statistical properties of armored gravel bed surfaces 1 roughness of successively developed armor layers in a large laboratory flume is analyzed considering gravel surfaces as two dimensional random fields of bed elevations statistically derived roughness parameters are evaluated from precise digital elevation models dems of bed surfaces and are discussed with respect to successive development of stable armor layers the key results relate to evolution of the probability distribution of bed elevations and its moments and structure functions of various orders with respect to armoring discharge our results suggest that statistical analysis of bed elevations is a helpful tool for defining roughness parameters quantifying armoring effects and identifying particle orientation flow direction and surface forming processes

regionally differentiated contribution of mountain glaciers and ice caps to future sea level rise the contribution to sea level rise from mountain glaciers and ice caps has grown over the past decades a projection of their melting during the twenty first century based on temperature and precipitation projections from ten climate models suggests that by 2100 these glaciers will lose about 21 of their total global volume

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

deformation and metamorphism associated with crustal rifting the permian to liassic evolution of the lake lugano lake como area southern alps abstract in connection with movements between europe and adria the southern alps underwent extension leading to the formation of the middle jurassic south alpine passive continental margin as a result of mainly s vergent alpine thrusting and folding a substantially preserved mesozoic crustal section ranging from the surface to a paleo depth of ca 15 km is exposed in the lugano lake como area tectonic processes associated with permo mesozoic extension can thus be investigated at different crustal levels rifting began with a thermal anomaly during which rocks at middle crustal levels were sheared at ca 650 750 c deformation was distributed on a several km wide zone and late kinematic pegmatites were emplaced at this stage temperatures then decreased and beginning in the norian extension was accommodated by a major e dipping normal fault the lugano val grande normal fault the fault which can be followed down to a paleo depth of ca 12 km was listric and flattened to 20 at ca 7 9 km depth in the upper 8 10 km deformation was only brittle whereas at deeper crustal levels greenschist mylonites were formed with continued normal faulting the colder hanging wall cooled the fault zone and greenschist mylonites were progressively replaced by lower temperature ultramylonites and cataclasites the thickness of the fault zone varies from some tens of meters in the upper 5 6 km to several hundred meters at deeper levels deformation was thus discrete at a crustal scale

towards a protocol for laser scanning in fluvial geomorphology advances in spatial analytical software allow digital elevation models dems to be produced which accurately represent landform surface variability and offer an important opportunity to measure and monitor morphological change and sediment transfer across a variety of spatial scales many of the techniques presently employed aerial lidar edm theodolites gps photogrammetry suffer coverage or resolution limitations resulting in a trade off between spatial coverage and morphologic detail captured this issue is particularly important when rates of spatial and temporal change are considered for fluvial systems this paper describes the field and processing techniques required for oblique laser scanning to acquire 0 01 m resolution digital elevation data of an upland reach of the river wharfe in the uk the study site is variable with rapidly changing morphology diverse vegetation and the presence of water and these are evaluated with respect to laser data accuracy scan location frequency and distance are discussed with reference to survey accuracy and efficiency and a field protocol is proposed scan data cloud merging was achieved with a high degree of precision sub centimetre and positional data are shown to be very accurate for exposed surfaces vegetation and water decrease the accuracy as the laser pulse is often prevented from reaching the ground surface or is not returned copyright 2006 john wiley sons ltd

effect of surface texture and structure on the development of stable fluvial armors abstract stable fluvial armors are found in river systems under conditions of partial sediment transport and limited sediment supply a common occurrence in nature stable armoring is also readily recreated in experimental flumes initially this bed stabilizing phenomenon was examined for different flow discharges and solely related to surface coarsening and bedload transport reduction the models developed suggest a specific armor composition i e texture dependent on the parent bed material and formative discharge following developments in topographic remote sensing recent research suggests that armor structure is an important control on bed stability and roughness in this paper replicated flume runs during which digital elevation models dems were collected from both exposed and flooded gravel beds are used to interpret armoring manifestations and to assess their replicability a range of methodologies was used for the analysis providing information on i surface grain size and orientation ii bed elevation distributions iii the spatial coherence of the elevations at the grain scale iv surface slope and aspect v grain imbrication and vi the spatial variability in dem properties the bed surface topography was found to be more responsive than bed material size to changes in flow strength our experimental results also provide convincing evidence that gravel beds response to water work during parallel degradation is unique i e replicable given the formative parameters based on this finding relationships between the armors properties and formative parameters are proposed and are supported by adding extensive data from previous research

metamorphic evolution and oxygen isotope geochemistry of rift precursor amphibolites from hole 1067a odp leg 173 off west iberian galicia bank rifted margin abstract the paper documents permian igneous rocks in the vicinity of an ocean continent transition in the west iberian abyssal plain odp leg 173 hole 1067a was drilled through a sequence of foliated to massive amphibolites of gabbroic protolithic origin the 270 3 ma to 246 5 ma rock sequence experienced several metamorphic events during the interval of time spanning from 138 ma up to 55 ma metamorphic parageneses record two major thermobarometric events for which the temperature and pressure conditions are 670 40 c and 0 7 0 1 gpa and 550 50 c and 0 5 0 1 gpa according to radiometric dating these metamorphic events might have occurred around 138 136 ma and 113 110 ma respectively the low cl content and the preserved igneous 18 o of amphibole imply seawater absent 580 c isothermal plagioclase amphibole equilibrium related to the development of the strong foliation of the amphibolite during the second metamorphic event late isotopic equilibration involved lower temperature seawater derived fluid and is younger than 110 ma the gabbroic intrusion is believed to be a precursor for initiation of continental rifting melting of such metamorphosed rocks in a rift setting would generate magmatic rocks with complex oxygen isotopic signatures

