displacement pile behaviour in glacial clay the paper describes a programme of field experiments with heavily instrumented displacement piles installed in a stiff lodgement till measurements of the effective stresses recorded at various le

surface stresses associated with arrested dykes in rift zones many theoretical models predict that arrested dykes may generate major grabens at rift zone surfaces arrested dyke tips in eroded rift zones however are normally not associated with major grabens or normal faults that could be generated by dyke induced stresses ahead of the tips and normal faults and grabens tend to be less common in those parts of eroded rift zones where dykes are comparatively abundant similarly there are feeder dykes as well as dykes arrested a few metres below the surface that do not generate faults or grabens at the surface here i propose that this discrepancy between theoretical models and field observations may be explained by the mechanical layering of the crust numerical models presented here show that abrupt changes in young s moduli layers with high dyke normal compressive stresses stress barriers and weak horizontal contacts have large effects on the dyke induced stress fields for the models considered the surface tensile stresses induced by arrested dykes are normally too small to lead to significant fault or graben formation at the rift zone surface the only significant dyke induced surface tensile stresses 2 mpa in these models are for a dyke tip arrested at 1 km depth below the surface of a rift zone with a weak contact at 400 m depth and subject to extension that tensile stress however peaks above the ends of the weak horizontal contact which in the model considered occur at distances of 4 km to either side of the dyke and shows no simple relation to the depth to the dyke tip thus for a layered crust with weak contacts straightforward inversion of surface geodetic data to infer dyke geometries may result in unreliable results

spatially integrated geodetic glacier mass balance and its uncertainty based on geostatistical analysis application to the western svartisen ice cap norway estimates of glacier mass balance using geodetic methods can differ significantly from estimates using direct glaciological field based measurements to determine if such differences are real or methodological there is a need to improve uncertainty estimates in both methods in this paper we focus on the uncertainty of geodetic methods and describe a geostatistical technique that takes into account the spatial correlation of the elevation differences when calculating spatially averaged elevation changes we apply this method to the western svartisen ice cap norway using elevation differences from the surrounding bedrock derived from stereophotogrammetry we show that the uncertainty is not only dependent on the standard error of the individual elevation differences but is also dependent on the size of the averaging area and the scale of the spatial correlation to assess if the geostatistical analysis made over bedrock is applicable to glacier surfaces we use concurrent photogrammetrical and laser scanning data from bedrock and a range of glacier surfaces to evaluate the dependency of the geostatistical analysis on the surface type the estimated geodetic mass balance and its uncertainty is 2 6 0 9 m w e for the period 1968 85 and 2 0 2 2 m w e for 1985 2002

greenland ice sheet motion coupled with daily melting in late summer 1 we use ground based and satellite observations to detect large diurnal and longer period variations in the flow of the greenland ice sheet gris during late summer that are strongly coupled with changes in its surface hydrology the diurnal signals are associated with periodic changes in surface melting and the longer period signals are associated with the episodic drainage of supra glacial lakes ice velocity doubles around 2 hours after peak daily melting and returns approximately to wintertime levels around 12 hours afterwards demonstrating an intimate link between the surface and basal hydrology during late summer the ice sheet accelerates by 35 per positive degree day of melting the observed link between surface melting and enhanced flow is typical of alpine glaciers which may provide an appropriate analogue for the evolution of the gris in a warming climate

fossil fluid reservoir beneath a duplex fault structure within the central range of taiwan implications for fluid leakage and lubrication during earthquake rupturing process in order to understand the kinematics which likely facilitated the speedy rupturing process of the 1999 mw 7 6 taiwan chichi earthquake we examined exposed rocks in the taiwan slate belt where the pressure and temperature conditions most resembled the hypocentre of the chi chi earthquake i e subgreenschist facies field observations and composition analyses of the silicified vein rich zones beneath the duplex structure suggest that impermeable slate layers may serve as cap rocks for confining deep seated fluids these fluids most likely come from the taiwan metamorphic complex at deeper depths by the dehydration and decarbonation reactions or partial melting in addition the gouge zone of a link fault above the detachment also indicates the presence of overpressured fluids during faulting it is probable that episodic leakage of the confined fluid reservoirs may provide essential fluids for fault lubrication during earthquake ruptures

effects of overpressure variations on fracture apertures and fluid transport abstract for an isolated rock fracture in a homogeneous isotropic rock subject to constant internal fluid overpressure or constant external driving stress the ideal opening displacement aperture profile or variation is that of a flat ellipse for many mineral veins dykes tension fractures normal faults and other rock fractures however the opening displacements show irregular aperture thickness variations very different from that of a flat ellipse here we present field data on typical fracture aperture variations as well as new numerical and analytical models to explain these data we present the overpressure variation by fourier cosine series a very flexible method that can be used to model abrupt overpressure and driving stress variations in vertical and lateral sections for fractures of various sizes and types we calculate the opening displacements of typical hydrofractures and discuss the results with reference to mineral veins and dykes we also present numerical models showing that when a fracture dissects layer or parts of a single layer such as a lava flow with different stiffnesses young s moduli the opening displacement may show irregular variation even when the overpressure is constant from the cubic law the volumetric flow rates in the large aperture segments of the mineral veins and dykes discussed in the paper may have been as much as 3 5 times the flow rates in the small aperture segments we propose that differences in volumetric flow rates are related to irregular opening displacement variations in feeder dykes is one principal reason for the development of crater cones a universal feature of volcanic fissures

estimating the ocr in uniform cohesive soil with cone penetrometer tests considering soil structure and index properties a basic empirical approach to estimate the preconsolidation stress and overconsolidation ratio ocr in uniform cohesive soils using the cone penetration and piezocone tests uses a correlation fact

propagation pathways and fluid transport of hydrofractures in jointed and layered rocks in geothermal fields abstract palaeofluid transporting systems observed as networks of mineral filled veins in deeply eroded parts of extinct geothermal fields indicate that hydrofractures commonly supply fluids to geothermal fields here we examine well exposed vein networks that occur at crustal depths of around 1 5 km below the initial surface of the tertiary lava pile in north iceland the veins are located in the damage zone of a major fault zone that dissects basaltic lava flows the most common host rocks of geothermal fields in iceland the lava flows contain numerous weaknesses particularly columnar cooling joints and contacts for hydrofractures to supply fluids to geothermal fields the fractures must be able to propagate and transport fluids to the surface we explore hydrofracture pathway formation using boundary element models of hydrofractures with fluid overpressure varying linearly from 10 mpa at the fracture centre to 0 mpa at the fracture tip or the fluid front the hydrofractures propagate through a vertically jointed and horizontally layered pile of lava flows with a general rock matrix young s modulus of 1 10 10 pa and a poisson s ratio of 0 25 the joints and contacts between layers are modelled as internal springs each with a stiffness strength of 6 mpa m the location and sizes of discontinuities as well as the location of the hydrofracture tip vary between the models the results indicate that tensile stresses generated at the tip of an overpressured hydrofracture can open up horizontal and vertical discontinuities out to a considerable distance from the tip and that these discontinuities eventually link up to form the hydrofracture pathway analytical models indicate that for a hot spring of a given yield associated with a fault the dimensions of the fluid transporting part of the fault are likely to be similar for a typical normal fault and a strike slip fault also a hot spring of yield 180 l s the maximum in the low temperature fields of iceland can be supplied through a hydrofracture of aperture 3 mm and trace length 1 2 m these dimensions are very similar to those of typical veins in the studied networks buoyancy rather than excess pressure in the fluid source appears to be the primary driving force of hydrofractures in the geothermal fields of iceland

