clast shape analysis and clast transport paths in glacial environments a critical review of methods and the role of lithology the reconstruction and tracing of transport paths in glaciated and other environments have a long tradition in the earth sciences we here present a dataset of clast shape samples from a worldwide selection of glaciated mountain environments in order to assess the reliability of this approach overall and the role of lithology on the performance of clast shape measurements in particular our findings demonstrate that the widely used ra c40 co variance approach is applicable to 63 of the 19 catchments investigated while the alternative rwr c40 approach is more widely applicable to 75 of these catchments a systematic assessment of mixing of lithologies at the catchment scale demonstrates that such mixing leads to pronounced overlaps between different control envelopes that had previously been separated thereby removing the discriminatory power of the method mixing of similar lithologies between different catchments shows an even more extreme loss of discriminatory power which strongly suggests that lithology plays a primary role in determining clast shape and that catchment specific processes are superimposed systematic analysis of the dataset also shows that nearly all catchments apart from two can be grouped into two types type i relates to sites in lesser mountain ranges and is characterised by dominantly blocky forms in the subglacial realm highlighting significant reworking processes type ii sites are dominantly in high mountain environments and characterised by a high similarity between subglacial and fluvial control envelopes this indicates that although reworking may be pronounced it is not necessarily effective enough to remove the platy shape that most likely results from extraglacial and supraglacial inputs our study highlights the potential of clast shape analysis as a tool that allows generic processes to be identified between catchments thereby enabling an understanding of debris cascades in glaciated mountain environments we finish with recommendations for ensuring that future clast shape studies are robust reproducible and comparable between different sites

dynamical properties of the venus mesosphere from the radio occultation experiment vera onboard venus express abstract the dynamics of venus mesosphere 60 100 km altitude was investigated using data acquired by the radio occultation experiment vera on board venus express vera provides vertical profiles of density temperature and pressure between 40 and 90 km of altitude with a vertical resolution of few hundred meters of both the northern and southern hemisphere pressure and temperature vertical profiles were used to derive zonal winds by applying an approximation of the navier stokes equation the cyclostrophic balance which applies well on slowly rotating planets with fast zonal winds like venus and titan the main features of the retrieved winds are a midlatitude jet with a maximum speed up to 140 15 m s 1 which extends between 20 s and 50 s latitude at 70 km altitude and a decrease of wind speed with increasing height above the jet cyclostrophic winds show satisfactory agreement with the cloud tracked winds derived from the venus monitoring camera vmc vex uv images although a disagreement is observed at the equator and near the pole due to the breakdown of the cyclostrophic approximation knowledge of both temperature and wind fields allowed us to study the stability of the atmosphere with respect to convection and turbulence the richardson number ri was evaluated from zonal field of measured temperatures and thermal winds the atmosphere is characterised by a low value of richardson number from 45 km up to 60 km altitude at all latitudes that corresponds to the lower and middle cloud layer indicating an almost adiabatic atmosphere a high value of richardson number was found in the region of the midlatitude jet indicating a highly stable atmosphere the necessary condition for barotropic instability was verified it is satisfied on the poleward side of the midlatitude jet indicating the possible presence of wave instability

wave analysis in the atmosphere of venus below 100 km altitude simulated by the lmd venus gcm a new simulation of venus atmospheric circulation obtained with the lmd venus gcm is described and the simulated wave activity is analysed agreement with observed features of the temperature structure static stability and zonal wind field is good such as the presence of a cold polar collar diurnal and semi diurnal tides at the resolution used 96 longitudes 96 latitudes a fully developed superrotation is obtained both when the simulation is initialised from rest and from an atmosphere already in superrotation though winds are still weak below the clouds roughly half the observed values the atmospheric waves play a crucial role in the angular momentum budget of the venus s atmospheric circulation in the upper cloud the vertical angular momentum is transported by the diurnal and semi diurnal tides above the cloud base approximately 1 bar equatorward transport of angular momentum is done by polar barotropic and mid to high latitude baroclinic waves present in the cloud region with frequencies between 5 and 20 cycles per venus day periods between 6 and 23 earth days in the middle cloud just above the convective layer a kelvin type wave period around 7 3 ed is present at the equator as well as a low latitude rossby gravity type wave period around 16 ed below the clouds large scale mid to high latitude gravity waves develop and play a significant role in the angular momentum balance

the formation of supraglacial debris covers by primary dispersal from transverse englacial debris bands glaciological controls on debris cover formation are investigated from the perspective of primary dispersal of supraglacial debris across a melting ice surface this involves the migration of angled debris septa outcrops across a melting thinning glacier ablation zone three measures of a glacier s ability to evacuate supraglacial debris are outlined 1 a concentration factor describing the focusing of englacial debris into specific supraglacial mass loads 2 the rate of migration of a septum outcrop relative to the local ice surface and 3 a downstream velocity differential between a slower septum outcrop and the faster ice surface velocity measures 1 and 2 are inversely related while measure 3 increases down glacier to explain why slow moving thinning ice rapidly becomes debris covered data from glacier d estelette italian alps are used to illustrate these processes and to explore the potential for debris cover formation and growth in different glaciological environments the transition from a clean transport dominated to a debris covered ablation dominated glacier is explained by the melting out of more closely spaced debris septa in combination with the geometric nteractions of angled septa and ice surface in a field of reducing flow and increasing ablation the growth and shrinkage of debris covers are most sensitive to glaciological changes at glaciers with gently dipping debris bearing foliation but less sensitive at high compression glaciers whose termini are constrained by moraine dams and other forms of obstruc tion these findings show that a variety of debris covered glacier types will show a spectrum of response characteristics to negative mass balance copyright 2013 john wiley sons ltd

venus express mission 1 venus express is well and healthy and has now been providing exciting new data from venus our nearby twin planet for over 2 years many of the new results are presented and discussed in the subsequent papers in this special section the overall scientific objective of venus express is to carry out a detailed study of the atmosphere of venus including the interaction of the upper atmosphere with the solar wind and the interaction of the lowest part of the atmosphere with the surface of the planet in addition the plasma environment and magnetic fields as well as some aspects of the surface of the planet are addressed for the first time investigations make systematic use of the transparent infrared spectral windows in order to probe the atmosphere in four dimensions three spatial dimensions plus time the spacecraft design is taken from mars express with some modifications necessary owing to the specific environment around venus the payload is composed of three spectrometers a camera a magnetometer an instrument for detecting energetic particles and a radio science package the orbit is polar and highly elliptic with a pericenter altitude of about 200 km over the northern polar region and an apocenter altitude of 66 000 km presently the coverage of the southern hemisphere is very good but important gaps still do exist the coverage of the northern hemisphere is much less dense venus express is a part of the european space agency s program for the exploration of the inner solar system which includes missions to study the sun mercury venus the moon mars and comets and asteroids

