bluuebunny/crossref_metadata_2025_split huggingface dataset:
Rainwater and ash leachate analysis as proxies for plume chemistry at Soufrière Hills volcano, Montserrat
Authors: Edmonds M. , Oppenheimer C. , Pyle D. M. , Herd R. A. 
Published: April 2008

Abstract

Chloride and sulphate concentrations in rainwater and water-soluble leachates from volcanic ash samples track the compositions of gas emissions at the Soufrière Hills Volcano, Montserrat, from 1996 to 2001. There are both systematic spatial and temporal variations in the chloride/sulphate ratio (expressed as the equivalent HCl/SO
2
mass ratio) in rainwater and ash leachates. Temporal variations reflect changes in eruption rate and eruptive style. Mass ratios of HCl/SO
2
in ash leachates correspond closely with those obtained by open-path Fourier transform infrared (OP-FTIR) spectroscopy, and reflect changes in volatile emissions throughout the eruption. Both leachate and OP-FTIR spectroscopic analyses show mass ratios of HCl/SO
2
> 1 during dome growth, and HCl/SO
2
< 1 during non-eruptive periods.

The HCl/SO
2
mass ratios in rainwater samples from 1996 and 1997 show temporal variations that correlate with changes in extrusion rate. The HCl/SO
2
ratios in plume-affected rainwater and ash leachates from June and July 2001 correlate positively with increasing rockfall energy, and with increasing eruption rate prior to a dome collapse event. The HCl/SO
2
mass ratios in water-soluble ash leachates and rainwater samples collected at the same time and from the same sites, are linearly correlated, with rainwater HCl/SO
2
ratios systematically two to three times higher than ash leachate ratios. Spatial patterns of rainwater pH, and HCl/SO
2
in rainwater and ash leachates are principally influenced by the proximity of the sampling sites to the active dome, and to the typical pattern of dispersion of the plume by tropospheric winds. These results demonstrate that rainwater chemistry and ash leachate analysis provides a useful indicator of volcanic activity, and represents a valuable supplement to volcano surveillance efforts.
The 12 900 years
BP
Laacher See eruption: estimation of volatile yields and simulation of their fate in the plume
Authors: Textor C. , Sachs P. M. , Graf H.-F. , Hansteen T. H. 
Published: April 2008

Abstract

We estimated the volatile emissions of the 12 900 years
BP
eruption of Laacher See volcano (Germany), using a modified petrological method. Glass inclusions in phenocrysts and matrix glasses sampled over the Laacher See tephra profile were analysed by synchrotron X-ray fluorescence microprobe and electron microprobe to obtain the emitted masses of halogens, sulphur, and water. These data were used to initialize the numerical plume model ATHAM in order to investigate the fate of volcanic gases in the plume, and to estimate volatile masses injected into the stratosphere. The scavenging efficiency of each volatile component depends on its interactions with both liquid water and ice. We found a scavenging efficiency of
c.
5% for the sulphur species, and of only
c.
30% for hydrogen halides, despite their high water solubility. Our simulations showed that the greatest fraction of hydrometeors freeze to ice, due to the fast plume rise and great height of the eruption column. For the dry atmospheric conditions of the Laacher See eruption, the amount of liquid water was not sufficient to completely scavenge HCl and HBr, so that a large proportion could reach the stratosphere.
Illness and elevated human mortality in Europe coincident with the Laki Fissure eruption
Authors: Grattan J. , Durand M. , Taylor S. 
Published: April 2008

Abstract
Volcanic eruptions represent a significant source of volatile gases that are harmful to human health. This chapter reviews and develops current understanding of the human health response to volcanogenic pollution and dry fog events; in particular it explores the health impact of the gases from the Laki fissure eruption, and presents data that point to a significant increase in the national death rate in England coincident with the early phases of the eruption. It is noted that many common symptoms of severe exposure to air pollution can be linked to the dry fog of 1783; these included difficulty in breathing, eye and skin irritation, headaches, loss of appetite and tiredness.
Modelling fracture systems in extensional crystalline basement
Authors: Sanders C. A. E. , Fullarton L. , Calvert S. 
Published: April 2008

