the interrelation of glaciotectonic and glaciodepositional processes within the glacial environment abstract in recent years it has been recognised that ice sediment coupling occurred beneath the quaternary ice sheets that advanced over the soft sediments of lowland areas this paper looks in detail at the effects of this coupling on the sediments which results in glaciotectonic deformation and also discusses the interaction of deformation and deposition within the subglacial environment two types of glaciotectonic deformation are discussed that are produced by the active movement of ice 1 proglacial tectonics at the margin which include compressive fold styles such as listric thrusts and faults and open folding 2 subglacial tectonics formed beneath the glacier which include fold styles resulting from simple shear and represent a soft rock purely dynamic shear zone styles of deformation associated with stagnant ice are also investigated we argue that glaciotectonic deformation is a common phenomenon and an integral part of geological record from continental ice sheets it is suggested that zones of deformation within the sediment are related to similar zones of strain in the ice sheet and complex deformation sequences are produced by the superimposition of these differing styles upon one another as the ice sheet advances and retreats it is also argued that subglacial deposition and deformation are related and that on soft beds underformed till is rare whilst deformed till is very common

an efficient and comprehensive method for drainage network extraction from dem with billions of pixels using a size balanced binary search tree abstract with the increasing resolution of digital elevation models dems computational efficiency problems have been encountered when extracting the drainage network of a large river basin at billion pixel scales the efficiency of the most time consuming depression filling pretreatment has been improved by using the o n log n complexity least cost path search method but the complete extraction steps following this method have not been proposed and tested in this paper an improved o n log n algorithm was proposed by introducing a size balanced binary search tree bst to improve the efficiency of the depression filling pretreatment further the following extraction steps including the flow direction determination and the upslope area accumulation were also redesigned to benefit from this improvement therefore an efficient and comprehensive method was developed the method was tested to extract drainage networks of 31 river basins with areas greater than 500 000 km 2 from the 30 m resolution aster gdem and two sub basins with areas of approximately 1000 km 2 from the 1 m resolution airborne lidar dem complete drainage networks with both vector features and topographic parameters were obtained with time consumptions in o n log n complexity the results indicate that the developed method can be used to extract entire drainage networks from dems with billions of pixels with high efficiency

strain path partitioning within thrust sheets microstructural and petrofabric evidence from the moine thrust zone at loch eriboll northwest scotland abstract quartz c axis fabrics and microstructures have been investigated within a suite of quartzites collected from the loch eriboll area of the moine thrust zone and are used to interpret the detailed processes involved in fabric evolution the intensity of quartz c axis fabrics is directly proportional to the calculated strain magnitude a correlation is also established between the pattern of c axis fabrics and the calculated strain symmetry two kinematic domains are recognized within one of the studied thrust sheets which outcrops immediately beneath the moine thrust within the upper and central levels of the thrust sheet coaxial deformation is indicated by conjugate mutually interfering shear bands globular low strain detrital quartz grains whose c axes are aligned sub parallel to the principal finite shortening direction z and quartz c axis fabrics which are symmetric both in terms of skeletal outline and intensity distribution with respect to mylonitic foliation and lineation non coaxial deformation is indicated within the more intensely deformed and recrystallized quartzites located near the base of the thrust sheet by single sets of shear bands and c axis fabrics which are asymmetric with respect to foliation and lineation tectonic models offering possible explanations for the presence of kinematic strain path domains within thrust sheets are considered

strain patterns in models of spreading gliding nappes three experiments have been carried out in order to study the progressive and finite strain in nappes where gravitational spreading and gliding occur together these experimental models were made from analogue materials able to collapse under their own weight on an inclined plane throughout most of the models the stretch trajectories in a vertical plane parallel to the flow show a low amplitude sigmoidal pattern consistent with a previous theoretical model other stretch trajectories exist at the front and back ends of each model the kinematic significance of all these trajectories is discussed in detail highest strain intensities are always found next to the base of the model strain paths calculated at different stages of flow indicate clearly that nowhere in the model is the motion simple there is a complex combination in time and space of simple and pure shear except at the base of the model where the motion approximates a simple shearing near the two parallel lateral sides of the model a lateral boundary effect can be observed from the strong curvature of the transverse markers surface grid and vertical layers strain paths have also been estimated in this complex zone where wrench shearing is superimposed upon vertical shortening and thrust shearing the geological implications of these experimental models are discussed in relation to recent theoretical studies and field work

