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

spatial variation of radar derived basal conditions on kamb ice stream west antarctica radar profiles of bed echo intensity can survey conditions at the ice bed interface and test for the presence or absence of water however extracting information about basal conditions from bed echo intensities requires an estimate of the attenuation loss through the ice we used the relationship between bed echo intensities from constant offset radar data and ice thickness to estimate depth averaged attenuation rates at several locations on and near kamb ice stream kis west antarctica we found values varying from 29 db km 1 at siple dome to 15 db km 1 in the main trunk region of kis in agreement with a previous measurement and models using these attenuation rate values we calculated the relative bed reflectivity throughout our kis surveys and found that most of the bed in the trunk has high basal reflectivities similar to those obtained in the location of boreholes that found water at the bed areas of lower bed reflectivity are limited to the sticky spot where a borehole found a dry bed and along the margins of kis these results support previous hypotheses that the basal conditions at locations like the sticky spot on kis control its stagnation and possible reactivation

geology and tectonics of the betic zone se spain abstract the southern margin of the iberian continent comprises a complex geological history which can be traced back into the proterozoic when a gneissic basement was formed a cover of nevado filabride rocks was deposited onto this proterozoic basement during the palaeozoic the permian intrusion of the bedar granite suggests that the palaeozoic sedimentary rocks now exposed in the betic cordilleras have been affected by the hercynian orogeny similar to that of palaeozoic rocks in the adjoining ossa morena zone the hercynian basement was probably covered by alpujarride carbonates in the mesozoic when rifting opened tethys and intruded 140 ma old basic dyke swarms the palaeozoic basement of the betic cordilleras comprises a suture of late cretaceous subduction 80 85 ma b p this can be inferred from hp lt metamorphic facies obducted in coeval thrust slices of nevado filabride rocks the nevado filabride nappes include mesozoic carbonates transformed into marbles macael the suture was probably annnealed after the closure of tethys the mesozoic boundary between africa and europe and the rifting in tethys ceased during the palaeogene when the atlas mountains were formed 36 ma b p subsequently relative movements between africa and europe in the neogene were accommodated by strike slip faults these define the iberian microplate moving eastward by atlantic spreading and possibly subducting under italy neogene deformation of iberia is most intensive in southeastern spain due to emplacement of a mantle diapir under the alboran area this occurred early in the neogene aquitanian and caused nappe spreading involving alpujarride and malaguide rocks the subsequent neogene history has now been studied in great detail and is reviewed here it involves clear examples of calc alkaline volcanism most probably not related to subduction seismic motion along strike slip faults within the iberian microplate and syntectonic deposition in intermontane neogene basins

surface melt driven seasonal behaviour englacial and subglacial from a soft bedded temperate glacier recorded by in situ wireless probes we investigate the spatial and temporal englacial and subglacial processes associated with a temperate glacier resting on a deformable bed using the unique glacsweb wireless in situ probes embedded in the ice and the till combined with other techniques including ground penetrating radar gpr and borehole analysis during the melt season spring summer and autumn high surface melt leads to high water pressures in the englacial and subglacial environment winter is characterised by no surface melting on most days base apart from a series of positive degree days once winter begins a diurnal water pressure cycle is established in the ice and at the ice sediment interface with direct meltwater inputs from the positive degree days and a secondary slower englacial pathway with a five day lag this direct surface melt also drives water pressure changes in the till till deformation occurred throughout the year with the winter rate approximately 60 that of the melt season we were able to show the bed comprised patches of till with different strengths and were able to estimate their size relative percentage and temporal stability we show that the melt season is characterised by a high pressure distributed system and winter by a low pressure channelized system we contrast this with studies from greenland overlying rigid bedrock where the opposite was found we argue our results are typical of soft bedded glaciers with low englacial water content and suggest this type of glacier can rapidly respond to surface driven melt based on theoretical and field results we suggest that the subglacial hydrology comprises a melt season distributed system dominated by wide anastomosing broad flat channels and thin water sheets which may become more channelized in winter and more responsive to changes in meltwater inputs

the interrelation of glaciotectonic and glaciodepositional processes within the glacial environment abstract in recent years it has been recognised that ice sediment coupling occurred beneath the quaternary ice sheets that advanced over the soft sediments of lowland areas this paper looks in detail at the effects of this coupling on the sediments which results in glaciotectonic deformation and also discusses the interaction of deformation and deposition within the subglacial environment two types of glaciotectonic deformation are discussed that are produced by the active movement of ice 1 proglacial tectonics at the margin which include compressive fold styles such as listric thrusts and faults and open folding 2 subglacial tectonics formed beneath the glacier which include fold styles resulting from simple shear and represent a soft rock purely dynamic shear zone styles of deformation associated with stagnant ice are also investigated we argue that glaciotectonic deformation is a common phenomenon and an integral part of geological record from continental ice sheets it is suggested that zones of deformation within the sediment are related to similar zones of strain in the ice sheet and complex deformation sequences are produced by the superimposition of these differing styles upon one another as the ice sheet advances and retreats it is also argued that subglacial deposition and deformation are related and that on soft beds underformed till is rare whilst deformed till is very common

a method for computing shallow ice core depths sipre style hand augers usually recover core sections whose bottom is somewhat shallower than the drill depth a procedure for calculating the range of possible core depths is presented in the field the drill barrel is lowered down the hole by means of a series of rigid extension rods the apparatus is then rotated to drill through debris left behind by the prior run and into fresh firn or ice care is taken to ensure that the total penetration of debris and firn does not exceed about half the length of the drill barrel otherwise the barrel s capacity for core and chips will be exceeded and the drill likely jammed the entire apparatus is then recovered the workers record the run number the total drill length barrel and extensions the exposed length of extensions above the hole top at the end of drilling and the length of recovered core the cycle is then repeated an example is shown in table i these data are then used to calculate drill depth which is drill length minus the exposed length plus an adjustment if drilling is from the base of a pit distance drilled is then obtained by comparison with the drill depth of the prior run the apparent core loss is the distallce drilled minus the length of recovered core the actual core loss is not readily calculated it is the sum of true core loss ground up core and the collapse of friable strata and the amount of core

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

ice speed of a calving glacier modulated by small fluctuations in basal water pressure ice flow acceleration has played a crucial role in the rapid retreat of calving glaciers in alaska greenland and antarctica high frequency measurements of ice speed and basal water temperatures from a calving glacier in patagonia show that changes in basal water pressure by a few per cent can significantly affect ice flow speed ice flow acceleration has played a crucial role in the rapid retreat of calving glaciers in alaska1 2 greenland and antarctica3 4 glaciers that calve in water flow much faster than those that terminate on land as a result of enhanced basal ice motion where basal water pressure is high5 however a scarcity of subglacial observations in calving glaciers limits a mechanistic understanding here we present high frequency measurements of ice speed and basal water pressures from glaciar perito moreno a fast flowing calving glacier in patagonia we measured water pressure in boreholes drilled at a site where the glacier is 515 5 m thick and where more than 60 of the ice is below the level of proglacial lakes we found that the mean basal water pressure was about 95 of the pressure imposed by the weight of the overlying ice moreover changes in basal water pressure by a few per cent drove nearly 40 of the variations in ice flow speed the ice speed was strongly correlated to air temperature suggesting that glacier motion was modulated by water pressure changes as meltwater entered the system we conclude that basal water pressure in calving glaciers is important for glacier dynamics and closely connected to climate conditions

digital optical televiewing of ice boreholes digital optical televiewing recently developed to log and map terrestrial boreholes provides a complete orientated image of borehole walls at a resolution of 1 mm along hole and typically

