occurrence of rocky and sedimentary glacier beds in the swiss alps as estimated from glacier inventory data the occurrence of rocky and sedimentary glacier beds in the swiss alps was investigated using two approaches 1 a detailed and systematic classification of glacier forefields in the completely revised swiss glacier inventory and 2 the application of an algorithm for estimating bed characteristics from glacier inventory data the algorithm is based on the assumption that the sediment balance of a glacierized catchment i e the ratio between debris input from the surrounding rock walls and debris evacuation by the meltwater stream determines the occurrence of rocky sedimentary or mixed beds the processes which govern the sediment balance within a glacierized catchment cannot be easily observed or measured in the field however the main factors reflecting them can be organized in the form of an erosion sedimentation index this index discriminates between glaciers eroding into bedrock and those building up thick sediment beds and thus allows for rough assessments concerning bed characteristics sedimentary and mixed sedimentary rocky glacier beds clearly predominate in the swiss alps but more detailed spatial analysis is required for better predictions

glacier shrinkage in the ebinur lake basin tien shan china during the past 40 years the ebinur lake basin tien shan china was described in the early 20th century as the green labyrinth this relatively productive area supports agriculture and stands in contrast to the regional aridity glacier melt runoff is an important source of water for this arid region and has played a significant role in its economic development however over the past 40 years the ecology and environment of the region have seriously degenerated due to human activity and climate change to investigate changes in glacier water supply measurements from two reference glaciers were performed and used to validate satellite data and historical data for glaciers in the water catchment variability in regional glacier total area and volume over the past 40 years was reconstructed from historical documents aerial photographs and remote sensing data our investigations of 446 glaciers showed that from 1964 to 2004 the total glacier area decreased by 14 7 0 4 a 1 corresponding to an estimated volume change of 20 5 during this period the most dramatic decrease in glacier area corresponded to a rapid rise in temperature this reduction in glacier area is accelerating and impacting the future sustainability of the region s water resources

the uplift history of the haiyuan liupan shan region northeast of the present tibetan plateau integrated constraint from stratigraphy and thermochronology abstractthe haiyuan liupan shan delimits the northeastern margin of the tibetan plateau we present the integrated results of new stratigraphic investigations apatite fission track analyses and related thermal history modeling tied to the structural fabric of this region these constraints provide insight into the timing of northward propagation of the plateau with 1 local relief creation and enhanced erosion in the latest jurassic to earliest cretaceous representing the local element of a complex regional far field deformation response to the lhasa qiangtang collision with the south asian margin 2 evidence for likely late cretaceous exhumation but this is uncertain given the regional sedimentary gap that exists across this interval 3 eocene relief generation as a first likely response to far field effects of the india asia collision and related to wider regional events recognized in this part of northwestern china and 4 the latest deformation episode propagating strongly into the haiyuan

the formation of supraglacial debris covers by primary dispersal from transverse englacial debris bands glaciological controls on debris cover formation are investigated from the perspective of primary dispersal of supraglacial debris across a melting ice surface this involves the migration of angled debris septa outcrops across a melting thinning glacier ablation zone three measures of a glacier s ability to evacuate supraglacial debris are outlined 1 a concentration factor describing the focusing of englacial debris into specific supraglacial mass loads 2 the rate of migration of a septum outcrop relative to the local ice surface and 3 a downstream velocity differential between a slower septum outcrop and the faster ice surface velocity measures 1 and 2 are inversely related while measure 3 increases down glacier to explain why slow moving thinning ice rapidly becomes debris covered data from glacier d estelette italian alps are used to illustrate these processes and to explore the potential for debris cover formation and growth in different glaciological environments the transition from a clean transport dominated to a debris covered ablation dominated glacier is explained by the melting out of more closely spaced debris septa in combination with the geometric nteractions of angled septa and ice surface in a field of reducing flow and increasing ablation the growth and shrinkage of debris covers are most sensitive to glaciological changes at glaciers with gently dipping debris bearing foliation but less sensitive at high compression glaciers whose termini are constrained by moraine dams and other forms of obstruc tion these findings show that a variety of debris covered glacier types will show a spectrum of response characteristics to negative mass balance copyright 2013 john wiley sons ltd

change in surface debris cover on mont blanc massif glaciers after the little ice age termination because of insulation by supraglacial debris the dynamics of debris covered glaciers differ from those of clean glaciers thus changes in debris cover have to be taken into account when interpreting glacier fluctuations in terms of climate forcing three large glaciers in the mont blanc massif were investigated for the period since the termination of the little ice age lia using historical and scientific documents of the eighteenth and nineteenth centuries although debris cover was limited to its frontal area until the 1840s miage glacier exhibited a continuous debris cover in the first decades after the lia increasing to its present extent by the 1930s on the mer de glace a partial debris cover formed by coalescence of two of the four medial moraines at the close of the lia until 1890 these moraines have formed the present veine noire black vein in contrast brenva glacier had a continuous debris cover at the end of the eighteenth century possibly following a rock avalanche in 1767 fo

