bluuebunny/crossref_metadata_2025_split huggingface dataset:
Constraints on sustainable development of arsenic-bearing aquifers in southern Bangladesh. Part 2: Preliminary models of arsenic variability in pumped groundwater
Authors: Cuthbert M. O. , Burgess W. G. , Connell L. 
Published: September 2007

Abstract

Numerical models of groundwater flow and arsenic transport to tubewells in southern Bangladesh have been developed, based on a conceptual model derived from field observations. The catchment of a single hand-pumped tubewell (HTW) is incorporated within a model domain 8110m
2
in area and 60m thick. Three tubewell specifications represent typical Bangladesh HTW designs. Constant-concentration cells act as a single-layered arsenic source, arranged to represent the observed depth distribution of arsenic in the aquifer and the range of possible patterns of overlap between HTW catchments and discontinuous zones of arsenic release from sediment to groundwater. A variety of sorption regimes is simulated, and sensitivity to sorption is illustrated. Boundary conditions are modified to simulate the effects of deep production wells. The models reproduce the observed scale and range of arsenic concentration in groundwater pumped from HTWs, and demonstrate likely long-term trends. Breakthrough of arsenic to HTWs may occur a few years after the start of pumping, but at many tubewells the concentration of arsenic could continue to rise significantly over tens to hundreds of years. Spatial distributions and depth profiles of arsenic in groundwater from tubewells should be viewed as transient in the long term. These preliminary models allow implications for the sustainability of the shallow alluvial aquifer to be quantified provisionally. The mechanisms and scale of sorption of arsenic by the aquifer sediments remain as significant uncertainties.
Assessing the impact of groundwater abstractions on river flows
Authors: Kirk S. , Herbert A. W. 
Published: September 2007

Abstract
Groundwater abstractions affect the water balance in catchments of rivers in hydraulic continuity with groundwater and may lead to reductions in river baseflow. The Environment Agency issues licences for groundwater abstractions and takes into account the risk of such adverse impacts when deciding whether to grant licences and what conditions to associate with each licence. Assessing the impact of a particular licence is a difficult task, but analytical solutions to idealizations of the complex river-aquifer interaction can help guide such judgements. This paper presents a brief review of available analytical solutions and discusses their applicability to real groundwater systems. The most useful analytical solutions (developed by Theis, Hantush and Stang) have been incorporated into a spreadsheet and a new methodology has been made available to support Environment Agency hydrogeologists working in abstraction licensing. This offers a consistent approach to making an initial evaluation of the impact of groundwater abstraction on river flow that may be applied across the diverse hydrogeological systems found throughout the Environment Agency Regions of England and Wales. The use of analytical solutions in this methodology inevitably represents a significant simplification of what is generally a very complex issue, and the limitations of the new methodology are emphasized.
Determination of hydraulic boundary conditions for the interaction between surface water and groundwater
Authors: Macheleidt W. , Nestler W. , Grischek T. 
Published: September 2007

Abstract

The main determinants of the interaction between surface water and groundwater are the distribution of areas with different infiltration rates, the thickness of sediment layers and the hydraulic head gradient. These conditions determine the volume and velocity of infiltrating water which, together with the direction of water flow, are required to model the interaction processes. Due to difficulties with measurement, only the direction of water flow is usually determined and boundary conditions are estimated from simplified assumptions. Field techniques have now been developed that help characterize surface water-groundwater interaction. Results from field experiments using a percussion probe and a large-scale laboratory column experiment set up to simulate infiltration processes are presented. Measurements of the
222
Rn distribution in the column are used to determine infiltration velocities.
A simple analytical solution for unsaturated solute migration under dynamic water movement conditions and root zone effects
Authors: Connell L. D. 
Published: September 2007

