hydrogeochemistry and geochemical simulations to assess water rock interactions in complex carbonate aquifers the case of aguadulce se spain abstract the hydrogeological unit of aguadulce campo de dalias aquifers se spain has a complex geometry this fact together with a continuous rise in water demand due to intensive agriculture and tourism create problems for groundwater quantity and quality in this paper classic geochemical tools managed by means of gis software and geochemical simulations are combined to delineate identify and locate the possible physicochemical processes acting in the aguadulce groundwater two main aquifers can be distinguished the carbonate or lower aquifer of triassic age and the calcodetritic or upper aquifer of plio quaternary age groundwaters from the latter are more saline and assuming all chlorinity originates from seawater intrusion the seawater contribution to their composition would be up to 7 nevertheless the carbonate aquifer appears not to be homogeneous it is compartmentalised into 4 zones where different processes explain the different groundwaters compositions zone 4 samples e margin of the carbonate aquifer resemble those of the plio quaternary aquifer where calcite precipitation dolomite and gypsum dissolution and some cation exchange water rock interaction together with seawater freshwater mixing occur in contrast water rock interaction predominates in zones 1 and 3 of the carbonate aquifer moreover zone 2 samples located between zones 1 and 3 are explained by water rock interaction in addition to mixing with plio quaternary aquifer waters the combination of geochemical simulations with gis and hydrogeochemical analyses has proven to be effective in identifying and locating the different physicochemical processes in the aquifer areas thus improving understanding of hydrogeochemistry in complex aquifers

the thermal and mineral springs of aitoloakarnania prefecture function mechanism and origin of groundwater the study area is located in the northwestern part of greece in aitoloakarnania prefecture in this region where no volcanic activity exists thermal springs such as kremasta and kokkino stefani well known for their healing properties occur the objective of this study was the investigation of these springs as well as the study of the chemical composition and origin of water relationships between these springs were also examined the geological setting of the area comprises sedimentary rocks of the pindos gavrovo tripolis and ionian geotectonic zones deformed by orogenic movements followed by neogene extensional tectonism the thermal and mineral springs were classified into three main groups the first group is characterized by ca hco3 water type and low water temperatures it corresponds to the springs that are hosted in the ionian zone and their possible enrichment in so4 is mainly attributed to the evaporites the other two groups consist of alkaline thermal water mainly hosted in the formations of gavrovo tripolis zone in these two groups the very strong reducing conditions that prevail are expressed by high amounts of nh3 and h2s moreover na f li sr and ba display elevated concentrations the second includes mineral waters of ca na hco3 type that are depleted in calcium their residence time is rather long and they originate from deep water circulation through siliceous rocks the third group includes thermal waters of ca mg na hco3 water type of higher water temperatures that reveal characteristics of deep circulation directly associated with the underlain limestones

ground deformation in askja iceland its source and possible relation to flow of the mantle plume abstract the volcano askja in east central iceland erupted several times between 1920 and 1930 following a very large caldera forming eruption in 1875 the last eruption occurred in 1961 measurements of the vertical component of ground deformation in askja were commenced in 1966 and made once each year 1966 to 1972 and 1983 to 1987 distance measurements with a geodimeter were first made in 1982 the measurements have shown alternating uplift and subsidence of the central part of the askja caldera two periods of uplift and three periods of subsidence have been identified during the 21 years of observations observed vertical displacements agree fairly well with a single point source model at a depth of 1 5 3 5 km below the surface near the center of the askja caldera deviation from a single point source model can be explained by a secondary source of subsidence beneath the site of the 1961 eruption this secondary source has been diminishing in intensity and appears to have been exhausted by 1983 1987 askja has been subsiding at a rate of 6 10 cm per year during the period 1983 1987 but in 1970 1972 rapid inflation was observed possibly as much as 20 cm per year the period of no levelings 1972 to 1983 is characterized by deflation but at a slower average rate than observed in 1983 1987 this suggests continuation of the 1970 1972 inflation into 1973 or 1974

evaluation of the domain state corrected multiple specimen absolute palaeointensity protocol a test of historical lavas from iceland summary palaeointensity estimates were made for a suite of five historical lava flows from mt askja iceland with the purpose of testing the newly proposed domain state corrections to the multispecimen parallel differential ptrm palaeointensity method msp where ptrm stands for partial thermoremanent magnetization before beginning the experimental procedure the chemical stability on heating to the determined ptrm induction temperature was assessed some flows were found to be unaltered by heating some displayed inconsistent repeatability while one flow was severely affected by heating to implement the domain state corrections and interpret the data successfully we had to implement two new approaches to the msp method 1 we used vector addition subtraction in our calculations and 2 we introduced a new selection rejection criterion that improves the robustness of the estimates by preferentially removing outliers based on the error analyses of the linear regression this rejection criterion typically rejected one or two points and was found to significantly improve the estimates with the exception of the one flow that displayed significant chemical alteration during the experiment the palaeointensity estimates determined using the original msp protocol yielded estimates within 3 t of the known field of 49 5 t the domain state corrected msp estimates were all within 4 t with no clear relationship between the uncorrected and domain state corrected palaeointensity estimates for this data set

controlling factors on earthquake swarms associated with magmatic intrusions constraints from iceland abstract the currently two most important surveying tools in volcano monitoring are observations of seismicity and surface deformation magma migration within the earth s crust is frequently associated with seismic activity often occurring as distinct earthquake swarms understanding the exact nature and significance of these swarms is important when evaluating volcanic crisis situations there seems however to be no general correlation between the amount of seismic energy release and the rate and volume of magma on the move which may complicate an immediate risk evaluation it has previously been shown that stressing rate appears as the controlling factor on the occurrence of seismicity during intrusion however in this paper we emphasize that this is only true under specific circumstances other factors influence the evolution and resulting seismic energy release and each intrusion scenario needs to be evaluated separately three icelandic cases where seismic swarms have been confirmed through deformation measurements to be related to magmatic movements were selected we show how the relationship between volume change and resulting seismicity varies greatly between cases and suggest that in a general approach the most important factor governing the level of seismic energy release is the background stress state tectonic setting regional stresses and tectonic history are therefore all of great importance when evaluating a magmatically induced seismic crisis the stressing rate only plays the dominant role when either a stress in the intruded area is close to the yield strength before intrusion or possibly b when the intrusion is extraordinarily voluminous and rapid

hydrochemistry and geothermometrical modeling of low temperature panticosa geothermal system spain abstract the chemical characteristics of the low temperature geothermal system of panticosa spain were investigated in order to determine the water temperature at the reservoir and to identify the main geochemical processes that affect the water composition during the ascent of the thermal waters in general the studied waters are similar to other geothermal systems in the pyrenees belonging to the group of granite related alkaline thermal waters high ph low total dissolved solids very low magnesium concentration and sodium as the dominant cation according to the alkaline ph of these waters they have a very low co 2 partial pressure bicarbonate is the dominant anion and silica is partially ionized as h 3 sio 4 the unusually active acid base pairs hco 3 co 3 2 and mainly h 4 sio 4 h 3 sio 4 act as homogeneous ph buffers and contribute to the total alkalinity in these alkaline waters on the basis of the study of the conservative elements a mixing process between a hot and a cold end member has been identified additionally in order to determinate the water temperature at the reservoir several geothermometric techniques have been applied including both geothermometrical modeling and classical geothermometrical calculations the geothermometrical modeling seems to indicate that thermal waters re equilibrate with respect to calcite and kaolinite during their ascent to the surface modeling results suggest that these thermal waters would be in equilibrium with respect to albite k feldspar quartz calcite kaolinite and zoisite at a similar temperature of 90 20 c in the reservoir which is in good agreement with the results obtained by applying the classical geothermometers

volcano geodesy and magma dynamics in iceland abstract here we review the achievements of volcano geodesy in iceland during the last 15 years extensive measurements of crustal deformation have been conducted using a variety of geodetic techniques including leveling electronic distance measurements campaign and continuous global positioning system gps geodesy and interferometric analysis of synthetic aperture radar images insar results from these measurements provide a comprehensive view of the behavior of icelandic volcanoes between inflation intrusion and eruption episodes volcanoes are likely to deflate or show no sign of seismic activity subsidence rates are often in the range of a few millimeters to a few centimeters a year reducing progressively with time since the last eruption or intrusion at the volcano subsidence can be caused by cooling and contraction of magma outflow of magma it can be related to plate spreading volcano subsidence or lack of deformation is often interrupted by episodic magma flow towards near surface locations such magma recharge has been observed geodetically at hengill hekla eyjafjallajokull katla grimsvotn and krafla volcanoes with inflow inferred to last from a few months up to two decades in the last 15 years five volcanic eruptions three intrusive events and two m6 earthquakes have occurred in recent years the grimsvotn and katla volcanoes have exhibited continuous inflation of a few centimeters per year which at grimsvotn culminated in an eruption on 1 november 2004 hekla and torfajokull volcanoes have inflated at rates an order of magnitude less subsidence is occurring presently at the askja and krafla volcanoes within the period of geodetic measurement signals consistent with no deformation are typical for most of the 35 active volcanoes in iceland

secondary processes determining the ph of alkaline waters in crystalline rock systems abstract the understanding of the main hydrogeochemical processes controlling the features and behaviour of crystalline rock environments considered for the deep geological storage of spent nuclear fuel is a key issue for the improvement of our knowledge and management of these systems and for a more accurate prediction of their future evolution in this paper some of the most important irreversible processes cooling mixing and co 2 exchange are studied and their effects quantified by combining classical geochemical calculations and geochemical modelling this methodology is applied to an alkaline thermal water system developed in crystalline rocks the caldas de boi groundwater system ne spain analogous to the deep geological environments expected for nuclear waste storage one of the most remarkable results obtained in this study is related to the high ph buffering capacity exhibited by these alkaline thermal waters during the mixing processes with colder and shallower waters taking place during the uprising of the hot waters from the deep reservoir even for high mixing proportions of cold water up to 60 the final ph remains as alkaline as in the thermal and deep end member although the rest of the physicochemical parameters including temperature change consistently with mixing another important secondary ph determining process detected in this study is the conductive cooling of the thermal waters suffered during their rise to surface conditions which is clearly responsible for a ph increase which enhances the typical alkaline character of these waters finally the existence of external inputs of edaphic or biogenic co 2 to the groundwater system producing a ph decrease in some of the springs has been proven to play a key role in their behaviour and evolution