evolution of magma conduits during the 1998 2000 eruptions of piton de la fournaise volcano reunion island 1 at basaltic volcanoes magma is transported to the surface through dikes magma filled fractures but the evolution of these dikes as eruptions proceed is rarely documented in march 1998 after five and a half years of quiescence piton de la fournaise volcano reunion island entered into a new eruptive phase characterized by intense eruptive activity coeruptive displacements recorded by interferometric synthetic aperture radar insar for the first five eruptions of the cycle are analyzed using 3 d boundary element models combined with a monte carlo inversion method we show that the eruptions are associated with the emplacement of lateral dikes rooted at depths of less than about 1000 m except for the first march 1998 event where an additional deeper source is required the dikes are located above preeruptive seismic swarms this is consistent with nearly isotropic stress caused by repeated dike intrusions and low confining pressure enhanced by the presence of pores in the shallowest 1000 m of the edifice the volumes of the modeled dikes represent 17 of the volume of emitted lava showing that exogenous growth plays a major role in building the volcano by taking into account the preeruptive seismicity and tilt data together with the results of insar data modeling we find that dikes first propagate vertically from a source region below sea level before being injected laterally at shallow depth this behavior is consistent with the presence of levels of neutral buoyancy at shallow depth in the edifice

surface deformation associated with a dipping hydrofracture crustal deformation associated with hydrofracture is modeled by a dipping rectangular dislocation beneath the surface of an elastic half space the burger s vector is taken normal to the rectangular surface analytical expressions for vertical displacements are obtained from integration of volterra s equation by using mindlin s point force solutions for the elastic halfspace in the limits of 0 and 90 dip the results agree with those obtained by maruyama 1964 for poisson s ratio 0 25 expressions for arbitrary poisson s ratio are given for elongate dislocations the displacement field agrees with curves given by pollard and holzhausen 1979 for two dimensional near surface fractures at various dips at dip 0 a deep square dislocation gives displacements indistinguishable from those of sun s 1969 model of a horizontal penny shaped crack beneath the surface of an elastic half space modifying his result for shallow depths shows that they correspond to a dislocation of semi elliptical cross section with the surface displacement field asymptotically approaching a semi elliptical shape as depth decreases to zero similarly the surface displacement field of the square dislocation approaches that of its rectangular cross section nonlinear inversion of surface tilt fields associated with hydrofracture of deep boreholes gives estimates of fracture geometry position and orientation along with their uncertainties two examples are presented one of a near horizontal and one of a near vertical fracture

mechanisms of dike propagation in layered rocks and in massive porous sedimentary rocks the mechanisms of dike propagation are analyzed through detailed examination of small structures associated with the dike intrusion exposures in the ramon area israel offer an opportunity to evaluate theoretical models of tensile fracture propagation and to better understand the factors governing the dike geometry dike related structures are studied in two jurassic units the ardon formation a well stratified sequence of shales and dolomites and the inmar formation which is composed of porous massive sandstones with a few shale lenses it is shown that for the different host rocks the propagation mechanisms and structures differ significantly dikes in the ardon formation are dominated by 1 20 m wide segments confined to distinct layers the mechanisms of segment containment are determined by calculating the stress intensity factor for an extension crack approaching a mechanical interface it is apparent that dike segmentation and containment is controlled mainly by in situ stress and shear moduli differences between adjacent layers and partly by bedding plane slippage dikes in the inmar formation are dominated by smaller segments and by 1 10 cm wide and 10 100 cm long fingers with intermittent smooth patches and slickensides opposite dike walls display exact mirror images of these features dikes propagate in alternating stages of viscous flow and brittle deformation the viscous stages include fluidization of the sandstone by the dike related fluids and increase of the pore pressure in the rock a viscous instability develops between the highly viscous fluidized sandstone and the less viscous dike related fluids forming a zone of viscous fingering in front of the dike stages of brittle fracturing occur when the pore pressure is released and the flux of fluids is insufficient to fluidize the rock

improving maps of ice sheet surface elevation change using combined laser altimeter and stereoscopic elevation model data we combine the complementary characteristics of laser altimeter data and stereoscopic digital elevation models dems to construct high resolution 100m maps of surface elevations and elevation changes over rapidly changing outlet glaciers in greenland measurements from spaceborne and airborne laser altimeters have relatively low errors but are spatially limited to the ground tracks while dems have larger errors but provide spatially continuous surfaces the principle of our method is to fit the dem surface to the altimeter point clouds in time and space to minimize the dem errors and use that surface to extrapolate elevations away from altimeter flight lines this reduces the dem registration errors and fills the gap between the altimeter paths we use data from icesat and atm as well as spot 5 dems from 2007 and 2008 and apply them to the outlet glaciers jakobshavn isbrae ji and kangerdlugssuaq kl we find that the main trunks of ji and kl lowered at rates of 30 35 and 7 20ma respectively the rates decreased inland the corresponding errors were 0 3 5 2ma 1 for ji and 0 3 5 1ma 1 for kl with errors increasing proportionally with distance from the altimeter paths

how hydrofractures become arrested fluids in the earth s crust are commonly transported by hydrofractures such as dykes and mineral veins many of which become arrested at various crustal depths hydrofractures are commonly arrested some showing blunt tips at contacts between soft low young s modulus and stiff high young s modulus layers for example many dyke tips are arrested at contacts between soft pyroclastic rocks and stiff basaltic lava flows and vein tips at contacts between soft marl and stiff limestone theoretical models indicate that overpressured buoyant hydrofractures in homogeneous isotropic host rocks should normally reach the surface in layered host rocks however abrupt changes in young s moduli horizontal discontinuities and layers with unusually high fracture perpendicular stresses encourage hydrofracture arrest it is proposed that for layer parallel loading stiff layers favour hydrofracture arrest during active compression but soft layers during extension it is concluded that for hydrofracture propagation to occur the stress field along its potential pathway must be essentially homogenous

the propagation and seismicity of dyke injection new experimental evidence to reach the surface dykes must overcome the inherent tensile strength of the country rock as they do they generate swarms of seismic signals frequently used for forecasting in this study we pressurize and inject molten acrylic into an encapsulating host rocks of 1 etna basalt and 2 comiso limestone at 30 mpa of confining pressure fracture was achieved at 12 mpa for etna basalt 7 2 mpa for comiso limestone the generation of radial fractures was accompanied by acoustic emissions ae at a dominant frequency of 600 khz during magma movement in the dykes ae events of approximately 150 khz dominant frequency were recorded we interpret our data using ae location and dominant frequency analysis concluding that the seismicity associated with magma transport in dykes peaks during initial dyke creation but remains significant as long as magma movement continues these results have important implications for seismic monitoring of active volcanoes