hydrochemistry as an indicator of subglacial drainage system structure a comparison of alpine and sub polar environments the anion compositions so 2 4 hco 3 and cl of runoff from the haut glacier d arolla switzerland and austre broggerbreen svalbard are compared to assess whether or not variations in water chemistry with discharge are consistent with current understanding of the subglacial drainage structure of warm and polythermal based glaciers these glacial catchments have very different bedrocks and the subglacial drainage structures are also believed to be different yet the range of anion concentrations show considerable overlap for so 2 4 and hco 3 concentrations of cl are higher at austre broggerbreen because of the maritime location of the glacier correcting so 2 4 for the snowpack component reveals that the variation in non snowpack so 2 4 with discharge and with hco 3 is similar to that observed at the haut glacier d arolla hence if we assume that the provenance of the non snowpack so 2 4 is the same in both glacial drainage systems a distributed drainage system also contributes to runoff at austre broggerbreen we have no independent means of testing the assumption at present the lower concentrations of non snowpack so 2 4 at austre broggerbreen may suggest that a smaller proportion of runoff originates from a distributed drainage system than at the haut glacier d arolla

global assessment of supraglacial debris cover extents rocky debris on glacier surfaces influences ice melt rates and the response of glaciers to climate change however scarce data on the extent and evolution of supraglacial debris cover have so far limited its inclusion in regional to global glacier models here we present global data sets of supraglacial debris cover extents based on landsat 8 and sentinel 2 optical satellite imagery we find that about 4 4 26 000 km2 of all glacier areas excluding the greenland ice sheet and antarctica are covered with debris but that the distribution is heterogeneous the largest debris covered areas are located in high mountain ranges away from the poles at a global scale we find a negative scaling relationship between glacier size and percentage of debris therefore the influence of debris cover on glacier mass balances is expected to increase in the future as glaciers continue to shrink

spatially variable response of himalayan glaciers to climate change affected by debris cover the present state and future evolution of himalayan glaciers has been controversial an analysis of remotely sensed frontal changes and surface velocities from glaciers in the greater himalaya between 2000 and 2008 shows large regional variability in the responses of himalayan glaciers to climate change

solute dynamics of meltwater of gangotri glacier garhwal himalaya india the present study investigates solute dynamics of meltwater of gangotri glacier system in terms of association of different chemical compounds with the geology of the area in the meltwater the presence of cations varied as c mg2 c ca2 c na c k while order of concentration of anions has been c hco3 c so42 c cl c no3 in years 2003 and 2004 the magnesium and calcium are found as the dominant cations along with bicarbonate and sulphate as dominant anions the high ratios of c ca2 mg2 total cations and c ca2 mg2 c na k indicate that the meltwater chemistry of the gangotri glacier system catchment is mostly controlled by carbonate weathering attempts are made to develop rating curves for discharge and different cations sporadic rise in discharge without corresponding rise in concentration of most of cations is responsible for their loose correlation in a compound valley glacier like gangotri glacier

suspended sediment and phosphorus in proglacial rivers bioavailability and potential impacts upon the p status of ice marginal receiving waters this paper adopts standard tests developed in temperate catchment research to determine the total phosphorus tp and the algal available base extractable phosphorus naoh p content of a wide range of glaciofluvial sediments from the northern hemisphere we find that the tp content of these sediments is broadly similar to the p content of major rock types in earth s crust 230 670 gp g and so the tp yields of glacier basins may be high owing to the efficacy of suspended sediment evacuation by glacial meltwaters we show that this is best achieved where subglacial drainage systems are present the naoh p pool of the sediments is found to be low 1 23 gp g relative to the tp pool and also to the naoh p pool of suspended sediments in temperate non glacierized catchments this most probably reflects the restricted duration of intimate contact between dilute meltwaters and glacial suspended sediments during the ablation season thus despite the high surface area volume ratio of glacial suspended sediments the potential for p adsorption to mineral surfaces following release by dissolution is also low further sorption experiments and sequential extraction tests conducted using glacial suspended sediments from two svalbard catchments indicate that the generation of reactive secondary minerals e g fe and other hydroxides with a strong capacity to scavenge p from solution and thereby promote the continued dissolution of p may also be limited by the short residence times most p is therefore associated with poorly weathered calcite apatite rich mineral phases however we use examples from the svalbard glacier basins austre broggerbreen and midre lovenbreen to show that the high sediment yields of glaciers may result in appreciable naoh p loading of ice marginal receiving waters again the importance of subglacial drainage is highlighted as it produces a major episodic release of naoh p at midre lovenbreen that results in a yield 8 2 kg naoh p km2 year more than one order of magnitude greater than that at austre broggerbreen where subglacial drainage is absent and the yield is 0 48 kg naoh p km2 year therefore as since both detrimental and beneficial effects of sediment bound p loading in ice marginal receiving waters are possible i e either reduced primary productivity owing to increased turbidity or p fertilization following desorption there is a pressing need to assess the ambient p status of such environments and also the capacity for ice marginal ecosystems to adapt to such inputs copyright 2004 john wiley sons ltd

glaciological response to distal tephra fallout from the 1947 eruption of hekla south iceland glacier responses to tephra deposition are shown to be highly variable where wind transported eruption plumes produce narrow distal fallout zones with steep lateral thickness gradients significant but short lived advances of faster flowing glaciers can be triggered by deposition from modest eruptions the 1947 eruption of hekla south iceland covered nearby glaciers with variable thicknesses of tephra causing dramatic spatial variations in ablation rate relative snow ablation increased by an estimated 80 at the eastern margin of eyjafjallajokull but decreased by 54 at the western margin relative ice ablation increased by only 4 in the east but decreased by 75 at the western margin only 15 km distant the effect on mass balance therefore depends on tephra distribution as well as on the nature of the glacier surface on gigjokull retardation of ablationwas greatest at the terminus associated with an anomalous advance of 328 m between 1947 and 1954 other glaciers in the fallout zone show either no recognizable response or accelerated retreat advances will be short lived due to the rapid redistribution of supraglacial tephra in a maritime climate and the potential for discriminating between volcanically and climatically forced advances in the glacio geomorphological record is low the long term glaciological effect of volcanism is to create thin low albedo covers after reworking which make conditions less favourable for glaciation

