shear margins in glaciers and ice sheets analytical and numerical techniques are used to examine the flow response of a sloped slab of power law fluid power n subjected to basal boundary conditions that vary spatially across the flow direction as for example near an ice stream margin with planar basal topography the primary assumption is that basal shear stress is proportional to the basal speed time a spatially variable slip resistance the ratio of mean basal speed to the speed originating from shearing through the thickness denoted as r gives a measure of how slippery the bed is the principal conclusion is that a localized disturbance in slip resistance affects the basal stress and speed in a zone spread over a greater width of the flow in units of ice thickness h the spatial scale of spreading is proportional to a single dimensionless number r n r n 1 1 n 1 derived from n and r the consequence for a shear zone above a sharp jump in slip resistance is that the shearing is spread out over a boundary layer with a width proportional to r n for an ice stream caused by a band of low slip resistance with a half width of wh the margins influence velocity and stress in the central part of the band depending on r n in comparison to w three regimes can be identified which for n 3 are quantified as follows low r defined as r 3 1w for which the boundary layers from both sides bridge across the full flow width and the driving stress in the center is supported almost entirely by side drag intermediate r for which the driving stress in the center is supported by a combination of basal and side drag shear zones that are narrower than predicted on the basis of this theory r 3 would require localized softening of the ice to explain the concentration of deformation at a shorter scale

modis based mosaic of antarctica moa data sets continent wide surface morphology and snow grain size abstract we present digital image mosaics of surface morphology and optical snow grain size for the antarctic continent and surrounding islands assembled from 260 moderate resolution imaging spectroradiometer modis images the products are derived from modis band 1 red light 647 nm and band 2 infrared 857 nm orbit swath data acquired during the 2003 2004 austral summer multiple images of all areas are combined in a data cumulation scheme to improve spatial resolution and increase radiometric content of the mosaics the component images were de striped geo registered and re sampled to the projection grid using the modis swath to grid toolbox ms2gt software a 125 m ground equivalent polar stereographic projection was used identical to previous radar image mosaics and similar to several other continent wide data sets geo location accuracy of the final mosaics is better than 125 m swath acquisition times were limited to the range 05 00 13 30 ut to provide broad but uniform mosaic illumination regions of cloud cover blowing snow and intense forward scattering were masked prior to compositing the moa snow grain size data set image provides the first continent wide semi quantitative map of mean summer snow firn and blue ice grain size optical grain size radius was determined using a normalized difference index derived from modis band 1 and band 2 rad values atmospheric correction adjustments for directional reflectance variation and snow grain size estimation were accomplished by a look up table generated by a combination of published models of snow spectral reflectance and atmosphere radiative transfer validation of the snow grain size image is provided by in situ spectra of snow covered sea ice made in october 2003 we use the new data sets to determine major ice shelf areas and shelf edge coastline and ice grounding line vector files and determine areas of selected blue ice regions these data sets are available for download at http nsidc org data moa

high arctic observations of mesospheric inversion layers 1 rayleigh lidar measurements of middle atmospheric temperatures obtained in the high arctic at eureka 80 n 86 w are examined for evidence of mesospheric inversion layers with overlying nearly adiabatic lapse rates inversion layers are identified in 5 4 0 5 of the measurements a rate considerably lower than is observed at midlatitudes the altitude distribution for the arctic inversions is similar to that found at midlatitudes no phase progression or relationship with stratospheric gravity wave activity was found the observations have important consequences for theories of the mesospheric inversion layer

inferring ice flow directions from single ice sheet surface images using the radon transform we present a new method for extracting the direction of surface flow for ice sheets based on the detection of flow induced features that are visible in satellite imagery the orientation of linear features is determined using a radon transform and only requires a single image the technique is demonstrated by applying it to the radarsat mosaic of antarctica over the lambert glacier amery ice shelf region of east antarctica comparisons with both existing flow direction fields and traced streamlines over the same area provide an evaluation of the method we also illustrate its application to landsat 7 imagery

preconsolidation pressures in the battleford formation southern saskatchewan canada soft surficial unoxidized till of the battleford formation overlies hard oxidized and unoxidized till of the floral formation the difference in hardness between these two formations is the result of preconsolidation pressures that range from 1500 to 2200 kpa in the floral formation and from 350 to 750 kpa in the lower till unit of the battleford formation the upper till and clay unit of the battleford formation which represents a conformable contact between this formation and the overlying glaciolacustrine clay is normally consolidated preconsolidation of the floral formation apparently took place upglacier where the potentiometric surface for subglacial beds was 170 240 m below the ice surface the lower till unit of the battleford formation was deposited from and consolidated under stagnant ice the upper normally consolidated till and clay unit of the battleford formation was let down upon the lower till unit by ablation the calculated minimum stagnant ice thickness required for consolidation

subglacial processes from drumlins in clew bay western ireland interpretation of subglacial processes and environments can be usefully informed by the stratigraphy and structures of sediments preserved within drumlins and the down ice variability of these sediments drumlins in clew bay western ireland were formed by westward late pleistocene ice flow onto the atlantic shelf but the depositional processes and environments of these sediments remain uncertain this study describes and interprets the drumlin stratigraphy and sediment properties and structures from two drumlins on the south side of clew bay drumlin sediments are dominated by massive to stratified diamicton deposited subglacially by deformation of flows of varying rheology folds shears and clastic dikes within the sediments suggest active subglacial water flow related to variations in ice flow and ice bed coupling the distal ends of the drumlins are dominated by stratified diamicton and gravel units with sandy interbeds these sediments reflect deposition in a leeside subglacial cavity formed coevally with bedform development a model is proposed that can account for sediment stratigraphic patterns and drumlin formation copyright 2015 john wiley sons ltd

modeling the basal melting and marine ice accretion of the amery ice shelf the basal mass balance of the amery ice shelf ais in east antarctica is investigated using a numerical ocean model the main improvements of this model over previous studies are the inclusion of frazil formation and dynamics tides and the use of the latest estimate of the sub ice shelf cavity geometry the model produces a net basal melt rate of 45 6 gt year 1 0 74 m ice year 1 which is in good agreement with reviewed observations the melting at the base of the ice shelf is primarily due to interaction with high salinity shelf water created from the surface sea ice formation in winter the temperature difference between the coldest waters created in the open ocean and the in situ freezing point of ocean water in contact with the deepest part of the ais drives a melt rate that can exceed 30 m of ice year 1 the inclusion of frazil dynamics is shown to be important for both melting and marine ice accretion refreezing frazil initially forms in the supercooled water layer adjacent to the base of the ice shelf the net accretion of marine ice is 5 3 gt year 1 comprised of 3 7 gt year 1 of frazil accretion and 1 6 gt year 1 of direct basal refreezing