geochemical investigations of saltwater intrusion into the coastal carbonate aquifer of mallorca spain abstract coastal aquifers often display seawater intrusion resulting in the formation of a salty water wedge progressing inland this study investigates the mass transfers in the mixing zone at the freshwater seawater interface where the water is out of equilibrium with the rock forming carbonates investigations were conducted in two boreholes separated by 5 m at the ses sitjoles test site mallorca island spain where repeated electrical conductivity logs of the formation and the saturating fluid as well as regular pore water sampling and permanent downhole multi parameter monitoring of the water were performed over a period of 9 a in the mixing zone the significant acidification the calcite saturation index profile and the ca concentration profile cannot be explained by conservative mixing nor by dissolution precipitation reactions only conversely the analysis of organic c content and of the distinctly different time resolved ph profiles measured in the two boreholes suggests the development of perennial biomass that triggers calcite dissolution moreover the presence of biomass seems to be correlated with the permeability and vertical connectivity at the meter scale it is speculated that the mechanism could be self activated because the microbiological activity induces calcite dissolution and tends to increase porosity and permeability that favors biomass development

origin of boron from a complex aquifer in southeast of spain a study of the boron content alongside cl s o 4 2 and no3 ions has enabled the factors that determine its origin to be distinguished in carbonate rocks with their higher saline content boron is associated with marine intrusion in the plioquaternary aquifer its origin is complex and is associated with three processes marine intrusion where there is a high cl content and the b cl ratio is close to that of seawater anthropogenic pollution at points with high b and no3 concentrations and where the b cl ratio is higher than that of seawater and the dissolution of evaporite deposits present in the plioquaternary strata at a series of sampling points where the so4 2 cl ratio is elevated and b

lower crustal earthquakes caused by magma movement beneath askja volcano on the north iceland rift the lower crust of magmatically active rifts is usually too hot and ductile to allow seismicity the icelandic mid atlantic rift is characterized by high heat flow abundant magmatism generating up to 25 30 km thick crust and seismicity within the upper 8 km of the crust in a 20 seismometer survey in july august 2006 within the northern rift zone around the askja volcano we recorded 1700 upper crustal earthquakes cutting off at 7 8 km depth marking the brittle ductile boundary unexpectedly we discovered 100 small magnitude ml 1 5 earthquakes occurring in swarms mostly at 14 26 km depth within the otherwise aseismic lower crust and beneath the completely aseismic middle crust a repeat survey during july august 2007 yielded more than twice as many lower crustal events geodetic and gravimetric data indicate melt drainage from crustal magma chambers beneath askja we interpret the microearthquakes to be caused by melt moving through the crust from the magma source feeding askja they represent bursts of magma motion opening dykes over distances of a few meters facilitated by the extensional setting of the active rift zone

groundwater chemistry and water rock interactions at stripa groundwaters from near surface to a depth of 1232 m in the stripa granite have been sampled and analyzed for major and trace constituents the groundwater composition consists of two general types a typical recharge water of ca hco3 type 700 m depth of high ph 8 10 that reaches a maximum of 1250 mg l in total dissolved solids tds intermediate depths show mixtures of the two types that are highly fracture dependent rather than depth dependent any borehole can vary significantly and erratically in tds for either a horizontal or vertical direction the general transition from ca hco3 type to na ca cl type correlates with the depth profile for hydraulic conductivity that drops from 10 8 m s to 10 11 m s or lower thermomechanical stress from heater experiments clearly shows an effect on the groundwater composition that could be caused by changing flow paths leakage of fluid inclusions or both dissolution and precipitation of calcite fluorite and barite aluminosilicate hydrolysis and addition of a saline source possibly fluid inclusion leakage play the major roles in defining the groundwater composition the low permeability of the stripa granite has produced a groundwater composition that appears intermediate between the dilute shallow groundwaters typical of recharge in a crystalline rock terrain and the saline waters and brines typical of cratonic shield areas at depth

formation of oskjuvatn caldera at askja north iceland mechanism of caldera collapse and implications for the lateral flow hypothesis the oskjuvatn caldera at askja volcano north iceland was formed as a result of an explosive eruption at askja on 28th 29th march 1875 oskjuvatn is one of the youngest collapse calderas on earth and its initiation and growth were observed and documented by explorers and geologists working in the askja region between 1875 and 1932 it is an example of caldera formation where the volume of the caldera collapse far exceeds the volume of associated erupted products the discrepancy between the collapse volume and associated erupted products has been used by previous workers as a justification for the hypothesis that the injection of lateral dykes from askja fed the february to october 1875 n jahraun fissure eruptions at the sveinagja graben some 60 km north of askja however historical accounts documenting the caldera formation in sufficient detail show clearly that oskjuvatn formed by piecemeal collapse taking over 40 years to reach its current form we use these accounts to undertake a detailed examination of the stages of caldera collapse and to compare them with the known magmatic output of askja in the years following the 1875 eruption arcgis software was used to calculate the volume of oskjuvatn during the various stages of collapse and the volume of material erupted after 1875 while a dyke extending between askja and sveinagja may be implied to account for the missing volume our results demonstrate that the volume of oskjuvatn in july 1875 closely corresponds to the volume of rhyolitic material erupted on 28th 29th march 1875 in addition geochemical evidence indicates that the n jahraun magmas were sourced from a deeper reservoir rather than by lateral injection from askja s shallow crustal magma chamber we therefore suggest that the injection of sills and dykes in a coherent intrusion complex beneath askja central volcano combined with background deflation of the magma storage zone beneath oskjuvatn caldera over 30 to 40 years following 1875 satisfactorily accommodates the volume required to form oskjuvatn caldera

the interaction of fissure swarms and monogenetic lava shields in the rift zones of iceland abstract the divergent plate boundaries of iceland are marked by rift zones that consist of fissure swarms i e areas with a high density of fractures faults and eruptive fissures generally considered to be the surface expressions of dikes monogenetic lava shields are common within the rift zones they are gently sloping circular cones created by eruptions from a single vent many of the shields were emplaced in the early holocene in response to increased mantle melting when the pleistocene glacier load on the crust was reduced in our studies of icelandic fissure swarms we have established that in most cases where a fissure swarm transects a lava shield there is an inverse correlation between surface elevation and the density of fractures the summit area of a shield is generally less fractured than the flanks fracture densities are also highest on one site of the lava shield but much lower and even approaching zero values on the other side this phenomenon is most clearly seen within early holocene lava shields i e between 4500 and 13 600 years bp of age lava shields younger than 4500 years bp of age have low fracture densities or are not fractured at all the lower fracture densities within holocene lava shields suggest that dike intrusions stop or remain deeper in the crust when they approach a lava shield various mechanisms may explain this the topographic load of the lava shield adds to the lithostatic stress thus increasing the strength and may affect the depth of a propagating dike a long lived eruption of a lava shield may also affect the stress field in the surrounding crust increase the horizontal compressive stress and thus create a stress barrier for propagating dikes for some time period following the eruption

mixing hydrology and chemical equilibria in bakreswar geothermal area eastern india abstract a group of alkaline thermal springs of bakreswar having varying temperatures 45 71 c and identical compositions emerges through a nearly n s trending fault in the gneissic basement the thermal springs are of na cl so 4 type and are rich in sio 2 and f contrary to the local groundwaters which are mostly of ca hco 3 type the springs undergo mild to moderate dilution by local groundwater which does not significantly affect their original compositions agnikund the main spring with the highest temperature mild dilution consistent composition and negligible tritium discharges almost pure deep seated thermal water original thermal water is at equilibrium with quartz in the deep reservoir and attains surface temperature largely by conductive cooling with no significant loss of dissolved sio 2 certain ionic ratios coupled with very low tritium contents in the springs are indicative of prolonged subsurface circulation of the original water xrd results of the spring site sediments and the bore hole rocks fairly corroborate the predicted saturation state of thermal water with respect to quartz feldspar calcite fluorite etc which is believed to control the major chemical compositions of the springs a geothermal reservoir having probable temperature of about 100 5 c and possibly occurring at a depth of 1 km is the source of thermal water for the springs the present study is aimed at understanding the mixing trend between thermal springs and local groundwaters as well as the water rock equilibria

from surface fault traces to a fault growth model the vogar fissure swarm of the reykjanes peninsula southwest iceland abstract the vogar fissure swarm is one of four en echelon fracture swarms that connect the reykjanes ridge to the south iceland seismic zone and the western volcanic zone occurring in an area of flat topography this fissure swarm is clearly visible at the surface where it can be seen to affect recent postglacial lavas using remote sensing methods to identify and measure all the faults and fractures in the swarm combined with additional field observations and measurements we measured 478 individual fractures 33 of them being faults and 67 being fissures the fracture lengths show roughly log normal distributions most of the individual fractures belong to 68 main composite fractures seven of which are longer than 2500 m and correspond to the main fault scarps of the fissure swarm we showed that these main faults are distributed along five equally spaced zones 500 m apart and a few kilometers long we drawn 71 across strike profiles to characterize the shape of the fault scarps and 5 along strike profiles to characterize the evolution of vertical throw along the main faults each fault consists of a coalescence of individual segments of approximately equal length fault throws are never larger than 10 m and are smallest at the junctions between individual segments analyses of along strike throw profiles allowed us to determine the early stages of growth after coalescence the earliest stage is characterized by an increase in the throw of the central parts of segments this is followed by a second stage during which the throw increases at the junctions between segments progressively erasing these small throw zones

using δ15n and δ18o values to identify sources of nitrate in karstic springs in the paris basin france abstract in many parts of the world groundwater quality deterioration is occurring often due to changes in land use along with overexploitation of some aquifers some of the drinking water distributed in paris france is collected from a karstic cretaceous chalk aquifer at two groups of springs located 80 km south of paris in the lunain catchment although geographically close to each other these springs sp1 and sp2 have quite different hydrogeochemical characteristics in sp1 an increase in the no 3 concentrations of 18 mg l 1 from 16 mg l 1 in 1965 to 34 mg l 1 in 2009 has been observed and in sp2 no 3 concentrations have increased by 26 mg l 1 from 20 mg l 1 in 1965 to 46 mg l 1 in 2009 the origin of the no 3 was however unclear the stable isotopic composition of no 3 was used to identify the sources causing the increase of no 3 concentrations and to assess seasonal variations the isotopic composition of two potential sources including agricultural effluents and wastewater was determined likewise two additional no 3 sources the chalk groundwater and the lunain river water were considered following the hydrogeological context of the lunain catchment determination the concentrations and the 15n and 18o values of spring water no 3 and the use of a bayesian isotopic mixing model siar stable isotope analyses in r allowed determination of the proportional contribution of respective no 3 sources in the springs in spring sp1 all the potential no 3 sources 4 contributed almost equally during the low flow period but higher no 3 contributions from the agricultural source and the chalk groundwater were observed during the high flow period for the sp2 group of springs elevated contributions of no 3 from the agricultural source and from the chalk aquifer were observed during the high flow period as well as during the low flow period knowledge of no 3 sources contributing to these springs is important for the implementation of remediation measures to protect the water resource and avoid further water quality deterioration

