rapid eocene extension in the chapedony metamorphic core complex central iran constraints from 40ar 39ar dating abstract the neybaz chatak detachment system accommodated nne directed extension along the southwest central iranian plateau during eocene time the detachment is mainly exposed as southeast and north west dipping low angle normal fault for more than 100 km along strike of a ne trending structural dome structural data and abundant migmatite granite and diorite show features typical for a mantled gneiss dome coupled with peak p t conditions of ca 3 kbar and 650 750 c new hornblende muscovite biotite and k feldspar 40ar 39ar ages together with published u pb zircon and u th he apatite and zircon ages imply rapid cooling from ca 750 c to 60 c of the chapedony complex between 49 and 30 ma the neybaz chatak detachment comprises low grade hydrous mylonites with 40ar 39ar white mica ages of ca 43 ma interpreted to date activity along the shear zone ca 20 100 m thick cataclasites and hydrothermal chlorite breccias separate the footwall from the overlying hangingwall unit the documentation of eocene coeval compression in the neotethyan suture and extension in central iranian plateau has important implications for the understanding of the dynamics of collisional orogenesis

magmatism as a response to exhumation of the priest river complex northern idaho constraints from zircon u pb geochronology and hf isotopes abstract zircon and monazite u pb geochronology and zircon hf isotopes place constraints on the temporal and source relationships between crustal anatexis magmatism and exhumation of the priest river metamorphic core complex northern idaho granitoids that intruded the migmatitic pelitic hauser lake gneiss include the

high temperature hydrothermal alteration of the boehls butte anorthosite origin of a bimodal plagioclase assemblage the boehls butte anorthosite consists predominantly of an unusual bimodal assemblage of andesine and bytownite anorthite oxygen isotope compositions of the anorthosite were profoundly altered by high temperature retrograde interaction with meteoric hydrothermal fluids that varied in composition from isotopically evolved to nearly pristine meteoric water oxygen isotope ratios of bulk plagioclase separates are in the range 7 0 to 6 2 v smow however secondary ion mass spectrometry indicates spot sized isotope values as low as 16 typical inter and intra plagioclase grain variability is 3 6 and extreme heterogeneity of up to 20 is noted in a few samples high temperature hydrothermal alteration of intermediate plagioclase is proposed to explain the origin of bytownite anorthite in the anorthosite and creation of its unusual bimodal plagioclase assemblage the anorthite forming reaction created retrograde reaction enhanced permeability which together with rapid decompression extension and unroofing of the anorthosite complex helped to accommodated influx of significant volumes of meteoric hydrothermal fluids into the anorthosite

changes in glacial meltwater alter algal communities in lakes of scoresby sund renland east greenland throughout the holocene abrupt reorganizations began 1000 years before present we investigated the response of lake algal communities to changes in glacial meltwater from the renland ice cap greenland through the holocene to assess whether influxes always elicit consistent responses or novel responses we measured sedimentary algal pigments in two proximal lakes snow fed raven and glacier and snow fed bunny lake and diatom community structure and turnover in bunny lake diatom data were not available in raven lake we also modeled lake level change in bunny lake to identify how glacial meltwater may have altered diatom habitat availability through time through a series of glacier advances and retreats over the holocene the algal response in bunny lake was relatively constant until approximately 1015 yr bp after which there were major changes in sedimentary algal remains algal pigment concentrations sharply declined and diatom species richness increased diatom community structure underwent three reorganizations until 1015 yr bp assemblages were dominated by pinnularia braunii and aulacoseira pffaffiana however approximately 1015 480 yr bp these species declined and tabellaria flocculosa and hannaea arcus became a significant component of the assemblage approximately 440 yr bp a pfaffiana increased along with species indicating elevated nitrogen in contrast the algal pigment records from nearby snow fed raven lake showed different and minimal change through time our results suggest that changes in the magnitude and composition of meltwater in our two study lakes were unique over the last 1000 yr bp and elicited a non linear threshold response absent during other periods of glacier advance and retreat deciphering the degree to which glaciers structure algal communities over time has strong implications for lakes as glaciers continue to recede

paleogeographic reconstruction of the eocene idaho river north american cordillera eocene lake gosiute in southwestern wyo ming was progressively fi lled in by volcani clastic sediment between 49 6 and 47 0 ma the source of this material has long been thought to have been the absaroka volcanic province immediately north of the greater green river basin lead isotope compositions of sandstone from this interval however are consistent with derivation from the challis volcanic fi eld the 40 ar 39 ar ages of single de trital k feldspar crystals from greater green river basin sandstones are nearly identical to 40 ar 39 ar eruptive ages for volcanic rocks of the challis volcanic fi eld 49 8 45 5 ma but we also identify mesozoic and proterozoic crystals that are consistent with cooling ages for rocks that were likely exposed in the idaho segment of the north american cordillera during the eocene most of these rocks are traversed by or are up gradient of a major eocene paleovalley in central idaho the sud den appearance of challis derived sediment in the greater green river basin indicates that a major river here named the idaho river connected the interior of the north american cordillera to the greater green river basin this connection requires 500 km to reach from central idaho to the greater green river ba sin the idaho river probably carried detritus that was stripped from distant uplifted moun tains above the active challis volcanic fi eld as far south as the piceance creek basin suggest ing a total length of at least 1000 km middle eocene metamorphic core complexes in the northern cordillera likely produced a major highland in the headwaters of the idaho river which generated river systems that drained both eastward into the wyoming foreland and westward into the oregon coast ranges

in stream uptake and retention of c n and p in a supraglacial stream supraglacial streams form annually during the melt season transporting dissolved solutes from the melting ice and snowpack to subglacial flow paths and the glacier terminus although nutrient and carbon processing has been documented in other supraglacial environments cryoconite holes snowpack little work has examined the potential for in stream nutrient retention in supraglacial streams here we carried out a solute nutrient injection experiment to quantify nh3 p o 4 3 and labile dissolved organic carbon doc retention in a supraglacial stream the experiment was performed on a 100 m stream reach on mendenhall glacier an outlet glacier on the juneau icefield southeastern alaska usa the study stream contained two distinct reaches of equal length the first reach had a lower velocity 0 04 m s 1 and contained abundant gravel sediment lining the ice water interface while the second reach was devoid of bedload sediment and had an order of magnitude higher velocity at the end of the second reach the stream emptied into a moulin which is typical of supraglacial streams on this and other temperate glaciers we found that n and p were transported largely conservatively although no3 increased along the reach suggestive of nitrification labile doc was retained slightly within the stream although rates were low relative to the travel times observed within the supraglacial stream although our findings show that these streams have low processing rates measurable in stream nitrification and dissolved organic matter uptake within this biologically unfavorable environment suggests that supraglacial streams with longer residence times and abundant fine substrate have the potential to modify and retain nutrients during transport to the glacier terminus

geometry bed topography and drainage system structure of the haut glacier d arolla switzerland as part of an integrated study of the hydrology meltwater quality and dynamics of the haut glacier d arolla switzerland the glacier s drainage network structure was determined from patterns of dye recovery in 342 injection experiments conducted from 47 moulins distributed widely across the glacier this structure was compared with theoretical predictions based upon reconstructed patterns of water flow governed by a the subglacial hydraulic potential surface and b the subglacial bedrock surface these reconstructions were based on measurements of ice surface and bedrock topography obtained by a combination of ground survey and radio echo sounding techniques the two reconstructions simulate the drainage system structures expected for a closed channels in which water is pressurized by the overlying ice and b gravity driven open channel flow the closed channel model provides the best fit to the observed structure even though theoretical calculations suggest that under summer discharge conditions open channel flow may be widespread beneath the glacier possible reasons for this apparent discrepancy are discussed

an integrated approach to modelling hydrology and water quality in glacierized catchments the results are summarized of an integrated investigation of glacier geometry ablation patterns water balance meltwater routing hydrochemistry and suspended sediment yield the ultimate objective is to evaluate the assumptions of lumped two component mixing models as descriptors of glacier hydrology and to develop a semi distributed physically based model as an alternative the results of the study demonstrate that a reconstruction of probable subglacial drainage alignments can be achieved through a combination of terrain modelling based on estimated potential surface and dye tracing experiments recession curve analysis evidence of the seasonal instability of the englacial and subglacial electrical conductivities assumed in a mixing model evidence of the non conservative behaviour of water chemistry in the presence of suspended sediment and evidence of the seasonal evolution of the subglacial drainage system based on dye tracing all indicate that an alternative to a lumped static model of the hydrology is necessary the alternative presented in this paper is based on the combination of an energy balance model for surface melt which operates on an hourly time step and accounts for the changing spatial distribution of melt through the day as shading patterns change and routing procedures that transfer surface melt to moulins on the basis of glacier surface gradients then route water through reconstructed conduit systems using a hydraulic sewer flow routing procedure

