crustal structure of the java margin from seismic wide angle and multichannel reflection data seismic investigations across the convergent sunda margin off indonesia provide a detailed image of the crustal architecture of the sunda plate boundary the combined analysis and interpretation of wide angle and reflection seismic data along two coincident profiles across the subduction zone are complemented by additional lines within the forearc domain which yield some three dimensional 3 d constraints on the velocity depth structure across the margin a detailed cross section of the subduction zone is presented which is confirmed by supplementary gravity modeling the sunda convergence zone is a prime example of an accretionary margin where sediment accretion has led to the formation of a massive accretionary prism with a total width of 110 km between the trench and the forearc basin it is composed of a frontal wedge which documents ongoing accretion and a fossil part behind the present backstop structure which constitutes the outer high moderate seismic velocities derived from wide angle modeling indicate a sedimentary composition of the outer high the subducting oceanic slab is traced to a depth of almost 30 km underneath the accretionary prism the adjacent forearc domain is characterized by a pronounced morphological basin which is underlain by a layer of increased seismic velocities and a shallow upper plate moho at 16 km depth we speculate that remnant fragments of oceanic crust might be involved in the formation of this oceanic type crust found at the leading edge of the upper plate beneath the forearc basin

glacial cirques and the relationship between equilibrium line altitudes and mountain range height a global gis and literature based analysis of the altitude and relief of more than 14 000 ice free glacial cirques in 56 study areas ranging from 69 n to 77 s shows that average cirque floor altitudes vary with latitude in a zone centered on the quaternary average equilibrium line altitude qa ela in addition relief above cirque floors averages 346 107 m and is rarely 600 m in regions where ice free cirques are abundant cirque relief is independent of modern precipitation rates tectonic regime and relative peak height limiting peaks to within a fixed distance above the qa ela and thus causing them to also parallel the ela we propose a physical process model where under suitable geologic and tectonic conditions climate exerts a first order control on mountain range height in this model glacial erosion excavates a zone of cirques with floors centered on the qa ela while climate driven weathering processes on adjacent slopes limit the peaks to within a few hundred meters above this zone

eolian deposition of trace elements onto taylor valley antarctic glaciers abstract the major ion and trace element chemistry in four 60 110 cm deep snow pits was examined from three antarctic taylor valley glaciers commonwealth canada and howard all located within 20 km of the ross sea taylor valley tv 77 30 s 163 15 e is part of the mcmurdo dry valleys mdv the largest ice free area in antarctica snow chemistry of these glaciers is strongly influenced by cross valley sw ne and ne sw winds that deposit eolian materials including mineral dust and soluble salts arsenic cd cu mo pb sb and sn in recent tv glacier snow are almost exclusively derived from eolian dust the relative magnitude of element variations with depth relate to the exposure of snow sites to prevalent winds eolian deposition is a primary source of these elements to canada glacier snow and supra and proglacial streams eolian processes are likely very important to the delivery and availability of nutrients and potentially toxic elements to dry valley antarctic ecosystems

surface energy balance and melt thresholds over 11 years at taylor glacier antarctica 11 years ablation 18 cm a 1 was dominated by sublimation with very few occurrences of melt 42 days during 11 years results also indicated that above freezing air temperatures did not necessarily result in melt and in turn melt occurred during subfreezing air temperatures under some conditions for air temperatures near freezing low wind speed was critically important for melt initiation according to the model subsurface melt away from rocks and sediment in the ice occurred three times more frequently than surface melt occurs no deeper than 50 cm below the glacier surface and was small never exceeding 8 by mass the magnitude of subsurface melting and the energy balance indicate that taylor glacier ice is intermediate in optical properties between snow and blue ice

cyclical behavior of thrust wedges insights from high basal friction sandbox experiments scaled sandbox experiments with high basal friction simulating the growth of accretionary wedges display cycles alternating between frontal imbricate thrusting and underthrusting of long undeformed sheets by contrast low basal friction experiments with otherwise similar and constant initial conditions produce a classic frontal imbricate fan through repeated failure along frontal thrusts the cyclical behavior observed in high basal friction experiments is expressed by three quantities 1 the average spacing between frontal thrusts 2 the advance and retreat of the deformation front and 3 the frontal slope alpha of the actively deforming wedge as a long sheet is underthrust the front is steepened through slumping until the maximum critical angle is reached then frontal thrusting resumes and the accretion of imbricate slices builds the wedge forward thereby lowering the taper to the minimum critical angle at shallow tapers a long unit is underthrust and subsequently uplifts shortens and steepens the overlying wedge through backthrust deformation thus completing the cycle underthrusting of long units offers a simple mechanism for underplating overlying units it also provides a possible explanation for temporally and spatially varying wedge geometries in nature when basal frictions attain 80 90 of the internal friction

a hydrological continuum in permafrost environments the morphological signatures of melt driven hydrology on earth and mars abstract this paper examines relationships between the morphology of cold desert hydrological features and the water sources and it relates the formation of diagnostic deposits and erosion patterns to environmentally controlled patterns of discharge in particular three sets of landforms found in the mcmurdo dry valleys of antarctica are compared to similar features on mars antarctic streams rivers to amazonian valleys terrestrial gullies to martian gullies and water tracks to recurring slope lineae similarities in landform morphology are highlighted for each set hydrological characteristics are aggregated or calculated and they are shown to scale comparably across the landforms for the terrestrial and martian groups accordingly a hydrological continuum is proposed linking the magnitude and the persistence of water sources in cold desert environments to flow response and the formation of diagnostic landforms this concept provides a framework for examining the relationships between climate hydrology and geomorphology in the cold desert environments of these two worlds

contractional tectonics and magma paths in volcanoes abstract this study aims to contribute a possible explanation for magma migration within volcanoes located in contractional tectonic settings based on field data and physically scaled experiments the data demonstrate the occurrence of large stratovolcanoes in areas of coeval reverse faulting in spite of the widely accepted idea that volcanism can develop only in extensional transcurrent tectonic settings the experiments simulate the propagation of deformation from substrate reverse faults with different attitudes and locations into volcanoes the substrate fault splits into two main shear zones within the volcano a shallow dipping one with reverse motion propagates towards the lower volcano flank and a steeper dipping one with normal motion propagates upwards in plan view the reverse fault zone is arcuate and convex outwards whereas the normal fault zone is rectilinear structural field surveys at volcanoes located in contractional settings show similar features the plio quaternary trohunco and los cardos centinela volcanic complexes argentina lie above plio quaternary reverse faults the late pleistocene holocene el reventador volcano ecuador is also located in a coeval contractional tectonic belt these volcanoes show curvilinear reverse faults along one flank and rectilinear extensional fracture zones across the crater area consistent with the experiments these data consistently suggest that magma migrates along the substrate reverse fault and is channelled along the normal fault zone across the volcano

temporal variations in physical and chemical features of cryoconite holes on canada glacier mcmurdo dry valleys antarctica cryoconite holes in the mcmurdo dry valleys are ice lidded thus isolating the pools of water from the atmosphere and from potential surface melt hourly measurements of ice and water temperature and water electrical conductivity ec were recorded to broadly characterize the physical and chemical changes on daily to seasonal timescales overall subsurface ice water temperatures were typically several degrees warmer than air temperatures underscoring the importance of subsurface solar heating at no time was surface melt observed and the holes melted from within detailed differences in the timing and magnitude of both temperature and ec variations during melt out and freezeup existed between holes despite short separation distances 1 m we attribute these differences to small scale changes in the optical characteristics of the ice and perhaps different efficiencies in hydrologic connections between holes the holes melt deepened quickly in the first half of the summer before slowing to a rate equal to the rate of surface ablation that kept hole depth constant for the remainder of the season the relatively constant ec of the hole waters during midsummer indicates that these holes were connected to a subsurface water system that flushed the holes with fresher meltwater the early and late season ecs are dominated by freeze thaw effects that concentrate dilute the solutes we speculate that high solute concentrations imply high nutrient concentrations in early summer that may help alleviate potential stresses caused by the production of new biomass after the winter freeze

