glaciological applications with landsat 7 imagery early assessments enhanced thematic mapper plus etm data from landsat 7 are providing glaciologists with an ever expanding data set that makes a comprehensive monitoring of the global cryosphere feasible for the first time in history examples of etm data illustrate its ability to satisfy major scientific needs in the glaciological subdisciplines of sea ice glacier ice cap and ice sheet research with high resolution optical satellite imagery examples shown include use as proxy ground truth positioning glacier termini and snowlines and determining snow facies boundaries the additional etm panchromatic band at a higher spatial resolution of 15 m improves the spatial accuracy of these applications the glaciological aspects of the landsat 7 long term acquisition plan are discussed to show how the timing and location of the image acquisitions will generate a cryospheric data set of unprecedented utility for future research

effect of surface roughness on bidirectional reflectance of antarctic snow the angular pattern of sunlight reflected by snow is altered by surface roughness which in the interior of antarctica is usually in the form of meter scale longitudinal erosional features sastrugi whose axes align with the direction of strong winds the bidirectional reflectance distribution function brdf changes over the course of a day as the solar azimuth changes relative to the sastrugi axis the normalized brdf or anisotropic reflectance factor r was measured at south pole station from a 22 m tower at 600 660 and 900 nm wavelengths the r pattern was similar at the three wavelengths it probably varies little from 300 to 900 nm measurements were made at solar zenith angles 0 from 67 to 90 over the full range of viewing zenith angle r azimuth angle between sun and view and azimuth angle between sun and sastrugi sas variation of r with sas was notable sastrugi oriented perpendicular to the solar beam cause a reduction of the forward peak and sastrugi at an oblique angle cause r to lose its symmetry about the solar azimuth however the effects of sastrugi are mostly restricted to large viewing zenith angles so remote sensing of albedo and atmospheric properties can be carried out accurately without knowledge of sastrugi height and orientation if only near nadir views are used this recommendation is opposite that for observations of broken clouds over dark surfaces for which large r is preferred a parameterization of r is developed valid for viewing angles r 50 sastrugi can cause a reduction of the snow albedo by altering the angle of incidence and by trapping of photons for the small sastrugi of the antarctic plateau the albedo is unaffected at visible wavelengths but can be reduced by a few percent at near infrared wavelengths when the sun is low

remote sensing of the albedo and detection of the slush line on the greenland ice sheet advanced very high resolution radiometer images of a section of the greenland ice sheet western part between 64 5 and 70 5 n with a size of 667 n s by 700 w e km were processed in order to retrieve the surface albedo the images were for the summer seasons of 1990 1997 inclusive and results were compared to simultaneous mass balance measurements carried out along the transect 67 n the main findings are as follows first many images show a distinct transition from low spatial variability of the albedo at higher elevations to higher spatial variability of the albedo at lower elevations it is argued that these transitions most likely correspond to transitions at the surface slush line in short from the area that is uniformly covered by snow to a mosaic of snow patches slush and ice second 70 of the interannual variations in the mean specific mass balance can be explained by interannual variations in the maximum elevation of the slush line i e the slush limit however a higher percentage 82 can be explained by interannual variations in the sum of positive degree days third in 3 years with a relatively large amount of melt the inland migration of the slush line stopped or slowed considerably down at a fixed distance from the ice sheet margin we believe that this so called maximum slush line coincides with an abrupt change in the density profile the maximum slush line forms an important limitation for the use of satellite data to monitor interannual variations in the mass balance its position is a climate indicator and was determined for the entire section of the greenland ice sheet investigated

thinning of the ice sheet in northwest greenland over the past forty years thermal expansion of the oceans as well as melting of glaciers ice sheets and ice caps have been the main contributors to global sea level rise over the past century the greatest uncertainty in predicting future sea level changes lies with our estimates of the mass balance of the ice sheets in greenland and antarctica1 satellite measurements have been used to determine changes in these ice sheets on short timescales demonstrating that surface elevation changes on timescales of decades or less result mainly from variations in snow accumulation2 here we present direct measurements of the changes in surface elevation between 1954 and 1995 on a traverse across the north greenland ice sheet measurements over a time interval of this length should reflect changes in ice flow the important quantity for predicting changes in sea level relatively unperturbed by short term fluctuations in snow accumulation we find only small changes in the eastern part of the transect except for some thickening of the north ice stream on the west side however the thinning rates of the ice sheet are significantly higher and thinning extends to higher elevations than had been anticipated from previous studies3

