strength and anisotropy of foliated rocks with varied mica contents abstract we have shortened 15 schists and gneisses with varying compositions 15 75 mica by volume at angles of 45 and 90 to foliation s to investigate the influence of micas on the strength and anisotropy of foliated rocks at the conditions tested t 25 c p c 200 mpa and e 10 5 s 1 compressive strengths vary by a factor 4 in the 45 and 90 orientations and individual rock types exhibit directional responses ranging from isotropic to strongly anisotropic trends of decreasing strength decreasing anisotropy and increasing ductility are observed with increasing mica content strains in all samples were localized within inclined shear zones accommodated by dislocation slip and grain scale microkinking in micas and microcracking in all other silicates stress strain response and grain scale deformation microstructures both indicate that mechanical behavior is strongly influenced by the concentration and spatial arrangement of micas shear zone formation is associated either with discrete brittle fracture transitional strain softening or steady strength ductile shear in both brittle and transitional samples extensive microcracking of strong quartzo feldspathic bridges occurs and stress drop magnitudes decrease with decreasing spacing and increasing overlap of adjacent critically oriented micas steady strength ductile shear zones develop in samples containing domains of interconnected micas and isotropic mechanical response is observed in those in which micas are contiguous in nearly all directions

the strength profile for bimineralic shear zones an insight from high temperature shearing experiments on calcite halite mixtures abstract shearing experiments on mixed halite calcite layers 0 7 mm thick have been performed to understand the behavior of bimineralic fault zones using a high temperature biaxial testing machine at a slip rate of 0 3 m s and shear strains to about 30 temperature was increased to 700 c in linear proportion to the normal stress with the experimental geotherm of about 22 c mpa simulating the natural geothermal gradient the experimental data clearly demonstrate that the effect of mineral composition on the ultimate frictional strength is distinctly different from that on the residual frictional strength tharp s framework model 1983 quantitatively accounts for the ultimate frictional strength whereas the residual frictional strength at large shear strains can be predicted by jordan s two block model 1988 thus the frictional behavior of a bimineralic shear zone changes from the framework model to the two block model with increasing displacement inclusion of halite the weaker member in quantities as small as 5 by volume reduces the friction almost to the level of pure halite and suppresses stick slip at large shear strains because halite grains are extremely sheared at the zone of strain concentration the strength profile and the slip mode including the lower limit of seismic behavior of bimineralic shear zones at large shear strains are controlled primarily by the weaker member the present results disprove strehlau s fault model 1986 the role of individual constituent mineral is not clarified in scholz s fault model 1988 and his model disagrees with existing experimental data

semi brittle deformation of anhydrite halite shear zones simulating mylonite formation abstract a series of new shear experiments on similar volume mixes of anhydrite and halite have been run at 100 and 400 c at the same constant loading rate and constant confining pressure of 200 mpa increasing temperature is found to decrease the viscosity contrast between anhydrite and halite the hard and soft phases respectively the mechanical response is similar at all temperatures regardless of volume proportions of mix an initial high stress steady state portion of the stress strain curve is followed by a stress drop and then by a second steady state stress interval at a much lower value that is nearly equal to the strength of the softer phase halite individual mineral behaviours and deformation mechanisms appear to correlate with specific portions of the stress strain curve as the fabric s evolve with increasing strain mechanism s of strain accomodation at all temperatures is semi brittle deformation mechanisms change gradually with conditions with shear dominated by stable sliding along r 1 and r 2 shear fracures especially in mixes of high anhydrite content at 100 c while homogeneous ductile flow along s and c surfaces is observed at 400 c in all variations of composition these features are very similar to those observed in natural shear zones

developments in monitoring and modelling small scale river bed topography recent research in fluvial geomorphology has emphasized the spatially distributed feedbacks amongst river channel topography flow hydraulics and sediment transport although understanding of the behaviour of dynamic river channels has been increased markedly through detailed within channel process studies less attention has been given to the accurate monitoring and terrain modelling of river channel form using three dimensional measurements however such information is useful in two distinct senses firstly it is one of the necessary boundary conditions for a physically based deterministic modelling approach in which three dimensional topography and river discharge drive within channel flow hydraulics and ultimately spatial patterns of erosion and deposition and therefore channel change secondly research has shown that an alternative means of estimating the medium term bedload transport rate can be based upon monitoring spatial patterns of erosion and deposition within the river channel this paper presents a detailed assessment of the distributed monitoring and terrain modelling of river bed topography using a technique that combines rigorous analytical photogrammetry with rapid ground survey the availability of increasingly sophisticated terrain modelling packages developed for civil engineering application allows the representation of topographic information as a landform surface intercomparison of landform surfaces allows visualization and quantification of spatial patterns of erosion and deposition a detailed assessment is undertaken of the quality of the morphological information acquired this allow some general comments to be made concerning the use of more traditional methods to monitor and represent small scale river channel morphology

flow laws for rocks containing two non linear viscous phases a phenomenological approach abstract mylonitic rocks and rock analogue materials reveal two basic types of structure 1 a load bearing framework lbf of strong phase contains isolated pockets of weak phase 2 interconnected layers of weak phase iwl separate boudins and clasts of strong phase aggregates with the lbf microstructure are characterized by nearly uniform strain rate stress is concentrated in the load bearing framework in aggregates with an iwl microstructure strain rate and sometimes also stress are higher in the interconnected weak phase than in the boudins and clasts of strong phase the degree of stress and strain partitioning depends strongly on the viscous strength contrast and on the relative amounts of the constituent mineral phases based on these observations the rheology of two phase rock is modelled with separate functions for lbf and iwl microstructures a new flow law is derived for rock with iwl structure in which two phases undergo dislocation creep the flow law expresses composite creep strength in terms of temperature bulk strain rate and the volume proportions and creep parameters of the minerals in the rock strain rate and stress are averaged in the constituent phases and slip along phase boundaries maintains strain compatibility within the aggregate composite strengths predicted with the iwl flow law fall well within the uniform stress and uniform strain rate bounds and are generally consistent with the viscous strengths of experimentally deformed bimineralic aggregates a hypothesis of viscous strain energy minimization is used to determine the relative stability of the lbf and iwl microstructures during steady state creep the iwl microstructure is predicted to be stable over a broad range of two phase compositions and mineral strength contrasts whereas the lbf microstructure is stable only in rocks with low volume proportions of weak phase and low to moderate mineral strength contrasts the iwl flow law indicates that rheological stratification in the lithosphere depends strongly on rock composition especially in rocks with low volume proportions of a weak phase and high mineral strength contrasts

assessment of erosion and deposition in steep mountain basins by differencing sequential digital terrain models abstract digital elevation models dems built from repeated topographic surveys permit producing dem of difference dod that enables assessment of elevation variations and estimation of volumetric changes through time in the framework of sediment transport studies dem differencing enables quantitative and spatially distributed representation of erosion and deposition within the analyzed time window at both the channel reach and the catchment scale in this study two high resolution digital terrain models dtms derived from airborne lidar data 2 m resolution acquired in 2005 and 2011 were used to characterize the topographic variations caused by sediment erosion transport and deposition in two adjacent mountain basins gadria and strimm vinschgau venosta valley eastern alps italy these catchments were chosen for their contrasting morphology and because they feature different types and intensity of sediment transfer processes a method based on fuzzy logic which takes into account spatially variable dtms uncertainty was used to derive the dod of the study area volumes of erosion and deposition calculated from the dod were then compared with post event field surveys to test the consistency of two independent estimates results show an overall agreement between the estimates with differences due to the intrinsic approximations of the two approaches the consistency of dod with post event estimates encourages the integration of these two methods whose combined application may permit to overcome the intrinsic limitations of the two estimations the comparison between 2005 and 2011 dtms allowed to investigate the relationships between topographic changes and geomorphometric parameters expressing the role of topography on sediment erosion and deposition i e slope and contributing area and describing the morphology influenced by debris flows and fluvial processes i e curvature erosion and deposition relations in the slope area space display substantial differences between the gadria and the strimm basins while in the former erosion and deposition clusters are reasonably well discriminated in the latter characterized by a complex stepped structure we observe substantial overlapping erosion mostly occurred in areas that show persistency of concavity or transformation from convex and flat to concave surfaces whereas deposition prevailingly took place on convex morphologies less expected correspondences between curvature and topographic changes can be explained by the variable sediment transport processes which are often characterized by alternation of erosion and deposition between different events and even during the same event

mechanisms for cessation of magmatic resurfacing on venus 1 proposed mechanisms of resurfacing on venus about 0 3 1 gyr ago usually involve either some form of tectonic resurfacing in which venusian lithosphere is recycled mechanically or magmatic resurfacing where essentially immobile lithosphere is covered by lava the focus of this study is mechanisms of magmatic resurfacing in the stagnant lid regime of mantle convection parameterized convection models suggest that cessation of magmatic resurfacing can occur in several ways 1 the mantle temperature drops sufficiently such that mantle rising adiabatically does not cross the solidus 2 the molten layer migrates below the solid melt density inversion at 250 500 km so that no melt can escape 3 sublithospheric small scale convection stops and conductive thickening of the lid suppresses melting in each case inability of magma to penetrate thickened venusian lithosphere may play a role the timing of melt cessation and duration of late stage resurfacing depend on various factors such as mantle rheology degree of mantle depletion and depth of resurfacing the models indicate that the waning stages of resurfacing which result in surface age variations can last 0 1 1 gyr a general trend of recent lithospheric thickening is also predicted some cases exhibit a rapid transition from relatively thin to thick lid as suggested by previous authors

microstructure development in an experimentally sheared orthopyroxene granulite abstract rheologies of the lower continental crust and overall contrast with the underlying upper mantle likely control the evolution of first order structures stress and strain partitioning between natural shear zones and wall rock s foliation development flow mechanism s and constitutive relations of rocks that make up the lower crust are poorly known we have undertaken an experimental study in which an orthopyroxene granulite is deformed in simple shear the starting material is a three phase plagioclase orthopyroxene amphibole equigranular granulite previously used in coaxial experiments wafers cut at 45 to the long axis of cores were placed between zircoa forcing blocks that have been cut obliquely at 45 at one end all experiments were run at 1 2 gpa pc and temperatures of 650 950 c specimens have been strained up to a maximum of 2 6 at shear strain rates of 7 10 5 to 7 10 7 s 1 most shear stress shear strain curves have a similar form they are characterised by an initial linear response that is followed by a work hardening region that leads to a level of quasi steady state the quasi steady state behaviour is followed by a gradual decrease in flow stress to a second quasi steady state stress level that very gradually decreases with increasing strain optical and tem examination of deformed samples indicates that an amphibole foliation develops during the first quasi steady state stress level by fragmentation and alignment of amphibole plagioclase and orthopyroxene undergo minimal crystal plastic strain at the onset of the second quasi steady state stress level plagioclase develops neoblasts orthopyroxene develops clinopyroxene lamellae and the amphibole foliation is better developed with increasing strain compositional lamination develops as in natural mylonites with extensive neoblast development in plagioclase and orthopyroxene and cataclastic grain refinement in amphibole strength data measured at the onset of the second quasi steady state level fit a power law with q 203 kj mole and n 2 3 these q and n values are significantly lower than those determined under similar conditions in previous coaxial experiments with increasing shear strain as under natural conditions there is a significant grain size reduction that may lead to a switch in flow mechanism from grain size insensitive flow at low strain to grain size sensitive flow at higher natural strains

