recovery of undisturbed highly fractured bench scale 30 cm diameter drilled samples for laboratory investigation investigation of the hydraulic parameters of fractured rock in the laboratory is often undertaken on a small scale sample diameter to 10 cm due to the difficulty of recovering undisturbed highly fractured rock samples usually such samples contain only one or at the most two discrete fractures when investigating the hydraulic or mechanical parameters important for geotechnical applications e g large scale triaxial tests it is necessary to have an understanding of the integrated effects of the fractures forming the fracture networks in this paper a method is presented whereby undisturbed samples with a diameter of 30 cm were recovered from a highly fractured porous rock mass and prepared for investigation of the fracture network properties in a laboratory most of the samples recovered contained several differently orientated fractures forming an interconnected network the undisturbed nature of the recovered samples allows the hydrogeological and geotechnical characteristics of the fracture network to be investigated

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

on the characterization of glacier response by a single time scale glacier response to climate can be characterized by a single time scale when the glacier changes sufficiently slowly then the derivative of volume with respect to area defines a thickness scale similar to that of johannesson and others and the time scale follows from it our version of the time scale is different from theirs because it explicitly includes the effect of surface elevation on mass balance rate which can cause a major increase in the time scale or even lead to unstable response the time constant has a dual role controlling both the rate and magnitude of response to a given climate change data from south cascade glacier washington u s a illustrate the ideas some of the difficulty in obtaining accurate values for the thickness and time scales and the susceptibility of all response models to potentially large errors

modelling glacier advances and related climate conditions during the last glaciation cycle in the kuzigun valley tashkurgan catchment on the north west tibetan plateau understanding regional climate during the last glaciation cycle lgc is far from complete for the north western tibetan plateau recent improvements in understanding glacial extents and chronologies in the tashkurgan catchment north west tibetan plateau present an opportunity to estimate the glacial climatic conditions of the lgc here we use a coupled mass balance and ice flow model to reconstruct glacier advances in the kuzigun valley during the lgc and quantify the related climate conditions in the tashkurgan hangdi and kuzigun glacial stages for the region the model results show that the kuzigun valley contained ice volumes of 5 713 0 005 4 874 0 005 and 3 631 0 004 km3 with equilibrium line altitude lowering values of 500 560 and 610 m in the three successive glacial stages respectively by referencing the climatic 18o proxy records we conclude that temperature decreased by 5 8 4 and 140 modern values in the kuzigun hangdi and tashkurgan glacial stages respectively our climatic estimates for the kuzigun stage are generally consistent with previous studies that showed the last glacial maximum climate was 4 9 c colder than today on the tibetan plateau more accurate climate proxies are needed for evaluating our modelled tashkurgan climatic conditions

on the climate geometry imbalance response time and volume area scaling of an alpine glacier insights from a 3 d flow model applied to vadret da morteratsch switzerland a two dimensional surface mass balance model is coupled to a three dimensional higher order ice flow model to assess the imbalance between climate and glacier geometry for the morteratsch engadine switzerland glacier complex the climate geometry imbalance has never been larger than at present indicating that the temperature increase is faster than the geometry is able to adapt to we derive response times from transient and steady state geometries and find that the volume response time is correlated to the magnitude of the mass balance forcing it varies between 22 and 43 years while the length response time is between 47 and 55 years subsequently the modelled response times are compared with different analytical methods from the literature the effect of a climatic perturbation on the response time which produces a spatially distributed mass balance forcing is also examined we investigate the effect of glacier size on the response time and project that the response time will decrease in the future due to a surface steepening finally volume area scaling methods with different parameters are tested and an alternative method is proposed that takes into account the surface slope the effect of a transient state on the method is also evaluated

effects of spatial discretization in ice sheet modelling using the shallow ice approximation this paper assesses a two dimensional vertically integrated ice model for its numerical properties in the calculation of ice sheet evolution on a sloping bed using the shallow ice approxi mation we discuss the influence of initial conditions and individual model parameters on the model s numerical behaviour with emphasis on varying spatial discretizations the modelling results suffer badly from numerical problems they show a strong dependence on gridcell size and we conclude that the widely used gridcell spacing of 20 km is too coarse the numerical errors are small in each single time step but increase non linearly over time and with volume change as a result of feedback of the mass balance with height we propose a new method for the calculation of the surface gradient near the margin which improves the results significantly furthermore we show that we may use dimension analysis as a tool to explain in which situations numerical problems are to be expected

estimating response times of vadret da morteratsch vadret da palu briksdalsbreen and nigardsbreen from their length records length records of two pairs of glaciers are used to reconstruct the equilibrium line altitude ela and to estimate glacier response times the method is based on the assumption that neighbouring glaciers should be subject to the same climatic forcing and that differences in the length records are thus caused by differences in response times and climate sensitivities by means of a control method in which the difference between the reconstructed histories of the ela is minimized realistic response times are found the pairs of glaciers studied are i vadret da morteratsch and vadret da paluin the swiss alps and ii briksdalsbreen and nigardsbreen in southern norway in both cases the reconstructed ela histories of the individual glaciers are very similar in spite of the large differences in the length records short e folding response times are found for the steep glaciers 4 4 years for vadret da palii 5 0 years for briksdalsbreen for the larger glaciers with a more gentle slope the response times are substantially larger 33 0 years for vadret da morteratsch 34 8 years for nigardsbreen

holocene evolution of hans tausen iskappe greenland and implications for the palaeoclimatic evolution of the high arctic abstract in this study the holocene evolution of hans tausen iskappe peary land north greenland is investigated constraints on the ice cap evolution are combined with climatic records in a numerical ice flow surface mass balance smb model to better understand the palaeoenvironmental and climatic evolution of this region our simulations suggest that after disconnecting from the greenland ice sheet gris the ice cap had roughly its present day size and geometry around 9 8 5 ka bp during the holocene thermal maximum htm the southern part of the ice cap is modelled to collapse while the northern part of the ice cap survived this warmer period the late holocene regrowth of the ice cap to its maximum neoglacial extent at the end of the little ice age lia can be reproduced from the temperature reconstruction the simulations suggest that over the last millennia the local precipitation may have been up to 70 80 higher than at present by coupling the pre industrial temperature forcing to a post lia warming trend it is suggested that the warming between the end of the lia and the period 1961 1990 was between 1 and 2 c in all experiments the ice flow model complexity and horizontal resolution have only a minor effect on the long term evolution of the ice cap we further conclude that the glacial isostatic adjustment has a significant effect on the modelled holocene ice cap evolution this suggests that modelling studies of millennial scale ice cap evolution should focus on smb and boundary conditions rather than on complex ice dynamics

true triaxial loading apparatus and its application to coal outburst prediction two generations of true triaxial loading ttal apparatuses are presented first generation apparatuses were intended primarily for true stress state imitation in rock or mineral specimens advanced second generation installations are designed to provide precise measurements in any stress and simulation of rock outburst at sudden relief of one sample face both ttal apparatuses can apply pressure up to 250 mpa corresponding to earth depth about 10 000 m independently along each of three axes experimental results are given on effect of absorbed water on ultimate state in coal as well as adsorbed methane influence on simulated coal outbursts

bayesian estimation of basal conditions on rutford ice stream west antarctica from surface data the determination of basal properties on ice streams from surface data is formulated as a bayesian statistical inference problem the theory is applied to a flowline on rutford ice stream west antarctica estimates of bed topography and basal slipperiness are updated using measurements of surface topography and the horizontal and vertical components of the surface velocity the surface topography is allowed to vary within measurement errors we calculate the transient evolution of the surface until rates of surface elevation change are within limits given by measurements for our final estimation of basal properties modelled rates of elevation change are in full agreement with estimates of surface elevation changes results are discarded from a section of the flowline where the distribution of surface residuals is not consistent with error estimates apart from a general increase in basal slipperiness toward the grounding line we find no evidence for any spatial variations in basal slipperiness in particular we find that short scale variability 10 ice thickness in surface topography and surface velocities can be reproduced by the model by variations in basal topography only assuming steady state conditions an almost perfect agreement is found between modelled and measured surface geometry suggesting that rutford ice stream is currently close to a steady state