a decade of change in the hydraulic connection between an antarctic epishelf lake and the ocean observations of the water level in beaver lake an epishelf lake in east antarctica show a regular tidal signal that is lagged and attenuated from the tides beneath the adjacent amery ice shelf the phase lag and amplitude attenuation can be created by a narrow inlet connection between beaver lake and the cavity beneath the amery ice shelf a forced linear damped oscillator is used to determine the inlet dimensions that are required to produce the observed phase lag and amplitude attenuation the model shows that the observations are consistent with a tidal flow that is restricted by the drag created by flow in the narrow inlet analysis shows that the phase lag and amplitude attenuation of the tides in beaver lake has increased over the years 1991 2002 probably due to a thickening of the overlying ice shelf the response is sensitive to subtle variations in the dimensions of the inlet

seismicity and deformation associated with ice shelf rift propagation previous observations have shown that rift propagation on the amery ice shelf ais east antarctica is episodic occurring in bursts of several hours with typical recurrence times of several weeks propagation events were deduced from seismic swarms detected with seismometers concurrent with rapid rift widening detected with gps receivers in this study we extend these results by deploying seismometers and gps receivers in a dense network around the tip of a propagating rift on the ais over three field seasons 2002 03 2004 05 and 2005 06 the pattern of seismic event locations shows that icequakes cluster along the rift axis extending several kilometers back from where the rift tip was visible in the field patterns of icequake event locations also appear aligned with the ice shelf flow direction along transverse to rift crevasses however we found some key differences in the seismicity between field seasons both the number of swarms and the number of events within each swarm decreased during the final field season the timing of the slowdown closely corresponds to the rift tip entering a suture zone formed where two ice streams merge upstream beneath the suture zone lies a thick band of marine ice we propose two hypotheses for the observed slowdown 1 defects within the ice in the suture zone cause a reduction in stress concentration ahead of the rift tip 2 increased marine ice thickness in the rift path slows propagation we show that the size frequency distribution of icequakes approximately follows a power law similar to the well known gutenberg richter law for earthquakes however large icequakes are not preceded by foreshocks nor are they followed by aftershocks thus rift related seismicity differs from the classic foreshock and aftershock distribution that is characteristic of large earth quakes

a landslide in clay shale in the north saskatchewan river valley canada abstract a case study of a landslide in heavily overconsolidated clay shale is analyzed to determine shear strength by back analysis the landslide apparently started during deglaciation about 11 000 years b p and is still active the infilling north saskatchewan river alluvium has altered the configuration of the shear zone of the landslide the implications of errors in field data on the results were examined the analysis was most sensitive to modelling the toe configuration and piezometric conditions the effective angle of shearing resistance was estimated at 8 7 degrees assuming zero cohesion

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

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

tide corrected flow velocity and mass balance of campbell glacier tongue east antarctica derived from interferometric sar abstract accurate measurement of ice flow velocity of floating glaciers is required to estimate ice mass balance from volume flux thinning thickening basal melting freezing and surface accumulation ablation we derived a tide corrected ice velocity map and mass budget of campbell glacier tongue cgt in east antarctica by using 14 cosmo skymed one day tandem differential interferometric sar dinsar pairs obtained from january to november 2011 the vertical tidal deflection of cgt was estimated and removed from the dinsar images by using a tide deflection ratio map generated by double differential insar ddinsar method we then generated averaged ice flow velocity v map and its standard deviation v map ice flow velocity increased from the upper part of the grounding line 0 20 m d 1 to the seaward edge of cgt 0 67 m d 1 with v less than 0 04 m d 1 in the main stream of cgt the eastern part of cgt flows slower than the western part because it is grounded along the flow line and thus experiences severe basal drag flux mass balance fmb i e ice thickness change by volume flux divergence of cgt was obtained by combining the v map and an ice thickness value of 340 18 m estimated by the icesat glas data we used mass conservation assumption in which total mass balance tmb 6 29 1 37 m a 1 observed by icesat glas data is attributed to fmb basal mass balance bmb and surface mass balance smb 0 24 0 02 m a 1 mass loss in the freely floating zone of cgt is mainly caused by basal melting bmb 144 5 39 9 mt a 1 while thinning by volume flux fmb 67 2 8 9 mt a 1 is relatively small in the hinge zone of cgt mass change is contributed to fmb of 147 3 25 2 mt a 1 and bmb of 15 3 39 8 mt a 1 however basal freezing derived for the hinge zone may be erroneous as a result of the constant ice thickness assumption extrapolated from the freely floating zone

episodic propagation of a rift on the amery ice shelf east antarctica 1 we investigate ice shelf rift propagation using a combination of gps and seismic measurements near the tip of an active rift in the amery ice shelf these measurements reveal that propagation occurs in episodic bursts which were identified based on swarms of seismicity accompanied by rapid rift widening the bursts last approximately 4 hours and are separated by 10 24 days in between bursts the rift widens at a rate comparable to that of ice shelf spreading comparison of automatic weather station data and tidal amplitudes show that the propagation bursts are not directly triggered by winds or tides suggesting that rift propagation is driven by the background glaciological stress in the ice shelf we show that the ice debris that partly fills the rift may play a role in controlling the rate of propagation

properties of a marine ice layer under the amery ice shelf east antarctica the amery ice shelf east antarctica undergoes high basal melt rates near the southern limit of its grounding line where 80 of the ice melts within 240 km of becoming afloat a considerable portion of this later refreezes downstream as marine ice this produces a marine ice layer up to 200 m thick in the northwest sector of the ice shelf concentrated in a pair of longitudinal bands that extend some 200 km all the way to the calving front we drilled through the eastern marine ice band at two locations 70 km apart on the same flowline we determine an average accretion rate of marine ice of 1 1 0 2 m a 1 at a reference density of 920 kg m 3 between borehole sites and infer a similar average rate of 1 3 0 2 m a 1 upstream the deeper marine ice was permeable enough that a hydraulic connection was made whilst the drill was still 70 100 m above the ice shelf base below this marine close off depth borehole video imagery showed permeable ice with water filled cavities and individual ice platelets fused together while the upper marine ice was impermeable with small brine cell inclusions we infer that the uppermost portion of the permeable ice becomes impermeable with the passage of time and as more marine ice is accreted on the base of the shelf we estimate an average closure rate of 0 3 m a 1 between the borehole sites upstream the average closure rate is faster at 0 9 m a 1 we estimate an average porosity of the total marine ice layer of 14 20 such that the deeper ice must have even higher values high permeability implies that sea water can move relatively freely through the material and we propose that where such marine ice exists this renders deep parts of the ice shelf particularly vulnerable to changes in ocean properties