interaction and linkage of extension fractures and normal faults examples from the rift zone of iceland abstract field and photogeological studies were made of 90 zones of interacting fracture segments along the rift zone of iceland each zone consists of a pair of extension fractures or a pair of normal faults with lengths from metres to kilometres these zones evolve from an underlapping stage through an overlapping stage the most common configuration and finally to a linkage stage of all the zones only 7 are underlapping whereas 93 are overlapping with hook shaped fracture pairs the length width ratios of the overlapping zones have a mean value of 3 5 the preferred geometry of the overlapping zones depends upon the initial configuration of the interacting fractures length overstep and the development of the interaction in the overlapping zones most fracture pairs show moderate shear strike slip components related to local variations in the extension opening directions vertical displacements on normal faults decrease as the overstep and length of overlapping zones increase both in turn are proportional to the total lengths of the faults forming the pair the geometrical and kinematic features of overlapping spreading centres at mid ocean ridges show close similarities to those reported here these similarities indicate that the architecture and evolution of overlapping zones are scale independent

recent changes on greenland outlet glaciers aircraft laser altimeter surveys during the 1990s showed near coastal parts of the greenland ice sheet to be thinning despite slow thickening at higher elevations the ice sheet lost mass to the ocean many outlet glaciers thinned more rapidly than could be explained by increased melting during the recent warmer summers indicating dynamic imbalance between glacier velocity and upstream snow accumulation results from more recent surveys presented here show that thinning rates have increased in most coastal regions for almost half of the surveys these increases might have resulted from increases in summer melting but rapid thinning on others is indicative of dynamic changes that increased with time in particular thinning rates on the three fastest glaciers increased to tens of m a 1 after 2000 and other observations show an approximate doubling in their velocities the deep beds of these glaciers appear to have a strong influence on rates of grounding line retreat and thickness change with periods of glacier acceleration and rapid thinning initiated by flotation and break up of lightly grounded glacier snouts or break up of floating ice tongues near simultaneous thinning of these widely separated glaciers suggests that warming of deeper ocean waters might be a common cause nearby glaciers without deep beds are thinning far more slowly suggesting that basal lubrication as a result of increased surface melting has only a marginal impact on greenland outlet glacier acceleration

seasonal speedup along the western flank of the greenland ice sheet it has been widely hypothesized that a warmer climate in greenland would increase the volume of lubricating surface meltwater reaching the ice bedrock interface accelerating ice flow and increasing mass loss we have assembled a data set that provides a synoptic scale view spanning ice sheet to outlet glacier flow with which to evaluate this hypothesis on the ice sheet these data reveal summer speedups 50 to 100 consistent with but somewhat larger than earlier observations the relative speedup of outlet glaciers however is far smaller 15 furthermore the dominant seasonal influence on jakobshavn isbrae s flow is the calving front s annual advance and retreat with other effects producing outlet glacier speedups an order of magnitude larger seasonal melt s influence on ice flow is likely confined to those regions dominated by ice sheet flow

advantageous goes ir results for ash mapping at high latitudes cleveland eruptions 2001 1 the february 2001 eruption of cleveland volcano alaska allowed for comparisons of volcanic ash detection using two band thermal infrared 10 12 m remote sensing from modis avhrr and goes 10 results show that high latitude goes volcanic cloud sensing the range of about 50 to 65 n is significantly enhanced for the cleveland volcanic clouds the modis and avhrr data have zenith angles 6 65 degrees and the goes has zenith angles that are around 70 degrees the enhancements are explained by distortion in the satellite view of the cloud s lateral extent because the satellite zenith angles result in a side looking aspect and longer path lengths through the volcanic cloud the shape of the cloud with respect to the goes look angle also influences the results the modis and avhrr data give consistent retrievals of the ash cloud evolution over time and are good corrections for the goes data

fusion of multi sensor surface elevation data for improved characterization of rapidly changing outlet glaciers in greenland abstract during the last two decades surface elevation data haven been gathered over the greenland ice sheet gris from a variety of sensor ranging from laser altimetry to stereoscopic dems derived from imaging sensors the spatio temporal resolution the accuracy and the spatial coverage among the data differ widely for example icesat a spaceborne laser profiler has a high temporal resolution but sparse spatial coverage which places the nearest ground track to the calving front of the kangerlussuaq glacier in east greenland our study site 30 km up stream on the other hand stereoscopic dems provide almost continuous spatial coverage but at a lower accuracy this is a typical scenario for many rapidly changing outlet glaciers in greenland where a fusion of the disparate data sets is highly desirable to construct detailed spatio temporal histories of elevation change we present in this paper how our recently developed serac method surface elevation reconstruction and change detection is well suited to cope with this fusion problem more specifically we describe a novel approach to adjust stereoscopic dems to the laser altimetry point cloud based on height corrections determined from the time series of elevation changes calculated by serac these corrections are then used in a height adjustment of the dems

thermal and mechanical aspects of magma emplacement in giant dike swarms we consider the thermal history and dynamics of magma emplacement in giant feeder dikes associated with continental flood basalts for driving pressure gradients inferred for giant dike swarms thicknesses of 10 m would enable dikes to transport magma laterally over the distances observed in the field up to thousands of kilometers without suffering thermal lock up using time dependent numerical solutions for the thermal evolution of a dike channel under laminar and turbulent flow conditions in the presence of phase transitions we investigate the possibility that the observed dike thicknesses of the order of 100 m result from thermal erosion of the country rocks during dike emplacement this implies that the observed range of dike widths in giant dike swarms may reflect variations in the source volume and not the excess magma pressure it is found that the total volume of intruded magma required to produce an order of magnitude increase in dike width via wall rock melting broadly agrees with the estimated volumes of individual flows in continental flood basalts the presence of chilled margins and apparently low crustal contamination characteristics of some giant dikes may be consistent with turbulent magma flow and extensive melt back during dike emplacement in this case measurements of the anisotropy of magnetic susceptibility most likely indicate magma flow directions during the final stages of dike intrusion shear stresses generated at the dike wall when the dike starts to freeze strongly decrease with increasing dike width which implies that thicker dikes may have less tendency to produce consistent fabric alignment our results suggest that if the dike was propagating downslope off a plume related topographic swell the mechanism responsible for flow termination could possibly have been related to underpressurization and collapse implosion of the shallow magma plumbing system feeding the intrusion radial dikes that erupted at the periphery of the topographic uplift might have increased rather than decreased extensional stresses in the crust within the topographic uplift upon their solidification

glacier volume changes using aster satellite stereo and icesat glas laser altimetry a test study on edgeoya eastern svalbard currently one of the major methodological gaps in the observation of glaciers from space is the measurement of volume changes of mountain glaciers and ice caps in this paper we present a case study of comparing a digital elevation model derived from advanced spaceborne thermal emission and reflection radiometer aster satellite optical stereo elevation data derived from ice cloud and land elevation satellite geoscience laser altimeter system glas laser altimetry and contour lines from a topographic map from the 1970s for two ice caps in eastern svalbard kvalpyntfonna and digerfonna we obtain an overall elevation change of 0 55 or 0 61 m year between 1970 and 2002 aster or glas 2006 respectively from comparison of different methods and from different quality checks we estimate the error of this numbers to be on the order of 5 this paper demonstrates that and on how long term glacier volume changes can be observed from space over a large number of ice caps and glaciers

insights of dyke emplacement mechanics from detailed 3d dyke thickness datasets abstract dyke thickness datasets offer new insights into the detailed 3d geometry of dyke swarms and an exceptional opportunity to evaluate theoretical emplacement models the swartruggens kimberlite dyke swarm extends over 7 km along strike and intrudes a dolerite quartzite shale and andesitic lava succession the star kimberlite dykes cut shales and sandstones intersect a large dolerite sill and extend 15 km along strike both dyke swarms comprise anastomosing en echelon segments each several hundred metres long in total 1532 swartruggens dyke thickness measurements were taken to 750 m below the surface over a 250 m depth range and 3354 star dyke thickness measurements were taken over a 520 m depth range the swartruggens dyke thicknesses are 0 05 1 95 m mean 0 64 m whereas the star kimberlites range from

