the geology of the terrestrial planets during the last four years our knowledge of the geology of the terrestrial planets has advanced rapidly the advances are particularly noticeable for venus and mars improved understanding of venus has come largely from the pioneer venus mission colin 1980 which has given us our first global view of the planet albeit at fairly low resolution the period was also one of almost continuous data gathering for mars as the viking orbiters and landers emplaced at the planet in 1976 continued to function

dark slope streaks on mars are aqueous processes involved 1 concentrations of dark slope streaks occur in the equatorial latitudes of mars mostly where magmatic driven activity dominates the geologic record although originally ascribed to wet debris flows all the most recent published hypotheses concerning these features focus on processes which disturb a brighter dusty mantle to expose a darker substrate these mechanisms invoke dry mass wasting or eolian processes excluding a role for water in light of the geographic geologic and morphologic considerations and the new information provided from the mars orbital camera and the mars orbital data altimeter we reexamine fluvial processes as a viable explanation for some of the dark slope streaks in our opinion two contrasting processes for the formation of dark slope streaks dust avalanching and spring discharge represent endpoints on a continuum of progenitors it may be that some of these features result from dry mass wasting or eolian processes some from fluvial processes and some from a mechanism s not yet conceived a spring discharge origin for the formation of the dark slope streaks has profound implications including mars having limited but currently active fluvial processes acting upon its surface as well as near surface aquifers

ice lubricated gravity spreading of the olympus mons aureole deposits abstract gravity sliding and spreading at low strain rates can account for the general morphology and structure of the aureoles and basal scarp of olympus mons detachment sliding could have occurred around the volcano if either pore fluid pressures were exceptionally high greater than 90 or the rocks had very low resistance to shear about 1 105 pa or 1 bar because of the vast areal extent and probable shallow depth of the detachment zone development of ubiquitous high pore fluid pressures beneath aureole forming material was unlikely however a zone of sufficiently weak material consisting of about 10 interstitial or interbedded ice could have been present if so a simple rheologic model for the aureole deposits can be applied that consists of a thin ductile layer overlain by a thicker brittle layer according to this model extensional deformation would have occurred near the shield and compressional deformation in its distal parts proximal grabens and distal corrugations on aureole surfaces support this model a submarine slide at kitimat arm british columbia is a valid qualitative analogy for the observed features and inferred emplacement style of the aureole deposits ground ice processes have been considered the cause of many geologic features on mars a 3 average concentration of ground ice in the regolith is predicted by theoretical models for the ice budget and cryosphere ice may have been deposited in higher concentrations below the aureole forming material the source of the ice could have been juvenile water circulated hydrothermally by olympus mons volcanism the basal scarp of olympus mons apparently demarcates the transition between the upper stable part of the shield and its lower part that decoupled and formed the aureole deposits this transition may reflect a change in the bulk shear strength of the shield caused either by a radial dependence in the abundance of ice or fluid in the shield materials or by the concentration of intrusive dikes within the volcano other martian volcanoes exhibit virtually no evidence of similar large scale gravity spreading and basal scarps perhaps such evidence if it existed has been buried by lava flows or perhaps the smaller size of other volcanoes did not permit the development of these features

seasonal formation rates of martian slope streaks abstract slope streaks are gravity driven dark or light toned features that form throughout the martian year in high albedo and low thermal inertia equatorial regions on mars these distinctive features have never been observed in a terrestrial environment although some analogs have been proposed based on diverse orbital observations a number of mechanisms including granular and aqueous flows have been proposed to explain their formation using multi temporal images taken by the context camera ctx aboard the mars reconnaissance orbiter mro we identified newly formed streaks in multiple martian years and estimated seasonal streak formation rates at intermediate latitudes as well as at the equator we found seasonal variations in streak activity in multiple consecutive martian years including high formation rates during autumn solar longitude ls 190 during this time slope streak activity exceeds the long term formation rate multiple times the highest seasonal formation rate of 0 16 per streak per martian day was observed in the olympus mons aureole in autumn ls 210 of mars year 30 in some sites slope streak formation rate at slopes of opposite orientation peaks at different seasons the seasonal variations of the formation rate are inconsistent with sporadic trigger mechanisms and revealed that changing conditions at the slopes affect the formation of the streaks throughout the martian year modelled environmental parameters at the streak bearing slopes indicate a correlation between seasonal streak activity and surface temperature as well as wind velocity seasonal variations of streak activity could be a result of varying intensities of both dry and wet mechanisms or could be explained by the interaction of multiple mechanisms

fluid dynamical implications of anastomosing slope streaks on mars 1 the mars global surveyor mission has imaged slope streaks some of which have formed in periods as short as 109 days these features are one of the most currently active surface processes on mars some slope streaks have flow like morphologic characteristics which include anastomosing patterns influenced by small topographic barriers in order to understand what processes gave rise to these specific features we applied viscoplastic flow numerical modeling techniques to simulated martian surfaces we simulate martian surfaces with observed slope streaks by using mars orbiter laser altimeter measurements to obtain large scale slope measurements and a photoclinometry technique on mars orbiter camera images to obtain meter scale topographic information our numerical simulations of slow moving plastic flows show that a fluid rheology and a short formation period are necessary to explain these features we estimate that the typical values of bulk viscosity and bulk yield strength are less than 10 pa s and less than 10 pa respectively the fluid rheology can be explained by a water related flow with a solid content less than about 20 an alternative explanation is a dry grain flow with extremely low cohesion and friction angle supported by dispersive pressure or a lubricant such as electric conditions of particles the continuous nature of anastomosing slope streaks that originate from point sources is best explained by continuous discharges of material or lubricant in this case the estimated flow rate is less than several cubic meters per second and the flow duration is estimated to be less than a day

further evidence for a mass movement origin of the olympus mons aureole analysis of the ridge graben and fracture patterns on the aureole material surrounding olympus mons lends further support to an origin by gravity sliding of the outer flanks of the shield the patterns provide evidence of the nature of sliding especially in the last stages of emplacement no part of the slide need have traveled the whole extent of the aureole for the slides to occur on a shallow slope reduction of shear strength of the materials involved is required possibly by melting of ground ice triggering mechanisms could be volcanically related marsquakes and possibly stresses induced on the surrounding area by the growing olympus mons volcano

devonian tetrapod trackways and trackmakers a review of the fossils and footprints abstract the earliest tetrapods are known from the upper devonian their remains are becoming better known from increasing numbers of specimens localities environments and ichnofossils each of the eight or possibly nine genera now represented by skeletal fossils is reviewed in its sedimentological faunal and stratigraphic context with an assessment of what might be inferred about the habitus and locomotory capabilities of each fossil trackways and their interpretations are then re examined in the context of the known body forms and consideration given to the degree of fit between the skeletal fossils the trackways and their interpretations the currently known devonian tetrapods are unlikely to have made any of the known tracks unless they were produced under water neither the skeletal fossils nor the trackways show good evidence of terrestrial locomotion among devonian tetrapods when the fossil material and recent phylogenetic analyses are taken in combination it appears that neither tetrapods nor limbs with digits are likely to have arisen before the frasnian this should be borne in mind in palaeoecological studies of these animals

cockroaches traverse crevices crawl rapidly in confined spaces and inspire a soft legged robot jointed exoskeletons permit rapid appendage driven locomotion but retain the soft bodied shape changing ability to explore confined environments we challenged cockroaches with horizontal crevices smaller than a quarter of their standing body height cockroaches rapidly traversed crevices in 300 800 ms by compressing their body 40 60 high speed videography revealed crevice negotiation to be a complex discontinuous maneuver after traversing horizontal crevices to enter a vertically confined space cockroaches crawled at velocities approaching 60 cm s 1 despite body compression and postural changes running velocity stride length and stride period only decreased at the smallest crevice height 4 mm whereas slipping and the probability of zigzag paths increased to explain confined space running performance limits we altered ceiling and ground friction increased ceiling friction decreased velocity by decreasing stride length and increasing slipping increased ground friction resulted in velocity and stride length attaining a maximum at intermediate friction levels these data support a model of an unexplored mode of locomotion body friction legged crawling with body drag friction dominated leg thrust but no media flow as in air water or sand to define the limits of body compression in confined spaces we conducted dynamic compressive cycle tests on living animals exoskeletal strength allowed cockroaches to withstand forces 300 times body weight when traversing the smallest crevices and up to nearly 900 times body weight without injury cockroach exoskeletons provided biological inspiration for the manufacture of an origami style soft legged robot that can locomote rapidly in both open and confined spaces

bubble growth and rise in soft sediments the mechanics of uncemented soft sediments during bubble growth are not widely understood and no rheological model has found wide acceptance we offer definitive evidence on the mode of bubble formation in the form of x ray computed tomographic images and comparison with theory natural and injected bubbles in muddy cohesive sediments are shown to be highly eccentric oblate spheroids disks that grow either by fracturing the sediment or by reopening preexisting fractures in contrast bubbles in soft sandy sediment tend to be spherical suggesting that sand acts fluidly or plastically in response to growth stresses we also present bubble rise results from gelatin a mechanically similar but transparent medium that suggest that initial rise is also accomplished by fracture given that muddy sediments are elastic and yield by fracture it becomes much easier to explain physically related phenomena such as seafloor pockmark formation animal burrowing and gas buildup during methane hydrate melting

burrowing mechanics burrow extension by crack propagation a worm minimizes its energy expenditure as it forges a path through mud sediment until now the analysis of burrowing mechanics has neglected the mechanical properties of impeding muddy cohesive sediments which behave like elastic solids1 here we show that burrowers can progress through such sediments by using a mechanically efficient previously unsuspected mechanism crack propagation1 2 in which an alternating anchor system of burrowing serves as a wedge to extend the crack shaped burrow the force required to propagate cracks through sediment1 2 in this way is relatively small we find that the force exerted by the annelid worm nereis virens in making and moving into such a burrow amounts to less than one tenth of the force it needs to use against rigid aquarium walls3

