characteristics and evolution of supraglacial ponds on debris covered tasman glacier new zealand supraglacial ponds on tasman glacier new zealand initiated the development of the large tasman lake during the 1980s and still play an important role for ice loss and further terminus disintegration limnological and glaciological measurements between 2001 and 2003 reveal distinct differences between ponds the hydraulic connection of a pond to the englacial water level exerts a key control on whether the pond contributes to longer term terminus disintegration in the earlier stages of pond development ice loss occurs predominantly in the horizontal dimension by subaerial melt subaqueous calving at later stages plays a major role for ice loss during the capture of a pond by the lake substantial limnological changes lead to changes in relative significance and rates of ice loss processes the most important being the change from melting to predominantly calving as a result ice loss accelerated from around 11 m a 1 of melt under partial debris cover to a retreat by calving and melting of 34 m a 1 ice loss at the ponds accounted for only 10 of the surface loss in the lower terminus area but is likely to increase in the future with enlargement and coalescence of ponds

extending the vostok ice core record of palaeoclimate to the penultimate glacial period the ice core record of local temperature dust accumulation and air composition at vostok station antarctica now extends back to the penultimate glacial period 140 200 kyr ago and the end of the preceding interglacial this yields a new glaciological timescale for the whole record which is consistent with ocean records temperatures at vostok appear to have been more uniformly cold in the penultimate glacial period than in the most recent one concentrations of co2 and ch4 correlate well with temperature throughout the record

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

on the accuracy of glacier outlines derived from remote sensing data deriving glacier outlines from satellite data has become increasingly popular in the past decade in particular when glacier outlines are used as a base for change assessment it is important to know how accurate they are calculating the accuracy correctly is challenging as appropriate reference data e g from higher resolution sensors are seldom available moreover after the required manual correction of the raw outlines e g for debris cover such a comparison would only reveal the accuracy of the analyst rather than of the algorithm applied here we compare outlines for clean and debris covered glaciers as derived from single and multiple digitizing by different or the same analysts on very high 1 m and medium resolution 30 m remote sensing data against each other and to glacier outlines derived from automated classification of landsat thematic mapper data results show a high variability in the interpretation of debris covered glacier parts largely independent of the spatial resolution area differences were up to 30 and an overall good agreement for clean ice with sufficient contrast to the surrounding terrain differences 5 the differences of the automatically derived outlines from a reference value are as small as the standard deviation of the manual digitizations from several analysts based on these results we conclude that automated mapping of clean ice is preferable to manual digitization and recommend using the latter method only for required corrections of incorrectly mapped glacier parts e g debris cover shadow

debris transport in a temperate valley glacier haut glacier d arolla valais switzerland hambrey m j goodsell becky glasser n f 2005 debris transport in a temperate valley glacier haut glacier d arolla valais switzerland journal of glaciology 51 172 pp 139 146

response of debris covered glaciers in the mount everest region to recent warming and implications for outburst flood hazards abstract in areas of high relief many glaciers have extensive covers of supraglacial debris in their ablation zones which alters both rates and spatial patterns of melting with important consequences for glacier response to climate change wastage of debris covered glaciers can be associated with the formation of large moraine dammed lakes posing risk of glacier lake outburst floods glofs in this paper we use observations of glaciers in the mount everest region to present an integrated view of debris covered glacier response to climate change which helps provide a long term perspective on evolving glof risks in recent decades debris covered glaciers in the everest region have been losing mass at a mean rate of 0 32 m yr 1 although in most cases there has been little or no change in terminus position mass loss occurs by 4 main processes 1 melting of clean ice close to glacier elas 2 melting beneath surface debris 3 melting of ice cliffs and calving around the margins of supraglacial ponds and 4 calving into deep proglacial lakes modelling of processes 1 and 2 shows that everest region glaciers typically have an inverted ablation gradient in their lower reaches due to the effects of a down glacier increase in debris thickness mass loss is therefore focused in the mid parts of glacier ablation zones causing localised surface lowering and a reduction in downglacier surface gradient which in turn reduce driving stress and glacier velocity so the lower ablation zones of many glaciers are now stagnant model results also indicate that increased summer temperatures have raised the altitude of the rain snow transition during the summer monsoon period reducing snow accumulation and ice flux to lower elevations as downwasting proceeds formerly efficient supraglacial and englacial drainage networks are broken up and supraglacial lakes form in hollows on the glacier surface ablation rates around supraglacial lakes are typically one or two orders of magnitude greater than sub debris melt rates so extensive lake formation accelerates overall rates of ice loss most supraglacial lakes are perched above hydrological base level and are susceptible to drainage if they become connected to the englacial drainage system speleological surveys of conduits show that large englacial voids can be created by drainage of warm lake waters along pre existing weaknesses in the ice roof collapses can open these voids up to the surface and commonly provide the nuclei of new lakes thus by influencing both lake drainage and formation englacial conduits exert a strong control on surface ablation rates an important threshold is crossed when downwasting glacier surfaces intersect the hydrological base level of the glacier base level lakes formed behind intact moraine dams can grow monotonically and in some cases can pose serious glof hazards glacier termini can evolve in different ways in response to the same climatic forcing so that potentially hazardous lakes will form in some situations but not others additionally the probability of a flood is not simply a function of lake volume but depends on the geometry and structure of the dam and possible trigger mechanisms such as ice or rockfalls into the lake satellite based measurements of glacier surface gradient and ice velocities allow probable future locations of base level lakes to be identified a base level lake has begun to grow rapidly on ngozumpa glacier west of mount everest and could attain a volume of 10 8 m 3 within the next 2 or 3 decades unless mitigation efforts are undertaken this lake could pose considerable glof hazard potential