dike induced faulting in rift zones of iceland and afar geodetic data and field observations demonstrate that the emplacement of dikes in volcanic rift zones frequently generates normal faulting and graben subsidence at the earth9s surface elastic modeling of the vertical ground surface displacements above dikes and faults indicates that the extent of graben subsidence can be achieved only if fault slip extends virtually to or beyond the dike plane at depth a mechanical model that includes dikes and frictional faults shows that dike opening tends to compress and lock faults located to either side of the dike therefore slip extending into or beyond the dike cavity must occur either 1 on faults that intersect the dike near its top above the zone of dike induced compression or 2 on faults that slip ahead of the dike as it propagates laterally data from iceland indicate that slip occurred on deep faults that presumably slipped in advance of the laterally propagating dike

extension fracture propagation in rocks with veins insight into the crack seal process using discrete element method modeling 1 we investigate how existing veins interact with extension fractures in rocks using 3 d discrete element method models with a geometry inspired by tension tests with notched samples in a sensitivity study we varied a the angle between the vein and the bulk extension direction and b the strength ratio between host rock and vein material results show a range of vein fracture interactions which fall into different robust structural styles veins which are weaker than the host rock tend to localize fracturing into the vein even at high misorientation angles veins which are stronger than the host rock cause deflection of the fracture tip along the vein host rock interface fractures are arrested at the interface from weak to stronger material when propagating from a stronger to a weaker material macroscopic bifurcation of the fracture is common complex interactions are favored by a low angle between the vein and the fracture and by high strength contrast the structural styles in the models show good agreement with microstructures and mesostructures of crack seal veins found in natural systems we propose that these structural styles form the basis for criteria to recognize strength contrasts and stress of crack seal systems in nature

stress estimates from the length width ratios of fractures the hypothesis is advanced that provided young s modulus and poisson s ratio of the rock are known the length width ratios of tension fractures can be used to estimate the tensile stress assumed constant along the length of each fracture at the time of fracture formation the hypothesis is tested on a fissure swarm in a 10 000 year old basaltic lava in iceland the length width ratios of the fissures give the average tensile stress as of the order of a few mpa

dynamics of volcanic systems in iceland example of tectonism and volcanism at juxtaposed hot spot and mid ocean ridge systems volcanic systems are swarms of tectonic fractures and basalt volcanoes formed as a result of plate pull as the plates are pulled apart associated with the mid ocean ridges and the magma dynamics of the iceland mantle plume most systems are 40 150 km long 5 20 km wide and develop a central volcano they supply magma to all eruptions in iceland data obtained in the last few years have greatly improved our knowledge of their volcanotectonic environment as a result the geometry of the plume is better constrained and the crust previously considered thin 10 km is now modeled as thick 20 40 km depending on the location of the volcanic systems their activity either decreases or increases faulting in the two main seismic zones from this we can infer that emplacement of the feeder dike to the largest historical eruption in iceland that of laki in 1783 increased shear stress in the south iceland seismic zone and almost certainly triggered the largest m 7 1 in 1784 historical earthquake in ic

an updated global review of solutional weathering processes and forms in quartz sandstones and quartzites abstract quartz is considered one of the less soluble minerals of the earth s crust and thus hardly affected by chemical weathering despite this for more than forty years it is clear that the formation of caves and peculiar solutional weathering dominated landforms in quartz rich lithologies is common and shares several similarities to the well known karstic ones in carbonate rocks in the last thirty years great strides have been made in furthering our knowledge of the distribution of these forms around the world and the geochemical processes involved these studies have clearly shown that solutional weathering is a fundamental process acting through intergranular dissolution of quartz increasing the rock porosity and decreasing the rock strength to erosion this process has been described in the concepts of arenization and phantomization and the widespread evidences of the fundamental role of quartz solution in landform genesis has even developed to the extent of several geomorphologists reassessing the definition of the term karst and its application to these peculiar lithologies nonetheless the process is complicated by several factors related both to environmental conditions water chemistry and availability as well as to the compositional and textural characters of the lithology presence of clays iron hydroxides carbonate cement etc all these aspects have to be taken carefully in consideration in order to understand if solution is a dominant or accessory process in the landscape evolution in this review the state of knowledge on the relevant chemical processes weathering mechanisms and speleogenesisk involved in the surface and underground karstification and clear examples of quartz solution and solutional landforms from different world locations are outlined and discussed

spread of ice mass loss into northwest greenland observed by grace and gps 1 greenland s main outlet glaciers have more than doubled their contribution to global sea level rise over the last decade recent work has shown that greenland s mass loss is still increasing here we show that the ice loss which has been well documented over southern portions of greenland is now spreading up along the northwest coast with this acceleration likely starting in late 2005 we support this with two lines of evidence one is based on measurements fromthegravityrecoveryandclimateexperiment grace satellite gravity mission launched in march 2002 the other comes from continuous global positioning system gps measurements from three long term sites on bedrock adjacent to the ice sheet the grace results provide a direct measure of mass loss averaged over scales of a few hundred km the gps data are used to monitor crustal uplift caused by ice mass loss close to the sites the grace results can be used to predict crustal uplift which can be compared with the gps data in addition to showing that the northwest ice sheet margin is now losing mass the uplift results from both the gps measurements and the grace predictions show rapid acceleration in southeast greenland in late 2003 followed by a moderate deceleration in 2006 because that latter deceleration is weak southeast greenland still appears to be losing ice mass at a much higher rate than it was prior to fall 2003 in a more general sense the analysis described here demonstrates that gps uplift measurements can be used in combination with grace mass estimates to provide a better understanding of ongoing greenland mass loss an analysis approach that will become increasingly useful as long time spans of data accumulate from the 51 permanent gps stations recently deployed around the edge of the ice sheet as part of the greenland gps network gnet citation khan s a j wahr m bevis i velicogna and e kendrick 2010 spread of ice mass loss into northwest greenland observed by grace and gps geophys res lett 37 l06501 doi 10 1029 2010gl042460

dykes faults and palaeostresses in the teno and anaga massifs of tenerife canary islands abstract a structural field study was made of 578 sheet intrusions mostly dykes and 153 mostly normal faults dissecting the anaga and teno massifs where a complex volcanic succession of tertiary age the old basaltic series representing the shield building stage of tenerife canary islands crops out many of the intrusions mostly sub vertical mafic dykes are emplaced by multiple magma injections with cumulative thicknesses mostly less than 2 m dyke tips are exposed and preserved for 12 of the dykes three differently oriented sets of dykes exist in the anaga massif nnw sse nne ssw e w whereas there is only one main set in teno trending nnw sse dyke swarms and other structural features having similar orientations also exist in other canary islands a minimum value of the horizontal component of extension induced by dykes is computed using a step of 5 of azimuth accounting also for the dip of dykes the cumulative crustal dilation is at least 300 m 4 in anaga and 270 m 6 in teno the maximum extension peaks at n75 in anaga and n60 in teno indicating a general prevailing extension in direction ene wsw most of the measured faults are normal and strike nnw sse computation of palaeostresses from inversion of fault slip data sets suggests the existence of a polyphase brittle deformation due to an extensional stress field with the minimum compressive principal axes trending ne sw and wnw ese

