a proton and electron microprobe study of gallium nickel and zinc distribution in chromian spinel abstract chromian spinels from a number of localities were analyzed by proton and electron microprobes to examine the variation of trace elements in different geological environments chromian spinels studied include those representing ophiolitic complexes layered intrusions in continental areas alaskan type complexes komatiitic subvolcanic sills ni sulfide ores and metamorphosed mafic and ultramafic rocks nickel concentrations range from 30 to 4690 ppm proton microprobe with a mean value of 943 ppm nickel favouring the octahedral sites in the spinel structure displays an overall increase with a decrease in the cr cr al fe 3 ratio nickel partitioning between chromian spinel and mantle silicates appears to be primarily dependent upon the major element composition of the chromian spinel zinc concentrations range from 230 to 9810 ppm proton microprobe with a cluster around 500 ppm ophiolitic chromian spinels display the lowest overall zn values zinc levels appear to discriminate between chromian spinels in chromitite samples from those occurring as accessory chromian spinel in dunites or other rock types chromian spinels that are enclosed in or adjacent to sulfide grains display higher concentrations of zn zinc strongly favouring the tetrahedral sites displays a crude negative correlation with the mg mg fe 2 ratio and appears to vary as a function of temperature all the chromian spinel grains analyzed contain measurable quantities of ga by proton microprobe ranging from 10 to 208 ppm there is a reciprocal relationship between the ga concentration and the cr cr al fe 3 ratio and a crude positive correlation between the ni and ga concentrations measured ga concentrations in chromian spinel and whole rock samples are supportive of the experimental mineral melt partition coefficient of malvin and drake 1987 similar to the peridotite xenoliths mid ocean ridge basalts and oceanic island basalts ga correlates well with al 2 o 3 in the case of the ophiolitic chromian spinels and most of those representing layered complexes the ophiolitic chromian spinels seem to have crystallized from melts whose compositions are similar to those of partial melts of the upper mantle

crustal deformation associated with glacial fluctuations in the eastern chugach mountains alaska the changes of the solid earth in south central alaska in response to two major glacial fluctuations on different temporal and spatial scales have been estimated and we evaluated their influence on the stress state and ongoing tectonic deformation of the region during the recent 1993 1995 bering glacier surge a large transfer of ice from the bagley ice field to the bering glacier terminus region occurred we estimated the elastic displacement of the solid earth due to ice mass redistribution from global positioning system gps measurements at sites near the surging glacier we can account for these displacements by transfer of an ice volume of about 14 km3 from the surge reservoir area to the terminus region we examined the background seismicity ml 2 5 before during and after the surge we found that the occurrence of small earthquakes ml 4 0 in the surge reservoir region increased during the surge time interval possibly in response to a decrease in ice mass this suggests that a small decrease in the vertical stress 3 could be enough to modulate the occurrence of small shallow earthquakes in this dominantly thrust fault setting during this century the southern alaska coastal glaciers have been undergoing an overall decrease in volume based on our compilation of changes in the extent and thickness of the coastal glaciers between the malaspina and bering we calculated surface displacements due to the earth s viscoelastic response to annual thinning and to the cumulative retreat over the last 100 years the uplift of the region due to an average annual thinning rate of 1 6 m yr in the ablation region is 1 12 mm yr for our reference model with a viscosity of 5 1019 pa s for depths between 40 and 200 km the total viscoelastic response due to the retreat over the last century may be as much as a couple of meters within the coastal ablation zone near icy bay the maximum decrease in v between 0 and 10 km was 1 0 mpa which is significant in relation to the stress drops in recent earthquakes 2 to 10 mpa but small in relation to the estimated tectonic stress magnitude therefore the occurrence of an earthquake such as the st elias 1979 ms 7 2 may have been advanced in time however most of the ongoing stress accumulation would be primarily due to tectonic forces

tide model accuracy in the amundsen sea antarctica from radar interferometry observations of ice shelf motion 1 this study assesses the accuracy of tide model predictions in the amundsen sea sector of west antarctica tide model accuracy in this region is poorly constrained yet tide models contribute to simulations of ocean heat transfer and to the removal of tidal signals from satellite observations of ice shelves we use two satellite based interferometric synthetic aperture radar insar methods to measure the tidal motion of the dotson ice shelf at multiple epochs a single difference technique that measures tidal displacement and a double difference technique that measures changes in tidal displacement we use these observations to evaluate predictions from three tide models tpxo7 1 cats2008a opt and fes2004 all three models perform comparably well exhibiting root mean square deviations from the observations of 9 cm single difference technique and 10 cm double difference technique care should be taken in generalizing these error statistics because 1 the dotson ice shelf experiences relatively small semidiurnal tides and 2 our observations are not sensitive to all tidal constituents an error analysis of our insar based methods indicates measurement errors of 7 and 4 cm for the single and double difference techniques respectively a model based correction for the effect of fluctuations in atmospheric pressure yields an 6 improvement in the agreement between tide model predictions and observations this study suggests that tide model accuracy in the amundsen sea is comparable to other antarctic regions where tide models are better constrained these methods can be used to evaluate tide models in other remote antarctic waters

surface velocity and mass balance of ice streams d and e west antarctica over 75 000 surface velocity measurements are extracted from sequential satellite imagery of ice streams d and e to reveal a complex pattern of flow not apparent from previous measurements horizontal and vertical strain rates calculated from surface velocity indicate that the bed experiences larger basal shear where the surface of these ice streams is rougher ten airborne radar profiles and one surface based radar profile of ice thickness make possible the calculation of mass balance for longitudinal sections of each ice stream improved data collection methods increase data density substantially reducing random errors in velocity however systematic errors continue to limit the ability of the flux differencing technique used here to resolve local variations in mass balance nevertheless significant local variations in mass balance are revealed while overall ice streams d and e are in approximate equilibrium an earlier estimate of the net mass balance for ice stream d is improved

calculation of ice velocities in the jakobshavn isbrae area using airborne laser altimetry abstract the ability to measure velocities of fast moving glaciers is essential to the understanding and interpretation of their dynamics and related processes this is especially important in the jakobshavn drainage basin of the greenland ice sheet where a significant portion of the ice sheet mass loss occurs and the iceberg calving rate is high in this article we present a method for using airborne laser altimetry data to determine surface velocities in portions of the jakobshavn drainage basin that have distinct elevation features by examining correlations between repeat elevation surveys the motion of these features the most distinct of which are crevasses is tracked results show that for areas with a standard deviation in elevation in excess of 1 m displacement of features can be tracked to a precision of 1 2 m and the corresponding velocities can be retrieved the maximum velocity of the jakobshavn isbrae at its calving front is found to be nearly 7 km yr 1 ice stream boundaries and flow patterns can also be observed in the derived velocity data

greenland ice sheet motion coupled with daily melting in late summer 1 we use ground based and satellite observations to detect large diurnal and longer period variations in the flow of the greenland ice sheet gris during late summer that are strongly coupled with changes in its surface hydrology the diurnal signals are associated with periodic changes in surface melting and the longer period signals are associated with the episodic drainage of supra glacial lakes ice velocity doubles around 2 hours after peak daily melting and returns approximately to wintertime levels around 12 hours afterwards demonstrating an intimate link between the surface and basal hydrology during late summer the ice sheet accelerates by 35 per positive degree day of melting the observed link between surface melting and enhanced flow is typical of alpine glaciers which may provide an appropriate analogue for the evolution of the gris in a warming climate

three dimensional surface velocities of storstrommen glacier greenland derived from radar interferometry and ice sounding radar measurements non steady state vertical velocities of up to 5 m y 1 exceed the vertical surface parallel flow components over much of the ablation area of storstrommen a large outlet glacier from the east greenland ice sheet neglecting a contribution to the vertical velocity of this magnitude results in substantial errors up to 20 also on the south north component of horizontal velocities derived by satellite synthetic aperture radar interferometry insar measurements in many glacier environments the steady state vertical velocity component required to balance the annual ablation rate is 5 to 10 m y 1 or more this indicates that the surface parallel flow assumption may be problematic also for glaciers in steady state here we derive the three dimensional surface velocity distribution of storstrommen by using the principle of mass conservation to combine insar measurements from ascending and descending satellite tracks with airborne ice sounding radar measurement of ice thickness the results are compared to insar velocities previously derived by using the assumption of surface parallel flow and to velocities obtained by inin situ gps measurements the velocities derived by using the principle of mass conservation are in better agreement with the gps velocities than the previously calculated velocities derived with the assumption of surface parallel flow

observations of ice sheet motion in greenland using satellite radar interferometry we present interferometric observations of ice sheet motion in western greenland based on pairs of ers 1 synthetic aperture radar sar images these observations provide the first detailed regional view of ice motion associated with dynamically supported topography near the margin of an ice sheet the interferograms of this area are much more complicated than other interferograms of ice sheets presented to date we devote the largest part of this paper to explaining the source of the complexity in these interferograms a synthetic interferogram based on a simple model helps to illustrate the effects of different components of the ice velocity field in interferometric data and suggests a method for estimating the large scale ice velocity field from such data