structural properties of mobile armors formed at different flow strengths in gravel bed rivers differences in the structure of mobile armors formed at three different flow strengths have been investigated in a laboratory flume the temporal evolution of the bed surfaces and the properties of the final beds were compared using metrics of surface grain size microtopography and bed organization at both grain and mesoscales measurements of the bed condition were obtained on nine occasions during each experiment to describe the temporal evolution of the beds structured mobile armors formed quickly in each experiment at the grain scale 1 45 mm 9 ds50 17 mm where ds50 is the median surface particle size surface complexity decreased and bed roughness increased in response to surface coarsening and the development of the mobile armor particles comprising the armor also became flow aligned and developed imbrication at a larger scale 100 200 mm the surface developed a mesoscale topography through the development of bed patches with lower and higher elevations metrics of mobile armor structure showed remarkable consistency over prolonged periods of near constant transport demonstrating for the first time that actively transporting surfaces maintain an equilibrium bed structure bed structuring was least developed in the experiments conducted at the lowest flow strength however little difference was observed in the structural metrics of the mobile armors generated at higher flows although the range of transport rates studied was limited the results suggest that the structure of mobile armors is insensitive to the formative transport rate except when rates are low 0 03 where is the dimensionless shear stress

the development of an automated correction procedure for digital photogrammetry for the study of wide shallow gravel bed rivers this paper develops an automated correction procedure for dealing with point errors associated with through water photogrammetry for application in the study of clear water shallow gravel bed rivers the procedure involves combining digital photogrammetry and image analysis techniques to i correct for the effects of refraction at an air water interface and ii eliminate and reinterpolate points where the bed has not been seen the correction procedure was applied to raw digital elevation models dems generated using digital photogrammetry from 1 3000 scale aerial photography of a small reach of the north ashburton river new zealand the accuracy of corrected and uncorrected dems is evaluated using an independent data set a measure of geomorphological usefulness as well as dem external reliability is obtained from calculations of water depth distributions and mean bed level results show that digital photogrammetry used in conjunction with image analysis techniques can successfully be used for extracting high resolution dems of gravel river beds in exposed areas errors are small and random tending to cancel out over large numbers of points where water is shallow and following correction point elevation errors are statistically no different from those for exposed zones in deeper water despite an improvement following application of the correction procedure elevation errors scale with water depth the geomorphological potential of photogrammetric survey of large gravel river beds is demonstrated by the ease and accuracy of calculations of water depth distribution important for the assessment of a river s ecological and recreational characteristics and mean bed level important for the calculation of reach scale sediment volumes copyright 2000 john wiley sons ltd

statistical characterization of bed roughness due to bed forms a field study in the elbe river at aken germany 1 bed form geometry and dynamics in a straight section of the elbe river in germany is analyzed considering the measured bed surfaces as two dimensional random fields of bed elevations statistically derived roughness parameters are evaluated from high resolution digital elevation models which were available for a range of flow rates from low flows to floods the key results relate to the identification of characteristic scaling regions in the bed surface spectra and to observed relationships between water discharge and both the standard deviation and a factor of the 3 spectral law of bed elevations two dimensional second order structure functions of bed elevations are also analyzed to gain further insight into the spatial structure of sand wave beds in addition the interrelations between flow rate hysteresis and the statistical structure of bed forms as well as effects of channel modification by groynes are highlighted and discussed the reported results demonstrate that statistical parameters of bed forms may be used for characterization and prediction of flow dependent sand bed roughness

a reconciled estimate of ice sheet mass balance we combined an ensemble of satellite altimetry interferometry and gravimetry data sets using common geographical regions time intervals and models of surface mass balance and glacial isostatic adjustment to estimate the mass balance of earth s polar ice sheets we find that there is good agreement between different satellite methods especially in greenland and west antarctica and that combining satellite data sets leads to greater certainty between 1992 and 2011 the ice sheets of greenland east antarctica west antarctica and the antarctic peninsula changed in mass by 142 49 14 43 65 26 and 20 14 gigatonnes year 1 respectively since 1992 the polar ice sheets have contributed on average 0 59 0 20 millimeter year 1 to the rate of global sea level rise

does the permeability of gravel river beds affect near bed hydrodynamics the permeability of river beds is an important control on hyporheic flow and the movement of fine sediment and solutes into and out of the bed however relatively little is known about the effect of bed permeability on overlying near bed flow dynamics and thus on fluid advection at the sediment water interface this study provides the first quantification of this effect for water worked gravel beds laboratory experiments in a recirculating flume revealed that flows over permeable beds exhibit fundamental differences compared with flows over impermeable beds of the same topography the turbulence over permeable beds is less intense more organised and more efficient at momentum transfer because eddies are more coherent furthermore turbulent kinetic energy is lower meaning that less energy is extracted from the mean flow by this turbulence consequently the double averaged velocity is higher and the bulk flow resistance is lower over permeable beds and there is a difference in how momentum is conveyed from the overlying flow to the bed surface the main implications of these results are three fold first local pressure gradients and therefore rates of material transport across the sediment water interface are likely to differ between impermeable and permeable beds second near bed and hyporheic flows are unlikely to be adequately predicted by numerical models that represent the bed as an impermeable boundary third more sophisticated flow resistance models are required for coarse grained rivers that consider not only the bed surface but also the underlying permeable structure overall our results suggest that the effects of bed permeability have critical implications for hyporheic exchange fluvial sediment dynamics and benthic habitat availability

