variability of tidal currents in a wide strait a comparison between drifter observations and numerical simulations the spatial variability of semidiurnal tidal currents throughout the waters of the northwest coast of canada is investigated by examination of velocities of surface drifters recording half hourly loran c positions time series are examined to remove any records with significant inertial currents the remaining records are segmented into sequential 25 hour blocks detrended and analyzed for semidiurnal energy tidal current ellipses are computed and compared with two different numerical models a finite element barotropic simulation and a finite difference baroclinic simulation that was initialized with horizontally uniform density surfaces models and observations show the dominance of negative rotation clockwise rotary with the amplification of currents shoreward of the continental slope in shallow waters both models agree well with the observations along the edge of the continental shelf in waters deeper than 200 m the baroclinic model provides better agreement with observations because of its ability to simulate internal tides however observations also reveal that internal tidal currents at and seaward of the shelf break may be irregular because of the presence of plumes and jets and a baroclinic model with horizontally uniform stratification cannot reproduce local features in these jets and plumes internal tidal currents in dixon entrance exceed those simulated by the baroclinic model by a significant degree this is likely due to the constraints of the density field used to initialize the model and to terrain smoothing in its 5 km grid

a tidal model for eastern juan de fuca strait and the southern strait of georgia a three dimensional barotropic finite element model is used to calculate the tidal flows in eastern juan de fuca strait and the southern strait of georgia the harmonics of eight constituents are computed and compared with those from previous finite difference models and those from historical tide gauge and current meter observations root mean square differences between observed and calculated sea level amplitudes are within 2 0 cm for all constituents and the phases are within 4 0 for all constituents except k2 horizontal currents from the model are found to reproduce the observed vertical variations in shear except in regions where stratification effects and internal tides exist in particular the model representation of currents at six stations in the canadian tide and current tables volume 5 is accurate the pattern of tidal residual currents has much more detail than previous coarser resolution models and numerous eddies are predicted computed energy flux fields reveal that over a 29 day period only 38 of the tidal power entering juan de fuca strait is transmitted into the southern strait of georgia and of the 39 entering haro strait 36 is dissipated within the strait itself

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

numerical simulation of internal kelvin waves and coastal upwelling fronts two three dimensional primitive equation numerical ocean models are applied to the problem of internal kelvin waves and coastal upwelling in the great lakes one is the princeton ocean model pom with a terrain following sigma vertical coordinate and the other is the dietrich center for air sea technology diecast model with constant z level coordinates the sigma coordinate system is particularly convenient for simulating coastal upwelling while the z level system might be better for representing abrupt topographic changes the models are first tested with a stratified idealized circular lake 100 km in diameter and 100 m deep two bottom topographies are considered a flat bottom and a parabolic depth profile three rectilinear horizontal grids are used 5 2 5 and 1 25 km the pom was used with 13 vertical levels while the diecast model was tested with both 13 and 29 vertical levels the models are driven with an impulsive wind stress imitating the passage of a weather system in the case of the flat bottom basin the dynamical response to light wind forcing is a small amplitude internal kelvin wave for both models the speed of the kelvin wave in the model is somewhat less than the inviscid analytic solution wave speed in the case of strong wind forcing the thermocline breaks the surface full upwelling and a strong surface thermal front appears after the wind ceases the edges of this thermal front propagate cyclonically around the lake quite similar to an internal kelvin wave in the case of parabolic bathymetry kelvin wave and thermal front propagation is modified by interaction with a topographic wave and a geostrophic circulation in both models higher horizontal resolution gives higher wave and frontal speeds horizontal resolution is much more critical in the full upwelling case than in the kelvin wave case vertical resolution is not as critical the models are also applied to lake michigan to determine the response to strong northerly winds causing upwelling along the eastern shore the results are more complex than for the circular basin but clearly show the characteristics of cyclonically propagating thermal fronts the resulting northward warm front propagation along the eastern shore compares favorably with observations of temperature fluctuations at municipal water intakes after a storm although the model frontal speed was less than the observed speed

