digital optical televiewing of ice boreholes digital optical televiewing recently developed to log and map terrestrial boreholes provides a complete orientated image of borehole walls at a resolution of 1 mm along hole and typically

early mesozoic southward migration of cordilleran transpressional terranes oblique plate convergence can cause forearc arc and back arc regions of active margin orogenic belts to behave as semi independent terranes relative to bordering continental and oceanic lithospheric plates these terranes called here transpressional terranes are bound by the subduction zone on one side by arc parallel strike slip faults in the forearc in the volcanic arc or in the back arc region on the other and are underlain by throughgoing basal decollements these terranes undergo shortening in a direction perpendicular to the subduction zone and migrate as coherent structural bodies parallel to the subduction zone along bounding strike slip faults many terranes of the north american cordillera may have behaved in this manner and perhaps did not travel across the pacific basin but rather were always peripheral to north america we propose that during the triassic to mid cretaceous portions of the cordillera borderland generally were displaced southward with respect to the north american craton due to left oblique convergence since the mid cretaceous they moved northward due to right oblique subduction the proposed displacements are consistent with structural paleomagnetic and paleontologic data and with the relative and absolute motions of north america and the pacific basin plates based on hotspot reference frame models

measuring suspended sediment concentrations using acoustic backscatter devices abstract in recent years the requirement to develop a technique for measuring suspended sediment concentration profiles with similar temporal and spatial resolution to that of electromagnetic current meter measurements of the flow has led to the development of an acoustic approach acoustic backscatter devices have been constructed and deployed in marine environments and measurements of backscattered signal profiles obtained however the translation from acoustic returns to suspended load has been an empirical procedure resulting in some uncertainty regarding the accuracy and reliability of the conversion process to address this problem a series of laboratory measurements of acoustic backscattering from marine suspensions were conducted using two acoustic backscatter instruments operating at 3 0 and 5 65 mhz a simple semi empirical backscattering theory has been developed to predict the form of the scattered signal and comparisons have been made of the concentrations predicted from the theory against concentration measurements made in laboratory tanks the results show that the main features of the backscattering signal can be explained and accurate concentration estimates can be made from the acoustic returns it is concluded that acoustic backscatter techniques are potentially powerful tools for examining at high resolution the structure of suspended sediment concentration profiles near the seabed

instruments and methods diamond wire saw cutting technique for investigating textures and fabrics of debris laden ice and brittle ice presents an original method for sampling special ice types like debris rich ice or brittle ice that cannot be prepared using the standard band saw microtome procedure the general working principles of the diamond wire sawing technique are explained and special adaptations for ice cutting thick sectioning and thin sectioning are discussed author

direct measurement of basal motion at a hard bedded temperate glacier glacier de tsanfleuron switzerland hubbard b 2002 direct measurement of basal motion at a hard bedded temperate glacier glacier de tsanfleuron switzerland journal of glaciology 48 160 pp 1 8 rae2008

strain rate enhancement at dye 3 greenland ice at depth in ice sheets can be softer in bed parallel shear than glen s flow law predicts for example at dye 3 greenland enhancement factors of 3 4 are needed in order to explain the rate of borehole tilting previous authors have identified crystal fabric as the dominant contributor but the role of impurities and crystal size is still incompletely resolved here we use two formulations of anisotropic flow laws for ice azuma s and sachs models to account for the effects of anisotropy and show that the measured anisotropy of the ice at dye 3 cannot explain all the detailed variations in the measured strain rates the jump in enhancement across the holocene wisconsin boundary is larger than expected from the measured fabrics alone dust and soluble ion concentration divided by crystal size correlates well with the residual enhancement indicating that most of the excess deformation may be due to impurities or crystal size while the major features of the deformation at dye 3 are explained by anisotropy and temperature results also suggest that further research into the role of impurities and crystal size is warranted

bedrock surface roughness and the distribution of subglacially precipitated carbonate deposits implications for formation at glacier de tsanfleuron switzerland two carbonate deposits are identified on the exposed bedrock surface in the forefield of glacier de tsanfleuron switzerland macrocrystalline sparite and microcrystalline micrite comparison of the distributions of these forms with lee side slope facets identified by high pass filtering of a flow parallel bedrock profile at a range of frequencies reveals two significant results first while the distribution of sparite is consistent with formation in the lee side of subglacial bedrock hummocks that of micrite is not this contrasts with previous investigations in which both sparite and micrite have been considered to form by mineral concentration and precipitation during the refreezing of regelation related basal meltwaters in the lee side of bedrock hummocks alternative mechanisms of micrite formation involving carbonate deposition and or precipitation within subglacial bedrock hollows are proposed second the distribution of sparite is most strongly correlated with the distribution of lee side slope facets identified by filtering at a frequency equivalent to a hummock wavelength of c 0 1 m this correspondence indicates empirically that pressure related melting and refreezing regelation operates most effectively around bedrock hummocks that are shorter than c 0 1 m 1998 john wiley sons ltd