multi track extraction of two dimensional surface velocity by the combined use of differential and multiple aperture insar in the amery ice shelf east antarctica abstract glaciers and ice streams drain the ice from the ice sheets to the ice shelves and contribute to global sea level changes therefore ice velocity is an essential parameter for the assessment of mass balance in this paper we propose an approach for the multi track extraction of two dimensional ice surface velocity by the combined use of multiple aperture interferometry mai and differential synthetic aperture radar interferometry dinsar the azimuth and ground range ice movements of each individual track are first estimated by the use of mai and dinsar respectively a seamless two dimensional ice velocity map is then achieved by calibration and mosaicking of the estimated velocity of the multi temporal and multi track measurements over a large area finally the dynamic behavior of the amery ice shelf is analyzed by formulating a long term series of ice flow velocities consisting of historical surface velocities 1968 1990 the estimated surface velocity by the proposed method with ers 1 2 data 1996 existing surface velocity products such as the radarsat 1 antarctic mapping project ramp velocities 1997 2000 and rignot s results 2007 2010 as well as the estimated velocities obtained by the use of the offset tracking method from landsat 8 images 2013 2014 the results show that the estimated velocity obtained by the use of the proposed method is superior to the other methods and the long term series of ice velocity measurements shows that the ice velocity in the amery ice shelf has hardly changed over the past 45 years 1968 2014 we conclude that the ice flow velocity of the amery ice shelf has showed a slight deceleration over the past 45 years

tracking subpixel scale sastrugi with advanced land imager high radiometric resolution imagery from the advanced land imager ali can detect the spatial reflectance variations associated with sastrugi snow dunes on ice sheets this is shown in theory by considering the appropriate snr ratio of ali as compared with eight bit optical sensors and in practice with multitemporal ali imagery comparison of ali imagery spanning 7 5 months also shows that the reflectance pattern associated with sastrugi can persist over this interval offering the potential of their use for measuring ice sheet velocity in uncrevassed regions

application of image cross correlation to the measurement of glacier velocity using satellite image data abstract image to image cross correlation software is applied to pairs of digital satellite images to map the velocity field of moving ice this technique uses small scale glacial surface features such as crevasse scars and snow dunes as markers on the surface of the moving ice displacements of the surface features are mapped by selecting small image areas centered on distinct features or by dividing a large area of densely featured glacial surface into a grid of areas and searching a subsequent image for matching areas using a cross correlation algorithm interpolation of the peak correlation values allows the displacements to be measured to subpixel accuracy resulting in very precise velocity measurements cross correlation is also applied to provide image coregistration in areas devoid of bedrock exposures in such areas subtle large scale topographic undulations in the ice surface related to underlying bedrock structure may be correlated by using large image areas and low pass filtered images both types of applications are demonstrated using ice stream d and ice stream e in west antarctica as test areas a high resolution map of the velocity field of the central portion of ice stream e generated by the displacement measuring technique is presented the use of cross correlation software is a significant improvement over previous manually based photogrammetric methods for velocity measurement and is far more cost effective than in situ methods in remote polar areas

satellite radar interferometry for monitoring ice sheet motion application to an antarctic ice stream satellite radar interferometry sri provides a sensitive means of monitoring the flow velocities and grounding line positions of ice streams which are indicators of response of the ice sheets to climatic change or internal instability the detection limit is about 1 5 millimeters for vertical motions and about 4 millimeters for horizontal motions in the radar beam direction the grounding line detected by tidal motions where the ice goes afloat can be mapped at a resolution of 0 5 kilometer the sri velocities and grounding line of the rutford ice stream antarctica agree fairly well with earlier ground based data the combined use of sri and other satellite methods is expected to provide data that will enhance the understanding of ice stream mechanics and help make possible the prediction of ice sheet behavior

estimation of glacier ice extinction using long wavelength airborne pol insar in the recent years there has been increased interest in using synthetic aperture radar sar to study and monitor glaciers and ice sheets for glaciological and climate change research this paper describes the estimation of ice extinctions through the modeling of polarimetric interferometric sar pol insar coherences as a combination of a surface contribution from the snow firn interface and wind induced sastrugi features and a volume response ground to volume scattering ratios derived from a novel polarimetric decomposition are used in conjunction with pol insar coherence magnitudes to invert the extinction of the ice layer the inversion is performed for experimental airborne pol insar data at l band and p band acquired by the german aerospace center s dlr e sar system over the austfonna ice cap in svalbard norway as part of the 2007 icesar campaign extinction dependences on frequency and glacier facie are investigated and validation is performed comparing ground penetrating radar data to sar backscatter and extinction values best extinction results are obtained at shallow incidence angles with small wavenumbers and for low ground to volume scattering ratios for swath areas in mid range to far range accuracies of 25 in extinction are anticipated when averaging over 100 effective looks for a four baseline inversion constraining solutions to vertical wavenumbers of 0 01 kz 0 1 to allow inversion using single baseline pol insar the proposed model is of limited complexity suggested extensions for a more realistic scattering scenario include incorporating multiple englacial ice scattering layers and improving the way multiple baselines are combined

satellite image derived velocity field of an antarctic ice stream the surface velocity of a rapidly moving ice stream has been determined to high accuracy and spatial density with the use of sequential satellite imagery variations of ice velocity are spatially related to surface undulations and transverse velocity variations of up to 30 percent occur such large variations negate the concept of plug flow and call into question earlier mass balance calculations for this and other ice streams where sparse velocity data were used the coregistration of images with the use of the topographic undulations of the ice stream and the measurement of feature displacement with cross correlation of image windows provide significant improvements in the use of satellite imagery for ice flow determination

numerical simulations of glacial valley longitudinal profile evolution glaciers shape alpine landscapes they broaden valley bottoms enhance local valley relief generate multiple steps overdeepen valley floors and cause tributary valleys to hang these distinctive glacial signatures result from 10 4 10 5 yr of erosion during which swings in climate drive advances and retreats of alpine glaciers we use a numerical model of glacial erosion to explore the development of the longitudinal profiles of glaciated valleys the model is driven by the past 400 k y of variable climate because both sliding speed which dictates abrasion rate and water pressure fluctuations which strongly modulate quarrying rate should peak at the equilibrium line altitude ela we expect the locus of most rapid erosion to follow the transient ela simulations of a single glacial valley show rapid flattening of the longitudinal profile inclusion of a tributary glacier creates a step immediately downvalley of the tributary junction that persists over multiple glaciations and commonly leaves the tributary valley hanging steps and overdeepenings result from an increase in ice discharge immediately below the tributary junction which is accommodated primarily by increased ice thickness and hence sliding rate the size of the step increases with the ratio of tributary to trunk ice discharge while the height of a hanging valley reflects the difference in the time integrated ice discharge in tributary and trunk valleys and therefore increases as the discharge ratio decreases

surface velocities and ice front positions of eight major glaciers in the southern patagonian ice field south america from 2002 to 2011 abstract the patagonian ice fields are known to have undergone rapid retreat of frontal positions and significant thinning of its glaciers over the past decades however surface velocities have been measured at only a few of these glaciers thus it remains uncertain if and to what extent the glacier dynamics has changed over time and contributed to ice loss in these ice fields in this study we examine the temporal evolution of flow velocities and ice front positions at eight major glaciers in the southern patagonian ice field spi hielo patagonico sur by using advanced synthetic aperture radar asar images from the environmental satellite envisat launched in 2002 by the european space agency and advanced land observation satellite phased array type l band synthetic aperture radar alos palsar data recorded from 2002 to 2011 the examined eight glaciers include glaciar jorge montt occidental pio xi or bruggen o higgins viedma upsala perito moreno and grey not all the glaciers revealed significant changes in frontal positions and flow velocities in the study period we detected significant temporal velocity changes at glaciar upsala jorge montt occidental and pio xi among these four glaciers glaciars upsala jorge montt and occidental revealed significant acceleration and terminus retreat and were undergoing dynamic thinning the markedly different absolute velocities but equally large longitudinal near terminus stretching at the three glaciers support a calving model based on crevasse depth criteria which predict a calving position where crevasse depths are equal to ice thickness crevasse depths are controlled by the longitudinal stretching rate meanwhile glaciar pio xi revealed complex spatial and temporal evolution in surface velocities without significant retreat and its dynamics remains enigmatic

