hydraulic modelling of subglacial tunnel channels south east alberta canada one of the key issues associated with the hypothesis of catastrophic subglacial drainage of the livingstone lake event is whether flows of such large magnitudes are physically feasible to explore this issue a one dimensional hydraulic network flow model was developed to investigate the range of peak discharges and associated flow parameters that may have been carried by a tunnel channel network in south east alberta canada this tunnel channel network has been interpreted elsewhere to carry large discharges associated with subglacial meltwater flows because of the convex longitudinal profiles of individual channels this computational modelling effort draws upon established and verified engineering principles and methods in its application to the hydraulics of this problem consequently it represents a unique and independent approach to investigating the subglacial meltwater hypothesis based on the modelling results it was determined that energy losses resulting from friction limit the maximum peak discharge that can be transported through the tunnel channel network to 10 7 m 3 s 1 which is in reasonable agreement with previous estimates of flood discharges for proposed megafloods results show that flow through channels with convex longitudinal profiles occurs when hydraulic head exceeds 910 m lost river and 950 m sage creek respectively these are considerably below the maximum head capable of driving flow through the system of 1360 m beyond which ice is decoupled from the bed across the pre glacial drainage divide therefore it is concluded that these model results support the hypothesis of catastrophic subglacial drainage during the livingstone lake event

the instability theory of drumlin formation and its explanation of their varied composition and internal structure despite their importance in understanding glaciological processes and constraining large scale flow patterns in palaeo glaciology there is little consensus as to how drumlins are formed attempts to solve the drumlin problem often fail to address how they are created from an initially flat surface in the absence of obvious cores or obstacles this is a key strength of the instability theory which has been described in a suite of physically based mathematical models and proposes that the coupled flow of ice and till causes spontaneous formation of relief in the till surface encouragingly model predictions of bedform height and length are consistent with observations and furthermore the theory has been applied to a range of subglacial bedforms and not just drumlins however it has yet to confront the myriad observations relating to the composition and internal structure of drumlins and this could be seen as a major deficiency this paper is a first attempt to assess whether the instability theory is compatible with the incredible diversity of sediments and structures found within drumlins we summarise the underlying principles of the theory and then describe and attempt to explain the main types of drumlin composition e g bedrock till glaciofluvial sediments and combinations thereof contrary to a view which suggests that the presence of some sedimentary sequences e g horizontally stratified cores is inconsistent with the theory we suggest that one would actually expect a diverse range of constituents depending on the inheritance of sediments that pre date drumlin formation the duration and variability of ice flow and the balance between erosion and deposition till continuity at the ice bed interface we conclude that the instability theory is compatible with and potentially strengthened by what is known about drumlin composition and as such offers the most complete and promising solution to the drumlin problem to date

subglacial meltwater origin and subaerial meltwater modifications of drumlins near morley alberta canada abstract drumlins in the bow valley west of calgary alberta are interpreted as the product of subglacial and subaerial meltwater erosion on the sides of the bow valley highly elongated streamlined first generation drumlins are aligned in an en echelon fashion and are not significantly modified by post glacial processes in the valley bottom scalloped stubby irregularly spaced second generation drumlins are found in close association with valley fill the drumlins are composed of bedrock and diamicton and some are overlain by a thin gravel veneer stratified gravel is found on the leeward flanks of some second generation drumlins meltwater erosional forms s forms found on the limestone bedrock up flow of the drumlins and crescentic furrows around their proximal ends indicate that subglacial meltwater beneath the bow valley ice was probably the main erosive agent responsible for the shaping of the drumlins the second generation drumlins are believed to be the remnants of the first generation drumlins that were dissected and reworked by postglacial subaerial meltwater flow s meltwater drainage from ice dammed glacial lake kananaskis and possibly other glacially dammed tributary valley lakes resulted in the deposition of megaripples 3 5 m high 40 m wavelength 8 km down flow from the drumlins and reverse eddy deposits on the flanks of the drumlins post glacial bow river incision and terrace development has continued to further sculpt these forms

lithology sedimentology and genesis of the wadena drumlin field minnesota u s a abstract studies on both the regional and small scales of the lithology sedimentology and stratigraphy of the wadena drumlin field in central minnesota u s a provide insights to the processes that operated within the wadena lobe during the drumlin forming phase horizontal changes in the down glacier direction in the nature of the drumlin till include an increase in the carbonate content decrease in grain size and magnetite content and variations in fine fraction mineralogy these changes also occur with depth at individual sites it is inferred that these patterns reflect progressive incorporation and mixing of the substrate which for much of the drumlin field is a till of northwestern origin with the till already in transit within the base of the wadena lobe derived from the northeast factors contributing to enhanced erosion within the wadena drumlin field include increased vertical strain rates over a major subglacial highland the presence of deformable bed material and a lowered ice profile which permitted elevated rates of bed deformation the patterns of mixing are generally consistent with substrate incorporation either by regelation or in the context of a deforming bed although neither of these processes adequately explain all of the observed features of the drumlin till where localized departures from the generalized pattern exist it can be shown that these are the result of either syn or post depositional processes primarily winnowing or the influence of a different substrate additional data are presented including macrofabric measurements and detailed site descriptions that are consistent with an accretionary progressive build up of the drumlin forms

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

the sedimentology of a late pleistocene drumlin near kingscourt ireland abstract an exposure in a late pleistocene drumlin near kingscourt ireland provides a good insight into some of the processes that give rise to such subglacial bedforms the drumlin is located on a ridge cored by red sandstone of carboniferous namurian age which rises to 150 m above m s l the drumlin itself is about 380 m long by 170 m wide and is 20 m in height it is orientated vvnw ese ice flow direction in the area as inferred from general drumlin orientation striae and erratic dispersal was nw se the drumlin is composed of diamicton with four constituent facies containing large scale up to 20 m long and 1 5 m high slabs of the sandstone bedrock which have been displaced tens of metres by ice dragging the thin diamicton matrix is sand rich with few clasts greater than pebble size it contains green sandstone erratics from west and northwest of the study site along with clasts of weathered namurian sandstone which have been sheared from local bedrock the diamicton attains a maximum thickness of 5 4 m the slabs are confined to the basal 2 5 m of the diamicton thus the drumlin is essentially rock cored parts of the matrix are interpreted as injection sediments that have been squeezed into fractures and voids in the bedrock and between rock slabs under high porewater pressures when the ice began to displace fractured substrate deformation structures at a variety of scales are seen in the matrix deformation erosion and deposition were all important in the formation of the drumlin much of the upper part of the diamicton has been sheared subsequent to initial deposition by ice action the sheared units are uppermost in the stratigraphic sequence the shearing is the last glacial process apparent in the drumlin sediment and may have been contemporaneous with drumlinisation both the squeezing process which deposited the injections within the matrix and the deflection in flow of ice were influenced by the obstructing bedrock ridge which in this case is also responsible for the anomalous orientation of the feature

synchronized observations of cloud to ground lightning using vhf broadband interferometer and acoustic arrays 1 a single station based lightning discharge channel reconstruction system by combining a two dimensional 2d vhf broadband interferometer and a three dimensional 3d acoustic lighting mapping system has been developed and used for lightning observations two cloud to ground cg flashes with highly branched leaders recorded by the system are analyzed and presented in this paper vhf radiation could well delineate the development of simultaneous leader branches while acoustic emissions mainly located on the main channel which was traversed by return stroke rs process localizations by vhf and acoustic emissions agree well with each other the mapping results confirm that audible acoustic emission of lightning discharge is mainly associated with high current process like rs leaders could generate detectable acoustic signals with amplitude at least an order weaker than ensuing rs but they are hard to identify except in closer ranges than the main channel as a significant phenomenon this paper provides the first 3d locations associated with sources of tearing sounds which are inferred to be generated by downward negative leaders when they approach ground the synchronized observation enable vhf interferometer locate lightning development in spatially quasi 3d and three stepped leaders five dart leaders and two dart stepped leaders are identified with the 3d velocity 1 3 3 9 105 m s 1 0 2 9 107 m s and from 1 0 1 3 107 m s to 2 4 2 6 106 m s respectively in addition the application of this approach in improving the accuracy of thunder ranging is discussed

search for active lava flows with virtis on venus express there are several lines of evidence suggesting that effusive volcanism still shapes the surface of venus but the rate is not well constrained the preservation of impact craters is consistent with a rate of 1 km year comparable to earth intraplate volcanism as well as a rate several orders of magnitude less it has been proposed to search images of the venus nightside near 1 m for the excess thermal emission of active lava flows the scattering of photons in the optically thick cloud cover is similar in effect to a gaussian blur with a full width half maximum fwhm of 90 km this reduces the maximum intensity of the anomalies introduced by eruptions making detection more difficult than in a clear atmosphere but also provides larger targets for imaging the virtis instrument on venus express observed surface thermal emission at 1 02 m wavelength between april 2006 and october 2008 at a spatial resolution of typically a few tens of km we have searched the 1000 images for the signatures of active lava flows in form of transient excess emission measured in several adjacent pixels we estimate that eruptions with 1gw m sr total excess specific thermal emission would be clearly visible compared to the instrumental and atmospheric noise but no such anomalies were detected it has been shown that the total thermal emission of eruptions on earth can be related to the lava discharge rate we adjust this model to the venus surface environment by adjusting observed lava surface temperature distributions and estimate that a discharge rate on the order of 1000 m s is required to produce an anomaly clearly identifiable in virtis data this is a relatively high value for effusive volcanism but a few historical eruptions on earth surpassed it adopting a fit to the discharge rates of historical eruptions on hawaii as a model 4 to 10 of the eruptions in the field of view of virtis images would have been detectable in addition to the low detection probability the low surface coverage of on average 1 of the surface per day over a period of 800 days indicates that the probability of an eruption imaged by virtis was low to begin with therefore the virtis data set fails to provide a useful constraint on the rate of volcanism on venus venus express continues to observe surface thermal emission with the venus monitoring camera for future missions near infrared imaging would profit from more frequent images of the same area than is possible from the excentric 24h orbit of venus express the superrotation of the cloud cover allows to reduce atmospheric noise by averaging of images taken hours apart and the detection of eruptions with 100 m s lava or less might then be possible nevertheless searching for lava flows emplaced between two observations of the same surface by high resolution radar imaging altimetry or interferometry generally provides a better constraints than infrared imaging for the same observation duration and surface coverage however high resolution radar and low resolution infrared observations are highly complementary and could be accommodated on the same mission preferably with a low circular polar orbit