rapid changes in ice discharge from greenland outlet glaciers using satellite derived surface elevation and velocity data we found major short term variations in recent ice discharge and mass loss at two of greenland s largest outlet glaciers their combined rate of mass loss doubled in less than a year in 2004 and then decreased in 2006 to near the previous rates likely as a result of fast re equilibration of calving front geometry after retreat total mass loss is a fraction of concurrent gravity derived estimates pointing to an alternative source of loss and the need for high resolution observations of outlet dynamics and glacier geometry for sea level rise predictions

effects of crustal scale mechanical layering on magma chamber failure and magma propagation within the venusian lithosphere understanding the connection between shallow subsurface magmatism and related surface expressions provides first order insight into the volcanic and tectonic processes that shape a planet s evolution when assessing the role of flexure previous investigations assumed homogeneous host rock but planetary lithospheres typically include crust and mantle material and the mechanical response of a layered lithosphere subjected to flexure may influence both shallow magma reservoir failure and intrusion propagation to assess the formation of giant radial dike systems such as those observed on venus we create axisymmetric elastic finite element models of a spherical reservoir centered at the contact between stiff dense mantle overlain by softer lighter crust we analyze magma chamber stability overpressure at rupture and resulting intrusion types for three distinct environments lithostatic upward flexure and downward flexure in the lithostatic case reservoir failure at the crust mantle contact favors lateral sill injection in the flexure cases we observe that failure location depends upon the crust lithosphere thickness ratio and at times will favor radial dike intrusion specifically upward flexure can promote the formation of giant radiating dike swarms a scenario consistent with a plume derived origin our results present a mechanical explanation for giant radial dike swarm formation showing that both the stability of magma chambers on venus and the type of intrusions that form are influenced by lithospheric layering furthermore where dike swarms occur our approach provides a powerful new way to constrain local crust mantle layering characteristics within the lithosphere at the time the swarm was forming

hydrofracturing stress measurements in the iceland research drilling project drill hole at reydarfjordur iceland two independent suites of hydrofracturing stress measurements were conducted in the top 600 m of the iceland research drilling project deep hole at reydarfjordur east iceland as indicated by the continuously extracted drill core the tested section consists of tertiary subaerial tholeiitic lava flows cut by many basaltic dikes the density of the basalt was used to estimate the vertical stress v in megapascals at depth d in meters v 0 027d in the 33 to 270 m depth range the horizontal principal stresses hmax and hmin as calculated from hydrofracturing results increase gradually with depth but at a lower rate than the vertical stress hmin 2 1 0 016d hmax 3 3 0 016d in the 300 to 550 m depth range a major perturbation occurs with both horizontal stress magnitudes rapidly rising between 300 and 400 m and then uniformly decreasing between 400 and 550 m to a level apparently predictable by the relationships obtained in the top 270 m conditions favoring normal faulting v hmax hmin were established in the 540 to 580 m range and are conjectured to persist at greater depths since the vertical stress gradient is higher than that of hmax and hmin this would be in accord with the predominant fault type in east iceland the relative low horizontal stress values and the small difference between them are supportive of ocean floor spreading theories and contradict near surface high compressive stresses previously determined by hast 1973 in east iceland the large increase in horizontal stress in the range of 300 to 500 m depth is not understood a correlation appears to exist between the zone of almost unintruded thick lava flows 200 500 m and that of high stresses an intuitive model suggesting locked in stresses in this zone is proposed the hydrofracturing determined overall mean direction of hmax is n50 e while a more selective sampling of results yields n40 e the measured stress directions appear to be reasonably compatible with the local structure such as dike direction nne and lava dip wsw significantly hmax direction is subparallel to the n20 e trend of the nearest fissure swarms in the axial rift zone this almost coincidence of directions like the measured stress magnitudes is also in agreement with the model of spreading lithospheric plates being pulled apart

mechanical controls on horizontal stresses and fracture behaviour in layered rocks a numerical sensitivity analysis in layered materials the deformation style orientation confinement and 3d connectivity of natural fractures is generally impacted by changes in sedimentary facies and alternations in mechanical properties in this study we address this effect and perform a numerical sensitivity analysis mechanical properties confining pressures and interfacial frictions are varied for a three layered model to investigate and quantify the relation between contrasting material properties the principal horizontal stresses and fracture behaviour i e deformation style and orientation firstly the results show that tensile stresses develop in the stiffer layers due to the contrasting elastic parameters the magnitude of these stresses is dependent on the ratio between the elastic parameters of stiffer and softer layers i e estiff esoft and stiff soft there are no horizontal tensile stresses when applying a compressive horizontal confining pressure approx 1 5 of the applied vertical stress implementing an interfacial friction lower than 0 2 will result in decoupling of the layers resulting in slip on the layer boundaries and no tensile stresses within the stiffer layers further the acquired numerical results are in good agreement with previously conducted laboratory work finally we discuss whether the presented results can be used for better relating contrasting mechanical properties to potential fracture deformation styles and orientations in layered outcrops or subsurface reservoirs

crustal spreading due to dikes and faults in southwest iceland abstract a 30 km long profile extending from 3 million year old pleistocene rocks to the holocene rocks of the rift zone in southwest iceland is dissected by 443 dikes and 156 normal faults nearly all the dikes are basaltic with an average strike of n26 e which is subparallel to the trend of fractures in the nearby rift zone their average dip is 69 and average thickness 1 37 m both values much lower than averages for regional tertiary dike swarms in iceland many dikes are seen to change into sills the great majority of the faults are pure dip slip with an average throw of 10 2 m their average strike n37 e is different from the average strike of the dikes in this area and the fractures in the nearby rift zone their average dip is 75 2 which is somewhat steeper than in the tertiary areas but the dips are less in the interbedded sedimentary layers than in the lava flows growth faults are very rare in the area and most of the faults appear to have completed their growth in less than 10 000 years in subsections crustal dilation due to dikes is 0 4 3 7 that due to faults is 0 6 5 3 and that due to both dikes and faults is 1 04 6 44 in these subsections average fault spacing is one fault per 170 563 m spacing decreases toward the active rift zone it is concluded that in typical fissure swarms of the rift zone the dilation at the surface is almost entirely due to extensional fractures and gaping vertical normal faults in the depth range of a couple of hundred metres to perhaps 1 km the non vertical faults contribute most to the dilation at deeper crustal levels however dilation due to dikes becomes dominant

emplacement of dikes sills and crustal magma chambers at divergent plate boundaries abstract a model of dike emplacement at divergent plate boundaries is developed which predicts that below the uppermost 1 3 km of the oceanic crust the number and lengths of dikes in any particular swarm should increase but that the thickness should decrease with depth in the crust these predictions are supported by field observations it is proposed that rapid injections of dikes at divergent plate boundaries may temporarily alter the normal stress field in such a way that at a certain level in the crust subsequent dikes change into sills such sills may develop into crustal magma chambers either when many nearby sills combine into a large one or when an initial sill absorbs the magma of many dikes that enter it in a rapid succession while the sill is liquid for the fastest spreading ridges the initial thickness of a sill that is to develop into a crustal chamber need only attain 20 m whereas at the slowest spreading ridges the initial thickness must exceed 170 m because thin sills are much more likely to form than thick sills the probability of sills developing into crustal chambers increases with dike intrusion frequency hence with spreading rate furthermore the model predicts first that with increasing spreading rate the length of the chamber along the ridge axis should increase and second that the most likely site for magma chambers is at depths of 2 4 km both these predictions are supported by available data

