structural evolution of the sarandi del yi shear zone uruguay kinematics deformation conditions and tectonic significance the sarandi del yi shear zone is a crustal scale shear zone that separates the piedra alta terrane from the nico perez terrane and the dom feliciano belt in southern uruguay it represents the eastern margin of the rio de la plata craton and consequently one of the main structural features of the precambrian basement of western gondwana this shear zone first underwent dextral shearing under upper to middle amphibolite facies conditions giving rise to the reactivation of pre existing crustal fabrics in the easternmost piedra alta terrane afterwards pure shear dominated sinistral shearing with contemporaneous magmatism took place under lower amphibolite to upper greenschist facies conditions the mylonites resulting from this event were then locally reactivated by a cataclastic deformation this evolution points to strain localization under progressively retrograde conditions with time indicating that the sarandi del yi shear zone represents an example of a thinning shear zone related to the collisional to post collisional evolution of the dom feliciano belt that occurred between the meso to neoproterozoic 600 ma and late ediacaran lower cambrian times

reequilibration of fluid inclusions bulk diffusion abstract bulk diffusion of fluid components through quartz which is a nominally anhydrous mineral is one of a series of processes that may alter fluid inclusions in crystals diffusion of water through quartz has been considered an important factor for re equilibration of fluid inclusions however the solubility of water in quartz the nature of the diffusing water related molecules and diffusion coefficients have not been adequately determined to calculate reliable rates of inclusion alteration a new three dimensional mathematical diffusion model is presented to characterize bulk diffusion in quartz with randomly distributed fluid inclusions this model assumes an infinite external fluid source and treats fluid inclusions as instantaneous point sources the computer program reqdif from the software package fluids http fluids unileoben ac at can be used to calculate the effect of diffusion with self defined parameters using a diffusion coefficient of 10 12 m2 s 1 60 the rate of h2o loss or gain of most inclusions is relatively high adapting them within several 10 000 of years to new pore fluid conditions however diffusion according to this model may be restricted and partly inhibited by several important factors such as the low porosity in metamorphic rock and relative low temperatures in sedimentary and diagenetic rocks the imprecision of estimated diffusion coefficients and the undetermined accuracy do not allow reliable diffusion calculations diffusion along micro cracks and dislocations is a more efficient process to transport fluid components through quartz

the mesoscale and microscale structure and organization of clouds and precipitation in midlatitude cyclones viii a model for the seeder feeder process in warm frontal rainbands abstract previous field studies have indicated that warm frontal rainbands form when ice particles from a seeder cloud grow as they fall through a lower level feeder cloud in this paper we present results from a parameterized numerical model of the growth processes that can lead to the enhancement of precipitation in a seeder feeder type situation the model is applied to two types of warm frontal rainbands in the first type 1 situation the vertical air motions are typical of those associated with slow widespread lifting in the vicinity of warm fronts in the second type 2 situation the vertical air motions are stronger and more characteristic of the mesoscale the model simulations show that in the type 1 situations the growth of the seed ice crystals within the feeder zone is due to vapor deposition the feeder zone in this case is slightly sub saturated with respect to water due to the presence of the seed crystals in regions where the feeder zone is not seeded from aloft snow cryst

modification of precipitation by coastal orography in storms crossing northern california abstract this study compiles and interprets three dimensional weather surveillance radar 1988 doppler wsr 88d data during a 2 5 yr period and examines the typical orographic effects on precipitation mainly associated with winter storms passing over coastal northern california the three dimensional mean reflectivity patterns show echo structure that was generally stratiform from over the ocean to inland over the mountains the flow above the 1 km level was strong enough to be unblocked by the terrain and the mean echo pattern over land had certain characteristics normally associated with an unblocked cross barrier flow both on the broad scale of the windward slopes of the coastal mountains and on the scale of individual peaks of the terrain on the windward side upward sloping echo contours on the scale of the overall region of coastal mountains indicated broadscale upslope orographic enhancement on a smaller scale the mean stratiform echo pattern over the mountains contained a strong embedded core

experimental study on the formation of faults from en echelon fractures in carrara marble abstract en echelon fractures have been commonly observed in a fault zone to better understand how en echelon fractures interact to produce a fault rock specimens containing multiple artificial flaws en echelon flaws under uniaxial compression are examined in the present study the fracture process zone white patch linking behaviors of flaws structures in fault tips and correlations between stress and flaw configuration are investigated in detail by the usage of an optical microscope and an image recording system the results suggest that two typical white patches characterized by different appearance in both unaided and microscopic observations would develop in carrara marble prior to the occurrence of visible cracks the linking behaviors are controlled by the regime of configurations where only tensile cracks occur in the extensional regimes and different types of shear cracks are involved in the contractional regimes although the linking coalescence behaviors between en echelon flaws are observed to be similar to those of two flaws in previous studies special linking phenomena are particularly observed in specimens of 15 and 30 where is the flaw array angle the influence of en echelon flaw geometries is also reflected by the structures in fault tip and the development of tensile wing cracks stress analysis shows that the configurations of en echelon flaws dictate the coalescence stress with the increase of flaw inclination angle the coalescence stress increases in the contractional regime but decreases in the extensional regime finally by comparing the coalescence stress and the corresponding linking behaviors of each en echelon flaw configuration a correlation between the coalescence stress and the linking crack types is proposed linking patterns of fault segments obtained from both experiments and field investigations are discussed towards the end of the paper

strain analysis of heterogeneous ductile shear zones based on the attitudes of planar markers using the simple measurement of the attitude of planar features such as foliation shear planes and displaced tabular markers such as veins or dykes fundamental information is obtained on deformation types and rheology in heterogeneous ductile shear zones the method outlined in this study is based on the subdivision of the shear zone in n deformed layers each of them being characterized by approximately homogenous deformation for each layer paired measurements of and are made where is the angle that the foliation forms with the shear plane and is the effective shear strain by means of suitable grids constructed according to strain boundary conditions values of stretch k shear strain strain ratio r and kinematic vorticity number wk are calculated the method has been tested on three ductile wrench zones exposed in a deformed granitoid pluton in the eastern alps italy the data indicate that the shear zones are of dominantly transtensional or transpressional type furthermore the finite shear strain and strain ratio peaked profiles suggest that in all instances shear zone evolution was characterized by strain softening analysis of the kinematic vorticity indicates that strain softening essentially affected the simple shear component of the deformation

embedded cellular convection in moist flow past topography abstract marginally unstable air masses impinging upon a mountain ridge may lead to the development of a nominally stratiform orographic cloud with shallow embedded convection rainfall amounts and distribution are then strongly influenced by the convective dynamics in this study the transition from purely stratiform orographic precipitation to flow regimes with embedded convection is systematically investigated to this end idealized cloud resolving numerical simulations of moist flow past a two dimensional mountain ridge are performed in a three dimensional domain a series of simulations with increasing upstream potential instability shows that the convective dynamics may significantly increase precipitation amounts intensity and efficiency to an extent that cannot be replicated by two dimensional simulations under conditions of uniform upstream flow the embedded convection is of the cellular type it is demonstrated that simple stability measures of the upstream profile are poor predictors for