wave attenuation and wave drift in the marginal ice zone abstract surface gravity waves in a viscous rotating ocean are studied theoretically when they penetrate an area covered by highly concentrated brashlike ice the motion is described by a lagrangian formulation and the brash is modeled by a viscous newtonian fluid results for wave attenuation and wave drift are obtained in the asymptotic limit of a thin very viscous upper layer the derived damping rate compares favorably with field data from the marginal ice zone miz the drift velocity in the ocean exhibits a marked maximum in the viscous boundary layer near the ice ocean interface at the outer edge of the boundary layer it exceeds the inviscid stokes drift by a factor of 7 4 computed values for the mean viscous drag on the ice induced by the wave motion show that this effect may compete with the frictional effected of the wind in packing the ice finally it is demonstrated that the integrated horizontal mass transports in the open ocean and under the ice do not match which leads to upwelling in

wave propagation in the marginal ice zone model predictions and comparisons with buoy and synthetic aperture radar data in this paper the ocean wave dispersion relation and viscous attenuation by a sea ice cover are studied for waves propagating into the marginal ice zone miz the derivation of the dispersion relation and the viscous attenuation by an ice sheet are discussed for waves under flexure and pack compression in the miz the flexure effect is important for short waves for a fixed wave period the changes in wavelength and group velocity as a function of ice thickness are significant in turn the exponential wave attenuation rate shows a rollover at short wave periods whereby the rapid increase in wave attenuation rate with decreasing wave period slows down or even turns into a decrease the labrador ice margin experiment limex conducted on the miz off the east coast of newfoundland canada in march 1987 provides us with aircraft synthetic aperture radar sar imagery wave buoy and ice property data on the basis of the wave number spectrum from the sar data and the concurrent wave frequency spectrum from the ocean buoy data and accelerometer data on the ice during limex 87 the dispersion relation has been estimated and compared with a model wave energy attenuation rates are estimated from sar data and the ice motion package data which were deployed at the ice edge and into the ice pack and compared with the model the model data comparisons are reasonably good for the ice conditions observed during limex 87 some previously reported data of wave attenuation in the miz are revisited for model comparison

initial rise of bubbles in cohesive sediments by a process of viscoelastic fracture 1 an understanding of the mechanics of bubble rise in sediments is essential because of the role of bubbles in releasing methane to the atmosphere and the formation and melting of gas hydrates past models to describe and predict the rise of other buoyant geological bodies through a surrounding solid e g magmas and hydrofractures appear not to be applicable to bubbles in soft sediments and this paper presents a new model for gas bubble rise in soft fine grained cohesive sediments bubbles in such sediments are essentially dry little if any free water and grow through a process of elastic expansion and fracture that can be described using the principles of linear elastic fracture mechanics which assume the existence of a spectrum of flaws within the sediment fabric by extending this theory we predict that bubbles initially rise by preferential propagation of a fracture in a sub vertical direction we present a criterion for initial bubble rise once rise is initiated the speed of rise is controlled by the viscoelastic response of the sediments to stress using this new bubble rise model we estimate rise velocities to be of the order of centimeters per second we again show that capillary pressure plays no substantive role in controlling bubble growth or rise

subterranean ant nests trace fossils past and future many species of ants excavate complex species typical nests in soil the basic structural units of many nests are descending tunnels connecting flattened generally horizontal chambers of oval to lobed outline the species typical structure of many nests results from variation in the size shape number and arrangement of these basic elements nest architecture can be rendered by filling subterranean nests with a thin slurry of orthodontal plaster then excavating and reconstructing the hardened cast photographs of such nest casts of nine species of ants from northern florida show the range and type of variation of architecture preservation conditions under which ant nests could form complex trace fossils are discussed and reports of such traces reviewed the images presented in this paper will help to alert trace fossil specialists to the potential range of appearance of such nest fossils 2002 elsevier science b v all rights reserved

debris covered piedmont glaciers along the northwest flank of the olympus mons scarp evidence for low latitude ice accumulation during the late amazonian of mars we use viking and new mgs and odyssey data to characterize the lobate deposits superimposed on aureole deposits along the west and northwest flanks of olympus mons mars these features have previously been interpreted variously as landslide pyroclastic lava flow or glacial features on the basis of viking images the advent of multiple high resolution image and topography data sets from recent spacecraft missions allow us to revisit these features and assess their origins on the basis of these new data we interpret these features as glacial deposits and the remnants of cold based debris covered glaciers that underwent multiple episodes of advance and retreat occasionally interacting with extrusive volcanism from higher on the slopes of olympus mons we subdivide the deposits into fifteen distinctive lobes typical lobes begin at a theater like alcove in the escarpment at the base of olympus mons interpreted to be former ice accumulation zones and extend outward as a tongue shaped or fan shaped deposit the surface of a typical lobe contains moving outward from the basal escarpment a chaotic facies of disorganized hillocks interpreted as sublimation till in the accumulation zone arcuate ridged facies characterized by regular subparallel ridges and interpreted as the ridges of surface debris formed by the flow of underlying ice and marginal ridges interpreted as local terminal moraines several lobes also contain a hummocky facies toward their margins that is interpreted as a distinctive type of sublimation till shaped by structural dislocations and preferential loss of ice blocky units are found extending from the escarpment onto several lobes these units are interpreted as evidence of lava ice interaction and imply that ice was present at a time of eruptive volcanic activity higher on the slopes of olympus mons other than minor channel like features in association with lava ice interactions we find no evidence for the flow of liquid water in association with these lobate features that might suggest 1 near surface groundwater as a source for ice in the alcoves in the lobe source region at the base of the scarp or 2 basal melting and drainage emanating from the lobes that might indicate wet based glacial conditions instead the array of features is consistent with cold based glacial processes the glacial interpretations outlined here are consistent with recent geological evidence for lowlatitude ice rich features at similar positions on the tharsis montes as well as with orbital dynamic and climate models indicating extensive snow and ice accumulation associated with episodes of increased obliquity during the late amazonian period of the history of mars

the effect of the marginal ice zone on the directional wave spectrum of the ocean abstract during the mizex 84 experiment in the greenland sea in june july 1984 a cooperative program was carried out between the scott polar research institute spri and the institute of oceanographic sciences ios to measure the change in the directional character of the ocean wave spectrum in the immediate vicinity of the ice edge the aim was to extend one dimensional spectral measurements made hitherto so as to study in full the processes of reflection and refraction directional spectrum analysis of these records shows that i significant reflection of wave energy occurs at the ice edge detected using long hasselmann analysis ii within the ice the directional spectrum at high frequencies where attenuation is rapid broadens to become almost isotropic whereas iii the directional spectrum at swell frequencies where the attenuation is slower becomes initially narrower before broadening more slowly than the high frequency energy an explanation of these effects is offered in terms of scatte

hydrovolcanic explosions the systematics of water pyroclast equilibration the initial contact of external water with erupting magma and the mass ratio of water to magma govern the development of hydrovolcanic phenomena the phase relations of water within the runout system and the separation of vapor or liquid from the pyroclasts explain gradational transitions between some pyroclastic flows base surges mud hurricanes mudflows and sheetfloods

hirise observations of slope streaks on mars 1 images from the high resolution imaging science experiment have revealed new details on the morphologic and topographic characteristics of slope streaks on mars over 1500 hirise images were analyzed with 78 unique image sites having slope streaks images with low sun illumination reveal that dark slope streaks have topographic relief where streaked surfaces are lower than their surroundings slope streaks often initiate below localized features such as rock outcrops individual boulders and impact craters they are also abundant in great numbers within the blast zones of small young impact craters 10 50 m in diameter these observations suggest that slope streaks can be triggered by localized disturbances such as rockfalls and impact blasts seismic activity from external e g impacts or internal forces could also trigger slope streaks the topographic relief and triggering mechanisms of slope streaks seem to best fit models that involve dry dust avalanches martian slope streaks and meters thick avalanche scars are part of a continuum of active mass wasting features at meter to sub meter scales

three decades of slope streak activity on mars slope streaks are surficial mass movements that are abundant in the dust covered regions of mars targeting of slope streaks seen in viking images with the mars orbiter camera provides observations of slope streak dust activity over two to three decades in all study areas new and persisting dark slope streaks are observed slope streaks disappeared in one area with persisting streaks nearby new slope streaks are found to be systematically darker than persisting streaks which indicates gradual fading far more slope streaks formed at the study sites than have faded from visibility the rate of formation at the study sites was 0 03 new slope streaks per existing streak per mars year bright slope streaks do not presently form in sudden events as dark slope streaks do instead bright streaks might form from old dark slope streaks perhaps transitioning through a partially faded stage

ignimbrites of amazonis planitia region of mars a series of postulated ignimbrite units is mapped in the amazonis memnonia and aeolis quadrangles of mars the units cover about 2 2 106 km2 within a broad but discontinuous and irregular belt trending east west along the highland lowland boundary the ignimbrites overlie parts of the western and southern aureole materials of olympus mons but are embayed in places by the lava plains of the lowlands stratigraphic relations between the basalt flows from the tharsis montes region and the ignimbrites are not clearly defined crater counts suggest that the younger ignimbrites postdate the lava flows crater counts per square kilometer for the ignimbrites range from 7 29 1 95 10 4 to 6 36 2 01 10 5 for craters larger than 1 km in diameter the ignimbrite materials form thick 100 m extensive relatively flat sheets that are smooth to grooved or gently undulating grooved surfaces appear to be yardangs and in most places are not alined with prevailing wind directions the seven mapped ignimbrite units are characterized by morphologic expression stratigraphic position and crater counts similarities to ignimbrites in the pancake range of central nevada include 1 rounded patches of smooth high albedo nonwelded material superposed on jointed low albedo welded material 2 local complementary joint sets in welded materials and 3 thick flow sheets of great areal extent that follow but subdue underlying topography four major eruptive centers occur in areas where units are thickest and where a dominant nnw sse structural trend is expressed locally by unit margins elongate collapse features and normal faulting a minimum volume of 3 85 106 km3 for the deposits has been calculated from thickness estimates based on shadow measurements and crater rim height relations