erosional power in the swiss alps characterization of slope failure in the illgraben landslides and rockfalls are key geomorphic processes in mountain basins their quantification and characterization are critical for understanding the processes of slope failure and their contributions to erosion and landscape evolution we used digital photogrammetry to produce a multi temporal record of erosion 1963 2005 of a rock slope at the head of the illgraben a very active catchment prone to debris flows in switzerland slope failures affect 70 of the study slope and erode the slope at an average rate of 0 39 0 03 m yr the analysis of individual slope failures yielded an inventory of 2500 failures ranging over 6 orders of magnitude in volume despite the small slope area and short study period the slope failures form a characteristic magnitude frequency distribution with a rollover and a power law tail between 200 m and 1 6 106 m with an exponent of 1 65 slope failure volume scales with area as a power law with an exponent of 1 1 both values are low for studies of bedrock landslides and rockfall and result from the highly fractured and weathered state of the quartzitic bedrock our data suggest that the magnitude frequency distribution is the result of two separate slope failure processes type 1 failures are frequent small slides and slumps within the weathered layer of highly fractured rock and loose sediment and make up the rollover type 2 failures are less frequent and larger rockslides and rockfalls within the internal bedded and fractured slope along pre determined potential failure surfaces and make up the power law tail rockslides and rockfalls of high magnitude and relatively low frequency make up 99 of the total failure volume and are thus responsible for the high erosion rate they are also significant in the context of landscape evolution as they occur on slopes above 45 and limit the relief of the slope copyright 2012 john wiley sons ltd

wrinkle ridges stress domains and kinematics of venusian plains wrinkle ridges are nearly ubiquitous landforms on the plains of venus by analogy with similar structures on other planets venusian wrinkle ridges are inferred to trend normal to the direction of maximum principal compression in the crust an inference that is verified by geometrical relationships with positive and negative relief features on venus because plains are the dominant terrain on venus wrinkle ridges provide an excellent opportunity to determine the orientations of shallow crustal principal stress trajectories over most of the planet in most places there are two or more sets of wrinkle ridges and commonly one of these persists over a very large area defining a regional stress domain intersection relationships indicate that these domains differ in age

tectonic and stratigraphic implications of the relative ages of venusian plains and wrinkle ridges abstract a major ongoing controversy concerns the style of crustal evolution on venus at one extreme is a directional model that proposes a sequence of depositional and deformational events that occur at specific times in the evolution of the crust and that are global in extent at the other extreme is a model that argues for different ages of these events in different places on the planet a test of the directional model is here focused on whether wrinkle ridges formed at a single time in the recorded crustal history of venus where sets of wrinkle ridges intersect it commonly is possible to determine that one set is older than the other also the deformation responsible for wrinkle ridges is in places clearly progressive with respect to stratigraphic material units these observations are not consistent with a specific single time for the formation of wrinkle ridges within the stratigraphic sequence within an area including about 1 3 of the surface of venus 15 of craters that are younger than regional plains are older than wrinkle ridges 85 are younger than wrinkle ridges taking 750 myr as a reasonable mean age for the regional plains this implies that the mean age of wrinkle ridges is 110 myr younger than the mean age of plains solomon et al 1999 science 286 87 propose that the emplacement of a large volume of plains lava would lead to a major atmospheric temperature increase their model predicts thermal stresses in the lithosphere that at shallow depth would reach peak compressive stresses in about 100 myr a number very similar to the time lag between plains emplacement and wrinkle ridge formation indicated by the crater data the thermal compressive stresses responsible for wrinkle ridges would be maintained at a level sufficient to deform basalt for at least 100 myr and possibly for as long as 350 myr these time intervals are not really short compared to the mean age of the plains finally because wrinkle ridges are demonstrably younger than the plains they deform they cannot be related to the processes that formed the plains and thus should not be used to define a plains with wrinkle ridges unit

feldspar influenced rock rheologies progressive fracture subsequent cataclasis and syntectonic alteration of feldspar to phyllosilicates transformed a massive granite into a quartz mica phyllonite during early tertiary deformation in a 20 30 m wide shear zone in southeastern arizona the ductile deformation proceeded at temperatures and pressures approximating middle to upper crustal levels most of the deformation was taken up by the feldspar and its alteration products quartz deformed by both brittle fracture and crystal plastic mechanisms these results show that under certain temperature pressure strain rate conditions feldspars are weaker than quartz the observed deformation mechanisms indicate that the brittle to ductile transition in fault zones is not simply a function of the onset of temperature activated plastic deformation in quartz nor of the frictional behavior of rocks as inferred in the familiar strength vs depth curves it is more likely that the transition is complex and depends on a variety of parameters one such factor delineated in this study is the fracture and fracture facilitated syntectonic alteration of feldspar under hydrated conditions

monitoring of high alpine mass movements combining laser scanning with digital airborne photogrammetry abstract airborne and terrestrial laser scanning are used in combination with digital airborne photogrammetry to monitor surface changes between 2009 and 2011 on rock glaciers and landslides at three mountain permafrost sites grabengufer schafberg and fluela pass in the swiss alps 3d surface changes detected through comparison of multitemporal laser scanning data as well as horizontal creep rates determined using laser scanning data and digital airborne photogrammetry are analyzed the methods applied allow comprehensive quantification of mass movements and volumetric changes which are presented in 2 5d gps ground truths are used as reference data at the grabengufer site on the basis of this a quality estimation is developed for the sites without gps reference data for changes with an extent of about 25 m 2 a level of significance of 3 cm was obtained for both horizontal and vertical displacements under optimal measurement conditions the complex dynamics of creeping and sliding permafrost features are investigated through analysis of their surface kinematics

correlating mechanical data with microstructural observations in deformation experiments on synthetic two phase aggregates abstract a simple method of analysing the results of deformation experiments on synthetic two phase aggregates is presented and applied to some tests on calcite halite aggregates the approach involves replacing the observed mechanical behaviour of real two phase materials of coarse microstructure with a phase volume fraction weighted mechanically equivalent representation in which each phase is assigned its own single valued stress and its own single valued strain such a representation can be solved for the stresses and strains in the two phases and the results compared with the stresses and strains as determined from the deformation microstructures in principle it is then possible to constrain which of the features of the microstructure are mechanically significant the stresses supported by the synthetic calcite halite aggregates suggest a strong partitioning of the deformation into the halite at all volume fractions of calcite and yet analysis of the halite strains from the deformation microstructures indicates that there is little or no strain partitioning between the phases however these conflicting results may be reconciled by using the calcite contiguous volume rather than the actual calcite volume fraction to characterize the strength of the aggregates with respect to those of their component phases

the effects of lateral variations in rock composition and texture on anhydrite caprock integrity of co2 storage systems abstract we investigated the effect of rock texture and composition on the mechanical strength and volumetric behaviour of anhydrite rich caprock conventional triaxial experiments were performed at 80 c confining pressures of 1 5 35 mpa and strain rates of 10 5 s 1 both dry and in the presence of fluids we determined the failure envelope and the effect of fluids upon it for anhydrite displaying an equigranular texture consisting of euhedral grains we observed a general pattern of increasing peak compressive strength with increasing confining pressure consistent with a previous study on anhydrite from the same formation which showed an irregular texture consisting of interlocking acicular grains embedded in a fine grained matrix the peak strength of euhedral anhydrite was found to be 15 65 lower than that of acicular anhydrite no chemical effects were observed for the fluids tested hydraulic fracturing experiments showed the tensile strength to be approximately 4 mpa for euhedral and 6 mpa for acicular anhydrite we combined the failure envelopes with simple analytical calculations on the effect of cooling on in situ stress showing that tensile caprock failure due to cooling would be unlikely for both types of anhydrite assuming a hypothetical reservoir at a depth of 3800 m however it should be noted that tensile failure may pose an issue for shallower reservoirs or weaker caprock formations

a stratigraphic study of small volcano clusters on venus recently proposed global stratigraphy and geologic history models have led to two end member volcanic evolution models for venus a directional model that proposes venus has progressed through a series of stages each characterized by a particular style of volcanic activity a t basilevsky and j w head 1997 j geophys res 103 8531 8544 and a nondirectional model that proposes a more earth like type of volcanic activity with different eruption styles occurring globally on a local scale throughout the recent history of the planet j e guest and e r stofan 1999 icarus139 55 66 the former infers that most small volcanoes d 20 km define a global unit referred to as the shield plains that predates emplacement of the widespread plains with wrinkle ridges or regional plains to test this hypothesis cross cutting and superposition relations were used to determine the stratigraphic positions of small volcano clusters in seven quadrangles 11 of the surface the seven quadrangles included 179 clusters containing over 22 000 constructs three materials were defined for each cluster 1 the constructs 2 the material immediately surrounding the constructs called the cluster material and 3 the regional plains where possible relative ages were established between the constructs cluster material and the regional plains there are six possible temporal relations between the constructs and regional plains emplacement 1 the constructs postdate regional plains emplacement 2 some constructs postdate regional plains emplacement and other constructs predate regional plains deformation but their ages relative to regional plains emplacement are ambiguous 3 the constructs predate regional plains emplacement 4 some constructs predate regional plains emplacement and other constructs predate regional plains deformation but their ages relative to regional plains emplacement are ambiguous 5 the constructs both predate and postdate regional plains emplacement and 6 the ages of the constructs relative to regional plains emplacement are ambiguous an age relative to regional plains emplacement could not be determined for almost half of the clusters studied of the clusters for which a relative age could be determined almost half postdate regional plains emplacement and an additional third contain at least some constructs that postdate regional plains emplacement less than a tenth of the clusters predate regional plains emplacement these observations indicate that many small constructs postdate the emplacement of the regional plains and therefore are consistent with the nondirectional volcanic evolution model in which small constructs represent a global process occurring locally throughout the recent history of venus

water controls the seasonal rhythm of rock glacier flow abstract rock glaciers are creeping periglacial landforms experiencing strong acceleration during recent atmospheric warming and raising concerns with regard to their future behaviour and stability high resolution kinematic observations show strong seasonal and multi annual variations in rock glacier creep but the linking mechanisms to environmental forcing remain poorly understood and lack quantitative models here we investigate the interaction between rock glacier creep and climatic forcing temperature and precipitation by developing a novel conceptual and numerical modelling approach the model is constrained and the results are compared with data from the dirru rock glacier vallis ch we are able to reproduce the observed velocity variations both in magnitude and phase on seasonal and inter annual time scales we find that water from liquid precipitation and snow melt rather than air temperature is the main driver of variations in rock glacier creep our results imply that the influence of water on rock glacier creep is fundamental and must be considered when investigating the historic and future evolution of rock glaciers

