character of the englacial and subglacial drainage system in the upper part of the ablation area of storglaciaren sweden on 4 july 1986 dye was injected at a point slightly above the equil ibrium line on storglac iliren a small valley glacier in northern sweden just below the equilibrium line the glacier bed is over deep ened the dye re appeared in a stream at the glacier terminus over the next 35 d this stream normally carries relatively little sediment in constrast to the situ ation in another nearby stream that also emerges from the glacier this sugge sts that the dye traveled in englacial rather than subglacial conduits tracer tests utilizing salt in bore holes in the overde epening support this interp retation as the bore holes were draining well above the bed the dye appeared during three distinct events suggesting that it became divided into at least three separate parcels shortly after iojection this probably occurred in the crevassed area in the vicinity of the inje ction point the englacial location of the drainage may be explained by the fact that in order to remain at the pressure melting p oint water in subg lacial conduits coming out of the overde epening may have had to warm up faster than would be possible by visc ous heating alone such

the significance of clathrates in fluid inclusions and the evidence for overpressuring in the broadlands ohaaki geothermal system new zealand the broadlands ohaaki geothermal system is host to an epithermal environment where gold silver transport and deposition involves deeply derived fluids containing up to 3 3 wt percent co 2 and 0 1 wt percent cl earlier fluid inclusion investigations show that most microthermometric data reflect boiling and mixing in the upper 2 km of the system under modern p t x fluid conditions here we report the microthermometric results for a single quartz crystal from 1 258 m depth well br 25 in the upflow zone of the geothermal system that reveal the presence of clathrates upon freezing due to anomalous concentrations of co 2 7 9 to 14 3 wt these inclusions occupy the core of the quartz crystal and have homogenization temperatures from 291 to 365 c but the anomalous concentrations of co 2 are likely artifacts of deep boiling and heterogeneous trapping of the resulting coexisting gas and liquid phases only a few fluid inclusions t h 300 t m of 1 4 to 1 6 c which lack clathrate reveal more realistic conditions of early quartz precipitation from a modestly overpressured fluid 140 bars relative to the prevailing hydrodynamic boiling conditions 110 bars microthermometric data t h 300 t m of 0 2 to 0 8 c for fluid inclusions in a later formed overgrowth of the quartz crystal match the modern p t x conditions at 1 258 m depth in the well the overall results of the study show that the clathrates are artifacts of two phase trapping of steam and liquid and that the deep liquid became overpressured locally probably due to mineral deposition and sealing of a permeable channel

the use of borehole video in investigating the hydrology of a temperate glacier a geovision micro colour video camera was used to investigate the internal structure of 11 boreholes at haut glacier d arolla switzerland the boreholes were distributed across a half section of the glacier with closest spacing towards the glacier margin the boreholes were used to investigate the hydrology of the glacier through automatic monitoring of borehole water level and electrical conductivity ec at the glacier bed ec profiling was undertaken in several boreholes to determine the existence of water quality stratification temporal variations in ec stratification were used to infer borehole water sources and patterns of water circulation borehole video was used to confirm the conclusions made from these indirect sources of evidence and to provide an independent source of information on the structure and hydrology of this temperate valley glacier the video showed variations in water turbidity englacial channels and voids conditions at the glacier bed and down borehole changes in ice structure based on the video observations englacial channels accounted for approximately 0 1 of the vertical ice thickness and englacial voids for approximately 0 4 overall the video images provided useful qualitative and semi quantitative data that reinforce interpretations of a range of physical and chemical parameters measured in boreholes 1997 by john wiley sons ltd

a stable isotope and fluid inclusion study of the qaleh zaricu au ag deposit khorasan province iran abstract the qaleh zari copper deposit located in south khorasan in the central lut region of iran is a polymetallic vein deposit with major amounts of cu au ag and minor amounts of pb zn and bi mineralization occurs in a series of nw se trending fault planes and breccia zones in paleogene andesitic to basaltic volcanic rocks argillization sericitization and propylitization characterize alteration halos bordering mineral veins the main ore minerals are chalcopyrite pyrite galena and sphalerite with quartz calcite and minor chlorite as the main gangue phases microthermometric measurements of fluid inclusions in cogenetic quartz indicate homogenization temperatures between 160 and 300 c and salinities from 1 to 4 wt nacl equiv boiling occurred in the mineralising fluids at 160 1000 m below the paleo water table at pressures of approximately 15 80 bar at various stages in the formation of the ore body the wide range of pressures and temperatures reflects the multi stage nature of the mineralization at qaleh zari the 18 o values in quartz relative to smow and 34 s values in chalcopyrite and galena relative to cdt range from 6 5 to 7 5 and 0 0 1 5 mean 7 0 respectively at 300 c calculated fluid 18 o values are close to 0 these data suggest a magmatic origin for sulfur and a surficial origin for the mineralizing fluid mineralization at qaleh zari is interpreted as epithermal and low sulfidation in style and was probably related to a deep seated magmatic system ore deposition was the result of boiling cooling and pressure reduction