an investigation of the deforming layer debris rich basal ice continuum illustrated from three alaskan glaciers three small alaskan glaciers with different bed conditions were studied exit glacier had a thin deforming layer and produced subglacial and proglacial glaciotectonic land forms childs glacier also had a thin deforming layer but the upper part was frozen to the ice matanuska glacier had no deforming layer but had subglacial debris rich ice since it has been shown that sediment at the base can account for the majority of ice movement it is suggested that there is a deforming bed debris rich continuum whereby similar processes occur throughout the different subglacial environments these include similar longitudinal deformation patterns compression at the margin extension and simple shear up glacier similar vertical deformation patterns increase in deformation and fabric strength upwards through the sequence leading to the attenuation of stratified ice into dispersed ice and similar and interrelated incorporation processes the major differences were that the processes occurred at a much faster rate within the deforming layer and that probably only the deforming layer will be recorded in the geological record

the deforming bed debris rich basal ice continuum and its implications for the formation of glacial landforms flutes and sediments melt out till abstract there are two potentially important shear zones at the base of the glacier the deforming layer and or the debris rich basal ice layer these two layers have a significant effect on glacier motion and glacial erosional depositional and sedimentary processes however it is shown that most of the processes operating within these two layers are very similar this includes compression at the ice margin longitudinal extension and simple shear upglacier similar styles of shear zone and associated fabric development and similar incorporation transport and depositional processes in the past many criterion have been developed to identify distinct deposition from the deforming layer and the debris rich basal ice layer however if the processes within these layers are similar then it makes the distinct identification of these two separate layers in the geological record very difficult however it is also shown that the main differences between the two layers include rates of sediment movement processes and preservation potential the later is very important as it appears that the two layers are interconnected and that material is melted out from the debris rich basal ice to form a significant component of the deforming layer in this way the final depositional imprint is from the deforming layer and there is little likelihood of the debris rich basal ice layer being preserved undeformed this is demonstrated from modern glacial environments pleistocene flute studies and studies of pleistocene melt out tills from the u k u s a and germany

automated recognition of valley lines and drainage networks from grid digital elevation models a review and a new method abstract the literature on valley and drainage line recognition from grid digital elevation models dems is reviewed two problems preventing the successful delineation of fully connected drainage networks of single line width are identified a the positioning of the ends of drainage networks and b the assignment of drainage directions to a dem in particular the assignment of drainage directions across flat areas and at closed depressions in the dem pits a new method for drainage network delineation is suggested which incorporates an alternative method for drainage direction assignment over a dem this method is found to produce realistic directions and performs well on two complex dems

stage dependent hydraulic and hydromorphologic properties in stream networks translated into response functions of compartmental models a distributed non uniform routing model was constructed and applied to two stream networks in southern sweden to investigate the effects of stage topology and morphology on advective travel times

progressive deformation in anisotropic rocks abstract field observations show that the majority of crustal rocks possess a penetrative foliation defined by either compositional layering preferred orientations of crystals or both ductile deformation involving planar anisotropy of viscosity can be characterized by an anisotropy factor q n r s the ratio of the bulk viscosities in pure and simple shear respectively this ratio of the normal and shear viscosities may be determined analytically if the anisotropy is resolvable in a multilayer sequence with individual laminae of isotropic viscosity in that case the resistance to normal compression will be largely controlled by the competent layers whereas the resistance to shear is controlled by the soft layers more specifically the viscosities of the individual laminae add up like resistances in series and in parallel in the expressions for the normal and shear viscosities respectively the reorientation of the bulk stress within an anisotropic multilayer is systematically investigated for a range of anisotropy factors the mode of progressive deformation is controlled only by the anisotropy factor and the orientation of the principal deviatoric stress the rate of deformation can be scaled if the bulk normal viscosity and the magnitude of the principal deviatoric stress are also known the results are illustrated in a series of nomograms showing the spectrum of strain and rotation histories possible in rock volumes deforming with planar anisotropy it appears that with increasing anisotropy factor the deformation spectrum will narrow on simple shear irrespective of the orientation of the background or bulk deviatoric stress axes plane strain and isochoric conditions are assumed throughout the analysis

determination of the drainage structure of a watershed using a digital elevation model and a digital river and lake network abstract distributed hydrological models require a detailed definition of a watershed s internal drainage structure the conventional approach to obtain this drainage structure is to use an eight flow direction matrix d8 which is derived from a raster digital elevation model dem however this approach leads to a rather coarse drainage structure when monitoring or gauging stations need to be accurately located within a watershed this is largely due to limitations of the d8 approach and the lack of information over flat areas and pits the d8 approach alone is also unable to differentiate lakes from plain areas to avoid these problems a new approach using a digital river and lake network drln as input in addition to the dem has been developed this new approach allows for an accurate fit between the drln and the modelled drainage structure which is represented by a flow direction matrix and a modelled watercourse network more importantly the identification of lakes within the modelled network is now possible the proposed approach which is largely rooted in the d8 approach uses the drln to correct modelled flow directions and network calculations for dem cells overlapped by the drln flow directions are determined using drln connections only the flow directions of the other dem cells are evaluated with the d8 approach which uses a dem that has been modified as a function of distance to the drln the proposed approach has been tested on the chaudiere river watershed in southern quebec canada the modelled watershed drainage structure showed a high level of coherence with the drln a comparison between the results obtained with the d8 approach and those obtained by the proposed approach clearly demonstrated an improvement over the conventionally modelled drainage structure the proposed approach will benefit hydrological models which require data such as a flow direction matrix a river and lake network and sub watersheds for drainage structure information