environmental assessment of the arsenic rich rodalquilar gold copper lead zinc mining district se spain data from soils and vegetation the rodalquilar mineral deposits se spain were formed in miocene time in relation to caldera volcanic episodes and dome emplacement phenomena two types of ore deposits are recognized 1 the el cinto epithermal au as high sulphidation vein and breccia type and 2 peripheral low sulphidation epithermal pb zn cu au veins the first metallurgical plants for gold extraction were set up in the 1920s and used amalgamation cyanide leaching began in the 1930s and the operations lasted until the mid 1960s the latter left a huge pile of 900 000 1 250 000 m3 of abandoned as rich tailings adjacent to the town of rodalquilar a frustrated initiative to reactivate the el cinto mines took place in the late 1980s and left a heap leaching pile of 120 000 m3 adverse mineralogical and structural conditions favoured metal and metalloid dispersion from the ore bodies into soils and sediments whereas mining and metallurgical operations considerably aggravated contamination we present geochemical data for soils tailings and wild plant species compared to world and local baselines both the tailings and soils of rodalquilar are highly enriched in as mean concentrations of 950 and 180 g g 1 respectively regarding plants only the concentrations of as bi and sb in asparagus horridus launaea arborescens salsola genistoides and stipa tenacissima are above the local baselines bioaccumulation factors in these species are generally lower in the tailings which may be related to an exclusion strategy for metal tolerance the statistical analysis of geochemical data from soils and plants allows recognition of two well differentiated clusters of elements as bi sb se sn te and cd cu hg pb zn which ultimately reflect the strong chemical influence of both el cinto and peripheral deposits mineral assemblages

in search of ice stream sticky spots the form drag of large bedrock bumps sticking into the base of an ice stream can produce effective sticky spots supporting large basal shear stress bedrock regions surrounded by lubricating till at the same topographic level can cause sticky spots but tend to collect lubricating water and thus are unlikely to support a shear stress of more than a few tenths of a bar unless they contain abundant large bumps raised regions on the ice air surface also can cause moderate increases in the shear stress supported on the bed beneath surveys of large scale bedrock roughness strain grids across the margins of ice surface highs and possibly water pressure measurements in regions of thin or zero till would help identify and characterize sticky spots

positive degree day factors for ablation on the greenland ice sheet studied by energy balance modelling ice ablation is related to air temperature by the positive degree day factor variations of the positive degree day factor in west greenland are studied using an energy balance model to simulate ablation under different conditions degree day factors for simulated and measured ice ablation at nordbogletscher and qaman rssup sermia agree well with values around 8 mm d 1 c 1 degree day factors for snow are less than half those for ice energy balance modelling shows that degree day factors vary with summer mean temperature surface albedo and turbulence but there is only evidence of large positive degree day factors at lower temperatures and with low albedo 0 3 the greatest effect of albedo variations 0 3 0 7 is at lower temperatures while variations in turbulence have greater effect at higher temperatures current models may underestimate runoff from the greenland ice sheet by several tenths because they use a degree day factor for melting ice that is too small for the colder parts of the ice sheet i e the upper ablation area and the northerly margin

sediment deformation beneath glaciers rheology and geological consequences experiments beneath breidamerkurjokull in iceland have led to development of flow laws for the subglacial till relating strain rate to shear stress and effective pressure and assuming either bingham fluid or nonlinearly viscous fluid behavior water pressures in the till are less than ice pressures and it is suggested that this may lead to infiltration of ice into the sediment which inhibits sliding at the ice sediment interface where water pressures are equal or near to ice pressures infiltration does not occur and sliding may result a one dimensional theory of subglacial deformation is developed in which the empirical flow law is coupled with a model of subglacial hydrology and consolidation this predicts stable states in which subglacial sediment either does not deform or a dilatant deforming horizon forms with positive effective pressures at the ice bed interface or unstable states where zero or negative effective pressures are predicted time dependent analyses show that response times following perturbations of the system may be of the order of 103 years and thus that unsteady behavior may be normal on glaciers flowing over unlithified sediment beds it is suggested that the natural variability of material properties in subglacial sediment beds leads to the development of drumlins on the glacier bed it is suggested that unstable deformation at zero or negative effective stress leads to piping in subglacial sediments at the glacier terminus and the growth of sediment floored subglacial tunnels their frequency is that which is sufficient to draw down subglacial water pressures so as to prevent unstable deformation where they discharge large water volumes subglacial sediments flow laterally toward them producing tunnel valleys this sediment is then removed by water flowing along the axial tunnel tunnel valleys can be regarded as the equivalent in soft sediment areas of eskers in bedrock areas

ice motion and mass balance at the allan hills blue ice area antarctica with implications for paleoclimate reconstructions we present a new surface balance and ice motion dataset derived from high precision gps measurements from a network of steel poles within three icefields of the allan hills blue ice area antarctica the surveys were conducted over a 14 year time period ice flow velocities and massbalance estimates for the main icefield mif are consistent with those from pre gps era measurements but have much smaller uncertainties the current study also extends these measurements through the near western icefield nwif to the eastern edge of the mid western icefield mwif the new dataset includes for the first time well constrained evidence of upward motion within the allan hills mif indicating that old ice should be present at the surface these data and terrestrial meteorite ages suggest that paleoclimate reconstructions using the surface record within the allan hills mif could potentially extend the ice core based record beyond the 800 000 years currently available in the epica

a method for determining ice thickness change at remote locations using gps ice thickness changes at remote locations on ice sheets can be determined by means of precise global positioning system gps surveys with interferometric solutions remote sites are precisely surveyed relative to gps receivers on rock repeat observations of the position of a remote site provide its vertical velocity the difference between this velocity and accumulation rate is an indicator of change in ice sheet thickness allowance must be made for the movement of survey markers due to firn compaction and down slope ice motion to allow for firn compaction very longpoles arc placed to a sufficient depth in the firn that the densification rate can be considered steady this assumption may be tested by measurements with poles set to different depths an analysis of errors in pilot studies indicates that the limit to precision is the determination of accumulation rate

basal drainage system response to increasing surface melt on the greenland ice sheet surface meltwater reaching the bed of the greenland ice sheet imparts a fundamental control on basal motion sliding speed depends on ice bed coupling dictated by the configuration and pressure of the hydrologic drainage system in situ observations in a four site transect containing 23 boreholes drilled to greenland s bed reveal basal water pressures unfavorable to water draining conduit development extending inland beneath deep ice this finding is supported by numerical analysis based on realistic ice sheet geometry slow meltback of ice walls limits conduit growth inhibiting their capacity to transport increased discharge key aspects of current conceptual models for greenland basal hydrology derived primarily from the study of mountain glaciers appear to be limited to a portion of the ablation zone near the ice sheet margin

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

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

genetic links between ash flow calderas and associated ore deposits as revealed by large scale thermo mechanical modeling abstract in addition to a number of epithermal ore deposits some porphyry type ore deposits are also hosted by ash flow calderas spatial correlation between ash flow calderas and these deposits is observed in several parts of the world but temporal correlation between the mineralization and the episode of caldera formation remains unclear especially because geochronological data indicate that the mineralization may date to several million years before or after caldera formation because caldera collapse represents only a very short event in a long time scale evolution between a silicic magma chamber and its host rocks we have developed a thermo mechanical model of upper crustal and magmatic system behavior during the pre and post caldera formation stages major petrophysical properties of ash flow caldera related rocks are incorporated into the model which accounts for brittle elasto ductile rheology and heat transfer and reproduces fault initiation and various caldera collapse scenarios large scale mechanisms of initiation of thermal and structural traps for epithermal ore deposits are described in particular we found that the outer sides of caldera border faults are associated with both anomalous heat transfer and a high fracture density the finite size of the insulating intracaldera units forces the accumulated heat excess to be laterally transferred across the border faults in most cases the model predicts y shaped fault geometry which is surprisingly similar to that of mineralized faults in the field variations in lithostatic pressure on the magma chamber roof and in the vicinity of the border faults can reach 10 to 20 mpa with deep overpressured zones close to the inner edge of the chamber corners despite the fact that hydrothermal convection and fluid geochemistry are not included in the model these thermal and mechanical results are believed to constrain the conditions for mineralization processes our results show that in the presence of regional extension the development of caldera border faults may be suppressed to the advantage of deep seated fractures clustered above the central part of the magma chamber thus favoring conditions for the formation of porphyry type ore deposits finally we demonstrate that well before the eruption the gradual emplacement of a hot and large silicic magma chamber may create significant extensional stress in the brittle upper crust resulting in breakup and pre eruptive normal faulting and thus allowing for conditions of pre caldera mineralization

