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

horizontal structures in granulite terrains a record of mountain building or mountain collapse in many high temperature 800 c granulite terrains the development of characteristic horizontal structures occurred during the metamorphic culmination and was followed by isobaric cooling the absolute magnitude of isobaric cooling commonly 300 c implies cooling intervals of the order of the thermal time constant of the continental lithosphere 100 m y such prolonged isobaric cooling implies that no significant erosional denudation followed the development of the horizontal structures and thus precludes the prograde deformation being responsible for significant crustal thickening rather the prograde deformation more probably records bulk crustal thinning during extensional collapse of a previously thickened crust possibly triggered by detachment of a thickened thermal boundary layer at the base of the lithosphere

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

pollen evidence for variations in the southern margin of the westerly winds in sw patagonia over the last 12 600 years we report pollen and charcoal records from vega nandu 51 0 s 72 45 w a small mire located near the modern forest steppe ecotone in torres del paine national park southern chile the record shows an open landscape dominated by low shrubs and herbs between 12 600 and 10 800 cal yr bp under cold and relatively humid conditions nothofagus experienced frequent large amplitude oscillations between 10 800 and 6800 cal yr bp indicating recurrent transitions between shrubland parkland environments under warm and highly variable moisture conditions a sustained increase in nothofagus started at 6800 cal yr bp punctuated by step wise increases at 5100 and 2400 cal yr bp implying further increases in precipitation we interpret these results as indicative of variations in the amount of precipitation of westerly origin with prominent increases at 6800 5100 and 2400 cal yr bp these pulses led to peak precipitation regimes during the last two millennia in this part of sw patagonia our data suggest variations in the position and or strength of the southern margin of the westerlies most likely linked to variations in the extent and or persistence of sea ice and sea surface temperature anomalies in the southern ocean over the last two centuries the record shows a forest decline and expansion of rumex acetosella an exotic species indicative of european disturbance 2007 university of washington all rights reserved

the acheron dorsum on mars a novel interpretation of its linear depressions and a model for its evolution abstract the acheron dorsum north of olympus mons on mars is a unique 800 km long arcuate ridge apparently unrelated to other adjacent morphologies acheron dorsum is crossed by deep and wide fractures fossae here referred to also as linear depressions or lds commonly interpreted as grabens formed by local lithosphere stress in response to endogenous mantle upwelling we suggest an alternate view that the linear depressions may result from gravitational self adjustment of a loose deposit similar to the deep seated gravitational slope deformations dsgsd or sackung a kind of slow mass movement well documented on earth numerical simulations based on a finite difference numerical model devised for terrestrial dsgsds reproduce the timing and position of lds reasonably well provided that the viscosity of the viscoplastic layer is between 7 10 15 and 10 17 pa s while rock masses typically exhibit much higher values based on comparison with glacial examples we find that these viscosities could be compatible to a rock ice mixture this leads to the hypothesis that the rock underneath acheron dorsum may be highly fragmented and that ice might have been involved in its deformation our hypothesis could shed light on the puzzling stress pattern on acheron dorsum which follows approximately the ridge without requiring the presence of hypothetical small scale endogenous currents

dinoflagellate cysts from sediment traps deployed in the bellingshausen weddell and scotia seas antarctica dinoflagellate cysts have been recovered from six long term 1 2 yr sediment trap moorings deployed in the bellingshausen weddell and scotia seas antarctica these traps mostly moored near the sea bed to sample the nepheloid layer were located both within and to the north of the maximum sea ice limit the numbers of cysts together with the composition of the assemblages reinforce the importance of the maximum sea ice limit as a modern biogeographic boundary for the distribution of dinoflagellate cysts cysts derived from heterotrophic dinoflagellates make up the highest proportions within the assemblages recovered from the traps one trap sampled the export production revealing little difference in cyst flux over those sampling the nepheloid layer cyst flux appears to be highest in areas closest to the antarctic convergence north of the maximum sea ice limit and to high nutrient availability there are however differences between the sediment trap assemblages and those recovered from core top samples at the same or nearby sites these differences in the greater number of cysts and in the higher numbers of round brown protoperidinium cysts in the traps may reflect annual differences in the primary productivity and or cyst production in the area in some areas the sediment record may preserve little information about local surface water productivity because of the activity of bottom water currents for example those arising from the antarctic circumpolar current

mars and earth comparison of cold climate features abstract on earth glacial and periglacial features are common in areas of cold climate on mars the temperature of the present day surface is appropriate for permafrost and the presence of water is suspected from data relating to the outgassing of the planet from remote sensing measurements over the polar caps and elsewhere on the martian surface and from recognition of fluvial morphological features such as channels these observations and the possibility that ice could be in equilibrium with the atmosphere in the high latitudes north and south of 40 latitude suggest that glacial and periglacial features should exist on the planet morphological studies based mainly on viking pictures indicate many features that can be attributed to the action of ice among these features are extensive talus aprons debris avalanches flows that resemble glaciers or rock glaciers ridges that look like moraines various types of patterned ground scalloped scarps and chaotically collapsed terrain that could be attributed to thermokarst processes and landforms that may reflect the interaction of volcanism and ice