ethology of the trace fossil chondrites form function and environment abstract the behaviour of the iconic ichnogenus chondrites is re evaluated based on review of existing literature and analysis of novel data macroscopic thin section and esem edx observations ct scans and resin peels of modern analogues computer controlled serial grinding morphometric analysis and theoretical morphology the bedding plane expression of chondrites is well constrained by morphometry 1 the angle of dichotomy formed by a pair of adjacent branches is typically between 30 and 56 interquartile range mean 47 2 branching order is between 1 and 9 3 branches are on average nine times longer than wide in the third dimension downward branching is dominant but bundled shafts and upward branching may be present the size of chondrites increased markedly from the late jurassic to the late cretaceous suggesting that the tracemakers became larger and larger microfabric analysis of chondrites shows active fill or alternatively passive fill of empty tunnels by currents or clay percolation a new mechanism proposed herein the tracemakers built chondrites to obtain food 1 vermiform deposit feeders produced chondrites for searching for food in the sediment fodinichnion 2 asymbiotic bivalves built chondrites for cultivating and directly ingesting bacteria agrichnion 3 chemosymbiotic bivalves produced chondrites to provide symbionts with chemical agents chondrites was modified through the life of the tracemaker or it represented a part of the producer s lifespan chondrites and its modern tracemaker s is associated with a range of marine settings including well oxygenated dysoxic and space limited nucleocave environments as such chondrites is regarded as an extremotolerant ichnotaxon

mass movement slope streaks imaged by the mars orbiter camera narrow fan shaped dark streaks on steep martian slopes were originally observed in viking orbiter images but a definitive explanation was not possible because of resolution limitations pictures acquired by the mars orbiter camera moc aboard the mars global surveyor mgs spacecraft show innumerable examples of dark slope streaks distributed widely but not uniformly across the brighter equatorial regions as well as individual details of these features that were not visible in viking orbiter data dark slope streaks as well as much rarer bright slope streaks represent one of the most widespread and easily recognized styles of mass movement currently affecting the martian surface new dark streaks have formed since viking and even during the mgs mission confirming earlier suppositions that higher contrast dark streaks are younger and fade brighten with time the darkest slope streaks represent 10 contrast with surrounding slope materials no small outcrops supplying dark material or bright material for bright streaks have been found at streak apexes digitate downslope ends indicate slope streak formation involves a ground hugging flow subject to deflection by minor topographic obstacles the model we favor explains most dark slope streaks as scars from dust avalanches following oversteepening of air fall deposits this process is analogous to terrestrial avalanches of oversteepened dry loose snow which produce shallow avalanche scars with similar morphologies low angles of internal friction typically 10 30i for terrestrial loess and clay materials suggest that mass movement of low cohesion martian dusty air fall is possible on a wide range of gradients martian gravity presumed low density of the air fall deposits and thin unresolved by moc failed layer depths imply extremely low cohesive strength at time of failure consistent with expectations for an air fall deposit of dust particles as speed increases during a dust avalanche a growing fraction of the avalanching dust particles acquires sufficient kinetic energy to be lost to the atmosphere in suspension limiting the momentum of the descending avalanche front the equilibrium speed where rate of mass lost to the atmosphere is balanced by mass continually entrained as the avalanche front descends decreases with decreasing gradient this mechanism explains observations from moc images indicating slope streaks formed with little reserve kinetic energy for run outs on to valley floors and explains why large distal deposits of displaced material are not found at downslope streak ends the mass movement process of dark and bright slope streak formation through dust avalanches involves renewable sources of dust only leaving underlying slope materials unaffected areas where dark and bright slope streaks currently form and fade in cycles are closely correlated with low thermal inertia and probably represent regions where dust currently is accumulating not just residing

geomorphological evidence for a dry dust avalanche origin of slope streaks on mars mars has several different types of slope feature that resemble aqueous flows however the current cold dry conditions are inimical to liquid water resulting in uncertainty about its role in modern surface processes dark slope streaks were among the first distinctive young slope features to be identified on mars and the first with activity seen in orbital images they form markings on steep slopes that can persist for decades and the role of water in their formation remains a matter of debate here i analyse the geomorphic features of new slope streaks using high resolution orbital images comparison of images before and after streak formation reveal how this process affects the surface and provides information about the cause these observations demonstrate that slope streaks erode and deposit material in some instances they also reveal that streaks can jump slopes and may be erosive very near their termini these observations support a formation model where dark slope streaks form as ground hugging low density avalanches of dry surface dust such streaks need not be treated as special regions for planetary protection patterns of erosion and deposition by some slope streaks on mars are consistent with a dry dust avalanche origin according to an analysis of orbital images before and after new streaks formed

autonomous underwater vehicles auvs and investigations of the ice ocean interface in antarctic and arctic waters limitations of access have long restricted exploration and investigation of the cavities beneath ice shelves to a small number of drillholes studies of sea ice underwater morphology are limited largely to scientific utilization of submarines remotely operated vehicles tethered to a mother ship by umbilical cable have been deployed to investigate tidewater glacier and ice shelf margins but their range is often restricted the development of free flying autonomous underwater vehicles auvs with ranges of tens to hundreds of kilometres enables extensive missions to take place beneath sea ice and floating ice shelves autosub2 is a 3600 kg 6 7 m long auv with a 1600 m operating depth and range of 400 km based on the earlier autosub1 which had a 500 m depth limit a single direct drive d c motor and five bladed propeller produce speeds of 1 2 m s 1 rear mounted rudder and stern plane control yaw pitch and depth the vehicle has three sections the front and rear sections are free flooding built around aluminium extrusion space frames covered with glass fibre reinforced plastic panels the central section has a set of carbon fibre reinforced plastic pressure vessels four tubes contain batteries powering the vehicle the other three house vehicle control systems and sensors the rear section houses subsystems for navigation control actuation and propulsion and scientific sensors e g digital camera upward looking 300 khz acoustic doppler current profiler 200 khz multibeam receiver the front section contains forward looking collision sensor emergency abort the homing systems argos satellite data and location transmitters and flashing lights for relocation as well as science sensors e g twin conductivity temperature depth instruments multibeam transmitter sub bottom profiler aqualab water sampler payload restrictions mean that a subset of scientific instruments is actually in place on any given dive the scientific instruments carried on autosub are described and examples of observational data collected from each sensor in arctic or antarctic waters are given e g of roughness at the underside of floating ice shelves and sea ice

the oldest evidence of bioturbation on earth detailed study of the khatyspyt formation in arctic siberia has shown that contrary to common expectations the earliest ichnofabric is of late ediacaran age records a food seeking behavior and is found in a distal carbonate ramp setting where it co occurs with fossils of avalon type ediacaran soft bodied organisms preserved depth of bioturbation reaches 5 cm the ichnofabric solely comprises nenoxites the oldest known meniscate trace fossil which is interpreted as burrows with terminal backfill structure formed as a result of active displacement of sediment to form a tunnel within the substrate followed by emplacement of the material behind the animal as it progressed through the sediment in addition to being the most reliable paleontological evidence for the existence of bilaterians at ca 555 ma the late ediacaran bioturbation is regarded as a key step in the escalatory engineering of phanerozoic ecospace leading to sudden diversification of macroscopic organisms and macrocommunities

a phenomenological model for precursor volcanic eruptions intense explosions of relatively short duration frequently precede large explosive and effusive volcanic eruptions by as much as weeks to months in the case of very viscous magmas1 2 3 4 5 6 in some cases such pre eruption activity has served as a sufficient warning to those living in the vicinity to evacuate and avoid calamity1 precursor events seem to be related to the formation of a magma pathway to the surface but their precise interpretation is a long standing puzzle it has been inferred from theoretical studies that exsolution of volatiles might create an almost separate gas pocket at the tip of a propagating dyke7 8 9 here we explain the role that such a process may have using a laboratory study of the transient propagation of a liquid filled crack with a gas pocket at its tip that grows with time we show that once the gas pocket acquires sufficient buoyancy to overcome the fracture resistance of the host solid the dynamics of the gas pocket rather than those of the liquid determine the velocity of the crack tip furthermore we find that the gas can ultimately separate from the liquid we propose that fast moving gas rich pockets reaching the surface ahead of the main liquid filled fissure could be the origin of many precursor eruptions

the olympus mons aureole formation by gravitational spreading new observations of the aureole deposits of olympus mons are in agreement with previous suggestions that the aureole lobes could have been formed by movement under gravity away from the observed scarps the characteristic corrugated morphology of the aureole is probably secondary formed by erosion along structural inhomogeneities geometries of the corrugations and translational faults in the aureole deposits favor a mechanism of emplacement that involves material with substantial shear strength rather than viscous flow estimates of the aspect ratios of terrestrial landslides nappes and ash flows suggest that the aureole deposits are more similar in overall shape to slide emplaced bodies than to pyroclastic flows although martian physical conditions permit the formation of ash flows there is no positive evidence for their existence a gravitational spreading mechanism is proposed that involves imbricate thrusting in distal regions analogous with terrestrial thrust sheets corrugations in the aureole developed by erosion along imbricate or listric faults basal shear stresses on the decoupling surface may have been of the order of 106 pa 10 bars the nature of the decoupling surfaces in the proximal regions is uncertain but is likely to have been the topographic surface in distal parts the aureole deposits were probably emplaced as a series of sheets by spreading under gravity from an ancestral olympus mons which extended farther to the northwest than does the present volcano as a result of the accumulation of lavas under the then prevailing stress conditions recent lava eruptions from the volcano have been concentrated in northeast and southwest sectors indicating a changed stress regime since aureole emplacement