geology fluid inclusion and stable isotope study of the yueyang ag au cu deposit zijinshan orefield fujian province china abstract the large yueyang ag au cu deposit is commonly regarded as a low sulfidation epithermal deposit in the zijinshan orefield fujian province southeastern china the ag ag cu orebodies hosted in the zijinshan granitic batholith are mainly stratoid and lens in shape and controlled by a series of nw trending listric faults with shallow dip angles four mineralization stages are recognized on the basis of mineral assemblage ore fabrics and crosscutting relationships of the ore veins namely pre ore pyrite sericite quartz chlorite main cu chalcopyrite pyrite sericite quartz bornite main ag au ag and au minerals pyrite quartz adularia calcite apatite chalcopyrite galena sphalerite and post ore quartz chalcedony calcite stages fluid inclusions fis in the deposit include aqueous liquid rich wl aqueous vapor rich wv and minor carbonic c and daughter mineral bearing s type ones wl subtype is the main inclusion type in the yueyang deposit accounting for more than 90 in proportion in each stage minor wv subtype inclusions occur in both the main cu and ag stages while the c type and s type ones are only observed in the main cu stage fluid inclusion and h o isotope study indicated that the ore forming fluid of the main cu stage is primarily magmatic vapor which further underwent fluid boiling and mixing with meteoric water while the ore forming fluid of the main ag stage is meteoric water dominated and the precipitation of silver and gold was mainly resulted from fluid boiling and the precipitation of other sulfides on the basis of the aforementioned geological fluid inclusion and stable isotope studies we proposed a two stage model for the yueyang deposit including a magmatic vapor related porphyry type cu mineralization and meteoric water related low sulfidation epithermal ag au cu mineralization although the porphyry cu mineralization is very limited in scale the mineralization and exhumation depths of the yueyang deposit are estimated to be 448 527 m and 18 97 m respectively by comparison with the exhumation depths of other deposits in the zijinshan orefield it is suggested that more epithermal deposits could be found in the southwest of the orefield due to less uplift and exhumation therein

diurnal variability of subglacial drainage conditions as revealed by tracer experiments 1 the morphology of the drainage system of unteraargletscher switzerland and the diurnal variability of drainage conditions were investigated by conducting a series of tracer tests over a number of discharge cycles during the ablation season 2000 dye injections into a moulin were repeated at intervals of a few hours and were accompanied by simultaneous measurements of discharge of supraglacial meltwater draining into the moulin and bulk runoff in the proglacial stream fast transit velocities in conjunction with low dispersion values suggest that the tracer was routed through a hydraulically efficient channelized drainage system however detailed analyses reveal a large diurnal variability in terms of transit velocity and dispersion coefficient this finding underlines the difficulty of detecting a possible drainage system evolution based on single tracer tests conducted at coarse temporal intervals furthermore the obtained velocity discharge relationships display pronounced hysteresis we suggest that the evolution of the cross sectional area of an ice walled conduit and the modulation of inflow at the junction of a tributary moulin to a main subglacial channel are responsible for the observed behavior

seasonal acceleration of inland ice via longitudinal coupling to marginal ice we use an ice flow model to demonstrate how flow variations initiated in the marginal zone of an ice sheet affect flow farther inland through longitudinal along flow coupling our findings allow for an alternate interpretation of seasonal accelerations observed near the equilibrium line of the greenland ice sheet zwally and others 2002 we demonstrate that these observations can be explained by accelerations initiated up to 12 km closer to the margin where the ice is 40 thinner is heavily crevassed experiences a seasonal doubling of velocity and where the ablation rate surface meltwater flux and ice temperature are likely higher our modeling and observations suggest that conditions and processes normally found near ice sheet margins are adequate for explaining the observations of zwally and others 2002 this and considerations of the likely subglacial hydrology in the marginal zone lead us to suggest that seasonal accelerations may have limited impact on ice sheet mass balance even in the face of climate warming