digital terrain modelling a review of hydrological geomorphological and biological applications the topography of a catchment has a major impact on the hydrological geomorphological and biological processes active in the landscape the spatial distribution of topographic attributes can often be used as an indirect measure of the spatial variability of these processes and allows them to be mapped using relatively simple techniques many geographic information systems are being developed that store topographic information as the primary data for analysing water resource and biological problems furthermore topography can be used to develop more physically realistic structures for hydrologic and water quality models that directly account for the impact of topography on the hydrology digital elevation models are the primary data used in the analysis of catchment topography we describe elevation data sources digital elevation model structures and the analysis of digital elevation data for hydrological geomorphological and biological applications some hydrologic models that make use of digital representations of topography are also considered

scale effects on the estimation of erosion thresholds through a distributed and physically based hydrological model abstract slope incision and subsequent development of rills gullies and channels are responsible for significant soil losses and are often irreversible with very high restoration costs particularly in semiarid environments the location of potential areas of erosion where these processes occur is vital to land management and conservation the study of the relationship between the local slope s and the drainage area a through the geomorphological relationship s a b combined with hydrologic simulation models has proved to be appropriate for the identification and characterisation of potential areas of incision especially when it takes into account the spatial distribution of soil properties and the evolution of hydrological processes however physical properties of soil digital elevation models dems and flow algorithms used may affect the results this study employs a distributed physically based hydrological model to evaluate the infiltration runoff relationships and their influence on selecting critical area from three dems with different resolutions the results show a significant scale effect on flow distribution and the location of threshold points on slopes the results obtained from a 30 m dem significantly differ from those obtained from 10 and 5 m dems because the former was unable to capture the spatial variability of geomorphic processes the selected set of critical points shows high s a correlations for different values of critical shear stress the physical model confirmed the dominance of surface runoff in the study site and was validated from field identification of erosion risk areas although for incision areas

the treatment of flat areas and depressions in automated drainage analysis of raster digital elevation models methods developed to process raster digital elevation models dem automatically in order to delineate and measure the properties of drainage networks and drainage basins are being recognized as potentially valuable tools for the topographic parameterization of hydrological models all of these methods ultimately rely on some form of overland flow simulation to define drainage courses and catchment areas and therefore have difficulty dealing with closed depressions and flat areas on digital land surface models some fundamental assumptions about the nature of these problem topographic features in dem are implicit in the various techniques developed to deal with them in automated drainage analysis the principal assumptions are 1 that closed depressions and flat areas are spurious features that arise from data errors and limitations of dem resolution 2 that flow directions across flat areas are determined solely by adjacent cells of lower elevation and 3 that closed depressions are caused exclusively by the underestimation of dem elevations it is argued that while the first of these assumptions is reasonable given the quality of dems generally available for hydrological analysis the others are not rather it seems more likely that depressions are caused by both under and overestimation errors and that flow directions across flat areas are determined by the distribution of both higher and lower elevations surrounding flat areas two new algorithms are introduced that are based on more reasonable assumptions about the nature of flat areas and depressions and produce more realistic results in application these algorithms allow breaching of depression outlets and consider the distribution of both higher and lower elevations in assigning flow directions on flat areas the results of applying these algorithms to some real and hypothetical landscapes are presented 1998 john wiley sons ltd

height above the nearest drainage a hydrologically relevant new terrain model summary this paper introduces a new terrain model named hand and reports on the calibration and validation of landscape classes representing soil environments in amazonia which were derived using it the hand model normalizes topography according to the local relative heights found along the drainage network and in this way presents the topology of the relative soil gravitational potentials or local draining potentials the hand model has been demonstrated to show a high correlation with the depth of the water table providing an accurate spatial representation of soil water environments normalized draining potentials can be classified according to the relative vertical flowpath distances to the nearest drainages defining classes of soil water environments these classes have been shown to be comparable and have verifiable and reproducible hydrological significance across the studied catchment and for surrounding ungauged catchments the robust validation of this model over an area of 18 000 km2 in the lower rio negro catchment has demonstrated its capacity to map expansive environments using only remotely acquired topography data as inputs the classified hand model has also preliminarily demonstrated robustness when applied to ungauged catchments elsewhere with contrasting geologies geomorphologies and soil types the hand model and the derived soil water maps can help to advance physically based hydrological models and be applied to a host of disciplines that focus on soil moisture and ground water dynamics as an original assessment of soil water in the landscape the hand model explores the synergy between digital topography data and terrain modeling presenting an opportunity for solving many difficult problems in hydrology