modification of clast shape in high arctic glacial environments abstract clast shape data from a range of different glacial environments at several high arctic valley glaciers in svalbard are presented these data add to the growing body of reference information about clast shape in modern glacial environments and is used to explore the role of lithology in clast morphogenesis and to evaluate the different methodological approaches to the analysis of clast shape data the following conclusions are drawn 1 it is possible to distinguish clasts transported subglacially from those moved supraglacially 2 it is not possible to differentiate among different types of subglacial sediment or to distinguish them collectively from glaciofluvial samples 3 lithology has some influence on clast shape although not as much as previously suggested and 4 covaria t plots of the ra percentage of angular and very angular clasts versus c40 percentage of clasts with c to a axial ratio 0 4 index give superior data visualization and discriminate more effectively among different glacial sediments than sphericity and roundness plots

south polar features on venus similar to those near the north pole venus has no seasons slow rotation and a very massive atmosphere which is mainly carbon dioxide with clouds primarily of sulphuric acid droplets infrared observations by previous missions to venus revealed a bright dipole feature surrounded by a cold collar at its north pole the polar dipole is a double eye feature at the centre of a vast vortex that rotates around the pole and is possibly associated with rapid downwelling the polar cold collar is a wide shallow river of cold air that circulates around the polar vortex one outstanding question has been whether the global circulation was symmetric such that a dipole feature existed at the south pole here we report observations of venus south polar region where we have seen clouds with morphology much like those around the north pole but rotating somewhat faster than the northern dipole the vortex may extend down to the lower cloud layers that lie at about 50 km height and perhaps deeper the spectroscopic properties of the clouds around the south pole are compatible with a sulphuric acid composition

ice bed interface and englacial properties of svalbard ice masses deduced from airborne radio echo sounding data un ensemble de donnees de sondages par echo radio ont ete collectees sur 44 masses de glace au spitsberg et les calottes glaciaires de nordaustlandet svalbard ces donnees ont permis de produire les coefficients de reflexion en puissance pour l interface glace manteau sur une grande etendue de svalbard nord

debris transport in a temperate valley glacier haut glacier d arolla valais switzerland hambrey m j goodsell becky glasser n f 2005 debris transport in a temperate valley glacier haut glacier d arolla valais switzerland journal of glaciology 51 172 pp 139 146

long term variation in the cloud tracked zonal velocities at the cloud top of venus deduced from venus express vmc images 1 we present observational evidence of the variation of the cloud tracked zonal velocity by 20 m s 1 with a timescale of a few hundred days in the southern low latitude region based on an analysis of cloud images taken by the venus monitoring camera on board venus express a spectral analysis suggests that the variation has a periodicity with a period of about 255 days although cloud features are not always passive tracers the periodical variation of the dynamical state is a robust feature superposed on this long term variation of the zonal velocity kelvin wave like disturbances tend to be observed in periods of relatively slow background velocity while rossby wave like disturbances tend to be observed in periods of fast background velocity since the momentum deposition by these waves can accelerate and decelerate the mean flow these waves may contribute to the suggested long term oscillation

mapping zonal winds at venus s cloud tops from ground based doppler velocimetry abstract the most significant aspect of the general circulation of the atmosphere of venus is its retrograde super rotation a complete characterization of this dynamical phenomenon is crucial for understanding its driving mechanisms here we report on ground based doppler velocimetry measurements of the zonal winds based on high resolution spectra from the uv visual echelle spectrograph uves instrument at eso s very large telescope under the assumption of predominantly zonal flow this method allows the simultaneous direct measurement of the zonal velocity across a range of latitudes and local times in the day side the technique based on long slit spectroscopy combined with the high spatial resolution provided by the vlt has provided the first ground based characterization of the latitudinal profile of zonal wind in the atmosphere of venus the first zonal wind field map in the visible as well as new constraints on wind variations with local time we measured mean zonal wind amplitudes between 106 21 and 127 14 m s at latitudes between 18 n and 34 s with the zonal wind being approximately uniform in 2 6 wide latitude bands 0 3 arcsec at disk center the zonal wind profile retrieved is consistent with previous spacecraft measurements based on cloud tracking but with non negligible variability in local time longitude and in latitude near 50 the presence of moderate jets is apparent in both hemispheres with the southern jet being stronger by 10 m s small scale wind variations with local time are also present at low and mid latitudes

former dynamic behaviour of a cold based valley glacier on svalbard revealed by basal ice and structural glaciology investigations large numbers of small valley glaciers on svalbard were thicker and more extensive during the little ice age lia demonstrated by prominent ice cored moraines up to several kilometres beyond present day margins the majority of these glaciers have since experienced a long period of strongly negative mass balance during the 20th century and are now largely frozen to their beds indicating they are likely to have undergone a thermal transition from a polythermal to a cold based regime we present evidence for such a switch by reconstructing the former flow dynamics and thermal regime of tellbreen a small cold based valley glacier in central spitsbergen based on its basal sequence and glaciological structures within the basal sequence the underlying matrix supported diamict is interpreted as saturated subglacial traction till which has frozen at the bed indicating that the thermal switch has resulted in a cessation of subglacial sediment deformation due to freezing of the former deforming layer this is overlain by debris poor dispersed facies ice interpreted to have formed through strain induced metamorphism of englacial ice the sequential development of structures includes arcuate fracture traces interpreted as shear planes formed in a compressive transpressive stress regime and fracture traces interpreted as healed extensional crevasses the formation of these sediment ice facies and structures is indicative of dynamic warm based flow most likely during the lia when the glacier was significantly thicker

