fracture propagation to the base of the greenland ice sheet during supraglacial lake drainage surface meltwater that reaches the base of an ice sheet creates a mechanism for the rapid response of ice flow to climate change the process whereby such a pathway is created through thick cold ice has not however been previously observed we describe the rapid 2 hours drainage of a large supraglacial lake down 980 meters through to the bed of the greenland ice sheet initiated by water driven fracture propagation evolving into moulin flow drainage coincided with increased seismicity transient acceleration ice sheet uplift and horizontal displacement subsidence and deceleration occurred over the subsequent 24 hours the short lived dynamic response suggests that an efficient drainage system dispersed the meltwater subglacially the integrated effect of multiple lake drainages could explain the observed net regional summer ice speedup

finite element simulation of fluid flow in fractured rock media fluid dynamics models are used by the petroleum industry to model single and or multi phase flow within fractured rock formations in order to facilitate extraction of fluids such as oil and natural gas and in other areas of engineering to study groundwater flow as well as to estimate contaminant seepage and transport in this paper the numerical modelling software comsol is used to simulate air and water flow through a specimen of granite with a single vertical fracture subjected to triaxial loading conditions the intent of the model is to simulate triaxial test findings on a rock specimen with a natural fracture fluid flow is simulated at various confining and inlet pressures using the cubic law model results were in good agreement with laboratory findings pressure distribution along the fracture and across the specimen are as expected with a near linear pressure distribution along the length of the fracture a drawdown effect on pressure distribution across the specimen in the vicinity of the fracture is also observed pressure gradient was largely uniform however some localised zones of high gradient along the fracture are observed

modelling the evolution of supraglacial lakes on the west greenland ice sheet margin we present a model study investigating the summer evolution of supraglacial lakes on the greenland ice margin using a one dimensional 1 d model we calculate the surface ablation for a bare ice surface and beneath supraglacial lakes for 30 days in the summers of 1999 and 2001 the surface ablation beneath the lake was enhanced by 110 in 1999 and 170 in 2001 compared with the ablation for bare ice we then use the results from the 1 d model to further model the vertical and horizontal evolution of the supraglacial lakes the results of which are compared with satellite images within the region of the ice sheet where supraglacial lakes presently occur the area covered by supraglacial lakes is found to be more or less independent of the summer melt rate but controlled by topography we therefore predict that inside this region the area covered by supraglacial lakes will remain constant even in a warmer climate however in a warmer climate surface melting will occur higher on the ice sheet where small surface slopes favour formation of large supraglacial lakes enhanced surface melting beneath such lakes is a hitherto overlooked feedback mechanism related to climate warming

measurement and modeling of ablation of the bottom of supraglacial lakes in western greenland 1 we report measurements of ablation rates of the bottom of two supraglacial lakes and of temperatures at different depths collected during the summers of 2010 and 2011 in west greenland to our knowledge this is the first time that such data sets are reported and discussed in the literature the measured ablation rates at the bottom of the two lakes are of the order of 6 cm day versus a rate of 2 5 3 cm day in the case of bare ice of surrounding areas though our measurements suggest the presence of a vertical temperature gradient it is not possible to draw final conclusions as the measured gradient is smaller than the accuracy of our temperature sensors in situ measurements are compared with the results of a thermodynamic model forced with the outputs of a regional climate model in general the model is able to satisfactorily reproduce the measured quantities with rmse of the order of 3 4 cm for the ablation and 1 5 c in the case of water temperature our results confirm that the ablation at the bottom of supraglacial lakes plays an important role on the overall lake volume with the ablation in the case of ice covered by a lake being 110 135 of that over bare ice at nearby locations beside ice sheet hydrological implications melting at the bottom of a supraglacial lake might affect estimates of lake volume from spaceborne visible and near infrared measurements

the tribology of cupules this paper describes a newly observed phenomenon a rare form of lamina protecting petroglyphs from weathering and it attempts an explanation of such features these laminae are not precipitates but represent the floors of the original cupules that have become more resistant to erosion through conversion to tectonite the process involves crystallization of the syntaxial quartz overgrowths on quartz grains that constitute the cement component of quartzite and silica rich schist it is attributed to the cumulative application of kinetic energy that derives from the tens of thousands of hammerstone blows that produced the cupule the tribological process results in products similar to those formed in ductile shear zones when sandstone has been subjected to great kinetic stresses in the cupules reported here the re metamorphosed lamina preserves their original surface and prevents the erosion of the protolith parent rock concealed by the modified layer the thickness of the layer is a function of the cumulative amount of energy applied to the rock s cement and the process of alteration is defined as kinetic energy metamorphosis

the physical properties of quartz micaschist and their application to freeze thaw weathering studies in the maritime antarctic as part of a study on freeze thaw weathering in the maritime antarctic an investigation was made of the physical properties of the local rock tests were made of point load compressive strength schmidt hammer in situ rock strength moisture content indentor resistance and the size range of weathering products the resulting data were used to consider the form of freeze thaw weathering operative in the field and its relationship to laboratory simulations a distinct difference between massive rock and intact rock is observed in the field it is suggested that future studies should generate a greater database pertaining to rock properties as it is an invaluable aid in the study of mechanical weathering