thermomechanical behavior of large ash flow calderas the fundamental thermal and mechanical processes that occur within the ash flow caldera magma chamber systems remain largely enigmatic to date the only models of caldera collapse are simple mostly elastic or viscoelastic mechanical models that can predict some of the conditions preceding the collapse they cannot however predict the collapse itself because they are incapable either of reproducing the formation of faults or of accounting for the brittle ductile transitions and fault related thermal anomalies we have constructed analytical and numerical therrnomechanical that account for both elastic plastic ductile rheology and physical properties of the caldera rocks the overpressured magma is evacuated through a central vent and transforms into ash flow units deposited within the forming caldera brittle deformation faulting and subsequent collapse of the structure are reproduced the results show that in the absence of a regional stress field the collapse on both sides will occur only for aspect ratios i e caldera diameter to the depth of the magma chamber exceeding 5 and that internal embedded faults may also appear when the aspect ratio exceeds 10 thermal conductivity contrasts in ash flow calderas give rise to strong heat refraction that localizes deep seated thermal anomalies to the outer sides of the faults in the presence of regional extension the border faulting can be attenuated or disappear and the faults tend to localize around the central part of the chamber roof coupled therrnomechanical modeling suggests that the outer sides of the border faults have high trapping capabilities for hydrothermal fluids the geometry of the brittle ductile transition largely controls that of the fractured zones within and around the chamber roof thus justifying a new mechanical definition of magma chamber geometry

manganese deposits in turkey distribution types and tectonic setting abstract manganese deposits in turkey are divided into four main groups on the basis of their age host rocks and processes of formation the first is hydrothermal hydrogenetic and rarely diagenetic type manganese deposits which are chiefly associated with radiolarian chert series these deposits occur as lenses and small ore beds within ophiolitic melanges zones of paleo tethyan karakaya and neo tethyan north anatolian and south anatolian suture belts the second is black shale hosted manganese deposits that is found in black shale calcareous shale and calciturbiditic limestone horizons of the passive margin sediments of late cretaceous age in the western taurides these deposits generally are metamorphosed to greenschist facies and include mn carbonate silicate and oxide minerals the third is volcanic arc hosted ores along the black sea margin which occur in different types of metasomatic hydrothermal and stratabound settings rock associations include upper cretaceous dacitic tuff reddish limestone marl and hemipelagic claystone the fourth is oligocene hosted ores in the thrace basin these deposits are similar to those of the paratethyan oligocene belt which occur on the eastern and northern margin of black sea and includes the chiatura georgia nikopol ukraine and varna bulgaria respectively the oligocene mn deposits of the thrace basin were formed by diagenetic replacement processes during a marine regression

a wireless subglacial probe for deep ice applications we present the design and first results from two experiments using a wireless subglacial sensor system wise that is able to transmit data through 2500 m thick ice energy consumption of the probes is minimized enabling the transmission of data for at least 10 years in july 2010 the first prototype of the system was used to measure subglacial pressure at the base and a temperature profile consisting of 23 probes in two 600 m deep holes at russell glacier a land terminating part of the west greenland ice sheet near kangerlussuaq the time series of subglacial pressure show very good agreement between data from the wise system and the wired reference system the wireless measured temperature data were validated by comparison with the theoretical decrease of melting point with water pressure inside the water filled hole directly after installation to test the depth range of the wise system a second experiment using three different probe types and two different surface antennas was performed inside the 2537 m deep hole at neem it is demonstrated that with the proper combination of transmission power and surface antenna type the wise system transmits data through 2500 m thick ice

abrupt glacier motion and reorganization of basal shear stress following the establishment of a connected drainage system three episodes of strong basal motion occurred at trapridge glacier yukon territory canada on 11 june 1995 following the establishment of a connected subglacial drainage system responses to these spring events are noted in the records for 42 instruments and were recorded throughout the 60 000 m study area strong basal motion during the events is indicated by ploughmeter load bolt and vertical strain records and abrupt pressure changes in several transducer records denote damage caused by extreme pressure pulses these pressure pulses generated by the abrupt basal motion also resulted in the failure of seven pressure sensors records for pressure turbidity and conductivity sensors indicate that basal drainage patterns did not change significantly during the events geophone records suggest that the episodes of basal motion were precipitated by the gradual failure of a sticky spot following hydraulic connection of part of the study area this failure resulted in the transfer of basal stress to the unconnected region of the bed during the course of the events no evidence for strong basal motion is seen in the instrument records for several weeks following the events suggesting that the mechanical adjustments resulted in a stable configuration of basal stresses this event illustrates how unstable situations can be quickly accommodated by mechanical adjustments at the glacier bed

thermochemically induced transformations in al smectites a spanish natural analogue of the bentonite barrier behaviour in a radwaste disposal abstract the thermal effect induced by the morron de mateo volcanic dome cabo de gata volcanic region spain on the adjacent bentonitised tuffaceous beds has been studied as a natural analogue of the thermal behaviour of the bentonite engineered barrier of a geological radwaste repository these bentonites consist mainly of fe rich smectites and were formed in equilibrium with seawater at temperatures between 75 and 95 c according to the 18o and d values in contrast bentonites from other localities in the region consist mainly of al smectites formed in equilibrium with meteoric water below 25 c this investigation is focussed on the detection of the chemical differences between smectites from proximal and distal zones to the dome as well as to test whether the temperatures calculated based on the o and h isotopic values correspond to their formation or transformation the initial hypothesis was that the chosen smectites could be formed under marine conditions being later transformed and isotopically re equilibrated as a result of the intrusion to check this hypothesis a detailed mineralogical chemical geochemical and isotopic study has been performed on the smectitised tuffaceous materials and the overlaying biocalcarenites outcropping near and far from the dome the results show that distal smectites are dioctahedral al smectites similar to those from other deposits in the region while proximal smectites are fe and mg rich smectites showing two evolutionary trends on a fe mg al ternary diagram similar features are observed when their structural formulae are plotted on the muscovite celadonite pyrophylite diagram thus they plot in the smectite domain with interlayer charge less than 1 which is mainly due to octahedral substitution for distal smectites while for proximal ones it is caused by both octahedral and tetrahedral substitutions in this ternary diagram the domains of both proximal and distal smectites are partially overlapped the coexistence of di and trioctahedral smectites was only detected in one proximal sample further proximal biocalcarenites are enriched in fe rich dolomite in relation to the distal ones the 87sr 86sr and 13c values in carbonates and d in smectites indicate equilibrium with seawater in contrast 18o values of carbonates and smectites indicate that they were transformed and re equilibrated between 40 and 90 c and between 55 and 66 c respectively independently of their location with respect to the dome these data suggest that the transformation of calcite into mg fe carbonates and the occurrence of fe and mg rich smectites near to the dome resulted from a chemically induced process at similar temperatures the compositional differences among samples suggests that fe mg and minor mn were supplied by a contaminant plume originated from the dome migrating through the sediments and becoming more diluted away from the source the absence of a well defined thermal gradient in the system could be due to the small size semi closed and shallow character of the basin as well as to its high underlying volcanic activity finally the results are discussed in terms of analogue processes that can be expected in the bentonite barrier of a radwaste geological repository