increasing rates of ice mass loss from the greenland and antarctic ice sheets revealed by grace 1 we use monthly measurements of time variable gravity from the grace gravity recovery and climate experiment satellite gravity mission to determine the ice mass loss for the greenland and antarctic ice sheets during the period between april 2002 and february 2009 we find that during this time period the mass loss of the ice sheets is not a constant but accelerating with time i e that the grace observations are better represented by a quadratic trend than by a linear one implying that the ice sheets contribution to sea level becomes larger with time in greenland the mass loss increased from 137 gt yr in 2002 2003 to 286 gt yr in 2007 2009 i e an acceleration of 30 11 gt yr2 in 2002 2009 in antarctica the mass loss increased from 104 gt yr in 2002 2006 to 246 gt yr in 2006 2009 i e an acceleration of 26 14 gt yr2 in 2002 2009 the observed acceleration in ice sheet mass loss helps reconcile grace ice mass estimates obtained for different time periods

close range digital photogrammetric analysis of experimental drainage basin evolution brasington james smart r m a 2003 close range digital photogrammetric analysis of experimental drainage basin evolution earth surface processes and landforms 28 3 pp 231 247 rae2008 special issue the generation of high quality topographic data for hydrology and geomorphology

antarctica greenland and gulf of alaska land ice evolution from an iterated grace global mascon solution we have determined the ice mass evolution of the antarctica and greenland ice sheets ais and gis and gulf of alaska goa glaciers from a new grace global solution of equal area surface mass concentration parcels mascons in equivalent height of water the mascons were estimated directly from the reduction of the inter satellite k band range rate kbrr observations taking into account the full noise covariance and formally iterating the solution the new solution increases signal recovery while reducing the grace kbrr observation residuals the mascons were estimated with 10 day and 1 arc degree equal area sampling applying anisotropic constraints an ensemble empirical mode decomposition adaptive filter was applied to the mascon time series to compute annual mass balances the details and causes of the spatial and temporal variability of the land ice regions studied are discussed the estimated mass trend over the total gis ais and goa glaciers for the time period 1 december 2003 to 1 december 2010 is 380 plus or minus 31 gt a exp 1 equivalent to 1 05 plus or minus 0 09 mma exp 1 sea level rise over the same time period we estimate the mass acceleration to be 41 plus or minus 27 gt a exp 2 equivalent to a 0 11 plus or minus 0 08 mm a exp 2 rate of change in sea level the trends and accelerations are dependent on significant seasonal and annual balance anomalies

contribution of alaskan glaciers to sea level rise derived from satellite imagery over the last 50 years retreating glaciers and ice caps gic contributed 0 5 mm yr to sea level rises slr and one third is believed to originate from ice masses bordering the gulf of alaska however these estimates of ice wastage in alaska are based on methods that measure a limited number of glaciers and extrapolate the results to estimate ice loss for the many thousands of others how these methods capture the complex pattern of decadal elevation changes at the scale of individual glacier and mountain range is unclear here combining a comprehensive glacier inventory with elevation changes derived from sequential digital elevation models dems we found that between 1962 and 2006 alaskan glaciers lost 41 9 8 6 km 3 yr water equivalent w e and contributed 0 12 0 02 mm yr to slr our ice loss is 34 lower than previous estimates reasons for our lower values include the higher spatial resolution of our glacier inventory and the reduction of ice thinning under debris and at the glacier margins which were not resolved in earlier work estimates of mass loss from gic in other mountain regions could be subject to similar revisions

derivation and analysis of a complete modern date glacier inventory for alaska and northwest canada we present a detailed complete glacier inventory for alaska and neighboring canada using multi sensor satellite data from 2000 to 2011 for each glacier we derive outlines and 51 variables including center line lengths outline types and debris cover we find 86 723 km 2 of glacier area 27 109 glaciers 0 025 km 2 similar to 12 of the global glacierized area outside ice sheets of this area 12 0 is drained by 39 marine terminating glaciers 74 km of tidewater margin and 19 3 by 148 lake and river terminating glaciers 420 km of lake river margin the overall debris cover is 11 with considerable differences among regions ranging from 1 4 in the kenai mountains to 28 in the central alaska range comparison of outlines from different sources on 2500 km 2 of glacierized area yields a total area difference of similar to 10 emphasizing the difficulties in accurately delineating debris covered glaciers assuming fully correlated systematic errors uncertainties in area reach 6 for all alaska glaciers but further analysis is needed to explore adequate error correlation scales preliminary analysis of the glacier database yields a new set of well constrained area length scaling parameters and shows good agreement between our area altitude distributions and previously established synthetic hypsometries the new glacier database will be valuable to further explore relations between glacier variables and glacier behavior

computations of the viscoelastic response of a 3 d compressible earth to surface loading an application to glacial isostatic adjustment in antarctica and canada s u m m a r y we develop a 3 d finite element model to study the viscoelastic response of a compressible earth to surface loads the effects of centre of mass motion polar wander feedback and selfconsistent ocean loading are implemented to assess the model s accuracy we benchmark the numerical results against a semi analytic solution for spherically symmetric structure we force our model with the ice 5g global ice loading history to study the effects of laterally varying viscosity structure on several glacial isostatic adjustment gia observables including relative sea level rsl measurements incanada and present day time variable gravity and uplift rates in antarctica canadian rsl observations have been used to determine the earth s globally averaged viscosity profile antarcticgps uplift rates have been used to constrainantarcticgia models and gia time variable gravity and uplift signals are error sources for grace and altimeter estimates of present day antarctic ice mass loss and must be modelled and removed from those estimates computinggia results for a 3 d viscosity profile derived from a realistic seismic tomography model and comparing with results computed for 1 d averages of that 3 d profile we conclude that 1 a gia viscosity model based on canadian relative sea level data is more likely to represent a canadian average than a true global average 2 the effects of 3 d viscosity structure on grace estimates of present day antarctic mass loss are probably smaller than the difference between gia models based on different antarctic deglaciation histories and 3 the effects of 3 d viscosity structure on antarctic gps observations of present day uplift rate can be significant and can complicate efforts to use gps observations to constrain 1 d gia models