architecture of normal faults in the rift zone of central north iceland this work examines the architecture and propagation of normal faults that accommodate extension in the rift zone of central north iceland it is based on a structural study of portions of three grabens their normal faults and dilational fractures in basaltic lavas of the fremri namur and dyngjufjol volcanic systems we analyzed the shape throw and dilation along faults in order to infer their possible evolution the shape of throw profiles departs from elliptical varying along each fault with throw being lower at the fault and segment tips propagation of fault segments is accommodated by dilational fractures nucleating at their respective tips segments link by lateral propagation of one or both tips or by the development of intervening linking segments two orders of fault segmentation indicate that the present throw accumulated by many increments as the fault scarps changed their geometries faults have large dilational components weakly correlated with fault throw and length

relative size of fluvial and glaciated valleys in central idaho quantitative comparisons of the morphometry of glaciated and fluvial valleys in central idaho were used to investigate the differences in valley relief and width in otherwise similar geologic and geomorphic settings the local relief width and cross sectional area of valleys were measured using gis software to extract information from usgs digital elevation models hillslope gradients were also measured using gis software power law relationships for local valley relief width and cross sectional area as a function of drainage area were developed local valley relief in glaciated valleys relates to drainage area with a power law exponent similar to fluvial valleys but glaciated valleys are deeper for a given drainage area local valley width in glaciated valleys is greater than in fluvial valleys but the exponent of the power law relationship to drainage area is similar in both valley types local valley cross sectional area in glaciated valleys increases with drainage area with a power law exponent similar to fluvial valleys however glacial valleys have roughly 80 greater cross sectional area steep valley walls in glaciated basins increase the potential for bedrock landsliding relative to fluvial basins both the olympic mountains of washington and valleys in central idaho show relationships in which glaciated valleys are up to 30 deeper than fluvial valleys despite differences in lithology tectonic setting and climate

ocean ridge discontinuities in iceland abstract the tjornes fracture zone in north iceland and the south iceland seismic zone are ocean ridge discontinuities that are partly exposed on land these are zones of high seismicity but contrasting style of crustal deformation detailed field studies and numerical modelling suggest that the tjornes fracture zone has all the characteristics of an oceanic transform fault is 7 9 ma old and developed along the zone of maximum shear stress between the nearby tips of the rift zones of the kolbeinsey ridge and north iceland conversely the results indicate that the south iceland seismic zone developed within an area of shear stress concentration between the overlapping rift zones in south iceland the development of the south iceland seismic zone is a consequence of the propagation of the eastern rift zone to the southwest during the past 3 ma

submarine springs and coastal karst aquifers a review this article reports on current knowledge of coastal karst aquifers in which conduit flow is dominant and its aim is to characterise the functioning of these systems which are closely linked to the sea first earlier and recent studies of these aquifers are discussed on the basis of their findings it can be shown that two essential mechanisms are involved in the functioning of these systems i e aquifer discharge through submarine springs and saline intrusion through conduits open to the sea then the conditions that give rise to these aquifers are described and particular emphasis is placed on the influence of deep karstification when the sea level falls the base level variations are attributed to the glaciations or in the specific case of the mediterranean to the salinity crisis in the messinian period it is this inherited structure sometimes containing very deep conduits below sea level that today conditions the aquifer flow the flow in the conduits open to the sea depends on the hydraulic head gradient between the aquifer and the sea and is therefore a function of the water density and head losses in the aquifer this survey of coastal karst aquifers has revealed some common characteristics that show the development and or functional capacity of their karstic drainage networks a classification of such systems into three categories is proposed with the aim of assisting in the decision making concerning potential exploitation of water resources in coastal regions

implications of fracturing mechanisms and fluid pressure on earthquakes and fault slip data in the east iceland rift zone comparison of the eroded off rift zone left inactive by plate motion with the inner active seismic rift zone allows us to constrain the fracturing mechanisms in eastern off rift zone we measured 423 fault slips including normal and strike slip faults inversion of fault slip data reveals the parallelism of the minimum stress 3 computed for the normal and for the strike slip faulting and consistency with the direction of plate divergence north of the vatnajokull in the active rift zone we analysed 14 250 earthquakes recorded by the icelandic meteorological office imo between 2004 and 2009 especially northeast of the askja volcano two main average focal depths were determined at 5 km her ubrei table mountain and 15 km upptyppingar hyaloclastite ridge the double couple focal mechanisms determined by imo revealed that more than half of the mechanisms are strike slip faulting type both in active and off rift zone reveals an unusual importance of strike slip regime in such an extensional tectonic context this can be explained by stress permutations 1 2 similarities in terms of stress orientations and type of faulting are observed both in the old and present day rift zones we assume that the seismic events may be generated by rapid deep magma intrusion also associated with shallower hydrothermal activities we thus propose that the presence of fluids shear failure double couple focal mechanism and stress permutations in both active and off rift zones are closely linked assuming a drucker prager failure criterion we evaluated analytically that a state near of lithostatic pore pressure is a necessary condition for shear failure at shallow 5 km and deep 15 km depth in a simple context of crustal extension that allows for stress permutations however processes favouring stress permutations cannot be further constrained from our observations since the dynamics of fluid materiel heterogeneity and post glacial rebound can also play a significant role

water temperature and conductivity variability as indicators of groundwater behaviour in complex aquifer systems in the south east of spain groundwater temperature and electrical conductivity logs were applied in this study to gain an understanding of the hydrogeological behaviour of a complex system this system compartmentalized by a large number of fractures which may even cause geothermal anomalies is that of the campo de dalias in the south east of the iberian peninsula in addition to this complexity one must consider the different levels with aquifer properties and their varying lithologies which in some cases are in direct contact with the sea vertical sections based upon the various logs allow lateral correlation to be made between the anomalies detected and provide information on the existence of both ascending and descending vertical flows and the inflow of sea water into the system analysis of environmental isotopes 18o and d indicate the areas of recharge with the greatest flow velocity no seasonal variation in the isotopes was observed which suggests that the residence time of the groundwater in the aquifer is several years radiocarbon dating gave estimates of generally long residence times although in some sectors it is possible to detect the current recharge based on its tritium content from rainwater infiltration or seawater intrusion copyright 2002 john wiley sons ltd

the fissure swarm of the askja volcanic system along the divergent plate boundary of n iceland divergent plate boundaries such as the one crossing iceland are characterized by a high density of subparallel volcanic fissures and tectonic fractures collectively termed rift zones or fissure swarms when extending from a specific volcano volcanic fissures and tectonic fractures in the fissure swarms are formed during rifting events when magma intrudes fractures to form dikes and even feeds fissure eruptions we mapped volcanic fissures and tectonic fractures in a part of the divergent plate boundary in northern iceland the study area is 1 800 km2 located within and north of the askja central volcano the style of fractures changes with distance from askja close to askja the swarm is dominated by eruptive fissures the proportion of tectonic fractures gets larger with distance from askja this may indicate that magma pressure is generally higher in dikes close to askja than farther away from it volcanic fissures and tectonic fractures are either oriented away from or concentric with the 3 4 identified calderas in askja the average azimuth of fissures and fractures in the area deviates significantly from the azimuth perpendicular to the direction of plate velocity as this deviation decreases gradually northward we suggest that the effect of the triple junction of the north american eurasian and the hreppar microplate is a likely cause for this deviation shallow tectonic earthquakes in the vicinity of askja are often located in a relatively unfractured area between the fissure swarms of askja and kverkfjoll these earthquakes are associated with strike slip faulting according to fault plane solutions we suggest that the latest magma intrusions into either the askja or the kverkfjoll fissure swarms rotated the maximum stress axis from being vertical to horizontal causing the formation of strike slip faults instead of the dilatational fractures related to the fissure swarms the activity in different parts of the askja fissure swarm is uneven in time and switches between subswarms as shown by a fissure swarm that is exposed in an early holocene lava nw of her ubrei but disappears under a younger 3500 4500 bp lava flow we suggest that the location of inflation centres in askja central volcano controls into which part of the askja fissure swarm a dike propagates the size and amount of fractures in the kollottadyngja lava shield decrease with increasing elevation we suggest that this occurred as the depth to the propagating dike s was greater under central kollottadyngja than under its flanks due to topography

relative importance of the saturated and the unsaturated zones in the hydrogeological functioning of karst aquifers the case of alta cadena southern spain summary from analysis of the hydrodynamic and hydrochemical responses of karst springs it is possible to know the behaviour of the aquifers they drain this manuscript aims to contribute to the characterization of infiltration process and to determine the relative importance of the saturated zone and of the unsaturated zone in the hydrogeological functioning of carbonate aquifers using natural hydrochemical tracers thus chemical components together with temperature and electrical conductivity both punctual and continuous records have been monitored in three springs which drain alta cadena carbonate aquifer southern spain an evaluation of the percentage of the electrical conductivity frequency peaks determined for each of the three springs is linked to the chemical parameters that comprise the conductivity signal one of these springs responds rapidly to precipitation conduit flow system due to the existence of a high degree of karstification in the unsaturated zone and in the saturated zone both of which play a similar role in the functioning of the spring another spring responds to precipitation with small increases in water flow somewhat lagged because the aquifer has a low degree of karstification even in the unsaturated zone which seems to influence its functioning more strongly than does the saturated zone the third spring drains a sector of the aquifer with a moderately developed degree of karstification one that is intermediate between the other two in which both the unsaturated zone and the saturated zone participate in the functioning of the spring but with the latter zone having a stronger influence these three springs show different hydrogeological functioning although they are in similar geological and climatic contexts which show the heterogeneity of karst media and the importance of an adequate investigation for groundwater management and protection in karst areas