cretaceous magnetizations in northwestern nevada and tectonic implications paleozoic and mesozoic arc related rocks of the black rock desert region of northwestern nevada have acquired a very stable postfolding secondary magnetization probably in late cretaceous time the remagnetization which appears to be of regional extent probably accompanied emplacement of granitic plutons in a northeast trending belt across northwestern nevada near the end of mesozoic time the region has experienced no appreciable tectonic rotation since that time

ice core evidence for the thickness and character of clear facies basal ice at glacier de tsanfleuron switzerland five ice cores have been retrieved from a transect close to the terminus of glacier de tsanfleuron switzerland the cores extend from the ice surface to the glacier bed and are 3 5 44 8 m long stratigraphic logging based on bubble size and density reveals the presence of a highly metamorphosed basal ice layer about 10 m thick from which all traces of bubble rich ice have been removed this bubble poor ice which corresponds closely with clear facies ice observed in cavities beneath numerous temperate based glaciers contrasts with the overlying bubble rich or bubble foliated englacial ice and the underlying debris rich and bubble free dispersed facies basal ice down core patterns in major ion composition stable isotope composition and total gas content and composition are generally consistent with formation of clear facies ice by deformation related metamorphism of bubbly englacial ice in addition isotopic data suggest that storage of downward percolating meltwaters occurs close to the upper surface of the clear facies ice layer perhaps reflecting a local variation in ice permeability across the transition from englacial to clear facies ice enrichment in crustally derived ionic species is noted in the lowermost decimetres of the debris free clear facies ice that immediately overlies debris rich dispersed facies basal ice this ionic enrichment in debris free ice is interpreted in terms of active inter granular meltwater flow within some decimetres of the glacier bed

structure and stability of the former subglacial drainage system of the glacier de tsanfleuron switzerland a well developed subglacial drainage system consisting of large cavities developed in the lee of bedrock steps connected together by a network of nye channels is exposed on an area of recently deglaciated limestone bedrock in front of glacier de tsanfleuron switzerland this system covers some 51 per cent of the bedrock surface area and is believed to have transported the bulk of supraglacially derived meltwaters through the glacier using the cavity hydraulics model of kamb 1987 it is shown that the geometry of the system rendered it stable against collapse by meltback of channel roofs into a tunnel dominated system for likely combinations of glacier geometry and meltwater discharge the steady state water pressure in this system would have been only a small fraction of that required for flotation and for discharges of less than about 0 5 5 m3 s 1 water would have flowed at atmospheric pressure the system appears to have adjusted to varying discharges by a combination of varying water pressure and changing the total cross sectional area of flow by altering the number of active channels connecting cavities glacier sliding velocity would have been independent of meltwater discharge for discharges at which water flowed at atmospheric pressure but would have risen with increasing discharge for higher flows velocities on the order of 0 1 m d 1 are predicted for a realistic range of discharges and effective pressures and these are believed to be plausible episodes of enhanced sliding in glaciers with similar drainage systems could be triggered by a rise in meltwater discharge across the threshold between flows at atmospheric pressure and flow under pressure from the glacier

optimising ice flow law parameters using borehole deformation measurements and numerical modelling chandler d m hubbard b hubbard a murray t rippin d 2008 optimising ice flow law parameters using borehole deformation measurements and numerical modelling geophysical research letters 35 l12502

paleomagnetic and structural evidence for middle tertiary counterclockwise block rotation in the dixie valley region west central nevada paleomagnetic data from late oligocene to early miocene ash flow tuffs at four localities in the northern dixie valley region west central nevada indicate that parts of the crust have rotated counterclockwise by at least 25 sup 0 and perhaps significantly more in late cenozoic time field relations in white rock canyon stillwater range suggest that rotation 1 was accommodated by right lateral slip on northwest trending faults 2 spanned ash flow tuff emplacement and 3 probably ceased before eruption of overlying middle miocene basalts accurate estimates of cenozoic extension as well as evaluation of earlier mesozoic structures must include the strain partitioned into rotation in the area

