a sea floor spreading event captured by seismometers two thirds of earth s surface is formed at mid ocean ridges yet sea floor spreading events are poorly understood because they occur far beneath the ocean surface at 9 50 n on the east pacific rise ocean bottom seismometers recently recorded the microearthquake character of a mid ocean ridge eruption including precursory activity a gradual ramp up in activity rates since seismic monitoring began at this site in october 2003 suggests that eruptions may be forecast in the fast spreading environment the pattern culminates in an intense but brief 6 hour inferred diking event on 22 january 2006 followed by rapid tapering to markedly decreased levels of seismicity

on the shape and velocity of fluid filled fractures in the earth summary in this paper i present a model to estimate the shape and velocity of slowly ascending buoyancy driven fluid filled fractures the model considers elastic deformation linear fracture mechanics and fluid flow an attempt is made to incorporate the effect ofthe 2 d fluid pattern on the viscous pressure drop most other models assume that the viscous pressure drop can be approximated by flow through a channel with constant width although the form of the fracture is known to deviate from such a simple shape the 2 d flow in my model has an important consequence for the mechanism of buoyancy driven fracture propagation it predicts a large pressure gradient at the tail of the propagating fracture indicating that the tail of the fracture is most important in hindering the fracture propagation a singularity at the tail of the fracture can be avoided when a small amount of fluid trails in the channel left behind the propagating fracture the trailing and decoupling of fluids at the tail seems to be accompanied by small flow and shape instabilities which is indicated by the jerky movement of the tail observed in propagating air filled fractures in solidified gelatine and by numerical boundary element solutions of the coupled flow deformation fracturing problem by comparing the predictions for propagation velocities with laboratory observations of buoyancy driven fracture propagation in gelatine i derive a non dimensional effective thickness at the tail of the fracture for which trailing of fluids may occur the model is applied to earth relevant problems such as oil and water filled fractures in pressurized sediments or magma filled dykes in the lithosphere which are discussed in the paper

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

jurassic magnetostratigraphy 4 early callovian through middle oxfordian of the krakow uplands poland a magnetic polarity pattern has been constructed for the early callovian through middle oxfordian stages of the jurassic from several ammonite rich magnetostratigraphy sections within the krakow czestochowa wielun region of southern poland these overlapping sections encompass portions of every ammonite from the late early callovian through late middle oxfordian however the presence of several hiatuses and condensed intervals within the shallow marine to pelagic sediments preclude reliable identification of the complete polarity pattern the mean callovian oxfordian pole from these sites is at 74 3 n 200 3 e 95 4 7 the callovian through early oxfordian is dominated by reversed polarity with a minimum of five normal polarity zones the early middle oxfordian is predominantly of normal polarity and the late middle oxfordian is characterized by reversed polarity with several relatively brief normal polarity episodes the callovian and oxfordian stages appear to average a minimum of two magnetic polarity reversals per million years this reversal frequency is similar to the average tertiary record but is less than the reported spacing of callovian and oxfordian magnetic anomalies in the pacific

magma propagation at piton de la fournaise from joint inversion of insar and gnss magma propagation is an unsteady process controlled by magma crust interaction to provide information on its dynamics we invert complementary ground deformation data spanning the 8 hr preceding the 26 may 2016 eruption at piton de la fournaise pdf volcano la reunion france data are inverted using 3 d boundary element models combined with a monte carlo inversion method the final geometry of the displacement source is determined based on four interferograms spanning the whole propagation phase while the dynamics of the propagation is inferred from temporal inversion of continuous global navigation satellite system gnss data using the final geometry as an a priori to constrain the source the best modeled magma path consists in a 2 700 m long sill located 800 m above sea level and connected to the eruptive fissure by a subvertical dike the quick opening of the horizontal part of the intrusion could have been favored by limited flank sliding during the early stage of propagation the intrusion then stalled for 5 hr while pressure increased slightly until final upward propagation and eruption volume budget suggests that the eruption was fed by a single batch of magma quickly disconnected from its source the delay prior to the eruption may reflect a limited magma supply finally two mechanisms potentially acting together might have favored the eruption a driving role of magmatic gas and or as often observed at piton de la fournaise an eastward flank slip

