active and passive microwave signatures of antarctic firn by means of field measurements and satellite data the angular dependence and polarization behaviour of back scattering and emission of polar firn at 5 2 ghz and 10 3 ghz were measured during an oversnow traverse in dronning maud land antarctica the signatures emphasize the importance of snow stratification in the interpretation of microwave remote sensing measurements highest backscattering coefficients and little angular variations were observed for refrozen firn near the coast in permanently dry snow areas with high accumulation rates and homogeneous snow morphology showed low backscattering coefficients and high emissivities pronounced layering and related density variations in low accumulation zones resulted in increased polarization differences of brightness temperatures and increased like polarized backscattering coefficients this behaviour is confirmed by the analysis of c band scatterometer measurements of the active microwave instrument aboard the european space agency s ers 1

on the use of the dual frequency envisat altimeter to determine snowpack properties of the antarctic ice sheet abstract the primary purpose of ice sheet altimetry is to monitor the changes in ice sheet topography which may impact on global sea level however the altimetric signal is sensitive to different properties of the snowpack and therefore can also be used to determine these properties the radar altimeter onboard the european space agency s envisat satellite provides a dual frequency dataset at ku 13 6 ghz and s band 3 2 ghz in this paper these signals are studied over the antarctic ice sheet during the 4 first years of the mission 2002 2006 in order to retrieve snowpack properties the altimeter signal can be described by 4 classical waveform parameters the 4 year time series of all these parameters are decomposed into a linear and a seasonal time component the linear component is almost constant the distribution of the mean parameters over the antarctic ice sheet shows that the altimeter signal is sensitive to small scale mm surface roughness for the first time the amplitudes and phases of the seasonal variations are characterized the s band amplitudes are greater than the ku band and the phase varies over the entire ice sheet previous studies suggested that the seasonal variations of the altitude from the altimeter are created by a decrease of the snowpack height through compaction the dual frequency observations shown here suggest that this hypothesis is too simple instead the altitude variations observed in the altimetric signal are not created by the snowpack height change but are more likely caused by the seasonal change of the snow properties which cause a different response between the s and ku bands therefore both the linear and the seasonal variations of the altimetric signal can be used to retrieve snowpack properties here we compare the dual frequency envisat signal with a model of the altimetric echo over the antarctic ice sheet the model combines a surface model with a sub surface model for both the s and ku bands the brown model brown g s 1977 the average impulse response of a rough surface and its applications ieee transactions on antennas and propagation 25 1 is used to describe the interaction of the radar wave with the snow surface the backscatter coefficient of the surface is derived using the iem method fung a k 1994 microwave scattering and emission models and their applications boston ma artech house the sub surface signal takes into account both the layering effects and the scattering caused by the homogeneous media which is composed of small snow grains the model is tested in two areas of the antarctic plateau which present very different waveform parameters the sensitivity of the radar signal to the different snowpack properties is investigated the analysis of the waveform behaviours shows that the sub surface signal can be completely masked by the small scale surface roughness signal finally the temperature and surface density effects are investigated in order to explain the seasonal variations of the altimetric signal both the temperature and the compaction rate of the snow change seasonally temperature is shown to impact on the ku band signal furthermore the compaction rate of the snow surface can explain all of the seasonal variation characteristics observed at both the s and ku bands the seasonal change of compaction rate in the snow creates a change in the waveform shape that can bias the altitude in particular the snow compaction can induce a bias in the retrieved altimetric altitude of more than 80 cm for the ku band and 1 5 m for the s band this work underlines that the altitude time series needs to be corrected for the shape of the altimetric echo over ice sheets

tectono geomorphic study of the karewa basin of kashmir valley abstract the karewa basin nestled between the pir panjal range and the great himalayan range in northwest india has been studied to understand its tectono geomorphic evolution on the basis of geomorphic indices and morphotectonic parameters supported by the field evidences satellite data topographic maps and digital elevation model dem were used to extract various parameters at various spatial scales four watersheds representative of the entire karewa basin were chosen for detailed studies on the basis of the researchable evidence of the complete sequence of the stratigraphic record and the preservation of geomorphic landscapes the integrated analysis of the geomorphic and morphometric data provides evidence of the relative variations in the tectonic activity among the watersheds geomorphic indices suggest a relatively high degree of tectonic activity along the pir panjal side of the karewa basin this variation in the relative degree of tectonic activity is consistent with the field evidence fault lineament locations and the landscape geometry of the karewa basin based on the results from this study it is suggested that late quaternary climate changes tectonic uplift and erosion of the pir panjal range and changing geometry of the karewa lake have played a key role in the evolution of the geomorphic landscape of the kashmir valley

thirty years of elevation change on antarctic peninsula ice shelves from multimission satellite radar altimetry 1 we use data acquired between 1978 and 2008 by four satellite radar altimeter missions seasat ers 1 ers 2 and envisat to determine multidecadal elevation change rates dhi dt for six major antarctic peninsula ap ice shelves in areas covered by the seasat orbit to 72 16 s regional averaged 30 year trends were negative surface lowering with rates between 0 03 and 0 16 m a 1 surface lowering preceded the start of near continuous radar altimeter operations that began with ers 1 in 1992 the average rate of lowering for the first 14 years of the period was typically smaller than the 30 year average the exception was the southern wilkins ice shelf which experienced negligible lowering between 2000 and 2008 when a series of large calving events began analyses of the continuous ers envisat time series to 81 5 for 1992 2008 reveal a period of strong negative dhi dt on most ice shelves between 1992 and 1995 based on prior studies of regional atmospheric and oceanic conditions we hypothesize that the observed elevation changes on larsen c ice shelf are driven primarily by firn compaction while the western ap ice shelves are responding to changes in both surface mass balance and basal melt rates our time series also show that large changes in dhi dt can occur on interannual time scales reinforcing the importance of long time series altimetry to separate long term trends associated with climate change from interannual to interdecadal natural variability

constructing improved decadal records of antarctic ice shelf height change from multiple satellite radar altimeters abstract antarctica s ice shelves the floating extensions of the ice sheet exert an important dynamic constraint on the flow of ice from the grounded ice sheet to the ocean and therefore on changes in global sea level thinning of an ice shelf reduces its ability to restrain the ice discharge from the grounded ice sheet however our understanding of how ice shelf processes couple ice sheet changes to climate variability is still rudimentary in part this is due to the brevity and low temporal resolution of surveys of ice shelf thickness relative to the broad range of time scales on which ice sheet mass fluctuates here we present improved procedures to construct 18 year 1994 2012 time series of antarctic ice shelf surface height at high spatial resolution 30 km by merging data from three overlapping satellite radar altimeter missions ers 1 ers 2 and envisat we apply an averaging scheme to enhance the signal to noise ratio of height changes over the floating ice shelves and extract low order polynomial trends using a robust approach regularized regression with cross validation that accounts for both bias and variance in the fit we construct formal confidence intervals by bootstrap resampling of the residuals of the fit the largest source of height error arises from the interaction of the radar signal with the snow and firn surface on annual time scales changes in surface and sub surface scattering and radar penetration lead to apparent height changes that are larger than the true surface height change arising from densification our 18 year time series of surface height provide an insight into how ice shelves respond to the changing atmospheric and oceanic conditions our methods could also be applied to grounded portions of the ice sheets both in antarctica and greenland

a comparison of greenland ice sheet volume changes derived from altimetry measurements we compare rates of surface elevation change on the greenland ice sheet derived from european remote sensing satellite 2 ers 2 radar altimeter data with those obtained from laser altimeter data collected over nearly the same time periods radar altimeter data show more rapid thickening 9 1 cm a 1 above 1500 m elevation in the north and 3 1 cm a 1 above 2000 m in the south than the laser estimates possibly caused by a lifting of the radar reflection horizon associated with changes in the snowpack such as those caused by progressively increased surface melting as summer temperatures rise over all the ice sheet above 2000m this results in an ers derived volume balance 75 15 km 3 a 1 more positive than that from laser data this bias between laser and radar estimates of elevation change varies spatially and temporally so cannot at present be corrected without independent surveys such as those presented here at lower elevations comparison of detailed repeat laser surveys over jakobshavn isbrae with ers results over the same time interval shows substantial ers underestimation of ice thinning rates this results partly from missing data because of bad radar waveforms over the very rough surface topography and partly from the tendency for large radar footprints to sample preferentially local high points in the topography thus missing regions of most rapid thinning along glacier depressions

changes in the extent of north american ice sheets during the late cenozoic magnetostratigraphy indicates that early pleistocene glaciations in north america instead of forming one continuous ice mass from atlantic to pacific as they did in the late pleistocene were characterized by eastern and western ice masses separated by a 2000 km wide north south ice free corridor down the centre of the continent we argue therefore that the area covered by ice during periods of glaciation and hence probably ice volume in north america was considerably less in the first 2 ma of the late cenozoic than it was in the last 0 7 ma this is consistent with delta 18o records of ocean cores indicating the ice volumes were much less in the earlier than in the later part of the cenozoic ice age

envisat derived elevation changes of the greenland ice sheet and a comparison with icesat results in the accumulation area abstract we show for the first time over the greenland ice sheet that an along track method for deriving rates of elevation change can successfully be applied to envisat radar altimetry data 2002 2010 the results provide improved resolution and coverage compared to previous results obtained from cross over methods also we find that temporal changes in the elevation change rate can be derived from envisat data and show clear examples of this by generating five year running means for selected areas of the greenland ice sheet for a period between 2003 and 2009 the elevation of the ice sheets was measured by both the laser altimeter on board icesat and the radar altimeter on board envisat we compare rates of elevation change derived from icesat and envisat for this time span in which both sensors were operating we focus on the area above the equilibrium line altitude in order to specifically derive information on snow parameters a comparison of the elevation changes observed by the two sensors shows a complex pattern which can be explained regionally by model output describing the changes in both firn air content and accumulation rates