tail use improves performance on soft substrates in models of early vertebrate land locomotors in the evolutionary transition from an aquatic to a terrestrial environment early tetrapods faced the challenges of terrestrial locomotion on flowable substrates such as sand and mud of variable stiffness and incline the morphology and range of motion of appendages can be revealed in fossils however biological and robophysical studies of modern taxa have shown that movement on such substrates can be sensitive to small changes in appendage use using a biological model the mudskipper a physical robot model granular drag measurements and theoretical tools from geometric mechanics we demonstrate how tail use can improve robustness to variable limb use and substrate conditions we hypothesize that properly coordinated tail movements could have provided a substantial benefit for the earliest vertebrates to move on land

volcanoes and volcanic provinces martian western hemisphere the recognition of some martian landforms as volcanoes is based on their morphology and geologic setting other structures however may exhibit classic identifying features to a varying or a less degree these may be only considered provisionally as having a volcanic origin regional geologic mapping of the western hemisphere of mars from viking images has revealed many more probable volcanoes and volcanotectonic features than were recognized on mariner 9 pictures these abundant volcanoes have been assigned to several distinct provinces on the basis of their areal distribution although the olympus tharsis region remains as the principal center of volcanism on mars four other important provinces are now also recognized the lowland plains tempe terra plateau southern highlands in the phaethontis and thaumasia quadrangles and a probable ignimbrite province situated along the highland lowland boundary in amazonis planitia volcanoes in any one province vary in morphology size and age but volcanoes in each province tend to have common characteristics that distinguish that particular group

the biostratigraphical and palaeogeographical framework of the earliest diversification of tetrapods late devonian the biostratigraphical and palaeogeographical framework of the earliest diversification of tetrapods late devonian

geologic context of the mars radar stealth region in southwestern tharsis stealth is a region on mars that has no distinguishable radar return stealth was discovered in 1988 by muhleman et al 1991 in 3 5 cm earth based radar images and it was found to extend 2000 km along the martian equator west of arsia and pavonis montes stealth was proposed to be a deposit of unconsolidated granular material with a minimum thickness of several meters with the most likely explanation being that stealth is a volcanic tephra deposit muhleman et al 1991 1995 stealth overlies some of the youngest geologic units on mars including lava flows and a giant curvilinear ridged lobate unit on the west flank of arsia mons stealth also overlies part of a region of smooth and wind scoured materials called the medusae fossae formation examination of high resolution viking orbiter images suggests that stealth is the youngest of several discontinuous wind worked mantles of fine grained 1 cm sediment older deposits of fine sediment appear to be interbedded with lava flows and show evidence of aeolian deposition dunes and deposits in the lee of topographic obstacles and erosion yardangs and pedestal craters the geologic context supports a volcanic ash origin for stealth if stealth is composed of tephra then its extent and the nature of landforms in the region indicate that it resulted from multiple eruptions that occurred relatively late in martian history possible source vents include linear depressions flanked by constructive volcanic landforms that are located on the lower western slopes of arsia and pavonis montes

fault propagation folds induced by gravitational failure and slumping of the central costa rica volcanic range implications for large terrestrial and martian volcanic edifices long sublinear ridges and related scarps located at the base of large volcanic structures are frequently interpreted as normal faults associated with extensional regional stress in contrast the ridges bordering the central costa rica volcanic range ccrvr are the topographic expression of hanging wall asymmetric angular anticlines overlying low angle thrust faults at the base of the range these faults formed by gravitational failure and slumping of the flanks of the range due to the weight of the volcanic edifices and were perhaps triggered by the intrusion of magma over the past 20 000 years the thrust fault underlying alajuela ridge rises from a depth of 700 m at a dip of 15 over a distance of a few kilometers it ramps up at 600 m depth on a 40 slope and terminates in the axis of the forward syncline 400 m below the surface the hanging wall of this fault has been thrusted about 200 m away from the volcanic range axis thrusting on the lower flanks of the ccrvr is compensated by extension on the range axis with formation of summit grabens shallow seismicity in the volcanic range suggests that thrusting is still active we postulate that at kilauea volcano hawaii the gravity and magma induced slumping of the southern flank on low angle thrust faults generates hanging wall anticlines similar to those observed in costa rica these anticlines are hypothesized to occur along the base of the volcano where the thrust faults ramp up toward the sea bottom ridges and scarps between 2000 and 5000 m below sea level are interpreted as the topographic expression of these folds we further suggest that the scarps of the ccrvr and kilauea are valid scaled terrestrial analogs of the perimeter scarp of the martian volcano olympus mons we suggest that the crust below olympus mons has failed under the load of the volcano triggering the radial slumping of the flanks of the volcano on basal thrusts the thrusting would have in turn formed the anticlinal ridges and scarps that surround the edifice the thrusting seems to be preferential toward the northwest and southeast and a northeast southwest rift zone seems to have developed perpendicular to the regional topographic gradient the thrust faults may extend all the way to the base of the martian crust about 40 km and they may have been active until almost the end of the volcanic activity we suggest that gravitational failure and slumping of the flanks of volcanoes is a process common to most large volcanic edifices in the ccrvr and at kilauea this slumping of the flanks is a slow intermittent process but it could evolve to rapid massive avalanching leading to catastrophic eruptions thus monitoring of uplift and displacement of the folds related to the slump tectonics could become an additional effective method for mitigating volcanic hazards

natural remanent magnetization acquisition in bioturbated sediment general theory and implications for relative paleointensity reconstructions we present a general theory for the acquisition of natural remanent magnetizations nrm in sediment under the influence of a magnetic torques b randomizing torques and c torques resulting from interaction forces dynamic equilibrium between a and b in the water column and at the sediment water interface generates a detrital remanent magnetization drm while much stronger randomizing torques may be provided by bioturbation inside the mixed layer these generate a so called mixed remanent magnetization mrm which is stabilized by mechanical interaction forces during the time required to cross the surface mixed layer drm is lost and mrm is acquired at a rate that depends on bioturbation intensity both processes are governed by a mrm lock in function the final nrm intensity is controlled mainly by a single parameter that is defined as the product of rotational diffusion and mixed layer thickness divided by sedimentation rate this parameter defines three regimes 1 slow mixing 10 with mrm acquisition and full drm randomization and 3 intermediate mixing because the acquisition efficiency of drm is larger than that of mrm nrm intensity is particularly sensitive to in case of mixed regimes generating variable nrm acquisition efficiencies this model explains 1 lock in delays that can be matched with empirical reconstructions from paleomagnetic records 2 the existence of small lock in depths that lead to drm preservation 3 specific nrm acquisition efficiencies of magnetofossil rich sediments and 4 some relative paleointensity artifacts

a generalized stochastic approach to particle dispersal in soils and sediments abstract we explore a generalized stochastic description for the dispersal of particles in soils and sediments the model is based on the continuous time random walk ctrw which enables a very general description of particle mixing due to biological activity a community of burrowing organisms is characterized by a bioturbation fingerprint that consists of two probability distributions the jump length distribution describes the distance a particle travels within a given bioturbation event the waiting time distribution describes the time interval a particle waits at a given location in between two bioturbation events our stochastic analysis provides insight on the applicability of the widely used biodiffusion model which forms the asymptotic limit of the ctrw model this asymptotic behaviour of diffusion is always reached independent of the shape of bioturbation fingerprint provided that the waiting time distribution has a finite mean and the jump length distribution has a finite variance the biodiffusion coefficient can be decomposed as the variance of the jump length distribution over the mean of the waiting time distribution since the variance enables a squared weighing of the jump distance long range displacements will contribute more to the mixing intensity d b than short range displacements therefore large macrofauna will contribute disproportionately to the mixing intensity relative to their abundance as they displace particles over longer distances than smaller organisms finally we review the potential for bioturbation of so called anomalous transport models where either the mean of the waiting time distribution or the variance of the jump length distribution becomes infinite

geochemistry of martian soil and bedrock in mantled and less mantled terrains with gamma ray data from mars odyssey 1 surficial materials including soil and dust are abundant in the upper tens of centimeters of the martian surface sensed by the mars odyssey gamma ray spectrometer grs seven large areas 14 of the martian surface that represent possible compositional end members were selected including three regions heavily mantled with surficial materials the selection process included mapping the ratio of exposed rocky terrain to surficial materials using high resolution imagery grs data for h cl fe si k and th were obtained for each area the areas are chemically homogeneous within each area given the spatial resolution and analytical uncertainty of the grs data however substantial chemical differences exist among the areas including the different mantled terrains contrary to earlier assumptions that surficial materials are globally homogeneous due to aeolian mixing the observed chemical differences among the areas may be due to variations in the protolith compositions extent of alteration of the protolith regions or post soil formation processes the abundances of cl k and th in rockier but still soil rich areas such as syrtis major planum can be explained by mixing between a soil with higher concentrations of cl k and th similar to the abundances in the mantled terrains and some of the landing sites and crustal rocks containing lower abundances of these elements similar to martian meteorites