ice surface morphology and flow on malaspina glacier alaska implications for regional tectonics in the saint elias orogen the saint elias mountains in southern alaska are located at a structural syntaxis where the coastal thrust and fold belt of the fairweather plate boundary intersects thrust faults and folds generated by collision of the yakutat terrane the axial trace of this syntaxis extends southeastward out of the saint elias mountains and beneath malaspina glacier where it is hidden from view and cannot be mapped using conventional methods here we examine the surface morphology and flow patterns of malaspina glacier to infer characteristics of the bedrock topography and organization of the syntaxis faults and folds beneath the eastern part of the glacier trend northwest and reflect dextral transpression near the terminus of the fairweather fault system those beneath the western part of the glacier trend northeast and accommodate folding and thrust faulting during collision and accretion of the yakutat terrane mapping the location and geometry of the structural syntaxis provides important constraints on spatial variations in seismicity fault kinematics and crustal shortening beneath malaspina glacier as well as the position of the collisional deformation front within the yakutat terrane we also speculate that the geometrical complexity of intersecting faults within the syntaxis formed a barrier to rupture propagation during two regional mw 8 1 earthquakes in september 1899

quantification of everest region glacier velocities between 1992 and 2002 using satellite radar interferometry and feature tracking quincey d j luckman a benn d 2009 quantification of everest region glacier velocities between 1992 and 2002 using satellite radar interferometry and feature tracking journal of glaciology 55 192 596 606 sponsorship knowledge transfer project no 3742

the role of lateral drag in the dynamics of ice stream b antarctica the partitioning of resistive force between the bed and sides of ice stream b antarctica is obtained for three large areas that have been measured using repeat aerial photogrammetry problems associated with data errors and local variations in ice strength and velocity are reduced by considering the areally averaged budget of forces for each photo block results indicate that the bed under ice stream b must be very weak and unable to provide muche resistance mechanical control on this ice stream emanates almost entirely from the lateral margins

the displacement field of the landers earthquake mapped by radar interferometry geodetic data obtained by ground or space based techniques can be used to infer the distribution of slip on a fault that has ruptured in an earthquake although most geodetic techniques require a surveyed network to be in place before the earthquake1 3 satellite images when collected at regular intervals can capture co seismic displacements without advance knowledge of the earthquake s location synthetic aperture radar sar interferometry first introduced4 in 1974 for topographic mapping5 8 can also be used to detect changes in the ground surface by removing the signal from the topography9 10 here we use sar interferometry to capture the movements produced by the 1992 earthquake in landers california11 we construct an interferogram by combining topographic information with sar images obtained by the ers 1 satellite before and after the earthquake the observed changes in range from the ground surface to the satellite agree well with the slip measured in the field with the displacements measured by surveying and with the results of an elastic dislocation model as a geodetic tool the sar interferogram provides a denser spatial sampling 100 m per pixel than surveying methods1 3 and a better precision 3 cm than previous space imaging techniques12 13

greenland ice sheet surface properties and ice dynamics from ers 1 sar imagery c band synthetic aperture radar sar imagery from the european space agency s ers 1 satellite reveals the basic zonation of the surface of the greenland ice sheet the zones have backscatter signatures related to the structure of the snowpack which varies with the balance of accumulation and melt at various elevations the boundaries of zones can be accurately located with the use of this high resolution imagery the images also reveal a large flow feature in northeast greenland that is similar to ice streams in antarctica and may play a major role in the discharge of ice from the ice sheet

measurement of ice sheet topography using satellite radar interferometry detailed digital elevation models dems do not exist for much of the greenland and antarctic ice sheets radar altimetry is at present the primary in many cases the only source of topographic data over the ice sheets but the horizontal resolution of such data is coarse satellite radar interferometry uses the phase difference between pairs of synthetic aperture radar sar images to measure both ice sheet topography and surface displacement we have applied this technique using ers 1 sar data to make detailed i e 80 m horizontal resolution maps of surface topography in a 100 km by 300 km strip in west greenland extending northward from just above jakobshavns isbrae comparison with a 76 km long line of airborne laser altimeter data shows that we have achieved a relative accuracy of 2 5m along the profile these observations provide a detailed view of dynamically supported topography near the margin of an ice sheet in the final section we compare our estimate of topography with phase contours due to motion and confirm our earlier analysis concerning vertical ice sheet motion and complexity in ers 1 sar interferograms

ice sheet motion and topography from radar interferometry both topography and motion information are present in repeat pass ers 1 interferograms over ice sheets the authors demonstrate that the topography is separable from the surface displacement field when a sequence of radar images are available if the velocity field is constant over the time span of observation the topography can be derived from differential interferograms formed from sequential observations with this measurement a pure displacement field can then be obtained by removal of the topographic contribution to the interferometric phase at each pixel further they discuss how the vertical and horizontal components of displacement affect the interferometrically derived motion field they illustrate their approach with four successive 3 day repeat ers 1 images of a flow feature in northeastern greenland

deformation during terrane accretion in the saint elias orogen alaska the saint elias orogen of southern alaska and adjacent canada is a complex belt of mountains formed by collision and accretion of the yakutat terrane into the transition zone from transform faulting to subduction in the northeast pacific the orogen is an active analog for tectonic processes that formed much of the north american cordillera and is also an important site to study 1 the relationships between climate and tectonics and 2 structures that generate large to great magnitude earthquakes the yakutat terrane is a fragment of the north american plate margin that is partly subducted beneath and partly accreted to the continental margin of southern alaska interaction between the yakutat terrane and the north american and pacific plates causes significant differences in the style of deformation within the terrane deformation in the eastern part of the terrane is caused by strike slip faulting along the fairweather transform fault and by reverse faulting beneath the coastal mountains but there is little deformation immediately offshore the central part of the orogen is marked by thrusting of the yakutat terrane beneath the north american plate along the chugach saint elias fault and development of a wide thin skinned fold and thrust belt strike slip faulting in this segment may be localized in the hanging wall of the chugach saint elias fault or dissipated by thrust faulting beneath a north northeast trending belt of active deformation that cuts obliquely across the eastern end of the fold and thrust belt superimposed folds with complex shapes and plunging hinge lines accommodate horizontal shortening and extension in the western part of the orogen where the sedimentary cover of the yakutat terrane is accreted into the upper plate of the aleutian subduction zone these three structural segments are separated by transverse tectonic boundaries that cut across the yakutat terrane and also coincide with the courses of piedmont glaciers that flow from the topographic backbone of the saint elias mountains onto the coastal plain the malaspina fault pamplona structural zone separates the eastern and central parts of the orogen and is marked by reverse faulting and folding onshore most of this boundary is buried beneath the western or agassiz lobe of the malaspina piedmont glacier the boundary between the central fold and thrust belt and western zone of superimposed folding lies beneath the middle and lower course of the bering piedmont glacier

ice velocity determined using conventional and multiple aperture insar abstract we combine conventional interferometric synthetic aperture radar insar and multiple aperture insar mai to determine the ice surface velocity on the langjokull and hofsjokull ice caps in iceland in 1994 this approach allows the velocity of the 20 principal ice cap outlet glaciers to be fully resolved we show that mai leads to displacement estimates of finer resolution 15 versus 150 m and superior precision 5 versus 15 cm to those afforded by the alternative technique of speckle tracking using sar data acquired in ascending and descending orbits we show that ice flows within 15 of the direction of maximum surface slope across 66 of the ice caps it is therefore possible to determine ice displacement over the majority of the ice caps using a single sar image pair thereby reducing errors associated with temporal fluctuations in ice flow

using multiple radarsat insar pairs to estimate a full three dimensional solution for glacial ice movement 1 multiple sar interferograms are used to solve for the full 3 dimensional displacement of the surface of the henrietta nesmith glacier in northern ellesmere island canada the approach exploits the incidence angle flexibility of different ascending and descending beam modes and the azimuth angle diversity which occurs when different incidence angles are used at high latitudes line of sight displacements are estimated in 3 different orientations from the terrain corrected unwrapped differential phase and used to solve for the displacements in a local east north up frame uncertainty in the absolute line of sight displacements limits the absolute accuracy for vertical displacement however the relative solution coupled with knowledge of the surface slope allows spaceborne mapping of relative glacier thickening or thinning with unprecedented spatial resolution and with an accuracy of order a millimeter per day

rapid discharge connects antarctic subglacial lakes a hidden subglacial world consisting of more than 140 lakes lies beneath the antarctic ice sheet it is widely assumed that these lakes are a static ecosystem cut off from each other and the rest of the world far from it according to a 16 month study of surface elevation changes in the region changes indicating a rapid discharge of water from one lake to another were detected and it is possible that the entire subglacial drainage basin is flushed through periodically by massive water transfers observation of surface elevation changes over 16 months in an area of the east antarctic ice sheet overlying subglacial lakes suggests a rapid discharge of one lake to at least two other lakes involving a water volume of 1 8 km3 in conflict with previous expectations that subglacial lakes have long residence times and slow circulations the existence of many subglacial lakes1 provides clear evidence for the widespread presence of water beneath the east antarctic ice sheet but the hydrology beneath this ice mass is poorly understood2 such knowledge is critical to understanding ice flow basal water transfer to the ice margin glacial landform development and subglacial lake habitats here we present ice sheet surface elevation changes in central east antarctica that we interpret to represent rapid discharge from a subglacial lake our observations indicate that during a period of 16 months 1 8 km3 of water was transferred over 290 km to at least two other subglacial lakes while viscous deformation of the ice roof above may moderate discharge the intrinsic instability of such a system3 suggests that discharge events are a common mode of basal drainage4 if large lakes such as lake vostok or lake concordia1 are pressurizing it is possible that substantial discharges could reach the coast5 6 our observations conflict with expectations that subglacial lakes have long residence times and slow circulations2 7 8 and we suggest that entire subglacial drainage basins may be flushed periodically the rapid transfer of water between lakes would result in large scale solute and microbe relocation and drainage system contamination from in situ exploration is therefore a distinct risk