on the frontal dynamics and morphology of submarine debris flows several submarine debris flows show an apparently chaotic frontal part with blocks of variable size from roughly tens to some hundreds of metres located some distance beyond the front of the main deposits this outrunner phenomenon was studied both in the field and in laboratory experiments depositional patterns in a field case finneidfjord northern norway are classified from the outer distal part of the debris flow to the outermost outrunner block similar patterns were found in experimental debris flows and we suggest that flow processes in the laboratory are applicable to the field example theoretical investigations are applied to assess frontal dynamics and especially the formation and motion of outrunner blocks as the front of the debris flow pushes through ambient water a combination of front pressure and lift force allows for intrusion of a water layer underneath the front hydroplaning this water layer reduces basal friction and induces tensile stresses farther behind the front leading to a possible detachment and decoupling with respect to the main slide body these outrunner blocks show an increased mobility compared to the main slide body and deposition of such blocks may occur far away from the main slide body

the angle of reach as a mobility index for small and large landslides the relations between the angle of reach fahrboschung and other indexes expressing the mobility of landslides and vertical drop horizontal reach and volume of landslide mass have been analyzed by means of simplified plots and regression equations results for 204 landslides of all sizes show that whatever the mechanism of motion all kinds of landslides experience a continuous reduction of the angle of reach with volume increase this reduction starts from the smallest sizes scattering in this relation is mostly due to mechanisms of motion and to both obstacles and topographic constraints on the path this synthesis indicates that small landslides less than 0 5 106 m3 in relative terms display excesses of travel distance similar to large landslides since most small landslides are not expected to develop any change in the mechanism of progression while moving the decrease in the reach angle with volume suggests that scale effects should be taken into account the angle of reach is found to be

coastal geomorphology of the martian northern plains the paper considers the question of the formation of the outflow channels and valley networks discovered on the martian northern plains during the mariner 9 mission parker and saunders 1987 and parker et al 1987 1989 data are used to describe key features common both in the lower reaches of the outflow channels and within and along the margins of the entire northern plains it is suggested that of the geological processes capable of producing similar morphologies on earth lacustrine or marine deposition and subsequent periglacial modification offer the simplest and most consistent explanation for the suit of features found on mars

oceans on mars an assessment of the observational evidence and possible fate the edges of the northern plains and interpreted to be shorelines remaining from these former standing bodies of water we examine the elevations and geologic relations along these contacts in detail and find little support for their interpretation as shorelines some contacts are clearly of volcanic origin and all have significant variations in elevation better support for the former presence of water over large parts of the northern plains is provided by the vastitas borealis formation vbf most of the post noachian fill within the northern basin is ridged plains of lower hesperian age interpreted to be volcanic in origin overlying the ridged plains is the vbf a thin veneer of material of upper hesperian age the vbf may have been deposited from large floods support for this interpretation is the similarity in age between the outflow channels and the vbf the presence of the vbf at the lower ends of the outflow channels and identification of numerous features in the outcrop areas of the vbf that are suggestive of basal melting of an ice sheet to cover all the area over which the vbf is exposed would require 2 3 10 7 km 3 of water spread over the entire surface of mars this volume is equal to a global layer global equivalent layer or gel 156 m deep we find no support for the larger estimates of ocean volumes that range up to 3 10 8 km 3 and which imply comparable amounts of water per unit area as are currently present on the surface of the earth under present climatic conditions on mars an ocean would freeze in a geologically short time period 10 4 years then would sublimate away at rates strongly dependent on the presence or absence of debris on the ice surface the present vbf is interpreted as a sublimation residue from the ponded outflow channel effluents the fate of a volume of water thought to have been emplaced by the outflow channels 2 3 10 7 km 3 is largely accounted for by the presence of other existing reservoirs on the planet an approximately 20 30 m gel of water is estimated to be in the present polar caps and a 50 m gel may have escaped to space since the hesperian leaving 80 m gel unaccounted for this amount may be partly trapped in other volatile rich deposits on the surface and a significant amount could have reentered the groundwater system by south polar basal melting and been progressively cold trapped at the base of a growing cryosphere on the basis of our assessment of the hesperian aged deposits we predict that testing of the clifford and parker 2001 hypothesis that a noachian aged ocean covered up to one third of the surface of mars will be made very difficult by the enhanced degradation rates in the noachian and subsequent geological events in the northern lowlands index terms 6225 planetology solar system objects mars 4267 oceanography general paleoceanography 5407 planetary sciences atmospheres evolution 5470 planetary sciences surface materials and properties 1635 global change oceans 4203 keywords mars oceans channels shorelines hesperian