genesis of acid sulfate alteration and au cu ag mineralization at summitville colorado the summitville au cu ag deposit occurs within a porphyritic quartz latite primarily in a zone of vuggy silica alteration characterized by leaching of all major elements except silica and iron vuggy silica is best developed between an elevation of 3 700 and 3 500 m where it occurs in irregular pipes and lenticular pods up to 70 m wide and is enclosed by up to 30 m of intense quartz alunite alteration the vuggy silica zones diminish in size with decreasing elevation and rarely exceed a width of 2 m below an elevation of 3 400 m these deep vuggy silica zones are enclosed by quartz kaolinite alteration with little or no alunite sulfide mineralization occurs primarily within the vuggy silica the sulfide assemblage changes with decreasing elevation from covellite luzonite or native gold to chalcopyrite tennantite sulfides occur lining voids or in microveinlets and are accompanied by minor kaolinitc but not by alunite gold also occurs in a near surface barite goethite jarosite assemblage that crosscuts the vuggy silica consideration of alunite kaolinitc and pyrite stability relations and of aluminum speciation at 250 degrees c indicates that a ph of 2 or below and a log f sub o 2 of 31 or 1 at 250 degrees c were necessary to produce vuggy silica alteration the chalcopyrite tennantite mineralization occurring at depth in the vuggy silica zone is indicative of less oxidizing and less acidic conditions the covellite luzonite or gold assemblage requires conditions intermediate between those necessary for vuggy silica alteration and for deep sulfide mineralization barite gold mineralization is interpreted as a near surface assemblage produced under highly acidic oxidizing conditions these textural and geochemical relationships indicate that sulfide and gold mineralization postdate the formation of vuggy silica alteration in the deposit and are not directly related to the highly acidic solutions necessary for this early acid leaching event the change from extreme acid leaching to copper sulfide and precious metal deposition may represent a transition from a magmatic vapor dominated to a liquid dominated system leading to more reducing and less acidic conditions during sulfide deposition

spatial patterns in mass balance of the siple coast and amundsen sea sectors west antarctica this is the publisher s version also available electronically from http www ingentaconnect com

supraglacial forcing of subglacial drainage in the ablation zone of the greenland ice sheet 1 we measure hydrological parameters in meltwater draining from an outlet glacier in west greenland to investigate seasonal changes in the structure and behaviour of the hydrological system of a large catchment in the greenland ice sheet gris our data reveal seasonal upglacier expansion and increase in hydraulic efficiency of the subglacial drainage system across a catchment 600 km2 to distances 50 km from the ice sheet margin this expansion occurs episodically in response to the drainage of surface meltwaters into a hitherto inefficient subglacial drainage system as new input locations become active progressively further upglacier this system is similar to alpine glaciers these observations provide the first synopsis of seasonal hydrological behaviour in the ablation zone of the gris

machine learning predictive models for mineral prospectivity an evaluation of neural networks random forest regression trees and support vector machines abstract machine learning algorithms mlas such us artificial neural networks anns regression trees rts random forest rf and support vector machines svms are powerful data driven methods that are relatively less widely used in the mapping of mineral prospectivity and thus have not been comparatively evaluated together thoroughly in this field the performances of a series of mlas namely artificial neural networks anns regression trees rts random forest rf and support vector machines svms in mineral prospectivity modelling are compared based on the following criteria i the accuracy in the delineation of prospective areas ii the sensitivity to the estimation of hyper parameters iii the sensitivity to the size of training data and iv the interpretability of model parameters the results of applying the above algorithms to epithermal au prospectivity mapping of the rodalquilar district spain indicate that the rf outperformed the other mla algorithms anns rts and svms the rf algorithm showed higher stability and robustness with varying training parameters and better success rates and roc analysis results on the other hand all mla algorithms can be used when ore deposit evidences are scarce moreover the model parameters of rf and rt can be interpreted to gain insights into the geological controls of mineralization

ice stream sticky spots a review of their identification and influence beneath contemporary and palaeo ice streams rapidly flowing ice streams are the arterial drainage routes in continental ice sheets and exert a major influence on ice sheet mass balance recent observations have revealed that ice stream flow exhibits considerable variability with relatively rapid changes taking place in speed and direction this spatial and temporal variability is intimately linked to the conditions at the base of the ice streams and the distribution of localised patches of basal friction known as sticky spots in this paper we provide a detailed review of sticky spot observations from both contemporary and palaeo ice stream beds in order to better understand their nature and influence observations and theoretical considerations reveal four primary causes of stickiness i bedrock bumps ii till free areas iii areas of strong well drained till and iv freeze on of subglacial meltwater these may act together in one location or in isolation and a progressive increase in their distribution could lead to ice stream shut down bedrock bumps are influential under active ice streams where they provide form drag and can create thinner ice which increases the likelihood of basal freeze on increased bed roughness may prevent the lateral migration of some ice streams but bedrock bumps are unlikely to cause ice stream shut down because over long time scales ice stream erosion might be expected to reduce their amplitude the influence of till free areas beneath an ice stream will depend critically on the amount of water that might be drawn out of the surrounding till to lubricate such areas they are likely to be most important in ice stream onset zones but their identification has proved difficult beneath active ice streams if an ice stream operates solely by till deformation it is conceivable that a progressive increase in the exposure of till free areas could lead to shut down through a process of sediment exhaustion areas of strong well drained till have been identified beneath both active and ancient ice streams and are most likely to result from the reorganisation of subglacial meltwater the collapse of an inefficient cannalised system to a more efficient channelised system can occur rapidly and this mechanism has been hypothesised as a candidate for ice stream shut down in both contemporary and palaeo settings basal freeze on has also been observed and inferred from beneath modern and palaeo ice streams and a reduction in basal meltwater supply coupled with ice stream drawdown and the advection of cold ice increases the likelihood of switching off an ice stream a paucity of data from ice stream sticky spots limits a better understanding of their nature distribution and evolution beneath ice streams future technological advances are likely to improve the resolution of the data collected from the beds of modern ice streams but well preserved palaeo ice stream beds also hold potential for investigating their influence on ice stream flow and we present simple landsystems models to aid their identification such data will considerably enhance the basal boundary condition in ice stream models which will ultimately refine our predictions of the response of contemporary ice sheets to future changes in climate

decadal slowdown of a land terminating sector of the greenland ice sheet despite warming ice flow along land terminating margins of the greenland ice sheet gis varies considerably in response to fluctuating inputs of surface meltwater to the bed of the ice sheet such inputs lubricate the ice bed interface transiently speeding up the flow of ice greater melting results in faster ice motion during summer but slower motion over the subsequent winter owing to the evolution of an efficient drainage system that enables water to drain from regions of the ice sheet bed that have a high basal water pressure however the impact of hydrodynamic coupling on ice motion over decadal timescales remains poorly constrained here we show that annual ice motion across an 8 000 km 2 land terminating region of the west gis margin extending to 1 100 m above sea level was 12 slower in 2007 14 compared with 1985 94 despite a 50 increase in surface meltwater production our findings suggest that over these three decades hydrodynamic coupling in this section of the ablation zone resulted in a net slowdown of ice motion not a speed up as previously postulated increases in meltwater production from projected climate warming may therefore further reduce the motion of land terminating margins of the gis our findings suggest that these sectors of the ice sheet are more resilient to the dynamic impacts of enhanced meltwater production than previously thought

basal conditions beneath a soft bedded polythermal surge type glacier bakaninbreen svalbard original article can be found at http www sciencedirect com science journal 10406182 copyright elsevier ltd and the international union for quaternary research inqua doi 10 1016 s1040 6182 01 00053 2 full text of this article is not available in the uhra

tv video observations of bed and basal sliding on storglaciaren sweden four boreholes in storglaciaren a small valley glacier in northernsweden were inspected with a video camera in two of the boreholes the apparentglacier bed was filmed in one borehole the bed was found to be composed of softsediment but in the other it consisted of bedrock in the latter the camera moved5 6 mm relative to the bed during an 80 min period the recorded camera movementshowed a background motion which is in the expected range of basal sliding superimposed on the background motion a jerky motion of a high speed spike wasfound the jerky motion is interpreted as a stress release induced by local topographyat the ice bed interface