lower jurassic magnetostratigraphy at the breggia gorge ticino switzerland and alpe turati como italy summary the breggia gorge ticino switzerland provides a continuous outcrop of mesozoic limestones covering the time between the lower jurassic and upper cretaceous the jurassic section from the lower pliensbachian to aalenian is well dated by ammonites the limestones of these stages are a good quality recorder of the polarity of the geomagnetic field during this time interval more than 500 cores have been drilled along a 120m thick section with a median distance between cores of about 20cm detailed thermal and af demagnetization and further rock magnetic studies were used to determine the characteristic nrm direction for each sample initial nrm intensities and low field susceptibilities reflect variations in oxidation potential and sedimentation rate during carbonate deposition the breggia section covers an estimated 12 myr of lower to middle jurassic time during which more than 60 distinct reversals of the geomagnetic field are recorded this corresponds to a comparatively high mean reversal frequency of about 5 reversals myr the breggia polarity zonation can be correlated with the nearby section at alpe turati como italy and comparable polarity patterns are recognized in other biostratigraphically well dated magnetostratigraphic profiles from hungary and umbria italy

evolution of magma conduits during the 1998 2000 eruptions of piton de la fournaise volcano reunion island 1 at basaltic volcanoes magma is transported to the surface through dikes magma filled fractures but the evolution of these dikes as eruptions proceed is rarely documented in march 1998 after five and a half years of quiescence piton de la fournaise volcano reunion island entered into a new eruptive phase characterized by intense eruptive activity coeruptive displacements recorded by interferometric synthetic aperture radar insar for the first five eruptions of the cycle are analyzed using 3 d boundary element models combined with a monte carlo inversion method we show that the eruptions are associated with the emplacement of lateral dikes rooted at depths of less than about 1000 m except for the first march 1998 event where an additional deeper source is required the dikes are located above preeruptive seismic swarms this is consistent with nearly isotropic stress caused by repeated dike intrusions and low confining pressure enhanced by the presence of pores in the shallowest 1000 m of the edifice the volumes of the modeled dikes represent 17 of the volume of emitted lava showing that exogenous growth plays a major role in building the volcano by taking into account the preeruptive seismicity and tilt data together with the results of insar data modeling we find that dikes first propagate vertically from a source region below sea level before being injected laterally at shallow depth this behavior is consistent with the presence of levels of neutral buoyancy at shallow depth in the edifice

using upper air conditions to estimate south cascade glacier washington u s a summer balance asimplemodelusesonce dailymeteorologicalvaluesintheu s national centers for environmental predictionand u s national center foratmospheric research ncep ncar re analysis databaseto estimate summerbalanceof south cascade glacier washington u s a each year over1959 99 the rms error 0 30mw e r 2 0 71 is com parable to measurement error the model relates summer balance linearly to temperature t 0 c at 2000m and to snow flux at1650m the altitudes in recent years of the equilib rium line and terminus the snow flux is the product of the humidity and westerly wind component at 850hpa when temperature t 2 c at 1650m temperatures are inter polated linearly betweenthe 850 and 700hpa levels boththe positive 2000mtemperature andthe snow flux are summedfrom 26 aprilto 4 october whenthe summerestimatesare combinedwiththosefromawinterbalancemodelusingthesamedatabase thermserrorin estimating netbalance is 0 40m r 2 0 81 the indicated sensitivities of balance to warm ing of 1 c are 0 51m for summerand 0 24m for winter onthe assumptionthatthetotal 0 75m c 1 sensitivityexists atall altitudes awarmingof only 0 7 c wouldbe sufficientto overcome the1986 98 averagenetbalance 0 5matthe top of theglacier

the deformation field of the august 2003 eruption at piton de la fournaise reunion island mapped by asar interferometry 1 three independent asar interferograms spanning the august 2003 piton de la fournaise eruption reveal a 3 by 3 km asymmetric pattern of range changes centred on the dolomieu crater northern flank it corresponds to 30 cm of displacement towards the satellite east of the eruptive fissures and 7 cm away from the satellite west of the fissures displacements are caused by dyke emplacement below fissures we model the deformation using a 3d mixed boundary element method for elastic media this consists of a dyke defined by six geometric parameters and an overpressure gradient a neighbourhood algorithm was applied to explore this 7 dimensional parameter space the best fit model is a 57 eastward dipping dyke with a base lying around 1520 m a s l the model provides new evidence of the dyke intrusion related seaward displacements of the volcano eastern flank