over winter persistence of supraglacial lakes on the greenland ice sheet results and insights from a new model we present a newly developed 1 d numerical energy balance and phase transition supraglacial lake model glacierlake glacierlake incorporates snowfall in situ snow and ice melt incoming water from the surrounding catchment ice lid formation basal freeze up and thermal stratification snow cover and temperature are varied to test lake development through winter and the maximum lid thickness is recorded average wintertime temperatures of 2 to 30 circ rm c and total snowfall of 0 to 3 45 m lead to a range of the maximum lid thickness from 1 2 to 2 8 m after sim 250 days with snow cover exerting the dominant control an initial ice temperature of 15 circ rm c with simulated advection of cold ice from upstream results in 0 6 m of basal freeze up this suggests that lakes with water depths above 1 3 to 3 4 m dependent on winter snowfall and temperature upon lid formation will persist through winter these buried lakes can provide a sizeable water store at the start of the melt season expedite future lake formation and warm underlying ice even in winter

supraglacial lakes on the larsen b ice shelf antarctica and at paakitsoq west greenland a comparative study we acknowledge the support of the u s national science foundation under grant ant 0944248

modeling supraglacial water routing and lake filling on the greenland ice sheet 1 during more intense melt years supraglacial lakes on the greenland ice sheet are found to fill more rapidly and to drain earlier in the melt season they also develop at higher latitudes and elevations since the rapid drainage of lakes has been shown to enhance basal sliding and since the lake volume can play an important role in determining if and when it drains understanding and modeling the processes which control lake filling rates forms a key development in successfully modeling the possible impacts of lake drainage events on ice motion we have developed a surface water routing and lake filling model and applied it to a 100 km2area of the paakitsoq region west greenland the model takes the time series of calculated runoff melt minus refreezing over the area and calculates flow paths and water velocities over the snow ice covered surface routing the water into topographic depressions which can fill to form lakes runoff is calculated from a distributed surface energy balance model coupled to a subsurface model which calculates changes in temperature density and water content in the snow firn and upper ice layers and hence refreezing and therefore net runoff the model is calibrated against field measurements of a filling lake in our study area during june 2011 and can be used to calculate the filling rate of the instrumented lake with a high degree of accuracy the filling rate of the instrumented modeled lake depends on melt and routing from the immediate lake catchment and from overflowing lakes in upstream catchments

simulation of groundwater flow in fractured rocks using a coupled model based on the method of domain decomposition groundwater flow in fractured rocks is modeled using a coupled model based on the domain decomposition method in the model the fractured porous medium is divided into two non overlapping sub domains one is the rock matrix in which the medium is described using a continuum model the other consists of deep fractures and fissure zones where the medium is described using a discrete fracture network dfn model the two models are coupled through the continuity of the hydraulic heads and fluxes on the common boundaries the coupled model is used to simulate groundwater flow in a hydropower station the results show that the model simulates groundwater levels that are in agreement with the measured groundwater levels furthermore the model s parameters relating to deep fractures and fissure zones are verified by comparing three different models the continuum model coupled model and dfn model the results show that the coupled model can capture and duplicate the hydrogeological conditions in the study domain whereas the continuum model overestimates and the dfn model underestimates the measured hydraulic heads a sensitivity analysis shows that fracture aperture has a considerable effect on the groundwater level so when the fracture aperture is large the coupled model or dfn model is more appropriate than the continuum model in the fracture domain

controls on rapid supraglacial lake drainage in west greenland an exploratory data analysis approach the controls on rapid surface lake drainage on the greenland ice sheet gris remain uncertain making it challenging to incorporate lake drainage into models of gris hydrology and so to determine the ice dynamic impact of meltwater reaching the ice sheet bed here we first use a lake area and volume tracking algorithm to identify rapidly draining lakes within west greenland during summer 2014 second we derive hydrological morphological glaciological and surface mass balance data for various factors that may influence rapid lake drainage third these factors are used within exploratory data analysis to examine existing hypotheses for rapid lake drainage this involves testing for statistical differences between the rapidly and non rapidly draining lake types as well as examining associations between lake size and the potential controlling factors this study shows that the two lake types are statistically indistinguishable for almost all factors investigated except lake area thus we are unable to recommend an empirically supported deterministic alternative to the fracture area threshold parameter for modelling rapid lake drainage within existing surface hydrology models of the gris however if improved remotely sensed datasets e g ice velocity maps climate model outputs were included in future research it may be possible to detect the causes of rapid drainage

seasonal evolution of supraglacial lakes on an east antarctic outlet glacier supraglacial lakes are known to influence ice melt and ice flow on the greenland ice sheet and potentially cause ice shelf disintegration on the antarctic peninsula in east antarctica however our understanding of their behavior and impact is more limited using 150 optical satellite images and meteorological records from 2000 to 2013 we provide the first multiyear analysis of lake evolution on langhovde glacier dronning maud land 69 11 s 39 32 e we mapped 7990 lakes and 855 surface channels up to 18 1 km inland 670 m above sea level from the grounding line and document three pathways of lake demise i refreezing ii drainage to the englacial subglacial environment on the floating ice and iii overflow into surface channels on both the floating and grounded ice the parallels between these mechanisms and those observed on greenland and the antarctic peninsula suggest that lakes may similarly affect rates and patterns of ice melt ice flow and ice shelf disintegration in east antarctica