Abstract
Using observations from the extensional basin setting in Vietnam, conceptual models were developed to simulate and analyse fracture systems typical of crystalline basement in such structural settings. Information from field observations, seismic surveys and three-dimensional (3-D) structural modelling were integrated and used to build geologically realistic 3-D fracture networks. A major advantage of the method used in this study is that it allows a better understanding of the apparently chaotic fracture networks characteristic of such rocks, and of the processes responsible for fracturing. Several fracture generating processes are discussed and modelled, with emphasis on tectonic fractures and the relation to structural modelling. An example is presented highlighting the differences in fracturing in the hanging wall and footwall during lithospheric extension superimposed on a primary (igneous) cooling fracture network. Results suggest that during flexural uplift, the hanging wall is significantly more deformed than the footwall, implying the former is more prone to fracturing than the footwall for both kinematic and flexural isostatic processes.
Computed tomography in petroleum engineering research
Authors: Akin S. , Kovscek A. R. 
Published: April 2008

Abstract
Imaging the distribution of porosity, permeability, and fluid phases is important to understanding single and multiphase flow characteristics of porous media. X-ray computed tomography (CT) has emerged as an important and powerful tool for non-destructive imaging because it is relatively easy to apply, can offer fine spatial resolution and is adaptable to many types of experimental procedures and flow conditions. This paper gives an overview of CT technology for imaging multiphase flow in porous media, the principles behind the technology and effective experimental design. By critically reviewing prior work using this important tool, we hope to provide a better understanding of its use and a pathway to improved analysis of CT-derived data. Because of the wide variety of image processing options, they are discussed in some detail.
Study of the microgeometry of porous materials using synchrotron computed microtomography
Authors: Jones K. W. , Feng H. , Lindquist W. B. , Adler P. M. , Thovert J. F. , Vekemans B. , Vincze L. , Szaloki I. , Van Grieken R. , Adams F. , Riekel C. 
Published: April 2008

Abstract
A series of measurements of the structure of a variety of porous materials has been made using synchrotron computed microtomography (SCMT). The work was carried out at the Brookhaven National Synchrotron Light Source (NSLS), the Argonne Advanced Photon Source (APS) and the European Synchrotron Radiation Facility (ESRF). The experiments at Brookhaven and Argonne were carried out on bending magnet beam lines using area detectors to obtain CT images based on determination of X-ray absorption coefficients. The work at the ESRF used an undulator beam line, a 13 KeV pencil X-ray beam of 2 µm and an energy dispersive X-ray detector to make tomographic sections of trace element distributions by X-ray fluorescence tomography. Most of the work was done with a pixel/voxel size ranging from 0.002 to 0.010 mm. We examined the structure of unconsolidated estuarine sediments, whose structure is relevant to transport of contaminants in rivers and estuaries. Fluorescent tomography with 2–3 µm resolution was used to ascertain whether or not metals were concentrated on the surface or throughout the volume of a single sediment particle. Sandstone samples were investigated to obtain a set of values describing their microstructures that could be useful in fluid flow calculations relevant to petroleum recovery or transport of environmental contaminants. Measurements were also made on sandstone samples that had been subjected to high-pressure compression to investigate the relation between the microgeometry and the magnitude of the applied pressure. Finally, a Wood’s metal-filled sample was scanned for demonstration of resolution enhancement and fluid flow studies.
Three-dimensional visualization of fractures in rock test samples, simulating deep level mining excavations, using X-ray computed tomography
Authors: Sellers E. , Vervoort A. , Van Cleynenbreugel J. 
Published: April 2008