Abstract
Vulnerability mapping involves an assessment of the potential for solute migration to the water table. Existing procedures rely on simple qualitative indices to calculate this migration potential. As an alternative to these vulnerability indices this paper presents a simple, analytical solution to the advection-dispersion equation. This solution is physically representative, in that it allows for the effects of root zone processes and climate-induced water movement variation on solute transport. The basis of this analytical solution is a spatially transformed advection-dispersion equation. The root zone is treated in a lumped fashion where a relation is developed for the solute concentration of water that has passed through the root zone that includes retardation, degradation and transpiration. This lumped root zone treatment is used in an existing analytical solution that is adapted so that it can be used for a transformed unsaturated advection-dispersion equation. The procedure is tested against hypothetical simulations with dynamic water movement conditions calculated using SWIMv2. The accuracy of the approach is found to be a function of the soil permeability. Where the dynamic variation is averaged out by the water movement process (such as in soils with moderate permeability) the method can accurately represent the transport process. For soils where surface conditions lead to significant variation in water content throughout the profile the technique is more approximate.
Groundwater pollution at a pulp and paper mill at Sjasstroj near Lake Ladoga, Russia
Authors: Schoenheinz D. , Grischek T. , Worch E. , Bereznoy V. , Gutkin I. , Shebesta A. , Hiscock K. , Macheleidt W. , Nestler W. 
Published: September 2007

Abstract

Lake Ladoga, situated in north-west Russia, is the main source of drinking water for more than 6 million people in the region of St Petersburg. During recent years eutrophication of Lake Ladoga has increased, with pollution of the lake water and sediments by heavy metals, phenols and chloro-organic substances. This paper reports the influence of effluents from a pulp and paper mill at Sjasstroj situated on the southern shore of Lake Ladoga. At Sjasstroj, contamination of a wide area of land, and the production of large volumes of wastewater requiring treatment and disposal, threaten the sustainability of surface and domestic well supplies and lake ecosystems. A tiered approach to risk assessment was adopted in this investigation beginning with a survey of historical data and an initial field reconnaissance followed by more detailed, targeted hydrogeological and hydrochemical investigations. Concentrations of dissolved organic carbon (DOC) as high as 44 mg 1
−1
and adsorbable organic halogens as high as 130 µg 1
−1
were found in groundwater samples. The detailed field reconnaissance survey contradicted toxicity index values for the wastewater, sludge and groundwater samples calculated using a Russian method of risk characterization, which would otherwise predict a high potential environmental pollution risk. In reality, there is good evidence for natural attenuation of organic compounds in groundwater, with as much as 40–50% removal of DOC. However, the residual DOC can be problematic when chlorination of raw surface and groundwaters creates organo-chlorine by-products in treated water.
Hydrocarbon contamination of groundwater at Ploiesti, Romania
Authors: Albu M. A. , Morris L. M. , Nash H. , Rivett M.O. 
Published: September 2007

Abstract
The area of Ploiesti in Romania was among the first oil producing regions in the world. The refineries and oil pipelines have leaked petroleum products over many years. An area of at least 500 ha is contaminated by free product light non-aqueous-phase liquid (LNAPL), affecting one third of Ploiesti’s water supplies. To date it has been possible to compensate by extending the well fields and using surface water, but the long-term sustainability of these measures has not been investigated. The Prahova and Teleajan rivers, tributaries of the River Danube, are also at risk. A conceptual map is presented to show the evolution of LNAPL contamination between 1980 and 2000, and the quantity of oil in each plume is estimated. Potential recovery of oil using a conventional pump-and-treat system is also calculated, with costs and possible revenue. An outline programme for investigation and remediation is presented, part of which is being implemented with a European Community grant. Although the severity of contamination was at least partly realised in the 1970s, only the recent move towards privatization could mobilize sufficient financial resources to address this problem and protect groundwater resources for future use.
Heat transfer and melting in subglacial basaltic volcanic eruptions: implications for volcanic deposit morphology and meltwater volumes
Authors: Wilson Lionel , Head James W. 
Published: September 2007