contemporary geomorphological activity throughout the proglacial area of an alpine catchment abstract quantification of contemporary geomorphological activity is a fundamental prerequisite for predicting the effects of future earth surface process and landscape development changes however there is a lack of high resolution spatial and temporal data on geomorphological activity within alpine catchments which are especially sensitive to climate change human impacts and which are amongst the most dynamic landscapes on earth this study used data from repeated laser scanning to identify and quantify the distribution of contemporary sediment sources and the intensity of geomorphological activity within the lower part of a glaciated alpine catchment odenwinkelkees central austria spatially geomorphological activity was discriminated by substrate class activity decreased in both areal extent and intensity with distance from the glacier becoming progressively more restricted to the fluvially dominated valley floor temporally geomorphological activity was identified on annual seasonal weekly and daily timescales activity became more extensive with increasing study duration but more intense over shorter timescales thereby demonstrating the importance of temporary storage of sediment within the catchment the mean volume of material moved within the proglacial zone was 4400 m 3 yr 1 which suggests a net surface lowering of 34 mm yr 1 in this part of the catchment we extrapolate a minimum of 4 8 mm yr 1 net surface lowering across the whole catchment these surface lowering values are approximately twice those calculated elsewhere from contemporary measurements of suspended sediment flux and of rates calculated from the geological record perhaps because we measure total geomorphological activity within the catchment rather than overall efflux of material repeated geomorphological surveying therefore appears to mitigate the problems of hydrological studies underestimating sediment fluxes on decadal annual time scales further development of the approach outlined in this study will enable the quantification of geomorphological activity alpine terrain stability and persistence of landforms

ambient effects on basalt and rhyolite lavas under venusian subaerial and subaqueous conditions both subaerial and subaqueous environments have been used as analog settings for venus volcanism to assess the merits of this the effects of ambient conditions on the physical properties of lava on venus the seafloor and land on earth are evaluated rhyolites on venus and on the surface of earth solidify before basalts do because of their lower eruption temperatures rhyolite crust is thinner than basalt crust at times less than about an hour especially on venus at later times rhyolite crust is thicker because of its lower latent heat relative to basalt the high pressure on the seafloor and venus inhibits the exsolution of volatiles in lavas vesicularity and bulk density are proportional so that lavas of the same composition should be more dense on the seafloor and less dense on land because viscosity depends partly upon the fraction of unvesiculated water in a melt basalts with the same initial volatile abundance will be least viscous on the seafloor and most viscous on land assuming the same preemptive h2o contents molten rhyolites on venus will have viscosities 10 that of rhyolites on land despite lower expected viscosities underwater flows are more buoyant and should have heights like subaerial and venusian lavas of the same composition and extrusive history in cases where the influence of crust is insignificant a volume of rhyolite will have a higher aspect ratio than the same volume of basalt no matter what the environment if flow rheology is dominated by the presence of strong crust aspect ratios differ little among environments or between compositions these analyses support a rhyolitic interpretation for the composition of venusian festooned flows and a basaltic interpretation for the composition of venusian steep sided domes although ambient effects are significant extrusion rate and eruption history must also be considered to explain analogous volcanic landforms on earth and venus

plains tectonism on venus the deformation belts of lavinia planitia high resolution radar images from the magellan spacecraft have revealed the first details of the morphology of the lavinia planitia region of venus a number of geologic units can be distinguished including volcanic plains units with a range of ages transecting these plains over much of the lavinia region are two types of generally orthogonal features that we interpret to be compressional wrinkle ridges and extensional grooves the dominant tectonic features of lavinia are broad elevated belts of intense deformation that transect the plains with complex geometry they are many tens to a few hundred kilometers wide as much as 1000 km long and elevated hundreds of meters above the surrounding plains two classes of deformation belts are seen in the lavinia region ridge belts are composed of parallel ridges each a few hundred meters in elevation that we interpret to be folds typical fold spacings are 5 10 km fracture belts are dominated instead by intense faulting with faults in some instances paired to form narrow grabens there is also some evidence for modest amounts of horizontal shear distributed across both ridge and fracture belts crosscutting relationships among the belts show there to be a range in belt ages in western lavinia in particular many ridge and fracture belts appear to bear a relationship to the much smaller wrinkle ridges and grooves on the surrounding plains ridge morphology tends to dominate belts that lie more nearly parallel to local plains wrinkle ridges and fracture morphology tends to dominate belts that lie more nearly parallel to local plains grooves we use simple models to explore the formation of ridge and fracture belts we show that convective motions in the mantle can couple to the crust to cause horizontal stresses of a magnitude sufficient to induce the formation of deformation belts like those observed in lavinia we also use the small scale wavelengths of deformation observed within individual ridge belts to place an approximate lower limit on the venusian thermal gradient in the lavinia region at the time of deformation

the sediment delivery problem abstract the linking of on site rates of erosion and soil loss within a drainage basin to the sediment yield at the basin outlet and improved knowledge and representation of the associated processes of sediment delivery represent a major research need within the field of erosion and sedimentation and also an important scale problem in drainage basin studies this paper reviews the limitations of the sediment delivery ratio concept by considering the problems of temporal and spatial lumping and its blackbox nature some recent advances in our understanding of the sediment delivery system and its modelling are described and the lack of detailed empirical investigations is highlighted the significance of recent concern for the role of sediments in the transport of nutrients and contaminants to sediment delivery studies is introduced and the need for further work in this field is emphasised

the global distribution of wrinkle ridges on venus abstract new digital mapping of over 65 000 wrinkle ridges of the plains of venus shows a strong correlation between the location and orientation of these long low amplitude compressive anticlines and major features of the geoid and long wavelength topography regions with wrinkle ridges occupy 43 of the plains and are strongly skewed toward low elevations and negative geoid anomalies about 93 of the wrinkle ridge plains lie below mean planetary radius and 72 have negative geoid anomalies in contrast the extensional rift zones of venus are strongly skewed toward high elevations and positive geoid anomalies thus compressive deformation dominates the topographic and geoid lows whereas extensional rifting is generally restricted to the highs these observations are consistent with geoid based stress models that predict compression in geoid lows and extension in geoid highs the orientations of wrinkle ridges are generally consistent over regions extending for 1000 10 000 km many regions have multiple sets of wrinkle ridges of different orientations reflecting multiple episodes and directions of compression however about 80 of the regions display a single dominant wrinkle ridge orientation with secondary orientations subordinate the dominant wrinkle ridge orientations in many regions follow the contours of long wavelength topography and geoid or lie along the axes of troughs in the geoid thus the maximum horizontal compression recorded by the folds is commonly parallel to the present day gradient in geoid and topography although some regions are strong exceptions perhaps reflecting changes in topography and geoid with time the dominant wrinkle ridge trends ring several major geoid and topographic swells especially western aphrodite terra and lada terra with ring diameters of 75 120 8000 13 000 km in addition there are smaller rings of wrinkle ridges around the swells in themis eistla and bell regiones especially gula mons with ring diameters of 25 45 2500 5000 km in contrast there are no rings of compressive deformation surrounding some other geoid topographic highs including beta and atla regiones which have been proposed to be the youngest swells and display the largest peak geoid topography ratios and largest geoid gradients these observations are consistent with the idea that not all the major topographic geoid swells existed on venus at the time of wrinkle ridge formation

a new view of the stratigraphic history of venus abstract studies of venus using magellan data have so far generated two views about the way venus has evolved on the one hand venus has been suggested to have had a history in which there was a series of epochs each represented by a different volcanic or tectonic process on a global scale basilevsky and head 1995 j w head et al 1996 lunar planet sci 27th 525 526 p t basilevsky et al 1997 in venus ii univ of arizona press tucson this we define as a directional history on the other hand there is evidence to suggest that coronae rifts wrinkle ridges small and large edifices and large flow fields have each formed throughout the portion of venus history revealed by presently exposed rock units we propose that the plains have been built up by lavas erupted in a number of different styles each occurring throughout the history represented by the exposed stratigraphy of the planet dates derived from crater counts accumulated from the combined area of specific types of feature such as coronae e g m h price et al 1996 j geophys res 101 4657 4672 must be interpreted with care as the method is based upon the assumption that features of like morphology have the same age detailed studies from full resolution magellan data indicate that venus has had a complex history in which most geologic processes have operated in a nondirectional fashion to a greater or lesser extent throughout the planet s history

evidence for rapid regional plains emplacement on venus from the population of volcanically embayed impact craters we have reexamined the population of craters on venus believed to be embayed by lava flows and discuss the reliability of criteria for determining the volcanic embayment state of a crater presenting nonvolcanic processes which may produce similar crater morphologies we conclude that 29 craters have been embayed by lava flows from the exterior and an additional 27 craters are ambiguous cases 3 6 of the total crater population all of the embayed craters are embayed by the stratigraphically youngest lava flows except for five to 11 craters embayed by stratigraphically older regional plains deposits which are typically deformed by wrinkle ridges through geologic mapping of an area covering over 8 of the surface we examined the spatial relationships between wrinkle ridged plains and stratigraphically older plains units and estimate that a large portion of the wrinkle ridged plains are thinner than 500 m which is thin enough for the rims of the largest half of preexisting craters to be preserved there are not enough craters embayed by the wrinkle ridged plains to support a model in which the plains were erupted directly onto an ancient surface given the number of large craters embayed by thin deposits of wrinkle ridged plains we develop a simple statistical model to overestimate the number of craters on the preplains surface this model suggests that the average age of the surface beneath the plains plus the average length of time over which the plains were emplaced was of the order of tens of millions of years the short exposure age for the preplains surface indicates that some event or events must have erased the ancient population of craters from the surface before the emplacement of the wrinkle ridged plains

monitoring and modelling morphological change in a braided gravel bed river using high resolution gps based survey recent research in fluvial geomorphology has emphasized the direct monitoring of channel topography as a useful tool to better understand the interrelationship between river form and process and in particular to estimate bedload transport rates and reach scale sediment budgets until recently however this morphometric approach has been limited to comparison of repeatedly surveyed cross sections with the associated problems of low frequency sampling and an emphasis on cross stream as opposed to downstream morphological dynamics recent advances in analytical photogrammetry have however permitted the acquisition of data at sufficient resolutions to represent macroform 101 m and microform 10 m channel geometry in fully three dimensions while inherently spatially distributed the photogrammetric approach to land surveying is however restricted to observable areas of the channel and is thus of limited use in the subaqueous zone especially if flows are turbid or highly coloured this paper presents an alternative approach to the study of three dimensional morphological dynamics of a divided reach of the gravelly river feshie scotland in which topographic survey of both exposed and submerged areas of the reach was undertaken using the global positioning system gps survey results from two field programmes in 1998 and 1999 are presented in which a geotronics geotracer 2000 real time kinematic gps receiving unit was used to survey a 200 80 m reach rapid radial survey methods were employed permitting the collection of 2000 survey points per day giving a mean density over the 13 ha reach of 1 1 points per square metre a detailed assessment of survey errors and dem quality is presented and a limit of detection of c 10 cm proposed as an upper threshold for the identification of significant change between dems preliminary interpretation of channel dynamics in 1998 99 reveals relatively little change to the overall macroscale reach structure dem differencing techniques however highlight important local changes including the progradation of submerged bar fronts bar head aggradation and scour along major channel thalwegs and the erosion of fines from sloughs copyright 2000 john wiley sons ltd