analysis of active lava flows on kilauea volcano hawaii using sir c radar correlation measurements precise eruption rates of active pahoehoe lava flows on kilauea volcano hawaii have been determined using spaceborne radar data acquired by the space shuttle imaging radar c sir c a coastal site downslope from the pu9u o9o vent was imaged once per day on each of the four days of october 7 10 1994 day to day decorrelation due to resurfacing was determined by interferometric combination of the data at 15 m resolution over a wide area on successive days new lava resurfaced 335700 m 2 368775 m 2 and 356625 m 2 assuming an average pahoehoe flow thickness of 50 cm a mean effusion rate for this period is approximately 2 m 3 s the radar observations show persistent surface activity at each site rather than downslope migration of coherent lava flows

a depositional model for outwash sediment sources and hydrologic characteristics malaspina glacier alaska a modern analog of the southeastern margin of the laurentide ice sheet the malaspina glacier on the southern coast of alaska is a partial analog of the late wisconsinan laurentide ice sheet that occupied new england and adjacent areas ice lobes of the malaspina are similar in size to end moraine lobes in southern new england and long island estimated ablation rates surface slopes and meltwater discharge per unit of surface area for the laurentide ice sheet are comparable to measured ablation rates surface slopes and meltwater discharge rates for the malaspina glacier meltwater moves from the surface of the malaspina down glacier and toward the bed of the glacier along intercrystalline pathways and through a series of tunnels regolith beneath the glacier which is eroded and transported to the margin of the glacier by subglacial and englacial streams is the source of essentially all fluvial and lacustrine deposits on the malaspina foreland by analogy a similar hydrologic system existed at the southeastern margin of the laurentide ice sheet subglacial regolith which was eroded from beneath the ice sheet by meltwater was the source of most stratified sediment deposited in new england and adjacent areas during the late wisconsinan similarly wisconsinan ice contact landforms in new england were built by the same processes that are constructing landforms composed of stratified sediments in contact with the malaspina glacier for the malaspina glacier and the laurentide ice sheet therefore we reject the concept of the dirt machine by which debris near the base of the glacier is carried to the surface of the glacier along shear planes and then washed off the surface to form ice contact stratified deposits

analysis of velocity field mass balance and basal melt of the lambert glacier amery ice shelf system by incorporating radarsat sar interferometry and icesat laser altimetry measurements 1 by incorporating recently available remote sensing data we investigated the mass balance for all individual tributary glacial basins of the lambert glacier amery ice shelf system east antarctica on the basis of the ice flow information derived from sar interferometry and icesat laser altimetry we have determined the spatial configuration of eight tributary drainage basins of the lambert amery glacial system by combining the coherence information from sar interferometry and the texture information from sar and modis images we have interpreted and refined the grounding line position we calculated ice volume flux of each tributary glacial basin based on the ice velocity field derived from radarsat three pass interferometry together with ice thickness data interpolated from australian and russian airborne radio echo sounding res surveys and inferred from icesat laser altimetry data our analysis reveals that three tributary basins have a significant net positive imbalance while five other subbasins are slightly positive or close to zero balance overall in contrast to previous studies we find that the grounded ice in lambert glacier amery ice shelf system has a positive mass imbalance of 22 9 4 4 gt a 1 the net basal melting for the entire amery ice shelf is estimated to be 27 0 7 0 gt a 1 the melting rate decreases rapidly from the grounding zone to the ice shelf front significant basal refreezing is detected in the downstream section of the ice shelf the mass balance estimates for both the grounded ice sheet and the ice shelf mass differ substantially from other recent estimates

compositions of chromite associated minerals and parental magmas of podiform chromite deposits the role of slab contamination of asthenospheric melts in suprasubduction zone environments abstract podiform chromitites in the mantle sections of ophiolites belong to either high cr metallurgical or high al refractory varieties their highly variable compositions are reflected by different cr s 100cr cr al and cr2o3 and al2o3 contents of the chromite falling in the boninitic and morb fields respectively parental magmas of high cr chromitites have higher sc mn co and ni and lower ti v zn and ga concentrations than morb melts their trace element patterns are similar to those of boninites except for ni and zn in contrast high al chromitites have parental magmas characterized by generally flat morb normalized patterns showing slight enrichments in v mn and co and depletion in ni and zn regardless of their compositions both types of chromitites have chondrite normalized platinum group element pge patterns showing enrichment in ipge and depletion in ppge a variety of platinum group minerals are typically present in both types occurring either as euhedral inclusions or along fractures in chromite grains these minerals have a wide span of re os isotopic compositions reflecting a variety of origins there is a diversity of unusual minerals and mineral inclusions associated with podiform chromitites the presence of these minerals suggest that grains of amphibolite plagioclase amphibole and zircon and eclogite coesite kyanite and garnet were present in the magmas from which chromite crystallized multiphase mineral inclusions demonstrate that podiform chromitites form from hydrous mafic magmas in suprasubduction zone environments ssz we propose a new model in which chromitite formation was involved in intra oceanic subduction zones initiated in closing oceanic basins continued subduction carries oceanic and possibly continental crustal materials to deep levels where they are metamorphosed under greenschist amphibolite and eclogite facies conditions the tearing and breakoff of the subducted slab possibly along the transitional contact between amphibolites and eclogites create a slab window through which the underlying asthenosphere rises and melts to generate cr rich mafic magmas these upward migrating magmas pass through the subduction zone and assimilate the subducted slab as a result of slab contamination these magmas become more siliceous more oxidized and more hydrous rapidly triggering chromite crystallization minute grains of chromite are suspended in the upward moving magmas as they migrate through the overlying metasomatized mantle wedge such chromite bearing magmas eventually deposit chromite in magma conduits in the uppermost mantle close to the moho where the upward flow changes from vertical to subhorizontal and velocity is greatly reduced highly reduced and ultrahigh pressure minerals including diamonds are reported in literature both in podiform chromitites and host peridotites of ophiolites some of these minerals in association with host peridotites may have been brought by the uprising asthenosphere at mid oceanic ridges due to the mantle convection it is also possible that some diamonds may have formed in the subducted slab below about 150 km some minerals of subducted slabs are preserved because they are encapsulated in chromite grains where they are protected from the ssz melts some of these ssz mantle wedges are emplaced on land to become podiform chromitite bearing ophiolites

tectonic model of the pacific north american plate boundary in the gulf of alaska from broadband analysis of the 1979 st elias alaska earthquake and its aftershocks the st elias alaska earthquake of 28 february 1979 ms 7 2 is reanalyzed using broadband teleseismic body waves and long period surface waves because of unresolved questions about its depth focal mechanism seismic moment and location in a seismic gap teleseismic waveforms are simultaneously inverted to determine the source mechanism seismic moment rupture history and centroid depth these data are well modeled with a point source propagating in the ese direction with an average kinematic rupture velocity of 2 5 km s the best fitting source mechanism indicates underthrusting on a ne dipping plane the mainshock depth of 24 km and the depth of aftershocks determined from inversions are consistent with locations on the gently dipping main thrust of the pacific north american plate boundary these depths are substantially different from those of earlier body wave studies and regional seismic network aftershock depth determinations but are in accord with the harvard centroid moment tensor and international seismological centre determinations the seismic moment determined from body waves is 9 4 1019 n m mw 7 3 the spatial and temporal distribution of moment release indicates that the st elias earthquake was a complex rupture consisting of two distinct subevents within 38 s of the initial onset followed by low moment release during the next 34 s earlier studies indicated an unusual amount of surface wave energy at very long periods 200 s that led some workers to suggest that st elias was a slow earthquake our broadband modeling does not require more than 34 s of additional moment release after the first two subevents moreover we are able to match the phase and amplitude of 200 s love and rayleigh waves with a thrust fault point source of moment 1 3 1020 n m mw 7 4 located at the body wave centroid the moment difference is not discernible with body waves for moment evenly distributed over 72 s thus the st elias earthquake is not slow with respect to 200 s surface waves but is complex with regard to the broadband body waves upper plate structure apparently controlled the gross characteristics of rupture the rupture direction parallels mapped upper plate faults rupture propagated unilaterally to the ese with little initial moment release as a shallow north dipping thrust that later changed to more steeply ne dipping with a large right lateral strike slip component the locations and source mechanisms of these subevents and locations of aftershocks define a shallow dipping surface at the eastern edge of the pacific plate moreover the component of strike slip motion increases with time in the mainshock implying that the transition to strike slip faulting occurs along the plate interface the estimated nucleation point of the second subevent coincides with a large concentration of aftershocks interpreted as representing a barrier to continuous rupture associated with the northern most boundary of the yakutat terrane joint relocation of aftershocks suggests that the main plate boundary may be offset vertically by 5 10 km as a result of this structure the southern part of the aftershock zone while containing many aftershocks appears not to have ruptured coseismically but may have failed later by aseismic creep as seen in geodetic measurements faults associated with the malaspina fault system the onshore extension of the aleutian trench appear to be the surface expression of the underthrusting plate boundary however upper plate deformation is widespread because of the collision of the yakutat terrane the convergence direction may explain the lack of a highly active wadati benioff zone downdip of the st elias zone the neotectonic deformation of the chugach st elias mountains is probably related to collision and subduction of the yakutat terrane a terrane in the process of accreting and subducting will cause considerable upper plate deformation over a wide zone once subduction of a terrane has begun deformation may then become localized