formation of olympus mons and the aureole escarpment problem on mars based on morphologic interpretation of viking orbiter images it is postulated that on the summit area of arsia mons mars there is a several kilometer thick ice cover in addition numerous linear striae on the flanks of arsia mons resemble terrestrial washboard moraines behind which there may be substantial dead ice deposits this implies that glacier phenomena are active in the tharsis region these features may have bearing on the formation of the aureole deposits of olympus mons olympus mons has been the cause of dispute among geologists for years and several contrasting models have been proposed to explain the up to 10 km high distal escarpment and broad lobate aureole deposits below one model by hodges and moore 1979 assumed 2 3 km thick ice under which volcanism proceeded at an early stage to build olympus mons thereby leading to the growth of the high cliff section it has been argued that the origin of the aureole has not been satisfactorily explained modifications of the hodges and moore hypothesis are proposed to explain some aspects of both the aureole formation and the escarpment at the lava aureole boundary the assumption is made that volcanism that persisted was mostly localized on the olympus mons massif throughout the aureole development and that a blanket of ice and wind blown dust covered the lower flanks of the volcano deposition of volcanic products on the flank blanket led to faulting and sliding of material away from the summit area thereby creating the aureole deposits and scarp further eruptions of lavas in the summit area substantially elevated the cliff segment and additions of lavas off the cliffs into the wing area led to further creeping of the lower flank region thus generating the vast aureoles therefore the aureole formation succeeded and resulted from olympus mons volcanic activity and is one of the youngest features of olympus mons and not older as has been postulated

the pristine shape of olympus mons on mars and the subaqueous origin of its aureole deposits abstract the tallest volcano in the solar system olympus mons on mars is bordered by at least ten enormous sub circular hummocky deposits forming a welded halo termed the aureole the aureole units or simply aureoles which are the deposits of landslides from olympus mons have dramatically transformed the pristine size and shape of the volcanic edifice topographic data are used to determine the amount of collapsed material and so reconstruct the original outline of olympus mons before the landslides took place under the assumption that the edifice did not start failing until it had reached this maximum size due to post aureole deposition on the eastern and southern flanks and to the uncertainty of the slippage level on the northern side the reconstruction is sufficiently precise along the western and north western olympus mons flank it is more uncertain for the northern flank while it is not feasible around the rest of the volcano it appears that the radius along the western and north western olympus mons before the collapse of the aureole landslides was approximately 200 km longer or more the results show that the volume of the aureoles even if enormous is insufficient to fill the ideal conical edifice which would be obtained prolonging the olympus mons flanks with present slope angles thus an overhang remains in the pre aureole reconstructed olympus mons which would also explain the onset of instability that led to the aureole collapse further a drape deposit blanketing the southern acheron fossae ridge just at the front of the western w aureole landslide deposit and a fan channel system carved on the same w aureole are investigated and it is suggested that these morphologies have been emplaced in subaqueous setting while the drape may indicate a landslide thrust water splash akin to a tsunami deposit caused by the fast travelling w aureole landslide the fan channel system is similar to certain morphologies in the terrestrial oceans a numerical model of the collapse of the western aureole unit in water shows final runouts on both acheron ridge and amazonis planitia compatible with observations provided that the friction angle is extremely small of the order of a tenth of degree simulations indicate that the w aureole could have reached acheron fossae ridge with velocities in excess of 100 m s which would explain the several tens of km long distance reached by the landslide thrust tsunami deposit in short morphological and numerical lines of evidence would indicate a subaqueous origin for the largest w aureole landslide

downslope sediment transport by boiling liquid water under mars like conditions experiments and potential implications for martian gullies gullies are widespread morphological features on mars for which current changes have been observed liquid water has been one of the potential mechanisms to explain their formation and activity however under present day martian conditions liquid water is unstable and should only be transiently present in small amounts at the surface yet little attention has been paid to the mechanisms by which unstable water transports sediment under low atmospheric pressure here we present the results of laboratory experiments studying the interaction between liquid water owing over a sand bed under mars like atmospheric pressure c 9 mbar the experiments were performed in a mars simulation chamber at the open university uk in which we placed a test bed of ne sand at a 25 slope we chose to investigate the in uence of two parameters the temperature of the water and the temperature of the sand we performed 27 experiments with nine different combinations of water and sand temperatures ranging from 278 to 297 k under all experimental conditions the water was boiling we investigated and compared the types and timing of sediment transport events and the shapes characteristics and volumes of the resulting morphologies in agreement with previous laboratory studies we found that more intense boiling increased the volume of sediment transported for a given volume of water we found four main types of sediment transport entrainment by overland ow grain ejection grain avalanches and levitation of saturated sand pellets our results showed that increasing sand temperature was the main driving parameter in increasing the sand transport and in modifying the dominant sediment transport mechanism the temperature of the water played a negligible or minor role apart from the duration of sand ejection and avalanches which lasted longer at low water temperature at low sand temperature the majority of the sand was transported by overland ow of the liquid water at higher sand temperatures the transport was dominated by processes triggered by the boiling behaviour of the water at the highest temperatures sediment transport was dominated by the formation of levitating pellets dry avalanches and ejection of the sand grains this resulted in a transport volume about nine times greater at a sand temperature of 297 k compared with 278 k our heat transfer scaling shows that the boiling behaviour will be enhanced under martian low gravity resulting in more ef cient transport of sediment by levitating sand pellets even at temperatures close to the triple point our results showed that the boiling intensity played an important role in the physics of sediment transport by liquid water this implied that the amount of water required to produce morphological changes at the surface of mars could be lower than previously estimated by assuming stable liquid water boiling is a critical process to be considered when assessing gully formation and modi cation mechanisms mobilized by liquid water our work could have similar implications for any water formed landform on mars which could include recurring slope lineae dark dune ows and slope streaks

global map of eolian features on mars ten basic categories of eolian features on mars were identified from a survey of mariner 9 and viking orbiter images the ten features mapped are 1 light streaks including frost streaks 2 dark streaks 3 sand sheets or splotches 4 barchari dunes 5 transverse dunes 6 crescentic dunes 7 anomalous dunes 8 yardangs 9 wind grooves and 10 deflation pits the features were mapped in groups not as individual landforms and recorded according to their geographic positions and orientations on maps of 1 12 5 million or 1 25 million scale in the north polar region light and dark streaks indicate winds from the west and northwest frost streaks show northeast and northwest winds barchan dunes show southwest and west winds transverse dunes show east and west winds local erosional features show winds from the northwest or southeast and northeast or southwest in the middle and low northern latitudes streaks show northeast winds yardangs and deflation pits show mostly easterly and northeasterly winds in the low southern latitudes light streaks and dunes record northwest and northeast winds dark streaks record southeast winds in high southern latitudes most streaks and dunes record southeast and east winds in the south polar region light and frost streaks record southwest and northwest winds whereas dark streaks and transverse dunes show southeast winds the patterns recorded for ephemeral features conform to global conditions of strong southern spring and summer northern fall and winter wind circulation erosional features in bedrock indicate long term and perhaps ancient wind trends whereas depositional features may record relatively more recent winds wind directions indicated by yardangs pits and other erosional features seldom correspond to those shown by streaks these erosional features indicating winds of different directions than those that formed the streaks may have been carved when the effective regional winds on mars were different due to relative hemisphere insolation differences which are related to obliquity variations alternatively many yardangs and pits may be largely controlled by structure and carved along surface structural patterns or features that channeled both ancient and present day winds deflation pits in the mantled terrain may contain the best record of ancient wind trends these pits seem to have stratigraphically related orientations different stratigraphic units composing the mantle contain wind erosion pits that possibly record large scale wind direction changes because of long term changes in the obliquity of the mars

climbing falling and jamming during ant locomotion in confined environments locomotion emerges from effective interactions of an individual with its environment principles of biological terrestrial locomotion have been discovered on unconfined vertical and horizontal substrates however a diversity of organisms construct inhabit and move within confined spaces such animals are faced with locomotor challenges including limited limb range of motion crowding and visual sensory deprivation little is known about how these organisms accomplish their locomotor tasks and such environments challenge human made devices to gain insight into how animals move within confined spaces we study the locomotion of the fire ant solenopsis invicta which constructs subterranean tunnel networks nests laboratory experiments reveal that ants construct tunnels with diameter d comparable to body length l 3 5 0 5 mm ants can move rapidly 9 bodylengths per s within these environments their tunnels allow for effective limb body and antennae interaction with walls which facilitate rapid slip recovery during ascending and descending climbs to examine the limits of slip recovery in artificial tunnels we perform perturbations consisting of rapid downward accelerations of the tunnels which induce falls below a critical tunnel diameter ds 1 31 0 02 l falls are always arrested through rapid interaction of appendages and antennae with tunnel walls to jam the falls ds is comparable to the size of incipient nest tunnels d 1 06 0 23 l supporting our hypothesis that fire ants construct environments that simplify their control task when moving through the nest likely without need for rapid nervous system intervention

rheomorphism of welded tuffs abstract peralkaline welded tuffs from the islands of gran canaria canary islands and pantelleria italy show abundant evidence for post depositional flow it is demonstrated that rheomorphism or secondary mass flowage can occur in welded tuffs of ignimbrite and air fall origin the presence of a linear fabric is taken as the diagnostic criterion for the recognition of the process deposition on a slope is an essential condition for the development of rheomorphism after compaction and welding internal structures produced during rheomorphic flow can be studied by the methods of structural geology and show similar dispositions to comparable features in sedimentary slump sheets it is shown that secondary flowage can occur in welded tuffs emplaced on gentle slopes provided that the apparent viscosity of the magma is sufficiently low compositional factors favor the development of rheomorphism in densely welded tuffs of peralkaline type

the attenuation rates of ocean waves in the marginal ice zone during field operations in the greenland and bering seas in 1978 1979 and 1983 a number of experiments were carried out in which wave energy was measured along a line of stations running from the open sea deep into an icefield wave buoys in the water and accelerometer packages on floes were the instruments employed with airborne vertical photography to supply information on floe size distribution it was found that the decay of waves is exponential with a decay coefficient which generally increases with frequency except for a roll over at the highest frequencies the observations can be fitted reasonably well to a theory of one dimensional scattering