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

tectonics and climate of the southern central andes the history of the southern central andes including the world s second largest plateau and adjacent intermontane basins and ranges of the eastern cordillera and the northern sierras pampeanas of argentina and bolivia impressively documents the effects of tectonics and topography on atmospheric circulation patterns the development of orographic barriers and their influence on erosion and landscape evolution at various timescales protracted aridity in the orogen interior has facilitated the creation and maintenance of the puna altiplano plateau contraction and range uplift filling of basins and possibly wholesale uplift of the plateau increased gravitational stresses in the orogen interior which caused the eastward migration of deformation into the foreland and successive aridification the uplift of the andean orogen has also had a far reaching influence on atmospheric and moisture transport patterns in south america this is documented by the onset of humid climate conditions on the eastern side of the andes in late miocene time which was coupled with the establishment of dramatic precipitation gradients perpendicular to the orogen and changes in tectonic processes in the andean orogenic wedge

consistent patterns of antarctic ice sheet interannual variations from envisat radar altimetry and grace satellite gravimetry summary interannual variations of the antarctic ice sheet due to surface mass balance smb fluctuations are important for mass balance estimates and interpretations to date these variations are primarily assessed by global or regional atmospheric modelling satellite altimetry and satellite gravimetry over the ice sheet provide complementary observations of the related volume and mass effects respectively yet so far the interannual signal contents of these observations have not been extensively studied we compare and jointly interpret envisat radar altimetry ra and grace satellite gravimetry results relying on ra products from the along track repeat satellite ra approach and on the grace 10 d solutions by cnes grgs ra results and grace results are expressed in terms of variations of ice sheet thickness z t and ice equivalent thickness zice t respectively in view of the different errors and limitations of both techniques and of differences between z t and zice t expected due to firn related processes our principal approach is a comparison of qualitative patterns in space and time to adjust the spatial resolution of both data sets we describe the spatial filtering inherent to the regularization of the cnes grgs grace solutions and apply this filtering to the envisat ra height changes in a consistent fashion after correction for glacial isostatic adjustment the spatial patterns of linear trends seen by envisat ra and grace over the period 2002 october to 2009 august agree well not only for the extreme ice losses in the west antarctic amundsen sea sector but also for an alternating sequence of gains and losses along the east antarctic coast our main focus is on interannual signals which we represent by the low pass filtered non linear non seasonal components of the z t and zice t time series these components should reflect interannual smb variations apart from effects of changes in ice flow we find an agreement between the interannual variation patterns from envisat ra and grace with temporal correlation coefficients typically in the order of 0 8 this qualitative agreement prevailing even in the theoretical absence of a simple proportionality between z t and zice t indicates that both observational signals primarily originate in common geophysical variations combining both geodetic data sets aids their interpretation and promises to be valuable for the reduction of smb uncertainties in a case study based on the analysis of both grace and envisat ra we identify a prominent interannual feature in west antarctica in 2005 september october as an event of excess snow accumulation with a mass effect of 82 31 gt

altimetric observations of surface characteristics of the antarctic ice sheet the aim of this paper is to investigate the geophysical characteristics of the antarctic ice sheet using radar altimetric observations to do this we use an altimetric waveform simulator in situ observations ers 1 european remote sensing satellite data and spot satellite pour l observation de la terre images the small scale study takes place at dome c terre adelie which is a relatively flat region with gentle undulations and low wind speed despite this the altimetric waveform parameters height energy leading edge and trailing edge are highly noisy the effect of undulations on the waveform parameters is found to be dominant the combination of a subsurface signal and a rough surface produces a linear effect on the altimetric backscattering or on the trailing edge of the waveform but a strongly non linear effect on the leading edge of the waveform or height estimation as a consequence the height measurement is very sensitive to the altimeter technical or orbital characteristics and is not reproducible from one mission to another observations show sastrugi fields that enhance the leading edge and affect the whole waveform observed local backscattering changes probably due to local variations in surface microroughness enhance the backscattered energy and may artificially create a topographic signal the continental scale study shows coherent patterns even if both surface and subsurface components affect the altimetric observation the large scale signal is mostly controlled by surface backscattering variations the surface or near subsurface characteristics of the snowpack may then be reached by altimetric observations

snow facies over ice sheets derived from envisat active and passive observations this paper aims to separate different snow regions over the terrestrial ice sheets based on their measured microwave signatures it takes advantage of coregistered data from passive and active sensors on the environmental satellite envisat to directly derive a snow facies indicator in a point by point basis this paper represents the first attempt of this kind in exploiting nadir viewing and dual frequency data from both altimeter and radiometer sensors the approach is based on a clustering method such representation of the data by means of fewer clusters necessarily loses fine details but achieves simplification in geographical representation and eases the description of the condition of the ice sheets in 2004 our approach broadens the description of the snow pack by taking into account characteristics such as surface roughness grain size stratification and snowmelt effects whereas the latter has often solely been considered in most previous work such partition of the ice sheets might help to better understand relationships between microwave signatures and snow morphology it could also be useful for estimating elevation uncertainty in altimeter data which in turn is essential to correctly interpret the significance of the rates of elevation change in a changing climate and to convert elevation change to snow mass change

different ers altimeter measurements between ascending and descending tracks caused by wind induced features over ice sheets the ers1 satellite provides a high resolution radar altimeter measurement up to 81 5 latitude for polar cap studies here we examine one particular effect of the interaction between the radar wave and the snowpack surface on height measurements measurements from ascending and descending tracks show systematic differences as large as 1 m such an artifact to be removed if it can be estimated the difference appears to be related to the way the altimeter perceives wind induced sculpting of the snowpack differences in the volume echo weight between ascending and descending passes appear to be the explanation seasat scatterometer allowed us to estimate independently the signal that could be inferred by wind features our results yield a map of the effect of wind on radar altimetric measurement finally we consider the possibility of long term variations in altimeter measurements caused by climatic changes

regional variations in tectonic geomorphology along a segmented convergent plate boundary pacific coast of costa rica abstract pacific coastal mountain piedmont landforms of costa rica extend across the tectonic boundary between the forearc and magnetic arc region of an active convergent margin this plate boundary became segmented circa 1 million years ago when the aseismic cocos ridge impinged upon the middle america trench offshore from the southernmost coastal area of costa rica morphometric analyses of 100 mountain fronts and numerous river long profiles radiometric dating and field studies were conducted in two study areas located arcward from the plate boundary where oceanic lithosphere of the cocos plate is being subducted beneath the caribbean plate region i and the partially subducted aseismic ridge is uplifting the plate margin by isostatic and collisional processes region ii values of tectonic geomorphic parameters mountain front sinuosity s percent dissected facets ffd river concavity k are not only different statistically in regions i and ii but are also different in the areas experiencing isostatic and collisional responses to the subducting aseismic ridge in the area experiencing collisional responses mountain fronts developed along ne dipping imbricate thrust and high angle reverse faults step upward and inland from the coast morphometric data along with the divergence of river terrace profiles from the coast piedmont inland toward the mountains indicates higher uplift rates along interior range mountain fronts isostatic uplift in the outer forearc area in region ii produces a distinctly different morphologic and neotectonic style characterized by regional uplift distributed across a number of blocks bounded by normal faults geomorphic analyses indicate a general southward trend of increasing tectonic uplift from region i into region ii where the highest frequency of mountain fronts with low values of s and ffd as well as rivers with the highest values of k occur over the crest of the subducted ridge field and historical seismic data for these regional trends include 1 fault scarps displacing late quaternary fluvial terraces and colluvial soils in areas of collisional responses 2 holocene latest pleistocene marine sediments uplifted tens of meters along normal faults in areas of isostatic response of region ii and 3 more frequent shallow high magnitude earthquakes in region ii this study indicates that spatial variations in the plate tectonic framework can be detected by regional morphometric analyses using techniques applied in extensional and compressional terranes of arid and semiarid regions but not previously applied to forearc systems along convergent plate boundaries in tropical areas