motion patterns of nabesna glacier alaska revealed by interferometric sar techniques abstract nabesna glacier is one of the longest land terminus mountain glaciers in north america however its flow has never been studied we derived detailed motion patterns of nabesna glacier in winter and spring 1994 1996 from the synthetic aperture radar sar images acquired by the european remote sensing satellites ers 1 and ers 2 using interferometric sar insar techniques special effort was made to assess the accuracy of the motion estimates and remove data points with high uncertainty from the motion profiles enabling us to obtain reliable glacier flow patterns along the highly curved main course of nabesna glacier the results covering 80 km of the 87 km main course of the glacier were used to delineate four distinctive sections in terms of spatial and temporal variability of the glacier speed 1 the upper section where glacier flow was apparently random both temporally and spatially presumably due to development of crevasses 2 the upper middle section with relatively steady flow around 0 27 to 0 4 m day 3 the middle section with a stable pattern of acceleration from 0 27 0 3 m day to the maximum about 0 67 0 73 m day followed by a general deceleration to 0 17 0 33 m day before reaching 4 the lower section where the glacier motion was generally slow yet highly variable although uncertainty in the estimation is high occurrence of the flow maximum as well as many local maxima and minima at consistent locations over different periods suggests that the valley geometry affect the overall flow pattern on top of this general trend many small scale temporal spatial variations in the glacier flow patterns were observed along the glacier especially in the lower sections on average the flow speeds were in the range of 0 3 to 0 7 m day however this lacks any measurements of summer flow speeds which are expected to be significantly higher

volcanic associated nickel deposits from around the widgiemooltha dome western australia volcanic peridotitc associated nickel sulfide deposits occur in archean komatiitic flow sequences around the widgiemooltha dome in the eastern goldfields region of western australia the deposits are typically small shoots 40 volatile free al 2 o 3 2 content of metamorphic fluids and the timing of fluid access to the rocks along the eastern side of the widgiemooltha dome host rocks have undergone serpentinization and variable but generally extensive prograde talc carbonate alteration e g redross dordie rocks north and widgiemooltha 3 deposits in the north munda deposit they have experienced serpentinization with minor carbonate alteration and in addition prograde metamorphic reconstitution to forsteritc talc rich assemblages dunitic units in the west wannaway and wannaway north deposits escaped prograde serpentinization talc carbonate alteration and significant metamorphic reconstitution but have been retrogressively serpentinized sulfides from the different alteration environments show systematic mineralogical and compositional differences at all deposits peak metamorphic temperatures 550 degrees 600 degrees c resulted in reversion of sulfides to a dominant fe ni co cu bearing monosulfide solid solution accompanied by pentlanditc or fe cu intermediate solid solution in some cases most of the present ore mineralogies and textures relate to exsolution of low temperature sulfides from metamorphic monosulfide solid solution with reequilibration and recrystallization during slow postmetamorphic cooling deformation produced a tectonite fabric in the ores characterized by preferred orientation of sulfide grains and mineral layering breccia ores were formed in response to brittle deformation in host rocks and continued ductile behavior in the sulfides deformation also affected the overall configuration of the ore shoots and led to significant sulfide mobilization and ore shoot distension after allowing for the metamorphic imprint a number of primary features of the ore environment can be isolated and there is strong evidence for the prior existence of magmatic sulfides the association of ores with early formed largely dunitic units similar bulk ni cu and ni co ratios for ores from different deposits precious metal data low s se ratios and distinctive magmatic spinels in the sulfides all point to a magmatic control on the ores strong positive correlation between ni and mgo in host units and similar ni mgo ratios in both mineralized and unmineralized units suggest that sulfide liquids formed and equilibrated with the parent magma at depth before being extruded as part of olivine rich crystal mushes

accuracy of topographic maps derived from ers 1 interferometric radar an interferometric radar technique for topographic mapping of surfaces promises a high resolution approach to the generation of digital elevation models the authors present analyses of data collected by the synthetic aperture radar instrument on board the ers 1 satellite on successive orbits use of a single satellite in a nearly repeating orbit is attractive for reducing cost and spaceborne hardware complexity also it permits inference of changes in the surface from the correlation properties of the radar echoes the data have been reduced to correlation maps and digital elevation models the correlation maps show that temporal correlation decreases significantly with time but not necessarily at a constant well defined rate likely depending on environmental factors when correlation among passes remains high however it is possible to form digital elevation models analyses of noise expected in ers 1 interferometric data collected over alaska and the southwestern united states indicate that maps with relative errors less than 5 m rms are possible in some regions however orbit uncertainties imply that tie points are required in order to reduce absolute height errors to a similar magnitude the authors find that about 6 tie points per 40 spl times 40 km scene with 5 m rms or better height accuracy are needed to keep systematic map height errors below 5 m rms the performance of the ers 1 radar system for topographic applications though useful for a variety of regional and local discipline studies may be improved with respect to temporal decorrelation errors and absolute height acuity by modifying the orbit repeat period and incorporating precise orbit determination techniques the resulting implementation will meet many but not all objectives of a global mapping mission

new gps constraints on the motion of the yakutat block global positioning system gps measurements were made at yakutat on the yakutat terrane of southern alaska to investigate the motion of the yakutat block with respect to the north american plate and to help constrain motion along the fairweather fault the velocity of yakutat derived from the gps data is 44 1 1 9 mm yr toward n37 4 w relative to stable north america the magnitude of this velocity is similar to that of the pacific plate predicted by nuvel1a although there is a significant difference in the azimuth of these two vectors the motion of yakutat relative to north america is almost exactly parallel to the strike of the fairweather fault suggesting that most deformation inboard of yakutat is right lateral strike slip on the fairweather fault or faults parallel to it and that significant motion normal to the fairweather fault occurs offshore of yakutat the gps velocity at yakutat is also used to help constrain the slip rate and locking depth of the fairweather fault

atmospheric limitations to repeat track radar interferometry in its recent radar imaging mission the shuttle imaging radar satellite sir c devoted three days to repeat track interferometry we have analyzed the data from a test site in the mojave desert of california although good topography 10 m on 21 m postings was obtained most of the error was caused by turbulent water vapor in the lower atmosphere spatial structure of 6 km and all smaller sizes was observed the rms one way time delay was found to be 0 24 cm essentially identical results were obtained at two wavelengths 24 and 5 7 cm

mapping small elevation changes over large areas differential radar interferometry a technique that uses synthetic aperture radar sar images to measure very small 1 cm or less surface motions with good resolution 10 m over large swaths 50 km is presented along with experimental results the method could be used for accurate measurements of many geophysical phenomena including swelling and buckling in fault zones residual displacements from seismic events and prevolcanic swelling the method is based on sar interferometry where two images are made of a scene by simultaneously flying two physically separated antennas then the phases of corresponding pixels are differenced and altitude formation is deduced from some simple computation and image rectification it is also possible to use one antenna flown twice over the same scene then if the second flight exactly duplicates the track of the first an interesting possibility occurs there would be no phase changes between the images at all unless there was a physical change in the scene such as ground swelling that would alter the distance from some resolution element to the antenna since the phase changes all occur at the short carrier wavelength the basic limitation on sensitivity is only the phase noise in the system when the two imaging passes are made from flight tracks that are separated which is the case with the seasat images used here it is no longer possible to distinguish surface changes from the parallax caused by topography however with some additional computation a third image made at some other baseline may be used to remove the topography and leave only the surface changes this method was applied using seasat data to an imaging site in imperial valley california where motion effects were observed that were ascribed to the expansion of water absorbing clays phase change images of this area are shown along with associated ground truth about the presence of water problems with the technique are explored along with a discussion of future experimental possibilities on upcoming sar missions like earth observing system eos earth resources satellite ers 1 sir c and the venus imaging radar magellan

