does folding accommodate europa s contractional strain the effect of surface temperature on fold formation in ice lithospheres 1 on europa the mechanism by which contractional strains are accommodated remains a mystery subtle folds have been observed in the polar regions but if folding is a dominant accommodation mechanism ubiquitous large amplitude folds might be expected across europa s surface here we use finite element modeling to show that fold growth rates are a strong function of surface temperature warm temperatures result in lower rates whereas cold temperatures result in higher rates combining diurnally averaged europan surface temperatures derived from galileo photopolarimeter radiometer data and new numerical simulations we show that forming moderate amplitude folds requires roughly twice the contraction or shortening in europa s equatorial latitudes relative to polar latitudes relatively large contractional strains in europa s equatorial and midlatitudes can therefore be accommodated primarily through passive shortening without producing obvious folds lithospheric folding and or passive shortening therefore remain plausible mechanisms for strain accommodation on europa

automated detection of unstable glacier flow and a spectrum of speedup behavior in the alaska range surge type glaciers are loosely defined as glaciers that experience periodic alterations between slow and fast flow regimes glaciers from a variety of mountain ranges around the world have been classified as surge type yet consensus of what defines a glacier as surge type has not always been met a common source of dispute is the lack of a succinct and globally applicable delimiter between a surging and nonsurging glacier the attempt is often a boolean classification however glacier speedup events can vary significantly with respect to event magnitude duration and the fraction of the glacier that participates in the speedup for this study we first updated the inventory of glaciers that show flow instabilities in the alaska range and then quantified the spectrum of speedup behavior we developed a new method that automatically detects glaciers with flow instabilities our automated results show a 91 success rate when compared to direct observations of speedup events and glaciers that are suspected to display unstable flow based on surface features through a combination of observations from the landsat archive and previously published data our inventory now contains 36 glaciers that encompass at least one branch exhibiting unstable flow and we document 53 speedup events that occurred between 1936 and 2014 we then present a universal method for comparing glacier speedup events based on a normalized event magnitude metric this method provides a consistent way to include and quantify the full spectrum of speedup events and allows for comparisons with glaciers that exhibit clear surge characteristics yet have no observed surge event to date our results show a continuous spectrum of speedup magnitudes from steady flow to clearly surge type which suggests that qualitative classifications such as surge type or pulse type behavior might be too simplistic and should be accompanied by a standardized magnitude metric

characterizing the surge behavior of alakesayi glacier in the west kunlun shan northwestern tibetan plateau from remote sensing data between 2013 and 2018

slope characteristics of europa constraints for landers and radar sounding 1 limited galileo derived topographic mapping of four major terrain types on europa provides slope characteristics useful for designing spacecraft instruments and for terrain comparisons topographic data are derived using stereo and photoclinometric analysis of galileo images at resolutions of 10 to 200 m with a few sites sampled at 500 m resolution similar data are also presented for dark and bright terrains on ganymede as well as preliminary results for polar terrains on enceladus rms slopes for ridged plains matrix and crater deposits on europa are typically between 10 and 15 at 10 100 m length scales significantly steeper overall than typical landing sites on mars terrains on ganymede may be even rougher smooth dilational bands on europa however have rms slopes of 5 the shallowest slope statistics of any major terrain type on europa aside from these areas almost no smooth areas larger than a few kilometers across occur on europa

karakoram glacier surge dynamics quincey d j braun m glasser n f bishop m p hewitt k luckman a 2011 geophysical research letters 38 article number l18504

model constraints on the opening rates of bands on europa a mid ocean ridge spreading analog is used to constrain the opening rates and brittle ductile transition depths for two axisymmetric ridged bands on europa estimates of brittle ductile transition depth based on the morphologies of yelland and ino lineae are combined with a conductive cooling model based on a mid ocean ridge analog to estimate the opening rates and active lifetimes of the bands this model limits local strain rates to 10 15 10 12 s 1 opening rates to 0 2 40 mm yr 1 and active lifetimes of the bands to 0 1 30 myr if the observed structures in the outer portions of ridged bands are indeed normal faults the estimated range for the tensile strength of ice on europa

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

forming europa s folds strain requirements for the production of large amplitude deformation abstract the surface of jupiter s iconic icy satellite europa is dominated by tectonic features that have formed in extension in contrast features that have formed in contraction appear to be rare thus there exists an apparent imbalance between the observed surface expression and relative magnitudes of extensional and contractional strain in this paper we reexamine the amount of strain that can be accommodated during fold formation on europa using a two dimensional finite element model that allows the examination of fold formation at large strains and under a broad range of initial conditions we find that in contrast to previous assessments relatively large strains can be accommodated by the development of relatively low amplitude folds under our nominal conditions creating peak to trough fold amplitudes of 200 m consistent with europa s astypalaea folds requires 7 contraction of the lithosphere decreasing either the strain rate or the ice grain size allows the formation of larger amplitude folds at smaller strains but we find no cases where 200 m amplitude folds form at less than 3 strain only if both of these conditions are met simultaneously do large amplitude folds form at contractional strains 3 the requirement of larger strains relative to previous analytical models results from the combined effects of an initial period of fold nucleation generally 1 2 contractional strain in which limited amplification occurs and smaller amplitude growth rates overall the requirement of several percent strain to produce even moderate amplitude folds is consistent with previous numerical models of single layer and lithospheric scale viscoelastic folding under terrestrial conditions because the formation of large amplitude folds requires relatively large strain small but significant amounts of contraction can be accommodated predominantly through uniform thickening of the lithosphere during the nucleation phase of fold growth without the formation of obvious surface deformation the accommodation of contractional strains via such pre folding lithospheric thickening provides at least a partial solution to europa s apparent strain imbalance