textural and mechanical evolution with progressive strain in experimentally deformed aplite determining meaningful flow laws for the polyphase aggregates that characterize the crust is difficult because the strength of such aggregates depends on the strengths volume proportions and geometrical arrangement of their constituent phases and all of those factors may change with progressive strain in order to investigate some of these factors we have performed a series of axial compression experiments on a fine grained granite aplite over a range of shortening strains 20 85 and temperatures 700 900 c at 1 5 10 6 s 1 and 1400 mpa we have also done comparison experiments on pure quartz and feldspar aggregates the aplite is composed of 1 3 quartz and 2 3 oligoclase and microcline with minor biotite and magnetite the quartz grains are dispersed in a continuous matrix of feldspar optical and tem scale microstructures indicate that the deformation mechanisms of the quartz and feldspar grains in the aplites are similar to those of pure quartz and feldspar aggregates deformed at the same conditions the feldspars deform by semi brittle flow at 700 and 800 c and by recrystallization accommodated dislocation creep at 900 c while quartz deforms by recrystallization accommodated dislocation creep at 700 c and by climb accommodated dislocation creep at 800 and 900 c pure albite aggregates are stronger than quartz aggregates over this range of conditions however in the aplite an apparent strength reversal is inferred from grain strain measurements and changes in phase distribution with increasing temperature at 700 c the dispersed quartz grains in the aplite remain less deformed than the feldspar grains because the scarcity of quartz quartz grain boundaries limits recovery by grain boundary migration recrystallization causing the quartz strength to rise above that of feldspar however the aplite is weaker than a pure feldspar aggregate because cracking is enhanced by stress concentrations at the quartz grains at 800 c the two phases undergo approximately equal strain because easy dislocation climb in quartz allows individual grains to strain homogeneously the aplite strength is close to that of a pure feldspar aggregate at 900 c the initially continuous feldspar grains deform inhomogeneously and undergo microboudinage while the quartz grains deform homogeneously and gradually become more interconnected and undergo higher strain than the feldspars the aplite strength is initially closer to that of a feldspar aggregate but with increasing strain it becomes closer to that of a quartz aggregate the aplite undergoes strain softening over the whole range of conditions at 700 and 800 c the weakening is due to grain boundary migration recrystallization of feldspar in the fine grained crush products along grain scale faults at 900 c the weakening is due to a combination of grain boundary migration recrystallization of the feldspars plus increasing interconnection of the weaker quartz grains these results demonstrate that the textural evolution of a polyphase aggregate with increasing strain is determined by both the phase distribution and the deformation mechanism of each phase and that very high strains may be required to approach microstructural and mechanical steady state therefore measuring or calculating a flow law appropriate for granite at mid crustal conditions is not simple

the rheology of polymineralic rocks an approach deduced from empirical and theoretical work a model is proposed for the rheology of bi and polyphase rocks based on the rheology of the components their volume fractions and their geometrical distribution the model is formulated for the common case where some minerals deform by crystall plasticity at steady state and others stronger ones deform in the vincinity of the brittle ductile transition

sediment transfer rates of two active rockglaciers in the swiss alps abstract high mountain geosystems are characterized by an extensive transfer of mass and energy reflected in its geomorphological processes shaping the landscape within the periglacial belt rockglaciers represent important sediment storages and transport components in this study sediment transfer rates are quantified for two rockglaciers with different characteristics based on a multi method approach combining geomorphological mapping dtm analyses digital photogrammetry and geodetic survey for the first time different velocity values resulting from a kinematic monitoring over two decades are included due to the different characteristics of the landforms especially thickness and horizontal velocity a wide range of sediment transfer rates results from this study between 0 24 and 1 1 million t a with the maximum value for a rockglacier with a relatively small mass but high deformation rates

the geomorphic significance of rock glaciers estimates of rock glacier debris volumes and headwall recession rates in west greenland to obtain knowledge on rockwall retreat rates at sites with rock glaciers an inventory of about 400 individual rock glacier sites in west greenland was carried out by means of field studies and using aerial photographs and topographic maps a number of sites with ice cored moraines beyond normal glaciers were included in the analysis for comparative purposes the estimated debris volume was compared with the size of the source headwall the result of the inventory suggests that the presence of rock glaciers indicates extraordinary high retreat rates for rock free faces above especially headwalls above glacier derived rock glaciers are exposed to high weathering rates and thereby presumably delimit critical ranges regarding altitude for headwall retreat rates the relation of such a critical altitudinal range to other regional concepts such as glaciation level gl and glacier equilibrium line is discussed from this comments are also made on the relation between various permafrost zones and the typical regional climate within the maximum headwall weathering altitude at sites with active rock glaciers finally the potential importance of this range of maximum weathering for understanding the long term evolution of high relief cold climate landscapes is emphasised

embayed intermediate volcanoes on venus implications for the evolution of the volcanic plains abstract volcanoes on venus are classified according to size with studies on the stratigraphic position of large volcanoes proposing that most of the large volcanoes postdate the regional volcanic materials some studies regarding intermediate volcanoes proposed that some of these volcanic features could be large volcanoes with embayed flow aprons a situation that would alter the previous stratigraphic considerations about large volcanoes on venus in this work i analyze the global population of embayed intermediate size volcanoes and compare their summits with that of other edifices classified as large volcanoes intermediate size volcanoes are considered embayed when 1 flows from another source clearly overlap the volcano slopes and 2 display scarps related to flank failure processes but with the associated collapse deposits being absent i e interpreted as covered as result of the survey 88 embayed intermediate size volcanoes have been catalogued and integrated into a geographic information system these embayed volcanoes have summit sizes and characteristics similar to large volcanoes and therefore could be interpreted as possible large volcanoes with their flow aprons embayed embayment materials for these volcanoes include all the units present in the history of the volcanic plains and would indicate that this type of central volcanic edifice would occur throughout the geologic history recorded in the venusian plains

mapping and quantifying sediment transfer between the front of rapidly moving rock glaciers and torrential gullies abstract the sedimentary connection which may occur between the front of active rock glaciers and torrential channels is not well understood despite its potential impact on the torrential activity characterizing the concerned catchments in this study dems of difference dods covering various time intervals between 2013 and 2016 were obtained from lidar derived multitemporal dems for three rapidly moving rock glaciers located in the western swiss alps the dods were used to map and quantify sediment transfer activity between the front of these rock glaciers and the corresponding underlying torrential gullies sediment transfer rates ranging between 1500 m3 y and 7800 m3 y have been calculated depending on the sites sediment eroded from the fronts generally accumulated in the upper sectors of the torrential gullies where they were occasionally mobilized within small to medium sized debris flow events a clear relation between the motion rates of the rock glaciers and the sediment transfer rates calculated at their fronts could be highlighted along with the size of the frontal areas rock glacier creep rates influence thus directly sediment availability in the headwaters of the studied torrents the frequency magnitude of debris flow events varied between sites and was mainly related to the concordance of local factors such as topography water availability sediment availability or sediment type

origin of periodically spaced wrinkle ridges on the tharsis plateau of mars ridged plains are a major geologic unit on mars and are a predominant unit on the tharsis plateau a region that has undergone uplift extension and extensive shield and flood volcanism these units probably flood volcanic in origin are characterized by landforms classed as wrinkle ridges wrinkle ridges are interpreted to be folds resulting from buckling followed by reverse to thrust faulting flexure fracture a prominent characteristic of many of the wrinkle ridges on mars particularly those in the tharsis ridge system is the periodic nature of their spacing the periodic spacing has been evaluated in six major provinces on the tharsis plateau with regions further divided into domains based largely on variation in ridge orientation the average spacing of the tharsis ridges based on 2934 measurements is 30 km in an effort to account for the periodic nature of the wrinkle ridges the ridged plains material is modeled as both a single member and a multilayer with frictionless contacts that has buckled at a critical wavelength of folding free slip between layers is assumed based on the possible existence of mechanically weak interbeds in the ridged plains sequence separating groups of flows the near surface mechanical structure in the area of ridged plains is approximated by a strong layer or layers overlying a weak megaregolith of finite thickness overlying a strong basement buckling of the ridged plains is assumed to be decoupled from the basement by the weak megaregolith decoupling is enhanced if the megaregolith were water or ice rich at the time of deformation the rheologic behavior of the ridged plains and megaregolith is approximated by a linear elastic and linear viscous material the models are examined for a range in 1 the strength contrast between the ridged plains material and the underlying megaregolith 2 thickness of the ridged plains material 3 thickness of the megaregolith and 4 number of layers the elastic model can explain the observed ridge spacing only if the ridged plains are relatively thick 2400 m with multiple layers n 1 and relatively high contrasts in young s modulus e e0 100 the high e e0 required is possible only if the megaregolith was water rich at the time of deformation over the same range in values of the parameters viscous buckling is much less restricted the viscous model can explain the observed ridge spacing over a wide range in ridged plains thickness 250 m to several kilometers megaregolith thickness number of layers n 1 to 8 and contrasts in viscosity 0 10 in addition viscous buckling is viable if the megaregolith were dry water rich or ice rich at the time of deformation the absence of folds with a cross sectional geometry in the shape of a sinusoid anticline syncline pairs may be the result of initial deformation of the ridged plains material into low amplitude folds in infinitesimal strain followed by plastic yielding in the cores of the anticlines in finite strain initial elastic or viscous buckling coupled with plastic yielding confined to the hinge area followed by the development of reverse to thrust faulting could account for the asymmetric fold geometry of many of the wrinkle ridges

effects of a third phase on the mechanical and microstructural evolution of a granulite to help constrain the rheology of and strain partitioning in composite silicates from lower contintental crust lcc opx hbl plag granulite samples were shortened coaxially 15 40 in a solid pressure medium nacl apparatus at pc 1 0 gpa t 650 950 c and strain rates from 10 5 to 10 7 s 1 the resultant mechanical behaviour and microstructures are compared with those of pikwitonei amphibolite 58 hbl 42 plag deformed by wilks and carter 1990 under similar conditions the opx hbl plag rock is stronger than the hbl plag rock at all conditions all samples strain soften beyond 10 strain and stress levels do not reach steady state once softening begins at low t and high strain rates relative mineral strength is plag opx hbl whereas at higher t and lower strain rates relative mineral strength is opx plag hbl opx grains are extensively kinked by glide on 010 001 at all conditions plagioclase deforms by translation glide and mechanical twinning that becomes more abundant with higher t and amphibole deforms by slip on 100 001 microcracking in all phases partially accommodates strain under all conditions recovery mechanisms are limited even at the highest temperature and lowest strain rates tubules along grain boundaries and within grains suggest that a fluid phase possibly related to amphibole breakdown was present during experiments semibrittle shear zones sszs comprising s c fabrics defined by elongate grains of all phases develop in all samples sszs initiation coincides with the onset of mechanical softening sszs initiate along grain boundaries and widen with increasing strain which accounts for progressive softening with time similar s c fabrics have been duplicated in simple shear tests under indentical conditions which in turn are comparable to fabrics in naturally deformed lcc rocks increasing the number of co existing hard phases in natural composite silicates promotes strain localisation by enhancing ductility contrast s between constituent phases

surface formation rates and impact crater densities on venus impact crater density has been used to estimate relative ages of major venus geologic units typically based on the assumption of short globally synchronous formation periods the total number density of craters is the only parameter which may be quantified for most venus subregions in contrast to the size frequency analysis often used for other planetary studies this paper examines the statistical limits on such crater counts and the predicted crater density for various possible time varying surface formation rate functions these results show that 1 the true mean crater density is poorly constrained due to the limited sample size provided by aggregate geologic units and 2 any given crater density can be accommodated by a very short pulse of unit formation at some age t gaussian distributed formation functions of mean age t exponential functions with initiation ages between t and 2t or a host of other more complicated rate functions these results when coupled with the unknown rate of crater removal by tectonic or volcanic activity indicate that the crater counts for specific landforms on venus offer little constraint on the relative timing or duration of their development the hypothesis of globally synchronous formation of landforms such as volcanoes or coronae cannot be validated with the available crater data