rapid large area mapping of ice flow using landsat 8 abstract we report on the maturation of optical satellite image based ice velocity mapping over the ice sheets and large glacierized areas enabled by the high radiometric resolution and internal geometric accuracy of landsat 8 s operational land imager oli detailed large area single season mosaics and time series maps of ice flow were created using data spanning june 2013 to june 2015 the 12 bit radiometric quantization and 15 m pixel scale resolution of oli band 8 enable displacement tracking of subtle snow drift patterns on ice sheet surfaces at 1 m precision ice sheet and snowfield snow drift features persist for typically 16 to 64 days and up to 432 days depending primarily on snow accumulation rates this results in spatially continuous mapping of ice flow extending the mapping capability beyond crevassed areas our method uses image chip cross correlation and sub pixel peak fitting in matching landsat path row pairs high pass filtering is applied to the imagery to enhance local surface texture the current high image acquisition rates of landsat 8 725 scenes per day globally reduces the impact of high cloudiness in polar and mountain terrain and allows rapid compilation of large areas or dense temporal coverage of seasonal ice flow variations the results rival the coverage and accuracy of interferometric synthetic aperture radar insar mapping

flow dynamics and iceberg calving rates of devon ice cap nunavut canada the surface velocity field of devon ice cap nunavut canada was mapped using interferometric synthetic aperture radar insar ascending european remote sensing satellite 1 and 2 ers 1 2 tandem mode data were used for the western and southeast sectors and 3 day repeat pass ers 1 imagery for the northeast sector speckle tracking procedures were used with radarsat 1 imagery to obtain surface velocities over the terminus of belcher glacier a major calving front where decorrelation between ers data occurred the insar data highlight a significant contrast in ice flow dynamics between the east and west sides of the ice cap ice movement west of the main north south divide is dominated by relatively uniform sheet flow but three fast flowing outlet glaciers that extend 14 23 km beyond the ice cap margin also drain this region several outlet glaciers that extend up to 60km inland from the eastern margin drain the eastern side of the ice cap the dominant ice flow regimes were classified based on the relationship between the driving stress averaged over a length scale often ice thicknesses and the ratio of surface velocity to ice thickness the mapped distribution of flow regimes appears to depict the spatial extent of basal sliding across the ice cap this is supported by a close relationship between the occurrence of flow stripes on the ice surface and flow regimes where basal sliding was found to be an important component of the glacier motion iceberg calving rates were computed using measured surface velocities and ice thicknesses derived from airborne radio echo sounding the volume of ice calved between 1960 and 1999 was estimated to be 20 5 4 7 km 3 or 0 57km 3 a 1 approximately 89 of this loss occurred along the eastern margin the largest single source is belcher glacier which accounts for 50 of the total amount of ice calved

differentiation of the cuthbert lake ultramafic dikes and related mafic dikes in the cuthbert lake region of north central manitoba northeasterly trending ultramafic mafic dikes part of the molson dike swarm show a range of composition from gabbro to olivine hornblende pyroxenite to hornblende peridotite the major dike which is ultramafic in composition is 60 m thick olivine and chromian spinel were the earliest cumulus phases formed in a subcrustal magma chamber before the emplacement of the dikes orthopyroxene and clinopyroxene were formed following emplacement at about 1120 c plagioclase and hornblende were the latest phases to crystallize from the intercumulus melt mineralogical and chemical variations across the major dike are interpreted to have resulted from flow differentiation of multiple injections of magma carrying suspended olivine crystals olivine phenocrysts changed their compositions from about fo87 to values ranging from fo80to fo73 as a function of the amount of intercumulus melt the composition of this melt is estimated to have been basaltic a mafic dike about 10 m thick and occurring about 20 m away from the main ultramafic dike is believed to have been formed from magmas that were tapped from an upper layer overlying the olivine rich zone in a subcrustal magma chamber separation must have occurred when clinopyroxene and plagioclase appeared on the liquidus

three dimensional glacial flow and surface elevation measured with radar interferometry outlet glaciers which serve to drain ice from ice sheets seem to be dynamically less stable in north greenland than in south greenland1 2 3 storstrommen a large outlet glacier in northeastern greenland which surged between 1978 and 1984 ref 2 has been well studied in general neither glacier surge mechanisms nor the geographical distribution of the surges are well known conventional satellite radar interferometry can provide large scale topography models with high resolution4 and can measure the radar line of sight component of ice flow vectors5 but cannot map full vector flow fields here we present an interferometry method that combines observations from descending and ascending satellite orbits which assuming ice flow parallel to the topographic surface allows us to use the differing view angles to estimate full three dimensional surface flow patterns the accuracy of our technique is confirmed by the good agreement between our radar based flow model and in situ global positioning system gps reference data at storstrommen radar measurements such as these made regularly and at high spatial density have the potential to substantially enhance our understanding of glacier dynamics and ice sheet flow as well as improve the accuracy of glacier mass balance estimates

existence of a marginal basin within the circum superior belt geochemical evidence from the churchill superior boundary in manitoba canada mafic volcanic rocks incorporated within the churchill superior boundary zone at ospwagan lake moak lake assean lake and the fox river belt constitute part of the circum superior belt major and trace element data have been obtained from mafic and ultramafic volcanic rocks from four localities the data provide a means of comparing and contrasting the geochemistry of the rocks from the portion of the circum superior belt surrounding the archean superior province in manitoba with other units from elsewhere in the belt and with rocks from the adjacent proterozoic churchill province major element geochemical data are consistent with the rocks having originally formed in a oceanic environment trace element and rare earth element data suggest that the environment was a marginal basin al2o3 tio2 ratios indicate that the magmas were derived from a mantle source by small degrees of partial melting high field strength element patterns show that the mantle source region giving rise to the rocks was relatively uniform in composition trace element mid ocean ridge basalt morb and chondrite normalized patterns indicate similarities in alkali element enrichment for the rocks at asean and ospwagan lakes virtually all the rocks have ti zr nb y and p levels morb which is consistent with the mantle source region having undergone a small degree of partial melting zr p ratios for the rocks from the fox river belt are consistently lower than those from the other localities and the assean lake rocks show slight enrichment in light rare earth elements which may suggest local compositional variability in the mantle source regions supplying the magmas to the fox river belt and the ospwagan assean and moak lake areas

the integration of jers 1 and ers sar in differential interferometry for measurement of complex glacier motion complex glacier motion in the grove mountains region antarctica is measured using four pass differential synthetic aperture radar sar interferometry insar the components of the motion vector field are resolved using a 44 day separation japanese earth resources satellite 1 jers 1 insar pair and a european remote sensing satellite 1 2 ers 1 2 tandem insar pair the 44 day temporal baseline provides the sensitivity required to observe the range of ice motion around 8 10 m a 1 and the 1 day short baseline provides the best choice for glacier digital elevation model reconstruction it is remarkable that the scattering field of the jers 1 pair remained coherent over the long time interval and the interferometric fringes are clear the overall ice flow is from east to west downslope and towards lambert glacier the regional flow is obstructed by nunataks extending north south with two wide gaps two narrow glaciers flow past the nunataks and rejoin each other at the downstream end regional morphology and the resolved flow in the grove mountains area suggests that ice flow is channeled throughout this eastern flank of lambert glacier

interferometric estimation of three dimensional ice flow using ascending and descending passes satellite radar interferometry sri provides an important new tool for determining ice flow velocity interferometric measurements made from a single track direction are sensitive only to a single component of the three component velocity vector observations from along three different track directions would allow the full velocity vector to be determined a north south looking synthetic aperture radar sar could provide these observations over large portions of the globe but not over large areas of the polar ice sheets the authors develop and demonstrate a technique that allows the three component velocity vector to be estimated from data acquired along two track directions ascending and descending under a surface parallel flow assumption this technique requires that there are accurate estimates of the surface slope which are also determined interferometrically to demonstrate the technique the authors estimate the three component velocity field for the ryder glacier greenland their results are promising although they do not have yet ground truth data with which to determine the accuracy of their estimates

analysis of the 1993 95 bering glacier alaska surge using differential sar interferometry differential spaceborne radar interferometry observations of west bagley icefield are used to measure surface velocity and topography bagley icefield is the accumulation area fur bering glacier which surged in two phases from spring 1993 through summer 1905 the observations presented are based on data collected during the winter of 1992 prior to the surge and during winter 1994 while the surge was in full progress both observation intervals correspond to 3 day repeat orbit phases of the ers i c band sar this paper gives an overview of the algorithms used to derive surface velocity vector fields and topography for valley glaciers from sar images the resulting high resolution velocity data clearly show west bagley icefield accelerating from its quiescent pre surge velocity by a factor of 2 7 in response to the bering glacier surge persistence of lnterfero metric phase coherence and the relatively moderate degree of acceleration on the western arm of bagley icefield suggest that the velocity increase may have been caused by increased longitudinal stress gradients resulting from coupling to the surging main trunk of bering glacier