random forest with semantic tie points for classifying landforms and creating rigorous shaded relief representations abstract in this study we tested random forest rf with semantic tie points to classify discrete landforms which would be ultimately useful for increasing the accuracy of shaded relief representations we therefore focused our efforts on the following landforms rock outcrops screes alluvial fans and low relief areas a characteristic of rf which makes it a good algorithm for geomorphological mapping is its ability to generate thousands of classification trees each tree provides a classification and the value classified by the majority of the trees is the final output of the algorithm furthermore having multiple classifications provides a measure of uncertainty this is very important because it gives practitioners an idea of areas where the method is less accurate which would require more effort in terms of sampling or surveying this method was applied in two mountainous areas of switzerland the first where we trained and calibrated it and the second where we used it for classification the results were validated using existing geomorphological maps and they show that this method can obtain good training accuracy with a relatively small starting dataset moreover both calibration and classification present a percentage of agreement with existing geomorphological maps of over 70 some geomorphological classes alluvial fans and screes present a classification accuracy that is lower than the calibration which is in line with previous tests found in the literature however for other classes i e rock outcrops and low relief areas the accuracy increases suggesting that this method can be employed extensively and relatively securely for these landforms

formation and interpretation of dilatant echelon cracks the relative displacements of the walls of many veins joints and dikes demonstrate that these structures are dilatant cracks we infer that dilatant cracks propagate in a principal stress plane normal to the maximum tensile or least compressive stress arrays of echelon crack segments appear to emerge from the peripheries of some dilatant cracks breakdown of a parent crack into an echelon array may be initiated by a spatial or temporal rotation of the remote principal stresses about an axis parallel to the crack propagation direction near the parent crack tip a rotation of the local principal stresses is induced in the same sense but not necessarily through the same angle incipient echelon cracks form at the parent crack tip normal to the local maximum tensile stress further longitudinal growth along surfaces that twist about axes parallel to the propagation direction realigns each echelon crack into a remote principal stress plane the walls of these twisted cracks may be idealized as helicoidal surfaces an array of helicoidal cracks sweeps out less surface area than one parent crack twisting through the same angle thus many echelon cracks grow from a single parent because the work done in creating the array as measured by its surface area decreases as the number of cracks increases in cross sections perpendicular to the propagation direction echelon cracks grow laterally each crack overlapping its neighbors until the mechanical interaction of adjacent cracks limits this growth dilation of each crack pinches the tips of adjacent cracks into an asymmetrical form and introduces local stresses that can cause lateral growth along a curving sigmoidal path sigmoidal echelon cracks may link at tip to plane intersections leaving a step in the through going crack wall the geometry of dilatant echelon cracks may be used to infer spatial or temporal changes in the orientation of principal stresses in the earth

vertical structures of precipitation in cyclones crossing the oregon cascades abstract the vertical structure of radar echoes in extratropical cyclones moving over the oregon cascade mountains from the pacific ocean indicates characteristic precipitation processes in three basic storm sectors in the early sector of a cyclone a leading edge echo lee appears aloft and descends toward the surface updraft cells inferred from the vertically pointing doppler radial velocity are often absent or weak in the middle sector the radar echo consists of a thick vertically continuous layer extending from the mountainside up to a height of approximately 5 6 km that lasts for several hours when the middle sector passes over the windward slope of the cascades the vertical structure of the precipitation exhibits a double maximum echo dme one maximum is associated with the radar reflectivity bright band the second reflectivity maximum is located approximately 1 2 5 km above the bright band the secondary reflectivity maximum aloft does not appear until the middle sector passes over the wi

the initiation and growth of en echelon veins abstract numerical models are used to understand the evolution of mode i opening fractures from spatially random distributions in a brittle elastic material en echelon arrays commonly develop because mechanical fracture interaction promotes growth for this geometry this provides a new mechanism for en echelon vein formation in rock which is distinctly different than previously proposed mechanisms it is suggested that some macroscopic en echelon vein arrays may have served as zones of weakness that localized later shear zone development in a manner analogous to that observed by experimentalists examining micro cracking and subsequent shear rupture of rocks loaded under compression sigmoidally shaped veins and vein fillings are explicitly modeled showing that they can form in response to the mechanical interaction of neighboring fractures which redirects the propagation path numerical comparison of sigmoidal veins formed by brittle fracture and by ductile shear zones demonstrates some of the pitfalls of failing to correctly identify the mechanism of formation

package fluids 1 computer programs for analysis of fluid inclusion data and for modelling bulk fluid properties the computer package fluids contains five sets of computer programs written in c for the calculation of fluid properties both model fluids and data from fluid inclusions can be analysed in the programs bulk density molar volume and composition of fluid inclusions are calculated with the program bulk which uses microthermometric data micro raman spectroscopic data cation ratios and volume fraction estimations as input the program offers a broad variety of equations of state which are selected according to the fluid system or the temperature and pressure conditions of interest the isochores that correspond to the output or test v x properties of fluid inclusions are calculated by the program isoc in calculating the isochores this program takes account of the compressibility and expansion of selected host minerals the program test allows different equations of state to be compared directly with experimental data thereby facilitating selection of the most adequate model in the programs bulk and isoc loner is a group of programs that handle individual equations of state eos for all fluid systems presented in the programs bulk and isoc aqso is a group of programs that allows purely empirical modelling of electrolyte bearing aqueous solutions henry s law for dilute gas bearing aqueous solutions and osmotic coefficients for dilute electrolyte bearing aqueous solutions the programs are available on the university of leoben web site at http www unileoben ac at buero62 minpet ronald

instability characteristics of radar derived mesoscale organization modes within cool season precipitation near portland oregon abstractthe instability characteristics associated with different radar derived mesoscale organization modes are examined using six cool seasons of operational scanning radar data near portland oregon and operational sounding data from salem oregon additionally several years of microwave rain radar ka band vertically pointing radar data from portland and merwin washington are used to characterize the nature and occurrence of generating cells and fall streaks the combination of a new metric convective stratiform intermittency with the classification of radar reflectivity maps into convective and stratiform precipitation types was applied to periods when the freezing level was 1 4 km altitude this method distinguishes periods with embedded convective within stratiform mesoscale organization from those that were mostly convective or mostly stratiform mesoscale organization occurs in a continuum of states with predominantly stratiform structure occurring most frequently generating cells in the s

microphysical properties of convectively generated fall streaks within the stratiform comma head region of continental winter cyclones abstractthis paper presents analyses of the microphysical structure of comma head stratiform precipitation in 14 continental cyclones focusing on fall streaks of hydrometeors produced by cloud top convective generating cells data were obtained at temperatures between 4 and 45 c using in situ instrumentation and the w band university of wyoming cloud radar all operated aboard the national science foundation national center for atmospheric research c 130 analyses are presented first for a case study of one cyclone followed by statistical analyses of the full dataset using radar based objective classifications the statistical percentile number concentrations averaged 1 9 times larger within the fall streaks compared to the regions between them and the corresponding ice water content and median mass diameter values averaged 2 2 and 1 1 times larger ice phase conditions were predominant within the stratiform precipitation with deposition and aggregation the primary ice growth mechanisms no distinc