the denholm landslide saskatchewan part i geology the denholm landslide whose surface is composed of scarps ridges and elongated depressions is 160 m high 2000 m wide and up to 100 m thick the shear zone is in silty montomorillonitic clay of the upper part of the lea park formation and upper colorado group unit the upper cretaceous judith river formation and the quaternary empress sutherland and saskatoon groups were affected by the landslide although these sediments were fractured and gravity faulted by tension when the landslide moved they can be readily traced through the landslide particularly the upper part the scarps gravity faults ridges horsts and elongated depressions grabens are the surface expression of tension resulting from the stretching of beds during the landslide the movement of the landslide is thought to have started when the north saskatchewan spillway eroded to the level of the present shear zone about 11 000 years ago established by radiocarbon dating and is believed to have stopped in recent time during th

dual frequency altimeter signal from envisat on the amery ice shelf in antarctica radar altimeter measurements are sensitive to dielectric and penetration properties of the sensed medium snow such that the spacecraft s altitude can be biased since 2002 relatively low frequency radar measurements over the amery ice shelf east antarctica have been acquired using the envisat dual frequency altimeter at s 3 2 ghz and ku 13 6 ghz bands which penetrate a few meters into the firn the altimeter signal is however modified in summer by the presence of snowfilled crevasses indeed the specularity of the snow surfaces in summer makes the altimetric signal sensitive mostly to nadir echoes that increases the ratio between the crevasse signal and the surrounding ice shelf signal at nadir crevasses are distinguished by differences in backscattering behavior compared with the surrounding ice shelf signal crevasses are characterized by a strong backscatter coefficient at ku band and anomalies in the s band altitude estimation these two characteristics make snowfilled crevasses detectable by the dual frequency altimeter of envisat we first retrieve the geometric properties of the crevasses using a hyperbolic shape function created by strong crevasse backscatter in the ku waveform measurements from this retrieved crevasse signal and further waveform analysis we assess the properties of the snow surface and its sub surface the crevasse due to its small size compared to the altimeter footprint is found to be an excellent target to study snow properties of the ice shelf the anomalies in the s band altitude measurements over crevasses can then be explained by the presence of a double echo in the s band waveforms this echo is attributed to a reflection at the base of the snowbridge where we see evidence of sub surface echos in the individual altimeter waveforms based on this observation a methodology is developed to estimate the thickness of the snowbridge we calculate the penetration depths in the summer snow surface of the amery at ku band that is found to be around 6 m

very high frequency tides observed in the airglow over eureka 80 the absolute brightness and spectral distributions of oh airglow meinel band near infrared emissions 1 0 1 7 were obtained from a michelson interferometer operating at eureka 80 0 n 85 56 w canada during polar night a cross spectral analysis of brightness and rotational temperature data from december 1 1993 to december 20 1993 shows spectral features with periods near 12 8 6 4 and 3 hours the periods tidal harmonics and persistence days to weeks of these features argue for a tidal interpretation tidal hough functions indicate that the dominant spectral features are most likely the manifestation of zonally symmetric tides the tides at eureka exhibit a high degree of transience there is a suggestion of an oscillation with a period close to 5 hours

pleistocene stratigraphy of the saskatoon area saskatchewan canada an update pleistocene deposits in the saskatoon area are divided into the sutherland and saskatoon groups the sutherland group is divided into the mennon dundurn and warman formations and the saskatoon group is divided into the floral and battleford formations the floral formation is subdivided into the lower till the riddell member and the upper till each formation is composed of a sequence of deposits including basal proglacial sediment till upper proglacial sediment and nonglacial sediment each formation is defined primarily on the basis of carbonate content and stratigraphic position of its till and commonly it is bounded by weathered zones and or nonglacial sediments the sutherland group is pre illinoian in age and the lower till of the floral formation is illinoian in age the riddell member between the lower and upper tills of the floral formation is late rancholabrean probably sangamon in age radiocarbon ages of sediments lying between the upper till of the floral formation early wis

a landslide in till near warman saskatchewan canada little information is available about typical shear strength parameters of tills in southern saskatchewan even though till is the most common earth material used for construction in this region the warman landslide in the south saskatchewan river valley provides some insight into the shear strength characteristics of a till and the results are compared with laboratory tests the till is from the upper till of the sutherland group which has a high clay content relative to the underlying and overlying tills a back analysis of the landslide produced 27 assuming c 0 comparison with laboratory test data and results from a similar landslide near lebret saskatchewan suggests that 22 5 with c 7 kpa may be appropriate residual shear strength parameters a rising water table appears to have been the main contributing factor to instability between 1969 and 1984 there is a possibility however that at the 1 50 return interval for flood levels on the river erosion at the toe of the landslid

preconsolidation of tills and intertill clays by glacial loading in southern saskatchewan canada preconsolidation of pre battleford tills and intertill clays resulted in a narrow range of effective pressures 1800 200 kpa at 10 sites along a 1300 km transect across southern saskatchewan these data suggest an almost invariant loading system that is independent of total ice thickness which ranged from 1150 to 2000 m the preconsolidation process apparently took place in a temperate glacier environment the loading system is characterized as a variable thickness of ice related to distance from the glacier terminus a steady hydraulic grade line sustained a potentiometric surface within the subglacial sediments at an elevation consistently 69 76 of the total ice thickness this mechanism maintains small fluctuations in effective stress

velocity and strain rates derived from insar analysis over the amery ice shelf east antarctica we use displacements derived from matching complex synthetic aperture radar data using maximum coherence to generate a dense network of velocity estimates over the amery ice shelf from these velocities we generate the horizontal strain rate components and resolve them with respect to the local flow direction we present the spatial distributions of velocity and transverse shear strain rate and use them to investigate features of the flow regime for the shelf from the southern end of the shelf velocity decreases from a high of about 800ma 1 to around 300 ma 1 and then increases to a maximum of about 1350ma 1 at the centre of the front strain rates vary systematically across and along the shelf the pattern of the transverse shear strain rate clearly identifies the shear margins where values exceed 0 1 a 1 in the southern section of the shelf the pattern also shows longitudinal bands of enhanced shear strain rate containing ice with a strong preferred crystal fabric that was advected from shear margins upstream in the northern section of the shelf significant values of longitudinal and traverse stresses lead to enhanced shear deformation through their effect on the octahedral shear stress term