influence of venus topography on the zonal wind and uv albedo at cloud top level the role of stationary gravity waves based on the analysis of uv images at 365 nm of venus cloud top altitude 67 2 km collected with vmc venus monitoring camera on board venus express vex it is found that the zonal wind speed south of the equator from 5 s to 15 s shows a conspicuous variation from 101 to 83 m s with geographic longitude of venus correlated with the underlying relief of aphrodite terra we interpret this pattern as the result of stationary gravity waves produced at ground level by the up lift of air when the horizontal wind encounters a mountain slope these waves can propagate up to the cloud top level break there and transfer their momentum to the zonal flow such upward propagation of gravity waves and influence on the wind speed vertical profile was shown to play an important role in the middle atmosphere of the earth by lindzen 1981 but is not reproduced in the current gcm of venus atmosphere from lmd in the equatorial regions the uv albedo at 365 nm varies also with longitude we argue that this variation may be simply explained by the divergence of the horizontal wind field in the longitude region from 60 to 10 where the horizontal wind speed is increasing in magnitude stretch it triggers air upwelling which brings the uv absorber at cloud top level and decreases the albedo and vice versa when the wind is decreasing in magnitude compression this picture is fully consistent with the classical view of venus meridional circulation with upwelling at equator revealed by horizontal air motions away from equator the longitude effect is only an additional but important modulation of this effect this interpretation is comforted by a recent map of cloud top h2o fedorova et al 2015 showing that near the equator the lower uv albedo longitude region is correlated with increased h2o we argue that h2o enhancement is the sign of upwelling suggesting that the uv absorber is also brought to cloud top by upwelling

variations of sulphur dioxide at the cloud top of venus s dynamic atmosphere a pulse of sulphur dioxide in venus s upper atmosphere was observed by the pioneer venus spacecraft in the 1970s and 1980s and attributed to volcanism recent sulphur dioxide measurements from venus express indicate decadal scale fluctuations in sulphur dioxide above venus s cloud tops in an atmosphere that is more dynamic than expected

palaeoglaciology of the last irish ice sheet reconstructed from striae evidence abstract a database comprising some 5200 individual striation measurements on bedrock surfaces across the island of ireland was used to produce maps of flowsets corresponding to individual ice flow events during the last late devensian glacial cycle these flowsets were identified on the basis of regional scale correspondence between striae orientations which when linked together spatially are able to identify consistent ice flow vectors four main chronological stages are identified on the basis of this evidence i incursion of scottish ice into ireland ii glacial maximum conditions iii ice retreat and dissolution and iv development of localised ice domes striae based reconstructions of the glaciology of the last irish ice sheet are qualitatively different from those based on bedform mainly drumlin and ribbed moraine evidence significant differences are apparent in upland areas which have fewer preserved bedforms and a higher concentration of striae combining bedform and striae datasets will enable a better understanding of the temporal evolution of the ice sheet it is likely that both datasets record a snapshot of ice flow direction and subglacial conditions and environments immediately prior to preservation of this directional evidence

on the reconstruction of pleistocene ice sheets a review abstract pleistocene ice sheets can be reconstructed through three separate approaches 1 evidence based on glacial geological studies such as erratic trains till composition crossing striations and exposures of multiple tills nonglacial sediments 2 reconstructions based on glaciological theory and observations these can be either two or three dimensional models they can be constrained by known ice margins at specific times or they can be open ended with the history of growth and retreat controlled by parameters resting entirely within the model 3 glacial isostatic rebound after deglaciation provides a measure of the distribution of mass ice across a region a best fit ice sheet model can be developed that closely approximates a series of relative sea level curves within an area of a former ice sheet in addition the model should also provide a reasonable sea level fit to relative sea level curves at sites well removed from glaciation this paper reviews some of the results of a variety of ice sheet reconstructions and concentrates on the various attempts to reconstruct the ice sheets of the last wisconsin weischelian wurm devensian glaciation evidence from glacial geology suggests flow patterns at variance with simple single domed ice sheets over north america and europe in addition reconstruction of ice sheets from glacial isostatic sea level data suggests that the ice sheets were significantly thinner than estimates based on 18 ka equilibrium ice sheets cf denton and hughes 1981 the review indicates it is important to differentiate between ice divides which control the directions of glacial flow and areas of maximum ice thickness which control the glacial isostatic rebound of the crust upon deglaciation recent studies from the laurentide ice sheet region indicate that the center of mass was not over hudson bay that a major ice divide lay east of hudson bay so that flow across the hudson bay and james bay lowlands was from the northeast that hudson bay was probably open to marine invasions two or three times during the wisconsin glaciation and that the laurentide ice sheet was thinner than an equilibrium reconstruction would suggest

a gps based three dimensional lightning mapping system initial observations in central new mexico a gps based system has been developed that accurately locates the sources of vhf radiation from lightning discharges in three spatial dimensions and time the observations are found to reflect the basic charge structure of electrified storms observations have also been obtained of a distinct type of energetic discharge referred to as positive bipolar breakdown recently identified as the source of trans ionospheric pulse pairs tipps observed by satellites from space the bipolar breakdown has been confirmed to occur between the main negative and upper positive charge regions of a storm and found to be the initial event of otherwise normal intracloud discharges the latter is contrary to previous findings that the breakdown appeared to be temporally isolated from other lightning in a storm peak vhf radiation from the energetic discharges is observed to be typically 30 db stronger than that from other lightning processes and to correspond to source power in excess of 100 kw over a 6 mhz bandwidth centered at 63 mhz

sediment deformation beneath glaciers rheology and geological consequences experiments beneath breidamerkurjokull in iceland have led to development of flow laws for the subglacial till relating strain rate to shear stress and effective pressure and assuming either bingham fluid or nonlinearly viscous fluid behavior water pressures in the till are less than ice pressures and it is suggested that this may lead to infiltration of ice into the sediment which inhibits sliding at the ice sediment interface where water pressures are equal or near to ice pressures infiltration does not occur and sliding may result a one dimensional theory of subglacial deformation is developed in which the empirical flow law is coupled with a model of subglacial hydrology and consolidation this predicts stable states in which subglacial sediment either does not deform or a dilatant deforming horizon forms with positive effective pressures at the ice bed interface or unstable states where zero or negative effective pressures are predicted time dependent analyses show that response times following perturbations of the system may be of the order of 103 years and thus that unsteady behavior may be normal on glaciers flowing over unlithified sediment beds it is suggested that the natural variability of material properties in subglacial sediment beds leads to the development of drumlins on the glacier bed it is suggested that unstable deformation at zero or negative effective stress leads to piping in subglacial sediments at the glacier terminus and the growth of sediment floored subglacial tunnels their frequency is that which is sufficient to draw down subglacial water pressures so as to prevent unstable deformation where they discharge large water volumes subglacial sediments flow laterally toward them producing tunnel valleys this sediment is then removed by water flowing along the axial tunnel tunnel valleys can be regarded as the equivalent in soft sediment areas of eskers in bedrock areas

the planar shape of drumlins abstract the asymmetry of the planar shape of drumlins is an established paradigm in the literature and characterizes drumlins as resembling tear drops with a blunt bullet shaped stoss end and a tapering pointed lee end it is widely cited and never been seriously questioned in this paper the planar shape of 44 500 drumlins mapped in various regional settings from drumlin fields in north america and northern europe were objectively analysed by means of geographic information system tools two parameters were considered the first denoted here as as pl focuses on the relative position of the point of intersection between the axes of the maximum length and the maximum width it is defined as the distance between the upstream i e beginning of the drumlin and the intersection point measured along the longitudinal axis divided by the entire length of the long axis results indicate that the intersection point of the majority of drumlins 64 is very close to the longitudinal midpoint 0 33 as pl as pl a is defined as the ratio between the area of the upstream half of the drumlin to that of the entire drumlin results show that for most drumlins 81 the upper half area is almost as large as the down half 0 45 as pl a

subglacial processes sediments and landforms an introduction this introduction provides an overview of research presented at the symposium on subglacial processes sediments and landforms held at the university of ulster july 1992 particular attention is focused on new developments in understanding the subglacial environment and elaboration of current controversies concerning the formation of subglacial landforms elements from the symposium show how the use of sediment dynamic principles offers new ways to examine subglacial sediment landform associations and how this sedimentary context is expressed in terms of ice sheet activity