influence of subglacial drainage system evolution on glacier surface motion haut glacier d arolla switzerland 1 the relationship between the evolution of subglacial drainage system morphology and spatial patterns of glacier surface velocity was investigated using dye tracing experiments and ground surveying throughout the 1995 melt season at haut glacier d arolla switzerland with the onset of high and variable melt season discharges subglacial drainage changed from a predominantly distributed system to a predominantly channelized system the change occurred later farther up glacier during the period of drainage evolution the glacier was subjected to three periods of rapidly rising meltwater discharge the magnitude and spatial pattern of the glacier s velocity response differed between these periods and can be explained in terms of the impact of the evolving drainage system morphology on the amplitude and spatial distribution of basal hydrological forcing increasing discharge through a distributed drainage system caused widespread basal forcing and high glacier velocity increasing discharge through incipient channels below moulins not yet connected to the main channel caused more localized basal forcing and slightly increased glacier velocity increasing discharge through a fully channelized drainage system caused no significant basal forcing and glacier velocity was not significantly different from the annual deformation flow pattern empirical orthogonal function analysis of flow patterns defined two distinct spatial modes of surface velocity which corresponded closely with the drainage system morphologies inferred to be present during each event the relative importance of these modes changed through the melt season suggesting a temporal change in the spatial pattern of hydrologically induced basal forcing

hydrological characteristics of the drainage system beneath a surging glacier a rare combination of natural circumstances permits assessment of current theories on water flow beneath glaciers outburst floods from the subglacial lake grimsvotn in iceland took place before during and after surging of skei ararjokull the glacier beneath which the outburst floods drain the observable drainage patterns associated with these floods show the different nature of the basal water conduit system of the glacier during surge and non surge phases during surge conditions basal water is dispersed slowly across the bed in a distributed drainage system but when the glacier is not surging water is transported rapidly through a system of tunnels

3d vsp migration by image point transform the common characteristic of the seismic methods involving downhole measurements is the difficulty of designing surveys able to image the subsurface space evenly migration schemes for these layouts are sensitive to reconstruction artifacts the defining property of the image point ip transform is its ability to accumulate amplitudes of curved reflection events appearing in time distance profiles into approximately discoidal or spherical in three dimensions vicinities in the ip domain due to the reflected wavefields collapsing into such vicinities in the ip domain the emphasizing of the reflectors consists of enhancing regions with higher amounts of accumulated amplitude true dip filtering can also easily be performed even for reflectors appearinginthetime distanceprofilesascurvedeventsduetotheirdip source offset or variable velocity field reflecting interfaces are definedassetsoflinkedpiecewiseplanar reflectorelementsrather than as collections of point diffractors true reflectors fitting this description are enhanced by the ip transform while diffraction patterns events produced by other wave types multiples and noise of any kind tend to be suppressed the inverse transformleadstofilteredversionsoftime distanceprofiles analternative to performing the inverse transform back to the original time distance representation is computing 2d 3d migrated imagesdirectlyfromthetransformedipspace althoughthe3dmigrationbyiptransformisapplicabletoanyseismicsurveygeometry we focused on procedures for enhancing prestack migrated images obtained by sparse multioffset multiazimuth vertical seismic profiling vsp surveys as typically performed for mining site characterization and mineral exploration the real data used were collected within an extensive mining seismic investigationprogramperformedincanada

vertical seismic profiling using distributed acoustic sensing with scatter enhanced fibre optic cable at the cu au new afton porphyry deposit british columbia canada abstract wireline logs and vertical seismic profile data were acquired in two boreholes intersecting the main mineralized zone at the cu au new afton porphyry deposit canada with the objectives of imaging lithological contacts fault zones that may have acted as conduits that channelled the mineralization and alteration zones log data provide physical rock properties for the main lithologies and alteration zones calliper logs reveal many faults and caved in zones generally indicating rocks with low integrity at the borehole wall the preponderance of these zones as indicated by the logs suggests that their response may dominate the seismic reflection wavefield outside fault zones compressional and shear wave velocities exhibit significant variability due to porosity the heterogeneity of volcanic fragmental rocks and alteration distributed acoustic sensing was used to acquire vertical seismic profiling data in the two boreholes surveyed with wireline logs straight and helically wound fibre optic cables housed standard fibres and a fibre engineered to increase the intensity of backscattering at the distributed acoustic sensing interrogator standard and engineered optical fibres placed in the two boreholes were daisy chained together to form two 5 km long continuous fibres that were interrogated at once with two interrogators a new generation of interrogator connected to the engineered fibres provided field data with lower noise level and higher signal to noise ratio these data with higher signal to noise ratio from straight fibre optic cable were processed and used for depth imaging depth images benefitted from new migration weights that account for the directional sensitivity of the straight fibre optic cable and limit the extent of migration artefacts migration results show several reflectors with shallow dips to the northwest some explained by faults intersecting the surveyed boreholes the main sub vertical lithological and alteration contacts at new afton generated downgoing reflections that were not considered in the migration