seasonal evolution of supra glacial lakes on the greenland ice sheet abstract a survey of supra glacial lakes on the western margin of the greenland ice sheet reveals a seasonally driven hydrological system culminating in widespread lake drainage in late summer we used satellite imagery to study the evolution of 292 lakes across two sites totalling 22 000 km 2 in area during 2001 the lakes combined area increased to 75 5 km 2 by the beginning of july over the following 25 days an area totalling 36 3 5 km 2 drained from 216 lakes at one study site we used meteorological data and a positive degree day model to calculate the volume of water generated by melting in the lake catchments based on this estimate the mean depth of filling lakes surveyed rose from 1 5 0 7 m on 7th july to 3 9 1 1 m on 1st august in agreement with a value for one lake of 4 4 0 9 m we have derived from airborne altimetry during this 25 day period we estimate that 38 18 10 7 m 3 of water drained from the surface at this site and that there was an average water flux of 1 3 0 3 m 3 s 1 passing through each lake that drained completely

a hydrologically coupled higher order flow band model of ice dynamics with a coulomb friction sliding law 1 the influence of hydrologic transience and heterogeneity on basal motion is an often neglected aspect of numerical ice flow models we present a flow band model of glacier dynamics with a coulomb friction sliding law that is coupled to a model of the basal drainage system by means of subglacial water pressure the ice flow model contains higher order stress gradients from the stokes flow approximation originally conceived by blatter 1995 the resulting system of nonlinear equations is solved using a modified picard iteration that is shown to improve the rate of convergence a parameterization of lateral shearing is included to account for the effects of three dimensional geometry we find that lateral drag has a discernible effect on glacier speed even when glacier width exceeds glacier length variations in flow band width are shown to have a greater influence on flow line speed than either different valley cross sectional shapes or the presence or absence of glacier sliding along valley walls modeled profiles of subglacial water pressure depart significantly from pressures prescribed as a uniform fraction of overburden thus producing profiles of glacier sliding that are distinctly different from those that would be described by a sliding law controlled by overburden pressures simulations of hydraulically driven glacier acceleration highlight the value of including a representation of basal hydrology in models aiming for improved predictive capability of glacier dynamics

the freeze thaw weathering regime at a section of the niagara escarpment on the bruce peninsula southern ontario canada the bedrock freeze thaw and moisture regimes at an actively eroding site on the niagara escarpment bruce peninsula southern ontario were monitored between december 1983 and april 1984 and the results compared with amounts of debris collected in an adjacent rock trap frost wedging in pre existing rock fissures is the primary mechanism responsible for the observed rockfall events hydration effects are negligible debris production was more closely related to the duration of the freezing leg of the freeze thaw cycle than to intensity or to cycle frequency release also coincided with periods of high pore saturation 60 per cent and the seepage of water from cracks and fissures fewer freeze thaw cycles were recorded in the air than at 1 and 3 5 cm in the bedrock the number of cycles that could be declared geomorphologically effective according to established temperature criteria was normally less than half the total number of freeze thaw cycles recorded in both air and bedrock under the current temperature regime at the field site few effective cycles are capable of penetrating more than 5 cm into the free face

validation of a method for determining the depth of glacial melt ponds using satellite imagery in situ measurements of water depth and optical properties of a melt pond in east greenland were collected to verify a previously developed algorithm for determining supraglacial water depths using satellite imagery that algorithm made five simplifying assumptions which we have tested using the in situ data and laboratory analysis of water samples we conclude that three assumptions were justified one was not and the remaining one substrate homogeneity requires further study but probably has a minor effect on the retrieved water depths and volumes measured water depths of 0 2 3 0m agree well with those derived from a satellite image using the algorithm numerically modeled depths also agree well with those from the satellite image this new analysis demonstrates the validity of our algorithm as a means for determining meltwater volumes in supraglacial ponds and lakes

some observations concerning the morphology and sedimentology of a protalus rampart okstindan norway a protaius rampart up to 4 75 m high and consisting largely of angular clasts up to boulder size is described bulk samples contained up to 35 per cent fines by weight compared with up to 68 per cent fines in adjacent till although the rampart material was clast dominated fines filled much of the void space in contrast with most other protalus ramparts described in the literature

breakup of the larsen b ice shelf triggered by chain reaction drainage of supraglacial lakes this research is supported by the u s national science foundation under grant geop ant 0944248 awarded to d r m and grants ant 0838811 and arc 0934534 awarded to o v s

basalt weathering in an arctic mars analog site abstract the martian surface has undergone chemical and physical weathering in the past and these processes may continue intermittently today to explore whether martian rocks are likely to retain features indicative of weathering we investigated how basaltic material weathers on earth specifically we investigated weathering of a quaternary aged basaltic flow at the sverrefjell volcano in svalbard above the arctic circle this flow weathered since deglaciation under cold dry