modelling a paleo valley glacier network using a hybrid model an assessment with a stokes ice flow model modelling paleo glacier networks in mountain ranges on the millennial timescales requires ice flow approximations hybrid models calculating ice flow by combining vertical shearing shallow ice approximation and longitudinal stretching shallow shelf approximation have been applied to model paleo glacier networks on steep terrain yet their validity has not yet been assessed quantitatively moreover hybrid models consistently yield higher ice thicknesses than last glacial maximum geomorphological reconstructions in the european alps here we compare results based on the hybrid parallel ice sheet model pism and the stokes model elmer ice on the rhine glacier a catchment of the former european alpine icefield for pism we also test two magnitudes of flux limitation in a scheme that reduces shearing velocities we find that the flux limitation typically used in pism yields significantly reduced shearing speeds and increases ice thicknesses by up to 500 m partly explaining previous overestimations however reducing the ice flux limitation allows the hybrid model to minimize this mismatch and captures sliding speeds ice thicknesses ice extent and basal temperatures in close agreement with those obtained with the stokes model

a level set method for modeling the evolution of glacier geometry a level set method is proposed for modeling the evolution of a glacier surface subject to a prescribed mass balance this leads to a simple and versatile approach for computing the evolution of glaciers the description of vertical fronts and overriding phenomena presents no difficulties topological changes are handled naturally and steady state solutions can be calculated without integration over time a numerical algorithm is put forth as a means of solving the proposed model of glacier surface evolution it is evaluated by comparing different numerical solutions of the model with analytical and published numerical solutions the level set method appears to be a reliable approach for dealing with different glaciological problems

transient response of idealized glaciers to climate variations the transient response of glaciers to climate variations is investigated with a novel low order model of an idealized glacier resting on uniformly inclined bedrock the model consists of two volumes representing the accumulation and ablation areas which are joined by a flux gate controlling mass flow according to the shallow ice approximation under the assumption of a constant vertical mass balance gradient a volume length scaling relation is derived which depends explicitly on mass balance gradient and bedrock slope analytic expressions for the volume and area timescales are given which are inversely proportional to the mass balance gradient and a geometric factor which is the ratio between the vertical extent of the ablation area and the ice thickness at the equilibrium line from the low order model a dynamical system in length and volume is obtained results from this system are in good agreement with solutions obtained from a transient finite element model solving the full force balance and mass conservation equations under periodic forcing there are significant deviations of the length response which show that the usual relaxation type parameterization of length change is not well suited for short term reactions switching on and off periodic climate forcing the model glaciers show surprisingly large initial and final transient responses that have not been investigated before these results are of significance for the interpretation of length and thickness changes observed on glaciers

sub moho seismic profile in the mariana basin ocean bottom seismograph long range explosion experiment abstract ocean bottom seismograph obs long range explosion experiments were carried out in the mariana basin in 1973 and 1976 seven large shots 8 5 1 5 ton as well as several tens of small shots were fired the maximum range of observation was about 1900 km as many as 25 obs stations were deployed in an array of about 800 km it is found that the sub moho p wave velocity structure is of stratified nature being composed of alternating high and low velocity layers high velocity layers with apparent velocities of 8 1 8 2 8 4 8 6 and 8 7 km s are identified low velocity layers sandwiched between the high velocity layers of 8 4 8 6 and 8 7 km s are very prominent the sub moho high velocity lid with an apparent velocity of 8 4 km s is very thin thinning of this lid thickening of the low velocity layer and the presence under it of another high velocity layer 8 6 km s appear to characterize the uppermost mantle structure beneath the mariana basin

on the relationship between surface and basal properties on glaciers ice sheets and ice streams the influence of basal disturbances on the steady state surface topography and on surface velocities of glaciers and ice sheets is investigated numerically this is done for finite amplitude basal perturbations in both bed topography and basal slipperiness using a nonlinear ice rheology and a nonlinear sliding law the effects of varying the exponent n in glen s flow law on transfer characteristics are mainly quantitative and do not affect qualitative aspects of the transfer amplitudes and phase shifts such as the number of maxima and inflection points when plotted as functions of wavelength in particular the well known maximum in bed to surface transfer amplitude for a newtonian medium at sufficiently high slip ratios ratio between mean sliding velocity and mean ice deformational velocity also forms for n 1 transfer amplitudes generally become smaller with increasing n for wavelengths less than about 3 times the mean ice thickness h for larger wavelengths the situation is reversed and transfer amplitudes increase with n for active ice streams characterized by high basal slipperiness low surface slopes 0 5 and fairly constant for all wavelengths longer than about 3 5h with increasing n and decreasing surface slope the lower limit of wavelengths over which horizontal stress gradients can be ignored increases markedly perturbation solutions for newtonian medium are found to give an accurate description of the transfer characteristics for bedrock amplitudes up to 50 ice thickness and for fractional amplitudes of slipperiness perturbations up to 0 5

glacier fluctuations of jostedalsbreen western norway during the past 20 years the sensitive response of maritime mountain glaciers the steep outlet glaciers of jostedalsbreen western norway are good examples of sensitively reacting maritime mountain glaciers their changes in length frontal position and lower tongue s morphology during the past 20 years have been well documented at first they experienced a strong frontal advance after ad 2000 glacier behaviour was dominated by a strong frontal retreat in some cases causing a separation of the lowermost glacier tongue in this paper the glacier length changes are presented both visually and numerically supplemented by mass balance and meteorological data the glacier behaviour is interpreted and its causes are discussed whereas the factors controlling the advance during the 1990s seem clear the interpretation of the most recent retreat still leaves some uncertainties the actual glacier front behaviour cannot fully be related to the mass balance data terminus response times and relations between individual mass balance and meteorological parameters have changed some hypoth

downscaled precipitation applied in modelling of mass balance and the evolution of southeast vatnajokull iceland simulations of the post little ice age evolution of three outlet glaciers of southeast vatnajokull iceland skalafellsjokull heinabergsjokull and flaajokull are presented a coupled shallow ice approximation ice flow and degree day mass balance model is applied that is calibrated with a 14 year record of in situ mass balance measurements the measured mass balance cannot be realistically represented by constant horizontal and vertical precipitation gradients high resolution 1 km precipitation fields derived from downscaled orographic atmospheric circulation models of precipitation are required to capture the spatial variation of the winter mass balance the observed ice volume around 1890 15 30 larger than in 2000 can be simulated with 1 c lower temperatures and a 20 reduction in the annual precipitation relative to the reference climate period 1980 2000 the sensitivity of each glacier s annual balance to a change in temperature is 1 51 to 0 97 m w e a 1 c 1 and 0 16 to 0 65 m w e a 1 for a 10 increase in precipitation a steady state experiment applying a step increase in temperature of 2 c 3 c and precipitation increase of 10 results in a 50 80 90 decrease in ice volume

climatic and morphometric controls on the altitudinal range of glaciers british columbia canada to examine the relation between climate and glacier extent we compared gridded monthly temperature and precipitation data to the altitudinal range of glaciers in british columbia canada we related glacier relief to ablation season temperature june august accumulation season precipitation september march and morphometric variables that included slope glacier order and a shape index for 523 alpine glaciers that ranged from 5 to 15 km2 in surface area a 1 c increase in mean june august temperature equates to a 109 to 182 m decrease in glacier relief and a 1 mm increase in mean monthly september march precipitation equates to a 0 78 to 2 20 m increase in glacier relief the most important morphometric controls on this glacier climate relation include average surface slope glacier order analogous to stream order and the ratio of upper accumulation area to lower ablation area width all of which are positively related to glacier relief we note strong relations between glacier relief and cli

transient glacier response with a higher order numerical ice flow model in this paper a higher order numerical flowline model is presented which is numerically stable and fast and can cope with very small horizontal grid sizes 10 m the model is compared with the results from blatter and others 1998 on haut glacier d arolla switzerland and with the european ice sheet modelling initiative benchmarks huybrechts and others 1996 results demonstrate that the significant difference between calculated basal drag and driving stress profiles in a fixed geometry disappears when the glacier profile is allowed to react to the surface mass balance conditions and reaches a steady state dynamic experiments show that the mass transfer in higher order models occurs at a different speed in the accumulation and ablation areas and that the front position is more sensitive to migration compared to the shallow ice approximation