observations on the distribution and characteristics of potholes on surging glaciers potholes are depressions often water filled 10 100 m across found on the surfaces of glaciers most fields of potholes are found on surging glaciers suggesting that potholes form as a result of surging a photographic inventory of hundreds of glaciers in alaska and yukon territory allowed this hypothesis to be tested out of 26 pothole fields observed 19 were on known surging glaciers two on probable surging glaciers and the rest in areas where surging glaciers are common the majority of pothole fields were found near the equilibrium line photographs show that potholes formed within several years following the 1937 surge of the black rapids glacier in a zone where there had been intense crevassing between 1949 and 1986 the total number of potholes on the glacier decreased from approximately 700 to less than 200 while their mean size increased from 20 to 30 m some of these potholes have been observed to drain englacially the movement of these potholes were measured photogrammetrically to be less than 10 m yr the majority of the motion resulting from ice flow intense crevassing resulting from surging appears to be necessary for the formation of potholes but not sufficient as only 21 out of 256 surging glaciers contain potholes

polar wander and surface convergence of europa s ice shell evidence from a survey of strike slip displacement two global issues regarding europa are addressed by a survey of strike slip faults first a common type of terrain that appears to represent convergent sites of surface removal which may help compensate for substantial widespread dilation along tectonic bands elsewhere thus helping resolve the problem of conserving global surface area is identified second evidence for polar wander may provide the first confirmation of that theoretically predicted phenomenon these results among others come from an extensive survey of strike slip faults over the portion of the surface where galileo images at 200 m pixel resolution were obtained for regional mapping purposes the images cover two broad swaths that run from the far north to the far south one in the leading hemisphere and the other in the trailing hemisphere among the faults that have been mapped are a fault 170 km long with a strike slip offset of 83 km the greatest yet identified on europa and a quasi circular strike slip fault that surrounds a 500 km wide plate which has undergone rotation as a rigid unit reconstruction of specific examples of strike slip reveals sites of lateral convergence because europa is unique in many ways these sites are not similar to compression features on other bodies which may explain why they had previously been difficult to identify the distribution of strike slip in both hemispheres when compared with predictions of the theory of tidal walking provides evidence for polar wander the crust of europa appears to have slid as a single unit relative to the spin axis such that the site on the crust that was previously at the north rotational pole has wandered probably during the last few million years to a location currently in the leading hemisphere about 30 away from the spin axis such polar wander probably also explains symmetry patterns in the distribution of chaotic terrain pits and uplift features

active formation of chaos terrain over shallow subsurface water on europa the galileo spacecraft revealed a number of chaos regions on jupiter s moon europa where the surface terrain appears to have been disrupted from below in many places the surface contains sharp edged blocks or rafts of ice that have at some point been flipped or rotated some characteristics of these regions have been hard to explain such as the fact that the archetypal conamara chaos stands above its surroundings and contains matrix domes schmidt et al apply lessons learned from analogous processes within earth s subglacial volcanoes and ice shelves to an analysis of archival data that suggests chaos terrain forms above liquid water lenses that are perched only 3 kilometres deep within the ice shell the data suggest that ice water interactions and freeze out give rise to the varied morphology of chaos terrains implying that more water is involved than has been previously appreciated for instance the sunken topography of thera macula a large chaos area may indicate that europa is actively resurfacing over a lens comparable in volume to north america s great lakes europa the innermost icy satellite of jupiter has a tortured young surface1 2 3 4 and sustains a liquid water ocean1 2 3 4 5 6 below an ice shell of highly debated thickness1 2 3 4 5 7 8 9 10 quasi circular areas of ice disruption called chaos terrains are unique to europa and both their formation and the ice shell thickness depend on europa s thermal state1 2 3 4 5 7 8 9 10 11 12 13 14 15 16 17 no model so far has been able to explain why features such as conamara chaos stand above surrounding terrain and contain matrix domes10 18 melt through of a thin few kilometre shell3 7 8 is thermodynamically improbable and cannot raise the ice10 18 the buoyancy of material rising as either plumes of warm pure ice called diapirs1 9 10 11 12 13 14 15 or convective cells16 17 in a thick 10 kilometres shell is insufficient to produce the observed chaos heights and no single plume can create matrix domes10 18 here we report an analysis of archival data from europa guided by processes observed within earth s subglacial volcanoes and ice shelves the data suggest that chaos terrains form above liquid water lenses perched within the ice shell as shallow as 3 kilometres our results suggest that ice water interactions and freeze out give rise to the diverse morphologies and topography of chaos terrains the sunken topography of thera macula indicates that europa is actively resurfacing over a lens comparable in volume to the great lakes in north america

