analysis of crack movements observed in an alpine bedrock cliff crack widths and rock temperatures were monitored on an andestic bedrock cliff in the summit area of the daisetsu mountains hokkaido northern japan sequential data recorded the gradual widening of a crack to the point of critical crack extension which resulted in catastrophic rock breakage the data indicate that a combination of liquid water in ltration into crack tip and subsequent freezing is the most signi cant factor contributing to critical crack extension the recorded sub critical crack movements involved a number of minor crack extensions and contractions the timing of which correlates well with the magnitude of the reconstructed thermal stresses at the crack tip derived from thermal deformation of the plate shaped rock fragment larger crack extensions occurred when stress at the crack tip exceeded a threshold value possibly re ecting the control of rock fracture mechanics by which cracks are thought to propagate when the stress intensity factor at the crack tip exceeds the threshold values for stress corrosion cracking and the fracture toughness of the material copyright 2004 john wiley sons ltd

aeolian activity at a giant sandstone weathering pit in arid south central utah aeolian abrasional depositional and deflational features indicate exceptionally strong southwesterly winds in a giant sandstone weathering pit in grand staircase escalante monument about 22 km southeast of escalante utah the 60 m wide 5 20 m deep pit has developed near the summit of a broad barren 160 m high dome on the lower jurassic navajo sandstone unlike other giant weathering pits 10 30 m diameter in the region the bedrock floor of this pit is undulatory and there is a cylindrical 10 m high rock pedestal in the centre of the pit an active dune surrounds the central pedestal and at times has as much as 8 m of local relief the dune shifts considerably over brief 250 m trapped in the pit dunal sand is typically derived from external sources other than the pit walls and floor centimetre to metre scale abrasional features such as grooves flutes and dedos occur on the bedrock walls and floor of the pit these dedos and other streamlined aeolian sculpted host rock features occur in clusters and typically form in the lee of iron concretions the dedos are similar to the controversial stalked blueberries on mars above the western rim of the pit there is a 29 m long 5 m wide aeolian groove with a fluted bedrock floor a 1 2 km long bedrock valley descends to the southwest from the pit and groove amplifying southwesterly winds data from hand held anemometers suggest that southwesterly winds can be accelerated 200 300 per cent or more by local topography copyright 2008 john wiley and sons ltd

porosity evolution and crystallization driven fragmentation during weathering of andesite 1 a 10 m thick andesitic sill intrusion from the neuquen basin argentina shows spectacular examples of spheroidal weathering and liesegang banding the liesegang patterns demonstrate how andesite blocks initially cut out by a preweathering joint set are subdivided by fractures formed during the spheroidal weathering process the stresses that cause fracturing originate from the growth of ferrihydrite and calcite in the pore space of the andesite partly at the expense of original ilmenite amphibole and plagioclase the porosity evolution and fracture formation during progressive weathering was characterized by scanning electron microscopy studies x ray computed tomography and he and hg porosimetry fresh andesite has a porosity of approximately 8 and a major fraction 80 of the pore volume is composed of pores less than 10 m in diameter the extent of pore filling during weathering increases with pore size pores more than 100 m are almost completely filled by an intimate intergrowth of calcite and ferrihydrite whereas pores less than 10 m are filled less than 50 the fracturing associated with spheroidal weathering is caused by mineral growth in the largest pores which account for 10 20 of the total porosity the periodic precipitation of the weathering product to form liesegang bands indicates a significant supersaturation threshold before nucleation commences the increase in the weathering product growth rate with increasing size is therefore most likely due to higher nucleation probabilities in larger pores

the chlorine isotopic composition of martian meteorites 1 chlorine isotope composition of martian mantle and crustal reservoirs and their interactions the martian meteorites record a wide diversity of environments processes and ages much work has been done to decipher potential mantle sources for martian magmas and their interactions with crustal and surface environments chlorine isotopes provide a unique opportunity to assess interactions between martian mantle derived magmas and the crust we have measured the cl isotopic composition of 17 samples that span the range of known ages martian environments and mantle reservoirs the 37cl of the martian mantle as represented by the olivine phyric shergottites nwa 2737 chassignite and shergotty basaltic shergottite has a low value of approximately 3 8 this value is lower than that of all other planetary bodies measured thus far the martian crust as represented by regolith breccia nwa 7034 is variably enriched in the heavy isotope of cl this enrichment is reflective of preferential loss of 35cl to space most basaltic shergottites less shergotty nakhlites chassigny and allan hills 84001 lie on a continuum between the martian mantle and crust this intermediate range is explained by mechanical mixing through impact fluid interaction and assimilation fractional crystallization

discussion on development of polygonal fault systems a test of hypotheses d m d james writes the mechanics of formation of polygonal faults are widely acknowledged as not yet fully understood and it is welcome that goulty swarbrick 2005 attempt a discriminatory test between rival hypotheses it is however important that such a test bears some relation to physical reality the test is based on the assumption that the ratio of horizontal to vertical effective stress as deduced from leak off tests in two wells in the north sea at depths of about 2 km yields the co efficient of earth pressure at rest therein and hence the residual friction governing the post nucleation development of polygonal faults apparently globally and at any depth it is not clear if the authors consider that the polygonal fault tiers at the well sites are currently active neither is it clear if they assume that the coefficient of residual friction along the fracture is a reasonable approximation to the coefficient of initial friction which governs the dip of the propagating fracture tip and the fault surface as a whole relative to the orientation of the vertical effective stress it is hardly surprising that the ratio of horizontal to vertical effective stress k is very high in the wells analysed the leak off tests are from highly overpressured horizons ratios of pore fluid pressure to total vertical stress approximately 0 80 and 0 84 and the effect of pore fluid pressure coupling hillis 2003 will inevitably decrease the value of the horizontal effective stress to lesser extent than it does the vertical effective stress it is certainly not yet demonstrated that polygonal faults require overpressures of this magnitude for their formation by any mechanism leak off tests tend to overestimate the horizontal effective stress if no correction is made for the excess mud pressure necessary to overcome the tensile strength of

erg margin of the permian white rim sandstone se utah the permian white rim sandstone of the canyonlands national park utah contains a wide variety of sedimentary structures and features that largely result from stages in erg migration and marine influence on an erg margin three spatially distinct lithological and depositional facies are recognized and can be distinguished as informal units within the formation the aeolian dune facies is composed predominantly of fine grained cross stratified sandstone of the white rim erg this facies is the most widespread and comprises the bulk of the formation within the aeolian dune facies are small subfacies that represent interdune deposits a sheet sand facies composed of parallel bedded sandstone makes up a significant part of the lowest part of the white rim formation this facies appears to have been the precursor or leading progradational edge to the main erg system the final facies is a reworked or veneer facies of rippled to disturbed sandstone that is localized in its extent it is restricted to the upper few metres of the formation and is transitional in some places to the triassic moenkopi formation this veneer facies contains many structures which indicate marine reworking as well as periods of desiccation or subaerial exposure some previous interpretations of the white rim sandstone have tended to classify the whole formation as one depositional setting it is clear that at the margin of a sand sea as shown in the white rim sandstone there are transitional facies due to the interactions with other environments additionally variation in the stratigraphic relationships of facies can be related to stages of erg migration erg margin deposits preceded central erg development erg initiation occurred during a probable relative sea level low sea level influence is recorded at the top of the formation because erg termination accompanied a relative sea level high with cut off of sand supply transgression of the permian kaibab sea over the white rim erg was probably the main process in preservation of original dune topographic relief sea level fluctuations also may have affected distribution of facies and the complexities of structures at the erg margin subsequent fluvial reworking of the veneer facies may have obliterated late permian features during lowest triassic moenkopi deposition