synoptic and topographic variability of northern california precipitation characteristics in landfalling winter storms observed during caljet abstract observations from northern california during the california landfalling jets caljet experiment are used to examine the mean characteristics of precipitation and their variances as functions of synoptic and topographic regimes ten cases involving the landfall of extratropical cyclones are analyzed with radar and rain gauge data collected at two sites one in the coastal mountains north of san francisco czd and the other in the central valley just west of sacramento kdax aside from the melting layer bright band the most striking feature in the 10 case composite vertical profile of radar reflectivity at czd was a distinct change in slope about 2 5 km above the bright band this shoulder is thought to represent a change in the growth rate of hydrometeors although the bright band was quite distinct about one third of the profiles in the composite did not exhibit this feature these nonbrightband nbb profiles had a low level slope where reflectivity increased with decreasing altitude a

the mesoscale and microscale structure and organization of clouds and precipitation in midlatitude cyclones xiii structure of a warm front abstract mesoscale measurement from radars aircraft and rawinsondes and synoptic and satellite data are used to provide a detailed description of a warm front as it approached the washington coast in many respects the warm front was consistent with the classical model temperature rises were concentrated within a forward sloping frontal zone winds veered with height and lapse rates were more stable within the frontal zone clouds and precipitation were produced by upglide over the warm frontal surface and as the warm front approached clouds lowered and precipitation generally increased however in several important respects the warm front differed from the classical picture air flowed through the warm front and the warm frontal zone also the warm frontal zone had a staircase profile with some segments nearly horizontal and other segments with steep slopes finally precipitation was by no means uniformly distributed instead it occurred in both irregular and banded shaped mesoscale features

dynamics of cloud top generating cells in winter cyclones part iii shear and convective organization abstractcloud top generating cells gcs are a common feature atop stratiform clouds within the comma head of winter cyclones the dynamics of cloud top gcs are investigated using very high resolution idealized wrf model simulations to examine the role of shear in modulating the structure and intensity of gcs simulations were run for the same combinations of radiative forcing and instability as in part ii of this series but with six different shear profiles ranging from 0 to 10 m s 1 km 1 within the layer encompassing the gcs the primary role of shear was to modulate the organization of gcs which organized as closed convective cells in simulations with radiative forcing and no shear in simulations with shear and radiative forcing gcs organized in linear streets parallel to the wind no gcs developed in the initially stable simulations with no radiative forcing in the initially unstable and neutral simulations with no radiative forcing or shear gcs were exceptionally weak with no clear organization

snow growth and transport patterns in orographic storms as estimated from airborne vertical plane dual doppler radar data abstractairborne vertical plane dual doppler cloud radar data collected on wind parallel flight legs over a mountain in wyoming during 16 winter storms are used to analyze the growth transport and sedimentation of snow in all storms the wind is rather strong such that the flow is unblocked the sampled clouds are mixed phase shallow and generally produce snowfall over the mountain only the 2d scatterers mean motion in the vertical along track plane below flight level is synthesized using one radar antenna pointing to nadir and one 30 forward of nadir this yields instantaneous cross mountain hydrometeor streamlines the dynamics of the orographic flow dominate the precipitation patterns across the mountain three patterns are distinguished the first two contain small convective cells either boundary layer bl convection or elevated convection the latter likely due to the release of potential instability in orographically lifted air in these patterns the cross mountain flow is relatively un

vertical velocity and physical structure of generating cells and convection in the comma head region of continental winter cyclones abstractthe vertical motion and physical structure of elevated convection and generating cells within the comma heads of three continental winter cyclones are investigated using the wyoming w band cloud radar mounted on the national science foundation national center for atmospheric research nsf ncar c 130 supplemented by analyses from the rapid update cycle model and weather surveillance radar 1988 doppler wsr 88d data the cyclones followed three distinct archetypical tracks and were typical of those producing winter weather in the midwestern united states in two of the cyclones dry air in the middle and upper troposphere behind the pacific cold front intruded over moist gulf of mexico air at lower altitudes within the comma head separating the comma head into two zones elevated convection in the southern zone extended from the cold frontal surface to the tropopause the stronger convective updrafts ranged from 2 to 7 m s 1 and downdrafts ranged from 2 to 6 m s 1 the horizontal scale of the

multiscale mountain waves influencing a major orographic precipitation event abstract this study combines high resolution mesoscale model simulations and comprehensive airborne doppler radar observations to identify kinematic structures influencing the production and mesoscale distribution of precipitation and microphysical processes during a period of heavy prefrontal orographic rainfall over the cascade mountains of oregon on 13 14 december 2001 during the second phase of the improvement of microphysical parameterization through observational verification experiment improve 2 field program airborne based radar detection of precipitation from well upstream of the cascades to the lee allows a depiction of terrain induced wave motions in unprecedented detail two distinct scales of mesoscale wave like air motions are identified 1 a vertically propagating mountain wave anchored to the cascade crest associated with strong midlevel zonal i e cross barrier flow and 2 smaller scale 20 km horizontal wavelength undulations over the windward foothills triggered by interaction

a simple model for the synoptic analysis of cold fronts a split cold front model with an over running upper front or humidity front ahead of a surface front or humidity front is shown to provide a useful representation of the principal characteristics of many katafronts the use of such a model leads to more consistent analyses especially of cloud and rain than are achieved using unmodified classical concepts

the mesoscale and microscale structure and organization of clouds and precipitation in midlatitude cyclones xi comparisons between observational and theoretical aspects of rainbands abstract comparisons are made between the characteristics of several types of rainbands observed in an extratropical cyclone and dynamical mechanisms relevant on the mesoscale the warm sector flow ahead of the cold front and above the cold frontal zone aloft was unstable to conditional symmetric instability and theoretical predictions for this mechanism am consistent with several aspects of the warm sector and wide cold frontal rainbands in the case of the warm sector rainbands other mechanisms e g wave cisk and mixed dynamic convective instabilities may have also played a role the core structure of the narrow cold frontal rainbands appeared to be affected by an instability that derived its energy from the horizontal shear across the surface front also many aspects of the narrow cold frontal rainband were similar to a density current shear induced gravity waves appeared to be responsible for the wavelike rainbands observed in the vicinity of the cold frontal zone aloft the orientation of the