surges of glaciers in iceland surges are common in all the major ice caps in iceland and historical reports of surge occurrence go back several centuries data collection and regular obser vationover thelast several decadeshave permitteda detailed descriptionof several surges fromwhich it is possible to generalize onthe nature of surging in icelandic glaciers com bining the historical records of glacier front variations and recent field research we sum marize the geographic distribution of surging glaciers their subglacial topography and geology the frequency andduration of surges changes in glacier surface geometry during the surge cycle and measured velocity changes comparedto calculatedbalance velocities wenotetheindicatorsofsurgeonsetanddescribechangesinice waterandsedimentfluxes duringa surge surgesaccomplishasignificantfractionofthetotalmasstransportthrough the main outlet glaciers of ice caps in iceland and have important implications for their hydrology ouranalysisof the data suggeststhat surge type glaciersin icelandarecharac terizedbygentlysloping surfacesandthatthey movetoo slowlytoremain inbalance given their accumulation rate surge frequency is neither regular nor clearly related to glacier size or massbalance steeply sloping glaciers whetherhard or soft bedded seemto move sufficiently rapidly to keep inbalance with the annual accumulation

hydrodynamic and suspended sediment transport controls on river mouth morphology 1 river mouths building into standing bodies of water have strikingly varied growth habits this presents a compelling pattern formation problem that is also of great practical relevance for subsurface prediction and managing coastal wetlands here we present a generalized 2 5 dimensional potential vorticity pv theory that explains sedimentation patterns of a sediment laden stationary jet by coupling an understanding of vorticity with suspended sediment concentration fields we explore the physical meaning of this new sediment pv definition and its impact on outflow depositional patterns by analyzing data from a shallow wall bounded plane jet experiment and by discussing new theoretical insights a key result is that lateral advection and diffusion of suspended sediment are directly proportional to jet vorticity a feature that reveals the mechanistic process that forms elongated channels by focused levee deposition the new pv theory constitutes a more generalized mathematical framework that expands the rouse theory for the equilibrium of suspended sediment

the triggering of aftershocks by the free oscillations of the earth analysis of the loma prieta aftershock sequence mainshock 18 october 1989 shows periodicities at the periods of two normal modes s 2 and t 2 about 10 of the small aftershocks in the fault zone are triggered by these two modes during the 6 days following the mainshock

one hundred km scale basins on enceladus evidence for an active ice shell 1 stereo derived topographic mapping of 50 of enceladus reveals at least 6 large scale ovoid depressions basins 90 175 km across and 800 to 1500 m deep and uncorrelated with geologic boundaries in contrast the south polar depression is larger and apparently shallower and correlates with active resurfacing the shape and scale of the basins is inconsistent with impact geoid surface deflections or with dynamically supported topography isostatic thinning of enceladus ice shell associated with upwellings and tidally driven ice melting can plausibly account for these basins thinning implies upwarping of the base of the shell of 10 20 km beneath the depressions depending on total shell thickness loss of near surface porosity due to enhanced heat flow may also contribute to basin lows alternatively the basins may overly cold inactive and hence denser ice but thermal isostasy alone requires thermal expansion more consistent with clathrate hydrate than water ice

surface area changes of glaciers in the tibetan plateau interior area since the 1970s using recent landsat images and historical maps the tibetan plateau interior area tpia often termed the qangtang plateau is distinguished by many dome like mountains higher than 6000 m a s l these mountains provide favourable conditions for the development of ice caps and glaciers of extreme continental subpolar type according to historical topographic maps 1959 80 and recent landsat images 2004 11 continuous retreat was observed and the glacierized part of this area decreased by 9 5 0 27 a 1 with respect to the total glacier area of 8036 4 km 2 in the 1970s glaciers in the zhari namco basin have experienced the highest area shrinkage with a reduction rate of 0 72 a 1 while the smallest reduction occurred in bangong co 0 12 a 1 and dogai coying basins 0 11 a 1 a regional gradient of area loss was found with a larger decrease in the south and a smaller decrease in the north of the plateau comparisons indicate glaciers have experienced smaller shrinkage in the tpia than in surrounding regions glacier shrinkage in the tpia is mainly attributed to an increase in air temperature while precipitation glacier size and positive difference of glaciation also played an important role

the new remote sensing derived swiss glacier inventory ii first results complete swiss glacier inventories are available for 1850 reconstructed and 1973 from aerial photography connected to the global land ice measurements from space project a new swiss glacier inventory for approximately the year 2000 sgi 2000 is compiled mainly based on satellite imagery the developed and applied remotesensing and geographical information system gis methods are described in part i of the contribution in part ii the inventory design first result analyses and comparisons with former glacial conditions are presented as basic entries sgi 2000 contains the individual glacier identification planimetric glacier boundaries as derived from image analysis digitized central flowlines and polygonal glacier basin maps all other parameters are automatically deduced from the above entries and a digital elevation model within a gis here we analyze a set of small bernese and valais glaciers of area 2 these glaciers lost about 21 of area from 1973 to 1998 in addition to about 80 during 1850 1973 both with respect to the 1973 area in order to track the latest trend in more detail anintermediate glacier condition has been compiled from satellite imagery of 1985 this analysis gave an increasing speed of area loss 19 for 1985 98