channel initiation and the problem of landscape scale since the 1940s it has been proposed that landscape dissection into distinct valleys is limited by a threshold of channelization that sets a finite scale to the landscape this threshold is equal to the hillslope length that is just shorter than that necessary to support a channel head a field study supports this hypothesis by showing that an empirically defined topographic threshold associated with channel head locations also defines the border between essentially smooth undissected hillslopes and the valley bottoms to which they drain this finding contradicts assertions that landscapes are scale independent and suggests that landscape response to changes in climate or land use depends on the corresponding changes in the threshold of channelization

experiments on folding in spreading gliding nappes abstract a small scale model of spreading gliding nappe was used to study the development of folds which are controlled by the geometry of external boundaries throughout in the model the deformation combines pure shear and simple shear recumbent folds are produced above irregularities of the base the cylindricity of folds is directly dependant on the cylindricity of basal irregularities models with homogeneous rheological properties produce only recumbent folds whereas models of contrasting rheological properties produce recumbent folds and en echelon upright folds in the zones of lateral shear the experiments demonstrate that 1 a large scale recumbent folds in nappes can result from passive amplification processes in unsteady shear flow 2 b upright folds and coaxial refolding result from mechanical instability due to contrasting rheological properties between layers and develop during a unique progressive deformation these laws can be directly applied to a spreading gliding nappe but also on a larger scale to all nappes in which the shear component dominates the deformation

determination of finite strain from passive initially planar markers deflected in ductile rocks undergoing simultaneous superposition of heterogeneous strains abstract from an empirical model of strain in ductile heterogeneous shear zones simultaneously undergoing a bulk pure shear we study the influence of the parameters of the deformation on the shape changes of passive initially planar markers and describe a method for determining the finite strain and even sometimes the instantaneous strain from these deflected markers

complex strain patterns developed at the frontal and lateral tips to shear zones and thrust zones abstract many of the complex strain patterns seen in shear zones and thrust zones such as variable fabric orientations refolded folds and fabrics together with folds with hinges almost parallel to the main transport direction can be explained in terms of differential movement within the shear zones these strains are developed at the frontal and lateral tips of the zones as they propagate examples are taken from the moine thrust zone of scotland which show variations in strains particularly at the lateral tips the form of differential movement described here may lead to complex strain paths and non plane strain ellipsoids and the spatial variations in finite strain may be used to delineate zones of extensional and compressional flow and differential movement in the shear zones or thrusts

automated segmentation of hillslope profiles across ridges and valleys using a digital elevation model abstract we developed a three step algorithm to automate the recognition and segmentation of hillslopes across ridges and valleys using a gridded digital elevation model dem the first step involves the delineation of a side slope profile by locating the lower and upper boundaries in the second step the cross profile pattern of a ridge or a valley floor which is defined and bounded by a pair of side slopes is examined in order to distinguish upland flats from ridges and lowlands from valley floors the width and gradient of these landform units are also measured in the third step a side slope profile is segmented into lower mid and upper slopes with a line simplification algorithm to identify changes and breaks in the slope in this step the footslope and crestslope can also be distinguished within the lower and upper slopes respectively using a 15 m dem this method was applied to five sites in low to high relief fluvial landscapes in japan the results showed good agreement 86 9 2 7 with manual slope segmentation indicating the effectiveness of our algorithm

rheology of the lithosphere selected topics we review recent results concerning the rheology of the lithosphere with special attention to the following topics 1 the flexure of the oceanic lithosphere 2 deformation of the continental lithosphere resulting from vertical surface loads and forces applied at plate margins 3 the rheological stratification of the continents 4 strain localization and shear zone development and 5 strain induced crystallographic preferred orientations and anisotropies in body wave velocities we conclude with a section citing the 1983 1986 rock mechanics literature by category