paleomagnetism of the cretaceous morelos and mezcala formations southern mexico a paleomagnetic study of platform facies carbonate rocks of the mid cretaceous morelos formation and deep water carbonate rocks of the overlying upper cretaceous mezcala formation sampled at zopilote canyon in guerrero state southern mexico indicates that their characteristic magnetization was acquired contemporaneously with folding of these rocks during the late cretaceous laramide orogeny the remanence carrier is interpreted to be magnetite although other mineral phases of high coercivity carry recent secondary overprints the overall mean is of dec 323 1j and inc 36 5j k 162 7 a95 2 7j n 18 sites 64 unfolding comparison with the north america reference direction indicates that this area has experienced a small yet statistically significant counterclockwise direction of 19 2f4 0j similar rotations are documented in other localities from southern mexico rotations are linked to mid tertiary deformation associated with the left lateral strike slip fault system that accommodated motion of the chortis and xolapa blocks d 2002 elsevier science b v all rights reserved

surface roughness and bulk heat transfer on a glacier comparison with eddy correlation more than 100 simultaneously measured profiles of wind speed and temperature were analyzed to determine the aerodynamic and thermal roughness lengths of glacier ice the results proved to be extremely sensitive to measurement height which is difficult to define precisely on the hummocky terrain of a glacier therefore aerodynamic roughness lengths were estimated from the microtopography of the surface yielding 2 46 mm for ice and 5 5 mm for snow despite the indeterminate nature of the profile analysis it did support the view that the thermal roughness length must decrease as the roughness reynolds number increases a relationship which has been modelled in the literature good agreement between bulk transfer estimates and eddy correlation measurements of fhe sensible heat flux density on melting ice and snow was obtained by combining the aerodynamic roughness length with a suitable model for thermal roughness length

upper air model of summer balance on mount rainier usa in 2003 07 summer balance was measured at altitudes between 1700 and 3382 m a s l on two glaciers on mount rainier washington state usa 46 85 n 121 72 w 4400 m a s l south facing nisqually glacier and east northeast facing emmons glacier upper air temperatures at the nearest gridpoint in the ncep ncar reanalysis database are used in a distributed over altitude positive degree day pdd model for each glacier the model used the same coefficients at all altitudes for all years the rms model error was 0 65 r 2 0 87 and 0 78 m a 1 w e r 2 0 93 for nisqually and emmons glaciers respectively although pdd work generally uses different coefficients for snow and ice surfaces and the duration of exposure of those surfaces varies with altitude error in this single coefficient model is nearly uncorrelated with altitude values of coefficients obtained are within the range of those found in other pdd work the degree day coefficient however differs markedly between the two glaciers and is shown to be controlled by the difference between them in vertical gradient of measured summer balance it is smaller for nisqually glacier where solar radiation is a stronger contributor to melt and larger for emmons glacier where it is a weaker contributor over 1948 2007 when the model calibrated over 2003 07 was applied to the upper air temperatures estimated summer balance was 0 4 m a 1 less negative over 1962 83 than before and 0 6 m a 1 less negative than after corresponding roughly with changes of the northeast pacific sea surface temperatures

the mass balance of mccall glacier brooks range alaska u s a its regional relevance and implications for climate change in the arctic mccall glacier has the only long term mass balance record in arctic alaska average annual balances over the periods 1958 72 and 1972 93 were 15 and 33cm respectively recent annual balances 1993 96 are about 60 cm and the mass balance gradient has increased for an arctic glacier with its low mass exchange rate this marks a significant negative trend recently acquired elevation profiles of mccall glacier and ten other glaciers within a 30 km radius were compared with topographic maps made in 1956 or 1973 most of these glaciers had average annual mass balances between 25 and 33 cm while mccall glacier averaged 28 cm for 1956 93 indicating that it is representative of the region in contrast changes in terminus position for the different glaciers vary markedly thus mass balance trends in this region cannot be estimated from fractional length changes at time scales of a few decades we developed a simple degree day accumulation mass balance model for mccall glacier the model was tested using precipitation and radiosonde temperatures from weather stations at inuvik canada and barrow kaktovik and fairbanks alaska and was calibrated with the measured balances the inuvik data reproduce all measured mass balances of mccall glacier well and also reproduce the long term trend towards more negative balances data from the other stations do not produce satisfactory model results we speculate that the arctic front oriented east west in this region causes the differences in model results