merging remote sensing images for geological environmental mapping application to the cabo de gata nijar natural park spain the cabo de gata nijar natural park in spain presents certain unique characteristics which make it of great geological ecological and environmental interest as a prior step to the environmental study of the park and the impact produced by the mining activities carried out up until ten years ago the mining and waste tip areas were defined and a lithological discrimination carried out for this purpose various remote sensing techniques were employed to create high resolution image documents on which the geological and environmental mapping of the area would be based with special attention being paid to the areas of former mining activity because of its implications for the local environment the merging of remote sensing images with different spatial spectral resolutions has become a highly useful tool due to their increasing availability such is the case of the spot panchromatic and landsat thematic mapper multispectral images which are two of the most commonly used images in geological and environmental studies based on remote sensing of the numerous techniques described for merging remote sensing image data this paper analyses those based on intensity hue saturation principal component analysis spherical coordinates high pass filters and colour normalized transform using spot panchromatic and landsat tm data the research goals were 1 to analyse and compare some of the most commonly used methods 2 to select the most appropriate method for a detailed geological environmental study and 3 to apply the methodology to the cabo de gata nijar area the site of one of the most distinctive natural parks in the country

glacial hydrological system characterization using ground penetrating radar hydrological systems near the terminus of a high arctic glacier and a proglacial icing on bylot island canada were investigated using ground penetrating radar gpr the ice thickness and the location and depth of tunnels within the glacier and icing were imaged modelling of the gpr response was utilized to predict the data quality and to assist in its interpretation the unique properties of the ice enabled velocity determinations from the diffraction patterns generated by point source reflectors as well as traditional velocity surveys the propagation velocity of the radar pulses through the ice depended on the air and water content in the ice the identification of drainage tunnels was attained through pulse polarity analysis and interpolation between the profiles in gridded surveys it was found that reflectivity analysis may enable gpr to be used for acquiring three dimensional information on the thermal structure of glaciers the much more complicated structure of the icing was imaged with higher frequency antennae and it was found that general ice types could be mapped using radar stratigraphical analysis both buried slush mounds and subsurface channel fills were identified within the icing a portion of the icing near the centre of the valley floor that has persisted perennially for over 50 years was found to be sitting on a slightly higher area of the valley bottom and thus was not subjected to the same hydrothermal erosional forces as the edges of the icing setting up a feed back loop encouraging the preservation of the central core of ice and promoting the destruction and rebuilding of the edges every year

mass balance and accumulation rate across siple dome west antarctica snow accumulation rates and rates of ice thickness change mass balance are studied at several sites on siple dome west antarctica accumulation rates are derived from analyses of grossbeta radioactivity in shallow firn cores located along a 60 km transect spanning both flanks and the crest of the dome there is a north south gradient in snow accumulation rate across the dome that is consistent with earlier radar mappingof internalstratigraphy orographicprocessesprobablycontrolthisdistribution mass balance is inferred from the difference between global positioning system gps derived vertical velocities and snow accumulation rates for sites close to the firn core locations results indicatethatthere is virtually no netthicknesschangeat fourof thefive sites the exception is at the northernmost site where a small amount of thinning is detected that appearstobe inconsistentwith other studies a possiblecause ofthisanom alousthinning is recent retreatof the grounding line of ice stream d

degree day glacier mass balance modelling with applications to glaciers in iceland norway and greenland a degree day glacier mass balance model is applied to three glaciers in iceland norway and greenland for which detailed mass balance measurements are available over a period of several years model results are in good agreement with measured variations in the mass balance with elevation over the time periods considered for each glacier in addition the model explains 60 80 of the year to year variance in the elevation averaged summer season mass balance measurements on the glaciers using a single parameter set for each glacier the increase in ablation on the glaciers due to a warming of 2 c is predicted to range from about 1 m w e year 1 at the highest elevations to about 2 5 m w e year 1 at the lowest elevations predicted changes in the winter balance measured between fixed date are relatively small except at the lowest elevations on the icelandic and norwegian glaciers where the winter balance is significantly reduced equilibrium line altitudes are raised by 200 300 m on the icelandic and norwegian glaciers except at the highest elevations the winter balance of the icelandic and norwegian glaciers is predicted to decrease even if the warming is accompanied by a 10 increase in the precipitation no firm evidence of a climate related variation in the degree day factors or in the temperature lapse rate on the same glacier could be found the model furthermore reproduces large variations in the mass balance with elevation and from year to year on each glacier using the same parameter set we assume therefore that these parameters will not change significantly for the climate scenarios considered here

evolution of the internal drainage system in the lower part of the ablation area of storglaci aren sweden during the 1989 melt season ten tracer experiments were conducted to investigate seasonal diurnal and spatial variations in the internal drainage system in the ablation area of storglaciaren sweden dye was injected into moulins and dye concentration and discharge were monitored in two streams at the glacier terminus sydjakk and nordjakk dye emerged only in sydjakk transit velocities ranged from 0 07 to 0 29 m s implying that drainage was through a well defined conduit system velocity and discharge relations suggest that these conduits are part of a multi branched arborescent network of individually braided wide low passages a progressive decline in dispersivity during the early part of the melt season reflects structural changes in these conduits presumably including a decrease in the degree of braiding and an increase in size the system reached its late season configuration in early august by which time the energy dissipated by the flowing water would have sufficed to melt between 0 7 and 21 m 3 of ice per meter of conduit length depending on conduit size potential closure rates exceed melt rates on conduit walls throughout most of the drainage system and so conduits are probably full of water during periods of higher daily discharge with water pressures exceeding atmospheric pressure variations in tracer return curves and dispersivity on a diurnal time scale also appear to reflect changes in the degree of braiding in this case resulting from drowning of low divides between channels as discharge increases

melt induced speed up of greenland ice sheet offset by efficient subglacial drainage fluctuations in surface melting are known to affect the speed of glaciers and ice sheets but their impact on the greenland ice sheet in a warming climate remains uncertain although some studies suggest that greater melting produces greater ice sheet acceleration others have identified a long term decrease in greenland s flow despite increased melting here we use satellite observations of ice motion recorded in a land terminating sector of southwest greenland to investigate the manner in which ice flow develops during years of markedly different melting although peak rates of ice speed up are positively correlated with the degree of melting mean summer flow rates are not because glacier slowdown occurs on average when a critical run off threshold of about 1 4 centimetres a day is exceeded in contrast to the first half of summer when flow is similar in all years speed up during the latter half is 62 16 per cent less in warmer years consequently in warmer years the period of fast ice flow is three times shorter and overall summer ice flow is slower this behaviour is at odds with that expected from basal lubrication alone instead it mirrors that of mountain glaciers where melt induced acceleration of flow ceases during years of high melting once subglacial drainage becomes efficient a model of ice sheet flow that captures switching between cavity and channel drainage modes is consistent with the run off threshold fast flow periods and later summer speeds we have observed simulations of the greenland ice sheet flow under climate warming scenarios should account for the dynamic evolution of subglacial drainage a simple model of basal lubrication alone misses key aspects of the ice sheet s response to climate warming

mineralized and unmineralized calderas in spain part ii evolution of the rodalquilar caldera complex and associated gold alunite deposits the rodalquilar caldera complex is located in the western part of the cabo de gata volcanic field in southeastern spain and is the first documented example of epithermal gold alunite mineralization within a caldera in europe the rodalquilar caldera is an oval collapse structure having a maximum diameter of 8 km and formed at 11 ma from eruption of the cinto ash flow tuff the oval lomilla caldera with a diameter of 2 km is nested within the central resurgent dome of the older rodalquilar caldera the lomilla caldera resulted from the eruption of the lazaras ash flow tuff which was ponded within the moat of the rodalquilar caldera the last phase of volcanic activity in the caldera complex was the emplacement of hornblende andesite flows and intru sions this magmatic event resulted in structural doming of the caldera opening of fractures and faults and pro vided the heat source for the large hydrothermal systems which deposited quartz alunite type gold deposits and base metal vein systems the gold alunite deposits are enclosed in areas of intense acid sulfate alteration and localized in ring and radial faults and fractures present in the east wall of the lomilla caldera like other acid sul fate type deposits the rodalquilar gold alunite deposits are closely related in time and space to porphyritic inter mediate composition magma emplaced along caldera structures but unrelated to the caldera forming magmatic system

