remote sensing of desert dune forms by polarimetric synthetic aperture radar sar abstract this report describes remote sensing experiments using highly capable polarimetric synthetic aperture radar sar in preparation for the launch of the sir c x sar mission nasa s jpl airborne polarimetric sar airsar was deployed over many locations worldwide the report describes sar observations of desert dune fields in north america bolivia and australia acquired by airsar and in namibia acquired by sir c x sar the use of polarimetric and multiwavelength sar is reviewed and comments on the advantages of the various combinations are noted sar data are very useful in mapping dunes because of the ability to control illumination parameters such as look angle wavelength and polarization furthermore the unique responses of sar to surface roughness are found very useful in mapping dune forms for most sites the longer wavelengths p and l band at 68 cm and 24 cm are advantageous over the shorter c band at 5 6 cm providing better contrast overall copolarized channels hh and vv are found best for mapping the dunes and dune types when trying to discriminate active from inactive dunes cross polarized channels provide essential information on vegetation

flow and bedform dynamics in an alluvial channel with downward seepage abstract in this paper we report the findings from an experimental study on a parabolic cross sectional sand bed channel with uniform fine sand under no seepage and downward seepage conditions through experiments we observed that an alluvial channel which remained at threshold condition of sediment movement during the no seepage experiment started transporting sediments with the application of seepage in the downward direction shields stress of the threshold channel increased significantly from its critical value after the application of downward seepage which led to the deformation of the cross sectional shape and consequent development of the bedforms the role of turbulence in the development of bedforms has also been analyzed measures of turbulent statistics show that the time mean velocities and reynolds stresses were increased significantly with the application of downward seepage under the action of seepage conditions increase in the flux of streamwise turbulent kinetic energy in the streamwise direction was observed in the region close to the channel boundary also quadrant analysis exhibited an increase in the contributions from all the bursting events and the thickness of the sweep dominated zone in near bed region after the application of downward seepage a bedform tracking tool has been used to evaluate the variability in the geometry of bedforms we have classified these developing bedforms as current ripples and linguoid ripples according to their evolution with time under the downward seepage condition it has been further observed that the variation in shields stress and corresponding bedform geometry reached an equilibrium state in the presence of downward seepage when the experiments were run over a longer period of time 24 31 h

evidence for a till layer beneath storglaciaren sweden based on electrical resistivity measurements evidence for a till layer beneath storglaciaren sweden based on electrical resistivity measurements

martian surface winds insensitivity to orbital changes and implications for aeolian processes aeolian features observed on the surface of mars provide insight into current and potentially past surface wind systems in some cases the features are clearly transient and related to the lifting and settling of atmospheric dust other features like dunefields yardangs and ventifacts are more persistent and likely require significant time to form in this study we analyze the observed directions of selected aeolian features with the aid of the geophysical fluid dynamics laboratory mars general circulation model gcm initially we examine bright and dark streaks which have been observed to form in association with global dust storms the ability to match these features with mars gcm wind directions provides an important validation of the model more important we are able to define best fit seasons and local times for both types of features which provide the basis for extension and modification of the veverka et al 1981 model of bright and dark dust streak formation in addition these best fit times correspond well with the dark streak wind storm model of magalhaes and young 1995 the primary focus of this paper is to provide constraints on the range of mechanisms proposed to explain inconsistencies between current wind direction patterns and long term wind indicators for example the misalignment of rock tail and ventifact orientations at the mars pathfinder landing site specifically we assess whether changes in planetary obliquity precession or global dust opacity could significantly alter patterns of surface wind directions in all cases we find the seasonal and annual average wind direction patterns to be highly invariable while changes in the dust loading hence the partitioning of solar absorption between the surface and atmosphere and in the surface latitude of maximum solstitial insolation cause the vigor of the large scale circulation to increase especially the hadley cell the spatial patterns of the surface wind orientations remain essentially unchanged in the case of perihelion during northern summer opposite of the current perihelion position the northern summer hadley cell remains weaker than the southern summer cell despite the strengthened heating in the northern hemisphere taken together these results cast significant doubt on orbital explanations for surface wind changes it is thus suggested that significant changes in topography e g tharsis uplift true polar wander or climate e g the existence of a significantly thicker atmosphere or an ocean at some point in the past are more likely explanations for long term wind indicators such as the ventifact orientations at the mars pathfinder landing site

electrical conductivity measurements from the gisp2 and grip greenland ice cores the direct current electrical conductivity of glacial ice depends on its acidity1 3 and can also indicate changes in climate as ice formed in cold dusty periods has a high concentration of alkaline dust1 4 5 which significantly reduces the conductivity6 7 compared to warmer less dusty periods here we present electrical conductivity records for the greenland ice sheet project 2 gisp2 and greenland ice core project grip ice cores drilled 28 km apart to enable direct comparison of the results the upper parts of both records are consistent with previous evidence from other greenland cores4 8 12 for a stable greenland climate during the holocene and a series of warm events punctuating the last glacial period however there is a significant discrepancy between the two records in the bottom 10 of the cores calling into question recent reports of climate variability in the last interglacial4 8 and the penultimate glaciation8 at this stage it is too early to say what exactly is causing the discrepancy although ice flow may have introduced some discontinuities into the records further work will be necessary to establish how much climatic information it will eventually be possible to extract from the lower parts of the two cores

mean and turbulent flow structure during the amalgamation process in fluvial bed forms 1 fluvial channels present bed forms such as dunes and ripples that alter instantaneous hydrodynamics parameters such as flow velocities water surface profiles bed shear stresses and reynolds stresses and create turbulent coherent structures that are significantly different from those presented in flat bed conditions it is known that les based models are more suitable than rans models to reproduce the complex hydrodynamics around bed forms herein a les model is applied to describe the mean and turbulent flow structure under superimposed bed forms three cases were simulated run i train of ripples run ii superimposed bed forms and run iii amalgamated bed forms the les modeling was performed using a free surface condition to allow the model to develop undulations and boils on the water surface caused by effect of the bed forms some important conclusions from this study are the division of high and low shear stresses on the stoss side of the dune the progression of the flow field topology from run i and run iii and the type of turbulent coherent structures found in each stage the region of high shear stresses was related to turbulence production in which the streamwise velocity fluctuations where strips structures are related to streaks were associated to the modification of the bed morphology the turbulence horseshoes vortices thv were more frequent in run i than in the other two cases where streamwise rolls were more frequent finally the frequency of the bursting events increased from run i to run ii and decreased from run ii to run iii implications of detailed hydrodynamics into bed forms processes are also presented and discussed

interpretation of borehole inclinometer data a general theory applied to a new instrument borehole inclinometers are standard equipment for field glaciologists and are commonly used for investigating the flow law of ice and for measuring the spatial position of englacial and sub surface sensors the recent development at the university of british columbia ubc of a prototype inclinometer that employs a three component fluxgate magentometer to obtain a compass bearing has stimulated our interest in borehole inclinometry following a review of various approaches to glacier inclinometry we present a unified theory of data interpretation that can be applied to all inclinometers discuss the application of the theory to the ubc inclinometer and discuss the sensitivity of the theory to error in the data

spatial variability in the flow of a valley glacier deformation of a large array of boreholes measurements of the deformation of a dense array of boreholes in worthington glacier alaska show that the glacier moves with generally bed parallel motion strain in the 200 m deep valley glacier is constant near the surface but follows a nonlinear vertical profile below a depth of about 120 m by a depth of 180 m the octahedral strain rate reaches 0 35 yr 1 the three dimensional velocity field shows spatial complexity with significant deviations from plane strain despite relatively simple valley geometry in the vicinity of the 6 10 6 m 3 study volume no evidence was found for time varying deformation or movement along localized shear planes observations were made by repeatedly measuring the long axis geometry of 31 closely spaced boreholes over a 70 day period and three additional holes after 1 full year of deformation the holes were spaced 15 to 30 m apart installation and measurement of such a large number of boreholes required the development of a semiautomated hot water drilling system that creates straight and vertical boreholes with uniform walls the equipment and procedures enables borehole profiles to be measured without the use of hole casing inclinometry measurements collected in the holes were processed analyzed for error and visualized as a fully three dimensional data set the new methods offer unique insight into small scale spatial and temporal variations in the pattern of flow in a valley glacier

life death and afterlife of the extrusion flow theory extrusion flow describes any velocity field where maximum horizontal velocity occurs below the surface by 1914 viscous flow and basal sliding over rough beds were accepted concepts between the world wars there was little communication between naturalists describing complicated ice sheets and physicists studying fundamental processes controlling flow max demorest brought concepts from mechanics into glaciology and glacial geology however his extrusion flow theory to explain how ice flowed out of central greenland overlooked force imbalance rudolf streiff becker found an apparent large imbalance between ice flux discharged through a gate and net accumulation in the upstream catchment at claridenfirn switzerland because he underestimated uncertainty in ice depth he had to propose a strong undercurrent extrusion flow to evacuate the excess mass reassessment of his assumptions shows that extrusion was actually unnecessary however confluence of two lines of evidence for extrusion flow added stature to the concept in 1952 john nye showed that free extrusion flow was impossible due to force imbalance two forms of extrusion flow survive capped extrusion flow is possible on local scales where longitudinal stress gradients allow upper ice to move slowly and rigid body rotational flow can allow deeper ice to move faster without strain

water pressure and basal sliding on storglaciaren northern sweden the subglacial hydrology of the ablation area of storglaciaren a small valley glacier in northern sweden is dramatically affected by a subglacial ridge or riegel water pressures above this riegel are relatively constant while down glacier from it they vary significantly the lower part of the glacier accelerates in response to peaks in basal water pressure the upper part may be weakly coupled to the lower part during these peaks a power law fit of observed basal water pressures and measured surface velocities yields where u s is the surface velocity and p e is the effective water pressure ice overburden pressure minus subglacial water pressure data from findelengletscher reported by iken and bindschadler 1986 yield an identical exponent and a coefficient one order of magnitude larger the similar exponent implies that the process producing the velocity variations on both glaciers is similar the variations in velocity are inferred to be due to hydraulic jacking on both glaciers