kilometer scale upward migration of hydrocarbons in geopressured sediments by buoyancy driven propagation of methane filled fractures several lines of evidence support kilometer scale upward migration of fluids in the gulf of mexico basin discharge of hypersaline brines at the sea floor long term natural hydrocarbon seeps and microseeps gas chimneys lead zinc mineralization in salt dome cap rocks and allochthonous brines in cenozoic sediments we explore the hypothesis that upward fluid transport in geopressured sediments is caused by buoyancy driven propagation of isolated methane filled fractures in other words instead of fluid migrating along a fixed network of interconnected pores or fractures fluid enclosed within an isolated fracture is transported upward by hydrofracturing the mechanically weak geopressured sediments thus the fluid filled fracture propagates upward through the sediments hydrofracture is driven by the pressure difference buoyancy between the enclosed methane and the surrounding sediments our results show that methane filled fractures with half lengths of a few meters should propagate upward through geopressured sediments with velocities of hundreds of meters per year or higher as methane filled fractures increase in volume and decrease in density with decreasing confining pressure they develop the potential to entrain and transport more than 1000 kg m3 of oil or brine methane filled fractures should propagate to the surface unless they are trapped beneath a layer that has high fracture toughness such as salt or are absorbed when they intersect a permeable 10 md sand layer

quantification of mechanical compaction and cementation during contact metamorphism of sandstone abstract both mechanical compaction and mineral reactions reduce the porosity and permeability of sedimentary rocks these processes occur during burial and diagenesis as well as during contact and regional metamorphism although the mechanisms governing porosity reduction have been studied extensively in diagenetic sedimentary systems relatively limited work has been carried out on metamorphic rocks here we present a petrographic method to isolate and quantify the effects of mineral cementation and mechanical compaction in sandstone altered during contact metamorphism we sampled rocks from the inmar formation in makhtesh ramon israel where indurated sandstone is present near contacts with dykes and analyzed them using high resolution scanning electron microscopy and cathodoluminescence using image segmentation to differentiate between quartz cement and detrital grains we observed both grain rearrangement and brittle fracturing near intrusive contacts at the highest level of porosity reduction mechanical compaction reduced porosity by 18 31 while cementation caused a reduction of 11 we also found that the maximal level of mechanical compaction as well as its spatial extent scale with the size of the intrusion by contrast the maximal level of cementation was unaffected by the size of the dyke our findings demonstrate that to model porosity and permeability evolution in contact aureoles both mechanical and chemical processes must be taken into account

spot5 hrs digital elevation models and the monitoring of glacier elevation changes in north west canada and south east alaska abstract monitoring the response of land ice to climate change requires accurate and repeatable topographic surveys the spot5 hrs high resolution stereoscopic instrument covers up to 120 km by 600 km in a single pass and has the potential to accurately map the poorly known topography of most glaciers and ice caps the acquisition of a large hrs archive over ice covered regions is planned by the french space agency cnes and spotimage france during the 2007 2008 international polar year ipy here we report on the accuracy and value of hrs digital elevation model dem over ice and snow surfaces a dem is generated by combining tools available from cnes with the pci orthoengine se software using hrs images acquired in may 2004 over south east alaska usa and northern british columbia canada the dem is evaluated through comparison with shuttle radar topographic mission srtm dem and icesat data on and around the glaciers a horizontal shift of 50 m is found between the hrs and srtm dems and is attributed to errors in the srtm dem over ice free areas hrs elevations are 7 m higher than those of srtm with a standard deviation of 25 m for the difference between the two dems the 7 m difference is partly attributed to the differential penetration of the electromagnetic waves visible for hrs microwave for srtm in snow and vegetation we also report on the application of sequential dems srtm dem in february 2000 and hrs dem in may 2004 for the monitoring of glacier elevation changes we map the topographic changes induced by a surge of one tributary of ferris glacier maximum surface lowering of 42 10 m and rising of 77 10 m are observed in the 4 years time interval thinning rates up to 10 2 5 m yr are observed at low altitudes and confirm the ongoing wastage of glaciers in south east alaska

assessment of glacier volume change using aster based surface matching of historical photography glaciated regions are known to be particularly sensitive to climate change historical archives of glacier volume change are important as they provide context for present day changes although photogrammetric archives exist for many regions their usefulness is often limited by a lack of contemporary ground control high quality digital elevation models dems underpin a range of change analysis activities this paper presents a cost effective solution which utilizes advanced spaceborne thermal emission and reflection radiometer aster dems as control for the scaling and orientation of archival data sets instead of relying upon ground control points a robust surface matching algorithm is employed to automatically determine the transformation required to register two overlapping dems through application to the slakbreen glacier system in svalbard norway the strategy is assessed by first matching an aster dem to a fixed lidar reference surface this demonstrates that aster dems are effectively correct in scale supporting their use as a control surface the second stage of the research implements this by matching an aerial photogrammetric dem to an aster reference surface resultant volumetric and annual elevation change rates are compared to those derived from lidar data which are considered in this paper as a truth data set aster based matching produced a mean annual elevation change rate of 4 12 ma 1 compared to a value of 4 11 ma 1 derived from the lidar data in volumetric terms this equates to a difference of 0 6 a major advantage of this approach is the near global coverage offered by aster data and the opportunity that this presents for remote glacial change analysis over regional extents

initial investigations of the soft clay test site at bothkennar this paper presents findings from a wide range of in situ tests and laboratory investigations of the soft silty clay at bothkennar many of which were undertaken prior to the purchase of the site the soft clays at bothkennar are unusual in being remarkably uniform compared to other similar deposits in the uk this is thought to result from their deposition under rather stable estuarine conditions during the period 8500 6000 years before present bp thus apart from the presence of a highly laminated zone in the south east corner the soft clay is generally consistent across the site with many engineering properties increasing linearly with depth in contrast with many other soft clays the bothkennar clay has high effective strength parameters and high undrained strength the site appears to be ideal for a wide range of research and the presence of the highly laminated zone only enhances its potential cet article presente les resultats d une grande variete d essais in situ et en laboratoire de l argile

registering imagery to icesat data for measuring elevation changes on byrd glacier antarctica 1 we present a new approach to derive control information from icesat data that enables rigorous registration of aerial and satellite imagery the technique based on matching terrain features identified from icesat measurements and aerial imagery opens the door to transform results of previous studies to a global reference frame we demonstrate the proposed methodology with historical aerial photographs to determine surface changes between 1979 and 2004 over byrd glacier this is important because there is no satellite radar altimetry coverage south of 81 5 s which limits mass balance knowledge of outlet glaciers draining the east antarctic ice sheet through the southern transantarctic mountains our study indicates that the grounded part of byrd glacier is close to being in balance however we observe large thinning on the floating part of the glacier probably induced by increased basal melting citation schenk t b csatho c j van der veen h brecher y ahn and t yoon 2005 registering imagery to icesat data for measuring elevation changes on byrd glacier antarctica geophys res lett 32 l23s05 doi 10 1029 2005gl024328