on estimating length fluctuations of glaciers caused by changes in climatic forcing the reaction of alpine glaciers to shifts in the equilibrium line altitude ela is calculated by using a two dimensional numerical model to solve the full equations for the velocity and stress fields full system model in the absence of basal motion rates of advance and retreat of the snout of typically sized alpine glaciers are found to be insensitive to the details of the flow at the snout even when the glaciers are far from steady state a comparison of results obtained with a full system model and a shallow ice approximation sia model yields no significant differences in advance or retreat rates this assumption has been implicitly made in numerous previous climatic studies and is here shown to be well justified using a realistic mass balance altitude feedback only slight model dependent changes in steady state lengths are found the relative importance of mass balance and glacier dynamics for the transient response of alpine glaciers to changes in the ela is given a precise meaning by determining the model dependent additional shifts in ela needed for the sia and the full system models to produce identical changes in length for alpine glaciers these additional shifts in ela are on the order of 10 m which is within the error range of ela estimates it follows that at least in the absence of significant basal motion there is no need to include the effects of horizontal stresses when calculating the reaction of alpine glaciers to climatic changes attention should focus on accurate determination of the mass balance distribution and model tuning to give realistic ice thickness distributions

a century of geometry and velocity evolution at eqip sermia west greenland rapid dynamic changes of ocean terminating outlet glaciers of the greenland ice sheet are related to atmospheric and oceanic warming but the detailed link to external forcing is not well understood observations show high variability in dynamic changes and are mainly limited to the past three decades with dense satellite observations here we compile a long term record of dynamic changes of eqip sermia glacier west greenland starting in 1912 we combine historical measurements of terminus positions ice surface elevation and flow velocity together with more recent in situ and remote sensing observations in the 20th century the glacier underwent small variations in terminus position and flow speed between 2000 and 2003 the terminus retreated substantially but stabilized thereafter in 2009 the northern terminus lobe started to retreat very rapidly the southern lobe collapsed in 2013 the present terminus position which has retreated by 4 km since 1920 is unprecedented in the historical record flow velocities were relatively stable until 2010 the recent acceleration reached threefold velocities in 2014 and rapidly affected the whole terminus region up to 15 km inland comparison with forcings from the atmosphere and the ocean over the past century shows that no dominant cause can be identified and that local effects of bed geometry modulate the glacier response

a three dimensional numerical model of the confluence area of unteraargletscher bernese alps switzerland with the use of a numerical three dimensional 3 d model the flow dynamics of the confluence area of unteraargletscher bernese alps switzerland are studied previous predictions based on conceptual two dimensional models about flow characteristics at confluence areas are tested against results from the fully 3 d model measured winter velocities are used for model verification despite some consistent systematic differences good overall agreement between measured and calculated surface velocities is obtained the calculated vertical strain rate variation with depth is in good agreement with available measurements from boreholes the ice is found to be almost three times stiffer than standard estimates of rheological parameters for glacier ice would predict the model predicts a complicated yet realistic pattern of vertical velocity variation along the surface the most noticeable features of the vertical velocity distribution across the surface are listed and their relation to topographic surface undulations and the overall dynamics of the confluence discussed in accordance with previous results from analytical models a strongly localized surface trough and a concomitant negative downward orientation vertical velocity anomaly develop at the junction point although depth integrated strain rates are positive extension the basal layer is compressed vertically the ice cored medial moraine is formed by differential ablation the flow mechanics of the confluence area play only an indirect role by enabling transfer of debris covered marginal ice towards the confluence center in the absence of differential ablation an elongated surface depression would be formed in the down glacier direction from the junction point instead of an elevated ice cored medial moraine

pyroxene orientation within the upper mantle petrofabric analyses of orthopyroxene and olivine for a suite of rocks from the bay of islands ophiolite newfoundland show systematic relationships between the minerals9 fabrics the plane of the mohorovicic discontinuity determined from the contact of the gabbro and ultramafic sections and the spreading direction inferred from the attitude of the sheeted dikes the orthopyroxene c crystallographic axes maxima which are aligned subparallel to the spreading direction coincide with olivine a axes maxima the orthopyroxene b axes and olivine c axes also lie approximately within the plane of the mohorovicic discontinuity but parallel the ridge whereas the orthopyroxene a axes maxima and olivine b axes maxima are approximately perpendicular to the mohorovicic discontinuity using olivine and orthopyroxene elastic constants and their pressure derivatives velocities have been calculated from composite petrofabric data and contoured for varying proportions of olivine and pyroxene the results of these calculations show that within a vertical direction compressional wave velocities change only slightly with increasing pyroxene content whereas parallel to the mohorovicic discontinuity velocities decrease with increasing pyroxene content anisotropy decreases from 4 for a rock with 100 olivine to 2 6 for a rock with 50 olivine and 50 orthopyroxene also within the plane of mohorovicic discontinuity the maximum and minumum velocities occur at approximately the same azimuth for differing percentages of orthopyroxene a comparison of the calculated anisotropy and the observed seismic anisotropy off the coast of california shows a striking agreement from this comparison it is estimated that the percentage of orthopyroxene within the upper mantle of this region varies between 0 and 30

numerical simulations of gurenhekou glacier on the tibetan plateau we investigate the impact of climate change on gurenhekou glacier southern tibetan plateau which is representative of the tens of thousands of mountain glaciers in the region we apply a three dimensional thermomechanically coupled full stokes model to simulate the evolution of the glacier the steep and rugged bedrock geometry requires use of such a flow model we parameterize the temperature and surface mass balance smb uncertainties using nearby automatic weather and meteorological stations 6 year measured smb data and an energy balance model for a nearby glacier summer air temperature increased at 0 02 k a 1 over the past 50 years and the glacier has retreated at an average rate of 8 3 m a 1 prognostic simulations suggest an accelerated annual average retreat rate of similar to 9 1 m a 1 along the central flowline for the next 25 years under continued steady warming however regional climate models suggest a marked increase in warming rate over tibet during the 21st century and this rate causes about a 0 9 0 3 a 1 loss of glaciated area and 1 1 0 6 a 1 shrinkage of glacier volume these results the rather high warming rates predicted and the small sizes of most tibetan glaciers suggest that significant numbers of glaciers will be lost in the region during the 21st century

a flow model for the polar caps of mars a mechanical model with circular symmetry is examined to test the hypothesis that the martian ice caps are composed of flowing water ice together with some rock debris in contrast with most or all previous models no assumption of a steady state is made instead the accumulation and ablation is assumed to be insignificant and it is suggested that after a sufficient time the profile would have settled down to a particular collapsing form calculated by halfar 1983 higher modes of flow would have decayed relatively quickly to calculate the time constant it is necessary to consider carefully the distribution of temperature with depth the time constant is sensitive to the grain size which is assumed to be 1 10 mm and is a significant unknown as is also the effect of preferred crystal orientation apart from this the main uncertainty is the value of the upward heat flux with a heat flux of 30 mw m 2 the water ice hypothesis is consistent with an age of about 10 7 years for both the north and the south polar caps the north cap being the younger by a factor of about 7

numerical modeling of the snowmass creek paleoglacier colorado and climate in the rocky mountains during the bull lake glaciation mis 6 abstract well preserved moraines from the penultimate or bull lake glaciation of snowmass creek valley in the elk range of colorado usa present an opportunity to examine the character of the high altitude climate in the rocky mountains during marine oxygen isotope stage 6 this study employs a 2 d coupled mass energy balance and flow model to assess the magnitudes of temperature and precipitation change that could have sustained the glacier in mass balance equilibrium at its maximum extent during the bull lake glaciation variable substrate effects on glacier flow and ice thickness make the modeling somewhat more complex than in geologically simpler settings model results indicate that a temperature depression of about 6 7 c compared with the present 1971 2000 ad would have been necessary to sustain the snowmass creek glacier in mass balance equilibrium during the bull lake glaciation assuming no change in precipitation amount or seasonality a 50 increase or decrease from modern precipitation would have been coupled with 5 2 c and 9 1 c bull lake temperature depressions respectively uncertainty in these modeled temperature depressions is about 1 c