a finite element model for tides and resonance along the north coast of british columbia a finite element barotropic tidal model is developed for the north coast of british columbia the model is run with eight tidal constituents and the results are compared with the flather 1987 finite difference model and with extensive tide gauge and current meter observations although the tidal potential earth tide and loading tide are included in the forcing their inclusion is shown to change the largest m2 amplitudes by only 2 5 and the largest k1 amplitudes by less than 1 root mean square differences between observed and calculated sea level amplitudes and phases are within 1 9 cm and 2 9 o for all but one constituent but the model currents do not in general compare as favourably the barotropic currents observed in hecate strait are reproduced well but elsewhere evidence is shown that model inaccuracies are due to baroclinic effects tidal residual currents calculated by the model suggest the existence of eddies off the tip of cape st james cape chacon and around goose island and learmonth banks the shallow water constituents in hecate strait are shown to have significant contributions from the constructive interference of signals propagating into dixon entrance and queen charlotte sound using the model the longest resonant period of the system is estimated to be 7 6 hours with an energy dissipation parameter q of 9 5

evaluating glacier dynamics using temporal remote sensing images a case study of hunza valley northern pakistan glaciers are the largest freshwater repository on the earth surface northern pakistan is covered with some of the largest midlatitude glaciers in the world most of the recent studies on the region lead to contradictory results that glaciers in the karakoram ranges have shown either advancement retreat or stable behaviors and therefore coin the term karakoram anomaly in the present study temporal landsat satellite images acquired in the years of 1977 1999 2001 2007 2009 and 2014 were used to evaluate the temporal dynamics of the selected glaciers in the hunza valley northern pakistan including the batura passu ghulkin and gulmit the glaciers outlines were extracted using ndsi and slope gradient followed by manual editing the landsat derived glacier inventories were verified through the fine resolution worldview 2 satellite image and field observations evaluating the temporal glacier inventories reveals that the selected glaciers are retreating however the melting rate is varying depending on the supra glacier debris cover the melting or advancing of glacier is also influenced by the mean annual temperature and precipitation records the study should assist in predicting the future climate of the region

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

modelling distributed and channelized subglacial drainage the spacing of channels models are proposed for channelized and distributed flow of meltwater at the base of an ice sheet the volumes of both channel and distributed systems evolve according to a competition between processes that open drainage space e g sliding over bedrock melting of the ice and processes that close it e g viscous creep of the ice due to a positive effective pressure channels are generally predicted to have lower water pressure and therefore capture water from the surrounding regions of distributed flow there is a natural length scale associated with the distributed system that determines the width of the bed from which water can be drawn into a channel it is suggested that this determines the spacing between major channels and that this may be reflected in the spacing of eskers a more permeable distributed system results in more widely spaced and therefore larger channels calculations of the flow into the head of a channel reveal that there is a critical discharge necessary for it to form and provide a criterion for where channels can exist

properties of natural supraglacial debris in relation to modelling sub debris ice ablation as debris covered glaciers become a more prominent feature of a shrinking mountain cryosphere there is increasing need to successfully model the surface energy and mass balance of debris covered glaciers yet measurements of the processes operating in natural supraglacial debris covers are sparse we report measurements of vertical temperature profiles in debris on the ngozumpa glacier in nepal that show i conductive processes dominate during the ablation season in matrix supported diamict ii ventilation may be possible in coarse surface layers iii phase changes associated with seasonal change have a marked effect on the effective thermal diffusivity of the debris effective thermal conductivity determined from vertical temperature profiles in the debris is generally 30 higher in summer than in winter but values depend on the volume and phase of water in the debris surface albedo can vary widely over small spatial scales as does the debris thickness measurements indicate that debris thickness is best represented as a probability density function with the peak debris thickness increasing down glacier the findings from ngozumpa glacier indicate that the probability distribution of debris thickness changes from positively skewed in the upper glacier towards a more normal distribution nearer the terminus although many of these effects remain to be quantified our observations highlight aspects of spatial and temporal variability in supraglacial debris that may require consideration in annual or multi annual distributed modelling of debris covered glacier surface energy and mass balance copyright 2012 john wiley sons ltd