Abstract

Subglacial volcanic eruptions can generate large volumes of meltwater that is stored and transported beneath glaciers and released catastrophically in jökulhlaups. At typical basaltic dyke propagation speeds, the high strain rate at a dyke tip causes ice to behave as a brittle solid; dykes can overshoot a rock-ice interface to intrude through 20–30% of the thickness of the overlying ice. The very large surface area of the dyke sides causes rapid melting of ice and subsequent collapse of the dyke to form a basal rubble pile. Magma can also be intruded at the substrate-ice interface as a sill, spreading sideways more efficiently than a subaerial flow, and also producing efficient and widespread heat transfer. Both intrusion mechanisms may lead to the early abundance of meltwater sometimes observed in Icelandic subglacial eruptions. If meltwater is retained above a sill, continuous melting of adjacent and overlying ice by hot convecting meltwater occurs. At typical sill pressures under more than 300 m ice thickness, magmatic CO
2
gas bubbles form
c.
25 vol% of the pressurized magma. If water drains and contact with the atmosphere is established, the pressure decreases dramatically unless the overlying ice subsides rapidly into the vacated space. If it does not, further CO
2
exsolution plus the onset of H
2
O exsolution has the potential to cause explosive fragmentation, i.e. a fire-fountain that forms at the dyke-sill connection, enhancing melting and creating another candidate pulse of meltwater. The now effectively subaerial magma body becomes thicker, narrower, and flows faster so that marginal meltwater drainage channels become available. If the ice overburden thickness is much less than
c.
300m the entire sill injection process may involve explosive magma fragmentation. Thus, there should be major differences between subglacial eruptions under local or alpine glaciers compared with those under continental-scale glaciers.
The 1969 subglacial eruption on Deception Island (Antarctica): events and processes during an eruption beneath a thin glacier and implications for volcanic hazards
Authors: Smellie J. L. 
Published: September 2007

Abstract

A short-lived eruption of basaltic andesite to andesite on Deception Island in 1969 occurred from a series of fissures underneath a glacier. The glacier was thin (
c.
100 m) and the eruption created a large and sudden discharge of meltwater that overflowed the glacier, severely damaging buildings on the island. The eruption was unusually well documented and it illustrates several features of subglacial eruptions that are only poorly known and not well understood. In particular, overflowing meltwater is contrary to predictions based on existing simple hydrological models for eruptions beneath thin glaciers. The eruption is analysed in this paper and used as a model for the fluid dynamics and thermodynamics of eruptions beneath a thin glacier mainly composed of impermeable ice. It is suggested that, in eruptions of relatively fluid magmas with a low magma rise rate, volatiles and magma are able to decouple and subglacial melting is strongly influenced by the superheated magmatic and hydrothermal gases (mainly steam). Thus, melting is much faster than that due solely to coupled conductive (magma) and convective (meltwater) heat transfer. The influence of gasdriven melting also has an important effect on the shape of the meltwater cavity and may be at least partly responsible for the cylindrical ice chimneys developed above vents on Deception Island. The results of the study are important for reconstructing the shapes of englacial cavities melted above a vent. They also highlight the importance of glacier structure and densification, rather than simply glacier thickness, in determining the hydraulic evolution of an eruption. Even eruptions beneath thin glaciers can generate significant meltwater floods.
Facies analysis of proximal subglacial and proglacial volcaniclastic successions at the Eyjafjallajökull central volcano, southern Iceland
Authors: Loughlin S. C. 
Published: September 2007

Abstract
The long-lived (at least 0.78 Ma) Eyjafjallajökull volcano has been constructed during a period of dramatic climatic shifts, and has produced subaerial lavas and cinder cones, pillow lavas, hyaloclastite, monogenetic volcaniclastic sediments and polygenetic glacio-fluvial sediments. Subaqueous lithofacies are dominant and nine distinct cogenetic lithofacies associations are identified within the successions that are interpreted as the proximal deposits of subglacial eruptions. These associations are typically bound by unconformities and lie directly on thin diamictites or glaciated surfaces; epiclastic sedimentary rocks are absent. The lithofacies include subaqueous sheet lava flows, lobate flows, pillow lavas, breccias, hyaloclastite and hyalotuff generated by eruption of mainly basaltic lavas. Lavas associated with massive hyaloclastite breccias commonly lie on or intrude cogenetic redeposited hyalotuff, indicating rapid changes in style of activity from explosive to effusive. This suggests that the vent was initially subaqueous but became subaerial as meltwater drained away down-slope beneath temperate ice sheets. In other instances, probably under thicker ice, the eruptions were effusive throughout but lava was subjected to intense steam explosivity. There is abundant evidence that volcaniclastic material was transported downslope by mass flow, grain flow and traction currents (i.e. by running water). Lithofacies associations that ponded in ice-dammed water commonly comprise thick redeposited tephra overlain by a ‘passage zone’ of hyaloclastite and then subaerial lavas. These deposits are voluminous but conditions suitable for ponding of large volumes of water were not common in the evolution of this large volcano.
During the early stages of volcano growth, eruptive deposits were emplaced on the gentle slopes of the growing cone during both glacial and interglacial periods. Glacial erosion modified the growing edifice and, as a result, younger deposits (<600 ka) tend to be valley-confined. The unconformities produced during glacial advance represent significant time gaps within the succession. Observations support the hypothesis that there were higher volcanic production rates during periods of deglaciation, probably as a result of the rapid decrease in lithostatic pressure as ice melted.
Glacial influences on morphology and eruptive products of Hoodoo Mountain volcano, Canada
Authors: Edwards B. R. , Russell J. K. 
Published: September 2007