gondwana derived microcontinents the constituents of the variscan and alpine collisional orogens abstract the european variscan and alpine mountain chains are collisional orogens and are built up of pre variscan building blocks which in most cases originated at the gondwana margin such pre variscan elements were part of a pre ordovician archipelago like continental ribbon in the former eastern prolongation of avalonia and their present day distribution resulted from juxtaposition through variscan and or alpine tectonic evolution the well known nomenclatures applied to these mountain chains are the mirror of variscan resp alpine organization it is the aim of this paper to present a terminology taking into account their pre variscan evolution at the gondwana margin they may contain relics of volcanic islands with pieces of cadomian crust relics of volcanic arc settings and accretionary wedges which were separated from gondwana by initial stages of rheic ocean opening after a short lived ordovician orogenic event and amalgamation of these elements at the gondwanan margin the still continuing gondwana directed subduction triggered the formation of ordovician al rich granitoids and the latest ordovician opening of palaeo tethys an example from the alps external massifs illustrates the gradual reworking of gondwana derived pre variscan elements during the variscan and alpine tertiary orogenic cycles

the physical basis of glacier volume area scaling ice volumes are known for only a few of the roughly 160 000 glaciers worldwide but are important components of many climate and sea level studies which require water flux estimates a scaling analysis of the mass and momentum conservation equations shows that glacier volumes can be related by a power law to more easily observed glacier surface areas the relationship requires four closure choices for the scaling behavior of glacier widths slopes side drag and mass balance reasonable closures predict a volume area scaling exponent which is consistent with observations giving a physical and practical basis for estimating ice volumes glacier volume is insensitive to perturbations in the mass balance scaling but changes in average accumulation area ratios reflect significant changes in the scaling of both mass balance and ice volume

a reconciled estimate of glacier contributions to sea level rise 2003 to 2009 glaciers distinct from the greenland and antarctic ice sheets are losing large amounts of water to the world s oceans however estimates of their contribution to sea level rise disagree we provide a consensus estimate by standardizing existing and creating new mass budget estimates from satellite gravimetry and altimetry and from local glaciological records in many regions local measurements are more negative than satellite based estimates all regions lost mass during 2003 2009 with the largest losses from arctic canada alaska coastal greenland the southern andes and high mountain asia but there was little loss from glaciers in antarctica over this period the global mass budget was 259 28 gigatons per year equivalent to the combined loss from both ice sheets and accounting for 29 13 of the observed sea level rise

variations in the earth s oblateness during the past 28 years 1 analysis of satellite laser ranging slr data indicates that the earth s dynamic oblateness j2 has undergone significant variations during the past 28 years the dominant signatures in the observed variations in j2 are 1 a secular decrease with a rate of approximately 2 75 10 11 yr 1 2 seasonal annual variations with a mean amplitude of 2 9 10 10 3 significant interannual variations with timescales of 4 6 years and 4 a variation with period of 21 years and an amplitude of 1 4 10 10 with minimum in december 1988 two large interannual variations are related to the strong el nino southern oscillation events during the periods of 1986 1991 and 1996 2002 and it appears that another interannual cycle may have started in late 2002 the superposition of the decadal variation on the interannual signal makes the j2 fluctuation appear to be anomalously large during the 1996 2002 period contemporary models of the mass redistributions in the atmosphere ocean and surface water can explain a major part of the 4 to 6 year fluctuations however the cause of the decadal variation remains unknown

detachment faulting and the evolution of passive continental margins major detachment faults play a key role in the lithospheric extension process in the basin and range province and may also be important in other continental extension terranes such detachment faulting leads to an inherent asymmetry of extensional structure and of uplift subsidence patterns detachment models developed for the formation of metamorphic core complexes can also be applied to the formation of passive continental margins we therefore suggest the existence of upper plate and lower plate passive margins these give rise to a complementary asymmetry of opposing margins after continental breakup transfer faults offset marginal features and allow margins to switch from upper plate to lower plate characteristics along strike

the gravity recovery and climate experiment mission overview and early results 1 the grace mission is designed to track changes in the earth s gravity field for a period of five years launched in march 2002 the two grace satellites have collected nearly two years of data a span of data available during the commissioning phase was used to obtain initial gravity models the gravity models developed with this data are more than an order of magnitude better at the long and mid wavelengths than previous models the error estimates indicate a 2 cm accuracy uniformly over the land and ocean regions a consequence of the highly accurate global and homogenous nature of the grace data these early results are a strong affirmation of the grace mission concept

widespread rapid grounding line retreat of pine island thwaites smith and kohler glaciers west antarctica from 1992 to 2011 we measure the grounding line retreat of glaciers draining the amundsen sea sector of west antarctica using earth remote sensing ers 1 2 satellite radar interferometry from 1992 to 2011 pine island glacier retreated 31 km at its center with most retreat in 2005 2009 when the glacier ungrounded from its ice plain thwaites glacier retreated 14 km along its fast flow core and 1 to 9 km along the sides haynes glacier retreated 10 km along its flanks smith kohler glaciers retreated the most 35 km along its ice plain and its ice shelf pinning points are vanishing these rapid retreats proceed along regions of retrograde bed elevation mapped at a high spatial resolution using a mass conservation technique that removes residual ambiguities from prior mappings upstream of the 2011 grounding line positions we find no major bed obstacle that would prevent the glaciers from further retreat and draw down the entire basin 2014 american geophysical union all rights reserved