recumbent folds key structural elements in orogenic belts abstract this review has two main parts the first of them presents existing ideas and data related to recumbent folds reviewing aspects such as the physical conditions of the development of these folds the strain inside the folded layers the kinematic mechanisms of their formation the role of gravitational forces the tectonic context of their development and the structures associated with them in the second part the above ideas are discussed and possible mechanisms for the development of these folds are presented it is proposed that initial perturbations of the layers are essential to give rise to the asymmetry of recumbent folds these perturbations may be non planarities of the layering or may be linked to the existence of a core or basement of competent rock that hinders the normal propagation of the deformation this could explain why many large recumbent folds have a root zone deformation with an important component of simple shear is a general condition for the formation of recumbent folds in areas with very low grade metamorphism competent layers often play an active role during the deformation and undergo buckling with the development of an overturned fold limb which can be stretched and thinned to finally produce a pair of recumbent folds separated by a thrust in areas with low or medium metamorphism buckling under a simple shear regime is probably the most important mechanism for producing large folds with gentle or moderately dipping axial surfaces subsequent kinematic amplification by coaxial strain components with vertical maximum shortening is important for the formation of recumbent folds these components involve a sub horizontal stretching that can cause a problem of strain compatibility and give rise to a basal thrust in areas deformed under high p and t conditions recumbent folds can develop by flow perturbations and kinematic amplification of folds this is probably a common mechanism in ductile shear zones

folding in the greenland ice sheet the deformation of layering into folds is modeled for a linear viscous medium moving over a decollement folds are generated by flow variations caused by relief on the decollement variations in friction or both the model is applied to folds forming now in the greenland ice sheet near dye 3 for which more complete data are available than for analogous solid earth situations and for which the decollement is at or near the bed the folds wavelength 4 8 km are detected by radio reflection sounding measured surface deformation and deformation rate are used with the radar results to test the theory calculated fold amplitude is only 20 less than that measured which indicates that the theory is substantially correct inversion of the data to calculate basal drag and velocity variations is not helpful for near dye 3 because many different basal boundary conditions can lead to the observed deformations

strain compatibility and shear zones is there a problem in analyzing deformation in rocks it is important to ensure that the solutions obtained satisfy strain compatibility this creates a challenge to understanding patterns of strain associated with shear zones in which measured strain may appear incompatible with the strain in the shear zone walls flattening strains are common in natural shear zones with locally straight and parallel boundaries to satisfy compatibility conditions such strains require volume loss across the shear zone or deviations from plane strain with or without discontinuities between the shear zone and the wall rock in the case of shear zones for which there is no evidence of volume loss or discontinuities along the shear zone walls problems of strain compatibility may be resolved if individual shear zones are linked together in an appropriate fashion shear zones commonly occur in anastomosing arrays and simple configurations of such arrays and the strains associated with them are examined it is shown that local transpression with strain compatibility can be accounted for in this way quite complex local strain patterns can develop in simple arrays

strain in an archean greenstone belt of minnesota abstract we measured strain at more than 60 locations in metasedimentary and metavolcanic rocks of the vermilion district an e w trending archean greenstone belt in minnesota strain ellipsoid orientations and shapes correlate strongly with n s location in the belt but magnitudes do not flattening strains occur near the present vermilion fault which bounds the greenstone belt to the north with constrictional strains to the south the observed strain patterns can be mathematically modeled by deformation paths which produce the flattening strains with west plunging 1 axes by dextral shear of the constrictional strains with east plunging 1 axes using reasonable geologic constraints the shear plane must dip to the north with a subhorizontal shear direction structures throughout the district also indicate dextral shear a geometrical finite element program uses the measured strains to destrain the rocks and find the configuration which most closely satisfies strain compatibility equations the linear e w strain patterns and minor rotations about horizontal axes during the deformation preclude origin of the greenstone belt by infolding and shear off the flanks of a rising granitic diapir by accounting for rotations which result in the deformed curvature of the original surface a true estimate of 50 n s shortening across the belt can be made the data and deformation models favor the origin of the vermilion district rocks at a convergent margin most likely as a n dipping subduction zone complex with shallow slab dip the origin of the constrictional strains remains enigmatic

hanging wall accommodation styles in ramp flat thrust models in this paper we study the dynamic and rheologic control of hanging wall accommodation in ramp flat thrust models in particular we vary the dimensionless ratio of shear strength to gravity stress to model hanging wall accommodation styles in different materials in all models we require that the flat ramp flat footwall provides a surface of low frictional resistance in viscous materials hanging wall accommodation progresses by wedge flow in bingham materials wedge flow is also the preferred mode in cases where the gravity stress exceeds the yield limit of materials such models simulate the flow of salt or snow glaciers above ramp obstructions at high ratios of shear strength to gravity stress the hanging wall blocks translate forward without bending and unbending to the form of the rigid footwall in elastic plastic strain hardening materials ramp flat accommodation progresses by fault bend folding in case there is a near balance between the yield stress and gravity stress in frictional materials hanging wall accomodation progresses by shear or kink band nucleation above fault bends the shear or kink bands which initially nucleate at the lower fault bend change shape and reactivate by normal faulting or tensile failure at the upper fault bend depending on the ratio of shear strength to gravity stress in nature hanging wall accommodation by thrust nucleation above ramps and their subsequent reactivation may be anticipated in frictional sediments at upper crustal levels where temperatures and pressures are low