turbulence as a mechanism for orographic precipitation enhancement this study examines the dynamical and microphysical mechanisms that enhance precipitation during the passage of winter midlatitude systems over mountain ranges the study uses data obtained over the oregon cascade mountains during the improvement of microphysical parameterization through observational verification experiment 2 improve 2 november december 2001 and over the alps in the mesoscale alpine program map september november 1999 polarimetric scanning and vertically pointing s band doppler radar data suggest that turbulence contributed to the orographic enhancement of the precipitation associated with fronts passing over the mountain barriers cells of strong upward air motion 2ms 1 occurred in a layer just above the melting layer while the frontal precipitation systems passed over the mountain ranges upstream flow appeared to be generally stable except for some weak conditional instability at low levels in the two improve 2 cases the cells occurred in a layer of strong shear at the top of a low level layer of apparently retarded or blocked flow shown by doppler radial velocity data the shear apparently provided a favorable environment for the turbulent cells to develop the updraft cells appeared at the times and locations where the shear was strongest 10 m s 1 km 1 the richardson number was slightly less than 0 25 at the level where the cells were observed suggesting shear generated turbulence could have been the origin of the updraft cells another possibility is that the rough mountainous lower boundary could have triggered buoyancy oscillations within the stable sheared flow the existence of turbulent cells made possible a precipitation growth mechanism that would not have been present in a laminar upslope flow the turbulent cells appeared to facilitate the rapid growth and fallout of condensate generated over the lower windward slopes of the mountains in a laminar flow over terrain upward motions would be unlikely to produce liquid water contents adequate to increase the density and hence the fall speed of precipitating ice particles by riming the turbulent updraft cells apparently create pockets of higher values of liquid water content embedded in the widespread frontal cloud system and snow particles falling from the parent cloud systems can then rapidly rime within the cells and fall out observations by polarimetric radar and direct aircraft sampling indicate the occurrence of rimed aggregate snowflakes and or graupel in the turbulent layer inasmuch as the shear layer is the consequence of retardation or blocking of the low level crossbarrier flow and the turbulence is a response to the shear the shear induced cellularity is an indirect response of the flow to the topography the turbulence embodied in this orographically induced cellularity allows a quick response of the precipitation fallout to the orography since aggregation and riming of ice particles in the turbulent layer produce heavier more rapidly falling precipitation particles without the turbulent cells condensate would more likely be advected farther up and perhaps even over the mountain range small scale cellularity has traditionally been associated with the release of buoyant instability by the upslope flow our results suggest that cellularity may be achieved even if buoyant instability is weak or nonexistent so that even a stable flow has the capacity to form cells that will enhance the precipitation fallout over the windward slopes

automated classifications of topography from dems by an unsupervised nested means algorithm and a three part geometric signature abstract an iterative procedure that implements the classification of continuous topography as a problem in digital image processing automatically divides an area into categories of surface form three taxonomic criteria slope gradient local convexity and surface texture are calculated from a square grid digital elevation model dem the sequence of programmed operations combines twofold partitioned maps of the three variables converted to greyscale images using the mean of each variable as the dividing threshold to subdivide increasingly subtle topography grid cells sloping at less than mean gradient of the input dem are classified by designating mean values of successively lower sloping subsets of the study area nested means as taxonomic thresholds thereby increasing the number of output categories from the minimum 8 to 12 or 16 program output is exemplified by 16 topographic types for the world at 1 km spatial resolution srtm30 data the japanese islands at 270 m and part of hokkaido at 55 m because the procedure is unsupervised and reflects frequency distributions of the input variables rather than pre set criteria the resulting classes are undefined and must be calibrated empirically by subsequent analysis maps of the example classifications reflect physiographic regions geological structure and landform as well as slope materials and processes fine textured terrain categories tend to correlate with erosional topography or older surfaces coarse textured classes with areas of little dissection in japan the resulting classes approximate landform types mapped from airphoto analysis while in the americas they create map patterns resembling hammond s terrain types or surface form classes srtm30 output for the united states compares favorably with fenneman s physical divisions experiments are suggested for further developing the method the arc info aml and the map of terrain classes for the world are available as online downloads

fabric development as the key for forming ductile shear zones and enabling plate tectonics abstract lithospheric deformation on earth is localized under both brittle and ductile deformation conditions as high temperature ductile rheologies are fundamentally strain rate hardening the formation of localized ductile shear zones must involve a structural or rheological change or a change in deformation conditions such as an increase in temperature in this contribution i develop a localization potential that quantifies the weakening associated with these changes the localization potential corresponds to the increase in strain rate resulting from that change under constant stress conditions i provide analytical expressions for the localization potential associated with a temperature increase grain size reduction an increase in water fugacity melt content or the abundance of a weak mineral phase i show that these processes cannot localize deformation from a mantle convection scale 103 km to a ductile shear zone scale 1 km to achieve this is it necessary to invoke a structural transition whereby the weak phase in a rock forms interconnected layers this process is efficient only if one phase is much weaker than the others or if the weakest phase has a highly non linear rheology micas melt and fine grained aggregates unless dry rheologies are used have the necessary characteristics as none of these phases is expected to be present in the dry lithosphere of venus this concept can explain why venus unlike the earth does not display a global network of plate boundaries the diffuse plate boundary in the central indian ocean may be as yet non localized because serpentinization has not reached the ductile levels of the lithosphere

deep orographic storms over the sierra nevada part i thermodynamic and kinematic structure abstract two deep orographic storms were documented over the sierra nevada with an instrumented aircraft and with a single doppler radar in both storms the geographic winds were normal to the barrier with speeds of 15 to 30 m s 1 because of blocking the measured wind component normal to the barrier was substantially less than the geostrophic wind component especially below barrier crest height in the very stable case a barrier jet was present below 1 km agl and had peak winds of 28 m s 1 in the slightly stable case a barrier jet was present at 1 km agl and had peak winds of 21 m s 1 other than the speed and altitude of the barrier jet the other measured characteristics of the airflow and thermal fields were rather similar between these two storms the forced ascent of stable air plus the diabatic process of melting caused the isotherms to descend near the barrier the barrier jet can be expressed by the thermal wind relation and is therefore a quasi geostrophic phenomenon the derived vertical

cross barrier flow during orographic precipitation events results from map and improve abstract ground based and airborne doppler radar data collected during passage of frontal rainstorms over the european alps and cascade mountains of oregon are found to exhibit characteristic cross barrier flow and precipitation patterns a stably stratified layer of blocked or partially blocked low momentum flow below mountain crest level is separated from strong cross barrier flow aloft by a concentrated layer of vertical wind shear this shear layer slopes upward toward the mountain crest and persists for several hours as the storm passes over the mountain range this pattern is remarkably similar from case to case and from one mountain range to the other the orographically enhanced precipitation in these cases exhibits stratiform structure marked by a radar bright band which often drops to a lower height indicating locally cooler conditions immediately adjacent to the windward mountain slopes a terrain induced gravity wave produces strong downslope flow and spillover of precipitation onto the