seismicity within a propagating ice shelf rift the relationship between icequake locations and ice shelf structure iceberg calving is a dominant mass loss mechanism for antarctic ice shelves second only to basal melting an important process involved in calving is the initiation and propagation of through penetrating fractures called rifts however the mechanisms controlling rift propagation remain poorly understood to investigate the mechanics of ice shelf rifting we analyzed seismicity associated with a propagating rift tip on the amery ice shelf using data collected during the austral summers of 2004 2007 we apply a suite of passive seismological techniques including icequake locations back projection and moment tensor inversion we confirm previous results that show ice shelf rifting is characterized by periods of relative quiescence punctuated by swarms of intense seismicity of 1 to 3 h even during periods of quiescence we find significant deformation around the rift tip moment tensors calculated for a subset of the largest icequakes mw 2 0 located near the rift tip show steeply dipping fault planes horizontal or shallowly plunging stress orientations and often have a significant volumetric component they also reveal that much of the observed seismicity is limited to the upper 50 m of the ice shelf this suggests a complex system of deformation that involves the propagating rift the region behind the rift tip and a system of rift transverse crevasses small scale variations in the mechanical structure of the ice shelf especially rift transverse crevasses and accreted marine ice play an important role in modulating the rate and location of seismicity associated with the propagating ice shelf rifts

variations in ice velocities of pine island glacier ice shelf evaluated using multispectral image matching of landsat time series data abstract pine island glacier pig in west antarctica drains out to the amundsen sea through pine island glacier ice shelf pigis as changes in ice velocities on pigis are strongly linked to changes in ice mass discharge from the west antarctic ice sheet it is very important to evaluate the spatiotemporal variations in ice velocities on the ice shelf this research estimated ice velocities of pigis from an ensemble of image matching of landsat time series multispectral data obtained from 2000 to 2014 orientation correlation was adopted for the image matching of blue green red near infrared panchromatic and the first principal image of the landsat multispectral data from which the results were combined and averaged the multispectral image matching proposed in this research produced 35 more ice velocity vectors than the use of a single band i e panchromatic band image matching the erroneous matches were filtered through simple but rigorous statistical evaluations the ice velocity of pigis accelerated by 55 during 2000 2010 and the acceleration of the image northing velocity component 1 3 km a 1 was higher than that of the image easting velocity component 0 8 km a 1 during 2010 2012 the ice velocity of pigis slowed down by 10 the ice velocity in 2014 increased by 5 from 2012 but was still lower than the peak values observed in 2010 the surface strain rate fields of pigis were derived from the ice velocity fields the longitudinal ice compression was observed near the grounding line and the geographically northern part of the central ice shelf of pigis while a fast flowing band was observed near the southern margin of the ice shelf the transverse strain rate showed that ice divergence in the hinge zone of the central ice shelf has increased since 2000 the width of the shear margins of the central ice shelf of pigis is 25 km which has been stable since 2000

preconsolidation pressures in intertill glaciolacustrine clay near blaine lake saskatchewan soft intertill glaciolacustrine clays are of concern for stability of slopes and foundations an intertill clay deposit between 32 and 54 m below the surface was continuously cored index properties were determined for 46 samples and 10 samples were tested on the oedometer stratigraphic evidence indicates that the glaciolacustrine clay blaine lake member lying between the till of the sutherland and saskatoon groups was glaciated three times however preconsolidation pressures of this intertill clay show the degree of consolidation is less than 20 based on a total stress from an estimated ice thickness extrapolated from the cypress hills this low preconsolidation pressure suggests there was insufficient time for dissipation of excess pore water pressure created by thickening of the advancing glacier key words preconsolidation pressure excess pore water pressure glaciers intertill clay

tidal variability of the geomagnetic polar cap mesopause above resolute bay variability in the geomagnetic polar cap neutral wind near the mesopause above resolute bay canada 74 9 n 94 9 w has been observed by a fabry perot interferometer using a circle to line detection technique fpi clio to observe the oh meinel emission we present an analysis of the first wind measurements obtained with the fpi clio from december 1995 to march 1996 the oh 7 3 892 0 nm doppler winds were analyzed for tidal oscillations defined herein as oscillations with periods which are sub harmonics of a solar day daily spectral analysis using 50 relatively clear days showed that oscillations between and including 12 h and 8 h were frequent throughout the winter season in both the meridional and the zonal winds a non linear least squares fit performed on the data from the jan 22 30 interval revealed that a 12 h tidal feature was dominant observations of the oh neutral winds show variations indicating strong tidal wave activity at the mesopause

ice thrust features and the maymont landslide in the north saskatchewan river valley the battleford glacier created shearing and softening of bedrock clays contributing to widespread slope instability along the valley of the north saskatchewan river the battleford glacier flowed southeastward down the valley of the north saskatchewan river during its final stage in west central saskatchewan it created flutings crevasse fillings folding and faulting in ice thrust ridges and extensive horizontal gouge zones filled with soft malleable clay extensive drilling and testing for the foundations of the maymont bridge provided definitive data outlining at least three gouge zones the shallowest gouge zone at an elevation of 465 m defines the base of the most severe glacial folding and deformation of the bedrock in at least one of the ice thrust ridges the deeper gouge zones are at about 433 and 438 m elevation postglacial landslides slumps along the southern side of the north saskatchewan river are controlled by the gouge zones which are low friction slide surfaces along which large ho

compression characteristics and index properties of tills and intertill clays in southern saskatchewan canada compression characteristics and index properties of unweathered tills and clays from repeated glaciations follow a predictable pattern at 10 sites along a 1300 km transect across southern saskatche

low frequency intraseasonal variations of the wintertime very high latitude mesopause regions 1 we have performed a spectral analysis of three fall and winter airglow data sets each for south pole station and for eureka canada 80 n these analyses show significant spectral features in the mesopause region at very high latitudes that are similar in period to low frequency intraseasonal is variations seen in analysis of length of day atmospheric angular momentum variations and outgoing long wave radiation as well as in height or wind fields up to 10 hpa 32 km these are fairly broadband spectral features centered approximately at 17 23 and 45 days the 17 day oscillation we find is more prominent than that found in the data sets reflecting variations mainly in the troposphere and stratosphere this oscillation is most likely associated with the second symmetric s 1 free rossby mode the data from south pole station should not reflect this mode as such because the spectral components that produce airglow variations should vanish at the pole unless they are zonally symmetric however free oscillations having zonal wave number zero with such long periods should not exist we suggest that at least at south pole station the 17 day oscillation is driven by interactions between the global rossby mode and stationary wave number one planetary waves in addition to the low frequency oscillations that have been reported in the is literature we see a wave in the 12 14 day period range at south pole station that wave may also reflect forcing by a global free mode

a new tide model for the antarctic ice shelves and seas we describe a new tide model for the seas surrounding antarctica including the ocean cavities under the floating ice shelves the model uses data assimilation to improve its fit to available data typical peak to peak tide ranges on ice shelves are 1 2 m but can exceed 3 m for the filchner ronne and larsen ice shelves in the weddell sea spring tidal ranges are about twice these values model performance is judged relative to the 5 10 cm accuracy that is needed to fully utilize ice shelf height data that will be collected with the geoscience laser altimeter system scheduled to be launched on the ice cloud and land elevation satellite in late 2002 the model does not yet achieve this level of accuracy except very near the few high quality tidal records that have been assimilated into the model some improvement in predictive skill is expected from increased sophistication of model physics but we also require better definition of ice shelf grounding lines and more accurate water column thickness data in shelf seas and under the ice shelves long duration tide measurements bottom pressure gauge or gps in critical data sparse areas particularly near and on the filchner ronne and ross ice shelves and pine island bay are required to improve the performance of the data assimilation model