fluid evolution wallrock alteration and ore mineralization associated with the rodalquilar epithermal gold deposit in southeast spain at rodalquilar gold mineralization is found in late tertiary volcanic rocks of the sierra del cabo de gata and is related to a caldera collapse radial and concentric faults were preferred sites for gold deposition hydrothermal activity produced a specific alteration zoning around gold bearing vein structures grading from an innermost advanced argillic via an argillic into a more regionally developed propylitic zone advanced argillic alteration with silica pyrophyllite alunite and kaolinite extends down to several hundred m indicating a hypogene origin high grade gold mineralization in vein structures is confined to the near surface part of the advanced argillic alteration fine grained gold is associated with hematite jarosite limonite or silica at a depth of about 120 m the oxidic ore assemblage grades into sulfide mineralization with pyrite and minor chalcopyrite covellite bornite enargite and tennantite two types of fluids from different sources were involved in the hydrothermal system overpressured and hypersaline fluids of presumably magmatic origin initiated the hydrothermal system subsequent hydrothermal processes were characterized by the influx of low salinity solutions of probable marine origin and by interactions between both fluids deep reaching advanced argillic alteration formed from high salinity fluids with 20 30 equiv wt nacl at about 225 c near surface gold precipitation and silification are related to fluids with temperatures of about 175 c and 3 4 equiv wt nacl gold was transported as au hs 2 and precipitation resulted from boiling with a concomitant decrease in temperature pressure and ph and an increase in fo2 all features of the rodalquilar gold deposit reveal a close relationship to acid sulfate type epithermal gold mineralization

constraining controls on carbonate sequences with high resolution chronostratigraphy upper miocene cabo de gata region se spain abstract a high resolution chronostratigraphy has been developed for miocene shallow water carbonate strata in the cabo de gata region of se spain for evaluation of local regional and global factors that controlled platform architecture prior to and during the messinian salinity crisis paleomagnetic data were collected from strata at three localities mean natural remanent magnetization nrm ranges between 1 53 10 8 and 5 2 10 3 am 2 kg incremental thermal and alternating field demagnetization isolated the characteristic remanent magnetization chrm rock magnetic studies show that the dominant magnetic mineral is magnetite but mixtures of magnetite and hematite occur a composite chronostratigraphy was derived from five stratigraphic sections regional stratigraphic data biostratigraphic data and an 40 ar 39 ar date of 8 5 0 1 ma for an interbedded volcanic flow place the strata in geomagnetic polarity chrons c4r to c3r sequence stratigraphic and diagenetic evidence indicate a major unconformity at the base of depositional sequence ds 3 that contains a prograding reef complex suggesting that approximately 250 000 yr of record subchrons c3br 2r to 3br 1r are missing near the messinian tortonian boundary correlation to the gpts shows that the studied strata represent five third to fourth order dss basal units are temperate to subtropical ramps ds1a ds1b ds2 these are overlain by subtropical to tropical reefal platforms ds3 which are capped by subtropical to tropical cyclic carbonates terminal carbonate complex tcc correlation of the cabo de gata record to the melilla area of morocco and the sorbas basin of spain indicate that early late tortonian ramp strata from these areas are partially time equivalent similar strata are extensively developed in the western mediterranean and likely were influenced by a cool climate or influx of nutrients during an overall rise in global sea level after ramp deposition a sequence boundary sb3 in cabo de gata correlates with a sequence boundary in morocco and a published third order eustatic fall suggesting at least a partial eustatic control for the sequence boundary coral reefs began to develop earlier in cabo de gata than at melilla or sorbas arguing for local factors affecting this major environmental transition later messinian reefs ds3 from all areas are time equivalent suggesting a regional or global control on their formation some halimeda rich horizons in the western mediterranean are not time equivalent event strata as hypothesized by others correlation of the relative sea level curve for the fringing reef complex ds3 with a published eustatic curve suggests at least a partial third order global eustatic control for the highstand part of the sequence downstepping ds3 reefs and initial subaerial exposure of earlier ds3 reef strata approximately correlate with initiation of a series of subaerial unconformities in the south pacific the longer term relative fall in sea level during ds3 downstepping reef progradation does not correlate with a published third order eustatic fall eustatic sea level fluctuations may have been associated with initiation of the mediterranean messinian salinity crisis but the longer term fall may have been linked to tectonic uplift in the mediterranean region widespread distribution of tcc style cycles of approximately the same age suggests a regional western mediterranean or global control on sea level change responsible for tcc cycles in addition four subaerial exposure capped tcc cycles may correlate with similar subaerial unconformities in the south pacific suggesting at least a partial eustatic control on tcc cyclicity the high rates of relative sea level change needed to generate a minimum of 25 30 m sea level changes associated with each cycle are consistent with glacio eustacy along with rapid evaporitic drawdown in the mediterranean

glacier mass balance determination by remote sensing and high resolution modelling an indirect methodology for determining the distribution of mass balance at high spatial resolution using remote sensing and ice flow modelling is presented the method based on the mass continuity equation requires two datasets collected over the desired monitoring interval i the spatial pattern of glacier surface elevation change and ii the mass flux divergence field at haut glacier d arolla valais switzerland the mass balance distribution between september 1992 and september 1993 is calculated at 20 m resolution from the difference between the pattern of surface elevation change derived from analytical photogrammetry and the mass flux divergence field determined from three dimensional numerical flow modelling constrained by surface velocity measurements the resultant pattern of mass balance is almost totally negative showing a strong dependence on elevation but with large localized departures the computed distribution of mass balance compares well r 2 0 91 with mass balance measurements made at stakes installed along the glacier centre line over the same period despite the highly optimized nature of the flow modelling effort employed in this study the good agreement indicates the potential this method has as a strategy for deriving high spatial and temporal resolution estimates of mass balance

marine ice sheet collapse potentially under way for the thwaites glacier basin west antarctica resting atop a deep marine basin the west antarctic ice sheet has long been considered prone to instability using a numerical model we investigated the sensitivity of thwaites glacier to ocean melt and whether its unstable retreat is already under way our model reproduces observed losses when forced with ocean melt comparable to estimates simulated losses are moderate 1 mm per year of sea level rise collapse in the different simulations within the range of 200 to 900 years

deformation of till beneath ice stream b west antarctica the behaviour and possible instability of the west antarctic ice sheet depend fundamentally on the dynamics of the large ice streams which drain it model calculations show that most ice stream velocity arises at the bed1 2 and radar sounding has shown the bed to be wet3 but the basal boundary condition is not well understood seismic evidence from the upstream b camp upb on the siple coast of west antarctica4 shows that the ice stream there rests on a layer of unconsolidated sediment averaging 5 or 6 m thick in which the water pressure is only 50 kpa less than the overburden pressure because this thin layer occurs well inland beneath an active ice sheet and rests on a surface showing flutes4 characteristic of glacial erosion5 we presume that it is glacial till we propose here that deformation within the till is the primary mechanism by which the ice stream moves and we discuss implications of this hypothesis

black box modeling of the subglacial water system measurements of water pressure beneath trapridge glacier yukon territory canada yield the following generalizations about subglacial conditions in the studied region 1 even over short distances the subglacial water system is highly heterogeneous 2 the subglacial water system consists of at least two distinct components which we refer to as the connected and unconnected water systems 3 regions of the glacier bed can switch back and forth from being part of the connected or part of the unconnected water system 4 large spatial pressure gradients can exist within the unconnected water system and between the connected and unconnected systems 5 rapid pressure variations can occur in the unconnected water system 6 pressure variations in the unconnected water system do not match those in the connected system and can in fact be strongly anticorrelated with pressure variations in the connected system if the water pressure variations in the connected system are viewed as a forcing and those in the unconnected system as a response to this forcing the input output relation between forcing and response can be efficiently represented as a low order nonlinear ordinary differential equation the response of the unconnected system to forcing from the connected system is governed by time constants having approximate magnitudes of 1 7 hours and 7 4 hours that we believe are associated with process rates for substrate compression and pore water diffusion respectively