hydro geochemical and isotopic fluid evolution of the los azufres geothermal field central mexico abstract hydrothermal alteration at los azufres geothermal field is mostly propylitic with a progressive dehydration with depth and temperature increase argillic and advanced argillic zones overlie the propylitic zone owing to the activity of gases in the system the deepest fluid inclusions proto fluid are liquid rich with low salinity with nacl dominant fluid type and ice melting temperatures t mi near zero 0 c and salinities of 0 8 wt nacl equivalent the homogenization temperature t h 325 5 c the boiling zone shows t h 300 c and apparent salinities between 1 and 4 9 wt nacl equivalent implying a vaporization process and a very important participation of non condensable gases ncgs mostly co 2 positive clathrate melting temperatures fusion with t h 150 c are observed in the upper part of the geothermal reservoir from 0 to 700 m depth these could well be the evidence of a high gas concentration the current water produced at the geothermal wells is nacl rich geothermal brine and is fully equilibrated with the host rock at temperatures between t 300 and 340 c the hot spring waters are acid sulfate indicating that they are derived from meteoric water heated by geothermal steam the ncgs related to the steam dominant zone are composed mostly of co 2 80 98 of all the gases the gases represent between 2 and 9 wt of the total mass of the fluid of the reservoir the authors interpret the evolution of this system as deep liquid water boiling when ascending through fractures connected to the surface boiling is caused by a drop of pressure which favors an increase in the steam phase within the brine ascending towards the surface during this ascent the fluid becomes steam dominant in the shallowest zone and mixes with meteoric water in perched aquifers stable isotope compositions 18 o d of the geothermal brine indicate mixing between meteoric water and a minor magmatic component the enrichment in 18 o is due to the rock water interaction at relatively high temperatures 13 c stable isotope data show a magmatic source with a minor meteoric contribution for co 2 the initial isotopic value 34 s res 2 3 which implies a magmatic source more negative values are observed for shallow pyrite and range from 34 s fes 2 4 to 4 9 indicating boiling the same fractionation tendencies are observed for fluids in the reservoir from results for 18 o

glaciohydraulic supercooling a freeze on mechanism to create stratified debris rich basal ice ii theory simple theory supports field observations lawson and others 1998 that subglacial water flow out of overdeepenings can cause accretion of layered debris bearing ice to the bases of glaciers the large meltwater flux into a temperate glacier at the onset of summer melting can cause rapid water flow through expanded basal cavities or other flow paths if that flow ascends a sufficiently steep slope out of an overdeepening the water will supercool as the pressure melting point rises and basal ice accretion will occur diurnal occasional or annual fluctuations in water discharge will cause variations in accretion rate debris content of accreted ice or subsequent diagenesis producing layers under appropriate conditions net accretion of debris bearing basal ice will allow debris fluxes that are significant in the glacier sediment budget

the transition from porphyry to epithermal style gold mineralization at ladolam lihir island papua new guinea a reconnaissance study the exceptionally large gold resource at ladolam 1 300 metric tons of gold lihir island resulted from the transition of an early stage low grade porphyry gold system to a low sulfidation epithermal gold event this transition was probably triggered by rapid decompression during the partial slope failure of luise stratovolcano and accompanied by the ingress of seawater the original porphyry stage is indicated by remnant hydrothermal breccia clasts of strongly biotite magnetite altered monzodiorite with disseminated pyrite chalcopyrite and poorly developed pyrite quartz stockwork veins the breccias are overprinted by biotite magnetite alteration and their matrix is strongly mineralized with disseminated auriferous pyrite the breccias are cut by late stage epithermal quartz chalcedony illite adularia pyrite veins and associated illite adularia alteration that locally contain bonanza gold grades of up to 120 g t isotope data suggest a magmatic source of sulfur in the gold bearing fluids at ladolam electronic supplementary material to this paper can be obtained by using the springer link server located at http dx doi org 10 1007 s00126 001 0230 y

modifications to the theory of intraglacial waterways for the case of subglacial ones on defend l idee que dans les glaciers de montagne temperes les voies d eau sont sous glaciaires pour un conduit noye sous glaciaire il faut introduire deux processus importants l accroissement de la deformation plastique sur les cotes amont des bosses et la chaleur apportee par l eau des sources qui en hiver rend compte de la plus grande partie du debit la theorie explique pourquoi rothlisberger 1972 dut adopter une valeur non realiste pour le parametre rheologique de la glace elle conduit a la conclusion que dans les zones non surcreusees la plus grande partie de l annee les conduits sous glaciaires doivent rester non noyes et a la pression atmospherique cas des surcreusements l incidence de ce nouveau modele sur la theorie du glissement des glaciers

mechanisms of englacial conduit formation and their implications for subglacial recharge abstract ideas about the character and evolution of englacial drainage systems have been deeply influenced by the theoretical model developed by shreve 1972 movement of water in glaciers journal of glaciology 11 62 205 214 the shreve model is based on three main assumptions 1 englacial drainage is in steady state 2 englacial water will flow along the steepest hydraulic gradient within the glacier and 3 pressure head equals the pressure of the surrounding ice minus a small component due to melting of the walls the shreve model has been widely adopted as a fundamental component of englacial drainage theory there is no evidence however that the model provides a realistic picture of actual glacial drainage systems to evaluate shreve s theory we used speleological techniques to directly survey englacial conduits we mapped a total of 8 25 km of passage in 27 distinct englacial conduits in temperate polythermal cold based and debris covered glaciers between 2005 and 2008 new information reported here is supplemented by published data on 40 other englacial conduits located worldwide and surveyed to ice depths of 176 m using speleological techniques in all cases englacial drainage systems consisted of a single unbranching conduit englacial conduit morphologies were found to be intimately linked to the orientation of a glacier s principal stresses or the presence of pre existing lines of high hydraulic conductivity if a sufficient supply of water is available hydrofracturing forms vertical conduits in zones of longitudinal extension and subhorizontal conduits where longitudinal stresses are compressive on unfractured glacier surfaces relatively shallow subhorizontal conduits with migrating nickpoints form by cut and closure provided channel incision is significantly faster than surface lowering conduits can also form along permeable debris filled crevasse traces that connect supraglacial lake basins of different potential our results suggest that shreve type englacial drainage systems do not exist and implies that englacial conduits can only penetrate through thick ice to recharge the bed where supraglacial water bodies either intersect or are advected through zones of acceleration