undulatory swimming in sand subsurface locomotion of the sandfish lizard the desert dwelling sandfish scincus scincus moves within dry sand a material that displays solid and fluidlike behavior high speed x ray imaging shows that below the surface the lizard no longer uses limbs for propulsion but generates thrust to overcome drag by propagating an undulatory traveling wave down the body although viscous hydrodynamics can predict swimming speed in fluids such as water an equivalent theory for granular drag is not available to predict sandfish swimming speed we developed an empirical model by measuring granular drag force on a small cylinder oriented at different angles relative to the displacement direction and summing these forces over the animal movement profile the agreement between model and experiment implies that the noninertial swimming occurs in a frictional fluid

the use of sar to measure ocean wave dispersion in frazil pancake icefields abstract icefields composed of frazil and pancake ice play important roles in both polar regions in winter during the early to midwinter period pancake ice is a major component of the antarctic sea ice cover while in the arctic the odden ice tongue in the greenland sea associated with deep convection is composed mainly of pancake ice the retrieval of sea ice thickness by remote sensing is in general a very difficult task in this paper the change in dispersion of ocean waves as they penetrate into pancake ice is considered so as to gain insight into its possible relationship with thickness spectral analysis of subscenes from ers 2 second european remote sensing satellite synthetic aperture radar sar images yields the wavelength and direction of the principal spectral component both outside and inside the ice cover there is a decrease of wavelength at the ice edge as well as refraction toward the normal and a loss of amplitude the analysis is complex because the true wave spectrum must be re

aureole deposits of the martian volcano olympus mons the aureole of grooved terrain that surrounds the large shield volcano olympus mons consists of several overlapping roughly circular sheets each 0 5 to 1 5 km thick the surfaces of these materials bear abundant curvilinear ridges and troughs 10 to 100 km long and 1 to 5 km wide which form anastomosing patterns that vary in length and width over the aureole the aureole is asymmetric to olympus mons extending almost 1000 km northwest from the center of the volcano but only 600 km southeast the lobate form of the deposits the pressure ridges on their surfaces and the deflection of aureole material around barriers indicate that the deposits were emplaced as viscous flows high resolution viking orbiter pictures show the aureole material to be unstratified and it is inferred to contain randomly distributed large dark blocks whose weathering products form dark streaks in the talus on the flanks of ridges a pyroclastic origin is proposed for the aureole the following sequence is suggested at least six great pyroclastic eruptions occurred prior to the construction olympus mons they formed very fluid ash flows that became viscous during late stages of emplacement and pressure ridges formed on the surfaces of the deposits before they finally came to rest the oldest and most extensive aureole deposit finely grooved terrain was considerably modified by erosion prior to being partly covered by later eruptions a positive gravity anomaly over the olympus mons area may define the site of a near surface magma chamber that was the source of the pyroclastic eruptions

the role of the wind transported dust in slope streaks activity evidence from the hrsc data abstract slope streaks are gravity driven albedo features observed on martian slopes since the viking missions the debated mechanism of formation could involve alternatively dry granular flow or wet mass wasting a systematic mapping of slope streaks from the high resolution stereo camera is presented in this paper two regions known for their slope streaks activity have been studied the first one is located close to cerberus lava flow and the second one is inside the olympus mons aureole the statistics of slope streaks shapes measured from orthorectified images confirm previous results from mars orbiter camera surveys preferential orientations of slope streaks are reported slope streaks occur preferentially on west facing slopes at latitudes lower than 30 n for olympus and on south west facing slopes for cerberus wind directions derived from a general circulation model during the dusty season correlate with these orientations furthermore west facing slopes at olympus have a thicker dust cover these observations indicate that slope streaks are dust avalanches controlled by the preferential accumulation of dust in the downstream side of the wind flow the paucity of slope streaks at high latitudes and their preferential orientation on south facing slopes have been presented as an evidence for a potential role of h 2 o phase transition in triggering or flow the potential role of h 2 o cannot be ruled out from our observations but the dust avalanche model together with the atmospheric circulation could potentially explain all observations the role of h 2 o might be limited to a stabilizing effect of dust deposits on northward facing slopes at intermediate latitudes 30 n 33 n and on all slopes further north

mars stratigraphy and gravimetry of olympus mons and its aureole olympus mons and its surroundings have been investigated using impact crater statistics crater retention ages of all major geological units show that their emplacement occurred during three time intervals the underlying fractured plains are part of the northern plains in general n 1 4 10 3 km 2 this time is followed by the time interval represented by crater retention ages n 1 8 10 4 to 3 10 3 km 2 some lava flows in the fractured plains the smooth plains and the aureole materials were emplaced during this time the aureole probably developed by some sort of collapse of the outer parts of an ancient volcano proto olympus mons underlying the present shield its remnants may show in the scarp and small parts of the shield not covered by younger lava flows the third interval covers crater retention ages n 1 5 10 5 to 3 10 4 km 2 this volcanic activity followed a period of dormancy a series of lava flows forming caldera and present shield surface and flooding a depression around the shield are distinguishable the regional stratigraphy is discussed as part of the global geological history the question of the genesis of the aureole material is addressed by gravity models the topographic mass of olympus mons contributes about 80 to the aureole gravity high northwest of the mountain the gravity high of the entire aureole can be explained by a density model consisting of the topographic masses of olympus mons and the aureole materials it does not require additional high density materials underneath the aureole thus aureole materials of an allochthonous origin by collapse are in agreement with the gravity data however the gravity data do not preclude an autochthonous and volcanic origin of the aureole materials in the latter case possible subsurface intrusions should have no density contrasts with the surroundings

mechanical response of sediments to bubble growth modeling the process of bubble growth in sediments requires an understanding of the physics that controls bubble shape and the interaction of the growing bubble with the sediment to acquire this understanding we have conducted experiments in which we have injected gas through a fine capillary into natural and surrogate sediment samples and have monitored pressure during bubble growth to provide information about stress and strain in gas injection studies with natural sediment samples we have observed two modes of bubble growth behavior one of these modes characterized by a saw tooth record of pressure as the bubble grows is consistent with fracture of the medium observations indicate that bubble growth by fracture should correspond to bubbles that are coin or disk shaped this shape is confirmed in observations of bubbles in natural sediments and in our studies of bubble injection into gelatin a surrogate sediment material interpretation of the stress strain results for bubble growth also required that we measure young s modulus e the measurements show e to be near 0 14 mn m2 which differs by more than 4 orders of magnitude from values that have been reported in the literature our measurements of e give substantially better estimates of bubble shape than are predicted using the literature values our data are interpreted with linear elastic fracture mechanics lefm which predicts that the critical pressure for bubble growth will depend on the bubble volume v raised to the 1 5 power while evidence of substantial heterogeneity in sediment properties is apparent in our results this v 1 5 dependence is confirmed through application of lefm theory we have determined the critical stress intensity factor k1c a material property and the principal determinant of bubble shape and growth by fracture our values of k1c range from 2 8 10 4 mn m 3 2 to 4 9 10 4 mn m 3 2 for our natural sediment samples from cole harbor nova scotia we have also estimated the critical stress intensity factor for eckernforde bay samples by analyzing published images of natural bubbles the k1c obtained in this way is similar to our cole harbor results and is 5 5 10 4 mn m 3 2

biophysical effects on soil crack morphology in a faunally active dryland vertisol abstract faunal behavior in dryland ecosystems may physically influence swelling soil hydrologic and pedologic processes due to its contributions to soil crack formation in order to provide a physical link between this faunal activity and pedological processes we use a resin visualization technique and x ray imaging to characterize the biomechanical influences of biocompaction mega meso herbivores and bioturbation termites on 3d crack morphology and topology in a faunally active dryland vertisol system results show increased soil cracking intensity due to faunal influence however this increased cracking diverged by faunal influence bioturbation creates surficial shallow extensive crack networks while biocompaction creates systematic deep narrow crack networks compared to a reference soil biocompacted soils also exhibit a memory of past wetting and drying events via vertically layered crack morphologies despite differences in these crack magnitudes between the faunal influences crack structures show morphological and topological similarity as a topological network these persistent differences in field crack systems may potentially create convectively driven hotspots of enhanced water and carbon gas transport in dryland ecosystems as a result of crack formation highlighting the importance of considering fracture behavior in both an ecological atmospheric and pedologic context

an ice water vortex at the edge of the east greenland current during the y mer 80 cruise in august 1980 we observed an ice feature of 60 km diameter having the shape of a breaking wave it lay at the edge of the east greenland drift ice in fram strait with its center at 79 15 n 00 38 e and the wave was breaking upstream relative to the east greenland current two conductivity temperature and depth sections across the feature in n s and e w directions revealed warm up to 4 3 c water some 60 km inside the polar front in lenses centered at 40 m depth but with an effect to beyond 600 m the temperature anomalies were accompanied by salinity anomalies so that there was little net effect on the density profile the form of the sections together with the ice distribution observed by vertical photography from a helicopter and surface motion observed by tracking four radar transponders all suggest that the feature is a vortex produced by an instability in the polar front it has similar characteristics to vortices investigated experimentally and theoretically by griffiths and linden 1981a b 1982 and observationally by wadhams et al 1979

geologically recent water flow inferred in channel systems in the ne sulci gordii region mars a series of fluid carved channels in the sulci gordii region of mars were investigated numerous channel networks exist in sulci gordii part of the olympus mons aureole and this area comprises some of the youngest volcanic terrain on mars the channels ranged in length from 43 to 155 km with widths of 128 288 m the morphology of the channels was analysed assuming both lava and water as possible agents for three of the four channels studied water appears to be the likely agent while one channel is probably lava formed for the water formed channels discharge rates were estimated at 8000 36 000 m3 s 1 the lava channel was probably formed from short lived episodic activity by a low viscosity lava the age of the channels and surrounding area was estimated using crater counting to be 100 ma water has appeared to have flowed for almost 150 km under the climatic conditions at this time there is some evidence for later tectonic activity possibly as recent as 10 ma but crater dating accuracy was limited by the lack of high resolution images of some areas sulci gordii is therefore a dynamic site with evidence of hydrological and volcanic activity extending into the recent geological past