pre cretaceous tectonic evolution of the pacific plate and extension of the geomagnetic polarity reversal time scale with implications for the origin of the jurassic quiet zone abstract linear magnetic anomalies resulting from seafloor spreading were mapped in the vicinity of the magnetic bight in the western pacific ocean new aeromagnetic data allowed the magnetic bight to be more accurately mapped from m21 to m28 and enabled the identification of low amplitude magnetic lineations in the jurassic quiet zone these lineations were formed by magnetic field reversals prior to m29 a revised jurassic geomagnetic polarity reversal time scale was constructed with nineteen reversals older than m29 numbered m30 m38 these reversals extend the record of geomagnetic polarity back in time by approximately 8 ma and are important constraints on the origin of the quiet zone in particular they imply that the jurassic was not a period of constant normal polarity an explanation offered by some authors further they cast doubt on a model of systematically decreasing geomagnetic field strength with increasing age during this period the early history of the northern pacific plate and pacific farallon izanagi p f i triple junction was traced by mapped magnetic isochrons the pacific plate seems to have evolved from a small plate that formed near the phoenix farallon izanagi triple junction about 180 188 m y ago at approximately 17 n 160 e in present coordinates until m21 time the evolution of the northern pacific plate was relatively simple and the p f i triple junction migrated north northwest with respect to the pacific

critical fluid injection volumes for uncontrolled fracture ascent hydro fracturing is a routine industrial technique whose safety depends on fractures remaining confined within the target rock volume both observations and theoretical models show that if the fluid volume is larger than a critical value pockets of fluid can propagate large distances in the earths crust in a self sustained uncontrolled manner existing models for such critical volumes are unsatisfactory most are two dimensional and depend on poorly constrained parameters typically the fracture length here we derive both analytically and numerically in three dimensions scale independent critical volumes as a function of only rock and fluid properties we apply our model to gas water and magma injections in laboratory industrial and natural settings showing that our critical volumes are consistent with observations and can be used as conservative estimates we discuss competing mechanisms promoting fracture arrest whose quantitative study could help to assess more comprehensively the safety of hydro fracturing operations

magnetostratigraphy of a middle jurassic red bed sequence from southern mexico abstract palaeomagnetic results for 178 oriented samples from five sections combined thickness of 75 m of the red bed tecomazuchil formation southern mexico are reported the formation has been assigned to the bathonian callovian and the sections studied cover its uppermost portion alternating field a f thermal combination of a f and thermal and chemical demagnetizations were used to investigate the magnetic stability and vectorial directions of all samples most samples showed apparent stable behaviour with dominantly single or two component magnetization reverse and intermediate polarity samples more often showed two and multi component remanences behaviour during demagnetization and rock magnetic experiments indicate that the remanences reside in magnetite haematite and goethite the magnetostratigraphic results reveal a polarity pattern characterized by frequent polarity changes

conditions for the arrest of a vertical propagating dyke magma ascent towards the earth s surface occurs through dyke propagation in the vast majority of cases we investigate two purely mechanical effects unrelated to cooling or solidification that lead to the arrest of propagation so that no eruption occurs the first is that the input of magma from the source is not maintained continuously such that a fixed volume of magma is released laboratory experiments show that in this case the dyke stops at a finite distance from the source this behaviour is specific to the fracturing process in 3 d we derive a relationship for the minimum magma volume required for an eruption as a function of magma buoyancy and source depth when large magma volumes are available eruption may also be prevented by a thick low density layer in the upper crust numerical studies of dyke propagation show that the dyke continues to rise even though it is negatively buoyant magma accumulates in a swollen nose region at the interface between the low density layer and the dense basement magma overpressure is largest at this interface and increases with increasing penetration into the upper layer it may become large enough to induce horizontal fractures in the dyke walls and lateral intrusion of a sill which prevents eruption this requires that the thickness of the low density layer exceeds a threshold value that depends on the density contrast between magma and host rock if the magma volume is smaller than a threshold value neither sill intrusion nor eruption are possible and magma gets stored in a horizontal blade shaped dyke straddling the interface scaling laws for variations of ascent rate and for the minimum magma volume allow diagnosis of a failed eruption