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

aster measurement of supraglacial lakes in the mount everest region of the himalaya we demonstrate an application of advanced spaceborne thermal emission and reflection radiometer aster images to detect and monitor supraglacial lakes on glaciers in the mount everest region in tibet xizang and nepal aster offers powerful capabilities to monitor supraglacial lakes in terms of 1 surface area growth and disappearance spatial resolution 15m 2 turbidity 15m resolution and 3 temperature 90m resolution preliminary results show an overall similarity of supraglacial lakes on three glaciers lakes have widely varying turbidity as indicated by color in visible near infrared bands 1 3 the largest lakes being bright blue highly turbid cold near 0 c and hydraulically connected with other lakes and supraglacial streams while small lakes are mostly darkblue relatively clear water warmer 4 c and appear hydraulically isolated high levels of turbidity in supraglacial lakes indicate high rates of meltwater input from streams or erosion of ice cliffs and thus are an indirect measure relating to the activity and hydraulic integration of the lake with respect to other lakes and streams in the glacier

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

glacial melt under a porous debris layer in this paper we undertake a quantitative analysis of the dynamic process by which ice underneath a dry porous debris layer melts we show that the incorporation of debris layer airflow into a theoretical model of glacial melting can capture the empirically observed features of the so called ostrem curve a plot of the melt rate as a function of debris depth specifically we show that the turning point in the ostrem curve can be caused by two distinct mechanisms the increase in the proportion of ice that is debris covered and or a reduction in the evaporative heat flux as the debris layer thickens this second effect causes an increased melt rate because the reduction in latent energy used for evaporation increases the amount of energy available for melting our model provides an explicit prediction for the melt rate and the temperature distribution within the debris layer and provides insight into the relative importance of the two effects responsible for the maximum in the ostrem curve we use the data of nicholson and benn 2006 to show that our model is consistent with existing empirical measurements

full wavefield migration of vertical seismic profiling data using all multiples to extend the illumination area vertical seismic profiling data can provide a high resolution reservoir image because the receivers are located close to the reservoir and hence the wavefield encounters less distortion in the overburden compared to surface seismic data however conventional migration of vertical seismic profiling data using only upgoing primary wavefields often suffers from poor illumination imaging artefacts and low image reliability especially at image locations away from the well we propose full wavefield migration to image vertical seismic profiling data using the primaries and all orders of surface multiples and internal multiples the downgoing internal or surface multiples are treated as an additional source of illumination in full wavefield migration we aim to estimate a high resolution reflectivity image of the subsurface with this extended illumination the algorithm is recursive in depth like conventional wavefield extrapolation based migration however it incorporates the non linear transmission and scattering effects at each depth level further full wavefield migration is posed as a constrained least squares inversion problem that could be solved using a conjugate gradient method we propose an iterative full wavefield forward modelling engine as the backbone of this inversion scheme the parameter used in the modelling is subsurface reflectivity full wavefield modelling iteratively incorporates the non linearity of the wavefield due to multiple scattering where every iteration utilizes one higher order of scattered wavefields to estimate the subsurface reflectivity in addition the constrained inversion helps in reducing the extrapolation artefacts and provides a high resolution image of the reservoir in this paper we discuss the concept of full wavefield migration and demonstrate its potential as an imaging tool for vertical seismic profiling data using synthetic examples key words vertical seismic profiling true amplitude migration inversion modelling illumination

glacier mass balance in the qinghai tibet plateau and its surroundings from the mid 1970s to 2000 based on hexagon kh 9 and srtm dems abstract in the context of global warming glacier changes in the qinghai tibet plateau qtp and its surroundings have attracted a great amount of public attention to date there have been many studies of glacier mass balance across the qtp however given that most of the previous studies have focused on a short observation period 2000 2015 and that long term mass change measurements are available only for some local regions we utilized declassified kh 9 images and 1 arc second shuttle radar topography mission srtm digital elevation models dems to provide the region wide mass balance from the mid 1970s to 2000 for a larger scale including 11 sample regions across the qtp and its surroundings the final results indicate that the glaciers in the northwest of the qtp have shown a less negative or near zero mass balance ranging from 0 11 0 13 m w e a 1 to 0 02 0 10 m w e a 1 compared to those in the southeast part with a mass balance range of 0 30 0 12 m w e a 1 to 0 11 0 14 m w e a 1 the most serious mass loss has emerged in the central eastern himalaya integrating our results with the observations after 2000 suggests that over the past four decades mid 1970s to the mid 2010s the glaciers in the himalaya nyainqentanglha and tanggula mountains as a whole have exhibited accelerated mass loss and the most significant acceleration has occurred in the eastern nyainqentanglha moreover the hindu raj glaciers have shown a stable rate of continuous mass loss while a nearly stable or slight mass gain state in the western kunlun region can be dated back to at least as far as the mid 1970s