comparison of thermal structure and evolution between neighboring subarctic glaciers 1 the distribution of cold and temperate ice within glaciers and ice sheets affects processes relevant to englacial and basal hydrology sliding and material rheology thermal regimes in turn are shaped by glacier and ice sheet dynamics as well as environmental setting we investigate the thermal structures of two small 7 km2 neighboring glaciers in the st elias mountains of southwestern yukon canada using ice penetrating radar and borehole temperature measurements our data reveal polythermal regimes in both glaciers that are strongly influenced by accumulation zone meltwater entrapment suggesting a climatic control on thermal structure differences in hypsometry and glacier dynamics nevertheless result in observed variations in the distribution of temperate ice between the two sites experiments with a thermomechanically coupled flow band model corroborate the strong control of meltwater entrapment on thermal structure and suggest a generally minimal role for strain heating an exception to this occurs where localized basal sliding produces lateral shearing and thus enhanced heat generation time dependent model simulations suggest that the future thermal evolution of the two glaciers may differ and therefore simple parameterizations of thermal response based on regional climate may not capture realistic variability between individual glaciers despite these differences both glaciers are ultimately expected to become fully cold prior to disappearing under negative mass balance conditions

major changes in ice stream dynamics during deglaciation of the north western margin of the laurentide ice sheet abstract victoria island lies at the north western limit of the former north american laurentide ice sheet in the canadian arctic archipelago and displays numerous cross cutting glacial lineations previous work suggests that several ice streams operated in this region during the last wisconsinan glaciation and played a major role in ice sheet dynamics and the delivery of icebergs into the arctic ocean this paper produces the first detailed synthesis of their behaviour from the last glacial maximum through to deglaciation 21 9 5 cal ka bp based on new mapping and a previously published radiocarbon constrained ice sheet margin chronology over 70 discrete ice flow events flow sets are fitted to the ice margin configuration to allow identification of several ice streams ranging in size from large and long lived thousands of years to much smaller and short lived hundreds of years the reconstruction depicts major ice streams in m clure strait and amundsen gulf which underwent relatively rapid retreat from the continental shelf edge at some time between 15 2 and 14 1 cal ka bp a period which encompasses climatic warming and rapid sea level rise meltwater pulse 1a following this overall retreat was slower and the ice streams exhibited asynchronous behaviour the amundsen gulf ice stream continued to operate during ice margin retreat whereas the m clure strait ice stream ceased operating and was replaced by an ice divide within 1000 years this ice divide was subsequently obliterated by another short lived phase of ice streaming in m clintock channel 13 cal ka bp the timing of this large ice discharge event coincides with the onset of the younger dryas subsequently a minor ice divide developed once again in m clintock channel before final deglaciation of the island shortly after 9 5 cal ka bp it is concluded that large ice streams at the nw margin of the laurentide ice sheet equivalent in size to the hudson strait ice stream underwent major changes during deglaciation resulting in punctuated delivery of icebergs into the arctic ocean published radiocarbon dates constrain this punctuated delivery as far as is possible within the limits imposed by their precision and we note their coincidence with pulses of meltwater delivery inferred from numerical modelling and ocean sediment cores

rapid soft bed sliding of the puget glacial lobe the puget lobe of the late pleis inferred to be lodgment till based on the tocene cordilleran ice sheet advanced into presence of oriented stones oriented stria western washington over a thick sequence of tions on stones overconsolidation and unlithified sediments the basal drag due to deformation features sliding over this surface was calculated by 1 this paper investigates the rapid motion of idealizing the sediment bed as a rigid planar the puget lobe over its bed of deformable sedi surface scattered with roughness elements cor ment studies of large vanished glaciers com responding to individual sedimentary particles plement basal motion studies of modern glaci and 2 taking the minimum reconstructed slid ers in which the glacier geometry and velocity ing velocity to be 500 m yr 1 the calculated are well constrained but the characteristics of basal drag minimized by choices of parameters the bed can only be inferred from observations is 400 kpa much higher than the reconstructed over very limited areas kamb et al 1985 gravitational driving stress of 40 kpa indi seismic measurements blankenship et al 1986 cating that a rigid bed and low water pressure or modelling lingle and brown 1987 obser are not consistent with the glacierfs rapid vations on glacier beds recently exposed by motion high subglacial water pressure aver glacial retreat can provide information about aging 90 of the ice overburden 10 mpa is conditions during a somewhat greater time span inferred from overconsolidation of subglacial but are restricted to the marginal environ clays the occurrence and deformation of ment in addition inferences about the bed of water deposited sediments within the till and modern glaciers are limited by the short dura the requirement to drain large quantities of tion and seasonality of the observations a water from the interface suggest that water notable benefit of studying the beds of pieis pressure reached 99 of the ice overburden tocene glaciers is that they record basal ploughing of till by ice entrained clasts per conditions for intervals spanning entire glaci vasive shearing and finally ice bed separa ations and accessible far from the glacier tion become possible as water pressure margins increases at the low inferred effective nor after a brief summary of data available from mal stress the basal drag is reduced from the previous reconstructions of the puget lobe the rigid bed case by water layers which decouple basal conditions of the lobe are explored along the smallest particles from the glacier sole two complementary lines we first present cal and ploughing which reduces the resistance culations of basal drag due to glacier sliding offered by the largest particles the limited for different models of till bed roughness that shear strain observed in much of the till indicate that rapid sliding requires very low implies pervasive shearing did not contribute effective stresses and extensive ice bed significantly to ice motion basal motion was decoupling or ploughing second we summarize confined to the ice bed interface or to dis geological and geotechnical data that indicate tinct faults within the substrate

ore deposits and epithermal evidences associated with intra magmatic faults at ain el araâr oued belif ring structure nw of tunisia hydrothermal ore deposits at ain el ara r oued belif location are classified as epithermal deposits type the ore bodies are hosted by upper turonian 8 9 m y volcanic rhyodacitic complex polymetallic sulfide orebodies are mainly concentrated within intra magmatic faults petrographic xrd and tem stem investigations revealed that ore minerals are essentially arsenopyrite pyrite chalcopyrite pyrrhotite hematite goethite and magnetite with au ag and pt trace metals gangue minerals are mainly adularia quartz sericite alunite tridymite chlorite phlogopite and smectite epithermal alteration is well zoned with four successive characteristic zones 1 zone of quartz adularia sericite and rare alunite 2 zone of kaolinite and plagioclase albitization 3 intermediate zone of illite sericite 4 sapropelic alteration type zone of chlorite smectite and rare illite this can be interpreted as a telescoping of two different acidity epithermal phases low sulfidation adularia sericite and high sulfidation quartz alunite separated in time or due to a gradual increase of fluids acidity and oxicity within the same mineralization phase brecciated macroscopic facies with fragments hosting quartz adularia sericite minerals low sulfidation phase without alunite support the last hypothesis geodynamic context and mineral alteration patterns are closely similar to those of maria josefa gold mine at se of spain which exhibit a volcanic hosted epithermal ore deposit in a similar vein system within rhyolitic ignimbrites altered to an argillic assemblage illite sericite abundant and subordinate kaolinite that grades outwards into propylitic alteration sanger von oepen et al 1990 mineralogical and lithologic study undertaken in the volcanic host rock at ain el ara r oued belif reveals a typical epithermal low sulfidation and high sulfidation ore deposits with dominance of low sulfidation host rocks in these systems range from silicic to intermediate for adularia sericite type low sulfidation to rhyodacite for quartz alunite type high sulfidation