earthquake genesis in nepal himalaya a perspective from imaging of the 25th april 2015 mw 7 8 earthquake source zone abstract the mw 7 8 earthquake in central nepal nucleated in the mid crustal ramp zone of the main himalayan decollement thrust mht and propagated eastward for 140 km where the largest triggered event of mw 7 3 occurred without any surface rupture although it is advocated that the slip and rupture dynamics are controlled by the structural configuration of the mht and the upper crust precise correlation between the seismic structure and seismogenesis is hitherto scarce in the himalaya to address the issue we imaged the crustal structure along three profiles covering the earthquake source region using receiver function analysis of the seismic data from the hiclimb and himnt seismic networks to understand the lateral variability a 5 km thick low velocity layer is observed at the mid crustal level that steepens in the mht ramp zone the bulk of the seismicity including large shocks after the 2015 nepal earthquake lies in the vicinity of this low velocity layer correlation of the seismic structure and aftershock distribution with the published crustal structure clearly suggests that the rupture involves a thicker zone extending for 40 km to the south of the source zone in the mht ramp we refined the structure of the mht zone incorporating published coseismic slip and ground deformation to suggest that the rupture terminated at the footwall imbricate horse on the floor thrust below the zone of maximum coseismic uplift and there was a two stage rupture towards the eastern margin of the rupture zone

force perturbation analysis of recent thinning and acceleration of jakobshavn isbrae greenland observations between 1997 and 2001 of a 30 velocity increase and up to 60 m thinning of downstream parts of jakobshavn isbrae greenland immediately following calving of about 4 km of its 15 km floating ice tongue suggest that acceleration may have been initiated by the calving assuming that the force perturbation associated with such weakening is swiftly transmitted far up glacier i develop equations to estimate the perturbation initially the observed changes are consistent with the comparatively small perturbation associated with the calving thereafter it was probably sustained by thinning of the remaining ice tongue at rates of about 80 m a 1 otherwise the force perturbation would soon have been balanced by reduction in the hydrostatic driving force for longitudinal creep as the glacier thinned with velocities dropping to their former values the calculated force perturbation increases to a maximum about 10 km inland of the grounding line consistent with decreasing weight forces as the glacier thins over bedrock that slopes uphill seawards further inland it progressively decreases probably because marginal drag increased as the glacier accelerated both here and on the floating tongue marginal ice appears to have been softened by the influence of locally intense shear on ice temperature and or fabric more recent observations show continued acceleration and thinning and most of the remaining ice tongue calved away in april 2003 so thinning is likely to continue

mass balance of the greenland ice sheet at high elevations comparison of ice discharge from higher elevation areas of the entire greenland ice sheet with total snow accumulation gives estimates of ice thickening rates over the past few decades on average the region has been in balance but with thickening of 21 centimeters per year in the southwest and thinning of 30 centimeters per year in the southeast the north of the ice sheet shows less variability with average thickening of 2 centimeters per year in the northeast and thinning of about 5 centimeters per year in the northwest these results agree well with those from repeated altimeter surveys except in the extreme south where we find substantially higher rates of both thickening and thinning

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

measuring snow and glacier ice properties from satellite satellite remote sensing is a convenient tool for studying snow and glacier ice allowing us to conduct research over large and otherwise inaccessible areas this paper reviews various methods for measuring snow and glacier ice properties with satellite remote sensing these methods have been improving with the use of new satellite sensors like the synthetic aperture radar sar during the last decade leading to the development of new and powerful methods such as sar interferometry for glacier velocity digital elevation model generation of ice sheets or snow cover mapping some methods still try to overcome the limitations of present sensors but future satellites will have much increased capability for example the ability to measure the whole optical spectrum or sar sensors with multiple polarization or frequencies among the methods presented are the satellite derived determination of surface albedo snow extent snow volume snow grain size surface temperature glacier facies glacier velocities glacier extent and ice sheet topography in this review emphasis is put on the principles and theory of each satellite remote sensing method an extensive list of references with an emphasis on studies from the 1990s allows the reader to delve into specific topics

