hydrological characteristics of the drainage system beneath a surging glacier a rare combination of natural circumstances permits assessment of current theories on water flow beneath glaciers outburst floods from the subglacial lake grimsvotn in iceland took place before during and after surging of skei ararjokull the glacier beneath which the outburst floods drain the observable drainage patterns associated with these floods show the different nature of the basal water conduit system of the glacier during surge and non surge phases during surge conditions basal water is dispersed slowly across the bed in a distributed drainage system but when the glacier is not surging water is transported rapidly through a system of tunnels

new insights into the subglacial and periglacial hydrology of vatnajokull iceland from a distributed physical model we apply a time dependent distributed glaciohydraulic model tovatna jo kull ice cap iceland aiming to determine the large scale subglacial drainage structure theimportance of basallyderivedmeltwater theinfluence ofapermeable glacierbedand vatnajo kull s discharge contribution to major rivers in iceland the model comprisestwo coupled layersthatrepresentthesubglacialhorizonperchedona subsurfaceaquifer inthe western sector and bedrock in the eastern sector to initialize and drive the simulations we use digital elevation models of the ice surface and bed the1999 2000 measured mass balance and an estimate of subglacial geothermal heat fluxes the modelled subglacial flow field differs substantially from that derived by hydraulic potential calculations and the corresponding distribution of basal effective pressure shows a strong correlation between low effective pressure and surge prone areas in northeastern and southern sectors of vatnajo kull simulations suggest that geothermally derived basal melt may account for upto 5 of the annualglacial discharge and buried aquifers may evacuate up to 30 ofsubglacialwater time dependenttestsyieldestimatesoftheglacialdischargecomponent in various outlet rivers and suggest a possible seasonal migration of subglacial hydraulic divides this study of present dayvatnajo kull hydrology formsthe starting point for inves tigationsof its future evolution

sedimentary pyrite a window into the microbial past early diagenetic pyrite forms as a result of microbial processes in sediments but has received little attention as a potential source of microbial fossils sedimentary pyrite grains archean to jurassic in age were examined by scanning and transmission electron microscopy tem ion milling was essential for the preparation of electron transparent tem samples most pyrite grains revealed coccoid rod shaped and even filamentous features that are interpreted as microbial identification of microbial remains in sedimentary pyrite may greatly expand our knowledge of microbial life in the sedimentary record combined with geochemical characterization the study of pyritized microbes in the geologic record may in the future enable us to interpret changes in geochemical signatures more realistically in terms of different sulfate reducing communities sedimentary pyrite grains may also represent a good prospect to further our knowledge of past life on mars

fluvial lacustrine interaction on skeiðararsandur iceland implications for sandur evolution abstract a complex assemblage of fluvial and lacustrine sediments is identified in a major section through proglacial sediments on skei ararsandur south iceland high magnitude low frequency events are identified in both the fluvial and lacustrine sediments however much of the sedimentary succession is composed of normal low magnitude high frequency sediments retreat of skei ararjokull following a surge event created a topographic basin occupied at various times by both fluvial and lacustrine depositional systems and also subjected to a high magnitude jokulhlaup previous studies have examined the processes and events occurring on skei ararjokull in isolation this paper improves the understanding of the way in which processes with varying magnitude and frequency regimes interact and contribute to the sedimentary record of proglacial environments

the precious metal rich south hercules mineralization western tasmania a possible subsea floor replacement volcanic hosted massive sulfide deposit south hercules is a newly delineated disseminated to semimassive base metal sulfide deposit with significant gold and silver grades the deposit lies a kilometer along strike south from the hercules mine a 2 0 mt polymetallic massive sulfide deposit in the mount read volcanics belt western tasmania the mineralization and alteration at the south hercules deposit has been divided into two major facies the mineralized sulfide facies and the carbonate facies the carbonate facies interfingers with and surrounds the upper part of the sulfide facies the mineralized sulfide facies includes three zones a massive pyrite or barite zone a siliceous or stringer sulfide zone and a sphalerite galena or pyrite zone the carbonate facies also consists of three zones a blebby carbonate chlorite zone a massive carbonate zone and a cherty carbonate zone the massive pyrite or barite zone contains significant gold grades and occurs mostly at the top of the sulfide facies this zone is characterized by colloform aggregates of pyrite and compact massive pyrite in chert the siliceous or stringer sulfide zone is a silicified and sericitized tuffaceous shale with disseminated to stringer pb zn mineralization the massive sphalerite galena or pyrite zone contains subordinate gold and silver and occurs as thin lenses toward the base of the sulfide facies significant zinc and lead values occur throughout the mineralized sulfide facies with the highest values occurring along stratigraphically controlled layers copper values are conspicuously low throughout the south hercules deposit rarely exceeding 0 5 percent the carbonate facies is conspicuous by its lack of significant precious metal and base metal grades mineragraphic investigations indicate that electrum occurs in two general associations with pyrite and with other sulfides such as sphalerite galena and tetrahedrite the electrum locked in the pyrite euhedra is generally fine grained 5 40 mu m whereas the electrum associated with other sulfides displays a range between 5 and 200 mu m microprobe analysis indicates that the fineness 1 000 au au ag wt for gold in the deposit ranges from 427 to 965 the delta 18 o isotope composition of the carbonate varies from 9 8 to 16 7 per mil and the delta 13 c values range from 3 5 to 0 6 per mil the calculated isotopic composition of the ore fluid at 150 degrees and 250 degrees c is consistent with derivation from evolved seawater sulfur isotope analyses of selected samples from the mineralized facies give delta 34 s values of 8 2 to 14 1 per mil which is in the same range as values from the rosebery deposit and consistent with values of sulfur derived from cambrian seawater the form texture mineralogy stable isotopes and fluid inclusion data for the south hercules deposit suggest that it was formed largely by a subsea floor replacement process from relatively low temperature 150 degrees 250 degrees c near neutral fluids the very low copper content and relatively high au ag pb zn ratio of the ores support a low temperature environment in which gold was transported as the au hs 2 super complex and pb and zn were transported as chloride complexes