spectral evidence for weathered basalt as an alternative to andesite in the northern lowlands of mars mineral abundances derived from the analysis of remotely sensed thermal emission data from mars have been interpreted to indicate that the surface is composed of basalt surface type 1 and andesite surface type 2 1 the global distribution of these rock types is divided roughly along the planetary dichotomy which separates ancient heavily cratered crust in the southern hemisphere basalt from younger lowland plains in the north andesite 1 but the existence of such a large volume of andesite is difficult to reconcile with our present understanding of the geological evolution of mars here we reinterpret martian surface rock lithologies using mineral abundances from previous work1 and new mineralogies derived from a spectral end member set representing minerals common in unaltered and low temperature aqueously altered basalts our results continue to indicate the dominance of unaltered basalt in the southern highlands but reveal that the northern lowlands can be interpreted as weathered basalt as an alternative to andesite the coincidence between locations of such altered basalt and a suggested northern ocean basin implies that lowland plains material may be composed of basalts weathered under submarine conditions or weathered basaltic sediments transported into this depocentre

the morphodynamics of fluvial sand dunes in the river rhine near mainz germany i sedimentology and morphology the dynamics of large isolated sand dunes moving across a gravel lag layer were studied in a supply limited reach of the river rhine germany bed sediments dune geometry bedform migration rates and the internal structure of dunes are considered in this paper hydrodynamic and sediment transport data are considered in a companion paper the pebbles and cobbles d50 of 10 mm of the flat lag layer are rarely entrained dunes consist of well sorted medium to coarse sand d50 of 0 9 mm small pebbles move over the dunes by overpassing but there is a degree of size and shape selectivity populations of ripples in sand d50 0 6 mm and small and large dunes are separated by distinct breaks in the bedform length data in the regions of 0 7 1 m and 5 10 m ripples and small dunes may have sinuous crestlines but primarily exhibit two dimensional planforms in contrast large dunes are primarily three dimensional barchanoid forms ripples on the backs of small dunes rarely develop to maximum steepness small dunes may achieve an equilibrium geometry either on the gravel bed or as secondary dunes within the boundary layer on the stoss side of large dunes secondary dunes frequently develop a humpback profile as they migrate across the upper stoss slope of large dunes diminishing in height but increasing in length as they traverse the crestal region however secondary dunes more than 5 m in length are rare the dearth of equilibrium ripples and long secondary dunes is probably related to the limited excursion length available for bedform development on the parent bedforms large dunes with lengths between 20 m and 100 m do not approach an equilibrium geometry a depth limitation rather than a sediment supply limitation is the primary control on dune height dunes rarely exceed 1 m high in water depths of 4 m dune celerity increases as a function of the mean flow velocity squared but this general relationship obscures more subtle morphodynamics during rising river stage dunes tend to grow in height owing to crestal accumulation which slows downstream progression and steepens the dune form during steady or falling stage an extended crestal platform develops in association with a rapid downstream migration of the lee side and a reduction in dune height these diminishing dunes actually increase in unit volume by a process of increased leeside accumulation fed by secondary dunes moving past a stalled stoss toe a six stage model of dune growth and diminution is proposed to explain variations in observed morphology the model demonstrates how the development of an internal boundary layer and the interaction of the water surface with the crests of these bedload dominated dunes can result in dunes characterized by gentle lee sides with weak flow separation this finding is significant as other studies of dunes in large rivers have attributed this morphological response to a predominance of suspended load transport

geometry and kinematics of dunes during steady and unsteady flows in the calamus river nebraska usa the geometry and kinematics of river dunes were studied in a reach of the calamus river nebraska during day long surveys dune height length steepness migration rate creation and destruction were measured concurrently with bedload transport rate flow depth flow velocity and bed shear stress within a survey individual dune heights lengths and migration rates were highly variable associated with their three dimensional geometry and changes in their shape through time notwithstanding this variability there were discernible changes in mean dune height length and migration rate in response to changing discharge over several days changes in mean dune height and length lagged only slightly behind changes in discharge therefore during periods of both steady and unsteady flow mean dune lengths were quite close to equilibrium values predicted by theoretical models mean dune steepnesses were also similar to predicted equilibrium values except during high falling flows when the steepness was above that predicted variations in mean dune height and length with discharge are similar to those predicted by theory under conditions of low mean dune excursion and discharge variation with a short high water period and long low water period however the calculated rates of change of height of individual dunes vary considerably from those measured rates of dune creation and destruction were unrelated to discharge variations contrary to previous results instead creations and destructions were apparently the result of local variations in bed shear stress and sediment transport rate observed changes in dune height during unsteady flows agree with theory fairly well at low bed shear stresses but not at higher bed shear stresses when suspended sediment transport is significant

age relationship of basaltic and andesitic surface compositions on mars analysis of high resolution tes observations of the northern hemisphere 1 previous mars global surveyor thermal emission spectrometer tes results have identified two principal surface compositions on mars basaltic surfaces are found primarily in the southern highlands while andesitic surfaces are found in the northern lowlands and in smaller concentrations distributed throughout the southern highlands in 1 pixel per degree composition maps the exact boundary between the basaltic and andesitic compositions is obscured by large amounts of equatorial surface dust in this work high resolution tes surface spectral data are used to identify and characterize isolated regions of basalt within the equatorial dust regions and northern lowlands generally between 20 s 60 n 0 360 w in an effort to better understand the nature of the boundary between the two compositions the purpose of refining this boundary is to more accurately determine the relationship of the compositional dichotomy with global surface morphology and derived crustal thickness results show that the basaltic surface composition is closely associated with the ancient cratered terrain morphology but is not well correlated with crustal thickness the northern extent of the tes basalt composition is also established with four exceptions there are no significant concentrations 30 surface cover of basalt greater than 400 km2 in area within the northern plains three are located within or adjacent to knobby terrain which has been suggested to be erosional remnants of the cratered highlands the fourth exception is in milankovic crater and may represent a local basalt flow or basaltic material excavated during crater formation results from this work suggest that there is a stratigraphic relationship between the basaltic and andesitic surface compositions with younger andesitic materials overlying older basaltic materials throughout the equatorial and northern plains regions

morphology and flow fields of three dimensional dunes rio parana argentina results from simultaneous multibeam echo sounding and acoustic doppler current profiling 1 most past studies of river dune dynamics have concentrated on two dimensional 2 d bed forms with constant heights and straight crest lines transverse to the flow and their associated turbulent flow structure this morphological simplification imposes inherent limitations on the interpretation and understanding of dune form and flow dynamics in natural channels where dune form is predominantly three dimensional for example studies over 2 d forms neglect the significant influence that lateral flows and secondary circulation may have on the flow structure and thus dune morphology this paper details a field study of a swath of 3 d dunes in the rio parana argentina a large 0 35 km wide 1 2 km long area of dunes was surveyed using a multibeam echo sounder mbes that provided high resolution 3 d detail of the river bed simultaneous with the mbes survey 3 d flow information was obtained with an acoustic doppler current profiler adcp revealing a complicated pattern of dune morphology and associated flow structure within the swath dune three dimensionality appears intimately connected to the morphology of the upstream dune with changes in crest line curvature and crest line bifurcations junctions significantly influencing the downstream dune form dunes with lobe or saddle shaped crest lines were found to have larger more structured regions of vertical velocity with smaller separation zones than more 2 d straight crested dunes these results represent the first integrated study of 3 d dune form and mean flow structure from the field and show several similarities to recent laboratory models of flow over 3 d dunes

thermal inertia of crater related wind streaks on mars data from the thermal emission spectrometer tes on board the mars global surveyor spacecraft are used to analyze the structure of and materials comprising crater related wind streaks comparisons of high resolution tes albedo and tes based thermal inertia values within and adjacent to the streaks allow us to constrain the properties of the streaks and gain insight into their physical structure the majority of the analyzed type i bright depositional streaks are distinct from the surrounding terrain in albedo but not in thermal inertia we conclude that these streaks consist of thin deposits of bright material greater than 1 pm thick but less than 1 3 mm thick the majority of the analyzed type i dark erosional streaks identified from viking images are now indistinct from the surrounding terrain in both albedo and thermal inertia we conclude that these streaks have been covered by a thin deposit of bright material greater than 1 m thick but less than 1 3 mm thick all of the analyzed type ii dark depositional streaks are distinct from the surrounding terrain in both albedo and thermal inertia we conclude that these streaks consist of deposits greater than a few centimeters thick in this case we were also able to use the thermal inertia values to estimate the particle sizes of the deposited material the values correspond to a broad range of sand sized particles easily mobilized by wind supporting the deflation deposition theory of type ii streak formation

reconstructing random topography from preserved stratification one of the fundamental problems of interpreting the sedimentary record is reconstructing the original heights of palaeotopographical features such as bedforms or river channels this requires an understanding of the relationship between topography and set thickness but at present an exact theory exists only for periodic topography of uniform height the applicability of this simple theory is severely limited by the random variability characteristic of many sedimentary systems in this paper we develop an exact theory for the probability density function pdf of sets generated from topography of random height we focus on the limiting case of zero net deposition in order to provide a lower bound for the set thickness and derive an analytical set thickness pdf that is determined by one parameter of the pdf for topographical height this parameter measures the breadth of the tail of the topographical pdf the mean set thickness is 0 8225 for bedforms and 1 645 for river channels if the topographical height is gamma distributed the preservation ratio defined as mean thickness of preserved sets mean topographical height is 0 8225 r2 for bedforms and 1 645 r2 for river channels where r is the coefficient of variation standard deviation mean of the generating topography in a comparison with data from laboratory current ripples our analytical predictions compare well with observations of both mean set thickness and thickness distribution the preservation ratio for the ripples is about 0 5 whilst measured dune heights give a preservation ratio of about 0 12 depth data from two modern braided streams yield preservation ratios ranging from 0 4 to 0 75 as more data on the distributions of topographical height in modern environments become available calculations such as these should help provide reliable error bounds for quantitative topographical reconstruction