a multicomponent coupled model of glacier hydrology 1 theory and synthetic examples 1 basal hydrology is acknowledged as a fundamental control on glacier dynamics especially in cases where surface meltwater reaches the bed for many glaciers at midlatitudes basal drainage is influenced by subaerial englacial and subsurface water flow one of the major shortcomings of existing basal hydrology models is the treatment of the glacier bed as an isolated system we present theoretical and computational models that couple glacier surface runoff englacial water storage and transport subglacial drainage and subsurface groundwater flow each of the four model components is represented as a two dimensional vertically integrated layer that communicates with its neighbors through water exchange governing equations are derived from the law of mass conservation and are expressed as a balance between the internal distribution of water and external sources the numerical exposition of this theory is a time dependent finite difference model that can be used to simulate glacier drainage in this paper we outline the theory and conduct simple tests using an idealized glacier geometry in the companion paper the model is tailored to trapridge glacier yukon territory canada where results are compared with measurements of subglacial water pressure

the hydrochemistry of runoff from a cold based glacier in the high arctic scott turnerbreen svalbard this article is restricted access it was published in the journal hydrological processes john wiley sons ltd and is available at http www3 interscience wiley com cgi bin issn descriptor printissn value 0885 6087

do debris covered glaciers demonstrate distinctive hydrological behaviour compared to clean glaciers abstract supraglacial debris is known to strongly influence the distribution of glacier surface melt since melt inputs drive the formation and evolution of glacial drainage systems it should follow that the drainage systems of debris covered glaciers will differ from those of debris free glaciers this would have implications for the proglacial runoff regime subglacial erosion and glacier dynamics this paper presents analysis of return curves from 33 successful dye injections into the extensively debris covered miage glacier italian alps it demonstrates that the spatial distribution of supraglacial debris influences the structure and seasonal evolution of the glacial drainage system where the debris cover is continuous melt is lower and the surface topography is chaotic with many small supraglacial catchments these factors result in an inefficient englacial subglacial drainage network beneath continuous debris which drains to the conduit system emanating from the upper ablation zone melt rates are high in areas of clean and dirty ice above the continuous debris runoff from these areas is concentrated by inter moraine troughs into large supraglacial streams which encourages the early season development of an efficient englacial subglacial conduit system downstream of this area drainage efficiency from the debris covered area increases over the melt season but dye trace transit velocity remains lower than from moulins on the upper glacier future runoff models should account for the influence of supraglacial debris on the hydrological system

hydrology of debris covered glaciers in high mountain asia abstract the hydrological characteristics of debris covered glaciers are known to be fundamentally different from those of clean ice glaciers even within the same climatological geological and geomorphological setting understanding how these characteristics influence the timing and magnitude of meltwater discharge is particularly important for regions where downstream communities rely on this resource for sanitation irrigation and hydropower such as high mountain asia the hydrology of debris covered glaciers is complex rugged surface topographies typically route meltwater through compound supraglacial englacial systems involving both channels and ponds as well as pathways that remain unknown low gradient tongues that extend several kilometres retard water conveyance and promote englacial storage englacial conduits are frequently abandoned and reactivated as water supply changes new lines of permeability are exploited and drainage is captured due to high rates of surface and subsurface change seasonal influences such as the monsoon are superimposed on these distinctive characteristics reorganising surface and subsurface drainage rapidly from one season to the next recent advances in understanding have mostly come from studies aimed at quantifying and describing supraglacial processes little is known about the subsurface hydrology particularly the nature or even existence of subglacial drainage in this review we consider in turn the supraglacial englacial subglacial and proglacial hydrological domains of debris covered glaciers in high mountain asia we summarise different lines of evidence to establish the current state of knowledge and in doing so identify major knowledge gaps finally we use this information to suggest six themes for future hydrological research at high mountain asian debris covered glaciers in order to make timely long term predictions of changes in the water they supply

lithospheric architecture and deformation of ne tibet new insights on the interplay of regional tectonic processes abstract gps measurements indicate rapid lateral extrusion of the ne tibetan plateau which causes active ne directed crustal shortening and has initiated oblique shearing along the margins of ne tibet however the tibetan highlands terminate around 103 e longitude and topographic relief disappears to the northeast the exact reasons for this drop in elevation remain obscure due to widespread tertiary sediments and quaternary loess which obscure details of the lithospheric structure this study describes a new 310 km long deep seismic reflection line striking ne sw across the interior of ne tibet integrating its data with a previously described 165 km long deep seismic profile of the tibet ordos transition zone together these datasets provide a complete picture of the crustal architecture of the north easternmost tibetan plateau gravity anomaly and previous geological evidence also help constrain complex deformation pattern in the region interpretations of these patterns indicate the importance of the large scale sinistral haiyuan fault zone and inherited vertical variation in mechanical properties of the lithosphere in the overall tectonic evolution of the ne tibetan plateau the overall crustal architecture obtained in this study provides spatial context for the neotectonic evolution of ne tibet and helps constrain the interplay of geologic and geodynamic processes affecting ne tibet and adjacent regions