classification of debris covered glaciers and rock glaciers in the andes of central chile in the dry andes of chile 17 to 35 s debris covered glaciers and rock glaciers are differentiated from true glaciers based on the percentage of surface debris cover thickness of surface debris and ice content internal ice is preserved by an insulating cover of thick debris which acts as a storage reservoir to release water during the summer and early fall these landforms are more numerous than glaciers in the central andes however the existing legislation only recognizes uncovered or semicovered glaciers as a water resource glaciers debris covered glaciers and rock glaciers are being altered or removed by mining operations to extract valuable minerals from the mountains in addition agricultural expansion and population growth in this region have placed additional demands on water resources in a warmer climate as glaciers recede and seasonal water availability becomes condensed over the course of a snowmelt season rock glaciers and debris covered glaciers contribute a larger component of base flow to rivers and streams as a result identifying and locating these features to implement sustainable regional planning for water resources is important the objective of this study is to develop a classification system to identify debris covered glaciers and rock glaciers based on the interpretation of satellite imagery and aerial photographs the classification system is linked to field observations and measurements of ice content debris covered glaciers have three subclasses surface coverage of semi class 1 and fully covered class 2 glaciers differentiates the first two forms whereas debris thickness is critical for class 3 when glaciers become buried with more than 3 m of surface debris based on field observations the amount of ice decreases from more than 85 to 65 85 to 45 65 for semi fully and buried debris covered glaciers respectively rock glaciers are characterized by three stages class 4 rock glaciers have pronounced transverse ridges and furrows that arch across the surface which indicates flow produced via ice class 5 rock glaciers have ridges and furrows that appear linear in the direction of flow indicating reduced flow from limited internal ice and class 6 rock glaciers have subdued surface topography because the movement of the rock glacier has ceased ice content decreases from 25 45 to 10 25 to 10 from class 4 to 6 respectively examples from digital imagery aerial photographs and field photographs are provided for each class the classification scheme can be used to identify and map debris covered glaciers and rock glaciers to create an inventory this will help improve recognition of these landforms as an important water resource in the dry andes of chile which will aid in sustainable planning and development in basins that hold the majority of the population and support a large share of the economic activity in chile

the influence of ground ice distribution on geomorphic dynamics since the little ice age in proglacial areas of two cirque glacier systems holocene glaciers have contributed to an abundance of unstable sediments in mountainous environments in permafrost environments these sediments can contain ground ice and are subject to rapid geomorphic activity and evolution under condition of a warming climate to understand the influence of ground ice distribution on this activity since the little ice age lia we have investigated the pierre ronde and rognes proglacial areas two cirque glacier systems located in the periglacial belt of the mont blanc massif for the first time electrical resistivity tomography temperature data loggers and differential global positioning systems dgps are combined with historical documents and glaciological data analysis to produce a complete study of evolution in time and space of these small landsystems since the lia this approach allows to explain spatial heterogeneity of current internal structure and dynamics the studied sites are a complex assemblage of debris covered glacier ice rich frozen debris and unfrozen debris ground ice distribution is related to former glacier thermal regime isolating effect of debris cover water supply to specific zones and topography in relation with this internal structure present dynamics are dominated by rapid ice melt in the debriscovered upper slopes slow creep processes in marginal glacigenic rock glaciers and weak superficial reworking in deglaciated moraines since the lia geomorphic activity is mainly spatially restricted within the proglacial areas sediment exportation has occurred in a limited part of the former rognes glacier and through water pocket outburst flood and debris flows in pierre ronde both sites contributed little sediment supply to the downslope geomorphic system rather by episodic events than by constant supply in that way during holocene and even in a paraglacial context as the recent deglaciation proglacial areas of cirque glaciers act mostly as sediment sinks when active geomorphic processes are unable to evacuate sediment downslope especially because of the slope angle weakness