continental fault structure and the shallow earthquake source plate boundaries in continental crust are generally less sharply defined than in the oceans with seismicity spread over broad areas interplate displacements appear to be largely accommodated by networks of major fault zones a simple 2 level model for these important structures accounts for the depth distribution of most continental earthquakes and for the observed range of faulting styles and associated rock deformation textures the model consists of a seismogenic frictional slip regime overlying quasi plastic mylonite belts wherein shearing is largely accommodated aseismically due mainly to the changing response of quartz to deformation with increasing temperature shear resistance increases with depth to a peak value in the vicinity of the frictiona1 quasi plastic transition and then decreases rapidly the depth to which microseismic activity extends appears inversely related to regional heat flow and can be satisfactorily modelled as the frictional quasi plastic transition for different geotherms using laboratory determined flow laws for quartz bearing rocks larger earthquake ruptures m 5 5 tend to nucleate near the base of the seismogenic regime in the region inferred to have the highest shear resistance and concentration of distortional strain energy consideration is also given to the depression of isotherms and seismic activity in regions of thrusting and to the question of the downward continuation of major fault zones through the lithosphere decoupling of the upper crust on flat lying shear zones may accompany higher level dip slip and perhaps in some circumstances strike slip faulting being favoured by above average continental heat flow and a high quartz content in the middle or deep crust the average level of deviatoric stress within the seismogenic regime remains an outstanding problem

insights into the mechanics of en echelon sigmoidal vein formation using ultra high resolution photogrammetry and computed tomography abstract two novel techniques photo based reconstruction photogrammetry and computed tomography ct are used to investigate the formation of an exceptional array of sigmoidal veins in a hand sample from cape liptrap southern victoria and to provide constraint on models for their development the accuracies of the photogrammetric models were tested by comparison with a laser scan generated three dimensional 3d model the photogrammetric model was found to be accurate to at least 0 25 mm and substantially more detailed than the laser scan a methodology was developed by which 3d structural measurements could be extracted from the photogrammetric model this was augmented with the ct model which through its capacity to elucidate internal structure was used to constrain the geometry and linkage of structures within the rock volume the photogrammetric and ct data were then combined with detailed photomicrographs to evaluate the evolution of the sigmoidal veins in the sample the angle between the sigmoidal vein margins and an inferred shear zone as well as the orientations of the crystal fibres were found to imply a rotation of 27 however coeval pressure solution seams and older veinlets in the rock bridges between the veins were only found to have rotated by 10 an observation not easily explained using existing models for sigmoidal vein formation a new model is proposed in which a significant component of sigmoidal vein geometry is due to localised dilation caused by slip on the pressure solution seams the process involves strain partitioning onto pressure solution seams which leads to exaggeration of sigmoidal vein geometries if not accounted for the apparent vein rotation due to slip partitioning introduces errors into calculations of simple shear and volume strain based on sigmoidal arrays of this type furthermore the ct data demonstrated that in 3d the veins are continuous and channel like implying a far higher degree of connectivity and fluid transport than is suggested by their 2d form

stability and charging characteristics of the comma head region of continental winter cyclones abstractthis paper presents analyses of the finescale structure of convection in the comma head of two continental winter cyclones and a 16 storm climatology analyzing the distribution of lightning within the comma head a case study of a deep cyclone is presented illustrating how upper tropospheric dry air associated with the dry slot can intrude over moist gulf air creating two zones of precipitation within the comma head a northern zone characterized by deep stratiform clouds topped by generating cells and a southern zone marked by elevated convection lightning when it occurred originated from the elevated convection a second case study of a cutoff low is presented to examine the relationship between lightning flashes and wintertime convection updrafts within convective cells in both storms approached 6 8 m s 1 and convective available potential energy in the cell environment reached approximately 50 250 j kg 1 radar measurements obtained in convective updraft regions showed enhanced spectral

enrichment of co2 in fluid inclusions in quartz by removal of h2o during crystal plastic deformation abstract ductile strain induced leakage of h 2 o from mixed co 2 h 2 o fluid inclusions in quartz is proposed as a mechanism for producing occurrences of pure co 2 fluid inclusions in metamorphic rocks the h 2 o needed for hydrolytic weakening of quartz under stress may be provided by the h 2 o in fluid inclusions with dislocation creep as dislocations nucleate on the walls of fluid inclusions or intersect them h 2 o can be transported with the dislocations from the inclusion to the grain boundaries the process should continue so long as there is stress on the host quartz and the inclusion contains h 2 o the h 2 o taken to the grain boundaries would due to its wetting properties be wicked out along the grain boundaries if the h 2 o is totally removed from an inclusion by a flux of dislocations through the quartz during the crystal plastic flow then a residual inclusion bearing components other than water should remain a mixed co 2 h 2 o inclusion would as a consequence of the process become a pure co 2 fluid inclusion during dynamic recrystallization the co 2 would collect at grain boundary triple junctions and following grain boundary migration would become incorporated into the recrystallized quartz as fluid inclusions this mechanism of generating pure co 2 inclusions could result in co 2 fluid inclusions having densities appropriate for the pressure temperature conditions during deformation using estimates of temperature of deformation the total confining pressure during deformation could be determined from the density of the co 2 fluid in these inclusions

the role of cloud top generating cells and boundary layer circulations in the finescale radar structure of a winter cyclone over the great lakes abstractdata from airborne w band radar are used in conjunction with thermodynamic fields from the weather research and forecasting model and air parcel back trajectories from the hysplit model to investigate the finescale reflectivity vertical motion and airmass structure of the comma head of a winter cyclone in the vicinity of the great lakes cloud top generating cells formed along an upper level frontal boundary vertically separating dry air which 48 h earlier was located in the upper troposphere over south central canada from moist air which was located in the lower troposphere over the southeast united states the stronger updrafts within the generating cells had vertical velocities ranging from 1 to 3 m s 1 the generating cells were important to precipitation production within the comma head precipitation trails formed within the generating cells could sometimes be followed to the boundary layer before merging boundary layer air beneath the cyclone s comma head exhibited convective circulati

fluid inclusions tectonic indicators abstract during the first half of the 20th century fluid inclusions have been studied in ore geology in order to determine the chemistry and physical parameters density of the mineralising fluids apart from a few pioneering works in the middle of the century fluid inclusions were not used as structural markers before the late 1980s during the same time experiments as well as observations of natural samples have shown that the volume shape and density of fluid inclusions may change when submitted to pressure temperature conditions different from their trapping isochores in view of these experiments and based on natural examples from the higher himalaya metamorphic rocks it is evident how fluid inclusions can be used as thermobarometric structural and tectonic markers points of interest for further studies on fluid inclusions in nature and experiments are also stressed

semi automated classification of exposed bedrock cover in british columbia s southern mountains using a random forest approach abstract knowledge of the spatial distribution of exposed bedrock eb is essential for natural resource inventories environmental monitoring and landscape evolution modelling this paper presents a method for the use of a random forest rf classifier and legacy land data to locate areas of eb in a mountainous landscape of southern british columbia canada eb map accuracy increased from 48 to 88 with the use of rf models in comparison to the legacy land cover maps reducing the total number of predictor variables from 43 to 17 had a negligible effect on prediction accuracy meaningful relationships between eb predictions and important predictor variables were observed in partial dependence plots these findings emphasize that substantial improvement in eb map accuracy is possible with a limited number of predictor variables and interpretation of such maps is improved where the relationships between specific predictor variables and predicted classes can be observed and evaluated