the last glacial maximum at 44 s documented by a 10be moraine chronology at lake ohau southern alps of new zealand abstract determining whether glaciers registered the classic last glacial maximum lgm 26 500 19 000 yrs ago coevally between the hemispheres can help to discriminate among hypothesized drivers of ice age climate here we present a record of glacier behavior from the southern alps of new zealand during the local lgm llgm we used 10 be surface exposure dating methods and detailed glacial geomorphologic mapping to produce a robust chronology of well preserved terminal moraines deposited during the llgm near lake ohau on central south island we then used a glaciological model to estimate a llgm glacier snowline and atmospheric temperature from the ohau glacier record seventy three 10 be surface exposure ages place culminations of terminal moraine construction and hence completions of glacier advances to positions outboard of present day lake ohau at 138 600 10 600 yrs 32 520 970 yrs ago 27 400 1300 yrs ago 22 510 660 yrs ago and 18 220 500 yrs ago recessional moraines document glacier recession into the lake ohau trough by 17 690 350 yrs ago exposure of an ice molded bedrock bench located inboard of the innermost llgm moraines by 17 380 510 yrs ago indicates that the ice tongue had receded about 40 of its overall length by that time comparing our chronology with distances of retreat suggests that the ohau glacier terminus receded at a mean net rate of about 77 m yr 1 and its surface lowered by 200 m between 17 690 and 17 380 yrs ago a long term continuation of ice retreat in the ohau glacier catchment is implied by moraine records at the head of irishman stream valley a tributary of the ohau glacier valley the irishman stream cirque glacier advanced to produce a set of lateglacial moraines at 13 000 500 yrs ago implying that the cirque glacier was less extensive prior to that advance we employed a glaciological model fit to these mapped and dated llgm moraines to derive snowline elevations and temperature parameters from the ohau glacier record the modeling experiments indicate that a snowline lowering of 920 50 m and temperature depression of 6 25 0 5 c below modern values allows for the ohau glacier to grow to an equilibrium position within the lgm moraine belt taken together with a glaciological simulation reported from the irishman stream valley snowlines and temperatures increased by at least 520 m and 3 6 c respectively between 18 000 and 13 000 yrs ago climate parameters derived from the ohau glacier reconstruction are similar to those derived from glacier records from patagonia to air temperature indicators from antarctica as well as to sea surface temperature and stratification signatures of the southern ocean we think that the best explanation for the observed southern llgm is that southern winter duration modulated southern ocean sea ice which in turn influenced southern ocean stratification and made the surface ocean cooler orbitally induced cooling of the southern ocean provides an explanation for the llgm in the southern alps having been coincident with the northern lgm we argue further that the global effect of north atlantic stadials led to disturbance of southern ocean stratification southward shifts of the subtropical front and retreat of southern alps glaciers collapse of southern ocean stratification during heinrich stadial 1 along with attendant sea surface warming triggered the onset of the last glacial termination in the southern alps of new zealand

the effect of the descending lithosphere beneath the tonga island arc on p wave travel time residuals at the warramunga seismic array abstract p wave travel time residuals at the warramunga seismic array wra in the northern territory australia have been studied from 49 earthquakes with epicenters south of 19 s in the fiji tonga region focal depths are between 42 and 679 km as determined from pp p using the jeffreys bullen and the herrin travel time tables the epicentral parameters have been redetermined by considering only normal seismic stations in the location procedure these are those stations where p wave travel times are probably not affected by lateral heterogeneities caused by the lithosphere descending beneath the tonga trench epicenters of deep earthquakes below 300 km have been relocated by using stations at 25 only epicenters from shallower depth earthquakes have been recalculated without using stations between 35

high frequency pn sn phases recorded by ocean bottom seismometers on the cocos plate data from ocean bottom seismometers located on the cocos plate indicate that high frequency pn sn phases are generated by earthquakes along the subducting margin of that plate and are propagated across the plate the sn phase appears to be severely attenuated as it approaches the ridge crest estimates of pn velocity are lower than previous extimates for western pacific paths which may indicate a relationship between pn sn velocity and lithospheric age high frequencies found in these phases suggest that q for pn sn propagation across the cocos plate is similar to that for the western pacific

draping or overriding the effect of horizontal stress gradients on internal layer architecture in ice sheets internal isochronic layers in ice sheets sensed by radar show two characteristic relationships to the basal topography either they override it with layers above the crests of rises lying essentially flat or they drape over it with the layers following rises and falls in basal topography a mechanical theory is presented which shows that overriding is the expected behavior when topographic wavelengths are comparable with or less than the ice thickness while draping occurs at longer wavelengths this is shown with analytical perturbation solutions for newtonian fluids numerical perturbation solutions for nonlinear fluids and finite element solutions for nonlinear fluids and large amplitude variations bed variation from topography and changes in the basal boundary condition are considered for fixed bed and sliding beds as well as three dimensional flows and thermomechanically coupled flows in all cases the dominant effect on draping overriding is the wavelength of the topography or variation in basal boundary conditions results of these full mechanical system calculations are compared with those from the shallow ice approximation and the longitudinal stress approximation some calculations are carried out for zero accumulation where the age of the ice and therefore isochrone geometry is not defined it is shown that there is a close relationship between isochrones and streamlines and that they behave similarly when bed wavelength divided by the ice thickness is small compared with the ratio of ice velocity and accumulation rate which is a useful approximation numerical comparisons of isochrones and streamlines show them to be virtually coincident

variation with age of anisotropy under oceans from great circle surface waves global great circle measurements of regionalized mantle love wave phase velocities are interpreted in terms of regional models the same study had been made by j j leveque 1980 for rayleigh waves and the resulting models for the two oceanic regions of different ages are used as a basis for comparison the observed love wave dispersion cannot be explained with these models if isotropic the models obtained by inversion of love wave data are compared with the models mentioned the discrepancy appearing in the 250km depth range between the velocities h and v of respectively sh and sv waves is indicative of polarization anisotropy moreover we put forward a significant variation from young to old oceans the difference between h and v is of the order of 1 for the former compared to 3 for the latter this variation can bring information about the behaviour of upper mantle materials in connection with the motion of oceanic plates

seismicity and seismic gap in the lesser antilles arc and earthquake hazard in guadeloupe summary a seismic study of the lesser antilles arc has been carried out first for the period 1950 1978 for which we can use local seismic networks to draw maps of instrumental seismicity then for the period 1530 1950 for which we have catalogues of felt earthquakes the striking feature of the spatial distribution of foci is the cluster of epicentres in the northern half of the arc all large earthquakes m 7 5 are located north of 14 latitude seismicity cross sections through the arc show a variable dipping subduction zone along the arc the deep seismic zone is steeper in the centre of the arc than on the extremity the time space diagram for historical seismicity and the evidence of a seismic gap at the east of guadeloupe lead us to consider the northern half arc as a likely site for a large earthquake in the near future the seismic slip rate calculated from all major earthquakes since 1530 is of much greater value than that obtained from recent plate tectonic models suggesting that the recurrence rate of earthquakes is more than many hundreds of years with a possible aseismic creep

the influence of sub glacial bed evolution on ice extent a model based evaluation of the last glacial maximum pukaki glacier new zealand abstract a potential complication in using glacier extent to estimate paleoclimatic conditions is the influence of glacier bed evolution on changes in ice extent over time here we examine this issue through model based reconstructions of the last glacial maximum lgm pukaki glacier southern alps new zealand whose lgm extents are exceptionally well defined by lateral and terminal moraines using the well dated moraine limits as an empirical constraint on maximum ice extents we employ a one dimensional glacier flowline model driven by a mass balance model in order to evaluate the influence of climate and glacier bed profile on the extent of the lgm pukaki glacier the lgm glacier bed is buried by lateglacial and post glacial sediment so we calculate bed profiles using a modified version of the one dimensional model and available geologic constraints a best fit to the moraine record occurs with a lgm temperature of 7 8 c cooler than present with precipitation ranging from 80 to 100 of present levels modeling of the bed profile evolution indicates that bed changes alone could account for kilometer scale changes in glacier width and length

quantifying the effects of climate and surface change on glacier mass balance when a mass balance is computed using an outdated map that computation does not reveal the actual mass change but older maps often must be used for practical reasons we present a method by which with a few additional measurements each year a mass balance computed with an outdated map can be transformed into an actual mass change this is done by taking into account the influence of changes in areal extent and changes in the surface elevation of the glacier since the map was made this method is applied to south cascade glacier washington u s a as an example the computed cumulative mass balance from 1970 to 1997 would have been 16 too negative if the 1970 map had not been updated while the actual volume change of a glacier is relevant to hydrological studies the change that would have occurred on a constant or static surface is more relevant to certain glacier dynamics problems and most climate problems we term this the reference surface balance and propose that such a balance which deliberately omits the influence of changes in area and surface elevation is better correlated to climatic variations than the conventional one which incorporates those influences

