contrasting patterns of early twenty first century glacier mass change in the himalayas glaciers are among the best terrestrial climate indicators an important water resource in mountains1 2 and a major contributor to global sea level rise3 4 in the hindu kush karakoram himalaya region hkkh a paucity of appropriate glacier data has prevented a comprehensive assessment of current regional mass balance5 however there are indirect evidences of a complex pattern of glacial responses5 8 in reaction to heterogeneous climate change signals9 here we provide the first coherent data set of detailed glacier thickness changes over the hkkh during 2003 2009 by combining satellite laser altimetry and a global elevation model in the eastern central and south western parts of the hkkh glacier wastage is widespread with regional thinning rates up to 0 66 0 09 m a 1 in the jammu kashmir region conversely in the karakoram glaciers are close to balance with only a slight thinning of 0 07 0 04 m a 1 regionally averaged thinning rates under debris mantled ice are similar to those of clean ice despite insulation by debris covers the 2003 2008 specific mass balance for our hkkh study region is 0 21 0 05 m a 1 water equivalent we significantly less negative than the global average of 0 7 m a 1 we for glaciers and ice caps4 10 this difference is mainly an effect of the balanced glacier mass budget in the karakoram the corresponding hkkh sea level contribution is 0 035 0 009 mm a 1 amounting to 1 of the present day sea level rise11 our 2003 2008 mass budget of 12 8 3 5 gt a 1 is more negative than recent satellite gravimetry based estimates of 5 6 gt a 1 over 2003 2010 ref 12 for the mountain catchments of the indus and ganges basins13 the glacier imbalance contributes 3 5 and 2 0 respectively to the annual average river discharge13 and up to 10 for the upper indus basin14

a physically based model of the year round surface energy and mass balance of debris covered glaciers debris covered glaciers respond to atmospheric conditions in different ways from debris free glaciers due to the presence of debris at the surface during the ablation season and at the snow ice interface during the accumulation season understanding the response of debris covered glaciers to a variety of meteorological conditions in a physically sound manner is essential to quantify meltwater discharge and to predict their response to climate change to tackle this issue we developed the crocus deb model as an adaptation of the detailed snowpack model crocus to simulate the energy and mass balance of debris covered glaciers including periods when debris is covered by snow crocus deb was evaluated with data gathered during a field experiment using artificial debris covering the snowpack at col de porte france with very good results in terms of conductive heat flux both at the surface and at the interface between the debris and the underlying dense snow taken as a surrogate for ice with and without snow overlying the debris the model was also evaluated using field data from the debris covered glacier changri nup nepal himalaya this paper introduces the design of the model its performance and its ability to explore relationships between model parameters meteorological conditions and the critical debris thickness

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

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

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

thickness estimation of supraglacial debris above ice cliff exposures using a high resolution digital surface model derived from terrestrial photography the thickness of supraglacial debris cover controls how it impacts the ablation rate of underlying glacier ice yet this quantity remains challenging to measure particularly at glacier scales we present a relatively straightforward and cost effective method to estimate debris thickness exposed above ice cliffs using simplified geometrical measurements from a high resolution digital surface model dsm derived from a terrestrial photographic survey and a structure from motion with multi view stereo workflow sfm mvs as the ice surface relief beneath the debris cover is unknown we assume it to be horizontal and provide error bounds based on characteristic ice surface slope at the visible debris ice interface debris thickness around the three sampled ice cliffs was highly variable interquartile range of 0 80 2 85 m and negatively skewed with a mean thickness of 2 08 0 68 m manual and high frequency radar determinations of debris thickness in the same area show similar thickness distributions but statistically different mean debris thickness due to local heterogeneity debris thickness values derived in this study all exceed estimates from satellite surface temperature inversions wider application of the method presented here would provide useful data for improving debris thickness approximations from satellite imagery

mass balance changes of the debris covered glaciers in the langtang himal nepal from 1974 to 1999 thick debris cover on glaciers can significantly reduce ice melt however several studies have suggested that debris covered glaciers in the himalaya might have lost mass at a rate similar to debris free glaciers we reconstruct elevation and mass changes for the debris covered glaciers of the upper langtang valley nepalese himalaya using a digital elevation model dem from 1974 stereo hexagon satellite data and the 2000 srtm shuttle radar topography mission dem uncertainties are high in the accumulation areas due to data gaps in the srtm and difficulties with delineation of the glacier borders even with these uncertainties we obtain thinning rates comparable to those of several other studies in the himalaya in particular we obtain a total mass balance for the investigated debris covered glaciers of the basin of 0 32 0 18 m w e a 1 however there are major spatial differences both between glaciers and within any single glacier exhibiting a very distinct nonlinear mass balance profile with elevation through analysis of surface velocities derived from landsat etm imagery we show that thinning occurs in areas of low velocity and low slope these areas are prone to a general dynamic decay of surface features and to the development of supraglacial lakes and ice cliffs which may be responsible for a considerable increase in overall glacier ablation