first in situ investigation of a dark wind streak on mars 1 prominent low albedo wind streaks issue from embayments at the north end of victoria crater in meridiani planum the site of surface investigations by the mars exploration rover opportunity opportunity was sent to examine the darkest of these wind streaks and compare it to the adjacent soil in the brighter corridor between the streaks two nearby sites inside and outside of the streak were selected for visible and infrared remote sensing and for elemental abundance measurements and images of the microscopic soil morphology the rover was next sent to study the interaction of the wind streak with an obstacle a small rock near the source of the streak opportunity s observations suggest that the victoria wind streaks are deposits of basaltic sand blown out of the crater from the dark dunes nestled below the crater rim particularly at the base of the alcove leading up to the darkest streak no local sources of sand have been identified within the victoria crater wall rock suggesting that the sand is supplied from outside the crater and is presently escaping its temporary topographic trap this process presents a possible explanation for the serrated margin of victoria crater through abrasion of the soft rock as trapped sands are blown out of the crater and carve alcoves under various seasonal winds some indication of the rate of activity of these wind streaks will be provided by continued monitoring of the erasure of the rover s tracks

effect of sediment transport boundary conditions on the numerical modeling of bed morphodynamics abstractexperimental sediment transport and river morphologic studies in laboratory flumes can use two sediment supply methods an imposed feed at the upstream end or a recirculation of sediment f

bed form initiation from a flat sand bed 1 bed form initiation in unidirectional flow is examined on a flat bed composed of a homogeneous 0 5 mm sand velocity profiles taken prior to bed form development indicate that the examined flows are typical of fully turbulent uniform open channel flows under these conditions two separate modes of bed form initiation are observed defect and instantaneous initiation defect initiation occurs at lower flow stages where sediment transport is sporadic and patchy and is characterized by defect propagation associated with flow separation instantaneous initiation occurs at larger flow strengths where sediment transport is general and widespread this form of bed form initiation begins with the imprinting of a cross hatch pattern on the flat sediment bed which leads to chevron shaped forms that migrate independently of the initial pattern the chevrons eventually align to form incipient crest lines this mode of bed form initiation does not appear to be linked to turbulent structures but integral scales derived from velocity measurements prior to bed form development are similar to the initial bed form length scales

extrusion flow demonstrated by bore hole deformation measurements over a riegel storglaciaren sweden inclinometry measurements in a 126 m bore hole slightly down glacier from the crest of a riegel on storglaciaren showed what appears to be indisputable extrusion flow during the last 3 weeks of july 1984 the velocity at the bed was about five times that at the surface and lay in a direction deviating 50 60 from that at the surface the increase in velocity with depth began more than 50 m above the bed in august and the first half of september the flow returned nearly to normal with only a slight tendency toward extrusion the flow in july appeared to be related to a period of large diurnal water pressure variation and cavity opening at the bed up glacier from the riegel decoupling of the ice from the bed on the lowest parts of the riegel may have permitted the extrusion the return to more normal conditions in august appears to have been related to a decrease in ice flux over the riegel and a widening of the zone of decoupling

the sedimentology and dynamics of crater affiliated wind streaks in western arabia terra mars and patagonia argentina abstract wind streaks comprise recent aeolian deposits that have been extensively documented on venus earth and mars martian wind streaks are among the most abundant surface features on the planet and commonly extend from the downwind margins of impact craters previous studies of wind streaks emerging from crater interior deposits suggested that the mode of emplacement was primarily related to the deposition of silt sized particles as these settled from plumes we have performed geologic investigations of two wind streaks clusters one situated in western arabia terra a region in the northern hemisphere of mars and another in an analogous terrestrial site located in southern patagonia argentina where occurrences of wind streaks emanate from playas within maar craters in both these regions we have identified bedforms in sedimentary deposits on crater floors along wind facing interior crater margins and along wind streaks these observations indicate that these deposits contain sand sized particles and that sediment migration has occurred via saltation from crater interior deposits to wind streaks in arabia terra and in patagonia wind streaks initiate from crater floors that contain lithic and evaporitic sedimentary deposits suggesting that the composition of wind streak source materials has played an important role in development spatial and topographic analyses suggest that regional clustering of wind streaks in the studied regions directly correlates to the areal density of craters with interior deposits the degree of proximity of these deposits and the craters rim to floor depths in addition some but not all wind streaks within the studied clusters have propagated at comparable yearly earth years rates extensive saltation is inferred to have been involved in its propagation based on the studied terrestrial wind streak that shows ripples and dunes on its surface and the martian counterpart changes orientation toward the downslope direction where it extends into an impact crater

new views of mars eolian activity materials and surface properties three vignettes from the mars global surveyor mars orbiter camera prior to the mars global surveyor mgs mission a very general view had emerged in which martian surface materials were seen as consisting of a mixture of bright dust dark sand and rocks the configuration of these materials and the winds that transport and deposit sand and dust have been thought to be directly linked to the albedo patterns that have been observed on mars for centuries high spatial resolution images 1 4 20 m pixel obtained by the mgs mars orbiter camera moc between september 15 1997 and july 4 1999 provide new information about the physical nature of the windblown material on the martian surface and show that the pre mgs view was much too simple in addition to bright dust and dark sand moc images show evidence of bright sediment that can be transported by saltation e g sand and dark material that can be transported in suspension e g silt new views of eolian wind streaks in daedalia planum show that part of this region thought to be mantled by bright dust based upon viking and mariner observations is instead covered by a thin veneer of bright windblown sand moc images of sinus sabaeus and parts of syrtis major two regions thought to be sandy based upon viking era observations exhibit thick mantles that are inferred to consist of fine grained sediment deposited from eolian suspension low albedo wind streaks in western arabia terra are also dark mantles and their association with eroded crater floors and megaripples dunes on these floors suggest that these particular wind streaks are deposits of silt sized material that was only briefly suspended before settling to the surface moc images also show evidence that some eolian dunes are active on mars today i e in 1998 and 1999 the evidence for activity is largely based upon wind and avalanche induced streaks superposed on or eroded into seasonal frost on high latitude dune fields moc images show that some other dunes are inactive but the albedo of dunes relative to surrounding terrain is not a good indicator of dune activity because some inactive dunes are not mantled by dust inactive dunes are best identified by superposed features such as impact craters landslide deposits and yardangs

numerical evaluation of the effects of planform geometry and inflow conditions on flow turbulence structure and bed shear velocity at a stream confluence with a concordant bed this study numerically investigates the effects of variations in inflow conditions and planform geometry on large scale coherent flow structures and bed friction velocities at a stream confluence with natural bathymetry and concordant bed morphology several numerical experiments are conducted in which either the kelvin helmholtz mode or the wake mode dominates within the mixing interface mi between the two confluent streams as the junction angle and alignments of the tributaries are altered in the kelvin helmholtz mode the mi contains mostly corotating vortices driven by the mean transverse shear across the mi while in the wake mode the mi contains counterrotating vortices forming by the interaction of the separated shear layers on the two sides of a zone of stagnant fluid near the junction corner a large angle between the two incoming streams is not necessary for the development of strongly coherent streamwise oriented vortical sov cells in the immediate vicinity of the mi results show that such sov cells can develop and produce high bed friction velocities even for cases with a low angle between the two tributaries and for cases where the downstream channel is approximately aligned with the axes of the two tributaries low curvature cases sov cells tend not to develop only when the incoming streams are parallel and aligned with the downstream channel junction angle of zero and the incoming flows produce a strong kelvin helmholtz mode under such conditions quasi 2 d mi vortices play the primary role in mixing and the production of high bed shear velocities simulations with and without natural bed morphology local bank line irregularities indicate that planform geometry and inflow conditions primarily govern the development of coherent flow structures but that bathymetric and bank line effects can locally modify details of these structures

on the relationship between flow and suspended sediment transport over the crest of a sand dune rio parana argentina the links between large scale turbulence and the suspension of sediment over alluvial bedforms have generated considerable interest in the last few decades with past studies illustrating the origin of such turbulence and its influence on flow resistance sediment transport and bedform morphology in this study of turbulence and sediment suspension over large sand dunes in the rio parana argentina time series of three dimensional velocity and at a point suspended sediment concentration and particle size were measured with an acoustic doppler current profiler and laser in situ scattering transmissometer respectively these time series were decomposed using wavelet analysis to investigate the scales of covariation of flow velocity and suspended sediment the analysis reveals an inverse relationship between streamwise and vertical velocities over the dune crest where streamwise flow deceleration is linked to the vertical flux of fluid towards the water surface in the form of large turbulent fluid ejections regions of high suspended sediment concentration are found to correlate well with such events the frequencies of these turbulent events have been assessed from wavelet analysis and found to concentrate in two zones that closely match predictions from empirical equations such a finding suggests that a combination and interaction of vortex shedding and wake flapping changing length of the lee side separation zone are the principal contributors to the turbulent flow field associated with such large alluvial sand dunes wavelet analysis provides insight upon the temporal and spatial evolution of these coherent flow structures including information on the topology of dune related turbulent flow structures at the flow stage investigated the turbulent flow events and their associated high suspended sediment concentrations are seen to grow with height above the bed until a threshold height ca 0 45 flow depth is reached above which they begin to decay and dissipate

preliminary analysis of shuttle radar laboratory srl 1 data to study aeolian features and processes in april 1994 the shuttle radar laboratory srl 1 obtained quad polarization data in l band spl lambda 24 cm and c band spl lambda 5 6 cm and vv polarized data in x band spl lambda 3 cm preliminary analyses show that radar backscatter coefficients spl sigma sup 0 can be used to map the aerodynamic roughness parameter z sub 0 over large areas from orbit as demonstrated by comparisons with measurements of z sub 0 obtained in the field although all wavelengths and polarizations show fairly good correlations with z sub 0 r 0 78 l band hv shows the best relationship r 0 81 this result has potential use in regional studies of sand and dust transport modeling atmospheric circulation and general climate studies srl images of aeolian landforms were also studied including dunes sand sheets and wind streaks dunes in the stovepipe wells area of death valley were clearly visible on l band hv images but not detected on c band images in the same area l band penetrated a sand sheet to reveal a buried fault scarp l band images in namibia showed the classic linear dunes near gobabeb and also revealed previously undetected sets of cross dunes wind streaks were imaged in several areas including namibia where streaks are associated with the impact crater roter kamm these features enable mapping of near surface wind patterns