landsat based inventory of glaciers in western canada 1985 2005 abstract we report on a glacier inventory for the canadian cordillera south of 60 n across the two western provinces of british columbia and alberta containing 30 000 km2 of glacierized terrain our semi automated method extracted glacier extents from landsat thematic mapper tm scenes for 2005 and 2000 using a band ratio tm3 tm5 we compared these extents with glacier cover for the mid 1980s from high altitude aerial photography for british columbia and from landsat tm imagery for alberta a 25 m digital elevation model dem helped to identify debris covered ice and to split the glaciers into their respective drainage basins the estimated mapping errors are 3 4 and arise primarily from seasonal snow cover glaciers in british columbia and alberta respectively lost 10 8 3 8 and 25 4 4 1 of their area over the period 1985 2005 the region wide annual shrinkage rate of 0 55 a 1 is comparable to rates reported for other mountain ranges in the late twentieth century least glacierized mountain ranges with smaller glaciers lost the largest fraction of ice cover the highest relative ice loss in british columbia 24 0 4 6 occurred in the northern interior ranges while glaciers in the northern coast mountains declined least 7 7 3 4

heterogeneity in karakoram glacier surges many karakoram glaciers periodically undergo surges during which large volumes of ice and debris are rapidly transported downglacier usually at a rate of 1 2 orders of magnitude greater than during quiescence here we identify eight recent surges in the region and map their surface velocities using cross correlation feature tracking on optical satellite imagery in total we present 44 surface velocity data sets which show that karakoram surges are generally short lived lasting between 3 and 5 years in most cases and have rapid buildup and relaxation phases often lasting less than a year peak velocities of up to 2 km a 1 are reached during summer months and the surges tend to diminish during winter months otherwise they do not follow a clearly identifiable pattern in two of the surges the peak velocity travels down ice through time as a wave which we interpret as a surge front three other surges are characterized by high velocities that occur simultaneously across the entire glacier surface and acceleration and deceleration are close to monotonic there is also no consistent seasonal control on surge initiation or termination we suggest that the differing styles of surge can be partly accounted for by individual glacier configurations and that while some characteristics of karakoram surges are akin to thermally controlled surges elsewhere e g svalbard the dominant surge mechanism remains unclear we thus propose that these surges represent a spectrum of flow instabilities and the processes controlling their evolution may vary on a glacier by glacier basis

late paleozoic strike slip faults and related vein arrays of cape elizabeth maine abstract strike slip faults and related quartz vein arrays of late paleozoic age cut gently dipping metasedimentary rocks at cape elizabeth in southern coastal maine and formed in response to regional dextral shearing along the norumbega fault system vertical quartz veins up to 20 m wide and 10s of meters long were emplaced orthogonal to the local shear zone parallel elongation fabric reflecting strain partitioning during transpression earlier veins were reoriented by clockwise rotation toward this ne trending regional shear direction the later brittle strike slip faults are oblique to the regional shear direction and interpreted as a 10 km scale r shear array on the southeast flank of the norumbega fault system these left stepping en echelon fault zones consist of the three two lights fault zones 200 m lengths and up to 5 m displacements and the richmond island fault zone 1 6 km length and 40 m displacement displacements on these fault zones have developed fine grained silicified obliquely foliated and laminated cataclasites and locally millimeter thin pseudotachylyte fault and injection veins individual fault core zones are up to 10s of centimeters thick as part of several complex anastamosing zones of faulting 10s of meters wide initial segments within each fault zone are typically terminated with oblique extension fractures in horsetail configurations the left stepping en echelon relationships between these segments led to dominantly contractional step over zones where p shear linkages created a through going fault that truncated the ends of the earlier formed terminated segments this linkage growth model for fault zone evolution works toward larger scales and longer fault lengths as displacement accumulates within a limiting maximum displacement length ratio characteristic of the host lithologies length frequency data for fault segments within these zones suggest a transition to linkage dominated growth once fault segments were longer than 15 m continued displacement was accommodated along the p shear linked en echelon faults through imbrication contractional duplexing and adhesive wear on the outcrop scale core zone processes on the micro scale reflect cataclasis and frictional sliding during coseismic slip as well as cataclastic flow and pressure solution during post seismic creep the development of foliated to laminated cataclasite was accompanied by pore volume collapse pressure solution and fluid expulsion that in turn triggered the development of the late fault related quartz vein arrays