Abstract

Hoodoo Mountain volcano (HMV), a Quaternary composite volcano in northwestern British Columbia, is a well-exposed example of peralkaline, phonolitic icecontact and subglacial volcanism. Its distinctive morphology and unique volcanic deposits are indicative of subglacial, within-ice, and/or ice-contact volcanic eruptions. Distinct ice-contact deposits result from three different types of lava-ice interaction: (1) vertical cliffs of lava, featuring finely jointed flow fronts up to 200 m in height, resulted from lava flows being dammed and ponded against thick masses of ice; (2) pervasively-jointed, dense lava flows, lobate intrusions, and domes associated with mantling deposits of poorly-vesiculated breccia are derived from volcanic eruptions contained beneath relatively thick ice; and (3) an association of pervasively-jointed, highly-vesicular lava flows or dykes encased by vesicular hyaloclastite of identical composition formed by eruption under and/or through relatively thin ice. The distribution of these three deposit types largely explains the distinctive morphology of Hoodoo Mountain and can be used to reconstruct variations in ice thickness surrounding the volcano since
c
.85 ka. Our analysis suggests that at
c
.85 ka Hoodoo Mountain erupted underneath ice cover of at least several hundred metres. At
c
.80 ka eruptions were no longer subglacial, but the edifice was surrounded by ice at least 800 m high that dammed lava flows around the perimeters of the volcano. After a period of eruptions showing no apparent evidence for ice interaction, from <80 to >40 ka, subglacial eruptions began again, signalling the build-up of regional ice levels. Local ice thickness during these eruptions may well have been over 2 km thick.
Effusive intermediate glaciovolcanism in the Garibaldi Volcanic Belt, southwestern British Columbia, Canada
Authors: Kelman M. C. , Russell J. K. , Hickson C. J. 
Published: September 2007

Abstract
The Garibaldi Volcanic Belt (GVB) in southwestern British Columbia is dominated by intermediate composition volcanoes in a setting that has been intermittently subjected to widespread glaciation. The glaciovolcanic features produced are distinctive, and include flow-dominated tuyas, subglacial domes, and ice-marginal flows. Flow-dominated tuyas, which are intermediate in composition, are unlike conventional basaltic tuyas; they consist of stacks of flat-lying lava flows, and lack pillows and hyaloclastite. They are inferred to represent subglacial eruptions that ultimately breached the ice surface. Subglacial domes occur as steep-sided masses of heavily-jointed, glassy lava, and represent eruptions that were entirely subglacial. Ice-marginal flows derive from subaerial flows that were impounded against ice.
Two unique aspects of GVB glaciovolcanic products are the presence of flow-dominated tuyas and the apparent scarcity of primary fragmental deposits. These unique features result from lava composition, the minimization of direct lava-water contact during eruptions, and topography. Composition influences morphology because eruption temperature decreases, and viscosity and glass transition temperature both increase with silica content. The result of this is that silicic subglacial volcanoes melt less water and are less likely to trap it near the vent, leading to the formation of structures whose shapes are strongly influenced by the surrounding ice. Topography also enhances meltwater drainage, favours lava flow impoundment in ice-filled valleys, and may, through erosion, influence the observed distribution of fragmental glaciovolcanic deposits.
Volatiles in basaltic glasses from a subglacial volcano in northern British Columbia (Canada): implications for ice sheet thickness and mantle volatiles
Authors: Dixon J. E. , Filiberto J. R. , Moore J. G. , Hickson C. J. 
Published: September 2007