direct observations of evolving subglacial drainage beneath the greenland ice sheet simultaneous observations of moulins and boreholes in western greenland show that water delivery to the base of the ice sheet via moulins affects short term ice velocity fluctuations but not late season ice velocity decelerations increased meltwater delivery to the base of the greenland ice sheet will increase the ice sheet velocity accelerating its inevitable rush towards the ocean and subsequent sea level rise or will it debate on this topic is at the forefront of cryospheric research but has been hampered by the lack of simultaneous observations of hydraulic head in moulins vertical shafts that deliver water to the base of the ice sheet and boreholes which monitor basal water pressure lauren andrews and colleagues now provide these observations from a small region in western greenland and reveal that water delivery by moulins into channelized basal flow is indeed linked to short term fluctuations in ice velocity late season decelerations in ice velocity however seem to be controlled by changes in unchannelized flow rather than any shifts in the moulin system seasonal acceleration of the greenland ice sheet is influenced by the dynamic response of the subglacial hydrologic system to variability in meltwater delivery to the bed1 2 via crevasses and moulins vertical conduits connecting supraglacial water to the bed of the ice sheet as the melt season progresses the subglacial hydrologic system drains supraglacial meltwater more efficiently1 2 3 4 decreasing basal water pressure4 and moderating the ice velocity response to surface melting1 2 however limited direct observations of subglacial water pressure4 5 6 7 mean that the spatiotemporal evolution of the subglacial hydrologic system remains poorly understood here we show that ice velocity is well correlated with moulin hydraulic head but is out of phase with that of nearby 0 3 2 kilometres away boreholes indicating that moulins connect to an efficient channelized component of the subglacial hydrologic system which exerts the primary control on diurnal and multi day changes in ice velocity our simultaneous measurements of moulin and borehole hydraulic head and ice velocity in the paakitsoq region of western greenland show that decreasing trends in ice velocity during the latter part of the melt season cannot be explained by changes in the ability of moulin connected channels to convey supraglacial melt instead these observations suggest that decreasing late season ice velocity may be caused by changes in connectivity in unchannelized regions of the subglacial hydrologic system understanding this spatiotemporal variability in subglacial pressures is increasingly important because melt season dynamics affect ice velocity beyond the conclusion of the melt season8 9 10

borehole water level variations and the structure of the subglacial hydrological system of haut glacier d arolla valais switzerland late summer subglacial water pressures have been measured in a dense array of boreholes in the ablation area of haut glacier d arolla switzerland interpolated surfaces of minimum diurnal water pressure and diurnal water pressure variation suggest the presence of a subglacial channel within a more widespread distributed drainage system the channel flows along the centre of a variable pressure axis vpa some tens of metres wide that is characterized by low minimum diurnal water pressures frequently atmospheric and high diurnal water pressure variations these characteristics are transitional over a lateral distance of c 70 m to higher and more stable subglacial water pressures in the adjacent distributed system water pressure variations recorded in boreholes located close to the centre of the vpa reflect the delivery of surface derived meltwater to the glacier bed and result in a diurnally reversing transverse hydraulic gradient that drives water out from the channel into the distributed system during the afternoon and back to the channel overnight subglacial observations suggest that such flow occurs through a vertically confined sediment layer borehole turbidity records indicate that the resulting diurnal water flows are responsible for the mobilization and transport of fine debris in suspension analysis of the propagation velocity and amplitude attenuation of the diurnal pressure waves suggests that the hydraulic conductivity of the sediment layer decreases exponentially with distance from the channel falling from c 10 4 m s 1 at the channel boundary to c 10 7 ms 1 70m away these apparent hydraulic conductivities are consistent with darcian flow through clean sand and typical glacial till respectively we suggest that fine material is systematically flushed from basal sediments located adjacent to large melt season drainage channels beneath warm based glaciers this process may have important implications for patterns of glacier erosion hydrochemistry and dynamics

potential of esa s sentinel 2 for geological applications abstract sentinel 2 is esa s medium spatial resolution 10 60 m super spectral instrument aimed at ensuring data continuity for global land surface monitoring of landsat and spot several simulation studies have been conducted that show the potential of sentinel 2 for estimating biophysical and biochemical parameters such as leaf area index chlorophyll and nitrogen and spectral products such as the red edge position and ndvi time series providing data continuity for a number of other operational sensors this paper aims at simulating sentinel 2 products that are relevant to the geology and soil science community and we compare these to well established band ratio products from aster as the basis for the simulation we use airborne hyperspectral imagery from the hymap sensor which were spectrally and spatially resampled to the resolutions of aster and sentinel 2 using actual spectral response functions and pixel aggregate respectively the simulated image products demonstrate a good correspondence between aster and sentinel 2 vnir and swir bands a number of band ratios are proposed for sentinel 2 to derive the following products ferric iron ferrous iron laterite gossan ferrous silicate and ferric oxides these are compared to established band ratios of real aster data as well as simulated from hymap aster data and they correlate favourably investigating the spatial patterns reveals that there is a good match between the proposed sentinel 2 band ratio products and those of aster the resulting band ratio products are compared to the local geologic map of the imaged hydrothermal area the rodalquilar mining area cabo de gata volcanic field se spain it is shown that they support the existing conceptual geologic model of the epithermal deposit

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

subglacial till a physical framework for its properties and processes the continuum theory of mixtures provides a framework around which present knowledge of subglacial till can be organized the proposed framework is provisional in two senses the constitutive description of till will require improvement and not all potentially significant processes have been included till is treated as a three component mixture of water clasts coarse grained solids and fine grained matrix solids these components obey mass balance equations and their behavior is subject to constitutive relations that describe such processes as darcian water transport fine grained sediment transport consolidation shear deformation dilatancy and comminution five state variables uniquely determine the compressibility permeability shear strength and other physical properties numerical solutions of the state evolutions equations illustrate that the properties of till are highly responsive to changes in the subglacial environment

review of subglacial hydro mechanical coupling trapridge glacier yukon territory canada abstract the interaction of basal processes with the subglacial drainage system is a critical issue in understanding glacier dynamics since the recognition that many glaciers and ice masses overlie soft sediments rather than hard bedrock much research has been undertaken to investigate how mechanical and hydrological conditions of a deformable substrate control the coupling at the ice bed interface and thus affect fast ice flow and glacier surging in research undertaken on trapridge glacier a small surge type glacier in the st elias mountains yukon territory canada we have combined extensive field investigations using novel measurement techniques and theoretical modelling to study hydro mechanical coupling processes measurements of subglacial water pressure indicate that the basal water system can be dramatically inhomogeneous both spatially and temporally since ice bed coupling is strongly influenced by subglacial water pressure the stresses at the bed are also markedly heterogeneous and are expected to form a patchwork distribution which mimics the pressure distribution of the basal water system this heterogeneity in the stress field at the ice bed interface introduces a pronounced variability to the basal motion mechanics as such basal sliding and subglacial sediment deformation are not steady and continuous processes instead the variability of the subglacial water system leads to a spatial and temporal interplay of increased ice bed coupling at low water pressures at one site or time with ice bed decoupling during rising water pressures at other sites or times thus on the one hand there is downglacier shear deformation of the bed and accumulation of elastic strain in ice and sediment while on the other hand there is enhanced slip sliding of the glacier and upglacier shear motion of the bed due to an elastic relaxation of the sediment

bedform topography and basal conditions beneath a fast flowing west antarctic ice stream a grid of seismic reflection lines has been used to image basal topography and infer basal conditions and flow processes beneath similar to 140 km 2 of rutford ice stream west antarctica the subglacial topography in this region consists of two troughs flanking a central high and the bed is composed of water saturated sediments the two troughs are filled with deforming sediment whereas the bed in the central region appears to undergo a transition from largely deforming conditions upstream to basal sliding downstream the deforming bed is very flat along flow but undulates across flow sliding areas show rougher bed topography cross stream bed topography is characterised by streamlined mounds of deforming sediment aligned in the ice flow direction these bedforms occur superimposed on the bed in regions of both basal sliding and sediment deformation in places they form finger like mounds of material which extend into the sliding region further downstream mean bedform height is 22 m mean width is 267 m and many of them extend for at least 1 2 km along flow we interpret most of these bedforms as drumlins and one as a mega scale glacial lineation the juxtaposition of different basal conditions is consistent with models proposed from terrestrial studies in which the glacier bed is a mosaic of stable and deforming bed areas variable both spatially and temporally any theory of subglacial sediment rheology must also be able to account for our conclusion that at any given time pervasive deformation extends at least a few metres into the bed and can persist over a considerable area many km 2 bedform geometry and basal conditions concur with interpretations of former ice streams with evidence for increasing elongation ratio with distance downstream however those studies also identified bedrock cropping out at the ice bed interface for which there is no evidence on rutford ice stream c 2008 elsevier ltd all rights reserved