Abstract
A series of experiments on cubic blocks of quartzite were performed to create fractures with three-dimensional characteristics so that they could serve as verification examples for numerical models that are being developed to analyse the fracture processes around mining excavations. The experiments proved to be very successful for creating 3D fracture patterns that have characteristics similar to those observed underground. The shape and position of the fracture surface is determined by the mining geometry and by the interaction with pre-existing discontinuities. However, variations of the fracture planes within the sample could not be determined from the visual study of the block surfaces. The application of a state-of-the-art medical X-ray computed tomography scanner and the development of automatic surface reconstruction software provided a method of producing a full three-dimensional, digital view of fractures within laboratory test samples. Software was developed to provide an interactive graphical method for studying the scans in three orthogonal planes simultaneously. By contouring below a selected density threshold, three-dimensional images of the fracture surfaces were produced. X-ray computed tomography was found to provide a unique means of visualizing the fractures within rock test samples, which can greatly assist the study of rock fracture processes.
Rock drying tests monitored by X-ray computed tomography — the effect of saturation methods on drying behaviour
Authors: Rousset-Tournier B. , Mazerolle F. , Géraud Y. , Jeannette D. 
Published: April 2008

Abstract
Drying experiments were conducted under controlled conditions (relative humidity, temperature, motionless atmosphere) using Fontainebleau sandstone. X-ray computed tomography images acquired at various stages of the drying show that the location of water in the pore network depends on the method of initial saturation. After capillary absorption, the trapped air, or free porosity, allows the water distribution to be homogeneous and independent of the pore structure. This is because it homogenizes the tensions that apply to the water in the pores, regardless of the pore dimensions. However, this is not the case after a total saturation under vacuum. These differences are visible from the beginning to the end of the drying experiments. These results are important for curators or restorers of the architectural heritage, because they show that before testing a conservation product for stones, the method of saturation of these stones must be considered and attention should be given to the required effect.
Assessment of soil structure using X-ray computed tomography
Authors: Rogasik H. , Onasch I. , Brunotte J. , Jegou D. , Wendroth O. 
Published: April 2008

Abstract
Assessment of soil structure, characterized by complex morphological and functional properties, is difficult because most conventional soil physical investigations are destructive and variable in spatial resolution. The use of X-ray computed tomography, as a non-destructive technique, presents significant progress. It can be used to study soil structure at the millimetre scale, e.g. with a resolution of 0.25 mm in the horizontal direction and 1 mm in the vertical direction for the reported study. The measured Hounsfield Unit (HU) values characterize X-ray attenuation for each volume element of the soil core samples. From HU values, soil physical properties of soil cores or their subunits can be derived. They enable: (i) visual assessment of the soil structural condition through inspection of the X-ray CT images; (ii) 3D visualization of air-filled macropores; and (iii) calculation of the mean dry bulk density and standard deviation of voxel-related HU values for successive slices of soil cores. The degradation of structure of loamy and silty soils by tillage could be assessed by CT through quantification of decreased air-filled porosity, destroyed macropore connectivity, increased dry bulk density and decreased standard deviation of HU values in horizontal slices. Small-scale compactions near earthworm burrows could also be detected.
How sediments become mobilized
Authors: Maltman Alex J. , Bolton Alistair 
Published: April 2008

Abstract
Geological sediments tend to strengthen during progressive burial but the interplay of porosity and permeability, strain and effective stress gives rise to numerous circumstances in which the strength increase can be temporarily reversed. The sediment becomes capable of bulk movement — sediment mobilization. Most explanations involve overpressuring, which results from additional loading being sustained by pore-fluid that is unable to dissipate adequately, leading to frictional strength reduction. The processes are highly heterogeneous, areally and with depth. The loads can be external (‘dynamic’) and both monotonic (e.g. a rapidly added suprajacent mass) and cyclic (e.g. the passage of waves), internal (e.g. the result of mineral reactions) and hydraulic (e.g. injection of external fluid). The sediments may become liquidized — that is, lose strength completely and behave as a fluid — through temporary fabric collapse (sensitive sediments) because loads are borne entirely by the pore-fluid (liquefaction), or by the grains becoming buoyant (fluidization), typically due to the ingress of externally derived fluids. In response to hydraulic gradients, buoyancy forces and reversed viscosity or density gradients, the weakened sediment may undergo bulk movement, though this requires failure of the enclosing material and sustained gradients. Mobilized but non-liquidized sediments retain some residual strength but can attain large shear displacements under critical state conditions.
Load structures: gravity-driven sediment mobilization in the shallow subsurface
Authors: Owen Geraint 
Published: April 2008