global scale analysis of martian landslide mobility and paleoenvironmental clues the mobility of landslides on mars is studied based on a database of 3 118 events to establish the volume of the landslides for the whole dataset based on the deposit area a new volume area relationship based on a representative dataset of 222 landslides is used plotting the h l ratio between fall height h and runout l versus volume landslide mobility is analyzed and compared with existing empirical relationships for martian and terrestrial landslides analyzing the mobility in terms of normalized residuals i e the relative deviation of the h l ratio from the dataset best fit line mobility is found to depend on both the landslide location on mars and landslide typology this allows us to identify four different types of high mobility hypermobile landslides three classes of high mobility landslides are associated respectively to meteoroid impact the olympus mons aureoles and landslides with toreva block failure style and their mobility can be explained by the peculiar flow mechanics the fourth class includes landslides associated with isolated craters those in the regions wetted by the putative oceanus borealis and the ones at high latitudes we suggest that the common factor behind all the hypermobile landslides of this fourth kind is the presence of ice this is confirmed by our data showing that landslides increase in mobility with latitude the latitudinal trend mirrors the distribution of ice as detected by radar neutron probes and the presence of glacial and layered ejecta morphologies because the overall landslide distribution supports the presence of ice lubricated conditions two ice lubrication models are presented showing how ice melting within or underneath the landslides could enhance mobility by proper analysis in terms of apparent friction residuals we find that the mobility of landslides in valles marineris with the largest landslide concentration is lower than average we explain this circumstance partly from the smaller role of ice in equatorial valles marineris and partly because the collapses from high slope relief imply high speed impact with the floor valley confinement loss of momentum and decrease in mobility environmental consequences imply that the present subsurface ice distribution may have been persistent throughout the amazonian period

reconstruction of sea surface conditions at middle to high latitudes of the northern hemisphere during the last glacial maximum lgm based on dinoflagellate cyst assemblages abstract a new calibration database of census counts of organic walled dinoflagellate cyst dinocyst assemblages has been developed from the analyses of surface sediment samples collected at middle to high latitudes of the northern hemisphere after standardisation of taxonomy and laboratory procedures the database comprises 940 reference data points from the north atlantic arctic and north pacific oceans and their adjacent seas including the mediterranean sea as well as epicontinental environments such as the estuary and gulf of st lawrence the bering sea and the hudson bay the relative abundance of taxa was analysed to describe the distribution of assemblages the best analogue technique was used for the reconstruction of last glacial maximum lgm sea surface temperature and salinity during summer and winter in addition to sea ice cover extent at sites from the north atlantic n 63 mediterranean sea n 1 and eastern north pacific n 1 three of the north atlantic cores from the continental margin of eastern canada revealed a barren lgm interval probably because of quasi permanent sea ice six other cores from the greenland and norwegian seas were excluded from the compilation because of too sparse assemblages and poor analogue situation at the remaining sites n 54 relatively close modern analogues were found for most lgm samples which allowed reconstructions the new lgm results are consistent with previous reconstructions based on dinocyst data which show much cooler conditions than at present along the continental margins of canada and europe but sharp gradients of increasing temperature offshore the results also suggest low salinity and larger than present contrasts in seasonal temperatures with colder winters and more extensive sea ice cover whereas relatively warm conditions may have prevailed offshore in summer from these data we hypothesise low thermal inertia in a shallow and low density surface water layer

laboratory simulation of debris flows over sand dunes insights into gully formation mars gully morphology often summarized as comprising an alcove channel and debris apron is one of the key elements used to support the argument for liquid water in the recent past on mars nevertheless the processes that create different gully morphologies on both mars and earth are not fully understood one of the puzzling morphologic attributes of martian dune gullies is their apparent lack of an apron or terminal deposit which has caused debate about their formation process several physical processes such as runoff debris flows granular flows and sliding blocks falling downslope could explain the formation of these gullies in this work we focus on the role of liquid in the substrate as well as in the flow and choose to experimentally test the plausibility of this hypothesis we performed a series of analogue experiments to investigate the formation of gullies on sand dune like substrates we used controlled flows of water over an inclined sand box to produce gully like forms ice rich sedimentary substrates were used including substrates that included a thin liquid water saturated thawed layer an active layer above the ice saturated zone to give an analogue for a periglacial environment we quantitatively demonstrate that debris flow processes in periglacial experiments are conducive to the formation of narrow and long channels with small terminal deposits with perched channels by re analysis of martian elevation data for dune gullies on mars we have found good evidence that such terminal deposits could exist our experiments revealed that increased water content in the thawed layer above the frozen bed increases flow length due to the subsequent reduction in infiltration capacity water is incorporated into the flow by erosion of the wet thawed layer sand plus water and by drainage of the thawed layer using a mars environment simulation chamber we found that atmospheric pressure conditions seem to have a limited influence on the morphology of the flows our experimental investigation allowed the reproduction of terrestrial debris flow and martian gully morphologies suggesting that a substrate that is resistant to infiltration could be present beneath the dune gullies on mars we suggest that like in our laboratory experiments the presence of ice at shallow depth is a possible explanation for the formation of these morphologies and that a wet thawed layer is a possible explanation for the long flow length