impact craters on regional plains on venus age relations with wrinkle ridges and implications for the geological evolution of venus 1 a global assessment of impact craters on venus 30 km in diameter shows that 146 craters are completely or partially superposed on the regional plains that dominate the surface and typically are deformed by wrinkle ridges in this study we found that 10 of these craters are deformed by wrinkle ridges pre wr 93 craters are superposed on wrinkle ridges post wr and 43 craters were found to be ambiguous cases we compared our findings with the results of a similar study by mcgill 2004 done for craters of all sizes but for 1 3 of the surface of venus we found that the percentage of pre wr craters found by mcgill 2004 among the unambiguous cases 15 is close to our percentage 10 but we are in disagreement on the classification of a significant number of specific craters and in this analysis we describe the major reason for the disagreements we then summarize published data on the crater densities for different plains on venus we assess monte carlo modeling of volcanic resurfacing which competed with the ongoing formation of impact craters on the basis of these data and analyses we conclude that the mean age of the regional plains is close to the mean global surface age of venus and that the potential time span of regional plains emplacement was relatively short we interpret our results as evidence that wrinkle ridging on venus was a distinct tectonic phase that occurred rather early in post regional plains time probably within the first 10 although the exact duration remains uncertain regional and global stratigraphic relationships strongly support the hypothesis that wrinkle ridging on venus predominantly occurred during a specific phase of history the geologic record of wrinkle ridging and post plains tectonic evolution of volcanic plains on the moon and mars show interesting similarities to those of venus

inventorying slope movements in an alpine environment using dinsar differential sar interferometry dinsar is a technique that can be used to detect and characterize slope movements it is investigated here as a tool for establishing a detailed overview of complex slope movements at a regional scale in an alpine context this paper gives specific recommendations to use and to understand dinsar signals in mountainous areas located above the tree line excluding glaciated areas it proposes a systematic procedure based on accurate interpretations of interferometric signals from a large dinsar dataset to locate and estimate the displacement rate of moving zones the methodology was successfully applied in the western swiss alps where about 1500 moving objects were detected above the tree line using a large dataset of ers and jers interferograms dating from the 1990s the dinsar detected movements had a displacement rate ranging from a few centimeters to several meters per year and were attributed to various types of mass wasting phenomena rock glaciers landslides etc this kind of inventory derived from dinsar can be used as a preliminary tool for natural hazard management and process understanding in mountain areas as automatic data archiving and systematic acquisition of sar data are ensured worldwide for most sar sensors a similar methodology can basically be applied in many other parts of the globe also by using data from current sar sensors as long as a high resolution dem is available copyright 2014 john wiley sons ltd

experimental investigation into the microstructural and mechanical evolution of phyllosilicate bearing fault rock under conditions favouring pressure solution abstract mature crustal fault zones are known to be zones of persistent weakness this weakness is believed to result from microstructural modifications during deformation such as grain size reduction and foliation development around the brittle ductile transition phyllosilicates are expected to have a significant effect on fault strength in particular under conditions favouring pressure solution to study such effects we performed rotary shear experiments on brine saturated halite kaolinite mixtures aimed at investigating the relation between microstructural and mechanical evolution in a system where pressure solution and cataclasis dominate the results show significant strain weakening and a transition with progressive strain towards more rate sensitive and less normal stress sensitive behaviour this was accompanied by a microstructural evolution from a purely cataclastic microstructure to a mylonitic microstructure consisting of elongate asymmetric clasts in a fine grained foliated matrix the results demonstrate that strain weakening and the development of a typical mylonitic microstructure can occur as a consequence of grain size reduction by cataclasis and a transition to pressure solution accommodated deformation even in the absence of dislocation creep the data raise questions regarding the reliability of microstructures as rheology indicators as well as on the use of low strain monomineralic flow laws for modelling crustal dynamics

fluid distribution in grain boundaries of natural fine grained rock salt deformed at low differential stress qom kuh salt fountain central iran implications for rheology and transport properties we used a combination of broad ion beam cross sectioning and cryogenic sem to image polished surfaces and corresponding pairs of fractured grain boundaries in an investigation of grain boundary microstructures and fluid distribution in naturally deformed halite from the qom kuh salt glacier central iran at the scale of observations four types of fluid filled grain boundary can be distinguished by morphology from straight to wavy thickness from 5000 to 50 nm and the presence of fluid inclusions the mobility of the brine is shown after cutting the inclusions by broad ion beam bib in vacuum and fine grained halite forms efflorescence and precipitates on internal walls of inclusions at cryogenic temperature grain boundary brine is shown either as continuous film or in isolated inclusions the halite halite grain boundary between isolated fluid inclusions is interpreted to have formed by fluid assisted grain boundary healing preliminary experiments on the samples at shear stress conditions of natural salt glacier show very slow strain rates 7 4 10 10 s 1 and 1 10 9 s 1 which are less than expected for pressure solution creep both microstructures and deformation experiments suggest interfacial energy driven grain boundary healing and therefore rendering inactive the pressure solution creep in our samples this result disagrees with previous microstructural studies of the same sample which showed microstructural evidence for pressure solution and dislocation creep different explanations are discussed which imply that both healing and reactivation of grain boundaries are important in salt glaciers leading to heterogeneous distribution of deformation mechanisms and strain rates in both space and time

methodological sensitivity of morphometric estimates of coarse fluvial sediment transport abstract the estimation of fluvial sediment transport rate from measurements of morphological change has received growing recent interest the revival of the morphological method reflects continuing concern over traditional methods of rate determination but also the availability of new survey methods capable of high precision high resolution topographic monitoring remote sensing of river channels through aerial digital photogrammetry is a potentially attractive alternative to labour intensive ground surveys however while photogrammetry presents the opportunity to acquire survey data over large areas data precision and accuracy particularly in the vertical dimension are lower than in traditional ground survey methods this paper presents results of recent research in which digital elevation models dems have been developed for a reach of a large braided gravel bed river in scotland using both digital photogrammetry and high resolution rtk gps ground surveys a statistical level of change detection is assessed by comparing surfaces with independent check points the methodological sensitivity of the annual channel sediment budget 1999 2000 to the threshold is presented results suggest that while the remote survey methods employed here can be used to develop qualitatively convincing moderate precision dems of channel topography rmse 0 21 m the remaining errors imply significant limits on reliable change detection which lead to important information losses tests at a 95 confidence interval for change detection show that over 60 of channel deposition and 40 of erosion may be obscured by the lower level of precision associated with photogrammetric monitoring when compared to ground survey measurements this bias reflects the difficulty of detecting the topographic signature of widespread but shallow deposition on bar tops

lips on venus venus a planet similar to earth in heat budget lacks plate tectonics yet displays ample evidence of extensive volcanic and tectonomagmatic processes including regions large enough to be considered lips thus venus provides an excellent opportunity to examine large scale magmatic processes outside a plate tectonic framework i discuss four groups of venus largest tectonomagmatic provinces volcanic rises large coronae artemis heng o quetzalpetlatl atahensik crustal plateaus and plains with wrinkle ridges unit pwr unit pwr widely interpreted as representing catastrophic resurfacing has been suggested to be the solar system s largest lip i argue herein that these features each covering 1 million km 2 or more and recording extensive volcanic activity record different evolutionary processes including both endogenic and exogenic processes volcanic rises represent surface manifestations of deep mantle plumes on thick lithosphere large coronae may record different evolutionary paths artemis represents a plume signature on thin lithosphere more mapping is required to determine if heng o formed by endogenic or exogenic processes preliminary mapping suggests quetzalpetlatl represents a young mantle plume atahensik marks a diapiric structure though buoyancy mode is unconstrained crustal plateaus record solidification of huge lava ponds formed by massive partial mantle melting caused by large bolide impact on thin lithosphere the status of unit pwr as the largest lip within the solar system is challenged based on geological considerations and results of a growing body of geologic mapping 2007 elsevier b v all rights reserved

grain growth in synthetic marbles with added mica and water evolution of grain size in synthetic marbles was traced from compaction of unconsolidated powder through primary recrystallization and normal grain growth to a size stabilized by second phases to form the marbles reagent grade caco3 was mixed with 0 1 and 5 volume mica and heat treated under pressure with added water densification with negligible recrystallization occurred within one hour at 500 c and 500 mpa confining pressure primary recrystallization occurred at 500 550 c causing increases of grain size of factors of 2 5 resulting samples had uniform grain size gently curved grain boundaries and near equilibrium triple junctions they were used subsequently for normal grain growth studies normal grain growth occurred above 550 c at 800 c grain size d increased from 7 m d0 to 65 m in 24 hours growth rates fit the equation d n d 0 n kt where k is a constant and n 2 6 minor amounts of pores or mica particles inhibit normal grain growth and lead to a stabilized grain size dmax which depends on the size of the second phases and the inverse of their volume fraction raised to a power between 0 3 and 1 once dmax is reached normal growth continues only if second phases are mobile or coarsen or if new driving forces are introduced that cause unpinning of boundaries normal grain growth in solnhofen limestone was significantly slower than in pure synthetic marble suggesting that migration is also inhibited by second phases in the limestone

microstructure and mechanical properties of halite coarse muscovite synthetic aggregates deformed in torsion abstract we investigated the behavior of a synthetic two phase aggregate composed of 80 halite 20 coarse muscovite under torsion deformation at 100 200 and 300 c a confining pressure of 250 mpa and a constant strain rate of 3e 4 s 1 at all temperatures the two phase aggregate deformed homogeneously at the sample scale the strength of the aggregate and muscovite deformation depended on temperature strain rate and initial orientation of muscovite greatest dimension relative to the shear plane with muscovite initially parallel to the shear plane halite flowed plastically and long muscovite grains were not strong enough to behave as a rigid inclusion rotating in a ductile matrix instead high aspect ratio grains deformed by folding which was visibly accomplished by slip along mica 001 cleavage and by great flattening of halite in the core of the folds when initially normal to the shear plane high aspect ratio muscovite grains passively rotated towards the shear plane in both cases small and low aspect ratio muscovite grains behaved mostly as mica fish with mica grains tilted opposite to shear sense similarly to natural mylonites porphyroclast systems and rolling structures were also common in the microstructure a strong foliation made of halite ribbons and aligned muscovite flakes rapidly developed but did not make the composite aggregate weaker when compared with single phase halite comparison with synthetic aggregates of single phase halite shows that the two phase aggregate was much stronger than single phase halite in all cases comparison with a synthetic aggregate with calcite porphyroclasts shows that the strength of the aggregate with muscovite at 100 c was lower below a strain of ca 2 6 and higher beyond this value and that the aggregate with calcite was stronger at 200 c strain rate stepping tests 1e 5 s 1 2e 3 s 1 indicate that the two phase aggregate behaved as power law viscous with stress exponents of ca 12 and 10 at 100 and 200 c respectively the mechanical data obtained in this study represent the actual rheological behavior of the aggregates because we used soft polymer jackets