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

greenland ice sheet melt extent 1979 1999 analysis of melt extent on the greenland ice sheet is updated to span the time period 1979 1999 and examined along with its spatial and temporal variability using passive microwave satellite data to acquire the full record the issue of continuity between the previous passive microwave sensors smmr ssm i f 8 and ssm i f 11 and the most recent ssm i f 13 sensor is addressed the f 13 cross polarized gradient ratio melt classification threshold is determined to be 0 0154 results show that for the 21 year record a positive melt trend of nearly 1 yr is observed but this trend falls just below the 90 significance level the observed melt increase does appear to be driven by conditions in the western portion of the ice sheet rather than the east where melt appears to have decreased slightly moreover the eruption of mount pinatubo in 1991 is likely to have had some impact on the melt but not so much as previously suspected the 1992 melt anomaly is 1 7 standard deviations from the mean finally the relationship between coastal temperatures and melt extent suggests an increase in surface runoff contribution to sea level of 0 31 mm yr for a 1 c temperature rise

variations in snowpack melt on the greenland ice sheet based on passive microwave measurements a simple microwave emission model is used to simulate 37 ghz brightness temperatures associated with snowpack melt conditions for locations across the greenland ice sheet the simulated values are utilized as threshold values and compared to daily gridded smmr and ssm i passive microwave data in order to reveal regions experiencing melt the spatial extent of the area classified as melting is examined on a daily monthly and seasonal may august basis for 1979 91 the typical seasonal cycle of melt coverage shows melt beginning in late april a rapid increase in the melting area from mid may to mid july a rapid decrease in melt extent from late july through mid august and cessation of melt in late september seasonal averages of the daily melt extents demonstrate an apparent increase in melt coverage over the 13 year period of approximately 3 8 annually significant at the 95 confidence interval this increase is dominated by statistically significant positive trends in melt coverage during july and august in the west and southwest of the ice sheet we find that a linear correlation between microwave derived melt extent and a surface measure of ablation rate is significant in june and july but not august so caution must be exercised in using the microwave derived melt extents in august nevertheless knowledge of the variability of snowpack melt on the greenland ice sheet as derived from microwave data should prove useful in detecting climate change in the arctic and examining the impact of climate change on the ice sheet

rapid thinning of parts of the southern greenland ice sheet aircraft laser altimeter surveys over southern greenland in 1993 and 1998 show three areas of thickening by more than 10 centimeters per year in the southern part of the region and large areas of thinning particularly in the east above 2000 meters elevation the ice sheet is in balance but thinning predominates at lower elevations with rates exceeding 1 meter per year on east coast outlet glaciers these high thinning rates occur at different latitudes and at elevations up to 1500 meters which suggests that they are caused by increased rates of creep thinning rather than by excessive melting taken as a whole the surveyed region is in negative balance

classification of glacier zones in western greenland using albedo and surface roughness from the multi angle imaging spectroradiometer misr the greenland ice sheet has been the subject of mass balance and melt measurements over the past two decades and its margins have shown significant thinning in recent years surface characteristics of the ice sheet margins are strongly modified by the annual process of snow accumulation and melt in this work we explore spatial and temporal relationships between near infrared albedo and surface roughness from the multi angle imaging spectroradiometer misr aboard nasa s terra satellite our study area is a region in western greenland in the vicinity of jakobshavn glacier and its upland drainage basin we compute near infrared albedo from misr data using imagery over the april to september period for 2000 through 2005 near infrared albedo is inversely related to both snow age and melt intensity we map surface roughness using the normalized difference angular index ndai applied to misr atmospherically corrected surface hemispherical directional reflectance in previous work the ndai has been correlated with surface roughness on the scale of about 70 m we have further substantiated that relationship here the ndai and albedo images for each of the six years are used in an isodata unsupervised classification classification results for the individual years show year to year differences which appear to depend on the number and temporal distribution of images with minimal cloud cover as well as interannual differences in ice sheet surface properties the year 2003 which had the greatest number of images with minimal cloud cover shows good correspondence with previously mapped glacier zones however we do not have an isodata class that corresponds to the dry snow zone and we see greater differentiation between zones at lower elevations within each isodata class distinct relationships between near infrared albedo and surface roughness emerge and in all cases but one there is an inverse temporal relationship between albedo and roughness the one class that shows a direct relationship between albedo and surface roughness is hypothesized to be the superimposed ice zone while still somewhat preliminary these results suggest that concurrent measurements of near infrared albedo and surface roughness have significant potential for ice sheet surface characterization as well as for ongoing monitoring