angles of friction and dilatancy of sand it is generally realized that the peakfriction angel depends not only on density but alsoon the stress path including differences betweenplane strain and triaxial testing conditions indeed plane strain and triaxial strain angles can differ bymore than 58 for a dense sand for a loose sand atthe critical density it is often suggested that similardifferences occur e g stroud 1971 lade 1984 however some authors have presented data thatsuggest a unique critical state angle e g rowe 1962 1971 bolton 1986 this technical note presents data on a uniquecritical state angle the implication is that thefailure criterion of a very loose sand is accuratelydescribed by the mohr coulomb condition whichgives the known six sided pyramid in principalstress space the test data on dense as well as loose hostunsand are also used to study the rate of dilation this topic was extensively treated by bolton 1986 and it is now generally accepted that thetriaxial rate of dilation coincides with the rate ofdilation found in plane strain tests followingroscoe 1970 bolton used an angle of dilatancyl

description of new dry granular materials of variable cohesion and friction coefficient implications for laboratory modeling of the brittle crust abstract cohesion and friction coefficient are fundamental parameters for scaling brittle deformation in laboratory models of geological processes however they are commonly not experimental variable whereas 1 rocks range from cohesion less to strongly cohesive and from low friction to high friction and 2 strata exhibit substantial cohesion and friction contrasts this brittle paradox implies that the effects of brittle properties on processes involving brittle deformation cannot be tested in laboratory models solving this paradox requires the use of dry granular materials of tunable and controllable brittle properties in this paper we describe dry mixtures of fine grained cohesive high friction silica powder sp and low cohesion low friction glass microspheres gm that fulfill this requirement we systematically estimated the cohesions and friction coefficients of mixtures of variable proportions using two independent methods 1 a classic hubbert type shear box to determine the extrapolated cohesion c and friction coefficient and 2 direct measurements of the tensile strength t 0 and the height h of open fractures to calculate the true cohesion c 0 the measured values of cohesion increase from 100 pa for pure gm to 600 pa for pure sp with a sub linear trend of the cohesion with the mixture gm content the two independent cohesion measurement methods from shear tests and tension extensional tests yield very similar results of extrapolated cohesion c and show that both are robust and can be used independently the measured values of friction coefficients increase from 0 5 for pure gm to 1 05 for pure sp the use of these granular material mixtures now allows testing 1 the effects of cohesion and friction coefficient in homogeneous laboratory models and 2 testing the effect of brittle layering on brittle deformation as demonstrated by preliminary experiments therefore the brittle properties become at last experimental variables

an innovative application of the kinect in earth sciences quantifying deformation in analogue modelling of volcanoes measuring surface deformation is critical in analogue modelling of earth science phenomena here we present a novel application of the microsoft kinect sensor to measure vertical deformation in a scaled analogue model of nisyros volcano greece simulating two magmatic sources and related surface deformation the kinect permits capture of real time 640 480 pixel true colour images rgb and a grid of distances to the modelled surface with a horizontal and vertical resolution of 1 mm using recorded distances permits quantification of vertical deformation in terms of maximum and average down and uplift during deflation and inflation phases respectively which is of crucial importance for defining the kinematics of faults formed during the modelling determined from interpretation of the rgb images although other techniques have demonstrated similar or higher accuracy our study demonstrates the cost effectiveness of the kinect in analogue modelling of volcanoes

spatial and temporal patterns of snow accumulation and aerial ablation across the mcmurdo dry valleys antarctica snow in the mcmurdo dry valleys is a potential source of moisture for subnivian soils in a cold desert ecosystem in a water limited environment enhanced soil moisture is expected to provide more favourable conditions for subnivian soil communities in addition snow cover insulates the underlying soil from air temperature extremes quantifying the spatial and temporal patterns of seasonal snow accumulation and ablation is necessary to understand these dynamics repeat high resolution imagery acquired for the 2009 2010 austral summer was used to map the seasonal distribution of snow across taylor and wright valleys southern victorialand antarctica an edge detection algorithm was used to perform an object based classification of snow covered area coupled with topographic parameters obtained from a 30 m digital elevation model unique distribution patterns were characterized for five regions within the neighbouring valleys time lapses of snow distribution in each region provide insight into spatially variable aerial ablation rates change in area of landscape covered by snow across the region a strong coastal to interior gradient of decreasing snow covered area was evident for both taylor and wright valleys the surrounding regions of lake fryxell lake hoare lake bonney lake brownworth and lake vanda exhibited losses of snow covered area of 9 61 km2 93 1 63 km2 72 1 07 km2 97 2 60 km2 82 and 0 25 km2 96 respectively as measured from peak accumulation in october to mid january differences in aerial ablation rates within and across local regions suggest that both topographic variation and regional microclimates influence the ablation of seasonal snow cover copyright 2012 john wiley sons ltd

the impact of analogue material properties on the geometry kinematics and dynamics of convergent sand wedges abstract simulation of geodynamic processes in sandbox experiments requires analogue materials with a deformation behaviour that reproduces the deformation mechanisms of typical crustal rocks we present data on the frictional strength of different sand types employing static and dynamic shear tests the sand types analysed are characterised by an elastic frictional plastic mechanical behaviour with a transient strain hardening and strain softening phase prior to transition to stable sliding this is in conflict with the standard assumption of an ideal cohesionless coulomb material with constant frictional properties the influence of the identified transient material properties on the kinematics growth mechanisms and internal deformation patterns of convergent sand wedges results in characteristic wedge segments which vary depending on material compaction between wedges with well defined segments i e frontal deformation zone frontal imbrication zone and internal accumulation zone with straight slopes and wedges with a continuous convex topographic profile for most materials only the frontal part of the wedge is critical during experimental runs taper and strength of the wedge segments can be shown to be controlled by the frictional properties of active faults wedge segmentation is controlled by a bulk strength increase toward the rear of the wedge due to fault rotation in mechanically less favourable orientations and plastic material hardening the limit between the frontal critical parts of a wedge and internal stable parts is largely controlled by a critical state of stress upon which either renewed failure or fault inactivation occurs on this basis we suggest that critical taper analysis of wedges must be restricted to specific kinematic segments comparison of the experimental results with the nankai accretionary wedge suggests that our interpretation also applies to natural convergent wedges moreover we provide constraints for the selection of adequate granular analogue materials to simulate typical crustal rocks in natural convergent wedges

constraining the recent history of the perennially ice covered lake bonney east antarctica using he kr and xe concentrations abstract lake bonney is a perennially ice covered lake in the mcmurdo dry valleys mdvs that has long been studied in order to provide constraints on the paleoclimate of west antarctica the lake is divided into two lobes west lake bonney wlb and east lake bonney elb that are separated by a narrow ridge the two lobes currently receive surface melt water during austral summers from glacier fed ephemeral streams and this meltwater enters the lake via a narrow ring or moat of liquid water that forms around the lake during summer the west lobe also receives water from direct input of melt water from taylor glacier and saline water from irregular subglacial discharge here we combine previously published he data from lake bonney with new kr and xe concentration data to examine the signatures of water recharge via the seasonal moat and these data are used to constrain a model for he kr and xe transport within both wlb and elb over about the last 5000 6000 yrs a detailed numerical simulation is presented that combines diffusive transport of noble gases within the stratified water column of lake bonney along with ice ablation at the top of the ice cover partitioning of noble gases between water and ice plus exchange of noble gases between wlb and elb results strongly suggest that open moats have only operated for about 2 3 centuries within the last millennium these results are corroborated by the high concentration of he especially within wlb which points to a history of ice cover with no open moats operating for both lobes for at least about 5 millennia in addition the distribution of he kr and xe suggest that a significant rise of the water level of lake bonney associated with a warmer period may have been interrupted by a roughly 4 5 century long cold period during which the moats were not large enough to allow air saturated water into the lake with this cold period ending about one century ago in addition during this cold period there is evidence for a thickening of the ice cover in the last century lake bonney levels have been rising pointing either to more extended austral summers or elevated summer temperatures a rise that is compatible with the heavy noble gas record in the upper portion of the lake a preliminary analysis that includes all stable noble gases heavier than he suggests that glacial melt water gmw directly from taylor glacier below the ice cover may have been a significant input into the deepest parts of wlb but not elb