laser microprobe sulphur isotope analysis of arsenopyrite experimental calibration and application to the boliden au cu as massive sulphide deposit abstract metamorphic remobilization of arsenopyrite rich ores is a globally important process which can lead to significant concentrations of gold in order to understand this and related processes relations of sulphur isotopes can give a number of important clues to resolve such relations in detail we have successfully calibrated and applied a laser combustion system for in situ analysis of sulphur isotopic compositions of arsenopyrite experimental calibration of the laser fractionation factor 0 4 was obtained by using compositionally and isotopically homogeneous natural samples from ore deposits at boliden sweden and freiberg germany subsequent to detailed microscopic study the s isotope ratios of these samples were measured by conventional and laser combustion techniques the present application to different types of arsenopyrite in the palaeoproterozoic metamorphosed vhms ores of the boliden au cu as deposit skellefte district northern sweden shows that the sulphur isotope composition of arsenopyrite is essentially unmodified during medium grade metamorphic recrystallization and remobilization here massive arsenopyrite ore is crosscut by later veins that carry a complex quartz sulphosalt sulphide assemblage the latter ore type is markedly au rich compared to the host ore and thus of significant economic interest we find that both ore types exhibit very similar sulphur isotope compositions ca 2 to 3 v cdt which is similar to most massive sulphide deposits in the skellefte district thus the crosscutting au rich vein ore has inherited the sulphur isotope composition from sulphur liberated by metamorphic reactions affecting the massive ore and most likely also inherited the au through this mechanism the latter finding clearly has important implications both for the general discussion on and the prospecting for similar high grade au ores in this world class mining region

hydraulic impacts of glacier advance over a sediment bed a sedimentary sequence of till overlying a gravel aquifer was instrumented with water pressure transducers prior to a small anticipated surge of the margin of the glacier brei amerkurjokull in iceland the records of water pressure at each transducer site show a well defined temporal sequence of hydraulic regimes that reflect the changing recharge of surface derived meltwater the pressure drop along the drainage pathway and the pattern of ice loading the poroelastic and water pressure response of glacially overridden sediments to the recharge rate is determined in the frequency domain through an analytic solution this permits the in situ conductivity compressibility and consolidation states of subglacial sediments to be derived and reveals aquifer scale compressibility that produces an important water pressure wave associated with the advancing glacier the model is then used to explore how varying conductivity compressibility largely determined by granulometry can determine drainage states and instabilities that may have a large impact on glacier ice sheet dynamics and how the drainage time of surface water to the bed can determine the frequency response of subglacial groundwater regimes and their influence on subglacial sediment stability mismatches between model predictions and specific events in water pressure records are used to infer processes that are not incorporated in the model hydrofracturing that changes the hydraulic properties of subglacial sediments the impact on groundwater pressure of subglacial channel formation upwelling beyond the glacier margin and rapid variations in the state of consolidation the poroelastic model also suggests how seismic methods can be developed further to monitor hydraulic conditions at the base of an ice sheet or glacier

geomorphic effectiveness sandur development and the pattern of landscape response during jokulhlaups skeiðararsandur southeastern iceland by contrast with other historical outburst floods on skeitararsandur the 1996 jokulhlaup was unprecedented in its magnitude and duration attaining a peak discharge of f53 000 m 3 s in 17 h using a combination of field sampling and remote sensing techniques landsat tm sar interferometry airphotos and laser altimetry we document the sandur wide geomorphic impacts of this event these impacts varied widely across the skeitararsandur and cannot be singularly attributed to jokulhlaup magnitude because pre jokulhlaup glacial dynamics and the extant setting largely conditioned the spatial pattern type and magnitude of these impacts topographic lowering and asymmetric retreat of the ice front during the late twentieth century has decoupled the ice sheet from the moraine sandur complex along the central and western sandur this glacial control in combination with the convex topography of the proximal sandur promoted a shift from a primarily diffuse source braided outwash system to a more point sourced channelized discharge of water and sediment deposition dominated within the proglacial depression with approximately 3 8 10 7 m 3 of sediment and along channel systems that remained connected to subglacial sediment supplies this shift to a laterally dissimilar channelized routing system creates a more varied depositional pattern that is not explicitly controlled by the concave longitudinal profile down sandur laterally contiguous units therefore may vary greatly in age and sediment character suggesting that current facies models inadequately characterize sediment transfers when the ice front is decoupled from its sandur water was routed onto the sandur in a highly organized fashion and this jokulhlaup generated major geomorphic changes including sandur incision in normally aggradational distal settings and eradication of proximal glacial landforms dating to fa d 1892 d 2002 elsevier science b v all rights reserved

sulfur isotope and trace element data from ore sulfides in the noranda district abitibi canada implications for volcanogenic massive sulfide deposit genesis we examine models for volcanogenic massive sulfide vms mineralization in the 2 7 ga noranda camp abitibi subprovince superior province canada using a combination of multiple sulfur isotope and trace element data from ore sulfide minerals the noranda camp is a well preserved vms deposit rich area that is thought to represent a collapsed volcanic caldera due to its economic value the camp has been studied extensively providing a robust geological framework within which to assess the new data presented in this study we explore previously proposed controls on mineralization within the noranda camp and in particular the exceptional au rich horne and quemont deposits we present multiple sulfur isotope and trace element compositional data for sulfide separates representing 25 different vms deposits and showings within the noranda camp multiple sulfur isotope data for this study have 34sv cdt values of between 1 9 and 2 5 and 33sv cdt values of between 0 59 and 0 03 we interpret the negative 33s values to be due to a contribution of sulfur that originated as seawater sulfate to form the ore sulfides of the noranda camp vms deposits the contribution of seawater sulfate increased with the collapse and subsequent evolution of the noranda caldera an inference supported by select trace and major element analyses in particular higher concentrations of se occur in samples with 33s values closer to 0 as well as lower fe zn ratios in sphalerite suggesting lower pressures and temperatures of formation we also report a relationship between average au grade and 33s values within au rich vms deposits of the noranda camp whereby higher gold grades are associated with near zero 33s values from this we infer a dominance of igneous sulfur in the gold rich deposits either leached from the volcanic pile and or directly degassed from an associated intrusion