frost action and hydration as rock weathering mechanisms on schist a laboratory study recently it has been proposed that stress generated by the adsorption of water to clay surfaces in argillaceous rocks may be an important agent of mechanical weathering in polar and alpine environments implying that long held views on the status of frost action in these areas may be in need of revision this study documents the response under controlled experimental conditions of aggregates of fresh and partlyweathered schist and fresh pre cut schist blocks to 500 accelerated 12 hour freeze thaw and hydration dehydration cycles aggregate samples subjected to freezing cycles produced the largest amounts of material in the less than 2 mm size range an average of 8 per cent and 16 per cent for the fresh and partly weathered aggregates respectively whereas humidity cycles above and below freezing yielded lesser amounts 3 per cent and 4 per cent respectively the fresh schist blocks were found to be highly resistant to both mechanisms only those experiencing freeze thaw oscillations produced measurable amounts of detritus although hydration effects were not as effective as frost action in causing particle size reduction in aggregates the two mechanisms may well reinforce one another in periglacial environments enhancing the ability of these areas to serve as source regions for loess

modeling weathering pathways and processes of the fragmentation of salt weathered quartz chlorite schist 1 the relationship between the rate of rock breakdown and environmental and geological factors must be understood in order to establish the conditions under which weathering limits erosion in this study qualitative and quantitative models of the rock fragmentation process are fitted to previously published data obtained from laboratory salt weathering trials of quartz chlorite schist weathering was modeled as a combination of 1 a fragmentation event that fragments the parent particle into a number of daughter particles while preserving mass and 2 a fracture probability that determines the probability that a fragmentation event will occur in a given time period we show that observations of the complex breakdown of salt weathered schist are consistent with model assumptions of a simple fracture geometry model and an increase in fracture probability with time for the fragmentation geometry the best fit to the experimental data was achieved by assuming that each fragmentation event involves splitting of the parent particle into two daughter fragments of equal volume for the fragmentation rate the data could best be described with a fracture probability and hence the weathering rate that increased linearly with time this paper shows that it is possible to use a physically based fragmentation model to infer the process of fragmentation for individual particles using a time evolving particle size distribution for the weathering rock fragments

characterization of two phase flow in a single rock joint abstract an experimental study using a triaxial apparatus was used to analyze the two phase flow patterns in jointed rock specimens rock specimens having a single natural fracture were tested for two phase flow of water and air triaxial tests were conducted to characterize the two phase flow through fractured granite specimens at low confining pressures it was found that for a relatively smooth joint jrc 0 25 mpa gas injection pressures the gas occupied the main part of the fracture and the liquid was able to flow as an unstable film forming an annular flow along the joint when the annular flow developed the mixture flow pattern was independent of the air flow velocity this was due to the fact that once the injected air velocity reached a critical value i e 20 m s water velocity inside the joint was negligible for a given confining pressure and injected water pressure further increase in inlet air pressures developed a single phase air flow with no water flow

laboratory simulation of the salt weathering of schist ii fragmentation of fine schist particles recent developments in long term landform evolution modelling have created a new demand for quantitative salt weathering data and in particular data describing the size distribution of the weathered rock fragments to enable future development of rock breakdown models for use in landscape evolution and soil production models laboratory work was undertaken to extend existing schist salt weathering fragmentation studies to include an examination of the breakdown of sub millimetre quartz chlorite schist particles in a seasonally wet tropical climate laser particle sizing was used to assess the impact of different experimental procedures on the resulting particle size distribution the results reveal that salt weathering under a range of realistic simulated tropical wet season conditions produces a significant degree of schist particle breakdown the fragmentation of the schist is characterized by splitting of the larger fragments into mid sized product with finer material produced possibly from the breakdown of mid sized fragments when weathering is more advanced salinity the salt addition method and temperature were all found to affect weathering rates subtle differences in mineralogy also produce variations in weathering patterns and rates it is also shown that an increase in drying temperature leads to accelerated weathering rates however the geometry of the fracture process is not significantly affected copyright 2006 john wiley sons ltd

extended finite element method for analysis of multi scale flow in fractured shale gas reservoirs economic exploration for shale gas is highly dependent on the complexity of the fracture network caused by hydraulic fracturing technology so it is necessary to accurately assess the effect of the fracture network on gas flow behavior and productivity having multiple scales is a remarkable characteristic of gas flow in fractured shale gas reservoirs which involves multiple flow regimes including the gas desorption from shale matrix knudsen flow in nanoscale pores darcy flow in general porous media darcy flow in the fracture networks and fluid exchange between the matrix system and the fracture system the extended finite element method xfem has been integrated with the dual permeability method dpm to investigate the multi scale problem some previous studies have adopted the same solution scheme but usually considered gas flow in the natural fracture network and in the hydraulic fractures as belonging to the same scale and in addition the coverage area of the stimulated reservoir volume srv was underestimated based on the xfem dpm this paper subsumes flow in the micro mecro fractures and macro hydraulic fractures under two scales because of their different effects on shale gas flow and then presents a new multi scale extended finite element model to study the multi scale flow problem in shale gas reservoirs moreover the lagrangian multiplier method is integrated to introduce the internal well boundary conditions into the xfem so the arbitrariness and the asymmetry of the complex fracture network can be taken into account easily to reflect the real flow mechanisms in fractured shale case studies indicate that the improved extended finite element model constructed in this paper is effective especially for complicated asymmetrical physical condition problems