hydrochemical dynamics of toc and no3 contents as natural tracers of infiltration in karst aquifers analysis of total organic carbon toc and no3 contents in the water at six springs in the province of malaga southern spain sampled under different hydrologic conditions revealed two different hydrochemical behaviour patterns for these natural tracers of infiltration toc content increased during every recharge period following the rapid arrival of water infiltrating through the soil on the other hand no3 content only rose during the first flood episodes normally in autumn and fell during the winter and spring ones this difference is consequence of the distinctive biogeochemical kinetics of nitrogen with respect to organic carbon both in the soil and within the aquifer unlike the mineralisation undergone by toc from the surface to the spring the no3 ion remains in the aquifer almost unaffected due to the oxidizing conditions prevailing within the karst medium which do not allow its denitrification and favour its preservation within the saturated zone in non polluted aquifers toc and no3 have a common origin in the soil and can be used to determine infiltration processes and the hydrogeological functioning of karst aquifers their different hydrochemical evolution provides information about mineralization and degradation processes of organic matter within karst aquifers which can be used to validate the vulnerability to contamination in this type of medium

hydrochemical indications of human impact on karst groundwater in a subtropical karst area chongqing china the application of combined isotopic and hydrochemical compositions may be useful for evaluating water quality problems in karst aquifers in which it is difficult to distinguish the sources of solutes from the natural background of those due to human activities multiple isotopes 13c dic 34s so4 2 and chemical parameters were measured in rainwater groundwater and sewage in order to elucidate the solute sources and impacts from human activities and natural background in the laolongdong karst catchment in chongqing municipality sw china overall the dissolution of carbonate rock controls ca2 mg2 and hco3 content in rainwater and karst groundwater so4 2 originated mainly from gypsum dissolution in karst groundwater carbonate rocks in the studied site could be dissolved jointly by h2co3 from the natural co2 h2o reaction and other acids organic acids and hno3 from sewage and soils sewage discharge from urban areas and agriculture activities lead to the increase of no3 po4 3 and cl in karst groundwater to protect and sustainably utilize the karst aquifer sewage originating from urban areas must be controlled and treated and the use of fertilizer should be limited

deflation of the askja volcanic system constraints on the deformation source from combined inversion of satellite radar interferograms and gps measurements the askja central volcano in northern iceland has been continuously subsiding at least since 1983 gps and optical leveling tilt measurements show subsidence of at least 75 cm from 1983 to 1998 in the center of the askja caldera without any eruptive activity we have performed an interferometric analysis of synthetic aperture radar images insar of the area utilizing data from the ers satellites we observe subsidence of the askja caldera and its fissure swarm up to a distance of 25 km from the volcano we evaluate the geometry of the magma chamber at askja from a combined inversion of satellite radar interferograms and gps measurements several models were tested including a mogi point source as well as an ellipsoidal source the use of an ellipsoidal source instead of a mogi source gives an estimate of the dimensions of the magma chamber and its deflating pressure whereas these parameters are not independently resolved if a mogi source is used two source models were also considered in order to explain the additional subsidence observed along the askja fissure swarm we tested a model using two mogi sources at different depths a shallow ellipsoidal cavity with a deeper mogi source and then a shallow mogi source with a deeper elongated ellipsoid oriented along the fissure swarm results indicate that an ellipsoidal source at about 3 km depth can accommodate most of the deflation occurring in the caldera residual subsidence occurs along the askja fissure swarm suggesting the existence of a deeper source of contraction we interpret this signal in terms of subsidence of the plate boundary

multiple sulfur isotope systematics of icelandic geothermal fluids and the source and reactions of sulfur in volcanic geothermal systems at divergent plate boundaries abstract multiple sulfur isotope systematics of geothermal fluids at krafla northeast iceland were studied in order to determine the source and reactions of sulfur in this system as an example of a geothermal system hosted on a divergent plate boundary fluid temperatures ranged from 192 to 437 c and the fluids have low cl concentration between 10 and 150 ppm with liquid water and vapor being present in the reservoir dissolved sulfide s ii and sulfate svi predominated in the water phase with trace concentrations of thiosulfate s 2 o 3 2 whereas sulfide s ii was the only species observed in the vapor phase the reconstructed sulfur isotope ratios of the reservoir fluids based on samples collected at surface from two phase and vapor only well discharges indicated that 34s and 33s of sulfide in the reservoir fluid ranged from 1 5 to 1 1 and 0 001 to 0 017 respectively whereas 34s and 33s of sulfate were significantly different and ranged from 3 4 to 13 4 and 0 000 to 0 036 respectively depressurization boiling upon fluid ascent coupled with progressive fluid rock interaction and sulfide mineral pyrite formation results in the liquid phase becoming progressively isotopically lighter with respect to both 34s and 33s in contrast h2s in the vapor phase and pyrite become isotopically heavier the observed 33s and 34s systematics for geothermal fluids at krafla suggest that the source of sulfide in the reservoir fluids is the basaltic magma either through degassing or upon dissolution of unaltered basalts at high temperatures insignificant so4 was observed in the fluids but below 230 c significant concentrations of so4 were observed the source inferred to be h2s oxidation the two key factors controlling the multiple sulfur isotope systematics of geothermal fluids are 1 the isotopic composition of the source material and 2 the isotope fractionation associated with aqueous and vapor speciation and how these change as a function of processes occurring in the system including boiling oxidation and fluid rock interaction

quantifying mixing boiling degassing oxidation and reactivity of thermal waters at vonarskard iceland abstract the chemical composition of geothermal fluids may be altered upon ascent from the reservoir to surface by processes including boiling degassing mixing oxidation and water rock interaction in an attempt to quantify these processes a three step model was developed that includes 1 defining the composition of the end member fluid types present in the system 2 quantifying mixing between the end members using non reactive elemental concentrations and enthalpy and 3 quantifying the changes of reactive elements including degassing oxidation and water rock interaction the model was applied to geothermal water at vonarskard iceland for demonstration having temperatures of 3 98 c ph of 2 15 9 95 and tds of 323 2250 ppm and was thought to be produced from boiled reservoir water condensed steam and non thermal water most geothermal water represented mixture of non thermal water and condensed steam whereas the boiled reservoir water was insignificantly mixed co2 and h2s degassing was found to be quantitative in steam heated water with oxidation of h2s to so4 also occurred in contrast major rock forming elements are enriched in steam heated water relative to their mixing ratios suggesting water rock interaction in the surface zone boiled reservoir water observed in alkaline hot springs have however undergone less geochemical changes upon ascent to surface and within the surface zone

geodetic gps measurements in south iceland strain accumulation and partitioning in a propagating ridge system 1 gps observations in south iceland between 1994 and 2003 are compared with two dimensional elastic half space and viscoelastic coupling models for two parallel rift zones representing the western and eastern volcanic zones wvz evz gps data from the hreppar block between the wvz and evz fit a rigid block model within uncertainties spreading rates across the wvz increase from 2 6 0 9 mm yr in the northeast to 7 0 0 4 mm yr in the southwest conversely spreading rates in the evz decrease from 19 0 2 0 mm yr in the northeast to 11 0 0 8 mm yr in the southwest the direction of ridge propagation summed extension rates across the two rift zones are approximately constant and equal to the total plate rate 18 20 mm yr consistent with a simple propagating ridge model whereby the wvz is deactivating in the direction of evz propagation the coupling model confirms results from the simple elastic half space model including relatively shallow locking depths 5 km beneath the rift zones and allows for an estimate of mean viscosity 1019 1020 pa s beneath the elastic layer the location of maximum surface velocity gradient in the evz presumably the locus of subsurface magma accumulation and future rifting does not coincide with the 1783 1784 lakagigar fissure eruption but is 20 km to the west on the bar abunga veidivotn fissure swarm this had a small volume eruption in 1862 1864 but a major eruption in 1477 a d

numerical modeling of the transient hydrogeological response produced by tunnel construction in fractured bedrocks abstract groundwater inflows into tunnels constructed in fractured bedrocks not only constitute an important factor controlling the rate of advancement in driving the tunnel but may pose potential hazards drawdowns caused by tunnel construction may also induce geotechnical and environmental impacts here we present a numerical methodology for the dynamic simulation of the hydrogeological transient conditions induced by the tunnel front advance the methodology is based on the use of a cauchy boundary condition at the points lying along the tunnel according to which water discharge q is computed as the product of a leakage coefficient and the head difference h h where h is the prescribed head at the tunnel wall and h is the hydraulic head in the fractured rock in the close vicinity of the tunnel at a given position of the tunnel is zero until the tunnel reaches such position when it is assigned a positive value the use of step wise time functions for allows an efficient and accurate simulation of the transient hydrogeological conditions at and around the tunnel during the excavation process the methodology has been implemented in tranmef 3 a finite element computer code for groundwater flow in 3d fractured media developed at the university of a coruna spain and has been used to simulate the impact of a tunnel on the groundwater system at the aspo island sweden this tunnel was constructed to access an underground laboratory for research on radioactive waste disposal the large amount of available data at this site provides a unique opportunity to test the performance of the numerical model and the proposed methodology for tunnel advance with just minor calibration the numerical model is able to reproduce accurately the measurements of inflows into the tunnel at several reaches and hydraulic heads at surface drilled boreholes these results obtained at the aspo site lead us to conclude that accurate predictions of the transient hydrogeological responses induced by tunneling works in fractured bedrocks can be achieved provided that a sound hydrogeological characterization of large scale fracture zones is available

effects of human activities on karst groundwater geochemistry in a rural area in the balkans abstract the geochemistry of three drinking water sources wells springs and tap in the vratza region of northern bulgaria was investigated to gain an understanding of how human activities influence natural geochemical processes in a carbonate aquifer system numerous villages have been identified within this highly agricultural area as endemic for the environmental disease balkan endemic nephropathy with some suggesting a link to the geochemistry of the region we observe that water quality varies significantly as a function of source hydrochemical facies analysis reveals trends not typical for limestone systems with cation trajectories falling along the ca2 mg2 axis and the anion trajectories lying along the hco 3 so 4 2 axis r mode factor analysis reveals i an increasing dominance of a cl na so 4 2 no 3 association from tap to spring to well waters ii a strong association between mg2 and u and iii a lack of associations between ca2 and mg2 and between ca2 and hco 3 that is atypical for limestone systems these observations are interpreted to indicate that human activities have influenced all sources across the vratza region and that mg and u concentrations result from the dissolution of limestone which is enhanced due to the input of anthropogenic chemicals geochemical modeling indicates that ca2 concentrations are in equilibrium with calcite but that mg2 concentrations remain conservative resulting in the decoupling of a ca2 and mg2 association uranium concentrations also appear to be conservative aided by a poised redox state due to high concentrations of no 3 and the formation of co 3 2 and po 4 3 ion pairs the similar source and conservative nature of both mg2 and u can account for their association finally cluster analysis indicates that the pattern of water geochemistry in the endemic area differs from the surrounding non endemic area may be explained by differences in the underlying geology this study has shown that the general water quality in this rural area whether in endemic or non endemic villages is poor and that agricultural activities have not only added chemicals to the groundwater system but that these chemicals have likely disrupted geochemical processes more work is required to understand the specific details of anthropogenic influences on geochemical processes on water quality in karstic terrains