geomorphic knobs of candor chasma mars new mars reconnaissance orbiter data and comparisons to terrestrial analogs high resolution imaging science experiment hirise imagery and digital elevation models of the candor chasma region of valles marineris mars reveal prominent and distinctive positive relief knobs amidst light toned layers three classifications of knobs types 1 2 and 3 are distinguished from a combination of hirise and thermal emission imaging system themis images based on physical expressions geometries spatial relationships and spectral data from compact reconnaissance imaging spectrometer for mars crism type 1 knobs are abundant concentrated topographically resistant features with their highest frequency in west candor which have consistent stratigraphic correlations of the peak altitude height these type 1 knobs could be erosional remnants of a simple dissected terrain possibly derived from a more continuous resistant capping layer of pre existing material diagenetically altered through recrystallization or cementation types 2 and 3 knobs are not linked to a single stratigraphic layer and are generally solitary to isolated with variable heights type 3 are the largest knobs at nearly an order of magnitude larger than type 1 knobs the variable sizes and occasional pits on the tops of type 2 and 3 knobs suggest a different origin possibly related to more developed erosion preferential cementation or textural differences from sediment water injection or intrusion or from a buried impact crater enhanced color hirise images show a brown coloration of the knob peak crests that is attributable to processing and photometric effects crism data do not show any detectable spectral differences between the knobs and the host rock layers other than albedo these intriguing knobs hold important clues to deducing relative rock properties timing of events and weathering conditions of mars history

cracks and fins in sulfate sand evidence for recent mineral atmospheric water cycling in meridiani planum outcrops gypsum dunes at white sands national monument new mexico provide an excellent analog to sulfate rich eolian outcrops on meridiani planum mars as characterized by the rover opportunity numerous outcrops imaged by opportunity contain polygonal cracks that crosscut bedding and extend across most surfaces of boulders some of these cracks are associated with millimeter thick platy fins that protrude as much as a few centimeters above outcrops similar cracks crosscut bedding at white sands on erosional stoss slopes and in pedestals of cemented dune sand the cracks at white sands form in response to cementation of damp gypsum sand followed by contraction due to dehydration during warm seasons cracked sand is dry and cracks rarely grow although some may form after rainstorms two types of fins form along cracks and differentially eroded laminae white fins represent subsurface differential cementation along cracks followed by differential erosion tan fins form due to cementation of crack edges and laminae on exposed dune surfaces wind blown sediment adheres to damp tan fins similar processes may be important for crack and fin formation in meridiani planum outcrops implying recent water cycling between sulfate outcrops and the martian atmosphere

dynamic liquefaction of jurassic sand dunes processes origins and implications soft sediment deformation occurs in ancient eolian dune deposits but understanding its extent and the conditions and forces behind the deformation often remains elusive here we gain insight into the aerial extent and environmental conditions related to intense soft sediment deformation based on an exceptional three dimensional 3d exposure of eolian dune deposits and preserved geomorphic landscape expressions in the jurassic navajo sandstone at white pocket vermilion cliffs national monument arizona deformation features include elongate northeast trending decameter scale mounds and raised ridges cored by deformed and upturned eolian dune sets overlain by a massive blanket sandstone with breccia blocks the geomorphic mounds display 40 60 m spacing roughly perpendicular to the southerly paleoflow dune foreset directions the geometry of the deformation is imaged by oblique aerial photography using cameras mounted on a remote control airplane and high resolution panoramas with a robotic camera mount we interpret the exquisitely preserved deformation features as liquefaction induced ground failure consistent with theoretical and laboratory studies of deformation in saturated sand a shallow water table affected by differential dune loading facilitated lateral spreading and failure the transition to steady state flow liquefaction near the top of the shallow water table destroyed original sedimentary structure creating a massive sand blanket that entrained brecciated blocks ripped up during flow the water pressurized upwelled sediment created the mounds a relief inversion in underlying deformed dune sets deformation was intense but sedimentary structure was not obliterated as deformation progressed from initial cyclic mobility to strain softening but ceased prior to steady state flow liquefaction the spatial extent topographic relief and intensity of dynamic deformation suggest an origin of strong ground motion driven by long duration surface waves of a large earthquake mw 7 8 possibly related to back arc thrusting from jurassic subduction of the pacific plate under north america copyright 2014 john wiley sons ltd

thermohaline circulation hysteresis a model intercomparison we present results from an intercomparison of 11 different climate models of intermediate complexity in which the north atlantic ocean was subjected to slowly varying changes in freshwater input all models show a characteristic hysteresis response of the thermohaline circulation to the freshwater forcing which can be explained by stommel s salt advection feedback the width of the hysteresis curves varies between 0 2 and 0 5 sv in the models major differences are found in the location of present day climate on the hysteresis diagram in seven of the models present day climate for standard parameter choices is found in the bi stable regime in four models this climate is in the mono stable regime the proximity of the present day climate to the stommel bifurcation point beyond which north atlantic deep water formation cannot be sustained varies from less than 0 1 sv to over 0 5 sv

application of data driven evidential belief functions to landslide susceptibility mapping in jinbu korea abstract evidential belief function ebf model was applied and validated for analysis of landslide susceptibility in the pyungchang area of korea using geographic information system areas of landslide occurrence in the study area were determined from the interpretation of aerial photographs and subsequent field surveys landslide locations were randomly allocated for landslide susceptibility map generation 70 and validation 30 purposes maps relevant to landslide occurrence topography geology soil and forest cover were assembled in a spatial database from which 17 landslide related factors were extracted the relationships between the observed landslide locations and these factors were identified and quantified using the ebf model three relationships were calculated disbelief dis uncertainty unc and belief bel the quantified relationships between each factor and landslide locations of each factor with known landslides were then used as factor ratings in an overlay analysis to create landslide susceptibility indices and maps the most representative of the resulting susceptibility maps the bel map was validated using the landslide data reserved for validation the landslide susceptibility map demonstrates 85 96 accuracy thus the ebf model was found to be effective in terms of prediction accuracy

sedimentology and climatic environment of alluvial fans in the martian saheki crater and a comparison with terrestrial fans in the atacama desert abstract the deflated surfaces of the alluvial fans in saheki crater reveal the most detailed record of fan stratigraphy and evolution found to date on mars during deposition of at least the uppermost 100 m of fan deposits discharges from the source basin consisted of channelized flows transporting sediment which we infer to be primarily sand and gravel sized as bedload coupled with extensive overbank mud rich flows depositing planar beds of sand sized or finer sediment flow events are inferred to have been of modest magnitude probably less than 60 m3 s of short duration and probably occupied only a few distributaries during any individual flow event occasional channel avulsions resulted in the distribution of sediment across the entire fan a comparison with fine grained alluvial fans in chile s atacama desert provides insights into the processes responsible for constructing the saheki crater fans sediment is deposited by channelized flows transporting sand through boulder sized material and overbank mudflows sand size and finer and wind erosion leaves channels expressed in inverted topographic relief the most likely source of water was snowmelt released after annual or epochal accumulation of snow in the headwater source basin on the interior crater rim during the hesperian to amazonian periods we infer the saheki fans to have been constructed by many hundreds of separate flow events and accumulation of the necessary snow and release of meltwater may have required favorable orbital configurations or transient global warming