discrimination of annealed and dynamic fabrics consequences for strain localization and deformation episodes of large scale shear zones abstract large scale shear zones are often characterized by long lasting deformation with complex strain localization behavior based on a drill core across polymineralic carbonate mylonites of the doldenhorn nappe helvetic alps switzerland the present study uses spatially resolved microstructural variations to discriminate unambiguously deformation microstructures from annealed ones to infer the deformation mechanisms and to reconstruct the strain localization history these goals require quantitative microstructural and textural analyses of sample suites in sections across the shear zone particularly the occurrence of two distinct zener trends i e the relationship between grain size and volume fraction of matrix and second phase grains allows for the identification of annealed from dynamic microstructures the data presented here indicate that continued shearing after peak metamorphic conditions and during exhumation induced cooling resulted in progressive strain localization at the base of the shear zone while the inactive parts of the formerly high temperature shear zone were progressively overprinted by annealing

fluid inclusion petrography abstract a procedure of fluid inclusion studies is proposed with emphasis on the criteria of selecting fluid inclusions for detailed microthermometry and spectroscopic analysis an overview of descriptive and genetic classifications of fluid inclusions in single crystals and in massive rocks is given with the intention of further differentiating the commonly used terms primary and secondary fluid inclusions some principles of fluid inclusion modification are explained cathodoluminescence cl studies of quartz with the optical high power cl microscope and the electron microprobe provided with a cl detector are an important help in fluid petrography cl textures are subdivided in primary growth textures and a wide variety of secondary microtextures which are in part induced by fluid inclusions the latter is grouped in textures indicative of local lower crystal order increasing defect structures and microtextures indicative of local quartz healing reduction of the defect structures microtextures showing the genetic relationship between fluid inclusions and the host mineral provide information about the possible post entrapment changes of fluid inclusions and therewith testify their geological relevance

development of sigmoidal en echelon microfractures in beryl and the role of strain localization evidenced by fluid inclusions abstract a combined fluid inclusion and microstructural study was carried out in beryl crystals from the san cayetano nb ta bearing pegmatite san luis argentina primary aqueous carbonic fluids t0 were subsequently re trapped during shearing resulting in en echelon microfractures the more brittle behaviour of beryl compared to quartz makes this mineral more suitable for the preservation of fluid inclusions and microstructures the primary inclusions t0 are preserved in strain free domains whereas the pseudo secondary t1 to t3 type inclusions occur in domains showing intracrystalline deformation co2 was relatively immobile or reacted to form carbonate in early t1 type inclusions whereas h2o preferentially migrated along microfractures and was trapped as t2 and t3 type inclusions short intragranular trails of fluid inclusions representing en echelon healed microfractures resulted from progressive strain localization contrary to previous proposals this new model implies the progressive thickness reduction of intracrystalline micro shear zones besides hydrolytic weakening linked to dislocation glide is the most likely mechanism to explain the evolution of fluid inclusions with intracrystalline deformation enhancing anisotropic diffusion this study highlights the potential of combined fluid inclusion and microstructural studies in order to understand the interaction between fluid activity and deformation in this way valuable insights can be provided into the progressive development of overprinted fabrics and low to medium temperature deformation mechanisms of minerals

cosmo skymed and terrasar x datasets for geomorphological mapping in the eastern of marajo island amazon coast abstract the amazon coast is marked by the high discharge of sediments and freshwater macrotidal influence a wide continental shelf extensive flood plains and lowered plateaus which make it unique as a delta and estuary landscape further the tropical climate imposes heavy rains and incessant cloudiness that render microwave systems more suitable for cartography this study proposed to recognize and map the amazon coastal environments through the x band synthetic aperture radar provided by cosmo skymed csk and terrasar x tsx systems the sar datasets consisted of interferometric and stereo pairs restricted to single revisit and obtained with small interval 1 11 days under steeper 0 60 during the rainy and dry season showing more suitability for radargrammetry on the amazon coast the rf models resulted in kappa coefficient between 0 39 to 0 70 indicating that the use of x band sar images at an incidence angle greater than 44 and obtained in the dry season is more appropriated for the morphological mapping the rf models given by tsx achieved the higher mapping accuracies per scenario of sar products in order of 0 48 to 0 63 despite this the best classification was carried out by 19 rf model with 0 70 provided by csk in shallow incidence composed by intensity texture coherence and stereo dsm the csk and tsx data allowed to map the amazon coast precisely based on x band at single polarization high spatial resolution and revisit which has demonstrated the support for detailed cartography scale 1 50 000 and frequent updating monthly up to yearly

notes and correspondence polarimetric radar observation of multiple freezing levels abstract an unusual multiple freezing level event observed with polarimetric radar during the second phase of the improvement of microphysical parameterization through observational verification experiments improve 2 field program is described the event occurred on 28 november 2001 when a warm front moved over the oregon cascade mountains as the front approached an elevated melting layer formed above a preexisting melting layer near ground continued warming of the lower atmosphere eventually dissipated the lower melting layer the polarimetric measurements are used to estimate the height of the freezing levels document their evolution and deduce hydrometeor habits the measurements indicate that when the two freezing levels were first observed melting was incomplete in the upper melting layer and characteristics of particles that passed through the two melting layers were similar as warming progressed the character of particles entering the lower melting layer changed possibly becoming ice pell

mesoscale organization and cloud microphysics in a bay of bengal depression abstract airborne radar and cloud microphysical data were obtained throughout a monsoon depression observed over the bay of bengal on 3 8 july 1979 during the summer monsoon experiment of the global atmospheric research programme the precipitation in the disturbance occurred in mesoscale rain areas 100 300 km in horizontal dimension with the largest areas tending to be elongated in the east west or northwest southeast direction these mesoscale precipitation features resembled the rain areas of equatorial cloud clusters each mesoscale precipitation feature contained intense convective cells but the area covered by rain was predominantly stratiform the convective cells in the mesoscale features were sometimes arranged in rapidly moving rather narrow arc shaped east west lines with the stratiform precipitation trailing the line in other cases the convective cells were more randomly embedded in the stratiform rain ice particle images obtained at flight level temperatures of 5 to 25 c indicated the

expert driven semi automated geomorphological mapping for a mountainous area using a laser dtm in this paper a semi automated method is presented to recognize and spatially delineate geomorphological units in mountainous forested ecosystems using statistical information extracted from a 1 m resolution laser digital elevation dataset the method was applied to a mountainous area in austria first slope angle and elevation characteristics were determined for each key geomorphological unit occurring in the study area second a map of slope classes derived from the laser dtm was used in an expert driven multilevel object oriented approach the resulting classes represent units corresponding to landforms and processes commonly recognized in mountain areas fluvial terrace alluvial fan slope with mass movement talus slope rock cliff glacial landform shallow incised channel and deep incised channel the classification result was compared with a validation dataset of geomorphological units derived from an analogue geomorphological map for the above mentioned classes the percentages of correctly classified grid cells are 69 79 50 64 32 61 23 and 70 respectively the lower values of 32 and 23 are mainly related to inaccurate mapping of rock cliffs and shallow incised channels in the analogue geomorphological map the accuracy increased to 76 and 54 respectively if a buffer is applied to these specific units it is concluded that high resolution topographical data derived from laser dtms are useful for the extraction of geomorphological units in mountain areas