response of meltwater runoff to air temperature fluctuations on keqikaer glacier south slope of tuomuer mountain western china flow records of meltwater runoff provide information about the movement of water through the ice and about glacial ablation this study indicates that the lag time required for a maximum correlation between daily discharge and air temperature and the sensitivity of meltwater response to air temperature changes during the ablation period for different proportions of the base flow to examine how glaciers respond to climatic changes and the hydrological characteristics of the large glaciers in the tuomuer mountain area western china observations have been undertaken in this region since june 2003 by means of correlation and cross spectral analysis the relationship between air temperature and meltwater runoff in different months of the ablation period may september on keqikaer glacier in 2004 has been evaluated data have been selected from the 1st to the 30th for every month and the calculated hourly discharges of the meltwater runoff for each day were utilized from these data we conclude that for keqikaer glacier the meltwater runoff has a greater sensitivity to air temperature in may july and august than in june and september however the lag time is shorter in june july and august than it is in may and september

role of the supraglacial snowpack in mediating meltwater delivery to the glacier system as inferred from dye tracer investigations the supraglacial snowpack plays an important role in mediating the delivery of meltwater produced at the snowpack surface to the rest of the glacier system with potential implications for both proglacial hydrograph form and the timing and magnitude of glacier movement induced by changes in subglacial water pressure however there remain few field observations of the hydrological behaviour of supraglacial snowpacks and its seasonal evolution during the melt season data collected during the 2004 melt season at haut glacier d arolla valais switzerland uses both qualitative and quantitative dye tracing techniques to enhance our understanding of supraglacial snowpack hydrology observations of the movement of dye stained water show the complexity of flow patterns and the influence of ice layers and preferential flow zones in controlling percolation through the snowpack and fluorometric techniques yield average flow rates for percolation through the snowpack of between 0 13 and 0 49 m h the changing form of dye return curves and increasing percolation rates reflect an increase over the course of the melt season in the efficiency with whichthesnowpacktransmitsmeltwater snowpackpermeabilitywasfoundtobesignificantlylower 1 67x10 m on average than that assumed in previous modelling studies of glacial hydrology showing the need for improved information about snowpack hydrology if its importance in controlling runoff is to be fully appreciated

glacier meltwater hydrochemistry abstract glacierised areas present an ideal environment in which to study water rock interaction since chemical weathering rates are high and anthropogenic impacts are often minimal detailed investigations of meltwater quality variations have suggested the importance of these environments in estimates of terrestrial chemical erosion and global biogeochemical cycles most notably the role of meltwaters in co2 sequestration during episodes of deglaciation has attracted considerable attention since this may impact on climate at glacial interglacial timescales however there is still considerable uncertainty surrounding estimates of co2 drawdown by meltwaters which remains to be resolved water flow through glaciers exerts an important control on ice mass dynamics and influences the quantity and quality of water delivered to environments downstream of glacierised basins thus the study of the configuration and dynamics of subglacial drainage systems is important not only to enhance scientific understanding but also to allow effective water resource utilisation in glacierised headwater catchments bulk meltwater quality characteristics draining terrestrial ice masses also offer the potential to provide unique information on hydrological and hydrochemical processes operating in the inaccessible subglacial environment here significant advances have been made in understanding the controls on chemical weathering reactions based on the identification of key dissolved indicator species this has allowed water quality variations to be exploited as a tool for both subglacial hydrochemical and hydrological investigations as a result this area of glaciology has received considerable attention in recent years utilising an increasing range of dissolved ions and integrating field and laboratory studies however uncertainty still surrounds certain areas of meltwater quality science including the role of microorganisms in a system which to date has largely been viewed as abiotic a better understanding of the processes and rates of chemical weathering in glacierised environments has the potential to enhance our understanding of the environment and to facilitate the exploitation of water quality variations for both scientific and applied objectives in this paper the development and current state of meltwater quality science as a tool for investigating subglacial hydrology and geochemistry is detailed and problems and future directions identified this will hopefully stimulate wider interest in an important area of aquatic chemistry with significant applied implications

evolution of glacial flow and drainage during the ablation season proglacial discharge is controlled by the geometry of the glacial drainage network and by meltwater processes the glacial drainage systems of some alpine glaciers have been characterised using a model based on a proglacial discharge analysis in this paper we apply high frequency systemic analysis to data collected from the baounet glacier french alps during two successive ablation seasons our approach is based on an analysis of the evolution of daily recession curves during the ablation period the observed data are fitted by a single coefficient dependant recession law changes in are compared to variations in the daily discharge amplitude and the time lag between air temperature and proglacial discharge the changes in the values do not appear to be related to changes in the time lag and the amplitude of the daily discharge there were significant variations in the coefficient during the two ablation periods studied here even if there was no time lag or the daily discharge amplitude change high values of correspond to high drainage velocities therefore increases in values can be used as an indicator of the evolution of the glacier s internal drainage network

chemical denudation and silicate weathering in himalayan glacier basins batura glacier pakistan original article can be found at http www sciencedirect com science journal 00221694 copyright elsevier b v doi 10 1016 s0022 1694 02 00036 7 full text of this article is not available in the uhra