recycling of cosmogenic nuclides after their removal from the atmosphere special case of appreciable transport of 10be to polar regions by aeolian dust abstract in this paper we discuss the general problem of recirculation of atmospheric cosmogenic isotopes after their initial removal from the atmosphere practically all nuclides are recycled after their removal from the atmosphere the noble gas radio nuclides re circulate between the atmosphere and the hydrosphere the fraction of time spent in these reservoirs depends on their solubility and half lives radiocarbon atoms spend most of their life time in the oceans before being removed to the sediments all cosmogenic nuclides which are removed from the atmosphere by wet precipitations spend most of their life time in the hydrosphere or in sediments a special exception arises in the case of nuclides such as 10 be and 26 al which are particle active and adhere to aerosols and top soils in the lithosphere strong winds dislodge surface particles and transport the smaller particles to great distances we discuss the special case of the transport of particle reactive 10 be via aeolian dust which can result in appreciable 10 be fluxes in polar regions in cold climates vis a vis its direct deposition from the atmosphere we compare estimated concentrations of dust transported 10 be with the measured total 10 be concentrations in antarctica in the vostok and taylor dome ice cores and atmospheric 10 be concentrations in greenland in the gisp and grip ice cores during certain epochs high aeolian dust concentrations contribute significantly to 10 be fluxes in greenland comparable to or greater than atmospheric 10 be fluxes in the antarctica however even during epochs of high dust fluxes the aeolian 10 be contributions are 10 be fluxes these results imply that great care should be taken in analyzing 10 be concentrations in greenland especially

a cut and closure origin for englacial conduits in uncrevassed regions of polythermal glaciers on uncrevassed regions of polythermal glaciers englacial conduits can form by incision of supraglacial stream channels followed by roof closure the origin and evolution of examples in longyearbreen svalbard and khumbu glacier nepal were determined by speleological survey the development of perennial incised channels requires that incision is significantly faster than glacier surface ablation and thus will be favoured by high meltwater discharges in combination with cool climatic conditions or thick debris cover incised canyons can become blocked by drifted winter snow refrozen meltwater ice rafting from non local sources allochthonous breccias and roof collapses autochthonous breccias conduit closure can also occur in response to ice creep particularly at depth following isolation from the surface englacial conduits continue to evolve by vadose incision down to local base level in the case of longyearbreen incision allowed the channel to reach the glacier bed but on khumbu glacier deep incision is prevented because an effectively impermeable terminal moraine provides a high base level for the glacier drainage system during our period of observations deeper parts of the longyearbreen conduit became blocked by a combination of ice accumulation and creep causing the stream course to be re routed to higher levels on that glacier incision blockage and upward re routing are cyclic we conclude that cut and closure is the dominant mechanism of englacial conduit formation on uncrevassed regions of polythermal glaciers

backwasting rate on debris covered koxkar glacier tuomuer mountain china a physically based energy balance model with improved parameterization of solar radiation for a sloped ice surface has been developed to estimate the backwasting rate of an ice cliff in a debris covered area the model has been tested against observations between 5 august and 5 september 2008 on 38 ice cliffs in the debris covered area of koxkar glacier tuomuer mountain china we calculated that the energy balance model gave a good estimate of the backwasting rates with errors in the range 1 96 cm d 1 and root mean square errors of 0 99 cm d 1 errors arising from setting of surface albedo and turbulent flux parameterization were limited we found that shortwave radiation is the most important heat source for ice cliff ablation contributing about 76 of the total heat available for ice melt while the sensible heat flux provides nearly 24 of the total heat for ice cliff wastage the latent heat flux and net longwave radiation are comparatively small according to the model calculation the mean backwasting rate of ice cliffs in the debris covered area of koxkar glacier is estimated at 7 64 m a 1 when the winter ablation is neglected with this annual backwasting rate and given a mean slope angle of 46 48 the backwasting of ice cliffs produces about 1 60 10 6 m 3 of meltwater accounting for about 7 3 of the total melt runoff from the debris covered area

a model of ablation dominated medial moraines and the generation of debris mantled glacier snouts medial moraines form striking dark stripes that widen non linearly steepen laterally and increase in relief down glacier from the equilibrium line coalescence of these low ablation rate features can feed back strongly on the mass balance of a glacier snout ablation dominated medial moraines originate from debris delivered to glacier margins producing a debris rich septum between tributary streams of ice below their confluence emergence of this ice below the equilibrium line delivers debris to the glacier surface which then moves down local slopes of evolving morainal topography a quantitative description of moraine evolution requires specification of the debris concentration field within the glacier treatment of the melt rate dependence on debris thickness and characterization of processes that transport debris once it emerges onto the ice surface debris concentration at glacier tributary junctions scales with the erosion rates and the lengths of the tributary valley walls and inversely with the tributary ice speeds melt rate is damped exponentially by debris with a 10 cm decay scale debris flux across the glacier surface scales with the product of debris thickness and local slope analytical and numerical results show that medial moraines should develop cross glacier profiles with parabolic crests and linear slopes and should widen with age and hence distance down glacier debris should be both thin and uniform over the moraine observed faster than linear growth of moraine widths with distance reflects the increasing ablation rate down glacier increase in medial moraine cover reduces the local average ablation rate allowing the glacier to extend further down valley than meteorology alone would suggest this feedback is especially effective when moraines merge