a 4 decade record of elevation change of the amery ice shelf east antarctica 1 we report on long term surface elevation changes of the central amery ice shelf ais by comparing elevation records spanning 4 decades 1968 2007 we use elevation records acquired with the following methods optical leveling 1968 1969 ers radar altimetry 1992 2003 gps 1995 2006 and ice cloud and land elevation satellite icesat laser altimetry 2003 2007 we compute multidecadal elevation trend dh dt values at crossovers between the leveling route and each of the gps and icesat tracks as well as shorter period dh dt at ers ers gps gps and icesat icesat crossovers at gps leveling crossovers the mean long term dh dt is 0 003 m a 1 and at icesat leveling crossovers the mean dh dt is 0 013 m a 1 neither trend is significantly different from zero the data do however exhibit variable trends near zero change between 1991 and mid 1996 then thickening to 2003 followed by thinning 2003 2007 with 5 year dh dt averages exceeding 0 1 m a 1 the changes in dh dt pattern in mid 1996 and again in 2003 occur with unexpected speed the ice shelf exhibits different dh dt patterns than does the surrounding grounded ice suggesting that surface mass balance variations or longer term variations in firn densification processes are unlikely to be major causes we conclude that these observed multiyear elevation changes must be due to currently unexplained or presently poorly quantified phenomena involving surface or basal processes and or ice dynamics with the multidecadal stability of the ais established the short term fluctuations that we observe suggests that for other ice shelves observed strong dh dt signals over short time periods do not necessarily indicate ice shelf instability

fine resolution radar altimeter measurements on land and sea ice satellite radar altimeter ra measurements are important for continued monitoring of rapidly changing polar regions in 2010 the european space agency launched cryosat 2 carrying siral a ku band ra with objectives of determining the thickness and extent of sea ice and the topography of the ice sheets one difficulty with ku band radar surveys over snow and ice is unknown penetration of ra signal into snow cover improving our understanding of the interactions of ra signals with snow and ice is needed to produce accurate elevation products to this end we developed a low power ultrawideband 12 18 ghz ra for airborne surveys to provide fine resolution measurements capable of detecting both scattering from the surface and layers within sea ice and ice sheets these measurements provide a means of identifying the dominant scattering location of lower resolution ra measurements comparable to satellite based instruments we generated two products a full bandwidth waveform fbw to identify scattering targets at fine resolution and a reduced bandwidth waveform rbw to represent conventional ra measurements retrackers are used to generate height estimates over various surface conditions for comparisons over ice sheets the leading edge tracker provided consistent ice surface elevation measurements between the fbw and rbw results however there were significant differences between the results from the centroid tracker over sea ice the location of the dominant return between the results from snow covered sea ice is highly variable this paper provides an overview of ra surveys in polar regions a description of the cresis system and a discussion of the results

tectonic evolution of kashmir basin in northwest himalayas abstract geomorphology has long been recognised as a key to evaluate the interplay between tectonics and landscape geometry in the regions of active deformation we use geomorphic signatures at varied spatial scales interpreted from srtm dem landsat etm data supplemented with field observations to review the tectonic evolution of kashmir basin in northwest himalayas geomorphic evidence is persuasive of a credible nnw sse trending dextral strike slip structure central kashmir fault ckf with the strike length of 165 km stretched centrally over the nnw sse length of the kashmir basin as a result of the strike slip motion and subsequent erosion significant deformation has taken place along the ckf in addition broad geomorphic architecture of the basin reveals typical pull apart characteristics hence we deduce that the kashmir basin has evolved as a pull apart quaternary sediment depression owing to the deformation along the central kashmir fault the spatial distribution pattern of seismic events neic catalogue 1973 2013 and gps measurements published collectively substantiate our geomorphic interpretations

earthquake geology of kashmir basin and its implications for future large earthquakes two major traces of active thrust faults were identified in the kashmir basin kb using satellite images and by mapping active geomorphic features the n130 e strike of the mapped thrust faults is consistent with the regional ne sw convergence along the indian eurasian collision zone the ne dipping thrust faults have uplifted the young alluvial fan surfaces at the sw side of the kb this created a major tectono geomorphic boundary along the entire strike length of the kb that is characterised by 1 a low relief with sediment filled sluggish streams to the se and 2 an uplifted region with actively flowing streams to the sw the overall tectono geomorphic expression suggests that recent activity along these faults has tilted the entire kashmir valley towards ne further the mw 7 6 earthquake which struck northern pakistan and kashmir on 8 october 2005 also suggests a similar strike and ne dipping fault plane which could indicate that the kb fault is continuous over a distance of 210 km and connects on the west with the balakot bagh fault however the geomorphic and the structural evidences of such a structure are not very apparent on the north west which thus suggest that it is not a contiguous structure with the balakot bagh fault therefore it is more likely that the kb fault is an independent thrust a possible ramp on the main himalayan thrust which has uplifting the sw portion of the kb and drowning everything to the ne e g madden et al 2011 furthermore it seems very likely that the kb fault could be a right stepping segment of the balakot bagh fault similar to riasi thrust as proposed by thakur et al 2010 the earthquake magnitude is measured by estimating the fault rupture parameters e g wells and coppersmith in bull seismol soc am 84 974 1002 1994 therefore the total strike length of the mapped kb fault is 120 km and by assuming a dip of 29 avouac et al in earth planet sci lett 249 514 528 2006 and a down dip limit of 20 km a mw of 7 6 is possible on this fault

changes in the velocity structure of the greenland ice sheet using satellite radar interferometry observations of greenland we detected widespread glacier acceleration below 66 north between 1996 and 2000 which rapidly expanded to 70 north in 2005 accelerated ice discharge in the west and particularly in the east doubled the ice sheet mass deficit in the last decade from 90 to 220 cubic kilometers per year as more glaciers accelerate farther north the contribution of greenland to sea level rise will continue to increase

influence of geomorphic and anthropogenic activities on channel morphology of river jhelum in kashmir valley nw himalayas abstract the srinagar reach of the river jhelum in kashmir valley india exhibits complex meandering and variable width 47 180m and depth 0 76 6 09m the reach is characterised by sharp bends in the river course channel sinuosity linearity of meander bends linear truncation of braid bars and concavities and convexities in the river channel reflecting varied river geomorphic processes during the extreme hydrological event of september 2014 a large number of river breaches occurred along the river jhelum particularly in the srinagar stretch of the river due to the floodwaters overflowing the banks and the consequent bank erosion the flooding situation was aggravated over the years by anthropogenic influences like the extensive urbanization of the jhelum floodplains encroachment of river banks and siltation of water courses due to the deforestation in the catchment and the shrinkage of wetlands which usually act as sponge during the flooding events to establish a relationship between the geomorphic processes and anthropogenic activities on river morphology we used various geomorphic parameters and techniques like river profiling bathymetric profiling lateral entrenchment ratio water velocity sinuosity index supported by gps and other field measurements the impact of the geomorphic and human induced changes on the channel morphology was corroborated with the data from the river breaches that occurred during the 2014 flooding a few of which occurred at the locations where geological structures lineaments faults cut across the river banks based on the investigations from this study it is suggested that varied geomorphic processes and the unchecked anthropogenic activities in the vicinity and catchment have significantly impacted the channel morphology of the river jhelum in kashmir valley increasing the vulnerability of the srinagar city to flooding

investigation of surface melting and dynamic thinning on jakobshavn isbrae greenland jakobshavn isbrae is the most active glacier in greenland with an annual discharge of about 30 km 3 of ice and it is one of the few recently surveyed glaciers to thicken between 1993 and 1998 despite locally warm summers repeated airborne laser altimeter surveys along a 120 km profile in the glacier basin show slow sporadic thickening between 1991 and 1997 suggesting a small positive mass balance but since 1997 there has been sustained thinning of several m a 1 within 20 km of the ice front with lower rates of thinning further inland here we use weather station data from the coast and the ice sheet to estimate the effects on surface elevation of interannual variability in snowfall and surface melt rates and thus to infer the temporal and spatial patterns of dynamic thinning these show the glacier to have been close to balance before 1997 followed by a sudden transition to rapid thinning initially confined to the lower reaches of the glacier below about 500 m elevation but progressively spreading inland until between 1999 and 2001 thinning predominated over the entire surveyed region up to 2000 m elevation if this continues the glacier calving front and probably its grounding line will retreat substantially in the very near future

intensity of satellite radar altimeter return power over continental ice a potential measurement of katabatic wind intensity au dessus de glace continentale antarctique des mesures d altimetrie radar par seasat commande automatique de gain ont ete effectuees les variations observees sont dues essentiellement a l intensite du vent catabatique