glacier mass changes over duxueshan burog kangri and zangser kangri in the inner tibetan plateau the variation of glacier mass balance during the past decades remains poorly known for duxueshan burog kangri and zangser kangri dbz which are located in the inner tibetan plateau itp a transition zone with shifting influences between the westerlies and the indian summer monsoon in the present study glacier area and mass changes were determined by topographic maps topo landsat imagery and multi temporal digital elevation models dems generated with topo srtm tandem x bistatic interferometric synthetic aperture radar insar images and high mountain asia 8 m dems on average the glaciers showed a slight retreat from 343 27 5 23 km2 in 1971 to 334 67 3 21 km2 in 2018 0 05 0 04 a 1 however glaciers lost mass at a rate of 0 32 0 03 m w e a 1 from 1971 to 2012 for the 1999 2012 and 2012 2017 periods mass balances of 0 03 0 16 and 0 09 0 04 m w e a 1 respectively were observed which represents an approximately equilibrium two glaciers also advanced in our investigation period and we confirmed one of them surged in 2015

ice velocity and climate variations for baltoro glacier pakistan quincey dj copland l mayer c bishop m luckman a belo m 2009 ice velocity and climate variations for the baltoro glacier pakistan journal of glaciology 55 194 1061 1071 sponsorship rcuk us national science foundation us national geographic society natural sciences and engineering research council of canada canadian foundation for innovation ontario research fund university of ottawa

stresses generated in cooling viscoelastic ice shells application to europa 1 a cooling viscoelastic ice shell overlying an ocean develops stresses due to two effects thermal contraction of the ice due to cooling and the expansion of the shell due to the ice water volume change the former effect generates near surface compression and deeper extension the second effect generates extension only in both cases stresses are smaller at depth due to viscous creep the resulting combined stresses are extensional except at shallow 1 km depths in thin ice shells for ice shells thicker than 45 km stresses are extensional throughout the extensional stresses exceed 10 mpa for shells thicker than 20 km and thus dominate all other likely sources of stress as long as shell cooling occurs the dominantly extensional nature of the stresses may help to explain the puzzling lack of compression observed on europa and other large icy satellites however after 100 myr of conductive cooling the maximum theoretical elastic strains for europa are 0 35 which are probably insufficient to explain the total amount of observed extension

hubbard glacier alaska 2002 closure and outburst of russell fjord and postflood conditions at gilbert point 1 hubbard glacier the largest temperate tidewater glacier in the world has been advancing since 1895 ad and has now twice dammed 60 km long russell fjord once in 1986 and more recently in 2002 this paper focuses on the 2002 event when a strong spring advance pushed shallow submarine proglacial sediments against gilbert point closing off russell fjord by late june as a consequence upstream ice flow decelerated from 5 m d 1 to 1 5 m d 1 with flow diverging to either side of gilbert point lake height reached 15 m asl before intense rains caused lake water to overtop the moraine dam on 14 august 2002 three cubic kilometers of water were released within 30 hours with peak discharge reaching 55 000 m3 s 1 24 hours after the flood began the discharge records for the 1986 and 2002 outbursts differ significantly and reflect differences in lake height 26 m versus 15 m and dam types ice versus moraine the 2002 outburst proceeded in two stages 1 relatively slow overtopping of the subaerial moraine with downward erosion rates of 1 2 m h 1 with little lateral expansion 2 followed by faster downward erosion of the submarine moraine up to 7 m h 1 with rapid lateral expansion of the channel by ice calving 7 m h 1 the annual average terminus position at gilbert point has remained constant since 2002 although there are seasonal variations of 100 200 m the deep channel strong tidal currents and seasonally warm ocean water appear to have prevented the advance of this segment of the terminus despite the glacier s continued advance elsewhere along its terminus sediments are slowly filling in the channel at a rate of about 4 m yr 1 and their steady accumulation may eventually trigger the next closure

characteristics of surge type glaciers glaciers can be divided into two classes according to their flow behavior normal relatively steady annually averaged flow rate and surge type pronounced cyclic flow variations having a typical periodicity of 10 100 years we have examined the population statistics of 2356 glaciers in the st elias mountains yukon territory canada and estimate that 151 6 4 of these glaciers are surge type to explore how various glacier attributes are associated with surging we compare the probability of surging associated with various subsets of the complete population to appropriate reference values in this way potential influences on surge tendency can be examined for the 55 drainage basins analyzed there is a pronounced spatial variation in the concentration of surge type glaciers but no obvious environmental control can be evinced within the study area the greatest concentration lies in the northern st elias mountains a region of high topographic elevation that is experiencing rapid tectonic uplift analysis of the influence of length on surge tendency reveals that long glaciers have a significantly greater probability of being surge type than short glaciers the surge probability increases monotonically from 0 61 for very short glaciers 0 1 km to 65 1 for long glaciers 10 75 km this result suggests that ice sheets and ice caps or at least portions of them should have a high probability of surging tributary glaciers have a greater tendency to surge than trunk glaciers presumably because they may themselves be surge type and may additionally participate in surges of the trunk glacier the nonrandom geographical distribution of surge type glaciers is not simply a consequence of the variation from basin to basin of the glacier length distribution surge type glaciers tend to have a higher overall elevation than normal glaciers the elevation of the highest point of the accumulation zone the elevation of the snow line and the elevation of the lowest point of the ablation zone on average exceed the corresponding elevations for normal glaciers there is no significant difference between the overall slopes of surge type and normal glaciers although there is a tendency for surge type glaciers to have greater slope in the accumulation zone and lesser slope in the ablation zone than normal glaciers although the prevalent flow direction for glaciers in the yukon data set is to the north surge type glaciers tend to flow to the east and southeast this orientation influence is probably explained by the fact that many of the longest glaciers also flow to the east and southeast