planetary scale waves and the cyclic nature of cloud top dynamics on venus abstract pioneer venus ocpp ultraviolet images spanning eight years have been analyzed objectively to derive quantitative information on the properties of planetary scale wave modes at the venus cloud tops we infer propagation characteristics for longitudinal wavenumber 1 by fourier analyzing time series of longitudinal mean normalized image brightness the dominant equatorial mode during 1979 80 was the 4 day periodicity associated with zonal motion of the y feature the difference between this and the 4 7 day equatorial rotation period derived from the tracking of small cloud features implies that the y is a propagating wave with a prograde phase speed of about 15 ms 1 relative to the wind simultaneous time series of cloud tracked wind fluctuations also exhibit a 4 day periodicity lending support to the wave interpretation the prograde propagation and equatorial confinement of the wave and the absence of analogous meridional wind fluctuations identify it as a kelvin wave zonal winds peak near the

late weichselian and holocene relative sea level history of broggerhalvoya spitsbergen abstract radiocarbon dated whalebones from raised beaches record a relative sea level history for broggerhalvoya western spitsbergen that suggest a two step deglaciation on svalbard at the end of the late weichselian glaciation the late weichselian marine limit was reached at about 13 000 yr b p and was followed by relatively slow emergence until about 10 000 yr b p either in response to ice unloading in the barents sea initial retreat of local fjord glaciers or some combination of the two rare whale skeletons dating between 13 000 and 10 000 yr b p indicate that the norwegian sea was at least seasonally ice free during that interval deglaciation of spitsbergen is recorded by the rapid emergence of broggerhalvoya after 10 000 yr b p this was followed by a transgression during the mid holocene here named the talavera transgression and another in modern times raised beach morphologies suggest striking differences in nearshore depositional processes before and after 10 000 yr b p that are probably related to changes in the rate of uplift and in sea ice conditions

venus s southern polar vortex reveals precessing circulation initial images of venus s south pole by the venus express mission have shown the presence of a bright highly variable vortex similar to that at the planet s north pole using high resolution infrared measurements of polar winds from the venus express visible and infrared thermal imaging spectrometer virtis instrument we show the vortex to have a constantly varying internal structure with a center of rotation displaced from the geographic south pole by 3 degrees of latitude and that drifts around the pole with a period of 5 to 10 earth days this is indicative of a nonsymmetric and varying precession of the polar atmospheric circulation with respect to the planetary axis

a chaotic long lived vortex at the southern pole of venus a whirling vortex has been observed in the atmosphere at the south pole of venus cloud motions tracked by the venus express spacecraft suggest that the south polar vortex is long lived erratic and baroclinic in character

glacier hydrology in svalbard norwegian high arctic abstract progress in glacier hydrology has focused on temperate glaciers although partly or wholly non temperate glaciers are found in many parts of the world and significant areas of former ice sheets were probably non temperate it has usually been assumed that drainage from non temperate glaciers consists of relatively dilute and invariable supraglacial runoff in this paper the hydrology of glaciers in the high arctic archipelago of svalbard is examined variations in the thermal regimes of glaciers and their implications for drainage are first addressed results from svalbard concerning meltwater discharge and storage and solute and suspended sediment dynamics are then reviewed in general meltwater penetration of non temperate ice is limited and drainage from non temperate glaciers in svalbard has many of the characteristics of sub aerial drainage however it would be erroneous to view this drainage simply as dilute supraglacial runoff as significant material transport occurs in suspension and solution furthermore twentieth century climate change has probably led to changes in the thermal regimes of some svalbard glaciers such that relict drainage structures are sometimes observed while meltwater yields are augmented by runoff which can be attributed to the loss of mass from glaciers at large spatial scales turbid plumes observed at the marine margins of polythermal ice caps indicate that meltwater can be routed subglacially through non temperate ice

zonal winds in the middle atmosphere of venus from pioneer venus radio occultation data abstract pioneer venus radio occultation data for four seasons between december 1978 and october 1981 are used to construct meridional cross sections of temperature and zonal wind velocity for the middle atmosphere of venus in the altitude range of 40 80 km and in the latitude range of 1 5 85 wind speeds are derived assuming cyclostrophic balance the wind field contains as many as three jets first a prominent one above the clouds situated between 50 and 55 latitude with a maximum speed of 140 m s 1 a second with a speed of 95 m s 1 centered at 70 and at 60 km altitude and a possible third jet at 15 and 65 km altitude with a speed of 100 m s 1 the notable midlatitude jet is associated with the cold polar collar wind speeds above 70 km generally decrease with height because of the warm pole at these levels however within the jet the speed is 100 m s 1 at 83 km the jets may be barotropically unstable and inertial instability may occur above the clouds on the equatorial side of the main

assessing the long term variability of venus winds at cloud level from virtis venus express abstract the venus express vex mission has been in orbit to venus for more than 4 years now the visible and infrared thermal imaging spectrometer virtis instrument onboard vex observes venus in two channels visible and infrared obtaining spectra and multi wavelength images of the planet that can be used to sample the atmosphere at different altitudes day side images in the ultraviolet range 380 nm are used to study the dynamics of the upper cloud at 66 72 km while night side images in the near infrared 1 74 m map the opacity of the lower cloud deck at 44 48 km here we present a long term analysis of the global atmospheric dynamics at these levels using a large selection of orbits from the virtis m dataset covering 860 earth days that extends our previous work sanchez lavega a et al 2008 geophys res lett 35 l13204 and allows studying the variability of the global circulation at the two altitude levels the atmospheric superrotation is evident with equatorial to mid latitudes westward velocities of 100 and 60 m s 1 in the upper and lower cloud layers these zonal velocities are almost constant in latitude from the equator to 50 s from 50 s to 90 s the zonal winds at both cloud layers decrease steadily to zero at the pole individual cloud tracked winds have errors of 3 10 m s 1 with a mean of 5 m s 1 and the standard deviations for a given latitude of our zonal and meridional winds are 9 m s 1 the zonal winds in the upper cloud change with the local time in a way that can be interpreted in terms of a solar tide the zonal winds in the lower cloud are stable at mid latitudes to the tropics and present variability at subpolar latitudes apparently linked to the activity of the south polar vortex while the upper cloud presents a net meridional motion consistent with the upper branch of a hadley cell with peak velocity v 10 m s 1 at 50 s the lower cloud meridional motions are less organized with some cloud features moving with intense northwards and southwards motions up to v 15 m s 1 but on average with almost null global meridional motions at all latitudes we also examine the long term behavior of the winds at these two vertical layers by comparing our extended wind tracked data with results from previous missions