frontal accretion an internal clock for bivergent wedge deformation and surface uplift 1 we propose a conceptual model of frontal accretion within bivergent wedges which is based on two dimensional sandbox simulations and the analysis of particle displacement fields each frontal accretion cycle consists of a thrust initiation an underthrusting phase and a reactivation phase the location and magnitude of deformation within a bivergent wedge and its associated surface uplift vary systematically with the phase of the frontal accretion cycle and are thus predictable therefore the frontal accretion cycle can be considered as an internal clock for wedge scaled deformation and surface uplift we further demonstrate that the geometry of the deformation front and the spatial distribution of surface uplift can be used to infer the currently active phase within a frontal accretion cycle surface uplift of the axial zone and the retrowedge may reach up to half of the thickness of the incoming sedimentary layer during a frontal accretion cycle we estimate cycle duration to range between 104 and 105 years which is thus similar to the time frame of climatic cycles the proposed conceptual model provides an explanation for the commonly observed transience of deformation and surface uplift and for the discrepancy between geodetic paleoseismologic and geologic estimates of fault slip

properties of granular analogue model materials a community wide survey we report the material properties of 26 granular analogue materials used in 14 analogue modelling laboratories we determined physical characteristics such as bulk density grain size distribution and grain shape and performed ring shear tests to determine friction angles and cohesion and uniaxial compression tests to evaluate the compaction behaviour mean grain size of the materials varied between c 100 and 400 m analysis of grain shape factors shows that the four different classes of granular materials 14 quartz sands 5 dyed quartz sands 4 heavy mineral sands and 3 size fractions of glass beads can be broadly divided into two groups consisting of 12 angular and 14 rounded materials grain shape has an influence on friction angles with most angular materials having higher internal friction angles between c 35 and 40 than rounded materials whereas well rounded glass beads have the lowest internal friction angles between c 25 and 30 we interpret this as an effect of intergranular sliding versus rolling most angular materials have also higher basal friction angles tested for a specific foil than more rounded materials suggesting that angular grains scratch and wear the foil most materials have an internal cohesion in the order of 20 100 pa except for well rounded glass beads which show a trend towards a quasi cohesionless c 20 pa coulomb type material the uniaxial confined compression tests reveal that rounded grains generally show less compaction than angular grains we interpret this to be related to the initial packing density after sifting which is higher for rounded grains than for angular grains ring shear test data show that angular grains undergo a longer strain hardening phase than more rounded materials this might explain why analogue models consisting of angular grains accommodate deformation in a more distributed manner prior to strain localisation than models consisting of rounded grains

below surface ice melt on the coastal antarctic ice sheet in the jutulgryta area of dronning maud land antarctica subsurface melting of the ice sheet has been observed the melting takes place during the summer months in blue ice areas under conditions of below freezing air and surface temperatures adjacent snow covered regions having the same meteorological and climatic conditions experience little or no subsurface melting to help explain and understand the observed melt rate differences in the blue ice and snow covered areas a physically based numerical model of the coupled atmosphere radiation snow and blue ice system has been developed the model comprises a heat transfer equation which includes a spectrally dependent solar radiation source term the penetration of radiation into the snow and blue ice depends on the solar radiation spectrum the surface albedo and the snow and blue ice grain sizes and densities in addition the model uses a complete surface energy balance to define the surface boundary conditions it is run over the full annual cycle simulating temperature profiles and melting and freezing quantities throughout the summer and winter seasons the model is driven and validated using field observations collected during the norwegian antarctic research expedition nare 1996 97 the simulations suggest that the observed differences between subsurface snow and blue ice melting can be explained largely by radiative and heat transfer interactions resulting from differences in albedo grain size and density between the two mediums

distributed modeling of ablation 1996 2011 and climate sensitivity on the glaciers of taylor valley antarctica here the mcmurdo dry valleys of antarctica host the coldest and driest ecosystem on earth which is acutely sensitive to the availability of water coming from glacial runoff we modeled the spatial variability in ablation and assessed climate sensitivity of the glacier ablation zones using 16 years of meteorological and surface mass balance observations collected in taylor valley sublimation was the primary form of mass loss over much of the ablation zones except for near the termini where melt primarily below the surface dominated microclimates in 10 m scale topographic basins generated melt rates up to ten times higher than over smooth glacier surfaces in contrast the vertical terminal cliffs on the glaciers can have higher or lower melt rates than the horizontal surfaces due to differences in incoming solar radiation the model systematically underpredicted ablation for the final 5 years studied possibly due to an increase of windblown sediment surface mass balance sensitivity to temperature was 0 02 m w e k 1 which is among the smallest magnitudes observed globally we also identified a high sensitivity to ice albedo with a decrease of 0 02 having similar effects as a 1 k increase in temperature and a complex sensitivity to wind speed

supraglacial and proglacial valleys on amazonian mars abundant evidence exists for glaciation being an important geomorphic process in the mid latitude regions of both hemispheres of mars as well as in specific environments at near equatorial latitudes such as along the western flanks of the major tharsis volcanoes detailed analyses of glacial landforms lobate debris aprons lineated valley fill concentric crater fill viscous flow features have suggested that this glaciation was predominantly cold based this is consistent with the view that the amazonian has been continuously cold and dry similar to conditions today we present new data based on a survey of images from the context camera ctx on the mars reconnaissance orbiter that some of these glaciers experienced limited surface melting leading to the formation of small glaciofluvial valleys some of these valleys show evidence for proglacial erosion eroding the region immediately in front of or adjacent to a glacier while others are supraglacial eroding a glacier s surface these valleys formed during the amazonian consistent with the inferred timing of glacial features based on both crater counts and stratigraphic constraints the small scale of the features interpreted to be of glaciofluvial origin hindered earlier recognition although their scale is similar to glaciofluvial counterparts on earth these valleys appear qualitatively different from valley networks formed in the noachian which can be much longer and often formed integrated networks and large lakes the valleys we describe here are also morphologically distinct from gullies which are very recent fluvial landforms formed during the last several million years and on much steeper slopes 20 30 for gullies versus 10 for the valleys we describe these small valleys represent a distinct class of fluvial features on the surface of mars glaciofluvial their presence shows that the hydrology of amazonian mars is more diverse than previously thought

coulomb theory applied to accretionary and nonaccretionary wedges possible causes for tectonic erosion and or frontal accretion based on observations from both modem convergent margins and sandbox modeling we examine the possible conditions favoring frontal accretion and or frontal and basal tectonic erosion mean characteristic parameters t t and are used to discuss the mechanical stability of 28 transects across the frontal part of convergent margins where the coulomb theory is applicable natural observations reveal that typical accretionary wedges are characterized by low tapers with smooth surface slope and subducting plate low convergence rates and thick trench sediment while nonaccretionary wedges display large tapers with irregular surface slopes and rough subducting plate high convergence rates and almost no trench fill sandbox experiments were performed to illustrate the effects of seamounts ridges in the subduction zone on the deformation of an accretionary wedge these experiments show that a wedge of sand is first trapped and pushed in front of the seamount which acts as a moving bulldozer this is followed by a tunnelling effect of the subducting seamount through the frontal wedge material which results in considerable sand reworking at an advanced subduction stage the d6collement jumps back from a high level in the wedge to its former basal position we conclude that a high trench sedimentation rate relative to the convergence rate leads to frontal accretion in contrast several conditions may favor tectonic erosion of the upper plate first oceanic features such as grabens seamounts or ridges may trap upper plate material during their subduction process second destabilization of the upper plate material by internal fluid overpressuring causing hydrofracturing is probably another important mechanism

modelling the geometry of coulomb thrust wedges internal geometry and detachment of coulomb thrust wedges is examined in a combined gravity and pressure force field under various boundary conditions and coulomb parameters frontally buttressed sand wedges accreted with narrow tapers above soles with negligible friction in these models serial imbricates stepped up in conjugate sets which operated synchronously or serially with increases in sole friction model coulomb wedges accreted in piggyback style with enhanced taper but narrower spacing of imbricates in this mode flat topped box fold anticlines nucleated at the frontal tip of a sole thrust prior to the fore limb failing as a ramp the initial ramp thrusts subsequently rotated and steepened to acquire concave upwards listric geometry when cohesion was a significant component of strength and the sand grains interlocked thoroughly ramp climb during piggyback thrusting occurred through the generation of a stack of backthrusts the taper of cohesionless sand wedges which lack any length scale was consistent with the critical cohesionless coulomb wedge taper in contrast the taper of experimental cohesive sand wedges which are scale dependent was consistent with the theoretical cohesive coulomb narrow taper only when the cohesive length scale was lr sr rar 10 6 this was constrained by comparing geometry of cohesive sand wedges shortened at different body force per unit mass