monitoring surging glaciers of the pamirs central asia from space the evolution of surging glaciers of the pamirs central asia has been studied using repeat remote sensing surveys in the institute of geography russian academy of sciences since the early 1970s we use images obtained from national resurs f satellites 1972 91 as well as landsat 7 and terra 1999 2006 to provide a basis for monitoring of surging glaciers aimed at developing their inventory studying the causes and mechanisms of surges and examining the timing and extent of glacial catastrophes the inventory from the early 1990s allows identification of 215 glaciers with a dynamically unstable regime we discovered 51 surging glaciers up until 2006 10 more surges had occurred we use stereoscopic deciphering and photogrammetric processing of consecutive satellite images to study the morphology and ice velocity changes of several compound surging glaciers we analyze the results of monitoring of bivachny and oktyabr sky glaciers from 1972 to 1991 and sugran glacier from 1972 to 2006 two surges of sugran glacier occurred during this time an internal surge in 1976 80 and a surge with glacier tongue advance as far as 4 5 km in 2000 05 the role of damming in compound glacier systems is examined satellite based monitoring is now the only method for obtaining initial information about the state and fluctuations of such glaciers

svalbard surge dynamics derived from geometric changes geometric changes on a sample of svalbard glaciers were studied using subtraction of repeat digital terrain models to determine early surge stage dynamics changes in surface features were also analyzed a number of new surges were found for glaciers not known to have surged previously the surge development could be followed through three stages of which the first two had not been previously described in svalbard the first two stages are mainly identified from glacier thickness changes and showed little visual evidence in stage 1 initial surface lowering was found in the upper part of the glacier followed by a thickening further down glacier in stage 2 stage 3 represents the period of well developed surge dynamics that is usually reported some surges ceased at stage 2 as a partial surge and never developed into a fully active surge these partial surges could be misinterpreted as rapid response to climate change the results of this study further support previous findings that the majority of svalbard glaciers are of surge type data archives have greatly facilitated the search for signs of surges and the recapturing of the course of events in this paper we present a number of new observations of svalbard surge type behaviour based on evidence from geometric changes and complemented by observations of newly developed crevasse fields two criteria are used to identify a surge either individually or in combination 1 mass displacement from the upper to the lower glacier part and 2 presence of new crevasse fields which indicate rapid or strong changes in stresses the aims of our study are to contribute to a more complementary picture and better understanding of the transition from build up stage via initial surge dynamics to the previously described mature stage where the changes are more pronounced we also investi gate whether all surges develop fully the implications of partial surges for interpretation of surface lowering related to varying climate conditions and finally the large spread in estimates for the number of surge type glaciers in svalbard

characterizing the may 2015 karayaylak glacier surge in the eastern pamir plateau using remote sensing we investigate an internal surge of karayaylak glacier which was reported by the media in may 2015 to differentiate the may 2015 glacier surge from other glacier advances we surveyed changes in velocity crevasses and glacier area using landsat 8 oli l1t zy 1 02c and gaofen 1 images from october 2014 to july 2015 the velocity measured by automatic feature extraction and tracking during the active phase was 10 100 times the velocity during the quiescent phase with a maximum of 20 2 0 9 m d 1 mean standard error from 8 to 15 may 2015 in the west branch of the glacier the surge initiation and termination took place from 13 april to 16 june 2015 ice in the west branch length 7 km area 6 8 km 2 of karayaylak glacier accelerated down to the east branch leading to the development of crevasses and ice covering an additional 0 1 km 2 of summer pasture on the northwestern side however we detected no advance of the glacier s terminus

how much do we really know about glacier surging some of the ideas about glacier surging are considered mainly but not entirely in the light of observations of temperate glaciers in alaska u s a made within the last 15 years climate has an influence on surge recurrence interval climate and weather also affect surge initiation termination and magnitude regional studies lead to the speculation that subglacial till plays a key role in surging and it has been found under all surge type glaciers studied so far including black rapids and variegated glaciers alaska in most of the glaciers studied till deformation processes dominate the motion in quiescence the linked cavity model of surge triggering and rapid motion is not consistent with these observations but the limited coverage of the observations does not rule it out under parts of the glaciers studied the till observations in alaska raise old questions about the interaction between till and the hydraulic systems of temperate glaciers the role of stored water which observations show to be active even in winter on black rapids glacier is noted

glacier motion estimation using sar offset tracking procedures two image to image patch offset techniques for estimating feature motion between satellite synthetic aperture radar sar images are discussed intensity tracking based on patch intensity cross correlation optimization and coherence tracking based on patch coherence optimization are used to estimate the movement of glacier surfaces between two sar images in both slant range and azimuth direction the accuracy and application range of the two methods are examined in the case of the surge of monacobreen in northern svalbard between 1992 and 1996 offset tracking procedures of sar images are an alternative to differential sar interferometry for the estimation of glacier motion when differential sar interferometry is limited by loss of coherence i e in the case of rapid and incoherent flow and of large acquisition time intervals between the two sar images in addition an offset tracking procedure in the azimuth direction may be combined with differential sar interferometry in the slant range direction in order to retrieve a two dimensional displacement map when sar data of only one orbit configuration are available