the structural glaciology of kongsvegen svalbard and its role in landform genesis mapping of the structural glaciology of kongsvegen svalbard reveals evidence for four main deformational structures these are stratification longitudinal foliation thrusts and crevasse traces these structures are considered in terms of their contribution to debris entrainment transport and subsequent landform development stratification is associated with small amounts of supraglacial debris that has been folded with flow parallel axes longitudinal foliation in places incorporates basal glacial sediments along folds with flow parallel axes and thrusts transport basal debris to the glacier surface crevasse traces are not significant in terms of debris entrainment the entrainment of basal debris along longitudinal foliation is not a universally recognised process at kongsvegen this process is attributed to the development of a transposition foliation in combination with incorporation of debris rich basal ice or soft basal sediment in the fold complex mapping of the landforms in the proglacial area shows that debris incorporated along longitudinal foliation is released as foliation parallel ridges and that transverse ridges mark debris bearing thrusts the role of longitudinal foliation in landform development has never been documented in this manner although the preservation potential of such ridges may be limited recognition of foliation parallel ridges in the pleistocene landform record has important implications for the interpretation of the dynamics of former ire masses

a model of ablation dominated medial moraines and the generation of debris mantled glacier snouts medial moraines form striking dark stripes that widen non linearly steepen laterally and increase in relief down glacier from the equilibrium line coalescence of these low ablation rate features can feed back strongly on the mass balance of a glacier snout ablation dominated medial moraines originate from debris delivered to glacier margins producing a debris rich septum between tributary streams of ice below their confluence emergence of this ice below the equilibrium line delivers debris to the glacier surface which then moves down local slopes of evolving morainal topography a quantitative description of moraine evolution requires specification of the debris concentration field within the glacier treatment of the melt rate dependence on debris thickness and characterization of processes that transport debris once it emerges onto the ice surface debris concentration at glacier tributary junctions scales with the erosion rates and the lengths of the tributary valley walls and inversely with the tributary ice speeds melt rate is damped exponentially by debris with a 10 cm decay scale debris flux across the glacier surface scales with the product of debris thickness and local slope analytical and numerical results show that medial moraines should develop cross glacier profiles with parabolic crests and linear slopes and should widen with age and hence distance down glacier debris should be both thin and uniform over the moraine observed faster than linear growth of moraine widths with distance reflects the increasing ablation rate down glacier increase in medial moraine cover reduces the local average ablation rate allowing the glacier to extend further down valley than meteorology alone would suggest this feedback is especially effective when moraines merge

terminal zone glacial sediment transfer at a temperate overdeepened glacier system continuity of sediment transfer through glacial systems is essential to maintain subglacial bedrock erosion yet transfer at temperate glaciers with overdeepened beds where subglacial fluvial sediment transport should be greatly limited by adverse slopes remains poorly understood complex multiple transfer processes in temperate overdeepened systems has been indicated by the presence of large frontal moraine systems supraglacial debris of mixed transport origin thick basal ice sequences and englacial thrusts and eskers at svinafellsjokull thrusts comprising decimetre thick debris rich bands of stratified facies ice of basal origin with a coarser size distribution and higher clast content than that observed in basal ice layers contribute substantially to the transfer of subglacial material in the terminal zone entrainment and transfer of material occurs by simple shear along the upper surface of bands and by strain induced deformation of stratified and firnified glacier ice below thrust material includes rounded and well rounded clasts that are also striated indicating that fluvial bedload is deposited as subglacial channels approach the overdeepening and then entrained along thrusts substantial transfer also occurs within basal ice with facies type and debris content dependent on the hydrological connectedness of the adverse slope a process model of transfer at glaciers with terminal overdeepenings is proposed in which the geometry of the overdeepening influences spatial patterns of ice deformation hydrology and basal ice formation we conclude that the significance of thrusting in maintaining sediment transfer continuity has likely been overlooked by glacier sediment budgets and glacial landscape evolution studies

a bulk cloud parameterization in a venus general circulation model a condensing cloud parameterization is included in a super rotating venus general circulation model a parameterization including condensation evaporation and sedimentation of mono modal sulfuric acid cloud particles is described saturation vapor pressure of sulfuric acid vapor is used to determine cloud formation through instantaneous condensation and destruction through evaporation while pressure dependent viscosity of a carbon dioxide atmosphere is used to determine sedimentation rates assuming particles fall at their terminal stokes velocity modifications are described to account for the large range of the reynolds number seen in the venus atmosphere two gcm experiments initialized with 10 ppm equivalent of sulfuric acid are integrated for 30 earth years and the results are discussed with reference to y shaped cloud structures observed on venus the gcm is able to produce an analog of the y shaped cloud structure through dynamical processes alone with contributions from the mean westward wind the equatorial kelvin wave and the mid latitude polar mixed rossby gravity waves the cloud top height in the gcm decreases from equator to pole and latitudinal gradients of cloud top height are comparable to those observed by pioneer venus and venus express and those produced in more complex microphysical models of the sulfur cycle on venus differences between the modeled cloud structures and observations are described and dynamical explanations are suggested for the most prominent differences

an advance of soler glacier north patagonian icefield at c ad 1222 1342 soler glacier is a temperate outlet glacier on the eastern side of the north patagonian icee eld in chile the glacier is currently receding from its little ice age maximum position attained sometime between ad 1600 and 1900 across the snout and foree eld of the glacier is an arcuate belt of well sorted granule gravel and coarse sand containing tree remains these sediments are interpreted as reworked glaciolacustrine material elevated to the glacier surface by thrusting and folding radiocarbon dating of samples of tree remains in these reworked glaciolacustrine sediments demonstrates that the glacier overrode this lake bed sometime between ad 904 and ad 1334 in situ tree remains plastered onto a large boulder in front of the glacier constrain this advance to the period between ad 1222 and ad 1342 this advance precedes by several hundred years the maximum little ice age extent of other north patagonian icee eld outlet glaciers suggesting either an early age for the onset of little ice age conditions or a previously unrecognized period of glacier advance prior to the advance at c ad 1222 to ad 1342 soler glacier was more recessed than at present cone rming the dynamic response of patagonian glaciers to holocene climatic e uctuations