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

the denholm landslide saskatchewan part ii analysis a procedure incorporating geological evidence with analytical methods was developed for the back analysis of a multiple retrogressive landslide in cretaceous clay shale the slide mass apparently inactive extends 2 km back from the toe at the river and is seated on a shear zone 100 m deep at the main scarp historical evidence of the slope movement was established from radiocarbon dating of the river alluvium over which the landslide moved the geometry of the landslide when the factor of safety was near unity was determined from historic and stratigraphic evidence and sensitivity analyses the stratigraphy of the slide mass showed that the beds are stretched with very little vertical displacement indicating a mainly translational mechanism along a nearly horizontal shear zone apparently movement has taken place at a slow but steady rate over 11 000 years resulting in a horizontal displacement of 390 430 m at the toe the landslide therefore was analyzed as a series of sliding blocks with a common f

the hepburn landslide an interactive slope stability and seepage analysis mechanisms of active landslides are continuous processes involving the dynamics of slope failure interacting with the groundwater regime this process is simulated in phases by combining stability calculations interactively with a seepage analysis to determine the factor of safety for a dormant landslide near hepburn saskatchewan the landslide is a multiple retrogressive failure with two parallel slip surfaces at different elevations the slip surfaces are in originally overconsolidated cretaceous and tertiary clays softened by shear from glaciation an artesian aquifer is present at the base of the slip surface causing saline springs at the base of the valley slope a residual effective friction angle of 6 7 with zero cohesion was found to best characterize the shear strength of the clays in the failure zone potential nets and head profiles from the seepage analysis illustrate the strong influence of changing topography on the groundwater flow system the present day factor of safety for the dormant

the marginal shear stress of ice stream b west antarctica to ascertain whether the velocity of ice stream b west antarctica may be controlled by the stress in its marginal shear zones the snake and the dragon we undertook a determination of the marginal shear stress in the dragon near camp up b by using ice itself as a stress meter the observed marginal shear strain rate of 0 14 a 1 is used to calculate the marginal shear stress from the flow law of ice determined by creep tests on ice cores from a depth of 300 m in the dragon obtained by using a hot water ice coring drill the test specimen orientation relative to the stress axes in the tests is chosen on the basis of c axis fabrics so that the test applies horizontal shear across vertical planes parallel to the margin the resulting marginal shear stress is 2 2 0 3 10 5 pa this implies that 63 100 of the ice stream s support against gravitational loading comes from the margins and only 37 0 from the base so that the margins play an important role in controlling the ice stream motion the marginal shear stress value is twice that given by the ice stream model of echelmeyer and others 1994 and the corresponding strain rate enhancement factors differ greatly e 1 2 vs 10 12 5 this large discrepancy could be explained by recrystallization of the ice during or shortly after coring estimates of the expected recrystallization time scale bracket the 1 h time scale of coring and leave the likelihood of recrystallization uncertain however the observed two maximum fabric type is not what is expected for annealing recrystallization from the sharp single maximum fabric that would be expected in situ at the high shear strains involved 20 experimental data from wilson 1982 suggest that if the core did recrystallize the prior fabric was a two maximum fabric not substantially different from the observed one which implies that the measured flow law and derived marginal shear stress are applicable to the in situ situation these issues need to be resolved by further work to obtain a more definitive observational assessment of the marginal shear stress

basal melting and freezing under the amery ice shelf east antarctica the basal melting and freezing rates under the amery ice shelf east antarctica are evaluated and their spatial distributions mapped ice velocity surface elevation and accumulation rate datasets are employed in the analysis along with a column averaged ice density model our analysis shows that the total area of basal melting is 34 700 km 2 with a total annual melt of 62 5 9 3 gt and an average melting rate of 1 8 0 3 m a 1 basal freezing mainly occurs in the northwestern part of the ice shelf over a total area of 26 100 km 2 and with a maximum freezing rate of 2 4 0 4 m a 1 the total marine ice that accretes to the ice shelf base is estimated to be 16 2 2 4 gt a 1 using a redefined grounding line and geometry of the amery ice shelf we estimate the net melt over the ice shelf base is about 46 4 6 9 gt a 1 which is higher than previous modeling and oceanographic estimates net basal melting accounts for about half of the total ice shelf mass loss with the rest being from iceberg discharge our basal melting and freezing distribution map provides a scientific basis for quantitative analysis of ice ocean interaction at the ice shelf ocean interface

stratigraphy and structure of a late wisconsinan salt collapse in the saskatoon low south of saskatoon saskatchewan canada an update the saskatoon low is a collapse structure that formed as a result of dissolution of salt from the middle devonian prairie evaporite formation in this study the collapse has affected the upper cretaceous lea park judith river and bearpaw formations of the montana group the early and middle pleistocene mennon dundurn and warman formations of the sutherland group and the late pleistocene floral battleford and haultain formations of the saskatoon group locally the collapse is about 180 m which is about equal to the thickness of the salt the first phase of collapse took place after deposition of the ardkenneth member of the bearpaw formation and before glaciation or during a pre illinoian glaciation the second phase of collapse occurred during the battleford glaciation late wisconsinan prior to deposition of the battleford formation the saskatoon low was glacially eroded removing the sutherland group and the floral formation after the glacial erosion up to 110 m of soft till of the battle