relocation analysis of earthquakes near nanga parbat haramosh massif northwest himalaya pakistan locations of earthquakes that have occurred between 1970 and 1988 in the northwest himalaya of pakistan as computed by the isc were analyzed to improve knowledge of the spatial distribution of seismicity near the nanga parbat haramosh massif nphm a set of 15 earthquakes were relocated using the multiple event relocation technique of jordan and sverdrup 1981 earthquakes located using records from at least 25 to 30 stations tend to be well located in the isc database smaller error ellipses and shorter distance of relocation these analyses indicate that earthquakes with magnitudes mb 4 0 have occurred since 1970 along the nphm

neotectonics of the nanga parbat syntaxis pakistan and crustal stacking in the northwest himalayas the northwest termination of the himalayan arc is marked by two large antiformal structures termed syntaxes and a nw se zone of intermediate depth earthquakes which have yielded both strike slip and thrust sense fault plane solutions this contribution presents new structural data from the nanga parbat area the northern syntaxis one of the fastest rising portions of the orogen 7 mm yr 1 our studies show uplift related to syntaxis growth to be accommodated by structures located along its western margin fault kinematics in the southern part of the margin indicate nw directed thrusting along a shear zone and high level cataclastic faults termed the liachar thrust zone this carries amphibolite facies basement rocks out onto quaternary sediments further north along the western margin active faults are dominantly dextral strike slip oriented north south e g the shahbatot fault overprinting relationships suggest that the strike slip fault zone has migrated southwards into the nw directed thrust zone these relationships are consistent with the northwest termination of the arcuate himalayan thrust belt at a lateral tip generating folding and radial thrust directions faulting patterns at nanga parbat suggest that this tip zone has migrated southwards active faulting is now concentrated in the northwest continuation of the hazara southern syntaxis along a seismogenic strike slip and thrust zone these deep level tips lie on the crustal stacking thrusts which cut through the higher level sse directed thrusts of pakistan

use of regression based models to map sensitivity of aquatic resources to atmospheric deposition in yosemite national park usa 1 an abundance of exposed bedrock sparse soil and vegetation and fast hydrologic flushing rates make aquatic ecosystems in yosemite national park susceptible to nutrient enrichment and episodic acidification due to atmospheric deposition of nitrogen n and sulfur s in this study multiple linear regression mlr models were created to estimate fall season nitrate and acid neutralizing capacity anc in surface water in yosemite wilderness input data included estimated winter n deposition fall season surface water chemistry measurements at 52 sites and basin characteristics derived from geographic information system layers of topography geology and vegetation the mlr models accounted for 84 and 70 of the variance in surface water nitrate and anc respectively explanatory variables and the sign of their coefficients for nitrate included elevation positive and the abundance of neoglacial and talus deposits positive unvegetated terrain positive alluvium negative and riparian negative areas in the basins explanatory variables for anc included basin area positive and the abundance of metamorphic rocks positive unvegetated terrain negative water negative and winter n deposition negative in the basins the mlr equations were applied to 1407 stream reaches delineated in the national hydrography data set for yosemite and maps of predicted surface water nitrate and anc concentrations were created predicted surface water nitrate concentrations were highest in small high elevation cirques and concentrations declined downstream predicted anc concentrations showed the opposite pattern except in high elevation areas underlain by metamorphic rocks along the sierran crest which had relatively high predicted anc 200 eq l 1 maps were created to show where basin characteristics predispose aquatic resources to nutrient enrichment and acidification effects from n and s deposition the maps can be used to help guide development of water quality programs designed to monitor and protect natural resources in national parks

a m gurnell and m j clark eds 1987 glacio fluvial sediment transfer an alpine perspective chichester etc john wiley and sons ltd

hydraulic properties of subglacial sediment determined from the mechanical response of water filled boreholes freezing of water filled boreholes drives water into the subglacial bed and the associated pressure effects yield information about subglacial hydraulic properties a numerical model describing the mechanical response of an unconnected borehole and the bed beneath it to this freezing forcing was developed using a nonlinear transient visco elastic ice flow law and an approximate model of top down freezing the resulting system of equations was solved using the method of lines results agreed well with analytic solutions when parameters were correctly chosen forward modelling of pressure records from three 1992 boreholes and three from other years indicated that the till underlying trapridge glacier has a hydraulic conductivity of 1 35 7 0 10 9 m s 1 the model was also used to investigate the response of a borehole to sudden pressure changes the response is very fast compared to pressure sensor sampling rates thus the true basal signal is essentially unaffected by the presence of the borehole except during the initial freeze in

influence of subglacial drainage conditions on the velocity distribution within a glacier cross section substrate properties and hydrological conditions at the base of haut glacier d arolla switzerland are nonuniform the thickness and grain size of subglacial sediment vary on length scales less than one ice thickness whereas hydrological conditions vary seasonally and on length scales of about one ice thickness transverse to ice motion there is a close relationship between the annually averaged velocity field and this nonuniformity of bed conditions basal motion dominates in an area with large water level variations in boreholes whereas ice deformation contributes significantly to total movement elsewhere localized enhanced basal motion occurs primarily in summer especially during a july spring event but this motion is barely discernible in annually averaged surface velocity measurements because transverse coupling suppresses surface expression of the basal motion discontinuity these results highlight the need to include representations of bed nonuniformity in models of glacier flow and to consider ice deformation and basal motion as interdependent processes

age and composition of dikes in southern tibet new constraints on the timing of east west extension and its relationship to postcollisional volcanism controversy exists over whether east west extension in southern tibet is related to plateau uplift or to the accommodation of plate boundary forces relationships between the onset of extension plateau uplift and the thermal state of the lithosphere are critical to this debate we present new data on postcollisional north south trending dikes in southern tibet their ages range from 18 3 2 7 ma to 13 3 0 8 ma and define the onset of regional east west extension in southern tibet dikes are compositionally indistinguishable from postcollisional lavas in southern tibet being either ultrapotassic having a source in the subcontinental lithospheric mantle or calc alkaline with a dominantly crustal origin the ultrapotassic dikes demonstrate that east west extension and subcontinental lithospheric mantle derived magmatism were temporally and spatially linked supporting models that relate the latest phase of plateau uplift to subcontinental lithospheric mantle thinning thus the onset of extension by 18 3 2 7 ma represents the time at which the potential energy of the plateau exceeded convergent boundary forces this places a new age limitation on the attainment of high elevation in southern tibet with implications for models that relate cenozoic monsoon intensification to plateau uplift

limits on the tectonic significance of rapid cooling events in extensional settings insights from the bitterroot metamorphic core complex idaho montana rapid cooling events deduced from thermochronologic data are often interpreted to be coincident with the age of extensional denudation in metamorphic core complexes 40 ar 39 ar data for mylonitic and nonmylonitic footwall rocks from the bitterroot core complex idaho montana united states challenge this view previous work brackets the age of the principal detachment in this area the bitterroot mylonite zone between 48 1 and 46 4 0 8 ma newly obtained hornblende 40 ar 39 ar cooling ages for samples collected from the mylonite zone are within this age range consistent with mylonitization at amphibolite facies conditions however muscovite biotite and potassium feldspar 40 ar 39 ar ages of 45 40 ma for rocks from the same area define a rapid cooling event that is significantly younger than the bitterroot mylonite zone if the 45 40 ma event is related to tectonic denudation by movement on the detachment then we can infer a time lag of 1 3 m y between the age of unroofing and the time of thermal reequilibration these data suggest caution in the use of 40 ar 39 ar data from the footwalls of metamorphic core complexes to suggest the precise age of tectonic denudation

seasonal reorganization of subglacial drainage inferred from measurements in boreholes the effect of the formation of a major subglacial drainage channel on the behaviour of the subglacial drainage system of haut glacier d arolla switzerland was investigated using measurements of borehole water level and the electrical conductivity and turbidity of basal meltwaters electrical conductivity profiles were also measured within borehole water columns to identify the water sources driving water level changes and to determine patterns of water circulation in boreholes prior to channel formation boreholes showed idiosyncratic and poorly coordinated behaviour diurnal water level fluctuations were small and driven by supraglacial englacial water inputs even when boreholes were connected to a subglacial drainage system this system appeared to consist of hydraulically impermeable patches interspersed with storage spaces and transmitted a very low water flux drainage reorganization which occurred around 31 july 1993 in response to rapidly rising meltwater and rainfall inputs seems to have involved the creation of a connection between an incipient channel and a well established channelized system located further down glacier once a major channel existed within the area of the borehole array borehole water level fluctuations were forced by discharge related changes in channel water pressure although a diversity of responses was observed these included i synchronous ii damped and lagged iii inverse and iv alternating inverse lagged responses synchronous responses occurred in boreholes connected directly to the channel while damped and lagged responses occurred in boreholes connected to it by a more resistive drainage system pressure variations within the channel resulted in diurnal transfer of mechanical support for the ice overburden between connected and unconnected areas of the bed producing inverse and alternating patterns of water level response 1998 john wiley sons ltd