comparison of single and multiple flow direction algorithms for computing topographic parameters in topmodel single flow direction sfd and multiple flow direction mfd algorithms were used to compute the spatial and statistical distributions of the topographic index used in the watershed model topmodel an sfd algorithm assumes that subsurface flow occurs only in the steepest downslope direction from any given point an mfd algorithm assumes that subsurface flow occurs in all downslope directions from any given point the topographic index in topmodel is in a tan 3 where in is the napierian logarithm a is the upslope area per unit contour length and tan 3 is the slope gradient the in a tan 3 distributions were computed from digital elevation model dem data for locations with diverse topography in arizona colorado louisiana nebraska north carolina oregon pennsylvania tennessee vermont and virginia the means of the in a tan 3 distributions were higher when the mfd algorithm was used for computation compared to when the sfd algorithm was used the variances and skews of the distributions were lower for the mfd algorithm compared to the sfd algorithm the differences between the mfd and sfd algorithms in the mean variance and skew of the in a tan 3 distribution were almost identical for the various dems and were not affected by dem resolution or watershed size topmodel model efficiency and simulated flow paths were affected only slightly when the in a tan 3 distribution was computed with the sfd algorithm instead of the mfd algorithm any difference in the model efficiency and simulated flow paths between the sfd and mfd algorithms essentially disappeared when the model was calibrated by adjusting subsurface hydraulic parameters

nappe emplacement direction in the central gneiss belt grenville province ontario canada evidence for oblique collision abstract the proterozoic grenville province in canada is widely regarded as a compressional orogen in which thrust transport occurred towards the northwest perpendicular to the orogenic front new structural data from an area near parry sound ontario lead to a re evaluation of this interpretation nappe structures in this area are consistent with northeast rather than northwest directed thrusting and imply that the southwestern part of the province experienced an early sinistral oblique collision which predated the emplacement of the 1 24 ga sudbury dike swarm two nappe piles which contain different rock types and have distinct stacking sequences are separated by a lateral ramp or ductile tear fault that coincides with the interior of the parry sound domain of davidson et al 1982 early nappes and associated structures f 1 are overprinted by nw se striking upright folds f 2 that formed between about 1 16 and 1 12 ga these later folds partially reorient rotated feldspar porphyroclast systems that formed during nappe emplacement and have axes that are consistently parallel to a well developed mineral lineation the orientation of this lin lineation reflects the two stage deformation history of the area rather than the thrusting direction during a single orogenic event

experimental work on the effect of pre existing anisotropy on fabric development in glaciers abstract localization of deformation in ice is known to be important at all scales in deforming glaciers however relatively little is known of the significance of shear localization and the influence of fabric development in anisotropic ice at microscopic scales c axis preferred orientation and the inclination of the primary layering in anisotropic ice masses during both plane strain compression and combined simple shear compression have been examined a series of creep tests in the temperature range of 5 to 1 c over a range of shortening strains varying from 10 to 40 and compressive stresses ranging from 0 to 0 7 mpa have been undertaken significant variations in the strain rate and microstructural development have been observed in the plane strain compression experiments that reflects the varying orientations of the anisotropy and its relationship to easy glide directions in the ice mass in the unconfined combined compression and shear experiments minimum shear stress rates vary between the variously oriented anisotropic ice masses and deviate from the normal power flow law for isotropic ice where annealing occurs such ice masses preserve the pre existing c axis fabric and hence may reflect a contribution from both the recrystallized and inherited ice components

strain distribution in a fold in the west norwegian caledonides abstract strain has been measured from clasts within a deformed conglomerate layer at 17 localities around an asymmetric fold in the rundemanen formation in the bergen arc system west norwegian caledonides strain is very high and a marked gradient in strain ellipsoid shape exists to either side of the fold strain within the conglomerate bed is of the extreme flattening type in the fold especially on the lower fold closure the strain is constrictional mathematical models of perturbations of flow in glacial ice have produced folds of the same geometry as this fold with a strikingly similar pattern of finite strain the fold geometry and strain pattern as well as other field observations suggest that the fold developed passively as the result of a perturbation of flow in a shear zone where the strain was accommodated by simple shear accompanied by extension along y