influence of debris rich basal ice on flow of a polar glacier at taylor glacier a cold based outlet glacier of the east antarctic ice sheet observed surface speeds in the terminus region are 20 times greater than those predicted using glen s flow law for cold 17 c thin 100 m ice rheological properties of the clean meteoric glacier ice and the underlying deformable debris rich basal ice can be inferred from surface velocity and ablation rate profiles using inverse theory here with limited data we use a two layer flowband model to examine two end member assumptions about the basal ice properties 1 uniform softness with spatially variable thickness and 2 uniform thickness with spatially variable softness we find that the basal ice contributes 85 98 to the observed surface velocity in the terminus region we also find that the basal ice layer must be 10 15 m thick and 20 40 times softer than clean holocene age glacier ice in order to match the observations because significant deformation occurs in the basal ice our inverse problem is not sensitive to variations in the softness of the meteoric ice our results suggest that despite low temperatures highly deformable basal ice may dominate flow of cold based glaciers and rheologically distinct layers should be incorporated in models of polar glacier flow

wind streaks on venus clues to atmospheric circulation magellan images reveal surface features on venus attributed to wind processes sand dunes wind sculpted hills and more than 5830 wind streaks have been identified the streaks serve as local wind vanes representing wind direction at the time of streak formation and allowing the first global mapping of near surface wind patterns on venus wind streaks are oriented both toward the equator and toward the west when streaks associated with local transient events such as impact cratering are deleted the westward component is mostly lost but the equatorward component remains this pattern is consistent with a hadley circulation of the lower atmosphere

large eddy simulation of turbulent flow over a fixed two dimensional dune turbulent open channel flow over a two dimensional dune is studied using an established large eddy simulation code the free surface is approximated as a shear free boundary turbulence statistics and instantaneous flow structures are examined numerical results from two computational grids agree with each other and are also in good agreement with recently obtained experimental data the mean velocity profiles show significant changes along the dune and there is no region that conforms to the standard law of the wall profiles of the reynolds stresses show distinct peaks marking the shear layer that originates from flow separation at the dune crest secondary peaks found further from the dune are ascribed to the shear layer over the upstream dune details of the separated flow and development of the flow after reattachment are well predicted quadrant analysis of the reynolds shear stress shows that turbulent ejections dominate the near wall motions complex water surface flow structures are visualized

structure of flow over alluvial bedforms an experiment on linking field and laboratory methods this paper presents results of a field study designed to examine the structure of flow over mobile and fixed bedforms in a natural stream and to compare the results with findings of previous laboratory studies within the framework of double time space averaging approach measurements of turbulence were obtained in a small river in illinois usa over a fine spatial grid of sampling points above a mobile sandy bedform and its artificially moulded replica flow structure over the artificial bedform is similar to that observed in laboratory studies but is markedly different from the flow structure over natural bedforms these differences are most pronounced in the roughness sublayer whereas flow in the logarithmic layer over natural and artificial sand waves is fairly similar and exhibits spatial uniformity the double time space averaged distributions of turbulence statistics conform to the multilayer model of flow structure over bedforms mean velocity distributions indicate neither classical flow recirculation nor substantial reduction of velocities in the lee of bedform crests however vertical patterns of turbulence statistics over depth suggest that stacked wakes similar to those observed in laboratory studies exist above the bedforms thus despite the absence of flow separation wake development seems to be induced by the systematic influence of upstream bedforms on the vertical structure of turbulence copyright 2006 john wiley sons ltd

red violet contrast reversal on mars significance for eolian sediments abstract albedo markings on mars can exhibit reversed contrast with their surroudings when imaged in red and violet light a complete search of viking orbiter images shows this phenomenon on scales less than 300 km is restricted to specific eolian features intracrater deposits and wind streaks originating from the deposits contrast reversal is not found between features such as lava flows of different ages that might expose different materials without a largely eolian influence laboratory simulations suggest that iron oxides are the most likely materials involved in contrast reversal on the martian surface red violet contrast reversal is achieved easily but not exclusively between samples from which very fine particles m in diameter have been removed and corresponding samples in which larger grains are coated by such fine particles substantial particle size dependent albedo and color viriations exist for material which can be carried in suspension on mars m thus all fine grained eolian deposits on mars need not be the same as the brighter parts of arabia which have colors and albedos similar to the fine m component of martian dust storms the observed contrast reversal characteristics and colors of the intracrater dunes and related sediments can be explained readily if they are essentially free of adhering dust as would be the case if such eolian features were subject toactive saltation

magellan initial analysis of venus surface modification initial magellan observations reveal a planet with high dielectric constant materials exposed preferentially in elevated regions with high slopes ejecta deposits extending up to 1000 kilometers to the west of several impact craters windblown deposits and features in areas where there are both obstacles and a source of particulate material and evidence for slow steady degradation by atmosphere surface interactions and mass movements

aeolian sediment transport pathways and aerodynamics at troughs on mars 1 interaction between wind regimes and topography can give rise to complex suites of aeolian landforms this paper considers aeolian sediment associated with troughs on mars and identifies a wider range of deposit types than has previously been documented these include wind streaks falling dunes lateral dunes barchan dunes linear dunes transverse ridges sand ramps climbing dunes sand streamers and sand patches the sediment incorporated into these deposits is supplied by wind streaks and ambient planitia sources as well as originating within the trough itself notably from the trough walls and floor there is also transmission of sediment between dunes the flow dynamics which account for the distribution of aeolian sediment have been modeled using two dimensional computational fluid dynamics the model predicts flow separation on the upwind side of the trough followed by reattachment and acceleration at the downwind margin the inferred patterns of sediment transport compare well with the distribution of aeolian forms model data indicate an increase of wind velocity by 30 at the downwind trough margin this suggests that the threshold wind speed necessary for sand mobilization on mars will be more frequently met in these inclined locations

interactions between bed forms topography turbulence and transport 1 results are presented examining the interaction between two sandy bed forms under low sediment transport conditions in a small laboratory flume the initial artificially made bed forms were out of equilibrium with the flow field temporal evolution of bed forms was monitored using time lapse photography in order to characterize bed form adjustment to the imposed flow velocity measurements were collected using an acoustic doppler velocimeter to characterize both mean flow and turbulence associated with different bed form geometries sandy bed forms all had identical initial geometries however the initial distance between bed form crests was varied between experiments overall deformation of the bed varied as a function of initial bed form spacing however bed forms evolved unpredictably as periods of relatively slow change were punctuated by periods of rapidly changing geometry subtle changes in bed form trough geometry were found to have a strong influence on turbulence and therefore sediment transport comparison with field studies suggests that the mechanisms described herein are active in natural systems

subglacial basins their origin and importance in glacial systems and landscapes closed topographic basins are found beneath contemporary ice masses and within the footprint of former ice masses in all glaciated regions we present the first integrated review of subglacial basin occurrence and formation and the implications of such basins for glaciological processes and the evolution of landscape our purpose is to motivate research in areas where understanding of basin origin and process significance is weak basins on the order of 10 102 m deep and 102 103 m long are produced by glacial erosion of subglacial rock and or sediment and are known as overdeepenings outlet and valley glaciers can overdeepen their beds far below sea level or local fluviatile base level larger basins typically in ice sheet contexts may have a pre glacial usually tectonic origin subglacial basins are important glaciologically because they require ice water and sediment to ascend an adverse subglacial slope in order to exit the glacial system the efficiency of which is dependent upon the gradient of the adverse slope and that of the ice surface basins thus influence subglacial drainage system morphology and transmissivity the thickness and distribution of basal ice and sediment layers and the mechanisms and dynamics of ice flow adverse gradients that exceed 11 times that of the ice surface may even permit the formation of subglacial lakes we speculate that in comparison to ice masses with few or no subglacial basins those with numerous or very large basins may respond to climatic changes with unexpected vigour in addition erosion rates and transport pathways of water and sediment through the glacial system and the expression of these processes in the sediment and landform record may be unexpectedly complex further our review shows that in a warming climate ice masses resting on adverse slopes will be vulnerable to rapid and potentially catastrophic retreat new lakes in subglacial basins exposed by mountain glacier retreat will present an increasing hazard and subglacial lakes may drain catastrophically on even longer time scales we speculate that the glacial excavation and post glacial filling of basins in mountainous regions should contribute importantly to climate related changes in isostasy and relief although the controls on overdeepening and their influence on other glacial and landscape processes remain uncertain we hypothesise that overdeepened glacial systems reflect an equilibrium ice bed geometry that maximises the efficiency of ice discharge improved understanding of overdeepening processes especially overdeepened bed hydrology is therefore necessary to understand fully the dynamic behaviour of valley and outlet glaciers and thus the fate of earth s largest ice masses

aeolian features on venus preliminary magellan results magellan synthetic aperture radar data reveal numerous surface features that are attributed to aeolian or wind processes wind streaks are the most common aeolian feature they consist of radar backscatter patterns that are high low or mixed in relation to the surface on which they occur a data base of more than 3400 wind streaks shows that low backscatter linear forms long narrow streaks are the most common and that most streaks occur between 17 s to 30 s and 5 n to 53 n on smooth plains moreover most streaks are associated with deposits from certain impact craters and some tectonically deformed terrains we infer that both of these geological settings provide fine particulate material that can be entrained by the low velocity winds on venus turbulence and wind patterns generated by the topographic features with which many streaks are associated can account for differences in particle distributions and in the patterns of the wind streaks thus some high backscatter streaks are considered to be zones that are swept free of sedimentary particles to expose rough bedrock other high backscatter streaks may be lag deposits of dense materials from which low density grains have been removed dense materials such as ilmenite or pyrite have dielectric properties that would produce high backscatter patterns wind streaks generally occur on slopes 2 and tend to be oriented toward the equator consistent with the hadley model of atmospheric circulation in addition to wind streaks other aeolian features on venus include yardangs and dune fields the aglaonice dune field centered at 25 s 340 e covers 1290 km 2 and is located in an ejecta flow channel from the aglaonice impact crater the meshkenet dune field located at 67 n 90 e covers 17 120 km 2 in a valley between ishtar terra and meshkenet tessera wind streaks associated with both dune fields suggest that the dunes are of transverse forms in which the dune crests are perpendicular to the prevailing winds dunes on venus signal the presence of sand size 60 to 2 000 m grains the possible yardangs are found at 9 n 60 5 e about 300 km southeast of the crater mead although most aeolian features are concentrated in smooth plains near the equator the occurrence of wind streaks is widespread and some have been found at all latitudes and elevations they demonstrate that aeolian processes operate widely on venus the intensity of wind erosion and deposits however varies with locality and is dependent on the wind regime and supply of particles