lightning leader characteristics in the thunderstorm research international program trip we have used high speed streaking photographic techniques to time resolve the luminous compnents of cloud to ground lightning flashes all recordings were made during our participation in the thunderstorm research international program trip conducted at the kennedy space center florida during the summers of 1977 and 1978 and at the langmuir laboratory near socorro new mexico during the summer of 1979 twenty one dart leaders four dart stepped leaders and three stepped leaders were recorded the majority under daylight conditions the mean two dimensional propagation speed of the dart leaders evaluated over channel lengths less than or equal to 0 8 km above ground is 11 106 m s with a range of 2 9 to 23 106 m s several of the dart leaders reveal a decrease in propagation speed as ground is approached however four of the dart leaders in two separate flashes show an increase in speed near the ground an observation not previously reported in the literature in two multistroke flashes we examine the variation of dart leader propagation speed along the channel and find very similar behavior for different strokes in the same flash the speed variations that we observe may be predominantly caused by geometrical variations of the channel the dart leader propagation speeds reported in this study are compared with the earlier works of schonland mceachron and kitagawa and brook agreement among the studies is good with a common range of observed dart leader propagation speed of 2 to 23 106 m s the major discrepancy among these studies is the observation by schonland of a distribution of dart leader propagation speeds positively skewed toward the lower limit of reported values eleven of the dart leaders are analyzed at upper and lower levels along the visible channel to give 22 dart lengths they range from 7 to 75 m with a mean of 34 m for these 22 determinations we calculate a correlation coefficient of 0 85 between the dart length and the dart leader propagation speed the correlation of greater dart length with higher propagation speed is consistent with the slower decay of channel luminosity due to the greater initial input of energy to the channel by the faster and presumably more energetic dart leader four dart stepped leaders are examined in detail with regard to variation of propagation speed step length stepping interval and luminous intensity during propagation between the cloud base and ground significant differences in the tendencies of these parameters are found within these four leaders for example one dart stepped leader recording shows a decreasing propagation speed and an increasing step interval near ground whereas another shows the opposite behavior in the best event recorded several of the individual steps reveal a photographic film density structure with the lower portion of the step exhibiting a distinct bright tip that fans out into a symmetrically diffuse image in the upper portion of the step our analysis indicates that this spread in the upper portion of the step image is not the result of streaking photography distortion but rather represents the luminous structure of the step we estimate that the step image is recorded in less than 1 s consequently with a measured step length of 20 m the luminous pulse must propagate along the step at a speed of at least 2 107 m s the mean propagation speed for three stepped leaders is found to be 1 1 106 m s all three stepped leaders are very faint and were recorded only in the last 100 200 m above ground two stepped leaders and one dart stepped leader do not propagate completely to ground before initiation of the return stroke apparently these leaders are met by an upward propagating discharge at heights above ground of 20 30 and 20 m respectively other stepped and dart stepped leader cases are indeterminate because an obstacle or the horizon prevent the recording of the leaders near the ground connecting discharges are not observed for any of the dart leader events with a resolution of 10 m at 5 km implying that upward discharges initiated by the approach of dart leader do not occur or are substantially less than a few tens of meters in length dart leaders apparently propagate completely to ground

the composition and internal structure of drumlins complexity commonality and implications for a unifying theory of their formation investigation of drumlins is significant to both glaciology and palaeoglaciology but the sheer diversity of their composition and internal structure is often cited as a major obstacle towards a satisfactory unifying explanation of their formation this paper presents the first systematic survey of the vast literature on this subject with the aim of concisely summarising observations and identifying any emergent patterns or commonality that theories of drumlin formation should be able to explain results confirm that investigations are often limited by availability of suitable sediment exposures 40 of studies report data from 5 drumlins and 44 do not specify sample size although borehole data and geophysical techniques can alleviate this problem however it is clear that the constituents of drumlins are incredibly diverse in terms of their composition e g a range of lithologies clast shapes sizes and fabrics structure e g sediments that are sorted homogeneous surface conformable unconformable and evidence of deformation e g ranging from pervasive to non pervasive limited to absent despite this diversity our review leads us to suggest that drumlin composition can be simplified to five basic types i mainly bedrock ii part bedrock part till iii mainly till iv part till part sorted sediments and v mainly sorted sediments this is a potentially significant step in that it reduces the oft cited complexity of drumlin composition and provides a more realistic goal for theories or numerical models of drumlin formation to target the various types can occur within the same drumlin field which leaves us with two possible implications for drumlin formation 1 different types of drumlin are formed seeded by different processes despite being morphologically similar equifinality investigation of drumlin composition may therefore reveal diagnostic processes explanations for these different types of drumlin and we argue that bedrock drumlins are an example 2 a single process occurs across large parts of the ice bed interface to create drumlinised terrain in a variety of sediments investigation of drumlin composition may in this case simply reflect pre existing sediments but importantly the way in which the drumlin forming mechanism modifies is modified by them we argue that the latter simpler explanation applies to all other types of drumlin excluding purely bedrock forms and conclude that the diversity in drumlin composition is no obstacle to a single unifying theory

thin film channelized drainage or sheetfloods beneath a portion of the laurentide ice sheet an examination of glacial erosion forms northern new york state usa abstract morphologic analyses of characteristic bedrock erosion forms found in northern new york state usa were used to reconstruct the subglacial conditions under which they may have been produced observations from sites on wellesley island n y at point salubrious n y and at an open pit mine near balmat n y were combined with regional mapping of a diverse suite of glacial erosion forms in order to establish the areal extent and significance of subglacial drainage in northern new york results of these site specific and regional studies are the basis for discussion of the probable role of subglacial meltwater in the region bedrock erosion forms preserved at various locations in northern new york are interpreted as products of flow separation of localized subglacial meltwater during ice bed decoupling the regional distribution of these forms indicates that they are largely restricted to pre existing subglacially modified bedrock valleys that served as subglacial tunnel channels regionally extensive deep subglacial meltwater flow characterized as sheetfloods is not required to account for the erosional features described from specific sites in northern new york state

recent drumlins flutes and lineations at vestari hagafellsjokull iceland in the foreland of the vestari hagafellsjokull glacier langajokull central iceland three scales of subglacial bed forms are found drumlins flutes and lineations the smaller bed forms are superimposed upon the larger these three bed forms probably formed as a result of the presence of a rigid subglacial core producing a lee side low pressure area into which sediment flowed and collected the cores of the drumlins are tumuli lava blisters whilst the cores of the flutes and lineations were large clasts differences between the three scales of bed forms are that a the flutes and lineations are far more mobile features as their cores could move within the deforming layer whilst the drumlin bedrock cores were fixed b the lineations formed in association with a clast pavement the change in scale of the bed forms may be related to changes in thickness of the deforming layer and size of the core at this site smaller bed forms were superimposed upon larger bed forms and these may have formed as the deforming layer progressively thinned in association with glacial retreat

origin of the active drumlin field at mulajokull iceland new insights from till shear and consolidation patterns abstract stratigraphic and morphologic data previously collected from the forefield of mulajokull iceland suggest that its recent surge cycles are responsible for the formation of drumlins there and that their relief reflects both deposition on drumlins and erosion between them we have tested these ideas and aspects of leading models of drumlin formation by studying past patterns of bed deformation and effective stress in basal tills of the glacier s forefield patterns of till strain indicated by the anisotropy of magnetic susceptibility ams of 2300 intact till samples indicate that till was deposited during shear deformation with shearing azimuths and planes that conform to the drumlin morphology thus till deposition occurred as drumlins grew in agreement with lidar data indicating that the degree of aggradation of the glacier forefield is largest in areas subjected to the most surges previously described unconformities on the drumlin flanks however indicate that drumlin relief at mulajokull has resulted in part from erosion given that the last surge deposited a till layer both on and between drumlins a reasonable hypothesis is that erosion between drumlins occurred during normal quiescent flow of the glacier between surges densities of till samples analyzed in conjunction with laboratory consolidation tests indicate that effective stresses on the bed during such periods were on the order of 100 kpa larger between drumlins than within them an observation consistent with subglacial channels at low water pressure occupying interdrumlin areas transport of sediment by turbulent flow in these channels or high effective stress adjacent to them causing enhanced till entrainment in ice or increased depths of bed deformation would promote the sediment flux divergence necessary to erode areas between drumlins the observation that effective stresses were higher between drumlins than within them is the opposite of that presumed in leading models of drumlin formation moreover the lack of ams fabric evidence of longitudinal compression in drumlin tills does not support some models of drumlin formation that invoke negative till flux gradients in a deforming bed

three dimensional imaging of upward positive leaders in triggered lightning using vhf broadband digital interferometers 1 upward positive leaders upls in two artificially initiated lightning flashes were imaged in three dimensions using vhf broadband digital interferometers and a high speed video camera with time synchronized channel base current measurements locatable vhf sources of the two upls began at 1 1 km and 1 5 km a few milliseconds after the upl inception and ascended to 2 4 km and 3 7 km respectively with average 3 d speeds on the order of 106 ms 1 the initial stage currents for both flashes were unusually large and had peak values of 6 ka and 18 ka vhf sources associated with positive leader propagation were located when the average current was higher than 3 ka and had significant pulse activity the source altitudes and channel base currents suggest that there might have been a region of significant negative charge at altitudes from 2 to 4 km which is below the freezing level of typical thunderstorms in florida

large scale ice moulding a discussion of genesis and glaciological significance abstract landsat images reveal a previously unsuspected large scale pattern of streamlining within drift which comprises a number of components drumlins and megaflutes form part of the pattern but in addition there are two previously undocumented ice moulded landform elements streamlined lineations of much greater proportions referred to as mega scale glacial lineations and a distinctive cross cutting topology within the grain consideration of the genesis and glaciological significance of such landforms leads to a number of conclusions it is suggested that mega scale glacial lineations were formed under conditions of fast ice flow and their presence may thus record former locations of ice streams or surge events many lineations of varying scales display a pattern that reveals that they were not formed in sub marginal positions extensive sets of lineations must have been formed approximately synchronously thus indicating that lineation generation occurs over a wide range of glaciodynamic conditions from sub marginal positions to interior portions of ice sheets subglacial deformation of tills has been widely invoked to account for rapid glacier motion criteria for identifying such tills are restricted to structures viewed in cross section and it is thus hard to assess how widespread the processes of deformation may have been lineations provide a surface marker of structure that records subsequent deformation from other ice flow events it is argued that the palaeo flow record including cross cutting patterns provides the surface or plan expression of subglacial deformation the degree of modification to pre existing lineations should permit the identification of zones favoured by deformation and thus assist in an assessment of how pervasive deforming bed processes were in influencing ice sheet dynamics