strain patterns in an ice cap and implications for strain variations in shear zones glacier flow is a form of gravity tectonics in thin sheets characterized by the development of large strains foliation and folds strain is difficult to measure in ice but numerical methods provide a good means of estimating cumulative strains in simple terms flow in an ice cap involves vertical flattening at the center with bottom parallel shear increasing in intensity downwards and outwards in steady state cumulative strains will be plane if flow is two dimensional as in parts of many valley glaciers and some ice caps and of flattening type if lateral extension occurs normal to the flow direction as in many ice sheets in both radial and plane flow strain gradients will be large vertically and low horizontally outwards cumulative strain magnitude can be extremely large near the base and at the margin z is everywhere sub vertical if flow is unsteady more complex strain patterns develop even if changes in the flow field are slight over bedrock ridges flow perturbations can lead locally to rotations greater than those of the quasi simple shear acting near the base in steady state flow this may cause the x direction of the cumulative strain to rotate through the shear plane in the neighborhood of the perturbation in which case strain magnitudes subsequently diminish leading to low or zero strains in plane flow and to constrictional strains in radial flow in the latter case x lies horizontal and perpendicular to the flow direction and we have local constrictional strain in an overall flattening field the zones of perturbed strain tend to be associated with the inverted limbs of recumbent folds shear zones in rocks are expected to show similar patterns of strain perturbation

channel head location and characteristics using digital elevation models the drainage network is the conduit through which much surface water and sediment are routed within a catchment in a catchment the position of where hillslopes begin and channels end has long been considered the position of transition between diffusive processes upslope and the more incisive fluvial processes downslope consequently understanding channel head location is an important issue in understanding catchment hydrology and geomorphology this study examines channel head position and characteristics in a catchment in arnhem land northern territory australia in this study the position of channel heads was mapped within the catchment and plotted on a reliable digital elevation model of the catchment it was found that the majority of channel heads have relatively small source areas and that graphical catchment descriptors such as the area slope relationship and cumulative area distribution can provide reliable measures of the field position of the heads of first order streams and the transition from hillslope to channel the area slope relationship and cumulative area distribution are also shown to be good tools for determining digital elevation model grid size which can capture hillslope detail and the transition from hillslope to channel copyright 2005 john wiley sons ltd

digital terrain modeling abstract this article examines how the methods and data sources used to generate dems and calculate land surface parameters have changed over the past 25 years the primary goal is to describe the state of the art for a typical digital terrain modeling workflow that starts with data capture continues with data preprocessing and dem generation and concludes with the calculation of one or more primary and secondary land surface parameters the article first describes some of ways in which lidar and radar remote sensing technologies have transformed the sources and methods for capturing elevation data it next discusses the need for and various methods that are currently used to preprocess dems along with some of the challenges that confront those who tackle these tasks the bulk of the article describes some of the subtleties involved in calculating the primary land surface parameters that are derived directly from dems without additional inputs and the two sets of secondary land surface parameters that are commonly used to model solar radiation and the accompanying interactions between the land surface and the atmosphere on the one hand and water flow and related surface processes on the other it concludes with a discussion of the various kinds of errors that are embedded in dems how these may be propagated and carried forward in calculating various land surface parameters and the consequences of this state of affairs for the modern terrain analyst

isotropic points and lines in strain fields abstract in heterogeneous strain fields the strain may be isotropic at some points or along some lines called isotropic points and isotropic lines these isotropic features are known in various strain environments such as folds diapirs nappes or shear zones mechanical instabilities involving flow cells diapirism and folding are able to produce simultaneously isotropic points and lines whose dimensions location and migration are controlled by the flow pattern and history many other isotropic points can be understood in terms of superposition of elementary flows some examples such as neighbouring diapirs synkinematic diapirs shear zone terminations and spreading sliding nappes are presented finally some three dimensional aspects and general properties of isotropic points and lines are discussed

shear wave reflectivity anisotropies poisson s ratios and densities of a southern appalachian paleozoic sedimentary sequence abstract the physical properties of a sequence of paleozoic sedimentary rocks have been examined in detail with an emphasis on laboratory measurements of density shear wave velocity shear wave splitting and vp vs ratios seismic properties of 147 cores from 49 rock samples collected from the thorn hill sedimentary sequence of eastern tennessee are examined in terms of implications for future seismic studies in the southern appalachians the shear wave velocities of these rocks are strongly influenced by the relatively high shear wave velocity of quartz shear wave velocity anisotropy is present in most of the lithologic groups it is highest in the shales while being almost insignificant in the dolostones the related phenomenon of shear wave splitting occurs to some degree in all of the lithologies studied and at high pressures originates from mineral orientation splitting due to preferred mineral orientation is most prominent in the shales but also is significant in some of the carbonates compressional to shear velocity vp vs ratios of approximately 1 82 dolostones and 1 95 limestones effectively characterize the carbonates while other lithologies display wider ranges of vp vs primarily due to the influence of accessory minerals such as quartz densities of the sample suite range from 2 34 g cm3 shale to 2 86 g cm3 dolostone using average data for each lithologic group to calculate normal incidence reflection coefficients significant differences in the shear and compressional reflectivity of hypothetical interfaces are found normal incidence shear and compressional wave synthetic seismograms approximating the subsurface reflectivity of the entire thorn hill section indicate that three zones of high amplitude reflections would be seen on reflection records obtained over this 3327 m thick sequence overall the shear and compressional synthetics are similar in appearance differences are seen at some interfaces in the mississippian devonian interval which are more reflective to shear waves and in the ordovician martinsburg formation which appears more reflective to compressional waves