evoluton of polygonal fracture patterns in lava flows cooling induced fractures also known as columnar joints divide basaltic lava flows into prismatic columns with polygonal cross sections the regularity and symmetry of the fracture patterns have long fascinated naturalists in view of the recent selection of two candidate nuclear waste sites in areas where polygonally fractured volcanic rocks are located a better understanding of the fracture patterns is required field data indicate that the tetragonal networks at flow surfaces evolve systematically to hexagonal networks as the joints grow inward during solidification of lava this evolution occurs by the gradual change of most orthogonal intersections to nonorthogonal intersections of about 120 degrees the surface features and intersection geometries of columnar joints show that joint segments at any given level form sequentially yet harmoniously

the control of stress history and flaw distribution on the evolution of polygonal fracture networks abstract we use boundary element models of fracture propagation and linkage to investigate the factors controlling the development of two dimensional multi directional polygonal fracture networks characterised by a large number of abutting intersections between fractures the position and orientation of a number of fracture seeds are prescribed in the model which propagate when the applied stress reaches a critical value according to linear elastic fracture mechanics theory the applied boundary condition is a remote isotropic horizontal tension where the stress is increased at a steady rate throughout each model to simulate continued fracture growth realistic polygonal systems are developed with the boundary element model simulations which are comparable with those observed in natural systems such as those found within eocene and oligocene mudrocks in the north sea and on the surface of mars if conditions exist where a small number of fracture seeds propagate and develop significant structures before others then these will dominate the resulting fracture network geometry not only do such early structures represent the largest fractures in the system they also significantly modify the stress field around them preventing some other seeds from developing and influencing the propagation paths of nearby fractures fracture seeding distribution and the rate at which the stress is increased are found to be the most significant parameters affecting the development of fracture network geometry these results suggest that the geometry of evolving fracture networks should be considered not only in terms of the mechanical properties of the deforming material but also in terms of the stress rate driving deformation

directivity of slope dynamic response to seismic shaking 1 a four year long accelerometric monitoring of a landslide prone slope area in italy provided evidence of amplifications with systematic directional differences in shaking energy by a factor of 2 3 apparently correlated with the directions of local topographic features the examination of regional scale data revealed similar site response directivity phenomena also on some steep rock slopes not affected by amplification the spectral properties of the site responses were investigated using hvsr analysis and a new approach based on the multiplication of spectra from several events the results suggest that such phenomena are caused by a directional redistribution of spectral energy controlled by a combination of interrelated topographic and geologic factors acting in similar directions

earthquake induced landslides and their effects on alluvial fans abstract earthquakes as small as magnitude 4 0 may dislodge landslides from susceptible slopes and larger earthquakes can generate tens of thousands of landslides throughout areas of hundreds of thousands of square kilometers producing billions of cubic meters of loose surficial sediment these landslides can have significant geomorphic effects that vary depending on the landslide characteristics and materials and on the settings in which the landslides occur a review of data from historical earthquakes indicates that the landslides they generated can be classified into 14 different types these include highly disaggregated and fast moving falls disrupted slides and avalanches more coherent and slower moving slumps block slides and earth slides and lateral spreads and flows that involve partly to completely liquefied material rock falls disrupted rock slides and disrupted slides of earth and debris are the most abundant types of earthquake induced landslides whereas earth flows debris flows and avalanches of rock earth or debris typically transport material the farthest because of their abundance or long distances of transport these landslides generally have the greatest effects on the landscape during and after earthquakes landslide effects on alluvial fans include direct deposition of material on fan surfaces fissuring and displacement of fan materials alterations in drainage basins such as devegetation denudation and changes in channel networks and generation of large amounts of sediment that may be transported to fans by post earthquake water flows or debris flows

statistical approach to earthquake induced landslide susceptibility susceptibility analysis for predicting earthquake induced landslides has most frequently been done using deterministic methods multivariate statistical methods have not previously been applied in this study however we introduce a statistical methodology that uses the intensity of earthquake shaking as a landslide triggering factor this methodology is applied in a study of shallow earthquake induced landslides in central western taiwan the results show that we can accurately interpret landslide distribution in the study area and predict the occurrence of landslides in neighboring regions this susceptibility model is capable of predicting shallow landslides induced during an earthquake scenario with similar range of ground shaking without requiring the use of geotechnical groundwater or failure depth data

convection in a catastrophic flood deposit as the mechanism for the giant polygons on mars a formational mechanism for the large scale polygons that are defined by intersecting fractures in the northern plains of mars is proposed in this work the presented model is based on rayleigh convection of interstitial water driven by an unstable density temperature gradient within a saturated porous medium catastrophic emplacement of water rich sediments into the martian northern plain basins could have provided a thick sedimentary layer in which rayleigh convection could have occurred convection within this active layer is proposed to have differentially thawed an underlying ice rich permafrost layer that had been at the planet s surface before being rapidly buried the resulting morphology of the permafrost subsurface is thought to have resembled the scalloped solid liquid interface morphology produced in terrestrial convective flow visualization studies the exact size and shape of the scallops on the frozen subsurface would have been controlled by the dimensions of the convection cells which are estimated to have had width to depth ratios of between 3 4 and 4 5 subsequent stresses e g gravity and bending stresses would have produced maximum tensile stresses in the overlying sediments preferentially above the subsurface topographic highs as described previously by mcgill and hills 1992 additional desiccation of the sediments would have required contraction of the sediment cover and would have produced large scale polygonal fractures along the preexisting weaknesses located above the raised subsurface topography thus the underlying subsurface geometric morphology would have been translated to the surface and would be represented by the large scale polygonal fractures visible in the viking orbiter and mars global surveyor images of the martian northern plains

origin of polygonal fractures in sand uppermost navajo and page sandstones page arizona abstract polygonal fractures in eolian sandstones occur along the upper surface of the navajo sandstone and along four additional surfaces within the page sandstone near page arizona the polygons are largely rectangular and range from 1 to 6 m across most of the fractures are less than 1 5 m deep and fracture widths range from hairlines to tens of centimeters or more fracture fill most commonly shows vertical layering and in some cases a series of layers is evident symmetrical about the midline of the fracture other fractures are filled with contorted or structureless deposits subhorizontal laminae and displaced or brecciated host strata in some cases surfaces marked by polygonal fractures can be shown to have been topographically low at the time of deposition and the fracture sandstone below these low areas contains calcite or siliceous nodules and siliceous cement interpreted as contractional in origin the polygonal fractures formed on an exposed evaporite encrusted surface in a manner similar to ice wedges irregularities in these fractures are attributed to erosion by wind or water evaporites evidenced by anhydrite inclusions pore shapes megaquartz replacement and pseudomorphs of evaporitic minerals provided the cohesion and contraction that caused the tensional stresses necessary for polygonal fracturing stresses were the result of thermal contraction such surfaces are thought to represent hiatuses in eolian sand sea development and probably represent deflation to near the water table during net deflationary conditions

physical weathering in arid landscapes due to diurnal variation in the direction of solar heating despite the prominent role of physical weathering in arid and semi arid landscapes there has been little study of the specifi c processes responsible for the rapid breakdown of subaerially exposed rocks for example many boulders and cobbles in deserts exhibit fi ne near vertical cracks although workers have hypothesized that these and other cracks are initiated by diurnal heating and cooling no convincing specifi c mechanism for their formation has been proposed we have characterized these cracks at eight sites on surfaces of different ages in the mojave sonoran and chihuahuan deserts and the high desert of central new mexico our data reveal four basic types of cracks longitudinal surfaceparallel fabric related and meridional the orientations of the fi rst three types are associated with clast shape and rock fabric the azimuths of meridional cracks however are preferentially aligned north south typically with a nonrandom multimodal distribution we propose that these cracks are caused by tensile stresses that arise in the interior of clasts due to strong radial gradients in temperature that evolve and rotate in alignment with the sun s rays we suggest that the multimodal nature of crack orientations may be in part attributable to the seasonally varying latitude dependent solar elevation angle over millennial time scales we suggest that this thermal cracking is an effi cient weathering process that together with cumulic soil epipedon development creates the key attributes of most desert pavements in addition to individual clasts exposed on desert surfaces this mechanism of cracking is potentially signifi cant in other climates and on other planets as well as for rock outcrops and for man made structures