atmospheric thermal structure and cloud features in the southern hemisphere of venus as retrieved from virtis vex radiation measurements thermal structure and cloud features in the atmosphere of venus are investigated using spectroscopic nightside measurements recorded by the visible and infrared thermal imaging spectrometer virtis aboard esa s venus express mission in the moderate resolution infrared mapping channel m ir 1 5 m new methodical approaches and retrieval results for the northern hemisphere have been recently described by haus et al haus r kappel d arnold g 2013 planet space sci 89 77 101 http dx doi org 10 1016 j pss 2013 09 020 now southern hemisphere maps of mesospheric temperature and cloud parameter fields are presented that cover variations with altitude latitude local time and mission time measurements from the entire usable data archive are utilized comprising radiation spectra recorded during eight venus solar days between april 2006 and october 2008 zonal averages of retrieved temperature altitude profiles in both hemispheres are very similar and give evidence of global n s axial symmetry of atmospheric temperature structure cold collar and warmer polar vortex regions exhibit the strongest temperature variability with standard deviations up to 8 5 k at 75 s and 63 km altitude compared with about 1 0 k at low and mid latitudes above 75 km the mesospheric temperature field strongly depends on local time at altitudes above about 75 km the atmosphere is warmer in the second half of night while the dawn side at lower altitudes is usually colder than the dusk side by about 8 k local minimum temperature of 220 k occurs at 03 00 h local time at 65 km and 60 s temperature standard deviation at polar latitudes is particularly large near midnight temperature variability with solar longitude is forced by solar thermal tides with a dominating diurnal component the influence of observed cloud parameter changes on retrieved mesospheric zonal average temperature structure is moderate and does not exceed 2 3 k at altitudes between 60 and 75 km the mesospheric thermal structure was essentially stable with julian date between 2006 and 2008 global n s axial symmetry is also observed in cloud structures cloud top altitude at 1 m slowly decreases from 71 km at the equator to 70 km at 45 50 and rapidly drops poleward of 50 it reaches 61 km over both poles average particle size in the vertical cloud column increases from mid latitudes toward the poles and also toward the equator resulting in minimum and maximum zonal average cloud opacities of about 32 and 42 and a planetary average of 36 5 at 1 m zonal averages of cloud features are similar at different solar days but variations with local time are very complex and inseparably associated with the superrotation of the clouds

quaternary geology and geomorphology of the dinosaur provincial park area and surrounding plains alberta canada the identification of former glacial lobes drainage diversions and meltwater flood tracks abstract the quaternary geology and geomorphology of the lower red deer river drainage basin centred on the dinosaur provincial park badlands provides information on pre late wisconsinan drainage patterns and the dynamics of former lobes of the laurentide ice sheet in western canada patterns of deglaciation proglacial lake evolution and spillway incision are also reconstructed based upon the distribution of surface materials and glacial glaciofluvial landforms the empress group fluvial and glaciolacustrine sediments which could be as young as 27 ka bp infill the precursor red deer river and its tributaries and document the initial advance of glacier ice into southern alberta glaciotectonic disturbance of older sediments and bedrock the production of deformation tills and the construction of a megafluting complex and cupola hills record the advances of a glacier lobe centred over the study area stratified inter and intra till beds record pulses of subglacial meltwater between phases of subsole deformation the thickening of tills towards the margin of the lobe represents a till wedge an expected product of sediment advection by glaciers moving over deformable beds the eastern margin of the glacier lobe is demarcated by the interlobate suffield hummocky moraine belt which contains overprinted thrust ridges which record diachronous oscillations of neighbouring lobes within the ice sheet proglacial and glaciofluvial sediments were deposited in the area in association with proglacial lake bassano patricia which drained eastwards when the suffield moraine was dissected by spillways changes in the size of glacial lake bassano patricia are clearly documented by a sequence of spillway incisions which culminated in the erosion of scabland topography and the initiation of a new course for the red deer river a 15 km southward diversion of the main channel in distinct contrast to the documented incision histories of other small rivers in alberta one tree creek and little sandhill creek did not start major incisions of the quaternary sediments over buried valley positions until the late holocene when environmental conditions were characterized by higher precipitation

on the formation of the tunnel valleys of the superior lobe central minnesota abstract when considering the formation of tunnel valleys most researchers have appealed to basal melting as the primary source of water erosion of the tunnel valleys can then be accomplished by steady state drainage over a long period or by storage and subsequent catastrophic release however field relationships in a large system of tunnel valleys formed by the superior lobe in central minnesota indicate that another source of water must be considered the minnesota tunnel valleys are composed of individual segments 10 20 km long and the segments commonly terminate in subaerial outwash fans at recessional ice margin positions eskers associated with the tunnel valleys are also composed of short segments frequently beginning at moulin kames and terminating at the head of outwash fans the dominant source of the water responsible for tunnel valley formation was seasonal meltwater from the glacier surface that reached the bed through moulins and crevasses the apparent continuity of the valleys resulted from the headward development of the englacial drainage system during ice retreat

melt out till in the edmonton area alberta canada till at two localities in the edmonton area alberta was formed mainly by passive melt out from glacier ice and not by lodgment by active ice or as a result of supraglacially derived flows this interpretation is based on the implications of in situ stratified glacial sediment below and within till and of large unlithified clasts of sediment derived from subtill deposits the interpretation is also supported by more general regional stratigraphic and structural observations such associated properties as subtill deformation a sharply planar till preglacial sediment contact sole marks and fabric support formation by melt out or illustrate local exceptions to this process regionally consistent preferred orientation of clasts is interpreted to represent preferred englacial orientation collective analysis of the principal eigenvectors of individual englacial fabrics and flow or resedimented till fabrics from a modem glacial environment and similar analysis for till at villeneuve near edmonton show the edmonton till to occupy the intermediate position in terms of orientation strength predicted by the melt out hypothesis in places preferred orientation is considered to have been disturbed by flow and diapirism induced by the process of thaw consolidation thus preferred clast orientation in till may show considerable deviation from a regional trend stratigraphy and sedimentology are used to classify the till and to relate individual exposures to regional environments of deposition

location and analysis of acoustic infrasound pulses in lightning acoustic vhf and electrostatic measurements throw new light onto the origin and production mechanism of the thunder infrasound signature 10 hz from lightning this signature composed of an initial compression followed by a rarefaction pulse has been the subject of several unconfirmed theories and models the observations of two intracloud flashes which each produced multiple infrasound pulses were analyzed for this work once the variation of the speed of sound with temperature is taken into account both the compression and rarefaction portions of the infrasound pulses are found to originate very near lightning channels mapped by the lightning mapping array we found that none of the currently proposed models can explain infrasound generation by lightning and thus propose an alternate theory the infrasound compression pulse is produced by electrostatic interaction of the charge deposited on the channel and in the streamer zone of the lightning channel

ice streams in the laurentide ice sheet identification characteristics and comparison to modern ice sheets this paper presents a comprehensive review and synthesis of ice streams in the laurentide ice sheet lis based on a new mapping inventory that includes previously hypothesised ice streams and includes a concerted effort to search for others from across the entire ice sheet bed the inventory includes 117 ice streams which have been identified based on a variety of evidence including their bedform imprint large scale geomorphology topography till properties and ice rafted debris in ocean sediment records despite uncertainty in identifying ice streams in hard bedrock areas it is unlikely that any major ice streams have been missed during the last glacial maximum laurentide ice streams formed a drainage pattern that bears close resemblance to the present day velocity patterns in modern ice sheets large ice streams had extensive onset zones and were fed by multiple tributaries and where ice drained through regions of high relief the spacing of ice streams shows a degree of spatial self organisation which has hitherto not been recognised topography exerted a primary control on the location of ice streams but there were large areas along the western and southern margin of the ice sheet where the bed was composed of weaker sedimentary bedrock and where networks of ice streams switched direction repeatedly and probably over short time scales as the ice sheet retreated onto its low relief interior several ice streams show no correspondence with topography or underlying geology perhaps facilitated by localised build up of pressurised subglacial meltwater they differed from most other ice stream tracks in having much lower length to width ratios and have no modern analogues there have been very few attempts to date the initiation and cessation of ice streams but it is clear that ice streams switched on and off during deglaciation rather than maintaining the same trajectory as the ice margin retreated we provide a first order estimate of changes in ice stream activity during deglaciation and show that around 30 of the margin was drained by ice streams at the lgm similar to that for present day antarctic ice sheets but this decreases to 15 and 12 at 12 cal ka bp and 10 cal ka bp respectively the extent to which these changes in the ice stream drainage network represent a simple and predictable readjustment to a changing mass balance driven by climate or internal ice dynamical feedbacks unrelated to climate or both is largely unknown and represents a key area for future work to address

glacial landsystems of the southwest laurentide ice sheet modern icelandic analogues landform assemblages and associated stratigraphy sedimentology and structure are used in the reconstruction of palaeo ice sheet dynamics in alberta western canada interpretations are based upon the modern analogues from four outlet glaciers at the margins of vatnajokull and myrdalsjokull iceland in the area between lloydminster and lac la biche central alberta an extensive landform assemblage of megaflutings crevasse squeeze ridges and thrust block moraine arcs document the former surging of part of the margin of the laurentide ice sheet during later stages of recession this landform assemblage including numerous exposures of glacitectonised bedrock and quaternary sediments is comparable to the landsystem of the surging glaciers eyjabakkajokull and bruarjokull in iceland near high river southern alberta the former existence of an ice lobe characterised by active recession is recorded by closely spaced low amplitude recessional push moraines that drape tunnel valleys these are comparable in form and pattern to annual push moraines and fluted till surfaces produced by breidamerkurjokull and sandfellsjokull iceland and also include rimmed depressions produced by the escape of artesian water during ice marginal pushing this study provides interpretations of the regional glacial geomorphology of alberta based upon comparisons of form and stratigraphy with modern glacial analogues and provides an alternative to recent models which invoke large floods of subglacial meltwater to explain many of these same features implications for ice dynamics and regional till stratigraphies are discussed copyright 1999 john wiley sons ltd