rising river flows throughout the twenty first century in two himalayan glacierized watersheds greater himalayan glaciers are retreating and losing mass a combination of the latest ensemble of climate models combined with a glacio hydrological model suggests that in two contrasting watersheds in the greater himalaya glaciers will recede but net glacier melt runoff is on a rising limb until at least 2050

englacial drainage systems formed by hydrologically driven crevasse propagation recent work has shown that surface to bed drainage systems re form annually on parts of the greenland ice sheet and some high arctic glaciers leading to speed up events soon after the onset of summer melt surface observations and geophysical data indicate that such systems form by hydrologically driven fracture propagation herein referred to as hydrofracturing although little is known about their characteristics using speleological techniques we have explored and surveyed englacial drainage systems formed by hydrofracturing in glaciers in svalbard nepal and alaska in hansbreen svalbard vertical shafts were followed through 60 m of cold ice and 10 m of temperate basal ice to a subglacial conduit deep hydrofracturing occurred at this site due to a combination of extensional ice flow and abundant surface meltwater at a glacier confluence the englacial drainage systems in khumbu glacier nepal and matanuska glacier alaska usa formed in areas of longitudinal compression and transverse extension and consist of vertical slots that plunge down glacier at angles of 558 or less the occurrence of englacial drainages initiated by hydrofracturing in diverse glaciological regimes suggests that it is a very widespread process and that surface to bed drainage can occur wherever high meltwater supply coincides with ice subjected to sufficiently large tensile stresses

thermo erosional notch development at fresh water calving tasman glacier new zealand controls on glacier calving rates are receiving increased scientific interest at fresh water calving glaciers limnological factors might be more important than glaciological ones measurements of thermo erosional notch development at the calving ice cliff of tasman glacier new zealand suggest that the calving rates at this glacier are directly controlled by the rate of thermal undercutting notch formation rates typically vary between 10 and 30 cm d 1 maximum rate 65 cm d 1 in summer corresponding to an average calving rate of 34 m a 1 notch formation is slower than waterline melt and is controlled by water temperatures and circulation cliff geometry debris supply and water level fluctuations the latter shift the position of undercutting resetting the level of the notch formation process and thereby slowing it the geometry of the notch and the debris supply determine the extent of influence of the lake on notch water temperatures and circulation hence water temperatures in the lake are not necessarily indicative of the rate of notch formation the prediction of rate of notch formation from far field variables is hampered by the complex interaction of the influencing factors the significance of thermal undercutting as a calving rate controlling process decreases with increasing ice velocities calving rates and surface gradients

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

rapid melting dynamics of an alpine glacier with repeated uav photogrammetry abstract glacial retreat is a major problem in the alps especially over the past 40 years unmanned aerial vehicles uavs can provide an unparalleled opportunity to track the spatiotemporal variations in rapidly changing glacial morphological features related to glacial dynamics the objective of this study is to evaluate the potential of commercial uav platforms to detect the evolution of the surface topography and morphology of an alpine glacier over a short time scale through the repeated acquisition of high resolution photogrammetric data two high resolution uav surveys were performed on the ablation region of the morteratsch glacier swiss alps in july and september 2016 first structure from motion sfm techniques were applied to create orthophotos and digital surface models dsms of the glacial surface from multi view uav acquisitions the geometric accuracy of dsms and orthophotos was checked using differential global navigation satellite system dgnss ground measurements and an accuracy of approximately 17 cm was achieved for both models high resolution orthophotos and dsms made it possible to provide a detailed characterization of rapidly changing glacial environments comparing the data from the first and the second campaigns the evolution of the lower part of the glacier in response to summer ablation was evaluated two distinct processes were revealed and accurately quantified an average lowering of the surface with a mean ice thinning of 4 m and an average horizontal displacement of 3 m due to flowing ice these data were validated through a comparison of different algorithms and approaches which clearly showed the consistency of the results the melt rate spatial patterns were then compared to the glacial brightness and roughness maps derived from the september uav acquisition the results showed that the dsm differences describing the glacial melt rates were inversely related to the glacial brightness in contrast a positive but weaker relationship existed between the dsm differences and glacial roughness this research demonstrates that uav photogrammetry allows the qualitative and quantitative appreciation of the complex evolution of retreating glaciers at a centimetre scale spatial resolution such performance allows the detection of seasonal changes in the surface topography which are related to summer ablation and span from the processes affecting the entire glacier to those that are more local