highly variable aerodynamic roughness length z0 for a hummocky debris covered glacier the aerodynamic roughness length z0 is an essential parameter in surface energy balance studies but few literature values exist for debris covered glaciers we use microtopographic and aerodynamic methods to assess the spatial variability of z0 for lirung glacier nepal we apply structure from motion to produce digital elevation models for three nested domains five 1 m2 plots a 21 300 m2 surface depression and lower 550 000 m2 of the debris mantled tongue wind and temperature sensor towers were installed in the vicinity of the plots within the surface depression in october 2014 we calculate z0 according to a variety of transect based microtopographic parameterisations for each plot then develop a grid version of the algorithms by aggregating data from all transects this grid approach is applied to the surface depression dem to characterize z0 spatial variability the algorithms reproduce the same variability among transects and plots but z0 estimates vary by an order of magnitude between algorithms across the study depression results from different algorithms are strongly correlated using monin obukov similarity theory we derive z0 values from the meteorological data using different stability criteria we derive median values of z0 between 0 03 m and 0 05 m but with considerable uncertainty due to the glacier s complex topography considering estimates from these algorithms results suggest that z0 varies across lirung glacier between 0 005 m gravels to 0 5 m boulders future efforts should assess the importance of such variable z0 values in a distributed energy balance model

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

modelling ice cliff backwasting on a debris covered glacier in the nepalese himalaya ice cliffs have been identified as a reason for higher ablation rates on debris covered glaciers than are implied by the insulation effects of the debris this study aims to improve our understanding of cliff backwasting and the role of radiative fluxes in particular an energy balance model is forced with new data gathered in may and october 2013 on lirung glacier nepalese himalaya observations show substantial variability in melt between cliffs between locations on any cliff and between seasons using a high resolution digital elevation model we calculate longwave fluxes incident to the cliff from surrounding terrain and include the effect of local shading on shortwave radiation this is an advance over previous studies that made simplified assumptions on cliff geometry and radiative fluxes measured melt rates varied between 3 25 and 8 6cm d 1 in may and 0 18 and 1 34 cmd 1 in october model results reproduce the strong variability in space and time suggesting considerable differences in radiative fluxes over one cliff in october the model fails to reproduce stake readings probably due to the lack of a refreezing component disregarding local topography can lead to overestimation of melt at the point scale by up to 9

high resolution monitoring of himalayan glacier dynamics using unmanned aerial vehicles himalayan glacier tongues are commonly debris covered and they are an important source of melt water however they remain relatively unstudied because of the inaccessibility of the terrain and the difficulties in field work caused by the thick debris mantles observations of debris covered glaciers are therefore scarce and airborne remote sensing may bridge the gap between scarce field observations and coarse resolution space borne remote sensing in this study we deploy an unmanned aerial vehicle uav before and after the melt and monsoon season may and october 2013 over the debris covered tongue of the lirung glacier in nepal based on stereo imaging and the structure for motion algorithm we derive highly detailed ortho mosaics and digital elevation models dems which we geometrically correct using differential gps observations collected in the field based on dem differencing and manual feature tracking we derive the mass loss and the surface velocity of the glacier at a high spatial accuracy on average mass loss is limited and the surface velocity is very small however the spatial variability of melt rates is very high and ice cliffs and supra glacial ponds show mass losses that can be an order of magnitude higher than the average we suggest that future research should focus on the interaction between supra glacial ponds ice cliffs and englacial hydrology to further understand the dynamics of debris covered glaciers finally we conclude that uav deployment has large potential in glaciology and it may revolutionize methods currently applied in studying glacier surface features

the sustainability of water resources in high mountain asia in the context of recent and future glacier change high mountain asia contains the largest volume of glacier ice outside the polar regions and contain the headwaters of some of the largest rivers in central asia these glaciers are losing mass at a mean rate of between 0 18 and 0 5 m water equivalent per year while glaciers in the himalaya are generally shrinking those in the karakoram have experienced a slight mass gain both changes have occurred in response to rising air temperatures due to northern hemisphere climate change in the westerly influenced indus catchment glacier meltwater makes up a large proportion of the hydrological budget and loss of glacier mass will ultimately lead to a decrease in water supplies in the monsoon influenced ganges and brahmaputra catchments the contribution of glacial meltwater is relatively small compared to the indus and the decrease in annual water supplies will be less dramatic therefore enhanced glacier melt will increase river flows until the middle of the twenty first century but in the longer term into the latter part of this century river flows will decline as glaciers shrink declining meltwater supplies may be compensated by increases in precipitation but this could exacerbate the risk of flooding