distribution of glaciofluvial sediment within and on the surface of a high arctic valley glacier marthabreen svalbard marthabreen is a 7 8km long valley glacier in sw spitsbergen the glacier is partially covered by a layer of angular debris derived from rockfall in its accumulation area pierced in places by pinnacles and ridges of glaciofluvial sediment these concentrations of glaciofluvial sediment fall into three categories 1 debris pinnacles 2 longitudinal sediment dykes 3 longitudinal ridge accumulations debris pinnacles are slabs of sediment predominantly sands gravels and cobbles elevated to the glacier surface along thrusts longitudinal sediment dykes are low 1m high ridges of sorted sand and gravels which are not associated with penetrative ice structures their occurrence downglacier of sediment dykes and debris pinnacles suggests that they originate as supraglacial or englacial channels or tunnels filled by sediment derived from the dykes or thrusts the presence of large quantities of glaciofluvial sediment on the surface of marthabreen does not imply englacial water flow at high levels within the glacier but is related to ice deformational processes such as thrusting and folding of debris rich stratification copyright 1999 john wiley sons ltd

controls on glacier surging in svalbard the geographical distribution of surge type glaciers worldwide displays a remarkably non random pattern surge type glaciers tend to be concentrated in certain glacierized areas and to be completely absent in others this observation suggests that special conditions are required for surges to occur however the factors controlling the spatial occurrence of surge type behaviour are not known to investigate this problem we performed probability statistical analysis on a sample population of 615 glaciers in svalbard the probability that a glacier in the sample population is surge type is 36 4 within the sampled area there is a spatial variation in the concentration of surge type glaciers several geometric and environmental factors associated with glaciers in the sample population were measured and tested to determine if they are related to the probability of surging of the geometric factors tested length slope elevation orientation and presence or absence of tributaries only glacier length is related to surging with surge probability increasing with increasing length elevated probabilities of surging were also found for glaciers associated with sedimentary subglacial rocks and sub polar thermal regimes the distributions of related factors were used to predict the spatial distribution of surge type glaciers however in each case the individual factors were unable to reproduce the observed pattern of surge type glacier distribution

waves in a venus general circulation model waves in the venus atmosphere are numerically investigated by extending a work of sugimoto et al 2014 fast superrotating zonal flow of 120 m s 1 at the equator is reproduced and maintained by solar heating for more than 10 earth years the meridional distribution of the obtained fast zonal flow is quite consistent with observations at the cloud levels in the cloud layer baroclinic waves develop continuously with a life cycle of 25 earth days at midlatitudes using available potential energy derived from a baroclinically unstable basic state rossby waves observed at the cloud top are generated by the baroclinic waves and induce spatio temporal variation of the superrotation with amplitude larger than 25 m s 1 further kelvin waves with a period of 6 2 days appear in the equatorial region below 50 km momentum and heat transports produced by these waves are discussed

vertical structure of the axi asymmetric temperature disturbance in the venusian polar atmosphere comparison between radio occultation measurements and gcm results vertical temperature profiles at 40 75 km around 80 n in the venus polar vortex are retrieved over 13 earth days almost continuously from radio occultation measurements vera in the venus express mission they show periodical variations with a dominant period of 3 1 earth days these fluctuations are confined in an altitude range of 45 65 km with a local minimum at 58 km altitude where the static stability abruptly increases with height the phase of the temperature fluctuations is almost reversed at the 58 km level and varies little above and below this altitude a numerical simulation of a venusian atmospheric general circulation model gcm shows that the axi asymmetric temperature disturbance with zonal wavenumber 1 is predominant at 50 75 km levels in the model atmosphere the vertical structure of the reproduced disturbance agrees quite well with that retrieved by the radio occultation measurement amplitude of the temperature fluctuation has a local minimum and its phase is reversed at the altitude 65 km in the model where the static stability rapidly changes as in the observations above and below this altitude the phase is almost constant in the vertical direction the relationship among the temperature horizontal winds and geopotential height associated with the simulated disturbance suggests that the axi asymmetric temperature disturbance observed in the venus polar region can be interpreted as neutral barotropic rossby waves related to barotropic instability in the polar region

the formation of a geometrical ridge network by the surge type glacier kongsvegen svalbard traditionally geometrical ridge networks are interpreted as the product of the flow of subglacial sediment into open basal crevasses at the cessation of a glacier surge crevasse fill ridges they are widely regarded as a characteristic landform of glacier surges understanding the range of processes by which these ridge networks form is therefore of importance in the recognition of palaeosurges within the landform record the geometrical ridge network at the surge type glacier kongsvegen in svalbard does not form by crevasse filling the networks consist of transverse and longitudinal ridges that can be seen forming at the current ice margin the transverse ridges form as a result of the incorporation of basal debris along thrust planes within the ice the thrusts were apparently formed during a glacier surge in 1948 longitudinal ridges form through the meltout of elongated pods of debris which on the glacier surface are subparallel to the ice foliation and pre date the surge this work adds to the range of landforms associated with glacier surges

debris entrainment and transfer in polythermal valley glaciers hambrey mj bennett mr dowdeswell ja et al 1999 debris entrainment and transfer in polythermal valley glaciers journal of glaciology 45 149 69 86 published 1999

the thermal regime of sub polar glaciers mapped by multi frequency radio echo sounding radio echo soundings provide an effective tool for mapping the thermal regimes of polythermal glaciers on a regional scale radar signals of 320 370 mhz penetrate ice at sub freezing temperatures but are reflected from the top of layers of ice which are at the melting point and contain water radar signals of 5 20 mhz on the other hand see through both the cold and the temperate ice down to the glacier bed radio echo soundings at these frequencies have been used to investigate the thermal regimes of four polythermal glaciers in svalbard kongsvegen uversbreen midre lovenbreen and austre broggerbreen in the ablation area of kongsvegen a cold surface layer 50 160m thick was underlain by a warm basal layer which is advected from the temperate accumulation area the surface ablation of this cold layer may be compensated by freezing at its lower cold temperate interface this requires that the free water content in the ice at the freezing interface is about 1 of the volume the cold surface layer is thicker beneath medial moraines and where cold based hanging glaciers enter the main ice stream on uversbreen the thermal regime was similar to that of kongsvegen a temperate hole was found in the otherwise cold surface layer of the ablation area in a surface depression between kongsvegen and uversbreen where meltwater accumulates during the summer near the subglacial lake setevatnet 250 m a s l lovenbreen was frozen to the bed at the snout and along all the mountain slopes but beneath the central part of the glacier a warm basal layer up to 50m thick was fed by temperate ice from two cirques on austre broggerbreen a temperate basal layer was not detected by radio echo soundings but the basal ice was observed to be at the melting point in two boreholes

glaciofluvial crevasse and conduit fills as indicators of supraglacial dewatering during a surge skeiðararjokull iceland