implications of middle eocene epizonal plutonism for the unroofing history of the bitterroot metamorphic core complex idaho montana petrologic and geochronologic limits on the progression of east directed extensional unroofing of the bitterroot metamorphic core complex provide a means to compare rates of denudation across the footwall during the earlystages of extensional denudation u pb and 4 0 ar 3 9 ar data from epizonal plutons in the northwestern and southwestern bitterroot metamorphic core complex demonstrate that much of the western footwall was exhumed to shallow levels 1 5 km by ca 49 ma while eastern footwall rocks remained at high temperatures following an episode of isothermal decompression u pb ages of epizonal plutons along the western margins of the footwall suggest that as much as 13 km of unroofing occurred between anatectic melting of belt supergroup metasedimentary rocks in the western footwall no later than 56 ma and emplacement of the adjacent epizonal lolo hot springs batholith at ca 49 ma in the northwestern bitterroot range tectonic denudation during this interval removed roughly the same amount of overburden from eastern footwall rocks suggesting that the initial stages of unroofing may have been accommodated by a planar moderately east dipping 30 50 shear zone 4 0 ar 3 9 ar cooling data show that cooling in the western footwall was synchronous with unroofing in contrast we suggest that a significant delay in cooling of eastern footwall rocks may have resulted from a slight increase in geothermal gradient following this unroofing stage exposure of a west dipping mylonitic shear zone along the western limb of the bitterroot complex may provide a key for interpreting the postmylonitic structural evolution of the core complex if this shear zone can be correlated to the bitterroot mylonite zone to the east then strong evidence for flexural uplift consistent with postmylonitic passage of a rolling hinge emerges

the differing biogeochemical and microbial signatures of glaciers and rock glaciers glaciers and rock glaciers supply water and bioavailable nutrients to headwater mountain lakes and streams across all regions of the american west here we present a comparative study of the metal nutrient and microbial characteristics of glacial and rock glacial influence on headwater ecosystems in three mountain ranges of the contiguous u s the cascade mountains rocky mountains and sierra nevada several meltwater characteristics water temperature conductivity ph metals nutrients complexity of dissolved organic matter dom and bacterial richness and diversity differed significantly between glacier and rock glacier meltwaters while other characteristics ca fe sio2 concentrations reactive nitrogen and microbial processing of dom showed distinct trends between mountain ranges regardless of meltwater source some characteristics were affected both by glacier type and mountain range e g temperature ammonium nh4 and nitrate no3 concentrations and bacterial diversity due to the ubiquity of rock glaciers and the accelerating loss of the low latitude glaciers our results point to the important and changing influence that these frozen features place on headwater ecosystems

the hydrochemistry of meltwaters draining a polythermal based high arctic glacier south svalbard i the ablation season solute and runoff time series at finsterwalderbreen svalbard provide evidence for considerable basal routing of water and the existence of at least two contrasting subglacial chemical weathering environments the hydrochemistry of a subglacial upwelling provides evidence for a snowmelt fed subglacial reservoir that dominates bulk runoff during recession flow high concentrations of cl and crustal ions high pco2 and ratios of so2 4 so2 4 hco 3 close to 0 5 indicate the passage of snowmelt through a subglacial weathering environment characterized by high rock water ratios prolonged residence times and restricted access to the atmosphere at higher discharges bulk runoff becomes dominated by icemelt from the lower part of the glacier that is conveyed through a chemical weathering environment characterized by low rock water ratios short residence times and free contact with atmospheric gases these observations suggest that icemelt is routed via a hydrological system composed of basal ice marginal englacial and supraglacial components and is directed to the glacier margins by the ice surface slope upwelling water flows relatively independently of icemelt to the terminus via a subglacial drainage system possibly constituting flow through a sediment layer cold basal ice at the terminus forces it to take a subterranean routing in its latter stages the existence of spatially discrete flow paths conveying icemelt and subglacial snowmelt to the terminus may be the norm for polythermal based glaciers on svalbard proglacial mixing of these components to form the bulk meltwaters gives rise to hydrochemical trends that resemble those of warm based glaciers these hydrochemical characteristics of bulk runoff have not been documented on any other glacier on svalbard to date and have significance for understanding interactions between thermal regime and glacier hydrology 1998 john wiley sons ltd

molecular characterization of dissolved organic matter associated with the greenland ice sheet abstract subsurface microbial oxidation of overridden soils and vegetation beneath glaciers and ice sheets may affect global carbon budgets on glacial interglacial timescales the likelihood and magnitude of this process depends on the chemical nature and reactivity of the subglacial organic carbon stores we examined the composition of carbon pools associated with different regions of the greenland ice sheet subglacial supraglacial proglacial in order to elucidate the type of dissolved organic matter dom present in the subglacial discharge over a melt season electrospray ionization esi fourier transform ion cyclotron resonance ft icr mass spectrometry coupled to multivariate statistics permitted unprecedented molecular level characterization of this material and revealed that carbon pools associated with discrete glacial regions are comprised of different compound classes specifically a larger proportion of protein like compounds were observed in the supraglacial samples and in the early melt season spring subglacial discharge in contrast the late melt season summer subglacial discharge contained a greater fraction of lignin like and other material presumably derived from underlying vegetation and soil these results suggest 1 that the majority of supraglacial dom originates from autochthonous microbial processes on the ice sheet surface 2 that the subglacial dom contains allochthonous carbon derived from overridden soils and vegetation as well as autochthonous carbon derived from in situ microbial metabolism and 3 that the relative contribution of allochthonous and autochthonous material in subglacial discharge varies during the melt season these conclusions are consistent with the hypothesis that given sufficient time e g overwinter storage resident subglacial microbial communities may oxidize terrestrial material beneath the greenland ice sheet

synconvergent exhumation of metamorphic core complexes in the northern north american cordillera continental metamorphic core complexes of the northern north american cordillera were exhumed during the early paleogene while the farallon north american plate convergence rate remained high such convergent boundary conditions can excite localized mid crustal exhumation in numerical simulations of collisions of softer accreted terranes with a rigid irregular craton margin resulting simulated temperature time t t paths match t t paths interpreted from observed footwall exposures in several core complexes of the northern north american cordillera including variability of maximum temperatures duration of exhumation and exhumation velocities among individual complexes

the occurrence of alpine permafrost in the front range of colorado abstract permafrost distribution or ground that remains frozen for at least 2 years has been modeled using a combination of geographic information system gis techniques digital elevation model dem variables and land cover in alpine regions of the world in the front range however no such empirical models have been developed and field data are restricted in spatial extent but rock glaciers are in abundance here i present a probabilistic logistic regression model that is based on topoclimatic information elevation and aspect for rock glaciers derived from u s geological survey usgs 10 m dems classes of land cover obtained from an enhanced thematic mapper plus etm image classification were assigned weights and were then multiplied by the regression results to refine estimates the effectiveness of the model was evaluated by comparing mean probability scores with rock glacier activity categories mean annual air temperature maat from climatic stations on niwot ridge and bottom temperature of winter snow bts measurements while a monte carlo simulation was used to detect uncertainty associated with the original dem permafrost scores 50 covered about 8 9 242 km 2 of the study area 2722 km 2 with the highest scores clustered around longs and rowe peaks permafrost locations showed a strong correlation with rock glacier activity classes the 1 0 c maat isotherm and bts measurements less than 3 0 c the uncertainty analysis revealed that slight global differences exist between the original and error prone dem however local variations in aspect caused the most uncertainty these results indicate that the model accurately represents regional distribution of permafrost therefore topoclimatic information from rock glaciers and land cover when combined with an uncertainty analysis can effectively be used to map the occurrence of front range permafrost providing an imperative tool for cartographers planners and geocryologists

teleseismic location techniques and their application to earthquake clusters in the south central pacific abstract improved methods for single and multiple event hypocenter determinations are developed and applied to the problem of locating earthquake clusters in the south central pacific ocean bayesian statistical methods are used to incorporate a priori information about arrival time variance into the derivation of hypocenter confidence ellipsoids permitting a more realistic calculation of critical parameters in the case where the number of stations is small the diagonal elements of certain projection operators called data importances by minster et al 1974 are used to evaluate network balance the hypocentroid of an event cluster is defined to be the average location of events within the cluster and the deviations of individual hypocenters from the hypocentroid are called cluster vectors the problem of estimating the cluster vectors can be decoupled from the problem of estimating the hypocentroid by a simple but fundamental mathematical result here termed the hypocentroidal decomposition theorem the algorithm based on this analysis appears to have many advantages over other published methods for multiple event location both in its efficient use of available information and its computational speed the application of this method to three clusters of shallow intraplate seismicity in the south central pacific designated regions a b and c demonstrates that the seismicity within each cluster is very localized the rms lengths of the cluster vectors for each group of epicenters are estimated to be only 9 6 and 12 km respectively estimates of the epicentroids are