mineralogy and stratigraphy of phyllosilicate bearing and dark mantling units in the greater mawrth vallis west arabia terra area constraints on geological origin 1 analyses of mro crism images of the greater mawrth vallis region of mars affirm the presence of two primary phyllosilicate assemblages throughout a region 1000 1000 km these two units consist of an fe mg phyllosilicate assemblage overlain by an al phyllosilicate and hydrated silica assemblage the lower unit contains fe mg smectites sometimes combined with one or more of these other fe mg phyllosilicates serpentine chlorite biotite and or vermiculite it is more than 100 m thick and finely layered at meter scales the upper unit includes al smectite kaolin group minerals and hydrated silica it is tens of meters thick and finely layered as well a common phyllosilicate stratigraphy and morphology is observed throughout the greater region wherever erosional windows are present this suggests that the geologic processes forming these units must have occurred on at least a regional scale sinuous ridges interpreted to be inverted channels and narrow channels cut into the upper clay bearing unit suggesting that aqueous processes were prevalent after and possibly during the deposition of the layered units we propose that layered units may have been deposited at mawrth vallis and then subsequently altered to form the hydrated units the fe mg phyllosilicate assemblage is consistent with hydrothermal alteration or pedogenesis of mafic to ultramafic rocks the al phyllosilicate hydrated silica unit may have formed through alteration of felsic material or via leaching of basaltic material through pedogenic alteration or a mildly acidic environment these phyllosilicate bearing units are overlain by a darker relatively unaltered and indurated material that has probably experienced a complex geological history

origin of giant martian polygons extensive areas of the martian northern plains in utopia and acidalia planitiae are characterized by polygonal terrane polygonal terrane consists of material cut by complex troughs defining a pattern resembling mudcracks columnar joints or frost wedge polygons on earth however the martian polygons are orders of magnitude larger than these potential earth analogues leading to severe mechanical difficulties for genetic models based on simple analogy arguments plate bending and finite element models indicate that shrinkage of desiccating sediment or cooling volcanics accompanied by differential compaction over buried topography can account for the stresses responsible for polygon troughs as well as the large size of the polygons although trough widths and depths relate primarily to shrinkage the large scale of the polygonal pattern relates to the spacing between topographic elevations on the surface buried beneath polygonal terrane material geological relationships favor a sedimentary origin for polygonal terrane material but our model is not dependent on the specific genesis our analysis also suggests that the polygons must have formed at a geologically rapid rate

polygonal cracks in bedrock on earth and mars implications for weathering polygonal crack systems with domal microrelief imaged by the mars exploration rover mer opportunity show remarkable similarity to terrestrial crack systems developed on outcrop surfaces study of jurassic navajo sandstone surfaces show development of crack systems in relatively isotropic host rock as a result of tensile weathering stresses these terrestrial analogs are utilized to understand potential weathering processes on mars

cavernous weathering dynamical instability and self organization cavernous weathering may be conceptualized as a self reinforcing process characterized by positive feedback within the weathering system a morphometric study of caverns in the valley of fire state park nevada usa demonstrates the applicability of a dynamically unstable or conditionally unstable model of cavernous weathering systems outcrop surfaces displaying caverns tend to show increasing fragmentation of the surface in the early stages of cavernous weathering succeeded by convergent evolution of the surface in which caverns tend to grow and coalesce a paradoxical relationship exists between the weathering system output at the scale of individual forms and the outcrop scale caverns tend toward minimum interior surface area by developing a spheroidal form yet the outcrop surface tends toward maximum exposed surface area by increasing the degree of fragmentation of the surface copyright 2004 john wiley sons ltd

a terrestrial weathering and wind abrasion analog for mound and moat morphology of gale crater mars a striking feature of gale crater is the 5 5 km high central layered mound called mount sharp aeolis mons the major exploration target for the mars science laboratory rover curiosity within the 154 km diameter crater low plains aeolis palous resemble a moat surrounding mount sharp there is a similar terrestrial analog in the jurassic navajo sandstone of southern utah usa where a distinctive weathering pit 60 m wide by 20 m deep contains a central pillar mound and moat strong regional and local winds are funneled to amplify their velocity and produce a venturi effect that sculpts the pit via wind abrasion although the navajo pit is orders of magnitude smaller than gale crater both show comparable morphologies accompanied by erosional wind features the terrestrial example shows the impact of weathering and the ability of strong winds and vortices to shape lithified sedimentary rock over long periods of time

mechanisms of abrupt climate change of the last glacial period 1 more than a decade ago ice core records from greenland revealed that the last glacial period was characterized by abrupt climate changes that recurred on millennial time scales since their discovery there has been a large effort to determine whether these climate events were a global phenomenon or were just confined to the north atlantic region and also to reveal the mechanisms that were responsible for them in this paper we review the available paleoclimate observations of abrupt change during the last glacial period in order to place constraints on possible mechanisms three different mechanisms are then reviewed ocean thermohaline circulation sea ice feedbacks and tropical processes each mechanism is tested for its ability to explain the key features of the observations particularly with regard to the abruptness millennial recurrence and geographical extent of the observed changes it is found that each of these mechanisms has explanatory strengths and weaknesses and key areas in which progress could be made in improving the understanding of their long term behavior both from observational and modeling approaches are suggested finally it is proposed that a complete understanding of the mechanisms of abrupt change requires inclusion of processes at both low and high latitudes as well as the potential for feedbacks between them some suggestions for experimental approaches to test for such feedbacks with coupled climate models are given

meter scale thermal contraction crack polygons on the nucleus of comet 67p churyumov gerasimenko we report on the detection and characterization of more than 6300 polygons on the surface of the nucleus of comet 67p churyumov gerasimenko using images acquired by the osiris camera onboard rosetta between august 2014 and march 2015 they are found in consolidated terrains and grouped in localized networks they are present at all latitudes from north to south and longitudes head neck and body sometimes on pit walls or following lineaments about 1 5 of the observed surface is covered by polygons polygons have an homogeneous size across the nucleus with 90 of them in the size range 1 5 m and a mean size of 3 0 1 4 m they show different morphologies depending on the width and depth of their trough they are found in networks with 3 or 4 crack intersection nodes the polygons observed on 67p are consistent with thermal contraction crack polygons formed by the diurnal or seasonal temperature variations in a hard mpa and consolidated sintered layer of water ice located a few centimeters below the surface our thermal analysis shows an evolution of thermal contraction crack polygons according to the local thermal environment with more evolved polygons i e deeper and larger troughs where the temperature and the diurnal and seasonal temperature range are the highest thermal contraction crack polygons are young surface morphologies that probably formed after the injection of 67p in the inner solar system typically 100 000 years ago and could be as young as a few orbital periods following the decreasing of its perihelion distance in 1959 from 2 7 to 1 3 a u meter scale thermal contraction crack polygons should be common features on the nucleus of jupiter family comets