aspect controls the survival of ice cliffs on debris covered glaciers supraglacial ice cliffs exist on debris covered glaciers worldwide but despite their importance as melt hot spots their life cycle is little understood early field observations had advanced a hypothesis of survival of north facing and disappearance of south facing cliffs which is central for predicting the contribution of cliffs to total glacier mass losses their role as windows of energy transfer suggests they may explain the anomalously high mass losses of debris covered glaciers in high mountain asia hma despite the insulating debris currently at the center of a debated controversy we use a 3d model of cliff evolution coupled to very high resolution topographic data to demonstrate that ice cliffs facing south in the northern hemisphere disappear within a few months due to enhanced solar radiation receipts and that aspect is the key control on cliffs evolution we reproduce continuous flattening of south facing cliffs a result of their vertical gradient of incoming solar radiation and sky view factor our results establish that only north facing cliffs are recurrent features and thus stable contributors to the melting of debris covered glaciers satellite observations and mass balance modeling confirms that few south facing cliffs of small size exist on the glaciers of langtang and their contribution to the glacier volume losses is very small 1 this has major implications for the mass balance of hma debris covered glaciers as it provides the basis for new parameterizations of cliff evolution and distribution to constrain volume losses in a region where glaciers are highly relevant as water sources for millions of people

growth and drainage of supraglacial lakes on debris mantled ngozumpa glacier khumbu himal nepal ablation of debris mantled glaciers in nepal has resulted in the formation of several potentially unstable moraine dammed lakes some of which constitute serious hazards ngozumpa glacier khumbu himal has undergone significant downwasting in recent decades and is believed to lie close to the threshold for moraine dammed lake formation the debris mantled ablation area of the glacier is studded with numerous supraglacial lakes the majority of which occupy closed basins with no perennial connections to the englacial drainage system perched lakes perched lakes can undergo rapid growth by subaerial and water line melting of exposed ice faces and calving subaerial and subaqueous melting beneath thick 1 m debris mantles is comparatively insignificant although lake expansion can contribute substantially to ablation of the glacier perched lakes cannot continue to grow indefinitely but are subject to rapid drainage once a connection is made to englacial conduits the level of one of the lakes on the ngozumpa however is controlled by the altitude of a spillway through the lateral moraine of the glacier this lake underwent only limited growth in the period 1998 2000 but is likely to experience monotonic growth if glacier mass balance continues to be negative

a grid based model of backwasting of supraglacial ice cliffs on debris covered glaciers ice cliffs might be partly responsible for the high mass losses of debris covered glaciers in the hindu kush karakoram himalaya region the few existing models of cliff backwasting are point scale models applied at few locations or assume cliffs to be planes with constant slope and aspect a major simplification given the complex surfaces of most cliffs we develop the first grid based model of cliff backwasting for two cliffs on debris covered lirung glacier nepal the model includes an improved representation of shortwave and longwave radiation and their interplay with the glacier topography shortwave radiation varies considerably across the two cliffs mostly due to direct radiation diffuse radiation is the major shortwave component as the direct component is strongly reduced by the cliffs aspect and slope through self shading incoming longwave radiation is higher than the total incoming shortwave flux due to radiation emitted by the surrounding terrain which is 25 of the incoming flux melt is highly variable in space suggesting that simple models provide inaccurate estimates of total melt volumes although only representing 0 09 of the glacier tongue area the total melt at the two cliffs over the measurement period is 2313 and 8282 m3 1 23 of the total melt simulated by a glacio hydrological model for the glacier s tongue

quantifying ice cliff evolution with multi temporal point clouds on the debris covered khumbu glacier nepal measurements of glacier ice cliff evolution are sparse but where they do exist they indicate that such areas of exposed ice contribute a disproportionate amount of melt to the glacier ablation budget we used structure from motion sfm photogrammetry with multi view stereo mvs to derive 3d point clouds for nine ice cliffs on khumbu glacier nepal in november 2015 may 2016 and october 2016 by differencing these clouds we could quantify the magnitude seasonality and spatial variability of ice cliff retreat mean retreat rates of 0 30 to 1 49 cm d 1 were observed during the winter interval november 2015 to may 2016 and 0 74 to 5 18 cm d 1 were observed during the summer may 2016 to october 2016 four ice cliffs which all featured supraglacial ponds persisted over the full study period in contrast ice cliffs without a pond or with a steep back slope degraded over the same period the rate of thermo erosional undercutting was over double that of subaerial retreat overall 3d topographic differencing allowed an improved process based understanding of cliff evolution and cliff pond coupling which will become increasingly important for monitoring and modelling the evolution of thinning debris covered glaciers