behaviour of major elements and some trace elements li rb cs sr fe mn w f in deep hot waters from granitic areas abstract analyses of selected hot springs in more than sixty areas in granites from europe are presented concentrations of major elements and of some trace elements li rb cs sr fe mn w f in high ph waters are not significantly affected by processes during uprise from the deep reservoir to the surface re equilibrations mixing with surficial waters normalized to k or na concentrations of all other elements are related to the aquifer temperature the knowledge of aquifer temperature and total electric charge of mobile elements cl s possibly f allows us to predict both major elements within 50 and trace elements within a factor 2 or 3 concentrations in alkaline waters from granites

estimating potential for exploitation of karst aquifer case example on two serbian karst aquifer rational use of karst water resources depends considerably on the existence of a successful approach to estimating karst groundwater potential for exploitation the term groundwater potential for exploitation involves the application of regulatory measures affecting natural outflow regime generally the concept of controlling the artificial discharge regime is based on two principles the first one the borrowing of water from deeper storage part of storage is based mainly on the construction of groundwater wells the second one considers increasing dynamic reserves by providing additional artificial water storage thereby controlling the groundwater discharge regime is based on the construction of underground dams this paper examines how these two concepts can be used to increase potential groundwater usage from two karst springs in serbia st petka and perucac the ability to potentially increase the amount of karst ground water available for future exploitation may facilitate and give important directions to the future research

contribution of correlation and spectral analyses to the regional study of a large karst aquifer charente france the purpose of the study is to demonstrate that correlation and spectral analyses can contribute to the regional study of a large karst aquifer an example is presented for the la rochefoucauld karst aquifer charente france different types of spatially distributed time series provide valuable spatio temporal information for the karst aquifer the available time series consist of the spring flow rates the flow rates at different locations in sinking streams the piezometric levels the electrical conductivity and temperature of the water the atmospheric pressure and the precipitation the analysis of the flow rates at the springs shows that the aquifer empties very slowly and has a large storage capacity hydrodynamic links were established between three of the four rivers flowing on the aquifer and the springs the results also demonstrate the important spatial heterogeneity of the aquifer and indicate that the most rapid flow occurs in the northern part of the aquifer hourly piezometric and electrical conductivity time series indicate that the transmissivity of the aquifer varies when some conductive channels become desaturated during the low water period the delays between the distributed recharge and the piezometric level between the localized river input and the flow rates at the springs and between the electrical conductivities in rivers and the main spring provide information on the travel times in the aquifer the observation of earth tides and barometric effects indicate that this apparently unconfined aquifer has a confined behaviour

1983 2003 decaying rate of deflation at askja caldera pressure decrease in an extensive magma plumbing system at a spreading plate boundary new deformation data from the askja volcano iceland show that the volcano s caldera has been deflating continuously for over 20 years and confirm that the rate of subsidence is slowing down the decay in subsidence rate can be fitted with a function of the form e t where is 39 years reanalysis of gps data from 1993 1998 show that these data can be fitted with a model calling for two mogi point sources one shallow and another one much deeper 16 2 km depth pressure decrease occurs in both sources the deeper source is responsible for observed horizontal contraction towards askja at distances that cannot be explained by the shallower source plate spreading of 19 mm year distributed evenly over about 100 km wide zone is also favoured by the data

karstic problems in the construction of milwaukee s deep tunnels a critical component of milwaukee s 2 8 billion water pollution abatement program is a 31 2 km inline storage system comprising three deep tunnel sections that were bored between 1984 and 1993 at a depth of 80 100 m within silurian aged niagara dolostone construction of these deep tunnels proved more difficult and expensive than estimated because the karstic nature of the dolostone particularly its hydrology had not been fully appreciated rock collapse subsidence and groundwater intrusion necessitated remedial grouting and lining of about 45 of the tunnels costing some 50 million above estimates and delaying completion by 9 months tunnel performance since completion continues to be controversial

determination of the sources of nitrate contamination in karst springs using isotopic and chemical indicators the sources of nitrate no3 in groundwater of the shallow karst aquifer in southwestern illinois sinkhole plain were investigated using chemical and isotopic techniques the groundwater in this aquifer is an important source of potable water for about half of the residents of the sinkhole plain area previous work has shown that groundwater from approximately 18 of the wells in the sinkhole plain has no3 concentrations in excess of the usepa s drinking water standard of 10 mg n l relative to background levels the no3 concentrations in water from 52 of the wells and probably all of the springs in the study area are anomalously high suggesting that sources other than naturally occurring soil organic matter have contributed additional no3 to groundwater in the shallow karst aquifer this information and the dominance of agriculture in the study area suggest that agrichemical contributions may be significant to test this hypothesis water samples from 10 relatively large karst springs were collected during four different seasons and analyzed for inorganic constituents dissolved organic carbon atrazine and 15n and 18o of the no3 ions the isotopic data were most definitive and suggested that the sources of no3 in spring water are dominated by n fertilizer with some possible influence of atmospheric no3 and to a much lesser extent human and or animal waste differences in the isotopic composition of no3 and some of the chemical characteristics were observed during the four consecutive seasons in which spring water samples were collected isotopic values for 15n and 18o of the no3 ranged from 3 2 to 19 1 and from 7 2 to 18 7 respectively the trend of 15n and 18o data for no3 also indicated that a significant degree of denitrification is occurring in the shallow karst hydrologic system within the soil zone the epikarst and the shallow karst aquifer prior to discharging to springs

comparative application of two methods cop and paprika for groundwater vulnerability mapping in mediterranean karst aquifers france and spain a comparative test of two vulnerability mapping methods cop and paprika specifically dedicated to for karst aquifers was carried out on two mediterranean carbonate aquifers the vulnerability maps obtained for each aquifer present important differences to identify and determine the origin of these differences the results were statistically analyzed using sensitivity analysis coefficients of determination and scatter graphs in addition the global vulnerability gv parameter was used to measure the general vulnerability of the aquifer and to compare the results obtained this statistical analysis led us to conclude that the main cause of differences between these two methods used to assess aquifer vulnerability lie in the relative importance of the parameters employed in calculating the vulnerability index for the paprika method the variable related to infiltration slope and karst features has the most influence with less weight being assigned to the protective capacity of layers overlying the aquifer for the cop method the most influent variable is defined by the layers overlying the aquifer together with infiltration characteristics determined by the relative importance of different forms of infiltration in each aquifer the vulnerability mappings performed using the cop method present greater coherence with the known hydrogeological behavior of the study areas especially the spanish aquifers nevertheless further hydrogeological investigations are needed such as ones to validate the obtained vulnerability maps

subsidence of askja caldera 2000 2009 modelling of deformation processes at an extensional plate boundary constrained by time series insar analysis abstract many calderas in the world show long term unrest in the form of elevated rates of deformation and seismicity related to pressure changes and magma movements within their magmatic plumbing systems we present new observations of the style of deformation at the askja caldera iceland since 2000 using interferometric analysis of synthetic aperture radar images insar acquired by the canadian radarsat 2 satellite when combined with previously acquired detailed geodetic observations by various techniques we obtain an overview of askja s behaviour through more than four decades the combined dataset reveals that during this non eruptive period askja continuously subsides at a rate of 2 5 3 cm yr in 2000 2009 somewhat lower than the 5 cm yr rate inferred for the 1983 1998 period this behaviour of askja is evaluated and compared to those of other restless calderas the wrapped interferograms show three main features 1 concentric fringes depicting subsidence in the centre of the main askja caldera 2 oval fringes elongated along the rift portraying subsidence and 3 subsidence in an area north of the vatnajokull glacier the average line of sight los velocity from ground to satellite was used as input for inverse modelling of a deflating pressure source beneath the caldera embedded in a homogeneous elastic half space two different source geometries were tested a point pressure source and a horizontal penny shaped crack the concentric fringes centred in the askja caldera are best fit by a point source located at 65 05 n 16 78 w at a depth of 3 2 3 8 km with a volume decrease of 0 0012 0 0017 km3 yr from 2000 to 2009 consistent with previous studies provisional 2d fem models including structural complexities in the crustal layers indicate that the tectonic setting of askja plays an important role in the continuous long term high subsidence rates observed there in order to fully understand the cause and effects of the complicated tectonic setting we encourage the use of a more realistic rheological model of the area which could lead to reinterpretation of previous model results

motion in the north iceland volcanic rift zone accommodated by bookshelf faulting along mid ocean ridges the extending crust is segmented1 on length scales of 10 1 000 km where rift segments are offset from one another motion between segments is accommodated by transform faults that are oriented orthogonally to the main rift axis where segments overlap non transform offsets with a variety of geometries2 accommodate shear motions here we use micro seismic data to analyse the geometries of faults at two overlapping rift segments exposed on land in north iceland between the rift segments we identify a series of faults that are aligned sub parallel to the orientation of the main rift these faults slip through left lateral strike slip motion yet movement between the overlapping rift segments is through right lateral motion together these motions induce a clockwise rotation of the faults and intervening crustal blocks in a motion that is consistent with a bookshelf faulting mechanism named after its resemblance to a tilting row of books on a shelf3 the faults probably reactivated existing crustal weaknesses such as dyke intrusions that were originally oriented parallel to the main rift and have since rotated about 15 clockwise reactivation of pre existing rift parallel weaknesses contrasts with typical mid ocean ridge transform faults and is an important illustration of a non transform offset accommodating shear motion between overlapping rift segments