reduction of icesat systematic geolocation errors and the impact on ice sheet elevation change detection 1 the ice cloud and land elevation satellite icesat has been acquiring unprecedented observations of our planet s varied surfaces with impressive precision however systematic errors remain in the data including orbital variation and long term bias trend pointing errors these errors are particularly troublesome because they cannot be separated from true surface elevation change and confound instrument range bias determination we present a method to correct these systematic pointing errors to the sub arcsecond level we demonstrate the impact of these errors and their corrections on greenland and antarctica ice sheet surface elevation change observations and sea surface anomaly observations as well as instrument range bias determination while further improvements in the icesat data will certainly be made the analysis presented here demonstrates a major error source can be significantly reduced resulting in improved surface elevation accuracies for ice sheet elevation change detection

geomorphic evidence of unrecognized balapur fault segment in the southwest kashmir basin of northwest himalayas abstract the balapur fault bf is a high angle thrust fault reverse dipping 60 ne with an established length of 40 km striking nw se of the kashmir basin however geomorphic traces suggest that the strike of the bf propagates beyond what has been documented previously the present investigation aims to identify the unrecognized segment of the bf in the sw of the kashmir basin using hypsometric variability in longitudinal profiles knickpoints zones followed by validation through stream gradient index sl calculations of the rivers draining the area the longitudinal profiles of all the streams indicate prominent and consistent anomalies in the upper and mid reaches even on the coarse resolution data survey of india topographic maps 1 50 000 40 m dem srtm 90 m the profile anomalies in the upper reaches hard rock zone of the streams may be attributed to lithological contacts i e panjal trap agglomeratic slate shale limestone however the river profile convex segments and course deflection specifically in the mid reaches soft rock zone are most likely associated with recent tectonic activity geomorphic signatures suggest that these anomalies coincide with the strike of the recognized segment of the bf moreover the sl values of each stream express a clear agreement with the anomalies shown by the long profiles of the rivers hence we infer that the strike of the bf extends for a significant distance 95 km over the northeastern flank of the pir panjal range in the nw se direction

quantitative analysis of relative tectonic activity in the sarvestan area central zagros iran neotectonics is a major factor controlling landform development in tectonically active regions and it has significantly affected fluvial systems and mountain front landscapes in the sarvestan area of the central zagros iran the area is located along the simply folded belt of the zagros and is an outcome of the sw ne oriented tectonic conversion that initiated in the late cretaceous and strengthened during the early miocene due to the collision of the arabian and eurasian plates to assess tectonic activities in the area we analyzed geomorphic indices the stream gradient index sl drainage basin asymmetry af hypsometric integral hi valley floor width valley height ratio vf drainage basin shape bs and mountain front sinuosity j these indices were combined to yield the relative active tectonics index iat using geographic information systems gis based on iat values the study area was divided into four parts class 1 very high relative tectonic activity 1 0 in area class 2 high 20 0 class 3 moderate 67 0 and class 4 low 12 0 the results are consistent with field observations on landforms and geology

satellite gravity measurements confirm accelerated melting of greenland ice sheet using time variable gravity measurements from the gravity recovery and climate experiment grace satellite mission we estimate ice mass changes over greenland during the period april 2002 to november 2005 after correcting for the effects of spatial filtering and limited resolution of grace data the estimated total ice melting rate over greenland is 239 23 cubic kilometers per year mostly from east greenland this estimate agrees remarkably well with a recent assessment of 224 41 cubic kilometers per year based on satellite radar interferometry data grace estimates in southeast greenland suggest accelerated melting since the summer of 2004 consistent with the latest remote sensing measurements

precision and accuracy of satellite radar and laser altimeter data over the continental ice sheets the unprecedented accuracy of elevations retrieved from the ice cloud and land elevation satellite icesat laser altimeter is investigated and used to characterize the range errors in the environmental satellite envisat and european remote sensing 2 satellite ers 2 radar altimeters over the continental ice sheets cross mission crossover analysis between time coincident ers 2 envisat and icesat retrieved elevations and comparisons to an icesat derived digital elevation map are used to quantify the radar elevation error budget as a function of surface slope and to investigate the effectiveness of a method to account for the radar altimeter slope induced error the precision and accuracy of the elevations retrieved from the icesat geoscience laser altimeter system and the european space agency radar altimeters on ers 2 and envisat are calculated over the greenland and antarctic ice sheets using a crossover analysis as a result of this work the laser precision is found to vary as a function of surface slope from 14 to 59 cm and the radar precision varies from 59 cm to 3 7 m for ers 2 and from 28 cm to 2 06 m for envisat envisat elevation retrievals when compared with icesat results over regions with less than 0 1deg surface slopes show a mean difference of 9plusmn5 cm for greenland and 40plusmn98 cm over antarctica ers 2 elevation retrievals over these same low surface slope regions differ from icesat results by 56plusmn72 cm over greenland and 1 12plusmn1 16 m over antarctica at higher surface slopes of 0 7deg to 0 8deg the envisat icesat differences increase to 2 27plusmn23 m over greenland and to 0 05plusmn26 m over antarctica

macroseismic intensity assessment of 1885 baramulla earthquake of northwestern kashmir himalaya using the environmental seismic intensity scale esi 2007 abstract kashmir has a long written history of 5000 years which provides a sketchy picture of historical earthquakes in all we collated details of 16 earthquakes from the historical scribes most of the earthquakes had their epicenters outside the kashmir valley the exceptions earthquakes with epicenters within the valley however caused severe damage to life and properties and were associated with ground ruptures and long periods of aftershocks among them only the 1885 event is adequately described we have analyzed environmental effects of this destructive earthquake which occurred in the northwestern kashmir himalaya along pir panjal range in the early morning 5 00 a m of 30 may 1885 using archival sources followed by field work the present attempt envisages applying the environmental seismic intensity scale esi 2007 for a macroseismic intensity assessment of the 1885 baramulla earthquake inferences primary and secondary reveal that the 1885 baramulla earthquake local intensity would have been vi x on the esi scale baramulla the macroseismic epicenter of the earthquake must have witnessed epicentral intensity of x on esi scale the intensity must have been variable severe at baramulla and less at srinagar because of the severity of damage decreased from nw to se

acceleration of greenland ice mass loss in spring 2004 in 2001 the intergovernmental panel on climate change projected the contribution to sea level rise from the greenland ice sheet to be between 0 02 and 0 09 m from 1990 to 2100 ref 1 however recent work has suggested that the ice sheet responds more quickly to climate perturbations than previously thought particularly near the coast here we use a satellite gravity survey by the gravity recovery and climate experiment grace conducted from april 2002 to april 2006 to provide an independent estimate of the contribution of greenland ice mass loss to sea level change we detect an ice mass loss of 248 36 km3 yr 1 equivalent to a global sea level rise of 0 5 0 1 mm yr 1 the rate of ice loss increased by 250 per cent between the periods april 2002 to april 2004 and may 2004 to april 2006 almost entirely due to accelerated rates of ice loss in southern greenland the rate of mass loss in north greenland was almost constant continued monitoring will be needed to identify any future changes in the rate of ice loss in greenland

response to no major active backthrust bounds the pir panjal range near kashmir basin nw himalaya by shah this article presents a rebuttal to the entirely ambiguous and unwanted commentary made by shah jaes d 15 00980 on dar et al 2014 the original article was aimed to evaluate the tectono geomorphic evolution of the kashmir valley using geomorphic indices obtained from satellite images and detailed fieldwork however shah while deviating from the core of the article has attempted to build an inexplicable tale about the structural configuration of the region the comment is primarily based on the misinterpretation regarding the dip direction of a thrust fault pertinently no major sw dipping frontal fault bounding the pir panjal range near kashmir valley is shown in the paper by dar et al 2014 the commentator has just recycled already documented text pertaining to general tectonic character of a few ne dipping thrusts i e the main frontal thrust mft and raisi fault rf moreover some unknown structure named as kashmir basin fault kbf by the commentator has been discussed which does not even exist in the region the commentary on the whole actually does not relate with the investigation reported by dar et al 2014 hence merits no consideration for publication

controls on ers altimeter measurements over ice sheets footprint scale topography backscatter fluctuations and the dependence of microwave penetration depth on satellite orientation we consider the reliability of radar altimeter measurements of ice sheet elevation and snowpack properties in the presence of surface undulations we demonstrate that over ice sheets the common practice of averaging echoes by aligning the first return from the surface at the origin can result in a redistribution of power to later times in the average echo mimicking the effects of microwave penetration into the snowpack algorithms that assume the topography affects the radar echo shape in the same way that waves affect altimeter echoes over the ocean will therefore lead to biased estimates of elevation this assumption will also cause errors in the retrieval of echo shape parameters intended to quantify the penetration of the microwave pulse into the snowpack using numerical simulations we estimate the errors in retrievals of extinction coefficient surface backscatter and volume backscatter for various undulating topographies in the flatter portions of the antarctic plateau useful estimates of these parameters may be recovered by averaging altimeter echoes recorded by the european remote sensing satellite ers 1 by numerical deconvolution of the average echoes we resolve the depths in the snowpack at which temporal changes and satellite travel direction effects occur both of which have the potential to corrupt measurements of ice sheet elevation change the temporal changes are isolated in the surface backscatter cross section while directional effects are confined to the extinction coefficient and are stable from year to year this allows the removal of the directional effect from measurement of ice sheet elevation change