rayleigh wave attenuation and its variation across the atlantic ocean summary fundamental mode rayleigh walies generated by several earthquakes situated on great circle paths traversing pairs of seismograph stations in american and european coastal regions and on atlantic islands have been analysed to obtain anelastic attenuation coefficients group and phase velocities and specific quality factors at periods between 15 and 100s inversions of the dispersion and attenuation data have yielded shear velocity and shear wave internal friction qj models of the upper mantle for regions of varying age in the atlantic ocean the attenuation coefficients and internal friction values can be related to the age of the atlantic ocean floor older regions being characterized by lower internal friction or higher q values a lowq zone is prominent in the upper mantle of all regions less than 65 myr in age but is poorly developed in older regions in contrast to the attenuation results no systematic variations of rayleigh or shear velocities with age can be resolved using the dispersion data of this study a comparison of internal friction models beneath the atlantic with those beneath the pacific indicates that for regions of similar age internal friction is smaller or q larger beneath the atlantic than beneath the pacific especially in the younger regions immediately contiguous with the ridges in particular the upper mantle low velocity low q zone is less prominent beneath the atlantic the fact that spreading rates of the lithospheric plates are also smaller in the atlantic suggests that internal friction and the rate of long term creep in the mantle are closely related

hintereisferner austria mass balance reconstruction and numerical modelling of the historical length variations in this study an attempt is made to simulate the historical length variations of hintereisferner austria key elements in the model are 1 reconstruction of the local climate vent 2 multiple linear regression analysis between measured climate and mass balance variations 3 reconstruction of the mass balance with 1 and 2 4 a one dimensional numerical ice flow model forced by the mass balance history

modeling the evolution of the juneau icefield between 1971 and 2100 using the parallel ice sheet model pism we study the evolution of the juneau icefield one of the largest icefields in north america 3700 km 2 using the parallel ice sheet model pism we test two climate datasets 20 km weather research and forecasting model wrf output and data from the scenarios network for alaska planning snap derived from spatial interpolation of observations good agreement between simulated and observed surface mass balance was achieved only after substantially adjusting wrf precipitation to account for unresolved orographic effects while snap s climate pattern is incompatible with observations of surface mass balance using the wrf data forced with the rcp6 0 emission scenario the model projects a decrease in ice volume by 58 68 and a 57 63 area loss by 2099 compared with 2010 if the modeled 2070 99 climate is held constant beyond 2099 the icefield is eliminated by 2200 with constant 1971 2010 climate the icefield stabilizes at 86 of its present day volume experiments started from an ice free state indicate that steady state volumes are largely independent of the initial ice volume when forced by identical scenarios of climate stabilization despite large projected volume losses the complex high mountain topography makes the juneau icefield less susceptible to climate warming than low lying alaskan icefields

transmission of basal variability to a glacier surface 1 transmission of basal variability to a glacier surface is investigated using analytical models for a linearly viscous medium the three dimensional transient response of the surface to both bedrock undulations and spatial variations in basal slipperiness for perturbations of arbitrary wavelengths is determined using perturbation methods both information transfer toward the surface and lateral transmission of horizontal stresses are strongly affected by the slip ratio that is the ratio of basal sliding to deformational velocity for any mean bedrock slope and above a minimum value of slip ratio the amplitude transfer of bedrock undulations toward the surface has a local maximum at undulation span corresponding to about 3 8 times the mean ice thickness the transmission of basal variability to a glacier surface increases quite significantly with increasing slip ratio this explains why the surfaces of fast flowing ice streams are more undulating than the slower moving bordering areas at slip ratios higher than about 100 the flow of glaciers and ice sheets becomes nonlocal in the sense that surface velocities and buildup and propagation of surface undulations cannot be calculated accurately on the basis of local thickness and slope using linearized long wave theories at these slip ratios instead of the more accurate arbitrary wavelength theory gives estimates of decay times that are an order of magnitude too small and phase velocities several times too large the problem of the propagation and decay of small amplitude surface undulations on glaciers in three dimensions is solved small amplitude surface waves on glaciers are strongly diffusive and dispersive redistribution of mass on ice sheets and glaciers is a diffusion process and it is misleading albeit not mathematically incorrect to describe the reaction of glaciers to surface perturbations in terms of a wave propagation

what do glaciers tell us about climate variability and climate change glaciers respond to long term climate changes and also to the year to year fluctuations inherent in a constant climate differentiating between these factors is critical for the correct interpretation of past glacier fluctuations and for the correct attribution of current changes previous work has established that century scale kilometre scale fluctuations can occur in a constant climate this study asks two further questions of practical significance how likely is an excursion of a given magnitude in a given amount of time and how large a trend in length is statistically significant a linear model permits analytical answers wherein the dependencies on glacier geometry and climate setting can be clearly understood the expressions are validated with a flowline glacier model the likelihood of glacier excursions is well characterized by extreme value statistics although probabilities are acutely sensitive to some poorly known glacier properties conventional statistical tests can be used for establishing the significance of an observed glacier trend however it is important to determine the independent information in the observations which can be effectively estimated from the glacier geometry finally the retreat of glaciers around mount baker washington state usa is consistent with but not independent proof of the regional climate warming that is established from the instrumental record

the p velocity within the tonga benioff zone determined from traced rays and observations p waves with travel time residuals between 0 s and 12 s are observed at regional stations in samoa afi and raoul island rao for 39 earthquakes in tonga with focal depths between 70 km and 300 km these anomalously large residuals apparently are produced because seismic phases travel along the strike of the tonga benioff zone within the high velocity subducted lithosphere for up to 1200 km before arriving at afi and rao to eliminate erroneous residuals caused by poor event locations we selected 11 stations and reread the available p times at these stations for the 39 events these arrivals and pp p intervals were used to relocate the events using a variant of the joint hypocenter determination method then the pattern of residuals at afi and rao not used in the relocation was compared to the pattern of residuals expected for various models of the subducted lithosphere as determined by ray tracing the observed pattern of residuals at afi is consistent with the ray traced models if some of the first arrivals are produced by rays traveling directly along the strike of the subducting lithosphere and if others are produced by rays which reflect once off the upper surface of the subducting lithosphere before arriving at afi the observed residuals can be explained by a model where the p velocity in the subducted lithosphere is 8 higher than the velocity in the herrin model the residuals are fit even better by a layered slab model in which the seismic velocity is about 6 higher than the herrin velocity at the upper surface of the subducted lithosphere and about 9 higher at the bottom of the slab these velocity contrasts could be produced if the temperature in the slab was 700 c cooler than the surrounding mantle and if there were no partially melted material within the slab the existence of these anomalously large residuals suggests that the high velocity region in the upper 300 km of the mantle beneath tonga must be fairly continuous over distances of 1000 km and more

flow dynamics of tidewater glaciers a numerical modelling approach the dynamics of grounded tidewater glaciers is investigated with a time dependent numerical flow model which solves the full equations for the stress and velocity fields and includes a water pressure dependent sliding law the calving criterion implemented in the model shifts the calving front at each time step to the position where the frontal ice thickness exceeds flotation height by a prescribed value with this model the linear relation between calving rate and water depth proposed on empirical grounds is qualitatively reproduced for the situation of a slowly retreating or advancing terminus but not for situations of rapid changes length changes of tidewater glaciers i e especially rapid changes are dominantly controlled by the bed topography and are to a minor degree a direct reaction to a mass balance change thus accurate information on the near terminus bed topography is required for reliable prediction of the terminus changes due to climate changes the results also confirm the suggested cycles of slow advance and rapid retreat through a basal depression rapid changes in terminus positions preferably occur in places where the bed slopes upwards in the ice flow direction

glacier based climate reconstructions for the last glacial interglacial transition arthur s pass new zealand 43 s geological records of mountain glacier fluctuations provide useful evidence for tracing the magnitude and rate of past temperature change in this study we present air temperature reconstructions for the last glacial termination in new zealand derived using snowline reconstructions and numerical glacier modelling we target the arthur s pass moraines in the otira river catchment which have previously been dated to the lateglacial using cosmogenic 10be recalculation of these exposure ages using a locally calibrated 10be production rate indicates that these moraines formed ca 16 14 ka our glacier modelling experiments and snowline reconstructions exhibit good agreement and show that the arthur s pass moraines formed in a climate that was 2 2 3 5 c colder than present combining our results with other proximal glacier records shows that ice in this catchment retreated ca 50 km from the coastal plain to the main divide during the interval 17 15 ka in response to a temperature increase of at least ca 3 c over half of this retreat occurred after the glacier had withdrawn from an overdeepened basin thus we conclude that temperature increase was the primary driver of widespread and rapid glacier retreat in new zealand at the onset of the last glacial termination