finite strain and deformation within the brianconnais castelvecchio cerisola nappe of the ligurian alps italy abstract the structural history of the castelvecchio cerisola brianconnais nappe ligurian alps italy was dominated by a southwestward overthrust shear that resulted in isoclinal folding and schistosity lineation fabric development within the nappe this deformation was due to the intracontinental shortening related to the collision of the european and adriatic plates during late cretaceous eocene times finite strain produced during the isoclinal folding and the schistosity lineation fabric development was determined from quartzites conglomerates and tuffs using fry s method strain type and intensities are strongly dependent on rock type other factors like the proximity to the major thrusts or the position in relation to the first phase recumbent folds seem to be of secondary importance the quartzites and conglomerates display a constrictional strain or else they approximate to plane strain while the pyroclastic rocks fall into the field of apparent flattening and are characterized by a higher intensity of deformation during nappe emplacement the deformation was not accommodated by simple shear alone the interpretation of strain patterns in the castelvecchio cerisola has led to a model in which longitudinal strain was superposed on layer parallel simple shear schistosity at a low angle to the major thrust faults incremental extension directions deduced from pressure shadows very frequent veins and stylolitic structures parallel to bedding support this hypothesis the data presented here emphasize that subvertical thinning associated with thrust shear and a small extension perpendicular to the emplacement direction occurred in the castelvecchio cerisola nappe

the assignment of drainage direction over flat surfaces in raster digital elevation models abstract drainage direction assignment over flat surfaces in raster digital elevation models dem has been a stubborn problem for dem processing methods a new approach that improves upon current methods of flat surface treatment is presented the approach is based on the recognition that in natural landscapes drainage is generally away from higher and towards lower terrain to produce such a drainage dem elevations of a flat surface are modified to impose two gradients one away from higher terrain and one towards lower terrain subsequent processing of the dem produces a drainage pattern over the flat surface that is topographically consistent and exhibits flow convergence properties the proposed approach is not restricted by the shape of the flat surface the number of outlets on its edge or the complexity of the surrounding topography a comparison with the drainage pattern of an established method that displays the parallel flow problem shows significant improvements in producing realistic drainage patterns the proposed approach extends automated dem processing to digital landscapes for which existing methods cannot provide adequate flow directions over flat surfaces to conduct a drainage analysis the necessary algorithmic details for implementation of the approach are provided 1997 elsevier science b v

extracting drainage networks and their connectivity using lidar data policies measures and models geared towards flood prevention and managing surface waters benefit from high quality data on the presence and characteristics of drainage ditches as a cost and labour effective alternative for acquiring such data through field surveys we propose a method a to extract vector data representing ditch drainage networks based on local morphologic features derived from high resolution digital elevation models dem and b to identify possible connections in the ditch network by calculating a probability of the connectivity using a logistic regression where the predictor variables are characteristics of the ditch centre lines or derived from the dem using light detection and ranging lidar derived dems with a 1m resolution the method was developed and tested for a mixed agricultural residential area in north eastern belgium the derived ditch segments had an error of omission of 8 and an error of commission of 5 the original positional accuracy of the centre lines of the extracted ditches was 0 6m and could be improved to 0 4m by shifting each vertex to the position of the lowest lidar point located within a radius equal to the spatial resolution of the used dem about 69 of the false disconnections in the network were identified and corrected leading to a reduction of the unconnected parts of the ditch network by 71 the extracted and connected network approximated the reference ditch network fairly well

the prediction of hillslope flow paths for distributed hydrological modelling using digital terrain models the accuracy of the predictions of distributed hydrological models must depend in part on the proper specification of flow pathways this paper examines some of the problems of deriving flow pathways from raster digital terrain data in the context of hydrological predictions using topmodel distributed moisture status is predicted in topmodel on the basis of spatial indices that depend on flow path definition the sensitivity of this index to flow path algorithm and grid size is examined for the case where the surface topography is a good indicator of local hydraulic gradients a strategy for the case where downslope subsurface flow pathways may deviate from those indicated by the surface topography is described with an example application