stable isotope evidence for microbial sulphate reduction at the bed of a polythermal high arctic glacier glacier beds may be host to a range of microbial communities which drive oxic waters towards anoxia along certain hydrological flowpaths chemical and isotopic signatures in meltwaters from finsterwalderbreen a polythermal glacier on sedimentary bedrock in svalbard show clear evidence for anoxia at the glacier bed increases in 34s and 18o of sulphate indicate that microbial sulphate reduction has resulted in significant decreases in sulphate concentration the 13c of the dissolved inorganic carbon dic is isotopically light 13c 8 which is consistent with the use of bedrock kerogen and or the necromass of sulphide oxidising bacteria as organic substrates for the sulphate reducing bacteria calculated rates of organic carbon mineralisation correspond to 10 of the total annual dic flux of the glacial meltwaters this microbial ecosystem is chemoautotrophically based ultimately being sustained by the kerogen and or bacterial necromass and sulphides in the bedrock this work suggests that glacier beds can be refugia for life when climatic and or atmospheric conditions are otherwise inclement and also supports the contention that microbial life is present in subglacial lake vostok

thermal effects of exhumation of a metamorphic core complex on hanging wall syn rift sediments an example from the rechnitz window eastern alps the removal of overburden by tectonic processes displaces the rock masses and their temperature with respect to the surface consequently high cooling rates and increased heat flow have been reported from rapidly exhuming terrains previous studies were mainly focused on the greenschist and amphibolite facies tectono thermal evolution of the footwall a two dimensional numerical thermal model presented in this study concentrates on the thermal history of the hanging wall and the footwall blocks and evaluates the variation of the near surface heat flow above an evolving metamorphic core complex based on structural thermobarometric and geochronological constraints from the rechnitz core complex of the eastern alps the modelling suggests that rapid movement along the extensional fault took place between 22 and 17 ma during this period the heat flow reached values of 140 150 mw m 2 in the hanging wall in a 10 15 km wide zone parallel to the fault trace the increased heat flow caused the high coal rank in the miocene syn rift sediments deposited on the hanging wall apatite fission track geochronology of the thermally overprinted sedimentary deposits gives the time at which the bottom of the syn rift sediment pile passed through 110oc 13 6 0 9 ma the vitrinite reflectance data rr 0 67 1 04 suggest significant burial of the margin of the hanging wall at the time of core complex formation considering the coal rank data and the thermal conductivity of the sedimentary deposits by modelling of the organic maturation we calculate syn rift early middle miocene burial of the hanging wall margin of the rechnitz core complex to be 1100 1600 m this value shows the importance of the post middle miocene erosion of the region which was related to the inversion of the pannonian basin 1998 elsevier science b v all rights reserved

seasonal changes in the morphology of the subglacial drainage system haut glacier d arolla switzerland dye tracing techniques were used to investigate the glacier wide pattern of change in the englacial subglacial drainage system of haut glacier d arolla during the ablation seasons of 1990 and 1991 analysis of breakthrough curve characteristics indicate that over the course of a melt season a system of major channels developed by headward growth at the expense of a hydraulically inefficient distributed system by the end of the melt season this channel system extended at least 3 3 km from the snout of the 4 km long glacier and drained the bulk of supraglacially derived meltwater passing through the glacier the upper limit of the channel system closely followed the retreating snowline up glacier rates of headward channel growth reached c 65 m d 1 although these rates decreased in the upper 1 km of the glacier where snowline retreat exposed a patchy firn aquifer it appears that the removal of snow with its high albedo and significant water storage capacity from the glacier surface resulted in a dramatic increase in the volume of runoff into moulins and in the peakedness of daily runoff cycles this induced transient high water pressures within the distributed drainage system which caused it to evolve rapidly into a channelised system it is therefore likely that at a local scale channel growth occurred down glacier from moulins and that the overall up glacier directed pattern of channel formation was caused by the retreating snowline exposing new moulins and crevasses to inputs of ice derived meltwater damping of diurnal melt inputs by storage in the firm aquifer accounts for the slowing of channel growth in the upper glacier 1998 john wiley sons ltd

late cenozoic evolution of the eastern margin of the tibetan plateau inferences from 40ar 39ar and u th he thermochronology high topography in central asia is perhaps the most fundamental expression of the cenozoic indo asian collision yet an understanding of the timing and rates of development of the tibetan plateau remains elusive here we investigate the cenozoic thermal histories of rocks along the eastern margin of the plateau adjacent to the sichuan basin in an effort to determine when the steep topographic escarpment that characterizes this margin developed temperature time paths inferred from 40 ar 39 ar thermochronology of biotite multiple diffusion domain modeling of alkali feldspar 40 ar release spectra and u th he thermochronology of zircon and apatite imply that rocks at the present day topographic front of the plateau underwent slow cooling 30 50 c m y coincident with exhumation from inferred depths of 8 10 km at denudation rates of 1 2 mm yr samples from the interior of the plateau continued to cool relatively slowly during the same time period 3 c m y suggesting limited exhumation 1 2 km however these samples record a slight increase in cooling rate from 1 to 3 c m y at some time during the middle tertiary the tectonic significance of this change remains uncertain regardless late cenozoic denudation in this region appears to have been markedly heterogeneous with the highest rates of exhumation focused at the topographic front of the plateau margin we infer that the onset of rapid cooling at the plateau margin reflects the erosional response to the development of regionally significant topographic gradients between the plateau and the stable sichuan basin and thus marks the onset of deformation related to the development of the tibetan plateau in this region the present margin of the plateau adjacent to and north of the sichuan basin is apparently no older than the late miocene or early pliocene 5 12 ma

modeling past and future alpine permafrost distribution in the colorado front range rock glaciers a feature associated with at least discontinuous permafrost provide important topoclimatic information active and inactive rock glaciers can be used to model current permafrost distribution relict rock glacier locations provide paleoclimatic information to infer past conditions future warmer climates could cause permafrost zones to shrink and initiate slope instability hazards such as debris flows or rockslides thus modeling change remains imperative this research examines potential past and future permafrost distribution in the colorado front range by calibrating an existing permafrost model using a standard adiabatic rate for mountains 0 5 c per 100 m for a 4 c range of cooler and warmer temperatures according to the model permafrost currently covers about 12 per cent 326 1 km2 of the entire study area 2721 5 km2 in a 4 c cooler climate 73 7 per cent 2004 4 km2 of the study area could be covered by permafrost whereas in a 4 c warmer climate almost no permafrost would be found permafrost would be reduced severely by 93 9 per cent a loss of 306 2 km2 in a 2 0 c warmer climate however permafrost will likely respond slowly to change relict rock glacier distribution indicates that mean annual air temperature maat was once at least some 3 0 to 4 0 c cooler during the pleistocene with permafrost extending some 600 700 m lower than today the model is effective at identifying temperature sensitive areas for future monitoring however other feedback mechanisms such as precipitation are neglected copyright 2005 john wiley sons ltd

trickle or treat the dynamics of nutrient export from polar glaciers cold based polar glacier watersheds contain well defined supraglacial ice marginal and proglacial elements that differ in their degree of hydrologic connectivity sources of water e g snow ice and or sediment pore water meltwater residence times allochthonous and autochthonous nutrient and sediment loads we investigated 11 distinct hydrological units along the supraglacial ice marginal and proglacial flow paths that drain joyce glacier in the mcmurdo dry valleys of antarctica we found that these units play unique and important roles as sources and or sinks for dissolved inorganic nitrogen and dissolved inorganic phosphorus and for specific fractions of dissolved organic matter dom as waters are routed from the glacier into nutrient poor downstream ecosystems changes in nutrient export from the glacial system as a whole were observed as the routing and residence times of meltwater changed throughout the melt season the concentrations of major ions in the proglacial stream were inversely proportional to discharge such that there was a relatively constant trickle of these solutes into downstream ecosystems in contrast no3 concentrations generally increased with discharge resulting in delivery of episodic pulses of dissolved inorganic nitrogen rich water treats into those same ecosystems during high discharge events dom concentrations or fluorescence did not correlate with discharge rate but high variability in dom concentrations or fluorescence suggests that dom may be exported downstream as episodic treats but with spatial and or temporal patterns that remain poorly understood the strong nutrient specific responses to changes in hydrology suggest that polar glacier drainage systems may export meltwater with nutrient compositions that vary within and between melt seasons and watersheds because nutrient dynamics identified in this study differ between glacier watersheds with broadly similar hydrology climate and geology we emphasize the need to develop conceptual models of nutrient export that thoroughly integrate the biogeochemical and