microscopic modelling of the hydraulic fracturing process a microscopic perspective is introduced in this study which offers a detailed insight at the inter particle level to the geo mechanical responses caused by fluid injection and the resulting pressure build up this was achieved by employing the discrete element method dem to model the pressure development and the subsequent fracturing and or cavity propagation this technique represents the formation material as an assembly of discrete particles linked to each other through contacts numerical experiments were carried out on two sample materials for the first instance tests were carried out on a bulk material representative of a generic intact rock with the breakage of inter particle bonds indicating the formation of cracks the second series of tests was carried out on granular type materials such as sand where particle separation signified cavity initiation and separation it was observed from the dem modelling results that the intact rock material showed a predominance of mode ii fracturing at high fluid velocities however when the fluid velocity is reduced considerably the fracturing behaviour tended towards more of mode i also records of the pressure development were taken from the numerical results and were used to monitor the fracturing events the outcome of this study highlights important aspects of the hydraulic fracturing process especially at the particle particle scale and thus provides a strong basis for more exhaustive studies involving larger scale reservoir modelling and more complex fracturing scenarios

influence of rock failure behaviour on predictions in sand production problems the mechanical strength of rock in terms of shear or compressive failure has been previously adopted as a criterion for sand production and when used solely has been proven to overestimate the process on the other hand ignoring the mechanical strength behaviour of the material increases the tendency for inaccurate estimations of the erosion process in this work an equally proportionated inclusion of the mechanical strength and erosion based criteria in sanding predictions is proposed and assessed by numerical models several rock failure models and their influences on the sanding process have been analysed including models such as the drucker prager dp the drucker prager hardening dp hardening the mohr coulomb mc and the mohr coulomb softening mc softening modelling outcomes show distinct differences in rock response to operating and boundary conditions e g flow rate and drawdown and predictions of sand production it was confirmed by modelling results that despite the low magnitude of stresses and strains developed at the well face and perforation regions post yield hardening behaviour increases the estimation of the amount and intensity of sand production also incorporating a post yield softening behaviour increases the magnitude of stresses and strains however this effect is observed to have a negligible impact on sand production the role of void ratio has been recognised as a dominant factor as its evolution significantly determines the pattern and intensity of sand production a more cautious selection and rigorous coupling of rock strength models in sand production modelling is therefore essential if accuracy of predictions is to be improved

evolution of melt pond volume on the surface of the greenland ice sheet 1 the presence of surface meltwater on ice caps and ice sheets is an important glaciological and climatological characteristic we describe an algorithm for estimating the depth and hence volume of surface melt ponds using multispectral aster satellite imagery the method relies on reasonable assumptions about the albedo of the bottom surface of the ponds and the optical attenuation characteristics of the ponded meltwater we apply the technique to sequences of satellite imagery acquired over the western margin of the greenland ice sheet to derive changes in melt pond extent and volume during the period 2001 2004 results show large intra and interannual changes in ponded water volumes and large volumes of liquid water stored in extensive slush zones

a laboratory simulation of rock breakdown due to freeze thaw in a maritime antarctic environment results of freeze thaw simulations on three large blocks of quartz micaschist are presented three types of water to ice phase change were identified from temperature and ultrasonic measurements it is suggested that the type of phase change results from a particular combination of rock moisture content solute concentration freeze amplitude and rate of fall of temperature the temperature at which ice thawed inside the rock 0 7 to 1 9 c was also found and this indicates the possibility of freeze thaw effects without positive temperatures approximately 80 per cent of the water that will freeze under natural conditions in the maritime antarctic environment under study appears to have done so by 6

recent changes in glacier velocities and thinning at novaya zemlya abstract ice loss from the glaciers of novaya zemlya nvz is the dominant contributor to sea level for the russian arctic here we present maps of glacier elevation change rates dh dt and velocities at novaya zemlya that reveal evidence of the impact of both calving flux and surface melt on ice mass loss dh dt are calculated by applying a weighted linear regression to stacked digital elevation models dems from a 1952 map and dems created from stereo pairs of worldview images acquired between 2012 and 2014 the 60 year average mass change rate is 0 23 0 04 m w e yr 1 the recent short term 2012 2013 2014 average mass change rate is 0 40 0 09 m w e yr 1 we apply the same weighted linear regression to stacked worldview dems and icesat elevations from 2003 to 2009 as well as stacked worldview dems and aster dems from 2000 to 2013 the dh dt from both datasets confirm that thinning has been more rapid than the 60 year average since 2000 average mass loss has accelerated at the lower elevations of land terminating glaciers suggesting that recent near surface warming and increased melt have led to greater thinning marine terminating glaciers along the barents sea coast have substantially higher thinning rates near their termini in recent years than adjacent land terminating glaciers suggesting that calving flux is an important contributor to overall ice mass loss in the region flow velocities are generated by feature tracking on optical and radar image pairs marine terminating glaciers along the barents sea coast have the highest frontal velocities of any glaciers on nvz our surface velocity measurements constrain the calving flux at the two fastest retreating glaciers inostrantseva ino and vil kitskogo vis which are both on the barents sea coast we find that the calving flux is high enough to drive frontal thinning and retreat at those two glaciers summer terminus speeds at inostrantseva glacier have accelerated from a 2006 maximum of 3 m day 1 to a 2012 maximum of 9 to 10 m day 1 and the front has retreated by more than 3 km between 2006 06 27 and 2013 08 17