complex spatial feedbacks of tephra redistribution ice melt and surface roughness modulate ablation on tephra covered glaciers tephra fallout from the 2011 grimsvotn eruption onto svinafellsjokull iceland created an ice ash landscape of a type that is rarely studied but is nevertheless common in glaciovolcanic regions we used terrestrial laser scanning tls to measure ice surface topography and absorption at high spatial resolution confirming ablation rates either reduce or increase under thick insulating and thin reduced albedo ash deposits respectively fourier transform analysis of the tls data identified that a three fold increase in aerodynamic roughness was attributable to an increase in larger 0 2m surface features moreover tls measurements revealed the importance of ash redistribution by meltwater in generating differential melting which modifies roughness and ash patchiness such that the net effect of these spatial ash ice feedbacks was to reduce ablation rates by up to 59 the modulating effects of these previously undocumented feedbacks on ablation rates are therefore significant and must be correctly parameterized if ashcovered glacier mass balances are to be predicted correctly

sensitivity of vatnajokull ice cap hydrology and dynamics to climate warming over the next 2 centuries 1 the sensitivity of vatnajokull ice cap to future climate change is examined using spatially distributed coupled models of ice dynamics and hydrology we simulate the evolving ice cap geometry mass balance velocity structure subglacial water pressures and fluxes and basin runoff in response to perturbations to a 1961 1990 reference climatology for a prescribed warming rate of 2 c per century simulated ice cap area and volume are reduced by 12 15 and 18 25 within 100 years respectively individual outlet glaciers experience 3 6 km of retreat in the first 100 years and a total retreat of 10 30 km over 200 years for the same applied warming our results suggest a maximum increase in glacier derived runoff of 25 after 130 years ice cap thinning and retreat alters vatnajokull s subglacial hydraulic catchment structure in the simulations with up to several kilometers of local hydraulic divide migration this serves to redistribute water among the major outlet rivers and in extreme cases to isolate river basins from glacially derived runoff glacier discharge from northern and northwestern vatnajokull distal from the coast appears to be the most robust to climate warming while discharge from vatnajokull s southern margin proximal to the coast is particularly vulnerable the latter reflects pronounced changes in the geometry of the southern outlet glaciers and has implications for glacier flood routing and frequency

buried glacier ice in southern iceland and its wider significance abstract geo electrical resistivity surveys have been carried out at recently deglaciated sites in front of three glaciers in southern iceland skei arajokull hrutarjokull and virkisjokull the results show the presence of old glacier ice beneath debris mantles of various thickness we conclude that buried glacier ice has survived for at least 50 years at virkisjokull and hrutarjokull and probably for over 200 years at skei arajokull additional data from a further site have identified a discontinuous ice core within 18th century jokulhlaup deposits photographic and lichenometric evidence show that the overlying debris has been relatively stable and hence melting of the ice at all four sites is proceeding slowly due to the heat shielding properties of the overburden the geomorphic implications are pertinent when considering the potential longevity of buried ice the possible implications for dating techniques such as lichenometry radiocarbon dating and cosmogenic surface exposure dating are also important as long term readjustments of surface forms may lead to dating inaccuracy finally it is recognised that landscape development in areas of stagnant ice topography may post date initial deglaciation by a considerable degree

the sulphur isotope and hydrochemical characteristics of skeiðararsandur iceland identification of solute sources and implications for weathering processes the hydrochemistry of sulphur in the active outwash plain of skeioararsandur se iceland shows considerable variety reflecting differences in sources and processes and is investigated in this article using 34 s values of dissolved sulphate and igneous sulphide minerals 18 o h2o and ionic concentrations in waters seawater derived sulphate is a notable component only in the lower sandur 34 s so4 6 8 vcdt 34 s so4 in the skeioara glacial melt river range from 3 4 to 8 8 34 s the higher values occur during a flood event and reflect geothermal sulphate contributions from the grimsvotn caldera kettle hole lakes formed since the november 1996 jokulhlaup form important ecological niches and show evidence of coupled sulphide oxidation and carbonate and possibly silicate dissolution and have the lowest 34 s so4 values average 0 8 attributed to higher proportions of sulphide oxidation derived so 4 2 and or bacterially mediated sulphide oxidation the hydrochemistry of eastern sandur groundwater is influenced by a hydrothermal source of reduced sulphur from the grimsvotn caldera or a localized area of geothermal springs and contrasts with the hydrochemistry of the majority of groundwaters and the sula and gigjukvisl rivers in western and central skeioararsandur these have lower ca 2 mg 2 na k and so 4 2 concentrations and 34 s values consistent with sulphate derived from the oxidation of igneous sulphides in comparison to catchments dominated by atmospherically transported sulphate catchments such as this where the sulphur system is dominated by internal sources rock derived and geothermal will not be sensitive to the temporal decreasing trends in contributions from long range airborne sulphate resulting from reductions of sulphur emissions in north america and europe