near surface hydraulic conductivity of northern hemisphere glaciers the hydrology of near surface glacier ice remains a neglected aspect of glacier hydrology despite its role in modulating meltwater delivery to downstream environments to elucidate the hydrological characteristics of this near surface glacial weathering crust we describe the design and operation of a capacitance based piezometer that enables rapid economical deployment across multiple sites and provides an accurate high resolution record of near surface water level fluctuations piezometers were employed at 10 northern hemisphere glaciers and through the application of standard bail recharge techniques we derive hydraulic conductivity k values from 0 003 to 3 519 m day 1 with a mean of 0 185 0 019 m day 1 these results are comparable to those obtained in other discrete studies of glacier near surface ice and for firn and indicate that the weathering crust represents a hydrologically inefficient aquifer hydraulic conductivity correlated positively with water table height but negatively with altitude and cumulative short wave radiation since the last synoptic period of either negative air temperatures or turbulent energy flux dominance the large range of k observed suggests complex interactions between meteorological influences and differences arising from variability in ice structure and crystallography our data demonstrate a greater complexity of near surface ice hydrology than hitherto appreciated and support the notion that the weathering crust can regulate the supraglacial discharge response to melt production the conductivities reported here coupled with typical supraglacial channel spacing suggest that meltwater can be retained within the weathering crust for at least several days not only does this have implications for the accuracy of predictive meltwater run off models but we also argue for biogeochemical processes and transfers that are strongly conditioned by water residence time and the efficacy of the cascade of sediments impurities microbes and nutrients to downstream ecosystems because continued atmospheric warming will incur rising snowline elevations and glacier thinning the supraglacial hydrological system may assume greater importance in many mountainous regions and consequently detailing weathering crust hydraulics represents a research priority because the flow path it represents remains poorly constrained

the seismicity of kohistan pakistan source studies of the hamran 1972 9 3 darel 1981 9 12 and patan 1974 12 28 earthquakes abstract long period body waves are examined to show that the hamran 1972 9 3 darel 1981 9 12 and patan 1974 12 28 earthquakes in kohistan had focal depths of about 8 10 km all involved high angle reverse faulting thrusting and had seismic moments of about 2 2 to 2 7 1025 dyne cm these shallow depths contrast with the deeper hypocentres found in the hindu kush and northeast karakoram to the north and in hazara to the south the hamran and patan shocks were assigned depths of 45 km by the isc indicating that even well recorded events in this region may have focal depths in error by 30 km

in situ measurements of basal water quality and pressure as an indicator of the character of subglacial drainage systems continuous subglacial measurements of turbidity and electrical conductivity two indicators of basal water quality can be used to help characterize subglacial drainage systems these indicators of water quality yield information that complements that provided by water pressure measurements quantitative attributes of subglacial drainage systems such as water velocity and subglacial residence time as well as qualitative behaviour for example spatial and temporal variations in system morphology can be deduced using water quality measurements interpretation is complicated by the many potential influences on turbidity and electrical conductivity but when these complications are appreciated a richer interpretation results to demonstrate the utility of basal water quality measurements observations from trapridge glacier yukon territory canada were examined the data reveal complex behaviour of the drainage system but constraints imposed by basal water quality measurements help to clarify the nature of the subglacial flow system the measurement and interpretation methods described and demonstrated are applicable to other glaciers as such they should prove useful for characterizing different subglacial drainage configurations and behaviours thereby improving our general understanding of the hydrology and dynamics of wet based glaciers

nitrogen production from geochemical weathering of rocks in southwest montana usa 1 a 30 day time course laboratory weathering experiment was conducted using rock samples collected from the west fork of the gallatin river watershed wfw in southwestern montana usa the goal of these experiments was to quantify the amount of labile nitrogen in rock samples collected from the watershed and determine if chemical weathering is a source of dissolved nitrogen in stream water several rock samples investigated produced nitrate in significantly higher concentrations than the silica bead control p 0 05 and the data were consistent with elevated no3 concentrations measured in associated wfw streams isotopic analyses of 15n no3 in 22 stream water samples from the wfw and four rock water extracts from the laboratory experiments indicated that the isotopic composition of no3 was comparable with rocks and stream water samples in the same watershed and differed strongly from waters downstream of development we suggest that the no3 measured in wfw streams includes nitrogen derived from mineral dissolution products from soils and rock the results presented herein further indicate that rock weathering is a source of stream water n in the west fork watershed and inform water quality assessment total maximum daily load development and the relative influences of natural and anthropocentrically derived n sources across this developing mountain watershed

dissolved oxygen variations in alpine glacial meltwaters recent models of chemical weathering in alpine glacial meltwaters suggest that sulphide oxidation is a major source of solute in the distributed component of the subglacial hydrological system this reaction requires o2 and may lower dissolved oxygen levels to below saturation with respect to the atmosphere this should result in an inverse association between so72 and dissolved oxygen saturation however measurements of o2 saturation in bulk meltwaters draining the haut glacier d arolla switzerland show that there is a positive association between so42 and o2 saturation the o2 content of glacial meltwaters depends on the initial content of snow and icemelt which may be controlled by the rate of melting and the kinetic balance between o2 losses e g sulphide oxidation microbial respiration and gains e g diffusion of o2 into solution

recent hydrologic change in a colorado alpine basin an indicator of permafrost thaw hydrologic and hydrochemical studies have been conducted in green lakes valley colorado front range usa above 3550 m since 1982 they show a classic seasonal hydrograph dominated by snowmelt and an earlier date for the start of spring flow and for peak flow over the period of record this is consistent with patterns found at lower elevations in colorado and throughout western north america they also show an increasing trend in flows in september and october of 2 6 0 7 mm a 1 which is not found elsewhere and cannot be accounted for by increased autumn precipitation and the melting of surface ice because this late season increase is not found at the highest elevations or in basins in which there is no evidence of permafrost it seems best explained by the thawing of alpine permafrost at intermediate elevations this is corroborated by an increase in the concentration of base cations and silica and particularly in ca 2 and so4 in the stream discharge starting in 2000 as with the physical hydrology the geochemical signals have not been detected at the higher elevations in the basin though they have previously been associated with streamflow from a small rock glacier in the valley the combined evidence suggests the degradation of ice rich permafrost on the north facing slopes of the valley below 3700 m where it has been detected at 3 m depth by geophysical surveys

statistical evaluation of glacier boreholes as indicators of basal drainage systems between 1988 and 1992 closely spaced arrays of boreholes were drilled at small river glacier british columbia the borehole arrays have been used to investigate the interannual and spatial consistency of patterns of basal hydraulics beneath the glacier a simple robust classification was devised identifying unconnected high standing low standing and dry base water levels in boreholes spatial and interannual comparisons were made using a simple nearest neighbour statistic corrected for differences in frequency of different borehole types and evaluated using monte carlo confidence intervals to compensate for array form arrays in the lower ablation zone showed spatial and interannual coherence with three distinct areas characterized by low water pressure till associated non connection and high pressure there was no indication of a dominant conduit slightly higher up glacier borehole patterns were less coherent and varied from year to year probably a result of subglacial karst capturing basal waters at a number of low pressure points at the bed therefore both the upper and lower arrays at small river glacier appear to encompass unusual drainage conditions the nearest neighbour analysis provides valuable constraints on more specific interpretation

multiple event relocation of earthquakes on and near the gorda ridge multiple event relocation of earthquakes associated with the gorda ridge and gorda basin indicates that activity tends to cluster spatially with some suggestion of linear trends in the epicenters of events near the central segment of the ridge sub parallel to the ridge axis events in the interior of the basin may be related to relic faults formed at the ridge crest that remain zones of weakness in the plate and are subject to periodic reactivation as well as the proposed gorda fault which crosses the plate in a nw se direction

extreme hydrochemical conditions in natural microcosms entombed within antarctic ice cryoconite holes are near vertical tubes that form in the surface of glaciers when solar heated debris melts into the ice those that form in the mcmurdo dry valleys of antarctica are distinctive in that they have ice lids and are closed to the atmosphere for periods of years to decades photoautotrophs and heterotrophs grow within this closed environment perturbing the poorly buffered water chemistry yet maintaining the potential for photosynthesis microbial excretion and decomposition of organic matter produces dissolved organic carbon doc dissolved inorganic carbon ratios of 1 2 much of the dissolved nitrogen pool 80 100 exists as dissolved organic nitrogen don the don doc ratio is 1 11 mol mol typical of organic particulate material at the earth s surface the combination of photoautotrophy heterotrophy and weak chemical buffering within these microcosms promotes values of ph pco2 o2 saturation and percentage total dissolved nitrogen as don that reach 10 99 10 7 6 atm 160 and 100 respectively which are a unique combination among the surface waters on earth these ice sealed cryoconite holes could be important analogues of refugia on snowball earth and other icy planets