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

digital elevation models for the lambert glacier amery ice shelf system east antarctica from ers 1 satellite radar altimetry the lambert glacier amery ice shelf system is a major component of the east antarctic ice sheet this paper presents two digital elevation models dems that have been generated for the lambert amery system from validated european remote sensing satellite ers 1 radar altimeter waveform data the first dem covers the amery ice shelf only and was produced using kriging on a 1 km grid the second is a coarser 5 km dem of the entire lambert amcry system generated via simple averaging procedures the dems provide unprecedented surface elevation information for the lambert amery system and allow new insight into the glaciology of the region

tidal oscillations of the arctic upper mesosphere and lower thermosphere in winter the upper mesosphere and lower thermosphere of the northern polar cap was investigated using fabry perot interferometer measurements of the horizontal wind velocity in the lower thermosphere meridian scanning photometer observations of atomic oxygen green line brightness in the lower thermosphere and michelson interferometer records of the infrared meinel oh bands brightness and rotational temperature in the upper mesosphere tidal airglow oscillations in the absence of local solar heating were studied using a superposed epoch analysis of observations obtained around three new moon intervals november 9 22 1993 december 7 20 1993 and january 4 17 1994 in eureka 80 n tidal harmonics were uncovered with an iterated least chi squared fit and their existence in the data tested using a goodness of fit probability against a null hypothesis of no oscillations no single dominant tide was found at all times and altitudes of the winter arctic upper mesosphere and lower thermosphere the horizontal wind velocity of the lower thermosphere exhibited all the first three harmonics of the tide with the largest amplitude oscillations shown by the diurnal component of the meridional wave speed the atmospheric layer near the mesopause that contributes to the oh airglow emission experienced terdiurnal oscillations throughout the winter season theoretical polarization relations for evanescent tides considerations of energy density propagation with altitude and a day by day analysis of the zonal and meridional wind speed and temperature all indicate that the terdiurnal tide observed on november was an evanescent zonally symmetric tide other data indicate propagating tides migrating tides or a mixture of both

simultaneous observations of the phase locked 2 day wave at adelaide cerro pachon and darwin the southern hemisphere summer 2 day wave tdw is the most dramatic large scale event of the upper mesosphere the winds accelerate over 1 week may attain 70 m s and are often accompanied by a near disappearance of the diurnal tide and stabilization of the period close to 48 h we denote this as the phase locked 2 day wave pl tdw we have examined airglow and meteor radar mr wind data from the andes lidar observatory cerro pachon chile 30 s 289 3 e mr data from darwin 12 5 s 131 e and airglow and medium frequency radar data from the university of adelaide 34 7 s 138 6 e for the behavior of the tdw during the austral summers of 2010 2012 and 2013 the cerro pachon and adelaide sites are located at similar latitudes separated in longitude by about 120 we find a remarkable coincidence between the tdw oscillations at chile and adelaide for the period january february 2010 the oscillations are nearly in phase in terms of local time and the minima and maxima repeat at nearly the same local time from cycle to cycle consistent with a phase locked wave number 3 tdw data for this and other years including darwin show that the amplitude of the diurnal tide decreases when the tdw is largest and that this occurs when the period is close to 48 h these observations support the proposal that the pl tdw is a subharmonic parametric instability wherein the diurnal tide transfers energy to a tdw that is resonant at nearly 48 h

observations and modeling of the 6 hour tide in the upper mesosphere 1 this paper presents observations and modeling of the 6 hour tide radar observations of horizontal winds at esrange 68 n 21 e indicate that this tidal periodicity is a consistent part of the diurnal variation and is largest during midwinter vertical structure and phase coherence provide strong support that the observed oscillations are tidal model simulations generate a tide that has many similarities to the observed tide at esrange diagnostic model tests indicate that the tide is forced primarily by the 6 hour component of solar heating globally the monthly mean simulated tide is dominated by the migrating component except near the poles although the contribution from nonmigrating modes is not negligible according to the model both migrating and nonmigrating 6 hour tides have small amplitude in low latitudes

meteoric and marine ice crystal orientation fabrics from the amery ice shelf east antarctica the northwestern sector of the amery ice shelf east antarctica has a layered structure due to the presence of both meteoric ice and a marine ice layer resulting from sub shelf freezing processes crystal orientation fabric and grain size data are presented for ice cores obtained from two boreholes 70 km apart on approximately the same flowline multiple maxima crystal orientation fabrics and large mean grain sizes in the meteoric ice are indicative of stress relaxation and subsequent grain growth in ice that has flowed into the amery ice shelf strongly anisotropic single maximum crystal orientation fabrics and rectangular textures near the base of the 200 m thick marine ice layer suggest accretion occurs by the accumulation of frazil ice platelets crystal orientation fabrics in older marine ice exhibit vertical large circle girdle patterns influenced by the complex stress configurations that exist towards the margins of the ice shelf post accumulation grain growth and fabric development in the marine ice layer are restricted by a high concentration of brine and insoluble particulate inclusions differences in the meteoric and marine ice crystallography are indicative of the contrasting rheological properties of these layers which must be considered in relation to large scale ice shelf dynamics

tide deflection of campbell glacier tongue antarctica analyzed by double differential sar interferometry and finite element method abstract a glacier tongue the terminus of a glacier projecting out from the coastline and floating over the ocean experiences vertical deflection due to the fluctuation of ocean tide accurate analysis of the tidal deflection of a glacier tongue is necessary to understand the elastic properties and dynamics of glacial ice we extracted the tidal deflection of campbell glacier tongue cgt one of the fast flowing glacier tongues in east antarctica by using 120 double differential interferometric sar ddinsar images from the 16 cosmo skymed one day tandem interferometric sar image pairs obtained during 2010 and 2011 a map of tide deflection ratio map defined as the ratio of the tidal deflection over tide height was generated by pixel based linear regression between the ddinsar derived tidal deflection and the tidal variation predicted by various tide models such as tpxo7 1 fes2004 cats2008a and ross inv after the inverse barometer effect correction we also generated the maps of r 2 root mean square error rmse and intercept of the linear regression model we confirmed that the horizontal flow of the campbell glacier is steady over the whole data acquisition period due to the fact that values were close to zero over the grounded part of the glacier ross inv provided the most reliable map with the highest r 2 0 97 and the smallest rmse 0 3 cm beyond the hinge zone than other tide models the spatial variation of the tidal response of the whole cgt was clearly defined from the map the grounding line retreated by 0 3 1 5 km in comparison with that in 1996 defined by rignot et al 2011a the ice thickness of cgt was estimated to be 397 71 m from icesat surface elevation data the young s modulus of cgt was found to be 0 5 1 3 gpa 0 8 gpa at an ice thickness of 397 m by simulating the in the hinge zone using a 2 dimensional finite element method

optimal measurement of ice sheet deformation from surface marker arrays surface strain rate is best observed by fitting a strain rate ellipsoid to the measured movement of a stake network or other collection of surface features using a least squares procedure error of the resulting fit varies as 1 l delta t square root of n where l is the stake separation delta is the time period between initial and final stake survey and n is the number of stakes in the network this relation suggests that if n is sufficiently high the traditional practice of revisiting stake network sites on successive field seasons may be replaced by a less costly single year operation a demonstration using ross ice shelf data shows that reasonably accurate measurements are obtained from 12 stakes after only 4 days of deformation it is possible for the least squares procedure to aid airborne photogrammetric surveys because reducing the time interval between survey and re survey permits better surface feature recognition