drumlin formation related to inverted melt water erosional marks drumlin forms are described from maps and air photographs of a part of the athabasca plains northern saskatchewan three major forms spindle parabolic and transverse asymmetrical are recognized these forms which may show superimposed minor elements depart from classical descriptions of drumlins but are similar to moulds of erosional marks created by separated fluid flows assemblages of drumlins also show characteristics similar to those of erosional marks the form analogy between drumlins and moulds of erosional marks is carried to a conclusion that drumlins may be formed by the infilling of erosional marks created on the under side of glaciers by separated subglacial melt water flows estimates of specific discharge are obtained by means of an expected range of reynolds number geomorphological evidence is given for large scale erosion by subglacial melt water a discussion of the sedimentology stratigraphy and deformational structure of the interiors of drumlins shows that they may be explained by the erosional mark hypothesis this paper emphasizes the importance of melt water as a geomorphic agent and may have broad implications for ice sheet dynamics and profiles rates of deglaciation and the occurrence of bedrock thrusting by ice

a glaciofluvial origin for drumlins of the livingstone lake area saskatchewan the livingstone lake drumlin field of northern saskatchewan is on the athabasca plains it is draped over high ground underlain by the precambrian athabasca sandstone the drumlins occur in spindle parabolic and transverse asymmetrical forms a map of individual drumlins shows that features of similar form occur together the drumlins are related on a regional scale to even larger landforms there is also an arrangement of drumlins in streams parallel to the assumed flow direction these patterns illustrate spatial organisation of the drumlin forming flows the livingstone lake drumlins are closely related to tunnel valleys large crescentic scours and eskers exposed bedrock reveals widespread scalloping and sichelwannen an argument is made that drumlins are related to these glaciofluvial forms but were created at different times and by different flows than those forming small scale flutings and other lodgment features sediments within the drumlins are mainly primary water sorted deposits some of wh

stratified flow deposits in a late pleistocene drumlin in northwest ireland abstract extensive stratified flow deposits are present within a drumlin exposed on the eastern shore of donegal bay northwest ireland the stratified deposits are located towards the central lee portion of the drumlin infilling a major depression within a basal diamicton association and are overlain by a sand rich diamicton association the stratified sequence consists of laminated silts cohesive diamictic muds stratified diamictons well sorted massive sands and clast supported gravels a discernible upward vertical facies transition is apparent within the stratified deposits from fines and matrix dominant sediments to well sorted clastic sediments these facies variations appear to reflect increased hydrodynamic activity and a prograding sequence the sediments are interpreted as a subglacial conduit infill formed at the point of debouchure into a glaciomarine environment the envisaged increase in water availability and flow energy may have resulted from progressive enlargement of the conduit by basal melting and scouring associated with the water sediment flux within the conduit the depression in the basal diamicton association appears to have resulted from scour at the base of the conduit

maintenance of strong rotational winds in venus middle atmosphere by thermal tides the cloud level atmosphere of venus takes little more than 4 days to complete one rotation whereas the solid planet below has a 243 day period computer simulations of the circulation of the venus middle atmosphere between 40 and 85 kilometers as driven by solar radiation absorbed in the clouds reproduce i the observed cloud level rotation rate ii strong vertical shears above and below the cloud tops and iii midlatitude jets and strong poleward flow on the day side simulated circulations converge to yield nearly the same zonal winds when initialized with both stronger or weaker rotation rates these results support the hypothesis that the observed cloud top rotation rate is maintained by statistical balance between fluxes of momentum by thermal tides and momentum advection by mean meridional circulation

semi automated extraction of longitudinal subglacial bedforms from digital terrain models two new methods abstract relict drumlin and mega scale glacial lineation positive relief longitudinal subglacial bedforms lsbs morphometry has been used as a proxy for paleo ice sheet dynamics lsb morphometric inventories have relied on manual mapping which is slow and subjective and thus potentially difficult to reproduce automated methods are faster and reproducible but previous methods for lsb semi automated mapping have not been highly successful here two new object based methods for the semi automated extraction of lsbs footprints from digital terrain models are compared in a test area in the puget lowland washington usa as segmentation procedures to create lsb candidate objects the normalized closed contour method relies on the contouring of a normalized local relief model addressing lsbs on slopes and the landform elements mask method relies on the classification of landform elements derived from the digital terrain model for identifying which lsb candidate objects correspond to lsbs both methods use the same lsb operational definition a ruleset encapsulating expert knowledge published morphometric data and the morphometric range of lsbs in the study area the normalized closed contour method was separately applied to four different local relief models two computed in moving windows and two hydrology based overall the normalized closed contour method outperformed the landform elements mask method the normalized closed contour method performed on a hydrological relief model from a multiple direction flow routing algorithm performed best for an assessment of its transferability the normalized closed contour method was evaluated on a second area the chautauqua drumlin field pennsylvania and new york usa where it performed better than in the puget lowland a broad comparison to previous methods suggests that the normalized relief closed contour method may be the most capable method to date but more development is required

late pleistocene tidewater glaciers and glaciomarine sequences from north county mayo republic of ireland late pleistocene deposits in north county mayo were deposited in three main glacigenic environments 1 drumlins and basal tills were formed when ice moved from the irish lowlands and local mountain catchments into donegal bay 2 gilbert type deltas accumulated up to 80m i o d on the lowlands and subaqueous moraines formed across minor valleys when marine based ice grounded inland 3 a thick drape of fossiliferous glaciomarine mud along the coastal fringe was deposited from meltwater plumes and by ice rafting immediately outside of these ice limits the muds contain an elphidium clavatum dominated low diversity microfauna which is characteristic of cold water conditions adjacent to glacier termini valves of macoma calcarea from the mud have been 14c dated at 16940 120 and 17300 100 bp the high level delta complex was deposited from tidewater glaciers in a peripheral depression adjacent to the drumlin ice limits of north county mayo although the field evidence cannot be used to determine former sea level history with any accuracy it poses general problems for sea level history and isostatic effects of the last major ice sheet in the west of ireland raised glaciomarine sequences commonly occur in close association with drumlin ice limits elsewhere in ireland and represent marine transgressions prior to glacial unloading it is suggested that the magnitudes and patterns of crustal depression are greater and geometrically more complex at the margins of ice sheets in ireland than hitherto realised

a pyroclastic flow deposit on venus explosive volcanism on venus is severely inhibited by its high atmospheric pressure and lack of water this paper shows that a deposit located near 16 s 144 e here referred to as scathach fluctus displays a number of morphological characteristics consistent with a pyroclastic flow deposit these characteristics particularly its lack of channelisation and evidence for momentum rather than cooling limited flow length contrast with fissure fed lava flow deposits the total erupted volume is estimated to have been between 225 km3 and 875 km3 but this may have been emplaced in more than one event interaction between scathach fluctus and a small volcanic cone constrain the flow velocity to 48 m s 1 and plausible volatile concentrations to at least 1 8 wt h2o 4 3 wt co2 or 6 1 wt so2 the latter two implying magma sourced directly from the mantle the deposit has radar characteristics particularly an exponential backscatter function that are similar to those of nearly half the planetary surface implying that pyroclastic deposits may be much more common on venus than has been recognised to date and suggesting both a relatively volatile rich mantle and a volcanic source for atmospheric so2

physical environment of drumlin formation review of published descriptions of drumlin fields suggests that the following conditions are important to drumlin growth 1 compressive longitudinal and possibly extending transverse strain rates in the ice 2 thin ice such as occurs near the glacier margin and 3 high pore water pressure in the subglacial sediments most drumlin fields display all of these and no fields of well developed drumlins were found that did not on the oilier hand the lithology of drumlin forming sediment appears not to be important in promoting drumlin growth since it varied widely nor are the lithology and large scale topography of the bed

statistical analysis of storm electrical discharges reconstituted from a lightning mapping system a lightning location system and an acoustic array in the framework of the european hydrological cycle in the mediterranean experiment project a field campaign devoted to the study of electrical activity during storms took place in the south of france in 2012 an acoustic station composed of four microphones and four microbarometers was deployed within the coverage of a lightning mapping array network on the 26 october 2012 a thunderstorm passed just over the acoustic station fifty six natural thunder events due to cloud to ground and intracloud flashes were recorded this paper studies the acoustic reconstruction in the low frequency range from 1 to 40 hz of the recorded flashes and their comparison with detections from electromagnetic networks concurrent detections from the european cooperation for lightning detection lightning location system were also used some case studies show clearly that acoustic signal from thunder comes from the return stroke but also from the horizontal discharges which occur inside the clouds the huge amount of observation data leads to a statistical analysis of lightning discharges acoustically recorded especially the distributions of altitudes of reconstructed acoustic detections are explored in detail the impact of the distance to the source on these distributions is established the capacity of the acoustic method to describe precisely the lower part of nearby cloud to ground discharges where the lightning mapping array network is not effective is also highlighted

landform and sediment imprints of fast glacier flow in the southwest laurentide ice sheet evidence for former fast glacier flow ice streaming in the southwest laurentide ice sheet is identified on the basis of regional glacial geomorphology and sedimentology highlighting the depositional processes associated with the margin of a terrestrial terminating ice stream preliminary mapping from a digital elevation model of alberta identifies corridors of smoothed topography and corridor parallel streamlined landforms megaflutes to mega lineations that display high levels of spatial coherency ridges that lie transverse to the dominant streamlining patterns are interpreted as a series of minor recessional push moraines b thrust block moraines or composite ridges hill hole pairs constructed during readvances surges and c overridden moraines cupola hills apparently of thrust origin together these landforms demarcate the beds and margins of former fast ice flow trunks or ice streams that terminated as lobate forms localised cross cutting and or misalignment of flow sets indicates temporal separation and the overprinting of ice streams lobes the fast flow tracks are separated by areas of interlobate or inter stream terrain in which moraines have been constructed at the margins of neighbouring competing ice streams outlet glaciers this inter stream terrain was covered by more sluggish non streaming ice during full glacial conditions thin tills at the centres of the fast flow corridors in many places unconformably overlying stratified sediments suggest that widespread till deformation may have been subordinate to basal sliding in driving fast ice flow but the general thickening of tills towards the lobate terminal margins of ice streams outlet glaciers is consistent with subglacial deformation theory in this area of relatively low relief we speculate that fast glacier flow or streaming was highly dynamic and transitory sometimes with fast flowing trunks topographically fixed in their onset zones and with the terminus migrating laterally the occurrence of minor push moraines and flutings and associated landforms because of their similarity to modern active temperate glacial landsystems are interpreted as indicative of ice lobe marginal oscillations possibly in response to seasonal climatic forcing in locations where meltwater was more effectively drained from the glacier bed further north the occurrence of surging glacier landsystems suggests that persistent fast glacier flow gave way to more transitory surging possibly in response to the decreasing size of ice reservoir areas in dispersal centres and also locally facilitated by ice bed decoupling and drawdown initiated by the development of ice dammed lakes copyright 2008 john wiley sons ltd