the origin of s c mylonites and a new fault zone model abstract this paper presents a synthesis of experimental data on mechanical behaviour and deformation textures of simulated halite shear zones with special regard to the internal structures of s c mylonites and their mechanical implications halite is the only mineral so far for which a complete transition between brittle shearing deformation to fully ductile shearing flow in the dislocation glide regime has been studied experimentally under large shear strains that may be encountered along faults or plate boundaries moreover deformation textures in the shear zones are similar to those of mylonites and cataclasites thus the experimental results provide an insight into the petrogenesis of fault rocks mylonites in particular and the establishment of a realistic fault model between the brittle regime and the fully ductile regime i e pressure insensitive inelastic regime there exists a wide and distinct regime called semiductile in which deformation textures are nearly identical to those developed in the ductile regime yet the shear resistance is pressure dependent and potentially unstable fault motion can occur in the low pressure part in cooking salt shear zone experiments the characteristic texture in the semiductile and ductile regimes is foliation resembling mylonitic foliation which formed in the direction of maximum elongation in the semiductile regime nearly homogeneous shearing deformation characterized by the formation of uniform and pervasive foliation changes into heterogeneous deformation after a critical shear strain and this strain localization induces potentially unstable fault motion the primary mode of internal slip after the strain localization is slip along y riedel shears parallel to the shear zone boundary interconnected with r 1 and some p riedel shears these shear surfaces of concentrated deformation are very similar to the internal structures of so called s c mylonites hence the semiductile regime is the primary candidate for the formation of s c mylonites and at least some s c mylonites must have formed at seismogenic depths this interpretation is consistent with recently reported interlaced pseudotachylytes and mylonites it is also shown that the size of recrystallized halite grains presumably mostly postdeformational decreases with increasing shear strains but not with the shear stress and this is consistent with the grain size reduction with strain concentration which has been confirmed for many mylonites in the world thus estimation of flow stress from recrystallized grains needs to be done with great care and might often be erroneous existing fault models are critically examined from the viewpoint of the halite experiments and a new fault model is proposed whereby fault zones are divided into brittle semibrittle semiductile and ductile regimes with increasing depth the shear resistance of faults is highest in the semiductile regime and the seismogenic depth is likely to extend down to the upper part of this regime the semiductile regime thus emerges as an area of primary interest with regard to the petrogenesis of many s c mylonites modelling of large and great shallow earthquakes along pre existing faults and plate boundaries and quantitative evaluation of the mechanical interactions of plates across their boundaries

venus s shield terrain plains planitiae or lowlands expanses of gentle long wavelength 1000 km basins cover 80 of venus s surface these regions are widely accepted as covered by volcanic fl ows although the mechanism s responsible for resurfacing remains elusive in addition a volcanic origin for the lowland surface may be open to question lowland resurfacing is typically attributed to catastrophic emplacement 10 100 m y of globally extensive thick 1 3 km fl ood type lava this model of resurfacing has been postulated on the basis of impact crater distribution taken together with a lack of obvious volcanic fl ows or edifi ces and a lack of viable alternative models ongoing geologic mapping of 15 000 000 km2 0 25n 90 150e using 225 m pixel and 75 m pixel nasa magellan sar synthetic aperture radar data indicates that small edifi ces called shields 1 15 km diameter edifi ces 1 km high play a major role in lowland resurfacing individual shields are radar smooth or rough quasi circular to circular features with or without a central pit shield shapes which have been previously documented range from shield dome or cone to fl at topped or fl at shield deposits typically coalesce forming a thin regionally extensive but discontinuous mechanically strong layer herein called shield paint shield paint conforms to delicate local topography providing evidence of its thin character and indicating generally low viscosity during emplacement shield terrain shields and shield paint covers more than 10 000 000 km2 within the study area detailed mapping of fi ve 2 2 regions using coregistered normal and inverted right and left illumination sar imagery indicates shield densities of 3500 33 500 shields 106 km 2 thus the map area hosts more than 35 000 335 000 shields shield terrain generally postdates but is also locally deformed by fractures and wrinkle ridges indicating time transgressive formation relative to local deformation and or reactivation the regional scale crust was strong throughout shield terrain formation shield terrain may extend across much of venus s surface

origin of planetary wrinkle ridges based on the study of terrestrial analogs wrinkle ridges linear asymmetric topographic highs are common physiographic features on the moon mars and mercury we describe here some terrestrial features of similar morphology and scale that have formed under compressional stress systems similar to planetary wrinkle ridges all of the terrestrial analogs are produced by the anticlinal folding of rocks above reverse faults that shallow and typically break the surface characteristics common to both terrestrial and planetary ridges include 1 a linear asymmetric antiformal shape 2 tension cracks and grabens along the hinges of the antiform 3 overlapping en echelon lobes 4 reversals of the sense of asymmetry along strike 5 occurrence in compressional environments and 6 similarity to features produced during compression of various materials in laboratory scale models these similarities strongly suggest that planetary wrinkle ridges result from deformation associated with shallow thrust faults that either break or come close to the surface kinematic models capable of explaining the development of wrinkle ridges include 1 anticlinal folding of rocks over a buried thrust fault that may subsequently propagate to the surface and 2 fault bend folding of upper plate rocks over the surface flattening bend of a thrust fault

rheology and deformation mechanisms of an isotropic mica schist we have investigated the transitional semibrittle deformation of a mica schist 75 biotite by shortening cylinders cored at 0 45 and 90 to foliation to varying strains at confining pressures pc to 500 mpa constant strain rates e from 1 5 10 7 to 1 6 10 4 s 1 and temperatures t from 25 to 400 c deformation is concentrated within one or more throughgoing millimeter wide shear zones at all conditions these localize at low strains e 2 through the nucleation and coalescence of dense sets of intragranular microkink bands mkbs despite distinct differences in the relative number of mica grains oriented favorably for slip and kinking in different loading directions the differential stresses required for shear zone development vary little with fabric orientation biotite schist undergoes a transition from strain softening to steady strength mechanical response at confining pressures in the range 75 to 150 mpa the pressure sensitivity of strength characterized by the slope of the mohr envelope decreases from 0 5 at pc 100 mpa to 0 1 at pressures greater than 200 mpa reflecting the increasing contribution of glide and kinking in biotite at higher pressures however dilatancy associated with microcracking and void formation along mkb boundaries persists to at least 500 mpa within the pressure insensitive regime 200 pc 500 mpa temperature and strain rate dependencies of strength determined in stepping tests reveal a strong history dependence to flow that cannot strictly be described by a steady state constitutive law samples deformed in steps from low to high temperatures or fast to slow strain rates consistently exhibit stronger temperature and strain rate sensitivities than those deformed along t decreasing or e increasing paths path dependent effects may reflect differences in the degree to which inherited dislocation substructures are utilized or overprinted during later deformation increments by assuming an exponential relationship between differential stress d and strain rate e of the form e c exp d exp q rt we fit the data with two end member flow laws with a single activation energy q 89 kj mol and exponential constants ss 0 15 0 01 mpa 1 and ws 0 55 0 04 mpa 1 that account for the different responses observed along stepping paths that are strongly sensitive or weakly sensitive to t and e respectively application of the results to crustal deformation suggests that mica rich aggregates are weaker than other common rock types throughout a broad midcrustal depth range supporting the inference that retrograde reaction to phyllosilicates may be important in localizing crustal deformations within large faults and shear zones

climate change as a regulator of tectonics on venus tectonics volcanism and climate on venus may be strongly coupled large excursions in surface temperature predicted to follow a global or near global volcanic event diffuse into the interior and introduce thermal stresses of a magnitude sufficient to influence widespread tectonic deformation this sequence of events accounts for the timing and many of the characteristics of deformation in the ridged plains of venus the most widely preserved volcanic terrain on the planet

rheological and kinematical responses to flow of two phase rocks abstract numerical simulations have been performed to investigate the strain dependent behaviour of rheological and kinematical responses to flow of two phase rocks using the commercial finite difference program flac2d it was assumed that the two phases have maxwell rheology plane strain and velocity boundary condition which produces a simple shear deformation were also assumed two types of geometries were considered strong phase supported sps and weak phase supported wps we calculated strain dependent variations of effective viscosity and partitioning of strain rate vorticity and kinematic vorticity number during deformation in both sps and wps structure models the results show that the strain dependent behaviour is largely influenced by the geometry of the composite sps models show both strain hardening and strain softening during the simulations with strain hardening preceding strain softening a critical shear strain is necessary to begin the strain softening behaviour strain hardening and strain softening are accompanied by a reduction and an increase of the partition of strain rate into the weak phase respectively on the other hand wps models show only weak strain hardening and strain softening being the strain dependent behaviour close to a steady state flow in addition the following results are obtained on vorticity and kinematic vorticity number 1 in both sps and wps models the partition of vorticity into weak phase increases with progressive shear strain i e the strong phase becomes less rotational 2 in sps models weak inclusions changes from sub simple shear to super simple shear with progressive strain whereas the strong matrix changes from super simple shear to sub simple shear 3 in wps models the strong inclusions with high viscosity contrasts are less rotational but can be in super simple shear condition to high strains the observed strain dependent behaviours have been compared with previous proposed analytical models the degree of agreement is variable balshin and ryshkewitch duckworth models are only applicable to sps models ji generalized mixture rule model is applicable to both models the results suggest that polyphase rocks with sps structure during ductile shear deformation respond as strain softening materials after an initial strain hardening stage that may drive to the strain localization into the material

venus astra novae estimates of the absolute time duration of their activity abstract in order to assess the age relations between astra novae features with extensive radial fracture graben systems and their surroundings and to determine the duration of their activity we undertook a photogeologic analysis of magellan images of 78 astra 49 dark parabola craters and 114 clear halo craters for seven of these 78 astra it was found that the astrum forming faulting started before or close to the time of emplacement of regional plains and extended into the second part of post regional plains time because the mean age of the regional plains is close to the mean surface age of venus which is estimated to be 750 m y this means that the duration of activity of these seven astra was several hundred millions of years this is longer than the duration of activity of ongoing mantle plumes on earth but shorter than the duration of activity of the plume feeding the martian volcano olympus mons the basic morphologic characteristics of these seven astra as well as their age relations with other geologic units are similar to those of the majority of other astra therefore such a long duration could also be typical of some other astra we confirm the two phase pre and post regional plains evolution of astrum forming faulting suggested in previous studies for the first phase we show evidence for purely tectonic faulting caused by the diapiric rise of a mantle plume for the second phase we find evidence supporting the interpretation of other studies that the observed faults resulted from subsurface dike intrusions produced by magmatism associated with the plume we also found that faulting during the second phase was not instantaneous but distributed over a long period of time

