higher levels of DO. Our study shows that by targeting high oxygen discharges the trout may thereby be avoiding emerging contaminants such as PFAS in groundwater recharged farther from the stream.     

Integrated Futures for Europe’s Mountain Regions: Reconciling Biodiversity Conservation and Human Livelihoods

Introduction Europe's mountains cover nearly half of the continent's area (Price et al. 2004) and land cover varies significantly (European Commission 2004). In most massifs, except for Sicily, southern Greece, and the British Isles, forest cover is dominant. In northern Europe, grassland is proportionately more important, and much of the mountains of the British Isles is covered by moorland. In central and southern Europe, arable land is of far greater importance than grassland, with Med…     

Porometric properties of siliciclastic marine sand: a comparison of traditional laboratory measurements with image analysis and effective medium modeling

During the 1999 sediment acoustics experiment (SAX99), porometric properties were measured and predicted for a well sorted, medium sand using standard laboratory geotechnical methods and image analysis of resin-impregnated sediments. Sediment porosity measured by laboratory water-weight-loss methods (0.372 /spl plusmn/ 0.0073 for mean /spl plusmn/1 standard deviation) is 0.026 lower than determined by microscopic image analysis of resin-impregnated sediments (0.398 /spl plusmn/ 0.029). Values of intrinsic permeability (m/sup 2/) determined from constant-head permeameter measurements (3.29 /spl times/ 10/sup -11/ /spl plusmn/ 0.60 /spl times/ 10/sup -11/) and by microscopic image analysis coupled with effective medium theory modeling (2.78 /spl times/ 10/sup -11/ /spl plusmn/ 1.01 /spl times/ 10/sup -11/) are nearly identical within measurement error. The mean value of tortuosity factor measured from images is 1.49 /spl plusmn/ 0.09, which is in agreement with tortuosity factor determined from electrical resistivity measurements. Slight heterogeneity and anisotropy are apparent in the top three centimeters of sediment as determined by image-based porometric property measurements. However, the overall similarity for both measured and predicted values of porosity and permeability among and within SAX99 sites indicates sediments are primarily homogeneous and isotropic and pore size distributions are fairly uniform. The results indicate that an effective medium theory technique and two-dimensional image analysis accurately predicts bulk permeability in resin-impregnated sands.