tectonic evolution of the northern pacific plate and pacific farallon izanagi triple junction in the late jurassic and early cretaceous m21 m10 abstract magnetic lineations in the northwestern pacific near the shatsky plateau were interpreted to trace the tectonic history of the northern pacific plate from the time of anomalies m21 to m10 at m22 time the pacific farallon izanagi p f i triple junction was located southwest of the plateau and migrating north northwest with respect to the pacific plate shortly thereafter the stress field acting on the three plates changed significantly and the pacific lzanagi ridge reacted by pivoting 24 clockwise from m21 to m19 time several ridge propagation events occurred while the ridge adjusted to the new spreading regime to the east of the m22 location of the junction it appears that this reorganization triggered a series of at least three ridge jumps along the pacific farallon ridge the geometry of magnetic isochron m21 suggests that several triple junctions existed simultaneously during the reorganization bordering one or more microplates differences in the spreading rate of the japanese magnetic lineations north of the plateau imply that one microplate which we call the shatsky microplate existed until about m15 m13 time it was probably captured by either the farallon or the izanagi plate and subsequently destroyed by subduction after m15 the p f i triple junction was reformed on seafloor that is now beneath the shatsky plateau the junction drifted generally northeast either in a ridge ridge ridge or in a ridge fault fault configuration perhaps alternating between the two from m11 m10 time the stress field on the three plates changed again and the pacific farallon ridge southeast of the plateau reoriented 15 clockwise at this time the p f i junction assumed a ridge ridge ridge geometry at the northeast end of the plateau

climate sensitivity of glaciers in southern norway application of an energy balance model to nigardsbreen hellstugubreen and alfotbreen three glaciers in southern norway with very different massbalance characteristics are studied with an energy balance model of the ice snow surface the model simulates the observed mass balance profiles in a satisfactory way and can thus be used with some confidence in a study of climate sensitivity calculated changes in equilibrium line altitude for a 1 k temperature increase are 110 108 and 135 in for nigardsbreen hellstugubreen and alfotbreen respectively the corresponding changes in mass balance averaged over the entire glacier area are 0 88 0 715 and 1 11 in year water equivalent runs with an ice flow model for nigardsbreen to which calculated mass balance profiles are imposed predict that the front will advance by 3 km for a 1 k cooling and will retreat by as much as 6 5 km for a 1 k warming the response to a 10 increase in precipitation would be a 2 km advance of the snout whereas a 4 km retreat is predicted for a 10 decrease this large sensitivity as compared to many other glaciers is to a large extent due to the geometry of nigardsbreen

eruption versus intrusion arrest of propagation of constant volume buoyant liquid filled cracks in an elastic brittle host received 9 january 2009 revised 31 march 2009 accepted 3 april 2009 published 5 june 2009 1 when a volume of magma is released from a source at depth one key question is whether or not this will culminate in an eruption or in the emplacement of a shallow intrusion we address some of the physics behind this question by describing and interpreting laboratory experiments on the propagation of cracks filled with fixed volumes of buoyant liquid in a brittle elastic host experiments were isothermal and the liquid was incompressible the cracks propagated vertically because of liquid buoyancy but were then found to come to a halt at a configuration of static mechanical equilibrium a result that is inconsistent with the prediction of the theory of linear elastic fracture mechanics in two dimensions we interpret this result as due to a three dimensional effect at the curved crack front horizontal cracking is necessary in order for vertical propagation to take place as the crack elongates and thins the former becomes progressively harder and in the end impossible to fracture we present a scaling law for the final length and breadth of cracks as a function of a governing dimensionless parameter constructed from the liquid volume the buoyancy and host fracture toughness an important implication of this result is that a minimum volume of magma is required for a volcanic eruption to occur for a given depth of magma reservoir

estimating south cascade glacier washington u s a mass balance from a distant radiosonde and comparison with blue glacier a simple flux model using twice daily measurements of wind humid ity and temperature from standard upper air levels in a distant radiosonde estimated winter balance of south cascade glacier over 1959 98 with error 0 24 m w e correla tion between net and winter balance is strong the model estimates net balance with error 0 53 m w e over the past 40 years average net balance of south cascade glacier has been strongly negative 0 46 m w e and it has been shrinking steadily in com parison 200 km wsw at blue glacier the average balance has been less negative 0 13 m w e that glacier has undergone little change over the 40 years balance histories of the two glaciers are positively correlated r 0 54 and south cascade has been more out of balance than blue presumably because it is still adjusting to climate change since the little ice age recent warming and drying has made the net balance of both glaciers strongly negative since 1976 0 84 m w e at south cascade 0 56 m w e at blue if south cascade glacier were in balance with the 1986 1998 climate it would be about 1 4 of its present area if conditions persist retreat of both glaciers is inevitable