hydrology and hydrochemistry of a deglaciating high arctic catchment svalbard summary the impact of deglaciation on contemporary hydrological and biogeochemical functioning in the rieperbreen foxfonna catchment in western svalbard was observed in 2007 2008 an overall negative mass balance was observed during 2007 mass loss was high below the equilibrium line altitude ela but spatially patchy mass increases due to superimposed ice and firn were evident above the ela runoff from above the ela was almost exclusively routed through low gradient hydraulically inefficient supraglacial flowpaths which fed steeper highly efficient supraglacial and englacial subglacial channels downstream as interaction with debris rich environments subglacial and proglacial was minimal and transit times were rapid below the ela runoff from supraglacial sources had a low solute content in addition two further parallel hydrological pathways existed snowmelt fed springs emerging from the glacier s contemporary marginal moraines and multiple shallow intermittent streams within recent moraines throughout the glacier forefield and along its northern moraine flank runoff from these additional pathways flowed through highly reactive sediments composed of shale carbonate and sandstones their intense chemical and physical weathering meant moraines were important sources of solute contribution to the catchment s bulk runoff chemistry ecological succession at the glacier margin is therefore highly likely to be dependent upon nutrient acquisition by hydrological processes within moraines as the catchment undergoes deglaciation

dynamics stratigraphy and proximal dispersal of supraglacial tephra during the ice confined 2004 eruption at grimsvotn volcano iceland the basaltic phreatomagmatic eruption of grimsvotn volcano iceland in november 2004 g2004 lasted for 5 days during which time two separate vents were active significant deposition of tephra occurred in the first 45 h only we have subdivided the deposit into seven units a g on the basis of differences in texture grain size and componentry and the presence of sharp contacts between the layers the distribution of tephra lobes was used to infer the vent of origin for each unit the g2004 deposit is poorly sorted overall and consists of non vesicular to highly vesicular juvenile components units a and b comprise almost exclusively non to poorly vesicular glass fragments whereas units c g contain at least 30 vol highly vesicular pumice the proportion of non juvenile fragments increases significantly in the final unit unit f of the main phase non juvenile fragments are restricted to the coarse 0 fraction of the deposit main phase units c and e account for 80 of the total deposit volume including the entire distal portion and are interpreted to represent a mixture of 1 a widely dispersed component that fell from the upper margins of a strongly inclined 45 6 10 km high plume and 2 a locally dispersed 3 km from source component originating from pyroclastic density currents and minor tephra jets

sensitivity to long term climate change of subpermafrost groundwater systems in svalbard deep subpermafrost aquifers are highly climate dependent with the permafrost as an aquitard preventing groundwater recharge and discharge a study from the high arctic island of spitsbergen svalbard shows that during a glacial to interglacial phase both the permafrost and the glacier regime will respond to climatic changes and a glacier fed groundwater flow system will vary accordingly a full glaciation results in the melting of permafrost and groundwater can flow through pores and fracture systems in the rocks and sediments below the temperate zones of glaciers these groundwater flow systems will mainly be localized to fjords and valleys and form low lying terrestrial springs when the relative sea level drops during deglaciation due to glacio isostatic rise during an interglaciation permafrost develops and thickens and the groundwater recharge and discharge areas will thereby be gradually reduced to a minimum reached at the warmest part of an interglaciation an already frozen spring system cannot reopen before the permafrost melts only groundwater springs related to permanently warm based glacial ice will persist into the next glaciation during a new glaciation flow systems that terminated during the previous interglaciation may become revitalized if overridden by warm based ice causing permafrost thawing

melt water driven stream and groundwater stage fluctuations on a glacier forefield dammagletscher switzerland in many mountain regions large land areas with heterogeneous soils have become ice free with the ongoing glacier retreat on these recently formed proglacial fields the melt of the remaining glaciers typically drives pronounced diurnal stream level fluctuations that propagate into the riparian zone this behaviour was measured on the damma glacier forefield in central switzerland with stage recorders in the stream and groundwater monitoring wells along four transects in spite of the large groundwater stage variations radon measurements in the near stream riparian zone indicate that there is little mixing between stream water and groundwater on daily time scales at all four transects including both losing and gaining reaches the groundwater level fluctuations lagged the stream stage variations and were often damped with distance from the stream similar behaviours have been modelled using the diffusion equation in coastal regions influenced by tidal sea level variations we thus tested the ability of such a model to predict groundwater level fluctuations in proglacial fields the model reproduced several key features of the observed fluctuations at three of four locations although discrepancies also arise due to non representative input data and model simplifications nevertheless calibration of the model for the individual transects yielded realistic estimates of hydraulic diffusivities between the stream and groundwater monitoring wells we conclude that studying diurnal groundwater fluctuations can provide important information about the subsurface hydrology of alpine watersheds dominated by glacier melt copyright 2012 john wiley sons ltd

geochemical characteristics of pyrite in the dabaozhuang deposit in the middle lower yangtze river metallogenic belt eastern china abstract dabaozhuang is a pyrite deposit in the luzong volcanic basin eastern china and has similar exhalation sedimentary features to volcanic massive sulfide deposits vms which commonly form in seawater to better understand the ore forming process of this special type of deposit we employed shrimp si and la icp ms to measure sulfur isotope and trace element compositions of anhydrite and four types of pyrite from the dabaozhuang deposit shrimp in situ sulfur isotope analysis indicates a narrow range in 34s of anhydrite 21 0 21 7 and variable ranges for pyrite 9 9 10 7 for pyrite vein in the deep py i 9 2 to 2 0 for cyclic annular and oval shaped pyrite in massive ore py ii 3 1 5 3 for massive or disseminated pyrite in the footwall tuff and hematite py iii and 29 7 to 30 4 for euhedral and coarse pyrite in the carbonate cement py iv 33s and 36s in four types of pyrite have no abnormal values indicating that sulfur isotope fractionation is mainly controlled by thermochemical sulfate reduction tsr the higher 34s values in type i pyrite and anhydrite indicate a mixing process of magmatic fluid and evaporates at depth py ii and iv have negative 34s data indicating the formation temperature of pyrite decreases because of the mixing of lake water 34s values in py iii are close to magmatic sulfur which shows the igneous sulfur tuff is an important sulfur source for the disseminated mineralization cobalt and ni content also show that the formation temperature of py i is highest and py iv is lowest this research indicates that the vms like deposits could be formed in continental volcanic lakes and are genetically related to so42 rich ioa iron oxide apatite deposits