debris thickness patterns on debris covered glaciers abstract many debris covered glaciers have broadly similar debris thickness patterns surface debris thickens and tends to transition from convex to concave up down glacier we explain this pattern using theory analytical and numerical models paired with empirical observations down glacier debris thickening results from the conveyor belt like nature of the glacier surface in the ablation zone debris can typically only be added but not removed and from the inevitable decline in ice surface velocity toward the terminus down glacier thickening of debris leads to the reduction of sub debris melt and debris emergence toward the terminus convex up debris thickness patterns occur near the up glacier end of debris covers where debris emergence dominates ablation controlled concave up debris thickness patterns occur toward glacier termini where declining surface velocities dominate velocity controlled a convex concave debris thickness profile inevitably results from the transition between ablation control and velocity control down glacier debris thickness patterns deviating from this longitudinal shape are most likely caused by changes in hillslope debris supply through time by establishing this expected debris thickness pattern the effects of climate change on debris cover can be better identified

medial moraines of the haut glacier d arolla valais switzerland debris supply and implications for moraine formation the haut glacier d arolla displays three medial moraines an ablation dominant moraine east of the glacier centre line an ice stream interaction moraine west of the glacier centre line and a medial lateral supraglacial moraine complex along the western margin of the glacier the eastern moraine is formed by the emergence of coarse angular clasts from a series of short longitudinal debris bands 1 km from the glacier terminus this debris is derived from rock falls at the glacier head wall and follows a low level transport path through the glacier the western moraine is formed partly by the direct fall of weathered debris on to the ice surface at a point 2 6 km from the snout but it receives further increments of sediment from extensive longitudinal englacial debris bands developed from the convergence of two ice streams with lateral englacial debris septa the medial lateral moraine complex is formed largely by rock falls from the western valley wall but is also nourished by a debris layer developed at the base of the small tributary glacier de la mitre this layer crops out at the eastern margin of the re sultant inset ice stream and releases more rounded abraded and comminuted rock fragments to supplement the surface debris cover of supraglacial origin

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

debris entrainment and transfer in polythermal valley glaciers hambrey mj bennett mr dowdeswell ja et al 1999 debris entrainment and transfer in polythermal valley glaciers journal of glaciology 45 149 69 86 published 1999

morphometric evolution of everest region debris covered glaciers abstract debris covered glaciers in the central himalaya have now experienced several decades of sustained ice loss manifested predominantly in glacier surface lowering in particular glacier surfaces of low longitudinal gradient and low ice surface velocity have developed locally complex surface topographies and undergone profound changes in supraglacial hydrology in this study we examine the development of complex ice surface topography across six debris covered glaciers in the everest region over the last four decades via a new metric of glacier surface relief applied to digital elevation models dems we focus in on khumbu glacier and use fine spatial and temporal resolution dems covering a period of 28 months to quantify the contemporary contribution of ice cliff and supraglacial pond expansion to overall mass loss from stagnant areas of ice on the broader scale we find three common long term changes in glacier surface topography 1 glacier wide expansion of high relief topography in response to ice cliff and supraglacial pond network evolution 2 up glacier expansion of high local relief zones that may be caused by differential sub debris melt beneath thin debris and 3 increase in glacier surface relief proximal to glacier termini caused by supraglacial stream incision where linked proglacial supraglacial hydrological networks exist overall we contend that these topographic measurements will be important for understanding glacier surface water storage and also the energy balance of a debris covered glacier surface both of which could exacerbate future ice loss and downstream meltwater supply

10be and 9be in marine sediments and their potential for dating using sequential leaching experiments we have measured the fraction of the cosmogenic isotope 10be half life 1 5 my and its stable isotope 9be co extracted with the following phases in marine sediments exchangeable calcium carbonate fe and mn oxyhydroxides organic opal and detrital the extraction of the authigenic phases typically release 70 of the 10be but only 40 of the 9be in order to test its potential for dating marine sediments we have measured the authigeniccally associated 10be 9be in 17 surface sediment samples from different ocean basins the observed spatial variability which appears to be influenced by proximity to continental input of 9be precludes the general and precise applications of leached 10be 9be for dating however the relatively constant value observed in surface sediments over large areas of the pacific indian and southern atlantic oceans shows considerable promise for approximate dating of open oceans sediments in order to test temporal variability a profile of the authigenically associated 10be 9be ratio has been measured in the independently dated central pacific core rc12 65 the observed variation in 10be 9be over the past nine my is approximately twice that expected on the basis of 10be decay alone several possible explanations for such behavior and their potential consequences for the use of leached 10be 9be for dating are discussed