seismic refraction profiles between cyprus and israel and their interpretation summary a long seismic refraction profile was carried out between southern israel and cyprus the seismic energy was generated by 33 sea shots each of 0 8 t explosives and was recorded by land stations in israel and cyprus and by ocean bottom seismographs deployed along the profile the results showed that the continental crust of southern israel thins towards the mediterranean underneath a northward thickening sedimentary cover cyprus is underlain by a 35 km thick continental crust thinning south wards and extending to mt eratosthenes between mt eratosthenes and the israel continental shelf the crystalline crust is composed of high velocity 6 5 km s 1 material and is about 8 km thick it is covered by 12 14 km of sediments and may represent a fossil oceanic crust

estimating rates of basal motion and internal ice deformation from continuous tilt measurements over a two year period continuous measurements of temporal changes in tilt conducted with a string of tilt meters in a borehole on unteraargletscher bernese alps switzerland have been used to estimate the basal motion component this estimation is based on a comparison of the measurements with synthetic tilt curves computed using a parameterization of a simplified flow field the best agreement is found for a ratio of basal motion to forward motion due to ice deformation slip ratio equal to about 1 2 measured tilt curves exhibit a number of different transient features while an overall increase in tilt angle is observed at every tilt meter location two of the sensors recorded anomalous tilt behaviour these anomalies are characterized by sudden and drastic variations in tilt a particularly intriguing example of such short term tilt variations was recorded with a tilt meter positioned 40 m above the bed during the 1997 summer melt season

glacier thickening and decay analysis from 50 years of glaciological observations performed on glacier d argentiere mont blanc area france numerous glaciological data have been obtained from measurements carried out on glacier d argentiere mont blanc area france since the beginning of the 20th century moreover data on annual mass balance ice flow velocity thickness variation and length fluctuation have been obtained from yearly measurements performed since 1975 this dataset provides an excellent opportunity to analyze the relationships between surface mass balance and dynamic response over time periods during which net mass balance changed from positive to negative following a positive specific net balance period between 1960 and 1981 the ablation zone experienced a large increase in thickness and ice flow velocities conversely the highly negative specific net balance period since 1982 has led to strong thinning deceleration and retreat of the tongue the response of these observed dynamics to surface mass balance is analyzed from ice flux calculations performed on three transverse cross sections our results reveal that the ice fluxes are largely accommodated by ice flow velocities velocity fluctuations are synchronous over the entire area studied in the largest part of the glacier no compressing extending flow change has been observed over the last 30 years and thickness changes are solely driven by surface mass balance changes however on the tongue of the glacier thickness changes do not depend on surface mass balance but are mainly driven by changes in the longitudinal strain rate

time step limits for stable solutions of the ice sheet equation various spatial discretizations for the ice sheet are compared for accuracy against analytical solutions in one and two dimensions the computational efficiency of various iterated and non iterated marching schemes is compared the stability properties of different marching schemes with and without iterations on the non linear equations are compared newton raphson techniques permit the largest time steps a new technique which is based on the fact that the dynamics of unstable iterated maps contain information about where the unstable root lies is shown to improve substantially the performance of picard iteration at a negligible computational cost

a composite focal mechanism for microearthquakes along the northeastern border of the caribbean plate seismograms from a local seismic network in the virgin islands portion of the northeastern caribbean are used to determine a composite focal mechanism for 26 microearthquakes along the north america caribbean plate boundary only one nodal plane of the focal mechanism could be constrained from p wave first motion data alone p sv amplitude ratios observed for these events were compared to theoretical amplitude ratios calculated for different focal mechanisms this procedure constrained the dip of the second nodal plane to be shallower than about 50 ruling out the possibility of a transform fault in this portion of the plate boundary the resulting focal mechanism indicates that oblique underthrusting of the north american plate beneath the caribbean plate occurs in the area this oblique motion is accommodated along a thrust plane that dips at a relatively shallow angle beneath the virgin islands platform

basal flow characteristics of a linear medium sliding frictionless over small bedrock undulations the basal deformation of a gravity driven linear creeping flow sliding frictionless over slowly varying bed undulations in two dimensions is analysed analytically using results from second order perturbation theory one of the key results is that close to sinusoidal bedrock undulations up to two different spatial regions of local extrusion flow may arise the offset and onset of extrusion flow is controlled primarily by the amplitude to wavelength ratio above the crest of a sinusoidal bed line a local maximum of the surface parallel velocity develops for e ak 0 138 where a is the amplitude and k is the wave number as e increases from zer to this critical value the vertical position of the velocity maximum moves from kz 1 to kz 1 98 where z is the vertical distance above the mean bed line within and above the trough of a sinusoid a region of local minimum of the surface parallel velocity component develops which shifts from kz 1 towards the bed line as e increases front zero to 1 2 below this velocity minimum and for some distance above the velocity maximum the surface parallel velocity increases with depth this type of extrusion flow will cause a reversal of borehole inclination profiles close to the bedrock

evaluation of lateglacial temperatures in the southern alps of new zealand based on glacier modelling at irishman stream ben ohau range abstract climate proxy records from the middle to high latitude southern hemisphere indicate that a lateglacial 15 000 11 500 years ago climate reversal approximately coeval with the antarctic cold reversal acr interrupted a warming trend during deglaciation in new zealand some palaeoclimate proxy records indicate a cool episode during the acr ca 14 500 12 500 years ago while others do not express a significant change in climate recently published moraine maps and ages present an opportunity to improve the palaeoclimate interpretation through numerical modelling of glaciers we use a coupled energy balance and ice flow model to quantify palaeoclimate from past glacier extent constrained by mapped and dated moraines in the headwaters of irishman stream a high elevation catchment in the southern alps first a suite of steady state model runs is used to identify the temperature and precipitation forcing required to fit the modelled glacier to well dated lateglacial moraine crests second time dependent glacier simulations forced by a nearby proxy temperature record derived from chironomids are used to assess the fit with the glacial geomorphic record steady state experiments using an optimal parameter set demonstrate that the conditions under which the 13 000 year old moraine formed were 2 3 3 2 c colder than present with the range in temperature corresponding to a 20 variance in precipitation relative to the present day this reconstructed climate change relative to the present day corresponds to an equilibrium line altitude of ca 2000 40 m above sea level asl which is ca 400 m lower than present time dependent simulations of glacier length produce ice advance to within 100 m of the 13 000 year old terminal moraine indicating that the chironomid based temperature forcing and moraine record provide consistent information about past climate our results together with other climate proxy reconstructions from pollen records and marine sediment cores support the notion that temperatures during the acr in new zealand were 2 3 c cooler than today

spatial distribution and mechanisms of earthquakes in the southern new hebrides arc from a temporary land and ocean bottom seismic network and from worldwide observations in 1977 a wide aperture seismic network of land and ocean bottom stations obs was operated for 6 weeks in the southern new hebrides island arc data on the spatial distribution and mechanisms of small events recorded by this local network were integrated with worldwide observations of moderate to large size new hebrides earthquakes of the past 17 years to study the structure and deformational processes in the new hebrides subduction zone surprisingly small differences less than about 10 km were found between the locations of shallow and intermediate depth earthquakes as located by the temporary local network and by the international seismological centre using worldwide stations analysis of the p wave travel time data from the obs station closest to the trench shows limited evidence for a high velocity zone about 5 higher than the surrounding mantle associated with the descending plate the thrust zone between the descending and upper plates is defined mainly by the spatial distribution and focal mechanisms of moderate to large size events and their aftershocks but it is not very well defined by the spatial distribution of small size events located in this study shallow seismic activity located beneath the trench and beneath the interplate thrust zone indicates a lower limit of about 40 km for the thickness of the seismically active part of the descending plate beneath the thrust zone focal mechanisms of moderate to large size earthquakes located within the upper plate and geological observations on the islands suggest that the upper plate in the region of erromango and tanna is divided into a series of blocks that are differentially uplifted along mainly nw se striking faults during the obs experiment several shallow events were well located beneath the coriolis trough a riftlike feature located to the east of the volcanic arc well determined depths of these events are between 11 and 22 km the well located intermediate depth events define a 20 km thick benioff zone that has a dip of about 70 the spatial distribution of events within the descending slab is very strongly clustered in a persistent pattern that is seen in both the short term sample of small events determined by the local network and the long term sample of locations based on worldwide data several focal mechanisms of moderate to large size intermediate depth events show components of lateral extension along the strike of the arc and some show components of lateral compression both of which could be interpreted as the result of a lateral bending of the descending plate in the part of the southern new hebrides arc where the trench begins to curve around to the east

the response of two icelandic glaciers to climatic warming computed with a degree day glacier mass balance model coupled to a dynamic glacier model a degree day glacier mass balance model is coupled to a dynamic glacier model for temperate glaciers the model is calibrated for two outlet glaciers from the hofsjokull ice cap in central iceland it is forced with a climate scenario that has recently been defined for the nordic countries for the purpose of outlining the hydrological consequences of future greenhouse warming the scenario for iceland specifies a warming rate of 0 25 c per decade in mid summer and 0 35 c per decade in mid winter with a sinusoidal variation through the year the volume of the glaciers is predicted to decrease by approximately 40 over the next century and the glaciers essentially disappear during the next 200 years runoff from the area that is presently covered by the glaciers is predicted to increase by approximately 0 5 m a 1 30 years from now due to the reduction in the volume of the glaciers the runoff increase reaches a flat maximum of 0 5 2 0 m a 1 100 150 years from now and levels off after that the predicted runoff increase leads to a significant increase in the discharge of rivers fed by meltwater from the outlet glaciers of the ice cap and may have important consequences for the operation and planning of hydroelectric power plants in iceland