meltwater pulse 1a from antarctica as a trigger of the bolling allerod warm interval meltwater pulse 1a mwp 1a was a prominent feature of the last deglaciation which led to a sea level rise of 20 meters in less than 500 years concurrent with mwp 1a was the onset of the bolling allerod interstadial event 14 600 years before the present which marked the termination of the last glacial period previous studies have been unable to reconcile a warm northern hemisphere with mwp 1a originating from the laurentide or fennoscandian ice sheets with the use of a climate model of intermediate complexity we demonstrate that with mwp 1a originating from the antarctic ice sheet consistent with recent sea level fingerprinting inferences the strength of north atlantic deep water nadw formation increases thereby warming the north atlantic region and providing an explanation for the onset of the bolling allerod warm interval the established mode of active nadw formation is then able to respond to subsequent freshwater forcing from the laurentide and fennoscandian ice sheets setting the stage for the younger dryas cold period the melting of continental ice sheets during the last deglaciation provided a freshwater source to the ocean that affected global sea level and the strength of the thermohaline circulation an exceptionally large melting event inferred from far field relative sea level records occurred

use of dinoflagellate cysts to determine changing quaternary sea surface temperature in southern australia abstract cluster analysis and principal component analysis of dinoflagellate cyst assemblage data from two cores so36 7 and v18 222 off southern australia clearly separate glacial from interglacial environments however those species causing much of the differentiation respond differently to changing sea surface temperature in the two cores this varying response emphasises the complexity of dinoflagellate interactions with the environment and underlines the need for caution in interpretation particularly with sea surface temperature

mobility and topographic effects for large valles marineris landslides on mars 1 recent experiments on dry granular flows over horizontal plane bare some similarities with large martian landslides observed in valles marineris vm however martian normalized runout are twice as large as those that observed in dry granular flow experiments numerical simulations on theoretical 2d and real 3d topographies reconstructed from remote sensing data show that slope effects significantly reduce the shift between experimental results and martian observation however topography effects are not strong enough to explain the high mobility of martian landslides as a result other physical and or geological processes should play a key role into the dynamics of martian landslides a new mobility is defined that makes it possible to characterize the dynamics of the flow regardless of the geometry of the released mass and of the underlying topography

tropical to mid latitude snow and ice accumulation flow and glaciation on mars images from the mars express hrsc high resolution stereo camera of debris aprons at the base of massifs in eastern hellas reveal numerous concentrically ridged lobate and pitted features and related evidence of extremely ice rich glacier like viscous flow and sublimation together with new evidence for recent ice rich rock glaciers at the base of the olympus mons scarp superposed on larger late amazonian debris covered piedmont glaciers we interpret these deposits as evidence for geologically recent and recurring glacial activity in tropical and mid latitude regions of mars during periods of increased spin axis obliquity when polar ice was mobilized and redeposited in microenvironments at lower latitudes the data indicate that abundant residual ice probably remains in these deposits and that these records of geologically recent climate changes are accessible to future automated and human surface exploration

lithospheric flexure and gravity spreading of olympus mons volcano mars the structural architecture of large volcanoes is governed substantially by gravity driven deformation that is manifest as distinct processes such as basement flexure or volcanic spreading temporal effects and the mutual interplay of these processes have been investigated only to a limited extent and so we present novel numerical models of the time dependent deformation associated with them the models simulate the combined effects of lithospheric flexure and volcanic spreading during growth increments of an elastoplastic volcanic cone different spreading scenarios are considered by a variable coupling decoupling behavior at the interface between volcano and basement we apply our models to olympus mons on mars which is characterized by upper to middle flank terraces on the shield is encircled by a basal scarp that has an average slope of 30 and is surrounded by distant deposits that resemble large scale slumping features on earth our results are consistent with the interpretation that terraces on olympus mons flanks form by thrust faulting that results from lithospheric flexure the presence and expression of terraces depend on the coupling of volcano and basement on the time of volcano growth relative to mantle relaxation and on the cohesion of the edifice the encircling scarp may be related to a very low friction detachment at the edifice base which leads to a normal fault regime on the lowermost flanks with time and volcano growth predicted stress and faulting regimes migrate only slightly indicating that the structural architecture of volcanoes is largely set in the very early stages of formation