the active temperate glacial landsystem a model based on breiðamerkurjokull and fjallsjokull iceland accurate interpretations of ancient glaciated terrains rely heavily on our knowledge of process form relationships in contemporary glacierized basins a landsystems model for temperate actively receding glaciers is presented based upon brei amerkurjokull and fjallsjokull iceland historical documentation maps and or aerial photography documenting recession since 1903 provide a unique series of snapshots of the evolving glacial geomorphology at these snouts this documentation is employed in association with sedimentological investigations to assess the evolution of sediment landform assemblages at active temperate glacier margins using the wealth of geomorphological and sedimentological information produced during the recent recession of brei amerkurjokull and fjallsjokull three depositional domains are recognized 1 areas of extensive low amplitude marginal dump push and squeeze moraines derived largely from material on the glacier foreland and often recording annual recession of active ice 2 incised and terraced glacifluvial forms such as recessional ice contact fans and hochsandur fans and simple and complex anabranched eskers and small areas of pitted outwash 3 subglacial landform assemblages of flutes drumlins and overridden push moraines located between ice marginal glacifluvial depo centres the lack of supraglacial sediment in active temperate glaciers like brei amerkurjokull and fjallsjokull generally precludes the widespread development of chaotic hummocky moraine the hummocky terrain previously termed kame and kettle topography has mostly evolved by melt out into a complex network of anabranched eskers over the period 1945 1998 or actually comprises pitted or kettled outwash sandar the tills across the foreland were emplaced by subglacial deformation and lodgement and comprise materials derived from pre existing stratified sediments in addition to localized abrasion of rock surfaces and patches of lake sediments till sequences thicker than 2 m have been constructed by the sequential plastering of till layers onto stratified sediments and bedrock because this stacking is a sub marginal process it is suggested that complex till sequences similar to those observed at brei amerkurjokull fjallsjokull may be employed in the reconstruction of ancient glacier margins additionally the geomorphology of the active temperate landsystem at east brei amerkurjokull may contain subtle surge signatures verifying the historical record of small surges by this part of the glacier this illustrates the danger of employing landform sediment associations from restricted study areas e g parts of landsystems as representative process form models for glaciated terrains

icelandic jokulhlaup impacts implications for ice sheet hydrology sediment transfer and geomorphology abstract glaciers and ice sheets erode entrain and deposit massive quantities of debris fluxes of subglacial meltwater exert a fundamental control on ice dynamics and sediment transport budgets within many glacial systems outburst floods jokulhlaups constitute high magnitude high frequency fluxes of meltwater relative to normal ablation controlled discharge this paper presents a synthesis of research on recent icelandic jokulhlaups and their geomorphological and sedimentary impact we identify jokulhlaup impacts within subglacial englacial and proglacial settings and discuss their wider significance for ice sheet hydrology sediment transfer and geomorphology because jokulhlaups erode deposit and re work sediment simultaneously they usually cause significant glaciological and sedimentological impacts jokulhlaups that propagate as subglacial flood waves often produce widespread hydromechanical disruption at the glacier base recent icelandic jokulhlaups have been recognised as highly efficient agents of reworking subglacial sediment and glacial sediment entrainment models of jokulhlaup impact therefore need to encompass the sub and englacial environment in addition to the proglacial zone where research has traditionally been focussed most jokulhlaups transport sediment to proglacial sandar and often directly to oceans where preservation potential of the impact is greater proglacial jokulhlaup deposits form distinctive sedimentary assemblages coupled with suites of high energy erosional landforms this study of modern jokulhlaup processes and sedimentary products may be useful for the interpretation of meltwater processes associated with quaternary ice sheets

effects of temperature sulfur and oxygen fugacity on the composition of sphalerite from submarine hydrothermal vents experimental studies have shown that temperature pressure sulfur fugacity fs2 and oxygen fugacity fo2 influence the fe content of sphalerite we present compositional in situ data on sphalerite from submarine volcanic hosted massive sulfide vhms ores of hydrothermal vents from different plate tectonic settings and with variable host rock compositions sphalerite from sediment hosted vents has systematically higher s contents and fe zn ratios than those of the sediment starved vents reflecting an influence of fs2 and fo2 on fe partitioning between fluid and sphalerite the fe zn ratios of sphalerite from sediment starved vent systems apparently increase systematically with the fluid temperatures of the corresponding vents we conclude that the composition of sphalerite can be used to 1 distinguish between sediment hosted and sediment starved hydrothermal processes and 2 estimate minimum fluid temperatures of sphalerite precipitation from inactive sediment starved hydrothermal vent sites and fossil vhms deposits

the hydrology of the proglacial zone of a high arctic glacier finsterwalderbreen svalbard sub surface water fluxes and complete water budget summary proglacial areas receive fluxes of glacial meltwater in addition to their own hydrological inputs and outputs while in high latitudes the seasonal development of the active layer also affects their hydrology this paper supplements a previous study of the surface and atmospheric water fluxes in the proglacial area of the svalbard glacier finsterwalderbreen 77 n by focusing on the sub surface water fluxes of the active layer and bringing together all the components of the proglacial water balance over a complete annual cycle particular attention is given to the transitional zone between the moraine complex and the flat sandur sub surface water in the moraine complex sourced mainly from snowmelt lake drainage and active layer thawing is exchanged with sub surface water from the sandur sourced mainly from glacier derived snow and ice melt across a largely distinct boundary hydraulic head and specific discharge were monitored in a transect of wells spanning this boundary a hydraulic gradient from the moraine complex to the sandur is maintained throughout the melt season although this is reversed first briefly when glacial runoff floods the sandur and then diurnally from mid melt season as peak daily flow in the proglacial channel network drives sub surface water in the sandur towards the moraine complex it is estimated that the active layer does not freeze up until mid december at this location so that sub surface water flow may be maintained for months after the cessation of surface runoff however the magnitude of sub surface flow is very small the total annual flux from the moraine complex to the sandur is 11 mm compared with 1073 mm of total annual runoff from the whole catchment glacier included furthermore when considering the water balance of the entire proglacial area there are unlikely to be significant seasonal storage changes in the active layer