basin scale patterns of subglacial sediment mobility implications for glaciological inversion modelling abstract patterns of glacial bedforms and their internal sediments are described from the omagh basin north central ireland here drumlins and ribbed moraines were variously formed preserved and remoulded during several late devensian ice flow stages and their patterns can be used as input into glaciological inversion models more detailed examination of the morphology and internal sediments of these bedforms shows a complex pattern of reworking driven by local scale basal thermal and hydrological regime sediment lithofacies associations and patterns of erratic carriage can be used to better evaluate ice bed conditions and basal processes than bedforms alone the sedimentary evidence suggests that bedforms were unlikely to have been formed during a single glacial episode as is implicit in glaciological inversion models and more likely formed during several episodes that cannot be resolved by crosscutting or superimposed bedform relationships alone

architectural element analysis applied to glacial deposits internal geometry of a late pleistocene till sheet ontario canada deposits left by continental ice sheets are characterized by sedimentological complexity and stratigraphic heterogeneity but stratigraphic descriptions of such deposits and resulting first generation facies models are still based primarily on one or two dimensional borehole or outcrop data reconstruction of depositional environments hydrogeological investigations of pleistocene glacial deposits and hydrocarbon exploration in pre pleistocene glaciated basin fills require a more detailed understanding of the form and heterogeneity of lithofacies sequences in three dimensions architectural element analysis is used widely by sedimentologists for categorizing internal stratigraphic heterogeneity in sandstones particularly those of fluvial origin this paper demonstrates the first application of architectural element analysis to glacial deposits such as tills outcrop borehole and a broad range of subsurface geophysical data were collected from a thick 60 m till sheet present across an 80 km 2 study area near toronto canada the till sheet is not homogeneous but is composed of three distinct architectural elements and associated lithofacies viz diamict elements interbeds of subglaciofluvial sediments and glaciotectonically deformed zones application of architectural element analysis to these subglacial strata provides insights into the origin of drumlin bedforms and subglacial processes below the laurentide ice sheet and creates a framework for understanding ground water and contaminant movement in underlying aquifers

evidence of cordilleran late wisconsinan glaciers in the ice free corridor abstract glaciers flowing down the athabasca river valley during the last glacial period were fed both by local montane glaciers and by cordilleran ice moving easterly across the continental divide from british columbia resulting in a major eastward surge into the ice free corridor the timing of this event has been disputed for many years and has important implications for the study of paleoenvironmental conditions and the north south migration of biota in the corridor chronologic and lithostratigraphic data from the jasper region suggest that this event took place in the late wisconsinan subtill radiocarbon dates on wood in the athabasca river valley indicate that non glacial alluvial sediments began accumulating there sometime before 48 ka a finite date of 29 100 560 bp gsc 3792 on wood under till near jasper provides a maximum age for the onset of the last glaciation in the region although ice from west of the rocky mountain trench probably did not cross the continental divide until after 21 5 ka the occurrence of supraglacial metamorphic erratics as well as the distribution and nature of mapped glacial deposits and the trend of subglacial paleoflow indicators in the region east of the rockies suggests that late wisconsinan glaciers flowing from the mountains coalesced with laurentide glaciers and were deflected southeasterly along the mountain front an even more extensive glacial event may have effected the region in pre late wisconsinan times the model of late wisconsinan glaciation presented here is in agreement with all known radiocarbon data from the area and is especially attractive when supratill dates on non woody lacustrine organics are viewed in light of possible contamination by old carbon

glaciofluvial erosional morphology and sediments of the coronation spondin scabland east central alberta spatially discontinuous meltwater channel networks on the canadian prairies are usually interpreted as having formed subaerially in front of the retreating laurentide ice sheet evidence in the coronation spondin scabland east central alberta supports an alternative formation by progressive channelization of a subglacial sheetflow of water the scabland is an integrated channel network with varying degrees of anabranching the channels having highly variable sizes shapes and orientations enhanced scour at some channel confluences reflects contemporaneous channel utilization channels also display convex up concave up and undulatory along channel profiles with some junctions at the same elevations longitudinal grooves in large scale channels are associated with numerous boulder deposits residual hills demarcated by channels display composite and streamlined forms superimposed on residuals are erosional transverse bedforms longitudinal grooves and undulating surfaces that indicate submergence

saginaw lobe tunnel channels laurentide ice sheet and their significance in south central michigan usa abstract a network of tunnel channels in southern michigan records substantial subglacial meltwater activity beneath the saginaw lobe of the laurentide ice sheet the channels are incompletely filled with outwash contain eskers and in many places crosscut and continue beyond upland ridges previously mapped as recessional moraines the presence of the tunnel channels and drumlins on these upland ridges indicate that the ridges are not recessional moraines instead outwash fans and minor ridges record deglaciation in the area a palimpsest relationship between buried bedrock valleys and tunnel channels records the presence of multiple generations of tunnel channels evidence for a subglacial meltwater sheetflow consists of sheets of boulder gravel in upland 15 km wide with a hummocky upper surface the hummocks transform down flow into erosional remnant drumlins possibly the result of flow acceleration on a negative slope tunnel channels at the distal end of the drumlin swarm suggest collapse of the sheetflow into a channelized flow the tunnel channels then end at the sturgis moraine at the heads of large outwash fans the observed geomorphic relationships between tunnel channels moraines and drumlins in south central michigan are applicable to glacial landform studies elsewhere and indicate the important role of meltwater in landscape evolution

glaciomarine facies from the western sector of the last british ice sheet malin beg county donegal ireland the coastal margins and mountainous core of county donegal republic of ireland have been areally scoured and deeply eroded along structural lineaments by major late devensian ice streams which moved generally westwards onto the continental shelf a raised glaciomarine sequence is selectively preserved along a gully at malin beg and comprises mud muddy diamict sand and diamict 1 the mud which was deposited from suspended sediment plumes passes upwards into muddy diamict which reflects an increase in ice rafting the muds contain a redeposited foraminiferal assemblage of ice proximal origin pumped into the water column by jets reworking previously deposited outwash the presence of middle devensian shells have been identified from the mud by amino acid analysis this suggests a late devensian age for the succession 2 the overlying sand indicates an increase in traction current activity at the site 3 there is a sharp planar contact between the sands and the overlying tabular diamict unit 4 a surficial sheet of coarse grained breccia is attributed to intense periglacial weathering along the slopes of leahan mountain this sequence and those at other sites in western ireland e g belderg co mayo provide a record of deep isostatic depression and sedimentation in a peripheral trough at the north western margin of the last british ice sheet directional indicators including drumlin fields and major troughs indicate that the north western sector of the ice sheet was drained by major ice streams these ended in calving bays ice marginal response to ice wastage depended largely on catchment factors such as the magnitude of the ice reservoirs and the length of flow lines ultimately calving led to accelerated ice flow and areal down draw and collapse of the north western sector of the ice sheet

recent hotspot volcanism on venus from virtis emissivity data the questions of whether venus is geologically active and how the planet has resurfaced over the past billion years have major implications for interior dynamics and climate change nine hotspots areas analogous to hawaii with volcanism broad topographic rises and large positive gravity anomalies suggesting mantle plumes at depth have been identified as possibly active this study used variations in the thermal emissivity of the surface observed by the visible and infrared thermal imaging spectrometer on the european space agency s venus express spacecraft to identify compositional differences in lava flows at three hotspots the anomalies are interpreted as a lack of surface weathering we estimate the flows to be younger than 2 5 million years and probably much younger about 250 000 years or less indicating that venus is actively resurfacing

transient subglacial hydrology of a thin ice sheet insights from the chasm esker british columbia canada abstract glacier drainage systems are never steady state instead they fluctuate over time and space in response to variation in water input in order to improve numerical models of glacier hydrology it is important to fully understand the processes controlling subglacial drainage system evolution but contemporary ice sheet beds are typically inaccessible thus esker distribution morphology and sedimentology have been used to infer the dynamics and hydrology of former ice sheets however debate remains as to the processes responsible for esker formation and most theoretical investigations have assumed that they formed due to processes that operated beneath thick ice despite many field investigations to the contrary we investigate esker formation during the final stages of the thin inactive and rapidly decaying cordilleran ice sheet cis in interior british columbia canada a combination of geomorphological ground penetrating radar gpr and electrical resistivity tomography ert data suggest esker ridge sedimentary architecture is consistent with synchronous formation during a glacial lake outburst flood glof these data reveal esker ridge deposition most likely took place within an ice tunnel that evacuated late waning stage flow following erosion and partial fill of a broader meltwater corridor esker ridge sedimentary architecture reveals this depositional environment was dynamic reflecting complex interaction between ice thickness ice structure ice tunnel geometry flow conditions and sediment supply under these thin inactive ice conditions ice tunnel location was initially governed by structural weaknesses in the ice and or equipotential gradient because creep closure rates were low the ice tunnel evolved through feedbacks between conduit growth via frictional melting mechanical ice excavation and conduit closure due to sediment infilling rather than ice creep this resulted in a non uniform ice tunnel that enlarged in an upglacier direction and locally unroofed to form open channels during its final stages these data suggest that eskers may record unsteady rather than steady flows in a drainage network and so the assumptions often made when using eskers to inform hydrological components of ice sheet models may not be applicable to all ice sheet settings