martian polar and circum polar sulfate bearing deposits sublimation tills derived from the north polar cap previous spectroscopic studies have shown the presence of hydrated minerals in various kinds of sedimentary accumulations covering and encircling the martian north polar cap more specifically gypsum a hydrated calcium sulfate has been detected on olympia planum a restricted part of the circum polar dune field to further constrain the geographical distribution and the process of formation and accumulation of these hydrated minerals we performed an integrated morphological structural and compositional analysis of a key area where hydrated minerals were detected and where the main polar landforms are present by the development of a spectral processing method based on spectral derivation and by the acquisition of laboratory spectra of gypsum ice mixtures we find that gypsum bearing sediment is not restricted to the olympia planum dunes but is also present in all kinds of superficial sediment covering the surface of the north polar cap and the circum polar dune field spectral signatures consistent with perchlorates are also detected on these deposits the interpretation of landforms reveals that this gypsum bearing sediment was released from the ice cap by sublimation we thus infer that gypsum crystals that are now present in the circum polar dune field derive from the interior of the north polar cap gypsum crystals that were initially trapped in the ice cap have been released by sublimation of the ice and have accumulated in the form of ablation tills at the surface of the ice cap these gypsum bearing sublimation tills are reworked by winds and are transported towards the circum polar dune field comparison with sulfates found in terrestrial glaciers suggests that gypsum crystals in the martian north polar cap have formed by weathering of dust particles either in the atmosphere prior to their deposition during the formation of the ice cap and or in the ice cap after their deposition

climatic implications of reconstructed early mid pliocene equilibrium line altitudes in the mcmurdo dry valleys antarctica early mid pliocene moraines in the mcmurdo dry valleys antarctica are more extensive than the present alpine glaciers in this region indicating substantial climatic differences between the early mid pliocene and the present to quantify this difference in the glacier climate regime we estimated the equilibrium line altitude ela change since the early mid pliocene by calculating the modern ela and reconstructing the elas of four alpine glaciers in wright and taylor valleys at their early mid pliocene maxima the area altitude balance ratio method was used on modern and reconstructed early mid pliocene hypsometry in wright and victoria valleys mass balance data identify present day elas of 800 1600 ma s l and an average balance ratio of 1 1 the estimated elas of the much larger early mid pliocene glaciers in wright and taylor valleys range from 600 to 950 170 m a s l and thus are 250 600 170 m lower than modern elas in these valleys the depressed elas during the early mid pliocene most likely indicate a wetter and therefore warmer climate in the dry valleys during this period than previous studies have recognized

minimal pliocene pleistocene uplift of the dry valleys sector of the transantarctic mountains a key parameter in ice sheet reconstructions we propose that there has been little or no pliocene pleistocene uplift of the dry valleys sector of the transantarctic mountains on the basis of isotopic dating and mapping of in situ cinder cone deposits on the walls of taylor valley twenty seven 40ar 39ar incremental heating analyses on whole rock samples from subaerially erupted olivine basanite volcanic outcrops of known elevations define 14 eruptions ranging in age from 3 89 to 1 50 ma because taylor valley opens directly onto the ross sea these results show that any surface uplift during the past 2 57 m y was 300 m our conclusion of minimal uplift contradicts previous models of dramatic uplift up to 3000 m since 3 ma and associated hypotheses that uplift caused climatic cooling and growth of a polar east antarctic ice sheet

map based methods for estimating glacier equilibrium line altitudes we examine the validity of two methods for estimating glacier equilib rium line altitudes elas from topographic maps the ela determined by contour inflection the kinematic ela andthe mean elevation of the glacier correlate extremely well with the ela determined from mass balance data observed ela however the range inglacierelevations above sea level is much larger thanthe variation in ela mak ing this correlation unhelpful the data were normalized and a reasonable correlation r 2 0 59 was found between observed and kinematic ela the average of the normal ized kinematic elas was consistently located down glacier fromthe observed ela con sistent withtheory thenormalized mean elevationoftheglacierexhibitedno correlation and suggests that the toe headwall altitude ratio is not a good approximation for the ela kinematic waves had no effect on the position of the kinematic ela therefore topographic maps of glacier surfaces can be used to infer the position of the ela and provide a method for estimating past elas from historic topographic maps

episodic growth of fold thrust belts insights from finite element modelling abstract the sequential development of a fold thrust belt was investigated using 2d finite element modelling fem the new model results show that a thrust system is typically composed of three distinct regions the thrust wedge pre wedge and undeformed region the thrust wedge involves growth that repeats episodically and cyclically a cycle of wedge building starts as frontal accretion occurs which is accompanied by a rapid increase in wedge width reducing the taper angle below critical in response to this the wedge interior tracked here by the 50 m displacement position rapidly propagates forwards into a region of incipient folding the taper angle progressively increases until it obtains a constant apparent critical value 10 during this period the wedge experiences significant shortening after a new thrust initiates at the failure front leading to a decrease in wedge width successive widening of the wedge and subsequent shortening and thrusting maintain a reasonably constant taper angle the fold thrust belt evolves cyclically through a combination of rapid advancement of the wedge and subsequent gradual slow wedge growth the new model results also highlights that there is clear although minor deformation 0 10 m horizontal displacement in front of the thrust wedge

lake ice ablation rates from permanently ice covered antarctic lakes in the mcmurdo dry valleys of antarctica three large permanently ice covered closed basin lakes exist along the floor of taylor valley lake ice ablation loss of ice mass is calculated as the sum of sublimation and surface melt and is the driver of ice cover turnover in these systems in taylor valley both manual and automated lake ice ablation rates have been calculated from 2001 to 2011 results indicate relatively consistent winter ablation of 0 07 0 21 m 0 2 0 7 mm w e d 1 summer ablation of lake ice is more variable and ranges from 0 25 to 1 62 m 5 31 mm w e d 1 over an average 51 day period previous to this study ablation rates have been cited as 0 35 m a 1 in the dry valleys from sublimation modeling based on meteorological variables we show that this value has significantly underestimated mean ablation and ice cover turnover on the taylor valley lakes

sandbox model simulation of forearc evolution and noncritical wedges convergent plate boundaries exhibit a wide range of behaviors ranging from sediment accretion and underplating to large scale erosion of the forearc we have used sandbox modeling to simulate the growth of thin skinned contractional wedges over a strong backstop at an accretionary margin the backstop in our model causes the growth of two distinct wedges with quite different growth histories analogous to the accretionary wedge and the inner deformation belt retrowedge found in at least some forearcs after starting with an initially steep slope the surface flattens as the accretionary wedge grows by frontal accretion until the wedge attains and maintains a minimum possible critical taper the retrowedge driven by uplift of the outer arc high increases its surface slope as it grows until a kinematic steady state is attained it exhibits a stable taper with slope larger than the minimum critical taper but never larger than the theoretical maximum critical taper when a basal decollement is present above the backstop in models in which the retrowedge has not developed a decollement it has a taper with a slope at the angle of repose when a basal decollement is present above the backstop the main body of the retrowedge acts as a bulldozer or a backstop pushing the sediments in front of it which then form an additional wedge with a small minimum critical taper a broad outer arc high stands above the toe of the backstop where maximum principal stresses rotate to meet the stress conditions in the two contractional belts on either side of it as these belts grow in opposite directions the accretionary wedge accretes large quantities of sediment at its front but the retrowedge does not because the retrowedge can exhibit a non critical stable taper in the absence of rapid erosion or accretion it is misleading to assume that active thin skinned wedges are necessarily at maximum or minimum critical taper