onset of calving at supraglacial lakes on debris covered glaciers of the nepal himalaya field surveys of supraglacial ponds on debris covered glaciers in the nepal himalaya clarify that ice cliff calving occurs when the fetch exceeds 80 m thermal undercutting is important for calving processes in glacial lakes and subaqueous ice melt rates during the melt and freeze seasons are therefore estimated under simple geomorphologic conditions in particular we focus on the differences between valley wind driven water currents in various fetches during the melt season our results demonstrate that the subaqueous ice melt rate exceeds the ice cliff melt rate when the fetch is 20 m and water temperature is 2 48c calculations suggest the onset of calving due to thermal undercutting is controlled by water currents driven by winds at the surface of the lake which develop with expanding water surface

on the influence of debris cover on glacier morphology how high relief structures evolve from smooth surfaces abstract debris covered glaciers receive increasing attention during the current period of sustained negative mass balance and expanding debris cover the debris cover induces various feedback mechanisms that shape the evolution of the glacier geometry and also the glacier surface although the surface morphology of many debris covered glaciers is markedly different from that of debris free glaciers only a few studies have combined different processes to investigate these characteristic glacier surfaces in order to improve our knowledge of glacier evolution on a wider spatial and temporal scale debris covered glacier tongues can consist of parts with a smooth surface as well as surfaces of high local relief with abundant ice cliffs in the lower end in this study we analysed the evolution of the surface features of zmuttgletscher a debris covered glacier in switzerland over a period of 140 years using time series of historic maps high resolution digital elevation models and glacier velocities as well as data on debris cover extent and thickness our results reveal insights into the up glacier expansion of the debris cover over time and the formation of medial moraines in the prolongation of the uppermost areas where debris emerged on the glacier surface moraine ridge prominence increased during periods of negative mass balance and troughs developed in debris free areas between ridges persisting even after a continuous debris cover had developed the changing surface morphology inhibits across glacier meltwater flow both supra and subglacially accordingly we found that large cryo valleys with ice cliffs have formed down glacier of the troughs where meltwater runoff accumulates the meanders of these valleys have enlarged over time especially by ice cliff backwasting at steep slopes and most of the glacier width today is affected by such high relief erosion features we find that about 75 of all ice cliffs are located in this high relief zone the volume lost at these erosion features has increased by a factor of five since the 1980s but is still very small in comparison to the high glacier wide thinning rates

a subglacial water flow model for west antarctica the current generation of continental scale ice sheet models cannot successfully reproduce the complex ice water sediment interactions of the west antarctic ice sheet wais in a physically meaningful manner the potential of a thin film based subglacial water flow model for incorporation into a continental scale coupled ice water flow model of the wais is evaluated in this paper the subglacial water flow model is applied to the ross sea sector of the wais in both a steady state and time dependent form to derive the equilibrium water depth for the present day configuration the potential for coupling the model to an ice flow model is then demonstrated using a variable sliding parameter that is a function of the subglacial water depth a coupled ice water flow model using the parameterization tested in this paper could have the potential for reproducing the surface elevation velocity and thermal regime of the wais successfully these requirements are crucial in modelling the evolution of the wais and must be addressed before reliable continental scale predictive models can be utilized

topographic characteristics in the ablation area of the khumbu glacier nepal himalaya topographic sketch mapping of the whole ablation area of the khumbu glacier east nepal himalaya is performed using a simple stereo photogrammetric method this map shows that the surface morphology can be classified into ii morphologic characteristics depending on their distribution and combination the ablation area can be divided into four morphologic areas detailed maps on a scale of i i 000 2500 of these four areas indicate that the distribution and combination of these i1 morphologic characteristics result from thickness of the debris cover supraglacial streams and ponds and glacier dynamics th irregularity in the ablation area of the khumbu glacier can be considered to be a consequence of the mass balance between rate of ice charge from upstream and irregular distribution of ablation rate depending on debris cover characteristics in situ