40ar 39ar laserprobe dating of mylonitic fabrics in a polyorogenic terrane of nw iberia the tectonothermal evolution of a polyorogenic terrane in the variscan belt of nw spain has been constrained by 40 ar 39 ar laserprobe incremental heating experiments on mylonitic fabrics developed in major structures transitional levels between hp ht and ip upper units in the ordenes complex where metamorphic and structural records demonstrate two cycles of burial and exhumation were selected for dating two groups of ages have been defined 1 silurian early devonian obtained from mylonites of the fornas extensional detachment here considered as the minimum age for the start of tectonic exhumation of the hp ht units and an upper age limit for the hp ht event itself 2 early to mid devonian from structures related to the variscan convergence in the area which include top to the east thrusts and extensional detachments a single younger carboniferous age obtained from the uppermost allochthonous sequences possibly reflects the final stages of emplacement of the allochthonous complexes our data indicate a polyorogenic character for a part of the iberian allochthonous complexes including variscan sensu stricto and early variscan convergence as well as an older early palaeozoic cycle

comments on the use of chemically based mixing models in glacier hydrology the assumptions involved in the use of chemically based mixing models for analysis of flow routing of meltwaters in glacierized basins are critically evaluated the assumption that glacial drainage systems consist of only two primary flow components is arbitrary and must be supported by independent evidence recent studies of the processes by which meltwaters acquire solute indicate that the assumption that flow components have unique and constant chemical compositions is unlikely to lie correct source water composition and weathering potential will vary over the course of a melt season and the extent of subglacial weathering is strongly dependent upon such factors as meltwater residence time and the availability of reactive sediment both of which are known to vary on diurnal to seasonal time scales mixing of flow components does not appear to be confined to the terminal regions of glaciers and is therefore unlikely to be conservative as assumed a multi parameter mixing model is applied to the analysis of data on the chemistry of waters sampled from bureholes drilled through haut glacier d arolla switzerland to demonstrate the range of dissolved species for which the assumption of conservative mixing is violated the consequences of this violation for quantitative hydrograph separation are shown to be highly significant the utility of mixing models as a tool for the investigation of glacier hydrological systems is questionable and the results of previous studies are unreliable

the thermal response of a metamorphic belt to extension constraints from laser ar data on metamorphic micas abstract metamorphic rocks may be exhumed to the surface either by isostatic rebound uplift and erosion or tectonically via thrusting or extension the latter mechanism is particularly important in the himalayas where a large extensional detachment system appears to be responsible for very fast unroofing at 20 ma here we present the results of a laser argon study of micas and quartz aimed at investigating the thermal response of an orogenic belt to such extension the data when combined with existing constraints on the prograde evolution lead to a uniquely complete thermal history for a metamorphic belt laser argon data are reported for quartz and micas from semi pelitic metamorphic rocks from the zanskar himalayas nw india the samples derive from three traverses extending from low grade rocks near the detachment to high grade rocks in the core of the belt most samples demonstrably contain no excess component and the ages of muscovite and biotite show a correlation with distance from the extensional detachment the ages themselves as well as the difference between the muscovite and biotite ages both increase as the detachment is approached muscovite and biotite ages from within the shear zone date deformation associated with extension at 20 25 ma the remaining data are most readily interpreted in terms of early slow cooling of the lower grade rocks near the detachment in response to erosional denudation before the detachment became active rocks in the core of the orogen were still heating at this time later fast cooling of the high grade rocks in the core of the belt ensued when the extensional regime became active simple heat transfer calculations based on the distance of the high grade rocks from the fault and the argon ages of their micas provide further constraints on the timing of extension and suggest that the fault first moved 23 25 ma ago and that it abruptly terminated metamorphism in the core of the metamorphic belt our analysis of the thermal history suggests that cooling and exhumation rates determined from metamorphic belts beneath extensional detachments will often be minima

absolute dating of brittle fault movements late permian and late jurassic extensional fault breccias in western norway 40ar 39ar geochronological and palaeomagnetic dating methods applied to fault breccias in western norway have isolated two brittle reactivation episodes of the syn post caledonian extensional nordfjord sogn detachment these events of latest permian and latest jurassic early cretaceous ages demonstrate temporal relationships between development of chemical remanent magnetism and partial resetting of ar isotopic systems during distinct breccia forming episodes a third event of carboniferous age was also identified in the breccias with the 40ar 39ar technique and is a relict unroofing signature inherited from the fault wall rocks these brittle faults are significant time markers and become relevant to interpretations of offshore seismic data which attempt to place ages on faults that have undergone multiple reactivation episodes

multiple event relocation of earthquakes near the gorda rise mendocino fracture zone intersection earthquakes along the southern edge of the gorda plate and the mendocino fracture zone that were relocated jointly generally tend to move 25 to 35 km southwest of their pde and isc locations this has the effect of reducing the number of events occurring deep in the plate and increasing the number of events located on the gorda rise as well as revealing a tightly grouped linear zone of activity extending along the mendocino fracture zone the resulting spatial pattern of seismicity is more consistent with recent models of the tectonics of the gorda plate and the mendocino fracture zone

geochemical weathering at the bed of haut glacier d arolla switzerland a new model waters were sampled from 17 boreholes at haut glacier d arolla during the 1993 and 1994 ablation seasons three types of concentrated subglacial water were identified based on the relative proportions of ca 2c h co 3 and so4 2 to si type a waters are the most solute rich and have the lowest relative proportion of si they are believed to form in hydrologically inefficient areas of a distributed drainage system most solute is obtained from coupled sulphide oxidation and carbonate dissolution so cd it is possible that there is a subglacial source of o2 perhaps from gas bubbles released during regelation because the high so4 2 levels found up to 1200 eq l are greater than could be achieved if sulphides are oxidized by oxygen in saturated water at 0 c c 414 eq l a more likely alternative is that sulphide is oxidized by fe 3c in anoxic environments if this is the case exchange reactions involving fe iii and fe ii from silicates are possible these have the potential to generate relatively high concentrations of hco3 with respect to so4 2 formation of secondary weathering products such as clays may explain the low si concentrations of type a waters type b waters were the most frequently sampled subglacial water they are believed to be representative of waters flowing in more efficient parts of a distributed drainage system residence time and reaction kinetics help determine the solute composition of these waters the initial water rock reactions are carbonate and silicate hydrolysis and there is exchange of divalent cations from solution for monovalent cations held on surface exchange sites hydrolysis is followed by so cd the so4 2 concentrations usually are 414 eq l although some range up to 580 eq l which suggests that elements of the distributed drainage system may become anoxic type c waters were the most dilute yet they were very turbid their chemical composition is characterized by low so4 2 h co3 ratios and high ph type c waters were usually artefacts of the borehole chemical weathering environment true type c waters are believed to flow through sulphide poor basal debris particularly in the channel marginal zone the composition of bulk runoff was most similar to diluted type b waters at high discharge and was similar to a mixture of type b and c waters at lower discharge these observations suggest that some supraglacial meltwaters input to the bed are stored temporarily in the channel marginal zone during rising discharge and are released during declining flow little of the subglacial chemical weathering we infer is associated with the sequestration of atmospheric co2 t he progression of reactions is from carbonate and silicate hydrolysis through sulphide oxidation by first oxygen and then fe iii which drives further carbonate and silicate weathering a crude estimate of the ratio of carbonate to silicate weathering following hydrolysis is 4 1 we speculate that microbial oxidation of organic carbon also may occur both sulphide oxidation and microbial oxidation of organic carbon are likely to drive the bed towards suboxic conditions hence we believe that subglacial chemical weathering does not sequester significant quantities of atmospheric co2 and that one of the key controls on the rate and magnitude of solute acquisition is microbial activity which catalyses the reduction of fe iii and the oxidation of fes2 copyright 2002 john wiley sons ltd

hydrochemistry of carbonate terrains in alpine glacial settings nearly 200 analyses of meltwaters ice and snow from three alpine glacial sites in carbonate terrain are summarized and discussed in terms of sources of solutes and kinetic controls on the progress of weathering reactions most data derive from the swiss glacier de tsanfleuron which is based on cretaceous and tertiary pure and impure limestones two other sites marmolada italian dolomites and the saskatchewan glacier alberta are based on a mixed calcitic dolomitic substrate most solutes originate from carbonate dissolution moreover where pyrite is present its oxidation supplies significant sulphate and forces more dissolution of carbonate the ratios sr2 ca2 and mg2 ca2 are much higher in tsanfleuron melt waters than local bedrock a phenomenon that can be reproduced in the laboratory at small percentages of dissolution these anomalous ratios are attributed to incongruent dissolution of traces of the metastable carbonates mg calcite and aragonite these phases also provide na to solution k is argued to originate mainly by ion exchange on clays with solute ca2 quartz and very minor feldspar dissolution are also inferred locally enhanced input from atmospheric sources is recognized by high cl and associated na the progress of weathering reactions has been evaluated by the trends in the data computer modelling and some simple laboratory experiments the most dilute samples show a trend towards removal of co2 to low partial pressures c 10 5 5 atmospheres reflecting initially rapid carbonate dissolution and relatively slow dissolution of gaseous co2 later addition of atmospheric co2 or acid from pyrite oxidation allows further carbonate dissolution but solutions show a wide range of saturations and co2 pressures as high as 10 2 2 where pyrite oxidation is important in a carbonate terrain measurement of electroconductivity corrected to 25 c and alkalinity in the field allows the following preliminary deductions where meq stands for milliequivalents formula presented where s is the minimum meq ca2 mg2 produced by simple dissolution of carbonate unconnected with pyrite oxidation as with any proxy method these deductions do not remove the need for chemical analysis of waters in a given study area copyright 1994 john wiley sons ltd