textural evolution of synthetic anhydrite halite mylonites the rheology and textural evolution of mylonites for both crustal and mantle rocks are generally poorly understood stress and strain partitioning between shear zones and wall rock foliation development flow mechanisms and constitutive relations are little known to address these problems we have begun an experimental study in which anhydrite and halite aggregates are deformed in simple shear homogeneous mixes at intervals of 10 vol of anhydrite and halite powders of 90 to 180 m grain size comprise the 1 mm thick zone between the 35 precut surfaces in 2 by 4 cm right circular cylinders of anhydrite all specimens are confined under 200 mpa pc and tested at 300 c t producing an aggregate of near zero porosity all specimens are shortened at an axial displacement rate of 5 l0 6 cm s to shear strains of about 2 0 most stress strain curves have a similar form they are characterized by an initial linear response that is followed by a work hardening region that leads to a plateau of constant stress whilst strain continues to accumulate this apparent steady state behavior is followed by a drop in stress to a second apparent steady state stress the strain at this stress drop and the magnitude of the drop increase with increasing anhydrite content the second lower steady state stress for all mixes approaches that of sheared pure halite optical examination of the fabrics shows that straining under the initial apparent steady state is accommodated by both mineral phases a foliation evolves as defined by mineral segregation and grain elongation of halite at 15 to 30 to the shear zone walls anhydrite grains rotate until their 001 010 slip system parallels the foliation the anhydrite also exhibits twin lamellae kinks and microfractures following the stress drop rheologic behavior is dominated by dynamic recovery in halite the recrystallized grain size increasing consistent with the lower stress level

comparison of gully erosion estimates using airborne and ground based lidar on santa cruz island california abstract gully erosion removes comparatively large volumes of soil from small areas it is often difficult to quantify the loss of soil because the footprint of individual gullies is too small to be captured by most generally available digital elevation models dems such as the usgs national elevation dataset airborne lidar light detection and ranging has the potential to provide the required data density but an even newer class of ground based sensors may provide better local resolution at lower cost in this study we compared digital elevation models produced by airborne and ground based lidar systems with ground based geomorphic and geodetic survey data to determine their utility in quantifying volumetric soil loss due to gully erosion in a heavily degraded watershed 7 55 10 2 km 2 on southwestern santa cruz island in southern california volumetric estimates of the eroded sediment were produced by comparing the lidar derived dems of the gully system to a modeled pre erosion surface average point densities were significantly higher for the ground based lidar system and provided more detailed information however its limited scanning footprint and side looking orientation presented serious challenges in collecting continuous data from deeply incised gullies making the airborne system preferable for this type of investigation and likely for most applications where heavy topographic shadowing is prevalent

rheology and microstructure of synthetic halite calcite porphyritic aggregates in torsion abstract polymer jacketed porphyritic samples of 70 halite 30 coarse calcite were subjected to torsion deformation to investigate the effects of a mixture of coarse calcite on the microstructure and mechanical properties of a two phase aggregate the experiments were run at 100 and 200 c a confining pressure of 250 mpa and a constant shear strain rate of 3e 4 s 1 ultimate strengths of single phase halite synthetic aggregates at 100 and 200 c were ca 32 and 8 nm respectively and of the two phase aggregate 39 and 18 nm respectively this shows that the two phase aggregate was much stronger especially at 200 c stepping strain rate tests show that the two phase aggregate behaved as power law viscous with stress exponents of ca 19 and 13 at 100 c at 200 c respectively from these high exponents we infer that the active deformation mechanisms were not efficient enough to rapidly relax the applied stress halite stress exponents at 100 and 200 c are typically much lower in the order of 4 6 which means that the calcite porphyroclasts were obstacles to halite plastic flow and hampered stress relaxation the drop of the stress exponent with temperature indicates that the main deformation mechanism s was temperature sensitive matrix halite deformed plastically while calcite rotated rigidly or deformed in a brittle fashion with grain size reduction by fracturing e g bookshelf and boudinage we conclude that halite was softer than calcite in the investigated temperature range strain was homogeneous at the sample scale but not at the grain scale where the foliation delineated by plastically flattened halite contoured the rigid calcite clasts the microstructures experimentally produced at 100 and 200 c are very similar and find their counterparts in natural mylonites rolling structures and porphyroclast systems bookshelf and boudinage in brittle calcite porphyroclasts and ductile y and c micro shear bands in the halite matrix

the geologic history of venus a stratigraphic view on the basis of regional and global stratigraphic analyses we outline the major events in the geologic history of venus determined by photogeological study of surface features because the morphological signatures of terrain emplaced prior to the time of tessera formation are not preserved the stratigraphic record presented comprises only the last 10 20 of the total history of venus the estimated range of the mean crater retention age of the surface from 200 to 1600 million years leads us to describe the timing and duration of different events in terms of fractions of the mean surface age t the beginning of the observed history of venus was characterized by intensive tectonic deformation of global or semi global scale which formed the tessera terrain termination of the compressional stage is estimated to have occurred at about 1 4t while the tensional stage lasted for another 0 1 0 2t after tessera formation several stages of extensive volcanism occurred burying vast areas of tessera and forming what are now observed as regional plains the combined duration of the emplacement of these plains is estimated to be about 0 2 0 3t with an implied average global rate of volcanism of a few cubic kilometers per year regional plains forming materials can be subdivided and are separated from each other and from underlying and overlying units by unconformities these unconformities are formed from oldest to youngest by tessera forming deformation dense fracturing broad ridging and finally wrinkle ridging these tectonic episodes are interpreted to be generally globally synchronous and to represent successive episodes characterized by the dominance of compression then tension then again compression and finally tension the last global scale tectonic episode extensive wrinkle ridging happened at about time t which was very close in time to the emplacement of the most areally abundant plains unit this marked the transition to the present stage of the history of venus which is characterized by a predominance of regional rifting and related volcanism this stage appears to have lasted from about time t to the present making it the longest time duration among the stratigraphic units considered although the resulting tectonic and volcanic features and deposits cover only 10 20 of the surface of venus these observations mean that the general intensity of tectonics and the flux of volcanism a few tenths of a cubic kilometer per year in this latest period were much lower than those in earlier times in summary the morphologically observable part of the history of venus was characterized by two key characteristics that stand in contrast to the comparable period of earth history approximately the phanerozoic when global geodynamic processes were dominated by plate tectonics 1 venus shows no signature of plate tectonics instead its global tectonic environment passed from an initial dominance of compression through tension then again compression and finally tension with the density of deformational structures and the strain rate declining with time 2 in the beginning of this period of time on venus plains forming volcanism occurred at a rate comparable to volcanism at mid ocean ridges but was emplaced in an entirely different style the predominant component of volcanism on earth during this time was the extrusive volcanism at mid oceanic ridges for the last few hundred million years venus has been dominated primarily by rift associated volcanism emplaced at a production rate comparable to or even lower than present intraplate volcanism production rates on earth

the deformational behaviour of bimineralic limestone halite aggregates abstract a compositional foliation banding develops within synthetic limestone halite aggregates experimentally deformed in axially symmetric compression and in simple shear the strength of the bulk aggregate decreases as the foliation becomes stronger foliation weakening in calcite rich specimens the development of foliation starts with the formation of cataclastic shear systems in calcite domains between isolated halite domains with increasing deformation halite is sheared into these systems the halite domains coalesce into halite rich shear systems and accommodate an increasing amount of the bulk deformation the bulk strength of bimineralic aggregates at a given amount of strain increases with decreasing halite content the influence of halite on the bulk strength is much greater than would be expected from its volume fraction and becomes dominant with increasing deformation due to the development of the foliation it is postulated that such processes also occur during natural deformation of polyphase rocks competent clasts within a weaker ductile matrix showing no recrystallization differ in shape and rotational behaviour from recrystallizing clasts such as feldspar augen these competent clasts denoted as type clasts may cause problems in deducing the sense and direction of shear when formed as almost exact mirror images of type recrystallizing clasts

monitoring in situ stress strain behaviour during plastic yielding in polymineralic rocks using neutron diffraction abstract attempts to use rock deformation experiments to examine the elastic and plastic behaviour of polymineralic rocks are hampered by the fact that usually only whole sample properties can be monitored as opposed to the separate contribution of each phase to circumvent this difficulty room temperature uniaxial compression experiments were performed in a neutron beam line on a suite of calcite halite samples with different phase volume proportions by collecting diffraction data during loading the elastic strain and hence stress in each phase was determined as a function of load to bulk strains of 1 2 in all cases the calcite behaved elastically while the halite underwent plastic yielding during the fully elastic part of the deformation the composite elastic properties and the within phase stresses are well described both by recent shear lag models and by analyses based on eshelby s solution for the elastic field around an ellipsoidal inclusion in a homogeneous medium after the onset of yielding the halite in situ stress total strain curve may be reconstructed using the rule of mixtures at calcite contents of greater than 30 the in situ halite response may be significantly weaker or stronger than that obtained at lesser calcite contents the results highlight the potential that such techniques offer for developing an explicitly experimental approach for determining the influence of microstructural variables on the mechanical properties of polymineralic rocks

the role of tectonic grain size reduction in the rheological stratification of the lithosphere with the aid of published constitutive flow laws for common crustal and upper mantle rock types it is possible to construct curves showing variation of rock strength with depth in the continental lithosphere assuming a particular crustal stratification of rock types and a particular geothermal gradient such exercises lead to the conclusion that marked changes in strength can occur at major petrological interfaces such as the moho discontinuity which are therefore likely to be associated with a tendency for major sub horizontal detachments to form constitutive flow laws used for such purposes are usually assumed to represent steady state flow at constant rock microstructure

microstructural and mechanical effects of strong fine grained muscovite in soft halite matrix shear strain localization in torsion 1 torsion experiments were performed on polymer jacketed samples of 80 halite 20 fine mica at 373 473 and 573 k a confining pressure of 250 mpa and a shear strain rate of 3 10 4 s 1 the strength of the aggregate depended on temperature strain rate mica distribution produced by cold pressing and mica orientation emerging during experiments comparison with synthetic aggregates of pure halite shows that halite mica mixtures were stronger in all cases from strain rate stepping tests we deduced stress exponents of 12 and 10 at 373 and 473 k respectively in contrast to values of approximately 4 and 3 for halite at the same temperatures strain localized only at 573 k except for one run at 373 k and high strain shear bands formed parallel to the applied shear plane at 573 k we infer that the strength contrast between halite and mica increased with temperature and promoted strain localization which occurred where the local mica content was low while unstrained domains persisted where the locally high mica content formed a strong framework mica reorientation and strain softening at 573 k increased with strain from which we deduce that mica alignment promoted softening we conclude that small amounts of a strong mineral phase can significantly increase the strength and stress dependence of a rock and that the heterogeneous connectivity between strong grains can trigger shear strain localization

sediment connectivity a framework for understanding sediment transfer at multiple scales a major challenge for geomorphologists is to scale up small magnitude processes to produce landscape form yet existing approaches have been found to be severely limited new ways to scale erosion and transfer of sediment are thus needed this paper evaluates the concept of sediment connectivity as a framework for understanding processes involved in sediment transfer across multiple scales we propose that the concept of sediment connectivity can be used to explain the connected transfer of sediment from a source to a sink in a catchment and movement of sediment between different zones within a catchment over hillslopes between hillslopes and channels and within channels using fluvial systems as an example we explore four scenarios of sediment connectivity which represent end members of behaviour from fully linked to fully unlinked hydrological and sediment connectivity sediment travel distance when combined with an entrainment parameter reflecting the frequency magnitude response of the system maps onto these end members providing a coherent conceptual model for the upscaling of erosion predictions this conceptual model could be readily expanded to other process domains to provide a more comprehensive underpinning of landscape evolution models thus further research on the controls and dynamics of travel distances under different modes of transport is fundamental copyright 2014 john wiley sons ltd