recent studies indicate that major structures in northeastern nevada and the golconda thrust in north central nevada are of jurassic or cretaceous age geologic mapping recently completed in four areas of northeastern nevada indicates that major folds and thrusts are of post early triassic age and probably are jurassic or cretaceous previously published data for northeastern nevada lead to or permit the same conclusion basinal deposits of early triassic age in the northern adobe range are easterly derived clay and carbonate the apparent lack of westerly derived siliceous orogenic sediments of sonoma age late permian to early triassic suggests that the sonoma orogeny took place at some unknown location far from northeastern nevada and that rocks deformed then the golconda allochthon were emplaced in northern nevada at a later date

on the special rheological properties of ancient microparticle laden northern hemisphere ice as derived from bore hole and core measurements on observe des differences dans le fluage des glaces a forte concentration en microparticules wisconsin recent qui sont plus douces que celles de la glace contemporaine ou holocene on analyse les parametres suivants concentration ou microparticules 18 o taille des cristaux axe c ca na conductivite et densite dans des carottes prelevees a agassiz iles ellesmere sur l ile devon et au groenland

spatial variability in the water content and rheology of temperate glaciers glacier de tsanfleuron switzerland the physical properties of eight ice coresrecovered from along a flowline at glacier detsanfleuron switzerland have led to the identification of three distinctive internal zones we use variations in the bulk ionic chemistry of these zonesto approximate their relative liquid water concentrations and ice viscosities results suggest that relative bulk water concentration and ice softness vary by over an order of magnitude between the zones implications of this variability for predictions of the glacier s response to climate change are evaluated by incorporating these relative softnesses into a multi layered two dimensional model of ice flow model output is compared with that from an identical model constrainedwith a spatially uniform ice viscosity under advance and retreatmodel ling scenarios the former scenario isusedto tuneviscosity by growinga glacier to itspres ent long section geometry resulting in best fit ice hardness values of 1 2a 1 bar 3 for the englacial ice in the multi layered model and 7 0a 1 bar 3 for all of the ice in the single layered model both result in close approximations to the current long profile yielding rmsdeviationsbetween measuredandmodelledicethicknessesthatare 55m in contrast a single layered model constrained with a hardness of 1 2a 1 bar 3 overestimates the current measured long section area by 31 having a rms ice thickness error of 15 0m under the retreat modelling scenario which gauges the response of the glacier to an imposed 75m rise in equilibrium line altitude ela the multi layered model predicts a long section area reduction of 78 this contrasts with a reduction of 64 for the single layered model hardness 7 0a 1 bar 3 and 85 forthe single layered model hardness 1 2a 1 bar 3

paleomagnetism of the late permian early triassic koipato volcanics nevada implications for latitudinal displacement abstract we have obtained paleomagnetic directions for 11 basalt flows of the probable early triassic koipato volcanics from the south tobin range of western nevada the mean direction for these flows d 350 3 i 39 0 95 8 0 is discordant with respect to the apw path for north america a positive fold test a consistency of reversal test the shape and amount of between site dispersion and other considerations strongly suggest that the magnetization is pre folding and probably primary the most likely explanation for this discordance is southward transport and clockwise rotation of the sampling area the most probable amount of displacement and net rotation are 1400 km and 25 respectively these observations have considerable significance for the early mesozoic tectonics of the great basin

a mechanism of basal ice layer formation involving major ice fabric changes an opportunity to analyse the mechanism for the formation of a basal ice layer was provided by glacier de tsanfleuron in the swiss alps this glacier has some lateral subglacial cavities in which a basal ice layer forms on the bedrock floor and is subsequently incorporated at the base of the glacier petrographic and crystallographic analyses of the different types of ice have provided a means of investigating the successive stages of the process these analyses show major structural changes which provide field confirmation of the deformation mechanisms studied by several authors in laboratory experiments

characterizing riverbed sediment using high frequency acoustics 1 spectral properties of scattering bed sediment classification using high frequency hydroacoustic instruments is challenging when sediments are spatially heterogeneous which is often the case in rivers the use of acoustic backscatter to classify sediments is an attractive alternative to analysis of topography because it is potentially sensitive to grain scale roughness here a new method is presented which uses high frequency acoustic backscatter from multibeam sonar to classify heterogeneous riverbed sediments by type sand gravel and rock continuously in space and at small spatial resolution in this the first of a pair of papers that examine the scattering signatures from a heterogeneous riverbed methods are presented to construct spatially explicit maps of spectral properties from georeferenced point clouds of geometrically and radiometrically corrected echoes backscatter power spectra are computed to produce scale and amplitude metrics that collectively characterize the length scales of stochastic measures of riverbed scattering termed stochastic geometries backscatter aggregated over small spatial scales have spectra that obey a power law this apparently self affine behavior could instead arise from morphological scale and grain scale roughnesses over multiple overlapping scales or riverbed scattering being transitional between rayleigh and geometric regimes relationships exist between stochastic geometries of backscatter and areas of rough and smooth sediments however no one parameter can uniquely characterize a particular substrate nor definitively separate the relative contributions of roughness and acoustic impedance hardness combinations of spectral quantities do however have the potential to delineate riverbed sediment patchiness in a data driven approach comparing backscatter with bed sediment observations which is the subject of part two of this manuscript