deglaciation and postglacial environmental changes in the teton mountain range recorded at jenny lake grand teton national park wy abstract sediments contained in lake basins positioned along the eastern front of the teton mountain range preserve a continuous and datable record of deglaciation and postglacial environmental conditions here we develop a multiproxy glacier and paleoenvironmental record using a combination of seismic reflection data and multiple sediment cores recovered from jenny lake and other nearby lakes age control of teton lake sediments is established primarily through radiocarbon dating and supported by the presence of two prominent rhyolitic tephra deposits that are geochemically correlated to the widespread mazama 7 6 ka and glacier peak 13 6 ka tephra layers multiple glacier and climate indicators including sediment accumulation rate bulk density clastic sediment concentration and flux organic matter concentration flux 13c 15n and c n ratios and biogenic silica track changes in environmental conditions and landscape development sediment accumulation at jenny lake began centuries prior to 13 8 ka and cores from three lakes demonstrate that teton glacier extents were greatly reduced by this time persistent ice retreat in cascade canyon was slowed by an interval of small glacier activity between 13 5 and 11 5 ka prior to the end of glacial lacustrine sedimentation 11 5 ka the transition to non glacial sediments marks the onset of holocene conditions at jenny lake and reflects a shift toward warmer summers increased vegetation cover and landscape stability in the tetons we discuss the teton lake sediment records within the context of other regional studies in an effort to construct a comprehensive overview of deglaciation and postglacial environmental conditions at grand teton national park

variability in the chemical composition of in situ subglacial meltwaters meltwaters collected from boreholes drilled to the base of the haut glacier d arolla switzerland have chemical compositions that can be classified into three main groups the first group is dilute whereas the second group is similar to though generally less concentrated in major ions than contemporaneous bulk glacial runoff the third group is more concentrated than any observed bulk runoff including periods of flow recession waters of the first group are believed to represent supraglacial meltwater and ice melted during drilling limited solutes may be derived from interactions with debris in the borehole the spatial pattern of borehole water levels and borehole water column stratification combined with the chemical composition of the different groups suggest that the second group represent samples of subglacial waters that exchange with channel water on a diurnal basis and that the third group represent samples of water draining through a distributed subglacial hydraulic system high no 3 concentrations in the third group suggest that snowmelt may provide a significant proportion of the waters and that the residence time of the waters at the bed in this particular section of the distributed system is of the order of a few months the high no 3 concentrations also suggest that some snowmelt is routed along different subglacial flowpaths to those used by icemelt the average so2 4 hco 3 so2 4 ratio of the third group of meltwaters is 0 3 suggesting that sulphide oxidation and carbonate dissolution which gives rise to a ratio of 0 5 cannot provide all the hco 3 to solution hence carbonate hydrolysis may be occurring before sulphide oxidation or there may be subglacial sources of co2 perhaps arising from microbial oxidation of organic c in bedrock air bubbles in glacier ice or pockets of air trapped in subglacial cavities the channel marginal zone is identified as an area that may influence the composition of bulk meltwater during periods of recession flow and low diurnal discharge regimes 1997 by john wiley sons ltd

widespread bacterial populations at glacier beds and their relationship to rock weathering and carbon cycling bacterial populations found in subglacial meltwaters and basal ice are comparable to those in the active layer of permafrost and orders of magnitude larger than those found in ice cores from large ice sheets populations increase with sediment concentration and 5 24 of the bacteria are dividing or have just divided suggesting that the populations are active these findings 1 support inferences from recent studies of basal ice and meltwater chemistry that microbially mediated redox reactions may be important at glacier beds 2 challenge the view that chemical weathering in glacial environments arises from purely inorganic reactions and 3 raise the possibilities that redox reactions are a major source of protons consumed in subglacial weathering and that these reactions may be the dominant proton source beneath ice sheets where meltwaters are isolated from an atmospheric source of co 2 microbial mediation may increase the rate of sulfide oxidation under subglacial conditions a suggestion supported by the results of simple weathering experiments if subglacial bacterial populations can oxidize and ferment organic carbon it is important to reconsider the fate of soil organic carbon accumulated under interglacial conditions in areas subsequently overridden by pleistocene ice sheets

chemical models of solute acquisition in glacial melt waters chemical models for the evolution of bulk melt waters can be constructed by assuming that rock mineral weathering and solute acquisition are controlled by carbonate equilibria different open and closed system models are defined by variations in the rates of weathering relative to the rate of hydrogen ion supply by the dissolution and dissociation of co2 and can be recognized by characteristic ph and relationships the observed and inferred compositions of englacial and subglacial melt suggest that mixing is unlikely to be conservative and that closed system conditions result where post mixing weathering reactions occur the final composition of bulk melt waters is determined by the mixing ratio between englacial and subglacial melt the extent of post mixing evolution and opportunity for mixing with ground waters or re equilibration with the atmosphere

the composition of the englacial and subglacial component in bulk meltwaters draining the gornergletscher switzerland a new method of hydrograph separation for bulk meltwaters draining alpine glaciers is proposed it is based on the two component subglacial and englacial mixing model of collins 1978 but allows the composition of the subglacial component to vary between ascending and descending lines of the hydrograph the mean englacial component can be derived from linear relationships between sulphate concentrations and other ions in bulk meltwaters on certain occasions during the ablation season the maximum concentration of ions in the subglacial component can be determined from the linear relationship between bulk meltwater sulphate concentrations and discharge the bulk discharge is then a direct measure of the mass fraction of the englacial component at maximum discharge the contribution of the subglacial component approaches zero which has implications for the storage and mixing of waters in subglacial reservoirs further the subglacial component is not of constant composition and may itself be a mixture of dilute supraglacial and concentrated subglacial water

the seismicity of northernmost pakistan abstract a portable seismic network was operated in the karakoram area of northern pakistan for over two months during the summer of 1980 the principal objectives were to record possible subcrustal earthquakes beneath the karakoram range and to monitor crustal activity throughout northernmost pakistan we confirm the existence of intermediate depth seismicity at a depth of about 140 km beneath the karakoram mountains shallow crustal activity also occurs in the karakoram range with events recorded from near the northwest end of the karakoram fault and near a number of smaller lineaments in baltistan seismicity in kohistan appears to be largely confined to the upper crust though occasional earthquakes at 65 km depth approximately the base of the crust occur beneath areas of higher topography nanga parbat rakaposhi an area close to the hamran 1972 and darel 1981 earthquakes showed intense activity in the depth range 0 25 km similar to that involved in the mainshocks themselves focal mechanisms for events in this area show thrusting on nw trending planes indicating ne sw compression

the hydrochemistry of bayelva a high arctic proglacial stream in svalbard major ion silica and ph data from a high arctic proglacial stream network are examined factor analysis shows that the major controls upon hydrochemistry in the basin include snowpack solute elution rapid alteration of minerals via surface reactions and slow incongruent silicate dissolution the importance of chemical weathering is found to increase downstream at the expense of solute acquisition from the transient snowpack data from a series of snow pits show that snowpack solute elution is characterised by the preferential elution of so42 evidence for the preferential elution of no3 is equivocal however no3 levels in proglacial runoff may be enhanced by the leaching of cryotic soils later in the ablation season chemical weathering is dominated by calcite dissolution at high elevations and a combination of calcite and dolomite dissolution in the downstream proglacial environment silicate weathering at high elevations is characterised by the enrichment of k relative to si concentrated active layer soil waters show less enrichment of k and constitute a potentially important source of dissolved silica to the river system na is also produced by silicate weathering but its mobility is believed to be largely governed by ion exchange with ca2 early in the ablation season all chemical weathering environments are characterised by high p co2 due to either respiration within the soil or at higher elevations within the catchment h provision from acid aerosol and sulphide oxidation however rates of sulphide oxidation are limited because the cold based thermal regime of the glaciers effectively prevents access of meltwaters to freshly comminuted sub glacial sulphide minerals the restricted sub glacial weathering therefore means that ice marginal and proglacial environments are the most important zones of solute acquisition by meltwaters causing significant enrichment of major ions silica and dissolved co2 within only a short distance of the contemporary ice margin

water flow through temperate glaciers understanding water movement through a glacier is fundamental to several critical issues in glaci ology including glacier dynamics glacier induced floods and the prediction of runoff from glacierized drainage basins to this end we have synthesized a conceptual model of water movement through a temper ate glacier from the surface to the outlet stream pro cesses that regulate the rate and distribution of water input at the glacier surface and that regulate water movement from the surface to the bed play important but commonly neglected roles in glacier hydrology where a glacier is covered by a layer of porous perme able firn the accumulation zone the flux of water to the glacier interior varies slowly because the firn tempo rarily stores water and thereby smooths out variations in the supply rate in the firn free ablation zone in con trast the flux of water into the glacier depends directly on the rate of surface melt or rainfall and therefore varies greatly in time water moves from the surface to the bed through an upward branching arborescent net work consisting of both steeply inclined conduits formed by the enlargement of intergranular veins and gently inclined conduits spawned by water flow along the bottoms of near surface fractures crevasses engla cial drainage conduits deliver water to the glacier bed at a limited number of points probably a long distance downglacier of where water enters the glacier englacial conduits supplied from the accumulation zone are quasi steady state features that convey the slowly varying water flux delivered via the firn their size adjusts so that they are usually full of water and flow is pressurized in contrast water flow in englacial conduits supplied from the ablation area is pressurized only near times of peak daily flow or during rainstorms flow is otherwise in an open channel configuration the subglacial drainage system typically consists of several elements that are distinct both morphologically and hydrologically an up glacier branching arborescent network of channels in cised into the basal ice conveys water rapidly much of the water flux to the bed probably enters directly into the arborescent channel network which covers only a small fraction of the glacier bed more extensive spatially is a nonarborescent network which commonly includes cav ities gaps between the glacier sole and bed channels incised into the bed and a layer of permeable sediment the nonarborescent network conveys water slowly and is usually poorly connected to the arborescent system the arborescent channel network largely collapses during winter but reforms in the spring as the first flush of meltwater to the bed destabilizes the cavities within the nonarborescent network the volume of water stored by a glacier varies diurnally and seasonally small temper ate alpine glaciers seem to attain a maximum seasonal water storage of 200 mm of water averaged over the area of the glacier bed with daily fluctuations of as much as 20 30 mm the likely storage capacity of subglacial cavities is insufficient to account for estimated stored water volumes so most water storage may actually occur englacially stored water may also be released abruptly and catastrophically in the form of outburst floods