surface melt induced acceleration of greenland ice sheet flow ice flow at a location in the equilibrium zone of the west central greenland ice sheet accelerates above the midwinter average rate during periods of summer melting the near coincidence of the ice acceleration with the duration of surface melting followed by deceleration after the melting ceases indicates that glacial sliding is enhanced by rapid migration of surface meltwater to the ice bedrock interface interannual variations in the ice acceleration are correlated with variations in the intensity of the surface melting with larger increases accompanying higher amounts of summer melting the indicated coupling between surface melting and ice sheet flow provides a mechanism for rapid large scale dynamic responses of ice sheets to climate warming

shuttle imaging radar sir c x sar reveals near surface properties of the south patagonian icefield shuttle imaging radar c x band synthetic aperture radar sir c x sar views of the south patagonian icefield in southern chile and argentina demonstrate the ability of spaceborne multiparameter radar to detect climatically driven intra annual changes in the snow and ice conditions on glaciers the sir c x sar system aboard space shuttle endeavor acquired images during two 11 day missions in april and october 1994 the radar signatures of differing snow and ice conditions are distinctive and homogeneous over large areas of the ice fields the signatures are characterized mainly by 1 backscatter amplitude levels 2 relative amplitudes of the c and l bands wavelengths of 5 7 and 24 cm respectively and 3 polarization properties indicative of volumetric or surface scattering the radar signatures are interpreted by correlating the radar characteristics with elevation of the snow and ice surfaces and with changes in the meteorological conditions we are able to define four radar glacier zones zone a a relatively dry snow zone with dominant c band returns zone b a moderately wet snow zone with dominant l band returns zone c a wet snow zone with weak returns in all bands and zone d bare ice and or heavily crevassed surfaces with strong returns in all bands the spatial changes in the radar glacier zones between april and october are consistent with colder temperatures recorded in october producing drier snow conditions at lower elevations than in april

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

comparison of avhrr derived and in situ surface albedo over the greenland ice sheet abstract this paper discusses a methodology for computing the clear sky surface albedo over the greenland ice sheet by using advanced very high resolution radiometer avhrr global area coverage visible and near infrared reflectances this approach is then used to map the monthly changes in albedo over the entire greenland ice sheet during the spring and summer months the methodology includes corrections for the intervening atmosphere by using the 6s radiative transfer model additional corrections for the anisotropic nature o f snow reflectance and the conversion from a marrow into a broadband albedo are made based on in site measurements from the swiss federal institute of technology university of colorado camp at 69 34 n 49 18 w comparison with surface albedo field ineasureinents indicates that before the onset of snoic melt agreement is good between the satellite derived and measured surface albedo after melt begins it is difficult to compare the satellite values with the field data owing to melt water ponding on the ice sheet surface with appropriate modifications the 6s radiative transfer model is suitable for atmospherically correcting avhrr visible and near infrared radiances atmospherically polar regions