changes in jokulhlaup sizes in grimsvotn vatnajokull iceland 1934 91 deduced from in situ measurements of subglacial lake volume a record of volumes of jokulhlaups from the subglacial grimsvotn lake vatnajokull iceland has been derived for the period 1934 91 the change in lake volume during jokulhlaups is estimated from the lake area ice cover thickness and the drop in lake level the jokulhlaup volumes have decreased gradually during this period of low volcanic activity and declining geothermal power the two jokulhlaups in the 1930s each discharged about 4 5 km peak discharge 25 30 10 3 m 3 s 1 in the 1980s jokulhlaup volumes were 0 6 1 2 km 3 peak discharge 2 10 3 m 3 s 1 the lake level required to trigger a jokulhlaup has risen as an ice dam east of the lake has thickened water flow in a jokulhlaup ceases when the base of a floating ice shelf covering grimsvotn settles to about 1160 m a s l apparently the jokulhlaups are cut off when the base of the ice shelf collapses on to a subglacial ridge bordering the lake on its eastern side the decline in melting rates has resulted in a positive mass balance of the 160 170 km grimsvotn ice drainage basin comparison of maps shows that the average positive mass balance rate was 0 12 km 3 a 1 25 of the total accumulation in the period 1946 87 a gradually increasing positive mass balance has prevailed since 1954 reaching 0 23 km 3 a 1 in 1976 86 48 of total accumulation

groundwater hydrochemistry in the active layer of the proglacial zone finsterwalderbreen svalbard abstract glacial bulk meltwaters and active layer groundwaters were sampled from the proglacial zone of finsterwalderbreen during a single melt season in 1999 in order to determine the geochemical processes that maintain high chemical weathering rates in the proglacial zone of this glacier results demonstrate that the principle means of solute acquisition is the weathering of highly reactive moraine and fluvial active layer sediments by supra permafrost groundwaters active layer groundwater derives from the thaw of the proglacial snowpack buried ice and glacial bulk meltwaters groundwater evolves by sulphide oxidation and carbonate dissolution evaporation and freeze concentration of groundwater in summer and winter respectively produce mg ca sulphate salts on the proglacial surface re dissolution of these salts in early summer produces groundwaters that are supersaturated with respect to calcite there is a pronounced spatial pattern to the geochemical evolution of groundwater close to the main proglacial channel active layer sediments are flushed diurnally by bulk meltwaters here mg ca sulphate deposits become exhausted in the early season and geochemical evolution proceeds by a combination of sulphide oxidation and carbonate dissolution at greater distances from the channel the dissolution of mg ca sulphate salts is a major influence and dilution by the bulk meltwaters is relatively minor the influence of sulphate salt dissolution decreases during the sampling season as these salts are exhausted and waters become increasingly routed by subsurface flowpaths

gold and trace element zonation in pyrite using a laser imaging technique implications for the timing of gold in orogenic and carlin style sediment hosted deposits laser ablation icp ms imaging of gold and other trace elements in pyrite from four different sedimenthosted gold arsenic deposits has revealed two distinct episodes of gold enrichment in each deposit an early synsedimentary stage where invisible gold is concentrated in arsenian diagenetic pyrite along with other trace elements in particular as ni pb zn ag mo te v and se and a later hydrothermal stage where gold forms as either free gold grains in cracks in overgrowth metamorphic and or hydrothermal pyrite or as narrow goldarsenic rims on the outermost parts of the overgrowth hydrothermal pyrite compared to the diagenetic pyrites the hydrothermal pyrites are commonly depleted in ni v zn pb and ag with cyclic zones of co ni and as concentration the outermost hydrothermal pyrite rims are either as au rich as in moderate to highgrade deposits such as carlin and bendigo or co ni rich and as au poor as in moderate to low grade deposits such as sukhoi log and spanish mountain the early enrichment of gold in arsenic bearing syngenetic to diagenetic pyrite within black shale facies of sedimentary basins is proposed as a critical requirement for the later development of carlin style and orogenic gold deposits in sedimentary environments the best grade sediment hosted deposits appear to have the gold climax event toward the final stages of deformation related hydrothermal pyrite growth and fluid flow

glacier surge mechanism 1982 1983 surge of variegated glacier alaska the hundredfold speedup in glacier motion in a surge of the kind the kind that took place in variegated glacier in 1982 1983 is caused by the buildup of high water pressure in the basal passageway system which is made possible by a fundamental and pervasive change in the geometry and water transport characteristics of this system the behavior of the glacier in surge has many remarkable features which can provide clues to a detailed theory of the surging process the surge mechanism is akin to a proposed mechanism of overthrust faulting

late quaternary fluvial sedimentation in the voidomatis basin epirus northwest greece abstract detailed morpho and lithostratigraphic investigations allied with radiometric dating in the voidomatis basin epirus northwest greece have identified four quaternary terraced alluvial fills that range from middle pleistocene to historic in age major periods of alluviation during the late quaternary were associated with valley glaciation ca 26 000 20 000 yr b p and subsequent deglaciation ca 20 000 15 000 yr b p in the pindus mountains during late wurmian times and more recently linked to overgrazing sometime before the 11th century ad the late quaternary alluvial stratigraphy of the voidomatis river is more complex than the older fill and younger fill model outlined previously and it is suggested that these terms should no longer form the basis for defining alluvial stratigraphic units in the mediterranean basin