progressive increase in ice loss from greenland 1 laser altimeter measurements over greenland show increasing thickening rates above 2000 m reflecting increasing snowfall in a warming climate but near coastal thinning rates have increased substantially since the mid 1990s and net mass loss more than doubled from an average of 4 50 gt yr 1 between 1993 4 and 1998 9 to 57 105 gt yr 1 between 1998 9 and 2004 this increasing trend is very similar to findings from independent mass budget studies but differs widely from ers radar altimeter results this may result from limitations associated with the large ers footprint over sloping and undulating surfaces that typify fast narrow glaciers where thinning is most pronounced

submarine melting of the 1985 jakobshavn isbrae floating tongue and the triggering of the current retreat 1 photogrammetric reanalysis of 1985 aerial photos has revealed substantial submarine melting of the floating ice tongue of jakobshavn isbrae west greenland the thickness of the floating tongue determined from hydrostatic equilibrium tapers from 940 m near the grounding zone to 600 m near the terminus feature tracking on orthophotos shows speeds on the july 1985 ice tongue to be nearly constant 18 5 m d 1 indicating negligible dynamic thinning the thinning of the ice tongue is mostly due to submarine melting with average rates of 228 49 m yr 1 0 62 0 13 m d 1 between the summers of 1984 and 1985 the cause of the high melt rate is the circulation of warm seawater thermal forcing of up to 4 2 c beneath the tongue with convection driven by the substantial discharge of subglacial freshwater from the grounding zone we believe that this buoyancy driven convection is responsible for a deep channel incised into the sole of the floating tongue a dramatic thinning retreat and speedup began in 1998 and continues today the timing of the change is coincident with a 1 1 c warming of deep ocean waters entering the fjord after 1997 assuming a linear relationship between thermal forcing and submarine melt rate average melt rates should have increased by 25 57 m yr 1 sufficient to destabilize the ice tongue and initiate the ice thinning and the retreat that followed

quaternary paleosol stratigraphy and paleomagnetic record near dreihausen central germany summary a succession of sediments and paleosols near dreihausen in central germany records a normal magnetic remanence throughout and appears to have formed during the brunhes chron this sequence of sediments and paleosols developed in bedrock loess colluvium and residual regolith exhibits no clear evidence for secular variation swings or excursions suggesting rather slow and intermittent sedimentation rates the paleosols are primarily alfisols with pronounced argillic horizons which formed during interglacial periods when climate was presumably warmer and certainly wetter than today the distribution of higher clay in the older paleosol of eemian age supports the hypothesis of strong interglacial paleoclimates relative to the present day climate clay mineral transformations in these paleosols suggest a weathering sequence of illite illite smectite vermiculite despite minor clay mineral transformations of this type the data supports the interpretation of a mixed deciduous coniferous forest during the eemian interglaciation

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

greenland 2012 melt event effects on cryosat 2 radar altimetry cryosat 2 data are used to study elevation changes over an area in the interior part of the greenland ice sheet during the extreme melt event in july 2012 the penetration of the radar signal into dry snow depends heavily on the snow stratigraphy and the rapid formation of refrozen ice layers can bias the surface elevations obtained from radar altimetry we investigate the change in cryosat 2 waveforms and elevation estimates over the melt event and interpret the findings by comparing in situ surface and snow pit observations from the north greenland eemian ice drilling project camp the investigation shows a major transition of scattering properties around the area and an apparent elevation increase of 56 26 cm is observed in reprocessed cryosat 2 data we suggest that this jump in elevation can be explained by the formation of a refrozen melt layer that raised the reflective surface introducing a positive elevation bias

stratigraphy and paleomagnetism of the jaw face section wellsch valley site saskatchewan the basal part of jaw face section at the wellsch valley site some 50 km north northwest of swift current saskatchewan contains mammalian fossils that are considered to be late blancan to early irvingtonian in age it has been sampled for paleomagnetic studies through a thickness of 11 m the section above 8 8 m has normal polarity that below has reversed polarity a tephra which has yielded a minimum fission track age of 0 69 0 11 ma lies within the reversely magnetized part near the top of the fossiliferous zone and just below the reversal at the 8 8 m level therefore the change from normal to reversed polarity at the 8 8 m level is probably the brunhes matuyama reversal at 0 73 ma earlier studies have indicated that the jaramillo 0 9 0 97 ma and olduvai 1 67 1 87 ma normal polarity subzones occur within the lower predominantly reversed part of the jaw face section in this more detailed study we find no evidence of these normal subzones we suggest that earlier results could have been

greenland mass balance from grace 1 we use 22 monthly grace gravity recovery and climate experiment gravity fields to estimate the linear trend in greenland ice mass during 2002 2004 we recover a decrease in total ice mass of 82 28 km3 of ice per year consistent with estimates from other techniques our uncertainty estimate is dominated by the effects of grace measurement errors and errors in our post glacial rebound pg correction the main advantages of grace are that it is sensitive to the entire ice sheet and that it provides mass estimates with only minimal use of supporting physical assumptions or ancillary data

modeling time series of microwave brightness temperature in antarctica this paper aims to interpret the temporal variations of microwave brightness temperature at 19 and 37 ghz and at vertical and horizontal polarizations in antarctica using a physically based snow dynamic and emission model sdem sdem predicts time series of top of atmosphere brightness temperature from widely available surface meteorological data era 40 re analysis to do so it successively computes the heat flux incoming the snowpack the snow temperature profile the microwaves emitted by the snow and finally the propagation of the microwaves through the atmosphere up to the satellite since the model contains several parameters whose value is variable and uncertain across the continent the parameter values are optimized for every 50 km 50 km pixel simulation results show that the model is inadequate in the melt zone where surface melting occurs on at least a few days a year because the snowpack structure and its temporal variations are too complex in contrast the accuracy is reasonably good in the dry zone and varies between 2 and 4 k depending on the frequency and polarization of observations and on the location at the antarctic scale the error is larger where wind is usually stronger suggesting either that meteorological data are less accurate in windy regions or that some neglected processes e g windpumping surface scouring are important at dome c in calm conditions a detailed analysis shows that most of the error is due to inaccuracy of the era 40 air temperature 2 k finally the paper discusses the values of the optimized parameters and their spatial variations across the antarctic

snow and ice facies variability and ice layer formation on canadian arctic ice caps 1999 2005 1 time series of enhanced resolution data from the seawinds scatterometer aboard quikscat were used to map the distribution of snow and ice surface facies and ice layer formation in the percolation zone on ice caps in the queen elizabeth islands during the period 1999 2005 iterative self organizing data analysis classification of the mean postfreeze up biweekly average 0 signal for the 7 year period resulted in the delineation of four snow and ice surface facies interpreted as the percolation saturation superimposed ice and glacier ice zones analysis with national centers for environmental prediction national center for atmospheric research reanalysis reveals that changes in geopotential height in the troposphere 700 500 and 300 hpa and air temperature 700 hpa level are positively negatively correlated with area changes in the glacier ice percolation and saturation zones and changes in facies boundary elevation the change in biweekly averaged backscatter following the freeze up periods between successive autumns was used to map changes in the distribution of ice layers formed by meltwater percolation and refreezing in the snowpack within the percolation zone strongly positive air temperature anomalies at the 700 hpa level in 2001 and 2005 are consistent with extensive ice layer formation in the percolation zones of all ice caps such large interannual changes in ice layer formation are likely associated with large changes to the density profile of the snowpack and may be associated with surface elevation changes that are unrelated to changes in surface mass balance

spatiotemporal interpolation of elevation changes derived from satellite altimetry for jakobshavn isbrae greenland estimation of ice sheet mass balance from satellite altimetry requires interpolation of point scale elevation change dh dt data over the area of interest the largest dh dt values occur over narrow fast flowing outlet glaciers where data coverage of current satellite altimetry is poorest in those areas straightforward interpolation of data is unlikely to reflect the true patterns of dh dt here four interpolation methods are compared and evaluated over jakobshavn isbrae an outlet glacier for which widespread airborne validation data are available from nasa s airborne topographic mapper atm the four methods are ordinary kriging ok kriging with external drift ked where the spatial pattern of surface velocity is used as a proxy for that of dh dt and their spatiotemporal equivalents st ok and st ked ked assumes a linear relationship between spatial gradients of velocity and dh dt which is confirmed for both negative pearson s correlation 0 85 and to a lesser degree positive 0 73 dh dt values when compared to atm data ked and st ked yield more realistic spatial patterns and higher thinning rates over 20 m yr 1 as opposed to 7 m yr 1 for ok spatiotemporal kriging smooths inter annual variability and improves interpolation in periods with sparse data coverage and we conclude therefore that st ked produces the best results using this method increases volume loss estimates from jakobshavn isbrae by up to 20 compared to those obtained by ok the proposed interpolation method will improve ice sheet mass balance reconstructions from existing and past satellite altimeter data sets with generally poor sampling of outlet glaciers