evolution of the hydrothermal system at los azufres mexico based on petrologic fluid inclusion and isotopic data abstract the los azufres geothermal reservoir formed in a fractured upper miocene to pliocene andesite and basalt base complex is sealed to the surface by a silicic mainly rhyolitic sequence of pleistocene age almost the entire sequence is affected by hydrothermal alteration to varying extent petrological and fluid inclusion studies confirmed vertical zonation of the reservoir by secondary processes hydrothermal alteration processes under low temperature conditions at a depth of 1200 1500 m the maximum ice melting temperatures tmi values of 0 7 to 4 c and salinities of 6 4 wt nacl eq indicate boiling conditions of the geothermal brine in a vapor rich zone chlorite calcite quartz zeolite anhydrite albite sphene pyrite hematite and illite form the hydrothermal mineral paragenesis with maximum temperatures of 250 c and pressure conditions of 150 bar below 1500 m tmi reach maximum values of 0 1 c and low salinities of 0 2 wt nacl eq the minerals epidote amphibole prehnite and garnet indicate temperatures above 250 c and pressure conditions between 150 and 200 bar the measured homogenization temperatures th of fluid inclusions fi are consistently higher than the in situ measured temperatures which indicates retrograde cooling of the los azufres geothermal reservoir since the time of the hydrothermal mineral formation updoming temperature isotherms at the center of the geothermal field below well az 9 az 23 and az 25 indicate the heating up of the fluids by a shallow magma chamber stable isotope data 18o d of the geothermal brine indicates mixing processes between meteoric water and a minor magmatic component secondary reactions forming sericite may have caused a further positive shift in 18o in the shallow part of the geothermal reservoir

geometry and flow conditions of subglacial water at south cascade glacier washington state u s a an analysis of tracer injections tracers were injected into south cascade glacier to determine the flow condition and geometry of the subglacial water system results indicate that two distincts drainage basins on the glacier feed the two main streams flowing from the glacier in the largest basin two parallel drainage networks exist one englacial and the other subglacial

englacial drainage systems formed by hydrologically driven crevasse propagation recent work has shown that surface to bed drainage systems re form annually on parts of the greenland ice sheet and some high arctic glaciers leading to speed up events soon after the onset of summer melt surface observations and geophysical data indicate that such systems form by hydrologically driven fracture propagation herein referred to as hydrofracturing although little is known about their characteristics using speleological techniques we have explored and surveyed englacial drainage systems formed by hydrofracturing in glaciers in svalbard nepal and alaska in hansbreen svalbard vertical shafts were followed through 60 m of cold ice and 10 m of temperate basal ice to a subglacial conduit deep hydrofracturing occurred at this site due to a combination of extensional ice flow and abundant surface meltwater at a glacier confluence the englacial drainage systems in khumbu glacier nepal and matanuska glacier alaska usa formed in areas of longitudinal compression and transverse extension and consist of vertical slots that plunge down glacier at angles of 558 or less the occurrence of englacial drainages initiated by hydrofracturing in diverse glaciological regimes suggests that it is a very widespread process and that surface to bed drainage can occur wherever high meltwater supply coincides with ice subjected to sufficiently large tensile stresses

the geometry of water veins and nodes in polycrystalline ice la glace polycristalline a son point de fusion renferme de l eau sous la forme d un reseau 3d de veines ces veines se rejoignent en n uds qui forment les jonctions a 4 grains la forme detaillee d un n ud est calculee a partir de considerations d energies de surface les volumes relatifs d eau dans les veines et dans les n uds en sont ensuite deduits