hyaloclastites and the slope stability of hawaiian volcanoes insights from the hawaiian scientific drilling project s 3 km drill core abstract core samples recovered during the hawaiian scientific drilling project hsdp drilling project reveal that the upper 1 km of the submarine flank of mauna kea is comprised mainly of hyaloclastites progressive very low temperature alteration of these hyaloclastites has been accompanied by systematic transformations in physical properties of these deposits hyaloclastite deposits which directly underlie ca 1 km of subaerially emplaced lavas are very poorly consolidated but over a depth interval of ca 500 m compaction and especially precipitation of zeolitic pore filling cements associated with palagonitization of sideromelane have eliminated porosity as well as promoted the consolidation of these hyaloclastites the latter is reflected in unconfined compressive strengths which increase from mean values respectively of 2 5 and 4 6 mpa in weakly consolidated smectite rich hyaloclastites from the incipient 1080 to 1335 mbsl and smectitic 1405 1573 mbsl alteration zones to a mean value of 10 0 mpa in the more highly consolidated hyaloclastites of the palagonitic zone of alteration from 1573 mbsl to the bottom of the drill hole conversely overlying intercalated and underlying lava flows are generally much less altered and have mean compressive strengths which are 1 to 2 orders of magnitude greater then hyaloclastites at equivalent depths the shear strengths of the hyaloclastites also increase with depth and grade of alteration but are uniformly and substantially lower in the lavas those hyaloclastites exhibiting the highest grade of alteration i e palagonitic also exhibit the highest measured strengths and thus the alteration of hyaloclastites appears to strengthen as opposed to weaken the flanks of the edifice however the contrast in strength between hyaloclastites and lavas may be a primary factor in localizing destabilization and the zones of weak and poorly consolidated hyaloclastites may facilitate slumping by servings as hosts for shallow detachment surfaces on the unsupported flanks of these volcanoes

southern ocean origin for the resumption of atlantic thermohaline circulation during deglaciation during the two most recent deglaciations the southern hemisphere warmed before greenland at the same time the northern atlantic ocean was exposed to meltwater discharge which is generally assumed to reduce the formation of north atlantic deep water yet during deglaciation the atlantic thermohaline circulation became more vigorous in the transition from a weak glacial to a strong interglacial mode here we use a three dimensional ocean circulation model to investigate the impact of southern ocean warming and the associated sea ice retreat on the atlantic thermohaline circulation we find that a gradual warming in the southern ocean during deglaciation induces an abrupt resumption of the interglacial mode of the thermohaline circulation triggered by increased mass transport into the atlantic ocean via the warm indian ocean and cold pacific ocean water route this effect prevails over the influence of meltwater discharge which would oppose a strengthening of the thermohaline circulation a southern ocean trigger for the transition into an interglacial mode of circulation provides a consistent picture of southern and northern hemispheric climate change at times of deglaciation in agreement with the available proxy records

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

rafted pumice a new model for the formation of the medusae fossae formation mars abstract the medusae fossae formation mff mars could be deposits of materials originally formed as hyaloclastites erupted from vents which formed the basal units of olympus mons volcano and subsequently collapsed as landslides to form the aureole materials these low density hyaloclastites subsequently floated on the northern sea as pumice rafts and drifted to the southwest where they encountered the boundary of the southern highlands to form the mff

rheological constraints on martian landslides we use a dynamic finite difference model to simulate martian landslides in the valles marineris canyon system and olympus mons aureole using three different modal rheologies frictional bingham and power law the frictional and bingham modes are applied individually fluidized rheology is treated as a combination of frictional and power law modes general fluidization can include pore pressure contributions whereas acoustic fluidization does not we find that general fluidization most often produces slides that best match landslide geometry in the valles marineris this implies that some amount of supporting liquid or gas was present in the material during failure the profile of the olympus mons aureole is not well matched by any landslide model suggesting an alternative genesis in contrast acoustic fluidization produces the best match for a lunar slide a result anticipated for dry crust with no overlying atmosphere the presence of pressurized fluid during valles marineris landsliding may be due to liquid water beneath a thin cryosphere 1 2 km or flash sublimation of co2

volcanic spreading and lateral variations in the structure of olympus mons mars the olympus mons volcano on mars is notable not only for its immense height and width but also for substantial asymmetries in its structure the gently sloped northwest flank extends to a much greater distance from the central caldera complex than the more steeply sloped southeast flank furthermore the northwest flank exhibits lower flank extensional faults whereas the southeast shows upper flank compressional terraces and lower flank upthrust blocks however both the northwest and southeast flanks exhibit characteristic concave upward profiles and steep bounding scarps in contrast to other sectors the nw se asymmetries are aligned with the regional slope from the tharsis rise but an understanding of the underlying causes has remained elusive we use particle dynamics models of growing spreading volcanoes to demonstrate that these flank structures could reflect the properties of the basement materials underlying olympus mons we find that basal slopes alone are insufficient to produce the observed concave upward slopes and asymmetries in flank extent and deformation style that are observed at olympus mons instead lateral variations in basal friction are required these variations are most likely related to the presence of sediments transported and preferentially accumulated downslope from the tharsis rise such sediments likely correspond to ancient phyllosilicates clays recently discovered by the mars express mission