recent glacier retreat in the caucasus mountains russia and associated increase in supraglacial debris cover and supra proglacial lake development this paper reports changes in supraglacial debris cover and supra proglacial lake development associated with recent glacier retreat 1985 2000 in the central caucasus mountains russia satellite imagery landsat tm and etm was used to map the surface area and supraglacial debris cover on six neighbouring glaciers in the adylsu valley through a process of manual digitizing on a false colour composite of bands 5 4 3 red green blue the distribution and surface area of supraglacial and proglacial lakes was digitized for a larger area which extended to the whole landsat scene we also compare our satellite interpretations to field observations in the adylsu valley supraglacial debris cover ranges from 25 on individual glaciers but glacier retreat between 1985 and 2000 resulted in a 3 6 increase in the proportion of each glacier covered by debris the only exception to this trend was a very small glacier where debris cover did not change significantly and remote mapping proved more difficult the increase in debris cover is characterized by a progressive up glacier migration which we suggest is being driven by focused ablation and therefore glacier thinning at the up glacier limit of the debris cover resulting in the progressive exposure of englacial debris glacier retreat has also been accompanied by an increase in the number of proglacial and supraglacial lakes in our study area from 16 in 1985 to 24 in 2000 representing a 57 increase in their cumulative surface area these lakes appear to be impounded by relatively recently lateral and terminal moraines and by debris deposits on the surface of the glacier the changes in glacier surface characteristics reported here are likely to exert a profound influence on glacier mass balance and their future response to climate change they may also increase the likelihood of glacier related hazards lake outbursts debris slides and future monitoring is recommended

a physically based method for estimating supraglacial debris thickness from thermal band remote sensing data in order to account for the effects of debris cover in model scenarios of the response of glaciers to climate change and water resource planning it is important to know the distribution and thickness of supraglacial debris and to monitor its change over time previous attempts to map surface debris thickness using thermal band remote sensing have relied upon time specific empirical relationships between surface temperature and thickness limiting their general applicability in this paper we develop a physically based model that utilizes advanced spaceborne thermal emission and reflection radiometer aster thermal band remotely sensed imagery and is based on a solution of the energy balance at the debris surface the model is used to estimate debris thickness on miage glacier italy and is validated using field debris thickness measurements and a previously published debris thickness map the temporal transferability of the model is demonstrated through successful application to a separate aster image from a different year using reanalysis meteorological input data this model has the potential to be used for regional scale supraglacial debris thickness mapping and monitoring for debris up to at least 0 50 m thickness but improved understanding of the spatial patterns of air temperature aerodynamic roughness length and thermal properties across debriscovered glaciers is needed

surface and subsurface hydrology of debris covered khumbu glacier nepal revealed by dye tracing abstract while the supraglacial hydrology of debris covered glaciers is relatively well studied almost nothing is known about how water is transported beneath the glacier surface here we report the results of sixteen fluorescent dye tracing experiments conducted in april may 2018 over the lowermost 7 km of the high elevation debris covered khumbu glacier nepal to characterise the glacier s surface and subsurface drainage system dye breakthroughs indicated a likely highly sinuous and channelised subsurface hydrological system draining water from the upper part of the ablation area this flowpath was distinct from the linked chain of supraglacial ponds present along much of the glacier s lower ablation area through which water flow was extremely slow 0 003 m s 1 likely reflecting the study s timing during the pre monsoon period subsurface drainage pathways emerged at the glacier surface close to the terminus and flowed into small near surface englacial reservoirs that typically delayed meltwater transit by several hours we observed rapid pathway changes resulting from surface collapse indicating a further distinctive aspect of the drainage of debris covered glaciers we conclude that the surface and subsurface drainage of khumbu glacier is both distinctive and dynamic and argue that further investigation is needed to refine the characterisation and test its regional applicability to better understand future himalayan debris covered glacier meltwater delivery to downstream areas

resolving sedimentological uncertainties using magnetostratigraphic correlation an example from the middle jurassic of burgundy france abstract magnetostratigraphic analysis was undertaken on a core 85 m long core from the shallow water carbonate platform of bathonian to late callovian age in burgundy france to establish high resolution magnetic correlations in a succession devoid of good stratigraphic markers and with diachronous lithofacies magnetic extracts reveal that the magnetic minerals carrying the characteristic remanence are mainly detrital titanomagnetites and fine grained biogenic magnetite of probable bacterial origin comparison of magnetic properties with lithologic data from wireline logs indicates that large grains are predominant in marly deposits whereas fine grained minerals are common mainly in pure limestones we have established a polarity sequence for the core that is independent of lithology and in ludes 17 polarity zones with the help of faunal zonation based on brachiopods and ammonites the polarity sequence was compared with the magnetostratigraphy established previously in four other sections from the same area the magnetostratigraphic correlation corroborates that platform flooding occurred during the early callovian an age in agreement with biostratigraphic interpretation constraining the age of successive onlaps a characteristic reverse polarity interval within the ammonite calloviense subzone is present in all the cores confirming the utility of magnetostratigraphy for stratigraphic correlation studies throughout the paris basin and burgundy

solute acquisition in glacial melt waters i fjallsjokull south east iceland bulk melt waters with closed system characteristics l etude de la composition des eaux de surface cations alcalinite sulfates et ph montre des modifications par rapport aux precipitations par l acquisition de substances dissoutes provenant de l alteration et de la dissolution de debris rocheux dans un systeme ouvert aux gaz carbonique atmospherique les eaux resurgentes ont des compositions variables calcite qui peuvent provenir de l eau de surface