on the role of mechanical energy in maintaining subglacial water conduits at atmospheric pressure recent theo retical studies of glacier hydrology have assumed that subglacial conduits are completely filled with water under steady state conditions this however is not necessarily the case where discharges are larger than a few tens of liters per second and the down glacier slope of the bed is more than a few degrees the potential energy released by water descending this slope may be capable of melting the walls of a subglacial conduit many times faster than the conduit can close by plastic flow of the ice as a result the pressure in such tunnels may normally be atmospheric or possibly even at the triple point pressure if there is no open connection to the glacier surface simple calcu lations suggest that such pressures in subglacial conduits may be more common than herclofore anticipated the positions of such open conduits may be unstable to small per turbations in discharge or ice veloci ty this is because the mechanical energy available in excess of that needed to balance closure can instead offset the gene ral flow of the ice cond ui ts can thus trend diago nally across the direction of ice aow if an increase in the angle which such a conduit makes with the ice flow direction also results in an increase in slope of he conduit more mechanical energy will become available resulting in a positive feedback process subglacial channels at atmospheric pressure may inauence the origin and morphology of certain glacial landforms such as eskers and plastically molded features resume sur le role de l inergie newtonnienne dam le maintien du riseau aquiflrl sous glaciaire cl la pression almosph irique de recentes etudes theoriques d hydrologie glaciaire ont suppose que le reseau sous glaci aire clait corn pletement rempli d eau en condition d cquil ibre stable ceci neanmoins n est pas necess airement le cas lorsque les debits sonl superieurs a quelques dizaines de litres par seconde et que la pente du lit du glacier est superieure a quelques degres i energie potentielle mise en oeuvre par i eau descendant celle pente peut ire capable de fondre les parois d un chenal sous glaciaire beaucoup plus vite que le chenal ne peut se refermer par le auage plastique de la glace il en resuhe que la pression dans de tels chenaux peut nor rnalement etre atrnospherique

geometric evolution and ice dynamics during a surge of bakaninbreen svalbard bakaninbreen svalbard started surging in 1985 and developed a steep surge front where fast moving ice impinged on stagnant non surging ice this front which was 20 25 m high in 1985 became a steep and heavily crevassed fcature about 60 m high the surge continued through 1986 95 annual surge front propagation rate was 1 0 1 8 km a 1 during 1985 89 this rate dropped considerably during 1989 95 and the front became less steep front propagation occurred largely by longitudinal compression and vertical extension of the ice and the effects of over riding appear minor ice velocities were slowe than the average propagation rate of the front the surge affected bakanin breen in four zones upper region where extensiv e flow fast propagation rates and negative vertical strain occurred resulting in widespread crevassing and stranded blocks tens of metres above the post surge ice surface 2 mid glacier region where initial strong compression was associated with ice thickening which started before the arrival of the surge front horizontal strain rates were very low but vertical strain rates were up to 300 mm d 1 as the front passed the horizontal velocity increased and about 500 m behind it became extensive negative vertical strain and ice down draw occurred as ice vclocities dropped 3 surge front where ice velocity w as high but vertical strain remained positive associated with compression 4 lower region below the front where only compression occurred resulting in the formation of a fore bulge a thickening of the ice of up to 50 m above pre surge levels the fore bulge affected the whole 1 7 km below the now halted surge front the glacier has not advanced ba kaninbreen s surge was characterized by a long active phase approximately 10 years low ice velocities and low basal shear stresses compared to glaciers in lower latitudes and an indistinet surge termination

volcanic stratigraphy of the los azufres geothermal area mexico abstract the los azufres volcanic center located 200 km northwest of mexico city is one of a number of pleistocene silicic volcanic centers with active geothermal systems that lie north of the axis of the mexican neovolcanic belt silicic volcanism began approximately 1 m y ago with eruption of the agua fria rhyodacite to high silica rhyolite lava domes and flows they are covered by rhyodacite and dacite lava domes and flows of the san andres volcano dated at 0 3 m y a north to northeast trending set of high angle normal faults is offset by a younger and more prominent east trending set that parallels the principal regional structural trend these faults cut all but the youngest volcanic rocks of the center the yerbabuena rhyodacites to high silica rhyolites these morphologically well preserved lava domes are approximately 0 15 m y old and are probably associated with air fall tuffs that blanket the western portion of the volcanic center two episodes of high heat flow suggested by studies of drill core samples and fluids from the los azufres geothermal field may correspond to two different episodes of magma injection to high levels the most recent one resulting in eruption of the yerbabuena lavas

ice fracturing during jokulhlaups implications for englacial floodwater routing and outlet development theoretical studies of glacial outburst floods jokulhlaups assume that i intraglacial floodwater is transported efficiently in isolated conduits ii intraglacial conduit enlargement operates proportionally to increasing discharge iii floodwater exits glaciers through pre existing ice marginal outlets and iv the morphology and positioning of outlets remains fixed during flooding direct field observations together with historical jokulhlaup accounts confirm that these theoretical assumptions are not always correct this paper presents new evidence for spatial and temporal changes in intraglacial floodwater routing during jokulhlaups secondly it identifies and explains the mechanisms controlling the position and morphology of supraglacial jokulhlaup outlets and finally it presents a conceptual model of the controls on supraglacial outbursts field observations are presented from two icelandic glaciers skei ararjokull and solheimajokull video footage and aerial photographs taken before during and after the skei ararjokull jokulhlaup and immediately after the solheimajokull jokulhlaup reveal changes in floodwater routing and the positioning and morphology of outlets field observations confirm that glaciers cannot transmit floodwater as efficiently as previously assumed rapid increases in jokulhlaup discharge generate basal hydraulic pressures in excess of ice overburden under these circumstances floodwater can be forced through the surface of glaciers leading to the development of a range of supraglacial outlets the rate of increase in hydraulic pressure strongly influences the type of supraglacial outlet that can develop steady increases in basal hydraulic pressure can retro feed pre existing englacial drainage whereas transient increases in pressure can generate hydraulic fracturing the position and morphology of supraglacial outlets provide important controls on the spatial and temporal impact of flooding the development of supraglacial jokulhlaup outlets provides a new mechanism for rapid englacial debris entrainment