drumlin evolution and ice sheet oscillations along the ne atlantic margin donegal bay western ireland abstract satellite imagery of donegal bay northwestern ireland reveals two streamlined subglacial bedform sets produced during the late devensian glaciation ca 22 000 15 000 yrs b p the first bedform set trends northeast southwest and records fast ice flow from inland ice domes onto the eastern atlantic continental shelf the second bedform set trending east west crosscuts and partially reorientates the first morphological and sedimentary evidence show that the second set corresponds to the last phase of fast ice flow drumlinization in northwestern ireland morphological characteristics of the donegal bay drumlin field and sedimentary characteristics of the mullinasole drumlin donegal bay support a two stage interpretation of drumlin evolution these are the following 1 deposition of glaciomarine mud and diamict facies at a tidewater glacier margin stratified diamicts record debris flow events and sediment reworking this facies sequence is erosionally truncated 2 deposition of subglacial diamict and sand facies recording ice readvance and drumlinization drumlinization sediment streamlining reflects ice mass balance destabilization episodic fast ice flow and ice marginal oscillation and may be correlated with millennial time scale climate changes in the circum north atlantic

ice keel seabed features in marine channels of the central canadian arctic archipelago evidence for former ice streams and iceberg scouring abstract the study area lies within the central part of the canadian arctic archipelago a region that was covered by the laurentide ice sheet during the late wisconsinan glaciation and earlier multibeam imagery from widely spaced transects indicates the presence of linear groove and ridge features on the seabed at several localities in peel sound franklin strait northern larsen sound and within m clintock channel these lineations resemble features in antarctica and in several formerly glaciated regions that have been interpreted to be sole marks emplaced beneath fast flowing ice streams based on these analogies a similar origin is inferred for the lineations on the channel floors within the study area the lineations are oriented parallel to the channel axes and margins they occur on all transects within the bathymetrically deeper area at the junction of franklin strait and peel sound northward in peel sound they occur extensively on the western and central transects and more locally on the eastern transect their north south orientation is normal to that of glacial flow features on somerset island and most of eastern prince of wales island which border peel sound to the east and west respectively the trend of the lineations is northeasterly parallel to the channel axis in franklin strait and mainly northerly in larsen sound and m clintock channel elsewhere the seabed imagery commonly displays scours of various sizes and orientations created by the keels of icebergs seabed sediments revealed by 3 5 khz sub bottom profiles are interpreted to consist primarily of ice contact sediments that in part are thinly mantled by draped water lain sediments the age of the lineations has not been established possibly their formation was coincident with an ice stream in the m clintock channel eastern victoria island region which formed an ice shelf in viscount melville sound that grounded on southern melville and byam martin islands at ca 10 4 9 6 14 c ka bp alternatively they could result from later glacial events

the role of meltwater in glacial processes abstract water plays a dominant role in many glacial processes and the erosional depositional and climatic significance of meltwaters and associated fluvioglacial processes cannot be overemphasized at its maximum extent c 20 000 years ago the volume of the laurentide ice sheet was 33 106 km3 about the same as the volume of all ice present today on planet earth the bulk of this was released as water in little more than 10 000 years pulses of meltwater flowing to the atlantic ocean from large ice dammed lakes altered thermohaline circulation of the world s oceans and global climate one such discharge event via hudson bay at 8200 years bp released 160 000 km3 of water in 12 months global sea levels recovered from glacial maximum low stands reached at about 20 000 years ago at an average rate of 15 m per thousand years but estimates of shorter term rates suggest as much as 20 m sea level rise in 1000 years and for short periods rates as high as 4 m per hundred years meltwaters played a key role in lubricating ice sheet motion and thus areal abrasion across the inner portions of the ice sheet where it slid over rigid crystalline bedrock of the canadian shield the recharge of meltwater into the ice sheets bed was instrumental in generating poorly sorted diamict sediments till by sliding induced shearing and deformation of overpressured sediment and soft rock the transformation of overpressured till into hyperconcentrated slurries in subglacial channels may have generated a highly effective erosional tool for selective overdeepening and sculpting of bedrock substrates some workers credit catastrophic subglacial megafloods with the formation of drumlins and flutes on till surfaces subglacial melt river systems were instrumental in reworking large volumes of glaciclastic sediment to marine basins it has been estimated that less than 6 of the total volume of glaciclastic sediment produced during the pleistocene remains on land fluvioglacial and glaciolacustrine sediments and landforms dominate large tracts of the glacial landscape in north america the recharge of subglacial meltwater into underlying bedrock and sediment aquifers created transient reversals in the long term equilibrium flow directions of basinal fluids with regard to pre pleistocene glacial record meltwaters moved enormous volumes of terrestrial glaciclastic sediment to marine basins and thus played a key role in preserving a record of glaciation a record otherwise almost entirely lost on land

themis regio venus evidence for recent volcanism from virtis data abstract themis regio is interpreted to be a hotspot rise underlain by one or more mantle plumes many volcanic features in the themis region have high emissivity anomalies in venus express visible and infrared thermal imaging spectrometer virtis data other high emissivity anomalies have been found to correspond to volcanic flows interpreted to be relatively recent smrekar et al 2010a science 328 605 608 similarly at themis the majority of the high emissivity anomalies closely correspond to flows associated with coronae and volcanic edifices consistent with the interpretation that they represent recent volcanism these volcanic features also have negative bouguer gravity anomalies indicating low density at depth consistent with hot mantle upwellings leading to pressure release melting in addition several volcanic features at themis have low emissivity anomalies suggestive of more evolved compositions combining geologic mapping data with gravity and emissivity data provide support that themis is an active hotspot swell with associated long lived volcanoes and coronae that are likely associated with small scale upwellings

characteristics and origins of lee side stratification sequences in late pleistocene drumlins northern ireland spindle and parabolic shaped drumlins examined at fifty five localities in northern ireland possess stratification sequences on their lee side flanks these forms lack the distinctive steep stoss and tapering lee ends of classical drumlins and tend to occur in linear zones transverse to late pleistocene ice flow in most cases 90 per cent the stratified deposits infill embayments excavated in the lee side of barkhanoid forms and in the remainder 10 per cent they are superimposed on the lee side of whaleback forms the stratification sequences developed as a result of sedimentation in interconnected subglacial water filled cavities and are unlike remanie proglacial sediments moulded by ice into drumlin form stratigraphic evidence indicates that the lee side sequences developed during drumlin streamlining which supports the view that subglacial hydraulic processes played an important role in drumlin formation

mesoscale modeling of venus bow shape waves abstract the akatsuki instrument lir measured an unprecedented wave feature at the top of venusian cloud layer stationary bow shape waves of thousands of kilometers large lasting several earth days have been observed over the main equatorial mountains here we use for the first time a mesoscale model of the venus s atmosphere with high resolution topography and fully coupled interactive radiative transfer computations mountain waves resolved by the model form large scale bow shape waves with an amplitude of about 1 5 k and a size up to several decades of latitude similar to the ones measured by the akatsuki spacecraft the maximum amplitude of the waves appears in the afternoon due to an increase of the near surface stability propagating vertically the waves encounter two regions of low static stability the mixed layer between approximately 18 and 30 km and the convective layer between 50 and 55 km some part of the wave energy can pass through these regions via wave tunneling these two layers act as wave filter especially the deep atmosphere layer the encounter with these layers generates trapped lee waves propagating horizontally no stationary waves is resolved at cloud top over the polar regions because of strong circumpolar transient waves and a thicker deep atmosphere mixed layer that filters most of the mountain waves

asymmetrical drumlins in patagonia chile abstract drumlins in south america are described and discussed in some detail for the first time they occur in the chilean part of southern patagonia close to the magellan straits here the majority of drumlins are spindle shaped and have asymmetric cross profiles with the steeper slopes consistently on the same side southeast elongated enclosed hollows are commonly associated with the steeper slopes till with blade shaped clasts showing preferred alignment roughly parallel with the drumlin long axes composes at least the outer 2 m and up to 6 m of the stoss end of some drumlins thick sequences of glaciofluvial and glaciolacustrine sediments may underlie much of the main drumlin field the subglacial deformation of earlier quaternary sediments may explain the spatial pattern and morphological characteristics of drumlins in patagonia

altimetry of the venus cloud tops from the venus express observations 1 simultaneous observations of venus by visible and infrared thermal imaging spectrometer and venus monitoring camera onboard the venus express spacecraft are used to map the cloud top altitude and to relate it to the ultraviolet uv markings the cloud top altitude is retrieved from the depth of co2 absorption band at 1 6 m in low and middle latitudes the cloud top is located at 74 1 km it decreases poleward of 50 and reaches 63 69 km in the polar regions this depression coincides with the eye of the planetary vortex at the same latitude and hour angle cloud top can experience fast variations of about 1 km in tens of hours while larger long term variations of several kilometers have been observed only at high latitudes uv markings correlate with the cloud altimetry however the difference between adjacent uv dark and bright regions does not exceed several hundred meters surprisingly co2 absorption bands are often weaker in the dark uv features indicating that these clouds may be a few hundred meters higher or have a larger scale height than neighboring clouds ultraviolet dark spiral arms which are often seen at about 70 correspond to higher altitudes or to the regions with strong latitudinal gradient of the cloud top altitude cloud altimetry in the polar region reveals the structure that correlates with the thermal emission maps but is invisible in uv images this implies that the uv optically thick polar hood is transparent in the near ir