relict mountain slope deposits of northern portugal facies sedimentogenesis and environmental implications this paper deals with the formation processes and the palaeoenvironmental significance of relict slope deposits located on the uppermost part of the north portugal mountains for this purpose seven key sites representative of the different lithofacies have been selected and analysed in detail the data show that three main dynamic processes are responsible for the emplacement of regional fossil slope deposits runoff debris flows and dry grain flows the ubiquity of these processes and the lack of frost related features or landforms do not support the existence of severe pleistocene climates in this part of the lberian peninsula as postulated by previous work pedological data gathered at one of the study sites show that a subalpine environment was probably present at 700 800 m altitude between 29 and 14 kyr using data from the pyrenees mountains a 6 5 to 12 c depression in mean annual temperature has been tentatively postulated for this pleniglacial period copyright 2003 john wiley sons ltd

analysis of flow path around the sealing section hg a experiment in the mont terri rock laboratory as part of the hg a experiment in the mont terri rock laboratory large scale in situ water gas injection experiments was conducted in a microtunnel this research work focuses on the numerical analysis of the experimental data and the in situ observations concerning a temporary change of the hydromechanical properties of opalinus clay during experimental operations three phases were numerically interpreted these included the generation of excavation damaged zone during tunnel excavation in which highly permeable flow paths around the tunnel have been formed the self sealing effect during water tests and the pressure evolution during a long term gas injection test a coupled two phase flow and mechanics model taking into account the strong anisotropic properties of opalinus clay was developed to interpret the measured data the hydraulic anisotropy was described by a transversely isotropic permeability tensor an elasto plastic model was established to consider both stiffness anisotropy and strength anisotropy anisotropic plasticity was studied using the microstructure tensor method

melt induced speed up of greenland ice sheet offset by efficient subglacial drainage fluctuations in surface melting are known to affect the speed of glaciers and ice sheets but their impact on the greenland ice sheet in a warming climate remains uncertain although some studies suggest that greater melting produces greater ice sheet acceleration others have identified a long term decrease in greenland s flow despite increased melting here we use satellite observations of ice motion recorded in a land terminating sector of southwest greenland to investigate the manner in which ice flow develops during years of markedly different melting although peak rates of ice speed up are positively correlated with the degree of melting mean summer flow rates are not because glacier slowdown occurs on average when a critical run off threshold of about 1 4 centimetres a day is exceeded in contrast to the first half of summer when flow is similar in all years speed up during the latter half is 62 16 per cent less in warmer years consequently in warmer years the period of fast ice flow is three times shorter and overall summer ice flow is slower this behaviour is at odds with that expected from basal lubrication alone instead it mirrors that of mountain glaciers where melt induced acceleration of flow ceases during years of high melting once subglacial drainage becomes efficient a model of ice sheet flow that captures switching between cavity and channel drainage modes is consistent with the run off threshold fast flow periods and later summer speeds we have observed simulations of the greenland ice sheet flow under climate warming scenarios should account for the dynamic evolution of subglacial drainage a simple model of basal lubrication alone misses key aspects of the ice sheet s response to climate warming

modelling channelized surface drainage of supraglacial lakes supraglacial lakes can drain to the bed of ice sheets affecting ice dynamics or over their surface relocating surface water focusing on surface drainage we first discuss observations of lake drainage in particular for the first time lakes are observed to drain 70 km across the nivlisen ice shelf east antarctica inspired by these observations we develop a model of lake drainage through a channel that incises into an ice sheet surface by frictional heat dissipated in the flow modelled lake drainage can be stable or unstable during stable drainage the rate of lake level drawdown exceeds the rate of channel incision so discharge from the lake decreases with time this can prevent the lake from emptying completely during unstable drainage discharge grows unstably with time and always empties the lake model lakes are more prone to drain unstably when the initial lake area the lake input and the channel slope are larger these parameters will vary during atmospheric warming induced ablation area expansion hence the mechanisms revealed by our analysis can influence the dynamic response of ice sheets to warming through their impact on surface water routing and storage

the negative effect of environmental geological conditions of some geo archaeological sites of north coast and alexandria three geo archaeological sites at the north coast and alexandria namely the alexandria wall el shalalat park site abu soir temple and marina excavations were investigated to determine the negative impact of a salty environmental condition the monuments suffer from rock decay of different rates the geo archaeological sites were built mainly from oolitic limestone blocks i e the alexandria wall at the el shalalat park site and abu soir temple or excavated on them i e marina excavations field inspection and a lab analysis were carried out to understand the weathering mechanism salt weathering criteria such as disintegration pitting scaling exfoliation and honeycomb are observed on the alexandria wall and upper parts of the abu soir temple while dangerous cracks are detected on the marina excavation tombs the petrographic study of the oolitic limestone samples shows that they consist mainly of oolities and drusy sparite as a cement oolitic grainstone some oolities have quartz grains as nuclei hydrochemical analysis shows that the total dissolved salts of extracted solutions of the north coast quarry samples range from 539 to 686 ppm and dramatically increase i e ten times for extracted solutions from monument samples ranging from 5395 to 6880 ppm the dominant cation is sodium while the dominant anion is chlorine acid insoluble residue analysis shows that the carbonate content ranges from 89 2 to 96 4 for fresh samples from quarries and from 9 2 to 94 8 for weathered monument samples the weight loss of the quarry oolitic limestone samples range from 30 7 to 32 7 and its physical and mechanical properties become worse after being subjected to 15 cycles of a durability simulation soundness test using a sodium sulphate solution our main recommendations are to use suitable grouting for binding the cracks high durability reconstruction rocks and suitable cleaning methods to remove salts from the monuments