hydrodynamics of mountain river confluences and its relationship to sediment transport mountain confluences are characterized by narrow and steep tributaries that provide important sediment load to the confluence whereas themain channel supplies the dominant flow discharge this results in a marked bed discordance between the tributary and main channel which induces key differences in the hydromorphodynamics of the confluence when compared to concordant bed and some common types of discordant bed confluences the processes of initiation and maintenance of the morphology of confluences are still unknown and research linking morphodynamics and hydrodynamics of river confluences is required to understand these phenomena in this paper eddy resolving simulations based on laboratory experiments made in a live bed model of a mountain river confluence are used to provide a detailed description of flow hydrodynamics and implications for morphodynamics the test case study corresponds to a confluence with an angle of 70 numerical simulations are performed for two extreme bathymetric conditions those at the start of the experiment and when equilibriummorphological conditions are reached results of the simulations and experimental observations are used tomake inferences on erosion mechanisms during the initial and final states of the erosion deposition process the relationship between the coherent structures present in the near bed region in the instantaneous and mean flow fields and sediment entrainment transport is described the present paper demonstrates the critical role played by large scale turbulence generated in the shear layers forming on the side of the tributary flow as it enters the main channel by the main vortex forming over the discordant bed region surrounding the downstream end of the tributary as well as by several near bed vortices induced by the deflection of the tributary flow by the incoming flow in the main channel the predicted patterns of bed shear stress are linked to pathways of sediment movement

the western qaidam basin as a potential martian environmental analogue an overview the early martian environment is interpreted as warmer and wetter before a significant change in its global climatic conditions irreversibly led to the current hyper arid environments this transition is one of the most intriguing processes of martian history the extreme climatic change is preserved in the salt deposits desiccated landscapes and geomorphological structures that were shaped by the evaporation of water however until a manned journey to mars is feasible many martian materials morphological structures and much of its evolutionary history will continue to be poorly understood in this regard searching and investigating martian analogues is still meaningful to find an earth environment with a whole set of martian structures distributed at a scale comparable to mars is even more important to test landing crafts and provide optimized working parameters for rovers the western qaidam basin in north tibetan plateau is such a martian analogue the area harbors one of the most extreme hyper arid environments on earth and contains a series of ancient lakes that evaporated at different evolutionary stages during the rise of the tibetan plateau large quantities of salts and geomorphological features formed during the transition of warmer and wet to colder and dry conditions provide unique references to study the modern martian surface and interpret the orbital data we present numerous similarities and results of investigations that suggest the qaidam basin as a potential analogue to study modern geomorphic processes on mars and suggest that this is an essential site to test future mars sample return missions

is the longitudinal profile of storglaciaren northern sweden in balance with the present climate the main perturbation in the mass balance of storglaciaren during the twentieth century was caused by a sudden 1 c increase in the summer mean temperature around 1910 later perturbations of the climate have been of minor importance in relation to the mass balance annual field surveys suggest that the mass budget on storglaciaren has been in near balance for the last 15 years because of this major step like change we can establish the validity of theoretical models giving response times for storglaciaren of the order of 50 years according to these models storglaciaren could by now have reached a profile in balance with the present climate to study this problem the emergence velocity was calculated and compared with the net balance the result shows that the emergence velocity either balances or exceeds the net balance for the entire tongue except for the lowermost part where it decreases to about half of the net balance a slight further recession of the front position would thus be expected with today s climate calculated balance velocities also suggest that most of the present profile is close to a steady state profile if the mean annual sliding velocity is about 50 of the surface velocity lower sliding velocities would imply a thickening

earth aeolian wind streaks comparison to wind data from model and stations wind streak is a collective term for a variety of aeolian features that display distinctive albedo surface patterns wind streaks have been used to map near surface winds and to estimate atmospheric circulation patterns on mars and venus however because wind streaks have been studied mostly on mars and venus much of the knowledge regarding the mechanism and time frame of their formation and their relationship to the atmospheric circulation cannot be verified this study aims to validate previous studies results by a comparison of real and modeled wind data with wind streak orientations as measured from remote sensing images orientations of earth wind streaks were statistically correlated to resultant drift direction rdd values calculated from reanalysis and wind data from 621 weather stations the results showed good agreement between wind streak orientations and reanalysis rdd r 0 78 a moderate correlation was found between the wind streak orientations and the weather station data r 0 47 a similar trend was revealed on a regional scale when the analysis was performed by continent with r ranging from 0 641 in north america to 0 922 in antarctica at sites where wind streak orientations did not correspond to the rdds i e a difference of 45 seasonal and diurnal variations in the wind flow were found to be responsible for deviation from the global pattern the study thus confirms that earth wind streaks were formed by the present wind regime and they are indeed indicative of the long term prevailing wind direction on global and regional scales

mars aeolian features and wind predictions at the terra meridiani and isidis planitia potential mars exploration rover landing sites 1 orientations of 11 497 aeolian wind related features at the potential mars exploration rover mer landing site in isidis planitia reflect formative winds from the northwest and are consistent with strong morning winds predicted by a regional scale atmospheric model for mars orientations of 3296 aeolian features mapped at the terra meridiani potential mer site suggest multidirectional wind patterns the results for the terra meridiani site are consistent with gentle winds which change direction as a function of martian season predicted by a general circulation model and erratic winds that occur diurnally predicted by a regional scale atmospheric model results for both sites give confidence that the predictions from the atmospheric models are basically correct when time of day and local topography are taken into account

low albedo surfaces and eolian sediment mars orbiter camera views of western arabia terra craters and wind streaks 1 high spatial resolution 1 5 to 6 m pixel mars global surveyor mars orbiter camera images obtained september 1997 to june 2001 show that each of the large dark wind streaks of western arabia terra originate at a barchan dune field on a crater floor the streaks consist of a relatively thin 1 m coating of sediment deflated from the dune fields and their vicinity in most cases this sediment drapes over a previous mantle that more thickly covers nearly all of western arabia terra no concurrent eolian bedforms are found within the dark streaks nor do any dunes climb up crater walls to deliver sand via saltation to the streaks the relations between dunes wind streak and subjacent terrain imply that dark toned grains finer than those that comprise the dunes are lifted into suspension and carried out of the craters to be deposited on the adjacent terrain previous eolian physics and thermal inertia studies suggest that under modern martian conditions such grains likely include silt 3 9 62 5 m very fine sand 62 5 125 m and possibly fine sand to 210 m the streaks change in terms of extent relative albedo and surface pattern over periods measured in years however through june 2001 very little evidence for recent eolian activity dust plumes storms dune movement was observed

surface properties of the pettit wind streak on mars implications for sediment transport abstract pettit crater 12 n 174 w is associated with a complex wind streak consisting of both type i bright streak and type ii dark streak materials broadband albedo measurements of the streak indicate a minimum of 20 and a maximum of 32 with 27 on the surrounding plains the darkest materials have the highest thermal inertias which can be related to an effective grain diameter typical of medium sand most of the dark streak materials have thermal inertias representative of fine sand the material most easily set in motion by the wind on mars the bright portions of the streak have thermal inertias higher than that of the surrounding plains the bright streak values are representative of very fine sand differences between temperatures measured at 11 and 20 m indicate there is no difference in the areal abundance of unresolved high thermal inertia materials e g blocks bedrock between the pettit streak and the surrounding plains the dark streak material is consistent with models involving sand saltation and transport but the bright streak thermal inertia is not consistent with a volumetrically significant enhancement of unconsolidated dust in the streak

instruments and methods borehole logging with an eight arm caliper inclinometer probe a newly designed eight arm caliper inclinometer probe for borehole logging is presented the caliper sounding gives eight points of cross sections of the borehole at 1 cm intervals along its axis regression circles and ellipses are calculated and used as obvious hypotheses to be tested in order to obtain information on strain rates in the horizontal planes and isotropic or anisotropic borehole closure the scratching of identifiable marks into the wall of the borehole enables material displacement to be tracked in particular in the vertical direction thus providing information for determining vertical strain rates along the borehole measurements in two boreholes drilled on high altitude glaciers in the swiss alps are used to demonstrate both the potential and the limitations of the probe and of the mathematical methods presented

character of the englacial and subglacial drainage system in the lower part of the ablation area of storglaciaren sweden as revealed by dye trace studies

tv video observations of bed and basal sliding on storglaciaren sweden four boreholes in storglaciaren a small valley glacier in northernsweden were inspected with a video camera in two of the boreholes the apparentglacier bed was filmed in one borehole the bed was found to be composed of softsediment but in the other it consisted of bedrock in the latter the camera moved5 6 mm relative to the bed during an 80 min period the recorded camera movementshowed a background motion which is in the expected range of basal sliding superimposed on the background motion a jerky motion of a high speed spike wasfound the jerky motion is interpreted as a stress release induced by local topographyat the ice bed interface