analysis of scaling methods in deriving future volume evolutions of valley glaciers volume area scaling is a common tool for deriving future volume evolutions of valley glaciers and their contribution to sea level rise we analyze the performance of scaling relationships for deriving volume projections in comparison to projections from a one dimensional ice flow model the model is calibrated for six glaciers nigardsbreen rhonegletscher south cascade glacier sofiyskiy glacier midre lovenbreen and abramov glacier volume evolutions forced by different hypothetical mass balance perturbations are compared with those obtained from volume area v a volume length v l and volume area length v a l scaling results show that the scaling methods mostly underestimate the volume losses predicted by the ice flow model up to 47 for v a scaling and up to 18 for v l scaling by the end of the 100 year simulation period in general v l scaling produces closer simulations of volume evolutions derived from the ice flow model suggesting that v l scaling may be a better approach for deriving volume projections than v a scaling sensitivity experiments show that the initial volumes and volume evolutions are highly sensitive to the choice of the scaling constants yielding both over and underestimates however when normalized by initial volume volume evolutions are relatively insensitive to the choice of scaling constants especially in the v l scaling the 100 year volume projections differ within 10 of initial volume when the v a scaling exponent commonly assumed 1 375 is varied by 30 to 45 0 95 2 00 and the v l scaling exponent q 2 2 is varied by 30 to 45 q 1 52 3 20 this is encouraging for the use of scaling methods in glacier volume projections particularly since scaling exponents may vary between glaciers and the scaling constants are generally unknown

spatial structure of near bed flow properties at the grain scale abstract expanding the existing knowledge of the role of roughness on near bed flow properties is vital to provide deeper insights into the interactions between the flow sediment transport morphology and ecology this study uses four fixed beds from both the laboratory and the field to characterise the structure of near bed flow properties dense measurements over a grid of 6 mm spacing were conducted across each cast using an acoustic doppler velocimeter these measurements followed the line of the bed topography with the sampling location being 2 mm away from the maximum bed elevations near bed flow properties were calculated across the surface including velocity turbulence intensity turbulent kinetic energy reynolds stress and quadrant analysis improved visualisation of flow properties involves contour plots of the spatial distribution of flow over the dem of the gravel bed to facilitate attributions of flow patterns to roughness and topography using the standard deviation of elevations as a proxy for grain roughness of each surface we observed that a decrease in roughness led to an increase in the average near bed velocity in contrast an increase in roughness resulted in an increase in both turbulence intensity and turbulent production tke analysis of quadrant events dominating across the surface can provide indications into the potential for erosion and or deposition across the natural mobile surfaces finally second order structure function analysis is used to quantify the spatial structure of flow properties presenting novel isopleth maps of flow properties for the majority of flow properties across all surfaces the range in the spatial extent of flow structures is between 1 and 2 25 d50a except for transverse and vertical velocities which have a wider range up to 3 5 d50a

water worked gravel beds in laboratory flumes a natural analogue an investigation has been conducted to identify the key parameters that are likely to scale laboratory sediment deposits to the field scale two types of bed formation were examined one where sediment is manually placed and screeded and the second where sediment is fed into a running flume this later technique created deposits through sequential cycles of sediment transport and deposition detailed bed surface topography measurements have been made over a screeded bed and three fed beds in addition bulk subsurface porosity and hydraulic conductivity have been measured by comparing the four beds results revealed that certain physical properties of the screeded bed were clearly different from those of the fed beds the screeded bed had a random organization of grains on both the surface and within the subsurface the fed beds exhibited greater surface and subsurface organization and complexity and had a number of properties that closely resembled those found for water worked gravel beds the surfaces were water worked and armoured and there was preferential particle orientation and direction of imbrication in the subsurface this suggested that fed beds are able to simulate in a simplified manner both the surface and subsurface properties of established gravel bed river deposits the near bed flow properties were also compared it revealed that the use of a screeded bed will typically cause an underestimation in the degree of temporal variability in the flow furthermore time averaged streamwise velocities were found to be randomly organized over the screeded bed but were organized into long streamwise flow structures over the fed beds it clearly showed that caution should be taken when comparing velocity measurements over screeded beds with water worked beds and that the formation of fed beds offers an improved way of investigating intragravel flow and sediment water interface exchange processes in gravel bed rivers at a laboratory scale copyright 2008 john wiley sons ltd

estimating geocenter variations from a combination of grace and ocean model output 1 in this study we estimate a time series of geocenter anomalies from a combination of data from the gravityrecoveryandclimateexperiment grace satellitemissionandthe outputfromoceanmodels amatrixequationisderivedrelating totalgeocentervariations to the grace coefficients of degrees two and higher and to the oceanic component of the degree one coefficients we estimate the oceanic component from two state of the art ocean models results are compared to independent estimates of geocenter derived from other satellite data such as satellite laser ranging and gps finally we compute degree one coefficients that are consistent with the processing applied to the grace level 2 gravity field coefficients the estimated degree one coefficients can be used to improve estimates of mass variability from grace which alone cannot provide them directly

roughness of a subglacial conduit under hansbreen svalbard hydraulic roughness exerts an important but poorly understood control on water pressure in subglacial conduits where relative roughness values are 5 here we report the first quantitative assessment of roughness heights and hydraulic diameters in a subglacial conduit we measured roughness heights in a 125 m long section of a subglacial conduit using structure from motion to produce a digital surface model and hand measurements of the b axis of rocks we found roughness heights from 0 07 to 0 22 m and cross sectional areas of 1 2 m 2 resulting in relative roughness of 3 12 and 5 for most locations a simple geometric model of varying conduit diameter shows that when the conduit is small relative roughness is 30 and has large variability our results suggest that parameterizations of conduit hydraulic roughness in subglacial hydrological models will remain challenging until hydraulic diameters exceed roughness heights by a factor of 20 or the conduit radius is 1 m for the roughness elements observed here