study on three dimensional fracture network connectivity path of rock mass and seepage characteristics based on equivalent pipe network nuclear waste repositories have extremely stringent requirements for geological environment however natural fractures in rock mass can be potential channels for nuclide migration therefore the influence of fractures on the permeability of rock mass must be assessed in this paper a well research was conducted on well exposed granite outcrops in the xinchang site the chinese high level radioactive waste repository the high precision three dimensional model of a typical outcrop is built to obtain fracture information combined with field measurement and then the three dimensional fracture network model is generated using the relevant parameters by monte carlo method to obtain more comprehensive fracture connectivity while avoiding the traditional method of searching the connectivity path in the complicated 3d fracture model taking up a lot of storage space and costing a lot of time this paper presents an approach using matlab cell array instead of traditional adjacency matrix to search and store fracture network connectivity paths in dfn model the fracture disc with certain thickness is equivalent to three dimensional pipe network model epnm with variable diameter and the equivalent path permeability coefficient epc is proposed to objectively study the permeability characteristics of the seepage path in fractured rock mass based on that especially noteworthy is that some fractures in a certain strike range belong to open type while those in another range belong to cemented closed fractures when fresh fractures were exposed by cutting off the surface rock to a certain depth the calculation of epc under different conditions shows that the order of magnitude of epc mean value is 1e 7m s and 1e 3m s respectively when fractures are cemented and not partly on this basis the size of the representative elementary volume rev of the fractured rock mass in the study area is determined to be about 25 m by rotating the matrix in model the spatial permeability tensor of the region including permeability principal value and main direction is obtained which is within the range of borehole data the predicted results may provide some reference for the related projects in the future

seasonal evolution of supraglacial lakes on a floating ice tongue petermann glacier greenland supraglacial lakes are known to trigger antarctic ice shelf instability and break up however to date no study has focused on lakes on greenland s floating termini here we apply lake boundary area and depth algorithms to landsat 8 imagery to analyse the inter and intraseasonal evolution of supraglacial lakes across petermann glacier s 81 n floating tongue from 2014 to 2016 while also comparing these lakes to those on the grounded ice lakes start to fill in june and quickly peak in total number volume and area in late june early july in response to increases in air temperatures however through july and august total lake number volume and area all decline despite sustained high temperatures these observations may be explained by the transportation of meltwater into the ocean by a river and by lake drainage events on the floating tongue further as mean lake depth remains relatively constant during this time we suggest that a large proportion of the lakes that drain do so completely likely by rapid hydrofracture the mean areas of lakes on the tongue are only 20 of those on the grounded ice and exhibit lower variability in maximum and mean depth differences likely attributable to the contrasting formation processes of lakes in each environment

laboratory simulation of the salt weathering of schist 1 weathering of schist blocks in a seasonally wet tropical environment data describing sediment generation focusing on the temporal evolution of size gradation are required for the prediction of long term landform evolution this paper presents such data for the salt weathering of a quartz chlorite schist obtained from the ranger uranium mine in northern australia rock fragment samples are subjected to three different climate regimes 1 a dry season climate 2 a wet season climate both based on observations at the ranger site and 3 an oven drying sequence designed to test the sensitivity of the weathering process by exposing the rocks to more extreme temperatures two mgso4 salt solutions are applied one being typical of wet season runoff and the other a more concentrated solution salt solution is applied daily in the wet season experiments and once only at the beginning of the dry season experiments results of the experiments reveal four stages of weathering the kinetics of each stage are described and related to the formation of sediment of different sizes wet season climate conditions are shown to produce greater moisture variability and lead to faster weathering rates however salt concentrations in the wet season are typically lower and so when climate is combined with observed salt concentrations the dry and wet season experiments weather at approximately equal rates finally small variations in rock properties were shown to have a large impact on weathering rates leading to the conclusion that rock weathering experiments need to be carefully designed if results are to be used to help predict weathering behaviour at the landscape scale copyright 2006 john wiley sons ltd

inland advance of supraglacial lakes in north west greenland under recent climatic warming the inland advance of supraglacial lakes sgls towards the interior regions of the greenland ice sheet gris may have implications for the water volumes reaching the subglacial drainage system and could consequently affect long term ice sheet dynamics here we investigate changes to the areas volumes and elevation distributions of over 8000 manually delineated sgls using 44 landsat images of a 6200 km 2 sector of north west greenland over three decades 1985 2016 our results show that sgls have advanced to higher maximum 418 m and mean 299 m elevations and that there has been a near doubling of total regional sgl areas and volumes over the study period accelerating after 2000 these changes were primarily caused by an increased sgl area and volume at high 1200 m a s l elevations where sgl coverage increased by over 2750 during the study period many of the observed changes particularly the post 2000 accelerations were driven by changes to regional surface temperature anomalies this study demonstrates the past and accelerating response of the gris s hydrological system due to climatic warming indicating an urgent need to understand whether the increasingly inland sgls will be capable of hydrofracture in the future thus determining their potential implications for ice sheet dynamics