Abstract

Dissolved H
2
O, CO
2
, S and Cl concentrations were measured in glasses from Tanzilla Mountain, a 500 m-high, exposed subglacial volcano from the Tuya-Teslin region, north central British Columbia, Canada. The absence of a flat-topped subaerial lava cap and the dominance of pillows and pillow breccias imply that the Tanzilla Mountain volcanic edifice did not reach a subaerial eruptive phase. Lavas are dominantly tholeiitic basalt with minor amounts of alkalic basalt erupted at the summit and near the base. Tholeiites have roughly constant H
2
O (
c.
0.56 ± 0.07 wt%), CO
2
(<30 ppm), S (980 ± 30 ppm) and Cl (200 ± 20 ppm) concentrations. Alkalic basalts have higher and more variable volatile concentrations that decrease with increasing elevation (0.62–0.92 wt% H
2
O, <30 ppm CO
2
, 870–1110 ppm S and 280–410 ppm Cl) consistent with eruptive degassing. Calculated vapour saturation pressures for the alkalic basalts are 36 to 81 bars corresponding to ice thicknesses of 400 to 900 m. Maximum calculated ice thickness (
c.
1 km) is at the lower end of the range of predicted maximum Fraser glaciation (
c.
1–2 km), and may indicate initiation of volcanism during the waning stages of glaciation. Temporal evolution from tholeiitic to alkalic compositions may reflect compositional gradients within a melting column, instead of convective processes within a stratified magma chamber. The mantle source region for the subglacial volcanoes is enriched in incompatible elements similar to that for enriched mid-oceanic ridge basalt (e.g. Endeavour Ridge) and does not contain residual amphibole. Thus, metasomatic enrichment most likely reflects small degree partial melts rather than hydrous fluids.
The hyaloclastite ridge formed in the subglacial 1996 eruption in Gjálp, Vatnajökull, Iceland: present day shape and future preservation
Authors: Gudmundsson M. T. , Pálsson F. , Björnsson H. , Högnadóttir ℋ 
Published: September 2007

Abstract

In the Gjálp eruption in 1996, a subglacial hyaloclastite ridge was formed over a volcanic fissure beneath the Vatnajökull ice cap in Iceland. The initial ice thickness along the 6 km-long fissure varied from 550 m to 750 m greatest in the northern part but least in the central part where a subaerial crater was active during the eruption. The shape of the subglacial ridge has been mapped, using direct observations of the top of the edifice in 1997, radio echo soundings and gravity surveying. The subglacial edifice is remarkably varied in shape and height. The southern part is low and narrow whereas the central part is the highest, rising 450 m above the pre-eruption bedrock. In the northern part the ridge is only 150–200 m high but up to 2 km wide, suggesting that lateral spreading of the erupted material occurred during the latter stages of the eruption. The total volume of erupted material in Gjálp was about 0.8 km
3
, mainly volcanic glass. The edifice has a volume of about 0.7 km
3
and a volume of 0.07 km
3
was transported with the meltwater from Gjálp and accumulated in the Grímsvötn caldera, where the subglacial lake acted as a trap for the sediments. This meltwater-transported material was removed from the southern part of the edifice during the eruption. Variations in basal water pressure may explain differences in edifice form along the fissure. Partial floating of the overlying ice in the northern part is likely to have occurred due to high water pressures, reducing confinement by the ice and allowing lateral spreading of the edifice. The overall shape of the Gjálp ridge is similar to that of many Pleistocene hyaloclastite ridges in Iceland. Future preservation of the Gjálp ridge will depend on the rate of glacial erosion it will suffer. Besides being related to future ice flow velocities, the erosion rate will depend on the rate of consolidation due to palagonitization and shielding from glacial erosion while depressions in the ice are gradually filled by ice flow directed towards the Gjálp hyaloclastite ridge.