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

assessing ice cliff backwasting and its contribution to total ablation of debris covered miage glacier mont blanc massif italy continuous surface debris cover strongly reduces the ablation of glaciers but high melt rates may occur at ice cliffs that are too steep to hold debris this study assesses the contribution of ice cliff backwasting to total ablation of miage glacier mont blanc massif italy in 2010 and 2011 based on field measurements physical melt models and mapping of ice cliffs using a high resolution 1 m digital elevation model dem short term model calculations closely match the measured melt rates a model sensitivity analysis indicates that the effects of cliff slope and albedo are more important for ablation than enhanced longwave incidence from sun warmed debris or reduced turbulent fluxes at sheltered cliff bases analysis of the dem indicates that ice cliffs account for at most 1 3 of the 1 m pixels in the glacier s debris covered zone but application of a distributed model indicates that ice cliffs account for 7 4 of total ablation we conclude that ice cliffs make an important contribution to the ablation of debris covered glaciers even when their spatial extent is very small

role of debris cover in the thermal physics of glaciers modele de fonte de la glace en presence de debris morainiques on en deduit une technique de noircissement de la surface des glaciers en vue d augmenter le debit d eau

stagnation and mass loss on a himalayan debris covered glacier processes patterns and rates the ablation areas of debris covered glaciers typically consist of a complex mosaic of surface features with contrasting processes and rates of mass loss this greatly complicates glacier response to climate change and increases the uncertainty of predictive models in this paper we present a series of high resolution dems and repeat lake bathymetric surveys on ngozumpa glacier nepal to study processes and patterns of mass loss on a himalayan debris covered glacier in unprecedented detail most mass loss occurs by melt below supraglacial debris and melt and calving of ice cliffs backwasting although ice cliffs cover only 5 of the area of the lower tongue they account for 40 of the ablation the surface debris layer is subject to frequent re distribution by slope processes resulting in large spatial and temporal differences in debris layer thickness enhancing or inhibiting local ablation rates and encouraging continuous topographic inversion a moraine dammed lake on the lower glacier tongue spillway lake underwent a period of rapid expansion from 2001 to 2009 but later experienced a reduction of area and volume as a result of lake level lowering and sediment redistribution rapid lake growth will likely resume in the near future and may eventually become up to 7 km long

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

paleo ocean chemistry records in marine opal implications for fluxes of trace elements cosmogenic nuclides 10be and 26al and biological productivity abstract here we provide evidence suggesting that marine diatom opal contains not only a high fidelity record of dissolved oceanic concentrations of cosmic ray produced radionuclides 10 be and 26 al but also a record of temporal variations in a large number of trace elements such as ti fe zn and mn this finding is derived from measurements in purified biogenic opal that can be separated from detrital materials using a newly developed technique based on surface charge characteristics initial results from a sediment core taken near the present day position of the antarctic polar front odp site 1093 show dramatic changes in the intrinsic concentrations of be al ti fe mn and zn in the opal assemblages during the past 140 kyr bp the results imply appreciable climatically controlled fluctuations in the level of bioreactive trace elements the time series of total be al ti fe and 10 be in the sediment core are all well correlated with each other and with dust records in the polar ice cores the observations suggest that a significant flux of these trace metals to oceans is contributed by the aeolian dust in this case presumably from the patagonia this observation also allows determination of fluxes of dust contributed 10 be to the antarctica ice sheets however our data show that the relationships among the various metals are not perfectly linear during periods of higher dissolved concentrations of trace elements indicated by fe and ti the relative concentrations of bioreactive elements be al mn and zn are decreased by contrast the fe zn and fe mn ratios decrease significantly during each transition from cold to warm periods the relative behavior could be consistent with any of the following processes i enhanced biological productivity due to greater supply of the bioreactive elements e g zn during cold periods ii increased biological and inorganic scavenging of particle active elements e g be and al during early interglacial periods iii differential uptake removal of the metals by the various diatom taxa whose relative productivity or growth rate changes with large scale climate in any case with one sedimentary phase and in single sedimentary sections we now have the potential to compare directly a proxy for aeolian input of micronutrients e g fe or ti with a proxy for production e g 26 al al ratios we expect that studies of the temporal records of trace elements and cosmogenic nuclides in contrasting regions of upwelling and productivity which exhibit different sensitivities to global climate fluctuations and micronutrient inputs would lead to a direct and comprehensive test of ideas such as the hypothesis of iron control of atmospheric carbon dioxide martin j h 1990 glacial interglacial co 2 change the iron hypothesis paleoceanography 5 1 13 our present data from a single site do not show that increases in dissolved fe concentrations per se were responsible for increased biological productivity however a much clearer picture of the effect of increased dust fluxes should emerge when we have data for trace elements and the cosmogenic nuclides 10 be and 26 al from various oceanic provinces