object based analysis of unmanned aerial vehicle imagery to map and characterise surface features on a debris covered glacier debris covered glaciers in the himalaya may have spatially averaged rates of surface height change that are similar to those observed on bare ice glaciers despite the insulating effects of thick debris spatially heterogeneous melt patterns caused by the development and evolution of ice cliffs and supraglacial pond systems result in substantial mass losses over time however mechanisms controlling the formation and survival of cliffs and ponds remain largely unknown to study the distribution and characteristics of these surface features we deploy an unmanned aerial vehicle uav over a stretch of the debris covered langtang glacier nepal acquired images are processed into high resolution orthomosaics and elevation models with the structure from motion sfm photogrammetry algorithm ice cliffs and ponds are classified using object based image analysis obia and their morphology and spatial distribution are analysed and evaluated using object pixel and point cloud approaches results show that ice cliffs are predominantly north facing and larger ice cliffs are generally coupled with supraglacial ponds which may affect their evolution considerably the spatial distribution of ice cliffs indicates that they are more likely to form in areas where high strain rates are expected the spatial configuration of ponds over the entire tongue reveals high pond density near confluences possibly due to closure of conduits via transverse compression we conclude that the combination of obia and uav imagery is a valuable tool in the semi automatic and objective analysis of surface features on debris covered glaciers the technique may also have potential for upscaling to the use of spaceborne imagery and the use of uav derived point clouds to analyse ice cliff undercuts is promising

elevation changes of glaciers revealed by multitemporal digital elevation models calibrated by gps survey in the khumbu region nepal himalaya 1992 2008 due to remoteness and high altitude only a few ground based glacier change studies are available in high mountain areas in the himalaya however digital elevation models based on remotely sensed data rs dems provide feasible opportunities to evaluate how fast himalayan glaciers are changing here we compute elevation changes in glacier surface total area 183 3 km in the khumbu region nepal himalaya for the period 1992 2008 using multitemporal rs dems and a map derived dem calibrated with differential gps survey data in 2007 elevation change is calculated by generating a weighted least squares linear regression model our method enables us to provide the distribution of uncertainty of the elevation change debris covered areas show large lowering rates the spatial distribution of elevation change shows that the different wastage features of the debris covered glaciers depend on their scale slope and the existence of glacial lakes the elevation changes of glaciers in the eastern khumbu region are in line with previous studies the regional average mass balance of 0 40 0 25mw e a for the period 1992 2008 is consistent with a global value of about 0 55mw e a for the period 1996 2005

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

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

refined energy balance modelling of a supraglacial pond langtang khola nepal supraglacial ponds on debris covered glaciers present a mechanism of atmosphere glacier energy transfer that is poorly studied and only conceptually included in mass balance studies of debris covered glaciers this research advances previous efforts to develop a model of mass and energy balance for supraglacial ponds by applying a free convection approach to account for energy exchanges at the subaqueous bare ice surfaces we develop the model using field data from a pond on lirung glacier nepal that was monitored during the 2013 and 2014 monsoon periods sensitivity testing is performed for several key parameters and alternative melt algorithms are compared with the model the pond acts as a significant recipient of energy for the glacier system and actively participates in the glacier s hydrologic system during the monsoon melt rates are 2 4 cm d 1 total of 98 5 m3 over the study period for bare ice in contact with the pond and 1 mm d 1 total of 10 6 m3 for the saturated debris zone the majority of absorbed atmospheric energy leaves the pond system through englacial conduits delivering sufficient energy to melt 2612m3 additional ice over the study period 38 4 m3 d 1 such melting might be expected to lead to subsidence of the glacier surface supraglacial ponds efficiently convey atmospheric energy to the glacier s interior and rapidly promote the downwasting process

structure from motion photogrammetry a low cost effective tool for geoscience applications abstract high resolution topographic surveying is traditionally associated with high capital and logistical costs so that data acquisition is often passed on to specialist third party organisations the high costs of data collection are for many applications in the earth sciences exacerbated by the remoteness and inaccessibility of many field sites rendering cheaper more portable surveying platforms i e terrestrial laser scanning or gps impractical this paper outlines a revolutionary low cost user friendly photogrammetric technique for obtaining high resolution datasets at a range of scales termed structure from motion sfm traditional softcopy photogrammetric methods require the 3 d location and pose of the camera s or the 3 d location of ground control points to be known to facilitate scene triangulation and reconstruction in contrast the sfm method solves the camera pose and scene geometry simultaneously and automatically using a highly redundant bundle adjustment based on matching features in multiple overlapping offset images a comprehensive introduction to the technique is presented followed by an outline of the methods used to create high resolution digital elevation models dems from extensive photosets obtained using a consumer grade digital camera as an initial appraisal of the technique an sfm derived dem is compared directly with a similar model obtained using terrestrial laser scanning this intercomparison reveals that decimetre scale vertical accuracy can be achieved using sfm even for sites with complex topography and a range of land covers example applications of sfm are presented for three contrasting landforms across a range of scales including an exposed rocky coastal cliff a breached moraine dam complex and a glacially sculpted bedrock ridge the sfm technique represents a major advancement in the field of photogrammetry for geoscience applications our results and experiences indicate sfm is an inexpensive effective and flexible approach to capturing complex topography