controls on englacial sediment deposition during the november 1996 jokulhlaup skeiđararjokull iceland this paper presents sedimentary evidence for rapid englacial debris entrainment during jokulhlaups previous studies of jokulhlaup sedimentology have focused predominantly on proglacial impact rather than depositional processes within glaciers however observations of supraglacial floodwater outbursts suggest that englacial sediment emplacement is possible during jokulhlaups the november 1996 jokulhlaup from skei ararjokull iceland presented one of the first opportunities to examine englacial flood deposits in relation to former supraglacial outlets using observations from skei ararjokull this paper identifies and explains controls on the deposition of englacial flood sediments and presents a qualitative model for englacial jokulhlaup deposition englacial jokulhlaup deposits were contained within complex networks of upglacier dipping fractures simultaneous englacial deposition of fines and boulder sized sediment demonstrates that englacial fracture discharge had a high transport capacity fracture geometry was an important control on the architecture of englacial jokulhlaup deposits the occurrence of pervasively frozen flood deposits within skei ararjokull is attributed to freeze on by glaciohydraulic supercooling floodwater flowing subglacially or through upglacier dipping fractures would have supercooled as it was raised to the surface faster than its pressure melting point could increase as glaciostatic pressure decreased evidence for floodwater contact with the glacier bed is supported by the ubiquitous occurrence of sheared diamict rip ups and intra clasts of basal ice within jokulhlaup fractures deposited englacially some 200 350 m above the bed of skei ararjokull evidence for fluidal supercooled sediment accretion is apparent within stratified sands deposited englacially at exceptionally high angles of rest in the absence of post depositional disturbance such primary sediment structures cannot be explained unless sediment is progressively accreted to opposing fracture walls ice retreat from areas of former supraglacial outbursts revealed distinct ridges characterized by localized upwellings of sediment rich floodwater these deposits are an important addition to current models of englacial sedimentation and demonstrate the potential for post jokulhlaup landform development copyright 2001 john wiley sons ltd keywords jokulhlaup englacial debris entrainment glaciofluvial sediment hydrofracturing iceland

cloud level winds from the venus express monitoring camera imaging abstract six years of continuous monitoring of venus by european space agency s venus express orbiter provides an opportunity to study dynamics of the atmosphere our neighbor planet venus monitoring camera vmc on board the orbiter has acquired the longest and the most complete so far set of ultra violet images of venus these images enable a study the cloud level circulation by tracking motion of the cloud features the highly elliptical polar orbit of venus express provides optimal conditions for observations of the southern hemisphere at varying spatial resolution out of the 2300 orbits of venus express over which the images used in the study cover about 10 venus years out of these we tracked cloud features in images obtained in 127 orbits by a manual cloud tracking technique and by a digital correlation method in 576 orbits total number of wind vectors derived in this work is 45 600 for the manual tracking and 391 600 for the digital method this allowed us to determine the mean circulation its long term and diurnal trends orbit to orbit variations and periodicities we also present the first results of tracking features in the vmc near ir images in low latitudes the mean zonal wind at cloud tops 67 2 km following rossow w b del genio a t eichler t 1990 j atmos sci 47 2053 2084 is about 90 m s with a maximum of about 100 m s at 40 50 s poleward of 50 s the average zonal wind speed decreases with latitude the corresponding atmospheric rotation period at cloud tops has a maximum of about 5 days at equator decreases to approximately 3 days in middle latitudes and stays almost constant poleward from 50 s the mean poleward meridional wind slowly increases from zero value at the equator to about 10 m s at 50 s and then decreases to zero at the pole the error of an individual measurement is 7 5 30 m s wind speeds of 70 80 m s were derived from near ir images at low latitudes the vmc observations indicate a long term trend for the zonal wind speed at low latitudes to increase from 85 m s in the beginning of the mission to 110 m s by the middle of 2012 vmc uv observations also showed significant short term variations of the mean flow the velocity difference between consecutive orbits in the region of mid latitude jet could reach 30 m s that likely indicates vacillation of the mean flow between jet like regime and quasi solid body rotation at mid latitudes fourier analysis revealed periodicities in the zonal circulation at low latitudes within the equatorial region up to 35 s the zonal wind show an oscillation with a period of 4 1 5 days 4 83 days on average that is close to the super rotation period at the equator the wave amplitude is 4 17 m s and decreases with latitude a feature of the kelvin wave the vmc observations showed a clear diurnal signature a minimum in the zonal speed was found close to the noon 11 14 h and maxima in the morning 8 9 h and in the evening 16 17 h the meridional component peaks in the early afternoon 13 15 h at around 50 s latitude the minimum of the meridional component is located at low latitudes in the morning 8 11 h the horizontal divergence of the mean cloud motions associated with the diurnal pattern suggests upwelling motions in the morning at low latitudes and downwelling flow in the afternoon in the cold collar region

debris characteristics and ice shelf dynamics in the ablation region of the mcmurdo ice shelf antarctica this paper presents observations and measurements of debris characteristics and ice shelf dynamics in the ablation region of the mcmurdo ice shelf in the ross sea sector of antarctica ice shelf surface processes and dynamics are inferred from a combination of sedimentological descriptions ground penetrating radar investigations and through ablation velocity and ice thickness measurements field data show that in the study area the ice shelf moves relatively slowly 1 5 18 3 m a 1 has high ablation rates 43 441 mm during 2003 04 summer and is thin 6 22 m the majority of debris on the ice shelf was originally transported into the area by a large and dynamic ice sheet ice shelf system at the last glacial maximum this debris is concentrated on the ice shelf surface and is continually redistributed by surface ablation creating an ice cored landscape of large debris rich mounds ice shelf flow forming medial moraines and meltwater streams locally reworking material and redistributing it across the ice shelf surface a conceptual model for supraglacial debris transport by contemporary antarctic ice shelves is presented which emphasizes these links between debris supply surface ablation and ice shelf motion low velocity ice shelves such as the mcmurdo ice shelf can maintain and sequester a debris load for thousands of years providing a mechanism by which ice shelves can accumulate sufficient debris to contribute to sediment deposition in the oceans