marine ice sheet collapse potentially under way for the thwaites glacier basin west antarctica resting atop a deep marine basin the west antarctic ice sheet has long been considered prone to instability using a numerical model we investigated the sensitivity of thwaites glacier to ocean melt and whether its unstable retreat is already under way our model reproduces observed losses when forced with ocean melt comparable to estimates simulated losses are moderate 1 mm per year of sea level rise collapse in the different simulations within the range of 200 to 900 years

reviewing pre transalp dss models abstract the interpretation of dss deep seismic soundings profiles in central and eastern alps is recalled in the paper and the models of the lower crust and moho proposed several years ago are compared to the results of the transalp seismic reflection profile this evaluation highlights a good agreement as far as the geometry of the deep crustal structure is concerned therefore the reliability of the interpretative models previously exclusively based on dss profiles becomes improved the deep structure beneath the whole alpine range is examined reconsidering the map of the moho boundary and the structural model already proposed for the central eastern sector five main interpretative transects are put side by side starting from the western alps and moving eastwards to the swiss lombardian central alps european geotraverse to the cross section from southern bavaria to the euganei hills to the transalp profile and finally to the easternmost profile available so far southern bavaria trieste the comparison outlines lateral variations of the deep crustal structure as well as a sharp contrast between the adria and the european lower crust and moho the transition from the adria plate to the dinaric domain remains up to now undefined

evolution of gravel surfaces in a sediment recirculating flume the assumption of the equilibrium state of gravel surfaces in flume experiments under feeding or recirculating conditions is generally justified by three equilibrium criteria based on sediment transport slopes and bed features when these parametersbecome stable an experiment is expected to reach equilibrium this equilibrium state however is based on a one dimensional 1d model the exner equation which may not truly reflect the equilibrium state of the system considering the complex flow and sediment processes in this paper the evolutionary process of a gravel surface is investigated based on a large scale recirculating flume experiment the performances of the three equilibrium criteria are evaluated first and then the evolution of the bed morphology is studied the key findings include the following 1 the sediment transport rate slopes of water and bed surfaces and 1d morphological features reach equilibrium roughly simultaneously 2 two dimensional 2d morphology continually evolves after these characteristics reach equilibrium which is confirmed by the characteristics of the sediment transport process and 3 the results from a numerical simulation suggest that a much longer time is required to reach an equilibrium state our results suggest that sufficient experimental time is required to investigate the equilibrium morphological characteristics of gravel surfaces which is much longer than the equilibrium time reflected by the 1d equilibrium criteria

estimation of flow resistance in gravel bedded rivers a physical explanation of the multiplier of roughness length the need to estimate velocity and discharge indirectly in gravel bedded rivers is a commonly encountered problem semilogarithmic friction equations are used to estimate mean velocity using a friction factor obtained from depth and grain size information although such equations have a semi theoretical basis in natural gravel bed channels an empirical constant 6 8 or 3 5 has to be introduced to scale up the characteristic grain size d50 or d84 to represent the effective roughness length in this paper two contrasting approaches are used to suggest that the multiplier of characteristic grain size is attributable to the effect of small scale form resistance reflecting the occurrence of microtopographic bedforms in gravel bedded environments first spatial elevation dependence in short detailed bed profiles from a single gravel bedded river is investigated using semivariogram and zero crossing analyses this leads to objective identification of two discrete scales of bed roughness associated with grain and microtopographic roughness elements second the autocorrelation structure of the three dimensional near bed velocity field is examined to identify regularities associated with eddy shedding and energy losses from larger grains and microtopographic bedforms apart from improving the capacity to determine friction factors for velocity and discharge estimation the findings have implications in general for the initial motion of gravelly bed material

in situ characterization of grain scale fluvial morphology using terrestrial laser scanning the grain scale morphology of fluvial sediments is an important control on the character and dynamics of river systems however current understanding of its role is limited by the difficulties of robustly quantifying field surface morphology terrestrial laser scanning tls offers a new methodology for the rapid acquisition of high resolution and high precision surface elevation data from in situ sediments to date most environmental and fluvial applications of tls have focused on large scale systems capturing macroscale morphologies application of this new technology at scales necessary to characterize the complexity of grain scale fluvial sediments therefore requires a robust assessment of the quality and sources of errors in close range tls data this paper describes both laboratory and field experiments designed to evaluate close range tls for sedimentological applications and to develop protocols for data acquisition in the former controlled experiments comprising high resolution scans of white grey and black planes and a sphere were used to quantify the magnitude and source of three dimensional 3d point errors resulting from a combination of surface geometry reflectivity effects and inherent instrument precision subsequently a methodology for the collection and processing of grain scale tls data is described through an application to a coarse grained gravel system the river feshie d50 32 to 63 mm this stepwise strategy incorporates averaging repeat scans and filtering scan artefact and non surface points using local 3d search algorithms the sensitivity of the results to the filter parameter values are assessed by careful internal validation of digital terrain models dtms created from the resulting point cloud data the transferability of this methodology is assessed through application to a second river bury green brook dominated by finer gravel d50 18 to 33 mm the factor limiting the resolution of dtms created from this second dataset was found to be the relative sizes of the laser footprint and smallest grains copyright 2009 john wiley sons ltd