fault growth by linkage observations and implications from analogue models abstract using time sequence analyses of extensional fault models we demonstrate the pivotal role played by fault segmentation in the accumulation of displacement and length during the growth of faults experiments are described in which incremental steps during the development of individual faults have been reconstructed from time lapse photographs taken during model deformation these records confirm the composite segment hierarchy of fault structure a pattern that is frequently recognised in many natural arrays they reveal the progressive enlargement of individual faults to be the product of a repetitive cycle of tip line propagation overlap and linkage between nearest neighbours by contrasting the displacement patterns of successive increments during growth convincing evidence is also presented to suggest that individual segments of faults may remain kinematically independent once they are physically linked this behaviour is shown to be responsible for the characteristic saw tooth patterns often recognised in strike parallel fault displacement profiles such patterns are believed to arise where relict segment boundaries remain preserved as asperities to slip so that displacement is confined to discrete parts of a fault plane surface growth in this way also causes the maximum displacement d and surface length l of faults to continually change by different proportions incremental displacement records presented here corroborate field evidence which shows that linkage between fault segments during growth is responsible for a significant component of the spread of values often recorded in d versus l compilations finally we speculate that linkage between fault segments also accounts for transient irregularities recorded in the frequency distribution of the fault length populations of each model

the mechanical contrast between layers controls fracture containment in layered rocks abstract open natural fractures allow fluids to flow which is necessary for the production of low permeable geothermal and petroleum reservoirs these reservoirs often consist of lithological layers with significant variation in rock strength which makes it difficult to predict fracture containment within the rock succession in this paper fractures are classified as contained when they do not cross the layer interface of the adjacent layer so that formation and growth are inhibited in the adjacent layer this study concerns the impact of the differences in rock strength i e mechanical contrast between two adjacent brittle layers on the fracture containment in finely layered rocks laboratory deformation tests and 2d finite element modelling were performed on three layered samples with varying mechanical contrasts to examine the behaviour of fractures at different stress conditions fractures initiate as shear fractures in weak layers and propagate with a steeper angle tensile fracture through the adjacent stronger layer the mechanical contrast within a layered rock does not always act as a containment barrier meaning that fractures do not cross the layer interface of the adjacent layer this is due to differences in differential stress between the weakest layer and strongest layer the mechanical contrast combined with the magnitude of the confining pressure has a significant influence on fracture containment an increase in mechanical contrast and confining pressure prevents fractures from propagating into stronger layers the results contribute to predict natural fracture containment in brittle sequences at shallow depth in the subsurface

infrastructure and mechanics of volcanic systems in iceland the divergent plate boundary in iceland consists of more than two dozen systems where most of the volcano tectonic activity takes place at the surface the volcanic systems are characterised by 5 20 km wide and 40 100 km long swarms of tension fractures 102 m long normal faults 103 m long and volcanic fissures the holocene fissure swarms are confined to less than 10 000 year old basaltic lava flows mostly pahoehoe occurring near the centre of the active rift zone in any particular swarm the number of tension fractures exceeds that of normal faults all tension fractures and normal faults are vertical at the surface indicating that the surface parts were generated by an absolute tension in addition to a fissure swarm many volcanic systems have a central volcano some of which have developed collapse calderas in the late tertiary and pleistocene lava pile of iceland extinct volcanic systems are represented by local sheet swarms and regional dyke swarms the sheet swarms are normally circular or slightly elliptical several kilometres in radius and are confined to the extinct central volcanoes many swarms are associated with large plutons exposed at 1 2 km depth beneath the initial top of the rift zone and presumably the uppermost parts of extinct crustal magma chambers and in short traverses up to 90 of the rock may consist of sheets the sheets have a very variable strike dip on average 45 65 mostly towards the centre of the associated volcano and have an average thickness of about 1 m the regional dykes occur outside central volcanoes in swarms that are commonly 50 km long and 5 10 km wide in several kilometre long traverses commonly 1 5 of the rock consist of dykes but occasionally as much as 15 28 most regional dykes are subparallel and subvertical the average dyke thickness in the pleistocene swarms is less than 2 m but 4 6 m in the tertiary swarms while active the volcanic systems in the rift zone are supplied with magma from reservoirs located at the depth of 8 12 km at the boundary between the crust and upper mantle the reservoirs are partially molten with totally molten top regions and of cross sectional areas similar to those of the volcanic systems that they feed some active volcanic systems especially those that develop central volcanoes high temperature areas and calderas have in addition to the deep seated magma reservoirs shallow crustal magma chambers located at 1 3 km depth which in turn are fed by the deeper magma reservoirs it is proposed that the regional dyke swarms are supplied with magma largely from the deep seated reservoirs whereas the local sheet swarms are mainly fed from the associated crustal magma chambers because the volume of a crustal chamber is less than that of its deeper source reservoir a single magma flow dyke intrusion from the reservoir may trigger tens of magma flows sheet intrusions from the chamber which is one explanation for the enormous number of sheets associated with many central volcanoes the sheets follow the stress trajectories of the local stress fields around the source chambers whereas the regional stress field associated with the divergent plate movements controls the emplacement of the regional dykes it is suggested that many dykes develop as self affine some as self similar structures when applied to the krafla volcanic system in northern iceland model calculations suggest that a magma flow from the krafla reservoir with regional dyke formation should occur on average once every several hundred years and that tens of sheets might be injected from the shallow krafla chamber and triggered by a single magma flow from the krafla reservoir these results are in broad agreement with the available data

structural and lithological guidance on speleogenesis in quartz sandstone evidence of the arenisation process a detailed petrographic structural and morphometric investigation of different types of caves carved in the quartz sandstones of the tepui table mountains in venezuela has allowed identification of the main speleogenetic factors guiding cave pattern development and the formation of particular features commonly found in these caves such as funnel shaped pillars pendants and floor bumps samples of fresh and weathered quartz sandstone of the mataui formation roraima supergroup were characterised through wds dispersive x ray chemical analyses picnometer measurements edax analyses sem and thin section microscopy in all the caves two compositionally different strata were identified almost pure quartz sandstones with content of silica over 95 and high primary porosity around 4 and phyllosilicate rich quartz sandstone with contents of aluminium over 10 and low primary porosity lower than 0 5 phyllosilicates are mainly pyrophyllite and kaolinite sem images on weathered samples showed clear evidence of dissolution on quartz grains to different degrees of development depending on the alteration state of the samples grain boundary dissolution increases the rock porosity and gradually releases the quartz grains suggesting that arenisation is a widespread and effective weathering process in these caves the primary porosity and the degree of fracturing of the quartz sandstone beds are the main factors controlling the intensity and distribution of the arenisation process weathering along iron hydroxide or silt layers which represent inception horizons or a strata bounded fracture network predisposes the formation of horizontal caves in specific stratigraphic positions the loose sands produced by arenisation are removed by piping processes gradually creating anastomosing open fracture systems and forming braided mazes geometric networks or main conduit patterns depending on the local lithological and structural guidance on the weathering process this study demonstrates that all the typical morphologies documented in these quartz sandstone caves can be explained as a result of arenisation which is guided by layers with particular petrographic characteristics primary porosity content of phyllosilicates and iron hydroxides and different degrees of fracturing strata bounded fractures or continuous dilational joints