formation of mega scale glacial lineations on the dubawnt lake ice stream bed 1 size shape and spacing from a large remote sensing dataset abstract mega scale glacial lineations msgls are the largest flow parallel bedforms produced by ice sheets and are formed beneath rapidly flowing ice streams knowledge of their characteristics and genesis is likely to result in an improved understanding of the rate at which ice and sediment are discharged by ice sheets but there is little consensus as to how they are formed and there are few quantitative datasets of their characteristics with which to formulate or test hypotheses this paper presents the results of a remote sensing survey of 46 000 bedforms on the dubawnt lake palaeo ice stream bed focussing on a central transect of 17 038 that includes highly elongate bedforms previously described as msgls within this transect lineations exceed 10 km in length max 20 km and 23 have elongation ratios 10 1 max 149 1 highly elongate features are interspersed with much shorter drumlin like features but longer bedforms are typically narrower suggesting that their length develops more quickly than or at the expense of their width bedforms are broadly symmetrical in plan form and have a preferred lateral spacing of 50 250 m which implies a regular rather than random pattern of corrugations comparison with drumlins reveals that the more attenuated msgls simply extend the tail of the distribution of data rather than plotting as a separate population taken together this supports the idea of a subglacial bedform continuum primarily controlled by ice velocity but existing hypotheses of msgl formation are either not supported or are insufficiently developed to explain our observations rather we conclude that under conditions of rapid ice flow msgls attain their great length relatively quickly decades through a probable combination of subglacial deformation which attenuates ridges and erosional processes that removes material from between them

an investigation of the so2 content of the venusian mesosphere using spicav uv in nadir mode using the spicav uv spectrometer aboard venus express in nadir mode we were able to derive spectral radiance factors in the middle atmosphere of venus in the 170 320 nm range at a spectral resolution of r 200 during 2006 and 2007 in the northern hemisphere by comparison with a radiative transfer model of the upper atmosphere of venus we could derive column abundance above the visible cloud top for so2 using its spectral absorption bands near 280 and 220 nm so2 column densities show large temporal and spatial variations on a horizontal scale of a few hundred kilometers typical so2 column densities at low latitudes up to 50 n were found between 5 and 50 m atm whereas in the northern polar region so2 content was usually below 5 m atm the observed latitudinal variations follow closely the cloud top altitude derived by spicav ir and are thought to be of dynamical origin also a sudden increase of so2 column density in the whole northern hemisphere has been observed in early 2007 possibly related to a convective episode advecting some deep so2 into the upper atmosphere

drumlins products of controlled or uncontrolled glaciodynamic response abstract two schools of thought on the process of drumlin formation have recently developed that have created a controversy within this ara of glacial geology one hypothesis contends that drumlins are in the main developed within a soft mobile subglacial debris zone the other school argues that for those drumlins that contain primary deposited stratified sediment formation during catastrophic subglacial flood events is necessary a classification of subglacial bed types is presented that allows for the accommodation of both schools it is proposed that a new paradigm for subglacial research may be needed in order that a closer relationship between glaciodynamics and sedimentological processes be established in future attempts at explaining glacial processes and froms

subglacial floods beneath ice sheets subglacial floods jokulhlaups are well documented as occurring beneath present day glaciers and ice caps in addition it is known that massive floods have occurred from ice dammed lakes proximal to the laurentide ice sheet during the last ice age and it has been suggested that at least one such flood below the waning ice sheet was responsible for a dramatic cooling event some 8000 years ago we propose that drainage of lakes from beneath ice sheets will generally occur in a time periodic fashion and that such floods can be of severe magnitude such hydraulic eruptions are likely to have caused severe climatic disturbances in the past and may well do so in the future

sedimentation in a drumlin lee side subglacial wave cavity northwest ireland abstract lee side stratification sequences in a late pleistocene drumlin in northwest ireland are used to assess sedimentation patterns in subglacial wave cavities formed on the lee sides of drumlins three major subglacial cavity sub environments are identified 1 high energy divergent trough like closed conduit characterised by channel fill pebbly sand facies 2 low energy closed conduit characterised by alternating sand silts 3 trough margin dominated by stratified diamicts facies arrangements suggest two major transient states reflecting variations in subglacial meltwater flux the active phase showed meltwater flow directed across the drumlin apex suggesting complete uncoupling from the glacier bed supercavitation as flow velocities waned pebbly sand facies were deposited by in situ freezing of within conduit sediment admixtures the later quiescent phase was characterised by meltwater flow directed transverse to ice flow cavity shrinkage and concomitant deposition of subglacial sheetwash and cohesive sediment flows along cavity margins cavity closure resulted in complete coupling at the ice substrate interface with localised glaciotectonic loading on underlying lee side stratification sequences and concomitant till deposition these late stage sedimentation events at shinnan hill produced a very complex polygene endform which cannot be simply attributed to one formative process more realistically they reflect the influence of a rather complex and very dynamic subglacial system subject to complex spatial and temporal variations in subglacial erosion deposition and meltwater flux at the time of drumlinisation

the tekapo glacier new zealand during the last glacial maximum an active temperate glacier influenced by intermittent surge activity abstract quaternary glaciations have created impressive landform assemblages that can be used to understand palaeo glacier extent character and behaviour and hence past global and local glacier forcings however in the southern hemisphere and especially in new zealand the quaternary glacial landform record is relatively poorly investigated with regard to glaciological properties in this study a 1 m digital elevation model dem was generated from airborne lidar data and supplemented with aerial imagery and field observations to analyse the exceptionally well preserved glacial geomorphology surrounding lake tekapo new zealand we describe a rich suite of last glacial maximum lgm and recessional ice marginal subglacial supraglacial glaciofluvial and glaciolacustrine landform assemblages these represent two landsystems comprising i fluted till surfaces with low relief push moraine ridges and ii crevasse squeeze ridges zig zag eskers and attenuated lineations the former landsystem records the behaviour of an active temperate glacier and the latter landsystem which is superimposed upon and inset within the former strongly suggests intermittent surge phases the two landsystem signatures indicate a sequential change in ice marginal dynamics during recession that was likely to have been partially non climatically driven overall we present the first evidence of surge type glacier behaviour in new zealand

morphology internal structure and genesis of the burtnieks drumlin field northern vidzeme latvia abstract the burtnieks drumlin field is one of the largest in the baltic countries it occupies a broad and uneven bedrock macrodepression the uneven distribution of drumlins is related to the relief of the bedrock surface needle shaped drumlinoids occur in the proximal part of the drumlin field and they gradually merge into typical drumlin forms downglacier this morphologic change reflects the differences in their genesis as suggested by internal structure the cores of drumlins consist mainly of glaciotectonically deformed pleistocene sediment and in some places also weakly cemented dislocated middle devonian sandstone all of them are folded into linear anticlines trending parallel to the crests of drumlins these anticlines contain the remains of preceding subglacial deformation structures superimposed imbricate overthrusts cover the flanks of drumlins drumlinoids contain diapiric folds in their cores trending parallel to their axes the burtnieks drumlin field was formed during the last activation of the north vidzeme tongue and three main phases may be distinguished in the development of its glaciotectonic structures two alternative genetic hypotheses are proposed for the formation of this drumlin field both involving multiphase glaciotectonic deformation

cloud top structure of venus revealed by subaru comics mid infrared images abstract we have investigated the cloud top structure of venus by analyzing ground based images taken at the mid infrared wavelengths of 8 66 m and 11 34 m venus at a solar phase angle of 90 with the morning terminator in view was observed by the cooled mid infrared camera and spectrometer comics mounted on the 8 2 m subaru telescope during the period october 25 29 2007 the disk averaged brightness temperatures for the observation period are 230 k and 238 k at 8 66 m and 11 34 m respectively the obtained images with good signal to noise ratio and with high spatial resolution 200 km at the sub observer point provide several important findings first we present observational evidence for the first time of the possibility that the westward rotation of the polar features the hot polar spots and the surrounding cold collars is synchronized between the northern and southern hemispheres second after high pass filtering the images reveal that streaks and mottled and patchy patterns are distributed over the entire disk with typical amplitudes of 0 5 k and vary from day to day the detected features some of which are similar to those seen in past uv images result from inhomogeneities of both the temperature and the cloud top altitude third the equatorial center to limb variations of brightness temperatures have a systematic day night asymmetry except those on october 25 that the dayside brightness temperatures are higher than the nightside brightness temperatures by 0 4 k under the same viewing geometry such asymmetry would be caused by the propagation of the migrating semidiurnal tide finally by applying the lapse rates deduced from previous studies we demonstrate that the equatorial center to limb curves in the two spectral channels give access to two parameters the cloud scale height h and the cloud top altitude zc the acceptable models for data on october 25 are obtained at h 2 4 4 3 km and zc 66 69 km this supports previous results determined from spacecraft observations

the meltwater hypothesis for subglacial bedforms this paper presents an historical and in places informal account of the meltwater hypothesis which invokes enormous outburst floods for the formation of subglacial bedforms it begins with a brief discussion of the difficulties of determining processes of formation for landforms which are not seen in formation analogy provides a solution to these difficulties analogy between erosional marks at the bases of turbidites and drumlins which were the starting point for this hypothesis rests on the idea that inverted erosional marks at the ice bed are subsequently infilled to form drumlins field tests on the sedimentology architecture and landform associations of drumlins in the livingstone lake drumlin field are outlined before more extensive work on bedrock erosional forms and flood routes is introduced bedrock erosional forms played a central part in establishing the hypothesis since their form and ornamentation are confidently interpreted as fluvial their form and genesis are discussed mainly with reference to sites at french river and wilton creek ontario though some remarkable bedrock erosional forms in antarctica support their regional extent initially in the meltwater hypothesis drumlins were thought to be cavity fills and erosional drumlins were recognized later this development is shown to be central to the realization that drumlin composition may be inferred from drumlin form the scale of drumlin fields measured at about 10 3 km 2 and the magnitude of the inferred floods require that the flood events were regional regional scale flood tracts in ontario quebec alberta and the northwest territories extending over 1000 km in length and several hundred kilometers in width support this suggestion floods had they occurred would have caused rapid rates of sea level rise and may have changed climate through their effects on ocean stratification and sea surface temperatures the meltwater hypothesis covers a range of bedforms besides drumlins and bedrock erosional marksffluting rogen moraine hummocky terrain and transverse ridges recent work shows how these forms are best explained by the meltwater hypothesis the roles of water storage and release which underpin the theory of the meltwater hypothesis remain poorly understood r 2002 published by elsevier science ltd