Abstract
Load structures are a type of soft-sediment deformation structure comprising synforms (load casts and pseudonodules) and antiforms (flame structures and diapirs) at an interface. They form in response to unstable density contrasts (density loading) or lateral variations in load (uneven loading) when sediment becomes liquidized or otherwise loses strength. They are here classified into five varieties: simple and pendulous load casts, in which the upper (denser) layer is laterally continuous; and attached pseudonodules, detached pseudonodules and ball-and-pillow structure, in which discrete masses of the upper layer are separated by matrix. Conceptual models demonstrate that there are several possible modes of formation for each type of load structure. One interpretation of the variation of load structure morphology is as a deformation series representing varying degrees of deformation, controlled by the magnitude of the driving force and/or the duration of its effective action. An interpretation of the commonly observed pattern of wide load casts and narrow flame structures is presented in terms of their differential growth. Fluidization has an important influence on the development of load structures and their relationship to other products of sediment mobilization.
Fluidization pipes and spring pits in a Gondwanan barrier-island environment: groundwater phenomenon, palaco-seismicity or a combination of both?
Authors: Draganits E. , Grasemann B. , Schmid H. P. 
Published: April 2008

Abstract
Cylindrical structures, cross-cutting stratification at right angles, occur in the Muth Formation, representing Lower Devonian barrier island arenites of the North Indian Gondwana coast. These structures are up to 1.5 m in height and 0.8 m in diameter, with an internal structure comprising concentric, cylindrical laminae. The pipes, which probably represent water conduits for laminar upward flow of ground water, initiate from relatively thin horizons, with upper terminations formed by spring pits. Thus, the structures in the Muth Formation represent a rarely observed combined occurrence of spring pits and their conduits below. Their formation is explained by rising ground water seepage in a coastal depositional environment that produced a relatively high hydrostatic head, resulting in the formation of springs. The rise in relative sea level might be related to tectonic subsidence caused by tectonic activity linked to the formation of conjugate deformation bands in the Muth Formation. This means, if tectonic activity was involved, it did not form the cylindrical structures by seismic liquefaction directly, but might be responsible indirectly through ground water seepage rise resulting from tectonic subsidence. Due to the little relief in this environment, the sea level rise affected a relatively large area and fluidization structures can be found widespread in distant sections.
Experimental evidence on the role of gas in sediment liquefaction and mud volcanism
Authors: Pralle Norbert , Külzer Michael , Gudehus Gerd 
Published: April 2008

Abstract
Mud volcanoes are structures that are formed through ‘cold volcanism’ and indicate soil liquefaction. Their evolution depends on the structure, state and excitation of fine-grained feeding sediments. The disturbance of the framework of a loose, fine-grained, saturated sediment causes shear deformation leading to a pore fluid pressure increase. Effective stresses are thereby reduced and can vanish; the soil is then totally liquefied. Small amounts of enclosed gas bubbles render the soil compressible and enhance local shearing, pore pressure build-up and structural damage. Liquefield, overpressurized sediments form mud chambers, whose excess pressure is released through cracks and other inherent weak channels caused, for example, by density variations in the overlying strata.
Experiments were conducted on small-scale soil columns and on model slopes, using quartz powder as model material. Soil column tests were aimed at determining the influence of gas bubbles with regard to the liquefaction process, whereas model slope tests were targeted at the collapsability of gentle slopes, subject to atmospheric pressure changes. Different initial porosities were achieved through ion content variation. Liquefaction of fine-grained sediments and subsequent volcano evolution could be produced.
Shallow bottom-simulating reflectors on the Angola margin, in relation with gas and gas hydrate in the sediments
Authors: Nouzé Hervé , Baltzer Agnès 
Published: April 2008