from geotechnical analysis to quantification and modelling using lidar data a study on rockfall in the reintal catchment bavarian alps germany in the year 2007 enhanced rockfall activity was observed within the scarp of a 500 bp rockslide in the reintal catchment northern calcareous alps germany the largest of a series of events took place in august when almost 50000 m of rock were detached from the subvertical rock face and deposited on a talus cone in this case study we focus on three aspects of rockfall research first we compile detailed geomorphological and geotechnical findings to explain the causes of the recent events the results of laboratory tests and stability estimations suggest that rockfall activity will persist in the future as the old rockslide scarp still contains unstable rock masses second we use digital elevation data from a pre event airborne lidar survey als and post event terrestrial laserscanning tls to quantify landform changes and the mass balance of the rockfall event s the widespread availability of als elevation data provides a good opportunity to quantify fresh events using a comparatively inexpensive tls survey this approach is complicated by uncertainties resulting from the difficult coregistration of als and tls data and the specific geometric problems in steep als and flat tls terrain it is therefore limited to at least medium sized events third the event s is simulated using the results of the lidar surveys and a modified gis based rockfall model in order to test its capability of predicting the extent and the spatial distribution of deposition on the talus cone results show that the model generally reproduces the process domain and the spatial distribution of topographic changes but frequently under and over estimates deposition heights copyright 2011 john wiley sons ltd

localization of bedding plane slip and backthrust faults above blind thrust faults keys to wrinkle ridge structure a mechanically based model for wrinkle ridge development is developed that combines wrinkle ridge morphologies regional topographic offsets suggestive of subsurface thrust faults and folding of near surface layers this model provides explicit relationships between observed morphologic elements characteristic of wrinkle ridges and plausible mechanisms in the subsurface a key component that is absent in previous qualitative fault based scenarios for these structures as developed in this paper wrinkle ridges are the surface expression of anticlines that grow above a blind thrust fault as a result of both flexural slip folding of near surface strata and the nucleation and growth of echelon arrays of backthrust faults calculations of displacements both horizontal shortening and vertical uplift and coulomb stress change related to slip along blind thrust faults in the model demonstrate physically important spatial inhomogeneities in these quantities with revealing and useful implications 1 the ratio of shortening due to folding at the surface to the shortening due to faulting at depth is characteristically small for coupled wrinkle ridge blind thrust fault systems and decreases with increasing fault depth the depth of the blind thrust fault s upper tip thus profoundly influences the surface strains 2 folding and uplifted topography forming the topographic ridge are produced above the area of the slipping blind thrust fault plane horizontal and vertical deformation at the surface extend over several ridge widths or a total of at least 50 km for a 10 km wide ridge implying that topographic profiles and geologic studies must extend sufficiently far from the wrinkle ridge to fully characterize the surface deformation 3 calculations of coulomb stress changes suggest that fault slip can localize both bedding plane slip in overlying strata and new backthrust faults that propagate upward to become wrinkles on the trailing side of the ridge initiation of bedding plane slip in association with slip along the blind thrust fault likely determines whether the resulting surface structure becomes a wrinkle ridge or a lobate scarp wrinkle ridge spacing may also be related to stress changes associated with slip along the underlying blind thrust fault

strength of two phase rocks a model based on fiber loading theory abstract in order to predict the strength of two phase rocks in terms of the component volume fraction the aspect ratio of the strong phase and the strength contrast between the strong and weak phases a simple model is developed according to a fiber loading theory modified for short fiber composites the analytical solution derived from elastic theory is found to hold in good approximation for rocks consisting of power law viscous minerals there is a good agreement between the predicted results and the experiments for two phase aggregates anhydrite halite calcite halite fe ag and clinopyroxene plagioclase the model is compared with several previous different models

fast deformation of perennially frozen debris in a warm rock glacier in the swiss alps an effect of liquid water 1 surface movement internal deformation and temperature were monitored over 5 years on buz north rock glacier a small rock glacier located at the lower limit of the permafrost belt in the swiss alps the permafrost in the rock glacier mainly consists of pebbles and cobbles filled with interstitial ice two inclinometers installed at 4 and 5 m depths showed fast deformation with large seasonal and interannual variations while the permafrost temperatures remained almost at the melting point the movement of the inclinometers coincided with changes in the surface velocities the deformation rapidly accelerated during snowmelt periods whereas it gradually decelerated below a dry snow cover in winter the frozen debris was more deformable than typical glacier ice at the melting point these phenomena suggest that the frozen debris is permeable to snowmelt water the fast deformation should result from significant annual relocation of debris particles which probably creates a network of air voids in the frozen debris that eventually allows water infiltration the meltwater infiltration accelerates the deformation by reducing effective stress resulting in the reduced strength of the frozen debris the refreezing of the pore water which depends on the cooling intensity in winter decelerates the deformation the combination of these processes controls the temporal variations in the deformation

impact of solid second phases on deformation mechanisms of naturally deformed salt rocks kuh e namak dashti iran and rheological stratification of the hormuz salt formation abstract viscosity contrasts displayed in flow structures of a mountain namakier kuh e namak dashti between weak second phase bearing rock salt and strong pure rock salt types are studied for deformation mechanisms using detailed quantitative microstructural study while the solid inclusions rich dirty rock salts contain disaggregated siltstone and dolomite interlayers clean salts reveal microscopic hematite and remnants of abundant fluid inclusions in non recrystallized cores of porphyroclasts although the flow in both the recrystallized dirty and clean salt types is accommodated by combined mechanisms of pressure solution creep ps grain boundary sliding gbs transgranular microcracking and dislocation creep accommodated grain boundary migration gbm their viscosity contrasts observed in the field outcrops are explained by 1 enhanced ductility of dirty salts due to increased diffusion rates along the solid inclusion halite contacts than along halite halite contacts and 2 slow rates of intergranular diffusion due to dissolved iron and inhibited dislocation creep due to hematite inclusions for clean salt types rheological contrasts inferred by microstructural analysis between both salt rock classes apply in general for the dirty salt forming lower hormuz and the clean salt forming the upper hormuz of the hormuz formation and imply strain rate gradients or decoupling along horizons of mobilized salt types of different composition and microstructure

effects of anhydrite and pressure on the mechanical behavior of synthetic rocksalt bimineralic polycrystalline rocksalt specimens ranging in composition from pure halite to pure anhydrite have been fabricated in hydrostatic compression at 150 mpa and 100 sup 0 c for 15 minutes resulting porosities of the compacted samples increased with increasing anhydrite content ranging from 02 for pure halite to 14 for pure anhydrite twenty three compacted samples were then deformed in triaxial compression experiments at confining pressures of 10 100 and 200 mpa a nominal strain rate of 10 sup 4 sec sup 1 and a temperature of 200 sup 0 c sample strength at 10 percent axial strain was directly related to both anhydrite content and pressure relatively small strength increases were observed for increases in anhydrite content up to 75 percent by weight and for all pressure increases much larger increases in strength were observed when the anhydrite content was increased from 75 to 100 percent ductilites of less than 10 percent were seen in only two sets of data the 100 and 75 percent anhydrite samples run at 10 mpa confining pressure and these data indicated a trend of increasing ductility with increasing halite content and or confining pressure all samples exhibited strain hardening except for the 75 percent halite samples at all three pressures andmore the 50 percent sample of 10 mpa which exhibited slight strain softening less

geomorphological activity at a rock glacier front detected with a 3d density based clustering algorithm abstract acquisition of high density point clouds using terrestrial laser scanners tlss has become commonplace in geomorphic science the derived point clouds are often interpolated onto regular grids and the grids compared to detect change i e erosion and deposition advancement movements this procedure is necessary for some applications e g digital terrain analysis but it inevitably leads to a certain loss of potentially valuable information contained within the point clouds in the present study an alternative methodology for geomorphological analysis and feature detection from point clouds is proposed it rests on the use of the density based spatial clustering of applications with noise dbscan applied to tls data for a rock glacier front slope in the swiss alps the proposed methods allowed the detection and isolation of movements directly from point clouds which yield to accuracies in the following computation of volumes that depend only on the actual registered distance between points we demonstrated that these values are more conservative than volumes computed with the traditional dem comparison the results are illustrated for the summer of 2015 a season of enhanced geomorphic activity associated with exceptionally high temperatures

investigating decadal scale geomorphic dynamics in an alpine mountain setting we know little about the effect of recent climate variability upon landscapes at the timescale of decades because of 1 the complex nonlinear and path dependent nature of the response of a landscape to climate forcing and 2 the difficulty of quantifying spatially distributed impacts at the timescale of decades to centuries despite this being the timescale over which significant hypotheses have been raised over human impacts upon climate change and hence geomorphic systems a unique resource to investigate the linkages between climatic variability and geomorphic response is provided by the extensive coverage of aerial imagery commonly available since the 1950s here we use archival digital photogrammetry to produce high precision digital elevation models over large spatial scales and so to reconstruct the quantitative history of surface downwasting and sediment flux in a high mountain alpine system over the timescales of decades propagation of error methods is used to identify locations of significant landscape response and to compute volumes of significant surface change orthorectified aerial images are used in an image correlation framework to detect horizontal and vertical displacements of components of the landscape results are coupled to extant climate data and modeled snow cover to show how the landscape responds to climate forcing and to geomorphological maps to understand how this response varies between landscape elements the results show distinct landscape response to both warming and cooling periods and a tendency for the acceleration of surface displacement under warming conditions precipitation and snow cover are critical in controlling glacier dynamics and rock glacier displacement velocities however while some landforms might lead to locally high sediment flux landscape heritage can disconnect zones of high change rates from the valley bottom hence the landscape response to climate forcing is not necessarily reflected in valley system processes or sediment deposits

a rock glacier pond system nw italian alps soil and sediment properties geochemistry and trace metal bioavailability abstract rock glacier sediment transfer and ice melting can impact surface waters located downstream however there is a lack of knowledge on the influence of rock glacier dynamics on the geochemical hydrochemical and ecological characteristics of adjacent impounded surface waters in the col d olen area long term ecological research site nw italian alps an intact rock glacier terminates into a pond and solute enriched waters originating from the rock glacier flow into the pond through a subsurface hydrological window in this study we performed geophysical and ground surface temperature measurements moreover we sampled soils and sediments in different compartments of the investigated rock glacier pond system and we further sampled benthic invertebrates in the pond cold ground thermal regime ground ice presence and coarse debris cover on the rock glacier together with its lithology serpentinites influence the rock glacier geochemistry and ecology with respect to surrounding areas pond geochemistry is affected by transfer of trace metal enriched fine grained debris and meltwaters from the rock glacier enhanced bioavailability of serpentinite associated trace metals was proved with concentrations of ni and cr in benthic invertebrates up to 384 and 110 mg kg 1 d w respectively potentially exerting toxic effects on pond biota the advancing movement of the rock glacier not only has delivered sediments to the pond but it has progressively filled the valley depression where the pond is located creating a dam that could have modified the level of impounded water this process likely constituted a sediment trap in which serpentinitic rock glacier sediments could be deposited at the pond bottom with related geochemical and ecological implications this study illustrates the importance of rock glaciers in influencing the characteristics of downstream freshwater bodies and highlights the need to improve our knowledge about climate change related impacts of rock glacier dynamics on alpine headwaters