initial stages of erosion and bed form development in a turbulent flow around a cylindrical pier 1 bed load transport and erosion in fine sediment beds are mainly driven by the dynamics of the near bed turbulent flow in situations when the shear stress is not sufficiently high to produce significant transport the presence of an obstacle can initiate erosion and trigger the development of bed forms which are produced by the emergence of the turbulent horseshoe vortex thv system we develop a numerical model to investigate the initial stages of erosion and the development of ripples produced by the thv system in the vicinity of a surface mounted cylindrical pier the flow is simulated using the detached eddy simulation approach which has been shown to accurately resolve most of the turbulent stresses produced by the thv to compute the erosion the exner equation is coupled to a new bed load transport model that directly incorporates the effect of the instantaneous flow field on sediment transport the morphodynamic model is integrated simultaneously with the flow equations using an arbitrary lagrangian eulerian method for moving boundaries even though the time rate of scour is slower compared to the observations the computed results exhibit essentially all the dynamics of erosion including the emergence of ripples reported in the experiments of dargahi 1990 the bed forms show similar velocities as reported in the experiments and are shown to be statistically similar to ripples measured in laboratory experiments and in nature to our knowledge this is the first three dimensional simulation to capture the ripple dynamics that evolve naturally from the nonlinear interactions between the flow and the bed

geomechanical and geochemical changes during early stages of weathering of karamu basalt new zealand abstract variations in geochemical and geomechanical characteristics were measured through a basalt weathering sequence exposed at an abandoned quarry at karamu near hamilton new zealand geochemical measurements show that at the early stages of weathering fresh to slightly weathered reductions in the concentrations cao and mgo are rapid although they are not accompanied by major mineralogical change during later stages of weathering secondary clay minerals form following well described mineralogical changes fresh basalt is strong uniaxial compressive strength 262 mn m 2 point load index 5 59 with well developed closely spaced columnar jointing slightly weathered material is distinguished in the field only by slight discolouration along joint planes but laboratory tests show a dramatic loss of strength in slightly weathered rock point load index 0 41 cbr 43 a causal relationship between the loss of cations and loss of strength in the early stages of weathering is suggested this stage of weathering is diffusion controlled whereby cations are lost from the constituent primary minerals and replaced by h this process disrupts the lattice structure and causes a marked loss of strength implications are that slightly weathered rock which appears competent in the field is likely to have much lower strength and durability than assumed from field evidence

martian intracrater splotches occurrence morphology and colors abstract martian intracrater splotches and related streaks are studied with global data on their occurrence and regional data on color and morphology the fraction of craters with splotches is greatest at high latitudes splotch occurrence is not strongly correlated with surface properties such as albedo and thermal inertia except where these correlate with substantial sediment cover large numbers of splotches are or include dunes especially at high southern latitudes color data show that the dune and nondune materials in splotches are part of one related group of materials that may be of similar composition but varying particle sizes the color data also show that some streaks are simply material deflated from splotches and mixed with local plains material while other streaks are more complex and may involve erosion of thin surface layers by material blown from the splotches splotches appear to be trapped eolian sand but probably have been formed by a great variety of mechanisms a large percentage of craters with splotches show evidence of complex histories of sediment deposition and erosion many splotches may be lag deposits from erosion of regional sediment cover present sediment budgets in splotches are not known but there is some evidence for loss of material and no evidence for resupply from outside the craters

the fluid dynamics of river dunes a review and some future research directions 1 dunes are present in nearly all fluvial channels and are vital in predicting flow resistance sediment transport and deposition within many rivers progress in understanding the fluid dynamics associated with alluvial dunes has been significant in the last 15 years and has witnessed huge advances in field laboratory and numerical investigations progress has been made in detailing the principal features of mean and turbulent flow over asymmetric dunes that possess flow separation in their leesides and how these forms affect both downstream boundary layer structure and stress partitioning over the dune additionally the links between sediment transport over dunes and instantaneous coherent flow structures are being increasingly understood with the feedback of dune three dimensionality upon flow and sediment dynamics over these bed forms beginning to be recognized as vital such research now provides an outstanding background for beginning to address areas of greater complexity that will enable a fuller understanding of these important natural features this review paper summarizes the principal features of mean and turbulent flow over alluvial sand dunes five areas are then highlighted and discussed as a possible focus for future research 1 the influence of dune leeside angle upon flow processes in the dune wake and downstream flow field 2 the influence of three dimensionality in dune shape upon the generation of turbulence and distribution of bed shear stress 3 flow field modification resulting from bed form superimposition and amalgamation 4 the scale and topology of dune related turbulence and its interactions with sediment transport and the flow surface and 5 the influence of suspended sediment on the dune flow field and dune morphology

the theoretical foundations and potential for large eddy simulation les in fluvial geomorphic and sedimentological research abstract large eddy simulation les is a method for resolving the time dependent structure of high reynolds number turbulent flows with les it is possible to model and track the behaviour of coherent turbulent structures and study their effect on the flow field hence les is potentially an important research tool in the fluvial sciences where flow mixing sediment entrainment and sediment transport are all affected by the presence of coherent vortices and their interactions with channel boundaries and other flow structures this paper introduces the les methodology discusses a variety of ways for representing small scale processes within les the subgrid scale modelling problem and provides some examples of early work into the use of les in a fluvial context a number of advances in computational power and numerical methods are required before les can be effectively applied at the river reach scale this paper considers some recent developments and their potential for providing validated large eddy simulations of river flow at the channel scale

patagonian origin of glacial dust deposited in east antarctica vostok and dome c during glacial stages 2 4 and 6 abstract the source area of continental dust deposited at both vostok and dome c sites east antarctica during the glacial stages stage 2 18 ka last glacial maximum stage 4 60 ka and stage 6 160 ka of the last two climatic cycles has remained constant the isotopic composition 87 sr 86 sr and 143 nd 144 nd of the ice core dust has been compared with the isotopic composition of the potential source areas antarctica new zealand southern africa australia and south america this comparison reveals the southern south american provenance of the dust for all three glacial periods as has already been shown for the lgm 1 we show that the patagonian loess and the marine shelf sediments from the argentine continental shelf which was variably emerged during glacial periods display different isotopic compositions and that the composition of the patagonian loess best matches the signature of the ice core dust the identification of the patagonian region as the source of the windblown dust deposited over east antarctica during all the latest glacial periods permits a better understanding of paleo atmospheric circulations of the last climatic cycles and a better constraint on the parametrization of dust sources for paleoatmospheric general circulation models

spatial structure of near bed flow properties at the grain scale abstract expanding the existing knowledge of the role of roughness on near bed flow properties is vital to provide deeper insights into the interactions between the flow sediment transport morphology and ecology this study uses four fixed beds from both the laboratory and the field to characterise the structure of near bed flow properties dense measurements over a grid of 6 mm spacing were conducted across each cast using an acoustic doppler velocimeter these measurements followed the line of the bed topography with the sampling location being 2 mm away from the maximum bed elevations near bed flow properties were calculated across the surface including velocity turbulence intensity turbulent kinetic energy reynolds stress and quadrant analysis improved visualisation of flow properties involves contour plots of the spatial distribution of flow over the dem of the gravel bed to facilitate attributions of flow patterns to roughness and topography using the standard deviation of elevations as a proxy for grain roughness of each surface we observed that a decrease in roughness led to an increase in the average near bed velocity in contrast an increase in roughness resulted in an increase in both turbulence intensity and turbulent production tke analysis of quadrant events dominating across the surface can provide indications into the potential for erosion and or deposition across the natural mobile surfaces finally second order structure function analysis is used to quantify the spatial structure of flow properties presenting novel isopleth maps of flow properties for the majority of flow properties across all surfaces the range in the spatial extent of flow structures is between 1 and 2 25 d50a except for transverse and vertical velocities which have a wider range up to 3 5 d50a

mars wind streak production as related to obstacle type and size abstract the characteristics of wind streaks associated with martian craters and hills in the size range of 100 m to 80 km corresponding to obstacle heights of a few to several hundred meters have been analyzed from viking orbiter images both dark erosional and bright depositional streaks form over the entire obstacle size range but there are preferred obstacle sizes for producing streaks bright streaks form more readily in association with relatively smaller obstacles than do dark streaks small obstacles produce both types of streaks more effectively than do large ones hills produce streaks as effectively as do craters of comparable height alternative explanations of bright streak formation are evaluated in terms of their ability to account for these observations the most satisfactory models invoke blocking of atmospheric flow downwind of an obstacle and consequent deposition of dust within the sheltered zone

seasonal variations in ice deformation and basal motion across the tongue of haut glacier d arolla switzerland records of surface motion englacial tilt and repeat inclinometry are used to determine patterns of surface internal and basal motion across the tongue of haut glacier d arolla switzerland over temporal scales ranging from days to months findings are interpreted with reference to contemporaneous measurements of subglacial water pressures and prior knowledge of the glacier s subglacial drainage system structure long term inclinometry results show pronounced extrusion flow over a subglacial drainage axis with basal velocities up to twice those measured at the glacier surface deformation profiles are more conventional away from the drainage axis with basal velocities 60 70 of surface velocities comparison of long term tilt rates from repeat inclinometry and englacial tilt meters shows close correspondence englacial tiltmeter data are used to reconstruct internal velocity profiles and to split surface velocities into internal deformation and basal motion contributions over spring summer and autumn winter periods although spatial patterns of surface movement are similar between periods patterns of internal and basal motion are not results are interpreted in terms of the location of sticky and slippery spots with temporally changing patterns of basal drag reflecting changing distributions of water pressure

shuttle radar images of wind streaks in the altiplano bolivia shuttle imaging radar sir a coverage across bolivia shows the major physiographic provinces including the andean altiplano the altiplano contains a variety of eolian features many of which are visible as radar dark radar mottled and radar bright streaks aligned parallel to the prevailing winds the streaks form downwind from hills and are as much as 15 km long and 800 m wide dark streaks originate between closely spaced hills whereas bright streaks form in the immediate lee of hills the radar brightness of the streaks is modulated by the proportion of sand cover vegetation and exposed substrate all of which relate to the local wind regime in the radar dark streaks vegetation is sparse and the sand is organized into dune forms some of which can be recognized as barchan dunes on the radar image by outlining of the dark dune by bright substrate radar mottled zones are covered by numerous 0 5 2 m high coppice dunes and in radarbright streaks the sand forms flat sheets but also includes sand mounds and abundant vegetation measurements indicate that winds are strongest and most turbulent in the region of active sand sheets and dunes inhibiting the growth of vegetation and the formation of mounds and resulting in a radar dark zone these results are consistent with previous studies that have demonstrated the existence of turbulent eddies in the wake of topographic obstacles that produce zones of increased surface wind shear and enhanced sand mobility the relation between the radar signature and the wind regime allows inferences to be drawn for the wind regime from image interpretation