seasonal surface velocities of a himalayan glacier derived by automated correlation of unmanned aerial vehicle imagery debris covered glaciers play an important role in the high altitude water cycle in the himalaya yet their dynamics are poorly understood partly because of the difficult fieldwork conditions in this study we therefore deploy an unmanned aerial vehicle uav three times may 2013 october 2013 and may 2014 over the debris covered lirung glacier in nepal the acquired data are processed into orthomosaics and elevation models by a structure from motion workflow and seasonal surface velocity is derived using frequency cross correlation in order to obtain optimal surface velocity products the effects of different input data and correlator configurations are evaluated which reveals that the orthomosaic as input paired with moderate correlator settings provides the best results the glacier has considerable spatial and seasonal differences in surface velocity with maximum summer and winter velocities 6 and 2 5ma 1 respectively in the upper part of the tongue while the lower part is nearly stagnant it is hypothesized that the higher velocities during summer are caused by basal sliding due to increased lubrication of the bed we conclude that uavs have great potential to quantify seasonal and annual variations in flow and can help to further our understanding of debris covered glaciers

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

synsedimentary diagenetic and metamorphic pyrite pyrrhotite and marcasite at the homestake bif hosted gold deposit south dakota usa insights on au as ore genesis from textural and la icp ms trace element studies the paleoproterozoic homestake deposit northern black hills south dakota is the largest banded iron formation bif hosted gold deposit in the world and one of the largest single gold deposits globally 1 300 t au mined at an average grade of 8 4 g t the origin of the deposit has remained in dispute from its discovery with views broadly falling into two groups 1 the gold and associated elements were externally sourced and deposited in a suitable structural and or chemical trap e g iron formation and 2 gold was indigenous to the host iron formation from which it was remobilized into dilatant structural zones during deformation and metamorphism in recent times most workers have favored the former model appealing to the broad synchroneity of paleoproterozoic metamorphism felsic magmatic activity and gold event timing la icp ms analysis of synsedimentary to early diagenetic sulfides at homestake and surrounding area indicates that the au in the orebodies may have originally had a significant syngenetic component in particular la icp ms mapping of multistage pyrites from carbonaceous shale in the upper poorman formation shows that au and a suite of trace elements co ni cu zn se mo ag sb te au hg tl pb and bi similar to those in diagenetic pyrite from around the globe are contained in anhedral sponge textured cores and nodules surrounded by relatively trace element barren au poor euhedral pyrite rims furthermore interelement ratios e g co ni ni ag of the trace element rich spongy and nodular pyrites are also similar to those of typical diagenetic pyrite la icp ms imaging of pyrrhotite in the same rocks reveals multistage growth in this mineral as well with the earlier generation having higher concentrations of ag sb pb tl and bi than its presumed metamorphic counterpart imaging of marcasite in the shales of the upper poorman formation demonstrates this mineral s high abundance of w and tl relative to all generations of pyrite and pyrrhotite mass balance calculations indicate that the volume of upper poorman formation in the mine area approx 12 km3 could potentially yield 4 500 t of au a value greater than the total mined resource by more than a factor of three these geochemical data and calculations suggest that a significant portion of the gold at homestake may have been sourced from the relatively thick carbonaceous and sulfidic black shale facies in the stratigraphic footwall to the host iron formation in a manner similar to other sediment hosted gold districts

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

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

so2 flux from stromboli during the 2007 eruption results from the flame network and traverse measurements abstract so 2 fluxes emitted by stromboli during the 27th february 2nd april 2007 effusive eruption were regularly measured both by an automatic network of scanning ultraviolet spectrometers and by traverse measurements conducted by boat and helicopter the results from both methodologies agree reasonably well providing a validation for the automatic flux calculations produced by the network approximately 22 000 t of so 2 were degassed during the course of the 35 day eruption at an average rate of 620 t per day such a degassing rate is much higher than that normally observed 150 200 t d because the cross sectional area occupied by ascending degassed magma is much greater than normal during the effusion as descending degassed magma that would normally occupy a large volume of the conduit is absent we propose that the hydrostatically controlled magma level within stromboli s conduit is the main control on eruptive activity and that a high effusion rate led to the depressurisation of an intermediate magma reservoir creating a decrease in the magma level until it dropped beneath the eruptive fissure causing the rapid end of the eruption a significant decrease in so 2 flux was observed prior to a paroxysm on 15th march 2007 suggesting that choking of the gas flowing in the conduit may have induced a coalescence event and consequent rapid ascent of gas and magma that produced the explosion