thermal evolution rate of exhumation and tectonic significance of metamorphic rocks from the floor of the alboran extensional basin western mediterranean high grade metamorphic rocks drilled at ocean drilling program site 976 in the alboran sea show a pt path characterized by decompression from about 1050 mpa 40 km depth to 350 mpa 13 km depth accompanied by an increase in temperature from about 550 50 c to 675 25 c the ar ar dating on muscovite and apatite fission track analysis indicate that the final stage of exhumation and cooling occurred very rapidly in the interval 20 5 18 ma which coincides with the initiation of sedimentation in the alboran sea basin the alboran sea formed by miocene extension on the site of a late cretaceous to paleogene contractional orogen and extension coincided with thrusting in the peripheral parts of the betic rif arc which surrounds the basin on three sides thermal modeling of the pt path was carried out with the aim of constraining geodynamic models for the formation of the basin variables considered in the modeling included 1 the thickness and thermal gradient of the postorogenic lithosphere 2 the radiogenic heat production in the thickened crust 3 the time gap pause between the end of contractional tectonics and the start of extension 4 removal of lithospheric mantle below 125 75 or 62 5 km and 5 the rate of extension the only combinations of variables that produce modeled pt paths with the observed characteristics involve high radiogenic heat production combined with a significant postcontractional pause to produce high temperatures in rocks initially at 40 km depth removal of lithosphere below 62 5 km to produce further heating during decompression extension by a factor of 3 in 6 m y to delay the attainment of the maximum temperature until the rocks reached shallow depths and final exhumation and cooling in about 3 3 m y to satisfy radiometric and petrological constraints this gives a maximum of about 9 m y for exhumation from 40 km depth to the surface lithospheric stretching in response to plate boundary forces such as trench rollback without removal of lithosphere cannot explain the late onset of heating and the high temperatures reached by these rocks removal of lithosphere at depths significantly greater than 62 5 km cannot explain the combination of high temperatures reached by these rocks and the shallow depth at which they attained the maximum temperature only a combination of significant postcollisional radiogenic heating then wholesale removal of lithospheric mantle below the orogenic crust followed by rapid stretching can explain the observed pt path these results appear to support some form of lithospheric delamination as the primary cause for the formation of the alboran sea basin

the impact of stress history on bed structure recent research has started to focus on how prolonged periods of sub threshold flows may be capable of imparting structural changes that contribute to increased bed stability to date this effect termed stress history has been found to be significant in acting to increase a bed s critical shear stress at entrainment threshold however it is supported by only limited qualitative and often speculative information on the mechanisms of this stabilisation process in grade specific studies as such this paper uses high resolution laser scanning to quantitatively ascertain the granular mechanics underpinning the relationship between stress history and entrainment threshold for beds of a range of grain size distributions employing a bed slope of 1 200 three grain size distributions with median grain sizes d50 of 4 8mm uniform g d84 d16 0 5 1 13 bimodal g 2 08 and unimodal g 1 63 were exposed to antecedent stress histories of 60 and 960 minutes duration antecedent shear stress magnitude was set at 50 of the critical shear stress for the d 50 when no stress history period was employed two laser displacement scans of the bed surface approximate area 100 x 117mm were taken one prior to the antecedent period and one after this period so that changes to surface topography could be quantified resolution of x 0 10mm y 0 13mm and z 0 24mm rearrangement of bed surface structure is described using statistical analysis and 2d semi variograms to analyse scaling behaviour results reveal vertical settlement changes to bed roughness and particle repositioning however the bed grain size distribution influences the relative importance of each mechanism in determining stress history induced bed stability this is the focus of discussion in this paper

rapid wastage of alaska glaciers and their contribution to rising sea level we have used airborne laser altimetry to estimate volume changes of 67 glaciers in alaska from the mid 1950s to the mid 1990s the average rate of thickness change of these glaciers was 0 52 m year extrapolation to all glaciers in alaska yields an estimated total annual volume change of 52 15 km 3 year water equivalent equivalent to a rise in sea level sle of 0 14 0 04 mm year repeat measurements of 28 glaciers from the mid 1990s to 2000 2001 suggest an increased average rate of thinning 1 8 m year this leads to an extrapolated annual volume loss from alaska glaciers equal to 96 35 km 3 year or 0 27 0 10 mm year sle during the past decade these recent losses are nearly double the estimated annual loss from the entire greenland ice sheet during the same time period and are much higher than previously published loss estimates for alaska glaciers they form the largest glaciological contribution to rising sea level yet measured

measurement of gravel bed topography evaluation study applying statistical roughness analysis abstractin this two part study experiments are conducted to evaluate available topography measurement techniques for gravel beds in a laboratory flume and to study their suitability for statistical roughness analysis the available instruments for this study include 1 an acoustic bed profiler 2 a hand held laser scanner and 3 two digital consumer cameras forming a stereophotogrammetric system and are employed to obtain digital elevation models dems of water worked gravel beds in the first part of the study the three measurement techniques are reviewed and their feasibilities for future grain scale roughness work assessed based on the obtained elevation datasets water worked gravel bed topographies are measured with all three available measurement techniques the analysis of the dems concentrates on using probability distribution functions pdfs and second order structure functions of bed elevations roughness coefficients are determined and used as a benchmark for comparison of the three