the accuracy of digital elevation models of the antarctic continent abstract the accuracy of two widely used digital elevation models of antarctica was assessed using data from the geoscience laser altimeter system onboard icesat the digital elevation models were derived from satellite radar altimeter and terrestrial data sets the first termed jlb97 was produced predominantly from ers 1 data while the second termed rampv2 included other sources of data in areas of high relief and poor coverage by ers 1 the accuracy of the models was examined as a function of surface slope and original data source large errors in excess of 100 m were ubiquitous in both models in areas where terrestrially derived elevation data had been used but were more extensive in rampv2 elsewhere the systematic error bias was found to be a monotonic function of slope for jlb97 with a more complex less predictable bias for rampv2 the magnitude of the global slope dependent bias ranged from less than a metre to slightly over 10 m but with much larger regional deviations the random error ranged from about 1 m to over 100 m depending on the dem and slope the random error was consistently over a factor two larger for rampv2 compared to jlb97

the potential of satellite radar interferometry and feature tracking for monitoring flow rates of himalayan glaciers abstract the stagnation of himalayan glaciers will only be exacerbated by a warming climate increasing hazards associated with glacier lake development frontal recession is a poor indicator of negative balance in this region where most glaciers are debris covered but reduced glacier flow rates provide a valuable warning of stagnation in situ measurements of velocity are understandably rare and remote sensing measurements have hitherto been limited by severe topography and lack of suitable data in this paper we compare two techniques to measure flow rates in everest region glaciers firstly satellite radar interferometry sri has recently become more viable because of improved digital elevation data and precision orbit models which now allow snapshots of velocities to be retrieved from ers imagery in the mid 1990s without ground control information secondly feature tracking between synthetic aperture radar sar images is found to be successful even on the small glaciers of this region because of the patterning associated with debris cover this technique extends through the 1990s and beyond the time frame over which velocities can be measured using the examples of the khumbu glacier flowing south into nepal and the kangshung glacier flowing east into china from the everest massif we compare sri and sar feature tracking in ers images consider the errors in these techniques and examine the potential to monitor flow rates across the region the techniques are found to be highly complementary and appropriate for monitoring flow rates in this region suggesting that routine monitoring of himalayan glaciers is possible the kangshung glacier appears to sustain relatively high flow rates of up to 10 cm day which along with a convex topographic profile indicates a healthy glacier not exhibiting significant negative mass balance in comparison much of the khumbu glacier appears to have stagnated the surface velocity at gorak shep is only 20 of a field based measurement in the 1970 s and the concave surface profile confirms the downwasting associated with a debris covered glacier in recession

petrogenesis of ultramafic and mafic rocks of the thompson nickel belt manitoba abundant sill like bodies of serpentinized ultramafic rocks with associated nickel sulfide deposits are found on the western side of the thompson nickel belt near the moak lake setting lake cataclastic fault zone the ultramafic rocks range in composition from dunite to orthopyroxenite and feature variable alteration chemical variation across the bodies is suggestive of in situ differentiation controlled mainly by olivine and orthopyroxene relative abundances of some elements incompatible for olivine and orthopyroxene suggest a parental liquid of komatiitic affinity ultramafic and mafic rocks are petrogenetically linked a high degree of partial melting of mantle material and subsequent low pressure crystal fractionation are responsible for the spectrum of composition from ultramafic to mafic

studies of multibaseline spaceborne interferometric synthetic aperture radars the authors have utilized a set of seasat synthetic aperture radar sar data that were obtained in nearly repeat ground track orbits to demonstrate the performance of spaceborne interferometric sar insar systems an assessment of the topography measurement capability is presented a phase measurement error model is described and compared with the data obtained at various baseline separations and signal to noise ratios finally the implications of these results on future spaceborne insar design are discussed

spatial distribution of glacial erosion rates in the st elias range alaska inferred from a realistic model of glacier dynamics glaciers have been principal erosional agents in many orogens throughout much of the recent geological past a modern example is the st elias mountains in southeastern alaska it is a highly convergent complex orogen which has been glaciated for much of its history we examine the seward malaspina glacier system which comprises two of the largest temperate glaciers in the world we focus on the pattern of erosion within its narrow passage through the st elias mountains the seward throat measured glacier surface velocities and elevations provide constraints for a full stress numerical flowband model that enables us to quantitatively determine the glacier thickness profile which is not easily measured on temperate glaciers and the basal characteristics relevant for erosion these characteristics at the bed namely the water pressure normal and shear stresses and sliding velocity are then used to infer the spatial variation in erosion rates using several commonly invoked erosion laws the calculations show that the geometry of the glacier basin exerts a far stronger control on the spatial variation of erosion rates than does the equilibrium line altitude which is often assumed to be important in studies of glaciated orogens the model provides a quantitative basis for understanding why erosion rates are highest around the seward throat which is generally consistent with local and large scale geological observations and thermochronologic evidence moreover model results suggest how glacier characteristics could be used to infer zones of active or recent uplift in ice mantled orogens 2012 american geophysical union all rights reserved

ice sheet velocity mapping a combined interferometric and speckle tracking approach the first and second radarsat antarctic mapping missions amm 1 and 2 have now acquired interferometric synthetic aperture radar sar overmuch of the ice sheet the radarsat 24 day repeat cycle is nearly ideal for measuring slow ice motion e g 1 but application of sar interferometry is limited in faster moving areas with a 1day repeat period ers 1 2 tandem sar data are much better matched to fast motion but are not always available fortunately several authors have demonstrated the ability to measure velocity in fast moving areas by tracking sar speckle from image to image which works well even in the absence of visible features while these estimates have intrinsically lower resolution and poorer accuracy than direct phase measurements they serve well in areas where there are no data suitable for conventional interferometry this paper describes algorithms i have developed for merging interferometric and speckle tracking data from multiple swaths to form a single seamless mosaic of velocity at each point in the mosaic all the available data are combined to produce estimates of the velocity and the associated error this technique is demonstrated using radarsat data collected over lambert glacier antarctica during amm 1 and 2

glacier surface velocities in alpine terrain from optical satellite imagery accuracy improvement and quality assessment the worldwide retreat of mountain glaciers has important consequences for the water food and power supply of large and densely populated areas in south and central asia successful mitigation of the hydrological impacts on societies as well as assessing glacier related hazards require large scale monitoring of glacier dynamics however detailed glaciological data from the asian highlands are lacking due to its size and difficult accessibility we have applied a novel technique for precise orthorectification co registration and sub pixel correlation of advanced spaceborne thermal emission and reflection radiometer aster satellite imagery to derive surface velocities of himalayan glaciers our approach allows for the correction of offsets due to attitude effects and sensor distortions as well as elevation errors if a digital elevation model dem from the shuttle radar topography mission srtm was used for orthorectification after post processing the error on the displacements is on the order of 2 4 m per correlation translated into annual velocities this error is reduced increased when the correlated images are more less than a year apart through application of a filtering procedure and several quality tests the consistency of the results is validated to provide confidence in the remotely sensed velocity measurements despite the lack of ground control this novel approach allows fast easy and economically viable acquisition of detailed glaciological data in areas of difficult access and provides a means for large scale monitoring of glaciers in high mountainous terrain

radar interferogram filtering for geophysical applications the use of sar interferometry is often impeded by decorrelation from thermal noise temporal change and baseline geometry power spectra of interferograms are typically the sum of a narrow band component combined with broad band noise we describe a new adaptive filtering algorithm that dramatically lowers phase noise improving both measurement accuracy and phase unwrapping while demonstrating graceful degradation in regions of pure noise the performance of the filter is demonstrated with sar data from the ers satellites over the jakobshavns glacier of greenland

interferometric radar observations of glaciar san rafael chile interferometric radar observations of glaciar san rafael chile were collected in october 1994 by nasa s spaceborne imaging radar c sir c at both l 24 cm and c band frequency 5 6 cm with vertical transmit and receive polarization the c band data did not yield good geophysical products because the temporal coherence of the signal was significantly reduced after 24 h the l band data were however successfully employed to map the surface topography of the icefield with a 10 m uncertainty in height and measure ice velocity with a precision of 4 mm d 1 or 1 4 ma 1 the corresponding error in strain rates is 0 05 a 1 at a 30 m horizontal spacing the one dimensional interferometric velocities were subsequently converted to horizontal displacements by assuming a flow direction and complemented by feature tracking results near the calving front the results provide a comprehensive view of the ice flow dynamics of glaciar san rafael the glacier has a core of rapid flow 4 5 km in width and 3 5 in average slope surrounded by slowermoving ice not by rock ice velocity is 2 6 m d 1 or 0 95 km a 1 near the equilibrium line altitude 1200 m increasing rapidly before the glacier enters the narrower terminal valley to reach 17 5 m d 1 or 6 4 km a 1 at the calving front strain rates are dominated by lateral shearing at the glacier margins 0 4 0 7 a 1 except for the terminal valley section where longitudinal strain rates average close to 1 a 1 this spectacular longitudinal increase in ice velocity in the last few kilometers may be a fundamental feature of tidewater glaciers