chemical composition of groundwater and surface water in the arctic environment petuniabukta region central spitsbergen summary the groundwater chemistry that occurs in the active layer and the chemistry of the surface water that recharges the active layer in the ebba valley area central spitsbergen were examined in order to explain the geochemical processes that influence water chemistry the most important factor that controls both surface water and groundwater chemistry is the dissolution of freshly weathered easily soluble rocks mainly gypsum anhydrite dolomite and limestone biological contamination of the water manifested by very high concentrations of nutrients was also documented this was caused by deep refreezing of the active layer and the activation of the flushing of birth faeces which was accumulated in the ground environment during recent years the investigation performed in two totally different hydrological years the ablation seasons of 2007 and 2008 shows distinct water chemistry differentiation caused by different hydrological conditions all these findings were then used to formulate a conceptual model of water circulation within the catchment

sediment deformation beneath glaciers and its coupling to the subglacial hydraulic system abstract the extent and style of shear deformation in sediments beneath modern glaciers and the geological evidence for such deformation in deposited sediments are reviewed new evidence is presented from beneath a modern glacier of the spatial and temporal patterns of water pressure fluctuation and of time dependent patterns of deformation in sediments it is concluded that in most experimental sites beneath soft bedded modern glaciers deformation is a significant or major contributor to glacier movement and the resultant discharge of till is large enough to make sediment deformation a major till forming process particular modes of deformation facilitate incorporation of underlying material into the till whilst the capacity of a deforming till to absorb strain can protect the underlying strata from deformation leading to the commonly found relationship where till overlies other strata with a sharp planar interface it is argued that the almost ubiquitous occurrence of drumlins on the beds of former ice sheets is a reflection of the widespread occurrence of sediment deformation beneath them with important implications for the coupling of ice sheet flow and bed properties it is argued that the mechanical behaviour of the subglacial system is not simply determined by till properties but largely controlled by the subglacial water pressure regime determined by the nature of subglacial drainage results of field experiments show how the nature of the basal hydraulic system can play a vital role in controlling the coupling between the glacier and till deformation processes they show that rapid glacier advances can produce undrained loading of sediments that effective pressure may increase either upwards or downwards in a till according to the direction of drainage and that interstitial water pressures in subglacial sediments can show large and rapid variations producing strong variations in the rate and distribution of strain and in the partitioning of basal movement between sliding and deformation

magnitude and frequency in proglacial rivers a geomorphological and sedimentological perspective abstract proglacial fluvial sedimentary systems receive water from a variety of sources and have variable discharges with a range of magnitudes and frequencies little attention has been paid to how these various magnitude and frequency regimes interact to produce a distinctive sedimentary record in modern and ancient proglacial environments this paper reviews the concept of magnitude and frequency in relation to proglacial fluvial systems from a geomorphic and sedimentary perspective rather than a hydrological or statistical perspective the nature of the meltwater inputs can be characterised as low magnitude high frequency primarily controlled by ablation inputs from the source glacier or high magnitude low frequency primarily controlled by exceptional inputs the most important high magnitude low frequency inputs are catastrophic outburst floods often referred to by the term jokulhlaup icelandic for glacier burst glacier surges are an additional form of cyclical variation impacting the proglacial environment which briefly alter the volumes and patterns of meltwater input the sedimentary consequences of low magnitude high frequency discharges are related to frequent variations in stage the greater directional variability that sediment will record and the increased significance of channel confluence sedimentation in contrast the most significant characteristics of high magnitude low frequency flooding include the presence of large flood bars and mid channel jokulhlaup bars hyperconcentrated flows large gravel dunes and the formation of ice block kettle hole structures and rip up clasts glacier surges result in a redistribution of low magnitude high frequency processes and products across the glacier margin and small floods may occur at the surge termination criteria for distinguishing magnitude and frequency regimes in the proglacial environment are identified based on these major characteristics studies of quaternary proglacial fluvial sediments are used to determine how the interaction of the various magnitude and frequency regimes might produce a distinctive sedimentary record consideration of sandur architecture and stratigraphy shows that the main controls on the sedimentary record of proglacial regions are the discharge magnitude and frequency regime sediment supply the pattern of glacier advance or retreat and proglacial topography a model of sandur development is suggested which shows how discharge magnitude and frequency in combination with sandur incision and aggradation controlled by glacier advance and retreat can control sandur stratigraphy

erratum to variations of sulphur isotope signatures in sulphides from the metamorphosed ming cu au volcanogenic massive sulphide deposit newfoundland appalachians canada the ming deposit is an early ordovician bimodal mafic cu au volcanogenic massive sulphide vms deposit in the newfoundland appalachians that was metamorphosed to upper greenschist lower amphibolite facies conditions and deformed in the silurian and devonian the ming deposit consists of several spatially proximal ore bodies of which the 1806 zone 1807 zone ming south up plunge and down plunge and the lower footwall zone are the focus of this paper the ore bodies have similar stratigraphic sequences the ore bodies can be divided into 1 a silicified horizon that caps the massive sulphides 2 semi massive to massive sulphides and 3 sulphide mineralization in a rhyodacitic footwall sulphide mineralization in a rhyodacitic footwall includes a sulphide stringers immediately below the semi massive to massive sulphides and b chalcopyrite pyrrhotite pyrite stringers distally from semi massive to massive sulphides in the lower footwall zone pyrite chalcopyrite pyrrhotite arsenopyrite and galena were analysed by in situ secondary ion mass spectrometry sims for sulphur isotope compositions the isotopic signatures of pyrite chalcopyrite pyrrhotite and arsenopyrite fall within a limited range of 2 8 to 12 0 for semi massive to massive sulphides and sulphide mineralization in the footwall the silicified horizon capping the semi massive to massive sulphides has higher 34s 5 8 19 6 especially for pyrrhotite mean 17 2 2 2 n 8 the sulphur isotope composition of galena is more heterogeneous especially within semi massive to massive sulphides and sulphide stringers ranging from 0 8 to 17 3 mean 6 1 4 3 n 35 and 7 6 to 17 1 mean 13 7 5 3 n 3 respectively geothermometric calculations give insufficient formation and metamorphism temperatures for neighbouring mineral pairs because sulphides were not in isotopic equilibrium while deposited in early ordovician or re equilibrated during silurian devonian metamorphism respectively therefore original isotopic compositions of sulphides at the ming deposit have been preserved modelling of the source of sulphur shows that 1 reduced seawater sulphate and 2 sulphur leached from igneous wall rock and or derived from magmatic fluids are the main sources of sulphur in the ming deposit the influence of igneous sulphur igneous wall rock magmatic fluids increases with temperature and is an important sulphur source for the semi massive to massive sulphides and footwall mineralization in addition to a contribution from thermochemical sulphate reduction tsr of seawater it is difficult to distinguish between sulphur leached from igneous rocks and magmatic fluid related sulphur and it is possible that both sources contributed to the ores at the ming deposit in addition to igneous sulphur the heavy isotopes of the silicified horizon are consistent with the sulphur in this horizon being derived only from thermochemical sulphate reduction of early ordovician seawater sulphate