englacial and proglacial glaciotectonic processes at the snout of a thermally complex glacier in svalbard many glaciers in svalbard which tend to be thermally complex with both warm and cold ice produced complex push moraines or thrust moraine complexes at the time of their maximum neoglacial advance and during their subsequent recession uv rsbreen which nearly reaches the coast of northwest spitsbergen has a push moraine 50 m high comprising gravel and sand of fluvial origin and diamicton derived from basal ice as well as thrust masses of dead ice the push moraine is almost entirely a product of the tectonic processes especially thrusting that occurred in the snout of the glacier and in the frozen sediments immediately in journal of quaternary science front thrusting is probably initiated where the glacier switches from a sliding mode to a state of being frozen to the bed thrusting in the foreland is an extension of the same processes that occur within the ice itself and a sole thrust probably extends from the frozen sediment that underlies the base of the glacier near its snout thrusting results in subglacial sediment being uplifted to a high level within the glacier or even to the surface subsidiary near horizontal thrusts parallel to the bedding plane link thrusts dipping up glacier and result in local thickening of individual subglacial sedimentary units gravels incorporated in this way retain their integrity but sands are folded whereas uplifted debris rich basal ice is intensely folded the distinctive tectonic style of low dip bedding in gravels truncated by high angle 30 40 thrusts and only localised folding in less competent material differs from most descriptions of such ridges but may be typical of many push moraines composed principally of fluvial material

a revised approach to discriminating sediment transport histories in glacigenic sediments in a temperate alpine environment a case study from fox glacier new zealand clast shape measurements have developed into a standard method for reconstructing the transport histories of sediments in glacial environments the majority of studies use the ra c40 covariance approach with some researchers routinely including clasts of varying lithologies within their samples the corollary is that variable lithological properties may control clast form and roundness rather than debris transport mechanisms despite this the role of lithology on clast shape in glacial environments has rarely been analysed furthermore some studies have reported difficulties in using the ra c40 co variance plot in discriminating clasts that have undergone subglacial transport and clasts that have been modified by fluvial activity results from a glacierized valley in a temperate alpine setting indicate that detailed analysis of clast shape where samples are of uniform lithology although time consuming is a useful tool in the investigation of deposits in glaciated environments copyright 2012 john wiley sons ltd

stable isotope δd δ18o relationships of ice facies and glaciological structures within the mid latitude maritime fox glacier new zealand relationships between stable isotopes d o ice facies and glacier structures have hitherto gone untested in the mid latitude maritime glaciers of the southern hemisphere here we present d o values as part of a broader study of the structural glaciology of fox glacier new zealand we analyzed 94 samples of d o from a range of ice facies to investigate whether isotopes have potential for structural glaciological studies of a rapidly deforming glacier the d o measurements were aided by structural mapping and imagery from terminus time lapse cameras the current retreat phase was preceded by an advance of 1 km between 1984 and 2009 with the isotopic sampling and analysis undertaken at the end of that advance 2010 11 stable isotopes from debris bearing shear planes near the terminus interpreted as thrust faults are isotopically enriched compared with the surrounding ice when plotted on co isotopic diagrams d o ice sampled from the shear planes appears to show a subtle but distinctive isotopic signal compared with the surrounding clean ice on the lower glacier hence stable isotopes d o have potential within the structural glaciology field but larger sample numbers than reported here may be required to establish isotopic contrasts between a broad range of ice facies and glacier structures

structure of the venus neutral atmosphere as observed by the radio science experiment vera on venus express 1 the european space agency venus express radio science experiment vera obtained 118 radio occultation measurements of the venusian atmosphere between july 2006 and june 2007 southern latitudes are uniformly sampled measurements in the northern hemisphere are concentrated near the pole radial profiles of neutral number density derived from the occultations cover the altitude range 40 90 km which are converted to profiles of temperature t and pressure p versus height h profiles of static stability are found to be latitude dependent and nearly adiabatic in the middle cloud region below the clouds the stability decreases at high latitudes at an altitude of 65 km the vera t p h profiles generally lie between the venus international reference atmosphere vira and vira 2 models the retrieved temperatures at any given pressure level typically are within 5 k of those derived from the pioneer venus orbiter radio occultation experiments a large equator to pole temperature contrast of 30 k is found at the 1 bar 1000 hpa level the vera observations reveal a distinct cold collar region in the southern hemisphere complementing that in the north at the latitudes of the cold collars the tropopause altitude increases relative to higher and lower latitudes by 7 km while the temperature drops roughly 60 k the observations indicate the existence of a wave number 2 structure poleward of 75 latitude at altitudes of 62 km

structural composition and sediment transfer in a composite cirque glacier glacier de st sorlin france robserson s 2008 structural composition and sediment transfer in a composite cirque glacier glacier de st sorlin france earth surface processes and landforms 33 13 1931 1947

eurasian mammal biochronology an overview abstract late cenozoic eurasian mammal biochronology has achieved a new and higher level of resolution this has been accomplished by correlation of eurasian mammal biochronology with an independent time frame the geomagnetic polarity time scale gpts the result is a tentative calibration for mn zones and their boundaries for the late miocene pliocene and pleistocene spanning mn zones 8 through 17 vallesian through villanyian villafranchian an interval of about 10 my 2 to 12 ma more or less an overview of papers presented in this special issue is organized under the following headings paleomagnetism and biochronology in spain chronologic resolution of eurasian mammal chronology and late cenozoic mammal chronology in asia excluding the siwaliks sequence of southern asia the chronologic framework presented in this issue should serve as a reliable temporal setting for late cenozoic mammal evolution in europe and asia it is not the last word in eurasian late cenozoic mammal biochronology but must be tested and revised as our knowledge advances

genesis of hummocky moraines by thrusting in glacier ice evidence from svalbard and britain irregular mounds of glacial debris commonly referred to as 9hummocky moraine9 until recently were linked to ice stagnation during rapid climatic amelioration however recent work in scotland has demonstrated that some hummocky moraine dating from the younger dryas event c 10 000 years bp was the product of deposition at active ice margins observations at modern high arctic glacier margins in svalbard 76 80 n indicate that some moraines of this type form under a dynamic glaciological regime mainly by thrusting in active polythermal ice undergoing strong longitudinal compression this situation is particularly common where there is a transition from warm based ice in the interior of a glacier to cold based ice at the margins or snout from their morphological similarity rectilinear slopes facing up glacier and irregular downglacier faces and apparent stacking of slabs of sediment of subglacial derivation it is concluded that some assemblages of british moraines are also the product of thrusting this process appears to be most dominant in polythermal glaciers rather than in temperate glaciers on this basis it is tentatively suggested that the younger dryas in britain was characterized by a climatic regime similar to that in svalbard today mean annual temperature 5 c 400 1000 mm precipitation and that the associated glaciers may have been of polythermal character