the kverkfjoll fissure swarm and the eastern boundary of the northern volcanic rift zone iceland rift zones at the divergent plate boundary in iceland consist of central volcanoes with swarms of fractures and fissures extending away from them fissure swarms can display different characteristics in accordance with their locations within the 50 km wide rift zones to better discern the characteristics of fissure swarms we mapped tectonic fractures and volcanic fissures within the kverkfjoll volcanic system which is located in the easternmost part of the northern volcanic rift zone nvz to do this we used aerial photographs and satellite images we find that rifting structures such as tectonic fractures holocene volcanic fissures and hyaloclastite ridges are unevenly distributed in the easternmost part of the nvz the kverkfjoll fissure swarm extends 60 km north of the kverkfjoll central volcano holocene volcanic fissures are only found within 20 km from the volcano the fjallgar ar area extending north of the kverkfjoll fissure swarm is characterized by narrow hyaloclastite ridges indicating subglacial volcanism we suggest that the lack of fractures and holocene volcanic fissures there indicates decreasing activity towards the north in the easternmost part of the nvz due to increasing distance from the long term spreading axis we argue that arcuate hyaloclastite ridges at the eastern boundary of the northern volcanic rift zone are mainly formed during deglaciations when three conditions may occur firstly eruption rate increases due to decompression of the mantle secondly the high tensile stresses accumulated during glaciations due to lack of magma supply may be relieved as magma supply increases during deglaciations thirdly faulting may occur during unloading due to differential movements between the thinner and younger northern volcanic rift zone crust and the thicker and older crust to the east of it

the evolution of the waiotapu geothermal system new zealand based on the chemical and isotopic composition of its fluids minerals and rocks abstract the waiotapu geothermal system is hosted by silicic rocks of the taupo volcanic zone new zealand exploration drilling in the late 1950s down to 1100 m provided physical information on the system measured temperatures show a boiling profile to 295 c with shallow inversions particularly in the north total discharge fluid samples were collected the geothermometry and measured temperatures show that fluids derive mainly from a shallow 400 m deep reservoir at about 225 c petrologic study of drillcore samples recovered from seven wells reveals an alteration assemblage of quartz and albite adularia with a variable distribution of chlorite pyrite calcite zeolites epidote pyrrhotite sphene leucoxene apatite and minor base metal sulfides white mica is a late overprint particularly well developed at shallow depths surficial alteration of kaolin cristobalite alunite and smectite clays reflect alteration by acid sulfate steam heated waters the activities of components in minerals determined from microprobe analyses and composition activity relations and fluids speciated to reservoir conditions indicate equilibrium now exists between the fluids and white mica the na k ratio of the fluid is being controlled by dissolution of albite and adularia while its h 2 h 2 s ratio is buffered by pyrite replacing pyrrhotite the fluids are now slightly undersaturated with respect to calcite the present deep fluids boil adiabatically from at least 300 c to 230 c at depths of 500 m this ascending chloride fluid is variably diluted by a steam heated water of zero chloride that lies over and occurs on the margin of the system like a discontinuous umbrella the steam heated water is relatively co2 rich 0 1 m the cooling at shallow levels by this mixing has shifted the alteration from albite adularia stability to white mica stability this shift is enhanced by the co2 rich nature of the diluent dilution of ascending chloride fluids by shallow waters is also supported by the oxygen and hydrogen isotopic composition of the mixture with the deep fluid being enriched in 18o and d from local meteoric by 7 and 10 respectively the patterns in whole rock 18o indicate that they were largely shifted in isotopic composition prior to incursion of steam heated waters possibly induced by a series of hydrothermal eruptions 900 years ago in contrast the 18o composition of late vug calcite indicates its formation is related to the initial incursion of steam heated groundwater and subsequent cooling this is supported by fluid inclusion evidence the d shift from local groundwater composition and the 13c composition of co2 determined from calcite 4 to 6 may be evidence for a magmatic input to the meteoric convection cell the shallow portion of the waiotapu geothermal system has recently evolved both chemically and physically by incursion of fluids from a steam heated carapace continued refluxing of these relatively cool hybrid fluids progressively deeper with their recycled co2 content will hasten hydrolytic leaching in contrast to a single pass of adiabatically cooling deep fluids this action accompanied by argillic alteration may eventually seal the deeper portions of the system hastening its demise there is evidence for similar events occurring in the fossil environment at epithermal depths

the anthropogenic impact on mediterranean karst aquifers cases of some spanish aquifers mediterranean karstic aquifers are a major source of water supply for drinking water and agricultural use in semiarid areas the risk of causing an intensive exploitation is high leading to degradation processes of water quality not only due to limited agricultural activities developed on the karstic rocks being generally poorly developed soils but to the presence of deep evaporates which can be mobilised or because of being coastal aquifers where seawater intrusion can progress rapidly moreover karstic massifs constitute often positive reliefs that can generate barriers for civil works more and more saved by building sophisticated tunnels such works can affect the quantity and quality of the waters from the karst five examples of human impacts on some karst aquifers in se of spain are shown in this paper three of them with impacts on water quality and the other two correspond to the impact of tunnels in high speed trains drilling below the water table

geometry oblique kinematics and extensional strain variation along a diverging plate boundary the example of the northern theistareykir fissure swarm ne iceland abstract the boundary between the american and european plates emerges in iceland an outstanding natural laboratory where it is possible to analyse ongoing rifting processes in the north volcanic zone we studied with unprecedented detail an active rift known as the theistareykir fissure swarm thfs we surveyed an area of 85 km2 with 694 measurement sites along 1537 post late glacial maximum extension fractures in the southern sector of the study area fractures strike n30 40 with opening directions about n120 fractures in the central sector strike about n00 and opening directions are n90 100 in the northern sector fractures strike about n30 with opening directions about n125 through a comparison with older faults cropping out in the substrate at the shoulder of the thfs we are able to suggest that variations in fracture strike are the effect of substrate structural inheritance as well as the possible interaction with the tjornes fracture zone with regard to kinematics we highlight that most fractures show a small but systematic strike slip component a more frequent right lateral component and a less common left lateral one this cannot be explained as the result of fracture strike rotation relative to the regional tectonic least principal stress we conclude that the net opening directions can result from the combination of tectonic offsets and events caused by shallow magma chamber inflation and or dyke intrusions the latter can produce transcurrent components of displacement along new or already existing fractures

human induced hydrogeological changes and sinkholes in the coastal gypsum karst of lesina marina area foggia province italy abstract in 1930 a canal was excavated to connect the lesina lagoon with the adriatic sea modifying the track of the previous existing acquarotta canal the 1100 m long stretch of the canal situated next to the coast exposed unknown highly cavernous gypsum bedrock underlying a loose sandy cover during the last two decades a large number of cover collapse and cover suffosion sinkholes have formed along two bands situated next to the canal impinging the adjacent lesina marina residential area the area affected by subsidence has increased exponentially from 1999 to 2009 the tight spatial correlation between the sinkholes and the canal reveals that the subsidence phenomenon has been induced by the local hydrogeological changes caused by the canal in the coastal evaporite aquifer 1 local lowering of the average water table 2 deflection of the groundwater flow lines towards the canal and increase in flow velocity 3 amplification of the groundwater level oscillations largely controlled by the tidal regime 4 local reversals in the groundwater flow changing the canal temporarily from effluent to influent these changes in the hydrogeological functioning of the system have favoured both internal erosion and karstification processes hydrochemical evidence reveals that gypsum dissolution is a currently active process favoured by fresh water and sea water mixing and cation exchange processes most likely the partial replacement of a concrete lining in the canal by pervious gabions in 1993 provided more adequate conditions for the evacuation of the sediments filling the karst conduits accelerating internal erosion and sinkhole development

non magmatic fracture controlled hydrothermal systems in the idaho batholith south fork payette geothermal system abstract non magmatic fracture controlled hydrothermal systems located within and near the idaho batholith have been examined and evaluated for potential application as natural analogues to high level nuclear waste repositories detailed geochemical petrologic and structural studies of hot springs along the south fork of the payette river sfpr in central idaho usa have been combined to assess the nature of a hydrothermal aquifer system along a major brittle shear zone geochemical modeling of thermal spring water chemistry with solveq reed m h 1992 solveq users manual unpublished report dept of geological sciences university of oregon eugene or indicates reservoir temperatures of 85 c to 160 c and an alteration assemblage consisting of several clays chlorite serpentinites quartz albite microcline and micas geothermometry calculations coupled with independent estimates of geothermal gradients based on heat flow and regional geology allow estimation of reservoir depths ranging from 2 4 to 6 7 km comparison of trace element rare earth element and solveq alteration assemblages supports the hypothesis that waters equilibrated with granitic rocks at depth and ascended to the surface in a short time span stable isotope data d 138 4 to 148 4 and 18 o 17 5 to 19 4 indicate that thermal waters of meteoric origin have interacted with country rocks at a very high water rock w r ratio systematic variations in d values and the amount of 18 o shift for thermal waters suggest that recharge probably occurs at much higher elevations than discharge fracture orientations petrologic relations and geochemical differences between adjacent springs delineate separate hydrothermal systems along the major structure defining the course of the sfpr hydrothermal systems along the sfpr exist primarily as small circulation cells which are probably influenced by minor changes in geothermal gradients associated with different rock types these subsystems are dependent on periodic seismic or microseismic activity to maintain flowpaths a working model of deep fracture controlled hydrothermal convection systems based on the sfpr geothermal system may be used to evaluate the long term behavior of artificial hydrothermal systems associated with high level nuclear waste repositories

the krafla fissure swarm iceland and its formation by rifting events fissure swarms at divergent plate boundaries are activated in rifting events during which intense fracturing occurs in the fissure swarm accompanied by intrusion of magma to form dikes that sometimes lead to eruptions to study the evolution of fissure swarms and the behaviour of rifting events detailed mapping was carried out on fractures and eruptive fissures within the krafla fissure swarm kfs fracture densities of dated lava flows ranging from 10 000 years bp to 30 years old were studied and the fracture pattern was compared with data on the historical m vatn rifting episode 1724 1729 and the instrumentally recorded krafla rifting episode 1975 1984 additionally the interaction of transform faults and fissure swarms was studied by analysing the influence of the husavik transform faults on the kfs during the historical rifting episodes eruptions on the fissure swarm occurred within 7 km from the krafla central volcano although faults and fractures were formed or activated at up to 60 70 km distance this is consistent with earlier rifting patterns as holocene eruptive fissures within the kfs are most common closer to the central volcano most fractures within the central krafla caldera are parallel to the overall orientation of the fissure swarm this suggests that the regional stress field is governing in the krafla central volcano while the local stress field of the volcano is generally weak a sudden widening of the graben in the northern kfs and a local maximum of fracture density at the junction of the kfs and the extrapolation of the husavik transform fault zone indicates possible buried continuation of the husavik transform fault zone which extends to the kfs eruptive fissures are found farther away from the krafla central volcano in the southern kfs than in the northern kfs this is either due to an additional magma source in the southern kfs the hei arspor ur volcanic system or caused by the husavik transform faults transferring some of the plate extension in the northern part fracture density within particular lava flow fields increases with field age indicating that repeated rifting events have occurred in the fissure swarm during the last 10 000 years bp the fracture density in the kfs is also generally higher closer to the krafla central volcano than at the ends of the fissure swarm this suggests that rifting events are more common in the parts of the fissure swarm closer to the krafla central volcano