high and low latitude climate control on the position of the southern peru chile current during the holocene 1 we reconstructed changes of temperature salinity and productivity within the southern peru chile current during the last 8000 years from a high resolution sediment core recovered at 41 s using alkenones isotope ratios of planktic foraminifera biogenic opal and organic carbon paleotemperatures and paleosalinities reached maximum values at 5500 years ago and thereafter declined to modern values whereas paleoproductivity continuously increased throughout the last 8000 years we ascribe these long term holocene trends primarily to latitudinal shifts of the antarctic circumpolar current acc the concurrence with shifts in the position of the southern westerlies points to a common response of atmospheric and oceanographic circulation patterns off southern chile millennial to centennial scale fluctuations of paleotemperatures and paleosalinities on the other hand lag displacements in the position of the southern westerlies but reveal a significant correlation to short term temperature changes in antarctica indicating a high latitude control of the acc at these timescales

the aureole of olympus mons mars as the compound deposit of submarine landslides abstract the enigmatic deposits building up the olympus mons aureole on mars are likely among the largest landslide remnants in the solar system these deposits exhibit an extraordinary run out distance up to nearly 700 km in spite of a fall height some 100 times smaller after quantifying the mobility of the olympus mons aureole lobes it is suggested based on dynamical considerations and morphological analysis that the aureole could be the consequence of a series of gigantic subaqueous landslides in order to bring evidence in favor of this interpretation comparisons are drawn between the different landslide deposits on earth and mars emphasizing the similarity with the rock avalanches of the canary islands and the hawaii the results of experimental subaqueous debris flows are also analyzed and numerical calculations are introduced to simulate the dynamics of flow in analogy with certain subaqueous landslides on earth it is possible that the outstanding run out of the aureole lobes was a consequence of hydroplaning a natural lubrication by water during flow

unusual july 10 1996 rock fall at happy isles yosemite national park california effects of the july 10 1996 rock fall at happy isles in yosemite national park california were unusual compared to most rock falls two main rock masses fell about 14 s apart from a 665 m high cliff southeast of glacier point onto a talus slope above happy isles in the eastern part of yosemite valley the two impacts were recorded by seismographs as much as 200 km away although the impact area of the rock falls was not particularly large the falls generated an airblast and an abrasive dense sandy cloud that devastated a larger area downslope of the impact sites toward the happy isles nature center immediately downslope of the impacts the airblast had velocities exceeding 110 m s and toppled or snapped about 1000 trees even at distances of 0 5 km from impact wind velocities snapped or toppled large trees causing one fatality and several serious injuries beyond the happy isles nature center a dense sandy cloud trailed the airblast and abraded fallen trunks and trees left standing the happy isles rock fall is one of the few known worldwide to have generated an airblast and abrasive dense sandy cloud the relatively high velocity of the rock fall at impact estimated to be 110 120 m s influenced the severity and areal extent of the airblast at happy isles specific geologic and topographic conditions typical of steep glaciated valleys and mountainous terrain contributed to the rock fall release and determined its travel path resulting in a high velocity at impact that generated the devastating airblast and sandy cloud the unusual effects of this rock fall emphasize the importance of considering collateral geologic hazards such as airblasts from rock falls in hazard assessment and planning development of mountainous areas

late quaternary environmental changes and latitudinal shifts of the antarctic circumpolar current as recorded by dinoflagellate cysts from offshore chile 41 s abstract the late quaternary organic walled dinoflagellate cyst record of site 1233 41 s offshore chile was studied with a 200 year resolution spanning the last 25 000 years the study provides the first continuous record of sub recent and recent dinoflagellate cysts in the southeast se pacific major changes in the composition of the cyst association cyst concentration and morphology of operculodinium centrocarpum reflect changes in sea surface temperature sst sea surface salinity sss palaeoproductivity and upwelling intensity these changes can be associated with latitudinal shifts of the circumpolar frontal systems the high cyst concentration high brigantedinium spp abundances low species diversity and the occurrence of certain cold water species are supportive for a 7 10 equatorward shift of the antarctic circumpolar current acc during the coldest phase of the last glacial maximum lgm between 25 and 21 1 cal ka bp deglacial warming initiated at 18 6 cal ka bp termination i 18 6 11 1 cal ka bp is interrupted by an unstable period of extreme seasonality rather than a cooling event between 14 4 and 13 2 cal ka bp synchronous with the antarctic cold reversal acr the holocene maximum is observed between 11 6 and 9 8 cal ka bp and is typified by the most southward position of the northern margin of the acc a cooling phase occurred during the early holocene until 7 cal ka bp and during the last 0 8 ka our data indicates that the se pacific 41 s climate has been influenced over the whole record by changes in the southern hemisphere sh high latitudes while during the mid to late holocene also a tropical forcing mechanism was involved including the el nino southern oscillation and the variable hadley cell intensity furthermore this study showed a relationship between the variable morphology of the spines processes of o centrocarpum and the combined variation of sea surface salinity and temperature sss sst ratio