nitrate content and potential microbial signature of rock glacier outflow colorado front range here we characterize the nutrient content in the outflow of the green lake 5 rock glacier located in the green lakes valley of the colorado front range dissolved organic carbon doc was present in all samples with a mean concentration of 0 85 mg l 1 a one way analysis of variance test shows no statistical difference in doc amounts among surface waters p 0 42 average nitrate concentrations were 69 moles l 1 in the outflow of the rock glacier compared to 7 moles l 1 in snow and 25 moles l 1 in rain nitrate concentrations from the rock glacier generally increased with time with maximum concentrations of 135 moles l 1 in october among the highest nitrate concentrations reported for high elevation surface waters these high nitrate concentrations appear to be characteristic of rock glacier outflow in the rocky mountains as a paired difference t test shows that nitrate concentrations from the outflow of 7 additional rock glaciers were significantly greater compared to their reference streams p 0 003 end member mixing analysis suggest that snow was the dominant source of nitrate in june soil solution was the dominant nitrate source in july and base flow was the dominant source in september fluoresence index values and parafac analyses of dissolved organic matter dom are also consistent with a switch from terrestrial dom in the summer time period to an increasing aquatic like microbial source during the autumn months copyright 2006 john wiley sons ltd

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

benchmarking classifiers to optimally integrate terrain analysis and multispectral remote sensing in automatic rock glacier detection abstract the performance improvements that can be achieved by classifier selection and by integrating terrain attributes into land cover classification are investigated in the context of rock glacier detection while exposed glacier ice can easily be mapped from multispectral remote sensing data the detection of rock glaciers and debris covered glaciers is a challenge for multispectral remote sensing motivated by the successful use of digital terrain analysis in rock glacier distribution models the predictive performance of a combination of terrain attributes derived from srtm shuttle radar topography mission digital elevation models and landsat etm data for detecting rock glaciers in the san juan mountains colorado usa is assessed eleven statistical and machine learning techniques are compared in a benchmarking exercise including logistic regression generalized additive models gam linear discriminant techniques the support vector machine and bootstrap aggregated tree based classifiers such as random forests penalized linear discriminant analysis plda yields mapping results that are significantly better than all other classifiers achieving a median false positive rate mfpr estimated by cross validation of 8 2 at a sensitivity of 70 i e when 70 of all true rock glacier points are detected the gam and standard linear discriminant analysis were second best mfpr 8 8 followed by polyclass for comparison the predictive performance of the best three techniques is also evaluated using 1 only terrain attributes as predictors mfpr 13 1 14 5 for best three techniques and 2 only landsat etm data mfpr 19 4 22 7 yielding significantly higher mfpr estimates at a 70 sensitivity the mfpr of the worst three classifiers was by about one quarter higher compared to the best three classifiers and the combination of terrain attributes and multispectral data reduced the mfpr by more than one half compared to remote sensing only these results highlight the importance of combining remote sensing and terrain data for mapping rock glaciers and other debris covered ice and choosing the optimal classifier based on unbiased error estimators the proposed benchmarking methodology is more generally suitable for comparing the utility of remote sensing algorithms and sensors

surface velocity and ice discharge of the ice cap on king george island antarctica glaciers on king george island antarctica have shown retreat and surface lowering in recent decades concurrent with increasing air temperatures a large portion of the glacier perimeter is ocean terminating suggesting possible large mass losses due to calving and submarine melting here we estimate the ice discharge into the ocean for the king george island ice cap l band synthetic aperture radar images covering the time span january 2008 to january 2011 over king george island are processed using an intensity tracking algorithm to obtain surface velocity measurements pixel offsets from 40 pairs of radar images are analysed and inverted to estimate a weighted average surface velocity field ice thicknesses are derived from simple principles of ice flow mechanics using the computed surface velocity fields and in situ thickness data the maximum ice surface speeds reach 225 m a 1 and the total ice discharge for the analysed flux gates of king george island is estimated to be 0 720 0 428 gt a 1 corresponding to a specific mass loss of 0 64 0 38 m w e a 1 over the area of the entire ice cap 1127 km 2

velocity structure of the pamir hindu kush region possible evidence of subducted crust the arrival times of compressional p and shear s waves from approximately 580 microearthquakes recorded by a temporary array in the pamir hindu kush region in central asia are used to deduce one and three dimensional velocity structures of this region the results for one dimensional structures imply that the moho is at 70 5 depth also there is a velocity reversal near 160 km depth which is inferred to be the beginning of the low velocity zone this reversal continues to depths of approximately 230 km below 230 km velocities are somewhat higher than those of normal mantle at similar depths 9 3 km s versus 8 4 km s for p waves the outstanding feature of the results for three dimensional velocity structures is a broad 40 km centrally located region with 8 to 10 lower velocities than those in the surrounding regions this low velocity region envelopes the seismic zone at depths between 70 and 150 km the region may actually extend beyond these depths but the results for shallower and deeper structure lack sufficient resolution to decide several tests using both hypothetical and real data were performed to estimate the reliability of the three dimensional solutions the results of these tests suggest that the inferred velocities are reasonably accurate representations of the average velocities in the blocks although one must be cautious of the effects of averaging in interpreting the solution the low velocity region is inferred to be a manifestation of substantial quantities of subducted continental crust therefore while subduction has occurred in the pamir hindu kush the results of the three dimensional inversions suggest that continental rather than only oceanic lithosphere has been subducted to depths of at least 150 km appendices are available with the entire article on microfiche order from american geophysical union 2000 florida avenue n w washington d c 20009 document j81 013 1 00 payment must accompany order

rates of chemical denudation and co2 drawdown in a glacier covered alpine catchment solute fluxes from a glacier covered alpine catchment are partitioned into components derived from sea salt acid aerosol dissolution of atmospheric co2 and crustal weathering the bulk of solute is crustally derived coupled sulfide oxidation and carbonate dissolution so cd and carbonation of carbonate minerals generate approximately equal amounts of solute chemical denudation constitutes 1 5 of solid denudation but is significantly higher than the continental average co2 drawdown by weathering reactions varies directly with discharge and suspended sediment load and inversely with meltwater p co2 if it is generally true that flushing rates control co2 drawdown in glacier covered catchments then glacially driven chemical weathering could be a significant factor in carbon cycling and climate change on glacial interglacial time scales

a rock glacier pond system nw italian alps soil and sediment properties geochemistry and trace metal bioavailability abstract rock glacier sediment transfer and ice melting can impact surface waters located downstream however there is a lack of knowledge on the influence of rock glacier dynamics on the geochemical hydrochemical and ecological characteristics of adjacent impounded surface waters in the col d olen area long term ecological research site nw italian alps an intact rock glacier terminates into a pond and solute enriched waters originating from the rock glacier flow into the pond through a subsurface hydrological window in this study we performed geophysical and ground surface temperature measurements moreover we sampled soils and sediments in different compartments of the investigated rock glacier pond system and we further sampled benthic invertebrates in the pond cold ground thermal regime ground ice presence and coarse debris cover on the rock glacier together with its lithology serpentinites influence the rock glacier geochemistry and ecology with respect to surrounding areas pond geochemistry is affected by transfer of trace metal enriched fine grained debris and meltwaters from the rock glacier enhanced bioavailability of serpentinite associated trace metals was proved with concentrations of ni and cr in benthic invertebrates up to 384 and 110 mg kg 1 d w respectively potentially exerting toxic effects on pond biota the advancing movement of the rock glacier not only has delivered sediments to the pond but it has progressively filled the valley depression where the pond is located creating a dam that could have modified the level of impounded water this process likely constituted a sediment trap in which serpentinitic rock glacier sediments could be deposited at the pond bottom with related geochemical and ecological implications this study illustrates the importance of rock glaciers in influencing the characteristics of downstream freshwater bodies and highlights the need to improve our knowledge about climate change related impacts of rock glacier dynamics on alpine headwaters