seasonal variation of ice ablation at the margin of the greenland ice sheet and its sensitivity to climate change qamanârssup sermia west greenland monthly ice ablation was measured at the margin of the greenland ice sheet for june july and august over 7 years 1980 86 the total winter ablation september may has also been measured and a simple ablation temperature model used to assign ablation values to individual months under the present climate the most ablation occurred in june august on average 81 of annual ablation moderate ablation took place in may and september 17 and very little ablation occurred in october april 2 the effect of climate change on ice ablation is simulated using the ablation model to recalculate ablation for higher temperatures summer ice ablation increases with temperature in the model but there is proportionally greater increase for may and september whereas the period from october to april is presently so cold that even a temperature rise of 5 c will hardly increase ablation the difference in annual ice ablation caused by future climate change will therefore depend upon the seasonal distribution of the temperature change changes in precipitation and accumulation will further modify the seasonal variation of ablation

theory of metamorphism of dry snow the growth of ice particles in dry seasonal snow is caused by vapor diffusion among particles due to temperature gradients imposed on the snow cover the diffusion is calculated by using the potential field solutions for electrostatically charged particles the stereography of snow is represented by using a log normal distribution function for a geometrical enhancement factor defined here reasonable crystal growth rates and supersaturations are found the transition between the growth of highly faceted crystals and the growth of highly rounded crystals is determined by the critical supersaturation for the onset of dislocation aided growth thermal convection and the continuous movement of vapor around the particles due to the imposed temperature gradient are accommodated in the theory although both have little effect relative to the interparticle diffusion the growth of a layer of faceted crystals just below semi permeable crusts is explained by showing that crusts can cause the local supersaturation to exceed the critical value faceted crystals are shown to grow most rapidly in the lower warmer portions of the snow cover because of temperature effects on growth rate

discrimination of glacier facies using multi temporal sar data glacier facies from the greenland ice sheet and the wrangell st elias mountains alaska are analyzed using multi temporal synthetic aperture radar sar data from the european space agency ers 1 satellite distinct zones and facies are visible in multi temporal sar data including the dry snow facies the combined percolation and wet snow facies the ice facies transient melt areas and moraine in greenland and south central alaska very similar multi temporal signatures are evident for the same facies although these facies are found at lower altitude in west greenland where the equilibrium line appears to be found at sea level at 71 30 n during the year analyzed 1992 93 probably because of the cooling effect of the eruption of mount pinatubo in greenland both the percolation and dry snow facies are excellent distributed targets for sensor calibration with backscatter coefficients stable to within 0 2 db however the percolation facies near the top of mount wrangell are more complex and less easily delineated than in greenland and at high altitude the glacier facies have a multi temporal signature which depends sensitively on slope orientation

the surface albedo of the greenland ice sheet satellite derived and in situ measurements in the sondre stromfjord area during the 1991 melt season the temporal and spatial variation in the surface albedo of the greenland ice sheet during the ablation season of 1991 is investigated the study focuses on an area east of sondre stromfjord measuring 200 km by 200 km and centred at 67 5 n 48 13 w the analysis is based on satellite radiance measurements carried out by the advanced very high resolution radiometer avhrr the broad band albedo is estimated from the albedos in channel 1 visible and channel 2 near infrared the results are calibrated with the surface albedo of sea and dry snow satellite derived albedos are compared with gimex ground measurements at three stations there is a high degree of consistency in temporal variation at two of the three stations large systematic differences are attributed to albedo variations on subpixel scale in the course of the ablation season four zones appear each parallel to the ice edge it is proposed that these are in order of increasing altitude i clean and dry ice ii ice with surface water iii superimposed ice and iv snow an extensive description of these zones is given on the basis of the situation on 25 july 1991 zones i iii and iv reveal fairly constant albedos 0 46 0 65 and 0 75 on average whereas zone ii is characterised by an albedo minimum 0 34 survey of the western margin of the greenland ice sheet up to 71 n shows that the zonation occurs between 66 and 70 n

recent atmospheric warming and retreat of ice shelves on the antarctic peninsula in 1978 mercer1 discussed the probable effects of climate warming on the antarctic ice sheet predicting that one sign of a warming trend in this region would be the retreat of ice shelves on the antarctic peninsula analyses of 50 year meteorological records have since revealed atmospheric warming on the antarctic peninsula2 3 and a number of ice shelves have retreated4 8 here we present time series of observations of the areal extent of nine ice shelves on the antarctic peninsula showing that five northerly ones have retreated dramatically in the past fifty years while those further south show no clear trend comparison with airtemperature data shows that the pattern and magnitude of ice shelf retreat is consistent with the existence of an abrupt thermal limit on iceshelf viability the isotherm associated with this limit having been driven south by the atmospheric warming ice shelves therefore appear to be sensitive indicators of climate change