distribution of organic walled dinoflagellate cysts in surface sediments from transects across the polar front offshore southeast greenland the polar front along the southeast greenland margin denotes the contrasting hydrographic properties of the polar and atlantic water masses on either side the remains of planktonic organisms in underlying sediments are expected to reflect these contrasts to test this we quantitatively analysed the organic walled dinoflagellate cyst dinocyst assemblages in surface sediments from transects across the present day polar front on the southeast greenland margin proportional differences are found between the composition of the dinocyst assemblages on either side of the polar front the influence of polar water can be traced in the dinocyst record as high abundances of algidasphaeridium minutum and the presence of pentapharsodinium dalei the influence of atlantic water is reflected in the presence of operculodinium centrocarpum and selenopemphix quanta all samples include taxa from both environments but the quantitative composition of the cyst assemblages clearly reflects the hydrographic features of the overlying surface water masses copyright 2001 john wiley sons ltd

a 70 kyr sea surface temperature record off southern chile ocean drilling program site 1233 1 we present the first high resolution alkenone derived sea surface temperature sst reconstruction in the southeast pacific ocean drilling program site 1233 covering the major part of the last glacial period and the holocene the record shows a clear millennial scale pattern that is very similar to climate fluctuations observed in antarctic ice cores suggesting that the southern hemisphere high latitude climate changes extended into the midlatitudes involving simultaneous changes in air temperatures over antarctica sea ice extent extension of the antarctic circumpolar current and westerly atmospheric circulation a comparison to other midlatitude surface ocean records suggests that this antarctic millennial scale pattern was probably a hemisphere wide phenomenon in addition we performed sst gradient reconstructions over the complete latitudinal range of the pacific eastern boundary current system for different time intervals during the last 70 kyr the main results suggest an equatorward displaced subtropical gyre circulation during marine isotope stages 2 and 4

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

recent geographical distribution of organic walled dinoflagellate cysts in the southeast pacific 25 53 s and their relation to the prevailing hydrographical conditions abstract forty eight surface sediment samples from the southeast se pacific 25 53 s are investigated for the determination of the spatial distribution of organic walled dinoflagellate cysts along the western south american continental margin fifty five different taxa are recorded and reflect oceanic or coastal assemblages the oceanic assemblages are characterised by low cyst concentrations and the dominance of autotrophs while the coastal assemblages generally contain a higher number of cysts which are mainly produced by heterotrophic species highest cyst concentrations are observed in the active upwelling system offshore concepcion 35 37 s brigantedinium spp echinidinium aculeatum echinidinium granulatum delicatum and cysts of protoperidinium americanum dominate assemblages related to upwelling echinidinium aculeatum appears to be the best indicator for the presence of all year round active upwelling cells other protoperidinioid cysts may also occur in high relative abundances in coastal regions outside active upwelling systems if the availability of nutrients co responsible for the presence absence of their main food sources such as diatoms and other protists is sufficient the importance of nutrient availability as a determining environmental variable influencing cyst signals on a regional scale se pacific is demonstrated through statistical analyses of the data because of the importance of nutrients uncertainties about the outcomes of quantitative sea surface temperature sst reconstructions modern analogue technique based on dinoflagellate cysts may arise since no interaction between different hydrographical variables is considered in this approach the combination of the se pacific surface sample dataset with other published cyst data from the southern hemisphere resulted in a database which includes 350 samples the sh350 database this database is used to test the accuracy of the quantitative reconstructions by calculating and comparing the estimated versus observed values for each site an attempt to perform quantitative sst reconstructions on the last 25 cal ka of site odp1233 41 s 74 27 w is made and again stresses the importance of other environmental variables such as nutrient availability in determining the dinoflagellate cyst assemblages

mobility of large rock avalanches evidence from valles marineris mars measurements of h l height of drop length of runout vs volume for landslides in valles marineris on mars show a trend of decreasing h l with increasing volume this trend which is linear on a log log plot is parallel to but lies above the trend for terrestrial dry rock avalanches this result and estimates of 10 4 to 10 5 pa yield strength suggest that the landslides were not water saturated as suggested by previous workers the offset between the h l vs volume trends shows that a typical martian avalanche must be nearly two orders of magnitude more voluminous than a typical terrestrial avalanche in order to achieve the same mobility this offset might be explained by the effects of gravity on flows with high yield strengths these results should prove useful to future efforts to resolve the controversy over the mechan ics of long runout avalanches