high latitude patterned grounds on mars classification distribution and climatic control patterned grounds such as polygonal features and slope stripes are the signature of the presence of ground ice and of temperature variations in cold regions on earth identifying similar features on mars is important to understand its past climate as well as the ground ice distribution in this study young patterned grounds are classed and mapped from the systematical analysis of mars observer camera high resolution images these features are located poleward of 55 latitude which fits the distribution of ground ice found by the neutron spectrometer onboard mars odyssey thermal contraction due to seasonal temperature variations is the predominant process of formation of polygons formed by cracks which sizes vary from 15 to 300 m the small 40 m widespread polygons are very recent and degraded by the desiccation of ground ice from the cracks which enhances the effect of ice sublimation the large polygons 50 to 300 m located only around the south co2 polar cap indicate the presence of ground ice and thus outline the limit of the co2 ice cap they could be due to the blanketing of water ice deposits by the advances and retreats of the residual co2 ice cap during the last thousand years large 50 250 m and homogeneous polygons similar to ice wedge polygons hillslope stripes and solifluction lobes may indicate that specific environments such as crater floors and hillslopes could have been submitted to freeze thaw cycles possibly related to higher summer temperatures in periods of obliquity higher than 35 these interpretations must be strengthened by higher resolution images such as those of the hirise mission of the mars reconnaissance orbiter because locations with past seasonal thaw could be of major interest as potential landing sites for the phoenix mission

reconciling channel formation processes with the nature of elevated outflow systems at ophir and aurorae plana mars 1 many hesperian outflow channels head at elevations compatible with aquifer recharge beneath the martian south polar cap and such channels are widely interpreted as the products of this recharge some outflow channels head at greater elevations that are inconsistent with southern recharge including three systems located in aurorae planum and eastern ophir planum these three systems have previously been interpreted as having formed through aqueous outbursts from local aquifers recharged by the meltwaters of ancient upland glaciers to the west however the viability of this interpretation is weakened by the lack of a geomorphic record supportive of past meltwater flow from western uplands inconsistencies between hypothesized processes and the nature of regional topography and mineralogy and the absence of satisfactory analog processes for catastrophic aqueous flow from the subsurface in contrast a volcanic origin for the ophir and aurorae systems appears to be in accord with the basic characteristics of constituent channels and associated landforms the volcanotectonic nature of the valles marineris system and adjacent upland plains and the nature of available analog landforms and processes though numerous uncertainties remain a volcanic interpretation of these outflow systems can more simply account for the existence of component channels the attributes of other elevated outflow systems on mars similarly appear to be most consistent with volcanic origins if the ophir and aurorae systems formed volcanically thermal considerations imply minimum erupted lava volumes of 6 4 103 km3 for allegheny vallis and 6 2 104 km3 for elaver vallis

mineralogy of the light toned outcrop at meridiani planum as seen by the miniature thermal emission spectrometer and implications for its formation 1 analysis of miniature thermal emission spectrometer mini tes data has led to the recovery of a pure end member spectral shape related to the light toned outcrop observed at meridiani planum data from the mer mossbauer spectrometer apxs and previous mini tes measurements were used to constrain a spectral library used to determine the mineralogy of the outcrop from this spectral shape linear deconvolution of the outcrop spectral shape suggests that it is composed primarily of al rich opaline silica mg ca and fe bearing sulfates plagioclase feldspar nontronite and hematite conversion of modeled mineralogy to chemistry shows good agreement with the chemical composition of the outcrops determined by apxs details of the analysis procedure and implications for the formation of the outcrop are discussed along with terrestrial analogs of the ancient environment at meridiani

two years at meridiani planum results from the opportunity rover the mars exploration rover opportunity has spent more than 2 years exploring meridiani planum traveling 8 kilometers and detecting features that reveal ancient environmental conditions these include well developed festoon trough cross lamination formed in flowing liquid water strata with smaller and more abundant hematite rich concretions than those seen previously possible relict hopper crystals that might reflect the formation of halite thick weathering rinds on rock surfaces resistant fracture fills and networks of polygonal fractures likely caused by dehydration of sulfate salts chemical variations with depth show that the siliciclastic fraction of outcrop rock has undergone substantial chemical alteration from a precursor basaltic composition observations from microscopic to orbital scales indicate that ancient meridiani once had abundant acidic groundwater arid and oxidizing surface conditions and occasional liquid flow on the surface

revisiting dirt cracking as a physical weathering process in warm deserts abstract a half century ago c d ollier proposed that insolation driven temperature changes expand and contract fill in fissures enough to widen cracks a process that would permit progressively deeper penetration of fissure fills that would in turn generate a positive feedback of greater and greater strain until desert boulders and bedrock shatters although desert physical weathering by dirt cracking has occasionally been cited this hypothesized process remains without support from subsequent research here field observations electron microscopy x ray powder diffraction particle size analysis and laboratory experiments shed new light on dirt cracking little clear evidence supports the original notion of expansive pressures from thermal fluctuations however mineralogical high resolution transmission electron microscopy back scattered electron microscopy and experimental evidence support two alternative processes of widening fractures wetting and drying of fills inside fissures and the precipitation and remobilization of calcium carbonate a re envisioned dirt cracking wedging process starts with calcium carbonate precipitating in fissures less than 5 m wide first precipitation and then ongoing dissolution of this laminar calcrete opens enough space for dust to penetrate into these narrow fractures wetting of expansive clays in the fissure fill exerts enough pressure to widen and deepen the fissure allowing the carbonate precipitation process to penetrate even deeper and allowing even more dust to move into a fracture as the dust infiltrates its texture changes from a chaotic mix of particles to an alignment of clays parallel to fissure sides this parallel alignment could increase the efficiency of fill wedging ollier s concept of a positive feedback remains supported each increment of fracture deepening and widening permits more even deeper infiltration of laminar calcrete and dust field and electron microscope observations of rock spalling in the winter of 2010 are consistent with ollier s hypothesis that dirt cracking is a common physical weathering process in deserts that splits rocks of all different sizes

earthquake induced rockfall hazard zoning abstract a methodology for quantitative probabilistic hazard zonation for earthquake induced rockfalls is presented and demonstrated in the area of friuli eastern italian alps affected by the 1976 mw 6 5 earthquake four rockfall datasets have been prepared both from historical data analysis and field surveys the methodology relies on a three dimensional hazard vector whose components include the rockfall kinetic energy the fly height and the annual frequency the values of the first two components are calculated for each location along the slope using the 3d rockfall runout simulator hy stone the rockfall annual frequency is assessed by multiplying the annual onset frequency by the simulated transit frequency the annual onset frequency is calculated through a procedure that combines the extent of unstable areas calculated for 10 different seismic hazard scenarios with different annual frequencies of occurrence and the magnitude relative frequency relationship of blocks as derived from the collected field data for each annual frequency of occurrence the unstable area is calculated as a function of morphometric and earthquake characteristics a series of discriminant analysis models using the rockfall datasets and dems of different resolution 1 and 10 m identified the controlling variables and verified the model robustness in contrast with previously published relationships we show that the slope curvature plays a relevant role in the computation of the unstable area

simulating weathering of basalt on mars and earth by thermal cycling physical weathering induced by heating and cooling may cause rock breakdown on mars and earth we report results from parallel weathering simulations on basalt blocks exposed to diurnal cycles representing mars like two simulation runs from 55 to 20 oc and 75 to 10 oc 1 100 relative humidity 4 8 mbar pressure co 2 atmosphere and hot arid earth 23 72o c 30 100 relative humidity conditions under earth conditions thermally pre stressed blocks showed measurable strength declines whilst salt pre treated blocks showed strength gains under mars like conditions pre stressed blocks recorded greater or similar strength declines and salt pre treated blocks showed more muted strength declines than under earth conditions the results imply that on earth and mars diurnal cycling of temperature alone can cause deterioration of basalt with a pre existing stress history the type of stress history is important with salt pre treatment affecting the response of thermally pre stressed blocks under both earth and mars conditions