strain accumulation in the yakataga seismic gap southern alaska strain accumulation in the yakataga seismic gap has been estimated from the deformation of a 60 km 40 km trilateration network surveyed in 1979 1980 1982 and 1984 the contraction in the approximate direction n19 w of plate convergence is 0 19 0 04 strain yr and there is a minor 0 07 0 04 strain yr orthogonal extension a significant right lateral shear 0 09 0 02 strain yr occurs across a vertical plane striking n71 e a simple dislocation representation of the plate interaction model proposed by lahr and plafker for the yakataga seismic gap quantitatively accounts for the observed n19 w contraction and qualitatively accounts for the right lateral shear the two strains being associated with the normal and transverse components respectively of the oblique convergence between the yakutat block and the north american plate the measurements are consistent with strain accumulation building up to a great thrust earthquake in the yakataga gap in addition there is a suggestion of right lateral shear strain accumulation across the contact fault but the interval over which data are available is probably too short to prove such accumulation

relation of ongoing deformation rates to the subduction zone process in southern alaska the rate and orientation of ongoing strain associated with subduction of the pacific plate and the accretion of the yakutat terrane to southern alaska has been estimated at 13 sites from global positioning system measurements made in june 1993 and 1995 along the gulf of alaska coast near cape yakataga the average rate of deformation relative to fairbanks was 38 mm yr at n32 w further inland above the region where the dip of the downgoing pacific plate changes from about 10 to 30 the deformation rate was 12mm yr at n26 w in the sourdough paxson area the deformation rate drops to 2 5 mm yr and suggests a low short term deformation rate across the denali fault elastic straining of the overriding plate due to back slip on a main thrust zone with an average dip of about 10 can account for the overall rate and distribution of short term compressional strain across south central alaska above the transitional region between unstable and stable sliding we suggest that strain associated with 15 mm yr of right lateral strike slip occurs also if the strain accumulated since the two 1899 earthquakes both mw 8 1 from the offshore pamplona fault zone to south of the border ranges fault down dip width 100 km was seismically released on a single fault it would correspond to a m 8 1 earthquake

balance velocities of the greenland ice sheet we present a map of balance velocities for the greenland ice sheet the resolution of the underlying dem which was derived primarily from radar altimetery data yields far greater detail than earlier balance velocity estimates for greenland the velocity contours reveal in striking detail the location of an ice stream in northeastern greenland which was only recently discovered using satellite imagery enhanced flow associated with all of the major outlets is clearly visible although small errors in the source data result in less accurate estimates of the absolute flow speeds nevertheless the balance map is useful for ice sheet modelling mass balance studies and field planning

the topsar interferometric radar topographic mapping instrument the authors have augmented the nasa dc 8 airsar instrument with a pair of c band antennas displaced across track to form an interferometer sensitive to topographic variations of the earth s surface during the 1991 dc 8 flight campaign data were acquired over several sites in the us and europe and topographic maps were produced from several of these flight lines analysis of the results indicate that statistical errors are in the 2 4 m range while systematic effects due to aircraft motion are in the 10 20 m range the initial results from development of a second generation processor show that aircraft motion compensation algorithms reduce the systematic variations to 2 m while the statistical errors are reduced to 2 3 m

estimation of ice sheet motion using satellite radar interferometry method and error analysis with application to humboldt glacier greenland satellite radar interferometry provides glaciologists with an important new tool for determining the motion and topography of large ice sheets we examine the sources of error in interferometrically derived ice motion measurements including those errors due to inaccurate estimates of the interferometric baseline several simulations are used to assess baseline accuracy in terms of tie point error and the number and distribution of tie points these results give insight into how best to select tie points and also demonstrate the level of accuracy that can be achieved examination of two representative cases likely to occur in mapping ice sheet motion leads to the conclusion that with adequate tie point information ice velocity can be measured accurately to within a few meters per year a method to correct horizontal velocity estimates for the effect of vertical displacement using surface slopes is also developed finally we estimate the single component velocity field for an area on humboldt glacier northern greenland using interferograms formed from ers i sar images we estimate that these velocity measurements are accurate to within 2 3 m year 1

polarimetric decomposition over glacier ice using long wavelength airborne polsar in recent years there has been increased interest in using synthetic aperture radar sar to study and monitor glaciers and ice sheets for glaciological and climate change research however due to the medium s complexity sar backscattering from ice remains poorly understood including the relative importance of scattering from surface and volume layers and also dependences on frequency and glacier zone extreme weather conditions can result in quickly changing surface conditions influencing backscatter signatures while leaving the underlying volume of interest unchanged surface and volume components must thus be separated in order to infer information regarding the properties of the ice volume this paper describes a three component scattering model to decompose polarimetric sar polsar images of glacier ice total backscatter is modeled as the incoherent summation of surface volume and sastrugi wind induced feature components the proposed model adapts and extends the freeman and durden decomposition for an ice volume scenario in which the volume is a dielectric medium forms of the model for both random and oriented volumes are considered and a new oriented sastrugi component is introduced which is able to explain backscatter behavior between different winter scenes validation is performed with airborne polsar data at l and p band collected using the e sar system of the german aerospace center over the austfonna ice cap in svalbard norway as part of the icesar campaign

direct dating of ultramafic sills and mafic intrusions associated with ni sulfide mineralization in the thompson nickel belt manitoba canada the paleoproterozoic thompson nickel belt a segment of the northwest margin of the archean superior craton in manitoba is one of the largest nickel producing regions in the world and the second largest ni cu pge platinum group elements mining camp in canada after sudbury the nickel sulfide ores are hosted in or associated with ultramafic sills of komatiitic affinity that were emplaced into sulfur rich metasedimentary rocks of the ospwagan group and subsequently strongly deformed and metamorphosed amphibolite to granulite facies during the trans hudson orogeny a u pb zircon age of 1880 2 1 4 ma for a metaperidotite olivine orthopyroxenite from the upper part of a boudinaged ultramafic sill at the pipe 2 deposit is interpreted as the age of crystallization of the intrusion the first age from an ultramafic sill containing mined nickel sulfide in the thompson nickel belt this age confirms a direct petrogenetic relationship between ni cu pge mineralization and widespread mafic ultramafic magmatic activity molson igneous events at ca 1 88 ga along the superior province craton margin e g thompson nickel belt fox river belt cape smith belt new quebec orogen at the south pit of the thompson mine a u pb zircon age of 1860 7 0 7 ma for a composite mafic intrusion garnet amphibolite to layered metagabbro identifies a new age of mafic magmatic activity in the thompson nickel belt that is unrelated to nickel sulfide mineralization the thermal effects of the trans hudson orogeny are recorded by a range of zircon dates and ca 1760 ma metamorphic titanite from the south pit intrusion and are consistent with interpretations that regional metamorphism occurred as a single progressive event the results of this study open up the possibility of using the high precision u pb geochronology of mineralized ultramafic rocks to precisely constrain the duration of mafic ultramafic magmatism in the thompson nickel belt and assess potential age differences between ultramafic sills across and along strike of this world class nickel metallotect

ice flow dynamics of the greenland ice sheet from sar interferometry synthetic aperture radar sar interferograms produced from esa s ers 1 satellite provide the first synoptic view of ice flow dynamics of the western sector of the greenland ice sheet glacial motion is detected in the radar ranging direction at millimetric scales across a complete sequence of snow accumulation and melting regimes despite significant variations in their radar scattering properties ice flow evolves from a slow regular motion at the higher elevations at lower elevations motion is strongly convoluted by meter scale undulations in surface topography which have a unique interferometric signature that enables a novel approach for retrieving flow direction inferred flow directions combined with surface displacements in the radar ranging direction yield ice velocity estimates that are within 6 of in situ measurements gathered along a 40 km survey line application of repeat pass sar interferometry to the entire greenland ice sheet should enable precise mapping of its ice flow dynamics at an unprecedented level of spatial detail

glaciological advances made with interferometric synthetic aperture radar spaceborne interferometric synthetic aperture radar insar techniques for measuring ice flow velocity and topography have developed rapidly over the last decade and a half revolutionizing the study of ice dynamics spaceborne interferometry has contributed to major progress in many areas of glaciological study by providing the first comprehensive measurements of ice stream flow velocity over the major outlets of greenland and antarctica revealing that ice stream and outlet glacier flow can change rapidly months to years improving understanding of several ice sheet and ice shelf processes providing velocity for flux gate based mass balance assessment mapping flow of mountain glaciers and capturing the geomorphic traces of past ice flow we review the basic technique development the measurement characteristics and the extensive set of results yielded by these measurements