glacier mass balances 1993 2001 taylor valley mcmurdo dry valleys antarctica mass balances were measured on four glaciers in taylor valley antarctica from 1993 to 2001 we used a piecewise linear regression which provided an objective assessment of error to estimate the mass balance with elevation missing measurements were estimated from linear regressions between points and showed a significant improvement over other methods unlike temperate glaciers the accumulation zone of these polar glaciers accumulates mass in summer and winter and the ablation zone loses mass in both seasons a strong spatial trend of smaller mass balance values with distance inland r 2 0 80 reflects a climatic gradient to warmer air temperatures faster wind speeds and less precipitation annual and seasonal mass balance values range only several tens of millimeters in magnitude and no temporal trend is evident the glaciers of taylor valley and probably the entire mcmurdo dry valleys are in equilibrium with the current climate and contrast with glacier trends elsewhere on the antarctic peninsula and in temperate latitudes

noncohesive critical coulomb wedges an exact solution active fold and thrust belts or submarine accretionary complexes can be modeled as critically tapered wedges of material on the verge of coulomb failure everywhere overlying a basal decollement where frictional sliding is occurring ignoring cohesion the four strength parameters needed to describe a critical coulomb wedge are its internal and basal coefficients of friction and b and its internal and basal hubbert rubey fluid pressure ratios and b an exact relation between surface slope and basal dip of a noncohesive critical wedge with uniform properties is derived the state of stress within such a wedge has the same orientation everywhere and is constant if is and vice versa a coefficient of internal friction 1 1 is consistent with the known surface slope basal dip and pore fluid pressures in the active fold and thrust belt of western taiwan assuming that byerlee s law b 0 85 is valid on the base the wide variety of tectonic styles observed to occur along convergent margins including subduction erosion active accretion subduction without accretion and even extension and normal faulting may be controlled by relatively small spatial or temporal variations in either b or b

the influence of an embedded viscoelastic plastic layer on kinematics and mass transport pattern within accretionary wedges abstract the major aim of this study was to examine the influence of an embedded viscoelastic plastic layer at different viscosity values on accretionary wedges at subduction zones to quantify the effects of the layer viscosity we analysed the wedge geometry accretion mode thrust systems and mass transport pattern therefore we developed a numerical 2d sandbox model utilising the discrete element method starting with a simple pure mohr coulomb sequence we added an embedded viscoelastic plastic layer within the brittle undeformed sediment package this layer followed burger s rheology which simulates the creep behaviour of natural rocks such as evaporites this layer got thrusted and folded during the subduction process the testing of different bulk viscosity values from 1 1013 to 1 1014 pa s revealed a certain range where an active detachment evolved within the viscoelastic plastic layer that decoupled the over and the underlying brittle strata this mid level detachment caused the evolution of a frontally accreted wedge above it and a long underthrusted and subsequently basally accreted sequence beneath it both sequences were characterised by specific mass transport patterns depending on the used viscosity value with decreasing bulk viscosities thrust systems above this weak mid level detachment became increasingly symmetrical and the particle uplift was reduced as would be expected for a salt controlled forearc in nature simultaneously antiformal stacking was favoured over hinterland dipping in the lower brittle layer and overturning of the uplifted material increased hence we validated that the viscosity of an embedded detachment strongly influences the whole wedge mechanics both the respective lower slope and the upper slope duplex shown by e g the mass transport pattern

ice dynamics and thermal regime of taylor glacier south victoria land antarctica les donnees glaciologiques recueillies sur le taylor glacier ont servi a reconstituer les principaux traits de la dynamique et du regime thermique du glacier les etudes du bilan de masse montrent que le glacier est proche de l equilibre les conditions thermiques de la glace basale sur une grande partie de la zone d ablation ont ete calculees a partir d estimation du flux de chaleur geothermique et de mesures des temperatures de la glace pres de la surface des vitesses et de l epaisseur de la glace on a trouve que jusqu a 50 de la zone d ablation la glace basale pouvait etre fondante

retreating glacier fronts on the antarctic peninsula over the past half century the continued retreat of ice shelves on the antarctic peninsula has been widely attributed to recent atmospheric warming but there is little published work describing changes in glacier margin positions we present trends in 244 marine glacier fronts on the peninsula and associated islands over the past 61 years of these glaciers 87 have retreated and a clear boundary between mean advance and retreat has migrated progressively southward the pattern is broadly compatible with retreat driven by atmospheric warming but the rapidity of the migration suggests that this may not be the sole driver of glacier retreat in this region

an experimental examination of the critical state and other similar concepts for granular soils measuring the critical state parameters of dense granular soil by drained triaxial tests is problematic as significant nonhomogeneous deformations can develop prior to approaching a critical state

solar heating rates and temperature profiles in antarctic snow and ice observations of temperature maxima at about 10 cm depth in cold antarctic snow during summer have previously been explained by proposing that solar heating is distributed with depth whereas thermal infrared cooling is localized at the surface the solid state greenhouse an increase in temperature from the surface to 10 cm depth t 4 k found by rusin 1961 on the antarctic plateau was successfully reproduced by schlatter 1972 in a combined radiative transfer and heat transfer model

effects of igneous intrusions on coal petrology pore fracture and coalbed methane characteristics in hongyang handan and huaibei coalfields north china article i nfo the effects of igneous intrusions have proved to be important for the exploration and development of coalbed methane in many coal basins however the studies of the influences of localized intrusions on coalbed meth ane reservoirs are still insufficient in the context of five typical dike sill intrusion patterns i e dike cut through dike cut in floor intrusion by sill roof intrusion by sill and dual intrusions of roof and floor by sills this study investigates the changes of coal organic composition and pores fractures resulting from igneous intrusions the influences of igneous intrusions on coal composition mainly include the decrease of vitrinites especially telocollinite and the increase of inertinites contents as well as the formation of secondary devolatilization vacuoles and of exogenous desiccation microfractures the vacuoles have size of 0 1 10 m and the microfractures are commonly developed with a wide space and a significantly short length the microfractures typically have irregular dendritic filamentous and turtleback textures and densi ties of hundreds per 9 cm 2 the influences of igneous intrusions on coal pores and fractures vary significantly depending on the intrusion patterns the coal ranks after the intrusion and the nature of the adjacent forma tion surrounding the intrusion for the coals with a vrr 4 2 the intrusion significantly reduced the coal pore development for the coals with a vrr from 2 1 4 2 the development of the coal pores improved with decreasing distance to the contact for the coals with a vrr b2 1 the intrusion resulted in a slight improvement of the coal pore development a possible explanation for the increasing gas content near the intrusion is that the secondary vacuoles and microfractures induced an increase in the gas storage capacity and in the permeability of the coal reservoir the detailed intrusion patterns of sills and dikes contribute to the formations of the coalbed methane accumulation in coal seams and to the coal generated gas accumula tion in the reservoir of the highly permeable surrounding rocks

pliocene paleoenvironment and antarctic ice sheet behavior evidence from wright valley investigations in wright valley adjacent to the transantarctic mountains in east antarctica shed light on the question of whether high latitude pliocene climate was warm enough to cause widespread deglaciation of the east antarctic craton with a concurrent magellanic moorland like environment if pliocene age diatoms presently in glaciogenic deposits high in the transantarctic mountains had come from seaways on the east antarctic craton an expanding late pliocene ice sheet must have first eroded them from marine sediments and then deposited the diatoms at their present high altitude locations this hypothetical expanding glacier would have had to have come through wright valley glacial drift sediments from the central wright valley were mapped sampled analyzed and 40ar 39ar whole rock dated our evidence indicates that an east antarctic outlet glacier has not expanded through wright valley and hence cannot have overridden the dry valleys sector of the transantarctic mountains any time in the pa

interpretation of recent southern hemisphere climate change climate variability in the high latitude southern hemisphere sh is dominated by the sh annular mode a large scale pattern of variability characterized by fluctuations in the strength of the circumpolar vortex we present evidence that recent trends in the sh tropospheric circulation can be interpreted as a bias toward the high index polarity of this pattern with stronger westerly flow encircling the polar cap it is argued that the largest and most significant tropospheric trends can be traced to recent trends in the lower stratospheric polar vortex which are due largely to photochemical ozone losses during the summer fall season the trend toward stronger circumpolar flow has contributed substantially to the observed warming over the antarctic peninsula and patagonia and to the cooling over eastern antarctica and the antarctic plateau