origin and significance of decameter scale polygons in the lower peace vallis fan of gale crater mars abstract decameter scale polygons are extensively developed in the bedded fractured bf unit of the lower peace vallis fan the polygons occur in a likely extension of the gillespie lake member north of yellowknife bay the section first drilled by the mars science laboratory msl mission we examine hypotheses for the origin of these polygons to provide insight into the history of gale crater the polygons are 4 30 m across square to rectangular and defined by 0 5 4 m wide generally straight troughs with orthogonal intersections polygon networks are typically oriented orthogonal systems with occasional nearly circular patterns hundreds of meters across potential origins include cooling of lava and for sedimentary units syneresis unloading weathering desiccation impact processes and cold climate thermal contraction cold climate thermal contraction is the hypothesis most consistent with the sedimentary nature of the bf unit and the polygon morphology geometry networks and apparent restriction to the coarse grained gillespie lake member a periglacial setting further provides the best analogs for the circular networks and is consistent with geologic context and msl data most of the decametric polygons appear to be ancient they are confined to the hesperian bf unit and only a few of their bounding fractures extend into younger or recently exposed units in this regard they differ from the majority of proposed thermal contraction polygons on mars as those are generally thought to be young features and accordingly the history of formation preservation and reactivation of the decametric polygons is likely to be more complex than that of any proposed young polygons on mars the decametric polygons in the bf unit may represent landforms developed in a cold but still comparatively wet interlude between a clement early mars and the much drier and colder planet of today

a method for producing digital probabilistic seismic landslide hazard maps abstract the 1994 northridge california earthquake is the first earthquake for which we have all of the data sets needed to conduct a rigorous regional analysis of seismic slope instability these data sets include 1 a comprehensive inventory of triggered landslides 2 about 200 strong motion records of the mainshock 3 1 24 000 scale geologic mapping of the region 4 extensive data on engineering properties of geologic units and 5 high resolution digital elevation models of the topography all of these data sets have been digitized and rasterized at 10 m grid spacing using arc info gis software on a unix computer combining these data sets in a dynamic model based on newmark s permanent deformation sliding block analysis yields estimates of coseismic landslide displacement in each grid cell from the northridge earthquake the modeled displacements are then compared with the digital inventory of landslides triggered by the northridge earthquake to construct a probability curve relating predicted displacement to probability of failure this probability function can be applied to predict and map the spatial variability in failure probability in any ground shaking conditions of interest we anticipate that this mapping procedure will be used to construct seismic landslide hazard maps that will assist in emergency preparedness planning and in making rational decisions regarding development and construction in areas susceptible to seismic slope failure

thermal fatigue and thermal shock in bedrock an attempt to unravel the geomorphic processes and products widespread acceptance in science at large notwithstanding the ability of thermal stresses to produce thermal fatigue tf and or thermal shock ts in bedrock and coarse debris in the field is often doubted commonly called insolation weathering in geomorphology the results of questionable laboratory experiments have led many geomorphologists to consider terrestrial temperatures to be inadequate to generate thermally induced stresses leading to rock failure the exceptions are the action of fire or lightning we comprehensively survey the general scientific literature on tf and ts while rigorously scrutinizing that relating to geomorphology findings indicate theoretical and experimental information is adequate to establish the feasibility of tf and ts in rock stemming from rock temperatures monitored in the field while ts may exhibit fracture patterns that are uniquely diagnostic those of tf lack any such attributes it would appear unlikely that tf can prepare or weaken rock to increase the likelihood of ts the question of whether widespread polygonal versus rectilinear cracking is diagnostic of ts is presently an open one as possible explanations invoke process es and or host material s and consequently to assign palaeoenvironmental significance to such fracture patterns is premature at this time further geomorphological laboratory research into tf and ts is merited as sufficient theoretical underpinning already exists however laboratory experimentation needs to be much more rigorously defined and executed and is faced with significant hurdles if it is to be effectively linked to field observations

in situ evidence for an ancient aqueous environment at meridiani planum mars sedimentary rocks at eagle crater in meridiani planum are composed of fine grained siliciclastic materials derived from weathering of basaltic rocks sulfate minerals including magnesium sulfate and jarosite that constitute several tens of percent of the rock by weight and hematite cross stratification observed in rock outcrops indicates eolian and aqueous transport diagenetic features include hematite rich concretions and crystal mold vugs we interpret the rocks to be a mixture of chemical and siliciclastic sediments with a complex diagenetic history the environmental conditions that they record include episodic inundation by shallow surface water evaporation and desiccation the geologic record at meridiani planum suggests that conditions were suitable for biological activity for a period of time in martian history

multiple equilibria of the global thermohaline circulation abstract a general circulation model with a highly idealized geometry is used to investigate which fundamentally different equilibria of the global thermohaline circulation may exist the model comprises two identical basins representing the atlantic and pacific oceans which are connected by a circumpolar channel in the south the model circulation is driven in addition to wind forcing by restoring the sea surface temperature to prescribed values and specified freshwater fluxes in the surface salinity budget mixed boundary conditions the boundary conditions are symmetric with respect to the equator and identical for both oceans four fundamentally different stable steady states are found under the same set of boundary conditions two of the equilibria show both oceans in the same state with high altitude deep water formation occuring either in both northern or in both southern oceans respectively two additional equilibria exist in which the thermohaline circulations of the basins differ fundament

potential desiccation cracks on mars a synthesis from modeling analogue field studies and global observations potential desiccation polygons pdps are polygonal surface patterns that are a common feature in noachian to hesperian aged phyllosilicate and chloride bearing terrains and have been observed with size scales that range from cm wide by current rovers to 10s of meters wide the global distribution of pdps shows that they share certain traits in terms of morphology and geologic setting that can aid identification and distinction from fracturing patterns caused by other processes they are mostly associated with sedimentary deposits that display spectral evidence for the presence of fe mg smectites al rich smectites or less commonly kaolinites carbonates and sulfates in addition pdps may indicate paleolacustrine environments which are of high interest for planetary exploration and their presence implies that the fractured units are rich in smectite minerals that may have been deposited in a standing body of water a collective synthesis with new data particularly from the hirise camera suggests that desiccation cracks may be more common on the surface of mars than previously thought a review of terrestrial research on desiccation processes with emphasis on the theoretical background field studies and modeling constraints is presented here as well and shown to be consistent with and relevant to certain polygonal patterns on mars

a seismic landslide susceptibility rating of geologic units based on analysis of characteristics of landslides triggered by the 17 january 1994 northridge california earthquake abstract one of the most significant effects of the 17 january 1994 northridge california earthquake m 6 7 was the triggering of thousands of landslides over a broad area some of these landslides damaged and destroyed homes and other structures blocked roads disrupted pipelines and caused other serious damage analysis of the distribution and characteristics of these landslides is important in understanding what areas may be susceptible to landsliding in future earthquakes we analyzed the frequency distribution and geometries of triggered landslides in the santa susana 7 5 quadrangle an area of intense seismic landslide activity near the earthquake epicenter landslides occurred primarily in young late miocene through pleistocene uncemented or very weakly cemented sediment that has been repeatedly folded faulted and uplifted in the past 1 5 million years the most common types of landslide triggered by the earthquake were highly disrupted shallow falls and slides of rock and debris far less numerous were deeper more coherent slumps and block slides primarily occurring in more cohesive or competent materials the landslides in the santa susana quadrangle were divided into two samples single landslides 1502 and landslide complexes 60 which involved multiple coalescing failures of surficial material we described landslide morphologies by computing simple morphometric parameters area length width aspect ratio slope angle to quantify and rank the relative susceptibility of each geologic unit to seismic landsliding we calculated two indices 1 the susceptibility index which is the ratio given as a percentage of the area covered by landslide sources within a geologic unit to the total outcrop area of that unit and 2 the frequency index given in landslides per square kilometer ls km2 which is the total number of landslides within each geologic unit divided by the outcrop area of that unit susceptibility categories include very high 2 5 landslide area or 30 ls km2 high 1 0 2 5 landslide area or 10 30 ls km2 moderate 0 5 1 0 landslide area or 3 10 ls km2 and low