a preisach method for estimating absolute paleofield intensity under the constraint of using only isothermal measurements 2 experimental testing 1 this paper reports an empirical test of a new nonheating preisach based protocol for determining the absolute ancient magnetic field intensity paleointensity using a selection of synthetic samples and a large suite of modern lavas and pyroclastic lithic samples generally the preisach paleointensity estimates compare favorably with the expected field intensities 1 for the synthetic samples displaying single domain like behavior the method returned the correct result for the known field while multidomain samples yielded an underestimate and 2 averaging 168 post 1850 a d lavas yielded a value 6 within the expected field value these preisach paleointensity estimates are also compared with paleointensity determinations made on the same suite of samples using standard thellier type heating protocols and the nonheating remanence rem method the preisach paleointensity estimates compare favorably for samples that yielded correct thellier type determinations including the synthetic single domain like samples in addition the preisach method produced estimates for cases where the thellier type estimates failed a possible selection criterion was identified median destructive field which was found to improve the paleointensity estimates in some sample suites for the investigated sample set the preisach method was found to be much more accurate than the rem method the importance of cooling rate on the preisach paleointensity estimate is also examined

description and interpretation of the composition of fluid and alteration mineralogy in the geothermal system at svartsengi iceland abstract the bulk composition and mineralogy of hydrothermally altered tholeiite along with the composition and speciation of fluid have been determined for a well defined alteration zone at 240 c and 110 bars at svartsengi iceland mass balances between the geothermal fluid and altered tholeiite relative to a seawater fresh water mixture and unaltered tholeiite indicate the overall reaction per 1000 cm 3 is 1325 gm plagioclase 1228 gm pyroxene 215 gm oxide minerals break down to form 685 gm chlorite 636 gm albite 441 gm quartz 249 gm epidote 266 gm calcite 201 gm oxide minerals 15 gm pyrite requiring an influx of 123 gm co 2 10 gm h 2 s and 4 gm na 2 o and a release of 57 gm sio 2 35 gm feo 21 gm cao 8 gm mgo and 4 gm k 2 o principal reactions deduced from textural evidence include na ca exchange in plagioclase precipitation of quartz calcite and anhydrite and formation of chlorite and epidote by reactions between groundmass minerals and fluid thermodynamic analyses of authigenic minerals and downhole fluid indicate that the fluid maintains a state close to equilibrium with the secondary mineral phases chlorite epidote albite quartz calcite prehnite anhydrite pyrite and magnetite whereas remnant primary labradorite and augite are out of equilibrium with the fluid water rock ratios for the system are determined under a variety of assumptions however the open nature of the system makes comparisons with experimental and theoretical closed system studies ambiguous

hydrodynamical changes and their consequences on groundwater hydrochemistry induced by three decades of intense exploitation in a mediterranean karst system the lez karst spring located in the mediterranean basin southern france supplies drinking water to the metropolitan area of montpellier france since the nineteenth century since 1981 an intense pumping is being performed directly in the main conduit with a maximum exploitation flow rate of about 1 700 l s to improve the understanding of groundwater origins and circulation dynamic in this karst system as well as the impact of three decades of intense water exploitation groundwater samples have been collected during various hydrologic conditions since march 2006 a previous hydrochemical study on the lez karst system had been carried out before the installation of the pumping plant this dataset was compared to the present one to identify possible changes on groundwater hydrochemistry the results of this analysis indicate the existence of historical changes in water hydrogeochemistry and evidence a decrease of the deep compartment participation to the lez spring outflow this change in spring water hydrogeochemistry may be attributed to the intense pumping of the karst system and in the absence of noticeable climatic changes expresses the direct consequences of anthropogenic forcing on the overall functioning of the aquifer this study aims to analyze the differences to understand the water chemistry changes and to better foresee the aquifer evolution for the future

building icelandic igneous crust by repeated melt injections observations of microseismicity provide a powerful tool for mapping the movement of melt in the crust here we record remarkable sequences of earthquakes 20 km below the surface in the normally ductile crust in the vicinity of askja volcano in northeast iceland the earthquakes occur in swarms consisting of identical waveforms repeating as frequently as every 8 s for up to 3 h we use template waveforms from each swarm to detect and locate earthquakes with an automated cross correlation technique events are located in the lower crust and are inferred to be the result of melt being injected into the crust during melt intrusion high strain rates are produced in conjunction with high pore fluid pressures from the melt or exsolved carbon dioxide these cause brittle failure on high angle fault planes located at the tips of sills moment tensor solutions show that most of the earthquakes are opening cracks accompanied by volumetric increases this is consistent with the failure causing the earthquakes by melt injection opening new tensile cracks analysis of the magnitude distribution of earthquakes within a swarm reveals a complicated relationship between the imposed strain rates and the fluids that cause brittle failure the magnitude of the earthquakes is controlled by the distance fluids can migrate along a fault whereas the frequency of the events is controlled by the strain rate faults at the tips of sills act to focus melt transport between sills and so must be an important method of transporting melt through the lower crust

environmental and hydrogeological problems in karstic terrains crossed by tunnels a case study the construction of one of the high speed railway tunnels between malaga and cordoba south spain beneath the abdalajis mountains occasioned a series of hydrogeological problems with geotechnical and environmental impacts the double tunnel 7 300 m in length runs south to north across several lines of small calcareous mountains that have a highly complex structure beneath the jurassic limestones lie triassic clays and evaporites overlying the limestones is an essentially marly and limestone marl cretaceous series which culminates with miocene marls containing some organic matter these mountains have generated springs that are used for urban water supply and irrigation as well as drinking fountains in the surrounding villages the initial water level in the aquifer series varied from 400 to 650 m above sea level after drilling approximately 2 900 m and intercepting a fracture zone within the carbonate rocks a sudden water eruption occurred that reached a peak flow of 800 l s after a short while spring discharges dried up leading to a public protest in this paper we describe the geological and hydrogeological settings the development of the aquifer as the drilling operation proceeded the measures adopted and the responses subsequent to completion of the tunnel including the effect of rainfall on the recovery of water levels lastly a generalized estimate is made of how the system functions and a forecast is made for recovery of its equilibrium

geothermal mineral equilibria the dominant reaction determining the chemistry of fluids in a geothermal system of the new zealand type consists of the conversion of primary plagioclase by co2 to calcite and clays with log pco2 15 26 7850 t 273 2 temperature t in c subsequent reactions involving secondary minerals control relative co2 h2s contents the distribution of mineral phases throughout a geothermal system reflects the stepwise conversion of thermodynamically unstable primary phases through a series of intermediate metastable phases to a thermodynamically stable secondary assemblage the relative stabilities of these phases was evaluated on the basis of their solubilities the least soluble aluminiumsilicate representing the thermodynamically most stable phase under a given set of conditions observed assemblages of secondary minerals in geothermal systems represent indicators allowing mineral fluidinteraction conditions to be evaluated on the basis of multi component mineral stability diagrams

correlation of homogenization temperatures of accessory minerals from sphalerite bearing deposits and ga ge model temperatures abstract the ga ge ratio in sphalerite can be related to the temperature of the initial fluids from which the sphalerite grew after mixing with various amounts of fluids from different origins the extent of mixing of the two fluids can be qualitatively derived from the pressure corrected homogenization temperature which represents the temperature after mixing of the fluids and the ga ge temperatures of sphalerite which indicates the temperature of the hot metal bearing initial fluids different temperature information strongly indicate that mixing of fluids did occur prior to sulphide formation

dike emplacement on venus and on earth many long linear troughs are visible in synthetic aperture radar images of the surface of venus their geometry closely resembles that of dike swarms on earth such troughs will be formed if dikes fail to reach the surface or if the magma in them is partially drained dikes that form closed ellipses in plan view can be produced by intrusions near a depression and intersecting dikes can result if the stress field changes with time because of the absence of erosion and sedimentation all these effects are better displayed on venus than they are on earth the magnitude of the regional stress on venus can be estimated from the dike patterns to be about 3 mpa or similar to that of earth dikes consisting of en echelon segments whose total length is 1500 km or more occur on both earth and venus on earth their widths are generally greater than 30 m and are sometimes as great as 250 m and they are likely to be similar on venus the melt velocity during their emplacement is predicted to be a few meters per second and the calculated rate of heat loss is sufficiently slow that they can remain molten as they propagate for distances of more than 1000 km the same calculations apply to sills though less is known about their geometry the results therefore suggest that magma intrusion in thin sheets extending over 1000 km or more could produce regional crustal thickening and uplift on both earth and venus

plate boundary deformation and continuing deflation of the askja volcano north iceland determined with gps 1987 1993 gps geodetic measurements were conducted around the askja central volcano located at the divergent plate boundary in north iceland in 1987 1990 1992 and 1993 the accuracy of the 1987 and 1990 measurements is in the range of 10 mm for horizontal components the accuracy of the 1992 and 1993 measurements is about 4 mm in the horizontal plane regional deformation in the askja region is dominated by extension points located outside a 30 45 km wide plate boundary deformation zone indicate a displacement of 2 4 0 5 cm a in the direction n 99 e 12 of the eurasian plate relative to the north american plate in the period 1987 1990 within the plate boundary deformation zone extensional strain accumulates at a rate of 0 8 strain a displacement of control points next to askja 7 km from the caldera center in the periods 1990 1993 and 1992 1993 show deflation and contraction towards the caldera these results are in accordance with the results obtained by other geodetic methods in the area which indicate that the deflation at askja occurs in response to a pressure decrease at about 2 8 km depth located close to the center of the main askja caldera a mogi point source was fixed at this location and the gps data used to solve for the source strength a central subsidence of 11 2 5 cm in the period 1990 1993 is indicated and 5 5 1 5 cm in the period 1992 1993 the maximum tensional strain rate according to the point source model occurs at a horizontal distance of 2 5 6 km from the source at the same location as the main caldera boundary discrepancies between the observed displacements and predicted displacements from the mogi model near the askja caldera can be attributed to the regional eastwest extension that occurs at askja