the role of moisture cycling in the weathering of a quartz chlorite schist in a tropical environment findings of a laboratory simulation long term weathering of a quartz chlorite schist via wetting and drying was studied under a simulated tropical climate cubic rock samples 15 mm 15 mm 15 mm were cut from larger rocks and subjected to time compressed climatic conditions simulating the tropical wet season climate at the ranger uranium mine in the northern territory australia fragmentation moisture content and moisture uptake rate were monitored over 5000 cycles of wetting and drying to determine the impact of climatic variables five climatic regimes were simulated varying water application temperature and drying one of the climatic regimes reproduced observed temperature and moisture variability at the ranger uranium mine but over a compressed time scale it is shown that wetting and drying is capable of weathering quartz chlorite schist with changes expected over a real time period of decades while wetting and drying alone does produce changes to rock morphology the incorporation of temperature variation further enhances weathering rates although little fragmentation occurred in experiments significant changes to internal pore structure were observed which could potentially enhance other weathering mechanisms moisture variability is shown to lead to higher weathering rates than are observed when samples are subjected only to leaching finally experiments were conducted on two rock samples from the same source having only subtle differences in mineralogy the samples exhibited quite different weathering rates leading to the conclusion that our knowledge of the role of rock type and composition in weathering is insufficient for the accurate determination of weathering rates copyright 2005 john wiley sons ltd

a scanning electron microscope study of bedrock microfractures in granites under high arctic conditions surface specimens obtained from highly weathered upland plateau outcrops at three localities in high arctic canada have been studied using the scanning electron microscope observations are given on factors influencing bedrock surface microfracturing processes evidence for the concentration of both salts and organic material in surface cracks which could enhance microfracturing is presented the importance of lithological parameters including mineralogy texture and structures present in influencing the actual processes of disintegration is reiterated under cold dry high arctic conditions the combined and apparently inseparable affects of frost action salt crystallization and organic activity may have contributed to microfracturing largely responsible for widely scattered examples of highly weathered bedrock terrain

remote sounding of greenland supraglacial melt lakes implications for subglacial hydraulics a supraglacial lake depth retrieval function is developed based on the correspondence between moderate resolution imaging spectroradiometer modis reflectance and water depth measured during raft surveys individual lake depth area and volume statistics including short term temporal changes for greenland s southwestern ablation region were compiled for 2000 05 the maximum area of an individual lake was found to be 8 9 km 2 the maximum volume 53 0 10 6 m 3 and the maximum depth 12 2 m sampling over 0 0625 km 2 pixel areas the total lake volume reaches 1 km 3 in this region by july each year the importance of melt lake reservoirs to greenland ice sheet flow may be a feedback between abrupt lake drainage events and ice dynamics lake outburst volumes up to 31 5 10 6 m 3 d 1 are capable of providing sufficient water via moulins to hydraulically pressurize the subglacial environment since the overburden pressure at the base of a flooded moulin is greater than that provided by ice lake outburst events seem capable of exerting sufficient upward force to lift the ice sheet locally if water flow in the subglacial environment is constrained laterally considering a moulin with a 10 m 2 cross sectional area basal pressurization can be maintained over lake outburst

rock moisture content in the field and the laboratory and its relationship to mechanical weathering studies rock moisture content is a major control of mechanical weathering particularly freeze thaw and yet almost no data exist from field situations this study presents moisture content values for rocks taken from a variety of positions and conditions in the maritime antarctic additional information regarding the amount of water the rock could take up as observed from laboratory experiments is also presented the results show that the approaches used in simulation experiments particularly that of soaking a rock for 24 hours may produce exaggerated results it was found that the saturation coefficient s value was a good indicator of frost susceptibility based on water content but that the derivation of that value may underestimate the potential of some rocks the distribution of moisture within rocks is seen as an important but unkown factor the results of these field moisture contents suggest that for simulations of freeze thaw or hydration to be meaningful then they should have rock water contents based on field observations

fast draining lakes on the greenland ice sheet 1 the rapid drainage of supraglacial lakes around the ablation zone of the greenland ice sheet forms an important link between water at the surface and the ice sheet base allowing surface meltwater to reach the bed and hence increase glacial velocity the conduits formed by lake drainages may remain open during the remainder of the melt season providing a pathway for further meltwater to reach the base we investigated the drainage behavior of lakes from all regions of the greenland ice sheet for the period 2005 2009 we mapped the evolution of 2600 lakes from 3704 modis images detecting a mean of 263 drainage events per year of which 61 occurred in the south west region only 1 of lake drainages occurred in the rapidly thinning south east region our results show marked differences between the hydrology of the different regions of the ice sheet with few lake drainages occurring in the regions where the highest dynamic mass loss is occurring in the south west and north east lake drainages are common and could impact glacier dynamics in the south east they are rare and are thus unlikely to do so