character of the englacial and subglacial drainage system in the lower part of the ablation area of storglaciaren sweden as revealed by dye trace studies

the temporal significance of transitions from melting to calving termini at glaciers in the central southern alps of new zealand termini of valley glaciers in the central southern alps are undergoing a three phase sequence of retreat that began in the 1950s an initial phase of melting and slow downwasting under thickening supraglacial debris mantles is associated with stationary or slowly retreating termini this is followed by a transitional phase of disruption of insulating debris mantles allowing the rapid growth of shallow thermokarst lakes the shape and location of which vary according to glacier gradient and marginal topography a third phase of rapid calving retreat of ice cliffs into deepening proglacial lakes develops from the transitional phase at no stage are terminal responses simply related to climate present transitions to calving retreat are related to the morphology of glacier termini particularly to large outwash heads landform evidence indicates that similar calving phases do not appear to have occurred since late pleistocene deglaciation so that present changes to glacier termini are of great significance

the formation and distribution of co2 enriched fluid inclusions in epithermal environments abstract fluid inclusions from two geothermal systems associated with volcanic activity were studied to document the distribution of co 2 in modern epithermal environments the fluid inclusion data combined with mineral distributions and chemical analyses of the production fluids from both systems provide a record of steam and gas flux to depths in excess of 1 to 2 km and of transient variations in the gas contents of the reservoirs the liquid rich fluid inclusions can be grouped into two types on the basis of their co 2 contents inclusions with co 2 contents of less than about 4 wt typically have calculated gas contents that are higher than the present day reservoir fluids however the calculated pressures and temperatures of these inclusions are consistent with their depth of formation indicating that they may have formed in response to boiling and mixing processes in the reservoir liquid rich fluid inclusions with co 2 contents between approximately 4 and 6 wt are characterized by co 2 clathrate dissociation temperatures greater than 0 0 c these inclusions occur on the margins of the thermal systems where they define umbrella shaped caps around the main zones of upwelling the co 2 contents of the inclusions require that they formed at pressures several tens of bars above hydrostatic elevated pressures and gas contents may have developed through compression and condensation of co 2 enriched steam by tectonic stress

gas souring by thermochemical sulfate reduction at 140 c reply natural gas in the permian triassic khuff formation of abu dhabi contains variable amounts of h2s gas souring occurred through thermochemical sulfate reduction of anhydrite by hydrocarbon gases sour gas is observed only in reservoirs hotter than a critical reaction temperature 140 c petrographic examination of core from a wide depth range showed that the anhydrite reactant has been replaced by calcite reaction product only in samples deeper than 4300 m gas composition data show that only reservoirs deeper than 4300 m contain large quantities of h2s i e 10 at present day geothermal gradients 4300 m is equivalent to 140 c fluid inclusion analysis of calcite reaction product has shown that calcite growth only became significan at temperatures greater than 140 c thus three independent indicators all show that 140 c is the critical temperature above which gas souring by thermochemical sulfate reduction begins the previously suggested lower temperature thresholds for other sour gas provinces 80 130 c derive from gas composition data that may not allow adequately either for the reservoir temperature history or for the migration of gas generated at higher temperatures into present traps conversely published proposals for higher threshold temperature 180 200 c derive from short duration experimental data that are not easily extrapolated to geologically realistic temperatures and time scales therefore the temperature of 140 c derived from our study of the khuff formation may be th best estimate of temperature required for in situ thermochemical sulfate reduction to produce the high h2s concentrations encountered in deep carbonate gas reservoirs

waterways ice permeability at depth and water pressures at glacier d argentiere french alps pour eclaircir les changements survenus a la prise d eau sous glaciaire du glacier d argentiere une etude approfondie a ete realisee en 1979 80 avec 31 forages et un carottage jusqu au fond 240m juste en amont de la prise dans une zone surcreusee on observe que la glace en dessous d environ 100 m de profondeur est legerement permeable on a mesure la pression interstitielle de l eau dans la glace profonde le gradient piezometrique entre les trous de forage et le dephasage entre les fluctuations du niveau d eau qui augmente lorsqu on s eloigne de la rive droite il n y a pas de torrent sous glaciaire au fond du surcreusement sauf a son extremite amont la plupart de l eau de fonte doit s ecouler entre glace et rocher le long de la rive droite sa surface libre s elevant d environ 150 m au moment de l engorgement de juin on n a pas trouve de correlation nette entre la pression de l eau interstitielle profonde et la temperature de l air ou le debit a la prise sous glaciaire en aval