sr nd o isotopic evidence of variable sources of mantle metasomatism in the subcratonic lithospheric mantle beneath the grib kimberlite northwestern russia abstract to provide new insights into the type and extent of mantle metasomatism in the subcratonic lithospheric mantle we examined the sr nd o isotopic compositions of orthopyroxene clinopyroxene garnet ilmenite and phlogopite from sheared garnet lherzolite granular garnet harzburgites and lherzolites and clinopyroxene phlogopite rocks from the grib kimberlite in the arkhangelsk diamond province in northwestern russia clinopyroxene and orthopyroxene from sheared garnet lherzolite initially have a close value of 87sr 86sr t 0 7034 and close weak positive end orthopyroxene and clinopyroxene are in oxygen isotope equilibrium with coexisting olivine clinopyroxene from a garnet harzburgite has a low 87sr 86sr t isotope ratio of 0 70266 clinopyroxene from granular garnet lherzolites has a relatively narrow variation in 87sr 86sr t 0 70456 0 70582 and considerably larger variations in end 4 3 1 0 isotope ratios garnet displays elevated initial 87sr 86sr t values 0 70540 0 70633 ilmenite shows a narrow range in 87sr 86sr t 0 70497 0 70522 coupled with end values of 0 4 and 3 5 these isotopic data suggest granular garnet lherzolite of mantle metasomatism took place during the interaction of kimberlite melts with sclm that contained mica amphibole rutile ilmenite diopside marid type metasomes clinopyroxenes from clinopyroxene phlogopite phlogopite wehrlite xenoliths display a broader range in 87sr 86sr t 0 70486 0 70813 that is significantly higher than the kimberlite values and a circa chondritic end 0 1 1 3 with a restricted 18o range 5 11 5 33 more radiogenic sr isotopic composition decoupled from nd isotopes could have been induced by metasomatic melt fluid related to a subducted material the isotopic compositions of mantle minerals preserve sr nd isotopic evidence of pre kimberlite metasomatic events that were probably due to incomplete reequilibration with ultramafic carbonated melt based on mineral pairs rb sr isochrons and a clinopyroxene based sm nd errochron these mantle metasomatic events correspond to 550 600 ma and 1200 ma episodes of magmatic thermal activity

large fluctuations in speed on greenland s jakobshavn isbrae glacier it is important to understand recent changes in the velocity of greenland glaciers because the mass balance of the greenland ice sheet is partly determined by the flow rates of these outlets jakobshavn isbrae is greenland s largest outlet glacier draining about 6 5 per cent of the ice sheet area and it has been surveyed repeatedly since 1991 ref 2 here we use remote sensing data to measure the velocity of jakobshavn isbrae between 1992 and 2003 we detect large variability of the velocity over time including a slowing down from 6 700 m yr 1 in 1985 to 5 700 m yr 1 in 1992 and a subsequent speeding up to 9 400 m yr 1 by 2000 and 12 600 m yr 1 in 2003 these changes are consistent with earlier evidence for thickening of the glacier in the early 1990s and rapid thinning thereafter our observations indicate that fast flowing glaciers can significantly alter ice discharge at sub decadal timescales with at least a potential to respond rapidly to a changing climate

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

an overview of seasonal snow metamorphism the grains in seasonal snow undergo rapid and radical transformations in size shape and cohesion these grain characteristics affect all of the basic properties of snow snow is characterized as either wet or dry depending on the presence of liquid water wet snow is markedly different at low and high liquid contents dry snow is characterized as either an equilibrium form or a kinetic growth form that is it is either well rounded or faceted of course many snow grains display either transitional features between two of these categories or features which arise from other processes snow is classified depending on the dominant processes of its metamorphism