hydrogeological implications of glacial landscape evolution at skeiðararsandur se iceland abstract patterns of groundwater recharge and flow in present day and palaeo glacial environments are governed by both geomorphology and subsurface sedimentology this paper assesses the hydrogeological implications of glacial landscape evolution and develops a conceptual model of glacial landscape evolution and hydrogeological interaction the ice marginal zone of skei ararsandur se iceland was selected as a case study of a temperate actively receding glacier landsystem that is affected by both surging behaviour and periodic glacier outburst floods jokulhlaups the groundwater table elevation was measured approximately every 2 5 days throughout two six week summer field seasons in 2000 and 2001 and once in march 2001 using a network of shallow piezometers and hydraulic conductivity was calculated based on grain size distribution analysis of sampled aquifer materials the hydraulic conductivity of the near surface aquifer at the study site spans three orders of magnitude and is highest and most varied in areas inundated by the november 1996 jokulhlaup the shallow water table in the study area responds dynamically to precipitation events with the greatest fluctuation in an enclosed moraine lake basin with a perched aquifer underlain by ice and in a zone of outwash fans proximal to the ice margin the seasonal decline in water table is greatest at the ice margin reflecting the reduced winter recharge from the stagnant ice zone landsystems with morainic relief are associated with localised moraine precipitation fed groundwater systems these localised groundwater systems are superimposed on the intermediate regional scale groundwater systems that discharge further down sandur and offshore and are dominated by the gently sloping geomorphologically uniform outwash plain groundwater fed lakes formed in depressions from ice blocks deposited during jokulhlaups may provide important ecological niches the investigations at this site demonstrate that glacial outburst floods and glacier margin fluctuations produce a suite of sediments landforms and environments that affect the hydrogeological system

long term variability of proglacial groundwater fed hydrological systems in an area of glacier retreat skeiðararsandur iceland proglacial groundwater fed features such as seeps substantially impact proglacial geomorphology hydrology and ecology however there is a paucity of research on the impacts of climate change and glacier retreat on the extent of these important features this paper aims to investigate the impact of glacier retreat on proglacial groundwater levels and on the extent of groundwater fed seeps research has taken place in western skei ararsandur the large proglacial outwash plain of skei ararjokull a retreating temperate glacier in southeast iceland changes in the extent of proglacial groundwater seeps were mapped using historical aerial photographs from 1986 1997 and 2012 proglacial groundwater levels were monitored in shallow boreholes between 2000 and 2012 the western margin of skei ararjokull has retreated approximately 1 km beyond its position in 1986 however this retreat was punctuated by short periods of readvance the geomorphology and groundwater systems at the site were substantially impacted by the november 1996 jokulhlaup whose deposits altered approximately 18 of the area of groundwater seeps the surface areas of groundwater seeps and lakes in the study area have declined by 97 between 1986 and 2012 most of the decline took place after 1997 when the mean annual rate of retreat increased three fold groundwater levels also declined substantially between 2000 and 2012 although this trend varies spatially the paper provides a conceptual model of the controls on proglacial shallow groundwater systems direct impacts of glacier retreat are suggested as the main cause for the declines in proglacial groundwater levels and in the extent of groundwater seeps these declines are expected to adversely impact sandur ecology copyright 2014 john wiley sons ltd

sulfur isotope characteristics of metamorphosed zn cu volcanogenic massive sulfides in the areachap group northern cape province south africa zn and cu rich massive sulfide ores of volcanogenic origin volcanogenic massive sulfide vms deposits occur as stratiform stratabound lenses of variable size hosted by gneisses amphibolites and schists of the areachap group in the northern cape province of south africa the areachap group represents the highly deformed and metamorphosed remnants of a mesoproterozoic volcanic arc that was accreted onto the western margin of the kaapvaal craton during the 1 0 1 2 ga namaquan orogeny sulfur isotope data 34s are presented for 57 sulfide separates and one barite sample from five massive sulfide occurrences in the areachap group although sulfides from each site have distinct sulfur isotope values all 34s values fall within a very limited range 3 0 to 8 5 barite has a 34s value of 18 5 very different from that of associated sulfides at one of the studied sites kantienpan a distinct increase in 34s of sulfides is observed from the massive sulfide lens into the disseminated sulfides associated with a distinct footwall alteration zone sulfide sulfide and sulfide barite mineral pairs which recrystallized together during amphibolite and lower granulite facies metamorphism are not in isotopic equilibrium sulfur isotope characteristics of sulfides and sulfates of the zn cu ores in the areachap group are however very similar to base metal sulfide accumulations associated with modern volcanic arcs and unsedimented mid ocean ridges it is thus concluded that profound recrystallization and textural reconstitution associated with high grade regional metamorphism of the massive sulfide ores of the areachap group did not result in extensive sulfur isotopic homogenization this is similar to observations in other metamorphosed vms deposit districts and confirms that massive sulfide ores remain effectively a closed system for sulfur isotopes for both sulfides and sulfates during metamorphism