karst and artificial recharge theoretical and practical problems a preliminary approach to artificial recharge assessment summary managed aquifer recharge mar is an emerging sustainable technique that has already generated successful results and is expected to solve many water resource problems especially in semi arid and arid zones it is of great interest for karst aquifers that currently supply 20 25 of the world s potable water particularly in mediterranean countries however the high heterogeneity in karst aquifers is too complex to be able to locate and describe them simply via field observations hence as compared to projects in porous media mar is still marginal in karst aquifers accordingly the present work presents a conceptual methodology for aquifer rechargeability assessment in karst referred to as arak the methodology was developed noting that artificial recharge in karst aquifers is considered an improbable challenge to solve since karst conduits may drain off recharge water without any significant storage or recharge water may not be able to infiltrate the aim of the arak method is to determine the ability of a given karst aquifer to be artificially recharged and managed and the best sites for implementing artificial recharge from the surface arak is based on multi criteria indexation analysis modeled on karst vulnerability assessment methods arak depends on four independent criteria i e epikarst rock infiltration and karst after dividing the karst domain into grids these criteria are indexed using geological and topographic maps refined by field observations arak applies a linear formula that computes the intrinsic rechargeability index based on the indexed map for every criterion coupled with its attributed weighting rate this index indicates the aptitude for recharging a given karst aquifer as determined by studying its probability first on a regional scale for the whole karst aquifer and then by characterizing the most favorable sites subsequently for the selected sites a technical and economic feasibility factor is applied weighted by the difficulties that could occur when trying to undertake a recharge operation at a selected site from the surface each site is finally rated by its rechargeability index the product of two factors the intrinsic rechargeability and the feasibility index arak was applied to the region of damour lebanon on the mediterranean coast where uncontrolled exploitation of public and private wells led to its partial salinization by seawater a mar system in damour region represents an interesting solution to cope with salinization and the insufficiency of the resource

mineralogical and fluid inclusion features of rock alterations in the seigoshi gold silver mining district western part of the izu peninsula japan abstract propylitic and advanced argillic alterations occur in the seigoshi gold silver mining district in the western part of the izu peninsula japan the propylitic alteration has the following zonal arrangement from the deeper portion to the shallower portion an epidote prehnite k feldspar chlorite zone a wairakite laumontite zone and a stilbite heulandite montmorillonite zone lateral and vertical zoning is conspicuous in the advanced argillic alteration the inner zone is silica rich and this grades laterally and vertically through alunite to clay rich zones fluid inclusions from the epidote prehnite k feldspar chlorite zone are liquid dominated and filling temperatures of this zone are in the range of 225 285 c filling temperatures for the zeolite zone are variable being in the range of 240 380 c this wide range suggests that boiling of the fluids was responsible for the zeolite zone filling temperatures of the advanced argillic alteration range widely from 210 to 430 c this wide range and the coexistence of liquid and vapor dominated fluid inclusions in a given sample suggest that liquid vapor separation simultaneously occurred during the advanced argillic alteration process it is deduced that the ranges of gaseous fugacity are quite different for each type of alteration for instance f s 2 and f o 2 of the advanced argillic alteration are estimated to be higher than those of the propylitic alteration based on the alteration mineral assemblage chemical composition and mode of occurrence of alteration minerals fluid inclusions estimated ranges of gaseous fugacities and comparison of these features with those of active geothermal systems it is concluded that the propylitic alteration minerals were probably precipitated due to the loss of gases such as co 2 and that the formation of advanced argillic alteration was caused by subsurface mixing of volcanic gas and or condensed hot water with groundwater these coexisting propylitic and advanced argillic alterations are commonly found in the other au ag mining districts in japan

revel a model for recent plate velocities from space geodesy 1 we present a new global model for recent plate velocities revel describing the relative velocities of 19 plates and continental blocks the model is derived from publicly available space geodetic primarily gps data for the period 1993 2000 we include an independent and rigorous estimate for gps velocity uncertainties to assess plate rigidity and propagate these uncertainties to the velocity estimates the velocity fields for north america eurasia and antarctica clearly show the effects of glacial isostatic adjustment and australia appears to depart from rigid plate behavior in a manner consistent with the mapped intraplate stress field two thirds of tested plate pairs agree with the nuvel 1a geologic 3 myr average velocities within uncertainties three plate pairs caribbean north america caribbean south america and north america pacific exhibit significant differences between the geodetic and geologic model that may reflect systematic errors in nuvel 1a due to the use of seafloor magnetic rate data that do not reflect the full plate rate because of tectonic complexities most other differences probably reflect real velocity changes over the last few million years several plate pairs arabia eurasia arabia nubia eurasia india move more slowly than the 3 myr nuvel 1a average perhaps reflecting long term deceleration associated with continental collision several other plate pairs including nazca pacific nazca south america and nubia south america are experiencing slowing that began 25 ma the beginning of the current phase of andean crustal shortening

interaction between central volcanoes and regional tectonics along divergent plate boundaries askja iceland activity within magmatic divergent plate boundaries mdpb focuses along both regional fissure swarms and central volcanoes an ideal place to investigate their mutual relationship is the askja central volcano in iceland askja consists of three nested calderas namely kollur askja and oskjuvatn located within a hyaloclastite massif along the nne ssw trending icelandic mdpb we performed an extensive field based structural analysis supported by a remote sensing study of tectonic and volcanic features of askja s calderas and of the eastern flank of the hyaloclastite massif in the massif volcano tectonic structures trend n 10 e to n 40 e but they vary around the askja caldera being both parallel to the caldera rim and cross cutting on the western side structural trends around the oskjuvatn caldera are typically rim parallel volcanic vents and dikes are preferentially distributed along the caldera ring faults however they follow the nne ssw regional structures when located outside the calderas our results highlight that the askja volcano displays a balanced amount of regional fissure swarm related and local shallow magma chamber related tectonic structures along with a mutual interaction among these this is different from krafla volcano to the north of askja dominated by regional structures and grimsvotn to the south dominated by local structures therefore askja represents an intermediate tectono magmatic setting for volcanoes located in a slow divergent plate boundary this is also likely in accordance with a northward increase in the spreading rate along the icelandic mdpb

hydrogeochemical effects of groundwater mining of the sierra de crevillente aquifer alicante spain the groundwater mining of the crevillente aquifer southeastern spain has resulted in the progressive deterioration of water quality with particularly significant increases in chloride sulfate and sodium the possibility of a vertical hydrochemical zoning is deduced that would require examining the importance of the geometry and lithology evaporitic materials in the salinization process the time of water rock contact residence time and dilution by infiltration of rainwater also influences the hydrogeochemistry of the aquifer the hydrochemical data are useful in defining the conceptual model of the aquifer completely karstified with relative homogeneity

the role of magma overpressure in suppressing earthquakes and topography worldwide examples in an extending terrane basaltic magma supplied at a pressure greater than the least principal stress overpressure may be capable of suppressing normal faulting and the earthquakes and topographic relief that commonly accompany normal faulting as vertical dikes intrude they press against their walls in the direction opposite the least principal stress and increase its magnitude the emplacement of tabular intrusions causes the internal magma pressure to act selectively in opposition to tectonic stresses this process tends to equalize the stresses and thus diminishes the deviatoric stress difference between maximum and minimum stresses that creates faults and causes earthquakes observations of the pattern of seismicity and magmatism worldwide indicate that magmatism commonly supplants large earthquakes as the primary mechanism for accommodating tectonic extension recognizing the extent of magmatic stress accommodation is important in assessing seismic and volcanic risks

nitrates as indicators of aquifer interconnection application to the campo de dalias se spain relatively high concentrations of no3 usually have their origin in processes of organic pollution and excessive use of inorganic fertilizers in the case of agricultural areas these activities may generate great quantities of nitrates this fact has enabled us to use the nitrate ion to characterize an exploited aquifer unit of a very complex aquifer system as is the case for the campo de dalias aquifer system se spain the shallow boreholes which draw water from intensively cultivated superficial formations yield waters with a high no3 content when the boreholes are deeper and penetrate low permeability formations in the superficial layers the waters contain little no3 similar to what happens in areas of recharge where agricultural activities are absent in addition using longitudinal sections it is possible to demonstrate the possible existence of connections between superficial and deep aquifers using no3 as a tracer similarly one can locate those sectors responsible for contamination caused by the poorly lined boreholes themselves when they perforate more than one aquifer in a multiple aquifer formation

the stress pattern of iceland moritz ziegler mojtaba rajabi oliver heidbach gylfi pall hersir kristjan agustsson sigurveig arnadottir arno zang

karst groundwater resources in the countries of eastern mediterranean the example of lebanon the hydrogeological study of some karst systems in lebanon shows important storage capacity up to 27 billions m3 for zarka system the spring of orontes river their geological and morphological settings as well as their hydrodynamic function show structures developed below the level of present springs probably up to several hundreds meters at depth since miocene those carbonate formations were subject to a remarkable instability of their base levels variations of sea level of which the messinian salinity crisis is the major phase and effects of the alpine orogenesis combined with climate variations to develop complex multiphased karst systems karstification occurs frequently in the whole formation often deeply below sea level or underneath sediment filling of continental basins the surface karst landscape is often intensely eroded those multiple superimposed karst phases give the carbonate aquifers their large extension and storage capacity these karst aquifers show the typical easy restoration of storage they have the ability to bear large interannual recharge variations and support exploitation under high pumping rates however these aquifers have some disadvantages for sustainable management in some regions successful boreholes which allow high pumping rates also induce uncontrolled exploitation another consequence is natural seawater intrusion as well as the submarine discharge of fresh groundwater in coastal aquifers those carbonate aquifers are subject to important economical stress which jeopardizes their durability the systematic study and understanding of carbonate aquifers in eastern mediterranean is a preliminary condition to any integrated and sustainable management of water resources studies in progress in lebanon may serve as examples to the whole region

rock fluid interactions in a temperature gradient biotite granodiorite h2o abstract a biotite granodiorite was reacted in a controlled temperature gradient with distilled water for 60 days at 1 3 kbar p tot p h 2 o polished rock prisms were placed in the gradient at 72 119 161 209 270 and 310 c scanning electron microscope and microprobe analyses show the appearance of several secondary phases ca montmorillonite at 72 c and 119 c zeolite either stillbite or heulandite at 161 c and another zeolite thomsonite at higher temperatures solution analyses show a constant composition after about 2 weeks of reaction the phase assemblages observed in this experiment are connected by reaction relationships the reactions show the transition from clay to zeolite i stilbite or heulandite to zeolite ii thomsonite with increasing temperature and decreasing chemical potential of silica additional relations can be used to predict mineral assemblages not directly observed in this experiment but which may occur at different pressures and temperatures as well as at different chemical potentials of water and silica