the potential of organic walled dinoflagellate cysts for the reconstruction of past sea surface conditions in the southern ocean abstract in this study we investigate the potential of organic walled dinoflagellate cysts dinocysts as tools for quantifying past sea surface temperatures sst in the southern ocean for this purpose a dinocyst reference dataset has been formed based on 138 surface sediment samples from different circum antarctic environments the dinocyst assemblages of these samples are composed of phototrophic gonyaulacoid and heterotrophic protoperidinioid species that provide a broad spectrum of palaeoenvironmental information the relationship between the environmental parameters in the upper water column and the dinocyst distribution patterns of individual species has been established using the statistical method of canonical correspondence analysis cca among the variables tested summer sst appeared to correspond to the maximum variance represented in the dataset to establish quantitative summer sst reconstructions a modern analogue technique mat has been performed on data from three late quaternary dinocyst records recovered from locations adjacent to prominent oceanic fronts in the atlantic sector of the southern ocean these dinocyst time series exhibit periodic changes in the dinocyst assemblage during the last two glacial interglacial cycles during glacial conditions the relative abundance of protoperidinioid cysts was highest whereas interglacial conditions are characterised by generally lower cyst concentrations and increased relative abundance of gonyaulacoid cysts the mat palaeotemperature estimates show trends in summer sst changes following the global oxygen isotope signal and a strong correlation with past temperatures of the last 140 000 years based on other proxies however by comparing the dinocyst results to quantitative estimates of summer ssts based on diatoms radiolarians and foraminifer derived stable isotope records it can be shown that in several core intervals the dinocyst based summer ssts appeared to be extremely high in these intervals the dinocyst record seems to be highly influenced by selective degradation leading to unusual temperature ranges and to unrealistic palaeotemperatures we used the selective degradation index kt index to determine those intervals that have been biased by selective degradation in order to correct the palaeotemperature estimates we show that after correction the dinocyst based ssts correspond reasonably well with other palaeotemperature estimates for this region supporting the great potential of dinoflagellate cysts as a basis for quantitative palaeoenvironmental studies

geographical distributions of organic walled dinoflagellate cysts in surficial sediments of the benguela upwelling region and their relationship to upper ocean conditions the organic walled cyst content of 41 surface sediment samples from the south eastern south atlantic ocean have been studied to create a dataset that can be used for palaeoceanographic reconstructions in order to obtain insight into which environmental factors influence the distribution of individual cyst species the cyst associations have been compared with oceanographic characteristics of the overlying water masses i e temperature salinity density and stratification gradients the associations and relationships have been established by visual examination of the dataset and the multivariate ordination techniques detrended correspondence analysis and canonical correspondence analysis special attention has been given to the factors of transport and preservation of the cysts five associations have been recognised as being characteristic of 1 areas influenced by coastal upwelling and or river outflow 2 open ocean 3 agulhas current and southern benguela current 4 benguela current and 5 walvis bay shelf break area the factors dominant in influencing either directly or indirectly the cyst distributions appear to be the stratification in the upper 50 m of the water column nutrient concentration and seasonality variations in sea surface temperatures and salinities have only minor effect on cyst distribution

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

distribution patterns of dinoflagellate cysts and other organic walled microfossils in recent norwegian greenland sea sediments dinoflagellate cysts and other organic walled microfossils have been studied in recent surface sediments from the entire norwegian greenland sea more than 30 taxa have been recognized of which only few show a distinct distribution pattern and allow description of four assemblages the occurrence of most taxa is related to the relatively warmer waters of the norwegian sea algidaspaeridium minutum s 1 brigantedinium simplex and impagidinium pallidum are the only species showing a preference for colder water masses two species i pallidum and nematosphaeropsis labyrinthus are mainly restricted to the oceanic environment whereas the other species have also been reported from neritic environments in previous studies due to the limited knowledge of the ecological and sedimentological factors influencing the occurrence of dinoflagellate cysts in oceanic environments their distribution in recent sediments can be only related to surface water masses in a broad sense although the distribution of assemblages correlates with specific surface water masses comparison with assemblages recovered from sediment traps deployed basinwide in the norwegian greenland sea dale and dale 1992 revealed some major discrepancies in species composition and percentage abundances the differences cannot be explained with certainty at the moment although there is some evidence that transport of dinoflagellate cysts and other fossilizable microplankton in water masses by currents in sea ice and sediments may modify the assemblages found in recent oceanic surface sediments from the norwegian greenland sea