glaciohydraulic supercooling a freeze on mechanism to create stratified debris rich basal ice i field evidence debris laden ice accretes to the base of matanuska glacier alaska u s a from water that supercools while flowing in a distributed drainage system up the adverse slope of an overdeepening frazil ice grows in the water column and forms aggregates while other ice grows on the glacier sole or on substrate materials sediment is trapped by this growing ice forming stratified debris laden basal ice growth rates of 0 1 m a 1 of debris rich basal ice are possible the large sediment fluxes that this mechanism allows may have implications for interpretation of the widespread deposits from ice that flowed through other overdeepenings including heinrich events and the till sheets south of the laurentian great lakes

the relationship between subglacial water pressure and velocity of findelengletscher switzerland during its advance and retreat findelengletscher switzerland advanced about 250 m between 1979 and 1985 and retreated thereafter subglacial water pressure surface velocity and surface strain rate were determined at several sites the measurements were made early in the melt seasons of 1980 1982 1985 and 1994 and in the autumn of 1983 and the winter of 1984 changes of surface geometry were assessed from aerial photographs the estimated basal shear stress changed little between 1982 and 1994 nevertheless large changes in the relationship of subglacial water pressure and surface velocity were observed which cannot be reconciled with the most commonly used sliding law unless it is modified substantially consideration of possible reasons indicales that a change in the subglacial drainage system occurred probably involving a change in the degree of cavity interconnection isolated cavities damp the variations in sliding velocity that normally result from changes in water pressure because the pressure in isolated cavities decreases as the sliding speed increases in contrast by transmitting water pressure fluctuations to a larger area of the bed interconnected cavities amplify the effect of water pressure fluctuations on sliding speed thus we suggest that an observed decrease in velocity for a given water pressure between 1982 and 1994 was a consequence of a decrease in the interconnectedness of the subglacial cavity system

subglacial drainage system structure and morphology of brewster glacier new zealand a global positioning system and ground penetrating radar surveys is used to produce digital elevation models of the surface and bed of brewster glacier these are used to derive maps of subglacial hydraulic potential and drainage system structure using three different assumptions about the subglacial water pressure pw i pw ice overburden ii pw half ice overburden iii pw atmospheric additionally 16 dye tracing experiments at 12 locations were performed through a summer melt season dye return curve shape together with calculations of transit velocity dispersivity and storage are used to infer the likely morphology of the subglacial drainage system taken together the data indicate that the glacier is underlain by a channelised but hydraulically inefficient drainage system in the early summer in which water pressures are close to ice overburden by mid summer water pressures are closer to half ice overburden and the channelised drainage system is more hydraulically efficient surface streams that enter the glacier close to the location of major subglacial drainage pathways are routed quickly to the channels and then to the glacier snout streams that enter the glacier further away from the drainage pathways are routed slowly to the channels and then to the snout because they first flow through a distributed drainage system copyright 2008 john wiley sons ltd

hydrological controls on patterns of surface internal and basal motion during three spring events haut glacier d arolla switzerland three early melt season high velocity events or spring events occurred on haut glacier d arolla switzerland during the melt seasons of 1998 and 1999 the events involve enhanced glacier velocity during periods of rapidly increasing bulk discharge in the proglacial stream and high subglacial water pressures however differences in spatial patterns of surface velocity internal ice deformation rates the spatial extent of high subglacial water pressures and in rates of subglacial sediment deformation suggest different hydrological and mechanical controls the data from two of the events suggest widespread ice bed decoupling particularly along a subglacial drainage axis creating the highest rates of basal motion and plug flow in the overlying ice the other event showed evidence of less extensive ice bed decoupling and sliding along the drainage axis with more mechanical support for ice overburden transferred to areas adjacent to decoupled areas we suggest that 1 plug flow may be a common feature on glaciers experiencing locally induced reductions in basal drag 2 under certain circumstances enhanced surface motion may be due in part to non locally forced enhanced bed deformation and 3 subglacial sediment deformation is confined to a depth of the order of centimetres to decimetres

internal geometry and evolution of moulins storglaciaren sweden depart ment of physical geog raphy university of stoc kholm s 106 91 stockholm sweden abstract the initial conditions needed for formation of moulins are crevasses and a supply of melt water water pouring into a crevasse may fill it until it ove rflows at the lowest point which is normally near the margin however as the crev asse deepens it intersects englacial chann els through which the water can drain these chann els may be finger tip tributaries in a dendritic system such as that described by shreve 1972 and observ ed by raymond and harrison 1975 when the cre vasse closes heat in the melt water keeps the conne ction open and a moulin is formed the englacial channel enlarges rapidly by melt ing utilizing mechanical energy released by the descending water descents into moulins and mapping of stru ctures exposed at the surface after many years of melting demonstrate that the drainage channels leading down from the bottoms of the moulins have incli nations of 0 450 from the vertical these channels trend in the dire ction of the original crevasse but appear to be deeper than the expected depth of the crevasse they have not