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

interactions between rock avalanches and glaciers in the mont blanc massif during the late holocene rock avalanches are common in the mont blanc massif which is bordered by valleys with large resident and tourist populations and important highways this paper combines historical data with detailed geomorphological mapping stratigraphic observation and absolute and relative dating to interpret several deposits resulting from rock avalanching onto glaciers nineteen rock falls and rock avalanches are described ranging in volume from 10 000 m3 to 10 106 m3 they occurred between 2500 bp and ad 2007 at six sites the events at three sites miage and drus glaciers and tour des grandes jorasses are characterised by short travel distances those at brenva triolet and frebouge glaciers exhibit excessive travel distances interactions between rock avalanches and glaciers are of four types i rock avalanche triggering where glacial and paraglacial controls include debuttressing of rockwalls due to glacier thinning and retreat oversteepening of rock slopes by glacial erosion and effects of glaciers on permafrost ii rock avalanche mobility in which mobility and travel distance are modified by channelling of rock avalanche debris by moraines and valleys incorporation of ice and snow often 50 for large events and irregularities on the glacier surface iii deposit sedimentology where melting of incorporated ice transforms the final deposit by reducing its thickness typically to 5 m and debris of variable thicknesses is juxtaposed in a hummocky deposit with chaotic piles of angular rock debris and iv glacier dynamics where insulating debris deposited upon a glacier produces a debris covered glacier of different dynamics and high elevated scars can favour the formation of small glaciers

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

glacier changes in the garhwal himalaya india from 1968 to 2006 based on remote sensing glacier outlines are mapped for the upper bhagirathi and saraswati alaknanda basins of the garhwal himalaya using corona and advanced spaceborne thermal emission and reflection radiometer aster satellite images acquired in 1968 and 2006 respectively a subset of glaciers was also mapped using landsat tm images acquired in 1990 glacier area decreased from 599 9 15 6 km 2 1968 to 572 5 18 0 km 2 2006 a loss of 4 6 2 8 glaciers in the saraswati alaknanda basin and upper bhagirathi basin lost 18 4 9 0 km 2 5 7 2 7 and 9 0 7 7 km 2 3 3 2 8 respectively from 1968 to 2006 garhwal himalayan glacier retreat rates are lower than previously reported more recently 1990 2006 recession rates have increased the number of glaciers in the study region increased from 82 in 1968 to 88 in 2006 due to fragmentation of glaciers smaller glaciers 2 lost 19 4 2 5 0 51 0 07 a 1 of their ice significantly more than for larger glaciers 50 km 2 which lost 2 8 2 7 0 074 0 071 a 1 from 1968 to 2006 the debris covered glacier area increased by 17 8 3 1 0 46 0 08 a 1 in the saraswati alaknanda basin and 11 8 3 0 0 31 0 08 a 1 in the upper bhagirathi basin climate records from mukhim 1900 m a s l and bhojbasa 3780 m a s l meteorological stations were used to analyze climate conditions and trends but the data are too limited to make firm conclusions regarding glacier climate interactions

seismic evidence for the north china plate underthrusting beneath northeastern tibet and its implications for plateau growth abstract lithospheric deformation of the tibetan plateau is caused by subduction of the indian northward and asian southward plates the effects of this interaction on inner reaches of the asian continent between the tibetan plateau and the north china craton ncc for example remain uncertain due to poor geophysical data coverage in northeastern tibet ne tibet we provide here detailed knowledge of the lithospheric structure beneath ne tibet as determined from a dense broadband seismic profile traversing ne tibet to the westernmost ncc receiver function imaging reveals several significant features including a north dipping intracrustal converter nc moho offset overlap beneath major fault zones and a low velocity layer lvl in the middle lower crust the lithosphere asthenosphere boundary lab is clearly defined and appears as a south dipping interface that runs continuously from the alxa interior to the qilian orogen interpretation of these observations combined with other seismic evidence implies that the ncc lithospheric mantle has been persistently underthrust beneath the qilian orogen this process forms the thick skinned crustal accretionary wedges which develop above a middle lower intracrustal decollement our results provide further deep geophysical constraints on the cenozoic post collisional evolution of the convergent boundary between ne tibet and the ncc and help clarify the mechanism of plateau growth in this boundary area

controls on the major ion chemistry of the dokriani glacier meltwaters ganga basin garhwal himalaya india a detailed study of the major ion chemistry of the dokriani glacier meltwaters feeding the bhagirathi river ganga basin garhwal himalaya india has been carried out to assess the role of active glaciers in the higher chemical denudation rate cdr in this area the cdr of the dokriani glacier catchment is 321 6 t km a higher than in other glacierized catchments of the world indicating intense chemical erosion in the glacierized catchments of the himalaya the dominance of ca 2 hco 3 and so 4 2 in meltwaters throughout the 6 month may october ablation period suggests that the chemical weathering is dominated by coupled reactions involving sulphide oxidation and carbonate dissolution good positive correlation between so 4 2 and suspended sediment concentration during july and august r 2 0 72 and 0 67 respectively suggests that the southwest monsoonal rainfall enhances the weathering of supraglacial moraine and contributes significant amounts of sulphate to the high meltwater discharges the sulphate flux as a proportion of combined so 4 2 hco 3 flux also increased from 45 at 2 m 3 s 1 to 63 at 10 m 3 s 1