tracer derived freshwater composition of the siberian continental shelf and slope following the extreme arctic summer of 2007 we investigate the freshwater composition of the shelf and slope of the arctic ocean north of the new siberian islands using geochemical tracer data 18o ba and po 4 collected following the extreme summer of 2007 we find that the anomalous wind patterns that partly explained the sea ice minimum at this time also led to significant quantities of pacific derived surface water in the westernmost part of the makarov basin we also find larger quantities of meteoric water near lomonosov ridge than were found in 1995 dissolved barium is depleted in the upper layers in one region of our study area probably as a result of biological activity in open waters increasingly ice free conditions compromise the quantitative use of barium as a tracer of river water in the arctic ocean

folds on europa implications for crustal cycling and accommodation of extension regional scale undulations with associated small scale secondary structures are inferred to be folds on jupiter s moon europa formation is consistent with stresses from tidal deformation potentially triggering compressional instability of a region of locally high thermal gradient folds may compensate for extension elsewhere on europa and then relax away over time

glacier velocities across the central karakoram optical matching of aster advanced spaceborne thermal emission and reflection radiometer satellite image pairs is used to determine the surface velocities of major glaciers across the central karakoram the aster images were acquired in 2006 and 2007 and cover a 60 120 km region over baltoro glacier pakistan and areas to the north and west the surface velocities were compared with differential global position system gps data collected on baltoro glacier in summer 2005 the aster measurements reveal fine details about ice dynamics in this region for example glaciers are found to be active over their termini even where they are very heavily debris covered the characteristics of several surge type glaciers were measured with terminus advances of several hundred meters per year and the displacement of trunk glaciers as surge glaciers pushed into them this study is the first synthesis of glacier velocities across this region and provides a baseline against which both past and future changes can be compared

the 2008 09 surge of central yulinchuan glacier northern tibetan plateau as monitored by remote sensing the 2008 09 surge of central yulinchuan glacier cyg on the northwestern slope of muztag mountain tibetan plateau is studied based on satellite remote sensing the widely used cross correlation feature tracking method was used to collect satellite image control points and validate their geometric accuracies as well as to derive glacier surface velocity changes in glacier length and area were also retrieved results show that the surge of cyg initiated in may 2008 and terminated in july 2009 two diffluent glacier termini advanced 590 26 m 5 1 0 2 of the 2004 length and 182 26 m 1 8 0 3 respectively and glacier area increased by similar to 1 41 0 11 km 2 4 6 0 4 of the 2004 area during this period the most significant surge period was october 2008 to march 2009 when most of the terminus advances and area increases occurred the glacier surface drastically crevassed during this time as much as 1657 297 m of horizontal surface displacements were produced by surge ice and maximum surface speed reached 13 1 5 m d 1 results of transverse and longitudinal velocity profiles revealed two surge waves during this surge of cyg

the new remote sensing derived swiss glacier inventory i methods a new swiss glacier inventory is to be compiled from satellite data for the year 2000 the study presented here describes two major tasks 1 an accuracy assessment of different methods for glacier classification with landsat thematic mapper tm data and a digital elevation model dem 2 the geographical information system gis based methods for automatic extraction of individual glaciers from classified satellite data and the computation of three dimensional glacier parameters such as minimum maximum and median elevation or slope and orientation by fusion with a dem first results obtained by these methods are presented in part ii of this paper kaab and others 2002 thresholding of a ratio image from tm4 and tm5 reveals the best suited glacier map the computation of glacier parameters in a gis environment is efficient and suitable for worldwide application the methods developed contribute to the u s geological survey led global land ice measurements from space glims project which is currently compiling a global inventory of land ice masses within the framework of global glacier monitoring haeberli and others 2000

glacier surges in the north west west kunlun shan inferred from 1972 to 2017 landsat imagery the west kunlun shan lie close to or are perhaps part of two significant glaciological phenomena the high mountain asia surge supercluster and the karakoram anomaly however glaciological studies and particularly surge studies in the range are limited here we extend the database of known surges in the region using landsat imagery and cross correlation feature tracking we examine 88 glaciers larger than 1 km2 in the hotan prefecture of xinjiang china and find evidence of nine surges occurring between 1972 and 2017 glaciers display low active phase velocities 0 2 1 5 km a 1 that show seasonal acceleration in the summer active phase periods as short as 2 years and build up and deceleration phases of months years although these observations display characteristics indicative of both the classic hydrological and thermal switch mechanisms the surging observed displays a close resemblance to that in the adjacent karakoram ranges furthermore the majority of the surges occur clustered at the end of a decadal scale warming period corroborating previously proposed causal links between climate and surging in the karakoram we suggest that the two regions should be considered part of one larger system when considering surge dynamics in high mountain asia

visible and near infrared digital images for determination of ice velocities and surface elevation during a surge on osbornebreen a tidewater glacier in svalbard