aquatic habitat bottom classification using adcp description of physical aquatic habitat often includes data describing distributions of water depth velocity and bed material type water depth and velocity in streams deeper than about 1 m may be continuously mapped using an acoustic doppler current profiler from a moving boat herein we examine the potential of using the echo signal strength from the bed as an indicator of bed material type mean signal strength from soft muddy beds was consistently 10 20 db lower than mean signal strength from noncohesive gravel or sand beds sand beds tended to have larger site to site variation means 30 to 19 db than for fines 43 to 38 db or gravel 23 to 20 db

flow law hypotheses for ice sheet modeling ice flow modeling requires a flow law relating strain rates to stresses in situ but a flow law cannot be measured directly in ice sheets microscopic processes such as dislocation glide and boundary diffusion control both the flow law for ice and the development of physical properties such as grain size and c axis fabric these microscopic processes can be inferred from observations of the physical properties and the flow law can then be estimated from the microscopic processes a review of available literature shows that this approach can be imperfectly successful interior regions of large ice sheets probably have depth varying flow law constants with the stress exponent n for power law creep less than 3 in upper regions and equal to 3 only in deep ice n probably equals 3 through most of the thickness of ice shelves and ice streams

evaluation of image based multibeam sonar backscatter classification for benthic habitat discrimination and mapping at stanton banks uk in recent years efforts have increased to develop quantitative computer directed methods for segmentation of multibeam mbes backscatter data this study utilises mbes backscatter data acquired at stanton banks uk and subsequently processed through the qtc multiview software environment in a bid to evaluate the program s ability to perform unsupervised classification statistical comparison with ground truth data grab stills and video enabled cross validation of acoustic segmentation and biological assemblages observed at the site 132 unspecified variables were extracted from user specified rectangular patches of the backscatter image reduced to three vectors by pca then clustered and classified by the software multivariate analyses of ground truth data were conducted on 75 stills images and 51 grab samples video footage coincident with the stills was divided into 30 s segments and coded by dominant substrate and species cross tabulation determined the interrelationship between software classifications multivariate analysis of the biological assemblages and coded video segments multiview optimally identified 19 classes using the automated clustering engine these were revised to 6 habitats a posteriori using combined analysis of ground truth data and multiview data products these habitats broadly correspond to major physiographic provinces within the region multivariate statistical analysis reveals low levels of assemblage similarity 35 for samples occurring within multiview classes irrespective of the mode of acquisition coded video data is more spatially appropriate than the other methods of ground truthing investigated although it is less well suited to the extraction of truly quantitative data multivariate analysis indicates assemblages within physiographically distinct multiview classes have a low degree of biological similarity supporting the notion that abiotic proxies may be contraindicative of benthic assemblage variations qtc multiview performs well as a mechanism for computer assisted segmentation of mbes backscatter imagery into acoustic provinces however a degree of caution is required prior to ascribing ecological significance to these classifications c 2008 elsevier ltd all rights reserved

paleomagnetism of middle tertiary volcanic rocks from the western cascade series northern california the western cascade series wcs is a 3 5 km thick crudely homoclinal east dipping calcalkaline volcanic sequence of mid oligocene to early miocene age that crops out near the southern tip of the cascade range in northern california the mean direction of remanent magnetization in the wcs is d 4 9 i 57 6 n 53 k 14 4 95 5 3 when compared to a reference direction for the north american craton the wcs direction indicates that the southern cascade range has rotated 14 0 9 0 since the wcs accumulated a difference in mean direction between the lower and upper halves of the wcs suggests that much of this rotation occurred during the late oligocene six other paleomagnetic studies of rock units of an age roughly comparable to the wcs also are available from western oregon northwestern california and southwestern washington all show statistically significant clockwise rotation inclinations of all but one are concordant comparison of directions indicates that the pacific northwest did not rotate as a rigid body but neither did it behave as a collection of small independently rotating domains the amount of rotation found throughout the area increases to the west or northwest suggesting a driving force for rotation operating at the continental margin