airborne remote sensing of ocean wave directional wavenumber spectra in the marginal ice zone interactions between surface waves and sea ice are thought to be an important but poorly understood physical process in the atmosphere ice ocean system in this work airborne scanning lidar was used to observe ocean waves propagating into the marginal ice zone miz these represent the first direct spatial measurements of the surface wave field in the polar miz data were compared against two attenuation models one based on viscous dissipation and one based on scattering both models were capable of reproducing the measured wave energy the observed wavenumber dependence of attenuation was found to be consistent with viscous processes while the spectral spreading of higher wavenumbers suggested a scattering mechanism both models reproduced a change in peak direction due to preferential directional filtering floe sizes were recorded using co located visible imagery and their distribution was found to be consistent with ice breakup by the wave field

olympus mons aureole deposits new evidence for a flank failure origin 1 the origin of the rough textured aureoles that surround the immense olympus mons volcano on mars is controversial we present data from the mars global surveyor and mars odyssey missions to demonstrate that at least two of the aureole lobes are derived from the volcano s flanks in large and probably catastrophic mass movement events leaving behind headwalls that constitute the basal scarp this evidence stems from the morphology and internal structure of aureole blocks which exhibit remnants of volcanic flow units on their surfaces our claim is supported by plausible reconstructions of the prefailure flanks structural analogs to known flank failure events at hawaiian volcanoes suggest that repeated cycles of flank growth and collapse at olympus mons allow generation of the observed aureoles from a protoedifice similar in size and shape to the present one

sidewinding with minimal slip snake and robot ascent of sandy slopes limbless organisms such as snakes can navigate nearly all terrain in particular desert dwelling sidewinder rattlesnakes crotalus cerastes operate effectively on inclined granular media such as sand dunes that induce failure in field tested limbless robots through slipping and pitching our laboratory experiments reveal that as granular incline angle increases sidewinder rattlesnakes increase the length of their body in contact with the sand implementing this strategy in a physical robot model of the snake enables the device to ascend sandy slopes close to the angle of maximum slope stability plate drag experiments demonstrate that granular yield stresses decrease with increasing incline angle together these three approaches demonstrate how sidewinding with contact length control mitigates failure on granular media

directional wave spectra estimation in a marginal ice zone using linear prediction abstract a synthetic aperature radar sar image of a wave field penetrating a marginal ice zone off newfoundland was analyzed in order to get insight into the physical processes responsible for the swell attenuation the analysis was done using a parameteric spectral density estimation technique based on linear prediction this approach allows the estimation of the directional spectrum of the swell on small images with a better low frequency definition than nonparametric spectral estimation methods like fast fourier transforms resulting in a greater number of estimations over the wave propagation length this increase in spatial resolution allowed the detection of physical phenomena occurring inside the ice pack that affected wave propagation evidence of wave refraction was observed inside the marginal ice zone as the waves encountered an area of different ice compaction finally results show that the parametric approach leads to an evaluation of the attenuation coefficient similar to fft analysis

in situ measurements and analysis of ocean waves in the antarctic marginal ice zone in situ measurements of ocean surface wave spectra evolution in the antarctic marginal ice zone are described analysis of the measurements shows significant wave heights and peak periods do not vary appreciably in approximately the first 80km of the ice covered ocean beyond this region significant wave heights attenuate and peak periods increase it is shown that attenuation rates are insensitive to amplitudes for long period waves but increase with increasing amplitude above some critical amplitude for short period waves attenuation rates of the spectral components of the wavefield are calculated it is shown that attenuation rates decrease with increasing wave period further for long period waves the decrease is shown to be proportional to the inverse of the period squared this relationship can be used to efficiently implement wave attenuation through the marginal ice zone in ocean scale wave models

slope streaks on mars correlations with surface properties and the potential role of water the mars orbiter camera on board the mars global surveyor spacecraft has returned images of numerous dark streaks that are the result of down slope mass movement occurring under present day martian climatic conditions we systematically analyze over 23 000 high resolution images and demonstrate that slope streaks form exclusively in regions of low thermal inertia confirming earlier results steep slopes and remarkably only where peak temperatures exceed 275 k the northernmost streaks which form in the coldest environment form preferentially on warmer south facing slopes repeat images of sites with slope streaks show changes only if the time interval between the two images includes the warm season surprisingly in light of the theoretically short residence time of h 2o close to the surface the data support the possibility that small amounts of water are transiently present in low latitude near surface regions of mars and undergo phase transitions at times of high insolation triggering the observed mass movements

ice properties in the greenland and barents seas during summer resultats d analyse de carotte de glace de mer dans l arctique europeen les proprietes de la glace sont mises en rapport avec les conditions generales de la distribution de glace leur epaisseur et leur relief dans la zone exploree interpretation de la salinite sur les glaces de premiere annee et pluri annuelles

a volcanotectonic survey of ascraeus mons mars 1 ascraeus mons is one of the largest volcanoes on mars it is replete with well preserved features that can be used to understand its volcanotectonic evolution previous studies of this volcano focused on specific features and were limited by the quality and coverage of contemporary data our objective is to review and enhance the existing developmental model for ascraeus by considering all endogenic surface features on the volcano we surveyed the volcano s caldera complex flank terraces pit structures sinuous rilles arcuate grabens and small vents we report the spatial and temporal distributions of these features appraise their proposed formation mechanisms in light of our mapping results and propose a detailed geological history for ascraeus mons an initial shield building phase was followed by the formation of a summit caldera complex and small parasitic cones while compression due to flexure of the supporting basement led to extensive terracing of the shield flanks an eruptive hiatus followed ending with the construction of expansive rift aprons to the northeast and southwest against later extensive flank resurfacing in the late amazonian continued flexure formed arcuate grabens concentric to the edifice localized eruption and surface flow of a fluid agent lava and or water from within the volcano then produced a population of rilles on the lower flanks finally in a change of flank tectonic regime from compression to extension pit crater chains and troughs developed on the main shield and rift aprons eventually coalescing to form large embayments at the northeast and southwest base of the volcano

slope streaks on mars a new wet mechanism slope steaks are one of the most intriguing modern phenomena observed on mars they have been mostly interpreted as some specific type of granular flow we propose another mechanism for slope streak formation on mars it involves natural seasonal formation of a modest amount of highly concentrated chloride brines within a seasonal thermal skin and runaway propagation of percolation fronts given the current state of knowledge of temperature regimes and the composition and structure of the surface layer in the slope streak regions this mechanism is consistent with the observational constraints it requires an assumption that a significant part of the observed chlorine to be in form of calcium and ferric chloride and a small part of the observed hydrogen to be in form of water ice this wet mechanism has a number of appealing advantages in comparison to the widely accepted dry granular flow mechanism potential tests for the wet mechanism include better modeling of the temperature regime and observations of the seasonality of streak formation

topographic measurements of slope streaks on mars abstract slope streaks are enigmatic actively forming albedo features occurring on slopes in high albedo low thermal inertia dust rich equatorial regions on mars they are a specifically martian phenomenon with no direct analogs on the earth their morphology suggests that the streaks are initiated at their upslope tips and propagate down to their termini however the physical mechanism of their formation is uncertain we performed a large series of measurements of slopes associated with slope streaks using stereo pairs of high resolution orbital images obtained by hirise camera and generated several digital elevation models for selected streaks we found that 1 slopes at the upslope streak tips range widely however there is a strong indication that streaks can be initiated only on slopes steeper than 20 2 slopes of the streak termini show an even wider range with some streaks terminating at slopes as steep as their tips while others propagate all the way down to horizontal surfaces 3 the streaks can propagate stably for long many hundreds of meters distances and can turn following the topographic gradient on 10 15 slopes 4 no uphill propagation of streaks is detected over baselines of tens of meters 5 the slope streaks often propagate over 1 2 m high obstacles and can climb 1 2 m uphill over short meters distances we used these findings to assess the viability of two classes of hypotheses about slope streak formation mechanisms proposed earlier 1 dry some kind of run away avalanche like dry granular flow and 2 wet some kind of run away propagation of a front of percolating brines in the shallow subsurface no specific observation unambiguously proves or rejects either of the two mechanisms several of our findings are readily explained by the dry mechanism and cannot be easily explained with any kind of wet mechanism while other findings are closely consistent with the wet mechanism and are difficult to reconcile with the dry mechanism this situation might be explained by equifinality meaning that the streaks despite their similarity are formed by different physical processes alternatively some modifications to either the dry or wet mechanisms may be able to provide a coherent explanation it is also possible that new ideas are needed to understand the processes involved

sediment segregation by biodiffusing bivalves the selective processing of sediment fractions sand and mud 63 mm and 63 mm median grain size by macrofauna was assessed using two size classes of inert uv fluorescent sediment fraction tracers luminophores the luminophores were applied to the sediment surface in 16 m 2 replicated plots defaunated and control and left to be reworked by infauna for 32 days as the macrofaunal assemblage in the ambient sediment and the control plots was dominated by the common cockle cerastoderma edule this species was used in an additional mesocosm experiment the diversity abundance and biomass of the defaunated macrobenthic assemblage did not return to control values within the experimental period both erosion threshold and bed elevation increased in the defaunated plots as a response to the absence of macrofauna and an increase in microphytobenthos growth in the absence of macrobenthos we observed an accretion of 7 mm sediment containing ca 60 mud image analysis of the vertical distribution of the different luminophore size classes showed that the cockles preferentially mobilised fine material from the sediment thereby rendering it less muddy and effectively increasing the sand mud ratio luminophore profiles and budgets of the mesocosm experiment under no waves no current conditions support the field data very well