3 d transport and acoustic properties of fontainebleau sandstone during true triaxial deformation experiments abstract fontainebleau sandstone specimens have been tested in a true triaxial geophysical imaging cell under hydrostatic 1 2 3 traditional triaxial 1 2 3 and true triaxial 1 2 3 stress regimes the research objectives are to recognize the effect of various stress ratios 2 3 under varying magnitudes of 2 and 3 on 3 d stress strain responses 3 d transport 3 d ultrasonic wave velocities and acoustic emission properties comparison of the variation of 3 d directional permeability between the specimens shows that higher magnitude of 3 and 2 disrupts the 3 d interconnectivity of the pore spaces and intergranular cracks irrespective of the magnitude of applied stress ratio 2 3 the observed permeability anisotropy between the two specimens is a function of inherent oriented pores and cracks stress ratio 2 3 and the magnitude of applied 3 and 2 stresses temporal and spatial evolution of the ae hypocenter locations combined with the examination of micro ct and thin section images shows the timely development of polymodal fault systems during peak to post peak stresses and validates the development of the source mechanism inferred from the acoustic emission events

modelling glacier response to measured mass balance forcing measurements of summer and winter mass balances have been carried out over the past 53 years on storglaciaren northern sweden repeated surveys of the glacier have resulted in several maps of surface topography as well as a map of the bed topography a new time dependent ice flow model allows us to compare the observed surface evolution of the glacier with that computed by the model using measured mass balance maps as input the computed volume change compares well with the measured change the model replicates the distribution of surface elevation to within 10 m over 30 years of integration on the model side these deviations can be attributed to the low resolution discretization of the model domain as well as to the limited accuracy of the ice rheology and omitted basal sliding on the other hand the uncertainties of the topography and mass balance maps match the model uncertainties in this sense the experiments are a validation of both model and observations

sampling and preparation of c 200 mm diameter cylindrical rock samples for geomechanical experiments abstract experimental investigation of rock mechanical properties of real and artificial samples often requires much care and attention to detail during sample preparation this especially applies to high fidelity state of the art complex experimental apparatuses where sample tolerance is low due to the complexity of the measuring and stress control devices as well as the nature of the experiments to be conducted although sometimes mundane the sample preparation methodology is as equally important as the experimental apparatus itself and can require several new technological developments the methodology and technical developments required to prepare realistic heterogeneous fractured and natural reservoir analogue rock samples for coupled thermo hydro mechanical chemical process experimental investigation is described here we present the sample recovery and preparation procedures for large c 200 mm diameter cylindrical samples of 200 mm 5 mm length with variable composition and mechanical properties e g rock strength existing fractures fracture networks macro porosity or lithic fragments although the technology demonstrated is for a specific application the procedures developed equipment and methodology are applicable to multiple sizes of sample requirements

last glacial climate reconstruction by exploring glacier sensitivity to climate on the southeastern slope of the western nyaiqentanglha shan tibetan plateau improvements in understanding glacial extents and chronologies for the southeastern slope of the western nyaiqentanglha shan on the tibetan plateau are required to understand regional climate changes during the last glacial cycle a two dimensional numerical model of mass balance based on snow ice melting factors and of ice flow for mountain glaciers is used to assess the glacier sensitivity to climatic change in a catchment of the region the model can reproduce valley glaciers wide tongued glaciers and a coalescing glacier within step temperature lowering and precipitation increasing experiments the model sensitivity experiments also indicate that the dependence of glacier growth on temperature and or precipitation is nonlinear the model results suggest that the valley glaciers respond more sensitively to an imposed climate change than wide tongued and coalescing glaciers guided by field geological evidence of former glacier extent and other independent paleoclimate reconstructions the model is also used to constrain the most realistic multi year mean temperatures to be 2 9 4 6 degrees c and 1 8 2 5 degrees c lower than present in the glacial stages of the last glacial maximum and middle marine oxygen isotope stage 3 respectively

committed retreat controls on glacier disequilibrium in a warming climate the widespread retreat of mountain glaciers is a striking emblem of recent climate change yet mass balance observations indicate that many glaciers are out of equilibrium with current climate meaning that observed retreats do not show the full response to warming this is a fundamental consequence of glacier dynamics mountain glaciers typically have multidecadal response timescales and so their response lags centennial scale climate trends a substantial difference between transient and equilibrium glacier length persists throughout the warming period we refer to this length difference as disequilibrium forcing idealized glacier geometries with gradual warming shows that the glacier response timescale fundamentally governs the evolution of disequilibrium comparing a hierarchy of different glacier models suggests that accurate estimates of ice thickness and climatology which control the timescale are more important than higher order ice dynamics for capturing disequilibrium current glacier disequilibrium has previously been estimated for a selection of individual glaciers our idealized modeling shows that sustained disequilibrium is a fundamental response of glacier dynamics and is robust across a range of glacier geometries this implies that many mountain glaciers are committed to additional kilometer scale retreats even without further warming disequilibrium must also be addressed when calibrating glacier models used for climate reconstructions and projections of retreat in response to future warming

the response of a glacier to a surface disturbance a case study on vatnajokull ice cap iceland in the course of a tremendous outburst flood jokulhlaup following the subglacial eruption in vatnajokull iceland in october 1996 a depression in the surface of the ice cap was created as a result of ice melting from the walls of a subglacial tunnel the surface depression was initially approximately 6 km long 800 m wide and 100 m deep this canyon represents a significant perturbation in the geometry of the ice cap in this area where the total ice thickness is about 200 400 m we present results of repeated measurements of flow velocities and elevation changes in the vicinity of the canyon made over a period of about 2 years the measurements show a reduction in the depth of the canyon and a concomitant decrease in surface flow towards it over time by calculating the transient evolution of idealized surface depressions using both analytical zeroth and first order theories as well as the shallow ice approximation sia and a finite element model incorporating all the terms of the momentum equations we demonstrate the importance of horizontal stress gradients at the spatial scale of this canyon the transient evolution of the canyon is calculated with a two dimensional time dependent finite element model with flow parameters the parameters a and n of glen s flow law that are tuned towards an optimal agreement with measured flow velocities although differences between measured and calculated velocities are comparable to measurement errors the differences are not randomly distributed the model is therefore not verified in detail nevertheless the model reproduces observed changes in the geometry over a 15 month time period reasonably well the model also reproduces changes in both velocities and geometry considerably better than an alternative model based on the sia

simulation of the historical variations in length of unterer grindelwaldgletscher switzerland the historical length variations in unterer grindelwaldgletscher have been simulated by coupling a numerical mass balance model to a dynamic ice flow model as forcing functions we used partly reconstructed local climatic records which were transformed by the mass balance model into a mass balance history the ice flow model then computes the length variations that have occurred over the course of time in a model run from ad 1530 to the present with both seasonal temperature and precipitation variations as forcing functions the observed maximum length of the glacier around ad 1860 and the subsequent retreat are simulated the observed ad 1600 maximum however does not show up in the simulation this is probably due to an incorrect reconstruction of the mass balance for this period as detailed climatic data are available only since 1865 the root mean square difference between the simulated and the observed front positions is 0 28 km the simulated glacier geometry for 1987 fits the observed geometry for that year reasonably well because of the success of the historical simulation an attempt is made to predict future glacier retreat on the basis of two different greenhouse gas scenarios for a business asusual scenario only 29 of the 1990 volume would remain in ad 2100