effect of amoc collapse on enso in a high resolution general circulation model we look at changes in the el nino southern oscillation enso in a high resolution eddy permitting climate model experiment in which the atlantic meridional circulation amoc is switched off using freshwater hosing the enso mode is shifted eastward and its period becomes longer and more regular when the amoc is off the eastward shift can be attributed to an anomalous eastern ekman transport in the mean equatorial pacific ocean state convergence of this transport deepens the thermocline in the eastern tropical pacific and increases the temperature anomaly relaxation time causing increased enso period the anomalous ekman transport is caused by a surface northerly wind anomaly in response to the meridional sea surface temperature dipole that results from switching the amoc off in contrast to a previous study with an earlier version of the model which showed an increase in enso amplitude in an amoc off experiment here the amplitude remains the same as in the amoc on control state we attribute this difference to variations in the response of decreased stochastic forcing in the different models which competes with the reduced damping of temperature anomalies in the new high resolution model these effects approximately cancel resulting in no change in amplitude

chemical variations in yellowknife bay formation sedimentary rocks analyzed by chemcam on board the curiosity rover on mars the yellowknife bay formation represents a similar to 5m thick stratigraphic section of lithified fluvial and lacustrine sediments analyzed by the curiosity rover in gale crater mars previous works have mainly focused on the mudstones that were drilled by the rover at two locations the present study focuses on the sedimentary rocks stratigraphically above the mudstones by studying their chemical variations in parallel with rock textures results show that differences in composition correlate with textures and both manifest subtle but significant variations through the stratigraphic column though the chemistry of the sediments does not vary much in the lower part of the stratigraphy the variations in alkali elements indicate variations in the source material and or physical sorting as shown by the identification of alkali feldspars the sandstones contain similar relative proportions of hydrogen to the mudstones below suggesting the presence of hydrous minerals that may have contributed to their cementation slight variations in magnesium correlate with changes in textures suggesting that diagenesis through cementation and dissolution modified the initial rock composition and texture simultaneously the upper part of the stratigraphy similar to 1m thick displays rocks with different compositions suggesting a strong change in the depositional system the presence of float rocks with similar compositions found along the rover traverse suggests that some of these outcrops extend further away in the nearby hummocky plains

origin of the polygons and the thickness of vastitas borealis formation in western utopia planitia on mars 1 many middle scale about 100m cracking space polygons are located between the area of the giant polygons and the thumbprint terrains in western utopia planitia most of the patterns are located on vastitas borealis formation the polygonal patterns have frequently been associated with collapsed features such as a covered trough like features the width of the underground crack is approximately 400 500 m the thickness of the surface materials 6 12 m where polygonal patterns occur was calculated based on the space of cracking relationship polygonal networks with strongly oriented features and parallel to the contour line are likely caused by structural geological origin as well as bending forces from the center of the basin

clastic polygonal networks around lyot crater mars possible formation mechanisms from morphometric analysis polygonal networks of patterned ground are a common feature in cold climate environments they can form through the thermal contraction of ice cemented sediment i e formed from fractures or the freezing and thawing of ground ice i e formed by patterns of clasts or ground deformation the characteristics of these landforms provide information about environmental conditions analogous polygonal forms have been observed on mars leading to inferences about environmental conditions we have identified clastic polygonal features located around lyot crater mars 50 n 30 e these polygons are unusually large 100 m diameter compared to terrestrial clastic polygons and contain very large clasts some of which are up to 15 metres in diameter the polygons are distributed in a wide arc around the eastern side of lyot crater at a consistent distance from the crater rim using high resolution imaging data we digi tised these features to extract morphological information these data are compared to existing terrestrial and martian polygon data to look for similarities and differences and to inform hypotheses concerning possible formation mechanisms our results show the clastic polygons do not have any morphometric features that indicate they are similar to terrestrial sorted clastic polygons formed by freeze thaw processes they are too large do not show the expected variation in form with slope and have clasts that do not scale in size with polygon diameter however the clastic networks are similar in network morphology to thermal contraction cracks and there is a potential direct martian analogue in a sub type of thermal contraction polygons located in utopia planitia based upon our observations we reject the hypothesis that polygons located around lyot formed as freeze thaw polygons and instead an alternative mechanism is put forward they result from the infilling of earlier thermal contraction cracks by wind blown material which then became compressed and or cemented resulting in a resistant fill erosion then leads to preservation of these polygons in positive relief while later weathering results in the fracturing of the fill material to form angular clasts these results suggest that there was an extensive area of ice rich terrain the extent of which is linked to ejecta from lyot crater

evaluation of camel comprehensive areal model of earthquake induced landslides abstract a new comprehensive areal model of earthquake induced landslides camel has been developed to assist in planning decisions related to disaster risk reduction camel provides an integrated framework for modeling all types of earthquake induced landslides using fuzzy logic systems and geographic information systems camel is designed to facilitate quantitative and qualitative representation of terrain conditions and knowledge about these conditions on the likely areal concentration of each landslide type camel has been empirically evaluated with respect to disrupted landslides category i using a case study of the 1989 m 6 9 loma prieta ca earthquake in this case camel performs best in comparison to disrupted slides and falls in soil for disrupted rock fall and slides camel s performance was slightly poorer the model predicted a low occurrence of rock avalanches when none in fact occurred a similar comparison with the loma prieta case study was also conducted using a simplified newmark displacement model the area under the curve method of evaluation was used in order to draw comparisons between both models revealing improved performance with camel camel should not however be viewed as a strict alternative to newmark displacement models camel can be used to integrate newmark displacements with other previously incompatible types of knowledge

mineralogy at meridiani planum from the mini tes experiment on the opportunity rover the miniature thermal emission spectrometer mini tes on opportunity investigated the mineral abundances and compositions of outcrops rocks and soils at meridiani planum coarse crystalline hematite and olivine rich basaltic sands were observed as predicted from orbital tes spectroscopy outcrops of aqueous origin are composed of 15 to 35 by volume magnesium and calcium sulfates a high silica component modeled as a combination of glass feldspar and sheet silicates 20 to 30 and hematite only minor jarosite is identified in mini tes spectra mini tes spectra show only a hematite signature in the millimeter sized spherules basaltic materials have more plagioclase than pyroxene contain olivine and are similar in inferred mineral composition to basalt mapped from orbit bounce rock is dominated by clinopyroxene and is close in inferred mineral composition to the basaltic martian meteorites bright wind streak material matches global dust waterlain rocks covered by unaltered basaltic sands suggest a change from an aqueous environment to one dominated by physical weathering