relating experimental and geological rheology this paper is concerned with the question of how to relate laboratory measurements of the rheology of rocks to the rheological assumptions that need to be made in geodynamic modelling first there is a brief resume of the principal types of rheological behaviour that have been studied in the laboratory both pressure dependent strain rate independent and pressure independent strain rate dependent then the generalization of the results from the relatively simple stress states of the experiments to general stress states is discussed followed by consideration of the extrapolation of the experimental results to geological strains and strain rates finally the problems associated with spatial scale are considered leading to the question of how to model the rheological behaviour of large scale rock masses using the rheological measurements of laboratory specimens and taking into account the heterogeneity of geological scale rock masses

evidence for subglacial ponding across taylor glacier dry valleys antarctica hubbard alun lawson w anderson b hubbard b p 2004 evidence for subglacial ponding across taylor glacier dry valleys antarctica annals of glaciology 39 1 79 84 rae2008

can climate warming induce glacier advance in taylor valley antarctica changes in the extent of the polar alpine glaciers within taylor valley antarctica are important for understanding past climates and past changes in ice dammed lakes comparison of ground based photographs taken over a 20 year period shows glacier advances of 2 100 m over the past 103 years the climate has warmed we hypothesize that an increase in average air temperature alone can explain the observed glacier advance through ice softening we test this hypothesis by using a flowband model that includes a temperature dependent softness term results show that for a 2 c warming a small glacier 50 km 2 advances 25m and the ablation zone thins consistent with observations a doubling of snow accumulation would also explain the glacial advance but predicts ablation zone thickening rather than thinning as observed problems encountered in modeling glacier flow lead to two intriguing but unresolved issues first the current form of the shape factor which distributes the stress in simple flow models may need to be revised for polar glaciers second the measured mass balance gradient in taylor valley may be anomalously low compared to past times and a larger gradient is required to develop the glacier profiles observed today

cold based debris covered glaciers evaluating their potential as climate archives through studies of ground penetrating radar and surface morphology we describe the morphology and internal structure of mullins and friedman glaciers two cold based debris covered alpine glaciers that occur in neighboring valleys in the mcmurdo dry valleys antarctica both glaciers are overlain by a single dry supraglacial debris layer 8 75 cm thick each mantling debris layer is marked with near identical patterns of arcuate ridges and steps as well as corresponding changes in bulk grain size meter scale surface topography and thermal contraction crack polygons results from 24 km of ground penetrating radar data show that the ice within the uppermost 1 2 km of mullins and friedman glaciers is essentially free of englacial debris 1 by volume but thereafter is interspersed with bands of englacial debris each 3 m thick and dipping up glacier that intersect the ice surface at all major surface ridges and steps the similarity in number and pattern of englacial debris bands and corresponding surface ridges and steps across both glaciers along with model results and observations that call for negligible basal entrainment is best explained by episodic environmental change at valley headwalls our working hypothesis is that layers of englacial debris originate as supraglacial lags that form in ice accumulation areas during times of reduced net ice accumulation following renewed net ice accumulation these lags are subsequently buried by snow and ice flow englacially and intersect the ice surface to impart distinctive changes in the texture of supraglacial debris and topographic relief the implication is that the englacial structure and surface morphology of these cold based debris covered glaciers preserves a consistent record of climate and environmental change

origin of convex accretionary wedges evidence from barbados the surface slopes of submarine accretionary wedges generally decrease away from the toe or defor mation front toward the arc this paper presents evidence that this characteristic convex cross sectional shape is a direct mechanical response to the lithification of sediments during accretion the recently accreted sediments near the toe which are typically unconsolidated and therefore very weak must deform until a critical taper is attained at which they are stable in the presence of the horizontal tectonic compression this critical wedge taper and thus the bathymetric slope of the accretionary prism is relatively high for the porous weak sediments near the toe in contrast the compacted sediments farther back in the wedge are stronger so they require a relatively modest critical taper and therefore a lower bathymetric slope to be stable under the same tectonic compression the result is a convex cross sectional wedge shape we investigate several possible causes of the increase in sediment strength within the wedge and conclude that the primary cause is an increase in cohesive strength with decreasing porosity a straightforward generalization of the exact critical taper model is combined with empirical cohesion porosity velocity relations to infer the distribution of porosity and p wave velocity within the barbados accretionary wedge we estimate that the porosity decreases from its near toe value of 70 to approximately 30 at a depth of 3 km below the seafloor and a distance of 60 km arcward from the front of the wedge

shear test results for cohesion and friction coefficients for different granular materials scaling implications for their usage in analogue modelling abstract laboratory tests have been carried out on dry granular materials such as quartz sand glass microspheres and sugar with different grain size rounding and sphericity the measurements have been made with a simple shear test machine for different values of normal stress 50 900 pa shear stress has been plotted against normal stress in order to determine the cohesion and coefficient of internal friction for the investigated materials resulting values of cohesion and coefficient of internal friction are mainly dependent on rounding and sphericity while grain size has a less significant influence further the behaviour of the materials for very small normal stresses 0 400 pa is more complex than previously assumed the fracture envelopes for all materials investigated are convex outward for this small range and converge towards a straight failure envelope with increasing normal stress finally in extensional faulting experiments there is no significant change in fault dip with increasing depth therefore the non linear behaviour for small normal stresses is best described as a dependence of the cohesion on the normal stress and not as a dependence of the coefficient of internal friction on the normal stress values for cohesion increase from 0 pa 15 pa at zero normal stress to 137 247 pa 15 pa for normal stresses greater than 250 400 pa the results show that well rounded spherical material is better suited to model brittle behaviour of rocks in crustal and lithospheric scale analogue models than less well rounded material since it has a smaller cohesion and a coefficient of internal friction which is closer to values of natural rocks

role of preexisting topography and overburden on strain partitioning of oblique doubly vergent convergent wedges 1 scaled sandbox modeling was used to analyze the three dimensional aspects of strain partitioning along obliquely convergent margins that underwent a subduction polarity reversal event in the experiments the first phase of shortening produced a preexisting topography that affected wedge kinematics during the second phase increasing degrees of obliquity during the first shortening phase produced different amounts of inherited topography and overburden giving way to different effects on wedge response during the second phase of shortening during the second phase the models with an inherited heavy overburden show an anomalous orientation for riedel shears predating the development of a margin parallel strike slip fault these shears are oriented at an angle that is higher than kinematically predicted with respect to the subduction slot suggesting a transient rotation of the stress applied by the obliquity of subduction in contrast experiments with a lighter overburden do not show this inconsistency in addition all the models displayed an unexpectedly high accretion rate during the second phase of shortening which we interpret to be dependent on topographical slope breaks inherited after the first phase of shortening and the critical asymmetrical architecture of doubly vergent wedges

shocks in a box an analogue model of subduction earthquake cycles with application to seismotectonic forearc evolution 1 we introduce and test an experimental approach to simulate elastoplastic megathrust earthquake cycles using an analogue model and apply it to study the seismotectonic evolution of subduction zones the quasi two dimensional analogue model features rate and state dependent elastic frictional plastic and viscoelastic material properties and is scaled for gravity inertia elasticity friction and viscosity the experiments are monitored with a high resolution strain analysis tool based on digital image correlation particle imaging velocimetry piv providing deformation time series comparable to seismologic geodetic and geologic observations in order to separate elastic and nonelastic effects inherent the experimental deformation patterns we integrate elastic dislocation modeling edm into a hybrid approach we use the analogue earthquake slip and interseismic locking distribution as edm dislocation input and forward model the coseismic and interseismic elastic response the residual which remains when the edm prediction is subtracted from the experimental deformation pattern highlights the accumulation of permanent deformation in the model the setup generates analogue earthquake sequences with realistic source mechanisms and elastic forearc response and recurrence patterns and reproduces principal earthquake scaling relations by applying the model to an accretionary type plate margin we demonstrate how strain localization at the rupture peripheries may lead to a seismotectonically segmented forearc including a tectonically stable shelf and coastal high 20 plate convergence accommodated by internal shortening overlying the area of large megathrust earthquake slip fifty to 75 of plate convergence is accommodated by internal shortening in the slope region where earthquake slip tapers out toward the trench the inner forearc region remains undeformed and represents a basin