late pleistocene glaciation and deglaciation in the crestone peaks area colorado sangre de cristo mountains usa chronology and paleoclimate abstract cosmogenic 10be surface exposure dating and numerical glacier modeling are used to reconstruct glacial chronology and climate in the colorado sangre de cristo mountains during the local last glacial maximum llgm and the subsequent deglaciation twenty two surface exposure ages on moraine boulders and polished bedrock outcrops in the willow creek valley and ten in two adjacent valleys indicate that glaciers were at or near their maxima from 21 ka until 17 16 ka and then retreated rapidly nearly deglaciating the willow creek valley entirely by 14 ka coupled energy mass balance and flow modeling of two of the glaciers indicates that if changing ice extent was driven only by temperature and insolation changes temperature depressions of 5 0 and 5 1 c from modern conditions with an uncertainty of approximately 1 5 1 0 c would have sustained the glaciers in mass balance equilibrium at their llgm extents doubling or halving of modern precipitation during the llgm would have been associated with 2 7 3 0 c and 6 9 7 0 c temperature depression respectively approximately half of the subsequent llgm to modern climate change was accomplished by 14 ka if the rapid main phase of deglaciation between about 16 ka and 14 ka was driven solely by temperature and insolation changes it would have been associated with a temperature rise of about 2 5 c at a mean rate of approximately 1 1 c ky this new chronology of the last glaciation is generally consistent with others developed recently in the colorado rocky mountains the numerical modeling however suggests a lesser llgm temperature depression from modern conditions than have most previous studies in colorado

exact solutions to the thermomechanically coupled shallow ice approximation effective tools for verification we describe exact solutions to the thermomechanically coupled shallow ice approximation in three spatial dimensions although artificially constructed these solutions are very useful for testing numerical methods in fact they allow us to verify a finite difference scheme that is to show that the results of our numerical scheme converge to the correct continuum values as the grid is refined in three dimensions comparison of numerical results with exact solutions has helped us to precisely quantify and understand some of the numerical errors we are making our verified numerical scheme shows the basal temperature spokes which arose in the eismint european ice sheet modelling initiative ii intercomparison payne and others 2000 a careful analysis describes these warm spokes as numerical errors which occur when the derivative of the strain heating term with respect to the temperature is large on the other hand the appearance of basal temperature spokes in a verified numerical scheme strongly suggests that they are a feature of the eismint ii experiment f continuum problem in fact they are clear evidence of an unstable equilibrium point of the continuum problem this paper is a sequel to bueler and others 2005 which addresses exact solutions and verification in the isothermal case

time scale for adjustment of glaciers to changes in mass balance the length of time tm over which a glacier responds to a prior change in climate is investigated with reference to the linearized theory of kinematic waves and to results from numerical models we show the following tm may in general be estimated by a volume time scale describing the time required for a step change in mass balance to supply the volume difference between the initial and final steady states the factor f in the classical estimate of m l u where i is glacier length and u is terminus velocity has a simple geometrical interpretation ft is the ratio of thickness change averaged over the full length i to the change at the terminus although both u and f relate to dynamic processes local to the terminus zone the ratio f u and therefore tm are insensitive to details of the terminus dynamics in contrast to conclusions derived from some simplified kinematic wave models a more robust estimate of tm independent of terminus dynamics is given by tm h b where h is a thickness scale for the glacier and b is the mass balance rate negative at the terminus we suggest that tm for mountain glaciers can be substantially less than the 1o2 103 years commonly considered to be theoretically expected

temperature and precipitation in the southern central andes during the last glacial maximum heinrich stadial 1 and the younger dryas abstract recent developments in terrestrial cosmogenic nuclide tcn exposure dating and the reinterpretation of tcn boulder ages from moraines have improved our understanding of the glacial chronology in the central andes according to these records glacial advances throughout the region correlate with insolation driven changes in the intensity of the south american summer monsoon and millennial scale climate events such as heinrich stadials and the younger dryas quantifying the temperature and precipitation shifts during these events helps to constrain past moisture pathways and associated changes in atmospheric circulation patterns yet particularly in the southern central andes where a wealth of glacigenic landforms attests to formerly cooler and or wetter conditions the magnitudes of past temperature and precipitation changes are only loosely constrained at a few sites here we present results from tcn dated moraines combined with the reconstruction of former glaciers and paleolakes within the eastern sector of the southern central andes 24 27 s for the last glacial maximum lgm heinrich stadial 1 hs1 and the younger dryas yd we performed monte carlo simulations with 2 dimensional models of ice flow and lake hydrology that are forced by a spatially distributed surface energy balance model our results indicate that temperatures were 3 0 4 2 c 2 0 3 3 c and 1 3 2 5 c cooler during the lgm hs1 and yd respectively in agreement with previous estimates elsewhere in the central andes we find that temperature changes during the late glacial are compatible with sea surface temperature anomalies derived from the tropical atlantic precipitation was only 5 27 greater than today which contrasts with larger anomalies reconstructed for the bolivian part of the andean plateau altiplano we attribute this discrepancy to the southerly position of our study region with respect to the bolivian high supporting the hypothesis that this atmospheric pressure system played a prominent role for south american summer monsoon dynamics during glacial episodes

on the imbalance and response time of glaciers in the european alps glaciers in the european alps rapidly lose mass to adapt to changes in climate conditions here we investigate the relationship and lag between climate forcing and geometric glacier response with a regional glacier evolution model accounting for ice dynamics the volume loss occurring as a result of the glacier climate imbalance increased over the early 21st century from about 35 in 2001 to 44 in 2010 this committed loss reduced to 40 by 2018 indicating that temperature increase was outweighing glacier retreat in the early 2000s but that the fast retreat effectively somewhat diminished glacier imbalances we analyze the lag in glacier response for each individual glacier and find mean response times of 50 28 years our findings indicate that the response time is primarily controlled by glacier slope and secondarily by elevation range and mass balance gradient rather than by glacier size

a lithospheric seismic refraction profile in the western north atlantic ocean summary a study of the seismic velocity structure of the subcrustal oceanic lithosphere was conducted in the western north atlantic north of the lesser antilles where the age of the lithosphere is 80 95 ma a 1000km long north south array of 18 ocean bottom seismographs obs spaced at 60 km intervals recorded arrivals from explosions at ranges up to 800km and arrivals from earthquakes in the northern caribbean region at ranges up to 1400 km analysis of the travel time and amplitude data from the explosions provided the velocity structure down to about 65 km below sea level the earthquake data were intended to extend the travel times to ranges over 1100 km and thus sample the deeper part of the lithosphere however the geometry and velocity structure of the downdipping slab beneath the puerto rico trench deflected the ray paths between the caribbean hypocentres and the obs array such that no rays travelling through the lower lithosphere were detected by the array only rays through the upper lithosphere reached the obs array the results show that the subcrustal oceanic lithosphere consists of two main regions the uppermost region starts just below the m discontinuity and exhibits velocities of 8 2 8 4 km s 1 this region is characterized by three alternating zones of low 8 2 km s 1 high 8 4 km s 1 and low 8 2 km s 1 velocity the second region lies below 53 km and exhibits high velocities of 8 5 8 6 km s 1 a sharp boundary separates these two regions suggesting that a major change in composition or phase occurs there the velocity structure within the upper region shows broad agreement with petrological models for the generation of oceanic lithosphere starting from a pyrolite composition the alternating zones of low and high velocity correspond to zones depleted of and enriched in the basaltic fraction of the primary mantle material respectively this is a consequence of the processes of migration and differentiation of the upwelling asthenosphere near the mid ocean ridge axis however none of the petrological models based on a pyrolite or peridotite initial composition can easily explain the high velocities of over 8 5 km s 1 observed for the lower region of the seismic velocity model we speculate that this region may consist instead primarily of eclogite which is acceted from the asthenosphere as the lithosphere cools and ages the results do not permit definition of the lower boundary of the lithosphere which probably lies below the 65 km maximum depth resolved in this study s wave observations were less reliable than the p wave data but generally support the p wave velocity model no evidence was found for azimuthal anisotropy within the upper region of the subcrustal lithosphere however the existence in the western north atlantic of a weakly anisotropic or even isotropic lower lithosphere with a significant component of eclogite requires verification by future experiments