the growth of northeastern tibet and its relevance to large scale continental geodynamics a review of recent studies recent studies of the northeastern part of the tibetan plateau have called attention to two emerging views of how the tibetan plateau has grown first deformation in northern tibet began essentially at the time of collision with india not 10 20 myr later as might be expected if the locus of activity migrated northward as india penetrated the rest of eurasia thus the north south dimensions of the tibetan plateau were set mainly by differences in lithospheric strength with strong lithosphere beneath india and the tarim and qaidam basins steadily encroaching on one another as the region between them the present day tibetan plateau deformed and its north south dimension became narrower second abundant evidence calls for acceleration of deformation including the formation of new faults in northeastern tibet since 15 ma and a less precisely dated change in orientation of crustal shortening since 20 ma this reorientation of crustal shortening and roughly concurrent outward growth of high terrain which swings from nne ssw in northern tibet to more ne sw and even ene wsw in the easternmost part of northeastern tibet are likely to be in part a consequence of crustal thickening within the high tibetan plateau reaching a limit and the locus of continued shortening then migrating to the northeastern and eastern flanks these changes in rates and orientation also could result from removal of some or all mantle lithosphere and increased gravitational potential energy per unit area and from a weakening of crustal material so that it could flow in response to pressure gradients set by evolving differences in elevation

chemical weathering in the foreland of a retreating glacier chemical denudation rates and strontium isotope ratios in streams vary substantially and systematically in the foreland of the retreating bench glacier in south central alaska to study weathering of young glacier sediments we sampled 12 streams draining a chronosequence of till and moraine soils derived from cretaceous metagraywacke metapelite bedrock both sediment age and vegetation cover increase with distance from the glacier cation denudation rates decline with increasing distance from the glacier whereas silica denudation rates increase carbonate dissolution and sulfide oxidation account for roughly 90 of the solute flux from the youngest sediments biotite alteration accounts for 5 11 of the solute flux its peak contribution is found in the glacier outlet stream silicate weathering is the dominant reaction only in the oldest sediments in a laboratory dissolution experiment using fresh glacial sediment carbonate dissolution dominated the solute flux during the first 700 hours paralleling the behavior of young sediments in the field in contrast to trends in the field the silica flux did not increase after the carbonate was exhausted from the reactor a possible reason for this difference is that establishment of vegetation causes an increase in silicate weathering the 87sr 86sr ratio in the glacier outlet stream is greater than that in proglacial streams and in bulk rock due to a greater contribution of biotite weathering in the outlet than in proglacial streams strontium isotope ratios decline with sediment exposure age in the proglacial streams and are consistent with a carbonate source because the dominant weathering reactions in the young sediments are of carbonate and sulfide rather than silicate minerals weathering at the glacier margin is not an important long term sink for atmospheric co2

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

far field lithospheric deformation in tibet during continental collision 1 crustal deformation along the present day northern margin of the tibetan plateau has occurred since mid to late eocene time soon after india collided with eurasia assuming that on these distance and time scales the lithosphere can be approximated using a thin viscous sheet we show that far field lithospheric deformation caused by an indenting boundary is expected to start shortly after collision begins when a strong region analogous to cratonic lithosphere like that of the tarim basin is included in the calculations shear and vertical strain rates concentrate along the southern edge of the strong region resulting in enhanced deformation there in calculations scaled to the dimensions of india and the tibetan plateau shear and vertical strain rates on the northern edge of the plateau increase soon after collision begins crustal thickening accelerates later in the calculations we propose that the apparent increased exhumation and perhaps surface uplift around 10 ma may signal the arrival of the thickening front

subglacial modulation of the hydrograph from glacierized basins the extent of basin glacierization has important implications for the hydrograph in part because snow firn and ice impart different delays in water transport through the system here the significance of subglacial drainage morphology in modulating the hydrograph is examined with a one dimensional physically based model the conceptual model of subglacial drainage comprises both fast and slow elements respectively associated with summer and winter drainage regimes the additional possibility of a permeable glacier substrate is taken into account by allowing water transport in a subglacial aquifer forced by prescribed rates of melt water delivery to the glacier bed the model predicts glacier discharge by drainage system provenance the effects of 1 hard versus soft glacier beds 2 subsurface permeability and groundwater flow and 3 glacier geometry are then investigated hydrograph character in the form of peak timing and amplitude symmetry with respect to the forcing and the amplitude of diurnal fluctuations is affected by the partitioning of water through the various flow elements hard beds and impermeable substrates maximize the discharge routed through the fast drainage system in the simulations generally resulting in higher seasonal discharge maxima and stronger diurnal variations in discharge high hydraulic transmissivities either at the glacier bed or in underlying strata hinder the development of the fast drainage system in the simulations producing hydrographs of lower amplitude glacier geometry has a modest effect with adverse bed slopes very thick or very thin ice and short glacier lengths favouring prolonged drainage through the slow system these results suggest that the morphology and evolution of the subglacial drainage system may play a significant role in determining the character of the hydrograph from glacierized basins

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

planimetric and volumetric glacier changes in the khumbu himal nepal since 1962 using corona landsat tm and aster data multitemporal space imagery from 1962 corona kh 4 1992 landsat tm 2001 and 2005 terra aster was used to investigate the glacier changes in the khumbu himal nepal the ice coverage in the investigation area decreased by about 5 between 1962 and 2005 with the highest retreat rates occurring between 1992 and 2001 the debris coverage increased concomitantly with the decrease in total glacier area the clean ice area decreased by 10 digital terrain model dtm generation from the early corona kh 4 stereo data in this high relief terrain is time consuming and the results still contain some elevation errors however these are minor in the snow free areas with gentle slopes thus comparison of the surfaces of the debris covered glacier tongues based on the corona dtm and an aster dtm is feasible and shows the downwasting of the debris covered glaciers the highest downwasting rates more than 20 m 0 5 m a 1 can be found near the transition zone between the active and the stagnant glacier parts of the debris covered glacier tongues the downwasting is lower but still evident in the active ice areas and at the snout with thick debris cover all investigated debris covered glaciers in the study area show similar behaviour the estimated volume loss for the investigated debris covered glacier tongues is 0 19 km 3