statistical analysis of an earthquake induced landslide distribution the 1989 loma prieta california event the 1989 loma prieta california earthquake moment magnitude m 6 9 generated landslides throughout an area of about 15 000 km2 in central california most of these landslides occurred in an area of about 2000 km2 in the mountainous terrain around the epicenter where they were mapped during field investigations immediately following the earthquake the distribution of these landslides is investigated statistically using regression and one way analysis of variance anova techniques to determine how the occurrence of landslides correlates with distance from the earthquake source slope steepness and rock type the landslide concentration defined as the number of landslide sources per unit area has a strong inverse correlation with distance from the earthquake source and a strong positive correlation with slope steepness the landslide concentration differs substantially among the various geologic units in the area the differences correlate to some degree with differences in lithology and degree of induration but this correlation is less clear suggesting a more complex relationship between landslide occurrence and rock properties

evidence of honeycomb weathering on mars features similar to honeycomb weathering are observed in some martian rocks at the pathfinder landing site honeycomb weathering on earth develops in a range of environments including extremely arid and cold areas in antarctica and on many types of rocks e g basalts and andesites subjected to physical and or chemical weathering salt weathering in combination with frost shattering and chemical weathering provides a viable explanation for the development of honeycomb features on mars under current environmental conditions data supporting this theory are presented and discussed these findings are important in understanding the present climate geology and in particular the geomorphology of mars they also suggest new paths for research and experimentation in future missions to mars

enhancement of enso variability by a weakened atlantic thermohaline circulation in a coupled gcm abstract a coupled ocean atmosphere general circulation model is used to investigate the modulation of el nino southern oscillation enso variability due to a weakened atlantic thermohaline circulation thc the thc weakening is induced by freshwater perturbations in the north atlantic and leads to a well known sea surface temperature dipole and a southward shift of the intertropical convergence zone itcz in the tropical atlantic through atmospheric teleconnections and local coupled air sea feedbacks a meridionally asymmetric mean state change is generated in the eastern equatorial pacific corresponding to a weakened annual cycle and westerly anomalies develop over the central pacific the westerly anomalies are associated with anomalous warming of sst causing an eastward extension of the west pacific warm pool particularly in august february and enhanced precipitation these and other changes in the mean state lead in turn to an eastward shift of the zonal wind anomalies associated with el nin

polygonal sandcracks unique sedimentary desiccation structures in bahamian ooid grainstone sandcracks which are ubiquitous in holocene eolian and beach backshore carbonate grainstone on alligator point cat island bahamas resemble polygonal mudcracks but formed in ooid sand without muddy matrix in experiments on cat island beach sand sediment surfaces cracked polygonally in the absence of mud or biofilms while drying at room temperature due to contraction generated by capillary effects related to surface tension attraction of interstitial water gravitational collapse of irregular open pores and repacking of sand grains due to loss of cohesion between particles caused by evaporation of water enhance the cracking process and appearance of polygons by providing space for cracks to expand the polygons are held together by any remaining capillary moisture and associated meniscus cement which precipitates as the sand dries polygonal sandcracks can be preserved by rapid lithification of carbonate sand but have been documented only rarely from other localities because their formation requires well sorted well rounded spherical grains rather than those making up the more common heterogeneous skeletal and peloidal sediment in carbonate settings interpretation of this primary sedimentary desiccation structure provides new insights into sedimentation and diagenesis of ooid rich deposits and can aid in recognizing ancient subaerial exposure horizons

viscoelastic thermal stress in cooling basalt flows polygonal fractures commonly form in basaltic lava flows during cooling of the molten lava a transient thermomechanical model is constructed to apply the temperature history in a cooling basalt flow as a boundary condition in a mechanical model of viscoelastic stress in cooling basalt nearly all past modeling of stress in cooling basalt has treated the material as purely elastic below a well defined glass transition temperature an important distinction of this model is that the viscosity of the material is allowed to be temperature dependent and the effects of viscoelastic relaxation are included on the basis of this research faster cooling and higher strain rates lead to markedly higher effective glass transition temperatures consistent with previous observations by researchers the total thermal strain in the system is constant yet the percentage of strain that is not relaxed by viscous flow varies with position relative to the cooling surface this elastic strain partition is the portion of the total strain that creates stress in the material and it is directly dependent on cooling rate thus a genetic link between cooling rate and magnitude of stress is identified

methods for measuring rock surface weathering and erosion a critical review studies of rates processes and modes of rock surface and near surface deterioration and also hardening are central to rock weathering and building stone research conservation and management there is a need to measure and monitor weathering at the rock atmosphere interface to facilitate understanding of climatic environmental and lithological controls on the evolution and development of surface weathering features this paper reviews long established and recently developed field and laboratory methods used by geomorphologists to monitor and measure the impact of weathering and erosion on physical and mechanical properties of exposed rock surfaces and their immediate subsurface key advances are highlighted their application to multi scalar understanding and modelling of rock surface weathering in different contexts is discussed and potential future advances to provide new insights into rock weathering durability and materials conservation are identified in highlighting key advantages and disadvantages of a wide range of methods to the broader earth science community the paper aims to contribute to further innovative thinking across disciplines to develop new methods for measuring and monitoring rock weathering

earthquake induced landslides in central america central america is a region of high seismic activity and the impact of destructive earthquakes is often aggravated by the triggering of landslides data are presented for earthquake triggered landslides in the region and their characteristics are compared with global relationships between the area of landsliding and earthquake magnitude we find that the areas affected by landslides are similar to other parts of the world but in certain parts of central america the numbers of slides are disproportionate for the size of the earthquakes we also find that there are important differences between the characteristics of landslides in different parts of the central american isthmus soil falls and slides in steep slopes in volcanic soils predominate in guatemala and el salvador whereas extensive translational slides in lateritic soils on large slopes are the principal hazard in costa rica and panama methods for assessing landslide hazards considering both rainfall and earthquakes as triggering mechanisms developed in costa rica appear not to be suitable for direct application in the northern countries of the isthmus for which modified approaches are required

linking emergence of the central pacific el nino to the atlantic multidecadal oscillation abstractthe ocean atmosphere coupling in the northeastern subtropical pacific is dominated by a pacific meridional mode pmm which spans between the extratropical and tropical pacific and plays an important role in connecting extratropical climate variability to the occurrence of el nino analyses of observational data and numerical model experiments were conducted to demonstrate that the pmm and the subtropical pacific coupling experienced a rapid strengthening in the early 1990s and that this strengthening is related to an intensification of the subtropical pacific high caused by a phase change of the atlantic multidecadal oscillation amo this pmm strengthening favored the development of more central pacific cp type el nino events the recent shift from more conventional eastern pacific ep to more cp type el nino events can thus be at least partly understood as a pacific ocean response to a phase change in the amo

origins of honeycomb weathering the role of salts and wind honeycomb weathering is a common surface phenomenon affecting a variety of rocks in a range of environments it develops on building stones and it shapes ocean cliffs rocks in hot deserts and arctic landscapes honeycomb weathering may also help alter rocks on other planets such as mars although first noted in the nineteenth century its origins are still not well understood and a dearth of laboratory experiments testing the many theories proposed for its development has added to the ambiguity incipient honeycomb weathering in a homogeneous limestone has been experimentally reproduced by wind exposure and salt crystallization our experiments show that heterogeneous wind flow over a stone surface is important in the development of this weathering pattern wind promotes evaporative salt growth between grains on a stone surface resulting in the development of small randomly distributed cavities a reduction in air pressure within the cavities results in increased wind speed and rapid evaporation a high evaporation rate and evaporative cooling of the saline solution in the cavity leads to more rapid and greater granular disintegration than in the surrounding areas it seems that this local supersaturation and subsequent buildup of salt crystallization pressure ultimately result in the formation of honeycomb features for the first time these experimental results demonstrate the close relationship between salts wind and honeycomb weathering they also offer new ways to understand the genesis of this striking and sometimes harmful weathering pattern