finding realistic dike models from interferometric synthetic aperture radar data the february 2000 eruption at piton de la fournaise dike intrusions often cause complex ground displacements that are not sufciently explained by simple analytical models we develop a method to nd complex and realistic dike geometries and overpressures from interferometric synthetic aperture radar insar data this method is based on a combination of a boundary element method with realistic topography and a neighbourhood algorithm inversion dike model geometry is roughly a quadrangle with its top reaching the ground the inversion has two stages search and appraisal the appraisal stage involves calculations of model marginal probability density functions using mist val ues calculated during the search stage the mist function takes into account the variance and correlation of data noise synthetic tests show that a model is successfully retrieved within predicted narrow condence intervals we apply the method on insar data of the february 2000 ank eruption at piton de la fournaise and get a trapezoid dike dipping seaward 61 0 n 67 3 with its bottom passing 800n1000 m beneath the summit a model with a basal slip plane does not better explain observed asymmetric displacements and thus this asymmetry is solely attributed to the dipping dike the dike lies above a narrow band of pre eruption seis micity suggesting that lateral magma propagation occurred neglecting topography results in poor modeling at depth and in overestimations of overpressure or opening height both about 30 and volume about 20

slip on wavy frictional faults is the 3rd dimension a sticking point abstract the formulation for the 3d triangular displacement discontinuity boundary element method with frictional constraints is described in detail its accuracy in comparison to analytical solutions is then quantified we show how this can be used to approximate stress intensity factors at the crack tips using this method we go on to quantify how slip is reduced on fault surfaces with topography where the asperities are approximated as a sinusoidal waveform i e corrugations we use stress boundary conditions compressive orientated such that frictional contacts shear we show that slip reductions relative to planar faults for 2d line and 3d penny shaped crack models are comparable within 10 when slip is perpendicular to the corrugations using the 3d model we then show how slip is reduced more when corrugation wavelengths are doubled compared to the reduction due to corrugation misalignment with the slip direction when slip is parallel with the corrugation alignment we show that reducing the out of plane stress from the normal traction acting on the fault when planar to that resolved on a perpendicular plane has the same effect as halving the length of the corrugation waveform in terms of slip reduction for a given amplitude

mass balance gradients and climatic change it is generally assumed that the mass balance gradient on glaciers is more or less conserved under climatic change in studies of the dynamic response of glaciers to climatic change one of the following assumptions is normally made i the mass balance perturbation is independent of altitude or ii the mass balance profile does not change it simply shifts up and down observational evidence for such an approach is not convincing on some glaciers the inter annual changes in mass balance seem to be independent of altitude on others not at all moreover it is questionable whether inter annual variation can be projected on different climatic states to see what a physical approach might contribute we developed an altitude dependent mass balance model it is based on the energy balance of the ice snow surface where precipitation is included in a parameterized form and numerical integrations are done through an entire balance year with a 30 min time step atmospheric temperature snowfall and atmospheric transmissivity for solar radiation are all dependent on altitude so a mass balance profile can be calculated slope and exposure of the ice snow surface are taken into account and the effects of these parameters studied in general the calculations were done for 100 m elevation intervals climatological data from the sonnblick observatory austria 3106 m a s l and from vent 2000 m a s l oetztal alps austria served as input for a number of runs simulation of the mass balance profiles for hinterseisferner north easterly exposure and kesselwandferner southeasterly exposure yields reasonable results the larger balance gradient on kesselwandferner is produced by the model so exposure appears to be an important factor here sensitivity of mass balance profiles to shading effects different slope and exposure are systematically studied another section deals with the sensitivity to climatic change perturbations of air temperature cloudiness albedo and precipitation are imposed to see their effects on the mass balance profiles the results clearly show that in general mass balance perturbations depend strongly on altitude they generally increase down glacier and are not always symmetric about the reference state for typical climatic conditions in the alps we found that a 1 k temperature change leads to a change in equilibrium line altitude of 130 m three factors contribute to this large value turbulent heat flux longwave radiation from the atmosphere and fraction of precipitation falling as snow here the albedo feed back increases the sensitivity in a significant way