experimental determination of a double valued drag relationship for glacier sliding the contribution of glaciers to sea level rise and their effects on landscape evolution depend on the poorly known relationship between sliding speed and drag at the ice bed interface results from experiments with a new rotary laboratory device demonstrate empirically for the first time a double valued drag relationship like that suggested by some sliding theories steady drag on a rigid sinusoidal bed increases peaks and declines at progressively higher sliding speeds due to growth of cavities in the lee sides of bed undulations drag decreases with increased sliding speed if cavities extend beyond the inflection points of up glacier facing surfaces so that adverse bed slopes in contact with ice diminish with further cavity growth these results indicate that shear tractions on glacier beds can potentially decrease due to increases in sliding speed driven by weather or climate variability promoting even more rapid glacier motion by requiring greater strain rates to produce resistive stresses although a double valued drag relationship has not yet been demonstrated for the complicated geometries of real glacier beds both its potential major implications and the characteristically convex stoss surfaces of bumps on real glacier beds provide stimulus for exploring the effects of this relationship in ice sheet models

ice deformation at the confluence of two glaciers investigated with conceptual map plane and flowline models using analytical and numerical techniques a two dimensional 2 d map plane model and a 2 d flowline model are utilized to elucidate the horizontal and vertical ice deformation at the confluence of two glaciers for a perfectly symmetrical confluence the junction point of the two tributaries can be modeled as a no slip free slip transition a strongly localized surface depression develops around the junction point accompanied by two broadly elevated zones positioned close to the margins of the tributaries facing the junction point the confluence center line is subjected to horizontal longitudinal extension and a transverse compression the compression generally exceeds the concomitant longitudinal extension in magnitude depth integrated vertical strain rates along the center line are positive extension but the strain rate variation with depth depends critically on the type of basal boundary conditions at the glacier bed for a no slip boundary condition vertical strain rates change from positive at the surface to negative close to the base whereas for a free slip boundary condition perfect sliding vertical strain rates are positive throughout the depth these theoretical results are compared with field measurements from unteraargletscher bernese alps switzerland

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

automated classification of debris covered glaciers combining optical sar and topographic data in an object based environment abstract satellite imagery is increasingly used to monitor glacier area changes and create glacier inventories robust and efficient pixel based band ratios have proven to be accurate for automatically delineating clean glacier ice however such classifications are restricted on debris covered ice due to its spectral similarity with surrounding terrain object based image analysis obia has emerged as a new analysis technique within remote sensing it offers many advantages over pixel based classification techniques due to the ability to work with multiple data sources and handle data contextually and hierarchically by making use of obia capabilities we automatically classify clean ice and debris covered ice in the challenging area surrounding mount manaslu in nepal using optical landsat 8 topographic void filled srtm and sar coherence alos palsar data clean ice was classified with a mean accuracy of 93 whilst debris covered ice was classified with an accuracy of 83 when compared to manually corrected outlines providing a total glacier accuracy of 91 with further developments in the classification steep tributary sections of ice could be contextually included raising the accuracy to over 94 one prominent advantage of obia is that it allows some post processing and correction of the glacier outlines automatically reducing the amount of manual correction needed obia incorporating sar coherence data is recommended for future mapping of debris covered ice

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

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

structural control of englacial conduits in the temperate matanuska glacier alaska usa fourteen englacial conduits were mapped within 2 km of the terminus of the temperate matanuska glacier alaska usa to ice depths of 65 m using speleological techniques detailed three dimensional maps of the conduits were made over 3 years to characterize conduit relationships with glacier structural features and to track conduit evolution through time all conduits consisted of single unbranching passages that followed fractures in the ice all conduits were either too constricted to continue or became water filled at their deepest explored point and were not able to be followed to the glacier bed conduit morphology varied systematically with the orientation of the glacier principal stresses allowing them to be categorized into two broad classes the first class of conduits were formed by hydrostatic crevasse penetration where a large supraglacial stream intersected longitudinal crevasses these conduits plunged toward the glacier bed at angles of 30 408 the second class of conduits formed where smaller streams sank into the glacier on shear crevasses many of these conduits changed direction dramatically where they intersected transverse crevasses at depth these results suggest that the conduits observed in this study formed along fractures and over their surveyed length were not affected by gradients in ice overburden pressure