forensic numerical analysis of gas venting in southwestern ontario abstract a forensic modeling study examines the potential causes of gas and water venting observed during the excavation of a landfill in a 40 m thick clayey till deposit in southwestern ontario canada the clayey till is known to be underlain by permeable natural gas bearing rock and gas has been diffusing through the clayey deposit over about the last 13 000 15 000 years attention is focused on 2d modeling of hydrofracturing as well as gassy soil behavior the model examines the predicted location of venting with and without the presence of gassy sand lenses and a discontinuous layer of basal till between the bedrock and the low permeability till the modeling shows that hydrofracturing alone can explain the occurrence and location of the observed venting in one of the sub cells in the other sub cell hydrofracturing explains the occurrence but not the location of the observed venting or the presence of the sand in the venting water at this location modeling of appropriately placed gassy sand lenses is shown to explain the occurrence and location of the observed venting as well as the presence of both waters with different geochemistry from the bedrock and the till in the venting waters

modelling time dependent behaviour of murro test embankment this paper investigates the time dependent behaviour of murro test embankment in finland the embankment was built in 1993 on a soft natural clay deposit which exhibits large strain anisotropy destructuration and viscosity the study is based on extensive experimental data from triaxial and oedometer tests on intact and reconstituted soil samples which shed light on the influence of time on mechanical properties including testing designed for studying soil anisotropy and destructuration the interpretation of the results is done in the framework of a recently developed elasto viscoplastic model evp sclay1s which is used to simulate the soft soil deposit coupled with biot s consolidation theory the determination of model parameters from the test results demonstrates that the model can be relatively easily used for practical applications using these parameters two dimensional finite element analyses have been made as large deformation analysis the comparisons between calculations and measurements de

comparison of field consolidation with laboratory and in situ tests settlement calculations for an earth embankment resting on soft compressible fraser river delta sediments were made from laboratory consolidation tests and in situ tests using a piezocone and a flat dilatometer the calculated values were compared with measured settlements there was rather good agreement among the three methods of calculation but the actual settlement was about 60 greater than the average calculated value calculated rates of settlement are also compared with observed values key words consolidation settlements piezocone dilatometer in situ tests constrained modulus pore water pressure settlement rate

scaling relationships of joint and vein arrays from the burren co clare ireland abstract we present a study of the systematics of veins and joints in carboniferous limestones of the burren ireland scaling relationships were established for fracture arrays mapped from low elevation aerial photographs that image fractures on numerous limestone pavements for areas up to ca 1 km2 the veins and joints occur in the same sequence but have contrasting scaling properties the veins strike north south and cut many beds to form vertically persistent non stratabound arrays they are strongly clustered and have scale invariant geometric properties vein geometries suggest they grew sub critically under relatively high differential stresses during north south directed variscan compression the joints form stratabound arrays with regular spacings that scale with bed thickness they show greater strike variation than the veins and have lognormal length distributions the joints formed during uplift under low differential stress conditions the contrasting scaling properties of the joints and veins are attributed to different overburden stresses at the time of formation the veins formed at greater depths than the joints in conditions that favoured fracture propagation across mechanical discontinuities resulting in the development of non stratabound scaling properties

three dimensional modeling of the 1983 1984 eruption at piton de la fournaise volcano reunion island displacement vectors on 125 points over a 6 km 2 area were calculated zlotnicki et al 1990 for piton de la fournaise volcano reunion island from photogrammetric surveys conducted in september 1981 and again in september 1984 an eruptive crisis with two episodes occurred during the 3 years between the surveys we modeled the displacements from the photogrammetric surveys using a three dimensional mixed boundary element method the model shows that both eruptive episodes were fed by a single dike oriented 165 from north as the dike approached the ground surface it divided into segments that rotated into an en echelon pattern the model that best fits all observations suggests that the stress state within the volcano is quasi isotropic such that horizontal stresses equal the overburden these high horizontal stresses are incompatible with an elastic edifice loaded merely by gravitational forces however they may be attributed to the cumulative effect of repeated dike intrusions

icesat validation of srtm c band digital elevation models 1 the geoscience laser altimeter system glas on the ice cloud and land elevation satellite icesat provides a globally distributed data set well suited for evaluating the vertical accuracy of shuttle radar topography mission srtm digital elevation models dems the horizontal error 2 4 7 3 m and vertical error 0 04 0 13 m per degree of incidence angle for the icesat data used are small compared to those for srtm using glas echo waveforms we document differences between the srtm c band phase center and the highest centroid and lowest elevations within icesat laser footprints in the western united states in areas of low relief and sparse tree cover the mean and standard deviation of elevation differences between the icesat centroid and srtm are 0 60 3 46 m the differences are 5 61 15 68 m in high relief sparse tree cover areas and 3 53 8 04 m in flat areas with dense tree cover the largest differences occur in rugged densely vegetated regions

effect of tensile stress concentration around magma chambers on intrusion and extrusion frequencies what controls the intrusion and extrusion frequencies associated with volcanoes is still poorly understood i propose that for volcanoes at divergent plate boundaries these frequencies may be largely determined by the tensile stress concentration around the magma chambers that feed them this stress concentration is mainly a function of the applied tensile stress associated with spreading and the aspect height width ratios of the chambers high spreading rates and or aspect ratios lead to high rates of tensile stress concentration around the chambers and to an increase in their intrusion frequencies it is found that for chambers at the same depth in a volcanic zone the one of the highest aspect ratio will normally intrude magma most frequently also if the chambers are of equal aspect ratios the one at the greatest depth will intrude magma most frequently because the extrusion frequency of a volcano is a fraction of its intrusion frequency the extrusion frequency may also be largely determined by the rate of tensile stress concentration around the magma chamber that feeds the volcano these results are applied to the divergent plate boundary in iceland where many of the volcanoes appear to be fed by double chambers that is shallow chambers fed by deep seated chambers it is found that except when the aspect ratio of the deep seated chamber is much less than that of the shallow chamber the intrusion frequency of the shallow chamber is normally largely controlled by that of the deep seated chamber it is concluded that whereas the short term i e 103 yrs extrusion frequencies of volcanoes at the plate boundary in iceland may be similar to the dike intrusion frequencies of the source chambers the long term i e 104 yrs extrusion frequencies may be about ten times lower than the intrusion frequencies

evaluation of undrained shear strength of swedish fine grained sulphide soils in swedish practice there is a long tradition of evaluating undrained shear strength from fall cone tests and field vane tests during the last 20 years cone penetration tests have also become wid

geometry formation and development of tectonic fractures on the reykjanes peninsula southwest iceland abstract a study was made of 903 fractures most of which are of postglacial age on the reykjanes peninsula some 120 fractures belonging to the vogar fissure swarm he completely within the same postglacial lava flow and were studied in great detail for the vogar fractures 75 are pure tension fractures and 25 are normal faults the average length of the vogar fractures is 611 m the average width is 0 6 m the average spacing measured perpendicular to the average strike n54e of fractures is 456 m the estimated average depth is of the order of several hundreds of meters and the average throw of the faults is 2 3 m all major fractures on the peninsula appear to have formed by coalescence of smaller fractures as a result of absolute tensile stress the fractures group into four fissure swarms each being a part of a volcanic system which it is proposed is fed by an elongated partially molten magma reservoir located at a depth of about 8 km beneath the peninsula it is suggested that a slight magmatic pressure increase in these reservoirs and resulting uplift and tensile stress at the surface is the main cause of postglacial fracture formation