episodic accretion and strain partitioning in a model sand wedge we model led thrust wedge accretion and deformation partitioning in a passively layered sand detached and shortened above a smooth rigid decollement the thrust wedge accretes in piggyback style during forward advance of a rear wall the passively layered sand accommodates the shortening penetratively by kinking ramp folding and by imbrication in single layers the style of compression changes with time and or stratigraphic position within the sand prism initial penetrative layer shortening above a slipped zone of decollement is succeeded by formation of monoclinal or conjugate shear bands at temporary terminations of decollement the shear bands subsequently narrow down and lock as thrust ramps the model sand wedge accrets episodically rather than steadily episodicity is controlled by the stick slip mode of decollement propagation and by volume loss and compaction of the wedge material in response to convergence this results in formation of a wedge with a convex upwards cross sectional topography

sublimation and surface energy budget of taylor glacier antarctica taylor glacier an outlet of the east antarctic ice sheet flows through the transantarctic mountains and terminates in the dry valleys understanding how this glacier fluctuates is important for studies of glacial geology paleoclimate ice dynamics and ecology sublimation is the primary mass loss process for most of the glacier four years of specific balance measurements from the ablation zone show sublimation rates up to 40 cma 1 we used data from an array of weather stations as inputs to a model for latent heat flux and hence sublimation rate calculated and measured ablation rates agree to within uncertainties indicating that wind speed and vapour pressure gradient a function of temperature and humidity are the governing variables as expected from theory measurements and model results together allowed us to examine the spatial and temporal variations of sublimation on the glacier on average sublimation is about two times faster in summer than winter rapid sublimation occurs during storms and katabatic wind events but such periods contribute less to the annual total than do slow persistent losses spatially sublimation reaches a maximum midway along the glacier where descending surface air currents are focused by the topography of the aptly named tributary windy gully

measurements of friction coefficients and cohesion for faulting and fault reactivation in laboratory models using sand and sand mixtures abstract simple laboratory tests have been made on dry quartz sand and on mixtures of sand and clay and sand and cement tests were made on both low and high density specimens of each mixture as determined by physical handling techniques the tests included measurements of density estimates of the coefficient of internal friction based on fault orientation and estimates of the friction coefficients and cohesion values for fault initiation and reactivation in a shear frame apparatus which was also used to test artificial fault zones made from pure clay glass microspheres and wheat flour the results suggest that density is determined more by handling technique than by composition and that friction coefficients and perhaps cohesion both increase with increasing density the shear testing revealed a consistent drop in cohesion for fault reactivation in all densely packed mixtures tested although small this drop may be significant for some types of laboratory models

insights into the effects of oblique extension on continental rift interaction from 3d analogue and numerical models abstract continental rifts often develop from linkage of distinct rift segments under varying degrees of extension obliquity these rift segments arise from rift initiation at non aligned crustal heterogeneities and need to interact to develop a full scale rift system here we test the effects of 1 oblique extension and 2 initial heterogeneity seed offset on continental rift interaction with the use of an improved analogue model set up x ray computer tomography ct techniques are used to analyse the 3d models through time and the results are compared with additional numerical models and natural examples the experimental results reveal that increasing extension obliquity strongly changes rift segment structures from wide rifts in orthogonal settings to narrower rifts with oblique internal structures under oblique extension conditions to narrow strike slip dominated systems towards the strike slip domain we also find that both decreasing seed offset and increasing extension obliquity promote hard linkage of rift segments through the formation of continuous rift boundary faults at the surface initial soft linkage through the formation of relay ramps is more likely when seed offset increases or extension is more orthogonal rather than linking at depth the rift boundary faults curve around each other at depth and merge towards the surface to form a continuous trough orthogonal extension promotes the formation of intra rift horsts which may provide hydrocarbon traps in nature

mechanism of decollement formation in subduction zones summary the mechanism of decollement formation was investigated through a particle based simulation model assuming homogeneity e g no weak layer or pore fluid a decollement like structure appeared as a spontaneously localized shear deformation near the bottom of the sediment when the thickness of the sediment was sufficient to balance the gravitational force and tectonic loading in contrast no such decollement like structure was formed when the sediment was too thin in this case the entire prism was deformed because of plate motion these results are consistent with various observations in real subduction zones a precise analysis of the stress state evolution during accretion reveals that the formation of a decollement like structure is controlled by the spatio temporal distribution of isotropic compression states

constraints on friction coefficients by an inverse analysis of sand box thrust dips abstract we measured the dips of thrusts forming in a uniform sand layer under horizontal shortening by a rigid emerging ramp in conditions of full erosion various ramp dips and four types of ramp material were used throughout the 12 experiments in three experiments the ramp was shortcut by a less steep thrust forming a spontaneous ramp in the sand the forward modelling proposed to predict these observations involves i computing the total dissipation in the structure by using global force equilibrium and a parameterised kinematic framework including the possibility of shortcut development and ii minimising the total dissipation of mechanical work with respect to the kinematic parameters i e the thrust dips for which two analytic solutions are found the inverse problem involves computing probability densities over the parametric space of friction coefficients including the internal friction angle of the sand and friction angles of the four materials used on the rigid ramps practically this involves computing a misfit using the l2 norm between the observed and predicted thrust dips for every possible value of the friction angles the resulting probability density provides all the quantitative information that can be retrieved from the experiments in the light of our forward modelling ramp friction angles exhibit sharp probability changes at values that trigger the occurrence of shortcuts thus yielding non trivial bounds on the ramp friction values that are directly related to the observations of ramp and back thrust geometry also the probability distribution of the internal sand friction and those of the ramp frictions is in good agreement with independent measurements this approach is designed to be applicable to field studies of brittle deformation where geometries are observed and rheological parameters are sought

the estimation of diffuse strains in the toe of the western nankai accretionary prism a kinematic solution arcward changes in the vertical spacing of seismically defined stratigraphic reflectors and sediment porosities determined from drill cores and seismic interval velocities suggest a compact kinematic solution for estimating diffuse deformation within accretionary prism toes the method involves the solution of the lagrangian form of the conservation of mass equation for the two dimensional finite deformation gradient field within discrete deforming domains we apply this technique to the unfaulted protothrust zone ptz along a western transect across the nankai accretionary prism in the vicinity of deep sea drilling project sites 582 and 583 the results yield horizontal shortening estimates of about 1 7 km or about 20 this shortening appears to be accommodated through different strain responses depending on the consolidation state of the sediments at the time of accretion shallow sediments respond to horizontal shortening dominantly by expelling pore fluids producing volume strains up to 30 while deeper sediments accommodate horizontal shortening dominantly through vertical extension reaching 70 in the footwall of the frontal thrust horizontal shear strains within the ptz are not well resolved by this solution due to uncertainties in the porosity distribution but they generally appear to be quite small

one million cubic kilometers of fossil ice in valles marineris relicts of a 3 5 gy old glacial landsystem along the martian equator abstract self consistent landform assemblages suggest that valles marineris the giant valley system that stretches along the martian equator was entirely glaciated during late noachian to early hesperian times and still contains huge volumes of fossil ice some of these glacial landform assemblages are illustrated here with representative examples selected in three regions ius chasma central candor chasma and the junction between coprates chasma and capri chasma a morphological boundary separating an upper spur and gully morphology from a smooth basal escarpment has been spectacularly preserved along valley walls throughout valles marineris the boundary winds around topographic obstacles and displays long wavelength variations in elevation it is associated with lateral benches hanging valleys and truncated spurs comparisons with terrestrial analogs indicate that it is most reasonably interpreted as a glacial trimline chasma floors are covered by various kinds of terrains including hummocky terrains platy terrains lateral banks layered benches and a draping mantle landforms in these terrains and their spatial relationship with the interpreted trimline suggest that they correspond to various disintegration stages of an ancient glacial fill currently protected by a superficial cover of ablation till altogether these landforms and terrains compose a full glacial landsystem with wet based glaciers that were able to flow and slide over their beds it was most probably fed by ice accumulating at low elevations directly from the atmosphere onto valley floors and walls with only minor contributions from tributary glaciers flowing down from higher elevations similar fossil glacial landsystems dating back from the early martian history are to be expected in many other low latitude troughs such as chasmata chaos valleys impact craters and other basins