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

supraglacial ice cliffs and ponds on debris covered glaciers spatio temporal distribution and characteristics ice cliffs and ponds on debris covered glaciers have received increased attention due to their role in amplifying local melt however very few studies have looked at these features on the catchment scale to determine their patterns and changes in space and time we have compiled a detailed inventory of cliffs and ponds in the langtang catchment central himalaya from six high resolution satellite orthoimages and dems between 2006 and 2015 and a historic orthophoto from 1974 cliffs cover between 1 4 0 4 in the dry and 3 4 0 9 in the wet seasons and ponds between 0 6 0 1 and 1 6 0 3 of the total debris covered tongues we find large variations between seasons as cliffs and ponds tend to grow in the wetter monsoon period but there is no obvious trend in total area over the study period the inventory further shows that cliffs are predominately north facing irrespective of the glacier flow direction both cliffs and ponds appear in higher densities several hundred metres from the terminus in areas where tributaries reach the main glacier tongue on the largest glacier in the catchment 10 of all cliffs and ponds persisted over nearly a decade

structural control of englacial drainage systems in himalayan debris covered glaciers englacial cave systems were mapped using speleological techniques in three debris covered glaciers in the khumbu himal nepal detailed three dimensional mapping of the cave systems and observations of relationships with structures in the surrounding ice show conduits formed by a mechanism directly analogous to speleogenesis in limestone karst the highest oldest parts of all passages developed along debris filled crevasse traces with hydraulic conductivity in the range 10 4 to 10 5 ms 1 conduits form when these hydraulically efficient pathways bridge between areas with different hydraulic potential they then evolve by grading through head ward migration of nick points and vertical incision to local base level often the surface of supraglacial lakes most supraglacial lakes on himalayan glaciers are perched above the elevation of the terminal stream and exist for a few years before draining through englacial conduits as a result near surface drainage evolution is frequently interrupted by base level fall and conduits may record multiple phases of incision conduits commonly migrate laterally during incision undermining higher levels of the ice and encouraging collapse voids can be created by fluvial processes and collapse of crevassed ice the oft noted resemblance of the surface morphology of debris covered glaciers to karst landscapes thus extends to the subsurface and karst hydrology provides a framework for understanding englacial drainage

large wood lw 3d accumulation mapping and assessment using structure from motion photogrammetry in the laboratory abstract a structure from motion sfm photogrammetry based methodology for precise mapping of large wood lw accumulations in fluvial systems is presented the technique may be useful for routine inventory and rapid volume estimation of complex lw structures that tend to divert or obstruct flow in rivers our methodology is validated by means of laboratory experiments ranging from elementary to complex arrangements of lw components and organic fine material ofm seven experimental setups were used as the basis for i manual approximations of 2 5d and 3d geometric reference volumes ii 2 5d volume models based on mesh geometry iii a closed watertight 3d mesh from an unorganized point cloud and iv estimates of porosity a commercially available sfm photogrammetry software package pix4dmapper was used for point cloud and simplified mesh generation in order to obtain more precise volumes 3d surface models are required accordingly we generated 3d watertight mesh models of the unorganized point cloud using the screened poisson surface reconstruction psr technique the pix4d volume tool 2 5d resulted in an overestimation 2 9 to 52 7 of the geometric volume 3d due to the convex hull approximation of the geometry normal to the surface plane psr 3d resulted in more precise volumes showing deviations from the geometric volume 3d in a range of 15 9 to 10 6 as the algorithm could capture concavities and involuted surfaces on the accumulation assuming that the difference between 3d and 2 5d volume models represents many of the voids visible within or on the surface of the deposit this volume can be used as an estimate of porosity our assessment suggests that image based sfm methodology is well suited for further investigations in lw research due to its time and cost efficiency in comparison with other conventional surveying techniques the methodology can be used to generate high quality point cloud and mesh models of log jam formations these may be used by river managers and researchers to quantify accumulation volume and thus gain a better understanding of lw composition and the influence of wood geometry on hydraulic flow conditions