contrasting medial moraine development at adjacent temperate maritime glaciers fox and franz josef glaciers south westland new zealand abstract medial moraines form important pathways for sediment transportation in valley glaciers despite the existence of well defined medial moraines on several glaciers in the new zealand southern alps medial moraines there have hitherto escaped attention the evolving morphology and debris content of medial moraines on franz josef glacier and fox glacier on the western flank of the southern alps is the focus of this study these temperate maritime glaciers exhibit accumulation zones of multiple basins that feed narrow tongues flowing down steep valleys and terminate 400 m above sea level the medial moraines at both glaciers become very prominent in the lower ablation zones where the medial moraines widen and develop steeper flanks coeval with an increase in relative relief medial moraine growth appears somewhat self limiting in that relief and slope angle increase eventually lead to transport of debris away from the medial moraine by mass movement related processes despite similarities in overall morphologies a key contrast in medial moraine formation exists between the two glaciers at fox glacier the medial moraine consists of angular rockfall derived debris folded to varying degrees along flow parallel axes throughout the tongue the debris originates above the ela coalesces at flow unit boundaries and takes a medium high level transport pathway before subsequently emerging at point sources aligned with gently dipping fold hinges near the snout in contrast at franz josef glacier the medial moraine emerges farther down glacier immediately below a prominent rock knob clasts show a mix of angular to rounded shapes representing high level transport and subglacially transported materials the latter facies possibly also elevated by supraglacial routing of subglacial meltwater our observations confirm that a variety of different debris sources transport pathways and structural glaciological processes can interact to form medial moraines within new zealand s southern alps

ice volume changes of selected glaciers in the swiss alps since the end of the 19th century the evolution of surface topography of glaciers in the swiss alps is well documented with high resolution aerial photographs repeatedly recorded since the 1960s and further back in time with topographic maps including elevation contour lines first surveyed in the mid 19th century in order to quantify and interpret glacier changes in the swiss alps time series of volume changes over the last 100 150 years have been collected the available datasets provide a detailed spatial resolution for the retreat period since the end of the little ice age the spatial distribution as well as temporal variations of the thickness change were analyzed a significant ice loss since the end of the 19th century was observed in the ablation area while the changes in the accumulation area were small we found moderate negative secular rates until the 1960s followed by steady to positive rates for about two decades and strong ice loss starting in the 1980s which has lasted until the present an evaluation of 19 glaciers revealed a total ice volume loss of about 13 km 3 since the 1870s of which 8 7 km 3 occurred since the 1920s and 3 5 km 3 since 1980 decadal mean net balance rates for the periods 1920 60 1960 80 and 1980 present are 0 29 0 03 and 0 53 m a 1 w e respectively

quantifying volume loss from ice cliffs on debris covered glaciers using high resolution terrestrial and aerial photogrammetry mass losses originating from supraglacial ice cliffs at the lower tongues of debris covered glaciers are a potentially large component of the mass balance but have rarely been quantified in this study we develop a method to estimate ice cliff volume losses based on high resolution topographic data derived from terrestrial and aerial photogrammetry we apply our method to six cliffs monitored in may and october 2013 and 2014 using four different topographic datasets collected over the debris covered lirung glacier of the nepalese himalayas during the monsoon the cliff mean backwasting rate was relatively consistent in 2013 3 8 0 3 cm w e d 1 and more heterogeneous among cliffs in 2014 3 1 0 7 cm w e d 1 and the geometric variations between cliffs are larger their mean backwasting rate is significantly lower in winter october 2013 may 2014 at 1 0 0 3 cm w e d 1 these results are consistent with estimates of cliff ablation from an energy balance model developed in a previous study the ice cliffs lose mass at rates six times higher than estimates of glacier wide melt under debris which seems to confirm that ice cliffs provide a large contribution to total glacier melt

initial results from a distributed physically based model of glacier hydrology this paper describes the development and testing of a distributed physically based model of glacier hydrology the model is used to investigate the behaviour of the hydrological system of haut glacier d arolla valais switzerland the model has an hourly time step and three main components a surface energy balance submodel a surface flow routing submodel and a subglacial hydrology submodel the energy balance submodel is used to calculate meltwater production over the entire glacier surface the surface routing submodel routes meltwater over the glacier surface from where it is produced to where it either enters the subglacial hydrological system via moulins or runs off the glacier surface the subglacial hydrology submodel calculates water flow in a network of conduits which can evolve over the course of a melt season simulation in response to changing meltwater inputs the main model inputs are a digital elevation model of the glacier surface and its surrounding topography start of season snow depth distribution data and meteorological data model performance is evaluated by comparing predictions with field measurements of proglacial stream discharge subglacial water pressure measured in a borehole drilled to the glacier bed and water velocities inferred from dye tracer tests the model performs best in comparison with the measured proglacial stream discharges but some of the substantial features of the other two records are also reproduced in particular the model results show the high amplitude water pressure cycles observed in the borehole in the mid melt season and the complex velocity discharge hysteresis cycles observed in dye tracer tests the results show that to model outflow hydrographs from glacierized catchments effectively it is necessary to simulate spatial and temporal variations in surface melt rates the delaying effect of the surface snowpack and the configuration of the subglacial drainage system itself the model s ability to predict detailed spatial and temporal patterns of subglacial water pressures and velocities should make it a valuable tool for aiding the understanding of glacier dynamics and hydrochemistry 1998 john wiley sons ltd