svalbard glacier elevation changes and contribution to sea level rise 1 we compare satellite altimetry from the ice cloud and land elevation satellite icesat 2003 2007 to older topographic maps and digital elevation models 1965 1990 to calculate long term elevation changes of glaciers on the svalbard archipelago results indicate significant thinning at most glacier fronts with either slight thinning or thickening in the accumulation areas except for glaciers that surged which show thickening in the ablation area and thinning in the accumulation areas the most negative geodetic balances occur in the south and on glaciers that have surged while the least negative balances occur in the northeast and on glaciers in the quiescent phase of a surge cycle geodetic balances are related to latitude and to the dynamical behavior of the glacier the average volume change rate over the past 40 years for svalbard excluding austfonna and kvitoya is estimated to be 9 71 0 55 km3 yr 1 or 0 36 0 02 m yr 1 w equivalent for an annual contribution to global sea level rise of 0 026 mm yr 1 sea level equivalent

greenland ice sheet high elevation balance and peripheral thinning aircraft laser altimeter surveys over northern greenland in 1994 and 1999 have been coupled with previously reported data from southern greenland to analyze the recent mass balance of the greenland ice sheet above 2000 meters elevation the ice sheet is in balance on average but has some regions of local thickening or thinning thinning predominates at lower elevations with rates exceeding 1 meter per year close to the coast interpolation of our results between flight lines indicates a net loss of about 51 cubic kilometers of ice per year from the entire ice sheet sufficient to raise sea level by 0 13 millimeter per year approximately 7 of the observed rise

elevation change measurement of the east antarctic ice sheet 1978 to 1988 from satellite radar altimetry seasat and geosat satellite radar altimeter measurements over the east antarctic ice sheet eais are analyzed to determine surface elevation change over the period from 1978 to 1988 the results show that the average elevation change over 1 7 spl times 10 sup 6 km sup 2 of the eais is 0 4 spl plusmn 1 8 cm yr and is therefore not significantly different than zero this result is in very good agreement with ers 1 2 radar altimeter estimates of eais elevation change from 1992 to 1996 the combined results suggest that the eais has been close to a state of balance for two decades this further reduces the likelihood that recent changes in snow accumulation have masked a long term mass imbalance in the eais

icesat range and mounting bias estimation over precisely surveyed terrain 1 prior to the launch of the geoscience laser altimeter system glas on the ice cloud and land elevation satellite icesat in january 2003 topographic surveys were made by nasa s airborne topographic mapper atm over regions of the western united states and the antarctic dry valleys to support calibration and validation of the range and pointing errors of glas lasers surveyed areas included terrain with large slopes allowing pointing bias estimation with as little as a few seconds of icesat data range errors over sloping irregular surfaces are calculated by computing the expected glas return waveform and comparing it with the actual waveform we conclude that the range bias is less than 2 cm and that pointing errors for the best available data set laser 2a have rss errors less than 2 arcsec

greenland ice sheet increased coastal thinning repeated laser altimeter surveys and modelled snowfall summer melt show average ice loss from greenland between 1997 and 2003 was 80 12 km3 yr 1 compared to about 60 km3 yr 1 for 1993 4 1998 9 half of the increase was from higher summer melting with the rest caused by velocities of some glaciers exceeding those needed to balance upstream snow accumulation velocities of one large glacier almost doubled between 1997 and 2003 resulting in net loss from its drainage basin by about 20 km3 of ice between 2002 and 2003 copyright 2004 by the american geophysical union

using the temporal variability of satellite radar altimetric observations to map surface properties of the antarctic ice sheet the problem of measuring surface height and snowpack characteristics from satellite radar altimeter echoes is investigated in this paper we perform an analysis of the ers1 altimeter dataset acquired during a 3 day repeat orbit the analysis reveals that there are temporal variations in shapes of the radar altimeter echo and that these variations are linked to meteorological phenomena the time and space scales over which these variations apply are a few to tens of days and a few hundred kilometres respectively this phenomenon if not accounted for can create error in the height measurement a numerical echo model is used to recover snowpack characteristics by taking advantage of the temporal variations of the radar echoes a map of penetration depth of the radar waves in the ku band over the antarctic continent is obtained and suggests that grain size produces the dominant effect on radar extinction in the snowpack at this frequency finally a procedure is proposed to correct the height measurement within the context of ice sheet mass balance survey

merging and analysis of elevation time series over greenland ice sheet from satellite radar altimetry spatial temporal variability and changes of greenland ice sheet elevation from 1992 to 2008 are analyzed from merged ers 1 ers 2 and envisat satellite radar altimeter data a methodology for determining intersatellite biases was developed and applied in order to merge measurements from these different satellites and to create continuous and consistent time series intersatellite biases of elevation and backscatter coefficient have shown to be significantly affected by the bias between measurements in ascending and descending orbits adjustment of elevation time series for its dependence on backscatter coefficient and other waveform parameters performed in this paper substantially reduced the amplitude of elevation seasonal variations and locally corrected elevation change rate estimates by up to several centimeters per year it was found that the correction depends not only on the variations in the waveform parameters but also on the temporal variations of the correlation gradients which represent the sensitivity of the elevation change to the change in the waveform parameters an elevation change rate of 2 8 0 2 cm year from 1992 to 2008 over 76 of the greenland ice sheet area was found increases in surface elevation from 1995 observed over the high elevation regions of greenland were followed by an elevation decrease from 2006 for the whole period of 1992 2008 the elevation increase is 4 0 0 2 cm year over 87 of the area above 1500 m in contrast over 38 of the low elevation areas below 1500 m the rate of elevation change is 7 0 1 0 cm year and the surface elevation decrease that started from 2000 has continued

mass balance of the antarctic ice sheet the antarctic contribution to sea level rise has long been uncertain while regional variability in ice dynamics has been revealed a picture of mass changes throughout the continental ice sheet is lacking here we use satellite radar altimetry to measure the elevation change of 72 of the grounded ice sheet during the period 1992 2003 depending on the density of the snow giving rise to the observed elevation fluctuations the ice sheet mass trend falls in the range 5 85gt yr 1 we find that data from climate model reanalyses are not able to characterise the contemporary snowfall fluctuation with useful accuracy and our best estimate of the overall mass trend growth of 27 29 gt yr 1 is based on an assessment of the expected snowfall variability mass gains from accumulating snow particularly on the antarctic peninsula and within east antarctica exceed the ice dynamic mass loss from west antarctica the result exacerbates the difficulty of explaining twentieth century sea level rise

paleomagnetic evidence for multiple late cenozoic glaciations in the tintina trench west central yukon canadathis article is a companion paper to duk rodkin et al also in this issue the tintina trench in west central yukon has preserved an extensive record of late cenozoic preglacial glacial and interglacial deposits these deposits comprise multiple sequences of tills outwash loesses and paleosols the sediments that were laid down directly by ice tills are of both local montane and regional cordilleran provenance the tintina trench area was impacted repeatedly by montane ice from the southern ogilvie mountains to the northwest 2500 m above sea level asl and also repeatedly along its southern extent by cordilleran ice from the selwyn mountains to the east 2759 m asl the latter forming the continental divide in this region we report here the magnetostratigraphy of three sections rock creek 64 13 n 139 07 w west fifteenmile river 64 29 n 139 55 w and east fifteenmile river 64 23 n 139 48 w the majority of the units identified at these sections record late pliocene to mid pleistocene glaciations although relatively thin surficial sequences of late mid

the late cenozoic chronologic and stratigraphic development of the kashmir intermontane basin northwestern himalaya abstract the intermontane basin of kashmir developed within the thrust faulted southern margin of the himalayan range detailed lithostratigraphies magnetic polarity stratigraphies and fission track dates on enclosed volcanic ashes were determined at four separate localities in order to develop a chronology of the late cenozoic evolution of the kashmir basin the results indicate that sedimentation had commenced by about 4 m y ago since then over 1300 m of sediments have aggraded at inferred average rates varying from 16 to 64 cm per 1000 yr lacustrine and deltaic sediments dominate the kashmiri sequences and appear to respond sensitively to tectonic events along the basin margins conglomerates shed from the faulted basin margins at about 1 7 2 1 2 7 and 3 0 3 5 m y ago punctuate the predominantly low energy fluviolacustrine depositional record paleocurrent analyses indicate a switch from northeasterly derived conglomeratic facies to southwesterly derived ones about 1 7 m y ago this transition reflects enhanced activity along the main boundary thrust complex to the southwest and an apparent diminution of faulting along the northeastern margin of the basin in the pir panjal range 1400 3000 m of uplift at inferred rates of up to 10 mm yr 1 have terminated widespread sedimentation within the kashmir basin since the middle pleistocene