estimating rates of basal motion and internal ice deformation from continuous tilt measurements over a two year period continuous measurements of temporal changes in tilt conducted with a string of tilt meters in a borehole on unteraargletscher bernese alps switzerland have been used to estimate the basal motion component this estimation is based on a comparison of the measurements with synthetic tilt curves computed using a parameterization of a simplified flow field the best agreement is found for a ratio of basal motion to forward motion due to ice deformation slip ratio equal to about 1 2 measured tilt curves exhibit a number of different transient features while an overall increase in tilt angle is observed at every tilt meter location two of the sensors recorded anomalous tilt behaviour these anomalies are characterized by sudden and drastic variations in tilt a particularly intriguing example of such short term tilt variations was recorded with a tilt meter positioned 40 m above the bed during the 1997 summer melt season

large scale patterns of eolian sediment transport on venus predictions for magellan the atmosphere of venus is likely to exert a major influence on the surface arecibo and venera 15 16 observations of the population of impact craters with bright halos give direct evidence of surface modification on the scale of centimeters to smooth the surface on time scales of 50 250 my both chemical and mechanical modifications probably occur diurnal winds in the planetary boundary layer can transport particles using boundary layer theory including the effects of topography surface stresses and resulting transport and deposition of sand size particles are calculated regional slopes are sites of largest surface stresses sand will be generally transported downhill although there is a preferential net transport from east to west in the same direction as the atmospheric superrotation it is predicted here that streaks may be seen in the magellan radar images which will indicate directions of net eolian transport on the surface of venus

subaerial salt extrusions in iran as analogues of ice sheets streams and glaciers abstract ice h20 and salt halite nacl share many physical properties and resemble each other in hand specimens and subaerial gravity driven flows however while most significant bodies of ice accumulate in cold highlands and gravity spread where and soon after they form most significant bodies of salt accumulate in tropical marine basins and have to be buried by 1 km of other rocks before they flow buried salt is driven by differential loading into various categories of piercing structures known as diapirs many diapirs extrude onto the surface as sheets of allochthonous out of place salt thousands of sheets of allochthonous salt have been interpreted in over 35 basins worldwide in the last 25 years mainly in the toes of passive continental margins and in orogenic belts where some are 103 km2 in area most former salt sheets are now submarine or subsurface but several active examples are beautifully exposed in iran these were compared to ice glaciers soon after they were introduced to western science a comparison that has been neglected since here we update this analogy and use modern understanding of flowing ice and salt to examine the similarities and differences that might be mutually beneficial to both fields of study as well as to extraterrestrial scientists the profiles internal structures and fabrics in flowing bodies of ice and salt are sensitive gauges of the histories of their budgets of supply and loss however whereas snow merely compacts where it accumulates salt sheets are fed from below by already deformed salt when salt diapirs first emerge on land they extrude domes that mature to the profiles of viscous fountains that often feed glacier like flows known as namakiers after locally exhausting their deep source layers salt fountains spread to the profiles of viscous droplets normal for ice caps ice typically deforms at 80 usually 90 of its absolute melting temperature while most salt deforms at

mean flow turbulence structure and bed form superimposition across the ripple dune transition 1 this paper describes a laboratory study of the dynamics of flow associated with three different stages of bed form amalgamation across the ripple dune transition measurements of flow velocity were obtained over simplified fixed bed forms designed to simulate conditions at the ripple dune transition using a 2d laser doppler anemometer this yielded information detailing the mean velocity field turbulence statistics local turbulence production local deviations from the mean pressure caused by dynamic effects turbulent kinetic energy and the contributions to the total reynolds stresses from different coherent turbulent events the results broadly confirm previous hypotheses that as bed form amalgamation proceeds across the ripple dune transition a superimposed bedstate can induce a series of critical changes to the flow structure with higher reynolds stresses being produced near and downstream of flow reattachment in particular quadrant 4 events turbulent flow structures with a downstream velocity greater than average and directed towards the bed dominate the vertical turbulent diffusion of longitudinal momentum in near bed regions close to the crest of the next downstream ripple thus providing the potential for increased erosion and sediment transport these experiments using simple fixed beds also provide support for recent measurements that document increased suspended sediment concentrations across the ripple dune transition schindler and robert 2004 2005 and that at the transition the largest bed forms are not necessarily those associated with the most intense shear layer activity schindler and robert 2005 bed form superimposition and amalgamation may thus significantly alter the mean and turbulent flow field as compared to bed forms without superimposition

basal flow characteristics of a linear medium sliding frictionless over small bedrock undulations the basal deformation of a gravity driven linear creeping flow sliding frictionless over slowly varying bed undulations in two dimensions is analysed analytically using results from second order perturbation theory one of the key results is that close to sinusoidal bedrock undulations up to two different spatial regions of local extrusion flow may arise the offset and onset of extrusion flow is controlled primarily by the amplitude to wavelength ratio above the crest of a sinusoidal bed line a local maximum of the surface parallel velocity develops for e ak 0 138 where a is the amplitude and k is the wave number as e increases from zer to this critical value the vertical position of the velocity maximum moves from kz 1 to kz 1 98 where z is the vertical distance above the mean bed line within and above the trough of a sinusoid a region of local minimum of the surface parallel velocity component develops which shifts from kz 1 towards the bed line as e increases front zero to 1 2 below this velocity minimum and for some distance above the velocity maximum the surface parallel velocity increases with depth this type of extrusion flow will cause a reversal of borehole inclination profiles close to the bedrock

new airborne imaging radar observations of sand dunes kelso dunes california abstract high resolution multiple wavelength and polarization radar data of kelso dunes were acquired during the mojave field experiment they offer the opportunity to develop criteria for the selection of optimal wavelengths and polarizations for imaging of dune areas the backscatter from unvegetated dune surfaces at all wavelenghts c l and p band with direct hh vv polarization is largely controlled by dune topography and incidence angle these data especially p band provide the best images of dune topography the best discrimination between active and inactive dunes is obtained by cross polarized c band data cvh chv as a result of multiple scattering from vegetation and small scale topography e g shadow dunes

a numerical investigation into the importance of bed permeability on determining flow structures over river dunes although permeable sediments dominate the majority of natural environments past work concerning bedform dynamics has considered the bed to be impermeable and has generally neglected flow between the hyporheic zone and boundary layer herein we present results detailing numerically modelled flow which allow the effects of bed permeability on bedform dynamics to be assessed simulation of an isolated impermeable bedform over a permeable bed shows that flow is forced into the bed upstream of the dune and returns to the boundary layer at the leeside in the form of returning jets that generate horseshoe shaped vortices the returning flow significantly influences the leeside flow modifying the separation zone lifting the shear layer adjoining the separation zone away from the bed simulation of a permeable dune on a permeable bed reveals even greater modifications as the flow through the dune negates the formation of any flow separation in the leeside with two dunes placed in series the flow over the downstream dune is influenced by the developing boundary layer on the leeside of the upstream dune for the permeable bed case the upwelling flow lifts the separated flow from the bed modifies the shear layer through the coalescence with vortices generated and causes the shear layer to undulate rather than be parallel to the bed these results demonstrate the significant effect that bed permeability has on the flow over bedforms that may be critical in affecting the flux of water and nutrients

sulfates in the north polar region of mars detected by omega mars express the observatoire pour la mineralogie l eau les glaces et l activite omega imaging spectrometer observed the northern circumpolar regions of mars at a resolution of a few kilometers an extended region at 240 e 85 n with an area of 60 kilometers by 200 kilometers exhibits absorptions at wavelengths of 1 45 1 75 1 94 2 22 2 26 and 2 48 micrometers these signatures can be unambiguously attributed to calcium rich sulfates most likely gypsum this region corresponds to the dark longitudinal dunes of olympia planitia these observations reveal that water alteration played a major role in the formation of the constituting minerals of northern circumpolar terrains

analysis of surface compositions in the oxia palus region on mars from mars global surveyor thermal emission spectrometer observations 1 we examine the distribution of thermal emission spectrometer tes derived surface compositions in the oxia palus region on mars through high spatial resolution mapping and integration with mars orbiter camera and mars orbiter laser altimeter data sets we also fit the basalt and andesite weathered basalt interpretations of tes surface type 1 and type 2 materials into multiple working hypotheses to describe the origin of surface compositions a mixing transition from surface type 1 to type 2 is observed in low albedo regions of southern acidalia planitia and may represent either 1 an influx of basaltic sediment from the southern highlands deposited on and mixed with andesitic volcanics 2 an influx of water transported basaltic sediment from the southern highlands that was altered and later deposited as a thin sedimentary veneer or 3 different degrees of weathering of indigenous basalt marking the geographic extent of submarine alteration of basaltic crust tes spectra of low albedo intracrater materials reveal that surface type 1 compositions form a central core on crater floors while type 2 compositions form a surrounding arc on the dark downwind sides of crater walls intracrater floor materials are interpreted as eolian sediment and wall materials are interpreted as either eolian sediment or eroded material from in place crater wall lithologies surface type 1 and type 2 compositions are also observed in adjacent low albedo wind streaks however a mixing trend is not as evident the mars pathfinder landing site and ares and tiu valles source regions are sufficiently blanketed by fine grained dust to prohibit the analysis of surface rock compositions