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

the randolph glacier inventory a globally complete inventory of glaciers the randolph glacier inventory rgi is a globally complete collection of digital outlines of glaciers excluding the ice sheets developed to meet the needs of the fifth assessment of the intergovernmental panel on climate change for estimates of past and future mass balance the rgi was created with limited resources in a short period priority was given to completeness of coverage but a limited uniform set of attributes is attached to each of the 198 000 glaciers in its latest version 3 2 satellite imagery from 1999 2010 provided most of the outlines their total extent is estimated as 726 800 34 000 km 2 the uncertainty about 5 is derived from careful single glacier and basin scale uncertainty estimates and comparisons with inventories that were not sources for the rgi the main contributors to uncertainty are probably misinterpretation of seasonal snow cover and debris cover these errors appear not to be normally distributed and quantifying them reliably is an unsolved problem combined with digital elevation models the rgi glacier outlines yield hypsometries that can be com bined with atmospheric data or model outputs for analysis of the impacts of climatic change on glaciers the rgi has already proved its value in the generation of significantly improved aggregate estimates of glacier mass changes and total volume and thus actual and potential contributions to sea level rise

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

effects of debris on ice surface melting rates an experimental study here we report a laboratory study of the effects of debris thickness diurnally cyclic radiation and rainfall on melt rates beneath rock avalanche debris and sand representing typical highly permeable supraglacial debris under continuous steady state radiation sand cover 50mm thick delays the onset of ice surface melting by 12 hours but subsequent melting matches melt rates of a bare ice surface only when diurnal cycles of radiation are imposed does the debris reduce the longterm rate of ice melt beneath it this is because debris 50 mm thick never reaches a steady state heat flux and heat acquired during the light part of the cycle is partially dissipated to the atmosphere during the nocturnal part of the cycle thereby continuously reducing total heat flux to the ice surface underneath the thicker the debris the greater this effect rain advects heat from high permeability supraglacial debris to the ice surface thereby increasing ablation where thin highly porous material covers the ice in contrast low permeability rock avalanche material slows water percolation and heat transfer through the debris can cease when interstitial water freezes during the cold night part of the cycle this frozen interstitial water blocks heat advection to the ice debris contact during the warm day part of the cycle thereby reducing overall ablation the presence of metre deep rock avalanche debris over much of the ablation zone of a glacier can significantly affect the mass balance and thus the motion of a glacier the length and thermal intensity of the diurnal cycle are important controls on ablation and thus both geographical location and altitude significantly affect the impact of debris on glacial melting rates the effect of debris cover is magnified at high altitude and in lower latitudes copyright 2010 elsevier b v all rights reserved

an interpretation of surface and borehole seismic surveys for mine planning at the millennium uranium deposit northern saskatchewan canada abstractthe millennium uranium deposit is located within the athabasca basin in northern saskatchewan canada the deposit is hosted within moderately dipping paleoproterozoic gneisses that are unconformably overlain by more than 500 m of flat lying porous paleoproterozoic to late mesoproterozoic athabasca group sandstones the deposit is associated with the sandstone basement unconformity post athabasca structure and hydrothermal alteration these features combine to create a complex 3d hydrogeologic setting that presents challenges with respect to mine development production and safety in 2007 as part of a prefeasibility study for potential mine development a seismic program consisting of a 3d surface survey vertical seismic profiling moving source profiling and side scan surveys was undertaken to map the complex geology the geometry and resolution of these different seismic surveys allowed for direct imaging of the geologic targets of interest regardless of orientation and size after int

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

slight mass gain of karakoram glaciers in the early twenty first century the mass balance of hindu kush karakoram himalaya glaciers has been debated partly because of a severe lack of observations from the region an analysis of the regional mass balance of karakoram glaciers by comparison of digital elevation models from 1999 to 2008 reveals a small glacier mass gain in the area

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

spatial seasonal and interannual variability of supraglacial ponds in the langtang valley of nepal 1999 2013 supraglacial ponds play a key role in absorbing atmospheric energy and directing it to the ice of debris covered glaciers but the spatial and temporal distribution of these features is not well documented we analyse 172 landsat tm etm scenes for the period 1999 2013 to identify thawed supraglacial ponds for the debris covered tongues of five glaciers in the langtang valley of nepal we apply an advanced atmospheric correction routine landcor 6s and use band ratio and image morphological techniques to identify ponds and validate our results with 2 5 m cartosat 1 observations we then characterize the spatial seasonal and interannual patterns of ponds we find high variability in pond incidence between glaciers may october means of 0 08 1 69 of debris area with ponds most frequent in zones of low surface gradient and velocity the ponds show pronounced seasonality appearing in the pre monsoon as snow melts peaking at the monsoon onset at 2 of debris covered area then declining in the post monsoon as ponds drain or freeze ponds are highly recurrent and persistent with 40 5 of pond locations occurring for multiple years rather than a trend in pond cover over the study period we find high interannual variability for each glacier after controlling for seasonality

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