quantifying the effects of glacier conduit geometry and recharge on proglacial hydrograph form summary the configuration of glacier hydrological systems is often inferred from proxy data such as hydrographs that are collected in proglacial streams seasonal changes in the peakedness of hydrographs are thought to reflect changes in the configuration of the subglacial drainage system however the amount of information that proglacial hydrographs contain about drainage system configurations depends critically on the degree to which the drainage systems modify recharge hydrographs if the drainage system does not modify recharge hydrographs then proglacial hydrographs primarily reflect the recharge conditions produced by supraglacial inputs here we develop a theoretical framework to determine the circumstances under which glacier drainage systems can modify recharge hydrographs and the circumstances under which recharge pulses pass through glaciers unchanged we address the capability of single conduits simple arborescent conduit networks and linked cavity systems to modify diurnal recharge pulses simulations of discharge through large sets of such systems demonstrate that unless large reservoirs or significant constrictions are present the discharge hydrographs of simple glacial conduit systems are nearly identical to their recharge hydrographs conduit systems tend not to modify hydrographs because the changes in storage within englacial and subglacial conduit networks on short time scales are typically small compared to their ability to transmit water this finding suggests that proglacial hydrographs reflect a variety of factors including surface melt rate surface water transfer and subglacial water transfer in many cases the influence of suglacial processes may be relatively minor as a result the evolution of proglacial hydrographs cannot be used unambiguously to infer changes in the structure or efficiency of englacial or subglacial hydrological systems without accurate knowledge of the nature of the recharge hydrograph driving the flow

an energy balance model for debris covered glaciers including heat conduction through the debris layer extensive covers of supraglacial debris are often present in glacier ablation areas and it is essential to assess exactly how the debris affects glacier melt rates this paper presents a physically based energy balance model for the surface of a debris covered glacier the model is driven by meteorological variables and was developed using data collected at miage glacier italy during the ablation seasons of 2005 2006 and 2007 the debris surface temperature is numerically estimated by considering the balance of heat fluxes at the air debris interface and heat conduction through the debris is calculated in order to estimate melt rates at the debris ice interface the predicted hourly debris surface temperatures and debris internal temperatures provide a good fit to temperatures measured on rock covered miage glacier r 2 0 94 and the tephra covered glacier on villarrica volcano chile r 2 0 82 the model can also be used to reproduce observed changes in melt rates below debris layers of varying types and thicknesses an important consideration for the overall mass balance of debris covered glaciers

a distributed energy balance melt model of an alpine debris covered glacier distributed energy balance melt models have rarely been applied to glaciers with extensive supraglacial debris cover this paper describes the development of a distributed melt model and its application to the debris covered miage glacier western italian alps over two summer seasons sub debris melt rates are calculated using an existing debris energy balance model deb model and melt rates for clean ice snow and partially debris covered ice are calculated using standard energy balance equations simulated sub debris melt rates compare well to ablation stake observations melt rates are highest and most sensitive to air temperature on areas of dirty crevassed ice on the middle glacier here melt rates are highly spatially variable because the debris thickness and surface type varies markedly melt rates are lowest and least sensitive to air temperature beneath the thickest debris on the lower glacier debris delays and attenuates the melt signal compared to clean ice with peak melt occurring later in the day with increasing debris thickness the continuously debris covered zone consistently provides 30 of total melt throughout the ablation season with the proportion increasing during cold weather sensitivity experiments show that an increase in debris thickness of 0 035 m would offset 1 c of atmospheric warming

the impact of supraglacial debris on proglacial runoff and water chemistry debris is known to influence the ablation topography and hydrological systems of glaciers this paper determines for the first time how these influences impact on bulk water routing and the proglacial runoff signal using analyses of supraglacial and proglacial water chemistry and proglacial discharge at miage glacier italian alps debris does influence the supraglacial water chemistry but the inefficient subglacial system beneath the debris covered zone also plays a role in increasing the ion contribution to the proglacial stream daily hydrographs had a lower amplitude and later discharge peak compared to clean glaciers and fewer diurnal hydrographs were found compared to similar analysis for haut glacier d arolla we attribute these observations to the attenuating effect of the debris on ablation smaller input streams on the debris covered area a less efficient subglacial system and possible leakage into a raised sediment bed beneath the glacier strongly diurnal hydrographs are constrained to periods with warmer than average conditions average weather conditions result in a hydrograph with reverse asymmetry conductivity and discharge commonly show anti clockwise hysteresis suggesting the more dilute rapidly routed melt component from the mid glacier peaks before the discharge peak with components from higher up glacier and the debris covered areas arriving later at the proglacial stream the results of this study could lead to a greater understanding of the hydrological structure of other debris covered glaciers with findings highlighting the need to include the influence of the debris cover within future models of debris covered glacier runoff

calculating ice melt beneath a debris layer using meteorological data generalized numerical models of sub debris ice ablation are preferable to empirical approaches for predicting runoff and glacier response to climate change as empirical methods are site specific and strongly dependent upon the conditions prevailing during the measurement period we present a modified surface energy balance model to calculate melt beneath a surface debris layer from daily mean meteorological variables despite numerous simplifications the model performs well and modelled melt rates give a good match to observed melt rates suggesting that this model can produce reliable estimates of ablation rate beneath debris layers several decimetres thick this is a useful improvement on previous models which are inappropriate for thick debris cover

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