isotopic and micromorphological studies of late quaternary loess paleosol sequences of the karewa group inferences for palaeoclimate of kashmir valley abstract pedogenic carbonates widespread in paleosols throughout the geological ages have been widely used to infer climatic conditions and vegetation type during their formation they are ubiquitous and widespread in the late quaternary loess paleosol sequence of the kashmir valley mostly in the form of carbonate nodules in the present study pedogenic carbonates are studied to analyze trends in the stable isotopic composition of carbonate nodules across three well developed loess paleosol sections in the kashmir valley the stable carbon isotopic 13 c analysis reveals a gradual increase of the c 4 vegetation towards the top of the sections the development of c 4 plant biomass towards the top of sections possibly reflects water stress and or reduced atmospheric pco 2 and increasing aridity the oxygen 18 o isotopic analysis reveals little variation with the values ranging from 6 37 to 7 75 reflecting stable climatic conditions during the development of pedogenic carbonate nodules the use of geospatial data including digital elevation model dem and landsat tm remote sensing imagery have added morphological characterization of the topographic and landform features observed in the area the tectonic uplift of the pir panjal range variation in the geometry of karewa basin and the slope gradient have played a key role in the spatial variation of loess paleosol sequences in the valley the late quaternary climate changes deposition of loessic sediments formation of the interbedded paleosol profiles and the subsequent denudation processes have resulted in the present day typical geomorphic landscape of the kashmir valley the micromorphological analysis of loess paleosol horizons reveals cold arid to semi arid climatic conditions prevailed during the late quaternary in the valley

implications of changing scattering properties on greenland ice sheet volume change from cryosat 2 altimetry abstract long term observations of surface elevation change of the greenland ice sheet gris is of utmost importance when assessing the state of the ice sheet satellite radar altimetry offers a long time series of data over the gris starting with ers 1 in 1991 esa s cryosat 2 mission launched in 2010 provides an invaluable radar altimetry dataset for monitoring the current changes of the ice sheets due to its dense spatial and temporal coverage of these areas here we investigate the effects of including different parameters which describe the shape of the return radar waveform waveform parameters in the elevation change algorithm to correct for temporal changes in the ratio between surface and volume scatter in cryosat 2 observations we present elevation and volume changes for the greenland ice sheet in the period from 2010 until 2014 the waveform parameters considered here are the backscatter coefficient and the leading edge width which are both available in the esa cryosat 2 level 2i data product investigations into relocation of radar reflection points are also included inter comparison of the cryosat 2 derived elevation changes with those derived from operation icebridge laser data suggests waveform parameters to be applicable for correcting for changes in volume scattering the best results in the synthetic aperture radar interferometric mode area of the gris are found when applying only the backscatter correction whereas the best result in the low resolution mode area is obtained by only applying a leading edge width correction using this approach to correct for the scattering properties a volume loss of 292 38 km 3 yr 1 is found for the gris for the time span november 2010 until november 2014 the inclusion of waveform parameter corrections and improved relocation for the gris helps to reconcile the satellite derived elevation changes with those observed by operation icebridge however the bias of temporal changes in the scattering horizons of cryosat 2 is not entirely removed and suggests that future improvements could be made by including climate data and or additional waveform parameters to make additional corrections in the cryosat 2 radar altimetry

snow accumulation variability from seasonal surface observations and firn core stratigraphy eastern wilkes land antarctica annual accumulation records were derived from two firn cores drilled at gd03 69 00 s 115 30 e 1835m and gd15 69 00 s 130 48 e 2155m which are separated by 750 km along the 2000 m contour in eastern wilkes land the accumulation records spanning the period 1930 85 show that annual accumulation has increased by 25 from 1960 to 1985 resulting in the highest accumulation rates in the 55 year records annual accumulation layers were identified in the firn cores using a firn stratigraphic model based on the observed characteristics and variability of the seasonal snow surface layer together with seasonal oxygen isotope ratios the accumulation records support other evidence for a similar recent increase across antarctica the greater increase over the long term mean for 1930 85 in eastern wilkes land was observed at gd15 which is located on a northeast aspect slope near terre adelie it is suggested that the increase is the result of changes in the general atmospheric circulation pattern which have produced a higher annual frequency of precipitation events

the melt anomaly of 2002 on the greenland ice sheet from active and passive microwave satellite observations 1 active and passive microwave satellite data are used to map snowmelt extent and duration on the greenland ice sheet the passive microwave pm data reveal the extreme melt extent of 690 000 km2 in 2002 as compared with an average extent of 455 000 km2 from 1979 2003 a statistical analysis of the melt time series affirms an increased melt extent earlier in the melt season the quikscat qscat or am analysis for 1999 to 2004 confirms the extreme melt situation in 2002 qscat data show a significant increase in melt season length over several areas in 2003 ssm i and qscat melt data reveal that the later detects melt earlier and is more sensitive to surface melt qscat detects an earlier stage of melt and ssm i detects a later stage of melt the ssm i xgpr melt extent is approximately confined to the qscat melt areas experiencing 2 weeks or more of melting time

observed and modeled greenland ice sheet snow accumulation 1958 2003 and links with regional climate forcing abstract annual and monthly snow accumulation for the greenland ice sheet was derived from ecmwf forecasts mainly 40 yr ecmwr re analysis era 40 and further meteorological modeling modeled accumulation was validated using 58 ice core accumulation datasets across the ice sheet and was found to be 95 of the observed accumulation on average with a mean correlation of 0 53 between modeled and observed many of the ice core datasets are new and are presented here for the first time central and northern interior parts of the ice sheet were found to be 10 30 too dry in era 40 in line with earlier ecmwf analysis although too much 50 locally snow accumulation was modeled for interior southern parts of greenland nevertheless 47 of 58 sites show significant correlation in temporal variability of modeled with observed accumulation the model also captures the absolute amount of snow accumulation at several sites most notably das1 and das2 in southeast greenland mean modeled accumulation over the

variable basal melt rates of antarctic peninsula ice shelves 1994 2016 we have constructed 23 year 1994 2016 time series of antarctic peninsula ap ice shelf height change using data from four satellite radar altimeters ers 1 ers 2 envisat and cryosat 2 combining these time series with output from atmospheric and firn models we partitioned the total height change signal into contributions from varying surface mass balance firn state ice dynamics and basal mass balance on the bellingshausen coast of the ap ice shelves lost 84 34 gt a 1 to basal melting compared to contributions of 50 7 gt a 1 from surface mass balance and ice dynamics net basal melting on the weddell coast was 51 71 gt a 1 recent changes in ice shelf height include increases over major ap ice shelves driven by changes in firn state basal melt rates near bawden ice rise a major pinning point of larsen c ice shelf showed large increases potentially leading to substantial loss of buttressing if sustained

surface height determination of crevassed glaciers mathematical principles of an autoadaptive density dimension algorithm and validation using icesat 2 simulator simpl data glacial acceleration is a main source of uncertainty in sea level change assessment measurement of ice surface heights with a spatial and temporal resolution that not only allows elevation change calculation but also captures ice surface morphology and its changes is required to aid in investigations of the geophysical processes associated with glacial acceleration the advanced topographic laser altimeter system aboard nasa s future icesat 2 mission launch 2017 will implement multibeam micropulse photon counting lidar altimetry aimed at measuring ice surface heights at 0 7 m along track spacing the instrument is designed to resolve spatial and temporal variability of rapidly changing glaciers and ice sheets and the arctic sea ice the new technology requires the development of a new mathematical algorithm for the retrieval of height information we introduce the density dimension algorithm dda that utilizes the radial basis function to calculate a weighted density as a form of data aggregation in the photon cloud and considers density an additional dimension as an aid in autoadaptive threshold determination the autoadaptive capability of the algorithm is necessary to separate returns from noise and signal photons under changing environmental conditions the algorithm is evaluated using data collected with an icesat 2 simulator instrument the slope imaging multi polarization photon counting lidar over the heavily crevassed giesecke braer in northwestern greenland in summer 2015 results demonstrate that icesat 2 may be expected to provide ice surface height measurements over crevassed glaciers and other complex ice surfaces the dda is generally applicable for the analysis of airborne and spaceborne micropulse photon counting lidar data over complex and simple surfaces