Abstract

Acoustic facies interpretation, high-resolution velocity analysis and amplitude
versus
offset modelling have been performed on high resolution seismic data acquired on the West African margin offshore Angola, in water depths of about 2000 m. The area has a complex structural, thermal and fluid-flow setting, in which sediments are affected by salt diapirism and faulting associated with sediment compaction. A discontinuous bottom-simulating reflector (BSR) at a depth of about 200 m below sea floor could mark the base of the gas hydrate occurrence zone, which does not always coincide with the top of the free gas zone. Within the gas hydrate stability zone, a shallow bottom-simulating reflector is observed at a depth of about 75 m below seafloor. This shallow bottom simulating reflector, that is termed ‘sheep back reflector’ (SR), correspond to a small amount of gas being trapped in the sediments. It could mark the top of the gas hydrate occurrence zone, where gas hydrate dissociation may occur. A reversed polarity reflector (R1) is also observed about 25 m below the sea floor. This reflector could correspond to a limit between normally compacted and underconsolidated sediments, possibly related to a permeability change in the sediments. Thus, the occurrence of excess pore pressure generated during gas hydrate dissociation could explain some subsurface sediment mobilization processes.
Mobile shale related deformation in large deltas developed on passive and active margins
Authors: Morley C. K. 
Published: April 2008

Abstract
Understanding the nature of mobile shale deformation in deltas requires appreciation of several critical factors: (1) the tectonic setting (deposition on an active or passive margin); (2) the range of potential structural styles and how to identify them on seismic reflection data; (3) how structural styles evolve with time; (4) how to apply and modify what is understood about salt deformation to mobile shale deformation; and (5) how delta structures influence sedimentation. Differences between active and passive margin settings include: (a) active margins tend to display shorter, higher gradient drainage systems associated with high rates of erosion per unit area when compared with passive margins; (b) active uplift of the hinterland will force delta progradation (not seen on passive margin); (c) uplift causes erosion and re-cycling of older deltaic deposits which can cause comparatively fine grained sandstone reservoirs; and (d) the development of large compression-related folds and thrusts in the shelfal region of deltas on active margins can create areas of active uplift. Consequently, structurally controlled embayments may develop that cause distinct changes in the dominant depositional process (wave, tidal, fluvial) along the margin. On both active and passive margins, growing gravity-driven structures locally create sea floor highs and depressions and create changes in the dip of slopes which influence depocentre location and sediment pathways from the shelf to deepwater. A wide range of mud diapir geometry can be found in deltas. Commonly mud diapirs exhibit reactive, active, passive and collapse features. Some diapirs develop as compressional features seaward of fault bounded depocentres. Also frequently associated with delta provinces are fluid pipes, shale intrusions, fluid fronts and gas clouds. All the overpressure phenomena can produce dimming, or disruption of reflections on seismic reflection data, however the characteristics of the different phenomena are sufficiently diverse that they can frequently be differentiated on good quality data.
Analogue models of delta systems above ductile substrates
Authors: McClay Ken , Dooley Tim , Zamora Gonzalo 
Published: April 2008

Abstract
Delta systems developed above ductile substrates such as overpressured shales and salt have been modelled using layered sand-packs above ductile silicone polymer layers. Gravity spreading of progradational sedimentary wedges produces delta-top and upper delta-slope grabens linked to delta-toe contractional fold-thrust and diapir zones. The delta-top grabens are bound by both regional and counter-regional listric growth faults. A basinward-stepping sequence of regional, counter-regional followed by regional faulting is commonly developed. Polymer pillows and ridges commonly develop in the footwalls of the major listric extensional faults and may evolve into reactive diapirs. Successive progradational loads generate new delta-top or upper delta-slope graben systems on top of older contractional belts where the ductile polymer layer has been thickened significantly. The analogue model results in cross-section show many similarities to examples of natural deltas and differential sedimentary load systems such as offshore Angola, the Niger and Nile Deltas, Kutai Basin, Kalimantan, the Baram delta, Brunei and the Orinoco delta, Columbus basin and offshore Trinidad.