supervised classification of types of glaciated landscapes using digital elevation data abstract automated approaches for identifying different types of glaciated landscapes using digitally processed elevation data were evaluated we tested the ability of geomorphic measures e g elevation relative relief roughness and slope gradient derived from digital elevation models dems to differentiate glaciated landscapes using maximum likelihood classification and artificial neural networks ann the automated methods were trained and validated using an existing quaternary geology map and a manual interpretation of the contour data portrayed on topographic quadrangles the need for such methods arises from efforts to classify types of landscapes e g ecoregions in michigan one fundamental control of the landscape structure in michigan including soil type and vegetation is the underlying sedimentary and landform assemblages produced by an array of glacial processes during the waning phase of the pleistocene traditional methods for identifying different landscapes e g ice contact landscapes stagnation landscapes have relied on printed topographic maps and have been very effective but time consuming the maps resulting from the four supervised classification trials had between 51 and 61 agreement with the original quaternary geology map the output from the maximum likelihood classification had slightly higher agreements than the output from the neural net which is attributed to the generalization inherent in the quaternary geology map compared with the nature of the classifier for the neural net the neural net however identifies significant detail and non linear relationships between classification inputs and output classes future work should incorporate a map of soils into the classification

airborne doppler observations of a landfalling cold front upstream of steep coastal orography abstract this study uses airborne doppler radar observations to describe the mesoscale structure and evolution of a cold frontal system as it made landfall on the mountainous coast of oregon and northern california on 1 december 1995 during the coastal observations and simulations with topography experiment this section of coastline constitutes a steep approximately two dimensional north south oriented orographic barrier the front exhibited a northeast southwest orientation and thus intersected the axis of high terrain at an acute angle the along barrier pressure gradient and low level winds increased with time along the coastal zone and reached a maximum as the front made landfall stably stratified prefrontal flow was strongly blocked by the orography resulting in a confluent transition from pervasive southwesterly winds offshore to a narrow zone of accelerated south southwesterly flow near the coast where wind speeds approached 30 m s 1 at a height of 750 m above mean sea level postfrontal flow

shear zone deformation determined from sigmoidal tension gashes the potential of using sigmoidal tension gashes as strain markers for assessing strain localisation in shear zones is discussed the appropriate analytical methods for this purpose depend on the assumed mechanism of tension gash formation two such models are considered the first is one in which the curvature of the gash is produced by passive rotation of different segments of the gash in response shear strain gradients across the shear zone the other model is one in which the curvature of the gashes is governed by the folding of the competent rock bridges between adjacent gashes in the latter case the tension gashes progressively grow within spaces created by the buckling bridges and therefore lead to a bulk dilatation of the shear zone however for the folded bridge mechanism to continue to operate beyond shear strains greater than unity requires a significant volume loss which in turn may signal the increase of the shear strength of the zone the geometrical characteristics of gash arrays resulting from these two mechanisms are described and criteria given for the recognition of the two types of gash arrays a new graphical method is proposed for the analysis of deformation in shear zones containing folded bridge tension gashes tension gash arrays from marloes west wales are used as examples of the procedures for shear zone analysis

the improve 1 storm of 1 2 february 2001 part ii cloud structures and the growth of precipitation abstract on 1 2 february 2001 a strong cyclonic storm system developed over the northeastern pacific ocean and moved onto the washington coast this storm was one of several that were documented during the first field phase of the improvement of microphysical parameterization through observational verification experiment improve in the 1 2 february case soundings and wind profiler measurements showed that a wide cold frontal rainband was coincident with the leading edge of an upper level cold front in a classical warm occlusion ground based radar observations revealed the presence of subbands within the wide cold frontal rainband and two layers of precipitation generating cells within this rainband one at 5 7 km msl and the other at 9 10 km msl the lower layer of generating cells produced fallstreaks that were traced from the cells down to the radar bright band at 2 km msl observations suggest a connection between the subbands and the lower layer of generating cells a research aircraft equipped

the mesoscale and microscale structure and organization of clouds and precipitation in midlatitude cyclones part v the substructure of narrow cold frontal rainbands abstract the organization and structure of a narrow cold frontal rainband ncfr on the small mesoscale and the microscale have been investigated through quantitative radar reflectivity doppler radar observations airborne observations and surface measurements the ncfr was composed of small mesoscale regions of heavy precipitation called precipitation cores pcs oriented at an angle to the synoptic scale cold front in horizontal cross section the pcs were roughly elliptical in shape areas of lighter precipitation called gap regions grs separated the pcs the pcs were so oriented that their loading edges were regions of strong low level convergence the weather associated with the passage of a pc resembled that of a squall line gust front with concurrent windshifts and pressure checks occurring 5 min before heavy precipitation and a fall in temperature the changes in surface weather that accompanied the passage of a gr were more variable but tended to be less marked than for pcs thus the se

a mechanism for preferential h 2 o leakage from fluid inclusions in quartz based on tem observations preferential leakage of h2o from fluid inclusions containing multiple gas components has been suspected in natural metamorphic rocks and has been demonstrated experimentally for synthetic h2o co2 rich inclusions in natural quartz knowledge of the physical and chemical characteristics of the leakage mechanism which may be very complex increases the value of natural fluid inclusions to metamorphic geology it is proposed that crystal defects play a major role in nondecrepitative preferential h2o leakage through quartz and remain effective during metamorphism inclusions with either an internal overpressure or underpressure produce strain in the adjacent quartz crystal via the nucleation of many dislocations and planar defects like dauphine twin boundaries these defects allow preferential loss of h2o from h2o co2 rich inclusions at supercritical conditions the transport capacity of this leakage mechanism is enhanced by nucleation of small bubbles on defect structures the nucleation of these bubbles seems to be a recovery process in strained crystals solubility gradients of quartz in water in a crystal with internally underpressurized inclusions may result in optical visible implosion halos in a three dimensional spatial arrangement caused by the growth of small bubbles at the expense of the larger original fluid inclusion natural fluid inclusions from naxos greece are always associated with numerous interlinked dislocations these dislocations may have been produced by plastic derormation or by crystal growth related processes e g crack healing the presence of small bubbles on these dislocations indicates that a similar leakage mechanism for h2o must have occurred in these rocks

airborne dual doppler observations of an intense frontal system approaching the pacific northwest coast airborne doppler radar data collected off the pacific northwest coast by a noaa wp 3d orion aircraft over an 8 h period on 8 december 1993 during the coastal observations and simulations with topography experiment reveal the mesoscale structure of an intense frontal system while it was well offshore and as it approached within 20 km of the oregon coastline during the offshore stage a portion of the narrow coldfrontal rainband was characterized by deep convective cores pseudo dual doppler analyses characterize the kinematic and precipitation structure of the deep convection pseudo dual doppler analyses describe the subsequent evolution of the narrow cold frontal rainband as it approached to within 20 km of the oregon coast deformation of the frontal zone appeared to cause the dissipation of one of three precipitation cores contained within the dual doppler area the precipitation cores and the strong convergence zone associated with the front conformed to some degree to the shape of the coastline near cape blanco oregon as the front neared the coast changes in the prefrontal flow that occurred as the front approached the coast were qualitatively consistent with theoretical and numerical studies of upstream orographic influence comparison of pseudo dual doppler derived velocity profiles with idealized numerical model calculations suggests that the nearshore evolution of the frontal rainband was significantly affected by an upstream influence of the coastal orography