displacement fields and finite strains in a sandbox model simulating a fold thrust belt this thesis uses geodetic satellite data to measure present day crustal deformation in the zagros fold thrust belt sw iran geodetic type measurements are also used in down scaled models that simulate the surface deformations seen in convergent settings like the zagros fold thrust belt global positioning system gps measurements of three surveys between 1998 and 2001 indicate 9 3 mm yr and 5 3 mm yr shortening across the se and nw zagros respectively gps results show that in addition to the different rates and directions of shortening on either side of the ns trending kazerun fault local along belt extension occurs to the east differential sar interferograms of ers1 2 images between 1992 and 1999 detect 8 4 mm yr uplift rate across a newly recognized fault in sw qeshm island this can be attributed to a steep imbricate thrust that may still represent the local zagros deformation front the salt diapirs in the zagros rise from a source layer that acts as a low frictional decollement that decouples the deformation of the cover sediments from their basement in the eastern zagros whereas the cover to the west deforms above a high friction decollement physical models were prepared to simulate cover deformation in the zagros by shortening a sand pack above adjacent high and low frictional decollements represented by a ductile layer the strain distributions differed above the two types of decollements it was more heterogeneous above the salt where local extension in the shortening direction was dominant a separate work also investigated systematically the role of basal friction on cover deformation in convergent settings accurate height measurements of the model surface by laser scanner indicated a deformation front more distal than usual particularly in the low basal frictional models the volume reduction in our shortened sand models correlated directly with their basal friction

dynamics and mass balance of taylor glacier antarctica 3 state of mass balance 1 taylor glacier flows from the east antarctic ice sheet and terminates in the mcmurdo dry valleys where it has left a geomorphologic record of past incursions here we use new data on the flow thickness and surface balance of taylor glacier to calculate ice fluxes and assess the current state of mass balance overall the glacier is close to a state of zero net balance and has largely adjusted to reduced snowfall on the taylor dome source region in the mid holocene one region of the upper ablation zone appears to be losing mass evidence from ice surface morphology and stable isotope profiles suggests that this mass loss is a long term phenomenon hence probably a lingering response to the earlier drying of taylor dome our data give a general indication of the size of ablation or accumulation changes needed for ice to advance far into taylor valley as occurred 70 to 130 ka ago

dynamics of orogenic wedges and the uplift of high pressure metamorphic rocks subduction accretion complexes can be approximated as wedge shaped continua with a rigid buttress behind and a subducting litho spheric slab beneath thick wedges undergoing prograde metamorphism have a negligible long term yield strength and are likely to exhibit a complex nonlinear viscous rheology such a wedge will tend to deform internally until it reaches a stable configuration in which the gravitational forces generated by the wedge geometry balance the traction exerted on its underside by the subducting slab accretion of material at the wedge front will lengthen the wedge and cause it to shorten internally to regain the stable geometry this shortening will be expressed as late out of sequence thrusting backthrusting and folding conversely underplating of sediment or crustal slices will thicken the wedge which may need to extend internally to regain stability extension will cause listric normal faults that may merge downward into zones of ductile extension continued underplating at depth and compensating extension above provides a mechanism for bringing high p low t metamorphic rocks to upper levels in the rear of the wedge where they are commonly observed many major tectonic boundaries in convergent orogens such as the coast range thrust in the franciscan complex major nappe contacts in the alps and the contact between the nevado filabride and higher betic nappe complexes in the betic cordillera show abrupt increases in metamorphic grade downward across them this is consistent with their origin or reactivation as uplift related extensional structures

the strength and dilatancy of sand the effects of stress path and loading direction in the triaxial test on strength and dilatancy of sand are investigated it is shown that the unique relationship observed between peak friction ang

investigating new materials in the context of analog physical models abstract to broaden the availability of granular materials that are suitable for the analog modeling of upper crustal deformation we investigated the mechanical behaviors of pure quartz sand and two sand mixtures quartz sand powdered barite and quartz sand mica crystals using ring shear tests and simple convergent sandbox experiments the ring shear test results indicate that the three materials have similar peak friction angles between 39 25 and 36 02 but the magnitude of the shear strain and the shear strength required to cause their failure are different the differences between the analog models are identified by distinct fault kinematics and different grain flows which are primarily related to differences in the plastic elasto frictional rheology we conclude that the use of the quartz mica mixture which showed the strongest distributed plastic deformation can improve analog models where different materials are required to simulate crystalline basement sand and supracrustal rocks sand mica mixture this is a common situation in extension and inversion tectonics such as for example in inversion tectonics when a granitic basement block acts as a buttress

late wisconsin and early holocene glacial history inner ross embayment antarctica abstract lateral drift sheets of outlet glaciers that pass through the transantarctic mountains constrain past changes of the huge ross ice drainage system of the antarctic ice sheet drift stratigraphy suggests correlation of reedy iii reedy glacier beardmore beardmore glacier britannia hatherton darwin glaciers ross sea mcmurdo sound and younger terra nova bay drifts radiocarbon dates place the outer limits of ross sea drift in late wisconsin time at 24 000 13 000 yr b p outlet glacier profiles from these drifts constrain late wisconsin ice sheet surface elevations within these constraints we give two extreme late wisconsin reconstructions of the ross ice drainage system both show little elevation change of the polar plateau coincident with extensive ice shelf grounding along the inner ross embayment however in the central ross embayment one reconstruction shows floating shelf ice whereas the other shows a grounded ice sheet massive late wisconsin holocene recession of grounded ice from the western ross embayment which was underway at 13 040 yr b p and completed by 6600 6020 yr b p was accompanied by little change in plateau ice levels inland of the transantarctic mountains sea level and basal melting probably controlled the extent of grounded ice in the ross embayment the interplay between the precipitation low late wisconsin and high holocene values and the influence of grounding on outlet glaciers late wisconsin thickening and late wisconsin holocene thinning with effects dying out inland probably controlled minor elevation changes of the polar plateau

seismic multiplet response triggered by melt at blood falls taylor glacier antarctica 1 meltwater input often triggers a seismic response from glaciers and ice sheets it is difficult however to measure melt production on glaciers directly while subglacial water storage is not directly observable therefore we document temporal changes in seismicity from a dry based polar glacier taylor glacier antarctica during a melt season using a synthesis of seismic observation and melt modeling we record icequakes using a dense six receiver network of three component geophones and compare this with melt input generated from a calibrated surface energy balance model in the absence of modeled surface melt we find that seismicity is well described by a diurnal signal composed of microseismic events in lake and glacial ice during melt events the diurnal signal is suppressed and seismicity is instead characterized by large glacial icequakes we perform network based correlation and clustering analyses of seismic record sections and determine that 18 of melt season icequakes are repetitive multiplets the epicentral locations for these multiplets suggest that they are triggered by meltwater produced near a brine seep known as blood falls our observations of the correspondingp wave first motions are consistent with volumetric source mechanisms we suggest that surface melt enables a persistent pathway through this cold ice to an englacial fracture system that is responsible for brine release episodes from the blood falls seep the scalar moments for these events suggest that the volumetric increase at the source region can be explained by melt input

the link between climate warming and break up of ice shelves in the antarctic peninsula a review of in situ and remote sensing data covering the ice shelves of the antarctic peninsula provides a series of characteristics closely associated with rapid shelf retreat deeply embayed ice fronts calving of myriad small elongate bergs in punctuated events increasing flow speed and the presence of melt ponds on the ice shelf surface in the vicinity of the break ups as climate has warmed in the antarctic peninsula region melt season duration and the extent of ponding have increased most break up events have occurred during longer melt seasons suggesting that meltwater itself not just warming is responsible regions that show melting without pond formation are relatively unchanged melt ponds thus appear to be a robust harbinger of ice shelf retreat we use these observations to guide a model of ice shelf flow and the effects of meltwater crevasses present in a region of surface ponding will likely fill to the brim with water we hypothesize building on weertman 1973 hughes 1983 and van der veen 1998 that crevasse propagation by meltwater is the main mechanism by which ice shelves weaken and retreat a thermodynamic finite element model is used to evaluate ice flow and the strain field and simple extensions of this model are used to investigate crack propagation by meltwater the model results support the hypothesis