double ridges on europa accommodate some of the missing surface contraction crosscutting relationships of tectonic lineaments on europa record the history of surface deformation we mapped the displacement and orientation of older features crosscut by two types of lineaments bands and double ridges these measurements allow us to determine both the strike perpendicular and strike parallel displacement along investigated features double ridges record both ridge perpendicular contraction and expansion with a mean of 0 16 0 06 km needs space of contraction based on the analysis of 16 double ridges bands record expansion with a mean of 3 33 0 27 km for the six bands analyzed but with perpendicular displacement less than their apparent morphologic widths of 3 24 km the implied global surface strain for double ridges including those that expand and bands is 2 22 0 76 contraction and 7 60 3 7 expansion respectively double ridges thus may accommodate part of the surface expansion recorded by bands most current models for double ridges do not predict contraction the models that satisfy the observations for bands are slow spreading models cryovolcanism and folding

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

glacier surge mechanism 1982 1983 surge of variegated glacier alaska the hundredfold speedup in glacier motion in a surge of the kind the kind that took place in variegated glacier in 1982 1983 is caused by the buildup of high water pressure in the basal passageway system which is made possible by a fundamental and pervasive change in the geometry and water transport characteristics of this system the behavior of the glacier in surge has many remarkable features which can provide clues to a detailed theory of the surging process the surge mechanism is akin to a proposed mechanism of overthrust faulting

the second chinese glacier inventory data methods and results the second chinese glacier inventory was compiled based on 218 landsat tm etm scenes acquired mainly during 2006 10 the widely used band ratio segmentation method was applied as the first step in delineating glacier outlines and then intensive manual improvements were performed the shuttle radar topography mission digital elevation model was used to derive altitudinal attributes of glaciers the boundaries of some glaciers measured by real time kinematic differential gps or digitized from high resolution images were used as references to validate the accuracy of the methods used to delineate glaciers which resulted in positioning errors of 10 m for manually improved clean ice outlines and 30 m for manually digitized outlines of debris covered parts the glacier area error of the compiled inventory evaluated using these two positioning accuracies was 3 2 the compiled parts of the new inventory have a total area of 43 087 km 2 in which 1723 glaciers were covered by debris with a total debris covered area of 1494 km 2 the area of uncompiled glaciers from the digitized first chinese glacier inventory is similar to 8753 km 2 mainly distributed in the southeastern tibetan plateau where no images of acceptable quality for glacier outline delineation can be found during 2006 10

does europa have a subsurface ocean evaluation of the geological evidence it has been proposed that jupiter s satellite europa currently possesses a global subsurface ocean of liquid water galileo gravity data verify that the satellite is differentiated into an outer h2o layer about 100 km thick but cannot determine the current physical state of this layer liquid or solid here we summarize the geological evidence regarding an extant subsurface ocean concentrating on galileo imaging data we describe and assess nine pertinent lines of geological evidence impact morphologies lenticulae cryovolcanic features pull apart bands chaos ridges surface frosts topography and global tectonics an internal ocean would be a simple and comprehensive explanation for a broad range of observations however we cannot rule out the possibility that all of the surface morphologies could be due to processes in warm soft ice with only localized or partial melting two different models of impact flux imply very different surface ages for europa the model favored here indicates an average age of 50 myr searches for evidence of current geological activity on europa such as plumes or surface changes have yielded negative results to date the current existence of a global subsurface ocean while attractive in explaining the observations remains inconclusive future geophysical measurements are essential to determine conclusively whether or not there is a liquid water ocean within europa today

a surge of north gasherbrum glacier karakoram china between 2003 and 2007 north gasherbrum glacier on the northeastern slope of the karakoram mountains in asia underwent a dramatic acceleration during which a velocity wave propagated down the glacier there was a significant transfer of ice from up glacier downstream which resulted in a strong surface elevation increase over the lower tongue but only a moderate advance of the glacier snout we interpret this behaviour as that of a glacier surge and we explain the observations by means of a simple version of the kamb drainage switching theory

large surface velocity fluctuations of biafo glacier central karakoram at high spatial and temporal resolution from optical satellite images despite global warming and unlike their himalayan neighbours glaciers in the karakoram mountains do not show signs of significant retreat here we report high velocity variations of biafo glacier central karakoram which occurred between 2001 and 2009 and which indicate considerable dynamics in its flow behaviour we have generated a dense time series of glacier surface velocities based on cross correlation of optical satellite images which clearly shows seasonal and interannual velocity variations reaching 50 in some places the interannual velocity variations resemble the passing of a broad wave of high velocities with peak velocities during 2005 and some diffusion down glacier over a period of at least 4 years high interannual velocity variations are also observed at other glaciers in the vicinity suggesting a common cause although these appear to partly comprise longer acceleration phases analysis of weather station data provides some indications of meteorological conditions that could have promoted sustained sliding events during this period but this does not explain the wave like nature of the acceleration at biafo glacier and the regular protracted velocity changes

evidence for subduction in the ice shell of europa despite widespread evidence for extension there have been few signs of contraction on the icy surface of jupiter s europa evidence for a subduction like convergent boundary suggests that europa may have active plate tectonics