recent contributions of glaciers and ice caps to sea level rise satellite measurements of earth s gravity field show that the mass loss of glaciers and ice caps contributed to sea level rise by approximately 0 4 millimetres per year between 2003 and 2010 the extent to which mass loss from ice covered land areas contributes to sea level rise is not known accurately in part because previous global estimates use different techniques for glaciers ice caps and ice sheets the gravity recovery and climate experiment grace satellite has provided monthly measurements of the global gravity field since 2002 using grace data jacob et al assess regional mass loss between 2003 and 2010 and conclude that mass loss from ice covered land areas contributed almost 1 5 mm per year to the sea level rise estimated mass loss from the high mountains of asia was negligible in contrast to some other reports glaciers and ice caps gics are important contributors to present day global mean sea level rise1 2 3 4 most previous global mass balance estimates for gics rely on extrapolation of sparse mass balance measurements1 2 4 representing only a small fraction of the gic area leaving their overall contribution to sea level rise unclear here we show that gics excluding the greenland and antarctic peripheral gics lost mass at a rate of 148 30 gt yr 1 from january 2003 to december 2010 contributing 0 41 0 08 mm yr 1 to sea level rise our results are based on a global simultaneous inversion of monthly grace derived satellite gravity fields from which we calculate the mass change over all ice covered regions greater in area than 100 km2 the gic rate for 2003 2010 is about 30 per cent smaller than the previous mass balance estimate that most closely matches our study period2 the high mountains of asia in particular show a mass loss of only 4 20 gt yr 1 for 2003 2010 compared with 47 55 gt yr 1 in previously published estimates2 5 for completeness we also estimate that the greenland and antarctic ice sheets including their peripheral gics contributed 1 06 0 19 mm yr 1 to sea level rise over the same time period the total contribution to sea level rise from all ice covered regions is thus 1 48 0 26 mm 1 which agrees well with independent estimates of sea level rise originating from land ice loss and other terrestrial sources6

preservation of permo triassic low pressure assemblages in the cretaceous high pressure metamorphic saualpe crystalline basement eastern alps austria metapelites and intercalated metapegmatites of the saualpe crystalline basement which forms part of the austroalpine nappe complex in the eastern alps display a polyphase tectonometamorphic history here we focus on the evolution that these rocks underwent prior to cretaceous eo alpine high pressure metamorphism and related penetrative deformation geothermobarometry on coarse grained porphyroclastic parageneses garnet biotite muscovite plagioclase sillimanite quartz which occur as relics in kyanite garnet two mica gneiss yielded 600 c 0 4 gpa results from a corundum bearing lithology suggest that higher temperatures may have been reached in very restricted areas the matrix of these rocks displays intense recrystallization during a pressure dominated metamorphic overprint microstructures and mineral chemistry indicate that this low pressure metamorphism was the first significant metamorphic imprint in these rocks mineral relics in all metapelitic rock types reflect low pressure conditions for this interkinematic crystallization phase the distribution macroscopic and microscopic observations and the mineralogical composition of intercalated metapegmatites point to regionally elevated temperature conditions during their emplacement therefore pegmatite formation is correlated with mineral formation in metapelites sm nd dating of magmatic garnet from the pegmatite gneiss yielded 249 3 ma which is interpreted to represent the age of pegmatite emplacement and low pressure metamorphism in the metapelites since the pegmatites are overprinted by mylonitisation and high pressure metamorphism this permo triassic age also sets an upper age limit to the eclogite facies metamorphic event which affected considerable parts of the saualpe crystalline basement

pre oceanic rifting in the alps abstract a review of mesozoic mainly earliest jurassic to mid jurassic rifting in the western and central alps normal faults with throws up to a few kilometers are moderately inclined and involve rotation of crustal blocks the amount of stretching and thinning of the crust by jurassic rifting is discussed the rifting 200 165 m y pre dates the opening of the alpine oceans by spreading and transform movements 165 110 m y

permian triassic high thermal regime in the alps result of late variscan collapse or continental rifting validation by numerical modeling 1 the permian triassic igneous activity associated with regional scale deformation developed under high temperature low pressure ht lp metamorphic conditions and widely recorded in the pre alpine crust of the european alps can result from late orogenic collapse of a collisional belt or from lithospheric thinning leading to a continental rifting process in order to reduce this ambiguity we use a two dimensional finite element model to give new insights on the sequence of mechanisms operating during active ocean continent convergence followed by continental collision and pure gravitational evolution and on the regional geodynamic interpretation of the paleozoic mesozoic evolution of the alpine area the modeling predictions are compared with the pt climax conditions of variscan and permian triassic metamorphism affecting the continental crust of the helvetic to southalpine domains the good agreement between model predictions and natural data realized for the early to neovariscan evolution indicates that during paleozoic the pre alpine crust of the alps was part of an active ocean continent convergence margin and an intracontinental suture zone furthermore modeling results support the interpretation envisaging a permian triassic lithospheric extension as responsible for the ht metamorphism and related intense igneous activity this evolution was precursor of the mesozoic oceanization during which the tectonic units coupled and accreted during the variscan subduction and collision were separated to form the two passive european and adriatic continental margins

evaluation of dem size and grid spacing for fluvial patch scale roughness parameterisation abstract surface roughness is a term used in fluvial research without a unanimous definition clarification of the term and improved parameterisation is needed in future research improvements to the collection of topographic data using photogrammetry have provided accurate digital elevation models dems of field and laboratory gravel bed patches of varied sediment size and surface structure in this study a moving window process is used for analysing spatial variability within dems using this information and in unison the effect of dem size and grid spacing are considered on an extensive range of roughness parameters in order to provide insights for obtaining grain roughness statistics it is shown that dem size influences the calculated roughness statistics and the observation of plateaus in statistics for dem window sizes above 16 d50a in both directions where d50a is the median grain size of the bed surface material suggests this as a minimum dem size for grain scale roughness analysis further the dem grid spacing should be 1 mm or below in order to adequately capture grain roughness as coarser resolutions failed to detect particle imbrication finally variability in roughness parameters was evident due to natural spatial variation in gravel bed microtopography suggesting using a single roughness parameter is not appropriate to holistically describe the roughness of a gravel patch as the importance of topographic information continues to grow in geomorphology the results of this study will assist researchers in the collection and subsequent analysis of dems