the formation of a forward tilting cold front with multiple cloud bands during superstorm 1993 abstract a mesoscale model simulation is used to examine the evolution of the cold front and accompanying cloud bands in eastern mexico associated with superstorm 1993 12 14 march the simulated cold front differed in structure and evolution from a classical cold front in agreement with evidence from observations and european centre for medium range weather forecasts analyses the surface cold front as defined by the leading edge of strong northerlies and cold advection initially possessed a rearward tilt with height over southern texas within 6 h the leading edge of the front moved equatorward and developed a large scale forward tilt of greater than 200 km in the horizontal from the surface to 700 hpa this forward tilt occurred as a mid to upper tropospheric baroclinic zone arrived from over the sierra madre descended into eastern mexico and interacted with the surface cold front embedded within this large scale forward tilt was a locally enhanced horizontal potential temperature gradient tha

statistical estimation and generalized additive modeling of rock glacier distribution in the san juan mountains colorado united states 1 our goal is to quantify rock glacier abundance and analyze the topographic controls of rock glacier distribution patterns for this purpose we use statistical estimation techniques and generalized additive models relating rock glacier occurrences to terrain attributes significant applied results include the ability to determine water equivalence and denudation rates the statistical estimation of regional rock glacier abundance based on local interpretation of air photos is an efficient alternative to costly rock glacier inventories these presence absence data n 2933 also allow us to analyze the partly nonlinear topographic controls on rock glacier distribution with generalized additive models we apply these techniques in the san juan mountains 2874 km2 above 3400 m colorado where we obtained a total rock glacier surface area of 70 km2 corresponding to a water equivalence in the order of 0 50 0 76 km3 estimated rock glacier debris volumes imply postglacial denudation rates on the order of 0 5 1 1 mm yr 1 within the talus sheds of rock glaciers the distribution model shows the nonlinear factors of local slope slope of the contributing area local curvature and size of the contributing area controlling the probability of rock glacier occurrence the model yields an area under the receiver operating characteristics curve of 0 91 which indicates an excellent fit on the basis of the present results the integration of terrain attributes with remote sensing data will be the next step toward automatic mapping of rock glaciers in vast mountain areas

geomorphons a pattern recognition approach to classification and mapping of landforms abstract we introduce a novel method for classification and mapping of landform elements from a dem based on the principle of pattern recognition rather than differential geometry at the core of the method is the concept of geomorphon geomorphologic phonotypes a simple ternary pattern that serves as an archetype of a particular terrain morphology a finite number of 498 geomorphons constitute a comprehensive and exhaustive set of all possible morphological terrain types including standard elements of landscape as well as unfamiliar forms rarely found in natural terrestrial surfaces a single scan of a dem assigns an appropriate geomorphon to every cell in the raster using a procedure that self adapts to identify the most suitable spatial scale at each location as a result the method classifies landform elements at a range of different spatial scales with unprecedented computational efficiency a general purpose geomorphometric map an interpreted map of topography is obtained by generalizing allgeomorphons to a small number of the most common landform elements due to the robustness and high computational efficiency of the method high resolution geomorphometric maps having continental and even global extents can be generated from giga cell dems such maps are a valuable new resource for both manual and automated geomorphometric analyses in order to demonstrate a practical application of this new method a 30 m cell 1 geomorphometric map of the entire country of poland is generated and the features and potential usage of this map are briefly discussed the computer implementation of the method is outlined the code is available in the public domain

microcracks in rocks a review abstract in the past decade the number of studies about microcracks in rocks has rapidly increased this review of recent work concentrates on microcracks in rock as separate entities emphasizing microcrack morphogenesis kinematics dynamics population statistics and observational techniques cracks are produced when the local stress exceeds the local strength the local stress may be augmented by twin lamellae interactions kink bands and deformation lamellae stress concentrations at grain boundary contacts and around intracrystalline cavities local strength may be reduced along cleavage planes along grain boundaries and along any internal surface as a result of corrosion by chemically active fluids dislocations appear not to be a significant factor for crack nucleation below about 500 c in silicates spatial and temporal changes in temperature can also induce microcracking as a result of differential thermal expansion between grains with different thermoelastic moduli and thermal conductivities the amount of quartz in the rock has a significant effect on thermally induced microcracks because of its large and variable thermal expansivity the application of hydrostatic pressure between 100 and 200 mpa effectively closes most cracks but the closure may not be uniform if crack wall asperities exist hydrostatic pressure appears to stabilize cracks and make crack growth more difficult the number and average size of mechanically induced microcracks is greater in rock deformed at higher pressures the application of a deviatoric stress field on the boundaries of a rock mass results on a microscopic scale in a very complex stress system which greatly affects nucleation and propagation paths the relative amount of intragranular and intergranular cracking appears to depend upon mineralogy rock type and stress state the vast majority of stress induced microcracks in rocks appear to be extensional statistically they are predominantly oriented within 30 of the macroscopic maximum stress direction crack densities increase as macroscopic deviatoric stress increases above a threshold level crack size distributions may be either lognormal or exponential fracture in rock under compressive boundary loads is a result of the coalescence of many microcracks not the growth of a single crack some crack configurations are more favorable for coalescence than others as deviatoric stress increases and rock failure is approached the microcrack population changes spatially from random to locally intense zones of cracking away from the fault the crack density dies off rapidly to the background level a few grains away under lesser deviatoric stresses slow subcritical microcrack growth can occur as a result of stress aided corrosion at the crack tip the rate governing mechanism may be either the chemical reaction rate or the rate at which water can get to the crack tip important details still remain to be worked out

low temperature intracrystalline deformation microstructures in quartz a review of numerous genetic interpretations of the individual low temperature intracrystalline deformation microstructures in quartz shows that there is no consensus concerning their formation mechanisms therefore we introduce a new purely descriptive terminology for the three categories of intracrystalline deformation microstructures formed in the low quartz stability field fine extinction bands feb wide extinction bands web and localised extinction bands leb the localised extinction bands are further subdivided into blocky bleb straight sleb and granular gleb morphological types a detailed polarised light microscopy study of vein quartz from the low grade metamorphic high ardenne slate belt belgium further reveals a series of particular geometric relationships between these newly defined intracrystalline deformation microstructures these geometric relationships are largely unrecognised or underemphasised in the literature and need to be taken into account in any future genetic interpretation based on our observations and a critical assessment of the current genetic models we argue that the interpretation of the pertinent microstructures in terms of ambient conditions and deformation history should be made with care as long as the genesis of these microstructures is not better confined