the glacier and land ice surface topography interferometer an airborne proof of concept demonstration of high precision ka band single pass elevation mapping as part of the nasa international polar year activities a ka band cross track interferometric synthetic aperture radar sar recently demonstrated high precision elevation swath mapping capability this proof of concept instrument was achieved by interfacing two ka band slotted waveguide antennas in a cross track geometry and ka band electronics with the jet propulsion laboratory s l band uninhabited aerial vehicle sar deployed on the nasa gulfstream iii initial engineering flights in march and april 2009 marked the first airborne demonstration of single pass cross track interferometry at ka band results of a preliminary interferometric assessment indicate height precisions that for a 3 m 3 m posting range from 30 cm in the near range to 3 m in the far range and greater than 5 km of swath over the urban areas imaged the engineering flights were followed by a comprehensive campaign to greenland in may 2009 for ice surface topography mapping assessment toward that end coordinated flights with the nasa wallops airborne topographic mapper lidar were conducted in addition to establishing ground calibration sites at both the summit station of the national science foundation and the swiss camp of the cooperative institute for research in the environmental sciences comparisons of the radar derived elevation measurements with both in situ and lidar data are planned for a subsequent paper however at this stage a single data example over rugged ice cover produced a swath up to 7 km with the desired height precision as estimated from interferometric correlation data while a systematic calibration including assessment and modeling of biases due to penetration of the electromagnetic waves into the snow cover has not yet been addressed these initial results indicate that we will exceed our system requirements

intermontane basin development in the past 4 myr in the north west himalaya the through the combined use of magnetic polarity stratigraphy with fission track dating of volcanic ashes a new chronology spanning 4 myr has been developed for the intermontane basin of kashmir in the northwestern himalaya

the 1958 2009 greenland ice sheet surface melt and the mid tropospheric atmospheric circulation in order to assess the impact of the mid tropospheric circulation over the greenland ice sheet gris on surface melt as simulated by the regional climate model mar an automatic circulation type classification ctc based on 500 hpa geopotential height from reanalyses is developed general circulation correlates significantly with the surface melt anomalies for the summers in the period 1958 2009 the record surface melt events observed during the summers of 2007 2009 are linked to the exceptional persistence of atmospheric circulations favouring warm air advection the ctc emphasizes that summer 500 hpa circulation patterns have changed since the beginning of the 2000s this process is partly responsible for the recent warming observed over the gris

evidence for early pleistocene glaciation from borecore stratigraphy in north central alberta canada pleistocene sediments collected in north central alberta canada were subsampled and studied for paleomagnetic remanence characteristics a magnetostratigraphy has been established for sediments previously assumed to represent multiple continental laurentide glaciations but for which no geochronology was available based on the quaternary record elsewhere in alberta and saskatchewan it was thought that some of these sediments were deposited during pre late wisconsinan glaciations the quaternary sedimentary successions of north central alberta have a thickness up to 300 m within buried valleys and are composed of diamicts interbedded with glaciolacustrine and outwash sediments most of the sampled units are not accessible from outcrop and their sedimentology and stratigraphy is derived from core data only in 4 of 16 borecores sampled to date diamict that correlates with the bronson lake formation till is reversely magnetized indicating an early pleistocene age this formation is underlain by eithe

on the recent elevation changes at the flade isblink ice cap northern greenland 1 we have used radar altimeter 2 ra 2 onboard esa s envisat and geosciences laser altimeter system glas onboard nasa s icesat to map the elevation change of the flade isblink ice cap fiic in northern greenland based on ra 2 data we show that the mean surface elevation change of the fiic has been near zero 0 03 0 03 m a between fall 2002 and fall 2009 we present the elevation change rate maps and assess the elevation change rates of areas above the late summer snow line 0 09 0 04 m a and below it 0 16 0 05 m a the glas elevation change rate maps show that some outlet glaciers previously reported to have been in a surge state are thickening rapidly using the ra 2 measured average elevation change rates for different parts of the ice cap we present a mass change rate estimate of 0 0 0 5 gt a for the fiic we compare the annual elevation changes with surface mass balance smb estimates from a regional atmospheric climate model racmo2 we find a strong correlation between the two r 0 94 and p 0 002 suggesting that the surface elevation changes of the fiic are mainly driven by net smb the correlation of modeled net smb and measured elevation change is strong in the southern areas of the fiic r 0 97 and p 0 0005 but insignificant in the northern areas r 0 38 and p 0 40 this is likely due to higher variability of glacier flow in the north relative to the south

geomorphic assessment of active tectonics in the acambay graben mexican volcanic belt spatial variations of quaternary deformation and tectonic activity of faults along the acambay graben are assessed using geomorphic and morphometric approaches the acambay graben is an east west trending structure of apparent quaternary age located in the central part of the mexican volcanic belt which gives rise to pronounced scarps over a distance of about 80 km continuing tectonic activity in the acambay graben is confirmed by recent well documented seismic episodes the intensity of active tectonics has been interpreted through a detailed geomorphic study of the fault generated mountain fronts and fluvial systems the combined geomorphic and morphometric data provide evidence for relative variations in tectonic activity among the acambay graben faults geomorphic indices suggest a relatively high degree of tectonic activity along the venta de bravo and the acambay tixmadeje faults followed in order of decreasing activity by the pastores temascalcingo and tepuxtepec faults spatial variations within faults have also been identified suggesting a higher level of tectonic activity at the tips of the faults this pattern of variation in the relative degree of tectonic activity is consistent with field evidence and seismic data for the acambay graben geomorphic evaluation of the acambay graben faults suggests that the acambay tixmadeje and venta de bravo faults and specifically the tips of these faults and a central segment near the town of venta de bravo should be considered as areas of potentially high earthquake risk 1998 john wiley sons ltd

mass changes of the greenland and antarctic ice sheets and shelves and contributions to sea level rise 1992 2002 changes in ice mass are estimated from elevation changes derived from 10 5 years greenland and 9 years antarctica of satellite radar altimetry data from the european remote sensing satellites ers 1 and 2 for the first time the dh dt values are adjusted for changes in surface elevation resulting from temperature driven variations in the rate of firn compaction the greenland ice sheet is thinning at the margins 42 2g t a 1 below the equilibrium line altitude ela and growing inland 53 2g t a 1 above the ela with a small overall mass gain 11 3g t a 1 0 03 mm a 1 sle sea level equivalent the ice sheet in west antarctica wa is losing mass 47 4g t a 1 and the ice sheet in east antarctica ea shows a small mass gain 16 11 gt a 1 for a combined net change of 31 12 gt a 1 0 08 mm a 1 sle the contribution of the three ice sheets to sea level is 0 05 0 03 mm a 1 t he antarctic ice shelves show corresponding mass changes of 95 11 gt a 1 in wa and 142 10 gt a 1 in ea thinning at the margins of the greenland ice sheet and growth at higher elevations is an expected response to increasing temperatures and precipitation in a warming climate the marked thinnings in the pine island and thwaites glacier basins of wa and the totten glacier basin in ea are probably ice dynamic responses to long term climate change and perhaps past removal of their adjacent ice shelves the ice growth in the southern antarctic peninsula and parts of ea may be due to increasing precipitation during the last century

understanding ice sheet mass balance progress in satellite altimetry and gravimetry satellite remote sensing has come to dominate the measurement of glacier and ice sheet change three independent methods now exist for assessing ice sheet mass balance and we focus on progress in two satellite altimetry icesat and gravimetry grace with improved spatial and temporal sampling and synergy with ice flow measurements both the mechanisms and causes changing mass balance can be investigated we present examples of mass losses due to widespread intensifying glacier dynamic thinning in northwest greenland but local ablation rates in the northeast that are unchanged for decades advances in grace processing reveal greenland net ice sheet mass loss continuing into 2010 at 19530 gt a 1 a similarly negative trend in the gulf of alaska has significant spatial and temporal variation that highlights the importance of intense summer melting here strong summer melt on the antarctic peninsula also precipitated recent ice shelf collapse and prompted rapid dynamic thinning of tributary glaciers at up to 70ma 1 thinning continued for years to decades after collapse and propagated far inland while understanding of the physical mechanisms of change continues to improve estimates of future behaviour and in particular the near future glacial sea level contribution still rely on projections from such observations we introduce the suite of new sensors that will monitor the ice sheets into the future

stratigraphy and paleomagnetism of late pliocene and pleistocene sediments in the wellsch valley and swift current creek areas southwestern saskatchewan canada the late pliocene and pleistocene are represented in southern saskatchewan by sequences of preglacial glacial and nonglacial deposits these have been studied in surface exposures and bore cores and have been subdivided and correlated on the basis of their lithologies in this study new observations of magnetic polarity are presented they reveal a lower preglacial sequence empress group with reversed polarity and an upper normally magnetized sequence which contains glacial deposits of pre illinoian illinoian and wisconsinan age and which are correlative with the saskatoon and sutherland groups of central saskatchewan the reversed preglacial sequence is referred to the matuyama zone late pliocene to early pleistocene 2 58 0 78 ma and the normal glacial sequence to the brunhes zone middle to late pleistocene and holocene 0 78 ma to present in southern saskatchewan there is no evidence of glaciation during the late pliocene and early pleistocene matuyama chron which is in marked contrast w