the morphodynamics of fluvial sand dunes in the river rhine near mainz germany ii hydrodynamics and sediment transport the dynamics of large isolated sand dunes moving across a gravel lag layer were studied in a supply limited reach of the river rhine during daylong surveys suspended sediment concentration bedload transport rate water depth flow velocity turbulence intensity near bed shear stress and water temperature were recorded over individual isolated dunes this paper considers the hydrodynamic environment and sediment transport over the dunes a companion paper details the sedimentology and morphology of the dunes flow over the flat gravel lag upstream of large dunes is more uniform than that over dunes and gravels are rarely entrained by in bank discharges unsteady and non logarithmic velocity profiles are common within the boundary layer above the stoss side of large dunes and the near bed flow demonstrates evidence of large scale coherent low frequency flow structures these may reflect stacked sequences of separated boundary layers generated by secondary dunes however the low amplitude morphology of large dunes does not affect the statistical properties of turbulence production over the stoss sides bed roughness and near bed shear stress commonly increase steadily over the stoss of dunes but may decrease near the crest especially where a crestal platform exists that is devoid of secondary bedforms bed roughness scales with the physical size of bed roughness elements however variability in roughness lengths is large owing to the composite nature of bed roughness bedload transport over stoss slopes is spatially variable but often shows an increase with increasing bed shear stress over the stoss well formed wakes only develop downstream of lee slopes which are close to the angle of repose otherwise separation is weak and suspension and settling of fine sediments is of little consequence to dune evolution wake flow is characterized by turbulence production one order of magnitude greater than over the stoss side which may be related to vortex shedding from the dune however wake current speeds are extremely low and variable in direction reverse flow is not sustained and no retrogressive bedforms occur in the lee of large dunes near bed shear stress and bed roughness are usually low within the wake reflecting low current speeds weak wake flow reattachment occurs at a variable distance downstream up to several times the duneform height a two dimensional numerical model for flow over dune topography calibrated using average parameter values provided a reasonable description of the flow upstream and over the backs of large dunes as far as the crestal region wake flow could not be modelled however the temporal and spatial complexity of natural three dimensional flow over the dunes resulted in variance in parameter estimates this variance precluded modelling of flow and bedload transport consequently it was not possible to model dune evolution in a deterministic sense

visual and infrared observations of wind streaks on mars abstract estimation of surface properties and physical setting of three common martian wind streak types bright dark and splotch related provides constraints on models of the formation and variability of streaks bright streaks form independently of surface properties other than local topography this is consistent with their formation being due to deposition of atmospheric dust in the lee of topographic features although they are widespread on mars dark streaks are noted as variable only in regions near 30 s latitude and elevations between 3 and 7 km and are associated with dark surfaces that have relatively high thermal inertias splotch related streaks occur at elevations between 0 and 6 km and in regions of relatively high thermal inertia splotch related streaks occur near the boundaries of thermally defined regions such as the south polar cap and other areas of either low or high thermal inertia these thermal conditions are responsible for the production of surface winds which form and modify these streaks the source of sidements which form splotch related streaks varies from dunes to well indurated stratified deposits regional studies of the various types in syrtis major syria planum claritas fossae oxia palus mesogea and pettit craters and noachis confirm that the correlations found at the global level occur at regional scales

nature and distribution of surficial deposits in chryse planitia and vicinity mars color images of bright red dust deposits at the mutch memorial station were acquired at variable incidence angles during sol 611 subsolar longitude 70 northern spring season after removing effects due to atmospheric scattering and absorption the data were used to estimate the independent variables in the hapke 1986 photometric function in blue green and red coordinates the vector representing the space radiance factor of the landing site extracted from viking orbiter images acquired on sol 609 is separated by a euclidean distance of only 0 022 units and an angle of only 1 5 from the vector estimated from the station data for the orbiter lighting and viewing geometries this result implies that light reflected from dust exposures dominates the orbiter signal multiplicative and additive atmospheric terms cancel one another and surface roughness is a second order effect in the orbiter data dust radiance factors computed from station data are most like laboratory spectra for fine grained hawaiian palagonite and are indistinguishable from earth based spectra of classical bright areas color composites of orbiter images show that the dust is found immediately south of acidalia planitia and in association with topographic barriers such as craters and cliffs examination of viking infrared thermal mapper data shows that the dust deposits typically do not have distinctive thermal inertia signatures implying that the deposits are optically thick hundreds of micrometers but thinner than the diurnal thermal skin depth centimeters dark gray material with thermal inertia values 8 12 10 3 cal cm 2 s 1 2 k 1 indicative of sand grain sizes 0 5 1 5 mm dominates the acidalia planitia lowlands and parts of kasei vallis this material also occurs as dark streaks extending from craters in xanthe terra and oxia palus space radiance factors of dark gray material are similar to spectra of mafic rock mixed with a minor amount of palagonitelike material material that is darker than but just as red as the dust deposits occurs in lunae planum xanthe terra and oxia palus areas of intermediate elevation multiple phase angle orbiter images suggest that the dark red exposures are a mixture of bright red and dark gray materials with the dark red exposures being relatively rough at a subpixel scale as compared to exposures of the other two materials thus only two types of materials can be detected in the data covering the study area palagonitelike dust and mafic rock fragments thermal inertia values 4 8 10 3 cal cm 2 s 1 2 k 1 for the dark red material are consistent with the presence of fine to medium sand size particles 0 10 0 5 mm such material should be easily moved by winds the lack of aeolian features implies that the dark red deposits are not composed of loose material rather they are probably more eroded versions of blocky soil or duricrust cemented dust and rock fragments exposed at the station both bright red dust aeolian suspension load and dark gray materials saltation traction loads migrate over the dark red substrate the overall distribution of the surficial units is controlled by topography at a variety of length scales lower wind threshold friction velocities associated with higher atmospheric densities in lowlands keep dust from accumulating and duricrust from forming while higher threshold velocities in highlands lead to net accumulation of dust local topographic obstacles craters walls ridges perturb wind flow and lead to local accumulation or erosion at a variety of elevations in addition the bright red dust ubiquitously found between exposures of dark gray and dark red materials may accumulate as the wind velocity gradient decreases at the transition from smoother dark gray exposures to rougher dark red exposures the distribution of the materials must also be modulated by climatic variations induced by quasi periodic oscillations in obliquity eccentricity and spin axis direction constraining these surficial deposits to be 1 ma

wind streaks geological and botanical effects on surface albedo contrast abstract two wind streaks in the eastern mojave desert of california were examined to gain insight into the origin of the surface brightness contrast that makes them visible both on the ground and in remote sensing data the two localities are a 4 km long dark streak oriented s43e from the amboy cinder cone 34 32 n 115 46 w located on a quaternary basalt flow covered with aeolian sand and a 2 km long dark streak oriented s22e from a low hill near the southwestern base of sleeping beauty mountain 34 48 n 116 20 w located on a sand covered alluvial surface in both cases the dark streaks have enhanced rock abundances on the streak surface relative to the surroundings at the amboy streak slope wash likely contributed to the rock concentration on the streak surface shielded from burial under aeolian sand by the cinder cone at the sleeping beauty streak the relative albedo contrast is strongly emphasized by the presence of big galleta grass only outside of the streak the albedo contrast of the sleeping beauty streak can be effectively eliminated by the seasonal presence of annual grass preferentially within the streak some plants may have reflectances that are strongly dependent upon viewing and illumination geometry raising the possibility that certain terrestrial aeolian features may appear variable on a diurnal basis alluvial processes appear to have been important at both localities for redistributing surface materials even given the infrequent rain conditions present in the mojave desert

comparison of remote sensing observations of planetary wind streaks abstract wind streaks are common aeolian features observed on terrestrial planets they were first identified on mars thus the associated terminology is based on mars related observations usually describing surface patterns with distinct albedos however terms related to reflected tones are only relevant to past knowledge for mars and not necessarily suitable for description of radar visible streaks located on venus titan or earth furthermore the sensor type used to observe wind streaks can influence the subsequent data analysis the purpose of this study was to examine the effects of sensor type on wind streak identification and interpretation six case studies featuring wind streaks on earth were performed using imaging by both radar and optical sensors the results indicate that wind streak identification is constrained to a specific combination of sensor settings appropriate for the local surface properties only half the optically visible wind streaks considered in this study were also radar visible but all the wind streaks observable in the radar images also appeared in the optical images furthermore bright and dark reflectance and backscatter are relative terms and should be used with caution these results suggest that the venusian wind streak database is most likely far from complete and that many more streaks exist

intra seasonal changes in deformation profiles revealed by borehole studies storglaciaren sweden in 1985 1987 and 1988 we measured deformation of bore holes in the ablation zone of storglaciaren a different hole was used each year deformation profiles were determined for four consecutive time periods between mid july and early september all three holes were in an area where the glacier lies in an overdeepened part of the bed up glacier from a riegel the first hole was approximately on the glacier center line while the others were midway between the center line and one or the other margin despite large standard errors variations in the deformation profiles during the melt season are broadly consistent with other data we thus believe that they are real and that they reflect changes in the stress field resulting from changes in drag at the bed a decrease in drag early in the melt season coupled with convergence of the bed contours towards the riegel is believed to be responsible for a previously documented increase in vertical velocity just up glacier from the riegal at this time of year also noteworthy but perhaps problematical was an abrupt transverse shear of m at a depth of 25 m near the center of the glacier injuly 1985 the shear took place in the zone in which cold ice near the surface gives way to temperate ice deeper in the glacier

potential effects of subglacial water pressure fluctuations on quarrying water pressure fluctuations beneath glaciers may accelerate rock fracture by redistributing stresses on subglacial bedrock and changing the pressure of water in bedrock cracks to study the potential influence of water pressure fluctuations on the fracture of subglacial bedrock ice flow over a small bedrock step with a water filled cavity in its lee is numerically modeled and stresses on the bedrock surface are calculated as a function of transient water pressures in the cavity stresses on the bed are then used to calculate principal stress differences within the step rapid reductions in cavity water pressure increase principal stress differences in the bed increasing the likelihood of crack growth in the step and the formation of predominantly vertical fractures relatively impermeable bedrock may be most susceptible to fracturing during water pressure reductions because high water pressure in cracks within the rock can be maintained as water pressure decreases in cavities these results when considered in conjunction with the strong likelihood that increases in water pressure accelerate the removal of rock fragments loosened from the bed suggest that in zones of ice bed separation where water pressure fluctuations typically are large rates of quarrying may be higher than along other parts of glacier beds