internal vein texture and vein evolution of the epithermal shila paula district southern peru the epithermal shila paula au ag district is characterized by numerous veins hosted in tertiary volcanic rocks of the western cordillera southern peru field studies of the ore bodies reveal a systematic association of a main e w vein with secondary n55 60 w veins two directions that are also reflected by the orientation of fluid inclusion planes in quartz crystals of the host rock in areas where this pattern is not recognized such as the apacheta sector vein emplacement seems to have been guided by regional n40 e and n40 w fractures two main vein filling stages are identified stage 1 is a quartz adularia pyrite galena sphalerite chalcopyrite electrum mn silicate carbonate assemblage that fills the main e w veins stage 2 which contains most of the precious metal mineralization is divided into pre bonanza and bonanza substages the pre bonanza substage consists of a quartz adularia carbonate assemblage that is observed within the secondary n45 60 w veins in veinlets that cut the stage 1 assemblage and in final open space fillings the two latter structures are finally filled by the bonanza substage characterized by a fe poor sphalerite chalcopyrite pyrite galena tennantite tetrahedrite polybasite pearceite electrum assemblage the ore in the main veins is systematically brecciated whereas the ore in the secondary veins and geodes is characteristic of open space crystallization microthermometric measurements on sphalerite from both stages and on quartz and calcite from stage 2 indicate a salinity range of 0 to 15 5 wt nacl equivalent and homogenization temperatures bracketed between 200 and 330 c secondary co2 n2 and h2s bearing fluid inclusions are also identified the age of vein emplacement based on 40ar 39ar ages obtained on adularia of different veins is estimated at around 11 ma with some overlap between adularia of stage 1 11 4 0 4 ma and of stage 2 10 8 0 3 ma a three phase tectonic model has been constructed to explain the vein formation phase 1 corresponds to the assumed development of e w sinistral shear zones and associated n60 w cleavages under the effects of a ne sw shortening direction that is recognized at andean scale these structures contain the stage 1 ore assemblage that was brecciated during ongoing deformation phase 2 is a reactivation of earlier structures under a nw se shortening direction that allowed the reopening of the preexisting schistosity and the formation of scarce n50 e striking s2 cleavage planes filled by the stage 2 pre bonanza minerals phase 3 coincides with the bonanza ore emplacement in the secondary n45 60 w veins and also in open space in the core of the main e w veins our combined tectonic textural mineralogical fluid inclusion and geochronological study presents a complete model of vein formation in which the reactivation of previously formed tectonic structures plays a significant role in ore formation

tv video observations of englacial voids in storglaciaren sweden tv video observations of four boreholes in storglaciaren sweden revealed that 1 3 of the observed ice column was composed of englacial voids the form of the voids is presented by photographs from the video it is suggested that they are openings into englacial channels and cavities which were intersected during drilling the observations further showed that about 11 of the ice column consisted of air bubble poor blue ice inclusions the observations show a relation between the blue ice inclusions and the voids which indicates that the origin and development of these features are coupled to each other it is suggested that crevasses in the accumulation area are an important factor in this process

combined measurements of subglacial water pressure and surface velocity of findelengletscher switzerland conclusions about drainage system and sliding mechanism interpretation des mesures de pression dans les forages et des vitesses superficielles la comparaison avec les modeles suggere que l on a neglige le frottement du aux debris dans les modeles et qu il n existe jamais de chenaux cylindriques rectilignes

changes in geometry and subglacial drainage of midre lovenbreen svalbard determined from digital elevation models digital elevation models dems of the bed and surface of the polythermal midre lovenbreen svalbard are used to identify changes in glacier geometry between 1977 and 1995 the calculated mean annual mass balance 0 61 m water equivalent w e a 1 is more negative than that derived from field measurements 0 35 m w e a 1 although the error associated with this value 0 7 m a 1 suggests that the difference may be accounted for by errors however similar discrepancies between dem based and field based measurements of mass balance have been reported elsewhere in svalbard although errors may be responsible patterns of surface elevation change may also be explained in terms of patterns of ablation accumulation and dynamics the theoretical structure of the subglacial drainage system is modelled using different assumptions about subglacial water pressure in 1977 and 1995 these reconstructions are compared with the observed positions of proglacial outlet streams decreasing subglacial water pressure results in a decrease in the influence of surface morphology and an increase in the role of the bed topography on drainage routing which generally leads to more dispersed drainage long term changes in the position of proglacial outlet streams occur as a result of changes in glacier geometry but short term changes may also occur in response to early season water pressures controlled by meteorological and hydrological conditions copyright 2003 john wiley sons ltd