the cavity under the amery ice shelf east antarctica ocean circulation under ice shelves and associated rates of melting and freezing are strongly influenced by the shape of the sub ice shelf cavity we have refined an existing method and used additional in situ measurements to estimate the cavity shape under the amery ice shelf east antarctica a finite element hydrodynamic ocean tide model was used to simulate the major tidal constituents for a range of different sub amery ice shelf cavity water column thicknesses the data are adjusted in the largely unsurveyed southern region of the ice shelf cavity by comparing the complex error between simulated tides and in situ tides derived from gps observations we show a significant improvement in the simulated tides with a combined complex error of 1 8 cm in comparison with past studies which show a complex error of 5 3 cm our bathymetry incorporates ice draft data at the grounding line and seismic surveys which have provided a considerable amount of new data this technique has particular application when the water column beneath ice shelves is inaccessible and in situ gps data are available

iceberg calving from the amery ice shelf east antarctica we investigate the iceberg calving cycle of the amery ice shelf ais east antarctica using evidence acquired between 1936 and 2000 the most recent major iceberg calving event occurred between late 1963 and early 1964 when a large berg totalling about 10000 km2 in area broke from the ice front the rate of forward advance of the ice front is presently 1300 1400 m a 1 at this rate of advance based on the present ice front position from recent radarsat imagery it would take 20 25 years to attain the 1963 pre calve position suggesting that the ais calving cycle has a period of approximately 60 70 years two longitudinal parallel to flow rifts approximately 25 km apart at the ais front are observed in satellite imagery acquired over the last 14 years these rifts have formed at suture zones in the ice shelf where neighbouring flow bands have separated in association with transverse spreading the rifts were 15 km rift a and 26 km rift b in length in september 2000 and will probably become the sides of a large tabular iceberg 25 km 25 km a transverse perpendicular to flow fracture visible at the upstream end of rift a in 1996 had propagated 6 km towards rift b by september 2000 when it meets rift b the iceberg will calve a satellite image acquired in 1962 shows an embayment of this size in the ais front hence we deduce that this calving pattern also occurred during the last calving cycle and therefore that the calving behaviour of the ais apparently follows a regular pattern

geology and diamond distribution of the 140 141 kimberlite fort a la corne central saskatchewan canada abstract the cretaceous age fort a la corne falc kimberlite province comprises at least 70 bodies which were emplaced near the edge of the western canadian interior seaway during cycles of marine transgression and regression many of the bodies were formed during a marine regression by a two stage process firstly the excavation of shallow but wide craters and then subsequent infilling by xenolith poor crater facies subaerial primary pyroclastic kimberlite the bodies range in size up to 2000 m in diameter but are mainly less than 200 m thick and thus comprise relatively thin but high volume pyroclastic kimberlite deposits each body is composed of contrasting types of kimberlite reflecting different volcanic histories and therefore are considered separately the 140 141 kimberlite is the largest delineated body in the province estimated to have an areal extent below glacial quaternary sediments in excess of 200 ha the infilling of the 140 141 crater is complex resulting from multiple phases of kimberlite the central part of the infill is dominated by several contrasting phases of kimberlite one of these phases is a primary pyroclastic airfall mega graded bed up to 130 m in thickness the constituents grade in size from very fine to coarse macrocrystic kimberlite through to a basal breccia the mega graded bed is a widespread feature within parts of the body examined to date and at this current stage of evaluation appears to explain a variable diamond distribution within a tested portion of the pipe a second different phase of kimberlite is interpreted as representing a younger nested crater within the mega graded bed centrally located thicker intersections 450 m of this younger kimberlite may indicate a vent for the kimberlite crater the thickness of the mega graded bed increases with proximity to the younger kimberlite in the study area macrodiamond minibulk sample grades from the mega graded bed have been obtained from nine large diameter drill holes located within the northwest part of the body from an area of 20 ha which represents approximately 10 of the currently modeled kimberlite outline diamond grade increases with depth within the mega graded bed and also increases within the same unit towards the centrally positioned younger kimberlite macrodiamond sample grades vary from low at the top of the mega graded bed to considerably higher grades near the base total sample grade per drill hole varies from moderate near the vent feature to lower grades 200 300 m from the vent feature macrodiamond stone frequency measured in stones per tonne shows a pronounced relationship with depth and proximity to the vent feature within the mega graded bed there is a strong correlation between depth and increased stones per tonne and a similar correlation between stones per tonne and proximity to the vent feature the data supports the emplacement model of the mega graded bed and in turn this information is useful in understanding the macrodiamond distribution within this bed

fire lake depression a glacially eroded feature in southwestern saskatchewan canada fire lake depression which is 9 km long 5 km wide and about 100 m deep was formed by surface removal of about 40 m of drift mainly till and 60 m of cretaceous sands silts and clays the depression which was formed during the last glaciation was partly filled with hummocky glaciolacustrine sands and silts the bedrock beneath the depression is slickensided folded brecciated softened and gouged typical of structures formed by shear the physical dimensions stratigraphy structure and age last glaciation indicate that the fire lake depression was formed by glacial erosion the folding faulting brecciation gouge and softening of the bedrock beneath the depression are indicative of shear and suggest glacial thrusting the process of glacial thrusting was not verified however because the sediments excavated from the depression were not found the fact that the base of the depression corresponds to the uppermost most clayey bed least shear resistance suggests that the depression was fo

large scale waves in the upper mesosphere at antarctic high latitudes upper mesosphere combined optical measurements of wind and temperature fields at amundsen scott station south pole and wind radar measurements at scott base 78 s 167 e show the presence of large scale waves in this region of the atmosphere at amundsen scott the largest amplitude wave observed with sub diurnal periodicity appears with a frequency near 2 4 day 10 1 hour period with a westward phase progression of wavenumber one the presence of a wave with this periodicity is confirmed by the observations at scott base the combination of the experimentally found period phase progression associated small temperature oscillations and theoretical considerations lead to the interpretation of this wave as a lamb wave the present combination of spatially resolved optical measurements and radar measurements illustrates the value of multiple station and multiple technique observations in elucidating the upper mesosphere dynamical state as well as the properties of the waves propagating through the medium where the observations are being made

the dirt hills structure an ice thrust feature in southern saskatchewan canada the dirt hills structure is expressed at the surface as a broad arcuate moraine 7 5 km wide 120 m high and 40 km long the structure is composed mainly of bedrock and drift consisting of three slabs stacked to form a single block 215 m thick the shear zones that bound the slabs are mainly in clays of the bearpaw formation the dirt hills structure originated during the last deglaciation when the glacier under compressive flow readvanced up the missouri coteau escarpment and stacked the subglacial slabs of bedrock and drift the subparallel arcuate ice thrust ridges are formed presumably by imbricate thrust faults originating from the uppermost shear zone