discriminating glacier thermal and dynamic regimes in the sedimentary record abstract this paper provides a description and evaluation of the sedimentary facies and environments associated with a range of glacier thermal and dynamic regimes with additional consideration given to the tectonic context new and previously published data are evaluated together and are presented from modern terrestrial and marine glacial sedimentary environments in order to identify a set of criteria that can be used to discriminate between different glacier thermal regimes and dynamic styles in the sedimentary record sedimentological data are presented from a total of 28 glaciers in 11 geographical areas that represent a wide range of contemporary thermal dynamic and topographic regimes in the context of landsystems representatives from terrestrial environments include temperate glaciers in the european alps patagonia new zealand the cordillera blanca peru cold glaciers in the dry valleys of antarctica and the antarctic peninsula region and polythermal valley glaciers in svalbard northern sweden the yukon and the khumbu himal nepal the glaciomarine environment is illustrated by data from cold and polythermal glacier margins on the east antarctic continental shelf and from a polythermal tidewater glacier in svalbard along with general observations from temperate glaciers in alaska these data show that temperate glacial systems particularly in high relief areas are dominated by rockfall and avalanche processes although sediments are largely reworked by glaciofluvial processes debris in polythermal glaciers is both thermally and topographically influenced in areas of moderate relief debris is mainly of basal glacial origin and the resulting facies association is dominated by diamicton in high relief areas such as the himalaya the debris load in polythermal glaciers is dominated by rockfall and avalanche inputs resulting in extensive accumulations of sandy boulder gravel cold glaciers are dominated by basal debris entrainment but sediments are little modified from the source materials which are typically sandy boulder gravel from older till and sand from glaciofluvial glaciolacustrine and aeolian sources similar facies associations but with different facies geometry and thickness occur in equivalent glaciomarine settings application of these concepts can aid the interpretation of glacier thermal regime and hence palaeoclimate in quaternary and ancient glacial systems

sedimentary facies and landform genesis at a temperate outlet glacier soler glacier north patagonian icefield glasser n f hambrey m j 2002 sedimentary facies and landform genesis at a temperate outlet glacier soler glacier north patagonian icefield 49 1 43 64

reconstructing the transport history of glacigenic sediments a new approach based on the co variance of clast form indices abstract two indices are used to describe the aggregate shape and roundness characteristics of glacially transported clasts the c40 index the percentage of clasts with c a ratios 0 4 and the ra index the percentage of very angular and angular clasts in a sample analysis of the between and within sample co variance of these indices provides a powerful tool for discriminating actively and passively transported clasts in glacigenic deposits use of these indices is illustrated in an analysis of the form characteristics of clasts from lateral and frontal moraines at storbreen jotunheimen these fall between those of actively transported clasts in basal till low c40 and ra values and those of unmodified frost weathered clasts high c40 and ra values both indices decline down moraine within sample analyses of clast shape demonstrates that these aggregate clast form gradients reflect changes in the relative proportions of actively and passively transported debris on the moraines rather than progressive modification of actively transported clasts these analyses also indicate that actively transported clasts form the dominant component of the moraines particularly near the former glacier terminus further applications of the approach developed here are suggested

sedimentation and stratigraphy at eyjabakkajokull an icelandic surging glacier a model for sedimentation by surging glaciers is developed from analysis of the debris load sedimentary processes and proglacial stratigraphy observed at the icelandic surging glacier eyjabakkajokull three aspects of the behavior of surging glaciers explain the distinctive landformsediment associations which they may produce a sudden loading of proglacial sediments during rapid glacier advances results in the buildup of excess pore pressures failure and glacitectonic deformation of the overridden sediments b reactivation of stagnant marginal ice by the downglacier propagation of surges is associated with large longitudinal compressive stresses these induce intense folding and thrusting during which basal debris rich ice is elevated into an englacial position in a narrow marginal zone as the terminal area of the glacier stagnates between surges debris from this ice is released supraglacially and deposited by meltout and sediment flows c local variations in overburden pressure beneath stagnant crevassed ice cause subglacial lodgement tills which are sheared during surges to flow into open crevasses and form crevasse fill ridges

potential vorticity of the south polar vortex of venus venus atmosphere shows highly variable warm vortices over both of the planet s poles the nature of the mechanism behind their formation and properties is still unknown potential vorticity is a conserved quantity when advective processes dominate over friction and diabatic heating and is a quantity frequently used to model balanced flows as a step toward understanding the vortices dynamics we present maps of ertel s potential vorticity epv at venus south polar region we analyze three configurations of the south polar vortex at the upper cloud level p 240 mbar z 58 km based on our previous analyses of cloud motions and thermal structure from data acquired by the visual and infrared thermal imaging spectrometer instrument on board venus express additionally we tentatively estimate epv at the lower cloud level p 2200 mbar z 43 km based on our previous wind measurements and on static stability data from pioneer venus and the venus international reference atmosphere vira model values of epv are on the order of 10 6 and 10 8 k m2 kg 1 s 1 at the upper and lower cloud levels respectively being 3 times larger than the estimated errors the morphology observed in epv maps is mainly determined by the structures of the vertical component of the relative vorticity this is in contrast to the vortex s morphology observed in 3 8 or 5 m images which are related to the thermal structure of the atmosphere at the cloud top some of the epv maps point to a weak ringed structure in the upper cloud while a more homogenous epv field is found in the lower cloud

the structural geology of a surge type glacier abstract the range of deformation structures found in surge type variegated glacier alaska is similar to that found in many thin skinned thrust belts and includes foliations folds dip slip and strike slip faults thrust faults and fractures the development of structural relationships and the overall structural assemblage can be related to the deformation histories of quiescent and surge phases of motion the surge phase dominates the formation of brittle structures because of the large stresses and strain rates associated with it the relationship between downglacier verging overturned folds with hinge lines transverse to flow and a family of transverse arcuate thrust faults is characteristic of structural development in the lower part of the glacier during the surge longitudinal foliation develops mainly from sedimentary stratification in the upper part of the glacier in a marginal transpressive deformation regime during quiescent phase flow from broad accumulation basins the structural relationships in this surge type glacier may aid in the interpretation of structures in other gravity driven tectonic settings