flank tectonics of martian volcanoes on the flanks of olympus mons is a series of terraces concentrically distributed around the caldera their morphology and location suggest that they could be thrust faults caused by compressional failure of the cone in an attempt to understand the mechanism of faulting and the possible influences of the interior structure of olympus mons we have constructed a numerical model for elastic stresses within a martian volcano in the absence of internal pressurization the middle slopes of the cone are subjected to compressional stress appropriate to the formation of thrust faults these stresses for olympus mons are 250 mpa if a vacant magma chamber is contained within the cone the region of maximum compressional stress is extended toward the base of the cone if the magma chamber is pressurized extensional stresses occur at the summit and on the upper slopes of the cone for a filled but unpressurized magma chamber the observed positions of the faults agree well with the calculated region of high compressional stress three other volcanoes on mars ascraeus mons arsia mons and pavonis mons possess similar terraces extending our analysis to other martian volcanoes we find that only these three and olympus mons have flank stresses that exceed the compressional failure strength of basalt lending support to the view that the terraces on all four are thrust faults

autonomous underwater vehicle measurements of surface wave decay and directional spectra in the marginal sea ice zone in march 2003 several autonomous underwater vehicle auv missions were carried out under sea ice in the western bellingshausen sea data from the upward looking acoustic doppler current profiler adcp on the autosub auv indicate a strongly oscillating horizontal velocity of the ice due to ocean swell swell period height direction and directional spread have been computed every 800 m from the ice edge to 10 km inward for three missions exponential period dependent attenuation of waves propagating through sea ice was observed mean period increased with distance from the ice edge the wave field refracted during propagation the directional wave spread does not seem to relate to distance from the ice edge although higher frequencies tended to be more spread if suitably deployed an ordinary adcp may be used with this technique to study both scalar and directional properties of waves in open or ice covered water

sar imaging of wave dispersion in antarctic pancake ice and its use in measuring ice thickness 1 a synthetic aperture radar sar image of the advancing winter marginal ice zone miz in the antarctic composed of frazil pancake ice has been analysed in a new way in order to test the predictions of a recently developed theory of wave dispersion in pancake ice which treats the ice as a viscous layer in the image obtained in april 2000 the structure of the wave spectrum in the miz and its change from the open water spectrum are consistent with a pancake layer 24 cm thick intensive in situ measurements of the pancake ice in the miz 280 km w of the image location were made from fs polarstern during a period covering the satellite imaging and also yielded a mean ice thickness of 24 cm we conclude that this technique gives realistic results for ice thickness whereas earlier work based on a different dispersion theory mass loading tended to over estimate thickness after further validation it is therefore possible that the sar wave technique can become an accepted method for monitoring ice thickness in pancake icefields

active tails enhance arboreal acrobatics in geckos geckos are nature s elite climbers their remarkable climbing feats have been attributed to specialized feet with hairy toes that uncurl and peel in milliseconds here we report that the secret to the gecko s arboreal acrobatics includes an active tail we examine the tail s role during rapid climbing aerial descent and gliding we show that a gecko s tail functions as an emergency fifth leg to prevent falling during rapid climbing a response initiated by slipping causes the tail tip to push against the vertical surface thereby preventing pitch back of the head and upper body when pitch back cannot be prevented geckos avoid falling by placing their tail in a posture similar to a bicycle s kickstand should a gecko fall with its back to the ground a swing of its tail induces the most rapid zero angular momentum air righting response yet measured once righted to a sprawled gliding posture circular tail movements control yaw and pitch as the gecko descends our results suggest that large active tails can function as effective control appendages these results have provided biological inspiration for the design of an active tail on a climbing robot and we anticipate their use in small unmanned gliding vehicles and multisegment spacecraft

response of a circular ice floe to ocean waves a new model is presented to reproduce the behavior of a solitary circular flexible ice floe brought into motion by the action of long crested sea waves the intended application of the work is ultimately a fully three dimensional analogue of a marginal ice zone miz through which ocean waves propagate allowing the attenuation and directional advance to be forecast and validated against observations existing theory does not treat directional changes correctly to enable a check to be made on the model two independent methods are developed an expansion in the eigenfunctions of a thin circular plate and the more general method of eigenfunctions used to construct a green s function for the floe displacement and three dimensional scattering patterns in the water surrounding the floe are given for several floe geometries the model is also used to investigate the strain field generated in the floe its surge response and the energy initiated in the water encircling it finally with the aim of understanding how floes herd together to form cohesive structures in the miz the force induced on floes of various thicknesses and diameters is plotted

mass movement within a slope streak on mars 1 slope streaks on mars represent a currently active geological process various theories for slope streak formation have suggested that slope streaks form by disturbing only a thin surface veneer or by staining of the surface preserving pre existing topography within the streak theories also vary as to whether the formation mechanism requires the presence of water or another liquid we present observations of a slope streak that reveal topographic mounds within the streak these mounds do not continue outside the streak and we suggest that they formed with or immediately after the slope streak we use estimates of the total volume of mounds in this particular streak compared with the estimated excavation volume to extrapolate to a global sediment transport rate from slope streak formation if this slope streak is typical then this calculated rate is greater than estimates of the total volume of material transported by dust storms each year

steady state tracer dynamics in a lattice automaton model of bioturbation the intensity of biogenic sediment mixing is often expressed as a biodiffusion coefficient db quantified by fitting a diffusive model of bioturbation to vertical profiles of particle bound radioisotopes the biodiffusion coefficient often exhibits a dependence on tracer half life short lived radioisotopes e g 234th tend to yield notably larger db values than longer lived radioisotopes e g 210pb it has been hypothesized that this is a result of differential mixing of tracers by particle selective benthos this study employs a lattice automaton model of bioturbation to explore how steady state tracers with different half lives are mixed in typical marine settings every particle in the model is tagged with the same array of radioisotopes so that all tracers experienced exactly the same degree of mixing two different estimates of the mixing intensity are calculated a tracer derived db obtained in the standard way by fitting the biodiffusion model to resulting tracer profiles and a particle tracking db derived from the statistics of particle movements the latter provides a tracer independent measure of mixing for use as a reference our simulations demonstrate that an apparent db tracer dependence results from violating the underlying assumptions of the biodiffusion model breakdown of the model is rarely apparent from tracer profiles emphasizing the need to evaluate the model s criteria from biological and ecological parameters rather than relying on obvious indications of model breakdown e g subsurface maxima simulations of various marine environments coastal slope abyssal suggest that the time scales of short lived radioisotopes such as 234th and 7be are insufficient for the tracers to be used with the biodiffusion model 210pb appears an appropriate tracer for abyssal sediments while 210pb and 228th are suitable for slope and coastal sediments

stability of bubbles in a linear elastic medium implications for bubble growth in marine sediments 1 methane bubbles in muddy fine grained sediments grow initially through a process of elastic expansion punctuated by discrete fracture events lefm growth the ability of the surrounding sediments to support a stress and actively resist expansion can under conditions of low gas production or high sediment toughness result in the cessation of growth and the presence of stable bubbles thus it is possible for a bubble to stop growing despite the presence of a source in the sediments that continues to produce gas this contrasts with growth of bubbles in a fluid medium which cannot support a stress and so will continue to grow as long as a surrounding source provides gas this no growth condition is the result of the coupling between gas supply methane production or supersaturation and the sediment mechanics here we quantify this condition and present a criterion for the switch between no growth and the lefm growth regimes we apply this theory to the sediments of eckernforde bay in the kiel bight germany and despite the absence of measurements for the key sediment mechanical properties we can provide a qualitative explanation for the sizes and shapes of the observed bubble population with depth in the sediment we also show how the release of hydrostatic pressure can stimulate growth by pushing otherwise stable bubbles into the lefm growth regime this could provide a mechanism for the release of bubbles during periods of low water such as during low tide or wave events

slope streak formation and dust deposition rates on mars 1 the mars orbiter camera moc has imaged sometimes repeatedly mass movements known as slope streaks which are abundant in the dust covered regions on mars they are among the few known examples of contemporary surface changes a survey of 173 collocated image pairs indicates that these features are currently forming at a high rate of 7 per existing streak per martian year either there is a complete turnover within a few decades or the streak population is currently increasing rapidly large spatial as well as possible temporal variations in the formation rate are obtained from these data streaks do not appear to fade over time periods comparable to their inverse formation rate of 28 years as seen by analysis of viking orbiter images containing streaks that are still visible in moc images gradual or stochastic variations in dust deposition may be needed to explain observations of changes in the formation rate and its current imbalance with the fading rate

airborne remote sensing of wave propagation in the marginal ice zone airborne scanning lidar was used to measure the evolution of the surface wave field in the marginal ice zone miz during two separate wave events in the beaufort sea in october 2015 the lidar data consisted of a 2 d field of surface elevation with horizontal resolutions between 17 and 33 cm over a swath approximately 150 220 m wide centred on the ground track of the aircraft those data were used to compute directional wavenumber spectra of the surface wave field comparison with nearly collocated buoy data found the lidar and buoy measurements to be generally consistent during the first event waves traveling from open water into the ice were attenuated by the ice the low spectral spreading and k7 4 spectral dependence of the attenuation was consistent with dissipative models that treat sea ice as a highly viscous fluid floating on a less viscous ocean upper ocean eddy viscosities calculated using that model were found to be significantly lower than those from previous work the second event was in off ice winds and cold temperatures allowing measurement of the wave fetch relation in ice forming conditions the wave growth rate was found to be slightly higher than previous measurements under unstable atmospheric conditions without ice formation comparison with wavewatch iii model output highlighted the importance of accurate ice information and fine geographic computational resolution when making predictions near the ice edge finally the very short scales over which the wave field was observed to evolve in the miz are discussed