measurement of temperature in a margin of ice stream b antarctica implications for margin migration and lateral drag ice temperature was measured in and around the chaotically crevassed south margin of ice stream b antarctica from 1992 to 1994 the temperatures at 30 m depth in the chaotic zone are about 12 k lower than in the adjacent uncrevassed ice due to the ponding of cold winter air at depths greater than 150 m there is clear evidence of internal heating of the ice due to the large shear deformation rate in the marginal zone analysis of the depth of cooling below the crevasses and of the internal heating gives two pieces of information first over the last half century the lateral shear stress averaged 2 0 x 10 5 pa in the top third of the margin and second the margin moved outward at an average rate of 7 3 m a these values do not involve any assumptions about the flow law of ice the uncertainties are roughly 20 the value of lateral shear stress indicates that the most of the drag on the ice stream is along its sides

simultaneous mesospheric wind measurements near south pole by optical and meteor radar methods simultaneous and co located measurements of mesospheric winds near south pole by high resolution optical and meteor radar methods show that these two methods determine very similar motions at slightly different heights of observation the measured atmospheric motions by the two techniques show that a the mean wind during 12 days in june 1995 was found to have a 7 m s amplitude flowing towards the 5 e longitude direction the latter direction is different from the 30e direction found earlier during august 1991 and 1992 b the observed dominant oscillations in the wind at both heights of observation are those of zonal wavenumber one character westward phase propagation was determined for the observed short period 0 hours oscillations and eastward phase propagation for the longer period 3 days oscillations respectively because of the neighboring heights of observation by the optical and meteor radar methods the in situ vertical wavelengths of propagation of the observed waves have been determined to be greater than 100 km for the 10 hr oscillations and near 65 km for the longer period oscillations with this new information we are able to independently establish the earlier assignment of the nearly 10 hr oscillations as the different meridional modes of a zonal wavenumber one lamb wave the determined vertical wavelength and eastward phase progression of the longer periodicity waves indicate these oscillations are likely to be the gravest inertio gravity wave which has the appropriate equivalent depths at these periods of oscillation the simultaneous absence of statistically significant kinetic temperature and optical tracer emission rate oscillations at the frequencies corresponding to the wind motions provides independent support to the earlier deductions on the ability of the atmosphere near the rotational poles to support only certain zonal character oscillations

topography of streaklines on an antarctic ice shelf from photoclinometry applied to a single advanced land imager ali image we investigate the usefulness of the experimental advanced land imager instrument onboard the earth observing 1 satellite and a shape from shading technique to study streaklines flow stripes on the amery ice shelf antarctica local variations in brightness in the image are directly related to surface topography because the snow surface reflectivity is mostly uniform image brightness values are combined with sun position and streakline orientation to calculate surface topography to centimeter level vertical precision the amplitude of the streaklines is typically 1 2 m and spacing is on the order of 1 km the streaklines show complex along flow changes in cross sectional shape that we interpret to be effects from temporal changes in grounding line dynamics and decay of ice topography due to flow cross sectional areas of the streaklines are calculated at various points along flow to investigate morphological evolution the study area subscene covers a 28 km spl times 90 km area and covers spl sim 350 years of ice flow

twelve hour tides in the winter northern polar mesosphere and lower thermosphere 1 an investigation of the tidal oscillations near the winter northern polar mesopause has been carried out at resolute bay canada 74 9 n 94 9 w the daily monthly and annual variations of the tidal field were studied using the 1995 1996 and 1996 1997 data ground based measurements were obtained using a fabry perot interferometer with a circle to line interferometric optical system fpi clio and the e region wind interferometer erwin the fpi clio observed the doppler winds of the oh emission near 86 km altitude the erwin provided simultaneous oh near 86 km and oi near 97 km wind measurements monthly data were compared to the global scale wave model gswm and the forbes vial solar semidiurnal tidal model predictions analysis of the 12 hour oscillation near 86 and 97 km altitudes indicates that it is persistent and characteristic of a semidiurnal propagating tide the semidiurnal tide was found to be highly variable in amplitude and phase from day to day the observations presented provide a continuous and extensive data set for the winter season index terms 3332 meteorology and atmospheric dynamics mesospheric dynamics 3334 meteorology and atmospheric dynamics middle atmosphere dynamics 0341 0342 3384 meteorology and atmospheric dynamics waves and tides keywords semidiurnal tide polar mesosphere polar thermosphere fabry perot interferometer resolute bay mesopause

the denholm landslide saskatchewan canada an update the lower block of the denholm landslide has moved 370 m over alluvium deposited by the north saskatchewan spillway and river during the last 11 500 years at an average rate of 32 mm year these values must be considered minimal because erosion of the toe of the landslide is required for the formation of retrogressive landslides the shear strength for the bedrock clay shale of the lea park formation was back calculated to be assuming zero cohesion key words retrogressive landslide clay shale residual strength movement rates geological age inclinometer

observations of a 12 h wave in the mesopause region at the south pole in december 1989 a na lidar was installed at the amundsen scott south pole station and was used to measure aerosol stratospheric temperature and mesospheric na profiles through october 1990 the mesospheric na data are used to characterize the gravity wave field in the mesopause region these first lidar observations of na layer dynamics at the south pole show strong wave activity during the antarctic winter data for 25 june and 19 august 1990 ut are presented here the total wave induced variances in atmospheric density are respectively 29 and 35 2 the na layer centroid height is very low during both observation periods on 25 june a strong 12 h oscillation is observed in the bottomside of the na layer which extends to altitudes as low as 74 km the vertical displacement and temperature amplitudes associated with the 12 h oscillation are respectively 1 9 km and 19 k the characteristics of the 12 h wave are similar to the pseudotide observed at svalbard by walterscheid et al 1986

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

red deer hill a drumlinized glaciotectonic feature near prince albert saskatchewan canada red deer hill is 5 km long 3 km wide and 70 m high the hill is a glaciotectonic structure formed by a single 106 m thick thrust block presumably derived from the 80 m deep upglacier holmes depression the thrust block became dislodged by displacement along a presheared horizontal gouge zone where the shearing resistance of the clay was reduced to a residual state by the first mennon glaciation the hill depression structure was formed by the battleford glacier which drumlinized red deer hill before depositing a veneer of till over the structure the holmes depression was filled with glacial lake saskatchewan lacustrine and deltaic sediments horizontal displacement along a decollement in the direction of the activating force resulted in a stress environment changing from extension to compression in the zone of extension holmes depression an active rankine state developed and beds stretched and thinned in the zone of compression red deer hill conversely a passive rankine state developed an